Materials by design for energy applications

Resume : From a computational point of view, materials by design has been largely focused on identifying compounds with specific electronic properties. While this approach is still in its infancy, recent successes clearly show that computational screening can accelerate significantly materials discovery. Yet, in most cases, a static characterization is far from sufficient to ensure the viability of proposed materials as kinetic properties, defining stability and evolution, can modify completely the materials' structure and behaviour. Using various examples, I will show how expanded computing powers and new approaches are now transforming how we characterize the potential energy landscape and kinetic properties of materials. Challenges remain, for sure, but it is now possible to beyond a static view of materials and what is we find then is, most often than not, very surprising.

Resume : Phosphorus, in several allotropic variations, is emerging as a high capacity anode candidate for lithium and sodium batteries. The theoretical capacity for Li3P/Na3P is 2596 mA·h·g-1, far exceeding carbon and on par with the best known lithium and sodium battery anodes. To date, some composites of carbon with red or black phosphorus, or phosphorene have been investigated; however, the amorphous or poorly crystalline nature of these composites has hindered the understanding of phosphide intermediates and reaction mechanisms. We use high-throughput computation and the ab initio random structure searching method (AIRSS) to predict the structure of lithium and sodium phosphides, then predict the properties of these systems using DFT, including NMR chemical shielding. We identify that specific ranges in the calculated shielding can be associated with specific ionic arrangements, results which play an important role in the interpretation of NMR spectroscopy experiments. Since the lithium-phosphides are found to be insulating even at high lithium concentrations we show that Li-P- doped phases with aluminium have electronic states at the Fermi level suggesting that using aluminium as a dopant can improve the electrochemical performance of P anodes.

Resume : Recent years witnessed considerable scientific and technological interest in rechargeable batteries for energy storage intended for several futuristic applications such as electrical vehicles. In addition to experimental studies, numerical and theoretical methods have become fundamental tools for the study of physical and chemical phenomena happening in rechargeable Li-ion batteries. Much effort was given to graphitic anodes to understand how and with what energy barrier lithium diffuses from one site to another. Also to elucidate edge effects on the characteristics of lithium diffusion in graphite. Efforts include a broad range of methodologies such as density functional theory (DFT), ab-initio molecular dynamics (AIMD), classical molecular dynamics (MD) and kinetic Monte Carlo (KMC). The KMC method, introduced 40 years ago is a stochastic approach that can be used to reach long time scales using a fixed and prebuilt catalogue containing information about the diffusion mechanisms identified beforehand. This standard KMC applied to materials science is limited to on-lattice configurations, which are not sufficient to study complex systems and off-lattice positions when elastic effects are important. The development of new KMC methods was of considerable scientific interest to overcome this limitation. This is the case of kinetic ART (k-ART), for example, which uses a very efficient transition-state searching method, ART nouveau, coupled with a topological tool, NAUTY, to offer an off-lattice KMC method with on-the-fly catalog building to study complex systems, such as ion-bombarded and amorphous materials, on timescales of a second or more. Here, we will show an on-the-fly off-lattice KMC method k-ART to study the diffusion mechanism into graphite sheets over long time scales and to characterize the surface effect on lithium diffusion in graphite. The method enables to simulate diffusion of lithium from site to site and evaluate possible reaction barriers as the system evolves and in the presence of structural defects.

Resume : Great research efforts are under way to develop cathode materials for Li-ion batteries able to improve battery performance in terms of voltage, energy density, kinetics, cyclability, and price. In this talk, I will show how first-principles simulations based on density functional theory can be used to predict the effect of low amounts of aluminium dopants on relevant functional properties of a cobalt-free oxide. The results show that this lithium-manganese-nickel oxide with low Al concentration is indeed promising for practical applications, leading to increased voltage and energy density, and band electronic conductivity. Moreover, the fundamental insight obtained might be useful for other systems as well.

Resume : There have been significant scientific and technological attentions to lithium-ion batteries (LIB) for many years because of their long cycle life, high energy density, and wider operating temperature range. LIB is a recyclable battery in which lithium ions move from cathode to anode through electrolyte during charging and back to cathode when discharging. Ethylene carbonate (EC) is one of the most common electrolyte because of its high compatibility with graphite electrodes, but the major disadvantage of EC is its high melting point of 36.4°C. Therefore, EC is used with other co-solvent such as dimethyl or diethyl carbonate to increase the melting point. In contrast, propylene carbonate (PC) is stable at lower temperature with melting point of –48.8°C despite the structural similarity to EC. Even though PC-based electrolyte would be more advantageous, however, the graphite of anode exfoliates in PC-based electrolyte that causes battery failure. Therefore, the understanding of the behavior of electrolytes is necessary step to design new batteries with better performance. To understand the different behavior of EC and PC electrolytes at the atomistic level, we performed molecular dynamics simulations of electrolyte intercalated graphene sheets. We observed no diffusion of electrolyte between graphene sheets when interlayer distance is less than 6 Å, but both of EC and PC form monolayer between graphene sheets with comparable density when interlayer distance is 7 ~ 8 Å. Because of the size difference, the intercalated PC molecules induce longer separation distance between graphene sheets compared to that of EC. The longer separation with PC intercalant induces more frequent sliding-exfoliation movement. We found that the exfoliation diffusion coefficient of the graphene sheet with PC intercalant is ~200 times larger than that with EC intercalant. One graphene diffuses and exfoliates from other graphene through sliding displacement rather than vertical separation because of steric interaction with electrolyte molecules in the bulk phase. For calculating the free energy changes of exfoliation, we constructed potential of means force using steered molecular dynamics simulations, and found that the energy barrier of exfoliation of EC intercalated graphene sheets is ~45 kcal/mol where it is ~4 kcal/mol for PC intercalated graphene sheets. We also analyzed the static and dynamic properties of electrolyte confined between two graphene sheets. The self-diffusion coefficient of confined PC is larger than that of EC, but smaller in the bulk phase. We also found that the decaying of the dipole rotation autocorrelation of confined electrolyte is slower than that in the bulk phase. The dynamic properties of the graphene in two different electrolytes reported in this paper can be used for designing new anode materials with better performance.

Resume : Graphene and its derivatives have attracted great attention owing to its highly appealing properties since its first isolation in 2004; however, it has been lately occasionally criticized as ‘graphene fever’ due to the shortage of ‘killer’ applications. Among all potential applications, electrochemical energy-storage devices, particularly lithium-ion batteries (LIBs), are one of the most popular fields for graphene. Despite huge efforts, graphene battery performance is still far from satisfactory in terms of capacity, rate-performance and long-term stability. Here we present a general and facile way to fabricate hierarchical graphene-based aerogels as binder-free anodes for ultra long-life LIBs. In this approach, different types of active anode materials can be easily incorporated as spacer/pillar between graphene layers, e.g. spinel-type metal oxides, or MoxSy/C hybrids. Benefitting from the hierarchical porosity of reduced graphene oxide (rGO) aerogel and its mechanical stability, the hybrid system synergistically enhances the intrinsic properties of each component, yet robust and flexible. As a result, the composite aerogels demonstrate outstanding electrochemical performance and ultra-long cyclability. For instance, the MoxSy/C/rGO composite aerogels were found to enable high capacity (1060 mAh g-1 at 0.35 A g-1), fast rate performance (425 mAh g-1 at 10 A g-1) and ultra-long stability. At 5 A g-1, the capacity can be retained at 336 mAh g-1 (71.3% of the initial) after 10,000 cycles. The excellent results pave an avenue for practical application for graphene in battery industry, and the versatile strategy developed here can be easily extended to the co-assembly of rGO with other functional materials for diverse applications as e.g. supercapacitors or in catalysis.

Resume : 2D structure materials are one of the promising material for use in electrochemical capacitor. There are several kind of 2D structure material, such as graphene, MXenes phase, and transition metal dichalcogenides (TMD). In here, we are focus on TMD material which is MoS2. There are two part of the fabrication of 2D structure of MoS2, which are by exfoliation from the bulk MoS2 or directly synthesis of 2D structure of MoS2. In the present study, we prefer to synthesis of 2D structure of MoS2 instead of exfoliation part. We utilized the various carbon template to forming the 2D structure of MoS2 such as graphene oxide (GO), reduced graphene oxide (RGO), N-doped graphene oxide (NDG), and carbon clothes with a facile method, microwave-assisted hydrothermal (MAH). Various degree oxidation of graphene would give nanoflower assembled by nanosheets morphology and carbon clothes would give nanoflakes morphology. These 2D structures would give excellent double layer capacitance. The effect of the time reaction and concentration of MoS2 precursor also were discussed. Physical and chemical properties were be investigated by using X-ray diffraction for the crystallinity, scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology, X-ray photoelectron spectroscopy (XPS) to confirm the chemical content, thermogravimetric analysis (TGA) to know the wt. % of MoS2 in the template. Electrochemical properties of materials were be investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic.

Resume : Lithium ion-batteries play an important role in rechargeable batteries technologies due to a number of advantages such as high energy storage and reduced gas emission. During the first charge cycle reduction of electrolyte leads to formation of a layer which adheres well to the anode, prevents further degradation and provides Li ions transport into the anode. Accessible experimental data reveal molecular composition of this solid electrolyte interphase (SEI), but almost nothing is known about its structural organization and how the SEI is connected with graphite and forms mutual interface between two materials. The latter is a crucial point determining stability and properties of the SEI and efficient battery operation as a result. Modeling of a “SEI - graphite” interface is not a trivial task due to lack of important structural details. Moreover such interface cannot be set simply as the sterical adjacency of two materials. Chemical and physical interactions between them must be taken into account. We demonstrate our approach to design step by step the SEI close to graphite. Performed within DFT framework, various types of graphite – SEI interfaces and their connections have been evaluated using various criteria such as the formation energy, the electrostatic potential, the dipole moment magnitude etc. The PBE functional, Grimme's dispersive forces and the wavelet basis set were applied using the BigDFT code (Genovese L. et al. J. Chem. Phys. 2008, 129 (1), 014109).

Resume : For the practical use of silicon nanowires (Si NWs) as anodes for Li-ion batteries, understanding their lithiation and delithiation mechanisms at the atomic level is of critical importance. Here, we report the mechanisms for the lithiation and delithiation of pristine Si and SiOx NWs determined using a large-scale (~100,000 atoms) molecular dynamics (MD) simulation with a reactive force field (ReaxFF). The ReaxFF is developed in this work using first-principles calculations. Our ReaxFF-MD simulation shows that an anisotropic volume expansion behavior of Si NWs during lithiation is dependent on the surface structures of the Si NWs; however, the volumes of the fully lithiated Si NWs are almost identical irrespective of the surface structures. During the lithiation process, Li atoms penetrate into the lattices of the crystalline Si (c-Si) NWs preferentially along the <110> or <112> direction, and then the c-Si changes into amorphous LixSi (a-LixSi) phases due to the simultaneous breaking of Si-Si bonds as a result of the tensile stresses between Si atoms. Before the complete amorphization of the Si NWs, we observe the formation of silicene-like structures in the NWs that are eventually broken into low-coordinated components, such as dumbbells and isolated atoms. On the other hand, during delithiation of the LixSi NWs, we observe the formation of a small amount of c-Si nuclei in the a-LixSi matrix below a composition of Li1.4Si~Li1.5Si, in which the volume fraction of formed c-Si phases relies on the delithiation rate. Our ReaxFF-MD simulation also reveals that SiOx NWs with thin surface oxide layers indeed provide smaller volume expansion rather than pristine NWs during lithiation. Here, oxide layers are more anchored than LixSi/Si interfaces during lithiation, which suppresses volume expansion of the NWs more effectively. And we observe that after lithiation of the SiOx NWs Li4SiO4 and Li2O clusters are formed in the oxide layers in which their concentrations is gradually increased during lithiation. Li atoms of Li4SiO4 clusters are moveable, in other words they can diffuse into c-Si and then form LixSi phases. Simultaneously, the dissociated SiO44- clusters bind to other Li atoms and then Li4SiO4 clusters reform. Moreover, we investigate solid-electrolyte interface (SEI) formation behaviors on Si and SiOx anodes by the ReaxFF-MD simulation, where various electrolytes (e.g. mixtures of EC/PC, EC/DEC and EC/DMC etc) along with a VC additive are considered. Our simulation is confirmed by several reported experiment. We expect that the developed ReaxFF will provide helpful guidelines in designing Si-based anodes to obtain better performing Li-ion batteries.

Resume : Lithium-ion batteries (LIBs) have been commercially applied in various portable electronic devices nowadays. Tremendous efforts have been devoted to explore new materials for both cathode and anode, and the operating techniques to controllably construct the admired structure. Engineering the surface properties of any new electrode material, including decreasing the particle size, modifying surface functions, controlling the morphology, in order to enhance the electrochemical compatibility with specific electrolyte and facilitate the electron transfer and ion diffusion, is of significance to improve the battery performance. A promising strategy is to develop composite material with adjustable surface chemistry, for example, the carbonaceous materials is greatly explored and intensively studied due to the superior electrochemical properties. However, the methodologies reported in the literature are often applicable only to specific active materials, involving rather complicated preparation routes that are unfavorable for large-scale production. Herein, we propose a generic methodology to generate hierarchical architecture for the active materials of LIB electrodes. Specifically, the nano-sized active material (<10 nm) are carbon-coated and encapsulated inside a conductive matrix derived from polymers, forming submicron-scale spheres. The carbon matrix inside the spheres improves the conductivity and mechanical properties and separates individual nanoparticles (NPs) to avoid their aggregation. Mesopores are generated within the carbon spheres through scarifying partial of the polymer component, necessary for facilitating the diffusion of Li ions in and out of the active material and for accommodating possible volume changes. The inter-space among the carbon spheres generates continuous channels, necessary for ease of electrolyte infiltration. Such a design concept is generic, applicable for various cathode/anode materials. To demonstrate the applicability of the proposed methodology, we have selected anatase TiO2 serving as active materials to be integrated within carbon matrix by applying the aforementioned approach. The as-synthesized TiO2 NPs are <10 nm and in-situ encapsulated into sub-micron poly-(styrene-acrylonitrile) (PSAN) spheres. The precursor of the anode material is obtained by drying properly dense-packed PSAN spheres, and the active anode material is obtained by pyrolysis of the precursor under desired conditions, where the poly-acrylonitrile (PAN) forms graphite-like carbons and the poly-styrene (PS) is sacrificed to contribute to mesopores inside each sphere. The LIBs based on such prepared active anode material exhibits good rate and cycling performance. A reversible capacity of 173 mAh g-1 at a current density of 500 mA g-1 lasts stably along 600 cycles with negligible fading. The high cycling stability demonstrates the advantages and applicability of the proposed methodology in preparation of electrode active materials. It should be also mentioned that the applied preparation route can be well utilized for large-scale production of high performed LIBs.

Resume : Owing to its high specific capacity (3579 mAh/g), silicon has become one of the most promising anode material candidates for use in lithium ion batteries. However, the poor cycle lifetime, caused by ~400% volume change during alloying is currently the biggest challenge toward their commercial application. The addition of graphene offers one potential method to overcome this problem. Due to its excellent mechanical properties, graphene is well suited to act as a buffer layer during large volume expansion. Hence, a facile route toward the optimization of graphene reduction is required. We demonstrate two different approaches leading to more efficient and low cost processes to reduce graphene oxide within few minutes. First, the proposed method, so-called “dry method” utilizes silicon carbide as an efficient microwave susceptor heat source. The second method, called “solution method” uses graphene oxide solution with the addition of a reducing agent. In both cases, under microwave radiation, graphene oxide undergoes a rapid heating and reduction to graphene. To characterize our materials, we utilize Fourier transform infrared spectroscopy (FTIR) and X-Ray photoelectron spectroscopy (XPS), the loss of C=O peaks and OH peaks confirm the reduction of graphene oxide and carbon-to-oxygen ratio is 30. The cell performance of our reduced graphene oxide shows capacity values of 1700mAh/g after 50 cycles compared to the 372mAh/g of commercial graphite anode material. Furthermore, by using the solution method, additional precursors can be easily combined into the solution for further material upgrade. We believe this work presents a highly promising technique toward the low-cost production of reduced graphene oxide suitable for future Si based Li-ion battery applications.

Resume : We perform atomic-scale simulations of electrolyte/electrode interfaces [1,2] to study structure and electrochemical properties of electrolytes that are of interest for the Li-ion battery and automotive industry, like Ethyl Methyl Carbonate (EMC) and LP57, which is a combination of EMC and Ethylene carbonate (EC). Ab-initio molecular dynamics (AIMD) and density functional theory (DFT) are used to calculate the structure of the electrolyte at different concentrations and chemical potentials of Li atoms and PF6 anions, and electrode potentials. We also investigate the effect of additives, like vinylene carbonate (VC). Several observable atomic-scale properties, such as phase diagrams and electrostatic potentials, are calculated for our model system, LP57|Au(111). [1] J. Rossmeisl, K. Chan, R. Ahmed, V. Tripkovic, and M. E. Bjorketun, Phys. Chem. Chem. Phys. 15, 10321 (2013). [2] Z. Zeng, M. H. Hansen, J. P. Greeley, J. Rossmeisl, M. E. Bjorketun, J. Phys. Chem. C 118, 22663 (2014).

Resume : With a high theoretical specific capacity of 3579 mAh/g, silicon has become one of the most favorable anode materials for lithium ion battery. Although the capacity value of Si is almost ten times larger than the commercial graphite anode; its poor cycle life caused by ~400% volume change when completely lithiated, is the major obstacle for commercial usage. One possible solution to overcome this issue is the use of porous Si. With a much higher surface-to-volume ratio, porous silicon can soak up lithium ions more easily and provide enough space to accommodate larger volume expansion, in turn improving the device cycle life. In this work, we propose a novel method using metal-assisted chemical etching of silicon powder increasing the porosity with high efficiency in a low cost process. Initiating the reaction at a temperature below 0 ºC, the reagent is placed in a metallic acid solution, facilitating pore nucleation and propagation within the particle. To characterize our materials, we utilize scanning electron microscope (SEM) to observe the porous morphology. The size of void space is estimated to be about 10~20 nanometers. In addition, Brunauer-Emmett-Teller (BET) analysis shows increased surface area after the porous formation. The Li-ion battery anode based on our porous Si particles offers an enhanced capacity with over 30% increase compared to anode prepared by intrinsic silicon powder. Furthermore, owing to its excellent mechanical properties, graphene can also act as a buffer layer further improving the Si based battery performance. In addition to the improved capacity and cycle life, we believe the combination of porous silicon powder and reduce graphene has the potential of large scale production for industrial applications.

Resume : Seeking high rate, high mass-loading and durable anode materials for lithium ion batteries (LIBs) has been a crucial aspect to promote the use of electric vehicles and other portable electronics. Silicon (Si) has been well-known as an outstanding candidate for LIBs, with a high lithium storage capacity of 4200 mAh/g and a relatively low lithium insertion potential. However, the process of lithium ions (Li-ion) insertion comes with a huge volume change as large as 420% that will cause a radical pulverization/fracture in the Si host and rapid capacity fading. A common strategy to address this issue is to explore various nanostructured Si materials, including nano particles, nanowires (NWs) and nanotubes, which can help to accommodate the large volumetric change during charge/discharge cycling. Among them, nanowire core-shell or hierarchical nano-branch structures have attracted particular interests, where the NW-core can be optimized to serve as efficient electric pathway, while the outer sidewall-coated Si thin film shell or SiNW branches enjoy a large interface for fast Li-ion interaction or insertion. In this presentation, we will first report a novel alloy-forming approach to convert amorphous Si (a-Si) coated copper-oxide (CuO) core-shell nanowires (NWs) into hollow and highly-interconnected Si-Cu alloy (mixture) nanotubes [1, 2]. The conformal coating of a thick a-Si (>120 nm) layer, in a fine-tuned plasma enhanced deposition, helps to forge a beneficial multipath network over the CuO NWs. Upon a simple H2 annealing, the CuO cores are reduced and diffuse out to alloy with the a-Si shell, producing highly-interconnected hollow Si-Cu alloy nanotubes, which can serve as high capacity and self-conductive anode structures with robust mechanical support. A high specific capacity of 1010 mAh/g (or 780 mAh/g) has been achieved after 1000 cycles at 3.4 A/g (or 20 A/g), with a capacity retention rate of ~84% (~ 88%), without the use of any binder or conductive agent. Remarkably, they can survive extremely fast charging rate at 70 A/g for 35 runs (corresponding to one full cycle in 30s) and recover 88% capacity. Then, we propose also a new hierarchical structure of fine-tuned crystalline Si (c-Si) nanowires (NWs) grafted upon ultra-long tin dioxide (SnO2) NW trunks [3], where the latter frame up a large, conductive and stable architecture to: i)host a high mass load of high capacity c-Si NWs medium for Li-ion storage, and ii) guarantee a good electric contact and fast charging process. The Si NWs branches are produced via a low-temperature vapor-liquid-solid (VLS) growth mediated by Sn catalyst droplets produced by a simple H2 plasma treatment upon the SnO2 trunks. Compared to other NW anodes structures, with different nanostructured storage mediums, the c-Si/SnO2 NWs hierarchical structure demonstrates an outstanding performance with a high mass-load (~1.5 mg/cm2 ) and a high areal capacity (~1.8 mAh/cm2) after 100 cycles, without the use of any additional polymer, conductive agent or binders. Finally, we will present our latest progresses in combing the hierarchical nanowire/nanotube structures to achieve simultaneously a high rate, high capacity, high mass-loading and durable nanostructured anode material to fulfill the true potential of Si-loaded LIB applications. References [1] Advanced Functional Materials, DOI: 10.1002/adfm.201504014 (2015), Highly-connected silicon-copper alloy mixture nanotubes as high rate and durable anode materials for lithium ion batteries, Hucheng Song, HongXiang Wang, Zixia Lin, Xiaofan Jiang, Linwei Yu*, Jun Xu*, Zhongwei Yu, Xiaowei Zhang, Yijie Liu, Ping He, Lijia Pan, Yi Shi, Haoshen Zhou and Kunji Chen [2] Nanoscale, advance article, DOI: 10.1039/C5NR06985H (2015), Highly cross-linked Cu/a-Si core–shell nanowires for ultra-long cycle life and high rate lithium batteries, Hongxiang Wang, Hucheng Song, Zixia Lin, Xiaofan Jiang, Xiaowei Zhang, Linwei YU*, Jun XU, Lijia Pan, Junzhuan Wang,* Mingbo Zheng, Yi Shi and Kunji Chen [3] Nano Energy 19, 511 (2016), Hierarchical Nano-branched c-Si/SnO2 Nanowires for High Areal Capacity and Stable Lithium-Ion Battery, Hucheng Song, HongXiang Wang, Zixia Lin, Linwei YU*, Xiaofan Jiang, Zhongwei Yu, Jun XU*, Lijia Pan, Mingbo Zheng, Yi Shi, and Kunji Chen

Resume : Silicon dioxide (SiO2) and zirconium dioxide (ZrO2) are earth abundant materials. SiO2 is studied as the potential replacement of silicon (Si), and ZrO2 is revealed as the material with buffering ability which can alleviate volume change of the host materials in lithium ion batteries (LIBs). This paper reports the novel nanocomposite anode materials of SiO2/ZrO2 (SSZ) with three different Si/Zr ratios of 0.5, 1, and 2.

Resume : The demand for high-energy storage systems is constantly increasing, as is the interest to explore alternatives to commercially available batteries. The rechargeable Li-air battery represents an exciting opportunity to design batteries that may satisfy some of the requirements of our future by coupling the light Li metal with the inexhaustible source of O2 of the surrounding air, resulting in high theoretical specific energy density. Currently, most of the researches on the Li-air battery comprise a cell fed with pure O2 allowing that way to maintain long-term operation, owing to the high O2 concentration free of contaminants. However, for many practical applications such as EV, air is the only viable option to supply the battery. In this context, moisture and gases other than O2 may cause side reactions and corrosion. Herein, we report a facile strategy to fabricate an effective oxygen selective membrane with poly(vinylidene fluoride co-hexafluoropropylene) (PVDF-HFP) via non-solvent induced phase separation, casted as a 240 micron thin sheets. The use of different additives helps enhancing the barrier properties as well as the membrane specificity toward O2. For instance, sacrificial silica nanoparticles (SiO2 NPs) were incorporated into the precursor solution to create a controlled alveolar-like structure inside the membrane and then load it with polydimethylsiloxane (PDMS) under vacuum. Galvanostatic charge-discharge tests in a potential/time controlled mode confirmed the ability of the cell with the membrane to reach, in ambient air, nearly the same performances that a dry oxygen fed cell.

Resume : Nowadays there is a scientific break trough finding a novel metal free redox flow battery based on bio-inspired organic molecules. It is due to low cost, environmental friendliness, as well as these compounds does not suffer from resource constraints as occurs with metals (i.e. lithium, cadmium or nickel). We have focused on quinone-based batteries, showing different molecules for cathode and anode in aqueous and also organic solvent in order to compare its electrochemical properties, voltage range and capacity. For that reason, we have been carried out 3 electrode, RDE (rotating disk electrode) and battery cycling. Therefore obtain an optimum organic redox flow battery by means of large voltage window, active species solubility, not forgetting about capacity and efficiencies. Comparatively, we were able to test some different molecules, as benzoquinones for cathode materials and anthraquinones for anode materials, in methanosulphonic acid as aqueous solvent. Although we could test them and obtain some relevant results in a 3 electrode cell, with a potential window up to 1.2 V, their solubility still remain inferior to build a battery to cope with lithium ion batteries. On that behave we switch to some organic solvents, as DMSO. Soluble amount of active material reaches 10 to 20 times more in these conditions, which lead us to a charge-discharge polarization curves exhibiting a good performance with our laboratory design flow cell (voltage above 2 V and 60% EE). It can be concluded that the metal-free redox flow batteries is a unique opportunity to boost this technology into the market as a cost-effective alternative (below 100$ kW/h) to the available products.

Resume : Fast, rich redox reactions in metal oxides have sparked an increasing interest for their utilization in electrochemical capacitors to boost up the available energy in traditional electrochemical double layer capacitors (EDLCs). In this regard, mixed transition metal oxides, specifically cobaltites, have attracted great attention due to their high specific capacitances.1 However, toxicity, relative high-cost, and scarcity of cobalt are considered main concerns of its employment as electrode material in energy storage applications. All these inspired researchers to partially substitute and reduce Co-content, resulted in development of high performance electrode materials such as NiCo2O4, CuCo2O4, etc.2,3 Therefore, introducing and developing materials with lower cobalt but superior or comparable energy storage performance is of great interest (i.e. ternary cobaltites). NiCoMnO4 is a spinel in which two third of metal sites in the lattice has been occupied by Ni and Mn ions which are known as high energy materials in their simple oxide analogues.4,5 However, to the best of our knowledge, the electrochemical properties of this particular spinel have never been examined in alkaline solutions for energy storage applications. Herein, we report facile hydrothermal synthesis of NiCoMnO4 nanoparticles and their evaluation as positive electrode materials for aqueous asymmetric supercapacitors.6 Structural and compositional features of the prepared samples were illuminated by X-ray diffraction (XRD), energy dispersive electron diffraction (EDX), and X-ray photoelectron spectroscopy (XPS), revealing the purity and presence of various oxidation states in the spinel phase. Transmission electron microscopy (TEM) shed light on morphological aspects of the samples and demonstrated very fine nanoparticles with clear crystallite domains. N2 sorption measurements showed a high specific surface area of 175 m2.g-1 with an average pore width centered in mesoporous region. The electrochemical behavior of the sample as a supercapacitor electrode material was investigated through different techniques including cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) in 3 M KOH solution. NiCoMnO4 nanoparticles showed a high specific capacitance of 510 F.g-1 at a current density of 1 A.g-1, capable of retaining 285 F.g-1 at 20 1 A.g-1 (~56% capacitance retention). Two-electrode asymmetric devices based on NiCoMnO4 nanoparticles as positive electrode and reduced graphene oxide nanosheets as negative electrode materials were assembled and subjected to different electrochemical evaluations. NiCoMnO4//RGO hybrid devices showed a high real specific energy of 20 Wh.kg-1 and a maximum specific power of 37.5 kW.kg-1. References: [1] C. Yuan, H. B. Wu, Y. Xie and X. W. Lou, Angewandte Chemie International Edition, 2014, 53, 1488-1504. [2] C. Yuan, J. Li, L. Hou, X. Zhang, L. Shen and X. W. Lou, Advanced Functional Materials, 2012, 22, 4592-4597. [3] A. Pendashteh, S. E. Moosavifard, M. S. Rahmanifar, Y. Wang, M. F. El-Kady, R. B. Kaner and M. F. Mousavi, Chemistry of Materials, 2015, 27, 3919–3926. [4] Y. Ren, Z. Ma and P. G. Bruce, Journal of Materials Chemistry, 2012, 22, 15121-15127. [5] S. Vijayakumar, S. Nagamuthu and G. Muralidharan, ACS Applied Materials & Interfaces, 2013, 5, 2188-2196. [6] A. Pendashteh, J. Palma, M. Anderson, R. Marcilla, RSC Advances, 2016, Under Review.

Resume : Layered-layered composites of xLi2MnO3-(1-x)LiMn0.375Ni0.375Co0.25O2 type shows electrochemical capacity ~300mAhg-1 which is above all the commercially available cathode materials. These composites have got potential for application in hybrid electric vehicles and electric vehicles where high energy density is required. These composites are poor in rate performance and cycleability, mainly because of structural transformation, low electronic and ionic conductivity. Li2MnO3 part transform into cubic spinel which causes capacity and voltage fade with cycling. The structural transformation involves movement of transition metal cations to lithium sites and as a result lithium ion mobility lowers down. Modification to the molecular stoichiometry by doping or surface coating of composite has led to considerable improvements in electrochemical performance of these composite cathodes. We have tried doping Li2MnO3 component with Zr on manganese site. Crystalline and phase pure samples were obtained using self-combustion synthetic route. Zr doped 0.5Li2MnO3-0.5LiMn0.375Ni0.375Co0.25O2 composites shows 86% capacity retention after 50 cycles compared to un-doped composite that is 76%. As the amount of dopant is increased, the first cycle capacity starts to fall but the capacity retention is maintained. The optimum amount of Zr doping was found to be 2 mol% at manganese site. xLi2Zr0.02Mn0.98O3-(1-x)LiMn0.375Ni0.375Co0.25O2, x = 0.25 and 0.75 composite show first cycle capacity 198mAhg-1 and 220mAhg-1 with 84% and 86% capacity retention after 50 cycles respectively. These samples exhibited lesser extent of spinel transformation compared to un-doped composite as confirmed from dQ/dV of discharge profiles after 50 cycles of galvanostatic charge-discharge.

Resume : The multiplication of the portable electronic market and also the development of environment-friendly transport motivate strongly the research in the field of the electric storage. Among different battery technologies, Lithium-Metal Batteries is very well positioned thanks to the high energy density of lithium vs its weight and volume. However, the main problem using Li metal, as an anode associated with a liquid electrolyte is the risk of dendrite growth during charge/discharge cycles. This can lead to internal short circuits possibly followed by dramatic explosion and fire. To overcome these drawbacks, solid polymer electrolytes (SPE) combining both high conductivity and suitable mechanical properties to prevent the dendritic growth are perfect candidates. Recently, we shown the remarkable potential of single-ion block copolymer based on polystyrene derivatives and poly(ethylene oxide) as SPE for Lithium-Metal battery technology. In order to constantly improve the SPE properties and to get a better insight in their mode of action, we present in this work the preparation and the use of a large series of SPE based on triblock copolymers. The triblock copolymers are composed of PEO as central block and polymethacrylate or polyacrylate backbone bearing Sulfonyl(trifluoromethylsulfonyl)imide group as external blocks. The thermal and mechanical properties, the conductivity data as well as the electrochemical performance of these block copolymers were measured and compared.

Resume : Plasmons are major collective excitations of valence electrons occurring in solids in the low-loss range (0 to 50 eV). Since valence electron states are primarily responsible for many intrinsic materials properties, plasmons externally induced e.g., by focused electron beams, can be used as an invaluable tool to probe optical, mechanical, cohesive, transport and thermal properties and phase compositions of nanoscale materials with a sub-nm lateral resolution. For materials with preferentially covalent and metallic bonding, which constitute the vast number of energy storage systems, the universal binding-energy relation (UBER) describes relationships between the cohesive energy, Ecoh, the bulk modulus, Bm, and the volume plasmon energy, Ep (valence electron density). The origin of universality and scaling lies in the nature of electron-ion interactions and in the essential exponential decay of electron density with interatomic distance. This opens opportunities to predict physical properties of materials and then to select materials with desired properties by measuring Ep. We will describe how to utilize these relations in order to determine and map nanoscale physical properties of prospective energy materials. Some applications will be illustrated by selected examples, including correlations between Ep, elastic moduli and microhardness, Hm, for nanophase silicon, Si-Li alloys, and conductive carbons used in composite electrodes for high-performance electrochemical batteries.

Resume : The routine access to power sources is an essential factor for developing our technology-oriented society and ensuring a better quality of life. In this context, while the implementation of renewable energy sources is in progress, electrical energy storage (EES) systems are set to play a central and potentially critical role in the next-generation energy infrastructure. Rechargeable (or secondary) batteries, which are already widely used for powering electrified vehicles and electronic devices of all kinds, appear also as particularly relevant for this future scenario. However, faced with such worldwide battery demand and beyond technical requirements in terms of capacity, energy density, cyclability, safety or cost, issues concerning the resource availability or the recyclability have also to be further addressed. A rapid overview shows that (i) chemistries currently employed are only based on inorganic elements for which some are scarce, expensive and energy greedy at the process level and (ii) none of them seems capable of satisfying our ongoing needs. Hence, it is an urgent need to accelerate progress and innovations in the development of new and potentially “greener” electrochemical storage devices. Based on the tailoring of naturally abundant chemical elements (C, H, N, O, S, in particular), organic chemistry provides great opportunities for finding innovative electrode materials able to operate in aqueous or nonaqueous electrolytes. Along this line, significant progress has been achieved these last ten years on redox-active organic compounds.1–3 Indeed, such greener and low-polluting systems were highlighted by the finding of efficient organic small-molecules and polymers that reach the performance of conventional inorganic composites, bringing them to the attention of the energy storage community.4–9 Nowadays the search of new organic materials is a burgeoning field and one of the remaining challenge relies on finding efficient insertion compounds for negative ions. Indeed, the accommodation of anionic counterions into composite materials is difficult due to their large size compared to the light metal cations (Li+, Na+, Mg+ ...). Reported examples beyond graphite intercalation compounds are rare and this lack of advanced materials for oxidative insertion (p-doping) is recently raising interest for promoting rechargeable batteries with anionic shuttle.10,11 For the first time, organic small molecules were applied as anionic insertion materials. The p-doping of these active compounds is based on the electrochemical activity of neutral amino groups that can (de)insert anion upon (dis)charging. Solvent-host features, intrinsically coming from their lamellar morphologies, were evidenced by spectroscopic, crystallographic and microscopic techniques. The (de)insertion reaction of anions were evaluated with typical battery electrolytes and showed good electrochemical performances vs lithium, with capacities > 75 mAh.g-1 at average operating voltages > 3.2 V vs Li+/Li.12 (1) Armand, M.; Grugeon, S.; Vezin, H.; Laruelle, S.; Ribière, P.; Poizot, P.; Tarascon, J.-M. Nat. Mater. 2009, 8 (2), 120–125. (2) Chen, H.; Armand, M.; Demailly, G.; Dolhem, F.; Poizot, P.; Tarascon, J.-M. ChemSusChem 2008, 1 (4), 348–355. (3) Renault, S.; Gottis, S.; Barrès, A.-L.; Courty, M.; Chauvet, O.; Dolhem, F.; Poizot, P. Energy Environ. Sci. 2013, 6 (7), 2124–2133. (4) Oyaizu, K.; Nishide, H. Adv. Mater. 2009, 21 (22), 2339–2344. (5) Poizot, P.; Dolhem, F. Energy Environ. Sci. 2011, 4 (6), 2003–2019. (6) Liang, Y.; Tao, Z.; Chen, J. Adv. Energy Mater. 2012, 2 (7), 742–769. (7) Song, Z.; Zhou, H. Energy Environ. Sci. 2013, 6 (8), 2280–2301. (8) Janoschka, T.; Hager, M. D.; Schubert, U. S. Adv. Mater. 2012, 24 (48), 6397–6409. (9) Haeupler, B.; Wild, A.; Schubert, U. S. Adv. Energy Mater. 2015, 5 (11), 1402034. (10) Aubrey, M. L.; Long, J. R. J. Am. Chem. Soc. 2015. (11) Reddy, M. A.; Fichtner, M. J. Mater. Chem. 2011, 21 (43), 17059–17062. (12) Deunf, E.; Moreau, P.; Quarez, E.; Dolhem, F.; Guyomard, D.; Poizot, P. Submitted.

Resume : From a theoretical analysis of the boundary conditions of efficient production of H2 by photoelectrochemical cells we propose buried p-i-n multijunction structures of highly absorbing thin film compound semiconductors as only (?) promising device structures. Results obtained so far with single absorber layers show that they do not provide the needed photovoltage for H2O splitting. But efficient thin film tandem or multijunction devices of suitable thin film materials with absorber layer bandgaps between 0.8 and 2.4 eV are not yet available besides very expensive 3-5 and medium efficient µc/-Si multijunction cells. Buried junction photoelectrochemical cell structures are needed to provide stable and loss free electrochemical contacts, which are based on electronically and chemically adjusted passivation layer(s) and electronically aligned co-catalysts. Because of these boundary conditions research and development of advanced thin film absorber materials for tandem and multijunction photovoltaics and efficient photoelectrochemical cells follow the same directions and are limited by the same shortcomings. Based on our past and present work on established and novel absorber materials we have identified a number of challenges for material’s development which must be addressed in future work. I will concentrate on two problems for which no easy solution is given yet as the kinetic control of nucleation and growth also at low substrate temperatures and the engineering of interface and contact properties. In most cases the bulk electronic properties of absorber materials are not of reasonable quality when the material growth is at lower sample temperature. But in these cases the morphology of the films shows the preferential morphology as flat films without detrimental pin-holes. For improving the electronic quality of the films annealing steps at elevated temperatures are applied which often lead to a detrimental restructuring of the crystallites in the film forming larger grains and pin-holes or grain boundary shunts and therefore deteriorates the conversion efficiencies. With respect to interface engineering dissimilar contacts are applied in most cases which are not appropriately adjusted in their chemical and electronic properties. As a consequence interface defects and only low built-in potentials due to the Fermi level pinning result. For electronic passivation of surface/interface states specifically engineered interfaces must be developed based on non-abrupt interdiffused or reactively adapted heterojunctions. With such multijunction solar cells based on thin film absorber materials promising research and development routes to highly competitive PV and PEC cells are given which need, however, systematic materials research strategy combining theoretical design concepts and high throughput experimental validation.

Resume : Aligned Ta3N5 nanotube (NT) photoanodes are formed by anodic oxide-tube growth on a Ta substrate, followed by a thermal conversion of the oxide to nitride in NH3. Here we introduce, prior to ammonolysis, a reductive heat treatment (in Ar/H2) to induce the controlled growth of a suboxide/subnitride (TaxNy) layer at the metal/Ta3N5-NT interface. This subnitride layer promotes electron transfer to the back contact and provides a drastic increase in solar conversion efficiency in photoelectrochemical water splitting, that is, a solar photocurrent of 4.2 mA cm-2 at 1.6 VRHE for the Ar/H2-treated Ta3N5 NTs is obtained under AM 1.5G simulated sunlight (100 mW cm-2) in 1 M KOH. Further modification with Co(OH)x co-catalyst leads to a record photocurrent of 11 mA cm-2 at 1.6 VRHE.

Resume : Oxygen reduction reaction (ORR) has been extensively studied due to its important role in energy conversion systems such as fuel cells and metal air batteries. Suntivich et al. reported that perovskite oxides could be optimized for ORR catalysis from molecular orbital principles. An M-shaped relationship between activity and the d-electron number per B cation was found. At the same time, a volcano shape plot is exhibited between the activity of oxides and the eg-filling of B ions, having a value of 1 for maximum activity. In this work, a structure-reactivity relationship is established for the oxygen reduction reaction (ORR) at carbon supported lanthanum based oxides employing rotating ring-disc electrodes. Highly phase pure LaCrO3, LaMnO3, LaFeO3, LaCoO3 and LaNiO3 nanoparticles were synthesised by an ionic liquid route, offering fine control over phase purity and composition. RRDE experimental data clearly reveal that LaMnO3 is by far the most active catalysts of the family. The nature of the active site is also discussed, concluding that the high activity of LaMnO3 is connected to changes in the redox state of the B-site close to the formal ORR potential. In order to strengthen our working hypothesis, the activity of LaxCa1-xMnO3 as a function of x is as well been studied. These results show that the onset potential for ORR decreases as x decreases. This trend is qualitatively consistent with the conclusion that Mn(III) is more active than Mn(IV). However, this issue is a lot more subtle as the extent of A-site segregation also decreases as x decreases, leading to more surface Mn sites in the case of CaMnO3, consistent with the larger voltammetric features and confirmed by quantitative XPS analysis.

Resume : CO2 is a source for the production of carbon based fuels, such as methanol, and presents an attractive alternative to fossil fuels. Copper is an ideal catalyst for the reduction of CO2, as it is able to direct reactions through stable intermediates, e.g. CO. An important question concerns the influence of oxygen on the catalytic activity and whether oxides are formed on the surface. As this system is an excellent material for the reduction of CO2 a detailed understanding of the basis of its catalytic activity is essential and absolutely necessary for any further development. X-ray photoelectron spectroscopy (XPS) is used widely in the solid-state sciences but due to its nature as an ultra high vacuum technique (pressure 10-9 mbar) it is not possible to study gas-solid interfaces. High-pressure XPS (HPXPS) is an advanced method which allows the measurement of solid samples at elevated pressures of between 1 and 30 mbar. This work presents results on the interaction of CO2 and CO2/O2 with the surface of polycrystalline Cu followed by HPXPS. Cu2p core levels, as well as the Cu Auger lines are used to investigate the state of the Cu surfaces. The C1s and O1s core levels are used to track the interaction between CO2/O2 and Cu and are compared to CO2/O2 gas phase measurements. Ultimately, the presented results provide a starting point for the detailed understanding of these catalysts and lead to the identification of possible ways to further improve and develop their properties.

Resume : The ability to electrolyze water into its elements in benign conditions at low cost will imply the exclusive use of cheap, abundantly available materials, instead of most advanced catalysts. Here, we demonstrate that iron oxide, the most abundant and least expensive transition metal compound, can be used as a catalytically active surface for the four-electron water oxidation to O2 at neutral pH which represents the kinetic bottleneck of the overall reaction. The geometric effects of nanostructuring a pure Fe2O3 surface on its electrochemical water oxidation performance were systematically explored. Atomic layer deposition was used to coat the inner walls of cylindrical “anodic” nanopores ordered in parallel arrays with a homogeneous Fe2O3 layer. The chemical nature of our iron oxide electrode surface was investigated by means of Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Combining electrochemical treatments and annealings with the “anodic” pore geometry can deliver an effective turnover increase by two to three orders of magnitude with respect to a smooth, planar Fe2O3 surface. However, the current density depended on the pore length in a non-monotonic manner. An optimal length was found that maximized turnover by equating the rate of transport in the electrolyte with that of charge transfer across the interface. Further optimization of the catalyst performance was achieved by bulk and surface doping of iron oxide.

Resume : Antimony-doped tin dioxide (ATO) is considered a promising support material for Pt-based fuel cell cathodes, displaying enhanced stability over carbon-based supports. In this work, the effect of Sb segregation on the conductance and catalytic activity at Pt/ATO interface was investigated through a combined computational and experimental study. It was found that Sb-dopant atoms prefer to segregate toward the ATO/Pt interface. The deposited Pt catalysts, interestingly, not only promote Sb segregation, but also suppress the occurrence of Sb3+ species, a charge carrier neutralizer at the interface. The conductivity of ATO was found to increase, to a magnitude close to that of activated carbon, with an increment of Sb concentration before reaching a saturation point around 10%, and then decrease, indicating that Sb enrichment at the ATO surface may not always favor an increment of the electric current. In addition, the calculation results show that the presence of Sb dopants in ATO has little effect on the catalytic activity of deposited three-layer Pt toward the oxygen reduction reaction, although subsequent alloying of Pt and Sb could lower the corresponding catalytic activity. These findings help to support future applications of ATO/Pt-based materials as possible cathodes for proton exchange membrane fuel cell applications with enhanced durability under practical applications.

Resume : Bimetallic nanoparticles have emerged as the new, leading edge of heterogeneous catalysts by enabling the combination of multiple materials in different compositions and arrangements to achieve both enhanced and selective catalytic performance. Three dimensional nanoparticles offer an exciting opportunity for bimetallic nanocatalysts; unlike two dimensional nanoparticles that lie flat on a substrate, the faceted surface features can be readily accessed by protruding outwards from a catalyst support. In this work, we present the synthesis and characterisation of three dimensional Pd-Ru and Au-Ru core-branched nanostructures with highly faceted surface features. The key to the formation of these novel structure is a three stage growth mechanism, which will be critical to the development of the next generation of complex nanostructures for oxygen evolution reaction electrocatalysis.

Resume : Complex binary hydrides involving light metals (e.g Li, Mg, Ca etc.) have been extensively studied as possible hydrogen storage materials because of their high gravimetric storage capacity. In particular, lithium nitride/imide/amide have been found to exhibit strong affinity for hydrogen. Unfortunately, though these materials can store sufficiently high amount of hydrogen, the desorption kinetics is poor for its on-board practical application. Making nano-structures of such materials ease the hydrogen release from the system. However, quest for designing new materials demands the accurate description of all their (meta)-stable structures under operational conditions. Unfortunately, not a single theoretical work (till date) related to designing hydrogen storage materials has addressed the challenging problem of the (meta)-stability of the materials under operational conditions. We find[1] from hybrid density functional theory and ab initio atomistic thermodynamics that the behavior of small LixNy clusters are very different than their bulk. Most importantly, while in bulk lithium nitride, the Li-rich phase [i.e. Li3N] is the stable stoichiometry; in small LixNy clusters, N-rich phases are more stable at thermodynamic equilibrium. Finally we find that these N-rich clusters are promising hydrogen storage material because of their easy adsorption and desorption ability at respectively low (≤ 300K) and moderately high temperature (≥ 600K). [1]A. Bhattacharya, S. Bhattacharya J. Phys. Chem. Lett. 6, 3726 (2015).

Resume : Solid state solar cells, derived from ETA cells are well known and represent a Vis-active heterostructures with at least one n-p hetero-junction. Most of these heterostructures involve TiO2 (as n-type window layer, with high chemical stability) and a p-type material, mainly a chalcogenide (as Vis-absorber). Following this concept the paper proposes the design principles of a Vis-active photocatalyst, for advanced oxidation processes, aiming at efficient wastewater treatment, targeting re-use. Basically, the heteorstructure should be a photovoltaic assembly with additional design pre-requisites: high stability in the working environment, high photo-corrosion resistance, etc. As case-studies, two heterostructures are analysed: TiO2/CIS and CIS/SnO2/TiO2; the heterostructures were deposited via spray pyrolysis and the optimised multilayers were characterised considering typical photovoltaic properties (I-V curves, photo-current) and typical photocatalytic properties in methylene blue removal, selected as standard pollutant (Total Organic Carbon and Total Nitrogen removal efficiencies). Correlations between these two groups of properties allows a reliable design of Vis-active photocatalysts, with high mineralization efficiencies in optimised conditions (92% of TOC removal). Additional, the effect of electrolyte addition (supporting the current flow in the local micro-electrochemical cells) is analysed by adding various amounts of NaCl (0.5….8%) in the aqueous pollutant system.

Resume : The preparation of nanostructured iridium oxide electrodes for the electrochemical oxygen evolution from water is explored. Due to its good electric conductivity and high catalytic activity, iridium oxide is used as active surface for the four-electron water oxidation to oxygen, which represents the kinetic bottleneck of the splitting of water. The use of anodic aluminum oxide templates, which are created according the usual two-step anodization procedure, lead to a well-defined and tunable geometry of electrodes. The coating of the inner walls of the cylindrical and parallel nanopores with iridium oxide catalyst is performed by atomic layer deposition from (1,3-cyclohexadiene)(ethylencyclopentadienyl)iridum and ozone, whereas the mechanism of the reaction can be monitored in situ by a piezoelectric crystal microbalance. The morphology of the generated nanostructured electrodes is characterized by scanning electron microscopy and helium ion microscopy and its elemental composition is confirmed by energy-dispersive X-ray spectroscopic analysis. The electrochemical characterization in acidic media is performed by cyclic voltammetry, bulk electrolysis and electrochemical impedance spectroscopy. This preparative method allows for a systematic tuning of the electrode’s geometric surface area by variation of the nanopores’ diameter and length. The electrocatalytic current densities vary accordingly.

Resume : Fuel cells can provide clean energy from hydrogen fuel and air. The main challenges for further improvement of the efficiency of polymer electrolyte membrane fuel cells are the activity and stability of the catalysts, typically Pt, used for the oxygen reduction reaction. Experiments on polycrystals and cluster-deposited nanoparticles have shown that Pt alloyed with rare earth (RE) metals has about 5 times improved specific activity compared to pure Pt, due to the formation of a strained Pt overlayer which changes the binding energies to the reactants. We have developed a generic method for single target co-sputtering of PtRE alloys. The method enables efficient fabrication of thin films with varying compositions and thicknesses down to few nanometers, while being compatible with mass-fabrication. To validate our approach we have measured the ORR-activities of PtY thin films with different thicknesses and compositions, which we found to be similar to the specific activities of polycrystals and to the mass activities of nanoparticles of the same alloy material. Characterization by XPS and EDX, before and after ORR-measurements, has confirmed the formation of a Pt-overlayer on the alloy thin films.

Resume : ABSTRACT: The production of hydrogen from abundant seawater is among the approaches being considered to better utilize renewable energy (e.g., solar and wind). The potential of “hydrogen economy” as the 21st century energy source target has made the search for viable alternatives to platinum (Pt) electrocatalyst an important area of research and development. The high cost of platinum and its instability in the electrochemical power systems for hydrogen generation are still predominant challenges [1-3]. Thus, the success would be consequent upon developing cost effective, stable and highly active Pt-free electrocatalysts. In this regard, a series of nanostructured catalysts based on cobalt-doped molybdenum carbide (Co-MoC) supported on carbon has been developed for electrolytic hydrogen evolution reaction (HER) from brine. The catalysts were synthesized by simple impregnation of metal salts on carbon support and followed by pyrolysis in CH4 atmosphere. The obtained catalysts showed impressive HER activities in both brine and alkaline media. The overpotential for these developed Co-MoC/C catalyst series was close to that of a commercial Pt/C catalyst, ranging from 63 to 89 mV and 15 to 148 mV in brine and alkaline solutions respectively. Such results for HER on Pt-free based materials seems to be very interesting, especially in brine media. Results reveal electrochemical desorption following the Volmer-Heyrovsky mechanism as the rate determining step. The superior HER activities of Co-MoC/C catalysts will be presented and discussed in details taking in consideration their properties, such as mesopore surface areas, composition, nanocrystallites, and low charge transfer resistances as confirmed by electrochemical impedance technique. KEYWORDS: electrocatalyst, hydrogen evolution reaction, brine water, molybdenum carbide, sustainable fuel REFERENCE: [1] Harnisch, F.; Sievers, G.; Schrӧder, U. Tungsten Carbide as Electrocatalyst for the Hydrogen Evolution Reaction in pH Neutral Electrolyte Solutions, Appl. Catal. B. Environ. 2009, 89, 455–458. [2] Wang, M.; Sun, L. Hydrogen Production by Noble-Metal-Free Molecular Catalysts and Related Nanomaterials, ChemSusChem. 2010, 3, 551–554. [3] Han, A.; Jin, S.; Chen, H.; Ji, H.; Sun, Z.; Du, P. A Robust Hydrogen Evolution Catalyst Based on Crystalline Nickel Phosphide Nanoflakes on Three Dimensional Graphene/Nickel Foam: High Performance for Electrocatalytic Hydrogen Production from pH 0–14, J. Mater. Chem. A. 2015, 3, 1941–1946.

Resume : Various bio-sensing systems have been suggested to be an efficient tool to investigate optical interactions and manipulating electromagnetic fields spatially distributed in the vicinity of an interface between a conductor and a dielectric. However, electromagnetic fields associated to surface-plasmons (SPs), resonant phenomena, have been analyzed both theoretically and numerically considering real dielectric gaps (with or without a periodic modulation) stacked between metallic films. Thus, properties of SPs have been controlled by the change of the metal film thickness and refractive index of a dielectric which is assumed to be the sensing medium. In the present work, we suggest a new tunable plasmonic cavity, consisting of a transparent conductor, i.e. indium tin oxide (ITO) embedded between two left-handed materials (LHMs) that exhibits high confinement energy of surface plasmon resonance (SPR) when geometric parameters are properly optimized. Here, each of the later LHMs is simulated by its complex permittivity and magnetic permeability expressed in a dependent-wavelength. Using the electromagnetic theory based on transfer matrix-method to express interface’s response, we carried out detailed analysis to design high performance of the nano-cavity by exploiting the advantage of the absorption effect of ITO gap. In addition, the performance of the designing SP sensor has been quantified in terms of sensitivity and detection accuracy. Finally, taking the sensing medium as glucose solution, in a spectral TM reflectance-mode, potential applications recognized to the designed sensor are discussed. Keywords: Imaging Sensor, Left-handed Materials, Dielectric Gap, Surface Plasmon Resonance, Performance Parameters, TM Reflectance-Mode

Resume : Pure and chromium doped titanium dioxide (TiO2) thin films at different atomic percentages (0.5 %, 1.3 % and 2.9 %) have been elaborated on ITO/Glass substrates by sol-gel and spin-coating methods using titanium (IV) isopropoxide as a precursor. The surface morphology of films was investigated by scanning electron microscopy (SEM), the structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission microscopy (HRTEM). SEM and HRTEM show homogenous and polycrystalline films. XRD patterns indicate a phase transition from anatase to anatase-rutile leading to expand the absorption band of TiO2 molecules around 520 cm-1 in FTIR spectra. The optical constants such as the refractive index (n), the extinction coefficient (K) and the band gap (Eg) as well as the film thickness are determined using spectroscopic ellipsometry technique and Fourouhi-Blommer dispersion model. Results show three major changes; i) the thickness of pure TiO2 layer is 54 nm, which linearly decreases when the layer is doped with chromium and reaches 33 nm for a doping concentration of 2.9 %, ii) the band gap energy (Eg) is also linearly reduced from 3.24 eV to 2.79 eV when the Cr-doping agent increases, and, iii) a phase transition from anatase to anatase-rutile is observed causing an increase in values of n() for wavelength greater than 350 nm.

Resume : We report a novel strategy to generate surface wrinkles with dimensions ranging from sub-micron to micron length-scales formed as a result of spontaneous buckling of an ultra-thin metal film thermally deposited on a viscoelastic polymer layer which forms due to significant mismatch in the thermal and mechanical properties of the constituent layers. We explore the dependence of the buckle morphology on the extent of viscous characteristics of the polymer layer, which is largely uninvestigated. Significant variation in the dimensions of the buckles has been achieved by varying the viscoelasticity of the polymer on tailoring the duration of thermal pre-curing of PDMS, a well-studied viscoelastic polymer whereby the buckles formed has a higher wavelength and amplitude in case of PDMS with greater viscous nature. Partial loss of the accumulated stress due to viscous dissipation results in a lower effective stress responsible for buckling which leads to the observed morphology. The relative magnitude of the stress loss depends on the viscoelasticity of the PDMS layer. This approach serves as a facile technique to fabricate multi-length scale surface structures having tremendous potential in enhancement of light harvesting efficiency in optical devices due to increased internal light scattering from the buckled metal surface when used as an electrode, amplifying the light absorption in those regions of the solar spectrum which otherwise shows minimal light absorption.

Resume : We report core-shell quantum dot (QDs) structures synthesized of ZnO-nanocarbon using a simple chemical method. The outer nanocarbon shell was analysed by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectra. The stable oxygen bridge bonds between the ZnO core QDs and the oxygen-related functional groups on the nanocarbon shell facilitated the efficient photoinduced charge separation of the core@shell QDs structure. The quenching ratio and Föster resonance energy transfer efficiency were significantly increased due to the conjugation of nanocarbon, as confirmed by photoluminescence (PL) and time-resolved photoluminescence measurements (TRPL). The efficient electron transfer between the ZnO core and the nanocarbon shell resulted in the improvement of the photocatalytic activity and the photoelectrochemical response.

Resume : Day to day increase in demand of energy increasing because of continuous increase in population and most of the population is dependent on fossil fuel. Since regular uses of these fossil fuels are getting deteriorating it and creating environmental issues. To solve these scarcity of energy and to overcome these environmental issues, the energy storage and generation devices with eco-friendly nature are getting an ample attention from researchers. In order to these energy devices, fuel cell, supercapacitor, Zinc-air batteries might be one of the most eligible candidate. But to make these devices, an efficient and low cost catalysts needed so that devices fabricated with these low cost materials can be easily promoted. The multifunctional materials which can be used for oxygen reduction (ORR) and evolution reaction (OER) and supercapacitors are very crucial for the energy generation from fuel cells, supercapacitor, water splitting and rechargeable zinc-air batteries.1 In case of bifunctional electrocatalyst for ORR and OER, the sluggish kinetics and stability of the catalysts are main technical barrier for the development and commercialization of those fuel cell and zinc-air battery technologies. So far, platinum and its derivatives with other non-noble transition metal are the best catalyst towards ORR and RuO2, IrO2 are state-of-the-art catalysts for OER. However, high cost and rare earth availability of these elements are hampering its extensive and large scale application. Therefore, an extensive research is being done by the researchers to develop highly efficient, low cost, and earth-abundant catalysts for both ORR and OER, to overcome the issues of high cost and low performance of conventional noble metal catalysts. There are many ways to develop these catalysts but a major attention of research and development is towards transition metals supported on highly conducting carbon (graphene, CNT, CNF and CNHs) due to their excellent electrocatalytic activity. Particularly non-noble transition metal supported on nitrogen doped carbon species i.e. metal@N-carbon exhibits prominent electrocatalytic activity towards ORR and OER. However, the synthesis of these catalysts at large scale is very difficult and it involves higher energy consumption which greatly limits their practical applications.2 Here in this report we have synthesized Co3O4 supported nitrogen doped graphene (NGr) catalysts by using very simple and scalable hydrothermal method. The synthesized catalysts are supported with three types of morphologies of Co3O4 (cubic, blunt edged cubes, spherical). Among these synthesized catalysts spherical Co3O4 supported catalyst have shown good activity towards ORR. Moreover, The catalyst supported with blunt edged Co3O4 nanocubes have shown excellent activity towards OER because of exposure of low surface energy (111) planes.3 The synthesized blunt edged Co3O4 nanoparticles supported on NGr (Co3O4-BC/NGr-12h) catalyst is showing overpotential of 280 mV @ 10 mAcm-2 current density in 1M KOH solution. Moreover spherical structured Co3O4 supported on NGr (Co3O4-SP/NGr-24h) hybrid exhibited better oxygen reduction activity (onset potential: 0.03 V (vs. Hg/HgO) with improved stability even after 5000 potential cycles, in a 0.1M KOH.4 Finally, to show the real application of the prepared catalyst, we have fabricated the zinc-air battery device with the ORR active material using as a cathode. References: 1. Liang, H.-W.; Zhuang, X.; Brüller, S.; Feng, X.; Müllen, K. Nat Commun 2014, 5, 1-7. 2. Zhang, J.; Zhao, Z.; Xia, Z.; Dai, L. Nat. Nano 2015, DOI: 10.1038/NNANO.2015.48. 3. Singh, S. K.; Dhavale, V. M.; Kurungot, S. ACS Appl. Mater. Inter. 2014, 7, 442. 4. Singh, S. K.; Dhavale, V. M.; Kurungot, S. ACS Appl. Mater. Interfaces, 2015, 7, 21138.

Resume : Goal of the present research is investigation of photoelectric and photomagnetic response of ITO (indium tin oxide) films under the UV laser irradiation. The ITO films were prepared by magnetron sputtering. Thickness of the ITO films was 300nm. Films were irradiated by UV laser light with 248 nm wavelength in laser pulse energy range from 10 mJ to 150 mJ using KrF excimer laser. Metallic electrodes were deposited on the films. Information about the topography was obtained using atomic force microscopy and scanning electron microscopy. Structure of the films was investigated by X-ray diffraction. It was shown that under the UV light the voltage appears between metallic contacts. The electric current was observed through resistive load. For the first time the anisotropy of photoelectric response electric field was observed. The appearance of magnetic field under the laser light irradiation was observed for the first time. The dependence of the voltage on the laser pulse energy was linear in whole measured energy range. For the description of the observed phenomenon the following physical was offered: electric voltage could be associated with non-uniform distribution of the average crystallite size along the film surface, and therefore mean free path of the charge carriers. Photomagnetic response could be associated with collective behavior of large number of charged particles, created due to high intensity laser irradiation. Investigated phenomenon could be used for creation of new optoelectronic devices, for e.g. modulators, optical detectors etc. Particularly, due to linear dependence of photoelectric response on the laser pulse energy, this phenomenon is attractive for manufacturing of simple and cheap excimer laser pulse energy detectors.

Resume : Hydrogen is a promising energy carrier, compatible with the sustainable energy concept. In this context, solid-state hydrogen-storage is the key challenge in developing hydrogen economy. The capability of absorption of large quantities of hydrogen makes intermetallic systems of particular interest. In this report, efforts have been devoted to the theoretical investigation of palladium-arsenic system. Beside hydrogen-storage considerations, a reinvestigation of cristal structures of this system was advisable. This binary system has been studied by an ab initio evolutionary algorithm for structure prediction and results are in good agreement with experimental data. On the compounds under consideration, particular attention has been paid to AsPd5 alloy, for which experience results were avalaible. Again, our calculations are in excellent concordance, demonstrating the efficience of evolutionary algorithm methods within the first-principles framework of density functional theory (DFT). A similar structure predicition has been performed to find possible hydrides. This analyse revealed one hypothetic stable hydride, experimentally unknown. We then aimed to provide explanation for this divergence and found clarification by considering the steps of hydride formation. Focus is finally made on investigation of hydrogen induced modifications to the structural and electronic properties of AsPd5.

Resume : High temperature Solid Oxide Fuel Cell (SOFC) is the most efficient and environmentally friendly energy conversion element used for generating electricity from an electrochemical reaction. The basis cell is a stack composed of a porous anode, a dense electrolyte, a porous cathode and interconnection. Typical operating temperature for SOFC are 800°C-1000°C, which generally leads to the material damage and decrease of the fuel cell lifetime by long-term operating mode. Therefore research trends to develop intermediate temperature SOFC (IT-SOFC) for lowering operating temperatures, typically from 600°C-800°C. But at these lower temperatures, the problems are the electrical efficiency decreases and ohmic loss increases. In order to compensate these problems, the research trends towards materials with better electrochemical properties or by changing the microstructure of the cathode to improve mass transfer and charge transfer. The cathode is a very important layer in the SOFC stack since it displays polarization resistance whose reduction makes quite an important challenge to be addressed. Strontium-doped Lanthanum Manganite (LSM) perovskite oxides possess many interesting properties such as good electronic conductivity, electro-catalytical activity, colossal magneto-resistivity and large magnetic moment. LSM has been extensively used as cathode material for high temperature SOFC. LSM presents several advantages such as good compatibility with along with high thermal and chemical stability. However, LSM-based cathode exhibits poor ionic conductivity and cathode polarization resistance dominates at intermediate temperature (<800°C). It is difficult to improve LSM cathode performance because in this type of material, electrochemical reaction occurs mainly at triple phase boundary where electrolyte, electrode and gas are in close contact. The microstructure of the cathode might play an important role in the performance of SOFC cathode, improving oxygen reduction that might, in turn, be related to grain size, tortuosity and porosity. In this study, we exploit LSM magnetic properties through application of a magnetic field that aligns LSM grains along the cross-section direction resulting in decrease of cathode polarization resistance. The magnetic field is applied during the drying process after deposition over a Gadolinium-doped Ceria (GDC) electrolyte. The microstructure of the LSM is analysed by scanning electron microscopy. The magnetic field produces without any ambiguity an important microstructure change. The performance of LSM cathode is investigated over a [700°C-800°C] temperature range by impedance spectroscopy. The measured electrode area specific resistance (ASR) of a LSM/GDC/LSM symmetric half-cell without and with magnetic field is 0.30 Ωcm² and 0.20 Ω.cm² respectively at 800°C. The ASR value has decreased by 33% after magnetic field application. This behaviour can be attributed to LSM grain reorientation, microstructure change and tortuosity of LSM cathode. The magnetic field effect has been further investigated with a composite cathode that displayed very promising results.

Resume : The introduction of metal has been demonstrated as efficient strategy to enhance the charge separation of semiconductor and thereby improve the photocatalytic activity. On the other hand, extensive focuses has been placed on the use of yolk@shell nanocrystals in catalysis applications. The unique structural features of interior, confined voids provide yolk-shell nanocrystals with homogeneous environment for reactant molecules, which is particularly favorable for catalytic reactions. Here we demonstrated the use of Au@Cu2Se yolk-shell nanocrystals as the photocathode for efficient photoelectrochemical water splitting. The samples were prepared by using Au@Cu2O core@shell nanocrystals as the growth template. The growth of yolk@shell nanocrystals was achieved by performing the selenization treatment on Au@Cu2O. Due to the higher diffusion rate of Cu2+ compared to Se2-, abundant voids would be generated inside the structure, leading to the formation of yolk@shell structures. To demonstrate the practical use of yolk@shell nanocrystals, the samples were employed as the photoelectrode in photoelectrochemical water splitting. The results showed that Au@Cu2Se yolk-shell nanocrystals exhibited substantially higher photocurrent of water reduction (-35µA/cm2) than the other counterpart samples such as pure Cu2O (-16µA/cm2), pure Cu2Se (-24µA/cm2) and Au@Cu2O (-26µA/cm2). This superiority was attributed to the pronounced charge separation caused by Au introduction as well as the homogeneous reaction environment rendered by the yolk@shell structures.

Resume : Ag is a promising candidate as an indispensable catalysts in alkaline medium due to its unique capability to resist against the corrosive environment and to enhance the ORR activity. Here, we have demonstrated shape-controlled synthesis of Ag catalysts by tailoring the reduction kinetics with adjusted electron densities in plasma. With low electron density of 7.11022 m-3, the Ag nanowires with the corrugated structure induced by twinning and stacking faults formation were observed along the entire longitudinal <111> direction of nanowires. Whereas, with high electron density of 13.71022 m-3, the Ag dendrites constructed via the coalescence between Ag nanoparticles could be obtained. These different kinetically-controlled growth behaviors were essential for achieving the shape transition between the nanowires and dendrites. From the linear sweep voltammetry, the Ag nanowires exhibited the highest kinetic current density with a value of 17.2 mA cm-2, and the electron transfer number was calculated to be 3.54, which is the indicative of a four-electron ORR pathway. This improvement in ORR activity could be mainly attributed to the lattice strain, derived from defective structures.

Resume : Nitrogen-doped onion-like carbon was synthesized using an arc discharge in a liquid phase in the presence of different ammonia concentrations. The nitrogen-doped onion-like carbon was investigated as a catalyst support material for a catalytic oxygen reduction reaction. With increasing ammonia concentrations up to 5 M, the nitrogen doping degree increased to 1.7 at.%, which created a highly defective onion-like structure. The edge and defective sites induced from nitrogen atoms effectively facilitated the nucleation of Pt clusters, which led to the stable dispersion and small size of Pt nanoparticles, as revealed via X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy and electron microscopy. From the results of the electrochemical characterization, the Pt nanoparticles supported on the nitrogen-doped onion-like carbon with a nitrogen content of 1.7 at.% exhibited the highest electrochemically active surface area, specific current density and half-wave potential. The enhanced oxygen reduction could be ascribed to the defective outermost layers and the electronic modification. Moreover, even after an accelerated durability test with 5,000 cycles, the nitrogen-doped onion-like carbon with a nitrogen of 1.7 at.% exhibited less degradation, indicating the excellent durability.

Resume : In this work, a more accurate, reliable method was proposed to evaluate the photoelectrochemical performance of semiconductor electrode toward water splitting. Conventionally, chronoamperometric measurements are conducted at a relatively fixed bias, e.g. 0 V vs. reference electrode, to monitor the photocurrent generation, which has been regarded as a direct index for performance comparison among different electrodes. Considering that the open-circuit potential of the cell varies from electrode to electrode, the direct photocurrent comparison at a relatively fixed bias may misrepresent the actual difference among samples. Here we studied the photoelectrochemical properties of the samples by applying two distinct external bias values, one at 0 V vs. Ag/AgCl deriving from the conventional practice and the other at 0.1 V vs. open-circuit potential representing the exactly fixed potential applied. Three experimental groups were designed to address the arguments, which included the influence of heat treatment for ZnO nanowire arrays, the quantitative effect of Au for Au nanoparticle-decorated ZnO nanowires and the global comparison between ZnO and TiO2 nanowires electrodes. Different trends in photocurrent generation were observed at the two distinct biases, with the results from 0.1 V vs. open-circuit potential being in conformity with the general considerations. The demonstrations from this work suggested that applying an exactly fixed potential from the open-circuit potential shall provide a more fair ground for accurate photoelectrochemical performance evaluation without under- or over-estimation.

Resume : The design of active and stable semiconducting composites with enhanced photoresponse from visible light to near infrared (NIR) is a key to improve solar energy harvesting for photolysis of water in photoelectrochemical cell or photocatalytic reaction. In this study, we prepared earth abundant semiconducting composites consisting of iron pyrite and Titanium oxide as a photoanode and photocatalyst for hydrogen evolution reaction. The detailed structure and atomic compositions of FeS2/TiO2 photoanode was characterized by high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), inductively coupled plasma with atomic emission spectroscopy (ICPAES) and Raman spectroscopy. Through the proper sulfurization treatment, the FeS2/TiO2 photoanode exhibited high photoresponse from visible light extended to near infrared range (900 nm) as well as stable durability test for 4 hours. We found that the critical factors to enhance the photoresponse are on the elimination of surface defect of FeS2 and on the enhancement of interface charge transfer between FeS2 and TiO2. Our overall results open a route for the design of sulfur-based binary compounds for photoelectrochemical applications.

Resume : Hydrogen produced by electrolysis is one of the promising means by which to store electricity coming from renewables and to address its intermittency. With the growing global electricity share from renewable energy sources, large-scale storage systems are required. Alkaline electrolysis can be a sustainable solution for the large-scale energy storage system. However, high overpotential and slow kinetics particularly of the oxygen evolution reaction (OER) still remains as a hurdle to limit efficiency of the system. To enhance efficiency of alkaline electrolysis cells, catalysts which have high electrocatalytic activity for OER should be developed. Platinum-like behavior of Tungsten carbide in surface catalysis was first reported by Levy and Boudart in 1973. In addition, tungsten carbide was reported to have Pt-like electronic structure by Colton in 1975. After that, tungsten carbide has been studied widely and expected to substitute noble metal catalysts which are used in many electrochemical reactions. Here, we studied tungsten carbide as a support for 3d-transition metals and make bi-metallic surfaces for developing a high activity OER catalyst. First, WC-Co was synthesized by heat treatment. Carbon nitride (g-C3N4) and tungsten chloride were used as a carbide precursor and cobalt acetate was also used for helping carbonization of tungsten. After heat treatment, acidic leaching process was followed to eliminate cobalt. Through additional mixing with Nickel precursor and heat treatment, Ni/WC was synthesized and to compare electrocatalytic activity Ni/C was also prepared. In addition, many different Ni/WC which have different Ni to WC ratios were synthesized and measured in electrochemical way. Finally, the optimal ratio was determined and it show better electrocatalytic activity than precious catalysts and any other non-noble catalysts. Cyclic voltammetry was measured to evaluate OER activity in 1 M KOH in potential range from 1 to 1.8 V. Pure WC and Ni/C have 394 mV and 413 mV overpotentials at 10 mA∙cm-2 respectively. In Metal/WC cases, Cobalt/WC shows only 417 mV. But Nickel/WC shows 340 mV overpotential at 10 mA∙cm-2 and higher electrocatalytic activity for OER than RuO2 in alkaline media.

Resume : Organic photovoltaics (OPVs) have attracted remarkable interest during the last decade because of their potential for low cost, printability and flexibility. Recent research has led to the report of power conversion efficiency (PCE) of over 10%. Nearly all reports involving OPV are based on a glass or polymeric substrate. However, for integration into building structures and exploitation by the building industry, other substrates need to be considered. Steel is one of the most suitable substrate materials for PVs, because their mechanical flexibility, robustness, thermal and chemical stability and excellent barrier properties against environmental factors. Several publications have analysed the OPV performance in which steel is used as back contact layer; however for industrial scale up, the substrate will need to be electrically isolated from the solar cell and therefore a dielectric barrier layer covering the steel surface is mandatory. This layer must exhibit multiple properties; firstly it must electrically isolate the steel substrate from the solar cell; secondly, it must planarise the surface to avoid pinholes and shunts; and finally it must avoid impurity diffusion from the steel substrate into the semiconductor layers. Herein we study the performance of OPV technology built on stainless steel coated with different barrier layers. This reports the first OPV fabricated onto a planarised steel substrate. In addition, the key performance parameters of an OPV are correlated with the variation in substrate/barrier layer properties. Additionally, the barrier layers proposed in this work will add certain optical functionalities to enhance the performance of the finished solar cell device.

Resume : Thermochromic materials change their transparency upon heating. The most studied thermochromic material is VO2, which undergoes a semiconductor to metal transition at a critical transition temperature Tc of 68oC. Below Tc VO2 is a semiconductor having a monoclinic structure and high IR transmittance, while above Tc it turns to metal with a rutile structure and high IR reflectance. In this work, VO2 thermochromic films were produced by rf sputtering technique using vanadium metal target. The O2 content in Ar/O2 plasma was 1 - 3%, while substrate temperature was 300oC. Film thickness was ranging 40 - 300nm. Three different types of glasses were used as substrate that is fused silica, Pilkington Float Glass and flexible Corning® Willow® glass with thickness 1mm, 4mm and 0.2mm, respectively. Thermochromic properties of films were identified measuring their transmittance at temperature well below and well above Tc. According this, variation of IR transmittance ΔTr, luminous transmittance Tlum, Tc and width of transmittance hysteresis loop ΔT can be calculated. Thermochromic properties were also verified by T-dependant micro-Raman technique. In as far as Pilkington Float Glass substrate is concerned, it was observed that only films with thickness below 50nm were thermochromic, having Tc=46oC, ΔT=9oC, ΔTr=15% and Tlum=46%, while films with thickness more than 100nm turned to thermochromic only after ex-situ annealing. In contrast, films deposited on fused silica glass were thermochromic, independent of their thickness, having Tc lower than 40oC and ΔT lower than 10oC. Finally, thermochromic VO2 films were deposited on flexible glass, for first time, having Tc=51oC, ΔΤ=12οC, ΔTr=36% and Tlum=40%.

Resume : The current technologies used in low temperature electrolysers and fuel cells rely on PGMs (platinum group metals) as catalysts in order to catalyse the reactions occurring in these devices. These materials are critical raw materials (CRMs) due to their low earth abundance and limited supply availability. Hence there is a critical need to avoid an increasing dependence on PGMs in the future. We aim to develop a cheap, stable and supported high surface area metal phosphide (MP) catalyst from readily-available, non-precious transition metals, via a facile synthesis method, to replace PGMs. Besides lower cost, alloying transition metals with phosphides has the advantages of increasing the stability and corrosion resistance of the pure transition metal [1]. In this work, solid-state microwave and high temperature pyrolysis methods were employed for the facile synthesis of supported MP catalysts via systematically varied phosphate anion-to-carbon (x(PO4)y/ zC) ratios. The electrochemical stability and catalytic activities of the MP catalyst obtained were analysed by testing in both alkaline and acidic solutions, using a rotating disc electrode and a PEMFC fuel cell test station. Physical characterisation was performed using XRD, TEM, SEM and XRF. The results obtained from using different transition metals, phosphate anion-to-carbon ratios and synthesis methods were correlated with the physical characteristics of the MP catalysts and their catalytic activities, to gain an insight into their catalytic performance. Reference: A. Alexander and J. S. J. Hargreaves, Chem. Soc. Rev., 2010, 39, 4388-4401 (DOI: 10.1039/b916787k).

Resume : Understanding the adsorption and desorption energetics of atoms and molecules on surfaces and the chemical reactions between them during catalytic processes is important for the development of new and more effective catalysis. Presently, the importance of oxygen exchange materials (e.g. CeO2, perovskites) for thermochemical splitting of H2O is in focus. In the present study, the effect of Nd3+ on the water adsorption and surface energetics of CeO2 was investigated. Nanoscale Nd doped CeO2 powders have been synthesized by a surfactant-based method. The as synthesized nano powders were found to be homogeneous solid solutions with a fluorite structure, where the lattice parameters increase linearly with Nd content. The water adsorption enthalpy and coverage found to increases with the dopant level, which imply increasing in the surface enthalpies and production of hydrogen. Interestingly, the measured surface enthalpies via differential scanning calorimetric method found to decrease with Nd content, and the grain size after coarsening decreased as well. The reasons for this behavior will be discussed.

Resume : Utilization of nanostructures on photovoltaic devices can significantly improve device energy conversion efficiency by enhancing device light harvesting capability as well as carrier collection efficiency. However, improvements in device mechanical robustness and reliability, particularly for flexible devices, have rarely been reported with in-depth understanding. In this work, we have fabricated high efficiency and flexible organometallic perovskite solar cells on plastic substrates with inverted nanocone (i-cone) structures. Compared with the reference cell that was fabricated on a flat substrate, it was shown that device power conversion efficiency could be improved by 37%, and reached up to 11.29% on i-cone substrates. More interestingly, it was discovered that the performance of an i-cone device remained more than 90% of the initial value even after 200 mechanical bending cycles, which is remarkably better than for the flat reference device, which degraded down to only 60% in the same test. Our experiments, coupled with mechanical simulation, demonstrated that a nanostructured template can greatly help to relax stress and strain upon device bending, which suppresses crack nucleation in different layers of a perovskite solar cell. This essentially leads to much improved device reliability and robustness and will have significant impact on practical applications.

Resume : Abstract Coal contributed 43% of CO2 emission, oil is responsible for 36% and natural gas is 20%, hence natural gas considered as potential fossil fuel as future source of energy. It has potential to produce an enormous amount of heat of combustion around 50.0MJ/kg with 44.5MJ/kg gasoline. Natural gas mainly contained methane but also involving carbon dioxide which affect the heating value and causing pipeline and equipment corrosion. Thus, in order to optimise the quality of natural gas, capture carbon dioxide is very important. This project is to use UiO-66 metal-organic- frameworks (MOFs) by adding amine groups inside the MOF pores to modulate the behaviour of MOFs , in order to separate the carbon dioxide from methane.

Resume : CsPbX3 (X=Cl, Br, I) perovskite quantum dots (PQDs) are synthesized via a novel halide precursor allowing solely carboxylic acid capped dots. The PQDs show enhanced surface stability against degradation with successive purification steps. Here we will demonstrate the application of CsPbX3 PQDs in light emitting diodes and hybrid (polymer:PQD) solar cell applications. The partial detachment of ligands during purification allowed solution processing light emitting diode fabrication. All inorganic PQDs show high brightness and realized in RGB (Red, Green and Blue) light-emitting diodes with 0.32% external quantum efficiency at 510 nm. We form hybrid nanocomposites by blending conjugated polymers and PQDs in solutions. The mixtures show high colloidal stability and preserving the PQD properties. We will demonstrate the application of these hybrid nanocomposites in solar cells.

Resume : Inconel 690 is widely used for steam generator(SG) tubes in nuclear power plants. Because SG tubes experience flow-induced vibration, fretting wear can occur between SG tubes and anti-vibration structures. Since the wear damage can reduce SG heat exchange efficiency in nuclear power plants by plugging the worn tube, investigation on the wear resistance of Inconel 690 SG tubes is necessary. During the operation of SG, Inconel 690 is oxidized due to high temperature and pressure of the secondary water. However, the effect of oxidation film on the wear behavior of Inconel 690 has not yet been studied, even though the oxidation film has important effects on the wear properties. Therefore, in this study, Inconel 690 tubes, oxidized under secondary water conditions, were used for fretting wear test. The results show that the spinel oxide, existent on the surface of Inconel 690, increases the room-temperature wear resistance, but decreases the high-temperature wear resistance.

Resume : Free-standing nanowire or nanorod arrays are of great interest for applications in photovoltaic device, surface-enhanced Raman scattering (SERS), biosensing, plasmonics, thermal electronics, high density data storage, and photocatalysts. In photovoltaics nanorod arrays are of particular interest for organic and hybrid solar cells, whose near-optimal architecture is proposed to consist of arrays of nanostructures (approximately 200 nm long) providing huge interfaces, efficient light harvesting and one-dimensional charge transport pathways [1]. Silver, scaled down to nanowire arrays, is considered one of the most exciting nanomaterials for organic and hybrid solar cells, because of its extremely high electrical conductivity, tunable surface plasmon resonance in the UV-Vis region and strong light scattering effects [2]. However, in the past years, large scale fabrication of such nanostructures on ITO glass and other rigid substrates was challenging. Here we present large-area free-standing silver nanorod arrays on ITO glass and other substrates by anodic aluminium oxide template (AAO) - assisted pulsed electrochemical deposition. We use an in situ oxygen plasma cleaning process and a sputtered Ti layer to enhance the adhesion between the template and ITO glass. An ultrathin gold (2 nm) layer is deposited as a nucleation layer for the electrodeposition of silver. An unprecedented high level of uniformity and control of the nanorod diameter (38–76 nm), spacing (84–133 nm) and length (98–208 nm) has been achieved. In addition, the absorption spectra of free-standing silver nanowire arrays shows tunable plasmon resonance peaks. We are currently investigating the optical and electronic effects of the silver nanorod arrays in SERS, biosensing, electrode for photoelectric devices and others. [1] Weickert J, Dunbar R B, Hesse H C, Wiedemann W and Schmidt‐Mende L 2011 Nanostructured organic and hybrid solar cells Advanced Materials 23 1810-28 [2] Zhuo X, Zhu X, Li Q, Yang Z and Wang J 2015 Gold Nanobipyramid-Directed Growth of Length-Variable Silver Nanorods with Multipolar Plasmon Resonances ACS Nano 9 7523-35

Resume : Inverted polymer solar cells have received a good deal of attention because of their compatibility with stability and large-scale roll-to-roll processing. In the inverted cell geometry, solution-processed metal-oxide films based on materials such as metal oxide nanoparticles are typically used as the electron-transporting layers. Here, We demonstrate enhanced charge collection in inverted Organic Photovoltaic solar cells (OPVs) using the surface modifier PEIE (Polyethyleneimine-ethoxylate), chemically functionalized ZnO/graphene core-shell type quantum dots (F-ZGQDs) monolayer as an electron transport layer(ETL). The mono-layered ZGQD plays the multi-functional role as surface modifier, photosensitizer and electron transport layer. We confirmed the internal structure of mono-layered F-ZGQDs by using the focused ion beam (FIB) milling technique. Additionally, we estimate the density of state (DOS) of F-ZGQDs using density functional theory (DFT). The inverted polymer solar cells with F-ZGQDs monolayer shows high power conversion efficiencies (∼10.3 %) due to effective interfacial properties and efficient charge transfer.

Resume : Charge transfer (CT) is an essential phenomenon relevant to numerous fields including biology, physics and chemistry.1-5 Here, we demonstrate that multi-layered hyperbolic metamaterial (HMM) substrates alter semiconductor CT dynamics.6 With triphenylene:perylene diimide dyad supramolecular self-assemblies prepared on HMM substrates, we show that both charge separation and recombination characteristic times are increased by factors of 2.5 and 1.6, respectively, resulting in longer-lived CT states. We successfully rationalise the experimental data extending Marcus theory framework with dipole image interactions tuning the driving force. The number of metal-dielectric pairs alters the HMM interfacial effective dielectric constant and becomes a solid analogue to solvent polarizability. The model and further PH3T:PCBM data show that the phenomenon is general and that molecular and substrate engineering offer a wide range of kinetic tailoring opportunities. This work opens the path toward novel artificial substrates designed to control CT dynamics with potential applications in fields including optoelectronics and chemistry.

Resume : Plasmonic nanostructured substrates have received a growing attention because of their potentials to tune optoelectronic properties of materials located inside or in their vicinity.1-4 These photophysical characteristics include emission or absorption, and charge transfer (CT) has been widely neglected. CT is, however, an essential phenomenon relevant to numerous fields including biology, physics and chemistry.5-8 Here, we demonstrate that multi-layered plasmonic (MLP) substrates can alter semiconductor CT dynamics.9 With donor-acceptor dyad supramolecular self-assemblies prepared on top of MLP substrates, we show that both charge separation and recombination characteristic times can be tuned, resulting in longer-lived CT states. We use Marcus theory framework to rationalize the experimental data and describe how the driving force is affected by the separation between the organic semiconductor and the MLP substrates. The phenomenon is general and this work paves the way toward molecular and substrate engineering to control CT dynamics with potential applications in fields including optoelectronics and chemistry.

Resume : Al2O3 surface passivation of p-type c-Si has proved its effectiveness and industrial compatibility thanks to (spatial-ALD) Al2O3 / (PECVD) SiN:H stack, providing cell efficiency of 20.2% (PERC). We reduced Al2O3 thickness down to 2 nm in order to benefit from its high fixed charge density at Al2O3/c-Si interface, which has been shown to be thickness independent. Such a thin Al2O3 layer raises concerns regarding ALD growth mode and electrostatic impact of the capping layer. We have grown an ultrathin chemical silicon oxide (<1 nm) on top of the c-Si surface to avoid the usual Volmer–Weber growth mode during the first ten ALD cycles. To provide good chemical passivation, at least 5 nm of Al2O3 are required to release enough hydrogen during annealing, so missing hydrogen had to be brought by the capping layer. We replaced standard SiN:H by SiOC:H to avoid field effect passivation lessening due to a high density of positive fixed charges within the SiN:H layer. We established the beneficial effect on passivation of the interfacial chemical oxide thank to HR-TEM, photoluminescence, µ-PCD and corona discharge. We added exo-diffusion and SIMS characterizations to highlight the usefulness of replacing SiN:H by SiOC:H. Taking into account the ALD growth mode and the electrostatic impact of the capping layer, we kept SRV below 10 cm/s, while increasing theoretical ALD throughput by factor of 3.

Resume : Increasing demand for clean energy have triggered researches on alternative energy sources and devices to reduce use of fossil fuel. Hydrogen has been considered as one of the most promising energy source for future due to its high energy density and no air pollutant emission. Splitting water into hydrogen and oxygen is an environmentally friendly method for producing hydrogen gas. This technology can store excess electric energy in the form of chemical bonds of hydrogen, which can resolve an issue about surplus electric power of present renewable energy systems caused by irregular energy source such as airflow and sunlight. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, especially OER has much higher overpotential than HER. Therefore, recently major efforts have been devoted to exploring active catalysts for the OER in water electrolysis cell. Among many kinds of candidate materials for OER catalyst, cobalt (Co) and various Co based materials, including nanostructured Co3O4, CoSe2, Co based perovskites, CoP, CoB and Co/N-doped carbon, have drawn much attention for use in the alkaline water electrolysis system. These Co based catalysts have high OER activity in alkaline media comparable with precious metal based catalysts, such as IrO2 and RuO2. However, previous studies has focused mainly on the exploring desirable composites for low OER overpotential without careful mechanistic study. OER mechanism on Co based catalysts and descriptors for designing more efficient catalysts have been unclear yet. Herein, we report novel hybrid type catalysts, which composed of Co and molybdenum carbide (Mo2C), as efficient OER catalysts for alkaline water electrolysis, and evaluate the OER mechanism by investigating the effects of surface acidity of the catalysts on the OER activity in alkaline media. Mo2C has very similar electronic structure with platinum (Pt) group metal. So, it can be promising candidate as an efficient electrocatalyst for water electrolysis system. We synthesized Co-Mo2C hybrids using facile solution based process. Synthesized Co-Mo2C hybrids exhibit enhanced activity and durability compared with Co and ruthenium dioxide (RuO2) catalysts in alkaline media (0.1 and 1 M KOH). This result is ascribed to increase in surface acidity by formation of Co-Mo bimetallic surface on the Co-Mo2C hybrids. Increase in surface acidity leads to increase in hydroxide ion (OH-) adsorption on the catalyst surface, which can promote the OER kinetics in alkaline media.

Resume : In recent years, much research was carried out in the field of fabrication and characterization of titania nanotubes (TiO2 NTs) due to their unique properties, such as high specific surface area, non-toxicity, chemical stability and high photocatalytic activity. As a result, TiO2 nanotubes have been often applied for photocatalytic processes or in dye sensitized solar cells. It has been found that TiO2 modification with metal, non-metal atoms or metal oxides considerable enhances its photoactivity in the visible range. We propose modification of titania surface region by indium tin oxide (ITO) that is usually known as a semitransparent conductive oxide deposited onto the glass plate. The proposed modification was realized via magnetron sputtering technique where ITO plate was used as a target material and anodized titania served as a substrate. Afterwards, TiO2NT/ITO samples were calcined at 450°C for 2h. The ordered nanostructure and ITO clusters growth onto the nanotubes were proved by scanning electron microscopy. EDX and XPS analysis show that apart from titanium and oxygen, indium and tin atoms are present in the sample. On the basis of Tauc plot, it was found that for ITO-modified titania, the bandgap energy was shifted towards lower energy values. Obtained materials exhibit much higher activity under illumination registered as a photocurrent than pristine TiO2. Financial support from the National Science Center (2012/07/D/ST5/02269) is gratefully acknowledged.

Resume : Conducting elastomers are generally prepared by either depositing a network of nano-conductors (typically carbon nanotubes or silver nanowire) onto a flexible substrate or blending conductive nano-fillers with a polymer matrix. Although recent advancement in fabrication based on these two methods has already shown great improvement in both electrical and mechanical properties, innovative methods are still required to improve material homogeneity (nano-filler aggregation) and multiaxial conductivity (eliminating the insulating substrate). Single wall carbon nanotubes (SWNTs) are excellent nano-fillers due to their exceptional conductivity (metallic SWNTs) and relatively low bending modulus. Their high aspect ratio means percolation threshold could be reached at lower filler content, maintaining the softness of the flexible matrix. We performed a one-step reductive dissolution process to purify and dissolve SWNTs. The purified and charged SWNTs can then react with monomeric cyclic siloxane to produce homogeneous polydimethylsiloxane/SWNTs composites via anionic ring opening polymerisation. The purity of SWNTs and the reactivity with siloxane can be controlled by the degree of charging. In general, low charging ratio tends to purify SWNTs whereas high charging ratio gives higher reactivity with siloxane. Since the charged SWNTs are individualised due to Coulomb repulsion, uniform distribution of SWNTs within the composite can be achieved easily.

Resume : The need to diminish greenhouse gas emissions opens the demand for discovery of very affordable and highly efficient materials with a unique structure for CO2 capture and energy storage (1-2). Recently, hybrid materials combining graphene or carbon nanotubes and inorganic-organic composites emerged as a new class of materials because of their unusual and superior properties including excellent thermal and chemical stability, high conductivity, outstanding oxidation and corrosion resistance, and tunable porosity (3). This study is focused on developing a highly conductive hybrid material with controllable surface characteristics and hierarchical structures using polysiloxanes as polymer backbone with graphene oxide (GO) as conductive nanofiller. Using emulsion based strategy with tetradecyltrimethylammonium bromide (TTAB) as surfactant we were able to create a monolithic structure made of polysiloxanes beads covered with reduced graphene oxide (rGO). From the AC impedance spectroscopic analysis, the electrical conductivity of SiOC ceramics increased with the incorporation of GO. In addition, the supercapacitor and CO2 adsorption behavior of the polysiloxane derived materials were tested. The CV curve shows the double layer capacitors with a high capacitance of 88 F/g at 2 mV s-1 in 0.5 M H2SO4 electrolyte solution and CO2 adsorption capacities up to 2 mmol/g, at 25 °C. Reference 1. Rutao Wang, Peiyu Wang, Xingbin Yan, Junwei Lang, Chao Peng, and Qunji Xue, ACS Appl. Mater. Interfaces 2012, 4, 5800−5806 2. Nilantha P. Wickramaratne, Jiantie Xu, Min Wang, Lin Zhu, Liming Dai, and Mietek Jaroniec, Chem. Mater. 2014, 26, 2820−2828 3. Luis Estevez, Rubal Dua, Nidhi Bhandari, Anirudh Ramanujapuram, Peng Wang and Emmanuel P. Giannelis, Energy Environ. Sci., 2013, 6, 1785–1790

Resume : Ceria (CeO2) has received considerable interest as an electrolyte for intermediate temperature solid oxide fuel cells. [1] Unfortunately, within this temperature range (~600-800°C), ceria displays poor ionic conductivity, while at high temperatures and low oxygen partial pressures Ce(IV) can be reduced to Ce(III), due to facile oxygen vacancy formation, [2] which results in electronic conductivity. In an attempt to improve the ionic conductivity of ceria aliovalent doping is commonly employed, with trivalent species (e.g. Gd(III), Sm(III)) a particular focus due to their creation of charge compensating vacancies which forms an oxide ion diffusion pathway without the presence of Ce(III). Experimental evidence [3] has corroborated the increased ionic conductivity from trivalent dopants, however a detailed understanding on the effect of the dopant on the electronic structure of ceria and a full exploration of the range of trivalent dopants has been lacking. This study considers two aspects of trivalent doping using density functional theory simulations: (i) the formation of charge compensating vacancies and their role in oxide ion conductivity, and (ii) their effect on the reducibility of ceria. These aspects are explored for a range of p-, d- and f-block ions. [1] Brett et al., Chem. Soc. Rev., 37, 1568 (2008). [2] Scanlon et al., J. Phys. Chem. C, 113, 11095 (2009). [3] Fu et al., Int. J. Hydrogen Energy, 35, 745 (2010).

Resume : Epoxy resins are important thermosetting polymers which have been used in composites as structural materials. They showed high thermal and chemical stability and good mechanical properties. However, there is no ionic conductivity in epoxy resin due to cross-linked structures of polymer chain restrict the transfer of small molecule like ion water, etc. There are some researches to fabricate ion conducting epoxy resin by the co-curing of epoxy resin and ionic liquid.[1,2] The mechanical properties and ionic conductivity are effected by morphology control of hybrid system. In this work, we used plastic crystal as electrolyte and crown-ether, and oligo-ethylene glycol as additive. Morphologies were controlled by change of volume ratio of epoxy resin/electrolytes and curing condition. The structure of cured epoxy resin was investigated by SEM. The cured polymer was shown about 10-6 S/cm of ion conductivity and 0.88 GPa of Young’s modulus. [1] B. G. Soares, A. a. Silva, J. Pereira, S. Livi, Macromol. Mater. Eng., 2014. [2] N. Shirshova, A. Bismarck, S. Carreyette, Q. P. V. Fontana, E. S. Greenhalgh, P. Jacobsson, P. Johansson, M. J. Marczewski, G. Kalinka, A. R. J. Kucernak, J. Scheers, M. S. P. Shaffer, J. H. G. Steinke, M. Wienrich, J. Mater. Chem. A, 2013, 1, 15300.

Resume : Mesoporous silica SBA-15 was exploited to synthesize a nanocomposite in which a nanoglass of composition 35Li2O.65SiO2 could be incorporated within the nanochannels of diameter 5.5 nm of the template. A dc electrical conductivity of 10-4 S-cm-1 was measured for the nanoglass at room temperature with an activation energy of 0.1 eV. This arose due to oxygen ion vacancies caused by the presence of Si2+ and Si4+ species in the mesoporous silica at its interface with the nanoglass. A repulsive interaction between the defects and the lithium ions reduced the attractive electrostatic force between the non-bridging oxygen ions and the lithium ions. These nanocomposites are expected to have applications in lithium ion batteries for storage of renewable energy.

Resume : SnS films as an alternative low cost chalcogenide absorber for thin film solar cells were grown by chemical spray pyrolysis. Acidic aqueous solutions consisted of tin chloride (SnCl2) and thiourea (SC(NH2)2) at molar ratios of 1:1 and 1:8 were deposited onto glass substrates at 200 °C in air. We studied the effects of post-deposition annealing treatments in nitrogen and vacuum at 450 °C for 60 min on properties of sprayed films. SnS films were examined by X-ray diffraction (XRD), Raman and UV-Vis spectroscopies, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). According to XRD and Raman studies, cubic SnS is the main crystalline phase of films independent of precursors’ molar ratio in the spray solution. 1:8 films annealed in nitrogen are composed of a mixture phases of Sn2S3 as the main and SnS as the minor phases. Annealing of 1:8 films in vacuum results in orthorhombic SnS phase, films show optical band gap of 1.4 eV. Thermal annealing of 1:1 films in vacuum leads to metallic Sn, while annealing in nitrogen results in films composed of a mixture of SnS and SnO2 phases. The formation of oxidized phases shows that oxygen containing phases are present additionally in the as-grown film. In this study we discuss the chemical reactions taking place during the thermal treatments, along with the optimal deposition conditions and optimal post-deposition treatment for fabrication of SnS single phase films.

Resume : Tungsten sulfides and selenides are materials with band gap energies are in a range of 1.2 to 2 eV, revealing a good match to solar energy materials [1]. Due to the potential for photovoltaic applications, we analyze the optical and electrical characteristics of the semiconductor compounds of tungsten chalcogenides WX2 and WX3 with X = S, Se, and Te. The different phases of the compounds are calculated within the density functional theory (DFT) using the generalized gradient approximation and a plane-wave basis set. The electronic structures of the phases are compared, and based on the investigation of the optical absorption and the density-of-states the most interesting compounds are further analyzed with a post-DFT approach [2]. [1] H. Jiang, J. Phys. Chem. C 116, 7664 (2012). [2] M. Dou, et al., Int. J. Hydrogen Energy 38, 16727 (2013).

Resume : The limitations of TiO2, known as photocatalyst for various pollutants, are related to the rapid rate of photogenerated electron-hole pairs and the light absorption in the UV domain hindering the processes up-scaling. The use of TiO2 deposited by cold spraying on flexible substrates and/or fabrics represents a twofold challenge of materials design: to enhance the TiO2 photoactivity and to formulate the ink. To improve the TiO2 photoactivity, the design strategy considers the Schotky diode concept, by developing TiO2/Ag heterostructures. The specific structure and composition of the developed materials corroborated with interface parameters influences the photodegradation ability of the system. In developing photocatalytic inks, fine control of the particles synthesis process and the dispersion rheological properties and stability were considered as optimization criteria. To obtain TiO2 - based photocatalytic dispersions, the particles were dispersed in aqueous and aqueous/alcoholic continuous medium and stabilized using surfactants (DTAB, PEG), polymers (polyvinylpyrrolidone, policrylamide) or capping agents (TODA). Based on transmittance spectra, the stability was discussed considering the stabilizer’s steric effect and the electrostatic repulsions between the particles. Methyleneblue photodegradation by TiO2 – based material deposited on fabrics from dispersion stabilized with TODA and DTAB provided removal efficiency higher than 75% under simulated solar radiation.

Resume : Carbon dioxide is one of the primary greenhouse gases implicated in global warming process. Alternative energy sources that make no contribution to CO2 emission are still in the development phase and not likely to replace current carbon-based energy sources during the few next decades. Therefore, sequestration process is of critical importance to maintain or even reduce the CO2 level in the atmosphere. To reach it one should gain understanding of possible microscale effects. In order to predict thermodynamic and transport properties of this system one should study the main components of the soils namely widely spread micaceous minerals like illite (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O). In the present study the structural and thermodynamic properties of the illite - CO2 system were investigated with the Car-Parinello molecular dynamics( CPMD). We relaxed several structures and found the one with the lowest adsorption energy, further we determined possible CO2 capture reactions from total energies and free energies from CPMD. Molecular dynamics calculations with canonical ensemble (NVT) were performed. The stability of such systems was also predicted as a function of certain temperature.

Resume : To explain the isomerization reaction mechanism of substitued polyacetylenes, we used an HF (ab-intio) and DFT (B3LYP) 6-31G and 3-21G** methods. The various (rotations, conversions, rearrangemnts) and the different intermediates (transition state) were investigated. The results were as following: * The studied bonds in the fragments (C10H12, C10H6F6, C10H6Cl6) showed an important stability, justified by the low HOMO-LUMO energetic gap observed. However, the stability of many conformations showed that, the trans form was the more stable than the cis form. * The different reactions profiles, reveled that the size and the nature of the dopant (substituant) play a major role in the evolution of the activation energy. * The calculated activation energy values indicated that the rates constants were in the order: kC10H12 >>kC10H6F6>> kC10H6Cl6. * Reaction intermediates during Cis-Trans transition showed that the geometrical parameters (angles and diedres angles) were amongst the most changed parameters, this was observed in the cases of substituted and unsubstitued PA.

Resume : (Na1-xKx)NbO3 (NKN) platelets synthesized at 600oC for 12 h have an Amm2 orthorhombic structure that is a stable NKN structure at room temperature. However, the structure of NKN platelets synthesized at 500oC for 1 h is a mixture of R3m rhombohedral and Amm2 orthorhombic structures. Formation of the rhombohedral structure is attributed to the presence of the OH- and H2O defects in the NKN platelet. The piezoelectric strain constant (d33) of the NKN platelets synthesized at 600oC for 12 h is 100 pmV-1 but the NKN platelets synthesized at 500oC for 1 h show a smaller d33 of 50 pmV-1 due to the presence of these defects. Piezoelectric energy harvesters (PEHs) are fabricated using composites consisting of NKN platelets and polydimethylsiloxane. A large output voltage of 20 V and output current of 3.0 μA are obtained by bending the PEH with NKN platelets synthesized at 600oC for 6.0 h with a strain of 2.13% and an average strain rate of 3.79 %s-1. Moreover, this PEH shows a high output electrical energy of 3.0 μW at an external load of 5.1 MΩ. In addition, an output voltage of 5.0 V and current of 400 nA are also obtained by softly tapping this PEH by hand.

Resume : A large number of perovskite (ABO3) materials exhibit a ferroelectric behaviour. A special attention has been given to the complex perovskite (AA’BB’O3) compounds with disorder cations leading to a new class of ferroelectric called relaxor. Materials having such characteristics are very interesting in the field of applications in electronics (1, 2) and in photocatalysis (3). The usual ferroelectric materials are lead-based ceramics and derived compounds which present disadvantage due to the toxicity and volatility of PbO during the manufacturing process. To protect the environment, researches are oriented towards lead-free materials. In the other hand, photocatalysis studies and particularly the photocatalytic hydrogen production represents a very promising contribution to a clean and renewable energy system. In this way, we present the ferroelectric properties of some lead-free perovskites compounds and their behaviour as photocatalyst. The concerned compositions are belonging to the systems BaTiO3-BaZrO3-A2O3 systems (A= rare earth or trivalent cations). As an example: - Typical relaxor behaviour and diffuse phase transition were observed in Ba0.975Eu0.017(Ti0.75 Zr0.25)O3, composition. The different characteristics of these ceramics present a real interest for environment applications. These compositions show a relaxor effect with unfortunately transition temperature below room temperature. Nevertheless, the photoelectrochemical investigation show an optical gap of 2.25 eV obtained from the diffuse reflectance spectrum. The energetic diagram clearly assesses the photoactivity of this perovskite. 95% of chromate (10-4 M) is reduced after 6 h of exposition to sunlight. - Ferroelectric relaxor with a phase transition close to room temperature was obtained for Ba0.785Bi0.127Y0.017TiO3, This composition is very interesting for electronic applications and can replace lead-based ferroelectric ceramics to prevent the environmental pollutions during the preparation step. In the other hand, Ba0.725Bi0.120Y0.033TiO3 (optical gap = 2.43 e.V) has been tested successfully for H2 production upon visible light when combined to the Delafossite CuFeO2 as sensitizer. An evolution rate of 24 micromol mn-1 and a quantum yield of 0.4% under polychromatic light were obtained. References 1. L.E. Cross, Ferroelectrics, 151, 305-3.., 1994 2. K. Uchino, Ferroelectrics, 151, 321-3.., 1994 3. Y. Yang, Y. Suna, Y. Jiang, C*hemistry and physics,96, 234-239, 2006

Resume : In order to improve the weight reduce potential of magnesium alloy in wind power equipment, green car and other fields related to energy and energy saving, a new melt treatment methods were developed to purify the alloy and to improve its mechanical properties. The Mg-8Al-0.7Zn-0.25Mn-1.0Y/1.6Ce-0.1Sr alloys melt with an extra holding treatment at temperature of 650℃ were used for die casting, the microstructure and mechanical properties of the products of the two kinds of alloys were investigated by optical microscopy, scanning electron microscopy, X-ray diffractometer and tensile test. The results show that the low-temperature holding treatment can reduce the content of Fe in magnesium alloys effectively and result in a bigger average grain size of the alloy as die-casting state. The average value of ultimate tensile strength, yield strength and elongation of the alloy contain Ce can be improved from 151.4 MPa, 121.6 MPa and 0.709% to 222.7 MPa, 143.8 MPa and 4.064%. And the electrical and thermal conductivity are improved significantly to attribute to the decrease of Fe impurity. This allows the alloy to be used in a wider range of energy fields.

Resume : Water splitting has attracted increasing attention for clean energy generation and efficient energy storage. Due to relatively high overpotential than hydrogen evolution reaction(HER), the oxygen evolution reaction(OER) is a key reaction in water splitting. To overcome this problem, current studies are focused on development of efficient, abundant and inexpensive OER catalyst. Although Nickel/iron(NiFe)-based compounds have been known as active OER catalysts for decades, NiFe-based materials such as NiFe LDH receiving attention recently. Here we report an approach to improve efficiency of water splitting electrodes based on flexible NiFe-based foil. Anodic oxidation method is applied to enhance the oxygen evolution activity of NiFe alloy foil. The anodized NiFe alloy foil exhibit significant higher activity than the corresponding Ni foam in base conditions. The anodic oxidation method generate NiFe oxide and hydroxide layers on NiFe alloy surface, act as electrocatalyst. Spontaneously, the anodic oxidation method widen the specific surface area of water splitting electrodes. Increased reaction sites and catalytic behavior of NiFe hydroxide is the reason of improved water splitting property. This work demonstrates the promising electrocatalysts of NiFe based materials for the oxygen evolution reaction.

Resume : Metal-organic frameworks and other nanoporous hybrid materials have widespread applications in energy and environmental applications, but the pathway from laboratory synthesis to practical implications is substantially challenging. More specifically, these framework materials often present an arduous challenge for structure determination due to their relatively poor crystallinity, low symmetry and large unit cell volumes that make the indexation of their powder X-ray patterns very complex and thus requires more efficient tools for step-wise modeling, screening and characterization. Inspired by the concept of molecular building units, we developed a software for such structure solution based on a revisited version of the AASBU (Automated Assembly of Structure Building Units) method. As a first step, this computational tool has been thoroughly validated on a series of experimentally-known MOF structures. The software has been further able to successfully predict some recently synthesized novel Zr-based MOFs characterized by the SBU present in the widely-studied UiO-66(Zr) MOF. As the software is under active development, we are confident that in the near future we will present a mature version of the software to the scientific community which will allow the determination and in silico prediction of novel structures that are created by more advanced and complex organic, inorganic and hybrid clusters.

Resume : Electrolytic high purity hydrogen production is still underuse (less than 4% of the global H2 production) because of its high price point when compared with steam reforming. Despite being a very sustainable method for H2 production, novel electrolytic technologies need to be develop to reach competitiveness in the world market. It is well accepted that the sluggish water oxidation kinetics is the limiting step in this process. To solve this drawback, many water oxidation catalysts (WOC) have been studied. One of the most promising candidates for the development of novel hydrolyzer technologies are the coordination polymers of the Prussian blue (PB) family [1]. These materials exhibit excellent stability, and processability, being active in a wide pH range. However, high current densities are still the major challenge because an appropriate electrode support for these novel WOC has not been identify yet. Here we present the development of stable high-surface area electrodes decorated with the Co-Fe PB for sustained and low-cost anodes in an electrolyzer architecture. The study of immobilization methods of the PB on substrates with high surface area, and the respectively characterization of the modified surface by ESEM, FTIR and XRD will be discussed. Finally, the electrochemical analysis of the surfaces, and the correlations between components, processing, catalytic activity and high stability will be highlighted. [1] Pintado, S. et al., J. Am. Chem. Soc, 135(36)( 2013)13270

Resume : We design a novel gas diffusion layer (GDL)/catalyst/membrane assembly using carbon xerogels as an alternative to the carbon paper which traditionally sustains the MEA assembly in proton exchange membrane Fuel Cells (PEMFCs). Xerogel synthesis reports a variation on the classical method for carbon xerogel synthesis, where the xerogel cross-linking process is performed in a centrifugal field, resulting in monolithic cylindrical configurations. We synthesize resorcinol-formaldehyde-GO (RFGO) xerogels by sol-gel polycondensation of resorcinol with formaldehyde in the presence of GO as the acidic catalyst in centrifugal fields of various magnitudes (125G/75G/37.5G) – the final pyrolysis stage of the method reduces GO into graphene. Platinum-ink, serving as FC catalyst, is directly sprayed on the carbonized xerogel cylinder and incorporated in the FC assembly by hot-pressing against a Nafion membrane. The integrated PEM fuel cell presents a maximum current density between 400 and 700 mA for the given catalyst loading ─ 0.6 mg/cm².

Resume : Vanadium redox flow battery offers not only a great promise to provide a robust and constant energy storage system, but also several advantages such as scalability, long cycle life, high efficiency, power and energy are independent. Despite all of its merits, VFBs have reached only a limited market presence after the continuous development the last 30 years. The improvements VFB performances require a better reversible kinetics with minimum side reactions (i.e hydrogen evolution) for a commercial outbreak. Our approach has been applied Rutile-TiO2 hydrogen-treated electrocatalyst for high performance all-vanadium redox flow batteries (VFRB) as a simple and eco-friendly strategy well-suited for large-scale applications. TiO2 hydrogen-treated shell in a graphite felt core (GF@TiO2:H) was prepared by a combination of hydrothermal synthesis followed by thermal treatments. Comparatively to commercial electrodes, rutile TiO2-based nanorods decorating graphite felt samples perform an abrupt inhibition of hydrogen-evolution reaction, which is a critical barrier for operating at high charge/discharge rate for long term cycling in VFRB. Moreover, significant improvements in charge and electron transfer processes towards V3+/V2+ redox reaction is achieved using GF@TiO2:H electrodes due to the enhancement in the electron donor properties of the TiO2 after hydrogen annealing, as a consequence of oxygen vacancies formation in the lattice structure. Keys performance indicators of VFRB have been increased not only in terms of high capability rates (200 mAcm-2) but also the electrolyte-utilization ratio achieved (82%), corresponding the best value reported up to date. A specific discharge capacity of around 31 WhL-1 with a 61% of energy efficiency was observed after more than 120 cycles. Taking into account all improvements mentioned above, it is a cost-effective way to boost this technology into the market.

Resume : In recent years, ceria based oxides have been widely used as catalysts or as electrolyte material for fuel cells. Moreover, it has been observed that interaction between noble metal such as Pt with ceria enhances its catalytic activity by improving the reducibility of the surface. Recently, DFT calculations have predicted that atomically dispersed platinum is stabilized in specific oxidation state Pt2+ at the surface of CeO2 {100} type nanofacets. This study was made in the context of recent approach which may make possible the observation of single Pt atoms in surface nanopockets through high resolution scanning transmission electron microscopy. Pt-CeO2 thin films were obtained by direct liquid injection CVD with a synthesis approach which allows direct observations of the layers on carbon coated Cu TEM grids. This approach does not require any prior preparation of the samples, which may damage or modify their structure and chemical state. In this way, the real chemical state and morphology of the deposits are preserved and quantification of very low Pt content is possible. TEM results show that the layers are composed of very well crystallized ceria particles with a homogeneous grain size (~10 nm). However, EELS measurements have revealed that the carbon membrane is consumed during deposition, even though its morphology is conserved after deposition. Finally, a very low Pt content (~1%) is revealed with cationic Pt localized at the extreme surface of the CeO2 particles.

Resume : Currently, UFCs (Urea Fuel Cells) became a promising alternative for new energy conversion and generation. The advantages of the urea fuel cell compared to the hydrogen fuel cell are that the fuel is non-toxic, non-flammable and easy to transport without pressurization. The fuel can also be recovered from waste water. Electro-decompostion of urea in the presence of a Ni catalyst is considered an effective approach for hydrogen production. In this work, three different catalysts based on Ni metallic were synthesized, characterized and used as anodic catalyst in urea fuel cells. The physico-chemical properties of electro-catalysts were investigated by SEM, FT-IR, TGA, DSC and CV. Electrochemical measurements showed that the Ni is an alternative catalyst material for applications in waste water remediation, hydrogen production and fuel cells.

Resume : The a II-VI semiconductor ZnS has been studied due to its unique optical properties and could be a promising candidate for p-type semiconductor materials. If the luminescence properties of Cu-doped ZnSare well known, the reports of Zn1-XCuXS films exhibiting a p-type behavior are scarce. In this work, Zn1-XCuXS thin films were synthetized by RF magnetron sputtering using ceramic ZnS and metallic Cu targets. The Cu target power was changed in order to vary the Cu content in the films while other experimental parameters remain constant. (0002)-oriented hexagonal ZnS films are obtained for all the conditions. XRD results suggest the Cu insertion in Zn atomic positions of the ZnS crystal lattice decreases the a and c lattice parameters and therefore the ZnS volume. Films with Cu contents above 6% show changes in the microstructural, optical and electronic properties of the films. Following the intensity of the (0002) ZnS diffraction peak, when decreasing the Cu content shows a striking loss in the preferential orientation growth is found also related with a loss in the ZnS crystal quality. The energy bandgap measured by optical absorption decreases with the Cu content.Moreover, an absorption in the near infrared region appears probably due to a plasmon resonance linked to an increase in the carrier concentration. The electrical measurements reveal that the films are conductive with a p-type behavior above a Cu concentration of 6%.

Resume : Ti1-xAlxN coatings with different compositions were deposited on steel and copper substrates in a cathodic arc physical vapor deposition system. To achieve the different coating compositions evaporation targets with different Ti and Al contents were used. Additional adjustments to the coating structure were realized by utilizing different modes of substrate bias, namely the DC mode, where a constant potential of -75 volts was applied to substrate, and a pulsed bias mode, where a unipolar pulse of 24 kHz and an amplitude of -1k volts was applied. After the deposition process, samples were subjected to a heat treatment in a high vacuum furnace. Samples were characterized optically, using a UV-Vis-NIR spectrophotometer both as deposited and heat treated states. Thermal emittance of the samples was measured using an emissometer. XRD measurements were also carried out to determine the changes to the structure and phase distribution induced by the heat treatment, separating TiN and AlN phases. The reflectance of the coatings in the 220-1500 nm range depends primarily on the Al/Ti ratio with higher Al content coatings showing lower reflectance. Additionally, coatings produced using pulsed high voltage bias exhibit lower reflectance values compared to the coatings deposited with DC bias and otherwise identical parameters. As a general behavior observed for all coatings, high vacuum heat treatment led to the decrease of reflectance and emissivity of the coatings. Keywords: TiAlN, Cathodic Arc, Physical Vapor Deposition, Optical Properties, Thermal Emissivity, Selective Solar Absorbers

Resume : Magnesium hydride is a very promising material for solid-state hydrogen storage. However,some drawbacks have to be overcome to use it in real applications. The use of catalysts is a viable solution to lower the desorption temperature and increase the overall kinetics. An accurate model has been developed to study the mechanism of action of the catalyst and how it interacts with the interface MgH2 - Mg, through which H atoms diffuse. The accurate evaluation of the work of adhesion and defect energy formation, versus the distance from the interface are linked to the atomic-scale structural distortion induced by the catalyst. Moreover, molecular dynamics simulations at several temperature provide a clear description of the desorption mechanism and an estimate of the desorption temperature.

Resume : Nowadays global warming and energy crisis has accelerated to develop renewable energy. Splitting water into hydrogen and oxygen molecules is an environmentally-friendly solar-to-energy conversion method which could produce hydrogen energy. However, the oxygen evolution reaction has been regarded as a bottleneck in overall water splitting reaction. The noble-metal catalyst shows remarkable catalytic activity, but their high cost gives limitation for realization of overall water-splitting systems. Therefore, developing cost-effective, abundant, and efficient water splitting catalysts under neutral condition is necessary. Although extensive studies have focused on the metal-oxide catalysts, the effect of metal coordination on the catalytic ability remains still elusive. Here we select four cobalt-based phosphate catalysts with various cobalt- and phosphate-group coordination as a platform to better understand the catalytic activity of cobalt-based materials. Although they exhibit various catalytic activities and stabilities during water oxidation, Na2CoP2O7 with distorted cobalt tetrahedral geometry shows high activity under neutral conditions, along with high structural stability. First-principles calculations suggest that the surface reorganization by the pyrophosphate ligand induces a highly distorted tetrahedral geometry, where water molecules can favourably bind, resulting in a low overpotential. In conclusion, we observed the importance of local cobalt coordination in the catalysis and suggest the possible effect of polyanions on the water oxidation chemistry.

Resume : Oxygen reduction reaction (ORR) is the electrochemical cathode process in polymer electrolyte fuel cells and Li-air batteries. Important for the construction of sustainable fuel cells is to identify candidates for novel ORR catalysts that not only satisfy the requirements for catalytic activity and durability under the cell operation conditions, but are also free of precious metals and rare elements. Recent development of alkaline polymer electrolytes opens up possibilities to use Ni alloys as an alternative cathode catalyst. One possibility to increase the poor catalytic activity of pure fcc Ni is modification with small amounts of Cr. In this study, we investigate different modifications of nickel catalyst with chromium combining density functional theory with established electrochemical models, and employing atomistic structure models of different sizes derived from available characterization data. We find that catalytic activity and stability of nickel surfaces can be enhanced via doping and decoration of the active Ni surface with chromium and chromium oxides. Based on the results we discuss the factors contributing to activity enhancement and to stabilization of ORR intermediates and suggest that specific modifications may increase catalyst performance considerably. Furthermore, we suggest a design strategy for improving the catalyst performance on the device level by coupling the atomistic model to a kinetic Monte Carlo simulation and a mass/charge transport model in fuel cell.

Resume : Photocatalytic water splitting is potentially a very attractive route to producing hydrogen fuel using the energy of sunlight. To this end, a large number of photocatalysts are being studied, but their efficiencies remain low. Graphitic carbon nitride (g-C3N4) is in many ways an ideal photocatalyst material: its structure and electronic properties can be tuned, it is non-toxic and cheap to synthesize. However, it is inefficient due to poor light-harvesting properties and low charge mobilities. Modifications to the g-C3N4 structure could greatly improve its optical and electronic properties and therefore its water splitting efficiency. Computational materials design is essential here: many candidate structures can be screened computationally before they are made, to direct experimental efforts to the structures with desirable properties. We use calculations to predict the effect of modifying the idealised g-C3N4 structure by replacing the three-coordinated nitrogen linker atom with a range of heteroatoms (phosphorus, boron) and aromatic groups (benzene, triazine and substituted benzenes). Electronic properties of the modified carbon nitride structures are studied using density-functional theory (DFT) calculations, focussing on the valence and conduction band positions and band gap energies. Both two-dimensional (2D) sheets and three-dimensional (3D) multilayer structures are explored. Our studies suggest that 3D g-C3N4 can catalyse only the hydrogen reduction half-reaction, in line with experimental reports. However, 2D sheets of g-C3N4 have suitable valence and conduction band for splitting water. Two new structures are found with smaller band gaps and better band positions than g-C3N4 for water splitting: benzene and s-triazine linked structures. The boron-doped structure is also interesting: it has the smallest band gap and is expected to absorb red light. Therefore, it may be useful as a component for photocatalytic Z-schemes. Thus, our computational study identifies boron-doped and benzene- and triazene-containing carbon nitrides as new promising materials for experimental studies.

Resume : Metal-Organic-Frameworks appear to be appealing platforms for immobilization of single-site organometallic catalysts. The first photosensitization of a rhodium-based catalytic system for CO2 reduction is reported, with formate as the sole carbon-containing product. Through post-synthetic ligand exchange methodology, we successfully proceeded to the heterogenization of this molecular catalyst via the synthesis of a new metal-organic framework (MOF) Cp*Rh@UiO-67. While the catalytic activities of the homogeneous and heterogeneous systems are found to be comparable, the MOF-based system is more stable and more selective for formate. Through the study of the behaviour of MOF systems having a controlled Rh loading, competitive catalytic reaction occurring inside the Cp*Rh@UiO-67 framework are postulated. Finally, a combined computational-experimetnal methodology allowed unravelling the band-gap as a new descriptor of the chemical compostion of the hybrid material, to assess ultimately the covalent incorporation of the organometallic catalyst within the framework.

Resume : When building physical models (truncated expansions, force-fields, etc.), one often employs the widely accepted intuition that the physics is determined by a few dominant terms. This reductionist paradigm is provides no recipe for how one develops intuition for identifying the dominant terms. A "Bayesian compressive sensing" technique provides simple, general, and computationally efficient solution to the challenge of picking out the relevant terms. Combined with the high-throughput first principles approach to materials, BCS makes it possible to automatically build models for binary alloy models without human monitoring. Furthermore, the method can automatically adjust to generate the simplest model (fewest terms) that meets a specific accuracy requirement. Beyond the alloy applications, our BCS code can readily be applied to other model building problems. One merely needs a basis representation and training data to build a model in just a few seconds.

Resume : Physical vapor deposition, such as reactive magnetron sputtering, allows for synthesis of metastable alloys, inaccessible through growth methods operating close to thermodynamic equilibrium. Thus, a huge chemical space is opened for property optimization. Sc0.5Al0.5N is an example of such an alloy, where the piezoelectric response is increased by more than 400% in comparison to AlN. This makes ScAlN an excellent candidate for use in micromechanical systems which are key components in modern electronic devices, such as radio frequency signal processing. Using an approach of theoretical prediction and experimental verification, we study the mechanisms behind phase formation and the piezoelectric increase in metastable nitrides. We show that the effect of high piezoelectric constants is general for the III-A nitrides (AlN, GaN, InN) alloyed with III-B nitrides (ScN, YN) [1,2]. Based on our determined criteria, we scan the periodic table for quaternary AlN-based alloys and map out new possible candidates suitable for metastable piezoelectric thin films, in particular, Tix/2Mgx/2Al1-xN, Zrx/2Mgx/2Al1-xN, and Hfx/2Mgx/2Al1-xN, and establish the energy difference EB3-EBk as a descriptor that can be used to find additional piezoelectric alloys in high-throughput studies [3]. [1] C. Tholander, I.A. Abrikosov, L. Hultman, and F. Tasnádi, Phys. Rev. B 87, 094107 (2013). [2] C. Tholander, J. Birch, F. Tasnádi, L. Hultman, J. Palisaitis, P.O.Å. Persson, J. Jensen, P. Sandström, B. Alling, and A. Zukauskaite, Acta Mater. 105, 199 (2016). [3] C. Tholander, F. Tasnádi, I.A. Abrikosov, L. Hultman, J. Birch, and B. Alling, Phys. Rev. B 92, 174119 (2015).

Resume : Molecular photoswitches capable of storing solar energy are interesting candidates for future renewable energy applications. In this context, substituted norbornadiene-quadricyclane systems have received renewed interest thanks to recent advances in their synthesis. Their properties can be tailored by introduction of functional side groups resulting in a very large number of potential compounds. Since this parameters space is practically impossible to navigate exclusively experimentally, we have followed a computational design approach to identify candidate compounds and delineate optimal design strategies. Specifically, using quantum mechanical calculations we carried out a systematic screening of critical optical (solar spectrum match) and thermal (storage energy density) properties of a matrix of more than 70 compounds and more than 800 structures. The substituents were chosen to be synthetically accessible thus providing realistic candidates for future experimental realization. It is shown that it is possible to design molecules that can reach the theoretical maximal solar power conversion efficiency. This, however, requires a strong red-shift of the absorption spectrum, which causes detrimental absorption by the higher-lying photo-isomer (quadricyclane) as well as a significantly reduced thermal stability. In addition, the respective compounds are typically based on two substituents and have a correspondingly large molecular mass, leading to storage densities below 400 kJ/kg. By contrast, single-substituted systems achieve a good compromise between efficiency and storage density reaching values in excess of 600 kJ/kg for the latter, while avoiding competing absorption by the photo-isomer. Based on these results we identified promising candidates along with general guiding principles for the future development of molecular solar thermal storage systems.

Resume : It is at the anode triple phase boundary between Ni, YSZ and fuel molecules that the reactions on which the efficiency and ageing of the fuel cell depend. Despite a significant body of research, the structure of the YSZ electrolyte surface has not been characterized at an atomic level and so the nature of the surface reaction sites is not known. In this study a systematic approach to the defect thermodynamics of YSZ is used to establish both the atomistic geometry of the Y and Ovac sites and an heuristic that facilitates the prediction of low energy structructues in more complex environments such as the surface and the TPB. This is used to construct an initial model of the interface between YSZ and the reactive gasses and to speculate about the nature of the reaction sites active in the oxygen reduction reaction and the carbon contamination reaction.

Resume : The double perovskite BaGd0.8La0.2Co2O6-δ (BGLC) shows excellent performance as oxygen electrode for Proton Ceramic Fuel Cells (PCFCs) and electrolyzer cells (PCEC), with polarization resistances in wet oxygen of 0.04 and 10 Ωcm2 at 650 and 350 ⁰C, respectively [1]. Compared with other reported PCFC cathodes [2], BGLC performs better both at high and low temperature. The high performance of BGLC is rationalized by a suggested partial proton conductivity at intermediate temperatures, and significant hydration is shown by thermogravimetry up to 400 ⁰C. To lower the A-site basicity and increase the chemical stability of BGLC in steam under PCEC operation, we substitute some La for Ba and a stable composition at 1.5 bar steam is reached with 50 % substitution of Ba. We investigate polarization resistance on symmetrical button cells, conductivity, and hydration vs x in Ba1 xGd0.8La0.2+xCo2O6-δ, with x = 0-0.5. Structural properties vs temperature and x in dry and hydrated samples are investigated by use of synchrotron and neutron powder diffraction and high temperature XRD. DC conductivity of BGLC vs x and temperature reaches a maximum of 1600 Scm 1. References [1] R. Strandbakke, V.A. Cherepanov, A.Y. Zuev, D.S. Tsvetkov, C. Argirusis, G. Sourkouni, S. Prünte, T. Norby, Solid State Ionics 278 (2015) 120. [2] J. Dailly, S. Fourcade, A. Largeteau, F. Mauvy, J.C. Grenier, M. Marrony, Electrochimica Acta 55 (2010) (20) 5847.

Resume : A Solid Oxide Fuel Cell (SOFC) is considered to be one of the electricity generation systems because of its high efficiency and fewer environmental loads during its operations. However, the present SOFC requires high operating temperatures of 800-1000 °C, which results in higher device cost. Therefore lowering the operating temperatures below 600 °C is indispensable to enhance the SOFC application fields. In the conventional SOFC, oxygen-ionic-conductor is used as an electrolyte; however, it needs high operating temperatures over 1000 °C to obtain sufficient ionic conductivity. Therefore, we have proposed a new SOFC structure with a proton-conductive oxide thin films de-posited on a Pt-plated porous stainless-steel (PSS) substrate as an electrolyte. The proton conductors show high conductivity at 400-600 °C. In this study, we will report the high quality deposition of these perovskites, such as Y-doped BaCeO3(BCYO) and SrZrO3(SZYO), and their application to SOFCs.

Resume : Ceria is an important material in many environmentally benign applications. In particular, it is a promising electrolyte in intermediate temperature solid oxide fuel cells (IT-SOFC). The characteristic high oxygen mobility is crucial to such applications. The optimization of this mobility has attracted many studies. Attempts at improving the ionic conductivity usually revolve around choosing the correct kind and concentration of dopants. We have approached the problem from a different direction: how does the conductivity depend on the lattice parameter? To justify this approach one can consider that most external parameters carry with them a volume change. The effect of volume change on the ionic conductivity in ceria has been studied in the framework of the density functional theory. We show that properly controlling external conditions one can treat the lattice constant of ceria as an adjustable parameter and change the topology of the energy landscape for the oxygen ion transport. We reveal the existence of a narrow range of lattice parameters, which lead to such a topology that the ionic conductivity in ceria is essentially enhanced. The tuning of the lattice parameter is possible via proper external conditions, such as oxygen pressure, concentartion of dopants and the choice of a substrate. This finding opens avenues for the future design of fast ionic conductors.

Resume : High-throughput computing has been emerging as a very powerful way to search for new materials. By building databases of thousands of computed materials properties, one can search for the few compounds with the exceptional properties for a given application. I will illustrate how this approach can be used to search for materials with specific opto-electronic properties (transparency, carrier mobility, conductivity) targeting two important applications: transparent conducting oxides and thermoelectric materials. I will especially focus on recent computational findings confirmed experimentally and stress the opportunities and challenges in computationally-driven materials design. In the last part of my talk, I will present how the data generated through high-throughput computing can be widely spread and introduce the Materials Project: a large publicly available database of computed materials properties (http://www.materialsproject.org).

Resume : Accurate ab initio electronic transport models can facilitate high throughput calculations and screening of semiconductor materials for energy applications. Previous attempts at screening new transparent conducting oxide (TCO) materials have focused on their average effective mass, due to the simplicity and speed of such calculations. This calculation is often simplified by being based solely on the shape of the band extrema. Although the approximate effective mass certainly gives a valuable prediction of material performance, it lacks sufficient complexity for accurate calculation of electronic properties, especially in degenerate semiconductors. In particular, electron-phonon interactions, which limit the mobility, particularly at room temperature, are ignored. Here we employ an ab initio transport Model in the Boltzmann Transport (aMoBT) framework, which accurately predicts the electrical mobility and conductivity of both n-type and p-type semiconductors. We screen more than 70 promising TCOs that were pre-screened using the average effective mass, and rank them based on their conductivity, as limited by ionized impurity scattering and electron-phonon scattering mechanisms. We now report the most promising candidates from each of the n- and p-type semiconductors, and assert the utility of aMoBT, as incorporated into an automated atomistic calculation framework, in designing new materials for solar cell applications.

Resume : III-IV semiconductor nanowires are promising building blocks of future electronic and optoelectronic devices. The nanowires are often doped with foreign impurity atoms to tune their electronic properties. In addition to this, native defects such as vacancies, interstitials and anti-sites may also form unintentionally. Moreover, during the growth of Au-seeded nanowires, Au impurities may also incorporate in the semiconductor. The aim of the current project is to study the energetics and concentrations of variety of native defects and foreign impurity atoms in the GaAs nanowires. We are calculating the formation energy of different point defects in GaAs including the Zn dopant, Au impurities and vacancies in different charged states through Density Functional Theory (DFT) calculations. Then, based on the relative stability of the defects, we will set up a thermodynamic model for the GaAs compound using a methodology which combines phase diagram and thermochemical experimental and first-principles information, so called CALPHAD method [1]. As a result of the current study, the existing thermodynamic model of the GaAs phase which does not take the impurity and native defect concentrations into account will be optimized. This model can eventually be used for modelling the growth of Zn-doped and Au-seeded GaAs nanowires [2]. [1] H.L. Lukas et. al., Computational thermodynamics: The Calphad method. Cambridge University Press 2007. [2] Yang et. al., J. Cryst. Growth, 414 (2015), 181.

Resume : A deep understanding of structure-property links is essential for the design of quantum dot solar cells (QDSCs), where interfacial recombination is a major source of current loss. However, the accurate characterization of semiconductor interfaces is so far challenging both from the experimental and theoretical point of view, especially in case of lattice-mismatched compounds. In this study, we combine theoretical and experimental methods to address this challenge. As an interesting alternative to spherical QDs, quasi 2D CdSe nanoplatelets (NPLs) of different thicknesses were linked to ZnO nanorods by SH- ligands. These systems were characterized by SEM, Raman and UV-VIS spectroscopy. The results confirm the presence of NPLs on the substrate, and suggest significant structural changes upon the interface formation between them. The latter was confirmed by a theoretical analysis using a highly efficient periodic density functional theory-based computational method. We also calculated the vibrational and electronic properties of this system, and the electron injection efficiency from the NPL towards the ZnO surface. This charge injection, in line with the working principle of QDSCs, turned out to be favored, but only partial. The proposed combined experimental/theoretical approach should be applicable for other lattice-mismatched semiconductor heterostructures in a wide range of optoelectronic devices to help rationalize their operating principles and thus design new systems.

Resume : In the past four years, the solar cell field has experienced an unprecedented meteoritic emergence of a new family of solar cell technologies; namely, perovskites solar cells (PSC) using (CH3NH3)PbI3 as absorber. [1] However, two main challenges prevent deploying PSC technology: the presence of the toxic element lead (Pb) and their structural instability. I will discuss our design strategy to increase the efficiency of hybrid halide perovskites which consists of understanding[2] designing then screening alternative stable, nontoxic, lead-free materials. Our efforts to design lead free family of hybrid materials demonstrate that hybrid materials containing organic cations might require careful considerations among them the size of the cell used during the screening process. Our strategy will be presented as well as some resulting promising compounds. Acknowledgement: Computational resources are provided by research computing at Texas A&M University at Qatar and the Swiss Super Computing Center(CSCS). This work is supported by the Qatar National Research Fund (QNRF) through the National Priorities Research Program (NPRP 8-090-2-047) References: [1] M. Peplow, “The perovskite revolution [news],” Spectrum, IEEE, vol. 51, no. 7, pp. 16–17, 2014. [2] C. Motta, F. El Mellouhi, S. Kais, N. Tabet, F. Alharbi, and S. Sanvito, Revealing the role of organic cations in hybrid halide perovskites CH3NH3PbI3, Nature Communications 6, Article number:7026 (2015) (doi:10.1038/ncomms8026)

Resume : A promising family of photovoltaic solar cells, based solely on metal oxide thin films, has recently been gaining interest. To improve the inadequate electrical properties of the pure metal oxide materials, various metal oxides are mixed, to create new composite materials that may exhibit enhanced properties. The new materials are then examined as light absorbing layers in photovoltaic cells, stacked between other metal oxide layers in multi-layered structure. The structure is consisting of different metal oxide layers: transparent conductive layer, electron transport layer, absorber layer and hole transport layer. Because of the multi-layered structure, it is difficult to resolve the operating mechanism of these solar cells. To meet this need, a home-built high-throughput incident photon to current efficiency (IPCE) measuring system was constructed. Using the new system and other high-throughput optical, electrical and structural scanning systems, we thoroughly studied the operating mechanisms of several all-oxide samples, including composite materials of Fe2O3, Co3O4, Bi2O3, TiO2 and others. In many of the cells we found evidence for two distinct processes with different operating mechanisms. The two mechanisms may work in parallel, compete, or even counter each other. As for their origin, the two mechanisms may result from photovoltaic activity of two different layers, or alternatively from activity of two separate bandgaps within the same material. Once the different mechanisms are understood, it is possible to enhance or to suppress one of them. This will allow for further improvement of the all-oxide cells’ photovoltaic performance.

Resume : In all practical photovoltaic cells, a major source of power conversion losses is the thermalization of carriers produced by the absorption of ultraviolet / blue light. The energy of photons in excess of the bandgap produces heat instead of electrical power. Artificial nanoscale materials, also known as metamaterials, are a potential platform to tackle this loss, because they can combine high spectral selectivity and quantum-confinement effects. Here we design and fabricate a metamaterial which can be incorporated on a traditional solar cell as an ‘add-on’ down-converter for solar radiation. This metamaterial provides absorption of photons from blue to ultraviolet, and emission via red / near-infrared photoluminescence. The light emission centers are Si nanocrystals, which are capable of efficient photoluminescence due to quantum confinement and enhancement through carrier multiplication processes. The metamaterial is obtained by combining semiconductor and dielectric nanostructures based on silicon, supporting electromagnetic resonances. We experimentally observe that the metamaterial photoluminescence is considerably boosted (> 200% time) by the enhancement of the Si-NCs absorption cross-section. Moreover, we investigate the opportunity to increase the emission rate and the probability of carrier multiplication. These results will facilitate the full control of optical transitions in an all-Si active metamaterial for energy applications.

Resume : We report an evidence of interfacial charge trapping mechanism in chemically synthesized polyaniline (PANI)/reduced graphene oxide (RGO) nanocomposites. The relative imaginary permittivity of the nanocomposites is carried out through broadband dielectric spectroscopy. Dielectric analyses indicate that the direct current (dc) conductivity (σ) decreases with increased RGO fraction and a Debye-like relaxation process which is analyzed within the framework of the Kohlrausch-William-Watts (KWW) model is observed at a frequency of ca. 5 kHz with increased RGO fraction in the nanocomposites. This relaxation can be explained by an electrical charge trapping mechanism which takes place at PANI/RGO interfaces. In addition, the dielectric relaxation dynamics and dc conductivity of the nanocomposites are studied as a function of temperature. The dielectric relaxation processes are interpreted according to Sillars approach and the results are consistent with the presence of conducting prolate spheroids (RGO) embedded into polymeric matrix (PANI). FE-SEM and TEM images confirm the multilayered nanostructural features of the composite and the numerous interactions between the RGO platelets and PANI aromatic rings through π-π stackings are evidenced by Raman spectroscopy and WAXRD studies. Such nanocomposite materials exhibiting charge trapping capabilities may find promising applications in supercapacitor or gate memory devices.

Resume : AlxGayIn1-x-yN III-nitrides semiconductor alloys have been widely studied for optoelectronic applications. Those alloys are interesting for solar cells absorbing layers. Nevertheless, the indium alloys suffer from the possible lack of indium in a close future. In this context, other alloys such as nitrides II and IV of the Zn-IV-N2 type have recently been proposed in which the IV element can be Sn, Ge or Si. These materials would present similar or superior properties while composed of abundant (then cheap) and non-toxic elements. Studies on ZnSnN2 are scarcer and the properties of this material are not well known. This work presents the development of ZnSnN2 thin films by reactive co-sputtering using zinc and tin metallic targets. The stoichiometry of the films was controlled by optimizing operating parameters such asthe target voltage, the nitrogen partial pressure or the total pressure.By modifying the growth parameters, we are able to obtain crystalline films.Advanced characterization techniques such as Mössbauer spectroscopy are used to get information about the chemical environment of tin.No contribution of metallic tin is observed. Fourier transform infrared spectroscopy and Raman spectrometry also reveal ZnSnN2 vibration modes. The opticalband gap has been deduced from UV-Visible spectroscopy measurements. Reference: [1] P. C. Quayle, J. He, J. Shan and K. Kash, MRS Communications, 3(03), 135-138 (2013).

Resume : Nowadays the idea to accomplish efficiencies buildings in which would possible combine green energy resources and efficiencies walls and windows to save the consumption is growing interest by scientific community. Photovoltachromic devices integrate photovoltaic and electrochromic functionalities allowing both their separate or conjugate use1. The recent development in the field of doped oxide nanocrystals may allow to develop a new class of transparent devices able to shield the infrared heat load carried by sunlight. Their optical features may be finely tuned by changing the nature of the nanomaterials engaged in the dynamic shift of the plasmonic scattering with specific parts of the solar spectrum. In this work, high-quality mesoporous electrodes based on Nb doped TiO2 nanocrystals made by colloidal synthesis2 has been studied and used to fabricated smart windows devices. This material present the possibility to be used in self-powered “plasmochromic” devices which are simultaneously capable of generating electric energy as a photovoltaic system, as well as controlling the energy fluxes by means of a smart variation of their optical transmittance. The effect of electrochemical charging on the optical features of the Nb doped TiO2-NCs mesoporous films has been systematically investigated by making them to work as anodes in a set of lab-scale EC cells filled with three different batches of electrolytes, respectively based on lithium iodide and 2-dimethyl-3-propylimidazolium iodide in propylencarbonate. Several devices has been fabricated and preliminary results shows a modulation of the NIR of around 90% and on the solar transmittance greater than 30%, accompanied with negligible reduction of the luminous transmittance, has been demonstrated in an optimized device. 1. Granqvist, C. G. Electrochromics for smart windows: Oxide-based thin films and devices. Thin Solid Films 564, 1–38 (2014). 2. De Trizio, L. et al. Nb-Doped Colloidal TiO2 Nanocrystals with Tunable Infrared Absorption. Chem. Mater. 25, 3383–3390 (2013).