Carbon and materials for energy applications

Resume : The insertion of guest species in graphite is the key feature utilized in applications ranging from energy storage and liquid purification to the synthesis of graphene. Recently, it was discovered that solvated-Naion intercalation can occur in graphite even though the insertion of Na ions alone is thermodynamically impossible; this phenomenon enables graphite to function as a promising anode for Na-ion batteries. In an effort to understand this unusual behavior, we investigate the solvated-Na-ion intercalation mechanism using in operando X-ray diffraction analysis, electrochemical titration, real-time optical observation, and density functional theory (DFT) calculations. The ultrafast intercalation is demonstrated in real time using millimeter-sized highly ordered pyrolytic graphite, in which instantaneous insertion of solvated-Na-ions occurs (in less than 2 s). The formation of various stagings with solvated-Na-ions in graphite is observed and precisely quantified for the first time. The atomistic configuration of the solvated-Na-ions in graphite is proposed based on the experimental results and DFT calculations. The correlation between the properties of various solvents and the Na ion co-intercalation further suggests a strategy to tune the electrochemical performance of graphite electrodes in Na rechargeable batteries.

Resume : The design of the next generation of efficient, high-performance secondary batteries requires an intimate understanding of the atomic-level mechanisms controlling ion migration, crystal structure stability, interface reactions, and so on. Atomic level computer simulation methods provide a powerful means of obtaining such information, and are becoming essential to many state-of-the-art studies where, in addition to helping interpret and explain experimental results, they are increasingly used to screen and search for novel battery materials prior to synthesis. In this paper, examples of computer modeling of novel Na-ion and Mg-ion conducting oxides will be presented that provide insights into fundamental phenomena pertinent to their use in secondary batteries. Examples include classical molecular dynamics simulations of NASICON-structured Na3V2(PO4)3 examining the effect of phase changes on Na-ion mobility; surface structures of olivine-structured NaFePO4; and electronic structure calculations of NaCrO2 and NaFeO2 polytypes.

Resume : Designing a highly efficient catalyst is essential to improve the electrochemical performance of Li-O2 batteries for long-term cycling. Furthermore, these batteries have significant capacity fading due to the irreversible reaction characteristics of the Li2O2 product. To overcome these problems, we propose a bi-functional composite catalyst composed of electrospun Co3O4 nanofibers (NF) immobilized on both sides of the non-oxidized graphene flakes (NOGFs) as an oxygen electrode in Li-O2 batteries. The NOGF-based electrodes show high discharge capacity (10500 mAh/g) and superior cyclability (>80 cycles with 1000 mAh/g) due to large surface area of Co3O4 NFs, facile electron transport via interconnected NOGFs, and fast O2 diffusion through the network formed with ultrathin NOGFs and porous Co3O4 NF. For fundamental improvement for Li-O2 battery, three-dimensional (3D) nanostructured catalyst is a very attractive candidate due to its large surface area, short electron diffusion length and effective mass transport. To realize highly efficient 3D nanostructured catalyst for Li-O2 battery, we propose a hierarchically porous, 3D nanostructured catalyst. Here we demonstrate successful fabrication of 3D nanostructured gold with hierarchical pore distribution over a large area (~1X1 inch2) via proximity field nanopatterning (PnP) and electroplating. The newly developed nanostructured material in this study is promising as an efficient electrode for Li-O2 battery.

Resume : The study of diffusion processes of small ions, such as lithium, sodium or even fluorine, in crystalline and amorphous solids has a long tradition in materials science. The studies published over the past years, either motivated by fundamental interest or driven because of applications behind, have brought out some quite interesting results in terms of mechanisms, fast diffusivity as well as spatially confined or interface-controlled motion. In particular, a thorough understanding of Li ion diffusion properties is indispensable if we want to develop new and powerful electrode materials and solid electrolytes for batteries. In order to meet this challenge ion dynamics are to be studied over a broad dynamic range. This purpose can be achieved by making use of complementary techniques such as Li nuclear magnetic resonance (NMR), such as echo and relaxation techniques, and conductivity spectroscopy. While the first, excluding field gradient techniques, gives access to jump rates and activation energies of the elementary hopping processes, ac and dc conductivity measurements, if recorded at median frequencies, are sensitive to overall macroscopic (ionic and electronic) transport. The present talk will spotlight latest results of studies focusing on (i) spatially confined Li diffusion in channel-structured and layered solids, e.g., LiC6 [1], and (ii) ion dynamics in (nano-)crystalline and single crystalline oxides such as garnet-type compounds [2]. Special emphasis will be put a) on materials offering extremely fast (liquid-like) translational diffusion, Li7P3S11, Li-argyrodites [3], and b) on compounds with ultraslow Li hopping processes, such as Li2O2 or Li2ZrO3 [4]. The NMR methods of choice mainly include frequency and temperature dependent relaxation measurements, 2D exchange spectroscopy as well as stimulated echo analyses preferably using both the Li(6) (spin-1) and Li(7) (spin-3/2) isotope. As an example, ultrafast Li ion dynamics with residence times as short as 1 ns at 263 K were probed for argyrodite-type Li6PS5Br [3a]. Such fast Li exchange correspond to conductivities of ca. 10 mS around room temperature. They are needed to develop all-solid-state lithium-based batteries taking advantage of highly conducting and inherently safe ceramic electrolytes. [1] a) B. Stanje, V. Epp, S. Nakhal, M. Lerch, M. Wilkening, ACS Appl. Mater Interfaces 7 (2015) 4089; b) V. Epp, S. Nakhal, M. Lerch, M. Wilkening, J. Phys.: Condens. Matter, 25 (2013) 195402; c) J. Langer, V. Epp, P. Heitjans, F. A. Mautner, M. Wilkening, Phys. Rev. B 88 (2013) 094304. [2] P. Bottke, D. Rettenwander, W. Schmidt, G. Amthauer, and M. Wilkening, Chem. Mater. 27 (2015) 6571. [3] a) V. Epp, O. Gün, H.-J. Deiseroth, M. Wilkening, J. Phys. Chem. Lett., 4 (2013) 2118. b) D. Wohlmuth, V. Epp, and M. Wilkening, ChemPhysChem. 16 (2015) 2582. [4] a) A. Dunst, V. Epp, I. Hanzu, S. Freunberger, M. Wilkening, Energy Environ. Sci. 7 (2014) 2739; b) P. Bottke, D. Freude, M. Wilkening, J. Phys. Chem. C, 117 (2013) 8114

Resume : Lithium ion battery has been rapidly developed for the applications in portable devices, electric vehicles (EV), and energy storage system (ESS) due to their high energy density and durable cycle life. From the practical viewpoint of electrode, high voltage charging and fast kinetics are essential to realize not only high power density but also high energy density for EV or ESS. However, it is quite challenging to improve both properties at the same time, especially for cathode materials. Thus, no matter what we develop for new cathode material, there have been severe limitations. Therefore, we devised a typical but synergistic way to fabricate a superb hybrid material in which the drawbacks of one material are completely covered by the advantages of the other material. In this synergistic way, we could successfully enhance the kinetic properties of Li3V2PO4 that is one of the representative high voltage cathode materials for Li ion battery, and utilize a conventional cathode material, LiCoO2, above 4.3 V. The detailed contents are as follows. Phosphate (PO4)3--based materials have been attracting tremendous interests due to their competitive energy density and remarkable thermal stability. Among these phosphates, monoclinic Li3V2(PO4)3 (LVP) was proposed as a highly promising cathode material, owing to its high operating voltage and very high theoretical capacity of 197 mAh g-1 when all three lithium ions are extracted/inserted between 3.0 and 4.8 V. In particular, its three-dimensional structure framework consisting of slightly distorted VO6 octahedral and PO4 tetrahedral sharing oxygen vertex provides large interstitial space that makes lithium ions capable of moving fast inside the structure [2]. However, just like the other metal phosphates, it shows a limited electron conductivity (10-8 - 10-9 S cm-1), which makes LVP to be difficult for practical applications [2]. Here, we present a sagacious design of LVP/carbon nanofiber with a distinctive morphology where LVP nanoparticles are anchored on the surface of carbon nanofiber. In general carbon-coated LVP 1D materials, there has been a problem that the carbon coating layer additionally interferes with lithium ion diffusion into LVP bulk. However, in our structure, LVP particles can directly contact with electrolytes leading to an improved lithium ion conductivity. Furthermore, carbon nanofiber can provide fast electron transport along its 1D pathway. As a result, it was demonstrated that this unique structure is favorable for simultaneously maximizing Li ion conductivity and electronic conductivity for great electrochemical improvement of LVP materials. LiCoO2 has the hexagonal α-NaFeO2 phase consisting of the layered rock-salt structure with the order of Li+ and Co3+ on alternating (111) planes in its cubic structure. When a Li/Li1-xCoxO2 cell is typically charged within limited composition range (0 < x < 0.5, 4.2V), it shows reasonably good capacity retention. However, the discharge capacity under the cut-off voltage of 4.2 V is around only 140 mAh/g, which is much lower than the theoretical value (274 mAh/g) of LiCoO2. Unfortunately, the practical use of LiCoO2 has been limited because its stability could be rapidly deteriorated at potentials higher than 4.2 V. Some research groups have reported that the poor cycling performance above 4.2 V is caused by structural instability induced by a phase transition from hexagonal phase to a monoclinic phase, which accompanies a volume change of ~2.6 % along the c-axis. To overcome the above problems, many researchers have developed lots of surface modifications that can improve the structural stability of LiCoO2. In this study, we tried to control the interlayer distance variation (lattice parameter c) though the substitution of phosphorus for Li+ sites by a phosphidation process. As a result, the unwanted phase transition could be suppressed by the existence of PO4 framework formed on the surface of LiCoO2 dramatically improving the cycleability and rate capability of LiCoO2 even above 4.5 V. Using this approach, we could easily change the surface O2-framework of LiCoO2 to PO4-framework. Consequently, phosphidated LiCoO2 came to retain very high structural stability and a stable surface film was formed in contact with electrolyte during charging/discharging. Phosphidated LiCoO2 exhibited greater bulk and surface stability compared to pristine LiCoO2 even in high voltage range, suggesting that this methodology will be also promising for other high-voltage cathode materials in lithium ion batteries.

Resume : Sodium-ion battery is a low cost energy storage device, which are similar in some ways to lithium-ion batteries. In both systems, Na/Li ions are shuttled between the battery’s positive and negative electrodes during charging and discharging. Taking into account recent concerns about a possible lithium shortage with the spread of electric vehicles, it is urgent to search for alternative energy storage systems that could complement the existing Li-ion technology. For this purpose, Na-ion technology can be a suitable choice in terms of battery cost, safety, and raw material abundance. Due to the increased size and heavier weight of the Na atom compared to the Li atom, the volumetric energy density and specific energy density obtainable for the sodium-ion battery would be significantly less than those obtainable with the lithium-ion battery. However, Na-ion batteries would be interesting for very low cost systems for grid storage, which could make renewable energy a primary source of energy rather than just a supplemental one. There are mainly three types of anode materials for sodium-ion batteries including carbon materials, alloy-based materials such as Sn, Sb, and P and insertion type sodium metal oxide materials. Alloy-based anode materials such as Sn, Sb, and P show high theoretical capacity of 847 (Na15Sn4), 660 (Na3Sb), 2,596 (Na3P) mAh g-1 towards sodium, but with more than 300% volume expansion. The theoretical capacity and the volume expansion ratio were shown in Figure 1. It can be found that the expansion ratio for Sodium based anode materials is more serious than Lithium based anode materials due to the bigger size of Na+ ions leading to poor cycle life. Several studies have shown that this massive volume expansion can lead to poor cycle life. Capacity fade can be caused by pulverization of the active particles or degradation of the electrode coating. Based on previous experience [1], the capacity fade of alloy-based negative electrodes is very sensitive to the choice of binder [2-4]. A good binder must ideally maintain adhesion of the electrode to the current collector, maintain ionic contact, and facilitate the formation of a stable interface with the electrolyte [5]. However, great efforts have to be made to find appropriate active materials for anodes of SIBs with cheaper price and environmental friendliness. Here, we will present our work on anode materials for sodium ion battery. The materials include carbon based materials, Sn-based materials and red phosphorous based composites with high specific capacity and excellent capacity retention [6-8]. 1. S. Komaba, Y. Matsuura, T. Ishikawa, N. Yabuuchi, W. Murata, S. Kuze, Electrochem. Commun. 2012, 21, 65. 2. J. F. Qian, Y. Chen, L. Wu, Y. L. Cao, X. P. Ai, H. X. Yang, Chem. Commun. 2012, 48, 7070 – 7072. 3. A. Darwiche, C. Marino, M. T. Sougrati, B. Fraisse, L. Stievano, L. Monconduit, J. Am. Chem. Soc. 2012, 134, 20805. 4. J. F. Qian, X. Y. Wu, Y. L. Cao, X. P. Ai, H. X. Yang, Angew. Chem., Int. Ed. 2013, 52, 4633-4636. 5. Y. Kim, Y. Park, A. Choi, N. S. Choi, J. Kim, J. Lee, J. H. Ryu, S. M. Oh, K. T. Lee, Adv. Mater. 2013, 25, 3045-3049. 6. W. J. Li, S. L. Chou, J. Z. Wang, H. K. Liu, and S. X. Dou, Nano Lett. 2013, 13(11), 5480-5484. 7. W.J. Li, S. L. Chou, J. Z. Wang, J. H. Kim, H.K. Liu, S.X. Dou, Adv. Mater. 2014, 26(24), 4037–4042. 8. Y. X. Wang, Y. G. Lim, M. S. Park, S. L. Chou, J. H. Kim, H. K. Liu, S. X. Dou, Y. J. Kim, J. Mater. Chem. A 2014, 2, 529-534.

Resume : Recently, Li4Ti5O12 (LTO), used as the negative electrode material in Li-ion batteries, has also been examined for the Na-ion battery. Na insertion in Li4Ti5O12 is accompanied with development of Na-substituted LTO phase with an about 4-5% larger unit cell volume which co-exists with Li4Ti5O12 in a single particle. In our work we studied Li and Na insertion into LTO of different particle size and synthetic history. The highest capacity and charging rate both for Li and Na insertion exhibited LTO prepared by sol-gel process pioneered in our laboratory. During testing of Li insertion by galvanostatic chronopotentiometry at 1C this material exhibited excellent stability over tens of cycles with almost 100% of theoretical capacity (175mAh/g). In contrary, commercial materials exhibited a capacity drop of about 30% after 50 cycles. In case of Na insertion, the charge capacity of sol-gel made LTO was 158mAh/g in the 1st cycle, however considerable capacity drop of about 40% was observed during cycling. This is obviously the consequence of irreversible structural changes induced by Na accommodation in the lattice. The best cycling stability for Na insertion exhibited commercial LTO from Altair. After 50 cycles at 1C the charge capacity decreased from initial 105mAh/g to 85mAh/g, i. e. of about 20%. This work was supported by the Grant Agency of the Czech Republic (contract No. 15-06511S) and by the Czech Ministry of Education, Youth and Sports (contract No. 8F15003).

Resume : Photon driven electrochemical reactions may contribute to future sustainable energy supply. Many different oxides (e.g. TiO2 or Fe2O3) have been tested so far to achieve photo-(electro-)chemical water splitting. Nevertheless, efficiency and/or materials stability are still not sufficient for widespread application of systems based on aqueous electrolytes. Photo-electrochemistry using solid oxide electrolytes, on the other hand, is an almost unexplored field. In such cells, operation temperatures of several hundred °C are required to enable sufficient oxide ion conduction. Very little knowledge is available on the experimental realization of such cells and on their problems. Here, we report results on the realization of a Solid Oxide Photo-Electrochemical Cell (SOPEC) using oxide ion conductors, operating at 400-500°C. The SOPEC includes a high temperature photovoltaic cell based on SrTiO3 in contact with La0.8Sr0.2CrO3, and a solid oxide electrolyte (Y doped zirconia). The photovoltaic cell part leads to open circuit voltages up to 920 mV at 400°C. The UV induced driving force is used in the electrochemical part of the cell to pump oxygen from low to high partial pressures, i.e. to convert radiation energy to chemical energy. This demonstrates the feasibility of high temperature photo-electrochemical cells for solar energy storage. The detailed characterization of the different resistance contributions in the system by DC and AC methods reveals the parts of the cell to be optimized for finally achieving high temperature photo-electrochemical water splitting. [1] G. C. Brunauer, B. Rotter, G. Walch, A. K. Opitz, G. Ponweiser, J. Summhammer, J. Fleig, Adv. Funct. Mater., 26 (2016) 120-128.

Resume : All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 22% and further improvements are expected up to 25%. These novel organometal halide perovskite absorbers which possess exceptionally strong and broad light absorption enable to approach the performances of the best thin film technologies. To commercialize these great solar cells, there are many bottlenecks such as long term stability, large scale fabrication process, and environmental issues. In this presentation, we demonstrate new fabrication processes for electron extraction layers such as electro-spray coating process and a novel 3-D nanopatterning technique that combines ion-assisted aerosol lithography (IAAL) and soft lithography. These processes are fairly suitable for realizing large scale fabrication of perovskite solar cells. In addition, we introduce a recycling technology of perovskite solar cells, which will facilitate the commercialization as well as solve the environmental issues of perovskite solar cells.

Resume : Recently, quantum dot solar cells (QDSCs) based on a depleted heterojunction structure achieved outstanding progress in power conversion efficiency (PCE). However, despite their promising potential, there are still remaining challenges to be solved for further improvement of their PEC. Here, we report that increasing the doping level of the metal oxide can significantly boost the depletion region width in the QD layer and improve the PCE of metal oxide/QD heterojunction solar cells. The performance of ZnO/PbS QDSCs with a lightly doped ZnO (n-ZnO, n ~ 1016 cm-3) film or a heavily doped ZnO (n+-ZnO, n ~ 1019 cm-3) layer was systematically characterized to elucidate the effect of the metal oxide doping level. The introduction of n+-ZnO instead of n-ZnO achieves an approximately 30% increase in the depletion region width in the QD layer from ~186 nm to ~242 nm, which was quantitatively estimated on the basis of current density-voltage (J-V) characteristics and capacitance-voltage (C-V) measurements. The optimum thickness of the QD layer therefore also increases from ~220 nm (n-ZnO device) to ~300 nm (n+-ZnO device). As a result, n+-ZnO/PbS QDSCs demonstrate a maximum PCE of 7.55% and a Jsc of 23.5 mA/cm2, which are significantly higher than those of n-ZnO/PbS QDSCs (PCE = 5.52%, and Jsc = 16.7 mA/cm2). Furthermore, the highly conductive n+-ZnO can have dual functionality as both a n-type layer and a transparent conducting oxide (TCO), and enables the successful fabrication and operation of QDSCs (PCE ~ 7.33%) without an additional bottom indium tin oxide (ITO) layer typically used as a TCO.

Resume : Graphene and titania find significant applications in dye sensitized solar cells as electrode materials for cathode and photoanode, respectively. The generic device is a liquid-junction photoelectrochemical cell with a dye-sensitized nanocrystalline TiO2 and Co-based electrolyte solutions. An alternative of this system is the solid-state dye sensitized solar cell in which the photogenerated holes are transported by a solid conductive material. Recently, this concept developed into the perovskite solar cell, exceeding 20 % conversion efficiency. Besides perovskite scaffold, titania is used for buffer layers in electron-collecting electrode. Here, the optimum blocking function is found for the sol-gel and ALD-made layers with thicknesses down to several nm. Accommodation of Li in TiO2¬ (anatase) and monoclinic TiO2(B) is applicable to the development of anodes for Li-ion batteries. The enhanced contribution of capacitive Li-storage in nanomaterials and faradaic pseudocapacitance in monoclinic TiO2(B) are of particular interest. These studies were further upgraded by investigation of titania nanomaterials labeled by oxygen isotopes 16, 17, 18 and insertion of Li 6 and 7 isotopes. Raman spectroelectrochemistry provided useful data about phase transitions during electrochemical Li-charging/discharging. The second-order Raman scattering in rutile, and the overlapping Raman features in anatase were addressed in detail. Acknowledgement: This work was supported and by the Czech Ministry of Education, Youth and Sports (contract No. 8F15003) and by the Czech National Science Foundation (contract No. 13-07724S).

Resume : Recently, the new technologies to produce renewable, sustainable energy have been invented such as wind energy, fuel cell, nuclear power, solar cells. Among those, organic photovoltaic cells (OPVs) have drawn a great attention due to its superior properties namely flexible, light weight, high efficiency, easy-making and low cost. The organolead halide perovskites have also emerged as an exciting material in photovoltaic research fields because of its large light-absorption coefficient, high carrier mobility and long carrier diffusion length. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely use as hole extraction layer (HEL) in OPVs and perovskite solar cells (PSCs) on account of its suitable band gap alignment with active layer and easy-fabrication via solution process. However, its acidic and hygroscopic nature makes it inappropriate for the real product [1]. To overcome the challenges caused by PEDOT:PSS, we have tried to use two dimensional materials instead of PEDOT:PSS as HEL in OPVs and PSCs, which include graphene oxide (GO), UV/ozone treated graphene, transition metal dichalcogenides (MoS2, WS2, TaS2, TiS2) and (NH4)2WS4. GO was synthesized by using Hummers’ method [2]. Graphene and transition metal dichalcogenides were prepared by chemical vapor deposition method or sonication process [3-5]. The lifetime comparison of OPV cells with UV/ozone-treated graphene and conventional PEDOT:PSS was conducted. The lifetimes were evaluated according to the ISOS-D-3 protocol with relative humidity of 90 % and temperature of 60 oC without encapsulation. The graphene underwent 5-min UV-ozone treatment. It is shown that the power conversion efficiency (PCE) of the PEDOT:PSS-based device rapidly decreased to ~ 0 % after 14-hour exposure in humid conditions while the UV/ozone-treated device continued to operate for 26 hours. This lifetime test suggests that more stable and efficient passivation can be achieved by replacing conventional PEDOT:PSS with UV/ozone-treated graphene. The current density-voltage characteristics of PSCs based on PEDOT:PSS, MoS2, WS2, and GO HEL are compared. The PCE of PEDOT:PSS based PSCs is 9.93%. The PCEs of MoS2, WS2, and GO based PSCs are 9.53, 8.02, and 9.62 %, respectively. Although PCE of WS2 based PSC was somewhat lower than that of PEDOT:PSS based ones, the PCE of GO and MoS2 based solar cell were similar to that of PEDOT:PSS based one, suggesting that GO and MoS2 HELs can be substituted for PEDOT:PSS. Therefore, it is considered that two dimensional materials could be used as HEL in OPVs and PSCs. [Acknowledgement] This research was supported in part by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2014R1A2A1A11051098) and in part by the International Cooperative R&D program through Korea Institute for Advancement of Technology (KIAT) funded by the Ministry of Trade, Industry and Energy (MOTIE) of Korea. [REFERENCES] 1. Jørgensen M., Norrman K., Krebs F. C.: Sol. Energy Mater. Sol. Cells 92, 686 (2008). 2. Park Y., Choi K. S., Kim S. Y.: Phys. Status Solidi A 209, 1363 (2012). 3. Kwon K. C., Dong W. J., Jung G. H., Ham J., Lee J.-L., Kim S. Y.: Sol. Energy Mater. Sol. Cells 109, 148 (2013). 4. Le Q. V., Nguyen T. P., Choi K. S., Cho Y.-H., Hong Y. J., Kim, S. Y.: Phys. Chem. Chem. Phys. 16, 25468 (2014). 5. Kwon K. C., Kim C., Le Q. V., Gim S., Jeon J.-M., Ham J., Lee J.-L., Jang H. W., Kim S. Y.: ACS Nano 9, 4146 (2015).

Resume : We present economical and versatile approaches to achieve structural precision, good scalability and novel periodicity of nanomaterials for energy applications. These novel approaches build on the bottom-up electrochemical techniques and are applicable to a wide range of materials and functions, including 1) electrochemically fabricated nanoporous metallic films, 2) electrochemically modified metal oxides, and 3) electrochemically treated bulk metal frameworks of large surface areas. For example, a convenient method is developed for mass producing monolithic porous metallic nanostructures of high specific surface area and improved mechanical performance. Alloys are first mechanically pretreated and grain-refined using the convenient surface mechanical attrition treatment (SMAT) and then dealloyed. The reactive metal component can be effectively removed at an accelerated rate, while the inert metal component forms a finer porous structure with the undesirable “self-coarsening” effect (the undesired structure rearrangement upon long-time soaking in the etchant that results in larger structural features to reduce the material overall surface area) largely suppressed. Monolithic supercapacitor electrodes of superior performance are enabled by the Cu-based bulk frameworks fabricated using the novel method reported in this study.

Resume : Colloidal semiconductor nanocrystals (NCs), also termed quantum dots (QDs), are composed of a core surrounded by different band gap material of its kind. With respect to core NCs, core/shell systems exhibit generally enhanced stability against photodegradation. So an important strategy to improve NCs’ surface passivation is their overgrowth with a shell of a second or third semiconductor, resulting in core/shell (CS) or core/shell/shell (CSS) heterostructured nanocrystals. Furthermore, by the appropriate choice of the core and shell materials, it is possible to tune the emission wavelength in a larger spectral window than with both materials alone. In this work we report a synthetic route to prepare ZnSe/Zn(Cd)S/Cd(Zn)S and CdSe/Zn(Cd)S/Cd(Zn)S Core/Shell/Shell heterostructured NCs. The synthesized nanocrystals were characterized by using high resolution TEM, x-ray diffraction (XRD) for structural properties and UV absorption and fluorescence techniques for optical properties. An ‘‘inverse’’ quantum dot quantim well (QDQW) structure has been realized with the synthesis of CdSe/ZnS/CdS and ZnSe/ZnS/CdS NCs, as here the larger-bandgap material is embedded between the lower-bandgap ones. In the case of CdSe/CdS/ZnS, CdS as a strain-reducing intermediate shell sandwiched between the core NC and the outer shell. The interest of such structures lies in the combination of low strain, provided by the intermediate layer (CdS) serving as a ‘‘lattice adapter’’ and the outer shell (ZnS) which assures efficient passivation and charge-carrier confinement. The effects of lattice mismatch induced interface strain on the first exciton energy, capped core diameter and conduction and valence band energies of the quantum dots investigated. The induced interface strain from lattice mismatch between core and shell(multishell) calculated from continuum elastic theory and included in effective mass aproximation (EMA) to calculate corresponding capped core diameter. The results compared with bare core images from TEM to evaluate squeeze (stretch) amount in core size after compressive (tensile) shell deposition.

Resume : Supercapacitor among many energy storage devices can realize fast charge discharge and long term cycling stability, however, its practical application is greatly restricted due to low energy density caused by limited electronic and ionic conductivity of electrode materials. The layered structure of NiMn layered double hydroxide (LDH) endows it as a promising supercapacitor electrodes, but low electronic conductivity limits the performance. In this work, the NiMn LDH is sulfidized to enhance the electronic conductivity, facilitate charge transfer and promote faster reversible redox reactions, while realizing enhanced specific capacitance. During the sulfidation process, the incorporated graphite oxide (GO) in GO/NiMn LDH composites can be simultaneously reduced, leading to an enhanced electronic conductivity, subsided defects and heteroatom S doping into graphitic structure. The sulfidized composite can achieve better long term stability due to mitigated phase transformation. As a result, specific capacitance as high as 2246.63 F/g can be realized by the sulfidized GO/LDH composite at current density of 1 A/g, while at increased current density of 10 A/g capacitance of 1670.83 F/g can be retained, manifesting an excellent capacitance and rate performance in comparison to other sulfide based electrode materials. The sulfidized composite also promises an enhanced cycling retention of ~ 67 % after 1500 cycles, compared to only ~ 44 % of pure NiMn LDH.

Resume : Hybrid halide perovskite based solar cells witnessed unprecedentedly rapid development in the past few years in terms of photoconversion efficiency. In spite of the progress achieved so far, a number of issues still remain to be solved, such as long term stability, toxicity induced by the presence of lead, cost effective and robust hole transport materials (HTMs) and a better understanding of the charge transfer at the interfaces, which governs the device operation. By far the most widely used HTM is 2,2',7,7'-Tetrakis(N,N-di-4-methoxyphenylamino)-9,9'-spirobiflourene, known as spiro-MeOTAD. Although spiro-MeOTAD has certified qualities as HTM, ensuring a barrier-free hole passage from the halide perovskite to the metallic (gold) contact, it also reveals some drawbacks: it may be responsible for the degradation of the perovskite layer by forming pinholes, as organic hole conductor long term stability is questionable and it is a relatively high cost material. Recent efforts to replace spiro-MeOTAD with an more stable and less expensive inorganic HTM, include cooper based compounds such as CuI, CuSCN or copper phthalocyanine, which however partly compromise the photoconversion efficiency (PCE). A promising inorganic HTM is Cu2O, with a high carrier mobility. Solar cells based on Cu2O were reported to yield reasonable PCEs [1]. Based on these recent promising experimental results we investigate by ab initio density functional theory (DFT) calculations the band alignment and charge transfer at the Cu2O/halide perovskite interface. We identify the band offsets using the approach introduced in Ref. [2] and discuss the charge distribution in the vecinity of the interface. Electronic structure modifications induced by point defects in the Cu2O layer are investigated. In this context we assess the conditions for a reliable hole transfer. [1] S. Chatterjee and A. J. Pal, J. Phys. Chem C 120, 1428 (2016). [2] G.A. Nemnes et al., Phys. Chem. Chem Phys. 17, 301417 (2015).

Resume : Keywords: Surface Mechanical Attrition Treatment (SMAT), titanium dioxide, photocatalysis, strain-induced defects, supercapacitors. Defect-based material engineering has found a niche in bandgap modification, photocatalysis and energy storage. Using a process called surface mechanical attrition treatment (SMAT)—normally reserved for deforming the surfaces of bulk material—we propose that this process can also be applied to delicate surfaces, allowing for the creation of strain and defect-based effects through stress concentration, vacancy creation, and/or dopant injection. Furthermore, with the great diversity of processing parameters of SMAT, one can deliver tailored treatment specific to the surface being modified as well as for the functionality being desired. In this work, we illustrate this concept by implementing SMAT in the modification of titanium dioxide (TiO2) nanotube arrays, leading to improved photocatalytic efficiency under solar radiation. We also suggest that with the further inclusion of surface dopants due to SMAT—when combined with the strain induced by said process—also yield a synergistic effect in light-harvesting in the modified TiO2, which has led to additional long-term operational stability on top of improved photocatalytic behavior being observed. Finally, with the enhanced defect creation via SMAT, the capacitance of the material has been enhanced from its original performance, demonstrating the value of using SMAT as a novel step in the functionalization process, as well as an effective post-treatment on already functionalized surfaces. a) yayutian-c@my.cityu.edu.hk b) yangli@cityu.edu.hk

Resume : Thermoelectric are perhaps the simplest technology for direct thermal to electric energy conversion. The conversion efficiency of a thermoelectric material is related to the dimensionless figure of merit ZT. High ZT is a counter-indicated property of matter. The tin diselenide (SnSe2) layered crystals are potential candidates for thermoelectric applications because of their high Seebeck coefficient and electrical conductivity. In this work, bulk SnSe2 single crystals were synthesized by gradient temperature method. The confirmation of single crystalline and composition determination of the grown crystals have been made by using X-ray diffraction and EPMA Quantitative Analysis techniques, respectively. The layered structure was observed via FE-SEM images. Thermoelectric response including electrical conductivity, Seebeck coefficients has been investigated in wide temperature range of 20-700K by using transport properties measurement system. Carrier concentration was evaluated by the Hall effect measurement with the van der Pauw method. The power factor value show obvious temperature dependences. Specific results will be discussed.

Resume : Like other semiconductor materials in III - VI compounds group (GaTe, In2Se3), Gallium Selenide (GaSe) appears to be a promising candidate material for thermoelectric applications in the future with high beta SE index which proportional to ZT value of thermoelectric material. In this work, the GaSe single crystal was grown from the high purity Ga and Se by vertical Bridgman method. The grown crystal can be cleaved in layer by layer without difficulty, confirmed the layered structure of GaSe. Meanwhile, the X-ray diffraction (XRD) result indicates the crystalline perfection of the grown single crystal as hexagonal structure. The absorption spectra analysis revealed the energy band gap of 1.98 eV, which is comparable to the reference value of 2.03 eV. We will discuss on transport properties of annealing GaSe samples.

Resume : Microbial Fuel Cells (MFCs) have been hailed as a promising technological solution for wastewater treatment in tandem with energy production. However, scaling MFC systems for high volume applications - as required in modern wastewater treatment facilities – has been impeded due to high internal resistances pertaining to the low efficiency of the oxygen reduction reaction (ORR) at the cathodic electrodes. To counter this issue, we developed a monochamber MFC employing highly conductive xerogel electrodes synthesized according to the resorcinol-formaldehyde method. Graphene oxide has been added into the precursor slurry, reducing into graphene in the xerogel matrix after thermal treatment. The cathodic electrode was treated with a strong peroxide solution to ease the ORR development; the anodic electrode was used as prepared. The MFC setup employed both electrolyte and microbiota collected from a functioning wastewater treatment facility in Romania. Finally, we characterized our system according to electrochemical activity, organic matter and nitrate removal efficiencies, as well as current and power density production.

Resume : The photocatalytic water splitting using solar light is a potentially clean and renewable source for the hydrogen production. Among several materials, TiO2 is one of the most promising photocatalyst due to its low cost, chemical inertness and high photostability, however in natural sunlight the photocatalytic efficiency of TiO2 is very low due to its large band gap (3.2 eV). Therefore, the development of efficient visible light active photocatalysts has been an attractive research field from the viewpoint of maximum utilization of solar energy. In very recent years, plasmonic photocatalytic composites have great potential for use in applications and is one of the most promising photocatalytic systems for high solar energy utilization efficiency [1-5]. In this work, Ag/TiO2/MWCNT ternary nanocomposite with optimal properties that enhance photo electrochemical (PEC) water splitting performance and photocatalytic activity is reported. Initially, TiO2/MWCNT nanocomposite was synthesized by hydrothermal method and then Ag nanoparticles were chemically grafted over the surface of as-synthesized TiO2/MWCNT nanocomposite for the formation of ternary nanocomposite system. Photocatalytic response of the prepared nanocomposite was studied through the degradation of a methylene blue solution using a solar irradiation source. The PEC property of the ternary hybrid electrode was also characterized by the linear sweep voltammetry. The results of both the methylene blue degradation and photocurrent tests indicated that the photocatalytic and PEC activities of the Ag/TiO2/MWCNT ternary hybrid are much higher than those of bare TiO2 and binary hybrids. The photocurrent density of Ag/TiO2/MWCNT photoanode under visible light illumination (20 mW/cm2) was 1 mA/cm2 (at 1 V vs Ag/AgCl), which is about 4 times higher than binary composite. The enhanced electron transfer within the Ag/TiO2/MWCNT was also confirmed by the electrochemical impedance spectroscopy. The efficient PEC water splitting of the ternary nanocomposite can be attributed to the synergetic effect of Ag nanoparticles and MWCNT, which enhances the photoresponse property of TiO2 in the visible region based on the surface plasmon resonance (SPR) effect and enhanced charge separation ability. This work demonstrates a feasible route to improve the PEC catalytic performance of TiO2 towards water splitting under sunlight irradiation. References [1] Z. Lian, W. Wang, S. Xiao, X. Li, Y. Cui, D. Zhang, G. Li and H. Li, Scientific Reports, 5 (2015) 10461. [2] E. Liu, L. Kang, Y. Yang, T. Sun, X. Hu, C. Zhu, H. Liu, Q. Wang, X. Li and J. Fan, Nanotechnology, 25 (2014) 165401. [3] W. Jiang, S. Bai, L. Wang , X. Wang, L. Yang , Y. Li, D. Liu, X. Wang, Z. Li, J. Jiang and Y. Xiong, Small, 12 (2016) 1640–1648. [4] D. Chaudhary, M. Z. Ansari, N. Khare , V. D. Vankar, Journal of nanoscience and nanotechnology, doi:10.1166/jnn.2016.12814. [5] M. M. Guia, W. M. P. Wong, S.-P. Chai, A. R. Mohamed, Chemical Engineering Journal 278 (2015) 272–278.

Resume : Due to the high redox voltage, low cost and sustainability, recently synthesized sulfate-based Na-ion batteries have become quite promising as the next generation cathode materials. Fe based kröhnkite-type material Na2Fe(SO4)2·2H2O has been synthesized under low temperature, showing high Fe3 /Fe2 redox potential at 3.25 V (vs Na/Na ). However, the fundamental insight regarding this material is still with limited understanding as far the electrochemical behaviour is concerned, especially about the intercalation processes, which play a significant role in the battery performance. In this study, Density Functional Theory (DFT) based calculation using GGA U approximation were performed to theoretically investigate the electronic properties and electrochemical behavior with respective magnetic configuration. To obtain diffusion barrier, nudge elastic band calculations were also systematically envisaged. During sodium removal, the oxidation state of Fe-centre gradually changes from 3 to 2 until half-desodiation is achieved and this has been nicely corresponded to the reported experimental observation. Na channel is primarily prevailed in the (001) plane, although the Na diffusions through several pathways are slow because of the presence of water molecules. Nevertheless, according to low defect formation energy, some intrinsic defects are likely to form and might participate in Na-ion diffusion of this material.

Resume : Bismuth vanadate (BiVO4) thin film for water-splitting in photoelectrochemical (PEC) cell has great potential in the design of low-cost, environmental friendly solar-hydrogen production. Presently, the solar-to-hydrogen conversion efficiency through PEC route is too low for the technology to be economically feasible. Bismuth vanadate (BiVO4) is an attractive material for its use in PEC cell for generation of hydrogen because of its suitable band gap (2.4-2.6 eV), abundance, stability and cost-effectiveness. But, its performance in a PEC cell is limited by high rate of charge recombination, unfavourable bandedge position with respect to water redox level and slow electron transport. This paper reports an improved photoelectrochemical response of Bismuth vanadate thin films after depositing FeOOH co-catalyst. Bismuth vanadate thin films were prepared by RF-sputtering technique and modified by FeOOH deposited by electrodepostion technique. X-ray diffraction, Raman spectroscopy and UV-Visible spectroscopy structural, optical and surface morphological characterization. XRD studies revealed the presence of monoclinic phase of BiVO4. The UV-Visible absorption curves showed extended absorbance in the visible region. The photoelectrochemical (PEC) studies were carried out in 0.1M Na2SO4 electrolyte in three electrode configuration. PEC results showed improvement in the photocurrent density of Bismuth vanadate from pristine and shift in onset potential (Von) for coupled photoelectrodes of BiVO4/FeOOH under visible light illumination. Detailed effect of FeOOH on surface morphology, optical absorption, electrical and photoelectrochemical properties will be discussed.

Resume : We have developed efficient nanostructures of Cu-Co-Ni alloy with varied stoichiometry as an alternative to the costly Pt-based alloys for hydrogen evolution reaction (HER). These nanoparticles were synthesized using reverse micellar method. The size of the alloy nanoparticles varied from 40-70 nm. An enhanced catalytic activity as evident from high current density was observed for these Cu-Co-Ni (111) alloys which follows the Volmer–Heyrovsky mechanism. They have excellent stability (up to 500 cycles) and significant activity in acid media which might be due to the low hydrogen binding energy.

Resume : In this study CuInSe2&CuInS2 (CIS) thin films were prepared on ITO glass substrate using electrodeposition technique in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS). The annealing effects on electrodeposited precursors were investigated. The chalcopyrite structure of CuInSe2/CuInS2 showed an enhancement of crystallinity after selenization/sulfurization treatment in Se/S atmosphere, respectively. XRD and SEM studies reveal a dramatic improvement of the crystalline quality of CIS films after annealing treatments. Mott-Schottky measurements were used to assess the conductivity type of the films and their carrier concentration.

Resume : Electrochemical water splitting has attracted substantial interest in the recent years as a key process in hydrogen production from sunlight and other sources of electricity. Recent experimental studies have demonstrated that Co3O4 is high-promising anode material for electrochemical water splitting due to its high catalytic activity in the oxygen evolution reaction (OER) [1]. In this context, understanding the interaction of Co3O4 surfaces with water is an essential preliminary step that can help to shed light on the atomic scale reaction mechanisms. Our attention is focused on investigation of Co3O4 (100) surface which are the most abundantly presented in Co3O4 nanoparticles [2]. Density functional method is applied to describe thermodynamics of electrocatalytic water splitting on the Co3O4 (100) surface. We calculated free energy changes along the reaction pathway using the computational standard hydrogen electrode (SHE) allowing us to replace a proton and an electron with half a hydrogen molecule at U = 0 V vs SHE. The analysis performed for the free energies is at standard conditions (pH = 0, T = 298.15 K) and U = 0. Using accurate DFT+U calculations, we shown that water adsorbs dissociatively on Co3O4 on the (100) surface [3]. Carbon doping of Co3O4 nanoparticles drastically changes their interaction with water. In this case the over potential decreased than in case of fluorine doping. In our investigations for water splitting on Co3O4 (100) surface carbon effectively than fluorine. References 1. I. C. Man, H.-Y. Su, F. Calle-Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, and J. Rossmeisl, ChemCatChem. 3, 1159 – 1165 (2011). 2. F. Zasada, W. Piskorz, S. Cristol, J.-F. Paul, A. Kotarba, and Z. Sojka, J. Phys. Chem. C. 114, 22245–22253 (2010). 3. G.A. Kaptagay, T.M. Inerbaev, Yu.A. Mastrikov, E.A. Kotomin, A.T.Akilbekov. Solid State Ionics 277 (2015) 77–82.

Resume : Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface performed by means of ultra-short pulse laser. Such a process represents a technologically easy process to fabricate ripples with a periodicity that depends on the laser wavelength on diamond surface, able to drastically modify the interaction with solar radiation from typical optical transparency up to solar absorptance values even higher than 90%. Here, we demonstrate that surface texturing gives rise to a strong enhancement of photo-responsivity in the visible range (up two orders of magnitude larger than the starting transparent diamond film). The operating mechanisms of black diamond is discussed and explained by disentangling the optical enhancement from an electronic increased density of states within the diamond bandgap corresponding to an actual intermediate band able to support an efficient photoelectronic conversion of sub-bandgap photons (<5.47 eV) [1]. The introduction of an intermediate band results in an enhanced external quantum efficiency up to 800 nm wavelengths, without affecting the film transport capabilities. Here, we further discuss recent results of process optimization on polyrcrystalline diamond, such as a reduced periodicity of the ripples and fabrication of 2D periodic structures [2]. This study is relevant for the developments of very well controlled periodic structures on single crystal diamond, opening the path for novel applications. [1] P. Calvani et al., "Black Diamond for Solar Energy Conversion”, Carbon 105 (2016) 401-407. [2]A. Bellucci et al., “Optimization of Black Diamond Films for Solar Energy Conversion”, Applied Surface Science (2016) in press, DOI: 10.1016/j.apsusc.2016.02.107.

Resume : Diamond-like carbon (DLC) have been produced by pulsed-laser deposition (PLD) of highly-oriented pyrolytic graphite (HOPG) target on transparent substrates, like quartz or glass, in order to use DLC as a buffer layer to obtain graphene-like films on top of the multilayer structure of DLC by thermal annealing process performed in Ultra High Vacuum (UHV) chamber using temperatures as high as 1373 K. The process of DLC production by PLD has been investigated using several techniques. The plasma dynamics have been studied by the Camille iCCD camera by Photonetics equipped with internal filter wheel using several optical filters and different time delays. The optical emission spectroscopy (OES) has been used for the spectral analysis of the plasma and the determination of the plasma parameters under different deposition conditions (e.g. laser fluence, laser wavelength). The Andor Mechelle ME 5000 OES spectrometer equipped with iCCD camera Andor iStar has been used for this purpose.

Resume : Graphene has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Furthermore, graphene oxide and graphene based nanocomposites with transition metal oxides nanoparticles (G-MOx NPs and GOx-MOx NPs) are considered as novel prospective materials for energy storage in batteries and supercapacitors. To make an essential impact toward sustainable development, the fabrication technologies of G-MOx NPs and GOx-MOx NPs should be as eco-friendly as possible. We report on the “green” chemical synthesis of graphene via i) chemical treatment of graphite by conventional modified Hummers method (MHM) followed by ii) eco-friendly reduction of obtained graphene oxide by several “green” reducers: ascorbic acid (vitamin C), caffeic acid, D-glucose and anthocyanine containing berries extract. The prepared graphene and its predeceasing oxide were mixed by combinatorial approach with nanoparticles of transition metal oxides (Co3O4, Fe2O3, ZnO, TiO2). The microstructure and crystal structure of the nanocomposited were investigated by Scanning Electron microscopy and X-ray Diffraction, while the electrochemical characterization of nanocomposites electrodes was performed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results obtained are discussed in terms of modern advance in energy storage devices.

Resume : Carbon-supported light metal hydrides are relevant for a range of applications including reversible hydrogen storage, batteries (in electrodes and solid state electrolytes), and ammonia capture. Nanosizing of light metal hydrides has in general yielded significant improvements to their functionality, such as enhanced Li+ ionic conductivity, or largely enhanced reversibility and sorption kinetics in hydrogen storage.[1,2] We highlight in this presentation carbon supported LiH nanoparticles which have been very little studied so far, most likely due to the fact that common preparation techniques cannot readily be applied to LiH. We identified for the first time a procedure to prepare supported LiH nanoparticles [3]. Impregnation of a porous carbon material with a butyllithium solution followed by reaction with hydrogen and driving off the solvent yielded carbon-supported LiH particles ranging in size from 2 nm to micrometer scale. The impact of particle size and the type of carbon support on the hydrogen storage properties was studied in detail [3,4]. The optimized preparation of the LiH/C gives a nanocomposite that begins hydrogen release as low as 100 °C and 10.4 wt% (wrt LiH) is released. Most remarkably hydrogen release was reversible: uptake of up to 5.2 wt% can be performed at 200 °C and as low as 0.1 bar H2 pressure, while full uptake can occur within 5 minutes at 26 bar. This unprecedented behaviour can be attributed to optimization of the preparation procedure as well as a specific interaction with the carbon support [3,4]. [1] de Jongh and Adelhelm, ChemSusChem, 3 (2010), 1332. [2] Blanchard et al., Adv. Funct. Mater. 25 (2015), 182. [3] Bramwell et al, submitted. [4] Ngene et al., Nano Energy 22 (2016), 169.

Resume : Due to limited natural abundance of lithium, novel battery technologies are needed for large-scale, stationary storage of electricity. Such batteries can then be combined with renewable sources of electricity, for the best integration of a variety of sources into electrical grid. We will discuss the utility of nanoscale inorganic materials as cathode and anode materials in Mg-ion batteries. In particular, the focus will be on a balance between the performance, material’s synthesis costs and natural abundance of the constituting elements. Owing to the reduced diffusivity of Mg-ions in most materials, nanostructuring has been identified to be of drastically higher importance than in the case of alkali-ion (Li, Na) batteries. The cathodic side of a battery remains the bottleneck. In this regard, we present several metal sulfides, delivering capacities of up to160 mAh g-1, with plateau voltages of 1.1-1.2V. On the anode side, we present Bi nanostructures as convenient anodes for research purposes. In particular, Bi-based anodes operate in a variety of electrolytes, in which metallic Mg is non-operational due to oxidative passivation.

Resume : Carbon obtained by pyrolysis of natural cellulosic precursors is hard or non-graphitizing as no subsequent heat process leads to ordered graphitic materials. However, the addition of a transition metal to the precursor induces graphitization within solid carbon materials during the pyrolysis at moderate temperatures in a single processing step. Catalytic graphitization has been intensively employed to produce graphitic materials, but the complex catalytic process by transition metals is not completely understood despite the intense research activity. In previous research, graphitic carbon monoliths from pyrolyzed wood were successfully obtained and this graphitization step was shown to enhance the electrochemical storage capacity and thermal conductivity of the material. In this work we perform a kinetic and structural characterization of the graphitization reaction in-situ through differential scanning calorimetry coupled with mass spectrometry in situ during the pyrolysis and x-ray diffraction, evaluating the intermediate compounds formed during the process and the temperature differences in the onset of graphitization to understand the mechanism and optimize the desirable characteristics of the graphitic material.

Resume : The reactivity of carbonaceous surfaces and its homogeneity are expected to be strongly dependent on the chemical and structural defects that, as reported in literature, can be induced by various treatments, including irradiation [1-4]. The present work is focused on surface properties and heterogeneity changes in carbonaceous materials induced by irradiation and investigated by Raman and photoluminescence (PL) spectrometry at the micro scale. The aim is to investigate more specifically the evolution of the Raman and PL spectra before and after different types of irradiation and their correlation. Irradiation tests are performed in dry conditions for different types of carbonaceous materials: graphene single layer on different substrates, highly oriented pyrolytic graphite (HOPG), carbon filled polyvinylidene fluorid (BMA5 (PVDF)). For HOPG and BMA5 in the as-received state, the Raman and PL spectra depend on the carbonaceous material nature. The spectra evolution shows that the concentration of defects increases during the electron irradiation. After UV irradiation, the evolution of spectra reveals a strong dependence on the irradiation conditions (UV light wavelength, flux and dose) and on defect concentration. Moreover, for the graphene single layer on Ni after 1 hour of UV irradiation, the Raman and the PL spectra vary independently with the increase in UV flux intensity. Keywords: graphene, carbon filled polyvinylidene fluorid, irradiation, UV, Raman spectroscopy, photoluminescence. References: 1. Teweldebrhan D. et al. Appl. Phys. Lett., 94,013101–013103, (2009) 2. Kotakoski J. et al. PRL 106, 105505 (2011) 3. Giannazzo F. et al. Nanoscale Research Letters (2011) 4. Pimenta M ;A. et al. Phys. Chem. Chem. Phys., 9, 1276-1290 (2007)

Resume : Research on novel carbon allotropes never loses momentum. The expectation of a larger variety than what is known so far is motivated by its ability to form tetrahedral sp3 compounds like diamond, as well as planar sp2 graphite. Between those two limiting geometries a manifold of intermediate cases is known, from fullerenes to nanotubes, from hyperbolic Schwarzites to carbon foams. While the planar sp2 unit implies layers of merged six-rings, as regular triangles tile the Euclidean plane, this is not necessarily true for structures based on sp3 centres. Diamond consists of adamantane-like cages of fused six-rings in chair conformation. On the other hand 3D structures with planar six-rings and tetrahedral centres seem to be intrinsically a problem, unless there is a certain amount of odd rings in the structure. Combination of odd and even rings is key to hard and transparent carbon materials, while entangling 1D nanotubes in regular pattern produces superior hydrogen storage materials. Dirac fermions appears in single sheet graphene, while electronic properties can be further tuned in few-layers gaphites. In the attempt to expand the catalogue of carbons, we have found novel graphenoid strcutures, based on sp2 centers, which nonetheless are not planar, i.e. they represent 3D gaphenes. They define a novel class of compounds, that can be derived from generalised graphite compounds, whereby different tilings of the plane can be used. Along this way, different graphites as well as graphenoid carbons can be obtained, which hosts interesting electronic properties. The chirality of some of them may represent the starting point towards pure carbon 3D Weyl fermion materials, which so far could be realised in exotic materials only. The possibility of experimentally accessing these materials from suitable precursors is also part of this study.

Resume : Assemblies of graphene oxide (GO) sheets into macroscopic membranes are of great interest because of their promising applications in energy conversion, gas separation, molecular filtration, nanofluidic system and so on. In particular, GO membranes have been demonstrated to have excellent mechanical properties and their extraordinary stability in water has been noted, which is a prerequisite for their membrane applications in solution. However, this is counterintuitive because GO sheets become negatively charged on hydration and the electrostatic repulsion between the sheets should make the membrane disintegrate. In this study, we have discovered a long-overlooked reason behind this apparent contradiction. Our findings show that while neat GO membranes do, indeed, readily disintegrate in water, the films become stable if they are crosslinked by multivalent cationic metal contaminants. Such metal contaminants can be introduced unintentionally during the synthesis and processing of GO. This new insight improves the understanding of interlayer interaction in GO membranes and their durability, which is crucial for proper use of GO thin films. Strategies to avoid and mitigate metal contamination are discussed. We also demonstrate that we can take advantage of the crosslinking effect for synthesizing layered oxide materials. This simple and versatile synthetic strategy holds great potential to prepare hybrid materials for energy applications including Li-ion batteries, supercapacitors, and photocatalysis. The finding has wide implications in interpreting the processing–structure–property relationships of GO and other lamellar membranes and opens up new opportunities to study wet-chemical reactions confined in the few nanometers of space between layers.

Resume : The photoelectrochemical (PEC) splitting of water for scalable and sustainable production of hydrogen (chemical fuel) requires a semiconductor to absorb light and generate electron?hole pairs, and a catalyst to enhance the kinetics of electron transfer between the semiconductor and solution. Therefore, building on high catalytic active hematite thin films based on oxygen evolution catalysts (OECs) are promising compounds as a high-performance Earth-abundant catalyst for photoelectrochemical hydrogen production. Here we present an experimental study on surface modification of hematite thin films with OECs to get enhanced PEC water splitting under visible light irradiation. We demonstrate that a dual modification, hydrogen treatment and OEC loading can achieve a considerably higher photocurrent density and more negative shift in the onset potential with respect to the pristine ?-Fe2O3 and exhibit long term stability under visible light illumination. The enhancement in PEC performance in OEC photoanode can be attributed due to the high electrocatalytic performance of OEC that facilitate the photo-generated electron mobilization which increases the amount of photo-generated holes involved in the water oxidation reaction and accelerates the kinetics of water oxidation.

Resume : Steam reforming are two processes which are used for the hydrogen and oxygen evolution reaction for production of energy. A large number of studies can be found in the literature regarding the production of new catalysts for steam reforming through copper-based and group 8?10 metal-based catalysts. Knowing that the boron sheet is the lightest 2D material and therefore exploring the catalytic activity of such monolayer system would be quite interesting, we use computational approach to explore the possibility for the same. Functionalization of the boron sheet with different elemental dopants has been explored and also determined the adsorption energy for each case. Thereafter, free energy calculated from the individual adsorption energy for each functionalized boron sheet subsequently guides us to predict which case of functionalization serves better for HER or OER. This in principle pave the way of extensive research in energy production using photocatalytic water splitting through oxygen and hydrogen evolution.

Resume : The solar water splitting is the third generation of solar energy utilizing technology for future energy problem. Through the past years, the technology has been amazingly meliorated, and theoretical basis has been enormously progressed. In recent days, much endeavor has been dedicated to enhancing solar water splitting efficiency. For further improvement, we need to deeply reflect a perspective of charge generation and transport in photoelectrodes and at interfaces between the electrodes and water. One of the most appropriate strategies for this concept would be grafting plasmonics to the photoelectrodes generally based on oxide semiconductors. We present photoelectrochemical properties of TiO2 thin films and TiO2 nanorods with 0-dimensional (0D) plasmonic Au nanoparticles. Our results clearly reveal the substantial enhancement of photoactivity in TiO2 by incorporating Au plasmonic nanoparticles. We show that the enhancement is strongly dependent on the shape of the 0D Au nanoparticles, suggesting that the localized surface plamonic resonances with high electromagnetic fields act as really effective hydrogen evolution catalysts on oxide-based photoanodes. Another appropriate strategy to develop efficient and stable water splitting photoelectrodes is the utilization of a surface protection layer which prevents photocorrosion of semiconductor photoelectrodes such as Si. We show that solution-processed 1D TiO2 nanorods can be used as protection and antireflective layer for Si photocathodes. It is also shown that 1D TiO2 nanorods themselves have catalytic effect to split water. Using the 1D TiO2 nanorods, we demonstrate the state-of-the-art performance of Si photocathodes. Finally, we are going to show chemical vapor deposition method to grow wafer-scale 2D transition metal disulfides (TMDs) such as MoS2 and WS2. We transfer large-area thin films composed of 2D TMDs to Si substrate to prepare efficient and stable photocathodes for solar water splitting. Atomically thin TMD films play important roles in hydrogen evolution reaction. We show the catalytic effect of 2D TMDs to dramatically lower charge transfer resistances at the semiconductor (p-Si)/electrolyte (water) interfaces. Compared with a bare Si photocathode, substantially enhanced stability of TMD/p-Si photocathodes is also presented.

Resume : Since the success story of lithium iron phosphate, other phosphate-based compounds have attracted a lot of interest as promising candidates for positive electrodes in lithium-ion or sodium-ion batteries. Their electronic conductivity usually has to be improved through the preparation of composite powders ensuring intimate contact between the active material and conductive carbon. We report on the one-step synthesis of composite precursors using spray-drying or hydrothermal synthesis routes, two techniques which offer easy scaling-up of production. We show that addition of a solid carbon source (carbon black or carbon nanotubes) into the solution has a strong influence on the powder microstructure and is very effective in improving the battery cycling performance, taking our recent results on phosphates [Fex(PO4)(OH)y.zH2O)] and fluorophosphates [Na2FePO4F, Na3V2(PO4)2F3] as examples. We also compare this approach with the addition of the carbon source as a soluble precursor (such as ascorbic acid or citric acid) where the in situ formation of carbon is achieved by a heat treatment in inert atmosphere (typically argon).

Resume : Structural batteries have emerged as a possible solution for reducing weight and volume of structures for a variety of applications [1], ranging from portable devices to space and electric vehicles. In view of multifunctional structural composite applications, this talk reports the findings of a reactive molecular dynamics study. The study explores the dependence of structural failure in SiO2- or Al2O3-coated Si nanotube anodes on Li concentration. In particular, the relation between the anode’s interface-debonding failure mechanisms and Li content at different battery charging levels is investigated. On microscale level, the effect of Li content is quantified in terms of the interface mechanical failure strains and stresses. Further considering the anode’s failure resistance properties, the size range for observable nanoscale size effects is estimated. The latter objective is achieved by comparing the failure responses of 3-D-periodic slab interface structures. Within the scope of the study, we anticipate that Al2O3/SiO2 softening due to Li charging [2, 3] may contribute to an improved failure resistance. Similarly, we also expect that a reduction in Si stiffness due to amorphization that occurs during Li charging [4] would result in larger deformations than those corresponding to crystalline phases and, as a result, Li concentration dependent structural response. References: [1] L. E. Asp and E. S. Greenhalgh. “Structural power composites”. In: Composites Science and Technology 101 (2014), pp. 41–61. [2] S.-Y. Kim et al. “Self-generated concentration and modulus gradient coating design to protect Si nano-wire electrodes during lithiation”. In: Phys. Chem. Chem. Phys. 18 (5 2016), pp. 3706–3715. [3] A. Ostadhossein et al. “Atomic Insight into the Lithium Storage and Diffusion Mechanism of SiO2/Al2O3 Electrodes of Lithium Ion Batter- ies: ReaxFF Reactive Force Field Modeling”. In: The Journal of Phys- ical Chemistry A 120.13 (2016), pp. 2114–2127. [4] Z. I. Popov et al. “A theoretical study of lithium absorption in amor- phous and crystalline silicon”. In: Journal of Structural Chemistry 52.5 (2011), pp. 861–869.

Resume : Due to their excellent mechanical properties and electrical conductivities, carbon nanofibers (CNFs) have been suggested for many applications including lithium ion battery electrodes. Since the specific capacity of electrode materials in nanoscale can approach to the theoretical values, macroscopic forms of these nanomaterials have been vastly researched that can have excellent properties in nanoscale at macroscale. In this study, CNF yarns were manufactured through a yarning process of composite CNFs (i.e., CNFs containing silicon (Si) nanoparticles or lithium iron phosphate (LFP) nanoparticles) for lithium ion battery microfiber electrodes. First, poly(acrylonitrile) (PAN) nanofibers containing Si or LFP nanoparticles were spun by coaxial electrospinning process. Then, PAN microfibers were pulled from the electrospun PAN nanofiber web and twisted. The PAN microfiber was hot-stretched to align PAN nanofibers and calcined into carbon nanocomposite yarns. The nanocomposite yarns were coated with polymer electrolytes by dip-coating method. The mechanical tests were carried out to quantitatively characterize the strength, stiffness, and flexibility of the carbon nanocomposite yarns and their electrochemical characterizations were carried out using freestanding yarns without conducting additives or binders.

Resume : Increasing demand in small, flexible electronic devices have promoted research and development of flexible electrodes. The fiber is the most promising form for flexible electrodes due to its flexibility and strength and applicability to textile fabrics. On the other hand, graphenes have excellent mechanical, thermal and electrical properties in nano-scale, being considered as preferred candidate of building blocks for such fiber electrodes. Due to the inertness of graphene, however, it is not routine to disperse and assemble them into a fiber. Instead, graphene oxide (GO) has been used for fiber manufacturing because it can form liquid crystals, which is important to make fibers through wet-spinning. This research is aimed to explore an efficient manufacturing method of strong GO fibers and their potential applications to flexible electrodes. In this study, GO fibers are manufactured via liquid crystal wet spinning process. First, liquid crystal GO spinning dope is prepared in aqueous solution and spun into rotating coagulation bath. During wet spinning process, GO is aligned in flow direction, forming into a bundle structure. Spun GO bundles are gathered, combined, and twisted into GO yarns. The GO yarns are expected to have enhanced strength due to densification and lateral pressure of GO fibers inside yarns. Finally, the mechanical and electrochemical properties of GO yarns are characterized to investigate their applicability to flexible electrodes.

Resume : The direct conversion of solar energy into fuels, H2 in particular, at a simple and low cost semiconductor/water junction is still a challenge. Despite the theoretical simplicity of such a device, limitations in suitable semiconductor materials have hindered its development. Recently, few authors started exploring the potential of organic and hybrid organic-inorganic semiconductors, as an alternative to the usual transition metal oxides or more costly III-V semiconductors, in photoelectrochemical systems. Most reports described performances in the order of 1 mA/cm2 at the reversible hydrogen electrode potential (RHE), relatively low onset potentials and limited stability. Here we report our recent results on the optimization of a hybrid organic-inorganic photocathode for the direct conversion of solar light into chemical energy. Starting from a prototypical P3HT:PCBM blend as photoactive element, we focused our attention on different interfacial layers and their influence on the photocathode performances. The photocatalytic activity and long-term stability of a simple, catalysed, bulk heterojunction is proven and the specific effect on hydrogen generation performances of electron- and hole- selective contacts is investigated. The relevance of our findings can be summarized in few key points: (i) high performances with a maximum photocurrent of 8 mA/cm2 at RHE and 50% IPCE; (ii) optimal process stability with 100% faradaic efficiency along the whole electrode’s lifetime; (iii) excellent energetics with onset potential as high as +0.7 V vs RHE; (iv) promising operational activity of several tens of hours and (vi) by-design compatibility for implementation in a tandem architecture. In addition, we realized a large area, all-solution processed device as the first proof of concept of the high versatility and up-scaling potential of our approach. Collectively, this set of features establish the hybrid architecture we developed well ahead of existing reports on organic photoelectrochemical systems and suggest the potential of the hybrid organic-inorganic photoelectrochemical (HOPEC) concept as real contender to the traditional inorganic counterpart.

Resume : InGaN semiconductors are promising for hybrid tandem solar cells due to their intrinsic properties and tuneable direct bandgap in the visible spectrum. Best solar cell efficiencies are obtained in structures with an active region consisting of InGaN/GaN multiple quantum-wells (MQWs), which delays the onset of misfit relaxation. However, to further improve the photovoltaic (PV) characteristics, it is necessary to optimize the active region design. In this work, we investigate the dependence of the PV performance of In0.1Ga0.9N/GaN (1.3/8.7 nm) MQW solar cells as a function of the number of wells (5-100, i.e. active region thickness of 50-1000 nm). The In content and QW/barrier thicknesses were chosen so as to limit the strain relaxation and the formation of structural defects. Increasing the number of wells from 5 to 40 significantly improves the PV characteristics (Voc and Jsc) under 1 sun of AM1.5 illumination, resulting in a 10 fold enhancement of the conversion efficiency (0.9%; maximum peak external quantum efficiency of 38% at 380 nm). A saturation of Jsc (and hence of the efficiency) is measured for cells with active regions above 40 MQWs. This feature is attributed to carrier collection losses and increased recombination in the MQW region associated with its incomplete depletion. A hole diffusion length in the MQW region of 48±6 nm is estimated from diffusion and drift current equations, taking into account the depletion width value extracted from capacitance measurements.

Resume : Scarcity of pure water worldwide is dramatically affecting the economic development of Third Countries but also the industrial growth of others. Electrochemical Advanced Oxidation Processes (EAOPs) are clean technologies for water recycling and reuse thanks to the production of hydroxyl radicals by electrolysis (i.e. needing an external energy source). We propose here an autonomous electrochemical cell fed by the direct green electrical energy coming from an abiotic electrode for glucose oxidation at gold anode (CF@Au) and oxygen reduction (Eq. 1) at a novel (Carbon Felt (CF)/porous Carbon (pC)) cathode. In this concept, electrons coming from glucose oxidation allow oxygen reduction, formation of hydrogen peroxide and then hydroxyl radicals generation through the Fenton reaction in presence of added iron (Eq. 2): O2 + 2H+ + 2e- → H2O2 (1) Fe2+ + H2O2 + H+ → Fe3+ + •OH + H2O (2) The highly active cathode is fabricated by an attractive route combining Atomic Layer Deposition (ALD) of metal oxide (ZnO) on commercial carbon felts (CF) followed by its subsequent solvothermal conversion to corresponding MOFs (ZIF-8). The as-prepared composite material was further calcined at high temperatures under controlled atmosphere forming porous carbon-based (pC) supports with high specific surface area and enhanced conductivity. The morphology, thickness and homogeneity of the obtained composite materials (CF/pC) were studied at different locations, using a high resolution scanning electron microscope (FESEM, Hitachi S-4800). X-ray diffraction analysis has been performed to investigate materials crystallinity. The N2 sorption-desorption isotherms of the virgin CF and porous carbon coated CF were measured. TGA, FTIR and XPS measurements of the as prepared composite materials were also conducted. Degradation kinetics of Acid Orange 7 (AO7) at CF/pC cathode by •OH radicals, a powerful oxidant, from Fenton reaction (Eq. 1), was monitored by UV-Vis spectrophotometry, HPLC and TOC analysis to prove the efficiency of the composite material for the mineralization of these bio-refractory model molecules. On the other hand, to supply electrons for the oxygen reduction reaction (ORR) into oxygen peroxide (Eq. 1), power was generated from glucose electro-oxidation at the anode manufactured by electrodeposition of gold particles, an efficient electrocatalyst for glucose oxidation. The CF@Au electrode was chosen because of its large electrochemical surface area, its excellent chemical stability, its high conductivity and the biocompatibility of the nanostructured gold films. The catalytic properties of both anode and cathode induce a stable output power maintained for at least one month. From that, pollutants are degraded efficiently, showing the high potential of this Fuel Cell-Fenton based system as a promising green technology for both environmental and energy areas. [1] Thi Xuan Huong Le, Mikhael Bechelany, Joffrey Champavert and Marc Cretin, A Highly Active Based Graphene Cathode for Electro-Fenton Reaction, RSC Advances, 2015, 5, 42536 – 42539

Resume : The application of fuel cell grade gas diffusion layer carbon paper (CP) electrodes in the all­ vanadium redox flow battery (VRFB) has allowed the maximum power density to be achieved for the system [1]. Up till today, the possible performance loss mechanisms of the electrodes due to poor micro-­structurally related mass transport of the electrolyte have not been understood nor been studied in much detail. In this work, time resolved 3D /4D imaging was used to study in-­situ the infiltration mechanism of the vanadium-­based electrolytes at four different concentrations. The wetting mechanisms have been analysed and the influence of respective parameters are discussed. The same CP electrodes are later subjected to electrophoresis in N,N'­dimethylformamide (DMF) consisting of reduced graphene oxide (rGO). EPD is conducted at a voltage of 300 V and an inter­-electrode distance of 15 mm. Thermal post­ treatment of the CP worsens electrochemical performance (measured in terms of cyclic voltammetry and electrochemical impedance spectroscopy). X­ ray computerized tomography (XCT) confirms an increase in the electrochemical surface area with rGO. Furthermore, XCT confirms that the deposition also penetrates into the substrate. Raman analysis shows that the rGO deposited is more amorphous than the CP electrode. An enhancement in the electrochemistry of the all­-vanadium redox flow battery catholyte is also observed when employing the modified samples for cyclic voltammetry and impedance tests. Polarisation tests show some marginal improvement of peak power densities in an all­vanadium redox flow battery after depositing rGO on the CP electrodes. Too much compression tends to clog up the pores of the CP by the deposited rGO and thus a torque of 4 Nm was used in most cases. Round­-trip efficiencies showed further improvements than peak power densities. Reference ======== [1] Q. H. Liu, G. M. Grim, A. B. Papandrew, A. Turhan, T. A. Zawodzinski and M. M. Mench. High Performance Vanadium Redox Flow Batteries with Optimized Electrode Configuration and Membrane Selection. Journal of the Electrochemical Society 159 (2012) A1246-­A1252.

Resume : One pot synthesis of MoS2 nanoflakes: Effect of temperature on structural & optical properties Navnita kumari1*, B. R. Mehta1 1Department of Physics, IIT Delhi, New Delhi Corresponding Author E mail:- k.navnita@gmail.com Abstract In family of Transition Metal Chalcogenides (TMDs), Molybdenum disulfide (MoS2) is a highly capable material for energy harvesting applications such as lithium ion batteries (LIBs), photocatalysis, photoelectrochemical as well as electronic device etc. MoS2 nanoflakes and nanoflowers were prepared by one step hydrothermal route with uniform morphology in temperature range 150-220°C. From XRD and HRTEM it has been clearly observed that grown nanoflakes have hexagonal primitive structure. Orientation of grown nanoflakes and flowers shows at (002) plane with interplanar spacing 0.61 nm and (100) plane having 0.32 nm which confirmed growth of MoS2 in desired pattern and signature of hexagonal arrangement. Temperature affects the formation of nanoflakes conversion towards 3D nanoflowers. FTIR transmission spectrum shows the vibrational bonding around wave number 467 cm-1 which is signature peaks of bonding between S-Mo-S with different morphology its showing shift in nature which may be due to another bonding of Mo-O at around 451 cm-1 which is grown at temperature 220°C. In Raman spectra prepared nanostructure shows a difference between two consecutive peaks is the range of 18 cm-1 to 24 cm-1 which indicates its change towards monolayer to few layers. The distance between two consecutive peaks is around 19 cm-1 which is clear signature of momolayer formation. Conversion of indirect band gap to direct band gap in monolayer structure has been confirmed by photoluminescence (PL) studies. This monolayer to few layers structures potentially important for different device application point of view.

Resume : Augmented thermoelectric performance of p-type Sb2Te3 films is investigated by introducing the interfacial energy-barrier scattering (i.e., barrier heights) occurring at both grain boundaries and interfaces between embedded second-phases. It’s postulated that the barrier heights filter the low energy carriers, thus favoring a high Seebeck coefficient. The Sb2Te3 nanocomposite films were formed via solid-state phase transition using amorphous Sb-Te electrodeposits as the starting materials. The initial composition and post-annealing profiles are varied to control the formation of the γ-SbTe and Te second nanophase. Electrical and thermoelectric properties are correlated with the physical properties, where the enhanced Seebeck coefficient at a given carrier concentration is interpreted that the energy-dependent carrier filtering effect is at play. The barrier height was indirectly manifested by measuring their difference in the valence band, advocating the possibility of a strong energy dependent charge scattering. On a promising note, the formation of the γ-SbTe/Sb2Te3 and Te/Sb2Te3 nanocomposites readily produces an effect on the interfacial energy-barrier scatterings along with the enhanced power factor – making it a candidate as a promising p-type thermoelectric material for room-temperature operational micro-thermoelectric power generator.

Resume : Due to limited conventional fossil energy and increasing greenhouse gas emission, highly efficient utilization of energy and developing new energy storage materials become more and more important. PCMs (Phase change materials) can provide high energy storage density and near isothermal heat storage, and contribute to more environmentally friendly energy use. As shell materials of encapsulated PCMs, organic–inorganic hybrids can combine the advantages of both organic and inorganic materials. In this work, we nanoencapsulated n-octadecane with PS–SiO2 (polystyrene–silica) hybrid shell in miniemulsion. FT-IR spectroscopy and XRD analysis were used to verify the chemical composition and crystallinity of the as-prepared nanocapsules, respectively. SEM and TEM results demonstrated that these nanocapsules possess regular bowl-like morphology (diameter: 320–440 nm) and well-defined core-shell structure. Phase change properties of the nanocapsules were characterized by DSC analysis, revealing that high melting enthalpies (79.5–126.0 J/g) and encapsulation ratios (37.3–59.1%) have been achieved. The crystallizing behaviors were clarified by means of temperature-dependent XRD measurements. TGA results revealed that the thermal stability of the nanocapsules is improved largely, compared with that of pristine n-octadecane. After 1000 melting/solidifying thermal cycles, the chemical structure, morphology, and phase change enthalpies of the nanocapsules were maintained perfectly, and supercooling behavior was mitigated obviously.

Resume : RPU (Rigid polyurethane) foams possess low thermal conductivity, high mechanical and chemical stability and high durability, and their thermoregulation property can be enhanced markedly by incorporation of various encapsulated PCMs (phase change materials). As a result, they can be used as ideal heat-insulated building materials, to enhance the energy efficiency and sustainability of buildings. The significant development of NanoPCMs (nanoencapsulated phase change materials) in recent years, especially that with inorganic shell materials, might offer new opportunity for the fabrication of advanced thermoregulated composite materials. Herein, thermoregulated RPU foams containing silica shelled NanoPCMs were fabricated, in order to improve their thermal energy storage capacity and mitigate the adverse effect of fillers on the morphology and mechanical properties. Chemical composition and morphology of the composite foams were characterized by FT-IR and SEM, respectively. Thermal properties of the composite foams were evaluated by DSC, TGA, and DMTA (dynamic mechanical thermal analysis) methods. The NanoPCMs are homogeneously dispersed in polyurethane matrix. Higher NanoPCMs contents in the composite foams lead to slightly increased cell size, minor decrease of glass transition temperature (Tg), and higher phase change enthalpies. The composite foams exhibit good thermal reliability, reasonable thermoregulation property, and fairly high compressive properties. In addition, the compressive property-density relationship for the composite foams agrees well with the Gibson-Ashby’s power law.

Resume : The structure of nanoporous carbon has a strong effect on the electrochemical characteristics of the devices like supercapacitors, polymer electrolyte fuel cells and electrolysers, Li-ion and Na-ion batteries. For that reason, it is crucial to have a good understanding of the porosity and structure of used carbon materials. As a standard method, the nitrogen adsorption measurements and various analysis theories (e.g Brunauer-Emmett-Teller and non-local density functional theory) are used. However, these models need the pore shape as an input parameter for detailed calculations and often the slit-shaped pore model is assumed without additional verification. This assumption is also very often transferred to the behaviour of carbon materials in different applications leading to some serious misinterpretations. Our research focuses on determining the pore shape and size in three carbide-derived carbon materials using various rather standardized methods, like nitrogen adsorption measurements, Raman spectra analysis etc., combined with small-angle neutrons scattering. The results obtained are compared to the behaviour of these materials in different energy storage/conversion related devices like supercapacitors and polymer electrolyte fuel cells. As a result, the importance of hierarchical porous structure and pore shape along with pore size of used carbon materials in these applications will be addressed and demonstrated.

Resume : Dominant technology of fabrication high quality of single layer graphene on large area is Chemical Vapor Deposition (CVD). The best results are obtained for metal substrates (Ni, Ci or MoNi). Much more sophisticated is graphene fabrication on the semiconductor and isulating substrates, which are commonly used in electronic and optoelectronic devices. Technology of graphene transfer on the arbitrary substrates will open wide range of new application. Combining the low-cost metal oxides thin films with single graphene layers allows to obtain multilayer structures with improve optoelectronic properties. Zinc oxide layers were obtained using decomposition of Zn(acac)2 hydrate method. Graphene layer was transferred from the copper foil on the zinc oxide layer by low temperature wet transfer method, using the PMMA as a temporary carrier medium. Etching processes of copper foil and PMMA were optimized to obtain the high quality of graphene on the zinc oxide surface without residuals of PMMA. Presence of graphene on the surface was confirmed using the Raman spectroscopy (2D peak at 2699 cm-1 and G peak at 1592 cm-1). Intensity of 2D peak was two times higher than for G peak. Optical and electrical properties of graphene single layer/ZnO structure were investigated. Combining of the transparent conductive oxide and electron transport layers for potential applications in organic photovoltaics are presented.

Resume : Burning fossil fuels that are in finite reserves globally triggers problems because of the emission of CO2 and other air pollutants. These issues have stimulated interest in hydrogen as a clean energy source. In these sense, the water electrolysis is a cost-effective method to produce hydrogen and environment-friendly. However, the design of oxygen electrodes is the main limiting factor, so the use of an electrocatalyst support different to conventional carbon support is an important aspect to study of this systems. For this reason, in this work we present the physicochemical and electrochemical characterization of Sb-doped SnO2 (ATO) synthesized by Sol-Gel method and assisted by microwave as a support for H2 production. Morphology, composition, crystallinity and surface area were investigated by SEM, EDS, XRD and BET. The results showed that the ATO has a homogeneous distribution and crystal sizes 5-6 nm with a preferential planes (110) and (101) corresponding to the tetrahedral rutile structure. The electrochemical characterization was evaluated for H2 production at E=1.8 V vs. NHE during 7 days of continuous operation and compared with Vulcan Carbon in a membraneless water microfluidic electrolyzer. The results show improved chemical stability when the ATO is subjected to these conditions, whereas Vulcan Carbon is corroded easily. As a perspective, this system can be integrated with a microfluidic fuel cell to supply energy to low-power devices.

Resume : Graphene thin films on Diamond-like carbon (DLC) films have been obtained on transparent substrates like quartz or glass by pulse laser deposition (PLD) of carbon at ambient temperature followed by either thermal annealing performed in Ultra High Vacuum condition up to 1273 K. The surface formation of a graphene-like film on top of the DLC, soon experimentally shown in Appl. Phys. A, Materials Science & Processing, 71, 433–439 (2000), has been investigated as a function of many parameters of the PLD and post-PLD processes (like laser fluence, DLC thickness, annealing temperature). The roughness of the films was find lower than 1 nm set over a rather large surface area. The density of the carbon has been measured both by XPS and Nuclear Reaction Analyses (NRA). The formation of graphene films on top of DLC have been characterized by X-ray photoemission (XPS) and Raman scattering. Under optimized conditions these films can exhibit high surface conductivity, optical transmission and work function performances, so that it can be achieved a high figure of merit (conductivity of transparency) as transparent conductors.

Resume : Thermoelectric (TE) materials are devices capable of converting energy from waste heat into an electrical potential when a temperature gradient is induced between the two ends of a material. The wide application range of TE materials includes the sectors of automotive, wearable electronics and power stations. However, current TE devices are composed of semiconductor materials which tend to be toxic, inorganic and expensive to manufacture such as Bismuth Telluride, thus, making the production of these devices into real-world applications challenging. In this project, carbon nanotubes (CNT) are shown to be an alternative TE material with properties that include mechanical flexibility, low manufacturing cost and non-toxicity. The process of functionalizing CNTs and doping them to n-type and p-type semiconductors is investigated. An efficient TE device should translate to a high figure of merit (ZT) which requires a high power factor and a low thermal conductivity. The latter is investigated and we reveal that nano-defects and phonon scattering in low dimensional structures can result in a low thermal conductivity by the inclusion of various concentrations of Polyethylenimine (PEI) which reduces the phonon mean free path without significantly affecting the power factor. The thermal conductivity of the synthesised CNT/PEI composites were measured and calculated to be as low as 20 W/mK at a temperature of 50°C.

Resume : An outstanding challenge in the realm of photocatalysis is the development of nanomaterials functional under visible region; to tackle the present plight of environment. Our work unfolds the design of core/shell nanostructures manifesting an appreciable photoelectrochemical water splitting and photocatalytic degradation of methylene blue, a noxious organic pollutant of dye waste water under visible light. Using core/shell geometry and the apposite sensitizer, we have tuned the absorption of NaNbO3 nanostructures to the visible region. The NaNbO3 core/shell nanostructures with the expanded light harvesting range are utilized for the destructive oxidation of noxious organic pollutants with the goal to ameliorate the environment. The remarkably enhanced photocatalytic activity of core/shell nanostructures could be interpreted in terms of efficient charge separation owing to core/shell geometry and resulting type-II band alignment between NaNbO3 and the sensitizer, which creates a step-like radial potential favoring the localization of one of the carriers in the core and the other in the shell.1 Our work unfolds the importance of core/shell nanostructures in leading toward new paradigms for developing highly efficient and reusable photocatalysts for the mitigation of noxious organic pollutants. Keywords: Photocatalysis, core/shell, NaNbO3, type-II band alignment, sensitizer 1. Kumar, S.; Singh, A. P.; Bera, C.; Thirumal, M.; Mehta, B. R.; Ganguli, A. K. Visible Light Driven Photoelectrochemical and Photocatalytic Performance of NaNbO3/Ag2S Core/Shell Heterostructure ChemSusChem, 2016 (Accepted)

Resume : Porous carbon materials are known for their applicability in important areas such as electrochemistry (e.g. fuel cell catalysts, where a lot of interest aroused due to possible coupling of advantageous structural properties and unique chemistry. The preparation of high content doped and conductive graphitic carbons can be achieved e.g. by employing ionic liquids (ILs) as precursors. We and others have shown that mesoporous carbon with structurally integrated nitrogen acts as an inexpensive and highly active metal-free catalyst in the oxygen reduction reaction (ORR).[1-3] A key-drawback was still the necessity of using silica templates and their hazardous removal to obtain porous high surface area materials. Our recent research focuses first on the porosity development in alternative fashion and second on the employment of naturally abundant carbon precursors, both for the perspective of large scale synthesis.[4, 5] Materials with very high surface areas and total pore volumes are accessible using alternative templates and molten salt syntheses and even completely new carbon morphologies are obtained throughout a carbonization from the wet state.[6, 7] The performance as non-noble electrocatalysts for the oxygen reduction reaction and the role of porosity will be discussed [1] W. Yang, T.-P. Fellinger, M. Antonietti, J. Am. Chem. Soc. 2011, 133, 206. [2] R. Liu, D. Wu, X. Feng, K. Müllen, Angew. Chem. Int. Ed. 2010, 49, 2565. [3] T.-P. Fellinger, F. Hasché, P. Strasser, M. Antonietti, J. Am. Chem. Soc. 2012, 134, 4072-4075. [4] N. Fechler, T.-P. Fellinger, M. Antonietti, Adv. Mater. 2013, 25, 75-79. [5] K. Elumeeva, N. Fechler, T.-P. Fellinger, M. Antonietti, Mater. Hor. 2014, 1, 588-594. [6] Y. Chang, M. Antonietti, T.-P. Fellinger, Angew. Chem. 2015, 54, 5507-5512. [7] J. Zhu, K. Sakaushi, G. Clavel, M. Shalom, M. Antonietti, T.-P. Fellinger, J. Am. Chem. Soc. 2015, 137, 5480-5485.

Resume : With the rapid growth of industrialization, huge amounts of dye effluents are often disposed into the environment causing significant pollution in water. Microwave (MW) irradiation in water treatment has gained attention due to its rapid and selective heating of materials. In this study, we have developed a two-step method involving impregnation and calcinations processes for the controllable synthesis of a porous Cu-Ni/C catalyst by using organic tissue paper as template. The sample was mesoporous and it exhibited macoporous networks composing of interwoven carbon fibers loaded with Cu-Ni nano-particles. The surface area of the sample was determined to be 538 m2/g. The product also exhibited high catalytic activity in the degradation of acid fuchsin dye during the microwave induced catalytic oxidation (MWICO) process. The degradation of acid fuchsin was a fast process under MW irritation. Not only in the chromophore group, but the naphthalene ring and benzene ring could also be destroyed. The presence of Ni had a significant effect on the degradation because it enhanced the formation of the hydroxyl radicals (•OH) under MW irritation. This outcome is important, not only because a hierarchically porous catalyst with high active sites has been developed using a simple bio-template route, it advanced the understanding of the roles of transition metals and activated carbon in dye degradation in water treatment under electromagnetic wave irradiation.

Resume : Graphene is a promising material for supercapacitor applications, both in electric double layer capacitors and as a conductive support for incorporating materials with large pseudocapacitance. Aerogels represent an attractive way to fabricate 3D graphene structures with large and accessible specific surface area suitable for supercapacitor electrodes. Freeze casting is a versatile route for aerogel fabrication that is scalable and has a relatively low production cost. However, most prior work on freeze casting graphene aerogels used graphene oxide (GO) as the source material because of the need to disperse it in water prior to freezing and vacuum sublimation. The resulting GO aerogel must be reduced to form the electrically conductive reduced graphene oxide (rGO) before it can be used as an electrode. Here we present a method to fabricate pristine graphene aerogels for supercapacitors using phenol as a room temperature sublimeable vehicle, without the need for a reduction step. These materials have electrical conductivity values reaching 0.9 S/cm, which is greater than equivalent rGO aerogels with similar densities produced by aqueous freeze casting. Alternative solvent systems have been identified using a solubility parameter approach and examples of aerogels fabricated with these materials that are more suitable for larger scale manufacture will be presented.

Resume : InGaN alloys are promising semiconductors for hybrid tandem solar cells due to their tuneable direct bandgap within the visible spectrum. Best solar cell efficiencies are obtained in structures grown by metalorganic vapour phase epitaxy (MOVPE) with active regions including InGaN/GaN multiple quantum-wells (MQWs). However, to further improve the photovoltaic characteristics the In content should be increased, being then the plasma-assisted molecular beam epitaxy (PAMBE) the most suitable growth technique. In this work we present results on solar cells based on InGaN/GaN MQWs grown by MOVPE and In-rich InGaN junctions grown by PAMBE. The design of the active region including QW, barrier and total thicknesses, and In mole fraction is critical for the success of the solar cells. We investigate the dependence of the photovoltaic performance on these parameters to limit the strain relaxation and the formation of structural defects while improving the conversion efficiency. Regarding In-rich InGaN devices, the PAMBE growth mechanisms that control the strain relaxation and In incorporation in thick layers is discussed. We demonstrate that the presence of Mg does not disturb the In incorporation and leads to a reduction of the stacking fault density in p-doped InGaN. The electrical characterization of p-i-n InxGa1-xN homojunctions (x = 0.10.4) is presented, which peak external quantum efficiency is 14±2% in the blue-to-orange spectral region with a cut-off from 465 nm to 600 nm.

Resume : Ammonia has been proposed as an efficient indirect hydrogen carrier, as it contains a large fraction of H2 (up to 18 wt% in liquid NH3) and it can be directly used as a fuel in SOFCs to produce energy, without greenhouse emissions. Nowadays, infrastructure for NH3 production, handling and transportation are well-established and developed, but the identification of a system for solid-state ammonia-storage would allow to further reduce hazards at a level below those of gasoline. Here we investigated the ability of lithium intercalated fullerides LixC60 (x = 3, 6, 12) to absorb large amount of ammonia, forming novel hyper-ammoniated phases, by letting react the fulleride with liquid NH3 at low T. The ammonia release from these compounds was investigated using high intensity neutron powder diffraction, in-situ/ex-situ manometric analyses and differential scanning calorimetry. We found that in (ND3)yLixC60 ammonia molecules are stored in their neutral state inside the inter-fullerene interstices and are coordinated to the intercalated Li ions, forming Li–ND3 clusters. In particular, Li6C60 was found to absorb up to 36.8 wt% ND3, corresponding to 14 ammonia molecules per C60. Ammonia desorption takes place in two main steps, at 350–410 K and 500–540 K, respectively, corresponding to two clear 1st order structural phase transitions, and absorption process is partially reversible. These findings suggest that these systems could be good candidates for ammonia-storage applications.

Resume : The adsorption equilibria of ethane (C2H6) and ethylene (C2H4) in the MIL-53(Al) metal organic framework are characterized using a self-consistent procedure combining experimental measurements and molecular simulation. Experimental single-component adsorption equilibrium data for C2H6 at 303 K, 323 K, 353 K, and 0–8 bar, and for C2H4 at 323 K, 353 K, 373 K, and 0–1.7 bar, are successfully interpreted using classical thermodynamics and statistical mechanics. An analysis of the experimental results shows that the large-pore form of the tested MIL-53(Al) sample is thermodynamically favoured in the pressure and temperature ranges spanned in the experiments. The adsorption equilibria of the two adsorbates are studied is detail by Monte Carlo (MC) simulation in the Canonical (NVT) and Grand-Canonical (GC) ensembles using the TraPPE united-atom force field to describe both the fluid–fluid and solid–fluid interactions. The good agreement between the GCMC results and experimental measurements shows that the adopted force field provides a good description of the dispersive solid–fluid interactions in MIL-53(Al). The molecular configuration of the confined ethylene molecules at different loadings is studied in the NVT ensemble and the preferential positions and orientations of the C2H4 molecules are determined. Binary C2H6/C2H4 adsorption equilibrium in the pressure and temperature ranges of the single-component experiments is predicted by GCMC using the validated force field. The ideal behaviour of the binary adsorbed mixture is demonstrated using the Ideal Adsorbed Solution Theory (IAST) and the multicomponent extension of the Toth isotherm model.