Materials, mechanism and devices in nano energy including one day on Carbon dioxide recovery and circular economy of carbon

Resume : High-efficiency solar-to-fuel energy conversion can be achieved using a photoelectrochemical (PEC) device consisting of an n-type photoanode in tandem with a p-type photocathode. However, the development of stable and inexpensive p-type photocathodes are needed to make PEC devices economically viable. In this presentation our group’s progress in the development of economically-prepared, high performance photoelectrodes will be discussed along with the application toward overall PEC water splitting tandem cells. Specifically, how the use of scalable solution-processing techniques (e.g. colloidal processing of nanoparticles) leads to limitations in charge transport and charge transfer in the resulting thin-film photoelectrode will be examined. Strategies to overcome these limitations such as using charge extraction buffer layers, catalysts, annealing/doping and nanoparticle self-assembly will be additionally presented. Materials of interest are delafossite CuFeO2, CZTS, CIGS, CdS and 2D-layered MoS2 and WSe2.

Resume : Enabling a new economy based on renewable energy sources requires finding new materials with different band gaps to work as photoabsorbers for Photoelectrochemical (PEC) water splitting. CIGS solar cells can be fabricated with band gaps from 1.0 to 1.7 eV modifying its stoichiometry, and can be deposited on flexible stainless steel sheets. Additionally, CIGS shows the highest conversion efficiency among the thin films technologies (21.7%), combined with extremely good stability even in hard conditions, being an ideal candidate for PEC water splitting applications. TiO2 protective layers can protect the photoabsorber material from degradation when put in contact with the electrolyte, and growing them by ALD reduces the possibility of pinholes being created. With a favorable band alignment, TiO2 can transport the photogenerated charges to the hydrogen evolution reaction catalyst while allowing a proper light transmission and low current and potential losses. In this work, we have demonstrated stability in acidic media, giving constant 10mA/cm2 at 0 V vs RHE with 100 mW/cm2 AM1.5G light and 0.4 V open circuit potential, using a 13% efficiency CIGS flexible based solar cell as photocathode. Protective layers play a crucial role into achieving stable high efficiency electrodes for PEC water splitting and implementing state-of-the-art photoactive materials. It shows that chalcogenides can be candidates and higher open circuit voltage can be obtained according to the composition.

Resume : Iron (III) oxides can be efficiently exploited for the sunlight-assisted photocatalytic hydrogen production from aqueous solutions, without the application of any external electrical bias. Favorable chemical and physical properties, coupled with high abundance, non-toxicity and low cost, make indeed Fe2O3 an ideal photocatalyst, in particular in the form supported material, overcoming the typical drawbacks related to the use of powdered systems. In the framework of iron(III) oxides, our group has recently demonstrated the high photocatalytic potential of the ε-Fe2O3 polymorph with respect to the commonly studied α-Fe2O3 one. In the present work, ε-Fe2O3 nanorod arrays have been grown on Si(100) by chemical vapor deposition, and tested as photocatalysts under simulated sunlight irradiation, resulting in hydrogen yields up to 20 mmol h-1 m-2. The material performances were further improved by iron oxidefunctionalization with metal (Ag, Au) aggregates via radio frequency sputtering. In particular, decoration with Au nanoparticles enabled to obtain a significant H2 evolution even under the sole Vis light, revealing the beneficial effects arising from the introduction of plasmonic structures.1 1 G. Carraro, et al. RSC Advances 2014, 4, 32174.

Resume : Efficient separation of the photoexcited electron-hole pairs is one of the major requirements for high solar energy to hydrogen conversion efficiency in photoelectrochemical cells based on semiconductor materials. Hence the controlled engineering of the electric potential profile across the photoactive semiconductor electrode promises considerable progress towards economic hydrogen production. Here we present our results from ab-initio calculations on the possibility of engineering the electronic properties of metal oxides by incorporation of various metal and nonmetal dopants. Additionally, an outlook will be given to the modelling of heterojunctions of promising semiconductor materials.

Resume : In very recent reports, ORR electrocatalysts based on different nitrogen-bearing compounds, such as, polyaniline, polypyrrole, and imidazolic framework with phenanthroline pyrolized with carbon, have been extensively explored. It has been established that the type of nitrogen precursor remains a key player in determining the property of the resulting ORR catalyst. In this regard and to further understand ORR mechanism, a new nitrogen precursor based on 2-vinyl-4, 5-dicyanoimidazole (called Vinazene) was for the first time used. Vinazene together with an iron source was impregnated into a carbon matrix and pyrolyzed at 900 °C in N2 atmosphere. The structure of the resulting Fe-N-C nanocomposite was analyzed by X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction spectroscopy. As expected, the catalyst was found to be rich in mesoporous structure along with predominant percentage of pyrrolic-N function with surface area of about 673 m2 g-1 and pore size of 4.2 nm Also, the catalyst was studied by electrochemical techniques; both rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) experiments showed excellent ORR activity with negligible H2O2 formation in alkaline solution. In addition to its excellent ORR activity, the catalyst exhibited remarkable tolerance towards methanol oxidation and good cycling stability over 10,000 potential cycles between 0.6 and 1.0 V Vs RHE). Details will be presented and discussed.

Resume : Water electrolysis represents a clean, sustainable and environmentally friendly way to produce H2, a fuel for energy-related applications in future. To enable large-scale deployment of electrolyzers, efficient, inexpensive and durable electrocatalysts for H2 evolution reaction (HER) must be developed. Since 2013, Ni2P has emerged as a promising HER catalyst and drawn great attention. In this presentation, we report an easy one-step approach to fabricating Ni2P-nanorods/Ni foam (Ni2P-NRs/Ni) hybrid electrode by direct phosphorization of a commercially available Ni foam current collector under solvothermal conditions. When tested as a cathode for H2 evolution, the as-fabricated Ni2P-NRs/Ni hybrid electrode exhibits an onset potential as small as -33 mV vs. RHE and a large cathodic current of 42 mA cm-2 at an overpotential of 200 mV. Moreover, to attain current densities of 10 and 20 mA cm-2, only small overpotentials of 131 and 162 mV are needed, respectively. Additionally, the electrode also shows reasonably good long-term stability. The excellent electrocatalytic performance of the hybrid Ni2P-NRs/Ni electrodes can be attributed to the unique 3D porous feature of Ni foam, which is not only beneficial for mass transfer of the electrolyte and release of H2 gas bubbles, but also greatly facilitates the electron transport. The Ni2P-NRs/Ni hybrid electrodes reported here hold substantial promise for use as efficient and low-cost cathodes in electrolyzers.

Resume : We coat the pore walls of an anodic nanoporous template with either galvanic deposition or atomic layer deposition (ALD) to obtain structured electrode surfaces that provide the experimentalist with a well-defined, tunable geometry. Indeed, the platform consists of a hexagonally ordered array of metallic or oxidic nanotubes of cylindrical shape, embedded in an inert matrix. The diameter of the tubes can be defined between 20 and 300 nm and their length between 0.5 and 100 μm, approximately. We utilize them as a model system in which the electrode's specific surface area can be increased and its effect on the electrocatalytic current characterized systematically. Diffusion-limited electrochemical transformations remain unaffected by changes in the length of the electrode's pores, whereas the steady-state galvanic current density observed for slow multielectron transformations increases linearly with the pore length. In particular, this approach enables us to increase the electrochemical water oxidation turnover at iron oxide surfaces by two to three orders of magnitude at the optimal point. These results highlight a strategy for optimizing electrochemical energy transformation devices which could be generalized: the geometric tuning of catalytically mediocre but abundant and cost-effective material systems.

Resume : Fe-doped NiOOH, is one of the best inexpensive catalysts for O2 evolution in photo/electrocatalytic water splitting [1], but its atomic and electronic features are not well understood as the material, with a structure in H bond-linked layers, is normally highly disordered. Here the electronic structure of the bulk system, Fe-doped or not, is modelled with a hybrid DFT method, able to give accurate bandgaps, in which the fraction of Fock exchange is tuned to the optical dielectric constant [2]. Several stackings of NiOOH layers and protons arrangements are studied. Lowest energy is found for a 3R-type stacking and distribution of Ni atoms in both NiO2(OH)4 and NiO4(OH)2 coordinations; other arrangements are near in energy, explaining the tendency to disorder. Bandgaps, the edges of which consist of Ni 3d levels, are in the ~1.0-1.4 eV range, depending on the exact atomic configuration. Substituting Ni by Fe introduces filled Fe 3d levels near the valence band edge, and in some configurations a redox process Ni(3+) + Fe(3+) -> Ni(2+) + Fe(4+) occurs, eventually with a jump of protons from Fe to Ni coordination spheres. This suggests a high electronic and protonic conductivity, which probably helps the electrocatalytic activity of the material. Modeling of its band alignment with other oxide semiconductors is under way. [1] L. Trotochaud et al., J. Am. Chem. Soc. 136 (2014) 6744. [2] E. Menéndez-Proupin et al., Phys. Rev. B 90 (2014) 045207 and references therein.

Resume : The global temperature rise related to greenhouse gas emissions must be kept within 2ºC below the pre-industrial times’ average for a sustainable growth. Therefore, valorization of carbon dioxide emissions and an alternative fuel synthesis is crucial. Herein, artificial photosynthesis holds a stimulating potential along with design challenges to adjust light dependent and independent reactions. To this end, we have designed a photoelectrochemical cell dedicated to serve both functions of a photosynthesis: (i) light dependent reaction by means of water splitting at the photoanode (ii) CO2 reduction into C1 – C2 hydrocarbon fuels via a catalyst loaded gas diffusion electrode (GDE) as cathode. This PEC configuration has been a distinctive design enabling direct solar-to-fuel conversion employing a catalyst loaded GDE coupled to an n-type photoanode within a continuous flow system. Through the adjustment of cathode features and solar concentration factors, we have demonstrated that cathode potential can be adjusted from -1.1 to -1.9 V vs Ag/AgCl to maximize CO2 conversion while keeping the cell voltage below -1.6 V improving the energy balance via diminution of electrical power consumption. The enhancement of the catalytic triple junction via GDE enables the use of various CO2 electrocatalysts within that potential window. Hence, fast and efficient conversion and storage capability is demonstrated for an uninterrupted carbon valorization assisted by AM 1.5G solar illumination.

Resume : There is an expanding interest in finding novel concepts for increasing the efficiency at reduced cost in solar energy conversion. In this regard, semiconductor nanowires (NWs) provide various paths towards this goal. The increased device freedom offered by NWs for optimizing carrier extraction and light absorption makes them prospective candidates as building blocks for future solar energy conversion devices. This talk will focus on two particular fundamental areas in nanowire-based solar energy conversion: (1) Exploration of the optical properties of semiconductor NWs and NW arrays. Electromagnetic simulations will be used to understand the different optical properties (absorption, Raman scattering, etc.) found in several types of nanowire systems. (2) The liquid/semiconductor interface. I will show the power of the built-in potential at the liquid-semiconductor interface, and that can be used not only as part of the energy conversion process, but also for fundamental studies on surface properties. In the latter, we will see how the combinatorial of optical, electrical and chemical techniques can serve as surface probes. Finally, the talk will conclude by proposing new concepts that combine the two factors described above, tailoring for highly efficient solar-to-fuel conversion. These new concepts involve the exploitation of the potential of semiconductor NWs submerged in water for the generation of fuel upon sunlight illumination.

Resume : Colloidal semiconductor nanoparticles hold great promise for efficient solar fuel generation. However, many of these systems suffer from low efficiencies, often determined by slow hole transfer processes. Furthermore, a failure to quickly remove the hole often leads to photooxidation, especially with Cd chalcogenides, even in presence of a sacrificial electron donor. Despite the progress in the field, many open questions remain regarding the charge transfer dynamics, recombination pathways, interfacial kinetics and chemical reactions of the fuel generation reactions. Here, we present a highly efficient system which achieves over 50% external quantum yield of H2 generation using CdS nanorods decorated with earth abundant nickel co-catalysts in highly alkaline environment.[1] The process relies on redox shuttle mechanism in which a mediator molecule relays the photoexcited hole from the surface to the hole scavenger present in solution. The fast hole removal allows for substantial increase in H2 production rate as well as conveys photostability on the photocatalyst. We show that the system retains high activity over more than 200 hours and discuss the applicability of the model to other prospective photocatalysts. We also demonstrate that it is possible to efficiently transfer the hole to the chemisorbed oxidation catalyst, allowing for the elimination of sacrificial agents and obtaining useful products from the oxidation half-reaction. 1.T.Simon et al.,Nat.Mater. 2014,13,1013

Resume : Thermal flow management has become a very important challenge due to the limited energy ressources and global warming issues. Indeed, engines or power plant produces large amount of heat which are usually wasted and rejected in the atmosphere. This heat could be advantageously used for example to heat buildings or domestic water. Moreover, numerous devices components, objects need to be maintained at a well established temperature in order to work properly. If tools already exist to manage heat such as heat pipe, heating and cooling devices, there is nothing in thermal science which allow to manage heat flows in a way electricity can be guided, ampliflied or modulated. Mastering electronic transport has been possible through the discovery of two components : the electronic diode and the transistor [1]. Diodes are able to regulate a tension whereas the transistor has three main functions : it can act as a switch, an amplifier or a modulator. The discovery of PN junction in semiconductors has paved the way to the miniaturization of such elementary components and has been one of the biggest scientific and technological breakthrough in the 20th century. It has allowed the conception and construction of circuits that now control most aspects of everyday life. Thermal rectifiers have been proposed mainly in conductors [2,3]. Rectification is obtained by managing phonon transport making the phonon flux asymmetric in the material. More recently radiative thermal rectifiers in the far-field [4] and the near-field [5] have been proposed as well as a radiative thermal transistor in the near-field [6]. If the rectification ratio achieved and the flux exchanged are very promising, experiments to demonstrate the effects are quite difficult since materials have to be maintained at subwavelength scale, i.e at micronic distances at ambient temperature. The goal of this study is to reconsider the configuration proposed in the near-field in order to propose experiments that would be able to demonstrate radiative thermal rectification as well as thermal transistor effects. We first consider the case of a system composed of a phase change material and a standard one. We derive an expression for the rectification ratio characterizing such a system. We discuss with simple considerations the properties that have to be exhibited by phase change materials in order to achieve a good rectification. Then, we consider the case of three body in plane-parallel configuration : a phase change material is introduced between two blackbodies put at different temperatures. We show that transistor effect can be achieved if the material critical temperature is close to the equilibrium temperature of a radiative screen. The transistor effect is also more efficient when the phase change material is very reflective. We finally take the example of vanadium oxyde (VO2) and show that both rectification and transistor effect should be observed with this material with simple far-field experiments. 1. J. Bardeen and W. H. Brattain, Phys. Rev. 74, 230 (1948). 2. L. Wang and B. Li, Phys. Rev. Lett. 99, 177208 (2007). 3. N. Li, J. Ren, L. Wang G. Zhang, P. Hänggi, and B. Li, Rev. Mod. Phys. 84, 1045 (2012). 4. E. Nefzaoui, K. Joulain, J. Drevillon and Y. Ezzahri, Appl. Phys. Lett. 104, 103905 (2014). 5. Y. Yang, S. Basu and L. Wang, Appl. Phys. Lett, 103, 163101 (2013) 6. P. Ben-Abdallah and S.-A. Biehs, Phys. Rev. Lett. 112, 044301 (2014).

Resume : Structural, morphological, electrical, thermal, and thermoelectric properties of chemically synthesized polyaniline (PANI)/reduced graphene oxide (RGO) nanocomposites are investigated and their potential use as organic thermoelectrics is presented and discussed. First, it is shown that the physical properties of the nanocomposites are strongly depending on volume fraction of RGO. It is observed that electrical percolation follows a 2D conduction process which takes place for samples having ~0.1% RGO content. Unlike electrical conductivity, the thermal conductivity evolves linearly with the RGO fraction. A modified MG-EMA model is used to estimate the interfacial resistance (Rk=4.9×10-10 m2KW-1) between the filler and the polymer host. The low Rk value is attributed to enhanced interactions between the planar geometry of RGO platelets and PANI aromatic rings through π-π stackings as evidenced by Raman spectroscopy and X-ray studies. Compared to that of pure PANI, the thermoelectric performance of PANI/RGO composites exhibits a ZT enhancement of two orders of magnitude.

Resume : Tailoring interfacial thermal transport in graphene-based nanoarchitectures is important for many applications including nanoelectronics, solid-state lighting, energy generation and nanocomposites. We demonstrate that interfacial thermal conductance G can be fivefold enhanced by introducing covalent bonds at the interfaces using molecular dynamics simulations. The simulations captured the trend of thermal transport enhancement with the increment of interfacial covalent bond density. The results confirm that the observed G enhancements at the interfaces are due to strong interfacial covalent bonds and resultant coupling in the atomic vibrational spectra near the interface. The spectral analysis indicates that the coupling between graphene out-of-plane motion and bonded linkage group motion at low frequencies serves as the most important channels for thermal transport across the interface. Thus, covalently bonding functionalization is an attractive approach to tune the heterointerfacial thermal transport in a variety of material systems.

Resume : CoSb3 based skutterudite materials are reported to be promising thermoelectric materials due to their high carrier mobility along with considerable Seebeck coefficient at high temperatures making them suitable candidates for high temperature thermoelectric applications. Although the thermal conductivity in undoped form is high due to strong covalent bonding in the lattice, the cubic skutterudite structure is representative of two voids or empty spaces which can be filled with external dopants as well as self-dopants (due to excess of either of Co or Sb atoms). The loosely bonded external dopant atoms are capable of rattling motion which results in phonon scattering and a consequent decrease in thermal conductivity. The self-dopants on the other hand also allow a wide range of electrical and thermoelectric properties to manifest within the samples. In this study, the effect of Sb content on thermoelectric properties of CoSb3 thin films without any intentional dopants is investigated. Sb excess, Co excess as well as stoichiometric CoSb3 thin films were deposited on oxidized Si (100) substrate at room temperature by radio frequency co-sputtering method using elemental sputtering targets. The as deposited samples, which were found to be amorphous by X-ray Diffraction (XRD) measurements, were heat treated in nitrogen atmosphere for about 14 hours where the temperature was slowly ramped from room temperature to 500?C with their thermoelectric properties measured during the process.

Resume : In the near future the technologies for the combined controlling of SOx and NOx have become a hot issue due to the serious environmental pollution. For removal of SOx and NOx, selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) are normally used in the desulfurization and denitrification equipment [1, 2], while it is quite difficult to realize the simultaneous remove. Nowdays, photocatalytic behavior of vanadium-titanium catalysts is considered to be an effective route to achieve the simultaneous desulfurization and denitrification [3]. To further improve the photocatalytic efficiency, rare-earth doping may be used as it could improve unsaturated link and enhance the surface adsorbed oxygen [4]. In the present work, La doped vanadium-titanium catalysts are prepared by hydrothermal synthesis method, and the influence of the reaction condition on the morphologies is systemically investigated. The removal processes of SOx and NOx from simulated flue gas are investigated in the photocatalysis reactor, and the influence of the doping and morphologies of the catalyst on the photocatalytic efficiency is also studied. It is found that the photocatalytic efficiency is greatly enhanced by the La doping, and it may realize the simultaneous desulfurization and denitrification. In conclusion, La doped vanadium-titanium catalysts are used to promote the photocatalytic efficiency, which achieve a simultaneous desulfurization and denitrification, as the doping may provide more surface adsorbed oxygen to favor for the photocatalysis. References: [1] Nick, D. H.; Renata, K.; Ravi, K. S. Ind. Eng. Chem. Res. 2008, 47, 5825. [2] Luis, C. C.; Emiliano, H.; Francisco, P.; et al. Catal. Today 2005, 107-108, 564. [3] Cheng, K.; Liu, J.; Zhang, T.; et al. J. Environ. Sci. 2014, 26(10), 2106. [4] Dalton, J. S.; Janes, P. A.; Jones, N. G.; et al. Environ. Pollution 2002, 120, 415.

Resume : Tungsten oxide is currently one of the most interesting materials for the preparation of photoanodes in water splitting devices, despite its intermediate band gap value (2.7 eV) which is higher than those of other oxides as Fe2O3 or BiVO4, and the short diffusion length of the charge carriers. In this work, highly crystalline WO3 films have been prepared by Pulsed Laser Deposition (PLD), thus reducing bulk recombination through grain boundaries and improving the carrier diffusion. This way, the limitations on the film thickness are overcome and thicker samples with improved optical absorption at longer wavelengths can be prepared, leading to WO3 systems with high photocurrent densities. A careful analysis on the connection between the thickness and the optical properties has been carried out and the results are well-explained through incident photon-to-current efficiency (IPCE) measurements. Additionally, we study the effect of surface passivation with Al2O3 layers prepared by Atomic Layer Deposition, in order to decrease recombination through surface states and the formation of intermediate peroxo-species.

Resume : The design of sunlight-activated, environmentally friendly photocatalysts for wastewater treatment and air purification is an open scientific and technological challenge. In the present work, two different iron(III) oxide polymorphs (α-Fe2O3 and β-Fe2O3) have been synthesized as supported materials by chemical vapor deposition (CVD). Subsequently, their nanostructure, composition, morphology and optical properties have been deeply characterized by a multi-technique approach. The obtained systems have been finally tested as photocatalysts under simulated solar light in the liquid phase methylene blue photo-degradation, as well as for the photo-oxidation of NO in air.1 The obtained results revealed the key role played by the material structure and morphology on the photocalytic performances, opening interesting perspectives for the tailored preparation of iron(III) oxide-based nanomaterials for water and air purification. 1 G. Carraro, et al. Thin Solid Films 2014, 564, 121.

Resume : The direct oxidation of methane into oxygenated and longer chain products is an interesting process, widely studied through different catalytic paths. Among these, the photocatalytic route might be promising because of the possibility of obtaining products as methanol and formaldehyde at milder conditions. Bismuth vanadate has attracted a lot of attention in photoelectrochemical and photocatalytic applications in the last years. Because of its band configuration and expected oxidizing potential, in the present work we evaluate the use of BiVO4 for the photocatalytic oxidation of methane to methanol with water. This material seems to be a good candidate for this reaction in comparison to other oxides as Bi2WO6 and TiO2. Besides CH3OH, C2H6 and CO2 are also obtained as reaction products. Higher selectivity to methanol is obtained with BiVO4 when compared to the other oxides. Several photocatalyst configurations are evaluated. For instance, coupling with TiO2 in a BiVO4/TiO2 heterostructure or doping with W lead to slight increases in methane conversion at expenses of decreases in the selectivity, as the complete oxidation to CO2 becomes favored. However, through the use of homogeneous additives as nitrite ion, which can act both as hydroxyl radical (•OH) scavenger and UV filter, C2H6 and CO2 formation are inhibited, leading to selectivity enhancement. Thus, an intimate link between the photocatalyst features and the media conditions must be considered.

Resume : Although electrodeposition from aqueous media has been widely used to obtain metallic deposits, there are cases where the application of non-aqueous solutions offers advantages over the traditional baths or it even represents the only way to electrodeposit some metals. A study of the electrodeposition of Ni from various alcoholic solutions was performed. Besides methanol and ethanol as solvents, Ni electrodeposition from ethylene glycol, glycerol, 1,2 propanediol and 1,3 propanediol was also the aim of our research. A detailed cyclic voltammetry study of these solutions has been carried out by establishing the polarization characteristics of Ni deposition and dissolution in each bath. Then the surface morphology, crystal structure and texture as well magnetic properties of the deposits have also been investigated. The best results were obtained with methanol as solvent and the deposit quality was investigated for various deposition potentials. Compact Ni deposits with metallic appearance and nanocrystalline grain size were obtained in the deposition potential range of ‒1.10 V to ‒1.40 V vs. SCE. A weak (111) texture of the deposits was observed by XRD and the lattice constant corresponded well to pure face-centred cubic (fcc) Ni. From the other solvents investigated, the Ni deposits were of lower quality in most cases. The Ni content in the deposits was in some cases fairly low and the characteristic fcc-Ni lines could also not always be observed.

Resume : Graphene has been the attraction center of research interests in many different perspectives. Among the many ways to make use of graphene, hybrids containing graphene have emerged as a promising class of materials. The unique geometrical, chemical, electronic, and electrical properties of graphene have been utilized to endow novel and desirable properties to the hybrids for specific applications. Recently, hybrids of graphene with noble metals or noble metal alloys have been investigated as electrocatalysts for the oxygen reduction reaction (ORR) or methanol oxidation reaction (MOR) of low temperature fuel cells. We report the a novel nanostructured Pt-Graphene (Pt-G) hybrid, which directly grown Pt nanowires (NWs) on intrinsic graphene without capping agents. The directly junction between the NWs and graphene and the defect free of the graphene grown by chemical vapor deposition enables the charge transfer from graphene to Pt in Pt-G. Through the interaction, the EF of Pt is raised by 0.3 eV. With the electronic structured altered, Pt-G shows an increased tolerance to CO-poisoning and, hence, enhanced MOR performance with increased If/Ib ratio and cycle stability. The present data demonstrate a novel way to exploit the unusual characteristics of graphene for useful applications.

Resume : An important approach towards an efficient and sustainable economy is storing solar energy into chemical fuels through Photoelectrochemical (PEC) water splitting. Silicon presents a 1.1 eV band gap, which allows it to absorb a large part of the visible spectra, what has made it the main photoabsorbing material for the photovoltaic industry for many years due to its abundance and high conversion efficiency. For tandem PEC cell configuration, silicon is a great candidate to work as low light energy photocathode in a non-biased cell configuration. Using it on an electrolyte is a challenge which faces important stability drawbacks due to the easy oxidation of Silicon. In this work, we demonstrate that Titanium Dioxide grown by ALD can be used as a transparent protective and conductive layer on a p/n Silicon electrode. It presented long term stability for over 24 hours while maintaining an excellent electron transport for water reduction with negligible potential losses due to a proper conduction band alignment between n-type Silicon, TiO2 and hydrogen evolution reaction. With 11 mA/cm2 at 0.4 V vs RHE and an almost 0.6 V open circuit potential with 100 mW/cm2 AM1.5 light, a Fill Factor of 0.65 can be obtained, meaning an excellent conversion from an industrial level Photovoltaic cell into a robust efficient Photocathode.

Resume : Carbon-based solid-state supercapacitors have a long history -both in research and in industry- that has seen the employment of various forms of carbon as electrode materials. Starting from porous activated carbon, current research efforts have shifted towards exploiting the properties of graphene to initiate a new chapter in supercapacitor technology. One of the latest trends has seen the use of laser technology to inscribe electrode designs directly onto carbon-based substrates by reducing the starting material to multi-layered porous graphene ? coupled with gel electrolytes produces maximized contact areas between the electrode and the electrolyte, thus leading to high energy densities for the full solid-state supercapacitor. Initial implementations of such methods have employed self-standing graphene oxide thin films and industrial laser cutters (CNCs); later implementations have succeeded to employ affordable commercial technology (LightScribe drives) to reduce graphene oxide films deposited on specialized media (LightScribe DVDs). The latest advances have abandoned graphene oxide as a precursor ?thus avoiding the time and cost for the production of the material- in favor of polyimide (i.e. Kapton) films inscribed using laser CNCs. In this research, we employ both materials to laser-scribe graphene electrodes for supercapacitors; dual-plane supercapacitor performances are tested for single and hybrid implementations. Finally, single-plane supercapacitors are produced by the reduction of both materials and novel designs are implemented to maximize internal active length-to-surface ratios in order to optimize single-plane supercapacitor form factors.

Resume : This study presents a new type of carbon-based polymer , synthesized via electric discharge in benzene-toluene mixtures. The new composite was investigated using Raman spectroscopy, FTIR and UV-VIS spectrophotometry. The structural analysis indicated a succession of aromatic nuclei intercalated by alkenic chaines, which formed a photosensitive array. The UV-VIS analysis allowed the calculation of the band gap width and the absorbance coefficient. The results showed promising application in the field of sensors and nanotechnology.

Resume : Graphene-based carbon xerogels are commonly synthesized via sol-gel polymerization of resorcinol with formaldehyde in the presence of graphene oxide (GO) and acidic or basic catalysts. This study reports a variation on the classical method for carbon xerogel synthesis, where the xerogel cross-linking process is performed in a centrifugal field, resulting in cylindrical configurations. We synthesize graphene-based xerogels (GX) by sol-gel polycondensation of resorcinol with formaldehyde in the presence of GO in centrifugal fields of various magnitudes (G force: 125G/75G/37.5G) ? the final pyrolysis stage of the method reduces GO to graphene. For comparison, we synthesize GX without centrifugation, so we can investigate the effects of the process on the electrochemical and physicochemical properties (i.e. density, mechanical strength, porous structure and specific surface area) of GX. The added centrifugation step resulted in an observable increase in both specific capacitance and material density. This method allows for the control of GX properties for applications of interest: electrodes for supercapacitors and batteries, gas diffusion layers in fuel cells.

Resume : Nanostructured GdxZn1-xO thin films with different Gd concentration from 0% to 4.5% deposited by spray pyrolysis technique on glass substrate at 350°C.The films were characterized by structural, surface, optical and electrical properties, respectively. X-ray diffraction analysis shows that the Gd doped ZnO films hexagonal structure and preferential orientation along (002) plane. Scanning electronic microscopy were used to study the films morphology. Optical analysis of the deposited films show an average optical transmittance of 90% in the visible region; meanwhile the band gap value oscillates around 3.27-3.22eV, with a shift towards higher values when the Gd concentration is decreased. The Hall effect electrical measurements showed that ZnO thin films not doped and have an electrical conductivity doped n-type. The best value of the electrical resistivity is of the order of 2.101 ohm.cm obtained in the layer of doped ZnO 1.5% Gd.

Resume : Silicon substrates are commonly used in microelectronics applications due to their interesting semi-conductor behaviour. Devices such as transistors, printed circuit boards and integrated circuits are some of the present and next future applications. But until recently it was not used for thermoelectric applications due to its high thermal conductivity (i.e. low value of the figure of merit), 156 W K−1 m−1 at room temperature. In the literature, numerous papers have shown that specific surface and or volume organisation at the micro and nano-scale(such as quantum wells, nanowires, and quantum dots…) make possible to improve the thermoelectric properties for several materials (super-lattices, oxide thin films for instance) by the interface scattering of phonons leading to lower the thermal conductivity. In this study we are investigating the effect of another kind of nano-structuring technique based on the irradiation by ultra-short laser beam of crystalline (c-Si) and mesoporous Si (p-Si) substrates. Laser-induced periodic surface structures (LIPSS) are formed on c-Si and p-Si surfaces using two ultra-short laser beams: Nd:YAG laser beam (pulse duration = 40 ps and central wavelength 266 nm) and Ti:Sapphire laser beam (pulse duration 100 fs and central wavelength 800 nm). The experimental conditions (laser fluency, number of pulses and beam energy) were optimized to achieve the LIPSS formation on those substrates. An automated scanning holder is employed to fabricate a wide surface structuration (25 X 25 mm2). The potential benefit of laser structuring for thermoelectric applications will be discussed in this work using a new laser based-micro-ZT meter for simultaneous estimation of electrical and thermal conductivities (σ, κ) in addition to the thermoelectric power coefficient (S). This study allows finally to correlate the thermoelectrical parameters to the morphology of the p-Si (porosity and pore sizes, depth etching, size distribution) and the doping rate for the c-Si substrates.

Resume : This work concerns Ferroelectrics , whose particularity is to have a variable dielectric permittivity under the effect of a static electric field , should achieve tunable frequency systems without the drawbacks of assets . The use of ferroelectric materials in the solid state, however, was limited until recent years, due to many disadvantages such as high losses . Indeed , the use of ferroelectric films eliminates many problems associated with solid material . Among those considered for this thesis, the ( PKN ) Gadolinium doped materials of general formula Pb 2 (x -1) +1 GdxNb5O15 Kx , has many advantages in the case of applications in the field of microelectronics. The purpose of our study is the preparation by sol- gel and characterization of ferroelectric thin films belonging to the APC family ( Tetragonal tungsten bronze). During the current year, we conducted a literature review on the subject and we prepared the same material PKN powdered solid route

Resume : Nanostructures are expected to give higher efficiency thermoelectrics due to a significant decrease in thermal conductivity compared to bulk (up to 80 % in Bi2Te3). Organic ligands and surfactants are used during colloidal nanoparticle synthesis for size and shape control. Impurities, such as carbon from these ligands, create an insulating surface. Standard methods of ligand removal include washing and annealing. We are currently investigating novel methods of ligand removal, without leaving a carbon coating on the surface. One method is based on complexation of crown ether ligands with metal ions. This was investigated by DOSY (Diffusion Ordered nuclear magnetic resonance Spectroscopy) and is presented here.

Resume : Benzene (Benz) derivatives are among the most common air and water pollutants emitted by chemical and related industries, and could be especially harmful to both environment and human life. There is an increasing attention to investigation of various types of adsorbents with selective interactions toward adsorbed molecules. The aim of this study is to obtain hydrolytically stable cyclodextrin(CD)-containing silicas, which will be used for the preparation of new sorbents for effective separation and removal of aromatic compounds from air or/and water. These silicas were synthesized via direct sol-gel method by hydrolysis and polycondensation of 3-chloropropyltriethoxysilane (CPTEOS) and tetraethoxysilane (TEOS) in the presence of β-CD. Silicas were characterized by IR spectroscopy, thermogravimetric and chemical analyses, nitrogen adsorption-desorption experiments. The possible effectiveness of CD-containing silicas for the removal of Benz molecules was investigated. Benz adsorption isotherms at 298 K from vapour phase were received. It was found out that adsorption of Benz on CD-containing silicas increases in comparison with silicas without supramolecular moieties. An increase in Benz adsorption for silica with supramolecular moieties could be explained by the β-CD ability to adsorb Benz through “host-guest” interaction. Hence, the number of the bonding sites for Benz molecules in CD-containing silicas increased, which leads to higher amount of adsorbed aromatics.

Resume : Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopies (XPS) have been used to study the bulk and surface compositions of Cu1.85(CdxZn1-x)1.1SnS4.1 (CCdZTS) (x=0 -1) monograin powders grown by molten salt synthesis, respectively. Monograin powder solid solutions were synthesized from binary compounds and elemental S in two different salts (KI, CdI2). Powder crystals, which have homogeneous composition in bulk, present clear indications of surface-enrichment by Cd at x=0.2-0.4. The ratio of [Cd]/([Cd]+[Zn]) in the bulk of powder crystals correlates to the input value of x in precursors independently from used salts, with the exception of the powder crystals with the x=0 synthesized in CdI2 salt. In this case the EDX showed that monograins contain 0.17 at% of Cd which incorporates to the crystals from the CdI2 salt. According to the XPS spectra the expected valence states of all the elements in the solid solutions of CCdZTS are confirmed. The peak deconvolution of high resolution XPS spectra indicate the presence of Cu(I), Zn(II), Cd(II), Sn(IV), and S(-II) valence states. The increase in Cd content in synthesized powders had no influence on the photoelectron peak positions of the elements on the top surface layer. In the bulk, there was a constant chemical shift of the Sn 3d and S 2p peak positions towards the smaller binding energies with increasing the Cd content. EDX showed the presence of additional CdS (x=1) and Zn1-xCdxS crystals among the solid solutions of CCdZTS.

Resume : Due to the increasing demand of alternative energy resources, considerable research interest has been devoted for the development of new thermoelectric materials. Thermoelectric materials are potential candidates for harvesting green energy, due to their ability to generate voltage upon exposure to a temperature difference. This so-called Seebeck-effect is also reported for polymer nanocomposites filled with carbon nanotubes (CNTs).[1] Herein, polymer/CNT nanocomposites processed by solvent or melt mixing have been tested for their thermoelectric performance. The highest obtained values have been found for the solvent mixed nanocomposites, which reacheda maximum power factor (PF) of ~1.8 μW/mK-2. Moreover, another interesting material used for engineering applications; glass fibers (GFs), were chemically grafted with single- and multi-wall carbon nanotubes and utilized also as a flexible thermoelectric power generator. CNT-networks were covalently attached onto the surface of intrinsically insulating glass fiber yarns (GF-yarns) following a dip-coating deposition process. The fiber/CNT functional yarns showed a maximum power factor (PF) of ~31.45 μW/mK-2.The PF values were found in general to be increased with the increased amount of CNTs grafted onto the fiber surface. The idea of fiber/CNT structures for thermal energy harvesting could be further applied toseveral consumer applications, such as to smart textiles for wearable applications with the potential of harvesting t

Resume : X-ray diffraction of particles of zinc oxide reveals a sub-stoichiometry that is inherent to this material at the nanoscale. Global optimisation methods [1] have been applied to identify the exact nature of this effect and showed that the zinc vacancies are disordered throughout the matrix of the wurtzite crystal, which can explain the observed drop in the second neighbour peak in the RDF. Next, global optimization and data-mining techniques have been used to generate the structures of Mg and Cd doped ZnO nanoclusters [2]. The final electronic solutions have been used for the prediction of optical absorption spectra. The excitonic energies have been obtained using time dependent density functional theory including asymptotic corrections. The optical behaviour of most stable clusters considered is contrary to the quantum confinement model. 1. Knowledge Led Master Code, e.g. Woodley, SM, JOURNAL OF PHYSICAL CHEMISTRY C, 2013, Volume: 117 Issue: 45 Pages: 24003-24014 DOI: 10.1021/jp406854j 2. Structural and optical properties of Mg and Cd doped ZnO nanoclusters, Woodley, SB; Sokol, AA; Catlow, CRA; Al-Sunaidi, AA; Woodley, SM, JOURNAL OF PHYSICAL CHEMISTRY C, 2013, Volume: 117 Issue: 51 Pages: 27127-27145 DOI: 10.1021/jp4084635

Resume : Many applications for conducting polymers have emerged since the discovery of polyacetylene in the 70s, including their use as organic light emitting diodes, sensors, transistors, solar cells, and, more recently, thermoelectric devices. Among the many advantages of these type of organic materials as compared to inorganic ones are: low cost, easy chemical modification, good mechanical properties, absence of toxicity. The nanostructuration could be the key to increase the performance of polymers for energy devices as in the case of thermoelectric and supercapacitor devices. On one hand by using nanostructures it is possible to reduce the thermal conductivity, therefore the thermoelectric efficiency increases. On the other hand, by using nanomaterials, it could be attained, important improvements for energy storage devices due to the size reduction of materials that increases the contact surface area between the electrode and the electrolyte and decreases the transport path length for both electrons and ions. In this work we have synthesized poly(3,4-ethylenedioxythiophene (PEDOT) nanowires by using alumina templates made by our group. The nanowires have been characterized as a function of their diameter and a study of their implantation in energy devices such as supercapacitors and thermoelectric modules have been developed.

Resume : Many materials are currently of great interest for light-emitting applications e.g. as spectral shapers for photovoltaics, for optoelectronics, photonics and bio-imaging. Despite their excellent optical characteristics, most of these materials are toxic and scarce/expensive. For future applications, the best candidates are quantum dots (QDs) based on benign and non-toxic elements like carbon and/or silicon. Unfortunately, the emission efficiency of these QDs in the visible spectral range (<620 nm) is comparatively low or is at the expense of limited spectral tunability of the photoluminescence (PL). These major limitations arise from complex interplay between the QD core and ligands/defects that reside on its surface; Properties that are difficult to study with ensemble characterisation techniques, as these yield properties that are averaged out over different sizes, so that information on individual QDs is obscured. Moreover, non-emitting QDs in the sample or leftover organic compounds from the chemical synthesis - which in many cases is used to prepare these materials – can pollute the ensemble properties of the studied material. To separate these influences and to quantify and find a solution to the spectral tunability and emission efficiency, single QD spectroscopy needs to be performed. In such case, photo-bleaching, PL spectrum, excitation power dependence and PL intermittency are studied to obtain solid understanding of the QD material limitations and potential.

Resume : Carrier multiplication can be realized in silicon nanocrystals (SiNCs) in SiO2 matrix. In order to obtain the maximal advantage of carrier multiplication in photovoltaics, the optimal bandgap value is around 0.8eV. This is below the bandgap energy of bulk Si. SiNCs with bandgap energies in this range can be obtained by co-doping, with the bandgap reduction being induced by donor and acceptor levels. In this report, we describe optical spectroscopy investigations of carrier multiplication in phosphorus and boron co-doped SiNCs as a function of excitation energy. We correlate the results obtained by measuring external quantum yield of photoluminescence, originating from radiative recombination between donor and acceptor levels, with those from ultrafast induced absorption, where dynamics of free carrier population is probed. Based on these we demonstrate carrier multiplication and then discuss its efficiency and threshold energy. These parameters we compare with those obtained for undoped SiNCs of similar size.

Resume : Self-organized tungsten oxide nanorods were formed on a mica substrate by thermal evaporation from an oxide source. Subsequently, mica samples were equipped with platinum electrodes and µ-wires prepared by means of electron beam lithography in order to contact the nanorods and to produce a functional conductometric gas sensor prototype. The manufacturing enabled measuring the resistance of either a percolating network of the nanorods but or a set of individually contacted nanorods. Comparison of both types of assemblies is given. Resistance of samples was measured as a function both of the concentration of hydrogen in synthetic air and of temperature; the minimum detected concentration was below 100 ppm. Time constants as well as relative response values are evaluated for various conditions.

Resume : As developments in the area of solution processable light absorber, flexible solar cells are tremendous attractive devices applicable to power generating plants, smart windows, mobiles and various textiles. Generally, flexible solar cells are based on flexible plastic substrates such as PET, PC, PES and PEN, however, these plastic substrates have critical issues in the weak stability due to high water permeation rate and low temperature process. Since stainless steel and metal based substrates have a lot of potential for mechanical robustness, thermal and chemical stability, top-illuminated solar cells based on these opaque substrates should be used to commercialize. In this work, we report the novel design of MoO3/Ag/PDMS (MAP) as a transparent electrode for highly efficient top-illuminated organic solar cells. To design advanced structure, PDMS, known as a hybrid polymer with dielectric property, was employed instead of an inorganic dielectric layer. With the low refractive index (n = 1.45, k = 0.0001) of PDMS, a transparency insensitive to the polymer thickness could be achieved even in on nanostructured electrode. Consequently, incident light could pass through the PDMS layer, without reflection loss, resulting in the enhanced transmittance. Additionally, we integrated inverted hexagonal pyramid patterned PDMS with on front side of MoO3/Ag by a simple lamination technique, which shows the enhanced omnidirectional optical characteristics and power conversion efficiency of 6.4 %.

Resume : Nanostructures including nanoparticles, nanowires and nanosheets are the ideal building blocks for the bottom-up fabrication of functional materials. They offer an immense variety of interesting properties, which not only depend on the composition, but also on the crystal structure, the particle size and shape and on the surface chemistry. Accordingly, potential synthesis routes have to provide full control over all these parameters. In addition, for most applications the nanoparticles have to be assembled and processed into useful geometries, architectures and bodies, and for this purpose, the surface properties of the nanoparticles have to be tailored carefully. The talk will cover the synthesis and assembly of nanoscale building blocks, mainly metal oxides, but also graphene oxide, in 2 and 3 dimensions and over several length scales. It will introduce the synthesis of a great variety of metal oxide nanocrystals by nonaqueous sol-gel chemistry, followed by discussing various strategies to fine-tune the surface chemistry, which is essential for the assembly of the nanoparticles into macroscopic aerogel monoliths and for their processing into films. Selected applications in the field of photoelectrochemical water splitting and lithium ion batteries will briefly be addressed, too.

Resume : Chemically synthesized inorganic nanocrystals are considered to be promising building blocks for a broad spectrum of applications in solid-state devices. Metal halides perovskites, such as hybrid organic-inorganic CH3NH3PbI3, are newcomer op-toelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors [1]. Their bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90% and radiative lifetimes in the range of 4-29 ns. Colloidal nanocrystals are also highly suitable as electrode materials for rechargeable batteries. We will discuss the utility of monodisperse metallic nanocrystals (Sn, Sb, Bi, SnSb nano-crystals and Sn/Ge nanoheterostructures) as anode material for Li-ion, Na-ion and Mg-ion batteries [2, 3, 4, 5]. Nanoscopic materials exhibit much greater electrochemical cycling sta-bility due to better mitigation of the impact of volumetric changes upon uptake and release of metal ions. As an example, Sb nanocrystals as Na-ion and Li-ion anode materials show high capacity retention of up to 80-85% even at 20C-rates of charge and discharge, which is com-parable to the best Li-intercalation anodes and is unprecedented for Na-ion storage. [1] L. Protesescu et al. submitted. [2] K. Kravchyk et al., J. Am. Chem. Soc., 2013, 135, 4199. [3] M. He et al., Nano Letters, 2014, 14, 1255. [4] M. Bodnarchuk et al. ACS Nano, 2014, 8, 2360 [5] M. He et al. Nanoscale, 2015, 7, 455-459.

Resume : The storage of energy is becoming crucial nowadays due to the increasing share of intermittent renewable energy sources like PV and wind in the total electricity production. This need has led to a search for higher capacity electrode materials than those available today. Silicon has been proposed as a promising anode material due its low cost, high theoretical lithium storage capacity and high volumetric capacity. Planar solid-state thin film silicon anodes reveal several drawbacks like the volume expansion upon Li insertion that causes cracking of Si particles as well as the fracture behavior Si electrode. In order to overcome the limitations, we have made a new nano-structured silicon material applied for anode Lithium-ion batteries. Self-organized nano-structured silicon has been deposited by microwave plasma-enhanced chemical vapor deposition (MW-PECVD). On top of a c-Si wafer, a Li diffusion barrier layer was deposited , in this case a RF-magnetron sputtered TiN layer. All samples have been characterized by optical measurement giving values for porosity of the layers in the range of 30-40 %, depending on the deposition conditions. Furthermore we performed Cyclic Voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT) vs a lithium electrode using Propylene Carbonate (PC) as electrolyte. The capacity of the layer and the cyclic performance for 50 nm thick layers are excellent with 3800 mAh/g and a retention of the capacity of 85% after more than 100 cycles. For a thicker layer of 800nm we observed a lower capacity of about 200-400 mAh/g, but with an equally good cyclic stability. We will discuss the various mechanisms which may be responsible for the different behavior of thinner and thicker silicon layers.

Resume : Semi-solid flow batteries (SSFBs) are a special class of redox flow batteries, in which anolyte and catholyte consist of flowable suspensions of solid active materials rather than dissolved redox species. Thus, the concen?tration of active redox centres of the SSFB can be significantly increased reached to 300 ? 500 Wh L-1 values of energy density, which is more than 10 times higher than that of all-vanadium RFBs (40 Wh L-1). Sodium-ion batteries (SIBs) attracted increasing attention in the past few years since sodium is abundant and inexpensive. We report the first proof of concept for a non-aqueous SSFB based on Na-ion chemistry using P2-type NaxNi0.22Co0.11Mn0.66O2 and NaTi2(PO4)3 as positive and negative electrodes, respectively. The proposed battery stores 80 mAh g-1NaNCM within the voltage range of 2.2 V ? 0.2 V. First results are encouraging but certainly indicate the need for a better understanding and control of irreversible charge losses in this type of battery. Although the energy density of this proof of concept was ca. 9 WhL-1 (6 WhKg-1), a proper selection and optimization active materials will certainly result in a significantly improved electrochemical performance of Na-SSFBs, e.g. a 2.5 V battery with 30 vol% of active material in the suspensions would deliver ca. 150 Wh L-1. Acknowledgements: The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n? 608621.?

Resume : In recent decades, supercapacitors could demonstrate their place in the market for high power demands and now huge efforts are dedicated to open their way towards high energy applications [1, 2]. Transition metal oxides are known as promising candidates in this path due to their high specific capacitances. Among them, binary or ternary metal oxides have attracted great interest due to their multiple oxidation states, resulting in high electrochemical performance. FeCo2O4 nanostructures have shown high Li-ion storage capacities as anode materials in Li-ion batteries [3], suggesting that they can offer high-charge storage capacity through redox reactions. However, few works have been carried out on application of FeCo2O4 as supercapacitor electrodes [4]. Herein, we report synthesis of porous FeCo2O4 rod-shape structures through a facile hydrothermal route on nickel foam (NF). The prepared sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction (EDX and SAED) analyses. Based on the obtained results, porous rod-shape structures are themselves comprised of very fine nanoparticles with the size of about 5 nm. The electrochemical behavior of the sample as a supercapacitor electrode material was investigated through different techniques including cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) in 3 M KOH solution. FeCo2O4 nanostructures showed a high specific capacitance of 420 F g-1 at a scan rate of 5 mV s-1. The rate capability of the sample was studied, showing that with a 20-fold increase in the scan rate from 5 to 100 mV s-1, around 60% of the initial capacitance was retained. Moreover, cycling performance of the sample was investigated during 5000 cycles, demonstrating high stability of the material. References: [1] M. F. El-Kady, V. Strong, S. Dubin, R. B. Kaner, Science 2012, 335, 1326. [2] G. A. Tiruye, D. Munoz-Torrero, J. Palma, M. Anderson, R. Marcilla, Journal of Power Sources 2015, 279, 472. [3] Y. Sharma, N. Sharma, G.V. Subba Rao, B.V.R. Chowdari, Solid State Ionics 2008, 179, 587. [4] S. G. Mohamed, C-J. Chen, C. K. Chen, S-F. Hu, R-S. Liu, ACS Applied Materials & Interfaces 2014, 6, 22701.

Resume : Carbon-based materials, such as carbon nanotubes and graphene, have attracted much attention due to their unique properties, mainly low dimensional effects, good structural integrity, high electrical and thermal conductivity. There are many potential applications of this material is in electronics, biomedical materials and clean energy. In this talk, we will like to give a review on the different types of carbon-based composite materials as an integrated electrode material encompassing gas-diffusion layer and catalyst support layer as a fully independent electrode with direct applications in PEM fuel cells energy generators. We will showthat we can further engineer 1D and 2D materials having unique advantages over the standard nanosized carbon black (VXC-72R) when applied directly on PEM fuel cells. We will further show and compare the fuel cell properties when other none carbon 2D materials are integrated. A series of in-situ tests are also performed which includes accelerated degradation test and electrochemical impedance spectroscopy to validate the effectiveness and robustness of these materials. This also forms the basis to extend these carbon electrodes into Li-air batteries and other applications

Resume : It is well known that the thermoelectric efficiency of a semiconductor is limited by the simultaneous increase of the conductivity and decrease of the Seebeck coefficient upon increasing carrier concentration. This interdependence results in low thermoelectric power factor and hence poor thermoelectric efficiency in conventional semiconductors. Theory predicts that the link between the conductivity and the Seebeck coefficient can be broken in composite semiconductor structures by energy filtering in the presence of energy barriers [1-3]. In order to exploit these predictions into applications, we need modeling that provides quantitative dependencies on the composite material parameters that can be engineered. To contribute to this need we have developed a simulation methodology on the thermoelectric transport properties of a composite semiconductor with non-uniform doping concentration. A non-uniform doping concentration results in non-constant carrier distribution in the semiconductor and the formation of energy barriers that directly affect the transport properties. The conductivity and Seebeck coefficient of the structure have been calculated using the Monte Carlo (MC) technique. Carrier scattering by phonons and by impurities have been taken into account. The conductivity is typically lower compared to that in the case of the uniform doping. The Seebeck coefficient is though sensitive to the doping concentration configuration and characteristic dimensions. Different transport regimes can take place simultaneously in the composite structure depending on the characteristic parameters and dimensions. The effective Seebeck coefficient depends drastically on the involved transport regimes. We have explored this dependence systematically with MC simulations as function of the relevant parameters of the material and of details of the doping profile. The MC simulations have been interpreted by Boltzmann transport equation calculations and a network model for the composite semiconductor structure. Characteristic dimensions of the doping concentration variation for optimized thermoelectric properties are identified. [1] R.Kim and M.S. Lundstrom, J.Appl.Phys. 110, 034511 (2011) [2] N. Neophytou and H.Kosina, J. Appl. Phys. 114, 044315 (2013) [3] X. Zianni and D. Narducci, J. Appl. Phys. (in print)

Resume : Understanding the laws that govern the phonon heat transport at atomic interfaces in crystalline superlattices has long been viewed as a key step toward efficient thermal-management strategy for high-performance superlattice-based thermoelectric devices. Therefore, several experimental studies on the phonon thermal conductivity in superlattice structures have been carried out, and many numerical techniques describing the phonon heat transport in multi-layer systems have been developed. Experimental studies have demonstrated that, in some circumstances, the phonons in a superlattice can propagate ballistically without being scattered at the interfaces as if the superlattice is a bulk material with no interfaces. This phonon mechanism is known as the coherent phonon transport mode, while the phonon heat transport mode in which phonons experience scattering at the interfaces is known as the incoherent phonon transport mode. Experiments have also demonstrated that when the interfaces between the layers that form the superlattice contain low amounts of irregularities, the superlattice cross-plane thermal conductivity presents a minimum value for a particular period thickness. However, in the case of diffusive interfaces, the cross-plane thermal conductivity increases monotonically with increasing the period thickness. Most theories for the superlattice thermal conductivity either rely on the solution of the Boltzmann transport equation that treats the phonons as particles or are based on the assumption that the phonons are plane waves. The existing Boltzmann models involve a rate at which particle-like phonons are scattered by interfaces. Thus, according to all Boltzmann models, the superlattice cross-plane thermal conductivity decreases monotonously as the interface density increases, which disagrees with the experimental measurements that demonstrated a minimum in the curve describing the cross-plane thermal conductivity versus the period thickness. On the other hand, by invoking the interference of phonon plane waves within thin periods, the models that consider the phonons as plane waves could describe the experimentally observed cross-plane thermal conductivity trend only at period thicknesses smaller than a few tens of Angstroms. At relatively large period thicknesses, these models overestimate the superlattice thermal conductivity. Thus, so far, the physics of the phonon heat transport in superlattices could not be fully explained by a single model. Indeed, it is highly desirable to have a wide scope model that can accurately predict the dependences of the period thickness and interface conditions on the thermal conductivity and phonon heat transport mode in superlattices. With such a theoretical tool in hand, one can gain insight into the physics of phonon heat transport across atomic interfaces and rationally design superlattices for many technological applications. In this contribution, we present an original approach for the determination of the phonon cross-plane thermal conductivity and heat transport mode in superlattices. It is based on the interpolation between two Boltzmann models: an incoherent Boltzmann transport model assuming that the cross-plane thermal conductivity of the superlattice is a weighted average of the thermal conductivities of the two bulk materials that form the superlattice period with the additional contribution of the interface thermal resistance, and a coherent Boltzmann transport model based on the assumption that the superlattice is a bulk material, free of interfaces, characterized by phonon dispersion relations determined by the Brillouin zone folding effects of the superlattice. We assess the reliability of the developed approach with reference to reported experimental data.

Resume : Solving safety issues related with the current liquid electrolyte based batteries face is highly desirable. Recently, there has been a great interest in developing solid electrolyte due to improved safety including non-flammability, reliability and leakage-free property. In addition, solid electrolyte could act as ion conducting media and separator between two contrary electrodes at the same time Among solid electrolyte materials, compounds with a composition of Li-La-M-O(M=Ta, Nb, Zr) have been widely studied as a fast lithium ion conductors over the last few years. Murugan and coworkers have successfully synthesized garnet-type Li7La3Zr2O12(LLZO) providing high lithium ion conductivity (3ⅹ10-4 S cm-1) as well as high chemical stability against lithium meta. However, their work requires several steps of thermal treatment and grinding as well as too high synthesis temperature and long time. In our work, we demonstrate a single step thermal process to prepare high Li-ion conducting cubic LLZO that would be adopted solid electrolyte in Li-ion battery. The adequate substitution of component element in LLZO could reduce synthesis temperature and time comparing to previous reports. Moreover, the optimized doping has led the enhanced ionic conductivity of Li7La3Zr2O12. Air stability (long time duration in air) and wide electrochemical window are also checked for indicating that LLZO is proper candidate for solid electrolyte under intense cell operating environment.

Resume : Rechargeable lithium-oxygen batteries with high theoretical energy density are considered a promising energy storage technology that could realize long-range electric vehicles. A cathode for a Li-O2 battery usually consists of carbon and polymeric binders; however, recent studies have confirmed that these main constituents become unstable in the presence of Li2O2 (desired discharge product), thereby causing significant performance degradation. In this paper, we report a cathode for Li-O2 batteries, which is comprised of binder-free carbon nanotubes (CNTs) coated with metal oxide (NiCo2O4) and decorated with metal (Au) nanoparticles (denoted as CNT/Au-NiCo2O4). A thin layer of NiCo2O4 is conformally coated onto CNT by a simple chemical deposition method. The thickness of the oxide layer is controlled to achieve improved cathode performance. The NiCo2O4-coated CNT electrode is further decorated with Au nanoparticles via sputtering. We demonstrate that the fabricated CNT/Au-NiCo2O4 electrode exhibits improved charging and cycling performances compared with pristine CNT. The roles of NiCo2O4 and Au in reducing overpotentials for charge and improving cyclability are discussed in detail with the help of various electrochemical and physicochemical analyses.

Resume : The electrochemical behavior of TiO2 anatase with a predominant (001) face (ANA001) was studied by cyclic voltammetry of Li insertion and chronoamperometry. Both methods proved its higher activity toward Li insertion compared to that of reference materials. The lithium diffusion coefficient of ANA001 calculated from cyclic voltammetry is by 1 order of magnitude higher than those of reference materials with a dominating (101) face. The same tendency, although not so large difference, exhibited the chronoamperometric diffusion coefficients and rate constants of ANA001 and reference samples. The enhanced activity of the anatase (001) face for Li insertion stems from synergic contributions of a faster interfacial charge transfer at this surface and a facile Li transport within a more open structure of the anatase lattice in the direction parallel to the c-axis. In addition to this, the solar conversion efficiency of the dye-sensitized solar cell employing ANA001 sensitized with C101 was measured and compared with that of standard nanocrystalline TiO2 anatase (101) sensitized with the same dye. The (001) face adsorbs a smaller amount of the used dye sensitizer (C101) but provides a larger open-circuit voltage of the solar cell. The negative shift of flatband potential is suggested to be responsible for the observed enhancement of Uoc. Acknowledgement: This research was supported by the Grant Agency of the Czech Republic (contract No. 15-06511S).

Resume : The demand for high-energy storage systems is constantly increasing, as is the interest to explore alternatives to commercially available batteries. The rechargeable Li-air battery represents an exciting opportunity to design batteries that may satisfy some of the requirements of our future by coupling the light Li metal with the inexhaustible source of O2 of the surrounding air, resulting in high theoretical specific energy density. Currently, most of the researches on the Li-air battery comprise a cell fed with pure O2 allowing the cell to maintain long-term operation, owing to the high O2 concentration free of contaminants. However, for many practical applications such as EV, air is the only viable option to supply the battery. In this context, moisture and gases, other than O2, may cause side reactions and corrosion. Thin-sheet poly(vinylidene fluoride co-hexafluoropropylene) (PVdF-HFP) based membranes with a controlled porosity are prepared and tested as an O2-selective membrane in a Li–air cell operating in ambient air. The membranes, prepared via non-solvent induced phase separation, are casted as 360 µm thin sheets. Optimal membrane porosity is achieved by adding sacrificial silica nanoparticles before casting, and removing them. The O2 selectivity is improved by entrapping silicone oil within the porous structure of the polymer. Electrochemical testing is performed and the results show an interesting increase of the cycle number.

Resume : Vanadium redox flow battery offers not only a great promise to provide a robust and constant energy storage system, but also several advantages such as scalability, long cycle life, high efficiency and independence between power and energy. Despite all of its merits, VFBs have reached only a limited market presence after the continuous development the last 30 years. VFB performance requires improvements in terms of a better reversible kinetics with minimum side reactions (i.e. hydrogen evolution). Our approach has been applied several, from “nano” to “macro”, architectures TiO2 (rutile) on the negative electrode of the VFBs enhancing the electrochemical performance of graphite felt (GF) electrodes. The low-cost TiO2-GFs electrodes have been synthesized by hydrothermal method with tetragonal phases. Linear sweep voltammetry (LSV) study confirmed hydrogen inhibition by rutile in the negative half-cell of the battery. Cyclic voltammetry (CV) confirmed that TiO2 has a catalytic effect towards the redox couple V2+/V3+ at the negative side. Even more, the presence of rutile allows obtaining 100% charge of the electrolyte, improving the energy efficiency up to 95 % at current density (12.5 mA/cm2) as compared with pristine GF. These results suggest rutile based electrodes, replacing expensive noble metals by an affordable material, uniformly decorating GFs holds great promise as high-performance electrodes for VRFB applications.

Resume : Vanadium redox flow batteries (VFB) are an appealing alternative for energy storage due to several attractive features including long cycle life, low maintenance cost, short response time, power and energy are independent and low self-discharge. In spite of the fact several MWh VFRB systems have been demonstrated the present of VFB technology still displays some drawbacks, limiting it to the pre-commercial phase, and preventing it from breaking into the industrial market place. The improvements vanadium redox flow battery (VFB) performances require a better reversible kinetics with maximized electron transfer properties. For attain this goal, electrode materials need to have higher active electrochemical properties in order to achieve a higher power of the VFB system. One-dimensional (1D) decorated carbon nanomaterials with several transition metals (i.e. Co, Fe, Mn….) have been developed as electrode materials synthesized by a combination of electrospinning and thermal process. These decorated nanofibers (NF) architectures demonstrate the existence of best electrocatalytic properties toward the V2+/V3+ and VO2+/VO2+ redox couples. Moreover, this composite electrode in the full cell exhibits substantially improved discharge capacity and energy efficiency around 90% at 50 mAcm−2, which constitutes a significant improvement compared to untreated electrode. This outstanding performance is due to a faster electron transfer together with an enhanced surface defect sites.

Resume : Graphene based materials such as composites of metal oxides/hydroxides and reduced graphene oxide for supercapacitors application have aroused tremendous interest in material science because of their unexpected property, high energy and power density. Nickel hydroxide has been proven to impart high pseudocapacitance due to its well-defined faradic reaction and several researches have been done on its composite with graphene. However, power densities of Ni(OH)2 composites is low due to the poor conducting nature of Ni(OH)2 which hinders charge transfer. Conversely, conductivity of the composites can be improved via cobalt addition. In this study, we report cobalt - nickel hydroxide precipitation on reduced graphene oxide (rGO) integrated with hydrothermal synthesis to improve specific capacitance and crystallinity. The cobalt - nickel hydroxide composites grown on rGO were synthesized by co-precipitation followed by hydrothermal synthesis. Different metal hydroxide precursor ratios, metal hydroxide to rGO ratio, and hydrothermal synthesis temperature were used as a parameter. The prepared samples morphology was characterized by X-ray diffraction, Energy dispersive x-ray spectroscopy and scanning electron microscopy. Moreover, electrochemical performance measurement was performed.

Resume : Here we present a unique core/shell nano-architecture based on α-Fe2O3 nanowires, designed specifically to prepare a high performance pseudocapacitor electrode. Bare α-Fe2O3 nanowires grown on Au substrate were coated with a thin MnO2 nanolayer to fabricate α-Fe2O3/MnO2 core/shell nanowire heterostructures arrays. The as-prepared α-Fe2O3/MnO2 nano-heterostructures have found to exhibit excellent specific capacitance, high-energy and power performance as compared to the bare α-Fe2O3 nanowires electrode. The unique geometry of this nano-heterostructures with highly porous surface morphology providing large platform for redox reactions by allowing facile electrolyte diffusion, incorporation of two highly redox active materials in a single structure for fast charge transfer kinetics and more importantly, introduction of a core material having higher electronic conductivity as compared to the shell for fast electron transport towards the current collector help in the superior electrochemical performance of the α-Fe2O3/MnO2 nano-heterostructure electrode. The maximum specific capacitance has been found to be 801 F g-1 at a discharge current density of 1 A g-1 in 1 M KOH aqueous solution. This hybrid nanocomposite electrode also exhibit good rate capability (nearly 68% capacitive retention at 50 A g-1) with excellent energy density of 17 Wh kg-1 and power density of 30.6 kW kg-1 at a current density of 50 A g-1 and good long-term cycling stability (almost 98.5 % retention of its initial capacitance after 1000 cycles) indicating its potentiality in applications for next generation high-performance pseudocapacitors.

Resume : ZnO, a wide band gap semiconductor with 3.3 eV band gap at room temperature, is intensively studied for photovoltaic (PV) applications mostly as a transparent conductive oxide (TCO) or as a n type partner for p-type materials (e.g. Si, CdTe, CIGS…). In this work, we study PV structures based on n type ZnO nanorods grown by hydrothermal method on top of p-type Si. For nanorods deposition, we developed a modified growth method, which allows us preparation of a new generation of low-cost and high efficiency solar cell structures. Vertically aligned zinc oxide nanorods (ZnONR) were grown on bare p-type silicon substrates using low temperature hydrothermal method. growth of ZnO nanorods is reproducible and controllable. As-grown ZnONR on Si surface were covered conformally with ZnO layer. Then, aluminum doped zinc oxide (AZO) layer was deposited on top as a transparent conductivity oxide. ZnO and AZO films were deposited by a low temperature atomic layer deposition (LT ALD) method. The PV efficiency for such new-generation structures (ZnO:Al/ZnO/ZnONR/Si/Al) is equal to 12.5%. This work was partially supported by the National Centre for Research and Development grant (PBS1/A5/27/2012), and (E. Zielony, P. Biegański and E. Popko) by the National Laboratory of Quantum Technologies (POIG. 02.02.00-00-003/08-00).

Resume : Integrating the increased light absorption and charge mobility of III-V compound semiconductors based solar cells into one-dimensional nanostructures such as nanowires (NWs), a substantial enhancement of the efficiency is expected, due to their high surface-to-volume ratio and defect-free crystal structure. Moreover, in NWs with a core-shell configuration light absorption is separated from carrier collection pathways and hence, longer carrier lifetimes can be achieved. GaAs/AlGaAs core-shell NWs were grown on Si (111) by molecular beam epitaxy (MBE) by the vapor-liquid-solid mechanism. High-resolution transmission electron microscopy (HRTEM) showed that NWs are zinc-blende single crystals with the occasional occurrence of wurtzite structure pockets. NWs emerge directly from the Si surface and grow by a continuous succession of (111) mirror twins. Diffraction contrast and annular dark-field (ADF) scanning TEM (STEM) imaging revealed the core-shell structure. A 0.35 Al mole fraction of the shell was estimated by energy dispersive X-ray (EDX) analysis. Furthermore, molecular dynamics (MD) simulations of plan-view NW slices were applied to calculate the variation of the energy, the displacement field, the stress tensors, and the strain components of the core-shell configuration. Acknowledgement Research co-financed by the European Union (European Social Fund–ESF) and Greek national funds - Research Funding Program: ARISTEIA II, project NILES.

Resume : Recent research on Graphene quantum dots (GQDs) properties indicates the emerging potential of these nanostructures towards various device applications, particularly in the energy conversion in organic optoelectronic devices. In this regard, two types of graphene quantum dots, namely glucose-derived (GQD-N) and PEGylated carbon nanoparticles (GQD-PEG1500N) were studied as photo and electro responsive materials in solar cells and LEDs, respectively. Both types of nanoparticles (NPs) are aqueous solution GQDs, with comparable structural morphologies but different surface functionalities, designed to be appropriate for the following device integration. While the GQD-N are obtained using bottom-up method starting from glucosamine as organic precursor, the second type of carbon nanoparticles are fabricated by a top-down method from graphite, subsequently separated, and uniform functionalized with PEG1500N. Physical-chemical characterizations were performed in order to determine the size, shape and functional groups attached on the surface. Consequently, GQD-N were used to sensitize the TiO2 photoanode of a typical QD-sensitized solar-cell (QDSSC) or hybrid (QD-dye) solar cell, and GQD-PEG1500N were deposited by spin casting and integrated as the electro-active layer into a multilayer organic LED structure (ITO/PEDOT-PSS/PVK/GQD-PEG1500N/Al). The effects of GQDs on each device performance were further investigated and the benefits of their presence were emphasized.

Resume : In this work novel emissive polymers with different emission characteristics within the visible region for the fabrication of organic light emitting diodes (OLEDs); namely Polyethers containing bis(styryl)anthracene units, Polyfluorenes, Polyphenylene vinylenes, etc have been dissolved in the appropriate solvent and polymer thin films were fabricated by spin coating. The photoluminescence (PL) of the polymeric thin films was evaluated by fluorescence spectroscopy revealing the characteristic emission of each material. Spectroscopic ellipsometry (SE) has been implemented in order to obtain further information about the optical properties and characteristics of the polymeric thin films. The fundamental optical band gap (ωg), as well as the optical gaps of the polymeric films determined by fitting the experimental spectra of the pseudodielectric function using the appropriate geometrical and dispersion models. The ωg and the energy of the first optical gap are correlated to the highest intensity peak wavelength position from the PL spectra, which determine the inherent color of emission. Thus, the prediction of the characteristic emission of the active polymer can be realized using SE data. Furthermore, the interpretation of the results gives insights to molecular structure of the polymers and to their performance as active layers in OLED devices.

Resume : We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.

Resume : Interest in the hybrid perovskite solar cells lies in their high performances and also in the low temperature that can be used for the layer deposition. These devices are mainly prepared by solution-processing and, consequently, they open the gate to a mass production at a very low-cost. In this context, ZnO is a major material candidate for the electron transport layer (ETL).[1] ZnO is a wide bandgap (3.3 eV) semiconductor which can be grown with a high structural quality with tailored nanostructures at low temperature by various techniques. We have explored the use of electrochemical techniques for the preparation of ETL.[2,3] The advantages of the technique include the deposition at low temperature of high quality material, the precise control of the (nano)structure morphology and thickness, the control of the electrical properties and the excellent electrical contact between the deposited layers and the substrate. Various ZnO nanostructures have been prepared and tested to perovskite solar cells. The effects of the structure and growth electrochemical bath on the cell performance and functioning have been investigated by various techniques. [1] D. Liu, T. L. Kelly, Nature Photonics, 2014, 8, 133-138. [2] J. Zhang, P. Barboux, T. Pauporté, Adv. Energy Mater., 4, (18) (2014) 1400932. [3] J. Zhang, E. J. Juárez-Pérez, I. Mora-Seró, B. Viana, Th. Pauporté, J. Materials Chemistry A. submitted