Energy Conversion and Storage

Controlled crystallization of GeSe₂-Sb₂Se₃-CuI glasses can lead to self-organized nano-heterojunction composed both of p-type Cu₂GeSe₃ and n-type Sb₂Se₃. Conductive channels are formed. This unique nanostructure leads to remarkable photoelectric properties because of their high absorption of visible light, high photocurrent and very long lifetime of charge careers. This work was initiated and continued through national collaborative programs (CNRS, Region Brittany) and above all international (PICS and PHC). These materials are protected by a CNRS patent (December 2013).

This thematic explores the formulation of new materials by introducing alkali (Li or Na) in matrices based on chalcogenide glasses or inorganic ceramics. Their synthesis is then implemented according to different ways: mechanical milling and sintering by hot-pressing or flash SPS sintering, or even by traditional melt-quenching.

Moreover, feasibility to prepare thin films of few microns deposited by CVD is studied. Ionic conductivity is finally characterized by impedance spectroscopy. Another axis consists in optimizing the quality of the electrode / electrolyte interface to enhance the exchanges.

Glass is a poor thermal conductor and a good electrical conductor, thus it constitutes an interesting starting point for developing compounds for the thermoelectricity. The main interest of a vitreous functional material will be its ability to be easily shaped compared to its crystallized counterpart. Thus glasses have been prepared and characterized mainly in the Te-As-Se-Cu system. Glass-ceramics were also elaborated with optimized heat treatment modifying their thermal and electrical behavior. These efforts will be pursued, in particular through a new European program (ITN Coach 2015-2019).

We use a powerful wet chemical tool to condense small inorganic nanoparticles (sizes between 2 nm and 20 nm) in water or ethanol. The main objectives of this work are the elaborations of superconcentrated stable nanocolloids (ZnO, TiO₂, Au, Ag) and their subsequent multiple doping, either cationic (Er, Fe, Al) or anionic (S, N). This approach delivers pre-doped sols which are useful for applied nanomaterials research. In addition, natural polysaccharides are used in bio-inspired synthesis of metallic/bi-metallic nanocolloids.

Non-aggregated nanoparticulate ZnO (or TiO₂) sols are cheap and easy to handle precursors for thin film technologies. Depending on the initial single or multiple doping of the colloidal nanoparticles, various photo-catalytical coatings have been successfully developed. For example, nitridated Zn_xTi_yO_zN_w – Spinel layers were used in visible light driven degradation of Methylene-Blue dyes. Furthermore, super-hydrophilic silica doped ZnTiO₃/TiO₂ coatings allow an efficient degradation of fatty acids deposited on glass surfaces.

Oxides and oxynitrides heterogeneous catalysts of the Al-P-O-N system have been studied in collaboration with the Institut Français du Pétrole Energies Nouvelles for the transesterification of vegetable oils. This reaction produces fatty acid methyl esters (FAME) entering the composition of biodiesel and glycerine, a recyclable by-product. The introduction of nitrogen within aluminophosphates (AlPO₄) involves a modification of the surface acid-base properties. AlPO₄ and corresponding nitrided phases (with N wt.% < 10) produce higher catalytic activities for this transesterification reaction compared to those of the reference catalyst ZnAl₂O₄.