Christel Laberty-Robert

Design and properties of functional hybrid organic–inorganic membranes for fuel cells

This critical review presents a discussion on the major advances in the field of organic-inorganic hybrid membranes for fuel cells application. The hybrid organic-inorganic approach, when the organic part is not conductive, reproduces to some extent the behavior of Nafion where discrete hydrophilic and hydrophilic domains are homogeneously distributed. A large variety of proton conducting or non conducting polymers can be combined with various functionalized, inorganic mesostructured particles or an inorganic network in order to achieve high proton conductivity, and good mechanical and chemical properties. The tuning of the interface between these two components and the control over chemical and processing conditions are the key parameters in fabricating these hybrid organic-inorganic membranes with a high degree of reproducibility. This dynamic coupling between chemistry and processing requires the extensive use and development of complementary ex situ measurements with in situ characterization techniques, following in real time the molecular precursor solutions to the formation of the final hybrid organic-inorganic membranes. These membranes combine the intrinsic physical and chemical properties of both the inorganic and organic components. The development of the sol-gel chemistry allows a fine tuning of the inorganic network, which exhibits acid-based functionalized pores (-SO(3)H, -PO(3)H(2), -COOH), tunable pore size and connectivity, high surface area and accessibility. As such, these hybrid membranes containing inorganic materials are a promising family for controlling conductivity, mechanical and chemical properties (349 references).

Advances in the recovering of spent lithium battery compounds

Advances in a process based on simple and environmentally compatible operations, aimed to the treatment and recycling of spent lithium-ion batteries, are reported in this paper. This process is safe, economic, and recovers as much of the battery materials as possible. It operates mainly in a selective dissolution in dilute acid, a chemical treatment of the filtrate and a thermal treatment of the solid residue. The validity of the process and its reproducibility have been evaluated at each step of the separation. This method involves very simple equipment and can be scaled-up for commercial production. Based on the projected quantities of lithium ion batteries available for recycling in the next few years, there is a significant market opportunity for a successful technology.

Mesoporous α-Fe2O3 thin films synthesized via the sol–gel process for light-driven water oxidation

This work reports a facile and cost-effective method for synthesizing photoactive α-Fe(2)O(3) films as well as their performances when used as photoanodes for water oxidation. Transparent α-Fe(2)O(3) mesoporous films were fabricated by template-directed sol-gel chemistry coupled with the dip-coating approach, followed by annealing at various temperatures from 350 °C to 750 °C in air. α-Fe(2)O(3) films were characterized by X-ray diffraction, XPS, FE-SEM and electrochemical measurements. The photoelectrochemical performance of α-Fe(2)O(3) photoanodes was characterized and optimized through the deposition of Co-based co-catalysts via different methods (impregnation, electro-deposition and photo-electro-deposition). Interestingly, the resulting hematite films heat-treated at relatively low temperature (500 °C), and therefore devoid of any extrinsic dopant, achieve light-driven water oxidation under near-to-neutral (pH = 8) aqueous conditions after decoration with a Co catalyst. The onset potential is 0.75 V vs. the reversible hydrogen electrode (RHE), thus corresponding to 450 mV light-induced underpotential, although modest photocurrent density values (40 μA cm(-2)) are obtained below 1.23 V vs. RHE. These new materials with a very large interfacial area in contact with the electrolyte and allowing for a high loading of water oxidation catalysts open new avenues for the optimization of photo-electrochemical water splitting.

Synthesis of YSZ powders by the sol-gel method: surfactant effects on the morphology

A colloid-emulsion route is established to prepare yttria stabilized zirconia (YSZ) powder, using cost-effective and commonly available inorganic salts as starting materials. Nanocrystalline, single-phase YSZ powders are prepared via calcinations of emulsion-derived precursor powder at 1000 °C for 2 hours. Formation of aggregates is detected, and the aggregates size and morphology depend on the chemical additives nature and milling. After chemical and mechanical treatments, the obtained powder has a spherical morphology, and the aggregates size is homogeneous and around 1 μm.

Room-Temperature Synthesis of Iron-Doped Anatase TiO2 for Lithium-Ion Batteries and Photocatalysis

Iron-doped nanocrystalline particles of anatase TiO2 (denoted x% Fe-TiO2, with x the nominal [Fe] atom % in solution) have been successfully synthesized at room temperature by a controlled two-step process. Hydrolysis of titanium isopropoxide is first achieved to precipitate Ti(OH)4 species. A fine control of the pH allows one to maintain (i) soluble iron species and (ii) a sluggish solubility of Ti(OH)4 to promote a dissolution and condensation of titanium clusters incorporating iron, leading to the precipitation of iron-doped anatase TiO2. The pH does then influence both the nature and crystallinity of the final phase. After 2 months of aging at pH = 2, well-dispersed nanocrystalline iron-doped TiO2 particles have been achieved, leading to 5-6 nm particle size and offering a high surface area of ca. 280 m(2)/g. This dissolution/recrystallization process allows the incorporation of a dopant concentration of up to 7.7 atom %; the successful incorporation of iron in the structure is demonstrated by X-ray diffraction, high-resolution transmission electron microscopy, and Mössbauer spectroscopy. This entails optical-band-gap narrowing from 3.05 to 2.30 eV. The pros and cons effects of doping on the electrochemical properties of TiO2 versus lithium are herein discussed. We reveal that doping improves the power rate capability of the electrode but, in turn, deserves the electrolyte stability, leading to early formation of SEI. Finally, we highlight a beneficial effect of low iron introduction into the anatase lattice for photocatalytic applications under standard AM1.5G visible-light illumination.

Sulfonic and Phosphonic Acid and Bifunctional Organic–Inorganic Hybrid Membranes and Their Proton Conduction Properties

Hybrid organic-inorganic approaches are used for the synthesis of bifunctional proton exchange membrane fuel cell (PEMFC) membranes owing to their ability to combine the properties of a functionalized inorganic network and an organic thermostable polymer. We report the synthesis of both sulfonic and phosphonic acid functionalized mesostructured silica networks into a poly(vinylidenefluoride-co-hexafluoropropylene) (poly(VDF-co-HFP) copolymer. These membranes, containing different amounts of phosphonic acid and sulfonic acid groups, have been characterized using FTIR and NMR spectroscopy, SA-XRD, SAXS, and electrochemical techniques. The proton conductivity of the bifunctional hybrid membranes depends strongly on hydration, increasing by two orders of magnitude over the relative humidity (RH) range of 20 to 100%, up to a maximum of 0.031 S cm(-1) at 60 °C and 100% RH. This value is interesting as only half of the membrane conducts protons. This approach allows the synthesis of a porous SiO(2) network with two different functions, having -SO(3)H and -PO(3)H(2) embedded in a thermostable polymer matrix.

New Fe2TiO5-based nanoheterostructured mesoporous photoanodes with improved visible light photoresponses

Triphasic nanocrystalline porous material based Fex–TiO2 anatase, pseudo-brookite and hematite are generated via a simple templated growth based strategy followed by carefully controlled temperature/atmosphere treatments. As shown by XRD, SEM, and TEM experiments the resulting nano-crystalline mesoporous films exhibit optimized bicontinuous pore-solid architectures and high surface-areas. Mossbauer spectroscopy and XPS analyses indicate that FeIII is the main iron oxidation state present in the films.

Nanoporous piezo- and ferroelectric thin films.

Nanoporous barium titanate and lead titanate thin films (∼100 nm calculated from ellipsometric data) are prepared starting from sol-gel solutions modified with a commercially available block-copolymer and evaporation-induced self-assembly methodology. The tuning of the thermal treatment followed by in situ ellipsometry allows the decomposition of the organic components and of the structuring agent leading to the formation of porous tetragonal crystalline perovskite structures as observed by XRD, HRTEM, SEM, and ellipsoporosimetry. Both nanoporous barium titanate and lead titanate thin films present local piezoelectric and ferroelectric behavior measured by piezoresponse force microscopy (PFM), being promising platforms for the preparation of the generation of new multifunctional systems.

Sol–gel route to advanced nanoelectrode arrays (NEA) based on titania gold nanocomposites

A simple sol–gel-coating strategy has been used to prepare below 10 nm thin nanostructured oxide (TiO2) membranes on conducting surfaces. Well calibrated (20 nm in diameter) and homogeneously dispersed nanoperforations are embedded into the membranes, altogether forming highly ordered and dense nanoelectrode arrays (NEAs) or patterns. Controlling the deposition conditions and the solution chemistry allowed for the formation of homogeneous membranes on very hydrophobic, and difficult to wet surfaces, such as gold. Calibrated pore size and interpore spacing are controlled through the self-assembly of macromolecular templates with the inorganic precursors upon evaporation. Structures were assessed by AFM and SEM-FEG, while XPS allowed us to estimate surface chemical state and composition. Cyclic voltammetry was used to describe the diffusion regime and the accessibility of the conducting nanosurfaces. We also show, using surface-tension measurement, that the ceramic matrix can be selectively chemically modified, which is an easy method to adjust the surface chemical nature of an electrode without altering its electron-transfer properties. It thus constitutes a novel route to hybrid organic–inorganic nanostructured surfaces with extended multifunctionality.

Nanocrystalline mesoporous LiFePO4 thin-films as cathodes for Li-ion microbatteries

Mesoporous LiFePO4 thin films prepared using a facile and low-cost synthesis approach have been studied as electrodes for Li-ion batteries. LiFePO4 mesoporous films (∼300 nm) were synthesized by a template-directed sol–gel chemistry coupled with the dip-coating approach, followed by heat-treatment under a reducing atmosphere (10% H2/N2) at temperatures ranging from 400 to 760 °C. These mesostructured LiFePO4 films are constituted of a connected network of mesopores (∼60 nm) and an assembly of crystalline nanoparticles (∼50 nm) in the pore wall. In addition, the presence of carbon, evidenced by Raman spectroscopy, provides efficient electron pathways along the 3-D nanoarchitectures. Cycling performance was evaluated for optimal nanocrystalline LiFePO4 thin films showing an excellent high rate performance after 1000 cycles (158 mA h g−1). These data provide important information on new types of porous architectures for the design of efficient electrodes for micro-batteries.