Sandrine Berthon-Fabry

Synthesis and Properties of Platinum Nanocatalyst Supported on Cellulose-Based Carbon Aerogel for Applications in PEMFCs

Platinum nanoparticles supported on nanostructured cellulose-based carbon aerogels (carbonized aerocellulose, CAC) were evaluated in proton exchange membrane fuel cell (PEMFC). The CAC substrate was synthesized through the dissolution, gelation, regeneration, supercritical CO2 drying and pyrolysis of cellulose. The Pt nanoparticles deposition was performed by impregnation of the CAC with H2PtCl6, followed by Pt z species reduction either under H2 at 300-400C or in basic NaBH4 solution. While H2 reduction leads to uniform Pt nanoparticles well-dispersed over the CAC surface, larger agglomerates form with NaBH4 reduction, as revealed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The reduction methods influences the quantity of platinum deposited, which may be increased by using multiple impregnation/reduction steps. The specific surface area of Pt and specific/mass activities towards oxygen reduction of the Pt/CAC materials, investigated using the rotating disk electrode setup, are similar to those of commercial Pt/Carbon Black (CB). Finally, PEMFC unit cell testing demonstrates that a Pt/CAC sample synthesized using three successive impregnation/reduction steps, loaded at ca. 14 wt Pt/(Pt C), competes with state-of-the-art Pt/CB electrocatalysts of comparable Pt loading

Synthesis of Highly Porous Catalytic Layers for Polymer Electrolyte Fuel Cell Based on Carbon Aerogels

Recent studies of the PEMFC catalytic layer electrocatalystsupport showed that high surface area carbon blacks cannot beused efficiently (1) because they have necessarily small primarypores that yield high diffusion limitation for the oxygenreduction reaction (ORR). In the present paper, we firstsynthesized and characterized carbon aerogels which exhibit highsurface area, high porous volume and adjustable pore-sizedistribution. In that way, they enable to decouple betweensurface area and porosity, while they are also promisingelectrocatalyst supports (2). Second, we elaborated newcatalytic layers made from 2 different carbon aerogels with 2different Nafion loadings. Finally, we characterized thestructure of such catalytic layers, and evaluated their activitytowards the oxygen reduction reaction (ORR). Finally, anappropriate catalyst support should display large pore-size andhigh surface area in order to reduce the PEMFC cathode platinumloadings without loosing activity, following the reduction ofoxygen diffusion limitation.

First Insight into Fluorinated Pt/Carbon Aerogels as More Corrosion-Resistant Electrocatalysts for Proton Exchange Membrane Fuel Cell Cathodes

This study evaluates the fluorination of a carbon aerogel and gives first insights into its durability when used as platinum electrocatalyst substrate for proton exchange membrane fuel cell (PEMFC) cathodes. Fluorine has been introduced before or after platinum deposition. The different electrocatalysts are physico-chemically and electrochemically characterized, and the results discussed by comparison with commercial Pt/XC72 from E-Tek. The results demonstrate that the level of fluorination of the carbon aerogel can be controlled. The fluorination modifies the texture of the carbons by increasing the pore size and decreasing the specific surface area, but the textures remain appropriate for PEMFC applications. Two fluorination sites are observed, leading to both high covalent C-F bonds and weakened ones, the quantity of which depends on whether the treatment is done before or after platinum deposition. The order of the different treatments is very important. Indeed, the presence of platinum contributes to the fluorination mechanism, but leads to amorphous platinum, which is demonstrated rather inactive towards the oxygen reduction reaction. On the contrary, a better durability was demonstrated for the fluorinated and then platinized catalyst compared both to the same but not fluorinated catalyst and to the reference commercial material (based on the loss of the electrochemical real surface area after accelerated stress tests).

Elaboration and Characterizations of Platinum Nanoparticles Supported on Cellulose-Based Carbon Aerogel

This work investigates the deposition of Pt nanoparticles onto carbonized aerocellulose (CAC), via impregnation of the CAC with H2PtCl6 followed by reduction either under H2 at 300-400{degree sign}C or in a basic NaBH4 solution. H2 reduction yields uniform Pt nanoparticles (average diameter < 2 nm) dispersed over the CAC surface, as revealed by transmission electron microscopy (TEM). Larger agglomerates can be seen in TEM images for NaBH4 reduced samples, which is confirmed by powder X-ray diffraction (XRD). A rotating disk electrode was employed to analyze the electrochemical properties of the Pt/CAC materials. The active area of the platinum nanoparticles was evaluated using hydrogen adsorption/desorption cyclic voltammetry and CO-stripping measurements. The oxygen reduction reaction kinetic parameters of the Pt/CAC materials compare well with those of commercial Pt/Carbon Black (CB). Finally, PEMFC unit cell testing demonstrates that a Pt/CAC electrocatalyst synthesized using 3 successive impregnation/reduction steps can compete with state-of-the-art Pt/CB electrocatalysts.

Synthesis of carbon nanospheres for the development of inkjet-printed resistive layers and sensors

Unitary carbon nanoparticles with a well-defined shape and a range of diameters between 50 nm and 300 nm have been synthetized from the pyrolysis of resorcinol formaldehyde copolymer. This divided solid has a molecular organization similar to carbon black with a more regular shape and a higher diameter. Thus, carbon nanospheres appear to be adapted to the development of accurate sensors. Inkjet-printable dispersion was prepared with this material and a mixture of N-methyl-2-pyrrolidone and N-cyclohexyl-2-pyrrolidone. This ink is the proof of concept that it is possible to form continuous layers on polyimide flexible substrate with resistive properties which exhibit temperature sensitivity.

SAXS Characterization of Carbon Aerogels for Catalytic Supports

Carbon aerogels are very promising substrates for electrocatalyst deposition involved in fuel cells. Their advantage over high surface area carbon blacks currently used, is the porous monolithic structure yielding large pore volumes with controlled pore sizes. By changing the synthesis parameters, it is possible to adjust their multi-scale structure which is strongly related to the electrochemical performances. The aim of the lecture is to give a survey of information about the multi-scale structure that can be obtained by small and wide angle X-ray scattering (SAXS and WAXS) techniques combined with contrast variation (CV). To this end, a series of SAXS experiments on carbon aerogels are described and the analysis of the experimental data is explained. Particular attention is paid to the determination of the specific surface area, SSAXS, and to the reasons why WAXS curves combined to SAXS ones make this determination more pertinent. The physical meaning of similarity or difference between SSAXS and surface area determined by gas adsorption, SADS, is discussed and information obtained by using contrast variation (CV) is described for two carbon aerogels prepared in different conditions.