Pt/carbon xerogel catalysts for PEM fuel cells

Abstract : Carbon xerogels have been used to replace carbon black as catalyst support at the cathode of proton exchange membrane (PEM) fuel cells in order to decrease the mass transport limitations in this electrode. Carbon xerogels are very clean nanostructured carbons with well-defined pore texture, which allows forbetter reactant/product diffusion. Pt/carbon xerogel catalysts with high metal dispersion (nanoparticles ca. 2 nm in size) and high metal content (~ 25 wt.%) can be engineered via rational synthesis methods such as the 'Strong Electrostatic Adsorption' technique. The results show that choosing correctly the average pore texture of the carbon xerogel allows for minimizing the diffusion overpotential of the H2/air cell. However, the catalyst characterization indicates that the presence of chlorine, coming from H2PtCl6, induces a dramatic decrease of the Pt utilization ratio in the final PEMFC catalytic layer. To remove chlorine, a reduction of the catalyst at 450°C, at least, is necessary.