Preparation of highly loaded Pt/carbon xerogel catalysts for Proton Exchange Membrane fuel cells by the Strong Electrostatic Adsorption method

Pt/carbon xerogel catalysts were prepared by the Strong Electrostatic Adsorption method: impregnation of the support was performed under optimal conditions, leading to maximum metal weight percentage while keeping the highest possible dispersion. After impregnation with H2PtCl6, the samples were filtered, dried and reduced. In order to increase the Pt weight percentage, up to three successive impregnation–drying–reduction cycles were performed. The final metal content of the catalysts was found to increase regularly: 7.5, 15.0 and 22.3 wt.%, after one, two and three cycles, respectively. This indicates that the adsorption sites were fully regenerated after the reduction treatment, and that they were available for the next impregnation step. In each case, the metal particles were found to be highly dispersed (particle size ∼2 nm); in addition, the average particle size did not change upon repeated impregnation. The 15.0 wt.% sample was tested as a cathodic catalyst in an H2/air Proton Exchange Membrane fuel cell: the cathode activity, expressed as a function of the mass of Pt involved, increased up to twice that of previous catalysts prepared by impregnation with H2PtCl6 and reduction in aqueous phase by NaBH4, provided the final reduction temperature of the catalyst was increased up to 450 °C.