Highly dispersed platinum on carbon aerogels as supported catalysts for PEM fuel cell-electrodes: comparison of two different synthesis paths

Pt-doped carbon aerogels have been prepared following two methods. In the first, the electrocatalytic material was synthesized from the sol-gel reaction precursors 2,4-dihydroxybenzoic acid and formaldehyde. The platinum precursor was Pt(NH3)(4)Cl-2, ion-exchanged onto the gel surface. The doped gel was dried supercritically and pyrolyzed at high temperature. This material was characterized with transmission electron microscopy (TEM) and by X-ray diffraction (XRD). The size distribution of the Pt nanoparticles changed with the pyrolysis temperature but the range of the size distribution did not. Platinum accessibility and electroactivity were evaluated with voltammetry. The second kind of Pt-doped carbon aerogels was synthesized from resorcinol and formaldehyde, supercritically dried, and pyrolyzed. The ground carbon aerogel was impregnated with a platinum precursor H2PtCl6 aqueous solution. This platinum salt was chemically reduced with NaBH4. Two carbon blacks, Vulcan XC-72 and BP2000, were doped following the same technique so that the influence of the carbon type on the properties of the deposited platinum nanoparticles could be investigated. The Pt-doped carbons so obtained were; characterized with TEM, XRD, hydrogen-adsorption/desorption cyclic voltammetry, CO-stripping voltammetry, and oxygen reduction reaction (ORR) activity. The Pt-doped carbon aerogel exhibited high ORR specific activity but comparable mass activity as compared with Pt-doped carbon blacks. (C) 2004 Elsevier B.V. All rights reserved.