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 CO(2) drying and pyrolysis of cellulose. The Pt nanoparticles deposition was performed by impregnation of the CAC with H(2)PtCl(6), followed by Pt(2+) species reduction either under H(2) at 300-400 degrees C or in basic NaBH(4) solution. While H(2) reduction leads to uniform Pt nanoparticles well-dispersed over the CAC surface, larger agglomerates form with NaBH(4) 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. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3585744] All rights reserved.