Two carbon aerogels with different nanopore size distributions but both with high surface area, high nanoporous volume and low bulk density have been compared as platinum support. The influence of the nanostructure of the carbon aerogel on the platinum nanoparticle deposit was investigated. The platinum was deposited on the carbon by means of two different techniques, one employing an anionic platinum precursor, the other using a cationic one. The porosity of the carbon aerogels was characterized by combining N-2-sorption and mercury porosimetry. The platinum deposit was characterized by transmission electron microscopy and rotating disk electrode experimentation to measure the platinum active surface area and its activity towards oxygen reduction reaction (ORR). The structural differences between the carbon aerogels did not yield any difference in platinum deposits in terms of Pt-surface area and ORR activity. Interestingly, the ORR mass activity of the high Pt-surface area samples, obtained by the cationic insertion technique, was several times lower than that of the samples obtained by the anionic technique. This observation was attributed to the particle size effect, detrimental in the case of platinum particle size around 1 nm.