On the Availability of Active Sites for the Hydrogen Peroxide and Oxygen Reduction Reactions on Highly Dispersed Platinum Nanoparticles

Abstract

AbstractCarbon‐supported platinum nanoparticles (Pt/C) were synthesized by the carbonyl chemical route. The obtained Pt/C catalysts with different Pt mass loadings, varying from 5 to 50 wt %, showed constant morphology with particle sizes of about 2 nm and a dispersion of around 50 %. The electrochemical surface area, determined from CO stripping and hydrogen underpotential deposition, increased with the Pt mass loading, which confirmed that agglomeration was negligible. The oxygen reduction reaction (ORR) half‐wave potential was positively shifted with an increase in the Pt mass loading, and the ORR kinetic current was (40±10) μA cm−2Pt. The data collected on a rotating ring‐disk electrode for the ORR pathway revealed a two‐electron serial mechanism (hydrogen peroxide), instead of the four‐electron transfer (water). The determined turnover frequency factor indicated good selectivity of the Pt active sites for the ORR with 1 or 2 mm H2O2 in the electrolyte for samples with mass loadings ranging from 15 to 40 wt %. The ORR was markedly affected by the mass loading (5–10 wt % Pt/C) in the presence of 2 mm H2O2.