Oxygen reduction on nanocrystalline ruthenia – local structure effects

Daniel F. Abbott, Sanjeev Mukerjee, Valery Petrykin, Zdeněk Bastl, Niels Bendtsen Halck, Jan Rossmeisl and Petr Krtil* Nanocrystalline ruthenium dioxide and doped ruthenia of the composition Ru1 xMxO2 (M1⁄4 Co, Ni, Zn) with 0 # x # 0.2 were prepared by the spray-freezing freeze-drying technique. The oxygen reduction activity and selectivity of the prepared materials were evaluated in alkaline media using the RRDE methodology. All ruthenium based oxides show a strong preference for a 2-electron oxygen reduction pathway at low overpotentials. The catalysts' selectivity shifts towards the 4-electron reduction pathway at high overpotentials (i.e. at potentials below 0.4 V vs. RHE). This trend is particularly noticeable on non-doped and Zn-doped catalysts; the materials containing Ni and Co produce a significant fraction of hydrogen peroxide even at high overpotentials. The suppression of the 4-electron reduction pathway on Ni and Co-doped catalysts can be accounted for by the presence of the Ni and Co cations in the cus binding sites as shown by the DFT-based analyses on non-doped and doped catalysts.