Electroreduction of nitrous oxide on platinum and palladium: Toward selective catalysts for methanol–nitrous oxide mixed-reactant fuel cells

The kinetics of N₂O electroreduction in the absence and presence of methanol was studied between 295 and 333 K on polycrystalline Pt and Pd electrodes in 0.1 M NaOH. In the absence of methanol the reduction of N₂O on Pd is more facile than on Pt as shown by the approximately four times lower apparent activation energy and lower Tafel slope (Pt: 0.111 ± 0.019 V dec⁻¹, Pd: 0.084 ± 0.007 V dec⁻¹ at 295 K). Two different electroreduction mechanisms are proposed for Pt and Pd with and without participation of underpotential deposited hydrogen, respectively. The selectivity of Pt and Pd electrodes toward both N₂O electroreduction and methanol (0.5 and 1 M) oxidation at 295 K was also investigated. Pt based electrocatalysts are promising candidates for the anode of a mixed reactant CH₃OH–N₂O fuel cell due to inhibition of N₂O reduction by chemisorbed methanol. Pd on the other hand is a selective cathode electrocatalyst since N₂O reduction takes place fairly actively in the presence of 1 M methanol, while methanol oxidation is inhibited.