Activation of Oxygen Reduction Reaction on Well-Defined Pt Electrocatalysts in Alkaline Media Containing Hydrophobic Organic Cations

The activity of the oxygen reduction reaction (ORR) is significantly affected by the nonspecifically adsorbed ions at the electrode/electrolyte interface as well as the surface structures of the catalytic substrate. In this study, we found that an organic cation activates the ORR on Pt single-crystal electrodes in alkaline media, and we evaluated ORR activity using shape-controlled Pt nanoparticles. The ORR activity on Pt(111) was significantly enhanced by a tetramethylammonium cation (TMA+), which correlates with its hydrophobicity as is the case for alkali metal cations. However, an alkylammonium cation with a long chain deactivated electrochemical reactions because these cations assemble at high concentrations on the surface through their hydrophobic interionic interactions with alkyl chains. The ORR activity on Pt nanoparticles was also enhanced by TMA+; cuboctahedral Pt nanoparticles with a (111) plane exhibit a markedly high rate of increase in ORR activity.