Effect of hydrophobic cations on the oxygen reduction reaction on single‒crystal platinum electrodes

Highly active catalysts for the oxygen reduction reaction are essential for the widespread and economically viable use of polymer electrolyte fuel cells. Here we report the oxygen reduction reaction activities of single‒crystal platinum electrodes in acidic solutions containing tetraalkylammonium cations with different alkyl chain lengths. The high hydrophobicity of a tetraalkylammonium cation with a longer alkyl chain enhances the oxygen reduction reaction activity. The activity on Pt(111) in the presence of tetra‒n‒hexylammonium cation is eight times as high as that without this cation, which is comparable to the activities on Pt₃Co(111) and Pt₃Ni(111) electrodes. Hydrophobic cations and their hydration shells destabilize the adsorbed hydroxide and adsorbed water. The hydrophobic characteristics of non‒specifically adsorbed cations can prevent the adsorption of poisoning species on the platinum electrode and form a highly efficient interface for the oxygen reduction reaction.