Correlation of the Adsorption Geometry of Melamine/Water Structure on the Low-Index Planes of Pt and the Activity in Oxygen Reduction Reaction

Abstract

It is important to enhance the activity of the oxygen reduction reaction (ORR) for the development of high-efficiency fuel cells. Hydrophobic species improve the ORR activity of Pt electrodes. In this study, we focused on melamine, which is known to increase the ORR activity of Pt nanoparticles and almost all single-crystal Pt electrodes. We estimated the adsorption geometry of melamine and the structure of water on the low-index planes of Pt by using infrared reflection absorption spectroscopy (IRAS). Melamine was adsorbed with one amino group on Pt(111) and Pt(110) electrodes, where the increase ratio of the ORR activity was higher. On Pt(100), where melamine had little effect on the ORR activity, the melamine was adsorbed with two amino groups. The structure of the ice-like water was destroyed after the adsorption of melamine on the Pt(111) and Pt(110) surfaces, whereas it remained intact on Pt(100). The order of the enhancement ratio of the ORR activity is rationalized based on the surface coverage of Pt–OH and melamine species, the adsorption geometry of melamine, and the destruction of the structure of the ice-like water.