Oxygen Reduction at the Pt/Recast-Nafion Film Interface at Different Temperatures and Relative Humidities

Abstract

The effects of temperature (20-80{degree sign}C) and relative humidity (~0- 100%) on the oxygen reduction reaction (ORR) on a Nafion®- covered platinum ultramicroelectrode were investigated using cyclic voltammetry and chronoamperometry. The cyclic voltammograms exhibited a significant hysteresis between the forward and reverse scans, which increased with either humidity or temperature increases. No hysteresis was observed for the fully hydrated film equilibrated with liquid water. It is postulated that the oxygen transport may be obstructed by water produced by oxygen reduction, which accumulates at the interface due to its hindered diffusion in the partially hydrated films. The charge transfer kinetics of ORR at both clean and oxide-covered platinum were found to slow down with increases in relative humidity. The effect was stronger for the oxide-covered platinum and was correlated with differences in platinum oxide coverage associated with changes in film hydration.