Electrode kinetics of oxygen reduction at carbon-supported and unsupported platinum microcrystallite/Nafion® interfaces

Abstract

The electrode kinetics of oxygen reduction at the platinum microcrystallite/Nafion® interface was investigated as a function of temperature and pressure. These studies were conducted using porous gas-diffusion electrodes, containing unsupported platinum (10 Mg cm −2) or carbon-supported platinum (0.4 mg cm −2), in proton exchange membrane fuel cells, using H 2 and O 2 as reactants. The effects of platinum loading and of Nafion impregnation on the electrode kinetic parameters were elucidated. Over the range of current densities from 1 to 1000 mA cm −2 (geometric), the Tafel slope was ca. −60 mV per decade and was practically independent of temperature, O 2 pressure, and type of electrode. The platinum electrode was still in the potential regime where oxygenated species are present on the surface (Temkin conditions). The reaction order with respect to O 2 is unity and the activation energy for O 2-reduction was ca. 80 kJ mol −1. These electrode kinetic parameters are in good agreement with those obtained at the platinum microelectrode/Nafion interface, as previously determined in our laboratories.