Temperature Dependence of the Electrode Kinetics of Oxygen Reduction at the Platinum/Nation Interface--A Microelectrode Investigation

A knowledge of the temperature dependence of the electrode-kinetic parameters for oxygen reduction at the platinum/ proton exchange membrane (PEM)interface and of mass-transport parameters of oxygen in the PEM is of vital importance in analyzing the performance of proton exchange-membrane fuel cells. The microelectrode technique which was previously developed to determine these parameters at the platinum/Nation activation energy for oxygen reduction at the platinum/Nation interface are nearly the same as those obtained at the platinum/trifluoromethane sulfonic acid (TFMSA)interface but less than values obtained at the Pt/H3PO4 and Pt/HC104 interfaces. The diffusion coefficient of oxygen in Nation increases with temperature while its solubility decreases with temperature. These parameters also depend on the water content of the membrane. The conductivity of the membrane increases with temperature until it reaches a plateau at a temperature of 80~ the dependence of the conductivity on temperature was correlated with the variation of water content of Nation with temperature.