Analysis of oxygen reduction on Pt microelectrode with polymer electrolytes of various exchange capacities

In order to obtain an improved design of a polymer electrolyte fuel cell cathode, the oxygen reduction reaction on a Pt micro-electrode with proton exchange membranes of various exchange capacities has been investigated. The measurements were performed by chronoamperometry for determination of the diffusion coefficient and oxygen solubility, and by slow scan voltammetry for reaction kinetics with the microelectrode in the temperature range 20 to 70degrees C. The results of chronoamperometry and slow scan voltammetry were analyzed by the fitting of analytic equations and digital simulation. The diffusion coefficients increased with temperature and exchange capacity. On the other hand, the solubilities increased with a decrease in temperature and exchange capacity. The dependences of the diffusion coefficient on temperature and exchange capacity were larger than those of the solubility. Accordingly, the permeabilities, which are the product of the diffusion coefficient and the solubility, increased with temperature and exchange capacity. Although the dependence of the exchange current densities on the exchange capacity was not clear, the exchange current densities were 10(-9) to 10(-8) A cm(-2) in the high potential region and about 10(-6) A cm(-2) in the low potential region. (C) 2002 The Electrochemical Society.