Determination of the Rate Constants of Oxygen Reduction in High‐Temperature Air Electrodes on Solid Oxide Electrolytes

The rate constants of electrochemical oxygen reduction by platinum electrodes on various solid oxide electrolytes have been determined from transient depolarization curves and steady‐state current‐potential curves free of ohmic drop. The rate equations used for the determination were derived on the basis of a mechanism involving dissociation of adsorbed oxygen into atomic species and subsequent diffusion of atomic oxygen through the electrolyte‐electrode interface. The rate constants were determined by comparison of the theoretical curves with the experimental ones. This analytical method has been applied to the air electrodes of doped ZrO 2 / Pt and doped CeO 2 / Pt systems. The latter electrode was found experimentally to be much less polarized than the former. The smaller polarization of the latter is due to a greater reaction area of the electrode and not due to the higher conductivity of the ceria electrolyte used. Addition of ceria to the electrode of the ZrO 2 / Pt system resulted in a marked decrease in polarization.