RELAXATION PHENOMENA OF THE CONCENTRATION POLARIZATION IN HIGH-TEMPERATURE AIR CATHODES

The transient depolarization curves of Pt/ZrO2 high temperature air cathodes have been measured and compared with theoretical curves calculated by assuming a diffusion mechanism of atomic oxygen. The decay equation used involves the limiting current density, time constant for the decay rate and effective reaction area, as parameters to be determined. These parameter values were obtained by curve fitting. The polarization loss was found to decrease with increasing O2 pressure at the rate expected from the diffusion mechanism. The performance of the electrodes was enhanced as the sintering temperature rose. This trend was reflected on an increase in the parameter of effective reaction area. The performance was improved by loading an excess current. This effect was explained as being due to an increase in the diffusivity of O(a).