To elucidate the mechanism of the electrode reaction at the interface of porous Pt/stabilized zirconia, measurements were made on the electrode interface conductivity, , and the steady‐state polarization current, , as a function of partial pressure, , and partial pressure, , up to 800°C. The rate of the electrode reaction at 700 to 800°C in atmospheres is faster than that in and slower than that in rich atmospheres by 1 to 2 orders of magnitude. The rate‐determining reaction process was the exchange of adsorbed OH radicals between the Pt‐ and the stabilized zirconia‐surface at the triple‐phase boundary (TPB) of gas/Pt/stabilized zirconia. When the oxygen activity, , ( vs. gas of ) on the zirconia surface at the TPB was higher than , the predominant rate‐determining reaction and the rate equation were given by and , respectively. Those in the region of were expressed by and , respectively. Here, , , , and are the rate constants, and θ denotes the coverage of the adsorbed species indicated by suffix on the surface of the solid shown in parentheses.
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Mizusaki et al. (1994) studied this question.