Separation of the polarization of a two-electron transfer reaction into those of consecutive one-electron transfer reactions by potential-step chronoamperometry in the oxidation of O 2− ion by Pt/YSZ oxygen electrodes

Abstract

Porous Pt electrodes prepared on a YSZ single crystal disk, which was used to take micrographs of the Pt-YSZ interface, were polarized in the anodic direction at 400 °C. The polarization vs log i plots fit Tafel's relationship with the slope corresponding to a two-electron transfer process which is most likely O 2− → O a + 2 e −. This study aims to separate the polarization of the reaction into those of consecutive one-electron transfer reactions, ie, O 2− → O − + e − and O − → O a + e −, using transient data obtained by potential-step chronoamperometry. A theoretical current decay equation was expressed by the sum of two exponential functions decaying with the time constants of the one-electron transfer reactions. The polarizations were determined by fitting the theoretical decay curves calculated by the equation to experimental ones. It was found that the first electron transfer step is of a pure charge transfer while the second involves the concentration polarization due to the accumulation of O a. The capacitance data calculated from the decay rates also supported these analytical results.