Oxygen Exchange on Platinum Electrodes in Zirconia Cells: Location of Electrochemical Reaction Sites

Abstract

Oxygen exchange kinetics on porous platinum electrodes in a zirconia electrochemical cell were measured at 600°–800°C in 10−5–0.21 atmospheres oxygen. Steady‐state polarization and potential‐step chronoamperometric experiments were performed. Steady‐state current‐voltage characteristics exhibited near‐exponential behavior at intermediate potentials and approached anodic and cathodic limiting currents at higher overpotentials. At and below 600°C, the initial decay of the current following anodic and cathodic potential steps was inversely proportional to the square root of time. This Cottrell‐type behavior indicates that the charge‐transfer step in the mechanism of oxygen exchange occurs at the three‐phase boundary where the electrode, electrolyte, and gas‐phase intersect.