ABSTRACT
When a potential difference is applied to a zirconia cell, an imbalance is sometimes observed at the transient state between the amount of oxygen gas incorporated at the cathode and that evolved at the anode. In this paper, the cause of this imbalance was clarified.
Three terminal zirconia cells were prepared using 8 m/o Y2O3 doped ZrO2 with porous La0.6Ca0.4MnO3 as the working electrode and porous Pt as the counter and the reference electrodes. Using the potentiostatic polarization method, measurements were made at 800°C in the stream of Ar–O2 gas mixtures with controlled oxygen partial pressures of 1×105 – 1×102 Pa on the transient current, the electrode impedance at the steady–state, and the oxygen partial pressure of the outlet gas. The amount of oxygen evolved or incorporated by the cell was calculated by the change in oxygen partial pressure of the outlet gas.
Under cathodic polarization, oxygen evolution was found to take place by the change in oxygen nonstoichiometry of La0.6Ca0.4MnO3. Under anodic polarization, the oxygen evolution takes place when the potential between the working and the counter electrodes exceeds the decomposition potential of ZrO2. The zirconia surface at the counter electrode is blackened due to partial reduction.
