Oxygen evolution on La0.5Ba0.5CoO3: Transient measurements

The recovery behavior of an aged La_0.5Ba_0.5CoO₃ electrode after interrupting a cathodic discharge current (forced decay, all starting from a high prepolarized state) at a still positive overpotential of 150 mV is discussed. It was found that the potential rises again after interrupting the cathodic current. This rise in potential decreases with decreasing cathodic currents when the electrodes are stabilized at the same starting overpotential before applying the cathodic current. The rise in potential also decreases with decreasing starting overpotential for the same cathodic discharge current. From these measurements it was concluded that higher oxides are present to a certain depth in the oxide layer at high positive overpotentials.Open-circuit decay measurements with different starting overpotentials were performed, all showing logarithmic slopes of ～ 50 mV/dec. The decay rates increased for lower starying overpotentials. Impedances were measured during a decay, from which effective capacitances were calculated. For a given overpotential, the capacitances during a decay were practically constant in the overpotential range from 220 to 150 mV for a given staring overpontential. But for higher starting overpotentials the capacitances were found to be higher. These effects are explained by a change in effective surface area for different starting overpotentials caused by the above-mentioned higher oxides blocking the surface.