Galvanostatic Polarization of Zinc Microanodes in KOH Electrolytes

摘要

This report includes a critical review of the current literature on the anodic passivation of zinc electrodes, a description of supplementary experimental studies to extend the data to a low-current-density region and to provide a basis for evaluating conflicting results of published work, and a new interpretation of the anodic passivation mechanism. This work provides a starting point for understanding passivation phenomena in battery electrodes. The utilization of a zinc electrode in alkaline batteries depends on the ability of the electrode to remain active during the anodic dissolution process. This dissolution period is often terminated by the onset of passivation. Experiments were conducted on the effects of current density on passivation time of a small zinc anode (6.6 x 10 exp -3 cm exp 2 ) in KOH at concentrations of 0.784, 2.92, 4.98 and 7.24M KOH as well as 7.24M KOH saturated with zinc oxide. It was concluded that there are two mechanisms for anodic passivation, one occurring at current densities below about 150 mA/cm exp 2 and another at higher current densities. Accordingly, in the overall mechanism, the total time to passivation includes the times to achieve the maximum zincate concentration as well as to form porous type I ZnO and compact type II ZnO. In Ni/Zn batteries under development for vehicle propulsion, the electrolyte is usually 30% KOH (7M) saturated with zinc oxide; and the zinc electrode is formed in-situ by electrodeposition of zinc onto the grid. For a current density of 20 mA/cm exp 2 in a Ni/Zn battery cycled at a 2-h rate and a zinc electrode with a porosity of 0.6 at the fully charged state, a current density of 338 mA/cm exp 2 was calculated to be that above which the passivation limits the utilization of the zinc electrode. 7 figures, 4 tables. (ERA citation 05:032346)