Passivation of Zinc Anodes in  KOH  Electrolytes

Passivation times of horizontally upward-facing and downward-facing Zn microanodes in KOH electrolytes of five concentrations are reported. These measurements extend passivation data into a low current-density region for evaluating conflicting interpretations of published work. To interpret these data, a new mechanism for anodic passivation is proposed. In high current-density regions, passivation occurs when compact ZnO covers the electrode surface; in low current-density regions, passivation occurs when the mass transfer of hydroxide ions across a porous ZnO layer is less than that required for anodization. Passivation in porous Zn battery electrodes is also discussed. 34 ref.--AA