Coupling Phenomena between Zinc Surface Morphological Variations and Ionic Mass Transfer Rate in Alkaline Solution

A horizontal upward-facing Zn anode was electrochemically dissolved in aqueous alkaline electrolyte. A plane-parallel upward-facing Ni(OH)2/NiOOH cathode was combined with the Zn anode in a single cell, divided by a polymer separator. This configuration can be regarded as a single pore model inside the porous space of a Zn-NiOOH battery cell. It also insures that the ionic mass transfer rate by diffusion and migration mechanism is dominant over that by natural convection. The morphological variations of the Zn anode surface were examined during the discharge operation of the Zn-NiOOH model cell. Two-dimensional transient concentration profiles of each ion accompanying the electrochemical dissolution of Zn anode in alkaline electrolyte were numerically calculated. The surface morphological variations of the Zn anode were discussed with the aid of numerical simulation. ZnO precipitation on the Zn anode surface was confirmed to be dependent on the horizontal distance from the separator. The present numerical model provides insight to the analysis of observed morphological variations along the Zn anode surface.