The Kinetics and Mass Transfer of Zinc Electrode in Acidic Zinc‐Chloride Solution

Abstract

The kinetics, mass transfer, and surface roughness of zinc electrode in acidic zinc chloride solutions have been investigated in order to understand and optimize its performance in the zinc‐chlorine hydrate battery. Polarization and limiting currents were measured using a rotating hemispherical zinc electrode. Exchange current densities and Tafel slopes are reported and the cathodic zinc deposition is confirmed to be first order. A cathodic mechanism of two consecutive one‐electron transfer steps are postulated where the first step is the rate‐determining step. A diffusion coefficient of zinc ion in , , is obtained from the kinetics‐diffusion mixed behavior. The surface roughness during the deposition depends strongly on the zinc‐chloride concentration, the fraction of the limiting current , and the deposition time. Two regions are observed: (i) at appreciable fraction of the limiting current where the roughness is determined by the hydrodynamic conditions, and (ii) at well below the limiting current where the roughness is governed by the microthrowing power of the zinc deposit. The growth of zinc dendrites at the edges of a rotating disk electrode was investigated potentiostatically. After an initiation period the current increased sharply and dendrites were detected. The growth direction of the dendrites is explained in terms of the hydrodynamic flow and the level of zinc ion concentration.