The macroscopic description of multicomponent diffusion serves as a basis for the development of equations in a useful form for electrochemical transport problems. A method is proposed for predicting the concentration dependence of the resulting transport parameters.

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A mathematical model which describes the transient behavior of porous zinc electrodes has been developed on the basis of concentrated ternary electrolyte theory. The model predicts the current distribution, potentials in the solution, concentrations of hydroxide ion and zincate ion, porosity, and volume fractions of zinc and zinc oxide as a function of time and position perpendicular to the surface of the electrode. Numerical techniques were used to predict zinc electrode behavior during galvanostatic operation of the cell with and without a membrane. During discharge of the cell without a membrane, much of the discharge product, zincate ions, are lost into the counter‐electrode compartment. For the cell with a membrane, this zincate loss is effectively restricted, but the utilization of zinc is severely limited by depletion of hydroxide ions within the zinc electrode compartment. In both cases, the reaction profiles are highly nonuniform and the reaction zone, located near the electrode surface, is very thin. This highly nonuniform reaction distribution accentuates the failure due to electrolyte depletion in the interior of the porous electrode, resulting in the low discharge capacity. On repeated cycling, the difference in anodic and cathodic reaction distribution causes the redistribution of solid zinc and zinc oxide species.

Shape change, the redistribution of active material over the zinc electrode surface as a result of cell cycling, is hypothesized to be caused by convective flows driven primarily by membrane pumping. A mathematical model is formulated based on the convective flow hypothesis for the zinc‐silver oxide secondary cell. The numerical solutions predict redistribution of zinc material over the zinc electrode, fluid flow rates, and variations of current distribution and cell potential with the number of cycles. These calculated results can be compared to experimental results. The results suggest that shape change can be eliminated if the convective flow in the zinc electrode compartment parallel to the electrode surface is stopped.