Multiphase mathematical model of a nickel/hydrogen cell

A mathematical model for a nickel/hydrogen cell is developed to investigate the dynamic performance of the cell's charge and discharge processes. Concentrated solution theory and the volume averaging technique are used to characterize the transport phenomena of the electrolyte and other species in the porous electrode and separator. Other physical fundamentals, such as Ohm's law, are employed to describe the electrical and other physical processes in the cell. The model is designed to predict the distribution of electrolyte, hydrogen, and oxygen concentrations within the cell, hydrogen and oxygen pressure, potential, current density, electrochemical reaction rates, and state of charge. The model can be used to evaluate the influences of all the physical, design, and operation parameters on the behavior of a nickel hydrogen cell. The model simulations show excellent agreement with experimental data for charge and discharge operations. The model simulations show the formation of a secondary discharge plateau by the end of discharge. This plateau is caused by oxygen reduction at the nickel electrode. It is the first model that predicts this feature, which is a characteristic of the nickel electrode. The model simulations also show the existence of an optimum charge rate that maximizes the charge efficiency, which can be used for the implementation of optimal operating conditions.