| 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, potential, current density, electrochemical reaction rates, and state of charge. Also, the model can be used to predict the hydrogen and oxygen pressures in the cell. 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 also shows the existence of an optimum rate of charge that maximizes the total charge uptake of the cell. Therefore, the model can be used to determine optimal operating conditions.; A sensitivity analysis on the model parameters revealed that the most relevant processes in the cell are the electrochemical reactions at the two electrodes. Mass transfer and ohmic losses have a secondary effect on the cell's performance. |
