Maxwell-Stefan modeling and experimental study on the ionic resistance of cation-selective membranes in concentrated lye solutions

Both experimental investigation and mathematical modeling have been combined to clarify the influence of membrane properties, temperature, electrolyte concentration, and current density on membrane resistance of Nafion 117 in concentrated lye solutions. The ionic resistance was measured with and without membrane using four electrodes for 15 wt% and 32 wt% sodium hydroxide, temperatures up to 90 °C, and current densities up to 25 kA/m². The results from the measurement using Direct Current (DC) method as well as Electrochemical Impedance Spectroscopy (EIS) method indicate that membrane resistance is a function of temperature and lye concentration but is independent of current density. A mathematical model based on the Maxwell-Stefan approach has been developed to predict the ionic membrane resistance, and the model has been validated using the measured experimental data. A more suitable semi-empirical correlation for Maxwell-Stefan diffusivities is proposed by replacing the expressions for binary diffusivities based on infinite dilution with the concentration-dependent binary diffusivities. The new proposed correlation performs better in the model validation with the experimental data than the expressions using infinite dilution diffusivities.