Abstract
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.
Highlights
Membrane resistance is a key parameter for the energy efficiency of electrochemical membrane-based technologies
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
With equal concentration at both anolyte and catholyte compartments, the DC results indicate that the membrane resistance is a function of temperature but is independent of current density
Summary
Membrane resistance is a key parameter for the energy efficiency of electrochemical membrane-based technologies. Previous studies have reported that measuring the membrane resis tance remains a challenge, as various reported methods and operating conditions lead to different results [1,2,3,6,7,8,9,10,11,12,13]. The EIS method is often preferred due to its ability to separate the boundary layer resis tance from the membrane resistance. When it comes to the experimental method, the choices are usually between a direct method with two electrodes and an indirect method with four electrodes. The indirect method offers an effective way of excluding the effects of electrode shielding, electrode reactions, and bubble formation The resistance, in this case, is measured between two reference electrodes instead of the current-generating electrodes. No single study exists which investigates the temperature profile as close as possible to the membrane for high cur rent density operation
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