Measurement of the Protonic and Electronic Conductivities of PEM Water Electrolyzer Electrodes

Reducing anode catalyst layer proton- and electron-transport resistances in polymer electrolyte membrane water electrolyzers is critical to improving its performance and maximizing catalyst utilization at high current density. A hydrogen pump technique is adapted to measure the protonic conductivity of IrO_x-based catalyst layers. The protonic resistance of the catalyst layer is obtained by subtracting the protonic resistance of an assembly of two NRE211 membranes hot-pressed together from an assembly of two NRE211 membranes with an IrO_x intermediate layer. The through-plane and in-plane electronic conductivities were also measured using two- and four-probe methods, respectively. Using these techniques, the protonic and electronic conductivities of the IrO_x catalyst layers with varying Nafion loading were measured. The results show that the limiting charge-transport phenomena in the IrO_x catalyst layer can be either proton or electron transport, depending on the ionomer loading in the catalyst layer. These results are validated by numerical simulation, as well as by comparison to the high-frequency resistance of an electrolyzer with the same layer.