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 IrOx-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 IrOx 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 IrOx catalyst layers with varying Nafion loading were measured.
The results show that the limiting charge-transport phenomena in the
IrOx 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.