Durability Testing of Low-Iridium PEM Water Electrolysis Membrane Electrode Assemblies

Lowering the iridium loading at the anode of proton exchange membrane (PEM) water electrolyzers is crucial for the envisaged GW-scale deployment of PEM water electrolysis. Here, the durability of a novel iridium catalyst with a low iridium packing density, allowing for low iridium loadings without decreasing the electrode thickness, is being investigated in a 10-cell PEM water electrolyzer short stack. The anodes of the membrane electrode assemblies (MEAs) of the first five cells utilize a conventional iridium catalyst, at loadings that serve as benchmark for today's industry standard (2 mg_Ir cm⁻²). The last five cells utilize the novel catalyst at 8-fold lower loadings (0.25 mg_Ir cm⁻²). The MEAs are based on Nafion^® 117 and are tested for 3700 h by load cycling between 0.2 and 2.0 A cm⁻², with weekly polarization curves and impedance diagnostics. For both catalysts, the performance degradation at low current densities is dominated by an increase of the overpotential for the oxygen evolution reaction (OER), whereby the OER mass activity of the novel catalyst remains ≈4-fold higher after 3700 h. The temporal evolution of the OER mass activities of the two catalysts will be analyzed in order to assess the suitability of the novel catalyst for industrial application.