Unveiling Iridium Degradation Pathways during Intermittent Operation of a Proton Exchange Membrane Water Electrolyzer

A deep understanding and mitigation of Ir catalyst degradation is crucial for effectively reducing the currently used high Ir loadings and deploying proton exchange membrane water electrolysis on a gigawatt scale. Here, we quantitatively and qualitatively track Ir dissolution within an electrolyzer cell through a combined mass spectrometry-microscopy approach. By mimicking various electrolysis operation modes, we empitrically correlate the formation and consumption of cation and anionic Ir species with potential changes during idle periods, while mathenmatical modelling allows for quantitative determination of the overall Ir loss. We found that the cationic Ir species precipitate at the anode-membrane interface and within a short timeframe limit the dissolved ions from accessing the cathode thereby further enhancing the formation of IrO2 deposits in the membrane. We also observed that the potential drops during idle periods of electrolyzer operation lead to an enhanced back-diffusion of the anionic Ir species to the anode catalyst layer, thus partially entrapping the dissolved Ir. This work suggests that the design of thicker catalyst layers with lower packing densities is an important key to an enhanced durability of the electrolyzer.