Experimental-modeling framework to unveil iridium degradation pathways during intermittent operation in PEMWE

A deep understanding and mitigation of Ir degradation are crucial for effectively reducing the currently used high catalyst loadings and deploying proton exchange membrane water electrolysis on a gigawatt scale. Here, we deconvolute the dynamics of Ir dissolution, transport, and deposition within an electrolyzer through a combined mass spectrometry-microscopy approach. The formation and consumption of cationic and anionic Ir species are empirically correlated with potential changes during idle periods, while mathematical modeling allows for the quantitative determination of the overall Ir loss. We found that the cationic species precipitate at the anode-membrane interface and, within a short time frame, limit the dissolved ions from accessing the cathode, while potential cycling leads to enhanced back-diffusion of the anionic species to the anode, thus partially entrapping the dissolved Ir. This work suggests that the design of thicker catalyst layers with lower Ir packing densities is an important key to an enhanced durability of electrolyzers.