Tracing Dissolved Iridium in Proton Exchange Membrane Water Electrolysis Using Operando Hard-X-Ray Fluorescence

Dissolution of iridium in proton exchange membrane water electrolyzer anodes is a critical challenge on the path towards low-cost and durable water electrolysis. While end-of-test analysis of electrolyzers showed that most of the dissolved catalyst redeposits in the membrane and the cathode catalyst layer, this approach offers only limited insight into the dynamics of iridium dissolution, transport, and redeposition mechanisms. By means of 2D-mapping with synchrotron-based operando X-ray fluorescence (XRF) spectroscopy, we detected dissolved iridium in the membrane electrode assembly (MEA) during electrolysis operation and traced the dynamics of its transport under varied operation conditions with reasonable temporal (20 min per map) and spatial (10 µm) resolution. During electrolysis, we observed an accumulation of dissolved iridium in the cathode catalyst layer. With the toggling flow of dry gas at the cathode, we can distinguish between mobile and redeposited iridium. Though thermodynamically favored, no significant deposition within the cathode was observed after ~1 h of electrolysis. The results obtained are another puzzle piece in the understanding of iridium dissolution in electrolyzers towards its possible mitigation.