Joint Forces: Time-resolved Analysis of Electrochemical Performance, Nanostructure, and Iridium Dissolution of PEM Water Electrolysis Cells with Low Iridium Loadings under Harsh on/off Cycling Conditions

Although proton exchange membrane water electrolysis technology is deployed at large scale for green hydrogen production, the reliance on iridium as an anode catalyst remains a key challenge for further scalability, competitiveness and sustainability. In this study, the degradation of Ir black and IrO 2 based anode catalyst layers (CL) with varying iridium loadings under harsh on/off cycling is examined. This protocol is considered as an accelerated stress test. A combined approach of operando and post-mortem analysis is applied comprising voltage breakdown analysis, oxygen evolution reaction mass activity determination, scanning transmission electron microscopy, and inductively coupled plasma mass spectrometry. Only minor performance losses are observed, which are particularly pronounced during an initial run-in phase. This phase, however, is followed by increasing iR-free cell voltage values leading to steady-state behavior. The overpotential changes are mostly of kinetic nature, and more evident for Ir black. Time-resolved post-mortem analysis reveals iridium dissolution and migration, with the highest deposition in the cathode CLs after 1 k cycles, coinciding with the run-in phase. However, no measurable effect on end of test performance is detected from anode CL dissolution. These results highlight the need for a combined operando and post-mortem analysis for accurate anode CL degradation analyses.