Fig. 1. Degradation processes of OER catalysts in aqueous and polymer electrolyte.

a Schematic drawing of degradation processes in a classical aqueous electrolysis cell in aqueous electrolyte and b schematic drawing of degradation processes in MEA. c Dissolution stability of IrO_x under OER conditions in aqueous electrolyte, measured in SFC-ICP-MS, and polymer electrolyte, measured in a precipitation-free MEA device, expressed in the S-number metric. Measurements were carried out with a 5 min chronopotentiometry hold in aqueous electrolyte and over several days for MEA, typical timescales for the devices. Source data are provided in the source data file.