Proton exchange membrane water electrolysis (PEMWE) is the ideal technology to transform renewable energy into green hydrogen. Due to the very strongly oxidizing environment in the anode of a PEMWE (low pH, high oxygen concentration, high potential and the presence of water), only catalysts based on Ir work. This reaction is the limiting process, requiring large amounts of electrocatalyst to take place at reasonable overpotentials. Therefore, strong efforts are being performed to reduce Ir content. Catalysts based on Ir mixed oxides are an alternative, since they display comparable or higher OER mass-normalized activities than Ir simple oxides. However, Ir mixed oxides lack structural stability during the OER, mainly due to the high solubility of the nonnoble elements in aqueous-acid solution. In the last years, many efforts have been devoted to understand and identify the species formed during the OER, that usually are Ir-O-OH, Ir-OH, IrO_x and/or IrO₂ phases with different levels of amorphization.

We prepared a highly active catalyst, Sr₂CaIrO₆ perovskite, and monitored its stability during the OER using in situ and ex situ approaches. We observed a progressive reconstruction of the perovskite surface that starts after immersion in the electrolyte and progresses during the OER, due to the rapid dissolution of Ca. Despite the removal of Ca, the skeleton of the original perovskite remains unaltered, with short-ordered corner and edge-sharing IrO₆ octahedra identified as IrO₂ and IrOOH, in a very open structure on the surface of the perovskite which may be responsible for the high OER activity of Sr₂CaIrO₆, which is among the highest reported in the literature.

A PEMWE cell with an extremely low amount of Ir (0.4 mg_Ir cm^-2) is developed and tested with Sr₂CaIrO₆ as the anode electrode. The cell achieves 2.40 V at 6 A cm^-2 (overload) and shows no loss in performance at a constant 2 A cm^-2 (nominal load). Thus, PEMWE with Sr₂CaIrO₆ reduces Ir use without compromising the efficiency and lifetime of the catalyst.