Iridates for PEM water electrolysis

Proton exchange membrane water electrolyzers (PEMWE) offer a promising solution to convert renewable energy into green hydrogen fuel, but their widespread implementation is significantly limited by the inadequate efficiency and durability of the anodic oxygen evolution reactions (OER) catalyst. In this regard, iridates have emerged as compelling candidates for the anodic catalysts in PEMWE due to their exceptional acidic OER activity and stability. However, the elusive structure-performance relationship of iridates renders the optimizations of catalyst performance in PEMWE challenging. This review highlights recent advancements in studying the surface evolutions of iridates under operational conditions via state-of-the-art in situ techniques, such as synchrotron radiation X-ray absorption fine structure (SR-XAFS), Fourier-transform infrared (FTIR), and Raman spectroscopy, with a focus on the in situ formation of active layers at the solid-liquid interface. We provide a comprehensive overview of the crystal structures, synthesis methods, and typical OER mechanisms of representative iridates. We discuss the theoretical links between the surface transformation and the OER performance of iridates. We also summarize the performance of iridates in PEMWE and conclude with future perspectives for rationally designing iridates with enhanced efficiency, durability, and reduced noble-metal iridium content. • We summarized more articles for the following sections in the manuscript: “Probing the in situ evolution by XAFS”, “Capturing the OER intermediates”, “OER theoretical analysis”, and “Iridates in PEMWE”. • We made some new figures for the manuscript and replaced some of the previous ones as requested. • We added a new subsection of “Design and Modification Strategies” and expanded the content of the “OER Mechanism in Acidic Media” section.