Strain‐Engineered Ir Shell Enhances Activity and Stability of Ir‐Ru Catalysts for Water Electrolysis: An Operando Wide‐Angle X‐Ray Scattering Study

Abstract Ir‐Ru alloys with high Ru content serve as stable and highly active catalysts for the Oxygen Evolution Reaction (OER) in Proton Exchange Membrane Water Electrolyzers (PEM‐WEs), enabling efficient operation with low Ir loadings (150 µg cm⁻²). Despite this, the mechanisms behind their enhanced stability remain unclear. In this study, operando Wide‐Angle X‐ray Scattering (WAXS) and ex situ techniques are utilized to investigate the structural evolution of these magnetron‐sputtered alloys during a PEM‐WE operation. The findings reveal that Ru leaches from the surface upon potential application, forming a dynamic Ir‐Ru@IrO_x core‐shell structure. The Ir shell, strained by the Ir‐Ru core, maintains a lower oxidation state than pure Ir catalyst, leading to superior catalytic activity and stability. Remarkably, the Ir‐Ru 25:75 catalyst demonstrates better stability over Ir‐Ru 50:50, despite its higher Ru content, due to the better protection of the subsurface Ir and Ru from oxidation and dissolution. This study not only clarifies the performance‐enhancing mechanisms of Ir‐Ru catalysts but also suggests that other, more economical materials, such as Co or Ti, could serve as effective cores in Ir‐M systems, offering a pathway to more cost‐effective catalysts for PEM‐WE applications.