In-situ total X-ray scattering reveals the structural evolution of SrIrO₃ during the oxygen evolution reaction

Despite the importance of oxygen evolution reaction (OER) catalysts in energy conversion applications, the time-resolved dynamics of their amorphous phases remain elusive. Understanding the structural evolution of OER catalysts is pivotal to improve their design and sustainability and increase the energy conversion efficiency. SrIrO₃ is a promising OER catalyst for achieving high energy conversion efficiencies, but it has not been sufficiently characterized in terms of its phase dynamics during operation. Herein, in-situ total X-ray scattering measurements and pair distribution function analysis are used to probe time-resolved structural changes in an IrO_x/SrIrO₃ catalyst during OER, revealing the occurrence of persistent Ir-O bond shortening and dynamic structural interconversions between multiple crystalline phases and an amorphous component. The relative contents of the main crystalline phases-3C-SrIrO₃ (Pnma) and 6H-SrIrO₃ (C2/c)-exhibited synchronized changes, whereas those of an additional C2/c phase and the amorphous component showed opposite trends, suggesting active structural interplay among the phases during the reaction. Furthermore, the observed Ir-O bond shortening under applied potential was attributed to a structural change associated with increased oxidation state of Ir, which is closely related to the local environment at the rate-determining step of OER. Our findings underscore the importance of precisely controlling bond distances and structural dynamics at the atomic scale for enhancing the activity of OER catalysts and provide valuable insights for future catalyst design.