In Situ Activation Endows Orthorhombic Fluorite-Type Samarium Iridium Oxide with Enhanced Acidic Water Oxidation

Developing electrochemical catalysts for acidic water oxidation with improved activity and stability has been the key to the further popularization of proton exchange membrane electrolyzers. In this work, an orthorhombic fluorite-type samarium iridium oxide (Sm₃IrO₇) catalyst is synthesized by a simple solid-state reaction. After in situ activation, the as-prepared Sm₃IrO₇ exhibits higher mass activity and durability than that of commercial IrO₂. The in-depth analyses indicate the formation of amorphous IrO_x species on the surface to evolve to a new heterostructure IrO_x/Sm₃IrO₇, along with Sm leaching during the in situ activation process. More importantly, strong electronic interactions exist between newborn IrO_x species and remaining Sm₃IrO₇, leading to the compressed Ir-O bonds in IrO_x compared to commercial IrO₂, thus reducing the energy barrier for oxygen evolution reaction (OER) intermediates to improve the OER process. Based on the above-mentioned analyses, it is speculated that the actual active species for enhanced acidic water oxidation should be IrO_x/Sm₃IrO₇, rather than Sm₃IrO₇ itself. Theoretical calculations confirm that the optimal energy level path of IrO_x/Sm₃IrO₇ follows the lattice oxygen mechanism, and the energy level of surface Ir 5d orbitals is lower than O 2p orbitals in IrO_x/Sm₃IrO₇, enabling it a superior OER activity.