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 (Sm 3 IrO 7 ) catalyst is synthesized by a simple solid-state reaction. After in situ activation, the as-prepared Sm 3 IrO 7 exhibits higher mass activity and durability than that of commercial IrO 2 . The in-depth analyses indicate the formation of amorphous IrO x species on the surface to evolve to a new heterostructure IrO x /Sm 3 IrO 7, along with Sm leaching during the in situ activation process. More importantly, strong electronic interactions exist between newborn IrO x species and remaining Sm 3 IrO 7, leading to the compressed Ir–O bonds in IrO x compared to commercial IrO 2, 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 /Sm 3 IrO 7, rather than Sm 3 IrO 7 itself. Theoretical calculations confirm that the optimal energy level path of IrO x /Sm 3 IrO 7 follows the lattice oxygen mechanism, and the energy level of surface Ir 5d orbitals is lower than O 2p orbitals in IrO x /Sm 3 IrO 7, enabling it a superior OER activity.