Identification of the Active-Layer Structures for Acidic Oxygen Evolution from 9R-BaIrO 3 Electrocatalyst with Enhanced Iridium Mass Activity

Iridium-based perovskites show promising catalytic activity for oxygen evolution reaction (OER) in acid media, but the iridium mass activity remains low and the active-layer structures have not been identified. Here, we report highly active 1 nm IrO particles anchored on 9R-BaIrO (IrO /9R-BaIrO ) that are directly synthesized by solution calcination followed by strong acid treatment for the first time. The developed IrO /9R-BaIrO catalyst delivers a high iridium mass activity (168 A g ), about 16 times higher than that of the benchmark acidic OER electrocatalyst IrO (10 A g ), and only requires a low overpotential of 230 mV to reach a catalytic current density of 10 mA cm . Careful scanning transmission electron microscopy, synchrotron radiation-based X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy analyses reveal that, during the electrocatalytic process, the initial 1 nm IrO nanoparticles/9R-BaIrO evolve into amorphous Ir O H /IrO octahedrons and then to amorphous Ir O /IrO octahedrons on the surface. Such high relative content of amorphous Ir O species derived from trimers of face-sharing IrO octahedrons in 9R-BaIrO3 and the enhanced metallic conductivity of the Ir O /9R-BaIrO catalyst are responsible for the excellent acidic OER activity. Our results provide new insights into the surface active-layer structure evolution in perovskite electrocatalysts and demonstrate new approaches for engineering highly active acidic OER nanocatalysts.