Identification of the Active-Layer Structures for Acidic Oxygen Evolution from 9R-BaIrO₃ Electrocatalyst with...

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-BaIrO₃ (IrO/9R-BaIrO₃) that are directly synthesized by solution calcination followed by strong acid treatment for the first time. The developed IrO/9R-BaIrO₃ catalyst delivers a high iridium mass activity (168 A g_Ir^-1), about 16 times higher than that of the benchmark acidic OER electrocatalyst IrO₂ (10 A g_Ir^-1), and only requires a low overpotential of 230 mV to reach a catalytic current density of 10 mA cm^-2_geo. 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-BaIrO₃ evolve into amorphous Ir⁴⁺OH/IrO₆ octahedrons and then to amorphous Ir⁵⁺O/IrO₆ octahedrons on the surface. Such high relative content of amorphous Ir⁵⁺O species derived from trimers of face-sharing IrO₆ octahedrons in 9R-BaIrO3 and the enhanced metallic conductivity of the Ir⁵⁺O/9R-BaIrO₃ 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.