Boosting Water Oxidation Performance of BiVO₄Photoanode by Vertically Stacked NiO Nanosheets Coupled with Atomically Dispersed Iridium Sites

Atomically dispersed oxygen evoution cocatalysts embedded on 2D metal oxide nanosheets are at the heart of the key to solar to chemical energy conversion applications. However, high photocurrent density, conversion efficiency, and durability remain grand challenges due to their photocorrosion in electrolyte solutions. To overcome these challenges, we designed a highly efficient and stable photoanode consisting of vertically stacked NiO nanosheets coupled with atomically dispersed iridium sites on a BiVO4 semiconductor as a water oxidation photoanode. A series of analyses, including scanning tunneling electron microscopy, X-ray spectroscopy, and density functional theory (DFT) calculations, demonstrated that the Ir atoms are atomically dispersed on the surface of vertically stacked NiO sheets with a favorable oxidation state and suitable band edge potentials for charge separation and transport. Owing to these properties, the designed BiVO4@NiO-Ir exhibited a stable water oxidation photocurrent of 4.33 mA·cm-2 at 1.23 V vs a reversible hydrogen electrode (RHE) under simulated solar light, which is much higher compared to those of BiVO4, BiVO4@NiO, and BiVO4@Ir photoanodes. In addition, we observed the evolution of stoichiometric amounts of oxygen and hydrogen with 96% Faradaic efficiency for greater than a 10 h duration. The DFT results showed that the potential determining step (PDS) of the oxygen evolution reaction at the BiVO4@NiO-Ir surface is only 0.68 eV compared to 1.78 eV at the BiVO4@NiO surface. The significant reduction of PDS on the order of 1 eV for BiVO4@NiO-Ir demonstrates superior photoelectrochemical (PEC) performance. We strongly believe that this work aids the design of atomically scaled nanocatalysts for solar-driven chemical fuel device applications.