Exposed Cocatalyst Interface with Cr–In Bonding for Efficient Solar‐Driven Fuel Production

Abstract In the realm of solar‐to‐hydrogen conversion, the technique of oxygen evolution cocatalyst (OEC) is comparatively sluggish relative to its electrocatalyst counterparts. This is mainly due to the absence of a novel cocatalyst with rapid reaction dynamics, optimal carrier transfer efficiency, and robust operation stability in the context of OEC applications. Here, a cocatalyst design is disclosed, composed of chromium oxide (CrO _x ) cluster with exposed junction interfaces (EJIs) for efficient OEC application, making the photoelectrocatalyst competitive to the electrocatalyst with excellent optoelectronic synergy. The experimental and theoretical results demonstrate that the formation of EJIs can simultaneously introduce abundant exposed catalytic sites and improve the photo‐assisted water dissociation kinetics with substantially reduced reaction barrier. Additionally, the Cr–In bonding at the exposed interface can eliminate the local defects, resulting in suppressed hole recombination and enhanced stability. Finally, a remarkable photocurrent density up to 6.26 mA cm ⁻² at 1.23 V _RHE is demonstrated, 920% higher than the pristine photoanode.