Bridging the Gap Between Photocatalytic Water Oxidation Half‐Reaction and Stoichiometric Pure Water Splitting Over Ta 3 N 5 via Cocatalyst Engineering

Despite significant progress in photocatalytic half‐reactions and photoelectrochemical water oxidation, achieving stable photocatalytic pure water splitting over Ta 3 N 5 remains a long‐standing challenge. Herein, the incompatibility of cocatalysts between alkaline photocatalytic water oxidation systems and pure water splitting is identified as a critical bottleneck, leading to serious N 2 generation through photocorrosion. To address this challenge, a highly dispersed RuCoO x cocatalyst is developed via a multi‐step incipient wetness impregnation strategy. The optimized Pt@Cr 2 O 3 /Ta 3 N 5 /RuCoO x achieves stoichiometric pure water splitting with an apparent quantum yield of 0.72% at 420 nm, representing the highest value reported for Ta‐based nitride/oxynitride photocatalysts to date. Mechanistic studies reveal that an enhanced interfacial electric field facilitates hole extraction, while a reduced formation barrier of key intermediates accelerates surface reaction kinetics, thereby overcoming the long‐standing bottleneck in photocatalytic pure water splitting over Ta 3 N 5 . This work establishes cocatalyst compatibility as a key design consideration for stable photocatalytic pure water splitting and provides mechanistic insight for the rational design of advanced nitride and oxynitride photocatalysts.