In Situ Synthesis of Chemically Bonded 2D/2D Covalent Organic Frameworks/O‐Vacancy WO₃ Z‐Scheme Heterostructure for Photocatalytic Overall Water Splitting

Abstract Covalent organic frameworks (COFs) have shown great promise for photocatalytic hydrogen evolution via water splitting. However, the four‐electron oxidation of water remains elusive toward oxygen evolution. Enabling this water oxidation pathway is critical to improve the yield and maximize atom utilization efficiency. A Z‐scheme heterojunction is proposed for overcoming fundamental issues in COF‐based photocatalytic overall water splitting (OWS), such as inefficient light absorption, charge recombination, and poor water oxidation ability. It is shown that the construction of a novel 2D/2D Z‐scheme heterojunction through in situ growth of COFs on the O‐vacancy WO₃ nanosheets (Ov‐WO₃) via the WOC chemical bond can remarkably promote photocatalytic OWS. Benefiting from the synergistic effect between the enhanced built‐in electric field by the interfacial WOC bond, the strong water oxidation ability of Ov‐WO_3, and the ultrathin structure of TSCOF, both separation and utilization efficiency of photogenerated electron–hole pairs can be significantly enhanced. An impressive photocatalytic hydrogen evolution half‐rection rate of 593 mmol h⁻¹ g⁻¹ and overall water splitting rate of 146 (hydrogen) and 68 (oxygen) µmol h⁻¹ g⁻¹ are achieved on the COF‐WO₃ (TSCOFW) composite. This 2D/2D Z‐scheme heterojunction with two‐step excitation and precisely cascaded charge‐transfer pathway makes it responsible for the efficient solar‐driven OWS without a sacrificial agent.