In-situ Synthesis of Chemically bonded 2D/2D Covalent Organic Frameworks/O-vacancy WO 3 Z-Scheme Heterostructure for Photocatalytic Overall Water Splitting.

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 heterojunctions through in-situ growth of COFs on the O-vacancy WO 3 nanosheets (Ov-WO 3 ) via W-O-C chemical bond can remarkably promote photocatalytic OWS. Benefiting from the synergistic effect between the enhanced built-in electric field by interfacial W-O-C bond, 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 were achieved on the COF-WO 3 (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. This article is protected by copyright. All rights reserved.