Spatially Separated Photoredox in a Covalent Organic Frameworks Heterostructure Boosting Overall Water Splitting

Covalent organic frameworks (COFs) with excellent structural tunability have emerged as fascinating photocatalysts to fulfill future energy demands. Here, we developed a COFs heterostructure by assembling two COFs for photocatalytic overall water splitting. The resulting heterostructure exhibited an effective spatial separation of photoredox sites originating from the efficient separation of photoinduced charge carriers through an orientated interfacial electron transfer pathway. Accordingly, the heterostructure of the COFs displays excellent activity for stoichiometric water splitting into H2 and O2 under 5 W white LED light irradiation. Our efficiencies of H2 and O2 evolution rates up to 120 and 58 μmol g–1 h–1 are significantly higher than those reported previously. The combination of experiments and theoretical calculations shows that water oxidation proceeds by a metal-free hydration-mediated pathway. This work sheds light on a rational design of the COF heterostructure with spatially separated photoredox for water splitting.