Build-in electric field in CuWO/covalent organic frameworks S-scheme photocatalysts steer boosting charge transfer for photocatalytic CO reduction.

Covalent organic frameworks (COFs) are crystalline porous materials with enormous potential for realizing solar-driven CO-to-fuel conversion, yet the sluggish transfer/separation of photoinduced electrons and holes remains a compelling challenge. Herein, a step (S)-scheme heterojunction photocatalyst (CuWO-COF) was rationally fabricated by a thermal annealing method for boosting CO conversion to CO. The optimal CuWO/COF composite sample, integrating 10 wt% CuWO with an olefin (C═C) linked COF (TTCOF), achieved a remarkable gas-solid phase CO yield as high as 7.17 ± 0.35 μmol gh under visible light irradiation, which was significantly higher than the pure COF (1.6 ± 0.29 μmol gh). The enhanced CO conversion rate could be attributable to the interface engineering effect and the formation of internal electric field (IEF) directing from TTCOF to CuWO according to the theoretical calculation and experimental results, which also proves the electrons transfer from TTCOF to CuWO upon hybridization. In addition, driven by the IEF, the photoinduced electrons can be steered from CuWO to TTCOF under visible light irradiation as well-elucidated by in-situ irradiated X-ray photoelectron spectroscopy, verifying the S-scheme charge transfer pathway over CuWO/COF composite heterojunctions, which greatly foster the photoreduction activity of CO. The preparation technique of the S-scheme heterojunction photocatalyst in this study provides a paradigmatic protocol for photocatalytic solar fuel generation.