Boosting CO 2 Photoreduction to Formate or CO with High Selectivity over a Covalent Organic Framework Covalently Anchored on Graphene Oxide.

Covalent organic frameworks (COFs) have been widely studied in photocatalytic CO 2 reduction reaction (CO 2 RR). However, pristine COFs usually exhibit low catalytic efficiency owing to the fast recombination of photogenerated electrons and holes. In this study, we fabricated a stable COF-based composite (GO-COF-366-Co) by covalently anchoring COF-366-Co on the surface of graphene oxide (GO) for the photocatalytic CO 2 reduction. Interestingly, in absolute acetonitrile (CH 3 CN), GO-COF-366-Co shows a high selectivity of 94.4 % for the photoreduction of CO 2 to formate, with a formate yield of 15.8 mmol/g, which is approximately four times higher than that using the pristine COF-366-Co. By contrast, in CH 3 CN/H 2 O (v : v=4 : 1), the main product for the photocatalytic CO 2 reduction over GO-COF-366-Co is CO (96.1 %), with a CO yield as high as 52.2 mmol/g, which is also approximately four times higher than that using the pristine COF-366-Co. Photoelectrochemical experiments demonstrate the covalent bonding of COF-366-Co and GO to form the GO-COF-366-Co composite facilitates charge separation and transfer significantly, thereby accounting for the enhanced catalytic activity. In addition, theoretical calculations and in situ Fourier transform infrared spectroscopy reveal H 2 O can stabilize the *COOH intermediate to further form a *CO intermediate via O-H(aq)⋅⋅⋅O(*COOH) hydrogen bonding, thus explaining the regulated photocatalytic performance.