Synergistic Bifunctional Covalent Organic Framework for Efficient Photocatalytic CO2 Reduction and Water Oxidation

The scientific community has been actively researching artificial photosynthesis to promote ecologically sustainable living and address environmental issues. However, designing photocatalysts with active sites that are effective for both CO2 reduction and water oxidation remains a significant challenge. Thus, we present the development of a donor-acceptor covalent organic framework (D-A COF), that integrates two distinct metal coordination environments through structure-activity relationships. Either cobalt or nickel ion is anchored on the D-A COF backbone to create N-metal-nitrogen and N-metal-sulfur coordination configurations, serving as bifunctional reduction and oxidation active sites, respectively. Remarkably, the as-synthesized Co-Btt-Bpy COF generated CO at a rate of 9,800 μmol g-1 h-1 and O2 at 242 μmol g-1 h-1 under visible light irradiation. The CO generation rate was 127 times higher than that of pristine D-A COF. More importantly, Co-Btt-Bpy COF facilitates artificial photosynthesis with a CO release rate of 7.4 μmol g-1 h-1. The outstanding photocatalytic performance can be attributed to the synergistic interaction between the dispersed single-atom sites and Btt-Bpy COF, as well as the rapid migration of photogenerated electrons. In situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectra and theoretical calculations indicated that introducing Co sites effectively lowered the reaction energy barriers for the crucial intermediates *COOH and *OH. This work provides state-of-the-art designs of photocatalysts at the molecular level and in-depth insights for efficient artificial photosynthesis.