Guanosine-derived atomically dispersed Cu-N3-C sites for efficient electroreduction of carbon dioxide.

Single-atom copper (Cu) embedded within carbon catalysts have demonstrated significant potential in the electrochemical reduction of carbon dioxide (CO2) into valuable chemicals and fuels. Herein, we develop a straightforward and template-free strategy for synthesizing atomically dispersed CuNC catalysts (CuG) by annealing the self-assembled guanosine. The CuG catalysts display two-dimensional morphology, tunable pore size and large surface areas that can be adjusted by changing carbonization temperature. Spherical aberration-corrected transmission electron microscopy reveals that single-atom Cu are homogeneously dispersed on the surface of carbon nanosheets. The optimum CuG-1000 catalysts achieve a high CO Faradaic efficiency (FEco) up to 99% and a high CO current density of 6.53 mA cm-2 (-0.65 V vs. RHE). Besides, the flow cell test of CuG-1000 shows a high current density up to 25.2 mA cm-2 and the FEco still exceeded 91% after more than 20 h of testing. Specifically, the existence of Cu-N3-C active sites was proved by extended X-ray absorption fine structure (EXAFS). Density functional theory evidences that tricoordinated copper with N can largely regulate the adsorption and desorption of key intermediates by transferring electrons to *COOH through Cu atoms, thereby improving selectivity toward CO. This work demonstrates the active origin of CuNC catalysts in CO2 electroreduction and offers a blueprint to construct atomically dispersed transition site catalysts by supramolecular self-assembly strategy.