Transition\nMetals Doped into g‑C<sub>3</sub>N<sub>4</sub> via N,O Coordination\nas Efficient Electrocatalysts\nfor the Carbon Dioxide Reduction Reaction

The electrochemical carbon dioxide reduction reaction\n(CO<sub>2</sub>RR) is a potential and efficient method that can directly\nconvert\nCO<sub>2</sub> into high-value-added chemicals under mild conditions.\nOwing to the exceptionally high activation barriers of CO<sub>2</sub>, catalysts play a pivotal role in CO<sub>2</sub>RR. In this study,\nthe transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and\nZn) is doped into g-C<sub>3</sub>N<sub>4</sub> with a unique N,O-coordination\nenvironment, namely, TM–N<sub>1</sub>O<sub>2</sub>/g-C<sub>3</sub>N<sub>4</sub>. Herein, the catalytic performance and reaction\nmechanism for the CO<sub>2</sub>RR on TM–N<sub>1</sub>O<sub>2</sub>/g-C<sub>3</sub>N<sub>4</sub> are systematically investigated\nby density functional theory methods. Especially, through the calculation\nof Δ<i>G</i><sub>*H</sub> and Δ<i>G</i><sub>*COOH</sub>/Δ<i>G</i><sub>*OCHO</sub>, the catalysts\nwith preference for the CO<sub>2</sub>RR over the hydrogen evolution\nreaction (HER) are selected for further study. Furthermore, Gibbs\nfree energy computation results of each elementary step for the CO<sub>2</sub>RR on these catalysts indicate that Ti–N<sub>1</sub>O<sub>2</sub>/g-C<sub>3</sub>N<sub>4</sub> has significant catalytic\nactivity and selectivity for reducing CO<sub>2</sub> to methanol (CH<sub>3</sub>OH) with the limiting potential (<i>U</i><sub>L</sub>) of −0.55 V. Finally, through frontier molecular orbital\ntheory and charge transfer analyses, the introduction of the O atoms\nillustrates that it is instrumental in regulating the electron distribution\nof the catalytic active site, thereby improving the catalytic performance.\nThis work provides insight into the design of single-atom catalysts\nwith unique coordination structures for the CO<sub>2</sub>RR.