Composite interfaces of g-C 3 N 4 fragments loaded on a Cu substrate for CO 2 reduction.

Designing an electrocatalyst with high efficiency and product selectivity is always crucial for an electrocatalytic CO 2 reduction reaction (CO 2 RR). Inspired by the great progress of two-dimensional (2D) nanomaterials growing on Cu surfaces and their promising CO 2 RR catalytic efficiencies at their interfaces, the unique performance of Cu-based 2D materials as high-efficiency and low-cost CO 2 RR electrocatalysts has attracted extensive attention. Herein, based on density functional theory (DFT) calculations, we proposed a composite structure of graphitic carbon nitride (g-C 3 N 4 ) fragments loaded on a Cu surface to explore the CO 2 RR catalytic property of the interface between g-C 3 N 4 and the Cu surface. Three composite interfaces of C 3 N 4 /Cu(111), C 3 N 4 /Cu(110) and C 3 N 4 /Cu(100) have been studied by considering the reaction sites of vertex nitrogen atoms, edge nitrogen atoms and the nearby Cu atoms. It was found that the C 3 N 4 /Cu interfaces where nitrogen atoms contact the Cu substrate present competitive CO 2 RR activity. Among them, C 3 N 4 /Cu(111)-N3 exhibited a better activity for CH 3 OH production, with a low overpotential of 0.38 V. For HCOOH and CH 4 production, C 3 N 4 /Cu(111)-Cu and C 3 N 4 /Cu(100)-N1 have overpotentials of 0.26 V and 0.44 V. The electronic analysis indicates the electron transfer from the Cu substrate to the g-C 3 N 4 fragment and mainly accumulates on the nitrogen atoms of the interface. Such charge accumulation can activate the adsorbed CO bond of CO 2 and lead to lower energetic barriers of CO 2 RR. DFT calculations indicate that the boundary nitrogen sites reduced the energy barrier of *CHO, which is crucial for CO 2 RR, compared with that of the pristine Cu surface. Our study explores a new Cu-based electrocatalyst and indicates that the C 3 N 4 /Cu interface can enhance the activities and selectivity of CO 2 RR and open a new strategy to design high-efficiency electrocatalysts for CO 2 RR.