Computational Evaluation of Defects in Fe–N4-Doped Graphene for Electrochemical CO2 Reduction

Single-atom catalysts supported by two-dimensional materials have been widely used in the electrochemical CO2 reduction reaction (CO2RR). Defects are inevitably generated during the preparation of two-dimensional materials. In this study, six Fe–N4-doped graphene catalysts (CAT1–CAT6) containing single carbon vacancy defects were designed and calculated using density functional theory (DFT) calculations. The stability, catalytic activity and product selectivity of these catalysts for CO2RR to C1 products CO, HCOOH, CH3OH and CH4 were discussed and compared with the defect-free Fe−N4-doped graphene catalyst (CAT0). The results show that CAT1–CAT6 all exhibit excellent thermodynamic and electrochemical stabilities. The possible reaction pathways for CO2 reduction to different C1 products were systematically investigated. The CAT2, CAT3 and CAT6 exhibit high selectivity for HCOOH, whereas the products of CAT1, CAT4 and CAT5 are HCOOH, CH3OH and CH4, the same as those of CAT0. Moreover, these six catalysts more effectively suppress the competing hydrogen evolution reaction (HER) compared to CAT0, indicating that the defect improves the catalytic selectivity of CO2RR. Among all of the catalysts, CAT2 demonstrates the most prominent catalytic activity and selectivity toward the CO2 reduction reaction (CO2RR). The large distortion of Fe−N4 in *HCOO with CAT2 contributes to the lower limiting potential UL. We hope that the finding that the large distortion of Fe−N4 could lower the limiting potential will provide theoretical insights for the design of more efficient CO2RR electrocatalysts.