Coordination environment engineering on nickel single-atom catalysts for CO2 electroreduction

Coordination engineering has recently emerged as a promising strategy to boost the activity of single atom catalysts (SACs) in electrocatalytic CO₂ reduction reactions (CO₂RR). Understanding the correlation between activity/selectivity and the coordination environment would enable the rational design of more advanced SACs for CO₂ reduction. Herein, via density functional theory (DFT) computations, we systematically studied the effects of coordination environment regulation on the CO₂RR activity of Ni SACs on C, N, or B co-doped graphene. The results reveal that the coordination environments can strongly affect the adsorption and reaction characteristics. In the C and/or N coordinated Ni-B_XC_YN_Z (B-free, X = 0), only Ni acts as the active site. While in the B, C and/or N coordinated Ni-B_XC_YN_Z (X ≠ 0), the B has transition-metal-like properties, where B and Ni function as dual-site active centers and concertedly tune the adsorption of CO₂RR intermediates. The tunability in the adsorption modes and strengths also results in a weakened linear scaling relationship between *COOH and *CO and causes a significant activity difference. The CO₂RR activity and the adsorption energy of *COOH/*CO are correlated to construct a volcano-type activity plot. Most of the B, C, and/or N-coordinated Ni-B_XC_YN_Z (X ≠ 0) are located in the left region where *CO desorption is the most difficult step, while the C and/or N coordinated Ni-B_XC_YN_Z (X = 0) are located in the right region where *COOH formation is the potential-determining step. Among all the possible Ni-B_XC_YN_Z candidates, Ni-B₀C₃N₁ and Ni-B₁C₁N_2-N-oppo are predicted to be the most active and selective catalysts for the CO₂RR. Our findings provide insightful guidance for developing highly effective CO₂RR catalysts based on a codoped coordination environment.