Theoretical and machine learning exploration of electronic factors governing Ni-centered CO₂ reduction catalysts

Carbon-based electrocatalysts are promising candidates for CO₂ reduction due to their intrinsic redox properties. However, achieving an in-depth understanding and rational design of the nickel site coordination environment and active site density remains a significant challenge. In this study, a single-atom catalyst supported on graphene was designed to reduce CO₂ to CO or HCOOH, based on density functional theory. The catalytic activity of the Ni_<i>n</i>-C_<i>x</i>N_<i>y</i>-<i>d</i> monolayer was systematically evaluated through charge density, density of states, and molecular dynamics analyses, verifying the conductivity and stability. Furthermore, an analysis of the Gibbs free energy pathway and electronic structure revealed that Ni₂-C₃N₁-1 exhibits excellent catalytic performance for CO production in the CO₂ reduction reaction, while Ni₂-C₂N₂-1 demonstrates superior performance for HCOOH, with relatively low limiting potentials of -0.27 V and -0.09 V, respectively. Molecular orbital theory analysis underscores the critical role of bonding states in explaining the adsorption energy of intermediate products. Moderate adsorption energy is shown to effectively suppress hydrogen evolution reactions, thereby enhancing both reaction activity and product selectivity. Leveraging the best-performing machine learning XGBoost model, the feature importance between HCOOH product and the Ni single-atom catalyst structure was predicted to be 0.568, allowing for the identification of optimal tuning strategies to achieve superior catalytic performance. This study provides novel theoretical insights and technological strategies for advancing sustainable CO₂ reduction.