First-Principles Study on the CO2 Reduction Reaction (CO2RR) Performance of h-BN-Based Single-Atom Catalysts Modified with Transition Metals

The reasonable design of low-cost, high-activity single-atom catalysts (SACs) is crucial for achieving highly efficient electrochemical CO₂RR. In this study, we systematically explore, using density functional theory (DFT), the performance of transition metal (TM = Mn, Fe, Co, Ni, Cu, Zn)-doped defect-type hexagonal boron nitride (h-BN) SACs TM@B_-1N (B vacancy) and TM@BN_-1 (N vacancy) in both CO₂RR and the hydrogen evolution reaction (HER). Integrated crystal orbital Hamiltonian population (ICOHP) analysis reveals that these catalysts weaken the sp orbital hybridization of CO₂, which promotes the formation of radical-state intermediates and significantly reduces the energy barrier for the hydrogenation reaction. Therefore, these theoretical calculations indicate that the Mn, Fe, Co@B_-1N, and Co@BN_-1 systems demonstrate excellent CO₂ chemical adsorption properties. In the CO₂RR pathway, Mn@B_-1N exhibits the lowest limiting potential (<i>U_L</i> = -0.524 V), and its higher d-band center (-0.334 eV), which aligns optimally with the adsorbate orbitals, highlights its excellent catalytic activity. Notably, Co@BN_-1 exhibits the highest activity in HER, while <i>U_L</i> is -0.217 V. Furthermore, comparative analysis reveals that Mn@B_-1N shows 16.4 times higher selectivity for CO₂RR than for HER. This study provides a theoretical framework for designing bifunctional SACs with selective reaction pathways. Mn@B_-1N shows considerable potential for selective CO₂ conversion, while Co@BN_-1 demonstrates promising prospects for efficient hydrogen production.