Symmetry-Dependent Orbital Involvement Governing C₂ Selectivity in CO/CO₂ Reduction on M-N_xB Single-Atom Catalysts

The lack of two active centers and simultaneous hydrogen evolution reaction (HER) restrict single-atom catalysts (SACs) to produce C₂ products in CO reduction reaction (CORR)/CO₂ reduction reaction (CO₂RR). In this work, we propose SACs with a N-B neighborhood, which can obtain ethylene and ethanol as desired C₂ products through CO₂RR in the presence of CO gas. We have identified Fe, Co, Rh, and Ni (tested 28 systems) as possible active centers in MN_xB SAC to produce a C₂ product with limiting potential as low as -0.66 V (FeN₃B) in CORR and CO/CO₂RR. The ↓d_yz orbital occupancy exhibited a significant correlation with E_{b_CO-CO} (R² = 0.74), explaining the origin of CO-CO coupling on M-N_xB systems. Further, we have provided geometrical analysis and σ-electron donation (CO) and π-electron back-donation (d_yz) to understand why MN_xB systems are suitable for producing C₂ products. This study opens the possibility of a future investigation in SAC for C₂ products in CORR beyond Cu.