Boosting Nitrogen Activation with Asymmetric Coordinated Ni–N₁–N₄ Site through p–d Hybridization

Single-atom catalysts (SACs) hold great promise for the electrocatalytic N2 reduction reaction (NRR), yet a comprehensive understanding of coordination microenvironment modulation remains elusive. Herein, Ni SACs with diverse Ni–Nx–C configurations (square-planar: Ni–N4, triangle-cone: Ni–N1–N3, pentagon-planar: Ni–N5, and square-cone: Ni–N1–N4) were theoretically studied. Ni SACs with the Ni–N1–N4 configuration demonstrated the highest stability and suitability for N2 adsorption, hydrogenation (*NN → *NNH), and inhibition of *H adsorption for H2 evolution. Notably, the additionally coordinated N disrupted the axisymmetric distribution of electrons in Ni–N1–N4, particularly in the z-direction of Ni dz2 orbitals, inducing the end-adsorbed N2 to adopt an inclined position. The variation in electronic states facilitated the simultaneous σ and π interaction between Ni dz2 and N2, forming a strong Ni–N bond (1.89 Å) and promoting N2 activation via p–d hybridization. In light of the calculation results, Ni SACs with the Ni–N1–N4 configuration (Ni20-FAN) were fabricated and displayed a superior NRR activity and Faradaic efficiency of 35.74% at −0.4 V vs RHE. In situ spectroscopic techniques together with density functional theory calculations further unraveled a facile distal pathway for ammonia evolution over Ni–N1–N4 SACs. This work offers an innovative perspective for theory-guided modulation of the SAC coordination microenvironment, introducing asymmetric coordination as an effective strategy for the activation of symmetric inert molecules.