Asymmetric Co 2+ –Ov–Co 3+ Sites With Strong d–π* Interactions for Activating Nitrogen Toward Photocatalytic Ammonia Synthesis

ABSTRACT Solar‐driven photocatalytic nitrogen reduction reaction (p‐NRR) offers a sustainable pathway for ammonia synthesis under ambient conditions. However, its efficiency is fundamentally hampered by the kinetic inertness of the N≡N triple bond. Herein, we construct oxygen‐vacancy‐induced asymmetric Co 2+ –Ov–Co 3+ units within two‐dimensional (2D) ultrathin LaCoO 3− x nanosheets to address this challenge. Oxygen‐vacancy‐induced symmetry breaking reconstructs the Co–O coordination field, forming Co 2+ sites with redistributed 3d energy levels that strongly couple with π* orbitals of N 2 . In situ spectroscopic measurements and theoretical calculations reveal that these asymmetric sites promote directional electron injection, stabilize the key *NNH intermediate, and decrease the transition‐state energy barrier of the rate‐determining step from 1.98 to 1.38 eV. Moreover, spin‐resolved orbital reconfiguration and orbital‐level modulation further guide the reaction pathway from the conventional distal pathway toward a more thermodynamically favorable alternating mechanism. Consequently, the optimized LaCoO 3− x exhibits a photocatalytic NH 3 production rate of 462.6 µg g −1 h −1 , which is 7.7 times higher than that of pristine LaCoO 3 . This work provides a fundamental insight into orbital‐level catalyst design for highly efficient p‐NRR.