Asymmetric Co2+–Ov–Co3+ 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 Co2+–Ov–Co3+ units within two‐dimensional (2D) ultrathin LaCoO3−x nanosheets to address this challenge. Oxygen‐vacancy‐induced symmetry breaking reconstructs the Co–O coordination field, forming Co2+ sites with redistributed 3d energy levels that strongly couple with π* orbitals of N2. 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 LaCoO3−x exhibits a photocatalytic NH3 production rate of 462.6 µg g−1 h−1, which is 7.7 times higher than that of pristine LaCoO3. This work provides a fundamental insight into orbital‐level catalyst design for highly efficient p‐NRR.