Lattice-Nitrogen-Mediated Electrochemical Nitrate Reduction Boosted by Single-Atom Antimony Doping

Stable lattice-nitrogen-mediated nitrate reduction could alleviate the intrinsically sluggish kinetics of ammonia synthesis, but sustaining this pathway remains challenging under reaction conditions. Here, in situ characterizations combined with theoretical calculations reveal that lattice nitrogen in a Co-N solid solution (CoNx) is directly involved in nitrate reduction. However, reconstruction driven by the coupled effects of the cathodic field and oxidative nitrate adsorption causes structural collapse and irreversible lattice-nitrogen loss, thereby interrupting the lattice-nitrogen-mediated pathway. Introducing Sb single atoms (SAs) into the CoNx matrix stabilizes the framework through Sb-Co interactions with appreciable covalent character. This stabilization enables a regenerative lattice-nitrogen cycle in which lattice-nitrogen is hydrogenated and released as ammonia, while the resulting nitrogen vacancies capture nitrate to replenish lattice-nitrogen and complete the cycle. Moreover, Sb SAs promote lattice-nitrogen activation, strengthen nitrate capture at nitrogen-vacancy sites, and thereby optimize the reaction kinetics. As a result, the CoNx-Sb catalyst achieves a maximum Faradaic efficiency for ammonia of 97.00 ± 2.58%, a maximum ammonia yield rate of 85.18 ± 2.37 mg h-1 cm-2, and stable operation in a membrane electrode assembly for over 200 h. These findings highlight the importance of structural stabilization in sustaining lattice-nitrogen-mediated nitrate reduction.