Co ₁ Zn Single‐Atom Alloy Boosts Active Hydrogen Spillover for Highly Efficient Electrosynthesis of Ammonia Over 2 A cm ⁻² Current Density

Electroreduction of nitrate to ammonia reaction (NO₃RR) involves a series of hydrogenation steps involving nitrate-derived intermediates. Consequently, accelerating the provision of active hydrogen is expected to enhance the reaction kinetics. In this work, we report a Co₁Zn single-atom alloy (SAA) catalyst that exhibits a pronounced hydrogen spillover effect. By virtue of this spillover phenomenon, the Co₁Zn SAA nanosheets (Co₁Zn NSs) achieve nitrate electroreduction at ampere-level current densities. Specifically, Co₁Zn NSs deliver a high current density of 2.4 A cm^-2 (corresponding to an ammonia yield rate of 204.5 mg h^-1 cm^-2) with a Faradaic efficiency of 98.7% for ammonia production, which is approximately 2.5-fold higher than that obtained with Zn nanosheets lacking hydrogen spillover effect. Moreover, Co₁Zn NSs demonstrate a great application potential in Zn-NO₃ ^- rechargeable battery. In situ electrochemical impedance spectroscopy (EIS), in situ electron paramagnetic resonance spectroscopy (EPR), and density functional theory (DFT) calculations reveal that the isolated Co atoms in Co₁Zn NSs served as a "hydrogen pump" for hydrogen spillover during NO₃RR, thereby increasing the coverage of active hydrogen on the catalyst surface and lowering the energy barrier of the rate-determining step of NO₃RR, and finally markedly enhanced the catalytic performance.