Unsaturated Cu Single-Atom Catalysts in COFs for Efficient Neutral Ammonia Electrosynthesis from Nitrate

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Electrocatalytic nitrate reduction reaction (NO3RR) offers a sustainable route for NH3 production and wastewater treatment. However, its efficiency is limited by weak nitrate affinity and complex multielectron/proton transfer. Herein, we incorporate unsaturated Cu single atoms into a bipyridine-functionalized, hydrazone-linked covalent organic framework (Cu@bpy-COF) for highly efficient NO3RR under neutral conditions. Combined experimental and theoretical analyses reveal that the unsaturated electron-deficient Cu centers promote the NO3– adsorption through charge polarization and key intermediate deoxygenation through the modulation of the surface binding energy of key intermediates. Beyond stabilizing the Cu sites, the Cu-bipyridine motifs facilitate water dissociation and OH– adsorption under neutral conditions, constructing a self-enhanced local alkaline environment to accelerate proton dynamics for the hydrogenation of nitrogenous intermediates at the Cu sites and suppress the competing hydrogen evolution reaction. As a result, Cu@bpy-COF exhibits a superior NH3 yield of 17.39 mg h–1 cm–2 at −0.90 V vs RHE and a Faradic efficiency (FE) of 93.63% at −0.85 V vs RHE in a 0.5 M K2SO4/0.1 M KNO3 electrolyte. Moreover, a coupled electrolyzer assembled with a Cu@bpy-COF cathode and an oxygen evolution reaction-active Co@bpy-COF anode delivers an exceptional NH3 FE of 88.80% at 100 mA cm–2 with a low cell voltage of 2.74 V. Given the feasibility of powering this system with renewable energy, this work opens a promising path toward green ammonia synthesis and environmental remediation.