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

Electrocatalytic nitrate reduction reaction (NO 3 RR) offers a sustainable route for NH 3 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 NO 3 RR under neutral conditions. Combined experimental and theoretical analyses reveal that the unsaturated electron-deficient Cu centers promote the NO 3 – 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 NH 3 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 K 2 SO 4 /0.1 M KNO 3 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 NH 3 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.