Spin‐State Modulation of Nickel Enables High‐Efficiency and Durable Nitrate Electroreduction to Ammonia

Electrocatalytic nitrate reduction to ammonia (NO 3 − RR) provides a sustainable pathway for nitrogen cycling and green ammonia (NH 3 ) synthesis. Copper‐based catalysts have attracted considerable attention due to their appropriate d ‐band energy level. However, their performance is restricted by imbalanced reaction energetics, where excessive adsorption of key nitrogen intermediates (*NO 2 , *NO, and *N) and insufficient active hydrogen (*H) availability lead to slow hydrogenation steps and poor selectivity. Herein, a sulfide‐template‐assisted electrochemical reconstruction strategy is developed to fabricate high‐spin Ni‐doped cuprous oxide (HS‐Ni‐Cu 2 O) catalysts. The HS‐Ni‐Cu 2 O achieves a Faradaic efficiency (FE) of 90.2% at −0.5 V RHE and an NH 3 yield rate of 2.19 mmol h −1 cm −2 at −0.8 V RHE , together with remarkable stability for over 160 h at −450 mA cm −2 in a membrane electrode assembly (MEA). In situ spectroscopy and DFT calculations reveal that HS‐Ni 2+ incorporation promotes the formation of *H, accelerates *NO 2 hydrogenation, and lowers the energy barrier of the rate‐determining step (*NO → *NOH) from 0.90 to 0.77 eV. Integrating NO 3 − RR with anodic glycerol oxidation further reduces the cell voltage, enabling energy‐efficient operation. This work demonstrates spin‐state engineering as an effective strategy for designing efficient, durable, and scalable catalysts for sustainable NH 3 synthesis and wastewater valorization.