Spin state and orbital engineering of cuprous oxide for efficient nitrate reduction

Electrocatalytic nitrate reduction provides a sustainable pathway for wastewater treatment and ammonia production, yet the complex multi‑electron transfer demands efficient catalysts to achieve both high selectivity and fast kinetics. Here we show that atomic substitution of magnetic transition metals (Cr, Mn, Fe, Co, Ni) into cuprous oxide enables systematic tuning of catalytic performance. Density functional theory calculations combined with experiments identify that catalytic activity is governed by nitrate adsorption strength, ammonia desorption energy, and d-p orbital hybridization. Cobalt‑substituted cuprous oxide delivers a near‑unity Faradaic efficiency of 96.5% and an ammonia yield rate of 2.8 mM h^-1 mg_cat^-1, showing favorable performance compared with the other metal‑doped counterparts. Mechanistic studies reveal that cobalt substitution alters the spin configuration at the active sites, which optimizes orbital hybridization and balances the adsorption and desorption of key intermediates. This work establishes a design principle linking atomic‑level spin and orbital engineering to catalytic performance, providing a framework for developing high‑performance nitrate reduction electrocatalysts.