Dual Ion Leaching‐Induced Reconstruction of CuCo₂S₄ Boosts Electrocatalytic Nitrate Reduction to Ammonia with Favorable Active Hydrogen Coverage

Electrochemical nitrate reduction (NO 3 ‒ RR) to ammonia (NH 3 ) offers a sustainable approach for NH 3 synthesis. However, inevitable catalyst reconstruction under NO 3 ‒ RR conditions complicates the identification of the true active species and the underlying reaction mechanisms. Herein, CuCo 2 S 4 nanoplates are fabricated as a model catalyst to investigate the reconstruction behavior and identify the active sites responsible for NO 3 ‒ RR. Experimental results reveal that the leaching of Cu and S triggers the transformation of CuCo 2 S 4 into Cu, S‐decorated Co(OH) 2 (denoted as Cu, S‐Co(OH) 2 ) during the NO 3 ‒ RR process. The derived Cu, S‐Co(OH) 2 exhibits a high NH 3 Faradaic efficiency of ≈99.5% across a broad potential range, with excellent cycling stability and chronopotentiometric durability. In situ Raman spectroscopy and kinetic analyses demonstrate that the superior performance is attributed to enhanced NO 3 − adsorption and optimal active hydrogen coverage. To demonstrate its practical application, a membrane electrode assembly (MEA) is assembled by incorporating Cu, S‐Co(OH) 2 as the cathode and IrO 2 as the anode, achieving stable operation at an industrial‐scale current density of 500 mA cm −2 with a Faradaic efficiency of ≈85% for green ammonia production.