Dual Ion Leaching‐Induced Reconstruction of CuCo ₂ S ₄ Boosts Electrocatalytic Nitrate Reduction to Ammonia with Favorable Active Hydrogen Coverage

Abstract 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.