Cracking the Activity–Stability Trade‐Off in CoFe Alloy Nanoparticles by Enhancing Metal–Support Interaction toward Selective Nitrate Electroreduction to Ammonia

Abstract The electrochemical nitrate reduction reaction (NO ₃ ⁻ RR) is a promising technology for converting NO ₃ ⁻ into ammonia (NH ₃ ) under mild conditions. However, enhancing the activity of NO ₃ ⁻ RR catalysts often entails a trade‐off with stability. This trade‐off can be overcome by tuning the metal–support interaction (MSI) in supported catalysts, thereby concurrently boosting catalyst activity and stability. However, research on this approach is currently limited. Herein, the MSI in a supported catalyst comprising a CoFe alloy embedded in CoFe ₂ O ₄ (CoFe/CoFeO) is tuned by altering the size of the CoFe alloy and oxygen vacancy concentration of CoFe ₂ O ₄ through an in situ exsolution process. The strong MSI (SMSI) optimizes the electronic structure of CoFe and suppresses its aggregation during the NO ₃ ⁻ RR, thereby simultaneously enhancing the NO ₃ ⁻ RR activity and stability. Consequently, CoFe/CoFeO with a SMSI displays twofold and sixfold enhancement of activity and stability compared with its counterpart with a weak SMSI. Furthermore, by integrating the NO ₃ ⁻ RR with plasma‐driven N ₂ oxidation for in situ generation of NO ₃ ⁻ from atmospheric N ₂ and O ₂ , this approach enables the efficient direct synthesis of NH ₃ from ambient air.