Unlocking Durable and Efficient Nitrate‐to‐Ammonia Electrocatalysis via Interface‐Stabilized Trivalent Cobalt

Abstract Although cobalt‐based materials are promising catalysts for electrochemical nitrate‐to‐ammonia reduction, achieving stable operation at high current densities remains challenging due to significant overpotential issues. To address this, we engineered a CoOOH/(Co x Sn 1‐ x ) 3 O 4 assembly to stabilize low‐spin Co 3+ ( t 2 g 6 e g 0 ) active centers, enabling highly durable performance under high current density operation. Sn doping in the underlying (Co x Sn 1‐ x ) 3 O 4 strengthens the stability of Co 3+ within the CoOOH catalytic layer by inducing an interfacial electric field at the CoOOH/(Co x Sn 1‐ x ) 3 O 4 junction. This field promotes electron transfer from Co 3+ species in CoOOH to (Co x Sn 1‐ x ) 3 O 4 , thereby stabilizing the critical Co 3+ active centers during high‐current operation. The enhanced interfacial electric field arises from the higher electronegativity of Sn 4+ (1.706) compared to Co 3+ (1.693). Consequently, the CoOOH/(Co x Sn 1‐ x ) 3 O 4 catalyst achieves a remarkable Faradaic efficiency of 96.7% for NH 4 + generation at −0.3 V versus RHE (110 mA cm −2 ) and demonstrates exceptional long‐term stability for 1000 h at 100 mA cm −2 . This work demonstrates that creating an interface electric field is an efficient strategy to stabilize electroreduction active centers at high currents.