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

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_xSn_1- _x)₃O₄ assembly to stabilize low-spin Co³⁺ (t₂ _g ⁶e_g ⁰) active centers, enabling highly durable performance under high current density operation. Sn doping in the underlying (Co_xSn_1- _x)₃O₄ strengthens the stability of Co³⁺ within the CoOOH catalytic layer by inducing an interfacial electric field at the CoOOH/(Co_xSn_1- _x)₃O₄ junction. This field promotes electron transfer from Co³⁺ species in CoOOH to (Co_xSn_1- _x)₃O₄, thereby stabilizing the critical Co³⁺ active centers during high-current operation. The enhanced interfacial electric field arises from the higher electronegativity of Sn⁴⁺ (1.706) compared to Co³⁺ (1.693). Consequently, the CoOOH/(Co_xSn_1- _x)₃O₄ catalyst achieves a remarkable Faradaic efficiency of 96.7% for NH₄ ⁺ 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.