Fe and Cu Double-Doped Co₃O₄ Nanorod with Abundant Oxygen Vacancies: A High-Rate Electrocatalyst for Tandem Electroreduction of Nitrate to Ammonia

The electrochemical nitrate reduction reaction (NO₃RR) is an attractive green alternative to the conventional Haber–Bosch method for the synthesis of NH₃. However, this reaction is a tandem process that involves multiple steps of electrons and protons, posing a significant challenge to the efficient synthesis of NH₃. Herein, we report a high-rate NO₃RR electrocatalyst of Fe and Cu double-doped Co₃O₄ nanorod (Fe₁/Cu₂-Co₃O₄) with abundant oxygen vacancies, where the Cu preferentially catalyzes the rapid conversion of NO₃^– to NO₂^– and the oxygen vacancy in the Co₃O₄ substrate can accelerate NO₂^– reduction to NH₃. In addition, the introduction of Fe can efficiently capture atomic H* that promotes the dynamics of NO₂^– to NH₃, improving Faradaic efficiency of the produced NH₃. Controlled experimental results show that the optimal electrocatalyst of Fe₁/Cu₂-Co₃O₄ exhibits good performance with high conversion (93.39%), Faradaic efficiency (98.15%), and ammonia selectivity (98.19%), which is significantly better than other Co-based materials. This work provides guidance for the rational design of high-performance NO₃RR catalysts.