Electrochemical Oxidation of Nitrogen towards Direct Nitrate Production on Spinel Oxides

Nitrates are widely used as fertilizer and oxidizing agents. Commercial nitrate production from nitrogen involves high-temperature-high-pressure multi-step processes. Therefore, an alternative nitrate production method under ambient environment is of importance. Herein, an electrochemical nitrogen oxidation reaction (NOR) approach is developed to produce nitrate catalyzed by ZnFe_xCo_2−xO₄ spinel oxides. Theoretical and experimental results show Fe aids the formation of the first N−O bond on the *N site, while high oxidation state Co assists in stabilizing the absorbed OH⁻ for the generation of the second and third N−O bonds. Owing to the concerted catalysis, the ZnFe_0.4Co_1.6O₄ oxide demonstrates the highest nitrate production rate of 130±12 μmol h⁻¹ g_MO⁻¹ at an applied potential of 1.6 V versus the reversible hydrogen electrode (RHE).