Electrochemical Oxidation of Nitrogen towards Direct Nitrate Production on Spinel Oxides

Abstract

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_x Co_2-x O₄ 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_0.4 Co_1.6 O₄ 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).

Keywords: electrocatalysis; electrochemical oxidation; nitrate; nitrogen oxidation; spinel oxides.