Side-Reaction Modulation and Surface Reconfiguration of CoSe in Nitrate-to-Ammonia Reduction Reactions

Electrocatalytic nitrate reduction to ammonia can not only effectively help realize the nitrogen cycle in the natural environment, but also be used for the industrial production of ammonia and the treatment of sewage containing nitric acid, thereby achieving wastewater reuse and environmental purification. Converting nitrate to ammonia involves the transfer of eight electrons and is a complex step. With the generation of by-products, exposure to an air environment increases the side reactions, thereby reducing the catalytic efficiency and limiting the application scenarios of the material. Therefore, it is crucial to select a nitrate reduction catalyst that is practical and can be applied to various scenarios. In this work, it is reported that CoSe catalysts have a high ammonia yield of 30.53 ± 3.15 mg h-1 cm-2 in an alkaline medium containing 0.5 mol L-1 NO3- exposed to air, and have a Faraday efficiency of up to 82.80 ± 2.64%, which is even higher than that of argon exposure. In this work, it was found that this phenomenon is due to the substitution of the oxygen reduction reaction (ORR) for the hydrogen evolution reaction (HER), which improves the catalytic efficiency through the modulation of side reactions.