Enhancing the electrocatalytic performance of nitrate reduction to ammonia by in-situ nitrogen leaching

Abstract

Electrochemical nitrate reduction reaction (NITRR) is regarded as a “two birds-one stone” method for the treatment of nitrate contaminant in polluted water and the synthesis of valuable ammonia, which is retarded by the lack of highly reactive and selective electrocatalysts. Herein, for the first time, nickel foam supported Co4N was designed as a high-performance NITRR catalyst by an in-situ nonmetal leaching-induced strategy. At the optimal potential, the Co4N/NF catalyst achieves ultra-high Faraday efficiency and NH3 selectivity of 95.4% and 99.4%, respectively. Ex situ X-ray absorption spectroscopy (XAS), together with other experiments powerfully reveal that the nitrogen vacancies produced by nitrogen leaching are stable and play a key role in boosting nitrate reduction to ammonia. Theoretical calculations confirm that Co4N with abundant nitrogen vacancies can optimize the adsorption energies of NO3- and intermediates, lower the free energy (ΔG) of the potential-determining step (*NH3 to NH3) and inhibit the formation of N-containing byproducts. In addition, we also conclude that the nitrogen vacancies can stabilize the adsorbed hydrogen, making H2 quite difficult to produce, and lowering ΔG from *NO to *NOH, which facilitates the selective reduction of nitrate. This study reveals significant insights about the in-situ nonmetal leaching to enhance the NITRR activity.