Study of a Fe₂N₄@graphene catalyst for electrocatalytic nitrogen reduction

Abstract

Ammonia is one of the most important raw materials in human industrial production and agricultural life. At present, the industrial ammonia production process needs to consume a large amount of fossil fuels to obtain a high-temperature and high-pressure reaction environment, which leads to serious environmental pollution caused by the synthetic ammonia industry. Electrocatalytic nitrogen reduction reaction (NRR) uses nitrogen and water resources as raw materials, and uses electricity generated by clean energy to provide power to achieve ammonia synthesis. It is one of the green and environmentally friendly ammonia production methods. However, the electrocatalytic synthesis of ammonia is still difficult to achieve large-scale industrial applications, mainly because the catalyst used in the reaction is difficult to meet the requirements of high activity and high selectivity. In this paper, a catalyst with four N-coordinated Fe atoms on graphene (Fe₂N₄@G) was designed to study the mechanism of electrocatalytic reduction. Firstly, the stability of Fe₂N₄@G catalyst at 300 K was studied by ab initio molecular dynamics. Secondly, the adsorption mode of N₂ on Fe₂N₄@G and its hydrogenation reduction reaction were studied. The best reduction mechanism of N₂ on Fe₂N₄@G was an enzymatic mechanism, which was consistent with the natural nitrogenase mechanism. And the free energy of the rate-determining step is only 0.50 eV, indicating that Fe₂N₄@G has excellent electrocatalytic activity. Finally, the side reaction energy of HER and lattice N atom with NRR is higher than that of NRR, indicating that Fe₂N₄@G catalyst has good selectivity and stability. This paper provides new insights into the design and preparation of diatomic catalysts for NRR.