Mechanism of MOF-derived Fe-doped TiO2 material enhanced by the AC magnetic field on electrochemical nitrogen reduction reaction (eNRR)

Electrochemical nitrogen reduction reaction(eNRR) is a promising strategy for ammonia production because of its mild reaction conditions, high theoretical conversion rate, and green pollution. However, the strong stability of N   N triple bond and competitive hydrogen evolution reaction (HER) limit the Faraday efficiency and ammonia conversion of eNRR. In recent years, the structural design of catalysts combined with external field enhancement to enhance the AC magnetic field electrocatalytic reaction has received extensive attention. In this study, an eNRR catalyst ( x Fe-M-TiO 2 ) with a high concentration of oxygen vacancies was constructed by the defect engineering strategy. The ammonia conversion rate of eNRR of 1.5Fe-M-TiO 2 was 7.35 μg h −1 mg cat −1 , and the Faraday efficiency was 22.69 %, which was 2 % higher than that before doping. The spin–orbit coupling effect induced by the AC magnetic field further improved the eNRR activity, in which the Faraday efficiency increased to 52.14 % (increased by 150 %), and the ammonia yield increased to 13.37 μg h −1 mg cat −1 (increased by 5 %). After 80 h of eNRR, the current density of the catalyst became 95 % of the initial current density, and the stability was good. Density functional theory calculation showed that Fe doping did not change the reaction mechanism of eNRR but increased the concentration of oxygen vacancy, resulting in a 0.62 eV decrease in the energy barrier of the first hydrogenation of eNRR, which was conducive to the occurrence of eNRR.