Single-Atom Fe-N₄ on a Carbon Substrate for Nitrogen Reduction Reaction

Ammonia plays an important role in production and life, but the high energy consumption of the industrial Haber–Bosch process encourages people to study nitrogenase, which can convert nitrogen into ammonia under environmental conditions. Here, we reported an atomically dispersed Fe-N4 fixed on a carbon substrate (Fe-N/C) with the Fe single atom loading up to 3.5 wt % and the specific surface area reaching up to 1088.96 m2 g–1. Furthermore, Fe-N/C was modified on carbon papers (CPs) to form Fe-N/C-CPs as effective electrochemical nitrogen reduction reaction (NRR) catalysts, achieving an RNH3 of 2.27 μg h–1 mg–1 with an FE of 7.67% at −0.2 V (vs RHE). The uniformly dispersed and high ratio Fe single atoms in Fe-N/C ensure that the active sites can be fully exposed, which has the ability to reduce the stable N≡N triple bond and facilitate subsequent activation and hydrogenation of nitrogen molecules, improving the electrocatalytic NRR activity. Density functional theory theoretical calculations proved that Fe-N/C-CPs with the Fe-N4 configuration, which catalyzes the reduction of nitrogen by the alternating mechanism, can effectively reduce the Gibbs free energy in the rate-determining step, thereby increasing the catalytic activity.