A simple approach to synthesize NiFe-LDH–Nb2C MXene for enhanced electrochemical nitrogen reduction reactions by a synergistic effect

Abstract

The main process for industrial ammonia synthesis is the Haber–Bosch process, which is highly energy intensive with large amounts of CO₂. The electrochemical ammonia synthesis is a potential alternative to the Haber–Bosch process because of its advantages of environmental friendliness; however, the inert N₂ molecule adsorption and activation are difficult and the competition of the hydrogen evolution reaction (HER) leads to a low Faraday efficiency (FE) and NH₃ yield of the nitrogen reduction reaction (NRR). The exploration of highly active and selective NRR catalysts that can efficiently adsorb and activate N₂, as well as effectively inhibit the HER, is the key point of current research. In this study, NiFe–Nb₂C catalysts were prepared by loading different Ni/Fe molar ratios of NiFe-LDH to Nb₂C MXene and successfully introducing the synergistic effect between Ni and Fe. NiFe–Nb₂C exhibited excellent NRR activity and the ammonia yield and FE hardly decreased in 4 consecutive cycle tests, and the current density remained stable in 24 h chronoamperometric tests, indicating that the NiFe–Nb₂C catalyst has excellent electrochemical stability. DFT calculations indicate that the excellent NRR activity originated from the synergistic effect between NiFe-LDH and Nb₂C MXene, which significantly promoted the activation of N₂ and the formation of *N₂H.