Controlled etching to immobilize highly dispersed Fe in MXene for electrochemical ammonia production

Electrocatalytic N2 reduction reaction (NRR), as an efficient and low-carbon NH3 production method, is highly desired to replace the traditional Haber–Bosch process under ambient conditions. Nevertheless, its industrial application remains hampered by the low Faradaic efficiency (FE) and an inferior ammonia yield mainly owing to the sluggish kinetics and the competing hydrogen evolution reaction (HER). Here, highly dispersed Fe immobilized in Ti3C2Tx MXene (HD-Fe-MXene) is for the first time developed by a controlled etching strategy to act as an efficient electrochemical ammonia production catalyst. In this process, the Al phase of MAX is firstly replaced by Fe through Lewis-acidic-melt selective etching, then the HD-Fe-MXene is obtained by etching with an HCl solution. The as-prepared HD-Fe-MXene delivers outstanding NRR activity with an FE of 21.8% at −0.1 V versus reversible hydrogen electrode (RHE) and a favorable NH3 yield of 18.25 µg h−1 mg−1 (−0.25 V vs. RHE) in 0.1 M Na2SO4 electrolyte. Notably, HD-Fe-MXene exhibits superior stability during the six times recycling tests and the 24 h chronoamperometric test. This excellent NRR electrocatalytic activity is mainly ascribed to the highly dispersed Fe immobilized in the fluorine-free Ti3C2Tx MXene, which inhibits Fe centers from aggregation for providing abundant active sites for NRR. Moreover, the two-dimensional structure and the fluorine-free property of Ti3C2Tx MXene benefit to provide abundant sites for N2 adsorption and promote the electron transfer thus boosting the NRR process. This study delivers a feasible strategy for adding transition metal into the MXene phase to enhance the electrocatalytic activity of MXene-based catalysts for nitrogen electroreduction to ammonia.