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

Abstract

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.

Fabricating freestanding electrocatalyst with bismuth‐iron dual active sites for efficient ammonia synthesis in neutral media

“…As depicted in Figure 5B, the electrochemical impedance spectroscopy (EIS) curves of BiFeO/FCC and BiFeO illustrate that the charge transfer resistance of BiFeO/FCC is much lower than that of BiFeO due to the in situ growth of BiFeO on FCC, which boosts the electron transfer from substrate (current collector) to catalysts. Second, in situ decoration BiFeO on FCC enlarges electrochemical active surface area and provides more active sites for NRR, which was determined by the electrochemical double‐layer capacitance (C dl ) as plotted in Figures 5C and 64 . In addition, the hydrophobicity of the BiFeO/FCC is conducive to inhibiting the occurrence of HER side reactions evidenced by water droplet contact angle measurement (Figure ) 33,65 .…”

“…Second, in situ decoration BiFeO on FCC enlarges electrochemical active surface area and provides more active sites for NRR, which was determined by the electrochemical double-layer capacitance (C dl ) as plotted in Figures 5C and S6. 64 In addition, the hydrophobicity of the BiFeO/FCC is conducive to inhibiting the occurrence of HER side reactions evidenced by water droplet contact angle measurement (Figure S7). 33,65 Above all, as illustrates in Figure 5D, the forementioned factors synergistically endow BiFeO/FCC with excellent NRR activity and selectivity.…”

Recent Advances and Perspectives of Lewis Acidic Etching Route: An Emerging Preparation Strategy for MXenes

“…For example, Wang et al prepared highly dispersed Fe immobilized in fluorine-free Ti 3 C 2 T x MXene (HD-Fe-MXene) as NRR electrocatalyst in 0.1 M Na 2 SO 4 electrolyte through FeCl 2 etching and HCl washing (Fig. 16f) [244]. The XRD pattern indicates that the formed Fe nanoparticles can be eliminated by HCl, and energy-dispersive spectroscopy and XPS analysis demonstrate that the remaining Fe atoms with a content of 3.12 wt% are highly anchored on the surface of Ti 3 C 2 T x MXene via Fe-O bond.…”

2D layered materials: structures, synthesis, and electrocatalytic applications

“…9e and f ). 180 Microstructural control is effective in exposing active sites and modulating the electronic structure and hence the adsorption ability. Qiao et al constructed a hybrid film composed of overlapped g-C 3 N 4 and Ti 3 C 2 nanosheets through homogeneous assembly.…”

“…(f ) NH 3 yields of HD-Fe-MXene and FEs during six cycles at −0.25 V versus RHE in 0.1 M Na 2 SO 4 (reproduced from ref. 180 with permission from Wiley, copyright 2022) 180.…”