Operando Exploring and Modulating Phase Evolution Chemistry from MAX to MXenes in Molten Salt Synthesis

Abstract

Lewis acidic molten salt method is a promising synthesis strategy for achieving MXenes with controllable surface termination from numerous MAX materials. Understanding the phase evolution chemistry during etching and post-processing is highly desirable but remains a key challenge due to the lack of suitable in-situ characterizations and the complexity of the reaction process. Herein, we introduce an operando synchrotron radiation X-ray diffraction (SRXRD) technique to unveil the phase evolution process of Nb2GaC MAX under a molten-salt ambient, proposing a controllable synthesis to achieve optimal etching through precise temperature and time adjustment. Subsequently, the phase structure of Nb2CT x MXenes is successfully tailored from hexagonal to amorphous by time-dependent persulfate oxidation. The resulting amorphous Nb2CT x with a well-patterned morphology and numerous chloride terminations exhibits highly improved specific capacity, rate capability, and long cycling for Li+ storage with a Cl-containing surface protective film. Addressing the time-related phase evolution during the entire molten salt strategy provides new insights into achieving higher efficiency and controllability in preparing MXenes and shows great potential in high-performance energy storage systems based on MXenes.

Regulating the Electronic Structure of MAX Phases Based on Rare Earth Element Sc to Enhance Electromagnetic Wave Absorption

“…For the synthesis of Ti 2 GaC, the same method was employed, with the only difference being the holding time at 1100 °C. It is worth noting that the preparation process for other Ga-MAX phases (V 2 GaC, 66 Cr 2 GaC, 67 Nb 2 GaC, 68 Mo 2 GaC, 69 and Mo 2 Ga 2 C 70 ) followed a similar procedure to that previously reported.…”

Opportunities of MXenes in Heterogeneous Catalysis: V2C as Aerobic Oxidation Catalyst

“…Another frequently used procedure to modify the surface terminal groups is APS oxidation. While prolonged treatments with APS for hours can damage MXene structure, producing amorphization and appearance of metal oxides, reaction of APS with MXenes for less than 1 h has been reported to introduce surface −O− groups without altering crystallinity and structure of the MXene [48,49] . Considering that V−O−H and V−O−V would behave differently as active sites, it was of interest to determine the influence of 30 min treatment of V 2 C with APS.…”

“…While prolonged treatments with APS for hours can damage MXene structure, producing amorphization and appearance of metal oxides, reaction of APS with MXenes for less than 1 h has been reported to introduce surface À OÀ groups without altering crystallinity and structure of the MXene. [48,49] Considering that VÀ OÀ H and VÀ OÀ V would behave differently as active sites, it was of interest to determine the influence of 30 min treatment of V 2 C with APS. Besides surface À OÀ functional groups being favored, it can also be envisioned that the V III/IV/V oxidation state distribution can also be modified towards higher valent V. The results of APS treatment of V 2 C are also included in Table 1 (entry 11) and, again, diminishes the catalytic activity of the original V 2 C sample for the aerobic oxidation of indane at 120 °C.…”

Ti2CTx MXene Cathode Host for Enhanced Zinc‐Bromine Battery Performance

“…This approach avoids the production of harmful compounds, eliminates the need for a protective atmosphere, and has recently gained widespread attention. [ 31,32 ]…”

“…This approach avoids the production of harmful compounds, eliminates the need for a protective atmosphere, and has recently gained widespread attention. [31,32] Here, we propose the utilization of 2D layered Ti 2 CT x MXene as the cathode host material for Zn-Br 2 battery. The Ti 2 CT x MXene, synthesized via the molten salt method, possesses a distinctive open layered structure, and is enriched with polar surface functional groups (Figure S2, Supporting Information).…”