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

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Lewis acidic molten salt synthesis is a key strategy for producing MXenes with tunable surface terminations from MAX phases.
• Understanding the complex phase evolution during MXene synthesis and post-processing is crucial but challenging due to limited in-situ characterization.
• Controlling MXene structure and surface chemistry is vital for enhancing their performance in energy storage applications.

Purpose of the Study:

• To investigate the phase evolution chemistry of Nb2GaC MAX during molten salt etching using operando synchrotron radiation X-ray diffraction (SRXRD).
• To develop a controllable synthesis strategy for MXenes by precisely adjusting temperature and time during the molten salt process.
• To tailor the phase structure of Nb2CTx MXenes for improved lithium-ion (Li+) storage capabilities.

Main Methods:

• Utilized an operando synchrotron radiation X-ray diffraction (SRXRD) technique to monitor phase evolution under molten salt conditions.
• Employed time-dependent persulfate oxidation to control the etching process and tailor the MXene phase structure.
• Characterized the synthesized Nb2CTx MXenes for morphology, surface termination, and electrochemical performance.

Main Results:

• Successfully unveiled the phase evolution of Nb2GaC MAX under molten salt conditions, enabling precise control over etching.
• Tailored the phase structure of Nb2CTx MXenes from hexagonal to amorphous by controlling etching time.
• Amorphous Nb2CTx MXenes with chloride terminations demonstrated significantly enhanced specific capacity, rate capability, and cycling stability for Li+ storage.

Conclusions:

• The study provides critical insights into time-dependent phase evolution during molten salt synthesis of MXenes.
• The developed controllable synthesis strategy enhances efficiency and precision in MXene preparation.
• The findings highlight the potential of tailored amorphous MXenes for advanced high-performance energy storage systems.