Amorphous Cu Intermediate Modification During Lewis Acid Etching of High-Entropy MAX to MXene Using CuCl₂.

Area of Science:

• Materials Science
• Nanotechnology
• Electrochemistry

Background:

• High-entropy MXenes (HE-MXenes) are advanced 2D materials with significant potential.
• Safe, fluorine-free synthesis routes for HE-MXenes are critically needed.
• Molten salt etching offers a safer alternative to traditional methods.

Purpose of the Study:

• To develop a fluorine-free synthesis for HE-MXenes.
• To investigate the reaction mechanism of molten salt etching on high-entropy MAX phases.
• To evaluate the electrochemical energy storage performance of the synthesized HE-MXenes.

Main Methods:

• Utilized anhydrous CuCl2 for molten salt etching of the (TiVNbMoW)3AlC2 high-entropy MAX phase.
• Investigated the formation of an amorphous intermediate structure (M3C2-ClCux).
• Optimized the etchant ratio to mitigate the intermediate phase's negative effects.

Main Results:

• Successfully synthesized accordion-like HE-MXenes via a fluorine-free route.
• Identified and characterized a novel amorphous intermediate phase (M3C2-ClCux).
• Demonstrated that optimizing the etchant ratio is crucial for mitigating performance degradation caused by the intermediate phase.

Conclusions:

• A viable fluorine-free synthesis for HE-MXenes was established using CuCl2 molten salt etching.
• A novel reaction mechanism involving an intermediate phase was uncovered, crucial for future material design.
• The synthesized HE-MXenes show promising electrochemical energy storage performance in various electrolytes.