Operando X-Ray Diffraction Study of MXene Electrode Structure in Supercapacitors with Alkali Metal Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• MXene materials exhibit promising properties for supercapacitor applications.
• The layered structure of MXene allows ion intercalation, crucial for energy storage.
• Understanding ion-MXene interactions is key to optimizing supercapacitor performance.

Purpose of the Study:

• Investigate the relationship between ion size and MXene interlayer spacing.
• Analyze structural changes in Ti-MXene electrodes during supercapacitor cycling.
• Determine the influence of different electrolytes on MXene electrode behavior.

Main Methods:

• Operando X-ray diffraction (XRD) on capillary-size supercapacitors.
• Electrochemical cycling of MXene electrodes in various alkali metal chloride and sulfuric acid electrolytes.
• Analysis of MXene c-lattice expansion and interlayer spacing variations.

Main Results:

• MXene electrodes showed significant c-lattice expansion in LiCl, NaCl, and KCl electrolytes with increasing voltage.
• Structural oscillations were observed in MXene electrodes correlating with polarity changes.
• Interlayer spacing remained largely unchanged in RbCl, CsCl, NH4Cl, and H2SO4 electrolytes.
• Ion insertion into MXene interlayers was found to be dependent on the ion's dehydrated state.

Conclusions:

• The degree of MXene interlayer expansion is dependent on the electrolyte composition and applied voltage.
• Ion size and hydration state critically influence ion intercalation within MXene structures.
• These findings provide insights for designing advanced MXene-based supercapacitors.