Calcium annealing approach to control of surface groups and formation of oxide in Ti3C2Tx MXene

Ti3C2Tx MXene, a 2D material, is known to exhibit unique characteristics that are strongly dependent on surface termination groups. Here, we developed a novel annealing approach with Ca as a reducing agent to simultaneously remove F and O groups from the surface of multilayered MXene powder. Unlike H-2 annealing that removes F effectively but has difficulty in removing O, annealing with Ca effectively removed both O and F. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy revealed that the proposed approach effectively removed F and O from the MXene powder. The results of O/N analyses showed that the O concentration decreased by 57.5% (from 2.66 to 1.13 wt%). In addition, XPS fitting showed that the volume fraction of metal oxides (TiO2 and Al2O3) decreased, while surface termination groups (-O and -OH) were enhanced, which could increase the hydrophilic and adsorption properties of the MXene. These findings suggest that when F and O are removed from the MXene powder, the interlayer spacing of its lattice structure increases. The proposed treatment also resulted in an increase in the specific surface area (from 5.17 to 10.98 m(2)/g), with an increase in oxidation resistance temperature in air from similar to 436 to similar to 667 degrees C. The benefits of this novel technology were verified by demonstrating the significantly improved cyclic charge-discharge characteristics of a lithium-ion battery with a Ca-treated MXene electrode.

Automated summary

This study developed a novel annealing approach using Ca as a reducing agent to remove both F and O groups from the surface of multilayered MXene powder. The proposed treatment effectively removed F and O, increased interlayer spacing, and enhanced the hydrophilic and adsorption properties of the MXene. The specific surface area increased, and the oxidation resistance temperature in air improved. The benefits of this novel technology were demonstrated by the improved cyclic charge-discharge characteristics of a lithium-ion battery with a Ca-treated MXene electrode.