Etching-driven evolution of Ti3C2Tx MXenes and its chemistry from a single Ti3AlC2 MAX phase for electrochemical energy storage performance

Here we study the variation of HCl reaction-medium volume at fixed LiF and MAX loading, with associated changes in reagent ratios and reaction-medium composition for the formation, structural evolution, and supercapacitor performance of Ti3C2Tx MXenes generated from a single Ti3AlC2 MAX phase. Ti3C2Tx MXenes were produced by lithium fluoride (LiF/HCl) based minimally intensive layer delamination (MILD) approach by adjusting the volume of HCl to 20, 30 and 40 mL, while maintaining other parameters such as Ti3AlC2, LiF, molarity of HCl, temperature and etching time constant. X-ray diffraction (XRD) validated the successful Al removal, as seen by the absence of the MAX-phase (104) peak and the shift of the (002) reflection to lower angles. Ti-MX-30 had the highest interlayer spacing, measuring 1.53 nm. Field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) showed a gradual transition of compact MAX particles into accordion-like single-to-few-layer MXene structures, whereas energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) corroborated the substantial depletion of Al and development of Ti-C frameworks ornamented with -O, -OH, and -F terminations. Electrochemical tests in 1 M H2SO4 revealed that Ti-MX-20 had the maximum three-electrode capacitance of 114.97 F g–1 at 5 mV s–1 and 57.29 F g–1 at 0.4 A g–1 confirmed by the prevalent surface-controlled kinetics. A symmetric Ti-MX-20//Ti-MX-20 device showed capacitance of 47.27 F g–1 at 5 mV s–1, 12.29 F g–1 at 0.1 A g–1, energy and power density of 1.092 Wh kg–1 and 40 W kg–1, respectively and 92.21% retention after 1500 cycles suggested reliable MXene-based energy-storage behaviour. These results suggest reaction-medium conditions can be tuned to balancing etching efficiency, interlayer accessibility, surface chemistry and electrochemical durability of Ti3C2Tx MXene electrodes for scalable supercapacitors.