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 Ti 3 C 2 T x MXenes generated from a single Ti 3 AlC 2 MAX phase. Ti 3 C 2 T x MXenes were produced by lithium fluoride (LiF/HCl) based minimally intensive layer delamination (MILD) approach by adjusting the volume of HCl as 20, 30 and 40 mL, while maintaining other parameters such as Ti 3 AlC 2 , 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 H 2 SO 4 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 at 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 Ti 3 C 2 T x MXene electrodes for scalable supercapacitors.