Upon etching, the color of the EE-Ti3C2 multilayer powder changed from grey to dark grey for both EE-Ti3C2 and EE-Ti3CN (Figure ). When treated with TMAOH, the EE-Ti3C2 water dispersion appeared as a dark green solution. electrolyte interface upon the first charge and discharge cycle. Yet, the Coulombic efficiency increases rapidly to 99.9 % and stabilised after a few cycles, with a specific capacity of 175 mAh g -1 for EE-Ti3C2, 195 mAh g - 1 for EE-Ti3CN, 190 mAh g -1 for HF/HCl-Ti3C2 and 210 mAh g -1 for HF/HCl-T3CN respectively. A tilted slope was observed during the charge and discharge process, indicating pseudocapacitance behaviour. Figure shows the cyclic performance of all MXenes at a rate of 0.1 and 1 A g -1 , respectively. Before the charge/discharge at 1 A g -1 , pre-cycling was done at 0.1 A g -1 for 20 cycles as an activation process. For all MXenes, no capacity losses were observed at 0.1 A g -1 after 250 cycle at 0.1 A g -1 . In fact, an increase of capacity was observed. Such an increase in capacity became more significant at a high current density that all MXenes only reach their maximum capacity around a few decades of cycles. At 1 A g -1 , the peak capacity was observed as followed: EE-Ti3C2= 140 mAh g -1 , EE-Ti3CN= 165 mAh g -1 , HF/HCl-Ti3C2= 142 mAh g -1 , HF/HCl-Ti3CN= 166 mAh g -1 . All MXenes exhibit superior cyclic performance, with a capacity retention of approximately 80 % after 2000 cycles. The trend of increase in capacity of MXene during cycling may be attributed to that the irreversible expansion of the interlayer spacing caused by lithiation. Thus, more lithium can be accomodate between the MXene layers. This trend was also observed for other MXene energy storage systems. Both, EE-Ti3C2 and EE-Ti3CN, showed slightly lower capacity than their HF/HCl etched analogues. Such difference is attributed to the small amount of chloride termination in the HF/HCl-MXene, which is bulkier