Synthesis of fluorine free MXene through lewis acidic etching for application as electrode of proton supercapacitors

MXenes are 2D materials dominated by carbides and nitrides , whose properties can be tailored for a wide range of applications. Here, generic method was adopted to etch MAX phases through direct redox coupling strategy between the A element and the cation of Lewis acid molten salt, allowing us to anticipate the MAX phase reactivity in molten salt. Fluorine free Ti 3 C 2 MXenes with halogen terminals, such as -Cl, -Br and -I, were synthesized using the molten salts synthesis method. Ti 3 C 2 Cl 2 , Ti 3 C 2 Br 2 and Ti 3 C 2 I 2 exhibit distinct charge-discharge rates and pseudocapacitive like behaviors in 3 M H 2 SO 4 electrolyte, with significant specific capacity of 92 C g −1 , 29 C g −1 and 63 C g −1 , respectively, corresponding to retention rates of 32%, 85.22% and 49.1%, respectively, after 10,000 cycles. The exceptional supercapacitive performances of the Ti 3 C 2 MXenes as electrodes with aqueous electrolytes are attributed to the high electrochemical activity of Cl, Br or I. This study demonstrates the efficacy of the Lewis-acidic-melt etching technique for fine tuning the surface chemistry and hence extending the applications of MXene family.