High capacitance of MXene (Ti3C2Tx) through Intercalation and Surface Modification in Molten Salt

Abstract MXenes (Ti3C2Tx) with –F surface terminations have a negative impact on electrochemical properties when used as potential electrodes in supercapacitors. In this study, Ti3C2Tx with –F surface terminations was one-step treated in LiCl-KCl-K2CO3 molten salt at atmospheric pressure to replace –F by –O surface terminations and simultaneously introduce the intercalation of potassium. Various potassium oxygenated complexes were intercalated into the interlayer of the Ti3C2Tx, resulting in the expansion of d-spacing from 0.96 to 1.05–1.21 nm, the decrease of F content from 11.23 to 3.43 at%, and the increase of O content from 0.79 to 24.18 at%. The modified Ti3C2Tx electrode (KM-Ti3C2Tx) showed an improved specific capacity of 323.6 F g−1 at 1 A g−1 in 1 M H2SO4 solution and excellent capacitance retention (97% after 10000 charging–discharging cycles at 10 A g−1). The storage mechanism is attributed to the reversible conversion of Ti3C2O2 / Ti3C2(OH)2 during the insertion/extraction of hydronium (H+). Therefore, the removal of –F by –O surface terminations can form more Ti3C2O2, leading to an increase in conductivity and electrochemical active surface area.