Influence of Surface Groups on Electrochemical Properties of Molten Salt Synthesized Ti3C2Tx in Mild Aqueous Electrolytes

MXene, notable for its excellent electrical conductivity and tunable surface groups, has garnered widespread attention in the field of electrochemical energy storage. Here, Ti3C2Tx MXene was synthesized by a Lewis acid molten salt-shielded synthesis (MS3). The surface groups (-Cl, -O) were modified by washing Ti3C2Tx samples with various solutions (deionized water, 0.5 M hydrochloric acid (HCl), 0.5 M ammonium persulfate solution (APS)) and/or thermal treatments under an argon atmosphere at 300 degrees C, 500 degrees C, and 700 degrees C. It is shown that deionized water and HCl solution washing have minimal impact on the surface groups, while APS washing can increase the content of -O surface group. Conversely, thermal treatment may remove the -O. Electrochemical charge storage behavior of these Ti3C2Tx variants were further investigated in a 1 M acetate electrolyte buffered at pH=5.0. It is indicated that the -Cl surface group is electrochemically inert, whereas the -O may significantly improve the charge storage performance. Ti3C2Tx with high -O content delivered an impressive maximum capacity of 155 C g(-1). This research underscores the crucial role of surface groups on the electrochemical performance of Ti3C2Tx in mild aqueous electrolytes, offering valuable insights for future modifications and applications of Ti3C2Tx in energy storage technologies.