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, Ti 3 C 2 T x MXene was synthesized by a Lewis acid molten salt‐shielded synthesis (MS 3 ). The surface groups (−Cl, −O) were modified by washing Ti 3 C 2 T x 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 °C, 500 °C, and 700 °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 Ti 3 C 2 T x 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. Ti 3 C 2 T x 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 Ti 3 C 2 T x in mild aqueous electrolytes, offering valuable insights for future modifications and applications of Ti 3 C 2 T x in energy storage technologies.