Surface Functional Groups and Electrochemical Behavior in Dimethyl Sulfoxide-Delaminated Ti₃ C₂ T_x MXene

Functional groups in two-dimensional (2D) Ti₃ C₂ T_x MXene are an important factor influencing electrochemical performance in many applications involving energy storage, electrochemical sensors, and water purification. However, after dimethyl sulfoxide (DMSO) delamination, the effect of surface functionalities in Ti₃ C₂ T_x is still unclear and there are no systematic reports on its capacitive behavior. Experiments and theoretical calculations confirm the relationship between different surface functionalities, the DMSO delamination effect, and the electrochemical behavior of the DMSO-delaminated Ti₃ C₂ T_x . The dominant -O and -OH terminations are attributed for surfaces delaminated by using HF [Ti₃ C₂ T_x  (HF)] and LiF/HCl [Ti₃ C₂ T_x  (LiF/HCl)], respectively. Theoretical results are also in agreement with experimental results in that -OH terminations are essential for the formation of a free-standing film. Compared to non-delaminated Ti₃ C₂ T_x  (HF) (similar O/F ratios of 1.37 and 1.42), there is a significant DMSO delamination effect for Ti₃ C₂ T_x  (LiF/HCl) because of different O/F ratios of 2.9 and 3.6. Additionally, the delaminated Ti₃ C₂ T_x  (LiF/HCl) electrodes deliver a higher capacitance of 508 F cm^-3 than that of 333 F cm^-3 for the delaminated Ti₃ C₂ T_x  (HF), although it exhibited lower equivalent series resistance, lower interlayer spacing, and slightly lower specific surface area. This study provides direct and systematic experimental evidence for different functional groups in Ti₃ C₂ T_x MXene based on the DMSO delamination effect.