Surface Functional Groups and Electrochemical Behavior in Dimethyl Sulfoxide-Delaminated Ti3C2Tx MXene

Functional groups in two-dimensional (2D) Ti3C2Tx 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 Ti3C2Tx 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 Ti3C2Tx. The dominant -O and -OH terminations are attributed for surfaces delaminated by using HF [Ti3C2Tx (HF)] and LiF/HCl [Ti3C2Tx (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 Ti3C2Tx (HF) (similar O/F ratios of 1.37 and 1.42), there is a significant DMSO delamination effect for Ti3C2Tx (LiF/HCl) because of different O/F ratios of 2.9 and 3.6. Additionally, the delaminated Ti3C2Tx (LiF/HCl) electrodes deliver a higher capacitance of 508 F cm(-3) than that of 333 F cm(-3) for the delaminated Ti3C2Tx (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 Ti3C2Tx MXene based on the DMSO delamination effect.