V2CTx-MXene partially derived hybrid VS2/V2CTx electrode for capacitive deionization with exceptional rate and capacity

MXenes have promising applications in capacitive deionization (CDI) due to their excellent electrical conductivity, tunable layer structure and hydrophilic surface. However, the electrochemical performance and water stability of MXenes would be limited by the large number of terminations on their surface. In this work, we obtained VS2/V2CTx nanocomposites by in situ partial derivatization of MXene to enhance electrochemical performance and slow down its own oxidation, and the resulting material was used as a cathode for CDI desalination. The TOPSIS-Entropy weight model was first used to achieve multi-objective optimization, realizing a salt adsorption capacity of 166.83 mg g−1, a salt removal rate of 3.67 mg g−1 min−1 and an energy consumption of only 0.256 kW h kg−1-NaCl. It also showed good stability over 60 CDI cycles. The fast salt removal rate and high desalination capacity of VS2/V2CTx can be explained by the synergy between the pseudocapacitive and battery behaviors of the VS2/V2CTx hybrid material. In situ electrochemical analysis based on electrochemical quartz crystal microbalance (EQCM) demonstrated that the desalination process is reversible and that the deionization mechanism is a combination of faradaic reaction (removal of Na+·4H2O) and intercalation pseudocapacitance (removal of desolvated Na+). This work shows that VS2/V2CTx, as a partially derived MXene material, provides a new solution to improve the stability and electrochemical properties of MXenes.