Free-standing 3D alkalized Ti 3 C 2 T x /Ti 3 C 2 T x nanosheet membrane electrode for highly efficient and stable desalination in hybrid capacitive deionization

To realize the industrial feasibility of capacitive deionization (CDI), many efforts have been made to improve the desalination performance. Since investment and daily maintenance issues have to be considered in the actual operation of CDI, which are related to the long-term operational stability of the system, the decline in the performance of electrode materials in long-term operation has seriously impeded the practical application of CDI systems. In this paper, we propose a binder-free Alk-Ti 3 C 2 T x MXene (Alk-Ti 3 C 2 T x -M) using 2D delaminated Ti 3 C 2 T x MXene (d-Ti 3 C 2 T x ) nanosheets and 3D porous Alk-Ti 3 C 2 T x via a simple vacuum-assisted filtration strategy. The alkali induces MXene to form a three-dimensional (3D) porous structure, which improves the stability of the electrode with open interconnected pores, while the high surface area guarantees fast ionic diffusion and high Na + loading. Moreover, d-Ti 3 C 2 T x sheets as a conductive binder replaces traditional conductive adhesives, which enhance the capacity and stability of the electrode by effectively accommodating the volume change and eliminating electrochemically inactive components of traditional conductive binders. As a result, the integrated Alk-Ti 3 C 2 T x -M cathode could be directly used for CDI and exhibited a high capacity (50 ± 3 mg g −1 at 30 mA g −1 ) and a long-life cycle stability (∼250 cycles, over more than 10 days). Therefore, this strategy of assembling electrodes can be readily extended to constructing a large number of 2D-derived materials for electrochemical applications.