A confinement strategy to in-situ prepare a peanut-like N-doped, C-wrapped TiO₂ electrode with an enhanced desalination capacity and rate for capacitive deionization

Capacitive deionization (CDI) technology has been considered a promising desalination technique, especially for brackish water, because of its relatively low energy consumption, facile operation, and easy regeneration of electrodes. However, the desalination capacity, cost, fabrication method, electrochemical stability, and environmental unfriendliness of the electrodes have restricted the practical application of the CDI technique. Herein, we reported the one-step in situ preparation of nitrogen-doped and carbon-decorated MXene-derived TiO₂ (termed N-TiO_2−x/C) through the confinement-growth strategy. The small particle size (~ 25 nm) and uniform distribution of a peanut-like N-TiO_2−x/C material could be ascribed to the confined growth space created by the nanoporous structure of melamine foam. The defects produced by N doping provide an enhanced electrical conductivity and more adsorption sites, while wrapping with a carbon shell layer increases the conductivity and offers protection for N-TiO_2−x to achieve an excellent electrochemical stability. The prepared N-TiO_2−x/C electrode is hydrophilic due to the abundant oxygen-containing functional groups (e.g., C-O, N-Ti-O, -NO_x, and -OH) and exhibits a high salt removal capacity (33.4 mg·g⁻¹), desalination rate (1.5 mg·g⁻¹·min⁻¹), and remarkable cycling stability (without declining after 100 cycles), which might be ascribed to the synergistic effects of the short ion diffusion path, more active adsorption sites, enhanced conductivity, pseudocapacitive behavior, and protection of the carbon shell layer. This work provides a confined-growth strategy to develop MXene-derived oxide electrodes for electrochemical desalination.