Freestanding Ti3C2Tx MXene/Prussian Blue Analogues Films with Superior Ion Uptake for Efficient Capacitive Deionization by a Dual Pseudocapacitance Effect

Exploring and designing high-performance Faradaic electrode materials is of great significance to enhance the desalination performance of hybrid capacitive deionization (HCDI). Herein, open and freestanding films (MXene/Prussian blue analogues (PBAs), specifically, MXene/NiHCF and MXene/CuHCF) were prepared by vacuum filtration of a mixed solution of PBAs nanoparticles and a Ti3C2Tx MXene dispersion and directly used as HCDI electrodes. The conductive MXene nanosheets bridge the PBAs nanoparticles to form a three-dimensional (3D) conductive network structure, which can accelerate the salt ion and electron diffusion/transport kinetics for HCDI. Additionally, the PBAs nanoparticles can prevent the restacking of MXene nanosheets, expand their interlayer spacing, and facilitate the rapid diffusion and storage of ions. Benefiting from the dual pseudocapacitance and synergistic effect of PBAs and MXene, the obtained MXene/PBAs films show superior properties, with a high desalination capacity (85.1 mg g-1 for the MXene/NiHCF film and 80.4 mg g-1 for the MXene/CuHCF film) and an ultrafast salt-removal rate, much higher than those of other Faradaic electrodes. The synergistic effect, the adsorption of Na+ ions, and the enhanced conductivity of MXene/PBAs films were demonstrated through first-principles calculations. This paper offers a simple and convenient method for the design of freestanding HCDI electrodes and promotes the rapid development of HCDI technology.