Ni-doping Cu-Prussian blue analogue/carbon nanotubes composite (Ni-CuPBA/CNTs) with 3D electronic channel-rich network structure for capacitive deionization

Intercalation materials are of considerable interest for capacitive deionization (CDI) due to the rigid open framework and energy storage ability. However, low conductivity and stability restrict its application. In this work, a redox-active intercalation cation electrode based on 3D network Ni-doping Cu-Prussian blue analogue NixCu1-x[Fe(CN)6]1-γ (NCP-2, γ < 1) interwoven with CNTs (NCP/CNT) is synthesized. Experiments illustrate that the dual strategy of Ni doping and the insert of CNTs reduce the vacancy and crystal water in the lattice, resulting in a maximum capacity of 373.6 F·g−1 and better cycling stability. NCP/CNT║active carbon (AC) cell delivers a high adsorption capacity of 41.25 mg·g−1 with less energy consumption of 0.1080 kWh·kg−1 in 500 ppm NaCl solution. The outstanding salt adsorption depends on the rapid Fe3+/Fe2+ and Cu2+/Cu+ redox cycle, shortened Na+ diffusion path and fast electron transport. The effect of Ni doping was explored by DFT calculations, which proved it enhanced the electron density of Fe atom, stabilized the skeleton structure, increased the conductivity of PBA materials and facilitated the insertion of Na+. After CNT inserting, abundant electronic conductive channels formed among PBA nanoparticles. Hence, this work provides a feasible strategy to construct highly efficient electrodes with less energy consumption for CDI applications.