Abstract: The substitution of transition metals and construction of conductive skeleton to improve the stability and conductivity were studied for high-efficiency hybrid capacitive deionization (HCDI). Herein, the carbon nanotubes composite nickel-doped manganese hexacyanoferrate three-dimensional material (MNHCF@CNT) with multiple redox electron pairs and high-speed ion transport channels was successfully synthesized by a one-step co-precipitation method. The synthesized MNHCF@CNT material exhibited high specific capacitance, low charge transfer resistance and excellent electrochemical stability. What is more, it achieved a high salt adsorption capacity of 71.28 mg g^-1, ultrahigh maximum salt adsorption rate of 31.89 mg g^-1 min^-1, and maintained 98.72 % of maximum salt adsorption capacity after 40 cycles. This exceptional HCDI performance primarily stems from the formation of robust Ni-N bonds via Ni substitution in MnHCF, improving the structural stability and ion diffusion kinetics. Meanwhile, efficient electron transport pathways are established through carbon nanotubes to suppress the volume expansion during the ion insertion/extraction process, thus improving the conductivity, ion storage capacity and cycle stability of the material. This work delivers actionable insights into the design of stable and highly efficient PBAs electrodes, critical for next-generation desalination technologies and hard water softening systems.

Key words: Hybrid capacitive deionization, Manganese hexacyanoferrate, Nickel doping, Carbon nanotubes, Stability