Ternary-metal Prussian blue analog hollow spheres/MXene electrode based on self-assembly enabling highly stable capacitive deionization

Mn-Fe Prussian blue analogues (PBAs) are a Faradaic material with high theoretical capacity due to their unique frame structure and adequate ion diffusion channels, demonstrating excellent salt adsorption performance as electrode materials in hybrid capacitive deionization (HCDI). However, Mn-Fe PBAs generally suffer from poor cycling reversibility and capacity retention during the phase transition from octahedral to tetragonal phases caused by Jahn-Teller distortion. Moreover, the electrical conductivity of PBAs is relatively inferior resulting in insufficient energy efficiency for practical desalination applications. In this study, a ternary-metal PBA hollow sphere is proposed to be integrated in the layered Ti₃C₂T_x MXene structure by an electrostatic interaction as the Faradaic electrodes of HCDI. The hollow sphere structure of PBA and the incorporation of Co in the ternary-metal PBA facilitate ion diffusion and mitigate structural distortion during charging/discharging processes. Furthermore, the ternary-metal PBA hollow spheres serve as the spacer to alleviate the self-stacking of MXene while benefiting from the enhanced electrical conductivity provided by MXene. Through the synergy between PBAs and MXene, the PBA/MXene composite exhibits fast ion transport, high salt adsorption capacity (185.25 mg g⁻¹ at 20 mA g⁻¹), and cycling stability (capacity retention of 100 % over 80 cycles). This new composite material offers a new strategy for the composite direction of functional PBA and MXene, harnessing the strengths of both materials to advance the development of HCDI technology.