Morphology-Controlled Synthesis of Co/Mn Co-Doped Ni-Fe Prussian Blue Analogues as Cathodes for All-Solid Zinc-Ion Hybrid Supercapacitors

Prussian blue analogues (PBAs), as favorable cathode materials for Zn-ion hybrid supercapacitors (ZHSs), are hindered by intrinsic limitations, including high electrical resistivity, relatively low specific capacitance, and structural instability during cycling. This work designs a Co/Mn bimetallic-doped Ni-Fe PBA cathode for ZHSs, with its morphology regulated through precise control of the co-precipitation pH. The PBA nanoparticles synthesized at pH 8.9 possess a higher specific surface area and a broader mesopore distribution than polyhedral PBAs, which facilitates a larger electrode–electrolyte contact area and provides rapid transport pathways for charge carriers. In a three-electrode system, the PBA nanoparticles exhibit optimal electrochemical performance, delivering a specific capacitance of 575.4 F g −1 (79.9 mAh g −1 ) at 1 A g −1 and retaining 72.3% of their initial capacitance after 5000 cycles. The resulting ZHS device, utilizing an activated carbon anode and ZnSO 4 gel electrolyte, achieves a specific capacity of 131 mAh g −1 at 0.25 A g −1 and an energy density of 116 Wh kg −1 at a power density of 252 W kg −1, while retaining 68.7% of its initial capacitance after 5000 cycles. This work demonstrates that synergistic bimetallic doping combined with morphological engineering effectively addresses the limitations of PBA cathodes, providing a viable strategy for developing high-performance and safe ZHSs.