Hollow multi-shelled CoFe Prussian blue analogues for high-performance aqueous potassium-ion batteries

Prussian blue analogues (PBAs) are promising cathodes for aqueous potassium-ion batteries (PIBs), yet their practical application is severely hindered by sluggish interfacial kinetics and solid-liquid interface degradation induced by large K⁺ intercalation. Herein, we report a kinetically controlled, citric acid-assisted self-templating strategy driven by interfacial dissolution-recrystallization to synthesize hollow multi-shelled CoFe PBA nanocubes (HoMS-CoHCF). This unique box-in-box architecture yields a high specific surface area (207.83 m²·g^-1), which optimizes the solid-liquid contact area for enhanced interfacial ion-exchange, while the internal cavities facilitate sufficient electrolyte penetration and accommodate volumetric variations. First-principles calculations suggest that d-orbital modulation in K₂CoFe(CN)₆ induces half-metallic characteristics, and a possible mechanism involving water-induced framework disorder is proposed to explain the transition to a semiconducting state. Benefiting from this dual structural-electronic modulation and a highly stable aqueous solid-liquid interface, the HoMS-CoHCF cathode delivers outstanding performance in a mild 2 M KNO₃ electrolyte. It achieves a high initial capacity of 71.5 mAh g^-1, robust cycling stability (81.54% retention after 500 cycles at 1C), and superior rate reversibility (96.2% capacity recovery). This work demonstrates that synergizing hollow multi-shell interfacial engineering with d-orbital modulation effectively resolves the surface and bulk kinetic bottlenecks of PIBs, advancing the design of stable interfaces for aqueous energy storage.