Controllable etching construction of nickel-based Prussian blue analog nanocages for stabilized energy storage in aqueous nickel-zinc batteries

Aqueous nickel-zinc batteries (NZBs) are well-suited for large-scale energy storage owing to their safety and low cost. Yet, their nickel-based cathodes encounter issues like particle fragmentation caused by lattice stress accumulation and irreversible phase changes during charge-discharge cycles. In this study, nickel-cobalt Prussian blue analog nanocages (NC-NiCo-PBA) with an octahedral cavity structure were successfully prepared using ammonia complex etching. Structural characterization revealed that the nanocage retained an intact PBA skeleton, with the specific surface area enhanced to 151.38 m 2 /g, which was a 5.2% increase over the original solid particles. The octahedral hollow cavity structure significantly reduces ion transfer distance and alleviates volume strain, thereby markedly improving electrochemical performance. This study provides a new approach for the structural design of PBA-based cathode materials and validates the critical role of hollow nanostructures in enhancing the energy storage performance of aqueous batteries. A strategy for the structural design of NC-NiCo-PBA based on ammonia complex etching is proposed. The nanocage architecture with octahedral cavities was successfully constructed by modulating the topology of PBA. The electrochemical tests show that the structure enables NC-NiCo-PBA//Zn battery to have excellent electrochemical performance. • Ammonia was used as a chemical etchant to selectively dissolve solid NiCo-PBA nanocubes into nanocage structures with octahedral cavities and 10 nm diameter windows. • The nanocage structure effectively shortens the ion diffusion path and enhances the contact between the electrolyte and the active centers, which achieves high efficiency of Ni-Zn batteries. • The etching process does not destroy the original NiCo-PBA, confirming the structural and chemical stability. • The ammonia etching strategy can be extended to other bimetallic Prussian blue analogues, providing a new method of “topology tuning - kinetics optimization” for the design of high-capacity energy storage devices, and contributing to the development of cathode materials for aqueous batteries.