Ammonia-Etched High-Entropy Prussian Blue Analogues Enabling Accelerated Zn²⁺ Transport for Aqueous Zinc-Ion Storage

Aqueous zinc-ion batteries (AZIBs) represent a promising energy-storage technology due to their inherent safety and low cost. High-entropy Prussian blue analogues (HEPBAs) have attracted considerable interest as AZIB cathode materials owing to their robust frameworks and multimetal synergy, yet their dense structure and excessive adsorbed and lattice water severely limit Zn²⁺ diffusion and active-site accessibility. Herein, a controlled ammonia-etching strategy is developed to optimize the microstructure of HEPBAs, effectively removing inactive water and creating accessible ion-transport pathways while preserving the primary framework. During etching, the coordinated NH₃ and in situ generated OH^- selectively dissolve weakly bonded metal centers, promoting the elimination of adsorbed and lattice water and inducing local structural relaxation. This preferential etching results in a hollow architecture, simultaneously enlarging the specific surface area and unmasking electrochemically accessible active sites that were previously inaccessible. As a result, the etched HEPBA cathode exhibits an enhanced Zn²⁺ diffusion coefficient of 6.78 × 10^-12 cm² s^-1, exhibiting excellent cycling stability with a capacity retention of 90.55% over 1000 cycles at 0.5 A g^-1. This work demonstrates that moderate ammonia etching can regulate the coordination environment and promote ion transport in high-entropy framework materials for advanced AZIBs.