Sodium-citrate-mediated crystal growth engineering of cobalt Prussian blue analogues for efficient Zn²⁺ storage

This study proposes a sodium citrate-mediated crystal growth regulation strategy to control the nucleation and growth process of cobalt-based Prussian blue analogues (CoPBAs), thereby fabricating CoPBA nanocubes with controllable particle size and applying them to high-performance aqueous zinc-ion batteries (AZIBs). Citrate regulates crystal growth through coordination with Co²⁺, resulting in CoPBA with appropriate particle size, abundant accessible active sites, and hierarchical mesoporous/large pore channels. These structural features facilitate the full infiltration of the electrolyte into the electrode, accelerate Zn²⁺ transport, and improve the utilization of active sites. The optimized P3 electrode delivers 249 mAh g^-1 reversibly under a current of 0.1 A g^-1 and maintains stable operation for over 2000 cycles under 1 A g^-1. In-situ and ex-situ characterization results indicate that a highly reversible Zn²⁺ insertion/deinsertion occurs during the electrochemical reaction, accompanied by Co³⁺/Co²⁺ redox reactions. Density functional theory (DFT) calculations further confirm that this material has good electron transport performance and a low Zn²⁺ diffusion energy barrier. This study demonstrates that crystal growth regulation is an effective strategy for optimizing PBA cathode materials, and establishes a theoretical basis for developing advanced AZIB cathodes.