Chemically Stable and Porous Cobalt‐Based Prussian Blue Analogue Metal–Organic Framework Serving as a Competent Cathode for Aqueous Zinc‐Ion Batteries

Aqueous zinc ion batteries (AZIBs) are emerging as safe, low-cost, and high-capacity devices for sustainable energy storage. Herein, Cobalt-based Prussian Blue Analogues (PBAs: a subclass of porous metal-organic frameworks-MOFs) have been strategically synthesized with different secondary transition metal ions: manganese, iron, and copper, namely MnCoPBA, FeCoPBA, and CuCoPBA for systematic performance evaluation as cathode materials for AZIBs. Among these, MnCoPBA demonstrates the most promising performance, attributed to its highest specific surface area, uniform cube-shaped particle morphology, and dual redox centers. It delivers a specific discharge capacity of approximately 117 mAh g^-1 at a current density of 0.2 A g^-1 within the voltage window of 0.3-2.0 V (vs. Zn²⁺/Zn), significantly outperforming FeCoPBA (60 mAh g^-1) and CuCoPBA (45 mAh g^-1). Moreover, the assembled Zn//MnCoPBA cell demonstrates excellent cyclic stability, with capacity retention of ∼89% after 1000 cycles, a coulombic efficiency of ∼99.7%, and superior rate capability, indicating its potential as a viable cathode material for AZIBs. Ex situ PXRD, FE-SEM, HR-TEM, and XPS measurements, along with device-level demonstrations, further confirm the structural robustness and reversibility of Zn²⁺ storage in the MnCoPBA electrode. This work represents the first methodical assessment of Co-based PBAs in AZIBs, providing valuable mechanistic insights into structure-property relationships.