Unified catalysis and confinement in a Prussian blue analogue via anisotropic lattice distortion

Abstract

Resolving the coupled challenges of parasitic polyiodide shuttling and sluggish redox kinetics is critical for advancing aqueous zinc-iodine (Zn-I2) batteries. This work demonstrates a unified physical solution within a Prussian blue analogue framework, where a single, targeted atomic substitution is shown to induce a functional anisotropic lattice distortion. The strategic replacement of framework Zn2+ with Co2+ simultaneously activates potent electrocatalytic sites for iodine conversion via enhanced π-backdonation and, through the resultant distortion, sculpts the sub-nanometer cages into geometric traps that physically confine polyiodide intermediates. This integrated mechanism is evidenced by a profound kinetic acceleration, halving both the charge-transfer resistance (to 8.98 Ω) and the intrinsic pseudocapacitive time constant (to 30.6 s). Consequently, the engineered cathode achieves a high capacity of 256 mAh g−1 at 1 A g−1 and exceptional durability. Crucially, a sustained Coulombic efficiency near 100% over 1000 cycles provides definitive proof of the shuttle effect's suppression. This study establishes how targeted lattice engineering can resolve coupled, multifunctional challenges in a monolithic material, offering a design principle for advanced energy storage systems.