Electrolyte-dependent structure–transport relationships in electrodeposited Prussian Blue analogue thin films

Understanding how electrolyte composition influences the structural factors governing charge storage in Prussian Blue analogues (PBAs) requires clarifying the coupled effects of ion desolvation, structural disorder, and transport pathway connectivity. Here, we demonstrate that electrolyte identity induces structural disorder, which correlates with transport dispersion measured under identical electrochemical conditions. To establish this relationship, Fe-, Co-, and Ni-based hexacyanoferrate thin films were electrodeposited from chloride electrolytes (KCl, NaCl, NH 4 Cl, and LiCl), enabling a comparative investigation of structure-transport correlations across multiple length scales. Although all systems crystallize in the cubic PBA structure, pronounced electrolyte-dependent variations in lattice parameters, defect concentration, and local coordination environments are observed. Na + induces lattice expansion but simultaneously promotes vacancy formation, microstrain, and structural heterogeneity, whereas K + and NH 4 + produce more structurally coherent frameworks with reduced disorder. Raman spectroscopy reveals that increasing structural disorder broadens the distribution of local coordination environments, which is accompanied by increasingly dispersed electrochemical behavior. Electrochemical impedance spectroscopy reveals that charge storage is governed by coupled ion-electron transport processes, with the impedance increasing by more than one order of magnitude from FeHCF to NiHCF. Importantly, the constant phase element (CPE) exponent decreases systematically with increasing Raman band broadening, revealing a strong correlation between structural disorder and transport dispersion. These results demonstrate that electrolyte identity controls not only lattice dimensions but, more importantly, the organization and connectivity of defect networks. Consequently, optimal electrochemical performance arises from a balance between structural coherence and accessible transport pathways rather than from lattice expansion alone.