Defect-Driven Electrochemical Domain Modulation in Prussian Blue Revealed by Single-Entity Analysis
He Zhang, Yang Tao, Lei Pan, Yufei Wang, Heekwon Lee, Xun Zhan, Hang Ren
Abstract
Electrochemical domains, defined as the spatial region of the electrode material where charge transfer occurs, are central to charge storage and electrocatalysis. In Prussian Blue (PB), a prototypical mixed-valence framework, these domains extend throughout the three-dimensional lattice and are shaped by structural accessibility and defect distribution. However, ensemble measurements obscure this spatial heterogeneity, averaging local variations in the electrochemical behavior. Here, we apply single-entity electrochemistry to individual PB nanocubes to resolve electrochemical domain behavior during K + insertion and H 2 O 2 reduction. Correlative electron microscopy and electrochemical analysis reveal a defect-driven reversal in function: smaller nanocubes exhibit a greater volumetric capacity for K + storage, whereas larger nanocubes show greater catalytic activity for H 2 O 2 reduction. This contrast originates from the dual role of structural defects, which limit ion-accessible volume by disrupting lattice connectivity and simultaneously expose coordinatively unsaturated Fe sites that promote catalytic activity. Our findings establish a mechanistic framework that connects structure, electrochemical domain accessibility, and function, demonstrating the power of integrating single-particle electrochemistry with high-resolution structural imaging in resolving spatially heterogeneous interfacial processes in redox-active materials.