3D‐Nanostructured ITO Enables High‐Loading Prussian Blue Cathodes for Zn‐Based Electrochromic Smart Windows

ABSTRACT Prussian Blue (PB) is an attractive electrochromic cathode material for aqueous electrochromic energy‐storage smart windows, but its performance remains limited by the low areal capacity of thin‐coatings deposited on planar transparent conductive oxides. Here, we overcome this limitation by combining galvanostatic electrodeposition with 3D‐nanostructured ITO electrodes, enabling conformal growth of PB with high‐loadings, while maintaining mechanical stability and fast electrochemical response. The resulting electrodes sustain charge densities up to 100 mC/cm 2 at relatively high rates. When integrated into Zn/PB smart window devices, they enable fast and homogeneous coloration/bleaching with enhanced optical contrast and charge storage capacity, while also exhibiting high cyclability. Device configurations based on reversible Zn electrodeposition onto a transparent ITO counter electrode enable improved control over optical contrast and electric field distribution, while a three‐electrode architecture incorporating a sacrificial Zn anode provides a route toward in situ regeneration of the electrochromic cathode and extended device lifetime.