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

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/cm² 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.