Bistable silver electrodeposition-based EC device with a Prussian blue counter electrode to maintain the mirror state without power supply

This article describes the design of a silver electrodeposition-based electrochromic (EC) device with excellent image retention properties by using the counter electrode reaction of Prussian blue (PB). We demonstrated silver electrodeposition-based EC device enabled various optical states without dyes and pigments. These optical states were explained by localized surface plasmon resonance (LSPR) absorption of silver nanoparticles electrodeposited on an indium tin oxide (ITO) electrode. However, the color retention property of the device was inadequate because of the presence of Cu²⁺ ions, which function as redox reaction materials at the counter electrode. That is, Cu²⁺ in the electrolyte oxidizes the silver deposits on the electrode, resulting in a lack of image retention property. To improve both the redox reactivity of the counter electrode and color retention property, here we utilized PB as the counter electrode material. We discuss the device properties of the silver electrodeposition-based EC device with the PB counter electrode in terms of charge density or its ability to change color. The device achieved both longer retention time in the colored state and reversibility. It has an advantage of maintaining the coloring state without electric power for practical applications.