Galvanic-driven deposition of large-area Prussian blue films for flexible battery-type electrochromic devices

The integration of electrochromic properties, energy storage, and mechanical flexibility in a multifunctional wearable electronic device is highly desirable yet challenging. Herein, we demonstrate a simple and scalable galvanic-driven strategy to deposit large-area Prussian Blue (PB) films on both rigid and flexible substrates. A flexible PB/Zn battery-type electrochromic device with multiple functions, including a flexible power source and capacity depletion visualization, was constructed. The finely tuned flexible electrochromic device exhibited excellent properties with a large optical contrast (ΔT_{700 nm} = 68.3%), high coloration efficiency (117.2 cm² C⁻¹), rapid switching (4.7 s/7.5 s for coloring/bleaching), and long-operation stability (>1000 cycles). The device also showed excellent flexibility and preserved the electrochromic properties under rigorous bending conditions. Therefore, the PB/Zn device can serve as a flexible power source with large capacity and good durability. Moreover, the discharge state of the battery can be monitored real time visually through the electrochromic changes. This work offers insights into the development of multifunctional smart devices toward real-world applications.