Three-Electrode Electrochromic Energy Storage Devices with Enhanced Multicolor Functionality

Electrochromic (EC) technology has garnered attention for its low energy consumption and aesthetic versatility. Among various EC materials, tungsten trioxide (WO₃) is notable for its high optical contrast, durability, and coloration efficiency. However, its single-color output limits its versatility in applications such as multicolor displays and windows. In addition, conventional complementary EC devices require the pairing of anodic and cathodic materials, restricting independent control of redox reactions on the electrodes. Hence, this study introduced a three-electrode EC energy storage device with various configurations: vanadium oxide/zinc/vanadium oxide (V₂O₅/Zn/V₂O₅) (energy status indicator) and V₂O₅/Zn/WO₃ (energy storage window and multicolor display). This design allowed independent redox control on both electrodes, enhanced multicolor functionality through V₂O₅, and incorporated zinc metal for efficient energy storage and discharge-induced coloration. The study revealed that V₂O₅/Zn/V₂O₅ configuration exhibited higher coloration depth (58.92% for orange, 32% for yellow-green, and 10.65% for blue) across all color states while achieving a high energy storage capacity of 185 mAh/m², making it ideal for energy status indicator applications. Conversely, the V₂O₅/Zn/WO₃ structure achieved a significantly higher optical contrast of 77.86%, excellent coloration efficiency of 46.24 cm²/C, and energy storage capacities of 104.8 mAh/m² (V₂O₅) and 142 mAh/m² (WO₃), making it suitable for multicolor energy storage windows. Additionally, the V₂O₅/Zn/WO₃ configuration demonstrated suitability for multicolor display applications. Overall, these three-electrode EC energy storage architectures address the intrinsic color limitations and redox control constraints of conventional devices, enabling high-capacity, tunable multicolor operation with significant potential for integration into advanced smart windows, energy indicators, and adaptive display technologies.