Bi-functional flexible electrodes based on tungsten trioxide/zinc oxide nanocomposites for electrochromic and energy storage applications

In this paper, the tungsten trioxide/zinc oxide (WO₃/ZnO) nanocomposites were formed on flexible substrates by combining facile hydrothermal process and pulsed laser deposition (PLD) method. As bi-functional electrodes, the WO₃/ZnO nanocomposites possess large specific surface area and a great number of micro channels, significantly increasing the area of WO₃ active layer and facilitating the diffusion of Li⁺ ions during the electrochemical process. Compared with dense WO₃ film, WO₃/ZnO nanocomposites exhibit enhanced electrochromic and capacitive performance of wider optical contrast (68.2%), greater coloration efficiency (80.6 cm²C⁻¹) and higher areal capacitance (15.24 mF cm⁻²). Furthermore, based on the WO₃/ZnO nanocomposites structure, a novel flexible electrochromic-supercapacitor was demonstrated, which functions as a smart energy storage device able to visually monitor the level of stored energy by rapid and reversible color variation. The results present great potential of WO₃/ZnO nanocomposites for electrochromic and energy storage applications.