High-performance electrochromic WO3/POM–MXene energy storage device with color-based energy indication

Abstract

Electrochromic energy storage devices (EESDs) with quantitative color-based visualization of their energy state have applications in smart displays and wearable intelligent electronics, as well as energy-efficient buildings. In addition, because of their ability to display their energy storage state accurately and in real time, the overcharging of energy-storage devices can be prevented, thus improving safety. WO3 is a classical electrochromic material, but EESDs based on WO3 can suffer from low coloration efficiencies and energy densities, as well as short cycle lives. However, compositing is a promising way to improve these properties. Therefore, in this study, an electrochromic WO3 nanoblock (NB)/Preyssler-type K12.5Na1.5[NaP5W30O110]-15H2O polyoxometallate (P5W30)//Ti3C2TX MXene energy storage device was prepared by a simple hydrothermal method. The WO3NB/P5W30 film was first deposited on a conductive substrate as the cathode and subsequently modified with the MXene film as the anode. The device exhibited a high coloration efficiency (145.02 cm2/C), excellent energy density (9.8 × 10−3 mWh/cm2), long cycle life (62.5 % retention rate after 5000 galvanostatic charge–discharge cycles), and excellent chromaticity difference (ΔE*, 25.91). These properties are not only due to the unique 2D layered structure of MXene but also the greater compatibility between the cathode and the anode (as shown by the q-values). In addition, compared to a WO3NB film alone, the composite WO3NB/P5W30 film had higher areal capacitance (12-times higher) and ΔE* (11-times higher), which is attributed to the synergism between the crystalline WO3 and amorphous polyoxometallate composite. This study provides an effective method for developing high-performance EESDs with quantitative color-based charge-state visualization and long cycle lives.