Electrochromic Asymmetric Supercapacitor Windows Enable Direct Determination of Energy Status by the Naked Eye

TLDR

Smart electronics drive interest in multifunctional energy storage, especially electrochromic supercapacitors. The study designs and fabricates a solid‑state electrochromic asymmetric supercapacitor window using WO3 and polyaniline electrodes. The device couples these electrodes in a solid‑state ASC window with commercial solar cells to create a self‑powered, color‑indicated system. The ASC delivers 28.3 mF cm⁻² capacitance, 7.7 × 10⁻³ mWh cm⁻² energy density, and a reversible light‑green to dark‑blue color shift, enabling visual energy‑status readout and promising use in smart electronics and buildings.

Abstract

Because of the popularity of smart electronics, multifunctional energy storage devices, especially electrochromic supercapacitors (SCs), have attracted tremendous research interest. Herein, a solid-state electrochromic asymmetric SC (ASC) window is designed and fabricated by introducing WO3 and polyaniline as the negative and positive electrodes, respectively. The two complementary materials contribute to the outstanding electrochemical and electrochromic performances of the fabricated device. With an operating voltage window of 1.4 V and an areal capacitance of 28.3 mF cm–2, the electrochromic devices show a high energy density of 7.7 × 10–3 mW h cm–2. Meanwhile, they exhibit an obvious and reversible color transition between light green (uncharged state) and dark blue (charged state), with an optical transmittance change between 55 and 12% at a wavelength of 633 nm. Hence, the energy storage level of the ASC is directly related to its color and can be determined by the naked eye, which means it can be incorporated with other energy cells to visual display their energy status. Particularly, a self-powered and color-indicated system is achieved by combining the smart windows with commercial solar cell panels. We believe that the novel electrochromic ASC windows will have great potential application for both smart electronics and smart buildings.