Novel Electrochromic Batteries: II. An InHCF-WO3 Cell with a High Visual Contrast

Upon the improvements in the electrodeposition of indium hexacyanoferrate (InHCF) thin film, another novel thin-film electrochromic battery (ECB) based on InHCF and WO3, namely IWECB, was proposed and investigated. By using the KCl-saturated poly-2-acrylamido2-methylpropane sulfonic acid (K-PAMPS) electrolyte, an IWECB can be charged/discharged between 0.70 V and 1.70 V and features a theoretical voltage of ca. 1.24 V. Moreover, an IWECB exhibits blue-to-colorless electrochromism, with a coloration efficiency of ca. 46.0 cm2/C at 650 nm during the discharging (bleaching) process; therefore, it offers a better visualization of the state of charge (SOC) than a Prussian blue-WO3 ECB (PWECB) does. In addition, it was revealed that the IWECB with such a high visual contrast possesses a dual energy-saving function, in which an IWECB can act as a rechargeable battery and/or a solar-attenuated window. Accordingly, an IWECB-based window can be charged and colored by a photovoltaic (PV) cell in the daytime to store the solar energy and to attenuate solar irradiation in the meantime. This elucidates that an IWECB can greatly enhance the use of the solar energy. Besides the above advantages, the dynamic and at-rest stabilities of an IWECB are discussed in this paper.