Enhanced Contrast of WO₃-Based Smart Windows by Continuous Li-Ion Insertion and Metal Electroplating

Abstract

The electrochromic WO3 smart window based on an aqueous electrolyte shows an excellent liquid/solid interface and thus can achieve a fast electrochromic response, while the aqueous electrolyte has a limited electrochemical window, which probably induces the H+ reduction and degrades the practical application. Here, we propose a strategy to modify the traditional Li+ acidic aqueous electrolyte by adding some selective inert metal ions, which not only improve the electrochromic performance but also avoid the possible production of hydrogen bubbles due to the broadened electrochemical window. Furthermore, reversible electroplating of inert metal ions will occur, leading to an enhanced optical transmission change of up to 77.5% at 500 nm and 70.4% at 700 nm. This combination of Li-ion insertion and metal electroplating in the ESW device makes it superior to all of the previous reports. The device also demonstrates high stability and high electrochromic efficiency after 1000 cycles. The current study not only emphasizes the rational design for aqueous electrolytes but also demonstrates a practical way to realize an excellent electrochromic window for practical applications.

Recent advances in electrochromic materials and devices for camouflage applications

“…For example, WO 3 , the most widely used inorganic EC material, exhibits only a monochromic color change from transparent to dark blue. 53 This problem can be effectively solved by the introduction of structural colors and the preparation of composite materials. 54,55 The great advantage of organic EC materials compared to inorganic materials is that the color can be tuned by means of molecular structural design.…”

Proton and Redox Couple Synergized Strategy for Aqueous Low Voltage-Driven WO3 Electrochromic Devices

“…25,37 Aqueous electrolytes often make it difficult for ECDs to operate consistently over long periods due to the reactive nature of water. 46,47 In the present work, all ECDs were tested for 5000 cycles. As can be seen from the current density curves (Figure S8), the NaClO 4 -ECD and LiClO 4 -ECD underwent a very significant decline, while the HClO 4 -ECD and HAc-ECD remained stable.…”

Design of Symmetric TiO2/LiI/TiO2 Electrochromic Devices for Gradient Shaded Smart Windows with Enhanced Switching and Cycling Properties

“…[10,11] In recent years, transition metal oxides such as WO 3−x , TiO 2−x , Nb 2 O 5−x , and their doped counterparts become candidates for commercialized smart windows. [12][13][14] TiO 2-x nanocrystal becomes a member of the family due to its dualband spectral change across the visible (vis) and near-infrared (NIR) regions, as well as ideal electrochemical and optical stabilities. TiO 2−x nanocrystals (NCs) are well-known Li + host materials because of their large ion-bearing capacity and can accommodate carrier concentrations exceeding 1.5 × 10 21 cm −3 upon charging.…”