Novel High-Performance and Low-Cost Electrochromic Prussian White Film

Preparation of Electrochromic Hydrogels Based on Anderson-Type POMs-Viologen Compounds with Photochromic and Thermochromic Properties

Currently, color-changing materials with multiple responses have emerged as a prominent research focus. In this work, two Anderson-type POMs-viologen compounds were successfully synthesized under solvothermal conditions, namely, (1,3-bcby)·[AlMo6(OH)6O18]·(en)0.5·H2O (1) and (1,3-bcby)·[Co2(H2O)6TeMo6O24]·2H2O (2) (1,3-bcby = 1,1'-bis(3-cyanobenzyl)-4,4'-bipyridine dichloride, en = ethylenediamine). Compound 1 shows a two-dimensional supramolecular lattice structure through the hydrogen bonding of dissociated water molecules. In compound 2, by utilizing the connection of Co atoms, a two-dimensional layered framework is constructed. Owing to the widespread application of viologen compounds in color-changing materials, an investigation was performed for exploration of the photochromic and thermochromic responses of 1 and 2 upon exposure to light and heat. The study reveals that compound 1 exhibits an exceptional reversible photochromic property, while compound 2 demonstrated equally impressive thermochromic behavior. The filter paper prepared by compound 1 was successfully applied to ink-free, erasable printing. Furthermore, ECH-1 and ECH-2 (two types of electrochromic hydrogels), were prepared through varying concentrations of compounds 1 and 2. Notably, ECH-1 exhibits a rapid response time and substantial coloring efficiency. ECH-1 and ECH-2 have been integrated into smart windows, demonstrating their capacity to modulate indoor temperatures effectively.

Homogeneous and Nanogranular Prussian Blue to Enable Long-Term-Stable Electrochromic Devices

The increasing demand for the state-of-the-art electrochromic devices has received great interest in synthesizing Prussian blue (PB) nanoparticles with a uniform diameter that exhibit excellent electrochromism, electrochemistry, and cyclability. Herein, we report the controllable synthesis of sub-100 nm PB nanoparticles via the coprecipitation method. The diameter of PB nanoparticles can be modulated by adjusting the reactant concentration, the selection of a chelator, and their purification. The self-assembled nanogranular thin films, homogeneously fabricated by using optimized PB nanoparticles with an average diameter of 50 nm as building blocks via the blade coating technique enable excellent performance with a large optical modulation of 80% and a high coloration efficiency of 417.79 cm2 C-1. It is also demonstrated by in situ and ex situ observations that the nanogranular PB thin films possess outstanding structural and electrochemical reversibility. Furthermore, such nanogranular PB thin films can enjoy the enhanced long-term cycling stability of the PB-WO3 complementary electrochromic devices having a 91.4% optical contrast retention after 16,000 consecutive cycles. This work provides a newly and industrially compatible approach to producing a complementary electrochromic device with extraordinary durability for various practical applications.

Flexible Inorganic All-Solid-State Electrochromic Devices toward Visual Energy Storage and Two-Dimensional Color Tunability

Multicolor display has gradually become a sought-after trend for electrochromic devices due to its broadened application scope. Meanwhile, the advantages of inorganic electrochromic devices such as stable electrochemical performance and good energy storage ability also have great attraction in practical production applications. However, there are still huge challenges for inorganic electrochromic materials to achieve multicolor transformation due to their single-color hue change. Herein, we design an inorganic and multicolor electrochromic energy storage device (MEESD) exhibiting flexibility and all-solid-state merits. Prussian blue (PB) and MnO₂, as the asymmetrical electrodes of this MEESD, show good pseudocapacitance property, matching charge capacity, and obvious color change. As a typical electrochromic device, the MEESD shows a fast response of 0.5 s and good coloration efficiency of 144.2 cm²/C. As an energy storage device, the MEESD presents excellent rate capability and volumetric energy/power density (84.2 mWh cm^-3/23.3 W cm^-3). Its energy level can be visually monitored by color contrast and optical modulation. In the charging/discharging process, its color can obviously change to various degrees of yellow, green, and blue along with 40% wide optical modulation at 710 nm. Meanwhile, the stability of the MEESD in a common and humidity environment was analyzed in detail from electrochemical, optical, and energy storage aspects. This work provides feasible thoughts to design multifunctional electrochromic devices integrated with inorganic, flexible, all-solid-state, multicolor, and energy storage properties.

Synergistic Electric and Thermal Effects of Electrochromic Devices

Electrochromic devices are the preferred devices for smart windows because they work independently of uncontrollable environmental factors and rely more on the user's personal feelings to adjust actively. However, in practical applications, the ambient temperature still has an impact on device performance, such as durability, reversibility and switching performance, etc. These technical issues have significantly slowed down the commercialization of electrochromic devices (ECDs). It is necessary to investigate the main reasons for the influence of temperature on the device and make reasonable optimization to enhance the effectiveness of the device and extend its lifetime. In recent years, with the joint efforts of various outstanding research teams, the performance of electrochromic devices has been rapidly improved, with a longer lifetime, richer colors, and better color contrast. This review highlights the important research on temperature-dependent electrochromic properties in recent years. Also, the reported structures, mechanisms, characteristics, and methods for improving electrochromic properties are discussed in detail. In addition, the challenges and corresponding strategies in this field are presented in this paper. This paper will inspire more researchers to enrich the temperature-dependent properties of ECDs and their related fields with innovative means and methods to overcome the technical obstacles faced.