Physical Simulation Model of WO₃ Electrochromic Films Based on Continuous Electron-Transfer Kinetics and Experimental Verification

Abstract

Tungsten oxide (WO 3 ) electrochromic devices have attracted a lot of interest in the energy conservation field and have shown a preliminary application potential in the market. However, it is difficult to quantitatively direct experiments with the existing electrochromic theoretical models, which can restrict the further development of electrochromism. Here, an electrochromic physical simulation model of WO 3 films was built to solve the above problem. Experimentally, the actual electrochromic kinetics of WO 3 in the LiClO 4 /propylene carbonate electrolyte was determined as a continuous electron-transfer process by cyclic voltammetry measurement and X-ray photoelectron spectroscopy analysis. Theoretically, the continuous electron-transfer process, Li + -ion diffusion process, and the transmittance change process were described by a modified Butler−Volmer equation, Fick's law, and charge versus coloration efficiency/bleaching efficiency coupling equation, respectively. The comparisons between theoretical and experimental data were conducted to verify this model. The shape of the simulated current curves was basically consistent with that of experiments. Besides, the difference of transmittance between the simulation and experiments was less than 8%. The difference between theory and experiment was attributed to the influence of the electric double layer and the actual reaction interface. The success of the simulation was attributed to the accurate description of the electrochromic process by continuous electron-transfer kinetics. This model can be applied in the research of electrochromic mechanisms, experimental result prediction, and novel device development due to its clear physical nature.

Wide-Spectrum Modulated Electrochromic Smart Windows Based on MnO2/PB Films

“…Energy saving, environmental protection, and green low-carbon living and technology have become crucially important not only to the environment but also to human health. − Buildings are responsible for about 40% of the world’s total annual energy consumption due to increased needs in interior lighting, cooling/heating, and ventilation. − An electrochromic smart window (ECW) offers dynamic and tunable transmission in response to a low voltage. − It can reduce energy consumption in buildings and simultaneously improve indoor comfort and offer an aesthetic design …”

Application of Tungsten-Oxide-Based Electrochromic Devices for Supercapacitors

“…With the continued interest in environmental protection and energy conservation, electrochromic technology with low voltage drive and dynamic control of solar heat and light input to buildings is developing rapidly as a very promising energy-saving technology [1][2][3][4][5][6][7]. Products such as smart windows, anti-glare mirrors, and aircraft portholes all involve electrochromic technology, which is already common in our daily life [3,8,9]. According to a study by David R. Roberts of the US Renewable Energy Laboratory, residential homes with electrochromic smart windows save 9.1% in total energy consumption and 13.5% in electricity consumption compared to homes with low-e glass and shaded glass [10].…”

“…[Reprinted with permission from Ref. [9] Copyright {2021} American Chemical Society.] General Electric patented the first supercapacitor in 1958, which used activated carbon as a substrate, where charge was not exchanged between the electrode and the electrolyte, and where the electrode simply stored charge.…”

“…Diagram showing the rate-determining step in the continuous electron-transfer process [9]. [Reprinted with permission from Ref [9]. Copyright {2021} American Chemical Society.…”

Determination of W(V) in WO3 Photochromism Using Localized Surface Plasmon Resonance of Ag Nanoparticles

“…The blue coloration occurs because of the absorption from the red region of the visible light to the near-infrared region. Among them, WO 3 is the most studied material due to the electrochemical reversibility and stability for a practical application such as smart windows, which control solar radiation transmitted through the windows. − Many efforts have been made to enhance the electrochromic performance by combining with conducting materials such as graphene and conductive polymers. , An important factor in estimating the electrochromic performance is the coloration efficiency, i.e., the change in optical density divided by charge density which is consumed per unit electrode area . High coloration efficiency means a large optical modulation range with small charge intercalation or extraction.…”