Novel tunneled phosphorus-doped WO3 films achieved using ignited red phosphorus for stable and fast switching electrochromic performances

Review on recent progress in WO3-based electrochromic films: preparation methods and performance enhancement strategies

Transition metal oxides have drawn tremendous interest due to their unique physical and chemical properties. As one of the most promising electrochromic (EC) materials, tungsten trioxide (WO₃) has attracted great attention due to its exceptional EC characteristics. This review summarizes the background and general concept of EC devices, and key criteria for evaluation of WO₃-based EC materials. Special focus is placed on preparation techniques and performance enhancement of WO₃ EC films. Specifically, four methods - nanostructuring, regulating crystallinity, fabricating hybrid films, and preparing multilayer composite structures - have been developed to enhance the EC performance of WO₃ films. Finally, we offer some important recommendations and perspectives on potential research directions for further study.

Towards two-dimensional color tunability of all-solid-state electrochromic devices using carbon dots

Electrochromic devices (ECDs) that display multicolor patterns have gradually attracted widespread attention. Considering the complexity in the integration of various electrochromic materials and multi-electrode configurations, the design of multicolor patterned ECDs based on simple approaches is still a big challenge. Herein, it is demonstrated vivid ECDs with broadened color hues via introducing carbon dots (CDs) into the ion electrolyte layer. Benefiting from the synergistic effect of electrodes and electrolytes, the resultant ECDs presented a rich color change. Significantly, the fabricated ECDs can still maintain a stable and reversible color change even in high temperature environments where operating temperatures are constantly changing from RT to 70°C. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of intelligent and portable electronics.

Defect engineering tuning electron structure of biphasic tungsten-based chalcogenide heterostructure improves its catalytic activity for hydrogen evolution and triiodide reduction

The design and exploration of high-efficiency and low-cost electrode catalysts are of great significance to the development of novel energy conversion technologies. In this work, metal and nonmetal heteroatoms co-doped biphasic tungsten-based chalcogenide heterostructured catalyst (Co-WS₂/P-WO_2.9) with rich defects is successfully synthesized by a vulcanization technique. The electrocatalytic performance of WS₂/WO₃ in the hydrogen evolution reaction (HER) and triiodide reduction reaction is significantly enhanced by modifying and optimizing its electronic structure through a defect engineering strategy. As an electrocatalyst for HER, the optimized Co-WS₂/P-WO_2.9 exhibits a low overpotential at 10 mA cm^-2 of 146 and 120 mV with small Tafel slopes of 86 and 74 mV dec^-1 in alkaline and acidic electrolyte, respectively. In addition, a Co-WS₂/P-WO_2.9 assembled solar cell yields a short circuit current density of 15.85 mA cm^-2, an open-circuit voltage of 0.74 V, a fill factor of 0.66, and a competitive power conversion efficiency (7.83%), which is comparable or higher than conventional Pt-based solar cell (16.02 mA cm^-2, 0.70 V, 0.63, 7.14%). The formation of a heterostructure in Co-WS₂/P-WO_2.9 leads to the presence of a built-in electric field in the interfacial region between Co-WS₂ and P-WO_2.9, which leads to an increased open-circuit voltage from 0.70 V for Pt to 0.74 V for Co-WS₂/P-WO_2.9. This work can provide a technical support for developing high-performance heterostructured catalysts, which open up a way for improving catalytic performance of heterostructured catalysts in the field of electrocatalysis.

Controllable Electrodeposition Adjusts the Electrochromic Properties of Co and Mo Co-Modified WO3 Films

Metal ion modification is considered to be an effective way to construct metal oxides with specific physical and chemical properties. In this paper, we prepare a tungsten oxide (WO3) film co-modified by Co-ion and Mo-ion to serve as the electrochromic material through a one-step electrodeposition method. The effect of electrodeposition time on film thickness, surface morphology and electrochromic properties is systematically studied as well. The results show that, compared with pure WO3 film, the surface morphology of the tungsten oxide film modified by Co-ion and Mo-ion (WO3: Co, Mo) is significantly different. The Co and Mo co-modified film possesses a higher transmission modulation (58.5% at 600 nm) and rapid switching speed (coloring and bleaching time are 2.7 s and 5.6 s, respectively), low impedance value and excellent cycle stability. The performance enhancement is mainly attributed to the coral-like structure of the membrane, which provides a larger specific surface area, more ion adsorption sites and faster ion diffusion. Therefore, this work provides a fast and low-cost method to prepare tungsten oxide electrochromic films co-modified with cobalt and molybdenum ions. At the same time, it also provides an idea to obtain films with different electrochromic properties by adjusting the film thickness.

Advances in Electrochemical Energy Devices Constructed with Tungsten Oxide-Based Nanomaterials

Tungsten oxide-based materials have drawn huge attention for their versatile uses to construct various energy storage devices. Particularly, their electrochromic devices and optically-changing devices are intensively studied in terms of energy-saving. Furthermore, based on close connections in the forms of device structure and working mechanisms between these two main applications, bifunctional devices of tungsten oxide-based materials with energy storage and optical change came into our view, and when solar cells are integrated, multifunctional devices are accessible. In this article, we have reviewed the latest developments of tungsten oxide-based nanostructured materials in various kinds of applications, and our focus falls on their energy-related uses, especially supercapacitors, lithium ion batteries, electrochromic devices, and their bifunctional and multifunctional devices. Additionally, other applications such as photochromic devices, sensors, and photocatalysts of tungsten oxide-based materials have also been mentioned. We hope this article can shed light on the related applications of tungsten oxide-based materials and inspire new possibilities for further uses.

Net-Patterned Fluorine-Doped Tin Oxide to Accelerate the Electrochromic and Photocatalytic Interface Reactions

In this study, the surface morphology of net-patterned fluorine-doped tin oxide (FTO) films was optimized with mesh sizes (60 mesh, 40 mesh, and 24 mesh) using the one-pot horizontal ultrasonic spray pyrolysis deposition (HUSPD) process. The 40M-FTO sample exhibited optimized electrical and optical properties due to the improved crystallinity and net-patterned surface morphology of FTO. The electrochromic (EC) electrodes fabricated with 40M-FTO showed superior EC performance, including transmittance modulation (ΔT, 58.7%), switching speeds (4.1 s for coloration and 5.9 s for bleaching), and coloration efficiency (CE, 52.4 cm2/C). These optimum values were attributed to the combined effect of the enhanced electrical properties from the improved crystallinity of the SnO2 and the high transmittance with a large surface area stemming from the optimization of the net-patterned FTO surface morphology. Moreover, the improved reaction sites with large surface area and enhanced electrical conductivity can facilitate the photocatalytic reaction. Accordingly, we suggest our novel strategy for use in creating promising transparent conducting electrodes that can be fabricated with net-patterned FTO to realize enhanced electrochromic and photocatalytic interface reactions.

Multifunctional inorganic nanomaterials for energy applications

Our society has been facing more and more serious challenges towards achieving highly efficient utilization of energy. In the field of energy applications, multifunctional nanomaterials have been attracting increasing attention. Various energy applications, such as energy generation, conversion, storage, saving and transmission, are strongly dependent upon the electrical, thermal, mechanical, optical and catalytic functions of materials. In the nanoscale range, thermoelectric, piezoelectric, triboelectric, photovoltaic, catalytic and electrochromic materials have made major contributions to various energy applications. Inorganic nanomaterials' unique properties, such as excellent electrical and thermal conductivity, large surface area and chemical stability, make them highly competitive in energy applications. In this review, the latest research and development of multifunctional inorganic nanomaterials in energy applications were summarized from the perspective of different energy applications. Furthermore, we also illustrated the unique functions of inorganic nanomaterials to improve their performances and the combination of the functions of nanomaterials into a device. However, challenges may be traced back to the limitations set by scaling the relations between multifunctional inorganic nanomaterials and energy devices.

Enhanced electrochromic switches and tunable green fluorescence based on terbium ion doped WO3 films

Multifunctional WO₃-based materials have been increasingly attracting attention due to their unique physical and electrochemical nature. In this work, the luminescent species, terbium (Tb) ions, were first successfully doped into WO₃ films by a hydrothermal method to incorporate their electrochromic and photoluminescent functions. The amorphous state and porous net structure are introduced, which can be attributed to the inhibited orientation growth caused by the occupation of Tb ions in the WO₃ lattice. Here, the optimal 13% Tb-WO₃ film exhibits enhanced electrochromic properties: a high transmittance modulation of 66.71%; a fast response speed of less than 10 s; an improved CE value of 48.33 cm² C^-1 at 680 nm; and cycling stability over 600 cycles without obvious degradation, arising from its larger active surface area. Meanwhile, its green-colored emission could be realized under 260 nm UV light and is electro-switchable upon applying voltage.