Two-Dimensional WO₃ Nanosheets Chemically Converted from Layered WS₂ for High-Performance Electrochromic Devices

Abstract

Two-dimensional (2D) transitional metal oxides (TMOs) are an attractive class of materials due to the combined advantages of high active surface area, enhanced electrochemical properties, and stability. Among the 2D TMOs, 2D tungsten oxide (WO) nanosheets possess great potential in electrochemical applications, particularly in electrochromic (EC) devices. However, feasible production of 2D WO nanosheets is challenging due to the innate 3D crystallographic structure of WO. Here we report a novel solution-phase synthesis of 2D WO nanosheets through simple oxidation from 2D tungsten disulfide (WS) nanosheets exfoliated from bulk WS powder. The complete conversion from WS into WO was confirmed through crystallographic and elemental analyses, followed by validation of the 2D WO nanosheets applied in the EC device. The EC device showed color modulation of 62.57% at 700 nm wavelength, which is 3.43 times higher than the value of the conventional device using bulk WO powder, while also showing enhancement of ∼46.62% and ∼62.71% in switching response-time (coloration and bleaching). The mechanism of enhancement was rationalized through comparative analysis based on the thickness of the WO components. In the future, 2D WO nanosheets could also be used for other promising applications such as sensors, catalysis, thermoelectric, and energy conversion.

Simplified All‐Solid‐State WO3 Based Electrochromic Devices on Single Substrate: Toward Large Area, Low Voltage, High Contrast, and Fast Switching Dynamics

“…[35][36][37] Recent reports of Azam et al, [35] showed for EC device based on 2D WO 3 nanosheets an optical modulation of 62.57% during +3 V (bleached state) and −3 V (colored state) and a color-switching response-time of 6.97 s for bleaching and 10.74 s for coloration, whereas Huo et al, [36] observed for devices based on hexagonal/amorphous WO 3 core/shell nanorod arrays an optical modulation of 67.7%, and response times of 15 s for coloring and 21 s for bleaching (±3 V), outperforming performances of ECDs based on pure hexagonal WO 3 nanorods. [35][36][37] Recent reports of Azam et al, [35] showed for EC device based on 2D WO 3 nanosheets an optical modulation of 62.57% during +3 V (bleached state) and −3 V (colored state) and a color-switching response-time of 6.97 s for bleaching and 10.74 s for coloration, whereas Huo et al, [36] observed for devices based on hexagonal/amorphous WO 3 core/shell nanorod arrays an optical modulation of 67.7%, and response times of 15 s for coloring and 21 s for bleaching (±3 V), outperforming performances of ECDs based on pure hexagonal WO 3 nanorods.…”

Flexible and High-Performance Electrochromic Devices Enabled by Self-Assembled 2D TiO2/MXene Heterostructures

“…The absorption coefficient change Δα can be obtained by Δα = αcαb ≈ [ln(Tc/Tb)]/L, which is a physical parameter independent of geometries of the film, thus can be used to compare different technologies. Δα of the LLIA TiO2 film is extracted to be 0.12 nm -1 , which is almost one order of magnitude higher than the previously reported TiO2-based EC materials assembled by other methods (Table S4) (20,(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54), suggesting a very high utilization of TiO2 in the LLIA films during the EC process.…”

“…First, these inorganic materials are long-lasting and robust against environmental factors such as high temperature, ultraviolet radiation, and mechanical wear (15)(16)(17), as compared to their organic counterparts (18). Second, the nanostructured TMO network, especially in the form of 2D nanosheets, improves electrical and ionic transport significantly, because: (a) the increased surface-to-volume ratio of nanosheets as compared to the bulk forms leads to larger interface areas with the electrolyte and the shorter ion diffusivity pathways within the nanostructured channels (3,19); and (b) the 2D formation of the nanostructures makes the contact area between adjacent nanosheets much bigger than that between 1D or 0D structures (nanowires or quantum dots) (20), which promotes the inter-nanosheets electron transfer (21). Finally, networks of 2D nanostructures also helps to redistribute the induced strain more evenly, thus improving both the mechanical strength and the flexibility of the film, which is fundamentally more advantageous than 1D or 0D nanostructures (22).…”

Layered Ternary and Quaternary Transition Metal Chalcogenide Based Catalysts for Water Splitting

“…In recent years, there has been increasing attention on renewable and environmentally friendly energy devices and energy sources as alternatives to fossil fuels [1,2]. In materials science research, two-dimensional (2D) layered materials such as graphene, transition metal chalcogenides (TMCs), MXenes and phosphorene have been heavily researched for many of these energy applications, including solar cells, batteries, light-emitting diodes, thermoelectric generators and so forth [3][4][5][6][7][8]. These layered 2D materials have also been studied as efficient catalysts for the production of hydrogen, which has been proposed as the ideal energy carrier by virtue of its highest gravimetric energy density with zero emission of carbon dioxide [9,10].…”