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

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 (WO₃) nanosheets possess great potential in electrochemical applications, particularly in electrochromic (EC) devices. However, feasible production of 2D WO₃ nanosheets is challenging due to the innate 3D crystallographic structure of WO₃. Here we report a novel solution-phase synthesis of 2D WO₃ nanosheets through simple oxidation from 2D tungsten disulfide (WS₂) nanosheets exfoliated from bulk WS₂ powder. The complete conversion from WS₂ into WO₃ was confirmed through crystallographic and elemental analyses, followed by validation of the 2D WO₃ 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 WO₃ 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 WO₃ components. In the future, 2D WO₃ nanosheets could also be used for other promising applications such as sensors, catalysis, thermoelectric, and energy conversion.