High-Performance Electrochromic Devices from Two-Dimensional WO₃ Nanosheets

Professor Seokwoo Jeon and his research team are working on the development of the two-dimensional (2D) WO₃ nanosheets for high-performance electrochromic (EC) devices. Two-dimensional WO₃ nanosheets are one of the best possible candidates for high-performance EC devices, due to higher surface area of the active material and extraordinary color-contrast. However, unlike other layered materials such as graphite or transition metal chalcogenides, exfoliation of 2D WO₃ from the bulk WO₃ counterpart is not successful because of the strong atomic bonding in the out-of-plane direction in the WO₃ crystal system. The absence of direct exfoliating methods of 2D WO₃ nanosheets from bulk WO₃ materials limits the use of such materials.

Herein, the research team demonstrated a novel strategy for solution phase synthesis of highly-crystalline and high-aspect-ratio 2D WO₃ nanosheets through sequential exfoliation and oxidation of layered WS2 powders for the first time. The water dispersed 2D WO₃ material can easily be coated on a conducting substrate to fabricate high-performance EC devices in a cost-effective manner for commercialization. From a performance point of view, 2D WO₃ nanosheets EC device showed color modulation 3.43 fold higher (62.57% at 700 nm wavelength), while also showing ∼46.62% and ∼62.71% faster switching response-time (coloration and bleaching), compared to the value of the conventional device using bulk WO₃ powder. Extraordinary device performance was shown by 2D WO₃ nanosheets because of fast electrolyte ion diffusion through more accessible 2D permeable channels, created by thin nanosheets of the device. Furthermore, the 2D WO₃ nanosheet EC device also showed exceptional stability, with no significant fading of capacitance after 1000 cycles, proving robustness to the developed EC device.

Finally, in a broader scope, this work has unveiled a guideline for synthesizing two-dimensional transition metal oxides (WO₃, MoO₃, TiO₂, and so on) for application to high-performance EC devices, as well as a potential wider range of electrochemical and optoelectronics applications.