Two-dimensional oxygen vacancy-doped tungsten oxide hydrate nanosheets for high-performance electrochromic device

Facile fabrication of advanced tungsten oxide (WO3) or WO3 hydrate materials with superior electrochemical and electrochromic properties is of great value in energy-related applications. Self-doping (oxygen vacancy doping) and nanostructure regulation are considered efficient strategies to enhance the performance of bulk WO3 materials. Herein, novel WO3-x hydrate nanosheets were prepared by a one-pot template/surfactant-free solvothermal method employing Na2WO4·2H2O as precursors and ethanol as solvent. The morphology, structure, and composition of the prepared WO3-x hydrate nanosheets were demonstrated by TEM, AFM, XRD, Raman spectrum, and XPS. Furthermore, WO3-x hydrate nanosheets films with mesostructured architecture were formed on FTO glass substrates by the dip-coating process, which exhibited excellent electrochemical and electrochromic performance. As a proof-of-concept example, an analog smart window device (ASWD) was assembled by using the WO3-x hydrate nanosheet film on FTO glass as the working electrode, an FTO glass as the counter electrode, and LiClO4 in propylene carbonate as the electrolyte. The fabricated ASWD presented fascinating electrochromic performance with a wide optical modulation range (82.1%) at the wavelength of 670 nm, moderate switching time (9.6/10.4 s for bleaching/coloration), high coloration efficiency (111.8 cm2/C) and good cyclic stability (maintains 71.6% of the maximum dynamic modulation range after 1000 cycles). Ascribed to the easy preparation process and outstanding electrochromic properties, this kind of WO3-x hydrate nanosheet and its corresponding electrochromic devices are believed to have great potential applications in energy-saving engineering.