Construction and characterization of tunable meso-/macroporous tungsten oxide-based transmissive electrochromic devices
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Recent developments in the processing of porous transition metal oxide thin films have opened up new opportunities in the construction of electrochromic (EC) devices with enhanced properties. Tungsten oxide (WO3) is one of the most promising materials for EC devices. In this work, we report on the synthesis of meso-/macroporous WO3 thin films using tungstic acid as precursor and organically modified silane (ORMOSIL) as a templating agent. Calcination of the film at 500 °C resulted in nanocrystalline monoclinic tungsten oxide (m-WO3) with crystallite sizes of ~16 nm. The meso-/macroporous structure is retained after calcination. An asymmetric EC device based on the meso-/macroporous m-WO3 thin film was constructed. Thus constructed EC device was characterized by micro-Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction (XRD). Detailed micro-Raman and XRD studies of the intercalation and deintercalation of lithium (Li) in the meso-/macroporous m-WO3 layer of the EC device as a function of the applied voltage were performed. The meso-/macroporous WO3 layer, which was found to be monoclinic before Li intercalation, transforms to its higher symmetric phase of tetragonal and toward cubic phase when Li is intercalated into it. Upon complete deintercalation, these phase transitions were reversed and m-WO3 is recovered. Optical transmission studies were performed in conjunction with Raman and XRD studies. This study shows that meso-/macroporous m-WO3 layer-based EC device exhibit a high color contrast during the coloration and bleaching.
KeywordsRaman Spectrum Tungsten Oxide Templating Agent Tungstic Acid Coloration Potential
The financial support of the Research Assistantships Initiative of New Brunswick Innovation Fund (NBIF), the Atlantic Innovation Fund (AIF—Round II), and National Science and Engineering Research Council (NSERC) of Canada is gratefully acknowledged. We thank Dr. Louise Weaver (Microscopy Microanalysis Facility, University of New Brunswick, Fredericton, NB, Canada) for the TEM measurements, and Zoulika Hadj—Sadok (Laboratoire de Chimie des matériaux inorganiques – FUNDP, Namur, Belgique) for BET and thermogravimetric measurements.
- 1.Granqvist CG (1995) Handbook of inorganic electrochromic materials. Elsevier, New YorkGoogle Scholar
- 23.Powder Diffraction Files Inorganic and Organic (Cards No: 43–1035 (Monoclinic-WO3), No: 89–1287 (tetragonal-WO3)) (1996) JCPDS-International Centre for Diffraction Data, PDF2 Data Base, SwarthmoreGoogle Scholar