A rapid and new technique describes synthesis technique of spherical and rod shaped tungsten trioxide (WO3) nanoparticles with similar band gap at visible wavelength. Acid catalyzed exothermic reaction and structure directing reagent follows the formation of two different morphologies and monoclinic WO3 phase. Rod shaped WO3 nanoparticle coated ITO glass electrode exhibits high current density at identical low voltage and scan rate due to its better adherence and coating uniformity in comparison with spherical nanoparticles. WO3-ITO electrode alters to blue tungsten bronze in color at low voltage, and further the color restores after removing the same applied voltage. 1. Introduction In recent years, different morphology nanostructured materials have stimulated great interest due to their importance in basic scientific research and technological applications [1, 2]. Tungsten trioxide (WO3), an important n-type semiconductor, has received much attention in the past few decades for it’s potential application in fabricating the miniature electrochromic and photochromic devices, gas sensors, and solar energy devices and also its usage as photoanode to generate hydrogen by photocatalytic splitting of water [3, 4]. The importance demands control over the dimension, size, and crystal structure of this class of particles for higher technology applications. Apart from being a promising electrochromic material, a great deal of effort has been made for improving the performance of WO3 films by several researchers. Thus, it is essential to control the morphology and also the surface coating over transparent coating oxide glass substrate [5]. Mostly, fabrication of WO3 films has been prepared by dip or spun coating of peroxopolytungstic acid on the Indium doped Tin Oxide (ITO) glass substrate and subsequent firing at optimum temperature [6, 7]. Leftheriotis et al. prepared sol-gel derived highly porous thick and opaque WO3 films. These films exhibited a similar reversible electrochromic property for 1st and 1000th cycle of cyclic voltammograms in 1？M LiClO4 with 0.2？mA/cm2 as current density [8]. Comparison of the electrochromic performance for orthorhombic rod and platelet type hydrated WO3 was investigated by Wei and Shen. Poly vinyl alcohol (PVA-124) and glacial acetic acid were used as structure directing agent and stabilizer for the preparation of single crystalline WO3 H2O nanorods, which exhibited highest current density of 40？mA/cm2 with fast response time and improved redox performance [5]. Peroxotungstic acid was used for the deposition of WO3.nH2O film on
References
[1]
X. Wang, J. Zhuang, Q. Peng, and Y. Li, “A general strategy for nanocrystal synthesis,” Nature, vol. 437, no. 7055, pp. 121–124, 2005.
[2]
J. Park, J. Joo, G. K. Soon, Y. Jang, and T. Hyeon, “Synthesis of monodisperse spherical nanocrystals,” Angewandte Chemie—International Edition, vol. 46, no. 25, pp. 4630–4660, 2007.
[3]
H. Zheng, J. Z. Ou, M. S. Strano, R. B. Kaner, A. Mitchell, and K. Kalantar-Zadeh, “Nanostructured tungsten oxide—properties, synthesis, and applications,” Advanced Functional Materials, vol. 21, no. 12, pp. 2175–2196, 2011.
[4]
J. Ma, J. Zhang, S. Wang et al., “Topochemical preparation of WO3 nanoplates through precursor H2WO4 and their gas-sensing performances,” Journal of Physical Chemistry C, vol. 115, no. 37, pp. 18157–18163, 2011.
[5]
X. Wei and P. K. Shen, “Electrochromics of single crystalline WO3 H2O nanorods,” Electrochemistry Communications, vol. 8, no. 2, pp. 293–298, 2006.
[6]
A. Chemseddine, F. Babonneau, and J. Livage, “Anisotropic WO3 nH2O layers deposited from gels,” Journal of Non-Crystalline Solids, vol. 91, no. 2, pp. 271–278, 1987.
[7]
P. Judeinstein and J. Livage, “Electrochromic properties of sol-gel derived WO3 coatings,” in Sol-Gel Optics, vol. 1328 of Proceedings of SPIE, pp. 344–351, July 1990.
[8]
G. Leftheriotis, S. Papaefthimiou, P. Yianoulis, A. Siokou, and D. Kefalas, “Structural and electrochemical properties of opaque sol-gel deposited WO3 layers,” Applied Surface Science, vol. 218, no. 1–4, pp. 275–280, 2003.
[9]
P. K. Biswas, N. C. Pramanik, M. K. Mahapatra, D. Ganguli, and J. Livage, “Optical and electrochromic properties of sol-gel WO3 films on conducting glass,” Materials Letters, vol. 57, no. 28, pp. 4429–4432, 2003.
[10]
Z. Jiao, X. Wang, J. Wang et al., “Efficient synthesis of plate-like crystalline hydrated tungsten trioxide thin films with highly improved electrochromic performance,” Chemical Communications, vol. 48, no. 3, pp. 365–367, 2012.
[11]
Y. Zhang, Y. Chen, H. Liu et al., “Three-dimensional hierarchical structure of single crystalline tungsten oxide nanowires: construction, phase transition, and voltammetric behavior,” Journal of Physical Chemistry C, vol. 113, no. 5, pp. 1746–1750, 2009.
[12]
Z. Gu, T. Zhai, B. Gao et al., “Controllable assembly of WO3 nanorods/nanowires into hierarchical nanostructures,” Journal of Physical Chemistry B, vol. 110, no. 47, pp. 23829–23836, 2006.
[13]
D. Sarkar, “Synthesis and properties of BaTiO3 nanopowders,” Journal of the American Ceramic Society, vol. 94, no. 1, pp. 106–110, 2011.
[14]
J. K. Kim, K. Shin, S. M. Cho, T.-W. Lee, and J. H. Park, “Synthesis of transparent mesoporous tungsten trioxide films with enhanced photoelectrochemical response: application to unassisted solar water splitting,” Energy and Environmental Science, vol. 4, no. 4, pp. 1465–1470, 2011.
[15]
B. Yang, Y. Zhang, E. Drabarek, P. R. F. Barnes, and V. Luca, “Enhanced photoelectrochemical activity of sol-gel tungsten trioxide films through textural control,” Chemistry of Materials, vol. 19, no. 23, pp. 5664–5672, 2007.
[16]
K. Bange, “Colouration of tungsten oxide films: a model for optically active coatings,” Solar Energy Materials and Solar Cells, vol. 58, no. 1, pp. 1–131, 1999.
[17]
M. A. Butler, “Photoelectrolysis and physical properties of the semiconducting electrode WO2,” Journal of Applied Physics, vol. 48, no. 5, pp. 1914–1920, 1977.
[18]
M. Regraguia, M. Addoua, A. Outzourhitc, E. E. Idrissia, A. Kachouanea, and A. Bougrinea, “Electrochromic effect in WO3 thin films prepared by spray pyrolysis,” Solar Energy Materials and Solar Cells, vol. 77, no. 4, pp. 341–350, 2003.
