Improved Electrochromic Properties of Vanadium Pentoxide Nanorods Prepared by Thermal Treatment of Sol-Gel Dip-Coated Thin Films

Abstract

Porosity in the sol-gel prepared vanadium pentoxide film is created by using templating methods. The morphology, optical and electrochromic properties of the macro-and mesoporous films, prepared in the presence of structure-directing agents such as polystyrene microspheres and triblock copolymer, have been compared with those of dense films. By using various methods to remove the template material, it was shown that the morphology of the vanadium pentoxide film can be controlled and new nanostructures can be created. The transformation of the lamellar into a nanorod structure, observed when the film is heated at 375-500 • C for several hours, resulted in the development of an elegant method for the synthesis of vanadium oxide nanostructures. The electrochromic performance of the nanorods prepared through the thermal treatment was found to be superior to that of the vanadium pentoxide with the layered structure, especially in the near-infrared region, demonstrating their potential for electrochromic applications.Due to the large lithium intercalation capacity, sol-gel derived vanadium pentoxide (V 2 O 5 ) has generated a significant research interest. V 2 O 5 gels can be used in energy storage/conversion devices such as electrochromic (EC) devices, rechargeable lithium ion battery technologies, and pseudocapacitor applications. 1-3 In addition, vanadium pentoxide showed good sensing and catalytic properties. 4 Vanadium pentoxide xerogel films have a layered structure; ions and molecules can be easily intercalated between adjacent layers without changing its structural integrity. Ion insertion/extraction is facilitated by the large contact area with the electrolyte and small sizes of nanostructures. Using nanostructured vanadium pentoxide with various morphologies in EC devices is expected to enhance their characteristics because of the inherently high surface area to volume ratio and short diffusion paths that facilitate ion and electron transfer.Among the different nanostructures for lithium intercalation applications, vanadium pentoxide nanotubes and nanorods have been found to be the most promising, especially as electrode material for lithium ion batteries. 5 Tubular host matrices for lithium intercalation have been prepared by using a sol-gel method, in combination with adequate structuredirecting molecules. The fabrication of vanadium oxide in a tubular form was first accomplished by Ajayan et al. in 1995 6 by using carbon nanotubes as templates. Later on, a new soft-chemistry (sol-gel) method was developed by Nesper et al. using vanadium oxide precursors and alkyl amines or α,ω-diamines with long alkyl chains as templates. Nanotubes were obtained in a high yield, after aging and a hydrothermal treatment. 7-11 They could be obtained from an ammonium metavanadate precursor as well, and a rolling mechanism for the formation of vanadium oxide nanotubes from lamellar structures has been described by Chen et al. 12 They have a scroll-type morphology and the vanadium oxide layers inside the walls have been found t...

Solution Processable Metal Oxide Thin Film Deposition and Material Growth for Electronic and Photonic Devices

“…The Raman scattering spectra for a dip‐coated V 2 O 5 thin film on ITO substrates deposited by Alsawafta et al is shown in Figure b, where the precursor solution was prepared from a mixture of vanadium oxytriisopropoxide, IPA and acetic acid . The Raman scattering spectra in Figure b shows the thin films in an as‐deposited state prior to annealing where no distinct Raman modes indicative of orthorhombic V 2 O 5 are noted, but are subsequently observed after crystallization at 500 °C …”

“…While the precursor that comprises two solutions may be the same, the mixture ratio of the individual components, alkoxide/solvent for example, is often altered for the specific purpose of the experiment. Chen et al prepared a vanadium pentoxide (V 2 O 5 ) alkoxide precursor solution for forming thin films with an IPA‐Alkoxide‐H 2 O mixture ratio of 76‐1‐19, whereas the same precursor solution is also used by others at different IPA‐Alkoxide ratios of 9‐1, 25‐1 and 100–1 . In each case, a V 2 O 5 thin film was formed from an alkoxide precursor solution where a best‐fit ratio can be chosen in order to attain desired deposit morphologies.…”

“…b) Raman scattering spectra of dip‐coated V 2 O 5 thin films as‐deposited (black) and annealed at both 300 °C (blue) and 500 °C (red). Reproduced with permission . Copyright 2015, The Electrochemical Society.…”

Subzero Temperature Dip-Coating of Sol-Gel Vanadium Pentoxide: Effect of the Deposition Temperature on the Film Structure, Morphology, and Electrochromic Properties

“…It has been reported that template sol-gel prepared vanadium oxide films yield, after removing the template, meso-(pores in the size range of 2 to 20 nm) or macroporous films with significantly enhanced electrochromic properties [23][24][25][26][27][28][29][30][31][32]. The morphology and optical and electrochromic properties of the macro-and mesoporous films, prepared in the presence of structure-directing agents, have been compared with those of dense films [23]. The transformation of the lamellar into a nanorod structure, observed when the film is heated at 400-500 ∘ C for several hours, resulted in the development of an elegant method for the synthesis of vanadium oxide nanorods [23].…”

Tungsten oxide–cellulose nanocrystal composite films for electrochromic applications

“…One of the more commonly utilized sol-gel methods is based on the reaction of the metallic tungsten with hydrogen peroxide that results in the formation of stable solutions of peroxopolytungstic acid, which contains the ðW 2 O 11 Þ 2− anion. [20][21][22][23] By using a dip-coating deposition technique and suitable annealing temperatures, our group and others have prepared nanostructured thin films of tungsten oxide and its golddoped composites that have very good EC properties.…”