Synthesis and Electrochromic Characterization of Graphene/V₂O₅/MoO₃Nanocomposite Films

Abstract

Graphene/V 2 O 5 /MoO 3 (GVM) films were fabricated by the sol-gel method. The structure, electrochemical and electrochromic properties were investigated by means of X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), cyclic voltammetry, chronoamperometry and UV-Visible spectrophotometer. The optical modulatory range of the GVM film was enlarged to 25.35%, which is 1.38 times larger than that of V 2 O 5 (V) films. The cyclic stability is improved significantly and the films perform well in the response rate. The bleaching time is 1.25 seconds, and the coloration time is 1.40 seconds. These results demonstrate that the GVM films are excellent candidates for the fast switching electrochromic materials. © 2016 The Electrochemical Society. [DOI: 10.1149/2.0031610jss] All rights reserved.Manuscript submitted May 24, 2016; revised manuscript received August 15, 2016. Published September 3, 2016 Electrochromism (EC) is a phenomenon in which materials are capable of changing their optical properties in a reversible and persistent way under the action of an electric field.1-3 Among the varieties of electrochromic materials, vanadium pentoxide (V 2 O 5 ) is one of the most promising electrochromic inorganic materials due to its exceptional electrochromic behavior. 4 Especially V 2 O 5 has not only both anodic and cathodic electrochromic properties but also large charge capacity.5,3 Furthermore, the V 2 O 5 -based films which contain mixed valence vanadium (V 5+ and V 4+ ) possess the multi-electrochromic behavior.6 However, the vanadium pentoxide (V 2 O 5 ) xerogel with ntype semiconducting properties has some disadvantages comparing with other metal oxides, such as low electrical conductivity, poor coloration efficiency and narrow color variation. Meanwhile, it shows a bad cycle stability by virtue of the interaction between the inserted Li + ions and the host structure of V 2 O 5 . 7,8All of these drawbacks prevent the commercialization of V 2 O 5 -based electrochromic devices, therefore various efforts have been made in order to improve their electrochromic and electrochemical properties. One of the effective ways to improve the electrochemical and electrochromic properties of V 2 O 5 is doped with other materials or combining with other electrochromic films.9 Previous report suggests that the doping of titanium ion (Ti 4+ ) could enhance the electrical conductivity of the film at room temperature.10 While the doping of CeO is responsible for the improvement of the cycling durability.11 Other studies showing the doping of the high-valence cations (W 6+ , Mo 6+ ) could increase the optical and electrical conductivity.12,13 MoO 3 is one of the main objects of electrochromic materials.14,15 It offers higher coloration efficiency and has richer colors. 16 The interaction between V 2 O 5 and MoO 3 is unique because their ionic radii and the structure in their highest oxidation state are similar.17 When the molybdenum ion (Mo 6+ ) was intercalated, the Mo 6+ generated a donor-like defect owing to providing quasi...

Low-Cost and Facile Synthesis of the Vanadium Oxides V2O3, VO2, and V2O5and Their Magnetic, Thermochromic and Electrochromic Properties

“…Indeed, facile intercalationdesintercalation of Li + ions into the V2O5 interlayer spaces leads to redox phenomena associated with reversible changes of the optical properties. As far as we know, vanadium pentoxide is the typical oxide that shows both anodic and cathodic colorations, even if the literature pointed up other compositions such as mixed oxides based on vanadium [34][35][36][37] thus offering the possibility of obtaining multicolor displays [30][31][32][33] . However, the lithiation process in V2O5 bulk is reported to be relatively limited due to a combination of low electrical conductivity (10 -3 -10 -2 S.m -1 ) and small Li + diffusion coefficients (10 -13 -10 -12 cm 2 .s -1 ) [29][30][31]33 .…”

“…Because of its anisotropic structural framework based on pentacoordinated vanadium (with square-pyramidal geometry), forming a “lamellar” structure (planes of edge-sharing pyramids isolated from each other with a interlayer length of about 4 Å), V 2 O 5 is one of the most popular materials for electrochromic applications. ,,,− Indeed, facile intercalation–desintercalation of Li + ions into the V 2 O 5 interlayer spaces leads to redox phenomena associated with reversible changes of the optical properties. As far as we know, vanadium pentoxide is the typical oxide that shows both anodic and cathodic colorations, even if the literature has pointed out other compositions such as mixed oxides based on vanadium, − thus offering the possibility of obtaining multicolor displays. − However, the lithiation process in V 2 O 5 bulk is reported to be relatively limited due to a combination of low electrical conductivity (10 –3 –10 –2 S m –1 ) and small Li + diffusion coefficients (10 –13 –10 –12 cm 2 s –1 ). − , …”

Using an Atmospheric Pressure Chemical Vapor Deposition Process for the Development of V2O5 as an Electrochromic Material

“…The maximum current density obtained for the as-grown coating at 550 • C (Figure 6) was lower than the colloidal crystal-assisted electrodeposited amorphous three-dimensional ordered macroporous (0.5 mA·cm −2 [4]), sol-gel (0.6 mA·cm −2 [16]), aerosol-assisted CVD (1.5 mA·cm −2 [34]) V 2 O 5 , and was comparable with APCVD (0.01 mA·cm −2 [18]) and hydrothermal growth (0.05 mA·cm −2 [17]) of V 2 O 5 . This value was also lower than the one obtained from the vacuum deposited (0.6 mA·cm −2 [35]) tungsten trioxide (WO 3 ), and comparable with APCVD (0.02 mA·cm −2 [36]), evaporation-induced self-assembly (0.06 mA·cm −2 [37]), low-pressure CVD (0.08 mA·cm −2 [38]), and hydrothermal (0.04 mA·cm −2 [39]) growth WO 3 .…”

“…Electrochromic V 2 O 5 coatings have been prepared by electrodeposition [11,12], "Doctor Blade" [13], reactive sputtering [14], polyol process [15], sol-gel [16], and hydrothermal growth [17]. Strategies…”

The determination of electrolyte stability and conditions for electrochromic WO3 films deposition

“…The color change of these materials is a result of an electrochemical reaction. The initial state, which is usually transparent, changes to colored as a result of electrochemical reduction (the so-called cathodic materials) [3,4] or electrochemical oxidation (the so-called anodic materials) [5,6]. The tungsten trioxide is a well-known cathodic material [7].…”