Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Abstract

The electrochromic properties of 90:10 WO 3 /TiO 2 thin films produced by anodizing co-sputtered W/Ti films in a fluorinated ethylene glycol solution are investigated in relation to corresponding pure WO 3 films. SEM images revealed that the TiO 2 content resulted in a more open honey-comb structure that increased the charge accommodation ability by 250%. The superior charge storage property of the WO 3 /TiO 2 meant that it had a better light modulation range, with transmittance of <1% at 800 nm in the colored state. The electrochromic kinetic processes associated with coloration and bleaching are also much faster in the presence of TiO 2 , with data generated by electrochemical impedance spectroscopy revealing that this is due to a reduction in the resistance to the insertion of Li + ions. Materials characterization techniques revealed that the WO 3 /TiO 2 composite maintains the monoclinic structure of the WO 3 and that the Ti atoms are substituted into the WO 3 matrix, rather than forming discrete 8 This especially important in the tropics where air-conditioning usage is high, in part due to architects making extensive use of aesthetically pleasing glass.However, unless the WO 3 is made via expensive high vacuum techniques, some of its properties, such electrochromic reversibility, stability or optical modulation, fall short of those required for a practical smart window. Since these drawbacks have proven difficult to overcome in a pure WO 3 system there have been a number of attempts to solve them by doping or mixing with other electrochromic materials, usually another transition metal oxide. [9][10][11][12][13][14][15][16] In 2005, Patil et al.17 investigated the effect of TiO 2 additions on the electrochromic properties of tungsten trioxide films prepared through spray pyrolysis, finding improved electrochromic reversibility, but not any real enhancement of the coloration efficiency. 17One possible way to improve electrochromic efficiency is to tailor the morphology of the oxide to have spacious channels that can aid charge/ion injection into and transport within the film.18-20 One approach to achieve this is by electrochemical anodization. In 2009 Zheng et al., 7 successfully formed a macro-porous WO 3 thin film by anodizing pure tungsten, which had been deposited onto conductive fluorine doped tin oxide (FTO) glass by a magnetron sputtering method, in NH 4 F aqueous electrolyte. This success provides and broadens the application of electrochromic WO 3 thin films on "Smart Windows" where the transparent substrate is essential. However, these authors only focused on the fabrication of WO 3 thin film with macro-porous structure on FTO glass, giving neither details nor further exploration of the electrochromic properties.Besides efforts have been directed at improving electrochromic properties by producing mixed transition metal oxide films, most notably WO 3 /TiO 2 , by techniques such as electron beam deposition, sputtering, hydrothermal and the sol-gel method. 17,[21][22][23] Although the synthesized film...

Reactive Sputter Deposition of WO3/Ag/WO3 Film for Indium Tin Oxide (ITO)-Free Electrochromic Devices

“…Tungsten oxide (WO 3 ) is the most widely studied EC material. − Currently, industrial-scale mass production of EC glass mainly relies on the sputter-deposited WO 3 film on indium tin oxide (ITO) transparent conductive (TC) glass. The continuous increasing of ITO price motivates people to exploit new TC materials such as aluminum-doped ZnO, silver nanowire films, graphene, and dielectric–metal–dielectric (DMD) trilayer films, etc., which may be potentially substituted for ITO.…”

Direct Observation of Photoinduced Higher Oxidation States at a Semiconductor/Electrocatalyst Junction

“…To follow the variation in the Ni oxidation state in real time, we perform FEXRAV, consisting of measuring the X-ray absorption coefficient (μ) at a fixed energy while scanning the potential (Figure d). The FEXRAV curves are recorded at 8350 eV, giving the maximum contrast between the different Ni oxidation states.…”

“…Therefore, our acronyms R interface and C interface correspond to the literature-reported C trap and R ct,trap that represent the capacitance of surface states and resistance to charge transfer from surface states, respectively. In the case of α-Fe 2 O 3 /NiO x -H, the EC is implemented with an additional Warburg element ( Z W ) because if compared with bare α-Fe 2 O 3 and α-Fe 2 O 3 /NiO x -L electrodes in the Bode/phase plot (Figure S13) it shows a non-negligible contribution of mass transport (diffusion), producing a straight line with a slope of 45° at low frequencies. The values of all parameters retrieved from EIS measurements are reported in Table .…”

Investigation on the Effect of Different Mild Acidic Electrolyte on ZIBs Electrode/Electrolyte Interface and the Performance Improvements With the Optimized Cathode

“…Furthermore, the platform extended farthest to 60 • describes a diffusion process, which is characterized by the size of warburg. The size of warburg time constant is inversely proportional to the square-root of Zn 2+ diffusivity (Gui and Blackwood, 2015). The fitting results based on the equivalent circuit displayed in Figure 2C were listed in Table 1, where R s represents the series resistance originated from electrode, electrolyte, and the contact; CPE DL denotes a constant phase element designating the double layer capacitance arising from the charges accumulated on the surface of electrode; R CT is the resistance produced by the charge transfer process from the electrolyte to Zn surface, which also associates with this process kinetics; and Wo is symbolized as an open circuit Warburg impedance reflecting ion diffusion from electrolyte to the electrode/electrolyte interface.…”