Nanostructured mesoporous tungsten oxide films with fast kinetics for electrochromic smart windows

Abstract

A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte-electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungsten oxide (WO(3)). Electron microscopy images revealed that the films are characterized by a hitherto unreported hybrid structure comprising nanoparticles and nanorods with a tetragonal crystalline phase of WO(3) with the measured lattice parameters: a = 0.53 nm and c = 0.37 nm. In addition to pentagonal voids characteristic of the tetragonal WO(3) phase at the lattice scale, open channels and pores of 5-10 nm in diameter lie between the nanoparticles, which cumulatively promote rapid charge transport through the film. This resulted in colouration efficiency (η(max)∼90 cm(2) C(-1) at λ = 900 nm) and switching kinetics (colouration time = 3 s and bleaching time = 2 s for a 50% change in transmittance) higher and faster than previously reported values for mesoporous WO(3) films. Repetitive cycling between the clear and blue states has no deleterious effect on the electrochromic performance of the film, which is suggestive of its potential as a cathode in practical electrochromic windows.

Nanochromics: old materials, new structures and architectures for high performance devices

“…40 cm 2 C -1 , and high durability, being exposed to more than 10,000 cycles. Deepa et al 29 showed the formation of mesoporous WO 3 electrodes (5-10 nm), presenting response times of 2-3 s and electrochromic efficiency of 90 cm 2 C -1 ; similar results were obtained by Nishio et al 30 In order to obtain more conductive electrodes, consequently enhancing electrochromic properties, WO 3 can be combined with other electrochromic materials, like hexacyanoferrates, 31 or metallic nanoparticles can be inserted into WO 3 matrix as shown by Park et al, 32 but surprisingly the electrode changed from cathodic coloration to anodic one. According to the authors this characteristic is related to forced ionic insertion due to the presence of metals, the response times reported for these electrodes were in the range of 3 to 5 s. Another study concerned the mixture of metallic nanoparticles and electrochromic materials, Ag and Au nanoparticles were incorporated on PEDOT conducting polymer, where higher absorbance was obtained.…”

Preparation, characterisation and electrochromic property of mesostructured tungsten oxide films via a surfactant templated sol–gel process from tungstic acid

“…It has been previously reported in studies of materials produced by other routes that mesostructured TOFs, allow rapid ion transport through the bulk of the film, and hence improve colouration efficiency and colour-bleach kinetics [11]. Deepa and co-workers also reported that the fast colour-bleach kinetics in mesostructured TOFs were associated with the mesopore morphology [12].…”

Large cation model of dissociative reduction of electrochromic WO3−x films

“…This analysis corroborates to the conclusions of Ramana et al [46] concerning WO 3 stability which pointed to the plane of oxygens (the plane containg only the bridging oxygens and no tungsten atoms) as the plane of adjustments during phase transitions. Interestingly, the recently reported syntheses of WO 3 films in the presence of surfactants [50,51] also showed low film stability. In contrast to this depletion effect, the intercalating cations, such as H 3 O + , Li + , etc., will cause the electron density increase in bridging oxygen of (WO) 4 rings since these oxygen atoms are the closest atoms to the intercalated cation localized in near the center of the (WO 6 ) 8 cage.…”