Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

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Tungsten trioxide hydrate (3WO 3 3 H 2 O) films with different morphologies were directly grown on fluorine doped tin oxide (FTO) substrate via a facile crystal-seed-assisted hydrothermal method. Scanning electron microscopy (SEM) analysis showed that 3WO 3 3 H 2 O thin films composed of platelike, wedgelike, and sheetlike nanostructures could be selectively synthesized by adding Na 2 SO 4 , (NH 4 ) 2 SO 4 , and CH 3 COONH 4 as capping agents, respectively. X-ray diffraction (XRD) studies indicated that these films were of orthorhombic structure. The as-prepared thin films after dehydration showed obvious photocatalytic activities. The best film grown using CH 3 COONH 4 as a capping agent generated anodic photocurrents of 1.16 mA/cm 2 for oxidization of methanol and 0.5 mA/cm 2 for water splitting with the highest photoconversion efficiency of about 0.3% under simulated solar illumination.

Section: Introductionmentioning

confidence: 99%

Morphology-Tailored Synthesis of Tungsten Trioxide (Hydrate) Thin Films and Their Photocatalytic Properties

Jiao

Wang

et al. 2011

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“…1,2 The standard large-area EC device embodies a W-oxide-based film separated from a Ni-oxide-based film by an electrolyte, and coloration and bleaching occur when ions are shuttled between these two films under the action of a voltage supplied to external transparent electrodes. [3][4][5] Moving charge from Ni oxide to W oxide makes them both dark, and reversing the charge transport bleaches them; hence oxides of Ni and W exhibit anodic and cathodic coloration, respectively.…”

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confidence: 99%

“…Extensive work has been carried out to achieve this goal by searching for novel EC materials with superior performance. However, methods to reverse degradation and hence rejuvenate existing lowcost EC materials are equally important and have attracted interest only recently, especially with regard to galvanostatic ion de-trapping which was shown to be able to refresh degraded WO 3 . [6][7][8] Titanium dioxide, TiO 2 , is an interesting alternative to the commonly used WO 3 as a cathodic EC material.…”

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confidence: 99%

Eliminating Electrochromic Degradation in Amorphous TiO₂ through Li-Ion Detrapping

Wen

Niklasson

Granqvist

2016

Self Cite

ABSTRACT:The quest for superior and low-cost electrochromic (EC) thin films, for applications in smart windows, remains strong owing to their large importance for energyefficient buildings. While the development of new EC materials for improved devices is important, diminishing or reversing degradation is another key issue, and electrical rejuvenation of degraded EC materials can offer new opportunities. Here we demonstrate that cathodically coloring EC thin films of TiO 2 , which normally suffer from ion-trapping-induced degradation of charge capacity and optical modulation upon extensive electrochemical cycling, can recover their initial EC performance by a rejuvenation procedure involving Li + ion de-trapping. Thus the initial performance can be regained, and refreshed TiO 2 films exhibit the same degradation features as as-deposited films upon prolonged electrochemical cycling. The rejuvenation was carried out by using either galvanostatic or potentiostatic treatments. Our study may open avenues to explore the recovery not only of EC materials and devices based on those but also for other ion-exchange-based devices.

“…[5][6][7] Optical modulation ensues when ions are shuttled between the WO 3 film, which colors cathodically by ion insertion, and the Ni-oxide-based film with complementary anodic coloration under ion extraction. 8 Large optical modulation span is required for most EC devices, which means that the inserted and extracted ion densities are also large, and this may lead to device degradation due to irreversible ion incorporation as well as structural rearrangements.…”

mentioning

confidence: 99%

Galvanostatic Ion Detrapping Rejuvenates Oxide Thin Films

Arvizu¹,

Wen²,

Primetzhofer³

et al. 2015

Self Cite

Ion trapping under charge insertion−extraction is wellknown to degrade the electrochemical performance of oxides. Galvanostatic treatment was recently shown capable to rejuvenate the oxide, but the detailed mechanism remained uncertain. Here we report on amorphous electrochromic (EC) WO 3 thin films prepared by sputtering and electrochemically cycled in a lithium-containing electrolyte under conditions leading to severe loss of charge exchange capacity and optical modulation span. Time-of-flight elastic recoil detection analysis (ToF-ERDA) documented pronounced Li + trapping associated with the degradation of the EC properties and, importantly, that Li + detrapping, caused by a weak constant current drawn through the film for some time, could recover the original EC performance. Thus, ToF-ERDA provided direct and unambiguous evidence for Li + detrapping.