Electrochromic smart windows: energy efficiency and device aspects

This paper covers three aspects of electrochromic smart windows. Their energy efficiency is discussed, and it is argued that a control strategy considering whether a room is in use or not can lead to large savings of the energy needed for space cooling. With regard to durability, it is shown that chemical compatibility between the electrolyte and electrochromic films of tungsten oxide and nickel oxide can be achieved without loss of optical transparency. Finally, we consider device manufacturability and present data on precharging of electrochromic nickel oxide films by ozone treatment. Electronic Publication     

氧化铑电致变色薄膜的制备、结构及性能

采用溶胶_凝胶方法在ITO导电基底上制备氧化铑电致变色薄膜 .当在碱性溶液中对薄膜分别施加阴极和阳极电位时 ,薄膜即呈现由亮黄到深绿的可逆变化 .采用原位XRD、TG_DTA、IR、XPS等方法对薄膜的结晶态、热处理过程以及膜的化学组成进行分析 .应用交流阻抗法计算了薄膜变色过程的扩散系数 ,结果表明该膜基本可以用于变色器件     

The role of thermal analysis in optimization of the electrochromic effect of nickel oxide thin films, prepared by the sol–gel method: Part II

Thin films and the corresponding xerogels were prepared from nickel acetate precursor using the sol–gel dip-coating technique. The differences in thermal stability of the two forms of samples were studied by dynamic and isothermal thermogravimetry. For thin films, the onset decomposition temperature of acetate groups was 230 °C and for the xerogel 250 °C. During thermal decomposition, the formation of nanosized nickel oxide took place. Carbonate ions, which were formed during thermal decompostion of acetate groups, remained either free or bidentately coordinated to nickel. In situ monochromatic optical transmittance changes showed that an optical stability up to the 100th cycle was already achieved for films heated for 15 min at the isothermal temperature (thermal decompositon 25%). Comparison of the results obtained for nickel sulfate (Part I) and nickel acetate precursors shows that at least two parameters, the precursor used and the degree of thermal treatment, have considerable influence on the thermal stability of the thin film and also on its electrochromic response during the cycling process.     

氧化铑变色薄膜的制备及其电变色研究

采用溶胶-凝胶方法制备了氧化铑电致变色薄膜。通过施加阴极或阳极电位, 薄膜在碱性电解液中呈现从亮黄（还原态）到深绿（氧化态）的可塑颜色变化,而 且可达到上千次循环而性能不变。采用XRD,SEM,TG,DTA,UVV,FTIR和循环伏安 等技术对薄膜的晶态、形貌、热处理过程和电变色过程进行了研究。得出100 ℃处 理的膜内含有一定量的结晶水,其性能最好。对薄膜的电致变色性能如：着色效率 、响应时间及循环寿命、开路记忆等进行了测试,并讨论了氧化铑薄膜电变色的反 应机理。     

Electrochromic nickel oxide films made by reactive r.f. sputtering from different targets

We describe the preparation and optical–electrical characterization of thin electrochromic layers based on nickel oxide (NiO_x). These layers were deposited by reactive radiofrequency (r.f.) sputtering from nickel or nickel oxide targets, maintaining the r.f. power and varying the oxygen flow in a gas mixture of Ar and O₂ from 5% up to 30%. The Ni/O ratio in the deposited thin films was determined by Rutherford backscattering spectroscopy (RBS) and the microstructure was investigated by x‐ray diffraction. The deposition rate was found to be strongly dependent on the type of target used. The electrochromic behaviour in aqueous alkaline electrolyte (0.1 N KOH solution) was investigated by electrochemical cyclization. Samples deposited by the NiO target exhibited the lowest N/O ratio (0.5) and the highest value of intercalated charge (～4.9 × 10^?2 mC cm^?2 nm^?1). Among the same samples the highest value of the intercalated charge was found for those deposited at low oxygen flow, but these samples exhibit the smallest reversible changes in optical absorption in the wavelength range 330–1200 nm. Samples deposited by the nickel target do not exhibit significant variations in the value of the exchanged charge; the measured Ni/O ratio indicates a stoichiometry closer to NiO. We also observed the switching behaviour by analysing the films in cyclic time mode at a fixed wavelength. The commutation response time is estimated by measurement under the application of a step waveform potential. Copyright © 2004 John Wiley & Sons, Ltd.     

MoO_3电致变色薄膜的XPS研究

近年来 ,随着人们提倡节能和使用洁净能源 ,无机电致变色材料在建筑物采光控制系统和反射率可调表面的应用研究 ,已成为材料领域的一个新热点 .WO3、 MoO3等过渡金属氧化物薄膜具有良好的电致变色效应 ,是人们研究的重点 .其中 MoO3的电致变色效果要好于 IrO2、 TiOx、 CoO及 NiOx等电致变色材料 [1],而且它在可见光区有比 WO3更柔和的色彩 ,使人眼更易于适应其颜色变化 .着色态的 MoO3称为钼青铜 ,其开路记忆也好于钨青铜 [2].故 MoO3电致变色薄膜是极有潜力用于实用化的电致变色器件 .MoO3薄膜常用的制备方法有真空蒸 发、化学气…     

MoO3电致变色薄膜的XPS研究

Molybdenum oxide films were fabricated successfully by spin coating from Li＋ doped peroxo polymolybdate solution via sol gel technique.Their electrochemical and electrochromic properties were investigated by cyclic voltammetry and in situ UV transmittance measurements.The results showed that the films possessed excellent electrochemical stability and reversibility.The electrochromic mechanism of the MoO3 was discussed by using results obtained from X ray photoelectron spectroscopy (XPS).The results showed that the most part of the Mo6＋ in MoO3 film was reduced to Mo5＋ and Mo4＋ ions during the Li＋ intercalation process,Mo4＋ was oxidized to Mo5＋ and part of Mo5＋ was oxidized to Mo6＋ again during the Li＋ deintercalation process.So it was considered that Mo4＋ ions existed in the colored MoO3 films.     

V2O5电致变色薄膜的Raman光谱

The amorphous V 2O 5 films prepared by vacuum evaporation are unstable and easily dissolved by electrolyte during the electrochromic process, so unfit to make electrochromic materials. We found that the annealed films have enhanced stability and electrochromic properties. We studied the microstructural changes during the electrochromic process by Raman spectra and discussed the mechanism for the enhancement. The results indicated that the amorphous films annealed by 400-500℃became polycrystalline and the films contained (V 2O 5)n ordered chains which prevented the films from solution effectively and enhanced the electrochromic characteristics. When colored and decolored, the microstructure of the polycrystalline V 2O 5 films changed inversely. During the cathodic polarization process, Li+ inserted into the V 2O 5 crystal cell , formed V-O-Li band, disordered the films and UV absorption of the films blue shifted. On the contrary , during the anodic polarization process, Li +escaped from the crystal cell. The films largely restored .     

The influence of annealing on electrochromic properties of Al–B–NiO thin films prepared by sol–gel

Al–B–NiO thin films were prepared using the sol–gel process and deposited on Indium tin oxide (ITO)-coated glass substrates via the dip-coating technique for the purpose of developing high performance electrochromic materials. The influence of the anneal on the structural and electrochromic properties of Al–B–NiO films is reported. Thermogravimetry (TG) and differential thermal analysis (DTA), cyclic voltammetry measurements (CV), UV spectrophotometer, atomic force microscopy (AFM) and X-ray diffraction (XRD) have been used to investigate the structural and electrochromic properties. The thickness of the films was determined by spectrophotometric analysis in 350–1,000 nm wavelength. Results showed that the Al–B–NiO thin films treated at high temperature have both the excellent electrochromic properties and good reversibility. The transmittance change (ΔT) of the film treated at 500 °C reaches still ~50% at the wavelength of 550 nm. The microstructure and the surface morphology were considered to play an important role in the electrochromic properties with different temperatures.     

Nanostructured NiO based all solid state electrochromic device

A nickel oxide film with a thickness of 445 nm was deposited from nickel acetate precursor using the sol–gel dip coating method. The NiO films exhibit optical transmission of 84% at 550 nm and direct energy gap (E _gd) value is 3.64 eV. The FTIR spectrum of the films confirms the formation of Ni–O bond. XRD spectrum reveals the formation of nano crystallites along (111) and (200) planes with a particle size of 17 nm. The electrochromic properties have been studied using cyclic voltammetric (CV) technique. The optical transmission of a glass/FTO/NiO/ZrO₂/FTO/glass EC device is reported.     

Electrochemical deposition of electrochromic niobium oxide films from an acidic solution of niobium peroxo complexes

Deposition of electrochromic niobium(V) oxide films from an acidic solution of niobium peroxo complexes on a transparent conducting cathode in the form of an SnO₂ film on glass was studied. With an increase in the negative potential of the deposition of niobium(V) oxide films from a solution of niobium peroxo complexes at pH 2.5, the structure and composition of the films changed. A study of the electrochromic properties of Nb₂O₅ films revealed broadening of the bands in the electrochromic coloration spectrum with an increase in the negative potential of the deposition.     

Synthesis and characterization of chemically grown electrochromic tungsten oxide

Tungsten oxide thin films, which are cathodic coloration materials that are used in electrochromic devices, were prepared by a chemical growth method and their electrochromic properties were investigated. The thin films of WO₃ were deposited onto electrically conducting substrates: fluorine doped tin oxide coated glass (FTO) with sheet resistance of about 10 Ω/cm. Transparent, uniform and strongly adherent thin film samples of WO₃ were studied for their structural, morphological, optical and electrochromic properties. The XRD data confirmed the monoclinic crystal structure of WO₃ thin films. The direct band gap Eg for the films was found to be 2.95 eV which is good for electrochromic device application. The electrochromism of WO₃ thin film was evaluated in 0.5 M LiClO₄/propylene carbonate for Li⁺ intercalation. Electrochromic properties of WO₃ thin films were studied with the help of Cyclic Voltammetry (CV), Chronoamperometry (CA) and Chronocoulometry (CC) techniques.     

In situ UV-Vis spectroelectrochemical studies to identify electrochromic sites in poly(1-naphthylamine) modified by diphenylamine

Poly(1-napthylamine) (PNPA) was modified by incorporation of diphenylamine (DPA) to result copolymer film on the indium tin oxide (ITO) coated glass electrode using cyclic voltammetry. Detailed static and dynamic UV-Vis spectroelectrochemical studies were performed on the copolymer films to identify the electrochromic sites corresponding to individual DPA and NPA units. Absorbance-wavelength-potential (AWP) profiles were constructed from the dynamic spectroelectrochemical results to infer the electrochromic sites. The advantages of using AWP profile in the analysis of electrochromic sites are discussed.     

A Study of the WO3/GO Electrochromic Films Obtained by the Electrochemical Deposition Route: Optical and Electromagnetic Method

Russian Journal of General Chemistry - The optical and electromagnetic properties of graphene oxide (GO)-modified WO3 electrochromic nanocomposite films obtained by electrochemical deposition of...     

Preparation and Characterization of Mixed‐Valent Nickel Oxide/Nickel Hexacyanoferrate Hybrid Films and Their Electrocatalytic Properties

Polynuclear mixed‐valent nickel oxide and nickel hexacyanoferrate hybrid film was prepared on glassy carbon electrode by multiple scan cyclic voltammetry. The film growth was monitored using electrochemical quartz crystal microbalance (EQCM). The cyclic voltammogram of the nickel hexacyanoferrate film is characterized by single redox couple whereas nickel oxide/nickel hexacyanoferrate hybrid film exhibits two redox couples. Cyclic voltammetric features suggest that the charge transfer process in both films resembles that of surface‐confined redox species. In stronger basic solution (pH ≥9), nickel hexacyanoferrate film was gradually converted into nickel oxide film during potentiodynamic cycling. The peak potential of nickel oxide redox couple moved into more negative side with increasing pH of contacting solution whereas the peak potential of nickel hexacyanoferrate redox couple remains the same. Electrocatalytic behavior of hybrid film coated electrodes toward ascorbic acid, hydrazine and hydroxylamine was investigated using cyclic voltammetry technique. Analytical application of nickel oxide/nickel hexacyanoferrate hybrid film electrode was tested in amperometry and flow injection analysis.     

Light-powered cell for detection of glucose with the naked eye

A concept for light-powered visual detection of glucose is developed. The detection mechanism is based on pairing a photo-active anode with an electrochromic counter electrode. The photoelectrochemical reaction changes the oxidation state of the analyte, leading to a change in the color of the electrochromic material, which makes visual detection possible. All of the electrical charge required to change the color of the electrochromic material is supplied by the photoelectrochemical reaction powered by visible light, so no conventional energy source is required. The proposed system consists of hematite modified with nickel hydroxide (Ni(OH)₂) as the photoanode, and Prussian blue deposited on a fluorine-doped tin oxide electrode as the electrochromic cathode. Under illumination, photo-oxidation of glucose at the photoanode is followed by reduction of Prussian blue to Prussian white at the cathode. The presence of glucose can therefore be detected visually as decolorization of Prussian blue occurs.     

Electrochemical and Electrochromic Properties of Ni Oxide Thin Films Prepared by a Sol–Gel Method

Nickel oxide thin films, which are well known anodic coloration materials that are used in electrochromic devices, were prepared by a sol–gel method, and their electrochemical and electrochromic properties were investigated. The sol was prepared from Ni(OH)₂ powder with an average size of 7 nm, in a mixture of ethylene glycol and absolute ethanol. The films were coated on an ITO substrate using the powder, dispersed in the solution. When additive materials, acetyl acetone and glycerol, were added to the sol its hardness and adhesion properties were improved. The optimized thin film formed an amorphous, porous structure, and showed a large current density during continuous potential and pulse potential cycling. The film also was transparent and had a high coloration efficiency (33.5 cm²/C) and a rapid response time (1.0–2.5 s) during the coloring/bleaching process.     

Potential-modulated, attenuated total reflectance spectroscopy of poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene methanol) copolymer films on indium-tin oxide

We report the first application of a potential-modulated spectroelectrochemical ATR (PM-ATR) instrument utilizing multiple internal reflections at an optically transparent electrode to study the charge-transfer kinetics and electrochromic response of adsorbed films. A sinusoidally modulated potential waveform was applied to an indium-tin oxide (ITO) electrode while simultaneously monitoring the optical reflectivity of thin (2-6 equivalent monolayers) copolymer films of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxythiophene methanol) (PEDTM), previously characterized in our laboratory. At high modulation frequencies the measured response of the polymer film is selective toward the fastest electrochromic processes in the film, presumably those occurring within the first adsorbed monolayer. Quantitative determination of the electrochromic switching rate, derived from the frequency response of the attenuated reflectivity, shows a linear decrease in the rate, from 11 x 10(3) s(-1) to 3 x 10(3) s(-1), with increasing proportions of PEDTM in the copolymer, suggesting that interactions between the methanol substituent on EDTM and the ITO surface slow the switching process by limiting the rate of conformational change in the polymer film.     

Fabricating polypyrrole/tungsten oxide hybrid based electrochromic devices using different ionic liquids

A facile approach of polypyrrole (PPy)/tungsten oxide (WO₃) composites electrosynthesized in ionic liquids for fabrication of electrochromic devices is discussed. The electrochromic properties of PPy/tungsten oxide nanocomposite films (PPy/WO₃) prepared in the presence of four different ionic liquids, 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF₄), 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIMTFSI), and 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMPTFSI) were investigated in detail. Cyclic voltammetry results revealed that PPy/WO₃ nanocomposite films have much more electrochemical activity than those of WO₃ and PPy film. The electrochromic contrast, coloration efficiency, and switching speed of the composite films were determined for electrochromic characteristics. The maximum contrast and the maximum coloration efficiency values were measured as 33.25% and 227.89 cm²/C for the PPy/WO₃/BMIMTFSI composite film. Copyright © 2015 John Wiley & Sons, Ltd.     

Metallopolymeric films based on a biscyclometalated ruthenium complex bridged by 1,3,6,8-tetra(2-pyridyl)pyrene: applications in near-infrared electrochromic windows

A biscyclometalated ruthenium complex bridged by the 2,7-deprotonated form of 1,3,6,8-tetra(2-pyridyl)pyrene was deposited onto indium-tin oxide glass electrodes by reductive electropolymerization. The resulting metallopolymeric films exhibited tricolor electrochromic behavior in the near-infrared region upon switching of the two well-separated Ru(II/III) processes at low potentials. A good contrast ratio (35%) at 2050 nm and a long memory time up to 100 min were recorded for this electrochromic behavior. The response time is typically of a few seconds.