Correlation between light absorption and electric charge in solid state electrochromic windows

Electrochromic windows based on different combinations of the electrochromic materials polyaniline (PANI), Prussian Blue (PB) and tungsten oxide (WO₃), with the solid state polymer electrolyte poly(2-acrylamido-2-methyl-propane-sulphonic acid) (PAMPS) as an ionic conductor, have been studied. These windows show a large transmission regulation both in the visible and in the near infrared wavelength region. Integrated over the solar spectrum, wind\ws with PB deposited on top of PANI, with WO₃ as a complementary coating, are typically able to regulate as much as 50% of the total solar radiation. The relationship between light absorption and charge extraction in electrochromic windows has been studied. The windows are coloured by applying a potential, which is then switched off, and the discharge process is followed by continuously measuring the light absorption and the charge extraction through a connected resistor. From the resulting linear relationship between the absorption and charge extraction, the overall absorption coefficient may be calculated.     

Deposition-order-dependent polyelectrochromic and redox behaviors of the polyaniline-prussian blue bilayer

This study thoroughly compared polyaniline (PANI)/prussian blue (PB) and PB/PANI bilayers with component films by electrochromic photographs, cyclic voltammograms, in situ transmittance spectra, in situ EQCM data and SEM pictures. It was found that both the electrochromic and redox behaviors of a PANI/PB bilayer strongly depended on which layer was deposited first. All of the experimental evidences disclosed that the inner PANI-outer PB bilayer would be superior to the inner PB-outer PANI arrangement and would display better synergistic effects, including better polyelectrochromism (colorless, light green, green/blue and deep blue) and higher redox activity and reversibility. It was also discovered by SEM that subsequent deposition of a PB film with submicron-crack openings on PANI yielded an ideal two-layer structure, but a non-idea bilayer that lacked an obvious boundary between PANI and PB layers was formed when PB was deposited first. In addition, the complex bilayer redox mechanism accompanied by a combinative K⁺, Cl⁻ and H⁺ doping process was studied quantitatively by in situ mass flux analysis and differential transmittance-potential curves. To sum up, this work has demonstrated a simple method to prepare a polyelectrochromic bilayer and provided various useful approaches to characterize bilayer electrodes, especially for those composed of a conducting polymer and a PB analogue.     

Electrodeposited Prussian blue films: Annealing effect

The correlation between the temperature-dependent electrochromic (EC) activity and other properties of galvanostatically deposited Prussian Blue (PB) films is presented here. Films subjected to annealing treatment in air at temperatures up to 500 °C were characterized by a variety of techniques which include TGA, XRD, FTIR, UV-vis spectrophotometry, SEM, XPS, cyclic voltammetry etc. The as-deposited X-ray amorphous hydrated PB films were blue in color and had Fe in both Fe^II and Fe^III valence states and were electrochromically active. Consequent to changes in the valence state, degree of hydration and coordination environment of the iron ions upon annealing, EC activity and morphology of the films exhibited dramatic changes. Annealing at moderate temperatures retained the blue color of the films and decreased the EC activity consistent with dehydration and decreased the Fe^II content. Lack of EC activity at higher temperatures was consistent with dehydration and quenching of Fe^II states accompanied with change of color from blue to rust (Fe^III) typical of Fe₂O₃. Independent of the annealing temperature, the films retained their amorphicity, however, prolonged annealing at 500 °C yielded hexagonal Fe₂O₃.     

New effective process to fabricate fast switching and high contrast electrochromic device based on viologen and Prussian blue/antimony tin oxide nano-composites with dark colored state

We developed a new electrochromic device by using compact Prussian blue (PB)/antimony tin oxide (ATO) nano-composites as anodic electrode and viologen anchoring on titanium dioxide (TiO₂) nano-particles as cathodic electrode. The anodic electrode was based on a transparent nanostructured ATO nano-particle film and was electro-deposited by Prussian blue to form compact Prussian blue/ATO nano-composites by means of galvanostatic electrodeposition process. Nanocrystalline TiO₂ thin films on conducting glass were modified with a mono-layer of viologen with two anchoring groups, which were much strongly adsorbed onto the surface of TiO₂ nano-particles. A polymer gel electrolyte sandwiched between the anodic and cathodic layers is used as the ionic transport layer. The 2.5 cm × 2.5 cm electrochromic device shows high contrast (64.8%, at 600 nm) very low transmittance at colored stage (0.1%, at 600 nm), fast switching time (600 and 720 ms for coloration and bleaching, respectively), high coloration efficiency of 912 cm² C⁻¹ at 600 nm and good stability. The enhanced performance of the electrochromic device can be attributed to the ATO nano-particles as inter-conductive materials.     

A tungsten-trioxide/prussian blue complementary electrochromic cell with a polymer electrolyte

Optically variable windows (smart windows), which control the transmission of light into buildings and vehicles, are of interest both for the control of solar heat load and for privacy applications. Such windows are likely to utilize electrochromic technology to achieve optical control. An electrochromic device consisting of a cathodically colouring tungsten trioxide (WO₃) film, an anodically colouring Prussian blue (PB) film, and a polymer electrolyte was made. The polymer electrolyte was prepared from polyvinyl alcohol doped with H₃PO₄ and KH₂PO₄ to accommodate the conduction of both H⁺ and K⁺ ions. The electrochromic WO₃ and PB films functioned in a complementary way such that the device was coloured or bleached by the application of –0.5 V or +0.5 V (WO₃ films vs PB film), respectively. The spectral characteristics of the coloured device confirmed the complementary colouration of WO₃ and PB in the device.     

Solid-state electrochromic devices using pTMC/PEO blends as polymer electrolytes

Flexible, transparent and self-supporting electrolyte films based on poly(trimethylene carbonate)/poly(ethylene oxide) (p(TMC)/PEO) interpenetrating networks doped with LiClO₄ were prepared by the solvent casting technique. These novel solid polymer electrolyte (SPE) systems were characterized by measurements of conductivity, cyclic voltammetry, differential scanning calorimetry and thermogravimetry.The incorporation of solid electrolytes as components of electrochromic devices can offer certain operational advantages in real-world applications. In this study, all-solid-state electrochromic cells were characterized, using Prussian blue (PB) and poly-(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT) as complementary electrochromic compounds on poly(ethyleneterphthalate) (PET) coated with indium tin oxide (ITO) as flexible electrodes. Assembled devices with PET/ITO/PB/SPE/PEDOT/ITO/PET “sandwich-like” structure were assembled and successfully cycled between light and dark blue, corresponding to the additive optical transitions for PB and PEDOT electrochromic layers. The cells required long cycle times (>600 s) to reach full color switch and have modest stability towards prolonged cycling tests. The use of short duration cycling permitted the observation of changes in the coloration-bleaching performance in cells with different electrolyte compositions.     

Preparation of PANI–PVA composite film with good conductivity and strong mechanical property

The polyaniline (PANI)–polyvinyl alcohol (PVA) conductive composite films [doped with hydrochloride (HCl), dodecylbenzene sulphonic acid and amino sulphonic acid (NH₂SO₃H) aqueous solution] were synthesised by ‘in situ’ polymerisation, and their conductivities were compared. Among these composite films, HCl–PANI–PVA composite film possessed the highest conductivity that reached 1360?S·m^??1 [w_(PVA)?=?40%]. Meanwhile, the effects of PVA content, HCl concentration, oxidant ammonium persulphate (APS) dosage, reaction time and film drying temperature on tensile strength of the HCl–PANI–PVA composite films were studied. The tensile strength of the film was improved greatly due to effective mixture of PANI and PVA. When the PVA content was 40%, C_(HCl)?=?1.0?mol·L^??1, reaction time was 4.0?h, n_(APS)/n_(aniline)?=?1.0 and film drying temperature was 80°C, and the tensile strength of the HCl–PANI–PVA composite film reached the maximum of 60.8?MPa. At the same time, the structure of composite materials was characterised and analysed through ultraviolet spectrum and SEM.     

Structure,electrical and optical properties of (PVA/LiAsF6) polymer composite electrolyte films

In this work, Li⁺ ion conducting polymer composite electrolyte films (PECs) were prepared based on poly (vinyl alcohol) (PVA), lithium hexafluoro arsenate (LiAsF₆), and ceramic filler TiO₂ using solution cast technique. The XRD and FTIR spectra were used to determine the complexation of the PVA polymer with LiAsF₆ salt. The ionic conductivities of the (PVA + LiAsF₆) and (PVA + LiAsF₆ + TiO₂) films have been determined by the A.C. impedance measurements in the temperature range 320–440 K. The maximum conductivity was found to be 5.10 × 10^?4 S cm^?1 for PVA:LiAsF₆ (75:25) + 5 wt% TiO₂ polymer composite film at 320 K. The calculation of Li⁺ ion transference number was carried out by the combination of A.C. impedance and D.C. polarization methods and is found to be 0.52 for PVA:LiAsF₆ (75:25) + 5 wt% TiO₂ film. Optical properties such as direct energy gap, indirect energy gap, and optical absorption edge values were investigated in pure PVA and salt complexed PVA films from their optical absorption spectra in the wavelength range of 200–600 nm. The absorption edge was found at 5.76 eV for undoped film, while it is observed at 4.87 and 4.70 eV for 20 and 25 wt% LiAsF₆ doped films, respectively. The direct band gaps for these undoped and salt doped PVA films were found to be 5.40, 5.12, and 4.87 eV, respectively, whereas the indirect band gaps were determined as 4.75, 4.45, and 4.30 eV. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Perturbation-correlation moving-window two-dimensional correlation spectroscopic studies on the heat treatment of poly(vinyl alcohol)/silver nitrate film

In this paper, poly(vinyl alcohol)/silver nitrate (PVA/AgNO₃) films were annealed at 180 °C for 1 h to prepare highly electrically conductive poly(vinyl alcohol)/silver (PVA/Ag) nanohybrids. Ultraviolet (UV)-visible absorption spectra, X-ray diffraction (XRD) scans, and scanning electronic microscopy (SEM) were applied to investigate the structures and morphology of the PVA hybrids. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to study the thermal property of PVA/AgNO₃ films. Furthermore, perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy combined with temperature-dependent Fourier transform infrared (FTIR) spectroscopy was used to investigate the conversion of AgNO₃ into Ag nanoparticles in PVA matrix. The results show that the chelates for AgNO₃ coordinated with hydroxyl groups are primarily decomposed in the temperature regions of 39.7–72.6 °C and 182.7–199.6 °C. AgNO₃ is reduced into Ag⁰ and the hydroxyl groups of PVA are oxidized into carbonyl groups. The PVA-AgNO₃ chelates are very rapidly decomposed in the temperature region of 182.7–199.6 °C. Large amounts of Ag⁰ produced by the reduction of AgNO₃ are aggregated into Ag nanoparticles which are homogeneously dispersed into the PVA matrix. When the temperature increases to 212.7 °C, the unhydrolyzed acetate groups in PVA chains are sharply decomposed.     

Synthesis and characterization of Ag nanoparticles embedded in PVA via UV-photoreduction technique for synthesis of Prussian blue pigment

Silver nanoparticles doped in polyvinyl alcohol (AgNps/PVA) were synthesized via polymer-promoted reductive reaction of AgNO₃ and PVA under time-dependent exposure to UV radiation. The AgNps/PVA composites were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, UV–Vis spectroscopy, and transmission electron microscopy to describe the structure, nuclearity, and distribution of Ag Nps within the PVA matrix. The UV–Vis spectrum of AgNps/PVA exhibited a broad surface plasmon absorption around 425–443 nm which originated from the formation of Ag NPs. Surface analysis by XPS indicated that the Ag NPs were grown solely on the PVA surface at UV exposure time of 2 h (2.0AgNPs/PVA). Increasing the UV exposure time to 4 h will cause the transformation of metallic nanosilver to oxidized nanosilver. UV–Vis absorption spectra were in situ recorded to follow the synthesis of Prussian blue (PB) on 2.0AgNPs/PVA (PB@2.0AgNPs/PVA). The colloidal dispersion of 2.0AgNPs/PVA in an acidic medium containing free Fe(III) ions and potassium hexacyanoferrate(III) revealed an additional band centered at 720 nm due to the intermetal charge-transfer absorbance of the polymeric Fe(II)-C-N-Fe(III) of the PB@2.0AgNPs/PVA nanocomposite. Control experiments were shown to involve a spontaneous electron transfer reaction between 2.0AgNPs/PVA and Fe(III) ions, with a concomitant decomposition of hexacyanoferrate(III) and formation of PB was observed. Moreover, IR gave clear cut evidence for the synthesis of PB@2.0AgNPs/PVA from the appearance of a band for the cyano group at 2090 cm^?1.     

Visualization of electrocatalytic activity of microstructured metal hexacyanoferrates by means of redox competition mode of scanning electrochemical microscopy (RC-SECM)

Transition metal hexacyanoferrates are versatile inorganic compounds widely employed for the assembling of sensors and biosensors in a variety of different electroanaytical applications. A modified version of the recently introduced redox competition mode of scanning electrochemical microscopy (RC-SECM) was exploited to visualize the local electrocatalytic activity of microstructured Prussian blue (PB) films towards the reduction of H₂O₂ with improved lateral resolution. The PB films were electrochemically deposited in a spot on glassy carbon surfaces using a droplet cell. The influence of the potential applied to the PB modified surface on the current at the SECM tip was evaluated when both the sample and the SECM tip were competing for H₂O₂ in solution. Thus, high local electrocatalytic activity is indicated by low currents at the SECM tip. The same strategy was successfully employed for the characterization of the performances of a biosensor employing the enzyme glucose oxidase (GOx) immobilized within a polymer hydrogel matrix on the top of PB-modified glassy carbon electrodes.     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

Electropolymerization of high quality electrochromic poly(3-alkyl-thiophene)s via a room temperature ionic liquid

Electrochemical polymerization in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆), has been used to prepare electrochromic poly(3-methylthiophene) (PMeT) and its more attractive derivatives: poly(3-hexylthiophene) (PHexT) and poly(3-octylthiophene) (POcT). Spectroelectrochemistry and electrochromic properties of the resulting polymers were characterized using various experiment techniques in [BMIM]PF₆/CH₃CN (1:1, v/v) solution. The thin films were bright red, orange red and orange yellow at its fully reduced state for PMeT, PHexT and POcT, respectively. After oxidization of these undoped polymers, the films underwent reversible change to the bright blue, blue or black blue form. These poly(3-alkylthiophene)s (PMeT, PHexT and POcT) films exhibit high chromatic contrast (46, 45 or 39%), comparative switching times (1.1, 1.4 or 1.9 s), great electrochromic efficiency (250, 220 and 230 cm² C⁻¹) and long-term switching stability. High quality electrochromic polymers were provided for the use of commercially available thiophene monomers, avoiding the use of other custom synthesized monomers.     

Effect of boric acid and heat treatment for the formation of poly(vinyl alcohol)/iodine complex films iodinated at solution before casting

This study examined the role of boric acid and the effect of heat treatment on PVA‐iodine polarizing films prepared in the solution state before casting (IBC) of PVA/iodine/boric acid films. The films were prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing boric acid with 0, 0.1, 0.3, and 0.5 mol/l of I₂/KI aqueous solution, and I₂/KI(1 : 2) with 5 wt % of PVA. The effect of boric acid and heat treatment on the durability of the IBC PVA polarizing sheet films was investigated by UV–vis absorption spectroscopy. Boric acid was found to be essential for the complex formation in PVA/iodine solutions at relatively low I₂/KI concentrations and high temperatures. The strength of the complex peak at ∼ 600 nm in UV–vis absorption spectra increased with increasing boric acid concentration. With increasing heating temperature over 90°C the intensity of the peak at 600 nm corresponding to the complex decreased due to the evaporation of I₂ decomposed from I₅⁻, but the peak at 355 nm corresponding to free I₂·I₃⁻ was remained unchanged. From heat treatment at 150°C, the intensity of the peak at 600 nm decreased but the intensity of the complex peak (600 nm) of the sample with 0.5 mol/l boric acid was unaffected. The transmittance and degree of polarization for the films increased and decreased with increasing heat treatment time under heat and a humid atmosphere, respectively. However, this tendency decreased with increasing boric acid concentration and heat treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Color change of an iodinated poly(vinyl alcohol) film by physical deformation

The color change of an iodinated poly(vinyl alcohol) (PVA) film caused by physical deformation was investigated in this study. The color of a PVA film soaked in an aqueous potassium iodide (KI)/I₂ solution was light yellow, but it turned light blue when the film was physically deformed. The ultraviolet–visible absorption spectrum of the iodinated PVA film extended uniaxially in air was measured at various extension levels. Without deformation, the film showed UV absorption bands at 210, 290, and 360 nm. However, under deformation, the film showed new visible light absorption bands at 440 and 620 nm. From the UV–vis absorption spectra of several iodinated solutions, we found that the absorption wavelength of iodine was affected by the cohesive energy of the solvents. The KI/I₂ diethyl ether solution showed an absorption band at 460 nm, and this provided a clue to understanding the color change of the PVA–iodine complexes caused by physical deformation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43036.     

聚苯胺-乙烯三叔丁基过氧硅烷复合膜的制备及其电致变色性能的研究

采用恒电位法在氧化铟导电玻璃上电聚合制备了聚苯胺(PAn),利用溶液复合法合成了掺杂态聚苯胺-乙烯三叔丁基过氧硅烷复合电致变色膜,并对其结构和电致变色性能研究。结果表明,复合电致变色膜在稳定态时仅出现第二氧化峰,在外加电压下其颜色在绿色至紫色之间可逆变化,聚合物中加入偶联剂,可提高电致变色膜与导电玻璃基底的粘结性及改善复合膜的耐溶剂性能。     

Electrochromic characteristics of a complementary tungsten trioxide/Prussian blue cell

Optically switchable electrochromic materials are of importance in the automobile industry for the control of solar heat load, glare reduction, and privacy applications. A complementary electrochromic cell consisting of a cathodically colouring tungsten trioxide (WO₃) film, an anodically colouring Prussian blue (PB) film, and a Li⁺ conducting polymer electrolyte was made. Cycling characteristics and colouration efficiency of the cell at various stages of cycling were evaluated. It was shown that the complementary cell requires less energy for operation compared to cells with a single film. The WO₃/PB was cycled up to 1300 times. A gradual decrease in the contrast between the coloured and the bleached states upon cycling was observed during the first 400 cycles. The colouration efficiency of 102 cm²C^–1 at the first cycle decreased to 67 cm²C^–1 after 387 cycles. The cause of degradation is attributed to the lack of K⁺ ions available to PB film.     

Synthesis and characterizations of magnetite nanocomposite films for radiation shielding

Polyvinyl alcohol (PVA) films containing magnetite Fe₃O₄ nanoparticles have been prepared by co‐precipitation method for use in gamma ray shielding and protection. Characterizations of the magnetite/PVA nanocomposite films were investigated by X‐ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis spectroscopy, and magnetization measurements. TEM images showed that the synthesized magnetite particles had about 6–11 nm dimensions. Optical study's results revealed that the optical energy band gaps of thin films range between 1.82 and 2.81 eV at room temperature using UV–visible absorption spectroscopy. The saturation magnetization (MS) value measured by vibrating sample magnetometer VSM was found to be 8.1 emu/g with superparamagnetic nature. The radiation shielding properties such as linear attenuation coefficients (μ ) and half‐value thickness (HVT) for the magnetite nanocomposite films have been obtained experimentally for different photon energies. The results imply that these nanocomposites films are promising radiation shielding materials. POLYM. COMPOS., 38:974–980, 2017. © 2015 Society of Plastics Engineers     

Molecular assembled self-doped polyaniline copolymer ultra-thin films

A self-assembly technique and copolymerization were used to buildup a self-doped polyaniline (SPANI) ultra-thin film on an indium-tin oxide (ITO) substrate. The monomers used were aniline and its derivative MSAN (m-aminobenzenesulfonic acid). Successful MSAN/AN copolymerization and film formation were simultaneously performed in aqueous solution with the addition of oxidant (APS, ammonium persulfate). The film deposition rate of a high AN/MSAN ratio system is generally higher than that of a low AN/MSAN ratio system. Cyclic voltammetry, UV-vis spectroscopy, and α-step instruments indicate a systematic dependence of the film thickness of these ultra-thin films on the assembly time and temperatures. The Auger depth profile reveals the elemental distribution in these films and exhibits different deposition rates between AN and MSAN. XPS N_1s spectra also show the variation of the degree of doping. This SPANI film can be used as an electrochromic electrode in a corresponding device. Carboxyl-terminated-butadiene-acrylonitrile (CTBN) blended with LiClO₄ was used as a solid polymer electrolyte. A total solid electrochromic device was assembled as ITO/SPANI/LiClO₄-CTBN/PEDOT:PSS/ITO, where PEDOT:PSS is poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) as the counter complementary electrode. The device was pale gray at −1.5 V and blue at +1.5 V.     

Role of CoBr2 on the structural,optical and magnetic properties of polyvinyl alcohol films

Polyvinyl alcohol (PVA) films filled with different concentrations of CoBr₂ were prepared using the casting method. These films were characterized by FTIR, UV–visible, XRD, and ESR techniques. FTIR spectra were used to clarify the structural variations due to the filling level from CoBr₂. The observed bands at 3484, 1733, and 1640 cm^?1 were assigned to O? H, C?O, and C?C stretching vibrations, respectively. UV–visible spectra shows the absorption band at 280 nm which is assigned to π → π* transition. This indicates the presence of unsaturated bonds in tail to head of PVA. Optical energy gap decreased with increasing the concentration of CoBr₂. X‐ray diffraction scans show some decrease in the degree of crystallinity in the filled films which reveals an increase in amorphous phase of PVA due to the interaction between Co⁺² and polymeric matrix causing a molecular rearrangement within the amorphous phase of PVA. The observed complex ESR spectrum due to hyperfine interactions confirms the role of free radicals. Spectroscopic and magnetic properties of PVA/CoBr₂ composite films were investigated and compared with those of PVA alone. The results show that the change of the structure due to the interaction of filler with the polymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010