Electrolyte For Electrochromic Devices Research Articles

Electrochromic windows based on luminescent acrylate/ionosilicas

AbstractPoly(methyl methacrylate) (PMMA)-based composite films doped with lanthanide-doped sol–gel derived imidazolium-based ionosilicas (IS-Ln) were recently proposed as active layers of luminescent down shifting (LDS) layers, but subsequent work demonstrated also their potential as electrolytes for electrochromic devices (ECDs) with foreseen application in smart windows of energy-efficient buildings. Nevertheless, some challenges remained to be addressed in the latter devices, the most critical one being the poor solubility of PMMA in the ionic liquid used in the formulation of these materials. To avoid this drawback, in the present work we propose novel lanthanide-containing acrylate/ionosilicas (AC/IS-Ln, Ln = Tb3+, Eu3+). The transparent, homogeneous, and luminescent hybrid materials synthesized are characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, atomic force microscopy, contact angle measurements, ionic conductivity, and photoluminescence spectroscopy. Optimized samples are successfully employed as electrolytes in luminescent ECD prototypes. The ECD device doped with AC/IS-Eu shows good cycling stability with reproducible bleaching/coloring over 50 chronoamperometry cycles, high coloration efficiency (CE) values CEin/CEout in the visible (−89/+98 cm2 C−1), and near-infrared (−126/138 cm2 C−1) spectral regions, and outstanding memory effect. Graphical Abstract

Hydrogel, the Next‐Generation Electrolyte for Electrochromic Devices

Hydrogel, the Next‐Generation Electrolyte for Electrochromic Devices

Hydrogel, the Next‐Generation Electrolyte for Electrochromic Devices

Electrolytes have become a research frontier in the electrochromic community owing to their widespread applications in advanced electronic devices especially in electrochromic devices (ECDs). However, traditional ECDs with liquid electrolytes commonly suffer from inflexibility, complicated configurations, and poor electrochromic properties. To achieve solid‐ or flexible‐state ECDs, an alternative method is to employ polymer electrolyte gels, which integrate the virtues of both liquid‐ and solid‐state electrolytes. In this review, first, the device configurations of conventional ECDs are introduced, where the classification of electrolytes for ECDs is comprehensively introduced. Then the current situation and applications of hydrogels for ECDs, where it is expected to reveal the developing trends of hydrogel‐based ECDs are specially reviewed. Finally, the insights on the design methods of hydrogel electrolytes for flexible and efficient ECDs are proposed.

Advances in the Study of Gel Polymer Electrolytes in Electrochromic Devices

The electrolytes in electrochromic devices (ECDs) serve as a conduction medium between electrodes and providing compensating ions for electrochromic reactions. Their characteristics directly affect the performance of electrochromic devices. Due to their ease of processing and encapsulation and high ionic conductivity, polymer gel electrolytes are widely used in electrochromic devices. As gel electrolyte polymers, polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF) are reviewed according to their polymer matrix. Furthermore, future development trends in gel polymer electrolytes are discussed.

Realisation of Solid-State Electrochromic Devices Based on Gel Electrolyte.

Background: In the last decade, there has been much interest in the area of solid polymer electrolyte (SPE) to address the issues of electrolyte leakage and evaporation in electrochromic devices (ECD). ECD is a state-of-the-art technology having the ability to change from transparent state to opaque state under the influence of a small applied voltage for energy saving applications. Methods: In this work, tungsten oxide (WO 3) films were fabricated via the sol-gel spin-coating method. Subsequently, ECDs were assembled based on SPE and liquid polymer electrolyte (LPE), respectively using indium doped tin oxide (ITO) coated glass as conducting electrodes and WO 3 films as working electrode. Results: Cyclic voltammetry (CV) results revealed reduced ionic conductivity of conducting ions in SPE based ECD (SECD) owing to increased viscosity by addition of PMMA. However, lesser time was required for the colouration process. LPE based ECD (LECD) showed higher colouration efficiency (CE) compared to its SECD counterpart. This is attributed to its larger optical modulation. Conclusions: This work presents a comparison between the performance of LECD and SECD in terms of electrochromic (EC) and optical properties. They were analysed through CV, chronoamperometry (CA) and ultraviolet-visible (UV-Vis) spectrophotometer. Furthermore, this work provides an insight on the employment of solid-state electrolytes in ECDs in view of the persistent leakage and evaporation problems in ECD implementation.

Realisation of Solid-State Electrochromic Devices Based on Gel Electrolyte

Background: In the last decade, there has been much interest in the area of solid polymer electrolyte (SPE) to address the issues of electrolyte leakage and evaporation in electrochromic devices (ECD). ECD is a state-of-the-art technology having the ability to change from transparent state to opaque state under the influence of a small applied voltage for energy saving applications. Methods: In this work, tungsten oxide (WO 3) films were fabricated via the sol-gel spin-coating method. Subsequently, ECDs were assembled based on SPE and liquid polymer electrolyte (LPE), respectively using indium doped tin oxide (ITO) coated glass as conducting electrodes and WO 3 films as working electrode. Results: Cyclic voltammetry (CV) results revealed reduced ionic conductivity of conducting ions in SPE based ECD (SECD) owing to increased viscosity by addition of PMMA. However, lesser time was required for the colouration process. LPE based ECD (LECD) showed higher colouration efficiency (CE) compared to its SECD counterpart. This is attributed to its larger optical modulation. Conclusions: This work presents a comparison between the performance of LECD and SECD in terms of electrochromic (EC) and optical properties. They were analysed through CV, chronoamperometry (CA) and ultraviolet-visible (UV-Vis) spectrophotometer. Furthermore, this work provides an insight on the employment of solid-state electrolytes in ECDs in view of the persistent leakage and evaporation problems in ECD implementation.

Realisation of Solid-State Electrochromic Devices Based on Gel Electrolyte.

Background: In the last decade, there has been much interest in the area of solid polymer electrolyte (SPE) to address the issues of electrolyte leakage and evaporation in electrochromic devices (ECD). ECD is a state-of-the-art technology having the ability to change from transparent state to opaque state under the influence of a small applied voltage for energy saving applications. Methods: In this work, tungsten oxide (WO 3) films were fabricated via the sol-gel spin-coating method. Subsequently, ECDs were assembled based on SPE and liquid polymer electrolyte (LPE), respectively using indium doped tin oxide (ITO) coated glass as conducting electrodes and WO 3 films as working electrode. Results: Cyclic voltammetry (CV) results revealed reduced ionic conductivity of conducting ions in SPE based ECD (SECD) owing to increased viscosity by addition of PMMA. However, lesser time was required for the colouration process. LPE based ECD (LECD) showed higher colouration efficiency (CE) compared to its SECD counterpart. This is attributed to its larger optical modulation. Conclusions: This work presents a comparison between the performance of LECD and SECD in terms of electrochromic (EC) and optical properties. They were analysed through CV, chronoamperometry (CA) and ultraviolet-visible (UV-Vis) spectrophotometer. Furthermore, this work provides an insight on the employment of solid-state electrolytes in ECDs in view of the persistent leakage and evaporation problems in ECD implementation.

Redox Electrolytes for Hybrid Type II Electrochromic Devices with Fe−MEPE or Ni1−xO as Electrode Materials

AbstractThe use of redox electrolytes in electrochromic devices (ECDs) based on cathodically coloring metallopolymers (MEPEs) and various redox mediators, including potassium hexacyanoferrate(II)/(III) (KHCF(II)/(III)), ferrocene/ferrocenium (Fc0/+) and tetramethyl thiourea/tetramethylformaminium disulfide (TMTU/TMFDS2+), was investigated. By decreasing the concentration of KHCF(III) in the electrolyte, it was possible to significantly reduce the loss current. Although the unpleasant yellow tint could be diminished with lower concentrations, Prussian blue (PB, Fe4[Fe(CN)6]3) was formed during cycling. Fc0/+ and TMTU/TMFDS2+ were studied as the basis of alternative redox electrolytes and characterized in terms of their electrochemical and optical properties. The maximum visible light transmittance changes (Δτv) of 50 % and 48 % were reached with the MEPE reference ECD and the MEPE‐ECD with 0.001 M TMTU/TMFDS2+, respectively. Finally, an ECD combining an anodically coloring non‐stoichiometric nickel oxide (Ni1−xO) electrode with a TMTU/TMFDS2+ (molar ratio: 1/0.1) containing electrolyte exhibits a maximum Δτv of 32 %, with τv ranging from 38 % in the dark state to 70 % in the bright state. These results imply that incorporating redox mediators into the electrolyte provides a straightforward and effective means of simplifying device structures and improving the performance of ECDs based on MEPEs and metal oxides.

Studies of bipyridinium ionic liquids and deep eutectic solvents as electrolytes for electrochromic devices

In this work, two bipyridinium di-cations based on [(allyl)2bpy]2+ and [(C10)2bpy]2+ combined with halogenate (I or Br), bistriflimide ([NTf2]) and dicyanamide [DCA] anions have been prepared and electrochemical characterized. These salts were studied using a conventional electrolyte (TBAP in acetonitrile) and alternative electrolyte based DES (LiTfO:6EG) for 3- and 2- electrodes configuration devices.In the 2-configuration device, [(allyl)2bpy][DCA]2 and [(C10)2bpy][DCA]2 showed different radical cation colorations particularly green and blue colors with different recovery times to original ones. In the case of [(C10)2bpy]I2 a blue and a red-violet colorations attributed to the electrogenerated radical cation and the dimer respectively was obtained in agreement with previous literature. In parallel, bipyridinium based DES by suitable combination between [(C10)2bpy]X2 and [(allyl)2bpy]X2 (X = Br, NTf2, DCA) with several hydrogen bond donors in 2-electrode configuration devices have been also studied. DES based on [(allyl)2bpy][NTf2]2:PEG200 and [(allyl)2bpy][DCA]2:PEG200 presented different coloration grades from pale brown to green taking longer times to recover the original color.The selected DES as alternative electrolytes or based bipyridinium derivatives can be promissory materials for efficient electrochromic devices.

A facile approach to prepare porous polyamide films with enhanced electrochromic performance.

Novel electroactive triphenylamine-based polyamide (PA) films with a purposeful porous structure have been designed and prepared by a simple route. Polymer thin films containing well dispersed electrolyte salts were prepared first, then channels of pores could be generated within the polymer film by washing the salts out. With the help of the porous channels, the diffusion rate between electroactive species and the electrolyte during the electrochemical process could be effectively increased. Consequently, the driving potential and electrochromic response time can be efficiently improved through this approach. Novel porous PA films with optimal results both in optical transparency and electrochemical properties could be readily obtained by choosing a commonly used supporting electrolyte TBABF4 as a salt in this study. When the PA films containing un-washed TBABF4 salt were further assembled into electrochromic devices (ECDs), the salt could then be leached out during the electrochemical redox switching process to form a porous film structure and also serves as a supporting electrolyte in ECDs simultaneously. Therefore, EC performance such as the driving potential and response time could be enhanced obviously by this simplified fabrication procedure of ECDs.

Complementary all Solid State Electrochromic Devices Using Carboxymethyl Cellulose Based Electrolytes

The paper presents the results of the research on a new polymer-membrane and gel electrolytes for electrochromic devices. A complementary solid-state electrochromic device consisting of cathodically coloring working electrode of WO3 and anodically coloring counter electrode of NiO films is prepared to compare the effects of gel or membrane forms of carboxymethyl cellulose (CMC) polymer electrolyte on the electrochromic properties of devices. The performance evaluations of the complementary solid-state electrochromic devices indicate good reversibility, low power consumption of ±3 V in colored state, high variation of transmittance changing of 64% in gel electrolyte, and lower 7% in membrane electrolyte and good memory effect under open-circuit conditions. CMC based electrolytes can be used as an ion-conducting medium and be a good candidate for complementary electrochromic devices owing to, the improved properties as well as its cheapness.

Tantalum oxide film prepared by reactive magnetron sputtering deposition for all-solid-state electrochromic device

Inorganic-solid-state electrolyte tantalum oxide thin films were deposited by reactive DC magnetron sputtering to improve the leakage and deterioration of traditional liquid electrolytes in electrochromic devices. O 2 at 1–20 sccm flow rates was used to deposit the tantalum oxide films with various compositions and microstructures. The results indicate that the tantalum oxide thin films were amorphous, near-stoichiometric, porous with a loose fibrous structure, and highly transparent. The maximum charge capacity was obtained at an oxygen flow rate of 3 sccm and 50 W. The transmission change of the Ta 2O 5 film deposited on a WO 3/ITO/glass substrate between colored and bleached states at a wavelength of 550 nm was 56.7%. The all-solid-state electrochromic device was fabricated as a multilayer structure of glass/ITO/WO 3/Ta 2O 5/NiO x/ITO/glass. The optical transmittance difference of the device increased with increasing applied voltage. The maximum change was 66.5% at an applied voltage of ± 5 V.

Plasticized pectin-based gel electrolytes

Pectin is a natural polymer present in plants and, as all natural polymers has biodegradation properties. Chemically, pectin is a polysaccharide composed of a linear chain of 1→4 linked galacturonic acids, which is esterified with methanol at 80%. The pectin-based gel electrolytes in a transparent film form were obtained by a plasticization process with glycerol and addition of LiClO 4. The films showed good ionic conductivity results, which increased from 10 −5 S/cm for the samples with 37 wt.% of glycerol to 4.7 × 10 −4 S/cm at room temperature for the sample with 68 wt.% of glycerol. The electrochemical behaviors of the samples were studied by electrochemical impedance spectroscopy (EIS), and Nyquist graphs are showed and discussed. The obtained pectin-based samples also presented good adherence to the glass, flexibility, homogeneity (SEM) and transparency (about 70% in the vis) properties. They are good candidates to be applied as gel electrolytes in electrochromic devices.

Optimization of performances of gelatin/LiBF 4-based polymer electrolytes by plasticizing effects

Gelatin is a cheap and abundant natural product with very good biodegradation properties and can be used to obtain acetic acid or LiClO 4-based gel polymer electrolytes (GPEs) with high ionic conductivity and good stability. This article presents results of GPEs obtained by the plasticization of gelatin and addition of LiBF 4, where the optimization of the system was achieved by using a factorial design type 2 2 with two variables: glycerol and LiBF 4. From this analysis it was stated that the effect of glycerol as a plasticizer on the ionic conductivity results is much more important than the effect obtained by varying the lithium salt content or the effect of the interaction of both variables. Also all the samples were characterized by X-ray diffraction measurements, UV–vis–NIR spectroscopy and scanning electron microscopy (SEM) and impedance spectroscopy. The ionic conductivity results of all analyzed samples as a function of temperature obey predominantly an Arrhenius relationship and the samples are stable up to 160 °C. Good conductivity results combined with transparency and good adhesion to the electrodes have shown that gelatin-based GPEs are very promising materials to be used as solid electrolytes in electrochromic devices.

Use of polymer/ionic liquid plasticizers as gel electrolytes in electrochromic devices

The dual polymer configuration is commonly used when constructing electrochromic devices (ECDs) due to the expected electrochemical stability and enhanced optical properties. In this configuration, two different polymers are used which are optically complementary. Herein we report the construction and characterization of dual-type ECDs using poly(3, 4-ethylenedioxythiophene) (PEDOT) and poly[3, 6-bis(2-(3, 4-ethylenedioxy)thienyl)-N-methylcarbazole] (PBEDOT-NMCz) as the two complementary electrochromic polymers for the device. A variety of gel electrolyte solutions were prepared and evaluated for these devices. The use of ionic liquids within these gels imparted interesting properties, including long lifetimes, and thermal stability of devices. Switching speeds for the various devices, as well as optical contrasts, were also obtained for the gel electrolytes containing different amounts of ionic liquid as plasticizer.

Ionic Conductivity Thermogravimetry Measurements of Starch-Based Polymeric Electrolytes

Natural polymers are a very interesting matrix to obtain solid polymeric electrolytes (SPE). The principal advantage comes from their particularly interesting biodegradation properties due to the natural origin and also very low cost and good physical and chemical properties. These polymers contain heteroatoms in their structure and for this reason can interact with protons or lithium ions leading to the ionic conduction. Among different natural polymers, starch-based SPEs show good opto-electrochemical characteristics and can be applied to electrochemical devices. This work presents the results of starch and starch derivatives-based electrolytes, which were characterized by impedance spectroscopy and thermal analysis. The ionic conductivity results obtained for these SPEs varied from 10−6 S/cm to 10−4 S/cm at room temperature, depending on the sample, and increased following Arrhenius model. The samples showed good stability up to 200°C evidenced by thermal analysis (TGA). Good conductivity results combined with transparency and good adhesion to the electrodes have shown that starch-based SPEs are very promising materials to be used as solid electrolytes in electrochromic devices.

A.C Impedance, X-ray Diffraction and DSC Investigation on Gelatin Based-Electrolyte with LiClO4

Natural polymers are particularly interesting due to their richness in nature, very low cost and principally biodegradation properties. For these reasons different solid polymeric electrolytes (SPE) have been obtained using cellulose derivatives, starch, chitosan and rubber. This work presents the results of gelatin-based electrolyte, which were characterized by impedance spectroscopy, X-ray diffraction and thermal analysis. The ionic conductivity results obtained for these SPEs were 1.5 × 10−5 S/cm and 4.9 × 10−4 S/cm at room temperature and 80°C, respectively. Temperature-dependence ionic conductivity measurements were taken to analyze the mechanism of ionic conduction in polymer electrolytes. Thermal analysis using differential scanning calorimetry (DSC) was performed in order to observe the change in transition temperature caused by the addition of salt to the electrolyte. Good conductivity results combined with transparency and good adhesion to the electrodes have shown that gelatin-based SPEs are very promising materials to be used as solid electrolytes in electrochromic devices.

Conductivity study of a gelatin-based polymer electrolyte

Natural polymers are particularly interesting due to their richness in nature, very low cost and principally biodegradation properties. For these reasons different solid polymeric electrolytes (SPE) have been obtained using cellulose derivatives, starch, chitosan and rubber. This work presents the results of gelatin-based protonic SPEs, which were characterized by impedance spectroscopy, X-ray diffraction, UV–vis-NIR spectroscopy and scanning electron microscopy (SEM). The ionic conductivity results obtained for these SPEs were 4.5 × 10 −5 S/cm and 3.6 × 10 −4 S/cm at room temperature and 80 °C, respectively. Temperature-dependent ionic conductivity measurements were taken to analyze the mechanism of ionic conduction in polymer electrolytes. Good conductivity results combined with transparency and good adhesion to the electrodes have shown that gelatin-based SPEs are very promising materials to be used as solid electrolyte in electrochromic devices.

DSC and solid state NMR characterization of hydroxyethylcellulose/polyether films

Thin solid films of hydroxyethylcellulose/oligoether were obtained by a grafting reaction of HEC with diisocyanates, and were then characterized by DSC, FTIR, NMR and complex impedance techniques. The transparency of these films in the visible range of the electromagnetic spectrum, the low T g , the good chain mobility and ionic conductivity of 8.8 x 10 -4 Scm -1 at 333 K, show that they can be used as solid electrolytes in electrochromic devices.

Aluminium oxide — Poly(vinyl acetate) composite electrolyte for electrochromic devices

This report describes composite proton electrolytes composed of nanosize activated aluminium oxide particles with different surface acidity suspended in a poly(vinyl acetate)/glycerine matrix. The conductivity of the composite was found to increase by going from basic to neutral to acidic aluminium oxide. Tests in laminated electrochromic devices with tungsten oxide and nickel hydroxide films showed that the acidic electrolyte is compatible with WO3, the basic electrolyte is compatible with Ni(OH)2, and the neutral electrolyte is compatible with both of the electrodes.