Electrochromic performance of a poly(3,4-ethylenedioxythiophene)-Prussian blue device encompassing a free standing proton electrolyte film

Electrochromic devices incorporating an electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film and a free standing, transparent film of a proton conducting polymer electrolyte with high ambient temperature ionic conductivity of 10⁻² S cm⁻¹ have been fabricated with and without the ion storage electrodeposited Prussian blue (PB) counter electrode layer. While coloration efficiency increases as a function of applied potential in the sole PEDOT device with largest values of CE_(max,VIS) ∼ 120 cm² C⁻¹ and CE_(max,NIR) ∼ 133 cm² C⁻¹ attained at V_c = −1.9 V, the PEDOT:PB device shows a digression from this trend. Much higher coloration efficiencies in the visible (247 cm² C⁻¹ at 570 nm) and NIR (116 cm² C⁻¹ at 1100 nm) regions are achieved for the PEDOT:PB device at a relatively lower reducing voltage of −0.8 V. The PEDOT:PB device shows fast switching redox process (t_c = 2.6 s and t_b = 1.3 s for a 50% optical contrast at 632.8 nm) and a highly reversible charge density as the ratio of Q_inserted to Q_extracted was found to vary between 0.8 and 1.0. When switched between the clear and blue states for 2000 cycles, the insignificant drop in peak current density maxima observed for the PEDOT:PB device, i.e. the good cycling stability, the facile fabrication of device assembly, the ease of scaling up the electrolyte and electrochromic coatings, indicate that this method can be adapted as a simple and inexpensive alternative to conventional electrochromic windows with high cost components.     

Performance of a single-phase hybrid and nanocomposite polyelectrolyte in classical electrochromic devices

In this paper, we discuss the high stability of a single-phase hybrid polyelectrolyte (SPHP) and nanocomposite hybrid polyelectrolyte (NHP) in a large electrochromic (EC) device (5 cm × 10 cm) mounted with different electrodes. The electrochromic device (K-glass/FTO/WO₃/SPHP/CeO₂-TiO₂/FTO/K-glass—ECI, K-glass/FTO/WO₃/NHP/CeO₂-TiO₂/FTO/K-glass—ECII,) exhibited excellent color and bleach reversibility, high coloration efficiency (CE) (>35 cm²/C) from the first cycle up to more than 60,000 CA cycles, and a maximum constant rate of deintercalation/intercalation (O_out/Q_in = 1). Also, the life time of the EC device with Nb₂O₅:Mo (K-glass/FTO/Nb₂O₅:O/SPHP/CeO₂-TiO₂/FTO/K-glass—ECIII) was prolonged to up to more than 10,000 cycles with a fairly stable coloration efficiency (around 19 cm²/C) and O_out/Q_in = 1. The SPHP and NHP were tested in a large EC device with different configurations to evaluate its successful performance. In conclusion, its remarkable behavior and high stability render this material an excellent candidate for application in EC devices.     

Ionic liquids in electrochromic devices

The ionic liquid (PYR₁₄TFSI) has proved to be the key material to make a Li-ion conducting element of a complete electrochromic device, when interposed between transparent film electrodes like WO₃ and Li-charged V₂O₅. The key features of this ionic liquid and its mixtures with LiTFSI are the excellent transparency in the visible and NIR optical regions, the good ionic conductivity and the electrochemical compatibility with inorganic Li-intercalation oxide thin film electrodes used in electrochromic devices. The higher optical contrast found during WO₃ colouration with PYR₁₄TFSI-LiTFSI, compared to that in a conventional non-aqueous electrolyte like PC-LiTFSI, was attributed to the larger inertness of the former one (no decomposition reaction at the lowest electrode potential). This highly conductive ionic liquid has been incorporated into a polymer matrix (P(EO)₁₀LiTFSI), in order to obtain a transparent solid electrolyte with high Li ion conductivity and good mechanical stability. Finally this solid PYR₁₄TFSI-P(EO)₁₀LiTFSI transparent ion conductor was interposed between the same electrodes as above in order to yield a fully solid-state, Li-ion electrochromic device. This new solid electrolyte was able to transfer reversibly a Li ionic charge between 5 mC cm⁻² and 10 mC cm⁻² from the lithium storage electrode Li_xV₂O₅ to the WO₃ electrochromic electrode in less than 100 s at room T, darkening the device from an initial 80% to a final 30% transmittance (at 650 nm). Such a device has been tested first under various constant current conditions, and later under potentiostatic control using ±2 V steps. The latter method allows not only for a faster response of the electrochromic system, but provides also an easier life stability test of the device, which withstood 2000 cycles with little changes in its optical contrast.     

Spray deposited titanium oxide thin films as passive counter electrodes

Titanium dioxide (TiO₂) thin films were deposited from methanolic solution onto fluorine doped tin oxide coated conducting glass substrates by spray pyrolysis technique. The electrochemical properties of TiO₂ thin films were investigated using cyclic voltammetry, chronoamperometry, chronocoulometry and iono-optical studies, in 0.1N H₂SO₄ electrolyte. Performance of the films deposited at three different substrate temperatures, viz. 350, 400 and 450 °C is discussed in view of their utilization in electrochromic devices, as counter electrode. The magnitude of charge storage capacity, Q/t (4.75-6.13 × 10⁻³ mC/(cm² nm)) and colouration efficiency (3.2-4.3 cm²/mC) of TiO₂ rank these films among the promising counter electrodes in electrochromic devices.     

A soluble conducting polymer: 1-Phenyl-2,5-di(2-thienyl)-1H-pyrrole and its electrochromic application

A thiophene-functionalized monomer 1-phenyl-2,5-di(2-thienyl)-1H-pyrrole (PTP) was synthesized. The chemical polymerization of PTP (CPTP) was realized by using FeCl₃ as the oxidant. The structures of both the monomer and the soluble polymer (CPTP) were investigated by Nuclear Magnetic Resonance (¹H and ¹³C NMR) and Fourier Transform Infrared (FTIR). The average molecular weight of the chemically synthesized polymer was determined by gel permeation chromatography (GPC) as Mn = 7.2 × 10³. The electrochemical oxidative polymerization of PTP was carried out via constant-potential electrolysis. Characterizations of the resulting polymer were done by cyclic voltammetry (CV), FTIR, Scanning Electron Microscopy (SEM) and UV-vis Spectroscopy. The conductivity of sample was measured by four-probe technique. Moreover, the spectroelectrochemical and electrochromic properties of the polymer film were investigated. Spectroelectrochemical analysis of P(PTP) revealed electronic transitions at 413, 577 and 884 nm corresponding to π-π^* transition, polaron, and bipolaron band formations, respectively. Kinetic studies evaluated the switching ability of the P(PTP); the percent transmittance T% was found as 27%. The homopolymer of PTP was used to construct dual-type polymer electrochromic devices (ECDs) against poly(3,4-ethylenedioxythiophene) (PEDOT). Spectroelectrochemistry, electrochromic switching and open circuit stability of the devices were investigated.     

The mediation reaction between the external couple Ferri/Ferrocyanide and Os(II) bipyridile poly-vinylpyridile films coated onto glassy carbon electrodes

The oxidation-reduction of the Ferri/Ferrocyanide couple in solution onto modified glassy carbon Rotating Disk Electrodes (RDE) covered by Os(II) bipyridile poly-vinylpyridile (OsBPP) polymer was studied at room temperature. Steady state polarization curves were carried out as a function of the rotation speed, the polymer thickness and the concentration of redox centers within the polymer. This system has the characteristic that the formal redox potentials of both the external redox couple (E⁰′(Fe(CN)₆^3−/4−) = + 0.225 V vs. SCE) and the mediator polymer (E⁰′(OsBPP) = 0.260 V vs. SCE) lie very close. It is demonstrated that diffusion of the Ferri/Ferrocyanide inside the polymer can be ruled out. Since the processes of charge transfer at the metal/polymer and the mediating reaction are fast, the experimental results can be interpreted in terms of a kinetics in which the charge transport in the polymer or the diffusion in the solution may be the rate determining step, according to the experimental conditions. A simple model is considered that allows interpreting the experimental results quantitatively. Application of this model allows the determination of the diffusion coefficient of the electrons within the film, D_e ≈ 10⁻¹⁰ cm² s⁻¹.     

A laccase-glucose oxidase biofuel cell prototype operating in a physiological buffer

Here we report on the design and study of a biofuel cell consisting of a glucose oxidase-based anode (Aspergillus niger) and a laccase-based cathode (Trametes versicolor) using osmium-based redox polymers as mediators of the biocatalysts’ electron transfer at graphite electrode surfaces. The graphite electrodes of the device are modified with the deposition and immobilization of the appropriate enzyme and the osmium redox polymer mediator. A redox polymer [Os(4,4′-diamino-2,2′bipyridine)₂(poly{N-vinylimidazole})-(poly{N-vinylimidazole})₉Cl]Cl (E⁰′ = −0.110 V versus Ag/AgCl) of moderately low redox potential is used for the glucose oxidizing anode and a redox polymer [Os(phenanthroline)₂(poly{N-vinylimidazole})₂-(poly{N-vinylimidazole})₈]Cl₂ (E⁰′ = 0.49 V versus Ag/AgCl) of moderately high redox potential is used at the dioxygen reducing cathode. The enzyme and redox polymer are cross-linked with polyoxyethylene bis(glycidyl ether). The working biofuel cell was studied under air at 37 °C in a 0.1 M phosphate buffer solution of pH range 4.4-7.4, containing 0.1 M sodium chloride and 10 mM glucose. Under physiological conditions (pH 7.4) maximum power density, evaluated from the geometric area of the electrode, reached 16 μW/cm² at a cell voltage of 0.25 V. At lower pH values maximum power density was 40 μW/cm² at 0.4 V (pH 5.5) and 10 μW/cm² at 0.3 V (pH 4.4).     

A simplified all-polymer flexible electrochromic device

New all-polymeric simplified electrochromic devices have been prepared based in an intrinsically conductive polymer, poly(ethylene dioxythiophene) (PEDOT). In these devices PEDOT acts simultaneously as electrochromic layer and current collector layer simplifying the construction of the classic devices from seven to five layers. The device presents a chromatic contrast in all the visible range with a maximum at 650 nm (ΔT=0.15) between 0 and 3 V. Representative bleaching and coloring times are 20 and 16 s, respectively, for  cm devices. The originality of this work is that advanced electrochromic devices can be constructed using commercially available materials and using simple experimental methods.     

Di-ureasil xerogels containing lithium bis(trifluoromethanesulfonyl)imide for application in solid-state electrochromic devices

In this study we report the characterization of a prototype solid-state electrochromic device based on poly(ethylene oxide) (PEO)/siloxane hybrid networks doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The polymer networks prepared, designated as di-ureasils and represented as d-U(2000), were produced by a sol-gel procedure and are composed of a siliceous framework to which both ends of polyether chains containing about 40 CH₂CH₂O units are covalently bonded through urea linkages. Samples with compositions of 200 ≥ n ≥ 0.5 (where n is the molar ratio of CH₂CH₂O to Li⁺) were characterized by thermal analysis, complex impedance measurements and cyclic voltammetry at a gold microelectrode. Electrolyte samples were obtained as self-supporting, transparent, amorphous films and at room temperature the highest conductivity was observed with the d-U(2000)₃₅LiTFSI composition (3.2 × 10⁻⁵ Ω⁻¹ cm⁻¹). We report the results of preliminary evaluation of these polymer electrolytes as multi-functional components in prototype electrochromic displays. Device performance parameters such as coloration efficiency, optical contrast and image stability were also evaluated. The electrolytes with n > 8 presented an optical density above 0.56 and display assemblies exhibited good open-circuit memory and stable electrochromic performances.     

Redox induced switching dynamics of a three colour electrochromic metallopolymer film

Thin films of a novel Ru-phenolate based metallopolymer, [Ru(terpy)(box)PVP₂₀]PF₆, in which one in every twenty of the 4-vinyl pyridine monomer units is labelled with the ruthenium complex have been formed on glassy carbon electrodes, terpy is 2,2′:6′,2″-terpyridine, box is 2-(2-hydroxyphenyl)benzoxazole, and PVP is poly(4-vinylpyridine). Cyclic voltammetry and Raman spectroscopy reveal that the Ru^2+/3+ couple is electrochemically reversible but that the phenolate ligand based oxidation is irreversible. These redox processes are associated with reversible colour changes from wine red (reduced) to red orange (mixed composition) then to light green (oxidized) in the visible region and an irreversible change in the near-IR region, respectively. Scanning electron microscopy reveals that repeated switching in LiClO₄ aqueous solution does not induce any significant structural change within the deposit films. Cyclic voltammetry has been used to determine the electrochromic switching rate under semi-infinite linear diffusion conditions. In aqueous LiClO₄, the homogeneous charge transport diffusion coefficient, D_CT, decreases from 3.6 ± 0.3 × 10⁻¹³ to 2.7 ± 0.2 × 10⁻¹³ cm² s⁻¹ as the LiClO₄ concentration increases from 0.1 to 1.0 M. This weak dependence of D_CT on electrolyte concentration suggests that counterion availability is not rate-determining and that the overall rate of charge transport through the metallopolymer film is limited by the rate of segmental polymer chain motion necessary to bring adjacent centres sufficiently close to allow electron transfer to occur. Also the impact of changing the identity of the charge compensating anion of the redox electrochromic switching rate has been investigated. Finally, the electronic conductivity has been determined using interdigitated array electrodes (IDAs).     

Gel electrolyte-based flexible electrochromic devices showing subtractive primary colors

We studied flexible electrochromic devices containing phthalate derivative which showed reversible color change between water transparent and subtractive primary color by electrochemical reaction. Poly(vinyl butyral) (PVB)-based gel electrolyte was prepared to apply the flexible electrochromic device. The ionic conductivity of the gel electrolyte depended on the polymer content, and was higher than 10⁻⁴ S/cm at 25 °C at the PVB content of 33 wt%. Redox reaction of phthalate derivatives was successfully achieved in the gel electrolyte. It is revealed that PVB-based gel electrolyte works well as the material for flexible electrochromic devices showing subtractive primary colors.     

Preparation and reversible photo-crosslinking/photo-cleavage behavior of 4-methylcoumarin functionalized hyperbranched polyester

A novel hyperbranched polymer endcapped with 4-methylcoumarin group (MCTH40) was prepared via thiol-ene addition reaction of thiol-modified hyperbranched polyester (fully thioglycolic acetate of Boltorn™ H40, TAH40) with a vinyl monomer (7-(4-vinyl-benzyloxyl)-4-methylcoumarin, VBMC), and characterized with ¹H NMR and FT-IR spectroscopies. Its reversible photo-crosslinking/photo-cleavage behavior was evaluated based on the UV-vis spectroscopic analysis, and compared with the linear polymer, poly(7-(4-vinyl-benzyloxyl)-4-methylcoumarin (PVBMC)). The absorbance at 319 nm in the UV-vis spectrum gradually decreased under UVA irradiation (λ_max = 365 nm), and then rapidly recovered under UVC irradiation (λ_max = 254 nm). The fluorescence intensity of MCTH40 (λ_max = 469 nm) recovered to 85.2% of original level after photo-cleavage under UVC irradiation, higher than 83.5% of PVBMC (λ_max = 472 nm). The UV-vis analysis results indicated that MCTH40 performs more rapid photo-response than linear PVBMC under the same conditions. Furthermore, the average doses of UVA irradiation for the maximum degree of photo-crosslinking were 22.08 J cm⁻² for MCTH40 and 28.29 J cm⁻² for PVBMC. The average UVC doses of complete photo-cleavage were 9.44 J cm⁻² for MCTH40 and 9.58 J cm⁻² for PVBMC. The GPC analysis indicated that the average molecular weight and its PDI of MCTH40 showed a slight increase after three reversible cycles.     

D-A type hybrid polymers based on EDOT and various benzodiazoles for electrochromic materials

Two donor units (D)-acceptor units (A) type monomers were synthesized by Stille coupling reaction, and then three D-A type hybrid polymers based on 3,4-ethylenedioxythiophene and various benzodiazoles were synthesized by electrochemical polymerization. Spectroelectrochemical and kinetic studies of these polymers showed that all polymer films exhibited excellent electrochromic behavior, obvious optical contrast, and excellent stability. Among them, the response time of P3 film was the shortest (t_c = 1.6 s, t_b = 2.2 s), the coloring efficiency of P2 film was the highest (CE = 333 cm²·C⁻¹), and the stability of P1 was the best (the ΔT loss of P1 after 1000 s cycles is only 2.3%). Therefore, these data prove that these new polymers have great potential in applications as electrochromic materials.     

Electrosynthesis and characterization of an electrochromic material from poly(1,4-bis(2-thienyl)-benzene) and its application in electrochromic devices

1,4-Bis(2-thienyl)-benzene monomer is successfully synthesized via coupling reaction. Poly(1,4-bis(2-thienyl)-benzene) (PBTB) is electrochemically synthesized and characterized. Resulting polymer film has distinct electrochromic properties. Its application in electrochromic devices (ECDs) is discussed. PBTB is switched between yellow in the neutral state and green in the oxidized state. Electrochromic switching of PBTB film is performed and the polymer film shows a maximum optical contrast (ΔT %) of 44.8% at 610 nm in visible region with a response time of 1.6 s. The coloration efficiency (CE) of PBTB is calculated to be 162 cm² C⁻¹. Electrochromic device (ECD) based on PBTB and poly(3,4-ethylenedioxythiophene) (PEDOT) is also constructed and characterized. Maximum contrast (ΔT %) and switching time of the device are measured as 29.5% and 0.43 s at 628 nm. The CE of the device is calculated to be 408.9 cm² C⁻¹. Clear change from green (at neutral state) to blue color (at full oxidized state) of this ECD is demonstrated with reasonable cycle life.     

Synthesis and electrochemical characterization of bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer

The synthesis and characterization of a novel donor acceptor donor type bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer and its electrochemically prepared polymer on carbon fiber, Pt button and ITO plate is reported in this paper. Cyclic voltammetry of the polymer in 0.1 M Et₄NBF₄/CH₂Cl₂ exhibits a very well defined and reversible redox processes and this co-monomer can be either p-doped or n-doped. The half-wave oxidation potentials of the polymer (E_1/2) were observed at 0.303 and 0.814 V versus Ag/AgCl. The polymer is electrochromic; the onset for the π-π^* transition (E_g) of 1.75 eV with a λ_max at 2.15 eV and the homogeneous and high quality film of the polymer is stable of its optical properties offering fast switching time which is less than 0.25 s. The morphological studies reveal that the polymer was deposited as a continuous and very well adhering film to surface of the carbon fiber microelectrode. All these properties make this polymer favorable for use in electronic devices.     

Poly(phenylacetylene) with bulky chiral germyl groups: synthesis and effects of measuring solvents and temperature on chiroptical properties

(+)-p-[{Methyl(1-naphthyl)phenyl}germyl]phenylacetylene, an acetylene with a bulky chiral germyl group, was polymerized with [(nbd)RhCl]₂-Et₃N to give a high-molecular-weight polymer in good yield. The CD spectrum of the polymer exhibited very large molar ellipticities [θ] in the UV region in non-aromatic solvents (e.g. THF and CHCl₃). In contrast, the CD signals of the polymer in aromatic solvents (e.g. toluene, tetralin, and benzene) became appreciably smaller: [θ]_max=6.4×10⁴ (330 nm) and −4.7×10⁴° cm² dmol⁻¹ (370 nm) in CHCl₃; [θ]_max=1.1×10⁴ (330 nm) and −0.7×10⁴° cm² dmol⁻¹ (370 nm) in toluene. The [θ]_max values of the polymer in aromatic solvents increased when the solutions were heated, which is attributed to decreased π-π interaction between the solvents and side groups.     

Electrochromism of dinitrobenzoyl-derivatised polypyrrole films deposited on ITO/glass electrodes

Poly[(R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate] films of various thicknesses were galvanostatically deposited on ITO/glass electrodes using different deposition charges (Q_dep), and their electrochromic properties were investigated. Depending on the Q_dep employed, the polymeric films presented green-yellow or green-brown colours in the reduced state (λ_max at 350 nm and shoulder at 390 nm) and a blue-grey colour in the oxidised state (λ_max at 460 nm) with high absorption in the near infrared region (λ_max > 800 nm). Whilst films deposited with a Q_dep of 40 mC cm⁻² presented the highest chromatic contrast (20%), films with a Q_dep of 50 mC cm⁻² exhibited greater stability to redox cycling (ca. 350 cycles), high coulombic efficiency (>73%) and good optical memory in the reduced state (E = 0.0 V).     

An approach to laminated flexible Dye sensitized solar cells

We have built TiO₂ Dye sensitized solar cells (DSSCs) that combined flexible TiO₂ photoanodes coated on ITO/PET substrates with a gel electrolyte based on PVDF-HFP-SiO₂ films. Titanium isopropoxide (TiP₄) was used as additive to TiO₂ nanoparticles for increasing power conversion efficiency in Dye sensitized solar cell electrodes prepared at low-temperature (130 °C). An efficiency η_AM1.5G = 3.55% on ITO/PET substrates is obtained at 48 mW/cm² illumination with a standard liquid electrolyte based on methoxypropionitrile. Among several solvents forming gels with PVDF-HFP-SiO₂, N-methyl (pyrrolidone) (NMP) was found to enable the most stable devices. A power conversion efficiency η_AM1.5G = 2% was obtained under 10 mW/cm² with flexible TiO₂-ITO-PET photoanodes and the PVDF-HFP-SiO₂ + NMP gel electrolyte.     

Modeling and design of transdermal drug delivery patches containing an external heating device

Process modeling and design concepts were implemented to aid in the manufacturing of heat-enhanced transdermal drug-delivery systems. The simulated prototype consists of a corticosterone-loaded polymer patch applied to the skin and connected to a heating device in which an exothermic reaction occurs. To achieve a desired transdermal flux of 1.2 × 10⁻⁵ mg/cm² h, this contribution focuses on the influences of the (1) initial reaction rate (−r_A0), (2) mass of filler material in the device (m), (3) initial concentration (C₀) of medicament in the patch and (4) overall heat transfer coefficient (U). A regression technique yielded the following results: −r_A0 = 3.000 × 10⁻² kg/m³ s, m = 1.251 × 10⁻⁸ kg, U = 6.124 × 10 J/m² K s and C₀ = 1.966 × 10⁻¹ kg/m³. When m was fixed at 12.5 g, the optimum design required the following specifications: r_A0 = 2.765 × 10⁻² kg/m³ s, U = 1.402 × 10³ J/m² K s and C₀ = 1.941 × 10⁻¹ kg/m³. The priority (S_i) of the input factors (i) in reaching the target delivery rate is: SC₀>S−rA0>Sm>SU.