Electrochemical supercapacitor electrode material based on poly(3,4-ethylenedioxythiophene)/polypyrrole composite

Poly (3,4-ethylenedioxythiophene)/polypyrrole composite electrodes were prepared by electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of polypyrrole (PPy) modified tantalum electrodes. The morphology observation of PPy and poly(3,4-ethylenedioxythiophene)/polypyrrole composite (PEDOT/PPy) was performed on Field Emission Scanning Electron Microscope (SEM). The electrochemical capacitance properties of the composite were investigated with cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques in the two- or three-electrode cell system. The results show that the PEDOT/h-PPy (PPy with horn-like structure) composite films were characterized with highly porous structure, which leads to their specific capacitance as 230 Fg⁻¹ in 1 M LiClO₄ aqueous solutions and even 290 Fg⁻¹ in 1 M KCl aqueous solutions. Moreover, the composite exhibits a rectangle-like shape of voltammetry characteristics even at scanning rate 100 mV s⁻¹, a linear variation of the voltage with respect to time without a clear ohm-drop phenomenon in galvanostatic charge–discharge process and almost ideal capacitance behavior in low-frequency in 1 M KCl solutions. Furthermore, specific power of the composite would reach 13 kW kg⁻¹ and it had good cycle stability. All of the above imply that the PEDOT/h-PPy composites were an ideal electrode material of supercapacitor.     

A complementary electrochromic device based on polyaniline and poly(3,4-ethylenedioxythiophene)

In this study, two conducting polymers, polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT), were used to construct an electrochromic device (ECD). PANI was employed as the anodic coloring polymer while PEDOT was used as the cathodic coloring polymer. The electrochemical and optical properties of PANI, which has a coloration efficiency of 25 cm²/C at 570 nm, were coupled with the complementary coloring material, PEDOT, which has a coloration efficiency of 206 cm²/C at 570 nm. A suitable operating potential window was switched between −0.6 and 1.0 V to explore the cycle life of the ECD. We tested the PANI–PEDOT ECD, which consisted of PANI, PEDOT, and an organic electrolyte containing 0.1 M LiClO₄ in propylene carbonate and 1 mM HClO₄. The transmittance of the ECD at 570 nm changed from 58% (−0.6 V) to 14% (1.0 V) with a coloration efficiency of 285 cm²/C. Within the selected operating voltage range, the PANI–PEDOT ECD could be cycled for up to 2×10⁴ cycles.     

An all-thiophene electrochromic device fabricated with poly(3-methylthiophene) and poly(3,4-ethylenedioxythiophene)

A novel all-organic electrochromic device (ECD) is presented. By electrodepositing poly(3-methylthiophene) (PMeT) in boron fluoride ethyl ether (BFEE), a strong Lewis acid, a good-quality PMeT film was obtained. On the basis of studies of PMeT, it can be regarded as a pseudo-anodic coloring material for ECDs. On the other hand, poly(3,4-ethylenedioxythiophene) (PEDOT) is an ideal cathodic coloring electrochromic material known for its high optical contrast, long-term stability, and high coloration efficiency. By combining these two thiophene derivatives, the application potential of this device was determined. The color of the ECD switches between deep blue at −1.4 V (PEDOT vs. PMeT) and light red at 0.6 V. The device exhibits stable electrochromic performance, with a maximum optical attenuation (ΔT_max) at 655 nm reaching 46% (from 9% to 55%), and achieves a high coloration efficiency of 336 cm²/C. After 100 repeated cycles, the cell still retained at 91.3% of its ΔT_max at 655 nm.     

Cycling and at-rest stabilities of a complementary electrochromic device containing poly(3,4-ethylenedioxythiophene) and Prussian blue

PEDOT-based electrochromic devices (ECDs) have been investigated intensively in recent years. In order to obtain an ECD having long cycle life, the counter electrode and electrolyte used should be compatible in the electrochemical environment. Prussian blue (PB) is proven to be electrochemically stable when cycling in non-aqueous solutions. Thus a new organic-inorganic complementary ECD was assembled in combination with a PMMA-based gel polymer electrolyte. This ECD exhibited deep blue-violet when applying −2.1 V and became light blue when applying 0.6 V. Under these conditions, the transmittance of the ECD at 590 nm changed from 13.8% (−2.1 V) to 60.5% (+0.6 V) with a coloration efficiency of 338 cm²/C. The cell retained 55% of its maximum transmittance window (ΔT_max) after 50,640 repeated cycles. Moreover, the at-rest stability test revealed a transmittance window (ΔT) decay of 9.6% over a period of 107 days. Therefore, the proposed PEDOT-PB ECD may have potential for practical applications.     

Porous NiO/poly(3,4-ethylenedioxythiophene) films as anode materials for lithium ion batteries

NiO/poly(3,4-ethylenedioxythiophene) (PEDOT) films are prepared by chemical bath deposition and electrodeposition techniques using nickel foam as the substrate. These composite films are porous, and constructed by many interconnected nanoflakes. As anode materials for lithium ion batteries, the NiO/PEDOT films exhibit weaker polarization and better cycling performance as compared to the bare NiO film. Among these composite films, the NiO/PEDOT film deposited after 2 CV cycles has the best cycling performance, and its specific capacity after 50 cycles at the current density of 2 C is 520 mAh g⁻¹. The improvements of these electrochemical properties are attributed to the PEDOT, a highly conductive polymer, which covers on the surfaces of the NiO nanoflakes, forming a conductive network and thus enhances the electrical conduction of the electrode.     

Improvement of the electrochemical properties via poly(3,4-ethylenedioxythiophene) oriented micro/nanorods

Arrays of oriented poly(3,4-ethylenedioxythiophene) (PEDOT) micro/nanorods are synthesized by electrochemical galvanostatic method at the current density of 1 mA cm⁻² in the cetyltrimethylammonium bromide (CTAB) aqueous solution whose pH value is 1. The CTAB is used both as the surfactant and the supporting salt in the electrolyte solution. The electrochemical properties of PEDOT films are characterized by cyclic voltammetry and galvanostatic charge/discharge techniques, which indicate that the arrays of oriented PEDOT micro/nanorods can be applied as the electrode materials of supercapacitors. In addition, the cycling performance of PEDOT micro/nanorods is much better than that of traditional PEDOT particles. The effects of the concentration of CTAB, the current density, and pH value of electrolyte solutions on the morphologies and electrochemical properties of PEDOT films are investigated. The mechanism of different morphologies formation is discussed in this study as well.     

Chemical modification of Nafion membrane with 3,4-ethylenedioxythiophene for direct methanol fuel cell application

Nafion 117 membranes were modified by in situ chemical polymerization of 3,4-ethylenedioxythiophene using H₂O₂ as oxidant for direct methanol fuel cell application. Methanol permeability and proton conductivity of the poly(3,4-ethylenedioxythiophene)-modified Nafion membranes as a function of temperature were investigated. An Arrhenius-type dependency of methanol permeability and proton conductivity on temperature exists for all the modified membranes. Compared with Nafion 117 membrane at 60 °C, the methanol permeability of these modified membranes is reduced from 30% to 72%, while the proton conductivity is decreased from 4% to 58%, respectively. Because of low methanol permeability and adequate proton conductivity, the DMFC performances of these modified membranes were better than that of Nafion 117 membrane. A maximum power density of 48.4 mW cm⁻² was obtained for the modified membrane, while under same condition Nafion 117 membrane got 37 mW cm⁻².     

Electropolymerization of high stable poly(3,4-ethylenedioxythiophene) in ionic liquids and its potential applications in electrochemical capacitor

Poly(3,4-ethylenedioxythiophene) (PEDOT) has been successfully electropolymerized using a purified 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) as both the growth medium and the supporting electrolyte. The electrochemical performance of the PEDOT thin film was investigated in 1 mol L⁻¹ H₂SO₄ solution. It possesses nearly ideal capacitive property, and its specific capacitance is about 130 F g⁻¹. Compared with other conducting polymers, enhanced cycling lifetime (up to 70,000 cycles), which is close to that of active carbon materials, was observed on repetitive redox cycling.     

Poly[dithio-2,5-(1,3,4-thiadiazole)] (PDMcT)–poly(3,4-ethylenedioxythiophene) (PEDOT) composite cathode for high-energy lithium/lithium-ion rechargeable batteries

We present a characterization of the redox behavior of organosulfur-based composite cathodes composed of poly[dithio-2,5-(1,3,4-thiadiazole)] (PDMcT), which is a polymer derived from 2,5-dimercapto-1,3,4-thiadiazole (DMcT), and poly(3,4-ethylenedioxythiophene) (PEDOT) in a carbonate-based mixed solvent containing 1.0 M LiBF₄. We have previously shown that PEDOT films, electrochemically generated at glassy carbon electrode surfaces, gave rise to a dramatic enhancement of the interfacial charge transfer kinetics of DMcT in solution. In a similar fashion, chemically prepared PEDOT films exhibited dramatic electrocatalytic activity towards the redox reactions of PDMcT in the composite cathodes. While the composite cathode exhibited a very high capacity of 205 mAh g⁻¹ (based on the electroactive mass) at the first discharge, in subsequent charge/discharge tests, the capacity of the PDMcT–PEDOT composite cathode (1:1 mole ratio) decreased significantly because of dissolution of the reduction products of PDMcT into the electrolyte solution. We also found that an ionic polymer, consisting of a mixture of PEDOT and polystyrene sulfonate (PEDOT–PSS) could electrostatically, but not physically, prevent, at least in part, leaching of the DMcT species into the electrolyte solution, thus improving the coulomb efficiency for the redox reactions of DMcT in a PDMcT–PEDOT composite film during charge/discharge cycles.     

Significant effects of poly(3,4-ethylenedioxythiophene) additive on redox responses of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) cathode for rechargeable Li batteries

Redox behaviors of the poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM)-coated electrodes composited with carbon black (CB) or poly(3,4-ethylenedioxy-thiophene) (PEDOT) are presented. Effects of PEDOT additive on the redox activity of PDBM were investigated to apply their composite materials as candidates of cathodes for rechargeable lithium batteries. The film having a PEDOT/PDBM with weight ratio of 1/1 shows a gravimetric capacity of 129 mAh g⁻¹ (corresponding to 188 mAh g⁻¹ for PDBM and 70 mAh g⁻¹ for PEDOT). The highest energy density observed was 140 mAh g⁻¹ (406 mWh g⁻¹) for the composite cathode. Good cycle-ability over 100 cycles was attained with a PEDOT/PDBM composite cathode.     

The effects of hyperbranched poly(siloxysilane)s on conductive polymer aluminum solid electrolytic capacitors

An aluminum solid electrolytic capacitor, using poly-(3,4-ethylenedioxythiophene) (PEDOT) as a counter electrode, was prepared with hyperbranched poly(siloxysilane)s (HBPSi) that has a large number of vinyl groups to improve the interfacial properties between aluminum oxide and PEDOT. Capacitance and equivalent series resistance (Rs) were significantly improved compared to untreated oxide film and vinyl terminated polydimethylsiloxane coated interfaces. From electrochemical measurement of the withstand voltage, damage to the oxide film from chemical polymerization of PEDOT was less with the HBPSi treatment. Frequency characteristics and electrical conductivity measurements of the polymer indicated that the resistance inside the etched porous layer was greatly reduced. These results show that the HBPSi pre-coating layer inhibited degradation of the oxide film by chemical polymerization of PEDOT and the conductivity of PEDOT in the etched porous oxide layer, and also enlarges the contact area by improving interfacial adhesion.     

Immobilization of Trametes hirsuta laccase into poly(3,4-ethylenedioxythiophene) and polyaniline polymer-matrices

The immobilization of Trametes hirsuta laccase (ThL) in the poly(3,4-ethylenedioxythiophene) (PEDOT) and polyaniline (PANI) matrices was carried out in order to study the catalytic effect of ThL in different biocathode structures in a biofuel cell application. By using 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) as a mediator compound, the immobilized ThL in both polymer matrices, exhibited catalytic activity for the reduction of oxygen into water. The amount of ThL was adjustable in the PEDOT matrix by controlling the working parameters, such as the charge density used in the electropolymerization of EDOT monomer and the ThL concentration used in the electropolymerization electrolyte. In the PEDOT biocathode structure, the utilization of porous material as the PEDOT supporting template was studied in order to improve the current density generated per unit area/volume. Reticulated vitreous carbon foam (RVC foam) was chosen as the PEDOT supporting template material and the biocathodes were manufactured by in situ entrapment of ThL into PEDOT films polymerized on the RVC foam. These biocathodes possessed a high cathodic open circuit potential and produced a large current density, reaching 1 mA cm⁻³ at 0.45 V when 19.5 μg ml⁻¹ of ThL was used in the electrolyte. The performance of these biocathodes was extremely sensitive to variations in pH and the optimal working pH was around 4.2. The biocathode reserved 80%, 50%, and 30% of the catalytic activity after storage in a +4 °C buffer solution for 1 day, 1 week, and 1 month, respectively. The PANI matrix was prepared in a form of printable ink where ThL was in situ entrapped in the PANI matrix during the laccase activated polymerization of aniline using a chemical batch reactor method. Different amounts of the ThL-containing printable PANI ink were then applied on carbon paper and the performance of the ink was subsequently electrochemically characterized. In this way, not only two different polymer matrices, but also two different matrix manufacturing procedures could be compared.     

A photovoltaic cell incorporating a dye-sensitized ZnS/ZnO composite thin film and a hole-injecting PEDOT layer

A photovoltaic cell containing a dye-sensitized ZnS/ZnO composite thin film was studied. ZnS was thermally evaporated or electrodeposited onto conducting fluorine-doped tin oxide glass; then a particulate ZnO layer was pasted and sintered to form a ZnS/ZnO composite layer. A visible light source was utilized to excite the Ru-dye, which was adsorbed onto the surface of the ZnO. The ZnS layer is believed to provide an alternative pathway for electrons to move across ZnO barriers. This alternative pathway with the composite layer structure provides higher power efficiency than does a single layer of ZnO or ZnS. A hole-injecting, p-type poly(3,4-ethylenedioxythiophene) (PEDOT) thin film was also introduced to substitute for the Pt catalytic layer which helps with the rejuvenation of I⁻ ions. Although the p-type semiconductor behavior increased the open circuit voltage (V_oc), the power efficiency decreased because the I⁻ rejuvenation rate was much slower on PEDOT than on Pt.     

Photoelectrochemical studies of the junction between poly[3-(4-octylphenyl)thiophene] and a redox polymer electrolyte

The photoelectrochemical properties of all-solid-state photoelectrochemical cell constructed from a conjugated polymer poly[3-(4-octylphenyl)thiophene] and an amorphous poly(ethylene oxide) complexed with iodide/triiodide redox couple were studied. In order to develop flexible photoelectrochemical cells, we have used a transparent polymeric metal, doped poly(3,4-ethylenedioxythiophene), as a counter electrode. It was shown that poly(3,4-ethylenedioxythiophene) improved the charge transfer between indium tin-oxide and iodide/triiodide redox couple. The spectral response, photocurrent time, and open-circuit voltage and short-circuit current dependence on light intensity have been studied. The photon to electron conversion efficiency obtained was low. The photocurrent and photovoltage dependence studies on light intensity indicate exciton recombination and/or traps as limiting factors.     

Development and characterization of polymer electrolyte membranes based on ionical cross-linked poly(1-vinyl-1,2,4 triazole) and poly(vinylphosphonic acid)

The fabrication, thermal and proton conducting properties of complex polymer electrolytes based on poly(vinylphosphonic acid) (VPA) and poly(1-vinyl-1,2,4-triazole) (PVTri) were investigated throughout this work. The membrane materials were produced by complexation of PVPA with PVTri at various concentrations to get PVTriP(VPA)_x where x designates the molar ratio of the polymer repeating units and varied from 0.25 to 4. The complexed structure of the polymers was confirmed by FT-IR spectroscopy. The TGA results verified that the presence of PVTri in the complex polymer electrolytes suppressed the formation of phosphonic acid anhydrides up to 150 °C. The DSC and SEM results demonstrated the homogeneity of the materials. Proton conductivity, activation energy and water/methanol uptake of these membranes were also measured. PVTriP(VPA)₂ showed a proton conductivity of 2.5 × 10⁻⁵ S cm⁻¹ at 180 °C in the anhydrous state. After humidification (RH = 50%), PVTri-P(VPA)₄ and PVTri-P(VPA)₂ showed respective proton conductivities of 0.008 and 0.022 S cm⁻¹ at 100 °C, where the conductivity of the latter is close to Nafion 117 at the same humidity level.     

Semi-interpenetrating network based on cross-linked poly(vinyl alcohol) and poly(styrene sulfonic acid-co-maleic anhydride) as proton exchange fuel cell membranes

A series of promising proton conducting membranes have been synthesized by using poly(vinyl alcohol), with sulfosuccinic acid (SSA) as a cross-linking agent and poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA) as proton source, which form a semi-interpenetrating network (semi-IPN) PVA/SSA/PSSA-MA membrane. A bridge of SSA between PVA molecules not only reinforces the network but also provides extra proton conducting paths. PSSA-MA chains trapped in the network were the major sources of protons in the membrane. FT-IR spectra confirmed the success of the cross-linking reaction and molecular interactions between PVA and PSSA-MA. Associated characteristics of a proton conducting membrane including ion-exchange capacity (IEC), proton conductivity and water uptake were investigated. The measured IECs of the membranes increased with increase of PSSA-MA content varying from 20 to 80% and correlated well with the measured uptake water and proton conductivity. The semi-IPN membranes with PSSA-MA over 60% exhibited a higher proton conductivity than Nafion-115 and also a reasonable level of water uptake. Fuel cell performance of membrane electrode assemblies (MEA) was evaluated at various temperatures with H₂/air as well as H₂/O₂ gases under ambient pressure. A power density of 0.7 W cm⁻² was obtained for the MEA using PVA/SSA20/PSSA-MA80 membrane using H₂/O₂ at 50 °C.     

A complementary electrochromic device based on polyaniline tethered polyhedral oligomeric silsesquioxane and poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonic acid)

A high-contrast complementary electrochromic device based on polyaniline (PANI) tethered polyhedral oligomeric silsesquioxane (POSS) (POSS-PANI) and poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonic acid) (PEDOT:PSS) is assembled. The electrochromic properties, cyclic voltammetry behavior and coloration efficiency of the device are studied. Due to the loosely packed structure, POSS-PANI gives rise to a significantly higher electrochromic contrast, coloration efficiency and faster switching speed than PANI. Despite its high contrast, the combination of POSS-PANI with PEDOT:PSS still shows synergy in terms of contrast enhancement, which can be attributed to the additional driving force for the diffusion of dopants into PEDOT:PSS provided by the dedoping of POSS-PANI.     

Novel cross-linked sulfonated poly (arylene ether ketone) membranes for direct methanol fuel cell

To prepare a cross-linked proton exchange membrane with low methanol permeability and high proton conductivity, poly (vinyl alcohol) is first blended with sulfonated poly (arylene ether ketone) bearing carboxylic acid groups (SPAEK-C) and then heated to induce a cross-linking reaction between the carboxyl groups in SPAEK-C and the hydroxyl groups in PVA. Fourier transform infrared spectroscopy is used to characterize and confirm the structure of SPAEK-C and the cross-linked membranes. The proton conductivity of the cross-linked membrane with 15% PVA in weight reaches up to 0.18 S cm⁻¹ at 80 °C (100% relative humidity), which is higher than that of Nafion membrane, while the methanol permeability is nearly five times lower than Nafion. The ion-exchange capacity, water uptake and thermal stability are investigated to confirm their applicability in fuel cells.     

Proton-conducting membranes with high selectivity from cross-linked poly(vinyl alcohol) and poly(vinyl pyrrolidone) for direct methanol fuel cell applications

A series of hydrocarbon membranes consisting of poly(vinyl alcohol) (PVA), sulfosuccinic acid (SSA) and poly(vinyl pyrrolidone) (PVP) were synthesized and characterized for direct methanol fuel cell (DMFC) applications. Fourier transform infrared (FT-IR) spectra confirm a semi-interpenetrating (SIPN) structure based on a cross-linked PVA/SSA network and penetrating PVP molecular chains. A SIPN membrane with 20% PVP (SIPN-20) exhibits a proton conductivity value comparable to Nafion^® 115 (1.0 × 10⁻² S cm⁻¹ for SIPN-20 and 1.4 × 10⁻² S cm⁻¹ for Nafion^® 115). Specifically, SIPN membranes reveal excellent methanol resistance for both sorption and transport properties. The methanol self-diffusion coefficient through a SIPN-20 membrane conducted by pulsed field-gradient nuclear magnetic resonance (PFG-NMR) technology measures 7.67 × 10⁻⁷ cm² s⁻¹, which is about one order of magnitude lower than that of Nafion^® 115. The methanol permeability of SIPN-20 membrane is 5.57 × 10⁻⁸ cm² s⁻¹, which is about one and a half order of magnitude lower than Nafion^® 115. The methanol transport behaviors of SIPN-20 and Nafion^® 115 membranes correlate well with their sorption characteristics. Methanol uptake in a SIPN-20 membrane is only half that of Nafion^® 115. An extended study shows that a membrane-electrode assembly (MEA) made of SIPN-20 membrane exhibits a power density comparable to Nafion^® 115 with a significantly higher open current voltage. Accordingly, SIPN membranes with a suitable PVP content are considered good methanol barriers, and suitable for DMFC applications.     

Inorganic-organic polymer electrolytes based on poly(vinyl alcohol) and borane/poly(ethylene glycol) monomethyl ether for Li-ion batteries

In this study, poly(vinyl alcohol) (PVA) was modified with poly(ethylene glycol) monomethyl ether (PEGME) using borane-tetrahydrofuran (BH₃/THF) complex. Molecular weights of both PVA and PEGME were varied prior to reaction. Boron containing comb-branched copolymers were produced and abbreviated as PVA1PEGMEX and PVA2PEGMEX. Then polymer electrolytes were successfully prepared by doping of the host matrix with CF₃SO₃Li at several stoichiomeric ratios with respect to EO to Li. The materials were characterized via nuclear magnetic resonance (¹H NMR and ¹¹B NMR), Fourier transform infrared spectroscopy (FT-IR), Thermogravimetry (TG) and differential scanning calorimeter (DSC). The ionic conductivity of these novel polymer electrolytes were studied by dielectric-impedance spectroscopy. Li-ion conductivity of these polymer electrolytes depends on the length of the side units as well as the doping ratio. Such electrolytes possess satisfactory ambient temperature ionic conductivity (>10⁻⁴ S cm⁻¹). Cyclic voltammetry results illustrated that the electrochemical stability domain extends over 4 V.