Electrochemical synthesis and structural studies of polypyrroles, poly(3,4-ethylene-dioxythiophene)s and copolymers of pyrrole and 3,4-ethylenedioxythiophene on carbon fibre microelectrodes

Polypyrrole, poly(3,4-ethylenedioxythiophene) and the copolymer of pyrrole and 3,4-ethylenedioxythiophene films were synthesized electrochemically on carbon fibre microelectrodes (CFME). Deposition conditions on the carbon fibre and the influence of monomer concentrations on the copolymerization, as well as the electrochemistry of the resulting polymers and copolymers, were studied. Structural studies of the polymers were conducted using different techniques such as cyclic voltammetry, in situ spectroelectrochemistry, FTIR and scanning electron microscopy. The effect of the monomer ratio on the formation of copolymer is reported. A high level of stability to overoxidation was also observed for poly(3,4-ethylenedioxythiophene) as the polymer on this CFME substrate shows limited degradation of its electroactivity at potentials 1.2 V above its half-wave potential.     

Effects of polymerization potential on the properties of electrosynthesized PEDOT films

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were prepared from an aqueous solution by electrooxidation at different anodic potential in the range 0.8-1.5 V (vs. SCE). The effect of polymerization potential on conductivity, electrochemical behavior and ESR response of PEDOT film has been investigated. The overoxidation peak of PEDOT exists near the polymerization potential of 3,4-ethylenedioxythiophene. The overoxidation behavior of PEDOT with polymerization potential yielded bell-shaped curve of the conductivity of PEDOT and the polymerization rate with the polymerization potential. This phenomenon has been reported for the first time.     

Different steps in the electrosynthesis of poly(3,4-ethylenedioxythiophene) on platinum

The initial stages of poly(3,4-ethylenedioxythiophene) (PEDOTh) film growth on platinum electrodes from TBAClO₄/acetonitrile solution are investigated by means of current-time transient measurements and tapping mode atomic force microscopy. It is shown that, for growth potentials in the range 1.17-1.29 V vs. SCE, the deposition process involves the formation of oligomers in the solution, progressive nucleation of centres of the new phase and three-dimensional growth of a first compact layer followed by a non-uniform distribution of granular-like clusters, whose number and size increase with the synthesis potential and charge. The obtained results reveal that PEDOTh films prepared at distinct potentials but with the same growth charge (Q_g) display similar electroactivities. They also depict that the electrochemical behaviour of the films is a function of the charge used for the synthesis, namely the reduction of tick PEDOTh layers (Q_g > 20 mC cm⁻²) includes more that one step, as a consequence of the formation of a two-layered polymer film.     

On the pH dependence of electroactivity of poly(methylene blue) films

The electrochemical behavior of poly(methylene blue) on different electrodes has been investigated by electrochemical quartz crystal microbalance and in situ spectrophotometric measurements coupled to cyclic voltammetry. Polymeric films were obtained potentiodynamically and the charge transport mechanism was analyzed. The electrochemical results show that polymer electroactivity depends not only on pH but also on the substrate. Charge compensation changes with both pH and the size of the anions showing a transition in the pH range of polymer pKa. It was demonstrated by spectroelectrochemical experiments that the electroactivity of the film depends on the radical/radical cation equilibrium. The potentials where the most electroactive species are formed have been determined.     

Synthesis and electrochemical characterization of new optoelectronic materials based on conjugated donor-acceptor system containing oligo-tri(heteroaryl)-1,3,5-triazines

A series of novel oligoarylenes based on donor-acceptor system, containing triazine moiety as an electron-transporting central core, have been prepared by electrochemical polymerization. The redox behaviour of poly(2,4,6-tri[p-(2-(3,4-ethylenedioxythienyl))-phenyl]-1,3,5-triazine) was studied by cyclic voltammetry and triple in situ ESR/UV-vis-NIR spectroelectrochemistry to get more details on the type of charge carriers within the film. To obtain desired oligoarylenes, triazine-core monomers possessing various electrochromic side groups have been synthesized by the Stille cross-coupling methodology. The structures have been confirmed by ¹H NMR, ¹³C NMR, and elemental analysis. Monomers show good chemical stability in common organic solvents such as chloroform, dichloromethane or toluene and also exhibit excellent thermal stability over wide range of temperatures. Furthermore, their photophysical properties have been established with the use of fluorescence spectroscopy. Electrochemical results accompanied with fluorescence spectroscopy suggest that these derivatives of triazine can be successfully used in the fabrication of organic light-emitting diodes (OLEDs).     

Quantitative in-situ EPR spectroelectrochemical studies of doping processes in poly(3,4-alkylenedioxythiophene)s: Part 1: PEDOT

Quantitative in-situ EPR spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) (PEDOT) have been carried out with an aim to gain new insights into the doping processes taking place in this polymer. Corroborating the findings made during previous studies of this polymer, absolute measurements conducted in this study provided new detailed information regarding some of the basic parameters characterising the doping process of this conjugated polymer. It was found that concentrations of paramagnetic centres in PEDOT vary from 0.02 spin per mer in the dedoped state up to a maximum of 0.12 spin per mer at 0.15 [e⁻/mer] doping level, corresponding to 1 spin per ca. 8.5 meric units. Such notable concentration values indicate that polarons represent a numerous charge carrier group in PEDOT, contrary to observations made for other members of polythiophene family. Furthermore polarons do not disappear at high doping levels of PEDOT but rather decrease their numbers gradually down to 0.08 spins per mer at a maximum doping level of 0.55 [e⁻/mer] attained in this study. Based on information about concentrations of spins and polymer doping charges, concentrations of bipolarons have been evaluated as a function of doping level. Results indicate that bipolaron formation starts at ca. 0.06 [e⁻/mer] doping level when spin generation efficiency begins to deviate from 1 and interspin interactions emerge as evidenced by doping level dependency of EPR signal linewidth (ΔB_pp). Decomposition of complex EPR spectra of PEDOT in its doped state corroborated the presence of two groups of paramagnetic centres in this polymer. Based upon doping level dependencies of their spectroscopic parameters (concentration, ΔB_pp linewidth and g-factor), the identity of these centres has been redefined compared to our previous reports, linking their properties with the type of polymer phase (crystalline or amorphous) they reside in.     

A novel EDOT–nonylbithiazole–EDOT based comonomer as an active electrode material for supercapacitor applications

A novel EDOT–nonylbithiazole–EDOT based bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer was synthesized and was electrochemically deposited onto carbon fiber electrode as an active electrode material. An electrochemical impedance study on the prepared electrodes is reported in this paper. Capacitive behavior of the carbon fiber microelectrode/poly(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) system was investigated with cyclic voltammetry (CV) experiments and electrochemical impedance spectroscopy. Variation of capacitance values by scan rate and specific capacitance values at different potentials are presented. Specific capacitance value for a galvanostatically prepared polymer film with a charge of 5 C cm⁻² was obtained about 340 mF cm⁻². Effect of the solvent and the deposition charge on the capacitive behavior of the film was investigated using electrochemical impedance spectroscopy. An equivalent circuit model was proposed and the electrochemical impedance data were fitted to find out numerical values of the proposed components. The galvanostatic charge/discharge characteristic of a film was investigated by chronopotentiometry and the morphology of the films electrodeposited at different deposition charges were monitored using FE-SEM.     

Fabrication of poly(3,4‐ethylenedioxythiophene)‐polysaccharide composites

Poly(3,4‐ethylenedioxythiophene) (PEDOT) doped with a series of anionic polysaccharides such as carboxymethyl cellulose, sodium hyaluronate, xanthan gum, pectin, gellan gum were prepared by electropolymerization in aqueous solutions. Some other dopants of potassium nitrate, potassium sulfate, sodium poly(styrenesulfonate), and sodium polyacrylate were used in comparison with the anionic polysaccharides. The electrochemical properties and stability of the obtained PEDOT films were also investigated. It was found that indium tin oxide (ITO) conductive glass could be used as the working electrode of the electropolymerization of EDOT and that the dopant had a great influence on polymerization potential and overoxidation potential. These charged biomolecules of anionic polysaccharides were found to facilitate electropolymerization of EDOT instead of common doping anions as counterion. The electroactive PEDOT films doped with anionic polysaccharides showed stable electrochemical properties, good texture, and adhesion properties to the ITO conductive glass. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphological and impedance studies on electropolymerized 3,4-(2,2-dibenzylpropylenedioxy)thiophene nanostructures on micron sized single carbon fiber

Micron sized single carbon fibers were cyclovoltammetrically coated with poly[3,4-(2,2-dibenzylpropylenedioxy)thiophene] resulting in a nanofiber network at the surface. The method provides conjugated polymer nanostructures covalently and uniformly bound to micron sized substrates. When the electropolymerization is carried out with different electrolytes in acetonitrile the dopant influences the structure of the coating layer what is proved by electrochemical impedance spectroscopy and electron microscopy. Electrodes based on poly[3,4-(2,2-dibenzylpropylenedioxy)thiophene] on single carbon fiber microelectrodes (SCFMEs) prepared in Bu₄NPF₆/ACN show the best capacitance performance due to their higher surface area. The improvement is attributed to the formed nanofiber network structure which results in a more efficient charge transport and collection.     

An in situ Raman spectroelectrochemical study of the controlled doping of single walled carbon nanotubes in a conducting polymer matrix

The interaction of single wall carbon nanotubes (SWCNT) and the conducting polymer poly(3,4-ethylendioxythiophene/polystyrenesulfonate) (PEDOT/PSS) was studied by in situ Raman spectroelectrochemistry. The mixing of SWCNT with PEDOT/PSS caused a partial doping of SWCNT which was indicated by the change of relative intensity of the SWCNT Raman features. We have demonstrated for the first time that in situ Raman spectroelectrochemistry is a method of choice for precise and effective control of doping level of composites of conducting polymers and SWCNT. For electrochemical doping of SWCNT embedded in PEDOT/PSS the bleaching of RBM and TG modes of the SWCNT is delayed as compared to that in pure SWCNT. The delay is of about 0.2 V. This potential difference vanishes at higher potentials. The delayed response to doping is observed for both the SWCNT and the polymer matrix features. In the latter case the response is specific for individual polymer bands. Furthermore, during p-doping most of the polymer bands exhibit a subsequent monotonous bleaching. This contrasts with the behavior of the pristine polymer where the intensity changes are non-monotonous.     

Identification of charge carriers in the conduction mechanism of an alternated copolymer of poly(aniline) and poly(phenylene sulfide)

In this paper, we have investigated the electrochemical behavior of a soluble copolymer of poly(aniline) (PANI) and poly(phenylene sulfide) in organic media. By using ‘in situ’ UV–vis and Raman spectroscopies, it was proved that during the oxidation of the first cycle, polarons and bipolarons are formed consecutively, due to the loss of electrons from the nitrogen and sulfur, respectively. In addition, it was verified that the formation of polarons is reversible while the formation of bipolarons is irreversible. In the second and subsequent cycles, only one reversible redox process is observed. This process corresponds to the transformation of polarons to bipolarons and vice versa. The ‘in situ’ resistance measurements have indicated that bipolarons are the charge carriers for doped PPSA, distinctly than it was observed for PANI.     

Electrochemical investigation of the effects of hydrogen on the stability of the passive film on iron

The effects of hydrogen on the stability of passive films on iron were investigated by electrochemical methods: open circuit potential decay, cathodic galvanostatic reduction, electrochemical impedance spectroscopy, and breakdown potential measurements. The results show that hydrogen decreases the final static open circuit potential, the cathodic charge for reduction and the charge transfer resistance of the passive film, indicating that hydrogen decreases the stability of the passive film. The charge transfer resistance of the passive film formed on the charged specimen does not change with increasing the film formation potentials, suggesting that increasing film formation potentials under hydrogen charging conditions cannot improve the stability of the passive film. Hydrogen decreases the breakdown potential of the passive film, especially at lower chloride ion concentrations, confirming that hydrogen promotes the susceptibility of the passive film on iron to pitting corrosion. The reasons why hydrogen decreases the stability of the passive film were discussed.     

Non-covalent modification of graphene sheets in PEDOT composite materials by ionic liquids

An ionic liquid (IL) supported composite of poly(3,4-ethylene dioxythiophene) (PEDOT) and graphene oxide (GO) is presented. GO was dispersed in ILs and electropolymerization carried out after loading of EDOT to the dried dispersion. The content of GO was optimized to obtain high electrical conductivity of the composite material. The IL acts as the dispersant for GO and as dopant in the synthesis of PEDOT leading to films with a highly porous structure indicated from the scanning electron microscopy (SEM) images. Subsequently, GO was reduced electrochemically by cyclic voltammetry to obtain PEDOT/rGO composite films. The successful formation of composite materials was confirmed using Raman and X-ray photoelectron spectroscopy (XPS) techniques. XPS was also used to verify removal of oxygen-containing functional groups upon electrochemical reduction of the composite films. The electrochemical properties of PEDOT, PEDOT/GO and PEDOT/rGO were studied using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results show that electrochemical reduction clearly increases the capacitance of the composite and furthermore the cycling stability. Such an increase could be obtained if >20 cycles, extending to highly negative potentials (−2.0 V), was used during the electroreduction of incorporated GO. Owing to the high porosity, favorable electrochemical properties and cycling stability these hybrid materials shows great potential towards supercapacitor applications.     

Multiple time constant modelling of a printed conducting polymer electrode

Constant phase elements (CPE) are routinely used to describe the frequency response of electrochemical systems. However, this approach is often scientifically unsatisfactory because the physical origin of the phase is unclear. Here we observe CPE-like behaviour in a conducting polymer poly(3,4-ethylenedioxythiophene)/poly(styrene-4-sulfonate) (PEDOT:PSS) film that was inkjet printed onto paper to form a flexible electrochemical double layer capacitor electrode. We show that the response of the electrochemically active film can also be described using a physical model with multiple parallel finite RC (resistor–capacitor) transmission lines whose lengths and time constants are determined by the distribution of the measured film thickness. The modeled volumetric capacitance and ionic conductivity match those determined experimentally, suggesting that the physical origin of the constant phase response is a distribution of mass transport limited time constants.     

Understanding of electrochemical and structural changes of polypyrrole/polyethylene glycol composite films in aqueous solution

Electrochemical monitoring of electrical and structural changes of both PPy and PPy–PEG films electrochemical deposited, in order to highlight if the structural stability offered by PEG has an influence on electrical properties and stability in aqueous solution over immersion time was investigated.Electrochemical analysis suggests that PPy–PEG film inserts cations easier than PPy film for a short immersion time probably due to ability of PEG to form complexes with metal cations.The FTIR spectra showed that the PEG incorporation decreases the rate of PPy overoxidation probably by restraining the electron release and by rendering O₂ inaccessible to PPy.Mott–Schottky analysis based on capacitance measurement reveal p-type conductance for both films.The in situ AFM analysis sustains electrochemical behaviour and has permitted elaboration of a model of PPy and PPy–PEG films behaviour during immersion in testing solution.     

Copolymer from electropolymerization of thiophene and 3,4-ethylenedioxythiophene and its use as cathode for lithium ion battery

Electropolymerizations (EPs) of thiophene (Th), 3,4-ethylenedioxythiophene (EDOT) and the mixed monomers of Th and EDOT in 0.05 M Et₄NClO₄/propylene carbonate (PC) solution were performed to prepare polymer films as potential cathode materials in lithium ion battery. The incorporation of EDOT units into pure polythiophene (PTh) chain leads to large alternations on the experimental conditions of EPs and the properties of the resulting polymer films. Onset potential of the EPs was reduced with the participation of EDOT component. The resulting polymers, PTh, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(thiophene-co-3,4-ethylenedioxythiophene) (PTh-EDOT) were then served as cathode materials to test their capabilities to transport lithium ion in 1.0 M LiPF₆/ethylene carbonate/dimethyl carbonate solution. With the inherent EDOT unit, PEDOT and PTh-EDOT have better charge capacity, stability and response rate than pure PTh. Among the copolymers, PTh-EDOT (1/1) even shows better stability than pure PEDOT homopolymer, advantage of using EDOT as copolymer component is thus evaluated.     

PEDOT solid-state polymer supercapacitor assembled with a KI-doped gel polymer electrolyte

Solid-state polymer supercapacitors (SSP-SCs) have vast potential for future development due to their compact, safe, environment-friendly, and facile designing. Thus, prevalent researches have been explored in this area. In this article, poly(3,4-ethylenedioxythiophene) (PEDOT) SSP-SCs were assembled by using poly(3,4-ethylenedioxythiophene)/carbon paper (PEDOT/CP) as electrodes and polyvinyl alcohol/sulfuric acid/potassium iodide (PVA/H₂SO₄/KI) as the gel polymer electrolyte. The effect of KI content on the electrochemical performance of the SC was studied by cyclic voltammetry, galvanostatic charge–discharge measurements (GCD), and electrochemical impedance spectroscopy. The results indicated that the PEDOT SSP-SC has excellent electrochemical properties when KI doping amount was 60 wt %. The introduction of KI increased the specific capacitance due to the improved ionic conductivity and additional pseudocapacitance reaction at the electrode–electrolyte interface. The PEDOT SSP-SC showed high energy and power densities of 451.32 Wh kg⁻¹ and 13.29 kW kg⁻¹, respectively, as well as a specific capacitance of 352.59 F g⁻¹ for a discharge current of 1 mA cm⁻². In addition, after 1000 GCD cycles, the PVA/H₂SO₄/KI-based PEDOT SSP-SC showed capacitance retention of 74.08%. Therefore, the SC exhibits outstanding energy and power density and good cycle stability and has great potential to be used in high-energy density equipment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48723.     

Fast electrochemistry of conductive polymer nanotubes: synthesis, mechanism, and application

Conductive polymers exhibit several interesting and important properties, such as metallic conductivity and reversible convertibility between redox states. When the redox states have very different electrochemical and electronic properties, their interconversion gives rise to changes in the polymers' conformations, doping levels, conductivities, and colors, useful attributes if they are to be applied in displays, energy storage devices, actuators, and sensors. Unfortunately, the rate of interconversion is usually slow, at best on the order a few hundred milliseconds, because of the slow transport of counterions into the polymer layer to balance charge. This phenomenon is one of the greatest obstacles toward building rapidly responsive electrochemical devices featuring conductive polymers. One approach to enhancing the switching speed is decreasing the diffusion distance for the counterions in the polymer. We have found that nanotubular structures are good candidates for realizing rapid switching between redox states because the counterions can be readily doped throughout the thin nanotube walls. Although the synthesis of conductive polymer nanotubes can be performed using electrochemical template synthesis, the synthetic techniques and underlying mechanisms controlling the nanotube morphologies are currently not well established. We begin this Account by discussing the mechanisms for controlling the structures from hollow nanotubes to solid nanowires. The applied potential, monomer concentration, and base electrode shape all play important roles in determining the nanotubes' morphologies. A mechanism based on the rates of monomer diffusion and reaction allows the synthesis of nanotubes at high oxidation potentials; a mechanism dictated by the base-electrode shape dominates at very low oxidation potentials. The structures of the resulting conductive polymer nanotubes, such as those of poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole, can be characterized using scanning electron microscopy and transmission electron microscopy. We also discuss these materials in terms of their prospective use in nanotube-based electrochemical devices. For example, we describe an electrochromic device incorporating PEDOT nanotubes that exhibits an ultrafast color switching rate (<10 ms) and strong coloration. In addition, we report a supercapacitor based on PEDOT nanotubes that can provide more than 80% of its own energy density, even at power demands as high as 25 kW/kg.     

Poly(aspartic acid) Biohydrogel as the Base of a New Hybrid Conducting Material

In the present study, a composite made of conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), and a biodegradable hydrogel of poly(aspartic acid) (PASP) were electrochemically interpenetrated with poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PHMeDOT) to prepare a new interpenetrated polymer network (IPN). Different cross-linker and PEDOT MPs contents, as well as different electropolymerization times, were studied to optimize the structural and electrochemical properties. The properties of the new material, being electrically conductive, biocompatible, bioactive, and biodegradable, make it suitable for possible uses in biomedical applications.     

Comparative study of photoelectric properties of regiosymmetrical poly(3,4-dialkoxythiophene)s

A series of regiosymmetrical poly(3,4-dialkoxythiophene)s: poly(3,4-diamyloxythiophene), poly(3,4-dioctyloxythiophene), poly(3,4-di(2-ethyl-1-hexyloxy)thiophene), and poly(3,4-didodecyloxythiophene) were synthesized by the FeCl₃-oxidative approach. All these polymers were evaluated with NMR, FT-IR, gel permeation chromatography (GPC), thermo-gravimetric analysis (TGA), UV–Vis spectroscopy, and photoluminescence (PL). The polymers have excellent solubility in common organic solvents, and TGA studies show that the polymers lost 5% of their weights on heating to 250 °C above. Investigations of the UV–Vis spectroscopy show that the absorption maxima of the polymer thin films are similar to those in solutions, and the optical band gaps of the polymer thin films are ranging from 2.27 to 2.69 eV. In PL spectra, maxima emission peaks of the polymer thin films lie at 527 to 589 nm, embodying colors from green to yellow, and the quantum yields of the polymers are in the range of 22–28%. All the data indicate that the polymers have good solubility, outstanding thermal stabilities, low band gaps, and high PL quantum yields, and they might be excellent polymeric materials for applications in organic light-emitting diodes (OLEDs), light-emitting electrochemical cells, polymer solar cells, and so on.