Electrosynthesis and characterization of poly(2-[(E)-2-azulen-1-ylvinyl] thiophene) using polyazulene as model compound

Electrochemical polymerization of azulene and 2-[(E)-2-azulen-1-ylvinyl] thiophene has been studied in this work. Characterization of the formed films was done by cyclic voltammetry (CV), in situ UV-vis absorption spectroscopy and by scanning electron microscopy (SEM). Polymerization was performed by CV in a three-electrode electrochemical cell in 0.1 M tetrabutylammonium hexafluorophosphate-acetonitrile (TBAPF₆-ACN) within two different potential ranges. The redox behavior of the films was studied by CV in monomer-free TBAPF₆-ACN electrolyte solution. The electrochemical response from the anodic charging (p-doping) in the different films consisted of symmetric and well-resolved redox peaks. During electrochemical doping changes in the UV-vis spectra can be seen due to transformation of the films from the neutral into the doped form. Poly(2-[(E)-2-azulen-1-ylvinyl] thiophene), in particular shows a very broad absorbance spectrum starting at 300 nm extending to 900 nm. Morphologies of the electrosynthesized films were studied by SEM.     

The photoelectrochemical behaviour of electrochemically deposited CdTe films

Cathodic photocurrents due to hydrogen evolution were observed at p-CdTe films deposited cathodically (?200 ≈ ?400 mV vs Ag/AgCl) from aqueous solution of pH = 1.4 containing 1 M CdSO₄ and 1 mM TeO₂ and it was demonstrated that the photocurrents were improved significantly by removing excess free Te metal and by increasing the crystalline size of CdTe.     

Thermoelectric properties of thin films of bismuth telluride electrochemically deposited on stainless steel substrates

Bismuth telluride thin films have been synthesized by electrochemical deposition onto stainless steel substrates from acidic solutions. The influence of deposition variables on film composition, morphology and crystal orientation associated with the growth of the film was investigated by means of constant potential deposition and pulsed potential deposition. In-plane thermoelectric and transport properties of the electrodeposited films were measured. The carrier concentration of the electrodeposited films was found to be one order of magnitude larger than typically reported for optimized bulk bismuth telluride, which explains the unusually low Hall mobility and Seebeck coefficient values found for the electrodeposited films. Pulse deposited films showed slightly lower electrical resistivity and higher Seebeck coefficient due to the lower porosity and less preferred crystal orientation of the films compared to the continuously deposited films. Improvements of the film properties are necessary to make them viable for applications.     

Studies of electrochemically deposited poly(N-methyl aniline) films

The effect of surface resistance of substrate and concentration of monomer on the properties of electrochemically deposited poly(N-methyl aniline) films has been investigated. The UV–visible spectra of the films show enhanced selectivity in the formation of the conducting phase (approximately 860nm) of polymer on lower surface resistance substrate (10Ω/□) over those with higher surface resistance (50Ω/□). The magnitude of selectivity increases with concentration of monomer. These results are further supported by IR analysis of the samples. From morphological studies it is noted that the films deposited on 10Ω/□ substrates exhibit an overall granular nature irrespective of concentration of monomer. In the case of films deposited on 50Ω/□ substrates sequential changes in patterning are observed with increasing concentration of monomer. Two redox couples are observed in the cyclic voltammograms together with distortion of peak potential in the films obtained on higher surface resistance substrates. © SCI 1998.     

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H₂SO₄ in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H₂SO₄, concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge‐discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Electrodeposition and electrochromic properties of N-ethyl substituted poly(3,4-ethylenedioxypyrrole)

N-Ethyl substituted poly(3,4-ethylenedioxypyrrole), a new electrochromic polymer, has been produced and its spectroelectrochemical properties have been investigated. This material displays multicolor electrochromism, switching between green, violet, and grey. Three different electrochromic devices have been laminated and evaluated using the electrochromic polymer, an ion-conducting polymer electrolyte, and one of the following counterelectrodes: tungsten oxide, polyaniline, or poly-di-methyl-(3,4-propylenedioxythiophene).     

Corrosion studies on electrochemically deposited PANI and PANI/epoxy coatings on mild steel in acid sulfate solution

The corrosion behavior of mild steel and mild steel covered by electrochemically deposited (a) polyaniline (PANI) film, (b) epoxy coating and (c) PANI/epoxy coating system in 0.1 M sulfuric acid solution were investigated by electrochemical impedance spectroscopy (EIS). Electrochemical deposition of PANI film was performed from aqueous solution of 0.5 M sodium benzoate and 0.1 M aniline at constant current density of 1.5 mA cm⁻². Epoxy coatings on mild steel and mild steel modified by PANI film were deposited at constant voltage. It was shown that thin PANI film had provided good corrosion protection of mild steel in 0.1 M sulfuric acid solution, and could be used for modification of mild steel prior to epoxy coating deposition. The increased corrosion protection of mild steel by PANI/epoxy coating system in the same solution was obtained.     

Preparation and characterization of the dopamine film electrochemically deposited on a gold template and its applications for dopamine sensing in aqueous solution

A dopamine polymer film was electrogenerated on the bare gold template from a 5 × 10⁻³ M dopamine solution in phosphate buffer at pH 7 and next subjected to overoxidation in 0.1 M sodium hydroxide solution. The overoxidized dopamine polymer film obtained shows good permeability to cationic species and was used for quantitative determination of dopamine. A linear relationship between dopamine concentration and current response was obtained in the range of 1 × 10⁻⁶ M to 6 × 10⁻⁴ M with the detection limit 2 × 10⁻⁷ M. The results have shown that using the overoxidized dopamine film it is possible to perform electrochemical analysis of dopamine without interference of ascorbic and uric acids, which is the major limitation in dopamine determination. The modified electrode shows good selectivity, sensitivity, reproducibility and high stability.     

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.     

Almost completely dedoped electrochemically deposited luminescent films exhibiting excellent LED performance

An improved method for electrochemical deposition (ED) of a novel precursor (peripheral carbazole substituted 9,9′-spirobifluorene (TCPC)) for fabricating highly efficient luminescent films and devices has been developed. Electrochemical deposition often leaves residual charged ion species within the film. These species can negatively impact the performance of these films in OLED applications. The amount of residual charged species in the films can be reduced by controlling the oxidation and reduction potentials, by using electrolytes with different counter anions, and by washing with solvents. An optimized ED process showed a significant decrease in the doping level; up to 0.07% in ED film. The films prepared under a scan potential range from 0.85 to −0.8 V, using TBAAsF₆ as the supporting electrolyte, and washed with solvent mixtures of acetonitrile and CH₂Cl₂ (V/V = 2/3) demonstrated excellent device performance. Light-emitting devices fabricated by electrochemical deposition achieved deep blue emission (x, y) = (0.16, 0.06) in CIE coordinates. High luminance efficiencies of 2.3 cd A⁻¹ were achieved for single-layer device; luminescence efficiencies of 4.4 cd A⁻¹ were achieved for a double-layer device. Finally, the problem that ED films usually exhibit low electroluminescent efficiency is solved.     

A potentiometric and voltammetric sensor based on polypyrrole film with electrochemically induced recognition sites for detection of silver ion

Conducting polypyrrole membranes were deposited on glassy carbon electrodes by electropolymerizing pyrrole in the presence of Eriochrome Blue-Black B (EBB) as the counter anion. The electrodes were then subjected to several oxidation/reduction potential steps in pure silver nitrate solution for successive accumulation/stripping of silver species. This electrochemically mediated doping/templating generated selective recognition elements in the EBB/PPy film for silver ions. The resulting sensor exhibited a considerable enhancement in the potentiometric and voltammetric response characteristics: extending the linear dynamic range and lowering the detection limit. In the potentiometric mode, the sensor showed highly reproducible response with a Nernstian slope of 58.5 ± 0.3 mV per decade of Ag⁺ activity over a linear range spanning seven orders of magnitude (1 × 10⁻⁸ to 1 × 10⁻¹ M Ag⁺), with a detection limit of ∼6 × 10⁻⁹ M. The electrodes demonstrated high selectivity over a large number of cations including alkali, alkaline earth and several transition and heavy metal ions, and could be used over a wide pH range of 1-8.5. The EBB/PPy modified electrode was also used for preconcentration and differential pulse anodic stripping voltammetric (DPASV) measurements. The DPASV peak current was dependent on the concentration of Ag⁺ over the range 3 × 10⁻¹⁰ to 1 × 10⁻⁴ M. The presence of 1000-fold excess of Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Pb²⁺ can be tolerated in the determination of silver ion.     

A comparative study on electrochemical co-deposition and capacitance of composite films of conducting polymers and carbon nanotubes

Composite films of carbon nanotubes (CNTs) with polyaniline (PANI), polypyrrole (PPY) or poly[3,4-ethylenedioxythiophene] (PEDOT) were prepared via electrochemical co-deposition from solutions containing acid treated CNTs and the corresponding monomer. In the cases of PPY and PEDOT, CNTs served as the charge carriers during electro-deposition, and also acted as both the backbone of a three-dimensional micro- and nano-porous structure and the effective charge-balancing dopant within the polymer. All the composites showed improved mechanical integrity, higher electronic and ionic conductivity (even when the polymer was reduced), and exhibited larger electrode specific capacitance than the polymer alone. Under similar conditions, the capacitance was enhanced significantly in as-prepared PPY-CNT and PEDOT-CNT films. However, the fresh PANI-CNT film was electrochemically similar to PANI, but PPY-CNT and PEDOT-CNT differed noticeably from the respective polymers alone. In continuous potential cycling tests, unlike the pure polymer and other composite films, PANI-CNT performed much better in retaining the capacitance of the as-prepared film, and the possible cause is analysed.     

Effect of deposition voltage on the microstructure of electrochemically deposited hydrogenated amorphous carbon films

Hydrogenated amorphous carbon (a-C:H) films were deposited on Si substrates by electrolysis in a methanol solution at ambient pressure and a low temperature (50 °C), using various deposition voltages. The influence of deposition voltage on the microstructure of the resulting films was analyzed by visible Raman spectroscopy at 514.5 nm and X-ray photoelectron spectroscopy (XPS). The contents of sp³ bonded carbon in the various films were obtained by the curve fitting technique to the C1s peak in the XPS spectra. The hardness and Young’s modulus of the a-C:H films were determined using a nanoindenter. The Raman characteristics suggest an increase of the ratio of sp³/sp² bonded carbon with increasing deposition voltage. The percentage of sp³-bonded carbon is determined as 33–55% obtained from XPS. Corresponding to the increase of sp³/sp², the hardness and Young’s modulus of the films both increase as the deposition voltage increases from 800 V to 1600 V.     

Control of locally deposited gold nanoparticle on polyaniline films

Local and bulk deposition of gold particles was accomplished by the spontaneous reaction between chemically reduced polyaniline (PAN) thin films and AuCl₄⁻ ions. PAN layers were electrodeposited on glassy carbon (GC). Characterization of the PAN films was carried out by microscopy and electrochemistry. Local deposition of gold particles was performed by means of scanning electrochemical microscopy, where a gold microelectrode was used to produce a flux of gold ions in close vicinity to an unbiased PAN film. We found that the nature of the gold particles was greatly affected by the potential applied at the microelectrode as well as the oxidation state of the PAN films.     

Optimization of the electropolymerization of 1-amino-9,10-anthraquinone conducting films from aqueous media

The optimum conditions for the electrochemical preparation of poly(1-amino-9,10-anthraquinone), PAAQ, films in environmentally safe aqueous solutions were investigated. The conducting polymer films were prepared by electrochemical oxidation of 1-amino-9,10-anthraquinone, AAQ, in sulfuric acid solutions in the potential range from 0.0 to +1.3 V. The influence of scan repetition, scan rate, and monomer concentration on the formation process and the properties of the polymer film were studied. The electrochemical response of the formed polymer film was investigated in both aqueous and non-aqueous media. The polymer films were found to be stable in aqueous acidic media. In non-aqueous solutions, like acetonitrile, dimethyl sulfoxide and dioxin, the polymer films showed remarkable degradation. The best electrochemical response of the PAAQ films was found to be in the potential range between +0.3 and +0.9 V. The presence of quinone units in the polymer film chain suggests promising applications of these conducting polymers in lightweight (rechargeable) batteries, electrochromic display devices, and biosensor and corrosion protection.     

Comparative studies of electrochemically deposited poly(o-toluidine) and poly(m-toluidine) films

Under galvanostatic deposition conditions poly(o-toluidine) exhibits a higher rate of polymerization than poly(m-toluidine). This observation is supported by results obtained by different characterization techniques such as spectrophotometry, scanning electron microscopy and thermogravimetric analysis. The monomer concentration was found to be the predominant parameter in obtaining selectively a conducting salt phase in both cases. However, the morphology of these polymeric films does not reveal any particular relationship with monomer concentration; instead a mixed morphology, i.e. a combination of granules and fibres, is observed. Finally, the thermal stability of poly(m-toluidine) is lower than that of poly(o-toluidine) with a shift of 190°C in the final decomposition temperature.     

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).     

Polymers of phenylenediamines

The chemical or electrochemical oxidation of phenylenediamines in acidic aqueous media yields the corresponding oligomers or polymers. Their structures and properties are discussed in relation to a closely-related conducting polymer, polyaniline. Depending on the reaction conditions, polyphenylenediamines are produced as powders, colloidal dispersions, thin films, or composites. In contrast to polyaniline, polyphenylenediamines are rated as non-conductors and their conductivities are low. Similarly to polyaniline, these polymers display a salt–base transition and they are redox-active. They act as reductants of noble-metal compounds to the corresponding metals or as precursors in the carbonization to nitrogen-rich carbons. Applications proposed in the literature are outlined; they include the corrosion protection of metals, catalysis, electrorheology, sensors, energy-conversion devices, electrochromism, noble-metal recovery, and water treatment.     

Supramolecular hydrogels of polyaniline-poly(styrene sulfonate) prepared in concentrated solutions

Polyaniline-poly(styrene sulfonate) (PAn-PSS) hydrogels have been synthesized via supramolecular self-assembly between positively-charged PAn chains and negatively-charged PSS chains. Phase diagram is plotted to systematically investigate the gelation conditions for the PAn-PSS system. A hierarchical porous microstructure consisting of oriented 1D nanofibers is observed in the hydrogels, and the phase structure, molecular structure and crystal structure are also characterized. Based on the investigation of a unique transformation of the hydrogels to colloidal particles in alkaline solutions, the electrostatic interaction is proposed to be the origin force for the gelation of the materials. Additionally, in comparison with conventional PAn-PSS colloids, as-prepared PAn-PSS hydrogels are demonstrated to possess improved capacitance performance, such as higher energy density, higher power density and better electrochemical stability. The present study gives valuable hints for achieving controlled fabrication of supramolecular materials with designed structures and outstanding properties.     

Synthesis and spectroelectrochemical properties of two new dithienylpyrroles bearing anthraquinone units and their polymer films

Two new kinds of dithienylpyrroles bearing anthraquinone units have been prepared by the Knorr-Paal condensation between 1,4-di(thiophen-2-yl)butane-1,4-dione and 1-/2-amino-anthraquinone. The corresponding polymer films were successfully synthesized via electropolymerization. The electrochemical, electro-optical properties and electrochromic behavior of the two polymer films were further investigated by thermogravimetric analysis, cyclic voltammetry and UV-vis absorption spectra. The results demonstrated that the two polymer films were thermally stable up to nearly 300 °C. Both the two electroactive polymer films presented a stable and well-defined reversible redox process as well as multicolor electrochromic change from yellow (in the reduced state) to grey (in the neutral state) and then to blue (in the oxidized state).