Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO₄ and PPy|ClO₄ films have been synthesized and investigated in K₂SO₄, ZnSO₄ and NaClO₄ aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10⁻⁶ to n × 10⁻⁴ μF cm⁻² for 1 μm film), independent of solution concentration, were established for PPy|SO₄ in ZnSO₄. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO₄ in NaClO₄ and PPy|SO₄ in K₂SO₄,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10⁻³ to n × 10⁻² μF cm⁻² and even somewhat higher for PPy|ClO₄ system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10⁻¹² to n × 10⁻¹⁴ cm² s⁻¹ for PPy|SO₄ in 0.1 M K₂SO₄ and PPy|ClO₄ in 0.1 M NaClO₄ aqueous solution. In the case of PPy|SO₄ film in ZnSO₄ solution the D values are essentially lower.     

Study of lithium/polypyrrole secondary batteries with Lithium as cathode and polypyrrole anode

Lithium/polypyrrole (Li/PPy) batteries were fabricated using lithium sheet as cathode, PPy as anode, microporous membrane polypropylene/polyethylene/polypropylene (PP/PE/PP) composite as separator and LiPF6/ethylene carbonate-dimethyl carbonate-methyl ethyl carbonate (EC-DMC-EMC) as electrolyte. Polypyrrole was prepared by chemical polymerization. Certain fundamental electrochemical performances were investigated. Properties of the batteries were characterized and tested by SEM, galvanostatic charge/discharge tests, cyclic voltammetry (CV), and a.c. impedance spectroscopy. The influences of separator, morphology, and conductivity of PPy anode, cold-molded pressure, and electric current on the performances of the batteries were studied. Using PP/PE/PP membranes as separator, the battery showed good storage stability and cycling property. The conductivity of materials rather than morphology affected the behavior of the battery. The higher the conductivity, the better performances the cells had. Proper cold-molded pressure 20 MPa of the anode pellet would make the properties of the cells good and the fitted charge/discharge current was 0.1 mA. The cells showed excellent performance with 97%-100% coulombic efficiency. The highest discharge capacity of 95.2 mAh/g was obtained.     

High molecular weight soluble polypyrrole

High molecular weight, soluble, doped polypyrrole containing no substituent on the pyrrole ring has been synthesized by the incorporation of the novel, versatile di(2-ethylhexyl) sulfosuccinate dopant anion which renders the polymer soluble in polar and also weakly polar or non-polar solvents. The M_w values corresponding to at least 303 pyrrole rings/polymer chain are observed in material which has at least 9 wt./vol.% solubility in NMP and significant solubility in solvents such as DMSO, DMF and m-cresol, etc. Free standing films exhibited conductivities ranging from ∼3 to 10⁻³ S/cm depending on the solvent from which they were cast. Films cast from NMP could be stretched to 2.5 times their original length to give a conductivity, σ, of ∼60 S/cm. The degree of crystallinity of films differed depending on the solvent from which they were cast. The TGA and DSC studies showed that the decomposition temperature was limited by the dopant anion.     

Electrochemically-induced fluid movement using polypyrrole

Initial studies on inherently conducting polymer-coated surfaces show that the surface energy can be controlled by electrochemically switching the polymer's oxidation state. This surface energy change was then used to induce fluidic movement in a 700 μm wide polymethylmethacrylate channel coated with a polypyrrole layer doped with dodecylbenzenesulfonate anions. By applying a reducing potential to the polymer-coated channel, electrolyte solution was seen to move along the channel.     

Conductivity of silver exposed polypyrrole films

Electrochemically prepared conducting polypyrrole tosylate films were exposed to silver in a wide range of concentrations. Four-probe measurements of the dc conductivity of these films as well as two-probe ac conductivity measurements were performed. Small silver exposures lead to a dramatic change in the surface potentials and electronic structure, whereas the ac- and dc-conductivities appear not to be influenced. In the range of high silver exposures metallic conductivities due to the formation of a massive silver overlayer on top of the polypyrrole films are observed.     

Intercalation of polypyrrole into graphite oxide

In this paper we report on the insertion of polypyrrole into layered graphite oxide. This was achieved by using the exfoliating and re-stacking properties of the host. The resulting intercalated product was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermogravimetric analysis and scanning electron microscopy.     

On the porosity of polypyrrole films

Polypyrrole (PPy) films doped with anions of various size, charge and chemical nature (inorganic, surfactant, with aromatic ring) were electrochemically synthesized and investigated by low-temperature N₂ sorption experiments at −196 °C. The specific surface area, total pore volume, average pore radius, pore size distribution and other parameters for oxidized PPy films using dodecylsulfate, 2-naphthalene sulfonate, 1,5-naphthalene disulfonate, poly(4-styrenesulfonate), tosylate, perchlorate, nitrate and chloride as dopant ions, were calculated. The obtained data show that although the average pore radius of investigated mesoporous PPy films (17–19 Å) is practically independent of the dopant anion used, however the latter determines the total pore volume and specific surface area values in different PPy materials investigated. As the total pore volumes for PPy films doped with large amphiphilic anions show the smallest values, the corresponding values for PPy/small inorganic anions, are up to 2 times higher.     

Polyaniline and polypyrrole oxygen reversible electrodes

The effect of oxygen on the potential of reduced forms of polyaniline and polypyrrole were investigated. These forms of polyaniline and polypyrrole were not stable in the presence of oxygen. Zinc–polyaniline, zinc–polypyrrole, polyaniline–polyaniline (PANI–PANI), and polypyrrole–polypyrrole (PPy–PPy) batteries were constructed and studied. The effect of oxygen on the short-circuit current of these batteries showed that the cathode material, i.e., polyaniline and polypyrrole, can be regenerated by oxygen oxidation after discharge. These materials are potential candidates for the use as O₂ “fuel cell” type electrocatalytic electrodes.     

Conducting polypyrrole with nanoscale hierarchical structure

Conducting polypyrrole (PPy) with nanoscale hierarchical structure is chemically synthesized in an aqueous solution in the presence of cetyltrimethylammonium bromide (CTAB) and 1,5-naphthalene disulfonic acid (1,5-NDA). The effect of synthetic conditions including concentration of CTAB and pyrrole, reaction temperature, oxidants and their introduced modes on the PPy hierarchical nanostructure is systematically investigated. A hypothesis for the hierarchical structure formation of PPy with the aid of CTAB/1,5-NDA/pyrrole supramolecular template is presented, in which the pyrrole is polymerized in imitation of the CTAB/1,5-NDA/pyrrole crystal shape. The electrochemical performances of representative PPy sample show that the PPy with hierarchical nanostructures has potential application as supercapacitor materials.     

Zinc modified polypyrrole coating on mild steel

Polypyrrole (PPy) films (∼ 1.7 μm thick) have been electrodeposited on mild steel (MS) substrates from 0.1 M pyrrole containing aqueous oxalic acid solution, by using cyclic voltammetry technique. Then, the polymer coatings were modified with deposition of zinc particles (∼ 1 mg/cm²), at a constant potential value of − 1.20 V in 0.2 M ZnSO₄ solution. The corrosion performance of zinc modified PPy coating has been investigated in 3.5% NaCl solution, by using electrochemical impedance spectroscopy and anodic polarisation curves. Also, the corrosion behaviours of zinc modified PPy coated platinum and single PPy coated MS samples have been investigated, for comparison. It was shown that zinc modified coating exhibited very low permeability and provided important cathodic protection to MS for considerably long immersion period. The voluminous zinc corrosion products are formed during exposure time in aggressive solution, giving rise to a blocking effect on the porous structure and led to effective barrier behaviour of zinc modified PPy coating, even after 96 h of exposure time to corrosive solution.     

Pressure dependence of electrical conductivity in polypyrrole

The electrical conductivity as a function of pressure to about 1.1 GPa is determined for p-toluenesulphonate-doped polypyrrole at two different doping levels and also for tetrafluoroborate-doped polypyrrole. A second-order polynomial is found to fit the observed data better than either of the existing models. The polynomial is of the form σ(P) = − aP² + bP+ σ(0).     

Conducting polypyrrole by chemical synthesis in water

Bulk quantities of polypyrrole (PP) can be obtained as fine powders using the oxidative polymerization of the monomer by selected transition metal ions in water. Short-term polymerization and low temperatures gave the best results as far as the electrical conductivity of the resulting PP powders is concerned.Positive effects on both conductivity and stability to aging were found when oxidations were carried out in the presence of selected organic compounds.     

Preparation of polypyrrole film with well-ordered corrugation

Polypyrrole (PPy) films with well-ordered corrugations were produced using the following three-step procedure. First, an elastic silicone sheet was stretched by 20% and fixed on a frame. Second, it was coated with gold using an ion sputtering technique. In this step, the gold coating spontaneously corrugated. Finally, PPy was synthesized by an electrochemical reaction on the gold coating that was used as the electrode. The obtained PPy film was corrugated because the corrugated gold coating worked as a template. The wavelength of the controlled corrugation ranged from 7.3 to 41.0 μm by controlling the thickness of the gold coating from 10 to 100 nm.     

Conductive composites from polyvinyl alcohol and polypyrrole

The electrochemical polymerization of pyrrole on a platinum electrode covered with a film of polyvinyl alcohol produces black, flexible films which are a composite of polypyrrole and polyvinyl alcohol. These composites incorporate some of the attractive electrical properties of the polypyrrole and some of the attractive mechanical properties of the polyvinyl alcohol.     

Electronic properties of metal/polypyrrole junctions

Metal contacts to conducting polypyrrole have been characterized. The results show that inert metals, i.e., Au, give ohmic contacts with no current limitations. Metals that can be oxidized form more or less insulating interphases of metal oxide at the metal/polymer interface. The electrical properties of these interphases control the charge transport through the junction, and generally symmetric, non-ohmic characteristics. No evidence of Schottky barrier formation is found.     

Multi-layered type hybrid glass/polypyrrole composite

Multilayer organic xerogel—polypyrrole composites have been prepared by alternate successive treatments of a glass substrate with a siloxane functionalized pyrrole, pyrrole, oxidant, and a sol precursor of the xerogel. An increase of the conductivity is seen upon the first depositions, but increasing the deposit numbers over three fourfold layers does not lead to a further improvement of the conductivity. The loss of conductivity upon aging in air of the composites is weaker than in the case of ordinary unprotected polypyrrole.     

Templating fabrication of polypyrrole nanorods/nanofibers

Nanostructured polypyrrole have been fabricated in high yield by chemical oxidation polymerization using one-dimensional rod-like aggregates of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS₄) as a template. This aggregate has the advantages of both soft and hard template such as stable, good versatility (for hard template), cheap, and easy removal (for soft template). Also, the molar ratio of TPPS₄ and pyrrole monomer could be as low as 1:1000, showing a high efficiency of the template. Polypyrrole nanorods with variational size have been achieved successfully by using this versatile template and cooperating with the oxidants with different redox potentials. Moreover, in the presence of TPPS₄ template and polyvinylpyrrolidone (PVP), Polypyrrole (PPy) nanofibers were obtained even though using a weak oxidant. The formation of PPy nanorods/nanofibers was discussed and their properties including conductivity and thermalstability were evaluated.     

Electrochemically deposited polypyrrole films and their characterization

Ionically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile/H₂O and NaBF₄ aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of thicker (< 30 micron) films on stainless steel allowed free-standing polypyrrole membranes to be produced. Well adherent and conductive films were deposited at constant potential in stirred solutions from acetonitrile electrolytes containing 1% (v/v) of water. The membrane resistivity of the reduced films in 0.5 mol dm^− 3 KCl_(aq) at 295 K was ≈ 1 × 10⁶ Ω cm, while the resistivity of the oxidised membrane was 2700 Ω cm.