Electrochemically instantaneous reduction of conducting polyaniline-coated latex particles dispersed in acidic solution

A cathodic voltammetric wave was observed in an aqueous suspension of mono-dispersed, spherical polyaniline-coated polystyrene particles, whereas no anodic wave was detected. This irreversibility was common to particles with eight different diameters ranging from 0.2 to 7.5 μm. Such irreversibility cannot be found at polyaniline-coated electrodes, and thus is a property of the dispersion of polyaniline latex. The reduction current was controlled by diffusion of dispersed particles. The reduction, being the conversion from the electrical conducting state to the resistive one, should begin at a point of contact between the conducting particle and the electrode in order to be propagated to the whole particle rapidly. In contrast, the oxidation proceeds slowly with the propagation of conducting zone, during which Brownian motion lets the particle detach from the electrode. The number of loaded aniline units per particle, determined by weight analysis, ranged from 6 × 10⁶ (Ø 0.2 μm) to 3 × 10¹¹ (Ø 7.5 μm) and was proportional to 2.9 powers of the particle diameter. The diffusion-controlled current of the cathodic wave was proportional to 2.4 powers of the diameter. The difference in these powers, 0.5, agreed with a theoretical estimation of the diffusion-controlled current, the diffusion coefficient for which was given by the Stokes-Einstein equation.     

An EPR investigation of electrospun polyaniline-polyethylene oxide blends

The EPR magnetic susceptibility behavior of the camphorsulfonic acid doped polyaniline (PANCSA) blends with polyethylene oxide (PEO) is reported in fibers and films. In particular, EPR investigations on electrospun (PANCSA)_0.72(PEO)_0.28 nanofibers, cast films of (PANCSA)_0.72(PEO)_0.28 and cast films of (PANCSA) were performed to investigate differences in the mesoscopic disorder as induced by the process of electrospinning. The changes observed in the Pauli susceptibility, EPR lineshape, EPR linewidth, and dc conductivity are interpreted as due to increased chain alignment in the fibers compared with the cast films.     

Ion-exchange kinetics and electrical conductivity studies of polyaniline Sn(IV) tungstoarsenate; (SnO2)(WO3)(As2O5)4(C6H5NH)2·nH2O: a new semi-crystalline ‘polymeric-inorganic’ composite cation-exchange material

A new and novel electrically conducting ‘polymeric-inorganic’ composite cation-exchange material; polyaniline Sn(IV) tungstoarsenate was prepared by incorporating polyaniline into inorganic ion-exchanger material. It possessed improved ion-exchange capacity, high chemical and thermal stabilities, reproducibility and selectivity for some specific metal ions. Kinetic study of exchange for some divalent metal ions of alkaline earths and transition metals was carried out under the conditions favoring a particle diffusion-controlled ion-exchange phenomenon and some physical parameters such as self diffusion coefficient D₀, energy of activation E_a and entropy of activation ΔS* were determined. The temperature dependence of electrical conductivity of this composite material with increasing temperatures was measured by using 4-in-line-probe DC electrical conductivity measuring-technique. The conductivity values lie in the semiconductor region, i.e. in the range of 10⁻³ S cm⁻¹ that follow the Arrhenius equation. The energy of activation of electrical conduction for the composite was also calculated.     

Spatially electrodeposited platinum in polyaniline doped with poly(styrene sulfonic acid) for methanol oxidation

Polyaniline (PANI) can be doped with poly(styrene sulfonic acid) (PSS) via doping–dedoping–redoping process. The specific characteristics of PANI doped with PSS (PANI-PSS) were checked by UV–vis spectroscopy, cyclic voltammetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). PANI-PSS was found to have spatial structure with minimum degradation products. Platinum can be potentiostatically deposited in a spatial layer of the PANI-PSS as evidenced by electron dispersive element analysis (EDS) and Auger electron spectroscopy (AES). The electrochemical measurements demonstrated that PANI-PSS-Pt exhibited a much higher electrocatalytic activity for methanol oxidation than PANI-Pt.     

Electrocatalytic oxidation of methanol on Pt modified polyaniline in alkaline medium

A comparative study of the electrocatalytic oxidation of methanol is made in NaOH, Na₂CO₃ and NaHCO₃ on bare Pt (Pt), polyaniline covered Pt (PANI) and Pt modified polyaniline film on Pt (Pt/PANI) using cyclic voltammetry, polarization, ac impedance spectroscopy and chronoamperometric techniques at 25 °C. The cyclic voltammetry and polarization studies show that the potentials at which methanol oxidation commences on different electrodes in each of the alkaline medium examined follow the trend Pt/PANI < Pt < PANI whereas the potentials for initiation of oxidation on each electrode in different alkaline media follow the order NaHCO₃ > Na₂CO₃ > NaOH. The oxidation current is highest and charge transfer resistance lowest for Pt/PANI films compared to Pt in all the media studied. However, for the same Pt loading Pt/PANI films exhibit larger oxidation currents in NaOH followed by Na₂CO₃ and NaHCO₃. The Tafel slope for methanol oxidation on Pt/PANI in NaOH, Na₂CO₃ and NaHCO₃ has a value of about 115 mV decade⁻¹. The chronoamperometric response of the Pt/PANI film at the peak potential for methanol oxidation shows lesser sensitivity to poisoning by CO compared to bare Pt and platinised Pt (Pt/Pt).     

Influence of charged tail groups of self-assembled monolayers on electrodeposition of polyaniline

Self-assembled monolayers (SAMs) of thiols with three different tail groups, −COOH, −SO₃Na, and −NH₂, were used to modify the Au substrates for electrodepositing polyaniline (PANI). Electrochemical quartz crystal microbalance (EQCM) results indicated a slower rate of deposition of PANI on a SAM surface consisting of positively charged amine groups compared to polymerization on bare gold and on a SAM of carboxyl acid groups. The properties of the SAM layers are dependent on the pH value of the solutions, and are effective only at very low pH values (pH < 2). A layer of the positively charged amino groups in acidic solution acted as a barrier for electron transfer in electro-oxidation of aniline monomer. The positively charged SAM of amine groups also increased repulsion between the coupled aniline species and the electrode surface and in this way hindered electrodeposition. Modification of the surface with pre-patterned SAMs have been demonstrated to be a convenient and practical way to fabricate selectively deposited thin films of polyaniline.     

Silver electrocrystallization at polyaniline-coated electrodes

The initial stage of silver electrocrystallization is studied at polyaniline (PANI)-coated platinum electrodes by means of potentiostatic current transients and electron microscopic observations. Data for the nucleation frequency and the number of active sites for nucleation are obtained by interpreting of current transients according to the theory for nucleation and 3D growth under diffusion limitations. It is found that depending on the PANI layers thickness, d, two different regimes for silver nucleation and growth exist. For thin PANI coatings (d<0.3 μm), the crystallization occurs with high nucleation frequency at active sites located at the polymer layer/metal electrode interface, the number of active sites decreasing sharply with increasing PANI coverage. For thick PANI layers (d>0.3 μm), silver nucleation occurs with a two orders of magnitude lower nucleation frequency at active sites located most probably at the polymer surface, their number remaining constant for thicknesses up to 1.4 μm. It is established that reduction of the PANI layer occurring in parallel with the silver electrodeposition does not influence the number of active sites for nucleation. The results obtained by interpretation of current transients are in good agreement with results for the number of crystals obtained by microscopic observation.     

Impedance characterization of the process of polyaniline first redox transformation after aniline electropolymerization

The paper presents the analysis of the aniline electropolymerization process by a recently developed experimental technique—dynamic electrochemical impedance spectroscopy. The process of the polyaniline first redox transformation was chosen for a detailed investigation. The technique used allowed to obtain the momentary impedance spectra for the potentiodynamic electrochemical reaction. The spectra were further analysed using the proposed electrical equivalent circuit. Thus, we were able to trace the electrochemical properties of the investigated system for potentiodynamic process. Results were in agreement with the expectations and confirmed the electrochemical nature of the analysed process.     

Polyaniline films containing electrolessly precipitated palladium

Polyaniline (PAni) films with similar electroactivity were potentiodynamically grown at selected different scan rates and number of cycles. Palladium particles were incorporated in the electroactive polymer by electroless precipitation. The polymeric matrix morphology and its effect on the distribution and size of Pd particles was analysed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was observed that the dispersion of metal clusters was imparted by the nature of the polymer matrix. The results allowed to state a correlation between the polymer topography and the size and spatial distribution of the catalytic particles.     

Synthesis of high-performance one-dimensional polyaniline nanostructures using dodecylbenzene sulfonic acid as soft template

High-performance one-dimensional polyaniline (PANI) nanostructures, i.e. nanotubes and nanofibers were synthesized in the presence of dodecylbenzene sulfonic acid (DBSA) and hydrochloric acid (HCl) aqueous solution, with ammonium peroxydisulfate (APS) as oxidant. And the resulting PANI nanotubes possessed the diameters of 350-650 nm and length up to tens of micrometers and PANI nanofibers with diameters of 120-160 nm, respectively. Especially, the PANI nanotubes had a very uniform structure (nearly 100% in nanotubes) and the reaction yield was about 110% (compared to the quantity of aniline in the reaction). The formation mechanism of 1D PANI nanostructures was also proposed. The guide effect of the initial “soft-template” formed by aniline and DBSA was greatly controlled by its content and chemical structures.