Role of carrier density and disorder on anisotropic charge transport in polypyrrole

Polypyrrole (PPy) has been synthesized electrochemically on platinum substrate by varying synthesis temperature and dopant concentration. The charge transport in PPy has been investigated as a function of temperature for both in-plane and out-of-plane geometry in a wide temperature range of 5K-300 K. The charge transport showed strong anisotropy and various mechanisms were used to explain the transport. The conductivity ratio, sigma(r) = sigma(300 K)/sigma(5 K) is calculated for each sample to quantify the relative disorder. At all the temperatures, the conductivity values for in-plane transport are found to be more for PPy synthesized at lower temperature, while the behavior is found to be different for out-of-plane transport. The carrier density is found to play a crucial role in case of in-plane transport. An effort has been made to correlate charge transport to morphology by analyzing temperature and frequency dependence of conductivity. Charge transport in lateral direction is found to be dominated by hopping whereas tunneling mechanisms are dominated in vertical direction. Parameters such as density of states at the Fermi level N(E-F)], average hopping distance (R), and average hopping energy (W) have been estimated for each samples in both geometry. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4775405]

Charge transport and magnetic properties of coaxial composite fibrils of polypyrrole/multiwall carbon nanotubes at low temperature

We report the low temperature electrical and magnetic properties of polypyrrole (PPy)/multiwall carbon nanotube (MWNT) coaxial composite fibrils synthesized by the electro-polymerization method. The iron-filled MWNTs were first grown by chemical vapor deposition of a mixture of liquid phase organic compound and ferrocene by the one step method. Then the PPy/MWNT fibrils were prepared by the electrochemical polymerization process. Electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length. The temperature dependent electrical resistivity and magnetization measurements were done from room temperature down to 5 and 10 K, respectively. The room temperature resistivity (rho) of PPy/MWNT composite fibril sample is similar to 3.8 Omega m with resistivity ratio R-5 K/R-300 K] of similar to 300, and the analysis of rho(T) in terms of reduced activation energy shows that resistivity lies in the insulating regime below 40 K. The resistivity varies according to three dimensional variable range hopping mechanism at low temperature. The magnetization versus applied field (M-H loop) data up to a field of 20 kOe are presented, displaying ferromagnetic behavior at all temperatures with enhanced coercivities similar to 680 and 1870 Oe at room temperature and 10 K, respectively. The observation of enhanced coercivity is due to significant dipolar interaction among encapsulated iron nanoparticles, and their shape anisotropy contribution as well.

Probing disorder and transport properties in polypyrrole thin-film devices by impedance and Raman spectroscopy

In the present study, impedance and Raman spectroscopy are adopted to probe the nature and extent of disorder to correlate with transport properties in doped polypyrrole (PPy) thin-film devices, synthesized electrochemically at different temperatures. A comparative study of the impedance spectroscopy is performed on PPy devices by both experimental and simulation approach with varying extent of disorder. The impedance measurements of PPy devices are well described by introducing a constant phase element (CPE) (Q) in modified RQ circuit, which accounts for frequency dependence of dielectric response. However, for the PPy grown at lower temperature, an equivalent circuit consisting of two such RQ elements in series is used for successful modelling of the impedance results, which accounts for the depletion region near the electrode. Raman spectroscopy and the de-convoluted spectra are successfully studied to probe the variation in C=C bond stretching and distribution of conjugation length, which relates to disorder in PPy films and the interpretation is well correlated to the impedance results.

Electric field activated nonlinear anisotropic charge transport in doped polypyrrole

Electric field activated nonlinear transport is investigated in polypyrrole thin film in both in-plane and out-of-plane geometries down to 5 K and strong anisotropy is observed. A morphological model is suggested to explain the anisotropy through inter-chain and intra-chain transport. The deviation from the variable range hopping at low temperature is accounted by fluctuation assisted transport. From Zabrodaskii plots, it is found that electric field can tune the transport from insulating to metallic regime. Glazman-Matveev model is used to describe the nonlinear conduction. Field scaling analysis shows that conductance data at different temperature falls on to a single curve. Nonlinearity exponent, m(T) and characteristic length, L-E are estimated to characterize the transport in both the geometries. (C) 2013 AIP Publishing LLC.

Reduced Graphene Oxide-Polypyrrole Composite as a Catalyst for Oxygen Electrode of High Rate Rechargeable Li-O-2 Cells

Polypyrrole (PPY) is grown on reduced graphene oxide (RGO) and the composite is studied as a catalyst for O-2 electrode in Li-O-2 cells. PPY is uniformly distributed on the two dimensional RGO layers. Li-O-2 cells assembled in a non-aqueous electrolyte using RGO-PPY catalyst exhibit an initial discharge capacity as high as 3358 mAh g(-1) (3.94 mAh cm(-2)) at a current density of 0.3 mA cm(-2). The voltage gap between the charge and discharge curves is less for Li-O-2(RGO-PPY) cell in comparison with Li-O-2(RGO) cell. The Li-O-2(RGO-PPY) cell delivers a discharge capacity of 550 mAh g(-1) (0.43 mAh cm(-2)) at a current density of 1.0 mA cm(-2). The results suggest that RGO-PPY is a promising catalyst of O-2 electrode for high rate rechargeable Li-O-2 cells. (C) 2014 The Electrochemical Society. All rights reserved.

Iminodiacetic acid functionalized polypyrrole modified electrode as Pb(II) sensor: Synthesis and DPASV studies

An electrochemical lead ion sensor has been developed by modification of carbon paste electrode (CPE) using polypyrrole functionalized with iminodiacetic acid (IDA-PPy) containing carboxyl group. The electrochemical response of Pb2+ ion on the IDA-PPy modified CPE has been evaluated and the controling parameters have been optimized using differential pulse anodic stripping voltammetry (DPASV). The IDA-PPy modified CPE shows a linear correlation for Pb2+ concentrations in the range of 1 x 10(-6) to 5 x 10(-9) M and the lower detection limit of Pb2+ has been found to be 9.6 x 10(-9) M concentration. Other tested metal ions, namely Cu2+, Cd2+, Co2+, Hg2+, Ni2+ and Zn2+, do not exhibit any voltammetric stripping response below 1 x 10(-7) M concentration. However, the Pb2+ response is affected in the presence of molar equivalents or higher concentrations of Cu2+, Cd2+ and Co2+ ions in binary systems with Pb2+, consequent to their ability to bind with iminodiacetic acid, while Hg2+, Ni2+ and Zn2+ do not interfere at all. A good correlation has been observed between the lead concentrations as analyzed by DPASV using IDA-PPy modified CPE and atomic absorption spectrophotometry for a lead containing industrial effluent sample. (C) 2014 Elsevier Ltd. All rights reserved.

Field dependent and disorder-induced nonlinear charge transport in electrochemically doped polypyrrole devices

Electric field activated charge transport is studied in the metal/polymer/metal device structure of electropolymerized polypyrrole down to 10 K with varying carrier density and disorder. Disorder induced nonlinear behaviour is observed in polypyrrole devices grown at room temperature which is correlated to delocalization of states. The slope parameter of currentvoltage characteristics (in log-log scale) increases as the temperature decreases, which indicates the onset of stronger field dependence. The field dependence of mobility becomes dominant as the carrier density decreases. The sharp dip in differential conductance indicates the localization of carriers at low temperatures which reduces the effective number of carriers involved in the transport.

Temperature dependent current-voltage characteristics of zinc oxide nanowire/polypyrrole nanocomposite

Temperature dependent current-voltage (I-V) measurements of electrochemically prepared zinc oxide nanowire/polypyrrole (ZnONW/PPy) nanocomposite yielded non-linear I-V characteristics at temperatures between 300 and 4.5 K. The low-field conductance (G) of the ZnONW/PPy film exhibits pronounced temperature dependence with room temperature conductance (G(300K)) similar to 10(-3) S and a conductance ratio (G(300)K/G(4.5K)) of similar to 10(4), indicating dominance of significant temperature dependent charge transport processes. The conduction mechanism of the film is satisfactorily understood by extended fluctuation induced tunneling (FIT) model as the non-linear I-V characteristics fit fairly well to the extended FIT model. Further, the temperature dependence of G(o) obtained from fitting followed Sheng's model also. (C) 2014 AIP Publishing LLC.

Nano-polypyrrole supercapacitor arrays prepared by layer-by-layer assembling method in anodic aluminum oxide templates

A novel method for preparing nano-supercapacitor arrays, in which each nano-supercapacitor consisted of electropolymerized Polypyrrole (PPy) electrode / porous TiO2 separator / chemical polymerized PPy electrode, was developed in this paper. The nano-supercapacitors were fabricated in the nano array pores of anodic aluminum oxide template using the bottom-up, layer-by-layer synthetic method. The nano-supercapacitor diameter was 80 nm, and length 500 nm. Based on the charge/discharge behavior of nano-supercapacitor arrays, it was found that the PPy/TiO2/PPy array supercapacitor devices performed typical electrochemical supercapacitor behavior. The method introduced here may find application in manufacturing nano-sized electrochemical power storage devices in the future for their use in the area of microelectronic devices and microelectromechanical systems.

Electrochemical fabrication and electronic behavior of polypyrrole nano-fiber array devices

Electrochemically active Polypyrrole (PPy) nano-fiber array device was fabricated via electrochemical deposition method using aluminum anodic oxide (AAO) membrane as template. After alkaline treatment electrochemically active PPy nano-fiber lost electrochemical activity, and became electrochemically inactive PPy. The electronic properties of PPy nano-fiber array devices were measured by means of a simple method. It was found that for an indium-tin oxide/electrochemically inactive PPy nano-fiber device, the conductivity of nano-fiber increased with the increase of voltage applied on the two terminals of nano-fiber. The electrochemical inactive PPy nano-fiber might be used as a nano-fiber switching diode. Both Au/electrochemically active PPy and Au/electrochemically inactive PPy nano-fiber devices demonstrate rectifying behavior, and might have been used for further application as nano-rectifiers. (c) 2005 Elsevier B.V. All tights reserved.

Characteristics of polypyrrole (PPy) nano-tubules made by templated ac electropolymerization

Electrochemical alternating current (ac) method designed for the synthesis of polypyrrole (PPy) nano-tubule arrays is the topic of this paper. Two-step anodic aluminum oxide (AAO) membrane is used as a template. The morphology of PPy nano-tubules is observed by SEM and discussed. FTIR spectra exhibit that the peaks of PPy nano-tubules shift compared to conventional PPy film. (c) 2005 Elsevier Ltd. All rights reserved.

Electrochemical polymerization and characterization of polypyrrole nanowires and nanotubules

Polypyrrole nanostructure arrays, including simultaneously large quantities of nanowires and small quantities of partially filled nanotubules have been electrochemically synthesized in home-made etched ion-track polycarbonate (PC) templates. Diameter of the prepared nanostructures varies from 45 to 320 nm with their lengths up to 30 microns. Morphological studies of these nanostructures were performed by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. While optical absorption properties were studied by ultraviolet-visible-near infrared spectrophotometry (UV-vis-NIR). It has been observed that the absorption maximum of polypyrrole shifts to the longer wavelength side as the diameter of these nanostructures (nanowires and nanotubules) increases. (C) 2010 Elsevier B.V. All rights reserved.

Preparation of a phosphopolyoxomolybdate P2Mo18O626- doped polypyrrole modified electrode and its catalytic properties

A phosphopolyoxomolybdate (P2Mo18) doped polypyrrole (PPy) modified electrode was prepared in aqueous solution by a one-step method. During the polymerization of PPy, P2Mo18 acted as both catalyst and dopant. The electrochemical behavior of the PPy/P2Mo18 modified electrode before and after the overoxidation of PPy was investigated. Both of these showed a catalytic effect toward bromate. The PPy/P2Mo18 composite film was characterized by chronoamperometry, cyclic voltammetry, the rotating disk electrode technique, X-ray photoelectron spectroscopy and Raman spectroscopy.

One-step synthesis of 3D dendritic gold/polypyrrole nanocomposites via a self-assembly method

Novel spherical three-dimensional (3D) dendritic gold-polypyrrole nanocomposites were successfully prepared in the presence of an amphiphilic p-toluene sulfonic acid (TSA) as dopant and surfactant via a self-assembly process which is based on the oxidation of pyrrole (Py) and the reduction of the chloroaurate ions, yielding PPy and Au(0) simultaneously. It was found that the probability of obtaining dendritic Au@PPy/TSA nanostructures depended on the concentration of TSA and the rate of addition of the oxidant (HAuCl4), It was also proposed that the supramolecular micelles formed by Py and TSA play the role of a 'soft template' to produce the dendritic Au@PPy/TSA nanocomposites.