Thick Polypyrrole Films Research Articles

Influence of processing parameters on the electric conductivity and on the mechanical properties of thick polypyrrole films

AbstractThe electric conductivity and the mechanical properties of electrochemically synthesized polypyrrole/p‐toluene sulfonic acid (PPy/pTSA) as a function of its processing parameters were investigated. The influence of polymerization current density, pyrrole concentration, and counter ion concentration on the electric conductivity of thick (≫100 μm) polymer films was examined and the electric conductivity was found to be in a range between 1.6 and 97 S · cm−1. Analysis of the polymer's chemical composition delivered a result in agreement with literature data of one counter ion for every 2.97 pyrrole rings for the best conducting samples. In mechanical tests, maximum values for Young's modulus, tensile strength, and elongation at break, were found to be 4.0 GPa, 72.6 MPa, and 11.2%, respectively. POLYM. ENG. SCI., 47:662–666, 2007. © 2007 Society of Plastics Engineers.

Towards High Power Polypyrrole/Carbon Capacitors

Conducting polymers demonstrate effective capacitances of more than 100 Farads per gram, 5 orders of magnitude higher than traditional capacitors. However polymer discharge times tend to be on the order of seconds, as opposed to the milli or microseconds of conventional capacitors, so that the overall power density is still at least an order of magnitude lower. The polypyrrole devices are essentially electrolytic capacitors in which charging times appear to be limited by rates of ionic mass transport and RC charging times. Electrochemical impedance measurements suggest diffusion time constants of 33 ms in 158 nm thick polypyrrole films with volumetric capacitances of 10 7 F/m 3. The impedance of a highly porous polypyrrole/carbon composite was measured to investigate the achievement of similarly fast response times in much thicker materials. It is shown that increasing the polypyrrole content of the film increases capacitance up to 60 F/g, but also increases the charging time constant. Analysis of the rate limiting factors suggests a method of optimizing capacitor geometry in order to maximize rates, including the prediction of device geometries that will lead to power delivery matching those of traditional capacitors.

Modification of Electronic Structure of Mesoscopic Perchlorate-Doped Polypyrrole Films by Ion Irradiation

The effects of low-energy (1−3 keV) argon ion irradiation on a 100 nm thick polypyrrole film deposited potentiostatically in an aqueous perchlorate solution have been studied by X-ray photoelectron spectroscopy (XPS). Dramatic spectral changes in the valence band structure and Cl 2p region with increasing ion impact energy and total ion dose have been observed for the perchlorate-doped conductive polymer surface. Higher impact energy (3 keV) is found to be more effective in modifying the polymer backbone, particularly in the breakage and formation of terminal bonding units, while higher ion flux (for impact energy above 1 keV) appears to produce complete dissociation of the perchlorate counterions, leaving behind only Cl atoms. These observations are also consistent with the spectral changes in the C 1s, N 1s, and O 1s regions observed under different ion irradiation conditions.

New electrochemical procedure for elaborating homogeneous and strongly adherent PPy films on zinc electrodes

Electropolymerization of pyrrole on zinc was investigated in sodium tartrate aqueous solution in order to obtain homogeneous and adherent polypyrrole films. The tartrate counter-anions inhibit the working electrode dissolution by leading to the formation of a passivation layer on its surface. Consequently, homogeneous and strongly adherent polypyrrole coating has been successfully achieved with different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. Polypyrrole coatings electrosynthesized on zinc electrodes have been characterized by several microscopic and spectroscopic techniques. Particularly, scanning electron microscopy (SEM) analysis has revealed a compact, homogeneous and thick polypyrrole film. X-ray photoelectron spectroscopy (XPS), IR and Raman analyses proved that the coatings obtained have globally the same structural features and elementary composition as those electrosynthesized on noble metals.

The Behavior of Polypyrrole-Coated Electrodes in Propylene Carbonate Solutions : II. Kinetics of Electrochemical Doping Studied by Electrochemical Impedance Spectroscopy

A family of Nyquist plots for 0.2 μm thick polypyrrole film was measured in a wide range of potentials in 0.25 M /propylene carbonate (PC) solution. This film was galvanostatically deposited onto the surface of a Pt electrode, and the film was continuously cycled in 0.25 M solution until a stable cyclic voltammetric response was reached. No irreversible changes occurred in the film during impedance measurements. Two alternative finite-space diffusion models were used to determine useful kinetic and equilibrium characteristics: the total charge-transfer resistance; partial electron and ion interfacial transfers; the low-frequency resistance related to the capacitive region of the impedance spectra; the binary chemical diffusion coefficient and the low-frequency differential capacitance related to the charging of the film’s bulk. All these quantities were determined as functions of potential and adequately interpreted. We also found that upon increasing the doping level, increases from to © 2002 The Electrochemical Society. All rights reserved.

Statistical Design to Optimize Specific Charges in Polypyrrole by Electrosynthesis

A design of experiments was employed to optimize the conditions of synthesis in order to electrogenerate thick polypyrrole films suitable for application as a cathode in polymeric batteries or supercapacitors. The influence of five main variables: potential of polymerization, generation time, monomer concentration, electrolyte concentration, and temperature, and their second‐order interaction on the specific charge were studied and optimized through three stages. The initial stage requires the synthesis of 16 films (design matrix). Every film is weighed and checked in the background solution to obtain the stored charge and the specific charge. The resulting statistical significance shows that optimization only is possible at low potentials. In a second stage a design matrix with eight new experiments allowed the determination of the variables of synthesis affecting the specific charge and the direction of change of those variables to optimize this property. By changing the conditions of synthesis in that direction three more experiments resulted in a designed film 0.5 μm thick and . © 1999 The Electrochemical Society. All rights reserved.

Electrochemical, thermal and spectral characteristics of thick polypyrrole films electropolymerized on active metal electrodes

Free-standing, thick polypyrrole (PPy) films were electrodeposited on active substrates (Fe, brass, Zn and Cu). The properties of the deposit grown on Fe resembled most closely that generated on an inert substrate (Pt). The conductivity, thermal stability and electrochemical properties of the films were seen to vary with substrate activity in the order Pt<Fe<brass<Zn<Cu. The low oxidation potential and high dissolution rate of Al hindered film formation. The redox reactions of the PPy films were electrochemically irreversible and were diffusion controlled. Raman spectra of the films were very similar.

Polypyrrole electrogeneration from a nucleophilic solvent (DMF)

In spite of difficulties pointed out in the literature thick polypyrrole film can be obtained on platinum from NaClO 4-DMF solutions. The polymerization rate increases at constant potential when the potential increases from 900 to 2400 mV(SCE) and the rate decreases at higher anodic potentials. The productivity of the consumed charge, as mg of polymer generated per mC of charge, decreases at increasing potentials. When temperature decreases the polymerization rate increases pointing to a high activation energy of parallel passivation reactions during polymerization. From the ‘ex situ’ microgravimetric method the following empirical kinetics was obtained: Rp = k[pyrrole] 0.5[ClO 4 −] 1.3. The formation of polymeric films was controlled by cyclic voltammetry in the background electrolyte. From the stored charge and the polymer weight the stored charge per mg of electrogenerated polymer for each film could be estimated. When the concentration of ClO 4 − ions increases both the polymerization rate and the capacity to store electrical charge in films increases, which indicates that ClO 4 − ions act as retarding agents of passivation processes during polymerization. In general, the ability to store electrical charge in polypyrrole electrogenerated in different solvents decreases when the donor ability of the solvent increases. At higher temperatures a faster nucleophilic attack of the solvent to the positively charged polymer is proposed to occur, promoting an increasing passivity of the film. The productivity of the polymerization charge decreases at increasing temperatures and increases at increasing concentrations of electrolyte and passes through a maximum when the concentrations of monomer increase.

Stability of thick polypyrrole films electrogenerated on stainless steel

Thick polypyrrole films (> 10 μm) were electrogenerated on steel electrodes, and their stability was checked through the variation of electrical charge stored in the film under different anodic potential limits and in different solvents. 0.1 M LiClO 4 acetonitrile, water and propylene carbonate solutions were used. Consecutive potential waves (square and triangular) were employed in the cycling. Water and acetonitrile solutions give higher charge storage efficacies (25–30 A h kg −1) than propylene carbonate solutions (0.7 A h kg −1). The stability is lower when the anodic potential is higher: polypyrrole films lose half of their charge storage efficacy after 250 cycles between - 500 and 1000 mV versus SCE, after 1100 cycles between -600 and 700 mV and after 1800 cycles between -600 and 400 mV.

Application of Polypyrrole Film Substrates for Characterization of Metallic Electrodeposits by Transmission Electron Microscopy and Electron Diffraction

The utility of polypyrrole is demonstrated as a substrate for characterization of metallic electrodeposits by transmission electron microscopy and electron diffraction. Copper and nickel crystallites are electrodeposited onto a polypyrrole film at a potential negative of the film undoping potential at which counterions are expelled and the film becomes an insulator (i.e., vs. ). The relatively slow process of undoping the counterions in the polypyrrole film at negative potentials enables the electrodeposition of thin samples of metals before the film becomes an insulator. Hence, both copper and nickel crystallites can be deposited in the first 30 s following the application of the cathodic potential. The insulating transition of the polypyrrole also insures that electrodeposits will be sufficiently thin for investigation by transmission electron microscopy (TEM). Conventional TEM using a 120 keV electron beam was used to study the morphological characteristics of the electrodeposits supported on a 110 nm thick polypyrrole film. The techniques of selected area electron diffraction (SAED) and energy dispersive x‐ray analysis were also used in conjunction with the TEM to confirm the structural and chemical identity of deposited structures as small as in dimension. The polypyrrole film serves as an acceptable substrate for electrodeposition and TEM characterization because of its mechanical stability, electrical conductivity, and electron transparency. Furthermore, the film can also be used for the TEM characterization of electrolessly deposited cadmium sulfide.

Structural effects in polypyrrole synthesis

Production of very thick polypyrrole films is an easy process, as the thickness can be controlled in a galvanostatic experiment by measuring the polymerization time. When using the p-toluene sulfonate anion, tough and flexible films with a high specific conductivity (70–90 Ω −1 cm −1) are produced. These properties are the same for films, produced in both acetonitrile and aqueous solutions. Both types of films contain a large amount of incorporated anion and solvent, even after drying in vacuo at room temperature. In aqueous solutions a polymer film with tube-like bulges are formed, probably caused by a spiralled microstructure of the chain. In acetonitrile no such tubes are found.