Characterization of polypyrrole/phosphotungstate membranes by electrochemical impedance spectroscopy

The aim of this study was to design and prepare multifunctional PPy/PW12O403- membranes useful for the development of smart textile fabrics and wastewaters treatments based on the application of electrochemical techniques. These PPy/PW12O403- membranes have been characterized by means of electrochemical impedance spectroscopy by using electrochemical cells with different configurations based on the use of two-, three-, or four-electrode experiments. The activation energy of the films in the temperature range 35-70 degrees C was 170 meV. It has been demonstrated that after measuring the PPy films in different NaCl solutions, both the rate of ionic exchange and the diffusion processes through the membrane are faster for more concentrated solutions. Ionic exchange and diffusion were very prevented with a large cation as tetramethylammonium. The impedance spectra obtained with metal/polymer/electrolyte configuration show that the electrical conduction developed through coatings in strong acid solution is controlled by finite-length diffusion processes with reflective boundary conditions. At pH 13, the electrical response proceeds through the oxide layer (Fe and Cr oxides) and the steel/electrolyte interface. In this case, the polymeric coating is very porous due to the counter-ion disintegration. The decomposition of the counter-ion was corroborated by means of energy dispersive X-ray and Fourier transform infrared spectroscopy. (C) 2013 Elsevier B.V. All rights reserved.Authors thank to the Spanish Ministerio de Ciencia e Innovacion (contract CTM2011-23583) and Universitat Politecnica de Valencia (Primeros Proyectos de Investigacion (PAID-06-10)) for the financial support. J. Molina is grateful to the Conselleria d'Educacio, Formacio i Ocupacio (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship.Bonastre Cano, JA.; Molina Puerto, J.; Galvan, JC.; Cases Iborra, FJ. (2014). Characterization of polypyrrole/phosphotungstate membranes by electrochemical impedance spectroscopy. Synthetic Metals. 187:37-45. https://doi.org/10.1016/j.synthmet.2013.10.020S374518

NANOPILLAR BASED ELECTROCHEMICAL BIOSENSOR FOR MONITORING MICROFLUIDIC BASED CELL CULTURE

In-vitro assays using cultured cells have been widely performed for studying many aspects of cell biology and cell physiology. These assays also form the basis of cell based sensing. Presently, analysis procedures on cell cultures are done using techniques that are not integrated with the cell culture system. This approach makes continuous and real-time in-vitro measurements difficult. It is well known that the availability of continuous online measurements for extended periods of time will help provide a better understanding and will give better insight into cell physiological events. With this motivation we developed a highly sensitive, selective and stable microfluidic electrochemical glucose biosensor to make continuous glucose measurements in cell culture media. The performance of the microfluidic biosensor was enhanced by adding 3D nanopillars to the electrode surfaces. The microfluidic glucose biosensor consisted of three electrodes - Enzyme electrode, Working electrode, and Counter electrode. All these electrodes were enhanced with nanopillars and were optimized in their respective own ways to obtain an effective and stable biosensing device in cell culture media. For example, the `Enzyme electrode\u27 was optimized for enzyme immobilization via either a polypyrrole-based or a self-assembled-monolayer-based immobilization method, and the `Working electrode\u27 was modified with Prussian Blue or electropolymerized Neutral Red to reduce the working potential and also the interference from other interacting electro-active species. The complete microfluidic biosensor was tested for its ability to monitor glucose concentration changes in cell culture media. The significance of this work is multifold. First, the developed device may find applications in continuous and real-time measurements of glucose concentrations in in-vitro cell cultures. Second, the development of a microfluidic biosensor will bring technical know-how toward constructing continuous glucose monitoring devices. Third, the methods used to develop 3D electrodes incorporated with nanopillars can be used for other applications such as neural probes, fuel cells, solar cells etc., and finally, the knowledge obtained from the immobilization of enzymes onto nanostructures sheds some new insight into nanomaterial/biomolecule interactions

Electrochemical properties and electrochemical impedance spectroscopy of polypyrrole-coated platinum electrodes

Polypyrrole (PPy) films of different thickness were characterized by electrochemical impedance spectroscopy (EIS) measurements in acetonitrile and aqueous solutions, containing 0.1 M NaClO4 or sodium dodecylsulfate as the dopant. The PPy films were electrochemically deposited on Pt, and their electrochemical properties studied by cyclic voltammetry. Impedance spectra were obtained at potentials ranging from 0 to 0.8 V/SCE. The EIS data were fitted using two different equivalent electrical circuits (depending on the nature of the dopant). They involve a diffusive capacitance, which increased with the passing charge during electrosynthesis (i.e. film thickness) for ClO4--doped PPy, but was practically unaffected by the film thickness in the case of SDS-doped PPy. Also, a double-layer capacitance was found only in the circuit of ClO4--doped PPy. It increased with the film thickness, and showed a minimum near the open-circuit potential. Finally the charge-transfer resistance (Rct) obtained with SDS is nearly 200-fold higher than that obtained with ClO4- in the same solvent (H2O). With the same dopant (ClO4-), Rct is about five times higher in acetonitrile relative to water. All these EIS results of the different types of PPy suggest a relation with the wettability of the polymer.KEY WORDS: Conducting polymers, Polypyrrole, Electrochemical impedance spectroscopy, Equivalent-electrical circuit, Micellar mediaBull. Chem. Soc. Ethiop. 2006, 20(2), 279-293

Long-Term Stable Adhesion for Conducting Polymers in Biomedical Applications: IrOx and Nanostructured Platinum Solve the Chronic Challenge

Conducting polymers (CPs) have frequently been described as outstanding coating materials for neural microelectrodes, providing significantly reduced impedance or higher charge injection compared to pure metals. Usability has until now, however, been limited by poor adhesion of polymers like poly(3,4-ethylenedioxythiophene) (PEDOT) to metallic substrates, ultimately precluding long-term applications. The aim of this study was to overcome this weakness of CPs by introducing two novel adhesion improvement strategies that can easily be integrated with standard microelectrode fabrication processes. Iridium Oxide (IrOx) demonstrated exceptional stability for PEDOT coatings, resulting in polymer survival over 10 000 redox cycles and 110 days under accelerated aging conditions at 60 °C. Nanostructured Pt was furthermore introduced as a purely mechanical adhesion promoter providing 10-fold adhesion improvement compared to smooth Pt substrates by simply altering the morphology of Pt. This layer can be realized in a very simple process that is compatible with any electrode design, turning nanostructured Pt into a universal adhesion layer for CP coatings. By the introduction of these adhesion-promoting strategies, the weakness of CP-based neural probes can ultimately be eliminated and true long-term stable use of PEDOT on neural probes will be possible in future electrode generations

Electrochemical synthesis of polypyrrole doped with graphene oxide and its electrochemical characterization as membrane material

Polypyrrole (PPy) doped with graphene oxide (GO) has been electrochemically obtained by potentiostatic synthesis and its electrochemical behavior as membrane material has been studied for the first time. Fourier transform infrared spectroscopy with attenuated total reflection showed the formation of the hybrid material due to presence of PPy and GO bands. Field emission scanning electron microscopy micrographs showed the effective incorporation of GO sheets and the formation of a 3-D porous material with high surface area. Scanning electrochemical microscopy of PPy/GO films showed positive feedback close to the ideal conducting behavior, indicating a good electroactivity. Electrochemical impedance spectroscopy (EIS) was employed to measure the electrochemical properties of the coatings by two-, three-, and four-electrode configurations. The electronic conductivity of PPy/GO film, measured between two metallic conductors, was 4.7·10−6 S/cm. Its ionic conductivity was superior (1.6·10−3 S/cm) due to the high porosity of the material as demonstrated by cyclic voltammetry and EIS measurements, where the PPy/GO film was employed as a free-standing membrane. The diffusion-migration rate of tetramethylammonium chloride was very similar to sodium chloride when present in the same concentration, which indicated no influence of the size of the electrolyte conductor due to the high porosity. © 2016 Elsevier B.V. All rights reserved.Authors wish to thank the Spanish Ministerio de Ciencia e Innovacion (contract CTM2011-23583) for the financial support. J. Molina is grateful to the Conselleria d'Educacio, Formacio i Ocupacio (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship (APOSTD/2013/056). A.I. del Rio is grateful to the Spanish Ministerio de Ciencia y Tecnologia for her FPI fellowship. Electron Microscopy Service of the UPV (Universitat Politecnica de Valencia) is gratefully acknowledged for help with FESEM and EDX characterization.Molina Puerto, J.; Bonastre Cano, JA.; Fernández Sáez, J.; Del Río García, AI.; Cases Iborra, FJ. (2016). Electrochemical synthesis of polypyrrole doped with graphene oxide and its electrochemical characterization as membrane material. Synthetic Metals. 220:300-310. https://doi.org/10.1016/j.synthmet.2016.06.028S30031022

Metallic bipolar plates for proton exchange membrane (PEM) fuel cells

With escalating oil prices and increasing environmental concerns, increasing attention is being paid to the development of proton exchange membrane fuel cells (PEMFCs). A significant part of the PEMFC stack is the bipolar plates (BPs), which account for about 80% of the total weight and 45% of the stack cost. Bipolar plates have traditionally been made of non-porous graphite, which suffers from high cost, heavy weight, low mechanical strength and the need to machine the flow channels. Metallic bipolar plates have many potential advantages, but in the operating environment of the fuel cell they are prone to corrosion or dissolution. To overcome these difficulties, six metals, including SS316L, SS347, SS410, A36 steel, A16061 and Grade 2 Ti, were investigated as potential bipolar plate materials in the simulated PEMFC working conditions. Based on the corrosion and interfacial contact resistance results and price, SS316L was chosen as the candidate bipolar plate material. TiN was coated on SS316L using a Plasma Assisted Physical Vapor Deposition (PAPVD) coating technology and the coatings were about 15μm thick. The TiN-coating increased the polarization resistance by a factor of 30 and reduced the corrosion current density by a factor of 40. Polypyrrole, a conductive polymer, has been coated on SS316L using electrochemical methods. Potentiodynamic tests showed that the corrosion current density is decreased by a factor of 17 and polarization resistance was increased by a factor of 10.5 by coating with polypyrrole. The nucleation and growth of polypyrrole can be divided into three stages. The first stage is the incubation period. The second stage is a combination of instantaneous nucleation with 2-D (IN2D) or 3-D growth (IN3D). The third stage is a combination of instantaneous nucleation or progressive nucleation and 3D growth (IN3D and PN3D). A Taguchi DOE method was then used to optimize the polypyrrole-coating parameters for SS316L for metallic bipolar plate application. In order to further improve the characteristics of polypyrrole coating, an Au interlayer was coated on SS316L before coating polypyrrole

Study of Epithelial Cells on Polypyrrole based Conducting Polymers using Electrochemical Impedance Spectroscopy

PhDPolypyrrole (PPy) is a conjugated polymer that displays special electronic properties including conductivity. It may be electrogenerated with the incorporation of any anionic species including negatively charged biological molecules such as proteins and polysaccharides. For this thesis, variously loaded-PPy films were prepared on gold sputter-coated coverslips. The growth and characteristics of epithelial cells, namely keratinocytes, were studied on these films by microscopy, biochemical assay, immunocytochemistry and electrochemical impedance spectroscopy. Keratinocyte viability was found to be PPy-load dependent. For chloride, polyvinyl sulphate, dermatan sulphate and collagen-loaded PPy films, polycarbonate and gold, keratinocyte viability, as assessed by the AlamarBlueTM assay, was respectively 47%, 60%, 88% and 23%, 75% and 61% of tissue culture polystyrene controls after 5 days. This was found to require a previously unreported polymer washing step prior to cell seeding due to the observed toxicity of untreated films. Keratinocytes stained positive for proliferation (PCNA), suprabasal differentiation (K10) and hyperproliferation (K16) markers although cell morphology was poor for organotypical cultures on dermatanloaded PPy compared with de-epidermalised dermis. Cell-induced impedance changes were detected in a three-electrode format over PPy modified electrodes. Results obtained showed the effects of cell density, cell type and monitoring frequencies. In particular, it was seen that lower cell densities could be detected on PPy compared to unmodified gold electrodes. Keratinocyte confluence as determined by impedimetric analysis was reached more rapidly on PPy than bare gold in agreement with AlamarBlueTM measurements. Electrical equivalent circuit analysis using parameters whose contributions may be directly mapped to intracellular and intercellular spaces, and membrane components suggested that the technique can be extended to cell morphology discrimination. This work shows that PPy biocomposites are attractive candidates for tissue engineering applications since they may incorporate biomolecules and are electrically addressable with the potential to both direct and report on cell activities

Aspects on Fundaments and Applications of Conducting Polymers

Since the establishment of the conductive properties of intrinsic conductive polymers, a huge variety of basic and applied research has been carried out, involving different polymers, copolymers, blends, mixtures and composites. Thus, fundamental understanding of physical and chemical properties of these materials has been sought, while the applied aspects have advanced very rapidly, crossing the boundaries between disciplines. Today, the applications of conducting polymers in various fields such as neuroscience, nanotechnology and green chemistry, are easily found. This development is dynamic and it needs to be updated and hence the motivation for the set of results presented in this book; which provides information about the development of fundamentals, and about some applications of conductive polymers

Conducting fabrics of polyester coated with polypyrrole and doped with graphene oxide

Polyester (PES) has been coated with polypyrrole (PPy) to produce conducting fabrics. Graphene oxide (GO) has been used in different concentrations (10, 20 and 30% weight) as counter ion to neutralize the positive charges of the PPy structure. Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) of the PPy/GO powders corroborated the incorporation of GO as counter ion due to the presence of O in the EDX spectrum, as well as an excess of C, arising from GO contribution. The doping level (N+/N) decreased with the GO content. Field emission scanning electron microscopy (FESEM) showed the formation of the PPy/GO coating and the incorporation of GO in the composite. Electrochemical impedance spectroscopy (EIS) in solid state and solution, cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) were used to test the electrical properties and electroactivity of the fabrics. There was a decrease in the electrical properties and electroactivity as the GO content increased. The conductivity of the fabrics could be tuned by varying the GO content.Spanish Ministerio de Ciencia e Innovación (contract CTM2011-23583) for the financial support. Conselleria d'Educació, Formació i Ocupació (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship. C2011-UMINHO-2C2T-01 FCT funding from Programa Compromisso para a Ciência 2008, Portugal. XPS studies were performed at CEMUP (University of Porto, Portugal) facilities. Electron Microscopy Service of the UPV (Universitat Politècnica de València) is gratefully acknowledged for help with FESEM and EDX characterization