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Throughout the globe, researchers are in quest of electro-catalysts for oxygen reduction reaction (ORR) in order to develop cathode materials for fuel cells (FCs). Although the anodic half-reactions of FCs are fast enough for oxidation of any fuel on cheap catalysts, ORR at the cathode is a slow process even with expensive platinum-based catalysts. Development of low-cost electro-catalysts with reasonably fast kinetics for (ORR) is desirable if fuel cell power is to be utilised in practice. The present study is based on the preparation and characterisation of silver-based electro-catalysts towards ORR. Simple chemical processes were developed to prepare three different electronically conducting nano-composites. Aniline, pyrrole or 3,4-ethyldioxythiophene (EDOT) in between the layer space of silver [Ag (I)] ion exchanged montmorillonite (MMT) undergoes spontaneous polymerisation. During the polymerisation process, Ag(I) cations are reduced to form metallic silver, while aniline, pyrrole or EDOT monomers are converted to polyaniline (PANI), polypyrrole (PPY) and poly (3,4-ethylenedioxythiphene) (PEDOT), respectively. The prepared composites were extensively characterised by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), conductivity measurements, AC-impedance and electrochemical analyses. Electrochemical studies showed that composites are good candidates towards ORR in alkaline electrolyte medium. Ag/MMT/PEDOT showed the best performance in catalytic properties. All three composites showed better performances than that of typical Ag/C composites with a similar mass loading of silver. Although the performances of the cheap composites are somewhat lower when compared to commercially available Pt/C, the performance is sufficient to use the materials as cheap alternatives for FC cathodes. [ABSTRACT FROM AUTHOR]

The properties of polymers are greatly enhanced when they are incorporated with silicate-layered clays as they find many applications in the fields of electronics, automobile industry, packaging, and construction. In this study a thermoplastic polymer poly(vinyl alcohol) (PVA) and montmorillonite (MMT) clay were used to prepare MMT-PVA nanocomposites and their mechanical properties were investigated. In general PVA is used in paper coating and packaging where their tensile strength and tearing strength are vital. The MMT-PVA nanocomposites displayed more than 60% increase in the tensile strength and young's modulus where as the tearing energy doubles the value of neat PVA. This is a substantial enhancement compared to that reported so far. The enhancement was achieved at low clay content probably due to its exfoliated structure. The dispersed clay layers are well embedded with PVA matrix via strong interatomic interactions leading to better material properties. [ABSTRACT FROM AUTHOR]

Cu(II)-exchanged montmorillonite [Cu(II)-MMT] takes up pyrrolium ions by ion exchange. Two pyrrolium ions are inserted for each Cu(II) ion expelled from its interlayers. These pyrrolium ions undergo spontaneous polymerization because of the remaining Cu(II) ions present within the intergalleries to form Cu(I)--polypyrrole--MMT nanocomposite. The polypyrrole (PPY) dispels any water already present within the intergalleries and the material becomes hydrophobic and reluctant to take up water. The inherent d-spacing due to anhydrous PPY present within the intergalleries is 16.0 Å, which is a 6.4 Å enhancement from the situation. which contains a bare inorganic ion. The material possesses unusually high mixed electrical conductivity. The conjugation length (and hence the electronic conductivity) decreases as the temperature is increased as confirmed by the Fourier transform infrared spectroscopy. However, the ionic component of the conductivity increases with temperature. The temperature dependence of conductivity shows Arrhenius behavior but two different activation regions are clearly visible. The activation energy for Cu(I) migration within the nanocomposite is much lower than 100°C (Ea=0.09eV). At the higher temperature region, the activation energy is 0.23 eV and this value is also comparatively low suggesting the favorable motion of Cu(I) ions within the PPY--MMT nanocomposite thus making it a fast Cu(I) ion conductor. The ionic conductivities are in the range 0.66--1.15 mS cm-1 in the temperature range from 25 to 120°C. [ABSTRACT FROM AUTHOR]

A series of nanocomposites of polyaniline-montmorillonite have been prepared in which polyaniline is present within the interlayers as well as adsorbed onto the external surfaces of the clay particles (i.e., emeraldine salt-montmorillonite, ES-MMT series). The composite materials show uniform texture as revealed by scanning electron microscopy. The ES-MMT members show high electronic conductivities. Under the identical conditions of sample preparation, the d-spacing enhancement upon the polymer intercallation is the same regardless of whether the polymer is present only within intergalleries or both inside and outside the intergalleries. The FTIR studies reveal that the OH stretching in the Al-Mg-OH infrared band appearing at 840cm-1 disappears upon polymer loading. Since the OH in Al-Mg-OH moieties are directed outward from the hexagonal cavities, this effect may be attributed to the interaction between the clay particles and the polymer that is present adsorbed to clay surfaces. The polymer present within the intergalleries influences strongly on the O-H vibrations, which are directing inward to the intergalleries. Cyclic voltammetric studies reveal that the electroactivity of the composite material is limited by the accessibility of solution species into the intergalleries in a diffusion-controlled manner. The electrochemical impedance spectroscopic (EIS) studies reveal that the ES-MMT members have both electronic and ionic conductivities with similar transport numbers even when the polymer is in its fully electronically conducting state. Four different and mutually independent techniques used to characterize the composites give strong evidence to confirm that there is a limit to the repetitive polymer loading within the intergalleries of the clay particles. The limited interspacing with all repeated polymer loading may be due to the saturation of all ion-exchangeable sites of montmorillonite by the cations of the polymer. [ABSTRACT FROM AUTHOR]

This paper describes the preparation and characterization of conducting polyaniline-montmorillonite (PANI-MMT) nanocomposites by the polymerization of anilinium ions within the interlayer space of MMT particles. A procedure for the successive introduction of PANI chains within the interlayer galleries of MMT is developed. The d-spacing, measured after heat treatment at various temperatures serves as a measure of the amount of polymer inserted in the clay intergalleries. The FTIR spectroscopy reveals the presence of host--guest interactions of a hydrogen-bonded nature. The DC conductivities were found to increase with the amount of PANI intercalated. Anilinium ions supported on kaolinite tended to dislodge from the surface upon repeated washings, as shown by the absence of polymer formation on such samples upon treatment with the oxidant. In MMT, however, polymerization is observed even with exhaustively washed samples, thus confirming that the successive polymerization processes occur within the interlayer galleries. Exclusion of the washing stage gives a composite material in which polyaniline is present on both the internal and external surfaces. This material is found to have significantly higher electronic conductivities than the composites where the polymer is restricted to interlayer galleries. The washed samples of the polymer once loaded into the clay (EMS1-MMT), twice loaded into the clay (EMS2-MMT) and thrice loaded into the clay (EMS3-MMT) have electrical conductivities of 4.5 x 10-5, 3.0 x 10-4, and 1.0 x 10-3 Scm-1, respectively in their dry states. The corresponding samples prepared by excluding the washing procedure had the values of 4.0 x 10-4, 1.0 x 10-2, and 1.0 x 10-1 Scm-1, respectively. [ABSTRACT FROM AUTHOR]