Polyelectrolyte complexes of chitosan and phosphotungstic acid as proton-conducting membranes for direct methanol fuel cells

Polyelectrolyte complexes (PECs) of chitosan and phosphotungstic acid have been prepared and evaluated as novel proton-conducting membranes for direct methanol fuel cells. Phosphotungstic acid can be fixed within PECs membranes through strong electrostatic interactions, which avoids the decrease of conductivity caused by the dissolving of phosphotungstic acid as previously reported. Scanning electron microscopy (SEM) shows that the PECs membranes are homogeneous and dense. Fourier transform infrared spectroscopy (FTIR) demonstrates that hydrogen bonding is formed between chitosan and phosphotungstic acid. Thermogravimetric analysis (TGA) shows that the PECs membranes have good thermal stability up to 210 degrees C. The PECs membranes exhibit good swelling properties and low methanol permeability (P, 3.3 x 10(-7) cm(2) s(-1)). Proton conductivity (sigma) of the PECs membranes increases at elevated temperature, reaching the value of 0.024 S cm(-1) at 80 degrees C.

Surface-modified Nafion (R) membrane by casting proton-conducting polyelectrolyte complexes for direct methanol fuel cells

Surface-modified Nafion (R) membrane was prepared by casting proton-conducting polyelectrolyte complexes on the surface of Nafion (R). The casting layer is homogeneous and its thickness is about 900 nm. The proton conductivity of modified Nafion (R) is slightly lower than that of plain Nafion (R); however, its methanol permeability is 41% lower than that of plain Nafion (R). The single cells with modified Nafion (R) exhibit higher open circuit voltage (OCV = 0.73 V) and maximal power density (P-max = 58 mW cm(-2)) than the single cells with plain Nafion (R) (OCV = 0.67 V, P x = 49 mW cm-2). It is a simple, efficient, cost-effective approach to modifying Nafion (R) by casting proton-conducting materials on the surface of Nafion (R).

Conducting probe atomic force microscopy investigation of anisotropic charge transport in solution cast PBD single crystals induced by an external field

2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxdiazole (PBD) is a good electron-transporting material and can form single crystals from solution. In this work, solution cast PBD single crystals with different crystallographic axes (b, c) perpendicular to the Au/S substrates in large area are achieved by controlling the rate of solvent evaporation in the presence and absence of external electrostatic field, respectively. The orientation of these single crystals on Au/S substrate was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting probe atomic force microscopy (CP-AFM) was used to measure the charge transport characteristics of PBD single crystals grown on Au/S substrates. Transport was measured perpendicular to the substrate between the CP-AFM tip and the Au/S substrate. The electron mobility of 3 x 10(-3) cm(2)/(V s) for PBD single crystal along crystallographic b-axis is determined. And the electron mobility of PBD single crystal along the c-axis is about 2 orders of magnitude higher than that along the b-axis due to the anisotropic charge transport at the low voltage region.

A room-temperature ionic-liquid-templated proton-conducting gelatinous electrolyte

Novel proton-conducting gelatinous electrolytes templated by room-temperature ionic liquid (RTIL) 1-butyl-3-methyl-imidazolium-tetrafluoroborate (BMImBF(4)) have been prepared in methylsisesquioxane backbone containing H3PO4, and the influences of the RTIL on the structure, morphology, thermal stability, and electrochemical properties of the gelatinous electrolytes have been examined. X-ray diffraction and scanning electron microscopy proved that BMImBF(4) acted as structure-directing template during the sol-gel process of methyl-trimethoxysilane. X-ray photoelectron spectra and infrared spectroscopy demonstrated that the hydrogen-bonding was formed between BMImBF(4) and H3PO4. The electrolytes had good thermal stability up to 300 degreesC and showed superior mechanical and electrochemical properties. A room-temperature conductivity of 1.2 x 10(-3) S cm(-1) was obtained for the electrolyte at the molar ratio of RTIL/Si/H3PO4 0.3/1/1, and its electrochemical window was up to 1.5 V.

Direct electrochemical generation of conducting polymer micro-rings

Self-doped polyaniline (PANI) micro-rings have been successfully generated electrochemically. The polymer forming rings were about 100 nm wide, and the ring diameter is tunable from several to dozens of micrometres depending on deferent current densities. The morphology of such nanostructured polyaniline rings was investigated and further confirmed with field-emission scanning electron microscopy (FE-SEM). Furthermore, the film was characterized using UV/visible spectroscopy and cyclic voltammetry. The bubble template formation mechanism of the micro-rings was also proposed. Such nanostructured materials synthesized electrochemically open up a new approach to surface morphology control.

Confining conducting polyaniline in a stable inorganic network

Water soluble conducting polyaniline with electrical conductivity of 10(-1)-10(-2) S/cm was prepared employing dopant induced water solubility technology. The water resistance of the conducting film was significantly improved employing,sol-gel hybrids method, especially when the conductive polyaniline loading was below 30 wt%. The reason for the improvement is that the conducting polyaniline chains are confined in a stable inorganic network.

Morphological study on water-borne conducting polyaniline-poly(ethylene oxide) blends

Conducting polyaniline-poly(ethylene oxide) blends were prepared from their aqueous solutions. The blends displayed an electrical conductivity percolation threshold as low as 1.83 wt % of polyaniline loading. As demonstrated by scanning electron microscopy, polarized optical microscopy, and wide-angle X-ray diffraction studies, the conducting polyaniline took a fibrillar morphology in the blend, and it existed only in the amorphous phase of poly(ethylene oxide). A three-phase model combining morphological factors instead of a two-phase model was proposed to explain the low-conductivity percolation threshold.

Conducting polyaniline confined in semi-interpenetrating networks

Communication: Conducting semi-interpenetrating network composites with low conductivity percolation threshold were synthesized from waterborne conducting polyaniline (cPAn) and melamine-urea resin, A perfect network of cPAn in the composite was observed by means of TEM (see Figure). The conductivity stability of cPAn in water was improved by confining the chain mobility of cPAn via in-situ crosslinking of melamine-urea resin. Cyclic voltammetry of the composites reveals electrochemical activities and reversibilities similarly to those of pure cPAn.

Formation of conducting layers on excimer-laser-irradiated polyimide film surfaces

Conducting layers on KrF excimer-laser-irradiated polyimide film surfaces were investigated by XPS, SEM and Fourier transform infrared (FTIR)-Raman spectroscopy, Analysis of polyimide residue after laser irradiation provided valuable insight into the nature of the formation of conducting layers. The subtle different between KrF laser irradiation and the pyrolysis of polyimide was found by comparison of the formation process of conducting layers. A physical picture was presented to describe better the formation of conducting layers. Under KrF laser irradiation, polyimide films underwent thermal decomposition assisted by photoinduced direct bond breaking. Polycrystalline graphite was subsequently formed as the product of the secondary addition reaction of carbon-enriched clusters, Such reaction was supported by the remaining energy on the irradiated polyimide film surface. This result shows that the thermal process played an important role that was not just restricted to the formation of conducting layers, Copyright (C) 2000 John Wiley & Sons, Ltd.

Preparation and properties of conducting polymer of doped polyaniline LB film

Stable monolayer of polyaniline doped with camphor sulfonic acid at the air-water interface has been obtained and has been successfully deposited by Langmuir-Blodgett technique onto CaF2 substrate. IR and UV-Vis-NIR spectra show that the doped molecules dedoped partially from the PANI backbone during the monolayer compression or deposition. Gas-sensing measurement indicates that the doped polyaniline LB film was sensitive to ethanol vapor at room temperature.

Covalently attached multilayer assemblies containing photoreactive diazo-resins and conducting polyaniline

We reported on the multilayer architecture containing diazo-resins (DAR) as polycations and polyaniline poly(aniline-co-N-propanesulfonic acid aniline) (PAPSAH) as polyanions held together by electrostatic interaction. Upon UV irradiation, the adjacent interfaces of the multilayer reacted to form a covalently crosslinking structure which greatly improved the stability of the films as confirmed by solvent etching experiments. These changes were confirmed by UV-Vis and FTIR spectroscopy. The thickness of the covalently attached films were characterized with small angle X-ray diffraction (SAXD) and a value of 30.0 Angstrom per bilayer was obtained. This type of film was further characterized by cyclic voltammetry which showed that the electroactive property of PAPSAH was still kept in the films after photoreaction. (C) 2000 Elsevier Science B.V. All rights reserved.

Poly(phenylene sulfide-tetraaniline): The soluble conducting polyaniline analogue with well-defined structures

A novel conducting polymer poly(phenylene sulfide-tetraaniline) (PPSTEA), with tetraaniline (TA) and phenylene sulfide (PS) segments in its repeat unit, has been synthesized through an acid-induced polycondensation reaction of 4-methylsulfinylphenyl-capped tetraaniline. The new polymer, which represents the first soluble conducting polyaniline analogue with well-defined structure, has high molecular weight, good solubility in common solvents, and good film-forming properties. Its electrical property is analogous to polyaniline. The conductivity of preliminarily, protonic-doping PPSTEA is up to 10 degrees S/cm. This synthetic strategy appears to be general for developing novel well-defined polyaniline analogue containing much longer fixed conjugation length.

Preparation and properties of water-based conducting polyaniline

A convenient way to make water-soluble or water-dispersible conducting polyaniline was given by employing protonic acid dopants containing hydrophilic ethyleneoxide oligomer as counter-anion. The conducting polyaniline possessed electrical conductivity in the range of 10(-3) to 10(-2) S/cm, depending on the dopant, and it displayed excellent electrochemical redox reversibility in non-aqueous system.

Preparation and properties of water-based conducting polyaniline

A convenient way to prepare water-soluble or water-dispersible conducting polyaniline was developed by employing protonic acid dopants containing hydrophilic ethyleneoxide oligomer as counter-ion. The conducting polyaniline possesses electrical conductivity in the range of 10(-3) to 10(-2) S/cm depending on the chosen dopant, and it displays an excellent electrochemical redox reversibility in non-aqueous systems.

Oxygen permeating properties of the mixed conducting membranes without cobalt

A new series of mixed conducting oxides, Sr10-n/2BinFe20Om (n = 4, 6, 8, 10), were synthesized by a solid state reaction method, and they have high oxygen permeability. The oxygen permeation rate at 1150 K is 0.41 ml(STD)/ cm(2).min for n = 6 and 0.90 ml(STD)/cm(2).min for n = 10, which is two times higher than that for Sr1-xBixFeO3 (x = 0.5). For the Sr1-xBixFeO3 (x = 0.1, 0.3, 0.5) series, the oxygen flux increases with increasing Bi content. (C) 1998 Elsevier Science Ltd.