Materials Science Forum Vol. 657

Abstract: Fuels are being considered an as environmental friendly technology and are making headlines across the globe as clean and reliable alternate energy source for transportation, stationary and portable power applications. The rapid developments taking place in all the leading research laboratories in the world are making fuel cell closer to the realization. The progress of PEM fuel cell is closely related to the development of solid polymer electrolyte membranes as it defines the properties needed for other components of the fuel cell. So far perfluorosulfonated membranes such as Nafion have been found useful in these fuel cells and are the only material of choice available commercially. But these membranes are very expensive and have other drawbacks, which acts as an impediment for the commercialization of this technology. As a result alternative cheaper membrane materials have been developed. For the development of new or novel membranes mainly three strategies have been used: (1) modifying the currently used ionomer membranes (2) synthesizing new polymeric membranes and (3) develop new polymer composites by blending the two polymers or composting with an inorganic material. The composite membrane approach (3) has been widely used to tackle the problem of methanol crossover and temperature stability.

Abstract: 40% Pt on carbon black was used to make various inks. Compositions were altered by changing the organic component (2-propanol vs 1,2-¬propanediol), the liquid to solid ratio, and addition of Fullerenes to alter electronic properties. Inks were printed onto Nafion® or bond paper substrates using a Presco screen printer. The inks rheological properties were thoroughly characterized, and screen printed electrodes were characterized using optical microscopy, and hall measurements. Ink formulation had a major effect on final film morphology, with high water ratio formulations optimum for the Nafion® substrate and low water ratios ideal for bond paper. The final film integrity influenced sheet hall coefficients with p-type carriers dominating inhomogeneous films, and n – type carriers dominating well formed films. However hall mobility did not correlate with film thickness. Rheological studies showed that increasing the solid ratios and changing the solvent increased the viscosity, and the storage modulus (G') of between 84 and 224 and viscoelastic behaviour of inks correlated with good print quality.

Abstract: Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Among the various types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) are considered to be at the forefront for commercialization for portable and transportation applications because of their high energy conversion efficiency and low pollutant emission. Cost and durability of PEMFCs are the two major challenges that need to be addressed to facilitate their commercialization. The properties of the membrane electrode assembly (MEA) have a direct impact on both cost and durability of a PEMFC. An overview is presented on the key components of the PEMFC MEA. The success of the MEA and thereby PEMFC technology is believed to depend largely on two key materials: the membrane and the electro-catalyst. These two key materials are directly linked to the major challenges faced in PEMFC, namely, the performance, and cost. Concerted efforts are conducted globally for the past couple of decades to address these challenges. This chapter aims to provide the reader an overview of the major research findings to date on the key components of a PEMFC MEA.

Abstract: This contribution discusses the deposition process and properties of intrinsic silicon thin films processed by the hot wire chemical vapour deposition technique. We review some fundamental characterization techniques that are used to probe into the quality of the material and thus decide its susceptibility to be used as the intrinsic layer in solar cells industry. This paper covers the optical, structural and electrical properties of the material. Results from UV-visible and IR spectroscopy, XRD and Raman scattering, X-section TEM as well as dark and photo-currents are given. It is shown that the thermal activation energy is a good measure of the quality of the sample.

Abstract: Dye doped polymers (DCPs) has a wide application based on their optical and electrochemical properties. Dye sensitisation of conducting polymeric materials has gained a wide theoretical interest and practical application in sensors and solar cell technology. This review gives a broad summary on synthesis, the effect of the presence of dye in the polymer (properties, structure and conductivity), application in sensors and dye sensitised solar cells. Different sensing modes are also discussed as well as the effects of post polymer modification with dyes in sensors. In solar cells, the role of DCPs in light harvesting is summarised using examples. Finally, perspectives and the advantages of dye modification or sensitisation of polymers in sensors and solar cells are included.

Abstract: Conducting and electroactive nanostructured poly(2, 5-dimethoxyaniline), PDMA, doped with anthracene sulphonic acid, ASA, and phenanthrene sulphonic acid, PSA, respectively, were prepared by oxidative polymerisation of 2, 5-dimethoxyaniline, DMA, with ammonium persulphate as oxidant. Scanning electron microscope, SEM, images of the polymers showed well defined nanotubes and fibrils with diameters of between 50 to 100 nm and 200 to 300 nm for PDMA-ASA and PDMA-PSA, respectively. Evidence of the incorporation of ASA and PSA into the PDMA backbone was provided by UV-Vis and FTIR analyses. Electrochemical interrogation of the sulphonic acid-doped polymers by cyclic voltammetry showed that both PDMA-ASA and PDMA-PSA exhibit quazi-reversible electrochemistry. The standard rate constant, ko, for the charge transfer reactions of PDMA-ASA and PDMA-PSA were 3.81 x 10-4 cm s-1 and 3.27 x 10-5 cm s-1, respectively. There was a relationship between the ko value and the formal potential, E0ʹ, of the polymeric nanomaterial. PDMA-ASA that had larger ko value gave an E0ʹ value of 134 mV which was lower than that of PDMA-PSA by 19 mV, indicating that PDMA-ASA has lower activation energy than PDMA-PSA for the electron transfer process Electrochemical impedance spectroscopy over a range of potentials showed that the polymeric nanotubues exhibited high conductivities, though the SA-doped polymer was more conducting.