Solid Oxide Fuel Cells (SOFCs) are high temperature solid-state electrochemical devices that convert fuel into electricity and heat with high efficiency. Many fuels suitable for SOFCs derive from hydrocarbon sources, such as natural gas or biogas; however, these contain significant impurities, most notably compounds containing sulphur, which can poison the nickel electrocatalyst in the anode of the fuel cell. Sulphur removal is usually carried out but it is complicated and expensive to achieve levels below 1 part per million (ppm). An enhanced scientific understanding of chemical interactions on the surface of SOFC electrodes is critical to the development of robust nickel-based anodes, but the mechanisms and effects of sulphur poisoning are not fully understood. The scope of this thesis is to advance the field of sulphur-poisoning research by studying the effect of current density on the sulphur-induced degradation, and focuses on intermediate-temperature (IT) conditions with nickel-gadolinia doped ceria (Ni-CGO), which is the most promising anode material for IT-SOFCs, operating between 600–800 °C. The work of this thesis is aimed at (i) investigating the kinetics of sulphur poisoning, and the effect of current density, by use of a specially built three-electrode electrochemical test rig; (ii) analysis of structural modifications to the anode microstructure as a result of exposure to fuel cell conditions and (iii) development and prototype testing of a miniature SOFC test rig with optical access for in situ Raman spectroscopy. Fuel cell operation at higher current density was found to partially mitigate the sulphur poisoning of up to 3 ppm H2S in H2 fuel, while microstructural analysis found that the presence of as little as 0.5 ppm H2S accelerated restructuring of nickel grain surfaces. Finally, preliminary proof-of-concept results were obtained for the in situ Raman rig, and suggestions for a future design are discussed.

A three dimensional computational fluid dynamics (CFD) model of a polymer electrolyte membrane fuel cell (PEMFC) stack has been developed in order to study heat transfer in single-cell and two-cell stacks. In order to simplify the computational model, the electrochemical and water transport aspects of fuel cell operation were decoupled from those of heat transfer; the PEMFC fuel cell membrane electrode assembly (MEA), which comprises the electrode and electrolyte functional layers, was substituted with an electrically heated-plate to simulate the heat generated by an MEA. A fuel cell stack was manufactured and instrumented with calibrated thermocouples to measure the temperature distribution. The effect of reactant gas flow rate and cell thermal power density on the temperature distribution within the stack was studied with a view to validating the CFD model over a broad range of operating conditions. Also, in order to study the effects of natural and forced convection on the temperature distribution in the stack, an infra-red imaging camera was used. The predicted temperature distribution showed good agreement with the experiment over a wide range of gas flow rates, both in terms of local temperature distribution and overall energy balance. Results show that increasing the number of cells in a stack from one to two causes in a larger temperature variation, and therefore heat management in the stack becomes increasingly critical. The validated computational model was used as a modelling framework to design and test different cooling plates for stacks in order to overcome this issue. As a result, the bipolar plate in the two-cell stack was replaced with an air-cooled cooling plate in order to minimise temperature variation and to improve overall stack performance.

Candidate organic semiconductor materials based on a,ro-dihexylquaterthiophene (dH4T) and a,ro-dihexylbis(phenylene)bithiophene (dHPTTP) core systems were synthesised. The tenninal positions of the alkyl substituents were substituted with, thioacetate, phosphonic acid, glycolic ester and allyl ether groups to enable the fonnation of self-assembled monolayers (SAMs) of the adsorbates onto Au, Ah03 and H-Si surfaces. These were then probed with x-ray photoelectron spectroscopy (XPS) and friction force microscopy (FFM). Analysis of the XPS spectra confirmed that the oligomers fonned monolayer films onto the respective substrates although the allyl-terminated oligomers were subject to oxidation when attached onto H-Si by thermally-initiated radical attachment. Comparison of this method with photochemical initiation highlighted a potentially competing photolysis reaction. FFM showed that the frictional properties of both the thiolate and phosphonic acid SAMs on Au and Ah03 for the oligomers depended on both the tail group polarity and the density of packing for the adsorbates, whilst the allyl-capped materials formed disordered monolayers on H-Si. Chemical patterns of the thioacetate and phosphonic acid-terminated oligomers were produced by the irradiation of methyl-tenninated alkanethiols and alkylphosphonic acids with 244 nm UV light. The irradiation and subsequent displacement of the exposed adsorbates with the dH4T and dHPTTP-based thioactetates and phosphonic acids resulted in areas of relatively high and low friction, which was imaged by FFM. The SAM photomodification process on Ah03 was monitored by XPS, and suggested C-P bond photolysis as a potential mechanism. Scanning near-field photolithography (SNP) was then used to generate dH4T and dHPTTP features into alkanethiol and phosphonate SAMs. The smallest features, of 40 nm fwhm demonstrate that SNP is a viable method for the preparation of organic semiconductors with nanometre resolution, with potential application in the production of self-assembled monolayer field-effect transistors (SAMFETs).

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