Abstract/Summary

Bicontinuous cubic phases are high surface area nanostructures formed spontaneously by amphiphilic lipids on contact with water. This thesis reports studies into the behaviour of thin lipid films, capable of forming bicontinuous cubic phases, and their use as soft templates for the electrodeposition of aligned platinum nanostructures. In addition, the suitability of these mesoporous films for use as catalysts in direct alcohol fuel cells is detailed. Through an experimental and theoretical study of thin films of lipid under controlled humidity, it was demonstrated that adding glycerol progressively lowers the humidity at which QII phase films are stable, without affecting their lattice parameter. These findings open up the possibility of utilising cubic phases in a much wider range of environments, where typically the structure would collapse due to dehydration. The addition of glycerol allowed for a study into the orientation adopted by these lipid films; the QIIG and the QIID phases were observed to be reproducibly orientated with the (110) and the (111) facets aligned parallel to the substrate respectively up to a measured thickness of 1.4 µm. These results agreed with theoretical predictions based on the minimization of interfacial energy. Self-assembled cubic phase films were used to template mesoporous platinum nanostructures 1-2 microns thick featuring uniaxial alignment with the (111) plane orientated parallel to the substrate and high surface area (42 ± 1 m2 /g). To investigate the electrodeposition process time resolved X-ray scattering measurements were taken in situ as the platinum nanostructures grew within the lipid template using a custom electrochemical cell developed for use on a synchrotron beamline. These measurements identified two surprising characteristics of the templated electrodeposition process. Firstly, the aligned platinum nanostructures are templated from polydomain lipid films, suggest that up to 3 µm away from the lipid/substrate interface, polydomain QII samples display a region of uniaxial orientation. Secondly, the platinum films are found to be cubic while the lipid template is in place but undergo a slight distortion of the lattice along the 111 direction once the template is removed resulting in a rhombohedral structure where α = 87 ˚ (α = 90˚ for cubic structures). Additionally, these phytantriol templated platinum nanostructures were assessed for use as anode catalysts in alcohol fuel cells. The catalytic response towards the oxidation of methanol and ethanol was found to be enhanced in phytantrioldirected nanostructured films in comparison to non-structured platinum. Lipid templated platinum was directly electrodeposited onto porous carbon gas diffusion layers as used in conventional fuel cell design. Platinum nanostructures on carbon and gold disc electrodes showed a comparable result towards the oxidation of ethanol. These findings present lipid templated electrodeposition as a practical method to incorporate nanostructured platinum materials into conventional fuel cell designs for enhanced catalytic response towards the oxidation of alcohols.