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New nanostructured catalytic Anodes for Solid Oxide fuel cells using hydrocarbon and Oxyhydrocarbon fuels

Final Activity Report Summary - NASOFC (New Nanostructured Catalytic Anodes for Solid Oxide Fuel Cells using Hydrocarbon and Oxyhydrocarbon Fuels)

The research conducted in the NASOFC Project was aimed at improving the efficiency of Solid Oxide Fuel Cells. SOFCs are electorchemical reactors in which chemical energy - from a fuel and air- is converted directly into electrical power. SOFCs contain catalyst materials which catalyse the activation of oxygen from the air at the cathode and the activation of the fuel - for example Hydrogen - at the anode. Our project concerned trying to improve the rate of reaction of the fuel at the anode. Our approach was to increase the surface area of the catalyst by deliberately preparing mesoporous materials. Mesoporous materials contain pores and channels just a few nanometers across. If we could make mesoporous structures of the same composition as the normal anode catalyst materials (Ni metal mixed with zirconium oxide) then we would greatly increase the surface area of the catalyst and so inprove the rate of reaction with the gas. In order to do this we used a technique sometimes called 'nanocasting'.

Here, a template or mould is made with a mesoporous structure. This is done in solution by mixing silicates with organic molecules which are able to form tubes a few nanometers wide. Under the right coditions the tubes assemble together to form three-dimensional structures with many parallel channels. The silicates can be incorporated into these and the orgainic mateiral removed to leave a mesoporous silica powder. This is what we used as one of our templates. We added Zr-containing solutions to the pores of this structure, heated it to form the zirconium oxide and then dissolved away the template. We successfully obtained the image of the template- where the template had channels our material had nanorods and where the template had walls our material had channels. We were able to confirm the structure using electron microscopy. This was the first time an ordered mesoporous zironium oxide had been made and this was published in the Journal of Materials Chemistry in 2008.

We used similar techniques to make a number of oxides of diffeirent compositions which would also be of interest in SOFC anode catalysts. We then tried a number of methods to introduce the Ni component into the mesoporous oxide materials. In some cases this did not work but we were successful with a number of methods. Again, we confirmed the structure using electron micrsocopy and we were able to study the distribution and type of Ni-containing material in our catalysts using a technique called temperature-programmed reduction. This allows the ease of chemical reduction of the NiO present in our samples to be determined and we were able to relate this to the chemical environment in which the NiO found itself in the samples.