Oxyanion doping strategies for Solid Oxide Fuel Cell Materials

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The drive for increasing energy efficiency and reducing greenhouse gas emissions has garnered increasing support for the use of fuel cell technology, which offers the potential for applications ranging from transport to stationary power generation. A number of different fuel cell systems have been investigated, with the electrolyte being crucial in dictating the temperature of operation. In terms of high temperature systems (>500C), a ceramic electrolyte is employed, and such solid oxide fuel cells (SOFCs) offer many benefits in terms of fuel flexibility and efficiency. A key requirement for an SOFC is a good ionic (oxide ion or proton) conductor as the electrolyte, and this has driven considerable research into the development of new oxide ion and proton conducting systems, along with accompanying electrode materials. In terms of the electrode materials, typically perovskite-related transition metal containing systems are targeted for the cathode. Research in this area has shown that in addition to the bulk characteristics of the material, the microstructure of the electrode is vitally important in ensuring optimum performance. This has led to considerable research into the design of nano-scale electrode structures, utilising low temperature synthesis techniques and carbon-based pore-formers. However, a feature that has not been considered is the fact that these strategies are likely to introduce residual carbonate into the electrode. This feature has been mostly overlooked due to the assumption that C is too small to be accommodated in the crystal structure of the electrode material. However, this is not necessarily the case, and indeed research from the high temperature cuprate superconductor area has shown that the perovskite structure will accommodate carbonate and a range of other oxyanions (sulphate, phosphate, borate). There is therefore a clear need to investigate the carbonate content of low temperature synthesised SOFC electrode materials, and examine how this affects the performance. In addition there is the potential to develop new materials with improved properties through the incorporation of carbonate or other oxyanions, as shown by recent work from our group on phosphate-doped electrolyte materials. In this project therefore, the possibility of oxyanion doping into a range of SOFC electrode and electrolyte materials will be examined, starting with perovskite systems, and then extending to investigate fluorite materials. In the case of carbonate incorporation, this will be achieved through low temperature synthesis from organic precursors, while in the case of sulphate and phosphate, both low and high temperature synthesis strategies will be employed (phosphate in particular is more thermally stable, allowing higher temperature synthesis strategies).