PITA Fiscal Year 2007 Projects

Nanotechnology

Novel synthesis of nanostructured materials for low temperature SOFC via in situ decomposition of sol-gel derived mixed metal oxides
A novel sol-gel process will be developed for synthesizing mixed transition metal (M) yttria stabilized zirconium oxide spinels (ZrM2O4) as well as perovskite structures corresponding to range of perovskite structures such as La4Sr8Ti12-xMnxO38-d. The resultant high surface area precursors will then be sintered to generate porous ceramics. The sintered ceramics will then be subsequently subjected to heat treatment in an Ar/H2 or air environment to generate a uniform nanoscale dispersion of the transition metals within the zirconia matrix or the perovskite oxide structure. The precursor structure (composition, surface area) and heat treatment parameters (environment, temperature, time) will dictate the range of the nanoscale microstructure and the volume fraction of the transition metals dispersed in the oxide matrix as well as the uniformity of the perovskite oxide cathodes. This novel approach exploits the following aspects. First, the ability of the late transition metals such as Ni, Cu and Co to form the spinel phase with zirconia. Second, the thermodynamic reduction potentials and the phase instability of the late transition metal oxides in the spinel phase thereby resulting in the phase separation of the metallic phase dispersed in the oxide matrix. Third, since the metal particles originate from oxide particulates that are sintered to zirconia, an adherent metal/ceramic interface will be obtained. Fourth, the use of Cu and Co and the solid solutions of these oxides in the spinel phase to generate coke resistant anodes for direct use of hydrocarbon fuels. The approach will also enable the generation of novel oxide anode structures that will be resistant to contamination by sulfur and carbon deposites.

The resultant nanostructured metal-oxide composites will be characterized for structure, composition and microstructure using X-ray diffraction (XRD) and high resolution scanning and transmission electron microscopy (HRSEM/HRTEM). The sintered discs containing varying volume fractions, porosity and nanoscale dispersions will then be tested initially for their electrochemical activity in half cell configurations by sintering a dense layer of yttria-stabilized zirconia (YSZ), the standard electrolyte on the porous anode nanocomposites using LSM (La0.8Sr0.2MnO3) as the cathode. Similar tests will be conducted on the oxide cathodes as well. Promising materials structures will then be tested in full fuel cell systems in collaboration with Dr. Vora at Siemens Power Generation.