A study of the conductive properties of nanostructured metal oxide films

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d'Olembert, Andre A.
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University of Guelph

Fuel cells which were first employed in spacecraft, producing both electricity and water for astronaut consumption during the mid-1960's, are part of the ongoing pursuit for renewable energy sources, and environmentally compatible electric power generation. Recent enhancements in design and materials might establish fuel cells in a 'sustainable hydrogen energy economy ' (SHEE) as viable alternatives to the internal combustion engine. In tune with our principal objectives, this study investigates the conductive properties of metal-oxide thin films by developing a new deposition technique called dual channel ultrasonic spray pyrolysis (DC-USP). The DC-USP process has proved to be a reliable and cost-effective method to fabricate thin films. Extending the DC-USP technique, we have created a novel mixed ionic electronic conductor (MIEC) composed of two metal-oxides: lanthanum strontium ferrite and copper-doped bismuth vanadate (LSF.40:BiCuVOx.10). When the two materials are mixed, their grain boundary regions are heavily defected because of the dissimilarity of the two crystal structures, which maintain their integrity in the formed heterogenous composite. Oxygen ion diffusion occurs as it migrates through an ionic crystal, hopping from defect site to defect site. Furthermore, a nanostructured material - with crystallite grains less than 100 nm in diameter - will improve oxygen diffusion by increasing the density of defect sites. The rate of diffusion is increased as well as the quantity of diffusion pathways. Ultimately, as the ionic current density is increased, the total efficiency ([nu]SOFCtotal) of the solid oxide fuel cell (SOFC) can be improved. Therefore, the LSF-40:BiCuVOx.10 material can contribute to solve the major outstanding problem of the three-phase boundary (TPB) that limits the oxygen reduction reaction to within a microscopic region near the cathode-electrolyte interface in the SOFC device. Materials were tested and analyzed using atomic force microscopy (AFM), interference microscopy (IM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and impedance spectroscopy to elucidate their structural features and energetic properties. Results show that the total bulk electrical conductivity of LSF.40:BiCuVOx.10 increases from 0.81 to 3 S/cm at 650°C when the content of BiCuVOx.10 increases from 10 to 50 vol.%. At a lower temperature of 550°C, the average bulk resistivity value for LSF.40:BiCuVOx.10 (50:50) films was as low as 2.08 0 cm (i.e. conductivity of 0.48 S/cm).

fuel cells, renewable energy sources, electric power generation, sustainable hydrogen energy economy, metal-oxide thin films