Treffer: Fabrication and Characterization of Novel Electrodes for Solid Oxide Fuel Cell for Efficient Energy Conversion

Solid oxide fuel cells (SOFCs) have been considered as one of the most promising technologies for future energy conversion since they can in principle be operated with fuels ranging from H2 to any hydrocarbon fuel. However, the system cost and coking (when using hydrocarbon as fuel) issues for the state-of-art electrode materials/designs often limit their further application. The objective of this Ph.D dissertation is aiming at overcoming these problems and accelerating SOFC commercialization. One approach to cost reduction is lowering the SOFC operating temperature to below 800 or even 600 oC, so that inexpensive materials can be used and quick start-up and SOFC durability can be improved. However, the overall electrochemical performance of an SOFC system will significantly decrease with a reduced operating temperature due to increased ohmic resistance of the electrolyte and polarization resistances of the electrode reactions. Ohmic resistance could be reduced by decreasing thickness of the electrolyte or using electrolyte with high ionic conductivity. Polarization resistance could be reduced by applying novel microstructured electrodes. Here we have fabricated a novel hierarchically oriented porous anode-supported solid oxide fuel cell with thin Gd0.1Ce0.9O2 (GDC) electrolyte by freeze-drying tape-casting and drop-coating. Three dimensional (3D) X-ray microscopy and subsequent analysis have demonstrated that the substrate has a graded open and straight pore/channel structure. The diameter of pore size on the bottom and top surface, porosity distribution along thickness direction and tortuosity factor have been determined by SEM and calculation with help of Matlab. The novel microstructure is expected to facilitate gas diffusion in the anode during fuel cell operation. The cell performance at low temperature ranging from 500-600 oC has been evaluated systematically. SOFCs with such Ni-GDC anode, GDC film (30 μm) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-GDC (LSCF-GDC) cathode show significantly enhanced cell ...