Solid oxide fuel cells (SOFCs) are electrochemical devices that convert fuels, such as hydrogen and natural gas, to electricity at high efficiencies, e.g., up to 90 %. SOFCs are emerging as a key technology for energy production that also minimize greenhouse gas emissions compared to conventional thermal power generation. SOFCs, which are normally based on nickel-yttria stabilized zirconia (YSZ) anodes, undergo degradation with time due to their high operating temperatures and their susceptibility to damage due to anode oxidation (redox cycling) and poisoning. Ni infiltration into porous YSZ scaffolds is considered to be a promising approach for overcoming some of these problems and enhancing their redox tolerance. However, long-term instability of the morphology of these types of anodes is an important problem. The focus of this thesis was therefore to develop methods to form porous YSZ scaffolds and attempt to construct stable Ni-YSZ anodes with reasonable electrochemical performance by infiltration.
In this work, the issue of long-term instability was considered to originate from both the porous YSZ scaffold microstructure and the Ni infiltration precursor employed. To study this more closely, two different porous YSZ scaffold microstructures were developed by using tape casting, followed by Ni infiltration using a polymeric precursor, known to form a continuous Ni phase, rather than electrically separated Ni particles.
Ni infiltration into porous YSZ scaffolds with large grains (0.5 µm) and large pores (two types of pores: ~0.5 µm and 5 µm) resulted in extensive Ni particle growth that resulted in poor stability and poor electrochemical performance (0.5 Ω cm2 per electrode at 800 °C). Ni infiltration into a scaffold having finer grains and pores (~200 nm each) resulted in anodes with a much lower polarization resistance of 0.11 Ω cm2 per electrode at 800 °C, increasing by ~ 5 % after 108 hours at this temperature.