Optimization Of Ceramic-glass Composite Seals For Planar Intermediate-temperature SOFC

Solid oxide fuel cell (SOFC) technology has many outstanding advantages including high efficiency, environment-friendly, high security and stability. Owing to its promising future in large-sized power station, distributed power supply system and military, many countries have been paying great attention to the SOFC technology. Though lots of difficulties have been overcome, the sealing problem has always been a technology barrier to hinder the spreading and application of that technology.This paper starts with the alumina-based sealing materials, which mingle with10-50wt%DT4glass powder, and then the tape-casting method is adopted to form the banding sealant. The influence of added glass powder content and forced pressure on the sealing property working at IT-SOFC operation temperature is analyzed. Then the microstructure is characterized by XRD pattern and SEM, respectively. The results show that better sealing properties, for example, lower leakage rate will be obtained as the increase of glass powder content and forced pressure. Furthermore, reaction sintering between glass and ceramics will appear when the content of glass powder is high enough, which helps to decrease the amount and size of the gas circulating channels and meanwhile increasing the tortuosity of channels, and by which means the sealing properties are improved. The leakage rate will drop with the increasing content of glass when the content of DT4achieves higher than30%, however, the thermal cycle properties of sealing materials will be affected as the possible creaking when cooling down to room temperature. So the composite of alumina and HGS glass (a kind of glass with more excellent performance which was developed by our laboratory) is researched.Glass-ceramic composite seals are fabricated by tape casting with AI2O3and20-60wt%HGS glass powers, and their sealing effectiveness and applicability in planar intermediate temperature solid oxide fuel cells are evaluated. The leakage rates are measured at the inlet pressure of3.5,7,10.5,14,17.5, and21kPa under different compressive stresses and temperatures respectively. The results reveal that the sealing performance and the deformation ability are better and better along with the increase of the content of glass. In the meantime, the leakage rate decreases with higher compressive stress and test temperature. The seal containing50wt%glass (AG50) shows the best sealing performance among the studied compositions. The initial leakage rate is below0.01sccem·cm-1under an inlet pressure of21kPa and the leakage rate during25thermal cycles are below0.02sccm·cm-1under the inlet gas pressure of10.5kPa. This seal and adjacent components have good compatibility, contributing to avoiding leakage from the interface. When the seal is applied for single cell testing, the open circuit voltage of1.18V and barely detectable degradation after6thermal cycles clearly demonstrate the applicability of glass-ceramic compressive seals in the planar intermediate temperature SOFCs.