Assessment of full ceramic solid oxide fuel cells based on modified strontium titanates

Todays’ solid oxide fuels cells based on composite Ni-cermet anodes have been developed up to reasonable levels of performance and durability. However, especially for small combined heat and power supply systems, known failure mechanisms e.g. re-oxidation, sulfur tolerance and coking have stimulated the development for full ceramic anodes based on strontium titanates. Furthermore, the Ni-cermet is primarily a hydrogen oxidation electrode and efficiency losses might occur when operating on carbon containing fuels.
In the European project SCOTAS-SOFC full ceramic cells comprising CGO/Ni infiltrated SrTiO3 anodes, and LSM/YSZ cathodes have been developed and tested as single 5 x 5 cm2 cells and up 100 cm2 circular cells. The initial performance exceeded 0.4 W/cm2 at 850 °C and redox tolerance has been proven. The cell concept provides flexibility with respect to the used electro-catalysts and various infiltrated metals including Ni and Ru have been studied. Stable power output has been observed for Ru and Ni-CGO as infiltrate. While redox tolerance is maintained, both types of cells degrade rapidly under exposure to sulfur. An initial assembly of a 60 cell stack in a one kW Hexis Galileo system indicates the necessity for further stack design adaptation in order to account for the lower electronic conductivity compared to Ni-cermet based cells.