Materials development for advanced planar solid oxide fuel cells

High-power density and high durability are the main targets for solid oxide fuel cell (SOFC) development at Forschungszentrum Julich. Power density has been further increased by variation of the material composition of perovskite-based cathodes (Sr content, Co content, substoichiometry) and by optimization of the diffusion barrier (Gd-substituted ceria) between an electrolyte and a cathode. The application of dense diffusion barrier layers significantly improved the performance. The associated avoidance of SrZrO3 formation, however, contributed only to a small extent to the improvement of durability of SOFCs with LSCF cathodes. The redox stability of anode-supported SOFCs has been addressed in two ways: (a) conventional Ni/yttria-stabilized zirconia anode substrates have been investigated to explore the limits of re-oxidation and to determine the degree of oxidation at which no damages occur. (b) Alternative anodes and anode substrates are under development, which basically consist of mixed-conducting ceramics. Avoiding the high amount of nickel decreases the probability of failure, but does not automatically lead to redox-stable anodes. The differences in the materials' properties of such ceramics in oxidizing and reducing environment are addressed.