Synthesis and characterization of novel Ge doped Sr1yCayFeO3 SOFC cathode materials

In this paper we report the successful incorporation of germanium into Sr1 yCayFeO3 d perovskite materials for potential applications as electrode materials for solid oxide fuel cells. It was observed that Ge doping leads to a change from a tetragonal cell (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). Annealing experiments in 5%H2/95%N2 (up to 800 C) also showed the stabilization of the cubic form in reducing conditions for the 15 mol% Ge-doped SrFeO3 d sample, in contrast to the undoped systems which showed a transition to an oxygen vacancy ordered brownmillerite-type phase. In order to examine the potential of these systems as SOFC cathodes, composite electrodes comprising 50% Ce0.9Gd0.1O1.95 and 50% Sr1 yCay(Fe/Ge)O3 d on dense Ce0.9Gd0.1O1.95 pellets were examined in air. The results showed an improvement in the area specific resistances (ASR) values for the Ge-doped samples with respect to the undoped ones, with the best performance for the Ge doped SrFeO3 d system (0.24 and 0.06 V cm at 700 and 800 C, respectively, for SrFe0.85Ge0.15O3 d). Thus, the results show that germanium can be incorporated into Sr1 yCayFeO3 dbased materials leading to materials with potential for use as cathode materials in solid oxide fuel cells