Synthesis and characterization of novel Ge doped Sr1−yCayFeO3−δ SOFC cathode materials

In this paper we report the successful incorporation of germanium into Sr1−yCayFeO3−δ 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−δ 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−δ 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−δ system (0.24 and 0.06 Ω cm2 at 700 and 800 °C, respectively, for SrFe0.85Ge0.15O3−δ). Thus, the results show that germanium can be incorporated into Sr1−yCayFeO3−δ-based materials leading to materials with potential for use as cathode materials in solid oxide fuel cells (SOFC).