Abstract
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 15mol% 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 0.06Ωcm2 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).
Highlights
Perovskite transition metal oxides have attracted considerable interest due to potential applications as cathode materials in the field of solid oxide fuel cells (SOFCs) [1,2,3,4,5]
In this paper we report the successful incorporation of germanium into Sr1ÀyCayFeO3Àd perovskite materials for potential applications as electrode materials for solid oxide fuel cells
In order to examine the potential of these systems as SOFC cathodes, composite electrodes comprising 50% Ce0.9Gd0.1O1.95 and 50% Sr1ÀyCay(Fe/Ge)O3Àd on dense Ce0.9Gd0.1O1.95 pellets were examined in air
Summary
Perovskite transition metal oxides have attracted considerable interest due to potential applications as cathode materials in the field of solid oxide fuel cells (SOFCs) [1,2,3,4,5]. An interesting aspect of the perovskite structure is the ability to accommodate a wide range of dopant sizes, and an unusual consequence of this has been prior observations on the successful incorporation of oxyanions into perovskite-type cuprate superconductors and related phases [6,7,8,9,10,11,12,13,14] Such studies demonstrated that the perovskite structure could incorporate significant levels of oxyanions (carbonate, borate, nitrate, sulfate, phosphate), with the C, B, N, P, S of the oxyanion group residing on the perovskite B cation site, while the oxide ions of this group fill 3 (C, B, N) – 4 (P, S) of the available 6 oxide ion positions around this site, albeit displaced so as to achieve the required geometry for the oxyanion. We have investigated whether Ge can be accommodated into these systems, and the consequent effect on the oxygen vacancy ordering and electrode performance
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