Investigation into the effect of Si doping on the performance of SrFeO3−δ SOFC electrode materials

Abstract

In this paper we report the successful incorporation of silicon into SrFeO 3Àd perovskite materials for potential applications as electrode materials for solid oxide fuel cells. It is observed that Si 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% H 2 /95% N 2 (up to 800 C) also showed the stabilization of the cubic form for the Si-doped samples under reducing conditions, suggesting that they may be suitable for both cathode and anode applications. In contrast to the cubic cell of the reduced Si doped system, reduction of undoped SrFeO 3Àd leads to the formation of a brownmillerite structure with ordered oxide ion vacancies. SrFe 0.90 Si 0.10 O 3Àd and SrFe 0.85 Si 0.15 O 3Àd were analysed by neutron powder diffraction, and the data confirmed the cubic cell, with no long range oxygen vacancy ordering. Mössbauer spectroscopy data were also recorded for SrFe 0.90 Si 0.10 O 3Àd , and indicated the presence of only Fe 3+ and Fe 5+ (i.e. disproportionation of Fe 4+ to Fe 3+ and Fe 5+) for such doped samples. Conductivity measurements showed an improvement in the conductivity on Si doping. Composite electrodes with 50% Ce 0.9 Gd 0.1 O 1.95 were therefore examined on dense Ce 0.9 Gd 0.1 O 1.95 pellets in two different atmospheres: air and 5% H 2 /95% N 2. In both atmospheres an improvement in the area specific resistance (ASR) values is observed for the Si-doped samples. Thus the results show that silicon can be incorporated into SrFeO 3Àd-based materials and can have a beneficial effect on the performance, making them potentially suitable for use as cathode and anode materials in symmetrical SOFCs.

Structural features and high-temperature properties of SrFe1−Si O3−

“…Therefore, one can conclude that the maximum solubility of silicon in 25. This is larger than x m = 0.15 in work [20]. However, the observed difference can be explained as a consequence of the higher synthesis temperature used in the present study.…”

“…6. The results obtained by authors [20] in air at 800°С are also shown for comparison. One can see a good correspondence of the data.…”

“…15 13 ± 1 18 ± 2 0. 20 12 ± 2 16 ± 1 0. 25 10 ± 2 14 ± 1 of silicon content may signal changes in the amount of oxygen ions and vacancies involved in the transport process.…”

“…Another approach was proposed recently for modification of SrFeO 3 − δ based materials and stabilization of the cubic structure through incorporation of silicate oxyanions (SiO 4 ) 4 − [20,21]. The obtained materials showed improved conductivity and decreased area specific resistance.…”

Progress and Prospects in Symmetrical Solid Oxide Fuel Cells with Two Identical Electrodes

“…[ 115 ] The cubic structure of SrFeO 3-δ was stabilized effectively by doping Si into the B-site of the oxide under a reducing atmosphere, making it a potentially useful anode material. [ 115 ] The cubic structure of SrFeO 3-δ was stabilized effectively by doping Si into the B-site of the oxide under a reducing atmosphere, making it a potentially useful anode material.…”