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Synthesis and Characterization of Oxyanion‐Doped Cobalt Containing Perovskites
Author(s) -
PorrasVazquez Jose M.,
Slater Peter R.
Publication year - 2012
Publication title -
fuel cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.485
H-Index - 69
eISSN - 1615-6854
pISSN - 1615-6846
DOI - 10.1002/fuce.201200081
Subject(s) - oxyanion , materials science , doping , conductivity , cobalt , oxide , analytical chemistry (journal) , inorganic chemistry , chemistry , metallurgy , catalysis , biochemistry , optoelectronics , chromatography
In this paper, we report the incorporation of borate, silicate and phosphate into La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3–δ (LSCF) and Sr 0.9 Y 0.1 CoO 3–δ (SYC) cathode materials for solid oxide fuel cells (SOFCs). In the former, an increase in the electronic conductivity was observed, which can be correlated with electron doping due to the oxyanion doping favoring the introduction of oxide ion vacancies. The highest conductivity was observed for La 0.6 Sr 0.4 Co 0.76 Fe 0.19 B 0.05 O 3–δ , 1190 S cm –1 at 700 °C, in comparison with 431 S cm –1 for undoped La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3–δ at the same temperature. For Sr 0.9 Y 0.1 CoO 3–δ series the conductivity suffers a decrease on doping, attributed to any effect of electron doping being outweighed by the effect of partial disruption of the electronic conduction pathways by the oxyanion. Composites of these cathode materials with 50% CGO10 were examined on dense CGO10 pellets and the area‐specific resistances (ASR) in symmetrical cells were determined. The ASR values, at 800 °C, were 0.20, 0.08 and 0.11 Ω cm 2 for La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3–δ , La 0.6 Sr 0.4 Co 0.76 Fe 0.19 B 0.05 O 3–δ and La 0.6 Sr 0.4 Co 0.78 Fe 0.195 Si 0.025 O 3–δ , respectively. For the SYC materials, the oxyanion‐doped compositions also showed an improvement in the ASR values with respect to the parent compounds, despite the lower electronic conductivity in these cases. This observation may be due to an increase in ionic conductivity due to oxyanion incorporation leading to the formation of oxide ion vacancies. In addition, the stability of these systems towards CO 2 was studied. For La 0.6 Sr 0.4 Co 0.8(1– x ) Fe 0.2(1– x ) M x O 3–δ series, all compositions showed no evidence for reactivity with CO 2 between RT and 1000 °C. On the other hand, for the Sr 0.9 Y 0.1 Co 1– x M x O 3–δ series, some reactivity was observed, although the CO 2 stability was shown to be improved on oxyanion doping. Thus, these results show that oxyanion doping can have a beneficial effect on the performance of perovskite cobaltite cathode materials.