Structural and electrical characterization of the Co-doped Ca2Fe2O5 brownmillerite: Evaluation as SOFC -cathode materials. (27th April 2015)

• Record Type: Journal Article
• Authors: Cascos, V.; Martínez-Coronado, R.; Alonso, J.A.; Fernández-Díaz, M.T.
• Is Part Of: International journal of hydrogen energy. Volume 40:Number 15(2015)
• Page Start: 5456
• Page End: 5468
• Publication Date: 2015-04-27
• Subjects: Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2015.01.067
• Languages: English
• ISSNs: 0360-3199

Abstract

<abstract xml:lang="en" abstract-type="author" id="abs0010"> <title id="sectitle0010">Abstract</title> <sec> <p id="abspara0010">Brownmillerite-type oxides Ca<sub>2</sub>Fe<sub>2-x</sub>Co<sub>x</sub>O<sub>5-δ</sub> (x = 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4) have been explored as possible cathodes for solid oxide fuel cells (SOFC). The samples have been prepared, characterized and tested as cathode materials in single solid-oxide fuel cells. As shown in a neutron powder diffraction (NPD) study at RT, for x = 0 and 0.2 the compounds crystallized in a single phase with brownmillerite-type structure (s.g. <italic>Pcmn</italic>), whereas for x = 0.4, 0.6, 0.8, 1, 1.2, and 1.4 the samples crystallized in a supercell, two times the c-axis and the volume of that for a typical brownmillerite (s.g <italic>Pcmb</italic>). This superstructure consists of Fe1O<sub>4</sub> and Co1O<sub>4</sub> tetrahedral layers containing Fe1 and Co1 atoms, which alternate with (Fe, Co)2O<sub>6</sub> and (Fe, Co)3O<sub>6</sub> octahedral layers. In an "in situ" NPD experiment of Ca<sub>2</sub>Fe<sub>0.8</sub>Co<sub>1.2</sub>O<sub>5-δ</sub> at the working temperature of the SOFC, this compound shows the presence of a sufficiently high oxygen deficiency, with large displacement factors for oxygen atoms that suggest a large lability and mobility. In single test cells these cathode materials generated a maximum power of 412 mW/cm<sup>2</sup> at 850 °C with pure H<sub>2</sub> as a fuel. The electrodes were supported on a 300-mm-thick pellet of the electrolyte La<sub>0.8</sub>Sr<sub>0.2</sub>Ga<sub>0.83</sub>Mg<sub>0.17</sub>O<sub>3-δ</sub> (LSGM). The measured thermal expansion coefficients between 300 and 850 °C exhibit an excellent chemical compatibility with the electrolyte. The obtained compounds display a semiconductor-like behavior with conductivity values at the SOFCs working temperatures (650–850 °C) that are sufficient to yield a good performance in IT-SOFC.</p> </sec> </abstract>