Katalytische und elektrochemische Eigenschaften von eisen- und kobalthaltigen Perowskiten als Kathoden für die oxidkeramische Brennstoffzelle (SOFC)

Mai, Andreas

Dissertation / PhD Thesis/Book

Katalytische und elektrochemische Eigenschaften von eisen- und kobalthaltigen Perowskiten als Kathoden für die oxidkeramische Brennstoffzelle (SOFC)

Mai, A. (Corresponding Author)FZJ*

2004
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 3-89336-356-4

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Energietechnik/Energy Technology 31, 100 S. (2004) = Universität Bochum, Diss., 2004

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Please use a persistent id in citations: http://hdl.handle.net/2128/300

Abstract: Solid oxide fuel cells (SOFCs) are highly efficient electrochemical energy converters. The main current issues in SOFC development are lowering the costs and increasing long-term stability. New cathode materials are therefore needed to increase power densities particularly at reduced temperatures. The aim of this work was to characterise iron- and cobalt-containing perovskites and to evaluate the applicability of these materials as SOFC cathodes in comparison to state-of-theart manganese-based perovskites. The main focus was on the characterisation of the catalytic activity for oxygen adsorption of the materials and on the determination of their electrochemical properties. The examination of the oxygen adsorption properties was not only carried out by the established method of temperature-programmed reduction (TPR), but for the first time also by temperature-programmed oxidation (TPO) of previously partially reduced perovskites. It was found that especially TPO is suitable to determine the concentration of oxygen defects in the perovskites, these defects being associated with the materials' electrochemical properties. By analysing the measured TPO data, the activation energy for oxygen adsorption could be determined. In comparison to other experimental methods, the preparative and instrumental effort is less extensive, because the materials can be used in powder form. The electrochemical properties of the materials were investigated on planar anode-supported SOFCs. The sintering temperatures of the cathodes were adapted for each of the materials to obtain similar microstructures. In comparison to the SOFCs with state-of-the-art manganesebased cathodes, SOFCs with La$_{1-x}$,Sr$_{x}$Co$_{1-y}$Fe$_{y}$O$_{3-\delta}$ cathodes achieved much higher current densities. A small A-site substoichiometry and a high strontium content had a particularly positive effect on cell performance. The measured current densities of cells with these cathodes were as high as 1.76 A/cm$^{2}$ at 800 °C and 0.7 V, which is about twice the current density of cells with LSM/YSZ cathodes. At temperatures of 700 °C and below, cells with the new cathodes achieved current densities that were nearly three times as high as for the LSM/YSZ cells. The achieved power density of 1.0 W/cm$^{2}$ at 750 °C is an outstanding value in comparison to other working groups. Endurance tests of SOFCs with La$_{0.58}$Sr$_{0.4}$Co$_{0.2}$Fe$_{0.8}$O$_{3-\delta}$ cathodes have shown that it is possible to operate the cells for more than 5000 h.

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