Novel oxide materials for solid oxide fuel cells applications

Simo, Frantisek
Novel oxide materials for solid oxide fuel cells applications. PhD thesis, University of Liverpool.

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The work of this thesis focuses on three perovskite-based compounds: YSr2Cu3−xCoxO7+δ cuprates, Gd2BaCo2O5+δ related phases and Sr2SnO4 Ruddlesden-Popper structures. Both YSr2Cu3−xCoxO7+δ and Gd2BaCo2O5+δ are cathode material candidates for solid oxide fuel cells (SOFCs). Doping of Sr2SnO4 aims to enhance the ionic conductivity of the parent phase and explore the phases as a potential SOFCs electrolyte material. The cobalt content in the layered perovskite YSr2Cu3−xCoxO7+δ has been increased to a maximum of x = 1.3. A slight excess of strontium was required for phase purity in these phases, yielding the composition Y1−ySr2+yCu3−xCoxO7+δ (where y = 0.03 and 0.05). The potential of Y1−ySr2+yCu3−xCoxO7+δ (where x = 1 to 1.3) as a cathode material for a solid oxide fuel cell has been explored through optimisation of processing parameters, AC impedance spectroscopy and DC conductivity measurements. The stability of Y0.95Sr2.05Cu1.7Co1.3O7+δ with commercial electrolytes has been tested along with the stability under CO2. This material exhibits a significant improvement in properties compared to the parent member, Y0.97Sr2.03Cu2CoO7+δ, and is compatible with commercially available doped ceria electrolytes at 900 °C. Energetics of Ln2BaCo2O7 (Ln = Gd, Nd, Ce) materials consisting of a layer of LnBaCo2O5+δ (Ln = Gd, Nd) and a fluorite layer (CeO2 or Ln2O3, Ln = Gd, Nd) have been studied using DFT calculations. Various reactions including binary oxides and double perovskites were taken into an account for the formation energy calculations. Phases favourable in DFT calculations were observed also in PXRD patterns of the materials prepared by a solid state synthesis. DFT prediction has been also used in the work with Ruddlesden-Popper phases. The structures of experimentally prepared Nb- and Ta-doped Sr2SnO4 phases were investigated using high resolution diffraction methods. The conductivity of single phased materials was studied by AC impedance spectroscopy. A significant improvement in conductivity was observed in Sr2Sn1−xTaxO4 compounds with x = 0.03 and 0.04. The origin of the enhancement has been studied using different techniques such as solid state Sn-NMR, UV-vis and NIR spectroscopy methods and it tends to be explained by an ionic contribution.

Item Type: Thesis (PhD)
Additional Information: Date: 2014-08 (completed)
Subjects: ?? QD ??
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 28 Jan 2016 09:38
Last Modified: 17 Dec 2022 01:37
DOI: 10.17638/00019353