New electrolyte materials for solid oxide fuel cells

Shin, J. Felix (2012). New electrolyte materials for solid oxide fuel cells. University of Birmingham. Ph.D.

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Abstract

Two general systems, brownmillerite-type Ba\(_2\)In\(_2\)O\(_5\) and apatite-type silicates have been investigated for potential solid oxide fuel cell electrolyte applications. The combination of powder diffraction, NMR, TGA, Raman and AC impedance spectroscopy indicated the successful incorporation of phosphate, sulphate and silicate into the Ba\(_2\)In\(_2\)O\(_5\) structure leading to a transition from an ordered brownmillerite-type structure to a disordered perovskite-type, which led to the conductivity enhancement below 800 °C, along with a significant protonic contribution in wet atmospheres. The CO\(_2\) stability was also shown to be improved on doping. This oxyanion doping strategy has been extended to the analogous system, Ba\(_2\)Sc\(_2\)O\(_5\), which resulted in samples with high conductivity and good stability towards CO\(_2\).
Neutron diffraction studies on La\(_9\)\(_.\)\(_6\)Si\(_6\)O\(_2\)\(_6\)\(_.\)\(_4\) indicated that the interstitial oxide ion is located near the channel centre. Further interstitial anions could be accommodated through hydration, which led to displacement of the interstitial site away from the channel centre, with an accompanying swelling of the channel. Although long term annealing of these apatite silicates showed no apparent significant structural change, a reduction in the bulk conductivity was observed, while the grain boundary conductivity was improved, thus resulting in a small enhancement in the total conductivity below 400 °C.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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