Synthesis and characterisation of new materials for use in solid oxide fuel cells and electrolysers

James, Matthew Samuel (2024). Synthesis and characterisation of new materials for use in solid oxide fuel cells and electrolysers. University of Birmingham. Ph.D.

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Abstract

In this thesis, the work presented focuses on the development of anion doping strategies (Oxyanions and Halides) into a variety of different structures for potential use as cathodes within solid oxide fuel cells and electrolysers.
The thesis examines the use of phosphate doping of the mixed perovskite Mn/Fe system, Sr¬2-xCaxMnFeO6-δ, to design a novel low-cost cathode material. The work shows the successful incorporation of phosphate into these systems and show that conductivities are higher than the previously reported silicon doped variant.
The work on Ba1-xSrxFeO3-δ systems demonstrates the successful incorporation of borate and characterises the effect on the structure and conductivity with a view to possible utilise as a cathode material in a ceramic fuel cell (H+ or O2- conducting). The incorporation of low levels of borate was shown to be sufficient to cause a change in cell symmetry to give a cubic perovskite structure.
Lanthanum germanate apatite was studied to try to confirm which oxide ion conduction mechanisms are present within the La10Ge6O27 and La10-xYxGe6O27 (x = 0, 1 and 2) structures with literature proposing two possible mechanisms; through the channel and perpendicular to the channel. Despite blocking the centre channel in the apatite structure with borate, the observation of high oxide ion conductivity provided support for an alternative oxygen interstitial conduction method perpendicular to the channel was presented. The addition of borate into the structure also introduced larger amounts of interstitial oxide ions, therefore increasing the conductivity in some of these systems.

The first use of two types of biopolymer, Iota and Kappa Carrageenan, was demonstrated as both a gelation agent and a precursor material with a novel sol-gel synthesis for the manufacture of SrFe1-xSxO3-δ materials with comparable results to the standard high-temperature solid-state synthesis.
Finally, the successful synthesis of a range of K2NiF4 structured La doped Sr2CoO3F phases was demonstrated. Contrary to undoped Sr2CoO3F which required high pressure synthesis, La doping was shown to allow synthesis under ambient pressure. We also evaluated these materials for their potential applications as SOFC cathode/ FIB electrode materials via conductivity and thermal characterisation, with some showing high conductivities.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):