Author

Shiqiang Hui

Date of Award

12-2000

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science

Supervisor

Professor Anthony Petric

Abstract

A number of perovskite oxides, typically, heavily doped SrTiO₃ samples, were synthesized and characterized with a view to establishing their potential as anode materials for solid oxide fuel cells (SOFCs). The structure, microstructure, electrical conductivity, reduction-oxidation behavior, phase stability, compatibility with electrolytes, and performance in SOFC operation were assessed.

Ceramic samples were prepared with the formula (Sr₁ᵪRᵪ)(Ti₁_yTy)O₃ (R = rare earth elements, T = transition metals) and with charge balance achieved by A-site deficiency. Electrical conductivities were examined by the do four-probe method and impedance spectroscopy. It was found that yttrium is soluble in SrTiO₃ (SYT) up to 8 mol% and has marked effects on conductivity. Electrical conductivities were observed to increase with increasing donor-doping level, on reduction in low oxygen partial pressures. Electrical conductivity with values as high as 82 S/cm was achieved at 800°C and P(O₂) = 10ˉ¹⁹ atm. Electrical conductivities were reversible upon reduction and oxidation. The thermal expansion coefficient is compatible with electrolyte materials such as yttria-stabilized ZrO₂ and doped LaGaO₃. Cobalt-doped SYT, which showed a relatively high resistance to oxidation, was tested as the anode material in a fuel cell. Yttrium-doped SrTiO₃ meets the requirements for the anode in SOFCs to a substantial degree, and is a promising alternative anode material.