dc.description.abstract | Generation of energy and supply to meet the ever-increasing demand without
damaging the environmental have contributed to research motivation of fuel
cells. This research is an effort in searching for efficient and environmentally
friendly alternative energy sources to replace burning of fossil fuels; which has
adverse implications in human health and climate change.
The current technology of solid electrolytes used in fuel cells allows operation
at lower temperature, < 200 0C, and temperatures > 700 0C. The former
requires expensive platinum catalysts and the latter needs considerable thermal
insulation and longer start-up times. The present challenge is therefore to
identify and synthesize electrolytes, which can efficiently operate at
intermediate temperatures. Proton conductors composed of perovskite oxides
doped with trivalent cations such as yttrium, have shown promising
conductivity results in this region. However, the effect of doping levels as well
as macro and micro-structural influences on proton mobility is not fully
understood.
The aim of this study was to use solgel and solid state reaction processes to
synthesize alkaline-earths zirconates doped with yttrium at varying percentage
levels. It involved characterization of their phase purity, crystal structures,
lattice parameters and proton conductivity at different to doping levels. The
synthesised samples were analysed using powder X-ray diffraction, electron
microscopy and impedance spectroscopy. In addition, complementary
techniques such as thermal gravimetric analysis and scanning electron
microscopy were to be used.
Synthesis of yttrium doped barium zirconate series, BaZr1-xYxO3-ı (BZYO),
was possible by use of modified Pechini process up to 50 % doping level (x =
0.5). However, synthesis of yttrium doped strontium and calcium zirconates
above 5 % doping level was not possible. Density of the sintered BZYO pellets
was 60 % to 74 % of the theoretical density. Rietveld analysis of BZYO was
used to prove unit cell expansion with increase in yttrium doping level thus
confirming that yttrium was being incorporated into the BZYO structure. The
cell parameter of the 20 % Y doped sample however showed an unexpected
contraction. | en |