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Title:	Structural and electrical properties of doped ceria based electrolyte materials for solid oxide fuel cells
Authors:	Mustafa Anwar (P77802)
Supervisor:	Andanastuti Muchtar, Prof. Dr.
Keywords:	Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia Solid oxide fuel cells Electrolytes
Issue Date:	8-Apr-2019
Description:	Doped ceria-based materials exhibit higher ionic conductivity than traditional yttria stabilized zirconia electrolyte, especially at lower operating temperatures (600-800 °C). However, the microstructure and ionic conductivity of these electrolytes can further be enhanced by two main approaches. First is the addition of another aliovalent cation in doped ceria, i.e., co-doping and second is the addition of some alkali carbonates in doped ceria, i.e., composite electrolytes. Therefore, the main aim of this work is to elucidate the effects of various co-dopants and carbonates on the structural and electrical properties of doped ceria electrolytes. Samarium-barium (Ce0.8Sm0.1Ba0.1O2-δ), erbium-strontium (Ce0.8Er0.2-xSrxO2-δ; x = 0, 0.025, 0.05, 0.075) and erbium-samarium (Ce0.8Er0.2-xSmxO2-δ; x = 0, 0.05, 0.1, 0.15, 0.20) codoped ceria electrolytes were synthesized by citric acid-nitrate combustion method. Co-doped ceria electrolyte powders were calcined to achieve the desired phase and the electrolyte pellets were sintered at high temperatures (> 1200 °C) for densification. In addition, doped ceria-based composite electrolytes were also synthesized by a two-step process. Initially, erbium-doped ceria (Ce0.85Er0.15O2-δ), lanthanum-doped ceria (Ce0.85La0.15O2-δ) and strontium-doped ceria (Ce0.95Sr0.05O2-δ) were synthesized by citric-acid nitrate combustion method. In the second step, the eutectic salt of ternary carbonate (LiNaK)2CO3 was prepared by solid-state mixing method. The composite electrolytes were prepared by the mechanical mixing of doped ceria electrolytes and ternary carbonate in the weight ratio of 4:1 followed by sintering at 680 °C. X-ray diffraction analysis, thermal gravimetric analysis, field emission scanning electron microscopy, transmission electron microscopy, UV-VIS spectrophotometry, and electrochemical impedance spectroscopy techniques were employed to analyse the prepared powders and pellets. The results revealed the cubic fluorite crystal structure of CeO2 for all the electrolytes. However, SrCeO3 impurity phase was formed for Ce0.8Er0.125Sr0.075O2-δ electrolyte due to the solubility limit of Sr2+ in ceria. Furthermore, the peak shifting was observed in X-ray diffractograms due to the addition of co-dopants and carbonates which indicated the change in lattice parameter. Microstructure analysis showed that the erbium-doped ceria-based co-doped ceria electrolytes exhibited higher sintered densities (89-98% of the theoretical densities) than that of singly-doped ones. Impedance analysis exhibited that the ionic conductivity of all the electrolytes increased with the increase in temperature. Furthermore, co-doped ceria electrolytes exhibited low ionic conductivity than that of singly-doped ones. The singly-doped Ce0.8Sm0.2O2-δ electrolyte exhibited the highest ionic conductivity of 0.0131 S cm-1 at 600 °C among all other co-doped electrolytes. However, the oxide ion conductivity of doped ceria electrolytes was increased by the addition of carbonates. Lanthanum-doped ceriabased composite electrolyte exhibited highest total ionic conductivity of 0.075 Scm-1 at 650 °C in air. In conclusion, this study proved that the choice of co-dopants and carbonates play a significant role in enhancing the structural and electrical performance of doped ceria electrolytes and not every co-dopant can increase the conductivity of ceria-based electrolytes.,Ph.D.
Pages:	149
Call Number:	TK2933.S65M857 2019 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Fuel Cell Institute / Institut Sel Fuel

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