Tailoring Perovskite- and Fluorite-Type Oxides for Solid Oxide Fuel Cells (SOFCs)
Abstract
A solid oxide fuel cell (SOFC) is a high temperature solid state energy conversion device that directly converts the chemical energy of fuels into electrical energy at high efficiency. The objective of thesis is to develop and tune fluorite- and perovskite-type metal oxides that serve as alternate anodes, electrolytes, and cathodes for intermediate temperature SOFCs. Here, the chemical reactivity between a fluorite-based Ce0.7RE0.2Mo0.1O2 (RE = Y, Sm) anode and 8 mol% yttria-stabilized zirconia electrolyte was evaluated at 1000 ºC. The electrical conductivity of the reaction product Ce1-x-y-zRExZrYMozO2 in air and wet H2 was found to be lower than that of Ce0.7RE0.2Mo0.1O2, due to the formation of defect associates and a decrease in concentration of charge carriers.
The effect of A-and B-site co-doping on the chemical and electrical properties of potential perovskite-type Ba0.5Sr0.5Ce1-x-y-zZrxGdyYzO3-δ (0 < x < 0.5; y = 0, 0.1, 0.15; z = 0.1, 0.2) proton conducting electrolyte was evaluated. Excellent chemical stability under water vapor for 24 h at 90 ºC was observed for all compositions. The electrical conductivity measurements under dry and humid atmospheres revealed the proton conductivity in these oxides. Among the samples investigated, Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ showed the highest proton conductivity of 10-3 S/cm at 600 ºC in humid air and H2. The effect of sintering temperature on the proton dynamics of Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ was evaluated by establishing a correlation between the grain boundary space charge effect, electrical conductivity, and dielectric loss of the samples sintered at 1300, 1400, and 1550 ºC. The proton dynamics in local motion and long-range motion appears to be different due to the difference seen in the relaxation time and activation energy of protons in local motion and bulk conduction properties.
Furthermore, the electrochemical performance of the layered perovskite-type Gd0.5Pr0.5BaCo2O5+δ and Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ composite cathode, and Ni and Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ composite anode for proton conducting SOFCs was evaluated through symmetrical cell studies. The symmetrical cell of Gd0.5Pr0.5BaCo2O5+δ-Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ composite cathode showed an area specific polarization resistance of 2.4 and 1.9 Ω.cm2 at 700 ºC for oxygen reduction reaction in the air and wet air, respectively, and exhibited an activation energy of 1.2 eV in both atmospheres.
Description
Keywords
Education--Physical, Education--Sciences, Anthropology--Physical, Energy
Citation
Singh, K. (2016). Tailoring Perovskite- and Fluorite-Type Oxides for Solid Oxide Fuel Cells (SOFCs) (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27971