Perovskite-type Cathode Material for Intermediate Temperature Solid Oxide Fuel Cells
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AbstractSolid oxide fuel cells (SOFCs) are an alternative energy device that transforms chemical energy to electrical energy without the conventional combustion step. SOFCs can do this with an efficiency of 60 - 80%. However, the temperature of operation (800 - 1000 oC) reduces the lifetime and puts sever restrictions on the material available for use. Ideally SOFCs would need to operate at a more intermediate temperature (IT) range between (500 – 750 oC) to maintain their fuel flexibility and have a reasonable lifetime to compete with conventional energy methods but, the reduction in temperature results in sluggish oxygen reduction reaction (ORR) activity for conventional SOFC cathodes. Due to the sluggish ORR of conventional cathodes, new materials are being introduced and studied to act as cathodes for SOFCs. The primary criteria for an SOFC cathode are the ability to act as a mixed ionic electronic conductor (MIEC), stability in an oxygen atmosphere, a porous microstructure, high catalytic activity towards the oxygen reduction reaction (ORR) and thermal cyclability. One material that has received attention is the perovskite-type structure because of its high tunability through doping while maintaining the same structure. The effect of Cu-substitution in Ba0.5Sr0.5Fe1-xCuxO3-δ (BSFCux, 0 ≤ x ≤ 0.20) on the phase, microstructure, cyclability and electrochemical performance was investigated using a series of methods to determine the feasibility of this material acting as a solid oxide fuel cell (SOFC) cathode. Powder X-ray diffraction showed the formation of a cubic perovskite (space group: Pm-3m, No. 221). This material has illustrated cyclable oxygen uptake and releasing properties that were studied using TGA. The microstructure was studied using SEM which showed a porous structure along with minor changes based on copper content. The symmetrical cells Ba0.5Sr0.5Fe1-xCuxO3-δ+LSGM|LSGM|Ba0.5Sr0.5Fe1-xCuxO3-δ+LSGM were tested for their electrochemical performance using EIS in ambient air. A trend of decreasing area specific resistance (ASR) with decreasing copper content was observed. 4-probe DC measurements were used to study the conductivity of Ba0.5Sr0.5Fe1-xCuxO3-δ in varying atmospheres. These measurements showed an increase in conductivity with increasing copper content and an increase in conductivity with an increasing pO2. The effect of sintering temperature (900-1100 °C) on the electrochemical performance and microstructure was studied for Ba0.5Sr0.5Fe0.95Cu0.05O3-δ+LSGM and Ba0.5Sr0.5Fe0.8Cu0.2O3-δ+LSGM. Plots of log ASR vs. pO2 were used to evaluate the rate determining steps in the oxygen reduction/oxygen evolution reactions (ORR/OER).
CitationAbubaker, O. A. (2020). Perovskite-type Cathode Material for Intermediate Temperature Solid Oxide Fuel Cells (Unpublished master's thesis). University of Calgary, Calgary, AB.
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