High Throughput Screening of Materials for Solid Oxide Fuel Cells
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High Throughput Screening of Materials for Solid Oxide Fuel Cells John P. Lemmon, Venkatesan Manivannan, Tracey Jordan, Lamyaa Hassib, Oltea Siclovan, Michelle Othon, and Mile Pilliod General Electric Global Research, Niskayuna, Schenectady, NY 12309, USA. ABSTRACT State of the art commercial cathodes for solid oxide fuel cells (SOFC) include LaMnO3 with a zirconia-based electrolyte. However, the vacancy concentration in A site doped LaMnO3 is low, thus ionic conductivity is also very low (10-7 – 10-8 S/cm at 800 ºC). The surface path dominates the reaction rate of the LaMnO3 cathode; therefore the optimized electrode is a porous composite material of both the cathode material and electrolyte and relies on triple-point boundaries for performance. The electrical conductivity and thermal expansion properties of this cathode material and other A3+B3+O3 perovskites can be tuned by substitution at the A and/or B site. The numerous combinations of composition, processing and microstructure needed for improved cathode performance is well suited for a high throughput screening (HTS) approach towards optimization and discovery. We present here a high throughput discovery process that includes, synthesis, performance testing and characterization techniques directed towards new low temperature SOFC cathode materials. INTRODUCTION Fuel cells are considered to be a potential future energy system expected to substitute existing energy conversion system which use fossil fuels. In this respect, (SOFCs) have attracted great attention due to the high-energy conversion efficiency and low or zero emission of air pollutants such as NOx. Significant gains in efficiency can be achieved when combining a SOFC stack with a conventional gas or steam turbine as shown in Figure 1. Steam Turbine
Combined Cycle
Micro- Fuel turbine Cell
Hybrid
Fuel cell mitigates combustion irreversibility and provides additional output Fuel
Efficiency
Advance Bottomin
80%
Stack
60%
Residual Exhaust Burner
Air
Compressor
Turbine
40%
Residual energy from stack recovered in GT
20% 0% Steam Turbine
Combined Cycle
Micro- Fuel turbine Cell
Hybrid
Figure 1 Fuel cells as viable source of "green energy" power generation.
A SOFC is an electrochemical device that converts chemical energy to electricity. They differ from other fuel cell technologies by their high operating temperature (1000 ºC) and efficiency (50-60%). The high operating temperature creates several issues for materials of construction such as oxidation, thermal expansion differences, and sealing. To reduce degradation and cost, lowering the operating temperature (700 – 800 ºC) while maintaining performance is one of the main goals of SOFC research today [1]. The performance of a fuel cell is dependent on several
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factors such as diffusion, mass transfer, and electronic, ionic, and catalytic properties. The focus of this paper will be on improving cathode performance, where the half reaction of the cell can be described as ½O2 +2e- O2-. There are several performance
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