Performance and Enhancement of Solid Oxide Fuel Cell Electrodes Via Surface Modification

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2020

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Abstract

Solid oxide fuel cells (SOFCs) electrochemically convert chemical fuels to usable electricity with high efficiency and can operate on any oxidizable fuel. SOFCs fuel flexibility is accompanied by clean conversion by only converting the fuel to H2O and CO2 without the production of NOx. Additionally, the design of the device allows for a facile integration of carbon capture because the exhaust from the anode and cathode are already separated, allowing for a separated CO2 stream for carbon capture. Technical limitations have prohibited the commercial deployment of SOFCs at an impactful scale and the SOFC market is currently worth <$1 billion. The high operating temperature (T>800 °C) of SOFCs limits possible applications due to high degradation rates within cell components and a high balance of plant costs to use the requisitespecialized high temperature materials. The primary limitation to using to a lower temperature SOFC is the sluggish kinetics of the air electrode or cathode oxygen reduction reaction (ORR) at lower temperatures. This work increases the activity and durability of SOFC electrodes at lower temperatures by utilizing a facile, effective, low cost surface modification technique, defect engineering, and universal cathode scaffold design. Surface modification of SOFC cathodes also prevents the deactivation of the SOFC cathode typically caused by contaminant gasses like CO2 in Sr0.5Sm0.5CoO3-δ (SSC) cathodes. The surface modification technique also shows breakthroughs in the activity of SOFC cathodes SSC and La1-xSrxCo1-yFeyO3-δ (LSCF), allowing the SOFC to operate below 600 °C. The use of an engineered porous functional layer is shown to reduce the electronic leakage current in ceria-based electrolytes. This type of functional layer also increases the overall performance and durability of a SOFC at lower temperatures. Additionally, an approach was developed to deposit any desired cathode electrocatalyst on a universal scaffold to enable low-temperature operation and is compatible with existing cell components. 1 W/cm2 at 550 °C is achieved by utilizing the scaffold infiltration approach and demonstrates that high performance operations at low temperatures is achievable. Finally, the fuel flexibility of metal-supported solid oxide fuel cells (MS-SOFCs) was demonstrated to highlight their potential applications for carbon neutral transportation.

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