Solid oxide fuel cells fueled by carbonaceous fuels: A thermodynamics-based approach for safe operation and experimental validation

Solid Oxide Fuel Cells (SOFCs) can operate with carbonaceous fuels. However, experiments indicate possible carbon deposition or coking on Ni-based anodes. Thermodynamic equilibrium calculations with NASA computer program CEA (Chemical Equilibrium with Applications) for typical SOFC operating temperatures predict graphitic carbon (C(gr)) formation. While fuel humidification eliminates coking, excess steam degrades Ni-based anode, necessitating suitable steam supply for safe operation. Thermodynamic approach is validated using experiments on 25 mm diameter electrolyte-supported NextCell-HP SOFC button cell fueled by H-2 and simulated syngas (CO and H-2). The use of 1 SLPM H-2 (fuel) with 4 SLPM air (oxidant) provides peak power density of similar to 1000 mW cm(-2). With simulated syngas fuel, cell performance drops. In-situ diagnosis with steam supply to anode suggests carbon deposition based on detection of H-2 and CO in tail gas. Equilibrium analysis suggests carbon-free operation by humidifying simulated syngas (CO:H-2 = 1:3 molar ratio) with similar to 5% steam by volume, at 973 K and above. Further experiments are conducted on a fresh cell. Simulated syngas (CO:H-2 = 1:3 volumetric ratio) with similar to 5% steam by volume provides safe cell operation. The study provides a pathway to safely utilize carbonaceous fuels in SOFC by suitable humidification, coupling thermodynamic analyses and experiments.

Automated summary

Solid Oxide Fuel Cells (SOFCs) can operate with carbonaceous fuels, but require suitable steam supply to prevent coking and ensure safe operation. This study validates a thermodynamic approach through experiments on electrolyte-supported SOFCs fueled by H2 and simulated syngas, providing insights on how to safely utilize carbonaceous fuels in SOFCs.