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Eric M. Stuve
Department of Chemical Engineering
University of Washington
Thursday, April 17, 2008
102 Chemistry Building
10:00 a.m. - 11:00 a.m.
Abstract
Solid oxide fuel cells (SOFC) provide an opportunity for fuel-flexible fuel cells that operate at higher efficiencies than other types of fuel cells.
These advantages arise from the high temperature of SOFC operation, 800-1000 0C, which facilitates direct oxidation and reforming of hydrocarbon fuels and a source of high quality waste heat.
Some of the issues faced in direct hydrocarbon oxidation are
To address these issues we have developed a SOFC mounted in a vacuum system with facilities for accurate control of fuel and oxygen partial pressures and measurement of reaction products by a calibrated mass spectrometer. The measurements highlight the interplay of fuel oxidation kinetics, carbon deposition on the anode, and transport of oxide ions through the electrolyte.
We have examined a wide range of fuels; H2, CH4, C2H4, CH3OH, C2H5OH, and C7H8; reacting at gadolinium-doped ceria (GDC), Pt/GDC, and CoO3/Pt/GDC anodes at temperatures of 800-1000 K and pressures of 5-50 Torr. The combined mass spectrometry and current measurements show some fascinating behaviors, including induction periods for electrocatalytic oxidation, spontaneous and forced oscillations, and coupled reforming with direct surface reaction. These effects are interpreted in terms of carbon formation on the anode and oxidation state and conductivity changes in the near surface layers of the electrolyte. The overall implication is that catalyst activity is a strong function of electrolyte structure, ionic flux, and adsorption kinetics of the fuel.