Operando optical studies of solid oxide fuel cells operating on CO and simulated syngas fuels

Abstract

Solid oxide fuel cells (SOFCs) are attractive devices for combined power and heat generation because they can operate with a variety of fuels. Syngas (CO + H2) is particularly attractive but many questions remain about its behavior on SOFC anodes including the relative oxidation efficiencies of CO and H2 and tendency to form carbon deposits. In this report, operando spectroelectrochemical measurements, including infrared emission spectroscopy, near infrared thermal imaging, and vibrational Raman scattering, combined with spectrochronopotentiometry, are performed using anode-supported SOFCs operating with simulated syngas at 800 °C. Results quantify the fate of syngas over Ni-YSZ anodes in SOFCs related to their performance. SOFCs operating with simulated syngas mixtures are compared with those for H2 and CO used separately. Thermal imaging shows more SOFC anode heating for H2-rich syngas than for operating on CO or H2 alone. We attribute this result to carbon gasification by water that is produced by H2 oxidation. Raman spectra together with spectrochronopotentiometry experiments illustrate that carbon is not observed on the anode surface at 800 °C – although it is at 750 °C and 700 °C – yet carbon is likely present in the spectroscopically inaccessible, electrochemically active region at the electrolyte-electrode interface.