Operando Studies of Carbon Removal and Partial Oxidation in Solid Oxide Fuel Cells

Operando methods, including thermal imaging, infrared emission and Raman spectroscopy, are combined with simultaneous electrochemical measurements to characterize carbon removal and partial oxidation of methane on Ni/YSZ anodes of operating solid oxide fuel cells (SOFCs). Results for carbon removal indicate that the CO2 to CO product ratio is higher for removal by oxygen than with steam. Also, steam removes carbon faster than oxygen and leads to slower oxidation of Ni in the cermet anode. Temperature changes are observed and explained in terms of the stronger adsorption for oxygen than water on the Ni anode. Related carbon oxidation studies are described for partial methane oxidation in operating cells in which Raman spectra show that graphite accumulation is strongly suppressed even at low ratios of oxygen or steam to methane (1:10). Simultaneous impedance measurements indicate that much of the effect is due to reduced polarization resistance.