Performance of nickel/cerium oxide/yttria stabilized zirconia SOFC anodes with carbonaceous fuels

This study explores the impact of ceria incorporation into Ni/YSZ cermet anode support layers on the performance of button-cell solid oxide fuel cells operating with syngas and n-butane/steam fuel feeds. Ceria is incorporated into the porous anode support layer by co-firing ceria powders with NiO, YSZ, and graphite pore formers. Comparison of the performance with and without the co-fired ceria indicated improvements for operation with doped ceria for both syngas (by almost 20% higher power density) and direct n-butane/steam feeds (by over 25% higher power density). For initial cell performance, ceria addition to the support layer offered improved performance at high current densities with syngas suggesting that ceria may enhance water-gas-shift reactions and thereby increase H2 availability for more effective electrochemical oxidation in the anode functional layer. For longer-term testing with direct-butane feeds, ceria doped cells not only showed better performance, but also indicated suppression of carbon deposition, thus improving long term operability. Ex situ characterization of the ceria-doped anodes using SEM and Raman spectroscopy indicated that ceria addition helped the anodes maintain structural integrity.;To better understand experimental results, a previous through-the-MEA 1-D model has been updated and used with C-H-O microkinetics for Ni/YSZ anodes to characterize the experimentally observed cell performance. The model was enhanced to account for gas leakage through the electrolyte and to incorporate non-isothermal effects due to endothermic internal reforming and exothermic oxidation within the anode layers. Studies with internal methane reforming in a Ni/YSZ anode showed that the non-isothermal effects in 1-D button cell experiments are very small. This through-the-MEA model was used to fit experimental data and provided a basis for assessing key micro-structural parameters for the Ni/YSZ cells tested in this study. The model fits with syngas at various compositions provided a basis for assessing the most sensitive micro-structural parameters on the fuel cell performance such as anode support layer porosity and tortuosity.