Numerical Study of Heterogeneous Reactions in an SOFC Anode With Oxygen Addition

Previous experimental studies have shown that addition of smallamounts of oxygen to a hydrocarbon fuel stream can controlcoking in the anode, while relatively large amounts of oxygenare present in the fuel stream in single-chamber SOFCs. Inorder to rationally design an anode for such use, it isimportant to understand the coupled catalytic oxidation /reforming chemistry and diffusion within the anode under SOFCoperating conditions. In this study, the heterogeneous catalyticreactions in the anode of an anode-supported SOFC running onmethane fuel with added oxygen are numerically investigated,using a model that accounts for catalytic chemistry, porousmedia transport, and electrochemistry at the anode/electrolyteinterface. Using an experimentally validated heterogeneousreaction mechanism for methane partial oxidation and reformingon nickel, we identify three distinct reaction zones atdifferent depths within the anode: a thin outer layer in whichoxygen is nearly fully consumed in oxidizing methane andhydrogen, followed by a reforming region, then a water-gas shiftregion deep within the anode. Based on these insights into thechemistry, the possibility of a composite anode with differentlayers of metal catalysts is also explored for the improvementof fuel cell performance.