Stability of Ni Base Anode for Direct Hydrocarbon SOFCs

Direct feeding of several hydrocarbon fuels was carried out at 800 degrees C for a SOFC with scandia stabilized zirconia (ScSZ) electrolyte and nickel-ScSZ (Ni-ScSZ) cermet anode. Liquid hydrocarbons as n-dodecane (paraffin type C12H26) and low sulfur content kerosene were used and fed to the anode at steam/carbon ratio (S/C) of 2. Continuous operation was achieved for more than 120 h with n-dodecane without anode degradation. However, the Ni-ScSZ anode completely detached from the electrolyte when low sulfur kerosene was used as fuel. After operation with the kerosene, nickel particles grew more than 3 mu m in diameter although particle growth was about 1 mu m under the n-dodecane. The nickel sintering seems to be enhanced by aromatic hydrocarbons and/or sulfur compounds in the kerosene. From thermodynamic consideration, liquid NiS could form under SOFC operation conditions with 30 ppm of sulfur containing hydrocarbon fuels.