Oxidation and steam deforming of CH4 on Ni and Fe anodes under low humidity conditions in solid oxide fuel cells

Oxidation and steam reforming of CH4 on Ni/YSZ and Fe/YSZ cermet anodes were examined, primarily under the condition of 0 less than or equal to H2O/CH4 less than or equal to 1. In the CH4 + H2O fuel system, steam reforming occurs on anodes, generating CO and H-2. The steam reforming activity of CH4 on Ni/YSZ was much higher than on Fe/YSZ at open circuit. The anodic polarization curves of an Ni/YSZ cermet electrode, both in dry CH4 and CH4 + H2O fuel systems, could be divided into two parts; one due to direct oxidation of C in the low overvoltage region, the other due to oxidation of H-2 and/or CO at higher overvoltages. On the other hand, the anodic polarization curves of an Fe/YSZ cermet electrode in CH4 fuel showed behavior different from that for Ni/YSZ in the dry CH4 or the CH4-H2O fuel systems. The polarization curve in the dry CH4 fuel system showed multiple reaction slopes, while that in the CH4-H2O fuel system showed only one slope. A thermochemical calculation was made to estimate the anode surface state and the equilibrium oxygen partial pressure between the anode/YSZ interface and the gas phase.