Investigation of Reaction Mechanism on Ni/YSZ Anodes and Pt/YSZ Anodes in Solid Oxide Fuel Cells with H_2and Dry CH_4

摘要

We investigated the reaction mechanism on the Ni/YSZ cermet anodes and the Pt/YSZ cermet anodes in H_2 fuel and dry CH_4 fuel. We propose a competitive adsorption reaction mechanism on the anodes of Ni/YSZ cermets in H_2-H_2O solid oxide fuel cells. With assuming competitive adsorption equilibrium of H_2, H_2O, and O on Ni surfaces at the three-phase boundary, the current density can be expressed as a function of the partial pressures of H_2 and H_2O and of the activity of O calculated from the anode potential. Our model successfully reproduces many observed characteristics of anodes. In dry CH_4 fuel, the current density was almost proportional to the activity of oxygen on the Ni/YSZ anodes at 800°C and on the Pt/YSZ anodes at 755°C. However, the reaction orders decreased with increasing operating temperature. The reactions on both the Ni/YSZ anodes and the Pt/YSZ anodes in dry CH_4 were also clarified.