The overpotential of nickel/yttria-stabilized zirconia cermet anodes used in solid oxide fuel cells

The overpotential of Ni/yttria-stabilized zirconia cermet anodes used in H- 2-H2O solid oxide fuel cells (SOFCs) was studied. We measured the current-d ensity dependence of the anodic overpotential at 850 degrees C operating te mperature using the inlet fuel,oases with compositions of 100% H-2, 80% H-2 + 20% H2O, and 20% H-2 + 80% Ar. It was found that the overpotential was l ower under wet-anode conditions than under dry conditions. We also showed t hat under wet-anode conditions the overpotential gradually increased with t he increase of the current density, whereas under dry anode conditions, the overpotential increased steeply with the increase of the current density u p to 20 mA/cm(2) and then showed a gradual increase with the current densit y. We related the overpotential of H-2-H2O SOFCs to the reaction rate const ants and to the operating conditions by using a reaction model and found th at the surface reaction model can successfully explain the experimental res ults. (C) 2000 The Electrochemical Society. S0013-4651(00)02-001-2. All rig hts reserved.