Fuel Composition and Diluent Effect on Gas Transport and Performance of Anode-Supported SOFCs

Anode-supported solid oxide fuel cells (SOFCs) with Ni+yttria-stabilized zirconia (YSZ) anode, YSZ-samaria-doped ceria (SDC) bilayer electrolyte, and Sr-doped (LSC)+SDC cathode were fabricated. Fuel used consisted of diluted with He, or mixtures of and CO, and mixtures of CO and Cell performance was measured at 800°C with the above-mentioned fuel gas mixtures and air as oxidant. For a given concentration of the diluent, cell performance was higher with He as the diluent than with as the diluent. Mass transport through porous Ni-YSZ anode for binary systems, and -diluent gas ternary systems was analyzed using multicomponent gas diffusion theory. At high concentrations of diluent, the maximum achievable current density was limited by the anodic concentration polarization. From this measured limiting current density, the corresponding effective gas diffusivity was estimated. Highest effective diffusivity was estimated for fuel gas mixtures containing mixtures (∼0.55 cm 2 /s), and the lowest for mixtures (∼0.07 cm 2 /s). The lowest performance was observed with mixture as a fuel, which in part was attributed to the lowest effective diffusivity of the fuels tested and higher activation polarization. © 2003 The Electrochemical Society. All rights reserved.