Ni Catalyst for Hydrogen Conversion in Gadolinia-Doped Ceria Anodes for Solid Oxide Fuel Cells

A gadolinia-doped ceria Ce 0.6 Gd 0.4 O 1.8 (CG4) is considered as anode material for solid oxide fuel cells with an yttria-stabilized zirconia electrolyte. Symmetrical cells are mounted in a novel setup geometry with auxiliary electrodes to avoid concentration polarization outside the electrode structure. The polarization resistance in H 2 /H 2 O mixtures is measured by impedance spectroscopy. Two rate-limiting processes are observed. The low frequency process is related to adsorption of hydrogen on the CG4 surface. This limiting process is effectively circumvented by the addition of small amounts of Ni. The high frequency process is related to oxygen ion transport in the CG4 electrode material, either in the bulk or in segregated surface layers. The pO 2 dependence of the electronic conductivity in CG4 is reflected in the series resistance.