Electrochemical behaviour of tungsten carbide-based materials as candidate anodes for solid oxide fuel cells

Tungsten carbide-based electrodes under mixed hydrogen–methane and methane fuels have been investigated as potential anode materials for solid oxide fuel cell (SOFC) application. Firstly, it was shown that hydrogen is not a suitable fuel for the carbide-based materials. A conventional WC–YSZ composite and a carbide infiltrated porous YSZ support were then studied. Ac impedance spectroscopy revealed that the ohmic resistance and the charge-transfer polarization of these cells were reasonably low. The chemical reaction polarization, however, was relatively large, particularly under methane fuel. The carbide-based electrodes were then modified by incorporation of ceria and/or ruthenium. Not only did the co-existence of CeO2 and Ru synergically enhance the cell performance, more importantly it also greatly improved the stability of the polarized cell. Although bulk phase analysis confirmed the presence of a minor amount of tungsten oxide, surface analysis showed that the oxide phase remained superficial. It was then proposed that surface oxidation of the carbide phase was essentially a part of the fuel oxidation process and, as long as the rate of carbide oxidation and that of oxide recarburization remained comparable, the cell performance was stable.