Development of SOFC Anodes for Internal Reforming of Methane

Abstract

Today the SOFC based power generation systems of Siemens Westinghouse operate on natural gas, which is converted to hydrogen by reformer units, thermally integrated into the SOFC stack. One possibility to reduce the still high costs of these systems is to avoid the reformer units by running the reforming reaction directly on the anodes of the cells. But the Ni-YSZ-cennet anodes applied in the past catalyze the endothermic reforming reaction to such an extent that the cell is undesirably cooled down towards the fuel entrance. This may cause cell failure by thermomechanical stress and in addition the electrochemically active cell area and hence the efficiency are decreased. Therefore new cermet structures have been successfully developed which show reduced reforming activity whilst keeping the fast kinetics for electrochemical hydrogen oxidation of conventional cermets. This was achieved in two steps: by decreasing the porosity of the cermets and by applying NiCr alloys instead of Ni to further decrease the free Ni surface by formation of a chromium oxide scale on the metal particles.