Catalytic behavior of Pd-Ni/composite anode for direct oxidation of methane in SOFCs

Electrocatalysis of a Pd-Ni/composite anode (small amounts of Pd-Ni catalyst on a lanthanum chromite-based porous composite anode) for direct oxidation of dry methane in solid oxide fuel cells (SOFCs) was studied at 1073-1173 K. Synergy of Pd and Ni catalysts was observed for the direct oxidation of dry methane. Maximum power densities with the Pd-Ni/composite anode were 150 and 420 mW cm(-2) at 1073 and 1173 K, respectively. Carbon deposition on the Pd-Ni/composite anode was quite low under both open- and closed-circuit conditions. Therefore, stable power generation was performed under the closed-circuit condition, and no physical damage was observed for the cell under the open- circuit condition with dry methane. XRD analysis suggested the formation of Pd-Ni alloy on the composite anode. A suitable reaction scheme for the direct oxidation of dry methane over the Pd-Ni/composite anode was proposed on the basis of the kinetic experiment, the gasification experiment of the deposited carbon by steam, and impedance spectra. The decomposition of CH4 to H-2 and C, and the gasification of C by H2O to H-2 and CO, are key reactions for the effective direct oxidation of dry CH4 over the Pd-Ni/composite anode. (c) 2005 The Electrochemical Society.