Syngas cogeneration in direct-methane solid oxide fuel cells with Ni-yttria-stabilized zirconia (YSZ) anodes was studied with temperature varying from 700 to 900 degrees C. A phenomenon of electrochemical promotion of bulk lattice-oxygen extraction from the YSZ electrolyte was observed. With increasing temperature, this promotion effect increases while both the rate enhancement ratios of CO and CO2 formations decrease. The activation energy of CO and CO2 formation under close circuit is lower than that under open circuit. The activation energy for the lattice-oxygen extraction from the YSZ bulk is higher than that for the oxygen transport through the YSZ bulk. The process of lattice-oxygen extraction from YSZ is rate determining in direct-methane oxidation under the condition of either close circuit or open circuit. The dependence of CO fort-nation rate on the oxygen supply rate is stronger than that of CO2 formation rate. Electrochemical promotion of bulk lattice-oxygen extraction enhances syngas cogeneration. (C) 2007 Elsevier B.V. All rights reserved.