Electrochemical promotion of bulk lattice-oxygen extraction for syngas generation over Ni-GDC anodes in direct-methane SOFCs

Gadolinia-doped ceria (GDC), a mixed ionic-electronic conductor, was used to fabricate a Ni-GDC/GDC/Pt solid oxide fuel cell (SOFC). The Ni-GDC anode has a composition of Ni:GDC = 3:5 in weight. A new phenomenon of electrochemical promotion of lattice-oxygen extraction from GDC bulk is observed during direct methane oxidation, in the absence of anode-side gas-phase oxygen, to generate syngas at 800 °C. The extraction of markedly higher amount of oxygen than that of the measured current is promoted. This effect increases as the potential (the generated voltage) increases. Both rates of CO and CO2 formations are linearly related to the measured current density but inversely linearly related to the voltage. The formation rate of CO depends on the rate of oxygen supply to the anode surface and its dependence is stronger than that of CO2. As the oxygen-supply rate increases, both methane conversion and CO selectivity increase. Electrochemical promotion of bulk lattice-oxygen extraction enhances the syngas generation.