Characteristics of Molten Metals as Anodes for Direct Carbon Solid Oxide Fuel Cells

Sn, Bi, In, Pb and Sb were examined as molten anodes for solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes. Cells were operated to characterize the electrochemical oxidation of these metals at the YSZ interface. For Sn and In, which form high-melting oxides, the performance of the cell drops due to formation of a thin solid oxide film on the YSZ interface, which prevents further oxidation. For Bi, such a drop is not observed because its oxide is O-2-conductive. For Pb, above the melting point of PbO, the oxide no longer hampers cell performance. For Sb, which forms low melting Sb2O3 (m.p. 929 K), the anode impedance remains low, making efficient fuel cells possible as Sb2O3 is also readily reduced by most types of solid fuels at 973 K. Finally, a high power direct carbon fuel cell (DCFC) is demonstrated with the Sb anode using sugar char fuel.