ELECTROCATALYTIC CELLS FOR CHEMICAL-REACTION

Solid oxide fuel cell technology has been successfully applied to the partial oxidation of methane to produce ethane and ethylene and to the oxydehydrogenation of ethane to produce ethylene. One electrocatalytic cell consists of a solid electrolyte (yttria-stabilized zirconia) coated on either side with a conductive metal to form electrodes. Air is passed over one side of the cell where it reacts with the cathode to form oxygen anions. The oxygen anions are transported through the zirconia to the anode where they oxidize the substrate. The cathode and anode are connected by an external circuit so that a current is generated. The choice of electrocatalyst on the anode affects the product selectivity. In the partial oxidation of methane, high selectivities to C2+ have been obtained using doped Ag or Au anodes. At 800-degrees-C under conditions of low conversion, the selectivity to C2+ was as high as 86% for a AgPb anode. In all cases selectivity decreases with increasing conversion. The highest yield was obtained with the AgPb anode at 850-degrees-C. Co-feed experiments using CH4-C2H4 mixtures shed light on the limit of the methane coupling yield. An advanced cell concept incorporating a second, conducting phase along with an oxygen conducting electrolyte to produce an internal short circuit will be described. High oxygen fluxes (current densities) have been measured that may permit these materials to be used as oxygen separating membranes in chemical reactors.