AG-COMPOSITE CATHODE FOR HIGH PERFORMANCE INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS

摘要

Solid oxide fuel cells have exhibited great potential as the next generation power generators for the following reasons: high efficiency when combined with other thermal power systems such as gas turbines, ability to use variety of hydrocarbon fuels, thermal and chemical stability of ceramic materials. Molten carbonate fuel cells (MCFCs) operating at >600°C are currently prevailing in the high temperature fuel cell market and several companies are earning decent profits out of the MCFC business. Many of fuel cell people expect that the MCFC will be replaced by SOFCs in a near future but there are still some technical huddles. Key in successful commercialization of SOFCs lies in lowering operation temperature to the intermediate temperature (IT) range (<500°C). Recent efforts in using a free-standing ultrathin membrane structure (total thickness <300 nm) have achieved power output up to 1.3 W cm~(-2) at 450°C. However, these approaches use expensive Pt as electrodes and require complicated fabrication processes which are not suitable for large-scale production. In mass-producible anode-supported SOFCs, it is essential to develop high performance cathodes since a significant portion of energy loss occurs at the oxygen reduction reaction (ORR). ORR at the conventional perovskite SOFC cathodes has a high activation energy (1.5-2.0 eV) implying that the cathodic resistance dramatically increases as temperature decreases. For this reason, most of conventional SOFCs have reported relatively low performance under 100 mW cm2 below 500°C. In this work, we propose novel Ag-composite cathodes for decent operation of SOFCs under 500°C. It has been reported that the ORR on the Ag surface can be as active as Pt in the IT regime but thermal instability of Ag due to decomposition of surface AgOx into metallic Ag with increasing temperature has limited the application of Ag at high temperature. We have fabricated the Ag-composite cathodes comprised of porous Ag mesh surface-decorated with ceramic electrolyte nano-particulates for thermal stabilization.