Partitioning of coal contaminants in the components of liquid tin anode solid oxide fuel cells

Abstract

Direct carbon fuel cells (DCFCs) electrochemically convert fossil fuels to electricity, resulting in higher efficiency and less pollution than traditional direct combustion technologies. This work focuses on direct use of coal in a liquid tin anode solid oxide fuel cell (LTA SOFC) where a layer of molten tin functions as the anode. In such a direct solid fueling scheme, a major technical concern is the ultimate disposition of trace materials naturally present in the coal. Trace contaminants introduced with the coal must be located in the functional portions of the LTA SOFC to ensure that any deleterious reactions are known and ultimately mitigated. This research effort determines the thermochemical contaminant partitioning between the tin anode, slag, or electrolyte material and examines the critical interfaces within the system. Contaminant partitioning was examined by TEM, SEM/EDS, and ICP–OES/MS. Sulfur is known to poison yttria-stabalized zirconia (YSZ) and appears to form a tin sulfide phase that is dispersed in the liquid tin during operation. Results show that tin oxide formed on and near the YSZ electrolyte, and could potentially degrade charge transfer. The slag was found to consist of the expected metal oxides, however, tin and tin oxide were intermixed with the slag component, indicating a probable need for a tin recovery process that will potentially increase the complexity of an LTA SOFC system.