The influence of normalH2S fuel impurity on power generation characteristics of solid oxide fuel cells (SOFCs) has been analyzed by measuring cell voltage at a constant current density, as a function of normalH2S concentration, operational temperature, and fuel gas composition. Reversible cell voltage change was observed around 1000°C , while fatal irreversible degradation occurred at a lower operational temperature, at a higher normalH2S concentration, and at a lower fuel normalH2∕CO ratio. Sulfur tolerance of SOFCs was improved by using normalSc2normalO3 -doped ZrnormalO2 instead of normalY2normalO3 -doped ZrnormalO2 as electrolyte and/or as electrolyte component in the anode cermets. It has been found that normalH2S poisoning consists of at least two stages, i.e., an initial cell voltage drop within a short time period to a metastable cell voltage, followed by a gradual larger cell voltage drop. Possible normalH2S poisoning processes are discussed.

While SOFCs are the most flexible fuel cells with respect to fuel selection, fuel impurities in practical SOFC fuels can cause degradation of electrodes and thus electrochemical performance. The understanding of fuel impurity poisoning and the increase in tolerance are therefore of technological relevance for SOFC commercialization. Along with thermochemical calculations on the stability of typical fuel impurities under SOFC operational conditions, fuel impurity poisoning of SOFCs is analyzed by using various impurity-containing fuel gases with respect to operational temperature, type and concentration of impurities, fuel composition, and steam-to-carbon ratio. We have revealed that poisoning depends on operational conditions and types of fuels and impurities. The poisoning effect becomes significant for internal-reforming SOFCs operated with humidified methane-based fuels. Poisoning mechanisms are discussed, based on cell voltage and durability data.

No abstract