Sulfur tolerance of solid oxide fuel cells

Influence of H₂S fuel impurity on power generation characteristics of SOFCs has been analyzed by measuring cell voltage at a given current density, as a function of operational temperature, H₂S concentration, and fuel gas composition. Reversible cell voltage drop was observed around 1000°C, but fatal irreversible degradation occurred at lower operational temperatures, at higher H₂S concentrations, and at lower fuel H₂/CO ratios. Sulfur tolerance of SOFCs improved by using Sc₂O₃-doped ZrO₂ instead of Y₂O ₃-doped ZrO₂ as electrolyte and/or as electrolyte component in the anode cermet. It has been found that H₂S poisoning consists of at least two stages, i.e. an initial cell voltage drop within a few minutes to a metastable cell voltage, followed by a gradual larger cell voltage drop associated with the agglomeration of Ni particles.