Understanding Performance Losses at Ni-Based Anodes Due to Sulphur Exposure

Abstract

While Ni-YSZ (yttria-stabilized zirconia) cermets have excellent properties for use as solid oxide fuel cell (SOFC) anodes, they are susceptible to performance loss in the presence of sulfur (S) in the fuel stream. In this work, we have electrochemically determined the extent of poisoning and recovery of Ni-YSZ electrolytesupported half-cells in 5 ppm H 2 S (in H 2 ) between 600 and 850°C, comparing these results with S adsorption/removal data obtained using TGA. It is shown by both approaches that the coverage of Ni by adsorbed S species (S ads ) increases as the temperature decreases, as expected. However, the extent of S ads coverage, determined from performance loss, is significantly less than predicted from the mass gain during S adsorption. Furthermore, anodes exposed to H 2 S at 600°C show an unusual irreversible S poisoning effect when polarized at 250 mV, not seen in TGA experiments.

Effect of Sulfur- and Tar-Contaminated Syngas on Solid Oxide Fuel Cell Anode Materials

“…12,14,15 Similar to carbon deposition, this becomes more of an issue at lower temperatures. 12,15,16 There are methods for reducing the tar and sulfur contents of gasifier outputs, 17,18 but these require energy and may reduce the heating value of the fuel gas. In addition, carbon monoxide itself can cause carbon deposition in certain conditions.…”

“…Carbon deposition can cause damage to the structural integrity of the anode as well as reduce the catalytic activity by poisoning the active sites . Sulfur-containing molecules, such as hydrogen sulfide, reduce the catalytic activity, again by poisoning the active sites. ,, Similar to carbon deposition, this becomes more of an issue at lower temperatures. ,, …”