Density functional theory study of sulfur poisoning on nickel anode in solid oxide fuel cells: Effects of surface and subsurface sulfur atoms

Impurities such as sulfur compounds cause performance degradation in solid oxide fuel cells (SOFCs). We have studied the sulfur poisoning mechanism on an SOFC nickel anode using density functional theory method, focusing on the effects of surface and subsurface sulfur atoms. The binding energy of surface sulfur atoms decreases with an increase in sulfur coverage on the nickel surface. Subsurface sulfur atoms become stable relative to surface sulfur atoms at high sulfur coverage. A subsurface sulfur phase also appears between sulfur adsorption phase and nickel sulfide phase in the calculated phase diagram for Ni–S systems. Influences of sulfur atoms on intermediate adsorbates during surface reactions are also investigated. Sulfur hinders the reaction by destabilizing the reaction intermediates on the nickel surface.