Abstract The most thermodynamically stable sulfur compound in the anode electrode at SOFC temperature is H 2 S, which dissociates on a nickel (Ni) surface according to a chemisorption mechanism. In this study, SOFC performance losses have been quantified in the presence of H 2 S contamination. The deactivation process has been well quantified by correlating it to Ni surface coverage by sulfur through a Temkin-like isotherm adsorption process. The detailed microscopic features of an Ni-based electrode have been taken into account to quantitatively predict atomic sulfur adsorption on the Ni surface. The results show that, in anode-supported cells, the entire available Ni surface is affected by sulfur contamination and not just the three-phase-boundary (TPB) region. Experiments on both commercial single-cells and on a stack have been described in this work. The H 2 S concentration was varied from 0.8 to 6.5 ppm(v) in the single-cell experiments, and between 0.01 and 25 ppm(v) in the stack experiment. The time-to-coverage evaluation has been established on the basis of the relationship between the sulfur capacity of the Ni anode and the sulfur flow rate through the fuel feed.