First-principles investigation of HS adsorption and dissociation on titanium carbide surfaces.

The adsorption and dissociation reactions of HS on TiC(001) are investigated using first-principles density functional theory calculations. The geometric and electronic structures of the adsorbed S-based species (including HS, SH and S) on TiC(001) are analyzed in detail. It is found that the HS is bound weakly, while SH and atomic S are bound strongly on the TiC(001) surface. The transition state calculations show that the formation of SH from HS (HS → SH + H) is very easy, while the presence of a co-adsorbed H will inhibit the further dissociation of SH (SH + H → S + H + H). In contrast, the hydrogenation of the adsorbed SH is rather easy (SH + H → HS). Therefore, the dissociative SH can be removed via the hydrogenation reaction. It is concluded that it is difficult for HS to dissociate completely to form atomic S and poison the TiC surface. The results will further provide understanding of the mechanism of the sulfur tolerance of the TiC anode of proton exchange membrane fuel cells (PEMFCs).