A first-principles analysis for sulfur tolerance of CeO2 in solid oxide fuel cells

The mechanism for H2S-CeO2(111) interactions in solid oxide fuel cells (SOFCs) has been investigated by using periodic density functional theory (DFT) calculations. In order to properly characterize the effect of the localization of Ce-4f states on the interactions, DFT + U calculations were applied. Adsorption of H2S, SH, and atomic S was initially examined to locate energetically favorable intermediates. The species adsorb favorably at the Ce-top, O-top, and Ce-O bridging sites, respectively. Potential energy profiles for the H2S-CeO2 (111) interactions along the three product channels producing H-2, H2O, and SO2 were constructed using the nudged elastic band (NEB) method. Calculations show that H2S weakly bounds on CeO2(111) with a small binding energy, followed by dehydrogenation processes, forming surface sulfur species with an exothermicity of 29.9 kcal/mol. Molecular-level calculations demonstrated that the SO2-forming pathway is energetically most favorable.