| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeM |
| Session: | Efficient Power Conversion/Cells |
| Presenter: | Kota Kuranari, Tohoku University, Japan |
| Authors: | K. Kuranari, Tohoku University, Japan N. Miyazaki, Tohoku University, Japan Y. Ootani, Tohoku University, Japan N. Ozawa, Tohoku University, Japan M. Kubo, Institute for Materials Research, Tohoku University, Japan |
| Correspondent: | Click to Email |
Pt catalysts are used as anode catalysts for polymer electrolyte fuel cell (PEFC). The fuel in PEFC contains a small amount of impurities such as CO and H2S. These impurities adsorb on active sites of Pt surfaces and degrade the hydrogen oxidation reaction activity of the anode catalyst. This loss of catalytic activity caused by impurities is known as impurity poisoning. Therefore, the development of the anode catalyst with the high impurity tolerance is strongly required. Takeguchi et al. experimentally found that adding SnO2 as support material improves the CO tolerance of the Pt-based catalyst[1]. Furthermore, it is known that adsorbed impurities on the Pt catalyst can be removed by oxidation reaction. Kakati et al. reported that oxidation reaction by O and OH can recover from the H2S poisoning[2]. In order to develop the high impurity tolerant catalyst, it is necessary to reveal the effect of SnO2 nano-particles on H2S tolerance and the recovery mechanism from H2S poisoning by oxidation reaction. In this study, we analyzed the adsorption states of H2S on Pt/SnO2(110) model and the recovery process from H2S poisoning by oxidation with OH using first-principles calculation.
For the calculation model, we put a Pt29 cluster on SnO2(110). The Pt29 cluster exposes Pt(111) on the top (See supplementary document Fig. 1). We calculated the adsorption energy of H2S on Pt/SnO2(110) and compared with the one on Pt(111) to reveal the effect of SnO2 on H2S poisoning process. The adsorption energies of H2S were -18.38 and -24.73 kcal/mol on the Pt cluster of Pt/SnO2(110) and Pt(111), respectively. Thus, it was found that the adsorption of H2S on Pt is suppressed by addition of SnO2. Next, we analyzed the recovery process from H2S poisoning by OH generated from dissociation of H2O. It is known that H2S adsorption on Pt is dissociative and adsorbed sulfur atom is generated. The sulfur atom adsorbed on the surface decreases the activity of the Pt catalyst. In this study, we considered the reaction process (See supplementary document Fig. 2) based on the intermediate stable species during the H2S oxidation cascade in the gas phase[3] and calculated the activation energies of each elementary process. We found that the water dissociation is the rate-determining step on both Pt/SnO2(110) and Pt(111) and the activation energies were 18.78 and 23.70 kcal/mol, respectively. Therefore, we demonstrated that an addition of SnO2 promotes an oxidation reaction of adsorbed sulfur on the Pt catalyst.
1) T. Takeguchi, et. al., Catal. Sci. Technol. 6, 3214 (2016).
2) B. K. Kakati, et al., J. Power Sources 252, 317 (2014).
3) F. Tureček, et al., J. Am. Chem. Soc. 118, 11321 (1996).