| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeM |
| Session: | Efficient Power Conversion/Cells |
| Presenter: | Nobuki Ozawa, Tohoku University, Japan |
| Authors: | N. Ozawa, Tohoku University, Japan K. Kuranari, Tohoku University, Japan M. Kubo, Tohoku University, Japan |
| Correspondent: | Click to Email |
Polymer electrolyte fuel cell (PEFC) needs anode materials with high tolerance to poisoning by impurities such as CO, NH3, and H2S in the fuel, which degrades performance of the PEFC. Recently, a composite of Pt and WO3 (Pt/WO3) is used as a catalyst in the anode, and this catalyst is effective for CO removal by oxidation [1]. For theoretical design of anode materials with high tolerance to impurity poisoning, the mechanism of high tolerance of Pt/WO3 to CO should be revealed. In this study, we investigated CO oxidation processes on Pt/WO3(001) by first-principles calculation. At first, we calculated the adsorption energies of CO on Pt/WO3(001) and an isolated Pt cluster, to discuss an effect of WO3 on CO tolerance of Pt. For a Pt/WO3(001) model, a Pt20 cluster is put on a WO3(001) surface. The adsorption energy of CO on the Pt20 cluster is 36.40 kcal/mol, while that on an isolated Pt20 cluster is 45.65 kcal/mol. These results indicate that the combination of the WO3 surface and Pt cluster decreases the adsorption energy of CO on the Pt cluster. To investigate the reason why the adsorption energy of CO decreases by the WO3 surface, we calculated d-band center [2] of the Pt atom on Pt/WO3(001) and Pt cluster. In general, downward shift of the d-band center increases the adsorption energy of CO. Here, the d-band center values of the Pt atom on Pt/WO3(001) and isolated Pt cluster are -2.28 and -2.15 eV, respectively. This means that WO3 modifies the electronic states of the Pt cluster and leads to the downward shift of the d-band center, which decreases the adsorption energy of CO. Next, we discuss CO oxidation on Pt/WO3(001). The CO oxidation by H2O proceeds as follows; (i) H2O → OH- + H+ and (ii) CO + OH-→ CO2 + H+ + 2e-. Here, we firstly investigated H2O dissociation on Pt/WO3(001). In this calculation, the H2O molecule adsorbs on the interface between the Pt cluster and WO3(001) surface, and dissociates to H+ on the Pt atom and OH- at the interface. The activation energy for the H2O dissociation is 19.87 kcal/mol, which is lower than that on a pure Pt(111) surface (23.70 kcal/mol). Thus, we suggest that WO3(001) can decrease an adsorption energy of CO and activation energy for H2O dissociation on Pt catalyst during CO oxidation process.
[1] P.-Y. Olu, et al., Electrochem. Commun., 71, 69 (2016).
[2] B. Hammer, et al., Catal. Lett., 46, 31 (1997).