| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuA |
| Session: | Catalysis on Metals and Alloys |
| Presenter: | HyungChul Ham, University of Texas at Austin |
| Authors: | H.C. Ham, University of Texas at Austin J.A. Stephens, University of Texas at Austin G.S. Hwang, University of Texas at Austin |
| Correspondent: | Click to Email |
In the oxidation reaction of fuels such as CO-contained hydrogen, methanol and formic acid at the low temperature region (300 ~ 400K) at the anode side of polymer electrolyte membrane fuel cell, the precious catalysts such as Pd and Pt have suffered the gradual loss in the catalytic activity due to the blocking of active sites (Pd/Pt) by CO molecules (the so-called CO poisoning effect). To handle this issue, alloying precious catalysts by other transition metals has been suggested as one of solutions since the synergetic alloying effects such as the creation of unique mixed-metal surface sites [ensemble effect] and electronic structure change by metal-metal interactions [ligand effect] can provide an avenue for preventing CO poisoning and enhancing CO oxidation at the low temperature.
In this talk, we will present our recent first-principles results on the role of Pd ensembles on the AuPd alloy in enhancing CO oxidation and tolerance at the low temperature. Using spin-polarized DFT-GGA calculations, for the first time, we elucidate that the reactivity toward CO+O2 oxidation at the low temperature on various CO-precovered Pd ensembles (such as monomer, dimer, trimers and tetramers) is a strong function of surface Pd arrangements on the AuPd surface. In particular, the small-sized ensembles like dimer or compact trimer are responsible for enhancing the low temperature CO+O2 oxidation by the increased availability of free Pd sites and facile O2 activation on CO-precovered Pd ensembles. We will also show the importance of the interplay of ensemble and ligand effects in reducing the CO poisoning of the catalysts through the comparison study on the energetics, charge transfer, geometric and electronic structures of CO between Pd and Pt ensembles. Finally, we will present geometric parameter effects (such as strain and facet) on the CO tolerance of Pd ensembles, which can provide the proper criteria for designing the nano-sized Au-based bimetallic catalysts.
This study hints on how the surface arrangements of atoms and the influence of ensembles on the reaction kinetics and energetics can offer insight to properly tailor CO-tolerant Au-based bimetallic catalysts for fuel cell applications.