Atomic and Electronic Structures of Pt Supported on Graphene
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Atomic and Electronic Structures of Pt Supported on Graphene Kazuyuki Okazaki-Maeda1, Yoshitada Morikawa2, Shingo Tanaka3, and Masanori Kohyama3 1
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan.
2
Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki
567-0047, Japan. 3
Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial
Science and Technology, 1-8-31 Midorigaoka, Ikeda 563-8577, Japan. ABSTRACT We examined atomic and electronic structures of Pt supported on graphene, using the first-principles calculations based on the density functional theory (DFT). First, we examined the interaction between graphene and a Pt(111) monolayer. The stable distance between graphene and the Pt-monolayer is 3.48Å and the adhesive energy is 0.09 eV/atom. The density of states (DOS) for the Pt(111)/graphene system is the same with the sum of respective DOS’s of the graphene sheet and the Pt monolayer. These results indicate that the interaction between graphene and a Pt(111) monolayer is very weak. Second, we examined the interaction between graphene and a Pt atom. The Pt-C bond length is 2.31Å and the adsorption energy is 2.82 eV/adatom, which means the stronger interaction. Finally, we examined the interaction between graphene and a Pt cluster consisting of ten atoms. The distance between graphene and the bottom layer of the cluster is about 2.7Å, which is shorter than that between graphene and the Pt(111) monolayer. This shows that the interaction between the Pt10 cluster and graphene is stronger than the Pt-monolayer/graphene interaction. The center atom in the hexagonal bottom layer of the Pt cluster has the nearest distance with graphene of about 2.5Å. If there is a defect on graphene, the center atom of the hexagonal bottom layer strongly interacts with that. INTRODUCTION Proton-exchange membrane fuel cells (PEMFCs) are attractive as a power source for mobile electronic equipment and zero-emission electrically powered vehicles [1,2]. In a PEMFC, nano-particles of Pt and Pt alloys supported on carbon materials are used as the electrode
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catalysts, and at present the catalysts using Pt and Pt alloy are considered to be the best for both hydrogen oxidation and oxygen reduction at low or intermediate temperature [3]. In order to understand the properties and reaction mechanism of the catalysts, it is essential to investigate the interactions between Pt or Pt-alloy particles and carbon materials. First of all, we have to understand to the interfacial interactions between graphene and Pt or Pt alloys at atomic scales. Recently, Okamoto has investigated the interface between graphene and Pt(111) or Pt(111)/RuML surfaces, where RuML means the monolayer of Ru, using density functional calculations [4]. He found that interfacial Ru atoms make the interface more stable and that carbon vacancies on graphene enhance the interactions between graphene and metal (111) surfaces. However, he examined o
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