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During past decades, fuel cells have become the focus of the scientific research area all over world is for the emissions of carbon dioxide and global greenhouse effect., so the higher energy conversion methods are needed badly. It is well known that electrode is one of important parts for the fuel cells. Electrode function quality is mainly determined by the property of catalyst, electrode materials and the manufacture craft[1-6]. Precious metals were most thought to be more applicable to most the electrode reaction of the fuel cell due to their special physics and chemistry property, especially the platinum and platinum-based alloy catalyst have higher electricity catalytic activity. During the electro-catalytic reaction of fuel cells, the adsorption activation and desorption of hydrogen on catalyst surface are the key steps of the catalytic reaction Hence, a wealth of experimental and theoretical data have been accumulated, and a clear picture of the features induced by the hydrogen adsorption has emerged. Gas-solid heterogeneous catalysis results from the fact that the forcefield of the atoms or molecules on the solid surface is unsaturated, which leads to the ability of attracting other molecules. There are mainly two kinds of attractions leading to absorption of gas molecules onto solid surface, physical adsorption and chemical adsorption. Furthermore, the chemical adsorption is much stronger than the physical one and can be regarded as a kind of chemical reaction resulting in some surface compounds. There are usually two kinds of models dealing with the activities of heterogeneous catalysis reaction of Pt including single crystal model and cluster model. The single crystal model is often employed when considering the periodic repetition of space for the research objects. But concerning adsorption activation on the Pt single-crystal surface for small gas molecules, such as hydrogen molecules, at present, most researcher pay more and more attention to the most stable adsorbed position for hydrogen molecules. As far as single-crystal Pt is concerned, the most stable adsorption position is related to the miller index of crystal planes. For example, for Pt(111), binding-energy which belongs to different adsorption is similar (about 0.40~0.50eV). Meanwhile, for Pt (100), it is belong to C4, local point group of symmetry. Because there are three kinds of non-equivalence potential surfaces, which are corresponding to three kinds of non-equivalence surface adsorption sites: atop site, bridge site, hollow site, respectively, it is an inevitable result that the adsorption energy of different adsorption sites is different. Yao calculated absorption situation at atop site, bridge site, hollow site, respectively by using density functional theory. It was indicated that H atom was most easily absorbed onto bridge site, with a maximum adsorption energy of 0.91eV. Xu proved that the adsorption energy was largest at bridge site using B3LYP cluster model. Arvia proved that it was more favorable for H atoms to absorb onto Pt surface at bridge sites by EHMO theoretical calculation. We draw the same conclusion by first-principles calculations, and it further proved it was favored for the reaction carrying on at bridge site.(此处需引出创新点) In order to reveal the nature of electrode reaction, we study the electrode reaction, adsorption site and electronic structure at the region of anode H atom on Pt(100) surface in this paper. This paper is organized as follows: 1, the computational methods are concisely described in section 2; 2, the results and analysis are presented and discussed in section 3; 3, the results are summarized in section 4. |
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zhangzhiweia(金币+5, 翻译EPI+1): 2010-12-17 01:18:32
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During past decades, fuel cells have become the focus of the scientific research area all over the world due to the emissions of carbon dioxide and global greenhouse effec, so that the higher energy conversion methods are needed badly. It is well known that electrode is one of important parts for the fuel cells. Electrode function quality is mainly determined by the property of catalyst, electrode materials and the manufacture craft[1-6]. Precious metals were most thought to be more applicable to most the electrode reaction of the fuel cell due to their special physics and chemistry property, especially the platinum and platinum-based alloy catalyst have higher electricity catalytic activity. During the electro-catalytic reaction of fuel cells, the adsorption activation and desorption of hydrogen on catalyst surface are the key steps of the catalytic reaction Hence, a wealth of experimental and theoretical data have been accumulated, and a clear picture of the features induced by the hydrogen adsorption has emerged. Gas-solid heterogeneous catalysis results from the fact that the forcefield of the atoms or molecules on the solid surface is unsaturated, which leads to the ability of attracting other molecules. There are mainly two kinds of attractions leading to absorption of gas molecules onto solid surface, physical adsorption and chemical adsorption. Furthermore, the chemical adsorption is much stronger than the physical one and can be regarded as a kind of chemical reaction resulting in some surface compounds. There are usually two kinds of models dealing with the activities of heterogeneous catalysis reaction of Pt including single crystal model and cluster model. The single crystal model is often employed when considering the periodic repetition of space for the research objects. But concerning adsorption activation on the Pt single-crystal surface for small gas molecules, such as hydrogen molecules, at present, most researcher pay more and more attention to the most stable adsorbed position for hydrogen molecules. As far as single-crystal Pt is concerned, the most stable adsorption position is related to the miller index of crystal planes. For example, for Pt(111), binding-energy which belongs to different adsorption is similar (about 0.40~0.50eV). Meanwhile, for Pt (100), it is belong to C4, local point group of symmetry. Because there are three kinds of non-equivalence potential surfaces, which are corresponding to three kinds of non-equivalence surface adsorption sites: atop site, bridge site, hollow site, respectively, it is an inevitable result that the adsorption energy of different adsorption sites is different. Yao calculated absorption situation at atop site, bridge site, hollow site, respectively by using density functional theory. It indicated that H atom was most easily absorbed onto bridge site, with a maximum adsorption energy of 0.91eV. Xu proved that the adsorption energy was largest at bridge site using B3LYP cluster model. Arvia proved that it was more favorable for H atoms to absorb onto Pt surface at bridge sites by EHMO theoretical calculation. We draw the same conclusion by first-principles calculations, and further proved it was favored for the reaction carrying on at bridge site.(此处需引出创新点) In order to reveal the nature of electrode reaction, we study the electrode reaction, adsorption site and electronic structure at the region of anode H atom on Pt(100) surface in this paper. This paper is organized as follows: 1, the computational methods are concisely described in section 2; 2, the results and analysis are presented and discussed in section 3; 3, the results are summarized in section 4. |
2楼2010-12-15 23:39:37
3楼2010-12-16 09:04:47
