Theoretical Studies On The Adsorption Of Pt On Graphene/Graphyne And Its Influence On Ethanol’s Adsorption

Carbon-supported platinum have been used as the direct ethanol fuel cell (DEFC) anode catalysts for years. Since the new members of the "carbon family", graphene and graphyne, were successfull developed, the adsorption mechanism of Pt on them have attracted the attention of researchers because there are more advantages for graphene/graphyne to adsord Pt than graphite. Graphene is a two-dimensional single carbon atomic layer, which has a unique electronic structure and stability. Although studies on platinum adsorded on graphene are numerous, the adsorption of Pt on pristine graphene is weak. Therefore, we will concentrate on Pt’s behavior on defective graphene and doped graphene. Graphyne, another new member of "carbon family", is a full two-dimensional network of carbon molecule formed by alkyne bonds and phenyl rings. It is a large conjugated system with rich carbon bonds, wide spacing, outstanding chemical stability and semiconductor properties. In this paper, the mechanisms of Pt on these two new carbon materials were discussed by using quantum chemistry computational methods. We want to investigate the adsorption behaviour of Pt on different carbon materials and the effect of adsporption systems on ethanol’s oxidation reaction.At first, the systems of Pt clusters (Pt/Pt4/Pt7) adsorded on different carbon supporting materials (graphene, β-and γ-graphyne, graphdiyne,5-8-5 defective graphene, and N/B/O doped grapheme) are extensively optimized by using pseudopotential LANL2DZ at the B3PW91/6-31G* level, based on density functional theory (DFT). Among the examined adsorption sites in graphyne, such as the hollow site (H), Csp-Csp(T), and Csp-Csp2 (D) bonds, it was found that the hollow site is the most attractive site to adsorb Pt/Pt4, regardless of β-GY, γ-GY, or GDY, because there are six bonds between Pt atom and carbon atoms, more than other adsorbed sites. Moreover, we found that the binding strength is proportional to the number of charges transferring from Pt cluster to carbon materials, through Mulliken charges analysis. It indicated that the charges took part in the information of Pt-C bonds. But Pt cluster prefers adsorbing on pristine graphene by Pt-Pt bond. It is the most interesting that the adsorption of Pt on both GY and GDY is much stronger than that on pristine graphene (binding energy,-3.23,-3.10 and-2.85 eV vs-1.11 eV), implying that the adsorption of Pt can be enhanced by the GY and GDY. The reason why the adsorption of Pt can be enhanced by GY and GDY is that there are more reactive Csp atoms in GY and GDY. the additional px-py π/π* states existing in the Csp-Csp bonds. Unlike the sp2 hybridization in graphene, where only out-of-plane pz π/π* states exist (here z is the direction perpendicular to the carbon plane), here there are also in-plane px-py π/π* states. This enables the π/π* states to rotate toward any direction perpendicular to the line of_Csp-Csp, thus making it possible for the π/π* states point toward the Pt atom. Pt atom prefers to adsorb on β-GY but Pt4 cluster is more like to adsorb on GDY. Both GY and GDY are deformed because of the adsorption of Pt4. The adsorption behaviour of Pt4 cluster on di-vacancy graphene (5-8-5-C102H28) was also investigated at the same computational level and found that Pt4 likes to stay at the center of defect position by Pt-Pt bond. Besides, it can be concluded from the frontier orbital theory that carbon materials make a great contribution to the adsorption system no matter in Pt or Ptt4 system. A preliminary study for the influence of catalytic properties of Pt4 nanoclusters for ethanol oxidation reduction reaction on different substrate materials was done in this paper. The binding of ethanol on β-, and γ-GY is slightly stronger than that on graphene (-0.44 and -0.46 eV vs -0.38 eV), while that on GDY is rather comparable to the latter (-0.40 vs. -0.38 eV), which are all weaker than it on the 5-8-5 defective graphene (-0.92 eV). The present first principle calculations indicate that β-/γ-graphyne, graphdiyne and defective graphene can be potential candidate materials to promote the catalytic performance for Pt catalysts.At the same time we also did a preliminary research on the behaviour of Pt7 cluster (CTP and PBP configuration) on N/B/O doped graphene sheet. It was found that the favourite adsorption site is not what we expected, the dopant atom, but the site adjacent to dopant atom. However, the adsorption stability of Pt7 on N/B/O doped graphene is weaker than it on the single vacancy defective graphene.Besides, the extensive application of single-walled carbon nanotubes (SWNTs) in biomedical terms stimulate the enthusiasm of researchers on the interaction between biological molecules and SWNTs. Recently, it was shown from theoretical and experimental studies that functional groups might largely adjust the electronic configuration and biological activities of CNTs. In this paper, we mainly investigate the substitution reaction between amino acids and functionalized SWNTs. Adsorptions of histidine on graphene and the functionalized single-walled carbon nanotube (SWNT), which were decorated by -COOH,-OH and -NH2 at edges and openings, were investigated using density function theory methods, M05-2x and DFT-D. The results show that the binding of the histidine ring to the functionalized SWNT is weaker than that to the pristine SWNT for both singlet and triplet complexes, regardless of the electron-donating (-OH,-NH2) or electron-withdrawing (-COOH) character and their attached sites. The present decreased binding is opposite to the well-known enhanced binding in the substituted benzene dimers. Since the atoms of the histidine are distant from the substituent atoms by over 6 A, there would be no direct interaction between histidine and the substituent as in the case of the substituted benzene systems. The decreased binding can be mainly driven by the aromaticity of the functionalized SWNT. The nucleus-independent chemical shift (NICS) index analysis for the functionalized SWNTs in deed shows that local aromaticity of SWNT is decreased because of the electron redistribution induced by functional groups, and the π-π stacking between the histidine ring and functionalized-SWNT is therefore decreased as compared to the pristine SWNT. However, the above trend does not remain for the binding between the histidine and graphene. The binding of the histidine to the functionalized graphene with -OH and -NH2 is just slightly weaker than that to the pristine graphene, while its binding to COOH-SWNT becomes a little bit stronger.