DFT Study of a graphene sheet decorated with nickel in contact with different adsorbates

AGUSTÍN SIGAL; MARIANA ISABEL ROJAS; EZEQUIEL PEDRO MARCOS LEIVA

Nice, France

Congreso; 61th Meeting of the International Society of Electrochemistry; 2010

International Society of Electrochemistry

DFT Study of a graphene sheet decorated with nickel in contact with different adsorbates A. Sigal1, M.I. Rojas2, E.P.M. Leiva2 1Facultad de Matemática Astronomía y Física, 2INFIQC, Departamento  de Matemática y Física, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina mrojas@fcq.unc.edu.ar   Carbon nanotubes may be decorated with different metals by different techniques. These surfaces obtained are of technological importance due to the fact that they may be a suitable material for gas storage. This property is especially worth being analyzed in the case of the hydrogen storage,since this gas is the optimal candidate as the energy carrier in an economy based on renewable resources. These surfaces have also been analyzed for low cost electrochemical hydrogen storage, with excellent perspectives [1]. In a recently theoretical study, Yildirim et al [2] found that titanium decoration of carbon nanotubes remarkably increases their capacity for hydrogen storage. For this system, we have demonstrated that a problem may arise during the manufacture of a titanium decorated graphene sheet, because titanium is irreversibly oxidized to titanium dioxide in the presence of small oxygen concentrations remaining in experimental vacuum [3], resulting in a strongly decreased storage capacity. Since graphene is a new carbonaceous material of high surface area, we studied the hydrogen storage capacity of a graphene layer decorated with nickel in order to contribute to the development of these storage materials. The present system appears as a potentially good candidate, since a single nickel atom in vacuum can coordinate until five hydrogen molecules and does not oxidize as easily as titanium. In order to anticipate the potential problems that could arise during the manufacturing process, handling and operation of the storage system, we studies by means of density functional theory (DFT): 1- The formation of on graphene, 2- The reduction reaction fromto , 3- The interaction of the  decorated graphene layer with the air components, 4- The possibility of hydride formation during the storage operation and 5- The hydrogen storage capacity. In all cases we investigate if the decorated structure remains stable and how the modification affects the storage capacity. The study of the minimum energy path for the different reactions was undertaken using nudged elastic band method (NEB) [4], the local minima where found through the conjugate gradient (CG) technique, employing Density Functional Theory (DFT) calculations with spin polarization (sp) as implemented in SIESTA [5] in all cases. References [1] C.C. Yang, Y.J. Li, W.H. Chen, Int. J. of Hydrogen Energy in press. [2] T. Yildirim, S. Ciraci, Phys. Rev. Lett. 94 175501 (2005). [3] M.I. Rojas, E.P.M. Leiva, Phys. Rev. B 76 155415 (2007). [4] G. Henkelman, B.P. Uberuaga, H. Jonsson, J. Chem. Phys. 113 (2000) 9901-04.   G. Henkelman, H. Jonsson, J. Chem. Phys. 113 (2000) 9978-85. [5] J. M. Soler, E. Artacho, J. D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal, J. Phys.: Condens. Matter 14 2745 (2002).