DFT study of the oxidation reaction of the Ti decoration adsorbed on a graphene layer

MARIANA ISABEL ROJAS; EZEQUIEL PEDRO MARCOS LEIVA

Bahía Blanca, Buenos Aires, Argentina

Congreso; Tercer encuentro de Física y Química de superficies; 2007

Encuentro de Física y Química de superficies

We study the oxidation reaction of the Ti decoration adsorbed on a graphene sheet in order to contribute to the Ti/nanotube system. Because it can be represented with a less number of atom and due to all the reaction studied here occur onto the titanium adatom. The study of the minimum energy path for the different reactions was undertaken using nudged elastic band method (NEB) [1], 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 [2] in all cases. In the case of the system is exposed only to hydrogen gas phase, the system can store up to four molecules per adatom, as it was found in the literature for single wall carbon NanoTubes [3]. Thus, titanium decoration improves considerably the hydrogen storage capacity of the carbon systems. The oxygen molecule is a very reactive species, present in air. As Nanotube modifications are performed in ultra high vacuum conditions. But even when the system is evacuated; it never turns to be completely free of oxygen, remaining a pressure of . For that reason, the interaction study of the system with the oxygen molecule is of potential technological relevance. However, small amounts of oxygen present in the gas phase should yield to the titanium oxidation to titanium dioxide. Others air components as nitrogen or water molecules could be also chemisorbed onto the titanium adatom. Dehydrogenate reaction from two adsorbed waters is found to exhibit a large activation energy barrier but appears as energetically favoured. The present results are relevant for hydrogen storage in Ti/carbon NanoTubes exposed to small amounts of air. [1] 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. [2] J. M. Soler, E. Artacho, J. D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal, J. Phys.: Condens. Matter 14  (2002) 2745. [3] T. Yildirim, S. Ciraci, Phys. Rev. Lett. 94 (2005) 175501.