Hydrogen Storage in Carbon Nanoscrolls: A Molecular Dynamics Study
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Hydrogen Storage in Carbon Nanoscrolls: A Molecular Dynamics Study V.R. Coluci1*, S. F. Braga1, R. H. Baughman2 and D. S. Galvão1 1 Applied Physics , State University of Campinas, 13083-970 Campinas, São Paulo, Brazil 2 NanoTech Institute and Department of Chemistry, The University of Texas, at Dallas, Richardson, TX 830688, USA ABSTRACT We carried out molecular dynamics simulations with Tersoff-Brenner potentials in order to investigate the hydrogen uptake mechanisms and storage capacity of carbon nanoscrolls (CNSs). CNSs are jelly roll-like structures formed by wrapping graphene layers. Interlayer adsorption is an option for this material, which does not exist for single and multiwalled carbon nanotubes. We analyzed the processes of hydrogen physisorption and uptake mechanisms. We observed incorporation of hydrogen molecules in both external and internal scroll surfaces. Insertion in the internal cavity and between the scroll layers is responsible for 40% of the total hydrogen adsorption at 77 K. * Corresponding author: [email protected] FAX: +551937885376 INTRODUCTION Hydrogen (H2) has attracted a great deal of attention as a possible energy source. It would be ideal as a synthetic fuel because it is lightweight, highly abundant and produces water as its oxidant product. It can be easily generated from renewable energy sources. However, the great promise of hydrogen as an energy source for batteries and fuel cells has been limited by difficulties in storing it for practical applications. The storage of H2 at modest pressures in low weight materials is a critically important problem for the use of hydrogen energy. The U.S. Department of Energy target for hydrogen storage is a gravimetric capacity (weight of stored H2 /system weight) of 6.5 wt% and a volumetric density of 62 kg H2 m3 [1]. The development of hydrogen-fueled vehicles and portable electronics will require new materials that can safely and reversibly store large amounts of hydrogen at ambient temperature at relatively low pressures in low weight and volume structures, and provide fast kinetics for discharge and recharge [2,3]. Among carbon-based structures for hydrogen storage, graphite, carbon nanotubes, and other nanofibers have been both theoretical and experimentally investigated as potential adsorbent structures [1,4-22]. Recently, Viculis et al. have developed a simple, low-temperature synthesis to a different type of carbon structure, named carbon nanoscrolls (CNSs) [23]. These structures are formed by the jelly roll-like wrapping of a graphite sheet to form a nanotubular structure. Theoretical studies of the structural and dynamical properties of carbon nanoscrolls revealed that the CNS formation is a selfsustained curling process after a critical overlap area is reached [24]. Because of the scroll topology, the properties of CNSs can differ from that of other related structures, such as carbon single walled nanotubes (SWNTs) or carbon multiwalled nanotubes (MWNTs). In contrast to SWNTs and MWNTs, CNSs provide inter-layer gal
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