xxiii πανελληνιο ÏƒÏ Î½ÎµÎ´ÏÎ¹Î¿ Ï†Ï ÏƒÎ¹ÎºÎ·Ï‚ στερεας καταστασης & επιστημης ...

Pillared Graphites – A New 3D Network Nanostructure for enhanced Hydrogen Storage
Dimitrakakis K. Georgios 1 , Tylianakis Emmanuel 2 and Froudakis George E. 1*
1 Department of Chemistry, University of Crete, P.O. Box 2208, Heraklion, Crete, 71003, Greece
2 Materials Science and Technology Department, University of Crete, P.O. Box 2208, Heraklion, Crete, 71003, Greece
* frudakis@chemistry.uoc.gr
Hydrogen is considered to be one of the most promising energy fuels. It can be stored in fuel cells in order to make easier
and safer its transportation and usage in mobile applications. After the synthesis of Carbon Nanotubes (CNTs) [1] the
scientific research has been focused on them, as they are believed to be a good candidate material for reversible hydrogen
storage [2-4]. So far, the results have shown [5-7] that in ambient conditions, the hydrogen storage capacity of pristine CNTs
is far below the gravimetric and volumetric targets that have been set by the U.S. Department of Energy (D.O.E.) [8].
Doping CNTs with alkali metals like Lithium has as a result higher storage capacity [9-13] but even that remains far away
from the D.O.E. targets. All these have lead to the proposal of new candidate structures based on carbon [14-16]. In the
present work a novel three dimensional (3D) carbon based architecture is proposed as a new enhanced hydrogen storage
material. The proposed structure consists of parallel graphite sheets build in such a way that they use CNTs as pillars for the
connection. The resulted 3D networked nanostructure can be seen in Figure 1. Ab-initio calculations were performed to
show the possibility of forming such a structure. They were done using the Density Functional Theory (DFT) level and the
PBE functional. Our calculations showed that something like this is theoretically feasible and thus we continued to see how
such a structure interacts with hydrogen atoms. In addition, more calculations were carried out when this structure was
doped with a lithium atom. Furthermore, Monte – Carlo calculations were conducted to measure the ability of this structure
to adsorb hydrogen. The uptake depends on both intertube and intersheet distance and also on the tube’s curvature. The
results were encouraging compared with previous studies. A 50% enhancement is observed related to graphene sheets and
nanotubes. Finally, when this novel material is doped with Li ions the volumetric uptake reaches 49 gr H 2 /Lit, fulfilling the
DOE’s target i.e. 45 gr H 2 /Lit [8].
Figure 1
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