Biomedical Engineering Reference
In-Depth Information
Similarly to other carbon nanostructures, fullerenes show low
binding energy values (few meV) for molecular hydrogen resulting
in poor uptake. In principle, charged fullerenes could improve the
uptake performance and
electronic structure calculations
of charged fullerenes have been performed accordingly [119].
As reported in Fig. 8.5a, the binding energy of a hydrogen molecule
adsorbed onto fullerene can be increased by a factor between 2 and
5 as the charge
ab initio
q
changes from -2 to +6, showing also that the H
2
orientation depends on the polarity. An uptake of 8.04 wt.% has
been predicted at best.
Figure 8.5
Binding energy of molecular hydrogen on charged or neutral
fullerenes (a). The DFT calculations (data points) are compared
with semi-classical calculations (solid lines), and for both cases
the binding energy increases as the square of the net charge.
Optimized hydrogen-fullerene complexes of 12H
28 3+
-C
(b)
2
82 6+
and 43H
(c) with a hydrogen uptake of 6.67 wt.% and
8.04 wt.%, respectively. From Ref. [119].
-C
2
Enhanced adsorption can be obtained also by fullerene decoration
with TMs [116] where the phenomena occurring can be described
through the Dewar-Chatt-Duncanson model [59] involving the
charge transfer from the H
highest occupied molecular orbital
2
(HOMO) to the metal empty
d
-states and from a metal
d
-state to the
H
decorated with light TMs
have been investigated extensively showing a hydrogen adsorption
up to 7.5 wt.% for Ti-doped fullerene. In this case, however, the
situation is slightly more complicated depending on the site occupied
by the metal atom. Sun and co-workers [98] have found that Ti,
similarly to other TMs, tend to agglomerate after the first desorption
lowest unoccupied orbital (LUMO). C
2
60
Search WWH ::




Custom Search