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Fig. 14 Top Bright field
TEM micrograph suggesting
that most of the Nb 2 O 5
particles are embedded in the
MgH 2 matrix (darker areas).
Bottom TEM micrograph of
the MgH 2 -Ni nanostructured
composite with (1) being
87.5 % Ni and (2) being only
5.2 % Ni by EDX.
Reproduced with permission
from Porcu 2008 and Hanada
2008
More recently Zeng et al. used a similar method to characterize another group of
3d transition metals, with a few different considerations taken into account [ 43 ].
As stated earlier, most of the above stated theoretical papers do not take into
account the effects of nanostructuring. More recently, Shevlin et al. used DFT and
many different exchange-correlation functionals, i.e., LDA, PBE, and PBESol, to
investigate the thermodynamics of nanostructuring and transition metal doping.
They found that unless the magnesium cluster contains less than three magnesium
atoms, it will have a higher dehydrogenation enthalpy than the bulk. Thus, for all
the experiments discussed thus far, all increased performance through nanostruc-
turing is purely kinetic. However, they did find that nickel doping is highly
effective in decreasing both dehydrogenation thermodynamics and kinetics [ 99 ].
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