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The compounds have been grouped based on the nature of the metal atom
‘M’ in MX2 i.e. the compounds have been put in the same group if the metal
atoms belong to the same group in the periodic table; based on this categorization
the plots for hydrogen adsorption energies are shown in the Figure
4.5.
Figure 4.5: Hydrogen adsorption energies of the individual groups. The compounds
have been grouped based on the nature of the metal atom ‘M’ in MX2
i.e. the compounds have been put in the same group if the metal atoms belong
to the same group in the periodic table. The missing data points represent
massive reconstruction upon the hydrogen adsorption thus omitted from the
plot. All the energies are in eV. The figure has been taken from the Paper-2.
The plot clearly shows that adsorption energies on the 2H and 1T structures
do not follow any systematic trend in most of the cases, therefore, a simple
systematic analysis cannot be performed to rationalize the different activities
of the different structures. However, the group containing Cr, Mo and W
(group-6) shows an opposite trend as the group containing Ti, Zr and Hf
(group-4). In the group-6 the 1T structure binds hydrogen strongly whereas
in the group-4 the 2H structure has higher binding energy. Therefore, only the
group-4 and group-6 have been selected to understand the origin of different