40
Table 4.3: Relevant energies for analysis of the stabilities of the obtained HER
candidates in the 2H-derived structures. H denotes the calculated standard
heat of formation. Hhull denotes the heat of formation of the most stable
compound (i.e. at the convex hull) in the OQMD database73. The symbol *
in superscript corresponds to the situation where no bulk structure with the
compound composition lies on the convex hull according to the database. In
that case Hhull is calculated as a linear combination of several structures.
Hhull denotes the difference between the two previous columns, i.e. it shows
how much the 2D compound lies above or below the convex hull. HExpt
indicates the experimental standard heats of formation as listed in the OQMD
database. Lebègue et. al. 74 have analyzed the possibilities for forming 2D
compounds based on the layered character of the bulk structures and their result
is also listed in the Table. H2H/1T is the difference between the energies
in the two (possibly distorted) 2H and 1T structures. Finally P(|G| 0.5 is
the probability that the free energy of hydrogen adsorption lies within 0.5 eV
from zero
2H-MX2 H Hhull Hhull HExpt. Ref. 74 H2H/1T P(|G| 0.5
RuS2 -0.31 -0.70 0.39 -0.71 No -0.01 1.00
NiSe2 -0.21 -0.34 0.13 -0.38 No 0.17 1.00
OsS2 0.34 -0.60 0.94 NA No -0.01 1.00
ReO2 -0.91 -1.42 0.51 -1.52 No 0.05 1.00
TaO2 -2.58 -3.00 0.42 NA No -0.07 1.00
PdS2 0.01 -0.31 0.32 -0.28 Yes 0.17 1.00
NbS2 -1.21 -1.20 -0.01 NA Yes -0.04 1.00
RhS2 -0.11 -0.48 0.37 NA No 0.07 0.99
ScS2 -1.46 -1.46 0.00 NA No -0.06 0.99
TiS2 -1.23 -1.37 0.14 -1.41 Yes 0.15 0.98
TaTe2 -0.32 -0.45 0.13 NA Yes 0.00 0.96
TaS2 -1.24 -1.22 -0.02 -1.22 Yes -0.02 0.93
IrS2 -0.11 -0.48 0.37 -0.46 No 0.22 0.92
RhSe2 -0.17 -0.45 0.28 NA No 0.07 0.92
ZrS2 -1.55 -1.73 0.18 -1.99 Yes 0.19 0.91
CoS2 -0.33 -0.48 0.15 -0.51 No 0.01 0.90
ScSe2 -1.30 -1.25 -0.05 NA No -0.01 0.60
PdSe2 -0.02 -0.33 0.31 NA Yes 0.22 0.57
VS2 -1.16 -1.14 -0.02 NA No -0.02 0.52
CrO2 -1.99 -2.15 0.16 -2.01 No 0.03 0.47
ScO2 -2.74 -3.17 0.43 NA No 0.05 0.40
HfS2 -1.62 -1.80 0.18 NA Yes 0.22 0.26
FeS2 -0.54 -0.73 0.19 -0.59 No 0.05 0.06