In the last years, the efforts to develop a clean and economically viable energy
source have been increased. This efforts arise as a response to the increasing con-
sumption of fuels and the high environmental and social impact of the exploration
and the use of hydrocarbons or nuclear power. One of the most promising alterna-
tives explored today is the use of H2 as energetic vector. However, there are some
limitations related with the production and storage that must be overcomed.
Focused in the problem of the H2 storage, in this research we have studied,
with computational chemistry techniques, the physical chemical properties that
promote the hydrogen adsorption in Metal-Organic Frameworks (MOFs). From
the analysis of the results, we have identified some parameters that can be used
as a reference to guide the design and synthesis of new MOFs with enhanced
properties for the H2 adsorption.
Along the study, the following aspects have been evaluated in detail: i. the na-
ture of the molecular interactions between the adsorbate and the different compo-
nents of the host and ii. the structural features which promote or limit the adsor-
ption. Such aspects were studied with computational chemistry techniques such
as quantum-chemistry calculations (with the semiempirical PM6 and MP2 met-
hods), molecular dynamic and Monte Carlo simulations. The results were analy-
zed as a function of the physical properties of the materials selected for the study.
In a first step, the interaction of the H2 molecules with the MOF-5 was studied
through quantum chemistry calculations. Given that the strongest adsorption si-
tes were located in positions close to the metal atoms (Zn(II)), a further study was
performed with four types of metallic centres commonly observed in the inorganic
building units of MOFs such as the UiO-66, MFU-1b, MIL-47 y MIL-48A(Pd).
By employing quantum chemistry calculations, particularly the MP2 method,
the maximum loadings of adsorbate molecules supported by the adsorption cen-
tres were estimated. With these results, the composition of each material and
their physical properties, the gravimetric and volumetric uptakes were computed.
As general result, it was found that a MOF with potential utility for the hydrogen
storage must have a density in a range of 0.7-1.0 g/cm3, a metal atoms density
∼0.004 M-atoms/Å and an adsorption centre whose topology and accessibility
allow the adsorption of more than 3 H2 molecules per metal atom.
Finally, the structural features which promote the H2 adsorption by confine-
ment effects were evaluated in the materials PCN-12, HKUST-1, MOF-505, NOTT-
103 y NOTT-112. With this goal, the adsorption centres were located in 3D occu-
pancy maps computed from the molecular trajectories, computed via molecular
dynamic simulations. From the occupancy maps it was observed that the confinement
effects play a significant role in the H2 adsorption in materials with cavities
of diameters around 8.0Å and with small windows where the weaker adsorption
centres are enhanced by the overlap of the attractive potentials.