Hydrogen storage is among the most demanding challenges in the hydrogen-based energy cycle. One proposedstrategy for hydrogen storage is based on physisorption on high surface area solids such as metal−organicframeworks (MOFs). Within this class of materials, MOF-5 has been the first structure studied for hydrogenstorage. The IR spectroscopy of adsorbed H2 performed at 15 K and ab initio calculations show that theadsorptive properties of this material are mainly due to dispersive interactions with the internal wall structureand to weak electrostatic forces associated with O13Zn4 clusters. Calculated and measured binding enthalpiesare between 2.26 and 3.5 kJ/mol, in agreement with the H2 rotational barriers reported in the literature. Aminority of binding sites with higher adsorption enthalpy (7.4 kJ/mol) is also observed. These species areprobably associated with OH groups on the external surfaces present as termini of the microcrystals.
