Modelling of hydrogen adsorption in the metal organic framework MOF5

Metal organic frameworks are formed by rigid organic spacer molecules linked by metal ions into a three-dimensional nano porous structure. The large internal surface (up to 4500 m2 g−1) provides abundant sites for the adsorption of small molecules like hydrogen, which currently generates significant interest for their potential application as reversible hydrogen storage matrix. A prerequisite for hydrogen storage at ambient conditions is that the interaction strength is sufficiently large. Using VASP ab initio computer calculations the adsorption interaction strength for MOF5 is found to be of the order of 70 meV per H2 molecule, where the main adsorption interaction is with the oxygen atoms. Such value compares well with adsorption experiments on MOF5 and it exceeds that obtained in nanostructured pure carbon materials. The J = 0 to J = 1 rotational transition of the H2 determined from inelastic neutron scattering results of Rosi et al. [N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O'Keeffe, O.M. Yaghi, Science 300 (2003) 1127] is compared to the simulation results, and a hydrogen self diffusion coefficient is estimated.