Hydrogen adsorption properties of metal-organic frameworks within the density-functional based tight-binding approach

Practical methods for hydrogen storage are still a prime challenge in the realization of an energy economy based on Hydrogen. Metal organic frameworks (MOFs) are crystalline ultra-porous materials with ability to trap and store voluminous amounts of gas molecules. MOFs represent an encouraging storage method relying on their enormous surface area. However, MOFs show reduced hydrogen uptake at room temperature due to low adsorption energy of hydrogen. To increase the adsorption uptake of MOFs at room temperature, the adsorption energy must be increased. In this contribution, materials exhibiting higher adsorption energy and enhanced hydrogen adsorption, namely MIL-53 (Al) and MOF-74, have been investigated using molecular dynamics (MD) simulation. MD simulations were performed within the density functional based tight binding method (DC-SCC-DFTB). Our results demonstrate that DC-SCC-DFTB method predicts structural parameters, adsorption sites, adsorption energies and diffusion factors with a very good accuracy, making this method a very powerful tool to investigate various types of MOF. Moreover, results show that the adsorption energy can be increased by incorporation of transition metals in MOF structures.