Theoretical investigation of mixed metal organic frameworks as H2 adsorbents

Molecular hydrogen (H2) is an environmentally friendly, renewable, and sustainable energy carrier. One of the biggest reasons for the limited use of molecular hydrogen (H2) in energy required applications is the inability to fully develop safe and high-performance hydrogen storage systems. New generation nanoporous materials, in principle, can store H2 which could be solution of the H2 storage challenge. Metal Organic Frameworks (MOF), which are new generation nanoporous materials are shown to be promising candidates for the H2 storage applications. MOFs that contain at least two different metal ions in their structures are called as mixed-metal MOFs (MM-MOF) and they could adsorb H2 in higher amounts compared to structures containing single metal nodes. In this thesis, the H2 adsorption capacities of the 27 MM-MOFs having different topological and chemical features have been theoretically investigated using Grand Canonical Monte Carlo (GCMC) and Density Functional Theory (DFT) simulations. Materials under consideration are divided into two groups. While the 1st group materials have been experimentally synthesized before, the 2nd group materials are hypothetical MM-MOFs designed by You et al. (2020). To the best of our knowledge, H2 storage performances of the selected MM-MOFs have not been studied in the literature before. H2 adsorption isotherms of the MM-MOFs have been predicted by GCMC simulations carried out at 233 K and at pressures between 1 and 100 bar. 5-site (anisotropic) atomic modeling has been used for modeling H2. The atomic point charges of the MM-MOF atoms required for calculating electrostatic interactions have been determined by applying the DDEC method. Correlation between H2 storage capacity of the MM-MOFs and their topological and chemical features have been established and six materials are determined to be the best performing MM-MOFs that can adsorb H2 both volumetrically and gravimetrically. Electronic structure analysis has been carried out for the top H2 adsorbing materials by applying DFT simulations. Keywords: Grand Canonical Monte Carlo Simulations, Density Functional Theory