Physisorption Processes on Graphene Related Surfaces with Applications to Solid State Hydrogen Storage

Abstract

This thesis investigates physisorption interactions of molecular hydrogen on graphene surfaces. The structure of graphene is outlined, followed by an overview of hydrogen storage materials. Focusing on hydrogen storage in a lightweight solid state material, molecular hydrogen is rst adsorbed onto a pure graphene surface and the binding energy of the physically adsorbed molecule is calculated using two di erent computational methods. In a primary cluster approach, polycyclic aromatic hydrocarbons (PAHs) are used as approximations to graphene. In the SLAB approach, periodic boundary conditions are used to represent an in nite graphene sheet in repeating units. A series of small molecules, including H2, are adsorbed on graphene and their corresponding physisorption energies are calculated. The results of the two methods are compared to develop a reliable yet e cient computational approach to lightweight physisorption systems. Then, lightweight alkali metals, halogens, and corresponding alkali halides are adsorbed onto graphene and their physisorption energies are calculated. Molecular hydrogen is then adsorbed to these structures and its physisorbed energy is reevaluated. LiF is shown to increase the magnitude of the H2 PSE to -15.3 kJ/mol as a result of 2 adsorbed H2 molecules, NaF is shown to increase the magnitude of the H2 PSE to -17.8 kJ/mol as a result of 3 adsorbed H2 molecules, LiCl is shown to increase the magnitude of the H2 PSE to -11.7 kJ/mol as a result of 4 adsorbed H2 molecules, and NaCl is shown to increase the magnitude of the H2 PSE to -10.3 kJ/mol as a result of 6 adsorbed H2 molecules. To our knowledge, this series of calculations has not been performed. These results provide potential novel coadsorbants that will increase the binding energy of the intact hydrogen molecule. The results can be used to propose a novel lightweight solidstate hydrogen storage system.