AB Initio study of reversible hydrogen storage in metal decorated Calix[4]arenes and porous materials

Abstract

The objective of this thesis is to investigate the hydrogen storage properties of various metal decorated materials by using rst principles calculations based on density functional theory (DFT). An increasing energy demand, and a limited supply of fossil fuels, their adverse e ect on the environment require the need for a clean and sustainable energy source. Hydrogen holds the promise to replace the widespread dependency on fossil fuels due to its renewable, light weight, highly abundant, the highest energy density per unit mass and produce water when used in fuel cells. High gravimetric and volumetric storage densities, optimal thermodynamics, and fast reaction kinetics are essential for an e ective hydrogen storage system. Thus the materials based hydrogen storage with an emphasis on the necessary properties for reversible hydrogen storage have been explored. A variety of di erent materials such as graphene, carbon nanotubes, fullerenes, graphynes, metal-organic frameworks and covalent organic frameworks reported for hydrogen storage experimentally and theoretically but none of them have met the ultimate target set by the US Department of Energy due to low e ciency in storage and release of hydrogen at ambient temperature and pressure conditions. DFT has been applied to explore the hydrogen storage properties of the systems by using two di erent methods, i.e., global hybrid functional M06 and generalized gradient approximation (GGA) based on the system size. The global hybrid functional M06 with 6-311G(d,p) basis set have been used to explore the hydrogen storage properties of metal decorated calix[4]arene and its derivatives. However, the hydrogen storage properties of metal􀀀organic and inorganic frameworks have been studied by GGA with double numeric polarization (DNP) basis set. The structural, thermochemical, and electronic properties have been studied. The hydrogen storage properties of light metals such as Li, Sc, and Ti decorated calix[4]arene and its derivatives have been explored. The hydrogen sorption properties of metal decorated metal-organic frameworks viz.; metal-graphyne framework (MGF), metal-carbyne framework (MCF) and metal inorganic framework made up of inorganic borazocine linker (MBF) have been studied. Metal atoms bind with CX systems, MGF, MCF, and MBF by Dewar coordination. The hydrogen molecules are adsorbed on the open metal sites of metal decorated systems by Kubas-Niu-Rao-Jena mechanism. It was observed that 3 to 6 H2 molecules adsorbed on per metal atom in the metal decorated system. The average hydrogen adsorption and sequential desorption energies are calculated and found in the required range for metal decorated CX, MGF, and MBF systems. The charge transfer mechanism during the hydrogen adsorption is studied by Hirshfeld charge analysis and electrostatic potential maps. The reversibility of adsorbed hydrogen and the stability of the metal decorated systems is studied by Born-Oppenheimer molecular dynamics simulations. Based on rst principles calculations, the hydrogen storage properties of di erent metal decorated materials have been explored, which can be considered as potential hydrogen storage materials. A summary of the present work is given at the end of the thesis along with the conclusions and the future direction of research followed by a bibliography.