Physisorption hydrogen storage, one of the solid-state hydrogen storage mechanisms, offers safe and reversible hydrogen storage for practical applications. The physisorption materials show high hydrogen uptake at cryogenic temperatures but possess challenges at commercialization. In this thesis, the most pertinent methods to synthesize and evaluate physisorption materials are performed to develop and enhance their hydrogen storage properties at room temperature. Also, the interactions between hydrogen and materials are investigated. Firstly, the hydrogen adsorption/desorption mechanism and its relation to physicochemical properties of acid functionalized carbon nanotubes (f-CNTs) under the influence of oxygen functional groups (OFGs) are investigated. The role of H2SO4:HNO3 mixture and 100 ºC combinedly influenced to develop the surface and structural properties which collectively enhanced ~75% in specific surface area (SSA) and ~150% in hydrogen uptake (at 298 K and 50 bar) with 51% reversibility. The OFGs are found to be appropriately influenced to obtain these properties; the effects of OFGs on the hydrogen storage mechanism are analyzed through kinetic analysis, which can be interpreted as the adsorption follows a 3D diffusion process, whereas desorption follows multiple diffusion processes. Secondly, high SSA of base zeolitic imidazolate frameworks (ZIFs) and their hybrid composites are explored. Remarkably, the base ZIF-8 exhibit a relatively high SSA of 2024 m2/g and hydrogen uptake of 1.01 wt.% with 100% reversibility at 298 K and 100 bar equilibrium pressure. The outcomes from X-ray photoelectron spectroscopy reveal that the high concentration of the Zn-N group in ZIF-8 created a suitable distribution of micropores along with proper crystalline alignment, hence remarkable results. Furthermore, ZIF-8 modulated with copper and structure-directing agent (trioctylamine) is exhibited an effective nitrogen deprotonation of ligand which facilitated favourable interactions between hydrogen and material, better cyclic stability. Finally, new ZIF topologies prepared by Zn and two ligands are also studied for H2 storage properties and observed reasonable results owing to their unique morphological structures and oxygen and nitrogen functional groups. Overall, a new development of hydrogen storage properties and hydrogen-materials interactions at room temperature is achieved for physisorption materials, which show good initial properties for physisorption based hydrogen storage tanks for practical applications.
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Thesis advisor: Kjeang, Erik
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