In this study, we used the Density functional theory (DFT) and Molecular dynamics (MD) to obtain the suitable hydrogen storage structure of Rh nanoclusters on the boron nitride sheet and Li atoms on the graphene. The reason of studying two type of nanoparticles is that there are two adsorption method in hydrogen storage, such as the adsorption of hydrogen molecules and hydrogen atoms. Using Rh nanoclusters on the boron nitride sheet to store hydrogen belong to the adsorption of hydrogen atoms. Using Li atoms on the graphene to store hydrogen belong to the adsorption of hydrogen molecules. We use these two models to simulate the hydrogen storage in this study. There were four parts in this study: The first part: The Density functional theory is utilized to obtain the configuration and corresponding energy of Rh nanoclusters, boron nitride sheet, Rh nanoclusters adsorbed on the boron nitride sheet, Li atoms adsorbed on the graphene, hydrogen adsorbed on the graphene and hydrogen adsorbed on the Li atoms. Then, we use the Force-matching method (FMM) to modify the parameters of potential function by the reference data which are obtained by Density functional theory. Finally, we use the modified parameters of potential function to perform Molecular dynamics in this study. The second part: In this part, the dynamical behavior of Rh nanoclusters with different sizes on the boron nitride sheet are investigated in temperature-rise period. The migration trajectory, square displacement and mean square displacement of the mass center of the Rh nanoclusters are used to analyze the dynamics behavior of Rh nanoclusters on the boron nitride sheet. The third part: In this part, the pristine graphene and graphen with Li atoms are investigated the efficiency of hydrogen storage at different temperature and pressure. In order to obtain the temperature (77K and 300K) and pressure effect of hydrogen storage, the densimetric distribution and gravimetric capacity (wt%) are analyzed. The fourth part: The Molecular dynamics is utilized to study the hydrogen storage and delivery when the distance between two graphene is different. Then, the temperature effect (77K and 300K) of hydrogen storage, the gravimetric capacity (wt%) are analyzed. In addition, the gravimetric capacity (wt%) of hydrogen delivery are also analyzed in the larger system space at 300K.

The design and production of efficient metal-hydrides for hydrogen storage is a long standing subject. Over the years, many different types of intermetallic hydride systems were studied and some of them came out to be operable. However, none of them meet all the storage criteria perfectly. In this study, total energies, hydrogen storage capacity and stability of AB (A = Al, Be, Cu, Fe, Ni, Sb, V and B = Ti) type intermetallics were investigated with the goal of spotting a potential hydrogen storage material. The relation between thermodynamic properties and the atomic and the electronic structure of hydrides are also pointed out. For this task, first principles pseudopotential method within the generalized gradient approximation (GGA) to density functional theory (DFT) was used. Calculations correctly predict experimentally determined structures except for CuTiH. Moreover, the atomic and cell parameter were found within the allowable error interval for DFT. In CuTi intermetallic, a structure having considerably lower formation energy than experimentally found mono-hydride was determined. This contradiction may be due to metastability of the experimental phase and high activation energy for the hydrogen movement in the system. It was found that AlTi and SbTi are not suitable candidates for hydrogen storage since their hydrides are too unstable. For the other intermetallic systems, the stability of the hydrides decreases in the order of VTi, CuTi, NiTi, BeTi, FeTi. For VTi, FeTi and NiTi, a change in metallic coordination around hydrogen from octahedron to tetrahedron is predicted when tetra-hydride (MTiH4) is formed. Additionally, at this composition, FeTi and NiTi have hydride structures with positive but near-zero formation energy which may be produced with appropriate alteration in chemical makeup or storage parameters. VTi is a promising intermetallic by means of storage capacity in that even VTiH6 is found to have negative formation energy but the hydrides are too stable which can be a problem during hydrogen desorption.

In recent decades, tremendous efforts have been made to obtain high hydrogen storage capacity in a stable configuration. In the literature there are plenty of experimental works investigating different materials for hydrogen storage and their storage values. In the first part of this thesis the available literature data have been collected and tabulated. In addition to the literature survey the hydrogen storage capacity of carbon nanotubes and carbon nanotubes doped with boron nitride (CBN nanotubes) with different chirality have been investigated by performing quantum chemical methods at semiempirical and DFT levels of calculations. It has been found that boron nitrite doping increases the hydrogen storage capacity of carbon nanotubes. Single wall carbon nanotubes (SWNT) can be thought as formed by warping a single graphitic layer into a cylindrical object. SWNTs attract much attention because they have unique electronic properties, very strong structure and high elastic moduli. The systems under study include the structures C(4,4), H2@C(4,4), C(7,0), C(4,0), and the BN doped C(4,4), H2@C(4,4), 2H2@C(4,4), C(7,0), H2@C(7,0), 2H2@C(7,0). Also, we have investigated adsorption and desorption of hydrogen molecules on BN doped coronene models by means of theoretical calculations.

A candidate hydrogen storing material should have high storage capacity and fast dehydrogenation kinetics. On this basis, magnesium hydride (MgH2) is an outstanding compound with 7.66 wt % storage capacity, despite its slow dehydriding kinetics and high desorption temperature. Therefore in this study, bulk and surface alloys of Mg with improved hydrogen desorption characteristics were investigated. In this respect, formation energies of alloyed bulk MgH2 as well as the adsorption energies on alloyed magnesium (Mg) and MgH2 surface structures were calculated by total energy pseudopotential methods. Furthermore, the effect of substitutionally placed dopants on the dissociation of hydrogen molecule (H2) at the surface of Mg was studied via Molecular Dynamics (MD). The results displayed that 31 out of 32 selected dopants contributed to the decrease in formation energy of MgH2 within a range of ~ 37 kJ/mol-H2 where only Sr did not exhibit any such effect. The most favorable elements in this respect came out to be / P, K, Tl, Si, Sn, Ag, Pb, Au, Na, v Mo, Ge and In. Afterwards, a systematical study within adsorption characteristics of hydrogen on alloyed Mg surfaces (via dynamic calculations) as well as calculations regarding adsorption energies of the impurity elements were performed. Accordingly, Mo and Ni yielded lower adsorption energies / -9.2626 and -5.2995 eV for substitutionally alloyed surfaces, respectively. MD simulations presented that Co is found to have a splitting effect on H2 in 50 fs, where the first hydrogen atom is immediately adsorbed on Mg substrate. Finally, charge density distributions were realized to verify the distinguished effects of most 3d and 4d transition metals in terms of their catalyzer effects.

In this study, the effect of surface crystallography on hydrogen molecule adsorption properties on FeTi surfaces is presented. Furthermore, the substitutional adsorption of 3d-transition metals on (001), (110) and (111) surfaces of FeTi is studied. Using ab initio pseudopotential methods, the adsorption energies of hydrogen and 3d-transition metals are calculated. In substitutional adsorption of 3d-transition metals, Fe-terminated (111) and Ti-terminated (001) surfaces, are found to express the lowest adsorption energies. The adsorption energy versus adsorbed elements&rsquo / curves are very alike for all the surfaces. According to this, going from the left to right of periodic table, the adsorption energies increase first. The maximum energy belongs to Cr, Mn and Fe for all the surfaces. Then a minimum is observed in Co for all the surfaces and after that the energy increases again. Adsorption energies of atomic and molecular hydrogen are calculated on high symmetry sites of surfaces. As a result, top and bridge sites came out to be the most stable positions for molecular and atomic hydrogen adsorption, respectively, for (001) and (111) surfaces in all terminations. In (110) surface / however, 3-fold (Ti-Ti)L-Fe and 3-fold (Ti-Ti)S-Fe hollow sites express the lowest adsorption energies for molecular and atomic hydrogen, respectively. Considering the minimum adsorption energy sites for hydrogen molecule and atom, a path of dissociation of hydrogen molecule on surfaces is represented. After that by fully relaxing the hydrogen molecule on the surface and using CI-NEB method the activation energy for hydrogen dissociation is calculated. So it has been found that on Fe-terminated (111) and FeTi (110) surfaces the dissociation of hydrogen molecule happens without activation energy. Meanwhile, the activation energy for Fe-terminated (001) surface and Ti-terminated (001) surface, is calculated to be 0.178 and 0.190 eV, respectively.

The aim of this study is the synthesis of hydrogen storage compounds by electrodeoxidation technique which offers an inexpensive and rapid route to synthesize compounds from oxide mixtures. Within the scope of this study, two hydrogen storage compounds, FeTi and Mg2Ni, are aimed to be produced by this technique. In the first part, effect of sintering conditions on synthesis of FeTi was studied. For this purpose, oxide pellets made out of Fe2O3-TiO2 powders were sintered at temperatures between 900 &deg / C &ndash / 1300 &deg / C. Experiments showed that by sintering at 1100 &deg / C, Fe2TiO5 forms and particle size remains comparatively small, which improve the reducibility of the oxide pellet. Experimental studies showed that the reduction of MgO rich MgO-NiO oxide pellet to synthesize Mg2Ni occurs only at extreme deoxidation conditions. Pure MgO remains intact after deoxidation. In contrast to these, pure NiO and NiO rich MgO-NiO mixtures were deoxidized successfully to Ni and MgNi2, respectively. Conductivity measurements address the low conductivity of MgO-rich systems as one of the reasons behind those difficulties in reduction. In the last part, a study was carried out to elucidate the low reducibility of oxides. It is considered that the oxygen permeability becomes important when the reduction-induced volumetric change does not yield fragmentation into solid-state. The approach successfully explains why MgO particles could not be reduced at ordinary deoxidation conditions. The study addresses that Mg layer formed at the surface of MgO particles blocks the oxygen transport between MgO and electrolyte as Mg has low oxygen permeability.

Magnesium (Mg) thin films with various thicknesses ranging from 50 to 1000 nm capped with nominally 20 nm Palladium (Pd) were prepared by a thermal evaporation unit. A total of 25 glass substrates were used in each experiment. The unit had a rotatable macro shutter, rectangular in shape, rotation axes opposite to the Mg source, which allowed controlled exposure of the substrates. Thin films of 50, 100, 150, 200, 300, 400, 500, 600, 800 nm and 1000 nm were produced in a single experiment. Hydrogenation and dehydrogenation of the films were examined using a gas loading chamber which allowed in-situ resistance measurement. Samples were hydrogenated isochronally up to 453 K with a heating rate of 1.5 K/min. Samples cooled to room temperature were subjected to dehydrogenation test. The chamber was taken under vacuum (~10-2 mbar) and the sample was heated up to 453 K at a rate of 1.5 K/min. The results showed that the hydrogenation and dehydrogenation temperatures correlate with the film thickness, thinner films reacting with hydrogen at low temperatures. While 200 nm thin film hydrogenated at 420 K and desorbed it at 423 K, 50 nm thin film hydrogenated at room temperature and desorbed it at 405 K. Thicker films needed higher temperatures to react with hydrogen. It is concluded that films thinner than 200 nm react fully with hydrogen / while a considerable portion of the thicker films remain unreacted. Significance of this is discussed with reference to the design of hydrogen storage systems based on thin films or nanoparticles.

Hydrogen is an appealing energy carrier for clean energy use. However, storage of hydrogen is still the main bottleneck for the realization of an energy economy based on hydrogen. Many materials with outstanding properties have been synthesized with the aim to store enough amount of hydrogen under ambient conditions. Such efforts need guidance from material science, which includes predictive theoretical tools. Carbon nanotubes were considered as promising candidates for hydrogen storage applications, but later on it was found to be unable to store enough amounts of hydrogen under ambient conditions. New arrangements of carbon nanotubes were constructed and hydrogen sorption properties were investigated using state-of-the-art simulation methods. The simulations indicate outstanding total hydrogen uptake (up to 19.0 wt.% at 77 K and 5.52wt.% at 300 K), which makes these materials excellent candidates for storage applications. This reopens the carbon route to superior materials for a hydrogen-based economy. Zeolite imidazolate frameworks are subclass of MOFs with an exceptional chemical and thermal stability. The hydrogen adsorption in ZIFs was investigated as a function of network geometry and organic linker exchange. Ab initio calculations performed at the MP2 level to obtain correct interaction energies between hydrogen molecules and the ZIF framework. Subsequently, GCMC simulations are carried out to obtain the hydrogen uptake of ZIFs at different thermodynamic conditions. The best of these materials (ZIF-8) is found to be able to store up to 5 wt.% at 77 K and high pressure. We expected possible improvement of hydrogen capacity of ZIFs by substituting the metal atom (Zn 2+) in the structure by lighter elements such as B or Li. Therefore, we investigated the energy landscape of LiB(IM)4 polymorphs in detail and analyzed their hydrogen storage capacities. The structure with the fau topology was shown to be one of the best materials for hydrogen storage. Its total hydrogen uptake at 77 K and 100 bar amounts to 7.8 wt.% comparable to the total uptake reported of MOF-177 (10 wt.%), which is a benchmark material for high pressure and low temperature H2 adsorption. Covalent organic frameworks are new class of nanoporous materials constructed solely from light elements (C, H, B, and O). The number of adsorption sites as well as the strength of adsorption are essential prerequisites for hydrogen storage in porous materials because they determine the storage capacity and the operational conditions. Currently, to the best of our knowledge, no experimental data are available on the position of preferential H2 adsorption sites in COFs. Molecular dynamics simulations were applied to determine the position of preferential hydrogen sites in COFs. Our results demonstrate that H2 molecule adsorbed at low temperature in seven different adsorption sites in COFs. The calculated adsorption energies are about 3 kJ/mol, comparable to that found for MOF systems. The gravimetric uptake for COF-108 reached 4.17 wt.% at room temperature and 100 bar, which makes this class of materials promising for hydrogen storage applications.

Computer simulations of metal-organic frameworks are conducted to both investigate the mechanism of hydrogen sorption and to elucidate a detailed, molecular-level understanding of the physical interactions that can lead to successful material design strategies. To this end, important intermolecular interactions are identified and individually parameterized to yield a highly accurate representation of the potential energy landscape. Polarization, one such interaction found to play a significant role in H 2 sorption, is included explicitly for the first time in simulations of metal-organic frameworks. Permanent electrostatics are usually accounted for by means of an approximate fit to model compounds. The application of this method to simulations involving metal-organic frameworks introduces several substantial problems that are characterized in this work. To circumvent this, a method is developed and tested in which atomic point partial charges are computed more directly, fit to the fully periodic electrostatic potential. In this manner, long-range electrostatics are explicitly accounted for via Ewald summation. Grand canonical Monte Carlo simulations are conducted employing the force field parameterization developed here. Several of the major findings of this work are: Polarization is found to play a critical role in determining the overall structure of H 2 sorbed in metal-organic frameworks, although not always the determining factor in uptake. The parameterization of atomic point charges by means of a fit to the periodic electrostatic potential is a robust, efficient method and consistently results in a reliable description of Coulombic interactions without introducing ambiguity associated with other procedures. After careful development of both hydrogen and framework potential energy functions, quantitatively accurate results have been obtained. Such predictive accuracy will aid greatly in the rational, iterative design cycle between experimental and theoretical groups that are attempting to design metal-organic frameworks for a variety of purposes, including H 2 sorption and CO2 sequestration.

In this dissertation, hydrogen storage enhancement in hypercrosslinked polystyrene, effects of single walled carbon nanotubes (SWCNTs) supported ruthenium (Ru) catalyst on the kinetics and ammonia suppression in the LiNH2-MgH2 complex hydride system and the accuracy of hydrogen storage measurements are investigated in detail. High surface area physisorption materials are of interest for room temperature hydrogen storage enhancement by spillover. Six different commercially available hypercrosslinked polystyrenes are screened by considering the specific surface area, average pore size, pore volume, and adsorption enthalpy. MN270 is selected mainly due to its high surface area and narrow pores for investigation of the spillover enhancement at room temperature. Two different platinum (Pt) doped MN270 samples are prepared by wet impregnation (MN270-6wt%Pt) and bridge building technique (MN270-bridged) with an average Pt particle size of 3.9 and 9.9nm, respectively, as obtained from X-ray diffraction analysis. Pt doping altered the surface property of MN270, and reduced the nitrogen and hydrogen uptake at 77 K and 1 atm due to pore blocking. The room temperature hydrogen uptake at 100 atm demonstrated a 10% enhancement for the MN270-bridged (0.36 wt. %) compared to the pristine MN270 (0.32 wt. %), but did not show any enhancement for the MN270-6wt%Pt under the same conditions. The hydrogen uptake of MN270-bridged has little value for practical applications; however, it showed the effectiveness of the bridge building technique. The LiNH2 - MgH2 (2:1.1) complex metal hydride system (Li-Mg-N-H), which is prepared by high energy ball milling, is investigated in terms of the hydrogen ab/desorption kinetics and the concomitant NH3 emission levels. By selecting more intense ball milling parameters, the hydrogen ab/desorption kinetics were improved and the NH3 emission reduced. However, it is shown that NH3 emission cannot be completely eliminated by ball milling. The hydrogen desorption kinetics of the Li-Mg-N-H system is much faster than the absorption kinetics at a specific T and P, but the desorption kinetics degraded considerably over a number of cycles as opposed to the stabilized absorption kinetics. Furthermore, SWCNTs and 20 wt. % Ru doped SWCNTs (SWCNT-20Ru) are utilized as catalysts to study their effects on NH3 emission and kinetics characteristics of the Li-Mg-N-H system. The SWCNT doped sample did not show any kinetics improvement, whereas the SWCNT-20Ru doped sample showed similar kinetics performance as that of the base sample. More importantly, the presence of SWCNT increased the NH3 emission as compared to the base sample. On the other hand, SWCNT-20Ru doping reduced the NH3 emission compared to the SWCNT doping, but did not eliminate it completely. As revealed from the mass spectrometry signals, the SWCNT-20Ru catalyst starts to decompose NH3 at a temperature as low as 200°C. However, an optimal catalyst still needs to be developed by fine tuning the Ru particle size and the SWCNT structural properties to maximize its effectiveness to suppress NH3 release in the Li-Mg-N-H system. The design of a volumetric measurement apparatus is studied by means of an uncertainty analysis to provide guidelines for optimum hydrogen sorption measurements. The reservoir volume should be as small as possible (i.e., 10 cc) to minimize the uncertainty. In addition, the sample mass loading has a profound effect on the uncertainty and the optimum loading is a function of the sample's intrinsic storage capacity. In general, the higher the sample mass loading the lower is the uncertainty, regardless of any other parameters. In cases where the material to be tested is not available in gram quantities, the use of high accuracy pressure and temperature transducers significantly mitigates the uncertainty in the sample's hydrogen uptake. Above all, the thermal equilibration time is an important parameter for high accuracy measurements and needs to be taken into consideration at the start of the measurements. Based on computational analysis, a 5 min wait time is required for achieving thermal equilibrium when the instrument enclosure temperature is different than the ambient temperature.