Abstract In order to make efficient hydrogen storage utilization as a fuel in fuel cell plant, there is need for its effective storage. Previous studies on hydrogen storage considered the hydrogen adsorption/ desorption in radial direction only which is one dimensional approach in this project, two dimensional computational model is implemented in CFD software to simulate the diffusion and heating of hydrogen in both radial and axial directions. The model consists of a system of partial differential equation (PDE) describing two-dimensional heat and mass transfer of hydrogen in porous matrix. Mathematical model was developed to simulate heat and mass transfer in a packed bed reactor with metal hydride as a material for hydrogen absorption and desorption. Importance of bed porosity radial distribution and correct equation for effective thermal conductivity is discussed.

Metal hydrides are used as anode material in nickel metal hydride batteries and are of particular interest because of the potential to be a part of energy systems completely involving renewable sources (e.g. solar power, wind power etc.). Preparation and electrochemical characterization of metal hydride electrodes have not previously been performed at the Department of Chemistry – Ångström Laboratory. Two basic techniques that are desired to be used in the characterization are cyclic voltammetry and chronopotentiometry. This thesis work is aimed at preparation and electrochemical characterization of a metal hydride electrode and, as a complement, study the electrode with X-ray diffraction. LaNi3.55Co0.75Mn0.4Al0.3, a standard material for metal hydride electrodes previously studied by Khaldi et al. was chosen, to ensure that electrochemical absorption of hydrogen was possible, and to be able to compare electrochemical results [1-3]. LaNi3.55Co0.75Mn0.4Al0.3 was synthesized with arc melting, with additional annealing at 900˚C for five days, ground in a cemented carbide ball mill and sieved to less than 56 µm. Electrodes were prepared containing 90 wt.-% of LaNi3.55Co0.75Mn0.4Al0.3 powder, 5 wt.-% of polytetrafluoroethylene and 5 wt.-% of carbon black. The hydrogen absorption and desorption capabilities of the electrode were studied electrochemically with cyclic voltammetry and chronopotentiometry, and the structural changes associated with absorption of hydrogen was studied with X-ray diffraction. The capacity increased, probably from activation of the material, during initial cycling up to the maximum capacity of 294 mAh/g, obtained after 9 cycles, followed by a small decrease, probably caused by corrosion and passivation of the material, in capacity of the remaining 11 cycles. Activation of the material causes the charge and the discharge potential to shift to a more positive and a more negative value, respectively. The final values for the charge potential and the discharge potential were -841mV and -945 mV vs. Hg/HgO, respectively, after 16 cycles. Khalid et al. [1-3]reported a maximum capacity of 300 mAh/g, a charge potential of about -960 mV and a discharge potential of about -840 mV after 16 cycles the results obtained in this study are considered to be in good agreement with those reported. X-ray diffraction of the electrodes revealed, as expected, a cell volume change of the charged electrode compared to the discharged electrode. The change in cell volume corresponds to an estimated capacity of 303 mAh/g, which is very close to the, above mentioned, electrochemically obtained maximum capacity of 294 mAh/g.

Dissertation (Ph.D.)--University of Toledo, 2005. / Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Engineering." Bibliography: leaves 61-63.

Thesis (M. Sc. (Chemistry)) --University of Limpopo, 2019. / Metal alloys are one of few materials that are capable of acting as catalyst precursors in Sabatier reactions, reducing poisonous CO2 gas into different useful hydrocarbons. However, optimal reduction of CO2 through these materials takes place at relatively elevated temperatures due to poisoning-intolerance and deterioration of hydrogen absorption/desorption kinetics resulting from the surface chemical action of electrophilic gases at lower or room temperature. This work presents results of the feasibility study focused on improving hydriding kinetics and poisoning-tolerance, which are prerequisites properties that a material should possess to be a suitable catalyst precursor for Sabatier reaction, of the metal hydride (MH) materials. The studies in this work included: (i) element substitution and (ii) surface modification procedure. The substrate alloys investigated had the compositions LaNi4.8-xSnx and TiMn1.52, where x was 0.2. The activation performances of the materials were estimated by measurement of H2 absorption kinetics in the absence of vacuum heating, after long-term exposure to air. The presence of oxide layers on the alloy surface resulted in the deterioration of H sorption kinetics for the parent alloys. To overcome impurity effects, surface-modification technique through autocatalytic palladium deposition was employed. The activation performances and kinetics of the surface-modified were found to be superior to that of the unmodified AB2 and AB5 alloys. Based on this observation, it was seen that surface-modified MH materials based on the alloy substrate and Pd nanostructured coatings may be utilised as catalysts precursors for CO2 reduction into hydrocarbons.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references.

Hydrogen diffusion is investigated in a 50 nm film of vanadium and a vanadium superlattice. Diffusion constants for three different temperature and pressure pairs are determined for the 50 nm film. The diffusion constants for the temperature and pressure pairs are determined to be 4.5 $\pm$ 0.1 $\cdot 10^{-5} \text{ cm}^{-2}$ at 463 K and 0.05 H/V, 5.6 $\pm$ 0.1 $\cdot 10^{-5} \text{ cm}^{-2}$ at 463 K and 0.12 H/V and 8.0 $\pm$ 0.2 $\cdot 10^{-5} \text{ cm}^{-2}$ at 493 K and 0.05 H/V. The temperature and concentration dependence of the diffusion constants are determined. A concentration dependence of the diffusion constant is found with a higher rate of diffusion for a higher hydrogen concentration. The activation energy of chemical diffusion is determined to be 0.38 $\pm$ 0.03 eV.

Thesis (Ph.D.)--University of Wollongong, 2003. / Typescript. Includes bibliographical references: leaf 151-160.

abstract: The discovery of the superconductor MgB2 led to the increase of research activity for more compounds adopting the AlB2 structure type and containing superconductive properties. The prominent successor compounds were the silicide systems, AeAlSi (Ae=Sr, Ba, Ca). Presented here is an extension of this investigation to the germanides, SrAlGe and BaAlGe. The ternary structures were synthesized through arc-melting elemental stoichiometric mixtures and structurally characterized by x-ray powder diffraction. Both crystallize as the hexagonal SrPtSb structure type, a variant of the AlB2 structure type. The low temperature region was measured on a Vibrating Sample Magnetometer (VSM) and both present the onset of superconductivity below 7K. These compounds are susceptible to hydrogen absorption and the new polyanionic hydrides, SrAlGeH and BaAlGeH, structural and dynamic properties are presented. The hydrides were synthesized via two distinct methods. One method is the reaction of SrH2 (BaH2) with elemental mixture of the Al and Ge under pressurized hydrogen and the other is a hydrogenation of the SrAlGe and BaAlGe. Both crystallize in the trigonal SrAlSiH structure type, as determined from Rietveld analysis on powder neutron diffraction measurements. The hydrogen is coordinated by both the active metal and aluminum atoms, providing a unique environment for studying metal-hydrogen interactions. When exposed to air, both the hydrides and alloys transform from a crystalline grey to an amorphous yellow powder accompanied by a dramatic volume increase. Infrared spectroscopy shows the disappearance of the bands associated with the Al-H bond and the appearance of Ge-H and O-H bands. This indicates the material reacts with atmospheric water. / Dissertation/Thesis / M.S. Chemistry 2011

Philosophiae Doctor - PhD / Today fossil fuels such as oil, coal and natural gas are providing for our ever growing energy needs. As the world’s fossil fuel reserves fast become depleted, it is vital that alternative and cleaner fuels are found. Renewable energy sources are the way of the future energy needs. A solution to the looming energy crisis can be found in the energy carrier hydrogen. Hydrogen can be produced by a number of production technologies. One hydrogen production method explored in this study is electrolysis of water.

Waste streams of hydrogen and helium mixtures are produced at the Kennedy Space Center during purging of the hydrogen systems and supply lines. This process is done prior to and after hydrogen servicing. The purged waste gases are lost to the atmosphere, resulting in an annual loss of 2 million and 0.1 million standard cubic meters of helium and hydrogen, respectively. Recovery of these gases will have an economic benefit. Metals, alloys, and intermetallics are known to react with hydrogen in favorable conditions; therefore, they have the possibility of serving as separating and recovery agents. In this study, Mg2Ni, VTiNi and LaNi5 were studied for the separation of H2 from He, using differential scanning calorimetry and thermal volumetric analysis. The ability of LaNi5 to react with hydrogen reversibly at room temperature was verified, and further analysis focused on this compound. Size reduction and activation of LaNi5 by mechanical milling was investigated using different milling parameters for the purpose of activating the material for hydrogen absorption. Because it has been shown that addition of aluminum to LaNi5 resulted in improved hydriding and dehydriding properties, that system was studied further here. In this study, aluminum was added to LaNi5 by mechanical milling. Hydriding properties and elemental compositions of the samples were determined afterwards. The hydrogen absorption rate and capacity were compared to that of LaNi5. Both LaNi5 and its Al doped derivatives exhibited a reduced rate of hydrogen uptake and a reduced hydrogen capacity in the presence of helium. The effects of coating the samples with either gold-palladium or platinum were investigated. It was observed that coating the samples with Pt reduced the negative effect of He, whereas AuPd coating did not have any effect. Larger scale studies were done using a continuous U-tube hydride reactor, built and tested for separation of H2¬ from a 20:80 H2:He mixture. The amount of hydrogen retained in the bed was determined and found to be less than that for the batch systems.