The present work reports a study of the effects of the formation of a nanostructure induced by high-energy ball milling, compositions, and various catalytic additives on the hydrogen storage properties of LiNH2-LiH and LiNH2-MgH2 systems. The mixtures are systematically investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and a Sieverts-type apparatus. The results indicate that microstructural refinement (particle and grain size) induced by ball milling affects the hydrogen storage properties of LiNH2-LiH and LiNH2-MgH2 systems. Moreover, the molar ratios of the starting constituents can also affect the dehydrogenation/hydrogenation properties. In the LiNH2-LiH system, high-energy ball milling is applied to the mixtures of LiNH2 and LiH with molar ratios of 1:1, 1:1.2 and 1:1.4 LiH. The lowest apparent activation energy is observed for the mixture of LiNH2-LiH (1:1.2) milled for 25 h. The major impediment in the LiNH2-LiH system is the hydrolysis and oxidation of LiH, which causes a fraction of LiH to be inactive in the intermediate reaction of NH3+LiH→LiNH2+H2. Therefore, the LiNH2-LiH system always releases NH3, as long as a part of LiH becomes inactive, due to hydrolysis/oxidation, and does not take part in the intermediate reaction. To prevent LiH from undergoing hydrolysis/oxidation during desorption/absorption, 5 wt. % graphite is incorporated in the (LiNH2+1.2LiH) system. The DSC curve of the mixture does not show a melting peak of retained LiNH2, indicating that graphite can prevent or at least substantially reduce the oxidation/hydrolysis of LiH. Moreover, compared to the mixture without graphite, the mixture with graphite shows more hydrogen capacity, thus this mixture desorbs ~5 wt.% H2, which is close to the theoretical capacity. This system is fully reversible in the following reaction: LiNH2+LiH→Li2NH+H2. However, the equilibrium temperature at the atmospheric pressure of hydrogen (0.1 MPa H2) is 256.8°C for (LiNH2+1.2LiH) mixture, which is too high for use in onboard applications. To overcome the thermodynamic barrier associated with the LiNH2/LiH system, LiH is substituted by MgH2; therefore, the (LiNH2+nMgH2) (n=0.55, 0.6 and 0.7) system is investigated first. These mixtures are partially converted to Mg(NH2)2 and LiH by the metathesis reaction upon ball milling. In this system, hydrogen is desorbed in a two-step reaction: [0.5xMg(NH2)2+xLiH]+[(1-x)LiNH2+(0.5-0.5x)MgH2]→0.5Li2Mg(NH)2+1.0H2 and 0.5Li2Mg(NH)2+MgH2→0.5Mg3N2+LiH+H2. Moreover, this system is fully reversible in the following reaction: Li2Mg(NH)2+2H2→ Mg(NH2)2+2LiH. Step-wise desorption tests show that the enthalpy and entropy change of the first reaction is -46.7 kJ/molH2 and 136.1 J/(molK), respectively. The equilibrium temperature at 0.1 bar H2 is 70.1°C, which indicates that this system has excellent potential for onboard applications. The lowest apparent activation energy of 71.7 kJ/mol is observed for the molar ratio of 1:0.7MgH2 milled for 25 h. This energy further decreases to 65.0 kJ/mol when 5 wt.% of n-Ni is incorporated in the system. Furthermore, the molar ratio of MgH2/LiNH2 is increased to 1.0 and 1.5 to increase the limited hydrogen storage capacity of the (LiNH2+0.7MgH2) mixture. It has been reported that the composition changes can enhance the hydrogen storage capacity by changing the dehydrogenation/hydrogenation reaction pathways. However, theoretically predicted LiMgN is not observed, even after dehydrogenation at 400°C. Instead of this phase, Li2Mg(NH)2 and Mg3N2 are obtained by dehydrogenation at low and high temperatures, respectively, regardless of the milling mode and the molar ratio of MgH2/LiNH2. The only finding is that the molar ratio of MgH2/LiNH2 can significantly affect mechano-chemical reactions during ball milling, which results in different reaction pathways of hydrogen desorption in subsequent heating processes; however, the reaction’s product is the same regardless of the milling mode, the milling duration and their composition. Therefore, the (LiNH2+0.7MgH2) mixture has the greatest potential for onboard applications among Li-Mg-N-H systems due to its high reversible capacity and good kinetic properties.

The present work reports a study of the effects of the formation of a nanostructure induced by high-energy ball milling, compositions, and various catalytic additives on the hydrogen storage properties of LiNH2-LiH and LiNH2-MgH2 systems. The mixtures are systematically investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and a Sieverts-type apparatus. The results indicate that microstructural refinement (particle and grain size) induced by ball milling affects the hydrogen storage properties of LiNH2-LiH and LiNH2-MgH2 systems. Moreover, the molar ratios of the starting constituents can also affect the dehydrogenation/hydrogenation properties. In the LiNH2-LiH system, high-energy ball milling is applied to the mixtures of LiNH2 and LiH with molar ratios of 1:1, 1:1.2 and 1:1.4 LiH. The lowest apparent activation energy is observed for the mixture of LiNH2-LiH (1:1.2) milled for 25 h. The major impediment in the LiNH2-LiH system is the hydrolysis and oxidation of LiH, which causes a fraction of LiH to be inactive in the intermediate reaction of NH3+LiH→LiNH2+H2. Therefore, the LiNH2-LiH system always releases NH3, as long as a part of LiH becomes inactive, due to hydrolysis/oxidation, and does not take part in the intermediate reaction. To prevent LiH from undergoing hydrolysis/oxidation during desorption/absorption, 5 wt. % graphite is incorporated in the (LiNH2+1.2LiH) system. The DSC curve of the mixture does not show a melting peak of retained LiNH2, indicating that graphite can prevent or at least substantially reduce the oxidation/hydrolysis of LiH. Moreover, compared to the mixture without graphite, the mixture with graphite shows more hydrogen capacity, thus this mixture desorbs ~5 wt.% H2, which is close to the theoretical capacity. This system is fully reversible in the following reaction: LiNH2+LiH→Li2NH+H2. However, the equilibrium temperature at the atmospheric pressure of hydrogen (0.1 MPa H2) is 256.8°C for (LiNH2+1.2LiH) mixture, which is too high for use in onboard applications. To overcome the thermodynamic barrier associated with the LiNH2/LiH system, LiH is substituted by MgH2; therefore, the (LiNH2+nMgH2) (n=0.55, 0.6 and 0.7) system is investigated first. These mixtures are partially converted to Mg(NH2)2 and LiH by the metathesis reaction upon ball milling. In this system, hydrogen is desorbed in a two-step reaction: [0.5xMg(NH2)2+xLiH]+[(1-x)LiNH2+(0.5-0.5x)MgH2]→0.5Li2Mg(NH)2+1.0H2 and 0.5Li2Mg(NH)2+MgH2→0.5Mg3N2+LiH+H2. Moreover, this system is fully reversible in the following reaction: Li2Mg(NH)2+2H2→ Mg(NH2)2+2LiH. Step-wise desorption tests show that the enthalpy and entropy change of the first reaction is -46.7 kJ/molH2 and 136.1 J/(molK), respectively. The equilibrium temperature at 0.1 bar H2 is 70.1°C, which indicates that this system has excellent potential for onboard applications. The lowest apparent activation energy of 71.7 kJ/mol is observed for the molar ratio of 1:0.7MgH2 milled for 25 h. This energy further decreases to 65.0 kJ/mol when 5 wt.% of n-Ni is incorporated in the system. Furthermore, the molar ratio of MgH2/LiNH2 is increased to 1.0 and 1.5 to increase the limited hydrogen storage capacity of the (LiNH2+0.7MgH2) mixture. It has been reported that the composition changes can enhance the hydrogen storage capacity by changing the dehydrogenation/hydrogenation reaction pathways. However, theoretically predicted LiMgN is not observed, even after dehydrogenation at 400°C. Instead of this phase, Li2Mg(NH)2 and Mg3N2 are obtained by dehydrogenation at low and high temperatures, respectively, regardless of the milling mode and the molar ratio of MgH2/LiNH2. The only finding is that the molar ratio of MgH2/LiNH2 can significantly affect mechano-chemical reactions during ball milling, which results in different reaction pathways of hydrogen desorption in subsequent heating processes; however, the reaction’s product is the same regardless of the milling mode, the milling duration and their composition. Therefore, the (LiNH2+0.7MgH2) mixture has the greatest potential for onboard applications among Li-Mg-N-H systems due to its high reversible capacity and good kinetic properties.

Over the past few years, the need for a clean and renewable fuel has sharply risen. This is due to increasing fossil fuel costs and the desire to limit or eliminate harmful by-products which are created during the burning of these fuels. Hydrogen is the most abundant element in the universe and can be used in either fuel cells or traditional internal combustion engines to produce energy with no harmful emissions. One of the main obstacles facing the implementation of a hydrogen economy is its storage. Classical methods of storage involve either high and unsafe pressures or liquid storage involving a large amount of energy. Two alternative hydrogen storage methods are investigated - physisorption, which is the weak chemical bonding to a material, as well as chemisorption, which is a strong chemical bond of hydrogen to a host material. Polyaniline, a conducting polymer, is investigated in both its bulk form as well as in nanostructured forms, more precisely nanofibers and nanospheres, to store hydrogen via physisorption. It is found the bulk form of polyaniline can store only approximately 0.5wt.% hydrogen, which is far short of the 6wt.% required for practical applications. Nanofibers and nanospheres, however, have been developed, which can store between 4wt.% and 10wt.% of hydrogen at room temperature with varying kinetics. A new complex metal hydride comprised of LiBH4, LiNH2 and MgH2 has been developed to store hydrogen via chemisorption. While the parent compounds require high temperatures and suffer of slow kinetics for hydrogen sorption, the work performed as part of this dissertation shows that optimized processing conditions reduce the hydrogen release temperature from 250°C to approximately 150°C, while the addition of nano sized materials has been found to increase the kinetics of hydrogen sorption as well as further decrease the hydrogen release temperature, making this one of the first viable hydrogen storage materials available. This is the first time that nanostructured polyaniline has been investigated for its hydrogen performance. Additionally, the thorough investigation of the effects of nano sized additives and processing parameter optimization of the multinary hydride are first reported in this dissertation.

The present work reports a study of the effects of the compositions, and various catalytic additives and nanostructuring by high-energy ball milling, on the hydrogen storage properties of LiBH4, NaBH4, LiNH2 and LiAlH4 complex hydrides and their composites. The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric nickel (n-Ni) added as a potential catalyst were synthesized by ball milling. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. In the (LiNH2+nMgH2) system, the phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2+nMgH2), having molar ratios n=0.5 to 2.0, have been thoroughly studied. The milling energy is estimated by a semi-empirical method. The results show that for the molar ratios n<1.0 three new phases such as LiH, amorphous Mg(NH2)2 (a-Mg(NH2)2) and Li2Mg(NH)2 are formed during ball milling depending on the injected energy. For the molar ratios n≥1.0 the new phase of MgNH forms whose formation is accompanied by a profound release of hydrogen. Addition of 5 %wt. KH can improve desorption rate of the LiNH2+0.5 MgH2 system. Furthermore this hydride system can be nearly fully rehydrogenated at 200°C and 50 bar H2 pressure. LiAlH4 containing 5 wt.% of nanometric Fe and Ni shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H2) during ball milling. X-ray diffraction studies show that Fe and Ni ions dissolve in the lattice, replacing the Al ions and forming a substitutional solid solution. Both Fe and Ni decrease the activation energies of stage I and II , but stage I is more sensitive to the particle size . The addition of 5 wt.% nano-size “interstitial compound” (n-TiC, n-TiN and n-ZrC) shows a continuous desorption of H2 is observed during high energy milling. Mechanical dehydrogenation rate of the doped samples increases noticeably during high-energy ball milling in the order of TiN > TiC > ZrC. The interstitial compound additives are able to strongly reduce the activation energy of Stage II dehydrogenation but do not substantially affect the apparent activation energy of Stage I .

The present work reports a study of the effects of the compositions, and various catalytic additives and nanostructuring by high-energy ball milling, on the hydrogen storage properties of LiBH4, NaBH4, LiNH2 and LiAlH4 complex hydrides and their composites. The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric nickel (n-Ni) added as a potential catalyst were synthesized by ball milling. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. In the (LiNH2+nMgH2) system, the phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2+nMgH2), having molar ratios n=0.5 to 2.0, have been thoroughly studied. The milling energy is estimated by a semi-empirical method. The results show that for the molar ratios n<1.0 three new phases such as LiH, amorphous Mg(NH2)2 (a-Mg(NH2)2) and Li2Mg(NH)2 are formed during ball milling depending on the injected energy. For the molar ratios n≥1.0 the new phase of MgNH forms whose formation is accompanied by a profound release of hydrogen. Addition of 5 %wt. KH can improve desorption rate of the LiNH2+0.5 MgH2 system. Furthermore this hydride system can be nearly fully rehydrogenated at 200°C and 50 bar H2 pressure. LiAlH4 containing 5 wt.% of nanometric Fe and Ni shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H2) during ball milling. X-ray diffraction studies show that Fe and Ni ions dissolve in the lattice, replacing the Al ions and forming a substitutional solid solution. Both Fe and Ni decrease the activation energies of stage I and II , but stage I is more sensitive to the particle size . The addition of 5 wt.% nano-size “interstitial compound” (n-TiC, n-TiN and n-ZrC) shows a continuous desorption of H2 is observed during high energy milling. Mechanical dehydrogenation rate of the doped samples increases noticeably during high-energy ball milling in the order of TiN > TiC > ZrC. The interstitial compound additives are able to strongly reduce the activation energy of Stage II dehydrogenation but do not substantially affect the apparent activation energy of Stage I .

Here we present the development of an aluminium alloy based hydrogen storage tank, charged with Ti-doped sodium aluminium hexahydride Na3AlH6. This hydride has a theoretical hydrogen storage capacity of 3 mass-% and can be operated at lower pressure compared to sodium alanate NaAlH4. The tank was made of aluminium alloy EN AW 6082 T6. The heat transfer was realised through an oil flow in a bayonet heat exchanger, manufactured by extrusion moulding from aluminium alloy EN AW 6060 T6. Na3AlH6 is prepared from 4 mol-% TiCl3 doped sodium aluminium tetrahydride NaAlH4 by addition of two moles of sodium hydride NaH in ball milling process. The hydrogen storage tank was filled with 213 g of doped Na3AlH6 in dehydrogenated state. Maximum of 3.6 g (1.7 mass-% of the hydride mass) of hydrogen was released from the hydride at approximately 450 K and the same hydrogen mass was consumed at 2.5 MPa hydrogenation pressure. 45 cycle tests (rehydrogenation and dehydrogenation) were carried out without any failure of the tank or its components. Operation of the tank under real conditions indicated the possibility for applications with stationary HT-PEM fuel cell systems.