Magnesium hydride is a promising candidate for solid-state hydrogen storage and thermal energy storage applications. A series of Ti-based intermetallic alloy (TiAl, Ti3Al, TiNi, TiFe, TiNb, TiMn2, and TiVMn)-doped MgH2 materials were systematically investigated in this study to improve its hydrogen storage properties. The dehydrogenation and hydrogenation properties were studied by using both thermogravimetric analysis and pressure–composition–temperature (PCT) isothermal to characterize the temperature of dehydrogenation and the kinetics of both desorption and absorption of hydrogen by these doped MgH2. Results show significant improvements of both dehydrogenation and hydrogenation kinetics as a result of adding the Ti intermetallic alloys as catalysts. In particular, the TiMn2-doped Mg demonstrated extraordinary hydrogen absorption capability at room temperature and 1 bar hydrogen pressure. The PCT experiments also show that the hydrogen equilibrium pressures of MgH2 were not affected by these additives.

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The effects of high-energy ball-milling on catalyst morphology and dispersion as a function of milling duration and on hydrogen desorption were investigated. Samples of MgH 2 doped with 0.05 Ni catalyst were examined after 1, 5, and 10 hours of milling. Longer milling durations produced finer catalyst particle sizes and more uniform dispersions, but yielded higher hydrogen desorption temperatures. This behavior is attributed to the formation of Mg 2 NiH 4 with increased milling times. Electron tomography was used to show that the Ni particles reside both inside and outside the MgH 2 particles. On dehydrogenation there was a redistribution of catalyst and continued formation of Mg 2 Ni. The formation of this phase is proposed to explain the reported degradation of hydrogen capacity and the change in kinetics of this system with cycling.

Thermodynamic destabilization of magnesium hydride is a difficult task that has challenged researchers of metal hydrides for decades. In this work, solid solution alloys of magnesium were exploited as a way to destabilize magnesium hydride thermodynamically. Various elements were alloyed with magnesium to form solid solutions, including: indium (In), aluminum (Al), gallium (Ga), and zinc (Zn). Thermodynamic properties of the reactions between the magnesium solid solution alloys and hydrogen were investigated. Equilibrium pressures were determined by pressure−composition−isothermal (PCI) measurements, showing that all the solid solution alloys that were investigated in this work have higher equilibrium hydrogen pressures than that of pure magnesium. Compared to magnesium hydride, the enthalpy (ΔH) of decomposition to form hydrogen and the magnesium alloy can be reduced from 78.60 kJ/(mol H 2 ) to 69.04 kJ/(mol H 2 ), and the temperature of 1 bar hydrogen pressure can be reduced to 262.33 °C, from 282.78 °C, for the decomposition of pure magnesium hydride. Further, in situ XRD analysis confirmed that magnesium solid solutions were indeed formed after the dehydrogenation of high-energy ball-milled MgH 2 with the addition of the solute element(s). XRD results also indicated that intermetallic phases of Mg with the solute elements were present along with MgH 2 in the rehydrogenated magnesium solid solution alloys, providing a reversible hydrogen absorption/desorption reaction pathway. However, the alloys were shown to have lower hydrogen storage capacity than that of pure MgH 2 .

Magnesium hydride is one of the most promising candidates for solid-state hydrogen storage and thermal energy storage applications. The effects of V-based solid solution alloys on the hydrogenation and dehydrogenation behavior of magnesium hydride are studied. Significant reduction of the dehydrogenation temperature and improvements of the kinetics of both absorption and desorption reactions were observed for MgH 2 with V-based additives. Those observations were made using thermogravimetric analysis (TGA) and pressure−composition−temperature (PCT) techniques. In situ synchrotron X-ray diffraction (XRD) measurements suggest that the additives functioned as catalysts during the reactions. The comparison of the characteristics of different additives suggested that the hydrogen equilibrium pressures of those additives themselves have a significant bearing on their effects on the kinetic behaviors of MgH 2 . The lower is the stability of an additive as a hydride, the more effective it would be as a catalyst.