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Abstract: The thermodynamics of hydrogenation for the Ti1−x Zr x MnCr (x =0, 0.1, 0.2, 0.32, 0.5, 0.7, 0.9, 1.0) alloys, which are characterized by the XRD Rietveld analysis as C14-type Laves phase, are evaluated by P–C isotherms measurements at different temperatures. Along with the increase of Zr content in the alloys, the pressure of the absorption/desorption plateau decreases monotonously; the average value of ǀΔHǀ increases linearly, and the average value of ǀΔSǀ decreases slightly; on the other hand, the hysteresis of hydrogenation reduces to a minimum at x =0.32, and then rises again; the slope of the plateau increases first, then decreases, forming a maximum at x =0.5. For the hydride formation of the Ti1−x Zr x MnCr alloys, the values of ǀΔHǀ and ǀΔSǀ increase with the hydrogen concentration, except for that of the Ti0.8Zr0.2MnCr, where an opposite trend occurs, but all the ǀΔHǀ values in the Ti1−x Zr x MnCr–H2 system are considerably lower than those in most Laves phase hydride systems. As combined effects of these trends, the Ti0.5Zr0.5MnCr alloy with the highest microstrain induced from the greatest mismatch of different atoms in the lattice, possesses the greatest plateau slope and the smallest variation width of ǀΔHǀ for the hydride formation; on the other hand, the Ti0.68Zr0.32MnCr alloy exhibits the best hydrogen storage properties, with a reversible hydrogen capacity of 216ml/g, and good plateau characteristics. [Copyright &y& Elsevier]

The increasing severity of global climate and energy problems has made renewable energy an inevitable choice for achieving a low-carbon society. Hydrogen is regarded as one of the most promising renewable energy due to its excellent characteristics, such as abundant and extensive resources, high calorific value, and non-pollution. How to achieve efficient hydrogen storage is one of the main hot spots of hydrogen energy research. For on-board hydrogen storage systems, which could be used for portable power sources and fuel cell vehicles, how to store hydrogen safely and effectively is one of the most urgent technological bottlenecks to overcome. The solid-state storage based on hydrogen storage materials has the advantages of low hydrogen storage pressure, high energy efficiency, safety and reliability, compared to conventional compressed hydrogen and cryogenic liquid hydrogen storage methods. It may be one of the most promising solutions to solve the above problems. Among the hydrogen storage materials, the lightweight composite hydrides Li–Mg–N–H system holds great promise for vehicular hydrogen storage applications owing to its moderate thermodynamic properties (∆Hdes ~ 44 kJ mol−1 H2 and ∆Sdes ~ 112 J mol−1 H2·K) and relatively high hydrogen capacity (~ 5.6 wt%). However, the Li–Mg–N–H material itself has poor cycling performance and a high energy barrier, resulting in a low dehydrogenation rate and high operating temperature. Apart from this, the multi-field coupling of mass and energy transfer also poses a challenge, hindering its on-board applications. In this paper, we present the modification methods and research status of the Li–Mg–N–H system's hydrogen storage materials. The effects of composition modification, nanocrystallization and catalyst addition on the thermal/kinetic properties of hydrogen storage materials in the Li–Mg–N–H system are expounded. The difficulties and directions for enhancing the hydrogen storage performance of Li–Mg–N–H system are discussed. [ABSTRACT FROM AUTHOR]

The research on safe and efficient hydrogen storage methods is the key scientific and technological issue which restricts the implementation of hydrogen economy. Lithium amidoborane (LiNH2BH3) has received extensive attention for its excellent hydrogen storage properties. It can desorb 10.9 wt% of hydrogen below 100 °C without deleterious by-product such as borazine. What is more, it is chemically stable at room-temperature conditions. The preparation methods and crystal structure of LiNH2BH3 were reviewed at length in this paper, and its dehydrogenation performance and mechanisms were analyzed combined with the theoretical calculation results. Moreover, the barriers and improvement measures in hydrogen release thermodynamics/kinetics and regeneration of the spent fuel were summarized. It is proposed that reducing the synthesis cost, decreasing dehydrogenation temperature with increased rates, and exploring high-efficiency, low-energy consumption, and low-cost regeneration techniques are the critical striving directions of lithium amidoborane. To the best of our knowledge, this work is the first review focusing on LiNH2BH3, one of the most promising materials for onboard hydrogen storage application, which is expected to give clues for the next advance of LiNH2BH3. [ABSTRACT FROM AUTHOR]

Mg-20 wt% Ti x Cr 0.8-x V 0.2 (x = 0.25, 0.35, 0.45, 0.55) nanocomposites were synthesized by Reactive Ball Milling (RBM) under 5.0 MPa H 2 for 8 h at room temperature. The morphology, crystal structure, and isothermal hydrogen ab-/desorption properties of the as-milled nanocomposites were investigated. X-ray diffraction confirms that the composites were composed of nanocrystalline β-MgH 2 , γ-MgH 2 and Ti-Cr-V 0.2 H y (1.91 < y < 2.01) phases. High-Resolution Transmission Electron Microscopy (HRTEM) images reveal that nanocrystalline β-MgH 2 , γ-MgH 2 and Ti 0.35 Cr 0.45 V 0.2 H y phases coexist on nano-level in the as-milled composites. Differential scanning calorimeter (DSC) results show that MgH 2 -20 wt% Ti 0.35 Cr 0.45 V 0.2 composite presents the minimum decomposition temperature (256 °C) among the studied composites and a relatively low activation energy of 86.43 kJ/mol. The hydrogen desorption capacity of MgH 2 -20 wt% Ti 0.35 Cr 0.45 V 0.2 composite reach to 5.30 wt% within 20 min at 270 °C under 0.01 MPa H 2 , compared with that only 0.1 wt% H 2 for pure MgH 2 powders under the same conditions. Besides, the hydrogenation and dehydrogenation enthalpies are determined to be −69.35 and 70.60 kJ/(mol⋅H 2) respectively, which show a significant decrease compared with that of Mg/MgH 2 systems. More importanly, the β-MgH 2 phase is found to decompose along with γ-MgH 2 and Ti-Cr-V 0.2 H y phases at the temperature ranging from 210 to 270 °C. It reveals the favorable synergetic desorption effect among γ-MgH 2 , β-MgH 2 and Ti 0.35 Cr 0.45 V 0.2 H y phases, which possibly leads to better dehydrogenation kinetics and thermodynamics properties of Mg/MgH 2 systems. Nanocrystalline Mg-20wt%Ti x Cr 0.8-x V 0.2 composites were synthesized. Highest content of metastable γ-MgH 2 phase(36.19wt%) was obtained. The desorption temperature of Mg-20wt%Ti 0.35 Cr 0.45 V 0.2 is 84 °C lowers than pure MgH2. Good synergetic desorption effect among Ti 0.35 Cr 0.45 V 0.2 Hy, γ-MgH2 and β-MgH2 phases. [ABSTRACT FROM AUTHOR]