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In this study, the hydrogen desorption properties for the reactions between 1 mol% MNH-added (M = Li, Na, and K) lithium hydride and NH (0.5 MPa, NH/LiH = 1 mol/mol) at 100 °C were systematically investigated to design a LiH-NH hydrogen storage system with better kinetic properties. It is found that all of the alkali metal amide additives can improve the hydrogen desorption kinetics of the LiH-NH system, among which, LiNH shows the best effect. As compared to the other LiNH-added composition, the 1 mol% LiNH-added composition shows the best effect on improving the desorption kinetics of the LiH-NH system. According to the kinetic analysis, it is proposed that the effect of LiNH on the hydrogen desorption kinetics would be mainly due to physical effect. [ABSTRACT FROM AUTHOR]

Reactions between alkali metal hydrides MH (M = Li, Na, or K) and carbon dioxide (CO 2 ) at room temperature were systematically investigated for the first time. It was found that the raw alkali metal hydrides did not react with CO 2 under static-pressure conditions at room temperature, but the mechanically activated alkali metal hydrides reacted with CO 2 and released large amounts of hydrogen (H 2 ). Under the same ball-milling conditions, the order of reactivity of the alkali metal hydrides with CO 2 was KH > NaH > LiH. The particle size of the activated alkali metal hydrides had a large influence on the reactivity of the alkali metal hydrides with CO 2 . During the reactions, CO 2 was reduced by alkali metal hydrides, generating elemental carbon, alkali metal oxides and H 2 , and it was consumed by alkali metal oxides, forming carbonates. [ABSTRACT FROM AUTHOR]

In this study, the superior effect of RbF on reducing the hydrogen desorption operating temperature of the Li N H system was demonstrated. By doping 5 mol% RbF in the LiNH 2 LiH system, we obtain the lowest hydrogen desorption peak temperature (211 °C) at a heating rate of 5 °C/min, which is approximately 69 °C lower than that of the pristine LiNH 2 LiH system. Moreover, the system starts to desorb H 2 at 120 °C, which is the lowest hydrogen desorption onset temperature. The hydrogen desorption peak and onset temperatures can be further decreased by doping more RbF. It is proposed that the RbH produced during heat treatment improves the dehydrogenation properties of the RbF-doped LiNH 2 LiH sample. [ABSTRACT FROM AUTHOR]

Ammonia is a vital intermediate in the hydrogen desorption process of Metal-N-H system. KH has strong reactivity with NH 3 to form KNH 2. We speculate that KNH 2 is also an intermediate formed during hydrogen desorption of the potassium-doped M-N-H systems. In this research, the dehydrogenation performance of the KNH 2 -doped LiNH 2 and LiH composition was first studied. Compared with the broad dehydrogenation curve of the composite material of LiNH 2 and LiH without the catalyst, the dehydrogenation curve of 0.05 mol KNH 2 -doped composite material was significantly narrowed. The initial and peak dehydrogenation temperature of the composite to which 0.05 mol of KNH 2 was added was lowered remarkably. Besides, the cyclic dehydrogenation properties of the LiNH 2 and LiH system was also significantly enhanced by the introduction of KNH 2. The cyclic conversion of KNH 2 to KH is the main reason for the enhancement of the hydrogen evolution performance of the LiNH 2 –LiH system doped with KNH 2. We found the KNH 2 -doped Li–N–H system exhibits similar dehydrogenation property with that of the KH-doped Li–N–H system. This work proves that KNH 2 plays a key role in improving the hydrogen desorption performances of the potassium-doped M-N-H systems. Image 1 • Hydrogen desorption properties of the KNH 2 -doped Li–N–H system was examined. • Hydrogen desorption kinetics are significantly enhanced by introducing KNH 2. • The dehydrogenation temperature is lowered drastically. • The improved properties induce from the cyclic conversion from KNH 2 to KH. • KNH 2 may be formed during dehydrogenation of the potassium-doped M-N-H system. [ABSTRACT FROM AUTHOR]

We report an efficient, convenient, solution-free method to achieve the room-temperature dehydrogenation of alkaline earth metal hydrides (MgH 2 and CaH 2). It is found, for the first time, that metal carbonates, which are readily available and cheap, can efficiently induce the hydrogen desorption of alkaline earth metal hydrides at room temperature under mechanical ball milling conditions. We demonstrate that the hydrogen yield and purity mainly depend on the nature of metal carbonates, rate and duration of ball milling, and reaction mixture composition. The best performances are obtained with the systems of MgCO 3 -MgH 2 and MgCO 3 -CaH 2 milled at 350 ​rpm for 12 ​h, with the CO x -free hydrogen yield of 94% and 90%. This work opens a new way to achieve the efficient dehydrogenation of alkaline earth metal hydrides at room temperature. It is found, for the first time, that metal carbonates can efficiently induce the hydrogen desorption of alkaline earth metal hydrides (MgH 2 and CaH 2) at room temperature under mechanical ball milling condition. Image 1 • Metal carbonates can induce the dehydrogenation of MgH 2 and CaH 2 at room temperature. • Hydrogen yield depends on the nature of metal carbonate and duration of ball milling. • Hydrogen yield also depends on rate of ball milling and reaction mixture composition. • For MgCO 3 -added MgH 2 and CaH 2 , hydrogen yields are achieved as high as 94% and 90%. • The work opens a new way to achieve the dehydrogenation of MgH 2 and CaH 2. [ABSTRACT FROM AUTHOR]