Hydrazine borane (N(2)H(4)BH(3)) is the novel boron- and nitrogen-based material appearing to be a promising candidate in chemical hydrogen storage. It stores 15.4 wt% of hydrogen in hydridic and protic forms, and the challenge is to release H(2) with maximum efficiency, if possible all hydrogen stored in the material. An important step to realize this ambitious goal is to synthesize HB with high yields and high purity, and to characterize it fully. In this work, we report a 2-step synthesis (salt metathesis and solvent extraction-drying) through which N(2)H(4)BH(3) is successfully obtained in 3 days, with a yield of about 80% and a purity of 99.6%. N(2)H(4)BH(3) was characterized by NMR, IR, XRD, TGA and DSC, its stability in dioxane and water was determined, and its thermolysis by-products were characterized. We thus present a complete data sheet that should be very useful for future studies. Furthermore, we propose a discussion on the potential of HB (with H(2) released by either thermolysis or hydrolysis) in chemical hydrogen storage.

SUMMARY The development of the hydrogen economy is hampered by many issues connected with production, storage, distribution, and end‐use. Although the hydrogen storage problem is particularly difficult, there are several attractive solutions under investigation, and chemical hydrogen storage (involving hydrogen‐rich materials) has shown much promising properties. The boron‐based materials are typical examples. They have high hydrogen densities, with up to four reactive B − H bonds. Most of the works have focused on dehydrogenation by hydrolysis or thermolysis so that it takes place in high extent in mild conditions. The first materials studied have been lithium borohydride, sodium borohydride, and ammonia borane. However, their development has been hindered by technical issues such as very high dehydrogenation temperatures, incomplete reaction, and purity of the produced hydrogen. To get round such problems, new materials have been proposed since the mid‐2000s. Interestingly, those materials present attractive attributes, but also drawbacks. This is illustrated in the present review. We believe that boron‐based hydrides have a significant potential in chemical hydrogen storage, but their implementation depends on the recyclability of the solid by‐products; this seems to be the key factor. Copyright © 2013 John Wiley & Sons, Ltd.

Herein, we present the successful synthesis and full characterization (by (11) B magic-angle-spinning nuclear magnetic resonance spectroscopy, infrared spectroscopy, powder X-ray diffraction) of sodium hydrazinidoborane (NaN2 H3 BH3 , with a hydrogen content of 8.85 wt %), a new material for chemical hydrogen storage. Using lab-prepared pure hydrazine borane (N2 H4 BH3 ) and commercial sodium hydride as precursors, sodium hydrazinidoborane was synthesized by ball-milling at low temperature (-30 °C) under an argon atmosphere. Its thermal stability was assessed by thermogravimetric analysis and differential scanning calorimetry. It was found that under heating sodium hydrazinidoborane starts to liberate hydrogen below 60 °C. Within the range of 60-150 °C, the overall mass loss is as high as 7.6 wt %. Relative to the parent N2 H4 BH3 , sodium hydrazinidoborane shows improved dehydrogenation properties, further confirmed by dehydrogenation experiments under prolonged heating at constant temperatures of 80, 90, 95, 100, and 110 °C. Hence, sodium hydrazinidoborane appears to be more suitable for chemical hydrogen storage than N2 H4 BH3 .

Metal amide and hydrogen (MNH2-H2) system is recognized as a promising reversible hydrogen storage system due to its high hydrogen capacity and lower operating temperature. However, slow reaction rate for the Li system with the highest hydrogen capacity is an important issue to be solved for practical use. In this thesis, modification of the reaction properties for the LiNH2-H2 system is carried out from thermodynamic and kinetic points of view. Particularly, the novel ammonia synthesis technique is proposed by applying the LiNH2-H2 system and Amide-imide system. Lithium hydride-Potassium hydride (LiH-KH) complex synthesized by ball-milling has been focused in order to modify the kinetic properties of the reaction between LiH and ammonia. The LiH-NH3 system is recognized as one of the most promising hydrogen storage system because it generates hydrogen at room temperature by ammonolysis reaction. Moreover, the starting system can be regenerated below 300 °C and possesses more than 8.0 wt.% hydrogen capacity. From the experimental results, it is confirmed that the hydrogen generation from the reaction between ammonia and the LiH-KH complex shows much higher reaction rate than that of the simple summation of each component as a synergetic effect. Then, a double-cation amide MNH2 (LiK(NH2)2) phase, which could not be assigned to any reported amides so far, is formed as the reaction product. Moreover, in the hydrogenation of LiK(NH2)2, two processes were confirmed at the different temperatures. After the low temperature hydrogenation, KH-lithium amide (LiNH2) composite is generated as the hydrogenated product. It is noteworthy that the hydrogenation temperature of the composite is dramatically lower than that of LiNH2 itself, which should be due to the interaction between LiNH2 and KH such as a eutectic melting phenomenon. II An ammonia synthesis technique from lithium nitride (Li3N) based on the reactions of "Amide-imide system" and "Amide-hydrogen system" is proposed. Namely, Li3N is hydrogenated below 300 °C under 0.5 MPa hydrogen atmosphere, and then LiNH2 and LiH are formed as products. Furthermore, the reaction between LiNH2 and hydrogen proceeds below 250 °C under 0.5 MPa of hydrogen flow condition, which results in the formation of ammonia and LiH. In this study, a new method of ammonia synthesis is proposed at laboratory scale using above two reactions. This method is capable of being operated under more moderate conditions than those of Haber-Bosch process. The proposed method is investigated for various reaction system such as open system, closed gas circuit system, and closed gas exchange system using couple of hydrogen storage alloys. As a result, it is experimentally clarified that the ammonia can be synthesized below 300 °C and 0.5 MPa with realistic reactions rate by non-equilibrium reaction field under certain hydrogen flow rate even in the closed system.

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Abstract:Hydrazine borane N2H4BH3 and alkali derivatives (i.e., lithium, sodium and potassium hydrazinidoboranes MN2H3BH3 with M = Li, Na and K) have been considered as potential chemical hydrogen storage materials. They belong to the family of boron-and nitrogen-based materials and the present article aims at providing a timely review while focusing on fundamentals so that their effective potential in the field could be appreciated. It stands out that, on the one hand, hydrazine borane, in aqueous solution, would be suitable for full dehydrogenation in hydrolytic conditions; the most attractive feature is the possibility to dehydrogenate, in addition to the BH3 group, the N2H4 moiety in the presence of an active and selective metal-based catalyst but for which further improvements are still necessary. However, the thermolytic dehydrogenation of hydrazine borane should be avoided because of the evolution of significant amounts of hydrazine and the formation of a shock-sensitive solid residue upon heating at >300 °C. On the other hand, the alkali hydrazinidoboranes, obtained by reaction of hydrazine borane with alkali hydrides, would be more suitable to thermolytic dehydrogenation, with improved properties in comparison to the parent borane. All of these aspects are surveyed herein and put into perspective.

This review describes recent research in the development of tank systems based on complex metal hydrides for thermolysis and hydrolysis. Commercial applications using complex metal hydrides are limited, especially for thermolysis-based systems where so far only demonstration projects have been performed. Hydrolysis-based systems find their way in space, naval, military and defense applications due to their compatibility with proton exchange membrane (PEM) fuel cells. Tank design, modeling, and development for thermolysis and hydrolysis systems as well as commercial applications of hydrolysis systems are described in more detail in this review. For thermolysis, mostly sodium aluminum hydride containing tanks were developed, and only a few examples with nitrides, ammonia borane and alane. For hydrolysis, sodium borohydride was the preferred material whereas ammonia borane found less popularity. Recycling of the sodium borohydride spent fuel remains an important part for their commercial viability.

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