The improved Hydrogen Storage Performances of the Multi-Component Composite: 2Mg(NH2)2–3LiH–LiBH4

De-hydrogenation/Rehydrogenation Properties and Reaction Mechanism of AmZn(NH2)n-2nLiH Systems (A = Li, K, Na, and Rb)

With the aim to find suitable hydrogen storage materials for stationary and mobile applications, multi-cation amide-based systems have attracted considerable attention, due to their unique hydrogenation kinetics. In this work, AmZn(NH2)n (with A = Li, K, Na, and Rb) were synthesized via an ammonothermal method. The synthesized phases were mixed via ball milling with LiH to form the systems AmZn(NH2)n-2nLiH (with m = 2, 4 and n = 4, 6), as well as Na2Zn(NH2)4∙0.5NH3-8LiH. The hydrogen storage properties of the obtained materials were investigated via a combination of calorimetric, spectroscopic, and diffraction methods. As a result of the performed analyses, Rb2Zn(NH2)4-8LiH appears as the most appealing system. This composite, after de-hydrogenation, can be fully rehydrogenated within 30 s at a temperature between 190 °C and 200 °C under a pressure of 50 bar of hydrogen.

Destabilization of Boron-Based Compounds for Hydrogen Storage in the Solid-State: Recent Advances

Boron-based materials have been widely studied for hydrogen storage applications. Examples of these compounds are borohydrides and boranes. However, all of these present some disadvantages that have hindered their potential application as hydrogen storage materials in the solid-state. Thus, different strategies have been developed to improve the dehydrogenation properties of these materials. The purpose of this review is to provide an overview of recent advances (for the period 2015–2021) in the destabilization strategies that have been considered for selected boron-based compounds. With this aim, we selected seven of the most investigated boron-based compounds for hydrogen storage applications: lithium borohydride, sodium borohydride, magnesium borohydride, calcium borohydride, ammonia borane, hydrazine borane and hydrazine bisborane. The destabilization strategies include the use of additives, the chemical modification and the nanosizing of these compounds. These approaches were analyzed for each one of the selected boron-based compounds and these are discussed in the present review.

Improved kinetic behaviour of Mg(NH2)2-2LiH doped with nanostructured K-modified-LixTiyOz for hydrogen storage

The system Mg(NH₂)₂ + 2LiH is considered as an interesting solid-state hydrogen storage material owing to its low thermodynamic stability of ca. 40 kJ/mol H₂ and high gravimetric hydrogen capacity of 5.6 wt.%. However, high kinetic barriers lead to slow absorption/desorption rates even at relatively high temperatures (>180 °C). In this work, we investigate the effects of the addition of K-modified Li_xTi_yO_z on the absorption/desorption behaviour of the Mg(NH₂)₂ + 2LiH system. In comparison with the pristine Mg(NH₂)₂ + 2LiH, the system containing a tiny amount of nanostructured K-modified Li_xTi_yO_z shows enhanced absorption/desorption behaviour. The doped material presents a sensibly reduced (∼30 °C) desorption onset temperature, notably shorter hydrogen absorption/desorption times and reversible hydrogen capacity of about 3 wt.% H₂ upon cycling. Studies on the absorption/desorption processes and micro/nanostructural characterizations of the Mg(NH₂)₂ + 2LiH + K-modified Li_xTi_yO_z system hint to the fact that the presence of in situ formed nanostructure K₂TiO₃ is the main responsible for the observed improved kinetic behaviour.

Enhancement Effect of Bimetallic Amide K2Mn(NH2)4 and In-Situ Formed KH and Mn4N on the Dehydrogenation/Hydrogenation Properties of Li–Mg–N–H System

In this work, we investigated the influence of the K2Mn(NH2)4 additive on the hydrogen sorption properties of the Mg(NH2)2 + 2LiH (Li–Mg–N–H) system. The addition of 5 mol% of K2Mn(NH2)4 to the Li–Mg–N–H system leads to a decrease of the dehydrogenation peak temperature from 200 °C to 172 °C compared to the pristine sample. This sample exhibits a constant hydrogen storage capacity of 4.2 wt.% over 25 dehydrogenation/rehydrogenation cycles. Besides that, the in-situ synchrotron powder X-ray diffraction analysis performed on the as prepared Mg(NH2)2 + 2LiH containing K2Mn(NH2)4 indicates the presence of Mn4N. However, no crystalline K-containing phases were detected. Upon dehydrogenation, the formation of KH is observed. The presence of KH and Mn4N positively influences the hydrogen sorption properties of this system, especially at the later stage of rehydrogenation. Under the applied conditions, hydrogenation of the last 1 wt.% takes place in only 2 min. This feature is preserved in the following three cycles.

Kinetic alteration of the 6Mg(NH2)2-9LiH-LiBH4 system by co-adding YCl3 and Li3N

The 6Mg(NH₂)₂-9LiH-LiBH₄ composite system has a maximum reversible hydrogen content of 4.2 wt% and a predicted dehydrogenation temperature of about 64 °C at 1 bar of H₂. However, the existence of severe kinetic barriers precludes the occurrence of de/re-hydrogenation processes at such a low temperature (H. Cao, G. Wu, Y. Zhang, Z. Xiong, J. Qiu and P. Chen, J. Mater. Chem. A, 2014, 2, 15816-15822). In this work, Li₃N and YCl₃ have been chosen as co-additives for this system. These additives increase the hydrogen storage capacity and hasten the de/re-hydrogenation kinetics: a hydrogen uptake of 4.2 wt% of H₂ was achieved in only 8 min under isothermal conditions at 180 °C and 85 bar of H₂ pressure. The re-hydrogenation temperature, necessary for a complete absorption process, can be lowered below 90 °C by increasing the H₂ pressure above 185 bar. Moreover, the results indicate that the hydrogenation capacity and absorption kinetics can be maintained roughly constant over several cycles. Low operating temperatures, together with fast absorption kinetics and good reversibility, make this system a promising on-board hydrogen storage material. The reasons for the improved de/re-hydrogenation properties are thoroughly investigated and discussed.

The effect of Sr(OH)2 on the hydrogen storage properties of the Mg(NH2)2–2LiH system

Sr(OH)₂ influences both the thermodynamics and kinetics of the Mg(NH₂)₂–2LiH system, lowering the dehydrogenation onset and peak temperatures by ca. 70 °C and 13 °C.