Potassium-Modified Mg(NH2)2/2 LiH System for Hydrogen Storage

Ti-Mn hydrogen storage alloys: from properties to applications

Efficient and safe storage of hydrogen is an important link in the process of hydrogen energy utilization. Hydrogen storage with hydrogen storage materials as the medium has the characteristics of high volumetric hydrogen storage density and good safety. Among many hydrogen storage materials, only rare earth-based and titanium-based hydrogen storage alloys have been applied thus far. In this work, current state-of-the-art research and applications of Ti-Mn hydrogen storage alloys are reviewed. Firstly, the hydrogen storage properties and regulation methods of binary to multicomponent Ti-Mn alloys are introduced. Then, the applications of Ti-Mn alloys in hydrogen storage, hydrogen compression and catalysis are discussed. Finally, the future research and development of Ti-Mn hydrogen storage alloys is proposed.

Directed Stabilization by Air-Milling and Catalyzed Decomposition by Layered Titanium Carbide Toward Low-Temperature and High-Capacity Hydrogen Storage of Aluminum Hydride

AlH₃ is a metastable hydride with a theoretical hydrogen capacity of 10.01 wt % and is very easy to decompose during ball milling especially in the presence of many catalysts, which will lead to the attenuation of the available hydrogen capacity. In this work, AlH₃ was ball milled in air (called "air-milling") with layered Ti₃C₂ to prepare a Ti₃C₂-catalyzed AlH₃ hydrogen storage material. Such air-milled and Ti₃C₂-catalyzed AlH₃ possesses excellent hydrogen storage performances, with a low initial decomposition temperature of just 61 °C and a high hydrogen release capacity of 8.1 wt %. In addition, 6.9 wt % of hydrogen can be released within 20 min at constantly 100 °C, with a low activation energy as low as 40 kJ mol^-1. Air-milling will lead to the formation of an Al₂O₃ oxide layer on the AlH₃ particles, which will prevent continuous decomposition of AlH₃ when milling with active layered Ti₃C₂. The layered Ti₃C₂ will grip on and intrude into the AlH₃ particle oxide layers and then catalyze the decomposition of AlH₃ during heating. The strategy employing air-milling as a synthesis method and utilizing layered Ti₃C₂ as a catalyst in this work can solve the key issue of severe decomposition during ball milling with catalysts economically and conveniently and thus achieve both high-capacity and low-temperature hydrogen storage of AlH₃. This air-milling method is also effective for other active catalysts toward both reducing the decomposition temperature and increasing the available hydrogen capacity of AlH₃.

Regulation of Kinetic Properties of Chemical Hydrogen Absorption and Desorption by Cubic K2MoO4 on Magnesium Hydride

Transition metal catalysts are particularly effective in improving the kinetics of the reversible hydrogen storage reaction for light metal hydrides. Herein, K₂MoO₄ microrods were prepared using a simple evaporative crystallization method, and it was confirmed that the kinetic properties of magnesium hydride could be adjusted by doping cubic K₂MoO₄ into MgH₂. Its unique cubic structure forms new species in the process of hydrogen absorption and desorption, which shows excellent catalytic activity in the process of hydrogen storage in MgH₂. The dissociation and adsorption time of hydrogen is related to the amount of K₂MoO₄. Generally speaking, the more K₂MoO₄, the faster the kinetic performance and the shorter the time used. According to the experimental results, the initial dehydrogenation temperature of MgH₂ + 10 wt% K₂MoO₄ composite is 250 °C, which is about 110 °C lower than that of As-received MgH₂. At 320 °C, almost all dehydrogenation was completed within 11 min. In the temperature rise hydrogen absorption test, the composite system can start to absorb hydrogen at about 70 °C. At 200 °C and 3 MPa hydrogen pressure, 5.5 wt% H₂ can be absorbed within 20 min. In addition, the activation energy of hydrogen absorption and dehydrogenation of the composite system decreased by 14.8 kJ/mol and 26.54 kJ/mol, respectively, compared to pure MgH₂. In the cycle-stability test of the composite system, the hydrogen storage capacity of MgH₂ can still reach more than 92% after the end of the 10th cycle, and the hydrogen storage capacity only decreases by about 0.49 wt%. The synergistic effect among the new species MgO, MgMo₂O_7, and KH generated in situ during the reaction may help to enhance the absorption and dissociation of H₂ on the Mg/MgH₂ surface and improve the kinetics of MgH₂ for absorption and dehydrogenation.

Pseudo-Binary Phase diagram of LiNH2-MH (M = Na, K) Eutectic Mixture

The hunt for a cleaner energy carrier leads us to consider a source that produces no toxic byproducts. One of the targeted alternatives in this approach is hydrogen energy, which, unfortunately, suffers from a lack of efficient storage media. Solid-state hydrogen absorption systems, such as lithium amide (LiNH₂) systems, may store up to 6.5 weight percent hydrogen. However, the temperature of hydrogenation and dehydrogenation is too high for practical use. Various molar ratios of LiNH₂ with sodium hydride (NaH) and potassium hydride (KH) have been explored in this paper. The temperature of hydrogenation for LiNH₂ combined with KH and NaH was found to be substantially lower than the temperature of individual LiNH₂. This lower temperature operation of both LiNH₂-NaH and LiNH₂-KH systems was investigated in depth, and the eutectic melting phenomenon was observed. Systematic thermal studies of this amide-hydride system in different compositions were carried out, which enabled the plotting of a pseudo-binary phase diagram. The occurrence of eutectic interaction increased atomic mobility, which resulted in the kinetic modification followed by an increase in the reactivity of two materials. For these eutectic compositions, i.e., 0.15LiNH₂-0.85NaH and 0.25LiNH₂-0.75KH, the lowest melting temperature was found to be 307 °C and 235 °C, respectively. Morphological studies were used to investigate and present the detailed mechanism linked with this phenomenon.

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.

Boosting carbonyl sulfide catalytic hydrolysis performance over N-doped Mg-Al oxide derived from MgAl-layered double hydroxide

Carbonyl sulfide (COS), the organic sulfur generated in the chemical industry, has been receiving more attention due to its environmental and economic influence. In this study N-doped MgAl-LDO catalyst was successfully prepared and tested for the COS hydrolysis reaction at low temperature, it was observed that the N species can be formed both in surface and bulk. Moreover, the basicity property and the H₂O adsorption-desorption property were remarkably improved due to the N-doping. Besides, the hydroxyl group can be formed more easily and more abundantly on N modified catalyst surface, which was beneficial to the COS adsorption and the remarkable improvement of catalytic performance. The catalytic hydrolysis performance can proceed for almost 1440 min without any deactivation at 70 °C. However, further increase of temperature was not beneficial to improve the catalytic performance due to the occurrence of H₂S oxidation side reaction. Furthermore, it was revealed that the surface hydroxyl groups were responsible for the adsorption of COS and then the formed surface transitional species reacted with the H₂O molecules. Hydrogen thiocarbonate and bicarbonate were the main reaction intermediate. The rate-determining step was IM6→IM7 i.e., a type transformation of bicarbonate.

Influence of K2NbF7 Catalyst on the Desorption Behavior of LiAlH4

In this study, the modification of the desorption behavior of LiAlH4 by the addition of K2NbF7 was explored for the first time. The addition of K2NbF7 causes a notable improvement in the desorption behavior of LiAlH4. Upon the addition of 10 wt.% of K2NbF7, the desorption temperature of LiAlH4 was significantly lowered. The desorption temperature of the LiAlH4 + 10 wt.% K2NbF7 sample was lowered to 90°C (first-stage reaction) and 149°C (second-stage reaction). Enhancement of the desorption kinetics performance with the LiAlH4 + 10 wt.% K2NbF7 sample was substantiated, with the composite sample being able to desorb hydrogen 30 times faster than did pure LiAlH4. Furthermore, with the presence of 10 wt.% K2NbF7, the calculated activation energy values for the first two desorption stages were significantly reduced to 80 and 86 kJ/mol; 24 and 26 kJ/mol lower than the as-milled LiAlH4. After analysis of the X-ray diffraction result, it is believed that the in situ formation of NbF4, LiF, and K or K-containing phases that appeared during the heating process promoted the amelioration of the desorption behavior of LiAlH4 with the addition of K2NbF7.

Hydrogen Pressure-Dependent Dehydrogenation Performance of the Mg(NH2)2-2LiH-0.07KOH System

The Mg(NH₂)₂-2LiH system with KOH additive is a promising high-capacity hydrogen storage material in terms of low dehydrogenation temperatures, good reversibility, and excellent cycling stability. Various mechanisms have been reported to elucidate the reasons for the K-containing additive improving the hydrogen storage performance. Herein, the dehydrogenation performance of Mg(NH₂)₂-2LiH-0.07KOH is found to be strongly associated with hydrogen pressures. The Li₂K(NH₂)₃ and KH produced from the reaction between KOH, LiH, and Mg(NH₂)₂ in the ball milling process are converted into Li₃K(NH₂)₄, MgNH, and LiNH₂ in the heating dehydrogenation process under Ar carrier gas or very low hydrogen pressure, exhibiting a two-peak dehydrogenation process. For the sample under high hydrogen pressure, Li₂K(NH₂)₃ can react with LiH to convert into Li₃K(NH₂)₄ and further to form KH and LiNH₂ in the heating process, showing a one-peak dehydrogenation process under 5 bar hydrogen. The hydrogen pressure-dependent reactions of K-containing additives in the Mg(NH₂)₂-2LiH system lead to a different hydrogen storage performance under different dehydrogenation conditions.

A Review of the MSCA ITN ECOSTORE—Novel Complex Metal Hydrides for Efficient and Compact Storage of Renewable Energy as Hydrogen and Electricity

Hydrogen as an energy carrier is very versatile in energy storage applications. Developments in novel, sustainable technologies towards a CO2-free society are needed and the exploration of all-solid-state batteries (ASSBs) as well as solid-state hydrogen storage applications based on metal hydrides can provide solutions for such technologies. However, there are still many technical challenges for both hydrogen storage material and ASSBs related to designing low-cost materials with low-environmental impact. The current materials considered for all-solid-state batteries should have high conductivities for Na+, Mg2+ and Ca2+, while Al3+-based compounds are often marginalised due to the lack of suitable electrode and electrolyte materials. In hydrogen storage materials, the sluggish kinetic behaviour of solid-state hydride materials is one of the key constraints that limit their practical uses. Therefore, it is necessary to overcome the kinetic issues of hydride materials before discussing and considering them on the system level. This review summarizes the achievements of the Marie Skłodowska-Curie Actions (MSCA) innovative training network (ITN) ECOSTORE, the aim of which was the investigation of different aspects of (complex) metal hydride materials. Advances in battery and hydrogen storage materials for the efficient and compact storage of renewable energy production are discussed.

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.

Complex Hydrides for Energy Storage, Conversion, and Utilization

Functional materials are the key enabling factor in the development of clean energy technologies. Materials of particular interest, which are reviewed herein, are a class of hydrogenous compound having the general formula of M(XH_n )_m , where M is usually a metal cation and X can be Al, B, C, N, O, transition metal (TM), or a mixture of them, which sets up an iono-covalent or covalent bonding with H. M(XH_n )_m is generally termed as a complex hydride by the hydrogen storage community. The rich chemistry between H and B/C/N/O/Al/TM allows complex hydrides of diverse composition and electronic configuration, and thus tunable physical and chemical properties, for applications in hydrogen storage, thermal energy storage, ion conduction in electrochemical devices, and catalysis in fuel processing. The recent progress is reviewed here and strategic approaches for the design and optimization of complex hydrides for the abovementioned applications are highlighted.

A dual borohydride (Li and Na borohydride) catalyst/additive together with intermetallic FeTi for the optimization of the hydrogen sorption characteristics of Mg(NH2)2/2LiH

The present study deals with the material tailoring of Mg(NH₂)₂-2LiH through dual borohydrides: the reactive LiBH₄ and the non-reactive NaBH₄. Furthermore, a pulverizer, as well as a catalyst FeTi, has been added in order to facilitate hydrogen sorption. Addition of LiBH₄ to LiNH₂ in a 1 : 3 molar ratio leads to the formation of Li₄(BH₄)(NH₂)₃ which also acts as a catalyst. However, the addition of NaBH₄ doesn't lead to any compound formation but shows a catalytic effect. The onset dehydrogenation temperature of thermally treated Mg(NH₂)₂-2LiH/(Li₄(BH₄)(NH₂)₃-NaBH₄) is 142 °C as against 196 °C for the basic material Mg(NH₂)₂-2LiH. However, with the FeTi catalyzed Mg(NH₂)₂-2LiH/(Li₄(BH₄)(NH₂)₃-NaBH₄, it has been reduced to 120 °C. This is better than other similar amide/hydride composites where it is 149 °C (when the basic material is catalyzed with LiBH₄). The FeTi catalyzed Mg(NH₂)₂-2LiH/(Li₄(BH₄)(NH₂)₃-NaBH₄ sample shows better de/re-hydrogenation kinetics as it desorbs 3.9 ± 0.04 wt% and absorbs nearly 4.1 ± 0.04 wt% both within 30 min at 170 °C (with the H₂ pressure being 0.1 MPa for desorption and 7 MPa for absorption). The eventual hydrogen storage capacity of Mg(NH₂)₂-2LiH/(Li₄(BH₄)(NH₂)₃-NaBH₄ together with FeTi has been found to be ∼5.0 wt%. To make the effect of catalysts intelligible, we have put forward in a schematic way the role of Li and Na borohydrides with FeTi for improving the hydrogen sorption properties of Mg(NH₂)₂-2LiH.

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.

Eutectic Phenomenon of LiNH₂-KH Composite in MH-NH₃ Hydrogen Storage System

Hydrogenation of a lithium-potassium (double-cation) amide (LiK(NH₂)₂), which is generated as a product by ammonolysis of litium hydride and potassium hydride (LiH-KH) composite, is investigated in details. As a result, lithium amide (LiNH₂) and KH are generated after hydrogenation at 160 °C as an intermediate. It is noteworthy that the mixture of LiH and KNH₂ has a much lower melting point than that of the individual melting points of LiNH₂ and KH, which is recognized as a eutectic phenomenon. The hydrogenation temperature of LiNH₂ in the mixture is found to be significantly lower than that of LiNH₂ itself. This improvement of reactivity must be due to kinetic modification, induced by the enhanced atomic mobility due to the eutectic interaction.

Catalytic Tuning of Sorption Kinetics of Lightweight Hydrides: A Review of the Materials and Mechanism

Hydrogen storage materials have been a subject of intensive research during the last 4 decades. Several developments have been achieved in regard of finding suitable materials as per the US-DOE targets. While the lightweight metal hydrides and complex hydrides meet the targeted hydrogen capacity, these possess difficulties of hard thermodynamics and sluggish kinetics of hydrogen sorption. A number of methods have been explored to tune the thermodynamic and kinetic properties of these materials. The thermodynamic constraints could be resolved using an intermediate step of alloying or by making reactive composites with other hydrogen storage materials, whereas the sluggish kinetics could be improved using several approaches such as downsizing and the use of catalysts. The catalyst addition reduces the activation barrier and enhances the sorption rate of hydrogen absorption/desorption. In this review, the catalytic modifications of lightweight hydrogen storage materials are reported and the mechanism towards the improvement is discussed.

The effect of KH on enhancing the dehydrogenation properties of the Li-N-H system and its catalytic mechanism

Although recent works demonstrated that some potassium compounds that can be converted to KH during ball-milling or heat-treatment have obvious effects on enhancing the dehydrogenation properties of the Li-N-H system, the effect of KH on enhancing the dehydrogenation properties of the Li-N-H system and its catalytic mechanism remain unclear. In this study, the hydrogen desorption properties of the LiNH2-LiH system with alkali metal hydrides (LiH, NaH, or KH) were investigated and discussed. We find that the three types of hydrides are effective for enhancing the hydrogen desorption properties of the LiNH2-LiH system, among which, KH shows the best effect. In comparison with the broad shaped hydrogen desorption curve of the LiNH2-LiH composite without additive, the hydrogen desorption curve of the LiNH2-LiH-0.05KH composite becomes narrow. The dehydrogenation onset temperature of the LiNH2-LiH-0.05KH composite is decreased by approximately 20 °C, and the dehydrogenation peak temperature is lowered by approximately 30 °C. Moreover, the reversibility of the LiNH2-LiH system is enhanced drastically by the addition of KH. On the basis of previous reports and present experimental results, the mechanism for the enhancement of the dehydrogenation properties in the KH-added Li-N-H system is proposed. The reason for the improvement of the hydrogen desorption kinetics is that KH has superior reactivity with NH3 and plays the role of a catalyst to accelerate hydrogen release by cyclic reactions.

Insights into the Rb-Mg-N-H System: an Ordered Mixed Amide/Imide Phase and a Disordered Amide/Hydride Solid Solution

The crystal structure of a mixed amide-imide phase, RbMgND₂ND, has been solved in the orthorhombic space group Pnma ( a = 9.55256(31), b = 3.70772(11) and c = 10.08308(32) Å). A new metal amide-hydride solid solution, Rb(NH₂) _xH_{(1- x)}, has been isolated and characterized in the entire compositional range. The profound analogies, as well as the subtle differences, with the crystal chemistry of KMgND₂ND and K(NH₂) _xH_{1- x} are thoroughly discussed. This approach suggests that the comparable performances obtained using K- and Rb-based additives for the Mg(NH₂)₂- 2LiH and 2LiN H₂-MgH₂ hydrogen storage systems are likely to depend on the structural similarities of possible reaction products and intermediates.

Enhanced hydrogen storage properties of 1.1MgH2–2LiNH2–0.1LiBH4 system with LaNi5-based alloy hydrides addition

The weakening of N–H bond and the homogeneous distribution of LaNi₅-based alloy hydrides in the Li–Mg–B–N–H composite enhance its hydrogen storage properties.

Metathesis of Mg2FeH6 and LiNH2 leading to hydrogen production at low temperatures

The metathesis reaction between Mg₂FeH₆ and LiNH₂ produces Li₄FeH₆, which provides an alternative route for synthesizing Li₄FeH₆ under mild conditions.

Improvements in the hydrogen storage properties of the Mg(NH2)2–LiH composite by KOH addition

KH thermodynamically destabilizes the Mg(NH₂)₂–LiH composite as it is actively involved in the dehydrogenation process.

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.

Improved overall hydrogen storage properties of a CsH and KH co-doped Mg(NH2)2/2LiH system by forming mixed amides of Li–K and Cs–Mg

Further improved overall hydrogen storage properties of a Mg(NH₂)₂/2LiH system is achieved by codoping CsH and KH.

Enhanced hydrogen sorption in a Li–Mg–N–H system by the synergistic role of Li4(NH2)3BH4 and ZrFe2

The present investigation describes the synergistic role of Li₄(BH₄)(NH₂)₃ and ZrFe₂ in the hydrogen storage behaviour of a Li–Mg–N–H hydride system.

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.

Improvement of hydrogen storage property of three-component Mg(NH2)2-LiNH2-LiH composites by additives

The three-component Mg(NH₂)₂-LiNH₂-4LiH composite reversibly stores hydrogen exceeding 5 wt% at a temperature as low as 150 °C. In this work, a number of additives such as CeF₄, CeO₂, TiCl₃, TiH₂, NaH, KBH₄ and KH are added to the Mg(NH₂)₂-LiNH₂-4LiH composite in order to improve its kinetics, thermodynamics and cycling properties. Addition of 3 wt% of KH reduces the dehydrogenation onset temperature of the Mg(NH₂)₂-LiNH₂-4LiH composite to below 90 °C without emission of NH₃ during the whole dehydrogenation process up to 450 °C. Moreover, the dehydrogenation kinetics and cycling ability are remarkably enhanced upon KH-addition. The reaction model of the Mg(NH₂)₂-LiNH₂-4LiH composite is altered upon KH-addition with the active molecule density improved by about 200 times. In addition, by optimization of the ratio of Mg²⁺ to Li⁺ in the Mg(NH₂)₂-LiNH₂-LiH system, several novel composites, e.g., Mg(NH₂)₂-2LiNH₂-5.9LiH-0.1KH and Mg(NH₂)₂-LiNH₂-5.9LiH-0.1KH, with the hydrogen storage capacity exceeding 6 wt% without emission of NH₃ below 250 °C are developed. Our study demonstrates that there are various undiscovered candidates with promising hydrogen storage properties in the three-component Li-Mg-N-H system.

A new potassium-based intermediate and its role in the desorption properties of the K-Mg-N-H system

New insights into the reaction pathways of different potassium/magnesium amide-hydride based systems are discussed. In situ SR-PXD experiments were for the first time performed in order to reveal the evolution of the phases connected with the hydrogen releasing processes. Evidence of a new K-N-H intermediate is shown and discussed with particular focus on structural modification. Based on these results, a new reaction mechanism of amide-hydride anionic exchange is proposed.

H3O(+) tetrahedron induction in large negative linear compressibility

Despite the rarity, large negative linear compressibility (NLC) was observed in metal-organic framework material Zn(HO₃PC₄H₈PO₃H)∙2H₂O (ZAG-4) in experiment. We find a unique NLC mechanism in ZAG-4 based on first-principle calculations. The key component to realize its large NLC is the deformation of H₃O⁺ tetrahedron. With pressure increase, the oxygen apex approaches and then is inserted into the tetrahedron base (hydrogen triangle). The tetrahedron base subsequently expands, which results in the b axis expansion. After that, the oxygen apex penetrates the tetrahedron base and the b axis contracts. The negative and positive linear compressibility is well reproduced by the hexagonal model and ZAG-4 is the first MOFs evolving from non re-entrant to re-entrant hexagon framework with pressure increase. This gives a new approach to explore and design NLC materials.

Enhanced hydrogen storage properties of MgH2 co-catalyzed with K2NiF6 and CNTs

The active species KF, KH and Mg₂Ni together with the unique structure of the CNTs functioned as a real catalyst.

Effective participation of Li4(NH2)3BH4 in the dehydrogenation pathway of the Mg(NH2)2–2LiH composite

The presence of Li₄(NH₂)₃BH₄ in the MgNH₂–LiH composite enhances the hydrogen sorption kinetics and its cycling stability.

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

Insights into the dehydrogenation reaction process of a K-containing Mg(NH2)2–2LiH system

KH and Li₂K(NH₂)₃, formed in situ during ball milling, participate as reactants in the dehydrogenation reaction of the Mg(NH₂)₂–2LiH system.

A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2

It was found that the MgH₂ + 10 wt% K₂ZrF₆ sample started to decompose at around 250 °C, which was 100 °C and lower than in as-milled MgH₂. The re/dehydrogenation kinetics had also improved significantly compared to the undoped MgH₂.

Hierarchical porous Li₂Mg(NH)₂@C nanowires with long cycle life towards stable hydrogen storage

The hierarchical porous Li₂Mg(NH)₂@C nanowires full of micropores, mesopores, and macropores are successfully fabricated via a single-nozzle electrospinning technique combined with in-situ reaction between the precursors, i.e., MgCl₂ and LiN₃, under physical restriction upon thermal annealing. The explosive decomposition of LiN₃ well dispersed in the electrospun nanowires during carbothermal treatment induces a highly porous structure, which provides a favourable way for H₂ delivering in and out of Li₂Mg(NH) nanoparticles simultaneously realized by the space-confinement of the porous carbon coating. As a result, the thus-fabricatedLi₂Mg(NH)@C nanowires present significantly enhanced thermodynamics and kinetics towards hydrogen storage performance, e.g., a complete cycle of H2 uptake and release with a capacity close to the theoretical value at a temperature as low as 105°C. This is, to the best of our knowledge, the lowest cycling temperature reported to date. More interestingly, induced by the nanosize effects and space-confinement function of porous carbon coating, a excellently stable regeneration without apparent degradation after 20 de-/re-hydrogenation cycles at a temperature as low as 130°C was achieved for the as-prepared Li₂Mg(NH)₂@C nanowires.

Superior dehydrogenation/hydrogenation kinetics and long-term cycling performance of K and Rb cocatalyzed Mg(NH(2))(2)-2LiH system

The coaddition of KH and RbH significantly improves the hydrogen storage properties of the Mg(NH2)2-2LiH system. An Mg(NH2)2-2LiH-0.04KH-0.04RbH composite was able to reversibly store 5.2 wt % H2 when the dehydrogenation operates at 130 °C and the hydrogenation operates at 120 °C. The isothermal dehydrogenation rate at 130 °C was approximately 43 times that of a pristine sample. During ball-milling, KH reacts with RbH to form a K(Rb)H solid solution. Upon heating, RbH first separates from the K(Rb)H solid solution and participates in the first step of dehydrogenation reaction, and then the remaining KH participates in the second dehydrogenation reaction. The presence of RbH and KH provide synergetic effects, which improve the thermodynamics and kinetics of hydrogen storage in the Mg(NH2)2-2LiH system. In particular, more than 93% of the hydrogen storage capacity (4.4 wt %) remains after cycling a sample with 0.04 mol of KH and RbH for 50 cycles, indicating notably better cycling stability compared with any presently known Li-Mg-N-H systems.

Catalytic modification in dehydrogenation properties of KSiH3

Hydrogen desorption activation energy of KSiH₃ is reduced by mesoporous Nb₂O₅, which drastically enhances the sorption kinetics.

The ternary amide KLi3(NH2)4: an important intermediate in the potassium compound-added Li–N–H systems

Formation mechanism of KLi₃(NH₂)₄ as an important intermediate in the potassium compound-added Li–N–H system was clarified.