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Hydrogen storage properties of K2Mn(NH2)4–8LiH were investigated by considering its de/re-hydrogenation properties and reaction mechanisms. Experimental results show that the dehydrogenated K2Mn(NH2)4–8LiH can be almost re-hydrogenated completely at 230 °C and 50 bar of H2 with a hydrogenation rate more than 1.0 wt%/min. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and FTIR investigations reveal that during ball milling K2Mn(NH2)4 reacts with LiH to form LiNH2 and K–Mn-species1 which is probably a K–Mn-containing hydride. The ball milled sample releases hydrogen in a multi-step reaction with the formation of K3MnH5 and K–Mn-species2 as intermediates and Li2NH, Mn3N2 and MnN as final products. The full hydrogenated products are LiH, LiNH2, and K–Mn-species2. The K–Mn-species2 may play a critical role for the fast hydrogeneration. This work indicates that transition metal contained amide-hydride composite holds potentials for hydrogen storage.

Over the last decade's magnesium and magnesium based compounds have been intensively investigated as potential hydrogen storage as well as thermal energy storage materials due to their abundance and availability as well as their extraordinary high gravimetric and volumetric storage densities. This review work provides a broad overview of the most appealing systems and of their hydrogenation/dehydrogenation properties. Special emphasis is placed on reviewing the efforts made by the scientific community in improving the material's thermodynamic and kinetic properties while maintaining a high hydrogen storage capacity.

Although Mg2FeH6 has drawn significant attention for storing hydrogen, its sluggish kinetics during hydrogenation and poor reversibility hinder practical uses. In this work, the replacement of Fe atoms in Mg2FeH6 with Ni atoms is attempted and the material properties are investigated. A detailed study of the de/rehydrogenation kinetics and reaction mechanisms of the Ni-doped Mg2FeH6 is carried out. The effects of Ni-loading contents on kinetic properties and behaviors as well as reversibility and reaction pathways are characterized. In addition, the crystal structure of a new Ni-substituted Mg2FeH6 phase is confirmed.

To find a solution to efficiently exploit renewable energy sources is a key step to achieve complete independence from fossil fuel energy sources. Hydrogen is considered by many as a suitable energy vector for efficiently exploiting intermittent and unevenly distributed renewable energy sources. However, although the production of hydrogen from renewable energy sources is technically feasible, the storage of large quantities of hydrogen is challenging. Comparing to conventional compressed and cryogenic hydrogen storage, the solid-state storage of hydrogen shows many advantages in terms of safety and volumetric energy density. Among the materials available to store hydrogen, metal hydrides and complex metal hydrides have been extensively investigated due to their appealing hydrogen storage properties. Among several potentials candidates, magnesium hydride (MgH2) and lithium borohydride (LiBH4) have been widely recognized as promising solid-state hydrogen storage materials. However, before considering these hydrides ready for real-scale applications, the issue of their high thermodynamic stability and of their poor hydrogenation/dehydrogenation kinetics must be solved. An approach to modify the hydrogen storage properties of these hydrides is nanoconfinement. This review summarizes and discusses recent findings on the use of porous scaffolds as nanostructured tools for improving the thermodynamics and kinetics of MgH2 and LiBH4.

The Mg(NH2)2–2LiH composite has been regarded as a promising on-board hydrogen storage material, due to its favorable thermodynamics and high H2 gravimetric capacity. In this paper, a new route to synthesize the Mg(NH2)2–2LiH composite, starting from hydrogenated Li2Mg(NH)2, is presented. Li2Mg(NH)2 is obtained from the decomposition of a mixture of a magnesium waste alloy (AZ91) and LiH, after a multi-step treatment. The as-prepared Mg(NH2)2–2LiH with Mg coming from AZ91 shows improved hydrogen storage properties, as compared with that synthesized from pure magnesium powder, with a lower dehydrogenation peak temperature of about 15 °C. The reaction pathways during the conversion of the AZ91 alloy to Mg(NH2)2–2LiH are investigated by ex situ and in situ XRD techniques. The obtained results confirm that this new approach is an effective way to recycle magnesium waste alloys into lightweight hydrogen storage materials. In addition, this new technology is easy to scale up and reduces the cost of Mg(NH2)2–2LiH, which has important significance for its practical applications.

Reversible solid-state hydrogen storage is one of the key technologies toward pollutant-free and sustainable energy conversion. The composite system LiBH4-MgH2 can reversibly store hydrogen with a gravimetric capacity of 13 wt%. However, its dehydrogenation/hydrogenation kinetics is extremely sluggish (~40 h) which hinders its usage for commercial applications. In this work, the kinetics of this composite system is significantly enhanced (~96%) by adding a small amount of NbF5. The catalytic effect of NbF5 on the dehydrogenation/hydrogenation process of LiBH4-MgH2 is systematically investigated using a broad range of experimental techniques such as in situ synchrotron radiation X-ray powder diffraction (in situ SR-XPD), X-ray absorption spectroscopy (XAS), anomalous small angle X-ray scattering (ASAXS), and ultra/small-angle neutron scattering (USANS/SANS). The obtained results are utilized to develop a model that explains the catalytic function of NbF5 in hydrogen release and uptake in the LiBH4-MgH2 composite system., The authors thank the great support from the BT5-Instrument staff at NIST center for Neutron Research. In particular, the authors are thankful to Dr David Mildner and Dr Steve Kline for the fruitful discussions and help for the USANS data evaluation and interpretation. The authors thank also CONICET (Consejo Nacional de Invetigaciones Científicas y Técnicas), ANPCyT – (Agencia Nacional de Promoción Científica y Tecnológica), for financial support to carry out this work. We would also like to thank the Metals Physics Division at Helmoltz-Zentrum Hereon for providing the TEM devices. The research leading to these results has received funding from Alexander von Humboldt Foundation, Fellowship number: ARG-1187279-GF-P. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and the Government of Catalonia's Agency for Business Competitiveness (ACCIÓ).

To improve the packing efficiency in tank scale, hydrides have been compacted into pellet form; however, poor hydrogen permeability through the pellets results in sluggish kinetics. In this work, the hydrogen sorption properties of compacted 2LiBH4 MgH2 doped with 30 wt % activated carbon nanofibers (ACNF) are investigated. After doping with ACNF, onset dehydrogenation temperature of compacted 2LiBH4 MgH2 decreases from 350 to 300 °C and hydrogen released content enhances from 55 to 87% of the theoretical capacity. The sample containing ACNF releases hydrogen following a two-step mechanism with reversible hydrogen storage capacities up to 4.5 wt % H2 and 41.8 gH2/L, whereas the sample without ACNF shows a single-step decomposition mainly from MgH2 with only 1.8 wt % H2 and 15.4 gH2/L. Significant kinetic improvement observed in the doped system is due to the enhancement of both hydrogen permeability and heat transfer through the pellet.

Binary combinations of borohydrides have been extensivly investigated evidencing the formation of eutectics, bimetallic compounds or solid solutions. In this paper, the investigation has been extended to ternary and quaternary systems in the LiBH4 -NaBH4 -KBH4 -Mg(BH4 )2 -Ca(BH4 )2 system. Possible interactions among borohydrides in equimolar composition has been explored by mechanochemical treatment. The obtained phases were analysed by X-ray diffraction and the thermal behaviour of the mixtures were analysed by HP-DSC and DTA, defining temperature of transitions and decomposition reactions. The release of hydrogen was detected by MS, showing the role of the presence of solid solutions and multi-cation compounds on the hydrogen desorption reactions. The presence of LiBH4 generally promotes the release of H2 at about 200 °C, while KCa(BH4 )3 promotes the release in a single-step reaction at higher temperatures.

Advanced engineering materials 23(11), 2100620 (2021). doi:10.1002/adem.202100620, The hydrogen storage performance of reactive hydride composite Mg(NH$_2$)$_2$+2LiH can be significantly improved by the addition of LiBH$_4$ and the subsequent formation of an amide���borohydride compound Li$_4$(BH$_4$)(NH$_2$)$_3$ during hydrogen release. Herein, an investigation into the structure and anion motions of Li$_4$(BH$_4$)(NH$_2$)$_3$ using synchrotron radiation powder X-ray diffraction (SR-PXD; 295���573 K) and quasielastic neutron scattering (QENS; 297���514 K) is described. The highest temperature studied with QENS (514 K) is above the melting point of Li$_4$(BH$_4$)(NH$_2$)$_3$. The neutron measurements confirm a long-range diffusive motion of hydrogen-containing species with the diffusion coefficient �������10$^{���6}$ cm$^2$ s$^{���1}$. Interestingly, this value is comparable to that of Li$^+$ diffusion inferred from conductivity measurements. SR-PXD confirms the recrystallization of Li$_4$(BH$_4$)(NH$_2$)$_3$ from the melt into the ��-phase upon cooling. At temperatures below 514 K, localized rotational motions are observed that are attributed to (BH$_4$)��� tetrahedra units mainly undergoing rotations around the ����$_3$ axes. The activation energy for this thermally activated process is found to be ����$_a$=15.5��0.9 and 17.4��0.9 kJ mol$^{���1}$ respectively for the two instrumental resolutions utilized in the QENS measurements, corresponding to observation times of 55 and 14 ps., Published by Deutsche Gesellschaft fu��r Materialkunde, Frankfurt, M.

Rechargeable solid-state magnesium batteries are considered for high energy density storage and usage in mobile applications as well as to store energy from intermittent energy sources, triggering intense research for suitable electrode and electrolyte materials. Recently, magnesium borohydride, Mg(BH4)2, was found to be an effective precursor for solid-state Mg-ion conductors. During the mechanochemical synthesis of these Mg-ion conductors, amorphous Mg(BH4)2 is typically formed and it was postulated that this amorphous phase promotes the conductivity. Here, electrochemical impedance spectroscopy of as-received γ-Mg(BH4)2 and ball milled, amorphous Mg(BH4)2 confirmed that the conductivity of the latter is ~2 orders of magnitude higher than in as-received γ-Mg(BH4)2 at 353 K. Pair distribution function (PDF) analysis of the local structure shows striking similarities up to a length scale of 5.1 Å, suggesting similar conduction pathways in both the crystalline and amorphous sample. Up to 12.27 Å the PDF indicates that a 3D net of interpenetrating channels might still be present in the amorphous phase although less ordered compared to the as-received γ-phase. However, quasi elastic neutron scattering experiments (QENS) were used to study the rotational mobility of the [BH4] units, revealing a much larger fraction of activated [BH4] rotations in amorphous Mg(BH4)2. These findings suggest that the conduction process in amorphous Mg(BH4)2 is supported by stronger rotational mobility, which is proposed to be the so-called “paddle-wheel” mechanism.

CO2 capture and conversion are a key research field for the transition towards an economy only based on renewable energy sources. In this regard, hydride materials are a potential option for CO2 methanation since they can provide hydrogen and act as a catalytic species. In this work, Mg2NiH4 complex hydride is synthesized by in situ monitoring of mechanical milling under a hydrogen atmosphere from a 2MgH2:Ni stoichiometric mixture. Temperature and pressure evolution is monitored, and the material is characterized, during milling in situ, thus providing a good insight into the synthesis process. The cubic polymorph of Mg2NiH4 (S.G. Fm3m) starts to be formed in the early beginning of the mechanical treatment due to the mechanical stress induced by the milling process. Then, after 25 hours of milling, Mg2NiH4 with a monoclinic (S.G. C12/c1) structure appears. The formation of the monoclinic polymorph is most likely related to the stress release that follows the continuous refinement of the material's microstructure. At the end of the milling process, after 60 hours, the as-milled material is composed of 90.8 wt% cubic Mg2NiH4, 5.7 wt% monoclinic Mg2NiH4, and 3.5 wt% remnant Ni. The as-milled Mg2NiH4 shows high reactivity for CO2 conversion into CH4. Under static conditions at 400 °C for 5 hours, the interactions between as-milled Mg2NiH4 and CO2 result in total CO2 consumption and in the formation of the catalytic system Ni-MgNi2-Mg2Ni/MgO. Experimental evidence and thermodynamic equilibrium calculations suggest that the global methanation mechanism takes place through the adsorption of C and the direct solid gasification towards CH4 formation. Fil: Grasso, María Laura. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Puszkiel, Julián Atilio. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Helmholtz-Zentrum Geesthacht GmbH; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Gennari, Fabiana Cristina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Santoru, Antonio. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Dornheim, Martin. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Pistidda, Claudio. Helmholtz-Zentrum Geesthacht GmbH; Alemania

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 LixTiyOz 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 LixTiyOz 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 LixTiyOz system hint to the fact that the presence of in situ formed nanostructure K2TiO3 is the main responsible for the observed improved kinetic behaviour., This work was funded by the CAS-HZG collaborative project ''RevHy'' – ''Study on the synthesis, structures and performances of complex hydrides systems for Reversible high capacity Hydrogen storage at low temperatures''. The authors thank CONICET (Consejo Nacional de Invetigaciones Científicas y Técnicas) and Alexander von Humboldt Foundation in the frame of the post-doctoral fellowship of Dr. J. Puszkiel (Fellowship number: ARG−1187279-GF-P). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and the Government of Catalonia's Agency for Business Competitiveness (ACCIÓ).

Mg2FeD6 is successfully synthesised with various degrees of purity using reactive ball milling and annealing under low pressure deuterium conditions to a maximum of 10 bar. The deuteride of the low cost ternary metal hydride Mg2FeH6, is synthesised to enable further characterisation studies such as isotopic exchange behaviour. Both on laboratory and industrial scales, keeping the pressure low reduces the need for expensive compression systems and also minimises the quantity of gas necessary for use; therefore it is important to assess synthesis under these cost effective conditions. This is especially the case when using a specialised gas such as high purity deuterium. The maximum pressure chosen is 10 bar, to comply with the High Pressure Safety Act in Japan. This Safety Act limits the use of any gas including hydrogen and deuterium to 10 bar eliminating the use of traditional synthesis methods for Mg2FeH6 or Mg2FeD6 synthesis at high pressure (120 bar). Ball milling parameters such as milling times, ball to powder ratios as well as sintering times were altered to achieve improved Mg2FeD6 yields under these low pressure conditions.

In this work, the hydrogen absorption and desorption properties of the system K2[Zn(NH2)4]-8LiH are investigated in detail via in situ synchrotron radiation powder X-ray diffraction (SR-PXD), Fourier transform infrared spectroscopy (FT-IR), and volumetric methods. Upon milling, K2[Zn(NH2)4] and 8LiH react to form 4LiNH2-4LiH-K2ZnH4, and then 4LiNH2-4LiH-K2ZnH4 releases H2 in multiple steps. The final products of the desorption reaction are KH, LiZn13, and Li2NH. During rehydrogenation, KH reacts with LiZn13 under 50 bar of hydrogen producing K3ZnH5. This phase appears to enhance the hydrogenation process which after its formation at ca. 220 °C takes place in only 30 s. The system 4LiNH2-4LiH-K2ZnH4 is shown to be reversible under the applied conditions of vacuum at 400 °C for desorption and 50 bar of H2 at 300 °C for absorption.

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. Fil: Cao, Hujun. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Zhang, Weijin. Chinese Academy of Sciences; República de China Fil: Pistidda, Claudio. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Puszkiel, Julián Atilio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Milanese, Chiara. Università di Padova; Italia Fil: Santoru, Antonio. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Karimi, Fahim. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Gizer, Gökhan. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Welter, Edmund. Deutsches Elektronen-Synchrotron a Research Centre of the Helmholtz Association; Alemania Fil: Bednarcik, Jozef. Deutsches Elektronen-Synchrotron a Research Centre of the Helmholtz Association; Alemania Fil: Etter, Martin. Deutsches Elektronen-Synchrotron a Research Centre of the Helmholtz Association; Alemania Fil: Chen, Ping. Chinese Academy of Sciences; República de China Fil: Klassen, Thomas. Helmholtz-Zentrum Geesthacht GmbH; Alemania Fil: Dornheim, Martin. Helmholtz-Zentrum Geesthacht GmbH; Alemania

CO2 emissions have been continuously increasing during the last half of the century with a relevant impact on the planet and are the main contributor to the greenhouse effect and global warming. The development of new technologies to mitigate these emissions poses a challenge. Herein, the recycling of CO2 to produce CH4 selectively by using Mg2FeH6 and Mg2NiH4 complex hydrides as dual conversion promoters and hydrogen sources has been demonstrated. Magnesium-based metal hydrides containing Fe and Ni catalyzed the hydrogenation of CO2 and their total conversion was obtained at 400 °C after 5 h and 10 h, respectively. The complete hydrogenation of CO2 depended on the complex hydride, H2:CO2 mol ratio, and experimental conditions: temperature and time. For both hydrides, the activation of CO2 on the metal surface and its subsequent capture resulted in the formation of MgO. Investigations on the Mg2FeH6-CO2 system indicated that the main process occurs via the reversed water-gas shift reaction (WGSR), followed by the methanation of CO in the presence of steam. In contrast, the reduction of CO2 by the Mg-based hydride in the Mg2NiH4-CO2 system has a strong contribution to the global process. Complex metal hydrides are promising dual promoter-hydrogen sources for CO2 recycling and conversion into valuable fuels such as CH4. Fil: Grasso, María Laura. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Puszkiel, Julián Atilio. Helmholtz zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Fernández Albanesi, Luisa Francisca. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Dornheim, Martin. Helmholtz zentrum Geesthacht; Alemania Fil: Pistidda, Claudio. Helmholtz zentrum Geesthacht; Alemania Fil: Gennari, Fabiana Cristina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina

In this work, the mechanical milling of a FeTiMn alloy for hydrogen storage purposes was performed in an industrial milling device. The TiFe hydride is interesting from the technological standpoint because of the abundance and the low cost of its constituent elements Ti and Fe, as well as its high volumetric hydrogen capacity. However, TiFe is difficult to activate, usually requiring a thermal treatment above 400 °C. A TiFeMn alloy milled for just 10 minutes in a 100 liter industrial milling device showed excellent hydrogen storage properties without any thermal treatment. The as-milled TiFeMn alloy did not need any activation procedure and showed fast kinetic behavior and good cycling stability. Microstructural and morphological characterization of the as-received and as-milled TiFeMn alloys revealed that the material, presents reduced particle and crystallite sizes, even after such short time of milling. The refined microstructure of the as-milled TiFeMn is deemed to account for the improved hydrogen absorption-desorption properties. Fil: Bellosta von Colbe, José. Helmholtz–Zentrum Geesthacht. ; Alemania Fil: Puszkiel, Julián Atilio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Capurso, Giovanni. Helmholtz–Zentrum Geesthacht. ; Alemania Fil: Franz, Andreas. ZoZ GmbH; Alemania Fil: Ulrich Benz, Hans. ZoZ GmbH; Alemania Fil: Zoz, Henning. ZoZ GmbH; Alemania Fil: Klassen, Thomas. Helmholtz–Zentrum Geesthacht. ; Alemania Fil: Dornheim, Martin. Helmholtz–Zentrum Geesthacht. ; Alemania

Lithium borohydride (LiBH4) and sodium borohydride (NaBH4) were synthesized via mechanical milling of LiBO2, and NaBO2 with Mg&ndash, Al-based waste under controlled gaseous atmosphere conditions. Following this approach, the results herein presented indicate that LiBH4 and NaBH4 can be formed with a high conversion yield starting from the anhydrous borates under 70 bar H2. Interestingly, NaBH4 can also be obtained with a high conversion yield by milling NaBO2&middot, 4H2O and Mg&ndash, Al-based waste under an argon atmosphere. Under optimized molar ratios of the starting materials and milling parameters, NaBH4 and LiBH4 were obtained with conversion ratios higher than 99.5%. Based on the collected experimental results, the influence of the milling energy and the correlation with the final yields were also discussed.

Metal hydrides are known as a potential efficient, low-risk option for high-density hydrogen storage since the late 1970s. In this paper, the present status and the future perspectives of the use of metal hydrides for hydrogen storage are discussed. Since the early 1990s, interstitial metal hydrides are known as base materials for Ni – metal hydride rechargeable batteries. For hydrogen storage, metal hydride systems have been developed in the 2010s [1] for use in emergency or backup power units, i. e. for stationary applications. With the development and completion of the first submarines of the U212 A series by HDW (now Thyssen Krupp Marine Systems) in 2003 and its export class U214 in 2004, the use of metal hydrides for hydrogen storage in mobile applications has been established, with new application fields coming into focus. In the last decades, a huge number of new intermetallic and partially covalent hydrogen absorbing compounds has been identified and partly more, partly less extensively characterized. In addition, based on the thermodynamic properties of metal hydrides, this class of materials gives the opportunity to develop a new hydrogen compression technology. They allow the direct conversion from thermal energy into the compression of hydrogen gas without the need of any moving parts. Such compressors have been developed and are nowadays commercially available for pressures up to 200 bar. Metal hydride based compressors for higher pressures are under development. Moreover, storage systems consisting of the combination of metal hydrides and high-pressure vessels have been proposed as a realistic solution for on-board hydrogen storage on fuel cell vehicles. In the frame of the “Hydrogen Storage Systems for Mobile and Stationary Applications” Group in the International Energy Agency (IEA) Hydrogen Task 32 “Hydrogen-based energy storage” different compounds have been and will be scaled-up in the near future and tested in the range of 500 g to several hundred kg for use in hydrogen storage applications, The research for the lab-scale compressor is part of the activities of SCCER HaE, which is financially supported by Innosuisse - Swiss Innovation Agency . The authors thank the Alexander von Humboldt Foundation in the frame of the post-doctoral fellowship of Dr. J. Puszkiel (No. 1187279 STP ) as well as the European Union for their funding of projects STORHY (contract Nr. SES6-CT-2004-502667 , FP6-2002-Energy-1, 6.1.3.2.2), NESSHY (contract Nr. 518271 , FP6-2004-Energy-3, 6.1.3.2.2) and the EU Horizon 2020 /RISE project HYDRIDE4MOBILITY. Financial support from the S02 and KP8 S05), the European Union's Seventh Framework Programme ( FP7/2007e2013 ) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no. 256653 (SSH2S), from the European Fuel Cells and Hydrogen Joint Undertaking in the framework of BOR4STORE (Grant agreement no. 303428 ), from the Australian Research Council for grants LP120101848 , LP150100730 , and LE0989180 , The Innovation Fund Denmark (project HyFill-Fast), DST within Hydrogen South Africa/HySA programme (projects KP3 National Research Foundation/NRF of South Africa , incentive funding grant number 109092 and the Research Council of Norway (project 285147 ) is thankfully acknowledged

Several different milling parameters (additive content, rotation velocity, ball-to-powder ratio, degree of filling, and time) affect the hydrogen absorption and desorption properties of a reactive hydride composite (RHC). In this paper, these effects were thoroughly tested and analyzed. The milling process investigated in such detail was performed on the 2LiH-MgB2 system doped with TiCl3. Applying an upgraded empirical model, the transfer of energy to the material during the milling process was determined. In this way, it is possible to compare the obtained experimental results with those from processes at different scales. In addition, the different milling parameters were evaluated independently according to their individual effect on the transferred energy. Their influence on the reaction kinetics and hydrogen capacity was discussed and the results were correlated to characteristics like particle and crystallite size, specific surface area, presence of nucleation sites and contaminants. Finally, an optimal value for the transferred energy was determined, above which the powder characteristics do not change and therefore the RHC system properties do not further improve. Fil: Jepsen, Julian. Helmholtz zentrum Geesthacht; Alemania. Helmut Schmidt University; Alemania Fil: Capurso, Giovanni. Helmholtz zentrum Geesthacht; Alemania Fil: Puszkiel, Julián Atilio. Helmholtz zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Busch, Nina. Helmholtz zentrum Geesthacht; Alemania Fil: Werner, Tobias. Helmholtz zentrum Geesthacht; Alemania Fil: Milanese, Chiara. Universita Degli Studi Di Pavia; Italia Fil: Girella, Alessandro. Universita Degli Studi Di Pavia; Italia Fil: Von Colbe, José Bellosta. Helmholtz zentrum Geesthacht; Alemania Fil: Dornheim, Martin. Helmholtz zentrum Geesthacht; Alemania Fil: Klassen, Thomas. Helmholtz zentrum Geesthacht; Alemania. Helmut Schmidt University; Alemania

As the world evolves, so does the energy demand. The storage of hydrogen using metal hydrides shows great promise due to the ability to store and deliver energy on demand while achieving higher volumetric density and safer storage conditions compared with traditional storage options such as compressed gas or liquid hydrogen. Research is typically performed on lab-sized samples and tanks and shows great potential for large scale applications. However, the effects of scale-up on the metal hydride’s performance are relatively less investigated. Studies performed so far on both materials, and hydride-based storage tanks show that the scale-up can significantly impact the system’s capacity, kinetics, and sorption properties. The findings presented in this review suggest areas of further investigation in order to implement metal hydrides in real scale applications.

The thermochemical energy storage properties of calcium hydride (CaH2) destabilised with either silicon (Si) or CaxSiy compounds at various molar ratios, were thoroughly studied by a combination of experimental and computer assisted thermodynamic calculations. Particularly, the destabilisation effect of Si on CaH2 at five different molar ratios (1:1, 1:2, 2:1, 3:4, 5:3 CaH2 to Si) was extensively investigated. Theoretical calculations predicted a multi-step thermal decomposition reaction between CaH2 and Si forming CaxSiy at varying temperatures, which was confirmed by in-situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and mass-spectroscopic measurements. The most suitable destabilisation reactions between CaH2 and Si or CaxSiy that meet the criteria of a thermal energy storage system for the next-generation of concentrated solar power (CSP) plants were identified. The CaH2 and CaSi system (in a 2:3 molar ratio of CaH2 to CaSi) showed desirable operating conditions with a decomposition temperature of 747 ± 33 °C at a hydrogen pressure of 1 bar. Pressure composition isothermal measurements were conducted on this system to determine its practical enthalpy of decomposition to form Ca5Si3. The calculated value (107.3 kJ mol−1 H2) was lower compared to the experimentally determined value (154 ± 4 kJ mol−1 H2). This mismatch was mainly due to the formation of CaO and a CaSi solid solution in addition to the desired Ca5Si3 phase.

Light metal complex borohydrides have high hydrogen storage capacities but suffer from drawbacks of slow hydrogen sorption kinetics, poor reversibility and high thermodynamic stability. The NaF + 9NaH + 5MgB2 composite has a theoretical hydrogen capacity of 7.7 wt% H assuming the formation of 10NaBH3.9F0.1 + 5MgH2. Hydrogenation and dehydrogenation properties as well as the effect of different ball milling times have been investigated. The in situ hydrogenation is faster in the composite ball milled for 87 h than the 5 h milled composite. A boron-rich phase with space group Pa-3, a = 7.4124(5) A was formed during hydrogenation at 325 °C and 50 bar hydrogen for both short and long milling times. In the long milled composite the boron-rich phase disappeared after 3 h of hydrogenation, whereas it became a major phase in the short milled composite after 1.5 h of hydrogenation. NaBH4 was formed at 206 °C. NaMgH1-xFx was formed at 290 °C instead of the assumed MgH2. The same phases formed at 268 °C and 325 °C, respectively, and only in minor amounts in the short milled composite. Ex situ hydrogenation in a Sieverts' type apparatus at the same temperature and hydrogen pressure conditions followed a different reaction pathway with formation of MgH2 in addition to NaBH4 and NaMgH3-xFx (0 ≤ x ≤ 1). The measured hydrogen uptake was 6.0 and 6.3 wt% for the long and short milled composites, respectively.

NaAlH 4 was melt infiltrated within a CO 2 activated carbon aerogel, which had been preloaded with TiCl 3 . Nanoconfinement was verified by Small Angle X-Ray Scattering (SAXS) and the nature of the Ti was investigated with Anomalous SAXS (ASAXS) and X-Ray Absorption Near Edge Structure (XANES) to determine its size and chemical state. The Ti is found to be in a similar state to that found in the bulk Ti-doped NaAlH 4 system where it exists as Al 1− x Ti x nanoalloys. Crystalline phases exist within the carbon aerogel pores, which are analysed by in-situ Powder X-Ray Diffraction (PXD) during hydrogen cycling. The in-situ data reveals that the hydrogen release from NaAlH 4 and its hydrogen uptake occurs through the Na 3 AlH 6 intermediate when confined at this size scale. The hydrogen capacity from the nanoconfined NaAlH 4 is found to initially be much higher in this CO 2 activated aerogel compared with previous studies into unactivated aerogels.

Mg₂FeH₆ is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m³) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg₂FeH₆ under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg₂FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH₂ is enhanced by the presence of Fe. However, MgH₂ does not take part as intermediate for the formation of Mg₂FeH₆ and acts as solid-solid diffusion barrier which hinders the complete formation of Mg₂FeH₆. This work provides novel insight about the formation mechanism of Mg₂FeH₆., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Reaction kinetic behaviour and cycling stability of the 2LiBH4-MgH2 reactive hydride composite (Li-RHC) are experimentally determined and analysed as a basis for the design and development of hydrogen storage tanks. In addition to the determination and discussion about the properties; different measurement methods are applied and compared. The activation energies for both hydrogenation and dehydrogenation are determined by the Kissinger method and via the fitting of solid-state reaction kinetic models to isothermal volumetric measurements. Furthermore, the hydrogen absorption-desorption cycling stability is assessed by titration measurements. Finally, the kinetic behaviour and the reversible hydrogen storage capacity of the Li-RHC are discussed. Fil: Jepsen, Julian. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania Fil: Milanese, Chiara. Università degli Studi di Pavia; Italia Fil: Puszkiel, Julián Atilio. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Girella, Alessandro. Università degli Studi di Pavia; Italia Fil: Schiavo, Benedetto. Università degli Studi di Palermo; Italia Fil: Lozano, Gustavo A.. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania Fil: Capurso, Giovanni. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania Fil: Von Colbe, José M. Bellosta. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania Fil: Marini, Amedeo. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Kabelac, Stephan. Leibniz Universität Hannover; Alemania Fil: Dornheim, Martin. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania Fil: Klassen, Thomas. Helmholtz-Zentrum Geesthacht Zentrum für Material- und Küstenforschung; Alemania

Hydrogen storage in the solid state represents one of the most attractive and challenging ways to supply hydrogen to a proton exchange membrane (PEM) fuel cell. Although in the last 15 years a large variety of material systems have been identified as possible candidates for storing hydrogen, further efforts have to be made in the development of systems which meet the strict targets of the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) and U.S. Department of Energy (DOE). Recent projections indicate that a system possessing: (i) an ideal enthalpy in the range of 20–50 kJ/mol H2, to use the heat produced by PEM fuel cell for providing the energy necessary for desorption; (ii) a gravimetric hydrogen density of 5 wt. % H2 and (iii) fast sorption kinetics below 110 °C is strongly recommended. Among the known hydrogen storage materials, amide and imide-based mixtures represent the most promising class of compounds for on-board applications; however, some barriers still have to be overcome before considering this class of material mature for real applications. In this review, the most relevant progresses made in the recent years as well as the kinetic and thermodynamic properties, experimentally measured for the most promising systems, are reported and properly discussed, European Marie Curie Actions under ECOSTORE grant agreement No. 607040

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH4 + MgH2/2LiH + MgB2 (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H2 and 45.9 kJ/mol H2). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl3·AlCl3 is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl3·AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl3·AlCl3 possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi3 phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB2 upon dehydrogenation and second suppressing the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling. Fil: Le, Thi-Thu. Helmholtz Zentrum Geesthacht; Alemania Fil: Pistidda, Claudio. Helmholtz Zentrum Geesthacht; Alemania Fil: Puszkiel, Julián Atilio. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Karimi, Fahim. Helmholtz Zentrum Geesthacht; Alemania Fil: Skibsted, Jørgen. University Aarhus; Dinamarca Fil: Gharibdoust, Seyedhosein Payandeh. University Aarhus; Dinamarca Fil: Richter, Bo. University Aarhus; Dinamarca Fil: Emmler, Thomas. Helmholtz Zentrum Geesthacht; Alemania Fil: Milanese, Chiara. Università di Pavia; Italia Fil: Santoru, Antonio. Helmholtz Zentrum Geesthacht; Alemania Fil: Hoell, Armin. Helmholtz Zentrum Berlin für Materialien und Energie; Alemania Fil: Krumrey, Michael. Physikalisch Technische Bundesanstalt; Alemania Fil: Gericke, Eike. Universität zu Berlin; Alemania Fil: Akiba, Etsuo. Kyushu University; Japón Fil: Jensen, Torben R.. University Aarhus; Dinamarca Fil: Klassen, Thomas. Helmholtz Zentrum Geesthacht; Alemania. Helmut Schmidt University; Alemania Fil: Dornheim, Martin. Helmholtz Zentrum Geesthacht; Alemania

International audience; The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH2, Ni has been added to form Mg2NiH4, which has been mixed with various borohydrides to further tune hydrogen release reactions. De-hydrogenation/re-hydrogenation properties of Mg2NiH4-LiBH4-M(BH4)(x) (M = Na, K, Mg, Ca) systems have been investigated. Mixtures of borohydrides have been selected to form eutectics, which provide a liquid phase at low temperatures, from 110 degrees C up to 216 degrees C. The presence of a liquid borohydride phase decreases the temperature of hydrogen release of Mg2NiH4 but only slight differences have been detected by changing the borohydrides in the eutectic mixture.

Materials today 10, 98 - 107 (2018). doi:10.1016/j.mtener.2018.08.008, Light metal hydrides are prone to react with oxygen and/or water to produce oxides and/or hydroxides leading to reduction of hydrogen capacities, and deterioration of the hydrogen storage properties. It is therefore critical to address these issues when the materials are to be exposed to air or moisture. In this work, the combination of light metal hydrides, Mg(NH$_{2}$)$_{2}$–nLiH with polymethylpentene (TPX™), an air/moisture protective barrier is presented. It was found that the fabricated composites exhibit significant improvement of the metal hydrides stability in air. No oxidation reactions in air can be proven even after air exposure for 90 min. Extending the air-exposure time to 12 h, the reversible hydrogen capacities of these composites are much higher and more stable than they are in the case of the pure metal hydrides. In comparison to the pure metal hydrides, the composites retain the same hydrogen loading capacities and kinetic properties, with respect to the metal hydrides contents. Further, in situ synchrotron radiation powder X-ray radiation diffraction (SR-PXRD) experiments reveal that the thermal decomposition reaction pathways of the 90 min air-exposed composites are the same under air or H$_2$ atmosphere. Moreover, morphology analysis confirms that the metal hydrides remain stable in the polymeric matrix and the three-dimensional integrity is retained, even after performing tens of de/re-hydrogenation cycles. The present study shows a promising way to fabricate air-stable metal hydride-polymer composite hydrogen storage materials that can be handled in ambient conditions., Published by Elsevier Ltd., Amsterdam [u.a.]

The present study aims at investigating, for the first time, a quinary mixture of light-metals borohydrides. The goal is to design combinations of borohydrides with multiple cations in equimolar ratio, following the concept of high entropy alloys. The equimolar composition of the LiBH4 NaBH4 KBH4 Mg(BH4)2 Ca(BH4)2 system was synthetized by ball milling. The obtained phases were analysed by X-ray diffraction and in-situ Synchrotron Radiation Powder X-ray Diffraction, in order to establish the amount of cations incorporated in the obtained crystalline phases and to study the thermal behaviour of the mixture. HP-DSC and DTA were also used to define the phase transformations and thermal decomposition reactions, leading to the release of hydrogen, that was detected by MS. The existence of a quinary liquid borohydride phase is reported for the first time. Effects of the presence of multi-cations compounds or a liquid phase on the hydrogen desorption reactions are described.

In the past decades, complex hydrides and complex hydrides-based materials have been thoroughly investigated as materials for energy storage, owing to their very high gravimetric and volumetric hydrogen capacities and interesting cation and hydrogen diffusion properties. Concerning hydrogen storage, the main limitations of this class of materials are the high working temperatures and pressures, the low hydrogen absorption and desorption rates and the poor cyclability. In the past years, research in this field has been focused on understanding the hydrogen release and uptake mechanism of the pristine and catalyzed materials and on the characterization of the thermodynamic aspects, in order to rationally choose the composition and the stoichiometry of the systems in terms of hydrogen active phases and catalysts/destabilizing agents. Moreover, new materials have been discovered and characterized in an attempt to find systems with properties suitable for practical on-board and stationary applications. A significant part of this rich and productive activity has been performed by the research groups led by the Experts of the International Energy Agreement Task 32, often in collaborative research projects. The most recent findings of these joint activities and other noteworthy recent results in the field are reported in this paper.

The alkali metal amidozincates Li4 [Zn(NH2)4](NH2)2 and K2[Zn(NH2)4] were, to the best of our knowledge, studied for the first time as hydrogen storage media. Compared with the LiNH2-2 LiH system, both Li4 [Zn(NH2)4](NH2)2-12 LiH and K2[Zn(NH2)4]-8 LiH systems showed improved rehydrogenation performance, especially K2[Zn(NH2)4]-8 LiH, which can be fully hydrogenated within 30 s at approximately 230 °C. The absorption properties are stable upon cycling. This work shows that ternary amides containing transition metals have great potential as hydrogen storage materials.

A mixture of 3NaH/AlB2 was prepared by ball-milling; its hydriding reaction was studied between 375–425 °C and 25–50 bar hydrogen pressure by means of volumetric titration. The hydriding reaction was characterized by means of in situ synchrotron radiation powder X-ray diffraction and high-pressure differential scanning calorimetry. Hydriding reaction took place at the molten state, and its reaction products were NaBH4 and Al. The scanning electron microscopy images of the material revealed that the material morphology changes after hydriding. A maximum hydrogen uptake of 4.7 wt % was registered for the hydriding experiment at 425 °C and 50 bar hydrogen pressure. Dehydriding reaction was studied by means of volumetric titration and differential scanning calorimetry. The dehydriding reaction at 425 °C and 1 bar argon pressure registered a release of 2.4 wt %. The low dehydriding level was attributed to the reduction of the available particle surface upon melting of the material during the hydriding reaction.

Ajuts: The authors are grateful to the Marie-Curie European Research Training Network (Contract MRTN-CT-2006-03 5366/COSY) In the last decade, alkaline and alkaline earth metal tetrahydroborates have been the focuses of the research due to their high gravimetric and volumetric hydrogen densities. Among them, Ca(BH4)2 and the Ca(BH4)2 + MgH2 reactive hydride composite (RHC), were calculated to have the ideal thermodynamic properties which fall within the optimal range for mobile applications.In this study, the addition of NbF5 or TiF4 to the Ca(BH4)2 + MgH2 reactive hydride composite system was attempted aiming to obtain a full reversible system with the simultaneous supression of CaB12H12. Structural characterization of the specimens was performed by means of in-situ Synchroton Radiation Power X-ray diffraction (SR-PXD) and 11B {1H} Solid State Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR). The evolution of the chemical state of the Nb- and Ti-based additives was monitored by X-ray Absorption Near Edge Structure (XANES). The addition of NbF5 or TiF4 to the Ca(BH4)2 + MgH2 system have not supressed completely the formation of CaB12H12 and only a slight improvement concerning the reversible reaction was displayed just in the case of Nb-doped composite material

Addition of multi-wall carbon nanotube (MWCNT) and NaAlH 4 into nanoconfined LiBH 4 –PcB (poly (methyl methacrylate)–co–butyl methacrylate) for improving thermal stability and reducing LiBH 4 /PcB interaction is proposed. The greater the amount of gases desorbed due to polymer (PcB) degradation, the less the thermal stability of polymer host. During dehydrogenation of nanoconfined LiBH 4 –PcB, combination of gases due to PcB degradation is 64.3% with respect to H 2 content, while those of nanoconfined samples doped with MWCNT and NaAlH 4 are only 9 and 7.9%, respectively. The LiBH 4 /PcB (i.e., B⋯OCH 3 ) interaction is quantitatively evaluated by FTIR technique. The more the ratio of peak area between υ(B–H) (from LiBH 4 ) and υ(C O) (from PcB), the lower the LiBH 4 /PcB interaction. It is found that by adding small amount of MWCNT and NaAlH 4 , this ratio significantly increases up to 78%. This is in agreement with B 1 s XPS results, where the relative amount of B x O y ( x /y = 3) to LiBH 4 decreases after adding MWCNT and NaAlH 4 into nanoconfined LiBH 4 –PcB. It should be remarked that significant improvement of thermal stability and decrease of LiBH 4 /PcB interaction after adding MWCNT and NaAlH 4 into nanoconfined LiBH 4 –PcB result in considerable amount of hydrogen release and uptake as well as hydrogen reproducibility during cycling. However, the dispersion of MWCNT is still one of the most critical factors to be concerned due to probably its hindrance for hydrogen diffusion.

In previous studies, complex hydrides LiBH4 and Mg2FeH6 have been reported to undergo simultaneous dehydrogenation when ball-milled as composite materials (1 − x)LiBH4 + xMg2FeH6. The simultaneous hydrogen release led to a decrease of the dehydrogenation temperature by as much as 150 K when compared to that of LiBH4. It also led to the modified dehydrogenation properties of Mg2FeH6. The simultaneous dehydrogenation behavior between stoichiometric ratios of LiBH4 and Mg2FeH6 is not yet understood. Therefore, in the present work, we used the molar ratio x = 0.25, 0.5, and 0.75, and studied the isothermal dehydrogenation processes via pressure–composition–isothermal (PCT) measurements. The results indicated that the same stoichiometric reaction occurred in all of these composite materials, and x = 0.5 was the molar ratio between LiBH4 and Mg2FeH6 in the reaction. Due to the optimal composition ratio, the composite material exhibited enhanced rehydrogenation and reversibility properties: the temperature and pressure of 673 K and 20 MPa of H2, respectively, for the full rehydrogenation of x = 0.5 composite, were much lower than those required for the partial rehydrogenation of LiBH4. Moreover, the x = 0.5 composite could be reversibly hydrogenated for more than four cycles without degradation of its H2 capacity.

A wide variety of metal borohydrides, MBH4, have been discovered and characterized during the past decade, revealing an extremely rich chemistry including fascinating structural flexibility and a wide range of compositions and physical properties. Metal borohydrides receive increasing interest within the energy storage field due to their extremely high hydrogen density and possible uses in batteries as solid state ion conductors. Recently, new types of physical properties have been explored in lanthanide-bearing borohydrides related to solid state phosphors and magnetic refrigeration. Two major classes of metal borohydride derivatives have also been discovered: anion-substituted compounds where the complex borohydride anion, BH4 -, is replaced by another anion, i.e. a halide or amide ion; and metal borohydrides modified with neutral molecules, such as NH3, NH3BH3, N2H4, etc. Here, we review new synthetic strategies along with structural, physical and chemical properties for metal borohydrides, revealing a number of new trends correlating composition, structure, bonding and thermal properties. These new trends provide general knowledge and may contribute to the design and discovery of new metal borohydrides with tailored properties towards the rational design of novel functional materials. This review also demonstrates that there is still room for discovering new combinations of light elements including boron and hydrogen, leading to complex hydrides with extreme flexibility in composition, structure and properties.

Chemistry - a European journal 23(41), 9766 - 9771 (2017). doi:10.1002/chem.201702728, A new complex ternary amide, Rb$_2$[Mn(NH$_2$)$_4$], which simultaneously contains both transition and alkali metal catalytic sites, is developed. This is in line with the recently reported TM-LiH composite catalysts, which have been shown to effectively break the scaling relations and achieve ammonia synthesis under mild conditions. Rb$_2$[Mn(NH$_2$)$_4$] can be facilely synthesized by mechanochemical reaction at room temperature. It exhibits two temperature-dependent polymorphs, that is, a low-temperature orthorhombic and a high-temperature monoclinic structure. Rb$_2$[Mn(NH$_2$)$_4$] decomposes to N$_2$, H$_2$, NH$_3$, Mn$_3$N$_2$, and RbNH$_2$ under inert atmosphere; whereas it releases NH3 at a temperature as low as 80 °C under H2 atmosphere. Those unique behaviors enable Rb$_2$[Mn(NH$_2$)$_4$], and its analogue K$_2$[Mn(NH$_2$)$_4$], to be excellent catalytic materials for ammonia decomposition and synthesis. Experimental results show both ammonia decomposition onset temperatures and conversion rates over Rb$_2$[Mn(NH$_2$)$_4$] and K$_2$[Mn(NH$_2$)$_4$] are similar to those of noble metal Ru-based catalysts. More importantly, these ternary amides exhibit superior capabilities in catalyzing NH3 synthesis, which are more than 3 orders of magnitude higher than that of Mn nitride and twice of that of Ru/MgO. The in situ SR-PXD measurement shows that manganese nitride, synergistic with Rb/KH or Rb/K(NH$_2$)$_x$H$_{1−x}$, are likely the active sites. The chemistry of Rb$_2$/K$_2$[Mn(NH$_2$)$_x$] and Rb/K(NH$_2$)$_x$H$_{1−x}$ with H$_2$/N$_2$ and NH$_3$correlates closely with the catalytic performance., Published by Wiley-VCH, Weinheim

This paper discusses and compares the different sub-processes that occur during the hydrogen sorption of practical systems based on metal hydrides, i.e. intrinsic kinetics, heat transfer and hydrogen transport. Derived from their modeling equations, a resistance analysis is developed on these hydrogen sorption sub-processes for the first time. This analysis allows quantifying how strongly each sub-process affects the overall sorption kinetics in a hydride bed and thereby the sorption-rate limiting sub-process can be identified. It was found that in the case of the hydrogen absorption of sodium alanate material the heat transfer resistance is the dominant and rate limiting sub-process, with the exception of small geometries. Besides, the resistance due to hydrogen transport is negligible in comparison to the overall absorption resistance. As a consequence, simulations and designs of scaled-up systems based on sodium alanate material always require heat transfer optimization as one of the foremost considerations.

In situ two-dimensional synchrotron X-ray powder diffraction investigation combined with Rietveld method data analysis were performed in order to yield a complete and quantitative phases structure evolution of the polycrystalline mixture 2LiNH 2 + KBH 4 + LiH during H 2 desorption. While a first-principles, purely thermodynamics approach of the system predicted a single dehydrogenation step reaction at relatively low temperatures, it is assessed experimentally that the reaction occurs in two steps with first the formation of Li 2 NH at ca. 230 °C due to the reaction between LiNH 2 and LiH plus hydrogen and ammonia evolution, followed by an additional reaction of the resulting phases with KBH 4 at 360 °C, which releases hydrogen and leads to the formation of the monoclinic and tetragonal Li 3 BN 2 polymorphs. Besides pointing out possible limits of a purely thermodynamics approach inevitably relying exact knowledge of experimental quantities, it is concluded that before assuming it viable for on-board vehicle use, additional stoichiometries may be worth of investigation in order to assess any existence of lower hydrogen desorption temperature of such system.

This review presents recent developments for effective heat management systems to be integrated in metal hydride storage tanks, and investigates the performance improvements and limitations of each particular solution. High pressures and high temperatures metal hydrides can lead to different design considerations, which are discussed in the paper. Studies analyzing design procedures based upon different geometrical solutions and/or operation strategies are considered, and their related advantages are explained. Restrictions to the validity of particular results are also evaluated.Major attention is here given to metal hydride storage tanks for light duty vehicles, since this application is the most promising one for such storage materials and has been widely studied in the literature. Enhancing cooling/heating during hydrogen uptake and discharge has found to be essential to improve storage systems capacities and minimize time requirements. Various fueling strategies are widely explained differing by the particular system approach taken into account.At the end, optimization criteria and outcomes for both geometry-oriented and operative strategies-oriented methods are analyzed and presented to the reader as a helpful tool for future design considerations. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen forms chemical compounds with most other elements and forms a variety of different chemical bonds. This fascinating chemistry of hydrogen has continuously provided new materials and composites with new prospects for rational design and the tailoring of properties. This review highlights a range of new boron and nitrogen based hydrides and illustrates how hydrogen release and uptake properties can be improved. © 2014 Elsevier Ltd.

The structure of an unknown crystalline phase observed during the hydrogen absorption reaction of the powder mixtures 2NaH + MgB2 at high pressure has been studied by ab-initio structure determination from powder diffraction. The sequence of un-overlapped peaks extracted from the X-ray powder diffraction pattern could be indexed with a primitive cubic cell with lattice parameter a = 7.319 A. The diffraction patterns of the peaks are matched with the Pa-3 space group. The stoichiometry of the hydrogen absorption reaction suggests the presence of a high-boron content phase in the compound under investigation. Assuming this phase to be composed only by boron atoms and therefore having a density similar to that found for boron polymorphs, the solution with a space group of Pa-3 leads to reasonable B–B interatomic distances.

Among different Reactive Hydride Composites (RHCs), the combination of LiBH4 and MgH2 is a promising one for hydrogen storage, providing a high reversible storage capacity. During desorption of both LiBH4 and MgH2, the formation of MgB2 lowers the overall reaction enthalpy. In this work, the material was compacted to pellets for further improvement of the volumetric hydrogen capacity. The influence of compaction pressure on the apparent density, thermal conductivity and sorption behaviour for the Li-based RHC during cycling was investigated for the first time. Although LiBH4 melts during cycling, decrepitation or disaggregation of the pellets is not observed for any of the investigated compaction pressures. However, a strong influence of the compaction pressure on the apparent hydrogen storage capacity is detected. The influence on the reaction kinetics is rather low. To provide explanations for the observed correlations, SEM analysis before and after each sorption step was performed for different compaction pressures. Thus, the low hydrogen sorption in the first cycles and the continuously improving sorption for low pressure compacted pellets with cycling may be explained by some surface observations, along with the form stability of the pellets.

Samples of nanoconfined Reactive Hydride Composites in resorcinol–formaldehyde aerogel scaffolds (RF–CAS) are prepared by (i) direct melt infiltration of bulk 2LiBH4–MgH2; and (ii) MgH2 impregnation and LiBH4 melt infiltration. The reaction mechanisms, kinetics and thermodynamics of the systems are concluded. Activation energy (EA) and dehydrogenation enthalpies of LiBH4 and MgH2 ( Δ H des , MgH 2 + Δ H des , LiBH 4 ) of nanoconfined 2LiBH4–MgH2 are in this work of interest. The hydrogen sorption reactions in both nanoconfined samples are reversible as shown by the recovering of LiBH4 and MgH2 after rehydrogenation. The titration results show the remarkable improvement in desorption kinetics of nanoconfined samples over the bulk material, such as more than 90% of overall hydrogen storage capacity is obtained within 2 h from the nanoconfined samples during the 1st dehydrogenation, while that of bulk material needs more than 16 h. The activation energy of the composites decreases by 27–170 kJ/mol (ΔEA) due to nanoconfinement. For thermodynamics, ( Δ H des , MgH 2 + Δ H des , LiBH 4 ) calculated from DSC results of the nanoconfined samples are in the range of 41–46 kJ/mol H2.

Transmission electron microscopy and in situ X-ray diffraction have been used to characterize the hydrogenation mechanism of ball-milled 2NaH + MgB2. Hydrogen absorption was performed under 50 bar hydrogen while heating from room temperature to 400 °C. A new and unknown hydride phase is observed at about 280 °C. This phase remains stable up to 320 °C and subsequently disappears, followed by the formation of perovskite-type NaMgH3 at about 330 °C. At 380 °C, crystals of NaBH4 appear and grow.

The desorption mechanism of as-milled 2NaBH 4 + MgH 2 was investigated by volumetric analysis, X-ray diffraction and electron microscopy. Hydrogen desorption was carried out in 0.1 bar hydrogen pressure from room temperature up to 450 °C at a heating rate of 3 °C min −1 . Complete dehydrogenation was achieved in two steps releasing 7.84 wt.% hydrogen. Desorption reaction in this system is kinetically restricted and limited by the growth of MgB 2 at the Mg/Na 2 B 12 H 12 interface where the intermediate product phases form a barrier to diffusion. During desorption, MgB 2 particles are observed to grow as plates around NaH particles.

The Ca(BH4)2–Mg2NiH4 system presented here is, to the best of our knowledge, the first described Ca(BH4)2-based hydride composite that reversibly transfers boron from the Ca-based compound(s) to the reaction partner. The ternary boride MgNi2.5B2 is formed upon dehydrogenation and the formation of Ca(BH4)2 upon rehydrogenation is confirmed.

Nanoconfinement of 2LiBH(4)-MgH2 composite into carbon aerogel scaffold (CAS) impregnated with zirconium (IV) chloride (ZrCl4) for reversible hydrogen storage is proposed. Nanoconfined samples prepared with hydride:ZrCl4-doped CAS weight ratios of 1:1, 1:2, and 1:3 are prepared by melt infiltration technique. Successful nanoconfinement of all samples is confirmed and it is found that the sample with high content of hydride with respect to ZrCl4-doped CAS (1:1 weight ratio) shows partial pore blocking. The most suitable hydride:ZrCl4-doped CAS weight ratio providing the best performance based on dehydrogenation temperature and kinetics as well as hydrogen storage capacity is 1:2. Reduction of dehydrogenation temperature and faster kinetics are obtained after doping with ZrCl4. Up to 97 and 93% of theoretical hydrogen storage capacity are released and reproduced after four cycles of nanoconfined sample with ZrCl4 (1:2 weight ratio). Deficient hydrogen content with respect to theoretical capacity can be due to partial dehydrogenation during melt infiltration and formation of thermally stable [B12H12](2-) phases during cycling. (C) 2015 Elsevier B.V. All rights reserved.