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Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized. Characteristic B-N stretching vibrations of low-dimensional BN were observed by infrared and Raman spectroscopies. The crystal structures were determined using a combination of X-ray diffraction and density functional theory with one and two one-dimensional zig-zag (BN)

Herein, we report the synthesis of the copper-based MOF, Cu3(SDBA)2(HSDBA), using a solvothermal method.

After various attempts, we present a new alkaline-earth derivative of hydrazine borane (N2H4BH3, HB), magnesium hydrazinidoborane (Mg(N2H3BH3)2, Mg(HB)2, 10.5 wt % H), that was undoubtedly identified by FTIR and 11B MAS NMR spectroscopy. Mg(HB)2 was obtained by an alternative synthesis route, which is the reaction between HB and di-n-butylmagnesium in THF. The dehydrogenation properties of this compound were evaluated by two different approaches: an “open” system by thermogravimetric analysis and differential scanning calorimetry, and in a closed system, by heating the compound under isothermal conditions. Different results were obtained depending on the approach. Unlike other boron- and nitrogen-based compounds, it is likely that when Mg(HB)2 is heated in a closed system, the dehydrogenation is limited and it occurs mainly due to the homopolar interaction between the protic hydrogen atoms of the molecule. Also, Mg(HB)2 presents a contrasting thermal behavior in comparison with previous HB derivatives. In addition, a characterization by X-ray photoelectron spectroscopy was performed, and we detected instability of Mg(HB)2 when it was irradiated with the X-ray beam. All of these results are presented and discussed in the context of materials for hydrogen storage in the solid-state.

Ammonia borane NH3BH3 (AB), a material for solid-state hydrogen storage, can be nanosized by confinement into the porosity of a scaffold like mesoporous silica, carbon cryogel, graphene oxide, ZIF-8 as a metal organic framework, poly (methyl acrylate), boron nitride and manganese oxide. In doing so, nanosized AB is destabilized and shows better dehydrogenation properties than bulk AB in terms of temperature, activation energy, enthalpy and kinetics. Such improvements are due to the confinement-driven nanosizing effect, but not only. A catalytic effect may also have a contribution and, in some cases, it even overpasses the nanosizing effect. These effects are explained in detail herein. The present review aims at reporting the outcomes of the AB confinement strategy to help understand the advantages and to identify the limitations which are still not adequately defined. Based on this analysis, the challenges ahead are listed and discussed, and it appears that there are new opportunities to explore. Though nanosized AB is not mature enough for implementation, it has the potential to be developed further. Avenues worth exploring are given.

This inorganic chemistry laboratory experiment, aimed at third-year undergraduate students, focuses on an energetic coordination compound, tris(hydrazine)nickel(II) nitrate [Ni(N2H4)3][NO3]2. As long as the solid is not subject to mechanical stimuli (impact and friction), it can be safely synthesized and handled. In our laboratory conditions (see supplementary information), the experiment includes synthesis of [Ni(N2H4)3][NO3]2 in two different morphologies, visual inspection of the samples, analysis by IR spectroscopy, checking the crystallinity by powder X-ray diffraction, 3D visualization of the crystal structure by means of a free program, and observation by scanning electron microscopy. In that respect, the experiment, as a whole, introduces students to nickel(II) complexes, coordination compounds, energetic materials, sonochemical and morphology-controlled syntheses, and a 3D visualization program for crystal structures and structural models. This laboratory experiment is also proposed in the form of alternate (light) versions so that it can be adopted in another inorganic chemistry laboratory that may have restrictions in terms of equipment, and in another third-year curriculum.

Methanolysis of sodium borohydride (NaBH4) is one of the methods efficient enough to release, on demand, the hydrogen stored in the hydride as well as in 4 equiv of methanol (CH3OH). It is generally reported that, in methanolysis, sodium tetramethoxyborate (NaB(OCH3)(4)) forms as single component of the spent fuel. It is, however, necessary to clearly investigate some critical aspects related to it. We first focused on the methanolysis reaction where NaBH(4)was reacted with 2, 4, 8, 16, or 32 equiv of CH3OH. With 2 equiv of CH3OH, the conversion of NaBH(4)is not complete. With 4 to 32 equiv of CH3OH, NaBH(4)is totally methanolized (conversion of 100%). The best conditions are those involving 4 equiv of CH3OH as they offer the highest effective gravimetric hydrogen storage capacity with 4.8 wt%, an attractive H(2)generation rate with 331 mL(H-2) min(-1)-a performance achieved without any catalyst-and the formation of NaB(OCH3)(4)as single product as identified by X-ray diffraction, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. We then focused on the transformation of this product NaB(OCH3)(4)into sodium metaborate (NaBO2), via the formation of sodium tetrahydroxyborate (NaB(OH)(4)). NaB(OCH3)(4)is easily transformed in water, by hydrolysis, at 80 degrees C and for 90 minutes, into NaB(OH)(4)and 4 equiv of CH3OH. In doing so, the cycle with CH3OH is closed. Subsequently, NaB(OH)(4)is recovered and converted into NaBO(2)under heating at 500 degrees C. This reaction liberates 4 equiv of H2O, which allows to close the cycle with water. Based on these achievements, we have finally proposed a triangular recycling scheme aiming at closing the cycle with the protic reactants of the aforementioned reactions. This scheme may be used as base for implementing a closed cycle with the couple NaBH4-CH3OH.

Dihydrogen Hδ+⋅⋅⋅Hδ− bonding that is accepted as an important unconventional hydrogen bonding could play a key role in molecular self-assembly of amine boranes. It is with this goal in mind that we have studied the behavior of n-dodecylamine borane nC12H25NH2BH3 (C12AB) dissolved in anhydrous THF. C12AB can be easily synthesized with a purity higher than 99% by Lewis acid-base reaction of a BH3 complex with n-dodecylamine nC12H25NH2. It is stable when dissolved in THF that is a good solvent of it. However, it is unstable in the presence of moisture, readily hydrolyzing and producing water-soluble borates. Molecular self-assembly of C12AB has thus to be studied in anhydrous conditions, which allows observing by DLS and SAXS-WAXS the formation of core-shell aggregates in anhydrous THF. The aggregates consist of about five self-assembling stretched C12AB molecules where the NH2BH3 groups are in the core of 3 A and the alkyl chains in an outer-shell.

International audience

Ammonia borane NH3BH3 (AB), in pristine or destabilized state, has been much investigated as a solid-state chemical hydrogen storage material. The potential of such compound for thermolytic dehydrogenation (and decomposition) can be fast and reliably screened and assessed by thermogravimetric (TG) analysis via descriptors like both the onset temperature of dehydrogenation and the overall weight loss over the temperature range 100–200 °C. However, comparisons to results reported in the open literature need to be done with caution. The objective of the present article is thus to show that the thermolytic properties of AB determined by TG analysis are much dependent on the operation conditions. We have observed that much different results are obtained by changing the analyzer, and especially the crucible (comparable to a semi-closed reactor in one case or similar to an open reactor in the second case). For example, a stable AB sample is able to suffer a weight loss of 18.4 wt% starting from 116.5 °C when a semi-closed crucible is used, versus a weight loss of 51.9 wt% starting from 91 °C with the utilization of an open crucible. Our main results are reported herein in the form of a short technical communication: it aims at sharing our experimental observations in order to avoid misinterpretation and misunderstanding as for the TG analyses of AB and of any kind of derivatives. The present work should help in comparing the data available in the open literature with care and, from now on, should be regarded as a key study to report comparable TG results for AB thermolytic dehydrogenation.

High-pressure X-ray diffraction and Raman spectroscopy in a diamond anvil cell were used to study the insertion of the chemical hydrogen storage material, ammonia borane, in the one-dimensional pores of the zeolite theta-1 TON. Heating of this material up to 300 °C under pressures up to 5 GPa resulted in the release of a significant amount of hydrogen due to the conversion of ammonia borane confined in the channels of TON and outside the zeolite to polyaminoborane and then polyiminoborane chains. The filling of TON with hydrogen resulted in a much greater increase in unit cell volume than that corresponding to thermal expansion of normal compact inorganic solids. This process at high temperature is accompanied by a phase transition from the collapsed high-pressure Pbn21 form to the more symmetric Cmc21 phase with expanded pores. This material has a high capacity for hydrogen adsorption under high-temperature, high-pressure conditions.

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

Following the seminal B–N–H compound ammonia borane NH3BH3, a series of derivatives have been developed as possible chemical hydrogen carriers. First, alkali and alkaline earth derivatives of ammonia borane, i.e. amidoboranes M(NH2BH3)n with n = 1 or 2, emerged. Then, hydrazine borane, which is actually a derivative of ammonia borane, was re-discovered and considered as a precursor of alkali and alkaline earth derivatives, i.e. hydrazinidoboranes M(N2H3BH3)n. A number of B–N–H ionic salts were, in this way, synthesized and reported. The present review provides the general background (e.g. syntheses, crystallographic structures, thermal stability, dehydrogenation properties, and decomposition mechanisms) relating to these alkali and alkaline earth amidoboranes and hydrazinidoboranes, and carries on two objectives. The first objective is to discuss the potential of these materials (for the application for which they have been primarily developed over the past decades, namely hydrogen storage) and the challenges they are facing. It is concluded that the light alkali amidoboranes, namely the lithium, sodium and potassium amidoboranes) should be further developed owing to better dehydrogenation properties in terms of the onset temperature of dehydrogenation, the extent of dehydrogenation, and the purity of the hydrogen released. They should, however, be further developed with the aim of upscaling, something that has not yet been achieved. Achieving high technological readiness levels is thereby the main challenge ahead. The second objective of the present review is to explore alternative uses because, as things stand, none of the developed materials have the expected features for hydrogen storage. We suggest that any of the discussed derivatives are potentially solid-state reducing agents, energetic materials, and/or precursors of boron nitride-based ceramics, bearing in mind that for this last use, if the targeted material is porous, it could be regarded as a reversible hydrogen sorbent. It is thus important to maintain efforts in the development of the current derivatives as well as in the discovery of novel ones.

Herein, we developed a precursor approach toward the design of a titanium nitride (TiN)/silicon nitride (Si3N4) nanocomposite with an activated carbon monolith as a support matrix forming a highly micro-/mesoporous component to be used as a Pt support for the catalytic hydrolysis of sodium borohydride (NaBH4) as a model reaction. The experimental data demonstrated that the amorphous Si3N4 matrix, the strong Pt-TiN nanocluster interaction and the synergistic effects between the three components contributed to the improved performance of the catalyst system. Thus, the use of this TiN/Si3N4 nanocomposite allowed to significantly reducing the noble metal loading (only ∼1 wt% of Pt) for the complete and fast dehydrogenation of NaBH4 under alkaline conditions at 80 °C. Additionally, the catalytic system displayed an excellent robustness and durability to offer reusability without collapsing and performance decrease under the harsh conditions imposed by the reaction.

Ammonia borane H3N−BH3 (AB) was re-discovered, in the 2000s, to play an important role in the developing hydrogen economy, but it has seemingly failed; at best it has lagged behind. The present review aims at analyzing, in the context of more than 300 articles, the reasons why AB gives a sense that it has failed as an anodic fuel, a liquid-state hydrogen carrier and a solid hydrogen carrier. The key issues AB faces and the key challenges ahead it has to address (i.e., those hindering its technological deployment) have been identified and itemized. The reality is that preventable errors have been made. First, some critical issues have been underestimated and thereby understudied, whereas others have been disproportionally considered. Second, the potential of AB has been overestimated, and there has been an undoubted lack of realistic and practical vision of it. Third, the competition in the field is severe, with more promising and cheaper hydrides in front of AB. Fourth, AB has been confined to lab benches, and consequently its technological readiness level has remained low. This is discussed in detail herein.

Alkali hydrazinidoboranes MN2H3BH3 (M = Li, Na, K, Rb) have been developed for hydrogen storage. To complete the family of MN2H3BH3, we focused on cesium hydrazinidoborane CsN2H3BH3 (CsHB). It has been synthesized by reaction of cesium with hydrazine borane (N2H4BH3) at −20 °C under inert atmosphere, and it has been characterized. A crystalline solid (monoclinic, s.g. P21 (No. 4)) has been obtained. Its potential for hydrogen storage has been studied by combining different techniques. It was found that, under heating at constant heating rate (5 °C min−1) or at constant temperature (e.g. 120 °C), CsHB decomposes rather than it dehydrogenates. It releases several unwanted gaseous products (e.g. NH3, B2H6) together with H2, and transforms into a residue that poses safety issues because of shock-sensitivity and reactivity towards O2/H2O. Though the destabilization brought by Cs+ onto the anion [N2H3BH3]− has been confirmed, the effect is not efficient enough to avoid the aforementioned drawbacks. All of our results are presented herein and discussed within the context of solid-state hydrogen storage.

Ammonia borane NH3BH3 is able to generate H2 by catalytic hydrolysis at ambient conditions. Such a potential has been much studied but the hydrolysis by-products, i.e. ammonium borates, have been little studied. As such we undertook a systematic work aiming at getting a sound understanding of the borates forming by hydrolysis. Contrary to what is commonly believed, NH3BH3 (10 M) in aqueous alkaline (pH = 8) solution is not completely stable. Spontaneous hydrolysis takes place, resulting in the formation of by-products and precipitation of borate crystals. This means that long-term storage of concentrated AB solution is not possible. The borate crystals were analyzed with the help of various techniques and was identified as being diammonium tetraborate dihydrate (NH4)2B4O5(OH)4⋅2H2O (263.39 g mol−1). The crystal structure was solved and found to be monoclinic with a space group P21. The borate is an analog of borax Na2B4O5(OH)4⋅8H2O. These results, among others, are reported in details hereafter and they are discussed in order to bring elements of response to the questions concerning storage of aqueous NH3BH3 and recyclability of such a borate.

International audience; Boron nitride, BN, for hydrogen storage emerged in the beginning of the millennium and there swiftly followed more than 15 years of efforts combining experimental laboratory works and to a greater extent computational predictions. BN has been considered mainly for the storage of molecular hydrogen, H-2, by physisorption and/or chemisorption over a wide range of temperatures, that is, between -196 degrees C and 300 degrees C. Yet its potential has gone beyond the sorption of H-2 as it has been also, although less extensively, involved in chemical H storage. The present review aims at giving a comprehensive overview of the main experimental results and findings as well as of the different avenues worth being explored. A key lesson of this survey is that boron nitride may turn out to be a promising material for hydrogen storage at room conditions provided all the predictions come true. The "ball" is now in the lab experimenters' court.

International audience; Mesoporous monolithic (3D) boron nitride (BN) structures are synthesized using a template‐assisted polymer‐derived ceramic route. Polyborazylene is selected to impregnate monolithic activated carbon, which is used as template. After pyrolysis and template removal, this method supplies BN compounds with controlled crystallinity and tunable textural properties controlled by the temperature at which they have been annealed (from 1000 to 1450 °C). Monoliths with an interconnected mesoporous network, high specific surface areas from 584 to 728 m2 g−1, significant pore volumes from 0.75 to 0.93 cm3 g−1, and a relatively high compressive strength are generated. These highly porous compounds are used as nanoscaffolds to confine ammonia borane (AB). The composites provide an effective gravimetric hydrogen capacity of up to 8.1 wt %, based on AB measured at 100 °C; this value demonstrates the high potential of this system as a safe potential hydrogen storage material.

The development of innovative methods for the effective removal of toxic organic pollutants from wastewater is of paramount importance. Removal of organic pollutants from aqueous media by chemical reduction using low cost metal-based nanocatalysts and in the presence of sodium borohydride (NaBH4), as a reducing agent, has become a very valuable approach in recent years. We report the advanced catalytic property of copper (0) nanoparticles (Cu NPs) supported on sulfonated reduced graphene oxide (Cu@rGO-SO3H) for the catalytic reduction of thioflavine-T (ThT) dye in the presence of NaBH4, at moderate conditions. Cu@rGO-SO3H catalyst was synthesized by the impregnation-reduction method and diverse characterization techniques were applied to explain the structure and morphology. The results show that the Cu NPs are perfectly dispersed on the surface of the rGO-SO3H support surface (d(mean) = 6.9 +/- 0.4 nm). The catalytic activity of the Cu@rGO-SO3H catalyst was tested in the reduction of ThT in water at 298 K in the presence of NaBH4 and the excellent activity of catalyst have been detected against ThT with 30.5 min(-1) initial turn-over frequency (TOFinitial) value. Another important point is that the catalyst has good reusability performance (at 5th reuse 68%) for the catalytic reduction of ThT. Our catalytic studies were also carried out at various temperatures in order to calculate the E-a, Delta H-not equal and Delta S-not equal.

International audience; Crystalline B–N–H compounds of low molecular weight have been intensively investigated over the past two decades owing to their promises for chemical hydrogen storage. Hydrazine borane NH2–NH2–BH3 is one of the most recent examples of this family of materials. In the present work, we explored its structural behaviour under mechanical stimulus by synchrotron high pressure X-ray diffraction. It has been evidenced that hydrazine borane shows a gradual pressure-induced decrease of its unit cell dimension and the process is reversible when the applied pressure is released. The compressibility of this material was established to be relatively low (high bulk modulus) and highly anisotropic. As revealed by molecular simulations based on Density Functional Theory calculations, the mechanical behaviour of NH2–NH2–BH3 was correlated to the pressure-induced changes of its crystal structure in terms of intra- and intermolecular bond lengths and angles parameters.

Aqueous hydrazine bisborane H3B N2H4 BH3 (HBB) might be a possible liquid-state chemical H storage material at the conditions that the compound totally dehydrogenates in mild conditions. Herein we demonstrate such a potential. We report for the first time a work about the dehydrogenation of aqueous HBB. The compound is not stable in water. Its stability is even lower in alkaline conditions because of the likely formation of the unstable intermediate [H3BOH]−. The use of a metal-based catalyst accelerates the hydrolysis of the BH3 groups but the bimetallic NiPt catalyst is more active, being also able to decompose the N2H4 moiety. The best kinetics is observed at 70 °C and in alkaline conditions. However, the dehydrogenation is not total, reaching a limit of 80% of conversion. Unfortunately the reason of that is not understood yet. As things stand, there are some challenges ahead, but HBB has shown to be a possible liquid-state chemical H storage material.

Viewing calcium hydrazinidoborane Ca(N2H3BH3)2 (9.3 wt% H) as a potential hydrogen storage material, we long sought to synthesize it by solid-solid reaction of calcium hydride CaH2 and hydrazine borane N2H4BH3. However, it was elusive because of unsuitable experimental conditions. In situ synchrotron thermodiffraction helped us to identify the key role played by the temperature in the formation of the new phase. From 45 °C, new diffraction peaks appear, and the DSC analysis shows an exothermic signal. Thermal activation is thus required to make solid-state CaH2 react with melted (liquid-state) N2H4BH3. The XRD pattern can be indexed using a mixture of two phases: (i) unreacted CaH2 as a minor phase (29 wt%) and (ii) the hitherto elusive Ca(N2H3BH3)2 (71 wt%). The as-formed Ca(N2H3BH3)2 crystallizes in a monoclinic Ic (No. 9) unit cell where the intermolecular interactions form chains (layers) along the a axis, resulting in intra-chain and inter-chain Ca⋅⋅⋅Ca distances as short as 4.39 and 7.04 A respectively. Beyond 90 °C, Ca(N2H3BH3)2 decomposes, as evidenced by the diffraction peaks fading, an exothermic signal revealed by DSC, a weight loss (5.3 wt% at 200 °C) observed by TGA, and a gas release (H2, and some N2, NH3, N2H4) monitored by MS. The as-formed thermolytic residue is amorphous and of complex polymeric composition. These results and the next challenges, are discussed herein.

The potential of the decahydro-closo-decaborate anion B10H102− in alkaline aqueous solution as anodic fuel was investigated by using cyclic voltammetry and three different bulk metal electrodes (platinum, gold and silver). The sodium salt NaB10H10 was first synthesized, fully characterized and assessed for its relative stability in alkaline medium for 25 days. Then, oxidation of B10H102− in alkaline aqueous solution was studied. With platinum, the electrochemical activity is nil. With gold and silver, oxidation takes place at >0 V vs. SCE, suggesting direct oxidation of B10H102−. A current density of e.g. 15.1 mA cm−2 at 0.51 V vs. SCE is produced, supporting an electrocatalytically activity for both electrodes. There is even some reversibility of the process (i.e. reduction of intermediate species) with silver. The most important oxidation products were identified as being B7-based anions for both silver and gold. Such results suggest the occurrence of partial oxidative degradation of B10H102− at positive potential and may open new application prospects to polyborate anions.

In this work we present rubidium hydrazinidoborane RbN2H3BH3 (RbHB), the newest and last member of the alkali metal derivatives of hydrazine borane N2H4BH3 (HB). It is shown that HB readily reacts with metallic rubidium in THF at room temperature to form RbHB under argon atmosphere. The molecular and crystal structures of this new compound are discussed on the basis of FTIR spectroscopy, 11B MAS NMR spectroscopy, and powder X-ray diffraction analyses. RbHB crystallizes in a monoclinic P21 (No. 4) unit cell where each Rb+ cation adopts octahedral coordination surrounded by six [N2H3BH3]− anions, which are two more than for e.g. LiN2H3BH3 (with tetrahedral coordination) in accordance with the larger size of Rb+. RbHB is isostructural to potassium hydrazinidoborane KN2H3BH3. Its dehydrogenation properties, evaluated by using thermogravimetric analysis, differential scanning calorimetry, and isothermal analysis, are compared to those of the parent HB as well as to analogous compounds in order to evaluate the potential of RbHB as hydrogen storage material. According to the presented data, the dehydrogenation properties of RbHB are much better than those of HB and are comparable to those of the lithium derivative. Our main results are reported therein.

International audience; The five-coordinate Ru-II hydride ((PNN)-P-tBu*) RuH(CO) (2) containing the dearomatized anionic form of the tridendate unsymmetrical pincer ligand (PNN)-P-tBu {(PNN)-P-tBu = 2-((di-tert-butylphosphino) methyl)-6-(3,5-dimethyl- 1H-pyrazol-1-yl) pyridine} has been exploited as an ammonia borane (NH3 center dot BH3, AB) and hydrazine bis(borane) (H3B center dot H2N-NH2 center dot BH3, HBB) dehydrogenation catalyst in THF solution at ambient temperature. Complex 2 releases two H-2 equivalents per AB monomer and 1.5 H-2 equivalent per HBB monomer, with concomitant generation of the corresponding polymeric "spent fuels" [poly(borazylenes) or poly(aminoboranes), respectively]. Complex 2 has been found to have excellent catalytic activity, with recorded TOF values of 171 h(-1) (AB) and 359 h(-1) (HBB) at ambient temperature. The reaction has been studied experimentally through multinuclear [11B, 31P{1H}, and 1H] variable-temperature (VT) NMR spectroscopy, kinetic rate measurements and kinetic isotope effect (KIE) determination with deuterated AB isotopologues. It was found that the pincer backbone is directly involved in the catalytic process, with the presence of both protonated ((PNN)-P-tBu) and deprotonated ((PNN)-P-tBu*)(-) forms in solution. Cooperative catalysis involving the pincer methylenic side-arm and the metal center at the same time is the most likely reaction mechanism, on the basis of the collected experimental data and the computational analysis of the process at the DFT//MN15//SMD level of theory. An unprecedented dearomatization path stemming from the reduction of Cg of the pyridine central ring has been found in the catalyst spent form formed at the end of the dehydrogenation process: ((PNN)-P-tBu#) RuH(CO)center dot BH3 (4). Complex 4 was independently synthesized from the hydrido-chloro compound ((PNN)-P-tBu) RuH(CO) Cl (1) with a large excess of NaBH4 at solvent reflux and it was characterized both in solution and in the solid state. The crystal structure revealed that the borane " ligand" bridges the Ru center and the pyridine N atom through one of its B-H bonds in a s-BH agostic fashion. It can be formally considered as a (more stable) structural isomer of the hydride-borohydride complex ((PNN)-P-tBu) RuH(CO)(eta(1)-BH4) (3), with the H and BH4 ligands trans to each other within the octahedral metal coordination sphere.

International audience; As the world shifts toward renewable energy, the need for an effective energy carrier is pressing. Hydrogen has often been touted as a universal clean energy vector and the fuel of the future. Unfortunately, mass adoption of the hydrogen economy is slow due to a lack of incentives and technical difficulties in storing hydrogen. Better materials capable of reversible hydrogen uptake/release with hydrogen capacity surpassing 5 mass% at the ambient must emerge. So far, finding such materials has been elusive; alloys capable of ambient hydrogen uptake/release have a low storage capacity while high capacity hydrides have a very high hydrogen release temperature. From metal alloys to complex hydrides, a better understanding of the behavior of hydrogen in hydrides is essential to fine-tune their properties toward application. Herein, the latest approaches to design hydrogen storage materials based on known hydrides are reviewed with the aim to facilitate the emergence of alternative thinking toward the design of better hydrogen storage materials. Synthetic methods and conceptual approaches to achieve particular hydrogen thermodynamics and kinetics are discussed. These include metallurgical alloying, mechanochemical modification, chemical destabilization, the nanosizing approach, and theoretical modeling and machine learning techniques to guide experimental work.

Nickel complexes have recently been presented as prospective catalytic materials for hydrogen H2 evolution by hydrolysis of sodium borohydride NaBH4. An attractive complex is nickel hydrazine nitrate [Ni(N2H4)3][NO3]2 for which little variations in the synthesis procedure result in different morphologies like hexagonal plates, clews and discs. In our conditions, the clews have the better catalytic activity owing to more defects and more active sites. There is an effect of the morphology on the catalytic activity. However, the H2 evolution curves (regardless the initial morphology) show an induction period during which the complex (purple violet in color) evolves into a catalytically active form (fine black powder). The evolution is featured by changes in morphology and chemical state of nickel. The catalytically active form is even more active than the pristine complex: it shows a higher H2 generation rate (three times higher in the best case). The starting complexes and the “reduced” counterparts have been then characterized (e.g. SEM, FTIR, XRD, XPS) to better understand the aforementioned evolutions. One of our main conclusions is that there are some marked analogies between our nickel-based catalysts and the much-investigated cobalt-based catalysts.

Catalyzed hydrolysis of sodium borohydride generates up to four molecules of hydrogen, but contrary to what has been reported so far, the humidified evolved gas is not pure hydrogen. Elemental and spectroscopic analyses show, for the first time, that borate by-products pollute the stream as well as the vessel.

Sodium borohydride (NaBH4) is an attractive hydrogen carrier owing to its reactivity with water: it can generate 4 equivalents of H2 by hydrolysis (NaBH4 + 4H2O → NaB(OH)4 + 4H2). Since using NaBH4 in the solid state is the most favorable way to achieve a high gravimetric hydrogen storage capacity (theoretical maximum of 7.3 wt%), we have investigated the possibility of developing a core@shell nanocomposite (NaBH4@Ni) where a metallic nickel catalyst facilitating the hydrolysis is directly supported onto NaBH4 nanoparticles. Following our initial work on core–shell hydrides, the successful preparation of NaBH4@Ni has been confirmed by TEM, EDS, IR, XRD and XPS. During hydrolysis, the intimately combined Ni0 and NaBH4 allow the production of H2 at high rates (e.g. 6.1 L min−1 g−1 at 39 °C) when water is used in excess. After H2 generation, the spent fuel is composed of an aqueous solution of NaB(OH)4 and a nickel-based agglomerated material in the form of Ni(OH)2 as evidenced by TEM, XPS and XRD. The effective gravimetric hydrogen storage capacity of nanosized NaBH4@Ni has been optimized by adjusting the required amount of water for hydrolysis and an effective hydrogen capacity of 4.4 wt% has been achieved. This is among the best reported values.

Ammonia borane NH

International audience; Ammonia borane NH3BH3 is a well-known thermolytic hydrogen storage material. However, the mechanism of dehydrogenation under heating is very complex. In this context, we have studied the thermolytic dehydrocoupling of solid, partially deuterated, ammonia borane NH3BD3 up to 200 degrees C, that is, up to the release of the second equivalent of hydrogen, by using thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry. Our results show that the process, resulting in the release of hydrogen (i.e., HD), is mainly driven by heteropolar hydrogen-deuterium interactions (N-H delta+center dot center dot center dot D delta--B). Homopolar dihydrogen interactions (N-H delta+center dot center dot center dot H delta+-N) appreciably contribute to hydrogen (i.e., H-2) release. In contrast, the contribution of homopolar dideuterium interactions (B-D delta-center dot center dot center dot D delta--B) is negligible. In summary, this work sheds new light on the mechanism governing the release of hydrogen from ammonia borane under thermolytic conditions.