Borohydride Mixtures Research Articles

Synthesis, properties and thermal decomposition particularities of magnesium borohydride ammoniates

An elemental analysis, as well as XPD, IR, XPS and TGA-DSC/TPD-MS methods are used to compare composition and properties of Mg(BH4)2(NH3)n (n = 1, 2, 3) complexes obtained by following methods: (1) mechanochemical treatment and (2) heating of magnesium borohydride hexaammoniate and unsolvated magnesium borohydride mixtures. A systematic study of the thermal decomposition features and gases composition released during the thermolysis of the synthesized compounds is carried out. The differences found are discussed.

Effective hydrogen release from ammonia borane and sodium borohydride mixture through homopolar based dehydrocoupling driven by intermolecular interaction and restrained water supply

Non-catalytic dehydrogenation of solid-state ammonia borane and sodium borohydride mixtures is achieved in this work by water vapor facilitated hydrothermolysis.

New gold standard: weakly capped infant Au nanoclusters with record high catalytic activity for 4-nitrophenol reduction and hydrogen generation from an ammonia borane-sodium borohydride mixture.

Increasing the surface area-to-volume ratio of materials through size reduction is a desired approach to access maximum possible surface sites in applications such as catalysis. However, increase in the surface energy with the decrease in dimension warrants strong ligands to stabilize nanosystems, which mask the accessibility of the active surface sites. Owing to this, the realization of the true potential of a catalyst's surface remains challenging. Here, we employed a rationally designed strategy to synthesize infant Au nanoclusters—that alleviates the requirement of any separate ligand removal step—to unleash their actual potential to register a record high maximum turn-over frequency (TOFmax) of 72 900 h−1 and 65 500 h−1 in the benchmark catalytic reduction of 4-nitrophenol and catalytic H2 generation from an ammonia borane–sodium borohydride mixture, respectively. Such a phenomenal catalytic activity has been realized via the synthesis and stabilization of Au nanoclusters using solid citric acid and a super-concentrated aqueous AuCl3 solution, a pathway entirely different from the conventional modifications of the Turkevich and Brust methods. The crux of the synthetic strategy lies in precise control of the water content and thereby ensuring that the final Au nanoclusters remain in the solid state. During the synthesis, citric acid not only acts as a reducing agent to yield ‘infant’ Au nanoclusters but also provides a barrier matrix to arrest their growth. In solution, its weak capping ability and rapid dissolution allows the reactants to easily access the active sites of Au nanoclusters, thus leading to faster catalysis. Our study reveals that the true potential of metal nanoclusters as catalysts is actually far higher than what has been reported in the literature.

Effective reduction of graphene oxide using sulfur dioxide-containing chemical compounds

The success of the graphene oxide reduction process depends on how similar the product is to pristine graphene. Sulfur oxide, which is a significant industrial waste gas, can be used in the reduction of graphene oxide. In this study, the graphene oxide reduction process was performed by using sulfur oxide with sodium tetraborate decahydrate, l-ascorbic acid, ammonium hydroxide, sodium hydroxide, lithium hydroxide, sodium borohydride and sodium thiosulfate. The carbon-to-oxygen atomic ratio and D-to-G peak ratio of the graphene oxide, which represent the degree of reduction, were 2.64–4 and 0.78–1.80 with the use of sulfur oxide, respectively. The sulfur oxide/sodium borohydride mixture increased the carbon-to-oxygen atomic ratio of the graphene oxide to 11.73, while improving the value of the D-to-G peak ratio at 3.14. The reduced graphene oxide with the highest specific heat capacity was obtained using sodium tetraborate decahydrate, with an improvement of 74.54% compared to graphene oxide. The results show that sulfur oxide, which is harmful to the environment and human health, can be utilized in an effective reduction process, together with other reducing chemicals, to obtain an industrially valuable material, such as reduced graphene oxide.

Hydrogen storage properties of eutectic metal borohydrides melt-infiltrated into porous Al scaffolds

Porous Al scaffolds were synthesised and melt-infiltrated with various eutectic metal borohydride mixtures (0.725LiBH4-0.275KBH4, 0.68NaBH4-0.32KBH4, 0.4NaBH4-0.6 Mg(BH4)2) to simultaneously act as both a confining framework and a reactive destabilising agent for H2 release. The scaffolds were synthesised by sintering a pellet of NaAlH4/2 mol%TiCl3 at 450 °C under dynamic vacuum. During the sintering process the sodium alanate (NaAlH4) decomposed to Al metal. The vacuum applied at elevated temperature promoted the Na metal to vaporise and be extruded from the pellet. The pores of the resulting Al scaffold were created during removal of the H2 and the Na from the body of the NaAlH4/2 mol%TiCl3 pellet. According to the morphological observations carried out by a Scanning Electron Microscope (SEM), melt-infiltrated eutectic mixtures of metal borohydrides were highly dispersed into the porous scaffolds. Temperature Programmed Desorption (TPD) experiments, revealed that the melt-infiltrated samples exhibited faster H2 desorption kinetics in comparison to bulk samples, with onset temperatures (Tdes) lower than the bulk by 150–250 °C. The as-synthesised porous Al scaffolds acted as a reactive containment vessel for these eutectic mixtures that simultaneously nanoconfined and destabilised the mixtures.

Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures

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 °C up to 216 °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.

Simultaneous desorption behavior of M borohydrides and Mg2FeH6 reactive hydride composites (M = Mg, then Li, Na, K, Ca)

Combinations of complex metal borohydrides ball milled with the transition metal complex hydride, Mg2FeH6, are analysed and compared. Initially, the Reactive Hydride Composite (RHC) of Mg2+ cation mixtures of Mg2FeH6 and γ-Mg(BH4)2 is combined in a range of molar ratios and heated to a maximum of 450 °C. For the molar ratio of 6 Mg2FeH6 + Mg(BH4)2, simultaneous desorption of the two hydrides occurred, which resulted in a single event of hydrogen release. This single step desorption occurred at temperatures between those of Mg2FeH6 and γ-Mg(BH4)2. Keeping this anionic ratio constant, the desorption behavior of four other borohydrides, Li-, Na-, K-, and Ca-borohydrides was studied by using materials ball milled with Mg2FeH6 applying the same milling parameters. The mixtures containing Mg-, Li-, and Ca-borohydrides also released hydrogen in a single event. The Mass Spectrometry (MS) results show a double step reaction within a narrow temperature range for both the Na- and K-borohydride mixtures. This phenomenon, observed for the RHC systems at the same anionic ratio with all five light metal borohydride mixtures, can be described as simultaneous hydrogen desorption within a narrow temperature range centered around 300 °C.

Eutectic melting of LiBH4-KBH4.

Eutectic melting in mixtures of alkali and alkali earth metal borohydrides can pave the way for new applications as fast ionic conductors, and facilitate hydrogen release by low temperature chemical reactions and convenient nanoconfinement. Here, we determine the eutectic composition for the lithium potassium borohydride system, 0.725LiBH4-0.275KBH4, with the lowest melting point, Tmelt ∼105 °C, of all known alkali and alkali earth metal borohydride mixtures. Mechanochemistry and manual mixing of LiBH4-KBH4 mixtures facilitate the formation of LiK(BH4)2. However, the melting or heat treatments used in this work do not produce LiK(BH4)2. The bimetallic borohydride dissociates into the monometallic borohydrides at ∼95 °C and partial melting occurs at ∼105 °C. Analysis of the unit cell volumes of LiBH4, KBH4 and LiK(BH4)2 in the temperature range 25 to 90 °C indicates that the formation of the bimetallic borohydride is facilitated by a more dense packing as compared to the reactants. Thus, LiK(BH4)2 is considered metastable and the formation is pressure induced. A phase diagram for the LiBH4-KBH4 system is established, which illustrates the low eutectic melting point and the stability range for the bimetallic borohydride, LiK(BH4)2.

Density functional theory simulations of complex hydride and carbon-based hydrogen storage materials

This critical review covers the mechanisms underlying density functional theory (DFT) simulations and their relevance in evaluating, developing and discovering new materials. It is intended to be of interest for both experimentalists and theorists in the expanding field of hydrogen storage. We focus on the most studied classes of materials, metal-hydride, -amide, and -borohydride mixtures, and bare and transition metal-doped carbon systems and the utility of DFT simulations for the pre-screening of thermally destabilised reaction paths (170 references).

Design, synthesis and glutathione peroxidase-Like properties of ovothiol-Derived diselenides

Eleven imidazole diselenides derived from the naturally occurring family of antioxidants, the ovothiols, were synthetised by cyclisation of selenoamides with trimethylsilyltrifluoromethanesulfonate or refluxing of cyanoamines in a selenium/sodium borohydride mixture. These compounds were assayed for their glutathione peroxidase-like (GSH Px-like) activity and their capacity to be reduced by glutathione. The most active molecules of the series were 4 times more potent in the GSH Px-like test than the widely known reference compound, ebselen. This catalytic activity was mediated by the formation of the antioxidant selenol intermediate upon partial but significant exchange reaction with glutathione.

Characterization of alkaline-degradation products of some 3,4-di- and 3,4,6-tri-methyl ethers of hexoses by G.L.C.-mass spectrometry of O-trimethylsilyl derivatives

G.l.c.-mass spectrometry has been used to provide information on the O-trimethylsilyl derivatives of the products of alkaline degradation of 3,4-di- and 3,4,6-tri- O-methyl- D-glucose, and 3,4,6-tri- O-methyl- D-galactose. During reaction with sodium hydroxide-sodium borohydride mixtures, reduction occurs more rapidly than β-elimination and the only detectable products were the corresponding alditols and the epimeric 3-deoxyalditols. Extended reaction with sodium hydroxide alone, followed by treatment with sodium borohydride, gives mixtures of aldonic acids including the epimeric 3-deoxy-4- O-methylaldonic acids (metasaccharinic acids), 3-deoxyaldonic acids (with loss of the 4- O-methyl substituent), and 3,4-dideoxy-aldonic acids. Possible reaction-pathways are discussed.

Combustion of Highly Reactive Fuels in Supersonic Airstreams

The feasibility of adding heat to supersonic airstreams by combustion was studied in a small wind tunnel. Aluminum borohydride, pentaborane, hydrocarbon-aluminum borohydride mixtures, trimethylaluminum, diethylaluminum hydride, alkylboranes, alkylboron hydrides and vinylsilane were tested. The first three ignited easily and burned well. The others either failed to ignite or burned only in the diffuser. Trimethylaluminum and diethylaluminum hydride produced light and other evidence of heat evolution when water was simultaneously injected into the tunnel. Gross effects on flow were studied by observation of shock patterns and water sprays injected from the tunnel walls. Examples are given which illustrate the use of these techniques in aerodynamic studies in larger wind tunnels.