Borohydride System Research Articles

Inducing One-Step Dehydrogenation of Magnesium Borohydride via Confinement in Robust Dodecahedral Nitrogen-Doped Porous Carbon Scaffold.

A dodecahedral activated N-doped porous carbon scaffold is synthesized and used for the nanoconfinement of Mg(BH4)2. The optimized mesoporous scaffold possesses an accumulated pore width of 2.65nm, high specific surface area (3955.9 m2g-1), and large pore volume (2.15 cm3g-1), providing ample space for the confinement of Mg(BH4)2 particles and numerous surface active sites for interactions with the same. The confined Mg(BH4)2 system features a dehydrogenation onset temperature of 81.5°C, an extremely high capacity of 10.2 wt% H2, and an almost single-step dehydrogenation profile. Moreover, the system exhibits superior capacity retention of 82.7% after 20 cycles at a moderate temperature of 250°C. Precise activation control enables a transformation from microporous carbon materials to mesoporous ones, and hence the efficient nanoconfinement of Mg(BH4)2 and realization of one-step dehydrogenation. The evolution of borohydride intermediates is systematically revealed throughout the cycling process. Density functional theory calculations demonstrate defective N heteroatoms within the scaffold are vital in reducing the strength of B─H bonds, and the N-doped carbon can facilitate decomposition of the irreversible MgB12H12 intermediate. This study opens up new avenues for designing robust carbon scaffolds doped with heteroatoms and analyzing intermediate evolution in nanoconfined Mg-based borohydride systems.

In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH4. The Li/Mg based dual-cation borohydride (LiMg2(BH4)5, LMBH) was successfully synthesized by wet chemical ball milling of LiBH4 and MgCl2. The optimal (LMBH (4.5:1) sample, LiBH4 and MgCl2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH4. The LMBH (4.5:1) doped with TiF3 system releases 7.98 wt% H2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB2 and TiH2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB2/TiH2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.

Ultrasensitive visualization detection of sodium borohydride based on surface treated transparent molybdenum oxide quantum dots

Sodium borohydride has attracted increasing attention as an energy source for direct borohydride fuel cells. But, to-date, the detection of borohydride concentration is still difficult in the research based on borohydride systems, especially the convenient visualization detection technology has not yet made a breakthrough. Herein, a transparent molybdenum oxide quantum dots (MoO3 QDs) was successfully prepared using a mild hydrothermal method. The as-prepared molybdenum oxide quantum dots achieved an ultrasensitive visualization response to sodium borohydride. Benefiting from the uniform size of molybdenum oxide quantum dots and less than 10 nm, the quantum dots dispersed in aqueous solution exhibit high transparency. When sodium borohydride appeared in the system, the solution quickly turned transparent blue. We anticipate that this work will provide a facile and cost-effective strategy based on the design of new materials for the visualization detection of compound concentration.

Unravelling the effect of alkali cations and halide anions on the de-hydrogenation properties of ammine zinc borohydrides

This work sheds light on the role of the alkali cations, halide anion substitution as well as borohydride anion vacancies on the de-hydrogenation properties of ammine zinc borohydrides. A new liquid ammonia-based synthesis approach employed in this study enabled direct solvothermal synthesis of several novel and previously reported ammine zinc borohydride compounds such as AxZn(BH4)2+x(NH3)2 for x = 0; 1 and M = Li; Na; K. The experimental results are supported by first principle calculations and molecular dynamics techniques for the interpretation of inherently complex hydrogen release mechanisms. We demonstrate that the salt metathesis reaction heavily relied upon in literature for synthesis of these compounds can result in preferential halide anion substitution of certain borohydride sites in the structure which have significant consequences for hydrogen storage properties. Conclusions of this work is applicable not only to zinc system but to any ammine metal borohydride system.

Ni-Doped Carbon Nanotube-Mg(BH4)2 Composites for Hydrogen Storage

Borohydride magnesium is widely studied as a promising hydrogen storage material due to its high gravimetric and volumetric density (14.9 wt % and 112 g/L, respectively). Different types of catalysts play a good catalytic role in enhancing the hydrogen desorption rates in borohydride systems. In the present paper, multiwalled carbon nanotubes supported Ni (Ni/MWCNTs) were synthesized by a chemical reduction method, and the catalyst was introduced into Mg(BH4)2 to enhance the dehydrogenation kinetics. The effect of Ni/MWCNTs on the microstructural evolution and hydrogen storage properties of Mg(BH4)2 is studied. The Mg(BH4)2-5wt% Ni/MWCNTs (95M@5NiMWCNTs) sample exhibits the best hydrogen storage performance; it starts to release hydrogen at 93 °C, which is 113 °C lower than that of the primary Mg(BH4)2 sample. Moreover, it takes only 3600 s to desorb hydrogen completely at 300 °C, showing a significant improvement on hydrogen desorption kinetics. In comparison with the primary Mg(BH4)2 sample, the dehydriding apparent activation energy of the 95M@5Ni3MWCNTs2 sample is significantly lowered to 119.5 kJ mol–1. Transmission electron microscopy analysis exhibits that the striking improvement of dehydriding properties of Mg(BH4)2 is mainly due to the synergistic catalysis of Ni and MWCNTs. This work provides a new method for designing and synthesizing high-performance catalysts in borohydride hydrogen storage materials, which is potentially utilized as a hydrogen supplier for hydrogen fuel cells.

Design and development of a laboratory for the study of PEMFC system for marine applications

Climate change is driving the introduction of strict emission limits in the shipping sector favoring the introduction of alternative fuels, among which hydrogen. While the storage energy density of this energy vector is a key challenge that makes way to a variety of different solutions, from fossil fuel reformers to sodium borohydride systems, fuel cell systems are generally considered among the future ideal energy converters. Nevertheless very few fuel cell marine applications are available worldwide, none of them is related to a ship application, mainly because of the high power requirements. Fuel cells are relatively new in the shipping sector, up to now no civil industrial system has been commercialized yet while military applications rely only on the U212 submarine of the Italian and German Navy. The lack of favorable niche markets coupled with the strong conservative and traditional design principles held back the investment for optimized marine systems. For this reason, present and past projects made use of conveniently adapted automotive technologies into pilot demos, with particular focus on Proton Exchange Membrane Fuel Cell (PEMFC). However, ships requirements are largely different from automotive ones, not only for the power size that are in the range of MWs instead of kWs. On the other side, in order to take advantage of large scale production as well as of the modularity of fuel cell technology, the integrations of automotive or stationary based fuel cell subsystems, already available on the market, inside a dedicate modular marine system seems to be the solution pursued by many shipbuilders and contemplated by regulatory authorities. In hybrid system configurations, fuel cells are considered in combinations with batteries, another important technology under development, in order to take advantage of the superior energy performances of fuel cell systems and the highly power discharge dynamics of batteries. The need of fuel cell power systems for ships is pushing towards the creation of knowledge that requires laboratories able to challenge the abovementioned issues in order to give answers to shipbuilders and at a lower level also to rule makers.

Hydrogen on-Demand from Sodium Borohydride Using Reactivated Co-Foams Catalysts

According to the World Health Organization, the use of fossil fuels has unequivocally originated climate changes with strong environmental and social impact at global scale. Simultaneously, global energy demand is predicted to rise about 30% by 2030 making the search for alternative greener fuels even more pressing. In this context, hydrogen has high potential as an energy carrier but unfortunately almost all of the H2 generation (95 %) stems from fossil fuels processing. Key factors for the development of reliable hydrogen-fueled systems comprise cost-effectiveness, greenness and safety on H2 production, storage, transportation and application [1]. Storage and transportation of H2 as a gas or in liquid state are widely used technologies. However, compressed H2 (gas state) demands high pressure and cryogenic H2 (liquid state) requires liquefaction, which turn both these options expensive (besides the volume occupied by the containers) [1]. From the point of view of the hydrogen economy, the International Energy Agency recognizes sodium borohydride (NaBH4) as a versatile route to be explored extensively. NaBH4 is a carbon free compound, nonflammable, with good stability in air and in alkaline aqueous solutions. It has a high gravimetric hydrogen storage capacity (10.8 wt.%) and can supply safe and clean H2 gas through a green approach. NaBH4 generates H2 through its hydrolysis, which is a spontaneous, exothermic reaction that can occur in ambient conditions [2]. Therefore, NaBH4 systems can solve multiple issues related with the storage, transportation and release of pure H2. However, the efficiency of borohydride hydrolysis systems depends on catalysts, to provide high enough hydrogen generation rates [2]. Noble metal-based catalysts, such as Pt and Ru, are effective for NaBH4 hydrolysis but they are scarce and expensive. On this regard, catalysts based on transition metals, such as Co and Ni, have been developed [3]. Interestingly, Co-based foam-like catalysts have been demonstrated to have better performances due to their highly porous nature with enhanced morphologies and large active surface areas [4]. Although different catalysts have been reported over the last decade, the catalyst durability is another important topic that is rarely addressed [5]. Borates by-product from borohydride hydrolysis can be strongly adsorbed at the catalyst surface, leading to its activity decrease and even deactivation [2]. So far, methods for borohydride hydrolysis catalysts reactivation involve ex-situ operations such as washing the catalyst with deionized water and acidic solutions [6], or catalyst thermal treatments [7]. Taking into account an integrated borohydride system to generate H2, these methods can be time-consuming, ineffective and not practical. The present work aims to produce tailored Co-based catalytic foams for H2 generation from borohydride source and develop in-situ electrolytic reactivation process to extend the durability of the catalysts. The optimized Co foams were submitted to several NaBH4 hydrolysis cycles to study their performance and durability (stability) before and after electro-reactivation. The foams shows highly porous three-dimensional structure and are able to catalyze borohydride hydrolysis. Reactivation of the catalytic foams through electrolytic in-situ procedure is proved to be a fast and practical approach of keeping catalysts efficiency and durability and thus for the advancement of integrated NaBH4 systems towards H2 on-demand applications. Figure 1. SEM image of the as-prepared cobalt foam.

Silver nanoparticles-containing dual-function hydrogels based on a guar gum-sodium borohydride system.

Dual-function hydrogels, possessing both stimuli-responsive and self-healing properties, have recently attracted attention of both chemists and materials scientists. Here we report a new paradigm using natural polymer (guar gum, GG) and sodium borohydride (NaBH4), for the preparation of silver nanoparticles (AgNPs)-containing smart hydrogels in a simple, fast and economical way. NaBH4 performs as a reducing agent for AgNPs synthesis using silver nitrate (AgNO3) as the precursor. Meanwhile, sodium metaborate (NaBO2) (from NaBH4) behaves as a cross-linking agent between GG molecular chains. The AgNPs/GG hydrogels with excellent viscoelastic properties can be obtained within 3 min at room temperature without the addition of other cross-linkers. The resultant AgNPs/GG hydrogels are flowable and injectable, and they possess excellent pH/thermal responsive properties. Additionally, they exhibit rapid self-healing capacity. This work introduces a facile and scale-up way to prepare a class of hydrogels that can have great potential to biomedical and other industrial applications.

Role of Ti doping and Al and B vacancies in the dehydrogenation of Al(BH4)3

Metal borohydrides such as Al(BH4)3 is thermodynamically very stable but has weak dehydrogenation property. In contrast, Ti(BH4)3 has less stability (25°C) but excellent dehydrogenation property. Hence, we have studied Ti-doped aluminium borohydride systems in order to improve the dehydrogenation property. Our density functional studies (DOS and pDOS) show that Ti interacts more strongly with the BH4 unit and such strong interaction weakens the B-H bond and improves the dehydrogenation property. Ti-doped Al(BH4)3 system improves the overall stability due to the formation of a stronger Ti-B bond. Our study on defects in Al(BH4)3 suggests that B-defect system has the best dehydrogenation property compared to the pure and Ti-doped Al(BH4)3 systems. The H2 molecular dehydrogenation (Ed) energies are presented for Ti-doped Al(BH4)3, and systems with Al/B-defects in Ti-doped and Al(BH4)3.

Effect of Eutectic Melting, Reactive Hydride Composites, and Nanoconfinement on Decomposition and Reversibility of LiBH4–KBH4

Eutectic melting, reactive hydride composites, and nanoconfinement have the potential to improve the reversible hydrogen storage properties in metal borohydrides. We study and compare the combined effect of all three methods on reversible hydrogen release and uptake of the eutectic melting lithium potassium borohydride system, 0.725LiBH4–0.275KBH4, with low melting temperature (Tm = 105 °C). The eutectic mixture and reactive hydride composites of the eutectic mixture with Mg or MgH2 are melt infiltrated into a CO2 activated nanoporous carbon scaffold, and their properties are compared to those of bulk samples. The decomposition of 0.725LiBH4–0.275KBH4 and the reactive hydride composites initiates simultaneously with the melting at 105 °C, but the decomposition remains slow until higher temperatures are reached (T > 300 °C). Eutectic melting appears to improve kinetics of hydrogen release and absorption, while nanoconfinement lowers the main hydrogen release temperature in the first cycle by up to 200 °C. ...

Optimization of hydrogen production by solid-state aluminum, calcium hydride, nickel, and sodium borohydride

ABSTRACTA novel solid-state aluminum-calcium hydride-nickel composite/sodium borohydride system was prepared by milling and its hydrolysis performance was characeterized. The optimized system provided 100% hydrogen yield, and the hydrogen generation rate was regulated by altering the calcium hydride concentration, nickel concentration, hydrolysis temperature, and milling time. Hydrogen generation measurements and microstructure analysis showed that improved hydrogen production was obtained by microgalvanic cell formation between nickel and aluminum, decreased grain size by milling, and improved catalytic activity of nickel deposited on the surface of aluminum hydroxide.

Flux-assisted single crystal growth and heteroepitaxy of perovskite-type mixed-metal borohydrides

Single crystals of mixed-metal perovskite-type borohydride KCa(BH4)3 are prepared by using an easily generalized flux melting procedure based on eutectic borohydride systems.

ChemInform Abstract: Amides and Borohydrides for High‐Capacity Solid‐State Hydrogen Storage‐Materials Design and Kinetic Improvements

AbstractReview: 88 refs.

Borohydrides: from sheet to framework topologies

The five novel compounds ALiM(BH4)4 (A = K or Rb; M = Mg or Mn) and K3Li2Mg2(BH4)9 crystallizing in the space groups Aba2 and P2/c, respectively, represent the first two-dimensional topologies amongst homoleptic borohydrides. The crystal structures have been solved, refined and characterized by synchrotron X-ray powder diffraction, neutron powder diffraction and solid-state DFT calculations. Minimal energies of ordered models corroborate crystal symmetries retrieved from diffraction data. The layered Li-Mg substructure forms negatively charged uninodal 4-connected networks. It is shown that this connectivity cannot generate the long sought-after, bimetallic Li-Mg borohydrides without countercations when assuming preferred coordination polyhedra as found in Mg(BH4)2 and LiBH4. The general properties of the trimetallic compound series are analogous with the anhydrous aluminosilicates. Additionally, a relationship with zeolites is suggested, which are built from three-dimensional Al-Si-O networks with a negative charge on them. The ternary metal borohydride systems are of interest due to their potential as novel hydridic frameworks and will allow exploration of the structural chemistry of light-metal systems otherwise subject to eutectic melting.

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.

Simple Reduction of Hydantoins with Sodium Borohydride

The reduction of various hydantoins with sodium borohydride gave the corresponding 4-hydroxy- 2-imidazolidinones in high yields. In contrast, reduction employing a boron trifluoride etherate-sodium borohydride system generated 2-imidazolidinones. In both reductions, the reactivity of the hydantoin was dependent on its substituents. The Lewis acid-promoted reactions of a 4-hydroxy-2-imidazolidinone with nucleophiles were also investigated.

Amides and borohydrides for high-capacity solid-state hydrogen storage—materials design and kinetic improvements

Abstract

Hydrolysis of AlLi/NaBH4 system promoted by Co powder with different particle size and amount as synergistic hydrogen generation for portable fuel cell

Hydrogen generation from the hydrolysis of aluminum lithium/sodium borohydride (referred to as AlLi/NaBH4) system activated by Co powder with different particle size and amount was evaluated in this paper. The designed aluminum–lithium–cobalt (referred to as Al–Li–Co/NaBH4) systems including Al-5 wt% Li-50 wt% nano Co, Al-7.5 wt% Li-25 wt% nano Co, Al-5 wt% Li-50 wt% micro Co, and Al-7.5 wt% Li-25 wt% micro Co had 100% hydrogen yield at 323 K. The hydrogen generation rates of these systems were regulated by Co species, Co amount, as well as consecutive runs of NaBH4 hydrolysis. The underlying activation mechanism, including the formation of Al0.94Co1.06 alloy and highly active and stable Co-based catalyst has been elaborated in this study. Experimental data present an inexpensive and highly efficient hydrogen source for portable fuel cell.

Understanding oscillatory phenomena in molecular hydrogen generation via sodium borohydride hydrolysis

The hydrolysis of borohydride salts represents one of the most promising processes for the generation of high purity molecular hydrogen under mild conditions. In this work we show that the sodium borohydride hydrolysis exhibits a fingerprinting periodic oscillatory transient in the hydrogen flow over a wide range of experimental conditions. We disproved the possibility that flow oscillations are driven by supersaturation phenomena of gaseous bubbles in the reactive mixture or by a nonlinear thermal feedback according to a thermokinetic model. Our experimental results indicate that the NaBH4 hydrolysis is a spontaneous inorganic oscillator, in which the hydrogen flow oscillations are coupled to an "oscillophor" in the reactive solution. The discovery of this original oscillator paves the way for a new class of chemical oscillators, with fundamental implications not only for testing the general theory on oscillations, but also with a view to chemical control of borohydride systems used as a source of hydrogen based green fuel.

A New Ammine Dual‐Cation (Li, Mg) Borohydride: Synthesis, Structure, and Dehydrogenation Enhancement

A new ammine dual-cation borohydride, LiMg(BH(4))(3)(NH(3))(2), has been successfully synthesized simply by ball-milling of Mg(BH(4))(2) and LiBH(4)·NH(3). Structure analysis of the synthesized LiMg(BH(4))(3)(NH(3))(2) revealed that it crystallized in the space group P6(3) (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three-dimensional architecture is built up through corner-connecting BH(4) units. Strong N-H···H-B dihydrogen bonds exist between the NH(3) and BH(4) units, enabling LiMg(BH(4))(3)(NH(3))(2) to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH(4))(3)(NH(3))(2)/LiBH(4) composite is able to release over 8 wt% hydrogen below 200 °C, which is comparable to that released by Mg(BH(4))(3)(NH(3))(2). More importantly, it was found that release of the byproduct NH(3) in this system can be completely suppressed by adjusting the ratio of Mg(BH(4))(2) and LiBH(4)·NH(3). This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.