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Hydrogen energy has been recognized as “Ultimate Power Source” in the 21st century. It is a boon in these days of energy crunches and concerns about climate change because of the characterized advantages, such as high energy density, large calorific value, abundant resource, zero pollution, zero carbon emission, storable and renewable. State-of-the-art perspectives on tuning the stable thermodynamics and sluggish kinetics of dehydrogenation and re-hydrogenation of LiBH4, which has been regarded as a promising hydrogen storage alternative for onboard energy carrier applications have been discussed. Five major technological approaches are involved, including nanoengineering, catalyst modification, ions substitution, reactant destabilization and a novel process termed as high-energy ball milling with in-situ aerosol spraying (BMAS). It is worth noting that BMAS has the potential to help overcome the kinetic barriers for thermodynamically favorable systems like LiBH4 ​+ ​MgH2 mixture and provide thermodynamic driving force to enhance hydrogen release at a lower temperature.

LiBH 4 which have attracted considerable attention from researchers due to the crystal structure characteristics is a metal hydride that can bind four hydrogen atoms. LiBH 4 which has high gravimetric and volumetric hydrogen density shows phase transitions at high pressures. In this regard, we created and analyzed LiBH 4 structure based on the first principles calculations, and then obtained the super-cell LiBH 4 structure. We achieved the phase transitions up to 20 GPa pressure with 2 GPa regular intervals for the super-cell LiBH 4 . We observed the Pnma to Pnma*, Pnma* to P2 1 /c, and P2 1 /c to C2/c phase transitions and calculated the volume contractions accompanying these phase transitions. According to the obtained volumetric values, one can conclude that LiBH 4 can minimize the volumetric requirements of the hydrogen storage for systems that can be used at high pressures. Thus, the hydrogen storage capacity of LiBH 4 may increase at particular phases. © 2019 The Physical Society of the Republic of China (Taiwan)

Hydrogen has become a promising energy source due to its efficient and renewable properties. Although promising, hydrogen energy has not been in widespread use due to the lack of high-performance materials for hydrogen storage. Previous studies have shown that the addition of Al-based compounds to LiBH4 can create composites that have good properties for hydrogen storage. In this work, the dehydrogenation performances of different composite systems of 2LiBH4+ M (M = Al, LiAlH4, Li3AlH6) were investigated. Results show that, under a ball to powder ratio of 25:1 and rotation speed of 300 rpm, the optimum ball milling time is 50 h for synthesizing Li3AlH6 from LiH and LiAlH4. The three studied systems destabilized LiBH4 at relatively low temperature, while the 2LiBH4-Li3AlH6 composite demonstrated excellent behavior. Based on the differential scanning calorimetry results, pure LiBH4 released hydrogen at 469 oC. The dehydrogenation temperature of LiBH4 is 416 oC for 2LiBH4-Li3AlH6, versus 435 oC for 2LiBH4-LiAlH4 and 445 oC for 2LiBH4-Al composite. The 2LiBH4-Li3AlH6, 2LiBH4-LiAlH4, 2LiBH4-Al samples released 9.1 wt.%, 8 wt.%, and 5.7 wt.% of H2, respectively. Additionally, the 2LiBH4-Li3AlH6 composite released 9.1 wt.% H2 within 150 min. An increase in the kinetics was achieved. From the results, it was concluded that 2LiBH4-Li3AlH6 exhibits the best dehydrogenation performance. Therefore, the 2LiBH4-Li3AlH6 composite is a considered hydrogen storage material.

Flexible, water-resistant and air-stable hydrogen storage material (named PMMA-LiBH4/GMF), consisting of LiBH4 nanoparticles confined by poly (methylmethacrylate) (PMMA) and reduced graphene oxide (rGO) modified melamine foam (GMF), were prepared by a facile method. PMMA-LiBH4/GMF can recover original shape after compression at the strain of 50 % and exhibits highly hydrophobic property (water contact angle of 123 °). Owing to the highly hydrophobic property and protection of PMMA, PMMA-LiBH4/GMF demonstrates outstanding water-resistance and air-stability. Significantly, the onset dehydrogenation temperature of PMMA-LiBH4/GMF at first step is reduced to 94 °C, which is 149 °C less than that of LiBH4/GMF, and the PMMA-LiBH4/GMF desorbs 2.9 wt% hydrogen within 25 min at 250 °C, which is obviously more than the dehydrogenation amount of LiBH4/GMF under the same conditions. It’s our belief that the flexible, water-resistant and air-stable PMMA-LiBH4/GMF with a simple preparation route will provide a new avenue to the research of hydrogen storage materials.

金沢大学ナノマテリアル研究所 / 金沢大学理工研究域数物科学系, This work examined the hydride transfer processes during the reduction of formaldehyde by LiAlH4 or LiBH4, including investigations of the geometries, solvent effects and charge transfer processes along the reaction coordinate, using density functional theory (DFT). The energy and geometry results demonstrate that the transition state (TS) structure for the LiAlH4-formaldehyde complex is reactant-like, while the structure generated by LiBH4 has a product-like geometry, consistent with the Hammond postulate. From a charge density analysis, we also found that both complexes undergo the same essential hydride transfer mechanism, which consists of: (1) single electron transfer to the carbonyl carbon, (2) formation of a bridge bond (X-H-C; X=Al or B) and (3) hydrogen transfer driven by electron transfer. Subsequently, in a fourth step, a single electron flows through the X-H-C bond during transfer of the hydrogen, such that hydrogen atom or proton-coupled electron transfer occurs. In both systems, the presence of tetrahydrofuran as a solvent affects the structure and energy values during the reaction, but not the charge transfer characteristics. We propose that the rate-determining steps during hydride transfer when employing LiAlH4 and LiBH4 are one electron transfer to the carbonyl carbon and B-H bond dissociation, respectively. © 2015 Elsevier B.V., Embargo Period 24 months

Lithium amideborohydrides Li[BH4](1x)[NH2](x) possess liquid-like Li superionic conductivity at nearly ambient temperature. The fast Li+ diffusion facilitated by the localized motions of the anions is proposed to occur through a network of vacant tetrahedral sites, acting as conduction channels. To study the reorientational dynamics of the anions, we have performed quasielastic neutron scattering experiments on samples with different compositions (x = 2/3, 0.722, 0.737, 3/4) over a broad temperature and time range. To unambiguously disentangle the contributions of the two species, [BH4](-) and [NH2](-), we took advantage of deuterium labeling and could clearly demonstrate that the quasielastic broadening is mainly determined by the [BH4](-) reorientations. With the help of a newly developed model, supported by ab initio molecular dynamics calculations, we have identified three relaxation components, which account for generally anisotropic C-3-rotations of the [BH4](-) tetrahedra including jumps by a small angle from the equilibrium position.

We investigate the diffusion mechanism of Li ions in LiCe(BH4)3Cl, which exhibits fast Li ion conduction. It was previously shown that eight Li ions partially occupy the 12d Wyckoff sites in the I43m structure and the Li ion diffusion takes place via jumping through the three-dimensional network of the 12d sites. In this study, we employ first-principles nudged elastic band simulation to elucidate the diffusion mechanism and discover that the Li ion does not directly jump to the neighboring 12d site, but instead passes through the closest 6b site. Moreover, the 6b site turns out to be another stable Li ion site, not just a transient point during a jump event. The occupation of the 6b site and the Li ion diffusion mechanism were assured by first-principles molecular dynamics simulations. The partial occupancy of the 12d site and 6b site at 500 K is approximately 1/2 and 1/3, respectively. The experimental diffraction data can be consistently interpreted. The peculiar crystal structure of LiCe(BH4)3Cl allo...

The hydrogen desorption/absorption behaviors of LiAlH4/LiBH4 with a focus on the effects of catalysts, namely TiCl3, TiO2, VCl3, and ZrCl4, were investigated using a thermal-volumetric apparatus. The hydrogen desorption was performed from room temperature to 300 °C with a heating rate of 2 °C min−1. The LiAlH4–LiBH4 mixture with a molar ratio of 2:1 decomposed between 100 and 220 °C, and the hydrogen desorption capacity reached up to 6.6 wt %. Doping 1 mol % of a catalyst to the mixture resulted in the two-step decomposition and a decrease in the hydrogen desorption temperature. All the doped samples provided lower amountz of desorbed hydrogen than that obtained from the undoped one. No hydrogen absorption was observed under 8.5 MPa of hydrogen pressure and 300 °C for 6 h. Despite the fact each of the catalysts may affect the hydrogen storage behaviors of the mixture differently, none resulted in a change in the sample reversibility.

In contrast to the traditional metal hydrides, in which hydrogen storage involves the reversible hydrogen entering/exiting of the host hydride lattice, LiBH4 releases hydrogen via decomposition that produces segregated LiH and amorphous B phases. This is obviously the reason why lithium borohydride applications in fuel cells so far meet only one requirement — high hydrogen storage capacity. Nevertheless, its thermodynamics and kinetics studies are very active today and efficient ways to meet fuel cell requirements might be done through lowering the temperature for hydrogenation/dehydrogenation and suitable catalyst. Some improvements are expected to enable LiBH4 to be used in on-board hydrogen storage.

Two bimetallic borohydrides, lithium yttrium tetraborohydride, LiY(BH4)4, and sodium yttrium tetraborohydride, NaY(BH4)4, have been synthesized by thermal treatment and quenching of ball-milled precursors. LiY(BH4)4 crystallizes in the space group P2c and NaY(BH4)4 in C2221 and the compounds are isostructural to LiSc(BH4)4 and NaSc(BH4)4, respectively. Both LiY(BH4)4 and NaY(BH4)4 are built from the complex anions of [Y(BH4)4]−. The unit cell volumes per formula unit of the bimetallic compounds LiY(BH4)4 and NaY(BH4)4 are significantly larger compared to those of the constituent components (14% and 7.5% unit cell expansion, respectively), which may contribute to the mobility of the Li+ and Na+ cations. The ionic conductivities of LiY(BH4)4 and NaY(BH4)4 at room temperature, measured by impedance spectroscopy, are σ = 1.26 × 10−6 and 6.92 × 10−7 S cm−1 respectively, and are improved compared to those of the precursors. DFT calculations were used to optimize the structures and identify a possible mechanism for the Na ion mobility. In addition, they provide the basis for assignment of the 11B NMR parameters determined by 11B MAS NMR for the two boron sites in NaY(BH4)4.

To improve nanoconfinement of LiBH4 and MgH2 in carbon aerogel scaffold (CAS), particle size reduction of MgH2 by premilling technique before melt infiltration is proposed. MgH2 is premilled for 5 h prior to milling with LiBH4 and nanoconfinement in CAS to obtained nanoconfined 2LiBH(4)-premilled MgH2. Significant confinement of both LiBH4 and MgH2 in CAS, confirmed by SEM-EDS mapping results, is achieved due to MgH2 premilling. Due to effective nanoconfinement, enhancement of CAS:hydride composite weight ratio to 1:1, resulting in increase of hydrogen storage capacity, is possible. Nanoconfined 2LiBH(4)-premilled MgH2 reveals a single-step dehydrogenation at 345 degrees C with no B2H6 release, while dehydrogenation of nanoconfined sample without MgH2 premilling performs in multiple steps at elevated temperatures (up to 430 degrees C) together with considerable amount of B2H6 release. Activation energy (E-A) for the main dehydrogenation of nanoconfined 2LiBH(4)-premilled MgH2 is considerably lower than those of LiBH4 and MgH2 of bulk 2LiBH(4)-MgH2 (Delta E-A = 31.9 and 55.8 kJ/mol with respect to LiBH4 and MgH2, respectively). Approximately twice faster dehydrogenation rate are accomplished after MgH2 premilling. Three hydrogen release (T = 320 degrees C, P(H-2) = 3-4 bar) and uptake (T = 320-325 degrees C, P(H-2) = 84 bar) cycles of nanoconfined 2LiBH(4)-premilled MgH2 reveal up to 4.96 wt. % H-2 (10 Wt. % H-2 with respect to hydride composite content), while the 1st desorption of nanoconfined sample without MgH2 premilling gives 4.30 wt. % of combined B2H6 and H-2 gases. It should be remarked that not only kinetic improvement and B2H6 suppression are obtained by MgH2 premilling, but also the lowest dehydrogenation temperature (T = 320 degrees C) among other modified 2LiBH(4)-MgH2 systems is acquired. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Nanoconfinement of 2LiBH4-NaAlH4 into a mesoporous carbon aerogel scaffold with a pore size, BET surface area and total pore volume of Dmax = 30 nm, SBET = 689 m2/g and Vtot = 1.21 mL/g, respectively is investigated. Nanoconfinement of 2LiBH4-NaAlH4 facilitates a reduction in the temperature of the hydrogen release by 132 °C, compared to that of bulk 2LiBH4-NaAlH4 and the onset of hydrogen release is below 100 °C. The reversible hydrogen storage capacity is also significantly improved for the nanoconfined sample, maintaining 83% of the initial hydrogen content after three cycles compared to 47% for that of the bulk sample. During nanoconfinement, LiBH4 and NaAlH4 reacts to form LiAlH4 and NaBH4 and the final dehydrogenation products, obtained at 481 °C are LiH, LiAl, AlB2 and Al. After rehydrogenation of the nanoconfined sample at T = 400 °C and p(H2) = 126 bar, amorphous NaBH4 is recovered along with unreacted LiH, AlB2 and Al and suggests that NaBH4 is the main compound that can reversibly release and uptake hydrogen.

A surprisingly high degree of structural and compositional dynamics is observed in the system LiBH4−LiCl as a function of temperature and time. Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data reveals that Cl− readily substitutes for BH4− in the structure of LiBH4. Prolonged heating a sample of LiBH4−LiCl (1:1 molar ratio) above the phase transition temperature and below the melting point (108 < T < 275 °C) can produce highly chloride substituted hexagonal lithium borohydride, h-Li(BH4)1−xClx, e.g., x ∼ 0.42, after heating from room temperature (RT) to 224 °C at 2.5 °C/min. LiCl has a higher solubility in h-LiBH4 as compared to orthorhombic lithium borohydride, o-LiBH4, which is illustrated by a LiBH4−LiCl (1:1) sample equilibrated at 245 °C for 24 days and left at RT for another 13 months. Rietveld refinement reveals that this sample contains o-Li(BH4)0.91Cl0.09 and LiCl. This illustrates a significantly faster dissolution of LiCl in h-LiBH4 as compared to a slower segr...

Interest in hydrogen as a future energy carrier in mobile applications has led to a strong increase in research on the structural properties of complex alkali metal and alkaline earth hydrides, with the aim to find structural phases with higher hydrogen densities. This contribution reviews recent work on the structural properties and phase diagrams of these complex hydrides under elevated pressures, an area where rapid progress has been made over the last few years. The materials discussed in greatest detail are LiAlH4, NaAlH4, Li3AlH6, Na3AlH6, LiBH4, NaBH4, and KBH4. All of these have been studied under high pressure by various methods such as X-ray or neutron scattering, Raman spectroscopy, differential thermal analysis or thermal conductivity measurements in order to find information on their structural phase diagrams. Based mainly on experimental studies, preliminary or partial phase diagrams are also given for six of these materials. In addition to this information, data are provided also on experimental results for a number of other complex hydrides, and theoretical predictions of new phases and structures under high pressures are reviewed for several materials not yet studied experimentally under high pressure. This is an OPEN ACCESS paper. The journal volume has also been published separately under the title "Solid Phase Transformations II", edited by J. Cermak and I. Stloukal