Hydrogen Storage Properties Of LiBH4 Research Articles

LiBH4 hydrogen storage system with low dehydrogenation temperature and favorable reversibility promoted by metallocene additives

LiBH4 is of great potential as hydrogen storage material due to its high theoretical hydrogen storage capacity. However, it suffers from high thermal stability, sluggish dehydrogenation/hydrogenation kinetics and poor reversibility. Introduction of catalysts is an effective way to improve the hydrogen storage properties of LiBH4. In the present study, chromocene and nickelocene are used as catalytic additives to LiBH4 by a simple ball-milling. Nickelocene is mostly decomposed, forming CNTs (carbon nanotubes) cross-linking the LiBH4 particles, while chromocene maintains stable during the ball-milling process. But they are fully decomposed to Cr and Ni nanoparticles after the initial dehydrogenation and further transferred to CrB2 and Ni2B nanoparticles after initial hydrogenation. The in situ formed CrB2 and Ni2B show superfine nanoparticles and are uniformly dispersed in the matrix, acting as highly active catalysts. The dehydrogenation temperature of the combined system is evidently reduced, and the hydrogen storage kinetics and reversibility are significantly improved. The highly thermal conductive CNTs are considered helpful in heat transfer during dehydrogenation and hydrogenation. The method for the introduction of the catalysts is facile and low cost. The present work provides a new insight into the design of novel catalysts for LiBH4.

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.

A nanoconfined-LiBH4 system using a unique multifunctional porous scaffold of carbon wrapped ultrafine Fe3O4 skeleton for reversible hydrogen storage with high capacity

LiBH4 with a capacity of 18.5 wt% H2, is a promising high-capacity hydrogen storage material; however, it suffers from high operation temperature and poor reversibility. Herein, a novel structural LiBH4 system prepared via a nanoconfinement technique, coupling with in-situ introduced catalysts, is developed. By using a unique passionfruit-like porous hybrid composed of carbon wrapped ultrafine Fe3O4 skeleton (p-Fe3O4@C) as scaffold, synergetic effects of nanoconfinement, catalysis and surface destablization are achieved, which significantly improve the overall hydrogen storage properties of LiBH4. With an optimized LiBH4 loading of 60 wt%, the confined system initiates dehydrogenation at a low temperature of 175 °C and rapidly desorbs 7.8 wt% H2 at 350 °C within 30 min. Moreover, the dehydrogenated system shows a high reversibility under relatively moderate hydrogenation conditions. A dehydrogenation capacity of 6.2 wt% remains after 20 cycles. The system can be flexibly compacted, showing a volumetric hydrogen density as high as 79.4 g L−1, where there is almost no dehydrogenation property deterioration compared with its powder counterpart. The present work provides new insights in developing advanced complex hydride-based hydrogen storage systems through functional and structural designs.

Enhanced Low-Temperature Hydrogen Storage in Nanoporous Ni-Based Alloy Supported LiBH4.

To reveal the synergistic effect of nanoconfinement and metallic catalysis on the hydrogen storage properties of LiBH4, the nanoporous Ni-based alloy (np-Ni) was prepared herein by dealloying of the Mn70Ni30 alloy in (NH4)2SO4 solution, and then LiBH4 was loaded into np-Ni to construct the LiBH4/np-Ni hydrogen storage system using wet impregnation. It was found that dehydrogenation of the LiBH4/np-Ni (1:5) system starts at around 70°C and ends before 400°C, with ~11.9 wt.% of hydrogen desorbed. The apparent dehydrogenation activation energy for the LiBH4/np-Ni (1:5) system was remarkable decreased to about 11.4 kJ/mol. After rehydrogenation at 450°C under 8 MPa hydrogen pressure, ~8.2 wt.% of hydrogen can be released from about 60°C upon second dehydrogenation. These obtained results would provide an efficient strategy for improving the hydrogen storage properties of other metal borohydrides.

New insights into the solid-state hydrogen storage of nanostructured LiBH4-MgH2 system

In this study, the nano-mixture of LiBH4 + MgH2 is prepared by ball milling (BM) of 1 mol MgH2 with in-situ aerosol-spraying (AS) of 1 mol of LiBH4 (called BMAS). It is shown, for the first time, that Mg(BH4)2 can be formed via the reaction between MgH2 and LiBH4 through the BMAS process and it contributes to H2 release at temperature ≤265 °C. Three parallel H2 release mechanisms have been identified from the BMAS powder. These include (i) H2 release from the decomposition of nano-LiBH4 and then Li2B12H12 decomposition product reacts with nano-MgH2 to release H2, (ii) H2 release from the decomposition of nano-Mg(BH4)2, and (iii) H2 release from the decomposition of nano-MgH2. Together, these three mechanisms result in 4.11 wt% H2 release in the solid-state at temperature ≤265 °C, which is among the highest quantities ever reported for LiBH4 + MgH2 mixtures to date. Furthermore, the H2 release temperature for each mechanism described above is lower than the corresponding temperature reported using other synthesis methods. In addition, the predicted property of a small amount of the Fe3B phase in the BMAS powder in absorbing more H2 than releasing is confirmed experimentally for the first time in this study. All these enhancements are achieved in the solid-state without any catalyst, which highlights the efficacy of mechanical activation and nanoengineering as well as the future opportunity to further improve the reversible hydrogen storage properties of LiBH4 + MgH2 in solid-state.

Hydrogen storage properties of activated carbon confined LiBH4 doped with CeF3 as catalyst

CeF3 as a catalyst is first added to activated carbon (AC) by ball milling under low rotation speed. Then the treated AC was used as the scaffold to confine LiBH4 by melt infiltration process. The combined effects of confinement and CeF3 doping on the hydrogen storage properties of LiBH4 are studied. The experimental results show that LiBH4 and CeF3 are well dispersed in the AC scaffold and occupy up to 90% of the pores of AC. Compared with pristine LiBH4, the onset dehydrogenation temperature for LiBH4-AC and LiBH4-AC-CeF3 decreases by 150 and 190 °C, respectively. And the corresponding dehydrogenation capacity increases from 8.2 wt% to 13.1 wt% for LiBH4-AC and 12.8 wt% for LiBH4-AC-CeF3, respectively. The maximum dehydrogenation speed of LiBH4-AC and LiBH4-AC-CeF3 is 80 and 288 times higher than that of pristine LiBH4 at 350 °C. And LiBH4-AC andLiBH4-AC-CeF3 show good reversible hydrogen storage properties. On the during 4th dehydrogenation cycle, the hydrogen release capacity of LiBH4-AC and LiBH4-AC-5 wt% CeF3 reaches 8.1 and 9.3 wt%, respectively.

Enhanced hydrogen storage properties of LiBH4 generated using a porous Li3BO3 catalyst

LiBH4 is considered a promising hydrogen storage material for automotive applications; however, its usage is limited because of unfavorable reversibility and sluggish kinetics. In this paper, we have improved the hydrogen storage properties of LiBH4 by doping with a porous Li3BO3 additive, which was prepared by a solid state synthesis method. The LiBH4–33 wt% Li3BO3 composite was prepared via mechanical milling. The composite exhibited an acceptable hydrogenation/dehydrogenation rate, high hydrogen storage capacity and superior reversibility. The initial dehydrogenation temperature of the composite was 105 °C, which is 205 °C lower than that of the pristine LiBH4, and the hydrogen desorption capacity was 4.12 wt% at 450 °C within 2000 s. The composite maintained its hydrogen absorption capacity of 2.8 wt% with a narrow gap after 5 de/hydrogenation cycles at 400 °C and 5.0 MPa. The Li3BO3 additive clearly enhanced the hydrogen storage properties of LiBH4 and facilitated the decomposition and formation of [BH4]−, thus accelerating de/rehydrogenation of LiBH4. At the same time, Li3BO3 offered numerous porous channels that enhanced hydrogen circulation.

Effect of nano-sized Ce2S3 on reversible hydrogen storage properties of LiBH4

Ce2S3 with a diameter ca. 100–200 nm was synthesized by a solvothermal method and doped into LiBH4. Ce2S3 reacts with LiBH4, forming Li2S and CeB6 as the dehydrogenated products, and they become active substances in the re-hydrogenation reaction to improve the reversibility of the LiBH4 system. The composite of LiBH4 with 20 wt.% Ce2S3 exhibits favorable re-hydrogenation ability, its hydrogen absorption still reaches 3.6 wt.% at the 4th cycle. After dehydrogenation, The initial dehydrogenation temperature of the LiBH4 + 20 wt.% Ce2S3 composite is decreased to 250 °C, which is 80 °C lower than that of the pristine LiBH4 system. Furthermore, within 3000 s, the LiBH4 + 20 wt.% Ce2S3 composite can release about 4.0 wt.% hydrogen at 400 °C, which is 1.67 times higher than that of the pristine LiBH4. The activation energy (Ea) of dehydrogenation reaction of LiBH4 is reduced from 181.80 kJ/mol to 157.82 kJ/mol.

Improved hydrogen storage properties of LiBH4 via nanoconfinement in micro- and mesoporous aerogel-like carbon

Herein, we present the effect of the nanoconfinement of LiBH4 within porous aerogel-like carbon on its hydrogen storage properties. The carbon scaffold is prepared by salt templating – a facile and sustainable technique for the production of micro- and mesoporous carbon-based materials. A loading of up to 40 wt. % of LiBH4 is achieved by melt infiltration, and the hydride remains amorphous as shown by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning transmission electron microscopy (STEM). Simultaneous thermogravimetry and mass spectroscopy (TG-MS) reveal that the nanoconfined LiBH4 starts to desorb hydrogen already at 200 °C with the main release at 310 °C. A partial rehydrogenation at moderate conditions (100 bar and 300 °C) is demonstrated. In contrast to recent reports, in-situ heating in the transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS) indicate that both decomposition products (B and LiH) remain within the carbon pores. Nuclear magnetic resonance (NMR) measurements reveal the presence of amorphous and partially oxidized boron in the dehydrogenated sample that may impede the reversibility of the (de)hydrogenation process.

Reversible hydrogen storage properties of LiBH4 combined with hydrogenated Mg11CeNi alloy

The hydrogenated Mg11CeNi alloy was utilized as a destabilizer to combine with LiBH4 in this paper. It was found that thermal dehydrogenation of the LiBH4/Mg11CeNi hydride system with a molar ratio of 17:2.5 proceeds in two-step reactions: one initiates at around 280 °C with about 4.0 wt.% of hydrogen released from MgH2 and Mg2NiH4, and the other occurs in the temperature range 350–425 °C that can be assigned to the decomposition of LiBH4 co-destabilized by Mg2Ni, CeH2 and Mg. These two-step dehydrogenation reactions for the LiBH4/Mg11CeNi hydride system are partially reversible, and about 4.9 wt.% of hydrogen can be reloaded at 400 °C under an initial hydrogen pressure of 9 MPa.

Enhanced hydrogen storage properties of LiBH4 modified by NbF5

Abstract In this work, the hydriding–dehydriding properties of the LiBH4–NbF5 mixtures were investigated. It was found that the dehydrogenation and reversibility properties of LiBH4 were significantly improved by NbF5. Temperature-programed dehydrogenation (TPD) showed that 5LiBH4–NbF5 sample started releasing hydrogen from as low as 60 °C, and 4 wt.% hydrogen could be obtained below 255 °C. Meanwhile, ∼7 wt.% H2 could be reached at 400 °C in 20LiBH4–NbF5 sample, whereas pristine LiBH4 only released ∼0.7 wt.% H2. In addition, reversibility measurement demonstrated that over 4.4 wt.% H2 could still be released even during the fifth dehydrogenation in 20LiBH4–NbF5 sample. The experimental results suggested that a new borohydride possibly formed during ball milling the LiBH4–NbF5 mixtures might be the source of the active effect of NbF5 on LiBH4.

Improved hydrogen storage properties of LiBH4 doped Li–N–H system

Remarkable improvement of hydrogen sorption properties of Li–N–H system has been obtained by doping with a small amount of LiBH4. The starting and ending temperatures of hydrogen desorption shift to lower temperatures and the release of NH3 is obviously restrained by 10 mol% LiBH4 doping. The kinetics of hydrogen desorption and absorption of Li–N–H system became faster by the addition of LiBH4. About 4 wt.% H2 can be released within 30 min and ∼4.8 wt.% H2 can be reabsorbed within 2 min by LiBH4 doped sample at 250 °C, while only 1.44 wt.% H2 is released and 2.1 wt.% is reabsorbed for pure Li–N–H system. The quaternary hydride (LiNH2)x(LiBH4)(1−x) formed by the reaction between LiBH4 and LiNH2 may contribute to the enhancement of the hydrogen sorption performances by yielding a ionic liquid phase and transferring LiNH2 from solid state to molten state with a weakened N–H bond.

Hydrogen storage properties of LiBH4 destabilized by SrH2

In this work, we have succeeded in destabilizing LiBH4 by the addition of SrH2, via the reaction 6LiBH4+SrH2→SrB6+6LiH+10H2 with a theoretical hydrogen capacity of 9.1wt.%. According to the van’t Hoff and Arrhenius equations, the dehydrogenation enthalpy change and activation energy for the LiBH4/SrH2 system were experimentally determined to be 48kJ/mol H2 and 64kJ/mol, respectively. Both are remarkably reduced in comparison with the pristine LiBH4, which is responsible for the improved dehydrogenation property of the LiBH4/SrH2 system. The dehydrogenated products SrB6+6LiH can be rehydrogenated to form LiBH4 and LiSrH3 at 723K under an initial hydrogen pressure of 8.0MPa.

NEXAFS study of 2LiF–MgB2 composite

Synthesis of lithium borohydridofluorides may pave a new way to pursue improved hydrogen storage properties of LiBH4 as reversible hydrogen storage materials that fit the fuel cell application. The main products of the hydrogen absorption by 2LiF–MgB2 composite are MgF2 and LiBH4. In addition to them, LiBH4−xFx compounds might be present during hydrogen absorption–desorptions and play important role on their kinetics and reversibility.First results of Near Edge X-ray Absorption Fine Structure (NEXAFS) at the B K-edge (193 eV) for LiF–MgB2 composite with molar ratio (2:1) are presented. Obtained results indicate a formation of mixed borohydrides/borofluorides of the type of LiBH4−xFx, thus suggesting fluorine substituting for hydrogen.

Combined Effects of Functional Cation and Anion on the Reversible Dehydrogenation of LiBH4

Catalyst doping has been widely employed as an effective method for improving the H-exchange kinetics of complex hydrides. However, a viable hydrogen storage material requires favorable properties on both kinetic and thermodynamic aspects to allow dehydrogenation and rehydrogenation reactions to proceed at moderate temperatures. In the present study, titanium halides (TiCl3 or TiF3) were mechanically milled with LiBH4 and examined with respect to their effects on the hydrogen storage properties of LiBH4. Experimental study showed that both halides are effective promoters. In particular, TiF3 exhibits a superior promoting effect to its analogue, TiCl3, on the reversible dehydrogenation of LiBH4. Phase characterization and chemical state analysis results showed that both halides react with the host LiBH4, resulting in the in situ formation of the catalytically active Ti hydride. However, the two halogen anions differ substantially from each other in terms of state and function. Associated with the dissolution of LiCl into LiBH4, the Cl– anion can readily replace [BH4]− and exerts a stabilizing effect on the hexagonal phase of LiBH4. By contrast, the F– anion may partially substitute the anionic H in both LiBH4 (hydrogenated state) and LiH (dehydrogenated state) lattices, resulting in a favorable modification of the hydrogen-exchange thermodynamics of LiBH4. The observed promoting effect of TiF3 on the reversible dehydrogenation of LiBH4 should be understood from the combined effects of functional cation and anion. In this regard, TiF3 provides a prototype catalyst that can simultaneously modify the H-exchange kinetics and thermodynamics of complex hydrides.

Superior hydrogen storage properties of LiBH4 catalyzed by Mg(AlH4)2

Mg(AlH(4))(2) is found to provide a synergistic effect on improving the de-/rehydrogenation properties of LiBH(4). The Mg(AlH(4))(2)-catalyzed LiBH(4) exhibits lower dehydrogenation temperature and faster de-/rehydrogenation kinetics than the individually MgH(2)- or Al-catalyzed LiBH(4).

Improved hydrogen storage properties of LiBH4 destabilized by carbon

The hydrogen storage properties of LiBH4 ball milled with various ratios of carbon nanotubes (Cnano) were investigated. The LiBH4∕Cnano mixtures showed superior dehydrogenation, hydrogen desorption starting at 250°C, and the majority of hydrogen being released below 600°C. The rehydrogenation results revealed that the Li2C2, formed during the dehydrogenation, could be reversed to LiH, in which the hydrogen capacity corresponds to 1∕4 of the original hydrogen content of LiBH4, and C at 10MPa hydrogen pressure and 400°C.

Hydrogen storage properties of LiBH4

Metal hydrides typically absorb 1–2 hydrogen atoms per metal atom and exhibit very large volumetric storage densities of up to 150 kg H2 m−3 (e.g. Mg2FeH6). However, due to the large atomic mass of the transition metals the gravimetric hydrogen density is limited to less than 5 mass%. Light weight group 3 metals, e.g. Al, B, are able to bind four hydrogen atoms and form together with an alkali metal an ionic or at least partially covalent compound. These compounds are rather stable and often desorb the hydrogen only above their melting temperature. LiBH4 has a gravimetric hydrogen density of 18.5 mass% and a volumetric hydrogen density of 121 kg H2 m−3. The compound was first synthesized by Schlesinger and Brown [J. Am. Chem. Soc. 62 (1940) 3429] in an organic solvent. According to the work of Stasinevich and Egorenko [Russian J. Inorg. Chem. 13(3) (1968) 341] hydrogen desorbs from LiBH4 at temperatures greater than 470°C. We have successfully identified the low temperature structure of LiBH4: orthorhombic, space group Pnma (#62), the unit cell contains four molecules and has the dimensions a=7.1730 Å, b=4.4340 Å, c=6.7976 Å at 25°C. A slight hydrogen desorption was observed during the structure transformation around 100°C and the major hydrogen desorption (13.5 mass%) starts at approximately 200°C when SiO2-powder is added to the LiBH4 sample.