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LiAlH4 is a potential solid-state H2 storage material, where safe and efficient H2 storage is of critical importance for the transition towards a sustainable emission-free economy. To improve the H2 release and storage properties of LiAlH4, confinement in porous media decreases the temperature of H2 release and improves the kinetics, where considerably improved H2 release properties are accompanied by a loss in the total amount of H2 released. The capability of mesoporous carbon black to improve the H2 storage properties of confined LiAlH4 is investigated with temperature-programmed desorption and time-stability measurements using X-ray diffraction and N2 gas adsorption measurements to characterize the composite materials’ composition and structure. Here, we present the capability of commercial carbon black to effectively lower the onset temperature of H2 release to that of near-ambient, ≥295 K. In addition, the confinement in mesoporous carbon black destabilized LiAlH4 to a degree that during ≤14 days in storage, under Ar atmosphere and at ambient temperature, 40% of the theoretically contained H2 was lost due to decomposition. Thus, we present the possibility of destabilizing LiAlH4 to a very high degree and, thus, avoiding the melting step before H2 release at around 440 K using scaffold materials with fine-tuned porosities.

LiAlH4 is a potential solid-state H2 storage material, where safe and efficient H2 storage is of critical importance for the transition towards a sustainable emission-free economy. To improve the H2 release and storage properties of LiAlH4, confinement in porous media decreases the temperature of H2 release and improves the kinetics, where considerably improved H2 release properties are accompanied by a loss in the total amount of H2 released. The capability of mesoporous carbon black to improve the H2 storage properties of confined LiAlH4 is investigated with temperature-programmed desorption and time-stability measurements using X-ray diffraction and N2 gas adsorption measurements to characterize the composite materials' composition and structure. Here, we present the capability of commercial carbon black to effectively lower the onset temperature of H2 release to that of near-ambient, ≥295 K. In addition, the confinement in mesoporous carbon black destabilized LiAlH4 to a degree that during ≤14 days in storage, under Ar atmosphere and at ambient temperature, 40% of the theoretically contained H2 was lost due to decomposition. Thus, we present the possibility of destabilizing LiAlH4 to a very high degree and, thus, avoiding the melting step before H2 release at around 440 K using scaffold materials with fine-tuned porosities. [ABSTRACT FROM AUTHOR]

The influence on the decomposition and reforming of the hydrogen storage material NaAlH 4 by adding relatively low amounts of mesoporous carbon black is investigated with in situ diffraction. A 60:40 NaAlH 4 /carbon black composite is prepared via ball milling and characterised ex situ via X-ray diffraction, gas adsorption, temperature-programmed decomposition, and dehydrogenation/hydrogenation cycling methods. The prepared composite is deuterated, and the crystalline phase composition is determined with in situ neutron powder diffraction method during multiple decomposition/deuteration cycles. Changes in the crystalline phase composition start slightly below the melting temperature of the pristine alanate, whereas the release of deuterium starts at considerably lower temperatures. The decomposition of Na 3 AlD 6 to NaD is almost completely reversible at the applied low deuterium pressures of ≥2 MPa. Thus, the strong effect of even low concentrations of a mesoporous carbon black on the capability to store H 2 reversibly is showcased and analysed in-depth. [Display omitted] • NaAlD 4 confined in a mesoporous carbon black. • In situ neutron powder diffraction during dedeuteration/deuteration cycles. • Crystalline composition determination at all experimental instances. • D 2 release at highly lowered temperatures from small-particulate/amorphous phase. • Full regeneration of Na 3 AlD 6 from NaD at low deuterium pressures (≤20 bar). [ABSTRACT FROM AUTHOR]

The present paper reports the effect of B- and BN-doped $$\hbox {C}_{60}$$ as catalysts for lowering the dehydrogenation energy in $$\hbox {MXH}_{4}$$ clusters (M = Na and Li, X = Al and B) using density functional calculations. $$\hbox {MXH}_{4}$$ interacts strongly with B-doped $$\hbox {C}_{60}$$ and weakly with BN-doped $$\hbox {C}_{60}$$ in comparison with pure $$\hbox {C}_{60}$$ with binding energy 0.56-0.80 and 0.05-0.34 eV, respectively. The hydrogen release energy $$(E_{\mathrm{HRE}})$$ of $$\hbox {MXH}_{4}$$ decreases sharply in the range of 38-49% when adsorbed on B-doped $$\hbox {C}_{60}$$ ; however, with BN-doped $$\hbox {C}_{60}$$ the decrease in the $$E_{\mathrm{HRE}}$$ varies in the range of 6-20% as compared with pure $$\hbox {MXH}_{4}$$ clusters. The hydrogen release energy of second hydrogen atom in $$\hbox {MXH}_{4}$$ decreases sharply in the range of 1.7-41% for BN-doped $$\hbox {C}_{60}$$ and decreases in the range of 0.2-11.3% for B-doped $$\hbox {C}_{60}$$ as compared with pure $$\hbox {MXH}_{4}$$ clusters. The results can be explained on the basis of charge transfer within $$\hbox {MXH}_{4}$$ cluster and with the doped $$\hbox {C}_{60}$$ . [ABSTRACT FROM AUTHOR]

Abstract: The formation of ultra-small Mg-based particles nanoconfined into the mesopores of a carbon template was studied by in situ synchrotron diffraction. Either Mg2Ni or Mg2NiH4 nanoparticles can be directly formed starting from separate Ni and MgH2 nano-species by tuning the H2 pressure and temperature. Both ultra-small Mg2Ni and Mg2NiH4 nanoparticles (∼4nm) are extremely stable against coalescence during hydrogen sorption cycling and prolonged exposure to high temperature as compared to Mg and MgH2 nanoparticles that show severe coalescence under same experimental conditions. The structural transition reported in bulk Mg2NiH4 from high temperature cubic to low temperature monoclinic structure is no longer observed for the nanoconfined particles. Hydrogen absorption/desorption in nanosized Mg2Ni is reversible and sorption kinetics proceed very quickly (∼5min) even at 483K. On the contrary, the thermodynamics properties are not altered by nanoconfinement. This study opens new routes for successful nanoconfinement of stoichiometric hydrides into the pores of carbon hosts along with a better understanding of the underlying nanochemistry. [Copyright &y& Elsevier]

Abstract: Li–N–H system, as a representative of metal-N–H system, is regarded as one of the most promising hydrogen storage materials. Motivated by the ammonia mediated mechanism of Li–N–H system, the effect of MgCl2 (which is an effective NH3 sorbent) on this system is systematically investigated in this work. Three different mechanisms are proposed to explain the effects of MgCl2 with different amount in the improvement of Li–N–H system. With small amount (<4 mol%), MgCl2 can improve the H-desorption properties of Li–N–H system as an NH3 sorbent. When the amount of MgCl2 increases, the H-desorption properties of Li–N–H system can be improved further though Mg2+ solid solution into LiNH2. With the amount of MgCl2 more than 25 mol%, the Li–N–H system changes into Li–Mg–N–H system by the reaction between MgCl2 and LiNH2. The Li–Mg–N–H system formed by this reaction exhibits a much better property than those of Li–Mg–N–H system reported before. It may provide a new idea to improve the metal-N–H system to meet the requirement of practical application. [Copyright &y& Elsevier]

Abstract: The effect of divalent metal-dopants, Mg, Ca, and Zn, on the stability of LiBH4 is studied by using the first-principles calculations and CALPHAD (CALculation of PHAse Diagram) modeling. The ground states of Mg1/2BH4, Ca1/2BH4, and Zn1/2BH4 are shown to be , F2dd, and , respectively, through first-principles calculations. Positive enthalpy of mixing between Li and the alloying element is predicted, indicating unfavorable solubility of alloying elements in LiBH4 and thus offering possibility to decrease the stability of LiBH4. The ionic sublattice model of (Li+, M2+, Va)1(BH4 −)1 is adopted for the metal substituted LiBH4 phase. It is observed that the addition of Mg or Zn has limited effect as the decomposition temperature is between those of LiBH4 and M1/2BH4 for Mg and Zn substitutions. LiBH4 is destabilized with magnesium borides or LiZn4 formation but its decomposition temperature is higher than that of M1/2BH4. On the other hand, the addition of Ca significantly reduces the H2 releasing temperature due to the formation of highly stable CaB6. [Copyright &y& Elsevier]

Abstract: Magnesium alanate Mg(AlH4)2 has been synthesized by mechanochemically activated metathesis reaction between NaAlH4 and MgCl2 without solvent, this metathesis reaction proceeded completely. The thermal decomposition behavior of solvent-free Mg(AlH4)2 has been analyzed by TG/MS and DSC. It has been confirmed that Mg(AlH4)2 decomposes in two steps: the first decomposition reaction Mg(AlH4)2 →MgH2 +2Al+3H2 is exothermic and starts at about 115°C. The second one is endothermic in total and starts at about 240°C, although the formation reaction of Al3Mg2 (3Al+2Mg→Al3Mg2) is exothermic. [Copyright &y& Elsevier]

Abstract: Some alkali and alkali-earth metal hydrides and their complex hydrides have very high hydrogen storage capacities and reversibility. Unfortunately, most of them have decomposition temperatures that are too high. This must be overcome before these hydrides can be considered seriously as practical hydrogen storage materials for on-board applications. In the present study, the CALPHAD approach has been adopted to evaluate thermodynamically the possibility of destabilizing these high temperature binary ionic hydrides and ternary complex hydrides by reacting them with light elements or other hydrides. The MgH2+Si, LiBH4+MgH2, and LiBH4+Al systems are predicted to show a significant decrease in decomposition temperature. On the other hand, the decrease in the decomposition temperatures of the MgH2+Al and NaBH4+Al systems is relatively small. The LiH+Si system also presents a considerable destabilization effect, which is consistent with experiment. [Copyright &y& Elsevier]

Abstract: Zinc borohydride Zn(BH4)2 (8.5wt% theoretical hydrogen storage capacity) has been synthesized by mechanochemical reaction between NaBH4 and ZnCl2 and its structure was analyzed by XRD and FT-IR. The thermal stability of Zn(BH4)2 in the presence of inert by-product NaCl was studied by TG/MS and DSC under flowing argon. It melts at about 85°C and starts to decompose almost at the same time producing diborane B2H6 and hydrogen gases between 85 and 140°C. The decomposition reaction is endothermic and the remaining solid product after decomposition is Zn with a trace of B. [Copyright &y& Elsevier]