Chemical activation of MgH2; a new route to superior hydrogen storage materials

Johnson, Simon R.; Anderson, Paul A.; Edwards, Peter P.; Gameson, I.; Prendergast, James W.; Al-Mamouri, Malek; Book, D. L.; Harris, I.R.; Speight, J.D.; Walton, Allan

doi:10.1039/b503085d

Cited by 117 publications

(67 citation statements)

References 14 publications

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“…On the contrary, the NaBH 4 dissociation takes place in the two mixtures with identical starting temperature and similar average rate (1.2 wt % H 2 /min vs. 0.9 wt % H 2 /min). The above consideration confirms the fact, already noticed in literature (Johnson et al [30], Czujko et al [21]), that NaBH 4 is a good catalyst towards the Mg/MgH 2 system. Desorption profile acquired on 2NaBH 4 :1MgH 2 mixture after milling under H 2 .…”

Section: Resultssupporting

confidence: 90%

H₂sorption performance of NaBH₄–MgH₂composites prepared by mechanical activation

Milanese¹,

Girella²,

Mulas³

et al. 2009

WIT Transactions on Ecology and the Environment

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The current research on solid state hydrogen storage materials for on-board applications is focused on reactive hydrides composites (RHC), i.e. systems based on the improvement of the dehydrogenation thermodynamic of a complex hydride when one (generally the light hydride MgH 2 ) or more hydrides take part to the reaction. The extent of the destabilization, as well as the sorption characteristics of the composites, strongly depends on the structural and nanostructural properties of the constituent hydrides, which are in turn affected by the preparation route. The aim of this work is to evaluate the influence of different mechanical activation conditions on the storage properties of NaBH 4 -MgH 2 composites, up to now scarcely explored in literature. The first results regard composites with 2:1 and 1:2 stoichiometry milled under different atmosphere (Ar or H 2 ). X-ray powders diffraction analysis shows that milling does not lead to the formation of any new phase, but it reduces the average crystallite size of the powders down to nanometric scale. All the mixtures release an H 2 amount close to the theoretical value expected for the full dissociation of both the hydrides and much higher than the target fixed by the US Department of Energy for on-board application. The thermal programmed desorption profiles of the mixtures clearly show two steps, with MgH 2 dissociating first and with higher rate and NaBH 4 gradually dehydrogenating at temperatures close to 400°C. Concerning the 2:1 stoichiometry, when the samples are processed under Ar the two dehydrogenation processes are characterized by a lower starting temperature but also by a lower average rate with respect to the sample milled in H 2 . The 1:2 sample milled under Ar shows the best kinetic performance. Unfortunately, also for this mixture more than 10 h are required to obtain full desorption at a temperature as high as 450°C.

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Section: Resultssupporting

confidence: 90%

H₂sorption performance of NaBH₄–MgH₂composites prepared by mechanical activation

Milanese¹,

Girella²,

Mulas³

et al. 2009

WIT Transactions on Ecology and the Environment

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“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The dehydrogenation of lithium and Group II borohydrides is plagued by severe kinetic limitations and irreversibility that precludes the utilization of these compounds under practical conditions, [2][3][4][5][6][7][8][9][10] even as components of binary hydride mixtures. [12][13][14][15][16][17][18] Many transition metal borohydride complexes also have suitable gravimetric hydrogen densities. 19 However, neutral transition metal borohydride complexes, such as Zr(BH 4 ) 4 , can be eliminated a priori from consideration as practical hydrogen carriers because of their high volatility under the conditions required for dehydrogenation.…”

Section: Introductionmentioning

confidence: 99%

LiSc(BH₄)₄: A Novel Salt of Li⁺ and Discrete Sc(BH₄)₄⁻ Complex Anions

et al. 2008

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LiSc(BH 4 ) 4 has been prepared by ball milling of LiBH 4 and ScCl 3 . Vibrational spectroscopy indicates the presence of discrete Sc(BH 4 ) 4 -ions. DFT calculations of this isolated complex ion confirm that it is a stable complex, and the calculated vibrational spectra agree well with the experimental ones. The four BH 4 -groups are oriented with a tilted plane of three hydrogen atoms directed to the central Sc ion, resulting in a global 8 + 4 coordination. The crystal structure obtained by high-resolution synchrotron powder diffraction reveals a tetragonal unit cell with a ) 6.076 Å and c ) 12.034 Å (space group P-42c). The local structure of the Sc(BH 4 ) 4 -complex is refined as a distorted form of the theoretical structure. The Li ions are found to be disordered along the z axis.

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“…MgH 2 shows several barriers for practical use in the hydrogen storage, mainly because it is characterized by high thermodynamic stability and slow decomposition kinetics [1][2][3][4][5][6]. The combination of these factors originates decomposition temperatures too high for most technological application so that the purpose of several research efforts is to find the way of facilitating the decomposition route of this compound.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Release and Microstructure of MgH₂Based Composite Powders Containing a Relevant Amount of LaNi₅

et al. 2010

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Micro-composite materials based on MgH 2 with the addition of a relevant amount of LaNi 5 have been synthesized by reactive ball milling. The powder microstructure has been studied by a combination of X-ray diffraction and scanning electron microscopy, while the decomposition behaviour and the hydrogen release properties have been obtained by differential thermal analysis and thermo-gravimetric measurements. Both temperature scans and constant temperature isotherms have been used to this purpose. Experimental results allow identifying optimum processing condition for synthesis of material that shows the onset of hydrogen release at temperatures as low as 450 K. The decomposition kinetics has been studied by isothermal measurements which show that the whole process cannot be described by just one mechanism limiting the reaction velocity. In fact in the first decomposition step the reaction is kinetically limited by the second phase nucleation, while, for partially decomposed samples the bulk diffusion appears to limit the process. On the basis of the experimental results we propose a mechanism of phase transformation where a percolating network of the two phases is formed.

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Chemical activation of MgH2; a new route to superior hydrogen storage materials

Abstract: We report the discovery of a new, chemical route for 'activating' the hydrogen store MgH2, that results in highly effective hydrogen uptake/release characteristics, comparable to those obtained from mechanically-milled material.

Cited by 117 publications

References 14 publications

H₂sorption performance of NaBH₄–MgH₂composites prepared by mechanical activation

H₂sorption performance of NaBH₄–MgH₂composites prepared by mechanical activation

LiSc(BH₄)₄: A Novel Salt of Li⁺ and Discrete Sc(BH₄)₄⁻ Complex Anions

Hydrogen Release and Microstructure of MgH₂Based Composite Powders Containing a Relevant Amount of LaNi₅

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Chemical activation of MgH2; a new route to superior hydrogen storage materials

Abstract: We report the discovery of a new, chemical route for 'activating' the hydrogen store MgH2, that results in highly effective hydrogen uptake/release characteristics, comparable to those obtained from mechanically-milled material.

Cited by 117 publications

References 14 publications

H2sorption performance of NaBH4–MgH2composites prepared by mechanical activation

H2sorption performance of NaBH4–MgH2composites prepared by mechanical activation

LiSc(BH4)4: A Novel Salt of Li+ and Discrete Sc(BH4)4− Complex Anions

Hydrogen Release and Microstructure of MgH2Based Composite Powders Containing a Relevant Amount of LaNi5

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H₂sorption performance of NaBH₄–MgH₂composites prepared by mechanical activation

H₂sorption performance of NaBH₄–MgH₂composites prepared by mechanical activation

LiSc(BH₄)₄: A Novel Salt of Li⁺ and Discrete Sc(BH₄)₄⁻ Complex Anions

Hydrogen Release and Microstructure of MgH₂Based Composite Powders Containing a Relevant Amount of LaNi₅