Regeneration of sodium alanate studied by powder in situ neutron and synchrotron X-ray diffraction

Humphries, Terry D.; Makepeace, Joshua W.; Hino, Satoshi; David, William I. F.; Hauback, Bjørn C.

doi:10.1039/c4ta02886d

Cited by 16 publications

(5 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From these results it can be concluded that the additive mainly speeds up the conversion from K 3 AlH 6 to KAlH 4 as compared to that of KH into K 3 AlH 6 . This concurs with recent “in situ” high-pressure RMN and synchrotron measurements during the thermal formation of NaAlH 4 showing that reactions and are not consecutive when Ti additives are used. , Therefore, the role of TiCl 3 on the H-absorption mechanism seems to be independent of the synthesis method (thermal or mechanochemical) and analogous for all monoalkali alanates. Reactions and during H absorption are better described by a single reaction in the presence of TiCl 3 Further milling for 25 min (marked as t 2 TiCl3 in Figure d) leads to a quick exhaust of crystalline KH (Figure b).…”

Section: Resultssupporting

confidence: 90%

“…This concurs with recent "in situ" high-pressure RMN and synchrotron measurements during the thermal formation of NaAlH 4 showing that reactions R1 and R2 are not consecutive when Ti additives are used. 30,31 Therefore, the role of TiCl 3 on the H-absorption mechanism seems to be independent of the synthesis method (thermal or mechanochemical) and analogous for all monoalkali alanates. Reactions R1 and R2 during H absorption are better described by a single reaction R3 in the presence of TiCl 3…”

Section: Resultsmentioning

confidence: 98%

See 1 more Smart Citation

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH₄)

et al. 2016

View full text Add to dashboard Cite

KAlH 4 is the unique monoalkali alanate that absorbs hydrogen reversibly with reasonable kinetics at moderate pressures without doping, offering an exciting playground to understand the role of additives. KAlH 4 was successfully synthesized by reactive ball milling (RBM) of a potassium hydride and aluminum 1:1 powder mixture under a hydrogen pressure of 8.5 MPa and low temperature (<65 °C). The synthesis without additives entails two consecutive hydrogenation steps through the formation of K 3 AlH 6 as intermediate. Among the different additives investigated (TiCl 3 , ScCl 3 , and LaCl 3 ), TiCl 3 is the most effective by reducing the hydrogenation time by a factor of 2. Moreover, it promotes the simultaneous formation of K 3 AlH 6 and KAlH 4 during mechanochemical synthesis before all KH is consumed. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis indicate that the additives do not modify the structural properties of the formed alanate. Independently of TiCl 3 addition, KAlH 4 is decomposed by three consecutive steps with K 3 AlH 6 and KH as intermediates. Thus, the absorption and desorption reaction paths are asymmetric when TiCl 3 is used as an additive. Moreover, the TiCl 3 additive efficiently reduces desorption temperatures and activation energies for KAlH 4 and K 3 AlH 6 decompositions, with that for KH remaining unchanged. These results suggest that TiCl 3 enhances the mobility of Al species during desorption, likely through the formation of species at the interphase and grain boundaries as NMR measurements suggest. Reaction kinetics is limited by nucleation and growth during absorption and by diffusion processes during desorption.

show abstract

Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 98%

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH₄)

et al. 2016

View full text Add to dashboard Cite

show abstract

“…[12][13][14] although the overall process was not reversible under more moderate conditions until 1997 [92]. This was achieved by the addition of a suitable titanium-based catalyst and since then multiple investigations have been undertaken into this process [34,[93][94][95][96][97][98][99][100][101][102]. Binary alkali aluminium hexahydrides (SBHs Category I) decompose via a very similar pathway (Eq.…”

Section: Nabhmentioning

confidence: 97%

Sodium-based hydrides for thermal energy applications

2016

View full text Add to dashboard Cite

Concentrating solar-thermal power (CSP) with thermal energy storage (TES) represents an attractive alternative to conventional fossil fuels for base-load power generation. Sodium alanate (NaAlH 4 ) is a well-known sodium-based complex metal hydride but, more recently, high-temperature sodium-based complex metal hydrides have been considered for TES. This review considers the current state of the art for NaH, NaMgH 3-x F x , Na-based transition metal hydrides, NaBH 4 and Na 3 AlH 6 for TES and heat pumping applications. These metal hydrides have a number of advantages over other classes of heat storage materials such as high thermal energy storage capacity, low volume, relatively low cost and a wide range of operating temperatures (100°C to more than 650°C). Potential safety issues associated with the use of high-temperature sodium-based hydrides are also addressed.

show abstract

“…[1][2][3] Because of its excellent dehy-drogenation reversibility under the influence of a catalyst at moderate conditions, 4 sodium aluminium tetrahydride NaAlH 4 is certainly one of the most studied potential hydrogen storage materials. Besides other methods, X-ray [5][6][7][8] and neutron diffraction, [6][7][8][9] Raman scattering [10][11][12] and X-ray absorption 13,14 and nuclear magnetic resonance (NMR) spectroscopy 5,[15][16][17] have been applied to study NaAlH 4 and its decomposition in great detail. Nevertheless, some important questions concerning the mechanism of hydrogen release and uptake remain open.…”

Section: Introductionmentioning

confidence: 99%

On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH₄

Zibrowius

Felderhoff

2019

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

Potassium aluminium tetrahydride KAlH 4 of high phase purity (space group Pnma (62)) was synthesized via a mechanochemical route. The thus obtained material was studied by 27 Al and 39 K MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T = 295 K were derived ( 27 Al: δ iso = (107.6±0.2) ppm, C Q = (1.29±0.02) MHz and η = 0.64±0.02; 39 K: δ iso = (6.1± 0.2) ppm, C Q = (0.562 ± 0.005) MHz and η = 0.74 ± 0.02). The straightforward NMR spectroscopic approach applied here should also work for other complex aluminium hydrides and for many other materials containing half-integer nuclei experiencing small to medium-sized quadrupole couplings. arXiv:1902.08540v3 [cond-mat.mtrl-sci]

show abstract

Regeneration of sodium alanate studied by powder in situ neutron and synchrotron X-ray diffraction

Abstract: The regeneration pathway of sodium alanate has been studied by in situ synchrotron powder X-ray diffraction and powder neutron diffraction.

Cited by 16 publications

References 54 publications

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH₄)

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH₄)

Sodium-based hydrides for thermal energy applications

On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH₄

Contact Info

Product

Resources

About

Regeneration of sodium alanate studied by powder in situ neutron and synchrotron X-ray diffraction

Abstract: The regeneration pathway of sodium alanate has been studied by in situ synchrotron powder X-ray diffraction and powder neutron diffraction.

Cited by 16 publications

References 54 publications

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH4)

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH4)

Sodium-based hydrides for thermal energy applications

On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4

Contact Info

Product

Resources

About

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH₄)

Asymmetric Reaction Paths and Hydrogen Sorption Mechanism in Mechanochemically Synthesized Potassium Alanate (KAlH₄)

On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH₄