Engineering considerations in the use of catalyzed sodium alanates for hydrogen storage

Sandrock, G.; Gross, Karl; Thomas, George J.; Jensen, Craig M.; Meeker, D.; Takara, Satoshi

doi:10.1016/s0925-8388(01)01505-5

Cited by 155 publications

(131 citation statements)

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“…2 This finding offers a clear potential to achieve >5 wt % hydrogen storage at a moderate temperature condition and thus quickly stimulates worldwide interest in developing catalytically enhanced TiNaAlH 4 and other related light metal complex hydrides as practical hydrogen storage media. [3][4][5][6][7][8][9][10][11][12][13][14][15] The hydrogen storage performance of the Ti-NaAlH 4 system at moderate temperature range is dominated by the catalytic enhancement arising upon doping with Ti catalyst. So far, however, the catalytic mechanism and even the nature of active Ti species have not been firmly established.…”

Section: Introductionmentioning

confidence: 99%

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH₄

2005

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Clarification of the nature of active Ti species has been a key challenge in developing Ti-doped NaAlH 4 as a potential hydrogen storage medium. Previously, it has been greatly hindered by the invisibility of Ticontaining species in conventional analysis techniques. In the present study, for the first time, the catalytically active Ti-containing species have been definitely identified by X-ray diffraction in the hydrides doped with metallic Ti. It was found that mechanical milling of a NaH/Al mixture or NaAlH 4 with metallic Ti powder resulted in the formation of nanocrystalline Ti hydrides. The variation of the preparation conditions during the doping process leads to a slight composition variation of the Ti hydrides. The catalytic enhancement arising upon doping the hydride with commercial TiH 2 was quite similar to that achieved in the hydrides doped with metallic Ti. Moreover, the cycling stability that was previously established in metallic Ti-doped hydrides was also observed in the hydrides doped with TiH 2 . These results clearly demonstrate that the in situ formed Ti hydrides act as active species to catalyze the reversible dehydrogenation of NaAlH 4 . The mechanism by which Ti hydrides catalyze the reversible de-/hydrogenation reactions of NaAlH 4 was discussed.

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Section: Introductionmentioning

confidence: 99%

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH₄

2005

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“…This indicates that thermal dissociation is more thermodynamically favorable for LiAlH 4 than for NaAlH 4 . Additionally, it has been shown that the activation energy for the decomposition of Li 3 AlH 6 is 54.8 kJ/mol H 2 , while that for Na 3 AlH 6 is 96.9 kJ/mol H 2 (Sandrock et al, 2002;Chen et al, 2001). Evidently, lithium alanate is less stable than sodium alanate; however, no conclusive studies have been done to show whether Eqs.…”

Section: Introductionmentioning

confidence: 99%

On the Reversibility of Hydrogen Storage in Novel Complex Hydrides

2005

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Abstract.A comparison of the hydrogen release and uptake (cycling) capability of Ti-doped NaAlH 4 , LiAlH 4 and Mg(AlH 4 ) 2 as a function of Ti dopant concentration, temperature, pressure, and cycle number is reported. Temperature programmed desorption revealed hydrogen release capacities of around 3 wt% at 140 o C, 3 wt % at 100 o C and 6 wt% at 150 o C, respectively for the Ti doped Na, Li and Mg alanates. In the same order, release capacities of 0.5, 2.0 and 1.5 wt% were obtained in 150, 6 and 150 min during constant temperature desorption at 90 o C. Although all three alanates exhibit striking characteristics that make them potential hydrogen storage materials, it remains that only Ti-doped NaAlH 4 exhibits around 3 wt % reversibility under reasonable conditions.

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“…In 2001, Jensen and Gross [2] reported that, the first decomposition occurs at 210-220 8C for a relative short time (%3 h) but the decomposition reactions of NaAlH 4 and Na 3 4 on NaAlH 4 . They concluded that a few mole percents of titanium compounds show superior kinetics for hydrogen absorption and desorption.…”

Section: Introductionmentioning

confidence: 99%

“…They concluded that a few mole percents of titanium compounds show superior kinetics for hydrogen absorption and desorption. Both alkoxide and chloride compounds have been used by different methods (wet doping, semi-doping and dry doping) to improve hydrogen storage of NaAlH 4 [4,5].…”

Section: Introductionmentioning

confidence: 99%

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Effect of metal type and loading on hydrogen storage on NaAlH₄

Termtanun

Rangsunvigit

Kitiyanan

et al. 2005

Science and Technology of Advanced Materials

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Although hydrogen has a great potential as clean energy, safe practical storage of hydrogen for applications such as fuel cells has been a major challenge. NaAlH 4 is one of the metal hydrides, which are candidates for hydrogen storage in vehicles. However, the rather slow absorption/desorption kinetics is still a significant drawback. To alleviate this problem, purified NaAlH 4 was ground with TiCl 3 , ZrCl 4 , or HfCl 4 . Desorption kinetics and capacities were observed under TPD-like operation. Absorption efficiency was determined by raising the temperature up to 125 8C. Of the three doped metals investigated for the positive effect on facilitating NaAlH 4 decomposition, TiCl 3 assists the best on the first reaction while ZrCl 4 and HfCl 4 do for the second one. Despite the kinetics enhancement directly involves with the ZrCl 4 amount, there is a threshold of ZrCl 4 -content which affects. 6% ZrCl 4 is considered as an appropriate amount to improve the hydrogen release because it simultaneously decreases the desorption temperature and gives the outstanding rate. In hydrogen desorption, ZrCl 4 provides the most amount of released hydrogen, but for hydrogen absorption TiCl 3 -doped NaAlH 4 possesses the highest capacity. It is believed that the metal size is one of the key factors resulting in such the behavior. q

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Engineering considerations in the use of catalyzed sodium alanates for hydrogen storage

Cited by 155 publications

References 10 publications

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH₄

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH₄

On the Reversibility of Hydrogen Storage in Novel Complex Hydrides

Effect of metal type and loading on hydrogen storage on NaAlH₄

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Engineering considerations in the use of catalyzed sodium alanates for hydrogen storage

Cited by 155 publications

References 10 publications

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH4

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH4

On the Reversibility of Hydrogen Storage in Novel Complex Hydrides

Effect of metal type and loading on hydrogen storage on NaAlH4

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Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH₄

Exploration of the Nature of Active Ti Species in Metallic Ti-Doped NaAlH₄

Effect of metal type and loading on hydrogen storage on NaAlH₄