Hydrogen storage of magnesium-based nanocomposites system

Hydrogen storage in traditional metallic hydrides can deliver about 1.5 to 2.0 wt pct hydrogen but magnesium hydrides can achieve more than 7 wt pct. However, these systems suffer from high temperature release drawback and chemical instability problems. Recently, big improvements of reducing temperature and increasing kinetics of hydrogenation have been made in nanostructured Mg-based composites. This paper aims to provide an overview of the science and engineering of Mg materials and their nanosized composites with nanostructured carbon for hydrogen storage. The needs in research including preparation of the materials, processing and characterisation and basic mechanisms will be explored. The preliminary experimental results indicated a promising future for chemically stable hydrogen storage using carbon nanotubes modified metal hydrides under lower temperatures.

Hydrogen storage properties of MgH2/SWNT composite prepared by ball milling

A systematic investigation was performed on the hydrogen storage properties of mechano-chemically prepared MgH2/Single-walled carbon nanotube (SWNT) composites. It is found that the hydrogen absorption capacity and hydriding kinetics of the composites were dependent on the addition amount of SWNTs as well as milling time. A 5 wt.% addition of SVVNTs is optimum to facilitate the hydrogen absorption and desorption of MgH2. The composite MgH2/5 wt.% SWNTs milled for 10h can absorb 6.7 wt.% hydrogen within about 2 min at 573 K, and desorb 6 wt.% hydrogen in about 5 min at 623 K. Prolonging the milling time over 10 h leads to a serious degradation on hydrogen storage property of the MgH2/SWNT composite, and property/structure investigations suggest that the property degradation comes from the structure destruction of the SWNTs. (c) 2005 Elsevier B.V. All rights reserved.

Mg-based nanocomposites with high capacity and fast kinetics for hydrogen storage

Magnesium and its alloys have shown a great potential in effective hydrogen storage due to their advantages of high volumetric/ gravimetric hydrogen storage capacity and low cost. However, the use of these materials in fuel cells for automotive applications at the present time is limited by high hydrogenation temperature and sluggish sorption kinetics. This paper presents the recent results of design and development of magnesium-based nanocomposites demonstrating the catalytic effects of carbon nanotubes and transition metals on hydrogen adsorption in these materials. The results are promising for the application of magnesium materials for hydrogen storage, with significantly reduced absorption temperatures and enhanced ab/desorption kinetics. High level Density Functional Theory calculations support the analysis of the hydrogenation mechanisms by revealing the detailed atomic and molecular interactions that underpin the catalytic roles of incorporated carbon and titanium, providing clear guidance for further design and development of such materials with better hydrogen storage properties.

Effect of carbon/noncarbon addition on hydrogen storage behaviors of magnesium hydride

Various Mg/carbon and Mg/noncarbon composite systems were prepared by mechanical milling and their hydrogen storage behaviors were investigated. It was found that all the carbon additives exhibited prominent advantage over the noncarbon additives, such as BN nanotubes (BNNTs) or asbestos in improving the hydrogen capacity and dehydriding/hydriding kinetics of Mg. And among the various carbon additives, purified single-walled carbon nanotubes (SWNTs) exhibited the most prominent catalytic effect on the hydrogen storage properties of Mg. The hydrogen capacities of all Mg/C composites at 573 K reached more than 6.2 wt.% within 10 min, about 1.5 wt.% higher than that of pure MgH2 at the identical operation conditions. Under certain operation temperatures, H-absorption/desorption rates of Mg/carbon systems were over one order of magnitude higher than that of pure Mg. Furthermore, the starting temperature of the desorption reaction of MgH2 has been lowered to 60 K by adding SWNTs. On the basis of the hydrogen storage behavior and structure/phase investigations, the possible mechanism involved in the property improvement of Mg upon adding carbon materials was discussed. (c) 2005 Elsevier B.V. All rights reserved.

Archaeological Identification and Significance of ÉSAG (Agricultural Storage Pits) at Kaman-Kalehöyük, Central Anatolia

Evidence for the presence of storage pits described in Hittite texts by the Sumerogram "ÉSAG" is presented from Kaman-Kalehöyük, a multi-period tell site in central Turkey occupied during the second and first millennia BC. Small earthen pits matching the description of "ÉSAG" were part of the normal suite of domestic installations at the site throughout the period. Similar to pits seen across western Eurasia, they were probably used to store seed corn or seed for trade. Large earthen pits (>7m in diameter) were also present that matched the description of the "ÉSAG" form, and in some cases contained archaeological cereal remains. Evidence from Kaman shows "ÉSAG" were part of Anatolian life for at least 4,000 years and suggests that the term was generic for lined, earthen storage pits. The presence of so many small pits at Kaman-Kalehöyük showed that it was an agricultural production site for much of its existence. The appearance of the large pits, confined to the Hittite period, reflects centralised control of grain supply, probably by the Hittite Kingdom, and fits a pattern seen at other sites in the region during the second millennium BC. /// Hitit metinlerinde Sumerogram "ÉSAG" ile tanimlanan depo çukurlarinin varliğina dair kanit, Orta Anadolu'da M.Ö. İkinci ve Birinci binde iskan edilmiş çok dönemli bir yerleşim alani olan Kaman-Kalehöyük'ten taninmaktadir. Küçük toprak çukurlar "ÉSAG" in tanimlamasina uygun olarak bu dönem süresince normal ev düzeninin bir parçasi olarak karşimiza çikmiştir. Çukurlar, Bati Avrasya'daki benzer çukurlar gibi olasilikla ticaret maksadi ile misir tohumu ya da tohum muhafaza etmişlerdir. "ÉSAG" formunun tanimina uyan büyük toprak çukurlara (çapi 7m. den büyük) rağmen bunlarin tahil depolama ile ilgili bağlantilari tam olarak belirlenmemiştir. Kaman'daki delil, "ÉSAG" in en az 4,000 yildir Anadolu yaşaminin bir parçasi olduğunu ve bu sözcüğün sivanmiş toprak çukurlar için kullanildiğini işaret etmektedir. Kaman-Kalehöyük'te ele geçen birçok küçük çukur, yerleşimin varliğini sürdürdüǧü sürecin büyük bir bölümünde zirai üretim yapildiğini göstermektedir. Hitit Döneminde büyük çukurlarin ortaya çikmasi muhtemelen Hitit Kralliği tarafindan gerçekleştirilen tahil tedarikinin merkezi kontrolünü yansitmakta ve M.Ö. İkinci binde bu bölgedeki diğer yerleşim alanlarinda görülen şekle uymaktadir.