Dehydrogenation/rehydrogenation mechanism in aluminum destabilized lithium borohydride
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Guanglin Xia Department of Materials Science, Fudan University, Shanghai 200433, China
Zaiping Guo and Huakun Liu Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia; and CSIRO National Hydrogen Materials Alliance, CSIRO Energy Centre, Mayfield West, NSW 2304, Australia (Received 12 August 2008; accepted 11 November 2008)
LiBH4/Al mixtures with various mol ratios were prepared by ball milling. The hydrogen storage properties of the mixtures were evaluated by differential scanning calorimetry/ thermogravimetry analyses coupled with mass spectrometry measurements. The phase compositions and chemical state of elements for the LiBH4/Al mixtures before and after hydrogen desorption and absorption reactions were assessed via powder x-ray diffraction, infrared spectroscopy, and x-ray photoelectron spectroscopy. Dehydrogenation results revealed that LiBH4 could react with Al to form AlB2 and AlLi compounds with a two-step decomposition, resulting in improved dehydrogenation. The rehydrogenation experiments were investigated at 600 C with various H2 pressure. It was found that intermediate hydride was formed firstly at a low H2 pressure of 30 atm, while LiBH4 could be reformed completely after increasing the pressure to 100 atm. Absorption/ desorption cycle results showed that the dehydrogenation temperature increased and the hydrogen capacity degraded with the increase of cycle numbers. I. INTRODUCTION
In order to use hydrogen as one of the clean fuels of the future, it is necessary to develop high-performance hydrogen-storage materials.1,2 Most of the complex hydrides, such as sodium alanate systems,3–5 the amide system,6–8 the borohydride system,9–13 and so on inevitably possess a high hydrogen storage capacity, so systematic investigations have vigorously been in progress in the past few years. Among them, lithium borohydride, LiBH4, is presently one of the most promising solid-state hydrogen-storage materials, because of its high hydrogen storage capacity of 18.5 wt%. However, the main evolution of gas starts at 380 C, and only half the hydrogen is released before 600 C.14 Recently, Zu¨ttel et al.14 reported that SiO2 may be used to destabilize the dehydrogenation of LiBH4, lowering the temperature of hydrogen evolution to 300 C. Pinkerton et al.15 also reported that LiBH4 could react with LiNH2 to form a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0328
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 8, Aug 2009 Downloaded: 10 Apr 2015
quaternary hydride Li–B–N–H. This quaternary hydride released hydrogen at just above 250 C. More recently, new approaches modify the hydrogenation/dehydrogenation reaction of LiBH4 by using additives to form compounds or alloys in the dehydrogenated state that are energetically favorable with respect to the products of the reaction without additives. This concept is known as destabilization. The principle underlying this concept is that having a stabiliz
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