Abstract
LiAlH4 and CaCl2 were employed for mechano-chemical activation synthesis (MCAS) of Ca(AlH4)2 and LiCl hydride composite. After short ball milling time, their X-ray diffraction (XRD) peaks are clearly observed. After ball milling for a longer duration than 0.5 h, the CaAlH5 diffraction peaks are observed which indicates that Ca(AlH4)2 starts decomposing during ball milling into CaAlH5+Al+1.5H2. It is estimated that less than 1 wt % H2 was mechanically dehydrogenated in association with decomposition reaction. After 2.5 h of ball milling, no Ca(AlH4)2 diffraction peaks were observed on XRD patterns which suggests that Ca(AlH4)2 was decomposed. Thermal behavior of ball milled powders, which was investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), indicates that a certain fraction of Ca(AlH4)2 could have been disordered/amorphized during ball milling being undetectable by XRD. The apparent activation energy for the decomposition of Ca(AlH4)2 and CaAlH5 equals 135 kJ/mol and 183 kJ/mol, respectively.
Highlights
The worldwide acceptance of the Hydrogen Economy would lead to a gradual elimination of the present fossil fuels-based economy and make a decisive turn to the economy based on renewable and clean resources [1,2]
Thermal dehydrogenation process of the (2LiAlH4+CaCl2) ball milled powders was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA)
Ca(AlH4)2 starts decomposing into the mixture of CaAlH5+2Al+1.5H2 during ball milling for at least 0.5 h and longer which is evidenced by the CaAlH5 diffraction peaks appearing on X-ray diffraction (XRD) patterns
Summary
The worldwide acceptance of the Hydrogen Economy would lead to a gradual elimination of the present fossil fuels-based economy and make a decisive turn to the economy based on renewable and clean resources [1,2]. For mass transportation by using automobiles, solid state hydrogen storage in hydrides has certain advantages over gas and liquid because most solid hydrides exhibit a higher H2 volumetric density than gas or liquid storage, and they don’t have serious safety problems such as a very high pressure of 70 MPa for H2 gas or large thermal losses for liquid H2 which requires a formidable insulation and an open storage system [3,4]. There is no solid hydride that can desorb under roughly 1.0–3.0 bar H2, at low temperatures, not exceeding the waste heat temperature of a FC stack (70–80 °C), which can be used for heating a hydride storage tank, has a capacity at least 11 wt % H2 and be reversible “on board”. Thermal dehydrogenation (thermolysis) experiments were conducted to shed more light on the understanding of the occurring mechanisms
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