Synthesis of calcium alanate and its dehydriding performance enhanced by FeF₃doping

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• 作者：Changxu Li ; Xuezhang Xiao ; Lixin Chen ; Kun Jiang ; Shouquan Li ; Qidong Wang
• 关键词：Calcium alanate ; Dehydriding performance ; Iron fluoride ; Ball-milling
• 刊名：Journal of Alloys and Compounds
• 出版年：2011
• 出版时间：21 January 2011
• 年：2011
• 卷：509
• 期：3
• 页码：590-595
• 全文大小：493 K

文摘

Ca(AlH₄)₂ was synthesized by ball-milling the mixture of NaAlH₄ and CaCl₂ in a molar ratio of 2:1 and under a hydrogen atmosphere of 1 MPa. The results indicate that the reactants have entirely transformed to Ca(AlH₄)₂ with a byproduct of NaCl after ball-milling for 48 h. Investigations of dehydriding behavior of the as-prepared Ca(AlH₄)₂ sample show that approximately 5.2 wt. % of hydrogen is desorbed during the first two dehydrogenation reactions of Ca(AlH₄)₂, which exhibit an exothermic event at 148 °C and an endothermic event at 267 °C, respectively. The high temperature dehydrogenation at 267 °C mainly concentrates on the thermolysis of CaAlH₅ intermediate. FeF₃-doped Ca(AlH₄)₂ system represents an improved dehydriding performance, the dehydrogenation temperature of CaAlH₅ intermediate is decreased about 43 °C. After FeF₃ doping, the apparent activation energy of CaAlH₅ is reduced from 153.4 kJ/mol (undoped) to 88.3 kJ/mol (doped), it renders a possibility to realize the rehydrogenation of CaAlH₅. The catalytic effect is attributed to a fluorine transfer reaction that occurred to generate CaF₂ and Fe catalysts.