Hydrogenation/Dehydrogenation Kinetics Study of Reacted Ball Milled (MgH₂)_100-x/(Ni)_y/(Nb₂O₅)_z)_x Nanocomposite Powders

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• 作者：M. Sherif El-Eskandarany ; H.S. AlMatrouk ; ^{hasan.almatrouk@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Ehab Shaban
• 关键词：Reactive ball milling ; metal hydrides ; Nanocomposites ; Nanocatalysts ; Gas-solid reaction ; Cycle-life-time
• 刊名：Materials Today: Proceedings
• 出版年：2016
• 出版时间：2016
• 年：2016
• 卷：3
• 期：8
• 页码：2735-2743
• 全文大小：2778 K

文摘

Nanocrystalline powders of MgH₂ was synthesized under a high hydrogen gas pressure (50 bar), using reactive ball milling technique operated at ambient temperature under 50 bar of a hydrogen gas atmosphere. The MgH₂ powders obtained after 200 h of continuous RBM time composed of β and γ phases. The powders possessed nanocrystalline characteristics with an average grain of about 10 nm in diameter. The time required for complete hydrogen absorption and desorption measured at 250°C was 500 s and 2500 s, respectively. In order to improve the hydrogenation/dehydrogenation kinetics, three different types of nanocatalysts (metallic Ni, Nb₂O₅ and (Ni)_x/(Nb₂O₅)_y) were utilized with different weight percentages and independently ball milled with the as-synthesized MgH₂ powders for 50 h under 50 bar of a hydrogen gas atmosphere. The results have shown that the as-prepared nanocomposite MgH₂/5Ni/5Nb₂O₅ powders possessed superior hydrogenation/dehydrogenation characteristics, indexed by low values of activation energy for β-phase (68 kJ/mol) and γ-phase (74 kJ/mol). Moreover, this nanocomposite system shows excellent hydrogenation/dehydrogenization behavior indexed by the short time required to uptake (41 s) and release (121 s) of 5 wt.% H₂ at 250°C.