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Effect of additives, ball milling and isotopic exchange in porous magnesium borohydride

机译：多孔硼氢化镁中添加剂，球磨和同位素交换的影响

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Magnesium borohydride (Mg(BH _(4) ) _(2) ) is a promising material for solid state hydrogen storage. However, the predicted reversible hydrogen sorption properties at moderate temperatures have not been reached due to sluggish hydrogen sorption kinetics. Hydrogen (H) → deuterium (D) exchange experiments can contribute to the understanding of the stability of the BH _(4) ~(?) anion. Pure γ-Mg(BH _(4) ) _(2) , ball milled Mg(BH _(4) ) _(2) and composites with the additives nickel triboride (Ni _(3) B) and diniobium pentaoxide (Nb _(2) O _(5) ) have been investigated. In situ Raman analysis demonstrated that in pure γ-Mg(BH _(4) ) _(2) the isotopic exchange reaction during continuous heating started at ～80 °C, while the ball milled sample did not show any exchange at 3 bar D _(2) . However, during ex situ exchange reactions investigated by infrared (IR) and thermogravimetric (TG) analyses a comparable H → D exchange during long exposures (23 h) to deuterium atmosphere was observed for as received, ball milled and γ-Mg(BH _(4) ) _(2) + Nb _(2) O _(5) , while the Ni _(3) B additive hindered isotopic exchange. The specific surface areas (SSA) were shown to be very different for as received γ-Mg(BH _(4) ) _(2) , BET area = 900 m ~(2) g ~(?1) , and ball milled Mg(BH _(4) ) _(2) , BET area = 30 m ~(2) g ~(?1) , respectively, and this explains why no gas–solid H(D) diffusion was observed for the ball milled (amorphous) Mg(BH _(4) ) _(2) during the short time frames of in situ Raman measurements. The heat treated ball milled sample partially regained the porous γ-Mg(BH _(4) ) _(2) structure (BET area = 560 m ~(2) g ~(?1) ). This in combination with the long reaction times allowing for the reaction to approach equilibrium explains the observed gas–solid H(D) diffusion during long exposure. We have also demonstrated that a small amount of D can be substituted in both high surface area and low surface area samples at room temperature proving that the B–H bonds in Mg(BH _(4) ) _(2) can be challenged at these mild conditions.
机译：硼氢化镁（Mg（BH _（4）_（2））是一种有前途的固态氢存储材料。但是，由于缓慢的氢吸附动力学，尚未达到在中等温度下可预测的可逆氢吸附性能。氢（H）→氘（D）交换实验可有助于理解BH _（4）〜（？）阴离子的稳定性。纯γ-Mg（BH _（4））_（2），球磨Mg（BH _（4））_（2）以及含三硼化镍（Ni _（3）B）和五氧化二铌（Nb）的复合材料_（2）O _（5））已被研究。原位拉曼分析表明，在纯γ-Mg（BH _（4））_（2）中，连续加热期间的同位素交换反应始于〜80°C，而球磨样品在3 bar D时未显示任何交换_（2）。但是，在通过红外（IR）和热重分析（TG）分析的异位交换反应过程中，观察到了长时间，氘气暴露于氘气中（23 h）时可比较的H→D交换，如接收，球磨和γ-Mg（BH_ （4））_（2）+ Nb _（2）O _（5），而Ni _（3）B添加剂阻碍了同位素交换。对于所接收的γ-Mg（BH _（4））_（2），BET面积= 900 m〜（2）g〜（？1）和球磨，显示出的比表面积（SSA）有很大不同。 Mg（BH _（4））_（2），BET面积分别为30 m〜（2）g〜（？1），这解释了为什么球磨时没有观察到气固H（D）扩散Mg（BH _（4））_（2）在原位拉曼测量的短时间范围内。经热处理的球磨样品部分恢复了多孔的γ-Mg（BH_（4））_（2）结构（BET面积= 560 m〜（2）g〜（？1））。结合较长的反应时间使反应达到平衡，这说明了长时间暴露期间观察到的气固H​​（D）扩散。我们还证明了在室温下高表面积和低表面积样品中都可以替换少量的D，证明Mg（BH _（4））_（2）中的B–H键可以在这些温和的条件。

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