El-Eskandarany M Sherif, Shaban Ehab
Nanotechnology and Advanced Materials Program, Energy and Building Research Center, Kuwait Institute for Scientific Research, Safat 13109, Kuwait.
Materials (Basel). 2015 Oct 10;8(10):6880-6892. doi: 10.3390/ma8105350.
Ultrafine MgH₂ nanocrystalline powders were prepared by reactive ball milling of elemental Mg powders after 200 h of high-energy ball milling under a hydrogen gas pressure of 50 bar. The as-prepared metal hydride powders were contaminated with 2.2 wt. % of FeCr-stainless steel that was introduced to the powders upon using stainless steel milling tools made of the same alloy. The as-synthesized MgH₂ was doped with previously prepared TiC nanopowders, which were contaminated with 2.4 wt. % FeCr (materials of the milling media), and then ball milled under hydrogen gas atmosphere for 50 h. The results related to the morphological examinations of the fabricated nanocomposite powders beyond the micro-and nano-levels showed excellent distributions of 5.2 wt. % TiC/4.6 wt. % FeCr dispersoids embedded into the fine host matrix of MgH₂ powders. The as-fabricated nanocomposite MgH₂/5.2 wt. % TiC/4.6 wt. % FeCr powders possessed superior hydrogenation/dehydrogenation characteristics, suggested by the low value of the activation energy (97.74 kJ/mol), and the short time required for achieving a complete absorption (6.6 min) and desorption (8.4 min) of 5.51 wt. % H₂ at a moderate temperature of 275 °C under a hydrogen gas pressure ranging from 100 mbar to 8 bar. van't Hoff approach was used to calculate the enthalpy (DH) and entropy (DS) of hydrogenation for MgH₂, which was found to be -72.74 kJ/mol and 112.79 J/mol H₂/K, respectively. Moreover, van't Hoff method was employed to calculate the DH and DS of dehydrogenation, which was found to be 76.76 kJ/mol and 119.15 J/mol H₂/K, respectively. This new nanocomposite system possessed excellent absorption/desorption cyclability of 696 complete cycles, achieved in a cyclic-life-time of 682 h.
在50巴氢气压力下对元素镁粉进行200小时高能球磨后，通过反应球磨制备了超细MgH₂纳米晶粉末。所制备的金属氢化物粉末被2.2 wt.%的FeCr不锈钢污染，这是在使用由相同合金制成的不锈钢研磨工具时引入到粉末中的。合成的MgH₂掺杂了先前制备的TiC纳米粉末，其被2.4 wt.%的FeCr（研磨介质材料）污染，然后在氢气气氛下球磨50小时。与制备的纳米复合粉末在微米和纳米尺度以上的形态学检查相关的结果表明，5.2 wt.% TiC/4.6 wt.% FeCr弥散体在MgH₂粉末的精细主体基质中分布优异。所制备的纳米复合MgH₂/5.2 wt.% TiC/4.6 wt.% FeCr粉末具有优异的氢化/脱氢特性，这由低活化能值（97.74 kJ/mol）以及在275°C的适中温度下、100毫巴至8巴的氢气压力下实现5.51 wt.% H₂完全吸收（6.6分钟）和解吸（8.4分钟）所需的短时间表明。采用范特霍夫方法计算MgH₂氢化的焓（DH）和熵（DS），分别为-72.74 kJ/mol和112.79 J/mol H₂/K。此外，采用范特霍夫方法计算脱氢的DH和DS，分别为76.76 kJ/mol和119.15 J/mol H₂/K。这种新型纳米复合体系在682小时的循环寿命内实现了696次完整循环的优异吸收/解吸循环稳定性。
