MgH_2-Nb_2O_5体系吸氢动力学性能

Rehydrogenation Performance of MgH_2-Nb_2O_5 System

采用高能球磨法成功制备了MgH_2+x mol%Nb_2O_5(x=0.1、0.5、1和2)材料,并研究了Nb_2O_5添加量对MgH_2吸氢动力学性能的影响规律.XRD结果显示,Nb_2O_5的加入未生成新相,晶粒大小约为30 nm.SEM结果表明,Nb_2O_5的加入使颗粒变小.TEM结果表明,该材料具有纳米/非晶态的混合结构.这些结构有利于氢的吸附和扩散,可提高其动力学性能.吸氢动力学结果显示,当Nb_2O_5含量达1 mol%时,动力学性能最佳.该体系在523 K时500 s内吸氢量达到4.0%,20 s即达到最大吸氢速率为0.09%/s;573 K时500 s内吸氢量为4.7%.研究还发现,在523 K时,随Nb_2O_5含量的增加,吸氢量逐渐降低,这主要是由于不吸氢的Nb_2O_5含量的增加造成的;而在473 K时,随Nb_2O_5含量的增加,吸氢量却随之增加,此时起主要作用的是其催化能力.

A MgH2＋x mol% Nb2O5 （x=0.1,0.5,1 and 2） system was successfully pre-pared by a high-energy ball milling process and the catalytic effect of the Nb2O5 content on the rehydrogenation performance of MgH2 was investigated. XRD and SEM results showed that no new phase was observed and the particle size was deceased to about 30 nm after the addition of Nb2O5, and TEM result indicated that this system had a nanocrystal and amorphous structure, which were believed to be beneficial for the improvement of the rehydrogenation performance of MgH2. The rehydrogenation results showed that a MgH2＋1 mol% Nb2O5 system had the most promising performance, and could reach the highest hydriding rate of 0.09%/s after 20 s and absorb 4% and 4.7% of hydrogen within 500 s at 523 K and 573 K, respectively. Further resuits revealed that the amount of rehydrogenation gradually decreased with the increase of Nb2O5 content at 523 K, which was mainly owing to the increase of the amount of the inactive Nb2O5. However, at 473 K, the amount of rehvdrogenation raised with the increase of Nh2O5 content, which was attributed to the catalytic ability of Nb2O5.