通过对MgH2+x%Ni(x=0,2,4,8,20,30)样品高能球磨不同时间,研究球磨时间及镍含量对MgH2/Ni体系放氢性能的影响.对合金在球磨过程中的结构变化、组织演变及放氢动力学进行了系统研究.结果表明,当放氢温度高于380°C时,MgH2的放氢动力学与晶粒尺寸、颗粒尺寸及合金中的缺陷数量无关,随着球磨时间增加,镍在MgH2表面分布更加均匀,放氢动力学性能越好.体系放氢后会生成Mg2Ni,从而降低复合体系在循环过程中的储氢性能.在MgH2放氢过程中,镍不仅有助于氢原子的重组,还可以帮助镁的形核长大.
The effects of ball milling time and Ni content on the dehydrogenation performance of MgH2/Ni composite were systematically investigated. The structural evolution of ball milled MgH2+x%Ni (x=0, 2, 4, 8, 20, 30, mass fraction) samples during mechanical milling process and dehydrogenation properties were investigated by a series of experimental techniques. The results show that the desorption kinetics is independent of particle size, grain size and defects as the temperature is above 380oC. The desorption kinetics is improved by prolonged milling time due to refined and uniformly distributed Ni. The formation of Mg2Ni after dehydrogenation is proposed to explain the degradation of hydrogen storage properties of MgH2 during de-/hydrogenation cycling process. The desorption activation energy of MgH2 decreases with the increase of Ni content due to the catalytic effect of Ni. It is found Ni favors the nucleation of magnesium phase and accelerates the recombination of hydrogen atoms.
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