球磨La_2Mg_(17)与Ni复合合金的电化学贮氢性能研究

Electrochemical hydrogen storage properties of ball milling La_2Mg_(17) and Ni composite

利用机械合金化法制备了La2Mg17+200%(质量分数)Ni复合储氢合金,并对不同球磨时间时合金的微观结构和电化学性能进行研究。结果发现,在球磨过程中Ni粉诱导了La-Mg-Ni非晶/纳米晶结构的形成。XRD和HRTEM结果共同表征了球磨80h时,合金中有Ni金属的存在,且XRD衍射峰强度较低,宽化严重,SAD为宽化的多环,表明形成非晶结构。电化学及其反应动力学测试结果发现,不同球磨时间的电化学反应的动力学控制机理是不同的。球磨60和80h后合金中不仅存在La-Mg-Ni非晶相,同时也有催化剂金属Ni,使合金的表面电荷转移反应电阻较小,氢在合金体相内的扩散系数D和极限电流密度I L均最大,最终导致80h的放电容量为最大值948.3mAh/g。然而,当合金的球磨时间为100和120h时,合金粉化到纳米级,100h的电荷转移反应电阻R ct最大,合金表面电化学反应缓慢,且合金体相内的极限电流密度和氢扩散系数均最小,属于合金电解液表面间的电荷转移和氢向体相内扩散联合控制的过程,必然导致其放电比容量较小。

Abstract： The microstructure and electrochemical hydrogen storage properties of La2Mg17 and Ni powders pre- pared by mechanical grinding method have been studied. It was found that Ni powder induced the formation of amorphous/ nanocrystalline structure of La Mg-Ni alloy. XRD and HRTEM results represent that when ball milling 80h, the alloy in the presence of metal Ni, and the intensity of XRD diffraction decreased and the peak- broad aggravation, forming to the amorphous structure. At the same time, transmission electron microscope and electron diffraction diagram （SAD） showing as the widen ring, which was further confirmed the amorphous structure. Electrochemical kinetics results indicated that the dynamic mechanism of electrochemical reaction was different with the different ball milling time. When ball milled 60 and 80h in the alloy not only exist amor- phous La-Mg-Ni alloys, but also catalyst Ni, make the smaller alloy surface charge transfer reaction resistance and higher the diffusion coefficient D and limiting current density IL, ultimately lead to the discharge capacity for maximum at 948. 3mAh/g. However, when the alloy ball milling time increased to 100 and 120h, alloy powders were in nanosized, the charge transfer reaction resistance Rot with 100h was the largest, the electro- chemical reaction of alloy surface was quite slow, and the limiting current density and the hydrogen diffusion coefficient D in the alloy bulk was minimum, which corresponding to charge transfer stage and the diffusion in alloy bulk combination controlling process. It was inevitably lead to the smaller discharge capacity.