MXene材料Nb_(2)CCl_(x)与Ti_(2)CCl_(x)对Mg储氢性能的改性研究

Modification of Mg hydrogen storage properties by MXene materials Nb_(2)CCl_(x) and Ti_(2)CCl_(x)

镁是众多固态储氢材料中一类深受关注的材料,具有很高的储氢容量(7.6%(质量分数))和可逆吸放氢等优点。但是Mg吸放氢所需温度高,放氢动力学缓慢等影响了其实用性。采用熔盐刻蚀法以n(Mg)∶n(MXene)=10∶1的比例制备了两种不同类型的MXene(Nb_(2)CCl_(x)和Ti_(2)CCl_(x)),并研究不同种类MXene的添加对金属Mg的微观结构和吸放氢性能的影响。结果表明,材料的相组成未发生改变,但球磨后材料的颗粒尺寸进一步减小,增大了其比表面积。Nb_(2)CCl_(x)和Ti_(2)CCl_(x)的引入则使Mg的性能得到明显提升,可以有效提高材料的吸放氢速率,Mg@Nb_(2)CCl_(x)在200 s内就可以放出5.0%(质量分数)的氢气,Mg@Ti_(2)CCl_(x)在250 s内也可以放出5.3%(质量分数)的氢气。同时也可以降低材料的初始吸放氢温度,10%(质量分数)Nb_(2)CCl_(x)使纯Mg的初始吸氢和放氢温度分别降低了125℃和175℃,10%(质量分数)Ti_(2)CCl_(x)则使纯Mg的初始吸氢和放氢温度分别降低了100和125℃。根据Chou模型进行吸放氢动力学拟合的结果表明,MXene的加入使Mg的控速步骤由表面渗透控制向扩散控制转变,从而提高了Mg的吸放氢动力学性能。

Magnesium is an interesting class of solid-state hydrogen storage materials with high hydrogen storage capacity(7.6wt%)and reversible hydrogen absorption and release.However,the high temperature required for Mg hydrogen absorption and release and the slow kinetics of hydrogen release affect its practicality.In this paper,two different types of MXene(Nb_(2)CCl_(x) and Ti_(2)CCl_(x))were prepared by the molten salt etching method with the ratio of Mg:MXene=10:1,and the effects of the addition of different types of MXene on the microstructure and hydrogen absorption and discharge properties of metallic Mg were investigated.The results showed that the phase composition of the materials remained unchanged,but the particle size of the materials was further reduced after ball milling,which increased their specific surface area.The introduction of Nb_(2)CCl_(x)and Ti_(2)CCl_(x),on the other hand,gives Mg a significant enhancement,which can effectively increase the hydrogen absorption and release rate of the material,with Mg@Nb_(2)CCl_(x)releasing 5.0 wt%hydrogen in 200 s,and Mg@Ti_(2)CCl_(x)releasing 5.3 wt%in 250 s.The introduction of Mg@Nb_(2)CCl_(x) can also reduce the initial hydrogen absorption and release temperature of pure Mg by 10wt%Nb_(2)CCl_(x).The initial hydrogen absorption and release temperatures of the materials can also be lowered,with 10wt%Nb_(2)CCl_(x) lowering the initial hydrogen absorption and release temperatures of pure Mg by 125℃ and 175℃,respectively,and 10 wt%Ti_(2)CCl_(x) lowering the initial hydrogen absorption and release temperatures of pure Mg by 100℃ and 125℃,respectively.The results of hydrogen absorption and release kinetic fitting based on the Chou model showed that the addition of MXene shifted the rate-control step of Mg from surface permeation control to diffusion control,which improved the hydrogen absorption and release kinetic performance of Mg.