Modification of Mg hydrogen storage properties by MXene materials Nb2CClx and Ti2CClx
Magnesium is an interesting class of solid-state hydrogen storage materials with high hydrogen stor-age 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(Nb2CClx and Ti2CClx)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 micro-structure 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 Nb2CClx and Ti2CClx,on the other hand,gives Mg a significant enhancement,which can effectively increase the hydro-gen absorption and release rate of the material,with Mg@Nb2CClx releasing 5.0 wt％hydrogen in 200 s,and Mg@Ti2CClx releasing 5.3 wt％in 250 s.The introduction of Mg@Nb2CClx can also reduce the initial hydrogen absorption and release temperature of pure Mg by 10wt％Nb2CClx.The initial hydrogen absorption and release temperatures of the materials can also be lowered,with 10wt％Nb2CClx lowering the initial hydrogen absorp-tion and release temperatures of pure Mg by 125 ℃ and 175 ℃,respectively,and 10 wt％Ti2CClx 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 hy-drogen absorption and release kinetic performance of Mg.
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