Study Of Preparation And Hydrogen Storage Performance Of Mg-Rich Mg_98.5Y₁Zn_0.5Alloy

With the continuous development of the world economy,energy crisis and environmental pollution issues have become increasingly prominent.In order to alleviate the dependence on fossil energy and environmental pollution,the governments began to develop renewable energy automotive.Hydrogen fuel cell vehicles possesses several characteristics,including short refueling time,long driving course,nonpollution,zero emission and strong environmental adaptability.The development of high efficiency and low energy consumption hydrogen storage technology is the key the wide application of hydrogen fuel cell vehicles.The Mg-based hydrogen storage materials are considered to be one of the most suitable materials for hydrogen carriers.The Mg-RE-TM alloys have a remarkable catalytic effect on the hydrogen ab/desorption properties of Mg-based materials dur to the in-situ formed of RE hydrides by hydrogenation.However,the research on this kind of alloy is only focused on a few kinds of materials,such as,Mg-Nd/Y/Ce-Ni.The research on Mg-Y-Zn alloy is rarely reported and the catalytic mechanism of rare earth hydrides on hydrogen storage alloys has not been fully clarified.By using a combination of theoretical calculations and experimental,the hydrogen storage properties of Mg-Y-Zn alloy are systematically investigated.The details are as follows:Firstly,the as-cast Mg98.5Y1Zn0.5 alloy was prepared by semi-continuous casting,and then the homogenized alloy was obtained by heat treatment.Then,the hot compression experiments were carried out on the homogenized alloy at deformation temperatures ranging from 380? to 500? and strain rates ranging from 0.001 s-1 to 1 s-1.The results show that the as-cast,homogenizated and ECAP states Mg98.5Y1Zn0.5 alloy is mainly composed of Mg and LPSO phases.The deformation activation energy Q value is 260 kJ/mol.In addition,the optimum deformation condition of the homogenized alloy was determined,which is 443?-500? and 0.001 s-1-0.003 s-1.Secondly,the hydrogen storage performance of as-cast,homogenized and ECAP processed Mg98.5Y1Zn0.5 alloy was tested.The results show that the hydrogen storage capacity of the alloy is 7.0wt%.The LPSO phases in the alloy decomposed into dispersed YHx by in-situ formed by hydrogenation,which can significantly promote the hydrogen storage performance of Mg alloy.In comparison,the Mg98.5Y1Zn0.5 alloy processed by ECAP has the best hydrogen storage performance.At 320?,the reversible hydrogen ab/desorption capacity is 6.5wt%,and it can be fully activated in two times.The kinetics of as-cast alloy is similar to that of ECAP processed sample,but the hydrogen storage capacity is lower.The hydrogen ab/desorption rate and capacity of homogenizated alloy were lower than those of as-cast and ECAP samples.Finally,the as-cast Mg98.5Y1Zn0.5 alloy chips with different morphologies were prepared by using three kinds of files with arc,triangle and flat cross sections,and the hydrogen storage peroperties of these chips were investiged.The results show that the chips with the best hydrogen abdorption rate and hydrogen storage capacity are obtained by the flat file.The hydrogen absorption capacity is close to 7.0wt%at 320?.The chips prepared by arc file were the second best,the chips prepared by triangular file have the worst hydrogen storage performance.This may be due to a combination of size,sawtooth density and dislocation density.The first-principles calculations show that the YH2 not only weakens the bond strength of H-H and Mg-H bonds,but also reduces the dissociation energy of H2 on the Mg surface and the activation energy of H atoms from MgH2 surface,which revealed the catalytic mechanisms of YH2 for hydrogen storage proformance of Mg98.5Y1Zn0.5 alloy.