Effect Of Element Substitution On Structure And Hydrogen Storage Properties Of AB₅ Rare Earth Hydrogen Storage Alloys

AB₅ type hydrogen storage alloys are important materials used for hydrogen storage and transportation.The influence of different elements on the hydrogen storage performance of the alloys need to be further clarified.In this paper,La Ni₅-based hydrogen storage alloy is taken as the research object,and multiple alloys are taken as the technical route.The series of(La Ce Ca)₁(Ni Mn Al)₅ and La_0.4Ce_0.4-xY_xCa_0.2Ni_4.9Mn_0.1(x=0-0.4)alloys are studied for the crystal structure and hydrogen storage properties.This research is expected to provide scientific basis and technical support for the development of diversified AB₅ hydrogen storage alloys.The series of(La Ce Ca)₁(Ni Mn Al)₅ alloys are designed by uniform design method in the interval[0-0.45]with the substitution of Ce,Ca,Mn and Al as variables,and then substituted Al for Mn in Al-free alloys in the design components.X-ray diffraction(XRD)analysis results show that all the alloys are single La Ni₅phase,Ca Cu₅ type crystal structure.The cell volume and hydride generation enthalpy|-?H_abs|are decrease with the increase of Ce content,with the increase of the content of Ca,Mn,Al.Hydrogen absorption rate quicken with the increase of Ca,Mn and Al content,and the effect of Mn is more obvious.The hydrogen absorption/desorption platform pressure of the alloys elevate with the increase of Ce content and reduce of the content of Ca,Mn,Al.Al can obviously reduce hysteresis,hydrogen storage capacity and resistance to pulverization.La_0.4Ce_0.4Ca_0.2Ni_4.9Mn_0.1,which is selected because of its best comprehensive hydrogen storage performance,has the minimum unit cell volume,minimum hydride generation enthalpy and the smallest hysteresis.It has the best effective hydrogen storage capacity,highest platform pressure of absorption/desorption.During the hydrogen absorption/desorption cycles,the hydrogen capacity of La_0.4Ce_0.4Ca_0.2Ni_4.9Mn_0.1decreased in the first 5 cycles significantly,the hydrogen absorption platform pressure,slope and hysteresis increased slightly in the first 10 cycles,after 30 cycles,the capacity retention rate was still above 97%.The series of La_0.4Ce_0.4-xY_xCa_0.2Ni_4.9Mn_0.1(x=0-0.4)alloys are use La_0.4Ce_0.4Ca_0.2Ni_4.9Mn_0.1 as the foundation,obtained by Y instead of Ce.XRD analysis shows that all the alloys are single La Ni₅phase,Ca Cu₅ type crystal structure.With the increase of substitute Y content,cell parameters c value and cell volume V all decreased slightly,the hydrogen storage capacity and hysteresis of the alloys decrease,and the platform pressure and platform slope increase.