Study On Microstructure And Electrochemical Properties Of La-Fe-B Based Hydrogen Storage Alloys

In this paper,the microscopic structure and electrochemical properties of La₁₅Fe₂Ni₇₂Mn₇B₂Al₂ type hydrogen storage alloys are studied.The main contents are as follows:The effect of different contents of graphene addition on the structures and electrochemical properties of La₁₅Fe₂Ni₇₂Mn₇B₂Al₂ hydrogen storage alloys are studied.The effect of ball-milling time on the structure and electrochemical of graphene/La₁₅Fe₂Ni₇₂Mn₇B₂Al₂ composite materials and La₁₅Fe₂Ni₇₂Mn₇B₂Al₂ alloy are also studied.The XRD analysis showed that the crystal structure of alloys did not change with ball-milling treatment and graphene addition.The alloys are composed of LaNi₅,La₃Ni₁₃B₂ and?Fe,Ni?phase.In these alloys,the LaNi₅ and La₃Ni₁₃B₂ are the hydrogen storage phase,LaNi₅ is the main hydrogen storage phase and?Fe,Ni?is the catalyze phase.The SEM analysis demonstrated that the particle decreased with the increase of ball-milling time and the structures of alloys did not be protected with graphene addition.Electrochemical analysis show that the maximal discharge capacity of the La₁₅Fe₂Ni₇₂Mn₇B₂Al₂ alloy increased with the increasing graphene contents in the same billing time.The activation cycles of alloys reduced from two cycles to one cycles with grapheneaddition.Withball-millingtreatment,theratecapabilityof La₁₅Fe₂Ni₇₂Mn₇B₂Al₂+x wt.%graphene?x=0,1,3,5?alloys are improved and electrochemical transfer resistance reduced.However,the charge retention ratio decreased.The maximal discharge capacity and rate capacity increased firstly and then decreased with the increasing of ball-milling time.This result can be explained that the smaller particles result in higher specific surface area and the alloys formed non-crystallizing because of ball-milling.The properties of alloys increased firstly and then decreased with changing ball-milling time and graphene addition.