The Influence Of The Phase Structure And Hydrogen Storage Properties Of Iron Compounds On Mangmesium Hydrides

In order to improve the hydrogen/dehydrogen properties of pure MgH2,theFeS/FeS2/Fe3S4/LaFeO3were respectively added into the pure MgH2throughmechanically ball milling methods, and the effect of the phase structures, kinetics anddehydrogenation thermal desorption on the MgH2were investigated.The MgH2+20wt.%FeS composite was prepared and the hydrogen absorption/desorption behavior was investigated systemically. Through the XRD pattern analysis, theMgS and Fe produced in the ball milling process played an co-catalytic role in improvingthe hydrogen kinetic of MgH2. At423K, the composite could uptake3.84wt.%ofhydrogen in1300s while pure MgH2was only about0.98wt.%. At623K, MgH2+20wt.%FeS composite put hydrogen amount was4.10wt.%, while pure MgH2was about1.23wt.%. The Kissinger equation was then used for MgH2+20wt.%FeS composite of DTAdata fitting, the fitting results showed that the activation energy of the composite was25.89kJ mol-1lower than MgH2.The FeS2was synthesized by a solvothermal method and the hydrogen kinetics ofMgH2+20wt.%FeS2composite was studied. The as-milled MgH2absorbed0.977%hydrogen within21min at423K. However, the FeS2-doped composite could absorb3.65%of hydrogen within21min. The composite could released1.02wt.%which washigher than MgH2at623K. The SEM reveraled that the addition of FeS2help to decreasethe particle size of the MgH2, which benefited the limitness of the cluster and favorablefor the kinetics performance.At423K, the MgH2+20wt%Fe3S4composites could absorb2.8wt%of hydrogenwithin200s while the pure MgH2is only0.3wt%. However, at573K, theMgH2+20wt.%Fe3S4composites could desorb1.2wt.%of hydrogen within800s, and theMgH2is0.12wt.%of hydrogen under the identical condition. The TPD results showedthat the hydrogen desorption temperature of MgH2+20wt.%Fe3S4composites is lower by90K than the pure MgH2Therefore, the hydrogen sorption behaviors and thermodynamicsproperties of MgH2were successfully enhanced by addition of the Fe3S4. The MgH2+20wt.%LaFeO3composite was prepared through the ball milling method.MgH2+20wt.%LaFeO3composite could absorb3.42wt.%of hydrogen within21min at423K while pristine MgH2only uptaked0.98wt.%hydrogen under the same conditions.MgH2+20wt.%LaFeO3also presented excellent dehydrogenation property with3.89wt.%of hydrogen released at623K, which was almost twice more than pure MgH2. Based onthe Kissinger plot analysis, the activation energy Edesfor hydrogen desorption process wasestimated to be36kJ/mol lower than that of MgH2. The XRD and SEM observationsdemonstrated that the highly dispersed LaFeO3in the MgH2, not only beneficial to the reduction of theparticle size but also acted as an inhibitor to keep the particles from clustering during the ball-milledprocess, which was accountable for the improved hydrogenation-dehydrogenation properties ofMgH2+20wt.%LaFeO3system.