Synthesis Of Ni,Fe,Zn MOFs Modified Materials And Their Effects On Hydrogen Storage Performance Of MgH₂

MgH₂ is considered as one of the most promising hydrogen storage materials because of its high theoretical hydrogen storage capacity(7.6 wt.%and 110 g/L).However,its development is hindered due to the high operating temperature and the slow kinetic speed.Doping additives can improve the hydrogen storage performance of magnesium based hydrogen storage materials.In this paper,three kinds of modified MOFs(Ni-MOF/Fe/Ni-MOF,Ni/Fe₃O₄@MIL and Ni/C/Zn O)were synthesized by wet chemical method,and the MgH₂-Ni-MOF/Fe/Ni-MOF,MgH₂-Ni/Fe₃O₄@MIL and MgH₂-Ni/C/Zn O composites were prepared by hydrogenation combustion and high-energy ball milling with magnesium powder,respectively.The hydrogen storage properties and mechanisms of the three composites were further studied.The study found that the MgH₂-Ni-MOF/Fe/Ni-MOF,MgH₂-Ni/Fe₃O₄@MIL and MgH₂-Ni/C/Zn O composite begin to release hydrogen at 500 K,517 K and 552 K,respectively.It is 151 K,96 K and 61 K lower than the initial hydrogen release temperature of pure MgH₂.The three composites all show excellent hydrogen absorption performance,among which,the hydrogen absorption capacity of MgH₂-Ni/Fe₃O₄@MIL can reach 4.2 wt.%at 373 K.Moreover,compared with pure MgH₂,the dehydrogenation activation energy of the three composites decreased to a certain extent,by 81.7 k J/mol,61.8 k J/mol and 81.0 k J/mol,respectively.Through structural characterization and mechanism analysis,it can be seen that Ni-MOF/Fe/Ni-MOF can produce Mg₂Ni H₄/Mg₂Ni and Fe H₆Mg₂/Fe conversion in the hydrogenation and dehydrogenation process of MgH₂,and synergistic catalytic improvement of hydrogen storage performance of MgH₂.In the MgH₂-Ni/Fe₃O₄@MIL composite,Mg₂Ni H₄ generated in situ can induce the hydrogen absorption and desorption of MgH₂,and the Fe phase generated in situ stably exists in the whole process of hydrogenation and dehydrogenation,which can increase more channels for the diffusion of hydrogen atoms.Besides,the unique core-shell structure plays a good dispersing role.For MgH₂-Ni/C/Zn O composites,Ni/C/Zn O can react with MgH₂ to form Mg Ni Zn alloy,and synergy with Mg₂Ni H₄ to catalyze the hydrogen absorption and desorption performance of magnesium based materials.In addition,the dispersion of carbon material effectively impedes the agglomeration of composites.