| Hydrogen as a kind of“green energy”can replace petrochemical resources.It is regarded one of the most hope for the future of new energy.The safe,efficient and economical hydrogen storage technology provides an ideal solution to solve the global problems such as energy.Considerable attention has been paid on LiBH4?18.5wt%?,which has the highest hydrogen storage capacity among the light metal complex hydrides.However,high dehydrogenated temperature and poor kinetics for re-/dehydrogenation prevent it from practical applications.In this paper,to further improve the hydrogen storage properties of Li BH4,stabilization by adding reactants and ions replace were systematically investigated.The valence of H in[BH4]-1 is-1,while that of H in[NH2]-1 is+1,and they are inclined to interact with each other to reduce the stability of the system.LiNH2,which contains[NH2]-1were added to LiBH4 and then by ball-milling method to prepare Li-N-B-H complex hydrogen storage system.In addition,this study also explores the function of Pauling electronegativity of the central metal ion in improving thermodynamics and kinetics of LiBH4.The effects of MCl2?M=Ca?Mg?added on the hydrogen storage behaviors and mechanisms of LiBH4 were elucidated.The performance of the composite is studied by means of XRD,FT-IR,TG-DTA-MS analysis and activation energy calculation?Achar differential method and Coats-Redfern integral method?.We discuss the thermodynamics and kinetics of the as-prepared complex hydrogen storage material by evaluating indicators of thermal decomposition temperature,hydrogen desorption capacity and activation energy.Research on 2LiNH2/LiBH4 composite indicated that liquid-phase ball milling is better than solid-phase ball milling in preparation Li-N-B-H composite.By comparing the TG diagrams of the two composites,we knew the total weight losses of both all greater the composite theoretical hydrogen storage capacity,but the value of gathered gas after liquid-phase ball milling was lower than that of solid-phase ball milling.It explained the composite after liquid-phase ball milling generating impurity gas in its thermal decomposition process was less than the composite after solid-phase ball milling.The gaseous products of the thermal decomposition were further decided by TG-DTA-MS,H2 is the main product and NH3 is the only byproduct.Hydrogen release took place from 220?to 340?.The mechanism of decomposition reaction of composite after liquid-phase ball milling was three-dimensional diffusion,activation energy was 132.6 KJ·mol-1,mechanism function was f???=3/2?1-??2/3[1-?1-??1/3]-1?Li-M-B-H?M=Ca,Mg?complex hydrogen storage material was also synthesized by machnically milling the mixture of Li BH4 and MCl2?M=Ca,Mg?at various ratio.The XRD,TG-DTA diagrams and calculation of activation energy results show that,main interval of hydrogen release of Li-Ca-B-H complex hydrogen storage material is380?to 450?,the total weight loss is 7.86wt%,activation energy was 95.1KJ·mol-1,and the mechanism of decomposition reaction of the composite was assumed random nucleation and its subsequent growth,machanism function was f???=[-ln?1-??]1/3;The main dehydrogenation rage of Li-Mg-B-H complex hydrogen storage material is 80?to 360?,accompanying by a total weight loss of 9.61wt%,activation energy was 44.3 KJ·mol-1,and the dehydrogenation process mechanism was three-dimensional diffusion,mechanism for function expression f???=3/2?1-??2/3[1-?1-??1/3]-1.The electronegativity of Mg?1.31?is greater than that of Ca?1.00?,while the central metal ion with higher electronegativity can play a role in weakening ionic bond in metal borohydride,so the thermal decomposition temperature and the values of activation energy of Li-Mg-B-H complex hydrogen material is lower than that of Li-Ca-B-H complex hydrogen material... |
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