The Synthesis And Hydrogen Release Properties Of Ammonia Borane-Metal Organic Framework Composite Materials

In recent years,with the growing concern about utilization of clean and environment friendly energy is due to the fact that fossil fuel cannot satisfy people's needs and carbon dioxide emissions must be cut down.Scientists have become increasingly interested in a hydrogen-based energy and considerable efforts have been put into it.Ammonia borane,is considered to be a promising candidate material for solid-state hydrogen source because of its extremely high hydrogen content?19.6 wt %?and favorable stability at room temperature.However there are some disadvantages for practical applications of AB attributed to its slow H2 releasing rate below 100?,irreversible H₂ loss and formation of volatile impurities [ammonia?NH₃?,diborane?B₂H₆?and borazine?B₃H₆N₃?].Actually,Metal-organic frameworks?MOFs?as proper materials combined with AB were applied into solid-state hydrogen storage to promote AB dehydrogenation property due to theirs high thermal stability,moderate pores size,and catalytic metal cites.In this thesis,the theory investigation work of AB@MOFs system was continued based on the previous research.The main research contents are as following:Firstly,AB particles were loaded into MOF-5 which do not possess unsaturated metal sites through infusion method.The dehydrogenation properties of this composite material were investigated.The results showed that MOF-5 could improve AB dehydrogenation properties in a degree.However,the unexpected byproduct NH₃ could not be inhabited.Compared to the AB@JUC-32-Y system,we discussed the unsaturated metal sites were played a key role in avoiding NH₃ gas.Secondly,three composite materials which contain the same metal center AB@Tm?BTC?-CH₃ OH,AB@Tm?BTC?-milled and AB@Tm₂O₃-milled were synthesized.Their thermal dehydrogenation properties were investigated and compared.The infused AB@Tm?BTC?-CH₃ OH sample showed the best ability to improve the thermal H₂ losing behavior including reducing dehydrogenation temperature,enhancing dehydrogenation kinetics and preventing unwished volatile byproducts.The mechanisms of AB@MOFs thermal dehydrogenation system have been deeply discussed.Furthermore,the interaction between AB between the unsaturated coordinated metal sites of MOFs is deemed to a key role for inhibiting ammonia during AB thermolysis.Thirdly,a series of rare earth AB@Re-MOF?Re = Sm,Eu,Tb,Er,Yb,Lu?composite materials were synthesized.Their thermal dehydrogenation properties were discussed detailedly.All these MOFs have the same skeletal structure but different metal center.The aim of this study was to explore the difference of themal decomposition properties of this series composite material and what effect the different metal centers in MOFs had on improving AB themal decomposition properties.