Theoretical Studies On Dehydrogenation Of Ammonia Borane

In recent years,world energy consumption is based on petroleum.If the energy structure remains,the greater energy and environmental crisis will inevitably occurs.Humanity is faced with the dual pressure on resources and the environment.From the long-term interests,the development of new energy is an effective way to solve these problems.Hydrogen as an efficient、clean、renewable energy gains great deal of attention.Hydrogen is highly explosive,and difficult to store.So the search for efficient hydrogen storage methods and materials is the greatest challenge for hydrogen use.In numerous of the hydrogen storage materials,ammonia borane(NH3BH3-AB)become a hotspot onboard hydrogen storage materials with a high hydrogen content、high stability and relatively low cost.It can provide a source of hydrogen for fuel cell electric vehicle etc.However,in practical application,the main disadvertages the hydrogen desorption are along with high temperature、slow rate and impurity gas liberation,limited use in a fuel cell.So this paper centered on AB which based on density functional theory(DFT),we separately explored the dehydrogenation mechanism of AB and AB under load,These works will help us to have a profound understanding of the dehydrogenation mechanism,and accelerate the market application of these hydrogen storage materials.The main conclusions are summarized as follows:1、Mechanisms for Alkali metal(Li、Na、K)and alkaline earth metal(Mg、Ca)ammonium borane derivatives(MAB AB).The calculation results show that:a.Indirect dehydrogenation path is superior to direct dehydrogenation path for MAB-AB,Dehydrogenation is easier than deamination for LiAB-AB and NaAB·AB;Exactly the opposite for KAB-AB;b.Indirect dehydrogenation path is most benefit for MgAB-AB,and the deamination occurs hardest,CaAB·AB is More likely to occur deamination,Direct dehydrogenation is superior to indirect deamination;c.When compared to the excellent indirect dehydrogenation of MAB(Li、Na、K、Mg、Ca),Indirect dehydrogenation is the best path for MAB-AB.The results can be fit well with the experimental phenomena.2、Mechanisms for Ammonia-Borane Dehydrogenation on mesoporous graphitic carbon nitride(M-C3N4---MGCN).The calculation results show that:a.the H(B)of AB transfering path is better than the H(the N)transfering path to form Chain polymerization or form DADB dehydrogenation with the cluster model.b.However,this phenomenon was not observed in the experiment.But the surface is easy to reconstruct in the calculation,so we take periodic model to further verify the reliability of this mechanism,The DADB forming process after H(B)/H(N)transfering is actually a competitive process,It illustrated the experimentally unobserved H(B)transfering dehydrogenation may also occur.3、Mechanisms for Ammonia-Borane Dehydrogenation on graphene oxide(GO).The calculation results show that:a.the calculation results of the cluster model and the periodic model are consistent;b.In this reactions mainly controlled by kinetics,the rate-determining step to generate four-membered ring dehydrogenation reaction is more favorable to generate borazine,This are agreeing with the experimental results.