Theoretical Study On The Dehydrogenation Properties Of Magnesium Hydride And The Reduction Mechanism Of Fluorinated Graphene

The electronic structure and dehydrogenation properties of Na Mg H 3 from metal(Li/K)substitution for parts of Na have been investigated using the density functional theory.It can be seen that the formation enthalpies of the M doped system are negative,which indicates they can exist stably in the thermodynamics.Further calculations of reaction enthalpies along with four possible dehydrogenation reaction pathways gain the most realistic ones.Comparing the result of reaction enthalpies finds that the Na Mg H3 doped by Li decreases the value of reaction enthalpy and improves thermodynamic properties,but the K substitution has little impact on ones.With the increasing of Li doping contents,the absolute value of the reaction enthalpies decrease slowly which indicate the structure present more excellent thermodynamic properties.The phonon spectrum of Li substitution system is computed that indicates the contents is less than 50.00%.The surface structure and desorption property of Mg H2(110)doped by C and Si atom are sdudied respectively.With the increasing of layer,the change of energy indicate that nine layers is of the bes t surface structure.The occupation energy of two doped position is calculated in the Mg H 2(110)surface finds Si is prior to occupy the interstitial site and C is easy to occupy the Mg site.The hydrogen desorption energy for Si occupying the interstitial site and C occupying the Mg site is computed in the outermost 3 layer of Mg H2(110)surface systems.When Si occupies the interstitial site and C occupies the Mg site,the hydrogen desorption energy is lower than pure systems,which indicate it is in favour of the hydrogen desorption.Further analysis of the result finds that Si doped interstitial site has the lower hydrogen desorption energy indicates Si doped system has a better hydrogen desorption performance than C doped.The reaction process of hydrazine(N2H4)and fluorinated graphene have been investigated using the density functional theory.N2H4 insert into the layer of graphite fluoride which increase the distance between the layers and weaken the interaction between the layers,so it is easy that the graphite fluoride translate into fluorinated graphene structure.Two kinds of reactions of N2H4 and fluorinated graphene are considered.One is four hydrogen atoms of the N2H4 react in turn with fluorinated graphene and the results show that the energy barrier value of reduction reaction is lower than the replacement reaction.The reaction path with the lowest reaction energy barrier is given: N2H4(reduction)→ N2H3(reduction)→N2H2(reduction)→ N2H(reduction)→ N2.Finally,the N2H4 is dissociated into N2.The F atoms on the surface of fluorinated graphene is reduced out which make fluorinated graphene convert into graphene structure.The other is two-NH2 group of the N2H4 react simultaneously with fluorinated graphene.Finally,the N2H4 is dissociated into N2 and then fluorinated graphene surface is hydrogenated,but the process requires a larger initial reaction energy and which indicate that the reaction is not easy to happen.Therefore,N2H4 react with fluorinated graphene,which can change into graphene structure.