Exploratory Reaearch On The Surface Structure And Performance Of Active Electrode Materials

First-principles calculation which based on the density functional theory is one of the important methods on materials science research.A serious of restrictions on the experiment can be overcomed by this way and essential properties of materials are discussed.The structures and properties of rutile RuO2,FCC Ni3Fe and Co-doped Ni3Fe have been researched and discussed in this study.The structure parameters,ground energies and formation energies of rutile RuO2,FCC Ni3Fe and(Cox,Fe1-x)Ni3 solid solutions were investigated by optimizting the crystal structures using plane-wave pseudopotential method within density functional theory(DFT).The electronic structure was also studied.Using the slab models,the low-index surface characteristic of rutile RuO2,FCC Ni3Fe and(Cox,Fe1-x)Ni3 systems were researched.The structural relaxation,surface energies and electronic structure were investigated.The thermodynamic stability of the various types of surfaces as functions of chemical potential variations for atoms was obtained,meanwhlie the inner reason caused the differences between the various surfaces performance were analyzed.The adsorption characteristics of C atoms on the surfaces of Ni3Fe and(Co0.5,Fe0.5)Ni3 system were studied in this work at the same time to explain the different performance of coke resistance theoretically.The ordered FM-Ni3Fe phase was also prepared using thermal decomposition method in order to acquire the lattice parameters of the experimental value.The results indicated that:1.As compared with the JCPDS cards and other researchs,the relative error is small for calculated lattice constants and electronic structure of rutile RuO2 and FCC Ni3Fe.2.For(110)and(100)surface of rutile RuO2 system,the relaxation mainly occur on the outmost three to five atomic layers,and generally the extent of relaxation follows in the sequence as(100)>(110).Surface energies are influenced by the chemical potential of oxygen,except for(110)-Ob and(100)-O1 termations of which are stoichiometric.In the O-rich limit,(110)-OCUS is the most energetically favorable plane while in the o-poor limit(110)-Ob exhibits the best stability as own importance of morphology.Investigation of the density of state shows that it is mainly contributed by 4d electronic orbit of Ru.3.For series surfaces of FCC Ni3Fe system,the relaxation mainly occur on the outmost two atomic layers,and generally the extent of relaxation follows in the sequence as(110)>(100)>(111).Surface energies are influenced by the chemical potential of nickel,except for(111)plane of which is stoichiometric.Ni3Fe(111)is the most energetically favorable plane,which owns importance of morphology.Investigation of the density of state for(111)plane shows that it is mainly contributed by 3d electronic orbit of Ni When doped with Co,the relaxation of surface structure was weakened which lead to a lower surface energy and better structural stability.4.The adsorption characteristics of C atoms on the surfaces of Ni3Fe and(Co0.5,Fe0.5)Ni3 shows us the best adsorption site.It indicates that it's easier for C atoms adsorbing on the surfaces of Ni3Fe(111)than(Co0.5,Fe0.5)Ni3(111)by comparing the caculated adsorption energy.This conclusion explained the reason why Co-doped Ni3Fe exhibits a better coke resistance performance intuitively.