Study On The Electronic Structure Of CoB,FeB And NiB Catalysts

Nanoparticle catalysts have different electronic and catalytic properties than bulk,which have attracted wide attention.CoB,FeB and NiB nanomaterials have good catalytic properties and have important applications in hydrogen storage of proton exchange membrane fuel cells.In this paper,the morphology,structure and properties of CoB,FeB,NiB nanocatalysts and CoBx@h-BN core-shell nanocatalysts were studied by using transmission electron microscopy and first-principles calculations.The electronic energy loss spectrum is correlated with the theoretically calculated density of the split-wave projection state to study the electronic structure of the material.The following conclusions were obtained:1.The prepared CoBx and CoBx@h-BN nanomaterials were characterized by high resolution transmission electron microscopy.The results show that:CoBx nanoparticles consist of irregular small particles with a diameter of about 100 nm.CoBx nanoparticles are disordered in three-dimensional space,and there are no defects such as grain boundaries,dislocations and segregation in the usual crystalline alloys,which are typical amorphous structures.The CoBx@h-BN nanocatalyst is encapsulated by an h-BN coating and is a nanoparticle having a core-shell structure.2.The CoBx samples at different ammoniation temperatures were tested by electron energy loss spectroscopy(EELS).The results showed that:Due to the different bonding environments,the fine structure of the B-K energy loss peak is different.There was no N element in the CoBx sample,and the CoBx@h-BN sample was coated with the h-BN nanocoating.The electron energy loss spectrum characteristics near the outer layer are consistent with the h-BN results,while the electron energy loss spectrum characteristics close to the inner layer are consistent with the CoBx nanoparticle results.A part of the B element in the CoBx@h-BN sample segregates to form an h-BN shell layer,and a part of B forms a bond with Co to form a Co-B compound.3.The microstructure and morphology of FeB nanocatalyst materials were studied by transmission electron microscopy.The samples were uniformly interconnected nanoparticles with a size of 50-100 nm,which were highly crystalline tetragonal single crystal phases.In the low energy loss spectrum,the～7.7 eV energy loss peak corresponds to the transition from B’s 2p orbit to Fe-3d or Fe-3p orbit,and the～12.6 eV energy loss peak corresponds to B’s 2p orbital to Fe’s 3d orbital transition,～19.8 The peak of eV broadening is a plasma peak,and the energy loss peak of～27.7 eV corresponds to the transition of the 2s orbital of B to the 3d orbit of Fe;The effect of Core-hole on the electron energy loss spectrum of Fe in FeB nanocatalyst was investigated.The results show that the simulation results under the effect of Core-hole are consistent with the experimental results.4.The microstructure of NiB nanocatalysts was studied by transmission electron microscopy(TEM).The irregular nano-particles with spherical or chain morphology were typical amorphous alloys.The electronic structure of the NiB nanocatalyst material was discussed.There is a strong interaction between the Ni atom p,d orbital and the B atom p orbital.The electron energy loss spectra of three kinds of nano-catalyst materials,CoB,FeB and NiB,were compared.It is known that the bonding environment is different and the fine structure of B-K energy loss peak is different.This study is the catalytic mechanism of CoB,FeB and NiB nanocatalyst materials.The research provides a theoretical basis.