Study On Synthesis And Properties Of The M-Al-B Ternary Compounds

In this paper,the density functional theory（DFT）calculations were carried out to study the crystal structure,stability,magnetic configuration,electronic structure,electrocatalytic activity,and elastic properties of a class of transition-metal borides.In addition,the bulk MoAlB samples with high purity were fabricated with the spark plasma sintering（SPS）technology.We also discussed the effect of chemical etching on the structure and activity for hydrogen evolution reaction（HER）of MoAlB powder.（1）We carried out the first-principle calculations on the structure,thermal stability,magnetic configuration,electronic structure,and electrocatalytic activity for hydrogen evolution reaction（HER）of a class of two-dimensional（2D）transition metal borides（MBenes,where M is Mn,Fe,Cr and Mo;B is boron）.The structural and thermal stability of the MBenes was estimated with the cohesive energy,the phonon dispersion curves as well as the ab initio molecular dynamics（AIMD）simulation calculations.The effects of functionalized groups on the structure of MBenes were also discussed.The magnetic configuration at ground state of both MBenes and their precursors was clarified and explored with a sample model.All stable MBenes exhibit metallic transport behaviors.The valence electrons are generally localized around B-B chains in the unit cell of MBenes,which results in the good stability of MBenes.The free energy of hydrogen adsorption of Mn₂B₂ at the coverage of 1/8 is 0.002 e V,implying that this 2D boride is a promising candidate for HER application.（2）The structure,thermal stability,elastic,and electronic properties of a class of ternary early-transition-metal borides with the general formula of h-M₂AB₂（M=3d,4d and 5d transition metal;A=Al,Ga,In;and h represents a hexagonal structure）are investigated with the first-principles calculations.The structural and thermal stability of the h-M₂AB₂ were estimated with the cohesive energy,formation energy and phonon dispersion curves.The lattice constants of h-M₂AB₂ borides are highly dependent on the chemical composition.The B-B bond lengths in the unit cell range widely from 1.68（?）for Mn₂Al B₂ to 1.94（?）for Y₂In B₂.All the stable borides are nonmagnetic or ferromagnetic,and exhibit metallic transport performance.The valence electrons are generally localized around the B-B rings,which contributed to the good stability and high bulk modulus of h-M₂AB₂.Finally,the correlations of the mechanical property of h-M₂AB₂ compounds with their chemical composition and electronic structure were also discussed.（3）The bulk MoAlB samples were successfully synthesized with SPS technology.The pure MoAlB bulk was synthesized at 1 250℃for 1 h under the pressure of 30 MPa.We also studied the etching behaviors of MoAlB powders in different aqueous solutions.The MoAlB powders can be effectively etched by Na OH aqueous solution.The as-etched MoAlB powders exhibit significantly improved HER activity and stability for HER...