Strain Engineering On The Hydrogen Evolution Reaction Activity Of Black Phosphorene:First-principles Study

Two-dimensional（2D）materials have become substitutes for platinum group noble metal catalysts due to their large specific surface area,unique physical and chemical properties and abundant adjustable active sites.Compared with others,black phosphorene（BP）is a kind of semiconductor with tunable direct bandgap,high mobility and anisotropy for electron transport,which has attracted extensive attention of scholars.However,its large-scale applications are limited by the poor activity of 2D BP surface for hydrogen evolution reaction（HER）.Strain engineering as a way without any introduction of exotic atoms,is more simple than other methods.Based on the first-principles method,the coupling effect caused by homogeneous strain and local strain induced by defect on HER activity and electronic properties of BP is studied in this paper.The main contents are as follows:1.The electronic properties of black phosphorus system and the strain effect of catalytic hydrogen evolution are investigated by applying uniaxial compression and tensile strain.The strain effect can adjust the Gibbs free energy(ΔG_H*)of BP.When the-10%compression strain is applied,theΔG_H*of the system decreases to 0.84 e V from the initial 1.23 e V,improving the catalytic activity of hydrogen adsorption.With the increase of the compression strain,the conduction band minimum of BP system decreases and the local charge density on the surface is larger than that of the original monolayer BP.The strains adjust the band gap value with the movement valence band and the conduction band in the BP system which enhances the interaction between hydrogen atom and catalyst.When the compression strain increases from 0 to-10%,the energy gap of the system decreases from the initial 0.90 e V to 0.23 e V,and the original direct band gap characteristics are maintained.Applying strain on BP can not only regulate its electronic structure,but also further improve the hydrogen evolution performance of BP for electrocatalysis.These results indicate that strain can regulate the electrocatalytic hydrogen evolution performance of 2D BP monolayer.2.Due to the strain itself does not provide more active sites,the HER performance of the system is still far from the ideal value(ΔG_H*≈0 e V).The effects of the vacancy defect on the HER for BP are investigated.Compared with the original monolayer BP,theΔG_H*of BP with defect is closer to the ideal value and negative,indicating that the vacancy brings better hydrogen evolution performance to the BP system.Through the study of its electronic properties,it is found that the BP with defect transfers from the initial semiconductor to the metal.The band structure shows that the number of electronic states near the Fermi level increases,and the local charge density near the defect site of BP increases,which improves the adsorption capacity of BP to hydrogen atom and thus improves the catalytic hydrogen evolution ability.In addition,the performance of electrocatalytic hydrogen evolution of BP with vacancy defect under homogeneous strain is also studied.It is found that the HER of the system was greatly improved,and itsΔG_H*can reach the relatively close value as noble metals catalyst.The results of this study can provide some theoretical supports for improving the HER performance of 2D materials in electro-catalysis.