First-principles Study On The Regulation Of Catalytic Activity Of Hydrogen Evolution In Two-dimensional Transition Metal Materials

Hydrogen is an ideal energy with the advantages of wide distribution,high combustion calorific value,high energy density,renewable,and pollution-free.Development a stable and efficient catalyst is the key to improving the hydrogen production.Two-dimensional?2D?MoS₂-based catalyst has been extensively studied,but its inherent low catalytic activity,poor structural stability,few catalytic active sites,low H⁺coverage that hinder the MoS₂ catalysts to practical application.In this dissertation,density functional theory?DFT?was used to systematically and deeply study the above constraints in the hydrogen evolution reaction?HER?process of two-dimensional MoS₂ catalyst from the atomic level.1.Studied the mechanical strain to enhance the inherent catalytic activity of1T'-MoS₂ for the HER.The results show that H has a stronger adsorption at the St site when H adsorbed on the surface of unstrained 1T'-MoS₂.The Gibbs free energy of the H adsorbed at the St site is reduced-0.04?0.12?eV,when strain of 9.55%?9.89%?is applied along the zigzag?armchair?direction.It finds that strains can change the bond lengths of Mo-S and Mo-Mo,and increasing the density of states near the Fermi energy will enhance the catalytic activity of the material.2.Investigated the effects of transition metal doping in 2H-MoS₂ on structural stability,electronic conductivity,and HER catalytic activity.The results show that the phase transition from 2H to 1T'is induced when Re doping concentration is larger than0.4.When H adsorbed on the surface of Mo_1-xRe_xS₂ alloy,the Gibbs free energy will decrease with the increases of Re doping.The Gibbs free energy is between 0.08-0.13eV,when the Re doping concentration range in 0.75-0.94.Transition metals with different valence electrons?Sc,Ti,V,Cr,Mn,Fe,Co,Ni and Cu?are doping MoS₂.It finds that dopants?Sc,Ti and V?with valence electrons less than Moatoms possess smaller formation energy,impurity atoms tend to togather to replace Moatoms rather than dispersed replacement.The dopant types and concentrations significantly affect the adsorption performance of H on the doping system.The results show that dopants?Sc,Ti and V?have closed to Gibbs free energy with 0 eV.It shows that this doping type is more suitable as HER catalyst.3.Investigated the catalytic activity of 2H-MoS₂ with high coverage H using non-metal atom decorate.This research shows that the O doping can significantly reduce the defect formation energy,e.g.,the atomic defect formation energies of S and Mohave a less than 0 eV when the O doping concentrations reached at 0.04.When H adsorbed on doped system with S vacancy,the Gibbs free energy is reduced to-0.01 eV;Gibbs free energies are also near the 0 eV when H adsorbed on doped system with Movacancy.In MoS_2?1-x?P_x alloy system,the electronic structure transformed from semiconductor to conductor when the P concentrations are greater than 0.25.Calculation results show that Gibbs free energy decreases from 2.13 eV to 0.03 eV,when the H adsorbed on MoS_0.5P_0.75 alloy.In additional,it remains a relatively suitable Gibbs free energy with the H coverage increasing from 1/12 to 7/12.It shows that P doping not only greatly improve the catalytic activity of MoS₂ surface,but also further improve the electronic conductivity.4.The mechanical and electronic properties of asymmetric MXY?M=Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W;X/Y=S,Se and Te?have been studied.Results show that breaking the out-of-plane symmetry can tune the electronic and mechanical behavior of monolayer transition metal dichalcogenides.Monolayer MXY?M=Mo,Ti,Zr,Hf and W?possess brittle characteristics,whereas both Cr XY and VXY have ductile characteristics.The in-plane stiffness of pristine and Janus monolayer MXY are in the range between 22 and 158 N/m.The catalytic performance of edge sites of Janus monolayer MoXY?X/Y=S,Se and Te?were investigated.The results show both Mo-edge and X/Y edge of Janus monolayer MoXY are catalytic active for HER,thus Janus monolayer MoXY exhibits the better catalytic performance than monolayer MoS₂.Janus monolayer MoSSe has predicted to be promising catalyst candidates for HER due to its inherent structural asymmetry.Calculations indicate that the formation energies of point defects and grain boundaries on MoSSe are lower than pristine MoS₂monolayer.MoSSe monolayer with 4|4,4|8a,5|7b,8|10a GBs,vacancies(V_S,V_Se,V_SSe,V_Mo,V_MoS3)and anti-site defects(Mo_SSe,Se _Mo,S_Mo)shows enhanced HER performance.