Theoretical Study On The Effect Of Edge Modification On Catalytic Hydrogen Evolution Of Monolayer Mos₂

The MoS₂ is a promising hydrogen evolution reaction?HER?catalyst due to its high chemical stability,excellent catalytic activity,low cost as well as abundant production.However,the HER catalytic efficiency of MoS₂ strongly depends on the activity of reaction sites including the basal plane and the edges,and there are still large space for the improvement because only the Mo edge sites are active but S boundary and surface are inert.Generally,it is very crucial for the edge effect on the HER catalytic activity.In this thesis,the first-principles calculation based on density functional theory is used to systematically study the influence of edge modification on the HER activity of monolayer 2H MoS₂.The main contents are as follows:?1?We calculated the formation energies of the substituted Mo edge structures of MoS₂nanoribbons by transition metal atoms?V,Cr,Co,W?with different edge concentrations.Based on the criterion of less than formation energy of MoS₂?E_f=1.24 eV?,it is found that the Mo edge structures with substituting V atoms below 100%concentrations(nV_Mo,n=1,2,3,4),Cr atoms below 50%concentrations(nCr _Mo,n=1,2)and Co below 25%concentrations(nCo_Mo,n=1)are thermodynamically stable under certain chemical potential conditions.Through the analysis of?G values,charge density differences and charge transfer,it is found that the substituted Mo edge strucutres of 2V_Mo,3V_Mo,4V_Mo and 2Cr_Mo can show high HER catalytic activity??G=-0.036⁰.069 eV?at 100%,75%,25%and 75%hydrogen coverage,respectively.For the S edge substituted by the transition metal atoms,the edge structures of S-2Cr_Mo and S-1Co_Mo can also show high HER catalytic activity??G=-0.084^-0.051 eV?at 75%and 100%hydrogen coverage,respectively.This shows that transition metal atoms substitution can indeed further increase the activity of Mo edge and activate the activity of S edge.?2?Based on the transition metal atoms substitution,we further studied the effect of S and Se atoms modification on the HER catalytic activity of MoS₂ nanoribbons.The results show that:for the S modification,the structures of Mo-S,4V_Mo-S,1Cr_Mo-S and 1Co_Mo-S exhibit high HER catalytic activity??G=-0.055⁰.101 eV?at 25%,100%,100%,75%hydrogen coverage;for the Se modification structures,the structures of 1V_Mo-Se?4V_Mo-Se?1Cr_Mo-Se and 2Cr_Mo-Se also exhibit high HER catalytic activity??G=-0.079⁰.083 eV?at 25%,100%,25%and 75%hydrogen coverage,respectively.This shows that S and Se modification can also improve the HER catalytic activity of Mo edge,and the Se modification structures have high activity at relatively low hydrogen coverage.?3?We finally also investigated the properties and?G values of the substituted S edge structures of MoS₂ nanoribbon by nonmetallic atoms?O,P,Se?.The results show that the total energy of substituted S edge structures?S-nSe_S,n=1,2,3,4?increases with the number of substituting Se atoms,while those substituted by O and P atoms decrease with the number of substituting O and P.And the smaller radius of the substitution atom is,the larger the energy decreases.O substitution can enhance the hydrogen adsorption strength and decrease the HER catalytic activity;P and Se substitution can weaken the hydrogen adsorption and increase the HER catalytic activity.This shows that the HER catalytic activity of S edge can be activated by the substitution of P and Se atoms,and particularly,the P substituted structures have high HER catalytic activity at low hydrogen coverage.This theoretic study can further deepen our insights into the MoS₂ edge modification both in the structural stability and the HER catalytic activity at the atomic level and provide us theoretic guidelines for the design of novel HER catalyst for application.