Study On Electronic Structure And Photocatalysis HER Performance Of Defective Monolayer WS₂

Monolayer transition Metal Dichalcogenides is one kind of two dimentional surface materials,and it is widely used in many fields,such as photoelectrocatalysis hydrogen evolution.The band edge potential is one of measure indexes for hydrogen evolution ability,in this article,electronic structure and band edge potentials of three different doped monolayer WS2 are investigated by Materials Studio 7.0,the results are showed below:When doped with O,the band gap value of WS2 decreases.Also,when the O-doped concentration is more,the band gap values decrease more dramatically.As a result,O 2p orbit is introduced to conduction band part,which results in lower conduction band position.So the doped oxygen is good for electronic movement from valence band to the conduction band,which improves the separation efficiency of photoproduction electronic and photoproduction hole.When WS2 is doped with O,the formation energy of the system is negative in the high or low sulfur environment,so the doped oxygen improves the stability of the system.After WS2 is doped with O,CBM potential(i.e.,reduction potential)of the doped state is more than that of eigen state,which means that the hydrogen evolution ability is reduced,so the doped oxygen reduces the hydrogen evolution ability of WS2 system.When WS2 is doped with vancancy,the band gap value is reduced,and the S vancancy doping makes band gap value decrease more dramatically.Vancancy doping leads to doping level,which makes the conduction band moves to low-energy to result in lower conduction band position,so vancancy doping is good for the electronic movement from the valence band to the conduction band,which improves the separation efficiency of photoproduction electron and photoproduction hole.After WS2 is doped with vancancy,the formation energy of S vancancy doped system is always positive,however,the formation energy of W vancancy doped system is negative,thus the stability of W vancancy monolayer WS2 is better than the other one.After WS2 is doped with S vancancy,CBM potential(that is,the reduction potential)of the system is more than that of the eigen state,which means that its hydrogen evolution ability is reduced.At the same time,VBM potential(that is,the oxidation potential)of the system is less than that of the eigen state,which means that S vancancy doping makes hydrogen evolution ability and oxygen evolution ability of the monolayer WS2 system both reduced.But W vancancy doping makes hydrogen evolution ability of the original system be improved,on the contrary,worse oxygen evolution ability.When WS2 is doped with Cr and Mo,the band gap value is reduced,and the Cr doping leads to smaller band gap value.After doped with metal,new doping level is introduced to conduction band part,which results in lower conduction band position.So the doped metal is good for electronic movement from the valence band to the conduction band,which improves the separation efficiency of photoproduction electron and photoproduction hole.After WS2 is doped with transition metal,the formation energies of the two doping systems are both positive,so the stabilities of Cr and Mo doped monolayer WS2 system are both worse.When WS2 is doped with Cr,the CBM potential(that is,the reduction potential)of the doping system is more than that of the eigen state,which means its hydrogen evolution ability is reduced,however,the VBM potential(that is,the oxidation potential)of the doping system is less than that of the eigen state,which means that the oxygen evolution ability is reduced.But the hydrogen evolution and oxygen evolution ability of Mo doped monolayer WS2 system are basically not changed.The theoretical basis for the experiment can be provided by the theoretical calculation,it can also predict the future new materials.The calculation results of three kinds of different doped system above show that the formation energies of oxygen doping system and W vancancy doping system are both negative,which means their stabilities are improved,and they are available in the experiment.But the formation energies of metal doping system and S vancancy doping system are both positive,which means their stabilities are worse.In addition,the absorption spectra of doping system can also show that:the "red shift" has taken place in the O doped monolayer WS2 system,which means that the light absorsion efficiency of O doped monolayer WS2 system is improved.So do vancancy doped and O doped monolayer WS2 system.However,the light absorsion efficiency of transition metal doped monolayer WS2 system is almost not changed.