The Study Of Photocatalytic Activity For Water-Splitting On ReS₂

With the acceleration of industrialization,people are facing two important problems:energy crisis and environmental pollution.As we all know,the reserves of fossil fuels are limited.According to the development intensity calculation,we predict that the total reserves will be exhausted in the next hundred years.Finding a clean and renewable energy is the focus of human research on energy and environmental issues.The photocatalytic water splitting by using semiconductor materials is an effective method.This whole process involve the production of hydrogen and oxygen just making use of water as raw materials.Ingeniously,after the combustion of hydrogen,water is naturally generated,becoming the raw materials of photocatalysis process again.Photocatalytic decomposition of aquatic hydrogen can not only solve the energy crisis problem,but also solve the problem of environmental pollution.Two-dimensional transition metal dichalcogenides materials(TMDCs)have attracted wide attention of reserchers due to its’ unique monolayer structure,good optical and electrical properties.Renium disulfide(ReS2)is an unique semi-conducting material different from traditional transition metal sulfides with a distorted 1T phase structure.The electronically and dynamically decoupling in the interface with weak van der Waals forces enable it to retain a direct band gap(～1.5 eV)almost independent of thickness.It also has the characteristics of anisotropy,high carrier mobility,good stability and so on.However,the conduction band minimum(CBM)of ReS2 is below the hydrogen redox potential of water,which limits its application in photocatalytic hydrogen evolution.In this paper,different methods were used to adjust the band position of ReS2 to achieve its photocatalytic decomposition of aquatic hydrogen.The detailed work is as follows:1.Density functional theory was used to calculate the band structure of two-dimensional 1T’-ReS2 by surface molecular modification.The changes of the band edge position were caused by the intrinsic electric dipole moment of the molecule and the induced electric dipole moment generated at the molecule/ReS2 interface.By selecting the appropriate polar molecules,and then controlling the adsorption concentration of polar molecules,doping the polar molecules and constructing the p-n type semiconductor heterostructures,the band edge position of ReS2 can be adjusted in a wide range.It was finally found that C6H5CN/ReS2/MoS2 and C6H5CH2NH2/ReS2/MoS2 van der Waals heterostructures are ideal candidate materials for water decomposition photocatalyst due to their strong absorption of visible light,suitable band edge position,less electron-hole pair recombination and good stability.2.To enhance photocatalytic water-splitting performance of 2D ReS2,we theoretically propose a feasible strategy to engineer its band structure by applying strain and vertical electric field.The density functional theory calculations show that the strains greatly tune the band gap and band edge positions of ReS2,because the strains significantly alter the crystal structure and then cause surface charge rearrangement.While the electric fields have little influence on band gap but obviously affect the band edge positions.This is because the electric fields have little effect on the crystal structure of ReS2 but easily produce in-plane electric dipole moment.The shifts of band edge position is mainly from the competition between surface charge and in-plane electric dipole.For applied strain,the shifts are dominated by surface charge rearrangement,for applied electric field,the shifts are determined by induced electric dipole moment.Importantly,the functionalized ReS2 with bi-axial strain of-4%and the electronic field of-0.1 V/A may be good candidates for water-splitting photocatalyst owing to their suitable band edge positions for water-splitting,ideal band gaps for visible light absorption,good stable,reduced electron-hole recombination and high carrier mobility.