| Aiming at the poor catalytic performance of two-dimensional van der Waals heterostructure in photocatalysis,this paper systematically studies the characteristics of the catalyst,such as band gap value,band edge position,visible light absorption range and catalytic efficiency,and simulates the polarization current characteristics of multi-scale atomic structure.The quantitative model of van der Waals heterostructure screening is mainly constructed,which realizes the in-depth study of the theoretical mechanism of two-dimensional van der Waals hetero structure and further improves the vacancy of photocatalytic theory of twodimensional van der Waals heterostructure.This study provides a new research idea for the application of two-dimensional van der Waals heterostructure in the field of photocatalysis,and greatly promotes the innovative development of photocatalytic green new energy technology.The main contents and results of this paper are summarized as follows:(1)Monolayer MXene and transition metal dichalcogenides(TMDCs)are new 2D semiconductor materials with good photoelectric properties.In this paper,we use a series of monolayer X2CT2(X=Cr,Hf,Mo,Sc,Ti,Zr;T=C1,F,O,OH)and MS2(M=Mo,W)construct two-dimensional van der Waals heterostructures,involving 20 heterostructures systems.Through the first-principles calculation,these 20 two-dimensional van der Waals heterostructures are screened by the fivefold photolysis water standard(first the band structure,second the band gap screening,third the band edge position matching,fourth the theoretical STH,and last the comparison PCE screening).Finally,two-dimensional Mo2CF2/WS2 van der Waals heterostructure is a potential high-performance photolysis catalyst.Phonon spectrum shows that Mo2CF2/WS2 heterostructure is stable.After forming the heterostructure,electrons at the interface are rearranged and the absorption range of visible light is greatly increased.These are all potential advantages of excellent photocatalytic materials.In this study,the characteristics of twodimensional X2CT2/MS2 van der Waals heterostructure are also explored,which provides a new idea for heterostructure screening of photolysis water.(2)Exciton dynamics and photocatalytic mechanism of two-dimensional Mo2CF2/WS2 van der Waals hetero structure have been studied.The stable interface structure was searched by adaptive genetic algorithm,and the dynamic processes such as electron-hole separation and electron-hole recombination at the interface of the stable structure were studied by non-adiabatic molecular dynamics method.After that,the change of Gibbs free energy of hydrogen evolution reaction was calculated,and the surface of Mo2CF2/WS2 is more inclined to adsorb and desorb at the S site to complete the reduction reaction.At the same time,by comparing the two paths of water splitting oxygen reaction:single-site adsorption path and doublesite adsorption path,it is known that the reaction energy barrier of single-site adsorption path is lower than that of double-site adsorption,and the oxygen evolution reaction of Mo2CF2/WS2 is more inclined to single-site adsorption path.Finally,the electronic structure of heterostructure is adjusted by applying strain.When biaxial stretching is 2%,the band edge position meets the needs of photocatalytic CO2,and the catalytic pathways of two kinds of photocatalytic CO2 products,CH3OH and CH4,are calculated.From the results,it can be seen that the product CH3OH is easier to generate and the reaction barrier is lower.To sum up,Mo2CF2/WS2 heterostructure is a potential photocatalyst with high exciton transfer efficiency and low energy barrier for catalytic reaction.(3)Finally,in order to deeply study the luminescence mechanism of twodimensional Mo2CF2/WS2 van der Waals heterostructure,and to find ways to improve the catalytic capacity.A two-dimensional Mo2CF2/WS2 van der Waals heterostructure large-scale photoelectric device is constructed to simulate the photoelectric effect of two kinds of natural light waves(elliptically polarized light and linearly polarized light)on the material surface.The photocurrent and rotation angle of polarized light in armchair direction and sawtooth direction are different,and the total photocurrent excited by polarized light in zigzag direction is better than that in armchair direction.The photocurrent and angle of polarized light in armchair direction and sawtooth direction are different,and the total photocurrent excited by polarized light in zigzag direction is better than that in armchair direction.In order to increase the photocurrent of heterostructure and improve the catalytic ability,small bias voltage and point defect are added to improve the photocurrent respectively.After adding a small bias voltage,the photocurrent increases obviously,but some photon energy will also be saturated with photocurrent in different photon energy.Then the effect of point defects on photocurrent is studied.By calculating the photocurrent of point defects,it is found that C,F and Mo have positive effects on improving photocurrent,while devices with W and S point defects cannot improve photocurrent.This phenomenon can be attributed to the increase of localized electrons caused by W and S point defects,which affects electron excitation.The above research provides theoretical basis and research ideas for improving the catalytic ability of two-dimensional Mo2CF2/WS2 van der Waals heterostructure,which is helpful to the development of large-area commercial catalytic materials in the future. |
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