Janus type heterojunction material and calculation method and application of Janus type heterojunction material in photocatalytic water decomposition

Abstract

The invention relates to a Janus type heterojunction material as well as a calculation method and application of the Janus type heterojunction material in photocatalytic water decomposition, and belongs to the technical field of heterojunction materials. The upper layer of the material is a 1T-phase GeSe single layer, the lower layer of the material is a 1T-phase SnSSe single layer, and the material is divided into two configurations of GeSe / SSnSe and GeSe / SeSnS according to interface atom arrangement. Modeling and simulation calculation are carried out through VESTA and VASP software, and the result shows that the material has the direct Z-type heterojunction characteristic, photon-generated carrier separation can be effectively promoted, the light absorption range is widened, the photocatalytic oxidation reduction capacity and the solar energy-hydrogen energy conversion efficiency are remarkably improved, and a new strategy is provided for developing efficient photocatalysts.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heterojunction materials, and relates to a Janus type heterojunction material and a calculation method and application thereof in photocatalytic water splitting. BACKGROUND

[0002] At present, the exploitation and utilization of traditional energy have caused serious environmental pollution and climate change problems. Therefore, exploring new clean energy production and utilization methods has become an urgent global demand. Solar energy and hydrogen energy, as important components of renewable green energy, have attracted widespread attention from researchers due to their safety and environmental friendliness. Using solar energy to drive photocatalytic water splitting to produce hydrogen is considered to be one of the most feasible industrial production methods.

[0003] However, traditional photocatalysts have many inherent defects, such as weak carrier separation and transport capacity, and narrow solar energy absorption range, which seriously restrict their photocatalytic efficiency. The design and application of heterojunction materials are considered to be an effective strategy to break this bottleneck. Heterojunctions not only broaden the spectral range of solar light capture, but also have unique band structures that allow photo-generated electrons to remain on the higher potential side with high reduction ability and photo-generated holes to remain on the lower potential side with high oxidation ability, thereby exhibiting stronger redox reaction driving force. These excellent properties make heterojunctions have great application prospects in the field of photocatalytic water splitting.

[0004] In recent years, Janus transition metal dichalcogenide monolayer materials have opened up a new field of regulating the properties of two-dimensional materials. This Janus structure is originally derived from theoretical prediction, which is achieved by replacing one layer in the original TMDs monolayer with another chalcogen atom layer. Janus TMDs break the out-of-plane mirror symmetry due to their structure, and exhibit enhanced Rashba spin-orbit coupling effect. Moreover, they have high basal plane hydrogen evolution reaction activity due to the synergistic effect of their inherent structural defects and structural strain. Most notably, the Janus structure of TMDs greatly enhances the spatial separation efficiency of photo-induced charged carriers due to the internal electric field, thereby effectively suppressing the recombination of electrons and holes.

[0005] Janus SnSSe is a representative material with out-of-plane polarization field. The stability of monolayer SnSSe is predicted by phonon spectrum calculation and ab initio molecular dynamics simulation, and the material is found to have high carrier mobility and high light absorption coefficient by calculation, showing great potential as an excellent photocatalyst. Among them, SnSSe has a relatively negative valence band position, making it have strong photocatalytic oxidation ability, but its ability to reduce protons to produce hydrogen is relatively limited. In addition, theoretical research has proved that germanium selenide is chemically stable and has photoelectric properties suitable for photovoltaic devices. At the same time, the band gap of GeSe is well matched with the solar spectrum, and it has a relatively high visible light absorption coefficient.

[0006] Therefore, monolayer GeSe and monolayer SnSSe are selected to construct a heterojunction, aiming to synergistically enhance the respective advantages of the two in the process of photocatalytic water splitting. According to the distance difference between the sulfur atoms and selenium atoms on both sides of the SnSSe layer and the GeSe layer, the heterojunction can be divided into two configurations: GeSe / SSnSe and GeSe / SeSnS. Because the different configurations will cause significant differences in the static potential and band edge position of the heterojunction, which will deeply affect its solar hydrogen production efficiency, hydrogen evolution reaction and oxygen evolution reaction path, therefore, in-depth study of the electronic properties and photocatalytic performance of the two different configurations of GeSe / SSnSe and GeSe / SeSnS has important theoretical guiding significance for designing the next generation of high-efficiency photocatalytic materials. SUMMARY

[0007] Therefore, monolayer GeSe and monolayer SnSSe are selected to construct a heterojunction, aiming to synergistically enhance the respective advantages of the two in the process of photocatalytic water splitting. According to the distance difference between the sulfur atoms and selenium atoms on both sides of the SnSSe layer and the GeSe layer, the heterojunction can be divided into two configurations: GeSe / SSnSe and GeSe / SeSnS. Because the different configurations will cause significant differences in the static potential and band edge position of the heterojunction, which will deeply affect its solar hydrogen production efficiency, hydrogen evolution reaction and oxygen evolution reaction path, therefore, in-depth study of the electronic properties and photocatalytic performance of the two different configurations of GeSe / SSnSe and GeSe / SeSnS has important theoretical guiding significance for designing the next generation of high-efficiency photocatalytic materials.

[0008] To achieve the above-mentioned purpose, the technical scheme provided by the present application is as follows:

[0009] A Janus-type heterojunction material, the upper layer material of the heterojunction material is a 1T phase of monolayer germanium selenide GeSe, and the lower layer material is a 1T phase of monolayer selenide tin SnSSe, and the middle layer tin atoms in the SnSSe are connected with different chalcogen elements sulfur atoms or selenium atoms on both sides.

[0010] Further, the heterojunction material has a space structure of P6 / mmm, and the interlayer spacing is

[0011] Further, the heterojunction material is divided into GeSe / SSnSe and GeSe / SeSnS configurations according to the distance between the sulfur atoms and selenium atoms on both sides of the SnSSe layer and the GeSe layer, the sulfur atoms of the SnSSe layer are on the side close to the GeSe layer in the GeSe / SSnSe configuration, and the selenium atoms of the SnSSe layer are on the side close to the GeSe layer in the GeSe / SeSnS configuration.

[0012] A simulation method of the Janus-type heterojunction material in photocatalytic water splitting, the simulation method comprising the following steps:

[0013] (1) Constructing a heterojunction model on VESTA software, setting the lattice constants a, b and c as 3.74, 3.74 and 25 respectively, and establishing a heterojunction model with a layered structure;

[0014] (2) Exporting the heterojunction model constructed by VESTA to obtain a POSCAR file, using the Generalized Gradient Approximation (GGA) method, calling the PWA-GGA library to generate a POTCAR file, calling the VASPKIT software, inputting the "101-LR" instruction to automatically generate an INCAR file, then setting the EDIFF parameter in the INCAR file to -0.01, using the Gamma Scheme method, selecting the K point as 9x9x1, and then obtaining a CONTCAR file through the Vienna Ab initio Simulation Package (VASP) for structure optimization;

[0015] (3) Self-consistent calculation of the heterojunction, using the input files in the structure optimization including CONTCAR, POTCAR and KPOINTS, renaming the CONTCAR file as POSCAR, calling the VASPKIT software, inputting the "101-ST" instruction to automatically generate an INCAR file, and then obtaining CHGCAR and WAVECAR files through VASP for static self-consistent calculation;

[0016] (4) The state density of the heterojunction is calculated by the PBE functional, the input files in the static self-consistent including POSCAR, POTCAR, INCAR, KPOINTS, CHGCAR and WAVECAR are used, the ICHARG parameter in the INCAR file is set to 11 and the appropriate energy band range is set, VASP is used for simulation calculation, after the calculation is completed, VASPKIT software is called, the "111" instruction is input, the TDOS.dat file is obtained, Origin software is imported, the total state density diagram calculated by the PBE functional is obtained; VASPKIT software is called, the "114" instruction is input, and the corresponding position of the atom is input again, the PDOS.dat file is obtained, Origin software is imported, and the partial wave state density diagram calculated by the PBE functional is obtained;

[0017] (5) The projected band structure, static potential and band edge position of the heterojunction are calculated by the HSE06 hybrid functional, the input files in the static self-consistent including POSCAR, POTCAR, CHGCAR and WAVECAR are used, VASPKIT software is called, the "101-H6" instruction is input to generate the INCAR file, then LORBIT=11 and LVHAR=.TRUE. are set in the INCAR file, VASPKIT software is called, the "302" instruction is input to generate the KPATH.in file, then VASPKIT software is called again, the "251-2-0.04-0.06" instruction is input to generate the KPOINTS file, VASP is used for simulation calculation, after the calculation is completed, VASPKIT software is called, the "256" is input, the PBAND ELEMENTS.dat file is obtained, Origin software is imported, and the projected band structure diagram calculated by the HSE06 hybrid functional is obtained; the "grep E-fermi OUTCAR" is input in the command line, the Fermi level is obtained, then qvasp software is called, the "qvasp-wkd" is input in the command line, then the corresponding Fermi level is input, and then the "3" is input, the vline.dat file is obtained, Origin software is imported, and the static potential diagram is obtained; VASPKIT software is called and the "927" instruction is input, and the band edge position of the heterojunction is obtained;

[0018] (6) Calculate the optical absorption coefficient of the heterojunction, extend the input files in the static self-consistent including POSCAR, POTCAR, KPOINTS, CHGCAR and WAVECAR and extend the INCAR file in the structure optimization, set LOPTICS=. TRUE., NBANDS=96, NEDOS=2000, CSHIFT=0.1 in the INCAR file, simulate and calculate by VASP, after the calculation is completed, call VASPKIT software and input "711" instruction, get ABSORPTION.dat file, import Origin software to get the optical absorption coefficient graph of the heterojunction;

[0019] (7) Calculate the Gibbs free energy of the heterojunction in the photocatalytic water splitting, first build the adsorption intermediate model of the heterojunction, then optimize the structure of the adsorption intermediate, set the ISIF parameter in the INCAR file of the structure optimization to 2, after the structure optimization is completed, input "cat OSZICAR|grep F|awk '{printf ("%.3f\n", $5)}'|tail-1" in the command line, get the total energy of the system, then extend the input files in the structure optimization including CONTCAR, INCAR, POTCAR and KPOINTS, rename the CONTCAR file as POSCAR, in addition to the adsorbed atoms, the atomic coordinates of the heterojunction in the POSCAR need to be fixed, set POTIM=0.015, EDIFF=1E-7, ALGO=VeryFast in the INCAR file, use VASP to perform frequency calculation, after the calculation is completed, call VASPKIT software and input "5-501-298.15" instruction, get the free energy correction value of the adsorption intermediate, then combine the total energy of the system, get the Gibbs free energy of the adsorption intermediate, calculate the Gibbs free energy of different adsorption intermediates according to the above steps, further process the data, and finally get the Gibbs free energy change graph of the hydrogen evolution reaction and the oxygen evolution reaction.

[0020] Further, the Gibbs free energy change ΔG in step (7) is calculated according to the following formula:

[0021] ΔG = ΔE + ΔE zpe -TΔS + ΔG pH + ΔG U

[0022] Wherein, ΔE represents the total energy difference between the adsorption state and the desorption state, ΔE zpe represents the zero-point energy difference, T represents the temperature, ΔS represents the entropy change, ΔG pH represents the free energy correction term considering the influence of pH value, ΔG U corresponds to the free energy correction term of the related electrode potential U.

[0023] Further, the Gibbs free energy change diagram of the hydrogen evolution reaction and the oxygen evolution reaction in step (7) is used to evaluate the photocatalytic redox ability of the Janus-type heterojunction material.

[0024] An application of the Janus-type heterojunction material, the material is applied as a photocatalyst in a photocatalytic water splitting reaction.

[0025] Further, the internal electric field generated by the direct Z-type heterojunction structure of the material realizes efficient separation and migration of photo-generated carriers.

[0026] Further, the solar-to-hydrogen conversion efficiency of the Janus-type heterojunction material is calculated according to the following formula:

[0027]

[0028] wherein, is the AM1.5G solar flux under the photon energy , ΔG represents the potential difference of water splitting, which is 1.23eV, ΔΦ represents the electrostatic potential difference of the SnSSe layer and the GeSe layer, E g represents the band gap of the heterojunction.

[0029] Further, when the Janus-type heterojunction material is in the GeSe / SSnSe configuration, the STH efficiency is 17.3%; when the Janus-type heterojunction material is in the GeSe / SeSnS configuration, the STH efficiency is 16.4%.

[0030] The beneficial effects of the present application are:

[0031] First, in terms of material design and structural innovation, the present application successfully constructs a new type of Janus heterojunction structure. The upper layer adopts 1T phase germanium selenide monolayer, and the lower layer adopts 1T phase tin selenide monolayer. By accurately controlling the stacking mode of the two layers of materials, two stable configurations of GeSe / SSnSe and GeSe / SeSnS are formed. This unique asymmetric structure design fundamentally breaks the mirror symmetry of the material out of plane, and induces a strong internal polarization electric field.

[0032] Secondly, in terms of photocatalytic performance, the heterojunction material exhibits excellent carrier separation and transport characteristics. Its staggered band arrangement structure makes the photo-generated electrons and holes be effectively separated and localized in different material layers, greatly suppressing the recombination probability of electron-hole pairs. At the same time, the material has a wide solar light absorption range, covering from ultraviolet to visible light and even infrared region, ensuring efficient use of the solar spectrum. More importantly, the calculation results show that the heterojunction is a direct Z-type heterojunction mechanism, while retaining strong oxidation and strong reduction active sites, providing sufficient driving force for the photocatalytic water splitting reaction.

[0033] Furthermore, in terms of research and development methods and efficiency, the present application establishes a complete and reliable simulation calculation system. Through the collaborative workflow of VESTA and VASP software, the whole process simulation from atomic structure modeling to electronic property calculation is realized. This calculation method has excellent calculation efficiency and high calculation accuracy, and the calculation results are in good agreement with the experimental data, providing a powerful theoretical tool for the design and performance prediction of new materials. This method greatly accelerates the research and development process, significantly reduces the high cost and time consumption brought by traditional trial-and-error experiments.

[0034] Finally, in terms of practical application prospects, the Janus heterojunction material exhibits great potential as a high-efficiency photocatalyst. Its excellent comprehensive performance indicates that it can effectively promote the hydrogen evolution and oxygen evolution processes in the water splitting reaction, providing a new material solution for solving energy conversion and environmental pollution problems. Compared with existing photocatalytic materials, the material of the present application has better stability and sustainability while maintaining high catalytic activity.

[0035] Other advantages, objects, and features of the present application will be in part apparent and in part pointed out hereinafter in the specification, and it is the intention, therefore, to be limited only as indicated by the scope of the claims. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred detailed description of the present application will be combined with the drawings to describe the present application, in which:

[0037] Figure 1 Fig. 1 is a schematic diagram of different configurations of GeSe / SSnSe heterojunction materials, wherein (a) is a top view and side view of S-A configuration, (b) is a top view and side view of S-B configuration, and (c) is a top view and side view of S-C configuration;

[0038] Figure 2Schematic diagrams of different configurations of GeSe / SeSnS heterojunction materials, wherein (a) is the top view and side view of Se-A configuration, (b) is the top view and side view of Se-B configuration, and (c) is the top view and side view of Se-C configuration;

[0039] Figure 3 AIMD simulation stability analysis diagrams of heterojunction materials at 300K, wherein (a) is the diagram of energy and configuration change of GeSe / SSnSe heterojunction, and (b) is the diagram of energy and configuration change of GeSe / SeSnS heterojunction;

[0040] Figure 4 Density of states analysis diagrams of heterojunction materials, wherein (a) is the total density of states and partial density of states diagram of GeSe / SSnSe heterojunction, and (b) is the total density of states and partial density of states diagram of GeSe / SeSnS heterojunction;

[0041] Figure 5 Projected energy band structure diagrams of heterojunction materials, wherein (a) is the projected energy band structure diagram of GeSe / SSnSe heterojunction, and (b) is the projected energy band structure diagram of GeSe / SeSnS heterojunction;

[0042] Figure 6 Static potential distribution diagrams of heterojunction materials, wherein (a) is the static potential diagram of GeSe / SSnSe heterojunction, and (b) is the static potential diagram of GeSe / SeSnS heterojunction;

[0043] Figure 7 Energy level band edge position distribution diagrams of heterojunction materials, wherein (a) is the distribution diagram of real band edge in energy level of GeSe / SSnSe heterojunction, and (b) is the distribution diagram of real band edge in energy level of GeSe / SeSnS heterojunction;

[0044] Figure 8 Light absorption property comparison diagrams of heterojunction materials, wherein (a) is the light absorption coefficient diagram of GeSe / SSnSe heterojunction, and (b) is the light absorption coefficient diagram of GeSe / SeSnS heterojunction;

[0045] Figure 9 Free energy change diagrams of photocatalytic water splitting reaction of heterojunction materials, wherein (a) is the adsorption structure and free energy change diagram of hydrogen evolution reaction of GeSe / SSnSe heterojunction, (b) is the adsorption structure and free energy change diagram of hydrogen evolution reaction of GeSe / SeSnS heterojunction, (c) is the adsorption structure and free energy change diagram of oxygen evolution reaction of GeSe / SSnSe heterojunction, and (d) is the adsorption structure and free energy change diagram of oxygen evolution reaction of GeSe / SeSnS heterojunction;

[0046] Figure 10FIG. 6 is a comparative diagram of STH efficiency of heterojunction materials, showing the STH efficiency of GeSe / SSnSe heterojunction and GeSe / SeSnS heterojunction compared with other heterojunction materials. DETAILED DESCRIPTION

[0047] Other advantages and effects of the present application can be easily understood by those skilled in the art from the description of the embodiments of the present application. The present application can also be implemented or applied by other different embodiments, and various modifications or changes can be made to the details of the description based on different views and applications without departing from the spirit of the present application. It should be noted that the diagrams provided in the following examples only illustrate the basic concept of the present application in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.

[0048] The accompanying drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual size of the product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0049] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0050] Figure 1 In (a), (b) and (c), respectively, are the top view and side view of different configurations of GeSe / SSnSe heterojunction material: S-A, S-B and S-C;

[0051] Figure 2 In (a), (b) and (c), respectively, are the top view and side view of different configurations of GeSe / SeSnS heterojunction material: Se-A, Se-B and Se-C;

[0052] Figure 3 In (a) and (b), respectively, are the energy and configuration change diagrams of GeSe / SSnSe heterojunction material and GeSe / SeSnS heterojunction during the AIMD simulation at 300K.

[0053] Figure 4 Fig. 1 (a) and (b) are total density of states and partial density of states diagrams of GeSe / SSnSe heterojunction materials and GeSe / SeSnS heterojunction materials, respectively;

[0054] Figure 5 Fig. 2 (a) and (b) are projected band structure diagrams of GeSe / SSnSe heterojunction materials and GeSe / SeSnS heterojunction materials, respectively;

[0055] Figure 6 Fig. 3 (a) and (b) are static potential diagrams of GeSe / SSnSe heterojunction materials and GeSe / SeSnS heterojunction materials, respectively;

[0056] Figure 7 Fig. 4 (a) and (b) are diagrams of the distribution of real band edges in the energy level of GeSe / SSnSe heterojunction materials and GeSe / SeSnS heterojunction materials, respectively;

[0057] Figure 8 Fig. 5 (a) and (b) are light absorption coefficient diagrams of GeSe / SSnSe heterojunction materials and GeSe / SeSnS heterojunction materials, respectively;

[0058] Figure 9 Fig. 6 (a), (b), (c) and (d) are adsorption structures and free energy change diagrams of GeSe / SSnSe heterojunction in hydrogen evolution reaction, adsorption structures and free energy change diagrams of GeSe / SeSnS heterojunction in hydrogen evolution reaction, adsorption structures and free energy change diagrams of GeSe / SSnSe heterojunction in oxygen evolution reaction, and adsorption structures and free energy change diagrams of GeSe / SeSnS heterojunction in oxygen evolution reaction, respectively;

[0059] Figure 10 Fig. 7 is a diagram of the STH efficiency of GeSe / SSnSe heterojunction materials and GeSe / SeSnS heterojunction materials compared with other heterojunction materials.

[0060] A Janus-type heterojunction material applied to photocatalytic water splitting, firstly verifies whether the Janus-type heterojunction material is stable and can meet the requirements for further performance research:

[0061] (1) Firstly, the lattice constants of single-layer GeSe and single-layer SnSSe were optimized. After optimization, the lattice constant of single-layer GeSe is a = b = 3.66, and the lattice constant of single-layer SnSSe is a = b = 3.77. The following formula defines the lattice mismatch between the two single-layer materials:

[0062]

[0063] a GeSe and a SnSSe respectively represent the lattice constants of GeSe and SnSSe after structure optimization. The calculated lattice mismatch between the two monolayer materials is 2.96%, which is within the allowable range (<5%), indicating that a stable heterostructure can be formed. The small lattice mismatch ensures that the heterojunction will not collapse easily and can be successfully prepared in experiments.

[0064] (2) The binding energy is used to evaluate the stability of the heterojunction, which is calculated by the following formula:

[0065] E b = E GeSe / SnSSe - E SnSSe - E GeSe

[0066] E GeSe / SnSSe represents the total energy of the GeSe / SnSSe heterojunction, E SnSSe and E GeSe represent the energy of the monolayer SnSSe and the monolayer GeSe, respectively. The GeSe / SnSSe heterojunction is formed by stacking the monolayer GeSe unit cell and the monolayer SnSSe unit cell. In order to select the most stable heterojunction, according to the distance between the S and Se atoms on both sides of the SnSSe layer and the GeSe layer, this heterostructure is divided into two configurations: GeSe / SSnSe and GeSe / SeSnS. Each configuration has 3 stacking modes, named S-A ~ C and Se-A ~ C, respectively. The top view and side view of the S-A, S-B, and S-C configurations are shown in Figure 1 , and the top view and side view of the Se-A, Se-B, and Se-C configurations are shown in Figure 2 . The lattice constants of the six configurations are all a = b = 3.74, among which S-A and Se-A are the stacking configurations with the smallest binding energy in the two interface types, respectively, and it is concluded that S-A and Se-A are the most stable stacking structures in the two interface types.

[0067] (3) In order to further verify the stability of the GeSe / SSnSe heterojunction and the GeSe / SeSnS heterojunction, AIMD is used to predict the thermodynamic stability of the S-A and Se-A configurations. As shown in Figure 3 , the structure of S-A and Se-A configurations is not destroyed after 5000 fs at a temperature of 300 K, and the bonding between atoms is not broken, and the total energy fluctuates on a horizontal line. This indicates that the heterojunction is stable at room temperature, i.e., the S-A and Se-A configurations have thermodynamic stability. Therefore, in the following calculations and discussions, the most stable structures S-A and Se-A configurations are selected as the research object for the next simulation.

[0068] The calculation steps of the electrical and photocatalytic properties of the GeSe / SSnSe and GeSe / SeSnS heterojunction materials will be illustrated below, and the calculation steps for materials with similar properties and structures are similar to the following steps.

[0069] Example 1

[0070] (1) Model construction: obtain stable GeSe and SnSSe structures through structure optimization, import them into VESTA to construct a GeSe / SSnSe heterojunction, wherein the S atoms in SnSSe are arranged on the side close to GeSe, and the S-A configuration in the selected Figure 1 POSCAR file is finally obtained.

[0071] (2) Structure optimization: use VASP to perform structure optimization calculation on the GeSe / SSnSe heterojunction based on first principles, use the generalized gradient approximation method, call the PWA-GGA library to generate the POTCAR file, call the VASPKIT software, input the "101-LR" instruction to automatically generate the INCAR file, then set the EDIFF parameter in the INCAR file to -0.01. Use the Gamma Scheme method, select K points as 9x9x1, and then perform structure optimization through VASP to obtain the CONTCAR file, which contains the crystal structure information in the stable state. The stable crystal structure information is shown in Table 1, wherein a and b represent the lattice constants, Sn-S represents the bond length between Sn and S elements, Sn-Se represents the bond length between Sn and Se elements, Ge-Se represents the bond length between Ge and Se elements, and d represents the interlayer spacing of the heterojunction.

[0072] Table 1 Lattice-related parameters after structure optimization of Examples 1-2

[0073]

[0074] (3) Static self-consistency: use the input files in the structure optimization including CONTCAR, POTCAR and KPOINTS. Rename the CONTCAR file as POSCAR, call the VASPKIT software, input the "101-ST" instruction to automatically generate the INCAR file, and then perform static self-consistency through VASP to obtain the CHGCAR and WAVECAR files, which can help to speed up the convergence of the electronic step in subsequent operations.

[0075] (4) Calculation of density of states using PBE functional analysis: The input files from the static self-consistent model include POSCAR, POTCAR, INCAR, KPOINTS, CHGCAR, and WAVECAR. Set the ICHARG parameter in the INCAR file to 11 and define a suitable bandgap range. Perform simulation calculations using VASP. After the calculations are complete, call the VASPKIT software, input the command "111", and obtain the TDOS.dat file. Import this file into Origin software to obtain the total density of states diagram of the GeSe / SSnSe heterojunction calculated using PBE functional analysis. Figure 4 As shown in 'a'; call the VASPKIT software, input the command "114", then input the corresponding position of the atom to obtain the PDOS.dat file. Import it into the Origin software to obtain the partial density of states diagram of the GeSe / SSnSe heterojunction calculated by PBE functional theory, as shown in 'a'. Figure 4 As shown in 'a'.

[0076] (5) Calculate the projected band structure, static potential, and band edge positions using the HSE06 hybrid functional: Using the input files from the static self-consistency model, including POSCAR, POTCAR, CHGCAR, and WAVECAR, call the VASPKIT software and input the command "101-H6" to generate the INCAR file. Then, set LORBIT=11 and LVHAR=.TRUE in the INCAR file. Call the VASPKIT software again and input the command "302" to generate the KPATH.in file. Then, call the VASPKIT software again and input the command "251-2-0.04-0.06" to generate the KPOINTS file. Use VASP for simulation calculations. After the calculation is complete, call the VASPKIT software again and input "256" to obtain the PBAND ELEMENTS.dat file. Import this file into Origin software to obtain the projected band structure diagram of the GeSe / SSnSe heterojunction calculated by the HSE06 hybrid functional. Figure 5 As shown in 'a', the band gap is 1.48 eV. Enter "grep E-fermi OUTCAR" in the command line to obtain the Fermi level. Then, launch the qvasp software by entering "qvasp-wkd" in the command line, followed by the corresponding Fermi level, and then "3". This will generate the vline.dat file. Importing this file into Origin software will yield the static potential diagram of the GeSe / SSnSe heterojunction, as shown in the image. Figure 6 As shown in a; by calling the VASPKIT software and entering the command "927", the band edge positions of the GeSe / SSnSe heterojunction can be obtained, as shown in Figure 'a'. Figure 7 As shown in 'a'.

[0077] (6) Calculation of optical absorption coefficient: The input files including POSCAR, POTCAR, KPOINTS, CHGCAR and WAVECAR in static self-consistency and INCAR file in structure optimization are extended, and in the INCAR file, LOPTICS=. TRUE., NBANDS=96, NEDOS=2000, CSHIFT=0.1 are set. VASP is used for simulation calculation. After the calculation is completed, VASPKIT software is called and the "711" instruction is input to obtain the ABSORPTION.dat file. Importing Origin software can obtain the optical absorption coefficient diagram of GeSe / SSnSe heterojunction, as shown in Fig. 6a. Figure 8

[0078] (7) Calculation of Gibbs free energy in photocatalytic water splitting: First, the GeSe / SSnSe heterojunction is expanded to 3x3x1 in VESTA, and then small molecules are added to the appropriate position in the heterojunction to finally build the adsorption intermediate model. Then the adsorption intermediate is structure optimized, and the ISIF parameter in the INCAR file in structure optimization is set to 2. After structure optimization, "cat OSZICAR|grep F|awk '{printf ("%.3f\n", $5)}'|tail-1" is input in the command line to obtain the total energy of the system. Then the input files including CONTCAR, INCAR, POTCAR and KPOINTS in structure optimization are extended, and the CONTCAR file is renamed as POSCAR. Except for the adsorbed atoms, the original atomic coordinates of the heterojunction in POSCAR need to be fixed. In the INCAR file, POTIM=0.015, EDIFF=1E-7, ALGO=VeryFast are set. VASP is used for frequency calculation. After the calculation is completed, VASPKIT software is called and the "5-501-298.15" instruction is input to obtain the free energy correction value of the adsorption intermediate. Combined with the total energy of the system, the Gibbs free energy of the adsorption intermediate can be obtained. According to the above method, the Gibbs free energy of different adsorption intermediates can be calculated. After further processing of the data, the free energy change diagram of GeSe / SSnSe heterojunction in hydrogen evolution reaction and oxygen evolution reaction can be obtained, as shown in Figs. 6a and 6c. Figure 9

[0079] Example 2

[0080] (1) Model construction: The stable SnSSe and GeSe structures obtained after structure optimization are imported into VESTA to construct GeSe / SeSnS heterojunction, wherein the Se atom in SnSSe is set on the side of GeSe, and Figure 2 ​​Se-A configuration in the middle, and finally get the POSCAR file.

[0081] (2) Structure optimization: based on the first principle, the structure of SeSnS / GeSe heterojunction is optimized by VASP, the generalized gradient approximation method is used, and the POTCAR file is generated by calling the PWA-GGA library. Call VASPKIT software, input "101-LR" instruction to automatically generate INCAR file, then set EDIFF parameter in INCAR file to-0.01. Gamma Scheme method is adopted, K point is selected as 9x9x1, and then CONTCAR file is obtained by structure optimization through VASP. CONTCAR file contains crystal structure information in stable state. The stable crystal structure information is shown in Table 1.

[0082] (3) Static self-consistency: the input files in the structure optimization include CONTCAR, POTCAR and KPOINTS. Rename the CONTCAR file as POSCAR, call VASPKIT software, input "101-ST" instruction to automatically generate INCAR file, and then obtain CHGCAR and WAVECAR files by static self-consistency through VASP, which can help to speed up the convergence of electronic steps in subsequent operation.

[0083] (4) Calculate the density of states by PBE functional: the input files in the static self-consistency include POSCAR, POTCAR, INCAR, KPOINTS, CHGCAR and WAVECAR. Set ICHARG parameter in INCAR file to 11 and set appropriate energy band range, use VASP for simulation calculation, after calculation, call VASPKIT software, input "111 instruction, get TDOS.dat file, import Origin software, can get the total density of states diagram of SeSnS / GeSe heterojunction calculated by PBE functional, as shown in Fig. Figure 4 (5) Calculate the partial density of states by PBE functional: call VASPKIT software, input "114" instruction, and then input the corresponding position of atoms, get PDOS.dat file, import Origin software, can get the partial density of states diagram of SeSnS / GeSe heterojunction calculated by PBE functional, as shown in Fig. Figure 4 (5) Calculate the partial density of states by PBE functional: call VASPKIT software, input "114" instruction, and then input the corresponding position of atoms, get PDOS.dat file, import Origin software, can get the partial density of states diagram of SeSnS / GeSe heterojunction calculated by PBE functional, as shown in Fig.

[0084] (5) Calculation of the projected band structure, static potential and band edge position by HSE06 hybrid functional: the input files including POSCAR, POTCAR, CHGCAR and WAVECAR in the static self-consistent stage are extended, VASPKIT software is called, INCAR file is generated by inputting "101-H6" instruction, LORBIT = 11 and LVHAR =.TRUE. are set in the INCAR file, VASPKIT software is called, KPATH.in file is generated by inputting "302" instruction, VASPKIT software is called again, KPOINTS file is generated by inputting "251-2-0.04-0.06" instruction, VASP is used for simulation calculation, after the calculation is completed, VASPKIT software is called, PBAND ELEMENTS.dat file is obtained by inputting "256", and HSE06 hybrid functional calculation of the projected band structure of SeSnS / GeSe heterojunction is obtained by importing Origin software, as shown in Fig. 2b. Figure 5 The band gap is 1.55 eV. "grep E-fermi OUTCAR" is input in the command line, the Fermi level is obtained, then qvasp software is called, "qvasp-wkd" is input in the command line, then the corresponding Fermi level is input, then "3" is input, vline.dat file is obtained, and the static potential diagram of SeSnS / GeSe heterojunction is obtained by importing Origin software, as shown in Fig. 2c. Figure 6 The band edge position of SeSnS / GeSe heterojunction is obtained by calling VASPKIT software and inputting "927" instruction, as shown in Fig. 2d. Figure 7 The band edge position of SeSnS / GeSe heterojunction is obtained by calling VASPKIT software and inputting "927" instruction, as shown in Fig. 2d.

[0085] (6) Calculation of optical absorption coefficient: the input files including POSCAR, POTCAR, KPOINTS, CHGCAR and WAVECAR in the static self-consistent stage and the INCAR file in the structure optimization stage are extended, LOPTICS =.TRUE., NBANDS = 96, NEDOS = 2000 and CSHIFT = 0.1 are set in the INCAR file, VASP is used for simulation calculation, after the calculation is completed, VASPKIT software is called and "711" instruction is input, ABSORPTION.dat file is obtained, and the optical absorption coefficient diagram of SeSnS / GeSe heterojunction is obtained by importing Origin software, as shown in Fig. 2e. Figure 8 The optical absorption coefficient diagram of SeSnS / GeSe heterojunction is obtained by importing Origin software, as shown in Fig. 2e.

[0086] (7) Calculation of Gibbs free energy in photocatalytic water splitting: First, the GeSe / SeSnS heterojunction was expanded to 3x3x1 in VESTA, then small molecules were added to the appropriate position in the heterojunction, and finally the adsorption intermediate model was constructed. Then the adsorption intermediate was optimized, and the ISIF parameter in the INCAR file in the structure optimization was set to 2. After the structure optimization, input "cat OSZICAR|grep F|awk '{printf ("%.3f\n", $5)}'|tail-1" in the command line to obtain the total energy of the system. Then use the input files including CONTCAR, INCAR, POTCAR and KPOINTS in the structure optimization, change the CONTCAR file to POSCAR, and fix the atomic coordinates of the heterojunction in POSCAR except the adsorbed atoms. Set POTIM=0.015, EDIFF=1E-7, ALGO=VeryFast in the INCAR file, use VASP for frequency calculation, and after the calculation, call VASPKIT software and input "5-501-298.15" instruction, then the free energy correction value of the adsorption intermediate can be obtained, and then the Gibbs free energy of the adsorption intermediate can be obtained. According to the above method, the Gibbs free energy of different adsorption intermediates can be calculated, and after further processing of the data, the free energy change diagram of GeSe / SeSnS heterojunction in hydrogen evolution reaction and oxygen evolution reaction can be obtained, as shown in FIG. 1 and FIG. 2. Figure 9

[0087] By analyzing the total density of states and the partial density of states of the GeSe / SSnSe and GeSe / SeSnS heterojunctions in Examples 1-2, it can be seen that the VBM is mainly contributed by the GeSe monolayer, and the CBM is mainly contributed by the SnSSe monolayer. Obviously, the conduction band and the valence band of the heterojunction are contributed by different semiconductor materials. This staggered band structure can effectively separate photo-generated electrons and holes, significantly prevent the recombination rate of carriers, and thus improve the catalytic efficiency of the heterojunction.

[0088] By analyzing the projected band structure of the GeSe / SSnSe and GeSe / SeSnS heterojunctions in Examples 1-2, it can be seen that the CBM of them is located at the M point, and the VBM is located at a point between the K and Γ points, indicating that the GeSe / SSnSe and GeSe / SeSnS heterojunctions are indirect semiconductors with band gaps of 1.48 eV and 1.55 eV, respectively. The VBM is mainly contributed by the GeSe monolayer, and the CBM is mainly contributed by the SnSSe monolayer, which is consistent with the analysis of the density of states, which indicates that the GeSe / SSnSe and GeSe / SeSnS heterojunctions have a type II band arrangement.

[0089] ​By analyzing the static potential of GeSe / SnSSe and GeSe / SeSnS heterojunctions in Examples 1-2, due to the asymmetry of the two sides of the heterojunction, a static potential difference ΔΦ is generated on the surface of SnSSe and GeSe, which will cause the change of the redox potential of water. The potential difference at the interface of GeSe / SnSSe heterojunction and GeSe / SeSnS heterojunction is 2.16 eV and 2.1 eV, respectively. This large potential difference has great benefits in promoting the recombination of interlayer photo-generated electron-hole pairs, inhibiting the charge transfer between GeSe and SnSSe layers, and promoting the formation of Z-type charge transfer path.

[0090] By analyzing the distribution of the real band edge in the energy level of GeSe / SnSSe and GeSe / SeSnS heterojunctions in Examples 1-2, due to the asymmetry of the vacuum level on the two sides of the heterojunction, compared with the SnSSe layer, the vacuum level and the redox potential of the GeSe layer are reduced by 0.58 eV and 0.97 eV, respectively. Therefore, in the GeSe / SnSSe and GeSe / SeSnS heterojunctions, the energy difference between the reduction potential of the GeSe layer and the oxidation potential of the SnSSe layer is reduced to 0.65 eV and 0.26 eV, respectively (calculated by ΔE = 1.23 eV - ΔΦ), which helps to enhance the redox ability of the heterojunction.

[0091] An important parameter for measuring the photocatalytic performance of semiconductor materials is the light absorption coefficient. Based on this, the light absorption coefficient of GeSe / SnSSe and GeSe / SeSnS heterojunctions in Examples 1-2 is analyzed. It can be seen that GeSe / SnSSe and GeSe / SeSnS heterojunctions have a wide light absorption range from ultraviolet light to visible light and even infrared light, and the light absorption intensity is about 10 5 cm. Moreover, in the visible light region, the integral area of sunlight absorption of GeSe / SnSSe and GeSe / SeSnS heterojunctions is larger than that of the two single-layer materials. This makes the two kinds of heterojunction materials have better application in the field of photocatalysis.

[0092] In the process of photocatalytic water splitting, photo-excited electrons and holes need to provide sufficient driving force to trigger the hydrogen evolution reaction and oxygen evolution reaction. It is necessary to calculate the Gibbs free energy change of hydrogen evolution reaction and oxygen evolution reaction to further illustrate the photocatalytic performance of GeSe / SnSSe and GeSe / SeSnS heterojunctions. The photo-generated electron potential (U e ) of hydrogen evolution reaction is defined as the energy difference between hydrogen reduction potential and CBM, and the photo-generated hole potential (U h ) of oxygen evolution reaction is defined as the energy difference between hydrogen reduction potential and VBM. U e and U hare calculated from the difference with the Standard Hydrogen Electrode (SHE). The two reactions of HER are as follows, where H* is an adsorbed intermediate and * is a heterogeneous junction in the non-adsorbed state:

[0093] * + H + + e - → H *

[0094] H * + H + + e - → * + H2

[0095] The steps of the oxygen evolution reaction are shown below, where OH*, O*, OOH* are adsorbed intermediates and * is a heterogeneous junction in the non-adsorbed state:

[0096] * + H2O → OH * + H + + e -

[0097] OH * → O * + H + + e -

[0098] O * + H2O → OOH * + H + + e -

[0099] OOH * → * + O2+ H + + e -

[0100] The Gibbs free energy change (AG) is calculated according to the following equation, where AE, AE zPe and AS represent the total energy difference, the zero-point energy difference and the entropy between the adsorbed and desorbed states, AG pH represents AG taking into account the influence of pH, AG U corresponds to the relevant electrode potential U, and the temperature is set to 298.15 K:

[0101] AG = AE + AE zpe - T AS + AG pH + AG U

[0102] Based on the above theory, the adsorption structure and free energy change diagram of GeSe / SSnSe and GeSe / SeSnS heterojunctions in the hydrogen evolution reaction and oxygen evolution reaction in examples 1-2 are analyzed. In the hydrogen evolution reaction, when pH=0 and there is no external potential, the free energy change of GeSe / SSnSe and GeSe / SeSnS heterojunctions is 1.166eV and 1.281eV respectively, and the curve shows an upward trend, which is an endothermic process and cannot be spontaneously carried out in the dark. Photogenerated carriers must provide an external potential greater than 1.166V (1.281v) to carry out the hydrogen evolution reaction. When pH=0, the photogenerated electron potential U e of GeSe / SSnSe and GeSe / SeSnS heterojunctions is 1.48V and 1.43V respectively. Thus, under the driving of the photogenerated electron potential, the curve becomes downward. Therefore, under light irradiation, photogenerated carriers can provide sufficient driving force to convert H2O under acidic conditions into H2. In the oxygen evolution reaction, when pH=0, the maximum free energy difference in the oxygen evolution reaction step of GeSe / SSnSe and GeSe / SeSnS heterojunctions is 2.605eV and 3.086eV respectively, and the photogenerated hole potential U h of GeSe / SSnSe and GeSe / SeSnS heterojunctions is 2.09V and 2.40V respectively, indicating that under light irradiation, an external potential of 0.515V (0.686V) is required to convert H2O into O2. When pH=7, the photogenerated hole potential U h of GeSe / SSnSe and GeSe / SeSnS heterojunctions is 2.50V and 2.81V respectively. It shows that under light irradiation, GeSe / SSnSe and GeSe / SeSnS heterojunctions can spontaneously carry out the oxygen reduction reaction under neutral conditions (pH=7). The Gibbs free energy proves that GeSe / SSnSe and GeSe / SeSnS heterojunctions can effectively improve the photocatalytic activity of single-layer materials and are strong competitors of high-efficiency photocatalysts.

[0103] In order to further analyze the practicability of the photocatalyst, the solar-to-hydrogen (STH) conversion efficiency (η STH ) of examples 1-2 is calculated. Since GeSe / SSnSe heterojunction and GeSe / SeSnS heterojunction generate a static potential difference of 0.58eV and 0.97eV respectively, η STH needs to be corrected. The corrected solar-to-hydrogen conversion efficiency calculation formula is:

[0104]

[0105] wherein is the photon energy AM1.5G solar flux, the integral of 0 to infinity represents the total power density of incident sunlight; AG represents the potential difference of water splitting, taking 1.23eV; A represents the electrostatic potential difference of the SnSSe layer and the GeSe layer; E g is determined by the position relationship between the actual band edge of the material and the lowest redox band edge of the photohydrolysis, and here the band width corresponding to the heterojunction is taken.

[0106] From Figure 10 It can be seen that the modified STH efficiency of the GeSe / SSnSe heterojunction material is 17.3%, and the modified STH efficiency of the GeSe / SeSnS heterojunction material is 16.4%. Figure 10 The GeSe / SSnSe heterojunction and the GeSe / SeSnS heterojunction are compared with other heterojunction STH efficiencies. They are significantly better than GaN / BS (5.4%), ZnSe / InSSe (8.9%), MoSe2 / SnSe2 (10.5%), B4C3 / MoS2 (12.3%) and beta-SnSe / HfS2 (14.3%). Therefore, the GeSe / SSnSe and GeSe / SeSnS heterojunctions both exhibit extremely high photocatalytic efficiency and are a very promising photocatalyst.

[0107] In summary, the present application discloses a Jauns type heterojunction material, the upper layer material of which is the 1T phase of GeSe, and the lower layer material is the 1T phase of SnSSe. According to the distance between the S atoms and Se atoms on both sides of the SnSSe layer and the GeSe layer, this heterojunction is divided into two configurations of GeSe / SSnSe and GeSe / SeSnS. The calculation of the density of states, the projected band structure, the work function and the band edge position shows that both configurations are direct Z-type heterojunctions, which have good photocatalytic redox ability. Among them, the STH efficiency of the GeSe / SSnSe heterojunction and the GeSe / SeSnS heterojunction is 17.3% and 16.4% respectively, which is significantly better than other heterojunctions, and has a broad application prospect in the field of photocatalysis. The present application uses VEST software to construct the heterojunction model, and then uses VASP software to simulate and calculate the electrical properties and photocatalytic performance of the heterojunction. VASP has excellent calculation efficiency and high calculation accuracy, and the calculation results are consistent with the experimental results. This method greatly reduces the research and development cost of new materials.

[0108] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A Janus heterojunction material, characterized in that: The upper layer material of the heterojunction material is a 1T phase of a single layer of germanium selenide GeSe, and the lower layer material is a 1T phase of a single layer of tin selenide SnSSe, and the middle layer tin atoms in the SnSSe are connected with different chalcogen atoms of sulfur or selenium on both sides.

2. The Janus heterojunction material of claim 1, wherein: The heterojunction material is a space structure of P6 / mmm, and the interlayer distance is 3. The Janus heterojunction material of claim 1, wherein: The heterojunction material is divided into two configurations of GeSe / SSnSe and GeSe / SeSnS according to the distance between the sulfur atoms and the selenium atoms on both sides of the SnSSe layer and the GeSe layer, the sulfur atoms of the SnSSe layer are on the side close to the GeSe layer in the GeSe / SSnSe configuration, and the selenium atoms of the SnSSe layer are on the side close to the GeSe layer in the GeSe / SeSnS configuration.

4. An artificial method of using the Janus heterojunction material of any one of claims 1 to 3 for photocatalytic water splitting, characterized by: The simulation method comprises the following steps: (1) constructing a heterojunction model on VESTA software, setting the lattice constants a, b and c to 3.74, 3.74 and 25 respectively, and establishing a heterojunction model with a layered structure; (2) exporting the heterojunction model constructed by VESTA to obtain a POSCAR file, using the Generalized Gradient Approximation (GGA) method, calling the PWA-GGA library to generate a POTCAR file, calling the VASPKIT software, inputting the "101-LR" instruction to automatically generate an INCAR file, then setting the EDIFF parameter in the INCAR file to -0.01, using the Gamma Scheme method, selecting K points as 9x9x1, and then obtaining a CONTCAR file through the Vienna Ab initio Simulation Package (VASP) for structure optimization; (3) performing self-consistent calculation on the heterojunction, using the input files in the structure optimization including CONTCAR, POTCAR and KPOINTS, renaming the CONTCAR file as POSCAR, calling the VASPKIT software, inputting the "101-ST" instruction to automatically generate the INCAR file, and then obtaining CHGCAR and WAVECAR files through VASP for static self-consistency; (4) calculating the state density of the heterojunction through the PBE functional, using the input files in the static self-consistency including POSCAR, POTCAR, INCAR, KPOINTS, CHGCAR and WAVECAR, setting the ICHARG parameter in the INCAR file to 11 and setting the appropriate energy band range, using VASP for simulation calculation, after the calculation is completed, calling the VASPKIT software, inputting the "111" instruction, obtaining the TDOS.dat file, importing the Origin software, and obtaining the total state density diagram calculated by the PBE functional; calling the VASPKIT software, inputting the "114" instruction, and then inputting the corresponding positions of the atoms, obtaining the PDOS.dat file, importing the Origin software, and obtaining the partial wave state density diagram calculated by the PBE functional; (5) The projection band structure, the static potential and the band edge position of the heterojunction are calculated by HSE06 hybrid function, the input files including POSCAR, POTCAR, CHGCAR and WAVECAR in the static self-consistency are extended, the VASPKIT software is called, the "101-H6" instruction is input to generate the INCAR file, then LORBIT=11 and LVHAR=.TRUE. are set in the INCAR file, the VASPKIT software is called, the "302" instruction is input to generate the KPATH.in file, then the VASPKIT software is called again, the "251-2-0.04-0.06" instruction is input to generate the KPOINTS file, VASP is used for simulation calculation, after the calculation is completed, the VASPKIT software is called, the "256" is input, the PBAND ELEMENTS.dat file is obtained, the HSE06 hybrid function calculated projection band structure diagram is obtained by importing the Origin software; the "grep E-fermi OUTCAR" is input in the command line, the Fermi level is obtained, then the qvasp software is called, the "qvasp-wkd" is input in the command line, then the corresponding Fermi level is input, then the "3" is input, the vline.dat file is obtained, the static potential diagram is obtained by importing the Origin software; the VASPKIT software is called and the "927" instruction is input, the band edge position of the heterojunction is obtained; (6) The optical absorption coefficient of the heterojunction is calculated, the input files including POSCAR, POTCAR, KPOINTS, CHGCAR and WAVECAR in the static self-consistency and the INCAR file in the structure optimization are extended, LOPTICS=.TRUE., NBANDS=96, NEDOS=2000 and CSHIFT=0.1 are set in the INCAR file, VASP is used for simulation calculation, after the calculation is completed, the VASPKIT software is called and the "711" instruction is input, the ABSORPTION.dat file is obtained, the optical absorption coefficient diagram of the heterojunction is obtained by importing the Origin software; (7) calculating the Gibbs free energy of the heterojunction in photocatalytic water splitting, first constructing an adsorption intermediate model of the heterojunction, then optimizing the structure of the adsorption intermediate, setting the ISIF parameter in the INCAR file in the structure optimization to 2, after the structure optimization is completed, inputting "cat OSZICAR|grep F|awk '{printf("%.3f\n", $5)}'|tail-1" in the command line to obtain the total energy of the system, then extending the input file including CONTCAR, INCAR, POTCAR and KPOINTS in the structure optimization, renaming the CONTCAR file as POSCAR, in addition to the adsorbed atoms, the atomic coordinates of the heterojunction in the POSCAR need to be fixed, setting POTIM=0.015, EDIFF=1E-7, ALGO=VeryFast in the INCAR file, using VASP to perform frequency calculation, after the calculation is completed, calling the VASPKIT software and inputting the "5-501-298.15" instruction to obtain the free energy correction value of the adsorption intermediate, then combining the total energy of the system to obtain the Gibbs free energy of the adsorption intermediate, according to the above steps, the Gibbs free energy of different adsorption intermediates is calculated, the data is further processed, and finally the Gibbs free energy change diagram of the hydrogen evolution reaction and the oxygen evolution reaction is obtained.

5. The simulation method in photocatalytic water splitting according to claim 4, characterized in that: The Gibbs free energy change ΔG in step (7) is calculated according to the following formula: AG = AE + AE zpe -TAS + AG pH + AG U wherein ΔE represents the total energy difference between the adsorbed and desorbed state, ΔE zpe represents the zero point energy difference, T represents the temperature, ΔS represents the entropy change, ΔG pH represents the free energy correction term considering the influence of the pH value, ΔG U corresponds to the free energy correction term for the electrode potential U.

6. The simulation method in photocatalytic water splitting according to claim 4, wherein: The Gibbs free energy change diagram of the hydrogen evolution reaction and the oxygen evolution reaction in step (7) is used to evaluate the photocatalytic redox ability of the Janus-type heterojunction material.

7. Use of the Janus heterojunction material according to any one of claims 1 to 3, characterized in that: The material is applied as a photocatalyst in a photocatalytic water splitting reaction.

8. Use according to claim 7, characterized in that: The internal electric field generated by the direct Z-type heterojunction structure of the material realizes efficient separation and migration of photo-generated carriers.

9. Use according to claim 7 or 8, characterized in that: The solar-to-hydrogen conversion efficiency of the Janus-type heterojunction material is calculated according to the following formula: wherein is the photon energy under AM1.5G solar flux, AG represents the potential difference for water splitting, having a value of 1.23 eV, AF represents the electrostatic potential difference between the SnSSe layer and the GeSe layer, E g represents the band gap of the heterojunction.

10. Use according to claim 9, characterized in that: When the Janus-type heterojunction material is in the GeSe / SSnSe configuration, the STH efficiency is 17.3%; when the Janus-type heterojunction material is in the GeSe / SeSnS configuration, the STH efficiency is 16.4%.

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