KR20220028808A - Hexagonal Ternary Sulfide Having Novel Structure And Photocatalysts Comprising The Same - Google Patents

Abstract

The present invention relates to ZnIn_2S_4, which is a hexagonal ternary sulfide having a novel structure that can be used as an anode active material in a water decomposition reaction and a photocatalyst comprising the same. According to the present invention, the hexagonal ternary sulfide has an energetically stable structure different from that of conventional ZnIn_2S_4, and exhibits semiconducting properties to have excellent photocatalytic properties, and thus can be usefully used as a photocatalyst for a water decomposition hydrogen generation reaction.

Description

Hexagonal Ternary Sulfide Having Novel Structure And Photocatalysts Comprising The Same

The present invention relates to ZnIn ₂ S ₄ , which is a hexagonal ternary sulfide having a novel structure that can be used as an anode active material in a water decomposition reaction, and a photocatalyst including the same.

The development of new energy sources to replace energy resources that are being depleted due to the steady increase in the use of fossil fuels is recognized as important. In particular, research to utilize solar energy, which is evaluated as an infinite energy source, in daily life through a commercial process, is being actively conducted in recent years. Although solar energy has a great advantage in preventing environmental pollution caused by the use of fossil fuels, it can be said that commercial application is in a very insignificant state due to significantly lower energy conversion efficiency and low economic feasibility compared to fossil fuels. The utilization of solar energy is largely possible through the development of solar cell materials that convert into electrical energy and photocatalytic materials that convert into chemical energy.

The photocatalytic reaction can be divided into two main categories: an organic matter decomposition reaction that is irreversible in the presence of oxygen and a water decomposition reaction that decomposes water to convert it into hydrogen and oxygen to produce chemical energy. A study of the water decomposition reaction using a photocatalyst was first reported by Fujishima and Honda in 1972. After the titanium dioxide (TiO ₂ )-based material was first reported, various materials have been developed and used for hydrogen production research. TiO ₂ has a band gap energy of 3.2 eV, so light corresponding to ultraviolet light is needed to excite electrons from a valence band to a conduction band. However, ultraviolet rays contained in sunlight itself are about 4%, which is undesirable in terms of the efficiency of using solar energy. Therefore, in order to improve TiO ₂ , attempts have been made to reduce the band gap by doping of various materials and to change the positions of the valence band and the conduction band. In order to solve this problem, attempts have been made to lower the band gap by doping metal ions, doping a non-metal material, or forming a composite material.

In addition to binary metal chalcogenides such as MoS ₂ for hydrogen evolution reactions, ternary and quaternary counterparts (CuInS ₂ , CuInSe ₂ , ZnIn ₂ S ₄ and Cu ₂ ZnSnS ₄ ) also have narrow band gaps (approximately 1-2 eV) and visible It has been proposed as a promising candidate as a photovoltaic material due to its high absorption in the light range. In particular, recent studies have shown that the hexagonal heterostructure of ZnIn ₂ S ₄ with polymeric carbon nitride, WO ₃ or In ₂ O ₃ , effectively minimizes the unwanted recombination of electron-hole pairs, resulting in a high photocatalyst for hydrogen evolution and CO ₂ reduction reactions. It has been reported to show activity.

On the other hand, polytypism is generally observed in various material systems. Materials having such polymorphism include, for example, graphite and diamond C ₆₀ as non-metals, and iron and manganese as metals. In addition, polymorphism can be found in materials such as TiO ₂ , rutile, anatase, and brookite. These polymorphs with the same stoichiometry, ie with the same repeating formula units, simply stack or combine differently to form various crystal symmetries and lattices with different physicochemical properties. In this context, polymorphic engineering, a sub-discipline of crystal engineering, can be used to tailor this structure-property relationship and design high-performance materials with target properties for technological advancement.

Controlled syntheses of cubic and hexagonal ZnIn2S4 nanostructures with different visible-light photocatalytic performance, Dalton Trans., 2011, 40, 2607

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconducting material having a novel structure that can be utilized as a photocatalyst for water decomposition and hydrogen generation reaction due to excellent electromagnetic and optical properties.

In order to achieve the above object,

The present invention is a crystal structure of ZnIn ₂ S ₄ , wherein a unit cell is composed of two S-In-S-In-S layers and one S-Zn-Zn-S layer, and the one S- The Zn-Zn-S layer provides a hexagonal ternary sulfide, disposed between the two S-In-S-In-S layers.

In addition, the present invention provides a photocatalyst comprising the hexagonal ternary sulfide.

The hexagonal ternary sulfide according to the present invention has an energetically stable structure different from that of conventional ZnIn ₂ S ₄ , and exhibits semiconducting properties and thus has excellent photocatalytic properties. there is.

1 shows the structures of the known ZnIn ₂ S ₄ polymorphs β, II _a and II _b .
FIG. 2 shows the structure of ZnIn ₂ S ₄ polymorph II _a ′, which is a hexagonal ternary sulfide according to the present invention, in comparison with the structure of the conventional polymorph II _a .
3 is a simulated XRD pattern for the polymorphs II _b , II _b @ICSD, II _a ′, II _a @DFT, II _a @EXPT, and II _a @ICSD of ZnIn ₂ S ₄ .
Fig. 4 shows the gradation/shading of color coding consistent with the intensity of the XRD peak shown in Fig. 3.
5 is a graph showing the phonon dispersion (left) of ZnIn ₂ S ₄ polymorph II _a ', a hexagonal ternary sulfide according to the present invention, and the corresponding total phonon state density (right) of the ZnIn ₂ S ₄ polymorph.
6 shows (a) COHP plots for Zn-S bonds, (b) Millikan charges calculated for II _a and (c) II _a ' and corresponding atomic structure models.
7 is a graph showing the result of estimating the optical band gap by calculating the linear optical absorption coefficient and calculating the linear slope extrapolated to the Tauc two-band model.
8 is a photocathode catalyst material (right ellipses: ZnIn2S4 polymorph; β , II _a ' and II based on the vacuum potential and relative potential (pH = 0) of a normal hydrogen electrode (NHE). _b ) and photoanodic catalyst materials (left ellipses: Rutile TiO ₂ , BiVO ₄ , δ-WO ₃ and γ-WO ₃ ) show schematic energy band alignment diagrams.

The technology to be described below may have various changes and may have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the technology described below to specific embodiments, and it should be understood to include all changes, equivalents, or substitutes included in the spirit and scope of the technology described below.

In one aspect, the present invention has a crystal structure of ZnIn ₂ S ₄ , wherein a unit cell is composed of two S-In-S-In-S layers and one S-Zn-Zn-S layer, The one S-Zn-Zn-S layer provides a hexagonal ternary sulfide disposed between the two S-In-S-In-S layers.

The S-In-S-In-S layer and the S-Zn-Zn-S layer may be coupled by a van der Walls force.

m1일 수 있다.The hexagonal ternary sulfide has a space group P

may be m1.

The hexagonal ternary sulfide may exhibit X-ray diffraction peaks including (005), (006), (102), (107) and (110) planes in powder X-ray diffraction (XRD) analysis.

The hexagonal ternary sulfide may have a calculated formation energy of -4.19eV/f.u.

The hexagonal ternary sulfide may have an optical band gap energy of 2.45 to 2.55 eV.

In another aspect, the present invention provides a photocatalyst comprising the hexagonal ternary sulfide.

In one specific embodiment, the photocatalyst may be a catalyst for water decomposition.

In another aspect, the present invention provides a Z-Scheme system including the photocatalyst as a hydrogen generating photoelectrode. The Z-scheme system is a system including a photoelectrode in which a catalyst for producing hydrogen and a catalyst for producing oxygen are combined.

In one specific embodiment, the Z-Scheme system may include a catalyst including at least one selected from the group consisting of TiO ₂ , BiVO ₄ and WO ₃ as an oxygen generating photoelectrode. More specifically, the TiO ₂ may include rutile TiO ₂ , and WO ₃ may include δ-WO ₃ or γ-WO ₃ .

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings in order to help the understanding of the present invention. However, the following examples are only provided for easier understanding of the present invention, and the contents of the present invention are not limited by the following examples.

Example 1: Existing hexagonal ternary sulfide structure review

Hexagonal polymorphs of ZnIn ₂ S ₄ are known to have various atomic and crystal structures, namely α, β, II _a and II _b . 1 shows the structure of the known polymorph of ZnIn ₂ S ₄ . In FIG. 1, (a) is β , (b) is II _a , and (c) is the structure of II _b polymorph, and unit cells are indicated by black squares. In Fig. 1, Zn, In and S atoms are indicated by white, gray and black circles, respectively.

m1인 II_a 및 도 1 (c)의 공간군이 P6₃mc인 갖는 II_b는 β의 경우와는 달리 7중 레이어 두 개가 적층되어 단위 셀을 구성하는 형태이다. II_a와 II_b는 중심 대칭과 회전 대칭의 보존 여부에 따라 형태가 달라진다. II_a는 중심 대칭이 보존된 두 개의 7중 레이어로 구성되며, II_b는 층 사이의 c-축을 따라 60°회전 대칭을 갖는 두 개의 7중 층으로 구성된다.As shown in FIG. 1 , the hexagonal polymorphs of ZnIn ₂ S ₄ mainly differ in the stacking order along the c-axis. The β polymorph in Fig. 1(a) is composed of a layer in the most basic repeating structural unit, S-Zn-S-In-S-In-S 7, along the c-axis separated by a van der Waals (vdW) gap. simply stacked. In the seven-layered layer, Zn atoms are tetrahedral bonded to four adjacent S atoms. Half of the In atom is bonded to the S atom and tetrahedron, and the other half is bonded to the S atom and octahedron. The space group of FIG. 1 (b) is P

Unlike the case of β , II _{a, which is m1, and II b ,} in which the space group of FIG. 1 (c) is P6 ₃ mc, forms a unit cell by stacking two 7-layer layers. _IIa and _IIb have different shapes depending on whether central and rotational symmetry are preserved. II _a consists of two 7-layers with preserved central symmetry, and II _b consists of two 7-layers with 60° rotational symmetry along the c-axis between the layers.

Example 2: DFT xc analysis

The crystal structure (II _a ') of ZnIn ₂ S ₄ , a hexagonal ternary sulfide according to the present invention, was analyzed through DFT exchange-correlation (xc) analysis.

The DFT calculation was performed using periodic boundary conditions using the projector augmented wave (PAW) method implemented in the Vienna ab initio Simulation Package (VASP) code. The Kohn-Sham orbit is extended on a plane wave basis set with a kinetic energy cutoff of 500 eV. The valence configurations of the Zn, In, and S PAW potentials are 4s ² 3d ¹⁰ , 4d ¹⁰ 5s ² 5p ¹ , and 3s ² 3p ⁴ , respectively. A Γ center k-point mesh with a grid spacing of 0.15 Å ⁻¹ is used to sample the Brillouin region. For the DFT xc function, a local-density approximation (LDA), Perdew, Burke, and Ernzehof (PBE) and Becke-Jones damped semi-empirical vdW to perform structural optimization of the ZnIn ₂ S ₄ polymorph. A generalized gradient approximation (GGA) resulting from a semiempirical vdW-corrected form (PBE + D3BJ) and a self-consistent vdW corrected GGA function (optB86b) were used. Electron band structure and chemical bond analysis were calculated using the hybrid DFT xc function by Heyd, Scuseria and Ernzerhof (HSE06) and optB86b xc function, respectively. To evaluate the energy stability of the ZnIn ₂ S ₄ polymorph, the formation energy (ΔH ^f _ZnIn2S4 , in eV/fu) for the bulk phases of Zn, In, and S was calculated as in Equation 1 below.

[Equation 1]

In Equation 1, E ^tot _ZnIn2S4 , E ^bulk _Zn , E ^bulk _In , and E ^bulk _S are the total energy of ZnIn ₂ S ₄ polymorph, bulk Zn, bulk In, and bulk S, respectively. Crystal orbital Hamilton population (COHP) and Mulliken charges were calculated using LOBSTER codes for chemical bonding analysis. Formally, the expected COHP (pCOHP) is considered as Equation 2 below.

[Equation 2]

In Equation 2 above, P ^(proj) _μυj and H ^(proj) _υμ (k) are the projected density matrix and projected Hamiltonian matrix elements for all bands j and all k-points, respectively. The delta function (δ) indicates that the density matrix has only non-zero values at a specific band energy ε _j (k).

The difference charge density (difference charge density) Δρ(r) _is used to specifically analyze the Zn-S bonding properties in the previously known polymorph IIa of ZnIn ₂ S ₄ and the polymorph II _a ' according to the present invention, and the following formula 3 is defined as

[Equation 3]

In Equation 3, ρ ^tot _ZnIn2S4 (r) is the total electron charge density of II _a and II _a ^' , and ρ ^U _ZnIn2S4 (r) and ρ ^L _ZnIn2S4 (r) are the nS bonds of II _a and II _a ^' , respectively. It's about the top and the bottom. To obtain the band offset and align the band edges of the stacked hexagonal structure of ZnIn ₂ S ₄ , first the 1s core level of Zn, conduction (ε _CBM ) and valence (ε _VBM ) band edges of the hexagonal ZnIn ₂ S ₄ polymorph was calculated using the HSE06 xc function. To obtain the absolute vacuum level in the bulk phase, the 1s core level of Zn was calculated in the bulk II _a ^′ and unrelaxed (001) surface.

The difference/offset of the core level Δε _c was obtained by comparing the Zn 1s core level of the bulk (ε ^bulk _c ) and the unrelaxed surface (ε ^slab _c ) of II _a ^' as shown in Equation 4 below.

[Equation 4]

Next, the ionization potential of the reference Zn 1s core level was calculated on the (001) non-relaxed surface (l ^slab _c ) with the energy required to bring electrons from the core level (ε ^slab _c ) to the vacuum level (V ^slab ). The ionization potential of the reference Zn 1s core level with respect to the bulk phase l ^bulk _c is calculated as in Equation 5 below.

[Equation 5]

Therefore, the hexagonal ZnIn ₂ S ₄ polymorphs can each be aligned at the absolute vacuum level. In addition, the effect of surface interaction was analyzed by adopting the continuum implicit solvation model implemented in the VASPsol code. To provide an estimate of the optical band gap, the optical absorption coefficient α(ω) was calculated in an independent particle approximation form without excitation and local effects, as shown in Equation 6 below.

[Equation 6]

In Equation 6, c and ω are the speed of light and the frequency of photons, and ε _re and ε _im are the real and imaginary parts of the dielectric function, respectively. Via a simple Tauc two-band model (no excitation effect), the optical band gap was approximated with an extrapolated linear slope along the onset of optical adsorption, as is commonly done in photoluminescence (PL) experiments.

The crystal structure and atomic geometry of hexagonal ZnIn ₂ S ₄ were systematically determined using various DFT xc functions (LDA, PBE, PBE+D3BJ and optB86b). The vdW-corrected optB86b xc function was found to be in best agreement with the available experimental lattice parameters (eg within 1% along the vdW c-axis direction). Data on the atomic structure and chemical thermodynamics of stacked hexagonal polymorphs were analyzed using the optB86b xc function.

Table 1 shows the optimized lattice parameters (a ₀ and c ₀ ), crystallographic space groups and formation energies per Formula Unit (fu) at 0 K of the layered hexagonal ZnIn ₂ S ₄ polymorph using the optB86b xc function ( Data for ΔH0K f, cf. Eq 1) are shown.

phase space group xc a ₀ (Å) c ₀ (Å) ΔH ^f _0K (eV/fu) β P3m1 optB86b 3.89 12.28 -4.22 II _a @DFT

m1P

m1 optB86b 3.96 24.74 -3.46 II _a ' P

m1 optB86b 3.90 24.76 -4.19 II _b P6 ₃ mc optB86b 3.89 24.58 -4.21

The lattice parameters a ₀ and c ₀ calculated using optB86b are 3.89 Å and 12.28 Å for β and 3.89 Å and 24.58 Å for II _b ), respectively, indicating that they are in good agreement with the experimental values within 2% error range. Confirmed. The calculated formation energies (ΔH ^f _0K ) were -4.22 eV/fu for β and -4.21 eV/fu for II _b , respectively, indicating that β and II _b polymorphs were considered to form competitively.

The crystallographic space groups determined for structurally optimized β and IIb are P3m1 and P6 ₃ mc, respectively, consistent with the standard inorganic crystal structure database (ICSD).

m1의 동일한 공간군을 유지하면서 IIa와는 완전히 새로운 층 구조를 형성한다. 이 새로운 구조의 II_a' 다형체는 2개의 In-S 5중 층과 한 개의 Zn-S 4중 층으로 구성된다. Zn 및 In PAW 전위에서 세미 코어 3d 궤도의 가능한 효과를 고려하기 위해 Hubbard U 보정을 포함하여 테스트한 결과 에너지적으로 선호되는 II_a'의 자발적 형성에 변화가 없음을 확인하였다. 또한 II_a 다형체의 상대적인 에너지 안정성을 조사하기 위해 II_a@DFT의 실험적 분수 좌표로 제한되는 원자를 사용하여 결정 격자의 최적화를 수행한 결과. IIa@DFT의 계산된 형성 에너지는 -3.46 eV/f.u.로 II_a'의 -4.19eV/f.u.보다 에너지적으로 덜 유리함을 확인하였다. On the other hand, as shown in FIG. 2, ZnIn ₂ S ₄ polymorph II _a ′, which is a hexagonal ternary sulfide according to the present invention, has II _a and P

While maintaining the same spatial group of m1, it forms a completely new layer structure with IIa. The II _a ' polymorph of this novel structure consists of two In-S quintuple layers and one Zn-S quaternary layer. Tests including Hubbard U correction to consider the possible effects of semi-core 3d orbitals on Zn and In PAW dislocations confirmed no change in the spontaneous formation of energetically favored _IIa '. Also, to investigate the relative energy stability of the II _a polymorph, we performed optimization of the crystal lattice using atoms constrained to the experimental fractional coordinates of II _a @DFT. The calculated formation energy of IIa@DFT is -3.46 eV/fu, confirming that it is less energetically favorable than _-4.19eV /fu of IIa'.

Example 3: X-ray diffraction analysis

The properties of the hexagonal ternary sulfide IIa' according to the present invention were analyzed through X-ray diffraction (XRD) analysis. 3 is a simulated XRD pattern for the polymorphs II _b , II _b @ICSD, II _a ′, II _a @DFT, II _a @EXPT, and II _a @ICSD of ZnIn ₂ S ₄ . Fig. 4 shows the gradation/shading of color coding consistent with the intensity of the XRD peak shown in Fig. 3.

As shown in FIG. 3 , it can be confirmed that the XRD plot of the new structure II _a ' does not match the XRD plot of the IIa structure. This can be seen more clearly in FIG. 4 . Through this, it can be confirmed that the polymorph of ZnIn ₂ S ₄ according to the present invention has a structure different from those of polymorphs of ZnIn ₂ S ₄ known in the prior art.

Example 4: Stability analysis

In order to evaluate the elastic stability of the polymorph of _{ZnIn 2} S ₄ according to the present invention, the bulk modulus ( B (GPa)), the shear modulus ( G (GPa)), the Young Mechanical modulus such as modulus ( E (GPa)) and position ratio (σ) were calculated by performing DFT calculations (using the optB86b xc function). The results are shown in Tables 2 and 3 below.

phase C ₁₁ C ₃₃ C ₄₄ C ₆₆ C ₁₂ C ₁₃ Spinel 119.94 128.323 24.68 33.07 53.81 45.42 α _One 96.22 61.81 11.19 25.85 44.50 25.88 β 98.46 61.50 9.88 28.06 42.33 26.45 II _a ' 90.66 40.20 7.19 25.53 39.60 17.81 II _a @DFT 59.44 5.72 2.01 11.09 37.26 24.97 II _b 96.10 61.58 10.43 25.90 44.30 26.15

phase B (GPa) G (GPa) E (GPa) σ Born-Huang criteria Spinel 73.06 30.76 80.98 0.32 Satisfy α _One 47.70 18.52 49.18 0.33 Satisfy β 47.91 18.16 48.34 0.33 Satisfy II _a ' 37.17 14.96 39.55 0.32 Satisfy II _a @DFT - - - - Not Satisfy II _b 47.73 17.98 47.91 0.33 Satisfy

From Tables 2 and 3, it can be seen that all hexagonal ZnIn ₂ S ₄ polymorphs except for II _a @DFT are elastically stable.

Next, the phonon band structure and related phonon state density of ZnIn ₂ S ₄ polymorph II _a ', a hexagonal ternary sulfide according to the present invention, were calculated using the density function perturbation theory implemented in the Quantum-Espresso package. The results are shown in FIG. 5 .

As shown in FIG. 5 , it can be confirmed that the ZnIn ₂ S ₄ polymorph II _a ' structure of the hexagonal ternary sulfide according to the present invention is elastically stable and dynamically stable. In contrast, a negative phonon mode was found in the calculated density of phonon states of II _a (shown in gray in Fig. 3 ), which is attributed to the In and Zn atoms closest to the vdW gap.

Example 5: Chemical Binding Analysis

Mulliken charges for II _a and II _a ' structures were calculated using COHP and LOBSTER codes. The COHP plot for the Zn-S bond is shown in FIG. 6 , the calculated Millikan charge for II _a and II _a ' and the corresponding atomic structure model.

In Fig. 6, (a) is the COHP for Zn-S bonds (i.e., bonds that contribute to structural reorganization) in II _a @DFT (red line) and II _a ' (blue line), and (b) is II _a @ The calculated Millikan charge and the corresponding atomic structure model of DFT, (c) is the calculated Millikan charge of IIa' and the corresponding atomic structure model. The difference charge density Δρ(r) is shown in FIGS. 6(b) and (c), respectively, where the electron charge depletion and accumulation are shown in cyan and yellow, respectively, and the isotropic value is 0.002e/Å ³ am. Zn, In and S atoms are indicated by white, gray and black circles, respectively.

Looking at the COHP of Figure 6 (a), it can be confirmed the characteristics of the covalent strength (covalent strength) of the Zn-S bond. Chemical bonding properties of Zn-S in II _a @DFT (red line) and II _a ' (blue line) appear similar overall, but unlike II _a ', II _a Zn-S near 0 to -3 eV It shows the strong antibonding properties of S. In terms of ionicity, the millicon charge shown in FIGS. 6 (b) and (c) indicates that the ionic charge of II _a ' is more ionic than the ionic charge of II _a , and this ionic property is the stability of the entire crystal of II _a ' It can be seen that this increases.

The positive charge of the Zn cation of II _a ' is +1.25e, and it can be seen that the positive charge of the Zn cation of II _a +1.23e is slightly higher than that of +1.23e. Similarly, the negative charge of the S anion adjacent to II _a ' is -1.17e, indicating more negative charge characteristics than the negative charge -1.03e of the S anion of II _a .

Example 6: Electronic Structure Analysis

The optical spacing was estimated by calculating the linear optical absorption coefficient and calculating the extrapolated linear slope with the Tauc twoband model. 7 shows the results.

As shown in FIG. 7 , in (a), the direct band gap of II _a ' was found to be 0.95 ev, but the direct band gap of II _a did not appear. As in (b), the linear optical coefficient α was calculated for the indirect bandgap IIa′ structure and the Tauc expression for the indirect bandgap material (αhν) 1/2 was plotted as a function of hν. Through the extrapolated linear slope, the optical bandgap of II _a ′ was confirmed to be 2.50 eV.

Example 7: Analysis of photocatalytic performance in the Z-Scheme system

The photocatalytic performance of the Z-Scheme system was studied to confirm the suitability of the ZnIn ₂ S ₄ polymorph, which is a hexagonal ternary sulfide according to the present invention, for a photocatalytic reaction including water decomposition.

8 is a photocathode catalyst material (right ellipses: ZnIn2S4 polymorph; β , II _a ' and II based on the vacuum potential and relative potential (pH = 0) of a normal hydrogen electrode (NHE). _b ) and photoanodic catalyst materials (left ellipses: Rutile TiO ₂ , BiVO ₄ , δ-WO ₃ and γ-WO ₃ ) show schematic energy band alignment diagrams. The horizontal line represents the redox potential of water and the carbon dioxide (CO ₂ ) reduction potential. The ionization potentials and band gap values of Rutile TiO ₂ , BiVO ₄ , δ-WO ₃ , and γ-WO ₃ were referred to as known values. The theoretical band edges for the ZnIn2S4 polymorph were determined using a surface slab considering the implicit solvation model. The hydrogen reduction potential of a normal hydrogen electrode (NHE) is 0 eV at pH = 0, and the redox potential of water in a vacuum is -4.44 eV (reduction) and -5.67 eV (oxidation), respectively. In the implicit solvation model, the ionization potentials of β , II _a ' and II _b are calculated to be 5.01 eV, 4.90 eV and 5.01 eV, respectively, which on average are 0.35 eV lower than the case without solvent effect. That is, considering the solvation effect, the ionization potentials of β , IIa′ and IIb are _5.36eV , _5.26eV and 5.36eV, respectively.

As shown in Fig. 5, the water reduction potential is located within the band gaps of β , II _a ' and II _b and the oxidation potential is located just below the valence band edge. As _a result, ZnIn2S4 polymorph IIa' according to the present invention can be used as an effective photocathode material to promote the photoreduction of water. In particular, since the reduction potential of CO ₂ is between the band edges of II _a ', ZnIn ₂ S ₄ polymorph II _a ', which is a hexagonal ternary sulfide according to the present invention, is not only a water decomposition reaction but also a CO ₂ reduction reaction (CO ₂ It can be seen that it can also be used for other important photocatalytic reactions such as RR).

In addition, the hexagonal ternary sulfide of ZnIn ₂ S ₄ polymorph II _a ′ according to the present invention can be utilized in a Z-scheme system for water decomposition when paired with a suitable photoanode catalyst material. As shown in the left ellipse of FIG. 8 , the conduction band edges of Rutile TiO ₂ , BiVO ₄ , δ-WO ₃ and γ-WO ₃ are -4.80, -4.90 eV, -4.58 eV and -4.64 eV, respectively. Since the valence band edges are -7.83 eV, -7.30 eV, -7.53 eV and -7.54 eV, respectively, when they are combined, a Z-scheme system for water decomposition photoreaction can be constructed.

The description of the present invention stated above is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. There will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (10)

With the crystal structure of ZnIn ₂ S ₄ ,
A unit cell is composed of two S-In-S-In-S layers and one S-Zn-Zn-S layer,
wherein the one S-Zn-Zn-S layer is disposed between the two S-In-S-In-S layers. The method of claim 1,
A hexagonal ternary sulfide, characterized in that the S-In-S-In-S layer and the S-Zn-Zn-S layer are coupled by a van der Walls force. The hexagonal ternary sulfide has a space group P

A hexagonal ternary sulfide, characterized in that m1. The method of claim 1,
The hexagonal ternary sulfide is characterized in that it exhibits X-ray diffraction peaks comprising (005), (006), (102), (107) and (110) planes in powder X-ray diffraction (XRD) analysis, Hexagonal ternary sulfide. The method of claim 1,
The hexagonal ternary sulfide is a hexagonal ternary sulfide, characterized in that the calculated formation energy is -4.19eV/fu. The method of claim 1,
The hexagonal ternary sulfide has an optical band gap energy of 2.45 to 2.55 eV, characterized in that the hexagonal ternary sulfide. A photocatalyst comprising the hexagonal ternary sulfide according to claim 1 . 8. The method of claim 7,
The photocatalyst is a catalyst for water decomposition reaction, a photocatalyst. A Z-Scheme system comprising the photocatalyst according to claim 7 as a hydrogen generating photoelectrode. 10. The method of claim 9,
The Z-Scheme system is TiO ₂ , BiVO ₄ and WO ₃ It characterized in that it comprises a photocatalyst including any one selected from the group consisting of oxygen generating photoelectrode, Z-Scheme system.

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