Water-splitting photocatalytic sheet, method for producing the same, and water-splitting device

Abstract

To achieve a photocatalytic sheet that can be provided easily and simply, and a water-splitting device applicable to hydrogen production.SOLUTION: A water-splitting photocatalytic sheet (1) has a mixed particle layer (3) on a substrate sheet (2). The mixed particle layer (3) includes a structure in which hydrogen-producing photocatalyst particles (4), oxygen-producing photocatalyst particles (5), and conductive material particles (6) are dispersed, with the conductive material particles (6) being interposed between the hydrogen-producing photocatalyst particles (4) and the oxygen-producing photocatalyst particles (5).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water-splitting photocatalyst sheet, a method for producing the same, and a water-splitting device. [Background technology]

[0002] From the viewpoint of curbing global warming and breaking away from dependency on fossil resources, technology is being considered for producing hydrogen by splitting water using solar energy with photocatalysts. A photocatalyst sheet is known as such a photocatalyst, in which a structure in which conductive material particles are interposed between photocatalyst particles for generating hydrogen and photocatalyst particles for generating oxygen in the presence of an organic medium such as acrylic resin (so-called Z-scheme photocatalyst) is fixed on a sheet-shaped substrate. Such a photocatalyst sheet is manufactured by fixing a mixed composition of the above-mentioned organic medium and particles on a substrate by coating or screen printing (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-74706 [Patent Document 2] Patent Publication No. 2022-58196 [Non-patent literature]

[0004] [Non-Patent Document 1] Qian Wang et. al.,Printable Photocatalyst Sheets Incorporating a Transparent Conductive Mediator for Z-Scheme Water Splitting, Joule 2, p.2667-2680, December 19, 2018 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned technology for producing hydrogen using photocatalysts requires that a large number of photocatalyst sheets be placed in an environment exposed to sunlight, and there is a demand for the photocatalyst sheets to be made easier to manufacture.

[0006] An object of one aspect of the present invention is to provide a photocatalyst sheet that can be easily provided and a water splitting device that can be applied to hydrogen production. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following aspects.

[0008] [1] A water-splitting photocatalyst sheet comprising a mixed particle layer in which two or more types of particles selected from photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, and which satisfies one of the following two conditions: (Condition 1) The mixed particle layer includes two types of particles selected from the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles dispersed therein, and a single particle layer of the remaining type of particle is directly superimposed on the mixed particle layer. (Condition 2) The mixed particle layer contains three types of particles, namely, the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles, dispersed therein.

[0009] [2] The water-splitting photocatalyst sheet according to [1], wherein the remaining type of particles under condition 1 are conductive material particles.

[0010] [3] The water-splitting photocatalyst sheet according to [1] or [2], wherein the conductive material particles contain one or both of reduced graphene oxide and carbon nanotubes.

[0011] [4] The water-splitting photocatalyst sheet according to any one of [1] to [3], further comprising a base sheet carrying on its surface the laminate of the mixed particle layer and the monoparticle layer of condition 1, or the mixed particle layer of condition 2.

[0012] [5] The water-splitting photocatalyst sheet according to [4], wherein the base sheet comprises one or more sheets selected from the group consisting of a fibrous sheet, a porous sheet and an adhesive sheet.

[0013] [6] The water-splitting photocatalyst sheet according to any one of [1] to [5], wherein the mixed particle layer under condition 2 has a thickness of 0.1 to 200 μm.

[0014] [7] A method for producing a water-splitting photocatalyst sheet, comprising a step of filtering a suspension in which two or more types of particles selected from among photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, to produce a mixed particle layer on a filter medium in which two or more types of particles selected from among photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, and which satisfies either of the following two conditions: (Condition A) The step of generating the mixed particle layer is a step of filtering a suspension in which two types of particles selected from the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles are dispersed, The method further comprises a step of directly superposing the resulting mixed particle layer on a single particle layer of the remaining type of particle. (Condition B) The step of producing the mixed particle layer is a step of filtering a suspension in which three types of particles, the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles, are dispersed.

[0015] [8] The method for producing a water-splitting photocatalyst sheet according to [7], wherein the remaining type of particles under condition A are conductive material particles.

[0016] [9] The method for producing a water-splitting photocatalyst sheet according to [7] or [8], wherein the conductive material particles include one or both of reduced graphene oxide and carbon nanotubes.

[0017]

[10] A roll-shaped fibrous sheet is used as the filter medium, The step of generating the mixed particle layer is a step of filtering the suspension on the continuously supplied fibrous sheet. A method for producing a water-splitting photocatalyst sheet according to any one of [7] to [9].

[0018]

[11] A method for producing a water-splitting photocatalyst sheet according to any one of [7] to

[10] , further comprising a step of contacting the laminate of the mixed particle layer and the single particle layer under condition A, or the mixed particle layer under condition B, with an adhesive surface of an adhesive sheet to support the laminate on the adhesive sheet.

[0019]

[12] The method for producing a water-splitting photocatalyst sheet described in

[11] , wherein the supporting step is a step of supporting the laminate of the mixed particle layer and the single particle layer under condition A, or the mixed particle layer under condition B, on the adhesive surface of the roll-shaped adhesive sheet, which is continuously supplied, by contacting the laminate.

[0020]

[13] The method for producing a water-splitting photocatalyst sheet according to any one of [7] to

[12] , wherein water is used as a dispersion medium for the suspension.

[0021]

[14] A water-splitting photocatalyst sheet that splits water into hydrogen and oxygen under light irradiation; a water splitting module that holds the water splitting photocatalyst sheet in a state in which water can be supplied to the water splitting photocatalyst sheet; a water supply mechanism for supplying water to the water-splitting photocatalyst sheet held in the water-splitting module; a gas recovery mechanism for recovering one or both of hydrogen gas and oxygen gas generated by the water-splitting photocatalyst sheet held in the water-splitting module; A water-splitting device, wherein the water-splitting photocatalyst sheet is the water-splitting photocatalyst sheet according to any one of [1] to [6].

[0022]

[15] The water splitting module comprises: A substrate portion supporting the water splitting photocatalyst sheet; a light-transmitting plate disposed opposite the substrate with the water-splitting photocatalyst sheet interposed therebetween; a water supply port for supplying water between the light-transmitting plate and the substrate portion; an exhaust port for discharging gas between the light-transmitting plate and the substrate portion; The water splitting apparatus according to

[14] , wherein water is supplied from the water supply port between the light-transmitting plate and the water-splitting photocatalyst sheet. Effect of the Invention

[0023] According to one aspect of the present invention, a photocatalyst sheet that can be easily provided can be realized, and a water decomposition device that can be applied to hydrogen production can be easily provided. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a water-splitting photocatalyst sheet according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a scanning electron microscope (SEM) photograph of a mixed particle layer in a water-splitting photocatalyst sheet according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a schematic configuration of a water-splitting photocatalyst sheet according to another embodiment of the present invention. [Figure 4] 1 is a diagram showing a schematic configuration of a water splitting apparatus according to one embodiment of the present invention. [Diagram 5] 5 is a plan view of a water splitting module in the water splitting apparatus of FIG. 4. [Figure 6] FIG. 6 is a cross-sectional view of the water splitting module of FIG. 5 taken along line AA. [Figure 7] FIG. 2 is a diagram showing a schematic diagram of the steps of the method for producing the photocatalyst sheet of Example 1. [Figure 8] FIG. 2 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 1. [Figure 9] FIG. 2 is a diagram showing a schematic diagram of the steps of the method for producing the photocatalyst sheet of Example 2-1. [Figure 10] FIG. 13 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 2-1. [Figure 11]FIG. 13 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 2-2. [Figure 12] FIG. 2 is a diagram showing a schematic diagram of the steps of the method for producing the photocatalyst sheet of Example 3-1. [Figure 13] FIG. 13 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 3-1. [Figure 14] FIG. 13 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 3-2. [Figure 15] FIG. 13 is a graph showing the relationship between the reaction system pressure and the initial rate of hydrogen production for the photocatalyst sheet of Example 3-2. [Figure 16] FIG. 13 is a graph showing the relationship between the reaction system pressure and the initial rate of hydrogen production for the photocatalyst sheet of Example 4-1. [Figure 17] FIG. 13 is a graph showing the relationship between the reaction system pressure and the initial rate of hydrogen production for the photocatalyst sheet of Example 4-2. [Figure 18] FIG. 5 is a diagram showing a schematic diagram of the steps of the method for producing the photocatalyst sheet of Example 5-1. [Figure 19] FIG. 13 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 5-1. [Figure 20] FIG. 13 is a graph showing the amount of hydrogen produced per hour in a reaction system of 5 kPaA for the photocatalyst sheet of Example 5-2. [Figure 21] FIG. 2 is a photograph showing an oblique image of the surface of the photocatalyst sheet of Example 1 observed with an optical microscope. [Figure 22] FIG. 2 is a photograph showing an image of the surface of the photocatalyst sheet of Example 1 viewed from above, observed with an optical microscope. [Diagram 23] FIG. 2 is a photograph of a secondary electron image taken with a scanning electron microscope (SEM) of a first portion of a cross section of the photocatalyst sheet of Example 1. [Figure 24] FIG. 2 is a photograph of a backscattered electron image taken by SEM of a first portion of a cross section of the photocatalyst sheet of Example 1. [Diagram 25] FIG. 25 is a photograph showing an enlarged view of part A surrounded by a dashed line in FIG. 24. [Figure 26] FIG. 25 is a photograph showing an enlarged view of part B surrounded by a dashed line in FIG. 24. [Figure 27] FIG. 25 is a photograph showing an enlarged view of part C surrounded by a dashed line in FIG. 24. [Figure 28] FIG. 4 is a photograph of a secondary electron image taken by SEM of a second portion of the cross section of the photocatalyst sheet of Example 1. [Figure 29] FIG. 4 is a photograph of a backscattered electron image taken by SEM of a second portion of the cross section of the photocatalyst sheet of Example 1. [Diagram 30] FIG. 13 is a photograph of a secondary electron image taken by SEM of a third portion of the cross section of the photocatalyst sheet of Example 1. [Diagram 31] FIG. 13 is a photograph of a backscattered electron image taken by SEM of a third portion of the cross section of the photocatalyst sheet of Example 1. [Diagram 32] FIG. 13 is a photograph showing an oblique image of the surface of the photocatalyst sheet of Example 5 observed with an optical microscope. [Diagram 33] FIG. 13 is a photograph showing an image of the surface of the photocatalyst sheet of Example 5 viewed from above, observed with an optical microscope. [Diagram 34] FIG. 13 is a photograph of a secondary electron image taken by SEM of a first portion of a cross section of the photocatalyst sheet of Example 5. [Diagram 35] FIG. 13 is a photograph of a backscattered electron image taken by SEM of a first portion of a cross section of the photocatalyst sheet of Example 5. [Diagram 36] FIG. 36 is a photograph showing an enlarged view of part D surrounded by a dashed line in FIG. 35. [Figure 37] FIG. 36 is a photograph showing an enlarged view of a part E surrounded by a dashed line in FIG. 35. [Figure 38] FIG. 36 is a photograph showing an enlarged view of part F surrounded by a dashed line in FIG. 35. [Figure 39] FIG. 13 is a photograph of a secondary electron image taken by SEM of a second portion of the cross section of the photocatalyst sheet of Example 5. [Diagram 40]FIG. 13 is a photograph of a backscattered electron image taken by SEM of a second portion of the cross section of the photocatalyst sheet of Example 5. [Diagram 41] FIG. 13 is a photograph of a secondary electron image taken by SEM of a third portion of the cross section of the photocatalyst sheet of Example 5. [Diagram 42] FIG. 13 is a photograph of a backscattered electron image taken by SEM of a third portion of the cross section of the photocatalyst sheet of Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the symbol "to" means a range including the numerical values ​​before and after it.

[0026] [Water-splitting photocatalyst sheet] A water-splitting photocatalyst sheet according to an embodiment of the present invention includes a mixed particle layer in which two or more types of particles selected from hydrogen generating photocatalyst particles, oxygen generating photocatalyst particles, and conductive material particles are dispersed.

[0027] In the water-splitting photocatalyst sheet, the mixed particle layer may be distributed in various ways within the range in which the effect of this embodiment can be obtained. From this viewpoint, the mixed particle layer may be distributed, for example, approximately uniformly in the spreading direction of the water-splitting photocatalyst sheet, and more specifically, may be continuous, may be intermittently present like an island structure, or may spread in a complex or irregular shape such as a fractal or mesh shape.

[0028] In addition, the mixed particle layer may have a substantially uniform thickness within the range where the effect of this embodiment can be obtained, or may have a thickness that changes continuously or intermittently. In addition, when the mixed particle layer is intermittently present in the spreading direction of the water-splitting photocatalyst sheet, each of the mixed particle layers may have a different thickness within the range where the effect of this embodiment can be obtained, or may be present at different positions in the thickness direction of the water-splitting photocatalyst sheet.

[0029] [Mixed particle layer] The mixed particle layer may be a layer in which the photocatalyst particles for hydrogen generation and the photocatalyst particles for oxygen generation are dispersed, or may be a layer in which the photocatalyst particles for oxygen generation and the conductive material particles are dispersed, or may be a layer in which the conductive material particles and the photocatalyst particles for hydrogen generation are dispersed. Alternatively, the mixed particle layer may be a layer in which three types of particles, namely, the photocatalyst particles for hydrogen generation, the photocatalyst particles for oxygen generation and the conductive material particles, are dispersed, or may be a layer in which three or more types of particles, namely, the photocatalyst particles for hydrogen generation, the photocatalyst particles for oxygen generation, the conductive material particles and other particles, are dispersed. "Dispersed" in the mixed particle layer means a state in which each of the particles constituting the mixed particle layer is substantially uniformly present in the mixed particle layer. Hereinafter, the particles constituting the mixed particle layer will be described.

[0030] <Photocatalyst particles for hydrogen generation> The photocatalyst particles for hydrogen generation are photocatalyst materials that can generate hydrogen by reducing water with excited electrons generated by irradiation with visible light. For the photocatalyst particles for hydrogen generation, particulate photocatalyst materials that are known to have such a function can be used.

[0031] The photocatalyst particles for hydrogen generation are semiconductor particles having an optical band gap. The photocatalyst particles for hydrogen generation generate excited electrons at the electron acceptor level present in the conduction band or band gap in the photocatalyst particles for hydrogen generation, and generate excited holes at the electron donor level present in the valence band or band gap. The photocatalyst particles for hydrogen generation are photocatalyst materials in which the excited electrons and excited holes can respectively reduce and oxidize the reaction target. The electron acceptor level present in the conduction band or band gap of the photocatalyst particles for hydrogen generation is, for example, more negative than the reduction potential of water (0V vs. NHE (standard hydrogen electrode potential) at pH=0). The electron donor level present in the valence band or band gap of the photocatalyst particles for hydrogen generation is, for example, more positive than the conduction band position of the photocatalyst particles for oxygen generation described later. The photocatalyst particles for hydrogen generation may be of one type or more.

[0032] The photocatalyst particles for generating hydrogen are, for example, particles having a composition represented by the following formula (I). M a Ti b O c S d (I)

[0033] In formula (I), M is one or more selected from Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Y. Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm are lanthanoid (Ln) elements, but these Ln elements and Y elements have a weak electronic effect on the hybrid orbital consisting of Ti, O, and S in the structure of M2Ti2O5S2, and in the case of lanthanoid elements, the outermost shell electrons do not change and only the number of electrons in the inner 4f orbital changes, so the effect of the Ln element entering the structure is small. For the above reasons, photocatalytic activity of almost the same level can be expected regardless of the use of any Ln element. Therefore, it is considered that any of the elements in the present invention can be applied as the Ln element, but from the viewpoint that the crystal particles obtained by adding the element tend to have a small particle size and the surface area of ​​the photocatalyst is easily secured, one or more of Gd, Sm, Er, Dy, Y, Nd, Ho, etc. are preferred, and Gd, Sm, Er, Dy, and Y are more preferred.

[0034] In formula (I), a is 1.7 to 2.3, b is 2, c is 4.7 to 5.3, and d is 1.7 to 2.3. For example, when the number of moles of Ti, b, is set to 2 as a standard, the molar ratios of a, c, and d can be a=1.7 to 2.3, c=4.7 to 5.3, and d=1.7 to 2.3. For the number of moles of Ti, b=2, a, c, and d are preferably a=1.8 to 2.2, c=4.8 to 5.2, and d=1.8 to 2.2, and more preferably a=1.85 to 2.15, c=4.85 to 5.15, and d=1.85 to 2.15.

[0035] Examples of photocatalyst particles for generating hydrogen represented by the above formula (I) include Sm2Ti2O5S2, Gd2Ti2O5S2 and Y2Ti2O5S2.

[0036] In addition, examples of photocatalyst particles for hydrogen generation include Rh-doped SrTiO3 (SrTi 1-x Rh x O3:x=0.002~0.1), Ir-doped SrTiO3 (SrTi 1-x Ir x O3:x=0.002~0.1), Cr-doped SrTiO3 (SrTi 1-x Cr x O3:x=0.002~0.1), Cr and Ta doped SrTiO3 (SrTi 1-x―y Cr x Ta y O3: x = 0.002-0.1, y = 0.002-0.1), and La- and Rh-doped SrTiO3 (Sr 1-x La x Ti 1―y Rh y The perovskite-type SrTiO3 doped with at least one transition metal or noble metal, such as SrTiO3: x = 0.005 to 0.2, y = 0.005 to 0.2, is included.

[0037] Examples of photocatalyst particles for hydrogen generation include Cu2O, CuO, CaFe2O4, NiO, Bi2O3, BiOX (X=Cl, Br, I), and GaN-ZnO solid solution.

[0038] Additionally, examples of photocatalyst particles for hydrogen generation include oxynitrides or nitrides containing transition metals or typical metals, such as LaTiO2N, BaTaO2N, SrTaO2N, CaTaO2N, BaNbO2N, TaON, Ta3N5, and Ge3N4.

[0039] Additionally, examples of photocatalyst particles for hydrogen generation include CuGaS2, CuInS2, Cu(Ga,In)S2, CuGaSe2, CuInSe2, Cu(Ga,In)Se2, and Cu2ZnSnS4 (CZTS).

[0040] Examples of photocatalyst particles for hydrogen generation include copper complex sulfide selenides containing typical metals such as Ga, In, and Al, such as Cu2ZnSn(S,Se)4.

[0041] Examples of photocatalyst particles for hydrogen generation include oxysulfur selenides such as La5Ti2CuS5O7, La5Ti2AgS5O7, La5Ti2CuSe5O7, and La5Ti2AgSe5O7. These are La5Ti2Cu 1-x Ag x S 5-y Se y Also included is a composition represented by the general formula O7 (0≦x, y≦1).

[0042] The average primary particle diameter of the photocatalyst particles for hydrogen generation is preferably 2000 nm or less, and more preferably 1000 nm or less. By having such a small particle diameter, the surface area per unit weight of the photocatalyst particles for hydrogen generation that can come into contact with water is increased. This increases the reduction reaction sites of water, and as a result, highly efficient hydrogen generation is possible. More preferably, the average primary particle diameter of the photocatalyst particles for hydrogen generation is 30 nm or more.

[0043] <Photocatalyst particles for oxygen generation> The oxygen generating photocatalyst particles are photocatalyst materials that can generate oxygen by oxidizing water with excited holes generated by irradiation with visible light. For the oxygen generating photocatalyst particles, particulate photocatalyst materials that are known to have such a function can be used.

[0044] The photocatalyst particles for generating oxygen are semiconductor particles having an optical band gap. When the photocatalyst particles for generating oxygen absorb visible light, excited electrons are generated in the conduction band and excited holes are generated in the valence band in the photocatalyst particles for generating oxygen. The photocatalyst particles for generating oxygen are photocatalyst materials in which the excited electrons and excited holes can respectively reduce and oxidize the reaction target. The valence band of the photocatalyst particles for generating oxygen is, for example, more positive than the oxidation potential of water (+1.23 V vs. NHE (standard hydrogen electrode potential) at pH = 0). In addition, the conduction band of the photocatalyst particles for generating oxygen is, for example, more negative than the valence band position of the photocatalyst particles for generating hydrogen. The photocatalyst particles for generating oxygen may be of one type or more.

[0045] Examples of photocatalyst particles for oxygen production include oxynitrides or nitrides containing transition metals or main group metals, examples of which include BiVO4, X-doped BiVO4 (X=Mo, W), SnNb2O6, WO3, Bi2WO6, Fe2TiO5, Fe2O3, Bi2MoO6, GaN-ZnO solid solution, LaTiO2N, BaTaO2N, SrTaO2N, CaTaO2N, BaNbO2N, TaON, Ta3N5 and Ge3N4.

[0046] The photocatalyst particles for generating oxygen are preferably one or more selected from the group consisting of BiVO4, X-doped BiVO4 (X=Mo, W), SnNb2O6, WO3, Bi2WO6, Bi2MoO6, Fe2O3, GaN-ZnO solid solution, LaTiO2N, BaTaO2N, BaNbO2N, TaON, Ta3N5 and Ge3N4. The photocatalyst particles for generating oxygen are more preferably one or more selected from the group consisting of BiVO4, Mo-doped BiVO4, WO3, SnNb2O6, Bi2WO6, BaTaO2N and Fe2O3.

[0047] The average primary particle diameter of the photocatalyst particles for generating oxygen is preferably 5000 nm or less, more preferably 2000 nm or less, and even more preferably 1000 nm or less. By having such a small particle diameter, the surface area per unit weight of the photocatalyst particles for generating oxygen that can come into contact with water is increased. This increases the number of oxidation reaction sites for water, and as a result, highly efficient oxygen generation is possible. More preferably, the average primary particle diameter of the photocatalyst particles for generating oxygen is 30 nm or more.

[0048] The average primary particle diameter of photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation can be defined as the average value, based on the circular approximation, of 50 crystal particles randomly selected when observed at a magnification of 40,000 times using a scanning electron microscope (SEM, for example, "SU-8220" manufactured by Hitachi High-Technologies Corporation).

[0049] The ratio of the photocatalyst particles for generating hydrogen and the photocatalyst particles for generating oxygen in the water splitting photocatalyst sheet may be appropriately determined based on the strength of activity for the water splitting reaction. For example, the ratio may be a ratio that can realize the total splitting of water at H2:O2=2:1.

[0050] <Co-catalyst> Although the photocatalyst particles for hydrogen generation and the photocatalyst particles for oxygen generation each exhibit sufficient photocatalytic activity by themselves, they are preferably used together with a co-catalyst. The co-catalysts include an oxidation reaction co-catalyst (oxygen generation side) and a reduction reaction co-catalyst (hydrogen generation side), and it is preferable to use one or both of these supported on one or both of the corresponding photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation.

[0051] (Oxidation reaction promoter) Examples of the oxidation reaction promoter include metals of Groups 2 to 14 of the periodic table, intermetallic compounds of the metals, alloys, or oxides, composite oxides, nitrides, oxynitrides, sulfides, oxysulfides, or mixtures thereof.

[0052] The term "intermetallic compound" refers to a compound formed from two or more metal elements, and the atomic ratio of the components constituting the intermetallic compound is not necessarily stoichiometric, but has a wide composition range. The term "oxides, composite oxides, nitrides, oxynitrides, sulfides, and oxysulfides of these" refers to metals in Groups 2 to 14 of the periodic table, intermetallic compounds of these metals, or oxides, composite oxides, nitrides, oxynitrides, sulfides, and oxysulfides of alloys. The term "mixtures of these" refers to a mixture of two or more of the compounds exemplified above.

[0053] The oxidation reaction promoter is preferably a metal such as Mg, Ti, Mn, Fe, Co, Ni, Cu, Ga, Ru, Rh, Pd, Ag, Cd, In, Ce, Ta, W, Ir, Pt or Pb, or an oxide or composite oxide thereof. The oxidation reaction promoter is more preferably a metal such as Mn, Co, Ni, Ru, Rh or Ir, or an oxide or composite oxide thereof, and further preferably Ir, MnO, MnO2, Mn2O3, Mn3O4, CoO, Co3O4, CoxOy, CoOOH, NiCo2O4, RuO2, Rh2O3 and IrO2.

[0054] The amount of metal carried by the oxidation reaction promoter is usually 0.01% by mass or more and 5% by mass or less, preferably 4% by mass or less, more preferably 3% by mass or less, and 0.05% by mass or more, based on the oxygen generating photocatalyst particles (100% by mass). The "amount of metal carried" refers to the amount of metal element in the supported promoter.

[0055] (Reduction reaction promoter) Examples of the reduction reaction promoter include metals of Groups 3 to 13 of the periodic table, intermetallic compounds of the metals, alloys, or oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, nitrides, or mixtures thereof. "Oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, and nitrides of the metals of Groups 3 to 13 of the periodic table, intermetallic compounds of the metals, and oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, or nitrides of alloys.

[0056] The reduction reaction promoter is preferably Pt, Pd, Rh, Ru, Ni, Au, Fe, NiO, RuO2, IrO2, Rh2O3, Cr-Rh composite oxide, core-shell type Rh / Cr2O3, Pt / Cr2O3, or the like.

[0057] The metal loading of the reduction reaction promoter is usually 0.01 mass % or more and 20 mass % or less, preferably the upper limit is 15 mass % or less, and more preferably the upper limit is 10 mass % or less, based on the hydrogen generation photocatalyst particles (100 mass %).

[0058] <Conductive material particles> The conductive material particles may be formed of a semiconductor component such as a nanocarbon material. For example, the conductive material particles may have a Fermi level that is more negative than the electronic energy level at the top of the valence band of the hydrogen generating photocatalyst particles and more positive than the electronic energy level at the bottom of the conduction band of the oxygen generating photocatalyst particles. Such conductive material particles can store excited holes generated in the valence band of the hydrogen generating photocatalyst particles and excited electrons generated in the conduction band of the oxygen generating photocatalyst particles, and enable the movement of holes and / or electrons between the hydrogen generating photocatalyst particles and the oxygen generating photocatalyst particles. When the conductive material particles have such a specific Fermi level, the photolysis of water by the water splitting photocatalyst sheet can be significantly improved by a mechanism described later. In addition, the Fermi level of the conductive material particles can also be expressed using electric potential as a reference instead of the electronic energy level, in which case the conductive material particles may have a Fermi level at a potential that is more negative than the top of the valence band of the hydrogen generation photocatalyst particles and more positive than the conduction band edge of the oxygen generation photocatalyst particles.

[0059] The conductive material particles may be one or more types, examples of which include reduced graphene oxide (rGO) and carbon nanotubes (CNT), and may include one or both. Both rGO and CNT have high electrical conductivity, and are therefore preferred from the viewpoint of increasing the efficiency of hydrogen production by the water splitting photocatalyst sheet.

[0060] The particle diameter of the conductive material particles is preferably, for example, 300 nm or more and 50 μm or less in major axis, and more preferably 1 μm or more and 50 μm or less. The particle diameter of the conductive material particles within this range is preferable from the viewpoint of enhancing the connectivity between the hydrogen generation photocatalyst particles and the oxygen generation photocatalyst particles by the conductive material particles, and is preferable from the viewpoint of realizing highly efficient water splitting (hydrogen generation) by the water splitting photocatalyst sheet. For the particle diameter of the conductive material particles, for example, the particle diameters (e.g., major axis) of 30 randomly selected conductive material particles when observing the cross section of the water splitting photocatalyst sheet with a scanning electron microscope (e.g., SU-8220, manufactured by Hitachi High-Technologies Corporation) at a magnification of 200,000 times can be obtained, and the average value of these can be used.

[0061] The conductivity of the conductive material particles is 0.1Scm -1 The volume resistivity of the conductive material particles is preferably, for example, 10 Ωcm or less.

[0062] The content of the conductive material particles in the water-splitting photocatalyst sheet may be appropriately determined, for example, from the viewpoint of satisfying the desired electrical connection between the hydrogen generation photocatalyst particles and the oxygen generation photocatalyst particles, and from the viewpoint of fully realizing light absorption by the hydrogen generation photocatalyst particles and the oxygen generation photocatalyst particles. From the viewpoint of enabling such highly efficient water splitting, the content of the conductive material particles in the water-splitting photocatalyst sheet is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 5% by mass or less, based on the total content of the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles.

[0063] Furthermore, the content of the conductive material particles in the water-splitting photocatalyst sheet is preferably high from the viewpoint of allowing the conductive material particles to also serve as a binder for the water-splitting photocatalyst sheet. From this viewpoint, the content of the conductive material particles in the water-splitting photocatalyst sheet is preferably 0.1 mass% or more, and more preferably 0.3 mass% or more, based on the total content of the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles.

[0064] The content of conductive material particles contained in the water-splitting photocatalyst sheet can be determined by measuring the water-splitting photocatalyst sheet with X-ray photoelectron spectroscopy (XPS). For example, if the conductive material particles are CNTs, the content can be determined from the amount of carbon-carbon double bonds by measuring the water-splitting photocatalyst sheet with X-ray photoelectron spectroscopy (XPS).

[0065] <Other particles> In the water-splitting photocatalyst sheet, particles other than the above-mentioned particles may be further dispersed within a range in which the effects of the present invention can be obtained. For example, the water-splitting photocatalyst sheet may further dispersed particles that function as a filler that enhances the adhesion between the mixed particle layer and the substrate sheet described later. Examples of such particles include glass frit and inorganic oxide fine particles. Examples of glass frit include low-melting glass frit. Examples of inorganic oxide fine particles include silica, alumina, ZrO2 and TiO2 fine particles. The average primary particle size of the particles is preferably small from the viewpoint of suppressing the influence on the photocatalytic activity and the diffusion of the generated gas in the water-splitting photocatalyst sheet, as well as from the viewpoint of increasing the wettability of the photocatalyst sheet and suppressing bubble adsorption, and is preferably, for example, 100 nm or less.

[0066] [Conditions that the water-splitting photocatalyst sheet according to the present invention must satisfy] The water-splitting photocatalyst sheet according to this embodiment satisfies either of the following two conditions.

[0067] <Condition 1> One of the two conditions (condition 1) is that "the water-splitting photocatalyst sheet includes a mixed particle layer in which two types of particles selected from photocatalyst particles for generating hydrogen, photocatalyst particles for generating oxygen, and conductive material particles are dispersed, and a single particle layer of the remaining type of particle directly superimposed on the mixed particle layer."

[0068] In a water-splitting photocatalyst sheet that satisfies condition 1, a configuration may occur in which conductive material particles are interposed between the hydrogen generating photocatalyst particles and the oxygen generating photocatalyst particles at the interface between the mixed particle layer and the single particle layer that are directly overlapped with each other. Therefore, the water-splitting photocatalyst sheet may function as a so-called Z-scheme photocatalyst. From the viewpoint of increasing the contact of the conductive material particles with both catalyst particles, it is preferable that the mixed particle layer in condition 1 is a layer in which the hydrogen generating photocatalyst particles and the oxygen generating photocatalyst particles are dispersed, and the single particle layer is a layer of conductive material particles.

[0069] <Condition 2> The other of the two conditions (condition 2) is that "the water-splitting photocatalyst sheet includes a mixed particle layer containing three types of particles dispersed therein: photocatalyst particles for generating hydrogen, photocatalyst particles for generating oxygen, and conductive material particles."

[0070] In a water-splitting photocatalyst sheet that satisfies condition 2, a configuration may occur in which conductive material particles are interposed between the hydrogen generating photocatalyst particles and the oxygen generating photocatalyst particles in both the spreading direction and the thickness direction of the mixed particle layer. Therefore, the mixed particle layer may function as a so-called Z-scheme photocatalyst. From the viewpoint of obtaining a higher water resolution ability, it is preferable that the water-splitting photocatalyst sheet satisfies condition 2.

[0071] In condition 2, if the mixed particle layer is too thin, the water decomposition ability by the photocatalytic reaction may be insufficient, and if it is too thick, the strength of the mixed particle layer may decrease. From the viewpoint of enhancing the water decomposition ability, the thickness of the mixed particle layer in condition 2 is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. Also, from the viewpoint of enhancing the strength of the mixed particle layer, the thickness of the mixed particle layer in condition 2 is preferably 300 μm or less, and more preferably 200 μm or less.

[0072] In addition, as described above, when a sufficient amount of conductive material particles is contained, the conductive material particles further exert the function of a binder in the mixed particle layer. Therefore, in the mixed particle layer of Condition 2, the content of the conductive material particles is preferably 0.1 mass% or more, and more preferably 0.3 mass% or more, based on the total content of the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles.

[0073] Also, from the viewpoint of electrical conductivity, it is preferable to form the mixed particle layer from only three types of particles, namely, photocatalyst particles for generating hydrogen carrying a co-catalyst, photocatalyst particles for generating oxygen carrying a co-catalyst, and conductive material particles, dispersed therein, and it is more preferable to sprinkle or coat the other particles mentioned above after formation and disperse them in the mixed particle layer.

[0074] [Other configurations] The water-splitting photocatalyst sheet may further include other configurations than the mixed particle layer and the monoparticle layer described above within the scope of obtaining the effects of the present invention. For example, the water-splitting photocatalyst sheet may further include a substrate sheet carrying the mixed particle layer or the monoparticle layer in condition 1, or the mixed particle layer in condition 2, on its surface. The substrate sheet may be appropriately selected from the scope capable of carrying the mixed particle layer or the monoparticle layer on its surface. For example, the substrate sheet may be one or more sheets selected from the group consisting of a fibrous sheet, a porous sheet, and an adhesive sheet.

[0075] The material of the substrate sheet is not limited, and may be an organic material or an inorganic material. The substrate sheet may be a commercially available product that exhibits the desired function. Examples of fibrous sheets include filter paper, nonwoven fabric sheets, glass fiber sheets, and glass paper. Examples of porous sheets include porous films made of resins such as ultra-high molecular weight polyethylene or polytetrafluoroethylene (PTFE). Examples of adhesive sheets include known adhesive sheets having an adhesive layer on one or both main surfaces of a resin sheet. These sheets can be subjected to hydrophilic treatment such as silica coating, hydrophilic polymer coating, or plasma treatment from the viewpoint of increasing the wettability of the photocatalyst sheet, suppressing bubble adsorption, and increasing the filtration efficiency during film formation. In addition, these sheets may be subjected to a conductive treatment from the viewpoint of imparting the same function as the conductive material particles. Alternatively, the above-mentioned sheet may be a sheet in which the fibers of the fibrous sheet themselves are conductive. Examples of sheets in which the fibers are conductive include carbon cloth and carbon paper.

[0076] The water-splitting photocatalyst sheet may be further supported by a supporting member such as a glass plate or a metal plate.

[0077] [Specific aspects] The water-splitting photocatalyst sheet according to the present embodiment will be described below with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of a water-splitting photocatalyst sheet according to one embodiment of the present invention. Fig. 2 shows a photograph of a mixed particle layer in a water-splitting photocatalyst sheet according to one embodiment of the present invention taken with a scanning electron microscope (SEM).

[0078] 1, the water-splitting photocatalyst sheet 1 is composed of a base sheet 2 and a mixed particle layer 3 supported on the base sheet 2. The base sheet 2 is, for example, an adhesive sheet, and an adhesive layer on a transparent resin film is adhered opposite to the mixed particle layer 3.

[0079] In the mixed particle layer 3, hydrogen generating photocatalyst particles 4, oxygen generating photocatalyst particles 5, and conductive material particles 6 are dispersed. The hydrogen generating photocatalyst particles 4 have a reduction reaction promoter 7 on their surfaces, and the oxygen generating photocatalyst particles 5 have an oxidation reaction promoter 8 on their surfaces. The conductive material particles 6 are, for example, reduced graphene oxide (rGO) particles. The mixed particle layer 3 has a substantially constant thickness, for example, about 0.1 to 300 μm. From the viewpoint that the mixed particle layer sufficiently receives light and does not transmit light, it is considered that this thickness may be a thickness of several particles. Therefore, although the thickness depends on the particle diameters of each photocatalyst particle (for oxygen generation and hydrogen generation) and the conductive material particle, it is usually preferable that the thickness is 1 μm or more, and more preferably 2 μm or more. On the other hand, from the viewpoint of reducing unnecessary particles (where light does not reach), although it depends on the diameter of each particle as described above, it is preferable that the thickness is 200 μm or less.

[0080] In the mixed particle layer 3, the above three types of particles are dispersed, and as shown in Fig. 1 and Fig. 2, the mixed particle layer 3 includes a state in which conductive material particles 6 are interposed between hydrogen generating photocatalyst particles 4 carrying a co-catalyst 7 and oxygen generating photocatalyst particles 5 carrying a co-catalyst 8, that is, a so-called Z-scheme photocatalyst structure. As is clear from Fig. 2, the mixed particle layer 3 has an extension in both the extension direction and the thickness direction of the base sheet 2. Therefore, the mixed particle layer 3 includes the Z-scheme photocatalyst structure everywhere in both the extension direction and the thickness direction. Note that in the form shown in Fig. 1, only the above three types of particles are dispersed in the mixed particle layer 3.

[0081] Alternatively, the configuration of a water-splitting photocatalyst sheet according to one embodiment of the present invention can be shown diagrammatically in Fig. 3. As shown in Fig. 3, a water-splitting photocatalyst sheet 10 is configured by stacking a base sheet 2, a monoparticle layer 12, and a mixed particle layer 11 in this order. The mixed particle layer 11 is a layer in which only hydrogen generating photocatalyst particles 4 carrying a co-catalyst 7 and oxygen generating photocatalyst particles 5 carrying a co-catalyst 8 are dispersed. The monoparticle layer 12 is a layer in which only conductive material particles 6 are aggregated.

[0082] The mixed particle layer 11 and the single particle layer 12 are directly overlapped with each other. Therefore, as shown in Fig. 3, at the interface between the two layers, a state in which the conductive material particles 6 are interposed between the hydrogen generation photocatalyst particles 4 and the oxygen generation photocatalyst particles 5, that is, a so-called Z-scheme photocatalyst structure, can be formed.

[0083] [Major effects] The water-splitting photocatalyst sheet 1 includes a mixed particle layer 3 in which only three types of particles, namely, photocatalyst particles 4 for generating hydrogen, photocatalyst particles 5 for generating oxygen, and conductive material particles 6, are dispersed. Thus, the water-splitting photocatalyst sheet 1 can have a Z-scheme photocatalyst structure at any point in the spreading direction and thickness direction of the mixed particle layer 3. This allows for higher activity in water splitting by the photocatalyst. Note that "substantially" means that it may include particles that inevitably enter the mixed particle layer 3 during manufacturing, such as when another layer, such as another protective layer, is provided on the mixed particle layer 3.

[0084] The water-splitting photocatalyst sheet 10 includes a structure in which a mixed particle layer 11 in which hydrogen generating photocatalyst particles 4 and oxygen generating photocatalyst particles 5 are dispersed is overlapped with a monoparticle layer 12 of conductive material particles 6. Thus, the water-splitting photocatalyst sheet 10 can have a Z-scheme photocatalyst structure at various places in the interface between the mixed particle layer 11 and the monoparticle layer 12. Thus, high activity of the water-splitting reaction by the photocatalyst can be obtained. In addition, since the monoparticle layer 12 is a layer of conductive material particles 6, the Z-scheme photocatalyst structure can be formed more at the above interface.

[0085] Both of the water-splitting photocatalyst sheets 1 and 10 include a base sheet 2 that supports the above-mentioned layers. Therefore, deformation or collapse of the above-mentioned layers is easily suppressed. Furthermore, the base sheet 2 is an adhesive sheet. Therefore, the supported layer (mixed particle layer 3 or single particle layer 12) is supported more firmly, and the positions between the particles in each layer are more easily maintained. Therefore, it is advantageous from the viewpoint of maintaining the above-mentioned layers and maintaining high activity of the water-splitting reaction by the catalyst.

[0086] Moreover, the conductive material particles 6 are made of reduced graphene oxide. Therefore, the conductive material particles 6 are made of an aggregate of fine fibrous particles. Therefore, the conductive material particles 6 are likely to be interposed between the hydrogen generation photocatalyst particles 4 and the oxygen generation photocatalyst particles 5, and are likely to be entangled with both particles. This is advantageous from the viewpoint of increasing the strength of the mixed particle layer 3, or the contact strength between the mixed particle layer 11 and the single particle layer 12.

[0087] The thickness of the mixed particle layer 3 is 0.1 to 300 μm. As described above, the mixed particle layer 3 may have a Z-scheme photocatalytic structure anywhere in its spreading direction and thickness direction. The structure of the mixed particle layer 3 in the spreading direction and thickness direction is easily maintained by the fixation by the base sheet 2 and the holding action between particles by the conductive material particles 6. This is therefore advantageous from the viewpoint of maintaining the layer structure of the mixed particle layer 3 and the high activity of the water splitting reaction by the catalyst.

[0088] [Method for producing water-splitting photocatalyst sheet] A manufacturing method for a water-splitting photocatalyst sheet according to one embodiment of the present invention includes a step of filtering a suspension in which two or more types of particles selected from among photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, to produce a mixed particle layer on a filter material in which two or more types of particles selected from among photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed.

[0089] The dispersion medium in the suspension is not limited, and examples thereof include organic solvents and aqueous media. The aqueous medium is water or an aqueous solution mainly composed of water. The solute of the aqueous solution may be any water-soluble component, and examples of the solute include water-soluble salts and water-soluble organic compounds.

[0090] Among these, using water as the dispersion medium of the suspension allows the suspension to be produced cheaply and easily even if it is a low-concentration suspension, and is also preferable from the viewpoint of the dispersibility of the above-mentioned particles.

[0091] The concentration of the suspension can be appropriately determined within a range in which the particles, which are the dispersoid, are uniformly dispersed in the dispersion medium. It can also be appropriately determined from the viewpoint that the dispersoid is accumulated on the filter medium in a uniformly dispersed state by filtration, which will be described later. From these viewpoints, the concentration of the dispersoid in the suspension may be, for example, 1 to 20 mg / mL.

[0092] When the suspension is filtered, the particles in the suspension are dispersed and accumulate in a layer on the filter media. This accumulation becomes the mixed particle layer described above.

[0093] The filter medium used for filtering the suspension is a member capable of accumulating particles in the suspension in layers by filtration, and only needs to have an appropriate mesh size and liquid permeability to realize such filtration. The filter medium may be the above-mentioned base sheet, and may be the base sheet. Examples of the filter medium include ordinary paper filter paper, glass fiber filter paper, glass filter, metal mesh, and the above-mentioned fibrous sheet and porous sheet.

[0094] A filter medium usually has uniform liquid permeability macroscopically, but may have uneven liquid permeability microscopically. Therefore, when the mixed particle layer is formed intermittently or unevenly in the spreading direction of the mixed particle layer, the thickness of the mixed particle layer may also have unevenness. For this reason, the thickness of the mixed particle layer may be, for example, 3 μm or more, 5 μm or more, 10 μm or more, or 100 μm or less, 90 μm or less, or 80 μm or less.

[0095] The mixed particle layer may be distributed almost uniformly at a specific position in the thickness direction of the water-splitting photocatalyst sheet, but the filter medium may have an affinity for various particles in this embodiment depending on the material. Therefore, microscopic deviation of the mixed particle layer in the thickness direction of the mixed particle layer may occur. For this reason, in the water-splitting photocatalyst sheet, the mixed particle layer may be unevenly distributed on the surface side of the water-splitting photocatalyst sheet (the surface and its vicinity), or may be unevenly distributed inside the surface of the water-splitting photocatalyst sheet.

[0096] The method for producing a water-splitting photocatalyst sheet satisfies the following condition A or B.

[0097] <Condition A> Condition A is that "the step of producing a mixed particle layer is a step of filtering a suspension in which two types of particles selected from photocatalyst particles for generating hydrogen, photocatalyst particles for generating oxygen, and conductive material particles are dispersed, and further includes a step of directly overlapping the resulting mixed particle layer with a monoparticle layer of the remaining type of particle."

[0098] A manufacturing method that satisfies condition A can manufacture a water-splitting photocatalyst sheet that satisfies the above-mentioned condition 1. In the manufacturing method that satisfies condition A, the step of preparing the monoparticle layer is not limited, and a commercially available product may be used if one is available, but it is preferable to prepare the monoparticle layer by preparing a suspension and filtering it, similar to the mixed particle layer, from the viewpoint of being able to appropriately design the monoparticle layer.

[0099] The particles constituting the monoparticle layer in condition A may be any of the above three types, but by using conductive material particles as the particles, a water-splitting photocatalyst sheet is obtained in which a mixed particle layer in which hydrogen generation photocatalyst particles and oxygen generation photocatalyst particles are dispersed and a monoparticle layer made of conductive material particles are directly superimposed. Therefore, using conductive material particles as the remaining type of particle in condition A is preferable from the viewpoint of increasing the contact of the three types of particles at the interface between the mixed particle layer and the monoparticle layer and forming more Z-scheme photocatalyst structures at the interface.

[0100] <Condition B> Condition B is that "the process of generating a mixed particle layer is a process of filtering a suspension in which three types of particles, namely, photocatalyst particles for generating hydrogen, photocatalyst particles for generating oxygen, and conductive material particles, are dispersed."

[0101] In the manufacturing method that satisfies the condition B, a water-splitting photocatalyst sheet that satisfies the above-mentioned condition 2 can be manufactured.

[0102] In both conditions A and B, using either or both of rGO and CNT as the conductive material particles is preferable from the viewpoint of increasing the efficiency of hydrogen production by the water-splitting photocatalyst sheet. In addition, the conductive material particles of both rGO and CNT are relatively easy to bridge between particles, so more Z-scheme photocatalyst structures are easily formed, and it is also advantageous from the viewpoint of increasing the shape retention (bonding strength between particles) of the water-splitting photocatalyst sheet.

[0103] The manufacturing method of the water-splitting photocatalyst sheet according to the present embodiment may further include other steps than the step of producing the mixed particle layer described above, within the scope of obtaining the effects of the present invention. For example, the manufacturing method may further include a step of supporting the laminate of the mixed particle layer and the single particle layer according to condition A, or the mixed particle layer according to condition B, on the adhesive surface of the adhesive sheet by abutting the laminate. The adhesive sheet described above in the description of the water-splitting photocatalyst sheet may be used as the adhesive sheet.

[0104] In the manufacturing method of the water-splitting photocatalyst sheet according to the present embodiment, it is also possible to manufacture the water-splitting photocatalyst sheet all at once. For example, in the manufacturing method, a roll-shaped fibrous sheet may be used as a filter medium, and in the step of generating a mixed particle layer, the suspension may be filtered with the continuously supplied fibrous sheet. Such a step can be performed by a conveying device that unfolds the fibrous sheet from the roll of the fibrous sheet, and a suspension supplying device that supplies the above-mentioned suspension at a specific speed onto the conveyed fibrous sheet. In this case, the continuously conveyed fibrous sheet carrying the mixed particle layer is cut as is or to an appropriate size to obtain a water-splitting photocatalyst sheet in which the mixed particle layer is supported on the fibrous sheet.

[0105] In addition, in the manufacturing method of the water-splitting photocatalyst sheet according to the present embodiment, the step of supporting the laminate or mixed particle layer on the adhesive sheet may be a step of supporting the laminate of condition A or the mixed particle layer of condition B on the adhesive sheet by contacting it with the adhesive surface of the continuously supplied roll-shaped adhesive sheet. According to this configuration, it is possible to continuously support the laminate or mixed particle layer on the continuous adhesive sheet. Such a step can be carried out, for example, by supplying a suspension onto a continuously transported porous conveyor belt to form a laminate or mixed particle layer, contacting an adhesive sheet with its adhesive surface facing the laminate or mixed particle layer on the conveyor belt while running in parallel, and pressing the overlapping conveyor belt and adhesive sheet with a roller as necessary. In this case, the adhesive sheet carrying the laminate or mixed particle layer that is continuously transported can be used as is or cut to an appropriate size to obtain a water-splitting photocatalyst sheet in which the mixed particle layer or the mixed particle layer and the single particle layer are supported on the adhesive sheet.

[0106] In addition, if there is an operation to enhance the photocatalytic activity of the components constituting the water-splitting photocatalyst sheet, the operation may be performed on the suspension. For example, if the photocatalytic activity of the particles constituting the water-splitting photocatalyst sheet is enhanced by irradiation with light, the manufacturing method of the water-splitting photocatalyst sheet according to this embodiment may further include a step of irradiating the suspension before filtration with light that enhances such photocatalytic activity. This step may be a step of irradiating the mixed particle layer, etc. with light in a part or all of the transport path of the base sheet when a mixed particle layer, etc. is formed on a base sheet that is continuously transported.

[0107] [Major effects] In the method for producing a water-splitting photocatalyst sheet according to the present embodiment, a mixed particle layer is generated on a filter medium by filtering the above-mentioned suspension. Thus, a layer in which the particles in the suspension are uniformly dispersed can be formed on the filter medium.

[0108] When the suspension is used as a paint and a mixed particle layer is produced by coating, the drying time is long, and layer separation due to an undesirable difference in sedimentation velocity may occur. In addition, impurities dissolved in the suspension may remain in the layer to be formed. In addition, if the slurry concentration of the suspension is low, uneven coating is likely to occur when the suspension is used as a paint. In the manufacturing method of the water-splitting photocatalyst sheet according to the present embodiment described above, the dispersion medium is removed in a short time by filtration, so the layer separation described above is unlikely to occur, and the impurities dissolved in the suspension pass through the particle layer as filtrate by filtration, and the photocatalyst particles can be uniformly developed even if the suspension is low in concentration. Therefore, according to the manufacturing method according to the present embodiment, a water-splitting photocatalyst sheet can be manufactured by an extremely simple operation of filtering a suspension of photocatalyst particles. In addition, this manufacturing method is simpler than filtering the suspension, preparing a coating liquid again using the filtered particles, and applying it to a substrate such as a substrate sheet to form a sheet.

[0109] In particular, since it is sufficient for the suspension to disperse the dispersoid, there is no need to increase the dispersion concentration, and therefore water can be suitably used as the dispersion medium for the suspension.

[0110] In addition, in the manufacturing method of the water-splitting photocatalyst sheet according to the present embodiment, a laminated water-splitting photocatalyst sheet is obtained, which is a mixed particle layer of two of the above three types of particles and a monoparticle layer of the remaining type of particle. By using conductive material particles as the particles of the monoparticle layer, more Z-scheme photocatalyst structures are easily formed at the interface between the two layers, and by using one or both of reduced graphene oxide and carbon nanotubes as the conductive material particles, more Z-scheme photocatalyst structures are easily formed at the interface.

[0111] Furthermore, the above-mentioned manufacturing method includes a step of contacting the laminate or mixed particle layer obtained by filtration with the adhesive surface of an adhesive sheet, so that these layers can be supported on the adhesive sheet. Therefore, the photocatalyst layer can be easily supported on the substrate sheet while the layer structure in the spreading direction and thickness direction is substantially maintained.

[0112] The manufacturing method according to this embodiment is applicable to a roll-shaped base sheet, and is suitable for enlarging the size of a water-splitting photocatalyst sheet by continuously supplying a suspension onto a roll-shaped fibrous sheet as described above and filtering it, or by continuously abutting a layer of photocatalyst particles against the adhesive surface of a roll-shaped adhesive sheet, or for mass production of water-splitting photocatalyst sheets of desired dimensions by cutting the continuous sheet.

[0113] In addition, regardless of which of the water-splitting photocatalyst sheets is used under the conditions described above, a further layer such as a protective layer or a hydrophilic layer can be formed by further flowing a liquid containing some kind of particle (e.g., silica particles) on top of the mixed particle layer or single particle layer substantially formed by filtration and filtering it.

[0114] [Water splitting device] The water splitting photocatalyst sheet according to this embodiment is applied to a water splitting device. The configuration of a water splitting device according to one embodiment of the present invention is shown in schematic form in Fig. 4. As shown in Fig. 4, a water splitting device 50 has three water splitting units 51, and a water supply mechanism 52 and a gas recovery mechanism 53 that are common to the three water splitting units 51.

[0115] The water splitting unit 51 has a base 54 and a plurality of water splitting modules 55 arranged on the base 54. The base 54 is a plate-like member having a substantially square shape when viewed in a plane, and is arranged at an angle to a horizontal plane at a desired angle, for example, 30°. The water splitting modules 55 are arranged in four rows on the base 54, and for example, as shown in the figure, a module group consisting of eight water splitting modules 55 in total, four in the horizontal direction and two in the vertical direction, is arranged in two vertical stages. In other words, 16 water splitting modules 55 are arranged in four rows on one base 54.

[0116] The water supply mechanism 52 is a mechanism for supplying water to the water splitting modules 55. The water supply mechanism 52 includes, for example, a main pipe through which a desired amount of water is supplied, four branch pipes branching off from the main pipe corresponding to the rows of water splitting modules 55 on the stand 54, and branch pipes further branching off from the branch pipes of each row and connected to the water splitting modules 55 of each row. In this manner, in this embodiment, the water supply mechanism 52 is configured to supply a desired amount of water to each of the water splitting modules 55.

[0117] The gas recovery mechanism 53 is a mechanism for recovering gas generated in the water splitting modules 55. The gas recovery mechanism 53 includes, for example, branch pipes connected to each of the water splitting modules 55, four branch pipes arranged corresponding to the rows of the water splitting modules 55 on the stand 54, and a main pipe to which the four branch pipes are connected. Each of the branch pipes in each row is connected to the branch pipe in the corresponding row. In this manner, in this embodiment, the gas recovery mechanism 53 is configured to recover gas generated from each of the water splitting modules 55 throughout the water splitting apparatus 50.

[0118] A plan view of the water splitting module 55 in the water splitting device 50 is shown in FIG. 5. A cross section of the water splitting module 55 in FIG. 5 cut along line AA is shown in FIG. 6. As shown in FIGS. 5 and 6, the water splitting module 55 has a substantially square shape when viewed in plan, and includes a plate-like substrate 61, a frame 62 arranged around the substrate 61, a seal 63 arranged inside the frame 62, a water splitting photocatalyst sheet 1 arranged inside the seal 63, a light-transmitting plate 64 arranged on the seal 63 inside the frame 62, a water supply port 65 opening at one end when viewed in plan through the substrate 61, and an exhaust port 66 opening at the other end when viewed in plan through the substrate 61.

[0119] In the cutting direction of the cross section, the substrate portion 61 and the sealing portion 63 are in close contact with each other, and the sealing portion 63 and the light-transmitting plate 64 are in close contact with each other. In this state, the light-transmitting plate 64 is disposed inside the water-splitting module 55 with a small gap 67 (for example, several hundred μm or less) between it and the water-splitting photocatalyst sheet 1. The water-splitting module 55 is disposed at an angle with one end side (the water supply port side) facing down. The inclination angle θ is the same as that of the base 54, for example, 30°. The water supply port 65 is connected to a branch pipe of the water supply mechanism 52, and the exhaust port 66 is connected to a branch pipe of the gas recovery mechanism 53.

[0120] Water from the water supply port 65 is introduced into the gap 67 via the water-splitting photocatalyst sheet 1. As a result, water from the water supply port 65 is supplied in the form of a film between the light-transmitting plate 64 and the water-splitting photocatalyst sheet 1. When the water-splitting photocatalyst sheet 1 is irradiated with light (e.g., sunlight) through the light-transmitting plate 64, the water is decomposed by the photocatalytic action, and hydrogen gas and oxygen gas are generated. The generated gas floats in the water filling the gap 67, reaches the exhaust port 66, and is discharged from the exhaust port 66 to the outside of the module. Water is consumed in accordance with the generation of gas, and water is supplied from the water supply port 65 to replenish the consumed water (e.g., to maintain a constant water level in the gap 67).

[0121] The generated gas is introduced through the main pipe of the gas recovery mechanism 53 into a gas purification mechanism, such as a gas separation device that separates hydrogen gas and oxygen gas, and a gas drying device that removes moisture from the gas. In this way, the final product, hydrogen gas or oxygen gas, is obtained from the water by the water decomposition device 50.

[0122] The water decomposition apparatus 50 may be an apparatus that produces only one of hydrogen gas and oxygen gas as a final product from the generated gas. For example, oxygen gas may be discharged to the outside during the gas purification process, and only hydrogen gas may be the final product. Alternatively, the water decomposition apparatus 50 may store the generated gas (a mixed gas of hydrogen gas and oxygen gas) in a container as the final product, and the hydrogen gas and oxygen gas may be separated from the mixed gas in a different facility.

[0123] [Major effects] As described above, the water splitting device according to the present embodiment includes the water splitting photocatalyst sheet according to the present embodiment described above, a water splitting module, a water supply mechanism, and a gas recovery mechanism, and is configured to supply water to the water splitting photocatalyst sheet under light irradiation conditions and recover the generated gas. Therefore, water can be split into hydrogen gas and oxygen gas by photocatalytic reaction, and the water splitting photocatalyst sheet can be easily manufactured, so that such a water splitting device can be more easily configured.

[0124] In addition, in this embodiment, the water splitting module is supplied with water from the water supply port to the water splitting photocatalyst sheet on the substrate part so that the water is in the form of a film between the light transmitting plate and the water splitting photocatalyst sheet. Therefore, in the water splitting module, sufficient water is gently supplied to the water splitting photocatalyst sheet, and the water splitting photocatalyst sheet is sufficiently exposed to light. Therefore, the photocatalyst layer is less likely to collapse due to the water flow of the supplied water, and the desired photocatalytic activity is easily expressed and maintained. Therefore, even in the water splitting photocatalyst sheet made of a mixed particle layer, which is a layer formed by filtering photocatalyst particles as described above, the desired photocatalytic activity is expressed over a long period of time, and hydrogen and oxygen can be efficiently generated. In addition, the water splitting module has a simple structure in which the water splitting photocatalyst sheet is sandwiched in an airtight space by the substrate part and the light transmitting plate, and even such a high-performance water splitting module can be easily manufactured.

[0125] As described above, the present invention makes it possible to more easily produce hydrogen and oxygen through a photochemical water splitting reaction. The present invention is expected to contribute to the achievement of Goal 7 of the Sustainable Development Goals (SDGs) proposed by the United Nations, "Affordable and Clean Energy."

[0126] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present invention. EXAMPLES

[0127] Examples of the present invention are described below. In the following examples, the following compounds may be abbreviated as follows. Sm2Ti2O5S2 → "STOS" BiVO4 → "BVO" Graphene oxide → "GO" Reduced graphene oxide → "rGO"

[0128] [Preparation of STOS (Sm2Ti2O5S2) powder] In a N2 glove box, Sm2O3 (manufactured by Fujifilm Wako Pure Chemical Industries), Sm2S3 (manufactured by Kojundo Chemical Laboratory), and TiO2 (manufactured by Rare Metallic Co., Ltd.) were mixed and crushed in a molar ratio of Sm2O3:Sm2S3:TiO2 = 1:2:6 to prepare a raw material mixture. Then, 10.0 mass% of sulfur powder (manufactured by Kojundo Chemical Laboratory) was added to the raw material mixture and further mixed to obtain a mixture of raw materials and sulfur (hereinafter also referred to as "raw material + sulfur mixture"). Then, a flux (hereinafter also referred to as "LiCl / CaCl2 mixed flux") in which LiCl (manufactured by Fujifilm Wako Pure Chemical Industries) and CaCl2 (manufactured by Fujifilm Wako Pure Chemical Industries) were mixed in a mass ratio of LiCl:CaCl2 = 42.4:57.6 was mixed and crushed in a mass ratio of (raw material + sulfur mixture):(LiCl / CaCl2 mixed flux) = 1:3. The prepared powder was then sealed in a vacuum quartz tube and fired for 24 hours at 973 K. After natural cooling, the product was dispersed in deionized water to dissolve the LiCl / CaCl2 flux, and the obtained STOS powder was filtered and dried under reduced pressure to obtain crude STOS powder.

[0129] To remove excess sulfur, the crude STOS powder was calcined in air at 473K for 1 h, then stirred in a 47% H2SO4 aqueous solution for 15 min and filtered. The sulfuric acid-treated sample was then washed several times with pure water, filtered, and dried under reduced pressure to obtain STOS powder.

[0130] [Preparation of Cr2O3 / Pt / IrO2 / STOS] STOS powder (0.2 g) was dispersed in 15 mL of H2O, and an aqueous solution of IrCl3 (Tokyo Chemical Industry Co., Ltd.) equivalent to 0.5 mass% Ir relative to STOS was added. The mixture was transferred to a glass microwave heating container, heated at 423 K for 15 min using a microwave reactor, filtered, and washed to obtain IrO2 / STOS. IrO2 / STOS was dispersed in 15 mL of ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.), and an aqueous solution of H2PtCl6-6H2O (Kanto Chemical Co., Ltd.) equivalent to 1.0 mass% Pt relative to STOS was added, heated at 423 K for 15 min using a microwave reactor, filtered, and washed to obtain Pt / IrO2 / STOS. The filtered Pt / IrO2 / STOS was immediately suspended in 150 mL of methanol aqueous solution (10 vol% methanol), and K2CrO4 (FUJIFILM Wako Pure Chemical Industries, Ltd.) was added as a precursor, equivalent to 0.5 mass% Cr relative to STOS, and photoprecipitation was performed under full spectrum irradiation of a 300W Xe lamp. The reaction was carried out for 1 hour, after which the Cr2O3 / Pt / IrO2 / STOS was collected by filtration and washed several times with pure water.

[0131] [Preparation of BVO powder] 10.0 mmol of NH4VO3 (FUJIFILM Wako Pure Chemical Industries, Ltd.) and 10.0 mmol of Bi(NO3)3·5H2O (FUJIFILM Wako Pure Chemical Industries, Ltd.) were dissolved in 100 mL of 2.0 mM aqueous nitric acid solution (FUJIFILM Wako Pure Chemical Industries, Ltd.), and the pH value was adjusted to about 0.5 with aqueous ammonia solution (28.0-30.0 mass%, FUJIFILM Wako Pure Chemical Industries, Ltd.). The solution was stirred for 2 hours until a pale yellow precipitate was formed, then transferred to a Teflon (registered trademark)-lined stainless steel autoclave and hydrothermally treated at 473 K for 24 hours. After natural cooling, the solution was filtered, washed, and dried under reduced pressure to obtain BVO powder.

[0132] [CoO x / Preparation of BVO powder] The cobalt promoter was supported on BVO by the photoprecipitation method. BVO powder was dispersed in 150 mL of phosphate buffer (pH 6.0, 50.0 mM) containing Co(NO3)2·6H2O (Kanto Chemical) equivalent to 0.5 mass% Co relative to BVO. This suspension was irradiated with full spectrum light from a 300 W Xe lamp for 1 hour. After filtration and washing, the CoO x / BVO was obtained.

[0133] [Activity evaluation] The water splitting activity of the prepared photocatalyst sheet was evaluated using a standard closed circulation system evaluation device equipped with a vacuum pump, a circulation pump, a cell to hold the photocatalyst sheet, a gas sampling valve, and a gas chromatograph (GC). A 300W xenon lamp (λ>420nm) was used as the light source, and the cell was cooled from the outside using cooling water (15℃). During the evaluation, the photocatalyst sheet was immersed in 40mL of pure water in the cell, and the reaction system was degassed several times in advance, and then Ar was introduced to adjust the pressure to a range of 5-90kPaA. The amount of gas generated was measured by irradiating the photocatalyst sheet with light without stirring. The analysis was performed using a TCD-GC (GC-8A, Shimadzu Corporation) with a column (molecular sieve 5A) and carrier gas (argon).

[0134] Example 1 [rGO / CoO x / Preparation of BVO] Two types of GO (graphene oxide) were used for photoelectrodeposition: G-21L (EM Japan graphene oxide) and graphene oxide (NiSiNa Materials (regular size)). 0.1 g of CoO was added to 150 mL of methanol aqueous solution (50.0 vol%). x / BVO decentralization and CoO x GO (normal size) was added in an amount equivalent to 0.5% by mass to the / BVO. A 2.5% by mass GO solution was used. It was then irradiated with a full spectrum of a 300W Xe lamp for 3 hours. The GO solution was converted to rGO by irradiating it with the Xe lamp, and an aqueous solution containing rGO was obtained.

[0135] [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of PO( / BVO) composite As-prepared 0.05 g Cr2O3 / Pt / IrO2 / STOS and 0.15 g rGO / CoO x / BVO was dispersed in 150 mL of ultrapure water and irradiated for 12 h with a 300 W Xe lamp equipped with a cutoff filter (L42, λ>420 nm).

[0136] [Preparation of photocatalytic sheet] The above (Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x The (BVO) composite was filtered through a φ5.5 cm filter paper (ADVANTECH, quantitative filter paper 5B, 55 mm) as shown in Figure 7. After drying, the thin layer of the sample was transferred to a glass plate with double-sided tape (Nissin EM, carbon double-sided tape for SEM) attached to one side of the thin layer. The area of ​​the thin layer was 28.3 cm 2 The thickness of the thin layer after transfer ranged from about 0.1 to 50 μm, with an average of 20 to 30 μm. In the following, when the layer thickness has a similar range, the maximum and minimum thickness values ​​are listed.

[0137] [Evaluation of photocatalytic sheet activity] The results of the activity evaluation using the above-mentioned activity evaluation method are shown in Figure 8. The area of ​​the photocatalyst sheet used for the evaluation was 28.3 cm. 2 As shown in the graph in Figure 8, in the water splitting reaction evaluation, total water splitting at H2:O2=2:1 progressed, and the hydrogen production rate in the reaction system at 5 kPaA was 36 μmol / h.

[0138] Example 2-1 [Preparation of photocatalytic sheet] As shown in Fig. 9, 0.05 g of as-prepared Cr2O3 / Pt / IrO2 / STOS and 0.15 g of CoO xThe rGO / BVO was dispersed in 50 mL of ultrapure water and filtered through a φ5.5 cm filter paper (ADVANTECH, quantitative filter paper 5B, 55 mm). An aqueous solution containing 2 mg of rGO was then supplied onto the filtered sample and filtered to form a layer containing rGO. The aqueous solution containing rGO was prepared by converting a given amount of GO (EM Japan G-21L) into rGO in a 10 vol% aqueous methanol solution by irradiating it with full spectrum light from a 300 W Xe lamp for 1 hour, and then isolating the aqueous solution containing 2 mg of rGO. After drying, the thin layer of the sample was transferred to a glass plate with double-sided tape attached to one side. The area of ​​the thin layer was 28.3 cm. 2 Since the amount of particles is the same as in Example 1, the thickness of the thin layer after transfer is estimated to be in the range of about 0.1 to 50 μm.

[0139] [Evaluation of photocatalytic sheet activity] The results of activity evaluation using the activity evaluation method described above are shown in Figure 10. As shown in the graph in Figure 10, in the water splitting reaction evaluation, total water splitting at H2:O2=2:1 progressed, and the hydrogen production rate in the 5 kPaA reaction system was 10 μmol / h. Note that in the graphs in the following figures, both hydrogen gas and oxygen gas temporarily become zero at the line indicating a specific time (the dashed line in Figure 10), which means that the generated gas was discharged from the system at a specific time.

[0140] The activity in Example 2-1 was lower than that in Example 1. However, it was shown that a photocatalyst sheet effective for total water splitting can be produced by forming a film of the photocatalyst mixture on filter paper and then permeating the film with rGO, rather than by forming a composite of rGO and the photocatalyst in advance.

[0141] Example 2-2 [Preparation of photocatalytic sheet] As-prepared 0.05 g Cr2O3 / Pt / IrO2 / STOS and 0.15 g CoO x / BVO was dispersed in 50 mL of ultrapure water and filtered through a φ5.5 cm filter paper (ADVANTECH, quantitative filter paper 5B, 55 mm). After this, an aqueous solution containing 2 mg of CNT (aqueous solution of single-walled carbon nanotubes, manufactured by Meijo Chemical) was supplied onto the filtered sample and filtered to form a thin layer containing CNT. After drying, this thin layer of the sample was transferred to a glass plate with double-sided tape attached to one side. The area of ​​the obtained photocatalyst sheet was 28.3 cm2. 2 Since the amount of particles is the same as in Example 1, the thickness of the thin layer after transfer is estimated to be in the range of about 0.1 to 50 μm, similar to Example 1.

[0142] [Evaluation of photocatalytic sheet activity] The results of activity evaluation using the activity evaluation method described above are shown in Figure 11. As in Example 2-1, the total decomposition of water proceeded at H2:O2=2:1 in the water-splitting reaction evaluation, as shown in the graph in Figure 11, and the hydrogen production rate in a reaction system of 5 kPaA was 10 μmol / h. Therefore, it was shown that a photocatalyst sheet effective for total water decomposition can be produced by using CNT instead of rGO in a photocatalyst sheet produced by forming a film of a photocatalyst mixture on filter paper and then permeating it with a conductive material, rather than by forming a composite of the photocatalyst and conductive material in advance.

[0143] Example 3-1 [rGO / CoO x / Preparation of BVO] G-21L (EM Japan graphene oxide) was used as GO for photoelectrodeposition. 0.15 g of CoO was added to 150 mL of methanol aqueous solution (50.0 vol%). x / BVO decentralization and CoO x GO was added in an amount equivalent to 0.5% by mass to the / BVO. A 2.5% by mass GO solution was used. After that, full spectrum irradiation was performed for 3 hours using a 300W Xe lamp.

[0144] [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of PO( / BVO) composite As-prepared 0.05 g Cr2O3 / Pt / IrO2 / STOS and 0.15 g rGO / CoO x / BVO was dispersed in 150 ml of ultrapure water and irradiated for 12 h with a 300 W Xe lamp equipped with a cutoff filter (L42, λ>420 nm).

[0145] [Preparation of photocatalytic sheet] As shown in FIG. 12, the above (Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x The (BVO) composite was filtered through a φ5.5 cm filter paper (Azfil, glass fiber filter paper, 055070N-SPGFF, 55 mm). To prevent the photocatalyst from peeling off from the filter paper, the sample was sandwiched between glass plates to form a photocatalyst sheet. The area of ​​the photocatalyst sheet was 23.7 cm. 2 The thickness of the catalyst layer was about 1 to 150 μm.

[0146] [Evaluation of photocatalytic sheet activity] The results of activity evaluation using the activity evaluation method described above are shown in Figure 13. As shown in the graph in Figure 13, the total decomposition of water proceeded at H2:O2=2:1 in the water-splitting reaction evaluation, and the hydrogen production rate in the 5 kPaA reaction system was 20 μmol / h. This shows that even if the sheet produced by filtration is used as is, without necessarily transferring it using double-sided tape, it can become an effective photocatalyst sheet for total water decomposition.

[0147] Example 3-2 [rGO / CoO x / Preparation of BVO] Graphene oxide (NiSiNa Materials (regular size)) was used for photoelectrodeposition as GO. 0.15 g of CoO was dissolved in 150 mL of methanol aqueous solution (50.0 vol%). x / BVO decentralization and CoO x GO was added in an amount equivalent to 0.5% by mass to the / BVO. A 2.5% by mass GO solution was used. After that, full spectrum irradiation was performed for 3 hours using a 300W Xe lamp.

[0148] [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of PO( / BVO) composite As-prepared 0.05g Cr2O3 / Pt / IrO2 / STOS and 0.15g rGO / CoO x / BVO was dispersed in 150 mL of ultrapure water and irradiated for 12 h with a 300 W Xe lamp equipped with a cutoff filter (L42, λ>420 nm).

[0149] [Preparation of photocatalytic sheet] The above (Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x The (BVO) composite was filtered through a φ5.5 cm filter paper (Azfil, glass fiber filter paper, 055070N-SPGFF, 55 mm). The top and bottom of this sample were sandwiched between glass plates to create a photocatalyst sheet. The area of ​​the photocatalyst sheet was 23.7 cm. 2 The thickness of the catalyst layer was about 1 to 150 μm.

[0150] [Evaluation of photocatalytic sheet activity] The results of activity evaluation using the above-mentioned activity evaluation method are shown in Figure 14. As in Example 3-1, the total decomposition of water proceeded at H2:O2=2:1 in the water-splitting reaction evaluation as shown in the graph in Figure 14, and the hydrogen production rate in the reaction system at 5 kPaA was 31 μmol / h. This shows that in a photocatalyst sheet that uses the sheet produced by filtration as is without transferring using double-sided tape, even if NiSiNaMaterials is used as GO instead of G21L, it can be an effective photocatalyst sheet for total water decomposition.

[0151] [Evaluation of photocatalytic sheet activity (2) Effect of pressure] The Ar introduction pressure at the start of the reaction of the photocatalyst sheet of Example 3-2 was changed in the range of 5 to 60 kPaA, and the effects of these were evaluated. The initial rate of hydrogen generation rate was plotted against the reaction start pressure, and the results are shown in FIG. 15. The initial rate was determined from the gas generation rate one hour after the start of the reaction. Although the hydrogen generation rate at a total pressure of 60 kPaA was lower than that at 5 kPaA, the water splitting reaction proceeded even at a total pressure of 60 kPaA. It was shown that the photocatalyst sheet of Example 3-2 proceeds with the water splitting reaction not only under near-vacuum conditions, but also under reduced pressure conditions close to normal pressure.

[0152] Example 4-1 [rGO / CoO x / Preparation of BVO] A regular-sized NiSiNaMaterials GO was used for photoelectrodeposition. 0.15 g of CoO was added to 150 mL of methanol aqueous solution (50.0 vol%). x / BVO decentralization and CoO x GO was added in an amount equivalent to 1.0 mass% to the / BVO. A 2.5 mass% GO solution was used. After that, full spectrum irradiation was performed for 3 hours using a 300W Xe lamp.

[0153] [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of (BVO)-SiO2 composite As-prepared 0.05 g Cr2O3 / Pt / IrO2 / STOS and 0.15 g rGO / CoO x The solution was dispersed in 150 mL of ultrapure water and irradiated with a 300 W Xe lamp equipped with a cutoff filter (L42, λ>420 nm) for 12 hours. SiO2 nanoparticles (NanoTeK (registered trademark) amorphous SiO2) were added to the solution. x The mixture was added to the (BVO / BVO) composite so as to give a concentration of 10 mass % and stirred for 1 hour.

[0154] [Preparation of photocatalytic sheet] The above (Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO xThe ( / BVO)-SiO2 composite was filtered through a φ5.5 cm filter paper (Azfil, glass fiber filter paper, 055070N-SPGFF, 55 mm). The top and bottom of this sample were sandwiched between glass plates to create a photocatalyst sheet. The area of ​​the photocatalyst sheet was 23.7 cm2. 2 It was.

[0155] [Evaluation of photocatalytic sheet activity] The activity of this catalyst was evaluated using the activity evaluation method described above. The Ar introduction pressure at the start of the reaction was also changed in the range of 5 to 90 kPaA to evaluate the effects of these changes. Figure 16 shows the initial rate of hydrogen generation plotted against the reaction start pressure. Although the hydrogen generation rate at a total pressure of 60 to 90 kPaA was lower than that at 5 kPaA, the water splitting reaction proceeded. The hydrogen generation rate in the reaction system at 5 kPaA was 20.1 μmol / h.

[0156] It was shown that the photocatalyst sheet of Example 4-1 proceeds with the water splitting reaction not only under near-vacuum conditions but also under near-normal pressure conditions. In addition, although the hydrogen generation rate at 5 kPaA is lower than that of Example 3-2, the difference in hydrogen generation rate at 90 kPaA and 60 kPaA, which are near normal pressures, is small, indicating that the inclusion of silica nanoparticles does not affect the performance of the photocatalyst sheet.

[0157] Example 4-2 [rGO / CoO x / Preparation of BVO] The normal size of GO from NiSinaMaterials was used for photoelectrodeposition. 0.15 g of CoO was added to 150 mL of methanol aqueous solution (50.0 vol%). x / BVO decentralization and CoO x GO was added in an amount equivalent to 1.0 mass% to the / BVO. A 2.5 mass% GO solution was used. After that, full spectrum irradiation was performed for 3 hours using a 300W Xe lamp.

[0158] [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of (BVO)-SiO2 composite As-prepared 0.05 g Cr2O3 / Pt / IrO2 / STOS and 0.15 g rGO / CoO x The solution was dispersed in 150 mL of ultrapure water and irradiated with a 300 W Xe lamp equipped with a cutoff filter (L42, λ>420 nm) for 12 hours. SiO2 nanoparticles (NanoTeK (registered trademark) amorphous SiO2) were added to the solution. x The mixture was added to the (BVO / BVO) composite at a concentration of 20 mass % and stirred for 1 hour.

[0159] [Preparation of photocatalytic sheet] The above (Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x The ( / BVO)-SiO2 composite was filtered through a φ5.5 cm filter paper (Azfil, glass fiber filter paper, 055070N-SPGFF, 55 mm). The top and bottom of this sample were sandwiched between glass plates to create a photocatalyst sheet. The area of ​​the photocatalyst sheet was 23.7 cm2. 2 It was.

[0160] [Evaluation of photocatalytic sheet activity] The activity of this catalyst was evaluated using the activity evaluation method described above. The Ar introduction pressure at the start of the reaction was also changed in the range of 5 to 60 kPaA to evaluate the effect of these changes. Figure 17 shows the results of plotting the initial rate of hydrogen evolution against the reaction start pressure. The hydrogen evolution rate in the reaction system at 5 kPaA was 12.7 μmol / h.

[0161] The hydrogen production rate in Example 4-2 was lower than those in Examples 3-2 and 4-1. However, it was shown that the photocatalyst sheet in Example 4-2 can perform a water splitting reaction not only under near-vacuum conditions but also under near-normal pressure conditions.

[0162] Example 5-1 [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of PO( / BVO) composite The normal size of NiSiNaMaterials was used for the photoelectrodeposition. 0.05 g of Cr2O3 / Pt / IrO2 / STOS and 0.15 g of CoO were added to 150 mL of methanol aqueous solution (50.0 vol%). x / BVO are dispersed in these Cr2O3 / Pt / IrO2 / STOS and CoO x GO was added in an amount equivalent to 1.0 mass% relative to the total amount of / BVO. A 2.5 mass% GO solution was used. After that, full spectrum irradiation was performed for 3 hours using a 300W Xe lamp.

[0163] [Preparation of photocatalytic sheet] As shown in FIG. 18, the above (Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x The (BVO) composite was filtered through a φ5.5 cm filter paper (ADVANTECH, quantitative filter paper 5B, 55 mm). This sample was used as a photocatalyst sheet. The area of ​​the photocatalyst sheet was 23.7 cm. 2 It was.

[0164] [Evaluation of photocatalytic sheet activity] The results of the activity evaluation using the above-mentioned activity evaluation method are shown in FIG. 19. As shown in the graph in FIG. 19, the total decomposition of water at H2:O2=2:1 progressed in the water splitting reaction evaluation, and the hydrogen production rate in the reaction system at 5 kPaA was ~130 μmol / h, which was a very high performance. In addition, this photocatalyst sheet did not show any signs of the photocatalyst layer peeling off from the filter paper, and the water splitting reaction could be carried out as it was without sandwiching the photocatalyst layer between glass plates as in Examples 3 and 4. This shows that a high-performance photocatalyst sheet can be obtained by simultaneously mixing the photocatalyst and GO and forming them into a sheet.

[0165] Example 5-2 [(Cr2O3 / Pt / IrO2 / STOS) / rGO / (CoO x Preparation of PO( / BVO) composite The same preparation as in Example 5-1 was performed except that CNT was used as GO. 0.05 g of Cr2O3 / Pt / IrO2 / STOS and 0.15 g of CoO were added to 150 mL of methanol aqueous solution (50.0 vol%). x / BVO are dispersed in these Cr2O3 / Pt / IrO2 / STOS and CoO x CNTs were added in an amount equivalent to 1.0 mass% relative to the total amount of / BVO. Then, full spectrum irradiation was performed for 3 hours using a 300W Xe lamp.

[0166] [Preparation of photocatalytic sheet] The above (Cr2O3 / Pt / IrO2 / STOS) / CNT / (CoO x The (BVO) composite was filtered through a φ5.5 cm filter paper (ADVANTECH, quantitative filter paper 5B, 55 mm). This sample was used as a photocatalyst sheet. The area of ​​the photocatalyst sheet was 23.7 cm. 2 It was.

[0167] [Evaluation of photocatalytic sheet activity] The results of the activity evaluation using the above-mentioned activity evaluation method are shown in FIG. 20. As shown in the graph in FIG. 20, the total decomposition of water at H2:O2=2:1 progressed in the water splitting reaction evaluation, and the hydrogen production rate in the reaction system of 5 kPaA was ~140 μmol / h, which was a very high performance. In addition, as in Example 5-1, this photocatalyst sheet did not show any signs of the photocatalyst layer peeling off from the filter paper, and the water splitting reaction could be carried out as it is without sandwiching the photocatalyst layer between glass plates. This shows that a high-performance photocatalyst sheet can be obtained by simultaneously mixing not only GO but also conductive CNT and photocatalyst and forming them into a sheet.

[0168] Table 1 shows the H2 production rate (μmol / h) at 5 kPaA in each example.

[0169] [Table 1]

[0170] [Cross-section observation of photocatalyst sheet] The photocatalyst sheets produced in Examples 1 and 5 were each observed with an optical microscope and a scanning electron microscope (SEM) to observe the distribution of the mixed particle layer.

[0171] [Sample preparation] Aron Alpha (registered trademark) was dropped onto the photocatalyst sheet prepared by the method described in Example 1, and then dried, and the double-sided tape and photocatalyst sample were fixed. Next, small pieces were cut out from the fixed double-sided tape and photocatalyst sample, and processed at -50°C using an ion mill (ArBlade5000: manufactured by Hitachi). A carbon coat was applied to the processed cross section to impart electrical conductivity. In this way, a sample of the photocatalyst sheet of Example 1 was prepared.

[0172] In addition, a photocatalyst sheet sample of Example 5 was prepared by the same procedure as above, except that the photocatalyst sheet prepared by the method described in Example 5-1 was used and a fixed object of filter paper and photocatalyst sample was prepared as the fixed object.

[0173] [Observation conditions] The optical microscope used was "DSX510" (Olympus). The SEM used was "SU5000" (Hitachi), and secondary electron images and backscattered electron images were obtained. The accelerating voltage for SEM observation was 3 kV, and the detectors used were a secondary electron detector (SE-L) and a backscattered electron detector (BSE-COMP).

[0174] [Observations] (1) Photocatalyst sheet of Example 1 Photographs of the surface of the photocatalyst sheet of Example 1 taken with an optical microscope are shown in Figures 21 and 22. As typically shown in the areas surrounded by dashed lines in Figures 21 and 22, in the photocatalyst sheet of Example 1, a mixed particle layer is present mainly at the bottom of the recesses in the unevenness caused by the filter medium.

[0175] Photographs of the first part of the image of the cross section of the photocatalyst sheet of Example 1 captured by SEM are shown in Figures 23 and 24. Figure 23 shows a secondary electron image, and Figure 24 shows a backscattered electron image. Also, Figure 25 is a view showing a magnified photograph of part A in Figure 24, Figure 26 is a view showing a magnified photograph of part B in Figure 24, and Figure 27 is a view showing a magnified photograph of part C in Figure 24.

[0176] The thickness of the mixed particle layer in part A (A) is about 40 μm. In part B, the thickness of the mixed particle layer on the left side of the paper surface (B1) is about 50 μm, and the thickness of the mixed particle layer on the right side of the paper surface (B2) is about 20 μm. In part C, the thickness of the mixed particle layer on the left side of the paper surface (C1) is about 4 μm, and the thickness of the mixed particle layer on the right side of the paper surface (C2) is about 1 μm.

[0177] The thickness of the mixed particle layer is the distance between a pair of parallel straight lines when the mixed particle layer is sandwiched in the thickness direction of the mixed particle layer by the pair of parallel straight lines in a cross-sectional image of the mixed particle layer in a backscattered electron image of the SEM such that each straight line extends longer along the direction in which each interface of the mixed particle layer extends.

[0178] Furthermore, a secondary electron image of a second portion of the image of the cross section of the photocatalyst sheet of Example 1 captured by SEM is shown in Fig. 28, and a backscattered electron image is shown in Fig. 29. A secondary electron image of a third portion of the image of the cross section of the photocatalyst sheet of Example 1 captured by SEM is shown in Fig. 30, and a backscattered electron image is shown in Fig. 31. Furthermore, the thicknesses of the mixed particle layers indicated by the numbers in Fig. 29 and Fig. 31 are shown in Table 2.

[0179] [Table 2]

[0180] (2) Photocatalyst sheet of Example 5 Photographs of the surface of the photocatalyst sheet of Example 5 taken with an optical microscope are shown in Figures 32 and 33. As typically shown in the areas surrounded by dashed lines in Figures 32 and 33, in the photocatalyst sheet of Example 5, a mixed particle layer is present mainly at the tops of the protrusions in the unevenness caused by the filter medium.

[0181] Photographs of the first part of the image of the cross section of the photocatalyst sheet of Example 5 captured by SEM are shown in Figures 34 and 35. Figure 34 shows a secondary electron image, and Figure 35 shows a backscattered electron image. Also, Figure 36 is a view showing a magnified photograph of part D in Figure 35, Figure 37 is a view showing a magnified photograph of part E in Figure 35, and Figure 38 is a view showing a magnified photograph of part F in Figure 35.

[0182] The thickness of the mixed particle layer in part D (D) is about 45 μm. The thickness of the mixed particle layer in part E (E) is about 80 μm. The thickness of the mixed particle layer on the left side of the paper surface in part F (F1) is about 10 μm, and the thickness of the mixed particle layer on the right side of the paper surface (F2) is about 0.6 μm.

[0183] Furthermore, a secondary electron image of a second portion of the image of the cross section of the photocatalyst sheet of Example 5 captured by SEM is shown in Fig. 39, and a backscattered electron image is shown in Fig. 40. A secondary electron image of a third portion of the image of the cross section of the photocatalyst sheet of Example 5 captured by SEM is shown in Fig. 41, and a backscattered electron image is shown in Fig. 42. Furthermore, the thicknesses of the mixed particle layers indicated by the numbers in Fig. 40 and Fig. 42 are shown in Table 3.

[0184] [Table 3]

[0185] [Consideration] In the photocatalyst sheet of Example 1, the mixed particle layer is mainly present in the concave portions of the unevenness of the carbon double-sided tape surface. Therefore, the mixed particle layer tends to be scattered in the spreading direction, like an island structure with the concave portions as islands. In addition, in the photocatalyst sheet of Example 1, the mixed particle layer present in the concave portions of the unevenness tends to be thicker, and the mixed particle layer present in the convex portions tends to be thinner. This is thought to be because the inorganic particles in the thin layer are easily inserted into the voids in the carbon double-sided tape, since the thin layer of the sample is transferred to the carbon double-sided tape in the preparation of the photocatalyst sheet.

[0186] In the photocatalyst sheet of Example 5, the mixed particle layer is mainly present in the convex parts of the surface unevenness caused by the filter paper. Therefore, the mixed particle layer tends to be present in a mesh shape that spreads along the convex parts in the spreading direction. In addition, in the photocatalyst sheet of Example 5, the thickness of the mixed particle layer present in the convex parts of the unevenness tends to be thicker, and the thickness of the mixed particle layer present in the concave parts tends to be thinner. This is thought to be because the filter paper after filtration in the production of the photocatalyst sheet is used as the photocatalyst sheet as it is, so the inorganic particles in the mixed particle layer adhere to the filter paper and tend to be preferentially deposited on the convex parts. [Industrial Applicability]

[0187] The present invention can be used to produce hydrogen gas by decomposing water through photocatalysis. [Explanation of symbols]

[0188] 1, 10 Water-splitting photocatalyst sheet 2. Base sheet 3, 11 Mixed particle layer 4. Photocatalyst particles for hydrogen generation 5. Photocatalyst particles for oxygen generation 6 Conductive material particles 7. Reduction reaction promoter 8. Oxidation reaction promoter 12 Single particle layer 50 Water splitting equipment 51 Water Splitting Unit 52 Water supply mechanism 53 Gas recovery mechanism 54 units 55 Water Splitting Module 61 Circuit Board 62 Frame 63 Seal part 64 Light transmission plate 65 Water supply inlet 66 Exhaust port 67 Gap

Claims

1. A water splitting photocatalyst sheet comprising a mixed particle layer in which two or more types of particles selected from photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, and which satisfies either of the following two conditions: (Condition 1) The mixed particle layer includes two types of particles selected from the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles dispersed therein, and a single particle layer of the remaining type of particle is directly superimposed on the mixed particle layer. (Condition 2) The mixed particle layer contains three types of particles, namely, the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles, dispersed therein.

2. 2. The water splitting photocatalyst sheet according to claim 1, wherein the remaining type of particles in condition 1 are conductive material particles.

3. The water splitting photocatalyst sheet according to claim 1 , wherein the conductive material particles include one or both of reduced graphene oxide and carbon nanotubes.

4. 2. The water splitting photocatalyst sheet according to claim 1, further comprising a substrate sheet carrying on its surface the laminate of the mixed particle layer and the single particle layer of condition 1, or the mixed particle layer of condition 2.

5. The water-splitting photocatalyst sheet according to claim 4 , wherein the substrate sheet comprises one or more sheets selected from the group consisting of a fibrous sheet, a porous sheet, and an adhesive sheet.

6. 2. The water splitting photocatalyst sheet according to claim 1, wherein the thickness of the mixed particle layer under condition 2 is 0.1 to 300 μm.

7. A method for producing a water splitting photocatalyst sheet, comprising a step of filtering a suspension in which two or more types of particles selected from among photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, to produce a mixed particle layer on a filter medium in which two or more types of particles selected from among photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and conductive material particles are dispersed, and which satisfies either of the following two conditions: (Condition A) The step of generating the mixed particle layer is a step of filtering a suspension in which two types of particles selected from the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles are dispersed, The method further comprises a step of directly superposing the resulting mixed particle layer on a single particle layer of the remaining type of particle. (Condition B) The step of producing the mixed particle layer is a step of filtering a suspension in which three types of particles, the hydrogen generation photocatalyst particles, the oxygen generation photocatalyst particles, and the conductive material particles, are dispersed.

8. The method for producing a water splitting photocatalyst sheet according to claim 7 , wherein the remaining type of particles under condition A are conductive material particles.

9. The method for producing a water splitting photocatalyst sheet according to claim 7 , wherein the conductive material particles are made of one or both of reduced graphene oxide and carbon nanotubes.

10. A roll-shaped fibrous sheet is used as the filter medium, The step of generating the mixed particle layer is a step of filtering the suspension on the continuously supplied fibrous sheet. A method for producing the water splitting photocatalyst sheet according to claim 7.

11. The method for producing a water-splitting photocatalyst sheet according to claim 7, further comprising a step of contacting the laminate of the mixed particle layer and the single particle layer under condition A, or the mixed particle layer under condition B, with an adhesive surface of an adhesive sheet, so as to support the laminate on the adhesive sheet.

12. The method for producing a water-splitting photocatalyst sheet according to claim 11, wherein the supporting step is a step of supporting the laminate of the mixed particle layer and the single particle layer under condition A, or the mixed particle layer under condition B, on the adhesive surface of the roll-shaped adhesive sheet, which is continuously supplied, by contacting the laminate.

13. The method for producing a water-splitting photocatalyst sheet according to any one of claims 7 to 12, wherein water is used as a dispersion medium for the suspension.

14. A water-splitting photocatalyst sheet that splits water into hydrogen and oxygen under light irradiation; a water splitting module that holds the water splitting photocatalyst sheet in a state in which water can be supplied to the water splitting photocatalyst sheet; a water supply mechanism for supplying water to the water-splitting photocatalyst sheet held in the water-splitting module; a gas recovery mechanism for recovering one or both of hydrogen gas and oxygen gas generated by the water-splitting photocatalyst sheet held in the water-splitting module; A water splitting device, wherein the water splitting photocatalyst sheet is the water splitting photocatalyst sheet according to any one of claims 1 to 5.

15. The water splitting module comprises: A substrate portion supporting the water splitting photocatalyst sheet; a light-transmitting plate disposed opposite the substrate with the water-splitting photocatalyst sheet interposed therebetween; a water supply port for supplying water between the light-transmitting plate and the substrate portion; an exhaust port for discharging gas between the light-transmitting plate and the substrate portion; The water splitting apparatus according to claim 14 , wherein water is supplied from the water supply port between the light-transmitting plate and the water-splitting photocatalyst sheet.

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