Photocatalyst, hydrogen production apparatus, and method for producing a photocatalyst

Abstract

The present invention provides a photocatalyst that can reduce the self-oxidation of a substrate made of a compound semiconductor. [Solution] A photocatalyst comprising a substrate made of a compound semiconductor and a graphene oxide layer covering the substrate.

Description

[Technical Field]

[0001] This invention relates to a photocatalyst, a hydrogen production apparatus, and a method for producing a photocatalyst. [Background technology]

[0002] Photocatalysts that exhibit catalytic activity when irradiated with light are known.

[0003] For example, Patent Document 1 describes a semiconductor photoelectrode comprising a first semiconductor layer made of a III-V compound semiconductor and a second semiconductor layer made of an oxide semiconductor formed by covering the reaction region of the first semiconductor layer that causes a reaction of the target substance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-101288 [Overview of the project] [Problems that the invention aims to solve]

[0005] In semiconductor photoelectrodes as described above, gallium nitride-based semiconductor thin-film electrodes degrade due to self-oxidation upon light irradiation, which can sometimes prevent the acquisition of a stable photocurrent. [Means for solving the problem]

[0006] One embodiment of the photocatalyst according to the present invention is: The device comprises a substrate made of a compound semiconductor and a graphene oxide layer covering the substrate.

[0007] One aspect of the hydrogen production apparatus according to the present invention is: The photocatalyst varies.

[0008] One embodiment of the photocatalyst according to the present invention is: A graphene oxide dispersion aqueous solution is applied to a substrate made of a compound semiconductor to form a graphene oxide layer. [Brief Description of the Drawings]

[0009] [Figure 1] A cross-sectional view schematically showing the photocatalyst according to the present embodiment. [Figure 2] A cross-sectional view schematically showing the photocatalyst according to a reference example. [Figure 3] A cross-sectional view schematically showing the photocatalyst according to a first modification of the present embodiment. [Figure 4] A cross-sectional view schematically showing the photocatalyst according to a first modification of the present embodiment. [Figure 5] A cross-sectional view schematically showing the photocatalyst according to a second modification of the present embodiment. [Figure 6] A cross-sectional view schematically showing the photocatalyst according to a second modification of the present embodiment. [Figure 7] A cross-sectional view schematically showing the photocatalyst according to a third modification of the present embodiment. [Figure 8] A diagram schematically showing the hydrogen production apparatus of the present embodiment. [Figure 9] A graph showing the potential and current density of a photoanode versus reversible hydrogen electrode potential. [Figure 10] A graph showing current density versus elapsed time. [Figure 11] A graph showing the potential and current density of a photoanode versus reversible hydrogen electrode potential. [Figure 12] A graph showing current density versus elapsed time. [Mode for Carrying Out the Invention]

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below improperly limit the content of the present invention described in the claims. . In addition, not all of the configurations described below are essential constituent requirements of the present invention.

[0011] 1. Photocatalyst 1.1. Configuration First, the photocatalyst according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the photocatalyst 100 according to the present embodiment.

[0012] As shown in FIG. 1, the photocatalyst 100 includes a base material 10 and a graphene oxide layer 20.

[0013] The base material 10 is, for example, layered. The base material 10 is made of a compound semiconductor. The base material 10 may be a compound semiconductor substrate. The material of the base material 10 is, for example, a III-V group semiconductor. Note that the material of the base material 10 may be a II-VI group semiconductor. The material of the base material 10 is, for example, a nitrogen-containing nitride semiconductor. The base material 10 has, for example, a wurtzite crystal structure. Specifically, the material of the base material 10 is GaN. The material of the base material 10 may be Si-doped n-type GaN.

[0014] The graphene oxide layer 20 covers the base material 10. In the illustrated example, the graphene oxide layer 20 is provided on the base material 10. A thickness T of the graphene oxide layer 20 is smaller than a thickness of the base material 10. The thickness T of the graphene oxide layer 20 is, for example, not less than 1 nm and not more than 10 nm, and preferably not less than 2 nm and not more than 5 nm. The thickness T of the graphene oxide layer 20 is measured using, for example, TEM (Transmission Electron Microscope).

[0015] 1.2. Operation The photocatalyst 100 constitutes, for example, a photoelectrode. The operation when the photocatalyst 100 is immersed in water and the photocatalyst 100 functions as a photoelectrode in water will be described below.

[0016] As shown in Figure 1, when the substrate 10 is irradiated with light L, the substrate 10 absorbs the light L and generates electrons and holes. The generated holes decompose water on the surface of the graphene oxide layer 20. Specifically, the generated holes undergo an oxidation reaction that oxidizes water, as shown in formula (1) below. However, formula (1) is for acidic to neutral conditions; in basic conditions, OH - This becomes the reactant. In this way, the photocatalyst 100 functions as a photoanode.

[0017] 2H₂O → O₂ + 4H + +4e - ...(1)

[0018] On the other hand, as shown in Figure 2, if a graphene oxide layer is not provided, the holes generated in the GaN substrate by light L self-oxidize the GaN as shown in equations (2) and (3) below. As a result, the GaN is etched and eventually disappears.

[0019] 2GaN → 2Ga 3+ +N2+6e - ...(2) 2Ga 3+ +6OH - →Ga2O3+3H2O ···(3)

[0020] 1.3. Effects The photocatalyst 100 comprises a substrate 10 made of a compound semiconductor and a graphene oxide layer 20 covering the substrate 10. Therefore, as described above, the photocatalyst 100 can reduce the self-oxidation of the substrate 10 by the graphene oxide layer 20.

[0021] In photocatalyst 100, the substrate 10 is a nitride semiconductor. Nitride semiconductors are prone to self-oxidation, but in photocatalyst 100, even though the substrate 10 is a nitride semiconductor, the graphene oxide layer The addition of 20 reduces the self-oxidation of the substrate 10.

[0022] In photocatalyst 100, the thickness T of the graphene oxide layer 20 is between 1 nm and 10 nm. Therefore, photocatalyst 100 can reduce the self-oxidation of the substrate 10 while suppressing the decrease in photocatalytic activity caused by the graphene oxide layer 20. For example, if the thickness T is greater than 10 nm, the graphene oxide layer inhibits the oxidation reaction of water, reducing photocatalytic activity.

[0023] The photocatalyst 100 constitutes a photoelectrode. Therefore, the photocatalyst 100 can function, for example, as a photoanode.

[0024] 2. Method for producing photocatalysts Next, the method for manufacturing the photocatalyst 100 according to this embodiment will be described with reference to the drawings.

[0025] As shown in Figure 1, a graphene oxide dispersion aqueous solution is applied to the substrate 10 to form a graphene oxide layer 20. The graphene oxide dispersion aqueous solution is applied, for example, by a spin coating method. The concentration of the graphene oxide dispersion aqueous solution is, for example, 5 mg / L to 20 mg / L, preferably 7 mg / L to 10 mg / L. For example, the thickness T of the graphene oxide layer 20 can be adjusted by the concentration of the graphene oxide dispersion aqueous solution.

[0026] Through the above process, photocatalyst 100 can be manufactured.

[0027] In the method for manufacturing the photocatalyst 100, a graphene oxide dispersion aqueous solution is applied to the substrate 10 to form a graphene oxide layer 20. Therefore, compared to, for example, the case where a coating layer is formed on the substrate by sputtering, damage to the substrate 10 caused by forming the graphene oxide layer 20 can be reduced. This makes it possible to maintain a good interface between the substrate 10 and the graphene oxide layer 20. For example, if crystal defects occur at the interface of the substrate, energy levels are formed, and electrons and holes generated by photoexcitation recombine via the interface energy levels, making it difficult for oxidation-reduction reactions to proceed. The method for manufacturing the photocatalyst 100 can solve this problem. Furthermore, as described in Patent Document 1, when an oxide semiconductor layer is formed on a substrate by the MOD (Metal Organic Decomposition) method, the quality of the oxide semiconductor layer is low and it contains many crystal defects, so there is a problem that electrons and holes generated by photoexcitation are prone to recombination. In the present invention, a thin graphene oxide layer is formed, so there is no such problem.

[0028] In the method for producing the photocatalyst 100, the concentration of the graphene oxide dispersion aqueous solution is between 5 mg / L and 20 mg / L. Therefore, it is possible to reduce the self-oxidation of the substrate 10 while suppressing the decrease in photocatalytic activity caused by the graphene oxide layer 20.

[0029] In the method for producing the photocatalyst 100, an aqueous solution of graphene oxide dispersion is applied by a spin-coating method. Therefore, the graphene oxide layer 20 can be easily formed.

[0030] 3. Modified examples of photocatalysts 3.1. First variation Next, a photocatalyst according to the first modified example of this embodiment will be described with reference to the drawings. Figure 3 is a schematic cross-sectional view showing the photocatalyst 200 according to the first modified example of this embodiment.

[0031] Hereinafter, in the photocatalyst 200 according to the first modified example of this embodiment, components having the same function as the components of the photocatalyst 100 according to the embodiment described above will be denoted by the same reference numerals, and their detailed descriptions will be omitted. The same applies to the photocatalyst according to the second modified example and the photocatalyst according to the third modified example of this embodiment, which will be described later.

[0032] Photocatalyst 200 differs from photocatalyst 100 described above in that it has a co-catalyst 30, as shown in Figure 3.

[0033] The co-catalyst 30 covers the graphene oxide layer 20. In the illustrated example, the co-catalyst 30 is provided on the graphene oxide layer 20. The graphene oxide layer 20 is provided between the substrate 10 and the co-catalyst 30. The co-catalyst 30 is, for example, layered. The material of the co-catalyst 30 is, for example, a metal oxide such as nickel oxide, iron nickel oxide, iridium oxide, manganese oxide, cobalt oxide, or rubidium oxide. The co-catalyst 30 is formed by, for example, sputtering, vacuum deposition, MOD method, spin coating, (photo)electrodeposition, or impregnation.

[0034] In the photocatalyst 200, the graphene oxide layer 20 suppresses the self-oxidation of the substrate 10, while the co-catalyst 30 improves the water splitting activity.

[0035] As shown in Figure 4, the co-catalysts 30 may be arranged in multiple island-like configurations. If the transmittance of the co-catalysts 30 to light L is low, arranging the co-catalysts 30 in island-like configurations makes it easier for light L to reach the substrate 10.

[0036] 3.2. Second Variation Next, a photocatalyst according to a second modified example of this embodiment will be described with reference to the drawings. Figure 5 is a schematic cross-sectional view showing a photocatalyst 300 according to a second modified example of this embodiment.

[0037] In the photocatalyst 300, as shown in Figure 5, the substrate 10 constitutes a base portion 12 and a plurality of columnar portions 14, which is different from the photocatalyst 100 described above.

[0038] The base material 10 has a base portion 12 and a plurality of columnar portions 14. The base portion 12 is, for example, plate-shaped.

[0039] The columnar portion 14 is provided on the base portion 12. In the illustrated example, the columnar portion 14 is provided on the base portion 12. The columnar portion 14 protrudes upward from the base portion 12. The columnar portion 14 is also called, for example, a nanocolumn, nanowire, nanorod, or nanopillar. The planar shape of the columnar portion 14 is, for example, a polygon such as a hexagon or a circle. The diameter of the columnar portion 14 is, for example, 1 nm or more and 1000 nm or less, preferably 10 nm or more and 500 nm or less. By setting the diameter of the columnar portion 14 to 1000 nm or less, the strain inherent in the columnar portion 14 can be reduced.

[0040] The "diameter of the columnar portion 14" refers to the diameter of the columnar portion 14 if its planar shape is a circle, and the diameter of the smallest inclusion circle if its planar shape is not a circle. For example, if the planar shape of the columnar portion 14 is a polygon, the diameter of the smallest circle that contains the polygon is the diameter of the smallest circle that contains the polygon is the diameter of the ellipse.

[0041] Multiple columnar sections 14 are provided. The multiple columnar sections 14 are spaced apart from each other. The number of columnar sections 14 is not particularly limited. The spacing between adjacent columnar sections 14 is, for example, 1 nm to 1000 nm, preferably 10 nm to 500 nm. The multiple columnar sections 14 are arranged in a predetermined direction at a predetermined pitch in a plan view. The multiple columnar sections 14 are arranged, for example, in a triangular lattice or a square lattice. Note that the multiple columnar sections 14 may not have a predetermined pitch and may be arranged randomly.

[0042] The "pitch of the columnar parts 14" refers to the distance between the centers of adjacent columnar parts 14 in a predetermined direction. The "center of the columnar portion 14" is the center of the circle if the planar shape of the columnar portion 14 is a circle, and the center of the smallest inclusion circle if the planar shape of the columnar portion 14 is not a circle. For example, if the planar shape of the columnar portion 14 is a polygon, the center of the smallest circle that contains the polygon is the center of the polygon, and if the planar shape of the columnar portion 14 is an ellipse, the center of the smallest circle that contains the ellipse is the center of the ellipse.

[0043] The graphene oxide layer 20 covers the substrate 10 and the columnar portion 14. In the illustrated example, the graphene oxide layer 20 is provided on the upper surface of the substrate 10, the side surface of the columnar portion 14, and the upper surface of the columnar portion 14. The upper surface of the columnar portion 14 is, for example, the c-plane.

[0044] The upper surface of the columnar portion 14 may be a faceted surface, as shown in Figure 6. Furthermore, although not shown, a co-catalyst may be provided in the graphene oxide layer 20, as in the photocatalyst 200 described above.

[0045] As a method for forming the columnar portion 14, for example, a mask layer (not shown) is formed on the base portion 12. The mask layer is formed by, for example, electron beam deposition or sputtering. Next, the mask layer is patterned to form a plurality of openings. Patterning is performed by, for example, EB (Electron Beam) exposure and etching.

[0046] Next, using the mask layer as a mask, multiple columnar portions 14 are formed on the substrate 10 by epitaxial growth. Examples of epitaxial growth methods include MOCVD (Metal Organic Chemical Vapor Deposition) and MBE (Molecular Beam Epitaxy). The mask layer may be removed after the multiple columnar portions 14 have been formed.

[0047] Through the above process, multiple columnar portions 14 can be formed.

[0048] In the photocatalyst 300, the substrate 10 has multiple columnar portions 14. Therefore, the surface area of ​​the substrate 10 can be increased in the photocatalyst 300. This allows, for example, oxidation reactions to be promoted.

[0049] 3.3. Third modified example Next, a photocatalyst according to a third modified example of this embodiment will be described with reference to the drawings. Figure 7 is a schematic cross-sectional view showing a photocatalyst 400 according to the third modified example of this embodiment.

[0050] In the photocatalyst 100 described above, the substrate 10 was layered, as shown in Figure 1.

[0051] In contrast, in the photocatalyst 400, as shown in Figure 7, the substrate 10 is particulate. For example, multiple substrates 10 are provided. The substrate 10 may also be crystalline grains. The size of the substrate 10 is, for example, 100 nm or more and 5 μm or less in diameter. Preferably, it is 100 nm or more and 500 nm or less in diameter. The photocatalyst 400 is, for example, in powder form.

[0052] In the method for producing the photocatalyst 400, for example, a graphene oxide layer 20 is formed by adding particulate substrate 10 to an aqueous graphene oxide dispersion solution, impregnating it, and then drying it.

[0053] In the photocatalyst 100 described above, an example was explained in which it functions as a photoanode that causes an oxidation reaction when immersed in water. In contrast, photocatalyst 400 functions as a photocatalyst that causes oxidation and reduction reactions when irradiated with light while immersed in water. Oxidation and reduction reactions occur with photocatalyst 400, producing hydrogen and oxygen. Similarly, in photocatalyst 100 described above, oxidation and reduction reactions occur when irradiated with light while immersed in water. It may function as a photocatalyst that induces a response. Furthermore, although not shown in the diagram, a co-catalyst may be provided in the graphene oxide layer 20, as in the photocatalyst 200 described above. The co-catalyst may include an oxygen-generating co-catalyst and a hydrogen-generating co-catalyst. The material of the oxygen-generating co-catalyst may be a metal oxide such as nickel oxide, iron-nickel oxide, iridium oxide, manganese oxide, cobalt oxide, or rubidium oxide. The material of the hydrogen-generating co-catalyst may be platinum, ruthenium, or rhodium.

[0054] In photocatalyst 400, the substrate 10 is particulate. Therefore, the surface area of ​​the substrate 10 can be increased in photocatalyst 400. This promotes oxidation and reduction reactions.

[0055] 4. Hydrogen production equipment Next, the hydrogen production apparatus according to this embodiment will be described with reference to the drawings. Figure 8 is a schematic diagram showing the hydrogen production apparatus 500 according to this embodiment.

[0056] As shown in Figure 8, the hydrogen production apparatus 500 includes, for example, a photocatalyst 100 as a photoanode, a counter electrode 40, a reference electrode 42, a container 50, a reaction solution 52, a potentiostat 60, and a light source 70. The hydrogen production apparatus 500 constitutes, for example, a triode photoelectrochemical cell.

[0057] The container 50 contains the reaction solution 52. In the illustrated example, the container 50 is filled with the reaction solution 52. The reaction solution 52 is, for example, an aqueous sodium hydroxide solution or water. The photocatalyst 100, the counter electrode 40, and the reference electrode 42 are immersed in the reaction solution 52. The material of the counter electrode 40 is, for example, platinum. The reference electrode 42 is composed of, for example, silver, silver chloride, and potassium chloride. In the illustrated example, the degassing member 44 is immersed in the reaction solution 52. The container 50 is placed on a stirrer 54. The stirrer 54 is, for example, a magnetic stirrer.

[0058] The potentiostat 60 is electrically connected to the photocatalyst 100, the counter electrode 40, and the reference electrode 42. The potentiostat 60 controls the potentials of the photocatalyst 100, the counter electrode 40, and the reference electrode 42.

[0059] The light source 70 faces the photocatalyst 100. The light source 70 irradiates the photocatalyst 100 with light L. The light source 70 is, for example, a xenon lamp.

[0060] When the photocatalyst 100 is irradiated with light L from the light source 70, as described above, the photocatalyst 100 absorbs the light L and generates electrons and holes. The generated holes cause an oxidation reaction that oxidizes the reaction solution 52, as shown in the above formula (1). On the other hand, the generated electrons move to the counter electrode 40 and cause a reduction reaction that reduces the reaction solution 52, as shown in the following formula (4). However, formula (4) corresponds to the case where the solution is acidic, and H₂O becomes a reactant when the solution is neutral to basic. Accordingly, the hydrogen production apparatus 500 can produce hydrogen.

[0061] 4H + +4e - →2H₂···(4)

[0062] The hydrogen production apparatus may be a two-electrode electrochemical cell that does not include the reference electrode 42. Further, the configuration may be such that the potentiostat 60 is not provided and the photocatalyst 100 and the counter electrode 40 are short-circuited.

[0063] Note that when the photocatalyst 100 is a photocatalyst that causes both an oxidation reaction and a reduction reaction, the configuration may be such that only the photocatalyst 100 is immersed in the reaction solution 52. When the photocatalyst 100 is irradiated with light L from the light source 70 in this state, the oxidation reaction of the above formula (1) and the reduction reaction of the above formula (4) occur in the photocatalyst 100, whereby hydrogen and oxygen are produced. Further, the light source 70 may not be provided, and sunlight may be used as the light L to irradiate the photocatalyst 100. Accordingly, miniaturization and energy saving of the apparatus can be achieved.

[0064] 5. Experimental Examples 5.1. Production of Photoanode An optical anode was fabricated by spin-coating a graphene oxide dispersion aqueous solution onto the surface of a GaN substrate, connecting wires with indium, and then sealing the wire connection area with epoxy resin. The spin-coating conditions were 1000 rpm for 10 seconds, followed by 5000 rpm for 30 seconds.

[0065] As the graphene oxide dispersion aqueous solution, we used "G-21L," a high-concentration single-layer graphene oxide dispersion aqueous solution manufactured by EM Japan Co., Ltd. The reaction solution for this high-concentration single-layer graphene oxide dispersion aqueous solution was water, with a concentration of 5 g / L. By diluting this high-concentration single-layer graphene oxide dispersion aqueous solution, graphene dispersion aqueous solutions with concentrations of 5 mg / L, 7.5 mg / L, 10 mg / L, and 50 mg / L were prepared. In addition, a photoanode was prepared without spin-coating with the graphene oxide dispersion aqueous solution. That is, this photoanode does not contain graphene oxide.

[0066] 5.2. Evaluation Method The photoanode prepared as described above was evaluated using a triode photoelectrochemical cell. The prepared photoanode was used as the sample electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode. A 0.1 M NaOH aqueous solution was used as the electrolyte. The pH of the NaOH aqueous solution was 13. The photoanode was irradiated with light from a 300 W Xe lamp, and the photocurrent was measured.

[0067] 5.3. Evaluation Results Figure 9 shows the potential V of the photoanode relative to the potential of the reverse hydrogen electrode (RHE). RHE This is a graph showing the current density. In other words, Figure 9 shows the potential-current density curve. Figure 10 is a graph showing the current density over time. In other words, Figure 10 shows the time-current density curve. In Figure 10, the potential is +0.8V. RHE The curve for this case is shown.

[0068] In Figures 9 and 10, photoanodes that do not contain graphene oxide are indicated as "no GO". Furthermore, the dip around 600 seconds in Figure 10 is due to the measurement being terminated once and is not essential. The same applies to Figure 12, which will be discussed later.

[0069] As shown in Figure 9, the photoanode coated with graphene oxide dispersion aqueous solution showed a lower photocurrent density compared to the "no GO" version. This is thought to be because the graphene oxide suppressed the self-oxidation of GaN, reducing the current flowing due to self-oxidation.

[0070] As shown in Figure 10, the photoanode coated with a graphene oxide dispersion aqueous solution showed a reduced decrease in photocurrent density over time compared to the "no GO" version. This is because the graphene oxide suppressed the self-oxidation of GaN. As self-oxidation progresses, the GaN is eventually etched away and disappears, and the photocurrent stops flowing.

[0071] At a graphene oxide dispersion aqueous solution concentration of 50 mg / L, the photocurrent density decreased considerably. This is because graphene oxide suppressed both the self-oxidation of GaN and the oxidation of water.

[0072] Figure 11 shows the potential V of the photoanode relative to the reversible hydrogen electrode potential at the photoanode when the concentrations of the graphene oxide dispersion aqueous solution are 5 mg / L, 7.5 mg / L, and 10 mg / L. RHE This is a graph showing the current density. Figure 12 is a graph showing the current density as a function of elapsed time at the photoanode when the concentrations of the graphene oxide dispersion aqueous solution are 5 mg / L, 7.5 mg / L, and 10 mg / L. In Figure 12, the potential is +0.8V. RHE The curve for this case is shown.

[0073] A photoanode with a graphene oxide dispersion aqueous solution concentration of 7.5 mg / L showed improved photocurrent density compared to the 10 mg / L concentration, and was comparable to that of the 5 mg / L concentration. Furthermore, the 7.5 mg / L photoanode exhibited improved stability of photocurrent density over time compared to the 5 mg / L concentration.

[0074] Based on the above, it is believed that in a photoanode coated with a graphene oxide dispersion aqueous solution, a graphene oxide layer is formed on the GaN surface, and as a result of the graphene oxide layer suppressing the progression of GaN self-oxidation, the temporal stability of the photocurrent is improved.

[0075] The embodiments and variations described above are examples only and are not limited thereto. For example, each embodiment and each variation can be combined as appropriate.

[0076] The present invention includes configurations substantially identical to those described in the embodiments, for example, configurations with the same function, method, and results, or configurations with the same purpose and effect. Furthermore, the present invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as those described in the embodiments. Finally, the present invention includes configurations that add known technology to the configurations described in the embodiments.

[0077] The following can be derived from the embodiments and modifications described above.

[0078] One aspect of photocatalysis is, The device comprises a substrate made of a compound semiconductor and a graphene oxide layer covering the substrate.

[0079] This photocatalyst allows for the reduction of self-oxidation of the substrate by utilizing a graphene oxide layer.

[0080] In one method of photocatalysis, The material of the substrate may be a nitride semiconductor.

[0081] According to this photocatalyst, even if the substrate is a nitride semiconductor, the graphene oxide layer can reduce the self-oxidation of the substrate.

[0082] In one method of photocatalysis, The thickness of the graphene oxide layer may be 1 nm or more and 10 nm or less.

[0083] This photocatalyst reduces the self-oxidation of the substrate while suppressing the decrease in photocatalytic activity caused by the graphene oxide layer.

[0084] In one method of photocatalysis, The base material may have a plurality of columnar portions.

[0085] This photocatalyst allows for an increase in the surface area of ​​the substrate.

[0086] In one method of photocatalysis, The substrate may be in particulate form.

[0087] This photocatalyst allows for an increase in the surface area of ​​the substrate.

[0088] In one method of photocatalysis, It may also constitute a photoelectrode.

[0089] This photocatalyst can function as a photoanode.

[0090] One embodiment of a hydrogen production apparatus is: It has one embodiment of the aforementioned photocatalyst.

[0091] This hydrogen production device can produce hydrogen.

[0092] One embodiment of a method for producing a photocatalyst is: A graphene oxide layer is formed by coating a substrate made of a compound semiconductor with an aqueous solution of graphene oxide dispersion.

[0093] This method for manufacturing photocatalysts reduces damage to the substrate caused by forming a graphene oxide layer.

[0094] In one embodiment of a method for producing a photocatalyst, The concentration of the graphene oxide dispersion aqueous solution may be 5 mg / L or more and 20 mg / L or less.

[0095] This method for producing photocatalysts can reduce the self-oxidation of the substrate while suppressing the decrease in photocatalytic activity caused by the graphene oxide layer.

[0096] In one embodiment of a method for producing a photocatalyst, The graphene oxide dispersion aqueous solution may be applied by spin coating.

[0097] This method for manufacturing photocatalysts allows for the easy formation of a graphene oxide layer. [Explanation of Symbols]

[0098] 10…Substrate, 12…Base, 14…Columnar part, 20…Graphene oxide layer, 30…Co-catalyst, 40…Counter electrode, 42…Reference electrode, 44…Degassing member, 50…Container, 52…Reaction solution, 54…Stirrer, 60…Potenstiostat, 70…Light source, 100, 200, 300, 400…Photocatalyst, 500…Hydrogen production device

Claims

1. A photocatalyst comprising a substrate made of a compound semiconductor and a graphene oxide layer covering the substrate.

2. In claim 1, The material of the aforementioned substrate is a photocatalyst, which is a nitride semiconductor.

3. In claim 1, The photocatalyst has a graphene oxide layer thickness of 1 nm to 10 nm.

4. In claim 1, The substrate is a photocatalyst having a plurality of columnar parts.

5. In claim 1, The aforementioned substrate is a particulate photocatalyst.

6. In claim 1, Photocatalysts are components of photoelectrodes.

7. A hydrogen production apparatus having a photocatalyst according to any one of claims 1 to 6.

8. A method for producing a photocatalyst, comprising coating a substrate made of a compound semiconductor with an aqueous solution of graphene oxide dispersion to form a graphene oxide layer.

9. In claim 8, A method for producing a photocatalyst, wherein the concentration of the graphene oxide dispersion aqueous solution is 5 mg / L or more and 20 mg / L or less.

10. In claim 8 or 9, A method for producing a photocatalyst, comprising applying the graphene oxide dispersion aqueous solution by a spin coating method.

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