Conductive laminate for water-splitting photocatalytic electrode, method for producing same, and water-splitting photocatalytic electrode

Abstract

To provide a conductive laminate for a water splitting photocatalytic electrode in which performance and productivity are improved.SOLUTION: The present invention relates to a conductive laminate for a water splitting photocatalytic electrode, a production method thereof, and the water splitting photocatalytic electrode. The conductive laminate for the water splitting photocatalytic electrode comprises a cationic polymer coated substrate and a silver particle layer which is formed on the surface of the substrate. The silver particle layer comprises a current collecting layer formed on the substrate and a contact layer formed on the current collecting layer. The current collecting layer comprises spherical silver particles. The silver particles in the current collecting layer exist in a dense manner. The contact layer comprises planar silver particles. The silver particles in the contact layer exist sparsely. The average particle diameter of the silver particles in the contact layer is larger than the average particle diameter of the silver particles in the current collecting layer. The cationic polymer is a polydiallyldialkylammonium salt.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive laminate for a water-splitting photocatalytic electrode, a method for producing the same, and a water-splitting photocatalytic electrode using the conductive laminate. [Background technology]

[0002] In recent years, water splitting technology that produces hydrogen and oxygen by splitting water using solar energy and photocatalysis has attracted attention from the perspective of reducing environmental impact. One of the photocatalytic water splitting technologies widely used is a photocatalytic electrode in which a conductive laminate having a metal layer as a conductive layer on a substrate is used and a photocatalyst is laminated on this conductive laminate, and photocatalytic electrodes and conductive laminates have been widely studied.

[0003] One known method for producing a conductive laminate for use in a photocatalytic electrode is the particle transfer method. Patent Document 1 discloses the fabrication of a photocatalytic electrode for water splitting using this method. The particle transfer method involves, for example, forming a metal layer as a conductive layer on a substrate coated with a photocatalyst; attaching and transferring the metal layer to another substrate; peeling off the substrate; and inverting the substrate and removing excess photocatalyst by ultrasonic treatment. However, photocatalytic electrodes fabricated using this method have problems such as unstable contact between the photocatalysts themselves and between the photocatalyst and the metal layer, resulting in reduced electrical conductivity and reduced water splitting efficiency, as well as reduced mechanical strength and durability. Furthermore, the need for two substrates leaves room for improvement in terms of productivity.

[0004] A photocatalytic electrode for water splitting can also be manufactured by photoelectrodeposition, as disclosed in Patent Document 2. However, when a photocatalytic electrode is manufactured by photoelectrodeposition, the metal layer sometimes does not have a uniform surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-43816 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-139616 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, there is room for improvement in performance and productivity in the production of conductive laminates for water-splitting photocatalyst electrodes by conventional methods. Therefore, an object of the present invention is to provide a conductive laminate for water-splitting photocatalyst electrodes with improved performance and productivity. [Means for solving the problem]

[0007] The inventors discovered that by using a substrate with a specific coating and silver nanoparticles and controlling the processing conditions, the metal layer in the resulting conductive laminate has a two-layer structure with different particle shapes, particle diameters, and densities, stabilizing the contact between the metal layer and the photocatalyst, improving the performance of a water-splitting photocatalytic electrode using this conductive laminate, and also improving productivity because it can be manufactured using a single substrate, thereby completing the present invention.

[0008] That is, the gist of the present invention is as follows. (1) A conductive laminate for a water-splitting photocatalyst electrode, comprising a substrate coated with a cationic polymer and a silver particle layer formed on the surface of the substrate, wherein the silver particle layer comprises a current collecting layer formed on the substrate and a contact layer formed on the current collecting layer, the current collecting layer comprising spherical silver particles, the silver particles being densely distributed in the current collecting layer, the contact layer comprising flat silver particles, the silver particles being sparsely distributed in the contact layer, the average particle size of the silver particles in the contact layer being larger than the average particle size of the silver particles in the current collecting layer, and the cationic polymer being a polydiallyldialkylammonium salt. (2) The conductive laminate for a water-splitting photocatalyst electrode according to (1) above, wherein the average particle size of the silver particles in the contact layer is 150 nm to 500 nm. (3) The conductive laminate for a water-splitting photocatalyst electrode according to (1) above, wherein the cationic polymer is polydiallyldimethylammonium chloride. (4) A method for producing a conductive laminate for a water-splitting photocatalyst electrode according to any one of (1) to (3), comprising immersing a substrate coated with the cationic polymer for 15 hours or more at room temperature and in the dark in an ink containing silver nanoparticles whose surfaces are coated with a protective agent having an anionic group, thereby forming the current collecting layer and the contact layer. (5) The method for producing a conductive laminate for a water-splitting photocatalyst electrode according to (4) above, wherein the protective agent having an anionic group is a compound having a carboxyl group. (6) The method for producing a conductive laminate for a water-splitting photocatalyst electrode according to (5) above, wherein the protective agent having an anionic group is citric acid. (7) A water-splitting photocatalytic electrode comprising a water-splitting photocatalytic nanosheet laminated on the conductive laminate for a water-splitting photocatalytic electrode according to any one of (1) to (3) above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a conductive laminate for a water-splitting photocatalyst electrode with improved performance and productivity. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows a schematic cross-sectional view of one embodiment of a conductive laminate of the present invention. [Figure 2] 1 shows a cross-sectional view of one embodiment of a water-splitting photocatalytic electrode of the present invention. [Figure 3] 3A to 3D are SEM images (20,000x magnification) of the surfaces of conductive laminates 1-1 to 1-4, respectively, showing the results of SEM observation of the surface morphology of the conductive laminate 1 in the example. [Figure 4] 4A to 4D show the results of SEM observation of the surface morphology of the conductive laminate 1 in the example, with SEM images (100,000x magnification) of the surfaces of the conductive laminates 1-1 to 1-4, respectively. [Figure 5] 5A to 5D show the results of SEM observation of the surface morphology of the conductive laminate 2 in the example, with SEM images (20,000 times magnification) of the surfaces of the conductive laminates 2-1 to 2-4, respectively. [Figure 6] 6A to 6D show the results of SEM observation of the surface morphology of the conductive laminate 2 in the example, with SEM images (100,000x magnification) of the surfaces of the conductive laminates 2-1 to 2-4, respectively. [Figure 7] 1 is a graph showing the results of measuring the particle diameter of silver particles in the silver particle layers of conductive laminates 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will now be described in detail.

[0012] The present invention relates to a conductive laminate for a water-splitting photocatalyst electrode (hereinafter also referred to as a conductive laminate) having a substrate coated with a cationic polymer and a silver particle layer formed on the surface of the substrate. In the conductive laminate of the present invention, the silver particle layer consists of two silver particle layers differing in particle shape, particle size, and density. Specifically, the silver particle layer consists of a current collecting layer formed on the substrate and composed of spherical silver particles, and a contact layer formed on the current collecting layer and composed of flat silver particles. In the conductive laminate of the present invention, the average particle size of the silver particles in the contact layer is larger than the average particle size of the silver particles in the current collecting layer.

[0013] FIG. 1 shows a cross-sectional schematic diagram of one embodiment of the conductive laminate of the present invention. As shown in FIG. 1, the conductive laminate 10 includes a substrate 11 coated with a cationic polymer (not shown) and a silver particle layer 12 formed on the surface of the substrate 11. The silver particle layer 12 includes a current collecting layer 12A composed of small, spherical silver particles and a contact layer 12B composed of large, flat silver particles formed on the current collecting layer 12A. The silver particles are densely distributed in the current collecting layer 12A, while the silver particles are sparsely distributed in the contact layer 12B. As shown in FIG. 1, the conductive laminate is composed of, from bottom to top, a substrate coated with a cationic polymer, a current collecting layer, and a contact layer. In one embodiment, the conductive laminate of the present invention includes a substrate coated with a cationic polymer and a silver particle layer formed on the surface of the substrate.

[0014] The substrate is not particularly limited, and a plate-shaped material such as glass, metal, ceramic, or plastic can be used. The substrate is preferably transparent and / or conductive. The substrate is preferably a glass plate. Examples of glass plates include those containing silica (SiO2) as a main component. Indium tin oxide (ITO)-coated glass and fluorine-doped tin oxide (FTO)-coated glass can also be used as the glass plate.

[0015] The thickness of the substrate is usually 1 μm to 30 mm, and preferably 2 mm to 7 mm.

[0016] In the conductive laminate of the present invention, the substrate is covered with a cationic polymer. Thus, the substrate has a cationic polymer coating on its surface. The thickness of the cationic polymer coating is usually 1 nm to 2 mm, and preferably 5 nm to 50 nm.

[0017] In the conductive laminate of the present invention, the cationic polymer is a polydiallyldialkylammonium salt, which is a polymer in which the repeating unit has a ring structure containing nitrogen. In the present invention, by using a polydiallyldialkylammonium salt as the cationic polymer, a sufficiently large electrostatic force (Coulomb force) is generated between the cationic functional groups of the cationic polymer and the anionic groups of the protective agent present on the surface of the silver nanoparticles in the raw ink during the manufacturing process of the conductive laminate, which is thought to enable a structure in which small-sized silver particles are densely stacked on the substrate. The cationic polymer is a polymer having a repeating unit represented by formula (1): [ka] (In the formula, R 1 and R 2 are each independently an alkyl group having 1 to 3 carbon atoms or a hydroxyalkyl group having 1 to 3 carbon atoms, and X - is the counterion.) and a repeating unit represented by formula (2): [ka] (In the formula, R 3 and R 4 are each independently an alkyl group having 1 to 3 carbon atoms or a hydroxyalkyl group having 1 to 3 carbon atoms, and X - is the counterion.) A polymer having one or more repeating units selected from the following is preferred, and a polymer having a repeating unit represented by formula (2) is more preferred.

[0018] The repeating units represented by formula (1) and formula (2) correspond to the repeating units in a polymer obtained by polymerizing a monomer component containing a diallyldialkylammonium salt represented by formula (3). [ka] (In the formula, R 5 and R 6 is R 1 and R 2 , R3 and R 4 and X - is the counterion.)

[0019] In the formulas (1) to (3), X - is not particularly limited, and examples thereof include halogen ions such as chloride ion and bromide ion, inorganic acid ions such as sulfate ion, nitrate ion and sulfite ion, and organic acid ions such as methyl sulfate ion, acetate ion and lactate ion.

[0020] As the cationic polymer, polydiallyldimethylammonium chloride is more preferable. 3 and R 4 is methyl and X - is a chloride ion.

[0021] The molecular weight of the cationic polymer is usually 100 to 20,000,000, and preferably 200 to 1,000,000 from the viewpoint of generating a sufficient electrostatic force between the cationic polymer and the anionic groups of the protective agent.

[0022] In the conductive laminate of the present invention, the silver particle layer is formed on the surface of the substrate. As described above, the substrate is coated with a cationic polymer, and the silver particle layer is formed on the surface of the cationic polymer coating on the substrate. The silver particle layer functions as a conductive layer, conducting electrons generated by the photocatalyst when the water-splitting photocatalyst electrode is used. The silver particle layer comprises a lower current collecting layer densely populated with small, spherical silver particles and an upper contact layer sparsely populated with large, flat silver particles. In the present invention, the silver particle layer has a two-layer structure with different particle shapes, particle sizes, and densities. This increases the number of contact points between the photocatalyst and the silver particle layer when the photocatalyst is laminated, thereby increasing the electrical conductivity and mechanical strength of the photocatalyst electrode and improving water-splitting efficiency and durability.

[0023] The silver particles may be particles containing at least one selected from silver, a silver compound, and a silver alloy, and are preferably particles made of silver. When a silver alloy is used, the metal element other than silver is not particularly limited, and examples thereof include gold, platinum, nickel, chromium, tin, zinc, indium, titanium, and copper.

[0024] In the conductive laminate of the present invention, the current collecting layer is formed on the surface of the substrate and constitutes a layer below the silver particle layer. The current collecting layer is made of spherical silver particles, and the silver particles are densely present in the current collecting layer. The entire surface of the substrate is preferably covered by the silver particles of the current collecting layer, or most of the surface, more preferably the entire surface.

[0025] The silver particles in the current collecting layer have the same shape as the silver nanoparticles in the raw ink, that is, spherical. In the present invention, "spherical" includes a true sphere and a shape similar to a sphere, such as an ellipsoid, and means that, for example, in an image obtained by scanning electron microscope (SEM) observation, the silver particles observed within a unit field of view of the image are rounded, and the value obtained by dividing the maximum particle diameter by the minimum particle diameter of the silver particles is approximately 1.0 to 2.0 (preferably approximately 1.0 to 1.5).

[0026] The average particle size of the silver particles in the current collecting layer is approximately the same as that of the silver nanoparticles in the raw ink, and is usually 1 to 100 nm. From the viewpoint of enabling good formation of a silver particle layer, it is preferably 10 to 50 nm, and more preferably 20 to 40 nm. In the present invention, the average particle size of the silver particles refers to the number-based average particle size determined by analyzing images obtained by scanning electron microscope (SEM) observation using Image J (manufactured by NIH).

[0027] In the current collecting layer, the silver particles are densely present, which means, for example, that there are no gaps between the silver particles and, in some cases, the silver particles overlap each other.

[0028] The thickness of the current collecting layer is usually 10 nm to 10,000 nm, and preferably 100 nm to 1,000 nm.

[0029] In the conductive laminate of the present invention, the contact layer is formed on the current collecting layer and constitutes the upper layer of the silver particle layer. The contact layer is made of flat silver particles, and the silver particles are sparsely present in the contact layer. Because the silver particles are sparsely present in the contact layer, part of the surface of the current collecting layer is covered with the silver particles of the contact layer.

[0030] The silver particles in the contact layer are flat. Each flat silver particle in the contact layer is formed during the manufacturing process by particle growth from multiple silver particles in the previously formed current collecting layer. In the present invention, "flat" refers to a shape having a substantially flat surface (XY plane) and a substantially uniform thickness (Z) in an image obtained by scanning electron microscope (SEM) observation. In the present invention, the particle diameter of the flat silver particles refers to the particle diameter of the substantially flat surface (XY plane).

[0031] The average particle size of the silver particles in the contact layer is larger than the average particle size of the silver particles in the current collecting layer and is usually 100 nm to 700 nm. In order to stabilize the contact between the silver particle layer and the photocatalyst, the average particle size is preferably 150 nm to 500 nm, more preferably 175 nm to 500 nm, and particularly preferably 200 nm to 500 nm.

[0032] The ratio of the average particle size of the silver particles in the contact layer to the average particle size of the silver particles in the current collecting layer (contact layer / current collecting layer) is preferably 2 or more, more preferably 5 or more, and particularly preferably 10 or more, from the viewpoint of stabilizing the contact between the silver particle layer and the photocatalyst.

[0033] In the contact layer, the silver particles are sparsely distributed. The sparse distribution of the silver particles means, for example, that there are gaps between the silver particles. In the contact layer, the gaps between the silver particles are usually 10 nm to 1000 nm, and preferably 100 nm to 500 nm.

[0034] The thickness of the contact layer is usually 1 nm to 1000 nm, and preferably 10 nm to 100 nm.

[0035] As will be explained below in connection with the method for producing the conductive laminate of the present invention, the current collecting layer and the contact layer are obtained by immersing the substrate in an ink containing silver nanoparticles for a predetermined period of time. In other words, the current collecting layer and the contact layer are obtained from a single silver nanoparticle ink, rather than from two silver nanoparticle inks with different particle sizes.

[0036] The present invention also relates to a method for producing the conductive laminate described above. The method for producing the conductive laminate of the present invention comprises immersing a substrate coated with a cationic polymer in an ink containing silver nanoparticles whose surfaces are coated with a protective agent having an anionic group (also referred to as silver nanoink or silver nanoparticle ink in this specification) at room temperature and in the dark for 15 hours or more to form a current collecting layer and a contact layer.

[0037] In the manufacturing method of the present invention, a substrate coated with a cationic polymer is immersed under predetermined conditions in an ink containing silver nanoparticles whose surfaces are coated with a protective agent having an anionic group. The substrate and cationic polymer may be the same as those described above for the conductive laminate.

[0038] The cationic polymer can be coated on a substrate by coating the cationic polymer solution on the substrate using a known coating method such as a nozzle flow method, a spray method, a dipping method, a roll method, or a spin method.

[0039] In one embodiment, when the cationic polymer is coated on the substrate by a dipping method, the treatment temperature is usually 1°C to 50°C, preferably room temperature (usually 1°C to 30°C), and more preferably ordinary temperature (usually 15°C to 25°C). In this embodiment, the treatment time is usually 10 seconds to 60 minutes, preferably 30 seconds to 30 minutes, and more preferably 1 minute to 10 minutes. After the treatment, the substrate is optionally washed with water or the like and used for producing a conductive laminate.

[0040] The ink containing silver nanoparticles is a dispersion in which silver nanoparticles are dispersed in a solvent such as water, acetone, methanol, ethanol, hexane, 1-butanol, methylcyclohexone, isohexadecane, or 1,3-propanediol. In the ink containing silver nanoparticles, the surfaces of the silver nanoparticles are coated with a protective agent having an anionic group. In the present invention, when a substrate coated with a cationic polymer is immersed in ink containing silver nanoparticles whose surfaces are coated with a protective agent having an anionic group, the silver nanoparticles are attracted to the substrate coated with the cationic polymer due to the electrostatic force between the anionic groups and the cationic functional groups of the cationic polymer, forming a current collecting layer in which the silver particles are densely stacked. While a silver particle layer may not be formed satisfactorily on a substrate not coated with a cationic polymer, in the present invention, such electrostatic force allows a silver particle layer to be formed satisfactorily on the surface of the substrate.

[0041] The protecting agent having an anionic group may be, for example, a compound having an anionic group. The anionic group is not particularly limited, and examples thereof include a carboxyl group, a sulfonic acid group, a phosphate group, a halogen group, and a sulfate group, with a carboxyl group being preferred.

[0042] Examples of compounds having a carboxyl group include, but are not limited to, formic acid, acetic acid, propionic acid, butyric acid, lactic acid, citric acid, etc., with citric acid being preferred as it can also function as a reducing agent. Examples of compounds having a sulfonic acid group include, but are not limited to, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, etc. Examples of compounds having a phosphate group include, but are not limited to, phosphoric acid, acidic phosphate esters, etc. Examples of compounds having a halogen group include, but are not limited to, hydrochloric acid, etc. Examples of compounds having a sulfate group include, but are not limited to, sulfuric acid, etc.

[0043] The content of silver nanoparticles in the ink containing silver nanoparticles is usually 0.1% by weight to 50% by weight, and preferably 1% by weight to 25% by weight.

[0044] In the manufacturing method of the present invention, the immersion treatment of the cationic polymer-coated substrate in the silver nanoink is carried out at room temperature (usually 1°C to 30°C) in the dark. By carrying out the immersion treatment in the dark, excessive growth of silver particles can be suppressed.

[0045] The immersion time of the cationic polymer-coated substrate in the silver nanoink is 15 hours or more, preferably 15 to 48 hours, and more preferably 24 to 48 hours. In the present invention, an immersion time of 15 hours or more allows the silver particles formed on the substrate to grow sufficiently, forming large, flat silver particles in an upper layer. In this way, a contact layer made of sparsely distributed, large, flat silver particles is formed on a current collecting layer made of densely distributed, spherical, small silver particles. The average particle size of the silver particles in the contact layer changes depending on the immersion time, so the immersion time can be appropriately selected depending on the desired average particle size.

[0046] As described above, the manufacturing method of the present invention can produce a conductive laminate using a single substrate, which is advantageous in terms of productivity compared to the particle transfer method, which requires two substrates.Furthermore, the manufacturing method of the present invention can form two silver particle layers with different particle sizes from a single silver nanoink, which is advantageous in terms of productivity compared to using two silver nanoinks with different particle sizes.

[0047] In one embodiment, the conductive laminate of the present invention is obtained by immersing a substrate coated with a cationic polymer in an ink containing silver nanoparticles whose surfaces are coated with a protective agent having an anionic group at room temperature and in the dark for 15 hours or more. In a preferred embodiment, the conductive laminate of the present invention is obtained by immersing a substrate coated with polydiallyldimethylammonium chloride in an ink containing silver nanoparticles whose surfaces are coated with citric acid at room temperature and in the dark for 15 hours or more.

[0048] The present invention also relates to a water-splitting photocatalytic electrode comprising the conductive laminate and a water-splitting photocatalyst nanosheet laminated thereon. Figure 2 shows a cross-sectional schematic diagram of one embodiment of the water-splitting photocatalyst electrode of the present invention. As shown in Figure 2, the water-splitting photocatalyst electrode 20 of the present invention comprises the conductive laminate 24 of the present invention and a water-splitting photocatalyst nanosheet 23. The conductive laminate 24 comprises a substrate 21 coated with a cationic polymer (not shown), and a silver particle layer 22 on the surface of the substrate 21, the silver particle layer 22 comprising a current collecting layer 22A and a contact layer 22B. In the present invention, the silver particle layer has a two-layer structure consisting of a lower current collecting layer densely populated with small, spherical silver particles and an upper contact layer sparsely populated with large, flat silver particles. In particular, the sparsely populated large, flat silver particles in the contact layer can fill the gaps between the photocatalyst nanosheets, increasing the number of contact points between the photocatalyst and the conductive silver particle layer. This increases the electrical conductivity and mechanical strength of the water-splitting photocatalyst electrode, improving water splitting efficiency and durability. Furthermore, in the water-splitting photocatalytic electrode of the present invention, silver ions may be eluted into the electrolyte from the silver particle layer in the portion not covered with the photocatalyst during use, which may increase the amount of oxygen produced.

[0049] The water-splitting photocatalyst nanosheet that can be used in the water-splitting photocatalyst electrode of the present invention is not particularly limited as long as it is a photocatalyst for water splitting, and examples thereof include nanosheets of oxides, sulfides, nitrides, and oxynitrides of metals such as tantalum, niobium, tungsten, molybdenum, vanadium, bismuth, titanium, zirconium, hafnium, tin, indium, yttrium, gallium, germanium, zinc, cadmium, copper, and silver, or alloys thereof. Furthermore, the photocatalyst disclosed in JP 2017-43816 A can also be used as the water-splitting photocatalyst.

[0050] Because the water-splitting photocatalyst nanosheet is a nanosheet, it can contact over a wider area than particulate photocatalysts and can maintain sufficient reactivity. The length of the water-splitting photocatalyst nanosheet is typically at least as large as the average particle size of the silver particles in the contact layer, for example, 100 nm to 1000 nm, and preferably 200 nm to 500 nm. In the present invention, the length of the water-splitting photocatalyst nanosheet refers to the long diameter in the horizontal direction. Furthermore, the thickness of the water-splitting photocatalyst nanosheet after one dip coating is typically 1 nm to 100 nm. The film thickness of the water-splitting photocatalyst nanosheet can be increased by repeating the dip coating process.

[0051] The water-splitting photocatalyst electrode of the present invention can be obtained by laminating a water-splitting photocatalyst nanosheet onto the conductive laminate of the present invention by a commonly known method. [Example]

[0052] The present invention will be described in more detail below using examples, although the technical scope of the present invention is not limited to these examples.

[0053] <Preparation of conductive laminate> Conductive laminate 1 A glass substrate (FP2, manufactured by Nippon Sheet Glass Co., Ltd.) was prepared with the following structure: [ka] A glass substrate was dip-coated with PDDA by immersing it in a polydiallyldimethylammonium chloride (PDDA) solution (100 g / ml, pH 9.1) containing 1,239 to 2,672 (where n is 1,239 to 2,1672) at room temperature for 5 minutes and then rinsing it three times with distilled water. The PDDA-coated glass substrate was then immersed in an ink containing silver nanoparticles coated with citric acid (10 wt% Ag nanodispersion, average particle size 50 nm, manufactured by Hamamatsu Nano Technology Co., Ltd.) at room temperature and in the dark for a predetermined time (4, 8, 24, or 48 hours) to obtain a conductive laminate (silver particle layer / glass substrate) in which a silver particle layer was formed on the surface of the glass substrate. The glass substrate immersed in the silver nanoink for 4 hours was designated Conductive Laminate 1-1, for 8 hours was designated Conductive Laminate 1-2, for 24 hours was designated Conductive Laminate 1-3, and for 48 hours was designated Conductive Laminate 1-4. As shown in the evaluation of the conductive laminates below, conductive laminates 1-1 and 1-2 are comparative examples, and conductive laminates 1-3 and 1-4 are examples.

[0054] Conductive laminate 2 PDDA may be prepared from a compound having the following structure: [ka] Conductive laminates 2-1 to 2-4 were obtained in the same manner as for producing conductive laminates 1-1 to 1-4, except that the compound was changed to polyethyleneimine (PEI) of formula (wherein n is 581). As will be shown in the evaluation of the conductive laminates below, conductive laminates 2-1 to 2-4 are comparative examples.

[0055] Conductive laminate 3 Conductive laminates 3-1 to 3-4 were obtained in the same manner as for the conductive laminates 1-1 to 1-4, except that PDDA was not used and the glass substrate coated with PDDA was replaced with a glass substrate. As will be shown in the evaluation of the conductive laminates below, conductive laminates 3-1 to 3-4 are comparative examples.

[0056] <Evaluation> The surface morphology of the cationic polymer-coated glass substrate and the conductive laminate (silver particle layer / glass substrate) was observed.

[0057] Microscopic observation of the surface morphology of a glass substrate coated with a cationic polymer The surface morphology of the glass substrate coated with a cationic polymer (PDDA or PEI) and the glass substrate was observed at the micrometer level using a microscope (VHX-D500, manufactured by Keyence Corporation). This observation revealed that there was no significant change in the surface morphology of the glass substrate coated with the cationic polymer and the glass substrate due to the cationic polymer coating.

[0058] Observation of the surface morphology of conductive laminates using a microscope The surface morphology of the conductive laminate was observed at the micrometer level using a microscope (VHX-D500, manufactured by Keyence Corporation). This observation revealed that in the case of Conductive Laminate 3, which did not contain a cationic polymer, there were unformed areas where the silver particle layer was not formed, even when the substrate was immersed in silver nanoink for 48 hours or more. However, in the case of Conductive Laminates 1 and 2, which used a cationic polymer, there were no unformed areas of the silver particle layer if the substrate was immersed in silver nanoink for 4 hours or more. This is thought to be due to the electrostatic force that brings the carboxyl groups of citric acid on the surface of the silver nanoparticles and the cationic functional groups of the cationic polymer into close proximity.

[0059] Observation of the surface morphology of conductive laminates using a scanning electron microscope (SEM) The conductive laminates 1 and 2 (silver particle layer / glass substrate) were subjected to nanometer-level surface morphology observation using an SEM (JSM-7100F, manufactured by JEOL Ltd.) Image analysis was performed using Image J (manufactured by NIH).

[0060] 3 and 4 show the results of SEM observation of the surface morphology of the conductive laminate 1. FIGS. 3A to 3D are SEM images (20,000x magnification) of the surfaces of conductive laminates 1-1 to 1-4, respectively. FIGS. 4A to 4D are SEM images (100,000x magnification) of the surfaces of conductive laminates 1-1 to 1-4, respectively. As shown in FIGS. 3A to 3D and 4A to 4D, when the cationic polymer was PDDA, the silver particle layers of conductive laminates 1-3 and 1-4 obtained by immersing the substrate in silver nanoink for 24 and 48 hours were found to consist of two layers with different particle shapes and particle sizes: a lower layer consisting of densely packed spherical small-diameter silver particles and an upper layer consisting of sparsely packed flat, large-diameter silver particles.

[0061] 5 and 6 show the results of SEM observation of the surface morphology of the conductive laminate 2. FIGS. 5A to 5D are SEM images (20,000x magnification) of the surfaces of conductive laminates 2-1 to 2-4, respectively. FIGS. 6A to 6D are SEM images (100,000x magnification) of the surfaces of conductive laminates 2-1 to 2-4, respectively. As shown in FIGS. 5A to 5D and 6A to 6D, when the cationic polymer was PEI, the silver particle layer of the conductive laminate obtained by immersing the substrate in silver nanoink for 4 to 48 hours was found to consist of a single layer with roughly the same particle diameter.

[0062] Particle size measurement The average particle size (by number) of the silver particles in the silver particle layer of Conductive Laminates 1 and 2 was measured by analyzing images obtained by scanning electron microscope (SEM) observation using Image J (manufactured by NIH). Figure 7 shows the measurement results of the particle size of the silver particles in the silver particle layer of Conductive Laminate 1 and Conductive Laminate 2 (PDDA and PEI, respectively, in Figure 7). The average particle size of Conductive Laminate 1 after immersion for 24 hours and 48 hours (Conductive Laminates 1-3 and 1-4, respectively) indicates the average particle size of the plate-like silver particles in the upper layer.

[0063] As shown in Figure 7, the average particle size of silver particles in conductive laminate 1, in which the cationic polymer was PDDA, was larger than the average particle size of silver particles in conductive laminate 2, in which the cationic polymer was PEI, after immersion for 24 and 48 hours. This is thought to be because PDDA has a larger positive charge than PEI, and the electrostatic force generated between the cationic functional groups of the cationic polymer and the carboxyl groups of citric acid is stronger than that generated by PEI. Also, as shown in Figure 7, when the cationic polymer was PDDA, the average particle size of silver particles in the upper layer after immersion for 48 hours (conductive laminate 1-4) was smaller than that after immersion for 24 hours (conductive laminate 1-3). This is thought to be because the decomposition rate of silver particles was faster than the growth rate during immersion for 24 to 48 hours.

[0064] <Layering of photocatalytic nanosheets> MoS2 nanosheets were laminated on a Si substrate coated with PDDA to prepare a laminate consisting of MoS2 nanosheets / PDDA / Si substrate, and the surface morphology was observed using an atomic force microscope (AFM). This observation revealed that the spacing between the MoS2 nanosheets was approximately 200 nm to 500 nm, and that the large, flat silver particles in the upper layer of the conductive laminates 1-3 and 1-4 were effective in filling the gaps between the MoS2 nanosheets.

[0065] <Reference example> Conductive laminates having a silver particle layer / cationic polymer-coated glass substrate configuration corresponding to Conductive Laminate 1 and 2, and a silver particle layer / glass substrate configuration corresponding to Conductive Laminate 3, were prepared by the photoelectrodeposition method disclosed in JP 2002-139616 A. Specifically, the cationic polymer-coated glass substrate or glass substrate was immersed in a 10 M silver nitrate aqueous solution for a predetermined time (4, 24, or 48 hours) at room temperature and in the dark, washed with a small amount of reducing agent (ethanol), and then irradiated with UV light to obtain a conductive laminate. The surface morphology of the conductive laminate obtained by the photoelectrodeposition method was observed using a microscope. This observation revealed that in the conductive laminates prepared by the photoelectrodeposition method, silver grew dendrites locally, and the silver particle layer did not have a uniform surface. [Explanation of symbols]

[0066] 10: conductive laminate, 11: substrate, 12: silver particle layer, 12A: current collecting layer, 12B: contact layer 20: Water-splitting photocatalytic electrode, 21: Substrate, 22: Silver particle layer, 22A: Current collecting layer, 22B: Contact layer, 23: Water-splitting photocatalytic nanosheet, 24: Conductive laminate

Claims

1. A conductive laminate for a water-splitting photocatalyst electrode, comprising: a substrate coated with a cationic polymer; and a silver particle layer formed on the surface of the substrate, the silver particle layer comprises a current collecting layer formed on the substrate and a contact layer formed on the current collecting layer, the current collecting layer is made of spherical silver particles, and the silver particles are densely present in the current collecting layer; the contact layer is made of tabular silver particles, and the silver particles are sparsely distributed in the contact layer; the average particle size of the silver particles in the contact layer is larger than the average particle size of the silver particles in the current collecting layer, The cationic polymer is a polydiallyldialkylammonium salt. Conductive laminate for water splitting photocatalytic electrodes.

2. 2. The conductive laminate for a water-splitting photocatalyst electrode according to claim 1, wherein the average particle size of the silver particles in the contact layer is 150 nm to 500 nm.

3. 2. The conductive laminate for a water-splitting photocatalyst electrode according to claim 1, wherein the cationic polymer is polydiallyldimethylammonium chloride.

4. A method for producing the conductive laminate for a water-splitting photocatalyst electrode according to any one of claims 1 to 3, comprising: and forming the current collecting layer and the contact layer by immersing the substrate coated with the cationic polymer in an ink containing silver nanoparticles whose surfaces are coated with a protective agent having an anionic group at room temperature and in the dark for 15 hours or more. A method for producing a conductive laminate for a water-splitting photocatalytic electrode.

5. The method for producing a conductive laminate for a water-splitting photocatalyst electrode according to claim 4 , wherein the protective agent having an anionic group is a compound having a carboxyl group.

6. The method for producing a conductive laminate for a water-splitting photocatalyst electrode according to claim 5 , wherein the protective agent having an anionic group is citric acid.

7. A water-splitting photocatalytic electrode comprising the conductive laminate for a water-splitting photocatalytic electrode according to any one of claims 1 to 3 and a water-splitting photocatalyst nanosheet laminated thereon.

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