Water splitting device

Abstract

This water splitting device produces hydrogen through irradiation with light and comprises: an electrolytic cell filled with an electrolyte solution and a water splitting cell immersed in the electrolyte solution. The water splitting cell has: a laminate in which an anode electrode, a hole transport layer, a perovskite battery layer, an electron transport layer, and a cathode electrode are stacked in this order; and an electrically insulating protective material that covers the outer periphery of the laminate. Two or more perovskite battery cells are connected in series in the perovskite battery layer.

Description

water splitting equipment

[0001] The present disclosure relates to a water splitting device that splits water into hydrogen and oxygen using light energy, and more specifically to a water splitting device in which, for example, a water splitting cell including an anode electrode and a cathode electrode is immersed in an electrolyte.

[0002] In order to reduce greenhouse gas emissions, which are considered to be the main cause of global warming, efforts are being made to switch to renewable energy. Electric energy can be obtained from solar power, wind power, tidal power, etc., but hydrogen is seen as a promising alternative fuel. Hydrogen can be used not only as a fuel alternative but also for power generation, so it is expected that demand for hydrogen will increase in the future.

[0003] Hydrogen can be produced by decomposing and reforming fossil fuels such as coal and natural gas at high temperatures, but this method is called gray hydrogen because it emits greenhouse gases during production. There is blue hydrogen, which captures and stores the greenhouse gases emitted, making it essentially zero-emission, but it still emits greenhouse gases. In contrast, the method of producing hydrogen by electrolyzing water using electricity generated from renewable energy sources such as solar power is called green hydrogen because it does not emit greenhouse gases.

[0004] A water electrolysis device uses electrical energy to split water into hydrogen and oxygen. It consists of a power supply that supplies power and an electrolyzer that performs the electrolysis. To obtain electricity from renewable energy, solar panels or wind power generators are used as power supplies. When water is electrolyzed in this device, oxygen is generated from the anode electrode and hydrogen is generated from the cathode electrode. Currently, commercially available water electrolysis devices are either alkaline or PEM types. However, alkaline types have low tolerance to power fluctuations and are incompatible with renewable energy. Furthermore, PEM types are expensive because they use precious metals for the electrodes. To widely disseminate water electrolysis devices, development of semiconductor materials for efficiently converting light energy into electricity, technology for transmitting electricity to the electrolyzer with low loss, and catalysts, electrode configurations, and device structures for efficiently electrolyzing water using electricity are required. Furthermore, because water electrolysis devices are complex systems consisting of a power supply, a power transmission mechanism, and an electrolyzer, a simple structure that integrates these components is required.

[0005] The water splitting device that realized this is TiO ２ A chemical conversion device has been proposed in which TiO, Pt, and Ti are stacked (see, for example, Patent Document 1 below). This chemical conversion device uses TiO, which exhibits high photocatalytic activity in the ultraviolet region. ２ By placing this at the anode electrode, the potential difference required for water splitting can be obtained, allowing water to be split into hydrogen and oxygen.

[0006] Also, TiO ２ A hydrogen generating photovoltaic device has been proposed that has an anode electrode made of stacked ITO, p-Si, and n-Si, and a cathode electrode made of Pt (see, for example, Patent Document 2 below). With this structure, TiO ２ The photocurrent can be shifted to a higher potential side and used, thereby increasing the efficiency of hydrogen generation.

[0007] Furthermore, TiO ２ and TiFe ２ O ３A hydrogen generating device has been proposed in which a series-connected Si solar cell is superimposed on an anode electrode made of a stack of TiO and a Pt cathode electrode is connected (see Patent Document 3 below). ２ and TiFe ２ O ３ When the two layers are made, the anode electrode can absorb energy up to 540 nm, and the electromotive force of the series-connected Si solar cells is generated by TiO ２ and TiFe ２ O ３ The photocurrent can be shifted to a higher potential side and used, thereby increasing the efficiency of hydrogen generation.

[0008] Japanese Patent Application Laid-Open No. 2001-213608 Japanese Patent Application Laid-Open No. 2003-238104 Japanese Patent Application Laid-Open No. 2009-50827

[0009] The water splitting device described above is ２ The band gap of ZnO is 3.0-3.2 eV, and the absorption wavelength edge is 388-413 nm, which is located in the ultraviolet region of the solar spectrum. Because the ultraviolet region accounts for only about 7% of solar energy, high-energy light is required for efficient water splitting.

[0010] The above-mentioned hydrogen generating photovoltaic device has a band gap of 1.2 eV and an absorption wavelength edge of 1033 nm, and exhibits activity at 74% of solar energy. However, when irradiated with light, TiO ２ Since the onset voltage of is higher than the open circuit voltage of Si, it is difficult to obtain the potential required for water electrolysis.

[0011] The above-mentioned hydrogen generating device uses TiFe, which absorbs up to the long wavelength side. ２ O ３ By stacking the series-connected Si solar cells, water can be decomposed into hydrogen and oxygen. However, the anode electrode is TiO ２ and TiFe ２ O ３ The two-layer structure reduces light transmittance and reduces the amount of light energy that reaches the Si solar cell, which reduces the current generated by the Si solar cell and prevents efficient water splitting.

[0012] The present disclosure aims to solve the problem of water splitting apparatuses being complex systems by providing a water splitting apparatus that is highly active with solar energy, has the potential necessary for water electrolysis, and has high photocatalytic activity.

[0013] As a result of extensive consideration of the above-mentioned problems, the water splitting device according to the present disclosure is a water splitting device that generates hydrogen when irradiated with light, and includes an electrolytic cell filled with an electrolyte, and a water splitting cell immersed in the electrolyte, the water splitting cell having a laminate in which an anode electrode on which a mesocrystalline film is formed, a hole transport layer, a perovskite battery layer, an electron transport layer, and a cathode electrode are stacked in this order, and an electrically insulating protective material that covers the outer periphery of the laminate, and the perovskite battery layer is made up of two or more perovskite battery cells connected in series.

[0014] The water splitting cell of the water splitting device according to the present disclosure has a band gap of 1.55 eV in the perovskite cell layer and an absorption wavelength edge of 800 nm, allowing it to utilize 55% of solar energy. In other words, the water splitting cell according to the present disclosure has a wider absorption wavelength range of solar energy than the water splitting device described above, can obtain sufficient potential for water electrolysis compared to the hydrogen generation device described above, and has a higher solar energy conversion efficiency than the hydrogen generation device described above.

[0015] It is a front view of the water splitting device according to Embodiment 1. It is a schematic cross-sectional view schematically showing the cross-sectional structure of a horizontal cross-section viewed in the 1B-1B direction of the water splitting device in FIG. 1A. It is a side cross-sectional view viewed in the 1C-1C direction of the water splitting device in FIG. 1A. It is a diagram showing the relationship between the number of series-connected perovskite battery cells constituting the perovskite battery layer and the current density. It is a diagram showing the relationship between the wavelength and transmittance of light irradiated on the anode electrode. It is a diagram showing the I-V curve of the anode electrode and the perovskite battery layer when the anode electrode and the perovskite battery layer having different transmittances are laminated. It is a diagram showing the relationship between the areal density of the anode electrode and the transmittance of the anode electrode with respect to light having a wavelength of 620 nm. It is a diagram showing the relationship between the transmittance of the anode electrode and the current flowing between the anode electrode and the cathode electrode when a water splitting cell in which the anode electrode and the perovskite battery layer are laminated is irradiated with 1 sun of light. It is Table 1 showing the transmittance of the water splitting cell using anode electrodes having different transmittances and the results of the current when irradiated with 1 sun of light.

[0016] The water splitting device according to the first aspect is a water splitting device that generates hydrogen when irradiated with light, and includes an electrolytic cell filled with an electrolytic solution, and a water splitting cell immersed in the electrolytic solution, the water splitting cell including a laminate in which a mesocrystalline film is formed on an anode electrode, a hole transport layer, a perovskite battery layer, an electron transport layer, and a cathode electrode are sequentially laminated, and an electrically insulating protective material covering the outer periphery of the laminate. The perovskite battery layer has two or more perovskite battery cells connected in series.

[0017] The water splitting device according to the second aspect may have a mesocrystalline film with an aligned orientation formed on the anode electrode in the first aspect.

[0018] The water splitting device according to the third aspect may be such that the anode electrode is a metal oxide in the first or second aspect.

[0019] The water splitting device according to the fourth aspect may be such that the anode electrode is a metal nitride in the first or second aspect.

[0020] A fifth aspect of the water splitting apparatus is the same as the third aspect, wherein the metal oxide is an oxide of Fe, Cu, Zn, or Ni.

[0021] A sixth aspect of the water splitting apparatus is the water splitting apparatus of the fourth aspect, wherein the metal nitride is a nitride of Ta, Ba, La, or Ti.

[0022] A seventh aspect of the present invention is a water decomposition apparatus according to the fifth aspect, wherein the metal oxide is TiFe ２ O ３ may be.

[0023] The water splitting device according to an eighth aspect is the water splitting device according to any one of the first to seventh aspects, wherein the hole transport layer has a hole mobility of 10 －４ ~10 －１ m ２ / s may also be used.

[0024] A ninth aspect of the water splitting device is the water splitting device of any one of the first to eighth aspects, wherein the perovskite battery cell may be a perovskite compound.

[0025] A tenth aspect of the present invention is a water splitting apparatus according to the ninth aspect, wherein the perovskite compound is (CH ３ NH ３ ) PbI ３ may be.

[0026] The water splitting apparatus according to an eleventh aspect is the water splitting apparatus according to any one of the first to tenth aspects, wherein the electron mobility of the electron transport layer is 10 －４ ~10m ２ / s may also be used.

[0027] A twelfth aspect of the water splitting device is the water splitting device of any one of the first to eleventh aspects, wherein a glass plate may be disposed between the anode electrode and the hole transport layer.

[0028] A water splitting apparatus according to a thirteenth aspect may be the water splitting apparatus according to the twelfth aspect, wherein conductive transparent electrode films are formed on both surfaces of the glass plate.

[0029] A water splitting apparatus according to a fourteenth aspect is the water splitting apparatus according to the twelfth or thirteenth aspect, wherein a conductive through electrode may be formed in the glass plate.

[0030] A fifteenth aspect of the water splitting apparatus is the second aspect, wherein the mesocrystal film has a light transmittance of 26 to 41% at 620 nm.

[0031] A sixteenth aspect of the present invention is a water decomposition apparatus according to any one of the first to fifteenth aspects, wherein the electrically insulating protective material is SiO ２ or Al ２ O ３ may be.

[0032] A seventeenth aspect of the water splitting apparatus is any one of the first to sixteenth aspects, wherein the cathode electrode is made of Pt, Ni, Ag, or C.

[0033] Hereinafter, a water splitting apparatus and a water splitting cell according to embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. The following description is an example of a specific embodiment for carrying out the present disclosure, but the present disclosure is not limited to such embodiment.

[0034] (Embodiment 1) <Water splitting apparatus> FIG. 1A is a front view of a water splitting apparatus 100 according to embodiment 1. FIG. 1B is a schematic cross-sectional view showing the horizontal cross-sectional structure of the water splitting apparatus 100 of FIG. 1A as seen in the direction 1B-1B. FIG. 1C is a side cross-sectional view of the water splitting apparatus 100 of FIG. 1A as seen in the direction 1C-1C. In the drawings, the vertically upward direction is the Z direction, the horizontal plane is the XY plane, and the direction in which the oxygen collection port 116 and the hydrogen collection port 115 are aligned is the X direction. In FIG. 1A, as will be described later, the electrolytic cell 102 and the electrolytic solution 103 transmit light, and the anode electrode 106 and the protective material 113 can be seen.

[0035] 1B and 1C , an example is shown in which a water-splitting cell 101 is immersed in an electrolyte 103 filled in an electrolytic cell 102. The water-splitting cell 101 has a first transparent electrode film 105 and an anode 106 disposed on one surface of a glass plate 104. A second transparent electrode film 107, a hole transport layer 108, a perovskite battery layer 109, an electron transport layer 110, and a cathode 111 disposed on the other surface of the glass plate 104. The first transparent electrode film 105 and the second transparent electrode film 107 may be electrically connected by a through electrode (not shown) provided in the glass plate 104. Furthermore, the edge of the laminate 112 consisting of the anode electrode 106, the first transparent electrode film 105, the glass plate 104, the second transparent electrode film 107, the hole transport layer 108, the perovskite battery layer 109, the electron transport layer 110, and the cathode electrode 111 is covered with a protective material 113.

[0036] The protective material 113 of the water splitting cell 101 is fixed to the inner wall 114 of the electrolytic cell 102, and the water splitting cell 101 divides the electrolyte 103 into two, an anode electrode side and a cathode electrode side. The electrolyte 103 on the anode electrode side and the electrolyte 103 on the cathode electrode side can move back and forth through a space (not shown) provided outside the electrolytic cell 102, so the structure allows ion exchange between the electrolyte 103 on the anode electrode side and the electrolyte 103 on the cathode electrode side.

[0037] The water splitting device according to the first embodiment is a device that splits water into hydrogen and oxygen using light energy. For example, when light energy is irradiated from the anode electrode 106 side, electrons are excited in the anode electrode 106 and the perovskite cell layer 109, and the electrons move to the cathode electrode 111, where they reduce hydrogen ions and generate hydrogen. Meanwhile, hydroxide ions are oxidized in the anode electrode 106 to generate oxygen. The generated hydrogen is collected through the hydrogen collection port 115, and the oxygen is collected through the oxygen collection port 116.

[0038] The water splitting cell of the water splitting device 100 according to the first embodiment has a band gap of 1.55 eV in the perovskite cell layer and an absorption wavelength edge of 800 nm, and is therefore capable of utilizing 55% of solar energy.

[0039] Furthermore, according to the water splitting device 100 of the first embodiment, the onset voltage of the anode electrode 106 when irradiated with light is lower than the open circuit voltage of the perovskite battery layer 109, and therefore, the potential required for water electrolysis can be obtained.

[0040] Furthermore, the anode electrode 106 has a mesocrystalline structure in which the metal oxides are oriented in a regular order, and therefore the photocatalytic activity can be improved.

[0041] In the water splitting device 100 according to the first embodiment, the anode electrode 106, hole transport layer 108, perovskite battery layer 109, electron transport layer 110, and cathode electrode 111 required for water splitting are stacked and immersed in an electrolyte. As a result, when the water splitting device 100 according to the first embodiment is used in a device that splits water into hydrogen and oxygen using light energy, an external power supply and power transmission mechanism are not required, and a simple configuration consisting of only the electrolytic cell 102 is possible. In addition, because hydrogen and oxygen are generated in different spaces, a gas separation device is not required. Furthermore, the stacked structure of the anode electrode 106, hole transport layer 108, perovskite battery layer 109, electron transport layer 110, and cathode electrode 111 enables efficient use of light energy.

[0042] The components that make up this water splitting apparatus 100 will be described below.

[0043] <Water Splitting Cell> The water splitting cell 101 includes a laminate 112 including an anode electrode 106, a first transparent electrode film 105, a glass plate 104, a second transparent electrode film 107, a hole transport layer 108, a perovskite battery layer 109, an electron transport layer 110, and a cathode electrode 111. Each layer, except for the glass plate 104, is electrically connected to the other layers. In FIGS. 1A to 1C, the laminate 112 has a structure in which each layer is in contact with the other layers, but this is not limited thereto. For example, the laminate may have a 1 mm gap between the glass plate 104 and the second transparent electrode film 107. Alternatively, a second glass plate with a through electrode may be added to hold the second transparent electrode film. In this case, additional electrical wiring is provided between the through electrode (not shown) of the glass plate 104 and the second transparent electrode film 107.

[0044] The size of the laminate 112 is, for example, 50 mm in length and 25 mm in width. Furthermore, the entire periphery of the edge of the laminate 112 is covered with a protective material 113. This structure prevents the electrolyte solution 103 from penetrating into the perovskite battery layer 109 disposed inside the laminate 112, thereby preventing deterioration of the perovskite battery layer 109. The size of the laminate 112 is not limited to 50 mm x 25 mm, and can be any size, such as 100 mm x 100 mm, 300 mm x 300 mm, etc.

[0045] <Anode Electrode> The material of the anode electrode 106 is, for example, TiFe. ２ O ３ The mesocrystals are made of TiFe, and have a thickness of, for example, 1 μm. Mesocrystals are particle aggregates in which crystalline nanoparticles are densely and regularly aligned and assembled. Metal oxide mesocrystals allow for more efficient charge transport than bulk metals because the crystalline nanoparticles are in regular contact with each other. ２ O ３ The average particle diameter of the anode electrode 106 is, for example, 100 nm, and the anode electrode 106 is formed as a thin film on the first transparent electrode film 105 using an electrostatic spray device. The thin film formation is not limited to electrostatic spraying, but may also be performed by spin coating, dip coating, die coating, bar coating, inkjet, or the like. The anode electrode 106 must be chemically stable in the electrolyte solution 103 so as not to react with the electrolyte solution 103 and corrode or cause a chemical reaction. The anode electrode 106 must also be capable of conducting excited electrons, and must also be reactive enough to cause an oxidation reaction on the anode electrode and generate oxygen. The anode electrode 106 is made of TiFe. ２ O ３ The metal oxide may be Cu, Zn, Ni, or the like. ３ N ５ , BaTaO ２ N, LaTiO ２ Metal nitrides such as N may also be used.

[0046] The anode electrode 106 has a mesocrystalline structure in which metal oxide particles are aligned and regularly arranged, and therefore can improve photocatalytic activity.

[0047] <Glass Plate> The glass plate 104 is made of, for example, aluminoborosilicate glass and has a thickness of, for example, 1.0 mm. In order for the perovskite battery layer 109 to absorb the light energy incident from the anode electrode 106 side, the average transmittance for wavelengths of 500 to 800 nm must be at least 60%, and an average transmittance of 70% is desirable. The material of the glass plate 104 is not limited to aluminoborosilicate glass, and quartz glass, aluminum oxide glass, soda-lime glass, etc. may also be used. The thickness is not limited to 1.0 mm, and may be 2.2 mm or 0.8 mm. In the manufacturing process of the laminate 112, the anode electrode 106, the perovskite battery layer 109, etc. are formed on both sides of the glass plate 104 by heat treatment, so the glass plate 104 needs to be heat-resistant enough to withstand the heat treatment.

[0048] <Hole Transport Layer> The material of the hole transport layer 108 is, for example, 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), and its thickness is 100 nm. The hole transport layer 108 is disposed to facilitate the movement of holes generated in the perovskite cell layer 109 by irradiation with light energy toward the anode electrode 106. To facilitate the movement of holes, the hole transport layer 108 has a hole mobility of 10 －４ ~10 －１ m ２ / s. Furthermore, to allow smooth hole movement between the second transparent electrode film 107 and the perovskite battery layer 109, which are disposed on both sides of the hole transport layer 108, the energy levels of these materials are adjusted. The material of the hole transport layer 108 is not limited to Spiro-OMeTAD, but may also be PEDOT:PSS or polyaniline. Furthermore, the thickness of the hole transport layer 108 is not limited to 100 nm, but may be any thickness within the range of 20 nm to 200 nm.

[0049] <Perovskite Battery Layer> The perovskite battery layer 109 is a solar cell that uses a semiconductor material (perovskite semiconductor) having a perovskite structure. ３ NH ３ PbI ３ The total thickness of the perovskite battery layer 109 is 0.3 μm. The perovskite structure has a chemical formula of ABX ３ In a typical perovskite structure, A is an alkali metal, B is a transition metal, and X is a halogen atom. ３ NH ３ PbI ３ So, A is a methylammonium ion (CH ３ NH ３ ) ＋ , B is lead (II) ion Pb ２＋ , and X is a halide ion I － is.

[0050] FIG. 2 is a diagram showing the relationship between the number of series-connected perovskite battery cells constituting the perovskite battery layer 109 and the current density.

[0051] In order to utilize the photocurrent generated in the anode electrode 106 on the high potential side, the perovskite battery layer 109 increases the voltage by forming a series structure within the layer. The series structure is formed by dividing the surface of the perovskite battery layer 109 into two or more parts, and connecting each perovskite battery cell in series. Here, the relationship between the number of series of perovskite battery cells and the current density will be explained using Figure 2. In Figure 2, the horizontal axis represents the number of series of cells, and the vertical axis represents the voltage and current density. When the number of series is 1, for example, the voltage is 1 V and the current density is 22 mA / cm. ２ If two of these cells are connected in series within a layer, the voltage will be 2 V, but the light-receiving area will be halved, so the current density will be 11 mA / cm ２ Furthermore, if three are connected in series, the voltage will be 3 V, but the light-receiving area will be 1 / 3, so the current density will be 7.3 mA / cm ２As described above, since there is a trade-off between voltage and current density, the number of series of perovskite battery cells when connecting from the metal oxide mesocrystal to the anode electrode 106 is preferably 2 or 3. Therefore, if the number of series is increased to 4 or more, the light receiving area per perovskite battery cell decreases, which is undesirable as it reduces the current value obtained. Laser patterning is a preferred method for forming a series structure of perovskite battery cells within a layer. The perovskite battery layer 109 is made of CH ３ NH ３ PbI ３ Not limited to CH ３ NH ３ PbCl ３ and CH ３ NH ３ PbBr ３ Perovskite semiconductors deteriorate due to moisture, so they need to be durable against water for long-term use.

[0052] <Electron Transport Layer> The material of the electron transport layer 110 is, for example, TiO ２ The electron transport layer 110 is disposed to facilitate the movement of electrons generated in the perovskite cell layer 109 by irradiation with light energy toward the cathode electrode 111. In order to facilitate the movement of electrons, the electron mobility of the electron transport layer 110 is set to, for example, 10 －４ ~10m ２ / s, and more preferably 10 －３ ~10 －１ m ２ / s. In order to smoothly transfer electrons between the perovskite battery layer 109 and the cathode electrode 111, which are disposed on both sides of the electron transport layer 110, the energy levels of these materials are adjusted. The material of the electron transport layer 110 is TiO ２ Not limited to ZnO and SrTiO ３ Furthermore, the thickness of the electron transport layer 110 is not limited to 80 nm, but can be selected arbitrarily within the range of 20 nm to 100 nm.

[0053] <Cathode Electrode> The cathode electrode 111 is made of, for example, Pt and has a thickness of, for example, 0.1 mm. The cathode electrode 111 needs to be chemically stable in the electrolyte solution 103 so as not to react with the electrolyte solution 103 and corrode or cause a chemical reaction. The cathode electrode 111 also needs to be capable of conducting excited electrons, and further needs to be reactive enough to cause a reduction reaction on the cathode electrode and generate hydrogen. The material of the cathode electrode 111 is not limited to Pt, but may be Ni, Ag, C (carbon), or the like. In the case of C (carbon), it is not limited to carbon, and may be in the form of graphite, graphene, or the like.

[0054] <Protective Material> The protective material 113 is, for example, SiO ２ The thickness is, for example, 2.0 mm. The thickness is the distance from the position where the protective material 113 contacts the laminate 112 to the surface of the protective material 113, and the protective material 113 is formed on the side of the laminate 112, the end on the anode electrode 106 side, and the end on the cathode electrode 111 side. The material of the protective material 113 is SiO ２ However, if water resistance can be obtained, SiO ２ Not limited to Al ２ O ３ , MgO, etc. may also be used.

[0055] The protective material 113 is fixed to an inner wall 114 of the electrolytic cell 102. As shown in FIG. 1C , the water splitting cell 101 and the protective material 113 divide the upper space of the electrolytic cell 102 into two sections, an anode electrode side and a cathode electrode side. As a result, hydrogen generated from the cathode electrode 111 and oxygen generated from the anode electrode 106 are generated in different spaces, and no gas separation device is required. In this case, as described above, the electrolytic solution 103 on the anode electrode side and the electrolytic solution 103 on the cathode electrode side can move back and forth through a space or the like (not shown), allowing ion exchange between the electrolytic solution 103 on the anode electrode side and the electrolytic solution 103 on the cathode electrode side.

[0056] <Electrolytic Cell> The electrolytic cell 102 is made of, for example, borosilicate glass and has a thickness of, for example, 4 mm. The electrolytic cell 102 is filled with an electrolyte 103, and the water-splitting cell 101 is immersed in the electrolytic cell 102. When light is irradiated from the anode electrode 106 side of the water-splitting cell 101, some of the light is absorbed by the anode electrode 106, and the unabsorbed light reaches the perovskite cell layer 109. At this time, electrons and holes are generated by photoexcitation in the anode electrode 106 and the perovskite cell layer 109. The electrons move toward the cathode electrode 111, and the holes move toward the anode electrode 106, and each participates in the oxidation-reduction reaction of hydrogen and oxygen. The material of the electrolytic cell 102 is borosilicate glass; however, it is not limited to borosilicate glass; soda-lime glass, quartz glass, transparent resin, and the like may be used as long as it is light-transmitting. Furthermore, since light is irradiated from the anode electrode 106 side, the five surfaces other than the anode electrode 106 side may be made of a material that does not transmit light. Examples of materials that do not transmit light include metals such as aluminum and stainless steel. If the material is one that does not transmit light but reflects it, the light energy that is not absorbed by the laminate 112 and is transmitted or reflected can be irradiated back onto the laminate 112, thereby increasing the efficiency of light energy utilization. Furthermore, the entire surface of the anode electrode 106 side of the electrolytic cell 102 does not need to be made of a material that transmits light; it is sufficient if at least the area of ​​the laminate 112 is made of a material that transmits light.

[0057] <Electrolyte> The electrolyte 103 is, for example, a sodium hydroxide solution, and the hydroxide ion concentration is 1 mol / L. The electrolyte 103 is not limited to a nanothorium hydroxide solution, and may be a potassium hydroxide solution, a sodium bicarbonate solution, or the like, as long as it is a conductive liquid.

[0058] <Transmittance of anode electrode> The water splitting cell 101 has a structure in which an anode electrode 106 and a perovskite cell layer 109 are stacked, and light is irradiated from the anode electrode 106 side. A part of the irradiated light is absorbed by the anode electrode 106, and the unabsorbed light passes through the anode electrode 106 and reaches the perovskite cell layer 109, where it is absorbed. As an example, ２ O ３ The weight per unit area of ​​Fe (hereinafter referred to as "weight") is 58 μg / cm２ The spectral transmittance of the anode electrode 106 fabricated in the above is shown in FIG. 3. Here, the basis weight was quantitatively analyzed by the fluorescent X-ray intensity of Fe using an energy dispersive X-ray fluorescence analyzer. In the wavelength range of 550 nm or less, the transmittance is 10% or less, and most of the light is absorbed. As the wavelength becomes longer, the transmittance increases, and in the wavelength range of 700 nm or more, the transmittance is 50% or more, and the transmitted light increases. TiFe ２ O ３ The band gap of is 1.97 eV and the absorption wavelength edge is 620 nm, so the absorption rate changes significantly around that wavelength. ２ The transmittance at this time is shown in Figure 3. As the basis weight increases, the amount of light absorbed increases, so the transmittance decreases, and as the basis weight decreases, the amount of light absorbed decreases, so the transmittance increases.

[0059] <I-V Curve> Because the anode electrode 106 and the perovskite battery layer 109 are stacked, when the amount of light absorbed by the anode electrode 106 is large, many electrons are excited in the anode electrode 106, but the number of excited electrons in the perovskite battery layer 109 decreases. On the other hand, when the amount of light absorbed by the anode electrode 106 is small, fewer electrons are excited in the anode electrode 106, and the number of excited electrons in the perovskite battery layer 109 increases. Figure 4A shows the I-V curves of anode electrodes 106 with different basis weights, and the I-V curves of the perovskite battery layer 109 alone when each anode electrode 106 and perovskite battery layer 109 are stacked. "High," "Intermediate," and "Low" in Figure 4 refer to the basis weight of the anode electrode 106. When the basis weight of the anode electrode 106 is "high," the current value of the anode electrode 106 is high, but the current value of the perovskite battery layer 109 is low. When the basis weight of the anode electrode 106 is reduced to "medium", the current value of the perovskite battery layer 109 increases. When the basis weight of the anode electrode 106 is reduced to "low", the current value of the perovskite battery layer 109 increases further.

[0060] When the anode electrode 106 and the perovskite battery layer 109 are electrically connected, a current flows as indicated by the intersection of the IV curves of the anode electrode 106 and the perovskite battery layer 109. An enlarged view of the area around the intersection of the IV curves in FIG. 4A is shown in FIG. 4B. The current value indicated by the intersection varies depending on the basis weight of the anode electrode 106, and the current value is highest when the basis weight is "medium." This indicates that the efficiency of water splitting is highest when the basis weight is "medium."

[0061] <Anode Electrode Coating Weight and Transmittance> The water splitting apparatus according to the first embodiment has a structure in which the anode electrode 106 and the perovskite cell layer 109 are stacked. For this reason, it is necessary to adjust the light energy that passes through the anode electrode 106 and reaches the perovskite cell layer 109 within an appropriate range, and the transmittance of the anode electrode 106 in particular plays an important role.

[0062] 5 shows the relationship between the basis weight of the anode electrode 106 and the transmittance of the anode electrode 106 for light with a wavelength of 620 nm. ２ The transmittance is 46% and the weight is 36 μg / cm ２ The transmittance decreases with increasing basis weight, and at a basis weight of 139 μg / cm ２ The transmittance at this time is 23%.

[0063] <Transmittance of Anode Electrode and Photocurrent> Figure 6 shows the current that flows between the electron transport layer 110 and the cathode electrode 111 when light of 1 sun is irradiated onto a water splitting cell stacked with an anode electrode 106, a first transparent electrode film 105, a glass plate 104, a second transparent electrode film 107, a hole transport layer 108, a perovskite battery layer 109, an electron transport layer 110, and a cathode electrode 111. The black circles indicate that the perovskite battery layer is made up of two perovskite battery cells connected in series (2-series), the triangle triangle indicates that the perovskite battery layer is made up of three perovskite battery cells connected in series (3-series), and the square square indicates that the perovskite battery layer is made up of four perovskite battery cells connected in series (4-series).

[0064] 6, the horizontal axis represents the transmittance of the anode electrode 106 to light of 620 nm, and the vertical axis represents the current value between the lead terminals of the electron transport layer 110 and the cathode electrode 111. In order to measure the current value, the electrical connection between the electron transport layer 110 and the cathode electrode 111 is cut off, and lead terminals are drawn out from the electron transport layer 110 and the cathode electrode 111 and connected to a multimeter to measure the current.

[0065] When two perovskite battery layers are connected in series, the current value is 41.9 mA when the transmittance of the anode electrode 106 is 34%, decreases to 37.7 mA when the transmittance is 32%, and decreases to 35.2 mA when the transmittance is 30%. This is thought to be because the decrease in transmittance reduces the amount of light energy reaching the perovskite battery layer 109, resulting in a decrease in the number of electrons excited in the perovskite battery layer 109. On the other hand, the current value is 41.9 mA when the transmittance of the anode electrode 106 is 34%, decreases to 39.8 mA when the transmittance is 36%, and decreases to 35.9 mA when the transmittance is 37%. This is thought to be because the amount of mesocrystals in the anode electrode 106 decreases, resulting in a decrease in the number of electrons excited in the anode electrode 106.

[0066] As can be seen from FIG. 6 , the current flowing between the electron transport layer 110 and the cathode electrode 111 decreases as the transmittance of the anode electrode 106 decreases. The current value is preferably 24 mA or more, more preferably 33 mA or more. Therefore, the transmittance of the anode electrode 106 needs to be 26% or more, preferably 30% or more. Furthermore, the current value also decreases when the transmittance of the anode electrode 106 increases. Since the current value is preferably 24 mA or more, more preferably 33 mA or more, the transmittance of the anode electrode 106 needs to be 41% or less, preferably 37% or less.

[0067] When three perovskite battery layers are connected in series, the current value is 33.1 mA when the transmittance of the anode electrode 106 is 34%, decreases to 30.2 mA when the transmittance is 32%, and decreases to 31.9 mA when the transmittance is 36%. The current value is 21.5 mA when the transmittance of the anode electrode 106 is 26%, and 19.0 mA when the transmittance is 44%.

[0068] The current value is preferably 24 mA or more, and more preferably 33 mA or more. Therefore, when three perovskite battery layers are connected in series, the transmittance of the anode electrode 106 needs to be 28% or more, and preferably 34%. Furthermore, when the transmittance of the anode electrode 106 is high, the current value also decreases. The current value is preferably 24 mA or more, and more preferably 33 mA or more, and therefore the transmittance of the anode electrode 106 needs to be 41% or less, and preferably 34%.

[0069] Therefore, in a preferred aspect of the first embodiment, when the perovskite battery layer is a two-series connection of two perovskite battery cells, the transmittance of the anode electrode 106 is 26 to 41%, and in a more preferred aspect, 30 to 37%. When the perovskite battery layer is a three-series connection of three perovskite battery cells, the transmittance of the anode electrode 106 is 28 to 41%, and in a more preferred aspect, 34%. When the transmittance of the anode electrode 106 falls within this range, the stacked structure of the anode electrode 106, first transparent electrode film 105, glass plate 104, second transparent electrode film 107, hole transport layer 108, perovskite battery layer 109, electron transport layer 110, and cathode electrode 111 enables efficient use of light energy.

[0070] In water splitting devices, it is necessary to utilize light energy efficiently to improve economic efficiency. To investigate this, water splitting cells with various anode electrode weights were fabricated in the same manner as above, and experiments were conducted to evaluate the current values. The results are shown in Table 1 of FIG. 7.

[0071] In the judgment column of Table 1 in FIG. 7, a more preferable current value is set to 24 mA or more, and "A" indicates a good evaluation, "S" indicates a current value of 33 mA or more, which is a sufficiently good evaluation, and "B" indicates a current value of less than 24 mA.

[0072] [Example 1] Weight per unit area: 80 μg / cm ２ The anode electrode was fabricated, and the transmittance was measured, which was 34%. A water splitting cell using this anode electrode was immersed in an electrolyte solution, and the current value between the electron transport layer and the cathode electrode was evaluated in the same manner as above. The current value measured in this water splitting device was 41.9 mA. This means that a sufficient amount of hydrogen was generated.

[0073] Examples 2 to 21 As in Example 1, a water splitting cell using an anode electrode having a transmittance shown in Table 1 of FIG. 7 was immersed in an electrolyte solution, and the current value between the electron transport layer and the cathode electrode was evaluated using a water splitting device. As can be seen from Table 1 of FIG. 7 , in the case of a two-series perovskite battery layer consisting of two perovskite battery cells connected in series, a more preferable current value was obtained when the anode electrode transmittance was 26% or more and 41% or less. Furthermore, a particularly preferable current value was obtained and high efficiency was realized when the anode electrode transmittance was 30% or more and 37% or less. Furthermore, in the case of a three-series perovskite battery layer consisting of three perovskite battery cells connected in series, a more preferable current value was obtained when the anode electrode transmittance was 28% or more and 41% or less. Furthermore, a particularly preferable current value was obtained and high efficiency was realized when the anode electrode transmittance was 34%.

[0074] [Comparative Examples 1 to 3] As in Example 1, the current value between the electron transport layer and the cathode electrode was evaluated using a water splitting device in which a water splitting cell using an anode electrode having a transmittance shown in Table 1 of FIG. 7 was immersed in an electrolyte. As can be seen from Table 1 of FIG. 7, when four perovskite battery layers were connected in series, a desirable current value of 24 mA or more could not be obtained. ２ O ３ Although the examples and comparative examples have been described, Fe ２ O ３This is true not only when Ti is doped but also when a metal other than Ti is doped.

[0075] These results demonstrate that a water splitting cell having a laminate including an anode electrode 106, a first transparent electrode film 105, a glass plate 104, a second transparent electrode film 107, a hole transport layer 108, a perovskite battery layer 109, an electron transport layer 110, and a cathode electrode 111, and in which the transmittance of the anode electrode is adjusted to fall within a predetermined range, can efficiently utilize light energy.

[0076] When the water splitting device according to the present disclosure is used, the anode electrode 106, the first transparent electrode film 105, the glass plate 104, the second transparent electrode film 107, the hole transport layer 108, the perovskite battery layer 109, the electron transport layer 110, and the cathode electrode 111, which are all required for water splitting, are stacked and immersed in an electrolytic solution. This eliminates the need for an external power supply and power transmission mechanism, allowing for a simple configuration consisting of only an electrolytic cell. Furthermore, because hydrogen and oxygen are generated in different spaces, a gas separation device is not required. Furthermore, the stacked structure of the anode electrode 106, the first transparent electrode film 105, the glass plate 104, the second transparent electrode film 107, the hole transport layer 108, the perovskite battery layer 109, the electron transport layer 110, and the cathode electrode 111 enables efficient use of light energy.

[0077] REFERENCE SIGNS LIST 100 Water splitting device 101 Water splitting cell 102 Electrolytic cell 103 Electrolyte 104 Glass plate 105 First transparent electrode film 106 Anode electrode 107 Second transparent electrode film 108 Hole transport layer 109 Perovskite cell layer 110 Electron transport layer 111 Cathode electrode 112 Laminate 113 Protective material 114 Inner wall 115 Hydrogen collection port 116 Oxygen collection port

Claims

1. A water splitting device that generates hydrogen when irradiated with light, comprising: an electrolytic cell filled with an electrolyte; and a water splitting cell immersed in the electrolyte, the water splitting cell having an anode electrode on which a mesocrystalline film is formed, a hole transport layer, a perovskite battery layer, an electron transport layer, and a cathode electrode stacked in that order; and an electrically insulating protective material covering the outer periphery of the stack, wherein the perovskite battery layer is two or more perovskite battery cells connected in series.

2. The water splitting apparatus according to claim 1, wherein a mesocrystalline film with uniform orientation is formed on the anode electrode.

3. The water splitting apparatus according to claim 1, wherein the anode electrode is a metal oxide.

4. The water splitting apparatus according to claim 1, wherein the anode electrode is a metal nitride.

5. The water splitting apparatus according to claim 3, wherein the metal oxide is an oxide of Fe, Cu, Zn or Ni.

6. The water splitting apparatus according to claim 4, wherein the metal nitride is a nitride of Ta, Ba, La or Ti.

7. The metal oxide is TiFe ２ O ３ The water splitting apparatus according to claim 5 , 8. The hole transport layer has a hole mobility of 10 －４ ~10 －１ m ２ 2. The water splitting apparatus of claim 1, wherein the ratio of the molten metal to the molten metal is 0.1 to 0.

2.

9. The water splitting apparatus of claim 1, wherein the perovskite battery cell is a perovskite compound.

10. The perovskite compound is (CH ３ NH ３ ) PbI ３ The water splitting apparatus according to claim 9, 11. The electron mobility of the electron transport layer is 10 －４ ~10m ２ 2. The water splitting apparatus of claim 1, wherein the ratio of the molten metal to the molten metal is 0.1 to 0.

2.

12. The water splitting apparatus of claim 1, wherein a glass plate is disposed between the anode electrode and the hole transport layer.

13. The water splitting apparatus according to claim 12, wherein conductive transparent electrode films are formed on both sides of the glass plate.

14. The water splitting apparatus according to claim 12, wherein the glass plate has a conductive through electrode formed therein.

15. The water splitting apparatus according to claim 2, wherein the mesocrystalline film has a light transmittance of 26 to 41% at 620 nm.

16. The electrically insulating protective material is SiO ２ or Al ２ O ３ The water splitting apparatus according to claim 1 , 17. The water splitting apparatus according to claim 1, wherein the material of the cathode electrode is Pt, Ni, Ag, or C.

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