Photo-driven fuel cell, catalyst for cathode thereof, catalyst for anode thereof, and methanol production method including step of converting methane into methanol

Abstract

Provided is a light-driven fuel cell having excellent power generation characteristics. The light-driven fuel cell includes a cathode, an anode, and a proton-permeable membrane between the cathode and the anode, the anode includes a light catalyst for an anaerobic methane oxidation reaction, methane and water are supplied to the anode, and light is irradiated, and through the anaerobic methane oxidation reaction, the methane and the water supplied to the anode generate methanol, protons, and electrons, the protons pass through the proton-permeable membrane and move to the cathode, the electrons move to the cathode via an external circuit, the cathode includes a light catalyst for an aerobic methane oxidation reaction, methane and oxygen are supplied to the cathode, and light is irradiated, and through the aerobic methane oxidation reaction, the methane and the oxygen supplied to the cathode, and the protons and the electrons moved from the anode generate methanol and water.

Description

Technical Field

[0001] This invention relates to a light-driven fuel cell, a catalyst for its cathode, a catalyst for its anode, and a methanol manufacturing method including the step of converting methane into methanol. Background Technology

[0002] Previously, various types of fuel cells, such as solid polymer fuel cells, alkaline electrolyte fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells, have been developed and put into practical use. More recently, fuel cells using photocatalysts (photocatalyst-driven fuel cells) have been proposed. These photocatalyst-driven fuel cells require light irradiation of the anode and can use organic compounds and nitrogen-containing compounds contained in biomass, waste, etc., as fuel. Therefore, photocatalyst-driven fuel cells have the advantage of effectively utilizing resources, a feature not found in previous fuel cells.

[0003] Non-Patent Document 1 describes a fuel cell in which a thin layer of titanium dioxide is used in the anode, platinum is used in the cathode, glucose is oxidized by photocatalysis on the titanium dioxide electrode, and the generated electrons are extracted to an external circuit to generate electricity (see [link to patent document]). Figure 1 ).

[0004] Existing technical documents

[0005] Non-patent literature

[0006] Non-patent literature 1: J. Appl. Electrochem., 37, 1039 (2007) Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Previous solar-driven fuel cells have not fully demonstrated the power generation characteristics of their counterparts.

[0009] Therefore, the object of the present invention is to provide a light-driven fuel cell with excellent power generation characteristics.

[0010] Methods for solving problems

[0011] To achieve the aforementioned objectives, the light-driven fuel cell of the present invention has the following characteristics:

[0012] [1] A light-driven fuel cell, comprising a cathode, an anode, and a proton-permeable membrane between the cathode and the anode.

[0013] The aforementioned anode is equipped with a photocatalyst for anaerobic methane oxidation. Methane and water are supplied to the aforementioned anode, and light is irradiated. Through the anaerobic methane oxidation reaction, methanol, protons, and electrons are generated from the aforementioned methane and water supplied to the aforementioned anode. The aforementioned protons pass through the aforementioned proton-permeable membrane and move towards the aforementioned cathode, while the aforementioned electrons move towards the aforementioned cathode via an external circuit.

[0014] The aforementioned cathode is equipped with a photocatalyst for aerobic methane oxidation reaction. Methane and oxygen are supplied to the aforementioned cathode and light is irradiated. Through aerobic methane oxidation reaction, methanol and water are generated from the aforementioned methane and oxygen supplied to the aforementioned cathode, as well as the aforementioned protons and aforementioned electrons moving from the aforementioned anode.

[0015] The present invention also includes the following inventions.

[0016] [2] As described in [1], the photocatalyst for the aforementioned anaerobic methane oxidation reaction comprises an organometallic complex.

[0017] [3] As described in [2], the light-driven fuel cell contains an organometallic complex in the aforementioned photocatalyst for anaerobic methane oxidation, which has pentamethylcyclopentadiene as a ligand and iridium as a metal center.

[0018] [4] As described in [2], the light-driven fuel cell contains an organometallic complex in the aforementioned photocatalyst for anaerobic methane oxidation, which has cyclopentadiene as a ligand and manganese or iron as a metal center.

[0019] [5] The light-driven fuel cell as described in any one of [1] to [4], wherein the aforementioned photocatalyst for aerobic methane oxidation reaction comprises an organometallic complex.

[0020] [6] As described in [5], the light-driven fuel cell contains an organometallic complex in the aforementioned photocatalyst for aerobic methane oxidation reaction, which has pentamethylcyclopentadiene as a ligand and ruthenium as a metal center.

[0021] [7] The light-driven fuel cell as described in any one of [1] to [6] has an anode-side transparent substrate and a cathode-side transparent substrate that are at least partially transparent.

[0022] The aforementioned anode is located between the aforementioned anode-side transparent substrate and the aforementioned proton-permeable membrane, and / or the aforementioned cathode is located between the aforementioned cathode-side transparent substrate and the aforementioned proton-permeable membrane.

[0023] [8] As described in [7], a light-driven fuel cell, wherein,

[0024] (1) The aforementioned cathode comprises a layer containing a photocatalyst for aerobic methane oxidation reaction and a cathode-side gas diffusion layer.

[0025] (2) The aforementioned anode comprises a layer containing a photocatalyst for anaerobic methane oxidation and an anode-side gas diffusion layer.

[0026] (3) The aforementioned cathode-side gas diffusion layer is disposed toward the aforementioned cathode-side light-transmitting substrate, the aforementioned anode-side gas diffusion layer is disposed toward the aforementioned anode-side light-transmitting substrate, the aforementioned layer containing the photocatalyst for aerobic methane oxidation reaction is disposed toward the cathode-side membrane surface of the aforementioned proton-permeable membrane, and the aforementioned layer containing the photocatalyst for anaerobic methane oxidation reaction is disposed toward the anode-side membrane surface of the aforementioned proton-permeable membrane.

[0027] [9] A photocatalyst for anaerobic methane oxidation reaction, comprising an organometallic complex having pentamethylcyclopentadiene as a ligand and iridium as a metal center.

[0028]

[10] A photocatalyst for anaerobic methane oxidation reaction, comprising an organometallic complex having cyclopentadiene as a ligand and manganese or iron as a metal center.

[0029]

[11] A method for producing methanol, comprising the step of contacting a photocatalyst for the anaerobic methane oxidation reaction described in [9] or

[10] with methane and water.

[0030]

[12] A photocatalyst for aerobic methane oxidation reaction, comprising an organometallic complex having pentamethylcyclopentadiene as a ligand and ruthenium as a metal center.

[0031]

[13] A method for producing methanol, comprising the step of contacting the photocatalyst for the aerobic methane oxidation reaction described in

[12] with methane and oxygen.

[0032] The effects of the invention

[0033] According to the present invention, a light-driven fuel cell with excellent power generation characteristics can be provided.

[0034] Furthermore, according to the present invention, a compact light-driven fuel cell can be provided that does not require a desulfurizer, reformer, CO converter, water vapor separator, etc. Additionally, according to the present invention, a catalyst for the cathode of a light-driven fuel cell, a catalyst for the anode of a light-driven fuel cell, and a methanol manufacturing method including the step of converting methane into methanol can be provided. Attached Figure Description

[0035] [ Figure 1 ] Figure 1A conceptual diagram illustrating the generator mechanism of dye-sensitized solar cells in the prior art.

[0036] [ Figure 2 ] Figure 2 A conceptual diagram illustrating the generator principle involved in this invention is provided.

[0037] [ Figure 3 ] Figure 3 This is a schematic diagram illustrating the structure and material conversion of a light-driven fuel cell according to one aspect of the present invention.

[0038] [ Figure 4 ] Figure 4 A conceptual diagram illustrating the energy diagram of the present invention.

[0039] [ Figure 5A ] Figure 5A This is a cross-sectional schematic diagram illustrating the main body of a reaction device for a light-driven fuel cell according to one aspect of the present invention.

[0040] [ Figure 5B ] Figure 5B This is a plan view of the current collector, which is a component of a light-driven fuel cell according to one aspect of the present invention.

[0041] [ Figure 6 ] Figure 6 The results of X-ray crystal structure analysis of the organometallic complexes involved in the embodiments of the present invention are shown.

[0042] [ Figure 7 ] Figure 7 A diagram illustrating the measurement system involved in this application.

[0043] [ Figure 8 ] Figure 8 A graph illustrating the power generation performance of an embodiment of the present invention. Detailed Implementation

[0044] To achieve the aforementioned objectives, the inventors of this application conducted a series of studies and discovered that the insufficient power generation characteristics of conventional photovoltaic fuel cells are caused by insufficient electron generation efficiency on the anode side and insufficient electron transfer efficiency on the cathode side. Based on this insight, in order to improve the electron generation efficiency on the anode side and the electron transfer efficiency on the cathode side, the inventors of this application envision using the following system (see...). Figure 2The protons generated by the anaerobic methane oxidation reaction in the anode pass through the proton permeation membrane and move from the anode to the cathode. Electrons generated by the anaerobic methane oxidation reaction in the anode through the external circuit pass through the photocatalyst and move from the anode to the cathode. In the cathode, in the presence of the protons that have moved from the anode, a redox reaction occurs in which oxygen is reduced by the electrons that have moved from the anode. This redox reaction is the aerobic methane oxidation reaction in the cathode based on the photocatalyst for aerobic methane oxidation. Figure 2 In the example system, the electromotive force is generated from the difference between the oxidation potential of the valence band of titanium oxide and the reduction potential of the oxidative addition complex (complex + O2).

[0045] Based on this concept, the inventors of this application conducted further and repeated research, and found that in a two-reaction field structure using a proton-permeable membrane divided into an anode and a cathode, if anaerobic methane oxidation reaction is generated using methane and water supplied to the anode under light irradiation, the electron generation efficiency in the anode can be improved. Furthermore, if aerobic methane oxidation reaction is generated using methane and oxygen supplied to the cathode under light irradiation, the electron donation and acceptance efficiency in the cathode can be improved. As a result, the power generation characteristics can be significantly improved, thus completing this invention (see [link]). Figure 3 ).

[0046] The superior power generation characteristics of the photovoltaic-driven fuel cell of the present invention are presumed to be based on the following mechanism. That is, a mechanism consisting of a combination of the catalytic reaction cycle described below and the catalyst activation and regeneration cycle described below can be cited.

[0047] First, the catalytic reaction cycle will be described. As a system related to the catalytic reaction cycle, for example, a "mechanism represented by a general formula" as shown in the following formula (1) (where M represents a metal and L represents a ligand). Thus, the following system can be cited, which includes: a catalytic reaction cycle based on anaerobic methane oxidation in the anode; and a catalytic reaction cycle based on aerobic methane oxidation in the cathode.

[0048] [Chemical Formula 1]

[0049] <Formula (1)>

[0050]

[0051] Next, the catalyst activation and regeneration cycle will be described. As a system related to the catalyst activation and regeneration cycle, for example, as shown in the "specific mechanism" of the following formula (2), the following system can be cited, which includes: a catalyst activation and regeneration cycle of an organometallic complex (specifically, for example, in the case where the ligand constituting the organometallic complex contains pentamethylcyclopentadiene and the transition metal that becomes the metal center in the organometallic complex is monovalent iridium; or in the case where the ligand constituting the organometallic complex contains cyclopentadiene and the transition metal that becomes the metal center in the organometallic complex is monovalent iron or monovalent manganese) in a photocatalyst for an aerobic methane oxidation reaction at the cathode; and a catalyst activation and regeneration cycle of an organometallic complex (specifically, for example, in the case where the ligand constituting the organometallic complex contains pentamethylcyclopentadiene and the transition metal that becomes the metal center in the organometallic complex is tetravalent ruthenium) in a photocatalyst for an aerobic methane oxidation reaction at the cathode.

[0052] [Chemical Formula 2]

[0053] <Formula (2)>

[0054]

[0055] It is hypothesized that, through the above mechanism, both electron generation efficiency and electron donation / acceptance efficiency can be improved. It should be noted that the aforementioned mechanism is hypothetical and does not limit the scope of this invention.

[0056] Photovoltaic-driven fuel cells

[0057] The light-driven fuel cell disclosed herein includes a cathode, an anode, and a proton-permeable membrane between the cathode and the anode.

[0058] The anode is equipped with a photocatalyst for the anaerobic methane oxidation reaction. Methane and water are supplied to the anode, and light is irradiated. Through the anaerobic methane oxidation reaction, methanol, protons, and electrons are produced from the methane and water supplied to the anode. Protons pass through the proton permeation membrane and move towards the cathode, while electrons move towards the cathode via an external circuit.

[0059] The cathode is equipped with a photocatalyst for aerobic methane oxidation reaction. Methane and oxygen are supplied to the cathode and light is irradiated. Through aerobic methane oxidation reaction, methanol and water are generated from the methane and oxygen supplied to the cathode, as well as the protons and electrons moving from the anode.

[0060] The light-driven fuel cell of the present invention will now be described in detail with reference to the accompanying drawings. However, the light-driven fuel cell of the present invention is not limited to the following description.

[0061] Photovoltaic-driven fuel cells

[0062] Figure 3 This is a schematic diagram illustrating an example of the configuration of the light-driven fuel cell of the present invention. Figure 3 For ease of understanding, the sizes and ratios of the components differ from the actual figures. As shown, the photovoltaic-driven fuel cell 10 has a cathode 11, an anode 12, and a proton-permeable membrane 14 between the cathode 11 and the anode 12. The cathode 11 and the anode 12 are electrically connected via an external circuit 15. Methane 16 and water 17 are supplied to the anode 12. Methane 16 and oxygen 18 are supplied to the cathode 11.

[0063] Figure 3 The anode 12 of the light-driven fuel cell has an electrode material 124, for example, titanium dioxide, and a photocatalyst 126 for anaerobic methane oxidation. Methane and water are supplied to the anode 12, and light is irradiated, thereby generating methanol, protons, and electrons from the methane and water supplied to the anode through an anaerobic methane oxidation reaction. The protons thus generated pass through the proton permeation membrane 14 and move toward the cathode 11, while the electrons move toward the cathode 11 via an external circuit 15.

[0064] Figure 3 The cathode 11 of the light-driven fuel cell has a photocatalyst for an aerobic methane oxidation reaction. Methane and oxygen are supplied to the cathode 11 and light is irradiated, thereby generating methanol and water through an aerobic methane oxidation reaction from the methane and oxygen supplied to the cathode 11, and protons and electrons moving from the anode 12.

[0065] The cathode reaction field 118, where the aerobic methane oxidation reaction occurs, and the anode reaction field 128, where the anaerobic methane oxidation reaction occurs, are isolated from each other by a proton permeable membrane, thus forming two reaction fields.

[0066] The power generation method of the light-driven fuel cell of the present invention will be described in more detail. It should be noted that the power generation method of the light-driven fuel cell of the present invention is not limited to this example.

[0067] An anode 12 containing a photocatalyst for the anaerobic methane oxidation reaction is irradiated with light of energy exceeding the band gap of the photocatalyst. This excites electrons in the valence band of the photocatalyst within the anode 12 to the conduction band, creating holes (h+) in the valence band. These holes (h+) then reach the methane interface. + In the presence of water, methane is oxidized to methanol, producing protons (H). + Furthermore, the excited electrons move along the potential gradient generated in the conduction band, pass through the external wire, and reach the cathode 11. This generates a photocurrent in the external circuit 15.

[0068] The reaction on the anode side is shown in the following equation (II):

[0069] CH4 + H2O → CH3OH + 2H++ +2e - (II)

[0070] The cathode 11, containing a photocatalyst for the aerobic methane oxidation reaction, is irradiated with light having an energy above the band gap of the photocatalyst. As a result, electrons in the valence band of the photocatalyst contained in the cathode 11 are excited to the conduction band, creating holes (h+) in the valence band. These holes (h+) reach the interface of methane 16. Meanwhile, protons (H+) generated in the anode 12... + Protons pass through membrane 14 and move toward cathode 11, thus being supplied to cathode 11. In the presence of holes (h+) at the interface of methane 16, protons (H+) supplied to cathode 11, and oxygen, methane is oxidized to methanol. Simultaneously, electrons generated in anode 12 move toward cathode 11 via external circuit 15, and through these electrons reaching cathode 11, oxygen is reduced to water. This completes the redox reaction on the cathode 11 side. At this time, protons (H+) at cathode 11... + It decreases due to redox reactions.

[0071] The reaction on the cathode side is shown in the following equation (III):

[0072] CH4+O2+2H + +2e - →CH3OH+H2O (III)

[0073] Thus, a complete circuit is achieved in the light-driven fuel cell of the present invention, which can generate photocurrent at a constant rate. Figure 4 A conceptual diagram of the energy diagram of the present invention is shown.

[0074] exist Figure 3 In the example embodiment shown, the cathode reaction field 118 and the anode reaction field 128 are divided by the proton permeable membrane 14 into fields of the same size. However, the proton permeable membrane 14 may also be configured closer to the cathode 11 or closer to the anode 12, thereby allowing the cathode reaction field 118 and the anode reaction field 128 to be of different sizes. Figure 3 In the example, there is one cathode 11 and one anode 12, but there can also be multiple cathodes 11 and multiple anodes 12.

[0075] The photo-driven fuel cell of the present invention can include: a mechanism for supplying methane 16 to the cathode 11 and anode 12; a mechanism for supplying water 17 to the anode 12; a mechanism for supplying oxygen 18 to the cathode 11; and a mechanism for removing or recovering the heat of oxidation reaction. Furthermore, the methane supplied to the cathode 11 and anode 12 can be recycled and reused. As a mechanism for supplying methane to the cathode 11 and anode 12, a device such as a diffuser that can supply methane to the solvent in the form of microbubbles can be cited. In order to maintain a high methane concentration in each chamber, a device capable of injecting methane into the cathode reaction field 118 and anode reaction field 128, and especially a device capable of injecting methane into the cathode 11 and anode 12, can be provided.

[0076] Furthermore, dissolved oxygen in methane 16 is preferably removed. For example, the removal of dissolved oxygen can be carried out by purging the inactive gas using an inactive gas introduction mechanism for the anode. The purging of the inactive gas is not limited to this example. For example, the purging of the inactive gas can be carried out before power generation, or it can be carried out during power generation after the prior purging, as in this example. It should be noted that the light-driven fuel cell of the present invention is not limited to this example. The light-driven fuel cell of the present invention may not have an inactive gas introduction mechanism.

[0077] Furthermore, the light-driven fuel cell of the present invention may have a light source that can change the wavelength and intensity of the irradiated light, and / or may have a function that can change the mixing ratio of methane and oxygen supplied to the cathode 11, and / or may have a function that can change the humidity of methane and oxygen supplied to the anode 12 and the cathode 11.

[0078] The operating temperature of the light-driven fuel cell of the present invention is not particularly limited during power generation. While the light-driven fuel cell can operate adequately even at room temperature, it is preferable to operate at a higher temperature from the viewpoint of increasing the oxidation rate of methane based on a photocatalyst. The operating temperature is, for example, in the range of 5°C to 95°C, preferably in the range of 10°C to 90°C, more preferably in the range of 20°C to 80°C, and particularly preferably in the range of 30°C to 70°C.

[0079] Next, the components of the light-driven fuel cell involved in this invention will be described.

[0080] <Cathode>

[0081] In the cathode of the light-driven fuel cell of the present invention, the aerobic methane oxidation reaction occurs in a light-dependent manner. "Aerobic methane oxidation reaction" refers to the aerobic oxidation of methane in the presence of oxygen.

[0082] The methane and oxygen supplied to the cathode can each be supplied in the form of a mixed gas diluted with argon or the like, wherein the concentration of methane and oxygen in the mixed gas can each be 1% to 10% by volume, preferably 2% to 8% by volume. The supply flow rate of the mixed gas can be, for example, 10 mL / min to 500 mL / min, or 50 mL / min to 200 mL / min. The mixed gas and argon are preferably humidified, for example, preferably by bubbling in ion-exchange water at room temperature.

[0083] In the light-driven fuel cell of the present invention, the conditions for the aerobic methane oxidation reaction are preferably in the range of 0.1 gas pressure to 50 gas pressure, and the oxygen concentration is in the range of 20% to 100%. The temperature of the aforementioned reaction is in the range of 5°C to 95°C, preferably in the range of 10°C to 90°C, more preferably in the range of 20°C to 80°C, and particularly preferably in the range of 30°C to 70°C.

[0084] In the photo-driven fuel cell of the present invention, the wavelength of the light irradiating the cathode is preferably in the range of 500 nm or less, more preferably in the range of 300 nm or less. The intensity of the light irradiating the cathode is preferably 1 mW / cm². 2 ~500mW / cm 2 The range is more preferably 1 mW / cm 2 ~200mW / cm 2 The range is further preferably 5mW / cm 2 ~100mW / cm 2 The range.

[0085] In the photo-driven fuel cell of the present invention, the cathode preferably contains a Teflon (registered trademark) dispersion. By including a Teflon (registered trademark) dispersion in the cathode, the hydrophobicity of the cathode can be improved, preventing the catalytic reaction from being hindered by water generated at the cathode. Therefore, the amount of catalyst can be reduced, thereby suppressing costs.

[0086] (Photocatalyst for aerobic methane oxidation reaction)

[0087] The cathode of the light-driven fuel cell of the present invention contains a photocatalyst for aerobic methane oxidation reaction.

[0088] The term "photocatalyst for aerobic methane oxidation reaction" refers to a photocatalyst that can be excited by ultraviolet or visible light and oxidize methane in a light-dependent and aerobic manner in the presence of oxygen. In the case of aerobic methane oxidation reaction photocatalysts, by irradiating with light having energy above the band gap of the photocatalyst, electrons in the valence band are excited to the conduction band, and methane can be oxidized in the presence of oxygen. It should be noted that in this invention, "ultraviolet light" refers to light with wavelengths, for example, in the range of 400 nm or less. Furthermore, "visible light" refers to light with wavelengths, for example, in the range of 400 nm to 800 nm.

[0089] Photocatalysts for aerobic methane oxidation reactions can contain organometallic complexes. Examples of organometallic complexes included in catalysts for aerobic methane oxidation reactions include organometallic complexes in which the ligand comprising pentamethylcyclopentadiene and the transition metal being tetravalent ruthenium, serving as the metal center in the organometallic complex. A single photocatalyst can be used, or two or more can be used in combination.

[0090] The photocatalyst for the aerobic methane oxidation reaction can be, for example, an organometallic complex film manufactured by depositing an organometallic complex onto a substrate. The organometallic complex film is particularly preferably manufactured by sputtering at a high temperature of 400°C or higher under a nitrogen-containing inactive gas atmosphere (nitrogen-replacement type). The nitrogen-containing inactive gas is preferably a mixture of nitrogen and argon. The mixing ratio of the mixed gas is not particularly limited. For example, the mixing ratio (volume ratio: nitrogen / argon) is in the range of 0.02 to 0.7, preferably in the range of 0.03 to 0.6, and more preferably in the range of 0.05 to 0.3. In the above manufacturing method, it is preferable to further calcine the (nitrogen-replacement type) organometallic complex film. The calcination temperature is, for example, 200°C or higher, preferably in the range of 200°C to 500°C, and more preferably in the range of 200°C to 400°C.

[0091] The organometallic complex ML contained in the photocatalyst for aerobic methane oxidation reaction can usually be manufactured by reacting M (metal) (specifically, metal salt) with L (ligand) in a solvent according to the chemical reaction formula shown in the following formula (3).

[0092] M (metal) + L (ligand) → ML (organometallic complex) ... Equation (3)

[0093] Chlorides are preferred as metal salts, but are not limited to chlorides; acetates, sulfates, etc., are also acceptable. As solvents, lower alcohols with 1 to 12 carbon atoms, such as methanol, ethanol, and propanol, are preferred.

[0094] Furthermore, in order to abstract a hydrogen atom from an organic compound that is acting as a ligand, it is ideal to add a base to the lower alcohol as a solvent to carry out the reaction. Suitable bases include, for example, ammonia, sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0095] The solvent is preferably used in an amount of 1 to 1000 times its weight relative to the reactants. Furthermore, the reaction temperature is preferably around, for example, the boiling point of the solvent used.

[0096] Pentamethylcyclopentadiene, as a ligand, can form complexes with substances such as Be, Mg, Sr, Mn, Zn, Co, Ni, Ru, Rh, Pd, Ir, Pt, and Eu.

[0097] As a method for synthesizing pentamethylcyclopentadiene, for example, a method can be given to obtain pentamethylcyclopentadiene from tetraldehyde (trans-2-methyl-2-butenal) via 2,3,4,5-tetramethyl-2-cyclopentenone. Another method can be given, for example, by adding two molecules of 2-butenyllithium to ethyl acetate to obtain an alcohol, and then dehydrating and cyclizing the alcohol using an acid catalyst.

[0098] It should be noted that pentamethylcyclopentadienyl has several advantages as a ligand. Firstly, pentamethylcyclopentadienyl is electron-rich, thus exhibiting high electron-donating ability and resisting desorption from the metal. Secondly, the steric hindrance of the methyl group provides kinetic stability to the complex, thereby preventing unwanted polymerization and attack by unwanted chemical species, and consequently improving solubility.

[0099] In particular, organometallic complexes having pentamethylcyclopentadiene as a ligand and ruthenium as the transition metal at the metal center can be synthesized, for example, based on known synthetic methods described in PJ Fagan, MD Ward, JCCalabrese, J. Am. Chem. Soc. 1989, 111, 1698, etc. Specifically, for example, they can be prepared according to the chemical reaction shown in the following formula (4).

[0100] [Chemical Formula 3]

[0101]

[0102] Of course, within the scope of being able to function as a "photocatalyst for aerobic methane oxidation reaction", the substituents and ligands in the above-mentioned specific compounds can be replaced with other substituents and ligands based on commonly known synthetic methods, thereby improving the above-mentioned specific compounds.

[0103] (Cathode photoelectrode)

[0104] The cathode of the light-driven fuel cell involved in this invention may have a cathode photoelectrode containing a photocatalyst for aerobic methane oxidation reaction. The cathode photoelectrode may be an electrode material-organometallic complex composite.

[0105] The electrode material constituting the electrode material-organic metal complex can be a known material used in cathode electrodes, such as carbon. The shape of the electrode material is not particularly limited; for example, it can be a film, a sheet, a mesh, or a paper.

[0106] Examples of organometallic complexes constituting electrode material-organometallic complexes include those contained in photocatalysts for aerobic methane oxidation reactions.

[0107] There are no particular limitations on the method for fabricating electrode material-organometallic complexes. For example, by immersing the electrode material in an organometallic complex solution dissolved in an organic solvent and then drying it, an electrode material-organometallic complex with an organometallic complex adhering to the surface of the electrode material can be fabricated.

[0108] Preferably, in the electrode material-organometallic complex, the ligands constituting the organometallic complex are bonded to the electrode material.

[0109] There are no particular restrictions on the bonding mode between the electrode material and the ligand. For example, the electrode material and the ligand can be bonded by covalent bonds, or the ligand can be simply adsorbed onto the electrode material.

[0110] There is no particular limitation on the amount of ligand introduced into the electrode material, but it is typically 0.01 mol% to 100 mol% relative to 1 mol of OH groups on the electrode material surface, preferably 0.1 mol% to 10 mol%, and more preferably 3 mol% to 10 mol%. Alternatively, it is relative to the unit surface area (m²) of the electrode material. 2 The amount of ligand introduced into the electrode material is typically 1 × 10⁻⁶. -4 mol~1×10 - 6 mol, preferably 1×10 -4 mol~1×10 -5 mol, more preferably 5 × 10 mol -5 mol~9×10 -5 mol.

[0111] Electrode materials can be either hydrophobic or hydrophilic. When the electrode material is hydrophobic, it can form a hydrophobic field around the complex. On the other hand, when the electrode material is hydrophilic, a hydrophobic field can be formed around the complex by bonding hydrophobic groups to the electrode material or ligands.

[0112] The process of introducing hydrophobic groups into hydrophilic electrode materials can be performed at any stage. For example, hydrophobic groups can be introduced during or after the manufacturing of the composite, or the composite can be manufactured using electrode materials pre-introduced with hydrophobic groups. In the case of introducing hydrophobic groups during the manufacturing of the composite, for example, the hydrophobic groups can be introduced after the ligands are introduced into the electrode material and before the metal center is introduced.

[0113] As a method for introducing hydrophobic groups into hydrophilic electrode materials, for example, a method of reacting an electrode material having hydroxyl groups with silane compounds such as alkoxysilanes and halosilanes, acyl halides, phenols, esters, alcohols, etc., can be exemplified.

[0114] To allow the hydroxyl groups on the electrode material surface to react with silane compounds, acyl halides, phenols, esters, alcohols, etc., they can be placed in solvents such as toluene, benzene, dichloromethane, or chloroform. Stirring can be performed as needed. The reaction temperature is not particularly limited, typically ranging from 50°C to 300°C, preferably from 100°C to 250°C. The reaction time is not particularly limited, typically ranging from 1 hour to 100 hours, preferably from 10 hours to 50 hours. The reaction pressure is not particularly limited, typically ranging from 0.1 MPa to 10 MPa, preferably from 1 MPa to 3 MPa.

[0115] The composite formed by the electrode material and the organometallic complex can be manufactured, for example, by mixing the electrode material, the ligand, and the metal source in one step; or by mixing the components in any order. As an example of the order of mixing the components, the following methods can be used: (1) first mixing the ligand with the electrode material and then introducing it into the metal center; (2) first forming a complex using the ligand and the metal source, and then mixing the resulting complex with the electrode material.

[0116] The method for bonding electrode materials to ligands can be appropriately selected depending on the type of electrode material used. For example, an example is a method in which an adsorption-promoting electrode material, such as activated carbon, is mixed with a ligand to adsorb the ligand onto the electrode material. Alternatively, as a method for covalently bonding electrode materials to ligands, an example is a method in which an electrode material having a hydroxyl group and a ligand precursor having an alkoxysilane site are used, and the hydroxyl group reacts with the alkoxysilane site.

[0117] To allow the hydroxyl groups on the electrode material surface to react with the ligand precursors, they can be placed in a solvent, etc. Stirring can be performed as needed. The reaction temperature is not particularly limited, typically ranging from 50°C to 200°C, preferably from 100°C to 150°C. The reaction time is not particularly limited, typically ranging from 1 hour to 50 hours, preferably from 10 hours to 30 hours. As a solvent, there are no particular limitations; examples include nitrile solvents such as acetonitrile and benzonitrile; and lower alcohols such as methane and ethanol.

[0118] The introduction of metal centers can be achieved by reacting ligands or ligands bonded to the same electrode material with the metal source.

[0119] To introduce the metal center, the ligand, or ligand bonded to the electrode material, is placed next to the metal source. A solvent may be added, and stirring may be performed, as needed. The reaction temperature is not particularly limited, typically ranging from 0°C to 100°C, preferably from 10°C to 50°C. The reaction time is not particularly limited, typically ranging from 1 hour to 50 hours, preferably from 10 hours to 30 hours. As a solvent, there are no particular limitations; examples include nitriles such as acetonitrile and benzonitrile; and lower alcohols such as methane and ethanol.

[0120] There are no particular limitations on the shape of the cathode photoelectrode. The cathode photoelectrode can be, for example, tubular, planar, linear, or rod-shaped. The aforementioned cathode photoelectrode is preferably porous. When the cathode photoelectrode is porous, for example, the contact area between methane and oxygen can be increased, and aerobic oxidation reactions in the cathode can be promoted. Methods for forming a porous cathode photoelectrode include, for example: forming the cathode photoelectrode in a state premixed with a volatile substance, and then vaporizing the volatile substance by heating; forming it using a porous mold; forming it by creating pinholes using a needle or the like after forming the cathode photoelectrode; forming the cathode photoelectrode on a substrate with uneven surfaces by vapor deposition or the like; and forming it by mixing gases during the formation of the cathode photoelectrode by vapor deposition, etc.

[0121] The cathode photoelectrode may contain materials other than those used for the aerobic methane oxidation reaction, provided that it does not obstruct the light irradiation necessary for the photocatalyst to function.

[0122] <Anode>

[0123] In the anode of the light-driven fuel cell of the present invention, a light-dependent anaerobic methane oxidation reaction occurs. In this invention, "anaerobic methane oxidation reaction" refers to the anaerobic oxidation of methane in the presence of water.

[0124] The methane supplied to the anode can be supplied in the form of a mixed gas diluted with argon or the like, and the methane concentration in the mixed gas can be 1% to 10% by volume, preferably 2% to 8% by volume. The supply flow rate of the mixed gas can be, for example, 1 mL / min to 500 mL / min, or 10 mL / min to 100 mL / min.

[0125] As for water, it can be supplied to the anode, for example, by humidifying the mixed gas and argon. Humidification can be performed, for example, by bubbling the mixed gas in ion-exchanged water at room temperature.

[0126] In the light-driven fuel cell of the present invention, the conditions for the anaerobic methane oxidation reaction are preferably, for example, a pressure of 0.01 oz or less and / or an oxygen concentration of 10% or less. The oxygen concentration is more preferably 5% or less, particularly preferably 1% or less, or 0.1% or less. The reaction temperature is in the range of 5°C to 95°C, preferably 10°C to 90°C, more preferably 20°C to 80°C, and particularly preferably 30°C to 70°C.

[0127] In the light-driven fuel cell of the present invention, the wavelength of the light irradiating the anode is preferably in the range of 500 nm or less, more preferably in the range of 300 nm or less. The intensity of the light irradiating the anode is preferably 1 mW / cm². 2 ~500mW / cm 2 The range is more preferably 1 mW / cm 2 ~200mW / cm 2 The range is further preferably 5mW / cm 2 ~100mW / cm 2 The range.

[0128] In the light-driven fuel cell of the present invention, the anode preferably contains a Teflon (registered trademark) dispersion. By including a Teflon (registered trademark) dispersion in the anode, the amount of catalyst can be reduced, thereby controlling costs.

[0129] The dissolved oxygen in the methane supplied to the anode is preferably removed, or substantially removed.

[0130] (Photocatalyst for anaerobic methane oxidation reaction)

[0131] The anode of the light-driven fuel cell of the present invention includes a photocatalyst for anaerobic methane oxidation. In the present invention, the term "photocatalyst for anaerobic methane oxidation" refers to a photocatalyst that can be excited by ultraviolet or visible light and anaerobically oxidize methane in the presence of water.

[0132] Photocatalysts for anaerobic methane oxidation can contain organometallic complexes. Examples of such organometallic complexes include: organometallic complexes in which the ligand comprising pentamethylcyclopentadiene and the metal center of the organometallic complex is iridium; and organometallic complexes in which the ligand comprising cyclopentadiene and the transition metal serving as the metal center of the organometallic complex is monovalent iron or monovalent manganese. A single photocatalyst can be used, or two or more can be used in combination.

[0133] The photocatalyst for the anaerobic methane oxidation reaction can be, for example, an organometallic complex thin film manufactured by depositing an organometallic complex onto a substrate. The aforementioned organometallic complex thin film is particularly preferably a (nitrogen-substituted) organometallic complex thin film manufactured by sputtering under high-temperature conditions of nitrogen-containing inactive gas atmosphere and substrate temperature of 400°C or higher. The nitrogen-containing inactive gas is preferably a mixture of nitrogen and argon. The mixing ratio of the mixed gas is not particularly limited. The mixing ratio (volume ratio: nitrogen / argon) is, for example, in the range of 0.02 to 0.7, preferably in the range of 0.03 to 0.6, and more preferably in the range of 0.05 to 0.3. In this manufacturing method, it is preferable to further calcine the aforementioned (nitrogen-substituted) organometallic complex thin film. The calcination temperature is, for example, 200°C or higher, preferably in the range of 200°C to 500°C, and more preferably in the range of 200°C to 400°C.

[0134] Organometallic complexes ML, which serve as photocatalysts for anaerobic methane oxidation, can typically be manufactured by reacting M (metal) (specifically, a metal salt) with L (ligand) in a solvent according to the chemical reaction shown in formula (5).

[0135] M (metal) + L (ligand) → ML (organometallic complex) ... Equation (5)

[0136] As a metal salt, chlorides are preferred, but not limited to chlorides; acetates, sulfates, etc., are also acceptable. As a solvent, lower alcohols with 1 to 12 carbon atoms, such as methanol, ethanol, and propanol, are preferred.

[0137] Furthermore, in order to abstract a hydrogen atom from an organic compound that is acting as a ligand, it is ideal to add a base to the lower alcohol as a solvent to carry out the reaction. Suitable bases include, for example, ammonia, sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0138] The amount of solvent used is preferably 1 to 1000 times the weight of the reactants. Furthermore, the reaction temperature is preferably around the boiling point of the solvent used.

[0139] Pentamethylcyclopentadiene, as a ligand, can form complexes with substances such as Be, Mg, Sr, Mn, Zn, Co, Ni, Ru, Rh, Pd, Ir, Pt, and Eu.

[0140] As a method for synthesizing pentamethylcyclopentadiene, for example, a method can be given to obtain pentamethylcyclopentadiene from tetraldehyde (trans-2-methyl-2-butenal) via 2,3,4,5-tetramethyl-2-cyclopentenone. Another method can be given, for example, by adding two molecules of 2-butenyllithium to ethyl acetate to obtain an alcohol, and then dehydrating and cyclizing the alcohol using an acid catalyst.

[0141] It should be noted that pentamethylcyclopentadienyl has several advantages as a ligand. Firstly, pentamethylcyclopentadienyl is electron-rich, thus exhibiting high electron-donating ability and resisting desorption from the metal. Secondly, the steric hindrance of the methyl group provides kinetic stability to the complex, preventing unwanted polymerization and attack by unwanted chemical species, thereby improving solubility.

[0142] For example, organometallic complexes having pentamethylcyclopentadiene as a ligand and iridium as the transition metal center can be manufactured according to the chemical reaction shown in the following chemical formula (6).

[0143] [Chemical Formula 4]

[0144] <Formula (6)>

[0145]

[0146] In addition, organometallic complexes having cyclopentadiene as a ligand and the transition metal as a monovalent iron or monovalent manganese as the metal center can be synthesized, for example, based on known methods described in Kang, JW; Moseley, K.; Maitlis, PM J Am. Chem. Soc. 1969, 91, 5970, etc.

[0147] Of course, within the scope of being able to function as a "photocatalyst for anaerobic methane oxidation reaction", the substituents and ligands in the above-mentioned specific compounds can be replaced with other substituents and ligands based on commonly known synthetic methods, thereby improving the above-mentioned specific compounds.

[0148] (Anode photoelectrode)

[0149] The anode of the light-driven fuel cell involved in this invention can have an anode photoelectrode containing a photocatalyst for anaerobic methane oxidation. The anode photoelectrode can be an electrode material-organometallic complex composite.

[0150] The electrode material constituting the electrode material-organic metal complex can be a known material used in the anode electrode. The electrode material can be titanium oxide. The shape of the electrode material is not particularly limited; for example, it can be in the form of a film, a sheet, a mesh, or paper.

[0151] Examples of organometallic complexes constituting electrode material-organometallic complexes include those contained in photocatalysts for anaerobic methane oxidation.

[0152] There are no particular limitations on the method for fabricating electrode material-organometallic complexes. For example, by immersing the electrode material in an organometallic complex solution dissolved in an organic solvent and then drying it, an electrode material-organometallic complex with an organometallic complex adhering to the surface of the electrode material can be fabricated.

[0153] There are no particular restrictions on the bonding mode between the electrode material and the ligands in the organometallic complex. For example, the electrode material and the ligands can be bonded by covalent bonds, or the ligands can be simply adsorbed onto the electrode material.

[0154] There is no particular limitation on the amount of ligand introduced into the electrode material. Typically, 0.01 mol% to 100 mol% is cited relative to 1 mol of OH groups on the electrode material surface; preferably, 0.1 mol% to 10 mol%; more preferably, 3 mol% to 10 mol%. Alternatively, relative to the unit surface area (m²) of the electrode material... 2 ), typically 1×10 -4 mol~1×10 -6 mol, preferably 1×10 -4 mol~1×10 -5 mol, more preferably 5 × 10 mol. -5 mol~9×10 -5 mol.

[0155] Electrode materials can be either hydrophobic or hydrophilic. When the electrode material is hydrophobic, it can form a hydrophobic field around the complex. On the other hand, when the electrode material is hydrophilic, a hydrophobic field can be formed around the complex by bonding hydrophobic groups to the electrode material or ligands.

[0156] The process of introducing hydrophobic groups into hydrophilic electrode materials can be performed at any stage. For example, hydrophobic groups can be introduced during or after the manufacturing of the composite, or the composite can be manufactured using electrode materials pre-introduced with hydrophobic groups. In the case of introducing hydrophobic groups during the manufacturing of the composite, for example, the hydrophobic groups can be introduced after the ligands are introduced into the electrode material and before the metal center is introduced.

[0157] As a method for introducing hydrophobic groups into hydrophilic electrode materials, for example, a method of reacting an electrode material having hydroxyl groups with silane compounds such as alkoxysilanes and halosilanes, acyl halides, phenols, esters, alcohols, etc., can be exemplified.

[0158] To allow the hydroxyl groups on the electrode material surface to react with silane compounds, acyl halides, phenols, esters, alcohols, etc., they can be placed in solvents such as toluene, benzene, dichloromethane, or chloroform. Stirring can be performed as needed. The reaction temperature is not particularly limited, typically ranging from 50°C to 300°C, preferably from 100°C to 250°C. The reaction time is not particularly limited, typically ranging from 1 hour to 100 hours, preferably from 10 hours to 50 hours. The reaction pressure is not particularly limited, typically ranging from 0.1 MPa to 10 MPa, preferably from 1 MPa to 3 MPa.

[0159] The composite formed by the electrode material and the organometallic complex can be manufactured, for example, by mixing the electrode material, the ligand, and the metal source in one step; or by mixing the components in any order. As an example of the order of mixing the components, the following methods can be used: (1) first mixing the ligand with the electrode material and then introducing it into the metal center; (2) first forming a complex using the ligand and the metal source, and then mixing the resulting complex with the electrode material.

[0160] The method for bonding electrode materials to ligands can be appropriately selected depending on the type of electrode material used. For example, an example is a method in which an adsorption-promoting electrode material, such as activated carbon, is mixed with a ligand to adsorb the ligand onto the electrode material. Alternatively, as a method for covalently bonding electrode materials to ligands, an example is a method in which an electrode material having a hydroxyl group and a ligand precursor having an alkoxysilane site are used, and the hydroxyl group reacts with the alkoxysilane site.

[0161] To allow the hydroxyl groups on the electrode material surface to react with the ligand precursors, they can be placed in a solvent, etc. Stirring can be performed as needed. The reaction temperature is not particularly limited, typically ranging from 50°C to 200°C, preferably from 100°C to 150°C. The reaction time is not particularly limited, typically ranging from 1 hour to 50 hours, preferably from 10 hours to 30 hours. The solvent is not particularly limited, examples include nitrile solvents such as acetonitrile and benzonitrile; and lower alcohols such as methane and ethanol.

[0162] The introduction of metal centers can be achieved by reacting ligands or ligands bonded to the same electrode material with the metal source.

[0163] To introduce the metal center, the ligand or a ligand bonded to the electrode material is placed next to the metal source. A solvent may be added, and stirring may be performed, as needed. The reaction temperature is not particularly limited, typically ranging from 0°C to 100°C, preferably from 10°C to 50°C. The reaction time is not particularly limited, typically ranging from 1 hour to 50 hours, preferably from 10 hours to 30 hours. The solvent is not particularly limited, and examples include nitriles such as acetonitrile and benzonitrile; and lower alcohols such as methane and ethanol.

[0164] There are no particular limitations on the shape of the anode photoelectrode. The anode photoelectrode can be, for example, tubular, flat, linear, or rod-shaped. A porous material is preferred for the anode photoelectrode. When the anode photoelectrode is porous, for example, the contact area between methane and water can be increased, and the anaerobic oxidation reaction in the anode can be promoted. Methods for forming a porous anode photoelectrode include, for example: forming the anode photoelectrode in a state premixed with volatile substances, and then vaporizing the volatile substances by heating; forming it using a porous mold; forming it by creating pinholes using a needle or the like after forming the anode photoelectrode; forming the anode photoelectrode on a substrate with uneven surfaces by vapor deposition or the like; and forming it by mixing gases during the vapor deposition process.

[0165] The anode photoelectrode may contain materials other than those used for anaerobic methane oxidation, provided that it does not obstruct the light irradiation necessary for the photocatalyst to function.

[0166] <Transparent Substrate>

[0167] In a preferred embodiment of the present invention, the light-driven fuel cell has an anode-side transparent substrate and a cathode-side transparent substrate, both of which are at least partially transparent. The anode is located between the anode-side transparent substrate and the proton-permeable membrane, and / or the cathode is located between the cathode-side transparent substrate and the proton-permeable membrane.

[0168] Materials that can be used as light-transmitting substrates include, for example, glass and transparent plastics. Examples of glass include quartz glass, borosilicate glass, and soda-lime glass. Examples of transparent plastics include acrylic resin, polycarbonate resin, polystyrene resin, rigid polyvinyl chloride, and polyphenylene ether.

[0169] In the preferred embodiments described in this disclosure,

[0170] (1) The cathode comprises a layer containing a photocatalyst for aerobic methane oxidation reaction and a cathode-side gas diffusion layer.

[0171] (2) The anode contains a layer of photocatalyst for anaerobic methane oxidation and an anode-side gas diffusion layer.

[0172] (3) The cathode-side gas diffusion layer is disposed toward the cathode-side light-transmitting substrate, the anode-side gas diffusion layer is disposed toward the anode-side light-transmitting substrate, the layer containing the photocatalyst for aerobic methane oxidation reaction is disposed toward the cathode-side membrane surface of the proton-permeable membrane, and the layer containing the photocatalyst for anaerobic methane oxidation reaction is disposed toward the anode-side membrane surface of the proton-permeable membrane.

[0173] (Gas supply port · Product outlet)

[0174] The photovoltaic-driven fuel cell disclosed herein can include a supply port and a supply mechanism for supplying methane and oxygen to the cathode. This enables a redox reaction in the cathode, where methane and oxygen react with protons and electrons moving from the anode. The methane-oxygen supply mechanism can use known mechanisms. For example, a gas tank containing methane and a gas tank containing oxygen can be connected to the gas supply port via connecting pipes, and the fuel supply can be adjusted using a mass flow controller (MFC) or similar device.

[0175] The photovoltaic-driven fuel cell disclosed herein can have a supply port and a supply mechanism for supplying methane and water to the anode. Known mechanisms can be used as the methane and water supply mechanism. For example, a gas tank containing methane can be connected to the methane supply port via a connecting pipe having a humidifier, and the fuel supply can be adjusted using a mass flow controller (MFC) or similar device.

[0176] (Inactive gas introduction mechanism)

[0177] The light-driven fuel cell disclosed herein preferably has an inactive gas introduction mechanism for the anode, thereby enabling further and better removal of dissolved oxygen from methane.

[0178] Examples of inert gases include nitrogen, helium, argon, krypton, methane, and ethane. One of these inert gases may be used alone, or two or more may be used in combination. Examples of inert gas introduction mechanisms include bubble generating devices, bubble jet nozzles, and foaming plates.

[0179] (Other components)

[0180] The light-driven fuel cell disclosed herein may include other components, such as encapsulation components for hermetically sealing the anode and cathode, and components having gas supply ports and reaction product outlets. The materials constituting such components are not particularly limited, as long as they are materials capable of being formed into the desired shape. From the viewpoint of preventing fuel consumption such as methane, examples of materials constituting components of the light-driven fuel cell disclosed herein include, for example, laminates obtained by coating a layer of low-moisture-permeability metals such as aluminum with an insulating polymer, polyvinylidene chloride resin, fluoropolymers, and glass fiber reinforced plastics.

[0181] <Proton permeation membrane>

[0182] A proton-permeable membrane simply needs to be a membrane that allows protons to pass through. Examples of materials that can form a proton-permeable membrane include, for example, polymeric acids, alumina hydrates, and solid electrolytes. Among these, polymeric acids are particularly preferred. Examples of polymeric acids include, for example, condensates of phenol sulfonic acid and formaldehyde, sulfonated polystyrene, trifluorostyrene sulfonic acid, mixtures of fluorocarbon sulfonic acid and polyvinylidene fluoride, and fluorocarbon sulfonic acid.

[0183] Proton permeation membranes can also be commercially available products. Examples of commercially available proton permeation membranes include "Nafion" (registered trademark) manufactured by DuPont, "Flemion" (registered trademark) manufactured by Asahi Glass Co., Ltd., and "Aciplex" manufactured by Asahi Kasei Corporation.

[0184] There is no particular limitation on the thickness of the proton-permeable membrane. The thickness of the proton-permeable membrane is, for example, in the range of 20 μm to 300 μm, preferably in the range of 30 μm to 250 μm, and more preferably in the range of 50 μm to 200 μm.

[0185] <Fuel>

[0186] As mentioned above, the fuel supplied to the anode comprises methane and water. Similarly, as mentioned above, the fuel supplied to the cathode comprises methane and oxygen. In this invention, "methane" refers to an organic compound used as fuel.

[0187] As mentioned earlier, dissolved oxygen in the methane supplied to the anode is preferably removed. This is because if oxygen (O2) is present in the methane, a photocatalyst, for example, might be used for the oxidation of oxygen (O2), hindering the photocatalytic oxidation of methane. It should be noted that "removal of dissolved oxygen" includes not only the complete removal of oxygen (O2) from the methane, but also the substantial removal.

[0188] <Solvent>

[0189] The cathode and anode, particularly the cathode photoelectrode and anode photoelectrode, may be in direct contact with methane gas at least partially, and / or may be in contact with the solvent in which methane is dissolved at least partially.

[0190] When the cathode and anode, particularly the cathode photoelectrode and anode photoelectrode, are in contact with a solvent that dissolves methane, the methane dissolved in the solvent is oxidized to methanol in the cathode and anode. To prevent the electrodes from drying out, the solvent can be introduced into the cathode and / or anode along with the methane gas. More specifically, a mist of solvent can be introduced into the cathode and / or anode along with the methane gas.

[0191] There are no particular restrictions on the solvent, and examples include water, liquid ammonia, hydrogen peroxide, hydrogen fluoride, acetonitrile, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, benzene, chlorobenzene, dichlorobenzene, diethyl ether, tetrahydrofuran, acetone, etc.

[0192] The electrolyte can be dissolved in the solvent. There are no particular limitations on the electrolyte; it can be either acidic or alkaline. For example, halides of alkali metals (sodium, potassium, etc.); halides of alkaline earth metals (magnesium, calcium, etc.); acids such as sulfuric acid, nitric acid, and carbonic acid, and their salts (alkali metal salts, alkaline earth metal salts, etc.); tetrafluoroborate-n-butylammonium, etc., can be used as electrolytes. The concentration of the electrolyte is not particularly limited, typically 0.01M to 0.3M, preferably 0.05M to 0.2M. When using alkali metal or alkaline earth metal chlorides as the electrolyte, a mechanism for recovering and reusing the generated chlorine gas can be provided in the light-driven fuel cell of the present invention. When introducing a solvent in the form of a mist along with methane gas, the solvent containing the electrolyte can be misted and introduced. Furthermore, the electrolyte membrane can be either acidic or alkaline.

[0193] <Light Source>

[0194] The light-driven fuel cell disclosed herein can have a light source for irradiating the anode and / or cathode with light. The light source is not particularly limited, but is preferably a light source that generates light in the wavelength range of 500 nm or less, preferably 300 nm, and / or, preferably, capable of irradiating the anode and / or cathode with 0.5 mW / cm² light. 2 ~500mW / cm 2 1.0mW / cm is preferred 2 ~200mW / cm 2 1.0mW / cm is particularly preferred 2 ~100mW / cm 2 A light source of light intensity.

[0195] From the perspective of effectively utilizing natural energy, sunlight is the preferred light source. For example, an artificial light source can be one capable of illuminating light with energy above the band gap of a photocatalyst. Examples of artificial light sources include xenon lamps, ultraviolet lamps, mercury lamps (high pressure, ultra-high pressure), incandescent lamps, and fluorescent lamps.

[0196] <External Circuit>

[0197] There are no particular limitations on the external circuit; any known circuit may be used. The external circuit may be connected to the cathode and anode, for example, via conductive wires.

[0198] <Other Components>

[0199] The light-driven fuel cell of the present invention may include other components in addition to the aforementioned components.

[0200] Manufacturing Method of Photovoltaic-Driven Fuel Cells

[0201] The light-driven fuel cell of the present invention can be manufactured, for example, by assembling the aforementioned components with other components to be added as needed using conventional methods.

[0202] The light-driven fuel cell of the present invention can also be manufactured by embedding the membrane electrode assembly into the reactor body of the light-driven fuel cell according to the following method.

[0203] Figure 5A and Figure 5B This is a schematic cross-sectional view showing one embodiment of the reaction device body of the light-driven fuel cell of the present invention. Figure 5A The main body 500 of the photo-driven fuel cell reactor shown includes a membrane electrode assembly 508. The membrane electrode assembly 508 includes: a solid electrolyte membrane 502 serving as a proton-permeable membrane; an anode photoelectrode 504 disposed on the solid electrolyte membrane 502; and a cathode photoelectrode 506 disposed on the side of the solid electrolyte membrane 502 opposite to the anode photoelectrode 504. The anode photoelectrode 504 and the cathode photoelectrode 506 are electrically connected to each other.

[0204] The anode photoelectrode 504 is disposed adjacent to one side of the first current collector (anode-side current collector) 572, which also functions as an anode-side gas diffusion layer, and is connected to the external circuit 525 through the first current collector 572. A quartz glass plate 516 serving as an anode-side light-transmitting substrate is disposed on the side of the first current collector 572 opposite to the anode photoelectrode 504.

[0205] The cathode photoelectrode 506 is disposed adjacent to one side of the second current collector (cathode-side current collector) 574, which also functions as a cathode-side gas diffusion layer, and is connected to the external circuit 525 through the second current collector 574. A quartz glass plate 518, serving as a cathode-side light-transmitting substrate, is disposed on the side of the second current collector 574 opposite to the cathode photoelectrode 506.

[0206] The main body 500 of the light-driven fuel cell also includes: components 540a and 550a with feed gas supply ports; and components 540b and 550b with outlet ports for discharging the generated hydrocarbons.

[0207] To deliver gas more evenly, the first current collector 572 and / or the second current collector 574 may have a gas flow path, which may be, for example, a meandering groove.

[0208] The first collector plate 572 and the second collector plate 574 respectively connect the anode photoelectrode 504 and the cathode photoelectrode 506 to the external circuit 525. The thickness of the first collector plate 572 and the second collector plate 574 can be, for example, 2 mm. The anode photoelectrode 504 and the cathode photoelectrode 506 are connected through the collector plates, thereby providing a more reliable electrical connection compared to the case where they are directly connected by wires without using collector plates.

[0209] There are no particular restrictions on the materials of the first collector board 572 and the second collector board 574; known materials can be used, such as gold-plated copper.

[0210] Figure 5A The collector plates (first collector plate 572 and second collector plate 574) are provided with openings for light illumination. Figure 5B A plan view of the current collectors (first current collector 572, second current collector 574) is shown. Figure 5A The middle is indicated by a white arrow. Figure 5B The direction of the field of vision. For example... Figure 5B As can be seen, the first collector board and the second collector board each have four square openings (572a, 574a) with a side length of 2cm for light illumination.

[0211] As described above, by contacting one side of the first current collector with an opening to the anode side of the membrane electrode assembly, and then covering the other side of the first current collector with a quartz glass plate, and by contacting one side of the second current collector with an opening to the cathode side of the membrane electrode assembly, and then covering the other side of the second current collector with a quartz glass plate, the membrane electrode assembly can be embedded into the reactor body of the photovoltaic fuel cell.

[0212] The reactor body of such a photovoltaic-driven fuel cell has, for example, the following structure:

[0213] (1) The cathode comprises a layer containing a photocatalyst for aerobic methane oxidation reaction and a cathode-side gas diffusion layer.

[0214] (2) The anode contains a layer of photocatalyst for anaerobic methane oxidation and an anode-side gas diffusion layer.

[0215] (3) The cathode-side gas diffusion layer is disposed toward the cathode-side light-transmitting substrate, the anode-side gas diffusion layer is disposed toward the anode-side light-transmitting substrate, the layer containing the photocatalyst for aerobic methane oxidation reaction is disposed toward the cathode-side membrane surface of the proton-permeable membrane, and the layer containing the photocatalyst for anaerobic methane oxidation reaction is disposed toward the anode-side membrane surface of the proton-permeable membrane.

[0216] Example

[0217] The embodiments of the present invention will be described below. It should be noted that the present invention is not limited or restricted in any way by the following embodiments and comparative examples.

[0218] Example

[0219] The light-driven fuel cell of the present invention is manufactured as described below, and its power generation characteristics and methane conversion efficiency are evaluated. The determination of various characteristics and physical properties, as well as the calculation of numerical values, are carried out using the methods shown below.

[0220] <Preparation of organometallic complexes contained in photocatalysts for anaerobic methane oxidation>

[0221] The organometallic complex (iridium complex) used as a photocatalyst for anaerobic methane oxidation reaction as an anode was synthesized according to the literature (Ball, RG; Graham, WAG; Heinekey, DM; Hoyano, JK; McMaster, AD; Mattson, BM; ST. Michel. Inorg. Chem. 1990, 29, 2023) as described below.

[0222] All operations were performed under a nitrogen atmosphere. 0.0800 g (0.100 mmol) of commercially available (Tokyo Chemical Industry Co., Ltd.) iridium(III) dichloride (pentamethylcyclopentadienyl) (dimer) was dissolved in 4.0 mL of dichloromethane. The resulting solution was stirred for 2 hours under a carbon monoxide atmosphere (0.3 MPa), and then 0.40 g (6.12 mmol) of zinc was added.

[0223] Next, the resulting solution was stirred for 16 hours under a carbon monoxide atmosphere (0.3 MPa), and then 3.0 mL of distilled water was added. The solution was then stirred for 1 hour, followed by filtration to recover the filtrate.

[0224] After washing the dichloromethane layer separated from the recovered filtrate three times with 1.0 mL of distilled water, the dichloromethane was removed by vacuum distillation, thereby obtaining the organometallic complex (formula (7) below) as the target compound in the form of a yellow powder (yield: 0.0310 g, 0.0808 mmol, yield: 81%).

[0225] [Chemical Formula 5]

[0226]

[0227] It should be noted that the use 1 Common analytical methods such as HNMR, IR, and X-ray crystal structure analysis are used to identify the obtained organometallic complexes and confirm that they are the desired target substances.

[0228] 1 HNMR (ppm, CDCl3): 2.2 (s, 15H, CH3)

[0229] IR (cm) -1 ): 2853-2915(CH), 2006(C≡O), 1922(C≡O)

[0230] X-ray structural analysis: See Figure 6 .

[0231] <Preparation of organometallic complexes contained in photocatalysts for aerobic methane oxidation>

[0232] The organometallic complex (ruthenium complex) used as a photocatalyst for anaerobic methane oxidation reaction on the cathode side was synthesized in the following manner based on the literature (PJ Fagan, MD Ward, JCC alabrese, J. Am. Chem. Soc. 1989, 111, 1698).

[0233] All operations were performed under a nitrogen atmosphere. 0.600 g (0.552 mmol) of commercially available tetrachlorotetra(pentamethylcyclopentadienyl)tetraruthenium (Tokyo Chemical Industry Co., Ltd.) was added to 10 mL of acetonitrile and heated under reflux at 90 °C for 1 hour to obtain a dark orange solution.

[0234] The temperature of the resulting solution was lowered to room temperature, and 0.374 mg (2.20 mmol) of silver nitrate was added. The mixture was stirred for 1 hour to obtain a mixture containing a white precipitate (white solid). The white solid was removed by filtration from the resulting mixture, and the filtrate was recovered. The recovered filtrate was passed through a gel filtration column, and the solvent was removed from the resulting solution under reduced pressure, thereby obtaining the organometallic complex (formula (8) below) as the target compound as a yellow powder (yield: 0.765 g, 1.82 mmol, yield: 82%).

[0235] [Chemical Formula 6]

[0236]

[0237] use 1 Common analytical methods such as HNMR, MS, and IR are used to identify the obtained organometallic complexes and confirm that they are the desired target substances.

[0238] 1 HNMR (ppm, THF-d8): 1.60 (s, 15H, CH3), 2.37 (s, 9H, CH3CN)

[0239] IR (cm) -1 ): 2845-3066(CH)

[0240] ESI-MS: m / z 360.

[0241] <Fabrication of the Anode Photoelectrode>

[0242] An electrode (“anodic photoelectrode”) is formed by a titanium mesh as the electrode material and a layer containing a photocatalyst for anaerobic methane oxidation reaction, in the manner described below.

[0243] Titanium mesh (5cm x 5cm) wire diameter The mesh is a 0.35mm, 20-mesh plain weave. After cleaning the mesh with an organic solvent, it is dried. Meanwhile, 5 mg of the iridium complex obtained above as a photocatalyst for anaerobic methane oxidation is dissolved in 3 ml of an organic solvent to obtain a photocatalyst solution for anaerobic methane oxidation.

[0244] Next, the cleaned and dried mesh is immersed in the anode catalyst solution at room temperature and then dried. This immersion and drying process is repeated three times to obtain the anode photoelectrode.

[0245] <Fabrication of Cathode Photoelectrodes>

[0246] An electrode (sometimes referred to as a "cathode photoelectrode") is formed by carbon paper as the electrode material and a layer containing a photocatalyst for aerobic methane oxidation reaction, in the manner described below.

[0247] As the carbon paper (5cm×5cm), Toray Industries' TGP-H-030 was used. On the other hand, 5mg of the ruthenium complex obtained as a photocatalyst for the aerobic methane oxidation reaction was dissolved in 3ml of organic solvent to obtain a photocatalyst solution for the aerobic methane oxidation reaction.

[0248] Next, the carbon paper was immersed in the photocatalyst solution for the aerobic methane oxidation reaction at room temperature, and then dried. This immersion and drying process was repeated three times to obtain the cathode photoelectrode.

[0249] <Fabrication of Membrane Electrode Connectors>

[0250] For the titanium mesh with photocatalyst for anaerobic methane oxidation and the carbon paper with photocatalyst for aerobic methane oxidation obtained in the above manner, the solution obtained by spraying 10 ml of propanol to dilute the sulfonic acid modified perfluorinated ionomer (10 wt% Nafion solution) was applied several times, and then dried.

[0251] Then, a Nafion membrane, serving as a solid electrolyte membrane, is inserted between a titanium mesh with a photocatalyst for anaerobic methane oxidation and a carbon paper with a photocatalyst for aerobic methane oxidation, with the spray surfaces facing each other, thereby obtaining a laminate.

[0252] Next, the resulting laminate is placed in a press and then pressed in a temperature range from room temperature to 140°C to produce the membrane electrode assembly of the embodiment.

[0253] <Manufacturing of Photovoltaic Fuel Cells>

[0254] Using the membrane electrode assembly prepared in the manner described above, refer to Figure 5A and Figure 5B The main body of the reaction device for the light-driven fuel cell involved in the embodiment is manufactured according to the above method.

[0255] Specifically, a first current collector plate is prepared, having four square openings with sides of 2 cm for light irradiation. One main surface of the first current collector plate is in contact with the anode side of the membrane electrode assembly, and the other main surface of the first current collector plate is covered with a quartz glass plate. A second current collector plate is also prepared, having four square openings with sides of 2 cm for light irradiation. One main surface of the second current collector plate is in contact with the cathode side of the membrane electrode assembly, and the other main surface of the second current collector plate is covered with a quartz glass plate. Furthermore, a component having a raw material gas supply port and a component having a reaction product outlet are then embedded.

[0256] The first and second collector boards are made of gold-plated copper. Each of the first and second collector boards is 2 mm thick. The anode and cathode photoelectrodes are electrically connected via the collector boards.

[0257] <Composition of the Experimental Apparatus>

[0258] Figure 7 This is a schematic diagram illustrating the overall structure of the system, which includes a gas supply mechanism and a measuring mechanism.

[0259] The reaction was monitored using an electrochemical measurement system consisting of a DVM (digital voltmeter). Furthermore, gas chromatography (GC) was used to quantitatively analyze the components of the gases emitted from the anode and cathode, respectively.

[0260] The short-circuit current density (JSC) and open-circuit voltage (VOC) were determined using the linear sweep voltammetry (LSV) method. LSV measurement was performed by plotting the photocurrent as the photoelectromotive force (PMF) changes from the initial photoelectromotive force (PMF) to 0V. Based on the results, the photocurrent flowing under zero resistance was taken as the short-circuit current density (JSC). The photoelectromotive force generated under open-circuit conditions (infinite resistance) was taken as the open-circuit voltage (VOC).

[0261] For light irradiation, a xenon lamp (300W, trade name "MAX-303" manufactured by Asahi Spectrophotometry Co., Ltd.) emitting light with a wavelength shorter than 300nm is prepared. The xenon lamp is adjusted using a water filter, resulting in approximately 100mW / cm². 2 Light is irradiated onto the anode and cathode (i.e., the photocatalyst for anaerobic methane oxidation and the photocatalyst for aerobic methane oxidation).

[0262] A mixed gas (equivalent to the feed gas) obtained by diluting the methane concentration in the mixed gas to 5% by volume using argon was supplied to the anode at a flow rate of 20 mL / min. The supplied mixed gas and argon were humidified by bubbling in ion-exchange water at room temperature.

[0263] A mixed gas, obtained by diluting the methane and oxygen concentrations in the mixed gas to 5% by volume using argon, was supplied to the cathode at a flow rate of 100 mL / min. The supplied mixed gas and argon were humidified by bubbling in ion-exchange water at room temperature.

[0264] While supplying the aforementioned mixed gas to the anode and cathode of the light-driven fuel cell, a xenon lamp emitting light with a wavelength shorter than 300 nm is used at 100 mW / cm². 2 The intensity of the light irradiated the anode and cathode respectively, causing the methane to react.

[0265] The following steps illustrate the measurement:

[0266] (0) Validation of the device and environment

[0267] • Prepare electrical measurement systems and gas analysis measurement systems.

[0268] • Measure the background voltage.

[0269] (1) Electromotive force measurement

[0270] 1-1. Supply gas. Measure the voltage. (0V)

[0271] 1-2. Irradiate the gas under a gas supply and measure the electromotive force. (~0.2V)

[0272] 1-3. Evaluate the stability of the electromotive force.

[0273] 1-4. While irradiating with light, stop the gas supply. Measure the electromotive force. (~0V)

[0274] 1-5. While irradiating with light, gas is supplied. The electromotive force is measured.

[0275] (2) Output power measurement

[0276] • Measure the voltage and current curves. Calculate the output electrical energy (0.061mW).

[0277] (3) Analysis of exhaust gases

[0278] • Determine the amount of methanol and water in the anolyte gas and cathode gas. (100cc / minute)

[0279] Calculate the methane-methanol conversion rate in the anode and cathode.

[0280] <Power Generation Characteristics>

[0281] Figure 8 A graph illustrating the current-voltage curves involved in the embodiment is provided.

[0282] The evaluation results of the light-driven fuel cell involved in the example, obtained by LSV measurement, are VOC=0.23V, JSC=1.24mA, and ff=0.21.

[0283] <Methane Conversion Efficiency>

[0284] The methane-methanol conversion rates in the anode and cathode were calculated, and the results confirmed that methane was converted into methanol in both the anode and cathode.

[0285] Specifically, regarding the anode, it was confirmed that 0.01% of the supplied methane is converted into methanol, including approximately 0.001% ethane, etc. Regarding the cathode, it was confirmed that 0.01% of the supplied methane is converted into methanol, including approximately 0.001% ethane, etc.

[0286] Industrial availability

[0287] As described above, the light-driven fuel cell of the present invention exhibits excellent power generation characteristics. Regarding the light-driven fuel cell of the present invention, (1) methane is anaerobically oxidized in the presence of water by irradiating the anode with light; and (2) methane is aerobically oxidized in the presence of oxygen by irradiating the cathode with light, thereby generating electricity. Therefore, the light-driven fuel cell of the present invention can be used in the form of small electronic devices used in an irradiated environment, such as mobile phones, e-notebooks, and laptops. Furthermore, the light-driven fuel cell of the present invention can use methane as fuel, and therefore can also be used as a fuel cell that efficiently utilizes resources to generate electricity. However, the light-driven fuel cell of the present invention is not limited to the aforementioned uses and can be applied to a wide range of fields.

[0288] Explanation of reference numerals in the attached figures

[0289] 10. Photovoltaic-driven fuel cells

[0290] 11 Cathode

[0291] 12 Anodes

[0292] 124 Electrode Material

[0293] 126 Photocatalyst

[0294] 118 Cathode Reaction Field

[0295] 128 Anode Reaction Field

[0296] 14. Protons permeate the membrane

[0297] 15 External Circuits

[0298] 16 Methane

[0299] 17 Water

[0300] 18 Oxygen

[0301] 19 External conductors

[0302] 500 Photovoltaic Fuel Cell Reactor Main Body

[0303] 502 Proton-permeable membrane (solid electrolyte membrane)

[0304] 504 Anode photoelectrode disposed on a proton-permeable membrane (solid electrolyte membrane)

[0305] 506 Cathode photoelectrode disposed on a proton-permeable membrane (solid electrolyte membrane)

[0306] 508 membrane electrode assembly

[0307] 572 First collector board

[0308] 516 and 518 quartz glass plates

[0309] 574 Second collector board

[0310] 540a is a component having a feed gas supply port for supplying feed gas to the anode.

[0311] The 550a is a component having a feed gas supply port for supplying feed gas to the cathode.

[0312] 540b has a component for removing hydrocarbons generated in the anode.

[0313] The 550b has a component for removing hydrocarbons generated in the cathode.

[0314] 572a The light-transmitting part of the first current collector for irradiating light onto the anode.

[0315] 574a The light-transmitting part of the second current collector for irradiating light onto the cathode.

Claims

1. A light-driven fuel cell, comprising a cathode, an anode, and a proton-permeable membrane between the cathode and the anode. The anode is equipped with a photocatalyst for anaerobic methane oxidation. Methane and water are supplied to the anode, and light is irradiated. Through the anaerobic methane oxidation reaction, methanol, protons, and electrons are generated from the methane and water supplied to the anode. The protons pass through the proton-permeable membrane and move towards the cathode, while the electrons move towards the cathode via an external circuit. The cathode is equipped with a photocatalyst for aerobic methane oxidation reaction. Methane and oxygen are supplied to the cathode and light is irradiated. Through aerobic methane oxidation reaction, methanol and water are generated from the methane and oxygen supplied to the cathode, as well as the protons and electrons moving from the anode.

2. The light-driven fuel cell as described in claim 1, wherein, The photocatalyst used in the anaerobic methane oxidation reaction comprises an organometallic complex.

3. The light-driven fuel cell as described in claim 2, wherein, The organometallic complex contained in the photocatalyst for the anaerobic methane oxidation reaction has pentamethylcyclopentadiene as a ligand and iridium as a metal center.

4. The light-driven fuel cell as described in claim 2, wherein, The organometallic complex contained in the photocatalyst for the anaerobic methane oxidation reaction has cyclopentadiene as a ligand and manganese or iron as a metal center.

5. The light-driven fuel cell according to any one of claims 1 to 4, wherein, The photocatalyst used in the aerobic methane oxidation reaction comprises an organometallic complex.

6. The light-driven fuel cell as described in claim 5, wherein, The organometallic complex contained in the photocatalyst for the aerobic methane oxidation reaction has pentamethylcyclopentadiene as a ligand and ruthenium as a metal center.

7. The light-driven fuel cell according to any one of claims 1 to 4, comprising a light-transmitting substrate on the anode side and a light-transmitting substrate on the cathode side, which are at least partially light-transmitting. The anode is located between the anode-side transparent substrate and the proton-permeable membrane, and / or the cathode is located between the cathode-side transparent substrate and the proton-permeable membrane.

8. The light-driven fuel cell as described in claim 7, wherein, (1) The cathode comprises a layer containing a photocatalyst for aerobic methane oxidation reaction and a cathode-side gas diffusion layer. (2) The anode comprises a layer containing a photocatalyst for anaerobic methane oxidation and an anode-side gas diffusion layer. (3) The cathode-side gas diffusion layer is disposed toward the cathode-side light-transmitting substrate, the anode-side gas diffusion layer is disposed toward the anode-side light-transmitting substrate, the layer containing the photocatalyst for aerobic methane oxidation reaction is disposed toward the cathode-side membrane surface of the proton-permeable membrane, and the layer containing the photocatalyst for anaerobic methane oxidation reaction is disposed toward the anode-side membrane surface of the proton-permeable membrane.

9. Application of organometallic complexes in photocatalysts for anaerobic methane oxidation, among which, The organometallic complex has pentamethylcyclopentadiene as a ligand and iridium as a metal center.

10. Application of organometallic complexes in photocatalysts for anaerobic methane oxidation, among which, The organometallic complex has cyclopentadiene as a ligand and manganese or iron as a metal center.

11. A method for producing methanol, comprising the step of contacting methane and water with a photocatalyst for the anaerobic methane oxidation reaction as described in the application of claim 9 or 10.

12. Application of organometallic complexes in photocatalysts for aerobic methane oxidation, among which, The organometallic complex has pentamethylcyclopentadiene as a ligand and ruthenium as a metal center.

13. A method for producing methanol, comprising the step of contacting methane and oxygen with a photocatalyst for the aerobic methane oxidation reaction described in claim 12.

Images