Electrode structure, gas diffusion layer, and water electrolysis device

Abstract

The invention provides a technology capable of reducing performance degradation of a gas diffusion layer and reducing the usage amount of a catalyst material. A cell (4), which is an electrode structure, has an electrolyte membrane (41), a gas diffusion layer (43), and a catalyst layer (45). The gas diffusion layer (43) is disposed on one side of the electrolyte membrane (41). The gas diffusion layer (43) is porous. The catalyst layer (45) is disposed between the electrolyte membrane (41) and the gas diffusion layer (43). The catalyst layer (45) is formed from a catalyst material. The gas diffusion layer (43) has a thickness of 1 [mu] m or less in a permeation portion (433) into which the catalyst material permeates.

Description

Technical Field

[0001] The subject matter disclosed in this specification relates to an electrode structure, a gas diffusion layer and a water electrolysis device. Background Art

[0002] Membrane and Electrode Assembly (MEA) is used in the fields of fuel cells and water electrolysis devices. MEA has high catalytic activity, promotes the reaction in the fuel cell or electrolytic hydrogen generation cell unit, and achieves high power generation efficiency. In addition, since MEA does not produce CO2 during the energy conversion process, the environmental load can be reduced by using MEA.

[0003] MEA generally has an electrode structure in which a catalyst layer and a gas diffusion layer (GDL: Gas Diffusion Layer) are in contact with both sides of a polymer electrolyte membrane (PEM: Polymer Electrolyte Membrane) in sequence. Such an electrode structure has been disclosed, for example, in Japanese Patent No. 5292729. In addition, Japanese Patent No. 5292729 discloses a technology in which a slurry composition for forming a flat layer is applied to the surface of a conductive porous substrate of a gas diffusion layer, and the slurry composition does not penetrate. Summary of the invention

[0004] As methods for manufacturing MEA, the following methods are known: a method in which a catalyst layer is provided on an electrolyte membrane and sandwiched by a pair of gas diffusion layers; a method in which a pair of gas diffusion layers formed with a catalyst layer are attached to the electrolyte membrane. In addition, as methods for forming a catalyst layer, a die coating method, a spray coating method, and a transfer method are known. The spray coating method is a method in which a liquid catalyst material is sprayed into a mist to form a coating on a substrate. The transfer method is a method in which a solid thin film or sheet catalyst material is directly attached to a substrate. These methods are generally difficult to improve productivity. On the other hand, the die coating method is a method in which a liquid catalyst material is directly applied to a substrate from a die nozzle, which is suitable for mass production of MEA.

[0005] However, when the liquid catalyst material is attached to the gas diffusion layer, the catalyst material will penetrate into the gas diffusion layer. When the catalyst material that penetrates into the gas diffusion layer increases, the performance of the gas diffusion layer such as gas diffusion efficiency decreases. In addition, in order to ensure the thickness of the catalyst layer, the amount of catalyst material used will increase.

[0006] An object of the present invention is to provide a technology capable of reducing the performance degradation of a gas diffusion layer and reducing the amount of catalyst material used.

[0007] The first mode is an electrode structure. The electrode structure of the first mode comprises: an electrolyte membrane; a porous gas diffusion layer disposed on one side of the electrolyte membrane; and a catalyst layer disposed between the electrolyte membrane and the gas diffusion layer and formed of a catalyst material. In the gas diffusion layer, the thickness of the permeation portion where the catalyst material permeates is 1 μm or less.

[0008] The second mode is an electrode structure. The electrode structure of the second mode comprises: an electrolyte membrane; a porous gas diffusion layer disposed on one side of the electrolyte membrane; and a catalyst layer disposed between the electrolyte membrane and the gas diffusion layer and formed of a catalyst material. In the gas diffusion layer, the thickness of the permeation portion where the catalyst material permeates is less than one tenth of the thickness of the catalyst layer.

[0009] A third aspect is the electrode structure according to the first aspect or the second aspect. In the third electrode structure, the gas diffusion layer has a barrier layer on the catalyst layer side for preventing penetration of the catalyst material.

[0010] The fourth aspect is a porous gas diffusion layer having a barrier layer on the side where the catalyst layer containing the catalyst material is arranged, and the barrier layer contains a barrier agent that prevents the penetration of the catalyst material.

[0011] A fifth aspect is a water electrolysis device for electrolyzing water. The water electrolysis device of the fifth aspect includes the electrode structure of any one of the first to third aspects.

[0012] According to the electrode structures of the first to third aspects, since the permeation of the catalyst material into the gas diffusion layer can be reduced, the reduction in gas diffusion efficiency can be reduced, and the amount of catalyst material used can be reduced.

[0013] According to the electrode structure of the third aspect, the barrier layer can reduce the permeation of the catalyst material into the gas diffusion layer.

[0014] According to the gas diffusion layer of the fourth aspect, the permeation of the catalyst material into the gas diffusion layer can be reduced by the barrier layer.

[0015] According to the water electrolysis device of the fifth aspect, since the permeation of the catalyst material into the gas diffusion layer can be reduced, the performance degradation of the gas diffusion layer can be reduced, and the amount of catalyst material used can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram which shows the water electrolysis apparatus 1 which concerns on one Embodiment.

[0017] Figure 2 It is schematically indicated Figure 1A perspective view of a cell unit of the water electrolysis device shown.

[0018] Figure 3 It is a magnified representation Figure 2 A cross-sectional view of a portion of a cell unit is shown.

[0019] Figure 4 Yes means Figure 2 Diagram of a first manufacturing flow of a cell unit is shown.

[0020] Figure 5 This is a diagram showing catalyst particles contained in a catalyst material for forming a catalyst layer.

[0021] Figure 6 Yes means Figure 2 A diagram of a second manufacturing flow diagram of a cell unit is shown. DETAILED DESCRIPTION

[0022] Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the components described in the embodiments are purely illustrative, and the scope of the present invention is not limited thereto. In the accompanying drawings, the size or quantity of each part may be exaggerated or simplified as needed for ease of understanding.

[0023] <1. Example>

[0024] Figure 1 Schematic diagram of a water electrolysis device 1 according to one embodiment. The water electrolysis device 1 is a device for producing hydrogen by solid polymer water electrolysis. Figure 1 As shown, the water electrolysis device 1 includes a cell stack 2 and a power source 3 .

[0025] The cell stack 2 has a plurality of cell cells 4 and a plurality of spacers 5. The cell stack 2 is formed by alternately stacking the cell cells 4 and the spacers 5. In the following description, the direction in which the cell cells 4 and the spacers 5 are stacked is referred to as a “stacking direction.” The power source 3 applies a voltage to the cell stack 2.

[0026] Figure 2 It is schematically indicated Figure 1 The cell unit 4 of the water electrolysis device 1 is shown in a perspective view. The cell unit 4 has an electrolyte membrane 41, a pair of gas diffusion layers 43 and a pair of catalyst layers 45. The stacked body composed of the electrolyte membrane 41, the pair of gas diffusion layers 43 and the pair of catalyst layers 45 is called a membrane electrode assembly (MEA). The membrane electrode assembly is an example of an "electrode structure".

[0027] The electrolyte membrane 41 is an ion-conductive thin film (ion exchange membrane) having insulating properties. For example, a fluorine-based or hydrocarbon-based polymer electrolyte membrane can be used as the electrolyte membrane 41, and more specifically, a polymer electrolyte membrane containing perfluorocarbon sulfonic acid can be used.

[0028] The gas diffusion layer 43 is disposed one at each side of the electrolyte membrane 41. The gas diffusion layer 43 is a member having electrical conductivity and is composed of a porous member. For example, carbon paper or carbon cloth can be used for the gas diffusion layer 43.

[0029] The catalyst layer 45 is disposed between the electrolyte membrane 41 and the gas diffusion layer 43. The catalyst layer 45 is formed of a catalyst material. The catalyst material includes, for example, catalyst metals such as platinum (Pt), platinum alloys, and platinum compounds. As a platinum alloy, for example, an alloy of platinum and at least one metal selected from ruthenium (Ru), palladium (Pd), nickel (Ni), molybdenum (Mo), iridium (Ir), iron (Fe), etc. can be cited.

[0030] like Figure 1 and Figure 2 As shown in FIG. 1 , when a voltage is applied between a pair of gas diffusion layers 43 in the cell unit 4 by the power supply 3 of the water electrolysis device 1, oxygen (O2) and hydrogen ions (H2O) are generated from water (H2O) in the catalyst layer 45 on the anode side. + ). The reaction is represented by the following formula.

[0031] Anode: 2H2O→4H + +O2+4e -

[0032] The oxygen generated on the anode side is discharged through the gas diffusion layer 43 on the anode side, and the generated hydrogen ions are transferred to the cathode side through the electrolyte membrane 41. In addition, in the catalyst layer 45 on the cathode side, the hydrogen ions (H + ) and electron (e - ) reaction, thereby generating hydrogen (H2). The reaction is represented by the following formula.

[0033] Cathode: 2H + +2e - →H2

[0034] The hydrogen gas generated on the cathode side passes through the gas diffusion layer 43 on the cathode side and is discharged.

[0035] Figure 3 It is a magnified representation Figure 2 FIG. 4 is a cross-sectional view of a portion of the pool unit 4 shown. Figure 3As shown in FIG. 1 , the gas diffusion layer 43 has an impermeable layer 431. The impermeable layer 431 is a layer that prevents the penetration of the catalyst material. The impermeable layer 431 is a surface layer on the catalyst layer 45 side of the gas diffusion layer 43. As described later, the impermeable layer 431 is formed by performing an impermeable treatment on the gas diffusion layer 43. In addition, the gas diffusion layer 43 does not necessarily have to have the impermeable layer 431, and it is also possible not to have the impermeable layer 431.

[0036] The gas diffusion layer 43 has a permeable portion 433. The permeable portion 433 is a portion formed by the catalyst material of the catalyst layer 45 penetrating into the gas diffusion layer 43. The thickness of the permeable portion 433 (thickness in the stacking direction) is, for example, 1 μm or less. The thickness of the permeable portion 433 is less than one tenth of the thickness of the catalyst layer 45. By setting the thickness of the permeable portion 433 to be less than 1 μm, or setting the thickness of the permeable portion 433 to be less than one tenth of the thickness of the catalyst layer 45, the penetration of the catalyst material into the gas diffusion layer 43 can be reduced. As a result, the performance degradation of the gas diffusion layer 43 can be reduced, and the amount of catalyst material used can be reduced.

[0037] Figure 4 Yes means Figure 2 1 is a diagram of a first manufacturing process of a cell unit 4 shown in FIG. First, an impermeability treatment is applied to the surface of the gas diffusion layer 43 (step S11). The impermeability treatment is, for example, a treatment of coating an impermeability agent that prevents the catalyst material from penetrating. After step S11, ink of a catalyst material (hereinafter referred to as "catalyst ink") is applied to the surface of the gas diffusion layer 43 that has been subjected to the impermeability treatment (step S12). After step S12, a drying treatment is performed to volatilize the solvent contained in the catalyst ink, thereby forming a catalyst layer 45 on the surface of the gas diffusion layer 43. Furthermore, the gas diffusion layer 43 formed with the catalyst layer 45 is respectively bonded to the anode side and the cathode side of the electrolyte membrane 41 (step S13). Thus, an electrode structure, i.e., the cell unit 4, is formed.

[0038] Figure 5 The figure shows the catalyst particles 6 contained in the catalyst material for forming the catalyst layer 45. The catalyst particles 6 include a carrier carbon 61 and an ionomer 63. The carrier carbon 61 supports a catalyst metal 611.

[0039] The ionomer 63 is an electrolyte polymer covering the carrier carbon 61. The ionomer 63 has a function of transporting hydrogen ions generated by electrolysis of water in the catalyst layer 45 on the anode side. For example, Nafion (perfluorocarbon sulfonic acid) can be used as the ionomer 63. The ionomer 63 has a polymer chain structure having an ion exchange group such as a sulfonic acid group. The hydrogen ions combine with water to form hydronium ions (H3O + ), propagates through the ion exchange groups of the ionomer 63. Figure 5As shown, the ionomer 63 is negatively charged. Therefore, in step S12, in the catalyst material ink applied to the gas diffusion layer 43, the catalyst particles 6 are dispersed with each other.

[0040] In step S11, as the anti-seepage agent applied to the gas diffusion layer 43, a coagulant can be used, which agglutinates the catalyst particles 6 in the catalyst ink, that is, causes solvent shock. In this case, an anti-seepage layer 431 containing a coagulant is formed on the gas diffusion layer 43. As the coagulant, for example, a cationic resin or a multivalent metal salt can be used. As described above, when the catalyst particles 6 are negatively charged, the catalyst particles 6 agglutinate by contacting the cationic coagulant. As a result, the agglomerated catalyst particles 6 block the micropores of the gas diffusion layer 43, thereby reducing the penetration of the catalyst ink in the gas diffusion layer 43.

[0041] In addition, when the catalyst ink is acidic, an alkaline metal salt can be used as a coagulant. The catalyst ink and the alkaline metal salt come into contact with each other, and the catalyst particles 6 agglomerate. As a result, the micropores of the gas diffusion layer 43 are blocked, and thus the penetration of the catalyst ink into the gas diffusion layer 43 can be reduced.

[0042] In addition, the impermeable agent is not limited to the coagulant. For example, the impermeable agent may be a waterproof material. In this case, an impermeable layer 431 containing a waterproof material is formed on the gas diffusion layer 43. As the waterproof material, for example, silicone resin, fluororesin, polyurethane, etc. can be used. By applying the waterproof material, the gas diffusion layer 43 can be given waterproofness, so the penetration of the catalyst ink in the gas diffusion layer 43 can be reduced.

[0043] In addition, the anti-seepage treatment in step S11 may be a treatment for imparting water repellency to the gas diffusion layer 43, specifically, a heating treatment. For example, when the gas diffusion layer 43 is made of carbon fiber, the hydrophilic groups (hydroxyl groups, carboxyl groups, etc.) on the surface thereof may be decomposed by heating to make the surface close to pure carbon. Thus, the gas diffusion layer 43 may be made water repellent.

[0044] Figure 6 Yes means Figure 2 1 is a diagram of a second manufacturing process of the cell unit 4. In the second manufacturing process, first, the catalyst ink is applied to the surface of the gas diffusion layer 43 (step S21). Then, the gas diffusion layer 43 just after the catalyst ink is applied is subjected to an anti-seepage treatment (step S22). Then, after step S22, a drying treatment is performed to volatilize the solvent contained in the catalyst ink, so that the catalyst layer 45 is formed on the surface of the gas diffusion layer 43. Then, the gas diffusion layer 43 formed with the catalyst layer 45 is respectively bonded to the anode side and the cathode side of the electrolyte membrane 41 (step S23). Thus, the cell unit 4 is formed.

[0045] The anti-seepage treatment in step S22 includes, for example, an annealing treatment of heating the catalyst ink applied to the gas diffusion layer 43. By heating the catalyst ink, the catalyst ink is fixed on the surface of the gas diffusion layer 43. Thus, the penetration of the catalyst ink into the gas diffusion layer 43 can be reduced.

[0046] In addition, the catalyst ink may be applied multiple times. In this case, in order to reduce the penetration of the catalyst ink into the gas diffusion layer 43, the amount of ink applied for the first time may be set to a very small amount. In addition, by drying the catalyst ink applied for the first time, the penetration of the catalyst ink applied for the second time and thereafter can be reduced. In addition, the catalyst ink applied for the first time may be made waterproof by including a waterproof material or the like in the catalyst ink. Thus, since the surface of the gas diffusion layer 43 can be made waterproof, the penetration of the catalyst ink applied for the second time can be further reduced.

[0047] <2. Modifications>

[0048] As mentioned above, although embodiment was described, this invention is not limited to the said content, Various deformation|transformation is possible.

[0049] For example, in the above-mentioned embodiment, the impermeable layer 431 is formed only on the surface portion of the gas diffusion layer 43. However, the impermeable layer 431 may be formed on the entire gas diffusion layer 43. For example, after the gas diffusion layer 43 is infiltrated with an impermeable agent, the impermeable agent is dried, thereby forming the impermeable layer 431 on the entire gas diffusion layer 43.

[0050] In the above embodiment, the catalyst layer 45 is formed on the gas diffusion layer 43 by applying the catalyst ink to the gas diffusion layer 43. However, the catalyst layer 45 may be formed by applying the catalyst ink on the electrolyte membrane 41. Furthermore, the gas diffusion layer 43 may be stacked on the catalyst layer 45.

[0051] The water electrolysis device 1 is not limited to a device that electrolyzes water to produce hydrogen. For example, the water electrolysis device 1 may also be a device that produces methylcyclohexane (MCH) by combining hydrogen ions after electrolysis of water with toluene. In addition, the electrode structure may also be applied to a fuel cell device that generates electricity from hydrogen or MCH.

[0052] Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It should be understood that many unillustrated variations can be thought of without departing from the scope of the present invention. As long as there is no contradiction, the various structures described in the above-mentioned embodiments and various variations can be appropriately combined or omitted.

Claims

1. An electrode structure, comprising: Electrolyte membrane; a porous gas diffusion layer disposed on one side of the electrolyte membrane; and a catalyst layer, disposed between the electrolyte membrane and the gas diffusion layer, and formed of a catalyst material, In the gas diffusion layer, a thickness of a permeation portion into which the catalyst material permeates is 1 μm or less.

2. An electrode structure having: Electrolyte membrane; a porous gas diffusion layer disposed on one side of the electrolyte membrane; and a catalyst layer, disposed between the electrolyte membrane and the gas diffusion layer, and formed of a catalyst material, In the gas diffusion layer, a thickness of a permeation portion into which the catalyst material permeates is one tenth or less of a thickness of the catalyst layer.

3. The electrode structure according to claim 1 or 2, wherein: The gas diffusion layer has a barrier layer on the catalyst layer side for preventing penetration of the catalyst material.

4. A gas diffusion layer, which is a porous gas diffusion layer, wherein: A barrier layer is provided on the side where the catalyst layer containing the catalyst material is arranged, and the barrier layer contains a barrier agent for preventing the penetration of the catalyst material.

5. A water electrolysis device for electrolyzing water, wherein: An electrode structure according to any one of claims 1 to 3.

Images