Electrode structure, gas diffusion layer, and water electrolysis device

Abstract

To provide a technology capable of reducing performance degradation of a gas diffusion layer while minimizing the amount of catalyst material used.SOLUTION: A cell 4, as an electrode structure, comprise an electrolyte membrane 41, a gas diffusion layer 43, and a catalyst layer 45. The gas diffusion layer 43 is arranged on one side of the electrolyte membrane 41. The gas diffusion layer 43 is porous. The catalyst layer 45 is arranged between the electrolyte membrane 41 and the gas diffusion layer 43. The catalyst layer 45 is formed by a catalyst material. Thickness of a permeated portion 433 of the catalyst material in the gas diffusion layer 43 is 1 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The subject matter disclosed herein relates to an electrode structure, a gas diffusion layer, and a water electrolysis device. [Background technology]

[0002] Membrane and Electrode Assembly (MEA) is used in fields such as fuel cells and water electrolysis equipment. MEAs have high catalytic activity, promoting reactions in fuel cells and electrolytic hydrogen generation cells, achieving high electricity generation efficiency. In addition, MEAs do not generate CO2 during the energy conversion process, so using MEAs can reduce the environmental impact.

[0003] An MEA generally has an electrode structure in which a catalyst layer and a gas diffusion layer (GDL) are in contact in order on both sides of a polymer electrolyte membrane (PEM). Such an electrode structure is disclosed, for example, in Patent Document 1. Patent Document 1 discloses a technique for preventing the penetration of a paste composition for forming a flat layer when the paste composition is applied to the surface of a conductive porous substrate of a gas diffusion layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5292729 Summary of the Invention [Problem to be solved by the invention]

[0005] Known methods for manufacturing MEAs include a method in which a catalyst layer is provided on an electrolyte membrane and sandwiched between a pair of gas diffusion layers, and a method in which a pair of gas diffusion layers on which a catalyst layer has been formed is attached to an electrolyte membrane. Known methods for forming a catalyst layer include a die coating method, a spray coating method, and a decal method. The spray coating method is a method in which a liquid catalyst material is sprayed to form a coating film on a substrate. The decal method is a method in which a solid film- or sheet-shaped catalyst material is directly attached to a substrate. These methods generally have difficulty in improving 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, and is suitable for mass production of MEAs.

[0006] However, when a liquid catalyst material is attached to the gas diffusion layer, there is a risk that the catalyst material will permeate into the gas diffusion layer. If an increase in the amount of catalyst material permeating into the gas diffusion layer occurs, the performance of the gas diffusion layer, such as gas diffusion efficiency, will decrease. In addition, there is a risk that the amount of catalyst material used will increase in order to ensure the thickness of the catalyst layer.

[0007] An object of the present invention is to provide a technique that can reduce the amount of catalyst material used while mitigating the deterioration of the performance of the gas diffusion layer. [Means for solving the problem]

[0008] In order to solve the above problems, a first aspect is an electrode structure comprising 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 from a catalyst material, wherein a thickness of a penetration portion of the gas diffusion layer into which the catalyst material has permeated is 1 μm or less.

[0009] A second aspect is an electrode structure comprising 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, wherein a thickness of a penetration portion of the gas diffusion layer into which the catalyst material has permeated is not more than one-tenth of a thickness of the catalyst layer.

[0010] A third aspect is the electrode structure of the first or second aspect, wherein the gas diffusion layer has a permeation prevention layer on the catalyst layer side, the permeation prevention layer preventing permeation of the catalyst material.

[0011] A fourth embodiment is a porous gas diffusion layer provided with a permeation prevention layer containing a permeation inhibitor that prevents permeation of the catalyst material on the side where the catalyst layer containing the catalyst material is disposed.

[0012] A fifth aspect is a water electrolysis device for electrolyzing water, comprising the electrode structure of the first or second aspect. Effect of the Invention

[0013] According to the electrode structures of the first to third aspects, the permeation of the catalyst material in the gas diffusion layer can be reduced, so that the amount of catalyst material used can be reduced while reducing the decrease in gas diffusion efficiency.

[0014] According to the electrode structure of the third aspect, the permeation prevention layer can reduce the permeation of the catalyst material in the gas diffusion layer.

[0015] According to the gas diffusion layer of the fourth embodiment, the permeation prevention layer can reduce the permeation of the catalyst material in the gas diffusion layer.

[0016] According to the water electrolysis device of the fifth aspect, the permeation of the catalyst material in the gas diffusion layer can be reduced, and therefore the amount of catalyst material used can be reduced while reducing the deterioration in performance of the gas diffusion layer. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing a water electrolysis device 1 according to an embodiment. [Diagram 2] FIG. 2 is a perspective view that typically illustrates a cell of the water electrolysis device shown in FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of a portion of the cell shown in FIG. 2. [Figure 4]FIG. 3 is a diagram showing a first manufacturing flow for the cell shown in FIG. 2. [Diagram 5] FIG. 2 is a diagram showing catalyst particles contained in a catalyst material for forming a catalyst layer. [Figure 6] FIG. 3 is a diagram showing a second manufacturing flow for the cell shown in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the components described in the embodiment are merely examples, and are not intended to limit the scope of the present invention. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary for ease of understanding.

[0019] <1. Embodiment> Fig. 1 is a schematic diagram showing a water electrolysis apparatus 1 according to one embodiment. The water electrolysis apparatus 1 is an apparatus for producing hydrogen by solid polymer water electrolysis. As shown in Fig. 1, the water electrolysis apparatus 1 includes a cell stack 2 and a power source 3.

[0020] The cell stack 2 has a plurality of cells 4 and a plurality of separators 5. The cell stack 2 is constructed by alternately stacking the cells 4 and the separators 5. In the following description, the direction in which the cells 4 and the separators 5 are stacked is referred to as the "stacking direction." The power source 3 applies a voltage to the cell stack 2.

[0021] Fig. 2 is a perspective view that typically illustrates a cell 4 of the water electrolysis apparatus 1 illustrated in Fig. 1. The cell 4 includes an electrolyte membrane 41, a pair of gas diffusion layers 43, and a pair of catalyst layers 45. A stacked body formed 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). This membrane electrode assembly is an example of an "electrode structure".

[0022] The electrolyte membrane 41 is a thin film (ion exchange membrane) having ion conductivity and has 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.

[0023] The gas diffusion layers 43 are disposed on both sides of the electrolyte membrane 41. The gas diffusion layers 43 are made of a conductive, porous material. The gas diffusion layers 43 may be made of, for example, carbon paper or carbon cloth.

[0024] 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, a catalyst metal such as platinum (Pt), a platinum alloy, a platinum compound, etc. An example of the platinum alloy is an alloy of platinum and at least one metal selected from the group consisting of ruthenium (Ru), palladium (Pd), nickel (Ni), molybdenum (Mo), iridium (Ir), iron (Fe), etc.

[0025] As shown in FIGS. 1 and 2, when a voltage is applied between a pair of gas diffusion layers 43 in a cell 4 by a power source 3 of a water electrolysis device 1, oxygen gas (O) and hydrogen ions (H + ) is produced. This reaction is represented by the following equation:

[0026] Anode: 2H2O → 4H + + O2+ 4e -

[0027] The oxygen gas 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 + ) is an electron (e -) produces hydrogen gas (H2). This reaction is represented by the following equation:

[0028] Cathode: 2H + + 2e - → H2

[0029] The hydrogen gas generated on the cathode side permeates through the gas diffusion layer 43 on the cathode side and is discharged.

[0030] 3 is an enlarged cross-sectional view of a portion of the cell 4 shown in FIG. 2. As shown in FIG. 3, the gas diffusion layer 43 has a permeation prevention layer 431. The permeation prevention layer 431 is a layer that prevents the permeation of a catalyst material. The permeation prevention layer 431 is a surface layer on the catalyst layer 45 side of the gas diffusion layer 43. The permeation prevention layer 431 is formed by subjecting the gas diffusion layer 43 to a permeation prevention treatment, as described below. It is not essential that the gas diffusion layer 43 has the permeation prevention layer 431, and the permeation prevention layer 431 may be omitted.

[0031] The gas diffusion layer 43 has a permeation portion 433. The permeation portion 433 is a portion formed by the permeation of the catalyst material of the catalyst layer 45 into the gas diffusion layer 43. The thickness (thickness in the stacking direction) of the permeation portion 433 is, for example, 1 μm or less. The thickness of the permeation portion 433 is 1 / 10 or less of the thickness of the catalyst layer 45. By making the thickness of the permeation portion 433 1 μm or less, or by making the thickness of the permeation portion 433 1 / 10 or less of the thickness of the catalyst layer 45, the permeation of the catalyst material into the gas diffusion layer 43 is reduced. This can reduce the performance degradation of the gas diffusion layer 43 and can reduce the amount of catalyst material used.

[0032] FIG. 4 is a diagram showing a first manufacturing flow of the cell 4 shown in FIG. 2. First, a permeation prevention treatment is applied to the surface of the gas diffusion layer 43 (step S11). The permeation prevention treatment is, for example, a treatment of applying a permeation inhibitor that prevents the permeation of a catalyst material. After step S11, an ink of a catalyst material (hereinafter referred to as a "catalyst ink") is applied to the surface of the gas diffusion layer 43 that has been subjected to the permeation prevention treatment (step S12). After step S12, a catalyst layer 45 is formed on the surface of the gas diffusion layer 43 by a drying treatment that volatilizes the solvent contained in the catalyst ink. Furthermore, the gas diffusion layer 43 on which the catalyst layer 45 is formed is bonded to each of the anode side and the cathode side of the electrolyte membrane 41 (step S13). In this way, the cell 4, which is an electrode structure, is formed.

[0033] 5 is a diagram showing a catalyst particle 6 contained in the catalyst material for forming the catalyst layer 45. The catalyst particle 6 includes a carrier carbon 61 and an ionomer 63. The carrier carbon 61 supports a catalyst metal 611.

[0034] The ionomer 63 is an electrolyte polymer that covers 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 sulfo group. The hydrogen ions combine with water to form oxonium ions (HO + ) and is propagated through the ion exchange group of the ionomer 63. As shown in Fig. 5, the ionomer 63 is negatively charged. Therefore, in the ink of the catalyst material applied to the gas diffusion layer 43 in step S12, the catalyst particles 6 are dispersed in one another.

[0035] In step S11, the permeation prevention agent applied to the gas diffusion layer 43 may be an aggregating agent that aggregates the catalyst particles 6 in the catalyst ink, i.e., that causes a solvent shock. In this case, a permeation prevention layer 431 containing an aggregating agent is formed on the gas diffusion layer 43. For example, a cationic resin or a polyvalent metal salt may be used as the aggregating agent. As described above, when the catalyst particles 6 are negatively charged, the catalyst particles 6 aggregate when they come into contact with the cationic aggregating agent. Then, the aggregated catalyst particles 6 block the micropores of the gas diffusion layer 43, thereby reducing the permeation of the catalyst ink into the gas diffusion layer 43.

[0036] In addition, when the catalyst ink is acidic, an alkaline metal salt can be used as the aggregating agent. When the catalyst ink comes into contact with the alkaline metal salt, the catalyst particles 6 aggregate. This causes the micropores in the gas diffusion layer 43 to be blocked, thereby reducing the penetration of the catalyst ink into the gas diffusion layer 43.

[0037] The permeation inhibitor is not limited to the flocculant. For example, the permeation inhibitor may be a water-repellent material. In this case, a permeation prevention layer 431 containing a water-repellent material is formed on the gas diffusion layer 43. Examples of the water-repellent material that can be used include silicone resin, fluororesin, and polyurethane. By applying the water-repellent material, the gas diffusion layer 43 can be made water-repellent, and therefore the permeation of the catalyst ink into the gas diffusion layer 43 can be reduced.

[0038] The permeation prevention treatment in step S11 may be a treatment for imparting water repellency to the gas diffusion layer 43, and specifically may be a heating treatment. For example, if the gas diffusion layer 43 is made of carbon fiber, hydrophilic groups (hydroxyl groups, carboxyl groups, etc.) on the surface are decomposed by heating, and the surface can be made closer to pure carbon. This makes it possible to impart water repellency to the gas diffusion layer 43.

[0039] FIG. 6 is a diagram showing a second manufacturing flow of the cell 4 shown in FIG. 2. In the second manufacturing flow, first, a catalyst ink is applied to the surface of the gas diffusion layer 43 (step S21). Then, a permeation prevention treatment is performed on the gas diffusion layer 43 immediately after the catalyst ink is applied (step S22). Then, after step S22, a catalyst layer 45 is formed on the surface of the gas diffusion layer 43 by a drying treatment for volatilizing the solvent contained in the catalyst ink. Then, the gas diffusion layer 43 on which the catalyst layer 45 is formed is bonded to each of the anode side and the cathode side of the electrolyte membrane 41 (step S23). In this way, the cell 4 is formed.

[0040] The permeation prevention process in step S22 includes, for example, an annealing process for heating the catalyst ink applied to the gas diffusion layer 43. By heating the catalyst ink, the catalyst ink is fixed to the surface layer of the gas diffusion layer 43. This reduces the permeation of the catalyst ink into the gas diffusion layer 43.

[0041] The catalyst ink may also be applied multiple times. In this case, the amount of ink applied the first time may be very small in order to reduce the penetration of the catalyst ink into the gas diffusion layer 43. The catalyst ink applied the first time is then dried, thereby reducing the penetration of the catalyst ink applied the second time and thereafter. The catalyst ink applied the first time may also be made water-repellent by including a water-repellent material or the like. This makes it possible to impart water-repellency to the surface of the gas diffusion layer 43, thereby further reducing the penetration of the catalyst ink applied the second time.

[0042] <2. Modification> Although the embodiment has been described above, the present invention is not limited to the above, and various modifications are possible.

[0043] For example, in the above embodiment, the permeation prevention layer 431 is formed only on the surface portion of the gas diffusion layer 43. However, the permeation prevention layer 431 may be formed on the entire gas diffusion layer 43. For example, the permeation prevention layer 431 may be formed on the entire gas diffusion layer 43 by impregnating the gas diffusion layer 43 with a permeation inhibitor and then drying the permeation inhibitor.

[0044] 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 onto the electrolyte membrane 41. Then, the gas diffusion layer 43 may be laminated on the catalyst layer 45.

[0045] The water electrolysis device 1 is not limited to one that produces hydrogen by electrolyzing water. For example, the water electrolysis device 1 may be a device that produces methylcyclohexane (MCH) by bonding hydrogen ions produced by electrolyzing water with toluene. The electrode structure may also be applied to a fuel cell device that generates electricity from hydrogen or MCH.

[0046] Although the present invention has been described in detail, the above description is merely illustrative in all respects, and the present invention is not limited thereto. It is understood that countless variations not illustrated can be envisioned without departing from the scope of the present invention. The configurations described in the above embodiments and variations can be appropriately combined or omitted as long as they are not mutually contradictory. [Explanation of symbols]

[0047] 1 Water electrolysis device 4 Cell (electrode structure) 6. Catalyst particles (catalyst materials) 41 Electrolyte membrane 43 Gas diffusion layer 45 Catalyst layer 431 Penetration prevention layer 433 Penetration part

Claims

1. An electrode structure comprising: An electrolyte membrane; a porous gas diffusion layer disposed on one side of the electrolyte membrane; a catalyst layer disposed between the electrolyte membrane and the gas diffusion layer and formed of a catalyst material; Equipped with An electrode structure, wherein a thickness of a permeated portion of the gas diffusion layer into which the catalyst material has permeated is 1 μm or less.

2. An electrode structure comprising: An electrolyte membrane; a porous gas diffusion layer disposed on one side of the electrolyte membrane; a catalyst layer disposed between the electrolyte membrane and the gas diffusion layer and formed of a catalyst material; Equipped with An electrode structure, wherein a thickness of a portion of the gas diffusion layer into which the catalyst material has permeated is one-tenth or less of a thickness of the catalyst layer.

3. The electrode structure according to claim 1 or 2, The gas diffusion layer has a permeation prevention layer on the catalyst layer side, the permeation prevention layer preventing the permeation of the catalyst material.

4. A porous gas diffusion layer, A gas diffusion layer comprising, on a side on which a catalyst layer containing a catalyst material is disposed, a permeation prevention layer containing a permeation inhibitor for preventing permeation of the catalyst material.

5. A water electrolysis device for electrolyzing water, comprising: A water electrolysis device comprising the electrode structure according to claim 1 or 2.

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