Electrochemical cell

Abstract

To provide an electrochemical cell having a good reactive performance.SOLUTION: An electrochemical cell according to the present invention comprises a polymer electrolyte, a catalyst layer, a gas diffusion layer, and a plate electrode in this order. Gaskets are arranged around the catalyst layer and around the gas diffusion layer. The thickness of the gasket is smaller than the thickness of the gas diffusion layer. The thickness of the gasket may be between 0.1 mm and 0.3 mm. The difference between the thickness of the gasket and the thickness of the gas diffusion layer may be 0.1 mm or more. The porosity of the gas diffusion layer may be 78% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to electrochemical cells. [Background technology]

[0002] Electrochemical cells (water electrolysis cells and fuel cells) consist of an electrolyte membrane, catalyst layer, gas diffusion layer (GDL layer), gasket, and separator. The GDL layer is made of a material with gas diffusivity and electrical conductivity, such as titanium fiber sintered compact. The sintered fiber has large irregularities, which can crush the catalytic electrolytic cell and electrolyte membrane, reducing their durability. For example, the diameter of titanium fiber is about 20 μm, while the electrolyte membrane is about 100 μm. However, if the fibers in the GDL layer are frayed, the electrolyte membrane can easily tear or collapse, causing a short circuit between the electrodes.

[0003] The following techniques have been proposed to prevent inter-electrode short circuits. Patent Document 1 discloses filling a microporous layer (MPL layer) with a thickness of 20 μm to 100 μm on the catalyst layer side of the GDL layer. Patent Document 2 discloses adopting a two-layer structure with different porosities for the GDL layer, with the porosity of the GDL layer on the catalyst side being low and the porosity of the outer GDL layer being high. It is also effective to cover the periphery of the GDL layer with a silicone gasket. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-159573 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-342587 Summary of the Invention [Problem to be solved by the invention]

[0005] To maintain the performance of water electrolysis and power generation, a structure suitable for water infiltration and gas evacuation is required, and the entire structure, including not only the GDL layer but also other components, must be appropriately designed. This ensures that the raw material water is sufficiently distributed over the catalyst surface, while the product gases, hydrogen and oxygen, are quickly removed, improving reaction efficiency and current-voltage characteristics. In other words, such structural design contributes to improving input power, making it a very important element for such devices.

[0006] An object of the present disclosure is to provide an electrochemical cell having better reaction performance than conventional electrochemical cells. [Means for solving the problem]

[0007] One aspect of the present disclosure is The fuel cell has an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a flat electrode in this order; a gasket is provided around the catalyst layer and the gas diffusion layer; The thickness of the gasket is smaller than the thickness of the gas diffusion layer. The electrochemical cell is characterized by:

[0008] The gasket thickness should be smaller than that of the gas diffusion layer, but it is more preferable if the difference in thickness between the gas diffusion layers is 0.1 mm or more. Although it depends on the thickness of the gas diffusion layer, for example, the gasket thickness is preferably 0.3 mm or less. Furthermore, the gasket thickness is preferably 0.1 mm or more.

[0009] In this embodiment, the above conditions regarding the thickness of the gasket and the thickness of the gas diffusion layer preferably hold true at least on the anode side, although the above conditions may also hold true on the cathode side.

[0010] In this embodiment, the porosity of the gas diffusion layer is preferably 78% or more. The gas diffusion layer may have a two-layer structure, in which case the porosity of the layer closest to the flat electrode, i.e., the layer opposite the catalyst layer, is preferably 78% or more.

[0011] In this embodiment, the gas diffusion layer comprises, for example, titanium fibers, and the gasket is made of, for example, silicone. [Effects of the Invention]

[0012] According to the present disclosure, the reaction performance of an electrochemical cell can be improved compared to conventional methods. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic configuration of a water electrolysis cell according to an embodiment. FIG. [Figure 2] FIG. 1 is a view showing an electron microscope photograph of a gas diffusion layer used in an experiment. [Figure 3] FIG. 10 is a diagram showing the results of an experiment measuring water electrolysis performance depending on the gasket thickness. [Figure 4] FIG. 10 is a diagram showing the results of an experiment measuring water electrolysis performance depending on the gasket thickness. [Figure 5] FIG. 10 is a diagram showing the results of an experiment measuring water electrolysis performance depending on the porosity of the gas diffusion layer. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments and examples of the present invention will be described below with reference to the drawings. However, the following embodiments and examples merely exemplify preferred configurations of the present invention, and the scope of the present invention is not limited to these configurations. Furthermore, unless otherwise specified, the scope of the present invention is not intended to be limited to only these.

[0015] <Configuration overview> This embodiment is a water electrolysis cell that electrolyzes water using electric power. In this embodiment, it is assumed that water is electrolyzed using electric power based on renewable energy, such as solar, wind, hydroelectric, or geothermal energy. However, this embodiment may also use electric power based on fossil fuels, nuclear power, or the like.

[0016] 1(A) is a diagram showing the schematic configuration of a water electrolysis cell 10 according to an embodiment. The water electrolysis cell 10 is a unit component that decomposes water (HO) into hydrogen (H) and oxygen (O), and a water electrolysis stack is formed by stacking such water electrolysis cells 10. The water electrolysis cell is supplied with raw materials such as pure water, water, or, in the case of an electrolyte solution, an aqueous solvent.

[0017] The water electrolysis cell 10 has multiple layers, with an electrolyte membrane (PEM) 11 sandwiched between them, one of which is an oxygen evolution electrode (anode) and the other is a hydrogen evolution electrode (cathode). The anode is composed of a catalyst layer 12, a gas diffusion layer (GDL) 13, and a flat plate electrode 14 stacked in this order from the electrolyte membrane 11 side. As shown in FIG. 1(B), a silicone gasket 15 is provided around the catalyst layer 12 and the gas diffusion layer 13. On the other hand, the cathode is composed of a catalyst layer 22, a gas diffusion layer (GDL) 23, and a flat plate electrode 24 stacked in this order from the electrolyte membrane 11 side. A silicone gasket 25 is provided around the catalyst layer 22 and the gas diffusion layer 23.

[0018] The electrolyte membrane 11 is made of an ion-permeable material, specifically an ion exchange membrane. In this embodiment, a known ion exchange membrane used in water electrolysis may be used. Specific examples of the electrolyte membrane 11 include a solid polymer electrolyte membrane such as perfluorocarbon with an ion exchange group introduced therein. Examples of the thickness of the electrolyte membrane 11 include a membrane. There are no particular limitations on the thickness of the electrolyte membrane 11, but it is preferably 50 to 200 μm, and more preferably about 100 μm. The thinner the electrolyte membrane 11, the lower the membrane resistance and the better the current-voltage characteristics, but hydrogen permeation from the cathode to the anode becomes a problem, so the appropriate thickness is determined by balancing these factors.

[0019] First, the anode-side catalyst layer 12, gas diffusion layer 13, flat plate electrode 14, and gasket 15 will be described.

[0020] The catalyst layer 12 is a layer made of an electrode catalyst containing at least one of a noble metal catalyst such as Pt, Ru, or Ir and its oxide. Specific materials include Pt, iridium oxide, ruthenium oxide, iridium-ruthenium oxide, and mixtures thereof. Examples of iridium oxide include iridium oxide (IrO2, IrO3), iridium tin oxide, and iridium zirconium oxide. Examples of ruthenium oxide include ruthenium oxide (RuO2, Ru2O3), ruthenium tantalum oxide, ruthenium zirconium oxide, ruthenium titanium oxide, and ruthenium titanium cerium oxide. Examples of iridium-ruthenium oxide include iridium-ruthenium cobalt oxide, iridium-ruthenium tin oxide, iridium-ruthenium iron oxide, and iridium-ruthenium nickel oxide. The catalyst layer 12 may be a transition metal catalyst such as manganese (Mn), iron (Fe), cobalt (Co), or nickel (Ni), or an oxide thereof, a transition metal oxide-carbon mixture, or a composite electrode material containing a transition metal oxide.

[0021] The gas diffusion layer 13 is made of a gas-permeable and conductive material, and known materials used in water electrolysis can be used. The gas diffusion layer 13 includes, for example, a porous conductive material made of metal fibers or metal particles. The gas diffusion layer 13 can be formed, for example, by layering fibrous titanium (Ti) like a nonwoven fabric. A titanium fiber sintered compact can be used for the gas diffusion layer 13. The titanium fibers may be coated with platinum. The thickness and porosity of the gas diffusion layer 13 will be described later.

[0022] The plate electrode 14 is a metal plate electrode that supplies current to the gas diffusion layer 13 and the catalyst layer 12 .

[0023] The gasket 15 is made of silicone (silicon resin), is provided around the catalyst layer 12 and the gas diffusion layer 13, and is an in-cell seal that seals the inside and outside of the water electrolysis cell.

[0024] Although not shown, the anode includes a separator that supplies water to the gas diffusion layer 13 and discharges the generated oxygen.

[0025] Next, the catalyst layer 22, gas diffusion layer 23, flat plate electrode 24, and gasket 25 on the cathode side will be described.

[0026] As the catalyst contained in the catalyst layer 22, known catalysts can be used, and examples thereof include platinum, platinum-coated titanium, platinum-supported carbon, palladium-supported carbon, cobalt glyoxime, and nickel glyoxime.

[0027] The gas diffusion layer 23 is composed of a member having gas permeability and conductivity, and known materials used in water electrolysis can be utilized. The gas diffusion layer 23 can use, for example, porous members such as carbon cloth or carbon paper. Since oxidation hardly occurs at the cathode, carbon can be used as described above, but it may have the same configuration as the gas diffusion layer 13 on the anode side.

[0028] The flat plate electrode 24 is a flat plate electrode made of metal that supplies current to the gas diffusion layer 23 and the catalyst layer 22.

[0029] The gasket 25 is made of silicone (silicon resin), is provided around the catalyst layer 22 and the gas diffusion layer 23, and is an in-cell seal that seals the inside and outside of the water electrolysis cell.

[0030] Although not shown, the cathode includes a separator that discharges the separated hydrogen and the accompanying water from the gas diffusion layer 23.

[0031] <GDL Layer and Silicon Gasket> The present inventors have investigated the influence of the GDL layer 13 and the gasket 15 on the water electrolysis performance, and have found the following.

[0032] The thickness of the gasket 15 is preferably smaller (thinner) than the thickness of the GDL layer 13. In other words, the thickness of the GDL layer 13 is preferably larger (thicker) than the thickness of the gasket 15. For example, if the thickness of the GDL layer 13 is 0.2 mm, the thickness of the gasket 15 is preferably 0.1 to 0.2 mm. Furthermore, if the thickness of the GDL layer 13 is 0.4 mm, the thickness of the gasket 15 is preferably 0.1 to 0.3 mm. Furthermore, the difference in thickness between the gasket 15 and the GDL layer 13 is preferably 0.1 mm or more. If the gasket 15 is too thick relative to the GDL layer 13, it is expected that pressure will not be applied appropriately, resulting in increased electrical resistance and reduced catalytic activity and water electrolysis reaction. On the other hand, if the thickness of the gasket 15 is too thin, it is also undesirable because it may cause leakage of water or gas inside, and therefore it is preferable that the thickness be at least 0.1 mm. Note that the thicknesses of the gasket 15 and the GDL layer 13 are measured under no load.

[0033] Furthermore, the porosity of the GDL layer 13 is preferably high, more preferably greater than 70%, and even more preferably 78% or greater. It has been found that not only the thickness of the GDL layer 13 but also its structure (porosity) has a significant effect on water supply and gas discharge. The GDL layer 13 can have a two-layer structure with different porosities. In this case, it is preferable that the layer closer to the catalyst (first layer) has a low porosity and the layer closer to the flat electrode (second layer) has a high porosity. In the case of a two-layer structure, the porosity of the outer layer is preferably greater than 70%, and even more preferably 78% or greater.

[0034] <Experiment> The present inventors conducted an experiment to examine the water electrolysis performance by changing the structures of the GDL layer 13 and the gasket 15 .

[0035] (GDL layer) Figure 2 shows scanning electron microscope (SEM) photographs of the GDL layer 13 used in the experiment. The SEM photographs were taken at 30x, 100x, 500x, and 800x magnifications. All of the GDL layers were formed by layering titanium fiber sintered compacts like nonwoven fabric.

[0036] Photo 31 is an image of a 0.2 mm thick GDL layer with a 56% porosity. Photo 32 is an image of a 0.4 mm thick GDL layer with a 78% porosity. Photo 33 is an image of the surface of a 78% porosity GDL layer with a two-layer structure, one 0.2 mm thick with a 78% porosity and the other 0.2 mm thick with a 56% porosity, for a total thickness of 0.4 mm. Photo 34 is an image of the surface of a 56% porosity GDL layer with the same two-layer structure. Photo 35 is an image of a 0.4 mm thick GDL layer with a 56% porosity. Photo 36 is an image of a 0.2 mm thick GDL layer with a 70% porosity.

[0037] (Experiment 1: Changing gasket thickness) First, the GDL layer 13 was fixed at a porosity of 56% and a thickness of 0.2 mm, and the thickness of the gasket 15 was changed to measure the electrolysis performance.

[0038] FIG. 3(A) shows the voltage-current characteristics when the applied voltage is increased at 500 mV / s. The voltage increase rate of 500 mV / s is relatively fast, and this is to evaluate the water electrolysis reaction itself while minimizing the effects of the supply and discharge of water and gas. Graph 41 shows the measurement results when the gasket 15 is 0.1 mm thick, graph 42 shows the measurement results when the gasket 15 is 0.2 mm thick, and graph 43 shows the measurement results when the gasket 15 is 0.3 mm thick. The vertical axis in the graphs of FIGS. 3 to 5 represents the generated current (electrode area 5 cm 2 ) is shown.

[0039] FIG. 3B is a diagram showing the change over time in the voltage-current characteristics when an applied voltage of 2.0 V is used.

[0040] As can be seen from the results in Figures 3(A) and 3(B), when the gasket 15 thickness is 0.1 mm and 0.2 mm, the water electrolysis performance is good. It can also be seen that the water electrolysis performance decreases a few seconds after the start of voltage application, but relatively good performance is maintained. On the other hand, when the gasket 15 thickness is 0.3 mm, the water electrolysis performance decreases significantly. Thus, it can be seen that it is preferable for the gasket 15 to be thinner than the GDL layer 13. This is thought to be because pressure is not applied appropriately when the gasket 15 is thick.

[0041] (Experiment 2: Changing the gasket thickness) Next, the GDL layer 13 was fixed at a porosity of 78% and a thickness of 0.4 mm, and the thickness of the gasket 15 was changed to measure the electrolysis performance.

[0042] Figure 4(A) shows the voltage-current characteristics when the applied voltage is increased at 500 mV / s. Figure 4(B) shows the change over time in the voltage-current characteristics when the applied voltage is 2.0 V. Graph 51 shows the measurement results when the gasket 15 is 0.1 mm thick, graph 52 when the gasket 15 is 0.2 mm thick, graph 53 when the gasket 15 is 0.3 mm thick, and graph 54 when the gasket 15 is 0.4 mm thick.

[0043] 4(A) and 4(B) show that, as in Experiment 1, good water electrolysis performance is obtained when the thickness of the gasket 15 is 0.1 to 0.3 mm, which is thinner than the thickness of the GDL layer 13 (0.4 mm). Furthermore, compared with Experiment 1, it was found that in Experiment 1, the water electrolysis performance deteriorated within a few seconds after the start of voltage application, whereas in this experiment, the water electrolysis performance was maintained without deterioration. Therefore, it was found that it is preferable to make the thickness of the gasket 15 thinner than the thickness of the GDL layer 13 and to increase the porosity of the GDL layer 13.

[0044] (Experiment 3: Change in GDL layer porosity) The water electrolysis performance was measured by changing the porosity of the GDL layer 13 and the thickness of the gasket 15. Here, the porosity and thickness of the GDL layer 13 and the thickness of the gasket 15 were measured under the following six conditions. (Condition 1) GDL layer: Thickness 0.2 mm, porosity 56% (Condition 2) GDL layer: Thickness 0.4 mm, porosity 78% (Condition 3) GDL layer: 0.4 mm thick, two-layer rough surface (*) (Condition 4) GDL layer: 0.4 mm thick, 2 layers, thin surface (*) (Condition 5) GDL layer: Thickness 0.4 mm, porosity 56%

[0045] The "two-layer rough surface" and "two-layer fine surface" have a structure with two layers of 0.2 mm thickness and porosity of 56% and 78% (33 and 34 in Figure 2). In the "two-layer rough surface," the porosity of 78% is on the catalyst side, and in the "two-layer fine surface," the porosity of 56% is on the catalyst side.

[0046] Furthermore, Experiments 1 and 2 have shown that the thickness of the gasket 15 should be determined according to the thickness of the GDL layer 13. Therefore, when the thickness of the GDL layer 13 is 0.2 mm, the thickness of the gasket 15 is set to 0.1 mm, and when the thickness of the GDL layer 13 is 0.4 mm, the thickness of the gasket 15 is set to 0.3 mm.

[0047] Fig. 5(A) shows the voltage-current characteristics when the applied voltage is increased at 500 mV / s. Fig. 5(B) shows the change over time in the voltage-current characteristics when the applied voltage is 2.0 V. Graphs 61 to 65 show the measurement results under the above conditions 1 to 5, respectively.

[0048] Figure 5(A) shows that relatively good water electrolysis performance is obtained under all conditions. Meanwhile, Figure 5(B) shows that the performance maintenance time varies depending on the porosity of the GDL layer 13, and that water electrolysis performance is particularly maintained under conditions 4 and 2. Condition 2 has a porosity of 78%, while condition 4 has a two-layer structure with a porosity of 56% on the catalyst side and 78% on the outside (the side opposite the catalyst). The experimental results show that a porosity of 78% on at least the outside of the GDL layer 13 is preferable. This structure is suitable for supplying water and discharging generated gas.

[0049] The results of Experiments 1 to 3 above revealed that the thickness of the gasket 15 is preferably smaller (thinner) than the thickness of the GDL layer 13, and that the difference between the two is preferably 0.1 mm or more. It was also found that the porosity of the GDL layer 13 is preferably high, for example, 78% or more. When the GDL layer 13 has a two-layer structure with different porosities, it is preferable that the layer closer to the catalyst (first layer) has a low porosity and the layer closer to the flat electrode (second layer) has a high porosity, and it is preferable that the porosity of the outer layer is 78% or more.

[0050] <Modification> Although the above embodiment is a water electrolysis cell, it may also function as a fuel cell. In the case of a water electrolysis cell, water is supplied as a raw material to perform electrolysis, while in the case of a fuel cell, oxygen and hydrogen are supplied as raw materials. In other words, the present invention is applicable to both water electrolysis cells and fuel cells. A fuel cell has a similar configuration to a water electrolysis cell, and similarly requires appropriate design of mechanical pressure and porosity. In particular, designing the porosity of the GDL layer is considered important to ensure smooth discharge of the gas raw material from the liquid discharge side without interruption of the supply. [Explanation of symbols]

[0051] 10: Water electrolysis cell 11: Electrolyte membrane 12: Catalyst layer 13: Gas diffusion layer 14: Flat plate electrode 21: Electrolyte membrane 22: Catalyst layer 23: Gas diffusion layer 24: Flat plate electrode

Claims

1. The fuel cell has an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a flat electrode in this order; a gasket is provided around the catalyst layer and the gas diffusion layer; The thickness of the gasket is smaller than the thickness of the gas diffusion layer. Electrochemical cell characterized by:

2. The thickness of the gasket is 0.3 mm or less.

2. The electrochemical cell of claim 1.

3. The thickness of the gasket is 0.1 mm or more.

2. The electrochemical cell of claim 1.

4. The difference between the thickness of the gasket and the thickness of the gas diffusion layer is 0.1 mm or more.

2. The electrochemical cell of claim 1.

5. the catalyst layer, the gas diffusion layer, and the flat plate electrode are provided on a cathode side and an anode side, respectively; At least for the gas diffusion layer and the gasket on the anode side, the thickness of the gasket is smaller than the thickness of the gas diffusion layer.

2. The electrochemical cell of claim 1.

6. The porosity of the gas diffusion layer is 78% or more.

2. The electrochemical cell of claim 1.

7. the gas diffusion layer includes a first layer close to the catalyst layer and a second layer close to the flat plate electrode; The second layer has a porosity of 78% or more.

2. The electrochemical cell of claim 1.

8. The gas diffusion layer includes titanium fibers.

2. The electrochemical cell of claim 1.

9. The gasket is made of silicone.

2. The electrochemical cell of claim 1.

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