Anode gas diffusion layer for water electrolysis cell, water electrolysis cell, and water electrolysis apparatus

Abstract

The present invention relates to an anode gas diffusion layer (1) for water electrolysis cells, the anode gas diffusion layer being provided with metal fibers; and the surface portions of the metal fibers are formed of nickel.

Description

[Technical Field] 【0001】 This disclosure relates to an anode gas diffusion layer for a water electrolysis cell, a water electrolysis cell, and a water electrolysis apparatus. [Background technology] 【0002】 In recent years, the development of anode gas diffusion layers used in water electrolysis devices has been anticipated. 【0003】 Patent Document 1 describes an electrolytic electrode using a porous metal having a metal skeleton and a thin film of metal oxide formed on at least a part of the surface of the metal skeleton. This electrolytic electrode is used, for example, as an electrolytic electrode in a hydrogen generator. Here, the metal skeleton is Ni or a Ni alloy, and the metal oxide is a metal oxide other than NiO. According to the manufacturing method of the porous metal described in Patent Document 1, a Ni plating film is formed on the surface of the porous substrate, and then a thin film of metal oxide such as Al2O3 is formed on the surface of this plating film. Therefore, it is understood that a thin film of metal oxide such as Al2O3 is formed on the surface of the porous metal described in Patent Document 1. 【0004】 Patent Document 2 describes a membrane electrode assembly comprising a pair of electrodes having a porous power supply layer made of a conductive material, and an electrolyte membrane disposed between the pair of electrodes. This membrane electrode assembly is used, for example, in an electrochemical cell of a hydrogen production apparatus. 【0005】 Non-patent document 1 describes a film electrode assembly using a material such as Ti or Ni foam coated with Pt as the anode gas diffusion layer. Non-patent document 1 does not describe the durability of the anode gas diffusion layer. [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] International Publication No. 2020 / 217668 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-49043 【Non-Patent Literature】 【0007】 【Non-Patent Literature 1】 Renewable and Sustainable Energy Reviews, Vol.81 (2018) p.1690-1704 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0008】 The present disclosure aims to provide an anode gas diffusion layer for a water electrolysis cell that has excellent durability while suppressing an increase in overvoltage of the water electrolysis cell. 【Means for Solving the Problems】 【0009】 The present disclosure includes metal fibers, and a portion forming the surface of the metal fibers consists of nickel, and provides an anode gas diffusion layer for a water electrolysis cell. 【Effects of the Invention】 【0010】 According to the present disclosure, it is possible to provide an anode gas diffusion layer for a water electrolysis cell that has excellent durability while suppressing an increase in overvoltage of the water electrolysis cell. 【Brief Description of the Drawings】 【0011】 [Figure 1] FIG. 1 is a diagram schematically showing an example of a water electrolysis cell according to the present embodiment. [Figure 2] FIG. 2 is a diagram schematically showing an example of the metal fibers according to the present embodiment. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the present embodiment. [Figure 4] FIG. 4 is a cross-sectional view schematically showing another example of a water electrolysis cell according to the present embodiment. [Figure 5] FIG. 5 is a cross-sectional view schematically showing another example of the water electrolysis apparatus according to the present embodiment. [Figure 6] FIG. 6 is a view showing the result of observing the nickel fiber sintered body with a scanning electron microscope. [Figure 7] FIG. 7 is a graph showing the result of the time change of the voltage derived from gas generation in the water electrolysis cell. [Figure 8] FIG. 8 is a graph showing the result of measuring the change in the contact resistivity of the anode gas diffusion layer with respect to pressure. 【MODE FOR CARRYING OUT THE INVENTION】 【0012】 (Knowledge on which the present disclosure is based) As a measure against global warming, the use of renewable energy such as sunlight and wind power has attracted attention. However, power generation using renewable energy has a problem of large output fluctuations. In addition, in power generation using renewable energy, a problem occurs that surplus power is wasted. Therefore, the utilization efficiency of renewable energy is not always sufficient. Thus, a method of effectively utilizing surplus power by producing and storing hydrogen from surplus power has been studied. 【0013】 Generally, electrolysis of water can be used as a method for producing hydrogen from surplus power. Electrolysis of water is also called water electrolysis. In order to produce hydrogen at low cost and stably, the development of a highly efficient and long-life water electrolysis apparatus is required. As a main component of the water electrolysis apparatus, a membrane electrode assembly (MEA) composed of a gas diffusion layer, an electrode catalyst layer, and an electrolyte membrane can be mentioned. 【0014】 To provide highly efficient and durable water electrolysis devices, it is particularly important to improve the performance and durability of the gas diffusion layers used in the anode and cathode. The gas diffusion layer can be formed, for example, by binding carbon fibers with a wire diameter of approximately 8 μm with a binder. However, carbon fibers are susceptible to oxidative decomposition at high potentials. Therefore, using a water electrolysis device with carbon fibers can reduce the function of the gas diffusion layer, potentially leading to a decrease in water electrolysis performance. For this reason, developing a gas diffusion layer that is less prone to oxidative degradation is crucial. 【0015】 Patent Document 1 describes a hydrogen production apparatus that uses a porous metal body as an electrolytic electrode, having a porous metal skeleton and a thin film of metal oxide formed on at least a portion of the surface of the metal skeleton. In Patent Document 1, a resin foam such as foamed urethane is used as the porous substrate for forming the porous metal skeleton. When such a resin foam is used, the resulting porous metal skeleton tends to be thick. For this reason, the use of this porous metal body is not particularly advantageous from the standpoint of improving electrolytic performance compared to the use of carbon fibers with a wire diameter of approximately 8 μm. In addition, since this porous metal body has a three-dimensional network structure, it is considered likely to damage the electrolyte membrane. 【0016】 Patent Document 2 describes an electrochemical apparatus using a titanium nonwoven fabric or titanium particle sintered body as the power supply layer as an example. Patent Document 2 also states that metals other than titanium can be used in the power supply layer in an embodiment, but this is not considered in the examples. 【0017】 On the other hand, water electrolysis devices generally have a current of 1 A / cm². 2 The device must also be able to operate as described above and remain stable when operated for extended periods. Non-patent document 1 describes a water electrolysis apparatus that uses a material such as Ni foam in the anode gas diffusion layer of the membrane electrode assembly. However, the current density of this water electrolysis apparatus is 0.5 A / cm². 2 It's a low degree. 【0018】 As described above, the water electrolysis apparatus described in Patent Document 1 and Non-Patent Document 1 has room for reconsideration from the viewpoint of durability. The electrochemical apparatus described in Patent Document 2 has room for reconsideration from the viewpoint of suppressing the increase of overvoltage. As a result of diligent research, the present inventors have newly discovered that the use of a gas diffusion layer containing predetermined metal fibers is advantageous from the viewpoint of suppressing the increase of overvoltage and durability, and have completed this disclosure. 【0019】 (Summary of one aspect of this disclosure) The anode gas diffusion layer for a water electrolysis cell according to a first aspect of this disclosure is: It contains metal fibers. Of the aforementioned metal fibers, the portion forming the surface of the metal fibers is made of nickel. 【0020】 According to the first embodiment, a gas diffusion layer with excellent durability can be provided while suppressing the increase in overvoltage of the water electrolysis cell. 【0021】 In a second aspect of this disclosure, for example, in the anode gas diffusion layer for a water electrolysis cell according to the first aspect, the average fiber diameter of the metal fibers may be 30 μm or less. According to the second aspect, the generated oxygen gas is easily discharged from the membrane electrode assembly. 【0022】 In a third aspect of this disclosure, for example, in an anode gas diffusion layer for a water electrolysis cell according to the first or second aspect, the anode gas diffusion layer for the water electrolysis cell may consist substantially of the metal fibers alone. According to the third aspect, the gas diffusion layer has better durability. 【0023】 In a fourth aspect of this disclosure, for example, in the anode gas diffusion layer for a water electrolysis cell according to any one of the first to third aspects, the purity of the nickel may be 90% by mass or more. According to the fourth aspect, the gas diffusion layer has better durability. 【0024】 A water electrolysis cell relating to the fifth aspect of this disclosure is A-scatter, Cathode and, The system comprises an electrolyte membrane disposed between the anode and the cathode. The anode includes an anode gas diffusion layer for a water electrolysis cell according to any one of the first to fourth embodiments. 【0025】 According to the fifth embodiment, the water electrolysis cell is likely to have excellent durability. 【0026】 In a sixth aspect of this disclosure, for example, in the water electrolysis cell according to the fifth aspect, the anode may further comprise a catalyst layer containing a catalyst. In addition, the catalyst may contain nickel as a constituent element. According to the sixth aspect, a water electrolysis cell advantageous from the viewpoint of reducing overpotential can be provided. 【0027】 In a seventh aspect of this disclosure, for example, in a water electrolysis cell according to the fifth or sixth aspect, the electrolyte membrane may include an anion exchange membrane. According to the seventh aspect, the oxygen gas generated at the anode and the hydrogen gas generated at the cathode are less likely to mix. 【0028】 The water electrolysis cell relating to the eighth aspect of this disclosure is A diaphragm separates the first space from the second space, an anode provided in the first space, The system comprises a cathode provided in the second space. The anode includes an anode gas diffusion layer for a water electrolysis cell according to any one of the first to seventh embodiments. 【0029】 According to the eighth aspect, the water electrolysis cell is likely to have excellent durability. 【0030】 In the ninth aspect of this disclosure, for example, in the water electrolysis cell according to the eighth aspect, the anode may further comprise a catalyst layer containing a catalyst. In addition, the catalyst may contain nickel as a constituent element. According to the ninth aspect, a water electrolysis cell advantageous from the viewpoint of reducing overpotential can be provided. 【0031】 The water electrolysis apparatus according to the tenth aspect of this disclosure is: A water electrolysis cell relating to any one of the fifth to ninth embodiments, The system includes a voltage injector connected to the anode and the cathode, which applies a voltage between the anode and the cathode. 【0032】 According to the tenth embodiment, the water electrolysis device is likely to have high durability. 【0033】 The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below. 【0034】 (First Embodiment) Figure 1 is a schematic diagram showing an example of a water electrolysis cell according to this embodiment. As shown in Figure 1, the water electrolysis cell 2 comprises an electrolyte membrane 31, an anode 100, and a cathode 200. The anode 100 comprises an anode gas diffusion layer 1. The anode gas diffusion layer 1 includes metal fibers 10, which will be described later. In the anode gas diffusion layer 1, the metal fibers are, for example, intertwined with each other. 【0035】 Figure 2 is a schematic diagram showing an example of a metal fiber according to this embodiment. As shown in Figure 2, the metal fiber 10 includes a portion 12. The portion 12, for example, forms the surface of the metal fiber 10 and is made of nickel. The portion 12 does not include an oxide film, for example. Since the anode gas diffusion layer 1 includes the metal fiber 10, the water electrolysis cell 2 can have excellent alkali resistance. In addition, the anode gas diffusion layer 1 can have excellent electronic conductivity. 【0036】 In this specification, "made of nickel" means, for example, that the purity of the nickel is 90% by mass or higher. The purity of the nickel in part 12 may be 92% by mass or higher, 95% by mass or higher, or 99% by mass or higher. This allows the anode gas diffusion layer 1 to have high electronic conductivity. The purity of the nickel in part 12 can be determined, for example, by X-ray photoelectron spectroscopy (XPS). 【0037】 Part 12 may be made of nickel plating. 【0038】 The thickness of part 12 is not limited to a specific value. For example, it may be 1 μm or more. The thickness of part 12 may be 5 μm or more, or 10 μm or more. The upper limit of the thickness of part 12 is not limited to a specific value. It may be 30 μm or 10 μm. By having part 12 with such a thickness, the anode gas diffusion layer 1 can have excellent alkali resistance. 【0039】 The metal fiber 10 may contain metals other than nickel. Examples of such metals include iron, cobalt, aluminum, stainless steel, gold, and platinum. 【0040】 The average fiber diameter of the metal fibers 10 is, for example, 30 μm or less. This ensures that the anode gas diffusion layer 1 has appropriate voids, allowing for the easy discharge of gases such as oxygen generated during the operation of the water electrolysis apparatus. In addition, the contact area between the anode gas diffusion layer 1 and the catalyst layer is improved, which can enhance the efficiency of water electrolysis. The average fiber diameter of the metal fibers 10 may also be 20 μm or less. The lower limit of the average fiber diameter of the metal fibers 10 is not limited to a specific value. It may be 5 μm or 10 μm. 【0041】 The average fiber diameter of the metal fiber 10 can be determined, for example, by observing the metal fiber 10 with a scanning electron microscope (SEM). Specifically, the maximum and minimum fiber diameters of the metal fiber 10 are measured, and their average value is defined as the fiber diameter of each metal fiber 10. Here, the fiber diameter of the metal fiber 10 refers to the fiber width in the direction perpendicular to the direction in which the fiber extends. Using the method described above, the fiber diameters of any 20 metal fibers 10 are calculated, and their average value is defined as the average fiber diameter. 【0042】 The anode gas diffusion layer 1 consists, for example, substantially only of metal fibers 10. The anode gas diffusion layer 1 may also be a sintered body of metal fibers 10. This allows the gas diffusion layer to have excellent electronic conductivity. The anode gas diffusion layer 1 may also contain components other than metal fibers 10. The content of components other than metal fibers 10 in the anode gas diffusion layer 1 is, for example, 10% by mass or less. 【0043】 The thickness of the anode gas diffusion layer 1 is not limited to a specific value. It may be between 50 μm and 1000 μm, or between 100 μm and 500 μm. 【0044】 The porosity of the anode gas diffusion layer 1 is not limited to a specific value. It may be 50% by volume or more, 60% by volume or more, or 80% by volume or more. The upper limit of the porosity of the anode gas diffusion layer 1 is not limited to a specific value. It may be 90% by volume or 85% by volume. Having such a porosity in the anode gas diffusion layer 1 allows gases such as water and oxygen to diffuse more easily. As a result, OH into the catalyst layer - The supply of the gas becomes easier. The porosity of the anode gas diffusion layer 1 can be determined, for example, by the method described in the examples. 【0045】 The method for forming part 12 is not limited to any particular method. Part 12 may be formed by methods such as vacuum technology, plating, and coating. Examples of methods using vacuum technology include vacuum deposition, DC sputtering, RF magnetron sputtering, pulsed laser deposition (PLD), atomic layer deposition (ALD), and chemical vapor deposition (CVD). 【0046】 As shown in Figure 1, the water electrolysis cell 2 comprises an electrolyte membrane 31, an anode 100, and a cathode 200. The electrolyte membrane 31 is, for example, positioned between the anode 100 and the cathode 200. The anode 100 includes the anode gas diffusion layer 1 described above. Since the water electrolysis cell 2 includes the anode gas diffusion layer 1, oxygen gas generated by the operation of the water electrolysis cell 2 is easily discharged from the membrane electrode assembly. The cathode 200 includes, for example, a cathode gas diffusion layer 34. The cathode gas diffusion layer 34 facilitates the discharge of hydrogen gas generated in, for example, the catalyst layer 32, from the membrane electrode assembly. 【0047】 The electrolyte membrane 31 may be an ion-conducting electrolyte membrane. The electrolyte membrane 31 is not limited to any particular type. The electrolyte membrane 31 may include an anion exchange membrane. The electrolyte membrane 31 is configured such that, for example, the oxygen gas generated at the anode 100 and the hydrogen gas generated at the cathode 200 do not mix easily. 【0048】 The anode 100 includes, for example, a catalyst layer 30. The catalyst layer 30 is responsible for, for example, the generation of oxygen gas. The catalyst layer 30 may be provided on one main surface of the electrolyte membrane 31. "Main surface" means the surface of the electrolyte membrane 31 that has the largest surface area. The anode 100 may have an anode gas diffusion layer 1 provided on top of the catalyst layer 30. The oxygen gas generation reaction occurs when water and electrons are supplied to the catalyst layer 30. 【0049】 The catalyst layer 30 may contain a catalyst that includes nickel as a constituent element. In this case, the catalyst layer 30 and the anode gas diffusion layer 1 contain the same type of metal. Such a configuration provides a water electrolysis cell that is advantageous in terms of reducing overpotential. 【0050】 The cathode 200 includes, for example, a catalyst layer 32. The catalyst layer 32 is responsible for, for example, the generation of hydrogen gas. The catalyst layer 32 may be provided on the other main surface of the electrolyte membrane 31. That is, the catalyst layer 32 may be provided on the main surface of the electrolyte membrane 31 opposite to the main surface on which the catalyst layer 30 is provided. The catalyst that can be used in the catalyst layer 32 is not limited to a specific type. This catalyst may be platinum. The cathode 200 may further have a porous and conductive gas diffusion layer 34 provided on top of the catalyst layer 32. The hydrogen gas generation reaction occurs when water and electrons are supplied to the catalyst layer 32. 【0051】 With the above configuration, the water electrolysis cell 2 can have high durability. 【0052】 (Second Embodiment) Figure 3 is a schematic cross-sectional view showing an example of a water electrolysis apparatus according to this embodiment. 【0053】 The water electrolysis apparatus 3 comprises a water electrolysis cell 2 and a voltage injector 40. The water electrolysis cell 2 is the same as the water electrolysis cell 2 of the first embodiment, so its description is omitted. 【0054】 The voltage injector 40 is connected to the anode 100 and cathode 200 of the water electrolysis cell 2. The voltage injector 40 is a device that applies a voltage between the anode 100 and cathode 200 of the water electrolysis cell 2. 【0055】 The voltage inductor 40 increases the potential at the anode 100 and decreases the potential at the cathode 200. The voltage inductor 40 is not limited to any particular type as long as it can apply a voltage between the anode 100 and the cathode 200. The voltage inductor 40 may also be a device that adjusts the voltage applied between the anode 100 and the cathode 200. Specifically, when the voltage inductor 40 is connected to a DC power source such as a battery, solar cell, or fuel cell, the voltage inductor 40 is equipped with a DC / DC converter. When the voltage inductor 40 is connected to an AC power source such as a commercial power supply, the voltage inductor 40 is equipped with an AC / DC converter. The voltage inductor 40 may also be a power supply that adjusts the voltage applied between the anode 100 and the cathode 200, as well as the current flowing between the anode 100 and the cathode 200, so that the power supplied to the water electrolysis device 3 is a predetermined set value. 【0056】 With the above configuration, the water electrolysis device 3 can have high durability. 【0057】 (Third embodiment) Figure 4 is a schematic cross-sectional view showing another example of a water electrolysis cell according to this embodiment. 【0058】 The water electrolysis cell 4 is, for example, an alkaline water electrolysis cell 4 that utilizes an alkaline aqueous solution. In alkaline water electrolysis, an alkaline aqueous solution is used. Examples of alkaline aqueous solutions are potassium hydroxide aqueous solution and sodium hydroxide aqueous solution. 【0059】 The alkaline water electrolysis cell 4 comprises an anode 300 and a cathode 400. The alkaline water electrolysis cell 4 further comprises an electrolytic cell 70, a first space 50, and a second space 60. The anode 300 is located in the first space 50. The cathode 400 is located in the second space 60. The alkaline water electrolysis cell 4 has a diaphragm 41. The diaphragm 41 is located inside the electrolytic cell 70 and separates the first space 50 and the second space 60. The anode 300 includes, for example, a catalyst layer and a gas diffusion layer. The catalyst layer and gas diffusion layer included in the anode 300 may be the same as the catalyst layer 30 and anode gas diffusion layer 1 described in the first embodiment. The cathode 400 includes, for example, a catalyst layer and a gas diffusion layer. The catalyst layer and gas diffusion layer included in the cathode 400 may be the same as the catalyst layer 32 and gas diffusion layer 34 described in the first embodiment. 【0060】 The diaphragm 41 is, for example, a diaphragm for alkaline water electrolysis. 【0061】 The anode 300 may be positioned in contact with the diaphragm 41, or there may be a gap between the anode 300 and the diaphragm 41. The cathode 400 may be positioned in contact with the diaphragm 41, or there may be a gap between the cathode 400 and the diaphragm 41. 【0062】 The alkaline water electrolysis cell 4 produces hydrogen and oxygen by electrolyzing an alkaline aqueous solution. An aqueous solution containing an alkali metal or alkaline earth metal hydroxide may be supplied to the first space 50 of the alkaline water electrolysis cell 4. An alkaline aqueous solution may be supplied to the second space 60 of the alkaline water electrolysis cell 4. Hydrogen and oxygen are produced by electrolysis while discharging an alkaline aqueous solution of a predetermined concentration from the first space 50 and the second space 60. 【0063】 With the above configuration, the alkaline water electrolysis cell 4 can have high durability. 【0064】 (Fourth Embodiment) Figure 5 is a schematic cross-sectional view showing another example of a water electrolysis apparatus according to this embodiment. 【0065】 The water electrolysis apparatus 5 according to this embodiment is, for example, an alkaline water electrolysis apparatus 5 that utilizes an alkaline aqueous solution. The alkaline water electrolysis apparatus 5 comprises an alkaline water electrolysis cell 4 and a voltage injector 40. The alkaline water electrolysis cell 4 is the same as the alkaline water electrolysis cell 4 of the third embodiment, so its description is omitted. 【0066】 The voltage injector 40 is connected to the anode 300 and cathode 400 of the alkaline water electrolysis cell 4. The voltage injector 40 is a device that applies voltage to the anode 300 and cathode 400 of the alkaline water electrolysis cell 4. 【0067】 With the above configuration, the alkaline water electrolysis device 5 can have high durability. [Examples] 【0068】 The present disclosure will be described in more detail below with reference to examples. Note that the following examples are merely examples of the present disclosure and are not limited to these examples. 【0069】 (Example 1) First, an electrode ink consisting of an anode catalyst, a binder, and a solvent was prepared. Ni-Fe LDH, a layered double hydroxide (LDH) containing Ni and Fe, was used as the anode catalyst. A mixed solvent of water and ethanol was used as the solvent. An anode catalyst layer was formed by spray coating the electrode ink onto an anion exchange film. On this anode catalyst layer, a nickel fiber sintered body NDF-17332-000 manufactured by Bekalt was laminated as an anode gas diffusion layer. This formed an anode on the anion exchange film. The average fiber diameter of the nickel fibers contained in the nickel fiber sintered body was approximately 14 μm. Table 1 shows the details of the materials used in the anode gas diffusion layer in Example 1. 【0070】 Toray Industries' TGP-H-120 carbon paper was used as the cathode gas diffusion layer. A cathode catalyst layer was formed on this carbon paper by spray coating with Pt-supported carbon. The Pt-supported carbon used was TEC10E50E from Tanaka Kikinzoku Co., Ltd. This resulted in a cathode with a cathode catalyst layer formed on the cathode gas diffusion layer. Next, a film electrode assembly according to Example 1 was fabricated by laminating the cathode catalyst layer and the anion exchange film so that they were in contact. 【0071】 Figure 6 shows the results of observing a nickel fiber sintered body with a scanning electron microscope. As shown in Figure 6, the nickel fiber sintered body contained fibers. 【0072】 (Example 2) An anode according to Example 2 was prepared in the same manner as in Example 1, except that Bekipor 2NI 18-0.25 nickel fiber sintered body manufactured by Bekart was used as the anode gas diffusion layer. Bekipor is a registered trademark of Bekart. 【0073】 (Comparative Example 1) An anode according to Comparative Example 1 was prepared in the same manner as in Example 1, except that Toray Industries' carbon paper TGP-H-120 was used as the anode gas diffusion layer. The average fiber diameter of the carbon fibers contained in this carbon paper was approximately 8 μm. A membrane electrode assembly according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the anode according to Comparative Example 1 was used. 【0074】 (Comparative Example 2) An anode according to Comparative Example 2 was prepared in the same manner as in Example 1, except that Pt-plated Ti 2GDL07N-030 manufactured by Bekart was used as the anode gas diffusion layer. The Pt-plated Ti had the surface of the titanium fibers plated with platinum. The average fiber diameter of this Pt-plated Ti was approximately 22 μm. A film electrode assembly according to Comparative Example 2 was prepared in the same manner as in Example 1, except that the anode according to Comparative Example 2 was used. 【0075】 (Calculation of Porosity) The porosity of the anode gas diffusion layers according to Example 1, Comparative Example 1, and Comparative Example 2 was determined using the gravimetric porosity method. First, the apparent volume V and the dry weight W of the anode gas diffusion layer were measured, and based on the following formula (1), the bulk density ρ a of the anode gas diffusion layer was calculated. ρ a = W / V Formula (1) 【0076】 Next, based on the following formula (2), the porosity P of the anode gas diffusion layer was calculated. The true density ρ t of the anode gas diffusion layer was measured by the gas displacement method. The results are shown in Table 1. P = (1 - ρ a / ρ t ) × 100 Formula (2) 【0077】 【Table 1】 【0078】 (Measurement of Cell Voltage) A water electrolysis cell was fabricated using the membrane electrode assemblies according to Example 1, Comparative Example 1, and Comparative Example 2, and the cell voltage of the water electrolysis cell was measured. For the measurement, a water electrolysis cell evaluation apparatus manufactured by Thermo Fisher Scientific was used to measure the time change of the voltage derived from gas generation in the water electrolysis cell under the following measurement conditions. The results are shown in Fig. 7. In Fig. 7, when the operating time of the water electrolysis cell is 0 hours, in other words, the cell voltage of the water electrolysis cell immediately after the start of the water electrolysis operation is defined as the initial voltage. The measurement results of the initial voltage are shown in Table 1. 【0079】 [Measurement Conditions] · Feed solution: 1 mol / liter KOH aqueous solution · Liquid supply rate to each of the anode and cathode electrodes: 10 cm 3 / min · Temperature of the water electrolysis cell: 80 °C · Pressure: Atmospheric pressure · Current density: 1 A / cm 2 · Effective electrode surface area: 1 cm 2 【0080】 Figure 7 is a graph showing the time change of the voltage originating from gas generation in a water electrolysis cell. The vertical axis represents the cell voltage, and the horizontal axis represents the operating time of the water electrolysis cell. As shown in Figure 7, in Example 1, the cell voltage remained low even after more than 1200 hours of operation. This indicates that the water electrolysis cell in Example 1 has excellent durability. 【0081】 As shown in Table 1, the current density is 1 A / cm². 2 At that time, the initial voltage of the water electrolysis cell according to Example 1 was 1.563V. On the other hand, the initial voltage of the water electrolysis cell according to Comparative Example 2 was 1.679V. Current density was 1 A / cm². 2 In this case, the initial voltage of the water electrolysis cell according to Example 1 was lower than the initial voltage of the water electrolysis cell according to Comparative Example 2. It was found that the water electrolysis cell using the gas diffusion layer according to Example 1 has excellent electrolysis performance. 【0082】 Here, the theoretical voltage in the electrolysis of water is 1.23V. In Example 1, the overvoltage relative to the theoretical voltage in the electrolysis of water was 0.333V. In Comparative Example 2, the overvoltage relative to the theoretical voltage in the electrolysis of water was 0.449V. In Example 1, the overvoltage was reduced by 0.116V (116mV) compared to Comparative Example 2. In Example 1, the overvoltage was reduced by 26% compared to Comparative Example 2. In Example 1, a nickel fiber sintered body was used in the anode gas diffusion layer. It was found that the increase in overvoltage can be suppressed according to the water electrolysis cell of Example 1. 【0083】 (Measurement of contact resistivity of the anode gas diffusion layer) The contact resistivity of the anode gas diffusion layers used in Example 1 and Comparative Example 2 was measured. A tensile and compression testing machine manufactured by Imada Seisakusho Co., Ltd. and a low-resistivity meter 3566 manufactured by Tsuruga Electric Co., Ltd. were used to measure the contact resistivity. The anode gas diffusion layer was placed between jigs, and the resistance value was measured. The contact resistivity was then calculated by subtracting the resistance value of the jigs. Specifically, an anode gas diffusion layer machined to a diameter of 30 mm was placed on a measuring jig, and the displacement and resistance values ​​were measured when a load of up to 4 kN was applied. The resistance value measured without the anode gas diffusion layer was then subtracted. Figure 8 shows the results of measuring the change in the contact resistivity of the anode gas diffusion layer with respect to pressure. 【0084】 Figure 8 is a graph showing the results of measuring the change in the contact resistivity of the anode gas diffusion layer with respect to pressure. In Figure 8, the vertical axis represents the contact resistivity of the anode gas diffusion layer [mΩ·cm]. 2 The horizontal axis shows pressure [MPa]. When the pressure is 1 MPa, the contact resistivity of the anode gas diffusion layer used in Example 1 is 0.2 mΩ·cm 2 The contact resistivity of the anode gas diffusion layer used in Comparative Example 2 was 0.4 mΩ·cm when the pressure was 1 MPa. 2 Therefore, the contact resistivity of the anode gas diffusion layer used in Example 1 was 0.2 mΩ·cm higher than that of the anode gas diffusion layer used in Comparative Example 2. 2 It was small. This is thought to be due to the difference in the type of metal contained in the anode gas diffusion layer between Example 1 and Comparative Example 2. 【0085】 According to the measurement results of the contact resistivity of the anode gas diffusion layer, the difference in contact resistivity of the anode gas diffusion layer between Example 1 and Comparative Example 2 was 0.2 mΩ·cm. 2 This was the case. From this difference in contact resistivity, the difference in overvoltage between the water electrolysis cell of Example 1 and the water electrolysis cell of Comparative Example 2 was the current density of 1 A / cm². 2 At that time, 0.2 [mΩ·cm 2 ]×1[A / cm 2It is expected that ] = 0.2mV. On the other hand, as described above, the difference between the overpotential of the water electrolysis cell according to Example 1 and the overpotential of the water electrolysis cell according to Comparative Example 2 was 116mV. Thus, the difference in overpotential between Example 1 and Comparative Example 2 was larger than the value expected from the contact resistivity. In Example 1, nickel is included in the anode gas diffusion layer. In addition, in Example 1, the catalyst layer also contains a catalyst that includes nickel as a constituent element. It is presumed that the difference in overpotential was larger than the value expected from the contact resistivity because the anode gas diffusion layer and the catalyst layer contain the same type of metal. 【0086】 (Measurement of current density-voltage characteristics of a water electrolysis cell) A water electrolysis cell was fabricated using the membrane electrode assemblies described in Example 1 and Example 2. The current density-voltage characteristics of the water electrolysis cell were measured under the same measurement conditions as described above (measurement of cell voltage), except for the following measurement conditions. The applied current was controlled by an external power supply and was set to 0 A / cm². 2 From 2A / cm 2 The current density-voltage characteristics of the water electrolysis cell were measured by gradually increasing the current density up to a certain point. 【0087】 Current density is 1 A / cm 2 At that time, the ratio X1 of the cell voltage of the water electrolysis cell according to Example 1 to the cell voltage of the water electrolysis cell according to Example 2 was 1.01. The current density was 2 A / cm². 2 At that time, the ratio X2 of the cell voltage of the water electrolysis cell according to Example 1 to the cell voltage of the water electrolysis cell according to Example 2 was 1.00. As shown in Table 1, the nickel fiber sintered body used in Example 1 and the nickel fiber sintered body used in Example 2 have different average fiber diameter and porosity values. That is, the structure of the anode gas diffusion layer is different in Examples 1 and 2. However, the current density is 1 A / cm². 2 The ratio X1 and current density at that time are 2A / cm². 2Based on the value of ratio X2 at that time, it can be understood that the cell voltage of the water electrolysis cell according to Example 1 and the cell voltage of the water electrolysis cell according to Example 2 were approximately the same. From these results, it can be inferred that differences in the structure of the anode gas diffusion layer do not significantly affect the cell voltage. [Industrial applicability] 【0088】 One aspect of this disclosure can be used in a water electrolysis reaction to provide a gas diffusion layer with higher resistance to oxidative degradation than conventional gases. [Explanation of Symbols] 【0089】 1. Anode gas diffusion layer 2, 4 Water electrolysis cell 3, 5 Water electrolysis equipment 10 Metal Fibers 12 parts 30, 32 Catalyst layer 31 Electrolyte membrane 34 Gas diffusion layer 40 Voltage Applyer 41 Diaphragm 50, 60 spaces 70 Electrolytic cell 100, 300 anodes 200, 400 cathode

Claims

[Claim 1] A-scatter, Cathode and, The system comprises an anion exchange membrane disposed between the anode and the cathode, The anode includes a catalyst layer provided on the anion exchange membrane and an anode gas diffusion layer provided on the catalyst layer. The anode gas diffusion layer comprises metal fibers, Of the aforementioned metal fibers, the portion forming the surface of the metal fibers is made of nickel. water electrolysis cell. [Claim 2] The average fiber diameter of the aforementioned metal fibers is 30 μm or less. The water electrolysis cell according to claim 1. [Claim 3] The anode gas diffusion layer consists substantially of the metal fibers. The water electrolysis cell according to claim 1 or 2. [Claim 4] The purity of the nickel is 90% by mass or higher. The water electrolysis cell according to claim 1. [Claim 5] (delete) [Claim 6] The catalyst layer includes a catalyst containing nickel as a constituent element. The water electrolysis cell according to claim 1. [Claim 7] (delete) [Claim 8] (delete) [Claim 9] (delete) [Claim 10] A water electrolysis cell according to claim 1, The system includes a voltage injector connected to the anode and the cathode, which applies a voltage between the anode and the cathode. Water electrolysis equipment.