Electrode, anode for water electrolysis, electrolytic cell, and method for producing hydrogen

Abstract

To provide an electrode having a low overvoltage for an oxygen evolution in a high-concentration alkaline electrolyte, an anode for water electrolysis, a bipolar electrolysis cell using the anode for water electrolysis, and a production method for hydrogen using the anode for water electrolysis.SOLUTION: An electrode comprises a substrate on which LaNixNbyO3-z (x+y is between 0.8 and 1.2, y is between 0 and 0.2, and z is between -0.5 and 0.5) layer is formed. In the area of 20 μm square on the LaNixNbyO3-z layer, the total sum of pores, each of which has the area of more than 0.785 μm2 and of 20 μm2 or less, is between 10 μm2 and 200 μm2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode, an anode for water electrolysis, a bipolar electrolytic cell using the anode for water electrolysis, and a method for producing hydrogen using the anode for water electrolysis. [Background technology]

[0002] In recent years, hydrogen produced using renewable energy has been attracting attention as a clean energy source that can solve problems such as global warming caused by CO2 and dwindling fossil fuel reserves. Hydrogen production using renewable energy is required to be as inexpensive as hydrogen production by conventional reforming of fossil fuels. Therefore, hydrogen production using renewable energy requires high levels of energy efficiency and inexpensive equipment that could not be achieved with conventional technologies.

[0003] One method for producing hydrogen that can meet the above requirements is the electrolytic decomposition of water (water electrolysis). For example, several proposals have been made to produce hydrogen by water electrolysis using power generated by natural energy sources such as wind or solar power, and then store or transport the hydrogen.

[0004] In water electrolysis, oxygen is generated at the anode and hydrogen is generated at the cathode by passing an electric current through the water. The main cause of energy loss in electrolysis is the overvoltage of the anode and cathode. Reducing this overvoltage makes it possible to produce hydrogen efficiently. In particular, the overvoltage of the anode is higher than the overvoltage of the cathode, and research and development into reducing the overvoltage of the anode is being widely pursued.

[0005] Among oxides having a perovskite structure, some are known to have high oxygen generating capacity and have attracted attention as anode materials for water electrolysis (Non-Patent Document 1). To use an oxide having a perovskite structure as an anode for alkaline water electrolysis, one method involves forming an oxide layer on the surface of a conductive substrate. For example, Patent Document 1 discloses a water electrolysis anode that has low oxygen overvoltage and high durability by forming a metal oxide layer with a high content of perovskite oxide in the crystalline components on the surface of a nickel porous substrate, and a water electrolysis device using the anode. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 155503 [Non-patent literature]

[0007] [Non-Patent Document 1] Science,2011,334,1383 Summary of the Invention [Problem to be solved by the invention]

[0008] It has been found that the anode described in Patent Document 1 has a problem in that when an electrolyte solution with a high alkaline concentration is used, the oxygen overvoltage does not become sufficiently low.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrode that exhibits a low overvoltage for oxygen evolution when an electrolytic solution with a high alkaline concentration is used, an anode for water electrolysis, a bipolar electrolytic cell using the anode for water electrolysis, and a method for producing hydrogen using the anode for water electrolysis. [Means for solving the problem]

[0010] The present inventors have conducted extensive research and experiments to solve the above problems. As a result, they have found that a LaNi x M y O 3-z The inventors have found that an electrode on which a layer is formed has a low overvoltage for oxygen evolution when an electrolyte solution with a high alkaline concentration is used, and can be used as an anode for water electrolysis, leading to the present invention.

[0011] That is, the present invention is as follows. [1] LaNi x Nb y O 3-z (x+y is 0.8 or more and 1.2 or less, y is 0 or more and 0.2 or less, z is -0.5 or more and 0.5 or less), and LaNi x Nb y O 3-z 0.785 μm in a 20 μm square area in the layer 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 The electrodes are as follows: [2] In the 20 μm square area, the average pore area is 0.785 μm 2 Ultra 10μm 2 The electrode according to [1], [3] The electrode according to [1] or [2], wherein the average number of pores in the 20 μm square area is 20 or more and 150 or less. [4] The electrode according to any one of [1] to [3], wherein the porosity in the 20 μm square region is more than 29% and not more than 55%. [5] An electrolytic cell, characterized by using the electrode according to any one of [1] to [4] as an anode. [6] A method for producing hydrogen by electrolyzing alkali-containing water in an electrolytic cell, the electrolytic cell comprising at least an anode and a cathode, the anode comprising a substrate having a LaNi x Nb y O 3-z (x+y is 0.8 or more and 1.2 or less, y is 0 or more and 0.2 or less, z is -0.5 or more and 0.5 or less), and LaNi x Nb y O3-z 0.785 μm in a 20 μm square area in the layer 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 A method for producing hydrogen, characterized in that: [Effects of the Invention]

[0012] According to the present invention, it is possible to obtain an electrode having a low oxygen overvoltage when an electrolyte solution with a high alkaline concentration is used, an anode for water electrolysis, and a water electrolysis cell including the anode for water electrolysis. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a side view showing an example of an entire electrolytic cell including an electrolytic cell equipped with the electrode of the present embodiment as an anode. [Figure 2] FIG. 2 is a diagram showing a cross section of the inside of an electrolytic cell of an electrolytic cell including an electrode of the present embodiment as an anode, the electrolytic cell being enclosed by a dashed square frame in FIG. [Figure 3] FIG. 1 is a diagram showing an outline of an electrolysis device used in Examples and Comparative Examples. [Figure 4] FIG. 1 is a diagram showing an outline of a bipolar electrolytic cell used in an electrolysis test. [Figure 5] This is a cross-sectional photograph of an electrode and an example of the setting of a 20 μm square area to be cut out. [Figure 6] This is an example of an image of a 20 μm square area cut out from Figure 5. [Figure 7] This is an example of an image in which pores are binarized and extracted from Figure 6. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention. Furthermore, the present invention can be modified in various ways without departing from the gist of the present invention.

[0015] (electrode) In this embodiment, the electrode is primarily characterized by having at least a substrate.

[0016] The substrate is preferably conductive. Examples of the material of the conductive substrate include nickel, materials containing nickel as a main component, titanium, GC (glassy carbon), tantalum, zirconium, gold, platinum, and palladium. Examples of materials containing nickel as a main component include nickel-based alloys such as Monel, Inconel, and Hastelloy.

[0017] From the viewpoint of heat resistance in the firing step during electrode preparation, the material of the substrate is more preferably a metal, and furthermore, nickel or a material containing nickel as a main component is even more preferred from the viewpoints of durability, conductivity, and economy, as these metals are not dissolved even at the oxygen generating potential in an alkaline aqueous solution and are available at lower cost than noble metals.

[0018] The conductive substrate of the electrode may be flat or may be a porous body having a plate shape with numerous holes. Specific examples of the porous body include expanded metal, punched metal, plain woven mesh, foam metal, and similar shapes. Among these, expanded metal is preferred. While its dimensions are not particularly limited, in order to achieve both an increase in the amount of gas generated by increasing the electrolysis surface area and efficient removal of gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferred that the mesh have a center-to-center distance (SW) of 2 mm to 5 mm, a center-to-center distance (LW) of 3 mm to 10 mm, a thickness of 0.2 mm to 2 mm, and an aperture ratio of 20% to 80%. More preferably, SW is 3 mm to 4 mm, LW is 4 mm to 6 mm, a thickness of 0.8 mm to 1.5 mm, and an aperture ratio of 40% to 60%.

[0019] In this embodiment, LaNi x Nb y O 3-zThe second characteristic is that x+y is 0.8 or more and 1.2 or less, y is 0 or more and 0.2 or less, and z is -0.5 or more and 0.5 or less.

[0020] LaNi x Nb y O 3-z is deposited directly on the substrate, and LaNi x Nb y O 3-z The substrate and the LaNi x Nb y O 3-z An interface may be formed between the layers. In this embodiment, a high oxygen generating capacity can be achieved by disposing Ni in at least a part of the B site of the metal oxide having a perovskite structure. Furthermore, disposing Nb in the B site together with Ni is preferable because it can provide a low oxygen generating overvoltage when an electrolyte with a high alkaline concentration is used. When an electrolyte solution with a high alkaline concentration is used, x+y is 0.8 or more and 1.2 or less from the viewpoint of providing a low oxygen evolution overvoltage, more preferably 0.8 or more and 1.05 or less, and even more preferably 1.0 or more and 1.05 or less. y is 0 or more and 0.2 or less, preferably 0.005 or more and 0.15 or less, and more preferably 0.01 or more and 0.1 or less. z is between -0.5 and 0.5.

[0021] In the present invention, z is determined by the composition ratio 3-z of O calculated so that the valence balance of the composition formula is balanced, with La being trivalent, Ni being trivalent, Nb being pentavalent, and O being divalent. For example, in the composition formula LaNi x Nb y O 3-z If x=0.8 and y=0.2, then z=-0.2 can be calculated from the equation 3-z=(3+3×0.8+5×0.2) / 2.

[0022] On the substrate, LaNi x Nb y O 3-z(x+y is 0.8 or more and 1.2 or less, y is 0 or more and 0.2 or less, z is -0.5 or more and 0.5 or less) can be used to, for example, x Nb y O 3-z The layer is peeled off and dissolved in aqua regia, and the composition is analyzed by ICP-AES (inductively coupled plasma atomic emission spectroscopy). x Nb y O 3-z The layer is peeled off and the composition is analyzed using an X-ray fluorescence analyzer. x Nb y O 3-z This can be confirmed by a known method such as SEM-EDX analysis of the layer.

[0023] In this embodiment, LaNi x Nb y O 3-z 0.785 μm in a 20 μm square area in the layer 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 The third characteristic is as follows.

[0024] If the pore is perfectly circular, the area of ​​a perfectly circular pore with a diameter of 1 μm is 0.5 × 0.5 × π ≒ 0.785 (μm 2 ) and the area of ​​a perfectly circular pore with a diameter of 5 μm is 2.5 × 2.5 × π ≒ 20 (μm 2 ) The area is 0.785 μm 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 The fact that the diameter is within the range below indicates that, when the pores are perfectly circular, pores having a diameter of more than 1 μm and not more than 5 μm are present within a certain area range in the cross section of the catalyst layer.

[0025] In this embodiment, 0.785 μm 2 Ultra 20μm 2The calculation of the sum of the areas of the following pores was carried out by embedding a small piece of the electrode in epoxy resin, cutting and polishing it to prepare a cross-sectional observation sample, observing the backscattered electron image at 500x magnification with an electron microscope, and cutting out an image to binarize and extract the pores using image processing software, setting it to a 20 μm square area, and then performing image processing on the cut-out image to binarize and extract the pores, determining the area of ​​each pore, and then 0.785 μm of the pore area was calculated. 2 Ultra 20μm 2 This is done by calculating the sum of the areas of the following pores. The 20 μm square area in which pores are binarized and extracted from the cross-sectional photograph is set so that the area does not include the outer surface or cracks that lead to the outer surface. When processing the image, it is preferable to perform appropriate filtering to remove noise. Specific methods for image processing will be described later in the Examples.

[0026] The present inventors have prepared a LaNi x Nb y O 3-z (x+y is 0.8 or more and 1.2 or less, y is 0 or more and 0.2 or less, z is -0.5 or more and 0.5 or less), and LaNi x Nb y O 3-z 0.785 μm in a 20 μm square area in the layer 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 We found that the overvoltage of an electrode with an area of ​​0.785 μm or less was surprisingly low when an electrolyte with a high alkaline concentration was used. 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 This is thought to be because, when the thickness is within the following range, even when an electrolyte solution with a high alkaline concentration is used, the decrease in the diffusion rate within the electrode due to the viscosity of the electrolyte solution is suppressed, and the electrode has sufficient stability against an electrolyte solution with a high alkaline concentration. From the viewpoint of providing a lower oxygen evolution overvoltage when using an electrolyte with a high alkaline concentration, 0.785 μm 2 Ultra 20μm 2The sum of the areas of the following pores is preferably 20 μm 2 More than 160μm 2 or less, and more preferably 30 μm 2 More than 130 μm 2 The following is the result.

[0027] In this embodiment, the average pore area in the 20 μm square area is 0.785 μm 2 Ultra 10μm 2 It is preferable that the above-mentioned range is not more than 10 ... The average pore area is the number average of the areas of each pore obtained by binarizing and extracting the pores from the cut-out image by image processing software, and a specific calculation method will be described later in the Examples. The average pore area is 1.2 μm from the viewpoint of providing a lower oxygen evolution overvoltage when an electrolyte with a high alkaline concentration is used. 2 More than 6.8μm 2 More preferably, it is 3.2 μm or less. 2 More than 4.5μm 2 It is even more preferable that:

[0028] In this embodiment, it is preferable that the average number of pores in the 20 μm square region is 20 to 150, from the viewpoint of imparting a low oxygen evolution overvoltage when an electrolyte with a high alkaline concentration is used. A specific method for calculating the average number of pores will be described later in the Examples. From the viewpoint of imparting a lower oxygen evolution overvoltage when an electrolyte solution with a high alkaline concentration is used, the average number of pores is more preferably 22 or more and 140 or less, even more preferably 29 or more and 140 or less, and most preferably 29 or more and 51 or less.

[0029] In this embodiment, it is preferable that the porosity is more than 29% and not more than 55% in a 20 μm square region from the viewpoint of providing a low oxygen evolution overvoltage when an electrolyte with a high alkaline concentration is used. A specific method for calculating the porosity will be described later in the Examples. The porosity is more preferably 41% or more and 55% or less, even more preferably 42% or more and 55% or less, and most preferably 45% or more and 55% or less.

[0030] The electrode of the present embodiment can be put to practical use as an anode for water electrolysis, and the present embodiment can provide an electrolytic cell for water electrolysis using the electrode of the present embodiment as an anode, and a method for producing hydrogen using the anode for water electrolysis. Water containing alkali may be used for water electrolysis.

[0031] (Electrode preparation method) The electrode of this embodiment is prepared by applying an aqueous solution (coating liquid) containing metal salts of La, Ni, and Nb to a substrate, drying and pre-baking the substrate, and depositing a predetermined weight of LaNi x Nb y O 3-z The precursor can be prepared by forming it and then subjecting it to main calcination.

[0032] The metal salt may be a water-soluble salt such as a nitrate, oxynitrate, chloride, oxalate, tartrate, acetate, sulfate, etc. The metal salt may be an anhydrous salt or a hydrate salt. For La, Ni, and Nb, a water-dispersible sol of an oxide or hydroxide may be used instead of a metal salt. As the metal salt of Nb, it is preferable to use niobium oxalate or ammonium niobium oxalate from the viewpoint of solubility.

[0033] Adding organic ligands such as amino acids like glycine, or carboxylic acids like oxalic acid and tartaric acid to the coating solution can result in LaNi ions that exhibit a lower overvoltage for oxygen evolution when using an electrolyte with a high alkaline concentration. x Nb y O 3-z This is preferable from the viewpoint of facilitating the preparation of the compound. Glycine is a preferred organic ligand, because the use of a coating solution containing glycine and a metal nitrate makes it easier to prepare electrodes that exhibit lower oxygen evolution overpotentials when using electrolytes with high alkaline concentrations.

[0034] The concentration of an aqueous solution containing metal salts of La, Ni, and Nb is LaNi x Nb y O 3-z The standard molar concentration is preferably 0.3 mol / kg or more and 4 mol / kg or less. 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 It is easy to keep the concentration below 4 mol / kg of solvent. At 4 mol / kg or less, metal salts and organic ligands are easily dissolved, which is preferable from the viewpoint of productivity of the coating solution. More preferably, it is 0.35 mol / kg or more and 2.0 mol / kg or less of solvent, and even more preferably, it is 0.4 mol / kg or more and 1.0 mol / kg or less of solvent.

[0035] After the coating liquid is applied to the substrate, the drying temperature is preferably 50°C or higher and 200°C or lower. If the temperature is 50°C or higher, drying can be completed in 3 minutes to 1 hour, which is preferable from the viewpoint of productivity. If the temperature is 200°C or lower, the cooling time of the substrate after drying is shortened, which is preferable from the viewpoint of productivity.

[0036] The method of applying the coating solution to the substrate is preferably a dip coating method in which the substrate is completely immersed in the coating solution. When coating is performed by the dip coating method, the coating solution can be applied to a thickness of 0.785 μm by controlling the concentration of the coating solution. 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 200μm 2 It is easy to do as follows: When immersing the substrate in the coating solution, if the substrate is placed at an angle and slowly inserted, it will be possible to completely immerse the substrate without forming any air bubbles. In addition, the voids in the metal oxide layer (pre-calcined layer) formed on the surface of the substrate will be completely replaced by the coating solution, resulting in a reproducible coating thickness of 0.785 μm.2 Ultra 20μm 2 This is preferable because it becomes possible to control the total area of ​​the following pores.

[0037] The temperature at which the dried substrate is pre-baked is preferably 300°C or higher and 500°C or lower. If the temperature is 300°C or higher, the pre-baking can be completed in 3 minutes to 1 hour, which is preferable from the viewpoint of productivity. If the temperature is 500°C or lower, the cooling time of the dried substrate can be shortened, which is preferable from the viewpoint of productivity.

[0038] Coating, drying, and pre-baking are performed to obtain the desired LaNi x Nb y O 3-z This process may be repeated to adjust the amount of electrode deposition. The deposition amount per one coating, drying, and pre-baking is 10 g / m 2 More than 20g / m 2 If it is less than 0.785 μm 2 Ultra 20μm 2 The sum of the areas of the following pores is 10 μm 2 More than 20μm 2 This makes it easier and more preferable to do the following:

[0039] The temperature for the main firing can be from 500° C. to 1000° C., but firing at 750° C. or higher is preferred. Firing at 750° C. or higher is preferred from the viewpoint of productivity, since it facilitates the preparation of an electrode that exhibits a lower oxygen evolution overvoltage when an electrolyte with a high alkaline concentration is used, for a firing time of from 10 minutes to 24 hours.

[0040] Nb may be added by a method in which a coating liquid containing a water-dispersible sol of a metal salt, or an oxide or hydroxide of La or Ni is applied in advance, dried, and pre-baked, and then a coating liquid containing a water-dispersible sol of a metal salt, or an oxide or hydroxide of Nb is applied to the electrode in a topcoat manner, dried, pre-baked, and then pre-baked. Alternatively, Nb may be added by first applying a coating liquid containing a water-dispersible sol of a metal salt, oxide, or hydroxide of La or Ni, followed by drying, pre-baking, and final baking, and then applying a coating liquid containing a water-dispersible sol of a metal salt, oxide, or hydroxide of Nb to the electrode in a topcoat manner, followed by drying, pre-baking, and final baking.

[0041] (electrolytic cell) FIG. 1 shows a side view of an example of an entire electrolytic cell including an electrolytic cell equipped with the electrode of this embodiment as an anode. FIG. 2 shows a cross section of the inside of an electrolytic cell in the part enclosed by the dashed square frame in FIG. 1, of an electrolytic cell including the electrolytic cell equipped with the electrode of this embodiment as an anode. In the bipolar electrolytic cell 50 of this embodiment (see FIG. 3), the diaphragm 4 is in contact with the anode 2a and the cathode 2c to form a zero-gap structure Z (see FIG. 2). An outline of the electrolysis device used in the examples and comparative examples is shown in Figure 3. An outline of the bipolar electrolytic cell used in the electrolysis tests is shown in Figure 4.

[0042] (element) As shown in FIG. 1, in a bipolar electrolytic cell 50, a bipolar element 60 is disposed between an anode terminal element 51a and a cathode terminal element 51c, and diaphragms 4 are disposed between the anode terminal element 51a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51c.

[0043] In this embodiment, the portion between the partition walls 1 between two adjacent bipolar elements 60 and the portion between the partition walls 1 between an adjacent bipolar element 60 and a terminal element in the bipolar electrolytic cell 50 are particularly referred to as the electrolytic cell 65. The electrolytic cell 65 includes the partition wall 1, anode chamber 5a, anode 2a, and diaphragm 4 of one element, and the cathode 2c, cathode chamber 5c, and partition wall 1 of the other element.

[0044] (electrode chamber) 2, in the bipolar electrolytic cell 50 of this embodiment, electrode chambers 5 through which the electrolytic solution passes are defined by the partition wall 1, the outer frame 3, and the diaphragm 4. Here, the electrode chamber 5 on the anode side across the partition wall 1 is the anode chamber 5a, and the electrode chamber 5 on the cathode side is the cathode chamber 5c.

[0045] In this embodiment, the header pipes of the bipolar electrolytic cell may be arranged in either an internal header type or an external header type, and the spaces occupied by the anode and cathode themselves may also be considered to be spaces inside the electrode chambers. In particular, when a gas-liquid separation box is provided, the space occupied by the gas-liquid separation box may also be considered to be spaces inside the electrode chambers.

[0046] (rib) In the bipolar electrolytic cell 65 for alkaline water electrolysis of this embodiment, the ribs 6 are preferably physically connected to the electrodes 2. With such a configuration, the ribs 6 serve as supports for the electrodes 2, making it easier to maintain the zero-gap structure Z. The ribs 6 are also preferably electrically connected to the partition wall 1. Furthermore, the provision of the ribs 6 can reduce convection that occurs in the electrode chambers 5 due to turbulence in the gas-liquid flow within the electrode chambers 5, thereby suppressing a local increase in the temperature of the electrolyte.

[0047] Here, an electrode may be provided on the rib, or a current collector, a conductive elastic body, and an electrode may be provided on the rib in this order.

[0048] In the above-described example of a bipolar electrolytic cell for alkaline water electrolysis, a structure is adopted in the cathode chamber, in which the cathode rib-cathode current collector-conductive elastic body-cathode are stacked in this order, and a structure is adopted in the anode chamber, in which the anode rib-anode are stacked in this order.

[0049] In the above-described example of the bipolar electrolytic cell for alkaline water electrolysis, the cathode chamber has the above-described "cathode rib-cathode current collector-conductive elastic body-cathode" structure, and the anode chamber has the above-described "anode rib-anode" structure; however, the present invention is not limited to this structure, and the anode chamber may also have an "anode rib-anode current collector-conductive elastic body-anode" structure.

[0050] Specifically, in the bipolar electrolytic cell for alkaline water electrolysis of this embodiment, as shown in FIG. 2, ribs 6 (anode ribs, cathode ribs) are preferably attached to the partition wall 1. The ribs (anode ribs, cathode ribs) preferably have a role not only to support the anode or cathode but also to transmit current from the partition wall to the anode or cathode.

[0051] In the bipolar electrolytic cell for alkaline water electrolysis of this embodiment, it is preferable that at least a portion of the ribs be electrically conductive, and it is more preferable that the entire ribs be electrically conductive. With this configuration, an increase in cell voltage due to electrode deflection can be suppressed.

[0052] The ribs are generally made of a conductive metal, such as nickel-plated mild steel, stainless steel, or nickel. The ribs are preferably made of the same material as the partition walls, and nickel is most preferred.

[0053] The distance between adjacent anode ribs or the distance between adjacent cathode ribs is determined taking into consideration the electrolysis pressure and the pressure difference between the anode chamber and the cathode chamber.

[0054] If the spacing between anode ribs or between adjacent cathode ribs is too narrow, it not only hinders the flow of electrolyte and gas but also increases costs. A rib pitch of 10 mm or more allows gas to escape to the back surface of the electrode well. On the other hand, if the spacing is too wide, disadvantages arise, such as deformation of the electrodes (anode and cathode) held in place by a slight pressure difference between the anode chamber and the cathode chamber, and increased electrical resistance due to a reduced number of anode ribs and cathode ribs. A rib pitch of 150 mm or less makes the electrodes less likely to warp. The number of ribs, the length of the ribs, the angle between the ribs and the partition wall, the number of through holes, and the spacing (pitch) of the through holes in a given direction along the partition wall may be determined appropriately as long as the effects of the present invention are achieved. The ribs are preferably arranged parallel to a given direction along the partition wall (for example, the vertical direction, or, if the partition wall has a substantially rectangular shape in a plan view, the same direction as one of two pairs of opposing sides). The rib pitch of the anode ribs and the rib pitch of the cathode ribs may be the same or different, and it is preferable that the rib pitch of the anode ribs and the rib pitch of the cathode ribs both satisfy the above range.

[0055] The anode ribs and cathode ribs are attached to the partition wall by laser welding or the like.

[0056] The thickness of the rib may be 0.5 mm or more and 5 mm or less, taking into consideration cost, manufacturability, strength, etc., and a thickness of 1 mm or more and 2 mm or less is easily used, but is not particularly limited.

[0057] The electrodes and current collectors are usually attached to the ribs by spot welding, but other methods such as laser welding may also be used, or they may be tied together with a wire or string-like member for close contact. The ribs are fixed to the partition wall by means of spot welding, laser welding, or the like, in the same way as the anode or cathode.

[0058] (Hydrogen production method) Next, a method for producing hydrogen by alkaline water electrolysis using the bipolar electrolytic cell of this embodiment will be described.

[0059] In this embodiment, water electrolysis is performed by applying a current to a bipolar electrolytic cell equipped with an anode and a cathode as described above and through which an electrolyte is circulated, thereby producing hydrogen at the cathode. In this case, for example, a variable power supply can be used as the power source. A variable power supply is a power source derived from a renewable energy power plant whose output fluctuates every few seconds to minutes, unlike a power source that provides a stable output, such as grid power. The method of generating renewable energy is not particularly limited, but examples include solar power generation and wind power generation.

[0060] For example, in the case of electrolysis using a bipolar electrolytic cell, cationic electrolytes in the electrolyte migrate from the anode chamber of one element through the diaphragm to the cathode chamber of the adjacent element, and anionic electrolytes migrate from the cathode chamber of one element through the diaphragm to the anode chamber of the adjacent element. Therefore, current during electrolysis flows in the direction in which the elements are connected in series. That is, current flows from the anode chamber of one element to the cathode chamber of the adjacent element through the diaphragm. As a result of electrolysis, oxygen gas is produced in the anode chamber and hydrogen gas is produced in the cathode chamber.

[0061] The bipolar electrolytic cell 65 for alkaline water electrolysis of this embodiment can be used in a bipolar electrolytic cell 50, an electrolysis device 70 for alkaline water electrolysis, etc. Examples of the electrolysis device 70 for alkaline water electrolysis include a device including the bipolar electrolytic cell 50 of this embodiment, a liquid feed pump 71 for circulating the electrolytic solution, a gas-liquid separation tank 72 for separating the electrolytic solution from hydrogen and / or oxygen, and a water replenisher for replenishing water consumed by electrolysis.

[0062] The alkaline water electrolysis apparatus may further include a rectifier 74, an oxygen concentration meter 75, a hydrogen concentration meter 76, a flow meter 77, a pressure meter 78, a heat exchanger 79, a pressure control valve 80, and the like.

[0063] In the alkaline water electrolysis method using the alkaline water electrolysis apparatus, the current density applied to the electrolytic cell is 4 kA / m 2 ~20kA / m 2 Preferably, it is 6 kA / m2 ~15kA / m 2 It is more preferable that:

[0064] The electrodes, electrolytic cells, and hydrogen production methods according to the embodiments of the present invention have been described above with reference to the drawings. However, the electrodes, electrolytic cells, and hydrogen production methods according to the present invention are not limited to the above examples, and appropriate modifications can be made to the above embodiments. [Example]

[0065] Example 1 Solutions A and B were prepared with the compositions of Example 1 in Table 1. Solution B was prepared by dissolving ammonium niobium oxalate in pure water, and the Nb concentration was confirmed by ICP-AES (inductively coupled plasma atomic emission spectroscopy). Solution A was placed in a rectangular polyethylene container measuring 6 cm x 10 cm in base and 11 cm in height, and solution B was slowly mixed in while stirring with a magnetic stirrer to prepare the coating solution of Example 1. A nickel expand metal with a SW of 3.0 mm, LW of 4.5 mm, thickness of 1.2 mm, and an opening ratio of 54% was prepared as the nickel porous substrate. This nickel expand metal was subjected to a blast treatment using a #100 white fused alumina abrasive, then acid-treated in 6N hydrochloric acid at 50°C for 6 hours, washed with water, and dried to prepare a substrate for application. The substrate was placed in a container with the coating solution in a vertical orientation, with the lower half immersed in the coating solution. The substrate was then lifted up, turned over, and the upper half was also immersed in the coating solution, coating the entire substrate with the coating solution. The substrate was then placed in a horizontal orientation, and excess coating solution was blown off using an air gun. The substrate was then dried at 60°C for 10 minutes and then baked at 400°C for 10 minutes, forming a metal oxide layer on the substrate surface. This cycle of coating, drying and baking was repeated 50 times, and then baking was carried out at 800°C for 1 hour, resulting in a coating weight of 503 g / m 2 Thus, the anode for water electrolysis of Example 1 was obtained.

[0066] Example 2 The same procedure as in Example 1 was carried out except that solutions A and B having the compositions of Example 2 in Table 1 were prepared, and the cycle of coating, drying, and baking was repeated 33 times. After that, baking was further carried out at 800°C for 1 hour, and a coating weight of 496 g / m was obtained on the coating substrate. 2 Thus, a metal oxide layer was formed on the anode for water electrolysis of Example 2.

[0067] Example 3 The same procedure as in Example 1 was carried out except that solutions A and B having the compositions of Example 3 in Table 1 were prepared, and the cycle of coating, drying, and baking was repeated 25 times. After that, baking was further carried out at 750°C for 1 hour, and a coating weight of 498 g / m was obtained on the coating substrate. 2 Thus, a water electrolysis anode of Example 3 was obtained.

[0068] Example 4 34.89 g of Ni(NO3)2·6H2O, 51.96 g of La(NO3)3·6H2O, and 45.04 g of glycine were dissolved in 400 g of pure water to prepare the coating solution of Example 4. This coating solution was then transferred to a polyethylene container with a base of 13 cm × 13 cm and a height of 10 cm. A substrate was prepared in the same manner as in Example 1. The substrate was completely immersed in the coating solution in a container, then lifted out, turned sideways, and air-blasted with an air gun to remove excess coating solution. The substrate was then dried at 60°C for 10 minutes and then baked at 400°C for 10 minutes to form a metal oxide layer on the substrate surface. This cycle of coating, drying, and baking was repeated 49 times. Niobium ammonium oxalate was dissolved in pure water to prepare an aqueous solution of niobium ammonium oxalate with a Nb concentration of 157 mmol / kg. This aqueous solution of niobium ammonium oxalate was transferred to a polyethylene container with a base of 13 cm x 13 cm and a height of 10 cm. The substrate, with a metal oxide layer formed on its surface, was completely immersed in an aqueous solution of ammonium niobium oxalate and then pulled out. After the coating solution was applied to the entire surface of the substrate, the substrate was turned sideways and a gentle blast of air was applied with an air gun to remove any coating solution clogging the pores of the substrate. Measuring the weight of the substrate after air gun treatment revealed that 1.3 g of the aqueous solution of ammonium niobium oxalate had been applied to the substrate. Since the amount of LaNiO3 supported on the substrate was 5.0 g and the weight of 1 mole of LaNiO3 is 245.6 g, applying 1.3 g of the aqueous solution of ammonium niobium oxalate with an Nb concentration of 157 mmol / kg revealed that 0.01 moles of Nb were applied to 1 mole of LaNiO3. The substrate coated with the niobium ammonium oxalate aqueous solution was dried at 60°C for 10 minutes, then baked at 400°C for 10 minutes and then baked at 800°C for 1 hour, resulting in a coating weight of 512 g / m 2 Thus, a water electrolysis anode of Example 4 was obtained.

[0069] Example 5 40.71 g of Ni(NO3)2·6H2O, 60.62 g of La(NO3)3·6H2O, and 52.55 g of glycine were dissolved in 400 g of pure water to prepare the coating solution of Example 5. This coating solution was then transferred to a polyethylene container with a base of 13 cm × 13 cm and a height of 10 cm. As in Example 4, the substrate was completely immersed in the coating solution in the container, then lifted out, turned sideways, and the excess coating solution was blown off using an air gun. The substrate was then dried at 60°C for 10 minutes and then baked at 400°C for 10 minutes to form a metal oxide layer on the substrate surface. This cycle of coating, drying, and baking was repeated 32 times. Niobium ammonium oxalate was dissolved in pure water to prepare an aqueous solution of niobium ammonium oxalate with an Nb concentration of 261 mmol / kg. This aqueous solution of niobium ammonium oxalate was transferred to a polyethylene container with a base of 13 cm x 13 cm and a height of 10 cm. The substrate with a metal oxide layer formed on its surface was completely immersed in an aqueous solution of ammonium niobium oxalate and then pulled out. After the coating solution was applied to the entire surface of the substrate, the substrate was turned sideways and a gentle breeze was applied with an air gun to remove the coating solution clogging the pores of the substrate. When the weight of the substrate was measured after the air gun treatment, it was found that 1.3 g of the aqueous solution of ammonium niobium oxalate was applied to the substrate. The substrate coated with the aqueous solution of ammonium niobium oxalate was dried at 60°C for 10 minutes and then baked at 400°C for 10 minutes. This process of applying 1.3 g of the aqueous solution of ammonium niobium oxalate, drying at 60°C for 10 minutes, and baking at 400°C for 10 minutes was repeated three times, followed by baking at 800°C for one hour, resulting in a coating weight of 492 g / m. 2 Thus, a water electrolysis anode of Example 5 was obtained. Since the amount of LaNiO3 supported on the substrate was 5.0 g and the weight of 1 mole of LaNiO3 is 245.6 g, it was found that by applying 1.3 g of an aqueous solution of ammonium niobium oxalate with an Nb concentration of 261 mmol / kg three times, for a total of 3.9 g, Nb was applied at a ratio of 0.05 moles per 1 mole of LaNiO3.

[0070] Example 6 The same procedure as in Example 1 was carried out except that solutions A and B having the compositions of Example 6 in Table 1 were prepared, and the cycle of coating, drying, and baking was repeated 24 times. After that, baking was further carried out at 750°C for 1 hour, and a coating weight of 486 g / m was obtained on the coating substrate. 2 A metal oxide layer was formed on the anode of Example 6 for water electrolysis.

[0071] (Comparative Example 1) A nickel expand metal with a SW of 3.0 mm, a LW of 4.5 mm, a thickness of 1.2 mm, and an aperture ratio of 54% was prepared as the nickel porous substrate. After blasting this nickel expand metal, it was acid-treated in 6N hydrochloric acid at 50°C for 6 hours, washed with water, and dried to prepare a substrate for application. Next, a coating solution was prepared by mixing lanthanum acetate 1.5 hydrate and nickel nitrate hexahydrate to concentrations of 0.20 mol / L and 0.20 mol / L, respectively. A tray containing the coating solution was placed at the bottom of the coating roll, and the coating solution was soaked into an EPDM coating roll. A roll was placed above it so that the roll and the coating solution were always in contact with each other, and a PVC roller was placed on top of that to apply the coating solution to the substrate (roll method). The substrate was quickly passed between two EPDM sponge rolls before the coating solution dried. After drying at 50°C for 10 minutes, the substrate was baked in a muffle furnace at 400°C for 10 minutes to form a metal oxide layer on the surface. This cycle of roll coating, drying and baking was repeated 75 times, and then the coating was further baked at 600°C for 1 hour, resulting in a coating weight of 303 g / m 2 Thus, a water electrolysis anode of Comparative Example 1 was obtained.

[0072] (Comparative Example 2) A substrate for application was prepared in the same manner as in Comparative Example 1. Next, coating solutions were prepared so that the concentrations of lanthanum nitrate hexahydrate, nickel nitrate hexahydrate, ammonium niobium oxalate n-hydrate, and glycine were 0.20 mol / L, 0.16 mol / L, 0.04 mol / L, and 0.36 mol / L, respectively. As in Comparative Example 1, the cycle of roll coating, drying and firing was repeated 40 times by the roll method, and then firing was carried out at 700°C for 1 hour to form a metal oxide layer, with a deposition weight of 145 g / m 2 Thus, an anode for water electrolysis of Comparative Example 2 was obtained.

[0073] (0.785μm 2 Ultra 20μm 2 (Calculation method for the sum of the pore areas, average pore area, average number of pores, and porosity below) A small piece of the electrode was embedded in epoxy resin, and then a cut surface was prepared. The cut surface was then processed using a broad-beam argon ion beam processing device (Hitachi High-Technologies Corporation, "E3500") at an acceleration voltage of 6 kV. The cut surface of the electrode to be observed was parallel to the expanded metal strand and passed through the center of the strand. The cross section was observed under an electron microscope (Hitachi High-Technologies Corporation, "S4800") at an accelerating voltage of 5 kV and a magnification of 500x. The cross section image taken using a YAG detector was saved as a BMP file with a data size of 1280 x 960 pixels. The size of one pixel was 198.4375 nm. Using the image processing software "ImageJ," 20 μm × 20 μm areas were cut out from the cross-sectional photographs according to the following steps 1) to 11). The pores in each cut-out area were binarized and extracted, and the area of ​​all pores was measured. After that, the area was divided into 0.785 μm 2 Ultra 20μm 2 The sum of the pore area, average pore area, number of pores, and porosity were calculated. Ten 20 μm × 20 μm areas were extracted from the cross-sectional photograph without overlapping, and the 0.785 μm area calculated from each of the 10 areas was used. 2 Ultra 20μm 2 The sum of the pore area, the average pore area, the number of pores, and the average porosity were calculated. 2 Ultra 20μm 2 The following measurement results were obtained: total pore area, average pore area, average number of pores, and porosity. The measurement results for Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 2.

[0074] 1) Open the BMP file of the cross-sectional image and select 8-bit in the Type submenu of the Image menu. Figure 5 shows an example of a cross-sectional image of an electrode. 2) In the Set scale submenu of the Analyze menu, set Distance in Pixels: 1, Known distance: 0.1984375, Pixel aspect ratio: 1.0, Unit of length: μm, and click OK. 3) From the Selection submenu of the Edit menu, select the Specify command, check the Scaled units (μm) checkbox, set Width: 20, Height: 20, and set the X coordinate and Y coordinate values ​​appropriately. Click OK to set a 20 μm square area within the cross-sectional image for image processing. Figure 5 shows an example of setting a 20 μm square area to be cut out from a cross-sectional image. The 20 μm square area for image processing should be set so that it does not include the outer surface or cracks that lead to the outer surface. 4) Execute the Crop command in the Image menu to cut out a 20 μm square area from which to extract the pores. Figure 6 shows an example of an image of a 20 μm square area cut out from Figure 5. 5) Name and save the cut 20 μm square area. 6) In the Filters submenu of the Process menu, select Median..., set Radius: 0.5, and click OK to perform the filtering process. 7) Select the Threshold command in the Adjust submenu of the Image menu, select Otsu as the automatic threshold setting method, select B&W as the display method, leave the Dark background checkbox unchecked, click the Auto button, and then click the Apply button to perform binarized extraction of the pores. Figure 7 shows an example of an image in which the pores have been binarized and extracted from Figure 6. 8) Select the Set Measurements... command from the Analyze menu and check the Area checkbox. 9) Select the Analyze Particles... command from the Analyze menu, set Size(Pixel^2):0-Infinity, Circularity:0.00-1.00, Show:Outlines, check the Display results, Clear results, and Summerize check boxes, uncheck the Exclude on Edges and Include Holes check boxes, and click OK. 10) The Count displayed in the Summary window is the number of pores (number), and the Average Size is the average pore area (μm 2 ), and %Area is the porosity (%). 11) The first column on the left side of the Results window shows the number of each pore, and the Area column shows the pore area (μm 2 ) is displayed. The number of each pore can be confirmed by looking at the image of the measured pore outline numbered and displayed in the "Drawing of image file name created in 5)" window. Of the pore area values ​​in the Area column, 0.785 μm 2 Ultra 20μm 2 Adding up all the areas below gives 0.785μm 2 Ultra 20μm 2 Calculate the sum of the areas of the following pores.

[0075] (Measurement of oxygen overvoltage in 55 wt% potassium hydroxide aqueous solution) The oxygen overvoltage in a 55 wt % aqueous potassium hydroxide solution was measured by the following procedure. An electrode measuring 2 cm x 2 cm was cut out from each of the electrodes of the Examples and Comparative Examples and fixed to a PTFE-coated nickel rod with a nickel screw. A platinum mesh was used as the counter electrode, and the electrode was measured at a current density of 6 kA / m in a 55 wt% potassium hydroxide aqueous solution at 80°C. 2The electrolyte was electrolyzed with 0.1% volts and the oxygen overvoltage was measured. The oxygen overvoltage was measured by the three-electrode method using a Luggin capillary to eliminate the effect of ohmic loss due to solution resistance. The distance between the tip of the Luggin capillary and the anode was always fixed at 1 mm. The device used to measure the oxygen overvoltage was a potentiogalvanostat "1470E System" manufactured by Solartron. A silver-silver chloride (Ag / AgCl) electrode was used as the reference electrode for the three-electrode method. The electrolyte resistance that could not be completely eliminated using the three-electrode method was measured using the AC impedance method, and the oxygen overvoltage was corrected based on the measured electrolyte resistance. Using a Solartron frequency response analyzer "1255B," a Cole-Cole plot was obtained by plotting the real and imaginary parts, and then the electrolyte resistance and double layer capacitance were calculated by analyzing using equivalent circuit fitting. The ohmic loss that could not be completely eliminated by the three-electrode method was measured by the AC impedance method, and the oxygen overvoltage was corrected based on the measured ohmic loss. The ohmic loss was measured using a frequency response analyzer "1255B" manufactured by Solartron.

[0076] The evaluation results for Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 2.

[0077] Example 7 An electrolytic cell for alkaline water electrolysis and a bipolar electrolytic cell were prepared as follows. -anode- It was prepared in the same manner as in Example 4. -cathode- The conductive substrate used was a plain-woven mesh substrate made of nickel thin wires with a diameter of 0.15 mm woven at 40 meshes, on which platinum was supported. -Partition walls, outer frames- The bipolar element used had a partition wall separating the anode and cathode and an outer frame surrounding the partition wall. All of the materials used for the partition wall and the bipolar element frame, which come into contact with the electrolyte, were nickel. -Conductive elastic body- The conductive elastic body used was made by weaving nickel wire with a wire diameter of 0.15 mm and corrugating it to a wave height of 5 mm. -diaphragm- A coating solution having the following component composition was obtained using zirconium oxide (trade name "EP Zirconium Oxide", manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.), N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.), polysulfone ("Udel" (registered trademark), manufactured by Solvay Advanced Polymers), and polyvinylpyrrolidone (weight average molecular weight (Mw) 900,000, manufactured by Wako Pure Chemical Industries, Ltd.). Polysulfone: 15 parts by mass Polyvinylpyrrolidone: 6 parts by mass N-methyl-2-pyrrolidone: 70 parts by mass Zirconium oxide: 45 parts by mass The coating solution was applied to both surfaces of a polyphenylene sulfide mesh (manufactured by Kureha Co., Ltd., film thickness 280 μm, mesh size 358 μm, fiber diameter 150 μm) as a substrate. Immediately after coating, the substrate coated with the coating solution was exposed to steam and then immersed in a coagulation bath to form a coating film on the substrate surface. The coating film was then thoroughly washed with pure water to obtain a porous film. -gasket- The gasket used was a square with an inner dimension of 504 mm square, 4.0 mm thick and 18 mm wide, with an opening on the inside that was the same size as the electrode chamber in a plan view, and a slit structure for inserting and holding the diaphragm. -Zero-gap type multi-pole element- The external header type zero gap cell unit 60 is a rectangle measuring 540 mm x 620 mm, and the area of ​​the current-carrying surfaces of the anode 2a and cathode 2c is 500 mm x 500 mm. The cathode side of the zero gap bipolar element 60 is composed of a laminate of the cathode 2c, conductive elastic body 2e, and cathode current collector 2r, connected to the partition wall 1 via the cathode rib 6, and has a cathode chamber 5c through which the electrolyte flows. On the anode side, the anode 2a is connected to the partition wall 1 via the anode rib 6, and has an anode chamber 5a through which the electrolyte flows (Figure 2). The depth of the anode chamber 5a (anode chamber depth, the distance between the partition wall and the anode in FIG. 2) was 25 mm, and the depth of the cathode chamber 5c (cathode chamber depth, the distance between the partition wall and the cathode current collector in FIG. 2) was 25 mm, and they were made of nickel. The thickness of the nickel partition wall 1 to which the nickel anode rib 6 with a height of 25 mm and a thickness of 1.5 mm and the nickel cathode rib 6 with a height of 25 mm and a thickness of 1.5 mm were attached by welding was 2 mm. A nickel expand base material that had been blasted in advance was used as the cathode current collector 2r. The base material was 1 mm thick and had an aperture ratio of 54%. A conductive elastic body 2e was fixed onto the cathode current collector 2r by spot welding. By stacking this zero-gap type bipolar element with a gasket that holds the diaphragm, a zero-gap structure Z in which the anode 2a and cathode 2c are pressed against the diaphragm 4 can be formed.

[0078] (Comparative Example 3) A zero-gap type bipolar element was produced in the same manner as in Example 7, except that an anode produced in the same manner as in Comparative Example 2 was used.

[0079] Using the electrolysis devices of Example 7 and Comparative Example 3, the electrolyte solution of 55 wt % potassium hydroxide aqueous solution was kept at 80°C and circulated, and the current density was 6 kA / m 2 Water electrolysis was performed by continuously applying positive current for 100 hours so that the voltage across each cell was 0.01 V. The voltage across each cell of Example 7 and Comparative Example 3 was monitored and recorded over time. The cell voltage of each cell was compared by taking the average value of three cells for each of Example 7 and Comparative Example 3. In Example 7, the three-cell average overvoltage after 100 hours of energization was a low value of 1.70 V, whereas in Comparative Example 3, the three-cell average overvoltage after 100 hours of energization was a high value of 1.90 V. Therefore, it can be concluded that the anode of Example 7 exhibited a lower oxygen overvoltage in a high-concentration alkaline electrolyte than Comparative Example 3, thereby achieving a low cell voltage even during long-term operation.

[0080] [Table 1]

[0081] [Table 2] [Industrial Applicability]

[0082] The electrode of the present invention has a low overvoltage for oxygen evolution in a highly concentrated alkaline electrolyte, and therefore can be suitably used as an anode in a water electrolysis cell for electrolyzing water containing a highly concentrated alkali. [Explanation of symbols]

[0083] 1 Bulkhead 2 electrodes 2a anode 2c cathode 2e Conductive elastic body 2r Cathode current collector 3 Outer frame 4 Diaphragm 5a Anode chamber 5c cathode chamber 6. Ribs 7 Gasket 50 bipolar electrolyzer 51g fast head, loose head 51i Insulating plate 51a Anode terminal element 51c Cathode Terminal Element 51r tie rod 60 Multi-pole element 65 Electrolysis Cell 70 Electrolyzer 71 Liquid transfer pump 72 Gas-liquid separation tank 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 77 Flow meter 78 Pressure Gauge 79 Heat exchanger 80 Pressure control valve Z Zero gap structure

Claims

1. On the substrate, LaNi ｘ Nb ｙ O ３－ｚ (x+y is 0.8 or more and 1.2 or less, y is 0.005 or more and 0.2 or less, z is -0.5 or more and 0.5 or less), ｘ Nb ｙ O ３－ｚ 0.785 μm in a 20 μm square area in the layer ２ Super 20μm ２ The sum of the areas of the following pores is 10 μm ２ 200 μm or more ２ Below are the electrodes.

2. In the 20 μm square area, the average pore area is 0.785 μm ２ Super 10μm ２ 2. The electrode of claim 1, wherein:

3. 3. The electrode according to claim 1, wherein the average number of pores in the 20 μm square region is 20 to 150.

4. The electrode according to any one of claims 1 to 3, wherein the porosity in the 20 µm square region is more than 29% and not more than 55%.

5. An electrolytic cell comprising the electrode according to any one of claims 1 to 4 as an anode.

6. In a method for producing hydrogen by electrolyzing alkali-containing water in an electrolytic cell, the electrolytic cell is provided with at least an anode and a cathode, and the anode is provided with a LaNi ｘ Nb ｙ O ３－ｚ (x+y is 0.8 or more and 1.2 or less, y is 0.005 or more and 0.2 or less, z is -0.5 or more and 0.5 or less), ｘ Nb ｙ O ３－ｚ 0.785 μm in a 20 μm square area in the layer ２ Super 20μm ２ The sum of the areas of the following pores is 10 μm ２ 200 μm or more ２ A method for producing hydrogen, characterized in that:

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