Electrode, method for producing electrode, electrolysis cell, electrolysis tank for alkaline water electrolysis, and method for producing hydrogen

Abstract

The objective of the present invention is to provide: an electrode in which an increase in overvoltage hardly occurs even when repeatedly turning on and off a power source and starting and stopping the generation of hydrogen; a method for producing the electrode; an electrolysis cell including the electrode; an electrolysis tank for alkaline water electrolysis including the electrolysis cell; and a method for producing hydrogen by means of alkaline water electrolysis using the electrolysis tank for alkaline water electrolysis. To achieve the above objective, an electrode according to the present invention has a nickel-containing conductive substrate and a platinum-containing catalyst layer, and is characterized by including a PtNi alloy and having a Ni atom concentration on the electrode surface of 20% or less.

Description

Electrode, electrode manufacturing method, electrolytic cell, alkaline water electrolysis cell, and hydrogen production method

[0001] The present invention relates to an electrode, a method for producing an electrode, an electrolytic cell including the electrode, an electrolytic cell for alkaline water electrolysis including the electrolytic cell, and a method for producing hydrogen by alkaline water electrolysis using the electrolytic cell for alkaline water electrolysis.

[0002] In recent years, renewable energy technologies such as wind power generation and solar power generation have been attracting attention in order to solve problems such as global warming caused by greenhouse gases such as carbon dioxide and dwindling fossil fuel reserves.

[0003] Renewable energy output is highly variable because it depends on weather conditions. As a result, it is not always possible to transport the electricity generated by renewable energy to the general power grid, raising concerns about the potential for imbalances in power supply and demand and the instability of the power grid.

[0004] Therefore, research is being conducted into converting electricity generated from renewable energy sources into a form that can be stored and transported, and using this electricity.Specifically, research is being conducted into generating storable and transportable hydrogen through the electrolysis of water using electricity generated from renewable energy, and using this hydrogen as an energy source or raw material.

[0005] Hydrogen is widely used industrially in oil refining, chemical synthesis, metal refining, etc., and in recent years, the possibility of its use has expanded in hydrogen stations for fuel cell vehicles (FCVs), smart communities, hydrogen power plants, etc. For this reason, there are high expectations for the development of technology to obtain hydrogen, especially from renewable energy sources.

[0006] Methods for electrolyzing water include solid polymer water electrolysis, high-temperature steam electrolysis, and alkaline water electrolysis. However, alkaline water electrolysis is considered to be one of the most promising methods because it has been industrialized for several decades, can be carried out on a large scale, and is inexpensive compared to other water electrolysis devices.

[0007] However, in order to adapt alkaline water electrolysis as a means for storing and transporting energy in the future, it is necessary to enable water electrolysis by efficiently and stably utilizing electric power, which has large output fluctuations as described above, and there is a need to solve various issues with electrolytic cells and devices for alkaline water electrolysis.

[0008] It is well known that adopting a so-called zero-gap structure, in which the gap between the diaphragm and the electrode is substantially eliminated, as the structure of the electrolysis cell is particularly effective for solving the problem of reducing the electrolysis voltage in alkaline water electrolysis and improving the power consumption rate of hydrogen production (see Patent Documents 1 and 2). In the zero-gap structure, generated gas is quickly released to the side of the electrode opposite the diaphragm through pores in the electrode, thereby reducing the distance between the electrodes and minimizing the occurrence of gas accumulation near the electrodes, thereby reducing the electrolysis voltage. The zero-gap structure is extremely effective in reducing the electrolysis voltage and is adopted in various electrolysis devices.

[0009] Patent No. 5553605 International Publication No. 2015 / 098058

[0010] However, although the electrodes described in the above patent documents can be used as cathodes in electrolysis devices for alkaline water electrolysis, they tend to deteriorate and cause an increase in overvoltage when the power supply to the device is repeatedly turned on and off, which poses a problem in using the electrolysis device for a long period of time.

[0011] Therefore, an object of the present invention is to provide an electrode that is resistant to an increase in overvoltage even when the power supply is repeatedly turned on and off, a method for manufacturing the electrode, an electrolytic cell including the electrode, an electrolytic cell for alkaline water electrolysis including the electrolytic cell, and a method for producing hydrogen by alkaline water electrolysis using the electrolytic cell for alkaline water electrolysis.

[0012] That is, the present invention is as follows. (1) An electrode having a conductive base material containing nickel and a catalytic layer containing platinum, wherein the electrode contains a PtNi alloy and the Ni atomic concentration on the surface of the electrode is 20% or less. (2) The electrode according to (1), wherein metallic Pt is present on the surface of the electrode. (3) The electrode according to (1) or (2), wherein the electrode contains Pt crystals. (4) The electrode according to any one of (1) to (3), wherein the catalytic layer is in contact with the conductive base material. (5) The electrode according to any one of (1) to (4), wherein the catalytic layer further contains one or more elements selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb. (6) The electrode according to any one of (1) to (4), wherein the catalytic layer further contains one or more elements selected from the group consisting of Y. ２ O ３ , La ２ O ３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ and NaNbO ３ (7) The electrode according to any one of (1) to (5), further comprising one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti and Zr. (8) The electrode according to any one of (1) to (6), further comprising one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti and Zr. (9) The electrode according to any one of (1) to (6), further comprising one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti and Zr. (10) The electrode according to any one of (1) to (6), further comprising one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti and Zr. (11) The electrode according to any one of (1) to (6), further comprising one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti and Zr. (12) The electrode according to any one of (1) to (6), further comprising one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti and Zr. Ｂ / Pt Ｂ is 0.2 or more and 1 or less. (9) The electrode according to any one of (5) to (7), wherein the molar ratio M of M (M represents Y, La, Ce, Pr, Nd, and Nb) to Pt on the surface of the catalyst layer is Ｓ / Pt Ｓ (10) The electrode according to any one of (5) to (8), wherein the molar ratio M of M (M represents Y, La, Ce, Pr, Nd, and Nb) to Pt in the catalyst layer is 0.5 or more and 40 or less. Ｂ / Pt Ｂ The molar ratio M of M (M represents Y, La, Ce, Pr, Nd, and Nb) to Pt on the surface of the catalyst layer, Ｓ / Pt Ｓ The ratio (M Ｓ / PtＳ ) / (M Ｂ / Pt Ｂ ) is 1.5 or more and 100 or less. (11) The electrode according to any one of (5) to (9), wherein the value of (R) is 1.5 or more and 100 or less. (11) A method for producing an electrode, comprising: a coating step of coating a nickel-containing conductive base material with a coating liquid containing at least a Pt compound and one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb; a precursor layer forming step of drying the coating liquid to form a precursor layer containing Pt and one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb on the conductive base material; and a firing step of heating the precursor layer at a temperature range of 300°C to 800°C to obtain an oxide layer, and further comprising a reduction step of reducing the conductive base material having the oxide layer with hydrogen at a temperature range of 400°C to 700°C to obtain a catalyst layer. (12) The method for producing an electrode according to (11), wherein hydrogen diluted with an inert gas to a hydrogen concentration of 100 ppm to 1% is used in the reduction step. (13) The method for producing an electrode according to (11) or (12), wherein the reduction step is carried out using a furnace, and hydrogen is supplied into the furnace at a reduced pressure so that the hydrogen partial pressure is 1333 Pa or less. (14) An electrolytic cell comprising, as a cathode, an electrode having a conductive substrate containing nickel and a catalytic layer containing platinum, the electrode comprising a PtNi alloy, and the Ni atomic concentration on the surface of the electrode being 20% ​​or less. (15) An electrolytic cell comprising, as a cathode, an electrode having a conductive substrate containing nickel and a catalytic layer containing platinum, the electrode comprising a PtNi alloy, the Ni atomic concentration on the surface of the electrode being 20% ​​or less. ｘ M'' ｙ O ３－ｚ(14) The electrolytic cell according to (14), comprising an electrode having, as an anode, the following formula: (x+y is 0.8 or more and 1.2 or less, y is 0.001 or more and 0.6 or less, z is −0.5 or more and 0.5 or less, and M″ includes at least one of Nb, Ta, Sb, Ti, Mn, and Zr). (16) The electrolytic cell according to (14) or (15), wherein the electrolytic cell is a bipolar electrolytic cell. (17) An electrolytic cell for alkaline water electrolysis, comprising 3 to 200 electrolytic cells according to (16), at least one cathode terminal cell, and at least one anode terminal cell. (18) A method for producing hydrogen by electrolyzing alkali-containing water using the electrolytic cell for alkaline water electrolysis according to (17). (19) The method for producing hydrogen by electrolyzing alkali-containing water using a variable power supply that repeatedly switches between positive current application and cessation of positive current application.

[0013] The present invention can provide an electrode that is resistant to an increase in overvoltage even when the power supply is repeatedly turned on and off, a method for manufacturing the electrode, an electrolytic cell including the electrode, an electrolytic cell for alkaline water electrolysis including the electrolytic cell, and a method for producing hydrogen by alkaline water electrolysis using the electrolytic cell.

[0014] 4 is a side view illustrating an example of an entire alkaline water electrolysis cell including the bipolar electrolytic cell of the present embodiment. It is a diagram illustrating a cross section of the interior of an electrolytic cell of an alkaline water electrolysis cell including the bipolar electrolytic cell of the present embodiment, the cross section being enclosed by a dashed-line square frame in FIG. 1 . It is a diagram illustrating an outline of an electrolysis device used in Examples and Comparative Examples. It is a diagram illustrating an outline of an alkaline water electrolysis cell used in an electrolysis test. It is a diagram illustrating a cross section of the interior of an electrolytic cell of an alkaline water electrolysis cell used in an electrolysis test, the cross section being enclosed by a dashed-dotted square frame X in FIG. 4 . It is a diagram illustrating a cross section of the interior of an electrolytic cell of an alkaline water electrolysis cell used in an electrolysis test, the cross section being enclosed by a dashed-dotted square frame Y in FIG. 4 . It is a diagram illustrating an X-ray diffraction (XRD) spectrum of the electrode of Example 1. It is a diagram illustrating a cross-sectional SEM image (backscattered electron image) of the electrode of Example 1.

[0015] Hereinafter, an embodiment for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to only the embodiment. In other words, the present invention can be modified in various ways without departing from the gist of the present invention.

[0016] [1] Electrode The electrode of this embodiment has a conductive base material containing nickel and a catalytic layer containing platinum, and is characterized in that it contains a PtNi alloy and the Ni atomic concentration on the surface of the electrode is 20% or less. The inventors have surprisingly found that an electrode having a conductive base material containing nickel and a catalytic layer containing platinum, which contains a PtNi alloy and has a Ni atomic concentration on the electrode surface of 20% or less, is less likely to experience an increase in overvoltage when the power supply is repeatedly turned on and off. Although the reason for this is not clear, a PtNi alloy has the same face-centered cubic structure as Pt and Ni, and its interplanar spacing is an intermediate value between that of Pt and Ni depending on the ratio of Pt to Ni. Therefore, when an electrode contains a PtNi alloy, adhesion between the catalyst layer and the conductive base material is good, thereby suppressing peeling of the catalyst layer when the power is turned on and off. In addition, when the Ni atomic concentration on the electrode surface is 20% or less, the Pt atomic concentration on the electrode surface becomes relatively high, suppressing a decrease in the conductivity of the electrode surface and a decrease in wettability of the electrolyte when the power is turned on and off. These combined effects are thought to make it less likely that an increase in overvoltage will occur when the power is turned on and off.

[0017] (1) Conductive Substrate The electrode of this embodiment has a conductive substrate containing nickel. The presence of nickel in the conductive substrate can be confirmed by performing cross-sectional SEM-EDX measurement of the electrode and EDX analysis of the cross-sectional portion of the conductive substrate, and obtaining results that indicate the presence of Ni. Furthermore, when the conductive substrate contains nickel, such as pure nickel NW2201 as specified in the JIS H4551 standard, X-ray diffraction (XRD) measurement of the electrode can yield a spectrum having a peak pattern attributable to nickel with PDF card number 00-004-0850, thereby confirming that the electrode contains nickel.

[0018] The elements constituting the conductive substrate are not particularly limited except for nickel, and may include C, O, N, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Cu, Mo, etc. If the material of the conductive substrate is pure nickel of NW2201 specified in JIS H4551, which contains C, Si, Mn, S, Cu, Fe, and Ni, deterioration of the electrode due to corrosion is suppressed when the electrode is used for alkaline water electrolysis, which is preferable.

[0019] The conductivity of the substrate can be confirmed by measuring the resistance of the substrate with a tester and confirming that the resistance is sufficiently low. For example, the resistivity of nickel is about 6.84×10 at 20° C. －８ (Ω m), and when the resistance value of a nickel substrate is measured with a tester, it is possible to measure a resistance value that corresponds to the dimensions and shape of the substrate. The higher the conductivity of the substrate, the lower the resistance overvoltage when the electrode is used in alkaline water electrolysis, and the lower the electrolysis voltage, improving the power consumption rate for hydrogen production.

[0020] The electrode of this embodiment is preferably porous in order to increase the surface area available for electrolysis and to efficiently remove gas generated by electrolysis from the electrode surface. In particular, in the case of a zero-gap electrolytic cell, it is necessary to degas the gas generated from the back side of the surface that contacts the diaphragm, and therefore it is preferable that the surface of the electrode opposite the surface that contacts the membrane is perforated. From this perspective, the form of the conductive substrate is not particularly limited, but is preferably a perforated metal, expanded metal, punched foil, mesh woven with metal wires, metal foam, metal sintered compact, metal fiber, metal paper, or the like, which has pores that allow gas bubbles to pass through.

[0021] Furthermore, the effect of improving the reverse charge resistance is enhanced when the conductive substrate has a configuration without corners or protrusions. This is because corners or protrusions can become the starting point for interfacial peeling between the catalyst layer and the substrate. Therefore, the conductive substrate is preferably a mesh composed of metal wires that do not have corners or protrusions, i.e., have a circular or elliptical cross section perpendicular to the axial direction. When a plain weave mesh is used for the conductive substrate, the dimensions are not particularly limited, but in order to achieve both an increase in the electrolytic reaction field due to an increase in the electrolytic surface area and efficient removal of gas generated by electrolysis from the electrode surface, the wire diameter is preferably 0.05 mm or more and 1.0 mm or less, and the pitch is preferably 20 mesh or more and 60 mesh or less. More preferably, the wire diameter is 0.1 mm or more and 0.3 mm or less, and the pitch is 30 mesh or more and 50 mesh or less.

[0022] (2) Catalyst Layer The electrode of this embodiment has a catalyst layer containing platinum. The presence of a catalyst layer in an electrode can be confirmed by performing cross-sectional SEM-EDX measurement of the electrode and finding, in the backscattered electron image obtained, that a layer with a different brightness from that of the conductive substrate is present on the conductive substrate, or by performing EDX analysis of the electrode and finding that a layer with a different composition is formed on the conductive substrate.

[0023] The inclusion of platinum in the catalytic layer can be confirmed by performing cross-sectional SEM-EDX measurement of the catalytic layer and EDX analysis of the cross-sectional portion of the catalytic layer, which reveals the presence of Pt. The inclusion of platinum in the catalytic layer increases the conductivity of the catalytic layer and improves the wettability of the electrolytic solution to the catalytic layer. In particular, when the electrode is used as a cathode for alkaline water electrolysis, the hydrogen generation overpotential is reduced, the electrolysis voltage is lowered, and the power consumption rate for hydrogen production is improved.

[0024] The Pt content in the electrode of this embodiment is 4.0 g / m ２ 10.0g / m or more ２ Preferably, the density is 4.0 g / m or less. ２ If the amount is 10.0 g / m or more, it becomes easy to prepare an electrode in which an increase in overvoltage due to turning on and off of the power supply is unlikely to occur. ２ When the Pt content is 5.0 g / m or less, it becomes easy to support Pt on the electrode, which is preferable from the viewpoint of productivity.２ 9.0g / m or more ２ If the concentration is less than 5.0 g / m, elution or peeling of Pt from the electrode is suppressed, and the possibility of recovering Pt from the used electrode in high yield increases, so this is more preferable. ２ 8.0g / m or more ２ More preferably, the Pt content is 5.0 g / m or less. ２ 9.0g / m or more ２ The reason why Pt elution and peeling from the electrode tend to be suppressed when the thickness is less than 1 / 2 cm is unclear, but it is thought that this is because the thickness of the catalyst layer on the electrode is appropriate and uniform, which reduces the likelihood of the catalyst layer peeling or wear occurring locally on the electrode surface due to repeated on / off switching. The Pt content in the electrode can be determined by cutting the electrode to a predetermined size, for example, 2 cm long x 1 cm wide, dissolving it in an acid such as aqua regia, diluting it, measuring the Pt concentration in the diluted solution by inductively coupled plasma optical emission spectroscopy (ICP optical emission spectroscopy), calculating the total mass of Pt contained in the dissolved electrode, and then dividing it by the geometric area of ​​the electrode. For example, the geometric area of ​​an electrode that is 2 cm long x 1 cm wide is 2 x 1 = 2 cm ２ 2 cm ２ If 1 mg of Pt is contained in an electrode with a geometric area of ​​5.0 g / m, the Pt content of the electrode is 5.0 g / m. ２ is.

[0025] In the electrode of this embodiment, the catalytic layer preferably contains, in addition to Pt, elements such as Y, La, Ce, Pr, Nd, and Nb. Two or more of these elements may be contained. Furthermore, other metal elements such as Na may also be contained. When these elements are contained in the catalytic layer, it becomes easier to prepare an electrode containing a PtNi alloy and having a Ni atomic concentration of 20% or less on the electrode surface. From the viewpoint of high element dissolution stability and increased electrode manufacturing productivity, it is more preferable that the catalytic layer contains, in addition to Pt, one or more elements selected from the group consisting of Y, La, Ce, Pr, and Nd. From the viewpoint of suppressing peeling and wear originating from large voids in the catalytic layer when the power supply is repeatedly turned on and off, it is even more preferable that the catalytic layer contains, in addition to Pt, one or more elements selected from the group consisting of La, Pr, and Nd.

[0026] If the catalytic layer has a bubble-like shape with large voids in its cross section, peeling and attrition are likely to occur from the voids when the power is repeatedly turned on and off, but if the catalytic layer contains one or more elements selected from the group consisting of La, Pr, and Nd in addition to Pt, large bubble-like voids are less likely to form in the catalytic layer, making peeling and attrition less likely.The reason why large bubble-like voids are less likely to form in the catalytic layer when the catalytic layer contains one or more elements selected from the group consisting of La, Pr, and Nd in addition to Pt is not clear, but it is thought to be because metal salts of La, Pr, and Nd are highly stable, and therefore gas generation in the thermal decomposition reaction of the metal salt is gentle and no foaming occurs in the (3) baking step of the [2] electrode manufacturing method described below, and large bubble-like voids are not generated in the oxide layer.

[0027] The less likely it is that peeling and wear originating from large voids in the catalyst layer will occur due to repeated on-off cycles of the power supply, the more likely it is that Pt can be recovered in high yield from the used electrode. From this perspective, the fact that the catalyst layer is less susceptible to peeling and wear is a practically desirable characteristic.

[0028] The presence of one or more elements selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb in the catalytic layer can be confirmed by performing SEM-EDX measurement of a cross section of the electrode and examining the composition of the catalytic layer by EDX analysis.

[0029] Y, La, Ce, Pr, Nd, and Nb in the catalyst layer may be in a metallic state. ２ O ３ , La ２ O ３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ , Nb ２ O ５ , NbO ２ , Nb ２ O ３ , NbO. Also, NaNbO ３ Also, a composite oxide such as Y ２ O ３ , La ２ O３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ reacts with moisture in the air to form Y(OH) ３ , La(OH) ３ , Ce(OH) ４ , Pr(OH) ３ , Nd(OH) ３ It may be in the form of a hydroxide such as

[0030] Y in the catalyst layer ２ O ３ , La ２ O ３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ , NaNbO ３ The inclusion of the above was confirmed by XRD measurement of the electrode, and the XRD spectrum was found to be Y of PDF card number 00-041-1105. ２ O ３ and PDF card number 01-071-5408 La ２ O ３ and CeO of PDF card number 00-004-0593 ２ and PDF card number 00-047-1111 Pr ２ O ３ and PDF card number 01-079-9858 Nd ２ O ３ and PDF card number 01-086-5414 NaNbO ３ This can be confirmed by having a peak pattern attributable to the peak positions and intensity ratios of the above.

[0031] In the entire catalyst layer, the relative element concentration of Pt Ｂ (atom %) of the added element M (M indicates a metal element selected from Y, La, Ce, Pr, Nd, and Nb) Ｂ The molar ratio M Ｂ / Pt Ｂ It is preferable that M is 0.2 or more and 1 or less, since the overvoltage after 1500 cycles of turning the power on and off is likely to be lower than 160 mV.Ｂ / Pt Ｂ Since the overvoltage after 1500 cycles of power on / off is likely to be lower than 150 mV, the lower limit is more preferably 0.25 or more, and since the overvoltage after 1500 cycles of power on / off is likely to be lower than 140 mV, the lower limit is even more preferably 0.30 or more. Ｂ / Pt Ｂ Since the overvoltage after 1500 cycles of power on / off is likely to be lower than 150 mV, the upper limit is more preferably 0.82 or less, and since the overvoltage after 1500 cycles of power on / off is likely to be lower than 140 mV, the upper limit is even more preferably 0.67 or less. Ｂ / Pt Ｂ When M is 0.2 or more and 1 or less, the overvoltage after repeatedly turning the power on and off becomes lower. The reason is not clear, but it is Ｂ / Pt Ｂ When M is 1 or less, the electrical conduction in the catalyst layer is sufficient even after the power is turned on and off repeatedly, and the overvoltage is low. Ｂ / Pt Ｂ This is thought to be because when M is 0.2 or more, the active surface of Pt exists at the interface between Pt and the additive element M in the catalyst layer even after repeated on / off cycles of the power supply, resulting in a low overvoltage. Ｂ / Pt Ｂ is the relative elemental concentration M of M and Pt to all elements measured in the bulk of the catalyst layer Ｂ (atom%) and Pt Ｂ (atom%), and M Ｂ Pt Ｂ In this specification, M Ｂ and Pt Ｂ The electrode is completely dissolved in aqua regia, and a composition analysis is performed by ICP emission spectrometry to determine the number of moles of each element contained per mass of the electrode, and then the Pt can be calculated by the following formula: Ｂ= (number of moles of Pt contained per electrode mass (mol / kg)) / (total number of moles of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per electrode mass (mol / kg)) × 100 M Ｂ = (Total number of moles (mol / kg) of Y, La, Ce, Pr, Nd, and Nb contained per electrode mass) / (Total number of moles (mol / kg) of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per electrode mass) × 100 Specific M Ｂ / Pt Ｂ The calculation method will be explained in the Examples below.

[0032] On the surface of the catalyst layer, the relative element concentration of Pt Ｓ (atom %) of the added element M (M indicates a metal element selected from Y, La, Ce, Pr, Nd, and Nb) Ｓ The molar ratio M Ｓ / Pt Ｓ Since the initial overvoltage is likely to be lower than 160 mV, it is preferable that M is 0.5 or more and 40 or less. Ｓ / Pt Ｓ Since the initial overvoltage tends to be lower than 150 mV, the lower limit of M is more preferably 1.0 or more, and since the initial overvoltage tends to be lower than 140 mV, the lower limit is even more preferably 2.0 or more. Ｓ / Pt Ｓ Since the initial overvoltage tends to be lower than 150 mV, the upper limit is more preferably 30 or less, and since the initial overvoltage tends to be lower than 140 mV, the upper limit is even more preferably 20 or less. Ｓ / Pt Ｓ When M is 0.5 or more and 40 or less, the reason why the initial overvoltage becomes lower is not clear. Ｓ / Pt Ｓ If M is 0.5 or more, Pt is highly dispersed due to the action of the additive element M present on the surface of the catalyst layer, and the overvoltage is reduced. Ｓ / Pt ＳThis is thought to be because, if M is 40 or less, Pt active sites with high catalytic activity are sufficiently secured on the surface from the beginning, resulting in a low overvoltage. Ｓ / Pt Ｓ The electrode was subjected to X-ray photoelectron spectroscopy (XPS) measurement, and the relative element concentrations M of M and Pt with respect to all elements measured on the electrode surface were calculated. Ｓ (atom%) and Pt Ｓ (atom%), and M Ｓ Pt Ｓ In the electrode of this embodiment, the electrode surface refers to the surface of the catalyst layer on the side opposite to the conductive substrate, and is a surface on which X-ray photoelectron spectroscopy (XPS) measurement can be performed. Ｓ / Pt Ｓ The calculation method will be explained in the Examples below.

[0033] M Ｂ / Pt Ｂ M against Ｓ / Pt Ｓ is the ratio of (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) is preferably 1.5 or more and 100 or less, since the Pt remaining rate after 1500 cycles of power on / off is likely to be 50% or more. Since the Pt remaining rate after 1500 cycles of power on / off is likely to be 60% or more, (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) has a more preferable lower limit of 2.4 or more, and since the Pt residual rate after 1500 cycles of power on / off is likely to be 70% or more, it is even more preferable that it is 3.3 or more. Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) is more preferably 80 or less since the Pt remaining rate after 1500 cycles of power on / off is likely to be 60% or more, and even more preferably 60 or less since the Pt remaining rate after 1500 cycles of power on / off is likely to be 70% or more. Ｓ / PtＳ ) / (M Ｂ / Pt Ｂ ) is 1.5 or more and 100 or less, the reason why the residual rate of Pt after repeatedly turning the power on and off is high is not clear, but it is thought that (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ When the value of (M) is 1.5 or more, the surface of Pt on the electrode surface is covered with the additive element M, and the Pt is less likely to be eluted even when the power supply is repeatedly turned on and off. Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ This is thought to be because, when the value of (M) is 100 or less, structural changes in the catalyst layer due to excessive compounding of Pt and the additive element M are suppressed, and peeling of the catalyst layer when the power is repeatedly turned on and off is less likely to occur. Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) is the aforementioned M Ｓ / Pt Ｓ The aforementioned M Ｂ / Pt Ｂ It can be calculated by dividing by .

[0034] In the electrode of this embodiment, the catalytic layer preferably further contains elements such as W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr. Two or more of these elements may be contained. More preferably, the catalytic layer contains one or more elements selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr. When these elements are contained in the catalytic layer, the overvoltage after repeated on-off switching of the power supply tends to be lower.

[0035] The presence of one or more elements selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr in the catalytic layer can be confirmed by performing SEM-EDX measurement of a cross section of the electrode and examining the composition of the catalytic layer by EDX analysis.

[0036] W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr in the catalyst layer may be in a metallic state. ２ O ３ , W.O. ２ , W.O. ３ , MoO ２ , MoO ３ , AgO, Ag ２ O, CuO, Cu ２ O, Au ２ O ３ , PdO, Bi ２ O ３ , IrO ２ , Ir ２ O ３ , RuO ２ , CoO, Co ２ O ３ , Co ３ O ４ , P ２ O ５ , TiO, TiO ２ , Ti ２ O ３ , ZrO ２ The oxides may be oxides such as those mentioned above. Also, composite oxides may be used. Furthermore, H ２ WO ４ , H ４ WO ５ , H ２ MoO ４ , H ４ MoO ５ , AgOH, Cu(OH) ２ , Au(OH) ３ , Pd(OH) ２ , Bi(OH) ３ , IrO ２ ・nH ２ O, RuO ２ ・nH ２ O, Co(OH) ２ , Co(OH) ３ , H ３ P.O. ４ , H ４ P ２ O ７ , H.P.O. ３ , Ti(OH) ４ , Zr(OH) ４ etc. may also be used.

[0037] In the entire catalyst layer, the relative element concentration M′ of the added element M′ (M′ represents W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr) Ｂ (atom%) and the relative element concentration of Pt Ｂ (atom %) and the relative element concentration M of the added element M (M indicates the metal elements Y, La, Ce, Pr, Nd, and Nb). Ｂ (atom%) (Pt Ｂ +M Ｂ ) and the molar ratio M' Ｂ : (Pt Ｂ +M Ｂ From the viewpoint of reducing the overvoltage after repeatedly turning the power on and off, the molar ratio M' is preferably 0.1:99.9 to 20:80, more preferably 0.5:99.5 to 10:90, and even more preferably 1:99 to 5:95. Ｂ : (Pt Ｂ +M Ｂ ) can be calculated by determining the relative element concentrations (atom %) of M', Pt, and M relative to all elements measured in the bulk of the catalyst layer. Ｂ The M' can be calculated by the following formula after completely dissolving the electrode in aqua regia and performing composition analysis by ICP emission spectrometry to determine the number of moles of each element contained per mass of the electrode. Ｂ = (Total number of moles (mol / kg) of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per electrode mass) / (Total number of moles (mol / kg) of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per electrode mass) × 100 Specific M' Ｂ : (Pt Ｂ +M Ｂ The calculation method of (a) will be explained in the Examples below.

[0038] In the electrode of this embodiment, the catalytic layer is preferably in contact with the conductive substrate. In the electrode of this embodiment, contact with the conductive substrate is preferable because it can suppress peeling and wear originating from the cut surface of the electrode when the power supply is repeatedly turned on and off. In this specification, "contact" between the catalytic layer and the conductive substrate refers to a state in which an interface is formed between the catalytic layer and the conductive substrate. By setting conditions such that a layer of an oxide or hydroxide composition different from that of the conductive substrate, such as a nickel oxide (NiO) layer, is not formed between the catalytic layer and the conductive substrate in the reduction step (4) of the electrode manufacturing method [2] described below, an electrode in which the conductive substrate and the catalytic layer are in contact can be manufactured. Contact of the catalytic layer with the conductive substrate can be confirmed by performing SEM-EDX measurement of a cross section of the electrode and observing, in the backscattered electron image obtained, that there is no layer darker than the conductive substrate between the conductive substrate and the catalytic layer and that an interface is present at a location.

[0039] The reason why peeling and wear starting from the cut surface of the electrode are less likely to occur when the catalyst layer is in contact with the conductive substrate, even when the power supply is repeatedly turned on and off, is not clear; however, it is thought that this is because, when the catalyst layer is in contact with the conductive substrate, cracks are less likely to occur between the catalyst layer on the cut surface of the electrode and the conductive substrate due to the mechanical stress that occurs when the electrode is cut, and therefore, peeling and wear of the catalyst layer starting from cracks on the cut surface of the electrode are suppressed even when electrolysis is performed using the cut electrode by repeatedly turning the power supply on and off.

[0040] The less likely the catalyst layer is to peel off and wear away from the cut surface of the electrode due to repeated on / off cycles, the more likely it is that Pt can be recovered in high yield from the used electrode. From this perspective, the fact that the catalyst layer is less likely to peel off and wear away is a practically desirable characteristic.

[0041] The electrode of this embodiment contains a PtNi alloy. When the electrode contains a PtNi alloy, the adhesion between the catalyst layer and the conductive substrate is improved, the conduction of the catalyst layer is maintained when the power supply is turned on and off, and an increase in overvoltage can be suppressed.

[0042] The presence of a PtNi alloy in an electrode can be confirmed by measuring the electrode's X-ray diffraction (XRD) and finding a peak between the 2θ = 44.508 ° peak of the Ni (111) plane (PDF card number 00-004-0850) and the 2θ = 39.765 ° peak of the Pt (111) plane (PDF card number 00-004-0802), or by finding a shoulder peak on the low-angle side of the 2θ = 44.508 ° peak of the Ni (111) plane. If an XRD peak appears near 2θ = 43.276 °, it is possible that this peak is a peak of the NiO (200) plane. However, if there is no 2θ = 37.249 ° peak of the NiO (111) plane, it can be determined that there is no NiO crystalline phase, and therefore the peak near 2θ = 43.276 ° is not a peak of the NiO crystalline phase, but a peak of the PtNi alloy. In the peaks of the PtNi alloy, the peak that appears between the 2θ = 44.508 ° peak of the Ni (111) plane according to PDF card number 00-004-0850 and the 2θ = 39.765 ° peak of the Pt (111) plane according to PDF card number 00-004-0802 is the peak of the (111) plane. If the peak intensity of the XRD spectrum of the PtNi alloy is high, the peak of the (200) plane of the PtNi alloy will also appear at a position corresponding to the interplanar spacing of the (200) plane of the PtNi alloy, between the 2θ = 51.847 ° peak of the Ni (200) plane according to PDF card number 00-004-0850 and the 2θ = 46.244 ° peak of the Pt (200) plane according to PDF card number 00-004-0802.

[0043] The Pt ratio of the PtNi alloy is preferably 50% or less, more preferably 45% or less, and even more preferably 35% or less, from the viewpoint of suppressing peeling and elution of Pt and increasing the possibility of recovering Pt in high yield from used electrodes. The reason why peeling and elution of Pt tend to be suppressed when the Pt ratio of the PtNi alloy is 50% or less is not clear, but it is thought that the lower the Pt ratio of the formed PtNi alloy, the more Ni is eluted preferentially over Pt when the power is turned on and off, according to the principle of bimetallic corrosion.

[0044] The PtNi alloy has a cubic crystal structure similar to Pt and Ni, and the Pt ratio x (%) is ＰｔＮｉ Using the lattice constant of Pt, 3.92310 (Å), and the lattice constant of Ni, 3.52380 (Å), it can be calculated according to Vegard's law using the following formula: ＰｔＮｉ = 3.92310 × x / 100 + 3.52380 × (100 - x) / 100 For example, the lattice constant a of a PtNi alloy ＰｔＮｉ is 3.72345 (Å), then "3.72345 = 3.92310 × x / 100 + 3.52380 × (100 - x) / 100" gives the Pt ratio x = 50 (%). Here, in a cubic crystal, the lattice constant a and the spacing d of the (hkl) planes are ｈｋｌ is d ｈｋｌ ２ = a ２ / (h ２ +k ２ +l ２ ) For example, the lattice constant a of the PtNi alloy is ＰｔＮｉ is 3.72345 (Å), the XRD peak of the (111) plane is 1.54060 (Å) of the Kα1 line of Cu in Black's law 2d sin θ = nλ, n = 1, d １１１ ２ = a ＰｔＮｉ ２ / (1 ２ +1 ２ +1 ２ ) relationship, it appears at 2θ=41.99°. Therefore, the PtNi alloy having an XRD peak at 2θ=41.99° has a lattice constant a ＰｔＮｉ Based on this principle, the Pt ratio of the PtNi alloy in the electrode of this embodiment can be calculated by calculating the lattice constant a of the PtNi alloy from 2θ of the XRD peak position of the PtNi alloy contained in the XRD spectrum of the electrode. ＰｔＮｉ It is possible to find and calculate

[0045] By reduction baking, which will be described later in the (4) reduction step of [2] Electrode manufacturing method, Pt in an oxidized state is ２＋ and Pt ４＋ and Ni ２＋ are metallic Pt０ and Ni ０ The Pt-Ni alloy is reduced to Pt, and further crystallization proceeds with heating, resulting in the formation of a Pt-Ni alloy crystalline structure. The inventors have discovered that this Pt-Ni alloy crystalline structure contributes to suppressing the rise in overvoltage caused by repeated on-off power cycles. When reduction without heating, such as liquid-phase oxidation or electrolytic reduction, is performed, the Pt-Ni alloy crystalline structure is not formed, and therefore the rise in overvoltage caused by repeated on-off power cycles cannot be suppressed.

[0046] The Ni in the conductive substrate can diffuse into the catalytic layer from the interface and react with the Pt in the catalytic layer to form a PtNi alloy. If an oxide layer (intermediate layer) containing nickel oxide such as NiO exists between the conductive substrate and the catalytic layer, the Ni in the conductive substrate cannot diffuse into the catalytic layer from the interface. However, the oxide layer (intermediate layer) containing nickel oxide is reduced by reduction firing, and the nickel returns to a metallic state substantially identical to that of the conductive substrate. This allows the Ni in the conductive substrate to diffuse into the catalytic layer from the interface and react with the Pt in the catalytic layer to form a PtNi alloy. When the PtNi alloy in the electrode of this embodiment is formed near the interface between the catalytic layer and the conductive substrate, peeling of the catalytic layer is suppressed, and elution and peeling of Pt from the electrode are suppressed, which is preferable from the viewpoint of increasing the possibility of recovering Pt with a high yield from the electrode after use.

[0047] By reduction firing, a PtNi alloy of uniform composition may be formed in the catalytic layer near the interface with the conductive substrate, and a layer containing Pt without the PtNi alloy may be formed on top of it. Alternatively, in a catalytic layer containing one or more elements selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb in addition to Pt, the diffusion range of Ni during reduction firing can be controlled near the interface, forming a concentration gradient in which the Ni concentration in the catalytic layer decreases from the interface between the conductive substrate and the catalytic layer toward the interior of the catalytic layer. In this case, the Ni ratio in the PtNi alloy formed in the catalytic layer is higher near the interface with the conductive substrate and lower the further away from the interface. Furthermore, by reduction firing, the Pt in the catalytic layer of this embodiment diffuses into the conductive substrate from the interface between the catalytic layer and the conductive substrate and reacts with the Pt in the conductive substrate to form a PtNi alloy. Due to the principle of diffusion, a concentration gradient occurs in which the Pt concentration in the conductive substrate decreases from the interface between the conductive substrate and the catalytic layer toward the interior of the conductive substrate. Therefore, in the PtNi alloy formed in the conductive substrate, the Pt ratio is higher near the interface with the catalytic layer and lower the further away from the interface.

[0048] The higher the ratio of Pt to Ni in a PtNi alloy, the closer the peak positions of the (111) and (200) planes of the PtNi alloy in XRD to the positions of the (111) and (200) planes of Pt, and the lower the ratio of Pt, the closer the peak positions of the (111) and (200) planes of the PtNi alloy in XRD to the positions of the (111) and (200) planes of Ni.

[0049] In the electrode of this embodiment, the Ni atomic concentration on the electrode surface is 20% or less. The Ni atomic concentration on the electrode surface is more preferably 15% or less, even more preferably 10% or less, and most preferably 8% or less. When the Ni atomic concentration on the electrode surface is 20% or less, the Pt atomic concentration on the electrode surface becomes relatively high, which suppresses a decrease in the conductivity of the electrode surface and a decrease in wettability of the electrolyte due to power on / off, and suppresses an increase in overvoltage. The Ni atomic concentration on the electrode surface is a value calculated by X-ray photoelectron spectroscopy (XPS) measurement as the relative elemental concentration (atom%) of Ni with respect to all elements measured. Details of the calculation method will be explained in the examples below.

[0050] The electrode of this embodiment has a metal Pt (Pt ０ ) is preferably present on the electrode surface. When metallic Pt is present on the electrode surface, peeling near the surface of the catalyst layer is less likely to occur even when the power is repeatedly turned on and off, and catalyst depletion is suppressed, which is preferable from the viewpoint of increasing the possibility of recovering Pt in high yield from the electrode after use. ０ ) is confirmed by XPS measurement. ７／２ This can be confirmed by the appearance of a peak at a binding energy of approximately 71.0 (eV). ０ The atomic concentration of metallic Pt (Pt) on the electrode surface is preferably 0.5% or more and 10% or less, more preferably 1% or more and 8% or less, and most preferably 2% or more and 7% or less, from the viewpoint of suppressing elution and peeling of Pt from the electrode and increasing the possibility of recovering Pt from the used electrode in high yield. ０ The atomic concentration of Pt relative to all elements measured by XPS measurement ０ The details of the calculation method will be explained in the examples below. ２＋ and Pt ４＋ When α is present, peaks also appear at 72.4 (eV) and 74.9 (eV), respectively. For such an electrode, the Pt atom concentration of each valence can be calculated by performing curve fitting and calculating the peak area for each valence.

[0051] In the electrode of this embodiment, the metal Pt (Pt ０ ) to metallic Ni (Ni ０ ) mole ratio (Ni ０ / Pt ０ ) is preferably 0 or more and 0.90 or less, more preferably 0 or more and 0.50 or less, and even more preferably 0 or more and 0.25 or less, from the viewpoint of suppressing elution or peeling of Pt from the electrode and increasing the possibility of recovering Pt in high yield from the used electrode.

[0052] The presence of metallic Pt on the electrode surface makes it difficult for peeling and wear within the catalyst layer to occur even when the power is repeatedly turned on and off. The reason is unclear, but the Pt in the catalyst layer is reduced by positive current, so the Pt ２＋ PtO having ４＋ PtO ２ Rather than Pt ０ The volume change of metal Pt due to the initial positive current is small. ０ ), cracks are less likely to occur in the catalyst layer near the electrode surface during the initial period of repeated on-off switching of the power supply, and as a result, interfacial peeling and depletion are less likely to occur between the catalyst layer near the electrode surface and the catalyst layer near the interface with the conductive substrate having a PtNi alloy even during subsequent repeated on-off switching of the power supply.

[0053] The less likely the catalytic layer is to be peeled off and worn away due to repeated on-off cycles of the power supply, the more likely it is that Pt can be recovered more efficiently from the electrode after use. From this perspective, the fact that the catalytic layer is less likely to be peeled off and worn away is a practically desirable characteristic. The degree of peeling and wear of the catalytic layer due to repeated on-off cycles of the power supply can be evaluated by the Pt remaining rate (%), which is calculated by the above-mentioned method for the Pt content of the electrode after use with repeated on-off cycles of the power supply, and divided by the Pt content of the electrode before use.

[0054] The electrode of this embodiment preferably contains Pt crystals. The inclusion of Pt crystals in the electrode of this embodiment is preferable because it reduces the likelihood of Pt elution even when the power supply is repeatedly turned on and off. The presence of Pt crystals in the electrode can be confirmed by performing XRD measurement of the electrode and finding that the XRD spectrum has a peak pattern attributable to the Pt peak position and intensity ratio of PDF card number 00-004-0802, such as 2θ = 39.765° for the Pt (111) plane or 2θ = 46.244° for the (200) plane. The reason why Pt elution is less likely to occur when the electrode contains Pt crystals, even when the power supply is repeatedly turned on and off, is not clear, but it is thought to be because Pt crystallizes, stabilizing it against dissolution, or because Pt crystals grow and efficiently capture dissolved Pt.

[0055] The less Pt elution occurs due to repeated on-off cycles of the power supply, the more likely it is that Pt can be recovered more efficiently from the electrode after use. From this perspective, being less prone to Pt elution is a practically desirable characteristic. The degree of Pt elution from the catalytic layer due to repeated on-off cycles can be evaluated, similar to the degree of peeling and wear of the catalytic layer, by the Pt residual rate (%), which is calculated by the above-mentioned method for the Pt content of the electrode after use with repeated on-off cycles of the power supply and divided by the Pt content of the electrode before use.

[0056] [2] Method for manufacturing an electrode Examples of methods for manufacturing an electrode by forming a catalyst layer on a conductive substrate include plating methods, thermal spraying methods such as plasma spraying methods, a coating and firing method in which a catalyst raw material solution is applied to a conductive substrate and then dried to form a precursor layer, and then the precursor layer is fired and further reduced and fired to form a catalyst layer, a method in which a catalyst substance is mixed with a binder component and fixed to a substrate, and a vacuum film formation method such as sputtering methods.

[0057] The coating and baking method allows a catalyst layer thin film of uniform thickness to be formed on a porous substrate. Therefore, the surface of the conductive substrate can be efficiently coated with a catalyst layer using a small amount of raw material. The coating and baking method preferably includes a coating step of coating a catalyst raw material solution (coating liquid) on the surface of the conductive substrate, a precursor layer formation step of drying the coating film (the coating liquid applied to the surface of the conductive substrate) to form a precursor layer, a baking step of heating the conductive substrate on whose surface the precursor layer has been formed to pyrolyze it to form an oxide layer, and a reduction step of reducing and baking the oxide layer to form a catalyst layer.

[0058] In preparing the electrode of this embodiment, a coating and baking method can be used. An oxide layer is formed by performing a coating step, a precursor layer formation step, and a baking step, and then a precursor layer is further laminated by performing a coating step and a precursor layer formation step, and then an oxide layer is laminated by a baking step. For the purpose of preparing an electrode with a predetermined platinum loading, a preparation method in which the coating step, the precursor layer formation step, and the baking step are repeated multiple times to laminate an oxide layer, and then a reduction and baking step is performed is preferable because this method improves bonding within the catalyst layer and makes it less likely that the electrode's overvoltage will increase when the power is repeatedly turned on and off. The number of times the coating step, the precursor layer formation step, and the baking step are repeated is not particularly limited as long as the desired platinum loading is obtained, but is preferably 2 to 30 times, and more preferably 5 to 20 times. After the reduction step, the electrode of this embodiment may be prepared by further performing a coating step, a precursor layer formation step, and a baking step. The method for producing the electrode of this embodiment using the coating and baking method is described in detail below.

[0059] (1) Coating Step In the coating step, a catalyst raw material solution containing a platinum compound is coated onto the substrate surface. In addition to the platinum compound, the catalyst raw material solution may contain one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb, and may further contain one or more compounds selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr. The form of the compound of the above elements in the catalyst raw material solution is not particularly limited, and may be fine particles of metal or metal compound, or a dissolved and ionized metal salt. In the case of a fine particle state, it is preferable that the compound is dispersed in the liquid to form a homogeneous precursor layer. Therefore, the particle size is preferably 100 nm or less. In the case of an ionized metal salt, examples of the metal salt include halide salts such as fluorides, chlorides, bromides, and iodides; inorganic compound salts such as nitrates, sulfates, and phosphates; and organic compound salts such as acetates. Among these, chlorides and nitrates are preferably used because the raw materials are industrially available. Furthermore, nitrates are more preferred because they minimize substrate degradation due to the anionic components remaining after decomposition, allowing for the production of electrodes with good storage stability. In particular, a nitric acid solution of a dinitrodiammine complex is preferably used as a platinum raw material, and a niobium oxalate solution, a niobium tartrate solution, or ammonium niobium oxalate or a solution thereof is preferably used as a Nb raw material. The solvent for the catalyst raw material solution may be any solvent capable of dissolving the solute, such as a metal salt. Since a high-concentration catalyst raw material solution can be prepared, the coating amount can be increased and productivity can be improved, and therefore, it is preferable for the catalyst raw material solution to contain at least one of water or an alcohol having 2 to 5 carbon atoms. If the concentration of the metal salt in the catalyst raw material solution is low, a lot of energy is required to volatilize the solvent. On the other hand, if the concentration of the metal salt is high, unevenness may occur, resulting in an uneven catalyst layer thickness. Therefore, the concentration of the metal salt in the catalyst raw material solution used in the coating step is preferably 0.001 mol / L or more and 1 mol / L or less, and more preferably 0.01 mol / L or more and 0.5 mol / L or less.

[0060] The catalyst raw material solution is such that the ratio of the number of moles of Pt in the platinum compound to the number of moles of the additive element M in the raw material compound of the additive element M, which is Y, La, Ce, Pr, Nd, and Nb, is M, which is the molar ratio of Pt to the additive element M in the entire catalyst layer. Ｂ / Pt Ｂ Furthermore, the catalyst raw material solution is preferably formulated and mixed so that the ratio of the total number of moles of the additional element M' in the raw material compound of the additional element M', which is W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr, to the total number of moles of Pt and the additional element M in the raw material compound is M', which is the molar ratio of Pt and the additional element M to the additional element M' in the entire catalyst layer. Ｂ : (Pt Ｂ +M Ｂ ) and mix them together.

[0061] In the coating process, various known methods can be used to coat the surface of the conductive substrate with the catalyst raw material solution. Examples include a dip method in which the substrate is immersed in the liquid, a brush method in which the liquid is applied to the substrate with a brush, a roll method in which a sponge roll is impregnated with the liquid and the substrate is coated with the liquid, a spray method in which the liquid is atomized using a two-fluid nozzle or the like and sprayed onto the substrate, and an electrostatic coating method in which the liquid and the substrate are oppositely charged and sprayed using a spray or the like. The roll method, spray method, and electrostatic coating method are particularly preferred in terms of productivity and the ability to uniformly coat the catalyst layer. Prior to coating the conductive substrate with the catalyst raw material solution, the conductive substrate may be subjected to a surface treatment to provide irregularities on the surface. Providing irregularities on the surface of the conductive substrate improves adhesion between the conductive substrate and the catalyst layer. The surface treatment method is not particularly limited, and examples include blasting and etching using a chemical solution.

[0062] (2) Precursor Layer Forming Step In the precursor layer forming step, the catalyst raw material solution (coating film) applied to the conductive substrate in the coating step is dried to heat and evaporate the solvent from the coating film, thereby forming a precursor layer containing the above-mentioned elements. Drying is preferably performed until the solvent in the coating film is completely evaporated. Furthermore, when the catalyst raw material is a metal salt such as a nitrate, drying is preferably performed until the metal salt becomes an anhydrous salt. The drying temperature in the precursor layer forming step is preferably 40°C or higher and 200°C or lower, more preferably 50°C or higher and 180°C or lower, and even more preferably 60°C or higher and 160°C or lower. A temperature of 40°C or higher facilitates drying of the solvent, shortening the time required for drying, which is preferable from the viewpoint of productivity. A temperature of 200°C or lower is preferable because bumping of the solvent contained in the coating film can be prevented during drying, allowing for the formation of a dried coating film without defects due to foaming. The drying time in the precursor layer forming step is preferably 1 minute to 1 hour from the viewpoint of productivity.

[0063] (3) Calcination Step In the calcination step, the precursor layer formed in the precursor layer formation step is heated to pyrolyze the precursor layer, thereby forming an oxide layer. Heating is preferably carried out at 300°C or higher and 800°C or lower, more preferably 350°C or higher and 750°C or lower, and even more preferably 400°C or higher and 700°C or lower. A temperature of 300°C or higher is preferable from the viewpoint of productivity, as pyrolysis of the precursor layer is completed in a short time. A temperature of 800°C or lower is preferable, as the formed oxide layer has high wettability with the catalyst raw material solution, and furthermore, it is easy to laminate a precursor layer without defects due to liquid repellency even after passing through the coating step and the precursor layer formation step.

[0064] The firing time per step is preferably 1 minute or more and 24 hours or less. When oxide layers are stacked by repeating the coating step, precursor layer formation step, and firing step, the firing step (pre-firing step) performed each time each layer is stacked may be short, for example, 1 minute or more and 2 hours or less, and after the oxide layer stack reaches a predetermined platinum loading, an additional long firing step (main firing step) may be performed, for example, 10 minutes or more and 24 hours or less. In this way, setting the firing time in the pre-firing step to a short time and the firing time in the main firing step to a long time is preferable because it improves the bonding within the catalyst layer obtained by the reduction step and makes peeling within the layer less likely to occur.

[0065] In the oxide layer obtained by the firing process, the Pt on the surface is Pt ２＋ or Pt ４＋ In the state of metallic platinum (Pt ０ ) is not present, and no Pt crystals are present. Furthermore, a NiO layer is formed between the oxide layer and the conductive substrate by the firing step, and the oxide layer is not in contact with the conductive substrate. In addition, a PtNi alloy formed by a reaction between Pt in the oxide layer and Ni in the conductive substrate is not present in the oxide layer and the conductive substrate. Note that, from the viewpoint of forming an oxide layer and / or NiO layer of sufficient thickness, it is preferable to repeat the coating step, precursor layer formation step, and firing step in this order two or more times. The more the number of times the coating step, precursor layer formation step, and firing step are repeated, the less likely cracks will occur in the catalyst layer, and the durability tends to improve. From the viewpoint of productivity, it is preferable that the number of times the coating step, precursor layer formation step, and firing step are repeated in this order is 30 or less.

[0066] (4) Reduction Step In the reduction step, a catalytic layer is formed by reducing the conductive substrate on which an oxide layer has been formed through the calcination step. The reduction step is preferably carried out by reduction calcination in the presence of a reducing gas at a temperature range of 400°C to 700°C. A temperature of 400°C or higher increases the diffusion rate of Ni from the conductive substrate, increasing the rate of PtNi alloy formation and shortening the time required for reduction calcination, which is preferable from the viewpoint of productivity. A temperature of 700°C or lower is preferable because it makes it easy to control the Ni atomic concentration on the electrode surface to 20% or less. The reduction calcination temperature is more preferably 450°C to 650°C, and even more preferably 500°C to 600°C.

[0067] Reducing gases include hydrogen, carbon monoxide, CH ４ , C ３ H ８ , C ４ H １０ Examples of the reducing gas include hydrocarbons such as methanol and ethanol, alcohols such as methanol and ethanol, ethers such as diethyl ether, and ammonia. As the reducing gas, hydrogen is preferred from the viewpoint of preventing deterioration of the catalyst layer and the conductive substrate, such as carburization, nitridation, and carbonylation. When performing reduction firing at atmospheric pressure, hydrogen is preferred. ２ It is preferable to dilute hydrogen with an inert gas such as HCl or HClO, and adjust the hydrogen concentration to 100 ppm or more and 1% or less before carrying out the reduction firing. If the hydrogen concentration is 100 ppm or more, the rate of formation of the PtNi alloy increases and the time required for the reduction firing is shortened, which is preferable from the viewpoint of productivity. If the hydrogen concentration is 1% or less, the amount of hydrogen used in the reduction firing can be reduced, which is preferable from the viewpoint of productivity.

[0068] The reduction firing may be performed using a vacuum furnace while supplying hydrogen into a vacuum. The hydrogen pressure can be appropriately selected depending on the temperature and reduction firing time, but setting it to 10 Torr (1333 Pa) or less makes it possible to reduce the amount of hydrogen gas used, which is preferable from the viewpoint of productivity.

[0069] The reduction firing time is preferably from 1 hour to 24 hours, more preferably from 1.5 hours to 15 hours, and even more preferably from 2 hours to 10 hours.

[0070] The reduction step converts the platinum in the oxide layer into metallic platinum Pt ０ The reduction step also reduces the NiO layer between the oxide layer and the conductive substrate to metallic nickel Ni. ０ is reduced to.

[0071] Furthermore, by carrying out the reduction step in a temperature range of 400° C. to 700° C., metallic nickel in the conductive substrate and metallic nickel generated from the NiO layer diffuse into the catalytic layer and react with metallic platinum in the catalytic layer to form a PtNi alloy. In some cases, Pt also diffuses from the catalytic layer into the conductive substrate and reacts with metallic nickel in the conductive substrate to form a PtNi alloy.

[0072] The generation of a PtNi alloy rapidly increases the Ni atomic concentration on the electrode surface. The inventors have found that even in an electrode containing a PtNi alloy, if the Ni atomic concentration on the electrode surface exceeds 20%, the electrode overvoltage rises significantly when the power supply is repeatedly turned on and off. On the other hand, an electrode containing a PtNi alloy and having a Ni atomic concentration on the electrode surface controlled to 20% or less is less likely to experience an increase in the electrode overvoltage when the power supply is repeatedly turned on and off. The inventors have also found that when a reduction step is performed using a catalyst raw material solution containing only a Pt compound as the catalyst raw material, it is difficult to control the Ni atomic concentration on the electrode surface to 20% or less because the diffusion rate of Ni in Pt is fast and the alloying reaction is rate-limiting. However, they have found that the Ni atomic concentration on the electrode surface can be easily controlled to 20% or less by using a catalyst raw material solution containing a Pt compound after the reduction step and performing a coating step, a precursor layer formation step, and a baking step to form a Pt-containing catalyst layer. It was also found that the electrode prepared in this manner was less susceptible to an increase in overvoltage when the power supply was repeatedly turned on and off.

[0073] The inventors further discovered that using a catalyst raw material solution containing, in addition to a Pt compound, one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb suppresses the increase in the Ni atomic concentration on the surface even when a PtNi alloy is formed in the reduction step, and thus makes it possible to easily prepare an electrode containing a PtNi alloy and having a Ni atomic concentration of 20% or less on the electrode surface without the need to further laminate a Pt-containing catalyst layer after the reduction step. The reason for this is unclear, but it is believed that the addition of one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb causes the Pt matrix formed in the firing step to become microcrystalline, and the numerous grain boundaries formed by these microcrystals act as resistance to the diffusion of nickel from the conductive substrate into the catalyst layer and to the electrode surface. Using a catalyst raw material solution containing, in addition to a Pt compound, one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb reduces the need to further laminate a Pt-containing catalyst layer after the reduction step, making it preferable from the standpoint of productivity.

[0074] In the reduction process, the higher the reduction baking temperature, the higher the hydrogen concentration and partial pressure, and the longer the reduction baking time, the more the Pt in the oxide layer is reduced and the more the metallic platinum Pt is formed on the electrode surface. ０ This leads to structural changes such as the formation of NiO, or the formation of Pt crystals from platinum in the catalytic layer. Furthermore, the reduction process reduces the NiO in the NiO layer between the oxide layer and the conductive substrate to metallic nickel, resulting in a structural change in which the catalytic layer formed by the reduction of the oxide layer comes into contact with the conductive substrate. When these structural changes occur, the electrode overvoltage tends to be less likely to increase when the power supply is repeatedly turned on and off.

[0075] For example, if the catalyst layer consists of a single layer obtained without carrying out a reduction step, the relative elemental concentration of platinum at the electrode surface, Pt Ｓ (atom %) of the added element M (M indicates a metal element selected from Y, La, Ce, Pr, Nd, and Nb) Ｓ The molar ratio M Ｓ / Pt Ｓ is the relative element concentration of Pt in the entire catalyst layer, Pt Ｂ(atom%), the relative element concentration M of the added element M Ｂ The molar ratio M Ｂ / Pt Ｂ On the other hand, when the catalyst layer is made of a single layer obtained by carrying out a reduction step, the higher the reduction firing temperature, the higher the hydrogen concentration and partial pressure, and the longer the reduction firing time, the more the reduction progresses and the added element M combines with Pt and coats its surface, so that M Ｓ is large Pt Ｓ becomes smaller, and the ratio M Ｓ / Pt Ｓ is M Ｂ / Pt Ｂ In particular, the reduction firing temperature has a greater effect on the reduction reaction rate than the hydrogen concentration or partial pressure. Ｓ / Pt Ｓ M Ｂ / Pt Ｂ The higher the hydrogen concentration and partial pressure, the easier the reduction will proceed, and it will be possible to carry out the reduction in a shorter time at the same reduction firing temperature. Ｓ / Pt Ｓ Ya (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ For example, even under the same reduction firing conditions, the hydrogen concentration and partial pressure can be adjusted appropriately depending on the type and amount of the added element M (Y, La, Ce, Pr, Nd, and Nb). Ｓ / Pt Ｓ Ya (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) will vary, so by appropriately adjusting the reduction firing temperature, hydrogen concentration, and partial pressure, M Ｓ / Pt Ｓ Ya (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) can be adjusted within a predetermined range. In the reduction step, when the reduction firing temperature is set to 400°C or higher and 650°C or lower, (M Ｓ / Pt Ｓ) / (M Ｂ / Pt Ｂ ) can be easily set to 1.5 or more and 100 or less, which is preferable from the viewpoint of increasing the Pt remaining rate after repeated on / off of the power supply. Furthermore, when the reduction firing temperature is set to 450°C or more and 650°C or less, M Ｓ / Pt Ｓ It is more preferable from the viewpoint that the initial overvoltage can be further reduced.

[0076] Y, La, Ce, Pr, Nd, and Nb contained in the catalyst layer may be reduced to a metallic state by reduction firing in the reduction step, but Y may remain in a metallic state even after reduction firing in the reduction step. ２ O ３ , La ２ O ３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ , Nb ２ O ５ , NbO ２ , Nb ２ O ３ , oxides such as NbO, or NaNbO ３ It may also be in the form of a composite oxide such as ２ O ３ , La ２ O ３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ reacts with moisture in the air to form Y(OH) ３ , La(OH) ３ , Ce(OH) ４ , Pr(OH) ３ , Nd(OH) ３ It may be in the form of a hydroxide such as

[0077] When the catalyst layer further contains one or more elements selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr, the W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained in the catalyst layer may be reduced to a metallic state by reduction firing in the reduction step. Furthermore, these elements may be alloyed with Pt. Furthermore, W may remain in a metallic state even after reduction firing in the reduction step. ２ O ３ , W.O. ２ , W.O. ３ , MoO ２ , MoO ３ , AgO, Ag ２ O, CuO, Cu ２ O, Au ２ O ３ , PdO, Bi ２ O ３ , IrO ２ , Ir ２ O ３ , RuO ２ , CoO, Co ２ O ３ , Co ３ O ４ , P ２ O ５ , TiO, TiO ２ , Ti ２ O ３ , ZrO ２ These oxides may be hydrated to produce H ２ WO ４ , H ４ WO ５ , H ２ MoO ４ , H ４ MoO ５ , AgOH, Cu(OH) ２ , Au(OH) ３ , Pd(OH) ２ , Bi(OH) ３ , IrO ２ ・nH ２ O, RuO ２ ・nH ２ O, Co(OH) ２ , Co(OH) ３ , H ３ P.O. ４ , H ４P ２ O ７ , H.P.O. ３ , Ti(OH) ４ , Zr(OH) ４ It may be something like this.

[0078] [3] Electrolytic cell, electrolytic cell for alkaline water electrolysis The electrolytic cell of this embodiment is characterized by including the electrode of this embodiment described above as a cathode. By including the electrode of this embodiment as a cathode, even when the power supply is repeatedly turned on and off to repeatedly start and stop hydrogen generation, high energy conversion efficiency can be maintained over a long period of time without an increase in overvoltage. The electrolytic cell of this embodiment is preferably a bipolar electrolytic cell.

[0079] The alkaline water electrolysis cell of this embodiment includes 3 to 200 electrolytic cells of this embodiment, at least one cathode terminal cell, and at least one anode terminal cell. By configuring the electrolytic cell from the alkaline water electrolysis cell of this embodiment, even when the power supply is repeatedly turned on and off to repeatedly start and stop hydrogen generation, high energy conversion efficiency can be maintained over a long period of time without an increase in overvoltage.

[0080] Hereinafter, the configuration of an example of an electrolytic cell for alkaline water electrolysis according to this embodiment will be described with reference to the drawings.

[0081] Fig. 1 shows a side view of an example of an entire alkaline water electrolysis cell including the bipolar electrolytic cell of this embodiment. Fig. 2 shows a diagram of the zero gap structure of an example of an alkaline water electrolysis cell including the bipolar electrolytic cell of this embodiment (a cross-sectional view of the part enclosed by the dashed square frame in Fig. 1 ). As shown in Figs. 1 and 2 , the alkaline water electrolysis cell 50 of this embodiment is preferably an alkaline water electrolysis cell in which a plurality of elements 60, each including an anode 2a, a cathode 2c, a partition wall 1 separating the anode 2a and the cathode 2c, and an outer frame 3 bordering the partition wall 1, are stacked with a diaphragm 4 sandwiched between them.

[0082] In the alkaline water electrolysis cell 50 of this embodiment, the diaphragm 4 is in contact with the anode 2a and the cathode 2c, forming a zero-gap structure Z (see FIG. 2).

[0083] The electrolytic cell for alkaline water electrolysis of this embodiment may be of a monopolar type or a bipolar type, and is preferably an electrolytic cell for alkaline water electrolysis in which bipolar elements are stacked with a diaphragm interposed therebetween. The monopolar type is a method in which one or more elements are each directly connected to a power source, and the bipolar type is a method in which many bipolar elements are arranged in series and the elements at both ends are connected to a power source.

[0084] In this embodiment, as shown in Fig. 1 , the alkaline water electrolysis cell 50 is configured by stacking the required number of bipolar elements 60. In the example shown in Fig. 1 , the alkaline water electrolysis cell 50 includes a fast head 51g, an insulating plate 51i, and an anode terminal element (anode terminal cell) 51a arranged in this order from one end, and further includes an anode side gasket portion, a diaphragm 4, a cathode side gasket portion, and a bipolar element 60 arranged in this order. The bipolar element 60 is arranged so that the cathode 2c faces the anode terminal element 51a. The anode gasket to the bipolar element 60 are arranged repeatedly the number of times required for the designed production volume. After the required number of anode gaskets to the bipolar element 60 are arranged repeatedly, the anode side gasket portion, the diaphragm 4, and the cathode side gasket portion are again arranged in a row, and finally the cathode terminal element (cathode terminal cell) 51c, the insulating plate 51i, and a loose head 51g are arranged in this order. The entire electrolytic cell 50 for alkaline water electrolysis is integrated by fastening it with tie rods 51r to form the electrolytic cell 50 for alkaline water electrolysis. The arrangement of the electrolytic cell 50 for alkaline water electrolysis can be selected as desired, either from the anode side or the cathode side, and is not limited to the above-mentioned order.

[0085] As shown in FIG. 1 , in an alkaline water electrolysis cell 50, a bipolar element 60 is disposed between an anode terminal element 51 a and a cathode terminal element 51 c, and diaphragms 4 are disposed between the anode terminal element 51 a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51 c.

[0086] In the alkaline water electrolysis cell 50 of this embodiment, as shown in Fig. 2 , the diaphragm 4 is in contact with the anode 2a and the cathode 2c, forming a zero gap structure Z. In this embodiment, in particular, 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 alkaline water electrolysis cell 50 are referred to as an 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.

[0087] In alkaline water electrolysis, if there is a gap between the diaphragm 4 and the anode 2a or the cathode 2c, a large amount of gas bubbles generated during electrolysis, as well as the electrolytic solution, will accumulate in this gap, resulting in a very high electrical resistance. In order to significantly reduce the electrolytic voltage in the electrolytic cell 65, it is effective to reduce the distance between the anode 2a and the cathode 2c (hereinafter also referred to as the "inter-electrode distance") as much as possible to eliminate the influence of the electrolytic solution and gas bubbles present between the anode 2a and the cathode 2c.

[0088] Therefore, a zero gap structure is adopted, which can maintain a state in which the anode 2a and the diaphragm 4 are in contact with each other and the cathode 2c and the diaphragm 4 are in contact with each other over the entire electrode surface, or a state in which the inter-electrode distance is substantially the same as the thickness of the diaphragm 4 and there is almost no gap between the anode 2a and the diaphragm 4 and between the cathode 2c and the diaphragm 4 over the entire electrode surface.

[0089] In the alkaline water electrolysis cell 50 of this embodiment, as shown in Fig. 2 , electrode chambers 5, through which the electrolytic solution passes, are defined by the partition wall 1, the outer frame 3, and the diaphragm 4. The header pipes, which are pipes for distributing or collecting the electrolytic solution and which are attached to the alkaline water electrolysis cell 50 shown in Figs. 1 and 2 , are typically of an internal header type or an external header type, but either type may be adopted in the present embodiment, and there is no particular limitation thereon.

[0090] The components of the bipolar electrolytic cell and alkaline water electrolysis cell of this embodiment will be described in detail below. Preferred embodiments for enhancing the effects of the present invention will also be described in detail below.

[0091] (Partition Wall) The partition wall 1 is preferably provided between the cathode 2c and the anode 2a, between the anode 2a and the cathode current collector 2r and / or between the cathode 2c and the anode current collector 2r. The shape of the partition wall in this embodiment may be a plate shape having a predetermined thickness, but is not particularly limited. The shape of the partition wall in a plan view is not particularly limited and may be a rectangle (such as a square or rectangle) or a circle (such as a circle or ellipse), and the rectangle may have rounded corners.

[0092] The size of the partition wall is not particularly limited and may be appropriately designed depending on the size of the electrode chamber. Furthermore, as the material of the partition wall, a material having high conductivity is preferred from the viewpoint of realizing a uniform supply of power, and nickel, a nickel alloy, mild steel, or a nickel alloy plated with nickel is preferred from the viewpoint of alkali resistance and heat resistance.

[0093] (Electrode) The size of the electrode is not particularly limited and may be determined according to the size of the electrode chamber, and may be 0.4 m to 4.0 m in length, 0.4 m to 6.0 m in width, and 0.1 mm to 3 mm in thickness.

[0094] In the bipolar electrolytic cell of this embodiment, at least one of the anode and cathode is preferably porous, and more preferably both the anode and the cathode are porous, in order to increase the surface area used for electrolysis and to efficiently remove gas generated by electrolysis from the electrode surface. In particular, in the case of a zero-gap electrolytic cell, it is necessary to degas the gas generated from the back side of the surface in contact with the diaphragm, so it is preferable that the surface of the electrode opposite to the surface in contact with the membrane is perforated.

[0095] The anode preferably includes a porous metal body, since the catalyst layer carried on the electrode is porous, increasing the effective electrolysis area and enabling a lower voltage.

[0096] Examples of porous bodies include plain weave and twill weave meshes, punched metals, expanded metals, and metal foams.

[0097] When a perforated metal is used, the dimensions are not particularly limited. However, in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferable that the hole diameter be 2 mm or more and 8 mm or less, the pitch be 2 mm or more and 10 mm or less, the opening ratio be 20% or more and 80% or less, and the thickness be 0.5 mm or more and 2 mm or less.

[0098] When an expanded metal is used, the dimensions are not particularly limited, but in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferable that the center-to-center distance in the short direction of the mesh (SW) is 2 mm or more and 5 mm or less, the center-to-center distance in the long direction of the mesh (LW) is 3 mm or more and 10 mm or less, the thickness is 0.5 mm or more and 2 mm or less, and the opening ratio is 20% or more and 80% or less.

[0099] When a metal foam is used, the dimensions are not particularly limited, but in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferable that the porosity be 80% or more and 95% or less, and the thickness be 0.5 mm or more and 2.0 mm or less.

[0100] The material of the substrate is not particularly limited, but in view of resistance to the use environment, it is preferable that the substrate contains mild steel, stainless steel, Ni, or a Ni-based alloy, and more preferably contains Ni.

[0101] The anode has holes, and the aperture ratio is preferably 30% or more and 70% or less in order to efficiently remove gas generated by electrolysis from the anode surface.

[0102] The catalytic layer of the anode preferably has a high oxygen generating capacity, and Ni, Co, Fe, or Pt group elements can be used. In order to achieve the desired activity and durability, the catalytic layer can be formed as a simple metal, a compound such as an oxide, a composite oxide or alloy made of multiple metal elements, or a mixture thereof. Specifically, Ni plating, alloy plating of Ni and Co, Ni and Fe, etc., LaNiO ３ and LaCoO ３ ,NiCo ２ O４ Examples of the material include composite oxides containing Ni or Co such as those mentioned above, compounds of Pt group elements such as Ir oxide, and carbon materials such as graphene. Organic materials such as polymers may be included to improve durability and adhesion to the substrate.

[0103] In particular, the anode is formed on a substrate by depositing LaNi ｘ M'' ｙ O ３－ｚ (x+y is 0.8 or more and 1.2 or less, y is 0.001 or more and 0.6 or less, z is −0.5 or more and 0.5 or less, and M″ contains at least one of Nb, Ta, Sb, Ti, Mn, and Zr) ｘ M'' ｙ O ３－ｚ It is preferable that the cathode is the electrode of the present embodiment described above, and the anode is a LaNi ｘ M'' ｙ O ３－ｚ An electrolytic cell equipped with LaNi electrodes is preferred because the overvoltage is less likely to increase even when the power is repeatedly turned on and off. ｘ M'' ｙ O ３－ｚ The electrodes are made of [5]LaNi, which will be described later. ｘ M'' ｙ O ３－ｚ Details will be given in the section on electrodes.

[0104] (Outer Frame) The shape of the outer frame 3 in the bipolar electrolytic cell of the present embodiment is not particularly limited as long as it can frame the partition wall 1, and may be a shape that has an inner surface that is perpendicular to the plane of the partition wall 1 and extends over the outer periphery of the partition wall 1. The shape of the outer frame is not particularly limited and may be determined appropriately in accordance with the shape of the partition wall in a plan view. The dimensions of the outer frame are not particularly limited and may be designed in accordance with the outer dimensions of the electrode chambers.

[0105] The material for the outer frame is preferably a conductive material, and from the standpoint of alkali resistance and heat resistance, nickel, nickel alloy, mild steel, or nickel alloy plated with nickel is preferred.

[0106] (Diaphragm) As the diaphragm 4 used in the bipolar electrolytic cell 65 of this embodiment, an ion-permeable diaphragm is used to separate the generated hydrogen gas and oxygen gas while conducting ions. This ion-permeable diaphragm can be an ion exchange membrane having ion exchange capacity or a porous membrane that is permeable to the electrolytic solution. This ion-permeable diaphragm preferably has low gas permeability, high ionic conductivity, low electronic conductivity, and high strength.

[0107] The porous membrane has a structure with multiple fine through-holes that allows the electrolyte to pass through the membrane. Since the electrolyte penetrates the porous membrane to exhibit ionic conduction, it is extremely important to control the porous structure, such as pore size, porosity, and hydrophilicity. On the other hand, it is also required to not only allow the electrolyte to pass through, but also the generated gas, i.e., to have gas barrier properties. From this perspective, control of the porous structure is also important.

[0108] The porous membrane has a plurality of fine through-holes, and examples thereof include polymer porous membranes, inorganic porous membranes, woven fabrics, nonwoven fabrics, etc. These can be produced by known techniques.

[0109] Ion exchange membranes include cation exchange membranes that selectively allow cations to pass through and anion exchange membranes that selectively allow anions to pass through, and either type of exchange membrane can be used. The material of the ion exchange membrane is not particularly limited, and known materials can be used. For example, fluorine-containing resins and modified resins of polystyrene-divinylbenzene copolymers can be suitably used. Fluorine-containing ion exchange membranes are particularly preferred because of their excellent heat resistance and chemical resistance.

[0110] Furthermore, in the zero-gap electrolytic cell 65, as a means for reducing the interelectrode distance, it is preferable to adopt a configuration in which a spring, which is an elastic body 2e, is disposed between the electrode 2 and the partition wall 1 and this spring supports the electrode. For example, in a first example, a spring made of a conductive material may be attached to the partition wall 1, and the electrode 2 may be attached to this spring. Furthermore, in a second example, a spring may be attached to the electrode rib 6 attached to the partition wall 1, and the electrode 2 may be attached to this spring. Note that when such a configuration using an elastic body is adopted, the strength, number, shape, and the like of the spring must be appropriately adjusted as necessary to prevent uneven contact pressure between the electrode and the diaphragm.

[0111] In addition, by increasing the rigidity of the other electrode that is paired with the electrode supported via the elastic body (for example, by making the anode more rigid than the cathode), a structure is achieved in which deformation is minimal even when pressed. On the other hand, by making the electrode supported via the elastic body a flexible structure that deforms when the diaphragm is pressed, it is possible to absorb unevenness due to tolerances in the manufacturing precision of the electrolytic cell and deformation of the electrodes, thereby maintaining the zero gap structure.

[0112] Examples of the zero gap structure Z include a zero gap structure formed between the anode terminal element 51a and an element, between elements, and between an element and the cathode terminal element 51c. In the bipolar electrolytic cell 65 of this embodiment, as shown in Fig. 2 , a conductive elastic body 2e and a cathode current collector 2r are preferably provided between the cathode 2c and the partition wall 1 such that the conductive elastic body 2e is sandwiched between the cathode 2c and the cathode current collector 2r. In addition, the cathode current collector 2r is preferably in contact with the rib 6 of the cathode.

[0113] The zero gap structure Z of the bipolar electrolytic cell 65 of the present embodiment preferably has a structure in which, as shown in FIG. 2 , a bipolar element 60 is formed by stacking an anode rib 6 and an anode 2a in this order on the anode 2a side of the partition wall 1, and a cathode rib 6, a cathode current collector 2r, a conductive elastic body 2e, and a cathode 2c in this order on the cathode 2c side of the partition wall 1, with the diaphragm 4 sandwiched between them, and the diaphragm 4 is in contact with the anode 2a and the cathode 2c.

[0114] (Current Collector) Examples of the current collector include a cathode current collector and an anode current collector. The current collector transmits electricity to the conductive elastic body and electrodes stacked thereon, supports the load received from them, and allows gas generated from the electrodes to pass through to the partition wall side without hindrance. Therefore, the shape of this current collector is preferably an expanded metal or a perforated plate. In this case, the aperture ratio of the current collector is preferably within a range that allows hydrogen gas generated from the electrodes to be released to the partition wall side without hindrance. However, if the aperture ratio is too large, problems such as a decrease in strength or a decrease in conductivity to the conductive elastic body may occur, and if the aperture ratio is too small, gas escape may be poor.

[0115] As the material for the current collector, nickel, nickel alloy, stainless steel, mild steel, etc. can be used from the viewpoints of electrical conductivity and alkali resistance, but nickel, mild steel, or stainless steel-nickel alloy plated with nickel is preferred from the viewpoint of corrosion resistance.

[0116] (Conductive elastic body) The conductive elastic body is located between the current collector and the electrode and is in contact with the current collector and the electrode. It is essential that it transmits electricity to the electrode and does not inhibit the diffusion of gas generated from the electrode. This is because inhibiting gas diffusion increases electrical resistance and reduces the electrode area used for electrolysis, thereby reducing the electrolysis efficiency. The most important role of the conductive elastic body is to evenly apply an appropriate amount of pressure to the electrode without damaging the diaphragm, thereby ensuring close contact between the diaphragm and the electrode.

[0117] (Electrode Chambers) In the alkaline water electrolysis cell 50 of this embodiment, as shown in Fig. 2 , electrode chambers 5, through which the electrolytic solution passes, are defined by the partition wall 1, the outer frame 3, and the diaphragm 4. 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.

[0118] (Ribs) In the bipolar electrolytic cell 65 of this embodiment, the ribs 6 are preferably physically connected to the electrodes 2. With this configuration, the ribs 6 serve as supports for the electrodes 2, making it easier to maintain the zero-gap structure Z. Furthermore, the ribs 6 are preferably electrically connected to the partition walls 1. In the example bipolar electrolytic cell described above, the cathode chamber has a structure in which the cathode rib-cathode current collector-conductive elastic body-cathode are stacked in this order, and the anode chamber has a structure in which the anode rib-anode are stacked in this order. However, the present invention is not limited to this, and the anode chamber may also have an "anode rib-anode current collector-conductive elastic body-anode" structure.

[0119] 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.

[0120] (Gasket) In the bipolar electrolytic cell 65 of the present embodiment, as shown in Fig. 2 , a gasket 7 is preferably sandwiched together with the diaphragm 4 between the outer frames 3 that frame the partition walls 1. The gasket 7 is used to seal the spaces between the bipolar element 60 and the diaphragm 4 and between the bipolar elements 60 against the electrolytic solution and the generated gas, and can prevent leakage of the electrolytic solution or the generated gas to the outside of the electrolytic cell and mixing of gases between the two electrode chambers.

[0121] A typical gasket structure is a rectangular or annular shape with the electrode surface hollowed out to match the surface of the element (such as a bipolar element, an anode terminal element, or a cathode terminal element) that contacts the frame. Diaphragms can be stacked between elements by sandwiching them between two such gaskets. Furthermore, the gasket preferably has a slit that can accommodate the diaphragm so that it can hold the diaphragm, and also has openings that allow the accommodated diaphragm to be exposed on both surfaces of the gasket. This allows the gasket to accommodate the edge of the diaphragm within the slit and cover the end faces of the edge of the diaphragm. This more reliably prevents electrolyte and gas from leaking from the end faces of the diaphragm.

[0122] The material of the gasket is not particularly limited, and can be selected from known insulating rubber materials, resin materials, etc. Specific examples of the rubber material and resin material include natural rubber (NR), styrene butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated polyethylene rubber (CSM); fluororesin materials such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE); and resin materials such as polyphenylene sulfide (PPS), polyethylene, polyimide, and polyacetal. Among these, ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) are particularly suitable from the viewpoint of elastic modulus and alkali resistance.

[0123] (Header) The electrolytic cell for alkaline water electrolysis preferably has a cathode chamber and an anode chamber for each electrolytic cell. In order to continuously perform the electrolysis reaction in the electrolytic cell, it is necessary to continuously supply an electrolyte containing a sufficient amount of raw materials to be consumed by electrolysis to the cathode chamber and the anode chamber of each electrolytic cell.

[0124] The electrolytic cells are connected to electrolyte supply and discharge pipes called headers, which are common to multiple electrolytic cells. Generally, the anode distribution pipe is called the anode inlet header, the cathode distribution pipe is called the cathode inlet header, the anode collection pipe is called the anode outlet header, and the cathode collection pipe is called the cathode outlet header. The elements are connected to each electrolyte distribution pipe and each electrolyte collection pipe via hoses, etc.

[0125] The material of the header is not particularly limited, but it is necessary to use a material that can sufficiently withstand the corrosiveness of the electrolyte used and the operating conditions such as pressure and temperature, etc. The header material may be iron, nickel, cobalt, PTFE, ETFE, PFA, polyvinyl chloride, polyethylene, etc.

[0126] The internal header type refers to a type in which an alkaline water electrolysis cell and a header (a tube for distributing or collecting the electrolyte) are integrated. An example of the internal header type is one in which an anode inlet header and a cathode inlet header are provided in a part of a lower portion of an outer frame at the edge of a partition wall, and similarly, an anode outlet header and a cathode outlet header are provided in a part of an upper portion of an outer frame at the edge of a partition wall. The outer frame and the anode chamber or the cathode chamber are connected by an electrolyte inlet or electrolyte outlet through which the electrolyte passes.

[0127] The external header type refers to a type in which the alkaline water electrolysis cell and headers (pipes for distributing or collecting the electrolyte) are independent. In an external header type alkaline water electrolysis cell, an anode inlet header and a cathode inlet header are provided independently, running parallel to the electrolytic cell in a direction perpendicular to the current-carrying surface of the electrolytic cell. The anode inlet header and cathode inlet header are connected to each element by hoses.

[0128] The internal header type and external header type electrolytic cells for alkaline water electrolysis may have therein a gas-liquid separation box that separates the gas generated by electrolysis from the electrolytic solution. The installation position of the gas-liquid separation box is not particularly limited, and the box may be installed between the anode chamber and the anode outlet header or between the cathode chamber and the cathode outlet header.

[0129] (Electrolyte) In the alkaline water electrolysis cell of this embodiment, a cathode chamber frame with a cathode attached thereto and an anode chamber frame with an anode attached thereto are arranged via a partition wall. That is, the anode chamber and the cathode chamber are separated by the partition wall. An electrolyte is supplied to the anode chamber and the cathode chamber. As the electrolyte, an electrolyte generally used in water electrolysis can be used. Examples include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution. The electrolyte concentration is preferably 1N or more and 12N or less, and more preferably 6N or more and 10N or less.

[0130] The alkaline water electrolysis cell of this embodiment includes the anode and cathode described above, and water electrolysis is performed by applying a current to the alkaline water electrolysis cell through which the 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 supply derived from a renewable energy power plant whose output fluctuates over a period of several seconds to several minutes, unlike power supplies that provide a stable output, such as grid power. The method of renewable energy power generation is not particularly limited, and examples include solar power generation and wind power generation. For example, in electrolysis using an alkaline water electrolysis cell, cationic electrolytes in the electrolyte migrate from the anode chamber of one element through a diaphragm to the cathode chamber of an adjacent element, and anionic electrolytes migrate from the cathode chamber of one element through a diaphragm to the anode chamber of the adjacent element. Therefore, the current during electrolysis flows in the direction in which the elements are connected in series. That is, the current flows from the anode chamber of one element to the cathode chamber of the adjacent element through the diaphragm. As the electrolysis proceeds, oxygen gas is produced in the anode chamber and hydrogen gas is produced in the cathode chamber.

[0131] The bipolar electrolytic cell 65 of this embodiment can be used in a bipolar electrolytic cell 50, an electrolysis apparatus for alkaline water electrolysis 70, etc. Examples of the electrolysis apparatus for alkaline water electrolysis 70 include an apparatus 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 during electrolysis. The electrolysis apparatus for alkaline water electrolysis 70 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, etc.

[0132] In the alkaline water electrolysis method using the alkaline water electrolysis apparatus, the current density applied to the electrolytic cell is 1 kA / m ２ ~20 kA / m ２ Preferably, it is 6 kA / m ２ ~15kA / m ２ In particular, when a variable power supply is used, it is preferable that the upper limit of the current density be within the above range.

[0133] [4] Hydrogen Production Method The hydrogen production method of the present embodiment involves electrolyzing alkali-containing water in an electrolytic cell to produce hydrogen, and can be carried out using the alkaline water electrolysis cell of the present embodiment.

[0134] The details of the alkaline water electrolysis cell of this embodiment are as described above. In the hydrogen production method of this embodiment, alkali-containing water can be electrolyzed to produce hydrogen using a variable power supply that involves repeating positive current application and stop of positive current application by repeatedly turning the power on and off.

[0135] The cathode of the present invention, the electrolytic cell of the present invention, the alkaline water electrolysis cell of the present invention, and the hydrogen production method of the present invention have been illustrated and described with reference to the drawings, but these are not limited to the above examples, and appropriate modifications can be made to the above embodiments.

[0136] [5] LaNi ｘ M'' ｙ O ３－ｚElectrode The electrode of the present embodiment described above is provided as a cathode, and a LaNi ｘ M ｙ O ３－ｚ (x+y is 0.8 or more and 1.2 or less, y is 0.001 or more and 0.6 or less, z is -0.5 or more and 0.5 or less, and M contains at least one of Nb, Ta, Sb, Ti, Mn, and Zr) ｘ M'' ｙ O ３－ｚ An electrolytic cell equipped with electrodes is preferred because the overvoltage is less likely to increase even when the power is repeatedly turned on and off.

[0137] The substrate preferably has electrical conductivity. Examples of the material of the conductive substrate include nickel, nickel-based materials, 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. The shape of the conductive substrate of the electrode may be a flat plate, or may be a porous body having a large number of holes. Specific examples of the shape of the porous body include expanded metal, punched metal, plain woven mesh, foam metal, and shapes similar to these. Among these, expanded metal is preferred, and although there are no particular restrictions on its dimensions, in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferred that the center-to-center distance in the short direction of the mesh (SW) be 2 mm to 5 mm, the center-to-center distance in the long direction of the mesh (LW) be 3 mm to 10 mm, the thickness be 0.2 mm to 2 mm, and the opening ratio be 20% to 80%. More preferably, SW be 3 mm to 4 mm, LW be 4 mm to 6 mm, the thickness be 0.8 mm to 1.5 mm, and the opening ratio be 40% to 60%.

[0138] LaNi ｘ M ｙ O ３－ｚ is directly deposited on the substrate, and LaNi ｘ M ｙ O ３－ｚ The substrate and the LaNi layer may be formed. ｘ Mｙ O ３－ｚ An interface may be formed between the layer and the M. Two or more of Nb, Ta, Sb, Ti, Mn, and Zr may be contained as M.

[0139] LaNi to substrate ｘ M ｙ O ３－ｚ The adhesion amount is 145 g / m ２ Super 3500g / m ２ It is preferable that the content is 200 g / m or less, and more preferably 200 g / m ２ More than 3000g / m ２ More preferably 350 g / m or less ２ More than 2500g / m ２ The area (m) used to calculate the adhesion amount is as follows: ２ ) is the geometric area of ​​the electrode. For example, when an electrode using an expanded metal substrate is cut out to have a square shape of 10 cm (0.1 m) long and 10 cm (0.1 m) wide when viewed from the thickness direction, the area of ​​the cutout is 0.01 m. ２ Then, 1 g of LaNi was added to the substrate. ｘ M ｙ O ３－ｚ When the adhesive is attached, the amount of adhesion is 100 g / m ２ The amount of adhesion is calculated by dividing the LaNi ｘ M ｙ O ３－ｚ After the catalyst is completely peeled off, the metal powder such as Ni derived from the substrate is removed from the powder obtained by peeling with a magnet, and the attached LaNi ｘ M ｙ O ３－ｚ The catalyst powder is obtained, its mass is measured using an electronic balance, and the mass is divided by the value of the above-mentioned fixed area of ​​the electrode, whereby the LaNi ｘ M ｙ O ３－ｚ The catalyst can be peeled off using various methods that can remove the catalyst without introducing foreign matter that cannot be removed with a magnet, such as using a file such as a precision file or an extra-fine file, using a spatula such as a microspatula or a spatula, or using a brush such as a wire brush.

[0140] (LaNi ｘ M'' ｙ O ３－ｚ Electrode manufacturing method) LaNi ｘ M'' ｙ O ３－ｚ The electrode is prepared by applying an aqueous solution (coating liquid) containing metal salts of La, Ni, and M″ (M″ includes at least one of Nb, Ta, Sb, Ti, Mn, and Zr) to a substrate, drying, and pre-baking the substrate, and depositing a predetermined mass of LaNi ｘ M'' ｙ O ３－ｚ The precursor can be prepared by forming it and then subjecting it to main calcination.

[0141] As the metal salt, water-soluble salts such as nitrates, oxynitrates, chlorides, oxalates, tartrates, acetates, and sulfates can be used. The metal salts may be anhydrous or hydrated. For La, Ni, and M", a water-dispersible sol of an oxide or hydroxide may be used instead of the metal salt. When Nb is used as M", it is preferable to use niobium oxalate or ammonium niobium oxalate from the viewpoint of solubility. Furthermore, when Sb is used as M", it is preferable to use antimony tartrate.

[0142] M" 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, followed by drying and pre-baking, and then a coating liquid containing a water-dispersible sol of a metal salt, or an oxide or hydroxide of M" is applied to the electrode in a topcoat manner, followed by drying, pre-baking, and final baking. Alternatively, M" 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, followed by drying, pre-baking, and final baking, and then a coating liquid containing a water-dispersible sol of a metal salt, or an oxide or hydroxide of M" is applied to the electrode in a topcoat manner, followed by drying, pre-baking, and final baking.

[0143] Adding organic ligands such as amino acids such as glycine, or carboxylic acids such as oxalic acid and tartaric acid to the coating solution can produce LaNi alloys that exhibit low oxygen overvoltage. ｘ M'' ｙ O ３－ｚFrom the viewpoint of facilitating the preparation of LaNi, which has high resistance to high-temperature alkalis, ｘ M'' ｙ O ３－ｚ From the viewpoint of facilitating the preparation of LaNi, and showing a lower oxygen evolution overvoltage even when an electrolyte with a high alkaline concentration is used, ｘ M'' ｙ O ３－ｚ In particular, when a coating solution in which glycine and a metal nitrate are dissolved is used, it becomes easy to prepare an electrode that exhibits a lower oxygen overvoltage, making it easy to prepare an electrode that has both durability to high-temperature alkali and an overvoltage, and it also becomes easy to prepare an electrode that exhibits a lower oxygen evolution overvoltage when an electrolyte solution with a high alkali concentration is used, so glycine is a preferred organic ligand.

[0144] The concentration of the aqueous solution containing metal salts of La, Ni, and M″ is LaNi ｘ M'' ｙ O ３－ｚ The standard molar concentration is preferably 0.1 mol / kg or more and 4.0 mol / kg or less.

[0145] A spray coating method is preferred as a method for applying the coating liquid to a substrate. In particular, if the coating liquid atomized from a spray nozzle is dried appropriately to become highly viscous before landing on the substrate, the coating liquid film does not move on the substrate after landing, and a coating film with a uniform thickness can be formed on the substrate, making it easy to prepare an electrode that exhibits a low oxygen overvoltage even after long-term current application. Furthermore, a dip coating method in which the substrate is completely immersed in the coating liquid is also a preferred method for applying the coating liquid to a substrate.

[0146] After the coating liquid is applied to the substrate, the drying temperature is preferably 50°C or higher and 200°C or lower. If it is 50°C or higher, drying is completed within 3 minutes to 1 hour, which is preferable from the viewpoint of productivity. If it is 200°C or lower, the cooling time of the substrate after drying is shortened, which is preferable from the viewpoint of productivity. If it is 300°C or higher, the pre-baking is completed within 3 minutes to 1 hour, which is preferable from the viewpoint of productivity. If it is 500°C or lower, the cooling time of the substrate after drying is shortened, which is preferable from the viewpoint of productivity. The coating, drying and pre-baking are carried out at a temperature of 300°C or higher and 500°C or lower. If it is 300°C or higher, the pre-baking is completed within 3 minutes to 1 hour, which is preferable from the viewpoint of productivity. ｘ M'' ｙ O ３－ｚ This process may be repeated to adjust the amount of deposition of the electrode. ２ 50g / m or more ２ If the temperature is less than 500° C., the number of coating times is reduced, which is preferable from the viewpoint of productivity. The temperature for the main baking can be 500° C. or higher and 1000° C. or lower, but baking at 650° C. or higher is preferable. Baking at 650° C. or higher is preferable from the viewpoint of productivity, because it makes it easy to prepare an electrode that exhibits a low oxygen overvoltage in a baking time of 10 minutes to 24 hours.

[0147] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0148] [Electrode Preparation] (Examples 1-9, Comparative Examples 1 and 2) A dinitrodiammine platinum nitrate solution with a Pt mass concentration of 8.35%, pure water, and additive reagents were mixed according to the formulations shown in Table 1 to prepare catalyst coating solutions (catalyst raw material solutions) for Examples 1-9 and Comparative Examples 1 and 2. The dinitrodiammine platinum nitrate solution used was subjected to neutralization titration to determine the acid content. Assuming that all of the acid contained in the solution was derived from nitric acid, the nitric acid mass concentration of the solution was calculated to be 180 g / L. A plain-woven mesh substrate was used as the conductive substrate, woven with 40-mesh thin nickel wires with a diameter of 0.15 mm. The conductive substrate was blasted with alumina powder with a weight-average particle size of 100 μm or less and cut into a 10 cm x 10 cm piece. It was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. After drying, the conductive substrate was subjected to heat cleaning at 500°C for 10 minutes using a muffle furnace ("FP412" manufactured by Yamato Scientific Co., Ltd.). Next, using a spray coater ("rCoater" sold by Asahi Sunac Corporation), the catalyst coating solution was applied to both sides of the conductive substrate, followed by drying for 10 minutes at 60 ° C. in a dryer ("DF412" manufactured by Yamato Scientific Co., Ltd.), and then calcination for 10 minutes at 500 ° C. in a muffle furnace to form an oxide layer on the surface of the conductive substrate. This coating, drying, and calcination were repeated the number of times listed in the "Number of Coatings" column of Table 2 to obtain electrode precursors with the Pt loadings shown in Table 2. The operating conditions of the spray coater, such as the delivery rate of the catalyst coating solution, were appropriately adjusted so that the Pt loadings listed in Table 2 could be obtained by the predetermined number of coatings, drying, and calcinations listed in Table 2. The obtained electrode precursors of Examples 1 to 9 and Comparative Examples 1 and 2 were calcined in a muffle furnace at 500 ° C. for 1 hour. Thereafter, for Examples 1 to 9 and Comparative Example 2, reduction calcination was performed in the atmosphere, temperature, and time listed in the "Reducing and Calcining Conditions" column of Table 2 to obtain electrodes. In Comparative Example 1, the electrode was used as is without reduction calcination. In addition, the normal pressure 1% H ２ / N ２ , 1000 ppmH ２ / N ２ , 100 ppmH ２ / N ２The reduction firing in the atmosphere was carried out by connecting a cylinder gas of the atmosphere composition to an atmosphere type electric furnace ("SKM-2030D" manufactured by Motoyama Corporation). After evacuating the air inside the furnace at room temperature, the cylinder gas was circulated through the furnace at 1 L / min, and the temperature was raised from room temperature to the temperature specified in the reduction firing conditions in Table 2 at a temperature increase rate of 3.5°C / min, and then maintained for the time specified in the reduction firing conditions in Table 2. Thereafter, the circulating gas was changed to N ２ The gas was switched to hydrogen and the mixture was slowly cooled to room temperature. The reduction firing in a hydrogen atmosphere of 100 Pa described in Table 2 was carried out by connecting a hydrogen cylinder to a horizontal vacuum furnace ("PQ-65 / 50 / 100" manufactured by IHI Corporation). After evacuating the air in the furnace at room temperature, hydrogen cylinder gas was circulated while controlling the furnace pressure to 100 Pa. The temperature was increased from room temperature to the temperature described in the reduction firing conditions in Table 2 at a rate of 3.5°C / min, and the mixture was maintained for the time described in the reduction firing conditions in Table 2. Thereafter, N was used as the cooling gas. ２ Gas was introduced and the mixture was rapidly cooled to room temperature.

[0149] (Example 11) For the electrode of Example 1, a spray coater ("rCoater" sold by Asahi Sunac Corporation) was used to apply the catalyst coating solution of Comparative Example 1 to both sides of the substrate, followed by drying at 60 ° C. for 10 minutes in a dryer ("DF412" manufactured by Yamato Scientific Co., Ltd.) and then baking at 400 ° C. for 10 minutes in a muffle furnace ("FP412" manufactured by Yamato Scientific Co., Ltd.). This application, drying, and baking were performed a total of five times to obtain an electrode precursor of Example 11 having the Pt loading amount listed in Table 2. The operating conditions of the spray coater, such as the liquid delivery rate of the catalyst coating solution, were set the same as in Comparative Example 1. The obtained electrode precursor was baked in a muffle furnace at 400 ° C. for 30 minutes to obtain the electrode of Example 11.

[0150] (Example 12) For the electrode of Comparative Example 2, a spray coater ("rCoater" sold by Asahi Sunac Corporation) was used to apply the catalyst coating solution of Comparative Example 1 to both sides of the substrate, followed by drying at 60 ° C. for 10 minutes in a dryer ("DF412" manufactured by Yamato Scientific Co., Ltd.) and then baking at 400 ° C. for 10 minutes in a muffle furnace ("FP412" manufactured by Yamato Scientific Co., Ltd.). This application, drying, and baking were performed a total of five times to obtain an electrode precursor of Example 12 having the Pt loading listed in Table 2. The operating conditions of the spray coater, such as the liquid delivery rate of the catalyst coating solution, were set the same as in Comparative Example 1. The obtained electrode precursor was baked in a muffle furnace at 400 ° C. for 30 minutes to obtain the electrode of Example 12.

[0151] Example 13 An electrode of Example 13 was obtained in the same manner as in Example 4, except that the dried conductive substrate was subjected to heat cleaning at 800°C for 1 hour using a muffle furnace. XRD measurement of the electrode of Example 13 showed the presence of a NiO crystalline phase. Furthermore, a cross-sectional SEM image showed the presence of a layer (NiO layer) with a darker contrast than the conductive substrate at the interface between the conductive substrate and the catalyst layer, indicating that the catalyst layer and the conductive substrate were not in contact.

[0152] Examples 14 to 16 As the conductive substrate, a nickel mesh substrate was used that had been blasted, acid-treated, washed and dried with water, and heat-cleaned in the same manner as in Examples 1 to 9. A dinitrodiammine platinum nitrate solution with a Pt mass concentration of 8.35%, pure water, and nickel (II) nitrate hexahydrate reagent as an additive reagent were mixed in the formulations shown in Table 5 to prepare the first catalyst layer coating liquids (first catalyst layer raw material solutions) of Examples 14 to 16. Using a spray coater ("rCoater" sold by Asahi Sunac Corporation), the first catalyst layer coating liquids of Examples 14 to 16 were applied to both sides of the conductive substrate, followed by drying at 60°C for 10 minutes in a dryer ("DF412" manufactured by Yamato Scientific Co., Ltd.), and then calcining for 10 minutes at 400°C in a muffle furnace ("FP412" manufactured by Yamato Scientific Co., Ltd.). This coating, drying, and calcination process was repeated five times to obtain a Pt loading of 3.0 g / m ２ The oxide layer of the first catalyst layer was formed by five coating, drying and baking processes. ２The operating conditions of the spray coater, such as the liquid feed rate of the catalyst layer first layer coating solution, were appropriately adjusted so that a Pt loading of 9.5 g / m was obtained. Thereafter, in the same manner as in Example 1, the application of the catalyst coating solution (catalyst raw material solution) of Example 1, drying, and firing were repeated five times as shown in the "Number of applications" column in Table 2. ２ The obtained electrode precursors of Examples 14 to 16 were fired in a muffle furnace at 500°C for 1 hour. Thereafter, reduction firing was carried out in the atmosphere, at the temperature, and for the time shown in the "Reduction firing conditions" column of Table 2, to obtain the electrodes of Examples 14 to 16.

[0153] Example 17 An electrode of Example 17 was obtained in the same manner as in Example 2, except that the reduction firing was carried out in a hydrogen atmosphere at 1333 Pa. In this example, the reduction firing in a hydrogen atmosphere at 1333 Pa was carried out by connecting a hydrogen cylinder gas to a horizontal vacuum furnace ("PQ-65 / 50 / 100" manufactured by IHI Corporation). After evacuating the air in the furnace at room temperature, hydrogen cylinder gas was circulated while controlling the pressure inside the furnace to 1333 Pa. The temperature was raised from room temperature to 500°C at a rate of 3.5°C / min and then maintained for 2 hours. Thereafter, N was used as a cooling gas. ２ Gas was introduced and the mixture was rapidly cooled to room temperature.

[0154] (Examples 18 to 28, Comparative Example 3) A dinitrodiammine platinum nitrate solution with a Pt mass concentration of 8.35%, pure water, and additive reagents were mixed in the formulations shown in Table 6 to prepare catalyst coating solutions (catalyst raw material solutions) for Examples 18 to 28 and Comparative Example 3. A nickel mesh substrate was used as the conductive substrate, which had been blasted, acid-treated, washed, dried, and heat-cleaned in the same manner as in Examples 1 to 9. Next, using a spray coater ("rCoater" sold by Asahi Sunac Corporation), the catalyst coating solution was applied to both sides of the conductive substrate, followed by drying at 60 ° C. for 10 minutes in a dryer ("DF412" manufactured by Yamato Scientific Co., Ltd.), and then calcined in a muffle furnace at 500 ° C. for 10 minutes to form an oxide layer on the conductive substrate surface. This coating, drying, and calcination were repeated the number of times shown in the "Number of Coatings" column of Table 7 to obtain an electrode precursor with the Pt loading shown in Table 7. The operating conditions of the spray coater, such as the liquid feed rate of the catalyst coating solution, were appropriately adjusted so that the Pt loading amount shown in Table 7 could be obtained by the predetermined number of coating, drying, and calcination steps shown in Table 7. The obtained electrode precursors of Examples 18 to 28 and Comparative Example 3 were calcined in a muffle furnace at 500°C for 1 hour. Thereafter, for Examples 18 to 28, reduction calcination was carried out in the atmosphere, temperature, and time shown in the "Reduction calcination conditions" column of Table 7 to obtain an electrode. In Comparative Example 3, the electrode was used as is without reduction calcination. The electrode precursors were calcined in a muffle furnace at 500°C for 1 hour at 500°C for 1 hour as shown in Table 7. ２ / N ２ Atmosphere: 1000 ppmH at normal pressure ２ / N ２ The reduction firing in the hydrogen atmosphere at 100 Pa was performed under the atmospheric pressure of 1% H ２ / N ２ Atmosphere: 1000 ppmH at normal pressure ２ / N ２ The atmosphere was the same as that of the reduction firing in a hydrogen atmosphere at 100 Pa.

[0155] (Examples 29 to 46) A dinitrodiammine platinum nitrate solution with a Pt mass concentration of 8.35%, pure water, and additive reagents were mixed in the formulations shown in Table 6 to prepare catalyst coating solutions (catalyst raw material solutions) for Examples 29 to 46. A nickel mesh substrate was used as the conductive substrate, which had been blasted, acid-treated, washed, dried, and heat-cleaned in the same manner as in Examples 1 to 9. Next, using a spray coater ("rCoater" sold by Asahi Sunac Corporation), the catalyst coating solution was applied to both sides of the conductive substrate, followed by drying at 60 ° C. for 10 minutes in a dryer ("DF412" manufactured by Yamato Scientific Co., Ltd.), and then calcined in a muffle furnace at 500 ° C. for 10 minutes to form an oxide layer on the conductive substrate surface. This coating, drying, and calcination were repeated the number of times shown in the "Number of Coatings" column of Table 7 to obtain electrode precursors with the Pt loadings shown in Table 7. The operating conditions of the spray coater, such as the liquid feed rate of the catalyst coating solution, were appropriately adjusted so that the Pt loading shown in Table 7 could be obtained by the predetermined number of coating, drying, and calcination steps shown in Table 7. The electrode precursor was calcined at 500°C for 1 hour in a muffle furnace. Thereafter, reduction calcination was carried out in the atmosphere, at the temperature, and for the time shown in the "Reduction calcination conditions" column of Table 7 to obtain an electrode.

[0156] [Measurement Methods] In Examples 1 to 46 and Comparative Examples 1 to 3, the measurements were carried out by the following measurement methods.

[0157] (ICP Atomic Emission Analysis Method) (1) Measurement of Pt Loading Amount on Electrode A 50 mL glass beaker was charged with 6 mL of ultrapure water, 4.5 mL of 30% hydrochloric acid, and 1.5 mL of 68% nitric acid to prepare an aqua regia solution. A 0.9 cm × 1.7 cm piece cut out from each electrode and having a geometric area of ​​1.53 cm was added to the aqua regia solution. ２ The test electrode was immersed in the solution and heated on a hot plate controlled at 100°C for 40 minutes to completely dissolve the test electrode. Ultrapure water was then added to make the total volume 100 mL to prepare a measurement solution. If any insoluble matter was generated, it was filtered off and heated in an atmospheric electric furnace at 1% H ２ / N ２After baking at 600 °C for 2 hours, the sample was again immersed in aqua regia using the method described above to completely dissolve the sample. A test solution was prepared to measure the Pt concentration in the insoluble matter. A 1000 mg / L Pt standard solution and a predetermined amount of ultrapure water were added to 4.5 mL of 30% hydrochloric acid and 1.5 mL of 68% nitric acid to make 100 mL. A calibration curve solution with Pt concentrations of 0, 1, 5, 10, and 20 mg / L was prepared. Using an ICP optical emission spectrometer (Hitachi High-Tech Science Corporation "SPS3520UV-DD"), the Pt concentration in the test solution was measured using the above test solution and the calibration curve solution. The total Pt mass contained in the test electrode with a size of 0.9 cm x 1.7 cm was determined, and the geometric area was 1.53 cm. ２ The Pt content was calculated by dividing the Pt content by the Pt content. The Pt content of each electrode is shown in the "Pt loading amount" column of Tables 2 and 7. (2) Calculation of Pt remaining rate after 1500 reverse current cycles + 2 hours of positive current treatment Furthermore, for each electrode, the Pt content after 1500 reverse current cycles + 2 hours of positive current treatment, which will be described later, was determined in the same manner as in (1) above, and the Pt remaining rate was calculated according to the following formula. The results are shown in the "Pt remaining rate (%) after 1500 reverse current cycles + 2 hours of positive current treatment" column of Tables 4 and 9. Pt remaining rate (%) = (Pt content (g / m) of electrode after 1500 reverse current cycles + 2 hours of positive current treatment) ２ )) / (Pt content (Pt supported amount) of electrode in non-energized state (g / m ２ ) × 100 (3) Relative element concentration (atom %) Pt in the bulk of the catalyst layer Ｂ , M Ｂ , M' ＢCalculation of 4.5 mL of 30% hydrochloric acid and 1.5 mL of 68% nitric acid were mixed with a standard solution of each measured element at a concentration of 1000 mg / L and a predetermined amount of ultrapure water to make 100 mL, and calibration curve solutions with measured element concentrations of 0, 1, 5, 10, and 20 mg / L were prepared. Using the method described in (1) Measurement of Pt Loading Amount on Electrode, the test electrode was completely dissolved in aqua regia, and then ultrapure water was added so that the measured element concentration was 0 mg / L or more and 20 mg / L or less to prepare a measurement solution. The content per test electrode mass (measured element mass (g) / test electrode mass (kg)) of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr was calculated. For Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr, the content per mass of the obtained test electrode (measured element mass (g) / test electrode mass (kg)) was divided by the atomic weight of each element to calculate the number of moles contained per mass of the test electrode (number of moles of measured element (mol) / test electrode mass (kg)). Relative element concentration of Pt Ｂ (atom %) was calculated by the following formula: Ｂ = (number of moles of Pt contained per test electrode mass (mol / kg)) / (total number of moles of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per test electrode mass (mol / kg)) × 100 Relative element concentration M of added element M (M indicates Y, La, Ce, Pr, Nd, and Nb) Ｂ (atom %) was calculated by the following formula: Ｂ = (Total number of moles (mol / kg) of Y, La, Ce, Pr, Nd, and Nb contained per test electrode mass) / (Total number of moles (mol / kg) of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per test electrode mass) × 100 Relative element concentration M' of added element M' (M' indicates W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr) Ｂ (atom %) was calculated by the following formula: Ｂ= (Total number of moles (mol / kg) of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per electrode mass) / (Total number of moles (mol / kg) of Pt, Y, La, Ce, Pr, Nd, Nb, W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr contained per electrode mass) × 100 Ｂ , M Ｂ , M' Ｂ Based on the value of Ｂ / Pt Ｂ , molar ratio M' Ｂ : (Pt Ｂ +M Ｂ The results are shown in Tables 3 and 8.

[0158] (XRD Measurement Method) A 1.7 cm x 1.8 cm test electrode was cut from each electrode and measured using an XRD measurement device ("D8 ADVANCE ECO" sold by Bruker Japan Co., Ltd.). The test electrode was placed in the center of a glass sample holder (groove φ30 mm, depth 0.2 mm), and tape was applied to the four corners of the test electrode, forming a right-angled isosceles triangle with a side length of 1 mm, to fix the test electrode. While rotating the test electrode at 15 rpm, the measurement range was set to 2θ = 5° to 70°, and 3,343 points were set so that the step interval was 2θ = approximately 0.02°. Measurements were performed for 0.5 seconds at each point. Cu Kα1 X-rays were used. The voltage of the X-ray source was 40 kV, and the current was 25 mA. A divergence slit of 0.3° and a Soller slit of 2.5° were used. The detector used was a LYNXEYE XE-T (manufactured by Bruker) to prevent the detection of peaks derived from Cu Kβ rays. Using the analysis software DIFFRAC.EVA (manufactured by Bruker), the "Kα2 removal" tool was used on the measured spectrum, with the intensity ratio set to 0.5, and calculations were performed to remove peaks derived from Cu Kα2 rays. Next, the "smoothing" tool was used, with the factor set to 0.146, and smoothing calculations were performed. Then, the "peak search" tool was used to determine the position of a high-intensity peak near 2θ = 44.508°, and the peak position of the measured spectrum was corrected using the "X-axis offset" tool so that the peak position coincided with 2θ = 44.508° of the Ni (111) plane according to PDF card number 00-004-0850. - Detection of PtNi alloy - If a peak other than NiO is observed between the 2θ = 44.508 ° peak of the Ni (111) plane according to PDF card number 00-004-0850 and the 2θ = 39.765 ° peak of the Pt (111) plane according to PDF card number 00-004-0802, or if a broad shoulder peak other than NiO is observed on the low-angle side of the 2θ = 44.508 ° peak of the Ni (111) plane, it can be determined that a PtNi alloy is present, and the column "Presence of PtNi alloy" in Tables 3 and 8 is recorded as "Presence". If the above-mentioned peak or shoulder peak is not present, the column is recorded as "Absence".- Detection of NiO crystals - When both the 2θ = 37.249 ° peak of the NiO (111) plane and the 2θ = 43.276 ° peak of the (200) plane were confirmed according to PDF card number 00-047-1049, the "Presence of NiO crystals" column in Tables 3 and 8 was recorded as "Yes." When neither peak was confirmed, the "Presence of NiO crystals" column in Tables 3 and 8 was recorded as "No." - Detection of Pt crystals - When the 2θ = 39.765 ° peak of the Pt (111) plane and the 2θ = 46.244 ° peak of the Pt (200) plane according to PDF card number 00-004-0802 were confirmed, the "Presence of Pt crystals" column in Tables 3 and 8 was recorded as "Yes." When neither peak was confirmed, the "Presence of Pt crystals" column in Tables 3 and 8 was recorded as "Yes." - Detection of crystalline phases of added elements - Also, La according to PDF card number 01-071-5408. ２ O ３ If a peak attributed to a crystalline phase was present, the column "Crystalline phase of added element" in Tables 3 and 8 should read "La ２ O ３ " Similarly, Y of PDF card number 00-041-1105 ２ O ３ If a peak attributed to a crystalline phase was present, it was marked as "Y ２ O ３ " and CeO of PDF card number 00-004-0593 ２ If a peak attributed to a crystalline phase was present, it was determined that the peak was "CeO ２ " and PDF card number 00-047-1111 Pr ２ O ３ If a peak attributed to a crystalline phase was present, it was classified as "Pr ２ O ３ " and PDF card number 01-079-9858 Nd ２ O ３ If a peak attributed to a crystalline phase was present, it was classified as "Nd ２ O ３ " and PDF card number 01-086-5414 NaNbO ３ If a peak attributed to a crystalline phase was present, it was classified as "NaNbO ３" was described. For peak assignment, the "Search / Match (Scan)" tool of the analysis software DIFFRAC. EVA was used, and the PDF-2 Release 2020 RDB was used as the database. - Calculation of Pt ratio in PtNi alloy - The peak position 2θ indicating the maximum value of the peak of PtNi alloy, which exists between the 2θ = 44.508 ° peak of the Ni (111) plane according to PDF card number 00-004-0850 and the 2θ = 39.765 ° peak of the Pt (111) plane according to PDF card number 00-004-0802, was used. ＰｔＮｉ (°), and the lattice constant a of the PtNi alloy was calculated using the following formula: ＰｔＮｉ asked for. The obtained lattice constant a ＰｔＮｉ The Pt ratio x (%) was calculated according to the following formula, and the results were entered in the "Pt ratio (%) of PtNi alloy" column in Tables 3 and 8. x = (a ＰｔＮｉ -3.52380) / (3.92310-3.52380)×100 However, when the Pt ratio of the PtNi alloy is very low and the peak of the PtNi alloy forms a broad shoulder peak on the low-angle side of the peak of the Ni(111) plane, it is recorded as "5 or less" (%).

[0159] Figure 7 shows the XRD spectrum of the electrode of Example 1. A peak (indicated by a ● mark in Figure 7) was observed near 2θ = 43.6°, but no peak was observed at 2θ = 37.249° on the NiO (111) plane, indicating that no NiO crystals were present, and that the peak near 2θ = 43.6° was different from the NiO crystalline phase and was therefore assigned to the PtNi alloy phase, indicating the presence of a PtNi alloy.

[0160] (XPS Measurement Method) Using a "VersaProbe II" manufactured by ULVAC-PHI, Inc., X-ray photoelectron spectroscopy (XPS) measurement of each electrode was performed under the following measurement conditions: Excitation source: Monochromated Al Kα 15 kV × 3.3 mA Analysis size: Approximately 200 μmφ Pass energy: 23.5 eV (narrow scan) Energy step: 0.1 eV The spectra acquired for each element were Pt 4f, Y3d, La 3d, Ce 3d, Pr 3d, Nd 3d, and Nb 3d. Ni ０For the electrode without La, Ni 2p ３／２ In the case of an electrode containing La, the La 3d peak and Ni 2p peak were observed. ３／２ Since the peaks of -Ni overlapped strongly, the spectrum of Ni LMM was acquired. ０ , Pt ０ , Pt ２＋ , Pt ４＋ , Pt Ｓ , M Ｓ Calculation of relative element concentration - The relative element concentration on the electrode surface was calculated by subtracting the background from the spectrum of each element to determine the peak area and using the following formula. When calculating the concentration, C was not contained in the electrode but was considered to be derived from a contaminant, so it was excluded from the calculation. C ｊ (atomic%)=100×(I ｊ / RSF ｊ ) / Σ(I ｊ / RSF ｊ ) where each parameter is as follows: C ｊ : Relative element concentration of element j (atomic%) I ｊ RSF: Spectral peak area of ​​element j (unit: cps eV) ｊ : Relative sensitivity coefficient of element j The relative sensitivity coefficient was the value registered in the library of the software MultiPak attached to the device. ０ In the case where Pt 4f is ７／２ The spectrum of Pt has a peak only at 71.0 eV. ２＋ and Pt ４＋ When Pt is present, there are also peaks at 72.4 eV and 74.9 eV, respectively. For such electrodes, curve fitting was performed to calculate the peak area for each valence, and the relative element concentration of Pt at each valence was calculated using the above formula. In addition, the relative element concentrations of Pt at each valence were summed to obtain the relative element concentration Pt Ｓ Similarly, the relative element concentrations of Y, La, Ce, Pr, Nd, and Nb were calculated and summed to obtain the relative element concentration M Ｓ The Ni on the surface of each electrode ０ , Pt ０ , Pt２＋ , Pt ４＋ , Pt Ｓ , M Ｓ The relative element concentrations (atomic %) are shown in the "Relative element concentrations (atomic %) on the electrode surface" column in Tables 3 and 8. The molar ratio of Ni ０ / Pt ０ , M Ｓ / Pt Ｓ , (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ ) were calculated and are shown in Tables 3 and 8.

[0161] (Cross-section SEM measurement method) Each electrode was trimmed to an appropriate size, sandwiched between cover glasses, and embedded in G2 epoxy resin manufactured by Gatan Corporation, followed by curing on a hot plate set at 120°C. The cured sample was polished to the vicinity of the target cross section using SiC polishing paper. At this time, polishing was performed using polishing paper with varying roughnesses of #400, #600, and #1000. Subsequently, ion milling processing of the target surface was performed using an ion milling processing device ("IM5000" manufactured by Hitachi High-Tech Corporation). The processing conditions were an acceleration voltage of 6 kV, a discharge voltage of 1.5 kV, a discharge current of 400 to 440 μA, a beam current of 130 to 170 μA, and an Ar gas volume of 0.2 cm. ３ / min. SEM observation of the processed cross section was carried out using "SU8220" manufactured by Hitachi High-Tech Corporation. The observation conditions were an acceleration voltage of 5 kV, an emission current of 10 μA, and a YAG BSE detector. - Detection of NiO layer - From the obtained cross-sectional SEM image, it was determined whether or not a NiO layer was present at the interface between the conductive substrate and the catalyst layer. When a NiO layer was present at the interface between the conductive substrate and the catalyst layer, the density of Ni (8.90 g / cm ３ ) and the density of NiO (6.67 g / cm ３ Due to the density difference of NiO, the NiO layer is visually recognized in backscattered electron (BSE) images as a layer with darker contrast than the conductive substrate.

[0162] 8 shows a cross-sectional SEM image (backscattered electron image) of the electrode of Example 1. No layer with a darker contrast than the conductive substrate was observed at the interface between the conductive substrate and the catalyst layer, indicating that no NiO layer was present.

[0163] (Initial Overvoltage of Electrode) A test electrode measuring 1.7 cm x 1.8 cm was cut out from each electrode 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 tested at a current density of 0.6 A / cm in a 5 M aqueous sodium hydroxide solution at 80°C. ２ Electrolysis was performed with 1000 kJ / min, and the hydrogen overvoltage was measured to determine the initial overvoltage of the electrode. The hydrogen overvoltage was measured by the three-electrode method using a Luggin capillary to eliminate the effects of ohmic loss due to solution resistance. The distance between the tip of the Luggin capillary and the cathode (test electrode) was always fixed at 1 mm. A potentiogalvanostat "1470E System" manufactured by Solartron was used as the hydrogen overvoltage measurement device. A silver-silver chloride (Ag / AgCl) electrode was used as the reference electrode for the three-electrode method. Ohmic loss that could not be completely eliminated using the three-electrode method was measured using the AC impedance method, and the hydrogen overvoltage was corrected based on the measured ohmic loss. Ohmic loss was measured using a frequency response analyzer "125 5B" manufactured by Solartron. The initial overvoltage of each electrode is shown in the "Initial overvoltage (mV)" column of Tables 4 and 9.

[0164] (Electrode reverse current treatment method: 1500 times + 2 hours of forward current treatment) Using the three-electrode method, the test electrode was subjected to 1500 times of reverse current treatment + 2 hours of forward current treatment as follows. The treatment device used was a potentiogalvanostat "PARSTAT MC 1000" manufactured by Princeton Applied Research. A 1.7 cm x 1.8 cm test electrode was cut out from each electrode and fixed to a PTFE-coated nickel rod with a nickel screw. A Pt mesh was used as the counter electrode, a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode, and a 5 M NaOH aqueous solution was used as the electrolyte. The temperature of this electrolyte was adjusted to 80°C. First, a current density of -6 kA / m ２ After applying a reduction current of +15 A / m for 1 minute, ２ An oxidation current of 0.16 V was passed through the cathode (test electrode). At this time, the potential of the cathode (test electrode) gradually increased from the hydrogen generation potential to a more noble potential. When the potential of the cathode reached +0.16 V (vs. Ag / AgCl), the current was stopped. This process of repeatedly passing a reduction current and an oxidation current (reverse current treatment) was repeated 1,500 times, and then the current density was set to −6 kA / m. ２A reduction current of 1500 times was applied for 2 hours (forward current application treatment). After this series of 1500 reverse current applications + 2 hours of forward current application treatment, the overvoltage of the cathode was measured. The overvoltage of each electrode after 1500 reverse current applications + 2 hours of forward current application treatment is shown in the "Overvoltage after 1500 reverse current applications + 2 hours of forward current application treatment (mV)" column of Tables 4 and 9.

[0165] The composition of each electrode, measurement results, etc. are shown in Tables 1 to 9. In the "Catalyst composition" column of each table, for example, "Pt65La35" means that the molar ratio is "Pt:La=65:35."

[0166]

[0167]

[0168]

[0169]

[0170]

[0171]

[0172]

[0173]

[0174]

[0175] [Fabrication of Zero-Gap Bipolar Element] (Example 10) A zero-gap bipolar element was fabricated according to the following steps. (1) Cathode: A 50 cm x 50 cm electrode was prepared in the same manner as in Example 2 and used as the cathode. (2) Anode: A Ni expanded metal with a SW of 3.0 mm, a LW of 4.5 mm, a thickness of 0.75 mm, and an aperture ratio of 54% was used as the anode 1. (3) Partition Wall and Outer Frame: A bipolar element was used that included a partition wall separating the anode and cathode and an outer frame surrounding the partition wall. All materials used for components that come into contact with the electrolyte, such as the partition wall and the frame of the bipolar element, were nickel. (4) Conductive Elastic Body: The conductive elastic body was made by weaving nickel wire with a wire diameter of 0.15 mm and corrugating it to a wave height of 5 mm. The thickness was 5 mm, and the repulsive force at 50% compression deformation was 150 g / cm. ２The mesh size was approximately 5 mesh. (5) Diaphragm: 135 g of zirconium oxide (trade name "EP Zirconium Oxide," manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) and 210 g of N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) were placed in a 1,000 mL ball mill pot containing 1 kg of 0.5 mm diameter SUS balls. These were stirred at 70 rpm in an atmosphere of 25°C for 3 hours to disperse the mixture, obtaining a mixture. The resulting mixture was filtered through a stainless steel sieve (30 mesh) to separate the balls from the mixture. To the mixture from which the balls were separated, 45 g of polysulfone ("Udel" (registered trademark), manufactured by Solvay Advanced Polymers) and 18 g of polyvinylpyrrolidone (weight average molecular weight (Mw) 900,000, manufactured by Wako Pure Chemical Industries, Ltd.) were added, and the mixture was stirred and dissolved at 60°C for 12 hours using a Three-One motor, obtaining a coating solution with the following component composition. 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 above coating liquid was applied to both surfaces of a substrate, a polyphenylene sulfide mesh (manufactured by Kureha Corporation, film thickness 280 μm, mesh size 358 μm, fiber diameter 150 μm), using a comma coater to a coating thickness of 150 μm on each side. Immediately after coating, the substrate coated with the coating liquid was exposed to steam from a coagulation bath containing a 30 ° C. pure water / isopropanol mixture (manufactured by Wako Pure Chemical Industries, Ltd., pure water / isopropanol = 50 / 50 (v / v)) for 2 minutes. Immediately thereafter, the substrate coated with the coating liquid was immersed in the coagulation bath for 4 minutes. Then, a coating film was formed on the surface of the substrate by coagulating the polysulfone. The coating film was then thoroughly washed with pure water to obtain a porous membrane. The average pore size of this porous membrane was 0.3 μm in terms of water permeation average pore size at 90° C. The thickness was 580 μm. The porosity was 43%. ２The mode diameter of the inorganic particles was 5.0 μm. The ratio of the mode diameter of the inorganic particles to the average pore diameter of the porous membrane (mode diameter / average pore diameter) was 2.6. (6) Gasket The gasket used was a rectangular gasket with a thickness of 4.0 mm, a width of 18 mm, and inner dimensions of 504 mm square. It had an opening on the inside with the same dimensions as the electrode chamber in a plan view and a slit structure for inserting and holding a diaphragm. The slit structure was configured so that a 0.4 mm gap was provided in the center of the thickness direction of the inner wall of the opening to insert and hold a diaphragm. This gasket was made of EPDM rubber and had a tensile stress of 4.0 MPa at 100% deformation. (7) Zero-gap bipolar element The external header type zero-gap cell unit 60 was a rectangle measuring 540 mm x 620 mm, and the area of ​​the current-carrying surfaces of the anode 2a and cathode 2c was 500 mm x 500 mm. The cathode side of the zero-gap bipolar element 60 includes a cathode chamber 5c in which a cathode 2c, a conductive elastic body 2e, and a cathode current collector 2r are stacked and connected to the partition wall 1 via a cathode rib 6, and an electrolyte flows through the cathode chamber 5c. The anode side includes an anode 2a connected to the partition wall 1 via an anode rib 6 and an anode chamber 5a in which an electrolyte flows (FIGS. 3 and 4). The depth of the anode chamber 5a (anode chamber depth, the distance between the partition wall and the anode in FIG. 4) 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. 4) was 25 mm and made of nickel. The nickel anode rib 6, 25 mm high and 1.5 mm thick, and the nickel partition wall 1 to which the nickel cathode rib 6, 25 mm high and 1.5 mm thick, was attached by welding, had a thickness of 2 mm. The cathode current collector 2r was a nickel expand substrate that had been pre-blasted. The substrate had a thickness of 1 mm and an aperture ratio of 54%. The conductive elastic body 2e was fixed to the cathode current collector 2r by spot welding. Furthermore, for the area X surrounded by the dashed-dotted line in Figure 4, a nozzle 9a leading to the cathode chamber was provided on the side of the element, as shown in Figure 5. A PFA resin-coated Pt wire 8 was inserted into an EPDM disk 9d and a PTFE disk 9c, each with a hole in the center that matched the diameter of the PFA-coated Pt wire 8, and then inserted into the nozzle 9a. The EPDM disk 9d and the PTFE disk 9c were then fastened together with a cap nut 9b.This allows the PFA-coated Pt wire to be introduced into the cell without leaking the electrolyte to the outside. The PFA coating of the PFA-coated Pt wire 8 was stripped off by approximately 10 mm from one end outside the element so that the Pt wire 8 could be grasped with an alligator clip. Furthermore, for the area Y surrounded by the two-dot dashed line in Figure 4 , as shown in Figure 6 , the tip of the PFA-coated Pt wire a introduced into the cathode chamber of the element was stripped off by approximately 0.5 mm so that the Pt wire would come into contact with hydrogen bubbles generated by electrolysis. This PFA-coated Pt wire a was bent inside the cathode chamber and fixed near the surface of the cathode 2c(2) opposite the diaphragm through the through-hole in the current collector 2r and the gap in the conductive elastic body 2e, so that the tip of the Pt wire would not come into contact with the cathode 2c(2), the conductive elastic body 2e, or the current collector 2r. (Figure 6) In this way, the Pt wire comes into contact with the hydrogen bubbles generated by electrolysis, forming an RHE reference electrode in which the potential of the Pt wire is at the hydrogen generation potential. By stacking this zero-gap type bipolar element via a gasket that holds the diaphragm, a zero-gap structure Z can be formed in which the anode 2a and cathode 2c are pressed against the diaphragm 4.

[0176] (Power-off cycle test of bipolar electrolytic cell) A bipolar electrolytic cell was fabricated as follows, using the zero-gap bipolar elements of Example 10, stacked in the order shown in Fig. 4. A bipolar electrolytic cell was constructed by stacking, in this order, an anode terminal element 51a using the anode described in Example 10, the above-mentioned diaphragm, a portion in which three sets of zero-gap bipolar elements of Example 10 were stacked with the above-mentioned diaphragm in between, the above-mentioned diaphragm, the above-mentioned diaphragm, and a cathode terminal cell 51c using the cathode described in Example 10. Then, using this bipolar electrolytic cell, the electrolytic device shown in Fig. 3 was fabricated. The electrolysis device includes a bipolar electrolytic cell 50, a liquid pump 71 for circulating the electrolyte, and a gas-liquid separation tank 72 for separating the electrolyte from hydrogen and / or oxygen. The gas-liquid separation tank 72 and the bipolar electrolytic cell 50 are filled with a 30% KOH aqueous solution of electrolyte. The liquid pump 71 circulates the electrolyte through the anode chamber 5a of the bipolar electrolytic cell 50, the anode gas-liquid separation tank 72, and the anode chamber 5a, and also through the cathode chamber 5c of the bipolar electrolytic cell 50, the cathode gas-liquid separation tank 72, and the cathode chamber 5c. The temperature was adjusted to 90°C. In the electrolysis device, gas separated in the gas-liquid separation tank 72 is recovered via a pressure gauge 78, a pressure control valve 80, an oxygen concentration meter 75, or a hydrogen concentration meter 76. Power can be controlled by a rectifier 74. A flow meter 77 and a heat exchanger 79 are provided in the path of the circulating electrolyte. The arrows in Fig. 3 indicate the flow directions of the circulating fluid (electrolyte) and gas. The circulation flow path uses 20A SGP carbon steel piping with a Teflon (registered trademark) lining on the inner surface for the electrolyte contact part. The gas-liquid separation tank 72 has a height of 1400 mm and a volume of 1 m. ３ The gas-liquid separation tank 72 had a height of 1400 mm and a volume of 1 m ３The liquid volume of each gas-liquid separation tank 72 was set to approximately 50% of the design volume. In the external header type electrolytic cell, four external pipes (anode inlet header 10ai, cathode inlet header 10ci, anode outlet header 10ao, and cathode outlet header 10co) for circulating the electrolyte are provided in the electrolysis frame, which serves as the housing of the bipolar element. Each of these external pipes is connected to each electrode chamber of the electrolytic cell via an external hose. This piping structure is called the external header structure. The external header pipes are divided into a cathode side external header pipe and an anode side external header pipe. Therefore, within each element, the electrolyte enters the cathode chamber 5c from the cathode inlet header 10ci via the external hose, and then flows from the cathode chamber 5c to the cathode outlet header 10co via the external hose. Similarly, on the anode side, the electrolyte enters the anode chamber 5a from the anode inlet header 10ai via an external hose, and then flows from the anode chamber 5a to the anode outlet header 10ao via the external hose. Because the inlet header of the external header is located below the electrolysis frame and the outlet header is located above the electrolysis frame, the electrolyte flows from bottom to top. It also rises in a direction approximately perpendicular to the electrode surface. Each cell's external hose is equipped with a thermocouple, allowing the temperature difference before and after passing through the element to be measured. In this example, there are four anode chambers 5a and four cathode chambers 5c, and the electrolyte flows from the inlet header to the outlet header in each of the four chambers. Hydrogen gas is generated by electrolysis in the cathode chamber 5c, and oxygen gas is generated in the anode chamber 5a. This results in a mixed-phase flow of electrolyte and hydrogen gas in the cathode outlet header 10co, and a mixed-phase flow of electrolyte and oxygen gas in the anode outlet header 10ao. Electricity was applied from the rectifier 74 to the bipolar electrolytic cell 50 with respect to the areas of the cathode and anode under the conditions of Electrolysis Test 1 or Electrolysis Test 2 described below. The pressure inside the cell after the start of energization was measured with a pressure gauge 78 and adjusted so that the cathode side pressure was 50 kPa and the oxygen side pressure was 49 kPa. The pressure was adjusted using a control valve 80 installed downstream of the pressure gauge 78. In the electrolysis device, the gas separated in the gas-liquid separation tank 72 is recovered through the pressure gauge 78, the pressure control valve 80, and the oxygen concentration meter 75 or hydrogen concentration meter 76. Furthermore, the power can be controlled by the rectifier 74.The flow path of the circulating electrolyte was equipped with a flow meter 77 and a heat exchanger 79. The electrolysis apparatus for alkaline water electrolysis was prepared using a rectifier, an oxygen concentration meter, a hydrogen concentration meter, a pressure gauge, a liquid feed pump, a gas-liquid separation tank, a water supply device, and other devices commonly used in the relevant technical field. During hydrogen generation electrolysis using the above electrolysis apparatus, the potential of the zero-gap bipolar element was equal to the potential of the cathode. Furthermore, the PTFE-coated Pt wire fixed near the cathode in the cathode chamber of the zero-gap bipolar element became an RHE electrode by contacting hydrogen generated by electrolysis and was at a hydrogen generation potential. Therefore, the potential difference between the zero-gap bipolar element and the PTFE-coated Pt wire was measured, and this potential difference was defined as the cathode overvoltage. Using the above electrolysis apparatus, a current density of 6 kA / m was measured. ２ After 100 hours of continuous water electrolysis with positive current, the electrolysis was stopped for 5 minutes. ２ This cycle of 5 minutes of positive current and 5 minutes of stop was counted as one cycle of current on / off, and 1500 cycles of current on / off were performed. ２ The average value of the cell voltages of the two cells not including the anode terminal element (anode terminal cell) 51a and the cathode terminal element (cathode terminal cell) 51c during the first five minutes of positive current application after 100 hours of positive current application was taken as the initial cell voltage, and the average value of the cathode overvoltages of the two cells at this time was taken as the initial overvoltage. ２ The average value of the cathode overvoltages of the two cells described above under positive current application was taken as the post-test overvoltage. In this power-on / off cycle test, the initial overvoltage was 110 mV, and the post-test overvoltage was 112 mV, and the increase in overvoltage was suppressed to 10 mV or less, demonstrating high durability against 1,500 power-on / off cycles.

[0177] (Example 47) A nickel expand metal having 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 a nickel porous substrate. After blasting this nickel expand metal, a substrate measuring 10 cm in length and 10 cm in width was cut out, and the substrate was acid-treated in 6N hydrochloric acid at 50°C for 6 hours, washed with water, and dried to obtain a substrate for coating the anode of Example 47. Ni(NO ３ ) ２ ・6H ２ 465.2g of O, La(NO ３ ) ３ ・6H ２ 692.8 g of 0, 90.08 g of glycine, and 94.12 g of an aqueous solution of ammonium niobium oxalate with a Nb concentration of 0.34 mol / kg were mixed, and the suspension was dispersed using a T18 Digital Ultra Turrax homogenizer (equipped with an S18N-19G shaft generator) sold by IKA Japan Co., Ltd., to prepare the coating solution for the anode of Example 47. Using a spray coater (rCoater sold by Asahi Sunac Corporation), the coating solution of Example 47 was applied to both sides of the substrate, 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. The cycle of application, drying, and baking of the coating solution was repeated 20 times, and then baked at 700 ° C. for 1 hour, resulting in a deposition amount of 1005 g / m ２ A metal oxide layer of 1000 kJ / cm2 was formed on the anode of Example 47, thereby obtaining the anode of Example 47. A zero-gap bipolar element was produced in the same manner as in Example 10, except that the anode of Example 47 was used as the anode. (Power-off cycle test of bipolar electrolytic cell) As in Example 10, a bipolar electrolytic cell was produced using the zero-gap bipolar element of Example 47, and an electrolytic device was produced using the obtained bipolar electrolytic cell. Using the above electrolytic device, a current density of 6 kA / m2 was measured. ２ After 100 hours of continuous water electrolysis with positive current, the electrolysis was stopped for 5 minutes. ２ This cycle of 5 minutes of positive current and 5 minutes of stop was counted as one cycle of current on / off, and 1500 cycles of current on / off were performed. ２In this power-on / off cycle test, the initial overvoltage was 110 mV and the overvoltage after the test was 110 mV, and the increase in overvoltage was kept to 10 mV or less, demonstrating high durability against 1,500 power-on / off cycles.

[0178] The electrode of the present invention is unlikely to experience an increase in overvoltage even when the power supply is repeatedly turned on and off and hydrogen generation is repeatedly started and stopped, and therefore can be suitably used as a cathode for hydrogen generation that maintains high energy conversion efficiency over a long period of time.

[0179] REFERENCE SIGNS LIST 1 Partition wall 2 Electrode 2a Anode 2c Cathode 2e Elastic body 2r Current collector 3 Outer frame 4 Diaphragm 5 Electrode chamber 5a Anode chamber 5c Cathode chamber 5i Electrolyte inlet 5o Electrolyte outlet 6 Rib 7 Gasket 8 PFA coated Pt wire 9a Nozzle 9b Cap nut 9c PTFE plate 9d EPDM plate 10 Header 10o External header 10ai Anode inlet header 10ao Anode outlet header 10ci Cathode inlet header 10co Cathode outlet header 50 Bipolar electrolytic cell 51g Fast head, loose head 51i Insulating plate 51a Anode terminal element 51c Cathode terminal element 51r Tie rod 60 Bipolar element 65 Electrolytic cell 70 Electrolysis device 71 Liquid transfer pump 72 Gas-liquid separation tank 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 77 Flow meter 78 Pressure meter 79 Heat exchanger 80 Pressure control valve Z Zero gap structure

Claims

1. An electrode having a conductive substrate containing nickel and a catalyst layer containing platinum, wherein the electrode comprises a PtNi alloy, and the Ni atomic concentration on the surface of the electrode is 20% or less.

2. The electrode of claim 1, wherein metallic Pt is present on the surface of the electrode.

3. The electrode of claim 1 or 2, wherein the electrode comprises Pt crystals.

4. The electrode according to claim 1 or 2, wherein the catalyst layer is in contact with the conductive substrate.

5. The electrode according to claim 1 or 2, wherein the catalyst layer further contains one or more elements selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb.

6. The catalyst layer is Y ２ O ３ , La ２ O ３ , CeO ２ , Pr ２ O ３ , Nd ２ O ３ and NaNbO ３ The electrode according to claim 1 or 2, further comprising one or more selected from the group consisting of:

7. The electrode according to claim 1 or 2, wherein the catalyst layer further comprises one or more selected from the group consisting of W, Mo, Ag, Cu, Au, Pd, Bi, Ir, Ru, Co, P, Ti, and Zr.

8. The molar ratio M of M (where M represents Y, La, Ce, Pr, Nd, and Nb) to Pt in the catalyst layer Ｂ / Pt Ｂ The electrode according to claim 5 , wherein is 0.2 or more and 1 or less.

9. The molar ratio M of M (where M represents Y, La, Ce, Pr, Nd, and Nb) to Pt on the surface of the catalyst layer Ｓ / Pt Ｓ The electrode according to claim 5 , wherein is 0.5 or more and 40 or less.

10. The molar ratio M of M (where M represents Y, La, Ce, Pr, Nd, and Nb) to Pt in the catalyst layer Ｂ / Pt Ｂ The molar ratio M of M (M represents Y, La, Ce, Pr, Nd, and Nb) to Pt on the surface of the catalyst layer, Ｓ / Pt Ｓ The ratio (M Ｓ / Pt Ｓ ) / (M Ｂ / Pt Ｂ 6. The electrode according to claim 5, wherein the value of (a) is 1.5 or more and 100 or less.

11. A method for manufacturing an electrode, comprising: a coating step of coating a conductive substrate containing nickel with a coating liquid containing at least a Pt compound and one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb; a precursor layer formation step of drying the coating liquid to form a precursor layer containing Pt and one or more compounds selected from the group consisting of Y, La, Ce, Pr, Nd, and Nb on the conductive substrate; a firing step of heating the precursor layer in a temperature range of 300°C to 800°C to obtain an oxide layer; and a reduction step of reducing the conductive substrate having the oxide layer with hydrogen in a temperature range of 400°C to 700°C to obtain a catalyst layer.

12. The method for producing an electrode according to claim 11, wherein hydrogen diluted with an inert gas to a hydrogen concentration of 100 ppm to 1% is used in the reduction step.

13. The method for producing an electrode according to claim 11, wherein the reduction step is carried out using a furnace, and hydrogen is supplied into the reduced pressure furnace so that the hydrogen partial pressure is 1,333 Pa or less.

14. An electrolytic cell comprising, as a cathode, an electrode having a conductive substrate containing nickel and a catalytic layer containing platinum, the electrode comprising a PtNi alloy, and the Ni atomic concentration on the surface of the electrode being 20% ​​or less.

15. LaNi on the substrate ｘ M'' ｙ O ３－ｚ (x+y is 0.8 or more and 1.2 or less, y is 0.001 or more and 0.6 or less, z is −0.5 or more and 0.5 or less, and M″ contains at least one of Nb, Ta, Sb, Ti, Mn, and Zr) as an anode.

16. The electrolytic cell according to claim 14 or 15, wherein the electrolytic cell is a bipolar electrolytic cell.

17. An electrolytic cell for alkaline water electrolysis, comprising 3 to 200 electrolytic cells according to claim 16, at least one cathode terminal cell, and at least one anode terminal cell.

18. A method for producing hydrogen, comprising electrolyzing alkali-containing water using the alkaline water electrolysis cell according to claim 17 to produce hydrogen.

19. The method for producing hydrogen according to claim 18, wherein hydrogen is produced by electrolyzing water containing alkali using a variable power supply that involves repeating positive current application and cessation of positive current application.

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