Electrode, membrane electrode assembly, electrochemical cell, stack, and electrolytic device

Abstract

To provide an electrode with excellent durability.SOLUTION: An electrode of an embodiment comprises a base material, and a catalyst layer provided on the base material and alternately laminated with a sheet layer and a gap layer. The catalyst layer is for electrolysis, and includes one or more kinds of a first metal selected from a group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr and one or more kinds of a second metal selected from a group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn. The catalyst layer includes a first region and a second region. The first metal of the first region is more oxidized than the first metal of the second region. The ratio of the second metal included in the first region is smaller than the ratio of the second metal included in the second region.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the invention relate to electrodes, membrane electrode assemblies, electrochemical cells, stacks and electrolyzers. [Background technology]

[0002] In recent years, electrochemical cells have been actively researched. For example, polymer electrolyte membrane electrolysis cells (PEMEC) are expected to be used to generate hydrogen in large-scale energy storage systems. To ensure sufficient durability and electrolytic properties, platinum (Pt) nanoparticle catalysts are generally used in the cathode of PEMEC, and precious metal catalysts such as iridium (Ir) nanoparticle catalysts are generally used in the anode. Methods of obtaining hydrogen from ammonia are also being investigated. They can also be used as the anode of electrolysis devices that electrolyze carbon dioxide to produce organic compounds such as methanol and ethylene, and carbon monoxide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2018-519420 Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments provide highly durable electrodes. [Means for solving the problem]

[0005] The electrode of the embodiment includes a substrate and a catalyst layer provided on the substrate, the catalyst layer being formed by alternately stacking sheet layers and gap layers. The catalyst layer is for electrolysis, and includes one or more first metals selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, and one or more second metals selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, the catalyst layer includes a first region and a second region, the first metal in the first region is more oxidized than the first metal in the second region, and the ratio of the second metal contained in the first region is smaller than the ratio of the second metal contained in the second region. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a schematic diagram of an electrode according to an embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a catalyst layer according to an embodiment. [Diagram 3] FIG. 2 is a schematic diagram of an electrode according to an embodiment. [Figure 4] FIG. 2 is a schematic diagram of an electrode according to an embodiment. [Diagram 5] FIG. 2 is a schematic diagram of an electrode according to an embodiment. [Figure 6] 4 is an analysis spot of an embodiment. [Figure 7] 1 is a schematic diagram of a membrane electrode assembly according to an embodiment. [Figure 8] FIG. 1 is a schematic diagram of an electrochemical cell according to an embodiment. [Figure 9] FIG. 2 is a schematic diagram of a stack according to an embodiment. [Figure 10] FIG. 1 is a conceptual diagram of an electrolysis device according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same components will be given the same reference numerals, and the description of components that have already been described will be omitted as appropriate.

[0008] The physical properties in the specification are values ​​at a temperature of 25°C and a pressure of 1 atom. The thickness and composition ratio of each component are the average values ​​for the distance in the stacking direction.

[0009] (First embodiment) The first embodiment relates to an electrode. A schematic cross-sectional view of an electrode 100 according to the embodiment is shown in FIG.

[0010] In the embodiment, the catalyst layer 2 is used as a catalyst for electrolysis. The electrolysis reaction produces, for example, hydrogen from water or ammonia. The electrolysis reaction produces, for example, carbon monoxide from carbon dioxide. The catalyst layer 2 is also used as an anode catalyst in the electrolysis of ammonia.

[0011] The electrode 100 of the first embodiment is used, for example, as an anode for water electrolysis. When the catalyst layer 2 further contains a catalyst for a fuel cell, the electrode 100 of the embodiment is also used as an oxygen electrode of a fuel cell. The electrode 100 of the embodiment can also be used as an anode for electrolytically generating ammonia. The electrode 100 of the embodiment can be used as an anode for an electrolytic device for ammonia synthesis. In the following, the first embodiment and other embodiments will be described using water electrolysis as an example, but the electrode 100 of the embodiment can be used as an anode of a membrane electrode assembly used for electrolysis for ammonia synthesis in which ultrapure water is supplied to the anode, water is decomposed at the anode to generate protons and oxygen, the protons generated in the electrolyte membrane pass through the electrolyte membrane, and nitrogen supplied to the cathode is combined with the protons and electrons to generate ammonia. The electrode 100 of the embodiment can also be used as a cathode for electrolyzing ammonia to generate hydrogen. The electrode 100 of the embodiment can be used as a cathode for electrolyzing ammonia to generate hydrogen. The electrode 100 of the embodiment can be used as a cathode for a hydrogen generating device. In the following, the first embodiment and other embodiments will be described taking water electrolysis as an example. However, the electrode 100 of the embodiment can be used as the cathode of a membrane electrode assembly used in electrolysis for ammonia decomposition, in which ammonia is supplied to the cathode, the ammonia is decomposed at the cathode to generate protons and nitrogen, the generated protons pass through an electrolyte membrane, and the protons and electrons combine at the anode to generate hydrogen.

[0012] It is preferable to use a porous, highly conductive material as the substrate 1. The substrate 1 is a porous member that allows gas and liquid to pass through. Since the electrode 100 is also used as an anode of a water electrolysis cell, for example, it is preferable to use a titanium substrate as the substrate 1.

[0013] The substrate 1 is preferably a porous conductive member containing a valve metal. The valve metal of the substrate 1 is preferably Ti, which has high durability. The substrate 1 is preferably porous and contains Ti. The substrate 1 is not particularly limited as long as it is, for example, a porous titanium substrate. The substrate 1 preferably contains, for example, a cloth (nonwoven fabric) made of Ti mesh or Ti fibers. The substrate 1 may have a coating layer provided on a part of the surface of the valve metal such as Ti to improve the characteristics.

[0014] Considering the movement of materials, the porosity of the substrate 1 may be from 20% to 95%, and more preferably from 40% to 90%.

[0015] For example, when the base material 1 is a metal nonwoven fabric in which Ti fibers are entangled, the fiber diameter is preferably 1 μm or more and 500 μm or less, and more preferably 1 μm or more and 100 μm or less in consideration of reactivity and power supply. When the base material 1 is a particle sintered body, the particle diameter is preferably 1 μm or more and 500 μm or less, and more preferably 1 μm or more and 100 μm or less in consideration of reactivity and power supply.

[0016] The substrate 1 may be partially oxidized.

[0017] The catalyst layer 2 contains one or more first metals selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, and one or more second metals selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn. An intermediate layer (not shown) may be provided between the catalyst layer 2 and the substrate 1. A configuration in which the catalyst layer 2 and the substrate 1 are in direct contact with each other is preferred.

[0018] The first metal contained in the catalyst layer 2 is preferably contained as an oxide. The second metal contained in the catalyst layer 2 is preferably contained as an oxide.

[0019] The catalytic layer 2 contains an oxide of a first metal and an oxide of a second metal. The catalytic layer 2 may contain a composite oxide of the first metal and the second metal. The catalytic layer 2 may contain the first metal and / or the second metal as metals that are not oxides.

[0020] Of the metal elements contained in the oxide of the first metal, it is preferable that 80 at % or more and 100 at % or less is the first metal, and it is preferable that 90 at % or more and 100 at % or less is the first metal.

[0021] Of the metal elements contained in the oxide of the second metal, it is preferable that 80 at % or more and 100 at % or less is the second metal, and it is preferable that 90 at % or more and 100 at % or less is the second metal.

[0022] Of the metal elements contained in the composite oxide of the first metal and the second metal, it is preferable that the combined total of the first metal and the second metal be 80 at % or more and 100 at % or less, and it is preferable that the combined total of the first metal and the second metal be 90 at % or more and 100 at % or less.

[0023] The amount of the first metal in the catalyst layer 2 (the mass of the metal element including compounds such as oxides present per unit area) is 0.02 [mg / cm 2 ] or more 1.0[mg / cm 2 ] or less, and more preferably 0.05 [mg / cm 2 ] or more 0.5[mg / cm 2 The amount of the first metal is 0.02 [mg / cm 2 ] or more 1.0[mg / cm 2 ] or less, and more preferably 0.05 [mg / cm 2 ] or more 0.5[mg / cm 2This sum of masses can be measured by ICP-MS.

[0024] The overall porosity of the catalyst layer 2 is preferably 10% or more and 90% or less, and more preferably 30% or more and 70% or less.

[0025] The catalyst layer 2 has a structure in which sheet layers 2A and gap layers 2B are alternately laminated. The laminated structure of the catalyst layer 2 is shown in the schematic cross-sectional view of the catalyst layer 2 in Fig. 2. The sheet layers 2A and the gap layers 2B are laminated substantially parallel to each other. Most of the gap layers 2B are hollow, but some of the sheet layers 2A protrude and connect the sheet layers 2A. The sheet layers 2A are connected by pillars 2C present in the gap layers 2B, and the laminated structure is maintained.

[0026] It is preferable that each sheet layer 2A is directly connected to the adjacent gap layer 2B. It is preferable that only one gap layer 2B exists between all the sheet layers 2A.

[0027] The sheet layer 2A is a layer in which catalyst particles, which are unsupported oxide particles aggregated into a sheet shape, are arranged. There are some voids in the sheet layer 2A. The sheet layer 2A is a dense layer containing a large amount of catalyst particles.

[0028] The gap layer 2B is a region sandwiched between the sheet layers 2A and contains catalyst particles, which are unsupported oxide particles. Unlike the sheet layers 2A, the gap layer 2B does not have a regular structure of catalyst particles. The gap layer 2B is a region with a low density of catalyst particles.

[0029] The average thickness of one layer of the sheet layer 2A is preferably 6 nm or more and 50 nm or less. The average thickness of one layer of the gap layer 2B is preferably 6 nm or more and 50 nm or less. The average thickness of one layer of the sheet layer 2A is preferably thicker than the average thickness of one layer of the gap layer 2B. Some gap layers 2B may be thicker than some sheet layers 2A.

[0030] The catalyst layer 2 contains, as an oxide of the first metal, an oxide containing one selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, or / and a composite oxide containing two or more selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr. The oxide containing one selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr is an oxide of one selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, and / or a composite oxide containing a metal element (excluding oxygen) other than the first metal in addition to the one selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr. The composite oxide containing two or more elements selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr is an oxide of two or more elements selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, and / or a composite oxide containing two or more elements selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr as well as a metal element (excluding oxygen) other than the first metal.

[0031] The catalyst layer 2 preferably contains Ir as the first metal. The catalyst layer 2 preferably contains an oxide containing Ir as the oxide of the first metal.

[0032] The catalytic layer 2 preferably contains an oxide containing Ir as the oxide of the first metal, and more preferably contains an oxide containing Ru. The sum of the concentrations of Ir and Ru among the precious metals contained in the catalytic layer 2 is preferably 90 wt% or more and 100 wt% or less. The precious metals contained in the precious metal oxide of the catalytic layer 2 are not limited to Ir and Ru.

[0033] The catalyst layer 2 preferably contains, as the oxide of the second metal, an oxide containing one selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, or an oxide containing two or more selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn. The oxide containing one selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn is an oxide containing one selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, or / and one selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, and a metal element other than the second metal. The oxide containing two or more selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn is an oxide containing two or more selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, or / and two or more selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, and a metal element other than the second metal.

[0034] The catalytic layer 2 preferably contains an oxide containing the second metal Ni. The second metal contained in the catalytic layer 2 preferably contains Ni and, optionally, Co and / or Mn. When the amount of non-precious metals contained in the catalytic layer 2 (the total mass of metal elements present as compounds such as oxides or in a metallic state) is taken as 100 [wt%], the total ratio of Ni, Co and Mn (the total mass of Ni, Co and Mn elements present as compounds such as oxides or in a metallic state relative to the total mass of metal elements present as compounds such as oxides or in a metallic state) among the non-precious metals contained in the catalytic layer 2 is preferably 80 [wt%] or more and 100 [wt%] or less. When the catalytic layer 2 contains Ni, the ratio of Ni contained in the first region 2D is preferably higher than the ratio of Ni contained in the second region 2E.

[0035] The catalyst layer 2 may contain a second metal in a metallic state.

[0036] The catalyst layer 2 includes a first region 2D and a second region 2E. The first metal in the first region 2D is preferably more oxidized than the first metal in the second region 2E. The ratio [at%] of the second metal contained in the first region 2D ([the number of atoms of the second metal contained in the first region 2D including compounds such as oxides] / [the number of atoms of all metals contained in the first region 2D including compounds such as oxides]) is preferably greater than the ratio [at%] of the second metal contained in the second region 2E ([the number of atoms of the second metal contained in the second region 2E including compounds such as oxides] / [the number of atoms of all metals contained in the second region 2E including compounds such as oxides]).

[0037] The distribution of the first region 2D and the second region 2E is obtained, for example, by XPS (X-ray photoelectron spectroscopy) or HAXPES (hard X-ray photoelectron spectroscopy) from the oxidation state of the first metal and the relative ratio of the second metal in the catalyst layer 2. Whether the first metal in the first region 2D is more oxidized than the first metal in the second region 2E is determined, for example, by analyzing the oxidation state of the first metal in the catalyst layer 2 by XPS (X-ray photoelectron spectroscopy) or HAXPES (hard X-ray photoelectron spectroscopy).

[0038] The first region 2D has lower activity than the second region 2E, but the first metal is less likely to dissolve and has excellent durability. The second region 2E has lower durability than the first region 2D, but has high activity. In order to obtain high activity and high durability of the catalyst layer 2, the catalyst layer 2 includes the first region 2D and the second region 2E, the first metal in the first region 2D is more oxidized than the first metal in the second region 2E, and the ratio of the second metal contained in the first region 2D is greater than the ratio [at %] of the second metal contained in the second region 2E.

[0039] The second metal in the first region 2D is preferably more oxidized than the second metal in the second region 2E. Whether the second metal in the first region 2D is more oxidized than the second metal in the second region 2E is determined by analyzing the oxidation state of the second metal in the catalyst layer 2 by, for example, XPS (X-ray photoelectron spectroscopy) or HAXPES (hard X-ray photoelectron spectroscopy).

[0040] It is preferable that both the first region 2D and the second region 2E are layered regions. It is preferable that the layered first region 2D and the layered second region 2E are alternately laminated. It is preferable that the layered first region 2D and the layered second region 2E are laminated in the lamination direction of the sheet layer 2A and the gap layer 2B of the catalyst layer 2. It is sufficient that the lamination direction of the layered first region 2D and the layered second region 2E generally coincides with the lamination direction of the sheet layer 2A and the gap layer 2B of the catalyst layer 2.

[0041] From the viewpoint of improving durability, it is preferable that the first region 2D is present on the surface of the catalyst layer 2 opposite to the substrate 1 side. The presence of the first region 2D on the surface of the catalyst layer 2 opposite to the substrate 1 side can suppress elution of the first metal having high electrocatalytic activity. The first metal is likely to be eluted from the surface of the catalyst layer 2 opposite to the substrate 1 side. When the first region 2D present on the surface of the catalyst layer 2 opposite to the substrate 1 side is layered, elution of the first metal of the catalyst layer 2 can be more effectively suppressed.

[0042] From the viewpoint of improving durability, it is preferable that the first region 2D is not exposed on the surface of the catalyst layer 2 opposite to the substrate 1 side.

[0043] 3 to 5 show schematic cross-sectional views of electrodes 101-103 of the first embodiment. The electrodes 101-103 are modified examples of the electrode 100. The modified examples of the electrode 100 are not limited to the electrodes 101-103.

[0044] Electrode 101 shown in the schematic cross-sectional view of Fig. 3 includes two layer-like first regions 2D and one layer-like second region 2E. From the viewpoint of improving durability, electrode 101 preferably has second region 2E sandwiched between first regions 2D.

[0045] 4 includes two layered first regions 2D and two layered second regions 2E. The first regions 2D and the second regions 2E of the electrode 102 are alternately stacked. From the viewpoint of improving durability, it is preferable that the second regions 2E of the electrode 102 are sandwiched between the first regions 2D.

[0046] 5 includes three layered first regions 2D and two layered second regions 2E. The first regions 2D and the second regions 2E of the electrode 102 are alternately stacked. From the viewpoint of improving durability, it is preferable that the electrode 103 has the second regions 2E sandwiched between the first regions 2D.

[0047] From the viewpoint of durability and catalytic activity, the average thickness of the first laminar region 2D is preferably thinner than the average thickness of the second laminar region 2E. If the thickness of the first laminar region 2D is thicker than the thickness of the second laminar region 2E, the durability is high but the electrolytic properties are likely to deteriorate. The average thickness of the first laminar region 2D is preferably 5% or more and 90% or less of the average thickness of the second laminar region 2E.

[0048] The average thickness of the layered first region 2D is the average value of the thicknesses of the layered first region 2D. The average thickness of the layered second region 2E is the average value of the thicknesses of the layered second region 2E.

[0049] The difference in thickness between the first layer region 2D and the second layer region 2E is due to, for example, a difference in the number of repetitions of the sheet layer 2A and the gap layer 2B, and / or a difference in the thickness of the sheet layer 2A and / or the thickness of the gap layer 2B.

[0050] The average thickness of the first layer region 2D and the average thickness of the second layer region 2E are determined by XPS (X-ray photoelectron spectroscopy) or HAXPES (hard X-ray photoelectron spectroscopy) from the oxidation state of the first metal and the relative ratio of the second metal in the catalyst layer 2. For example, the central portion of the electrode 100 is analyzed to determine the average thickness of the first layer region 2D and the average thickness of the second layer region 2E.

[0051] From the viewpoint of durability, the porosity of the laminar first region 2D is preferably lower than the porosity of the laminar second region 2E. The relatively high porosity of the first region 2D preferably improves the durability of the electrode 100. The porosity of the laminar first region 2D is preferably 40% or more and 80% or less of the porosity of the laminar second region 2E (when the porosity of the laminar second region 2E is X%, the porosity of the laminar first region 2D is preferably 0.4X% or more and 0.8X% or less).

[0052] The first region 2D and the second region 2E preferably contain Ni. The ratio [at %] of Ni contained in the first region 2D is preferably higher than the ratio [at %] of Ni contained in the second region 2E.

[0053] The first region 2D has a structure in which sheet layers 2A and gap layers 2B are alternately laminated. The sheet layers 2A of the first region 2D and the gap layers 2B of the first region 2D are laminated side by side and approximately parallel to each other. The gap layers 2B of the first region 2D are mostly hollow, but some of the sheet layers 2A protrude and connect to each other. The sheet layers 2A of the first region 2D are connected by the columns 2C of the first region 2D that exist in the gap layers 2B of the first region 2D, and the laminated structure is maintained.

[0054] The second region 2E has a structure in which sheet layers 2A and gap layers 2B are alternately laminated. The sheet layers 2A in the second region 2E and the gap layers 2B in the first region 2D are laminated side by side and approximately parallel to each other. The gap layers 2B in the second region 2E are mostly hollow, but some of the sheet layers 2A protrude and connect to each other. The sheet layers 2A in the second region 2E are connected by the columns 2C of the second region 2E present in the gap layers 2B in the second region 2E, and the laminated structure is maintained.

[0055] It is preferable that the sheet layer 2A of the first layered region 2D is directly connected to the gap layer 2B of the second layered region 2E, or that the gap layer 2B of the first layered region 2D is directly connected to the sheet layer 2A of the second region 2E.

[0056] The layered first region 2D preferably includes two or more sheet layers 2 A. The layered first region 2D preferably includes 2 to 50 sheet layers 2A.

[0057] The layered second region 2E preferably includes two or more sheet layers 2 A. The layered second region 2E preferably includes 2 to 50 sheet layers 2A.

[0058] It is preferable that the composition ratio of the first metal be similar in the first region 2D and the second region 2E. It is preferable that the elements of the first metal contained in the first region 2D are the same as the elements of the first metal contained in the second region 2E.

[0059] It is preferable that the composition ratio of the second metal be similar in the first region 2D and the second region 2E. It is preferable that the elements of the second metal contained in the first region 2D are the same as the elements of the second metal contained in the second region 2E.

[0060] A transition region may be included between the first region 2D and the second region 2E. The transition region is a region that does not satisfy the conditions of the first region 2D and the second region 2E. The thickness of the transition region is preferably 0 nm or more and 100 nm or less. The thickness of the transition region is preferably less than one tenth of the thickness of the first region 2D and less than one tenth of the thickness of the second region 2E.

[0061] When a transition region is included between the first region 2D and the second region 2E, it is preferable that the first region 2D and the second region 2E are connected via the transition region (one surface of the transition region is in direct contact with the first region 2D, and the surface opposite to the one surface of the transition region is in direct contact with the second region 2E). When the thickness of the transition region is less than one tenth of the thickness of the first region 2D and less than one tenth of the thickness of the second region 2E, the state in which the first region 2D and the second region 2E are connected via the transition region can be regarded as the state in which the first region 2D and the second region 2E are directly connected.

[0062] The distribution of the transition region can be determined from the oxidation state of the first metal and the relative proportion of the second metal in the catalyst layer 2, for example by XPS (X-ray Photoelectron Spectroscopy) or HAXPES (Hard X-ray Photoelectron Spectroscopy).

[0063] A number of spots can be analyzed to determine the sheet layer 2A and the gap layer 2B. Each spot is square and at least 1 mm 2As shown in FIG. 6, when the length of the electrode 100 is D1 and the width of the electrode 100 is D2 (D1≧D2), imaginary lines are drawn from two opposing sides of the electrode 100 in the width direction at a distance of D3 (=D1 / 10) inward, and from two opposing sides of the electrode 100 in the length direction at a distance of D4 (=D2 / 10) inward. Furthermore, imaginary lines parallel to the width direction passing through the center of the electrode 100 are drawn, and imaginary lines parallel to the length direction passing through the center of the electrode 100 are drawn. The analysis spots A1 to A9 are areas centered on nine intersections of the imaginary lines. The cross section observed by SEM is perpendicular to the plane of FIG. 3 and parallel to the width direction. The thickness of each gap layer 2B of the analysis spots A1 to A9 is obtained at 50 [nm] intervals in the width direction of the SEM image. Then, the ratio of the gap layer 2B thickness less than 2 [nm] is obtained. The average thicknesses of the gap layer 2B and the sheet layer 2A are obtained in the same manner. A similar analysis using a similar SEM-EDX can be performed to observe the cross section of the substrate 1. By observing the cross section of the substrate 1, the thickness of the oxide film of the substrate 1 and the composition of the substrate 1 can be obtained.

[0064] The catalyst layer 2 is formed by alternately sputtering a sheet layer precursor that is substantially a precursor of the sheet layer 2A and contains an oxide of a first metal and a gap layer precursor that is substantially a precursor of the gap layer 2B and mainly contains an oxide of a second metal on the substrate 1. At this time, the sheet layer precursor and the gap layer precursor are formed in an oxidizing atmosphere. When forming the sheet layer precursor and the gap layer precursor in an oxidizing atmosphere, for example, the layered first region 2D and the layered second region 2E can be made separately by changing the oxygen concentration. The oxide of the second metal is dissolved by an acid treatment such as sulfuric acid. After dissolving the oxide of the second metal, it is preferable to perform a heat treatment in an oxidizing atmosphere. After the heat treatment, an electrode 100 is obtained in which an oxide film of a suitable thickness is provided on the surface of the substrate 1. The heat treatment in an oxidizing atmosphere improves the adhesion between the catalyst layer 2 and the substrate 1.

[0065] The portion where the sheet layer precursor and the gap layer precursor are alternately formed under conditions of high oxygen concentration is the precursor of the first region 2D. The portion where the sheet layer precursor and the gap layer precursor are alternately formed under conditions of low oxygen concentration is the precursor of the first region 2D.

[0066] An example will be described in which the second region 2E and the first region 2D are alternately arranged from the substrate 1 side in an oxidizing atmosphere, and the first region 2D exists on the surface of the catalyst layer 2 opposite to the substrate 1 side. When the oxygen concentration for forming the precursor of the sheet layer 2A of the precursor of the first region 2D is X1 and the oxygen concentration for forming the precursor of the gap layer 2B of the precursor of the first region 2D is Y1, the oxygen concentration for forming the precursor of the sheet layer 2A of the second region 2E is preferably 0.2 to 0.8 times X1, and the oxygen concentration for forming the precursor of the gap layer 2B of the second region 2E is preferably 0.2 to 0.8 times Y1.

[0067] An example will be described in which the first region 2D and the second region 2E are alternately arranged from the substrate 1 side in an oxidizing atmosphere, and the first region 2D exists on the surface of the catalyst layer 2 opposite to the substrate 1 side. When the oxygen concentration for forming the precursor of the sheet layer 2A of the precursor of the first region 2D is X1 and the oxygen concentration for forming the precursor of the gap layer 2B of the precursor of the first region 2D is Y1, the oxygen concentration for forming the precursor of the sheet layer 2A of the second region 2E is preferably 0.2 to 0.8 times X1, and the oxygen concentration for forming the precursor of the gap layer 2B of the second region 2E is preferably 0.2 to 0.8 times Y1.

[0068] Second embodiment The second embodiment relates to a membrane electrode assembly (MEA). Fig. 7 shows a schematic diagram of a membrane electrode assembly 200 of the embodiment. The membrane electrode assembly 200 has a first electrode 11, a second electrode 12, and an electrolyte membrane 13. The first electrode 11 is preferably an anode electrode, and the second electrode 12 is preferably a cathode electrode. The electrodes 100 to 103 of the first embodiment are preferably used for the first electrode 11. The membrane electrode assembly 200 of the embodiment is preferably used in an electrochemical cell or stack that generates hydrogen or oxygen.

[0069] It is preferable to use the electrodes 100 to 103 of the first embodiment as the first electrode 11. The catalyst layer 2 of the electrode 100 used as the first electrode 11 is provided on the electrolyte membrane 13 side. It is preferable that the catalyst layer 2 is in direct contact with the electrolyte membrane 13. It is preferable that the first region 2D of the catalyst layer 2 is in direct contact with the electrolyte membrane 13.

[0070] The second electrode 12 has a second substrate 12B and a second catalyst layer 12A. The second catalyst layer 12A is provided on the second substrate 12B. The second catalyst layer 12A is provided on the electrolyte membrane 13 side. The second catalyst layer 12A is preferably in direct contact with the electrolyte membrane 13.

[0071] The second substrate 12B is preferably made of a porous material having high conductivity. The second substrate 12B is a porous member that allows gas and liquid to pass through. The second substrate 12B is, for example, carbon paper or a metal mesh. As the metal mesh, a porous substrate made of a valve metal is preferable. As the porous substrate made of a valve metal, a porous substrate containing one or more metals selected from the group consisting of titanium, aluminum, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony, or a porous substrate made of one metal selected from the group consisting of titanium, aluminum, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony is preferable. The second substrate 12B has a carbon layer (MPL layer) containing carbon fine particles and a water-repellent resin (fluororesin such as PTFE or Nafion). The carbon layer is provided, for example, between the carbon paper and the second catalyst layer 12A.

[0072] The second catalytic layer 12A has a catalytic metal. The second catalytic layer 12A is preferably a catalytic metal particle, and the catalytic metal is not supported on a carrier. The second catalytic layer 12A is preferably a porous catalytic layer. The catalytic metal is not particularly limited, but includes, for example, one or more selected from the group consisting of Pt, Rh, Os, Ir, Pd, and Au. It is preferable to include one or more selected from the group consisting of such catalytic materials. The catalytic metal is preferably a metal, an alloy, or a metal oxide. The second catalytic layer 12A preferably has a plurality of catalytic units in which, for example, sheet-like catalytic layers and gap layers are alternately laminated.

[0073] The amount of metal per area of ​​the second catalyst layer 12A is 0.02 [mg / cm 2 ] or more 1.0[mg / cm 2 ] or less, and more preferably 0.05 [mg / cm 2 ] or more 0.5[mg / cm 2 This sum of masses can be measured by ICP-MS.

[0074] The porosity of the second catalyst layer 12A is preferably 10% or more and 90% or less, and more preferably 30% or more and 70% or less.

[0075] The electrolyte membrane 13 is preferably a proton conductive membrane. The electrolyte membrane 13 is preferably a fluorine-based polymer or an aromatic hydrocarbon-based polymer having one or more selected from the group consisting of a sulfonic acid group, a sulfonimide group, and a sulfate group. The electrolyte membrane 13 is preferably a fluorine-based polymer having a sulfonic acid group. Examples of the fluorine-based polymer having a sulfonic acid group that can be used include Nafion (trademark, manufactured by DuPont), Flemion (trademark, manufactured by Asahi Kasei), Selemion (trademark, manufactured by Asahi Kasei), Aquivion (trademark; Solvay Specialty Polymers), and Aciplex (trademark, manufactured by Asahi Glass). Note that instead of the proton conductive membrane, various conductive membranes such as anion exchange membranes and porous membranes can be used in some cases.

[0076] The thickness of the electrolyte membrane 13 can be appropriately determined in consideration of the membrane's properties such as permeability and durability. From the viewpoints of strength, dissolution resistance, and output properties of the MEA 200, the thickness of the electrolyte membrane 13 is preferably 20 μm or more and 500 μm or less, more preferably 50 μm or more and 300 μm or less, and even more preferably 80 μm or more and 200 μm or less.

[0077] The electrolyte membrane 13 preferably includes a precious metal region on the first electrode 11 side. The precious metal region includes precious metal particles. The precious metal region is preferably present on the surface of the electrolyte membrane 13. The precious metal region is preferably composed of one region, but may be composed of multiple separate regions.

[0078] The precious metal particles are preferably particles of one or more precious metals selected from the group consisting of Pt, Re, Rh, Ir, Pd, and Ru. The precious metal particles may include alloy particles containing one or more selected from the group consisting of Pt, Re, Rh, Ir, Pd, and Ru. The precious metal particles are preferably particles of one precious metal selected from the group consisting of Pt, Re, Rh, Ir, Pd, and Ru. The precious metal particles are preferably Pt particles. The precious metal particles are preferably Re particles. The precious metal particles are preferably Rh particles. The precious metal particles are preferably Ir particles. The precious metal particles are preferably Pd particles. The precious metal particles are preferably Ru particles.

[0079] The precious metal particles oxidize hydrogen that is generated on the cathode side and passes through the electrolyte membrane 13. The precious metal particles can suppress hydrogen leakage. Because the precious metal particles are present on the anode side, they do not easily oxidize hydrogen discharged from the cathode side. The region where the precious metal particles are present may also be present in the electrolyte membrane 13 on the second electrode 12 (cathode) side.

[0080] The average circumscribed circle diameter of the precious metal particles is preferably 0.5 nm or more and 50 nm or less, more preferably 1 nm or more and 10 nm or less, and even more preferably 1 nm or more and 5 nm or less.

[0081] By using the highly durable electrodes 100 to 103 as the anode of the membrane electrode assembly 200, long-term operation with high activity becomes possible.

[0082] Third embodiment The third embodiment relates to an electrochemical cell. Fig. 8 shows a cross-sectional view of an electrochemical cell 300 according to the second embodiment. The electrochemical cell 300 will be described below using water electrolysis as an example, but hydrogen can also be generated by decomposing ammonia or the like other than water.

[0083] 8, an electrochemical cell 300 of the second embodiment includes a first electrode (anode) 11, a second electrode (cathode) 12, an electrolyte membrane 13, a gasket 21, a gasket 22, a separator 23, and a separator 24. A sealing material for the first electrode 11 may be used as the gasket 21. A sealing material for the second electrode 12 may be used as the gasket 22.

[0084] It is preferable to use a membrane electrode assembly 200 in which a first electrode (anode) 11, a second electrode (card) 12, and an electrolyte membrane 13 are joined together. An anode power supply may be provided separately from the separator 23. A cathode power supply may be provided separately from the separator 24.

[0085] In the electrochemical cell 300 of FIG. 8, a power source (not shown) is connected to the separator 23 and the separator 24, and a reaction occurs at the anode 11 and the cathode 12. For example, water is supplied to the anode 11, and the water is decomposed into protons, oxygen, and electrons at the anode 11. The electrode support and the power supply are porous, and this porous body functions as a flow path plate. The generated water and unreacted water are discharged, and the protons and electrons are used in the cathode reaction. In the cathode reaction, the protons and electrons react to generate hydrogen. Either or both of the generated hydrogen and oxygen are used, for example, as fuel for the fuel cell.

[0086] (Fourth embodiment) The fourth embodiment relates to a stack. Fig. 9 is a schematic cross-sectional view showing a stack 400 of the fourth embodiment. The stack 400 of the third embodiment shown in Fig. 9 has a plurality of MEAs 200 or electrochemical cells 300 connected in series. Clamping plates 31 and 32 are attached to both ends of the MEA 200 or the electrochemical cell 300.

[0087] Since the amount of hydrogen produced in an electrochemical cell 300 consisting of one MEA 200 is small, a large amount of hydrogen can be obtained by forming a stack 400 in which a plurality of MEAs 200 or a plurality of electrochemical cells 300 are connected in series.

[0088] Fifth embodiment The fifth embodiment relates to an electrolysis device. Fig. 10 shows a conceptual diagram of an electrolysis device 500 of the fifth embodiment. The electrolysis device 500 uses an electrochemical cell 300 or a stack 400. The electrolysis device 500 in Fig. 10 is for water electrolysis. The electrolysis device 500 for water electrolysis will be described. For example, when hydrogen is generated from ammonia, it is preferable to adopt a device with a different configuration using the electrode 100. The electrodes of the embodiment can also be used in an electrolysis device that electrolyzes carbon dioxide to generate organic substances such as methanol and ethylene, and carbon monoxide.

[0089] As shown in FIG. 10, a stack 400 is formed by stacking unit cells for water electrolysis in series. A power source 41 is attached to the stack 400, and a voltage is applied between the anode 12 and the cathode 11. A gas-liquid separator 42 for separating generated gas from unreacted water and a mixing tank 43 are connected to the anode 11 side of the stack 400. Water is sent from an ion-exchanged water production device 44, which supplies water, to the mixing tank 43 by a pump 46, and the water is mixed in the mixing tank 43 through a check valve 47 from the gas-liquid separator 42 and circulated to the anode 11. Oxygen generated at the anode 11 passes through the gas-liquid separator 42 to obtain oxygen gas. On the other hand, a hydrogen purifier 49 is connected to the gas-liquid separator 48 on the cathode 12 side to obtain high-purity hydrogen. Impurities are discharged through a path having a valve 50 connected to the hydrogen purifier 49. In order to stably control the operating temperature, it is possible to control the heating of the stack 400 and the mixing tank 43, the current density during pyrolysis, and the like.

[0090] In the specification, some elements are represented only by their element symbols.

[0091] The technical solutions of the embodiments are described below. Technical proposal 1 A substrate; a catalyst layer provided on the substrate, the catalyst layer being formed by alternately laminating sheet layers and gap layers; having The catalyst layer is for electrolysis, The catalyst layer contains one or more first metals selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, and one or more second metals selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, The catalyst layer includes a first region (high durability) and a second region (high activity), the first metal in the first region is more oxidized than the first metal in the second region; An electrode in which the ratio of the second metal contained in the first region is smaller than the ratio of the second metal contained in the second region. Technical proposal 2 The first region is layered, The second region is layered, The electrode according to Technical Scheme 1, in which the layered first region and the layered second region are laminated in the lamination direction of the sheet layer and the gap layer. Technical proposal 3 The electrode according to Technical Solution 1 or 2, wherein the first region is present on the surface of the catalyst layer opposite the substrate side. Technical proposal 4 The first region is layered, The second region is layered, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, The laminar first region is included in two or more of the catalyst layers, An electrode described in any one of technical proposals 1 to 3, wherein the layered second region is present between the two or more layered first regions. Technical proposal 5 The first region is layered, The second region is layered, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, An electrode according to any one of technical proposals 1 to 4, wherein the average thickness of the first layer region is thinner than the average thickness of the second layer region. Technical proposal 6 The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers; An electrode according to any one of technical proposals 1 to 5, wherein the layered first region and the layered second region are laminated in the lamination direction of the sheet layer and the gap layer. Technical proposal 7 The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers; the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, An electrode described in any one of technical proposals 1 to 6, wherein the layered first region is in direct contact with the layered second region. Technical proposal 8 The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers; the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, An electrode described in any one of technical proposals 1 to 7, wherein the sheet layer of the first layered region is directly connected to the gap layer of the second layered region, or the gap layer of the first layered region is directly connected to the sheet layer of the second region. Technical proposal 9 The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers; The first layer region and the second layer region contain Ni as the second metal, An electrode described in any one of technical proposals 1 to 8, wherein the Ni ratio contained in the first region is higher than the Ni ratio contained in the second region. Technical proposal 10 The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers; 10. The electrode according to any one of technical proposals 1 to 9, wherein the porosity of the first layer region is lower than the porosity of the second layer region. Technical proposal 11 The first region is layered, The second region is layered, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, The laminar first region is included in two or more of the catalyst layers, the laminar second region is present between the two or more laminar first regions, the average thickness of the first laminar region is less than the average thickness of the second laminar region; the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, the first layer region is in direct contact with the second layer region; The first layer region and the second layer region contain Ni as the second metal, a ratio of Ni contained in the first region is higher than a ratio of Ni contained in the second region, 11. The electrode according to any one of Technical Schemes 1 to 10, wherein the porosity of the first layer region is lower than the porosity of the second layer region. Technical proposal 12 An electrode according to any one of technical proposals 1 to 11; An electrolyte membrane is provided, The electrolyte membrane is a membrane electrode assembly that is in direct contact with the first region. Technical proposal 13 An electrochemical cell using the membrane electrode assembly described in Technical Proposal 12. Technical proposal 14 A stack using the membrane electrode assembly described in Technical Proposal 12. Technical proposal 15 An electrolysis device using the stack described in Technical Proposal 14.

[0092] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. Although a PEMEC has been described as a water electrolysis cell, the present invention can be similarly applied to other electrolysis cells. These novel embodiments described above can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included within the scope and spirit of the invention, and are included in the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0093] 1 Base material 2 Catalyst layer 2A Sheet layer 2B Gap layer 2C columnar body 2D 1st area 2E 2nd area 11 1st electrode 12 2nd electrode 13 Electrolyte membrane 21 Gasket 22 Gasket 23 Separator 24 Separator 31 Clamping plate 32 Clamping plate 41 Power supply 42 Gas-liquid separation equipment 43 Mixing Tank 44 Ion exchange water production equipment 46 Pump 47 Check valve 48 Gas-liquid separation equipment 49 Hydrogen purification equipment 50 valves 100 electrodes 101 Electrode 102 electrode 103 Electrode 200 Membrane electrode assembly 300 Electrochemical Cells 400 Stack 500 Electrolyzer

Claims

1. A substrate; a catalyst layer provided on the substrate, the catalyst layer being formed by alternately laminating sheet layers and gap layers; having The catalyst layer is for electrolysis, The catalyst layer contains one or more first metals selected from the group consisting of Ir, Ru, Pt, Pd, Hf, V, Au, Ta, W, Nb, Zr, Mo, and Cr, and one or more second metals selected from the group consisting of Ni, Co, Mn, Fe, Cu, Al, and Zn, The catalyst layer includes a first region (high durability) and a second region (high activity), the first metal in the first region is more oxidized than the first metal in the second region; An electrode in which the ratio of the second metal contained in the first region is smaller than the ratio of the second metal contained in the second region.

2. The first region is layered, The second region is layered, 2. The electrode according to claim 1, wherein the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer.

3. The electrode according to claim 1 , wherein the first region is present on a surface of the catalyst layer opposite to the substrate side.

4. The first region is layered, The second region is layered, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, The laminar first region is included in two or more of the catalyst layer, The electrode of claim 1 , wherein the layered second region is present between two or more of the layered first regions.

5. The first region is layered, The second region is layered, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, 2. The electrode of claim 1, wherein the average thickness of the first layer region is less than the average thickness of the second layer region.

6. The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers, The electrode according to claim 1 , wherein the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer.

7. The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, The electrode of claim 1 , wherein the first layer region is in direct contact with the second layer region.

8. The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, The electrode of claim 1 , wherein the sheet layer of the first layered region is directly connected to the gap layer of the second layered region, or the gap layer of the first layered region is directly connected to the sheet layer of the second region.

9. The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers, The first layer region and the second layer region contain Ni as the second metal, The electrode according to claim 1 , wherein a ratio of Ni contained in the first region is higher than a ratio of Ni contained in the second region.

10. The first region is layered, The second region is layered, the first layered region and the second layered region include a plurality of the sheet layers and a plurality of the gap layers, The electrode of claim 1 , wherein the porosity of the first layer region is lower than the porosity of the second layer region.

11. The first region is layered, The second region is layered, the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, The laminar first region is included in two or more of the catalyst layer, the layered second region is present between the two or more layered first regions, the average thickness of the first layer region is less than the average thickness of the second layer region; the first layered region and the second layered region are laminated in a lamination direction of the sheet layer and the gap layer, the first layer region is in direct contact with the second layer region; The first layer region and the second layer region contain Ni as the second metal, The ratio of Ni contained in the first region is higher than the ratio of Ni contained in the second region, The electrode of claim 1 , wherein the first layer region has a lower porosity than the second layer region.

12. An electrode according to any one of claims 1 to 11; An electrolyte membrane is provided, The electrolyte membrane is a membrane electrode assembly that is in direct contact with the first region.

13. An electrochemical cell using the membrane electrode assembly according to claim 12.

14. A stack using the membrane electrode assembly according to claim 12.

15. An electrolysis device using the stack according to claim 14.

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