Electrodes, membrane electrode assemblies, electrochemical cells, stacks, electrolyzers

Abstract

Embodiments provide electrodes that are highly durable. [Solution] An electrode according to an embodiment includes a substrate and a catalyst layer formed on the substrate, in which sheet layers and gap layers are alternately laminated. The gap layer includes a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb.

Description

[Technical Field]

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

[0002] Electrochemical cells have been the subject of intensive research in recent years. 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 typically used in the cathode of PEMEC, and precious metal catalysts such as iridium (Ir) nanoparticle catalysts are typically used in the anode. Methods for 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, as well as carbon monoxide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-167620 Summary of the Invention [Problem to be solved by the invention]

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

[0005] The electrode of the embodiment includes a substrate and a catalyst layer formed on the substrate, the catalyst layer being composed of alternately stacked sheet layers and gap layers. The gap layer includes a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb. [Brief explanation of the drawings]

[0006] [Figure 1] Schematic diagram of an electrode according to an embodiment. [Figure 2] FIG. 2 is a partial schematic cross-sectional view of an electrode according to an embodiment. [Figure 3] FIG. 2 is a partial schematic cross-sectional view of an electrode according to an embodiment. [Figure 4] Analysis spot of the embodiment. [Figure 5] 1 is a schematic diagram of a membrane electrode assembly according to an embodiment. [Figure 6] 1 is a schematic diagram of an electrochemical cell according to an embodiment. [Figure 7] FIG. 2 is a schematic diagram of a stack according to an embodiment. [Figure 8] 1 is a conceptual diagram of an electrolysis device according to an embodiment. [Figure 9] Table of Examples. DETAILED DESCRIPTION OF THE INVENTION

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

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

[0009] (First embodiment) The first embodiment relates to an electrode. Fig. 1 shows a schematic cross-sectional view of an electrode 100 according to the embodiment. The electrode 100 has a substrate 1 and a catalyst layer 2. The catalyst layer 2 is provided on the substrate 1.

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

[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 fuel cell catalyst, the electrode 100 of the embodiment can also be 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 of the embodiment can be used as an anode for an electrolysis device for ammonia synthesis. In the following, the first embodiment and other embodiments will be described using water electrolysis as an example. However, the electrode 100 of the embodiment can also be used as the anode of a membrane electrode assembly used in electrolysis for ammonia synthesis, in which ultrapure water or an electrolyte solution is supplied to the anode, water is decomposed at the anode to generate protons and oxygen, the generated protons pass through an electrolyte membrane, and nitrogen supplied to the cathode combines 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 of the embodiment can be used as a cathode for a hydrogen generation 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 also 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 gases and liquids to pass through.

[0013] The substrate 1 includes metal fibers or metal particles. The substrate 1 preferably includes metal fibers or metal particles of a valve metal. The metal fibers and metal particles may be plated.

[0014] The substrate 1 containing metal fibers is preferably a cloth containing metal fibers, and the cloth containing metal fibers is preferably a mesh of metal fibers or a nonwoven fabric of metal fibers.

[0015] The substrate 1 containing metal particles is preferably a sintered body in which the metal particles are aggregated. The metal particles are preferably layered in the thickness direction of the substrate 1.

[0016] The metal fibers preferably contain one or more metals selected from the group consisting of titanium, aluminum, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony, more preferably titanium, and even more preferably titanium.

[0017] The fiber diameter (diameter) of the metal fibers 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. The average fiber diameter (average diameter) of the metal fibers is preferably 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.

[0018] The metal particles preferably contain one or more metals selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi and Sb, more preferably contain Ti, and even more preferably are Ti.

[0019] The primary particle size (diameter) of the metal particles 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. The average primary particle size (average diameter) of the metal particles 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.

[0020] The substrate 1 is a conductive porous body. Taking into consideration the movement of substances, the porosity of the substrate 1 is preferably 20% or more and 95% or less, and more preferably 40% or more and 90% or less.

[0021] The substrate 1 has a first surface A and a second surface B located on the opposite side to the first surface A. The first surface A and the second surface B are main surfaces of the substrate 1. The first surface A and the second surface B of the substrate 1 are flat or approximately flat surfaces. The catalyst layer 2 is provided on the first surface A side of the substrate 1.

[0022] The catalytic layer 2 preferably contains one or more elements selected from the group consisting of Ir, Ru, Pt, Pd, Ni, Co, Mn, Fe, Cu, V, Au, Cr, Sr, Y, Ag, Sn, Mo, Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb. The catalytic layer 2 preferably contains an oxide containing one or more elements selected from the group consisting of Ir, Ru, Pt, Pd, Ni, Co, Mn, Fe, Cu, V, Au, Cr, Sr, Y, Ag, Sn, Mo, Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb.

[0023] The catalyst layer 2 preferably contains one or more oxides of a noble metal selected from the group consisting of Ir, Ru, Pt, and Pd.

[0024] The catalyst layer 2 is preferably a porous body. The 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 amount of precious metal in the catalyst layer 2 is 0.01 [mg / cm 2 ] or more 1.0[mg / cm 2 ] or less, and more preferably 0.03 [mg / cm 2 ] or more 0.5[mg / cm 2 ] or less, and even more preferably 0.04 [mg / cm 2 ] or more 0.1[mg / cm 2 This sum of masses can be measured by ICP-MS.

[0026] The thickness of the catalyst layer 2 is preferably 0.1 μm or more and 2 μm or less, and more preferably 0.5 μm or more and 1 μm or less.

[0027] The catalyst layer 2 preferably has a structure in which sheet layers 2A and gap layers 2B are alternately laminated. The laminate structure of the catalyst layer 2 provided on the substrate 1 is shown in the partial schematic cross-sectional views of the electrode in Figures 2 and 3. The sheet layers 2A and gap layers 2B are laminated side by side and approximately parallel to each other. Most of the gap layer 2B is 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 layer 2B, maintaining the laminate structure. The difference between the schematic diagram in Figure 2 and the schematic diagram in Figure 3 is whether the layer present on the substrate 1 side is a sheet layer 2A (Figure 2) or a gap layer 2B (Figure 3).

[0028] The structure in which the sheet layers 2A and the gap layers 2B are alternately laminated can also be identified from the shading of the layers in a cross-sectional SEM image of the catalyst layer 2, for example.

[0029] The sheet layer 2A is a layer in which unsupported catalyst particles, such as metal oxide particles, are arranged in a sheet shape. There are some voids within the sheet layer 2A. The sheet layer 2A is a dense layer containing many catalyst particles.

[0030] The gap layer 2B is a region sandwiched between the sheet layers 2A and contains catalyst particles, which are unsupported metal 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. Columnar bodies 2C exist in the gap layer 2B. The columnar bodies 2C present in the gap layer 2B are aggregates of unsupported particles, for example, metal oxide particles, that extend in the stacking direction of the sheet layers 2A and 2B, connecting the sheet layers 2A.

[0031] The average thickness of one sheet layer 2A is preferably 10 nm to 200 nm, more preferably 10 nm to 100 nm, and even more preferably 10 nm to 50 nm.

[0032] The porosity of the sheet layer 2A is preferably 20% or more and 80% or less, more preferably 30% or more and 70% or less, and even more preferably 40% or more and 60% or less.

[0033] The average thickness of one layer of the gap layer 2B is preferably 10 nm to 200 nm, more preferably 10 nm to 100 nm, and even more preferably 10 nm to 50 nm.

[0034] The porosity of the sheet layer 2A is preferably 20% or more and 80% or less, more preferably 30% or more and 70% or less, and even more preferably 40% or more and 60% or less.

[0035] When the average thickness of one layer of the gap layer 2B is d1, the thickness of one layer of the sheet layer 2A is preferably 0.5 to 10 times d1, more preferably 1 to 5 times, and even more preferably 2 to 4 times.

[0036] When the porosity of the gap layer 2B is d2, the porosity of the sheet layer 2A is preferably 0.5 to 5 times d2, more preferably 1 to 4 times, and even more preferably 2 to 3 times.

[0037] The gap layer 2B preferably contains an oxide (oxide of the first element) containing one or more elements (first elements) selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb. The first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb is preferably an oxide of one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb. The oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb is an oxide that is difficult to dissolve in the dissolution treatment that is performed when forming the gap layer 2B.

[0038] The gap layer 2B preferably contains an oxide (second element) containing one or more elements (second elements) selected from the group consisting of Ni, Co, Mn, and Fe. The second oxide containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe is preferably an oxide of one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe. The second oxide containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe is an oxide that is easily dissolved in a dissolution treatment during the formation of the gap layer 2B.

[0039] The gap layer 2B preferably contains a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb, and further contains a second oxide containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe.

[0040] By including a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb in the gap layer 2B, the increase in diffusion overvoltage is small even when the electrolysis operation time is extended, that is, the structural stability of the entire catalyst layer 2 is improved. The improved structural stability of the entire catalyst layer 2 can suppress deterioration of the catalyst layer 2. Even when the amount of precious metal catalyst used in electrode fabrication is reduced, a catalyst layer 2 containing a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb in the gap layer 2B can maintain a low cell voltage.

[0041] The preferred ratios shown below are the ratios at which the electrode 100 was fabricated.

[0042] The total mass of the first oxides containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb contained in the gap layer 2B is preferably 20 wt% or more and 80 wt% or less, more preferably 20 wt% or more and 70 wt% or less, and even more preferably 30 wt% or more and 60 wt% or less of the total mass of the gap layer 2B.

[0043] The total mass of the first oxides containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb contained in the gap layers 2B containing the first oxides among all the gap layers 2B is preferably 20 wt% or more and 80 wt% or less, more preferably 30 wt% or more and 70 wt% or less, and even more preferably 40 wt% or more and 60 wt% or less of the mass of the gap layers 2B containing the first oxides.

[0044] For example, when the initial cell voltage of a catalyst layer in which the gap layer 2B does not contain a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb but has a large amount of Ir is taken as 100, the cell voltage of a catalyst layer 2 in which the gap layer 2B contains a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb and has a small amount of Ir is greater than 100. However, after long-term operation, the cell voltage of the catalyst layer 2 in which the gap layer 2B contains a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb and the amount of Ir is small becomes smaller than that of the catalyst layer in which the gap layer 2B does not contain a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb but the amount of Ir is large. Therefore, the electrode 100 of the embodiment has a low cell voltage even when the amount of precious metal is small (for example, when the amount of precious metal in the catalyst layer 2 is 0.01 [mg / cm 2 ] or more 0.1[mg / cm 2 ] or below), the effect of improving durability becomes significant.

[0045] For example, the amount of precious metal such as Ir in the catalyst layer 2 can be reduced by reducing the thickness of the sheet layer 2A or by reducing the number of times the sheet layer 2A and the gap layer 2B are repeatedly laminated.

[0046] The total mass of the first oxides containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb contained in the sheet layer 2A is preferably 0 wt% or more and 80 wt% or less, more preferably 20 wt% or more and 70 wt% or less, and even more preferably 30 wt% or more and 60 wt% or less of the total mass of the first oxides containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb contained in the gap layer 2B.

[0047] The first element contained in the first oxide is preferably one or more selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb, more preferably one or more selected from the group consisting of Ti, Ta, Nb, Hf, Zr, Zn, W, and Sb, and even more preferably one or more selected from the group consisting of Ti, Ta, Nb, Hf, Zr, and W.

[0048] It is preferable that the first oxide containing the first element is present in a small amount in the sheet layer 2A and in a large amount in the gap layer 2B. If the sheet layer 2A contains a large amount of the first oxide containing the first element, the catalytic activity of the catalyst layer 2 decreases. It is preferable that the first oxide of the first element is selectively contained in the gap layer 2B, rather than the entire catalyst layer 2 containing the first oxide of the first element.

[0049] The total mass of the second oxides containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe contained in the sheet layer 2A is preferably 20 wt% or more and 80 wt% or less, more preferably 30 wt% or more and 70 wt% or less, and even more preferably 40 wt% or more and 60 wt% or less, of the total mass of the second oxides containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe contained in the gap layer 2B.

[0050] The second element contained in the second oxide is preferably one or more selected from the group consisting of Ni, Co, Mn and Fe, more preferably one or more selected from the group consisting of Ni and Co, and even more preferably Ni.

[0051] It is preferable that the second oxide containing the second element is present in a small amount in the sheet layer 2A and in a large amount in the gap layer 2B. If the sheet layer 2A contains a large amount of the second oxide containing the second element, the catalytic activity of the catalyst layer 2 will decrease. It is preferable that the second oxide of the second element is selectively contained in the gap layer 2B, rather than the entire catalyst layer 2 containing the second oxide of the second element.

[0052] The total mass of the first oxides containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb contained in the sheet layer 2A is preferably 10 wt% or more and 90 wt% or less, more preferably 20 wt% or more and 80 wt% or less, and more preferably 30 wt% or more and 70 wt% or less of the total mass of the first oxides containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb contained in the gap layer 2B. The total mass of the second oxides containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe contained in the sheet layer 2A is preferably 10 [wt] or more and 90 [wt] or less, more preferably 20 [wt] or more and 80 [wt] or less, and even more preferably 30 [wt] or more and 70 [wt] or less, of the total mass of the second oxides containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe contained in the gap layer 2B.

[0053] The total mass of the first oxides contained in the gap layer 2B and containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb is preferably 20 wt% or more and 80 wt% or less, more preferably 30 wt% or more and 70 wt% or less, and even more preferably 40 wt% or more and 60 wt% or less, of the total mass of the second oxides contained in the gap layer 2B and containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe.

[0054] From the viewpoint of achieving both high catalytic activity and improved structural stability of the catalytic layer 2, it is preferable that the relationship between the ratio of the total of the first oxides containing the first element to the total of the second oxides containing the second element in the gap layer 2B satisfies the above. When the ratio of the first oxide of the first element in the gap layer 2B is relatively high, the porosity of the gap layer 2B increases. When the ratio of the second oxide of the second element in the gap layer 2B is relatively high, the porosity of the gap layer 2B decreases.

[0055] The first oxide containing the first element and the second oxide containing the second element may be separate oxides, or may be present in the catalytic layer 2 as a composite oxide of the first oxide and the second oxide, or the first oxide containing the first element, the second oxide containing the second element, and a composite oxide of the first oxide and the second oxide may be present in the catalytic layer 2. The ratio of oxides in the specification is a ratio that takes composite oxides into consideration.

[0056] The catalyst layer 2 includes two or more gap layers 2B. Preferably, one or more gap layers 2B contain a first oxide of the first element. When the number of gap layers 2B is n, the number of gap layers 2B containing the first oxide of the first element is preferably 1×n (1 time n) to 10×n (10 times n), more preferably 3×n (3 times n) to 7×n (7 times n), and even more preferably 4×n (4 times n) to 6×n (6 times n).

[0057] The total mass of oxides (third oxides) of precious metals (third elements) selected from the group consisting of Ir, Ru, Pt, and Pd contained in the gap layer 2B is preferably 10 wt% or more and 80 wt% or less, more preferably 20 wt% or more and 70 wt% or less, and even more preferably 30 wt% or more and 60 wt% or less of the total mass of third oxides of third elements selected from the group consisting of Ir, Ru, Pt, and Pd contained in the sheet layer 2A.

[0058] The third oxide of the third element is preferably present in a small amount in the gap layer 2B and in a large amount in the sheet layer 2A. It is more preferable that the third oxide of the third element is selectively contained in the sheet layer 2A than that the third oxide of the third element is contained throughout the entire catalyst layer 2.

[0059] The identity of the sheet layer 2A and gap layer 2B of the catalyst layer 2, and the distribution of the first oxide, second oxide, and third oxide can be determined by observing the cross sections of multiple analysis spots. As shown in Figure 4, assuming that the length of the electrode 100 is D1 and the width of the electrode 100 is D2 (D1 ≥ D2), imaginary lines are drawn inward from each of two opposing sides of the electrode 100 in the width direction at a distance of D3 (= D1 / 10), and imaginary lines are drawn inward from each of two opposing sides of the electrode 100 in the length direction at a distance of D4 (= D2 / 10). Further, imaginary lines are drawn parallel to the width direction through the center of the electrode 100, and imaginary lines are drawn parallel to the length direction through the center of the electrode 100. The analysis spots A1 to A9 are defined as areas centered on the intersections of the imaginary lines. Each spot is square and has a size of at least 10 μm. 2 ] area. The image of each spot may be a mosaic image obtained by combining (mosaicing) multiple raster images. The cross section observed by SEM-EDX or TEM-EDX is perpendicular to the plane of FIG. 1 and parallel to the width direction. The thickness of each gap layer 2B of analysis spots A1 to A9 is determined at 50 nm intervals in the width direction of the SEM or TEM image. The ratio of catalyst layer 2 provided at a specific location is the average value for each spot. The ratio of catalyst layer 2 provided at a specific location can be determined from the volume and ratio of catalyst layer 2.

[0060] Next, an example of a method for producing the electrode 100 is shown. A sheet layer precursor, which is essentially a precursor of the sheet layer 2A, and a gap layer precursor, which is essentially a precursor of the gap layer 2B, are alternately sputtered onto the substrate 1. The target used to form the sheet layer precursor contains a third element. The target used to form the gap layer precursor contains a first element and a second element. The sheet layer precursor and the gap layer precursor are formed in an oxidizing atmosphere. The laminate, in which the sheet layer precursor and the gap layer precursor are alternately stacked, is treated with a solution that selectively dissolves the second oxide containing the second element of the precursor of the gap layer 2B. The dissolving solution is, for example, sulfuric acid, hydrochloric acid, or nitric acid. After the solution treatment, optionally, a heat treatment is performed in an oxidizing atmosphere to obtain the electrode 100.

[0061] The electrode 100 of the embodiment has improved structural stability of the catalyst layer 2. As an electrode for electrolysis, the electrode 100 of the embodiment has high durability and excellent electrolysis properties.

[0062] (Second embodiment) The second embodiment relates to a membrane electrode assembly (MEA). Fig. 5 shows a schematic diagram of a membrane electrode assembly 200 of this 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 electrode 100 of the first embodiment is preferably used for the first electrode 11 or the second electrode 12. The membrane electrode assembly 200 of this embodiment is preferably used in an electrochemical cell or stack that generates hydrogen or oxygen.

[0063] The first electrode 11 has a first substrate 11B and a first catalyst layer 11A. The first catalyst layer 11A is provided on the first substrate 11B. The first catalyst layer 11A is preferably in direct contact with the electrolyte membrane 13. When the electrode 100 is used as the first electrode 11, the first catalyst layer 11A is the catalyst layer 2, and the first substrate 11B is the substrate 1.

[0064] 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.

[0065] The second substrate 12B is preferably made of a porous, highly conductive material. The second substrate 12B is a porous member that allows gases and liquids to pass through. The second substrate 12B is, for example, carbon paper or a metal mesh. A preferred metal mesh is a porous substrate made of a valve metal. A preferred porous substrate made of a valve metal is 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. The second substrate 12B has a carbon layer (MPL layer) containing carbon fine particles and a water-repellent resin (a fluororesin such as PTFE or Nafion). The carbon layer is provided, for example, between the carbon paper and the second catalyst layer 12A.

[0066] The second catalytic layer 12A contains a catalytic metal. The second catalytic layer 12A is preferably made of catalytic metal particles, 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 that the second catalytic layer 12A contains one or more selected from the group consisting of such catalytic materials. The catalytic metal is preferably a metal, alloy, or metal oxide. The second catalytic layer 12A preferably has a plurality of catalytic units, for example, in which sheet-like catalytic layers and gap layers are alternately stacked.

[0067] 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.

[0068] 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.

[0069] 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 groups selected from the group consisting of sulfonic acid groups, sulfonimide groups, and sulfate groups. The electrolyte membrane 13 is preferably a fluorine-based polymer having sulfonic acid groups. Examples of fluorine-based polymers having sulfonic acid groups include Nafion (trademark, manufactured by DuPont), Flemion (trademark, manufactured by Asahi Kasei Corporation), Selemion (trademark, manufactured by Asahi Kasei Corporation), Aquivion (trademark; Solvay Specialty Polymers), and Aciplex (trademark, manufactured by Asahi Glass Co., Ltd.). Instead of a proton-conductive membrane, various conductive membranes such as anion exchange membranes and porous membranes may be used.

[0070] The thickness of the electrolyte membrane 13 can be appropriately determined taking into consideration the membrane's properties such as permeability and durability. From the viewpoints of strength, dissolution resistance, and MEA output properties, the thickness of the electrolyte membrane 13 is preferably 20 μm to 500 μm, more preferably 50 μm to 300 μm, and even more preferably 80 μm to 200 μm. It is preferred that the composition does not contain an ionomer that has been modified.

[0071] 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 a single region, but may be composed of multiple separate regions.

[0072] 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 particles of an alloy containing one or more precious metals 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.

[0073] The precious metal particles oxidize hydrogen generated on the cathode side and passing 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 exist may also be present on the electrolyte membrane 13 on the second electrode 12 (cathode) side.

[0074] The average circumscribed circle diameter of the noble 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.

[0075] By using the electrode 100 with high durability and characteristics as the anode of the membrane electrode assembly 200, it becomes possible to operate the membrane electrode assembly 200 with high activity for a long period of time.

[0076] (Third embodiment) The third embodiment relates to an electrochemical cell. Fig. 6 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 in addition to water.

[0077] 6, an electrochemical cell 300 of the second embodiment includes a first electrode (anode) 11, a second electrode (card) 12, an electrolyte membrane 13, a gasket 21, a gasket 22, a separator 23, and a separator 24. The gasket 21 may be a sealing material for the first electrode 11. The gasket 22 may be a sealing material for the second electrode 12.

[0078] 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. The anode power supply may be provided separately from the separator 23. The cathode power supply may be provided separately from the separator 24.

[0079] In the electrochemical cell 300 of FIG. 6, a power supply (not shown) is connected to separators 23 and 24, and a reaction occurs between first electrode 11 and second electrode 12. For example, water is supplied to first electrode 11, where the water is decomposed into protons, oxygen, and electrons. The electrode support and power supply are porous, and this porous body functions as a flow path plate. The produced water and unreacted water are discharged, and the protons and electrons are used in the cathode reaction. In the cathode reaction, protons and electrons react to produce hydrogen. Either or both of the produced hydrogen and oxygen are used, for example, as fuel for the fuel cell.

[0080] (Fourth embodiment) The fourth embodiment relates to a stack. Fig. 7 is a schematic cross-sectional view showing a stack 400 of the fourth embodiment. The stack 400 of the third embodiment shown in Fig. 7 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 or electrochemical cell.

[0081] Since the amount of hydrogen produced by an electrochemical cell 300 consisting of one MEA 200 is small, a large amount of hydrogen can be obtained by connecting a plurality of MEAs 200 or a plurality of electrochemical cells 300 in series to form a stack 400.

[0082] (Fifth embodiment) The fifth embodiment relates to an electrolysis device. Fig. 8 shows a conceptual diagram of the electrolysis device of the fifth embodiment. An electrolysis device 500 uses an electrochemical cell 300 or a stack 400. The electrolysis device of Fig. 8 is for water electrolysis. An electrolysis device for water electrolysis will be described. For example, when generating hydrogen from ammonia, it is preferable to employ a device with a different configuration using an electrode 100. The electrodes of the embodiment can also be used in an electrolysis device that electrolyzes carbon dioxide to produce organic substances such as methanol and ethylene, or carbon monoxide.

[0083] As shown in Figure 8, a stack 400 is formed by stacking unit cells for water electrolysis in series. A power supply 41 is attached to the stack 400, and a voltage is applied between the anode and cathode. A gas-liquid separator 42, which separates the generated gas from unreacted water, and a mixing tank 43 are connected to the anode side of the stack 400. Water is delivered to the mixing tank 43 by a pump 46 from an ion-exchange water production system 44, and the water passes through a check valve 47 from the gas-liquid separator 42 and mixed in the mixing tank 43 before being circulated to the anode. Oxygen generated at the anode passes through the gas-liquid separator 42 to produce oxygen gas. Meanwhile, a hydrogen purifier 49 is connected to the gas-liquid separator 48 on the cathode side to produce high-purity hydrogen. Impurities are discharged via a pathway with a valve 50 connected to the hydrogen purifier 49. To stably control the operating temperature, the stack and mixing tank can be heated, and the current density during pyrolysis can be controlled.

[0084] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0085] Example 1 A nonwoven fabric of titanium metal fiber is used as the substrate, and a catalyst layer is formed on the substrate. The catalyst layer has a structure in which sheet layers and gap layers are alternately stacked, 40 layers each. A sheet layer precursor containing Ir oxide and a gap layer precursor containing Ni oxide and Ta oxide are alternately formed by sputtering in an oxidizing atmosphere. The loading density of the precious metal is 0.05 mg / cm. 2Then, most of the gap layer precursor is selectively dissolved with sulfuric acid to obtain the electrode of the embodiment. The obtained electrode is used as an anode.

[0086] Carbon paper is used as a substrate, and a porous catalyst layer containing Pt is formed on the substrate to obtain an electrode. The resulting electrode is used as a cathode. The loading density of the precious metal is 0.4 mg / cm. 2 ].

[0087] A Nafion membrane is sandwiched between the resulting anode and cathode as an electrolyte membrane and pressed together to obtain a membrane electrode assembly. The resulting membrane electrode assembly is placed between two separators with flow channels, and the membrane electrode assembly, sealed with a gasket, is fixed in place to obtain an electrochemical cell. The resulting electrochemical cell is measured at a temperature of 80°C and a current density of 2 A / cm. 2 ] for 48 hours to evaluate durability and cell voltage.

[0088] The cell voltages were evaluated 100 hours, 200 hours, 300 hours, 400 hours, 500 hours, and 600 hours after the start of operation. The difference between the rate of increase in cell voltage of Example 1 (rate of increase in cell voltage after each time has elapsed since the start of operation) and the rate of increase in cell voltage of Comparative Example 1 (rate of increase in cell voltage after each time has elapsed since the start of operation) ([rate of increase in cell voltage of Comparative Example 1] - [rate of increase in cell voltage of Example 1]) was evaluated as A if it was 0% or more and less than 0.5%, B if it was 0.5% or more and less than 1.0%, C if it was 1.0% or more and less than 1.5%, D if it was 1.5% or more and less than 2.0%, E if it was 2.0% or more and less than 2.5%, and F if it was 2.5% or more and less than 3.0%.

[0089] (Comparative Example 1) An anode is fabricated in the same manner as in Example 1, except that the gap layer precursor does not contain Ta oxide and instead contains Ni oxide, and an electrochemical cell is fabricated using the fabricated anode. The cell voltage is measured under the same conditions as in Example 1 using the fabricated electrochemical cell.

[0090] The rate of increase in cell voltage of Example 1, which was compared with Comparative Example 1, is summarized in the table of FIG. 9. The rate of increase in cell voltage of Example 1 was smaller than that of Comparative Example 1. As shown in the table of FIG. 9, the rate of increase in cell voltage of the Comparative Example increases over time, while the rate of increase in Example 1 does not change much over time, and therefore it can be seen that the difference between the rate of increase in cell voltage of Example 1 and that of Comparative Example 1 increases over time. Furthermore, when the diffusion overvoltages of Example 1 and Comparative Example 1 are evaluated, the increase in diffusion overvoltage of Example 1 is smaller than that of Comparative Example 1. The diffusion overvoltage can be used to evaluate the collapse of the catalyst layer structure, and the diffusion overvoltage also indicates that the electrode of Example 1 has high durability.

[0091] Example 2 An electrochemical cell was fabricated using the fabricated anode in the same manner as in Example 1, except that the ratio of Ta oxide in the gap layer precursor was increased compared to Example 1. Using the fabricated electrochemical cell, the cell voltage was measured under the same conditions as in Example 1. The rate of increase in the cell voltage of Example 2 was evaluated by comparing the rate of increase in the cell voltage of Comparative Example 1, which serves as a comparison for Example 2.

[0092] Example 3 An electrochemical cell was fabricated using the fabricated anode in the same manner as in Example 1, except that the ratio of Ta oxide in the gap layer precursor was reduced compared to Example 1. Using the fabricated electrochemical cell, the cell voltage was measured under the same conditions as in Example 1. The rate of increase in the cell voltage of Example 3 was evaluated by comparing the rate of increase in the cell voltage of Comparative Example 1, which serves as a comparison for Example 3.

[0093] In Examples 2 and 3, as in Example 1, the difference over time between the rate of increase in cell voltage in Example 1 and the rate of increase in cell voltage in Comparative Example 1 becomes larger. Example 3, which has a relatively small amount of Ta oxide in the gap layer, has a relatively large rate of increase in cell voltage, but Example 3 also effectively suppresses the increase in cell voltage compared to Comparative Example 1. In the Examples, Ta oxide was used, but if a first oxide of a first element other than Ta is used, it is similarly more difficult to dissolve than the oxide of the second element, and the first oxide remains in the gap layer. Therefore, Examples in which Ta oxide was used but a first oxide of a first element other than Ta also had a low rate of increase in cell voltage and high durability, similar to Example 1 and the like.

[0094] In the specification, some elements are represented only by element symbols.

[0095] The technical solutions of the embodiments are described below. Technical proposal 1 A substrate; a catalyst layer formed by alternately laminating sheet layers and gap layers provided on the substrate; Equipped with The gap layer is an electrode comprising a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb. Technical proposal 2 The electrode according to Technical Scheme 1, wherein the gap layer contains a second oxide containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe. Technical proposal 3 The electrode according to Technical Scheme 1 or 2, wherein the total mass of the first oxide contained in the gap layer is 20 wt% or more and 80 wt% or less of the total mass of the gap layer. Technical proposal 4 An electrode described in any one of Technical Proposals 1 to 3, wherein the total mass of the first oxide contained in the gap layer containing the first oxide is 20 wt% or more and 80 wt% or less of the mass of the gap layer containing the first oxide. Technical proposal 5 An electrode described in any one of technical proposals 1 to 4, wherein the total mass of the first oxide contained in the sheet layer is 0 [wt%] or more and 80 [wt%] or less of the total mass of the first oxide contained in the gap layer. Technical plan 6 An electrode according to any one of technical proposals 1 to 5, wherein the first element contained in the first oxide is one or more selected from the group consisting of Ti, Ta, Nb, Hf, Zr and W. Technical proposal 7 An electrode according to Technical Proposal 2, wherein the total mass of the second oxide contained in the sheet layer is 20 wt% or more and 80 wt% or less of the total mass of the second oxide contained in the gap layer. Technical proposal 8 An electrode described in any one of technical proposals 1 to 7, wherein when the number of gap layers is n, the number of gap layers containing the first oxide is 1×n or more and 10×n or less. Technical proposal 9 The average thickness of one of the sheet layers is 10 [nm] or more and 200 [nm] or less, The electrode according to Technical Proposal 1, wherein the average thickness of one layer of the gap layer is 10 nm or more and 200 nm or less. Technical proposal 10 The electrode according to any one of Technical Schemes 1 to 9, wherein the thickness of the catalyst layer is 0.1 μm or more and 2 μm or less. Technical proposal 11 An electrode according to any one of technical proposals 1 to 10; and a membrane electrode assembly comprising an electrolyte membrane in direct contact with the electrode. Technical proposal 12 The membrane electrode assembly according to Technical Scheme 12, comprising the catalyst layer not in contact with the membrane electrode assembly. Technical proposal 13 An electrochemical cell comprising the membrane electrode assembly described in Technical Proposal 12. Technical proposal 14 A stack comprising a plurality of electrochemical cells as described in Technical Proposal 13. Technical proposal 15 An electrolysis device comprising an electrochemical cell according to technical proposal 13 or a stack according to technical proposal 14.

[0096] 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 and scope of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the invention and its equivalents as defined in the accompanying claims. [Explanation of symbols]

[0097] 1: Base material 2: Catalyst layer 2A: Sheet layer 2B: Gap layer 2C: columnar body 11: 1st electrode 11A: 1st catalyst layer 11B: 1st base material 12:Second electrode 12A: 2nd catalyst layer 12B: 2nd base material 13: Electrolyte membrane 21: Gasket 22: Gasket 23: Separator 24: Separator 31: Clamping plate 32: Clamping plate 41:Power supply 42: Gas-liquid separation device 43: Mixing tank 44: Ion exchange water production equipment 46: Pump 47: Check valve 48: Gas-liquid separation device 49: Hydrogen purification equipment 50: Valve 100: Electrode 200: Membrane electrode assembly 300: Electrochemical cell 400: Stack 500: Electrolysis unit

Claims

1. A substrate; a catalyst layer formed by alternately laminating sheet layers and gap layers provided on the substrate; Equipped with The gap layer is an electrode comprising a first oxide containing one or more first elements selected from the group consisting of Ti, Al, Ta, Nb, Hf, Zr, Zn, W, Bi, and Sb.

2. 2. The electrode of claim 1, wherein the gap layer comprises a second oxide containing one or more second elements selected from the group consisting of Ni, Co, Mn, and Fe.

3. 2. The electrode according to claim 1, wherein the total mass of the first oxide contained in the gap layer is 20 wt % or more and 80 wt % or less of the total mass of the gap layer.

4. 2. The electrode according to claim 1, wherein a total mass of the first oxide contained in the gap layer containing the first oxide is 20 wt % or more and 80 wt % or less of a mass of the gap layer containing the first oxide.

5. 2. The electrode according to claim 1, wherein a total mass of the first oxide contained in the sheet layer is 0 wt % or more and 80 wt % or less of a total mass of the first oxide contained in the gap layer.

6. 2. The electrode according to claim 1, wherein the first element contained in the first oxide is at least one element selected from the group consisting of Ti, Ta, Nb, Hf, Zr, and W.

7. 3. The electrode according to claim 2, wherein the total mass of the second oxide contained in the sheet layer is 20 wt % or more and 80 wt % or less of the total mass of the second oxide contained in the gap layer.

8. 2. The electrode according to claim 1, wherein the number of the gap layers containing the first oxide is 1×n or more and 10×n or less, where n is the number of the gap layers.

9. the average thickness of one of the sheet layers is 10 nm or more and 200 nm or less; The electrode according to claim 1 , wherein the average thickness of one of the gap layers is 10 nm or more and 200 nm or less.

10. 2. The electrode according to claim 1, wherein the thickness of the catalyst layer is 0.1 μm or more and 2 μm or less.

11. An electrode according to any one of claims 1 to 10; and a membrane electrode assembly comprising an electrolyte membrane in direct contact with the electrode.

12. The membrane electrode assembly according to claim 11 , comprising the catalyst layer not in contact with the membrane electrode assembly.

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

14. A stack comprising a plurality of electrochemical cells according to claim 13.

15. Electrolysis device comprising the stack according to claim 14.

Images