Electrode, method for manufacturing the same, water electrolysis device, and fuel cell

Abstract

The electrode 10 has an alloy as a catalyst, the alloy being composed of three or more base metal elements, the atomic composition ratio of the three or more base metal elements being substantially equal, and the three or more base metal elements forming a solid solution. In addition, the electrode 12 has a carbon fiber and a catalyst composed of a base metal, at least a part of the elements of the catalyst being chemically bonded to the carbon fiber. Furthermore, the water electrolysis device has an anode, a cathode, and a solid polymer electrolyte membrane provided between the anode and the cathode, the anode being the electrode 10, and / or the cathode being the electrode 12.

Description

Technical Field

[0001] This invention relates to electrodes, methods for manufacturing them, water electrolysis devices, and fuel cells. Background Technology

[0002] In water electrolysis devices, fuel cells, secondary batteries, and electrodes of double-layer capacitors, noble metals such as platinum are used as catalysts. Base metal alloys that form graphene films in NiMo (nickel-molybdenum) alloys are known (e.g., Non-Patent Literature 1). Alloys containing Cr, Mn, Fe, Co, and Ni are known to be used as catalysts for oxygen reduction reactions (ORR) (e.g., Non-Patent Literature 2).

[0003] Existing technical documents

[0004] Non-patent literature

[0005] Non-Patent Document 1: "Base metal electrode with corrosion resistance and high hydrogen production efficiency," [online], March 30, 2013, National University Corporation of Tsukuba, National University Corporation of Osaka, National University Corporation of Tohoku, [searched on September 16, 2013], Internet<URL:http: / / www.tsukuba.ac.jp / wp-content / upload s / 180330ito-1.pdf>

[0006] Non-patent literature 2: Adv. Energy Mater. 2018, 8, 1802269 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Precious metals are expensive, making the device costly if used in the electrodes. Base metals are inexpensive but have low chemical stability. Therefore, using base metals in the electrodes results in poor durability and reduced long-term performance. Using graphene films, as in Non-Patent Document 1, increases manufacturing costs. It is common knowledge to those skilled in the art that different types of reactions require different catalyst characteristics; ORR catalysts are not used for oxygen evolution reaction (OER) or hydrogen evolution reaction (HER). Applying overvoltage to the OER catalyst to allow OER to proceed and achieve the desired current density exposes it to high potential, making it susceptible to oxidation and degradation. Therefore, ORR catalysts are generally not used as OER catalysts. Devices using HER catalysts are also prone to oxidation and degradation. Therefore, ORR catalysts are generally not used as HER catalysts. Furthermore, catalysts for hydrogen oxidation reaction (HOR) have CO poisoning problems. Therefore, ORR catalysts are not typically used as HOR catalysts.

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide an inexpensive electrode with improved durability, a method for manufacturing the electrode, and a water electrolysis apparatus.

[0010] Methods for solving problems

[0011] The present invention is an electrode comprising an alloy as a catalyst for an oxygen evolution reaction or a hydrogen evolution reaction, wherein the alloy is composed of three or more base metal elements, the atomic ratios of the three or more base metal elements are approximately equal, and the three or more base metal elements form a solid solution.

[0012] In the above composition, the above three or more base metal elements can be at least three elements selected from Fe, Cu, Ni, Al, Pb, Zn, Sn, W, Mo, Ta, Mg, Co, Bi, Cd, Ti, Zr, Sb, Mn, Be, Cr, Ge, V, Ga, Hf, In, Nb, Re, and Tl.

[0013] In the above configuration, the three or more base metal elements can be configured to be five or more base metal elements.

[0014] In the above configuration, the three or more base metal elements can be configured to be six or more base metal elements.

[0015] In the above configuration, the catalyst can be a catalyst used for the oxygen evolution reaction.

[0016] The present invention is an electrode comprising an alloy as a catalyst for a hydrogenation reaction, wherein the alloy is composed of three or more base metal elements, the atomic ratios of the three or more base metal elements are approximately equal, and the three or more base metal elements form a solid solution.

[0017] In the above composition, the above three or more base metal elements can be at least three elements selected from Fe, Cu, Ni, Al, Pb, Zn, Sn, W, Mo, Ta, Mg, Co, Bi, Cd, Ti, Zr, Sb, Mn, Be, Cr, Ge, V, Ga, Hf, In, Nb, Re, and Tl.

[0018] In the above configuration, the three or more base metal elements can be configured to be five or more base metal elements.

[0019] In the above configuration, the three or more base metal elements can be configured to be six or more base metal elements.

[0020] The present invention is an electrode comprising: carbon fiber; and a catalyst made of base metal, at least a portion of which is chemically bonded to the carbon fiber.

[0021] In the above configuration, the catalyst may be an alloy composed of at least two elements selected from Cr, Mn, Fe, Co, Ni, and Mo.

[0022] In the above configuration, the catalyst can be a NiMo alloy.

[0023] The present invention is a water electrolysis device comprising: an anode containing an alloy as a catalyst for an oxygen evolution reaction or a hydrogen evolution reaction, wherein the alloy is composed of three or more base metal elements, the atomic ratios of the three or more base metal elements being approximately equal, and the three or more base metal elements forming a solid solution; a cathode; and a solid polymer electrolyte membrane disposed between the anode and the cathode.

[0024] In the above configuration, the cathode may be an electrode containing an alloy as a catalyst for an oxygen evolution reaction or a hydrogen evolution reaction, wherein the alloy is composed of three or more base metal elements, the atomic ratios of the three or more base metal elements are approximately equal, and the three or more base metal elements form a solid solution.

[0025] In the above configuration, the cathode may be an electrode comprising carbon fiber and a catalyst made of base metal, wherein at least a portion of the elements of the catalyst are chemically bonded to the carbon fiber.

[0026] In the above configuration, the anode may be an electrode containing an alloy as a catalyst, wherein the alloy is composed of at least five elements selected from Fe, Cu, Ni, Al, Pb, Zn, Sn, W, Mo, Ta, Mg, Co, Bi, Cd, Ti, Zr, Sb, Mn, Be, Cr, Ge, V, Ga, Hf, In, Nb, Re, and Tl, wherein the atomic ratios of the at least five elements are approximately equal, and the at least five elements form a solid solution.

[0027] The present invention is a water electrolysis device comprising: an anode; a cathode comprising an electrode having carbon fibers and a catalyst made of base metal, wherein at least a portion of the elements of the catalyst are chemically bonded to the carbon fibers; and a solid polymer electrolyte membrane disposed between the anode and the cathode.

[0028] The present invention is a fuel cell comprising: an anode, which is an electrode containing an alloy as a catalyst for a hydrogenation reaction, wherein the alloy is composed of three or more base metal elements, the atomic ratios of the three or more base metal elements are approximately equal, and the three or more base metal elements form a solid solution; a cathode; and an electrolyte membrane disposed between the anode and the cathode.

[0029] The present invention is a method for manufacturing an electrode, comprising: a step of attaching an oxide of a base metal to the surface of a carbon fiber; and a step of heat-treating the carbon fiber under a reducing gas atmosphere to form a catalyst containing a base metal that is chemically bonded to the carbon fiber.

[0030] In the above configuration, the process of attaching the oxides may include arranging the carbon fibers in an aqueous solution containing a variety of base metals and using a hydrothermal synthesis method to attach the oxides of the various base metals to the surface of the carbon fibers; the process of forming the catalyst may include forming an alloy of the various base metals.

[0031] Invention Effects

[0032] According to the present invention, it is possible to provide an inexpensive electrode with improved durability, a method for manufacturing the electrode, and a water electrolysis apparatus. Attached Figure Description

[0033] Figure 1 : Figure 1 (a)~ Figure 1 (d) is a schematic diagram illustrating the method for manufacturing the electrode according to Embodiment 2.

[0034] Figure 2 : Figure 2 This is a cross-sectional view of the device according to Embodiment 3.

[0035] Figure 3 : Figure 3This is a cross-sectional view of the PEM-type water electrolysis device according to Embodiment 3.

[0036] Figure 4 : Figure 4 (a) and Figure 4 (b) is a diagram showing the X-ray diffraction patterns of the 5-element HEA and the 6-element HEA in the embodiments.

[0037] Figure 5 : Figure 5 This is a SEM image of a 5-component HEA loaded with carbon black in the embodiment.

[0038] Figure 6 : Figure 6 This is a diagram showing the X-ray diffraction pattern of the NiMo alloy in the embodiment.

[0039] Figure 7 : Figure 7 (a)~ Figure 7 (c) is a SEM image of the NiMo alloy supported on carbon fiber in the embodiment.

[0040] Figure 8 : Figure 8 This is a graph showing the current-voltage characteristics of batteries A, C, and D.

[0041] Figure 9 : Figure 9 This is a graph showing the current-voltage characteristics of battery B.

[0042] Figure 10 : Figure 10 This is a graph representing the constant voltage characteristics of battery C.

[0043] Figure 11 : Figure 11 This is a diagram showing the constant voltage characteristics of batteries D and E.

[0044] Figure 12 : Figure 12 This is a graph showing the current-voltage characteristics of the battery's C, D, and F terminals.

[0045] Figure 13 : Figure 13 (a)~ Figure 13 (c) are graphs showing the impedance test results of batteries C, D and F respectively.

[0046] Figure 14 : Figure 14 (a) and Figure 14 (b) is a graph showing the current-voltage characteristics of a battery that uses 5-cell HEA to 9-cell HEA at the anode or cathode.

[0047] Figure 15 : Figure 15This is a graph showing the current-voltage characteristics of a battery that uses a 9-element HEA at the anode and cathode.

[0048] Figure 16 : Figure 16 This is a graph representing the constant voltage characteristics of a 9-yuan HEA battery. Detailed Implementation

[0049] The embodiments of the present invention will be described below.

[0050] (Implementation Method 1)

[0051] Base metals are inexpensive metals with a lower ionization tendency than hydrogen. Therefore, catalysts using base metals as electrodes have been investigated. It should be noted that although Cu has a higher ionization tendency than hydrogen, it is included in the category of base metals in this specification due to its low cost. In Embodiment 1, high-entropy alloys are considered as catalysts that use base metals and have high durability. High-entropy alloys are solid solutions that increase the entropy of the mixture by setting the atomic composition of five or more constituent elements to approximately equal amounts. A solid solution is a state in which the constituent elements are fused together to form a homogeneous solid phase, and it has a crystal structure such as a face-centered cubic (FCC) lattice or a body-centered cubic (BCC) lattice.

[0052] High-entropy alloys have high strength. By using high-entropy alloys in electrodes, improved durability can be expected. From the perspective of increasing entropy, even if the constituent elements are not more than five, using three or more base metal elements can increase entropy.

[0053] Based on the above viewpoints, the electrode of Embodiment 1 comprises a catalyst containing an alloy, wherein the alloy contains three or more base metal elements, the atomic ratios of the three or more base metal elements are approximately equal, and the three or more base metal elements form a solid solution. Therefore, an electrode that uses inexpensive base metals and has high durability can be provided.

[0054] Having approximately equal atomic ratios for three or more base metal elements means that the elemental ratios only need to be equal in terms of entropy change, allowing for variations in the degree of manufacturing error. For example, if the atomic ratio of the element with the highest atomic ratio among three or more base metal elements is set as Cmax, and the atomic ratio of the element with the lowest atomic ratio is set as Cmin, then (Cmax-Cmin) / (Cmax+Cmin)≤0.2, preferably (Cmax-Cmin) / (Cmax+Cmin)≤0.1.

[0055] Base metals include Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Mo (molybdenum), Zr (zirconium), Ti (titanium), Nb (niobium), Zn (zinc), Al (aluminum), Cu (copper), Sb (antimony), Be (beryllium), Bi (bismuth), Cd (cadmium), Ga (gallium), Ge (germanium), Hf (hafnium), In (indium), Pb (lead), Mg (magnesium), Re (rhenium), Ta (tantalum), Tl (thallium), Sn (tin), W (tungsten), V (vanadium), Sc (scandium), Y (yttrium), and the lanthanides.

[0056] As base metal elements that are easy to alloy, the three or more base metal elements preferably include at least three elements selected from Cr, Mn, Fe, Co, Ni, Mo, Zr, Ti, Nb, Zn, Al and Cu.

[0057] From the viewpoint of increasing the entropy of the alloy, the base metal elements contained in the alloy are preferably four or more, more preferably five or more. From the viewpoint of functioning as a catalyst and increasing the entropy of the alloy, the five or more base metal elements preferably include at least five elements selected from Cr, Mn, Fe, Co, Ni, and Mo.

[0058] Alloys containing three or more base metals can be supported on carbon, such as carbon black or carbon fibers. The alloy is preferably porous. This improves the catalytic performance and electrode performance of the alloy. The average pore size of the porous body is, for example, 1 nm to 100 μm, and the average size of the ligaments is, for example, 1 nm to 100 μm. The porous body is formed, for example, using a dealloying method.

[0059] (Implementation Method 2)

[0060] In Non-Patent Literature 1, corrosion of NiMo alloy caused by electrolyte was suppressed by covering it with a graphene film. However, the manufacturing cost of forming the graphene film is high. Furthermore, the graphene film hinders the movement of protons and other ions within the electrolyte, thus reducing electrode characteristics.

[0061] In Embodiment 2, the electrode comprises: carbon fibers; and a catalyst containing a base metal, at least a portion of which is chemically bonded to the carbon fibers. Furthermore, the electrode comprises: carbon fibers; and a catalyst composed of a base metal, at least a portion of which is chemically bonded to the carbon fibers. Thus, because at least a portion of the catalyst is chemically bonded to the carbon fibers, the contact resistance between the carbon fibers and the catalyst is low, improving the electrode performance. Additionally, because the catalyst is firmly bonded to the carbon fibers, the electrode durability is improved. Furthermore, since a graphene film can be omitted, manufacturing costs can be reduced. Moreover, since a graphene film, which hinders ion movement within the electrolyte, can be omitted, electrode performance can be further improved.

[0062] Carbon fiber is a fiber obtained by heating and carbonizing organic fibers, and is composed of 90% carbon by mass. The diameter of carbon fiber is, for example, 0.1 μm to 100 μm, preferably 1 μm to 20 μm. Carbon fiber can also be carbon cloth woven from multiple carbon fibers, or carbon paper made by forming multiple carbon fibers into a paper-like form. From the viewpoint of improving the permeability to liquids such as water or electrolytes, the porosity of the carbon cloth or carbon paper is preferably 50% or more, more preferably 70% or more.

[0063] Catalysts containing base metals are alloys or compounds of at least two elements selected from Cr, Mn, Fe, Co, Ni, Mo, Zr, Ti, Nb, Zn, Al, Cu, Sb, Be, Bi, Cd, Ga, Ge, Hf, In, Pb, Mg, Re, Ta, Tl, Sn, W, V, Se (selenium), Te (tellurium), Si (silicon), P (phosphorus), Sc, Y, and the lanthanides, or compounds of these base metals (e.g., carbides, nitrides, sulfides, selenium compounds, tellurium compounds, chalcogenide alloys). Examples of carbides include TiC, ZrC, VC, NbC, TaC, MoC, WC, V₂C, Ta₂C, Mo₂C, W₂C, Mn₃C, Te₃C, Co₃C, Ni₃C, or Cr₃C₂. Nitrides include, for example, Si3N4, Ge3N4, GaN, P2N3, TiN, ZrN, NbN, TaN, Cr2N, CrN, VN, V2N, Mn2N, Mn3N, Mn4N, Mn6N, FeN, Fe2N, Fe3N, Fe4N, CoN, Co2N, Co3N, Co4N, Ni2N, Ni3N, Ni4N, Cu3N, Zn3N2, MoN, Mo2N, InN, Sn3N4, or Sn3N2.

[0064] Sulfides are, for example, layered chalcogenide compounds, such as MoS2, WS2, ReS2, SnS2, SeS2, ZrS2, NiS2, HfS2, PdS2, TaS2, TiS2, VS2, or NbS2. Selenium compounds are, for example, layered chalcogenide compounds, such as MoSe2, WSe2, ReSe2, SnSe2, ZrSe2, NiSe2, HfSe2, PdSe2, TaSe2, TiSe2, VSe2, or NbSe2. Tellurium compounds are, for example, layered chalcogenide compounds, such as MoTe2, WTe2, ReTe2, SnTe2, SeTe2, ZrTe2, NiTe2, HfTe2, PdTe2, TaTe2, TiTe2, VTe2, or NbTe2. Chalcogenide alloys contain two or more metallic elements other than S, Se and Te, or contain two or more of S, Se and Te, such as MoWS2, MoWSe2, MoWSeS or SnSeS.

[0065] To improve the performance of the catalyst, the base metal-containing catalyst preferably contains at least one element selected from Cr, Mn, Fe, Co, Ni, and Mo. Furthermore, the catalyst is preferably an alloy containing at least two elements selected from Cr, Mn, Fe, Co, Ni, and Mo. More specifically, the catalyst is preferably an alloy composed of at least two elements selected from Cr, Mn, Fe, Co, Ni, and Mo. Even more specifically, the catalyst is preferably a NiMo alloy.

[0066] The NiMo alloy composition ratio is, for example, a Ni:Mo atomic ratio of 2:1 to 1:2. The NiMo alloy is preferably porous. This improves catalyst performance and electrode performance. The average size of the micropores in the porous body is, for example, 1 nm to 100 nm / μm, and the average size of the ligaments is, for example, 1 nm to 100 μm.

[0067] Figure 1 (a)~ Figure 1 (d) is a schematic diagram illustrating the method for manufacturing the electrode according to Embodiment 2. Figure 1 As shown in (a), carbon fibers 50, such as carbon cloth or carbon paper, are immersed in an aqueous solution 54 containing a base metal compound within a container 55. Examples of base metal compounds include nickel chloride hexahydrate (NiCl2·6H2O) and Mo-containing compounds such as sodium molybdate (Na2MoO4·2H2O). A base metal oxide is generated from the base metal compound using a hydrothermal synthesis method.

[0068] like Figure 1 As shown in (b), a base metal oxide 51 is impregnated in carbon fiber 50. The oxide 51 is, for example, NiMoO4. Figure 1 As shown in (c), carbon fiber 50 impregnated with oxide 51 is arranged inside a cylindrical furnace 56. The carbon fiber 50 is heat-treated in a reducing gas atmosphere 57. The reducing gas 57 is, for example, hydrogen or a mixture of hydrogen and other inert gases such as rare gases. Figure 1 As shown in (d), the base metal oxide 51 is reduced, and the base metal-containing catalyst 52 is directly bonded to the carbon fiber 50. The catalyst 52 is, for example, a NiMo alloy. The catalyst 52 is not only physically bonded to the carbon fiber 50, but at least a portion of the elements of the catalyst 52 are chemically bonded to the carbon of the carbon fiber 50.

[0069] like Figure 1 (a) and Figure 1 As shown in (b), base metal oxide 51 is attached to the surface of multiple carbon fibers 50. Then, as... Figure 1 (c) and Figure 1As shown in (d), by heat-treating the carbon fiber 50 in a reducing gas atmosphere, a catalyst 52 containing base metals is formed in which at least a portion of the elements are directly chemically bonded to the carbon fiber 50. The electrode manufactured in this way exhibits improved performance and durability because the catalyst 52 is firmly fixed to the carbon fiber 50.

[0070] exist Figure 1 In step (a), during the process of attaching oxide 51, carbon fibers 50 are arranged in an aqueous solution 54 containing multiple base metals, and an oxide of the multiple base metals is attached to the surface of the carbon fibers 50 using a hydrothermal synthesis method. An alloy of the multiple base metals is formed by heat treatment in a reducing gas atmosphere. This allows the formation of an electrode with excellent performance and durability. In the process of attaching oxide 51 to the surface of multiple carbon fibers 50, it is preferable to impregnate the surface of the carbon fibers 50 with oxide 51. It should be noted that impregnation refers to the penetration of oxide 51 deep into the structure of the multiple carbon fibers.

[0071] (Implementation Method 3)

[0072] Embodiment 3 is an example of a water electrolysis device, fuel cell, secondary battery, and double-layer capacitor that uses the electrodes of Embodiments 1 and 2. Figure 2 This is a cross-sectional view of the device in Embodiment 3. (As shown) Figure 2 As shown, a device 100, including a water electrolysis apparatus, a fuel cell, a secondary battery, and an electric double-layer capacitor, includes electrodes 10 and 12, and an electrolyte 11 disposed between the electrodes 10 and 12. Electrodes 10 and 12 are, for example, an anode and a cathode. At least one of electrodes 10 and 12 uses electrodes from embodiments 1 and 2. This improves the durability of electrodes 10 and 12. Furthermore, by using base metals, an inexpensive device can be provided.

[0073] (Implementation Method 4)

[0074] Embodiment 4 is an example of a solid polymer electrolysis type (PEM: Polymer Electrolyte Membrane) water electrolysis device using the electrodes of Embodiments 1 and 2. Water electrolysis, which electrolyzes water, is highly regarded because it produces hydrogen gas (H2) without emitting CO2. As water electrolysis methods, alkaline water electrolysis and PEM-type water electrolysis are known. Alkaline water electrolysis uses an alkaline aqueous solution. While alkaline water electrolysis can use base metal electrodes, it suffers from poor energy efficiency and the generation of harmful alkaline waste liquid. PEM-type water electrolysis uses a solid polymer electrolyte, through 2H... + +2e - →H2 is a method of generating hydrogen gas from protons. The PEM-type water electrolysis method has good energy efficiency and does not produce alkaline waste liquid. However, if base metals are used as electrodes, there is a problem of poor electrode durability.

[0075] Figure 3 This is a cross-sectional view of the PEM-type water electrolysis device according to Embodiment 3. Figure 3 As shown, in the water electrolysis apparatus 102, catalysts 16 and 18 are arranged to sandwich a solid polymer electrolyte membrane 14. The solid polymer electrolyte membrane 14 is a polymer membrane with ion (proton) conductivity, such as a fluorinated polymer with sulfonic acid groups (e.g., Nafion). The thickness of the solid polymer electrolyte membrane 14 is, for example, 0.1 mm to 1 mm. Catalyst 16 is, for example, the alloy described in Embodiment 1, and catalyst 18 is, for example, the base metal-containing catalyst bonded to carbon fibers described in Embodiment 2.

[0076] Gas diffusion layers 20 and 21 are provided in a manner that sandwiches catalysts 16 and 18. Gas diffusion layer 20 supplies water to electrode 10, and gas diffusion layer 21 discharges the generated hydrogen gas. Furthermore, gas diffusion layers 20 and 21 are conductive. Gas diffusion layers 20 and 21 are, for example, carbon paper or carbon cloth. The thicknesses of gas diffusion layers 20 and 21 are, for example, 0.01 mm to 1 mm. Gas diffusion layers 20 and 21 are respectively disposed within openings 22a and 23a formed in insulating gaskets 22 and 23.

[0077] Electrode 10 includes a catalyst 16 and a gas diffusion layer 20, and electrode 12 includes a catalyst 18 and a gas diffusion layer 21. Catalyst 16 and / or 18 can be supported on the surface of electrolyte membrane 14, or on gas diffusion layers 20 and / or 21. The method of coating catalyst 16 and / or 18 on the surface of electrolyte membrane 14 is called the CCM (Catalyst Coated Membrane) method. The method of coating catalyst 16 and / or 18 on the surface of gas diffusion layers 20 and / or 21 is called the CCE (Catalyst Coated Electrode) method.

[0078] Current collectors 24 and 25 are disposed such that they sandwich gas diffusion layers 20 and 21. Current collectors 24 and 25 supply current to electrodes 10 and 12 via gas diffusion layers 20 and 21, respectively. Since current is supplied, current collectors 24 and 25 are technically power supply bodies, but are conventionally referred to as current collectors here. Water channels 24a and 25a may also be provided on the surfaces of current collectors 24 and 25. Current collectors 24 and 25 are conductive materials, such as Ti. Insulating gaskets 26 and 27 are disposed such that they sandwich current collectors 24 and 25, and a frame 28 is disposed such that it sandwiches gaskets 26 and 27.

[0079] Terminals 30 and 31 are electrically connected to current collectors 24 and 25, respectively. When a positive voltage is applied between terminals 30 and 31, hydrogen gas 36 is generated in electrode 12. An inlet path 32 and an outlet path 33 are provided, penetrating the frame 28, gasket 26, and current collector 24. Water 35 is introduced into water passage 24a via inlet path 32, and water 35 is discharged from water passage 24a via outlet path 33. An outlet path 34 is provided, penetrating the frame 28, gasket 27, and current collector 25. Hydrogen gas 36 is discharged from water passage 25a via outlet path 34.

[0080] The water electrolysis apparatus 102, as long as it includes the catalyst 16 at the anode, the catalyst 18 at the cathode, and the solid polymer electrolyte membrane 14, can be appropriately designed with other configurations. By using the electrodes of Embodiments 1 and 2 in the PEM-type water electrolysis apparatus 102, the durability of electrodes 10 and 12 can be improved even when using base metals. Thus, a water electrolysis apparatus 102 that is inexpensive and has excellent durability can be provided. At least one of electrodes 10 and 12 can be an electrode of Embodiment 1 or 2.

[0081] Catalysts 16 and 18 can be arranged using either the CCM method or the CCE method, but it is preferred to use the CCM method when the catalyst of Embodiment 1 is used as the anode and the CCE method when the catalyst of Embodiment 2 is used as the cathode. This reduces the contact resistance between the electrolyte membrane 14 and the electrodes 10 and 12.

[0082] Example

[0083] As an example, a PEM-type water electrolysis device was fabricated.

[0084] (anode)

[0085] Five-element HEA welding wire composed of Mn, Co, Ni, Cr, and Fe was prepared. The atomic percentages of Mn, Co, Ni, Cr, and Fe were all approximately 20 atomic percent. Additionally, six-element HEA welding wire composed of Mo, Mn, Co, Ni, Cr, and Fe was prepared. The atomic percentages of Mo, Mn, Co, Ni, Cr, and Fe were all approximately 16.7 atomic percent. The HEA welding wire was pulverized using a planetary ball mill at 600 rpm for 3 hours. The pulverized HEA was mixed with carbon black CB at a 1:1 weight ratio, and the HEA was physically pressed onto the CB using a planetary ball mill. Vulcan XC72R manufactured by Cabot, Ketjen Black EC600JD manufactured by Lion Specialty Chemicals, or 05-1530 manufactured by Sigma-Aldrich were used as the carbon black. Other carbon blacks may also be used. The planetary ball mill was operated at 600 rpm for 25 hours, resulting in a mixture of HEA and CB, HEA-CB. 30 mg of HEA-CB was dispersed in 0.6 ml of a mixture of 1-propanol and water (1-PrOH:H₂O = 4.56:0.55 by weight). Nafion (Nafion 115) was added, followed by ultrasonic treatment. The concentration of Nafion was 5% by weight, and the C:Nafion ratio was 1:0.8 by weight. The solution containing HEA-CB and Nafion was coated onto an electrolyte membrane 14 (CCM method). Electrolyte membrane 14 was Nafion. Thus, HEA was loaded onto CB, and CB was loaded onto electrolyte membrane 14.

[0086] Figure 4 (a) and Figure 4 (b) is a diagram showing the X-ray diffraction (XRD) patterns of the 5-element HEA and 6-element HEA in the embodiments. Figure 4 (a) and Figure 4 (b) shows the XRD patterns of the HEA welding wire and the pulverized HEA powder. 1h, 3h, and 6h represent the pulverization time of HEA (excluding CB). The peaks at 2θ of 43°–52° represent the FCC crystal structure.

[0087] like Figure 4As shown in (a), the 5-component HEA welding wire exhibits an FCC crystal structure. In the HEA powder obtained by pulverizing the HEA welding wire, although the peaks are wider than those of the HEA welding wire, it still possesses an FCC crystal structure. This indicates that the 5-component HEA powder is a solid solution of a 5-component base metal, forming a high-entropy alloy. Even with a pulverization time of 6 hours, the FCC crystal structure is maintained. The peak with 2θ ranging from 24° to 37° is a zirconium oxide peak. Since the balls in the ball mill are zirconium oxide, it is assumed that zirconium oxide is mixed into the HEA powder as an impurity. If the pulverization time increases, it is assumed that the surface area of ​​the HEA increases.

[0088] like Figure 4 As shown in (b), the 6-component HEA welding wire exhibits an FCC crystal structure. In the HEA powder obtained by pulverizing the HEA welding wire, the peaks broaden with longer pulverization times, but the FCC crystal structure is still present. This indicates that the 6-component HEA powder is a high-entropy alloy. Longer pulverization times result in increased zirconium oxide content.

[0089] Figure 5 This is a SEM (Scanning Electron Microscope) image of the 5-component HEA loaded with carbon black in the embodiment. Figure 5 As shown, HEA is supported on carbon black CB. The particle size of HEA is approximately 1 μm to 10 μm.

[0090] (cathode)

[0091] like Figure 1 As shown in (a), 1.5 mM NiCl2·H2O and 1.5 mM Na2MoO4·2H2O were dissolved in 30 ml of water to prepare aqueous solution 54. A 2 cm × 2 cm piece of carbon paper (TGP-H-090 manufactured by Toray) was impregnated in aqueous solution 54. Hydrothermal synthesis was performed at 150 °C for 6 hours. After drying, a product was formed as shown in (a). Figure 1 (b) shows carbon paper impregnated with NiMoO4. Sometimes, when using only carbon paper impregnated with NiMoO4, the NiMo content is insufficient. In this case, a pre-prepared NiMoO4 solution, or a NiMoO4 solution that has not adhered to the carbon paper in the aqueous solution 54, is placed on the carbon paper. This adjusts the NiMo alloy content. The area is 4 cm² relative to the carbon paper area. 2 The amount of NiMoO4 solution subsequently loaded is, for example, 1 ml to 10 ml. Figure 1 As shown in (c), NiMoO4 is heat-treated for 20 minutes at 950°C in a tubular furnace 56 under a mixed atmosphere of Ar and H2 gases. This reduces NiMoO4 to form a structure as shown in (c). Figure 1(d) NiMo alloy supported on carbon paper. A solution containing NiMo alloy and Nafion (NiMO:Nafion weight ratio of 1:0.22) was coated onto the gas diffusion layer 21 (CCE method).

[0092] Figure 6 This is a diagram showing the X-ray diffraction pattern of the NiMo alloy in the embodiment. (Example) Figure 6 As shown, the NiMo alloy before energization contains NiMo and Ni4Mo. The ratio of NiMo is greater than that of Ni4Mo. It also contains some Mo2C. Thus, at least a portion of the Mo element in NiMo is chemically bonded to the carbon in carbon fiber 50. The Ni to Mo ratio of the prepared NiMo alloy is Ni:Mo = 1:1.5 by weight and Ni:Mo = 1.09:1 atomic ratio.

[0093] Figure 7 (a)~ Figure 7 (c) is a SEM image of the NiMo alloy supported on carbon fibers in the embodiment. Figure 7 As shown in (a), multiple carbon fibers 40 are arranged in a mesh pattern in carbon paper. The diameter of the carbon fiber 40 is several μm. Figure 7 As shown in (b), the NiMo alloy 42 is supported in a manner that surrounds each of the multiple carbon fibers 40. Figure 7 As shown in (c), NiMo alloy 42 is directly bonded to carbon fiber 40 and grown directly from carbon fiber 40. NiMo alloy 42 is a porous body. The pore and ligament sizes of NiMo alloy 42 range from 0.1 μm to 3 μm.

[0094] (Water electrolysis battery)

[0095] The electrolyte membrane 14 is clamped by gas diffusion layers 20 and 21. Catalysts 16 and 18 are formed by CCM or CCE methods. The electrolyte membrane 14, gas diffusion layers 20 and 21 are pressed for 3 minutes at 130°C and a load of 250 kg using a hot press. Gas diffusion layers 20 and 21 are clamped by current collectors 24 and 25, and gaskets 26 and 27. Gaskets 26 and 27 are clamped by the plates of frame 28 and fastened with approximately 4 N, thereby fabricating the membrane. Figure 3 Such a water electrolysis battery.

[0096] Make the following 4 batteries.

[0097] Battery A

[0098] Cathode catalyst: Pt / C; Anode catalyst: IrO2

[0099] Battery B

[0100] Cathode catalyst: NiMo alloy monomer; Anode catalyst: IrO2

[0101] Battery C

[0102] Cathode catalyst: NiMo alloy; Anode catalyst: IrO2

[0103] Battery D

[0104] Cathode catalyst: Pt / C; Anode catalyst: quinary HEA

[0105] Battery E

[0106] Cathode catalyst: Pt / C; Anode catalyst: Hexavalent HEA

[0107] Battery F

[0108] Cathode catalyst: NiMo alloy; Anode catalyst: 5-component HEA

[0109] Weight density per unit area

[0110] Pt / C: 1 mg / cm 2

[0111] IrO2: 1 mg / cm 2

[0112] NiMo alloy: 3mg / cm 2

[0113] 5 yuan HEA: 3mg / cm 2

[0114] 6 yuan HEA: 3mg / cm 2

[0115] Other materials

[0116] Electrolyte membrane 14: Nafion (registered trademark) 115 or 117 manufactured by Merck.

[0117] Gas diffusion layers 20 and 21: Toray Industries carbon paper TGP-H-090

[0118] Battery A is a comparative example where both the cathode and anode catalysts use noble metals. Battery B is a battery equivalent to the comparative example, in which a porous NiMo alloy is pressed and placed on a gas diffusion layer 21. In battery B, the NiMo alloy and the carbon fibers within the gas diffusion layer 21 are only physically bonded, without chemical bonding. Battery C uses the NiMo alloy of the examples in the cathode. Batteries D and E use the quinary HEA and hexavalent HEA of the examples in the anode. Battery F uses the NiMo alloy of the examples in the cathode and the quinary HEA of the examples in the anode.

[0119] For batteries A, B, and C, water electrolysis cells with an active area of ​​2 cm × 2 cm were constructed, and their current-voltage characteristics were measured. The measurement conditions were: battery temperature 80℃, water flow rate 5 ml / min, and current-voltage characteristics of 4 A / cm². 2 After aging at current density for 25 hours, the current and voltage characteristics were measured.

[0120] Figure 8 This is a graph showing the current-voltage characteristics of batteries A, C, and D. The horizontal axis represents current density, and the vertical axis represents battery voltage. Figure 8 As shown, compared to battery A (used as a comparison example), battery C has approximately the same battery voltage, while battery D has a slightly higher battery voltage. A current density of 1 A / cm² is used. 2 The battery voltage is used as an indicator of electrolytic characteristics. A lower battery voltage indicates better efficiency. In the comparative example battery A, which uses precious metals, 1 A / cm 2 The battery voltage is 1.6V. In battery C, it is 1.75V, roughly the same as battery A. In battery D, it is 1.95V, slightly higher than battery A.

[0121] As a comparison with battery C, for battery B, the active area is fabricated to be 4 cm. 2 The current and voltage characteristics of a water electrolysis battery were measured. The measurement conditions were: battery temperature 25℃ and water flow rate 1 ml / min. Figure 9 This is a graph showing the current-voltage characteristics of battery B. (For example...) Figure 9 As shown, although the measurement conditions are different, the battery voltage in battery B is significantly higher than that in battery C. Thus, battery B, obtained by physically pressing NiMo alloy onto carbon fiber, exhibits poor electrode performance. This is attributed to the increased contact resistance during physical contact alone.

[0122] The change in current density over time was measured for battery C. The measurement conditions were: battery voltage of 2V, battery temperature of 80℃, and water flow rate of 20ml / min. Figure 10 This is a graph representing the constant voltage characteristics of battery C. (Example) Figure 10 As shown, even after 250 hours, the current density did not decrease; in fact, it increased. No decrease in current density was observed after 250 hours. This suggests that under these conditions, the area surrounding the cathode catalyst is strongly acidic (pH 1-2). The fact that no decrease in current density was observed after 250 hours in such a strongly acidic environment indicates surprising durability. Figure 6 After 250 hours of energization, the XRD pattern showed that the crystal structure of the NiMo alloy had not deteriorated.

[0123] The change in current density over time was measured for batteries D and E. The measurement conditions were: battery voltage 2.4V, battery temperature 80℃, and water flow rate 5ml / min. Figure 11This is a graph representing the constant voltage characteristics of batteries D and E. (For example...) Figure 11 As shown, the increase in current density is a common phenomenon resulting from the swelling of the electrolyte membrane 14 and improved electrolytic performance. In battery D, the maximum current density is 3.0 A / cm². 2 The current density after 150 hours of energization is 2.72 A / cm². 2 After 150 hours of energization, the current density is 90.6% of the maximum current density.

[0124] In battery E, the battery voltage was temporarily disconnected and then reapplied after approximately 75 hours. With each voltage disconnection and reapplication, the current density recovered by 6%. The maximum current density was 4.15 A / cm². 2 The current density after 130 hours of energization is 3.7 A / cm². 2 After 150 hours of energization, the current density is 89% of the maximum current density. For example, if the NiMo alloy used in the cathode catalyst of battery C is used as the anode catalyst, the NiMo alloy dissolves within 1 minute. In contrast, batteries D and E also exhibit very high durability.

[0125] For batteries C, D, and F, water electrolysis cells with an active area of ​​1 cm × 1 cm were constructed, and their current-voltage characteristics were measured. The measurement conditions were: battery temperature 80℃, water flow rate 5 ml / min, and current-voltage characteristics of 4 A / cm². 2 After aging at current density for 25 hours, the current and voltage characteristics were measured.

[0126] Figure 12 This is a graph showing the current-voltage characteristics of the battery's capacitors C, D, and capacitor F. (Example) Figure 12 As shown, due to the active region and Figure 8 The voltages of batteries C and D are different, therefore the voltage ratios are different. Figure 8 High. It can. Figure 12 Internal comparison. Current density is 1 A / cm². 2 The battery voltage is 2.0V in battery C, 2.6V in battery D, and 2.8V in battery F. The battery voltage of battery F is slightly higher than that of battery D. Thus, water electrolysis can also be carried out in battery F, where both the cathode and anode catalysts are base metals.

[0127] Figure 13 (a)~ Figure 13 (c) are graphs showing the impedance test results of batteries C, D and F respectively. Figure 13 (a)~ Figure 13 In (c), the -Z″ intercept represents the contact resistance from terminals 30 and 31 to catalysts 16 and 18. Figure 13 As shown in (a), the contact resistance in battery C is estimated to be approximately 200 mΩ to 650 mΩ. Figure 13As shown in (b), the contact resistance in battery D is estimated to be approximately 300 mΩ. Figure 13 As shown in (c), the contact resistance in battery F is estimated to be between 350 mΩ and 1.6 Ω. Thus, the contact resistance is high in batteries C, D, and F. The contact resistance should be able to be reduced depending on battery manufacturing conditions, etc., and it is believed that with optimization, the performance of batteries C, D, and F could be improved to the same level as battery A, which uses precious metals.

[0128] As described above, by using batteries C to F, the performance and durability of the electrodes are improved, and the performance and durability of the water electrolysis device are also improved.

[0129] A water electrolysis cell with an active region of 2 cm × 2 cm was fabricated, using high-entropy alloys (HEAs) of 5 to 9 elements as catalysts for the anode and / or cathode. The elements used in each HEA are as follows.

[0130] 5 yuan HEA: Co, Cr, Mn, Ni, Fe

[0131] 6 yuan HEA: Co, Cr, Mn, Ni, Fe, Mo

[0132] 7 yuan HEA: Co, Cr, Mn, Ni, Fe, Mo, Nb

[0133] 8 yuan HEA: Co, Cr, Mn, Ni, Fe, Mo, Nb, Zr

[0134] 9 yuan HEA: Co, Cr, Mn, Ni, Fe, Mo, Nb, Zr, Ti

[0135] Cells were constructed using quinary to quinary HEA catalysts for the anode and IrO2 catalysts for the cathode. Additionally, cells were constructed using Pt / C catalysts for the anode and quinary to quinary HEA catalysts for the cathode. The current-voltage characteristics of these cells were measured. Measurement conditions were: cell temperature 80°C, water flow rate 5 ml / min, and current at 4 A / cm². 2 After aging at current density for 25 hours, the current and voltage characteristics were measured.

[0136] Figure 14 (a) and Figure 14 (b) is a graph showing the current-voltage characteristics of a battery that uses 5-cell HEA to 9-cell HEA at the anode or cathode. Figure 14 (a) is a graph showing the current-voltage characteristics of a Pt / C-5-9 HEA cell with a Pt / C cathode and a 5- to 9-ary HEA anode. As a comparative example, the current-voltage characteristics of a Pt / C-IrO2 cell with a Pt / C cathode and an IrO2 anode are also shown. Figure 14As shown in (a), the Pt / C-5- to 9-ary HEA batteries have slightly higher voltages compared to Pt / C-IrO2 batteries. For example, the current density is 1 A / cm². 2 The battery voltage is 1.60V in a Pt / C-IrO2 battery, compared to 2.20V in a Pt / C-9-element HEA battery. The battery voltage decreases as the number of elements increases from 5 to 9. This decrease is particularly noticeable in batteries using 8-element HEA or higher elements.

[0137] Figure 14 (b) is a graph showing the current-voltage characteristics of a cell using a quinary to quinary HEA cathode and an IrO2 anode (quinary to quinary HEA-IrO2). As a comparative example, the current-voltage characteristics of a Pt / C-IrO2 cell are also shown. Figure 14 As shown in (b), the 5- to 9-element HEA-IrO2 batteries have slightly higher voltages compared to Pt / C-IrO2 batteries. For example, the current density is 1 A / cm². 2 The battery voltage is 1.60V in Pt / C-IrO2 batteries and 2.06V in HEA-IrO2 batteries with elements ranging from 5 to 9. The battery voltage decreases as the element number increases from 5 to 9. This decrease is particularly noticeable in batteries using HEA elements of 8 or higher.

[0138] Figure 15 This graph shows the current-voltage characteristics of a battery using a 9-element HEA at both the anode and cathode. The 9-element HEA battery uses a 9-element HEA at both the anode and cathode. As a comparative example, the current-voltage characteristics of a Pt / C-IrO2 battery are shown. The current-voltage characteristics of each battery in the first cycle and from 0 A / cm are also shown. 2 Up to 1A / cm 2 The current-voltage characteristics were obtained after 10,000 scan cycles. For example... Figure 15 As shown, the battery voltage is higher in the 9-cell HEA-9-cell HEA batteries compared to the Pt / C-IrO2 batteries. In the Pt / C-IrO2 batteries, the current-voltage characteristics after 10,000 cycles are almost unchanged from the first cycle. In the 9-cell HEA-9-cell HEA batteries, the current-voltage characteristics after 10,000 cycles are slightly higher than the first cycle.

[0139] For 9-yuan HEA batteries, the change in current density over time was measured. Figure 16 This graph shows the constant voltage characteristics of a 9-cell HEA battery. As a comparative example, the characteristics of a Pt / C-IrO2 battery are shown. The voltage of the 9-cell HEA battery is 3V, while the voltage of the Pt / C-IrO2 battery is 2.5V. Figure 16As shown, the current density of both the 9-yuan HEA-9-yuan HEA battery and the Pt / C-IrO2 battery remained almost unchanged until 130-140 hours of operation. Even after stopping the power supply for about 10 hours and then restarting it, the current density remained almost unchanged.

[0140] The reaction at the anode of a water electrolysis unit is OER, and at the cathode it is HER. At the anode, an overvoltage is applied to obtain the desired current density for OER to occur. Exposed to a high potential, the OER catalyst is oxidized and easily degraded. Therefore, if a catalyst without oxidation durability is used at the anode, the catalyst at the anode dissolves instantaneously when the water electrolysis unit is energized. Therefore, apart from IrO2, there are no practical catalysts for the anode of PEM-type water electrolysis units. Figure 11 and Figure 16 As shown, by using HEA as the anode, a durable OER catalyst can be achieved. While using HEA as the anode catalyst results in a higher cell voltage compared to IrO2, the use of base metal HEA makes it cheaper and more practical than IrO2. Furthermore, in water electrolysis devices, the cathode is oxidized when the current is stopped. If a catalyst without oxidation durability is used at the cathode, the catalyst will dissolve after the current is stopped. To suppress this, for example, in alkaline water electrolysis devices using base metal catalysts, a low current is continuously flowing when the water electrolysis device is stopped. Figure 16 As shown, by using HEA as the cathode, the cathode does not deteriorate even after power is turned on again after power has been turned off.

[0141] By using an alloy composed of three or more base metal elements with approximately equal atomic ratios and forming a solid solution of the three or more base metal elements as a catalyst for the oxygen evolution reaction (OER) or hydrogen evolution reaction (HER), the durability of the electrode can be improved.

[0142] In fuel cells, a catalyst for hydrogen refrigerant (HOR) is used at the anode. When hydrogen is produced from hydrocarbons such as methanol or natural gas, the fuel gas in the fuel cell contains carbon monoxide (CO). For example, when Pt is used as the catalyst at the anode of a fuel cell, Pt becomes poisoned by CO. To enhance CO tolerance, a Pt-Ru alloy is used as the anode catalyst, but after prolonged use, CO tolerance decreases due to Ru dissolution, etc. This causes problems not present in HOR catalysts compared to ORR catalysts. Therefore, ORR catalysts are generally not used as HOR catalysts.

[0143] By using an alloy composed of three or more base metal elements in approximately equal atomic ratios, forming a solid solution of the three or more base metal elements, as a catalyst for the hydrogen oxidation reaction (HOR), the durability of the electrode can be improved. In particular, by using the catalyst of Embodiment 1 at the anode of the fuel cell, the durability of the anode can be improved.

[0144] The three or more base metal elements are preferably at least three elements selected from Fe, Cu, Ni, Al, Pb, Zn, Sn, W, Mo, Ta, Mg, Co, Bi, Cd, Ti, Zr, Sb, Mn, Be, Cr, Ge, V, Ga, Hf, In, Nb, Re, and Tl. The number of base metal elements is preferably five or more, more preferably six or more. Figure 14 (a) and Figure 14 As shown in (b), it is further preferred to have 8 or more types.

[0145] Here, "a catalyst or alloy composed of a plurality of base metal elements" means that the catalyst or alloy is intentionally designed to be free of elements other than the plurality of base metal elements. That is, the catalyst or alloy may also contain unavoidable elements other than the plurality of base metal elements. When the atomic percentage of the element with the smallest atomic percentage among the plurality of base metal elements is set as Cat, the total atomic percentage of unavoidable nonmetallic elements such as oxygen, carbon, and hydrogen in the catalyst or alloy is preferably Cat / 2 or less, more preferably Cat / 5 or less. The total atomic percentage of unavoidable metallic elements other than the plurality of base metal elements in the catalyst or alloy is preferably Cat / 10 or less, more preferably Cat / 100 or less. Furthermore, the total composition percentage of unavoidable elements in the catalyst or alloy is preferably 10 atomic% or less, more preferably 1 atomic% or less.

[0146] The preferred embodiments of the invention have been described in detail above, but the invention is not limited to this specific embodiment. Various modifications and alterations can be made within the scope of the spirit of the invention as described in the claims.

[0147] Symbol Explanation

[0148] 10 and 12 electrodes

[0149] 11 Electrolytes

[0150] 14 Electrolyte Membrane

[0151] 16, 18 catalysts

[0152] 20 and 21 Gas diffusion layers

[0153] 24, 25 collectors

[0154] 22, 23, 26, 27 gaskets

[0155] 50 carbon fiber

[0156] 51 oxide

[0157] 52 catalyst

[0158] 54 aqueous solution

[0159] 57 Reducing Gas

Claims

1. An electrode comprising an alloy as a catalyst for an oxygen evolution reaction, a hydrogen evolution reaction, or a hydrogen oxidation reaction, said alloy being an octet HEA composed of Co, Cr, Mn, Ni, Fe, Mo, Nb, and Zr, or a nintet HEA composed of Co, Cr, Mn, Ni, Fe, Mo, Nb, Zr, and Ti, wherein the atomic ratios of the elements in the octet HEA or the nintet HEA are equal, and the elements in the octet HEA or the nintet HEA form a solid solution.

2. A water electrolysis device, comprising: The anode is the electrode as described in claim 1; cathode; and A solid polymer electrolyte membrane is disposed between the anode and the cathode.

3. The water electrolysis device according to claim 2, wherein, The cathode is the electrode as described in claim 1.

4. The water electrolysis device according to claim 2, wherein, The cathode comprises: carbon fiber; and A catalyst composed of base metals, wherein at least a portion of the elements of the catalyst are chemically bonded to the carbon fiber. The catalyst is a NiMo alloy with a Ni to Mo atomic ratio of 2:1 to 1:2, wherein at least Mo is chemically bonded to the carbon fiber. The NiMo alloy is a porous material.

5. A fuel cell, comprising: The anode is the electrode as described in claim 1; cathode; and An electrolyte membrane is disposed between the anode and the cathode.

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