Electrocatalyst, anion exchange membrane electrochemical cell

Abstract

Provided is an electrode catalyst which is excellent in durability, substance conductivity and electric conductivity, and which can be produced inexpensively.　According to the present invention, provided is an electrode catalyst comprising a void-containing structure having a void, wherein: the void-containing structure is provided with a core part, and a skin layer that covers the core part; the core part comprises metal; and the skin comprises an oxide containing Ni.

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst and an anion exchange membrane electrochemical cell. The electrode catalyst of the present invention can be used, for example, as a catalyst for electrochemical reactions in an anion exchange membrane electrochemical cell. Examples of anion exchange membrane electrochemical cells include anion exchange membrane water electrolysis cells and anion exchange membrane fuel cells. [Background technology]

[0002] In the production of hydrogen by water electrolysis using an anion exchange membrane, the hydrogen reaction (H2O+e - →1 / 2H2+OH - ) occurs at the anode opposite to the electrode, and the oxygen reduction reaction (OH - →1 / 4O2+1 / 2H2O+e - Currently, noble metal oxides (IrO x ) is used as an electrode catalyst. x IrRuO x Attempts have been made to reduce the amount of Ir used by 30% and the overvoltage to approximately 0.2 V (Non-Patent Document 1). However, there is a need for the development of non-precious metal-supported catalysts that do not use Ir, which is expensive and has limited reserves. Patent Document 1 develops a catalyst in which non-precious metal Ni(OH)2 nanoparticles are supported on conductive carbon, but the addition of carbon is required to provide conductivity and form gas diffusion paths. Carbon accelerates degradation at the operating potential (1.7-1.8 V), which poses a major practical challenge. The use of NiFe metal nanoparticles has overcome the conductivity issue and succeeded in reducing the overvoltage compared to IrOx. However, the electrode is prone to densification, and the addition of carbon is essential to provide diffusion paths (voids) for the generated oxygen (Non-Patent Document 2). In NiCoO-based and NiFeO-based catalysts, the overvoltage at the anode is reduced by using IrO. xHowever, in the case of NiCoO-based materials, the formation of gas diffusion paths and the improvement of the specific surface area increase the resistance to 30 Ω at the operating potential (1.6 V), causing a problem in electrical conductivity (Non-Patent Document 5), and in the case of NiFeO-based materials, there is a problem of deterioration due to oxidation of Fe as the potential increases (Non-Patent Document 6). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special table number 2017-527693 [Non-patent literature]

[0004] [Non-Patent Document 1] Appl. Catal B 164 (2015) 488-495 [Non-patent document 2] ACS Catal. 10 (2020) 4019-4047 [Non-patent document 3] JACS 134(2012)17253-17261 [Non-patent document 4] JACS 135 (2013) 16977-16987 [Non-patent document 5] ACS Appl. Mat. Interfaces (2017) 44567 [Non-patent document 6] ACS Catal. 9(2019)7-15 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and provides an electrode catalyst that is excellent in durability, material conductivity and electrical conductivity, and that can be produced at low cost. [Means for solving the problem]

[0006] According to the present invention, there is provided an electrode catalyst comprising a porous body having voids, the porous body having a core portion and a skin layer covering the core portion, the core portion being composed of a metal, and the skin layer being composed of an oxide containing Ni.

[0007] The electrode catalyst of the present invention does not require the addition of carbon and is composed of a metal core and an oxide skin layer, and therefore has excellent durability. Furthermore, since this electrode catalyst is composed of a porous body with a porosity of 20% or more, it has excellent material conductivity. Furthermore, since the core of this electrode catalyst is metal, it has excellent electrical conductivity. Furthermore, since this electrode catalyst does not require a precious metal as an essential component, it can be produced inexpensively. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a configuration diagram showing a state in which the electrochemical cell 10 is performing a water electrolysis operation. [Figure 2] FIG. 1 is a configuration diagram showing a state in which an electrochemical cell 10 is operating to generate electricity. [Figure 3] FIG. 2 is a cross-sectional view of a porous body 60 that constitutes the electrode catalyst 50. [Figure 4] FIG. 2 is a cross-sectional view of a powder 70 that constitutes the electrode catalyst 50. [Figure 5] FIG. 1 is a perspective view of a particle 80 having a beaded structure. [Figure 6] FIG. 1 is a cross-sectional view of a particle 80 having a bead-and-loop structure. [Figure 7] 1 is a cross-sectional view of a manufacturing apparatus 1 for manufacturing powder, passing through the center of a burner 2. FIG. [Figure 8] FIG. 8 is an enlarged view of an area X in FIG. [Figure 9] 8 is a cross-sectional view taken along the line AA in FIG. 7. [Figure 10] FIG. 10 is an enlarged view of an area Y in FIG. [Figure 11] FIG. 11A is a TEM image of oxide fine particles obtained in the example, and FIG. 11B is a diagram in which arrows indicating the primary particle diameters of the primary particles in the TEM image of FIG. 11A are superimposed. [Figure 12] 1 is a graph showing the relationship between the Co ratio x and the electrical conductivity of the electrode catalyst 50. [Figure 13] 1 shows the configuration of an electrochemical measurement device 15 used to measure OER activity and HER activity. [Figure 14] 1 is a graph showing the results of measuring the OER activity of the electrode catalysts 50 of Examples 1 to 4. [Figure 15] 1 is a graph showing the results of measuring the OER activity of the electrode catalysts 50 of Examples 1-2 and 5-6. [Figure 16] 1 is a graph showing the results of measuring the HER activity of the electrode catalysts 50 of Examples 1 to 4. [Figure 17] 1 is a graph showing the results of measuring the HER activity of the electrode catalysts 50 of Examples 1-2 and 5-6. [Figure 18] 1 is a graph showing the results of an evaluation of the voltage-voltage characteristics of a water electrolysis cell in which the electrode catalyst 50 (Ni0.8Co0.2O) of Example 2 was used as the anode catalyst. [Figure 19] 10 is a graph showing the results of a long-term evaluation of a water electrolysis cell in which the anode catalyst was the electrode catalyst 50 (Ni0.8Co0.2O) of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently.

[0010] 1. Electrochemical Cell 10 1 shows the configuration of an anion exchange membrane electrochemical cell 10 according to one embodiment of the present invention. The electrochemical cell 10 includes a cathode 20, an anode 30, and an anion exchange membrane 40 disposed therebetween.

[0011] 1, when a voltage is applied between the cathode 20 and the anode 30 and water is supplied to the cathode 20, the following cathode and anode reactions occur, generating hydrogen at the cathode 20 and water and oxygen at the anode. Electrons move from the anode 30 to the cathode 20 through the wiring, generating OH - moves from the cathode 20 to the anode 30 through the anion exchange membrane 40. In this case, the electrochemical cell 10 becomes an anion exchange membrane water electrolysis cell and performs water electrolysis operation. Cathodic reaction: H2O+e - →1 / 2H2+OH - Anode reaction: OH - → 1 / 2H2O+1 / 4O2+e -

[0012] 2, the electrochemical cell 10 has a load R connected between the cathode 20 and the anode 30, and when water and oxygen are supplied to the cathode 20 and hydrogen is supplied to the anode 30, an electromotive force is generated and water is produced by the cathode and anode reactions shown below. The generated electromotive force causes electrons to move from the anode 30 to the cathode 20 through the load R, and OH - moves from the cathode 20 to the anode 30 through the anion exchange membrane 40. In this case, the electrochemical cell 10 becomes an anion exchange membrane fuel cell and operates to generate electricity. Cathode reaction: 1 / 2H2O + 1 / 4O2 + e - →OH - Anode reaction: 1 / 2H2+OH - →H2O+e -

[0013] The cathode reaction in the power generation operation is the reverse reaction of the anode reaction in the water electrolysis operation, and the anode reaction in the power generation operation is the reverse reaction of the cathode reaction in the water electrolysis operation.

[0014] In this way, the electrochemical cell 10 can be operated both as a water electrolysis cell and as a fuel cell. For this reason, for example, surplus power generated by solar power generation or the like can be used to operate the electrochemical cell 10 as a water electrolysis cell to generate hydrogen and oxygen, which can be stored, and when power is needed, the stored hydrogen and oxygen can be used to operate the electrochemical cell 10 as a fuel cell to generate electromotive force, thereby enabling the electrochemical cell 10 to be operated efficiently.

[0015] The cathode 20 includes a diffusion layer 21, a microporous layer 22, and a catalyst layer 23. The anode 30 includes a diffusion layer 31, a microporous layer 32, and a catalyst layer 33. The diffusion layers 21, 31 are made of a porous material and function to diffuse a fluid (liquid or gas) supplied to the catalyst layers 23, 33. The microporous layers 22, 32 function to further diffuse the fluid supplied to the catalyst layers 23, 33 and to efficiently remove liquid generated in the catalyst layers 23, 33. The catalyst layers 23, 33 function to promote an electrochemical reaction (cathode reaction or anode reaction) by means of a catalyst.

[0016] One or both of the catalyst layers 23, 33 are formed of the electrode catalyst 50 of the present invention, which will be described later. When one of the catalyst layers 23, 33 is formed of the electrode catalyst 50, the other of the catalyst layers 23, 33 can be formed of any catalyst that can promote the desired electrochemical reaction, and for example, a catalyst such as those listed in the prior art (e.g., IrOx) can be used. When both of the catalyst layers 23, 33 are formed of the electrode catalyst 50, the composition and structure of the electrode catalyst 50 may be the same or different.

[0017] 2.Electrode catalyst 50 The electrode catalyst 50 is composed of a porous body having voids. Examples of the porous body include a porous body 60 as shown in Fig. 3 and a powder 70 as shown in Fig. 4. In the present invention, the porous body is formed by the catalyst itself, so there is no need to support the catalyst on a support as in the conventional case.

[0018] The porous body 60 has a large number of pores 62 formed in a base 61, and the pores 62 serve as voids. The pores 62 may be arranged regularly or irregularly. The pores 62 may have a regular shape (for example, a linear shape) or an irregular shape. The pores 62 may or may not penetrate the base 61. The powder 70 is an aggregate of fine particles 80, and the gaps 81 between the fine particles 80 and the gaps inside the fine particles serve as voids. The fine particles 80 may be spherical or have another shape. When the void-containing body is a powder 70, the void-containing body is composed of the fine particles 80 themselves, which act as a catalyst.

[0019] The porosity of the porous body is preferably 20% or more, and more preferably 50% or more. This porosity is, for example, 20 to 90%, specifically, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90%, and may be within a range between any two of the values ​​exemplified here. The porosity can be calculated by dividing the bulk density by the true density. The porosity of the powder can be measured after molding (molded body size: 5 mm × 5 mm × 30 mm, molding pressure 2 MPa or less) using a uniaxial pressure molding machine.

[0020] The void-containing body has a core portion 90 and a skin layer 91 that covers the core portion 90. When the void-containing body is a porous body 60, the porous body 60 has a core portion 90 and a skin layer 91. When the void-containing body is a powder 70, each fine particle 80 has a core portion 90 and a skin layer 91.

[0021] The core portion 90 is formed of a metal, and the skin layer 91 is composed of an oxide containing Ni. The skin layer 91 contains NiO bonds, which generate NiOOH (active sites) in an alkaline aqueous solution and promote the electrochemical reaction. On the other hand, the core portion 90 is formed of a metal, and therefore has high electrical conductivity. The metal of the core portion 90 may or may not contain Ni. However, if the metal of the core portion 90 contains Ni, the skin layer 91 composed of an oxide containing Ni can be formed by reducing the entire void-containing body and then oxidizing only its surface, which makes production easy. The skin layer 91 may also be formed by coating the core portion 90 with an oxide containing Ni. In this case, the core portion 90 does not need to contain Ni.

[0022] The thickness of the skin layer 91 is, for example, 0.1 to 50 nm, and preferably 1 to 10 nm. Specific examples of this thickness include 0.1, 0.5, 1, 5, 10, 15, 20, 30, 40, and 50 nm, and may be within a range between any two of the values ​​exemplified here.

[0023] The electrical conductivity of the electrode catalyst 50 is preferably 0.001 S / cm, more preferably 0.01 S / cm or more, and even more preferably 0.1 S / cm or more. This electrical conductivity is, for example, 0.001 to 1 S / cm, specifically, for example, 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, or 1 S / cm, and may be within a range between any two of the values ​​exemplified here.

[0024] The metal of the core region 90 and the skin layer 91 preferably contains, in addition to Ni, a transition metal with an atomic number smaller than that of Ni. Examples of such transition metals include Co, Fe, Mn, Cr, V, Ti, and Sc, with Co or Fe being preferred. The inclusion of such a transition metal lowers the Fermi level, facilitating electrochemical reactions. The ratio of the transition metal to the total of Ni and the transition metal is preferably 5 to 95 atomic %, more preferably 10 to 80 atomic %, and specifically, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 atomic %, and may be within a range between any two of the values ​​exemplified here.

[0025] In the oxygen evolution reaction (hereinafter referred to as "OER") of water electrolysis, the ratio of the transition metal to the total of Ni and the transition metal is preferably 5 to 80 atomic %, and particularly preferably 5 to 35 atomic %. In the hydrogen evolution reaction (hereinafter referred to as "HER") of water electrolysis, the ratio of the transition metal to the total of Ni and the transition metal is preferably 25 to 80 atomic %, and particularly preferably 25 to 50 atomic %. Co is particularly preferred as the transition metal.

[0026] As shown in FIG. 5, the microparticles 80 preferably have a structure having chain portions 83 formed by fusion-bonding a plurality of primary particles 82 in a chain shape (hereinafter referred to as a "beaded structure"). In this case, the area surrounded by the chain portions 83 becomes voids 84. The beaded structure preferably has a branched structure in which the chain portions 83 branch at branch points 85. In this case, voids 84 are more likely to be formed. Furthermore, because the beaded structure is formed by the catalyst itself, it is not necessary to support the catalyst on a support, as in the past.

[0027] 6, it is preferable that each of the multiple primary particles 82 constituting the chain portion 83 has a core portion 90 and a skin layer 91, and that the core portions 90 of adjacent primary particles 82 are connected to each other. In this case, the conductivity is particularly good.

[0028] The average size of the primary particles 82 is preferably 1 to 100 nm, more preferably 5 to 40 nm, and even more preferably 10 to 20 nm. Specifically, the average size may be, for example, 1, 5, 10, 15, 20, 25, 30, 35, 40, 50, or 100 nm, or may be within a range between any two of the values ​​exemplified here. The average size of the primary particles 82 can be determined by the arithmetic mean of the primary particle diameters of 10 or more primary particles. The primary particle diameter can be measured using a TEM image such as that shown in FIG. 11. In the TEM image shown in FIG. 11A, dark areas indicate overlapping of multiple primary particles. In measuring the primary particle diameter, a relatively light-colored particle whose periphery is visible is focused on, and the value at which the distance between two points on the periphery of the particle is greatest (the length of the arrow in FIG. 11B) is taken as the primary particle diameter.

[0029] The average particle size of the fine particles 80 is 0.1 μm to 4 μm, and preferably 0.5 μm to 2 μm. The average particle size of the fine particles 80 can be measured by a laser diffraction / scattering particle size distribution measuring device.

[0030] The specific surface area of ​​Powder 70 is 10m 2 This specific surface area is preferably 10 to 50 m / g or more. 2 / g, specifically, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50 m 2 / g and may be within a range between any two of the values ​​exemplified herein.

[0031] The powder 70 preferably has an angle of repose of 50 degrees or less, and more preferably 45 degrees or less. In this case, the powder has the same fluidity as wheat flour and is easy to handle. The angle of repose is, for example, 20 to 50 degrees, specifically, for example, 20, 25, 30, 35, 40, 45, or 50 degrees, and may be within a range between any two of the values ​​exemplified here. The angle of repose can be determined by the falling volume method.

[0032] 3. Method for manufacturing the electrode catalyst 50 When the electrode catalyst 50 is made of powder 70, which is an aggregate of fine particles 80 having a bead-and-loop structure, the electrode catalyst 50 can be manufactured by a method including a powder formation step and a reduction and surface oxidation step. Each step will be described in detail below.

[0033] 3-1. Powder formation process First, a manufacturing apparatus 1 that can be used to manufacture powder will be described with reference to Figures 7 to 10. The manufacturing apparatus 1 includes a burner 2, a raw material supply unit 3, a reaction tube 4, a recovery vessel 5, and a gas storage unit 6. The raw material supply unit 3 includes an outer tube 13 and a raw material distribution tube 14.

[0034] The burner 2 is cylindrical, and the raw material supply unit 3 is disposed inside the burner 2. Burner gas 2a flows between the burner 2 and the outer casing 13. The burner gas 2a is used to form a flame 7 at the tip of the burner 2 upon ignition. The flame 7 forms a high-temperature region of 1000°C or higher. The burner gas 2a preferably contains a flammable gas such as propane, methane, acetylene, hydrogen, or nitrous oxide. In one example, a mixed gas of oxygen and propane can be used as the burner gas 2a. The temperature of the high-temperature region is, for example, 1000 to 2000°C, specifically, for example, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, or 2000°C, and may be within a range between any two of the values ​​exemplified here.

[0035] A raw material solution 14a for producing powder flows through the raw material flow tube 14. The raw material solution 14a contains a Ni compound and, if necessary, a compound of a transition metal (e.g., Co, Fe). Examples of the compound include fatty acid metal salts (e.g., fatty acid Ni, fatty acid Co, fatty acid Fe). The number of carbon atoms in the fatty acid is, for example, 2 to 20, preferably 4 to 15, and more preferably 6 to 12. The fatty acid is preferably octylic acid.

[0036] In the raw material solution 14a, the fatty acid metal salt is preferably dissolved or dispersed in a non-aqueous solvent. Examples of the non-aqueous solvent include organic solvents such as turpentine. If the raw material solution 14a contains water, the fatty acid metal salt may be hydrolyzed and deteriorated.

[0037] A mist-forming gas 13a used to atomize the raw material solution 14a flows between the outer cylinder 13 and the raw material flow cylinder 14. When the mist-forming gas 13a and the raw material solution 14a are ejected together from the tip of the raw material supply unit 3, the raw material solution 14a is atomized. A mist 14b of the raw material solution 14a is sprayed into the flame 7, and the fatty acid metal salt in the raw material solution 14a undergoes a thermal decomposition reaction in the flame 7, producing an oxide powder that is an aggregate of oxide microparticles 9 having chain-like portions formed by oxide crystallites 8 fused and bonded together in a chain shape. These crystallites 8, oxide microparticles 9, and oxide powder undergo reduction and surface oxidation processes to become primary particles 82, microparticles 80, and powder 70, respectively. One example of the mist-forming gas 13a is oxygen.

[0038] The reaction tube 4 is provided between the collector 5 and the gas storage section 6. A flame 7 is formed in the reaction tube 4. The collector 5 is provided with a filter 5a and a gas outlet 5b. Negative pressure is applied to the gas outlet 5b. As a result, an airflow toward the gas outlet 5b is generated in the collector 5 and the reaction tube 4.

[0039] The gas storage section 6 is cylindrical and includes a cooling gas inlet 6a and a slit 6b. A cooling gas 6g is introduced into the gas storage section 6 through the cooling gas inlet 6a. The cooling gas inlet 6a is oriented in a direction tangent to the inner peripheral wall 6c of the gas storage section 6, so that the cooling gas 6g introduced into the gas storage section 6 through the cooling gas inlet 6a swirls along the inner peripheral wall 6c. A burner insertion hole 6d is provided in the center of the gas storage section 6. A burner 2 is inserted through the burner insertion hole 6d. The slit 6b is positioned adjacent to the burner insertion hole 6d and surrounds the burner insertion hole 6d. Therefore, when the burner 2 is inserted through the burner insertion hole 6d, the slit 6b surrounds the burner 2. The cooling gas 6g in the gas storage section 6 is driven by the negative pressure applied to the gas outlet 5b and discharged from the slit 6b toward the reaction tube 4. The cooling gas 6g may be any gas capable of cooling the produced metal oxide, and is preferably an inert gas, such as air.

[0040] After the oxide fine particles 9 emerge from the flame 7, they are immediately cooled by the cooling gas 6g, so that the structure having chain-like portions is maintained. The cooled oxide fine particles 9 are captured and collected by the filter 5a. The captured oxide fine particles 9 may be heat-treated at 400 to 1000°C to adjust them to a desired primary particle size.

[0041] 3-2. Reduction and surface oxidation process The oxide particles 9 constituting the oxide powder obtained in the above step are entirely oxide and therefore do not have good conductivity. Therefore, in this step, the oxide particles 9 are reduced to a state in which they are entirely metallic, and then only the surface is oxidized to form a metal core 90 and an oxide skin layer 91. This results in an electrode catalyst 50 composed of a powder 70 that is an aggregate of particles 80 having a bead-like structure.

[0042] The reduction of the oxide microparticles 9 can be carried out by heat treating the oxide microparticles 9 in a hydrogen-containing atmosphere. The hydrogen-containing atmosphere is an atmosphere containing hydrogen, and is preferably an atmosphere in which the hydrogen is diluted with an inert gas (e.g., nitrogen). The hydrogen content in the atmosphere is, for example, 0.5 to 50%. The heat treatment temperature is preferably 20 to 500°C. This process reduces the oxide microparticles 9 to obtain metal microparticles. Next, after the reduction, when the mixture is slowly cooled to room temperature, the surface of the metal microparticles can be oxidized by holding the mixture in nitrogen containing a trace amount of oxygen. The oxygen concentration is preferably 0.5 to 50 ppm. [Example]

[0043] An electrode catalyst was produced by the method described below, and various evaluations were carried out.

[0044] 1. Preparation of Electrocatalyst 50 1-1. Examples 1 to 4 (Ni 1-x Co x O) 1-1-1. Powder formation process An electrode catalyst 50 was produced using the production apparatus 1 shown in FIGS. 7 to 10. A gas mixture of 5 L / min of oxygen and 1 L / min of propane gas was used as the burner gas 2a, and this gas was ignited to form a flame (chemical flame) 7 of 1600°C or higher at the tip of the burner 2. The raw material solution 14a was prepared by mixing and dissolving Ni octylate and Co octylate in mineral split turpentine at a predetermined ratio. The Ni octylate and Co octylate were mixed so that the atomic ratio x of Co to the total of Ni and Co was 0, 0.2, 0.4, or 0.6 (Example 1, Example 2, Example 3, and Example 4, respectively). Oxygen was used as the mist-forming gas 13a. A mixture of 9 L / min of mist-forming gas 13a and 3 g / min of raw material solution 14a was sprayed from the tip of raw material supply unit 3, which is a spray nozzle (atomizer), into the center of the flame and burned, producing oxide powder, which is an aggregate of oxide microparticles 9. At this time, negative pressure was applied to gas outlet 5b, and air was sucked through slit 6b at a flow rate of 170 L / min, thereby collecting the produced powder in collector 5 (with filter 5a). Raw material supply unit 3 has a double-tube structure (total length 322.3 mm), and oxygen gas is supplied from outer tube 13, and raw material solution 14a is supplied to raw material flow tube 14, which has a fluid nozzle and an air nozzle at the tip, where raw material solution 14a is converted into mist 14b.

[0045] The general formula of the obtained oxide powder is Ni 1-x Co x 11A shows a TEM image of oxide microparticles 9 contained in the powder obtained when x=0.4. It can be seen that these oxide microparticles 9 have chain-like portions formed by crystallites 8 fused and bonded in a chain-like manner.

[0046] 1-1-2. Reduction and surface oxidation process Next, the oxide powder obtained in the above step was subjected to reduction and surface oxidation to form a metal core 90 and an oxide skin layer 91. This resulted in an electrode catalyst 50 composed of powder 70, which is an aggregate of microparticles 80 having a beaded structure.

[0047] The reduction was carried out by heat treating the oxide microparticles 9 in a hydrogen-containing atmosphere (a mixed gas atmosphere of hydrogen and nitrogen, with a hydrogen content of 1%) at 400°C for 2 hours. The surface oxidation was carried out by holding the particles in nitrogen containing a trace amount of oxygen while slowly cooling them to room temperature after the reduction. The oxygen concentration was set to 5 ppm.

[0048] 1-2. Example 5 (Ni 0.8 Mn 0.2 O), Example 6 (Ni 0.8 Fe 0.2 O) The electrode catalysts 50 of Examples 5 and 6 were produced under the same conditions as in Example 2, except that Mn octylate (Example 5) or Fe octylate (Example 6) was used instead of Co octylate.

[0049] 2. Electrical Conductivity Measurement of Electrocatalyst 50 The electrical conductivity of the electrode catalysts 50 of Examples 1 to 4 obtained by the above method was measured by the following method. The results are shown in Figure 12. As shown in Figure 12, it was found that when the Co ratio x was around 0.2, the electrical conductivity was particularly high, reaching 0.1 S / cm or more.

[0050] (Method for measuring electrical conductivity) Eight samples of electrode catalysts (hereinafter referred to as "target samples") precisely weighed using a precision electronic balance were filled into eight sample holders (3 mm in diameter, 5 mm deep) in the measurement jig. The measurement jig filled with the target samples was set into a pressure device, and the target samples were compressed with a force of 1.1 kN. Using electrodes set into the compression tool of the pressure device, the resistance of the target samples when compressed was measured using the DC two-terminal method, and the length when compressed was also measured at the same time. This operation was performed on four or more target samples of different weights, and the relationship between the length (x-axis) and resistance (y-axis) of the target samples when compressed was determined, and this was extrapolated along the y-axis to determine the value of the y-intercept. The resistivity of the target sample was determined from the value of the y-intercept and the length and cross-sectional area of ​​the compact, and the electrical conductivity, which is its reciprocal, was calculated.

[0051] 3. OER Activity Measurement of Electrocatalyst 50 The OER activity of the electrode catalysts 50 of Examples 1 to 6 was measured using a three-electrode electrochemical measurement apparatus 15 shown in FIG. 13. The apparatus 15 includes a glass cell 15a, a working electrode 15b, a counter electrode 15c, and a reference electrode 15d. The potential of the working electrode 15b relative to the reference electrode 15d can be adjusted by a potentiostat (not shown). A KOH solution 15e with a concentration of 0.1 mol / L is contained in the glass cell 15a. Nitrogen or oxygen can be blown into the KOH solution 15e. The working electrode 15b is made of glassy carbon (GC) and has a cylindrical shape, and the electrode catalyst 50 is applied to its lower surface. The lower surface of the working electrode 15b and the counter electrode 15c are immersed in the KOH solution 15e. The reference electrode 15d is liquid-junction with the KOH solution 15e via a salt bridge 15f.

[0052] The electrode catalyst 50 was dispersed in a mixed solution of 80 wt% water and 20 wt% ethanol, which was then applied to the underside of the working electrode 15b and dried. Nitrogen was blown into the KOH solution 15e before measurement to purge the KOH solution 15e. During measurement, oxygen was blown in at a flow rate of 100 ml / min, and the reference electrode 15d was rotated around its central axis. The current value was measured while varying the potential (Potential / V vs. RHE) of the working electrode 15b relative to the reference electrode 15d. The results are shown in Figure 14 (Examples 1-4) and Figure 15 (Examples 1-2 and 5-6). Figure 14 also shows the results for a Pt / C catalyst (manufactured by Tanaka Kikinzoku Kogyo Kogyo, model TEC10E50E) and an IrOx catalyst (manufactured by Tanaka Kikinzoku Kogyo Kogyo Kogyo).

[0053] 14 and 15, it was found that the electrode catalyst 50 exhibited catalytic activity comparable to that of IrOx. Furthermore, the performance was improved by adding Co, and was particularly high when the proportion x of Co was around 0.2.

[0054] 4. HER Activity Measurement of Electrocatalyst 50 Using the same apparatus as in the above-described OER activity measurement, the potentiostat was set so that the potential of the working electrode 15b was a negative value, and the HER activity of the electrode catalyst 50 was measured. The results are shown in Fig. 16 (Examples 1 to 4) and Fig. 17 (Examples 1 to 2 and 5 to 6).

[0055] 16 and 17, it was found that the electrode catalyst 50 exhibited excellent catalytic activity, intermediate between that of IrOx and Pt / C. Furthermore, the addition of Fe or Co significantly improved performance, with the addition of Fe resulting in a particularly significant improvement. Furthermore, when Co was added, performance was particularly high when the Co ratio x was near 0.4.

[0056] 5. Evaluation of voltage-voltage characteristics of water electrolysis cell In the water electrolysis cell shown in FIG. 1, the cathode catalyst was Pt / C (manufactured by Tanaka Kikinzoku Kogyo, model TEC10E50E), and the anode catalyst was the electrode catalyst 50 (Ni 0.8 Co 0.2 The relationship between the voltage applied between the anode and cathode and the current flowing during the water electrolysis reaction was measured at 80°C using electrode catalyst 50 of Example 2 (IrOx catalyst) or a commercially available IrOx catalyst (Tanaka Kikinzoku Kogyo Kogyo). The results are shown in Fig. 18. As shown in Fig. 18, the water electrolysis cell using electrode catalyst 50 of Example 2 had a higher water electrolysis reaction rate and better catalytic performance than the water electrolysis cell using an IrOx catalyst.

[0057] 6. Long-term evaluation of water electrolysis cells The water electrolysis cell (anode catalyst was the electrode catalyst 50 (Ni 0.8 Co 0.2 O)) was evaluated for a long term.

[0058] In this evaluation, the resistance between the anode and cathode (cell resistance) was measured while a voltage (cell voltage) was applied between the anode and cathode at 80°C. The results are shown in Figure 19. As shown in Figure 19, even after 600 hours had passed, neither the cell voltage nor the cell resistance changed significantly, indicating that the electrode catalyst 50 of the present invention has excellent durability. [Explanation of symbols]

[0059] 1: manufacturing equipment, 2: burner, 2a: burner gas, 3: raw material supply section, 4: reaction tube, 5: recovery vessel, 5a: filter, 5b: gas discharge section, 6: gas storage section, 6a: cooling gas inlet section, 6b: slit, 6c: inner peripheral wall, 6d: burner insertion hole, 6g: cooling gas, 7: flame, 8: crystallite, 9: oxide fine particles, 10: anion exchange membrane electrochemical cell, 13: outer tube, 13a: mist-forming gas, 14: raw material flow tube, 14a: raw material solution, 14b: mist, 15: electrochemical measurement device, 15a: glass cell, 15b: working electrode, 15c: counter electrode, 15d: reference electrode, 15e: KOH solution, 15f: salt bridge, 20: cathode, 21: diffusion layer, 22: microporous layer, 23: catalyst layer, 30: anode, 31: diffusion layer, 32: microporous layer, 33: catalyst layer, 40: anion exchange membrane, 50: electrode catalyst, 60: porous body, 61: substrate, 62: pores, 70: powder, 80: fine particles, 81: gaps, 82: primary particles, 83: chain portions, 84: voids, 85: branch points, 90: core portion, 91: skin layer

Claims

1. An electrode catalyst for an anion exchange membrane electrochemical cell, which is composed of a porous body having pores, The void-containing body has a core portion and a skin layer covering the core portion, the core portion is made of metal, the skin layer is made of an oxide containing Ni, The porous body is composed of fine particles that act as a catalyst, The fine particles are composed of a plurality of primary particles fused and bonded in a chain form, The electrode catalyst for an anion exchange membrane electrochemical cell, wherein the fine particles have the core portion and the skin layer.

2. 2. The electrode catalyst according to claim 1, The electrode catalyst includes primary particles in which the core portions of adjacent primary particles are connected to each other.

3. The electrode catalyst according to claim 1 or claim 2, The anion exchange membrane electrochemical cell is a water electrolysis cell.

4. The electrode catalyst according to claim 1 or claim 2, The anion exchange membrane electrochemical cell is a fuel cell.

5. The electrode catalyst according to any one of claims 1 to 4, The oxide comprises a transition metal having an atomic number smaller than that of Ni.

6. The electrode catalyst according to claim 5, The electrode catalyst, wherein the transition metal is Co or Fe.

7. The electrode catalyst according to any one of claims 1 to 6, The porous body has a porosity of 20% or more.

8. An electrochemical cell comprising a cathode, an anode and an anion exchange membrane disposed therebetween, An anion exchange membrane electrochemical cell, wherein at least one of the cathode and the anode is provided with a catalyst layer made of the electrode catalyst according to any one of claims 1 to 7.

9. 9. The anion exchange membrane electrochemical cell according to claim 8, The anion exchange membrane electrochemical cell is a water electrolysis cell.

10. 9. The anion exchange membrane electrochemical cell according to claim 8, The anion exchange membrane electrochemical cell is a fuel cell.

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