Electrode catalyst, water electrolysis cell

Abstract

Provided is an electrode catalyst having high activity as a catalyst for a water electrolysis cell anode, as well as excellent electrical conductivity.　Through the present invention, there is provided an electrode catalyst comprising a carrier powder and active particles supported on the carrier powder, the carrier powder being an aggregate of carrier fine particles provided with chain parts formed by fusion bonding of a plurality of crystallites into chains, the carrier fine particles including a metal oxide doped with a doping element, the main elements of the metal oxide including tin, the active particles including a platinum-group oxide including a platinum-group element, and the carrying rate of the active particles being 25 mass% or greater.

Description

Technical Field

[0001] The present invention relates to an electrode catalyst and a water electrolysis cell using the same.

Background Art

[0002] Patent Document 1 discloses a catalyst for water electrolysis in which active particles containing platinum or iridium are supported on a carrier containing tin oxide doped with a pentavalent metal.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although the catalyst of Patent Document 1 has excellent activity, its conductivity cannot be said to be sufficiently high. Therefore, in order to reduce the internal resistance of the water electrolysis cell, improvement of the conductivity of the catalyst is desired.

[0005] The present invention has been made in view of such circumstances, and provides an electrode catalyst having high activity as a catalyst for the anode of a water electrolysis cell and excellent conductivity.

Means for Solving the Problems

[0006] As a result of intensive studies by the present inventor, it has been found that by setting the loading rate of the active particles to 25% by mass or more, the conductivity of the catalyst is remarkably improved, and the present invention has been completed.

[0007] According to the present invention, the following inventions are provided. [1]An electrode catalyst comprising carrier powder and active particles supported on the carrier powder, wherein the carrier powder is an aggregate of carrier fine particles having chain-like portions formed by fusion bonding of a plurality of crystallites in a chain-like manner, the carrier fine particles contain a metal oxide doped with a doping element, the main element of the metal oxide contains tin, the active particles contain a platinum group oxide containing a platinum group element, and the loading rate of the active particles is 25% by mass or more. [2]The electrode catalyst according to [1], wherein the ratio of the halogen element to the platinum group element in the active particles is 2.0 atomic% or less. [3]The electrode catalyst according to [1] or [2], wherein the catalyst has a conductivity of 0.5 S / cm or more. [4]The electrode catalyst according to any one of [1] to [3], wherein the ratio of tin to the total main elements contained in the metal oxide is 50 atomic% or more. [5]The electrode catalyst according to any one of [1] to [4], wherein the ratio of iridium to the total platinum group elements contained in the platinum group oxide is 50 atomic% or more. [6]The electrode catalyst according to any one of [1] to [5], wherein the loading rate is 30% by mass or more. [7]The electrode catalyst according to any one of [1] to [6], wherein the active particles have a crystallite size determined from the XRD pattern of 2 to 10 nm. [8]A water electrolysis cell comprising a cathode, an anode, and a proton-conductive polymer electrolyte membrane disposed therebetween, wherein the anode comprises a catalyst layer composed of the electrode catalyst according to any one of [1] to [7].

Brief Description of the Drawings

[0008]

Figure 1

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Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Various characteristic matters shown in the following embodiments can be combined with each other. Also, an invention can be established independently for each characteristic matter.

[0010] 1. Electrode catalyst 100 As shown in FIGS. 1 to 4, the electrode catalyst 100 includes a carrier powder and active particles 130 supported on the carrier powder. The carrier powder is an aggregate of carrier fine particles 150 having a chain-like portion formed by chain-like fusion bonding of a plurality of crystallites 120. Hereinafter, each configuration will be described.

[0011] 1-1. Carrier fine particles 150 and carrier powder As shown in FIGS. 1 to 3, the carrier fine particles 150 have a three-dimensional void 110 surrounded by the branches 160 and the pores existing between the plurality of branches. The branch 160 is a portion where a chain-like portion formed by the fusion bonding of a plurality of crystallites 120 constituting the carrier fine particles 150 in a chain-like manner is divided as a branch.

[0012] As shown in FIGS. 1 to 3 as an example of the structure model of the electrode catalyst, the carrier fine particles 150 include a first pore portion surrounded by points (branch points, which may be simply referred to as branches hereinafter) b1, b2, b5, b4, b1 where the branches are connected to each other, a second pore portion surrounded by branch points b1, b2, b3, b1, a third pore portion surrounded by branch points b2, b3, b6, b7, b5, b2, and a fourth pore portion surrounded by branch points b1, b3, b6, b7, b5, b4, b1. Here, if the surface surrounded by the branch points of each pore portion (the first to fourth pore portions) is defined as a pore surface, the void 110 is a three-dimensional space surrounded by these four pore surfaces. The carrier fine particles 150 include a plurality of pore portions surrounded by a plurality of branch points where the plurality of branches are connected to each other. And the three-dimensional spaces (voids) surrounded by the plurality of pore portions are continuously provided with each other.

[0013] Note that, as a simple configuration of the carrier fine particles 150, it may simply include one pore portion (for example, the first pore portion surrounded by branch points b1, b2, b5, b4, b1). In this case, the void 110 having a thickness of the crystallite grains of the crystallites 120 will be provided. As an even simpler configuration, the carrier fine particles 150 may have one or more branches. Even in this case, since there are branches between the carrier fine particles 150, they cannot be in close contact with each other and the void 110 can be provided therebetween.

[0014] Note that the pore portion described above may be rephrased as a closed curve (closed loop). Alternatively, it can also be rephrased as having a void 110 surrounded by a closed surface including a plurality of the above-described branch points (for example, branch points b1 to b7). The branch points b1 to b7 can be regarded as the centers of gravity of the crystallites of the metal oxide constituting the carrier fine particles 150 where the branches are connected to each other, or may be any one point on this crystallite.

[0015] The size of the crystallite 120 is preferably 10 to 30 nm, more preferably 10 to 15 nm. Specifically, this size can be, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30 nm, and may also be within the range between any two of the numerical values exemplified herein. The size (crystallite diameter) of the crystallite 120 can be determined based on the Scherrer equation from the half-width of the peak in the XRD pattern. If the crystallite 120 is too small, the oxide is likely to elute, and there is a risk of deterioration in the durability of the catalyst. If the crystallite 120 is too large, the secondary pore volume becomes small, and there is a risk of deterioration in the diffusibility of substances.

[0016] The aggregate of the carrier fine particles 150 is in powder form. Such an aggregate is referred to as "carrier powder".

[0017] The average particle diameter of the carrier fine particles 150 in the carrier powder is preferably 0.1 μm to 4 μm, more preferably 0.5 μm to 2 μm. The average particle diameter of the carrier fine particles 150 can be measured by a laser diffraction / scattering type particle size distribution measuring device.

[0018] The BET specific surface area of the carrier powder is preferably 12 m 2 / g or more, more preferably 25 m 2 / g or more. This BET specific surface area is, for example, 12 to 100 m 2 / g, and specifically, for example, 12, 15, 20, 25, 30, 35, 40, 45, 50, 100 m 2 / g, and may also be within the range between any two of the numerical values exemplified herein.

[0019] The carrier powder preferably has a porosity of 50% or more, more preferably 60% or more. The porosity is, for example, 50 to 80%, and specifically, for example, 50, 55, 60, 65, 70, 75, 80%, and may also be within the range between any two of the numerical values exemplified herein. The porosity can be determined by mercury intrusion porosimetry or FIB-SEM.

[0020] The carrier powder preferably has an angle of repose of 50 degrees or less, more preferably 45 degrees or less. In this case, the carrier powder has fluidity comparable to that of flour and is easy to handle. This angle of repose is, for example, 20 to 50 degrees, specifically, for example, 20, 25, 30, 35, 40, 45, 50 degrees, and may be within the range between any two of the values exemplified herein. The angle of repose can be determined by the falling volume method.

[0021] The conductivity of the carrier powder is preferably 0.001 S / cm or more, more preferably 0.01 S / cm or more. This conductivity is, for example, 0.01 to 1000 S / cm, specifically, for example, 0.01, 0.1, 1, 10, 100, 1000 S / cm, and may be within the range between any two of the values exemplified herein. The conductivity can be measured based on the JIS standard (JIS K 7194).

[0022] The carrier fine particles 150 have branches 160 each consisting of a chain-like part formed by fusing and bonding a plurality of crystallites 120 in a chain-like manner, and each of them has the property of conducting electrons. As shown in FIGS. 1 to 3, the carrier fine particles 150 have a plurality of branches 160, and the branches are connected to each other through branch points (b1 to b7) to form a network state, and the spaces between them have electrically conductive properties. Therefore, the branch 160 of the carrier fine particles 150 indicated by the dotted line from the point P0 in FIG. 1 itself constitutes an electron conduction path (electron conduction path) 140.

[0023] The carrier fine particles 150 contain a metal oxide doped with a doping element. The carrier fine particles 150 are preferably composed only of the metal oxide, but may contain a small amount of other components. The proportion of the metal oxide in the carrier fine particles 150 is, for example, 90 to 100% by mass, specifically, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100% by mass, and may be within the range between any two of the values exemplified herein.

[0024] The doping element is an element with a valence different from that of the main element. The main element includes tin and may also include titanium, cerium, zirconium, etc. Examples of the doping element include elements at least partly having a valence of 5 or higher. Specifically, at least one is selected from among rare earth elements typified by yttrium, group 5 elements typified by niobium and tantalum, group 6 elements typified by tungsten, and group 15 elements typified by antimony. "At least partly having a valence of 5 or higher" means that part or all of the doping element has a valence of 5 or higher, and part of the doping element may have a valence of 4 or lower. By doping with such a doping element, conductivity can be imparted to the carrier fine particles. Among such elements, group 5 elements typified by niobium and tantalum, group 6 elements typified by tungsten, or group 15 elements typified by antimony are preferable, and tantalum, niobium, antimony, or tungsten is particularly preferable.

[0025] The ratio of the doping element to the total metal contained in the metal oxide is preferably 1 to 30 atomic %. In this case, the electrical conductivity of the electrode catalyst 100 becomes particularly high. Specifically, this ratio is, for example, 1, 5, 10, 15, 20, 25, 30 atomic %, and may be within the range between any two of the values exemplified herein.

[0026] The ratio of tin to the total main element contained in the metal oxide is preferably 50 atomic % or more. In this case, the electrical conductivity of the electrode catalyst 100 becomes particularly high. This ratio is, for example, 50 to 100 atomic %, and specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 atomic %, and may be within the range between any two of the values exemplified herein.

[0027] 1-2. Active particle 130 The active particles 130 are particles that can function as a catalyst (preferably, a catalyst for the anodic reaction of a water electrolysis cell). The active particles 130 contain a platinum group oxide containing a platinum group element. The active particles 130 are preferably composed of only the platinum group oxide, but may contain a small amount of other components. The proportion of the platinum group oxide in the active particles 130 is, for example, 90 to 100% by mass, specifically, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100% by mass, and may be within the range between any two of the values exemplified herein.

[0028] Examples of the platinum group element include ruthenium, rhodium, palladium, osmium, iridium, and platinum. The platinum group oxide contains one or more of these elements. From the viewpoint of catalytic activity, the platinum group oxide preferably contains iridium, and the proportion of iridium in the total platinum group elements contained in the platinum group oxide is more preferably 50 atomic% or more. This proportion is, for example, 50 to 100 atomic%, specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 atomic%, and may be within the range between any two of the values exemplified herein.

[0029] The platinum group oxide is an oxide of the platinum group element. In one example, the platinum group element in the platinum group oxide has a mixed valence of tetravalent and trivalent. When the platinum group element is M (= Ru, Rh, Pd, Os, Ir, Pt), the platinum group oxide can be expressed as MOx. x is, for example, 1.4 to 2.0, and 1.6 to 2.0 is preferable. Specifically, x is, for example, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and may be within the range between any two of the values exemplified herein.

[0030] The active particles 130 may contain a halogen element. However, if a halogen element is present at the active sites on the surface of the active particles 130, the activity of the active particles 130 may decrease. Therefore, it is preferable that the content of the halogen element contained in the active particles 130 is low. Specifically, the ratio of the halogen element to the platinum group element in the active particles 130 is preferably 2.0 atomic% or less. This ratio is, for example, 0 to 2.0 atomic%, and specifically, for example, 0.001, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0 atomic%, and may be within the range between any two of the numerical values exemplified herein. Examples of the halogen element include fluorine, chlorine, bromine, iodine, and the like. The ratio of the halogen element to the platinum group element can be calculated based on the peak area ratio by XPS analysis.

[0031] The loading rate of the active particles 130 is 25 mass% or more, and more preferably 30 mass% or more. When the loading rate of the active particles 130 becomes 25 mass% or more, the conductivity of the electrode catalyst 100 significantly increases, and when it becomes 30 mass% or more, the conductivity of the electrode catalyst 100 further significantly increases. The loading rate can be calculated by (mass of the active particles 130) / (mass of the electrode catalyst 100). This loading rate can be calculated by calculating the concentration (mass%) of the platinum group element by ICP analysis and converting the concentration of the platinum group element to the concentration of the platinum group oxide assuming that the platinum group element is in the form of a tetravalent oxide. The loading rate is, for example, 25 to 75 mass%, and specifically, for example, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 mass%, and may be within the range between any two of the numerical values exemplified herein.

[0032] The active particles 130 have a crystallite size of 2 to 10 nm as determined from the XRD pattern. If this crystallite size is too small, they are likely to dissolve as the electrode reaction proceeds. If the crystallite size is too large, the electrochemically active surface area becomes small and it is difficult to obtain the desired electrode performance. Specifically, this crystallite size is, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10 nm, and may also be within the range between any two of the values exemplified herein. This crystallite size can be determined based on the Scherrer equation from the half-width of the peak in the XRD pattern.

[0033] For the active particles 130, when the peak intensity of the (111) plane in the XRD pattern is I1 and the peak intensity of the (200) plane is I2, it is preferable that I1 / I2 ≧ 2, more preferably I1 / I2 ≧ 5, and even more preferably I1 / I2 ≧ 7. Since the (111) plane of the active particles 130 has higher catalytic activity than the (200) plane, the higher the value of I1 / I2, the higher the catalytic activity. Also, since the (111) plane has a smaller surface energy than the (200) plane, the higher the loading rate of the active particles 130, the more preferentially the (111) plane with a smaller surface energy is formed. As a result, the value of I1 / I2 increases. Therefore, by increasing the loading rate of the active particles 130, the value of I1 / I2 can be increased. The value of I1 / I2 is, for example, 2 to 15, specifically, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, and may also be within the range between any two of the values exemplified herein or any value or more. In this specification, the peak intensity ratio means the intensity ratio at the peak top.

[0034] 3. Electrode Catalyst 100 In the electrode catalyst 100 of the present embodiment, a low-resistance region is likely to be formed in the vicinity of the region where the active particles 130 are supported by electron donation from the active particles 130 supported on the carrier powder to the carrier powder. Further, in the electrode catalyst 100 of the present embodiment, since the loading rate of the active particles 130 is high, even if the low-resistance regions formed in the vicinity of each of the adjacent active particles 130 are connected to each other or not, the distance between the adjacent low-resistance regions becomes short, so the conductivity of the electrode catalyst 100 is likely to be high. Further, as the loading amount of the active particles 130 increases, the adjacent active particles 130 are self-organized and are likely to be connected to each other. Also in this regard, the electrode catalyst 100 is likely to have a high conductivity. Therefore, the conductivity of the electrode catalyst 100 is preferably 0.5 S / cm or more. In this case, the internal resistance of the water electrolysis cell configured using the electrode catalyst 100 becomes particularly low. This conductivity is 0.5 to 1000 S / cm, and specifically, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 100, 1000 S / cm, and it may be within the range between any two of the values exemplified here or any value or more. The conductivity can be measured based on the JIS standard (JIS K 7194).

[0035] 3. Water electrolysis device As shown in FIG. 4, a water electrolysis device 10 according to an embodiment of the present invention includes a DC voltage source 11 and a water electrolysis cell 3. The water electrolysis cell 3 includes an anode 3a, a cathode 3c, and a proton-conductive polymer electrolyte membrane 3e disposed therebetween. The DC voltage source 11 is configured to apply a DC voltage between the anode 3a and the cathode 3c. The DC voltage source 11 applies a voltage so as to move electrons from the anode 3a toward the cathode 3c. An anode flow path 3a1 is provided adjacent to the anode 3a. A cathode flow path 3c1 is provided adjacent to the cathode 3c.

[0036] At the anode 3a and the cathode 3c, the following anodic reaction and cathodic reaction occur. Specifically, the water supplied to the anode 3a through the anode flow path 3a1 is electrolyzed, oxygen is generated from the anode 3a, and hydrogen is generated from the cathode 3c. Oxygen is discharged through the anode flow path 3a1, and hydrogen is discharged through the cathode flow path 3c1. Protons move from the anode 3a to the cathode 3c through the polymer electrolyte membrane 3e. (Anodic reaction) 2H2O → 4H + + O2 + 4e - (Cathodic reaction) 4H + + 4e - → 2H2

[0037] As the catalyst for the anode 3a, the electrode catalyst 100 of the present embodiment can be used. As the catalyst for the cathode 3c, platinum, a platinum alloy, or the like can be used.

[0038] 3. Method for manufacturing carrier powder First, with reference to FIGS. 5 to 8, the manufacturing apparatus 1 available for manufacturing the carrier powder will be described. The manufacturing apparatus 1 includes a burner 2, a raw material supply unit 8, a reaction cylinder 4, a collector 5, and a gas storage unit 6. The raw material supply unit 8 includes an outer cylinder 13 and a raw material flow cylinder 23.

[0039] The burner 2 is cylindrical, and the raw material supply unit 8 is disposed inside the burner 2. Burner gas 2a flows between the burner 2 and the outer cylinder 13. The burner gas 2a is used to form a flame 7 at the tip of the burner 2 by ignition. A high-temperature region of 1000 °C or higher is formed by the flame 7. The burner gas 2a preferably contains a combustible 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, 2000 °C, and may be within the range between any two of the values exemplified herein.

[0040] In the raw material flow tube 23, a raw material solution 23a for generating carrier powder is circulated. As the raw material solution 23a, those containing a metal compound are used. Examples of the metal compound include fatty acid metal (such as Sn, Ti, Ce, Sb, Nb, Ta, W, etc.) salts. The number of carbon atoms of the fatty acid is, for example, 2 to 20, preferably 4 to 15, and more preferably 6 to 12. As the fatty acid metal salt, octylic acid metal salts (such as tin octylate, titanium octylate, cerium octylate, antimony octylate, niobium octylate, tantalum octylate, tungsten octylate, etc.) are preferred. In the raw material solution 23a, the metal compound is preferably dissolved or dispersed in a non-aqueous solvent.

[0041] Between the outer cylinder 13 and the raw material flow tube 23, an atomizing gas 13a used for atomizing the raw material solution 23a is circulated. When the atomizing gas 13a and the raw material solution 23a are ejected together from the tip of the raw material supply unit 8, the raw material solution 23a is atomized. The mist 23b of the raw material solution 23a is sprayed into the flame 7, and the metal compound in the raw material solution 23a undergoes a thermal decomposition reaction in the flame 7 to generate a carrier powder, which is an aggregate of carrier particles 150 having a chain-like portion formed by fusion bonding of crystallites 120 in a chain-like manner. The atomizing gas 13a is, in one example, oxygen.

[0042] The reaction cylinder 4 is provided between the recovery unit 5 and the gas storage unit 6. A flame 7 is formed in the reaction cylinder 4. The recovery unit 5 is provided with a filter 5a and a gas discharge part 5b. A negative pressure is applied to the gas discharge part 5b. For this reason, an air flow toward the gas discharge part 5b is generated in the recovery unit 5 and the reaction cylinder 4.

[0043] The gas storage section 6 is cylindrical and includes a cooling gas introduction section 6a and a slit 6b. Cooling gas 6g is introduced into the gas storage section 6 from the cooling gas introduction section 6a. Since the cooling gas introduction section 6a is directed in a direction along the tangent to the inner peripheral wall 6c of the gas storage section 6, the cooling gas 6g introduced into the gas storage section 6 through the cooling gas introduction section 6a swirls along the inner peripheral wall 6c. A burner insertion hole 6d is provided at the center of the gas storage section 6. The burner 2 is inserted into the burner insertion hole 6d. The slit 6b is provided at a position adjacent to the burner insertion hole 6d so as to surround the burner insertion hole 6d. Therefore, in a state where the burner 2 is inserted into the burner insertion hole 6d, the slit 6b is provided so as to surround the burner 2. The cooling gas 6g in the gas storage section 6 is driven by the negative pressure applied to the gas discharge section 5b and is discharged from the slit 6b toward the reaction cylinder 4. The cooling gas 6g may be any gas that can cool the generated oxide, and an inert gas is preferable, for example, air. The flow rate of the cooling gas 6g is preferably at least twice the flow rate of the burner gas 2a. The upper limit of the flow rate of the cooling gas 6g is not particularly defined, but for example, it is 1000 times the flow rate of the burner gas 2a. The flow rate of the cooling gas 6g / the flow rate of the burner gas 2a is, for example, 2 to 1000, specifically, for example, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, 500, 1000, and it may be within the range between any two of the values exemplified here. In this embodiment, a negative pressure is applied to the gas discharge section 5b to flow the cooling gas 6g, but a positive pressure may be applied to the cooling gas introduction section 6a to flow the cooling gas 6g.

[0044] In this embodiment, since the cooling gas 6g is supplied around the flame 7 through the slit 6b, the cooling gas 6g forms a laminar flow and flows around the flame 7. For this reason, the mist 23b, the crystallites 120, and the carrier fine particles 150 are not disturbed by the cooling gas 6g, and while moving along the flame 7, they are sufficiently heated by the flame 7 and the reaction proceeds. Further, after the carrier fine particles 150 exit the flame 7, the carrier fine particles 150 are immediately cooled by the cooling gas 6g, so that the structure having the chain-like portion is maintained. The cooled carrier fine particles 150 are captured and recovered by the filter 5a.

[0045] In this embodiment, the carrier powder, which is an aggregate of the carrier fine particles 150, can be produced by using the production apparatus 1, forming a high-temperature region of 1000°C or higher by the flame 7 at the tip of the burner 2, supplying the cooling gas 6g around the high-temperature region through the slit 6b, and thermally decomposing the metal compound in this high-temperature region. The high-temperature region may be formed by a plasma or the like in addition to the flame 7.

[0046] 4. Method for manufacturing the electrode catalyst 100 The method for manufacturing the electrode catalyst 100 includes a carrier powder generation step, a colloid adsorption step, and a heat treatment step.

[0047] <Carrier powder generation step> In the carrier powder generation step, the carrier powder is generated by the method described above.

[0048] <Colloid adsorption step> In the colloid adsorption step, platinum group colloid particles are adsorbed onto the carrier powder. More specifically, a dispersion in which platinum group colloid particles prepared by the colloid method are dispersed in an aqueous solution is prepared, and the carrier powder is added to and mixed in the dispersion to adsorb the colloid particles onto the surface of the carrier powder. The carrier powder adsorbed with the colloid particles can be separated from the dispersion medium through filtration and drying. The platinum group colloid particles can be prepared, for example, by adding a reducing agent to a liquid containing a precursor of a colloid containing a platinum group element to reduce the precursor, but the precursor of the colloid containing a platinum group element may be used directly as the platinum group colloid particles.

[0049] <Heat Treatment Step> In the heat treatment step, heat treatment is performed after the adsorption step to oxidize the platinum group colloid particles, thereby converting them into active particles 130. The heat treatment temperature is, for example, 150 to 750 °C, and specifically, for example, 500, 550, 600, 650, 700, 750 °C, and it may also be within the range between any two of the values exemplified here.

[0050] The heat treatment time is, for example, 0.1 to 20 hours, and preferably 0.5 to 5 hours. Specifically, this time is, for example, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 hours, and it may also be within the range between any two of the values exemplified here.

[0051] The heat treatment can be carried out in an inert gas atmosphere such as nitrogen.

Example

[0052] The electrode catalyst was manufactured by the method shown below and various evaluations were carried out.

[0053] 1. Manufacture of Electrode Catalyst 100 <Example 1> (Manufacture of Carrier Powder) Using the manufacturing apparatus 1 shown in FIGS. 5 to 8, carrier powder was manufactured. As the burner gas 2a, a gas obtained by mixing 5 L / min of oxygen and 1 L / min of propane gas was used, and this gas was ignited to form a flame (chemical flame) 7 of 1600° C. or higher at the tip of the burner 2. As the raw material solution 23a, a solution obtained by mixing tin octylate and antimony octylate at a molar ratio of 0.95:0.05 in mineral split terpene and dissolving them was used. As the atomizing gas 13a, oxygen was used. 9 L / min of the atomizing gas 13a and 3 g / min of the raw material solution 23a were mixed and sprayed from the tip of the raw material supply unit 8, which is a spray nozzle (atomizer), into the center part of the flame and burned to generate carrier powder, which is an aggregate of carrier fine particles 150. At that time, by making the gas discharge part 5b into a negative pressure and sucking air from the slit 6b at a flow rate of 170 L / min, the generated carrier powder was collected in the collector 5 (with a filter 5a). The raw material supply unit 8 has a double-tube structure (total length 322.3 mm), oxygen gas is supplied from the outer cylinder 13, the raw material solution 23a is supplied to the raw material flow cylinder 23, and there are a fluid nozzle and an air nozzle at the tip of the raw material flow cylinder 23, where the raw material solution 23a was made into mist 23b. The recovery amount of the carrier powder was 10 g or more in a 60-minute operation.

[0054] (Supporting of active particles 130) Next, the active particles 130 were supported on the carrier powder.

[0055] <Colloid adsorption step> First, 4.5 mL of an Ir chloride acid solution (Tanaka Precious Metals Industry, 100 g / L) was dissolved in 500 ml of ultrapure water, and further 7.2 g of sodium bisulfite (Kanto Chemical), which is a reducing agent, was added and stirred to generate colloid particles.

[0056] The solution was diluted with 150 ml of water, and a sodium hydroxide (Kanto Chemical) solution prepared to 5 mass% was dropped using an automatic potentiometric titrator (manufactured by KEM, AT-500) to adjust the pH of the precursor solution to 5. Then, about 54 ml of hydrogen peroxide (Kanto Chemical, 35%) was added at about 2 mL / min, and the pH was readjusted to 5 with NaOH.

[0057] To the obtained dispersion, a dispersion in which 0.15 g of carrier powder was dispersed in 15 mL of ultrapure water was added, and the mixture was stirred at 90 °C for 18 hours to adsorb colloidal particles onto the carrier powder. Next, after cooling to room temperature, it was filtered to take out the solid content. This solid content was washed with ultrapure water. This washing was carried out by adding 15 mL of ultrapure water to the solid content, stirring and then filtering, and observing whether a white precipitate occurred when an aqueous silver nitrate solution (manufactured by Kanto Chemical, 1M) was dropped into the filtrate. This operation was repeated until no white precipitate was observed.

[0058] <Heat treatment step> In the heat treatment step, the washed sample was heat-treated at 400 °C for 2 hours in nitrogen to oxidize the colloidal particles to obtain active particles 130.

[0059] Through the above steps, an electrode catalyst 100 in which active particles 130 were supported on the carrier powder was obtained.

[0060] <Other examples and comparative examples> The electrode catalyst 100 was produced in the same manner as in Example 1 except that the loading rate of the active particles 130 was changed as shown in Table 1.

[0061]

Table 1

[0062] 2. Various measurements

[0063] For the electrode catalysts of the examples and comparative examples, various measurements were carried out according to the methods shown below.

[0064] <Measurement of loading rate> For each catalyst, the concentration of iridium was determined by performing inductively coupled plasma atomic emission spectrometry (ICP - AES) measurement, and assuming that iridium is a tetravalent oxide, the concentration of iridium was converted by the concentration of iridium oxide. This concentration was taken as the loading rate of the active particles 130.

[0065] <Conductivity measurement> The resistance was measured when each catalyst was filled in a uniaxial pressing device and compressed at a pressure of 16 MPa. Catalysts in different amounts were measured at four levels, and the electrical resistance of the catalyst was calculated from the slope of the straight line obtained from the correlation between the obtained electrical resistance and the sample thickness or weight, and converted to conductivity. The results are shown in Table 1 and FIG. 9.

[0066] As shown in Table 1 and FIG. 9, when the loading rate was 25% by mass or more, the conductivity was significantly high, and when the loading rate was 30% by mass or more, the conductivity was even more significantly high.

[0067] <Electron Microscopy Observation> The electron micrograph obtained by observing the catalyst of Example 1 with an electron microscope is shown in FIG. 10A. Looking at FIG. 10A, it can be seen that the active particles 130 composed of iridium oxide particles of 3 to 5 nm are supported on the carrier powder. Further, the electron micrograph of the catalyst of Example 4 is shown in FIG. 10B. Referring to FIG. 10B, it can be seen that the adjacent active particles 130 are connected by self-organization to form a continuous phase.

[0068] <OER (Oxygen Evolution Reaction) Activity> The OER activities of the electrode catalyst 100 and a commercially available IrOx catalyst (manufactured by Furuya Metal) were measured. Since OER corresponds to the anodic reaction of a water electrolysis cell, the OER activity indicates the activity as an anodic catalyst for water electrolysis.

[0069] Specifically, for the electrode catalyst 100 and the commercially available catalyst, FIG. 11 shows a graph indicating the change in current density when swept up to 2.0 V under OER activity test conditions (80 °C, in 0.1 M HClO4, sweep rate: 10 mV / s). 27 wt%, 35 wt% and 49 wt% in the figure indicate the loading rate of the active particles 130.

[0070] As shown in FIG. 11, it can be seen that the electrode catalyst 100 of the present invention has significantly higher OER activity than the commercially available IrOx catalyst.

[0071] <XPS Measurement> XPS measurement was performed on the catalyst of Example 1. The results are shown in Fig. 12. Figs. 12A and 12B show the analysis results for Ir and Cl, respectively. As shown in Fig. 12B, Cl was hardly detected, and it was found that the ratio of Cl to Ir was 0.1 atomic% or less.

[0072] <Peak intensity ratio of active particles> XRD measurement was performed on the electrode catalyst 100, and the peak intensity ratio of the active particles 130 (= ((111) peak intensity I1 / (200) peak intensity I2)) was calculated from the XRD pattern. Also, the crystallite size of the metal fine particles was calculated based on the Scherrer equation from the half-width of the (200) peak. The results are shown in Table 1 and Fig. 13. As shown in Table 1 and Fig. 13, it can be seen that as the loading rate of the active particles 130 increases, the (111) peak intensity I1 increases significantly, and as a result, the peak intensity ratio increases.

Description of symbols

[0073] 1: Manufacturing apparatus, 2: Burner, 2a: Burner gas, 3: Water electrolysis cell, 3a: Anode, 3a1: Anode flow path, 3c: Cathode, 3c1: Cathode flow path, 3e: Polymer electrolyte membrane, 4: Reaction cylinder, 5: Recoverer, 5a: Filter, 5b: Gas discharge part, 6: Gas storage part, 6a: Cooling gas introduction part, 6b: Slit, 6c: Inner peripheral wall, 6d: Burner insertion hole, 6g: Cooling gas, 7: Flame, 8: Raw material supply part, 10: Water electrolysis device, 11: DC voltage source, 13: Outer cylinder, 13a: Mist gas, 23: Raw material flow cylinder, 23a: Raw material solution, 23b: Mist, 100: Electrode catalyst, 110: Void, 120: Crystallite, 130: Active particle, 150: Carrier particle, 160: Branch

Claims

1. Comprising a carrier powder and active particles supported on the carrier powder, The carrier powder is an aggregate of carrier fine particles, The carrier fine particles include a chain-like part formed by fusion bonding of a plurality of crystallites in a chain-like manner and a branch composed of the chain-like part, The crystallite size of the crystallites is 10 to 30 nm, The carrier fine particles contain a metal oxide doped with a doping element, At least a part of the doping element has a valence of 5 or more, The main element of the metal oxide contains tin, The ratio of tin to the whole of the main element is 50 atomic% or more, The active particles contain a platinum group oxide containing a platinum group element, The active particles are supported on the carrier fine particles, An electrode catalyst having a loading rate of the active particles of 25% by mass or more.

2. The electrode catalyst according to Claim 1, The electrode catalyst in which the ratio of the halogen element to the platinum group element in the active particles is 2.0 atomic% or less.

3. The electrode catalyst according to Claim 1, The electrode catalyst having a conductivity of 0.5 S / cm or more.

4. The electrode catalyst according to Claim 1, The electrode catalyst in which the ratio of iridium to the whole of the platinum group element contained in the platinum group oxide is 50 atomic% or more.

5. The electrode catalyst according to Claim 1, The electrode catalyst in which the loading rate is 30% by mass or more.

6. The electrode catalyst according to Claim 1, The electrode catalyst in which the active particles have a crystallite size determined from the XRD pattern of 2 to 10 nm.

7. A water electrolysis cell comprising a cathode, an anode, and a proton-conductive polymer electrolyte membrane disposed therebetween, The anode includes a catalyst layer composed of the electrode catalyst according to any one of Claims 1 to 6.

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