Method for producing catalytic precious metal-supported conductive oxide particles

Abstract

This method for producing catalyst particles, which are for an electrochemical reaction and in which catalytic noble metal particles are carried on conductive oxide particles, comprises: using metal atom-containing organic compounds as a precursor of the conductive oxide particles and a precursor of the catalytic noble metal particles, and dissolving the metal atom-containing organic compounds in an organic solvent to obtain a precursor solution; and spraying and combusting the precursor solution.

Description

[Technical Field]

[0001] The present invention relates to a method for producing catalytic noble metal-supported conductive oxide particles.

[0002] Electrode catalysts used in electrodes of electrochemical cells such as fuel cells generally have a structure in which catalytic noble metal particles are supported on the surface of support particles made of a conductive carbon material, such as carbon black, and the catalytic noble metal is, for example, platinum.

[0003] The use of such catalysts poses a problem of deterioration in the performance of the electrochemical cell over time, which is thought to be due to the oxidation of the conductive carbon material that supports the electrode catalyst due to potential changes during operation of the electrochemical cell, causing aggregation and detachment of the supported precious metal particles.

[0004] In order to avoid the above-mentioned disadvantages caused by the use of conductive carbon materials, it has been proposed to use a non-carbon conductive metal oxide support as a support for an electrode catalyst in an electrochemical cell. For example, Patent Document 1 proposes using Sb-doped SnO2 as a support for an electrode catalyst.

[0005] Recently, it has been proposed to synthesize composite particles in which catalytic noble metal particles are supported on a conductive metal oxide support by flame spray pyrolysis (FSP).

[0006] For example, Non-Patent Document 1 describes the synthesis of Pt / TiO2 particles with a Pt loading of 1 wt% or less by FSP using an acetonitrile solution of Ti(OiPr)4 and Pt(acac)2, and the use of these Pt / TiO2 particles as a catalyst for photocatalytic NOx removal.

[0007] Furthermore, Non-Patent Document 2 describes the synthesis of Au-Pt / TiO2 particles with a total loading of Au and Pt of 1 wt% by FSP using a precursor solution prepared by dissolving HAuCl4, HPtCL6, and Ti(OBu)4 in a mixed solvent of xylene / EtOH (volume ratio 4 / 1), and the use of these Au-Pt / TiO2 particles as a catalyst for the oxidation of CO with oxygen. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2012-514287 [Non-patent literature]

[0009] [Non-Patent Document 1] Appiled Catalysis B:Environmental,226(2018),127-134 [Non-patent document 2] Applied Surface Science,521(2020),146447 Summary of the Invention [Problem to be solved by the invention]

[0010] When a conductive metal oxide support is used as a support for an electrode catalyst in an electrochemical cell, there is a problem that the catalytic activity is insufficient and the output of the resulting electrochemical cell is low.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing catalytic noble metal-supported conductive oxide particles that have high electrochemical activity and can maintain high initial activity for a long period of time. [Means for solving the problem]

[0012] The present invention is as follows.

[0013] Aspect 1: A method for producing catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on conductive oxide particles, comprising: a metal atom-containing organic compound is used as a precursor of the conductive oxide particles and a precursor of the catalytic noble metal particles, and the metal atom-containing organic compound is dissolved in an organic solvent to obtain a precursor solution; and atomizing and burning the precursor solution; Including, A method for producing catalyst particles for electrochemical reactions. Aspect 2: The production method according to Aspect 1, wherein the amount of the catalytic noble metal particles supported is 1.5% by mass or more, when the total mass of the catalytic particles is taken as 100% by mass. Aspect 3: The method according to Aspect 1 or 2, wherein the catalytic noble metal particles are platinum particles. Aspect 4: The method according to aspect 3, wherein the precursor of the catalytic noble metal particles is a platinum complex compound. Aspect 5: The method according to any one of Aspects 1 to 4, wherein the metal atom-containing organic compound is at least one selected from the group consisting of metal alkoxides, organic acid salts, and complex compounds. Aspect 6: The method according to any one of Aspects 1 to 5, wherein the conductive oxide particles are tin oxide particles doped with one or more elements selected from niobium, tantalum, tungsten, antimony, and bismuth. Aspect 7: The method according to aspect 6, wherein the conductive oxide particles are niobium-doped tin oxide particles. Aspect 8: The method according to aspect 7, wherein the precursor of the conductive oxide particles is a tin carboxylate and a niobium alkoxide. Aspect 9: The method according to any one of aspects 1 to 8, wherein the organic solvent includes a solvent having a combustion enthalpy of 3,000 kJ / mol or more. Aspect 10: The method according to any one of Aspects 1 to 9, wherein the catalyst particles are an electrode catalyst for a fuel cell. <Embodiment 11> Catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on conductive oxide particles, When cyclic voltammetry (CV) measurements were performed in a nitrogen atmosphere using an electrode containing the catalyst particles as a working electrode, a reversible hydrogen electrode (RHE) as a reference electrode, and a platinum wire electrode as a counter electrode, When the potential is swept upward and downward, a peak is observed around 0.4 V (vs. RHE). Catalyst particles for electrochemical reactions. Aspect 12: The particle according to aspect 11, which is an electrode catalyst for a fuel cell. [Effects of the Invention]

[0014] According to the present invention, there is provided a method for producing catalyst particles for electrochemical reactions that have high electrochemical activity and can maintain this high initial activity for a long period of time. The catalyst particles for electrochemical reactions obtained by the method of the present invention have high electrochemical activity and a long life, and are suitable as catalysts for electrochemical reactions, particularly as electrode catalysts for fuel cells. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a CV chart obtained for the electrochemical reaction catalyst particles of Example 1 and Comparative Examples 1 to 3. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] <<Method for producing electrochemical reaction catalyst particles>> The method for producing catalyst particles for electrochemical reactions of the present invention includes the steps of: A method for producing catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on conductive oxide particles, comprising: a metal atom-containing organic compound is used as a precursor of the conductive oxide particles and a precursor of the catalytic noble metal particles, and the metal atom-containing organic compound is dissolved in an organic solvent to obtain a precursor solution; and atomizing and burning the precursor solution; Including, It is a method.

[0017] The present invention is a method for conducting electrochemical reaction catalyst particles by dissolving specific metal-atom-containing organic compounds as precursors for conductive oxide particles and catalytic noble metal particles in an organic solvent, preferably an organic solvent with a high combustion enthalpy, followed by FSP. This method produces electrochemical reaction catalyst particles in which catalytic noble metals are supported on conductive oxide particles. These highly loaded electrochemical reaction catalyst particles have high electrochemical activity and can maintain their high initial activity for a long period of time.

[0018] Hereinafter, each element of the method for producing catalyst particles for electrochemical reactions of the present invention will be described in order.

[0019] Precursor solution The precursor solution in the method of the present invention is a solution containing a precursor of conductive oxide particles and a precursor of catalytic noble metal particles dissolved in an organic solvent.

[0020] Here, a metal atom-containing organic compound is used as the precursor of the conductive oxide particles and the precursor of the catalytic noble metal particles, respectively. Here, "metal atom-containing organic compound" means a compound, salt, or complex compound containing a metal atom, a carbon atom, and a hydrogen atom. The metal atom-containing organic compound may optionally further contain one or more atoms selected from an oxygen atom, a nitrogen atom, and a sulfur atom. The metal atom-containing organic compound in the present invention does not need to contain a halogen atom or a silicon atom.

[0021] The number of metal atoms in one metal atom-containing organic compound may be 1 or 2 or more, but a typical metal atom-containing organic compound in the present invention may contain one metal atom.

[0022] The precursors of the conductive oxide particles and the catalytic noble metal particles may each be a metal-atom-containing organic compound that is liquid at room temperature (25°C) and atmospheric pressure (1 atm). In conventional particle synthesis by FSP, the cause of particle heterogeneity or coarsening is thought to be the precipitation (solidification) of the precursor compound in the sprayed droplets. Therefore, by using a metal-atom-containing organic compound, particularly a metal-atom-containing organic compound that is liquid at room temperature and atmospheric pressure, as the precursor, decomposition of the precursor compound is promoted and precipitation (solidification) of the precursor compound is suppressed, resulting in the production of homogeneous, nanosized electrochemical reaction catalyst particles.

[0023] The metal atom-containing organic compound that is liquid at room temperature and pressure may be, for example, one or more compounds selected from metal alkoxides, metal organic acid salts, metal complex compounds, and the like.

[0024] (Precursor of conductive oxide particles) The conductive oxide particles in the catalyst particles for electrochemical reactions produced by the method of the present invention may be, for example, tin oxide particles doped with one or more elements selected from niobium, tantalum, tungsten, antimony, and bismuth.

[0025] In the method of the present invention, such doped tin oxide particles are obtained by using a precursor solution containing a precursor of one or more elements (doping elements) selected from niobium, tantalum, tungsten, antimony, and bismuth, and a precursor of tin oxide.

[0026] The precursor of the doping element may be, for example, an alkoxide of a predetermined metal. When the predetermined metal can have multiple stable oxidation states, the oxidation state of the metal in the metal alkoxide may be any of the stable oxidation states. The number of carbon atoms in the alkoxide of the alkoxyl group may be 1 or more, 2 or more, 3 or more, or 4 or more, and may be 10 or less, 8 or less, 6 or less, 4 or less, or 3 or less. When the number of carbon atoms in the alkoxyl group is 3 or more, the alkoxyl group may be linear or branched.

[0027] The precursor of the tin oxide particles may be, for example, a tin carboxylate. In the tin carboxylate, the tin may be divalent or tetravalent. The number of carbon atoms in the alkyloxycarbonyl group in the tin carboxylate, including the carbonyl carbon, may be 2 or more, 4 or more, 6 or more, or 8 or more, and may be 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10 or less. When the alkyloxycarbonyl group has 4 or more carbon atoms, the alkyloxycarbonyl group may be linear or branched.

[0028] The conductive oxide particles in the catalyst particles for electrochemical reactions produced by the method of the present invention may be, in particular, niobium-doped tin oxide particles, in which case the precursor solution may contain, for example, a niobium alkoxide and a tin carboxylate, in particular, niobium(V) ethoxide and tin(II) 2-ethylhexanoate.

[0029] The mixing ratio of the tin oxide particle precursor to the doping element precursor in the precursor solution may be the same as the ratio of tin to doping element in the desired electrochemical reaction catalyst particles. The molar ratio of the doping element to the total molar ratio of tin and doping element may be, for example, 0.5 mol% or more, 1 mol% or more, 2 mol% or more, 3 mol% or more, 4 mol% or more, or 5 mol% or more, or 10 mol% or less, 8 mol% or less, 6 mol% or less, or 5 mol% or less.

[0030] (Precursor of catalytic noble metal particles) The catalytic noble metal particles in the electrochemical reaction catalyst particles produced by the method of the present invention may be, for example, platinum particles. In this case, the precursor of the catalytic noble metal particles may be a platinum complex compound.

[0031] The precursor of the catalytic noble metal particles in the method of the present invention may specifically be, for example, platinum bisacetylacetonate.

[0032] The content of the precursor of catalytic noble metal particles in the precursor solution may be appropriately set depending on the amount of catalytic noble metal particles supported in the desired electrochemical reaction catalyst particles. The amount of catalytic noble metal particles supported in the electrochemical reaction catalyst is desirably relatively high from the viewpoint of ensuring sufficient electrochemical activity. Therefore, the content of the precursor of catalytic noble metal particles in the precursor solution used in the method of the present invention may also be relatively high accordingly.

[0033] The content of the precursor of catalytic noble metal particles in the precursor solution may be, for example, 1.5 mass% or more, 2.0 mass% or more, 5.0 mass% or more, or 8.0 mass% or more, as a ratio of the mass of the catalytic noble metal particle precursor in metal equivalent to the total mass of the conductive oxide particle precursor in oxide equivalent and the mass of the catalytic noble metal particle precursor in metal equivalent, or may be, for example, 50 mass% or less, 45 mass% or less, or 40 mass% or less.

[0034] (organic solvent) The organic solvent in the precursor solution used in the method of the present invention may be one that can dissolve the precursor of the conductive oxide particles and the precursor of the catalytic noble metal particles.

[0035] Specific examples of organic solvents include aromatic compounds, aliphatic hydrocarbons, alcohols, polar organic solvents, etc., and one or more selected from these may be used. Examples of aromatic compounds include benzene, toluene, ethylbenzene, xylene, cumene, durene, etc.; examples of aliphatic hydrocarbons include pentane, cyclopentane, hexane, cyclohexane, etc.; examples of alcohols include methanol, ethanol, 2-propanol, isopropanol, n-butanol, benzyl alcohol, etc.; and examples of polar organic solvents include tetrahydrofuran, acetonitrile, diethylhexanoic acid, etc.

[0036] The organic solvent may include one having a high combustion enthalpy, which is desirable because the conductive oxide particle precursor and the catalytic noble metal particle precursor are instantly converted into the target products during spray combustion of the precursor solution, thereby suppressing problems such as precipitation and aggregation of the precursors.

[0037] From this viewpoint, the organic solvent may contain a high combustion enthalpy solvent having a combustion enthalpy of 3,000 kJ / mol or more. The organic solvent used in the method of the present invention may contain the high combustion enthalpy solvent in an amount of 30 mass % or more, 50 mass % or more, 70 mass % or more, 80 mass % or more, 90 mass % or more, or 95 mass % or more based on the total amount of the organic solvent. Alternatively, all of the organic solvent may be high combustion enthalpy solvents.

[0038] The combustion enthalpy of the high combustion enthalpy solvent may be 3,500 kJ / mol or more, 4,000 kJ / mol or more, or 4,500 kJ / mol or more, and may be 6,000 kJ / mol or less, 5,500 kJ / mol or less, or 5,000 kJ / mol or less.

[0039] The combustion enthalpy of the high combustion enthalpy solvent may typically be 3,000 kJ / mol or more and 6,000 kJ / mol or less. Examples of high combustion enthalpy solvents having such a combustion enthalpy include aromatic compounds and aliphatic hydrocarbons.

[0040] Due to the high solubility and high combustion enthalpy of the precursors of the conductive oxide particles and catalytic noble metal particles, the organic solvent of the precursor solution used in the method of the present invention may be an aromatic compound, in particular toluene, ethylbenzene, xylene, etc.

[0041] In this specification, the combustion enthalpy refers to the combustion enthalpy of a liquid at 25°C.

[0042] The amount of organic solvent used in the precursor solution may be such that the total concentration of the precursor of the conductive oxide particles and the precursor of the catalytic noble metal particles in the precursor solution is 0.05 mol / L or more and 0.5 mol / L or less.

[0043] <Spray flame method> In the method of the present invention, the above-mentioned precursor solution is sprayed and combusted to obtain catalyst particles for electrochemical reactions.

[0044] In the method of the present invention, the combustion of the precursor solution may be carried out by a flame spray method (FSP method). In the flame spray method, a precursor solution atomized by a flow of a dispersion gas is ignited by a pilot flame to form a flame. The flame formed at this time is a spray flame in which the atomized precursor solution is combusted. This spray combustion method using a spray flame differs from particle synthesis methods using a diffusion flame, in which droplets of raw material are supplied to an already formed flame and combusted.

[0045] When a flame spray method is applied to a precursor solution containing a conductive oxide particle precursor and a catalytic noble metal particle precursor, catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on the surfaces of conductive oxide particles, are formed in a single step.

[0046] This is thought to be because, when the conductive oxide particle precursor and the catalytic noble metal particle precursor contained in the precursor solution are once thermally decomposed and then reconstituted into particles, the metal elements constituting the conductive oxide are first particle-formed, followed by the catalytic noble metal. The reason why there is a time lag in particle formation is thought to be because the metal elements constituting the conductive oxide and the catalytic noble metal elements have different vapor pressures at the particle formation temperature.

[0047] The dispersion gas may be an oxidizing gas, such as air or oxygen. The pilot flame is not particularly limited as long as it can ignite the atomized precursor solution, and may be formed, for example, from methane and air or oxygen. The flow rate of the dispersion gas (i.e., the velocity of the precursor solution droplets introduced into the flame) may be, for example, 500 m / min or more, 1,000 m / min or more, 1,500 m / min or more, 2,000 m / min or more, 2,500 m / min or more, or 3,000 m / min or more, and may be, for example, 10,000 m / min or less, 8,000 m / min or less, 6,000 m / min or less, 5,000 m / min or less, 4,000 m / min or less, or 3,500 m / min or less.

[0048] The method of the present invention has the advantage that the amount of catalytic noble metal particles supported on the electrochemical reaction catalyst particles can be freely controlled. According to the method of the present invention, the amount of catalytic noble metal particles supported on the electrochemical reaction catalyst particles can be set to, for example, 1.5 mass % or more, 2.0 mass % or more, 5.0 mass % or more, or 8.0 mass % or more, and can be set to, for example, 50 mass % or less, 45 mass % or less, or 40 mass % or less.

[0049] <Catalyst particles for electrochemical reactions> According to another aspect of the present invention, a catalyst particle for an electrochemical reaction is provided.

[0050] The catalyst particles for electrochemical reactions of the present invention are Catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on conductive oxide particles, When cyclic voltammetry (CV) measurements were performed in a nitrogen atmosphere using an electrode containing the catalyst particles as a working electrode, a reversible hydrogen electrode (RHE) as a reference electrode, and a platinum wire electrode as a counter electrode, When the potential is swept upward and downward, a peak is observed around 0.4 V (vs. RHE). Catalyst particles for electrochemical reactions.

[0051] The amount of catalytic noble metal particles carried in the electrochemical reaction catalyst particles of the present invention is determined by the ratio of the conductive oxide particle precursor to the catalytic noble metal particle precursor in the precursor solution.

[0052] The amount of catalytic noble metal particles supported in the electrochemical reaction catalyst particles of the present invention may be 1.5 mass% or more, 2.0 mass% or more, 5.0 mass% or more, or 8.0 mass% or more, and may be 50 mass% or less, 45 mass% or less, or 40 mass% or less, when the total mass of the catalyst particles is 100 mass%.

[0053] The particle size of the conductive oxide particles in the electrochemical reaction catalyst particles may be 5 nm or more, 7 nm or more, 10 nm or more, or 12 nm or more, or may be 60 nm or less, 40 nm or less, 20 nm or less, or 15 nm or less. The particle size of the conductive oxide particles can be adjusted by changing the initial concentration of the conductive oxide particle precursor in the precursor solution when performing the flame spray method, changing the supply rate of the precursor solution, or the like.

[0054] The particle size of the catalytic noble metal particles in the electrochemical reaction catalyst particles may be smaller than the particle size of the conductive oxide particles, and may be 0.5 nm or more, 1 nm or more, 2 nm or more, 3 nm or more, or 4 nm or more, and may be 20 nm or less, 15 nm or less, 10 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, or 5 nm or less. The particle size of the catalytic noble metal particles can be adjusted by changing the initial concentration of the catalytic noble metal particle precursor in the precursor solution when performing the flame spray method, changing the supply rate of the precursor solution, etc.

[0055] When cyclic voltammetry (CV) measurements were performed in a nitrogen atmosphere using an electrode containing the electrochemical reaction catalyst particles of the present invention as a working electrode, a reversible hydrogen electrode (RHE) as a reference electrode, and a platinum wire electrode as a counter electrode, When the potential is swept upward and downward, a peak is observed around 0.4 V (vs. RHE).

[0056] This CV measurement may be carried out by the method described in the Examples below.

[0057] The catalyst particles for electrochemical reactions of the present invention exhibit the above-mentioned properties in CV measurements, and are therefore suitable as catalyst particles for electrochemical reactions. The catalyst particles for electrochemical reactions of the present invention are suitable, for example, as electrode catalysts for fuel cells, and are particularly suitable as electrode catalysts for air electrodes of fuel cells. [Example]

[0058] "reagent" The raw material reagents used in the following examples and comparative examples are as follows. SnCl2: Sigma-Aldrich, purity 99.9% NbCl5: Sigma-Aldrich, purity 99.9% Nb(OC2H5)5: Sigma-Aldrich, purity 99.9% HPtCl: Sigma-Aldrich, purity 99.9% Platinum bisacetylacetonate (Pt(C5H7O2)2): Sigma-Aldrich, purity 99.9% Tin(II) 2-ethylhexanoate (Sn(CH 15 O2)2): Sigma-Aldrich, 99.9% purity Ethanol: Sigma-Aldrich, 99.9% purity Xylene: Sigma-Aldrich, 99.9% purity, isomer mixture

[0059] Example 1 1. Particle Synthesis Tin(II) 2-ethylhexanoate (Sn(CH)) was dissolved in xylene so that the total concentration of Sn and Nb was 0.1 mol / L and the atomic ratio of Sn to Nb was 96:4. 15 In the above, platinum bisacetylacetonate (Pt(C5H7O2)2) and niobium ethoxide (Nb(OC2H5)5) were dissolved in the solution, and platinum bisacetylacetonate (Pt(C5H7O2)2) was added to the resulting solution in an amount such that the Pt loading was 10 mass % to prepare a precursor solution.

[0060] Using a syringe pump, the resulting precursor solution was supplied at a flow rate of 3 mL / min to a two-fluid nozzle "AM6 type nozzle" manufactured by Atmax Co., Ltd. The precursor solution was atomized using an oxygen flow rate of 1.5 L / min and ignited using a methane / air mixture pilot flame of 1 L / min methane and 10 L / min air to form a spray flame of the precursor solution, synthesizing the Pt-supported Nb-doped tin oxide (Pt / NTO) particles of Example 1.

[0061] The height of the spray flame at this time was approximately 16 cm, and the gas flow velocity (the velocity of droplets of the precursor solution carried into the flame) was 3,080 m / min.

[0062] The generated Pt / NTO particles were collected using a bag filter manufactured by Hokos Corporation.

[0063] 2.Analysis The particle size of the NTO particles calculated from the XRD of the obtained Pt / NTO particles using the Scherrer equation was 12 nm, and the particle size of the Pt particles calculated from the SEM image of the Pt / NTO particles was 5 nm.

[0064] 3. Electrochemical Measurements 88.9 mg of Pt / NTO particles were dispersed in a mixture of 16 mL of ultrapure water and 9 mL of 2-propanol (Cica-reagent, manufactured by Kanto Chemical Co., Ltd.). 81.6 mL of Nafion (registered trademark) dispersion (5% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the resulting dispersion. The resulting mixture was ultrasonically dispersed in an ice bath for 1 hour.

[0065] 10 μL of the mixture after ultrasonic dispersion was placed on a polished glassy carbon disk, and the solvent was evaporated to form a catalyst thin film containing Pt / NTO particles, which was used as a measurement electrode.

[0066] An electrochemical measurement cell was prepared using a rotating electrode device "HR-301" manufactured by Hokuto Denko Corporation. The measurement electrode obtained above was used as the working electrode, a reversible hydrogen electrode (RHE) as the reference electrode, a Pt wire electrode as the counter electrode, and a 0.1 mol / L HClO4 aqueous solution as the electrolyte. Cyclic voltammetry (CV) measurements were performed on this electrochemical measurement cell in a N2-saturated atmosphere. The solvent temperature was set to 30°C.

[0067] In this CV measurement, the potential was swept in the noble direction (potential increasing direction) from 0 V to 1.2 V (vs. RHE) at a potential sweep rate of 50 mV / s, and then continuously in the less noble direction (potential decreasing direction) from 1.2 V to 0 V (vs. RHE) at a potential sweep rate of 50 mV / s. The effective platinum surface area (ECSA) was calculated from the peak area of ​​the peak due to hydrogen adsorption wave near the potential of 0.05 V to 0.4 V (vs. RHE) when the potential was swept in the less noble direction.

[0068] The CV chart obtained by the above CV measurement is shown in FIG.

[0069] Subsequently, O2 gas was bubbled into the electrolyte in the electrochemical measurement cell to saturate the electrolyte with O2, and then rotating electrode measurements were performed as follows.

[0070] Rotating electrode measurements were performed in an oxygen atmosphere by rotating the measurement electrode at 400 rpm, sweeping the potential in the noble direction (potential increasing direction) from 0.1 V to 1.2 V (vs. RHE) at a potential sweep rate of 10 mV / sec, followed by sweeping the potential in the less noble direction (potential decreasing direction) from 1.2 V to 0.1 V (vs. RHE) at a potential sweep rate of 10 mV / sec.

[0071] The ORR (Oxygen Reduction Reaction) activity of the catalyst was determined using the current value at a potential of 0.9 V (vs. RHE) when the potential was swept in the negative direction. iR compensation was performed using the liquid resistance of the electrolyte.

[0072] The rotating electrode measurements were repeated, except that the rotation speed of the measurement electrode was changed to 800 rpm, 1,200 rpm, 1,600 rpm, 2,000 rpm, and 2,400 rpm. The ORR activity per unit mass of Pt (MA) was calculated from a Koutecky-Levich plot using the current value at a potential of 0.9 V (vs. RHE) when the electrode was swept in the less noble direction. The ORR activity per unit area of ​​Pt (SA) was also calculated using the Koutecky-Levich plot and the effective platinum area (ECSA) calculated above.

[0073] Furthermore, from the results of the rotating electrode measurements, the activity per unit mass of Pt (ORR mass activity, "MA") and the activity per unit surface area of ​​Pt (ORR area specific activity, "SA") in ORR (Oxygen Reduction Reaction) were determined. The results are shown in Table 1.

[0074] Comparative Example 1 In "1. Synthesis of particles," Nb-doped tin oxide (NTO) particles not carrying Pt were synthesized by forming a spray flame of the precursor solution in the same manner as in Example 1, except that platinum bisacetylacetonate was not used when preparing the precursor solution.

[0075] To a dispersion of 2 g of the NTO particles obtained above in 80 g of ultrapure water, a nitric acid solution of dinitrodiammine platinum in an amount to provide a Pt loading of 10 mass % was added and stirred for 15 minutes. 30 g of ethanol as a reducing agent was then added and stirred for 15 minutes, followed by heating and stirring at 90°C for 2 hours to reduce the Pt ions and precipitate them as Pt particles on the NTO particles, yielding Pt / NTO particles for Comparative Example 1.

[0076] The obtained Pt / NTO particles were analyzed and subjected to electrochemical measurements in the same manner as in Example 1. The results are shown in Table 1 and FIG.

[0077] Comparative Example 2 1. Particle Synthesis SnCl2 and NbCl5 were dissolved in ethanol so that the total concentration of Sn and Nb was 0.1 mol / L and the atomic ratio of the two was Sn:Nb = 96:4. To the resulting solution, hexachloroplatinic (IV) acid (HPtCl6) was further added in an amount such that the Pt loading amount was 10 mass % to prepare a precursor solution.

[0078] The obtained precursor solution was liquefied into droplets using an ultrasonic nebulizer "NE-U17" manufactured by Omron Healthcare Co., Ltd. The obtained droplets were transported by N2 carrier gas at a flow rate of 3 L / min, and a diffusion flame of the precursor solution was formed using a methane / air mixture gas of 21 L / min of methane as fuel and 5 L / min of air as an oxidant, to attempt the synthesis of Pt-supported Nb-doped tin oxide (Pt / NTO) particles of Comparative Example 2.

[0079] 2. Analytical and Electrochemical Measurements The obtained particles were analyzed and electrochemically measured in the same manner as in Example 1. The results are shown in Table 1 and Fig. 1. In the rotating electrode measurement using the particles obtained in Comparative Example 2, an analyzable polarization curve could not be obtained, and MA and SA could not be calculated.

[0080] Comparative Example 3 In "1. Synthesis of particles," Nb-doped tin oxide (NTO) particles not carrying Pt were synthesized by forming a diffusion flame of the precursor solution in the same manner as in Comparative Example 2, except that hexachloroplatinic (IV) acid was not used when preparing the precursor solution.

[0081] Pt / NTO particles of Comparative Example 3 were obtained by precipitating Pt particles on NTO particles in the same manner as in Comparative Example 1, except that the NTO particles obtained above were used.

[0082] The obtained Pt / NTO particles were analyzed and subjected to electrochemical measurements in the same manner as in Example 1. The results are shown in Table 1 and FIG.

[0083] [Table 1]

[0084] As can be seen in Table 1, Comparative Example 1, in which an organometallic compound was used as the raw material for the conductive particles and catalytic noble metal particles, and the flame synthesis of the conductive particles and the support of the catalytic noble metal particles were carried out in two steps; The Pt / NTO particles obtained in Comparative Example 3, in which inorganic metal compounds (chlorides) were used as raw materials for the conductive particles and catalytic precious metal particles, and the flame synthesis of the conductive particles and the loading of the catalytic precious metal particles were carried out in two steps, had insufficient MA and SA values.

[0085] Furthermore, as described above, the particles of Comparative Example 2, which were synthesized by using inorganic metal compounds (chlorides) as raw materials for the conductive particles and catalytic precious metal particles and burning them together using a flame method, did not provide an analyzable polarization curve in rotating electrode measurements, and MA and SA could not be calculated. It is believed that the particles of Comparative Example 2 do not form a structure in which catalytic precious metal particles are supported on conductive oxide (NTO) particles.

[0086] In contrast, the Pt / NTO particles of Example 1, which were obtained by using organometallic compounds as raw materials for the conductive particles and catalytic noble metal particles and burning them together by a flame method, had high MA and SA values.

[0087] Furthermore, in the CV measurement of the Pt / NTO particles of Example 1, a peak was observed around 0.4 V when the potential was swept in both the increasing and decreasing directions. This peak is thought to be attributable to a change in the valence of Sn or Nb atoms in the NTO particles. This phenomenon is thought to be due to the fact that the NTO particles of Example 1 are doped with Pt, making the valence of Sn or Nb atoms more likely to change.

[0088] From the above, it was verified that the catalyst particles synthesized by the method of the present invention exhibit excellent activity as an electrode catalyst for the air electrode of a fuel cell.

Claims

1. A method for producing catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on conductive oxide particles, comprising: a metal atom-containing organic compound is used as a precursor of the conductive oxide particles and a precursor of the catalytic noble metal particles, and the metal atom-containing organic compound is dissolved in an organic solvent to obtain a precursor solution; and spraying the precursor solution and burning it by a spray flame method; Includes The organic solvent includes a high combustion enthalpy solvent having a combustion enthalpy of 3,000 kJ / mol or more. A method for producing catalyst particles for electrochemical reactions.

2. 2. The method according to claim 1, wherein the amount of the catalytic noble metal particles supported is 1.5% by mass or more when the total mass of the catalytic particles is taken as 100% by mass.

3. The method according to claim 1 , wherein the catalytic noble metal particles are platinum particles.

4. The method according to claim 3 , wherein the precursor of the catalytic noble metal particles is a platinum complex compound.

5. The method according to claim 1 , wherein the metal atom-containing organic compound is at least one selected from the group consisting of metal alkoxides, organic acid salts, and complex compounds.

6. The method according to claim 1 , wherein the conductive oxide particles are particles of tin oxide doped with one or more elements selected from niobium, tantalum, tungsten, antimony, and bismuth.

7. The method of claim 6, wherein the conductive oxide particles are niobium-doped tin oxide particles.

8. The method according to claim 7, wherein the precursor of the conductive oxide particles is a tin carboxylate and a niobium alkoxide.

9. The method according to claim 1, wherein the high combustion enthalpy solvent has a combustion enthalpy of 3,500 kJ / mol or more and 6,000 kJ / mol or less.

10. The method according to any one of claims 1 to 9, wherein the catalyst particles are an electrode catalyst for a fuel cell.

11. Catalyst particles for electrochemical reactions, in which catalytic noble metal particles are supported on conductive oxide particles, the conductive oxide particles are niobium-doped tin oxide particles; The catalytic noble metal particles are platinum particles, and When cyclic voltammetry (CV) measurement was performed in a nitrogen atmosphere using an electrode containing the catalyst particles as a working electrode, a reversible hydrogen electrode (RHE) as a reference electrode, and a Pt wire electrode as a counter electrode, During the potential sweep both upward and downward, peaks including 0.4 V (vs. RHE) are observed. Catalyst particles for electrochemical reactions.

12. A catalyst particle for an electrochemical reaction, comprising catalytic noble metal particles supported on conductive oxide particles, the conductive oxide particles are niobium-doped tin oxide particles; The catalytic noble metal particles are platinum particles, and Produced by the production method according to claim 1. Catalyst particles for electrochemical reactions.

13. 13. The particle according to claim 11 or 12, which is an electrocatalyst for a fuel cell.

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