JP2018060790A - Electrocatalyst production method - Google Patents

Abstract

The present invention provides a method for easily producing an electrode catalyst excellent in catalyst performance such as activity-dominated current density. A method for producing an electrode catalyst having a dispersion preparation step and a supporting step. In the dispersion preparation step, (i) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, and (iv) a transition metal compound are mixed and dispersed. Make a liquid. In the supporting step, the dispersion is heated to support a platinum alloy of platinum and a transition metal on the surface of the catalyst carrier powder. The supporting step is performed in a state in which formic acid species are present in the dispersion. [Selection figure] None

Description

  The present invention relates to a method for producing an electrode catalyst suitably used for a fuel cell.

  The polymer electrolyte fuel cell has a proton conductive polymer membrane such as a perfluoroalkylsulfonic acid type polymer as a solid electrolyte, and an oxygen electrode in which an electrode catalyst is applied to each surface of the solid polymer membrane. A membrane electrode assembly having a fuel electrode is provided.

  The electrode catalyst is generally formed by supporting various precious metal catalysts such as platinum on the surface of a conductive carbon material such as carbon black as a carrier. In the electrode catalyst, it is known that carbon is oxidized and corroded due to a potential change during operation of the fuel cell, and the supported metal catalyst is aggregated or dropped off. As a result, the performance of the fuel cell decreases as the operating time elapses. Therefore, in the manufacture of a fuel cell, a larger amount of noble metal catalyst than is actually required is supported on a carrier, so that the performance is increased and the life is extended. However, this is not advantageous from an economic point of view.

  Accordingly, various studies on electrode catalysts have been made for the purpose of improving the performance, extending the life and improving the economic efficiency of polymer electrolyte fuel cells. For example, it has been proposed to use a conductive oxide carrier that is a non-carbon material instead of the conductive carbon that has been used as a carrier until now (see Patent Document 1). In this document, tin oxide is used as a support for the electrode catalyst. On the surface of the carrier, fine particles of noble metal such as platinum are supported. This electrode catalyst is described in the same literature as having excellent electrochemical catalytic activity and high durability. In this document, noble metal fine particles are generated by heat-treating a noble metal colloid at 80 ° C. to 250 ° C. in a reducing atmosphere.

International Publication No. 2009/060582 Pamphlet

  When this inventor examined about the performance of the electrode catalyst of patent document 1, it was found that there is room for improvement in catalyst performance, such as activity dominant current density. Therefore, it is thought that the catalytic performance of the electrode catalyst is improved by supporting a platinum nickel alloy having a higher catalytic activity than platinum on the tin oxide, and the platinum nickel alloy is supported on the surface of tin oxide by the method described in Patent Document 1. An attempt was made to produce an electrode catalyst. However, in the method described in the document, for the purpose of dissolving nickel in platinum, a sample in which a platinum metal and a precursor of nickel metal are supported on tin oxide is, for example, 200 ° C. or higher in a reducing atmosphere. Since it is necessary to perform a heat treatment at a high temperature, platinum was alloyed with tin in tin oxide as well as nickel during the heat treatment, and the desired catalyst performance could not be obtained.

  Therefore, the subject of this invention is providing the method which can manufacture the electrode catalyst which can eliminate the various fault which the prior art mentioned above has.

The present invention provides a dispersion obtained by mixing (i) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, and (iv) a transition metal compound. A dispersion preparation process for preparing
Heating the dispersion to support a platinum alloy of platinum and a transition metal on the surface of the catalyst support powder, and the step is performed in a state in which formic acid species are present in the dispersion. A loading process;
The manufacturing method of the electrode catalyst which has this is provided.

The present invention also includes (i) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, (iv) a transition metal compound, and (v) water or A dispersion preparation step of preparing a dispersion by mixing a water-containing compound;
A supporting step of heating the dispersion and supporting a platinum alloy of platinum and a transition metal on the surface of the catalyst carrier powder;
The manufacturing method of the electrode catalyst which has this is provided.

  According to the present invention, an electrode catalyst excellent in catalyst performance such as activity-dominated current density can be easily produced.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The electrode catalyst to be produced in the present invention has a structure in which a catalyst is supported on the surface of a carrier. As the carrier, a conductive metal oxide is preferably used. In the present invention, “having conductivity” means that the volume resistivity of the metal oxide under a pressure of 57 MPa is 1 × 10 ⁴ Ω · cm or less. As the catalyst supported on the surface of the support, a platinum alloy of platinum and a transition metal is preferably used. The electrode catalyst produced by the method of the present invention is suitably used as a catalyst for various fuel cells. A typical example of such a fuel cell is a polymer electrolyte fuel cell.

  The production method of the present invention comprises mixing (i) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, and (iv) a transition metal compound. A dispersion preparation step for preparing a dispersion, and a step of heating the dispersion to support a platinum alloy of platinum and a transition metal on the surface of the catalyst carrier powder, the step being performed by adding formic acid in the dispersion. And a supporting step performed in the presence of chemical species.

  The reason why an electrode catalyst having excellent catalytic performance can be obtained by adopting the production method of the present invention is that the platinum compound and transition at a lower temperature can be obtained by heating the dispersion liquid and reducing the organic compound having a formamide group. The present inventor believes that the metal compound can be reduced to form an alloy of both, and the alloying of platinum and the metal oxide constituting the catalyst support with the metal element can be suppressed. Further, heating the dispersion in the presence of formic acid is currently not necessarily clear, but the reduction of platinum compounds and transition metal compounds contained in the dispersion is promoted by the formic acid species. Therefore, the present inventor believes that the solid solution of the alloy is promoted and the catalytic activity of the platinum alloy is increased.

  As described above, the production method of the present invention is broadly divided into (a) a dispersion preparation step and (b) a supporting step. Each step will be described in detail below.

In the dispersion preparation step (a), the dispersion is prepared by mixing the following (i)-(iv) as its constituent components.
(I) A solvent for an organic compound having a formamide group.
(Ii) Metal oxide catalyst carrier powder.
(Iii) Platinum compound.
(Iv) Transition metal compounds.

  In (i)-(iv), for example, these can be put together in a container or the like and mixed. Alternatively, (ii)-(iv) can be added to (i) and mixed. The order of addition is not critical in the present invention, and the order of addition can be appropriately determined according to the properties of each component and the blending ratio.

  In the dispersion preparation step, the ratio of the solvent of the organic compound having the formamide group (i) is preferably 30% by mass or more and 99.9% by mass or less, more preferably, with respect to the total mass of the target dispersion. Is preferably added in an amount of 40 mass% to 99.7 mass%, more preferably 50 mass% to 99 mass%. In addition, the dispersion liquid may contain a solvent other than the above solvent as long as the effect of the present invention is achieved.

  In the dispersion preparation step, the ratio of the metal oxide catalyst support powder of (ii) to the solvent volume of the target dispersion is preferably 0.1 g / L or more and 500 g / L or less, more preferably The carrier powder is preferably added so as to be 1 g / L or more and 150 g / L or less, more preferably 2 g / L or more and 100 g / L or less.

In the dispersion preparation step, the ratio of the platinum compound (iii) to the solvent volume of the target dispersion is preferably 2.5 × 10 ⁻⁴ mol / L or more and 1.2 mol / L or less, Preferably it is 6.0 × 10 ⁻⁴ mol / L or more and 8.0 × 10 ⁻¹ mol / L or less, more preferably 1.5 × 10 ⁻³ mol / L or more and 8.0 × 10 ⁻² mol / L or less. It is preferable to add the platinum compound so that

In the dispersion preparation step, the ratio of the transition metal compound (iv) to the solvent volume of the target dispersion is preferably 4.0 × 10 ⁻⁴ mol / L or more and 2.0 × 10 ^−1. mol / L or less, more preferably 6.0 × 10 ⁻⁴ mol / L or more and 1.2 × 10 ⁻¹ mol / L or less, more preferably 2.0 × 10 ⁻³ mol / L or more and 6.0 × 10. It is preferable to add the transition metal compound so as to be ⁻² mol / L or less.

  In the dispersion preparation step, an aromatic compound containing a carboxyl group may be further mixed in addition to the above components. By containing an aromatic compound containing a carboxyl group in the dispersion, platinum and transition metals are more successfully reduced in the loading step (b), resulting in solid solution of the alloy. The state becomes more uniform. As a result, the catalytic performance of the target electrode catalyst is further improved.

In the dispersion preparation step, the ratio of the aromatic compound containing a carboxyl group to the solvent volume of the target dispersion is preferably 4.0 × 10 ⁻⁴ mol / L or more and 4.0 mol / L. Hereinafter, the fragrance is more preferably 2.0 × 10 ⁻² mol / L or more and 3.0 mol / L or less, more preferably 4.0 × 10 ⁻² mol / L or more and 2.0 mol / L or less. It is preferable to add a group compound.

In the dispersion preparing step, the solvent of the organic compound having the formamide group (i) is used as a solvent for dissolving the platinum compound (iii) and the transition metal compound (iv). It is also used as a reducing agent for reducing the platinum compound (iii) and the transition metal compound (iv). From these viewpoints, examples of the solvent of the organic compound having a formamide group (i) include formamide, N, N-dimethylformamide, N-methylformamide, N, N-diethylformamide, and N-ethylformamide. It is done. These solvents can be used alone or in combination of two or more.

  In the dispersion preparation step, the metal oxide catalyst carrier powder (ii) is composed of aggregates of metal oxide carrier particles (hereinafter also referred to as “carrier particles”). As the carrier particles, conductive metal oxide particles can be used. Examples of the conductive metal oxide include indium oxide, tin oxide, titanium oxide, zirconium oxide, selenium oxide, tungsten oxide, zinc oxide, and vanadium oxide. Tantalum oxide, niobium oxide and rhenium oxide. More preferable inorganic oxides include, for example, tin oxide containing one or more elements selected from halogens such as fluorine and chlorine, niobium, tantalum, antimony, and tungsten. Specifically, tin-containing indium oxide, antimony-containing tin oxide, fluorine-containing tin oxide, tantalum-containing tin oxide, antimony and tantalum-containing tin oxide, tungsten-containing tin oxide, fluorine and tungsten-containing tin oxide And non-metal-containing (doped) tin oxide such as niobium-containing tin oxide. In particular, the carrier particles are preferably a ceramic material containing tin oxide from the viewpoint of the stability of the substance in the power generation environment of the polymer electrolyte fuel cell.

  Carrier particles made of a conductive metal oxide can be produced by various methods. Manufacturing methods are roughly classified into wet methods and dry methods. From the viewpoint of producing fine carrier particles, it is advantageous to employ a wet method. As an example of the wet method, it is preferable to employ the following method to produce carrier particles made of tin oxide containing halogen. Details of this production method are described in, for example, WO2016 / 098399.

  The primary particle size of the carrier particles is preferably 5 nm to 200 nm, more preferably 5 nm to 100 nm, and still more preferably 5 nm to 50 nm. The primary particle diameter of the carrier can be obtained by an average value of the primary particle diameter of the carrier measured from an electron microscope image or small angle X-ray scattering. For example, it is obtained by observing carrier particles with an electron microscope image, measuring the maximum transverse length for 500 or more particles, and calculating the average value.

  In the dispersion preparation step, the platinum compound (iii) is preferably one that can be dissolved in a solvent of an organic compound having a formamide group (i), but is not limited thereto. As the platinum compound (iii), for example, a platinum complex or a platinum salt can be used. Specific examples of platinum compounds include bis (acetylacetonato) platinum (II), a kind of platinum complex, hexachloride platinum (IV) acid, tetrachloride platinum (II) acid, dinitrodiammine platinum (II), dichloro Examples include tetraammineplatinum (II) hydrate, hexahydroxoplatinum (IV) acid, and the like.

  In the dispersion preparation step, the transition metal compound (iv) is preferably one that can be dissolved in the solvent of the organic compound having the formamide group (i), but is not limited thereto. As the transition metal compound (iv), for example, a transition metal complex or a transition metal salt can be used. Examples of transition metals include, but are not limited to, nickel, cobalt, iron, chromium, titanium, vanadium, manganese, copper, zinc, scandium, and the like. Moreover, a transition metal compound can also be used individually by 1 type, or can also be used in combination of 2 or more type. Of the above transition metals, it is preferable to use a compound of nickel, cobalt, iron or chromium from the viewpoint of high catalytic activity of an alloy with platinum.

  As described later, the transition metal compound (iv) may have crystal water. Examples of the transition metal compound having crystal water include bis (2,4-pentandionato) nickel (II) dihydrate and hexafluoroacetylacetonatonickel (II) hydrate which are a kind of nickel complex, Further, for example, nickel acetate tetrahydrate, nickel nitrate hexahydrate and nickel chloride hexahydrate which are nickel salts are included.

  The aromatic compound containing a carboxyl group used additionally has at least one aromatic ring and has at least one carboxyl group bonded directly to the aromatic ring or indirectly via a bonding group. It is a compound having a number. Examples of the aromatic ring include a benzene ring, a naphthalene ring, and an anthracene ring. In addition, a heterocyclic ring containing at least one nitrogen or oxygen and having aromaticity is also included in the category of the aromatic ring. Specific examples of the aromatic compound containing a carboxyl group include benzoic acid, phthalic acid, terephthalic acid, salicylic acid, acetylsalicylic acid, and the like. These aromatic compounds can be used individually by 1 type or in combination of 2 or more types.

  The dispersion prepared using each of the above components is subjected to the supporting step (b), and a catalyst made of a platinum alloy of platinum and a transition metal is supported on the surface of the catalyst carrier powder particles. Catalyst loading is achieved by heating the dispersion. Heating of the dispersion can be performed under open pressure to atmospheric pressure, or can be performed in a sealed state. When heating is performed at an open pressure to atmospheric pressure, heating may be performed while refluxing volatile components.

  Prior to heating the dispersion in the supporting step, it is preferable that the components contained in the dispersion are sufficiently uniformly dispersed from the viewpoint that the catalyst can be uniformly supported on the surface of the carrier particles. For this purpose, it is preferable to perform a dispersion treatment in which ultrasonic waves are applied to the dispersion prior to heating the dispersion in the supporting step. The dispersion treatment using ultrasonic waves is preferably performed without heating, for example, preferably at 15 ° C. or more and 25 ° C. or less.

  It is preferable to pre-stir the dispersion after the dispersion treatment of the dispersion and before heating the dispersion in the supporting step. The preliminary stirring is performed mainly for the purpose of uniform mixing of the support and other raw materials and adsorption of the precursor onto the support. Pre-stirring can be performed, for example, by submerging a magnetic stirring bar in the dispersion and rotating it with a magnetic stirring device installed outside. Or it can carry out by arrange | positioning a stirring blade in a dispersion liquid and rotating this. In any case, the preliminary stirring is preferably performed without heating, for example, preferably at 15 ° C. or more and 25 ° C. or less.

  The pre-stirring time is appropriately set according to the volume of the dispersion, the properties such as viscosity, the concentration of the catalyst carrier powder contained in the dispersion, etc., and is generally preferably 30 minutes to 120 hours. More preferably, the time is not less than 120 hours and not more than 120 hours, and more preferably not less than 12 hours and not more than 120 hours.

  Pre-stirring can be performed under various atmospheres. For example, the reaction can be performed in an oxygen-containing atmosphere such as the air or an inert gas atmosphere such as argon or nitrogen. From the viewpoint of not deactivating the reducing agent that reduces the platinum compound and the transition metal compound, it is preferable to pre-stir the dispersion in an inert gas atmosphere.

  After completion of the pre-stirring, the process proceeds to the supporting step and the dispersion is heated. Similar to the pre-stirring, the dispersion can be heated in various atmospheres. For example, the reaction can be performed in an oxygen-containing atmosphere such as the air or an inert gas atmosphere such as argon or nitrogen. From the viewpoint of not deactivating the reducing agent that reduces the platinum compound and the transition metal compound, and from the viewpoint of minimizing the activity of the catalyst supported on the carrier particles, the dispersion is heated in an inert gas atmosphere. Is preferred. From the viewpoint of simplification of operation, it is preferable that the pre-stirring atmosphere and the heating atmosphere be the same.

  In the supporting step, if the heating temperature of the dispersion is equal to or less than the temperature at which platinum and the metal element of the metal oxide constituting the support are not excessively alloyed, the type and the mixing ratio of each component included in the dispersion are used. Accordingly, it can be appropriately selected, and is generally preferably 120 ° C. or higher and lower than 200 ° C., more preferably 120 ° C. or higher and 175 ° C. or lower. On the condition of this heating temperature, the heating time is preferably 3 hours or longer and 120 hours or shorter, more preferably 6 hours or longer and 72 hours or shorter, and further preferably 12 hours or longer and 48 hours or shorter.

  By heating the dispersion, the platinum compound and the transition metal compound contained in the dispersion are thermally decomposed, and the reduction of the organic compound having a formamide group reduces the platinum and the metal oxide constituting the catalyst support. Without excessively alloying the metal element, platinum and the transition metal are reduced to form an alloy of both. The produced platinum alloy adheres to the surface of the carrier particles, and the intended electrode catalyst is obtained.

  In the supporting step, the supported amount of platinum alloy of platinum as a catalyst and the transition metal is preferably 0.1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 30% by mass with respect to the mass of the electrode catalyst. The catalyst is supported so as to be not more than mass%. Adjustment of the amount of catalyst supported can be achieved by appropriately adjusting the concentrations of the metal oxide catalyst support powder, platinum compound, and transition metal compound in the dispersion preparation step, and controlling the heating temperature and heating time in the loading step, for example. Achieved.

  From the viewpoint of further improving the catalytic performance of the electrode catalyst obtained in this way, particularly the activity-dominated current density, it is advantageous to heat the dispersion in a state where formic acid species are present in the dispersion. As a result of examination by the present inventors, it has been found. The reason why the electrocatalytic performance of the electrocatalyst is further improved by heating the dispersion in the presence of formic acid is not necessarily clear at present, but the reduction of platinum compounds and transition metal compounds contained in the dispersion is formic acid chemistry. The present inventor thinks that the solid solution state of the platinum alloy becomes more uniform due to the promotion by the seed.

Examples of the formic acid chemical species include formic acid (HCOOH), formate ((HCOO) _n X (X represents an anion, and n represents the valence of X)), formate ion (HCOO ⁻ ), and the like. These formic acid chemical species may be used alone or in combination of two or more. The total concentration of formic acid species present in the dispersion during heating, the solvent volume of the dispersion is preferably not more than 1 × ¹⁰ -5 mol / L or more 1mol / L, 1 × ^{10 -4} more preferably to less mol / L or more 1 × ¹⁰ -1 mol / L, and more preferably be 1 × ¹⁰ -1 mol / L or less 1 × ¹⁰ -3 mol / L or more. The presence of the formic acid species in the dispersion within this concentration range further improves the catalyst performance such as the activity-dominated current density in the target electrode catalyst.

  The total concentration of formic acid species present in the dispersion being heated can be measured, for example, by liquid chromatography.

  In order to make the formic acid species present in the dispersion during heating, (a) a method of adding a predetermined amount of formic acid species to the dispersion is an example. As another method, in the (b) dispersion preparation step, water or a water-containing compound is mixed and water is present in the prepared dispersion. According to the method of (b), the organic compound which has the formamide group of (i) which is a solvent contained in a dispersion liquid by heating a dispersion liquid in the state in which water or the water-containing compound existed in the dispersion liquid. The formic acid chemical species (for example, formic acid) is generated by the reaction of the solvent with water.

  When the method (b) is adopted, the amount of formic acid in the dispersion gradually increases during the heating process in the supporting step as compared with the case where the method (a) is adopted. And the transition metal are likely to be gradually alloyed. As a result, it may be possible to produce a catalyst in which platinum atoms and transition metal atoms are alloyed more uniformly and platinum alloy fine particles are uniformly dispersed on the surface of the carrier particles. .

  When the method (b) is employed, as the water-containing compound, a compound capable of causing water to be present in the dispersion by preparing the dispersion can be used. As such a compound, for example, a transition metal compound (iv) that is a substance contained in a dispersion can be used having a crystal water, and the compound serves as both a transition metal compound and a water-containing compound. It is simple. By producing a dispersion using a transition metal compound having crystal water, the crystal water is eluted in the dispersion and water is present in the dispersion. This water reacts with the organic compound having a formamide group (i) as a solvent in the heating step of the dispersion. As a result of this reaction, formic acid species are generated in the dispersion.

  When the method (b) is adopted, the addition of a transition metal compound having crystal water rather than the addition of water further promotes the alloying of platinum with the transition metal, and the transition between the platinum atom and the transition. In some cases, an electrode catalyst in which metal atoms are uniformly alloyed can be produced. The reason for this is that when a transition metal compound having crystal water is added, water is easily coordinated around the transition metal ion, and formic acid generated during the supporting process is also easily arranged around the transition metal ion. Become. As a result, more reducing agent is present around the transition metal ion, which is an element that is harder to reduce than platinum, so that the alloying of platinum and the transition metal is further promoted. Thinks.

When the method (b) is employed, the amount of water or water-containing compound added is such that the concentration of water present in the dispersion is 1 × 10 ⁻³ mol / L with respect to the solvent volume of the dispersion. The amount is preferably 10 mol / L or less, more preferably 1 × 10 ⁻² mol / L or more and 5 mol / L or less, and further preferably 1 × 10 ⁻² mol / L or more. The amount is more preferably 5 × 10 ⁻¹ mol / L or less. By adopting such an added amount, the formic acid species can be present in the dispersion at a desired concentration.

As described above, the method for producing an electrode catalyst of the present invention is roughly divided into the following two embodiments <I> and <II>.
<I>
A dispersion in which a dispersion liquid is prepared by mixing (i) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, and (iv) a transition metal compound. Liquid preparation process;
A supporting step of heating the dispersion and supporting a platinum alloy of platinum and a transition metal on the surface of the catalyst carrier powder.
The supporting step is performed in a state in which formic acid species are present in the dispersion.
<II>
(I) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, (iv) a transition metal compound, (v) water or a water-containing compound, A dispersion preparation step of preparing a dispersion by mixing
And a supporting step of supporting the platinum alloy of platinum and a transition metal on the surface of the catalyst carrier powder by heating the dispersion.

  When the electrode catalyst is obtained by the above method <I> or <II>, a solid-liquid separation step of separating the electrode catalyst which is a dispersoid from the dispersion is performed. Through this step, an electrode catalyst in which a platinum alloy of platinum and a transition metal is supported on the catalyst carrier powder is obtained. In the solid-liquid separation step, various known solid-liquid separation means can be used without particular limitation. Examples thereof include filtration using a filter, centrifugation, and decantation.

  When the electrode catalyst is separated in this manner, it is preferable to perform leaching to remove a trace amount of impurities present on the surface of the platinum alloy fine particles. By performing this operation, the catalytic activity of the electrode catalyst is further improved. The leaching is generally achieved by acid-treating the electrode catalyst. By the acid treatment, a very small amount of impurities present on the surface of the platinum alloy fine particles are eluted and removed. Examples of the acid used for leaching include perchloric acid, nitric acid, sulfuric acid, hydrochloric acid, and hydrogen peroxide. The acid concentration is preferably 0.01 mol / L or more and 10 mol / L or less, and more preferably 0.1 mol / L or more and 1 mol / L or less.

  The leaching can be performed while the dispersion is heated, or can be performed without heating. When leaching is performed under heating, the dispersion can be heated preferably to 30 ° C. or higher and 100 ° C. or lower. Leaching without heating can be performed at, for example, 15 ° C. or more and 25 ° C. or less. For example, in the case of heating, the leaching time can be 0.1 hour or more and 100 hours or less.

  The electrode catalyst after leaching can be used as an electrode catalyst for a fuel cell. Or it can also heat-process as a post-process, and can further improve catalyst performance. The heat treatment can be performed in a vacuum, a reducing gas atmosphere, or an inert gas atmosphere, for example. By subjecting the electrode catalyst to heat treatment, the surface alloy state of platinum alloy fine particles of platinum and transition metal changes, and the catalytic activity of the platinum alloy is further improved. In particular, the catalytic activity of the platinum alloy is further improved by performing the heat treatment in a vacuum or a reducing gas atmosphere.

When heat-treating the electrode catalyst under vacuum, the degree of vacuum in the system is preferably 10 Pa or less, more preferably 1 × 10 ⁻³ Pa or less in absolute pressure. When heat-treating the electrode catalyst in a reducing gas atmosphere, it is preferable to heat the electrode catalyst in a state where the reducing gas is circulated in the system. As the reducing gas, for example, hydrogen gas, carbon monoxide gas, and a mixed gas thereof can be used.

  The temperature when heating the electrode catalyst under vacuum is preferably set to 60 ° C. or higher and 400 ° C. or lower, and more preferably set to 60 ° C. or higher and 200 ° C. or lower. The temperature when heating the electrode catalyst in a reducing gas atmosphere is preferably set to 25 ° C. or higher and lower than 200 ° C., more preferably 60 ° C. or higher and lower than 200 ° C. In any case, the heating time is preferably set to 0.1 hours or more and 20 hours or less, and more preferably 0.5 hours or more and 10 hours or less.

  By the method as described above, an electrode catalyst excellent in catalyst performance such as activity-dominated current density can be easily produced. Examples of the properties of the electrode catalyst include powder. The electrode catalyst thus obtained is, for example, an oxygen electrode or a fuel electrode in a membrane electrode assembly having an oxygen electrode arranged on one surface of a solid polymer electrolyte membrane and a fuel electrode arranged on the other surface. It can be used in at least one of them. The electrode catalyst can be preferably contained in both the oxygen electrode and the fuel electrode.

  In particular, the oxygen electrode and the fuel electrode preferably include a catalyst layer containing the electrode catalyst of the present invention and a gas diffusion layer. In order for the electrode reaction to proceed smoothly, the electrode catalyst is preferably in contact with the solid polymer electrolyte membrane. The gas diffusion layer functions as a supporting current collector having a current collecting function. Furthermore, it has a function of sufficiently supplying gas to the electrode catalyst. As the gas diffusion layer, those similar to those conventionally used in this kind of technical field can be used. For example, carbon paper and carbon cloth which are porous materials can be used. Specifically, it can be formed by, for example, a carbon cloth woven with yarns having a predetermined ratio of carbon fibers whose surfaces are coated with polytetrafluoroethylene and carbon fibers that are not coated.

  As the solid polymer electrolyte, those similar to those conventionally used in this kind of technical field can be used. For example, a perfluorosulfonic acid polymer-based proton conductor film, a hydrocarbon polymer compound doped with an inorganic acid such as phosphoric acid, or an organic / inorganic hybrid polymer partially substituted with a proton conductor functional group And proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution.

  The membrane electrode assembly is provided with a separator on each surface to form a polymer electrolyte fuel cell. As the separator, for example, a separator in which a plurality of protrusions (ribs) extending in one direction are formed at a predetermined interval on the surface facing the gas diffusion layer can be used. Between adjacent convex parts, it is a groove part with a rectangular cross section. The groove is used as a supply / discharge flow path for an oxidant gas such as fuel gas and air. The fuel gas and the oxidant gas are supplied from the fuel gas supply unit and the oxidant gas supply unit, respectively. Each separator disposed on each surface of the membrane electrode assembly is preferably disposed so that the grooves formed therein are orthogonal to each other. The above configuration constitutes the minimum unit of the fuel cell, and a fuel cell can be configured from a cell stack in which several tens to several hundreds of this configuration are arranged in parallel.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, in the above-described embodiment, the example in which the electrode catalyst manufactured by the method of the present invention is used as an electrode catalyst of a solid polymer electrolyte fuel cell has been mainly described. However, the electrode catalyst manufactured by the method of the present invention Can be used as an electrode catalyst in various fuel cells such as fuel cells other than solid polymer electrolyte fuel cells, such as alkaline fuel cells, phosphoric acid fuel cells, and direct methanol fuel cells.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
(1) Production process of carrier Based on Example 1 described in WO2016 / 098399, tungsten / fluorine-containing tin oxide particles having a primary particle diameter of 20 nm were obtained.

(2) Dispersion Preparation process capacity 500mL volumetric flask to 337mL of N, N- dimethylformamide (abbreviated: DMF, 049-32363, manufactured by Wako Pure Chemical Industries, _{^{Ltd.), 1.22 × 10 -2 mol /}} L -DMF Bis (acetylacetonato) platinum (II) (Pt (acac) ₂ , 028-16853, manufactured by Wako Pure Chemical Industries, Ltd.), 9.37 × 10 ⁻³ mol / L- _DMF bis (2,4-pentane) Dionato) nickel (II) dihydrate (Ni (acac) ₂ .2H ₂ O, 343-01981, manufactured by Dojindo Laboratories) 2.99 × 10 ⁻¹ mol / L- _DMF benzoic acid (204-00985, manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the carrier obtained in (1) was added at a concentration of 16 g / L- _DMF . Thereafter, the liquid obtained by mixing each component was dispersed at room temperature (25 ° C.) for 30 minutes using an ultrasonic disperser to obtain a dispersion. While purging the volumetric flask containing this dispersion with argon gas, preliminary stirring was performed at room temperature and 400 rpm for 20 hours using a football-type stirrer having a major axis of about 2 cm and a minor axis of about 1 cm. In addition, said each value which makes a unit "mol / L- _DMF " or "g / L- _DMF " means the ratio with respect to DMF which is a solvent of a dispersion liquid.

(3) Supporting step With the pre-stirred dispersion flask containing the dispersion liquid kept purged with argon gas, submerged in an oil bath whose oil temperature was controlled at 160 ° C. Heating started. At this time, it took about 7 minutes for the solvent in the volumetric flask to boil. After boiling, the mixture was heated to reflux for 12 hours while the oil temperature in the oil bath was controlled at 160 ° C. Thereafter, the oil bath was removed and the mixture was cooled to room temperature, followed by filtration. Next, the mixture was washed 5 times with a mixed solvent of acetone and ethanol (mixed solvent of 1: 1 by volume ratio) and once with a mixed solvent of water and ethanol (mixed solvent of 1: 1 by volume ratio) and then dried. . The obtained dried powder was dispersed in 400 mL of 0.5 mol / L perchloric acid, heated and stirred at 60 ° C. for 2 hours, filtered, washed and dried to obtain a platinum-nickel alloy-supported electrode catalyst. The proportion of formic acid in the dispersion was 0.1%.

[Example 2]
A platinum-nickel alloy-supported electrode catalyst was obtained in the same manner as in Example 1, except that the dispersion preparation step in Example 1 was changed to the following method. In this example, bis (2,4-pentanedionato) nickel (II) and pure water are used instead of bis (2,4-pentandionato) nickel (II) .dihydrate.

(2) Dispersion Preparation Step To a 500 mL volumetric flask, add 337 mL of N, N-dimethylformamide (abbreviation: DMF, 049-32363, manufactured by Wako Pure Chemical Industries, Ltd.) to 0.8 × 10 ⁻² mol / L _−. After adding pure water of _DMF , bis (acetylacetonato) platinum (II) of 1.22 × 10 ⁻² mol / L- _DMF (Pt (acac) ₂ , 026-16853, manufactured by Wako Pure Chemical Industries, Ltd.) 9.37 × 10 ⁻³ mol / L- _DMF bis (2,4-pentanedionato) nickel (II) (Ni (acac) ₂ 283657-25G, manufactured by Sigma-Aldrich), 2.99 × 10 ^-1 mol / L- _DMF of benzoic acid (204-00985, manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the carrier obtained in (1) was added at a concentration of 16 g / L- _DMF . Thereafter, the liquid obtained by mixing each component was dispersed at room temperature (25 ° C.) for 30 minutes using an ultrasonic disperser to obtain a dispersion. While purging the volumetric flask containing this dispersion with argon gas, preliminary stirring was performed at room temperature and 400 rpm for 20 hours using a football-type stirrer having a major axis of about 2 cm and a minor axis of about 1 cm.

Example 3
The same procedure as in Example 2 was performed, except that 1.9 × 10 ⁻² mol / L- _DMF pure water was used instead of 0.8 × 10 ⁻² mol / L- _DMF pure water. In the same manner as in Example 2, a platinum-nickel alloy-supported electrode catalyst was obtained.

Example 4
In the dispersion preparation process of Example 2, it was carried out except that pure water of 2.5 × 10 ⁻² mol / L- _DMF was used instead of pure water of 0.8 × 10 ⁻² mol / L— _DMF. In the same manner as in Example 2, a platinum-nickel alloy-supported electrode catalyst was obtained.

Example 5
In the dispersion preparation process of Example 2, it was carried out except that pure water of 3.3 × 10 ⁻² mol / L- _DMF was used instead of pure water of 0.8 × 10 ⁻² mol / L— _DMF. In the same manner as in Example 2, a platinum-nickel alloy-supported electrode catalyst was obtained.

Example 6
In the dispersion preparation process of Example 2, 0.6 × 10 ⁻² mol / L- _DMF formic acid (063-05895, Wako Pure Chemical Industries) was used instead of 0.8 × 10 ⁻² mol / L- _DMF pure water. A platinum-nickel alloy-supported electrode catalyst was obtained in the same manner as in Example 2 except that Kogyo Co., Ltd. was used.

Example 7
In the dispersion preparation step of Example 2, 1.2 × 10 ⁻² mol / L- _DMF formic acid (063-05895, Wako Pure Chemical Industries) was used instead of 0.8 × 10 ⁻² mol / L- _DMF pure water. A platinum-nickel alloy-supported electrode catalyst was obtained in the same manner as in Example 2 except that Kogyo Co., Ltd. was used.

[Comparative Example 1]
This comparative example is an example in which a platinum-nickel alloy catalyst is supported by a colloid method according to the description in Patent Document 1.
5 ml of H ₂ PtCl ₆ solution (corresponding to 1 g of Pt) and 295 mL of distilled water were mixed, platinum was reduced with 15.3 g of NaHSO ₃ , and then diluted with 1400 mL of distilled water. Next, a 5% aqueous solution of NaOH was added to adjust the pH to about 5, and 35% hydrogen peroxide (120 mL) was added dropwise to obtain a liquid containing platinum colloid. At this time, NaOH 5% aqueous solution was appropriately added to maintain the pH of the solution at about 5. The liquid containing the colloid obtained by this procedure contains 1 g of platinum. Nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) was added to this liquid. The amount added was 1.49 g so that Pt / Ni, which is the molar ratio of Pt to Ni, was 1. Thereafter, 8.7 g of the carrier obtained in the step (1) of Example 1 was added and mixed at 90 ° C. for 3 hours. After mixing, the liquid was cooled and further solid-liquid separated. In order to remove chloride ions from the water-containing powder obtained by solid-liquid separation, it was diluted again with 1500 mL of distilled water and boiled at 90 ° C. for 1 hour, and the liquid was cooled and solid-liquid separated. This washing operation was performed four times. Finally, after solid-liquid separation, it was dried at 60 ° C. for 12 hours in the atmosphere. As a result, platinum containing non-stoichiometric oxide and nickel containing non-stoichiometric oxide were supported on the surface of the support. The support was heat-treated at 200 ° C. for 2 hours under a 4% by volume hydrogen atmosphere diluted with nitrogen.

[Comparative Example 2]
_Instead of 9.37 × 10 ⁻³ mol / L- _DMF bis (2,4-pentanedionato) nickel (II) · dihydrate in the dispersion preparation step of Example 1, 9.37 × 10 ⁻ _{Except that} ³ mol / L- _DMF of bis (2,4-pentanedionato) nickel (II) (Ni (acac) ₂ , 283657-25G, manufactured by Sigma-Aldrich) was used, the same procedure as in Example 1 was performed. A platinum-nickel alloy-supported electrode catalyst was obtained.

[Evaluation]
About the electrode catalyst obtained by each Example and the comparative example 1 and the comparative example 2, Pt loading rate (mass%) measured by ICP mass spectrometer (ICP-MS), Ni loading rate (mass%), Pt And Ni molar ratio [Pt / Ni], diffraction angle 2θ (°) of peak of (200) plane of platinum alloy in diffraction pattern obtained by powder X-ray diffraction measurement (XRD), rotating disk electrode (RDE) cyclic voltammetry was used (CV: cyclic voltammetry) and convection voltammetry (LSV: Linear Sweep voltammetry) activity dominates current density at 0.64V (VS.Ag/AgCl) determined by _j k of (mA ^/ _{cm 2 -Pt)} Values are shown in Table 1 below. Specifically, operations were performed in the following order of “electrode preparation”, “CV measurement”, and “ORR activity evaluation”. The Pt loading rate and the Ni loading rate are values defined by Pt mass / (Pt mass + Ni mass + carrier mass) × 100 and Ni mass / (Pt mass + Ni mass + carrier mass) × 100, respectively.
XRD was measured by using RINT-TTR III manufactured by Rigaku Corporation and using Cu Kα (0.15406 nm, 50 kV, 300 mA) as an X-ray source.

Electrode preparation A glassy carbon (GC) disk electrode having a diameter of 5 mm was polished with 0.05 μm alumina paste, and then ultrasonically cleaned with pure water. A sample carrying platinum-nickel alloy was 90 vol. In addition to an aqueous ethanol solution, the mixture was dispersed with an ultrasonic homogenizer. This was applied onto a GC disk at a density such that the amount of Pt metal per area of the disk was 12 μg- _Pt / cm ² _-GC, and dried at room temperature. After drying, a 5% Nafion (registered trademark) solution (274704-100ML, manufactured by Sigma-Aldrich) was added dropwise to the catalyst on the GC disk so as to have a film thickness of 50 nm and dried at room temperature.

CV measurement The measurement was carried out using an electrochemical measurement system HZ-7000 manufactured by Hokuto Denko Corporation. After purging N ₂ into a 0.1 mol / L HClO ₄ aqueous solution for 1 hour or longer, a silver-silver chloride electrode (Ag / AgCl) was used as a reference electrode, and a potential range of −0.25 to 0.742 V (VS. Ag). / AgCl) and cleaning was performed 300 times at a sweep rate of 0.5 V / s. Thereafter, CV measurement was performed in a potential range of −0.25 to 0.74 V, and this measurement was performed. Electrochemical active surface area (ECSA) analysis was performed using an adsorption wave of hydrogen found at 0.4 V or less.

ORR activity evaluation After the oxygen solution was purged for 1 hour or more in the electrolyte solution (HClO ₄ aqueous solution) used in the CV measurement, LSV was performed. Data for a total of six conditions were acquired at a temperature of 25 ° C., a potential range of −0.20 to 1.00 V (VS. Ag / AgCl), a sweep speed of 10 mV / s, and a rotational speed from 400 rpm to 2500 rpm. The obtained result was analyzed using the Koutecky-Levic plot, and the value of the active dominant current density j _k (mA / cm ² ) at 0.64 V (VS. Ag / AgCl) was obtained.

As is apparent from the results shown in Table 1, each of the examples using the production method of the present invention is a comparative example 1 using the production method of Patent Document 1 and a Ni compound having no crystallization water as a transition metal compound. It can be seen that the active dominant current density j _k is higher than that of Comparative Example 2 using
In addition, it was found that the diffraction angle 2θ (°) of each example obtained by XRD shifts to a higher angle side with respect to Comparative Example 2. Usually, it is known that 2θ shifts to the high angle side when Ni is dissolved in Pt having a face-centered cubic lattice structure. From these facts, it can be interpreted that the platinum nickel alloy produced in each example promoted the solid solution of Ni in Pt more than that of Comparative Example 2.

On the other hand, although the active dominant current density j _k of each example is higher than that of Comparative Example 1, the diffraction angle 2θ (°) is not necessarily shifted to the higher angle side than Comparative Example 1. The reason for this is that in Comparative Example 1, heat treatment is performed at 200 ° C. in a reducing atmosphere, so that Ni easily dissolves in Pt and the diffraction angle 2θ (°) tends to shift to the high angle side. In this case, the active dominant current density j _{k of} Comparative Example 1 is lower than the value of the diffraction angle 2θ (°). Thinks.

  In addition, the preliminary stirring performed in each example contributes in the form of uniform mixing of the support and other raw materials, adsorption of the precursor to the support, etc., and rapid temperature increase contributes in the form of promotion of nucleation, etc. For this reason, the present inventor presumes that it works favorably in increasing ECSA.

Claims (7)

A dispersion in which a dispersion liquid is prepared by mixing (i) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, and (iv) a transition metal compound. Liquid preparation process;
A step of heating the dispersion and supporting a platinum alloy of platinum and a transition metal on the surface of the catalyst support powder, wherein the step is performed in the presence of formic acid chemical species in the dispersion. Process,
The manufacturing method of the electrode catalyst which has this. In the dispersion preparation step, water or a water-containing compound is mixed, and water is present in the dispersion,
The method for producing an electrocatalyst according to claim 1, wherein in the supporting step, the formic acid chemical species is generated by reacting the water and the organic compound present in the dispersion.   The method for producing an electrode catalyst according to claim 2, wherein the transition metal compound having crystal water is used as the water-containing compound. (I) a solvent of an organic compound having a formamide group, (ii) a catalyst support powder of a metal oxide, (iii) a platinum compound, (iv) a transition metal compound, (v) water or a water-containing compound, A dispersion preparation step of preparing a dispersion by mixing
A supporting step of heating the dispersion and supporting a platinum alloy of platinum and a transition metal on the surface of the catalyst carrier powder;
The manufacturing method of the electrode catalyst which has this.   The method for producing an electrode catalyst according to claim 4, wherein the transition metal compound having crystal water is used as the water-containing compound.   The method for producing an electrode catalyst according to any one of claims 1 to 5, wherein an aromatic compound containing a carboxyl group is further mixed in the dispersion preparation step.   The method for producing an electrode catalyst according to any one of claims 1 to 6, wherein a ceramic material containing tin oxide is used as the catalyst carrier powder.