WO2018047968A1

WO2018047968A1 - Electrode catalyst

Info

Publication number: WO2018047968A1
Application number: PCT/JP2017/032730
Authority: WO
Inventors: 谷口　浩司
Original assignee: 三井金属鉱業株式会社
Priority date: 2016-09-12
Filing date: 2017-09-11
Publication date: 2018-03-15
Also published as: JP6983785B2; JPWO2018047968A1

Abstract

This electrode catalyst comprises: a carrier which has a core part that is formed of a tin oxide containing a specific element and a shell part that is arranged on the surface of the core part; and a catalyst which is supported by the carrier and contains a platinum group element. The shell part contains an oxide of at least one metal element that is different from the above-mentioned specific element and is selected from the group consisting of Ti, Ta, Nb and Zr. This electrode catalyst is used for an anode of a fuel cell or a cathode for electrolysis. It is preferable that the oxide is in an amorphous state. It is also preferable that the oxide is zirconium oxide.

Description

Electrocatalyst

The present invention relates to an electrode catalyst.

A polymer electrolyte fuel cell has a proton conductive polymer membrane such as a perfluoroalkyl sulfonic 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 in which a cathode) and a fuel electrode (anode) are formed 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 serving as a carrier. In the electrode catalyst, it is known that carbon is oxidized and corroded due to a change in potential during operation of the fuel cell, and the noble metal catalyst supported is agglomerated 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.

Therefore, various studies on electrode catalysts have been made for the purpose of improving the performance and life of solid polymer fuel cells and improving the economic efficiency. 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. This document describes that this tin oxide is doped with Sb. On the surface of the carrier, fine particles of noble metal such as platinum are supported. According to the document, the acid resistance of Sb-doped tin oxide is increased by setting the ratio of Sb to the sum of Sb and Sn within a specific range.

Special table 2012-514287

The inventors conducted a follow-up test of the electrode catalyst described in Patent Document 1, and found that when the electrode catalyst was used in a reducing environment, the catalytic activity was significantly reduced.

An object of the present invention is to improve an electrode catalyst, and more specifically, to provide an electrode catalyst in which a decrease in catalytic activity is suppressed when used in a reducing environment.

In order to solve the above-mentioned problems, the present inventor has intensively studied, and in a reducing environment, tin constituting the support of the electrode catalyst and a noble metal such as platinum constituting the catalyst are alloyed, resulting in that. It was found that the catalytic activity was lost.

The present invention has been made on the basis of the above knowledge, and a support provided with a core part of tin oxide containing a predetermined element, and a shell part located on the surface of the core part,
A catalyst containing a platinum group element supported on the carrier;
Have
The shell part includes an oxide of at least one metal element selected from the group consisting of Ti, Zr, Nb, and Ta and different from the predetermined element;
The above-described problems are solved by providing an electrode catalyst.

FIG. 1 is a graph showing the power generation characteristics of the fuel cell obtained in Example 1. FIG. 2 is a graph showing the power generation characteristics of the fuel cell obtained in Example 5. FIG. 3 is a graph showing the power generation characteristics of the fuel cell obtained in Example 7. FIG. 4 is a graph showing the power generation characteristics of the fuel cell obtained in Example 8. FIG. 5 is a graph showing the power generation characteristics of the fuel cell obtained in Comparative Example 1.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The electrode catalyst of the present invention has a support and a catalyst containing a platinum group element supported on the surface of the support. The carrier includes a core part and a shell part located on the surface of the core part. The shell part may cover the entire surface of the core part evenly, or may cover the surface discontinuously so that a part of the surface of the core part is exposed. From the viewpoint of effectively preventing alloying of tin and platinum group elements, the shell portion preferably covers the entire core portion so that the surface of the core portion is not exposed.

The core part in the carrier is configured to contain tin oxide. The tin oxide used in the present invention is composed of an oxide of tin. It is known that tin oxide is a highly conductive substance. Examples of the tin oxide include SnO ₂ which is a tetravalent tin oxide and SnO which is a divalent tin oxide. In particular, the tin oxide is preferably composed mainly of SnO ₂ from the viewpoint of increasing the acid resistance of the electrode catalyst. “Mainly composed of SnO ₂ ” means that 50 mol% or more of tin oxide is composed of SnO ₂ .

The form of the carrier is not particularly limited, but preferably, the carrier is in the form of secondary particles in which primary particles are aggregated, and the primary particles of the carrier are primary particles of a composition containing tin oxide. And a shell portion disposed on the surface thereof. In this specification, the primary particle is an object recognized as the smallest unit as a particle, judging from the apparent geometric form, and the secondary particle is obtained by agglomeration of two or more primary particles. It is configured. Aggregation of primary particles is caused by, for example, intermolecular force, chemical bonding, or binding by a binder. The primary particle size of the carrier is preferably 5 nm or more and 200 nm or less, and more preferably 5 nm or more and 50 nm or less. 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 with an electron microscope image, measuring the maximum transverse length for 500 or more particles, and calculating the average value. The particle size of the secondary particles of the carrier is preferably from 0.1 μm to 10 μm, and more preferably from 0.5 μm to 5 μm. The particle size refers to a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measuring method.

As described above, the core portion constituting the support contains tin oxide, and it is preferable that the tin oxide contains a predetermined element from the viewpoint of further improving the performance of the electrode catalyst. A predetermined element is an element which can improve the electroconductivity of a tin oxide by containing in a tin oxide. Examples of the predetermined element include one or more elements selected from the group consisting of Ta, Nb, Sb, W, In, F, and V (hereinafter, this element is referred to as “addition element”). . The additive element is dissolved in the tin oxide, or is mixed in the state of the compound of the additive element (for example, an oxide of the additive element) in the tin oxide. The fact that the additive element is dissolved in the tin oxide means that the tin site in the tin oxide is replaced by the additive element. It is preferable that the additive element is dissolved in the tin oxide because the conductivity of the tin oxide containing the additive element is increased.

The content ratio of the additive element contained in the tin oxide containing the additive element is represented by X (mol) / (Sn (mol) + X (mol)) × 100, preferably 0.1 mol, where X is the additive element. % Or more and 10 mol% or less. Hereinafter, this value is referred to as “additional element content ratio”. When two or more kinds of additive elements are used, the additive element content ratio is calculated based on the total amount of all the additive elements. By setting the additive element content ratio to 0.1 mol% or more, the conductivity of tin oxide containing the additive element can be sufficiently increased. Even when the additive element content exceeds 10 mol%, the conductivity as a carrier is not greatly improved. From the viewpoint of further increasing the conductivity of tin oxide containing an additive element and sufficiently increasing the specific surface area, the additive element content is more preferably 0.1 mol% or more and 5 mol% or less, and still more preferably 0.5 mol% or more. 5 mol% or less.

The additive element content ratio of tin oxide containing additive elements can be measured, for example, by the following method. The electrode catalyst is dissolved by an appropriate method to form a solution, and this solution is analyzed by inductively coupled plasma (ICP) emission analysis, and the concentration of tin and the concentration of added elements are measured. Instead of ICP emission analysis, fluorescent X-ray (XRF) analysis can also be used. It can also be calculated by measuring the elemental composition of the core part by scraping the shell part of the carrier by X-ray photoelectron spectroscopy (XPS) combined with ion sputtering. In particular, when the additive element is F, the content of F can be measured using combustion-ion chromatography (for example, an automatic sample combustion apparatus (AQF-2100H) manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

As described above, it is preferable to use one or more elements selected from the group consisting of Ta, Nb, Sb, In, W, F, and V as the additive element. Among these elements, it is preferable to use one or more elements selected from the group consisting of Ta, Nb, Sb, W and F from the viewpoint of balance between performance and price, and a group consisting of Ta, Sb, W and F It is more preferable to use one or more elements selected from more.

The shell part located on the surface of the core part including tin oxide is configured to include an oxide of a specific element. Hereinafter, this specific element is also referred to as “shell element”. In the present invention, as the shell element, a metal element that is at least one metal element selected from the group consisting of Ti, Ta, Nb, and Zr and that is different from the additive element described above is employed. Even when the electrode catalyst of the present invention is used in a reducing environment, an alloy of tin and a platinum group element is formed by disposing a shell portion containing an oxide of these shell elements on the surface of the core portion. As a result of the study of the present inventor, it has been found that the conversion can be effectively suppressed. As a result, the catalytic activity of the electrode catalyst in a reducing environment is maintained over a long period of time. In order to make this advantage even more remarkable, it is preferable that the oxide constituting the shell portion is insoluble under the operating environment of the fuel cell or in the environment of use in the acidic electrolyte in the electrolysis process. It is. “Insoluble” means that no metal is eluted from the oxide, and that even if it is eluted, the amount is extremely small. The elution amount is extremely small means that the elution mass of the shell element after operation for 24 hours is 1% by mass or less with respect to the mass of the shell element before operation of the fuel cell. In particular, it is preferable that the shell portion contains zirconium oxide as an oxide constituting the shell element from the viewpoint of more effectively preventing a decrease in catalyst activity under a reducing environment.

As described above, the shell element is a metal element different from the additive element contained in the core portion. In this case, when two or more kinds of additive elements contained in the shell element and / or the core portion are present, it is necessary that they are completely different. For example, as in Comparative Example 3 described later, when the core portion contains tantalum and antimony and the shell portion contains tantalum, it is not said that the shell element and the additive element are different. The difference between the shell element and the additive element contained in the core part has the advantageous effect of suppressing the diffusion of tin element contained in the core part into the shell part when an electrode catalyst is used in a reducing environment. Played.

The content ratio of the shell element constituting the oxide to the tin element contained in the support is preferably 1 mol% or more and 60 mol% or less in terms of molar ratio. That is, when the total number of moles of shell elements is M (mol), M (mol) / Sn (mol) × 100 is preferably 1 mol% or more and 60 mol% or less. Hereinafter, this value is also referred to as “shell element content ratio”. By setting the content ratio of the shell element within this range, alloying of tin and a platinum group element can be effectively suppressed without impairing the conductivity as a carrier. From the viewpoint of making this effect even more remarkable, the content ratio of the shell element is more preferably 2 mol% or more and 50 mol% or less, and further preferably 5 mol% or more and 45 mol% or less.

The content ratio of the shell element is measured by X-ray photoelectron spectroscopy (XPS). Specifically, semi-quantitative values of tin element and shell element are calculated by XPS, and the content ratio of shell element is calculated from the ratio. XPS is preferably measured under the following conditions (A1) to (A5).
(A1) X-ray source: Kα of Al (hν = 1486.6 eV).
(A2) Angle between sample and detector: θ = 45 °.
(A3) Detector calibration: implemented using Cu2p and Au4f.
(A4) Analysis region: a circle with a diameter of 0.1 mm.
(A5) Chamber pressure during analysis: on the order of 10 ⁻⁷ to 10 ⁻⁶ Pa.

The shell part preferably further contains fluorine in addition to the above-described oxide of the shell element. As a result, the conductivity of the shell portion is improved, and the conductivity of the entire carrier is improved. Whether or not the shell contains fluorine can be confirmed by line analysis of energy dispersive X-ray spectroscopy (TEM-EDX) or electron energy loss spectroscopy (TEM-EELS) attached to the transmission electron microscope. it can. From the viewpoint of further improving the conductivity of the shell part, the fluorine content in the shell part is 0 with respect to the total number of moles of the shell element constituting the oxide and fluorine in the shell part. It is preferably 1 mol% or more and 20 mol% or less, more preferably 0.5 mol% or more and 15 mol% or less, and further preferably 1 mol% or more and 10 mol% or less.

The fluorine content contained in the shell portion can be measured by combustion-ion chromatography using combustion-ion chromatography (for example, an automatic sample combustion apparatus (AQF-2100H) manufactured by Mitsubishi Chemical Analytech Co., Ltd.). Separately from this, the content ratio of fluorine is calculated from the molar amount with the shell element calculated by ICP analysis according to the formula of F (mol) / (shell element ((mol)) + F (mol)) × 100. . When fluorine is contained in both the shell part and the core part, the content of fluorine contained in the shell part is measured by energy dispersive X-ray spectroscopy (TEM-EDX) attached to a transmission electron microscope or electron energy. It can be calculated from the semi-quantitative values of fluorine and shell elements in the shell by spot analysis of loss spectroscopy (TEM-EELS).

The reason why alloying of tin and platinum group elements is suppressed by disposing a shell part including a specific oxide on the surface of the core part is not clear at present, but the present inventor According to the above investigation, it was found that the effect of suppressing alloying between tin and a platinum group element is higher when the oxide is in an amorphous state than in a crystalline state. Whether the oxide constituting the shell part is crystalline or amorphous is determined by the diffraction peak of the oxide constituting the shell part in the diffraction pattern obtained by X-ray diffraction measurement of the electrode catalyst. Judgment can be made based on whether or not it is confirmed. Moreover, the shell part containing an amorphous oxide can be suitably manufactured, for example by the liquid phase precipitation method mentioned later.

The shell part preferably has a predetermined thickness and separates the core part of the support from the catalyst containing the platinum group element, and the thickness of the shell part is preferably 1 nm or more and 50 nm or less. By setting the thickness of the shell portion within this range, alloying of tin and a platinum group element can be effectively suppressed without impairing the conductivity as a carrier. From the viewpoint of making this effect even more remarkable, the thickness of the shell portion is more preferably 1 nm or more and 20 nm or less. The thickness of the shell part can be measured by observation with a transmission electron microscope (TEM). It can also be measured by X-ray photoelectron spectroscopic analysis combined with ion sputtering. For example, the analysis is performed until the signal intensity of the shell element reaches 50% of the signal intensity of the outermost surface, and the etching thickness by ion sputtering at that time can be defined as the shell thickness.

A catalyst containing a platinum group element is supported on the surface of the support. The platinum group element is a general term for elements belonging to Groups 8, 9, and 10 of the fifth period and the sixth period in the periodic table. Specific examples include platinum, ruthenium, rhodium, palladium, osmium, and iridium. Examples of the catalyst containing a platinum group element include an alloy of platinum and another element. Alloys of platinum and other elements include platinum and platinum group elements other than platinum (ruthenium, rhodium, iridium, etc.), platinum and base metals (vanadium, chromium, cobalt, nickel, iron, titanium, molybdenum) And alloys with manganese). These catalysts preferably have an average particle size of 1 nm or more and 10 nm or less on the surface of the support from the viewpoint of efficient expression of catalytic ability.

When attention is paid to the platinum group element contained in the catalyst, the supported amount of the platinum group element is 1 with respect to the total mass of the electrode catalyst, that is, the total mass of the support and the mass of the catalyst containing the platinum group element. It is preferable to set it as mass% or more and 30 mass% or less, and it is still more preferable to set it as 1 mass% or more and 20 mass% or less. By setting the loading amount within this range, the electrode reaction can be performed sufficiently smoothly. The supported amount of the platinum group element can be determined by dissolving the electrode catalyst by an appropriate method to form a solution and analyzing the solution by ICP emission analysis.

The catalyst containing the platinum group element may cover the entire surface of the support evenly according to the amount of the catalyst supported, but the catalyst is discontinuously coated so that the surface of the support is exposed at an appropriate distance. Is good.

Next, a preferred method for producing the electrode catalyst of the present invention will be described. This production method is roughly divided into (i) a production process of the core part, (ii) a formation process of the shell part, and (iii) a support process of a catalyst containing a platinum group element. Hereinafter, each process will be described.

First, the manufacturing process of the core part (i) will be described. The core part can be suitably manufactured by, for example, a wet synthesis method or a plasma synthesis method. In the wet synthesis method, a core portion can be obtained by generating a tin precipitate from a solution containing a tin source and, if necessary, an additive element source, and then firing the precipitate. When an additive element source is also used, a core part can be obtained by producing a coprecipitate containing tin and the additive element and then firing the coprecipitate. The obtained core part may be granulated by subjecting it to a spray drying method as necessary. In the plasma synthesis method, powder for spray drying may be synthesized, and the powder may be granulated by spray drying. Regardless of which method is employed, the obtained granulated product can be fired. Firing can be performed, for example, in an air atmosphere.

Next, the process of forming the shell part (ii) will be described. The shell portion is preferably formed by a liquid phase precipitation method (LPD method). The LPD method is a method of directly synthesizing an oxide thin film from an aqueous solution onto a base material using a hydrolysis equilibrium reaction of a metal fluoro complex in the aqueous solution. The outline of the reaction in the LPD method can be expressed by the following chemical reaction formula.

<Precipitation equilibrium reaction>
_{^{_{MF x (x-2n) -}}} + nH 2 O = MOn + xF - + 2nH + (1)
(In the formula, M represents an oxide element.)
<Deposition driven reaction>
H ₃ BO ₃ + 4H ⁺ + 4F ⁻ = HBF ₄ + 3H ₂ O (2)
Al ³⁺ + 6H ⁺ + 6F ⁻ = H ₃ AlF ₆ (3)

In the LPD method, the hydrolysis equilibrium reaction (ligand exchange reaction) of the metal fluoro complex MF _x ^{(x-2n) — in} the aqueous solution represented by the above formula (1) is the main reaction. To this reaction system, an agent for forming a fluorine compound that is more stable than the metal fluoro complex (hereinafter also referred to as a fluoride ion scavenger) and the core, that is, tin oxide particles, are added. For example, by adding boric acid or aluminum ions, which are fluoride ion scavengers, to the reaction system, a more stable complex is formed according to the reaction of the formula (2) or (3). The formation of this complex consumes free fluoride ions and shifts the equilibrium of equation (1) toward the direction of metal oxide precipitation. As a result, the reaction of formula (1) proceeds spontaneously, and the oxide supersaturated in the aqueous solution gradually forms a thin film on the surface of the core portion added to the aqueous solution.

When the shell portion contains an oxide of Ti, diammonium titanate ((NH ₄ ) ₂ TiF ₆ ) is used as a Ti source, and boric acid (H ₃ BO as a fluoride ion scavenger) is used in this aqueous solution. ₃ ) is added, and the core portion may be further added thereto.
Further, when the shell portion contains Ta oxide, tantalum pentoxide (Ta ₂ O ₅ ) is used as a Ta source, and boric acid (H ₃ BO ₃ ) as a fluoride ion scavenger is added to this aqueous solution. Then, the core portion may be further added thereto.
Further, when the shell portion contains an oxide of Nb, niobium pentoxide (Nb ₂ O ₅ ) is used as the Nb source, and boric acid (H ₃ BO ₃ ) as a fluoride ion scavenger is added to this aqueous solution. Then, the core portion may be further added thereto.

Even in the case where the shell portion contains an oxide of Zr, fluorinated zirconic acid (H ₂ ZrF ₆ ) is used as a Zr source, and aluminum ions (Al ³⁺ ) as a fluoride ion scavenger are added to this aqueous solution. What is necessary is just to add a core part to this.

When the carrier having the core portion and the shell portion is obtained as described above, the catalyst supporting step (iii) is performed. There is no particular limitation on the method for supporting the catalyst on the surface of the carrier, and methods similar to those known so far in the art can be employed. For example, chloroplatinic acid hexahydrate (H ₂ PtCl ₆ .6H ₂ O), dinitrodiammine platinum (Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ), etc. are used as the platinum group element source, and these are used in the liquid phase. A platinum group element is supported on a carrier by reduction using a known method such as a chemical reduction method, a gas phase chemical reduction method, an impregnation-reduction pyrolysis method, a colloid method, or a surface-modified colloid pyrolysis reduction method. Can do. In the colloid method, a carrier is dispersed in a liquid containing a colloid containing a platinum group element, and the colloid is supported on the carrier. Specifically, a reducing agent is added to a liquid containing a platinum group element-containing colloidal precursor to reduce the precursor, thereby generating a colloid containing a platinum group element. Then, the carrier is dispersed in the liquid containing the colloid containing the platinum group element, and the colloid is supported on the carrier as fine particles containing the platinum group element. Details of the ethanol method are described, for example, in JP-A-9-47659. Details of the colloid method are described in, for example, WO2009 / 060582 and JP-A-2006-79904.

After the fine particles containing the platinum group element are adhered to the surface of the carrier in this way, the reduction treatment is performed next. This reduction treatment is preferably performed in a reducing atmosphere for the purpose of activating the catalyst. Examples of the reducing atmosphere include hydrogen and carbon monoxide. When hydrogen is used, it may be used at a concentration of 100%, or preferably 0.1 to 50% by volume, more preferably 1 to 10% by volume with an inert gas such as nitrogen, helium or argon. You may dilute and use. The temperature of the reduction treatment is preferably set to 10 ° C. or higher and 200 ° C. or lower, more preferably 10 ° C. or higher and 150 ° C. or lower, from the viewpoint of successfully activating the catalyst.

Thus, the target electrode catalyst is obtained. This electrode catalyst is preferably used in a membrane electrode assembly having an oxygen electrode (cathode) disposed on one surface of a solid polymer electrolyte membrane and a fuel electrode (anode) disposed on the other surface of the fuel cell. It can be used by containing at least the fuel electrode (anode). If necessary, the electrode catalyst of the present invention may be used for an oxygen electrode (cathode). In addition, the electrode catalyst of the present invention can be applied to uses other than fuel cells. For example, it can be suitably used as a cathode catalyst in various aqueous electrolysis processes.

In order to make the electrode reaction proceed smoothly, the electrode catalyst is preferably in contact with the solid polymer electrolyte membrane. Specifically, it is preferable to directly form a catalyst layer containing the electrode catalyst of the present invention on at least one surface of the solid polymer electrolyte membrane. Thereby, CCM (CatalystataCoated Membrane) is obtained. This catalyst layer is preferably a catalyst layer of the fuel electrode (anode). On the other hand, when the electrode catalyst of the present invention is used as an electrode catalyst in an aqueous electrolysis process, the catalyst layer is preferably a cathode catalyst layer. When the catalyst layer is used as an anode catalyst layer of a fuel cell, the catalyst layer preferably contains an ionomer in addition to the electrode catalyst of the present invention. As the ionomer, for example, it is preferable to use the same type of compound as the solid polymer electrolyte membrane. Specifically, when the solid polymer electrolyte membrane is a fluorine-containing polymer compound, the same kind of compound as the fluorine-containing polymer compound can be used as the ionomer contained in the catalyst layer.

A gas diffusion layer is disposed on each surface of the CCM, whereby an MEA (membrane electrode assembly) is obtained. 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 made into a polymer electrolyte fuel cell by providing a separator on each surface. 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 formed by arranging several tens to several hundreds of this configuration 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 electrode catalyst of the present invention has been mainly described as an example of using an electrode catalyst of a solid polymer electrolyte fuel cell or an electrode catalyst of an electrolysis process. It 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) Formation of anode catalyst layer (a) Manufacturing process of core part-Manufacturing process of tantalum-containing tin oxide particles-
148 g of Na ₂ SnO ₃ was dissolved in 1630 g of pure water to prepare a tin-containing aqueous solution. Separately from this operation, a tantalum-containing solution in which 5.1 g of TaCl ₅ was dissolved in 140 mL of ethanol was prepared, and this tantalum-containing solution was mixed with an aqueous nitric acid solution (116 g of nitric acid dissolved in 1394 g of pure water). The tin-containing aqueous solution was added to the liquid after mixing and mixed and stirred. Stirring was continued for 1 hour, then stirring was stopped, and the mixture was allowed to stand for 12 hours. As a result, a tin oxide precursor containing tantalum was produced and precipitated. The liquid was filtered and the solid was washed with water and then dried at 60 ° C. The precursor after drying was fired at 450 ° C. for 5 hours in an air atmosphere to obtain tantalum-containing tin oxide particles. The ratio of tantalum represented by Ta (mol) / (Sn (mol) + Ta (mol)) × 100 was 2.6 mol%.

-Manufacturing process of granulated product of tantalum-containing tin oxide particles-
The tantalum-containing tin oxide particles were coarsely crushed with an agate mortar to an average particle size of 100 μm or less, and then pulverized with a ball mill using yttrium-stabilized zirconia balls. In pulverization with a ball mill, 40 g of tantalum-containing tin oxide particles were mixed with 700 mL of pure water and 40 g of ethanol to form a slurry, and this slurry was used for pulverization. After pulverization, the slurry and the ball were separated and granulated by a spray drying method using the separated slurry to obtain a granulated product. The granulation conditions were as follows: inlet temperature: 220 ° C., outlet temperature 60 ° C., spray pressure: 0.15-0.2 MPa, liquid feed rate: 8.3 mL / min, slurry concentration: 10 g / 250 mL.

~ Firing process of granulated product ~
The obtained granulated material was fired under conditions of 680 ° C. and 5 hours in an air atmosphere. The obtained tantalum-containing tin oxide granulated product was substantially spherical with an average particle size of 2.68 μm. In this way, a core part in the carrier was obtained.

(B) Shell part formation step 50 mol of 0.5 mol / L diammonium fluoride (NH ₄ ) ₂ TiF ₆ solution is mixed with 100 mL of 0.5 mol / L boric acid and 100 mL of pure water to obtain a reaction solution. It was. 5 g of the core part was added to this solution and reacted for 4 hours. Then, filtration washing was performed and it was made to dry overnight in a 120 degreeC dryer. Thus, a support provided with a shell portion containing Ti oxide and a core portion made of tantalum-containing tin oxide was obtained.

(C) Catalyst loading step Platinum was loaded on the carrier obtained in the step (b). The loading was performed according to the method described in Examples of Japanese Patent Application Laid-Open No. 2006-79904. Specifically, it is as follows. First, a platinum solution containing 1 g of platinum was prepared using chloroplatinic acid. Sodium bisulfite was added thereto as a reducing agent, diluted with pure water, and a 5% aqueous sodium hydroxide solution was added to adjust the pH to 5. Further, hydrogen peroxide solution was added dropwise to oxidize and remove excess sulfite ions. The liquidity was maintained at pH 5 using a 5% aqueous sodium hydroxide solution. The carrier was dispersed in the colloidal solution thus obtained to adsorb the platinum colloid, followed by filtration, washing and drying to obtain a platinum-supporting carrier. Thereafter, heat treatment was performed at 80 ° C. for 2 hours in a weak reducing atmosphere of 4% by volume H ₂ / N ₂ to obtain an electrode catalyst. As a result of analysis, the amount of platinum supported was 7.5%. The supported amount is defined as [platinum / (platinum + carrier)] × 100 on a mass basis. Further, from the result of XRD measurement, it was confirmed that the Ti oxide was amorphous.

(2) Anode catalyst layer formation step 1.24 g of the electrode catalyst was placed in a container, and pure water, ethanol and 2-propanol were added in order at a mass ratio of 35:45:20 (1.61 g as a mixed solution). The ink thus obtained was dispersed with ultrasound for 3 minutes. Next, a yttrium-stabilized zirconia ball having a diameter of 10 mm was placed in the container, and stirred for 20 minutes at 800 rpm with a planetary ball mill (Sinky ARE310). Further, 5% Nafion (registered trademark) (274704-100ML, manufactured by Sigma-Aldrich), which is an ionomer, was added to the ink, and the same stirring was performed by ultrasonic dispersion and a planetary ball mill. The amount of Nafion added was such that the mass ratio of Nafion / carrier was 0.074. The ink thus obtained was applied onto a polytetrafluoroethylene sheet using a bar coater, and the coating film was dried at 60 ° C. to form a catalyst layer.

(2) Formation of cathode catalyst layer 1.00 g of platinum-supported carbon black (TEC10E50E) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. was put into a container, and pure water, ethanol and 2-propanol were mixed at a mass ratio of 45:35:20 (mixed solution As 12.8 g). The ink thus obtained was dispersed with ultrasound for 3 minutes. Next, a yttrium-stabilized zirconia ball having a diameter of 10 mm was placed in the container, and stirred at 800 rpm for 20 minutes by a planetary ball mill (Sinky ARE310). Further, 5% Nafion (registered trademark) (274704-100ML, manufactured by Sigma-Aldrich), which is an ionomer, was added to the ink, and the same agitation as described above was continued by ultrasonic dispersion and a planetary ball mill. The amount of Nafion added was such that the mass ratio of Nafion / carbon black support was 0.70. The ink thus obtained was applied onto a polytetrafluoroethylene sheet using a bar coater, and the coating film was dried at 60 ° C.

(3) Manufacture of CCM (membrane electrode assembly) The obtained sheet of polytetrafluoroethylene with cathode catalyst layer and sheet of polytetrafluoroethylene with anode catalyst layer were cut into a square shape of 54 mm square, and Nafion (registered) (Trademark) (NRE-212, manufactured by Du Pont Co., Ltd.) was superposed on the membrane and heat-pressed in air at 140 ° C. and 25 kgf / cm ² for 2 minutes for transfer. In this way, the cathode and anode catalyst layers were formed on each surface of the solid polymer electrolyte membrane made of Nafion. The amount of the platinum in the electrode catalyst layer, the cathode catalyst layer in the anode catalyst layer at _0.165mg -Pt / cm ² was _0.035mg -Pt / cm ^2.

(4) Assembly of fuel cell A fuel cell was assembled using the CCM and JARI standard cell obtained in (3) above. SIGRACE (registered trademark) 29BC (manufactured by SGL) was used as the gas diffusion layer. Further, Si / PEN / Si (180 μm) was used as the gasket.

[Example 2]
In the production of the carrier in Example 1, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 1 except that the production of the core part and the formation of the shell part were changed to the following methods. Moreover, it was confirmed from the result of the XRD measurement of the electrode catalyst that the Ti oxide is amorphous.
(A) Manufacturing process of core part Based on the description of Example 1 of WO2016 / 098399, tungsten and fluorine-containing tin oxide particles having a primary particle diameter of 20 nm were obtained. The ratio of tungsten represented by W (mol) / (Sn (mol) + W (mol) + F (mol)) × 100 is 2.5 mol%, and F (mol) / (Sn (mol) + W (mol) The ratio of fluorine represented by + F (mol)) × 100 was 3.8 mol%. The obtained tungsten and fluorine-containing tin oxide particles were substantially spherical with an average particle size of 2.1 μm. In this way, a core part in the carrier was obtained.

(B) Shell part forming step 0.5 mol / L diammonium fluoride (NH ₄ ) ₂ TiF ₆ solution 0.5 mL was mixed with 0.5 mol / L boric acid 100 mL and pure water 149.5 mL. A reaction solution was obtained. 5 g of the core part was added to this solution and reacted for 4 hours. Then, filtration washing was performed and it was made to dry overnight in a 120 degreeC dryer. As a result, a support provided with a shell portion containing Ti oxide and a core portion made of tungsten and fluorine-containing tin oxide was obtained.

Example 3
In the step of forming the shell portion in Example 2, 0.5 mL / L boric acid 100 mL and pure water 145 mL were mixed with 0.5 mL / L diammonium fluoride (NH ₄ ) ₂ TiF ₆ solution 5 mL, After obtaining the reaction solution, 20 g of the core part was added to the solution and reacted for 4 hours. Except for these, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 2. Moreover, it was confirmed from the result of the XRD measurement of the electrode catalyst that the Ti oxide is amorphous.

Example 4
In the shell portion forming step in Example 2, 0.5 mol / L boric acid titanate (NH ₄ ) ₂ TiF ₆ solution 10 mL was mixed with 0.5 mol / L boric acid and 100 mL pure water 140 mL, A reaction solution was obtained. Except for these, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 2. Moreover, it was confirmed from the result of the XRD measurement of the electrode catalyst that the Ti oxide is amorphous.

Example 5
The formation of the shell portion in Example 2 was performed in the same manner as the formation of the shell portion in Example 1. Except this, it carried out similarly to Example 2, and obtained the electrode catalyst and the fuel cell. Moreover, it was confirmed from the result of the XRD measurement of the electrode catalyst that the Ti oxide is amorphous.

Example 6
In the shell portion forming step in Example 5, 100 mL of 0.5 mol / L boric acid and 100 mL of pure water were mixed with 50 mL of 0.5 mol / L diammonium fluoride (NH ₄ ) ₂ TiF ₆ solution and reacted. After obtaining the solution, 3.5 g of the core part was added to the solution and reacted for 4 hours. Except for these, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 5. Moreover, it was confirmed from the result of the XRD measurement of the electrode catalyst that the Ti oxide is amorphous.

Example 7
In the production of the carrier in Example 5, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 5 except that the production of the shell part was changed to the following method. Further, as a result of XRD measurement of the electrode catalyst, it was confirmed that the Ta oxide was amorphous.
(B) Shell part forming step 3 g of tantalum pentoxide (manufactured by Mitsuwa Chemicals) was dissolved in 500 mL of a 1 mol / L hydrofluoric acid solution to prepare a raw material solution. After 110 mL of this raw material solution was mixed with 40 mL of pure water, 100 mL of 0.5 mol / L boric acid was mixed to obtain a reaction solution. 5 g of the core part was added to this solution and reacted for 4 hours. Then, filtration washing was performed and it was made to dry overnight in a 120 degreeC dryer. Thus, a support provided with a shell portion containing Ta oxide and a core portion made of tungsten and fluorine-containing tin oxide was obtained.

Example 8
In the production of the carrier in Example 5, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 5 except that the production of the shell part was changed to the following method. Further, as a result of XRD measurement of the electrode catalyst, it was confirmed that the Nb oxide was amorphous.
(B) Shell part forming step 4.5 g of niobium pentoxide (manufactured by Mitsuwa Chemical Co., Ltd.) was dissolved in 500 mL of a 1 mol / L ammonium hydrogen fluoride solution to prepare a raw material solution. 50 mL of this raw material solution was mixed with 200 mL of 0.25 mol / L boric acid to obtain a reaction solution. 5 g of the core part was added to this solution and reacted for 4 hours. Then, filtration washing was performed and it was made to dry overnight in a 120 degreeC dryer. As a result, a support including a shell portion containing Nb oxide and a core portion made of tungsten and fluorine-containing tin oxide was obtained.

Example 9
In the production of the carrier in Example 5, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 5 except that the production of the shell part was changed to the following method. As a result of XRD measurement of the electrode catalyst, it was confirmed that the Zr oxide was amorphous.
(B) Shell part forming step 3.4 mL of fluorinated zirconate H ₂ ZrF ₆ (manufactured by Sigma-Aldrich) was diluted with pure water to 250 mL, and then mixed and dissolved 15 g of aluminum chloride was used as a reaction solution. . 5 g of the core part was added to this solution and reacted for 4 hours. Then, filtration washing was performed and it was made to dry overnight in a 120 degreeC dryer. As a result, a support including a shell portion containing Zr oxide and a core portion made of tungsten and fluorine-containing tin oxide was obtained.

Example 10
In the production of the carrier in Example 5, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 5 except that the production process of tantalum and fluorine-containing tin oxide particles in the production process of the core part was changed to the following method. . From the result of XRD measurement of the electrode catalyst, it was confirmed that the Ti oxide was amorphous.
(A) Manufacturing process of core part-Manufacturing process of tin oxide particles containing antimony and tantalum-
(1) Preparation of tantalum-containing solution 5 g of TaCl ₅ was dissolved in 115 ml of ethanol, and 115 ml of water was subsequently added to obtain a tantalum-containing transparent liquid. To this transparent liquid, 25% aqueous ammonia was added dropwise until the pH reached 10. This caused precipitation in the liquid. The precipitate was collected by filtration and washed, and then 22.5 g of 30% hydrogen peroxide water, 10.5 g of oxalic acid dihydrate, and 117 g of pure water were added. Thus, a tantalum-containing transparent liquid was obtained again.

(2) Production of Tin Oxide by Sol-Gel Method 250 ml of 40% nitric acid aqueous solution was added to a mixture of 10 g of Sn foil containing 2.2% Sb and 33.3 g of citric acid. This gave a clear liquid. To this transparent liquid, 10.6 g of the tantalum-containing transparent liquid obtained in (1) was added and mixed. 25% aqueous ammonia was added dropwise to the resulting mixture until the pH of the solution reached 8. The liquid immediately after the dropping remained transparent. The solution was refluxed at 100 ° C. for 2 hours. This caused the liquid to become cloudy. After the liquid had cooled, it was centrifuged to recover the solids and washed with water. The obtained solid was dried in the atmosphere at 120 ° C. overnight and then pulverized in a mortar. The solid content after pulverization was calcined at 730 ° C. for 2 hours in the air. Thus, particles of tin oxide containing antimony and tantalum were obtained. (Sb (mol) + Ta (mol)) / (Sn (mol) + Sb (mol) + Ta (mol)) × 100 was 2.7%.

Example 11
In the production of the carrier in Example 8, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 8, except that the production of the core part was the same as in Example 10. From the result of XRD measurement of the electrode catalyst, it was confirmed that the Nb oxide was amorphous.

Example 12
In the production of the carrier in Example 9, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 9, except that the production of the core part was the same as in Example 10. From the results of XRD measurement of the electrode catalyst, it was confirmed that the Zr oxide was amorphous.

Example 13
An electrode catalyst and a fuel cell were obtained in the same manner as in Example 8, except that in the catalyst supporting step in the production process of the electrode catalyst in Example 8, chloroplatinic acid was changed to chloroiridic acid. From the result of XRD measurement of the electrode catalyst, it was confirmed that the Nb oxide was amorphous.

[Comparative Example 1]
In the manufacture of the carrier in Example 1, the core part itself was used as the carrier without forming a shell part on the surface of the core part. Except for this, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 1.

[Comparative Example 2]
In the production of the carrier in Example 2, the core part itself was used as a carrier without forming a shell part on the surface of the core part. Except this, it carried out similarly to Example 2, and obtained the electrode catalyst and the fuel cell.

[Comparative Example 3]
This comparative example is an example in which the additive element included in the core portion and the type of the shell element included in the shell portion overlap. Specifically, in the production of the carrier in Example 7, an electrode catalyst and a fuel cell were obtained in the same manner as in Example 7 except that the production of the core was the same as in Example 10.

[Comparative Example 4]
This comparative example is an example in which the shell element contained in the shell portion is different from the element used in the present invention. Specifically, in the shell portion forming step in Example 5, 0.5 mol / L hydrosilicofluoric acid was used instead of 0.5 mol / L diammonium fluoride (NH ₄ ) ₂ TiF ₆ solution. An electrode catalyst and a fuel cell were obtained in the same manner as in Example 5 except that an H ₂ SiF ₆ solution (manufactured by Kanto Chemical) was used.

[Comparative Example 5]
This comparative example is an example in which the shell element contained in the shell portion is different from the element used in the present invention. Specifically, in the shell portion forming step in Example 5, 1.8 g of molybdic acid H ₂ MoO ₄ (instead of 0.5 mol / L diammonium titanate (NH ₄ ) ₂ TiF ₆ solution) was used. Kanto Chemical Co.) was dissolved in 500 mL of a 0.55 mol / L hydrofluoric acid solution, and an electrode catalyst and a fuel cell were obtained in the same manner as in Example 5 except that the prepared raw material solution was used.

[Evaluation]
About the shell part of the electrode catalyst obtained in the Example and the comparative example, the content rate (M / Sn) of the shell element and the content rate of fluorine (F / (M + F)) were measured by the above-mentioned method. The results are shown in Table 1 below. The fluorine content was measured for each of Examples 1 and 10 to 12 and Comparative Example 3 by a combustion-ion chromatograph using an automatic sample combustion apparatus (AQF-2100H) manufactured by Mitsubishi Chemical Analytech. Examples 2 to 9 and 13 and Comparative Examples 4 and 5 were measured by spot analysis by electron energy loss spectroscopy (TEM-EELS).
In addition, the power generation characteristics of the fuel cells obtained in Examples and Comparative Examples were evaluated. In the evaluation, after heating to 80 ° C. and stabilizing nitrogen gas humidified to 100% RH to the anode and cathode of the fuel cell, humidified hydrogen is supplied to the anode and humidified oxygen is supplied to the cathode. I went. Under these conditions, the power generation characteristics (current-voltage characteristics) were measured for three cycles in the current value range of 0 to 1.5 A / cm ² . The cell resistance at that time was measured using a low resistance meter (MODEL 356E) manufactured by Tsuruga Electric Co., Ltd. The initial (first cycle) 0.5 A / cm ² cell voltage value (V), cell resistance (Ω · cm ² ), and evaluation results thereof, and the third cycle 0.5 A / cm The cell voltage value (V) at ² o'clock and the evaluation results are shown in Table 1 below. Moreover, the graph of the measurement result of Example 1, 5, 7, and 8 and the comparative example 1 is shown to FIG. Further, for Examples 4, 7, 8 and 9, 15 cycles of measurement were performed. Table 2 shows the cell voltage value (V) and the evaluation result at 0.5 A / cm ² at the 15th cycle.

The evaluation criteria in Table 1 are as follows.
<Initial voltage>
A: Cell voltage is 0.7V or more B: Cell voltage is 0.68V or more and less than 0.7V C: Cell voltage is 0.66V or more and less than 0.68V D: Cell voltage is 0.64V or more and less than 0.66V E: Cell voltage is less than 0.64V <Initial resistance>
A: 90mΩ · cm ² or less B: 90mΩ · cm ² ultra 95mΩ · cm ² or less C: 95mΩ · cm ² ultra 100 m [Omega · cm ² or less D: 100mΩ · cm ² ultra 105mΩ · cm ² or less E: 105mΩ · cm ² greater <Voltage at the third cycle>
A: Cell voltage is 0.7V or more B: Cell voltage is 0.68V or more and less than 0.7V C: Cell voltage is 0.66V or more and less than 0.68V D: Cell voltage is 0.64V or more and less than 0.66V E: Cell voltage is less than 0.64V

As is apparent from the results shown in Table 1 and FIGS. 1 to 5, in each example (product of the present invention), no significant decrease in power generation characteristics is observed even when the cycle is repeated three times. On the other hand, in each comparative example, power generation was not possible in the second cycle. That is, the electrode catalyst of each example did not lose the hydrogen oxidation activity (catalytic activity), whereas the electrode catalyst of each comparative example lost the hydrogen oxidation activity (catalytic activity).

In particular, as is clear from the comparison of Examples 4, 7, 8 and 9 shown in Table 2, when zirconium is used as the shell element, the cell voltage is higher than when other shell elements are used, and the durability is high. Can be seen to be even higher.

As described above in detail, according to the present invention, it is possible to effectively prevent a decrease in catalytic activity in a reducing environment.

Claims

A support comprising a core portion of tin oxide containing a predetermined element, and a shell portion located on the surface of the core portion;
A catalyst containing a platinum group element supported on the carrier;
Have
The shell part includes an oxide of at least one metal element selected from the group consisting of Ti, Ta, Nb and Zr and different from the predetermined element;
Electrocatalyst.
2. The electrode according to claim 1, wherein a content ratio of the metal element constituting the oxide with respect to a tin element contained in the carrier, measured by X-ray photoelectron spectroscopy (XPS), is 1 mol% or more and 60 mol% or less. catalyst.
The electrode catalyst according to claim 1 or 2, wherein the shell portion further contains fluorine.
The content ratio of fluorine in the shell part is 0.1 mol% or more and 20 mol% or less with respect to the total number of moles of the metal element constituting the oxide and fluorine in the shell part. The electrode catalyst according to any one of the above.
The electrode catalyst according to any one of claims 1 to 4, wherein the oxide is zirconium oxide.
The electrode catalyst according to any one of claims 1 to 5, wherein the oxide is in an amorphous form.
The electrode catalyst according to claim 1, which is used for an anode of a fuel cell or an electrolysis cathode.
An anode catalyst layer for a fuel cell comprising the electrode catalyst according to any one of claims 1 to 6.
A cathode catalyst layer for electrolysis comprising the electrode catalyst according to any one of claims 1 to 6.
A method for producing an electrode catalyst according to any one of claims 1 to 7,
An agent for forming a fluorine compound more stable than the fluoro complex in a solution of a metal fluoro complex of at least one metal element selected from the group consisting of Ti, Ta, Nb and Zr, and tin oxide particles A method for producing an electrode catalyst, comprising the step of adding and forming an oxide film of the metal element on the surface of the tin oxide particles.