JP2015199002A - Apparatus and method for production of core-shell catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core-shell catalyst production apparatus capable of reducing the over-voltage during an electrode reaction and a core-shell catalyst production method capable of reducing production costs.SOLUTION: A core-shell production apparatus 10 for producing a core-shell catalyst comprising a core containing a core metal 9 and a shell which contains a shell metal and covering the core by under-potential deposition includes a first tank 6 which contains an acidic solution 1 containing an acidic compound, based on the Arrhenius's definition, and has an action electrode 3 and a reference electrode 4, a second tank 7 which contains an acidic solution 2 containing the acidic compound in a concentration higher than the concentration in the first tank 6 and has a counter electrode 5 containing a precious metal selected from gold and platinum and a potential control mechanism for controlling the potentials of the action electrode 3, the reference electrode 4 and the counter electrode 5, and the first tank 6 and the second tank 7 are separated from each other with a cation exchange membrane 8. A core-shell catalyst production method using the apparatus 10 is also provided.

Description

  The present invention relates to a core-shell catalyst manufacturing apparatus and a core-shell catalyst manufacturing method.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Therefore, since the fuel cell is not subject to the Carnot cycle, it exhibits high energy conversion efficiency. A fuel cell is usually configured by laminating a plurality of single cells having a basic structure of a membrane electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes.

Conventionally, platinum and platinum alloy materials have been employed as electrode catalysts for the fuel electrode (anode electrode) and oxidant electrode (cathode electrode) of fuel cells. However, the amount of platinum required for current state-of-the-art electrocatalysts is still expensive to make mass production of fuel cells commercially feasible. Therefore, studies have been made to reduce the amount of platinum contained in the fuel electrode and oxidant electrode of a fuel cell by combining platinum with a cheaper metal.
For example, Patent Document 1 describes a method of manufacturing a core-shell catalyst including a core that is attracting attention as an electrode catalyst for a fuel cell and a shell that covers the core by displacement plating using underpotential deposition (UPD). ing.

JP 2013-215701 A

Underpotential deposition (UPD) is caused by the relative redox potential of the base metal on the surface of the core metal (for example, Pd) material having a stronger binding force than the core metal (hereinafter referred to as a relative base metal). This is a phenomenon in which a monoatomic layer of a relative base metal is formed at a more noble potential.
The core metal material having a relative base metal atomic layer formed by UPD on the surface is dipped in a solution containing shell metal ions, and the relative base metal (for example, Cu) is converted into the shell metal (for example, Pt using the difference in ionization tendency). ), A core-shell catalyst in which the surface of the core metal material is coated with a shell metal-containing shell can be produced.
When removing oxides and impurities on the surface of the core metal material as a pretreatment of UPD and UPD, by applying a voltage between the working electrode and a counter electrode using a corrosion-resistant noble metal such as platinum, the counter electrode side in water oxidation reaction _{^{(2H 2 O → O 2 +}} 4H + + 4e - E 0 = + 1.23V) it is necessary to cause.
When the apparatus is enlarged to produce a large amount of the core-shell catalyst, the distance between the working electrode and the counter electrode is widened, so that the overvoltage increases accordingly, and the water oxidation reaction on the counter electrode side as described above can be advanced. There is a problem that it becomes difficult.
Therefore, in order to reduce overvoltage and promote the oxidation reaction of water on the counter electrode side, it is necessary to increase the counter electrode area. There is a problem of increasing.

  The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to produce a core-shell catalyst production apparatus capable of reducing overvoltage during electrode reaction and production of a core-shell catalyst capable of reducing production cost. Is to provide a method.

The core-shell catalyst production apparatus of the present invention is an apparatus for producing a core-shell catalyst comprising a core containing a core metal and a shell containing the shell metal and covering the core by an underpotential deposition method,
A first tank containing an acidic solution containing an acidic compound according to the definition of Arrhenius and having a working electrode and a reference electrode;
A second tank containing an acidic solution containing the acidic compound at a concentration higher than the concentration in the first tank, and having a counter electrode containing a noble metal selected from gold and platinum;
A potential control mechanism for controlling the potential of the working electrode, the reference electrode, and the counter electrode;
The first tank and the second tank are separated from each other by a cation exchange membrane.

In the core-shell catalyst production apparatus of the present invention, the acidic compound is preferably sulfuric acid.
In the core-shell catalyst production apparatus of the present invention, it is preferable that the sulfuric acid in the second tank is 10 to 100 times higher in concentration than the sulfuric acid in the first tank.
In the core-shell catalyst production apparatus of the present invention, the first tank may function as the working electrode.

A method for producing a core-shell catalyst of the present invention is a method for producing a core-shell catalyst comprising: a core containing a core metal; and a shell containing the shell metal and covering the core,
An acidic solution containing an acidic compound according to the definition of Arrhenius and containing a working electrode, a first tank provided with a reference electrode, and an acid containing the acidic compound at a concentration higher than the concentration in the first tank A second tank containing a solution and including a counter electrode containing a noble metal selected from gold and platinum, and a potential control mechanism for controlling the potential of the working electrode, the reference electrode, and the counter electrode, Preparing a device in which the first tank and the second tank are separated from each other by a cation exchange membrane;
Supplying a base metal ion-containing solution containing a core metal material and ions of a metal relatively lower than the core metal to the first tank;
The step of precipitating the relative base metal on the surface of the core metal material by applying a noble potential higher than the oxidation-reduction potential of the relative base metal in the mixed solution containing the base metal ion-containing solution and the acidic solution. When,
After the deposition step, the shell metal ion-containing solution containing the shell metal ions is brought into contact with the core metal material on which the relative base metal is deposited, thereby replacing the relative base metal with the shell metal. Forming the shell.

In the method for producing a core-shell catalyst of the present invention, the acidic compound is preferably sulfuric acid.
In the method for producing a core-shell catalyst of the present invention, the sulfuric acid in the second tank is preferably 10 to 100 times higher in concentration than the sulfuric acid in the first tank.
The core shell catalyst production method of the present invention is characterized in that, in the supplying step, after supplying the core metal material, before supplying the base metal ion-containing solution, in the acidic solution in the first tank, the core metal material has a potential. Is preferably applied.
In the method for producing a core-shell catalyst of the present invention, the first tank may function as the working electrode.

According to the core-shell catalyst production apparatus of the present invention, it is possible to reduce overvoltage during electrode reaction.
According to the manufacturing method of the core-shell catalyst of the present invention, the manufacturing cost can be reduced.

It is a cross-sectional schematic diagram which shows an example of the core-shell catalyst manufacturing apparatus of this invention. It is a cross-sectional schematic diagram which shows an example of the core-shell catalyst manufacturing apparatus of this invention. It is a cross-sectional schematic diagram which shows an example of the core-shell catalyst manufacturing apparatus of this invention. It is a flowchart which shows an example of the manufacturing method of the core-shell catalyst of this invention. It is a figure which shows the analysis result by (A) STEM photograph and (B) EDS of a core-shell catalyst. It is a figure which shows the relationship between the acidic compound density | concentration at the time of (A) supply process, and (B) precipitation process, and an applied voltage. It is a figure which shows the relationship between the preparation core metal material mass and an applied voltage. It is a figure which shows the relationship between a counter electrode area and an applied voltage.

1. Core-shell catalyst production apparatus The core-shell catalyst production apparatus of the present invention is an apparatus for producing a core-shell catalyst comprising a core containing a core metal and a shell containing the shell metal and covering the core by an underpotential deposition method. ,
A first tank containing an acidic solution containing an acidic compound according to the definition of Arrhenius and having a working electrode and a reference electrode;
A second tank containing an acidic solution containing the acidic compound at a concentration higher than the concentration in the first tank, and having a counter electrode containing a noble metal selected from gold and platinum;
A potential control mechanism for controlling the potential of the working electrode, the reference electrode, and the counter electrode;
The first tank and the second tank are separated from each other by a cation exchange membrane.

According to the present invention, the overvoltage can be reduced by separating the first tank and the second tank by a cation exchange membrane, and the acidic solution in the second tank having a higher concentration than the first tank. It is presumed that the inclusion of can increase only the reaction rate on the counter electrode side, and further can reduce the activation energy of the electrode reaction due to the presence of the acidic compound.
According to the present invention, overvoltage can be reduced even if the apparatus is enlarged.
According to the present invention, since the first tank and the second tank are separated from each other by the cation exchange membrane, the concentration of the acidic compound contained in the acidic solution of the first tank is the acid solution of the second tank. Since the overvoltage can be reduced even if the concentration is lower than the concentration of the acidic compound to be contained, the amount of the acidic compound used can be reduced.
In the present invention, the shell covers the core is not only a form in which the entire surface of the core is covered by the shell, but a part of the surface of the core is covered by the shell, and a part of the surface of the core is exposed. The form which is doing is also included.

FIG. 1 is a schematic cross-sectional view showing an example of the core-shell catalyst production apparatus of the present invention.
The apparatus 10 shown in FIG. 1 has an acidic solution 1, a working electrode 3, a first tank 6 that accommodates a reference electrode 4, an acidic solution 2, and a second tank 7 that accommodates a counter electrode 5. The first tank 6 and the second tank 7 are adjacent to each other, a part of the adjacent portion is formed by the cation exchange membrane 8, and the first tank 6 and the second tank 7 are cation exchange. They are separated from each other by a membrane 8.
The working electrode 3 and the reference electrode 4 are disposed so as to be sufficiently immersed in the acidic solution 1, and the counter electrode 5 is disposed so as to be sufficiently immersed in the acidic solution 2. The working electrode 3, the reference electrode 4 and the counter electrode 5 are electrically connected to a potential control mechanism (for example, a potentiostat, etc., not shown) so that the potential of the working electrode 3 can be controlled.
The acidic solution 2 contains an acidic compound having a higher concentration than the acidic solution 1.
The core metal material 9 is added only to the acidic solution 1 in the first tank 6.

As another form of the core-shell catalyst production apparatus of the present invention, the one shown in FIGS. 2 and 3, the same reference numerals are given to the same components as those in FIG. 1, and the description thereof is omitted.
In the apparatus 20 shown in FIG. 2, the counter electrode 5 is arrange | positioned in the 1st tank 6 in the state accommodated in the 2nd tank 7 which has the cation exchange membrane 8 in the bottom part.
In the apparatus 30 shown in FIG. 3, the counter electrode 5 is disposed in the first tank 6 in a state of being accommodated in the second tank 7 having the cation exchange membrane 8 at the bottom. The first tank 6 is made of a highly conductive material, and its inner surface also functions as the working electrode 3.

The apparatus is not particularly limited as long as it has a first tank, a second tank, and a potential control mechanism, and the first tank and the second tank are separated from each other by a cation exchange membrane.
In the present invention, “the first tank and the second tank are separated from each other by a cation exchange membrane” means that the first tank and the second tank are adjacent to each other. It suffices that at least a part of the portion adjacent to the tank and the second tank is formed of a cation exchange membrane, and when the second tank is accommodated in the first tank, the second tank The tank should just be formed by the cation exchange membrane at least a part (for example, bottom part) where the 2nd tank is contacting the acidic solution of the 1st tank, and the 1st tank is the 2nd tank. When accommodated in the tank, at least a part (for example, the bottom part) of the first tank in contact with the acidic solution of the second tank is formed of a cation exchange membrane. Just do it.
Examples of the cation exchange membrane include a polyether ether as well as a fluorine polymer electrolyte membrane containing a fluorine polymer electrolyte such as a perfluorosulfonic acid polymer electrolyte membrane such as Nafion (registered trademark: DuPont). Hydrocarbon polymers such as ketones, polyetherketone, polyethersulfone, polyphenylene sulfide, polyphenylene ether, polyparaphenylene, and other general purpose plastics such as polyethylene, polypropylene, polystyrene, etc., sulfonic acid groups, carboxylic acid groups, Examples thereof include a hydrocarbon polymer electrolyte membrane including a hydrocarbon polymer electrolyte into which a proton acid group (proton conductive group) such as a phosphate group or a boronic acid group is introduced. The cation exchange membrane allows only the cations to move between the first tank and the second tank, and prevents the core metal material from contacting the counter electrode. For example, when a Nafion membrane is used as a cation exchange membrane and sulfuric acid is used as an acidic compound described later, protons pass through the Nafion membrane, but the concentration of sulfuric acid in the first tank and the sulfuric acid in the second tank Although the concentration depends on the scale of the apparatus, it does not change so much in a few days.
The potential control mechanism is not particularly limited as long as it can control the potential of the working electrode, the reference electrode, and the counter electrode, and a potentiostat, a potentiogalvanostat, or the like can be used.

The first tank is not particularly limited as long as it contains an acidic solution and includes a working electrode and a reference electrode, and if necessary, a second tank at least partially formed of a cation exchange membrane. Accommodate. Moreover, a 1st tank can also form at least one part of the inner surface of a 1st tank with the electroconductive material used for the working electrode mentioned later, and can also function as a working electrode.
The acidic solution is not particularly limited as long as it contains an acidic compound.
An acidic compound will not be specifically limited if it corresponds to the acid by the definition of Arrhenius, and it is preferable that it is a thing which is oxidized and reduced more easily than water. Specific examples of the acidic compound include those containing at least one selected from the group consisting of sulfuric acid, perchloric acid, nitric acid, hydrochloric acid and phosphoric acid. It is preferable to use only one type, and sulfuric acid is particularly preferable.
Although the density | concentration of the acidic compound in a 1st tank is not specifically limited, When an acidic compound is a sulfuric acid, it is preferable that it is 0.01-1.00M.
As the working electrode, for example, a material that can ensure conductivity, such as a metal material such as titanium, a conductive carbon material such as glassy carbon, or a carbon plate, can be used. The working electrode may be separate from the first tank, may be at least part of the inner surface of the first tank, or may be the entire surface.
As the reference electrode, a reversible hydrogen electrode (RHE), a silver-silver chloride electrode, a silver-silver chloride-potassium chloride electrode, or the like can be used.
The material of the portion other than the cation exchange membrane of the first tank is not particularly limited, and glass, plastic, ceramics, etc. can be used, and when the first tank functions as a working electrode, the working electrode described above is used. The conductive material used can be used. When the first tank of metal material is used as the working electrode, it is preferable to coat the inner surface of the first tank with a corrosion-resistant material such as RuO ₂ from the viewpoint of suppressing corrosion. When the first tank of conductive carbon material is used as a working electrode, it can be used as it is without coating.

The second tank is not particularly limited as long as it contains an acidic solution and is provided with a counter electrode. If necessary, the second tank contains a first tank at least partially formed of a cation exchange membrane.
The acidic solution in the second tank is not particularly limited as long as it contains an acidic compound at a concentration higher than that in the first tank.
The concentration of the acidic compound in the second tank is not particularly limited as long as it is higher than the concentration in the first tank. When the acidic compound is sulfuric acid, it is 10 to 100 times higher than the concentration in the first tank. The concentration is preferred. In addition, even if the concentration of the acidic compound contained in the acidic solution in the first tank and the second tank is the same, overvoltage can be reduced by increasing the concentration of the acidic compound, Acidic compounds are required. Therefore, from the viewpoint of saving acidic compounds, it is preferable to increase only the concentration of acidic compounds contained in the acidic solution of the second tank.
The counter electrode is not particularly limited as long as it contains a noble metal selected from gold and platinum, and examples thereof include platinum, gold, a platinum alloy, a gold alloy, a mixture containing at least one of gold and platinum, and another metal. .
In the case of a platinum alloy, an alloy with a metal material selected from the group consisting of iridium, ruthenium, rhodium and gold can be used, and the metal other than platinum constituting the platinum alloy may be one type or two or more types.
When a platinum alloy is used, the platinum content is preferably 80% by mass or more when the mass of the entire alloy is 100% by mass.
In the case of a gold alloy, an alloy with a metal material selected from the group consisting of iridium, ruthenium, rhodium, and platinum can be used, and the metal other than gold constituting the gold alloy may be one type or two or more types.
When a gold alloy is used, the gold content is preferably 80% by mass or more when the mass of the entire alloy is 100% by mass.
Specific examples of the counter electrode include a gold plate, a platinum plate, platinum black, a platinum mesh plated with platinum black, and the like.
The material of the portion other than the cation exchange membrane in the second tank is not particularly limited, and glass, plastic, ceramics and the like can be used.

2. A method for producing a core-shell catalyst according to the present invention is a method for producing a core-shell catalyst comprising: a core containing a core metal; and a shell containing the shell metal and covering the core,
An acidic solution containing an acidic compound according to the definition of Arrhenius and containing a working electrode, a first tank provided with a reference electrode, and an acid containing the acidic compound at a concentration higher than the concentration in the first tank A second tank containing a solution and including a counter electrode containing a noble metal selected from gold and platinum, and a potential control mechanism for controlling the potential of the working electrode, the reference electrode, and the counter electrode, Preparing a device in which the first tank and the second tank are separated from each other by a cation exchange membrane;
Supplying a base metal ion-containing solution containing a core metal material and ions of a metal relatively lower than the core metal to the first tank;
The step of precipitating the relative base metal on the surface of the core metal material by applying a noble potential higher than the oxidation-reduction potential of the relative base metal in the mixed solution containing the base metal ion-containing solution and the acidic solution. When,
After the deposition step, the shell metal ion-containing solution containing the shell metal ions is brought into contact with the core metal material on which the relative base metal is deposited, thereby replacing the relative base metal with the shell metal. Forming the shell.

According to the production method of the present invention, the electrode reaction can proceed without increasing the counter electrode area, and the production cost can be reduced.
FIG. 4 is a flowchart showing an example of the method for producing the core-shell catalyst of the present invention.
The manufacturing method of the core-shell catalyst shown in FIG. 4 includes (1) preparation step, (2) supply step, (3) precipitation step, (4) substitution step, (5) washing step, and (6) drying step.
The method for producing a core-shell catalyst of the present invention has at least (1) a preparation step, (2) a supply step, (3) a precipitation step, and (4) a substitution step, and (5) washing after the substitution step as necessary. A process, and (6) a drying process.
Hereinafter, each process is demonstrated in order.

(1) Preparatory step The preparatory step accommodates an acidic solution containing an acidic compound according to the definition of Arrhenius, and has a working electrode, a first tank provided with a reference electrode, and the acidic compound in the first tank. A second tank containing a counter electrode containing a noble metal selected from gold and platinum and containing an acidic solution containing a higher concentration than the concentration; and a potential for controlling the potential of the working electrode, the reference electrode, and the counter electrode And a control mechanism, and preparing a device in which the first tank and the second tank are separated from each other by a cation exchange membrane.
Since the apparatus prepared in the preparation step is the above-described core-shell catalyst manufacturing apparatus of the present invention, description of the apparatus is omitted.

(2) Supplying process The supplying process is a process of supplying a base metal ion-containing solution containing ions of a metal that is relatively baser than the core metal material and the core metal to the first tank.

The core metal is at least one selected from the group consisting of at least one metal selected from palladium, iridium, ruthenium, rhodium, iron, cobalt, nickel, copper, silver and gold, and an alloy containing the metal. Are preferred, palladium and palladium alloys are particularly preferred, and palladium is more preferred.
In the case of a palladium alloy, an alloy with a metal material selected from the group consisting of iridium, ruthenium, rhodium, iron, cobalt, nickel, copper, silver, and gold can be mentioned. The metal other than palladium constituting the palladium alloy is 1 Two or more species may be used.
When using a palladium alloy, it is preferable that the content rate of palladium is 50 mass% or more when the mass of the whole alloy is 100 mass%. This is because when the content ratio of palladium is 50% by mass or more, a uniform platinum-containing shell can be formed when the shell metal described later is platinum.

In the present invention, the form of the core metal material is not particularly limited, and examples thereof include particles and plates.
The core metal material may be supported on a carrier. In particular, when the core-shell catalyst obtained by the present invention is used for an electrode catalyst layer of a fuel cell, the carrier is preferably a conductive material from the viewpoint of imparting conductivity to the electrode catalyst layer. Further, since the core metal material is supported on the conductive carrier, a potential can be efficiently applied to the core metal material.
Specific examples of conductive materials that can be used as carriers include Ketjen Black (trade name: manufactured by Ketjen Black International), Vulcan (trade name: manufactured by Cabot), Norit (trade name: manufactured by Norit), and Black. Examples thereof include carbon particles such as pearl (trade name: manufactured by Cabot) and acetylene black (trade name: manufactured by Chevron), conductive carbon materials such as carbon fibers, and metal materials such as metal particles and metal fibers.

The base metal ion-containing solution is not particularly limited as long as it is a solution capable of depositing a relative base metal on the surface of the core metal material.
The base metal ion-containing solution is usually composed of a solution in which a predetermined amount of a base metal salt is dissolved in an acidic solution containing an acidic compound, but is not particularly limited to this configuration, and part or all of the base metal ions are in the liquid. Any solution that has been dissociated and present may be used.
As the acidic compound used for the base metal ion-containing solution, those exemplified as the acidic compound contained in the acidic solution in the first tank can be used.
Examples of the relative base metal include Cu, Pb, Bi, Sn, Ce, Ag, Sb, Tl and the like, and Cu is preferable.
Examples of the relative base metal salt include copper sulfate, copper nitrate, copper chloride, copper chlorite, copper perchlorate, and copper oxalate when the relative base metal is copper.
In the base metal ion-containing solution, the relative base metal ion concentration is not particularly limited and can be appropriately set according to the amount of the core-shell catalyst to be produced.
The counter anion of the relative base metal salt and the counter anion in the acidic solution may be the same or different, but are preferably the same.
The base metal ion-containing solution is preferably bubbled with an inert gas in advance. Nitrogen gas, argon gas, etc. can be used as the inert gas.

In the supplying step, the supply of the core metal material and the supply of the base metal ion-containing solution may be performed at the same time or either one may be performed first, but the supply of the core metal material is preferably performed first.
In the supplying step, it is preferable to apply a potential to the core metal material in the acidic solution in the first tank after supplying the core metal material and before supplying the base metal ion-containing solution. This is because the oxide on the surface of the core metal material can be removed by the potential application treatment, and the shell metal-containing shell can be uniformly coated on the core metal material.
According to the present invention, it is possible to reduce overvoltage at the time of electrode reaction in the supplying step.

When applying a potential to the core metal material in the supplying step, the core metal material may be immersed and dispersed in the acidic solution by adding it to the acidic solution in the first tank in a powder state, or dispersed in the solvent in advance. You may make it soak and disperse | distribute to an acidic solution by adding what was made to add to the acidic solution in a 1st tank. As the solvent, for example, water or an organic solvent can be used, and the solvent may contain an acidic compound. As an acidic compound, what was illustrated as an acidic compound contained in the acidic solution in said 1st tank can be used.
In addition, the core metal material is fixed on the conductive base material or the working electrode, and the conductive base material or the working electrode is immersed in an acidic solution. And a method of applying a potential to the substrate. As a method for fixing the core metal material, for example, a core metal material paste is prepared using an electrolyte resin (for example, Nafion (trade name) or the like) and a solvent such as water or alcohol, and the conductive base material or action The method of apply | coating to the surface of a pole is mentioned.
The method for applying a potential to the core metal material is not particularly limited, and examples include a method in which a working electrode, a counter electrode, and a reference electrode are connected to a potential control mechanism, and a potential is applied to the working electrode.

In the supply step, after supplying the core metal material, before supplying the base metal ion-containing solution, in the acidic solution in the first tank, when applying a potential to the core metal material, from the viewpoint of promptly proceeding with oxide removal, It is preferable to reciprocate the potential a plurality of times in a certain potential range. Examples of the potential application signal pattern include a triangular wave, a rectangular wave, and a trapezoidal wave.
The range of the potential can be appropriately set depending on the type of the core metal. When the core metal is palladium, it is preferably 0.05 to 1.2 V (vs. RHE). The number of potential cycles when the potential application signal pattern is a triangular wave is not particularly limited, but is preferably 500 to 3000 cycles, and the potential sweep rate can be, for example, 5 to 500 mV / sec.
The application of potential in the supply step removes oxygen in the acidic solution as much as possible and allows the oxide removal to proceed promptly. In the acidic solution, inert gas such as nitrogen gas or argon gas is used. It is preferable to bubble the gas.
Moreover, it is preferable that the acidic solution in the first tank in the case of applying a potential in the supplying step is appropriately stirred as necessary. For example, when the core metal material is immersed and dispersed in an acidic solution, each core metal material is brought into contact with the surface of the working electrode by stirring the acidic solution, and a potential is applied uniformly to each core metal material. Because it can. In this case, stirring may be performed continuously during potential application, or may be performed intermittently. The method for stirring the acidic solution in the first tank is not particularly limited, and examples thereof include stirring with a magnetic stirrer.

(3) Precipitation step In the precipitation step, the surface of the core metal material is applied by applying a potential higher than the oxidation-reduction potential of the relative base metal in the mixed solution containing the base metal ion-containing solution and the acidic solution. And depositing the relative base metal.
According to the present invention, it is possible to reduce overvoltage during electrode reaction in the deposition step.

The method of applying a potential to the core metal material in the precipitation step can be the same as the supply step described above.
The potential to be applied is not particularly limited as long as it is a potential at which a relative base metal can be deposited on the surface of the core metal material, that is, a potential nobler than the oxidation-reduction potential of the relative base metal. For example, when the relative base metal is copper, 0.75 to 0.30 V (vs. RHE) is preferable, and 0.37 V (vs. RHE) is particularly preferable.
The time for applying the potential is not particularly limited, but is preferably 2 hours or more, particularly preferably 15 hours or more, and more preferably until the reaction current becomes steady and approaches zero.

The deposition step is preferably performed in an inert gas atmosphere such as a nitrogen atmosphere from the viewpoint of relative base metal stability.
In the precipitation step, the mixed solution is preferably stirred as necessary. The stirring method can be the same as in the supplying step.

(4) Substitution step The substitution step is performed by bringing the shell metal ion-containing solution containing ions of the shell metal into contact with the core metal material on which the relative base metal is deposited after the precipitation step. Is a step of forming the shell by substituting for the shell metal.
In the replacement step, the method of replacing the relative base metal deposited on the surface of the core metal material with the shell metal is not particularly limited. Usually, the base metal material and the shell metal can be replaced due to the difference in ionization tendency by contacting the shell metal ion-containing solution with the core metal material on which the surface base metal is deposited.

The shell metal is preferably at least one selected from the group consisting of at least one metal selected from platinum, iridium, ruthenium, rhodium and gold, and an alloy containing the metal, and platinum and platinum alloys are particularly preferable. More preferred is platinum.
In the case of a platinum alloy, an alloy with a metal material selected from the group consisting of iridium, ruthenium, rhodium, nickel and gold can be used, and the metal other than platinum constituting the platinum alloy may be one type or two or more types.
When a platinum alloy is used, the platinum content is preferably 40% by mass or more when the mass of the entire alloy is 100% by mass. This is because if the platinum content is less than 40% by mass, sufficient catalytic activity and durability cannot be obtained.

The shell metal ion-containing solution is not particularly limited as long as it is a solution that can replace the relative base metal with the shell metal.
The shell metal ion-containing solution is usually composed of a solution obtained by dissolving a predetermined amount of a salt of a shell metal in an acidic solution containing an acidic compound, but is not particularly limited to this configuration. Any solution that is dissociated in the liquid may be used.
When the shell metal is platinum, for example, K ₂ PtCl ₄ , K ₂ PtCl _6, etc. can be used as the salt of the shell metal used in the shell metal ion-containing solution, and ([PtCl ₄ ] [Pt Ammonia complexes such as (NH ₃ ) ₄ ]) can also be used.
In the shell metal ion-containing solution, the shell metal ion concentration is not particularly limited, and can be appropriately set according to the amount of the core-shell catalyst to be produced.
As the acidic compound that can be used in the shell metal ion-containing solution, those exemplified as the acidic compound contained in the acidic solution in the first tank can be used.

It is preferable that the shell metal ion-containing solution is sufficiently agitated in advance and an inert gas such as nitrogen gas is bubbled in advance from the viewpoint of the stability of the precipitated base metal.
The replacement time (contact time between the shell metal ion-containing solution and the core metal material) is not particularly limited, but is preferably 120 minutes or more.
In addition, when performing a precipitation process and a substitution process in the same apparatus, you may add a shell metal salt and a shell metal ion containing solution to the liquid mixture used for the precipitation process.

(5) Washing process The washing process is a process of washing the core-shell catalyst after the replacement process.
The washing of the core-shell catalyst is not particularly limited as long as it can remove impurities without impairing the core-shell structure of the produced core-shell catalyst. As an example of the cleaning, a method of suction filtration using water, perchloric acid, dilute sulfuric acid, dilute nitric acid or the like can be mentioned.

(6) Drying step The drying step is a step of drying the obtained core-shell catalyst after the substitution step.
The drying of the core-shell catalyst is not particularly limited as long as it is a method capable of removing the solvent and the like, and examples thereof include a method of holding a temperature of 50 to 100 ° C. for 6 to 12 hours in a vacuum or in an inert gas atmosphere. It is done.
The core-shell catalyst may be pulverized as necessary. The pulverization method is not particularly limited as long as it is a method capable of pulverizing solids. Examples of the pulverization include pulverization using an inert gas atmosphere or an atmospheric mortar, and mechanical milling such as a jet mill, a ball mill, and a turbo mill.

(Example 1)
[Preparation process]
The first tank and the second tank are adjacent to each other, and a part of the adjacent part is formed of a cation exchange membrane (Nafion (registered trademark: DuPont) membrane), and the first tank and the second tank Were prepared with cation exchange membranes separated from each other.
In the first tank, an acidic solution (0.05 M sulfuric acid solution) containing sulfuric acid as an acidic compound is used so that the working electrode (carbon electrode area 707 cm ² ) and the reference electrode (silver / silver chloride) are immersed in the acidic solution. Installed.
In the second tank, an acidic solution (0.5 M sulfuric acid solution) containing sulfuric acid having a concentration 10 times higher than that of the first tank is used as the acidic compound, and the counter electrode (platinum mesh with platinum black, electrode area 6.5 m ^2). ) Was soaked in an acidic solution.

[Supply process]
10 g of palladium-supported carbon (Pd / C Pd support rate 28% by mass) was prepared, and Pd / C was added to the acidic solution in the first tank to suspend Pd / C. Subsequently, the apparatus was sealed, and the acidic solution was sufficiently bubbled with nitrogen gas to degas oxygen.
Next, a potentiostat (manufactured by Hokuto Denko Co., Ltd.) was connected to the working electrode, the counter electrode, and the reference electrode, and with respect to the working electrode, a potential sweep range of 0.05 V to 1.0 V (vs. RHE), a sweep speed of 50 mV / Second, cyclic voltammetry (CV) was carried out for 800 cycles to remove impurities and oxides on the surface of the palladium particles. In addition, the electric potential of the silver-silver chloride electrode was described in terms of RHE.
Then, while bubbling the acidic solution in the apparatus with nitrogen, as a base metal ion-containing solution, a copper ion-containing solution prepared by dissolving 300 g of copper sulfate in 1 L of 0.05 M sulfuric acid aqueous solution deoxygenated was added to the first tank. added.

[Precipitation process]
The potential of the working electrode was fixed at 0.37 V (vs. RHE), and copper was deposited on the palladium particles. The potential was applied until the reaction current became steady and approached zero.

[Replacement process]
The potential control was stopped, and a platinum ion-containing solution in which 5.5 g of K ₂ PtCl ₄ was dissolved in 1 L of 0.05 M sulfuric acid aqueous solution that had been degassed as a shell metal-containing ion was gradually added to the first tank. . After completion of the addition, stirring was continued until the natural potential in the apparatus reached a plateau (that is, until the fluctuation of the natural potential disappeared), and copper on the surface of the palladium particles was replaced with platinum.

[Washing and drying process]
After the replacement step, the solution in the apparatus was filtered, and the filtrate was washed with ultrapure water.
The filtrate washed with ultrapure water was put into a 1.0 M nitric acid aqueous solution at 50 ° C. The filtrate was sufficiently dispersed in an aqueous nitric acid solution using an ultrasonic homogenizer, and then the dispersion was stirred for 1 hour. Thereafter, the solution was filtered again, and the filtrate was washed with ultrapure water and dried to obtain a core-shell catalyst.
The obtained core-shell catalyst was analyzed by energy dispersive x-ray spectroscopy (EDS) using a scanning transmission electron microscope (STEM). The results are shown in FIG. FIG. 5A is a STEM photograph, and FIG. 5B is a diagram showing a Pt / Pd / C atomic concentration ratio obtained by observing the core-shell catalyst shown in FIG. 5A in the arrow direction. As shown in FIG. 5B, it was confirmed that the produced core-shell catalyst had a platinum shell formed on the surface of the palladium core.

(Examples 2 to 7)
In the second tank, a 1.0 M sulfuric acid solution was used as the acidic solution, and Pd / C was 1 g (Example 2), 7 g (Example 3), 10 g (Example 4), 20 g (Example 5), and 50 g. (Example 6) A core-shell catalyst was produced in the same manner as in Example 1 except that 100 g (Example 7) was used.

(Example 8)
A core-shell catalyst was produced in the same manner as in Example 1 except that a 5.0 M sulfuric acid solution was used as the acidic solution in the second tank.

Example 9
A core-shell catalyst was produced in the same manner as in Example 1 except that the area of the counter electrode was 3.5 m ² .

(Example 10)
A core-shell catalyst was produced in the same manner as in Example 1 except that the area of the counter electrode was 1 m ² .

(Comparative Examples 1-2)
Example 1 except that both the acidic solution in the first tank and the acidic solution in the second tank were made 0.05M sulfuric acid solution and 1 g (Comparative Example 1) and 7 g (Comparative Example 2) of Pd / C were used. A core-shell catalyst was produced in the same manner.

(Comparative Example 3)
A potential application and precipitation step in the supply step was tried in the same manner as in Example 1 except that both the acidic solution in the first tank and the acidic solution in the second tank were made 0.05M sulfuric acid solution. However, the voltage necessary for proceeding with the reaction exceeded the upper limit of the potentiostat output, and the potential could not be applied.

(Comparative Example 4)
Application of electric potential in the supplying step in the same manner as in Example 1 except that the area of the counter electrode was 3.5 m ² and both the acidic solution in the first tank and the acidic solution in the second tank were made 0.05M sulfuric acid solution. And a precipitation step was attempted. However, the voltage necessary for proceeding with the reaction exceeded the upper limit of the potentiostat output, and the potential could not be applied.

(Comparative Example 5)
Application and deposition of potential in the supplying step in the same manner as in Example 1 except that the area of the counter electrode was 1 m ² and the acidic solution in the first tank and the acidic solution in the second tank were both 0.05M sulfuric acid solution. Tried process. However, the voltage necessary for proceeding with the reaction exceeded the upper limit of the potentiostat output, and the potential could not be applied.

(Comparative Example 6)
Second tank, using an acid solution (0.05M sulfuric acid solution) containing sulfuric acid of the same concentration as the first bath as the acidic compound, methanol _{(CH 3 OH + H 2 O} → CO 2 + 6H + + 6e - E 0 = A potential application and deposition step in the supply step was attempted in the same manner as in Example 1 except that 1.21 V) was added to a concentration of 50 g / L.
However, the treatment was stopped because methanol moved to the first tank through the cation exchange membrane during the reaction.

[Effect when using acidic compound with higher concentration than the first tank in the second tank]
FIG. 6 shows voltages applied between the working electrode and the counter electrode during the supply process (FIG. 6A) and the deposition process (FIG. 6B) in Examples 1, 4, 8 and Comparative Example 3. . In any step, in Comparative Example 3, the overvoltage was too large to allow the reaction to proceed. On the other hand, in Examples 1, 4, and 8, the applied voltage when scanning the potential in the supplying process is about 10V to -10V, and the applied voltage when fixing the potential of the working electrode during the deposition process is 10V. It can be seen that the overvoltage decreased as the concentration of sulfuric acid in the second tank increased in any step.

[Relationship between charged core metal material mass and voltage]
FIG. 7 shows voltages applied between the working electrode and the counter electrode in the deposition steps of Examples 2 to 7 and Comparative Examples 1 to 3. From the results of Comparative Examples 2 and 3, it can be seen that when the charged core metal material mass exceeds 7 g, the overvoltage is too large to allow the reaction to proceed. On the other hand, in Comparative Example 3 and Example 4 in which the charged core metal material mass is the same, compared with Comparative Example 3, the applied voltage when fixing the potential of the working electrode during the deposition step is about 10 V, It can be seen that the overvoltage was lowered and the reaction could proceed. Further, even in Example 7 in which the mass of the charged core metal material was 100 g, the applied voltage when the potential of the working electrode during the deposition step was fixed was about 10 V, and the overvoltage was lowered to advance the reaction. I understand that I was able to. Further, it is presumed from FIG. 7 that the reaction can proceed even when the charged core metal material is 1 kg or more.

[Relationship between counter electrode area and voltage]
FIG. 8 shows voltages applied between the working electrode and the counter electrode during the deposition steps of Examples 1, 9, and 10 and Comparative Examples 3 to 5. In Comparative Examples 3 to 5, the overvoltage was too large to allow the reaction to proceed. On the other hand, in Example 10 where the counter electrode area was 1 m ² and the charged core metal material mass was 10 g, the applied voltage when the potential of the working electrode during the deposition step was fixed was about 10 V, and the overvoltage was reduced. From the results of Examples 1, 9, and 10, it can be seen that the reaction can proceed even if the counter electrode area is reduced from 6.5 m ² to 1 m ² , and the manufacturing cost can be reduced.

DESCRIPTION OF SYMBOLS 1 Acidic solution of 1st tank 2 Acidic solution of 2nd tank 3 Working electrode 4 Reference electrode 5 Counter electrode 6 1st tank 7 2nd tank 8 Cation exchange membrane 9 Core metal material 10 Apparatus 20 Apparatus 30 Apparatus

Claims (9)

An apparatus for producing a core-shell catalyst comprising a core containing a core metal and a shell containing a shell metal and covering the core by an underpotential deposition method,
A first tank containing an acidic solution containing an acidic compound according to the definition of Arrhenius and having a working electrode and a reference electrode;
A second tank containing an acidic solution containing the acidic compound at a concentration higher than the concentration in the first tank, and having a counter electrode containing a noble metal selected from gold and platinum;
A potential control mechanism for controlling the potential of the working electrode, the reference electrode, and the counter electrode;
The core-shell catalyst manufacturing apparatus, wherein the first tank and the second tank are separated from each other by a cation exchange membrane.   The core-shell catalyst manufacturing apparatus according to claim 1, wherein the acidic compound is sulfuric acid.   The core-shell catalyst manufacturing apparatus according to claim 2, wherein the sulfuric acid in the second tank is 10 to 100 times higher in concentration than the sulfuric acid in the first tank.   The core-shell catalyst manufacturing apparatus according to any one of claims 1 to 3, wherein the first tank also functions as the working electrode. A core-shell catalyst manufacturing method comprising: a core including a core metal; and a shell including a shell metal and covering the core,
An acidic solution containing an acidic compound according to the definition of Arrhenius and containing a working electrode, a first tank provided with a reference electrode, and an acid containing the acidic compound at a concentration higher than the concentration in the first tank A second tank containing a solution and including a counter electrode containing a noble metal selected from gold and platinum, and a potential control mechanism for controlling the potential of the working electrode, the reference electrode, and the counter electrode, Preparing a device in which the first tank and the second tank are separated from each other by a cation exchange membrane;
Supplying a base metal ion-containing solution containing a core metal material and ions of a metal relatively lower than the core metal to the first tank;
The step of precipitating the relative base metal on the surface of the core metal material by applying a noble potential higher than the oxidation-reduction potential of the relative base metal in the mixed solution containing the base metal ion-containing solution and the acidic solution. When,
After the deposition step, the shell metal ion-containing solution containing the shell metal ions is brought into contact with the core metal material on which the relative base metal is deposited, thereby replacing the relative base metal with the shell metal. Forming the shell, and a method for producing a core-shell catalyst.   The method for producing a core-shell catalyst according to claim 5, wherein the acidic compound is sulfuric acid.   The method for producing a core-shell catalyst according to claim 6, wherein the sulfuric acid in the second tank is 10 to 100 times higher in concentration than the sulfuric acid in the first tank.   In the supply step, a potential is applied to the core metal material in the acidic solution in the first tank after supplying the core metal material and before supplying the base metal ion-containing solution. The manufacturing method of the core-shell catalyst as described in any one.   The method for producing a core-shell catalyst according to any one of claims 5 to 8, wherein the first tank also functions as the working electrode.