JP7139567B2 - Oxidation catalyst for fuel cell, method for producing the same, and fuel cell - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to an oxidation catalyst for a fuel cell, a method for producing the same, and a fuel cell.

In recent years, the spread of mobile devices such as notebook computers and mobile phones has been accelerating. Along with the development of mobile devices, their functions are becoming more sophisticated, and their power consumption tends to increase more and more. At present, secondary batteries such as lithium ion batteries are mainly used as power sources for these portable devices, but it is difficult to dramatically increase the theoretical energy density of these batteries. It is known. Therefore, it is necessary to develop a new compact power supply that has a higher energy density and that can be made smaller and lighter.

A direct methanol fuel cell (DMFC) using methanol as a fuel is attracting attention as one of the new energy devices to replace conventional secondary batteries.
Direct methanol fuel cells have been extensively researched because they use a liquid fuel and therefore have a large theoretical energy density, which is thought to facilitate miniaturization.

For example, in a solid polymer electrolyte fuel cell in which an anode layer and a cathode layer are formed on both sides of a solid polymer electrolyte membrane with catalyst layers interposed therebetween, at least one of the catalyst layers is formed without using a solvent. A polymer electrolyte fuel cell is disclosed (see, for example, Patent Document 1).
Further, for example, a catalyst layer of a polymer electrolyte fuel cell having a solid polymer electrolyte membrane, an electrode, and a catalyst layer provided between the solid polymer electrolyte and the electrode, the catalyst layer having a dendritic structure. and a polymer electrolyte fuel cell having the catalyst layer are disclosed (see, for example, Patent Document 2).

Japanese Patent Application Laid-Open No. 2002-289206 Japanese Patent Application Laid-Open No. 2006-049278

In the case of using a catalyst layer by electron beam evaporation described in Patent Documents 1 and 2, for further development of DMFC, improvement of alcohol oxidation activity is required for further improvement of output. . Moreover, in DMFC, there is also concern about the high cost of precious metals used in anode catalysts. In DMFC anode catalysts, it is required to reduce the amount of noble metal used and to improve the alcohol oxidation activity.

As a result of intensive studies, the inventors of the present invention have found that fuel cell oxidation catalysts using a carrier containing cerium oxide with a widened interplanar spacing due to irradiation with a specific amount of ion beams exhibit excellent fuel oxidation activity.

The present disclosure has been made in view of the circumstances described above, and an object of the present disclosure is to provide a fuel cell oxidation catalyst having excellent fuel oxidation activity, a method for producing the same, and a fuel cell using the same. do.

That is, the means for solving the above problems includes the following embodiments.
<1> Cerium oxide having a 111 plane spacing of 0.3129 nm to 0.3160 nm as determined by X-ray diffraction, and a cerium oxide having a 110 plane spacing of 0.3195 nm to 0.3244 nm as determined by X-ray diffraction a carrier containing at least one oxide selected from the group consisting of titanium oxide;
a catalyst metal supported on the carrier;
An oxidation catalyst for fuel cells.
<2> The fuel cell oxidation catalyst according to <1>, wherein the carrier further contains a carbon material.
<3> The fuel cell oxidation catalyst according to <1> or <2> above, wherein the cerium oxide contains the particulate cerium oxide, and the particulate cerium oxide has a crystallite size of 1 nm to 1 μm. .
<4> The titanium oxide according to any one of <1> to <3>, wherein the titanium oxide contains particulate titanium oxide, and the particulate titanium oxide has a crystallite size of 1 nm to 1 μm. Oxidation catalyst for fuel cells.
<5> The fuel cell oxidation catalyst according to any one of <1> to <4>, which is used in a fuel cell using alcohol or ether as a fuel for a direct methanol fuel cell.
<6> a polymer electrolyte membrane;
an electrode;
a catalyst layer having the fuel cell oxidation catalyst according to any one of <1> to <5> provided between the polymer electrolyte membrane and the electrode;
A fuel cell.
<7> an irradiation step of irradiating a carrier containing a transition metal oxide with an ion beam at a dose of 1.0×10 ¹⁰ ions/cm ² to 8.0×10 ¹² ions/cm ² ;
A step of supporting a catalyst metal on the support containing the transition metal oxide obtained in the irradiation step;
A method for producing an oxidation catalyst for a fuel cell, comprising:
<8> The method for producing a fuel cell oxidation catalyst according to <7>, wherein the support further contains a carbon material.
<9> The transition metal oxide is selected from the group consisting of cerium oxide, titanium oxide, molybdenum oxide, vanadium oxide, tungsten oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, manganese oxide, tin oxide and zirconium oxide. The method for producing an oxidation catalyst for a fuel cell according to <7> or <8> above, including at least one of
<10> Any one of <7> to <9>, wherein the transition metal oxide obtained in the irradiation step has an absolute value of a rate of change in interplanar spacing of 0.15% to 0.65%. 2. The method for producing the oxidation catalyst for fuel cells according to 1.

Advantageous Effects of Invention According to the present disclosure, it is possible to provide a fuel cell oxidation catalyst having excellent fuel oxidation activity, a method for producing the same, and a fuel cell using the same. In addition, it is possible to provide a fuel cell with high output even when the amount of catalyst metal used is suppressed.

FIG. 1 is a diagram showing an example of a method for producing a carrier containing cerium oxide by an electrostatic spinning method. FIG. 2 is an enlarged view of the peak of the cerium oxide (111) plane. FIG. 3 is a diagram showing the relationship between the ion beam dose and the mass activity of the catalyst. FIG. 4 is a diagram showing the relationship between the interplanar spacing value d [Å] of the cerium oxide (111) plane and the mass activity of the catalyst. FIG. 5 is a diagram showing an example of the configuration of a fuel cell membrane electrode assembly.

Hereinafter, an oxidation catalyst for a fuel cell according to embodiments of the present disclosure will be described.
In this specification, a numerical range represented by "to" means a range including the numerical values before and after "to" as lower and upper limits.
In the numerical ranges described step by step in the present disclosure, the upper limit value or lower limit value described in one numerical range may be replaced with the upper limit value or lower limit value of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
In this specification, the term "process" is not only an independent process, but also includes the term if the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. be

《Oxidation catalyst for fuel cells》
An oxidation catalyst for a fuel cell according to the present disclosure includes a carrier containing fine particles of a transition metal oxide with adjusted interplanar spacing (that is, lattice spacing of crystals), and a catalyst metal supported on the carrier. As an embodiment of the present disclosure, cerium oxide having a 111 plane spacing of 0.3129 nm to 0.3160 nm determined by X-ray diffraction, and a 110 plane spacing of 0 determined by X-ray diffraction A carrier containing at least one oxide selected from the group consisting of titanium oxide having a diameter of 0.3195 nm to 0.3244 nm, and a catalyst metal supported on the carrier.
The transition metal oxide has the same meaning as the transition metal oxide used in the method for producing an oxidation catalyst for fuel cells, which will be described later, and preferred embodiments are also the same.
A catalyst metal supported on a carrier containing cerium oxide with a 111 plane spacing of 0.3129 nm to 0.3160 nm as determined by X-ray diffraction, and a 110 plane spacing of 0 as determined by X-ray diffraction. A fuel cell oxidation catalyst having a catalyst metal supported on a carrier containing at least one oxide selected from the group consisting of titanium oxide having a diameter of 0.3195 nm to 0.3244 nm has excellent oxidation activity for fuel, Supports containing transition metal oxides with controlled spacing (specifically cerium oxide and/or titanium oxide) can reduce the amount of catalytic metal.
Although the effect of obtaining such an effect is not clear, it is presumed as follows.

For example, in a direct methanol fuel cell (DMFC), when methanol is completely oxidized, the following electrode reaction formula is shown
Anode reaction: _CH3OH + _H2O → _CO2 + 6H ⁺ + 6e ^－ (1.1)
Cathode reaction : O ₂ + 4H ⁺ + 4e ^－ → 2H ₂ O (1.2)
Total reaction : _CH3OH + 3/ _2O2 → _{CO2 +} 2H2O (1.3)
When methanol is completely oxidized, methanol and water supplied to the anode layer react as shown in formula (1.1). At the cathode, the supplied oxygen reacts with the electrons and protons generated in the anode layer as shown in formula (1.2). At this time, due to the properties of the solid polymer electrolyte membrane, the electrons do not pass through the membrane but pass through an external circuit to the cathode, and this mechanism generates electricity. The overall reaction formula is shown in formula (1.3).

Generally, in direct methanol fuel cells, it is known that the electrode reaction rate of the anode (anode) layer is slow. The reason for this is poisoning of reaction intermediates (such as CO) to Pt contained in the anode layer. When Pt is poisoned by CO species, the number of reaction sites decreases and the reaction rate decreases. Therefore, for example, by adding Ru or the like to Pt and alloying it, the CO poisoning is reduced, and the methanol oxidation reaction (MOR) activity is improved, but the activity is not necessarily sufficient, and the activity is even higher. is required.

Cerium oxide and titanium oxide that have been subjected to ion beam irradiation under appropriate conditions have a cerium oxide 111 plane spacing of 0.3129 nm to 0.3160 nm as determined by an X-ray diffraction method. The interplanar spacing of the 110 plane of titanium oxide obtained by the X-ray diffraction method is 0.3195 nm to 0.3244 nm.
It is presumed that when cerium oxide or titanium oxide is irradiated with an ion beam in this way, the interplanar spacing is expanded or decreased compared to the interplanar spacing of cerium oxide or titanium oxide before irradiation. That is, since it is presumed that oxygen atom vacancies are formed in cerium oxide or titanium oxide exhibiting a specific interplanar spacing value, a fuel cell oxidation catalyst having a support containing this cerium oxide or a support containing titanium oxide In , the supply of oxygen species from cerium oxide or titanium oxide to the surface of the catalyst metal (hereinafter sometimes referred to as "OH group supply ability") is promoted, so the oxidation of fuel such as methanol on the surface of the catalyst metal It is speculated that the conductivity of cerium oxide or titanium oxide improves as the reaction is activated.
Therefore, in the fuel cell oxidation catalyst according to the present disclosure, even if the amount of catalyst metal used is reduced, high oxidation activity for fuel is likely to be obtained.
Details of each component constituting the fuel cell oxidation catalyst will be described below.

<Carrier>
The carrier possessed by the fuel cell oxidation catalyst according to the present disclosure is cerium oxide (hereinafter also referred to as “specific cerium oxide”) having a 111 plane spacing of 0.3129 nm to 0.3160 nm as determined by X-ray diffraction. and at least one oxide selected from the group consisting of titanium oxide (hereinafter also referred to as “specific titanium oxide”) having a 110-plane spacing of 0.3195 nm to 0.3244 nm as determined by X-ray diffraction. include.
Since the specific cerium oxide and the specific titanium oxide have a relatively large number of oxygen atom vacancies, a fuel cell catalyst having a carrier containing these specific oxides has an improved OH group supplying ability and conductivity. is improved, the oxidation activity for fuel can be improved, and the amount of catalyst metal, which will be described later, can be reduced.

The degree of generation of oxygen atom vacancies in cerium oxide and titanium oxide can be confirmed by, for example, XRD measurement (X-Ray Diffraction). For example, in the case of cerium oxide, in XRD measurement, the degree of generation of oxygen atom vacancies can be confirmed by the deviation of the peak position of the 111 plane, which generally exhibits the maximum peak intensity.
In the case of titanium oxide, the degree of generation of oxygen atom vacancies can be similarly confirmed by the deviation of the peak position of the 110 plane.

(specific cerium oxide)
The specific cerium oxide has a 111 plane spacing of 0.3129 nm to 0.3160 nm as determined by X-ray diffraction. The interplanar spacing is more preferably 0.3130 nm to 0.3150 nm, even more preferably 0.3140 nm to 0.3145 nm.

The interplanar spacing of the 111 plane of the specific cerium oxide is obtained by, for example, the following method.
Using a powder X-ray diffractometer using CuKα (product name: Rint2100, manufactured by Rigaku Co., Ltd.), the fuel cell catalyst carrier was irradiated under the conditions of V = 32 kV and I = 20 mA, and the diffraction line at this time Using a goniometer (product name: Rinto 2000 vertical goniometer, manufactured by Rigaku Co., Ltd.), the diffraction peak position (that is, the interplanar spacing value). From the diffraction angle 2θ [Degree] of this peak position, the interplanar spacing d [nm] of the 111 plane of the specific cerium oxide can be obtained from the following formula.
d [nm] = λ/(2·sin θ)
In the above formula, λ (=0.154056 nm) represents the X-ray wavelength.

The carrier preferably contains particulate cerium oxide, and the particulate cerium oxide preferably has a crystallite size of 1 nm to 1 μm. When the crystallite diameter is within the above range, a strong interaction between the catalyst metal such as platinum described later and the cerium oxide is likely to be obtained.
From the above viewpoint, the crystallite size of the particulate cerium oxide is preferably 1 nm to 1 μm, more preferably 5 nm to 500 nm, still more preferably 5 nm to 100 nm, and particularly preferably 10 nm to 20 nm. be.
As used herein, the crystallite size is the size (maximum size) of the smallest crystal unit that constitutes a crystal, and can generally be measured using an X-ray diffraction (XRD) apparatus.

In the present disclosure, the crystallite size is obtained by the following measurement method and calculation method.
First, the sample is measured using powder X-ray diffraction using CuKα, and in the range of 2θ = 5 ° to 90 °, the peak showing the maximum intensity, or a large intensity that can be separated from adjacent peaks. The half width of the peak is measured, and the crystallite size is determined using the Scherrer formula below.

D=K·λ/(β·cos θ)

D; crystallite diameter [nm]
K; Scherrer constant λ; measured X-ray wavelength [nm]
θ; Bragg angle of diffraction line (half of diffraction angle 2θ) [rad (radian)]
β; half width of diffraction line of crystal lattice [rad (radian)]

The specific cerium oxide is preferably obtained by irradiating a carrier containing cerium oxide with an ion beam at a dose of 1.0×10 ¹⁰ ions/cm ² to 8.0×10 ¹² ions/cm ² . From the viewpoint of better oxidation activity of the fuel cell oxidation catalyst for fuel, the ion beam irradiation dose for cerium oxide is 1.0×10 ¹¹ ions/cm ² to 5.0×10 ¹² ions/cm ² . A dose of 1.0×10 ¹¹ ions/cm ² to 4.0×10 ¹² ions/cm ² is even more preferred.

The cerium oxide used for ion beam irradiation is not particularly limited, and may be a commercially available product or a compound obtained by heat-treating (oxidizing) cerium.

Ion species used for ion beam irradiation are not particularly limited, but examples include rare gases such as Ar and Kr, halogen atoms such as Br and I, hydrogen, nitrogen, and oxygen.

The accelerator for accelerating the ion species and the irradiation dose can be appropriately selected depending on the ion species.
For example, it is preferable to irradiate with an electrostatic accelerator when Ar ⁺ or H ⁺ is used as the ion species, and with a cycloton accelerator when Ar ⁹⁺ and Kr ²⁰⁺ are used.

The content of the specific cerium oxide in the carrier is preferably 10% by mass to 60% by mass, preferably 20% by mass to 40% by mass, with respect to the total mass of the carbon nanofiber carrier described later containing cerium oxide. It is more preferable to have

(specific titanium oxide)
The specific titanium oxide has an interplanar spacing of 0.3190 nm to 0.3250 nm between the 110 planes determined by the X-ray diffraction method. The interplanar spacing is preferably 0.3195 nm to 0.3244 nm.
The interplanar spacing of the 110 plane of the specific titanium oxide can be obtained by the same method as that for the cerium oxide described above.

The crystal structure of the specific titanium oxide includes rutile type, anatase type, brookite type, and the like, but the rutile type is preferable from the viewpoint of excellent oxidation activity for fuel.
The presence of the rutile-type specific titanium oxide in the carrier can be confirmed by a method using a powder X-ray diffractometer.

The crystallite size of the specific titanium oxide is preferably 1 nm to 1 μm, more preferably 10 nm to 500 nm, still more preferably 10 nm to 100 nm, and particularly preferably, from the viewpoint of excellent fuel oxidation activity. 15 nm to 40 nm.
The particle size of the specific titanium oxide can be obtained by the same method as that for the specific cerium oxide.

The specific titanium oxide is preferably obtained by irradiating a carrier containing titanium oxide with an ion beam at a dose of 1.0×10 ¹⁰ ions/cm ² to 8.0×10 ¹² ions/cm ² . From the viewpoint of the oxidation activity of the fuel cell oxidation catalyst for fuel, the ion beam irradiation dose for titanium oxide is 1.0×10 ¹¹ ions/cm ² to 5.0×10 ¹² ions/cm ² . more preferably 1.0×10 ¹¹ ions/cm ² to 4.0×10 ¹² ions/cm ² .
Titanium oxide used for ion beam irradiation is not particularly limited, and may be a commercially available product or a compound obtained by heat-treating (oxidizing) titanium.
Also, the ion species of the ion beam irradiated to titanium oxide and the accelerator for accelerating the ion species are the same as the ion species of the ion beam and the accelerator used for the cerium oxide described above.

The content of the specific titanium oxide in the carrier is preferably 40% by mass to 70% by mass with respect to the total mass of the later-described carbon nanofiber carrier containing the specific titanium oxide.

The carrier of the fuel cell oxidation catalyst according to the present disclosure may contain transition metal oxides other than specific cerium oxide and specific titanium oxide, that is, transition metal oxides whose interplanar spacing is not adjusted. However, from the viewpoint of catalytic activity, it is preferable not to contain a transition metal oxide whose interplanar spacing is not adjusted.

(carbon material)
Preferably, the carrier further contains a carbon material. Conductivity can be further improved by including a carbon material in the carrier.
Examples of carbon materials include carbon black, carbon nanotubes, carbon nanofibers (CNF), fullerenes, and the like.
Note that the carbon material refers to, for example, a material containing 90% or more by number of carbon elements with respect to all elements contained in the carbon material.

Examples of carbon black include known carbon blacks such as channel black, furnace black, thermal black and lamp black.
When the carbon material is carbon black, the average primary particle size of the carbon black is, for example, 1 nm to 100 nm, preferably 20 nm to 80 nm.

The carbon material is preferably a sheet-like carbon material from the viewpoints of having a large surface area, more easily forming crystal structural defects on the surface, and easily obtaining an interaction between the carbon material and the transition metal oxide. Carbon nanofibers (CNF) are more preferred.

When the carbon material is carbon nanofibers, the diameter thereof is, for example, in the range of 50 nm or more and 500 nm or less, preferably 200 nm to 300 nm.

When carbon nanofibers (CNF) are used as the carbon material, a representative method for producing the carbon nanofibers is, for example, an electrostatic spinning method, but the method is not limited to this.

The electrostatic spinning method is a method of obtaining fibrous carbon nanofibers by performing an electrostatic spinning operation in which a high voltage is applied while ejecting a solution of a polymer compound as a raw material from an ejection port such as a nozzle.
Examples of polymer compounds used as raw materials include polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyimide (PI), polyvinylidene fluoride (PVDF), pitch, and phenolic resins. . The solvent used for the solution of the polymer compound is not particularly limited as long as it dissolves the polymer compound as a raw material. , sodium thiocyanate aqueous solution, etc., and N,N-dimethylformamide is preferably used from the viewpoint of electrostatic spinning properties such as solubility, viscosity and conductivity.

After the electrospinning operation, for example, a stabilization treatment may be performed in a constant temperature bath in a high-temperature air atmosphere, a carbonization treatment may be performed in a high-temperature nitrogen atmosphere, and after carbonization, a high-temperature steam atmosphere or a carbonization treatment may be performed. Activation treatment may be performed in a carbon dioxide atmosphere, and after carbonization, nitrogen doping treatment may be performed in an ammonia atmosphere at a high temperature, and any one or combination of stabilization treatment, carbonization treatment, activation treatment, nitrogen doping treatment may be performed. may be performed.

When producing a carrier containing transition metal oxides such as cerium oxide and titanium oxide, and carbon nanofibers, for example, a solvent is mixed with the polymer compound and the transition metal oxide as a carbon source. A support containing the transition metal oxide and carbon nanofibers may be prepared by electrostatic spinning using the liquid.

When the carrier of the fuel cell oxidation catalyst contains a carbon material, the content ratio of the carbon material to the transition metal oxide (carbon material: transition metal oxide) is The ratio is preferably 10:1 to 1:1, preferably 5:1 to 1:1, on a standard basis.
When the carrier of the fuel cell oxidation catalyst contains a carbon material, the content ratio of the carbon material and cerium oxide (carbon material: cerium oxide) is 10 on a volume basis from the viewpoint of improving the oxidation activity for the fuel. :1 to 1:1, preferably 5:1 to 1:1.

From the same point of view, when the carrier of the fuel cell oxidation catalyst contains a carbon material, the content ratio of the carbon material and titanium oxide (carbon material: titanium oxide) is from 10:1 on a volume basis. 1:1 is preferred, preferably 5:1 to 1:1.

<Catalyst metal>
A fuel cell catalyst according to the present disclosure has a catalyst metal supported on a support.
The catalyst metal is not particularly limited, and preferably includes platinum (Pt), palladium (Pd), ruthenium (Ru), nickel (Ni), or copper (Cu), and the catalyst metal is a composite containing these metals. may be
Examples of the composites include composites made of at least one metal selected from the group of metals consisting of platinum, palladium, ruthenium, nickel and copper, and other metals different from the metals of the metal group. Other metals include zinc (Zn), manganese (Mn), etc., preferably zinc or manganese, or zinc and manganese.

When the catalyst metal is a composite, the composite includes, for example, Ni—Ru (1:1), Ni—Cu (1:1), Pt—Ru (1:1), Cu—Ru (2:1 ), Cu—Mn (12:1), and the like. The numbers in parentheses indicate the molar ratios of the elements.
As the composite, a solid solution is preferable, and a solid solution containing at least one of platinum, ruthenium and nickel is preferable in that electronic interaction can be expected.

The particle size of the catalyst metal is preferably 1 nm to 10 nm from the viewpoint of increasing the specific surface area. The particle size of the catalyst metal can be obtained by the same method as for the crystallite size described above.
A catalyst metal having a particle size within such a range may be used, for example, by producing it by a microwave polyol method.

The amount of catalyst metal supported on the oxidation catalyst for fuel cells according to the present disclosure depends on the type or temperature of the catalyst metal. , 0.1 mg/cm ² to 100 mg/cm ² .
When the catalyst metal contains platinum, the amount of the catalyst metal supported is preferably 0.1 mg/cm ^{2 to 50 mg/cm 2 from} the viewpoint of maintaining high oxidation activity, and more preferably 0.5 mg/cm ² to 50 mg/cm 2 . More preferably 10 mg/cm ² .

The fuel cell oxidation catalyst according to the present disclosure is not particularly limited as a fuel for direct methanol fuel cells, but can be suitably used for fuel cells using alcohol or ether as fuel.
From the viewpoint of excellent fuel oxidation activity, the fuel cell oxidation catalyst is more preferably used in a direct methanol fuel cell using alcohol as the fuel for the direct methanol fuel cell.

<<Method for Producing Oxidation Catalyst for Fuel Cell>>
A method for producing an oxidation catalyst for a fuel cell according to the present disclosure includes irradiation in which a carrier containing a transition metal oxide is irradiated with an ion beam at a dose of 1.0×10 ¹⁰ ions/cm ² to 8.0×10 ¹² . process and
a step of supporting a catalyst metal on the support containing the transition metal oxide obtained in the irradiation step (hereinafter also referred to as a "supporting step");
have
Since the production method of the present disclosure includes the above steps, the fuel cell oxidation catalyst obtained by the production method of the present disclosure exhibits excellent fuel oxidation activity.
Hereinafter, each step of the method for producing a fuel cell oxidation catalyst according to the present disclosure will be described, but detailed descriptions of the same components as those contained in the fuel cell oxidation catalyst described above will be omitted.

<Irradiation process>
The irradiation step is a step of irradiating the carrier containing the transition metal oxide with an ion beam at a dose of 1.0×10 ¹⁰ ions/cm ² to 8.0×10 ¹² ions/cm ² , preferably 1. 0×10 ¹¹ ions/cm ² to 5.0×10 ¹² ons/cm ² , more preferably 1.0×10 ¹¹ ions/cm ² to 4.0×10 ¹² ions/cm ² . A step of irradiating is included.
In the irradiation step, a carrier containing a transition metal oxide whose interplanar spacing is adjusted by irradiation with an ion beam is obtained. As shown in FIG. 1, for example, in cerium oxide or titanium oxide with an adjusted interplanar spacing, it is thought that relatively many oxygen atom vacancies are formed therein. The supply ability can be improved, and the conductivity can also be improved.

The carrier used in the irradiation step has the same definition as the carrier described above, and the preferred range is also the same.
Further, the description of the ion beam irradiation conditions, the accelerator used for the ion beam irradiation, and the like are the same as those described above, and are therefore omitted.

The transition metal oxide obtained in the irradiation step preferably has an absolute value of the rate of change in interplanar spacing of 0.15% to 0.65%.
When the absolute value of the rate of change in interplanar spacing is adjusted within the above range, a large number of oxygen atom vacancies are formed, the OH group supplying ability is improved, and the oxidation activity for fuel is excellent.
more preferred.

The rate of change (%) of the interplanar spacing is obtained, for example, as follows.
Change rate of interplanar spacing (%) = ((interplanar spacing of oxide after ion beam irradiation - interplanar spacing of oxide before ion beam irradiation) / interplanar spacing of oxide before ion beam irradiation) x 100 (%)

As transition metal oxides, cerium oxide, titanium oxide, molybdenum oxide, vanadium oxide, tungsten oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, manganese oxide, oxide It preferably contains at least one selected from the group consisting of tin and zirconium oxide, and more preferably contains at least one selected from the group consisting of cerium oxide, titanium oxide, molybdenum oxide, and vanadium oxide.
The transition metal oxide may be used alone or in combination of two or more.

The transition metal oxide may contain a particulate transition metal oxide.
When the transition metal oxide contains a particulate transition metal oxide, crystals of the particulate transition metal oxide are used from the viewpoint of easily obtaining a strong interaction between the catalyst metal such as platinum and the transition metal oxide. The particle diameter is preferably 1 nm to 1 μm.
The crystallite size of the particulate transition metal oxide is obtained by the same method as the method for measuring the crystallite size described above.

In the method for producing an oxidation catalyst for a fuel cell according to the present disclosure, when a carrier containing cerium oxide is used, the cerium oxide (transition metal oxide) obtained in the irradiation step can be treated with X-rays from the viewpoint of excellent fuel oxidation activity. The interplanar spacing of the 111 plane determined by the diffraction method is preferably 0.3129 nm to 0.3160 nm, more preferably 0.3140 nm to 0.3150 nm.

In the method for producing an oxidation catalyst for a fuel cell according to the present disclosure, when a carrier containing titanium oxide is used as a transition metal oxide, the titanium oxide obtained in the irradiation step is measured by an X-ray diffraction method from the viewpoint of excellent fuel oxidation activity. The interplanar spacing of the 110 plane obtained by the formula is preferably 0.3190 nm to 0.3250 nm, more preferably 0.3195 nm to 0.3244 nm.

<Supporting process>
The supporting step is a step of supporting the catalyst metal on the carrier containing the transition metal oxide obtained in the irradiation step.
The method for supporting the catalyst metal on the carrier is not particularly limited, and known methods can be used.
As a method for supporting the catalyst metal, for example, the catalyst metal may be supported by a microwave polyol method.

As an example of supporting a catalyst metal using a microwave polyol method, a carrier is added to polyethylene glycol, ultrasonic treatment is performed for 30 minutes to prepare a mixed solution, then a catalyst metal is added, and after stirring for 3 hours, Heat in microwave (600 W) for 5 minutes and stir overnight. This solution was filtered and washed with methanol and distilled water. It can be prepared by drying the obtained precipitate in a vacuum dryer at 70° C. for 24 hours.

The method for producing an oxidation catalyst for a fuel cell according to the present disclosure may have other steps as necessary in addition to the irradiation step and the supporting step.

The fuel cell oxidation catalyst according to the present disclosure can be used, for example, in both anode and cathode catalyst layers in fuel cells described later.
Since the oxidation catalyst for fuel cells according to the present disclosure is excellent in OH group supplying ability, that is, oxidation activity for fuel, it is preferably used for a cathode catalyst layer, particularly a cathode catalyst layer of a direct methanol fuel cell.

"Fuel cell"
The fuel cell according to the present disclosure includes a polymer electrolyte membrane 10, an electrode 20, and a catalyst layer 31 having the fuel cell oxidation catalyst provided between the polymer electrolyte and the electrode.
Since the fuel cell has the above-mentioned fuel cell oxidation catalyst as a catalyst layer, it is excellent in oxidation activity for fuel and also excellent in electrical conductivity.
Each configuration of the fuel cell will be described below with reference to FIG. 5, but the description of the oxidation catalyst for the fuel cell will be omitted.

(Catalyst layer (electrode))
A catalyst layer 31 is provided between the polymer electrolyte membrane 10 and the electrode 20 . For example, a direct methanol fuel cell usually has a structure in which a fuel electrode (anode) and an air electrode (oxidant electrode: cathode) sandwich a polymer electrolyte membrane from both sides.
The catalyst layer 31 may contain optional components used in ordinary fuel cells in addition to the fuel cell oxidation catalyst and conductive material described above.
The fuel electrode (anode) may have a gas diffusion layer 32 in addition to the catalyst layer 31 . Examples of the gas diffusion layer include sintered bodies of polyacrylonitrile, sintered bodies of pitch, carbon materials such as graphite and expanded graphite, and conductive materials such as stainless steel, molybdenum, and titanium.

(polymer electrolyte membrane)
The polymer electrolyte membrane 10 is preferably a solid polymer electrolyte membrane having proton conductivity, such as polyperfluorosulfonic acid membrane, sulfonic acid type polystyrene-graft-ethylenetetrafluoroethylene copolymer (ETFE). Fluorine-based solid polymer electrolyte membranes such as membranes can be mentioned.

The fuel cell may have, in addition to the configuration described above, a configuration normally provided for a fuel cell.

The fuel cell oxidation catalyst according to the present disclosure is excellent in oxidation activity for fuel, and thus can be suitably used particularly in fuel cells using alcohol fuels such as methanol and ethanol or ethers such as dimethyl ether as fuels.

EXAMPLES The present disclosure will be described below using examples, but the present disclosure is not limited to these examples. In the following description, "%" is based on mass unless otherwise specified.

-Production Example 1-
[Preparation of CeO ₂ /CNF carrier]
9 g of dimethylformamide (DMF) (Wako Pure Chemicals Ind. Ltd.) and cerium oxide (CeO ₂ ) nanoparticles (product name; Nano Tek (registered trademark), manufactured by C.I. Kasei Co., Ltd., average primary particle size 14 nm) as a solvent0. 3 g, and sonicated for 30 minutes.
Next, 1 g of polyacrylonitrile (PAN) (manufactured by Sigma-Aldrich, Co. Ltd.), which is a polymer compound as a carbon source, was added to the mixed solution of dimethylformamide (DMF) and cerium oxide, and the mixture was stirred overnight at 80°C. , to prepare a stock solution.

The prepared raw material solution was filled in a syringe (2 mL), and the syringe pump (Future Science Co. Ltd.) was fixed so that the distance from the tip of the syringe to the current collector was 15 cm, and the tip of the syringe and the current collector were fixed. A high voltage of 18 kV was applied between the plate and the electrostatic spinning as shown in FIG. 1 at a flow rate of 0.025 mL/min to form carbon nanofibers on the current collector plate.
The carbon nanofibers (CNF) on the current collector plate were stabilized at 250°C for 10 hours in an air atmosphere, and then carbonized at 900°C for 1 hour in a nitrogen atmosphere. , a sheet of cerium oxide-embedded carbon nanofibers (CECNF) was obtained.

A cerium oxide-embedded carbon nanofiber (CECNF) sheet cut to a size of 2.5 cm×5.0 cm was placed on an aluminum plate. A polyimide film was placed on the CECNF sheet, the edge of the polyimide film was fixed to an aluminum plate with an imide tape, and the CECNF sheet was fixed on the aluminum plate.

－Irradiation of ion beam－
Using an AVF (azimuthal varying field) cyclone accelerator, under the irradiation conditions described in Table 1 below, the obtained CECNF was irradiated with an ion beam to obtain carrier 1, carrier 2-1, carrier 2-2, carrier 3- 1, Carrier 3-2, Carrier 4-1 and Carrier 4-2 were prepared.

-Production Example 2-
[Preparation of TiO ₂ /CNF carrier]
A raw material solution was prepared in the same manner as in Production Example 1, except that titanium oxide (TiO ₂ ) nanoparticles (P25, manufactured by Nippon Aerosil Co., Ltd.) were used instead of cerium oxide (CeO ₂ ). Carbon nanofibers containing titanium oxide were produced by heating to 850° C. in nitrogen gas in an electric furnace and then exposing them to a nitrogen stream containing steam pressure at 70° C. for 1 hour to perform steam activation treatment. The obtained carbon nanofibers containing titanium oxide were irradiated with an ion beam under the irradiation conditions shown in Table 1 below to prepare carriers 5-1 and 5-2.

In the table, "No ion" means a condition in which no ion beam was irradiated. Also, "-" means that there is no applicable data.

(Example 1)
-Supporting catalyst metal by microwave polyol method-
Carrier 2-1 was added to ethylene glycol and subjected to ultrasonic treatment for 30 minutes to prepare a mixed solution. Next, a precursor compound of Pt and Ru was added to the mixed solution so that the atomic ratio of Pt to Ru (Pt:Ru) was 1:1, and the mixture was stirred for 3 hours. Then, the mixture was heated in a microwave oven (600 W) for 5 minutes and stirred overnight. This solution was filtered and washed with methanol and distilled water. The resulting precipitate was dried in a vacuum dryer at 70° C. for 24 hours to obtain fuel cell catalyst 1 in which PtRu nanoparticles were supported on CNF (PtRu/CECNF).

[Evaluation of catalyst characteristics]
Using a powder X-ray diffractometer (product name: Rint2100, manufactured by Rigaku Corporation) using CuKα, the fuel cell catalyst 1 was irradiated under the conditions of V=32 kV and I=20 mA. Using a goniometer (product name: Rinto 2000 vertical goniometer, manufactured by Rigaku Co., Ltd.), the diffraction peaks appearing near 2θ = 5° to 90° at a scanning speed of 1.0°/min. investigated. The results are shown in Table 2 and FIG.

[Catalyst characteristics in methanol oxidation reaction]
As an evaluation test of the methanol oxidation activity of the catalyst, a mass activity evaluation was performed using a rotating disk electrode (RDE; AFMSRCE).
As a working electrode (WE), a glassy carbon electrode (GCE; glassy carbon electrode, inner diameter: 5.0 mm, manufactured by BAS Inc.) produced by the following method was used. A platinum mesh was used as a counter electrode (CE), and an Ag/AgCl electrode (manufactured by BAS Inc.) was used as a reference electrode (RE).

-Preparation of working electrode-
Fuel cell catalyst 1, water, ethanol, and a 5% by mass fluororesin copolymer solution (Nafion (registered trademark), Sigma-Aldrich, Co., Ltd.) were mixed so that the amount of catalyst supported was 1.0 mg/cm ² . Ltd.) was applied to the surface of a glassy carbon electrode and dried to prepare a working electrode.

-Oxidation activity for methanol solution-
A mixed solution of 0.5 mol/L H ₂ SO ₄ and 0.5 mol/L methanol was used as the fuel solution of the direct methanol fuel cell.
After purging the fuel solution with N ₂ at 100 ml / min for 30 minutes, N ₂ is introduced at 50 ml / min, while the working electrode is rotated at 1600 rpm (revolutions per minute), the scan speed is 0.02 V / s, the scan range made measurements over a range of electrode potentials from 0 V to 1.2 V vs. a reversible hydrogen electrode (RHE) and continued until the oxidation peak began to decline.
The oxidation activity was evaluated in terms of mass activity (current value per 1 mg of PtRu on the working electrode; mA/mg ⁻ _PtRu ).
Table 3 and FIGS. 3 and 4 show the results of the mass activity of the fuel cell catalyst 1 with respect to the methanol solution from the measured cyclic voltammogram.
The higher the mass activity, the better the oxidation activity for fuel.

Using the diffraction angle 2θ [Degree] at the peak position of the 111 plane of cerium oxide in the X-ray diffraction (XRD) pattern shown in FIG. rice field.

d [nm] = λ/(2·sin θ)
In the above formula, λ indicates the X-ray wavelength. The interplanar spacing value d [nm] of the 111 plane of cerium oxide was obtained using 0.154056 [nm] as the value of λ.

Using the half width of the XRD peak, the crystallite diameter D of the cerium oxide was obtained from the following Scherrer's formula.

D [nm]=K·λ/(β·cos θ)

In the above formula, β represents the half width [rad (radian)] of the XRD peak of the corresponding component.
D; crystallite diameter K; Scherrer constant 0.9
λ; X-ray wavelength, 0.154056 nm
θ; Bragg angle of diffraction line (half of diffraction angle 2θ) [rad (radian)]
β; half width of diffracted X-ray of crystal lattice [rad (radian)]

The results are shown in Table 3, and FIG. 4 shows the relationship between the interplanar spacing value d [nm] of the 111 plane of cerium oxide and the mass activity.

(Examples 2 to 6 and Comparative Examples 1 to 3)
Fuel cell catalysts 2 to 9 were prepared by the microwave polyol method in the same manner as in Example 1, except that the carrier 2-1 in Example 1 was changed to the carrier shown in Table 2. Each evaluation was performed using the obtained fuel cell catalysts 2 to 9. The results are shown in Tables 2 to 4 and FIGS. 2 to 4.

In the table, "ND" means not measured. Also, "-" means that there is no applicable data.

In Table 3 and FIG. 2, the 2θ value [Deg.] and d value [nm] are the diffraction angle 2θ of the 111 plane of untreated (Non ion) cerium oxide, which is the literature value (NIMS database, J. Am. Ceram Soc., 1993, 76, 1745-1750, Yamashita M., Morimoto K., Ishizawa N., Yoshimura M.).

In Table 4, the 2θ value [Deg.] and the d value [nm] are the diffraction angle 2θ of (110) of untreated (non-ion) titanium oxide, and the literature value (NIMS database, J. Am. Ceram. Soc ., 1996, 79, 1095, Kim D.W., Enomoto N., Nakagawa Z., Kawamura K.) 27.431 [Degree] and recalculated.

As shown in Table 3 and FIG. 4, it can be seen that the mass activity, that is, the fuel oxidation activity increases as the interplanar spacing of the 111 planes of the cerium oxide of Examples 1 to 5, that is, the d value increases.
On the other hand, in Comparative Examples 1 and 2, in which the d value of the 111 plane of cerium oxide is outside the range of 0.3129 nm to 0.3160 nm, the mass activity value is smaller than that of the example, and the fuel It can be seen that the mass activity, that is, the oxidation activity for fuel is inferior.

Further, as shown in Table 4, the d value of the 110 plane spacing of titanium oxide in Example 6 is 0.3195 nm to 0.3244 nm, and the d value of the 110 plane spacing is 0.3195 nm to 0.3244 nm. Compared to the 110 plane spacing of titanium oxide in Comparative Example 3, which is out of the range, the plane spacing is smaller, and it can be seen that the oxidation activity for fuel is improved.

As described above, cerium oxide having a 111 plane spacing of 0.3129 nm to 0.3160 nm obtained by X-ray diffraction and a cerium oxide having a 110 plane spacing of 0.3195 nm to 0.3244 nm obtained by X-ray diffraction The fuel cell oxidation catalysts of Examples containing a certain titanium oxide are excellent in oxidation activity for fuel.

10 polymer electrolyte membrane 20 electrode 31 catalyst layer 32 gas diffusion layer

Claims (9)

Cerium oxide having a 111 plane spacing of 0.3129 nm to 0.3160 nm determined by X-ray diffraction, and oxide having a 110 plane spacing of 0.3195 nm to 0.3244 nm determined by X-ray diffraction a carrier containing at least one oxide selected from the group consisting of titanium;
a catalyst metal supported on the carrier;
and an oxidation catalyst for direct methanol fuel cells. 2. The oxidation catalyst for direct methanol fuel cells according to claim 1, wherein said carrier further contains a carbon material. 3. The oxidation catalyst for a direct methanol fuel cell according to claim 1, wherein said cerium oxide contains said particulate cerium oxide, and said particulate cerium oxide has a crystallite size of 1 nm to 1 μm. The direct methanol fuel according to any one of claims 1 to 3, wherein the titanium oxide contains particulate titanium oxide, and the particulate titanium oxide has a crystallite size of 1 nm to 1 µm. Oxidation catalyst for batteries. The oxidation catalyst for a direct methanol fuel cell according to any one of claims 1 to 4, which is used in a fuel cell using alcohol or ether as a fuel for the direct methanol fuel cell. a polymer electrolyte membrane;
an electrode;
a catalyst layer having the direct methanol fuel cell oxidation catalyst according to any one of claims 1 to 5, provided between the polymer electrolyte membrane and the electrode;
A fuel cell. an irradiation step of irradiating a carrier containing a transition metal oxide with an ion beam at a dose of 1.0×10 ¹⁰ ions/cm ² to 8.0×10 ¹² ions/cm ² ;
A step of supporting a catalyst metal on a support containing the transition metal oxide obtained in the irradiation step;
has
The transition metal oxide is at least one selected from the group consisting of cerium oxide and titanium oxide,
the ion species of the ion beam are Ar ions, Kr ions, or Xe ions;
the ion beam is an Ar ion beam having an energy of 127 MeV and a dose of 5.0×10 ¹¹ ions cm ⁻² to 1.0×10 ¹² ions cm ⁻² ;
a Kr ion beam with an energy of 310 MeV and a dose of 3.0×10 ¹¹ ions cm ⁻² to 3.0×10 ¹² ions cm ⁻² ;
Alternatively, a Xe ion beam with an energy of 350 MeV and a dose of 2.0×10 ¹¹ ions cm ⁻² to 2.0×10 ¹² ions cm ⁻² ,
The obtained transition metal oxide is cerium oxide having a 111 plane spacing of 0.3129 nm to 0.3160 nm determined by an X-ray diffraction method, and a 110 plane spacing determined by an X-ray diffraction method. At least one selected from the group consisting of titanium oxide having a diameter of 0.3195 nm to 0.3244 nm,
A method for producing an oxidation catalyst for a direct methanol fuel cell. 8. The method for producing an oxidation catalyst for a direct methanol fuel cell according to claim 7, wherein said carrier further contains a carbon material. The direct methanol fuel according to claim 7 or claim 8, wherein the transition metal oxide obtained in the irradiation step has an absolute value of a change rate of the interplanar spacing of 0.15% to 0.65%. A method for producing an oxidation catalyst for a battery.

Images