JP2002358971A - Fuel cell electrode and its manufacturing method and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fuel cell electrode that has a high CO toxication resistance performance. SOLUTION: The fuel cell electrode comprises a positive ion exchange resin, carbon particles, and a catalyst metal, and the quantity of the catalyst metal carried by the contact face of the proton conductive passage of the positive ion exchange resin and the carbon particle surface is more than 50 wt.% of the total catalyst metal carrying quantity. The above catalyst contains platinum and ruthenium, and the ratio of the number of ruthenium atoms to the total number of atoms of platinum and ruthenium is 60-90%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell electrode, a method of manufacturing the same, and a fuel cell using the same.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell comprises a solid polymer electrolyte membrane and an anode and a cathode which are arranged so as to sandwich the membrane. When this apparatus is operated by supplying hydrogen and oxygen to the anode and the cathode, respectively, the following electrochemical reaction proceeds on each electrode.

Anode: 2H ₂ → 4H ⁺ + 4e ⁻ Cathode: O ₂ + 4H ⁺ + 4e ⁻ → H ₂ O As is clear from this reaction formula, the reaction of a gas (hydrogen or oxygen) as an active material is , Proton (H ⁺ ) and electron (e
⁻ ) Only progresses in places where the transfer with) can take place at the same time. By paying attention to this, an electrode with a significantly reduced platinum catalyst loading has been proposed (Sumitomi Hitomi et al., The 40th Battery Symposium, 167-168, (1)
999)).

In this electrode, first, an electrode containing a cation exchange resin and carbon particles is manufactured, and then, a platinum cation is adsorbed on the electrode, and then the adsorbed platinum cation is chemically converted. Can be produced by reduction.

[0005] The electrode manufactured by this method has a structure in which the amount of platinum carried on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon particles exceeds 50 wt% of the total amount of platinum carried. The contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon particles is a place where the transfer of protons (H ⁺ ) and electrons (e ⁻ ) as described above can be performed at the same time. Electrodes have significantly higher platinum utilization. Therefore, this electrode shows the same activity with an extremely small amount of loaded platinum as compared to an electrode made of carbon particles preloaded with platinum and a cation exchange resin.

[0006] As a fuel for a polymer electrolyte fuel cell, a reformed gas produced from methanol, natural gas, or the like, which is easily stored and transported, is used. This gas is mainly composed of hydrogen and contains 10 to 100 ppm of CO. It is known that when such a fuel is used, the platinum catalyst provided on the electrode is poisoned by CO.

On the other hand, as a catalyst which is less susceptible to CO poisoning, there is a binary alloy of platinum and ruthenium (M. Watanabe, Journal of E.).
Electroanalytical Chemistr
y 229, (1987) 395). In particular, an alloy of platinum and ruthenium containing about 50 atomic% of ruthenium is resistant to C.
Due to the remarkably high O poisoning performance, electrodes with alloys of such composition show little CO effect (M.
Iwase, Electrochemical Soc
iety Proceedings Volume 95
-23, (1995) 12).

[0008]

SUMMARY OF THE INVENTION The present inventors have found that the amount of the catalyst metal supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon particles is 50 w of the total amount of the supported catalyst metal.
An electrode was fabricated in which the catalytic metal exceeded t% and whose catalytic metal was a binary alloy of platinum and ruthenium containing 50 atomic percent ruthenium. However, in the fuel cell provided with this electrode, the catalyst is C-resistant.
When the reformed gas was used as a fuel, the output decreased due to CO poisoning, despite the fact that the alloy had a conventional composition which was considered to be highly poisonous. In other words, there is a problem in that an electrode having a special structure as used by the present inventors cannot impart sufficient CO poisoning resistance when a catalyst having a conventional composition is supported.

Therefore, the present inventor has proposed that the amount of catalyst metal supported on the interface between the proton conduction path of the cation exchange resin and the surface of the carbon particles exceeds 50 wt% of the total amount of supported catalyst metal. In order to improve the CO poisoning performance, the amount of ruthenium contained in the catalyst containing platinum and ruthenium was examined. As a result, the present inventor has found that the catalyst exhibits the highest CO poisoning resistance when the catalyst has a completely different amount of ruthenium than the conventional one, and furthermore, the performance of the fuel cell using this electrode is The present invention has been accomplished by finding a unique property that is significantly higher than that of the present invention.

[0010]

The invention of claim 1 includes a cation exchange resin, carbon particles and a catalyst metal, and is supported on a contact surface between a proton conduction path of the cation exchange resin and the surface of the carbon particles. The amount of catalyst metal is 5 times the total amount of catalyst metal carried.
In a fuel cell electrode exceeding 0 wt%, the catalyst contains platinum and ruthenium, and the ratio of the number of ruthenium atoms to the total number of platinum and ruthenium atoms is 60 to 90%.

According to the first aspect of the present invention, it is possible to obtain an electrode for a fuel cell having excellent resistance to CO poisoning.

A second aspect of the present invention relates to a method for producing the above-mentioned fuel cell electrode, wherein a mixture containing a cation exchange resin and carbon particles adsorbs a cation containing platinum and a cation containing ruthenium. And a second step of reducing each cation in the mixture obtained in the first step.

[0013] The invention of claim 3 relates to a method of manufacturing the fuel cell electrode, wherein in the first step, the cation containing platinum is a platinum ammine complex cation, and the cation containing ruthenium is a ruthenium ammine complex cation. It is an ion.

The invention according to claim 4 relates to a method for producing the above-mentioned fuel cell electrode, wherein in the first step, a mixture containing a cation exchange resin and carbon particles is mixed with a tetraammine Pt (divalent) cation. And hexaammine Ru (3
Hexammine R based on the total number of moles with the cation
The ratio of the number of moles of u (trivalent) cation is 40 to 95 mol%
According to the invention of the second, third and fourth aspects, the electrode for a fuel cell can be easily manufactured.

According to a fifth aspect of the present invention, in the fuel cell, the fuel cell is used as the fuel cell electrode or the fuel cell electrode anode produced by the above-described manufacturing method. Claim 5
According to the invention, a fuel cell exhibiting excellent characteristics can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One example of an electrode for a fuel cell according to the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing the relationship between a cation exchange resin, carbon particles, and a catalyst contained in the fuel cell electrode of the present invention. In FIG. 1, reference numeral 11 denotes carbon particles, 12 denotes a proton conduction path of a cation exchange resin, and 13 denotes Teflon (registered trademark) of a cation exchange resin.
The skeleton portion 14 is a catalytic metal containing platinum and ruthenium.

This electrode forms the surface layer of the carbon particles 11
A cation exchange resin composed of a proton conduction path 12 and a Teflon skeleton 13 is coated, and a catalyst metal 14 is supported on a contact surface between the proton conduction path 12 of the cation exchange resin and the surface of the carbon particles 11. The structure is such that the amount of catalyst metal supported on the contact surface between the proton conduction path 12 of the ion exchange resin and the surface of the carbon particles 11 exceeds 50 wt% of the total amount of catalyst metal supported. At the interface between the proton conduction path 12 of the cation exchange resin and the surface of the carbon particles 11, the existence of the electron conduction channel formed by the carbon particles and the proton conduction channel formed by the cation exchange resin, It is a place where the transfer of electrons (e ⁻ ) and protons (H ⁺ ) can be performed simultaneously.

That is, since the reaction of the active material supplied from the outside proceeds only at that location, the amount of the catalyst metal carried on the interface between the proton conduction path of the cation exchange resin and the surface of the carbon particles is reduced by the total amount of the catalyst. The electrode of the present invention exceeding 50 wt% of the metal loading has a high catalyst utilization. In the electrode of the present invention, in order to exhibit high activity while having a very small amount of catalyst carried, the amount of catalyst carried on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon particles must be equal to the total amount of catalyst carried. It is preferably at least 80 wt%,
More preferably, it exceeds 90 wt%.

Further, the catalyst containing platinum and ruthenium of the fuel cell electrode according to the present invention is preferably such that the ratio of the number of ruthenium atoms to the total number of platinum and ruthenium atoms is 60 to 90%, that is, its CO resistance. It is preferable because poison performance is increased. Since the performance is further remarkably improved, the ratio is particularly preferably 70 to 90%.

The catalyst for an electrode for a fuel cell according to the present invention comprises:
It may contain not only platinum and ruthenium but also other platinum group metals. For example, rhodium, iridium, palladium, and osnium. By including these metals, the catalytic activity can be increased.

Further, the catalyst for an electrode for a fuel cell of the present invention includes magnesium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc,
At least one element selected from the group consisting of silver, tungsten and gold may be contained. In this case, there are effects such as improvement in catalytic activity of platinum and ruthenium and inexpensive production.

However, when the total weight of platinum and ruthenium with respect to all metal elements contained in the catalyst is 50% or more, excellent CO poisoning resistance can be obtained.

Here, ruthenium in the catalyst exists in a state of forming a solid solution with another metal, a state of ruthenium oxide represented by RuOx, or a state of a complex such as an ammine complex, a phthalocyanine complex or a porphyrin complex. You may. The shape of the catalyst is preferably in the form of particles having a particle size of 4 nm or less, since the mass activity of the catalyst is increased, and more preferably 1.5 nm or less, in which the activity is significantly improved.

The cation exchange resin used in the electrode of the present invention is preferably a perfluorocarbon sulfonic acid type or a styrene-divinylbenzene type sulfonic acid type cation exchange resin. Among them, the cation exchange resin contained in the electrode may be 2.5 meq / g or less, and is more preferably 1.0 meq / g or more because a catalyst having high activity can be obtained. As the carbon particles, carbon black can be used. For example, Denka Black, Vul
can XC-72, Black Pearl 2000
And the like are particularly preferred.

The fuel cell of the present invention has a structure in which the fuel cell electrode of the present invention is disposed on at least one surface of the solid polymer electrolyte membrane. In particular, the fuel cell of the present invention has a C
Since the O poisoning performance is high, it is preferable to provide the electrode as an anode.

The fuel cell electrode of the present invention can be manufactured, for example, by the following method. The cation containing the metal element is adsorbed on the cation exchange resin by the ion exchange reaction between the counter ion of the cation exchange resin and the cation containing the metal element in the mixture containing the cation exchange resin and the carbon particles. A first step and a second step of chemically reducing a cation containing a metal element in the mixture obtained in the first step.
And a process for producing an electrode for a fuel cell.

Specifically, a first step of adsorbing a cation containing platinum and a cation containing ruthenium on a mixture containing a cation exchange resin and carbon particles, and a first step obtained by the first step. And a second step of reducing each cation in the mixture obtained.

Here, in the first step, for example, a compound that generates a cation containing a metal element in an aqueous solution or a solution containing an alcohol is dissolved in a solution containing water or an alcohol, and the cation exchange resin is dissolved. The mixture is prepared by immersing a mixture containing carbon and carbon particles in a solution containing water or alcohol.

In the first step, the mixture may be immersed in a solution containing those various cations in order to adsorb two or more cations having different metal elements to the mixture. After dipping in a solution containing a cation containing a metal element, it may be further dipped in a solution containing a cation containing a different metal element.

In particular, when the mixture is immersed in a solution containing two or more cations, the ratio of each metal carried on the electrode is controlled by adjusting the ratio of each cation in the solution. Can be. For example, when the mixture is immersed in a solution containing a cation containing platinum and a cation containing ruthenium, by controlling the ratio of each cation, the total number of atoms of platinum and ruthenium supported on the electrode is controlled. The atomic ratio of ruthenium can be controlled to 60 to 90%.

The second step is performed by leaving the mixture under a reducing atmosphere. In this step, it is preferable to use a chemical reduction method using a reducing agent suitable for mass production. In particular, a gas phase reduction method using hydrogen gas or a gas containing hydrogen or a gas phase reduction method using an inert gas containing hydrazine is preferable. The method is preferred.

Here, the gas containing hydrogen gas is preferably a mixed gas of hydrogen gas and an inert gas such as nitrogen, helium, or argon.
It is preferable to include the above. Since the carbon particles are active in the reduction reaction of the cation containing the metal element, the cations containing the metal element adsorbed on the cation exchange resin and those existing near the carbon particle surface are ,
It is preferentially reduced compared to cations present elsewhere.

Therefore, in this step, by appropriately adjusting the type of the reducing agent, the reducing pressure, the reducing agent concentration, the reducing time, and the reducing temperature, the cation containing the metal element in the vicinity of the carbon particle surface can be positively changed in other places. The reduction can be performed more preferentially than the ions, so that the catalyst can be supported mainly on the interface between the proton conduction path of the cation exchange resin and the surface of the carbon particles.

Specifically, the temperature is lower than the temperature at which cations containing a metal element adsorbed on the cation exchange resin and not present near the surface of the carbon particles are reduced. Is reduced at a temperature higher than the temperature at which the cations present in the vicinity of the cation exchange resin are reduced. It is preferable that the amount exceeds 80 wt% of the supported amount.

In the production method of the present invention, after the first step and the second step are performed, the first step and the second step are further repeated once or more, so that the metal in the catalyst can be obtained. And the ratio of the amounts of the metals supported can be adjusted. Further, by repeating this series of steps, it is possible to further increase the size of the catalyst using the previously supported catalyst metal as a nucleus, and to support a catalyst of an arbitrary size. Further, in order to improve the activity of the electrode of the present invention, the mixture obtained through the first step and the second step is mixed under an atmosphere containing an oxidizing gas, under an atmosphere containing a gas mainly containing an inert gas, Aging may be performed in an acidic solution or an alkaline solution.

The cation containing a metal element used in the production method of the present invention is a cation that can be used as a catalyst by reducing the cation, and the shape of the catalyst is not particularly limited. . The above manufacturing method includes, for example,
Platinum, ruthenium, rhodium, iridium, palladium, osmium, magnesium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel,
A cation containing at least one element selected from the group consisting of copper, zinc, silver, tungsten, and gold can be used.

Above all, the cation containing the metal element used in this method is hardly adsorbed on the carbon surface not coated with the cation exchange resin, and is subjected to cation exchange reaction with the counter ion of the cation exchange resin. It is preferable that the resin preferentially adsorbs to the proton conduction path of the resin.

For example, as a cation containing platinum or ruthenium having such adsorption characteristics, [Pt (N
H ₃ ) ₄ ] ²⁺ , [Pt (NH ₃ ) ₆ ] ^4+, etc., or an ammine complex ion of platinum, or [R
u (NH ₃ ) ₄ ] ²⁺ and [Ru (NH ₃ ) ₆ ] ³⁺ .

Therefore, in the first step of the method for producing a fuel cell electrode according to the present invention, the cation containing platinum may be a platinum ammine complex cation and the cation containing ruthenium may be a ruthenium ammine complex cation. preferable.

Further, in the first step of the method for producing an electrode for a fuel cell according to the present invention, the mixture containing a cation exchange resin and carbon particles is mixed with tetraammine Pt (2
Immersion in a solution in which the ratio of the number of moles of hexaammine Ru (trivalent) cation to the total number of moles of (valent) cation and hexaammine Ru (trivalent) cation is 40 to 95 mol%. More preferred.

In the first step of the method for producing a fuel cell electrode according to the present invention, a step of immersing the mixture in the above solution is included. It is easy to make the ratio of the number of ruthenium atoms to the total number of atoms 60 to 90%.

On the other hand, the mixture containing the carbon particles and the cation exchange resin is preferably prepared as a porous body in which the cation exchange resin, the carbon particles and, if necessary, the PTFE particles are dispersed. The mixture is preferably in the form of a film, and the thickness of the film is preferably 3 to 30 μm, more preferably 3 to 20 μm. Further, as the carbon particles, carbon black exhibiting a high activity for a reduction reaction of a cation containing a metal element is preferable. For example, Denka Black, Vulcan XC
-72, carbon black such as Black Pearl 2000 is particularly preferred.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to preferred embodiments. [Example 1] A cation exchange resin (manufactured by Aldrich, Nafion 5 wt% solution) and carbon particles (Vul
can XC-72), heated and concentrated to form a paste, formed into a film (about 13 μm in thickness) on a polymer (FEP) film, and then dried at room temperature. This mixture is combined with [Pt (NH ₃ ) ₄ ] Cl ₂ and [Ru (NH ₃ ) ₆ ] C
immersed l ₃ and 24 hours in an aqueous solution prepared by dissolving, 200 ° C.
Was left in a hydrogen atmosphere for 7 hours to produce an electrode.

Here, electrodes using solutions in which the mixing ratio of [Pt (NH ₃ ) ₄ ] Cl ₂ and [Ru (NH ₃ ) ₆ ] Cl ₃ were variously changed were manufactured, and their platinum was used. And the supported amount of ruthenium were examined. The result is shown in FIG. FIG. 2 is a diagram showing the relationship between the atomic ratio of ruthenium to the total number of platinum and ruthenium atoms in the raw material solution and the obtained electrode during the production of the electrode, as is clear from this figure. By using solutions of platinum and ruthenium having different compounding ratios, the ratio of each metal supported can be adjusted.

In the above method, the ratio of the number of ruthenium atoms to the total number of platinum and ruthenium atoms is 0.0,
1.0, 5.0, 10, 20, 30, 40, 50, 6
Electrodes carrying 0, 70, 80, 90, 95, 99 and 100% of the catalyst were produced. The catalyst carrying amount of each electrode was adjusted to 0.05 mg / cm ² .

[Comparative Example 1] Pt-Ru-supported carbon (manufactured by Tanaka Kikinzoku Co., Ltd., platinum 18.6 wt%, ruthenium 14.4 wt%, carrier: Vulcan XC-72) and a cation exchange resin (manufactured by Aldrich, Nafion) 5w
t% solution) and heat-concentrate to form a paste,
Film formation on polymer (FEP) film (thickness about 13μm)
Thereafter, drying was performed at room temperature to obtain an electrode A of a comparative example. By adjusting the amount of Pt-Ru supported carbon at the time of paste production, the amount of supported catalyst of this electrode was reduced to about 0.05 mg / c.
It was made to be m ^2. In the electrode A, the ratio of the number of ruthenium atoms to the total number of platinum and ruthenium atoms is 60%.

[Comparative Example 2] Pt-Ru supported carbon (E
TEK, platinum 20.0wt%, ruthenium 10.3
wt%, carrier: Vulcan XC-72) and a cation exchange resin (manufactured by Aldrich, Nafion 5 wt% solution) are kneaded, heated and concentrated to form a paste, and formed into a film on a polymer (FEP) film ( After drying at room temperature, an electrode B of Comparative Example was obtained. By adjusting the amount of Pt-Ru supported carbon during paste production, the amount of catalyst supported on this electrode was adjusted to about 0.05 mg / cm ² . In the electrode B, the atomic ratio of ruthenium to the total number of atoms of platinum and ruthenium is 50%.
It is.

[Comparative Example 3] Platinum-supported carbon (manufactured by Tanaka Kikinzoku Co., Ltd., platinum 30 wt%, carrier: Vulcan
XC-72) and a cation exchange resin (manufactured by Aldrich,
Nafion 5 wt% solution), and then heat-concentrated to form a paste, formed on a polymer (FEP) film (thickness: about 13 μm), and dried at room temperature to obtain electrode C of Comparative Example. Was. By adjusting the amount of platinum-carrying carbon during paste production, the platinum amount of this electrode was reduced to about 0.05.
mg / cm ² .

A fuel cell was manufactured using the electrodes manufactured in the examples and the electrodes A, B and C of the comparative example as anodes.
At that time, each fuel cell has, as a cathode,
The electrode C of Comparative Example 3 was used. Next, the current density in a steady state when operating at a cell voltage of 0.5 V using hydrogen (2 atm, 80 ° C.) containing 20 ppm of CO as a fuel was measured for each cell. The result is shown in FIG.

FIG. 3 shows the ratio of the number of ruthenium atoms to the total number of platinum and ruthenium atoms in the catalyst when the fuel cell including the electrodes of the example and the electrodes of the comparative example was operated at 0.5 V. %) And the current density at 0.5 V. In FIG. 3, the symbol は indicates the electrode of the embodiment,
The symbol ▲ indicates the relationship of the electrode A of Comparative Example 1, the symbol ◆ indicates the relationship of the electrode B of Comparative Example 2, and the symbol ■ indicates the relationship of the electrode C of Comparative Example 3.

As shown in FIG. 3, as is generally known, the electrode A of Comparative Example 1, the electrode B of Comparative Example 2, and the electrode C of Comparative Example 3 have, as generally known, the ratio of ruthenium to the total number of platinum and ruthenium atoms. The tendency to show the highest current value when the atomic ratio was 50% was obtained. On the other hand, the electrode of the example showed a particularly high current value when the atomic ratio of ruthenium to the total atomic number of platinum and ruthenium was 60 to 90 atomic%. These results indicate that when the electrode of the present invention has a specific ruthenium content, the resistance to CO poisoning is high, and the performance of the fuel cell using the electrode of the present invention is significantly higher than that of the conventional one. ing.

[0052]

By using the fuel cell electrode of the present invention, it is possible to provide a fuel cell capable of generating a high output even when hydrogen containing CO is used as fuel. Further, according to the fuel cell of the present invention, it is possible to provide a power supply system that supplies large power even when hydrogen containing CO is used as fuel.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the relationship between a cation exchange resin, carbon particles, and a catalyst contained in a fuel cell electrode of the present invention.

FIG. 2 is a diagram showing the relationship between the atomic ratio of ruthenium to the total number of platinum and ruthenium atoms in a raw material solution and an obtained electrode during electrode production.

FIG. 3 is a diagram showing the relationship between the atomic ratio (%) of ruthenium to the total number of platinum and ruthenium in the catalyst and the current density at 0.5 V when the fuel cell is operated at 0.5 V. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Carbon particle 12 Cation exchange resin 13 Ion exchange membrane 14 Catalyst

Claims (5)

[Claims] 1. A catalyst comprising a cation exchange resin, carbon particles and a catalyst metal, wherein the amount of catalyst metal supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon particles is 50 wt. %, Wherein the catalyst contains platinum and ruthenium, and the ratio of the number of ruthenium atoms to the total number of platinum and ruthenium atoms is 60 to 90%. . 2. A first step of adsorbing a cation containing platinum and a cation containing ruthenium on a mixture containing a cation exchange resin and carbon particles, and a mixture obtained in the first step. 2. The method for producing an electrode for a fuel cell according to claim 1, further comprising: a second step of reducing each cation therein. 3. The fuel cell electrode according to claim 2, wherein, in the first step, the cation containing platinum is a platinum ammine complex cation, and the cation containing ruthenium is a ruthenium ammine complex cation. Manufacturing method. 4. In a first step, a mixture containing a cation exchange resin and carbon particles is mixed with tetraammine Pt.
Hexammine Ru (trivalent) based on the total number of moles of (divalent) cations and hexaammine Ru (trivalent) cations
The method for producing an electrode for a fuel cell according to claim 3, further comprising a step of immersing in a solution having a molar ratio of cations of 40 to 95 mol%. 5. A fuel cell, wherein the fuel cell electrode according to claim 1 or the fuel cell electrode produced by the manufacturing method according to claim 2, 3 or 4 is used as an anode.