JP2000188110A - Solid high polymer electrolyte fuel cell and its gas diffusion electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid high polymer electrolyte fuel cell having a high output. SOLUTION: This gas diffusion electrode for a solid high polymer electrolyte fuel cell contains a catalyst and a carbon sulfonic acid type ion exchange resin containing fluoride, the ion exchange resin can be obtained by hydrolyzing and oxidizing the precursor of the ion exchange resin having -SO2F and the precursor has a fused extrusion temperature of 80-170 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer electrolyte fuel cell and a gas diffusion electrode thereof.

[0002]

2. Description of the Related Art A hydrogen / oxygen fuel cell has attracted attention as a power generation system whose reaction product is only water in principle and has almost no adverse effect on the global environment. Solid polymer electrolyte fuel cells were once mounted on spacecraft in the Gemini and Biosatellite programs, but the power density at that time was low. Since then, higher performance alkaline fuel cells have been developed, and up to the present space shuttle, alkaline fuel cells have been adopted for space applications.

However, in recent years, attention has been paid again to solid polymer electrolyte fuel cells due to technological advances. The reasons are as follows. (1) A highly conductive film was developed as a solid polymer electrolyte. (2) By supporting the catalyst used for the gas diffusion electrode layer on carbon and coating this with an ion-exchange resin, an extremely large activity can be obtained.

[0004] Many studies have been made on a method for manufacturing an electrode-solid polymer electrolyte membrane assembly (hereinafter simply referred to as an assembly) of a solid polymer electrolyte fuel cell. The solid polymer electrolyte fuel cells currently being studied have a drawback that the operating temperature is as low as 50 to 120 ° C., so that the exhaust heat cannot be used effectively for the auxiliary power of the fuel cell. To compensate for this, the solid polymer electrolyte fuel cell is required to have a particularly high output density. In addition, as a challenge for practical use, high energy efficiency, even under operating conditions with high fuel and air utilization rates,
There is a demand for the development of a joined body that can obtain a high power density.

[0005]

Under operating conditions of low operating temperature and high gas utilization, mass transfer, especially on the catalyst, tends to be the rate limiting of the electrode reaction. Specifically, it is necessary that the gas be rapidly diffused onto the catalyst coated with the ion exchange resin, but satisfactory characteristics cannot be obtained with the conventional ion exchange resin material.

The ion exchange resin contained in the electrode is
Usually contained in the electrode using a solution dissolved in a solvent,
Conventional materials are difficult to dissolve in a solvent at normal temperature and normal pressure, and have a problem that they must be dissolved at a high temperature in an autoclave. Furthermore, the ion exchange resin solution obtained in this way has a high viscosity, and there is a problem that the catalyst cannot be coated sufficiently.

On the other hand, as a method of forming a joined body, a method of hot-pressing and joining an air electrode and a fuel electrode comprising a layer containing an ion exchange resin and a catalyst to a membrane which is a solid polymer electrolyte is generally used. The ion exchange resin is melted during hot pressing and also functions as a binder for bonding the membrane and the electrode. However, with conventional materials, it is known that unless the temperature of hot pressing is a relatively high temperature of 150 to 180 ° C., the ion exchange resin does not melt and the membrane and the electrode cannot be sufficiently bonded. At that time, since the ion exchange membrane and the ion exchange resin are exposed to the temperature, the water content decreases, and as a result, the electric resistance increases, and there is a problem that the output as a battery decreases.

Accordingly, the present invention provides a gas diffusion electrode containing an ion-exchange resin having a high water content and capable of rapidly moving a gas onto a catalyst even under operating conditions of a low operating temperature and a high gas utilization rate. It is another object of the present invention to provide a polymer solid oxide fuel cell having a high output by having the gas diffusion electrode.

[0009]

The present invention comprises a catalyst and a fluorinated carbon sulfonic acid type ion exchange resin, wherein the ion exchange resin has a structure of -SO ₂ F at the terminal. The precursor is obtained by hydrolyzing and acidifying the precursor, and the precursor has a melt extrusion temperature of 80
A gas diffusion electrode for a solid polymer electrolyte fuel cell, wherein the temperature is from 170 to 170 ° C.

Further, according to the present invention, a gas diffusion electrode containing a catalyst and an ion exchange resin is used as a fuel electrode and an air electrode, and the fuel electrode is provided on one surface of the membrane-shaped solid polymer electrolyte, and the other is provided on the other surface. In the solid polymer electrolyte fuel cell in which the air electrode is respectively disposed, the ion exchange resin contained in at least one of the air electrode and the fuel electrode has -SO ₂ F at an end thereof. A solid obtained by hydrolyzing and acid-forming a resin precursor, and wherein the precursor is a fluorine-containing carbon sulfonic acid type ion exchange resin having a melt extrusion temperature of 80 to 170 ° C. Provided is a polymer electrolyte fuel cell.

[0011] The fluorine-containing carbon sulfonic acid type ion exchange resin contained in the gas diffusion electrode of the present invention has a terminal of -SO
₂ F precursor comprising a resin (hereinafter, simply referred to as precursor.) Obtained by the processes hydrolysis and acid form. The precursors include CF ₂ = CF ₂ and CF ₂ = CF- (OCF _{2
CFX) m -O p - (CF} 2) n fluorovinyl compound represented by -SO ₂ F (wherein, m is an integer of from 0 to 3, n represents 1
12 integer, p is 0 or 1, X is F or CF _3. ) Are preferred. Preferred examples of the fluorovinyl compound include the following compounds. However, in the following formula, q is an integer of 1 to 8, and r is 1 to 8
, S is an integer of 1 to 8, and t is an integer of 1 to 3.

[0012]

Embedded image CF ₂ ＣＦCFO (CF ₂ ) _q SO ₂ F, CF ₂ ＣＦCFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _r SO
_{2 F, CF 2 = CF (} CF 2) s SO 2 F, CF 2 = CF (OCF 2 CF (CF 3)) t O (CF 2) 2 S
O ₂ F.

The above-mentioned copolymer is based on a fluorinated olefin such as hexafluoropropylene or chlorotrifluoroethylene, a polymerized unit based on perfluoro (alkyl vinyl ether), or a non-fluorinated olefin such as ethylene or vinylidene chloride. If the polymerized unit is 25% by weight or less of the polymerized unit based on tetrafluoroethylene, it may be included in place of a part of the polymerized unit based on tetrafluoroethylene.

[0014] precursor, after being hydrolyzed by an aqueous solution such as a -SO ₂ F, for example NaOH or KOH, is converted to the acid type resin is an acid form with an aqueous solution such as hydrochloric acid or sulfuric acid. For example, when hydrolyzed by KOH aqueous solution, -SO ₂
The desired ion exchange resin is obtained by converting F to —SO ₃ K and then replacing the K ion with a proton.
Further, the hydrolysis and the acidification treatment may be performed simultaneously.

The ion-exchange resin contained in the gas diffusion electrode of the present invention has a melt extrusion temperature of the precursor of 80 to 170 ° C., preferably 100 to 160 ° C. In the present invention, the melt extrusion temperature is 1 mm in length and 1 m in inner diameter.
When the resin was melt-extruded using a 30-m nozzle under an extrusion pressure of 30 kg / cm ² , the extrusion amount was 100 m
It indicates the temperature at which m ³ / sec. In this specification,
Hereinafter, this melt extrusion temperature is referred to as T _Q. T
_Q is a numerical value which is a measure of the molecular weight of the resin, generally T _Q
The higher is the higher the molecular weight.

Since the resin having a T _Q of less than 80 ° C. and the resin using the resin as a precursor are structurally difficult to maintain a solid state, the ion exchange resin contained in the gas diffusion electrode of the present invention is Not suitable. Further, if T _Q of the precursor exceeds 170 ° C., the water content is lowered to increase the molecular weight of the ion-exchange resin, together with electrical conductivity is decreased, hardly solutionizing for difficult to dissolve in a solvent, effective catalyst particles It is difficult to cover the surface.

When the T _{Q of the} precursor is in the above range, the catalyst particles are effectively coated, and the water content of the ion exchange resin is increased, so that the gas can be easily dissolved and diffused in the ion exchange resin. Become. Therefore, an increase in overvoltage due to mass transfer in an electrode reaction on the catalyst, that is, an increase in voltage loss due to a decrease in gas concentration at a reaction site of the electrode can be suppressed, and a fuel cell with high voltage and high current density can be obtained.

Further, since the T _Q precursors melting temperature of the ion exchange resin is lowered when the above-mentioned range, forming a bonded body of the electrode layer containing an ion exchange resin and a catalyst to hot pressing ion exchange membrane In this case, bonding can be performed so as to have sufficient strength at a considerably lower temperature than conventional materials. For this reason, especially when the air electrode and the fuel electrode are both formed of the gas diffusion electrodes of the present invention, not only the production of the joined body is facilitated, but also the ion exchange membrane and the ion exchange resin, which are solid polymer electrolytes, become hot at the time of hot pressing. This is preferable because the water content does not decrease and a high output can be achieved as a battery.

Further, if the T _Q of the precursor of the ion exchange resin is set lower than the T _Q of the precursor of the ion exchange membrane, hot pressing can be performed in a temperature range where the fluidity of the ion exchange membrane is not easily reduced. Therefore, the ion exchange membrane is not easily deformed, and a short circuit between the fuel electrode and the air electrode and a decrease in membrane strength due to a local thinning of the ion exchange membrane can be avoided.

Further, since T _Q of the precursor molecular weight is the ion exchange resin in the above range is not extreme large, the ion exchange resin becomes easy to solution by being dissolved in a solvent, and a solution viscosity of Therefore, the catalyst particles can be effectively coated, and a high output can be obtained as a battery.

The ion exchange resin contained in the gas diffusion electrode of the present invention has an ion exchange capacity (hereinafter referred to as _AR ).
Is preferably 0.5 to 2.0 meq / g dry resin. Generally, the ion exchange resin, A _R is large enough moisture content is high, high proton conductivity, high gas permeability. When _AR is less than 0.5 meq / g dry resin, the resistance of the ion exchange resin increases. When _AR exceeds 2.0 meq / g dry resin, the ether side chains become too large in the structure of the resin and it becomes difficult to maintain a solid state. Is inappropriate. In particular, it is preferably from 0.7 to 1.4 meq / g dry resin.

[0022] To supply smoothly the reaction gas to the catalyst from the gas phase, it is preferable moisture content with high ion-exchange resins, i.e. T _Q is lower ion exchange resin precursor covers the catalyst. By using a gas diffusion electrode having an ion-exchange resin having a low precursor T _Q , the fuel cell can stably obtain a high output.

In addition, during power generation, the electroosmotic water moves from the fuel electrode to the air electrode, and the ion exchange resin coating the catalyst tends to be dehydrated at the fuel electrode to increase the resistance. However, to prevent drying of the membrane, the gas to be supplied to the fuel electrode and the air electrode is usually humidified, water from the water vapor in the gas phase the use of T _Q low water content high ion exchange resin precursor The resistance of the ion exchange resin can be prevented from increasing even at the fuel electrode.

The catalyst and the ion exchange resin contained in the gas diffusion electrode of the present invention are expressed by weight ratio of catalyst: ion exchange resin =
The ratio of 0.40: 0.60 to 0.95: 0.05 is preferable from the viewpoint of electrode conductivity and water repellency. In addition,
In the case of a supported catalyst supported on a carrier such as carbon, the catalyst herein includes the weight of the carrier.

The gas diffusion electrode of the present invention can be formed by a known method such as spraying, coating, or filtering a liquid in which an ion exchange resin and a catalyst are dissolved or dispersed in a solvent (hereinafter, referred to as a liquid for forming an electrode). The electrodes may be formed directly on the ion exchange membrane, or may be formed in layers on a current collector made of carbon paper or the like and then joined to the ion exchange membrane.
Instead of carbon paper, a sheet in which a carbon layer made of carbon and fluororesin is formed on a carbon fiber woven fabric may be used. Alternatively, an electrode may be formed on a separately prepared flat plate and transferred to an ion exchange membrane. When the electrode is not formed directly on the ion-exchange membrane, a known hot pressing method and a bonding method (Japanese Patent Application Laid-Open Nos.
254420) and the like.

The preferred range of the viscosity of the above liquid for forming an electrode varies depending on the method of forming the electrode, and ranges from a dispersion of about several tens cP to a paste of about 20,000 cP.
A wide viscosity range can be used. In order to adjust the viscosity, the liquid for forming an electrode may contain a thickener or a diluting solvent. Ethylcellulose, methylcellulose or cellosolve-based thickeners can be used as the thickener, but it is desirable not to use it because a removal operation is required. As the diluting solvent, alcohols such as methanol, ethanol and isopropyl alcohol, fluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, water and the like can be used.

In the present invention, it is preferable that a water-repellent agent is contained in the electrode, particularly in the air electrode from which water is generated, because it is possible to suppress clogging (flooding) of the electrode porous body due to condensation of water vapor. As the water repellent, for example, tetrafluoroethylene (hereinafter, referred to as PTFE), a tetrafluoroethylene / hexafluoropropylene copolymer, a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, or the like can be used. Further, a fluorine-containing resin that can be dissolved in a solvent is preferable because the electrode is easily water-repellent. The water repellent is preferably contained in the electrode in an amount of 0.01 to 30% by weight.

Although the membrane solid polymer electrolyte in the present invention is not particularly limited, it is preferably made of a resin having, for example, a sulfonic acid group, a phosphoric acid group or a phenolic hydroxyl group as a cation exchange group. Specifically, for example, it is preferable to use a fluorinated cation exchange resin having the same structure as that of the fluorinated carbon sulfonic acid type ion exchange resin in the present invention. It is formed into a membrane by a known method such as press molding, roll molding, or extrusion molding, and is subjected to hydrolysis and acidification to obtain a membrane-shaped solid polymer electrolyte. Further, it can be obtained by a solvent casting method from a solution in which a fluorine-based cation exchange resin is dissolved in a solvent such as alcohol.

Further, the membrane solid polymer electrolyte may be made of an ion exchange resin such as a hydrocarbon resin having a sulfonic acid group or a phosphonic acid group or a partially fluorinated hydrocarbon resin. Specifically, for example, a resin obtained by graft-polymerizing styrene onto an ethylene / tetrafluoroethylene copolymer and then introducing a sulfonic acid group into a polymerization unit based on styrene, a resin obtained by sulfonating polysulfone or polyetheretherketone, or the like. It may be composed of

Further, the membrane solid polymer electrolyte may be formed of a membrane in which the above cation exchange resin is combined with a reinforcing material. Examples of the reinforcing material include polyethylene, polytetrafluoroethylene, tetrafluoroethylene / perfluoro (propyl vinyl ether) copolymer, and tetrafluoroethylene / hexafluoropropylene copolymer. These reinforcing materials are used in the form of fibrils, woven fabrics, nonwoven fabrics and porous bodies.

The thickness of the membrane solid polymer electrolyte is, for example, 1
Those having a size of 0 to 300 μm are used. If the thickness is less than 10 μm, pinholes are likely to occur and a short circuit may occur. If the thickness is more than 300 μm, the electric resistance of the membrane increases, and the output characteristics of the fuel cell deteriorate. In particular, a thickness of 20 to 100 μm is preferable.

[0032]

EXAMPLES The present invention will be described in detail with reference to Examples (Examples 1 to 3) and Comparative Examples (Examples 4 and 5), but the present invention is not limited to these.

The stainless steel autoclave, and azobisisobutyronitrile as CF ₂ ClCF ₂ CHClF and a polymerization initiator as a polymerization solvent, CF ₂ = CF-O
CF ₂ CF (CF ₃₎ were charged and -OCF ₂ CF ₂ SO ₂ F. Next, after the inside of the autoclave was sufficiently degassed with liquid nitrogen, CF ₂ = CF ₂ was charged and solution polymerization was started at 70 ° C. During the polymerization, the pressure inside the autoclave was kept constant by introducing CF ₂ = CF ₂ from outside the system. 10
After a period of time, unreacted CF ₂ = CF ₂ is purged to terminate the polymerization, and the obtained polymer solution is aggregated with methanol, washed and dried to obtain CF ₂ = CF ₂ / CF ₂ = CF-OCF ₂ C.
F (CF ₃₎ to give the -OCF ₂ CF ₂ SO ₂ F copolymer.

After measuring the T _Q of the copolymer, the copolymer is hydrolyzed in a mixed aqueous solution containing 30% by weight of dimethyl sulfoxide and 15% by weight of KOH, washed with water, and then immersed in 1N hydrochloric acid. Thus, a perfluorocarbon sulfonic acid type ion exchange resin was obtained.

By adjusting the amount of the polymerization initiator, the concentration of the raw materials in the charged solution, and the pressure during the polymerization, T _Q
4 ion exchange resins having the values shown in Table 1 were synthesized. These ion exchange resins, both A _R 1.0
Metric equivalents / gram dry resin.

Next, a catalyst comprising platinum supported on carbon black powder so as to contain 40% by weight of platinum and the ion exchange resin obtained as described above were mixed in a weight ratio of 3: 1.
Thus, a catalyst paste for forming an air electrode and a fuel electrode was prepared.

As the current collector for both the fuel electrode and the air electrode, carbon paper (trade name: TGP-H-060, manufactured by Toray Industries, Inc.) was used after water-repellent treatment. As a gas diffusion layer,
A mixture consisting of 60% by weight of carbon black powder and 40% by weight of PTFE powder is kneaded and then rolled to a thickness of 100%.
A sheet in which PTFE was fibrillated with a μm of 70% porosity was used.

For both the fuel electrode and the air electrode, a catalyst paste was applied to the gas diffusion layer and dried to form an electrode sheet. At this time, the catalyst paste was applied such that the amount of platinum contained in the electrode sheet was 0.5 mg / cm ² . The electrode sheet was cut out to have an effective electrode area of 28 cm ^{2 for} both the fuel electrode and the air electrode.

As a solid polymer electrolyte, a perfluorocarbon sulfonic acid type ion exchange membrane (trade name: Flemion H)
R, manufactured by Asahi Glass Co., Ltd., ion exchange capacity: 1.1 meq / g dry resin, film thickness: 50 μm) was used. The air electrode and the fuel electrode are opposed to each other with the surface coated with the catalyst paste facing inward, and the electrode sheet and the membrane are joined by hot pressing with the ion exchange membrane sandwiched therebetween,
A joined body was produced. The temperature of the hot press in Examples 1 to 5 is
It is shown in Table 1.

The above joined body was placed in a measuring cell sandwiched between two carbon papers as current collectors, and was placed under normal pressure (1 at.
a) The gas was continuously operated at a constant current of 0.5 A / cm ^{2 at} a hydrogen / air system at a cell temperature of 80 ° C., and the output voltage of the cell was measured. Table 1 shows the results.

[0041]

[Table 1]

[0042]

According to the gas diffusion electrode of the present invention, since the gas can be easily dissolved and diffused in the ion exchange resin coating the catalyst in the electrode, the gas is quickly supplied onto the catalyst. Therefore, an increase in voltage loss due to a decrease in gas concentration at the reaction site of the electrode is suppressed. Therefore, a solid polymer electrolyte fuel cell capable of obtaining high output stably for a long period of time is obtained.

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Claims (5)

[Claims] Claims: 1. An ion exchange resin comprising a catalyst and a fluorinated carbon sulfonic acid type ion exchange resin,
A solid obtained by subjecting a precursor of the ion-exchange resin having —SO ₂ F to a terminal to hydrolysis and acidification, and wherein the precursor has a melt extrusion temperature of 80 to 170 ° C. Gas diffusion electrode for polymer electrolyte fuel cells. 2. The gas diffusion electrode for a solid polymer electrolyte fuel cell according to claim 1, wherein the ion exchange resin is a dry resin having an ion exchange capacity of 0.5 to 2.0 meq / g. 3. A gas diffusion electrode containing a catalyst and an ion exchange resin is used as a fuel electrode and an air electrode. The fuel electrode is provided on one surface of the solid polymer electrolyte membrane and the air electrode is provided on the other surface. However, in the solid polymer electrolyte fuel cells arranged respectively, the ion exchange resin contained in at least one of the air electrode and the fuel electrode has -SO ₂ F
The precursor of the ion-exchange resin having is obtained by hydrolysis and acidification, and the precursor is a fluorocarbon sulfonic acid-type ion-exchange resin having a melt extrusion temperature of 80 to 170 ° C. A solid polymer electrolyte fuel cell comprising: 4. The solid polymer electrolyte fuel cell according to claim 3, wherein said ion exchange resin is a dry resin having an ion exchange capacity of 0.5 to 2.0 meq / g. 5. The solid polymer electrolyte fuel cell according to claim 3, wherein both the air electrode and the fuel electrode contain the ion exchange resin.