JPH09219206A - Electrochemical element - Google Patents

Abstract

(57) Abstract: Provided is an electrochemical device capable of stably increasing the output without causing an electrode to penetrate the membrane to cause a short circuit even if the thickness of the ion exchange membrane is reduced. An ion exchange membrane made of a fluorocarbon polymer having a sulfonic acid group or a carboxylic acid group containing non-conductive pillar particles is used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrochemical device such as a solid polymer electrolyte fuel cell and an air-zinc battery.

[0002]

2. Description of the Related Art A hydrogen / oxygen fuel cell has been attracting attention as a power generation system that has a reaction product of only water in principle and has little adverse effect on the global environment. Above all,
The solid polymer electrolyte type using a perfluorosulfonic acid type cation exchange membrane has been able to achieve higher output density due to the rapid progress of research in recent years, and has features such as compact size and low temperature operation, and an in-vehicle power supply. It is highly expected that it will be put into practical use.

Further, in an air-zinc battery or the like, one using an ion-exchange resin film as a separator has already been put into practical use.

As the electrolyte membrane used in the solid polymer electrolyte fuel cell, a proton conductive ion exchange membrane having a thickness of 50 to 200 μm is usually used, and in particular, an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group. Has excellent basic characteristics and has been widely studied.

In this type of fuel cell, gas diffusion electrode layers are formed on both surfaces of an electrolyte membrane, and hydrogen is supplied as fuel and oxygen or air serving as an oxidant is supplied to each electrode to generate electricity. Is. In order to further improve the output characteristics, studies have been made on improving the electrocatalytic activity, improving the characteristics of the gas diffusion electrode, and reducing the resistance loss. The resistance loss includes conductor resistance loss, contact resistance loss, and film resistance loss.

[0006]

The resistance of the ion exchange membrane tends to be smaller as the water content of the membrane is higher, the ion exchange group concentration in the membrane is higher, and the thickness of the membrane is thinner. The water content of the membrane changes depending on the operating conditions such as the humidity of the supplied gas, and the concentration of ion-exchange groups available in the ion-exchange membrane naturally has a certain limit. It is expected to reduce membrane resistance loss by using an exchange membrane.

However, when the ion-exchange membrane thickness is made thin, the strength of the membrane itself is reduced, and an electrode short circuit occurs due to the electrode penetrating the ion-exchange membrane during the production of the electrode-membrane assembly or during the use of the fuel cell. There is such a problem.

In the case of a conventional cellophane film, the separator of the air-zinc battery has a thickness of 100 to 200 μm.
When the ion-exchange membrane is used, it can be made thinner than a conventional separator film such as cellophane, but this case also has the same problem as above.

Porous polytetrafluoroethylene (P) is used as a method for improving the dimensional stability and mechanical strength of an ion exchange membrane when it is thinned to reduce the membrane resistance.
An ion exchange membrane in which a TFE film is impregnated with a perfluoro ion exchange resin and reinforced has been proposed (Japanese Patent Publication No. 5-75835, Japanese Patent Publication No. 6-10277, etc.), but it is not always sufficient.

The present invention has been made to solve the above problems, and it is an object of the present invention to prevent a short circuit between electrodes, which is caused by the electrodes penetrating an ion exchange membrane.

[0011]

The present invention provides an electrochemical device in which an anode is placed on one side of an ion exchange membrane made of a fluorocarbon polymer and a cathode is placed on the other side of the ion exchange membrane.
The electrochemical element is characterized in that the ion exchange membrane contains non-conductive pillar particles.

The thickness of the ion exchange membrane used in the electrochemical device of the present invention is not particularly limited, but the effect is particularly large in an ion exchange membrane having a thickness of 100 μm or less, particularly 5 to 50 μm.

The pillar particles contained in the ion exchange membrane in the present invention mean particles which retain the thickness of the ion exchange membrane due to the presence thereof even when the ion exchange membrane is softened and function as so-called pillars. To do. The material of the pillar particles is non-conductive in order to prevent short circuit of the electrodes, preferably hydrophilic, and more preferably those having corrosion resistance even under strongly acidic conditions such as perfluorosulfonic acid. is there.

Examples thereof include oxides such as silica, titania and alumina, composite oxides such as spinel and perovskite, glasses such as silicate glass, carbides such as silicon carbide and titanium carbide, silicon nitride and boron nitride. Nitride of
A plastic such as a fluororesin such as nylon or PTFE is preferable.

The shape of the pillar particles may be any, and spherical particles are preferable in that a uniform shape can be easily obtained. The size of the pillar particles changes depending on the thickness of the ion exchange membrane,
10 to 90% of the thickness of the ion exchange membrane, especially 30 to 70
% Is preferable. If it is smaller than the above range, a sufficient effect of preventing electrode short-circuiting cannot be obtained, while if it is larger, defects such as pores penetrating the ion exchange membrane are likely to occur, which is not preferable.

The above-mentioned ion exchange membrane contains 5 to 5 pillar particles.
It is preferably contained in an amount of 50% by volume, particularly 10 to 40% by volume. If it is less than the above range, the effect of adding pillar particles is reduced due to the small amount of pillar particles present in the membrane, and a sufficient electrode short-circuit prevention effect cannot be obtained. Since the content ratio decreases, the mechanical strength of the ion exchange membrane decreases and the membrane resistance increases, which is not preferable.

The ion exchange membrane in the present invention is preferably made of a fluorocarbon polymer having a cation exchange group such as a sulfonic acid group or a carboxylic acid group. As such a fluorocarbon polymer, CF ₂ =
CF ₂ and _{CF 2 = CF- (OCF 2 CFX} ) m -O p -
(CF _{2) n} -A (wherein, m is 0-8 integer, n represents 0
An integer of 12, p is 0 or 1, X is F or CF ₃ , A
Represents an SO ₃ H group, a COOH group or a precursor functional group thereof. ) A fluorocarbon copolymer with a fluorovinyl compound represented by

As a preferred example of the above fluorovinyl compound, the compound of Chemical formula 1 is mentioned. R represents an alkyl group.

[0019]

Embedded image CF ₂ ═CFO (CF ₂ ) _1-8 —SO ₂ F, CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _{1-8
-SO 2 F, CF 2 = CF} (CF 2) 0-8 -SO 2 F, CF 2 = CF (OCF 2 CF (CF 3)) 1-5 - (CF
_{2) 2 -SO 2 F, CF} 2 = CFO (CF 2) 1-8 -CO 2 R, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) 1-8
_{-CO 2 R, CF 2 = CF} (CF 2) 0-8 -CO 2 R, CF 2 = CF (OCF 2 CF (CF 3)) 1-5 - (CF
_{2) 2} -CO ₂ R.

The fluorocarbon copolymer is
It may be a copolymer containing a perfluoroolefin such as hexafluoropropylene or chlorotrifluoroethylene, or a third component such as perfluoroalkyl vinyl ether.

The ion exchange membrane can also be reinforced with a fibril, fibrous or non-woven fluorocarbon polymer.

Various methods can be adopted as the method for producing the ion exchange membrane containing the pillar particles in the present invention. For example, a mixture of a fluorocarbon polymer having a sulfonic acid type functional group or a carboxylic acid type functional group and a pillar particle is extruded by heating to obtain a film-shaped molded body, and then a sulfonic acid is prepared with an aqueous solution of alkali hydroxide or the like. Examples of the method include hydrolyzing a functional group of carboxylic acid type or a functional group of carboxylic acid type, further washing with water, and then treating with an inorganic acid such as hydrochloric acid.

As another method, a solvent is evaporated from a dispersion liquid in which pillar particles are dispersed in a solution or dispersion liquid of the above-mentioned fluorocarbon polymer having a sulfonic acid type functional group or a carboxylic acid type functional group to form a film. After obtaining the molded product of (1), the sulfonic acid type functional group or the carboxylic acid type functional group is hydrolyzed with an aqueous solution of alkali hydroxide, further washed with water, and then treated with an inorganic acid such as hydrochloric acid.

As still another method, the sulfonic acid type functional group or carboxylic acid type functional group of the fluorocarbon polymer having the above sulfonic acid type functional group or carboxylic acid type functional group is hydrolyzed with an aqueous solution of alkali hydroxide or the like. Then, after further washing with water, the solvent is evaporated from the dispersion liquid in which the pillar particles are dispersed in the solution obtained by dissolving the fluorocarbon sulfonic acid polymer or fluorocarbon carboxylic acid polymer obtained by treating with an inorganic acid such as hydrochloric acid. Examples thereof include a method of obtaining a film-shaped molded product.

The ion exchange membrane thus obtained contains pillar particles almost uniformly throughout the membrane. However, in the present invention, the pillar particles do not necessarily have to be uniformly present in the entire film, and the pillar particles are allowed to be present in a layered form along a direction perpendicular to the thickness direction of the film, which is present as a so-called pillar particle-containing layer. May be. Examples of such an ion exchange membrane include a membrane having a pillar particle-containing layer on one side, a three-layer membrane in which a pillar particle-containing layer is sandwiched by two ion exchange membranes not containing pillar particles, and an ion exchange membrane containing pillar particles. There are multi-layer membranes of layers and ion-exchange membrane layers that do not contain pillar particles.

In such a multi-layer membrane, an ion exchange membrane layer containing pillar particles and an ion exchange membrane layer containing no pillar particles are separately formed into films, preferably 12
It can be produced by adhering and laminating at 0 to 230 ° C. and 0.5 to 30 kg / cm ^{2 by a} hot pressing method or the like.

After forming the ion-exchange membrane layer containing the pillar particles on one surface of the ion-exchange membrane layer not containing the pillar particles by a coating method, a spray method, a printing method or the like, if necessary, further pillar particles are further formed. It is also possible to stack the ion-exchange membrane layer-containing pillar-particle-containing layers that do not contain the so as to sandwich them and to adhere them by a hot pressing method or the like.

When the electrochemical device of the present invention is, for example, a solid polymer electrolyte fuel cell, a gas diffusion electrode is bonded to the surface of the ion exchange membrane according to a commonly known method, and then a carbon paper or the like is collected. An electric body is attached. An ion exchange membrane having an electrode and a current collector on its surface is
A fuel cell is assembled by being sandwiched between a pair of electrically conductive chamber frames in which a groove serving as a passage for fuel gas (hydrogen gas or the like) or oxidant gas (oxygen gas or air or the like) is formed.

The gas diffusion electrode used in the above solid polymer electrolyte fuel cell is not particularly limited. For example, a porous sheet in which platinum-supporting carbon black powder is held by a water-repellent resin binder such as PTFE can be used, and the porous sheet is made of a sulfonic acid type perfluorocarbon polymer or fine particles coated with the polymer. May be included. This porous sheet is bonded as a gas diffusion electrode to the ion exchange membrane, which is a solid polymer electrolyte, by a hot pressing method or the like.

In another example, on both sides or one side of carbon paper or the like forming an ion exchange membrane or a current collector,
A layer of a gas diffusion electrode composed of a mixture of platinum-carrying carbon and a sulfonic acid type perfluorocarbon polymer is formed by a coating method, a spray method, a printing method, or the like, and these are preferably 120 to 350 ° C. and ² to 100 kg / cm ² . Then, the ion-exchange membrane or the current collector having the electrode layer on the surface can be produced by bringing them into close contact with each other by a hot pressing method or the like.
Next, the current collector or the ion exchange membrane layer is bonded to the ion exchange membrane layer or the current collector, respectively.

When the electrochemical device of the present invention is an air-zinc battery or the like, it can be used by replacing the conventionally used separator with the ion exchange membrane of the present invention. For example, in the case of an air-zinc battery, a diffusion sheet made of cellulose for diffusing oxygen from air holes to a catalyst layer in a cathode (positive electrode) container made of stainless steel → a water repellent film made of porous PTFE etc. → activated carbon , A cathode catalyst layer made of a carbon material having a large specific surface area such as carbon black or a material having a catalyst component such as manganese and cobalt supported on the carbon material, and a separator made of the ion exchange membrane of the present invention To be done. On the other hand, a zinc anode made of zinc powder, a gelling agent and an electrolytic solution is housed in a stainless steel anode (negative electrode) container. Then, the air-zinc battery is formed by sealing the cathode container and the anode container via a gasket.

[0032]

In the present invention, a good electrochemical device can be obtained in which a short circuit between electrodes does not occur even if the thickness of the ion exchange membrane is reduced to reduce the membrane resistance loss. The mechanism is as follows. Conceivable.

An ion exchange membrane made of a fluorocarbon sulfonic acid polymer or a fluorocarbon carboxylic acid polymer containing no pillar particles is softened by an increase in temperature or water content, and therefore, it is used for forming an electrode-membrane assembly by hot pressing or the like. The film thickness is further reduced by the pressure and the tightening pressure of the fuel cell chamber frame, the cell anode and cathode containers, and the gas diffusion electrode formed on the surface of the ion exchange membrane and the cell anode and cathode that contact both sides of the ion exchange membrane are membranes. By digging into, finally a short circuit of the electrodes occurs.

On the other hand, since the ion exchange membrane of the present invention contains non-conductive pillar particles, the fluorocarbon sulfonic acid polymer or fluorocarbon carboxylic acid polymer is softened under the operating conditions of the electrochemical device. Also, it does not collapse below the particle size of the non-conductive pillar particles, and the short circuit of the electrodes can be prevented. For this reason, the thickness of the ion exchange membrane can be reduced without causing a problem due to a short circuit of the electrodes, and as a result, the membrane resistance loss is reduced and the electrochemical element can achieve a high output.

[0035]

EXAMPLES Specific embodiments of the present invention will be described below with reference to Examples (Example 1,
Example 3) and comparative examples (Examples 2 and 4) will be described.
The present invention is not limited to these.

[Example 1] CF ₂ = CF ₂ and CF ₂ = CFO
Ion exchange capacity of 1.1 meq / g dry resin copolymer particles consisting of a copolymer with CF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F, 30% by weight of dimethyl sulfoxide
Was hydrolyzed in a mixed aqueous solution of 15% by weight of caustic potash, washed with water, and immersed in 1N hydrochloric acid. Next, the particles were washed with water and dried at 60 ° C. for 1 hour, and the obtained copolymer particles were dissolved in ethanol to prepare an ethanol solution containing 5% by weight of the copolymer.

Alumina particles having a particle size of 7 μm were dispersed in this solution, the dispersion was coated on a glass plate, air-dried at room temperature for 1 hour, and further dried at 80 ° C. for 1 hour to obtain a thickness of 10
An ion exchange membrane for a fuel cell having a thickness of μm was obtained. This ion exchange membrane contained 30% by volume of alumina uniformly throughout the membrane.

On both sides of this ion exchange membrane, a gas diffusion electrode (Pt carrying amount: 0.5 mg / cm ² ) having a thickness of about 150 μm and consisting of 60 parts by weight of carbon black supporting Pt and 40 parts by weight of PTFE was placed at a temperature of 150 ° C. , Pressure 10kg /
Bonding was performed by the hot pressing method under the condition of cm ² for 10 seconds.

This electrode-membrane assembly was incorporated into a cell for measuring battery performance, and humidified hydrogen and air were supplied to the anode and the cathode at a cell temperature of 80 ° C., and a discharge test was conducted at a current density of 0.5 A / cm ^2. I went. The terminal voltage is 0.
It was 69V.

[Example 2] An electrode-membrane assembly was obtained in the same manner as in Example 1 except that the alumina particles were not used. This electrode-membrane assembly was incorporated in a cell for measuring battery performance, and a discharge test was conducted in the same manner as in Example 1, but the open electromotive force was extremely low and the voltage could not be extracted. When the electrode-membrane assembly was examined, a short circuit of the electrode occurred inside the assembly.

[Example 3] CF ₂ = CF ₂ and CF ₂ = CFO
Ion exchange capacity of 1.0 meq / g copolymer of CF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F, 80% by volume of dry resin copolymer, and silica particles having a particle size of 10 μm A 20% by volume mixture was extruded at 220 ° C to form a film having a thickness of 20
A μm film was obtained.

The above film was treated with dimethyl sulfoxide 3
Hydrolysis was performed in a mixed aqueous solution of 0% by weight and 15% by weight of caustic potash, washed with water, and immersed in 1N hydrochloric acid. Then, it was washed with water, and its four sides were restrained by dedicated jigs and then dried at 60 ° C. for 1 hour to obtain an ion exchange membrane for a fuel cell. Gas diffusion electrodes were bonded to both sides of this ion exchange membrane in the same manner as in Example 1.

This electrode-membrane assembly was incorporated into a cell for measuring battery performance, and humidified hydrogen and air were supplied to the anode and the cathode at a cell temperature of 80 ° C., and continuous discharge was performed at a current density of 0.5 A / cm ^2. The test was conducted. The initial terminal voltage was 0.68 V, and the decrease in the terminal voltage after 1000 hours was about 5%.

Example 4 An ion exchange membrane having a thickness of 20 μm was obtained in the same manner as in Example 3, except that silica particles were not used. After hydrolyzing this ion exchange membrane in the same manner as in Example 3, the gas diffusion electrode was further joined in the same manner as in Example 3 to obtain an electrode-membrane assembly.

This electrode-membrane assembly was incorporated into a cell for measuring battery performance, and a continuous discharge test was conducted in the same manner as in Example 1. The initial terminal voltage was 0.69 V, which was equivalent to that of Example 3, but after about 500 hours, the terminal voltage drastically dropped, and discharge at 0.5 A / cm ² became impossible. When the electrode-membrane assembly was examined, a short circuit of the electrode occurred inside the assembly.

[0046]

INDUSTRIAL APPLICABILITY The electrochemical device of the present invention is effective in short-circuiting caused by the non-conductive pillar particles contained in the ion exchange membrane, which softens the ion exchange membrane and causes the electrode to penetrate through the membrane. The thickness of the ion exchange membrane can be reduced because it can be effectively prevented. Further, by using hydrophilic particles as the pillar particles, the water content in the film can be kept high. When the water content is high, the conductivity of the membrane is improved, and the membrane resistance loss can be made extremely small in combination with the thin film thickness.
Further higher output of the electrochemical device can be achieved.

Furthermore, when the pillar particles are hydrophilic, it has the effect of preventing the membrane from drying, and in the case of the solid polymer electrolyte fuel cell, it is less susceptible to the change in humidity of the outside of the ion exchange membrane, Operation of the fuel cell becomes easy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinji Terazono 1150, Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Central Research Institute, Asahi Glass Co., Ltd. (72) Haruhisa Miyake 1150, Hazawa-machi, Kanagawa-ku, Yokohama Kanagawa (72) Inventor Tetsuji Shimohira, 1150, Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd.

Claims (3)

[Claims] 1. An electrochemical element in which an anode is placed on one side of a fluorocarbon polymer ion exchange membrane and a cathode is placed on the other side of the ion exchange membrane, and the ion exchange membrane contains non-conductive pillar particles. An electrochemical device characterized by: 2. The ion exchange membrane contains 5 to 50% by volume of non-conductive pillar particles, and the particle diameter of the non-conductive pillar particles is 10 to 90% of the thickness of the ion exchange membrane. 1 electrochemical device. 3. The electrochemical device according to claim 1, wherein the ion exchange membrane is made of a perfluorocarbon polymer having a sulfonic acid group, the anode and the cathode are gas diffusion electrodes, and the electrochemical device is a fuel cell.