JPH11135135A - Electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain drying of an ion exchange membrane and prevent short- circuit of an electrode by containing non-conductive pillar particles in an ion exchange membrane consisting of a fluorocarbon polymer having a phosphonic acid and allocating a positive electrode, in contact with one side face thereof and negative electrode in contact with the other side face. SOLUTION: On both side faces of an ion-exchange membrane, consisting of a fluorocarbon polymer having a phosphonic acid group, a positive electrode and a negative electrode such as a gas dispersion electrodes are disposed respectively, and a slide poly electrolyte type fuel cell is obtained. In this electrochemical element, in the above ion-exchange membrane, non-conductive, hydrophilic, acid resistant pillar particles of 10 to 90% in particle size of thickness of the ion exchange membrane, and preferably about 30 to 70% is made to be contained in 5 to 50% by volume, preferably 10 to 40% uniformly. As the pillar particles, oxide such as silica, a composite oxide such as spinel, and glass such as silicate are preferred. Thereby, even if an ion exchange membrane is thinned, penetration of an electrode can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 As a typical polymer electrolyte fuel cell using hydrogen as a fuel, a type using a fluororesin-based ion exchange membrane as a solid electrolyte has been conventionally known.
It can be operated from room temperature, has a high output density, and has the characteristic that only water is generated in principle. For this reason, with increasing social demands for energy and global environmental issues in recent years, great expectations have been placed. In addition, air
In a zinc battery or the like, a separator using an ion-exchange resin film as a separator has already been put to practical use.

As a solid electrolyte used in a polymer electrolyte fuel cell, a proton-conducting ion exchange membrane having a thickness of 50 to 200 μm is usually used. In particular, an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group is used. Excellent in basic characteristics and widely studied.

A polymer electrolyte fuel cell using this ion exchange membrane operates while supplying a humidified gas in order to maintain the conductivity of the ion exchange membrane. Therefore, when the operating temperature is set to 100 ° C. or more at normal pressure, the vapor pressure of water sharply increases, the ion exchange membrane dries, the membrane resistance increases, and the partial pressure of the reaction gas decreases, and the battery performance decreases. Therefore, it is operated under a temperature condition of less than 100 ° C. at normal pressure.

[0005] This type of fuel cell generates gas by forming gas-diffusing electrode layers on both sides of an electrolyte membrane and supplying hydrogen as a fuel and oxygen or air as an oxidant to each electrode. It is. For the purpose of further improving the output characteristics, studies have been made on improving the electrode catalyst activity, improving the characteristics of the gas diffusion electrode, reducing the resistance loss, and the like. The resistance loss includes a conductor resistance loss, a contact resistance loss, and a film resistance loss.

[0006]

As described above, a polymer electrolyte fuel cell using an ion exchange membrane is operated by supplying a humidified gas. On the other hand, when water is generated by the reaction at the air electrode and condensed in the air electrode (so-called flooding), oxygen, which is a reactant, cannot be supplied sufficiently and battery performance deteriorates. Need to be quickly removed. As described above, in order to obtain a cell output with the polymer electrolyte fuel cell, the opposing operations of humidifying the system and removing water from the system must be performed in a well-balanced manner.

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

However, when the thickness of the ion exchange membrane is reduced, the strength of the membrane itself is reduced, and the electrode is short-circuited when the electrode penetrates the ion exchange membrane during production of the electrode-membrane assembly or during use of the fuel cell. There is a problem.

When the separator of an air-zinc battery or the like is a conventional film such as cellophane, the thickness is 100 to 200 μm.
m, and when an ion exchange membrane is used, it can be made thinner than a conventional separator film such as cellophane. However, in this case, the same problem as described above occurs.

As a method for improving the dimensional stability and mechanical strength of an ion-exchange membrane when the ion exchange membrane is made thinner to reduce the membrane resistance, porous polytetrafluoroethylene (P)
Ion exchange membranes in which a TFE) film is impregnated with a perfluoro-based ion exchange resin and reinforced have been proposed (Japanese Patent Publication No. 5-75835, Japanese Patent Publication No. 6-10277, etc.), but are not always sufficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In particular, it is an object of the present invention to suppress an increase in membrane resistance due to drying of an ion exchange membrane and to prevent a short circuit of an electrode caused by the penetration of an electrode through the ion exchange membrane. Aim.

[0012]

The present invention relates to an electrochemical device comprising an ion exchange membrane comprising a fluorocarbon polymer having a phosphonic acid group, wherein an anode is arranged on one side and a cathode is arranged on the other side. An electrochemical device wherein 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 when it is 100 μm or less, particularly 5 to 50 μm, the effect of preventing short-circuiting of the electrodes is particularly large and is preferable.

In the present specification, the term "pillar particles" refers to pillars that maintain the thickness of an ion exchange membrane due to its presence even when the ion exchange membrane is softened.
Refers to particles that function as The pillar particles in the present invention are preferably non-conductive, hydrophilic, and have corrosion resistance even in the presence of a strong acid such as perfluorophosphonic acid for the purpose of preventing a short circuit of the electrode.

Specifically, oxides such as silica, titania, and alumina; composite oxides such as spinel and perovskite; glass such as silicate glass; carbides such as silicon carbide and titanium carbide; silicon nitride; Preference is given to nitrides, plastics such as nylon and fluororesins such as PTFE. Among them, the above oxides, composite oxides and glasses are particularly preferred.

The pillar particles may have any shape, but are preferably spherical in that a uniform shape can be easily obtained. The size of the pillar particles depends on the thickness of the ion exchange membrane,
10 to 90% of the thickness of the ion exchange membrane, especially 30 to 70%
%. When the diameter is smaller than the above range, a sufficient effect of preventing short-circuiting of the electrode cannot be obtained. The particle size of the pillar particles is specifically 0.5 to 50 μm, and particularly preferably 1 to 30 μm.

In the above-mentioned ion exchange membrane, the number of pillar particles is 5 to 5.
The content is preferably 50% by volume, particularly preferably 10 to 40% by volume. When the content ratio is smaller than the above range, the effect of adding the pillar particles is reduced due to the small amount of the pillar particles in the film, and a sufficient electrode short-circuit preventing effect cannot be obtained. Is small, the mechanical strength of the ion exchange membrane is reduced and the membrane resistance is increased, which is not preferable. Further, it is preferable that the pillar particles are uniformly contained in the entire film.

The ion exchange membrane of the present invention comprises a fluorocarbon polymer having a phosphonic acid group. As the fluorocarbon polymer, CF ₂ ＝ CF— (OC
_{F 2 CFX) m -O p -} (CF 2) in _n -A (wherein, m is an integer of 0 to 8, n is from 0 to 12 integer, p is 0 or 1,
X represents a fluorine atom or a trifluoromethyl group, and A represents a phosphonic acid group (—PO ₃ H ₂ ) or a precursor functional group thereof. ) And CF ₂ ＣC
A copolymer of F ₂ is preferred.

Preferred examples of the above fluorovinyl compound include the following compounds. R and R 'represent an alkyl group, and R and R' may be the same alkyl group or different alkyl groups. The alkyl group preferably has 1 to 3 carbon atoms. Also, q and r are integers of 1 to 8, s is an integer of 0 to 8, t
Is an integer of 1 to 5.

[0020]

## STR1 ## _{CF 2 = CFO (CF 2)} q -PO 3 RR ', CF 2 = CFOCF 2 CF (CF 3) O (CF 2) r -
_{PO 3 RR ', CF 2 =} CF (CF 2) s -PO 3 RR', CF 2 = CF (OCF 2 CF (CF 3)) t - (CF
_{2) 2} -PO ₃ RR '.

The above fluorocarbon copolymer is
It may be a perfluoroolefin such as hexafluoropropylene or chlorotrifluoroethylene, or a copolymer containing a third component such as perfluoro (alkyl vinyl ether).

The ion exchange membrane may be reinforced with a fibril-like, fibrous or non-woven fabric fluorocarbon polymer. Various methods can be adopted as a method for producing an ion exchange membrane containing pillar particles. For example, a method in which a mixture of the fluorocarbon polymer having the phosphonic acid type functional group and the pillar particles is extrusion-molded to obtain a film-shaped molded body, and then the phosphonic acid type functional group is hydrolyzed with an aqueous solution of an inorganic acid or the like. Is mentioned.

As another method, a solvent is evaporated from a dispersion in which pillar particles are dispersed in a solution or dispersion of the fluorocarbon polymer having a phosphonic acid type functional group to obtain a film-shaped molded body. And a method of hydrolyzing a phosphonic acid-type functional group with an aqueous solution of an inorganic acid.

As still another method, a fluorocarbon polymer having a phosphonic acid group obtained by treating the above fluorocarbon polymer having a phosphonic acid type functional group with an aqueous solution of an inorganic acid or the like and hydrolyzing the phosphonic acid type functional group can be used. There is a method in which a solvent is evaporated from a dispersion in which pillar particles are dispersed in a solution in which a polymer is dissolved in a solvent to obtain a film-shaped molded body.

The ion exchange membrane obtained as described above contains pillar particles almost uniformly throughout the membrane. However, in the present invention, the pillar particles do not necessarily need to exist uniformly in the entire film, but exist as a so-called pillar particle-containing layer in which pillar particles are present in a layer along a direction perpendicular to the thickness direction of the film. You may. Examples of such an ion exchange membrane include a membrane having a pillar particle-containing layer on one side, a multilayer film having a three-layer structure in which a pillar particle-containing layer is sandwiched between two ion exchange membranes not containing pillar particles, and a pillar particle. There is a multi-layer membrane of an ion exchange membrane containing the ion exchange membrane and an ion exchange membrane not containing the pillar particles.

Such a multilayer membrane is formed by separately forming an ion exchange membrane containing pillar particles and an ion exchange membrane not containing pillar particles into a film.
It can be manufactured by closely contacting and laminating at 0 to 230 ° C. and 0.5 to 30 kg / cm ^{2 by a} hot press method or the like.

After forming an ion-exchange membrane layer containing pillar particles on one side of the ion-exchange membrane containing no pillar particles by a coating method, a spraying method, a printing method or the like, if necessary, further forming another pillar particle. Can be produced by laminating ion-exchange membranes containing no particles so as to sandwich the pillar particle-containing layer and bringing them into close contact by a hot press 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 generally known method, and then a current collector such as carbon paper is collected. The body is attached. The ion exchange membrane having the electrodes and the current collector on its surface is formed on a pair of conductive chamber frames in which grooves serving as passages for a fuel gas (eg, hydrogen gas) or an oxidizing gas (eg, oxygen gas or air) are formed. By being sandwiched, it is assembled as a fuel cell.

The gas diffusion electrode used in the solid polymer electrolyte fuel cell is not particularly limited. For example, a porous sheet in which platinum-supported carbon black powder is held by a water-repellent resin binder such as PTFE can be used, and the porous sheet is coated with a perfluorocarbon polymer having a phosphonic acid group or the polymer. It may contain fine particles.
This porous sheet is bonded to the ion exchange membrane as a solid polymer electrolyte by a hot press method or the like as a gas diffusion electrode.

As another method of manufacturing the gas diffusion electrode, platinum-supported carbon is applied to both sides or one side of a carbon paper or the like forming an ion exchange membrane or a current collector by a coating method, a spraying method, a printing method, or the like. To form a layer of a gas diffusion electrode made of a mixture with a perfluorocarbon polymer having a phosphonic acid group or a sulfonic acid group, preferably at 120 to 350 ° C. and 2 to 100 kg / cm.
There is a method of hot pressing in ² , whereby an ion exchange membrane or a current collector having a gas diffusion electrode layer on the surface can be manufactured. The current collector having the gas diffusion electrode layer is further joined to the ion exchange membrane with the gas diffusion electrode layer facing the ion exchange membrane.

When the electrochemical element of the present invention is an air-zinc battery or the like, it can be used by replacing a conventionally used separator with the ion exchange membrane of the present invention. For example, in the case of an air-zinc battery, 1) a diffusion paper made of cellulose for diffusing oxygen from an air hole to the catalyst layer, and 2) a repellent material made of porous PTFE or the like in a cathode (positive electrode) container made of stainless steel. Water film; 3) a cathode catalyst layer comprising a carbon material having a large specific surface area such as activated carbon and carbon black; or a material in which a catalyst component such as manganese or cobalt is carried on the carbon material; 4) an ion exchange membrane of the present invention. It is constituted by being accommodated in the order of the separator. On the other hand, a stainless steel anode (negative electrode) container contains a zinc anode made of zinc powder, a gelling agent and an electrolytic solution. Then, the cathode container and the anode container are sealed via a gasket to form an air-zinc battery.

[0032]

In the present invention, the use of an ion exchange membrane comprising a fluorocarbon polymer having a phosphonic acid group (hereinafter, referred to as a phosphonic acid type membrane) enables water control for preventing drying in the ion exchange membrane of a fuel cell. Becomes easier. The reason for this is not clear, but is considered as follows.

The ion exchange group of a conventional sulfonic acid group-containing fluorocarbon polymer having a sulfonic acid group (hereinafter referred to as sulfonic acid type membrane) has a monovalent ion exchange group, whereas the phosphonic acid type membrane has a monovalent ion exchange group. Is divalent. Therefore, a phosphonic acid type membrane having a high ion exchange capacity can be easily obtained. In ion exchange membranes,
The higher the ion exchange capacity, the higher the water content. Therefore, even under conditions in which the ion exchange membrane is easily dried, the phosphonic acid type membrane can maintain a higher water content than the sulfonic acid type membrane, and can suppress an increase in membrane resistance. That is, even if the supply of the humidifying gas is insufficient, the change in the film resistance is small, and thus it is considered that a stable output voltage can be obtained.

In the present invention, a good electrochemical element can be obtained without causing a short circuit between electrodes even if the film thickness of the ion exchange membrane is reduced in order to reduce the membrane resistance loss. It is thought to be.

Since the perfluoro-based ion exchange membrane containing no pillar particles is softened by an increase in temperature or water content, the molding pressure of an electrode-membrane assembly such as a hot press, the anode of a fuel cell chamber frame or a cell, and the like. The film thickness is reduced by the clamping pressure by the cathode container. Further, the gas diffusion electrode formed on the surface of the ion exchange membrane and the anode and the cathode of the battery in contact with both sides of the ion exchange membrane bite into the membrane, and eventually the electrodes are short-circuited.

On the other hand, since the ion exchange membrane of the present invention contains non-conductive pillar particles, even if the fluorocarbon polymer having a phosphonic acid group is softened, the ion exchange membrane will not be crushed below the particle size of the pillar particles. In addition, it is possible to prevent a short circuit of the electrode. Further, the phosphonic acid type membrane in the present invention,
Since it is harder to soften than the sulfonic acid type membrane, this is also effective for preventing short circuit of the electrode. Therefore, the thickness of the ion exchange membrane can be reduced without causing a problem due to the short circuit of the electrode, and as a result, the membrane resistance loss is reduced, and a high output of the electrochemical element is achieved.

[0037]

The present invention will be described in more detail with reference to Examples (Examples 1 and 3) and Comparative Examples (Examples 2, 4 and 5).
The present invention is not limited to these.

Example 1 CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ )
_{O (CF 2) 2 PO 3} (CH 3) Ion exchange capacity 2 comprising a copolymer of _2.
The copolymer particles of 1 meq / g dry resin were hydrolyzed in a mixed aqueous solution of 1N hydrochloric acid and 1N acetic acid, washed with water, and immersed in 1N hydrochloric acid. The particles are then washed with water,
After drying at 0 ° C. for 1 hour, copolymer particles were obtained.

Using a mixture of the above copolymer particles and titania particles having a particle size of 5 μm, a thickness of 8 μm was obtained by a melt casting method.
m of an ion exchange membrane for a fuel cell was obtained. This ion exchange membrane contained 30% by volume of titania uniformly throughout the membrane.

A gas diffusion electrode (Pt carrying amount: 0.5 mg / cm ² ) having a thickness of about 150 μm and comprising 60 parts by weight of Pt-supported carbon black and 40 parts by weight of PTFE was hot-pressed on both surfaces of the ion exchange membrane. And joined.

This electrode-membrane assembly was assembled in 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 current density of 0.5 A
/ Cm ² was subjected to a discharge test. The terminal voltage was 0.69V.

Example 2 An electrode-membrane assembly was obtained in the same manner as in Example 1, except that the titania particles were not mixed. This electrode-membrane assembly was assembled in a cell for measuring battery performance and subjected to a discharge test in the same manner as in Example 1. However, the open electromotive force was extremely low, and no voltage could be taken out. 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 = CFOCF ₂ CF (CF ₃ )
Ion exchange capacity 2.0 meq / g of a copolymer of O (CF ₂ ) ₂ PO ₃ (CH ₃ ) ₂ and CF ₂ ＣＦCFOC ₃ F ₇ / g 80% by volume of a dry resin copolymer and an average Silica particles 2 having a particle size of 10 μm
A mixture of 0% by volume was extruded at 230 ° C. to a thickness of 20 μm.
m was obtained.

The above film was hydrolyzed in a mixed aqueous solution of 1N hydrochloric acid and 1N acetic acid, washed with water, and immersed in 1N hydrochloric acid. Next, the substrate was washed with water, and its four sides were restrained by special 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 surfaces of the ion exchange membrane in the same manner as in Example 1.

This electrode-membrane assembly was assembled in a cell for measuring battery performance, and dried hydrogen and air were supplied to the anode and the cathode at a cell temperature of 60 ° C., respectively, and the current density was 0.5 A / cm ² without humidification. A continuous discharge test was performed.
The initial terminal voltage was 0.65 V, and the decrease in terminal voltage after 1000 hours was about 5%.

Example 4 CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ )
An ion exchange capacity of 1.0 meq / g of a copolymer with O (CF ₂ ) ₂ SO ₂ F / 80 volume% of a copolymer of dry resin, and an average particle size of 10 μm
A mixture of 20% by volume of silica particles was extruded at 220 ° C. to obtain a film having a thickness of 20 μm. The above film was hydrolyzed in a mixed aqueous solution of dimethyl sulfoxide 30% by weight and potassium hydroxide 15% by weight.
The same treatment was performed.

Next, after obtaining an electrode-membrane assembly in the same manner as in Example 3, the electrode-membrane assembly was assembled into a cell for measuring battery performance, and a continuous discharge test was performed under the same conditions as in Example 3. The initial terminal voltage was 0.66 V, which was slightly higher than that of Example 3, but the terminal voltage after 1000 hours decreased by about 10%.

Example 5 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. This ion exchange membrane was subjected to hydrolysis and post-treatment in the same manner as in Example 3.

Next, after an electrode-membrane assembly was obtained in the same manner as in Example 3, the electrode-membrane assembly was assembled in a cell for measuring battery performance, and a continuous discharge test was performed under the same conditions as in Example 3. The initial terminal voltage was 0.65 V, but after a lapse of about 800 hours, the terminal voltage suddenly dropped, and discharge at 0.5 A / cm ² was impossible. When the electrode-membrane assembly was examined, a short circuit of the electrode occurred inside the assembly.

[0050]

According to the electrochemical device of the present invention, the thickness of the ion exchange membrane can be reduced because the ion exchange membrane is softened and a short circuit caused by an electrode penetrating the membrane can be effectively prevented. In addition, since the water content in the film can be kept high and the conductivity of the film can be improved, the film resistance loss can be extremely reduced in combination with the thin film thickness, and a higher output of the electrochemical device has been achieved. it can.

Further, by keeping the water content of the ion exchange membrane high, drying of the membrane can be prevented. In the case of the solid polymer electrolyte fuel cell, the water content of the ion exchange membrane is affected by the change of the humidity in the external environment. And operation of the fuel cell is facilitated.

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 12/08 H01M 12/08 K (72) Inventor Tetsuji Shimohira 1150 Hazawacho, Kanagawa-ku, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Inside Asahi Glass Co., Ltd.

Claims (3)

[Claims] 1. An electrochemical device comprising an ion-exchange membrane comprising a fluorocarbon polymer having a phosphonic acid group, wherein an anode is disposed on one side of the ion-exchange membrane and a cathode is disposed on the other side thereof. An electrochemical device comprising: pillar particles of 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. 2. The electrochemical device according to 1. 3. The electrochemical device according to claim 1, wherein the anode and the cathode are gas diffusion electrodes, and the electrochemical device is a fuel cell.