JP2001085019A - High polymer solid fuel cell and manufacture of electrode therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability while having high open circuit voltage by forming a gas diffusion layer by flattening the surface by applying a hot press, oppositely arranging a pair of water repellent carbon layers, and arranging a catalyst layer in contact with the surface of the water repellent carbon layers after forming the water repellent carbon layers on the surface of carbon cloth. SOLUTION: A solid high polymer fuel cell is composed of an ion exchange membrane and an electrode in contact with both sides of it, the electrode is composed of a gas diffusion layer and a catalyst layer, and the gas diffusion layer is composed of a carbon cloth and water repellent carbon layers formed on the surface. The carbon cloth is desirably 100 to 600 μm a thick, and the water repellent carbon layers include a water repellent fluororesin and carbon black, and has a thickness of 10 to 100 μm. A hot press is desirably applied to the carbon cloth at 100 to 250 deg.C and 15 to 150 kg/cm2. The surface is flattened so that damage of the ion exchange membrane is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel polymer electrolyte fuel cell and a method for manufacturing an electrode therefor.

[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. Among these, solid polymer fuels, in particular, have been able to achieve high output densities due to rapid progress in research in recent years, and are expected to be put to practical use.

As a material of a gas diffusion layer used for such an electrode of a fuel cell, carbon cloth is widely used as well as carbon paper because carbon cloth is particularly excellent in gas diffusivity in a plane direction. However, when carbon cloth is actually used as a gas diffusion layer material, the carbon cloth is essentially a woven cloth, and has openings and irregularities. Hard to be retained. As a method for improving this, a method of plugging with a mixture of carbon black and a water-repellent fluororesin on the surface or in a state of being partially penetrated into carbon cloth (see Japanese Patent Application Laid-Open No. 10-261421) has been proposed.

[0004]

The present inventors have studied the above-mentioned conventional method. In this method, in order to take advantage of the good gas diffusivity of the carbon cloth, the portion filled with the water-repellent carbon layer must be used. Since the thickness of the carbon cloth is reduced to about half or less, the influence of the shape of the carbon cloth main body is large, and it has been found that considerable irregularities still remain.

Further, when a polymer electrolyte fuel cell is manufactured, at the time of bonding the electrode and the ion exchange membrane, the catalyst layer is directly placed on the gas diffusion layer having the water-repellent carbon layer formed on the carbon cloth as described above. Form and join the catalyst layer to the ion exchange membrane (eg, by hot pressing)
The catalyst layer is integrally formed on both sides of the ion-exchange membrane. The catalyst layer / ion-exchange membrane / the catalyst layer is directly sandwiched between two sets of gas diffusion layers from both outer sides, or the catalyst layer / ion-exchange membrane / Gas diffusion layers are bonded to both outer sides of the catalyst layer body. In this case, it has also been found that unevenness in the thickness of the water-repellent carbon layer in contact with the ion exchange membrane occurs due to unevenness of the surface. The degree of the irregularities can vary greatly depending on the thickness of the carbon cloth and the thickness of the water-repellent carbon layer.For example, for a gas diffusion layer material having a carbon cloth thickness of 400 μm and a carbon layer thickness of 60 μm, It was confirmed that the portion where the yarns did not overlap was as thin as 230 μm.

Furthermore, the membrane is often damaged by locally existing projections, and it is presumed that this has an effect on the durability of the polymer fuel cell produced. .

Under the circumstances described above, there is a need to improve a conventional gas diffusion layer to provide a polymer electrolyte fuel cell having excellent durability. Accordingly, an object of the present invention is to provide a polymer electrolyte fuel cell having an improved gas diffusion layer and excellent durability, and an electrode therefor.

[0008]

That is, the present invention relates to a method for producing an electrode for a polymer electrolyte fuel cell comprising a catalyst layer and a gas diffusion layer, wherein a water-repellent carbon layer is formed on the surface of a carbon cloth. Electrode for polymer electrolyte fuel cell, characterized in that the surface is flattened by hot pressing to form a gas diffusion layer, and the catalyst layer is disposed in contact with the surface of the water-repellent carbon layer, and solid polymer using the same In the method of manufacturing a fuel cell.

[0009]

Next, an embodiment of the present invention will be described.

In the present invention, the gas diffusion layer comprises a carbon cloth and a water-repellent carbon layer formed on the surface of the carbon cloth.
The water-repellent carbon layer preferably contains a water-repellent fluororesin and carbon black.

The carbon cloth is a woven cloth made of twisted carbon short fibers, and any carbon cloth known, or developed, can be used.

The water-repellent carbon layer formed on the surface of the carbon cloth can be formed by a conventionally known method, and a water-repellent carbon layer may be formed. In this case, a layer containing carbon black and a resin having water repellency is preferably employed. More preferably, a carbon cloth whose surface is partially filled with a water-repellent carbon layer, which is a mixture containing carbon black and a water-repellent fluororesin, is used. The water-repellent fluororesin in this case is not particularly limited, and may or may not be soluble in a solvent.

The water-repellent carbon layer has a thickness of preferably about 10 to 100 μm. The water-repellent carbon layer is formed on the surface of the carbon cloth, and is at least one third of the thickness of the carbon cloth. It is preferable to form it so that the components of the water-repellent carbon layer do not enter therein. It is preferable because the water repellent carbon layer has an anchor effect by penetrating in the thickness direction from the surface of the carbon cloth. However, when the carbon cloth penetrates more than one-third of the thickness of the carbon cloth, good gas diffusivity of the carbon cloth is obtained. It is not preferable because it is lost.

The hot press conditions in the present invention are preferably such that the carbon cloth on which the water-repellent carbon layer is formed is subjected to hot press preferably at a temperature of 100 to 250 ° C. and a press pressure of about 15 to 150 kg / cm ² , A step of flattening the surface of the gas diffusion layer on the side of the water-repellent carbon layer can be performed.

The step of arranging the catalyst layer adjacent to the gas diffusion layer that has been flattened by hot pressing preferably includes forming the catalyst layer on the surface of the gas diffusion layer on the side of the water-repellent carbon layer as an electrode. A step of bonding the two electrodes with the respective catalyst layers facing inward and bonding them with an ion exchange membrane therebetween, or forming a catalyst layer on both surfaces of the ion exchange membrane, A polymer electrolyte fuel cell in which a catalyst layer is placed in contact with the surface of the water-repellent carbon layer by sandwiching the two gas diffusion layers so that the catalyst layer is in contact with the surface of the water-repellent carbon layer from both outer sides thereof Can be manufactured.

In the present invention, the polymer electrolyte fuel cell comprises an ion exchange membrane and electrodes (cathode and anode) present on both sides thereof. The electrode is composed of a gas diffusion layer and a catalyst layer, and the ion exchange membrane is in contact with the electrode in contact with the catalyst layer side of the electrode.

In the present invention, when the catalyst layer is formed on the gas diffusion layer, the catalyst layer is formed on the surface of the flattened water-repellent carbon layer of the gas diffusion layer. Need to be prepared in two sets. In the step of joining these to the ion exchange membrane, the catalyst layer is arranged so as to be in contact with both outer sides of the ion exchange membrane so as to be in contact with each other, whereby the intended fuel cell is produced.

When a catalyst layer / ion exchange membrane / catalyst layer body having a catalyst layer formed on both sides of an ion exchange membrane is used and sandwiched between two gas diffusion layers from both outer sides,
The gas diffusion layer is sandwiched so that the flattened surface is in contact with the catalyst layer. At this time, it is also preferable that the catalyst layer / ion exchange membrane / catalyst layer body is bonded to the gas diffusion layers disposed on both outer sides.

In the present invention, the surface of the water-repellent carbon layer of the gas diffusion layer is flattened by the hot pressing step, and the protrusions due to the powder mass on the surface are smoothed out. Damage to the membrane due to unevenness and fuzzing of the carbon cloth is reduced, and an electrode-ion exchange membrane assembly having a flat joint surface can be manufactured.

In the manufacturing method of the present invention, the degree of flattening of the gas diffusion layer by hot pressing and the state of the flattening are determined by observing the cross section of the gas diffusion layer with an optical microscope, an electron microscope or the like. Can be easily confirmed by comparison.

As a method of forming the electrode-ion exchange membrane assembly, a general hot press bonding (for example, Japanese Patent Application Laid-Open No.
See No. 897. ) Or heat fusion passing between rolls (see Japanese Patent Application Laid-Open No. 8-329962), and a bonding method for bonding an ion exchange membrane and an electrode using a special adhesive (Japanese Patent Application Laid-Open No. 7-254420). Various methods have been proposed, but these methods can be used as appropriate.

The ion exchange membrane used in the present invention is not particularly limited. Either a reinforced membrane or a non-reinforced membrane can be used. For example, Nafion (trade name) manufactured by DuPont or Gore Select (trade name) manufactured by Japan Gore-Tex Corporation can be used.

The hot pressing conditions for forming the gas diffusion layer are preferably 100 to 100 in consideration of the ease of deformation of the water-repellent carbon layer on the carbon cloth surface.
It is necessary to carry out at 250 ° C, more preferably at 150 to 200 ° C.

At a pressing temperature of less than 100 ° C., the effect of reducing the distance between the carbon fibers constituting the carbon cloth can be obtained, but since the temperature is low, it is difficult to obtain the fluidity of the carbon layer containing a relatively large amount of fluororesin. It is difficult to make the unevenness of the surface uneven. On the other hand, the pressing temperature exceeding 250 ° C., considering that there is a possibility of chemically adversely affecting the water-repellent fluororesin in the water-repellent carbon layer,
It is not preferable from the viewpoint of heat resistance.

The above-mentioned preferable temperature range was determined in consideration of the fact that the composition of the water-repellent carbon layer was 2: 8 to 5: 5 (weight ratio) between the water-repellent fluororesin and carbon black. This composition is determined so that the binder effect and the porosity, conductivity and water repellency of the fluororesin can be obtained in a well-balanced manner.

In this case, if the content of the fluororesin is less than 20%, the water repellency is not sufficiently sustained, the water is easily wetted, the water produced by the battery reaction is hardly discharged, and the flooding easily occurs. Further, in this case, it is difficult to obtain the binder effect of the fluororesin, and the powder layer collapses, which is not preferable from this point.

On the other hand, if the proportion of the fluororesin exceeds 50%, the water repellency is sufficient, but the fluororesin is an insulator, so that the resistance is increased and the conductivity is greatly reduced, which is not preferable.

As the fluororesin used here,
Preferably, polytetrafluoroethylene (PTFE) and ethylene / tetrafluoroethylene copolymer (ET)
FE) can be employed.

The press pressure is 15 to 150 kg
/ Cm ² is preferred. If it is less than 15 kg / cm ² , the gap between the carbon fibers constituting the carbon cloth is not narrowed, and large irregularities of the carbon cloth itself remain. Meanwhile, 1
When it exceeds 50 kg / cm ² , a flatter material can be obtained, but the thickness of the gas diffusion layer is considerably reduced, the pores of the carbon layer are crushed, and the gas diffusibility is greatly reduced.

Although the pressing time is not particularly limited, it is preferably about 30 seconds to 10 minutes, and particularly preferably about 2 to 5 minutes in consideration of the time required for the carbon layer to be deformed.

[0031]

After the surface of the carbon cloth is filled with a water-repellent carbon layer and pressed, the spacing between the bundles of carbon fibers constituting the yarn of the carbon cloth is reduced, so that the entire carbon cloth becomes flat. In addition, the clogged water-repellent carbon layer is likely to have fluidity when heated, and is deformed in accordance with the flattening of the carbon cloth, so that the irregularities thereof become gentle. Further, the protrusion-like powder mass of the water-repellent carbon layer is crushed and smoothed, so that the entire gas diffusion layer obtained is reduced in unevenness and the surface is flattened.

By forming an electrode-membrane assembly using the gas diffusion layer thus flattened, damage to the ion exchange membrane and unevenness of the film thickness can be greatly reduced. Thereby, when the electrode-membrane assembly is formed by hot pressing or the like, it is possible to suppress the partial thinning of the ion-exchange membrane, so that it becomes easy to secure mechanical strength and increase in hydrogen cross leak is prevented, As a result, the durability can be greatly improved while maintaining a high open circuit voltage.

[0033]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<Example 1> An integrated joined body is manufactured in the following procedure.

As a gas diffusion layer material, a carbon cloth having a thickness of 460 μm is filled with a water-repellent carbon layer which is a mixture of carbon black and a water-repellent fluororesin (trade name: CARBEL-CL, Japan Gore-Tex Co., Ltd.). Was used. This is cut into a predetermined size, sandwiched between polyimide sheets (trade name: Kapton sheet, manufactured by DuPont) in the air, and the thickness change when hot pressing at 160 ° C. for 5 minutes at various pressing pressures is shown. 1
Shown in The thickness was measured after removing from the press.

[0036] It pressing pressure becomes gentle slope at 20-30 kg / cm ^2, and at 150 kg / cm ² or more for the degree to which the pores of the water-repellent carbon layer is crushed is increased, where the 50 kg / cm ² Press Pressure was chosen. The thickness after taking out from the press machine is about 410μm
Met. Table 1 shows the results of changes in the thickness of the gas diffusion layer before and after hot pressing. After hot pressing, the components of the water-repellent carbon layer that had penetrated into the carbon cloth were up to a depth of about 30 μm from the surface of the carbon cloth.

[0037]

[Table 1] Change in thickness of gas diffusion layer before and after hot pressing

It is considered that mainly the carbon cloth is thinned and flattened by narrowing the filament interval in the portion where the yarns in which the filaments are bundled overlap each other. The thickness of the water-repellent carbon layer hardly changes, but with the flattened carbon cloth,
The undulations became smooth.

To form the catalyst layer on the anode side,
Medium ink was used. Such an anode catalyst ink
As perfluorosulfonic acid type ion exchange resin (C
F_Two= CF_TwoPolymerized unit based on CF and CF_Two= CFOCF_TwoCF
(CF_Three) O (CF_Two)_TwoSO _ThreeFrom polymerized units based on H
25% by weight and 40% Pt-supported carbon
(Pt / C = 40/60) from 75% by weight solids composition
Was used. Pt this anode catalyst ink
0.5mg / cm^TwoSo that the gas diffusion
Electrode coating on the water-repellent carbon layer side surface of the layer and drying
Was prepared.

As the catalyst ink for forming the cathode-side catalyst layer, a perfluorosulfonic acid type ion exchange resin (ion exchange capacity 0.91 meq / g dry resin; trade name “Nafion” manufactured by DuPont) ) 25% by weight
And 40% Pt-supported carbon (Pt / C = 40/60)
A solution having a solid content of 75% by weight was used. This cathode catalyst ink is treated with Pt in the same manner as the anode-side catalyst layer.
The above-mentioned carbon cloth was coated on the surface of the water-repellent carbon layer side and dried so that the amount of adhesion was 0.5 mg / cm ² , thereby producing an electrode.

Each of the electrodes obtained in this way is referred to as 5.
An electrode sheet was cut out into a 3 cm square. As the ion exchange membrane, a perfluorosulfonic acid type ion exchange resin membrane (dry film thickness 50 μm, 1.1 meq / g dry resin; trade name “Flemion” manufactured by Asahi Glass Co., Ltd.) was used. Hot press bonding with the ion exchange membrane sandwiched inward to prepare a gas diffusion layer-catalyst layer-ion exchange membrane-catalyst layer-gas diffusion layer integrated assembly did.

Using this single cell, normal pressure, cell temperature 80
℃, use hydrogen / air as fuel gas, fuel utilization rate is hydrogen 7
A power generation test was performed with 0% and air at 40%. The open circuit voltage, the cell voltage, and the hydrogen concentration in the air outlet line were measured at the initial stage and after 100 hours in a continuous power generation test at a constant current of 0.5 A / cm ^{2. The} results are shown in Table 2.

<Comparative Example 1>
Example 1 was repeated in the same manner as in Example 1 except that the step of hot-pressing the gas diffusion layer itself before application to ARBEL-CL was omitted. This was incorporated into a cell to produce a single cell,
A continuous power generation test was performed under the same conditions as in
The result after 0 hour is also shown in Table 2.

[0044]

[Table 2] Results of continuous test of Example 1 and Comparative Example 1

In the joined body prepared in Comparative Example 1, the open circuit voltage reflecting the amount of hydrogen cross leak was already as low as 0.82 V in Example 1 compared to 0.88 V in Example 1. On the other hand, with respect to the hydrogen concentration in the air outlet line, there was almost no difference between the example 1 and the comparative example 1, but it is considered that the leaked hydrogen was burned by the Pt catalyst on the air electrode. Can be It is presumed that the open circuit voltage dropped due to the large amount of energy expended in this reaction.

In the open circuit voltage after 100 hours in the continuous test, the product of the present invention (Example 1) shows no change at 0.88 V, but the conventional product (Comparative Example 1) shows no change.
It dropped to 77V. This is because the hydrogen concentration in the air outlet line of the product of the present invention is about 10 ppm, which is not different from the initial time, whereas that of the conventional product is extremely increased to several thousands ppm from about 10 ppm at the initial time. This is considered to be due to the film being torn or extremely thinned. That is, in the joined body according to Comparative Example 1, the thickness of each part was reduced to several μm due to unevenness of the electrode and unevenness of the surface due to surface protrusions at the time of hot press joining of the electrode, and the part was formed into a separator. It is supposed that they were pushed out during power generation due to being pressed, or were extremely thinned. On the other hand, in the bonded body according to Example 1, the bonding surface between the ion-exchange membrane and the electrode was flat at the time of bonding, so that the thickness of the ion-exchange membrane was small and approximately 40 μm or more. As a result, it was possible to prevent the film from being pushed out and the film from being broken.

[0047]

By using the flattened gas diffusion layer according to the present invention to form an electrode-ion exchange membrane assembly, damage to the ion exchange membrane and unevenness in film thickness can be greatly reduced. As a result, it is possible to provide a polymer electrolyte fuel cell in which the ion-exchange membrane is prevented from being thinned or the membrane is pushed out in the state of the joined body, and the durability is greatly improved while having a high open circuit voltage. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a pressing pressure at 160 ° C. and a thickness of a gas diffusion layer after pressing in Example 1.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/10 H01M 8/10 (72) Inventor Eiji Eiji 1150 Hazawacho, Kanagawa-ku, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Asahi Glass Co., Ltd. In-company F term (reference) 5H018 AA06 AS02 AS03 BB01 BB03 DD06 EE05 EE08 EE18 HH03 HH05 HH08 HH09 5H026 AA06 BB00 BB01 BB02 CX03 EE05 EE19 HH03 HH05 HH08 HH09

Claims (6)

[Claims] In a method for manufacturing an electrode for a polymer electrolyte fuel cell comprising a catalyst layer and a gas diffusion layer, after forming a water-repellent carbon layer on the surface of a carbon cloth, the surface is flattened by hot pressing. A method for producing an electrode for a polymer electrolyte fuel cell, comprising: forming a gas diffusion layer; and arranging a catalyst layer in contact with the surface of the water-repellent carbon layer. 2. The hot pressing condition is a temperature of 100 to 25.
The method for producing an electrode for a polymer electrolyte fuel cell according to claim 1, wherein the temperature is 0 ° C and the pressing pressure is 15 to 150 kg / cm ² . 3. The water-repellent carbon layer, wherein the carbon cloth has a thickness of 100 to 600 μm, the water-repellent carbon layer contains a water-repellent fluororesin and carbon black, has a thickness of 10 to 100 μm, and 3. The method for producing an electrode for a polymer electrolyte fuel cell according to claim 1, wherein the component does not penetrate into the carbon cloth more than one third of the thickness of the carbon cloth. 4. 4. The mixing ratio of the water-repellent fluororesin and carbon black contained in the water-repellent carbon layer is from 2: 8 to weight ratio.
The method for producing an electrode for a polymer electrolyte fuel cell according to claim 3, wherein the ratio is 5: 5. 5. After forming a water-repellent carbon layer on the surface of a carbon cloth, the surface is flattened by hot pressing to form a gas diffusion layer, and a catalyst layer is formed on the surface of the gas diffusion layer on the side of the water-repellent carbon layer. Two pieces were made as electrodes using
The two electrodes face each other with the respective catalyst layers facing inward, and the two electrodes are joined with an ion exchange membrane interposed therebetween.
A method for producing a polymer electrolyte fuel cell, comprising arranging a catalyst layer in contact with the surface of the water-repellent carbon layer. 6. After forming a water-repellent carbon layer on the surface of the carbon cloth, the surface is flattened by hot pressing to form a gas diffusion layer, and catalyst layers are formed on both surfaces of the ion exchange membrane, respectively. A method for manufacturing a polymer electrolyte fuel cell, wherein a catalyst layer is disposed in contact with the surface of the water-repellent carbon layer by sandwiching the two gas diffusion layers so that the catalyst layer is in contact with the surface of the water-repellent carbon layer.