JPS6247966A - Manufacture of fuel cell - Google Patents

Abstract

PURPOSE:To make sure seal to prevent gas leakage from the end side of electrode by forming sealing grooves at the end of electrolyte, and impregnating slurry made of hydrophilic material on the opposite side of the grooves, and filling paste made of hydrophilic material in the grooves. CONSTITUTION:An electrode is prepared by bonding a catalyst layer on one side of a conductive porous substrate having gas flow grooves on its other side. Sealing grooves B having similar width and depth to the gas flow groove are formed at each end A of the electrode. Slurry mainly comprising hydrophilic material powder such as carbon and silicon carbide powder is impregnated under vacuum to the end A of the electrode, and dried. Paste made of the same hydrophilic material powder, having slightly higher viscosity than the slurry, is filled in the groove B, dried and backed. Phosphoric acid electrolyte is impregnated in the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell, and more particularly to a method for manufacturing a fuel cell that can reliably prevent gas leakage at the ends of electrodes.

[Technical Background of the Invention and Problems Therein] Fuel cells have conventionally been known as devices that directly convert chemical energy contained in fuel into electrical energy.

This fuel cell usually has a pair of porous electrodes placed opposite each other with an electrolyte layer in between, and a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidizing agent such as oxygen is brought into contact with the back surface of the other electrode. Electrical energy is extracted between the pair of electrodes by bringing gases into contact and utilizing the electrochemical reaction that occurs.As long as the fuel gas and oxidant gas are supplied, the conversion efficiency is high. It is dust from which electrical energy can be extracted.

FIG. 2 is an exploded perspective view showing an example of the structure of a unit cell in a ribbed electrode type fuel cell based on the above principle and using phosphoric acid as an electrolyte.

In the figure, 1 is an electrolyte layer formed by impregnating a matrix with phosphoric acid as an electrolyte, and 3a and 3b are this electrolyte layer 1.
The anode electrode and the cathode electrode are made of porous carbon material and are placed between the electrodes, and the catalysts 2a and 2b are respectively coated on the side in contact with the electrolyte layer 1, and the rib 4 is applied on the back side.
a, 4b, and a groove 5a through which fuel gas and oxidizing gas flow.
, 5b, respectively. Here, the grooves 5a through which the fuel gas flows and the grooves 5b through which the oxidant gas flows are regularly formed in parallel in a direction orthogonal to each other. A unit cell is formed as described above, and a unit cell laminate is constructed by stacking a plurality of such unit cells with separators 6 made of dense carbon material sandwiched therebetween.

In addition, as shown in FIG. 3, the unit cell laminate has a current collecting plate 7, an insulating plate 8, a clamping plate 9, and a terminal 10 on its upper and lower ends, respectively. Furthermore, a pair of manifolds 12 for supplying and discharging fuel gas and oxidizing gas through pipes 16 are provided on the side surfaces of the unit cell stack through gaskets 11. A fuel cell is constructed by arranging 13, 14 and 15 facing each other and tightening them with appropriate pressure.

Now, in the fuel cell having such a configuration, the anode electrode 3a
, The cathode electrode 3b is made of a carbonaceous porous material because it requires air permeability. Therefore, the groove 5a
The fuel gas flowing through the anode electrode 3a freely passes through the inside of the edge 17a of the anode electrode 3a and reaches the manifold 14 on the oxidizing gas side.
and 15 chambers, or the oxidant gas flowing through the groove 5b freely passes inside the edge 17b of the cathode electrode 3b and leaks into the manifolds 12 and 13 chambers on the fuel gas side, resulting in both This is extremely dangerous as the gases will mix. Therefore, it is necessary to seal the edges 17a and 17b of the anode electrode 3a and cathode electrode 3b to prevent gas leakage, and the edges 17a and 17b may be impregnated with resin or rubber material, or The edges are sealed using the so-called wet sealing method, which involves wrapping a heat-resistant and electrolyte-resistant resin film in a U-shape, or applying silicon carbide powder to make it hydrophilic and impregnating it with the same phosphoric acid as the electrolyte. has been done. However, although the last wet seal method is a simple method, its sealing performance is incomplete and its reliability is poor.

Normally, the electrode end is impregnated with a hydrophilic material by immersing the electrode end in an aqueous solution of hydrophilic powder, reducing the pressure to impregnate the powder, drying it, and then retaining the electrolyte. In this case, even if a hydrophilic material with a fairly small particle size is used, it aggregates in an aqueous solution and forms secondary particles, so it is difficult to fill the inside of the electrode end, and the surface layer becomes polarized. It is impregnated only up to the vicinity. Therefore, when phosphoric acid was impregnated here, the sealability was not sufficiently ensured.

Therefore, recently, as shown in the perspective view in Figure 4,
A method has been proposed in which the electrode end A is first impregnated with a hydrophilic material, and then the groove for gas flow at the end is filled with a paste-like hydrophilic material, and then the electrolyte is retained and sealed. It's coming.

In this method, the hydrophilic material is filled only in a relatively thin part (approximately 0.5
mm), the hydrophilic abrasive material is sufficiently impregnated, and the processed groove B section above it is filled with baset, so if the electrolyte is retained here, its sealing performance is improved. , gas leakage from the electrode end A can be sufficiently prevented. However, in this method, the electrode end A
Although it is possible to sufficiently prevent gas leakage from
If the laminated surface of the hydrophilic material filled in the groove B processing portion is not sufficiently exposed, there is a problem in that gas leakage from the electrode laminated surface becomes large. In addition, if the process of drying and baking 1q is performed after filling the processed groove B with a hydrophilic material, 1
．． Cracks may form in the hydrophilic material of the filled powder and gas leakage may occur therethrough, which is a particular problem in the later stages of cell operation when the retention electrolyte is lost. Furthermore, because the liquid junction between the electrolyte held at the electrode end A and the electrolyte held in the electrolyte layer is not sufficiently established, the electrolyte at the electrode end disappears relatively quickly, ensuring long-term sealing performance. The problem is that it cannot be done.

[Object of the Invention] The present invention was made to solve the above-mentioned problems, and its purpose is to reliably seal the electrode end to prevent gas leakage from the side of the electrode end and the battery stack surface. It is an object of the present invention to provide a method for manufacturing a fuel cell, which can prevent such problems, stably hold the electrolyte held at the end of the electrode over a long period of time, and improve reliability.

[Summary of the Invention] In order to achieve the above object, the present invention provides an electrolyte impregnated between a pair of electrodes, which is formed by coating a catalyst layer on one side of a conductive porous substrate having grooves for gas flow. In a method for manufacturing a fuel cell configured with an electrolyte layer in between, grooves for sealing are formed at the ends of the electrodes (with approximately the same width and depth as the gas flow grooves) from the catalyst layer side. a first step of applying;
A second step of vacuum impregnating the end of the electrode with a slurry mainly composed of hydrophilic powder such as carbon powder or silicon carbide powder and drying it; It is characterized by a third step of filling a highly viscous paste into the sealing grooved portion of the electrode end, drying and firing, and then impregnating it with an electrolyte.

[Embodiments of the invention] First, the characteristics of the wet sealing method for end sealing are as follows:
Compared to the above-mentioned method of impregnating resin or rubber, this method produces less stress and fluctuations in lamination pressure due to differences in material expansion between the room temperature when the battery is stopped and the high temperature exceeding 200°C during operation. The weak point is that the seal is unreliable. In this wet seal method, the groove at the end of the electrode is filled with a hydrophilic material such as silicon carbide or carbon powder, which is then impregnated with phosphoric acid to prevent gas from passing through due to the surface tension of the phosphoric acid. Therefore, it can be said that the reliability of the sealing performance is determined by how the hydrophilic powder is filled into the groove at the end of the electrode.

In order to fill the groove of the electrode end with the hydrophilic powder, a so-called slurry made by mixing the powder with a liquid such as water or a solvent may be prepared and the slurry may be press-fitted. However, with this method, particles such as carbon powder and silicon carbide, which are currently candidates for hydrophilic materials, cannot be sufficiently impregnated into a thick porous substrate. The impregnating treatment is applied to the grooved remaining flesh, and the groove is filled with a paste-like hydrophilic material having a higher viscosity than the impregnating liquid.
After drying and firing, an electrolyte is impregnated and held there to ensure sealing performance.

Hereinafter, a specific example thereof will be described with reference to the drawings. In this example, the end seal of the electrode is constructed as follows.

That is, as shown in the perspective view of FIG. 1, in the first step, a catalyst layer is coated on one side of a conductive porous substrate having grooves for gas flow. , Process a sealing groove B using a diamond bur from the surface on the catalyst layer side with approximately the same width and depth as the above-mentioned gas circulation groove. Here, the porous substrate is generally a material made by bonding carbon fibers with phenolic resin and carbonizing them at a high temperature of 1000°C or higher.
Use one of about 5.

Next, as a second step, a slurry mainly composed of hydrophilic powder such as carbon powder or silicon carbide powder is impregnated into the end portion A of the electrode under reduced pressure and dried. That is, for example, the end A of the electrode is immersed in the slurry, and after repeating the operation between reduced pressure and normal pressure in a vacuum container about 2 to 3 times, the deposits on the substrate surface are removed and the electrode is heated at 200°C for 1 to 3 hours.
Dry for about an hour. In this case, the film may be dried while being evacuated using a vacuum dryer. In the above, the impregnating liquid used has the following composition, for example.

(Part 1) Vulcan XC-72R (Cabot) (average particle size 30 μm) ...30g pure water
...420m1Tef Io
n 30-J (Mitsui Fluorochemical Company)
...5 m1Triton
X-100 (Rhom & Hass) (nonionic surfactant)...19m1 (Part 2) SiC (Showa Denko) (average particle size 1 μm)...120
g Pure water...75m1Te
flon 30-J (Mitsui Fluorochemical Co., Ltd.)
...1.9gTriton
XX-100 (Rho & Hass) (nonionic surfactant)...8g Furthermore, as a third step, a slightly viscous paste-like hydrophilic powder similar to the second step was added to the above 18 It is filled into the sealing groove B processed part of the extreme part A, dried and fired, and then impregnated with phosphoric acid as an electrolyte. In this case, after filling the sealing groove B with the paste, drying (200
℃, 1 hour) and baking (320℃, 6 minutes), the filled paste may shrink and cause cracks in the filling, so perform the paste filling and drying operations at least twice. It is preferable. And from this point,
It has been found that it is more preferable to use silicon carbide as the hydrophilic material because it is less likely to cause cracks. In the above, as the highly viscous paste-like hydrophilic agent for filling grooves, for example, one having the following composition is used.

(Part 1) Vulcan XC-72R (Cabot)...
30g pure water...300 m1Te
f Ion 30-J (Mitsui Fluorochemical Company)
...0.9m1Carb
opol (thickener) -0.45g (Part 2) SiC...130g Pure water...60ml1Tef
ion 30-J (Mitsui Fluorochemical Company)
...3.5g Carbo
pol (thickener) - 0.26g By a method that requires 0.26g, electrodes impregnated with silicon carbide as a hydrophilic agent and sealed are sandwiched between flat interconnectors, and a surface pressure of 2
After tightening to kg/ci, attach the manifold, fill the electrode with air at a constant pressure, close one side of the electrode end A, and measure the air flow rate from the opposite side at 180°C. 3.7X10-4cc/sec at sealing pressure 10cmAq per seal length 10cm
-cmAq. Moreover, the rate of this leakage hardly changed even when the air sealing pressure was increased to 20 cmHg. From this, it has become clear that gas leakage from the electrode end A can be sufficiently prevented even when the supply gas pressure suddenly increases during actual battery operation.

As described above, in this example, the end A of the electrode is processed with a sealing groove B, and the end A of the electrode, including the remaining thickness, is soaked in a slurry of a hydrophilic material such as carbon powder or silicon carbide powder. Since the sealing groove B is further filled with a paste of a hydrophilic material after being soaked and impregnated, the electrode end A can be reliably sealed.
It is possible to completely prevent gas leakage from one side of fti'.

In addition, since the sealing groove B is formed on the side of the catalyst layer that is in contact with the electrolyte layer, there is no gas leakage from the grooved area before lamination, as in the conventional case, and there is no leakage at the electrode end. With the electrolyte held in part A, the liquid junction between the phosphoric acid and the electrolyte layer is sufficiently established, and 'i, ji F'j (electrolyte is also supplied to end part A in a well-balanced manner over a long period of time, making it reliable. As a result, a fuel cell using an electrode provided with such an end seal can operate extremely stably over a long period of time θ1.

It should be noted that the present invention is not limited to the above embodiments, and can be implemented with various modifications without changing the gist thereof.

"Effects of the Invention - 1 - Explanation [7] According to the present invention, between a pair of electrodes, a catalyst layer is coated on one side of an electrically conductive porous substrate forming a groove for gas circulation. In the case of manufacturing a fuel cell consisting of an electrolyte layer impregnated with an electrolyte on both sides, at the end of the electrode (with approximately the same width and depth as the gas flow groove)
A sealing groove is formed from the surface on the catalyst layer side, and then a slurry mainly composed of hydrophilic powder such as carbon powder or silicon carbide powder is vacuum impregnated into the end of the electrode and dried. The same hydrophilic powder as above in the form of a paste with a slightly higher viscosity is filled into the sealing groove at the end of the electrode, dried and fired, and then impregnated with electrolyte to seal the end of the electrode. As a result, the electrode end is reliably sealed to prevent gas leakage from the side of the electrode end and the battery stack surface, and the electrolyte held at the electrode end is stably maintained over a long period of time. Therefore, it is possible to provide a method for manufacturing a fuel cell that can improve reliability.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an electrode manufactured according to an embodiment of the present invention, FIG. 2 is an exploded perspective view showing the configuration of a unit cell of a ribbed electrode type fuel cell, and FIG. 3 is a perspective view showing the configuration of a fuel cell. FIG. 4 is an exploded perspective view showing an electrode manufactured by a conventional method. A... Electrode end, B... Machining groove, 1... Electrolyte layer, 2a, 2b... Catalyst, 3a... Anode electrode, 3
b... Cathode electrode, 4a, 4b... Rib, 5a,
5b... Groove, 7... Current collector plate, 8... Insulating plate, 9...
...Tightening plate, 11...Gasket, 12-15...
Manifold, 16... Oxidizer (air) supply pipe, 17
a, 17b...edge, 21...terminal. Applicant's agent Patent attorney Takehikomi Suzue Figure 1 Figure 2 Figure 3 B Figure 4

Claims (3)

[Claims] (1) A method for manufacturing a fuel cell in which an electrolyte layer impregnated with an electrolyte is sandwiched between a pair of electrodes, each of which has a catalyst layer coated on one side of a conductive porous substrate having grooves for gas flow. In this step, a first step of forming a sealing groove on the end of the electrode from the surface facing the catalyst layer, and vacuum impregnating the end of the electrode with a slurry mainly composed of hydrophilic powder and drying it. In the second step, a similar hydrophilic powder with a slightly higher viscosity in the form of a paste is filled into the sealing groove of the electrode end, dried and fired, and then impregnated with electrolyte. A method for manufacturing a fuel cell, comprising a third step of: (2) The method for manufacturing a fuel cell according to claim (1), wherein carbon powder or silicon carbide powder is used as the hydrophilic powder. (3) A method for manufacturing a fuel cell according to claim (1), characterized in that the sealing grooves are formed to have approximately the same width and depth as the gas circulation grooves. .