JPH07120532B2 - Method for producing carbonaceous composite electrode substrate for fuel cell - Google Patents

Description

The present invention relates to a phosphoric acid type carbonaceous composite electrode substrate for a fuel cell in which a porous electrode plate composed of a carbonaceous material and a dense separator plate are integrated. To a method of manufacturing.

[Conventional technology]

When manufacturing a phosphoric acid fuel cell using carbonaceous material as a member, the mechanical strength was improved and the electrical
In order to reduce the thermal resistance and simplify the laminated assembly, a structure in which both members of the separator plate and the porous electrode plate are combined and integrated in advance has been developed and is in the stage of practical application.

As a simple and highly practical means for producing such a composite electrode substrate, a bonding and firing method is used in which an electrode plate, a separator plate, and a side seal plate are bonded to each other in a predetermined form with an adhesive and then baked (Japanese Patent Laid-Open No. Sho 60). -20471 and Jitsukai Sho 60-15759).

However, in the case of the bonding and firing method described above, a phenomenon occurs in which the adhesive penetrates into the tissue of the porous electrode, which reduces the porosity of the electrode member, while the adhesive strength at the interface decreases and the electrode plate and the separator plate are reduced. There was a defect that and peeled off.

Therefore, the present inventors have previously proposed a method of preventing the electrode from penetrating the adhesive at the time of bonding and treating the electrode base material with a substance that volatilizes and disappears during the firing step (Japanese Patent Laid-Open No. 62-126562).

However, if this method is adopted,
Since the process is added, there is a problem that the production efficiency is reduced.

[Problems to be Solved by the Invention]

Recently, with the increase in cell size, there has been an increasing demand for an increase in member adhesive force and uniform electric resistance inside the substrate. In order to meet this performance requirement, it is essential to increase the adhesive strength of the adhesive and to form a uniform adhesive interface by making the adhesive interface uniform. There is no composition that satisfies the requirements. Especially with conventional adhesives, there is a strong tendency for non-uniformity of the adhesive layer to appear, which is due to shearing force acting on the adhesive layer during processing, as well as fluctuations in electrical resistance, so that the electrode member from the thin layer It also becomes a problem in processing such as missing.

The present invention aims to solve the above problems by improving the composition of the adhesive, and the object thereof is to provide excellent adhesive strength and uniform electric resistance between the interfaces even in a large size electrode member and a separator. (EN) It is possible to provide a method for producing a carbonaceous composite electrode substrate for a fuel cell, which is capable of high production efficiency.

[Means for Solving the Problems]

The method for producing a carbonaceous composite electrode substrate for a fuel cell according to the present invention for achieving the above-mentioned object has an average particle size of 1 to 10 μm.
10 to 40 parts by weight of carbonaceous powder and 60 to 90 parts by weight of carbonaceous powder having an average particle diameter of 20 to 80 μm are mixed, and then kneaded with a liquid thermosetting resin having a residual carbon ratio of 40% or more to have a viscosity of 500 to 5000 poises. The adhesive is prepared, and the adhesive is uniformly applied to the surface of the carbonaceous separator member so that the thickness of the adhesive layer is 50 to 200 μm, bonded to the porous carbonaceous electrode plate, and bonded under pressure and heating. The structural feature is that after the layer is cured, it is fired and carbonized in a temperature range of 800 ° C. or higher in a non-oxidizing atmosphere.

As the carbonaceous separator plate which is a constituent member of the present invention, a graphite substrate is impregnated with a thermosetting resin liquid such as a phenol-based or furan-based resin and cured, and graphite fine powder is mixed with phenol resin, furan resin or tar pitch. A thin plate with an impermeable dense structure and surface smoothness obtained by, for example, a method of kneading with the above to form a plate and then firing, or a method of firing a molded plate of phenol resin or furan resin to form a glassy carbon. Materials are used together.

For the porous carbonaceous electrode plate, carbon fibers or organic fibers such as polyacrylonitrile and cellulose are molded into a thin plate together with a thermosetting resin such as a phenol resin, and then carbonized by firing and carbonization. Material is used.

The gist of the present invention is to mix a carbonaceous separator and a porous carbonaceous electrode plate with 10 to 40 parts by weight of carbonaceous powder having an average particle diameter of 1 to 10 μm and 60 to 90 parts by weight of carbonaceous powder having an average particle diameter of 20 to 80 μm. After that, they are bonded together with an adhesive having a viscosity of 500 to 5000 poise prepared by kneading with a liquid thermosetting resin having a residual carbon rate of 40% or more.

Mixing and using carbonaceous powders having different average particle diameter ranges in a specified mixing ratio is a composition condition for improving the adhesive strength after firing and carbonization and giving a low electric resistance. If the range is not satisfied, effective increase in adhesive strength and provision of low electrical resistance cannot be expected.

As the carbonaceous powder, it is possible to apply coke, carbon, natural graphite, artificial graphite, glassy carbon, or the like crushed to a predetermined particle size range, but especially artificial graphite powder having high purity and good electrical conductivity is effective. Can be used well.

Liquid thermosetting resin with a residual carbon ratio of 40% or more refers to a thermosetting resin liquid having a property that 40% by weight or more of carbon content remains when baked at a temperature of 1000 ° C. in a non-oxidizing atmosphere, For example, an initial condensate such as a phenol resin, a furan resin, or a polyimide resin is applicable.

The reason for setting the viscosity of the adhesive in the range of 500 to 5000 poise is that at a viscosity below 500 poise, the adhesive penetrates into the porous structure of the electrode plate and causes a decrease in adhesive strength, and when it exceeds 5000 poise, it is applied. This is because the adhesive layer becomes difficult and the thickness of the adhesive layer becomes non-uniform. In order to secure this viscosity range, the liquid thermosetting resin may be adjusted in an amount of about 50 to 150 parts by weight and kneaded with 100 parts by weight of the mixture of carbonaceous powder.

The adhesive having the above composition is uniformly applied to the surface of the carbonaceous separator plate so that the thickness of the adhesive layer is 50 to 200 μm, and bonded to the porous carbonaceous electrode plate. When the thickness of the adhesive layer is less than 50 μm, the adhesive force is insufficient and partial peeling is likely to occur, and when the thickness of the adhesive layer exceeds 200 μm, peeling of the adhesive interface frequently occurs.

The application of the adhesive is preferably carried out by using a mechanical means such as a doctor blade method, and it is desirable that the variation in the thickness of the adhesive layer is within ± 0.03 mm. If the variation is out of the range, local peeling of the member is likely to occur and variation in electric resistance increases.

The member after the bonding treatment cures the adhesive layer under pressure and heating.
In this case, the preferred conditions are pressure 1-20 kg / cm ² , temperature
50 to 300 ° C.

Then, transfer the joint members to a firing furnace and place them in a non-oxidizing atmosphere.
Carbonizes by firing in a temperature range of 800 ° C or higher. In addition, a side seal portion is installed and required processing (processing of flat surface, outer circumference, groove, etc.) is performed to obtain a carbonaceous composite electrode substrate for a fuel cell.

[Work]

According to the present invention, 10 to 40 parts by weight of carbonaceous powder having an average particle diameter of 1 to 10 μm and an average particle diameter of 20 are used as a filler component of an adhesive.
By mixing and using 60 to 90 parts by weight of carbonaceous powder of -80 μm, a unique adhesive layer is formed in which conductive fine particles whose particle size distribution has two peaks during firing and carbonization are mixed inside the carbonized structure of the thermosetting resin. However, this adhesive layer functions to improve the adhesive strength and at the same time reduce the electric resistance.

In addition, the viscosity of the adhesive is set to 500 to 5000 poise, and the thickness of the coating is set to 50 to 200 μm for the adhesive layer.
It secures the uniformity of the adhesive layer to reduce the fluctuation of electric resistance and also serves to prevent the peeling of the adhesive interface.

By such synergistic effects, it becomes possible to effectively impart the strengthening of the adhesive layer portion and the uniformization of electric resistance required for a large-sized composite electrode substrate for a fuel cell.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 5, Comparative Examples 1 to 10 (1) Preparation of Adhesive Artificial graphite fine powder having an average particle diameter of 3 μm and an average particle diameter of 40 μm
The artificial graphite fine powder of was prepared, and both were mixed at various compounding ratios. Each mixed powder was added to a phenol resin initial condensate [PR940 manufactured by Sumitomo Durres Co., Ltd.] and kneaded sufficiently with a kneader to prepare paste adhesives having different viscosities.

(2) Manufacture of composite electrode substrate As a porous carbon electrode plate, a pitch-based carbon fiber chop (average length 20 mm) was mixed with phenol resin, molded, and then baked at 2000 ° C. to obtain 1010 mm in length and 10 mm in width. 920m
m, thickness 2 mm, porosity 64%, average pore diameter 50 μm
A plate-like body having the property of was used. As the carbonaceous separator plate, a square thin plate with a side length of 1000 mm and a thickness of 0.6 mm obtained by rolling and molding a phenol resin in which graphite fine powder (average particle size 5 μm) is kneaded, followed by hardening and then firing at 1300 ° C. Was used.

An adhesive was applied to the surface of this separator plate by the doctor blade method, and the porous carbonaceous electrode plates were joined to both surfaces. The joining was performed so that the front and back surfaces of the separator plate were orthogonal to each other in the length direction of the electrode plate and there was a space of 45 mm at both ends.

The member after joining is heated to 80 ℃ and pressed at 5kg /
A pressure of cm ² was applied to cure the resin component of the adhesive.

Next, the joint member was transferred to an electric firing furnace, covered with coke powder, and then heated to 1000 ° C. at a heating rate of 5 ° C./min to perform a firing treatment.

Side seals made of the same material as the separator plate were joined to both ends of the integrated member obtained by firing and carbonizing the adhesive layer via the joining agent. Continuously, the length of one side is 1000 mm and the thickness is 2.8 m.
The outer periphery and the flat surface are processed so that the cell size becomes m, and the groove (width 2 mm,
A carbonaceous composite electrode substrate for a phosphoric acid fuel cell was manufactured by setting a depth of 1 mm).

(3) Evaluation of characteristics The characteristics and properties measured for each of the obtained composite electrode substrates are shown in Table 1 in comparison with the composition of the adhesive.

The methods for measuring various properties and characteristics shown in Table 1 were as follows.

Thickness of adhesive layer: The test piece is divided into 16 equal parts, and the side surface is observed with an optical microscope to measure the layer thickness.

Electrode porosity, electrode porosity-: The porosity of the electrode member after adhesion is measured up to 0.01 μm by the mercury porosimetry.
Pore size was shown as 50% of pre-pore volume.

Electric resistance: The resistance value per area is measured by the voltage drop method, and the product is calculated by multiplying the area by the total resistance.

Adhesive strength-: Separator plate specimen (30 x 50 x 0.8 mm)
An adhesive (width: 3 mm) is applied to the two, the two test pieces are joined, cured, and then fired at a temperature of 1000 ° C. in a non-oxidizing atmosphere. The bonding interface between the two sheets is pulled and the force required for peeling is defined as the adhesive strength.

From the results of Table 1, the examples satisfying the requirements of the present invention have relatively high adhesive strength and low electric resistance with little variation, even though they are large-sized electrode substrates, and are found in the comparative examples. No phenomena such as a decrease in the porosity of the electrode structure due to the permeation of the adhesive and a reduction in the processing yield due to the peeling of the adhesive interface are observed.

[Advantages of the Invention] As described above, according to the present invention, by applying the adhesive having the specified composition and the adhesion conditions, it is possible to always provide excellent adhesive strength and uniform and low electric resistance even in a large size. A carbonaceous composite electrode substrate for a fuel cell can be manufactured.

In addition, it does not require an extra processing step, and there is no reduction in processing yield due to the peeling phenomenon, so that productivity is excellent.

Claims (1)

[Claims] 1. A carbonaceous powder having an average particle size of 1 to 10 μm 10 to 40.
After mixing 60 parts by weight and 60 to 90 parts by weight of carbonaceous powder having an average particle size of 20 to 80 μm with a liquid thermosetting resin having a residual carbon ratio of 40% or more to prepare an adhesive having a viscosity of 500 to 5000 poises, The adhesive is applied to the surface of the carbonaceous separator plate so that the thickness of the adhesive layer is 50
~ 200μm evenly applied and bonded to a porous carbonaceous electrode plate, the adhesive layer is cured under pressure and heating, then carbonized in a temperature range of 800 ℃ or more in a non-oxidizing atmosphere Of manufacturing carbonaceous composite electrode substrate for fuel cell.