JPH04169070A - Manufacture of carbonaceous composite electrode substrate for fuel cell - Google Patents

Abstract

PURPOSE:To obtain a carbonaceous composite electrode substrate for a fuel cell constantly having excellent adhesive strength and uniform and low electric resistance even in a large size by applying an adhesive, having specific composition, and a specific adhesion condition. CONSTITUTION:Carbonaceous powders, having mean particle diameters of 1-10mum, of 10-40wt. parts and carbonaceous powders, having mean particle diameters of 20-80mum, of 60-90wt. parts are mixedly used as the filler component of an adhesive. By this, an adhesion layer is formed in which conductive fine particles, whose particle size distribution has two piles at the time of baking and carbonization, mixedly exist in the inside of the carbonization organization of a thermosetting resin. Also on condition that the viscosity of the adhesive is 500-5000 poises and the thickness of the adhesive application forms an adhesion layer of 50-200mum in thickness, and adhesion layer is joined to a porous carbonaceous electrode plate to be hardened under pressurization and heating, and then is baked and carbonized in temperature region of 800 deg.C or more in a non-exidizing atmosphere. This permits the giving of excellent adhesive strength and uniform electric resistance between interfaces even in large size electrode members and separators.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a carbonaceous composite electrode substrate for a phosphoric acid fuel cell in which a porous electrode plate made of a carbonaceous material and a dense separator plate are integrated. Relating to a method of manufacturing.

[Prior art] In manufacturing phosphoric acid fuel cells using carbonaceous materials as components, improvements in mechanical strength and electrical and
In order to reduce thermal resistance and simplify lamination assembly, a structure in which the separator plate and porous electrode plate are integrated into a composite structure has been developed and is now in the stage of practical application.

A simple and highly practical means for manufacturing such composite electrode substrates is the bonding and firing method (Japanese Patent Application Laid-Open No. 1983-1996), in which electrode plates, separator plates, and side seal plates are bonded in a predetermined shape with an adhesive and then fired. -20471 Publication, Utility Model Publication 1986-
15759).

However, when using the bonding and firing method described above, a phenomenon occurs in which the adhesive permeates into the structure of the porous electrode, reducing the porosity of the electrode member and reducing the adhesive strength at the interface, causing the electrode plate and separator to deteriorate. There was a drawback that the plate would peel off.

Therefore, the present inventors previously proposed a method of pre-treating the electrode base material with a substance that prevents the adhesive from penetrating into the electrode during bonding and evaporates during the firing process (Japanese Patent Laid-Open No. 62-1265
Publication No. 62).

However, when using this method, 1
The disadvantage is that production efficiency decreases due to the addition of additional steps.

(Problems to be Solved by the Invention) Recently, with the increase in cell size, there has been a growing demand for increased member adhesive strength and uniform electrical resistance within the substrate. To meet this performance requirement, it is essential to increase the adhesive strength of the adhesive and to make the adhesive interface uniform to form a consistent adhesive layer. There is no one with a composition that satisfies the requirements. In particular, with conventional adhesives, there is a strong tendency for non-uniformity of the adhesive layer to appear, and this is not only caused by fluctuations in electrical resistance, but also by shearing force acting on the adhesive layer during processing, which causes electrode members to separate from the layered areas. It also causes problems in processing, such as chipping.

The present invention aims to solve the above problems by improving the composition of the adhesive, and its purpose is to provide excellent adhesive strength and uniform electrical resistance between the interfaces even in large-sized electrode members and separators. An object of the present invention is to provide a method for manufacturing a carbonaceous composite electrode substrate for a fuel cell with high production efficiency.

[Means to solve the problem]

The method for manufacturing a carbonaceous composite electrode substrate for fuel cells according to the present invention to achieve the above object includes an average particle size of 1 to 10 μm.
m carbonaceous powder 10 to 40 parts by weight and average particle size 20 to 8
After mixing 60 to 90 parts by weight of carbonaceous powder with a diameter of 0 μm, the mixture is kneaded with a liquid thermosetting resin having a residual carbon content of 40% or more to obtain a viscosity of 50%.
An adhesive having a poise of 0 to 5000 is prepared, and the adhesive is applied to the surface of a carbonaceous separator member so that the thickness of the adhesive layer is 50 to 20.
The structure is such that the adhesive layer is coated uniformly to a thickness of 0 μm and bonded to the porous carbonaceous electrode plate, the adhesive layer is cured under pressure and heat, and then fired and carbonized in a non-oxidizing atmosphere at a temperature of 800°C or higher. The characteristics of

The carbonaceous separator plate, which is a component of the present invention, can be produced by impregnating a graphite substrate with a thermosetting resin liquid such as phenolic or furan, and then curing it, or by applying fine graphite powder to a phenolic resin, furan resin, or tar pitch. A thin sheet with an impermeable dense structure and a smooth surface obtained by kneading it with other materials, forming it into a plate shape, and then firing it, or firing a molded plate of phenol resin or furan resin to form a glassy carbon, etc. Materials will be made available.

In addition, porous carbonaceous electrode plates are made by forming carbon fibers or organic fibers such as polyacrylonitrile or cellulose into a thin plate together with a thermosetting resin such as phenolic resin, and then firing and carbonizing carbon fibers with a porous structure. material is used.

The key points of the present invention are the carbonaceous separator and the porous carbon l! The electrode plate is made of carbonaceous powder 10 to 4 with an average particle size of 1 to 10 μm.
Carbonaceous powder 60 with 0 parts by weight and an average particle size of 20 to 80 μm
After mixing ~90 parts by weight, the mixture is bonded via an adhesive having a viscosity of 500 to 5000 poise prepared by kneading with a liquid thermosetting resin having a residual carbon content of 40% or more.

The mixing and use of carbonaceous powders with different average particle size ranges in a specified blending ratio is a compositional condition for improving adhesive strength after firing and carbonization and providing low electrical resistance. If the range is not met, effective increase in adhesive strength and provision of low electrical resistance cannot be expected.

As the carbonaceous powder, it is possible to use coke, carbon, natural graphite, artificial graphite, glassy carbon, etc. that have been crushed into a specified particle size range, but artificial graphite powder with high purity and good conductivity is particularly effective. Can be used often.

A liquid thermosetting resin with a residual carbon content of 40% or more means a residual carbon content of 40% by weight when fired at a temperature of 1000"C in a non-oxidizing atmosphere.
Refers to a thermosetting resin liquid with a residual carbon content of
For example, initial condensates such as phenolic resins, furan resins, and polyimide resins are applicable.

The reason why the viscosity of the adhesive is set in the range of 500 to 5000 poise is that if the viscosity is lower than 500 poise, the adhesive will penetrate into the porous structure of the electrode plate, resulting in a decrease in adhesive strength.
This is because if it exceeds 0.00 poise, coating becomes difficult and the thickness of the adhesive layer becomes non-uniform. In order to ensure this viscosity range, the amount of liquid thermosetting resin may be adjusted to approximately 50 to 150 parts by weight per 100 parts by weight of the carbonaceous powder mixture and kneaded.

The adhesive having the above composition is uniformly applied to the surface of the carbonaceous separator plate so that the adhesive layer has a thickness of 50 to 200 μm to bond it to the porous carbonaceous electrode plate. Adhesive layer thickness is 50μ
If the thickness is less than 200 μm, the adhesive strength will be insufficient and partial peeling will easily occur, and if the thickness of the adhesive layer exceeds 200 μm, peeling at the adhesive interface will occur frequently.

The adhesive is preferably applied 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 a range of ±0.03 mm. Outside this range of variation, local peeling of the member tends to occur and the electrical resistance fluctuates significantly.

After the bonding process, the adhesive layer of the member is cured under pressure and heat.

In this case, the preferable conditions are a pressing force of 1 to 20 kg/cm.
”, the temperature is 50-300°C.

Next, the joining member is transferred to a firing furnace and fired and carbonized in a non-oxidizing atmosphere at a temperature of 800° C. or higher. In addition, a side seal portion is installed and required processing (processing of the flat surface, outer periphery, grooves, etc.) is performed to obtain a carbonaceous composite electrode substrate for a fuel cell.

[For production]

According to the present invention, by mixing and using 10 to 40 parts by weight of carbonaceous powder with an average particle size of 1 to 10 μm and 60 to 90 parts by weight of carbonaceous powder with an average particle size of 20 to 80 μm as a filler component of the adhesive. During firing and carbonization, conductive fine particles with a two-peak particle size distribution form a unique adhesive layer mixed inside the carbonized structure of the thermosetting resin, and this adhesive layer improves adhesive strength and reduces electrical resistance at the same time. function to make it happen.

In addition, setting the viscosity of the adhesive to 500 to 5000 poise and applying conditions such that the thickness of the adhesive layer becomes 50 to 200 μm ensures uniformity of the adhesive layer and reduces fluctuations in electrical resistance. , which acts to prevent peeling of the adhesive interface.

These effects combine to effectively provide reinforcement of the adhesive layer portion and uniform electrical resistance required for large-sized composite electrode substrates for fuel cells.

〔Example] Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 5, Comparative Examples 1 to 10 (1) Preparation of adhesive Artificial graphite fine powder with an average particle size of 3 μm and an average particle size of 40 μm
m of artificial graphite fine powder were prepared, and both were mixed at various blending ratios. Each of the mixed powders was added to a phenolic resin initial condensate (manufactured by Sumitomo Durez ■, PR940) and sufficiently kneaded with a niegu to prepare paste adhesives having different viscosities.

(2) Manufacture of composite electrode substrate As a porous carbonaceous electrode plate, chopped pitch-based carbon fiber (average length 2011cm) was mixed with phenol resin, molded, and then baked at 2000°C.
A plate-like body having a size of 0Il+w, a width of 920 mm, a thickness of 2 mm, a porosity of 64%, and an average pore diameter of 50 μm was used. The carbonaceous separator plate was prepared by rolling a phenol resin kneaded with fine graphite powder (average particle size 5 μm), hardening it, and then baking it at 1300°C. A square thin plate was used.

An adhesive was applied to the surface of this separator plate using a doctor blade method, and the porous carbonaceous electrode plates described above were bonded to both sides. The joining was performed so that the longitudinal direction of the electrode plate was perpendicular to the front and back surfaces of the separator plate, and a 45-1 interval was left at both ends.

After joining, the members are heated to 80°C and pressed for 55 minutes.
The resin component of the adhesive was cured by applying a pressure of "kg/cab".

Next, the joining members were transferred to an electric firing furnace and encapsulated with coke powder, and then fired at a temperature increase rate of 5° C./min to 1000° C.

Side seals made of the same material as the separator plates were bonded to both ends of the integrated member whose adhesive layer was carbonized by firing, via the bonding agent. Subsequently, the outer periphery and plane were machined so that the cell size was 1100K in length on the negative side and 2.8mm in thickness, and grooves (
A carbonaceous composite electrode substrate for a phosphoric acid fuel cell was manufactured by installing a carbonaceous composite electrode substrate having a width of 2 mm and a depth of 1 cm + s.

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

The various properties and characteristics shown in Table 1 were measured in the following manner.

(1) Thickness of adhesive layer: Divide the specimen into 16 equal parts, observe the side surface with an optical microscope, and measure the layer thickness.

■Electrode porosity, bridge pore diameter: The electrode member after adhesion was measured with mercury pressure method to obtain a pore diameter of 0. Measure the porosity down to 01 μm. Pore diameter was expressed as 50% of the previous pore volume.

■Electrical resistance: Measure the resistance per area using the voltage drop method, and calculate the value by multiplying the area and total resistance.

■Adhesive strength: Separator plate (30x50xO.

811-) was coated with adhesive (width 3 s+m), the two specimens were joined, and after hardening, they were fired at a temperature of 1000° C. in a non-oxidizing atmosphere. The bonding interface between these two sheets is pulled, and the force required for peeling is defined as the adhesive strength.

From the results in Table 1, the examples that meet the requirements of the present invention have relatively high adhesive strength and low electrical resistance with little variation despite the large size electrode substrate, and the comparative examples have relatively high adhesive strength and low electrical resistance with little variation. No phenomena such as a decrease in the porosity of the electrode structure due to penetration of the adhesive or a decrease in processing yield due to peeling of the adhesive interface were observed.

[Effects of the Invention] As described above, according to the present invention, by applying the adhesive with the specified composition and the adhesive conditions, even large sizes can always have excellent adhesive strength and uniform and low electrical resistance. A carbonaceous composite electrode substrate for fuel cells can be manufactured.

Moreover, since no extra processing steps are required and there is no reduction in processing yield due to peeling phenomena, productivity is excellent.

Applicant: Tokai Carbon Co., Ltd. Agent: Patent Attorney Masaya Takahata

Claims (1)

[Claims] 1. 10 to 40 parts by weight of carbonaceous powder with an average particle size of 1 to 10 μm and 60 to 9 parts of carbonaceous powder with an average particle size of 20 to 80 μm
After mixing 0 parts by weight with a liquid thermosetting resin having a residual carbon content of 40% or more, an adhesive having a viscosity of 500 to 5000 poise is prepared. Apply uniformly to a thickness of 50 to 200 μm, bond to a porous carbonaceous electrode plate, harden the adhesive layer under pressure and heat, and then sinter and carbonize in a non-oxidizing atmosphere at a temperature of 800°C or higher. A method for manufacturing a carbonaceous composite electrode substrate for fuel cells, characterized by: