JP4656370B2 - Separator for polymer electrolyte fuel cell, method for producing the same, and polymer electrolyte fuel cell - Google Patents

Description

The present invention relates to a method for producing a polymer electrolyte fuel cell separator and a polymer electrolyte fuel cell.

  There are various types of fuel cells depending on the type of electrolyte, fuel, oxidant, etc. Among them, solid polymer electrolyte membranes that use solid polymer electrolyte membrane as electrolyte, hydrogen gas as fuel, and air as oxidant, and fuel cells A methanol direct fuel cell that directly extracts hydrogen from methanol and uses it as fuel can efficiently generate power at a relatively low temperature of 200 ° C. or lower during operation.

  A polymer electrolyte fuel cell generates electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and a fuel gas containing oxygen such as air. In the structure, first, a catalytic reaction layer composed mainly of carbon powder carrying a platinum-based metal catalyst is formed on both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions. Next, a diffusion layer having both fuel gas permeability and electronic conductivity is formed on the outer surface of the catalytic reaction layer, and the diffusion layer and the catalytic reaction layer are combined to form an electrode.

  Next, a gas seal material or a gasket is disposed around the electrode with a polymer electrolyte membrane interposed so that the fuel gas to be supplied leaks outside or the two kinds of fuel gases are not mixed with each other. This sealing material or gasket is integrated with an electrode and a polymer electrolyte membrane and assembled in advance, and this is called an electrode electrolyte membrane assembly (MEA). On the outside of the MEA, a conductive separator plate for mechanically fixing the MEA and electrically connecting adjacent MEAs to each other in series is disposed. In the portion of the separator plate that contacts the MEA, a reaction gas is supplied to the electrode surface, and a gas flow path for carrying away the generated gas and surplus gas is formed. Although the gas flow path can be provided separately from the separator plate, a method of providing a gas flow path by providing a groove on the separator surface is general. In such a polymer electrolyte fuel cell, the separator is required to have high conductivity, and to have high corrosion resistance against the reaction during oxidation / reduction of hydrogen / oxygen.

  The separators constituting these polymer electrolyte fuel cells have a role of ensuring the supply path for the reaction gas flowing into the fuel cells and transmitting the electricity generated by the fuel cells to the outside. In order to sufficiently fulfill the above role, the separator in the battery is required not only to have high conductivity in the surface direction and thickness direction, but also to reduce the contact resistance with the electrode portion.

In response to this demand, a separator having a low contact resistance with an electrode portion and a manufacturing method thereof have been proposed (see, for example, Patent Document 1). This separator forms a mixture of a conductive material, a thermoplastic resin, and a thermosetting resin, and controls the surface roughness of the separator surface to 1.5 μm to 9 μm by polishing.
However, the separator has a rough surface and the contact resistance with the electrode part is not sufficiently reduced.
JP 2002-270203 A

It is an object of the present invention to provide a method for producing a polymer electrolyte fuel cell separator having a low contact resistance with an electrode portion and a polymer electrolyte fuel cell in a separator formed by molding a mixture of a conductive material and a resin. And

  In order to solve the above problems, the influence of the state of the separator surface in contact with the electrode part on the contact resistance has been examined. It was found that the roughness is low, the contact resistance is low, and the conductivity is high.

That is, the present invention forms a composition containing (A) conductive material 95 to 50% by weight and vinyl ester resin 5 to 50% by weight into a desired shape,
(B) Surface roughness when the surface of the obtained molded body was measured by a blasting method using a 4 μm front end diameter probe with a polishing substance containing a spherical abrasive having an average particle diameter of 40 μm or less. Polished to less than 1.5 μm,
(C) Next, a method for producing a separator for a polymer electrolyte fuel cell is provided, wherein the roughened surface is washed.
Furthermore, the present invention provides a polymer electrolyte fuel cell having a laminated structure in which electrodes are disposed on both surfaces of an electrolyte membrane, and the electrolyte in which the electrodes are disposed is sandwiched between fuel cell separators . be by molding a composition containing a conductive material 95 to 50 wt% and 5 to 50 wt% vinyl ester resin, does not have a film of a vinyl ester resin surface of the molded article by the removal of the resin layer, In addition, the present invention provides a polymer electrolyte fuel cell having a surface roughness of less than 1.5 μm when measured using a 4 μm front end diameter probe.
Furthermore, the present invention is a molding comprising a composition containing 95 to 50% by weight of a conductive material and 5 to 50% by weight of a vinyl ester resin, and the surface of the molded product has a vinyl ester resin film by removing the resin layer. In addition, the present invention provides a separator for a polymer electrolyte fuel cell, which has a surface roughness of less than 1.5 μm when measured using a 4 μm front end diameter probe.

The polymer electrolyte fuel cell separator obtained by the production method of the present invention has a low contact resistance and can provide a fuel cell having high conductivity.

  Embodiments of the present invention will be described below.

  Although it does not specifically limit as an electroconductive material used for this invention, For example, a carbon material, a metal, a metal compound can be mentioned, and it uses combining 1 type, or 2 or more types of these electroconductive materials. it can. Further, a composite material of a non-conductive material and a conductive material may be used.

Examples of the carbon material include particulates and powders such as artificial graphite, natural graphite, glassy carbon, carbon black, acetylene black, and ketjen black. There are no particular restrictions on the shape of the particles and powder, and any of fibrous, particulate, foil, scaly, spherical, and amorphous shapes may be used. Also, expanded graphite obtained by chemically treating graphite can be used. Considering conductivity, artificial graphite, natural graphite, and expanded graphite are preferable in that a high level of conductivity can be achieved with a smaller amount. As the fibrous carbon material, any of pitch-based, PAN-based, and rayon-based carbon fibers can be used. In view of conductivity, carbon fibers produced through a carbonization and graphitization process at a high temperature of 2000 ° C. or higher are preferable. Although there is no restriction | limiting in particular in the length and form of carbon fiber, If the kneadability with resin is considered, the filament whose fiber length is 1 inch or less, a chopped strand, and a milled fiber are preferable.

Examples of the metal and metal compound include powders such as aluminum, zinc, iron, copper, nickel, silver, gold, stainless steel, palladium, and titanium, particles, fibers, foils, and amorphous. I can do it. Further, boron compounds such as titanium, zirconium and hafnium can also be used.

Examples of the resin used in the present invention include synthetic resins such as thermosetting resins and thermoplastic resins.
Such a resin not only needs to act as a main raw material conductive material and / or a binder that anchors the conductive material, but also the operating temperature of the fuel cell and the fuel, oxidant, water, etc. supplied to the fuel cell. It is desired to be stable to the product. Considering the above, the resin is preferably a thermosetting resin having heat resistance and acid resistance. Examples of the thermosetting resin include phenol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, silicone resin, diallyl phthalate resin, maleimide resin, polyimide resin, and the like. Two or more types of mixtures can be used.
The form of the resin is not particularly limited as long as it can be mixed and dispersed with the conductive material. When the resin is a liquid, it is preferable that the viscosity is as low as possible because it is easy to mix and disperse with the conductive material. The solid resin is preferably in a powder form and has an average particle size of 1000 μm or less.

Examples of the thermoplastic resin include polyethylene, polystyrene, polypropylene, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyether sulfone, polycarbonate, polyoxamethylene, polyamide, polyimide, polyamideimide, polyvinyl alcohol, polyvinyl chloride, and fluorine resin. , One or a mixture of two or more selected from polypenissulfone, polyetheretherketone, polysulfone, polyetherketone, polyarylate, polyetherimide, polymethylbenden, etc. There is no limitation.

  The content of the resin in the composition is preferably 5 to 50% by weight, and particularly preferably 10 to 30% by weight in order to develop the strength and conductivity of the separator.

  The method for molding the composition is preferably a method that includes a gas flow path and can be integrally molded. Examples of such molding methods include press molding, injection molding, transfer molding, and the like.

The polymer electrolyte fuel cell separator obtained by the production method of the present invention does not have a resin film. Usually, a separator obtained by molding a composition containing a conductive material and a resin has a resin film on its surface. The separator of the present invention can be obtained by using a method such as surface polishing described later. It does not have a film.
Further, the polymer electrolyte fuel cell separator obtained by the production method of the present invention is characterized in that the surface roughness is a value measured by a surface roughness meter having a probe tip diameter of 4 μm and Ra is less than 1.5 μm. There is.

When the surface roughness in the polymer electrolyte fuel cell separator obtained by the production method of the present invention is Ra = 1.5 μm or more as measured above, the surface is too rough, so the electrode portion There is a tendency for the contact portion to decrease and the contact electrical resistance to increase.

The surface roughness of the separator can be measured with a surface roughness meter having a probe tip diameter of 4 μm in accordance with JIS B 0601 (1994).
The parameters representing the surface roughness include arithmetic average roughness (Ra), maximum height (Ry), ten-point average roughness (Rz), etc. The surface roughness of the present invention is the arithmetic average roughness (Ra ). Ra is a value expressed in μm in terms of the standard length 1 and the roughness curve expressed as y = f (x) as defined in the above JIS. is there.
Ra = 1 / l × ∫ ₀ ^l | f (x) | dx

  Examples of the method for removing the resin layer on the surface of the molded product in which the gas flow path is integrally molded by the molding method include removal methods such as an acid treatment method, a sandpaper method, and a blast treatment method. Among these methods, the blasting method is particularly preferable in order to uniformly remove the resin layer on the surface of the molded product.

  In the acid treatment method, depending on the resin group to be selected, the treatment is insufficient and the reduction in the desired contact resistance cannot be realized, and the treatment time is increased. Further, in the sandpaper method, it is very difficult to uniformly remove the resin layer on the surface of the molded product.

  In order to obtain the above-mentioned surface roughness, an abrasive substance containing a spherical abrasive having an average particle diameter of 40 μm or less is used as an abrasive substance used for blasting. When an abrasive substance containing a large spherical abrasive having an average particle diameter exceeding 40 μm is used, Ra may exceed 1.5 μm, which is not preferable.

  Examples of the polishing substance used for the blast treatment include iron, stainless steel, aluminum, zinc, copper, alumina, carbon silicon, glass, resin, and silica sand.

The blasting refers to processing a product by flying particles such as sand or iron powder at high speed using compressed air or the power of a motor. Commonly called sand blasting, shot blasting, and air blasting, when the average particle size of the abrasive is 40 μm or less as in the present invention, air blasting in which the abrasive is blown using compressed air is preferred.
By adjusting the air blasting and blasting conditions, that is, air pressure, the amount of abrasive sprayed per unit time, the distance between the spray nozzle and the molded product, etc., the surface roughness of the molded product can be arbitrarily adjusted. it can.

The fuel cell stack is operated at about 80 ° C. and often circulates cooling water. It is necessary to prevent the solid polymer film from being soiled by the eluate from the hot water separator and from being electrically short-circuited by the cooling water. It is said that trace metal ions contaminate the polymer electrolyte membrane, resulting in a decrease in battery characteristics and a decrease in power generation efficiency.

Although an example was given as an abrasive material used for blasting, there are many metal materials. If these abrasive substances remain on the separator surface, the polymer electrolyte membrane is contaminated, causing deterioration of battery characteristics.

In order not to cause deterioration of battery characteristics after blasting, it is necessary to clean the separator and completely remove the residual abrasive and polishing powder.
If an abrasive substance or the like remains on the surface of the separator, it causes interference with electrical contact, catalyst poison during fuel cell operation, and film deterioration, resulting in increased contact resistance and decreased fuel cell performance.

  Examples of the cleaning method include a method of spraying compressed air on the separator surface, a method of brushing with a brush, a method of cleaning with distilled water, a method of cleaning with an organic solvent such as ethanol, and the like.

The fuel cell of the present invention may be composed of only a single cell, which is a basic structural unit in which an electrolyte is sandwiched between electrodes and the separator is disposed on the outside, and a plurality of such single cells are laminated. It will be.
Here, the fuel cell uses a power generation system in which hydrogen obtained by reforming the fuel is used as a main fuel, and chemical energy obtained when this hydrogen reacts with oxygen is used as electric power. Is formed by collecting a single cell, which generates power, in a single or a stacked structure in series and collecting current with current collecting plates provided at both ends of the stack.

  An example of the structure of the polymer electrolyte fuel cell is shown in FIG. A single cell, which is a basic structural unit of a fuel cell, has a structure in which a separator 1 sandwiches both surfaces of an electrolyte membrane electrode assembly 6 including a solid polymer electrolyte membrane 3, a fuel electrode 4, and an oxidizer electrode 5. The flow path 7 formed on the surface of the separator is suitable for stably supplying fuel and an oxidant to the electrode. Further, by introducing water as a heat source to the opposite surface of the separator installed in the oxidizer electrode 5, heat can be taken out from the fuel cell. FIG. 3 shows an example of a cell stack (fuel cell stack) in which a plurality of single cells configured as described above are stacked in series.

  The fuel cell of the present invention described above can be used as various mobile power sources such as artificial hygiene, airplanes, spacecrafts, etc. in addition to electric vehicle power supplies, portable power supplies, emergency power supplies, and the like.

  Examples of the present invention will be described below.

With respect to the molded plates obtained in the examples described later, the measurement methods of resistance value, surface roughness and metal analysis are as follows.
<Measurement of resistance value>
A test piece obtained by cutting the molded plate obtained in Example 1 into 50 mm × 50 mm was used as a test piece, and pressure was applied in a state in which both sides were sandwiched between carbon papers of the same size (Toray TGPH-120). The resistance value of the paper was measured.

  After measuring the resistance value, this molded plate was blasted with an air blast machine (manufactured by Nichu, PAMD-102). The blasting conditions were a pressure of 0.2 MPa, a distance of 150 mm, a nozzle moving speed of 20 m / min, a spray amount of 150 g / min, and glass beads having an average particle size of 40 μm were used as the polishing substance.

  After the blast treatment, compressed air was sprayed onto the surface of the treated molded plate to remove abrasive substances and abrasive powder, and then immersed in distilled water for 2 hours. This washing with distilled water was repeated 4 times to complete the washing.

After washing the molded plate, the resistance value was measured again by the above method, and the resistance reduction rate was measured by the following formula. The resistance reduction rate was calculated by the following formula.
Resistance reduction rate = [1− (resistance value before blast treatment−resistance value after blast treatment) / resistance value before blast treatment] × 100

<Measurement of surface roughness>
Measurement was performed by the method described in JIS B0601-1994 using the molded plate as a test piece and using a surface roughness measuring instrument having a probe tip diameter of 4 μm (Surfcoder SE3500, manufactured by Kosaka Laboratory).

<Metal analysis>
The obtained molded plate and distilled water were placed in a Teflon (registered trademark) container at a weight ratio of 1: 2, immersed in a 95 ° C. oil tank, and heated for 24 hours. After heating, it was cooled to room temperature, the metal analysis of the outer water phase was performed, and the analysis of silicon (Si) was performed.
The analysis of Si was based on JIS K 0101, and inductively coupled plasma (ICP) emission spectroscopic analysis was performed. An Optima 3300 DV manufactured by Perkin Elmer was used as the ICP emission spectroscopic analyzer.
If the surface of the molding plate is not sufficiently cleaned, silicon contained in the glass, which is a polishing material for blasting, should remain on the surface of the molded product. Whether or not the separator is a separator that does not deteriorate the battery performance without metal elution is determined based on whether or not silicon is detected.

Example 1
Scale-like graphite having an average particle diameter of 100 μm is used as graphite particles, and vinyl ester resin is mixed as a resin at a ratio of 75% by weight of scale-like graphite powder and 25% by weight of vinyl ester resin by a mixer for 20 minutes. The composition used as the raw material of was prepared.

  A predetermined amount of this composition was weighed, filled in a mold, and press-molded at 150 ° C. and 10 MPa for 10 minutes to produce a molded plate having a thickness of 3 mm.

Example 2
In Example 1, the resistance reduction rate, the surface roughness, and the metal analysis of the molded plate were measured in the same manner except that the average particle size of 40 μm of the blasting polishing material was changed to 20 μm.

Example 3
In Example 1, the resistance reduction rate, the surface roughness, and the metal analysis of the molded plate were measured in the same manner except that the distance of 150 mm in the blasting condition was changed to 200 mm.

Example 4
In Example 1, the reduction rate, surface roughness, and metal analysis of the molded plate were measured in the same manner except that the distilled water under washing conditions was ethanol. The results are shown in Table-1.

Comparative Example 1
In Example 1, the resistance reduction rate, the surface roughness, and the metal analysis of the molded plate were measured in the same manner except that the average particle size of 40 μm of the blasting polishing material was changed to 80 μm.

Comparative Example 2
The resistance reduction rate, surface roughness, and metal analysis of the molded plate were measured in the same manner except that the blast treatment in Example 1 was immersed in a 30% by weight sulfuric acid aqueous solution. It was immersed in a sulfuric acid aqueous solution for 24 hours.

Comparative Example 3
The resistance reduction rate, surface roughness, and metal analysis of the molded plate were measured without performing the cleaning step in Example 1. The results are shown in Table-2.

  As shown in the evaluation results in Tables 1 and 2, the contact resistance is low by blasting using an abrasive having an abrasive of 40 μm or less and removing any residual abrasive and abrasive powder on the surface of the molded product, and It was found that a molded product with less elution components from the separator can be obtained.

It is a perspective view which shows the separator for fuel cells of this invention. It is a perspective view which shows the fuel cell structure of this invention. It is a perspective view which shows the fuel cell stack structure of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separator 2 Fuel, oxidant, cooling water flow path 3 Single cell 4 Solid polymer electrolyte membrane 5 Fuel electrode 6 Oxidant electrode 7 Electrolyte membrane electrode assembly 8 Fuel cell stack 9 Oxidant flow path 10 Fuel flow path 11 Cooling water flow Road

Claims (3)

(A) A composition containing 95 to 50% by weight of a conductive material and 5 to 50% by weight of a vinyl ester resin is molded into a desired shape,
(B) Surface roughness when the surface of the obtained molded body was measured by a blasting method using a 4 μm front end diameter probe with a polishing substance containing a spherical abrasive having an average particle diameter of 40 μm or less. Polished to less than 1.5 μm,
(C) A method for producing a separator for a polymer electrolyte fuel cell, wherein the roughened surface is then washed. In a polymer electrolyte fuel cell having a laminated structure in which electrodes are disposed on both surfaces of an electrolyte membrane, and the electrolyte in which the electrodes are disposed is sandwiched between fuel cell separators, the separator includes conductive materials 95 to 95. A composition containing 50% by weight and 5 to 50% by weight of vinyl ester resin is molded, the surface of the molded product does not have a vinyl ester resin film by removing the resin layer , and has a front end of 4 μm. A polymer electrolyte fuel cell having a surface roughness of less than 1.5 μm as measured using a diameter probe. A composition comprising 95 to 50% by weight of a conductive material and 5 to 50% by weight of a vinyl ester resin is molded, and the surface of the molded product does not have a vinyl ester resin film by removing the resin layer, And a separator for a polymer electrolyte fuel cell, having a surface roughness of less than 1.5 μm when measured using a 4 μm front end diameter probe.

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