JP2004213997A - Pretreatment method of separator for fuel cell, and fuel cell laminating that plate having carried out pretreatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a pretreatment method of a separator that enables to produce a assembled fuel cell which has no initial operation trouble and can maintain stable generating capacity from operation start, by applying a pretreatment after processing of a separator constituting a unit cell of the fuel cell. <P>SOLUTION: The separator after completion of processing is set in a vibrating tank, and a pure water with a conductivity of 5 μS/cm or less or a mixture of pure water and ethanol having a conductivity of 5 μS/cm or less is supplied to the vibrating tank, and ultrasonic vibration with an oscillation frequency 20-50 kHz and an effective ultrasonic power density of 5-20 kW/m<SP>3</SP>is applied for 30 minutes. This ultrasonic vibration is applied three times while exchanging the water solution, and by applying working-up cleaning, the pretreatment process is completed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for pretreating a separator constituting a single cell of a fuel cell.
[0002]
[Prior art]
In a fuel cell, an electrolyte membrane is sandwiched between a fuel electrode comprising a fuel electrode catalyst layer and a porous support layer on one side and an air electrode comprising an air electrode catalyst layer and a porous support layer on the other side. Are sandwiched by separators which also serve as supply paths for reaction gases such as hydrogen and oxygen. Hydrogen gas supplied to the reaction gas supply passage of the separator provided on the fuel electrode side is diffused in the porous support layer, absorbed by the fuel electrode catalyst layer and separated into hydrogen ions and electrons. At the air electrode, oxygen supplied to the reaction gas supply path of the separator is diffused in the porous layer, absorbed by the air electrode catalyst layer, and formed by hydrogen ions moving through the electrolyte membrane and electrons moving through the external circuit. Produces water. In this reaction, the electrons separated in the fuel electrode catalyst layer move through an external circuit, so that a current flows. The unit cell having this configuration is called a unit cell. However, since the electromotive force is as small as about 1 volt, in order to use it as a power source for electric equipment, a large number of such unit cells are stacked to form a stack, and a battery having a required output is formed. Assemble. In the unit cell having such a configuration, the role of the separator is to separate the fuel gas entering the fuel electrode and the oxidizing gas (such as air) entering the air electrode when the unit cells are stacked, and to separate the unit cells from each other. It has two roles of electrical connection. As a separator that can stably fulfill these roles and reduce cost, there is a separator formed by molding using carbon as a material (for example, see Reference Document 1).
[0003]
[Patent Document 1]
JP-A-2000-223133 (pages 2-3)
[0004]
[Problems to be solved by the invention]
However, the molded article has a high binder resin content, and has a lower carbon density than a carbon plate having a lower binder resin content used in cutting, resulting in lower electric conductivity. . Therefore, in order to improve this, a process of roughening the surface of the carbon plate of the molded article was performed, and a single cell was formed using the carbon plate. As a result, a black effluent (black solid matter) was observed at the outlet pipe of the reaction gas and the cooling water. Therefore, when operating a fuel cell system including a fuel cell assembled by stacking single cells using this carbon plate, clogging in the system piping and failure of the pump may cause problems in the fuel cell system. This can be a factor that causes In order to prevent the generation of this black effluent, electric conductivity can be secured by simple washing, for example, washing with running water, washing with water, washing with a cleaning agent, or blowing with air or nitrogen. When the battery cannot be completely removed and an operation test is performed as a battery, occurrence of the black outflow portion described above is inevitable. On the other hand, when high energy such as laser is applied to the surface, the surface may be stabilized, but conversely, the surface may be disturbed and the electrical conductivity may be reduced, and the manufacturing cost may be increased.
In view of the above, the present invention has been made in view of the above-described problems. By taking effective measures to prevent the generation of black effluent due to the operation of a fuel cell, stable power generation at low cost is achieved. It is to realize a separator that makes it possible.
[0005]
[Means for Solving the Problems]
Therefore, in order to achieve both the conductivity and the stability of the surface, which are seemingly contradictory, which are the above-mentioned problems, and as a means for obtaining a simple and reliable effect, surface treatment is performed by applying energy by ultrasonic vibration. Has been found to be the easiest and most effective.
[0006]
That is, in order to solve the above-mentioned problem, the invention described in claim 1 of the present invention is to sandwich a membrane-electrode assembly formed by joining an oxygen electrode and a hydrogen electrode on both surfaces of an electrolyte membrane. A pretreatment method after processing a separator having a supply path of a reaction gas or cooling water containing carbon as a main component, wherein the pretreatment method includes immersing the separator in an aqueous solution and ultrasonically vibrating the aqueous solution. It is characterized by the following.
[0007]
Further, in the invention described in claim 2 of the present invention, in claim 1, the aqueous solution is a mixture of pure water having a conductivity of 5 μS / cm or less, or pure water having a conductivity of 5 μS / cm or less and ethanol. It is a mixed liquid.
[0008]
Also, in the invention described in claim 3 of the present invention, in claim 1 or 2, the frequency of the ultrasonic vibration is 20 to 50 kHz, and the effective ultrasonic output density is 5 to 20 kW / m ³ . It is characterized by the following.
[0009]
Further, in the invention described in claim 4 of the present invention, in any one of claims 1 to 3, the pre-processing step by the ultrasonic vibration has an effective ultrasonic output amount density of 5 to 30 kWh / m ^3. It is characterized by being.
[0010]
Further, in the invention described in claim 5 of the present invention, in any one of claims 1 to 4, the pretreatment step by the ultrasonic vibration uses the new aqueous solution every time the ultrasonic vibration is applied. In addition, ultrasonic vibration for 30 minutes is repeated three times.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. The embodiment described below is a preferred specific example of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. The embodiments are not limited to these embodiments unless otherwise described.
[0012]
FIG. 1 is a flowchart of a pretreatment process showing a first embodiment of a fuel cell separator pretreatment method according to the present invention and a fuel cell in which plates subjected to the pretreatment are stacked. In addition, as one means for applying ultrasonic vibration energy in the pretreatment step, specifically, an aqueous solution is subjected to ultrasonic vibration and energy is applied through the aqueous solution. One vibration tank is used in this step, and this is a step of applying the ultrasonic vibration energy to a relatively small amount of the vibrating object. The separator of the vibrating object is obtained by dispersing carbon powder in a resin binder, molding the resultant, molding it into a desired shape by press working, baking and consolidating the resin film formed on the surface. This is obtained by shaving off by surface treatment such as sand blasting to expose carbon on the surface to increase the conductivity of the surface. However, other manufacturing methods include, but are not limited to, cutting, injection molding, etching, electric discharge, ultrasonic processing, engraving, and the like.
[0013]
In the pretreatment step 1 for applying ultrasonic vibration energy to the separator prepared by the above-described method, the separator is set S1 in a vibration tank, and then the aqueous solution is supplied S2 to the vibration tank to fill the vibration tank with the aqueous solution. As the aqueous solution, pure water having a conductivity of 5 μS / cm or less, or a mixed solution of pure water having a conductivity of 5 μS / cm or less and ethanol is used. The reason for this is that the conductivity meter attached to the ion-exchanged water outlet indicates 5 μS / cm or less, so that the conductivity can be strictly controlled and the cost is not high because it is not a special solution. Things. Next, the oscillation frequency of the ultrasonic vibration is 20 to 50 kHz, preferably 24 to 40 kHz, and the effective ultrasonic output density (kW / m ³ ) is obtained by dividing the ultrasonic output output from the ultrasonic oscillator by the volume of the vibration tank. And represents an ultrasonic output corresponding to a unit volume, and the first ultrasonic vibration 30 is applied for 5 minutes to 20 kW / m ³ , preferably 9 to 16 kW / m ³ for 30 minutes. This is performed during the application time. When the first ultrasonic vibration S3 is completed, the solution is replaced with a new aqueous solution S4, and the second ultrasonic vibration S5 is performed under the same ultrasonic application conditions and application time as those of the first ultrasonic vibration. The third ultrasonic vibration S7 is performed under the same ultrasonic application conditions and application time as the first and second ultrasonic vibrations. The ultrasonic vibration is divided into three times. When the ultrasonic vibration is terminated, by observing the aqueous solution as a result of applying the energy by the ultrasonic vibration, unstable components on the surface are removed and the surface does not float. This is to confirm. The total effective ultrasonic output density given by the energy of the total of three ultrasonic vibrations is the effective ultrasonic output density × the total ultrasonic application time, and this is expressed as an effective ultrasonic output amount density (kWh / m ³ ). in 5~30kWh / ^{m 3,} preferably 9~24kWh / ^{m 3.} Thereafter, the separator is pulled up from the vibrating tank S8, and the pretreatment step is completed through the finish cleaning S9. Pure water having a conductivity of 5 μS / cm or less or a mixed solution of pure water having a conductivity of 5 μS / cm or less and ethanol is also used for the finish cleaning.
[0014]
FIG. 2 is a schematic diagram of a pretreatment step showing a second embodiment of a fuel cell in which a fuel cell separator pretreatment method according to the present invention and plates subjected to the pretreatment are laminated. The number of the vibrating tanks used in this step is three, and this is a step of applying the ultrasonic vibration energy to a relatively large amount of the vibrating object. The separator of the vibrating object is formed by the method of the first embodiment described above. First, three vibration tanks 10, 11, and 12 are prepared, and pure water having a conductivity of 5 μS / cm or less or pure water having a conductivity of 5 μS / cm or less is used in each of the vibration tanks. Fill with a mixture of water and ethanol. Then, first, the separator is immersed in the first vibration tank 10, and ultrasonic vibration is performed under the same ultrasonic application conditions and application time as in the first embodiment. Next, the energy of the ultrasonic vibration is sequentially applied to the second vibration tank 11 and the third vibration tank 12, and finally, the energy is lifted up from the third vibration tank 12, and the finish cleaning is performed.
[0015]
The effective ultrasonic output density, which gives energy by ultrasonic vibration, is that if the ultrasonic waves are too weak, the carbon barely adhered to the binder resin on the surface remains without being separated, and if it is too strong, the coarse carbon exposed on the surface separates However, when the resin surface is largely exposed, the conductivity of the surface decreases instead of stabilizing the surface. Also, if the time for applying the ultrasonic vibration is too short, the surface treatment becomes incomplete and carbon remains on the surface, and the energy effect given by the ultrasonic vibration cannot be sufficiently obtained. The energy effect by the ultrasonic vibration cannot be obtained as much as the corresponding cost. The same can be said for the number of vibrations. Based on the above, the pretreatment method according to the present invention was repeated while changing the conditions of the ultrasonic oscillation frequency and the application time, verifying the results, and deriving while confirming the matching between the surface treatment effect and the operation cost. Was found based on
[0016]
【The invention's effect】
As described above, the pretreatment method of the fuel cell separator of the present invention and the separator pretreated in the fuel cell in which the plates subjected to the pretreatment are stacked, the carbon bonded to the binder by a weak bonding force is removed. Therefore, a single cell is created using a separator surface-treated with the energy of ultrasonic vibrations through an aqueous solution, and in a fuel cell that is assembled by stacking the single cells, a high-speed Even if gas or liquid flows, the carbon does not desorb.Therefore, the operation that occurs due to the deterioration of the power generation reaction due to the blockage of the respective flow paths and the contamination or blockage in the pipes through which the gas and liquid flow. There is no problem such as a decrease in power generation capacity due to a failure or a trouble in the device. Therefore, there are no initial driving troubles, and excellent effects such as stable power generation capability from the start of operation can be obtained.
[Brief description of the drawings]
FIG. 1 is a flow chart of a pretreatment process showing a first embodiment of a fuel cell separator according to the present invention, which is a pretreatment method for a fuel cell separator and a fuel cell in which plates subjected to the pretreatment are stacked.
FIG. 2 is a schematic view of a pretreatment process showing a second embodiment of a fuel cell in which a pretreatment method for a fuel cell separator according to the present invention and a plate subjected to the pretreatment are stacked.
[Explanation of symbols]
Reference Signs List 1 Pretreatment step S1 Set S2 Supply of aqueous solution S3 First ultrasonic vibration S4 Replacement of aqueous solution S5 Second ultrasonic vibration S6 Replacement of aqueous solution S7 Third ultrasonic vibration S8 Pull-up S9 Finish cleaning 10 First vibration tank 11 Second vibration tank 12 Third vibration tank

Claims (5)

After processing of a separator which is arranged so as to sandwich a membrane-electrode assembly formed by joining an oxygen electrode and a hydrogen electrode to both surfaces of an electrolyte membrane and has a supply path of a reaction gas or cooling water containing carbon as a main component. A pretreatment method, wherein the pretreatment method comprises immersing the separator in an aqueous solution, and ultrasonically vibrating the aqueous solution, and laminating a fuel cell separator pretreatment method and a plate subjected to the pretreatment. Fuel cell. 2. The fuel cell separator according to claim 1, wherein the aqueous solution is pure water having a conductivity of 5 μS / cm or less, or a mixed solution of pure water having a conductivity of 5 μS / cm or less and ethanol. 3. A fuel cell in which a pretreatment method and plates subjected to the pretreatment are laminated. ^{3. The method} of claim 1, wherein a frequency of the ultrasonic vibration is 20 to 50 kHz, and an effective ultrasonic power density is 5 to 20 kW / m ^{3. 4.} And a fuel cell in which plates pre-treated are stacked. 4. The pretreatment of the fuel cell separator according to claim 1, wherein in the pretreatment step by the ultrasonic vibration, the effective ultrasonic output amount density is 5 to 30 kWh / m ^{3. 5.} A method and a fuel cell in which plates pretreated are laminated. 5. The pre-treatment step by ultrasonic vibration, wherein a new aqueous solution is used every time the ultrasonic vibration is applied, and ultrasonic vibration for 30 minutes is repeated three times. A method for pre-treating a fuel cell separator according to claim 1 and a fuel cell obtained by stacking plates subjected to the pre-treatment.

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