JPS6062063A - Activation method of electrode for fuel cell - Google Patents

Abstract

PURPOSE:To prevent an electrode catalyzer from being poisoned and enable to maintain electrode performance highly by removing chlorine ion, fluorine ion, etc. from the electrode before operation of a fuel cell after assembling it and at the time of stopping the operation of the fuel cell. CONSTITUTION:An electrode catalyzer is activated by removing halogen system composition from an electrode catalyzer which is poisoned by halogen system composition such as chlorine ion, fluorine ion, etc. An activation treatment like this can be operated before operation of a fuel cell and after assembling it or at the time of stopping operation of the fuel cell. An electro-chemical method is to perform an anode reaction at a potential higher than the predetermined level, by an outisde electric power against a fuel pole which is incorporated into the cell. Further, a cleaning method is to circulate de-ionized water, electrolyte and liquid fuel or composite liquid composed of these three through a fuel chamber and to clean the electrode catalyzer. Removing efficiency for the poisoned component of the catalyzer can be improved by using such electro-chemical method and cleaning method together.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for activating an electrode for a fuel cell, and in particular to a method for activating an electrode for a fuel cell such as a methanol/oxygen fuel cell, which prevents deterioration in electrode performance due to poisoning of the electrode catalyst. This invention relates to a method for activating an electrode.

[Background of the invention]

Fuel cells, which supply fuel and cause an electrochemical reaction to occur on electrodes to directly extract electrical energy, are expected to be put into practical use as a new type of power source that is expected to be highly efficient. Fuel cells, which are currently being researched for practical use, include:
Oxygen-hydrogen fuel cells that use phosphoric acid as the electrolyte are relatively large-capacity power sources, while methanol-oxygen fuel cells that use sulfuric acid as the electrolyte and potassium hydroxide aqueous solutions are used as small, portable power sources. There are oxygen-hydrogen or oxygen-hydrazine fuel cells that use hydrogen as an electrolyte. In all of these fuel cells, the electrodes must have catalytic ability, and the most practical electrode catalysts are noble metals such as platinum and palladium, used alone or in combination. Platinum group elements have high catalytic activity and are effective, but
When these catalysts are used, substances that coexist with the fuel or oxidizer, or electrochemically generated by-products, can cause
There is a problem in that the catalyst is poisoned and the electrode performance is significantly reduced.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a method 1c for activating an electrode for a fuel cell, which prevents poisoning of an electrode catalyst and maintains a high level of electrode performance.

[Summary of the Invention] The present inventors have discovered that the catalytic ability of a fuel cell electrode is significantly reduced when halogen components such as chlorine or chlorine ions, or fluorine or fluorine ions coexist in the catalyst. In particular, in methanol/oxygen fuel cells that use methanol liquid fuel,
When chloride is used as a raw material for a catalyst, chlorine or chlorine ions may remain in the catalyst, and chlorine ions may be mixed into the catalyst from battery constituent materials.

That is, for example, when chloroplatinic acid is reduced with formaldehyde by a deposition method, the reaction proceeds according to the fi1 formula.

H2PtCmu+HCHO+H*0→Pt+CO2↑+6
l-ICt...ill In this reaction, hydrochloric acid is produced and the reaction does not proceed if it becomes acidic, so it is neutralized with potassium hydroxide or the like and reduced to an alkaline solution.

HC7+KOH→ H20+KC1・・・・・・・・・
(2) Potassium chloride of formula (2) dissociates in an aqueous solution,
Chlorine ions in the solution are adsorbed on the reduced platinum.

KCl −* K”+C1−・・・・・・・・・(3)
Pt10C1''' →pt...Ct-(ad)
(4) When a platinum catalyst adsorbs chlorine, it loses its catalytic ability due to adsorption poisoning.

Historically, the ηi electrolyte and liquid fuel are usually adjusted to a predetermined molar density before use. When a fuel cell is operated continuously, relatively large amounts of electrolyte and liquid fuel are used, so they are generally diluted with tap water. Tap water generally contains chlorine ions, fluoride ions, etc. Therefore, small amounts of chlorine ions, fluorine ions, etc. from the electrolyte and liquid fuel mix into the catalyst.

The present invention is an activation method for removing halogen components from an electrode catalyst that has been poisoned by halogen components such as chlorine ions and fluoride ions.

Such activation treatment is performed during the preparation of the fuel electrode catalyst.

This can be carried out either after the fuel cell is assembled and before operation, or when the fuel cell is stopped.

Examples of the activation treatment method during preparation of the electrode catalyst include electrochemical and washing methods. As an example of the electrochemical method, there is, for example, a method of performing an anodic reaction on the fuel electrode at a predetermined potential or higher using an external power source when manufacturing the fuel electrode. When removing chlorine ions from the fuel electrode, an anode reaction is performed at a potential higher than the oxidation potential of chlorine ions.

In addition, chlorine ions are removed by washing during electrode catalyst preparation.

Examples of methods for removing fluorine ions include cleaning the electrodes with deionized water, an electrolyte-liquid fuel that does not substantially contain the above ions, or a mixed solution of deionized water, electrolyte, and liquid fuel.

When an electrolyte or a liquid fuel is used as the cleaning liquid, even if these liquid components remain in the electrode, there will be no problem with the electrode performance after battery assembly.

There are also electrochemical and cleaning methods for removing chlorine ions, fluorine ions, etc. from the electrodes and activating the electrode catalysts after assembly and before operation of the fuel cell and when stopping the operation of the fuel cell. In the electrochemical method, an anode reaction is performed on a fuel electrode incorporated in a battery at a predetermined potential or higher using an external power source. Further, in the cleaning method, deionized water, electrolyte, liquid fuel, or a mixture of deionized water, electrolyte, and liquid fuel is circulated in the fuel chamber to clean the electrode catalyst. In such a cleaning method, even if the liquid used for cleaning remains in the fuel chamber, the engine can be started or restarted without any problem.

Note that the electrochemical method and the cleaning method can be used together to enhance the effect of removing catalyst poisoning components.

The electrode catalyst of the present invention contains at least one member of Group Ⅰ of the periodic table, and has remarkable electrode performance due to poisoning by halogen-based components such as chlorine ions and fluoride ions, and has no effect due to the above-mentioned activation treatment. is large.

In methanol/oxygen fuel cells, catalysts are used in which platinum or ruthenium is supported on a porous carbon carrier such as graphite or furnace black. The supporting method may be any of the usual catalyst preparation methods such as a deposition method, an impregnation method, and a crosstalk method. The electrodes are made by adding distilled water to the catalytic rice to make it into a paste, and then adding colloidal polytetrafluoroethylene as a binder after mixing.
The catalyst paste prepared by further kneading is applied onto a conductive porous substrate, dried, and then fired.

[Embodiments of the invention]

Methanol l Ill□t/t, sulfuric acid 3 mol/
Potassium chloride in each 1.25 x 1 t of fuel solution
0-'rno7/l* 2.5X10-'mot/41
．． The monopolar potential was measured at a constant current density of 601 nm/crtl in a fuel added to 25xlO-3mo, /:/l, and 'jAte potassium 6.25x 10-' mot/lKe. The results are shown in Figure 1. From Figure 1, potassium chloride was present (code in the figure: potassium chloride 1.25xl O-'mot/l
2.2.5X10-'m07/l 3.1.25X
10-3 mot/l 4, potassium sulfate 6.25X10
It can be seen that the electrode performance of -' mat/L of 5 and no additive of 1) is significantly reduced.

Catalyst Preparation Example 1 After adding 4.92 g of carbon powder (graphite: AUP), 5 ml of 35% formaldehyde solution and 12 ml of 50% potassium hydroxide bath solution, H2O was added and the mixture was stirred to make 6 Q ml. The solution is cooled to +2 to -2C while stirring in a dry ice-ethanol refrigerant. To this solution, add 0.57 g of platinum chloride DI1 0.57 g of ruthenium chloride
．． Approximately 1 m of a solution of 32 g dissolved in H2O to make 23 m1
Add at a rate of l'/rmn. During this time, the temperature of the liquid is maintained at +2 to -2C. After the addition is complete, the solution is returned to room temperature and further heated to 35-40C, and stirred at this temperature for about 30 minutes. Further, after stirring this solution at 55 to 60 C for about 30 minutes, the solid matter is washed with distilled water, and the washing is repeated until the pH of the slurry becomes 7 or less. The washed cake was sufficiently dried at 80C in a dryer to obtain fuel electrode catalyst A. The chlorine contained in this catalyst A was analyzed by colorimetric analysis and was found to be at the detection limit (0,005% by weight or less 1).

Catalyst Preparation Example 2 Catalyst B was a fuel electrode catalyst prepared under the same conditions as Catalyst Preparation Example 1, except that washing with distilled water was repeated until the pHI was OK. The chlorine content in this catalyst is 0.
It was 012% heavy view.

Example 1 Take 0.375 g of catalyst A powder obtained in Catalyst Preparation Example 1, add 0.4 ml of distilled water, and knead well. After thorough kneading, 0.2 ml of a colloidal tetrafluoroethylene liquid (Polyflon Dispersion D, manufactured by Taikin Industries, diluted 1°5 times, containing 12% by weight of tetrafluoroethylene) was added and mixed well. 'This paste catalyst was placed on a porous carbon substrate (Kurekamat E715, manufactured by Guigen Kagaku) 50 x 50 m.
Apply evenly to m.

After drying this, it is fired for 30 minutes in an aooc nitrogen stream.

The obtained electrode was made of platinum 1. □ m9/crL Ruthenium 0.5 m? / Contains cni. This was designated as electrode 1.

Example 2 Electrode 2 was an electrode prepared under the same conditions as Example 1, except that the catalyst B powder obtained in Catalyst Preparation Example 2 was used.

Example 3 The electrode performances of the fuel electrode and the oxidizer electrode are evaluated based on the flow density-potential (t-E) characteristics. A model of current density-potential characteristics is shown in FIG. When a current is applied, the potential of the fuel electrode A moves in the negative direction (in the figure, upward) due to reaction delays and internal resistance. On the other hand, the potential of the oxidizer electrode B is in the base direction, which is downward in the figure. The difference in potential between the fuel electrode A and the oxidizer electrode B is the battery voltage C, and this is large, and a battery whose voltage does not drop much even when current is drawn out is an excellent battery, which improves performance. In order to achieve this, it is necessary to lower the characteristic curve of the fuel electrode downward and push the characteristic curve of the oxidizer electrode upward.

Therefore, the electrodes (1, 2
) was cut out to a size of 2c4, and the electrode performance (i-E% property) was measured in fuel with a methanol concentration of 1 mo7/ts and a sulfuric acid concentration of 3 mo, /:/l.

The results are shown in Figure 3. In FIG. 3, 6 indicates the electrode performance of electrode 1, and 7 indicates the electrode performance of electrode 2.

As is clear from Figure 2, electrode performance deteriorates when chlorine or chlorine ions are present, as in electrode 2, but electrode performance is high in electrode 1, which was thoroughly cleaned during catalyst preparation and avoided chlorine contamination. Recognize.

Miyamashio 114 Electrodes 1 and 2 were energized in a 3 mol/t sulfuric acid solution at a potential of 0.76 V (based on standard hydrogen electrodes) for 5 minutes to cause an anode reaction, and then washed with distilled water.

These were designated as electrode 3 and electrode 4, respectively. Using this electrode, methanol concentration is 1 mol/l, phosphoric acid concentration is 3
The monopolar position was measured at a current density of 60 mA/cnf in a fuel of mA/L. As a result, based on standard hydrogen electrode standards,
The unipolar potential was 0.35V at iJ#3 and 0.35V at electrode 4.
It was 36V. Note that the chlorine content of electrode 3 and electrode 4 was below the detection limit.

Example 5 The monopolar potential was measured using the electrodes treated at Higashioki as in Example 4, using electrodes 5 and 6, except that the potential was 1.36 V (standard hydrogen electrode reference) and electricity was applied for 2 minutes to cause an anode reaction. did. As a result, the current density was 60 mA/art, electrode 5 was 0.36 V, and electrode 6 was 0.36 V based on a standard hydrogen electrode. The chlorine content was below the detection limit for each electrode.

Catalyst Preparation Example 3 Carbon powder (manufactured by Capot Co., Ltd., Palcan XC72R1 (
121) 500 ml of methanol-water was added, 5.3 g of chloroplatinic acid (H2PtC1,6.6HzO) was dissolved, and the mixture was heated under reflux at 70C for reduction to obtain an air electrode catalyst.

This was designated as catalyst C.

Example 6 1 g of Catalyst C was mixed with distilled water, and 0.4 g of Polyflon dispersion (manufactured by Daikin) was added and kneaded. The mixture was applied to a conductive porous carbon substrate of 100 cvt, dried, and then air-flowed. The mixture was fired at 300C for 30 minutes to obtain an air electrode. This was designated as electrode 7.

Example 7 The electrode 4 for the fuel electrode obtained in Example 4 and the electrode 7 for the air electrode obtained in Example 6 were cut out to a size of 50×50 mm, and a unit cell A was constructed using these. 3 mol between the electrodes
/L of sulfuric acid immersed in a cation exchange membrane (manufactured by DuPont,
Nafion) was used as an electrolyte. The oxidizing agent was air, the fuel was 1mo7/, /, and a solution containing methanol and 3mot/sulfuric acid was used, and each was continuously supplied from outside the cell by a fan and a pump. Battery temperature is 6
It was held at 0C. Initial output is electrode density 60mA/c
rl was 0.45■. When this operation was repeated for 100 hours by repeatedly stopping the fuel supply every 8 hours, the output was 0.44 V.

Comparative Example 1 A battery was constructed under the same conditions as in Example 7 except that electrode 2 for the fuel electrode obtained in Example 2 was used (referred to as "Battery B"), and the battery voltage was measured.The initial output was , current density 60
mAlcy! It was 0.34 V at 100 hours, and 0.21 V after 100 hours.

Example 8 Three cells of the rechargeable battery B produced in Comparative Example 1 were stacked to form a battery C. Before operating this battery, the fuel is 1 mot/
t methanol, 3 mol/L sulfuric acid 10ml/
After pretreatment was carried out by increasing the potential of the fuel electrode until the adsorbed species was oxidized while flowing through the battery at a speed of 10 min, fuel was injected and the cell voltage was measured under the same conditions as in Example 7. The initial output is
It is 1.27 V at 100 hours, and 1.25 V after 100 hours.
Met.

〔Effect of the invention〕

According to the present invention, a fuel cell can be operated with an electrode from which halogen-based components that are poisonous components in electrode reactions have been removed, so that the cell performance can always be maintained at the sieving performance.

[Brief explanation of drawings]

Figure 1 shows the concentration of components interfering with the electrode reaction at 60 m
Relationship diagram between A/cnl current density energization time and potential change,
Figure 2 shows current density-potential (
t-E) characteristic diagram, and FIG. 3 shows current density-potential (i-E) % spout of electrodes according to the present invention and the conventional method. Agent Patent Attorney Tatsuyuki Unuma 1 Figure 60 Claws/cT11? -4 electric hours (i) Tank 2 height, electric 7℃ seat (to m/C Ayu) Continued from page 1 ■ Inventor State name Hidejibu Hitachi City Saiwai-cho Shonai 0 Inventor Kuniko Kitami Inside Saiwai-cho, Hitachi City0 Inventor Tomo Kamo - Inside Saiwai-cho, Hitachi City @Inventor Hiroki Enso Inside Hitachi Wheelworks

Claims (1)

[Scope of Claims] 1. A fuel characterized in that halogen-based components are removed from the electrode catalyst during preparation of the fuel cell electrode catalyst, after assembly and before operation of the fuel cell, and when stopping operation of the fuel cell. Method for activating battery electrodes. 2. The method for activating a fuel cell electrode according to claim 1, wherein the halogen-based component is chlorine or chlorine ions. 3. The method for activating an electrode for a fuel cell according to claim 1, wherein the electrode catalyst contains at least one element from Group Ⅰ of the periodic table. 4. A method for activating an electrode for a fuel cell according to claim 1, characterized in that an anode reaction is performed on the electrode via an external power source to remove halogen components. 5. Claim 1 provides that the electrode is cleaned with an electrolyte used in the fuel cell, deionized water, liquid fuel, or a mixed solution of two or more thereof to remove halogen components. Characteristic method for activating electrodes for fuel cells. 6. In claim 1, the fuel cell comprises:
A method for activating a cylinder single pole for a fuel cell, characterized in that methanol is used as a liquid fuel.