JPS59127372A - Electrode for fuel cell - Google Patents

Abstract

PURPOSE:To obtain a high mechanical intensity electrode for a fuel cell from which a catalyst is not separated and in which no cracks are caused and a high performance is maintained over a long period by adding a fibrous substance to make a catalyst layer. CONSTITUTION:A catalyst principally consisting of one or more platinum group elements is supported on a porous conductive carrier such as active carbon, furnace black, graphite powder or the like so that mixture of a given concentration of the catalyst is prepared. After a fibrous substance is added to the carrier catalyst powder, a sufficient amount of water is added to the mixture before it is kneaded to prepare a paste. The thus prepared paste, after being sufficiently mixed, is combined with colloidal polytetrafluoroethylene used as a binder before being kneaded again. The thus prepared paste is applied to a porous conductive base material before this is dried and sintered, thereby obtaining an electrode for a fuel cell. As the fibrous substance, polytetrafluoroethylene also used as the binder can be used since it resists a sintering temperature of 200- 300 deg.C and any substances which can not be activated by electrolyte, fuel and an oxidizing agent may be used. For example glass wool, silica wool, silica, alumina wool, alumina-wool, acid-proof metal wools of tantalum and the like and carbon wool can be used.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an electrode for a fuel cell, and in particular, in a fuel cell that directly uses liquid fuel, the present invention relates to an electrode for a fuel cell, and in particular, a conductive porous substrate and one or both surfaces thereof. When using an electrode consisting of a catalyst layer formed on
The present invention relates to a novel structure for having strength and long life.

[Prior art]

Fuel cells, which supply fuel, oxidize it electrochemically on electrodes, and directly extract all electrical energy, have been studied for a long time. Recently, with the diversification of energy sources and fuels progressing, many researchers are promoting the practical application of fuel cells, and they are attracting attention. An oxygen/hydrogen fuel cell that uses phosphoric acid as an electrolyte is one that will enter the practical stage in the near future. This is effective as a relatively large power generation system. On the other hand, a fuel cell that uses methanol directly as a fuel is also considered to be an effective alternative to the conventional twin-engine generator as a portable small power generator.

The basic structure of a fuel cell consists of two electrode plates and an electrolyte layer provided between the electrodes.

The electrodes each include a conductive porous base material, for example, a net-like or cloth-like material made of platinum, gold, tantalum, carbonaceous material, etc., and a catalyst containing one or more platinum group elements as a main component on this base material.
Alternatively, the catalyst layer may include a catalyst layer in which the catalyst is coated and bound on a conductive porous carrier, for example, a carbonaceous carrier such as activated carbon, graphite, or furnace black. When fuel is supplied to the fuel cell, the fuel and oxidant react electrochemically in the catalyst layer on the electrode, and the associated mass transfer between the electrodes occurs as ion movement through the electrolyte. . Further, the electrical energy accompanying the reaction is taken out to an external circuit through the conductive base material. In particular, in a fuel cell that uses an acidic electrolyte, such as an aqueous sulfuric acid solution, and directly uses methanol as fuel, the fuel electrode is the electrode where the liquid fuel and the liquid electrolyte are in contact, and the other electrode is the electrode where the liquid electrolyte and the oxidized n (1. For example, it is a gas electrode that comes into contact with a gas such as oxygen or air. Conventional electrodes are catalyst powders whose main component is one or more platinum group elements, or catalyst powders whose main component is one or more platinum group elements. A dispersible binder, such as colloidal polytetrafluoroethylene, is mixed with a powder of a catalyst supported on a conductive porous carrier to form a paste, and this is applied onto a surface of a paste and dried for 200 minutes. ~320C
It is prepared by firing at a temperature of .

Polytetrafluoroethylene, which is used as a binder here, is itself inert and does not get wet with acidic aqueous solutions, so it is important as a component of the oxygen electrode of methanol fuel cells. It is also effective in promoting the elimination of carbon dioxide gas generated with the oxidation of carbon dioxide.

The 'fc electrode prepared by this method has excellent performance, and can be said to be an effective method that provides a practically usable battery output with a small amount of catalyst. However, when assembling a fuel cell or operating a fuel cell using this electrode, a phenomenon occurs in which the catalyst layer peels off from the base material and the particles constituting the catalyst layer are detached, resulting in a failure to obtain output from the fuel cell. There were problems such as a decrease in output due to long-term operation. The binding force with the base material and the binding force between the catalyst powders increase as the amount of binder increases, but the binder used has the above-mentioned water repellency (property not to get wet with water bath liquid). It has a function and generally has a large electrical resistance, so the electrical resistance of the electrode becomes large. Furthermore, in the electrode preparation process, the catalyst and binder are applied in the form of a paste, but in the process of drying the paste, the catalyst layer shrinks and cracks occur.

Although the degree of cracking varies depending on the nature of the catalyst powder used, it is essentially unavoidable when coated on a substrate with little shrinkage. These cracks also greatly reduce the performance of the fuel cell.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art described above,
It is an object of the present invention to provide an electrode for a fuel cell that has high strength and maintains high performance for a long time without peeling off the catalyst from the electrode and without cracking.

[Key points of invention]

For the above purpose, the inventors have made extensive studies! As a result of the il-superposition, the present invention was achieved. The present invention will be explained in detail in 11 above.

In the present invention, a catalyst containing one or more platinum group elements as a main component, or a material in which this catalyst is supported on a porous conductive carrier, is formed as a catalyst layer on a conductive porous thin plate-like substrate.

The electrode for a fuel cell using liquid fuel is characterized in that the catalyst layer contains a fibrous material. The electrode according to the present invention can be prepared as follows, for example.

A predetermined concentration of a catalyst containing one or more platinum group elements as a main component is supported in advance on a porous conductive carrier such as activated carbon, 7-Arnes black, graphite powder, or the like. The supporting method may be any method commonly used in catalyst preparation, such as impregnation, deposition, and kneading. All of the fibrous material is added to this supported catalyst powder, and sufficient water is added to form a paste, followed by kneading. After thorough mixing, colloidal polytetrafluoroethylene is added as a binder and further kneaded. The prepared paste is applied onto a conductive porous substrate, dried, and then fired to obtain a base electrode for a fuel cell. Key according to the present invention! Method A is not limited to the above-mentioned preparation method, but can be prepared by various methods. For example, as a modification, a carrier layer consisting of a conductive porous carrier, a fibrous material, and a binder is formed on a conductive porous base material according to the above method, and then a catalyst component is applied to the carrier layer. Impregnating and supporting methods are effective methods. The fibrous material used in the present invention is fired at a firing temperature of 200 to 300, in order for polytetrafluoroethylene to function as a binder.
Any material may be used as long as it is resistant to C and is inert to electrolytes, fuels, and oxidizers. For example, glass wool, silica wool, silica/alumina wool, alumina wool, tantalum and other acid-resistant metal wool, carbon wool, etc. can be used. In particular, conductive metal wool and carbon wool are preferred materials. The diameter of the fibers depends on the thickness of the catalyst layer formed on the porous base material, but since the catalyst layer is usually 1 + IR or less, the diameter of the fibers is preferably 0.1+++m or less, considering the strength and cost of the fibers. -0.1 diameter is preferred.

A diameter of 0.1 m or more is not preferable because the dispersion into the catalyst powder becomes uneven, but on the other hand, even if fibers with a diameter of 0.01 m or less are used, the effects of the present invention can be obtained. The length of the fibers is not particularly limited since they are cut by kneading the catalyst powder, but if the fibers are too long, kneading takes a long time, which is undesirable. In addition, if it is short, the effect of the present invention will not be noticeable and the most preferable range is 0.1~
It is 10m. The optimum amount of the fibrous material to be added varies slightly depending on the material of the catalyst layer, but it is preferably added in an amount of 5 to 30% by weight. However, this is not necessarily limiting, and as the amount added becomes smaller, the effect of the present invention gradually decreases.
If the amount exceeds 1% by weight, the resistance of the electrode will increase if a non-conductive fibrous material is added. If the size of the obtained paste is to be applied, the commonly used doctor blade method, roller pressure bonding method, screen printing method, etc. can be used, or the paste can be applied with a spatula or a spatula. As the conductive porous base material used in the present invention, a conventionally used electrode base material can be used. . For example, acid-resistant metal wire mesh, expanded metal, metal screen, porous carbon plate, carbon cloth, carbon fiber nonwoven fabric, etc. can be used.

As the binder used in the present invention, any conventionally used binder is effective, but it is particularly preferable to use polytetrafluoroethylene or a derivative thereof. The amount added is 95 to 50%, preferably 5 to 20%, based on the weight of the catalyst layer.

If less than 5% is added, the effect of the binder is not significant;
If it is more than 0%, the -Ei electrode performance will deteriorate due to an increase in the electrical resistance of the electrode. The firing temperature during preparation varies depending on the properties of the binder, but for example, in the case of polytetrafluoroethylene or its derivatives, it is preferably in the range of 200 to 320C. Furthermore, since polytetrafluoroethylene or its derivatives have water repellency, they can also be used to form gas electrodes by coating the surface of a conductive porous base material that will come into contact with gas in advance to form a water repellent layer. It will be done.

The electrode prepared according to the present invention has a strong binding force between the catalyst layer and the conductive base material, and a fibrous substance is interposed between the catalyst layer particles to increase the binding force, and at the same time, the binding force between the catalyst layer and the conductive base material is increased. No more cracking due to dryness. The electrode obtained in this way is not damaged during assembly of the fuel alpha wave, and maintains high performance for a long time without the catalyst falling off even after long-term operation.

[Embodiments of the invention]

A more detailed explanation will be given below using examples.

Example 1 Carbon powder (furnace black: CC8X150A2
) 5 and H4F tc161.05g, RuCt
Add 300 ml of H2O to 30.51 g' and stir. After the H2P tC74, uC13 has dissolved, add 15 mt of 35% HCHO solution. While stirring this in a dry ice-ethanol refrigerant, cool the solution from +2 to -2 times. To this solution, add 50% by weight. K
Add the OH water bath at a rate of about 2 mtl. The opening temperature is maintained at +2 to -2 ic. After the addition, the solution was returned to room temperature and then gradually raised to 30-40C, and stirred and maintained at this temperature for about 30 seconds to dissolve H2P.
t Reduce Cts and RLIC13. Further, this solution is stirred for about 30 minutes using a 5-needle OC, and then the solid matter is washed with water, and washing is repeated until the pH of the slurry becomes 7 or less. The cake after washing is thoroughly dried in a true nitrogen dryer at 100C. The dried solids are crushed.

The obtained catalyst powder used carbon as a carrier and contained 10M% of Pt.
, contained 5% by weight of RLI.

Example 2 Take 0.75 g of the catalyst powder obtained in Example 1, add 11 g of carbon fiber (manufactured by Toshi, trading card chipped fiber, length 3) to it, and add 5 m of H2O2 in a mortar. Knead. After the fibers were sufficiently dispersed, a colloidal tetrafluoroethylene liquid (Polyflon Dispersion DI manufactured by Daikin Industries, Ltd.) was used.

5-fold dilution: Contains 12% by weight of tetrafluoroethylene)
'! Add i=0.2 mL and mix well. This paste-like substance is uniformly applied to a 50×100 mm porous carbon paper (Kurekamant E715, manufactured by Kureha Chemical Co., Ltd.). After drying this, 300C in a nitrogen stream
Bake separately. The resulting catalyst contained 1.5 mg of platinum/a
rt? , containing 0.75 mg of ruthenium and carbon fI1. Contains 15M amount% of fiber K. This was used as electrode 1 for methanol electrode.

Comparative Example 1 A catalyst prepared in exactly the same manner as in Example 2 except that carbon fiber was not added to 0.75 g of the catalyst powder obtained in Example 1 was used as Comparative Electrode 1 for methanol electrode.

Example 3 0.75 g of catalyst powder prepared in Example 1 was added with 0.11 g of silica alumina wool (manufactured by Isolite Industries, Kao Wool).
An electrode prepared in the same manner as in Example 2 except that g was added was used as Electrode 2 for methanol electrode.

Example 4 To 0.75 g of the catalyst powder prepared in Example 1, 0.023 g of the carbon fiber used in Example 2 was added.

0.038g, 0.075g, 0.15g, 0.22g
.

was prepared in the same manner as in Example 2 by adding
They were designated as methanol electrodes 3, 4, 5, 6, and 7.

Example 5 A catalyst peeling test was conducted to compare the bonding strength of the electrode with the seven types of electrodes obtained in Examples 1 to 4. The above electrode 25×50m+n was cut out as a test piece, and a contact tape (Scotch Trafting Tape, manufactured by Sumitomo 3M) having a width of 12 was adhered to the surface of the catalyst layer, and then this tape was peeled off.

The change in electrode weight after Ail in this operation is taken as the amount of peeling,
The Mt specific yield was calculated. The results are shown in Table 1. In the electrode of Comparative Example 1, a large amount of the catalyst layer peels off. In addition, many cracks were observed in the electrode before the test, and in some cases, cracks were observed in the base material. One electrode I for methanol electrode
``i, No cracks were observed in the melting medium layer, and the amount of catalyst peeled off in the peel test was about 1
Rarely below /1o. Furthermore, the amount of peeling was significantly reduced for methanol electrode 2 as well.

In the 3rd to 7th electrodes for methanol and other uses, the structure of the added fibers was changed. In the electrode containing 3% by weight, slight cracks were observed on the surface of the catalyst layer, but there was less peeling. It can be seen that the amount of peeling decreases as the amount of fiber added increases, and becomes noticeable when the amount added is 5% by weight or more. From the above results, it can be seen that the electrode according to the present invention has a catalyst layer with a high binding power and no cracks on the surface of the catalyst layer.

Example 6 Carbon powder (manufactured by Cabot, Palkan XC72R,) 0
A paste was prepared in the same manner as in Example 2 by adding 0.075 g of the carbon fiber used in Example 2 to this paste. , 50X 100rnm used in Example 2
One side of the carbon vapor was coated in advance so that the amount of colloidal polytetrafluoroethylene impregnated was 1.5 mg glt-, and then it was coated between the other side of the dried carbon vapor. After drying, it was IHJ fired at 300C in full air for about 30 minutes.

Then H4F tcza o, 11 g f 1.5
ml of a solution in ethanol is impregnated onto the carbon powder coating side of the plate-shaped molded article, and dried in 100C% air.

Add this to a 1:1 mixture of water and ethanol with 10% Na
It was immersed in a solution in which BH4 was dissolved for 2 to 3 minutes, the L was taken out, thoroughly washed with water, and then dried in 80C1 air for 10 hours to obtain an electrode 8 for an air electrode.

Comparative Example 2 An electrode prepared in the same manner as in Example 6 in the actual F16 except that the carbon fiber used was not added was used as a comparative electrode for air electrode 2.

Example 7 The electrodes obtained in the actual peak side 6 and comparative example 2 were
A peel test was performed using the same method as in Example 5. The results are shown in Table 2.

It can be seen that the amount of peeling of the electrode 8 for air etc. is smaller than that of the 4-metre electrode 2, and the strength is greater.

EXAMPLE Cut out the methanol electrode 2 and the small gas electrode 8 obtained in Example 7 into 50 x 50 ii pieces, and use this 'J''L to make a first leather battery. Configured.

! The methanol electrode obtained in Comparative Example 1 and the air electrode obtained in Comparative Example 2 were cut into 50×50 m+n pieces, and used to construct a second single cell.

In each cell, between a pair of magnetic poles, 3 mo
A cation exchange membrane (DuPont, Nafion) soaked in t/l H2S04 was interposed as an electrolyte.

Brightening agent is air, fuel is 1m0A/7 CH30H and 3m
A solution containing 017L H2804k was used, and was continuously supplied from outside the battery using a pump and a pump.

The operating temperature of the battery was maintained at 60C. In the initial stage, the current density was 60 mvd, the first single cell U0.40V, and the second single cell U0.43V. When this operation was repeated for 200 hours by repeatedly stopping the fuel supply every 10 hours, the first single cell voltage was 0.33V, and the second single cell voltage was 0.42V.

Chapter 1 Table Part 2 Clothes Hitachi City Saiwaicho 3-1-1 Stock %formula% Hitachi City Saiwaicho 3-1-1 Stock Hitachi Research Institute, Hitachi, Ltd.

Claims (1)

[Scope of Claims] 1. A conductive porous thin plate-like base material and a catalytic material containing one or more platinum group elements as a main component on the base material, or the catalytic material is formed into a conductive porous phase. 1. An electrode for a fuel cell using a liquid fuel formed by forming a catalyst layer containing a supported substance, characterized in that the catalyst layer absorbs a fibrous substance. 2. The electrode for a fuel cell according to claim 1, wherein the fibrous material has electrical conductivity. 3. A fuel cell electrode according to claim 2, characterized in that a hostile electrolyte is used as the fuel cell electrolyte. 4. The electrode for a fuel cell according to claim 3, characterized in that the conductive fibrous material is contained in an amount of 5 to 30% based on the weight of the catalyst layer.