JPH08106915A - Electrode of solid polymer fuel cell and manufacture of fuel cell - Google Patents

Abstract

PURPOSE: To provide a solid polymer fuel cell with high output by forming the contact part of reaction gas, an electrode catalyst layer, and a solid polymer electrolyte film in three-dimensional structure. CONSTITUTION: A solid polymer electrolyte film 22 and a polytetrafluoroethylene layer 21 are formed in a supporting body made of carbon paper fibers 41 having a three-dimensional network, an electrode catalyst film layer 23A is formed on the solid polymer electrolyte film by chemical plating to obtain three- dimensional structure with high density in an electrode 40. One side of the carbon paper fibers is coated with a solid polymer electrolyte solution, then a solid polymer electrolyte film 32 is integrally bonded thereto with a hot press.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a polymer electrolyte fuel cell, and more particularly to a structure of an electrode of a fuel cell.

[0002]

2. Description of the Related Art Fuel cells are classified into solid polymer fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid electrolyte fuel cells, etc., depending on the type of electrolyte used and the operating temperature. Be separated. The polymer electrolyte fuel cell is limited to special applications because of its high cost, but it is easier to control the differential pressure between both electrodes and to pressurize the cell compared to other fuel cell systems, so high output density can be obtained. In addition, since it is an acidic electrolyte, it has a feature that a carbon dioxide-containing gas can be used as it is. Further, since it is a low temperature operation type, there are few restrictions on the material constituting the battery, and it can be started at room temperature in a short time.

FIG. 2 shows a sectional view of the basic structure of a conventional polymer electrolyte fuel cell unit cell. The unit cell 8 has an anode 74a and a cathode 74b on both surfaces of the solid polymer electrolyte membrane 7, and electrode base materials 75a and 75b on the outer surfaces thereof. Furthermore, the gas-impermeable separator 76 is provided on the outer side.
The separator 76a has a fuel gas passage 29a, and the separator 76b has an oxidant gas passage 29b.

Such a polymer electrolyte fuel cell unit cell is manufactured, for example, as follows. Incidentally, FIG. 3 schematically shows a conventional electrode structure of a polymer electrolyte fuel cell.
Carbon 23 carrying catalyst particles and a dispersion solution of polytetrafluoroethylene 21 are dispersed and mixed, and the solution is applied to an electrode base material 31 made of porous carbon paper, dried and heated to form an electrode substrate. The electrode 50 in which the electrode catalyst layer 30 is laminated on the material 31 is obtained. Next, a polymer electrolyte solution is applied onto the electrode catalyst layer 30 to form a solid polymer electrolyte coating film 22, and the solid polymer electrolyte membrane 32 is sandwiched between the surfaces on which the electrode catalyst layer 30 is formed and heated by hot pressing. After pressure bonding and integration, it is sandwiched by separators.

As the solid polymer electrolyte membrane, a perfluorosulfonic acid resin membrane resistant to oxidation and heat (for example, Nafion, trade name, manufactured by DuPont, USA) is used, and this cation exchange membrane is a fluorocarbon-based membrane. It consists of a hydrophobic main chain, which is a polymer, and a hydrophilic exchange group, which is a side chain made of fluorocarbon with a sulfone group at the tip, and these exchange groups associate in the fluorocarbon matrix to form clusters. There is. This solid polymer electrolyte membrane has a cluster portion of 20 Ω · cm at room temperature when saturated with water.
It exhibits the following specific resistance and functions as a proton conductor and a gas separator. Therefore, the reaction gas is humidified in advance and then supplied to the cell.

The electrode base material is a porous body, and functions as a reaction gas diffusion path and a path forming means for removing generated water to the outside of the system together with the reflux gas, and further functions as a current collector. The electrode catalyst layer is integrally joined with the solid polymer electrolyte membrane, which is an acidic electrolyte with strong corrosivity, by the hot pressing method,
The catalyst is limited to precious metals such as platinum, and CO becomes a catalyst poison.

The fuel gas and the oxidant gas supplied to the cell are consumed by the following electrochemical reaction at the three-phase interface formed by the catalyst in each electrode catalyst layer and the solid polymer electrolyte coating.

[0008]

[Chemical formula 1] H ₂ → 2H ⁺ + 2e ^- anode

[0009]

(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O cathode As described above, water is produced as a whole reaction, and protons move in the solid polymer electrolyte membrane in a hydrated state. In order to
Water is produced at the cathode.

Further, in order to improve the battery characteristics that enable a high output, the density of the three-phase interface per unit area of the electrode is increased so that the reaction sites, that is, the reaction gas, the electrode catalyst layer and the solid polymer electrolyte coating are It is necessary to increase the contact area of the metal and the three-dimensional structure of the reaction site is generally attempted.

[0011]

In the above, the electrode catalyst layer and the solid polymer electrolyte membrane are heated and pressure bonded to form a three-phase interface. At this contact portion, the electrode catalyst layer and the solid polymer for the reaction gas are formed. Under the present circumstances, the structure of the electrolyte coating is not completely three-dimensional, and the formation of a high-density three-phase interface has not been achieved. That is, the reaction gas can contact only the portion near the carbon paper in the electrode catalyst layer, and the amount of the catalyst that can contribute to the reaction is limited.

It is an object of the present invention to provide a polymer electrolyte fuel cell capable of achieving high output by three-dimensionally contacting the reaction gas, the electrode catalyst layer and the polymer electrolyte membrane.

[0013]

In order to achieve the above object, first of all, a cell which receives a supply of a fuel gas and an oxidant gas to generate a direct current power is provided with a solid polymer electrolyte body and a cell sandwiching the electrolyte body. A fuel cell (anode) and an oxidizer electrode (cathode), and a plurality of the cells are laminated with a separator interposed therebetween to form a unit cell integrated body (stack) of a polymer electrolyte fuel cell. The electrode comprises a support made of carbon paper fibers having a three-dimensional network structure, a solid polymer electrolyte coating and a polytetrafluoroethylene layer formed on the surface of the carbon paper fibers of the support, and the solid polymer. This is achieved by comprising an electrode catalyst layer formed on the surface of the electrolyte coating.

Further, in the above electrode of the solid polymer electrolyte fuel cell, the electrode catalyst layer formed on the surface of the solid polymer electrolyte coating is achieved when the thickness thereof is within the range of 3 μm to 10 μm. Furthermore, a cell that receives the supply of the fuel gas and the oxidant gas to generate direct current power is a solid polymer electrolyte body, and a fuel electrode (anode) and an oxidant electrode (cathode) that are respectively disposed with the electrolyte body interposed therebetween. ) And a plurality of the cells are laminated via a separator to form a unit cell integrated body (stack) in a method for producing a polymer electrolyte fuel cell, the first step, the second step, and the third step. The first step includes immersing the carbon paper fiber in a mixed solution of an alcohol solution of a polyelectrolyte and a dispersion solution of polytetrafluoroethylene, and a second step. Dry the carbon paper fiber to form a solid polymer electrolyte coating and a particulate polytetrafluoroethylene layer. The third step is chemical plating of the carbon paper fiber. An electrode catalyst layer is formed from the carbon paper fiber, the fourth step is to apply the polyelectrolyte containing solution to one surface of the carbon paper fiber surface, and the fifth step is to apply the two polyelectrolyte solution of the carbon paper fiber to one surface. And the solid polymer electrolyte membrane are adhered and integrated by hot pressing.

Further, it has a first step, a second step, a third step, a fourth step, a fifth step, a sixth step and a seventh step, the first step being carbon paper. Immerse the fiber in a dispersion solution of polytetrafluoroethylene,
In the second step, the carbon paper fibers are dried and then heated to form a partially fibrillated polytetrafluoroethylene layer. In the third step, the carbon paper fibers are converted into a polyelectrolyte alcohol solution. Immersion, the fourth step is to dry the carbon paper fiber to form a solid polymer electrolyte coating, the fifth step is to form an electrode catalyst layer on the carbon paper fiber by chemical plating, the sixth step is The surface of the carbon paper fibers is coated with a polyelectrolyte-containing solution on one side, and the seventh step is to hot-press the one side of the carbon paper fibers coated with the polyelectrolyte solution and the solid polymer electrolyte membrane respectively. It is achieved by close contact and integration.

[0016]

Since the reaction gas freely flows through the voids in the carbon paper fiber, the contact area between the reaction gas, the electrode catalyst layer and the solid polymer electrolyte coating at the electrode becomes large.
As a result, a high-density three-phase interface can be obtained, and high output can be achieved in the solid polymer electrolyte fuel cell.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 FIG. 1 is one of the examples of the present invention, and schematically shows the structure of electrodes in a polymer electrolyte fuel cell. The same parts as those in the schematic diagram shown in FIG. 3 are designated by the same reference numerals.

In FIG. 1, a carbon paper fiber 41 having a three-dimensional stitch structure is used as a support, and a polymer electrolyte coating 22 and a polytetrafluoroethylene layer 2 are provided on the surface.
1 and the electrode catalyst coating layer 23A is further formed on the surface to form the electrode 40. Further, a solid polymer electrolyte membrane 32 is arranged on the electrode 40. Here, the reaction gas is carbon paper fiber 4
The three-phase interface is formed by freely flowing through the voids in 1.

Although the carbon paper fibers 41 are schematically shown in FIG. 1, the carbon fibers actually have a random three-dimensional structure. Example 2; An example of a method for producing a polymer electrolyte fuel cell of the present invention according to claim 3 will be described. A solution of a perfluorosulfonic acid resin diluted with alcohol (for example, a product name Nafion membrane manufactured by DuPont, USA) and a dispersion solution of polytetrafluoroethylene in a volume ratio of 7: 3 was mixed with 0 After soaking the carbon paper fiber having a thickness of 4 mm and sufficiently impregnating the solution component, it is dried in a vacuum dryer for 24 hours to form a solid polymer electrolyte coating and a polytetrafluoroethylene layer. .

Here, as a result of observing the surface and cross section of the carbon paper fiber with a scanning electron microscope (SEM), a Nafion solution film (solid polymer electrolyte film) and a particulate polytetrafluoroethylene layer were formed on the carbon paper fiber. It was confirmed that the film was formed at a ratio of 7: 3. Then, the carbon paper fiber was immersed in a plating bath for 1 hour. As a solution in the bath, an ammonia solution of 0.01 mol / l chloroplatinic acid thermostated at 80 ° C. is used, and platinum metal ions are adsorbed on the Nafion solution film formed on the surface of the carbon paper fiber. A 30 mol% ammonia solution of sodium borohydride is immersed in a bath kept at 50 ° C. for 30 minutes to reduce platinum metal ions on the Nafion solution coating to form a platinum metal layer (electrode catalyst layer).

After washing with water, the surface and the cross section of the carbon paper fiber were observed by SEM. As a result, it was confirmed that a platinum metal layer having a thickness of 5 to 10 μm was formed on the Nafion solution coating film. Further, prepare two sheets of carbon paper fiber coated with a Nafion solution on one side, and hold the Nafion membrane (solid polymer electrolyte membrane) containing pure water on one side at 120 ° C. for 10 days. Hot press for a minute to adhere and integrate.

Embodiment 3; An embodiment of the method for producing a polymer electrolyte fuel cell of the present invention according to claim 4 will be described. After the carbon paper fiber was immersed in a dispersion solution of polytetrafluoroethylene to sufficiently impregnate the solution components, it was dried in a vacuum drier for 24 hours and further heated at 300 ° C. for 10 minutes to obtain a polytetrafluoroethylene dispersion solution. Form a tetrafluoroethylene layer.

As a result of observing the surface and the cross section of the carbon paper fiber with an SEM, it was confirmed that a fibrillar polytetrafluoroethylene layer was formed on the carbon paper fiber. Further, the carbon paper fiber is dipped in a Nafion solution diluted with alcohol, and then dried to form a Nafion solution coating film.

Next, the carbon paper fiber was immersed in a plating bath for 1 hour. 60 ℃ as the solution in the bath
Using a 0.01 mol / l ammoniacal solution of chloroplatinic acid stored at constant temperature, platinum metal ions are adsorbed on the Nafion solution coating film formed on the surface of the carbon paper fiber. 60 mol of 25 mol% ammonia solution of sodium borohydride
The platinum metal ion on the Nafion solution coating is reduced by immersing in a bath kept at 0 ° C. for 30 minutes to form a platinum metal layer.

After washing with water, the surface and the cross section of the carbon paper fiber were observed by SEM. As a result, it was confirmed that a platinum metal layer having a thickness of 3 to 5 μm was formed on the Nafion solution coating film. Further, prepare two sheets of carbon paper fibers coated with a Nafion solution on one side and brush the Nafion membrane containing pure water on one side at 120 ° C.
At 10 minutes, hot press for 10 minutes to integrate.

[0026]

According to the present invention, by adopting the above-described structure, the contact portion with the reaction gas, the electrode catalyst layer and the solid polymer electrolyte coating is three-dimensionalized, so that a high density three-phase The interface can be obtained, and high output in the solid polymer electrolyte fuel cell is possible.

Since the solid polymer electrolyte membrane is the same as the solid polymer electrolyte membrane and is formed not only on the surface of the carbon paper fiber but also inside thereof, it is projected into the carbon paper fiber by hot pressing. A part of the solid polymer electrolyte membrane and the solid polymer electrolyte coating inside are thermocompression-bonded, and the adhesion is improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrode structure in a polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a single cell of a conventional polymer electrolyte fuel cell.

FIG. 3 is a schematic diagram of an electrode configuration in a conventional polymer electrolyte fuel cell.

[Explanation of symbols] 21 polytetrafluoroethylene layer 22 solid polymer electrolyte coating 23 catalyst particle supporting carbon 23A electrode catalyst layer 30 electrode catalyst layer 31 electrode substrate 32 solid polymer electrolyte membrane 40 electrode 50 electrode 41 carbon paper fiber 7 solid Polymer electrolyte membrane 74 a Anode 74 b Cathode 75 a, 75 b Electrode substrate 29 a Fuel gas passage 29 b Oxidant gas passage 76 a, 76 b Separator

Claims (4)

[Claims] 1. A solid polymer electrolyte body, and a fuel electrode (anode) and an oxidizer, each of which is provided with a solid polymer electrolyte body sandwiching the electrolyte body. An electrode of a polymer electrolyte fuel cell having an electrode (cathode), wherein a plurality of the cells are laminated via a separator to form a unit cell integrated body (stack), wherein the electrode has a three-dimensional mesh structure. A support comprising the carbon paper fiber having, a solid polymer electrolyte coating and a polytetrafluoroethylene layer formed on the surface of the carbon paper fiber of the support, and an electrode catalyst layer formed on the surface of the solid polymer electrolyte coating. An electrode for a polymer electrolyte fuel cell, comprising: 2. The electrode of the polymer electrolyte fuel cell according to claim 1, wherein the electrode catalyst layer formed on the surface of the polymer electrolyte membrane has a thickness within a range of 3 μm to 10 μm. An electrode for a polymer electrolyte fuel cell. 3. A solid polymer electrolyte body, and a fuel electrode (anode) and an oxidizer, each of which is provided with a solid polymer electrolyte body sandwiching the electrolyte body. A method for producing a polymer electrolyte fuel cell, comprising an electrode (cathode), a plurality of the cells being stacked via a separator to form a unit cell integrated body (stack), comprising: a first step; The method includes a step, a third step, a fourth step, and a fifth step, and the first step is to immerse the carbon paper fiber in a mixed solution of an alcohol solution of a polyelectrolyte and a dispersion solution of polytetrafluoroethylene. Then, in the second step, the carbon paper fiber is dried to form a solid polymer electrolyte coating and a particulate polytetrafluoroethylene layer, and in the third step, the carbon paper fiber is chemically treated. An electrode catalyst layer is formed by plating, a fourth step applies a polyelectrolyte-containing polymer electrolyte solution to one surface of the carbon paper fiber surface, and a fifth step applies two polyelectrolyte solutions of the carbon paper fiber. A method for producing a polymer electrolyte fuel cell, characterized in that one surface and a polymer electrolyte membrane are adhered and integrated by hot pressing. 4. A solid polymer electrolyte body, and a fuel electrode (anode) and an oxidizer, each of which is provided with a solid polymer electrolyte body sandwiching the electrolyte body. A method for producing a polymer electrolyte fuel cell, comprising an electrode (cathode), a plurality of the cells being stacked via a separator to form a unit cell integrated body (stack), comprising: a first step; It has a process, a 3rd process, a 4th process, a 5th process, a 6th process, and a 7th process, and the 1st process immerses carbon paper fiber in the dispersion solution of polytetrafluoroethylene. Then, in the second step, the carbon paper fibers are dried and then heated to form a partially fibrillated polytetrafluoroethylene layer, and in the third step, the carbon paper fibers are mixed with a polymer electrolyte alcohol. In a fourth step, the carbon paper fibers are dried to form a solid polymer electrolyte coating, and in a fifth step, an electrode catalyst layer is formed on the carbon paper fibers by chemical plating. The sixth step is to apply the polyelectrolyte-containing solution on one side of the carbon paper fiber surface, and the seventh step is to apply the two-side polyelectrolyte solution of the carbon paper fiber and the solid polyelectrolyte membrane respectively. A method for producing a polymer electrolyte fuel cell, characterized in that they are adhered and integrated by hot pressing.