JP2008041467A - Device and method of manufacturing electrode for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance uniformity or the like of film thickness, and to suppress occurrence or the like of a crack in forming an electrode (catalyst layer) for a fuel cell. <P>SOLUTION: This device of manufacturing the electrode for the fuel cell is provided with: a coating supply part 4 supplying a certain quantity of an electrode forming coating 2 prepared by dispersing a carbon species with a noble metal catalyst supported thereto in a solvent; and a nozzle part 3 discharging the electrode forming coating 2 supplied from the coating supply part 4 onto a surface of a conductive porous base material 1. A suction part 5 is arranged on the back side of the conductive porous base material 1, and a solvent constituent in the electrode forming coating 2 is depressurized and sucked through the conductive porous base material 1 simultaneously with application of the electrode forming coating 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell electrode manufacturing apparatus and a fuel cell electrode manufacturing method.

  Fuel cells are attracting attention as a power generation technology with low carbon dioxide emissions and low environmental impact. In a fuel cell, a cathode current collector / cathode electrode (cathode catalyst layer: air electrode) / proton (hydrogen ion) conductive electrolyte membrane / anode electrode (anode catalyst layer: fuel electrode) / anode current collector A membrane electrode assembly (MEA) having a laminated structure is used as a fuel cell stack.

  In a fuel cell having a membrane electrode composite, a fuel such as methanol or hydrogen gas supplied to the anode electrode side is decomposed and ionized by a catalyst contained in the electrode to form a proton conductive electrolyte membrane as hydrogen ions. It moves to the cathode electrode via, and combines with oxygen in the air supplied to the cathode electrode to generate water. Electric power is generated based on the movement of hydrogen ions from the anode electrode to the cathode electrode in this reaction, and current is extracted from the cathode current collector and the anode current collector.

  In such an electrode reaction, reducing the resistance of proton and electron diffusion is an important factor for improving the electrode efficiency, that is, the efficiency of the entire fuel cell. As an electrode of a fuel cell, a material in which a conductive material such as carbon carrying fine particles of a noble metal that is a catalyst for a fuel cell is laminated on a current collector is used. Here, in a fuel cell that extracts electrical energy from hydrogen or methanol, a catalyst that promotes dissociation of protons and electrons is required at the fuel electrode in order to generate an electromotive force between the fuel electrode and the air electrode. In the air electrode, a catalyst that promotes the combination of protons with electrons and oxygen is required.

  In order to efficiently perform the above-described chemical reaction, the fuel electrode (anode catalyst layer) and the air electrode (cathode catalyst layer) are required to have gas diffusibility and permeability. For this reason, carbon paper or the like in which carbon fibers are woven and sintered is used for the current collector forming each electrode. That is, an electrode is formed by applying a coating for forming an electrode prepared by dispersing a carbon powder or the like carrying a noble metal catalyst for each electrode in a solvent to the surface of carbon paper or the like (see, for example, Patent Document 1). ). Since base materials such as carbon paper are used for the purpose of collecting current and diffusing gas, they have a structure in which the pores of the film are relatively large.

  When an electrode forming coating is applied on a current collector made of a conductive porous substrate such as carbon paper to form an electrode, the electrode forming coating passes through the pores of the substrate. It is necessary to give the material a water repellent treatment. By using a base material that has been subjected to water repellent treatment, it is possible to form a coating film of the electrode forming paint, but there is a problem that the film thickness of the coating film tends to be non-uniform. A catalyst layer having a non-uniform film thickness is a cause of deterioration in battery characteristics. Furthermore, there is a problem that cracks are likely to occur in the catalyst layer during drying after the coating film is formed. Cracks in the catalyst layer cause crossover when a fuel cell is configured as a membrane electrode assembly.

On the other hand, the electrode-forming coating material is once applied to a temporary support such as a polyethylene terephthalate (PET) film to form a coating film, and the coating film is transferred onto the electrolyte film, or the electrolyte film is formed on the coating film. A method of forming an electrolyte membrane by applying a polymer composition for use (see, for example, Patent Document 2), and a method of forming an electrode by directly applying a coating material for forming an electrode on the electrolyte membrane are proposed. . The method of applying the electrode forming paint on the temporary support has a problem that the process becomes complicated and the productivity of the electrode is lowered. In addition, when an electrode-forming paint is applied on the electrolyte membrane, it is difficult to improve the adhesion of the coating film, and thus there is a problem that the catalyst layer is easily peeled off after drying.
JP2003-036860 JP 2005-507150 A

  The object of the present invention is to produce an electrode having excellent quality and characteristics at a low cost by improving the uniformity of the thickness of the catalyst layer as an electrode for a fuel cell and suppressing the occurrence of cracks. An object of the present invention is to provide a fuel cell electrode manufacturing apparatus and a fuel cell electrode manufacturing method.

  An electrode manufacturing apparatus for a fuel cell according to an aspect of the present invention includes a paint supply unit that quantitatively supplies an electrode-forming paint in which a carbon species supporting a noble metal catalyst is dispersed in a solvent, and the above-described supply supplied from the paint supply unit A nozzle part for discharging and applying an electrode-forming coating material onto the surface of the conductive porous substrate, and a back surface side of the conductive porous substrate, and the electrode through the conductive porous substrate And a suction part for suctioning the solvent component in the forming paint under reduced pressure.

  In the method for producing an electrode for a fuel cell according to an embodiment of the present invention, an electrode is formed by applying a coating material for forming an electrode in which a carbon species supporting a noble metal catalyst is dispersed in a solvent to the surface of a conductive porous substrate. In applying the electrode-forming paint to the surface of the conductive porous substrate, the electrode-forming paint in the electrode-forming paint from the back side of the conductive porous substrate through the conductive porous substrate. The method includes a step of suctioning the solvent component under reduced pressure.

  According to the fuel cell electrode manufacturing apparatus and electrode manufacturing method of the present invention, when the electrode forming paint is applied to the surface of the conductive porous substrate, the solvent in the electrode forming paint from the back side Since the components are sucked under reduced pressure, the coating film formation accuracy and drying accuracy can be increased. By these, it becomes possible to obtain an electrode (catalyst layer) having a uniform film thickness with good reproducibility while suppressing the occurrence of cracks in the coating film.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, although embodiment of this invention is described based on drawing below, those drawings are provided for illustration and this invention is not limited to those drawings.

  FIG. 1 is a perspective view showing a configuration of a fuel cell electrode manufacturing apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a conductive porous base material that functions as a base material and a current collector during electrode formation. As the conductive porous substrate 1, a nonwoven fabric or a woven fabric using carbon fibers is used. Specifically, carbon paper, carbon cloth, or the like can be used. Such a conductive porous substrate 1 is preferably used after being subjected to, for example, a water repellent treatment, or formed by forming a microporous carbon coat layer on the surface.

  As the water repellent treatment for the conductive porous substrate 1 made of carbon paper, carbon cloth, or the like, for example, treatment using a polytetrafluoroethylene (PTFE) emulsion or the like can be applied. The carbon coat layer formed on the surface of the conductive porous substrate 1 is preferably a carbon layer having a pore size of about 5 to 6 nm and a pore volume of about 40%, for example. Such a carbon coat layer exhibits the same effect as the water repellent treatment. Depending on the carbon species in the electrode-forming coating material, it is possible to use the conductive porous substrate 1 made of carbon paper, carbon cloth or the like without performing a water repellent treatment or the like.

  On the conductive porous substrate 1 described above, a nozzle portion 3 is disposed for discharging and applying the electrode forming paint 2 onto the conductive porous substrate 1. The nozzle unit 3 has, for example, an extrusion type nozzle head. The nozzle part 3 is supplied with a fixed amount of the electrode forming paint 2 from the paint supply part 4. A metering pump or the like is used as the paint supply unit 4. The electrode forming coating 2 is formed by dispersing carbon species carrying a noble metal catalyst in a solvent.

  As the noble metal catalyst constituting the electrode forming paint 2, for example, a single element of a platinum group element such as Pt, Ru, Rh, Ir, Os, Pd, an alloy containing the platinum group element, or the like is used. These noble metal catalysts are appropriately selected according to each electrode (fuel electrode (anode) or air electrode (cathode)). For example, it is preferable to use Pt—Ru, Pt—Mo or the like having strong resistance to methanol or carbon monoxide for the fuel electrode (anode), and platinum or Pt—Ni or the like for the air electrode (cathode). .

  As the carbon species supporting the noble metal catalyst as described above, carbon powder, carbon nanofiber, or the like can be used. In particular, it is preferable to use a mixture of carbon powder and carbon nanofibers. This makes it possible to use the conductive porous substrate 1 made of carbon paper, carbon cloth or the like without performing a water repellent treatment. Moreover, any of an aqueous solvent and an organic solvent may be used as the solvent, and a mixed system of an aqueous solvent and an organic solvent may be used. Furthermore, the electrode-forming paint 2 may contain a proton conductive resin solution as required.

  The electrode forming paint 2 is produced according to a conventional method. An example of producing the electrode forming paint 2 is shown below. First, an aqueous solvent is added to a carbon species carrying a noble metal catalyst and stirred well. A proton conductive resin solution is added to this as necessary, and then an organic solvent and a conductive material are added and dispersed as necessary to prepare a slurry (electrode-forming paint 2). As the organic solvent, a single solvent or a mixed solvent of two or more kinds is used.

  In the dispersion described above, a slurry composition that is a dispersion is prepared using a commonly used disperser (ball mill, sound mill, bead mill, paint shaker, nanomizer, or the like). The amount of solvent in the dispersion (slurry composition) is preferably adjusted so that the solid content is in the range of 5 to 60%. When the solid content is less than 5%, the coating film is easily peeled off. On the other hand, when the solid content exceeds 60%, the applicability to the conductive porous substrate 1 decreases. The water-repellent treatment for carbon paper, carbon cloth, or the like is adjusted within a range where the electrode-forming coating material 2 made of the slurry composition can be applied.

  The electrode-forming coating material 2 made of the slurry composition is supplied in a fixed amount from the coating material supply unit 4 to the nozzle unit 3 and further discharged from the nozzle unit 3 onto the surface of the conductive porous substrate 1. On the other hand, a suction unit 5 connected to a vacuum suction device (not shown) is disposed on the back side of the conductive porous substrate 1. Then, the electrode forming paint 2 is ejected and applied from the nozzle portion 3 onto the conductive porous substrate 1 and simultaneously, the solvent component in the electrode forming paint 2 is sucked through the conductive porous substrate 1. While the vacuum suction is performed at 5, the coating film 6 of the electrode forming paint 2 is formed on the conductive porous substrate 1.

  As described above, the application accuracy of the electrode-forming paint 2 is improved by sucking the solvent component under reduced pressure simultaneously with the application of the paint 2. Therefore, the film thickness uniformity of the coating film 6 that becomes the anode catalyst layer (fuel electrode) and the cathode catalyst layer (air electrode) can be improved. In addition, since the drying proceeds in a uniform state simultaneously with the formation of the coating film 6, the amount of cracks generated can be reduced even when the coating film 6 is finally dried to form an electrode (anode catalyst layer or cathode catalyst layer). Can be suppressed. By reducing the amount of cracks generated in the anode catalyst layer and the cathode catalyst layer, it is possible to suppress the crossover amount when the membrane electrode assembly is constructed.

  Further, by simultaneously sucking the solvent component under reduced pressure simultaneously with the application of the paint 2, a part of the carbon species supporting the noble metal catalyst enters the inside of the conductive porous substrate 1, thereby improving the reaction efficiency of the fuel cell. Can do. This contributes to an improvement in output. In this way, by applying vacuum suction of the solvent component, an electrode (anode catalyst layer or cathode catalyst layer) with excellent film thickness uniformity, catalyst distribution, etc. and reduced cracking can be manufactured at low cost. It can be obtained with good reproducibility in the process. Therefore, by manufacturing a membrane electrode assembly using such an electrode, it becomes possible to manufacture a fuel cell having excellent characteristics and reliability.

  The fuel cell electrode manufacturing apparatus of this embodiment can be applied to the production of various fuel cell electrodes. An example in which an electrode manufactured using a fuel cell electrode manufacturing apparatus is applied to a membrane electrode assembly (MEA) will be described with reference to FIG. FIG. 2 shows a configuration example of a membrane electrode assembly used in a direct methanol fuel cell (DMFC). The membrane electrode assembly (MEA) 11 includes a cathode current collector 12 / cathode catalyst layer (air electrode) 13 / proton (hydrogen ion) conductive electrolyte membrane 14 / anode catalyst layer (fuel electrode) 15 / anode collector. It has a laminated structure of the electric bodies 16.

  In addition to the function of the cathode catalyst layer 13 as a current collector, the cathode current collector 12 has a function of uniformly supplying air (oxidant) to the cathode catalyst layer 13. On the other hand, the anode current collector 16 has a function of uniformly supplying fuel to the anode catalyst layer 15 in addition to the function of the anode catalyst layer 15 as a current collector. A cathode conductive layer is laminated on the cathode current collector 12 as necessary, and an anode conductive layer is laminated on the anode current collector 16 as needed. These conductive layers are composed of, for example, a mesh, a porous film, or a thin film made of a conductive metal material such as gold.

  In the membrane electrode assembly (MEA) 11 described above, the cathode current collector 12 and the anode current collector 16 are each made of a conductive porous substrate 1 such as carbon paper or carbon cloth, on which a cathode catalyst is formed. As the layer (air electrode) 13 and the anode catalyst layer (fuel electrode) 15, a coating film 6 of the electrode forming paint 2, that is, a coating film mainly composed of carbon carrying a noble metal catalyst is formed. The cathode catalyst layer 13 and the anode catalyst layer 15 are formed using the fuel cell electrode manufacturing apparatus of the above-described embodiment.

  Examples of the proton conductive material constituting the electrolyte membrane 14 include fluorine-based resins (Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by Asahi Glass Co., Ltd.) such as a perfluorosulfonic acid polymer having a sulfonic acid group. Etc.), organic materials such as hydrocarbon resins having sulfonic acid groups, or inorganic materials such as tungstic acid and phosphotungstic acid. However, it is not restricted to these.

In the DMFC using the membrane electrode assembly (MEA) 11 described above, for example, methanol fuel in the fuel tank is vaporized, and this vaporized component is supplied to the membrane electrode assembly (MEA) 11. In the membrane electrode assembly (MEA) 11, the vaporized component of the methanol fuel is diffused by the anode current collector 16 and supplied to the anode catalyst layer 15. The vaporized component supplied to the anode catalyst layer 15 causes an internal reforming reaction of methanol represented by the following formula (1).
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)

Protons (H ⁺ ) generated by the internal reforming reaction are conducted through the electrolyte membrane 14 and reach the cathode catalyst layer 13. Air (oxidant) taken into the membrane electrode assembly (MEA) 11 diffuses through the cathode current collector 12 and is supplied to the cathode catalyst layer 13. The air supplied to the cathode catalyst layer 13 causes the reaction shown in the following formula (2).
(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
This reaction causes a power generation reaction that accompanies the generation of water.

  Next, specific examples of the present invention and evaluation results thereof will be described.

(Example 1)
As raw materials for preparing electrode-forming coating materials, 66 g of carbon carrying platinum, 24 g of glycerin, 120 g of perfluorocarbon sulfonic acid solution (20% solution of Nafion (trade name)), 252 g of 1,2-propanol, and 160 g of pure water were prepared. . A mixture of carbon nanotubes and carbon powder was used as carbon as a support. Moreover, the carbon paper which performed the water-repellent process was prepared as an electroconductive porous base material.

First, carbon carrying platinum was dispersed in pure water and stirred well. To this was added a perfluorocarbon sulfonic acid solution, and further glycerin and 1,2-propanol were added and well dispersed to form a slurry. A stirring blade type disperser was used for dispersion. In this way, a slurry composition was prepared as a coating material for electrode formation. The viscosity of the paint was about 330 mPa · s (under a condition of 100 ⁻¹ s). Such a paint was applied onto carbon paper using the electrode manufacturing apparatus shown in FIG. At this time, a coating film was formed by suction under reduced pressure from the back side of the carbon paper simultaneously with application of the paint. The electrode (catalyst layer) thus obtained was subjected to the characteristic evaluation described later.

(Comparative Example 1)
A paint film (slurry composition) having the same composition as in Example 1 was used to form a coating film in the same manner as in Example 1 except that vacuum suction from the back side of the carbon paper was not performed. This electrode (catalyst layer) was subjected to characteristic evaluation described later.

(Comparative Example 2)
In Comparative Example 1 described above, a coating film was formed in the same manner as Comparative Example 1 except that water-repellent carbon paper was used. This electrode (catalyst layer) was subjected to characteristic evaluation described later.

  The film thickness distribution of each electrode produced in Example 1 and Comparative Examples 1 and 2 described above was measured. As a result, it was confirmed that the electrode according to Example 1 was superior in film thickness uniformity as compared with the electrodes according to Comparative Examples 1 and 2. Furthermore, the surface state of each electrode was observed. The surface state of the electrode according to Example 1 is shown in FIG. 3, and the surface state of each electrode according to Comparative Examples 1 and 2 is shown in FIGS. As is clear from these observation results, large cracks are generated in the electrodes according to Comparative Examples 1 and 2. On the other hand, it can be seen that the amount of cracks in the electrode according to Example 1 is reduced.

Next, using each electrode of Example 1 and Comparative Examples 1 and 2, a membrane electrode assembly (MEA) 11 for DMFC shown in FIG. 2 was produced. The shape of each MEA was 30 × 40 mm (1200 mm ² ). A 1M methanol solution was allowed to flow at 0.72 mL / min on the anode side of each MEA, and air was allowed to flow at 120 mL / min on the cathode side. In this state, a load of 1.8 A was applied, and the amount of CO ₂ in the air discharged from the air outlet was measured. The crossover rate (CO) was calculated from the amount of CO ₂ as follows.

  The crossover rate (C.O) is expressed as a ratio of the amount of fuel methanol that has passed through the electrolyte membrane and moved from the anode side to the cathode side. The formula: [amount of methanol transferred to the cathode / (amount of methanol transferred to the cathode + ideal) The amount of methanol consumed in the reaction)] × 100 (%) was calculated.

Here, the amount of methanol consumed in the ideal reaction (ideal reaction methanol amount) can be obtained from the reaction equation (1) described above, the Faraday constant, and the load current value (1.8 A) by the following equation.
Ideal reaction amount of methanol = 1.8 (A) x 60 (sec) / 96485/6 [mol / L]
The methanol crossed over to the cathode side undergoes a combustion reaction based on the following reaction formula to generate CO ₂ .
CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O (3)
The amount of methanol transferred to the cathode (moved methanol amount) can be obtained from the following equation from the amount of CO ₂ in air (mass% / measured value) and the crossover reaction equation.
Movement amount of methanol [mol / mim] = (CO 2 amount / 100) × 120 (ml / min) / 22400 (mL)

Table 1 shows the calculated crossover rate (CO) of each DMFC.

  As is apparent from Table 1, the DMFC using the electrode according to Example 1 has a lower crossover rate (C.O) than the DMFC using each electrode according to Comparative Examples 1 and 2. This agrees well with the observation result (crack amount) of the surface state of each electrode. That is, by performing vacuum suction simultaneously with application of the paint, an electrode with a reduced crack amount can be obtained, and as a result, crossover of a fuel cell such as a DMFC can be suppressed.

  Although an example in which the present invention is applied to a DMFC electrode has been described here, the present invention is not limited to this. The fuel cell electrode manufacturing apparatus and the fuel cell electrode manufacturing method of the present invention can be applied to the manufacture of various fuel cell electrodes.

1 is a perspective view showing a fuel cell electrode manufacturing apparatus according to an embodiment of the present invention. It is sectional drawing which shows the example of 1 structure of the membrane electrode composite to which the electrode produced by embodiment of this invention is applied. It is an enlarged photograph which shows the observation result of the surface state of the electrode by Example 1 of this invention. 6 is an enlarged photograph showing an observation result of a surface state of an electrode according to Comparative Example 1. 10 is an enlarged photograph showing an observation result of a surface state of an electrode according to Comparative Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electroconductive porous base material, 2 ... Paint for electrode formation, 3 ... Nozzle part, 4 ... Paint supply part, 5 ... Suction part, 6 ... Coating film (electrode / catalyst layer).

Claims (10)

A paint supply unit for quantitatively supplying an electrode forming paint in which a carbon species supporting a noble metal catalyst is dispersed in a solvent;
A nozzle part for discharging and applying the electrode-forming paint supplied from the paint supply part onto the surface of the conductive porous substrate;
A fuel, comprising: a suction part that is disposed on a back surface side of the conductive porous substrate and sucks the solvent component in the electrode forming paint under reduced pressure through the conductive porous substrate. Battery electrode manufacturing equipment. In the fuel cell electrode manufacturing apparatus according to claim 1,
The electrode manufacturing apparatus for fuel cells, wherein the conductive porous substrate is carbon paper or carbon cloth using carbon fibers. In the fuel cell electrode manufacturing apparatus according to claim 1 or 2,
A fuel cell electrode manufacturing apparatus, wherein the conductive porous substrate is subjected to a water repellent treatment. In the fuel cell electrode manufacturing apparatus according to claim 1 or 2,
The electroconductive porous substrate has a microporous carbon coat layer formed on the surface thereof, and the fuel cell electrode manufacturing apparatus. In the fuel cell electrode manufacturing apparatus according to any one of claims 1 to 4,
The electrode forming coating apparatus according to claim 1, wherein the electrode forming paint contains carbon nanofibers and carbon powder as the carbon species. In forming an electrode by applying a coating material for forming an electrode in which a carbon species supporting a noble metal catalyst is dispersed in a solvent to the surface of a conductive porous substrate,
The solvent in the electrode forming paint from the back side of the conductive porous base material through the conductive porous base material while applying the electrode forming paint to the surface of the conductive porous base material A method for producing an electrode for a fuel cell, comprising the step of sucking a component under reduced pressure. In the manufacturing method of the electrode for fuel cells of Claim 6,
The method for producing a fuel cell electrode, wherein the conductive porous substrate is carbon paper or carbon cloth using carbon fibers. In the manufacturing method of the electrode for fuel cells of Claim 6 or Claim 7,
A method for producing an electrode for a fuel cell, wherein the conductive porous substrate is subjected to a water repellent treatment. In the manufacturing method of the electrode for fuel cells of Claim 6 or Claim 7,
The method for producing an electrode for a fuel cell, wherein the conductive porous substrate has a microporous carbon coat layer formed on a surface thereof. In the manufacturing method of the electrode for fuel cells of any one of Claim 6 thru | or 9,
The method for producing an electrode for a fuel cell, wherein the electrode-forming paint contains carbon nanofibers and carbon powder as the carbon species.