JP2010257739A - Method for manufacturing electrode for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase productivity when forming an electrode on an electrolyte membrane, and to enhance durability of a fuel cell. <P>SOLUTION: The method for manufacturing an electrode for a fuel cell includes the steps of: (a) preparing the electrolyte membrane; (b) producing electrode material powder by kneading catalyst particles carrying a catalyst on carbon particles, a binder, a pore forming agent, crushing, removing the pore forming agent to make the binder porous, and interposing the porous binder among many catalyst particles; (c) forming an electrode precursor layer made of the electrode material powder by applying the electrode material powder to the electrolyte membrane by an electrostatic splay method; (d) fixing the electrode precursor layer onto the electrolyte membrane by conducting photoirradiation to the electrode precursor layer, softening the binder by heat generation of the carbon particles or melting a part of the binder; and (e) applying or impregnating a polymer electrolyte solution to or into the electrode precursor layer fixed onto the electrolyte membrane. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a fuel cell electrode.

  Conventionally, as a method for producing an electrode for a fuel cell, for example, an electrode catalyst ink (paste) containing carbon particles supporting a noble metal as a catalyst is prepared, and this ink (paste) is applied onto an electrolyte membrane and then dried. The method is known. Alternatively, a configuration has been proposed in which an electrode catalyst powder containing carbon particles supporting a noble metal as a catalyst is electrostatically charged and attached to at least one surface of a polymer electrolyte membrane (for example, Patent Document 1). reference). The method of electrostatically attaching the electrode catalyst powder onto the electrolyte membrane is different from the method of applying the electrode catalyst ink in that it does not use a solvent and does not require a drying step after application. Has advantages.

JP-A-11-288728 International Publication No. 2003/033566 JP 2005-116308 A

  However, in the method of forming an electrode by electrostatically charging an electrode catalyst powder and adhering it to the electrolyte membrane, a method for fixing the electrode on the electrolyte membrane has not been sufficiently studied. . It is important to sufficiently fix the electrode on the electrolyte membrane in order to ensure the performance of the fuel cell. For example, when heating is performed when fixing the electrode on the electrolyte membrane, the electrolyte is heated by heat. It is conceivable that the membrane is deteriorated and the durability of the fuel cell becomes insufficient. Further, if the fixing process is complicated, it may be possible that the productivity in manufacturing the electrode cannot be sufficiently increased.

  The present invention has been made in order to solve the above-described conventional problems, and further improves productivity and further improves the durability of the fuel cell when an electrode is formed on the electrolyte membrane. The purpose is to plan.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A method for producing a polymer electrolyte fuel cell electrode,
(A) preparing an electrolyte membrane comprising a polymer electrolyte;
(B) The catalyst particles having the catalyst supported on the carbon particles, the binder that can be melted by heating, and the pore former are kneaded and then pulverized, and the pore former is removed, Making the binder porous, and producing the electrode material powder comprising the porous binder interposed between the plurality of catalyst particles;
(C) applying the electrode material powder onto the electrolyte membrane by electrostatic spraying to form an electrode precursor layer made of the applied electrode material powder;
(D) irradiating the electrode precursor layer with light to heat the carbon particles, thereby softening the binder contained in the electrode precursor layer or melting a part of the binder. Fixing the electrode precursor layer on the electrolyte membrane;
(E) A method for producing a fuel cell electrode, comprising: applying or impregnating a polymer electrolyte solution to the electrode precursor layer fixed on the electrolyte membrane.

  According to the manufacturing method of the fuel cell electrode described in Application Example 1, when forming the electrode on the electrolyte membrane, the electrode material powder is applied on the electrolyte membrane by the electrostatic spray method and light irradiation is used. By combining with the fixing of the electrode material to the electrolyte membrane, the productivity at the time of manufacturing the electrode can be improved, and the durability of the obtained electrode and the fuel cell incorporating the electrode can be improved.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of an electrode manufactured by a method for manufacturing an electrode for a fuel cell or a fuel cell including such an electrode. is there.

It is process drawing showing the manufacturing method of the electrode for fuel cells of an Example. It is explanatory drawing showing the main processes in the manufacturing method of the electrode for fuel cells. It is explanatory drawing which shows the composition ratio of an electrode material. It is explanatory drawing which shows an example of the conditions of the light irradiation in step S140.

  FIG. 1 is a process diagram showing a method of manufacturing a fuel cell electrode as an embodiment of the present invention. Moreover, FIG. 2 is explanatory drawing showing the mode of the main processes in the manufacturing method of the electrode for fuel cells of a present Example.

  In the fuel cell electrode manufacturing method of the present embodiment, first, the electrolyte membrane 10 is prepared (step S100). The fuel cell assembled using the electrode manufactured by the electrode manufacturing method of the present embodiment is a polymer electrolyte fuel cell. Therefore, as the electrolyte membrane 10, a solid polymer electrolyte membrane, for example, a proton conductive ion exchange membrane formed of a fluorine-based resin is prepared. Such a polymer electrolyte membrane has substantially no electrical conductivity, but in this embodiment, in particular, by adding a conductive agent to the raw material when the electrolyte membrane 10 is produced, the polymer electrolyte membrane 10 is electrically conductive. Has been given sex. As the conductive agent to be mixed with the electrolyte film 10, it is desirable to use a transparent or white conductive agent so that an increase in temperature of the electrolyte film 10 can be suppressed in a photofixing process using a flash lamp described later. For example, iridium oxide can be used as the transparent conductive agent. In this case, for example, the electrolyte membrane 10 may be manufactured by mixing iridium oxide at a weight ratio of about 2% with respect to the raw material of the electrolyte membrane 10. The amount of the conductive agent mixed in the electrolyte membrane 10 is within a range in which the influence of the conductive agent on the fuel cell including the electrolyte membrane 10 can be tolerated, and the application efficiency of the catalyst fine particles 20 in the electrostatic spray method by adding the conductive agent. What is necessary is just to set suitably so that it may become the range from which the improvement effect of this is fully acquired. The photofixing process will be described in detail later.

Next, the electrode material is adjusted (step S110). In this embodiment, adjustment of the electrode material is performed by a kneading and pulverizing method, and the step S110 includes a process of metering, mixing, kneading, pulverizing, classifying or sieving raw materials for producing an electrode. The In this example, as a raw material of the electrode material, a binder for fixing the electrode to the electrolyte membrane, carbon particles carrying platinum as an electrode catalyst, a pore former, and a polymer electrolyte are used. However, in step S110, materials other than the polymer electrolyte are mixed to adjust the electrode material. In this embodiment, polytetrafluoroethylene (PTFE) is used as the binder, and calcium carbonate (CaCO ₃ ) is used as the pore former. FIG. 3 shows the composition ratio of the electrode material of this example.

  In step S110, the binder, the platinum-supporting carbon, and the pore-forming agent are weighed so as to have the ratio shown in FIG. 3, and the weighed raw materials are combined and mixed using, for example, a Henschel mixer. When the raw materials are mixed together, further kneading is performed using a kneader while heating at 330 to 350 ° C. By heating and kneading, the binder is melted, and the platinum-supporting carbon and the pore-forming agent are finely divided, and the raw materials thus finely divided are uniformly mixed. After each raw material is heat-kneaded, the kneaded raw material is cooled and pulverized to obtain an electrode material. The operation of pulverization may be carried out after coarse pulverization and then finely pulverized to an average particle size of 5 to 13 μm using, for example, a dry jet mill. The electrode material obtained by pulverization is classified using, for example, a centrifugal classifier, and fine particles having a particularly small particle size and coarse particles having a particularly large particle size are removed to sharpen the particle size distribution. Such classification operation may be performed by sieving.

  Next, the pore-forming agent is removed from the particulate electrode material that has undergone the classification step, and the porous binder coats the catalyst-supporting carbon particles and binds in a state of being interposed between the catalyst-supporting carbon particles. Catalyst fine particles as electrode material powder in which the agent and the catalyst-supporting carbon particles are mixed are prepared (step S120). The pore-forming agent can be removed, for example, by washing the particulate electrode material that has been subjected to the classification step with nitric acid, followed by further washing with water and drying to remove nitric acid.

  Once the catalyst fine particles are produced, the catalyst fine particles are then applied onto the electrolyte membrane 10 prepared in step S100 using an electrostatic spray method (step S130), and an electrode precursor layer made of catalyst fine particles is applied to the electrolyte membrane. 10 is formed. Electrostatic spraying means applying a high voltage to the electrode at the tip of the spray gun when spraying powder (catalyst particles in this example) onto an object to be coated (electrolyte film in this example) with a spray gun. Is a well-known technique in which the powder supplied into the spray gun together with the compressed carrier air is charged, and the charged powder is sprayed on the grounded object to be adhered to the object to be coated. . The powder can be charged by the spray gun by corona charging or friction charging. FIG. 2 shows the state of each step after step S130. As step (A) in FIG. 2, corresponding to step S130, the spray gun 30 provided with the high-voltage power supply 32 is applied to the electrolyte membrane 10. The catalyst fine particles 20 are sprayed to form an electrode precursor layer 22 on the electrolyte membrane 10. In the present embodiment, as described above, the electrolyte membrane 10 is produced by previously mixing a conductive agent. Therefore, by grounding the electrolyte membrane 10 as an object to be coated, it is possible to efficiently suck and apply the charged powder discharged from the spray gun onto the electrolyte membrane 10. Become.

  Next, the electrode precursor layer 22 formed on the electrolyte membrane 10 is irradiated with light using a flash lamp to soften the binder in the electrode precursor layer 22 or melt a part of the binder. Thus, the electrode precursor layer 22 is fixed on the electrolyte membrane 10 (step S140). 2B shows a state in which light irradiation is performed on the electrode precursor layer 22 on the electrolyte membrane 10 using the flash lamp 40 including the flash reflector 42 corresponding to step S140. Yes. A xenon lamp used as a flash lamp has a strong emission intensity in the infrared region. When irradiation is performed using such a flash lamp, the black carbon particles carrying the catalyst contained in the electrode precursor layer 22 absorb the irradiated light and convert it into heat, and the temperature is reduced within a short time. To rise. An example of the light irradiation conditions in step S140 is shown in FIG. Using the flash lamp under such irradiation conditions, the electrode precursor layer 22 is irradiated for 0.3 milliseconds, for example, to raise the temperature of the carbon particles in the electrode precursor layer 22 to about 500 ° C. Can do. Here, since the melting point of PTFE used as the binder constituting the electrode precursor layer 22 is about 327 ° C., the binder constituting the electrode precursor layer 22 is melted by the above-described light irradiation to the electrode precursor layer 22. Thus, the electrode precursor layer 22 and the electrolyte membrane 10 are bound.

  As described above, in step S140, the carbon particles are locally heated within the electrode precursor layer 22 by irradiation with a flash lamp, and the binder existing inside the electrode precursor layer 22 is heated by being mixed with the carbon particles.・ Melting. On the other hand, the electrolyte membrane 10 is a separate member from the electrode precursor layer 22 and is separated from the carbon particles in the electrode precursor layer 22. Therefore, even when the carbon particles generate heat, the electrolyte membrane 10 is less affected by heat generation. The light absorption rate of the electrolyte membrane 10 itself is about 35%, and the electrolyte membrane 10 itself hardly generates heat due to light irradiation. In particular, in this embodiment, a transparent or white conductive agent is used as a conductive agent to be mixed in order to give conductivity to the electrolyte membrane 10, and the increase in light absorption of the electrolyte membrane 10 due to the conductive agent is suppressed. ing.

  In step S140, the binder is melted by light irradiation using a flash lamp, and the light irradiation amount is adjusted so that the porosity of the binder remains to some extent. As described above, in the electrode precursor layer 22, the binder is made porous by removing the pore forming agent in step S120. When the binder is melted by heating in step S140, the output in the flash lamp and the irradiation time are adjusted to control the degree of temperature rise in the electrode precursor layer 22, thereby leaving the porosity in the binder. I am letting. In addition, the melting of the binder by light irradiation is not complete melting but partial melting or partial melting of the surface. Or a considerable part remains. Further, in the electrode precursor layer 22 after the binder is melted, the porosity of the electrode precursor layer 22 is also maintained by leaving a part of the voids between the powdery catalyst fine particles.

  Next, the electrode precursor layer 22 that has been subjected to photofixing is coated and impregnated with a polymer electrolyte solution (step S150) to complete a fuel cell electrode. The polymer electrolyte solution used in step S150 can be, for example, a fluorine resin having proton conductivity. Such a polymer electrolyte solution can be, for example, a solution containing an electrolyte resin of the same type as the electrolyte membrane 10. Various methods can be used as a method for applying and impregnating the polymer electrolyte solution to the electrode precursor layer 22. In FIG. 2 (C), the state in which the polymer electrolyte solution 24 is applied onto the electrode precursor layer 22 by dropping from the electrolyte solution applying device 45 is shown corresponding to step S150. Thus, by applying the polymer electrolyte solution to the electrode precursor layer 22, the polymer electrolyte solution can be contained in the pores of the electrode precursor layer 22 (in the pores of the binder and in the molten catalyst fine particles). It is impregnated in the voids remaining between them. In addition, when completing an electrode in step S150, after apply | coating a polymer electrolyte solution, it may dry further and the solvent in a polymer electrolyte solution may be removed.

  As described above, the polymer electrolyte solution is impregnated in the pores of the electrode precursor layer 22, but in the electrode finally obtained after the polymer electrolyte solution is impregnated in the pores, In step S150, the polymer electrolyte solution is applied and impregnated so that the porosity still remains. When power generation is performed in the fuel cell, in the catalyst provided in the electrode, supply and discharge of electrons through the carbon particles carrying the catalyst, supply and discharge of protons through the polymer electrolyte impregnated in step S150, It is necessary to supply and discharge the gas containing the electrode active material without delay. In order to ensure supply / discharge of gas to / from such a catalyst, it is desirable that the electrode has a porous property. Therefore, when manufacturing an electrode in this embodiment, the amount of the binder and pore former added when adjusting the electrode material in step S110, and the degree of loss of porosity due to melting of the binder. By adjusting the light irradiation amount in step S140 involved and the application amount of the polymer electrolyte solution in step S150 related to the degree to which the pores of the electrode precursor layer 22 are blocked, an electrode having a desired porosity is obtained. Is desirable.

  In FIG. 2, the steps of electrostatic application of catalyst fine particles using a spray gun, photofixing using a flash lamp, and application of an electrolyte solution are carried out in series while the electrolyte membrane 10 is conveyed in a certain direction. The operation is sequentially performed as the operation. In such a case, since a plurality of electrodes can be sequentially formed on the larger electrolyte membrane 10, the electrolyte membrane 10 may be appropriately cut after forming the plurality of electrodes. When the method of applying and impregnating the polymer electrolyte solution to the electrode precursor layer 22 is adopted as a method of dropping from the electrolyte solution application device 45 as shown in FIG. 2, the electrode as shown in FIG. This is desirable because it can be easily incorporated into a series of steps for manufacturing the substrate. In FIG. 2, the state in which the electrode is formed on one surface of the electrolyte membrane 10 is shown. After the electrode is formed on one surface, the electrode is formed on the other surface in the same manner, thereby forming the membrane. -An electrode assembly (Membrane Electrode Assembly, MEA) can be produced. When assembling a fuel cell, a conductive porous body such as carbon cloth is laminated as a gas diffusion layer on each electrode surface of the membrane-electrode assembly, and, for example, a groove is provided on the laminated gas diffusion layer. A single cell in which a gas flow path is formed between the gas diffusion layer and the separator may be manufactured by further laminating the separator. By stacking a plurality of such single cells, a fuel cell having a stack structure can be assembled.

  According to the method of manufacturing the fuel cell electrode of the present embodiment configured as described above, the electrode material is applied onto the electrolyte membrane using an electrostatic method when the electrode is formed on the electrolyte membrane. In combination with the fixing of the electrode material to the electrolyte membrane using light fixing with a flash lamp, the productivity at the time of manufacturing the electrode is improved and the durability of the fuel cell incorporating the electrode and the electrode is improved. Can do.

  In particular, since the electrostatic spray method is a method of spraying and applying a powdered electrode material, when applying the electrode material on the electrolyte membrane, a solvent is used as in the case of spraying the electrode material into an ink. There is no need to use it. Therefore, it is not necessary to consider environmental pollution caused by using a solvent. In addition, since it is not necessary to dry the electrode material after application as in the case of spraying the catalyst ink in which the electrode material is converted to ink, the manufacturing process can be simplified and shortened to increase productivity. In addition, since the electrostatic spray method applies a powder electrode material onto the electrolyte membrane, the physical property value of the applied electrode material does not vary, and the electrode material can be more easily and uniformly applied. . On the other hand, when the catalyst ink is sprayed, physical properties such as the adjusted ink particle size and viscosity can change with time, so the basis weight of the catalyst ink (coating amount) due to changes in the physical properties of the ink. As a result, battery performance may be reduced or varied. Furthermore, according to the electrostatic spray method, the oversprayed powder can be easily collected and reused, so that the utilization efficiency of the electrode material can be increased.

  There is an electrostatic copying method as another method for electrostatically applying a powdered electrode material. The electrostatic spraying method in this embodiment is simpler and less expensive than the electrostatic copying method. The electrode material can be applied by the apparatus. As described above, the electrostatic spray method has a simple mechanism for charging and applying powder, so that variation in the amount of charge in the powder is unlikely to occur, suppressing variation in the amount of application, and improving electrode performance. Can do. On the other hand, the electrostatic copying method has a complicated apparatus structure, so that the amount of charge varies depending on the shape and particle size of the catalyst fine particles, which causes the amount of adhesion on the electrolyte membrane to vary, As a result, streaks occur, and the electrode performance may vary.

  Further, in this embodiment, in order to fix the applied electrode material on the electrolyte membrane, light fixing using a flash lamp is performed, so that the bonding is performed by non-contact heating for a short time (for example, 0.3 milliseconds). The electrode can be fixed by melting the adhesive. During the short heating time, the temperature is, for example, 500 ° C., but otherwise, the treatment is performed at a low temperature of 100 ° C. or less. Therefore, deterioration of the electrolyte membrane due to heat caused by heating for fixing the electrode can be suppressed, and durability of the electrolyte membrane can be improved. On the other hand, when the electrode material applied on the electrolyte membrane is baked and fixed in a drying furnace, for example, it is necessary to perform heating for about 30 minutes to 2 hours under a temperature condition of about 320 to 350 ° C. . In such a case, there is a possibility that the deterioration of the electrolyte membrane due to the heating is not negligible. Further, in the case where the optical fixing using the flash lamp is performed as in the present embodiment, the heating time for fixing can be shortened, so that the effect of increasing the productivity in manufacturing the electrode can be obtained.

  In this embodiment, the electrode precursor layer 22 is fixed after the porous electrode precursor layer 22 made of an electrode material other than the polymer electrolyte is fixed on the electrolyte membrane 10. It is arranged in the electrode by applying and impregnating the electrode. As described above, since the polymer electrolyte solution is applied and impregnated after the fixing step, the polymer electrolyte included in the electrode is not affected by the heating in the fixing step and deteriorates due to the heating. There is no. Therefore, durability of the electrode can be improved.

  Furthermore, according to the present embodiment, since the electrolyte membrane 10 formed by mixing a transparent or white conductive agent is used, the conductivity required in the step of applying the electrode material by the electrostatic spray method is improved. It is possible to achieve both application to the electrolyte membrane 10 and suppression of an undesired temperature rise in the electrolyte membrane 10 when performing photofixing using a flash lamp. Further, in this embodiment, since the catalyst metal included in the electrode is dispersedly supported on the carbon particles, a substance for absorbing the light of the flash lamp is used as the electrode material in order to perform light fixing using the flash lamp. Therefore, there is no need to mix them separately, and the use of photofixing does not complicate the electrode material adjustment process and the electrode configuration.

DESCRIPTION OF SYMBOLS 10 ... Electrolyte membrane 20 ... Catalyst fine particle 22 ... Electrode precursor layer 24 ... Polymer electrolyte solution 30 ... Spray gun 32 ... High voltage power supply 40 ... Flash lamp 42 ... Flash reflector 45 ... Electrolyte solution coating apparatus

Claims (1)

A method for producing a polymer electrolyte fuel cell electrode,
(A) preparing an electrolyte membrane comprising a polymer electrolyte;
(B) The catalyst particles having the catalyst supported on the carbon particles, the binder that can be melted by heating, and the pore former are kneaded and then pulverized, and the pore former is removed, Making the binder porous, and producing the electrode material powder comprising the porous binder interposed between the plurality of catalyst particles;
(C) applying the electrode material powder onto the electrolyte membrane by electrostatic spraying to form an electrode precursor layer made of the applied electrode material powder;
(D) irradiating the electrode precursor layer with light to heat the carbon particles, thereby softening the binder contained in the electrode precursor layer or melting a part of the binder. Fixing the electrode precursor layer on the electrolyte membrane;
(E) A method for producing a fuel cell electrode, comprising: applying or impregnating a polymer electrolyte solution to the electrode precursor layer fixed on the electrolyte membrane.

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