JP2009093929A - Method of manufacturing electrode, and method of manufacturing electrolyte membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably form pores in an electrode of an electrochemical device while restraining deterioration of electrode performance. <P>SOLUTION: First, catalyst particles and electrolytes as materials for an anode electrode 21 and a cathode electrode 22 are mixed with water and ethanol as solvents at a predetermined ratio to prepare catalyst ink. Then, agitating them to keep the uniformity of the elements of the catalyst ink, the catalyst ink is cooled to prepare a catalyst slurry CS being a sherbet-like or ice cream-like solvent slurry SS whose water and ethanol contained in the catalyst ink are solidified by the status change. Then, after the catalyst slurry CS is coated on both faces of an electrolyte film 20 under the condition of temperature to keep the solvent slurry SS solid, the pressure is reduced and the solvent slurry S is sublimated to form pores H. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode used in an electrochemical device.

  In fuel cells, electrodes are generally formed on both surfaces of an electrolyte membrane having proton conductivity, and an electrochemical reaction proceeds at the three-phase interface between the reaction gas supplied to the electrode, the electrolyte, and the electrode. To do. In order to improve the power generation efficiency of the fuel cell, it is effective to secure this wide three-phase interface. For this purpose, the electrode needs to have appropriate pores. From this point of view, for example, the following Patent Document 1 and Patent Document 2 are known as techniques for suitably forming the pores of the electrode.

JP 2005-302665 A JP-A-9-199138

  In Patent Document 1, an electrode paste containing an electrode material and a polymer pore-forming agent is prepared, and this is applied to an electrolyte membrane, and then the polymer pore-forming agent is eluted with a solvent such as high-temperature water to form an electrode. A technique for forming pores is disclosed.

  In Patent Document 2, an electrode paste containing an electrode material and camphor is prepared on an electrolyte membrane, and this is applied to the electrolyte membrane, and then camphor is deposited as a pore-forming agent, and further sublimated to form an electrode. A technique for forming pores is disclosed. Also disclosed is a technique in which a catalyst paste in which an electrode material and a solvent are mixed is prepared, applied onto an electrolyte membrane, and then frozen, and the frozen solvent is further sublimated to form pores in the electrode. .

  However, in the method using a pore-forming agent, part of the pore-forming agent remains on the electrode, and the performance of the electrode may be deteriorated. Alternatively, in order to prevent the pore-forming agent from remaining, it is necessary to dissolve and sublimate the pore-forming agent for a long time, which hinders the efficiency of the manufacturing process. Moreover, in the method of freezing and sublimating the solvent contained in the electrode paste applied to the electrolyte membrane, it is difficult to adjust the size of the pores, and a great effect cannot be obtained. Such a problem is not limited to fuel cells, but is a problem common to various electrochemical devices.

  Based on the above-described problems, the problem to be solved by the present invention is to suitably form pores in the electrode of the electrochemical device.

  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] An electrode manufacturing method for use in an electrochemical device,
A preparation step of preparing a catalyst slurry in which a solvent slurry in which at least a part of a predetermined solvent is in a solid state due to a state change and the material of the electrode are mixed;
An application step of applying the catalyst slurry to a predetermined substrate under a temperature condition capable of maintaining the solid state;
A sublimation step of reducing the pressure under a predetermined temperature condition and sublimating the solvent slurry in the solid state contained in the applied catalyst slurry.

  Such an electrode manufacturing method includes applying a catalyst slurry in which a solvent slurry in which at least a part of a predetermined solvent is in a solid state and an electrode material are mixed to a substrate, sublimating the solvent slurry in a solid state, The pores are formed in the. Therefore, by controlling the amount and particle size of the solvent slurry, the amount and size of pores formed in the electrode can be adjusted, and an electrode having desired pores can be manufactured.

[Application Example 2] A method for producing an electrode according to Application Example 1, wherein the preparation step is to prepare a mixed solution of the electrode material and a predetermined solvent, cool the mixed solution while stirring, and remove the solvent. A method for producing an electrode, which is solidified to prepare a catalyst slurry.

  In such an electrode manufacturing method, a mixed solution of an electrode material and a predetermined solvent is cooled while stirring to prepare a catalyst slurry, so that uniform dispersibility of the electrode material can be secured and a suitable electrode is manufactured. Can do.

Application Example 3 The method for manufacturing an electrode according to Application Example 1 or Application Example 2, wherein the predetermined solvent is a mixed solution of water and a predetermined hydrophilic solvent.

  Such an electrode manufacturing method uses only water and a predetermined hydrophilic solvent as a solvent, and does not use a pore-forming agent. Therefore, the pore-forming agent does not remain on the electrode and the performance of the electrode is not deteriorated.

[Application Example 4] A method for producing an electrode used in an electrochemical device, comprising: preparing a predetermined slurry substance in which at least a part is maintained in a solid state; and mixing the slurry substance and the electrode material; Included in the applied catalyst slurry, a preparation process for preparing the catalyst slurry, an application process for applying the catalyst slurry to a predetermined substrate under a temperature condition capable of maintaining a solid state, and a reduced pressure under the predetermined temperature condition And a sublimation step of sublimating the solid slurry material.

  In such an electrode manufacturing method, a catalyst slurry obtained by mixing at least a part of a predetermined slurry substance maintained in a solid state and an electrode material is applied to a substrate, and the solid slurry substance is sublimated to form an electrode. Creates pores. Therefore, by controlling the amount and particle size of the solvent slurry, the amount and size of pores formed in the electrode can be easily adjusted, and an electrode having desired pores can be manufactured.

Application Example 5 The method for manufacturing an electrode according to Application Example 4, wherein the predetermined slurry material is ice slurry.

  Such an electrode manufacturing method uses ice slurry as the slurry material, and therefore does not use an unnecessary material for the electrode. Therefore, the electrode performance is not deteriorated.

Application Example 6 The method for manufacturing an electrode according to any one of Application Examples 1 to 5, wherein the electrochemical device is a fuel cell.

[Application Example 7] A method for producing an electrolyte membrane / electrode assembly for use in an electrochemical device, comprising a step of preparing a predetermined electrolyte membrane, and a solvent in which at least a part of the predetermined solvent is in a solid state due to a state change A preparation step for preparing a catalyst slurry in which the slurry and the electrode material are mixed, a coating step for applying the catalyst slurry to at least one surface of the electrolyte membrane under a temperature condition capable of maintaining a solid state, and a predetermined temperature condition And a sublimation step of sublimating the solvent slurry in a solid state contained in the applied catalyst slurry under reduced pressure.

Examples of the present invention will be described.
A. Example:
A-1. Fuel cell configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell 10 using an electrode of the present invention. The fuel cell 10 is a polymer electrolyte fuel cell, and is formed by laminating an electrolyte membrane 20, an anode electrode 21, a cathode electrode 22, gas diffusion layers 23 and 24, and separators 25 and 26, as shown.

  The electrolyte membrane 20 is made of a solid polymer that exhibits proton conductivity in a wet state. The anode electrode 21 and the cathode electrode 22 are electrodes in which a catalyst is supported on a carrier having conductivity, and in this embodiment, carbon particles supporting a platinum catalyst, a polymer electrolyte constituting the electrolyte membrane 20, and With the same electrolyte. The anode electrode 21 and the cathode electrode 22 together with the above-described electrolyte membrane 20 constitute an MEA (electrolyte membrane / electrode assembly) 30.

  The gas diffusion layers 23 and 24 can be formed of a conductive member having gas permeability, such as carbon paper or carbon cloth, metal mesh, or foam metal. The gas diffusion layers 23 and 24 of the present embodiment are both formed as flat plate members. Such a gas diffusion layer 24 serves as a flow path for a gas used for an electrochemical reaction and collects current.

  The separators 25 and 26 are formed of a gas impermeable conductive member, for example, a member made of compressed carbon or stainless steel. The separators 25 and 26 each have a predetermined uneven shape. Due to the uneven shape, a single-cell fuel gas flow path 27 through which a fuel gas containing hydrogen flows is formed between the separator 25 and the gas diffusion layer 23. In addition, due to the uneven shape, an in-single cell oxidizing gas flow path 28 in which an oxidizing gas containing oxygen flows is formed between the separator 26 and the gas diffusion layer 24.

A-2. Manufacturing method of MEA:
An example of the procedure of the manufacturing method of the MEA 30 constituting the fuel cell 10 described above is shown in FIG. In order to manufacture the MEA 30, first, a solid polymer electrolyte membrane to be the electrolyte membrane 20 is prepared (step S110). In this example, an electrolyte membrane made of a perfluorosulfonic acid electrolyte was prepared.

  Then, a catalyst ink for forming the anode electrode 21 and the cathode electrode 22 is prepared (step S120). Specifically, the catalyst ink is prepared by mixing catalyst particles and an electrolyte as materials for the anode electrode 21 and the cathode electrode 22, and water and ethanol as a solvent at a predetermined ratio. The weight mixing ratio of each component of the catalyst ink was water: ethanol: catalyst particles: electrolyte = 10: 10: 1: 0.5. The weight mixing ratio is not limited to the above example, and may be set as appropriate in consideration of required electrode performance, polarity of catalyst particles, and the like. For example, water or ethanol may be about “4” to “20” instead of the above-mentioned ratio “10”.

  In this example, water and ethanol were used as the solvent for the catalyst particles and the electrolyte. However, the type of the solvent is not limited to this, and a combination of water and another solvent having hydrophilicity may be used. There may be. For example, a combination of water and an alcohol solvent such as methanol, propanol, or isopropanol is preferable. Of course, the solvent is not limited to a combination with water, and any solvent that can ensure uniform dispersibility of catalyst particles and the like may be used.

  In addition, the catalyst particles (carbon particles carrying platinum) of this example are obtained by, for example, converting carbon particles made of carbon black into platinum compound solutions (for example, tetraammine platinum salt solution, dinitrodiammine platinum solution, platinum nitrate solution, or In a chloroplatinic acid solution, etc.) and can be prepared by an impregnation method, a coprecipitation method, or an ion exchange method.

  Once the catalyst ink is prepared, the catalyst slurry CS is then cooled by injecting liquid nitrogen while stirring so as to maintain the uniform dispersibility of the components of the catalyst ink, thereby preparing the catalyst slurry CS (step S130). . Specifically, the prepared catalyst ink is put into a stirring tank and stirred by a rotating plate-shaped stirrer provided in the stirring tank. However, the stirring method is not limited to this, and the container rotating type is used. For example, various stirring devices can be used. The catalyst slurry CS refers to a mixture of water and ethanol as a solvent contained in the catalyst ink that is solidified by a change in state to form a sherbet or ice cream. In this example, the cooling temperature was set to −40 ° C. in consideration of the fact that the freezing point of the mixed solution of water and ethanol having the above mixing ratio was about −32 ° C., and the electrolyte was added thereto. This cooling temperature should just be the temperature below the freezing point of the liquid mixture of water and ethanol, and can be made into -10-70 degreeC according to the mixing ratio of water and ethanol, for example. The cooling temperature is set to be lower as the mixing ratio of ethanol having a lower freezing point than water is increased. Thus, by controlling the mixing ratio of the solvent and the cooling temperature, the viscosity of the solvent can be adjusted, and the uniform dispersibility of the catalyst particles and the like can be improved. Hereinafter, the mixed solution of water and ethanol coagulated as described above is referred to as “solvent slurry SS”.

  Once the catalyst slurry CS is prepared, next, the catalyst slurry CS is applied to both surfaces of the electrolyte membrane 20 (step S140). In step S130, this application is performed under temperature conditions where the solidified solvent slurry SS can maintain a solid state. In the present embodiment, the application is performed using a doctor blade method suitable for application of a slurry-like substance, but various application methods such as spraying and screen printing can be used. Thereby, on the surface of the electrolyte membrane 20, as shown in FIG. 3A, the carbon particles C carrying the platinum catalyst P, the electrolyte E, and the solvent (here, a mixture of water and ethanol) are present. A layer of catalyst slurry CS in which the coagulated solvent slurry SS is uniformly mixed is formed.

  Once the catalyst slurry CS is applied, the electrolyte membrane 20 to which the catalyst slurry CS is applied is then set in a freeze dryer and, under a predetermined temperature condition (in this embodiment, the triple point or less of the mixed liquid of water and ethanol). At a temperature of −40 ° C., the inside of the vessel is depressurized with a vacuum pump to sublimate the solvent slurry SS (step S150). By doing so, as shown in FIG. 3B, the space occupied by the solvent slurry SS in the catalyst slurry CS of FIG. 3A becomes pores H as the solvent slurry SS sublimates. The pore H has a three-dimensionally communicating structure, and in FIG. 3B, the void portion displayed so as to exist independently between the electrolyte E and the like is also illustrated with other void portions. It communicates on the cross section that does not.

  The amount and size of the pores H formed in this way can be easily controlled. For example, the amount of pores H can be controlled by adjusting the ratio between the catalyst particles and the solvent in step S120. Further, if the solvent concentration is adjusted in step S120 or the type of the solvent is changed, the slurry of the solvent slurry SS can be adjusted by changing the binding force between the molecules. Can be controlled. Alternatively, the size of the pores H can be controlled by adjusting the cooling rate in step S130. In general, when the cooling rate is increased, the particle size of the solvent slurry SS is reduced, and the pores H can be reduced. In this way, the size of the pores H can be controlled in the range of about 50 nm to 10 μm, for example.

  When the solvent is almost sublimated, the cooling / depressurization state is canceled and the solvent is completely dried (step S160). Note that this step is not always necessary, and conversely, heating may be performed for speeding up. In this way, the MEA 30 in which the anode electrode 21 and the cathode electrode 22 having the pores H are formed on both surfaces of the electrolyte membrane 20 is obtained.

  In this example, the catalyst slurry CS was prepared so that a part of the mixed liquid of water and ethanol was solidified. All of these solvents need not be solidified, and some of them may be liquid.

  The MEA 30 obtained in step S160 may be further subjected to a bonding process such as hot pressing to improve the bonding property between the electrolyte membrane 20, the anode electrode 21, and the cathode electrode 22. Even when such treatment is performed, the pores H can be kept relatively large because the shapes of the anode electrode 21 and the cathode electrode 22 are maintained by the skeleton of the carbon particles.

  The manufacturing method of the MEA 30 having such a configuration prepares a catalyst slurry CS in which a solvent slurry SS that has become a solid state due to a state change, catalyst particles, and an electrolyte are mixed. Therefore, the viscosity of the catalyst particle dispersion solution is increased, and the catalyst particles that are relatively difficult to ensure uniform dispersibility can be uniformly dispersed.

  In the method for manufacturing the MEA 30 having such a configuration, the catalyst slurry CS is applied on the surface of the electrolyte membrane 20, and the solvent slurry SS is sublimated to form the pores H. Therefore, it is possible to form an electrode that can take a wide three-phase interface. Further, since no pore forming agent is used, no excess compound remains in the electrode, and the performance of the electrode is not deteriorated. Furthermore, the amount and size of the particles of the solvent slurry SS can be easily controlled by the concentration of the solvent, the cooling rate, etc., and the size of the solvent slurry SS becomes the size of the pores H as they are. Easy to control the number of pods.

  In addition, although the above-mentioned Example was shown as a manufacturing method of MEA30, it cannot be overemphasized that this invention can also be comprised as a manufacturing method of the anode electrode 21 or the cathode electrode 22. FIG. In the embodiment, in order to efficiently manufacture the MEA 30, the anode electrode 21 and the cathode electrode 22 are formed by applying the catalyst slurry CS on the surface of the electrolyte membrane 20 as a base material. In the case of constituting as a manufacturing method of the cathode electrode 22, for example, a sheet of polyethylene terephthalate (PET) or polytetrafluoroethylene (PTFE) is used as a base material, and the catalyst slurry CS is applied on the base material. The anode electrode 21 and the cathode electrode 22 may be formed. In such a case, for example, the anode electrode 21 and the cathode electrode 22 may be transferred to the electrolyte membrane 20 by hot-pressure transfer, and the substrate may be peeled and removed to manufacture the MEA 30.

B. Variations:
In the above embodiment, the catalyst particles and the electrolyte are dispersed in a solvent, and the solvent is stirred and cooled to prepare the catalyst slurry CS. However, the catalyst slurry CS can be prepared by another method. . FIG. 4 shows a procedure of a method for manufacturing the MEA 30 as a modification. The difference from the embodiment shown in FIG. 2 is step S220 and step S230, and the same reference numerals as those in FIG. Below, step S220 and step S230 are demonstrated.

  After preparing the electrolyte membrane (step S110), the slurry is stirred while cooling water below the freezing point to prepare an ice slurry (step S220). Then, the ice slurry, the catalyst particles, and the electrolyte are mixed to prepare the catalyst slurry CS (step S230). The subsequent steps are the same as those in FIG.

  In this way, from the viewpoint of uniform dispersibility of the catalyst particles and the like, although inferior to the examples, there is no restriction on the mixing ratio of the solvent such as water and ethanol, and the ice slurry is prepared alone, The particle diameter of the ice slurry contained in the catalyst slurry CS can be easily adjusted, and as a result, the size of the pores H formed in the anode electrode 21 and the cathode electrode 22 can be easily adjusted. In addition, since unnecessary solvents and pore forming agents are not used for the anode electrode 21 and the cathode electrode 22, excess components remain in the anode electrode 21 and the cathode electrode 22 and the performance is not deteriorated.

  In this modification, a predetermined slurry substance maintained in a solid state is prepared, and this is regarded as a solvent, and the slurry substance, catalyst particles, and electrolyte are mixed to prepare a catalyst slurry CS. The slurry substance is not limited to ice, and a mixture of water and an organic solvent in a solid state, a mixture of only an organic solvent in a solid state, dry ice, or the like may be used. Further, the slurry material does not necessarily have to be in a solid state, and may be in a mixed state of a solid and a liquid.

  The embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, the electrode manufacturing method of the present invention is not limited to the electrode for the polymer electrolyte fuel cell shown in the embodiment. It can be configured as a method for producing electrodes used in various electrochemical devices such as various types of fuel cells, water electrolytic cells, salt electrolytic cells, hydrochloric acid electrolytic cells and the like. Further, the present invention can be configured as an electrode and an electrolyte membrane / electrode assembly in addition to the configuration as a method for manufacturing an electrode and an electrolyte membrane / electrode assembly.

It is explanatory drawing which shows schematic structure of the fuel cell 10 using the electrode of this invention. It is process drawing which shows an example of the procedure of the manufacturing method of MEA30 which comprises the fuel cell 10 as an Example. FIG. 6 is an explanatory view showing a state in which pores H are formed in the anode electrode 21. It is process drawing which shows an example of the procedure of the manufacturing method of MEA30 which comprises the fuel cell 10 as a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 20 ... Electrolyte membrane 21 ... Anode electrode 22 ... Cathode electrode 23, 24 ... Gas diffusion layer 25, 26 ... Separator 27 ... Fuel gas flow path in a single cell 28 ... Oxidation gas flow path in a single cell P ... Platinum catalyst C: Carbon particles E ... Electrolyte SS ... Solvent slurry CS ... Catalyst slurry H ... Pore

Claims (7)

A method for producing an electrode for use in an electrochemical device, comprising:
A preparation step of preparing a catalyst slurry in which a solvent slurry in which at least a part of a predetermined solvent is in a solid state due to a state change and the material of the electrode are mixed;
An application step of applying the catalyst slurry to a predetermined substrate under a temperature condition capable of maintaining the solid state;
A sublimation step of reducing the pressure under a predetermined temperature condition and sublimating the solvent slurry in the solid state contained in the applied catalyst slurry. A method for producing an electrode according to claim 1,
The preparation step prepares a catalyst slurry by preparing a mixed liquid of the electrode material and the predetermined solvent, cooling the mixed liquid while stirring, and solidifying the predetermined solvent. Manufacturing method.   The method of manufacturing an electrode according to claim 1, wherein the predetermined solvent is a mixed solution of water and a predetermined hydrophilic solvent. A method for producing an electrode for use in an electrochemical device, comprising:
Providing a predetermined slurry material at least partially maintained in a solid state;
A preparation step of preparing a catalyst slurry by mixing the slurry substance and the electrode material;
An application step of applying the catalyst slurry to a predetermined substrate under a temperature condition capable of maintaining the solid state;
A sublimation step of reducing the pressure under a predetermined temperature condition and sublimating the slurry material in the solid state contained in the applied catalyst slurry.   The method of manufacturing an electrode according to claim 4, wherein the predetermined slurry material is ice slurry.   The electrode manufacturing method according to claim 1, wherein the electrochemical device is a fuel cell. A method for producing an electrolyte membrane / electrode assembly for use in an electrochemical device,
A step of preparing a predetermined electrolyte membrane;
A preparation step of preparing a catalyst slurry in which a solvent slurry in which at least a part of a predetermined solvent is in a solid state due to a state change and the material of the electrode are mixed;
An application step of applying the catalyst slurry to at least one surface of the electrolyte membrane under a temperature condition capable of maintaining the solid state;
And a sublimation step of sublimating the solvent slurry in the solid state contained in the applied catalyst slurry under reduced pressure under a predetermined temperature condition.

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