JP2010044949A - Method for manufacturing electrolyte layer of fuel battery, and method for manufacturing fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain changes on pH of a paste used as a precursor of an electrolyte layer of the fuel battery. <P>SOLUTION: A method for manufacturing a single cell of a fuel battery includes a step of forming the electrolyte layer on a first electrode 20, and a step of positioning a second electrode 60 on the electrolyte layer. The step of forming the electrolyte layer has a step of controlling pH of moisture at a level of 6-8 by cleaning the electrolyte layer formation surface of the first electrode 20 at the time of existence of the moisture on an electrolyte layer formation surface, and a step of forming the electrolyte layer by applying the paste on the electrolyte layer formation surface. pH of the paste is controlled at a designated range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an electrolyte layer for a fuel cell and a method for producing a fuel cell, which include a step of forming an electrolyte layer by applying a paste.

  When manufacturing a fuel cell, it is necessary to form an electrolyte layer. The electrolyte layer is sandwiched between the fuel electrode and the air electrode while being impregnated with an electrolyte such as an electrolytic solution. In order to improve the power generation efficiency of the fuel cell, it is necessary to reduce the electric resistance (ion transfer resistance) in the electrolyte layer and to efficiently perform the power generation reaction. In order to reduce the electrical resistance in the electrolyte layer, the thickness of the electrolyte layer can be reduced and the porosity can be increased. However, if the thickness of the electrolyte layer is too thin or the porosity is too high, it will be difficult to keep the reactant gas secret on the fuel electrode side and the air electrode side. In this case, since the fuel system gas that is the reaction gas on the fuel electrode side and the oxidant gas that is the reaction gas on the air electrode side directly react, the efficiency of the power generation reaction decreases. From such points, there are appropriate ranges for the thickness and the porosity of the electrolyte layer.

  As a method of forming the electrolyte layer, in addition to a method of sandwiching the electrolyte layer formed into a sheet between the fuel electrode and the air electrode, a method of applying a paste as a precursor to the surface of the catalyst layer of the electrode, followed by drying and heat treatment ( For example, see Patent Documents 1 to 5.

  When forming an electrolyte layer using a paste, it is important to control the viscosity of the paste in order to control the thickness and porosity of the electrolyte layer. That is, when the paste viscosity decreases, the electrolyte layer becomes thinner, and when the paste viscosity increases, the electrolyte layer becomes thicker. Moreover, when the paste viscosity is too low, the thickness of the applied paste, that is, the thickness of the electrolyte layer tends to be non-uniform. If the paste viscosity becomes too high, the binder contained in the paste is consolidated due to an increase in the shear stress at the coating roll, and aggregated particles that exceed the thickness of the electrolyte layer are generated, or the transfer defect of the paste occurs. Sometimes.

Patent Document 6 discloses a technique for controlling the viscosity of a paste within a certain range by controlling the pH of the paste within a certain range. Patent Document 7 discloses that the pH of the catalyst-supported carbon slurry for fuel cells is less than 6. Further, in Patent Document 8, when an electrode catalyst layer of a fuel cell is formed, an agglomerated slurry containing a catalyst is placed on a porous carbon base material, washed with pure water, and dried to obtain a fuel cell. Making an electrode is disclosed.
Japanese Patent No. 2991377 Japanese Patent Publication No. 1-58831 JP-A-4-284364 JP-A-64-41174 JP-A-1-217858 JP 2005-294179 A JP 2003-317726 A JP 2002-184413 A

  However, even if the pH of the paste serving as the precursor of the electrolyte layer is controlled within a certain range in advance, if an alkaline substance or an acidic substance adheres to the electrode surface, these substances are mixed in the paste. The pH of the paste sometimes changed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing an electrolyte layer for a fuel cell and a fuel cell capable of suppressing a change in pH of a paste serving as a precursor of the electrolyte layer. It is to provide a manufacturing method.

According to the present invention, by washing the electrolyte layer forming surface of the electrode, the step of setting the pH of the water when the moisture is present on the electrolyte layer forming surface to 6 or more and 8 or less,
Forming an electrolyte layer by applying a paste whose pH is controlled within a predetermined range on the electrolyte layer forming surface;
The manufacturing method of the electrolyte layer for fuel cells provided with this is provided.

According to the present invention, the step of forming the electrolyte layer on the first electrode by the method for manufacturing an electrolyte layer for a fuel cell,
Positioning a second electrode on the electrolyte layer;
A method for manufacturing a fuel cell is provided.

  According to the present invention, even if an alkaline substance or an acidic substance adheres to the electrode surface, these substances can be prevented from being mixed into the paste. For this reason, it can suppress that the pH of a paste changes.

  Hereinafter, a method for manufacturing a fuel cell according to an embodiment of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  The fuel cell manufacturing method according to the present embodiment includes a step of forming the electrolyte layer 40 on the first electrode 20 and a step of positioning the second electrode 60 on the electrolyte layer 40. The step of forming the electrolyte layer 40 is a step of cleaning the electrolyte layer forming surface of the first electrode 20 to make the pH of the water 6 to 8 when water is present on the electrolyte layer forming surface; A step of forming an electrolyte layer by applying a paste to the electrolyte layer forming surface. The pH of the paste is controlled within a predetermined range. Details will be described below.

  FIG. 1 is a schematic cross-sectional view showing the configuration of a single cell of a fuel cell manufactured according to this embodiment. This fuel cell is a phosphoric acid fuel cell, and includes a first electrode 20, an electrolyte layer 40, and a second electrode 60. The first electrode 20 is one of an air electrode and a fuel electrode, and the second electrode 60 is the other of the air electrode and the fuel electrode. The first electrode 20 and the second electrode 60 are obtained by providing a catalyst layer on a porous substrate (for example, carbon paper). The electrolyte layer 40 is formed on the catalyst layer of the first electrode 20.

  FIG. 2 is a flowchart showing a method for manufacturing a single cell of the fuel cell according to the present embodiment. First, a paste for forming the electrolyte layer 40 is generated (S20). The paste includes, for example, an aqueous solution containing 70% by weight of alkylene glycol (for example, diethylene glycol) that is a solvent, silicon carbide particles that are electrolyte layer forming particles, and a fluororesin that is a binder (for example, polytetrafluoroethylene (PTFE)). It is formed by mixing. The average particle diameter of the silicon carbide particles is, for example, about 1 μm.

  Next, the pH of the catalyst layer surface that is the electrolyte layer forming surface of the first electrode 20 is adjusted to 6 or more and 8 or less. Here, the pH of the catalyst layer surface is the pH of the moisture when moisture is present on the catalyst layer surface. (S40).

  Next, the paste is applied to the surface of the catalyst layer of the first electrode 20 using, for example, a natural roll coater (S60). The thickness of the applied paste is adjusted so that the finally formed electrolyte layer 40 has a thickness of 30 μm or more and 80 μm or less. When the thickness of the electrolyte layer 40 is less than 30 μm, it is difficult to keep the reactant gas secret on the fuel electrode side and the air electrode side. Moreover, when the thickness of the electrolyte layer 40 is more than 80 μm, the electric resistance in the electrolyte layer 40 is increased, and the power generation efficiency is lowered. The porosity of the electrolyte layer 40 is preferably 40% or more and 60% or less.

  The thickness of the paste can be adjusted by the viscosity of the paste. The viscosity of the paste can be adjusted by the pH of the paste. The viscosity of the paste is preferably 0.5 Pa · s or more and 1.5 Pa · s or less, for example. In order to control the viscosity of the paste within this range, for example, the pH of the paste may be controlled to be 5.2 or more and 5.8 or less.

  FIG. 3 is a graph showing an example of the relationship between the pH of the paste and the viscosity of the paste. The composition of the paste is the same as that described above. As shown in this graph, when the pH of the paste is smaller than 5.1, the viscosity rapidly increases as the pH decreases (that is, the acidity increases). In the example shown in this figure, the viscosity of the paste can be reduced to 1 Pa · s or lower by setting the pH of the paste to 4.9 or higher.

  Returning to FIG. The paste is held in the paste holding unit after the pH is adjusted in advance to a predetermined range in the paste generation step (S20) described above. In the step of forming the electrolyte layer, the paste is supplied from the paste holding unit to the surface of the catalyst layer of the first electrode 20 by a roll. At this time, the paste that has been supplied to the surface of the catalyst layer but has not formed the electrolyte layer 40 is collected in the paste holding unit.

  For this reason, when an alkaline substance or an acidic substance adheres to the surface of the catalyst layer, as shown in the example of Table 1, for example, it is held in the paste holding portion while the formation of the electrolyte layer 40 is repeated. The pH of the paste is gradually changed, and the viscosity of the paste is gradually changed.

  Table 1 is a table showing the effect of the pH of the catalyst layer surface of the first electrode 20 on the pH and viscosity of the paste held in the paste holding part.

  In this table, the pH of the catalyst layer surface was measured at five locations using pH test paper in which pure water was immersed. The pH of the paste immediately after starting the paste application was 5.2, and the viscosity of the paste was 0.52 (Pa · s). When the average pH of the catalyst layer surface was 6, even after the paste was applied, the pH of the paste in the paste holding part was 5.1 and the viscosity of the paste was 0.53 (Pa · s). However, when the average pH of the catalyst layer surface is 4.5, the pH of the paste in the paste holding part after the paste application was 4.74, and the viscosity of the paste was 2.09 (Pa · s). .

  In contrast, in the present embodiment, the pH of the catalyst layer surface is adjusted to 6 or more and 8 or less immediately before applying the paste. Therefore, even if the formation of the electrolyte layer 40 is repeated, the pH of the paste held in the paste holding part can be suppressed from changing.

  Returning to FIG. Next, the paste on the surface of the catalyst layer of the first electrode 20 is dried (S80). This drying process is performed at 45 ° C. for about 15 hours, for example. Next, the paste and the first electrode 20 are heat-treated to form the electrolyte layer 40 (S100). This heat treatment is performed at 270 ° C. for about 20 minutes, for example. Thereafter, the second electrode 60 is positioned on the electrolyte layer 40 (S120).

  FIG. 4 is a flowchart showing details of the paste generation process (S20) in FIG. First, silicon carbide particles that are electrolyte layer forming particles are mixed in a 70 wt% diethylene glycol aqueous solution that is a solvent (S21). Subsequently, the process which disperse | distributes electrolyte layer formation particle | grains in a solvent is performed. Thereby, a slurry is formed (S22). This dispersion treatment is performed, for example, by applying ultrasonic waves to a solvent in which electrolyte layer forming particles are mixed and stirring. Next, PTFE as a binder is mixed with the slurry and stirred. Thereby, a paste is formed (S23). Next, the pH of the paste is controlled within a predetermined range (S24). The pH of the paste is controlled, for example, by dropping a low concentration alkaline solution or acidic solution. As the alkaline solution, for example, an aqueous ammonia solution is used, and as the acidic solution, for example, acetic acid or nitric acid is used.

  FIG. 5 is a flowchart showing in detail the step (S40) of adjusting the pH of the surface of the catalyst layer of the first electrode 20 shown in FIG. First, the electrolyte layer forming surface of the first electrode 20 is washed with pure water (S41).

  Next, the pH of moisture located on the electrolyte layer forming surface is measured (S42). This measurement may be measured, for example, by quickly bringing a pH test paper immersed in pure water into contact with the electrolyte layer forming surface, or immediately after contacting the pH electrode after supplying moisture to the electrolyte layer forming surface. May be measured. In the latter case, after washing with pure water, the pH may be measured using moisture remaining in the electrolyte layer, or moisture may be newly supplied to the electrolyte layer forming surface.

  A process is complete | finished when the pH of the water | moisture content located in an electrolyte layer formation surface is 6-8 (S43: Yes). When the pH of water located on the electrolyte layer forming surface is less than 6 (S43: No), the electrolyte layer forming surface is washed with an alkaline solution, for example, an aqueous ammonia solution or an aqueous sodium hydroxide solution (S44). When the pH of the water located on the electrolyte layer forming surface is more than 8 (S43: No), the electrolyte layer forming surface is washed with an acidic solution, for example, phosphoric acid-containing water or carbonated water (S44). Thereafter, the process returns to S42.

  Next, the effect of this embodiment is demonstrated. In this embodiment, before applying the paste for forming the electrolyte layer to the surface of the catalyst layer (electrolyte layer forming surface), the catalyst layer surface is washed, and the pH of the moisture when moisture exists on the catalyst layer surface Is 6 or more and 8 or less. For this reason, even if an alkaline substance or an acidic substance adheres to the surface of the catalyst layer, these substances are removed before applying the paste. Therefore, it can suppress that these substances mix in a paste and the pH of a paste changes. For this reason, even if the fuel cells are continuously formed, it is possible to suppress variations in the quality of the electrolyte layer, and it is possible to suppress variations in the power generation efficiency of the fuel cells.

  In particular, as in this embodiment, when a paste that has been supplied to the surface of the catalyst layer but has not formed the electrolyte layer 40 is collected in the paste holding unit, an alkaline substance or an acidic substance adheres to the surface of the catalyst layer. As the electrolyte layer 40 is repeatedly formed, the pH of the paste held in the paste holding portion gradually changes. On the other hand, in this embodiment, since the alkaline substance and the acidic substance adhering to the electrode surface before applying the paste can be removed before applying the paste, this change in pH can be suppressed.

  In addition, since the electrolyte layer forming surface is first cleaned with pure water, the pH of water on the electrolyte layer forming surface is easily set to 6 or more and 8 or less compared to the case where the electrolyte layer forming surface is first cleaned with an alkaline or acidic liquid. Become. When the pH of the water is higher than 8 after washing with pure water, the electrolyte layer forming surface is rewashed with an acidic solution, and when the pH of the water is less than 6, the electrolyte layer forming surface is rewashed with an alkaline solution. Therefore, even if a large amount of an alkaline substance or an acidic substance adheres to the electrolyte layer forming surface, the pH of water on the electrolyte layer forming surface can be made 6 or more and 8 or less.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

It is a section schematic diagram showing the composition of the single cell of the fuel cell manufactured by this embodiment. It is a flowchart which shows the manufacturing method of the single cell of the fuel cell concerning this embodiment. It is a graph which shows an example of the relationship between pH of a paste, and the viscosity of a paste. It is a flowchart which shows the detail of the paste production | generation process in FIG. It is a flowchart which shows in detail the process of adjusting pH of the electrolyte layer formation surface shown in FIG. 2 to 6-8.

Explanation of symbols

20 First electrode 40 Electrolyte layer 60 Second electrode

Claims (10)

Cleaning the electrolyte layer forming surface of the electrode to bring the pH of the water to 6 or more and 8 or less when water is present on the electrolyte layer forming surface;
Forming an electrolyte layer by applying a paste whose pH is controlled within a predetermined range on the electrolyte layer forming surface;
The manufacturing method of the electrolyte layer for fuel cells provided with. In the manufacturing method of the electrolyte layer for fuel cells of Claim 1,
The paste is held in the paste holding unit after the pH is adjusted to a predetermined range,
In the step of forming the electrolyte layer, the paste is supplied from the paste holding part to the electrolyte layer forming surface, and the paste that has been supplied to the electrolyte layer forming surface but does not form the electrolyte layer is the paste. A method for producing an electrolyte layer for a fuel cell recovered in a holding part. In the manufacturing method of the electrolyte layer for fuel cells of Claim 1 or 2,
The pH of the moisture when moisture is present on the electrolyte layer forming surface is a value measured by bringing a pH test paper immersed in pure water into contact with the electrolyte layer forming surface. Production method. In the manufacturing method of the electrolyte layer for fuel cells of Claim 1 or 2,
The method for producing an electrolyte layer for a fuel cell, wherein the pH of the moisture when moisture is present on the electrolyte layer forming surface is a value measured by bringing a pH electrode into contact with the electrolyte layer forming surface where the moisture is located. In the manufacturing method of the electrolyte layer for fuel cells as described in any one of Claims 1-4,
The step of adjusting the pH of the moisture on the electrolyte layer forming surface to 6 or more and 8 or less includes the step of washing the electrolyte layer forming surface with pure water. In the manufacturing method of the electrolyte layer for fuel cells according to claim 5,
The step of setting the pH of the water on the electrolyte layer forming surface to 6 or more and 8 or less is the step of washing the electrolyte layer forming surface with pure water.
Measuring the pH at the electrolyte layer forming surface;
Washing the electrolyte layer forming surface with an acidic solution when the pH is greater than 8, and washing the electrolyte layer forming surface with an alkaline solution when the pH is less than 6; and
The manufacturing method of the electrolyte layer for fuel cells provided with.   The method for producing an electrolyte layer for a fuel cell according to claim 6, wherein the acidic solution is phosphoric acid-containing water or carbonated water, and the alkaline solution is an aqueous ammonia solution. In the manufacturing method of the electrolyte layer for fuel cells as described in any one of Claims 1-7,
The said paste is a manufacturing method of the electrolyte layer for fuel cells which contains alkylene glycol as a solvent and contains a fluororesin as a binder. In the manufacturing method of the electrolyte layer for fuel cells of Claim 8,
The method for producing an electrolyte layer for a fuel cell, wherein the alkylene glycol is diethylene glycol and the fluororesin is polytetrafluoroethylene. A step of forming the electrolyte layer on the first electrode by the method for producing an electrolyte layer for a fuel cell according to any one of claims 1 to 9,
Positioning a second electrode on the electrolyte layer;
A method for manufacturing a fuel cell comprising:

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