JP4407308B2 - Method for producing catalyst electrode for direct methanol fuel cell, method for producing membrane electrode assembly for direct methanol fuel cell, and method for producing direct methanol fuel cell - Google Patents

Description

The present invention relates to a method of manufacturing a catalytic electrode for DMFC suitably used for the direct methanol solid polymer electrolyte fuel cell or the like, the membrane electrode assembly (MEA: Membrane-Electrode Assembly) The method of manufacturing And a method of manufacturing the fuel cell .

  A fuel cell is a device that makes it possible to convert combustion heat generated when fuel is oxidized into electrical energy with high efficiency, and it is clean without producing environmental pollutants such as nitrogen oxides. Therefore, it has been attracting attention as a next-generation electric energy generator and is being actively developed in various fields.

  One of them, a solid polymer electrolyte fuel cell (hereinafter abbreviated as PEFC), is mainly composed of a fuel electrode, an oxygen electrode, and a hydrogen ion (proton) conductive membrane sandwiched between both electrodes. An electromotive force is generated between the fuel electrode and the oxygen electrode due to the reaction between the fuel and oxygen supplied to the electrode.

For example, when the fuel is hydrogen, the hydrogen supplied to the fuel electrode is expressed by the following (formula 1):
2H ₂ → 4H ⁺ + 4e ⁻ (Formula 1)
Oxidized by this reaction, electrons are given to the fuel electrode. The generated hydrogen ions H ⁺ (protons) move to the oxygen electrode through the hydrogen ion conductive membrane.

The hydrogen ions that have moved to the oxygen electrode are the oxygen supplied to the oxygen electrode and the following (formula 2)
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (Formula 2)
To produce water. At this time, oxygen takes in electrons from the oxygen electrode and is reduced.

In this way, hydrogen is oxidized at the fuel electrode and oxygen is reduced at the oxygen electrode.
2H ₂ + O ₂ → 2H ₂ O (Formula 3)
The hydrogen combustion reaction proceeds. At this time, an electric current flows from the oxygen electrode to the fuel electrode, and electric energy can be extracted from the fuel cell.

  The solid polymer electrolyte fuel cell uses a solid polymer hydrogen ion conductive membrane for the electrolyte, so there is no scattering of the electrolyte, it is resistant to vibration, can be reduced in size and weight, and has a high output density. Excellent characteristics not found in fuel cells.

  Conventionally, as the hydrogen ion conductive membrane, a perfluoroalkyl sulfonic acid resin membrane (such as Nafion (registered trademark) (trade name) manufactured by Du Pont) is generally used. Research and development of various hydrogen ion conductive membranes, such as a hydrocarbon-based ion exchange membrane and a fullerene derivative membrane having hydrogen ion conductivity even under non-humidified conditions, has been actively conducted.

  By the way, although the reaction of (Formula 3) is a reaction that proceeds spontaneously, the activation energy is large. For this reason, in order to achieve a sufficient reaction rate at a general PEFC operating temperature, the assistance of a catalyst such as platinum is required. Therefore, in many PEFCs, platinum or a platinum alloy, which is a catalyst, is supported on carbon fine particles, and this is applied to the surface of a conductive porous support such as a carbon sheet or carbon cloth as a fuel electrode and an oxygen electrode. These are joined to a hydrogen ion conductive membrane to form a membrane-electrode assembly (MEA).

  It is desirable that the catalyst layer has a high power density when the MEA is formed and can extract energy from the fuel as efficiently as possible. For this purpose, it is desirable that the catalyst layer has a porous structure continuously formed from the gas diffusible electrode so that the gas diffusibility is improved. Further, it is desirable that the electrolyte enters the catalyst layer in a three-dimensional structure so that a three-phase interface of the reaction gas / catalyst / electrolyte is sufficiently secured and the area of the reaction site is increased.

  FIG. 6 is a schematic cross-sectional view showing a manufacturing process of a catalyst electrode and MEA generally used in a conventional PEFC.

  First, as shown in FIG. 6A, a paint obtained by kneading carbon black and a water-repellent resin, for example, a fluorine-based resin (polytetrafluoroethylene PTFE or polyfluoroethylene FEP) is used as a carbon sheet or carbon cloth. The conductive porous bodies 1 and 5 having the water-repellent diffusion layers 2 and 6 are prepared by applying the conductive porous bodies 1 and 5 on the surface of the conductive porous bodies 1 and 5 and heating them to a temperature at which the resin melts.

  Next, as shown in FIG. 6B, carbon fine particles carrying a catalyst such as a platinum-based catalyst and a hydrogen ion conductive polymer material (for example, Nafion (registered trademark) manufactured by DuPont) are used. An oxygen electrode catalyst is prepared by preparing a kneaded mixture by dispersing in a solvent such as alcohol and applying the mixture onto the water-repellent conductive porous bodies 1 and 5 and then heating the mixture to 60 to 80 ° C. to evaporate the solvent. The layer 3 and the fuel electrode catalyst layer 7 are formed, and the gas diffusible catalyst electrode 54 (oxygen electrode) and the gas diffusible catalyst electrode 58 (fuel electrode) are respectively produced.

  Next, as shown in FIG. 6C, a hydrogen ion conductive membrane 9 such as Nafion (registered trademark) is sandwiched between the catalyst layer 3 of the oxygen electrode 54 and the catalyst layer 7 of the fuel electrode 58, and thermocompression bonded. Then, the MEA 60 is manufactured.

  It is generally accepted that the above process is effective in forming a catalyst layer having a gas diffusible porous structure and a reaction gas / catalyst / electrolyte three-phase interface. No fixed method has been established for the treatment of the catalyst layer after forming the catalyst layer.

  For example, in many cases, after applying a mixture containing a catalyst to a conductive porous body and evaporating the solvent at 60 to 80 ° C. in the atmosphere to form a catalyst layer, the catalyst layer is left as it is without any special treatment. It is bonded to an ion conductive membrane (Japanese Patent Laid-Open No. 2003-109606).

  Alternatively, there is an example in which the catalyst layer is formed by evaporating the solvent from the mixture containing the catalyst at 145 ° C. However, there is no description about the atmosphere (Journal of The Electrochemical Society, 147 (1), 92-98 (2000)).

  In Patent Documents 1 and 2 to be described later, after applying a mixture of carbon black powder carrying platinum, a fluorine-containing ion exchange resin, a dispersant and ethanol to an ion exchange membrane made of a perfluoroalkyl polymer, In this example, the solvent is evaporated at 120 ° C. for 1 hour to form a catalyst layer.

  In Patent Document 3 described later, a mixture of a carbon powder carrying a platinum-based catalyst, an ion exchange resin made of a perfluoroalkyl polymer, and a mixed dispersion medium (mass ratio of 1: 1) of ethanol and water. The catalyst layer is formed by evaporating the dispersion medium at 80 ° C., and an ion exchange resin film is formed thereon by the same method. Then, the membrane / catalyst layer assembly is combined with nitrogen gas not containing oxygen. An example is shown in which heat treatment is performed at 60 to 240 ° C. in an atmosphere for 5 seconds or longer, for example, at 120 ° C. for 30 minutes.

JP 2003-45437 A (pages 5 and 6) JP 2003-45440 A (page 6) Japanese Patent Laid-Open No. 2003-17086 (pages 2, 4 and 5; FIG. 1)

The present invention has been made in view of the above circumstances, and its purpose is to produce a catalyst electrode that is effective in improving output particularly when applied to a direct methanol type solid polymer electrolyte fuel cell. The object is to provide a method, a method for producing a membrane electrode assembly, and a method for producing a fuel cell .

  The present inventor has reached the following invention while examining optimization of various manufacturing processes of electrochemical devices.

That is, the present invention
After applying a liquid layer containing catalyst particles, an ion conductive resin and a solvent on the conductive porous body,
The liquid layer is dried at a temperature of less than 100 ° C. to evaporate the solvent to form a catalyst layer;
Thereafter, the catalyst layer is heat-treated at a temperature of 100 to 140 ° C. for 0.2 to 6 hours in an atmosphere having a total pressure of 1 atm or less in which oxygen having an oxygen partial pressure of 2 × 10 Pa or more and an oxygen partial pressure in the air is present. To
The present invention relates to a method for producing a catalyst electrode for a direct methanol fuel cell .

Further, by the manufacturing method of this catalyst electrodes, the liquid layer is formed on the conductive porous body, a process of forming the catalyst electrode through the drying process and the heat treatment, the between the pair of the catalyst electrode The present invention relates to a method of manufacturing a membrane electrode assembly for a direct methanol fuel cell , which includes a step of contacting and integrating an ion conductive membrane in contact with a catalyst layer.

Furthermore, the present invention relates to a method for manufacturing a direct methanol fuel cell , comprising a step of sandwiching the membrane electrode assembly obtained by the above manufacturing method between a methanol supply unit and an oxygen supply unit.

The present inventor has found that when a catalyst electrode, a membrane electrode assembly, and a fuel cell are produced by the above-described method and a fuel cell such as a solid polymer electrolyte fuel cell is configured using the catalyst electrode, the output increases. .

After forming a liquid layer containing catalyst particles, an ion conductive resin and a solvent, the liquid layer is dried at a temperature of less than 100 ° C. to evaporate the solvent to form a catalyst layer, 2 × 10 Pa or more, The catalyst layer is heat-treated at a specific temperature and time of 100 ° C. or higher and 140 ° C. or lower and 0.2 to 6 hours in a specific atmosphere having a total pressure of 1 atm or less in which oxygen having an oxygen partial pressure of atmospheric pressure or less exists. It has been found that the output is improved when the direct methanol fuel cell is used.

As an effect of the heat treatment in the presence of oxygen having a specific partial pressure, when a liquid layer to be formed on the catalyst layer is applied on the conductive porous body, the catalyst substance penetrates into the porous body, Organic compounds and carbon adhering to the catalyst surface that do not contribute to the formation of the catalyst / electrolyte three-phase interface and hinder gas diffusion are not removed by simple heat treatment. It is effectively and sufficiently oxidized and removed by heat treatment at 100 ° C. or higher and 140 ° C. or lower for 0.2 to 6 hours in an atmosphere with a partial pressure of oxygen of 1 atm or less under the partial pressure of oxygen. It can be considered to be formed effectively.

Regardless of the mechanism of action, the important point of the present invention is that the temperature and time are from 100 ° C. to 140 ° C. and from 0.2 to 6 hours in an atmosphere having a total partial pressure of 1 atm or less in the presence of oxygen at a specific partial pressure. In the heat treatment to be performed, the positive action for increasing the output and the negative action for reducing the output are competing, but according to the present invention, the oxygen pressure, total pressure, and heating during the heat treatment are competing. For the first time, it has been found that there is an optimum range for the treatment temperature (and also the heat treatment time).
In addition, before the heat treatment, the drying treatment for evaporating the solvent to form the catalyst layer is performed at less than 100 ° C., so that the ion conductive resin constituting the catalyst layer is not deteriorated. .

The method of manufacturing a catalytic electrode of the present invention, as shown in the Examples below, have rows the heat treatment at a temperature of 100 to 140 ° C., also performs the heat treatment 0.2-6 hours.

  In addition, the drying process for evaporating the solvent to form the catalyst layer is performed at a temperature lower than 100 ° C. (preferably 60 to 80 ° C.) before the heat treatment, which is the same as in atmospheric air. It is preferable to carry out in an atmosphere having an oxygen partial pressure. Removal of the solvent by evaporation is preferably performed at 60 to 80 ° C., which does not cause deterioration of the hydrogen ion conductive resin constituting the catalyst layer. Since the temperature is low, there is no particular limitation on the atmosphere in which this treatment is performed, and it is convenient to perform in the air.

  The catalyst electrode is preferably formed as a catalyst electrode for a membrane electrode assembly, and a hydrogen ion conductive membrane is preferably sandwiched between the catalyst electrodes of the membrane electrode assembly.

In the fuel cell manufacturing method of the present invention, the catalyst electrode on the methanol ( fuel ) supply unit side and the catalyst electrode on the oxygen supply unit side are preferably connected to an external load, whereby the fuel cell is manufactured. It is good to do.

  Next, preferred embodiments of the present invention will be described in more detail with reference to the drawings.

Embodiment 1
FIG. 1 is a schematic cross-sectional view showing a production process of a catalyst layer and an MEA based on Embodiment 1 of the present invention.

  First, as shown in FIG. 1 (a), a mixture obtained by kneading carbon black and a water-repellent resin such as a fluorine-based resin (polytetrafluoroethylene PTFE or polyfluoroethylene FEP) is used as a carbon sheet or carbon cloth. Conductive porous bodies 1 and 5 having water-repellent diffusion layers 2 and 6 are applied to the surface of a conductive porous porous body and heated to a temperature at which the resin melts, for example, FEP, to 380 ° C. Is made.

  Next, as shown in FIG. 1 (b), a mixture of catalyst particles, a hydrogen ion conductive resin and a solvent is prepared and applied onto the water-repellent conductive porous bodies 1 and 5, and then less than 100 ° C. The temperature is raised to, for example, 60 to 80 ° C. to evaporate the solvent, thereby forming the oxygen electrode catalyst layer 3 and the fuel electrode catalyst layer 7.

  Here, as the oxygen electrode side catalyst, for example, platinum, and as the fuel electrode side catalyst, for example, a platinum ruthenium alloy is preferably used by being supported on carbon fine particles.

  Further, as the hydrogen ion conductive resin, for example, perfluoroalkyl sulfonic acid resin is preferably used, specifically, Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass, Asahi Kasei Co., Ltd. Aciplex (registered trademark) and the like.

  As the solvent, an alcohol (for example, ethanol or 1-propanol) or a mixed solvent of alcohol and water is preferably used.

  Next, as shown in FIG. 1 (c), the oxygen electrode catalyst layer 3 and the fuel electrode catalyst layer 7 have oxygen of 2 × 10 Pa or more and oxygen partial pressure or less in the atmosphere at a temperature of 100 to 140 ° C. In the atmosphere, the heat treatment is performed for 0.2 to 6 hours to form the heat-treated oxygen electrode catalyst layer 3a and the fuel electrode catalyst layer 7a, and the gas diffusible catalyst electrodes 4 (oxygen electrode) and 8 (fuel electrode) Are produced respectively.

  Next, as shown in FIG. 1 (d), the hydrogen ion conductive film 9 is sandwiched between the oxygen electrode 4 and the fuel electrode 8 and bonded by thermocompression bonding (hot pressing) at a temperature of 100 to 150 ° C. Then, a membrane electrode assembly (MEA) 10 is produced. As the hydrogen ion conducting membrane, for example, a perfluoroalkyl sulfonic acid resin membrane is preferably used. Specifically, a Nafion (registered trademark) membrane manufactured by DuPont, a Flemion (registered trademark) membrane manufactured by Asahi Glass, Aciplex (registered trademark) membrane manufactured by the company can be mentioned.

  If the hydrogen ion conductive resin forming the catalyst layers 3a and 7a and the hydrogen ion conductive film 9 are made of the same material, when the MEA is formed, the hydrogen ion conductive film 9 is continuously connected to the catalyst layers 3a and 7a. A hydrogen ion conduction path can be formed.

  FIG. 2 is a schematic cross-sectional view showing a configuration of a direct methanol fuel cell (DMFC) 20 manufactured using the MEA 10 described above.

  In the DMFC 20 shown in FIG. 2, the MEA 10 is sandwiched between the upper cell half 13 and the cell lower half 14 and incorporated in the DMFC 20. The cell upper half 13 and the cell lower half 14 are respectively provided with a fuel supply pipe 15 and an oxygen (air) supply pipe 16. A methanol aqueous solution is supplied from the fuel supply pipe 15, and oxygen (air) ) Oxygen or air is supplied from the supply pipe 16.

  The methanol aqueous solution and oxygen (or air) are supplied to the fuel electrode 8 and the oxygen electrode 4 through the fuel supply unit 11 and the oxygen supply unit 12 having vent holes (not shown), respectively. The fuel supply unit 11 electrically connects the fuel electrode 8 and the cell upper half 13, and the oxygen supply unit 12 also functions to electrically connect the oxygen electrode 4 and the cell lower half 14. Further, an O-ring (not shown) may be disposed in the cell upper half 13 to prevent fuel leakage.

Power generation can be performed by closing the external circuit 17 connected to the cell upper half 13 and the cell lower half 14 while supplying an aqueous methanol solution and oxygen (or air). At this time, on the surface of the fuel electrode 8, the following (formula 4)
2CH ₃ OH + 2H ₂ O → 12H ⁺ + 2CO ₂ + 12e ⁻ (Formula 4)
As a result of the reaction, methanol is oxidized and electrons are given to the fuel electrode 8. The generated hydrogen ions H ⁺ move to the oxygen electrode 4 through the hydrogen ion conductive film 9.

The hydrogen ions moved to the oxygen electrode 4 are oxygen and the following (formula 5) supplied to the oxygen electrode 4.
3O ₂ + 12H ⁺ + 12e ⁻ → 6H ₂ O (Formula 5)
To produce water. At this time, oxygen takes in electrons from the oxygen electrode 4 and is reduced.

In this way, methanol is oxidized at the fuel electrode 8 and oxygen is reduced at the oxygen electrode 4.
2CH ₃ OH + 3O ₂ → 2CO ₂ + 6H ₂ O (Formula 6)
The methanol combustion reaction proceeds. At this time, an electric current flows from the oxygen electrode 4 to the fuel electrode 8, and electric energy can be taken out from the fuel cell 20.

  Moreover, if hydrogen is supplied instead of methanol, it can be used as a hydrogen-oxygen fuel cell.

  A description will be given of a result obtained by fabricating a catalyst electrode and an MEA by the method described in the first embodiment, forming a direct methanol fuel cell (DMFC) using the catalyst electrode, and examining output characteristics of the DMFC. The experiment is performed by changing the oxygen pressure, the heat treatment temperature, and the heat treatment time when performing the heat treatment, and an example in which optimum conditions are found for these will be described.

<Comparative Example 1>
First, as shown in FIG. 6A, a mixture obtained by kneading carbon black and polyfluoroethylene resin (FEP) as a water-repellent resin is applied on carbon paper, and this is a temperature at which the resin melts 380. The conductive porous bodies 1 and 5 having the water-repellent diffusion layers 2 and 6 were produced by heating to ° C. Next, as shown in FIG. 6B, platinum-supported carbon fine particles (manufactured by Tanaka Kikinzoku) and Nafion (registered trademark) solution (manufactured by Aldrich) are mixed in a mixed solvent of water and 1-propanol. After the uniformly dispersed mixture is applied onto the conductive porous body 1, the solvent is evaporated by heating in the atmosphere at 80 ° C. for 5 minutes to form the oxygen electrode catalyst layer 3, and the gas diffusing catalyst. An electrode 54 (oxygen electrode) was produced. Similarly, a fuel electrode catalyst layer 7 is formed on the conductive porous body 5 using carbon fine particles (produced by Tanaka Kikinzoku Co., Ltd.) carrying platinum ruthenium alloy instead of carbon fine particles carrying platinum, and gas diffusion is performed. The catalytic electrode 58 (fuel electrode) was produced.

  Next, as shown in FIG. 6C, a Nafion (registered trademark) 115 membrane is sandwiched between the oxygen electrode 54 and the fuel electrode 58 as a hydrogen ion conductive membrane, and thermocompression bonding (hot press) at 150 ° C. And joined to produce an integrated MEA 60.

  The MEA 60 was incorporated in a DMFC similar to the DMFC 20 shown in FIG. 2, a 3 mass% methanol solution was passed through the fuel electrode 58, and air was passed through the oxygen electrode 54, and the output of the DMFC was measured. In this case, the maximum output is 100 (reference).

<Examples 1 to 6, Comparative Examples 2 and 3>
First, as in the comparative example, as shown in FIG. 1A, conductive porous bodies 1 and 5 having water repellency were prepared, and as shown in FIG. An oxygen electrode catalyst layer 3 was formed on 1, and a fuel electrode catalyst layer 7 was formed on the conductive porous body 5.

Next, unlike Comparative Example 1, as shown in FIG. 1C, the heat treatment time was 0.1 to 8 at a temperature of 120 ° C. in the atmosphere (partial pressure of oxygen 2 × 10 ⁴ Pa). The catalyst layer was heat-treated in various ways during the time.

  Next, similarly to Comparative Example 1, as shown in FIG. 1D, a Nafion (registered trademark) 115 film as a hydrogen ion conductive film is sandwiched between the oxygen electrode 4 and the fuel electrode 8 and heated. Bonded (hot press) and bonded to produce an integrated MEA 10.

  Similarly to the comparative example, this MEA 10 was incorporated in the DMFC 20 shown in FIG. 2, a 3 mass% methanol solution was passed through the fuel electrode 8, and air was passed through the oxygen electrode 4, and the output of the DMFC 20 was measured. The maximum output in this case was determined and expressed as a relative value with the maximum output in Comparative Example 1 being 100 (reference). The results are shown in Table 1 and FIG. 3 together with the results of Comparative Example 1.

  According to FIG. 3 and Table 1, the maximum output of DMFC is the same as that of Comparative Example 1 in which the heat treatment time is 0.1 hours in Comparative Example 2 in which the heat treatment time is 0.1 hour. It can be seen that the time starts to increase rapidly from Example 1. In addition, when the heat treatment time exceeds 1 hour, the maximum output of DMFC starts to decrease, and when the heat treatment time exceeds 6 hours, the decrease is abrupt, but the heat treatment time is 8 hours. In Comparative Example 3, there is no difference from Comparative Example 1 in which no heat treatment is performed.

  From the above, it can be seen that the heat treatment time of the catalyst layer is preferably 0.2 to 6 hours. If further limited, the heat treatment time is more preferably 0.5 to 4 hours, and most preferably 1 to 2 hours.

  As mentioned above, after drying and evaporating the solvent to form a catalyst layer, heating the catalyst layer at a temperature of 100 ° C or higher in an atmosphere containing oxygen is effective for improving the output of the fuel cell. The obvious reason for this is not clear. However, in the heat treatment, a positive action for increasing the output of the fuel cell competes with a negative action for reducing the output of the fuel cell, and as a result, there is an optimum range for the heat treatment time. This is clear from FIG.

  As a positive effect, organic compounds and carbon adhering to the catalyst surface, etc., which do not contribute to the formation of the reaction gas / catalyst / electrolyte three-phase interface and hinder gas diffusion, are removed by oxidation, It is conceivable that the gas diffusion path and the three-phase interface are formed more effectively. Negative effects include a decrease in the effective three-phase interface due to excessive progress of oxidation, or a decrease in water repellency due to oxidation of the surface of the gas diffusion path, resulting in a reduction in the efficiency of removing water generated in the battery reaction. Can be considered.

<Examples 7 to 10, Comparative Examples 4 and 5>
Also in this example, the same process as in Comparative Example 1 was performed except that the catalyst layer was heat-treated, and a catalyst layer and MEA 10 were produced. The heat treatment of the catalyst layer was carried out in the atmosphere (partial pressure of oxygen 2 × 10 ⁴ Pa) in a heat treatment time of 1 hour and variously changing the heat treatment temperature between 80 to 150 ° C.

  Next, as in Comparative Example 1, the above MEA 10 was incorporated in the DMFC 20 and the output of the DMFC 20 was measured. The maximum output in this case was determined and expressed as a relative value with the maximum output in Comparative Example 1 being 100 (reference). The results are shown in Table 2 and FIG.

図４および表２によれば、ＤＭＦＣの最大出力は、加熱処理温度が８０℃の比較例４では、加熱処理を行わない比較例１と差はないが、加熱処理温度が１００℃の実施例７から急激に増加し始めることがわかる。また、加熱処理温度が１２０℃をこえると、ＤＭＦＣの最大出力は減少に転じ、加熱処理温度が１４０℃付近で減少は最も急激であり、加熱処理温度が１５０℃の比較例５では、加熱処理を行わない比較例１と変わりがない。

According to FIG. 4 and Table 2, the maximum output of the DMFC, in Comparative Example 4 heat treatment temperature of 80 ° C., although Comparative Example 1 and the difference will not not heat treatment, the heat treatment temperature is 100 ° C. Example It turns out that it starts to increase rapidly from 7. Further, when the heat treatment temperature exceeds 120 ° C., the maximum output of DMFC starts to decrease, and the decrease is the fastest when the heat treatment temperature is around 140 ° C. In Comparative Example 5 where the heat treatment temperature is 150 ° C., the heat treatment temperature No difference from Comparative Example 1 in which

  From the above, it can be seen that the temperature at which the catalyst layer is heat-treated is preferably 100 to 140 ° C. If further limited, the heat treatment time is more preferably 105 to 135 ° C, and most preferably 120 to 130 ° C.

  As described above, the clear reason has not been elucidated, but the heat treatment competes with the positive effect of increasing the output of the fuel cell and the negative effect of reducing the output of the fuel cell. As a result, it is clear from FIG. 4 and Table 2 that there is an optimum range for the heat treatment temperature.

<Examples 11-14, Comparative Example 6> and <Examples 15-18, Comparative Example 7>
Also in this example, the same process as in Comparative Example 1 was performed except that the catalyst layer was heat-treated, and a catalyst layer and MEA 10 were produced. The heat treatment of the catalyst layer was performed at a heat treatment temperature of 120 ° C. and a heat treatment time of 1 hour by changing the oxygen partial pressure in the atmosphere in which the heat treatment was performed between 2 to 2 × 10 ⁴ Pa.

  However, Examples 11 to 14 and Comparative Example 6 are cases where the total pressure was also changed with the oxygen partial pressure, and Examples 15 to 18 and Comparative Example 7 were to change the total amount of nitrogen by changing the amount of coexisting nitrogen. This is when it is kept at atmospheric pressure.

  Next, as in Comparative Example 1, the above MEA 8 was incorporated in the DMFC 20 and the output of the DMFC 20 was measured. The maximum output in this case was determined and expressed as a relative value with the maximum output in Comparative Example 1 being 100 (reference). The results are shown in Table 3, Table 4, and FIG.

  Comparing Table 3 and Table 4, it can be seen that the maximum output of DMFC depends on the oxygen partial pressure in the atmosphere in which the heat treatment is performed, but does not depend on the total pressure. Therefore, FIG. 5 shows Table 3 and Table 4 together.

According to FIG. 5 and Tables 3 and 4, the maximum output of DMFC is not different in Comparative Example 6 or 7 in which the oxygen partial pressure in the atmosphere in which the heat treatment is performed is 2 Pa, compared with Comparative Example 1 in which the heat treatment is not performed. However, it can be seen that the oxygen partial pressure starts to increase rapidly from Examples 11 and 15 where the oxygen partial pressure is 2 × 10 Pa. When the oxygen partial pressure exceeds 2 × 10 ⁴ Pa, the maximum output of DMFC starts to decrease. Therefore, introducing oxygen in the atmosphere at or above the atmospheric partial pressure of atmospheric pressure increases the burden on the apparatus and operation and does not improve the output.

From the above, it can be seen that the oxygen partial pressure in the atmosphere during the heat treatment of the catalyst layer is preferably 2 × 10 Pa or more and not more than the oxygen partial pressure in the atmospheric pressure atmosphere. If further limited, the oxygen partial pressure during the heat treatment is more preferably 1 × 10 ² Pa or more and less than or equal to the oxygen partial pressure in the atmospheric pressure atmosphere, and 2 × 10 ² Pa or more in the atmospheric pressure atmosphere. More preferably, the oxygen partial pressure is less than or equal to.

  As described above, the clear reason has not been elucidated, but the heat treatment competes with the positive effect of increasing the output of the fuel cell and the negative effect of reducing the output of the fuel cell. As a result, it is clear from FIG. 4 and Table 2 that there is an optimum range for the heat treatment temperature.

  In Examples 1 to 18, the direct methanol fuel cell (DMFC) was described as an example, but the same effect was observed in the hydrogen-oxygen fuel cell.

  Although the present invention has been described based on the embodiments and examples, it is needless to say that the present invention is not limited to these examples and can be appropriately changed without departing from the gist of the invention. .

The present invention, hydrogen ion conductor is sandwiched between the counter electrodes constitute an electrochemical reaction section, can be applied to direct methanol fuel cells, it is preferably used to improve the performance of it.

It is a schematic sectional drawing which shows the production process of a catalyst layer and MEA based on Embodiment 1 of this invention. It is a schematic sectional drawing which shows the structure of DMFC. It is a graph which shows the relationship between the maximum output of DMFC, and the heat processing time of a catalyst layer by Examples 1-6 of this invention, and Comparative Examples 1-3. It is a graph which shows the relationship between the maximum output of DMFC, and the heat processing temperature of a catalyst layer by Examples 7-10 and Comparative Examples 4 and 5 of this invention. It is a graph which shows the relationship between the maximum output of DMFC and the oxygen partial pressure in the case of the heat processing of a catalyst layer by Examples 11-16 and Comparative Examples 6 and 7 of this invention. It is a schematic sectional drawing which shows the structure of the conventional MEA.

Explanation of symbols

3 ... oxygen electrode catalyst layer, 3a ... heat-treated oxygen electrode catalyst layer, 4 ... oxygen electrode,
5 ... Fuel electrode catalyst layer, 7a ... Heat-treated fuel electrode catalyst layer, 8 ... Fuel electrode,
DESCRIPTION OF SYMBOLS 9 ... Hydrogen ion conductive film, 10 ... Membrane electrode assembly (MEA), 11 ... Fuel supply part,
12 ... Oxygen supply part, 13 ... Cell upper half part, 14 ... Cell lower half part, 15 ... Fuel supply pipe,
16 ... Oxygen (air) supply pipe, 17 ... External circuit (output circuit), 20 ... Fuel cell

Claims (6)

After applying a liquid layer containing catalyst particles, an ion conductive resin and a solvent on the conductive porous body,
The liquid layer is dried at a temperature of less than 100 ° C. to evaporate the solvent to form a catalyst layer;
Thereafter, the catalyst layer is heat-treated at a temperature of 100 to 140 ° C. for 0.2 to 6 hours in an atmosphere having a total pressure of 1 atm or less in which oxygen having an oxygen partial pressure of 2 × 10 Pa or more and an oxygen partial pressure in the air is present. To
A method for producing a catalyst electrode for a direct methanol fuel cell .   The method for producing a catalyst electrode according to claim 1, wherein the drying treatment is performed at 60 to 80 ° C.   The method for producing a catalyst electrode according to claim 1, wherein the drying treatment is performed in an atmosphere having the same oxygen partial pressure as that in atmospheric air. A step of forming the liquid layer on a conductive porous body by the manufacturing method according to any one of claims 1 to 3 and producing the catalyst electrode through the drying treatment and the heat treatment; A method of manufacturing a membrane electrode assembly for a direct methanol fuel cell , comprising the step of contacting the catalyst layer between the catalyst electrodes, sandwiching an ion conductive membrane, and joining and integrating them. A method for producing a direct methanol fuel cell , comprising a step of sandwiching a membrane electrode assembly obtained by the production method according to claim 4 between a methanol supply unit and an oxygen supply unit. The method for producing a direct methanol fuel cell according to claim 5, wherein the catalyst electrode on the methanol supply unit side and the catalyst electrode on the oxygen supply unit side are connected to an external load.

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