JP4923271B2 - Method for manufacturing a direct methanol fuel cell - Google Patents

Description

The present invention, fuel in liquid methanol direct methanol fuel cell using (direct methanol fuel cell, DMFC) process for the preparation of.

  For example, the power source of portable electronic devices has been composed of a primary battery or a secondary battery. A primary battery must be replaced when it consumes predetermined power, but a secondary battery can be reused. As secondary batteries, lead batteries, Ni / Cd batteries, Ni / hydrogen batteries, Li ion batteries, and the like have been used. Secondary batteries need to be charged after using a certain amount of power.

  In recent years, power consumption tends to increase as the functionality of portable electronic devices increases. For this purpose, high energy density and high output density of the battery are strongly demanded. It is difficult to achieve much higher energy density than Li-ion batteries. Further, a secondary battery that requires charging is not convenient.

  The fuel cell has the potential to provide a convenient power supply by compensating for the shortcomings of these conventional energy devices. A fuel cell is excellent in convenience because it does not need to be charged as in a secondary battery because an electric energy is extracted by electrochemically reacting a fuel containing hydrogen and oxygen in the air. There is also a possibility of realizing an energy density exceeding that of the secondary battery.

  The fuel cell has a configuration in which an electrolyte is sandwiched between a fuel electrode and an air electrode. A fuel cell using a polymer thin film as an electrolyte has a low operating temperature and is regarded as a promising power source for portable electronic devices. As an electrode of a fuel cell, a metal having a catalytic function, for example, an alloy of platinum and another element is supported on a carrier such as conductive carbon powder (for example, Patent Documents 2, 3, and 4).

  In the case of a polymer solid electrolyte using hydrogen as a fuel, a method of adding iron, cobalt, nickel, etc. to platinum has been studied by Watanabe et al. 1). It has been described that the addition of iron, cobalt, nickel or the like to platinum affects the electronic structure of the platinum surface, which is a catalyst, and can form an active surface. However, in the case of an alloy catalyst, if the alloy particle size is reduced to about 2 nm to 5 nm, which is the particle size of platinum in a practical platinum-supported catalyst, dealloying occurs, so the catalytic activity decreases. Arise. Note that dealloying refers to a phenomenon in which platinum dissolves and reprecipitates on the adjacent particle surfaces.

  Attempts have been made to control the particle size of platinum as a method for improving the activity of platinum catalysts other than alloying. There is a report that the activity as a catalyst improves as the particle size of platinum increases. There is also a report that the activity per unit weight decreases when the particle size of the supported particles is 3 nm or less. However, an increase in particle diameter tends to cause a decrease in the surface area involved in the reaction, which can cause a decrease in electrical characteristics.

  Among fuel cells, the direct methanol fuel cell (DMFC) generates electricity by supplying a methanol aqueous solution directly to the fuel electrode, so the configuration is simplified compared to the case of using hydrogen as the fuel. In addition, it is easy to handle fuel (for example, Patent Document 1).

In DMFC, the following reactions are considered to occur at the fuel electrode and the air electrode:
Fuel electrode: CH ₃ OH + H ₂ O → 6H ⁺ + 6e ⁻ + CO ₂ (1)
Air electrode: (3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
The currently known DMFC has a lower operating potential for the air electrode and the fuel electrode than other fuel cells, for example, hydrogen fuel cells with hydrogen gas as the operating voltage of 0.8V to 0.9V. Is 0.3V to 0.4V, and sufficient output power is not obtained. Since a decrease in cell voltage means a decrease in output, an increase in cell voltage is important for securing output. In order to improve the output of the DMFC, it is desired to improve the reactivity of the formulas (1) and (2).

  As shown in FIG. 5, the cell voltage is given as a difference between the operating voltage (Vair) of the air electrode and the operating voltage (Vfuel) of the fuel electrode. In FIG. 5, the horizontal axis indicates the current value supplied from the fuel cell, and the vertical axis indicates the electrode potential. When the current value is 0, the difference between the equilibrium potential of the air electrode and the equilibrium potential of the fuel electrode is supplied as the cell potential. The potential of the electrode when an electric current is passed through the fuel cell (during operation) is called the operating potential. As the extracted current value increases, the operating potentials of the air electrode and the fuel electrode change away from the equilibrium potential and approach each other, causing a voltage drop in the cell voltage. The difference between the equilibrium potential and the working potential is called polarization.

  Assuming that the equilibrium potential of the air electrode is 0.85 V and the equilibrium potential of the fuel electrode is 0.10 V, the cell voltage when the current is 0 is 0.85−0.10 = 0.75 (V). When the polarization of the air electrode is 0.15 V, the working potential of the air electrode is 0.75−0.15 V = 0.6 (V). When the polarization of the fuel electrode is 0.20 V, the operating potential of the fuel electrode is 0.10 + 0.20 = 0.30 (V). The cell voltage is 0.70−0.30 = 0.40 (V). In order to improve the output characteristics of the DMFC, it is desired to improve the reactivity of the equations (1) and (2), increase the equilibrium potential, and reduce the polarization. Since the reaction at the fuel electrode and the air electrode proceeds on the surface of each catalyst, it is considered that the improvement in reactivity can be realized by improving the catalyst activity.

  The reaction at the fuel electrode actually proceeds in multiple stages, and the platinum catalyst is poisoned by CO produced during the progress of the reaction. In order to improve the reactivity of the fuel electrode reaction, it is necessary to consider the avoidance of CO poisoning (carbon monoxide resistance) in addition to the original decomposition activity of methanol. For this reason, the reactivity improvement as a catalyst becomes complicated. On the other hand, in the air electrode, problems such as CO poisoning in the fuel electrode do not occur, so that the improvement in catalytic activity is directly linked to the improvement in reactivity.

JP 2002-343378 A JP 2003-142112 A JP 2000-215899 A JP-A-10-92441 Japanese Patent Application No. 2003-195092 (filed on July 10, 2003) Watanabe et al .; J. Electrochem. Soc., 146, 3750 (1999) L. J. Bregoli et al; Electrochem. Acta, 23, 489 (1978)

An object of the present invention is to provide a DMFC having improved output characteristics by improving the catalytic activity of the air electrode.
Another object of the present invention is to provide a DMFC with a high cell voltage during operation.

According to one aspect of the present invention,
A method for producing a direct methanol fuel cell in which a fuel electrode supporting a metal catalyst and an air electrode are disposed with a solid polymer electrolyte interposed therebetween, and liquid methanol is used as a fuel,
(A) measuring a work function X (eV) of a carbon material that is a carrier of the metal-supported catalyst of the air electrode;
(B) supporting a metal catalyst on the carbon material under various conditions, and measuring a work function Y (eV) of the metal-supported catalyst after supporting the metal catalyst;
(C) extracting a manufacturing condition satisfying a relationship of Y−X ≦ 0.25 (eV);
(D) adjusting the air electrode catalyst under the extracted conditions;
A direct methanol fuel cell manufacturing method is provided.

  It was found that when the difference between the work function of the catalyst carrier before supporting the catalyst on the air electrode and the work function of the metal-supported catalyst after supporting the catalyst is 0.25 eV or less, a high output density can be obtained. Furthermore, when the coordination number extracted by EXAFS analysis is selected to be 6.5 or more, a high output density can be obtained.

  The activation of the platinum catalyst is considered to be closely related to the atomic state on the surface of the platinum particles acting as a catalyst. Moreover, it is considered that the platinum surface state in the platinum-supported catalyst appears as a result of various states of platinum acting in a complicated manner. The present inventors first focused on the work function of the platinum-supported catalyst. Platinum-supported catalysts were prepared under different conditions, and the work function and electrochemical characteristics were measured.

Sample A
As shown in FIG. 1A, 200 g of nitric acid aqueous solution 12 of dinitrodiamine platinum having a platinum concentration of 1 wt% is contained in a container 11, 2 g of carbon material 13 (Ketjen Black EC), and a small amount of ethanol 14. In addition, the mixed solution is adjusted by stirring until the carbon material 13 is well dispersed.

  As shown in FIG. 1B, the ethanol solution was added as a reducing agent while stirring the mixed solution 15, and then the solution temperature was raised to 85 ° C. and held for 12 hours while stirring. The resulting solid is collected by filtration. The collected solid was thoroughly washed with distilled water and then dried in a constant temperature bath at 100 ° C. to obtain Sample A.

Sample B
The weight of carbon material (Ketjen Black EC) added to 200 g of nitric acid aqueous solution of dinitrodiamine platinum having a platinum concentration of 1 wt% was 1.33 g. Sample B was prepared in the same manner as Sample A under the other conditions.

FIG. 1C is a table collectively showing the characteristics of each sample. Samples A and B have different carbon weights of 2 g and 1.33 g, but other conditions are the same.
Sample C
As in Sample A, the ethanol solution was added as a reducing agent while stirring the nitric acid aqueous solution of dinitrodiamine platinum in which the carbon material was dispersed, and the solution was kept boiling for 8 hours while stirring. Sample C was prepared in the same manner as Sample A except for the other requirements. As shown in FIG. 1C, the heat treatment temperature is changed from 85 ° C. to boiling compared to sample A.

Sample D
In 200 g of nitric acid solution of dinitrodiamine platinum having a platinum concentration of 1 wt%, the weight of the carbon material to be added (Ketjen Black EC) is 3 g, and after adding an ethanol solution as a reducing agent, the solution is boiled. Hold for 8 hours with stirring. Sample D was prepared in the same manner as Sample A with other requirements. Compared to sample C, only the carbon weight is different.

Sample E
The amount of carbon material (Ketjen Black EC) to be added was 1.33 g with respect to 200 g of nitric acid aqueous solution of dinitrodiamine platinum having a platinum concentration of 1 wt%, and after adding an ethanol solution as a reducing agent, the solution was boiled. The mixture was kept for 8 hours while stirring. Other conditions were the same as those of Sample A, and Sample E was prepared. Compared to sample C, only the carbon weight is different.

Sample F
The carbon material used as the catalyst support was acetylene black, and an ethanol solution was added as a reducing agent. Then, the temperature was raised to 75 ° C. and held for 24 hours with stirring. Sample F was prepared in the same manner as Sample A with other requirements.

  As shown in FIG. 1C, with respect to 200 g of nitric acid aqueous solution having a platinum concentration of 1 wt%, the weight of the carbon material to be added is changed to 1.33 g, 2 g, and 3 g, and after adding an ethanol solution as a reducing agent, The stirring temperature was changed to 85 ° C, boiling, and 75 ° C. In this way, six types of platinum-supported catalysts were obtained.

  The air electrode catalyst paste was prepared by mixing 1 g of each of Samples A to F thus prepared, 2.5 g of water, 4 g of 2-propanol, and 4 g of a 20 wt% Nafion solution with a ball mill for 1 hour.

As shown in FIG. 1D, the adjusted air electrode catalyst paste was applied onto a Teflon (registered trademark) sheet 16 with a bar coater while adjusting the platinum amount per unit area to 1.0 mg / cm ² . It dried at 100 degreeC after application | coating, cut out to 3 cm x 3 cm, and was set as the air electrode catalyst membrane.

By using the same procedure, a supported catalyst of platinum ruthenium alloy (TEC61E54 made by Tanaka Kikinzoku) was used to prepare a fuel electrode catalyst paste.
As shown in FIG. 1E, while adjusting the amount of platinum ruthenium alloy to 2.0 mg / cm ² on the Teflon sheet 18, the anode catalyst paste was applied onto the Teflon sheet 18 using a bar coater, A fuel electrode catalyst film 19 was formed. After drying at 100 ° C., it was cut into 3 cm × 3 cm, and used as a fuel electrode catalyst membrane for testing.

  It arrange | positions so that the air electrode catalyst film 17 and the fuel electrode catalyst film 19 may oppose through the Nafion film | membrane 20, and it crimps | bonds by 160 degreeC and a hot press for 2 minutes, peels off the Teflon sheets 16 and 18, and on the electrolyte membrane 20 Then, the catalyst films 17 and 19 were transferred. Carbon paper 28 and 29 are superposed on both sides of the Nafion membrane to which the catalyst membrane is transferred instead of the Teflon sheet so as to coincide with the catalyst membrane, and hot pressing is performed at 160 ° C. for 2 minutes to form an electrode electrolyte assembly (MEA). did.

As shown in FIG. 1F, the produced MEA was incorporated into an evaluation cell to form a fuel cell.
In FIG. 1F, the electrolyte membrane 20, the air electrode catalyst layer 17, the fuel electrode catalyst layer 19, the air electrode current collector layer 22, and the fuel electrode current collector layer 23 are formed by the above-mentioned MEA. The box body 27 forms a fuel storage portion 26 at a position where it comes into contact with the fuel electrode catalyst layer 19. The fuel storage unit 26 accommodated 5 ml of a 10% by volume methanol aqueous solution. The fuel cell operation test was performed at room temperature.

FIG. 2A shows the output characteristics measured for each sample AF. The horizontal axis indicates the current density in the unit mA / cm ² , and the vertical axis indicates the cell voltage in the unit V. For each sample, the cell voltage decreases as the current density increases, but the characteristics differ from cell to cell. The output characteristics are arranged in the order of B, A, C, E, and F from the superior one. Maximum power density was obtained from the cell voltage at a given current density.

The work function was measured for samples A to F. As a measuring device, AC-1 manufactured by Riken Keiki was used.
As shown in the graph of FIG. 2B, a catalyst sample 33 was fixed to a stainless steel plate 31 of 20 mm × 30 mm × 1 mm using a carbon tape 32 to obtain a measurement sample. The measurement was performed under the conditions of a counting time of 10 seconds, a light amount of 20 nW, a measurement range of 4.2 eV to 6.2 eV, and a measurement interval of 0.1 eV. The measurement was carried out by scanning the energy of the irradiated ultraviolet rays and counting the emitted photoelectrons.

FIG. 2B is a graph showing an example of measurement results. The horizontal axis indicates the energy of irradiated ultraviolet rays in units of eV, and the vertical axis indicates the count of emitted photoelectrons in units (cps) ^1/2 . As shown in the figure, the square root of the count changes almost linearly. The intersection of this extension and the extension of the background portion was taken as the work function.

  In the same procedure, the work function of the carbon material used for preparing the platinum-supported catalyst sample was measured. A work function difference ΔWF was obtained by subtracting the work function X of the carbon material used as the carrier from the work function Y of the platinum-supported catalyst.

FIG. 3 is a table summarizing the obtained maximum power density and the work function difference of the air electrode catalyst for each sample. As is clear from the table of FIG. 3, the maximum power density tends to increase as the work function difference ΔWF decreases. Samples A to D have a work function difference ΔWF of 0.25 eV or less and a maximum output density of 25 mW / cm ² or more, while Samples E and F have a work function difference ΔWF of 0.3 eV or more. The maximum power density is 22 mW / cm ² or less.

A typical application in which the direct methanol fuel cell of the present invention is used is a portable electronic device such as a PDA (Personal Digital Assistance).
Currently, the average power required to operate the PDA is about 1W, but the PDA consumes most of the power from the liquid crystal backlight in addition to high performance, so the required output is smaller than this value. Is unlikely.

The space in which the battery can be placed inside the PDA is a space in which a current lithium battery is built, but the installation area of the lithium battery with respect to the PDA body is approximately 40 cm ² . Even if the PDA is not significantly reduced in size for operational reasons, it is not expected to become any larger. Therefore, the space (and installation area) of the fuel cell built in the PDA is 40 cm ^2. One guideline.

Under such conditions, when the direct methanol fuel cell of the present invention is applied to a PDA, one side of the fuel cell is in contact with the inside of the apparatus and air is taken in on the other side. It becomes equal to the electrode area of the fuel cell. Therefore, the electrode area is assumed to be 40 cm ^2, and obtaining electric power of 1 W or more with this electrode area is a condition for using the fuel cell in a portable electronic device such as a PDA.

When this condition is converted as a required power (output density) per 1 cm ² of electrode area, the required power is 1 W ÷ 40 cm ² = 0.25 mW / cm ² . As shown in the table of FIG. 3, samples A to F having a work function difference ΔWF of 0.25 eV or less satisfy the above criteria, but the sample E having a work function ΔWF larger than 0.25 eV, The above criteria are not cleared for F. Since a clear difference in performance is recognized between the samples D and E, it is considered that the maximum output density shows an excellent value when the work function difference ΔWF is 0.25 eV or less.

Among samples A to D, sample B shows particularly excellent characteristics. In order to investigate the cause, the EXAFS analysis was conducted focusing on the crystallinity. EXAFS (X-ray absorption wide-area fine structure) refers to a damped wave-like vibration structure that is observed at a wavelength shorter than the absorption edge in an X-ray absorption spectrum. The EXAFS analysis is an analysis method capable of obtaining knowledge about a local structure of an atom from a fine structure appearing in an obtained absorption spectrum by irradiating a sample with X-rays while continuously changing energy. In the sample irradiated with X-rays, inner-shell electrons are emitted as photoelectrons according to the energy, and the photoelectrons are scattered by hitting adjacent atoms. This scattering state appears as a fine structure of the absorption spectrum. By analyzing this, it is possible to obtain structural information about the periphery of the target atom. The coordination number obtained by this method represents the local arrangement state of the platinum particles at the atomic level. As the coordination number increases, the regularity of the local arrangement of the platinum particles increases. It is thought that there is.
The EXAFS analysis was carried out by the transmission method using the BL16B2 beam line of Spring-8, a large synchrotron radiation facility. The measurement was performed by changing the energy of the X-ray incident on the sample from the low energy side to the high energy side by scanning the angle of the two-crystal monochromator with X-rays monochromatized by the monochromator. The measurement range was 11 keV to 13 keV. The coordination number was extracted by analyzing the spectrum obtained by the measurement.

FIG. 4A shows the configuration of the sample used for EXAFS analysis. The air electrode catalyst film 17 was pressure-bonded on the Nafion film 20 by hot pressing and cut into a predetermined size to obtain a measurement sample.
FIG. 4B is a table showing the coordination number of platinum obtained as a result of the EXAFAS analysis together with the maximum power density. Looking at samples A to D having a high maximum power density, it can be seen that the larger the platinum coordination number, the larger the maximum power density. It can be considered that Sample B was able to provide a higher maximum power density than Sample A, although the coordination number of platinum was higher than Sample A and the work function difference was lower than Sample A. When the work function difference ΔWF is 0.25 eV or less, if the coordination number extracted from the EXAFS analysis is 6.5 or more, excellent characteristics are obtained. If the coordination number extracted from the EXAFS analysis is selected to be 7.4 or more, particularly excellent characteristics can be obtained.

  The regularity regarding the atomic arrangement in the crystal can also be discussed by calculating the crystallite size from the half width of the powder X-ray diffraction peak. Here, the result of the powder X-ray diffraction measurement reflects a longer-period arrangement than the EXAFS analysis result. As a result of performing powder X-ray diffraction measurement on samples A to F, the crystallite size of the obtained platinum was about 2.4 nm to 2.6 nm, and no significant difference was observed. It is considered that powder X-ray diffraction and EXAFS analysis give different findings. Although the platinum particle size was measured to be 3 nm or less, the fact that an excellent maximum output density was obtained is also interpreted as a result contrary to the prediction of Bregoli et al.

  The reason why excellent characteristics are obtained when the work function difference ΔWF between the platinum-supported catalyst and the carrier is 0.25 eV or less is not necessarily clear. It can be considered as follows.

  In general, when materials having different work functions are joined, electrons move in a direction that relaxes the work function deviation. In an air electrode catalyst of a fuel cell, platinum is supported on a carbon material as a carrier, but the work function of platinum is larger than that of a carbon material. When platinum is supported on a carbon material, electrons move from the carbon material to platinum. As a result, the electronic states of the platinum and carbon materials constituting the platinum-supported catalyst also change. This change due to the platinum loading on the carbon material is associated with the difference ΔWF between the work function of the carbon material serving as the support and the work function of the catalyst after the platinum loading, and in the state where ΔWF ≦ 0.25 eV is established, The platinum-supported catalyst is considered to show a highly active state.

  The correlation between the local arrangement of platinum and the catalyst activity is not necessarily clear, but in a catalyst state where ΔWF is 0.25 eV or less, the regularity of the local arrangement of platinum increases, It is considered that the state becomes more highly active.

  In addition, the adjustment method of a platinum carrying catalyst is not reduced to the above-mentioned method. Any platinum-supported catalyst that satisfies the requirement that the work function change ΔWF after platinum support with respect to the work function of the support is 0.25 eV or less may be used.

The platinum-supported catalyst of the present invention can be applied to other fuel cells using hydrogen gas as fuel.
In addition, the ratio of platinum to the total weight of the carbon material and platinum in the platinum-supported catalyst is preferably 20 wt% to 80 wt%. If the platinum ratio is less than 20 wt%, the amount of platinum in the electrode will be insufficient, and sufficient output characteristics will not be obtained. When the amount is more than 80 wt%, the aggregation of platinum particles is likely to occur, and the surface area is likely to decrease. If the surface area is reduced, sufficient output characteristics will not be obtained.

  Typical examples of the carbon material used as the carrier include carbon black typified by ketjen black, Vulcan, and acetylene black, activated carbon, and graphite material. Other carbon materials can also be used.

  In the cell shown in FIG. 1F used for the measurement of electrochemical characteristics, the electrode electrolyte assembly is disposed on one side surface of the fuel storage unit. However, the electrode electrolyte assembly may be disposed so as to surround the fuel storage unit. The good will be obvious to those skilled in the art.

  When manufacturing a direct methanol fuel cell, air electrode catalyst membranes are prepared under various manufacturing conditions, and the difference between the work function after carrying platinum on the air electrode catalyst carrier and the work function before carrying the carrier is determined. It is preferable to obtain the air electrode by obtaining a condition that the current is 0.25 eV or less. Further, the coordination number by EXAFS measurement is obtained, and the air electrode catalyst is preferably prepared under the condition that the coordination number is 6.5 or more, preferably 7.4 or more. The features of the present invention will be described below.

(Supplementary note 1) A direct methanol fuel cell in which a fuel electrode carrying a metal catalyst and an air electrode are arranged with a solid electrolyte sandwiched between them and liquid methanol is used as the fuel, and the carrier of the metal-supported catalyst in the air electrode When the work function of the carbon material is X (eV) and the work function of the metal-supported catalyst after supporting the metal catalyst is Y (eV),
Y−X ≦ 0.25 (eV)
A direct methanol fuel cell that satisfies the above relationship.

(Supplementary note 2) The direct methanol fuel cell according to supplementary note 1, wherein the metal of the metal-supported catalyst is platinum, and the carbon material as the carrier includes carbon black, graphite, or activated carbon.
(Additional remark 3) The direct methanol type fuel cell of Additional remark 1 or 2 whose value of the coordination number extracted by EXAFS analysis is 6.5 or more in the said metal supported catalyst. Polymer solid electrolyte fuel cell.

(Additional remark 4) The direct methanol fuel cell of Additional remark 1 or 2 whose value of the coordination number extracted by EXAFS analysis is 7.4 or more in the said metal supported catalyst.
(Appendix 5) The direct methanol fuel cell according to any one of appendices 1 to 4, wherein the metal loading of the metal-supported catalyst is 20 wt% to 80 wt%.

(Appendix 6) A direct methanol fuel cell manufacturing method in which a fuel electrode carrying a metal catalyst and an air electrode are arranged with a polymer solid electrolyte interposed therebetween, and liquid methanol is used as a fuel,
(A) measuring a work function X (eV) of a carbon material that is a carrier of the metal-supported catalyst of the air electrode;
(B) supporting a metal catalyst on the carbon material under various conditions and measuring a work function Y (eV) of the metal-supported catalyst after supporting the metal catalyst;
(C) extracting a manufacturing condition that satisfies a relationship of Y-X ≦ 0.25 (eV);
(D) adjusting the air electrode catalyst under the extracted conditions;
A method for producing a direct methanol fuel cell comprising:

    (Supplementary note 7) The method for producing a direct methanol fuel cell according to supplementary note 6, wherein the metal of the metal-supported catalyst is platinum, and the carbon material as the carrier includes any one of carbon black, graphite, and activated carbon.

(Supplementary Note 8) Furthermore, (e) a step of performing EXAFS analysis on the metal-supported catalyst prepared under various conditions and extracting a coordination number;
(F) a step of selecting a condition in which the value of the coordination number is 6.5 or more among the production conditions satisfying the relationship of Y−X ≦ 0.25 (eV);
The manufacturing method of the direct methanol fuel cell of Additional remark 6 or 7 containing these.

    (Additional remark 9) The manufacturing method of the direct methanol fuel cell of Additional remark 8 which selects the conditions whose value of a coordination number is 7.4 or more in the said process (f).

It is sectional drawing and the table | surface explaining the procedure which produces the various samples of an air electrode catalyst, and sectional drawing which shows the structure of the cell used for measuring an electrochemical characteristic. It is a graph which shows the measurement result of an electrochemical characteristic and a work function. It is a table | surface which shows the maximum power density and work function difference with respect to each sample collectively. It is sectional drawing which shows the structure of the sample used for EXAFS measurement. It is a table | surface which shows the number of ligands extracted from the result of the EXAFS measurement with the maximum output density. It is a graph which shows the relationship of the equilibrium potential of a fuel cell, an operating potential, and a cell voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Container 12 Nitric acid aqueous solution of dinitrodiamine platinum 13 Carbon material 14 Ethanol 15 Mixed solution 16 Teflon sheet 17 Air electrode catalyst film 18 Teflon sheet 19 Fuel electrode catalyst film 20 Nafion film 22 Air electrode current collector 23 Fuel electrode current collector 26 Fuel Storage unit 27 Box 28 Carbon paper 29 Carbon paper 31 Stainless steel plate 32 Carbon tape 33 Catalyst sample A to F sample

Claims (3)

A method for producing a direct methanol fuel cell in which a fuel electrode supporting a metal catalyst and an air electrode are disposed with a solid polymer electrolyte interposed therebetween, and liquid methanol is used as a fuel,
(A) measuring a work function X (eV) of a carbon material that is a carrier of the metal-supported catalyst of the air electrode;
(B) supporting a metal catalyst on the carbon material under various conditions, and measuring a work function Y (eV) of the metal-supported catalyst after supporting the metal catalyst;
(C) extracting a manufacturing condition that satisfies a relationship of Y-X ≦ 0.25 (eV);
(D) adjusting the air electrode catalyst under the extracted conditions;
A method for producing a direct methanol fuel cell comprising: Furthermore, (e) a step of performing EXAFS analysis on the metal-supported catalyst prepared under various conditions and extracting a coordination number;
(F) a step of selecting a condition in which the value of the coordination number is 6.5 or more among the production conditions satisfying the relationship of Y-X ≦ 0.25 (eV);
Method for producing a direct methanol fuel cell according to claim 1 comprising a. The method for producing a direct methanol fuel cell according to claim 2 , wherein in the step (f), a condition in which the value of the coordination number is 7.4 or more is selected.

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