JP2008210581A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell in which output reduction due to fuel crossover is suppressed, excessive heat generation is also suppressed, and which can also take countermeasures against heat dissipation easily. <P>SOLUTION: The fuel cell comprises a cathode catalyst layer, an anode catalyst layer, a proton conductive membrane arranged between the cathode catalyst layer and the anode catalyst layer, and a mechanism in order to supply the fuel to the anode catalyst layer. In the fuel cell, the cathode catalyst layer contains a palladium based catalyst obtained by carrying palladium block or palladium alloy on a carrier having electronic conductivity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly, to a fuel cell in which a decrease in output due to a fuel crossover or excessive heat generation when a high concentration fuel is used is suppressed.

  In recent years, various small electronic devices such as personal computers and mobile phones have been miniaturized with the development of semiconductor technology, and attempts have been made to use fuel cells for these power sources. Fuel cells have the advantage that they can generate electricity simply by supplying fuel and oxidant, and can continuously generate electricity if only the fuel is replaced. This is a very advantageous system. In particular, direct methanol fuel cells (DMFCs) use methanol with high energy density as fuel, and can take out current directly from methanol on the electrocatalyst, eliminating the need for a reformer. It is promising as a power source for small electronic devices.

  As a fuel supply method in the DMFC, for example, a gas supply type in which a liquid fuel is vaporized is fed into the DMFC with a blower, a liquid supply type in which the liquid fuel is directly fed into the DMFC with a pump or the like, and the liquid fuel is in the DMFC. An internal vaporization type for vaporization is known.

For example, as an internal vaporization type DMFC, a membrane electrode assembly in which a proton conductive membrane is disposed between a cathode catalyst layer and an anode catalyst layer, a liquid fuel storage chamber, and these membrane electrode assemblies and a liquid fuel storage chamber And a fuel vaporization layer composed of a gas-liquid separation membrane that allows only the vaporization component of the liquid fuel to pass therethrough is known (for example, see Patent Document 1).
International Publication No. 2005/112172 Pamphlet

  However, conventional fuel cells such as the above internal vaporization type DMFC do not always have sufficient output characteristics. That is, when a high-concentration fuel with a concentration of 50 mol% or more is used, the vapor pressure of the fuel component, which is the main component, increases, so that a so-called fuel crossover occurs in which the fuel component permeates directly to the cathode side. It becomes easy. When fuel crossover occurs, the cathode side potential decreases, so that sufficient output characteristics cannot be obtained, and heat generation increases, so that sufficient heat dissipation measures are required.

  The present invention has been made in order to solve the above-described problems. Particularly, when high-concentration fuel is used, output reduction due to fuel crossover is suppressed, excessive heat generation is also suppressed, and heat dissipation measures are easy. It aims to provide a simple fuel cell.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor uses a palladium-based catalyst having at least low methanol oxidation activity as a catalyst for the cathode catalyst layer, thereby suppressing a decrease in output due to fuel crossover. The inventors have found that excessive heat generation can be suppressed and heat dissipation measures can be simplified, and the present invention has been completed.

  That is, the fuel cell of the present invention supplies a cathode catalyst layer, an anode catalyst layer, a proton conductive membrane disposed between the cathode catalyst layer and the anode catalyst layer, and fuel to the anode catalyst layer. The cathode catalyst layer includes a palladium-based catalyst in which palladium alone or a palladium alloy is supported on a carrier having electron conductivity.

  The cathode catalyst layer in the fuel cell of the present invention preferably further includes a platinum catalyst in which platinum is supported on a non-electron conductive carrier, or a platinum catalyst in which platinum is supported on a carrier having electron conductivity.

  Further, in the fuel cell of the present invention, instead of including such a platinum catalyst in the cathode catalyst layer, a platinum catalyst layer containing such a platinum catalyst on at least the side opposite to the proton conductive membrane of the cathode catalyst layer. May be provided. Moreover, it is preferable that the platinum catalyst in such a platinum catalyst layer is contained in a non-electron conductive and non-proton conductive binder.

  According to the present invention, by using at least a palladium-based catalyst as a catalyst in the cathode catalyst layer, it is possible to suppress a decrease in output due to fuel crossover, to suppress excessive heat generation, and to provide a fuel cell with easy heat dissipation measures. it can. In addition, according to the present invention, by further including a platinum catalyst in the cathode catalyst layer, or by providing a platinum catalyst layer containing a platinum catalyst separately from the cathode catalyst layer, the output characteristics are further improved, and heat dissipation measures are taken. An easy fuel cell can be obtained.

  Hereinafter, the fuel cell of the present invention will be described by taking an internal vaporization type direct methanol fuel cell as an example. FIG. 1 is a cross-sectional view showing a fuel cell 1 of the present invention. The membrane electrode assembly (MEA) 2 constitutes an electromotive portion, and includes a cathode composed of the cathode catalyst layer 3 and the cathode gas diffusion layer 4, an anode composed of the anode catalyst layer 5 and the anode gas diffusion layer 6, and these cathode and anode. And a proton conductive membrane 7 disposed between the two.

  The cathode gas diffusion layer 4 is laminated on the cathode catalyst layer 3, and the anode gas diffusion layer 6 is laminated on the anode catalyst layer 5. The cathode gas diffusion layer 4 serves to uniformly supply the oxidant to the cathode catalyst layer 3 and also serves as a current collector for the cathode catalyst layer 3. The anode gas diffusion layer 6 also serves to supply fuel to the anode catalyst layer 5 uniformly, and also serves as a current collector for the anode catalyst layer 5. The cathode gas diffusion layer 4 and the anode gas diffusion layer 6 are made of, for example, carbon paper.

  Further, a cathode conductive layer 8 is laminated on the cathode gas diffusion layer 4, and an anode conductive layer 9 is laminated on the anode gas diffusion layer 6. The cathode conductive layer 8 and the anode conductive layer 9 are porous layers (for example, mesh) made of a metal material such as gold.

  A cathode seal between the proton conductive membrane 7 and the cathode conductive layer 8 and around the cathode catalyst layer 3 and the cathode gas diffusion layer 4 is, for example, an O-shaped cross section and a rectangular frame shape in plan view. A material 10 is provided. Further, between the proton conductive membrane 7 and the anode conductive layer 9 and around the anode catalyst layer 5 and the anode gas diffusion layer 6, for example, the cross section is O-shaped and the planar shape is a rectangular frame shape. An anode sealing material 11 is provided. These cathode sealing materials 10 and 11 prevent fuel leakage and oxidant leakage from the membrane electrode assembly 2 and are made of an elastic body such as rubber.

  A liquid fuel storage chamber 12 is disposed on the anode side of the membrane electrode assembly 2. The liquid fuel storage chamber 12 stores a methanol aqueous solution or pure methanol as the liquid fuel F. At the open end of the liquid fuel storage chamber 12, a gas-liquid separation membrane that allows only the vaporized component of the liquid fuel F to permeate but does not allow the liquid component to permeate is disposed as the fuel vaporized layer 13, for example. Here, the vaporized component of the liquid fuel F means a vaporized component of methanol when pure methanol is used as the liquid fuel F, and a vaporized component of methanol when an aqueous methanol solution is used as the liquid fuel. It means a mixed gas composed of water vaporized components.

  A resin frame 14 is stacked between the membrane electrode assembly 2 and the fuel vaporization layer 13. The space surrounded by the frame 14 functions as a vaporized fuel storage chamber 15 (so-called vapor pool) that temporarily stores the vaporized fuel that has diffused through the fuel vaporized layer 13. Due to the effect of suppressing the amount of permeated fuel in the fuel vaporized layer 13 and the vaporized fuel storage chamber 15, rapid inflow of vaporized fuel to the membrane electrode assembly 2 is suppressed, and the occurrence of fuel crossover is suppressed. Note that the frame 14 has a lattice shape in a planar shape, and also has a role of suppressing deformation and reducing contact resistance by pressing the membrane electrode assembly 2. Therefore, the material used for the frame 14 is made of an engineering plastic having excellent chemical resistance such as PEEK.

  On the other hand, a moisturizing plate 16 is laminated on the cathode conductive layer 8 of the membrane electrode assembly 2. The moisturizing plate 16 has a function of suppressing the transpiration of water generated in the cathode catalyst layer 3, introduces an oxidant uniformly into the cathode gas diffusion layer 4, and uniformly diffuses the oxidant into the cathode catalyst layer 3. It also has a function as an auxiliary diffusion layer to promote. On the moisturizing plate 16, a surface layer 17 in which a plurality of air introduction ports 17a for taking in air as an oxidant is formed is laminated. The surface layer 17 also serves to pressurize the membrane electrode assembly 2 and the moisture retaining plate 16 and increase their adhesion, and is made of a metal such as SUS304.

  The cathode catalyst layer 3 in the present invention includes at least a palladium-based catalyst 20 as shown in FIG. More specifically, the palladium-based catalyst 20 is obtained by supporting catalyst fine particles 22 made of palladium alone or a palladium alloy on a carrier 21 having electron conductivity. Such a palladium-based catalyst 20 is in a state of being contained in, for example, a proton-conductive polymer electrolyte 23.

  Such a palladium-based catalyst 20 has a lower oxidation activity of methanol than a conventionally used platinum catalyst. That is, in the present invention, by using at least such a palladium-based catalyst 20 having a low oxidation activity of methanol as a catalyst in the cathode catalyst layer 3, it is possible to suppress a decrease in output due to fuel crossover and to suppress excessive heat generation, Heat dissipation measures can also be made easy.

  In particular, since a fuel crossover is likely to occur for a liquid fuel F using a high concentration fuel, for example, a methanol aqueous solution or a pure methanol having a concentration of 50 mol% or more, a cathode catalyst layer for such a high concentration fuel. By using at least the palladium-based catalyst 20 as the catalyst in No. 3, it is possible to effectively suppress output reduction due to fuel crossover, effectively suppress excessive heat generation, and facilitate heat dissipation measures.

  The carrier 21 in the palladium-based catalyst 20 is not particularly limited as long as it has electron conductivity. For example, carbon black such as ketjen black, vapor grown carbon fiber, carbon nanofiber, carbon nanotube, etc. Are preferably used.

  Further, the catalyst fine particles 22 in the palladium-based catalyst 20 are made of palladium alone or a palladium alloy. In the present invention, the palladium alloy means 50 at. Percentage containing more than%. The alloy component other than palladium in the palladium alloy is not necessarily limited as long as it dissolves in the face-centered cubic structure (FCC) of palladium. For example, platinum, iridium, and the like are preferable. The content of alloy components other than palladium in the palladium alloy is 50 at. It can be appropriately changed within a range of less than%, and is preferably determined in consideration of heat generation during power generation.

  On the other hand, the proton conductive polymer electrolyte 23 is not particularly limited as long as it is generally used for constituting the cathode catalyst layer. For example, a sulfonic acid group such as Nafion (registered trademark of DuPont) is used. Perfluorocarbon polymer having an inorganic acid such as phosphoric acid doped with a hydrocarbon polymer compound, organic / inorganic hybrid polymer partially substituted with a proton conductive functional group, phosphorus in a polymer matrix Examples thereof include polymer electrolytes such as proton conductors impregnated with an acid solution or a sulfuric acid solution.

  The cathode catalyst layer 3 preferably contains a platinum catalyst 24 or 25 as shown in FIGS. Here, the platinum catalyst 24 shown in FIG. 3 is one in which catalyst fine particles 27 made of platinum are supported on a non-electron conductive carrier 26. The platinum catalyst 25 shown in FIG. A catalyst fine particle 27 made of platinum is supported on a carrier 21 having a catalyst. Here, as the carrier 21 having the electron conductivity in the platinum catalyst 25 shown in FIG. 4, a carrier having the same electron conductivity as that of the carrier 21 in the palladium catalyst 20 can be used. ing.

  The palladium-based catalyst 20 is slightly inferior in oxygen reduction characteristics as compared with conventionally used platinum catalysts. For this reason, when only the palladium-based catalyst 20 is used as the catalyst of the cathode catalyst layer 3, water generated by the oxygen reduction reaction may be reduced. As a result, the internal reforming of the liquid fuel F in the anode catalyst layer 5 may occur. The water required for the reaction may be insufficient, and the output characteristics may not always be excellent. In the present invention, by using the platinum catalyst 24 or 25 together with the palladium-based catalyst 20, the water generated in the cathode catalyst layer 3 can be increased, and as a result, the output characteristics can be excellent.

  In addition, when only the palladium-based catalyst 20 is used as the catalyst of the cathode catalyst layer 3, since the heat generation is small and the temperature does not rise, the catalytic activity may not always be sufficient. By using the catalyst 24 or 25 in combination, the heat generation can be increased and the catalytic activity can be improved. Furthermore, the palladium-based catalyst 20 is inferior in terms of exhaust gas treatment capacity as compared with conventionally used platinum catalysts. However, by using the platinum catalyst 24 or 25 together as in the present invention, the exhaust gas treatment capacity is reduced. Can also be improved.

  The non-electron conductive carrier 26 in the platinum catalyst 24 is not particularly limited as long as it does not have electron conductivity. For example, alumina, silica, zeolite, and the like are preferably used. The carrier 21 having electron conductivity in the platinum catalyst 25 is not particularly limited as long as it has electron conductivity. For example, the same carrier 21 in the palladium catalyst 20 can be used. . On the other hand, the catalyst fine particles 27 in the platinum catalysts 24 and 25 are both made of platinum, and specifically, those made of platinum alone are preferable.

  Here, the platinum catalysts 24 and 25 to be contained in the cathode catalyst layer 3 may be either, but preferably a platinum catalyst 24 in which catalyst fine particles 27 made of platinum are supported on a non-electron conductive carrier 26 is preferable. . This is because the non-electron conductive carrier 26 that carries the catalyst fine particles 27 made of platinum suppresses the movement of electrons from the catalyst fine particles 27 to the carrier 26 and easily suppresses the occurrence of side reactions. It is.

  When the platinum catalyst 24 or 25 is added to the cathode catalyst layer 3 together with the palladium-based catalyst 20, palladium alone or a palladium alloy supported on the palladium-based catalyst 20, platinum supported on the platinum catalyst 24 or 25, and It is preferable to add such that the platinum content supported on the platinum catalyst 24 or 25 is 1 wt% or more and 20 wt% or less. When the platinum catalyst 24 or 25 is added, if the platinum content is less than the lower limit, the addition effect of the platinum catalyst 24 or 25 is small, and the addition effect is small. When the upper limit is exceeded, side reactions due to the platinum catalyst 24 or 25 tend to increase.

  3 and 4, instead of containing the platinum catalyst 24 or 25 in the cathode catalyst layer 3, as shown in FIG. 5, a platinum catalyst layer 30 or 31 is provided separately from the cathode catalyst layer 3, More preferably, platinum catalyst 24 or 25 is contained therein. FIG. 6 is a schematic diagram schematically showing the platinum catalyst layer 30, and FIG. 7 is a schematic diagram schematically showing the platinum catalyst layer 31. As shown in FIG. 6, the platinum catalyst layer 30 contains a platinum catalyst 24, and as shown in FIG. 7, the platinum catalyst layer 31 contains a platinum catalyst 25. As for the platinum catalyst layers 30 and 31, it is preferable that both of the platinum catalysts 24 and 25 are contained in the non-electron conductive binder 32.

  Thus, by providing the platinum catalyst layer 30 or 31 separately from the cathode catalyst layer 3, the platinum catalysts 24 and 25 are contained in the non-electron conductive binder 32 separately from the palladium-based catalyst 20. It is possible to suppress the movement of electrons between the platinum catalysts 24 or 25 while generating water, generating heat, treating exhaust gas, and the like, and more effectively suppressing the occurrence of side reactions. Note that generation and heat generation of water in the platinum catalyst layer 30 are performed using fuel or the like by fuel crossover.

  The non-electron conductive binder 32 constituting the platinum catalyst layers 30 and 31 is not particularly limited as long as it does not have electron conductivity. For example, a perfluorocarbon-based non-electron conductive binder, specifically, Tetrafluoroethylene (PTFE) or the like is preferably used. Further, from the viewpoint of more effectively suppressing the occurrence of side reactions due to the platinum catalysts 24 and 25, it is preferable that the non-conductive binder 32 has no proton conductivity. The perfluorocarbon-based non-electron conductive binder, specifically, tetrafluoroethylene (PTFE) and the like are preferably used as the non-conductive binder 32 because they are non-electron conductive and non-proton conductive. It is done.

  In the platinum catalyst layer 30 and the platinum catalyst layer 31, it is preferable to provide the platinum catalyst layer 30 including the platinum catalyst 24. That is, as the platinum catalyst 24, which supports the catalyst fine particles 27 made of platinum is the non-electron conductive carrier 26, the movement of electrons from the catalyst fine particles 27 to the carrier 26 is suppressed, and the side reaction occurs. This is because the generation is easily suppressed.

  Although not shown, the positions of the platinum catalyst layers 30 and 31 are not necessarily limited to the cathode electron conductive layer 8 side of the cathode gas diffusion layer 4. That is, even if the platinum catalyst layer 30 or 31 is laminated on the cathode conductive layer 7 side of the cathode gas diffusion layer 4 and further the cathode catalyst layer 3 is laminated on the proton conductive membrane 7 side of the platinum catalyst layer 30 or 31. Good. Also in this case, the same effect as that obtained by laminating the cathode catalyst layer 3 on one side of the cathode gas diffusion layer 4 and laminating the platinum catalyst layer 30 or 31 on the other side can be obtained. Can do.

  The membrane electrode assembly 2 other than the cathode catalyst layer 3 is not particularly limited, and those similar to those in the conventional fuel cell can be used. That is, examples of the proton conductive material constituting the proton conductive membrane 7 include a fluorine-based resin having a sulfonic acid group (for example, perfluorosulfonic acid polymer), a hydrocarbon resin having a sulfonic acid group, and the like. It is done.

  The anode catalyst layer 5 contains a catalyst in which catalyst fine particles are supported on a carrier having electron conductivity in a proton conductive polymer electrolyte. The carrier having electron conductivity in such a catalyst is not particularly limited, but for example, carbon black such as ketjen black, vapor grown carbon fiber, carbon nanofiber or carbon nanotube is suitable. As mentioned. Further, the catalyst fine particles supported on such a carrier are made of a single element of a platinum group element such as platinum, iridium, osmium, or an alloy containing the platinum group element. Among these, catalyst fine particles made of a platinum-ruthenium alloy or a platinum-molybdenum alloy having strong resistance to methanol or carbon monoxide are particularly suitable.

  The proton conductive polymer electrolyte in the anode catalyst layer 5 is not particularly limited as long as it is generally used as a material constituting the anode catalyst layer. For example, sulfonic acid such as Nafion (registered trademark of DuPont) is used. Perfluorocarbon polymer having a group, a hydrocarbon polymer compound doped with an inorganic acid such as phosphoric acid, an organic / inorganic hybrid polymer partially substituted with a proton conductive functional group, a polymer matrix Examples thereof include a polymer electrolyte such as a proton conductor impregnated with a phosphoric acid solution or a sulfuric acid solution.

  Although the fuel cell 1 of the present invention has been described above, in terms of output characteristics, the one provided with the platinum catalyst layer 30 or 31 separately from the cathode catalyst layer 3 (FIGS. 6 and 7) is the best, and then the cathode catalyst. The layer 3 containing the platinum catalyst 24 or 25 (FIGS. 3 and 4) is excellent. This is because, by providing the platinum catalyst layers 30 and 31 separately from the cathode catalyst layer 3, the binder constituting the layers can be made non-electron conductive, and further non-proton conductive. It is because generation | occurrence | production of a side reaction can be suppressed effectively.

  Further, among those provided with the platinum catalyst layer 30 or the platinum catalyst layer 31 (FIGS. 6 and 7), the one carrying the catalyst fine particles 27 made of platinum includes the platinum catalyst 24 that is made non-electron conductive. The one provided with the platinum catalyst layer 30 (FIG. 6) is superior in output characteristics. This is because, as already described, what supports the catalyst fine particles 27 made of platinum is a non-electron conductive carrier, so that the movement of electrons from the catalyst fine particles 27 to the carrier is suppressed, and the occurrence of side reactions occurs. It is because it is easy to be suppressed. Similarly, of the cathode catalyst layer 3 containing the platinum catalyst 24 or 25 (FIGS. 3 and 4), the one containing the platinum catalyst 24 (FIG. 3) is superior in output characteristics.

  On the other hand, in terms of productivity, those not provided with such platinum catalyst layers 30 and 31 (FIGS. 2 to 4) are superior to those provided with platinum catalyst layers 30 or 31 (FIGS. 6 and 7). Yes. This is because in the case where the platinum catalyst layers 30 and 31 are provided, the number of steps for forming the platinum catalyst layer 30 or 31 is increased as compared with the case where the platinum catalyst layers 30 and 31 are not provided. Among the cathode catalyst layers 3 containing the platinum catalysts 24 and 25 (FIGS. 3 and 4), the carrier containing the platinum catalyst 25 which is the carrier 21 having electron conductivity (FIG. 4). Is excellent in productivity. This is because the carrier 21 of the palladium-based catalyst 20 and the carrier 21 of the platinum catalyst 24 contained in the cathode catalyst layer 3 both have electronic conductivity, and the wettability and the like are likely to be similar. This is because mixing in preparation of the slurry for forming the cathode catalyst layer at the time of forming the electrode becomes easy.

  The liquid fuel F used in the fuel cell 1 of the present invention is preferably an aqueous methanol solution or pure methanol, but is not necessarily limited to this, for example, an aqueous ethanol solution or pure ethanol. Ethanol fuel such as propanol, propanol fuel such as propanol aqueous solution and pure propanol, glycol fuel such as glycol aqueous solution and pure glycol, dimethyl ether, formic acid, and other fuels can also be used.

In such a fuel cell 1, power generation is performed as follows. First, the vaporized component of methanol aqueous solution or pure methanol, which is the liquid fuel F in the liquid fuel storage chamber 12, diffuses in the fuel vaporization layer 13 and is stored in the vaporized fuel storage chamber 15. The vaporized component of the liquid fuel F stored in the vaporized fuel storage chamber 15 is gradually diffused through the anode conductive layer 9 and the anode gas diffusion layer 6 and supplied to the anode catalyst layer 5. The vaporized component of the liquid fuel F supplied to the anode catalyst layer 5 causes an internal reforming reaction of methanol represented by the following reaction formula (1).
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)

  Here, when pure methanol is used as the liquid fuel F, there is no supply of water from the liquid fuel F. In this case, water generated in the cathode catalyst layer 3 or the platinum catalyst layers 30 and 31 described later, The internal reforming reaction of methanol shown in the reaction formula (1) is performed using water or the like contained in the proton conductive membrane 7, or the reaction mechanism of methanol not using the reaction formula (1) does not use water. An internal reforming reaction takes place.

Protons (H ⁺ ) generated by the internal reforming reaction diffuse through the proton conductive membrane 7 and reach the cathode catalyst layer 3. On the other hand, the air taken in from the air inlet 17 a of the surface layer 17 is sequentially diffused through the moisture retaining plate 16, the cathode conductive layer 8 and the cathode gas diffusion layer 4 and supplied to the cathode catalyst layer 3. In the cathode catalyst layer 3, water is generated by the reaction shown in the following reaction formula (2). That is, a power generation reaction occurs. Further, when the platinum catalyst layers 30 and 31 are provided, water is also generated by the platinum catalysts 24 and 25 in the platinum catalyst layers 30 and 31.
3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)

  As the power generation reaction proceeds, the water generated in the cathode catalyst layer 3 and the platinum catalyst layers 30 and 31 by the reaction shown in the reaction formula (2) reaches the moisture retention plate 16. Since the water that has reached the moisturizing plate 16 is prevented from being evaporated by the moisturizing plate 16, the amount of water stored in the cathode catalyst layer 3 increases as a result. As a result of the water retention amount of the cathode catalyst layer 3 being larger than the moisture retention amount of the anode catalyst layer 5, the movement of water from the cathode catalyst layer 3 to the anode catalyst layer 5 is promoted by the osmotic pressure phenomenon. Thereby, the internal reforming reaction of methanol shown in the reaction formula (1) is promoted, the output characteristics are improved, and the high output characteristics are maintained for a long time.

  Further, as already described, since the cathode catalyst layer 3 includes at least the palladium-based catalyst 20, a decrease in output due to fuel crossover is suppressed and excessive heat generation is also suppressed. In particular, when the liquid fuel F is a high-concentration fuel, fuel crossover is likely to occur. Therefore, when such a high-concentration fuel is used, the output reduction is remarkably suppressed and excessive heat generation is also suppressed. The

  Further, when the platinum catalyst 24 or 25 is contained in the cathode catalyst layer 3 or the platinum catalyst layer 30 or 31 is provided separately from the cathode catalyst layer 3, the insufficient water and heat generation are compensated for, and the exhaust gas is treated. The capacity can also be improved, and the output characteristics can be further improved.

  Such a fuel cell 1 of the present invention can be manufactured using a known manufacturing method except that the cathode catalyst layer 3 contains at least a palladium-based catalyst 20. Hereinafter, the manufacturing method of the fuel cell of this invention is demonstrated.

  First, the palladium-based catalyst 20 is manufactured as follows, for example. That is, the carrier 21 having electron conductivity is brought into contact with an aqueous solution or slurry containing a compound of each metal component constituting palladium or a palladium alloy, and this metal compound or its ion is adsorbed or impregnated on the carrier 21. Then, while stirring the slurry at a high speed, a suitable fixing agent, for example, sodium hydroxide, ammonia, hydrazine, formic acid, citric acid, formalin, methanol, ethanol, propanol, etc. is slowly added dropwise as a metal salt, Alternatively, it is supported on the carrier 21 as partially reduced metal fine particles. Further, the obtained product is dried and heat-treated in a reducing gas or inert gas atmosphere to produce the palladium-based catalyst 20. Further, if necessary, the platinum catalyst 24 or 25 is also produced using a substantially similar method.

  Next, the produced palladium-based catalyst 20 is mixed with a suspension of the proton conductive polymer electrolyte 23, and the viscosity is adjusted with alcohols such as methanol, ethanol, propanol, and glycerin, ethylene glycol, etc. A slurry for layer formation is obtained. When the cathode catalyst layer 3 contains the platinum catalyst 24 or 25, the platinum catalyst 24 or 25 is mixed with the cathode catalyst layer forming slurry.

  Then, the cathode catalyst layer forming slurry is applied to an electron conductive porous substrate such as carbon paper or carbon cloth to be the cathode gas diffusion layer 4 by a suction filtration method, a spray method, a roll coater method, and the like, and is dried. A cathode having the cathode catalyst layer 3 formed on the cathode gas diffusion layer 4 is manufactured. If necessary, the cathode catalyst layer 3 may be applied directly on the proton conductive film 7 or thermally transferred.

  Further, when the platinum catalyst layer 30 or 31 is provided, the platinum catalyst 24 or the non-electron conductive binder 32, for example, a perfluorocarbon-based non-electron conductive binder, specifically, a suspension of tetrafluoroethylene (PTFE) or the like is suspended. 25 is dispersed to prepare a slurry for forming a platinum catalyst layer, which is applied to the cathode gas diffusion layer 4 side of the already produced cathode and dried. When the platinum catalyst layer 30 or 31 and the cathode catalyst layer 3 are formed on one side of the cathode gas diffusion layer 4, first, an electron conductive porous material such as carbon paper or carbon cloth that becomes the cathode gas diffusion layer 4 is used. After the platinum catalyst layer forming slurry is applied to the porous substrate to form the platinum catalyst layer 30 or 31, the cathode catalyst layer forming slurry is applied onto the platinum catalyst layer 30 or 31 to form the cathode catalyst layer 3. To do.

  Then, after sandwiching the proton conductive membrane 7 between the cathode manufactured in this manner and the separately manufactured anode, the membrane electrode assembly 2 is manufactured by thermocompression bonding with a roll or a press. Further, a cathode conductive layer 8 and an anode conductive layer 9 are laminated on the membrane electrode assembly 2. Then, the fuel vaporization layer 13, the membrane electrode assembly 2, the moisture retention plate 16, the surface layer 17 and the like are overlapped and integrated on the liquid fuel storage chamber 12, so that the fuel as shown in FIG. 1 or FIG. Battery 1 can be manufactured.

  Next, the present invention will be specifically described with reference to examples.

(Example 1)
A Pd—Pt alloy (Pt 10 at.%) Was supported on Ketjen ECP (trade name, manufactured by Lion Corporation) as a carrier having electron conductivity to produce a Pd—Pt alloy catalyst (a catalyst loading amount of about 40 at%). Then, this Pd—Pt alloy catalyst is mixed with a suspension of a perfluorocarbon-based proton electron conductive binder Nafion 20% solution DE2020 (manufactured by DuPont, trade name), 1-propanol, 2-propanol, and glycerin, and the cathode A slurry for forming a catalyst layer was prepared. Further, this cathode catalyst layer forming slurry was applied to carbon paper to be a cathode gas diffusion layer and dried to form a cathode catalyst layer (FIG. 2) to be a cathode. Further, a membrane electrode assembly as shown in FIG. 1 was produced using this cathode.

  The proton conductive membrane was NRE-212 (manufactured by DuPont, trade name). Moreover, the anode catalyst layer carried a Pt—Ru alloy (Pt60 at.%) On KetjenECP (product name of Lion Corporation) as a carrier having electron conductivity in a perfluorocarbon-based proton electron conductive binder. A Pt—Ru alloy catalyst was included. Further, the anode gas diffusion layer was carbon paper.

(Example 2)
In the preparation of the cathode catalyst layer forming slurry, the same procedure as in Example 1 was conducted except that a Pt catalyst (catalyst support amount of about 10 wt%) supporting Pt on Al ₂ O ₃ as a non-electron conductive support was further added. Thus, a membrane / electrode assembly was produced. The cathode catalyst layer in this membrane electrode assembly is schematically shown in FIG. Further, the Pd—Pt alloy catalyst and the Pt catalyst in the cathode catalyst layer are the Pt catalyst in the total amount of the Pd—Pt alloy supported on the Pd—Pt alloy catalyst and the Pt supported on the Pt catalyst. The supported Pt was 10 wt%.

(Example 3)
In the preparation of the cathode catalyst layer forming slurry, except that a Pt catalyst (catalyst supported amount of about 10 wt%) supporting Pt on Ketjen ECP (product name of Lion Corporation) as an electron conductive carrier was further added. A membrane / electrode assembly was produced in the same manner as in Example 1. The cathode catalyst layer in this membrane electrode assembly is schematically shown in FIG. Further, the Pd—Pt alloy catalyst and the Pt catalyst in the cathode catalyst layer are the Pt catalyst in the total amount of the Pd—Pt alloy supported on the Pd—Pt alloy catalyst and the Pt supported on the Pt catalyst. The supported Pt was 10 wt%.

Example 4
A cathode was produced in the same manner as in Example 1. On the other hand, a Pt catalyst (catalyst supported amount of about 10 wt%) in which Pt is supported on Al ₂ O ₃ as a non-electron conductive carrier and a suspension of PTFE as a non-electron conductive binder are mixed. A slurry for forming a platinum catalyst layer was prepared. And this platinum catalyst layer formation slurry was apply | coated to the cathode gas diffusion layer side of the cathode manufactured previously, it was made to dry, and the platinum catalyst layer (FIG. 6) was formed. Thereafter, a membrane / electrode assembly as shown in FIG. 5 was produced in the same manner as in Example 1 except that the cathode on which the platinum catalyst layer was formed was used. The cathode on which the platinum catalyst layer was formed was arranged such that the cathode catalyst layer side was the proton conductive membrane side.

(Example 5)
In the preparation of the slurry for forming a platinum catalyst layer, instead of using a Pt catalyst having Pt supported on Al ₂ O ₃ as a non-electron conductive carrier, KetjenECP (manufactured by Lion Corporation, manufactured by Lion) A membrane / electrode assembly was manufactured in the same manner as in Example 4 except that a Pt catalyst (catalyst carrying amount: about 70 wt%) on which Pt was supported on a product name) was used. The platinum catalyst layer in this membrane electrode assembly is schematically shown in FIG.

(Comparative Example 1)
A membrane / electrode assembly was produced in the same manner as in Example 1 except that a Pt catalyst was used instead of the Pd catalyst. As the Pt catalyst of Comparative Example 1, TEC10E70TPM (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., trade name, catalyst loading 70 wt. %) Was used.

  Next, a fuel cell as shown in FIG. 1 or FIG. 5 is manufactured using the membrane electrode assemblies of Examples and Comparative Examples manufactured as described above, and pure methanol is used as the liquid fuel in the liquid fuel storage chamber. The current-voltage characteristics were measured by actually generating power. The results are shown in FIG.

  As shown in FIG. 8, the fuel cell of Example 1 using a Pd—Pt alloy catalyst has better output characteristics than the fuel cell of Comparative Example 1 using a Pt catalyst as the catalyst in the cathode catalyst layer. I understand. In addition, the fuel cells of Examples 2 and 3 using a Pt catalyst in combination with the Pt catalyst are more excellent in output characteristics than the fuel cell of Example 1 in which the catalyst in the cathode catalyst layer is only a Pd—Pt alloy catalyst. It can be seen that the fuel cells of Examples 4 and 5 in which a platinum catalyst layer is provided separately and a Pt catalyst is contained therein are superior in output characteristics.

  Furthermore, it can be seen that, among the fuel cells of Examples 2 and 3, the fuel cell of Example 2 in which the carrier carrying Pt is non-electron conductive has better output characteristics. Similarly, it can be seen that, among the fuel cells of Examples 4 and 5, the fuel cell of Example 4 in which the carrier carrying Pt is non-electron conductive has better output characteristics.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  For example, in the above description, the structure of the fuel cell has been described with a structure having a fuel storage chamber below the membrane electrode assembly (MEA), but the fuel supply from the fuel storage section to the MEA is provided with a flow path. It may be a connected structure. In addition, the configuration of the fuel cell body has been described by taking a passive fuel cell as an example, but for an active fuel cell, and also a semi-passive fuel cell that uses a pump or the like in part such as fuel supply The present invention can also be applied. Even if it is these structures, the effect similar to the above-mentioned description is acquired. The liquid fuel vapor supplied to the MEA may be all supplied as a liquid fuel vapor, but the present invention can be applied even when a part of the liquid fuel vapor is supplied in a liquid state.

Sectional drawing which shows an example of the fuel cell of this invention. The schematic diagram which shows typically the cathode catalyst layer containing a palladium-type catalyst. The schematic diagram which shows typically an example of the cathode catalyst layer containing a palladium-type catalyst and a platinum catalyst. The schematic diagram which shows typically the other example of the cathode catalyst layer containing a palladium-type catalyst and a platinum catalyst. Sectional drawing which shows an example of the fuel cell which has a platinum catalyst layer. The schematic diagram which shows an example of a platinum catalyst layer typically. The schematic diagram which shows the other example of a platinum catalyst layer typically. The figure which shows the current-voltage characteristic of the fuel cell which concerns on an Example and a comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 2 ... Membrane electrode assembly, 3 ... Cathode catalyst layer, 4 ... Cathode gas diffusion layer, 5 ... Anode catalyst layer, 6 ... Anode gas diffusion layer, 7 ... Proton conductive membrane, 8 ... Cathode conductive layer , 9 ... Anode conductive layer, 12 ... Liquid fuel storage chamber, 13 ... Fuel vaporization layer, 15 ... Fuel vaporization layer, 20 ... Palladium-based catalyst, 21 ... Electronic conductive support, 22 ... Palladium alone or palladium alloy Catalyst fine particles, 23 ... proton conductive polymer electrolyte, 24 ... platinum catalyst (support has electron conductivity), 25 ... platinum catalyst (support has non-electron conductivity), 26 ... non-electron conductivity Support, 27 ... catalyst fine particles made of platinum, 30 ... platinum catalyst layer (the carrier contains a non-electron conductive platinum catalyst), 31 ... platinum catalyst layer (the carrier contains an electron conductive platinum catalyst)

Claims (6)

A fuel cell comprising a cathode catalyst layer, an anode catalyst layer, a proton conductive membrane disposed between the cathode catalyst layer and the anode catalyst layer, and a mechanism for supplying fuel to the anode catalyst layer Because
The cathode catalyst layer includes a palladium-based catalyst in which palladium alone or a palladium alloy is supported on a carrier having electron conductivity.   2. The fuel cell according to claim 1, wherein the cathode catalyst layer further includes a platinum catalyst in which platinum is supported on a non-electron conductive carrier.   2. The fuel cell according to claim 1, wherein the cathode catalyst layer further includes a platinum catalyst in which platinum is supported on a carrier having electron conductivity.   2. The fuel according to claim 1, further comprising a platinum catalyst layer including a platinum catalyst in which platinum is supported on a non-electron conductive carrier on at least a side of the cathode catalyst layer opposite to the proton conductive membrane. battery.   2. The fuel according to claim 1, further comprising a platinum catalyst layer including a platinum catalyst in which platinum is supported on a carrier having electron conductivity on at least a side opposite to the proton conductive membrane of the cathode catalyst layer. battery.   6. The fuel cell according to claim 4, wherein the platinum catalyst in the platinum catalyst layer is contained in a non-electron conductive and non-proton conductive binder.

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