JP2011071062A - Direct oxidation type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which is superior in fuel utilization efficiency and power generation performance such as power generation voltage and power generation efficiency. <P>SOLUTION: The fuel cell includes at least one unit cell equipped with a membrane-electrode assembly including an anode, a cathode, and an electrolyte membrane arranged between them, an anode-side separator in contact with the anode, and a cathode-side separator in contact with the cathode. The anode-side separator has fuel flow passages in order to supply fuel to the anode, and the anode includes an anode catalyst layer in contact with the electrolyte membrane, and an anode diffusion layer in contact with the anode-side separator. The anode catalyst layer contains an anode catalyst and a polyelectrolyte. The volume expansion coefficient of the polyelectrolyte on the upstream side is larger than that on the downstream of the fuel flow passages in the anode catalyst layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a direct oxidation fuel cell such as a direct methanol fuel cell, and more particularly to an improvement in the cell structure of a direct oxidation fuel cell.

  Fuel cells are classified into solid polymer fuel cells, phosphoric acid fuel cells, alkaline fuel cells, molten carbonate fuel cells, solid oxide fuel cells, etc., depending on the type of electrolyte used. Among them, the polymer electrolyte fuel cell (PEFC) is being put into practical use as an in-vehicle power source, a household cogeneration system power source and the like because of its low operating temperature and high output density.

  In recent years, the use of fuel cells as power sources in portable small electronic devices such as notebook personal computers, mobile phones, and personal digital assistants (PDAs) has been studied. Since the fuel cell can continuously generate power by replenishing fuel, it is expected that the convenience of the portable small electronic device can be further improved by using the fuel cell instead of the secondary battery that needs to be charged. As described above, PEFC is attracting attention as a power source for portable small electronic devices because of its low operating temperature.

  Among PEFCs, a direct oxidation fuel cell uses a liquid fuel at room temperature, and directly oxidizes the fuel without reforming it into hydrogen to extract electric energy. For this reason, the direct oxidation fuel cell does not need to include a reformer, and thus can be easily downsized. Among direct oxidation fuel cells, a direct methanol fuel cell (DMFC) using methanol as a fuel is most promising as a power source for portable small electronic devices from the viewpoint of energy efficiency and output. .

Reactions at the anode and cathode of DMFC are represented by the following reaction formulas (1) and (2), respectively. The oxygen introduced into the cathode is generally taken from the atmosphere.
Anode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
Cathode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)

A solid polymer fuel cell such as DMFC has a configuration as shown in FIG. FIG. 1 shows a conventional general configuration of a polymer electrolyte fuel cell.
The fuel cell 10 in FIG. 1 includes an electrolyte membrane 11 and an anode 23 and a cathode 25 arranged so as to sandwich the electrolyte membrane 11. The anode 23 includes an anode catalyst layer 12 and an anode diffusion layer 16. The anode catalyst layer 12 is in contact with the electrolyte membrane 11. The anode diffusion layer 16 includes an anode water repellent layer 14 and an anode porous substrate 15. The anode water repellent layer 14 and the anode porous substrate 15 are laminated in this order on the surface of the anode catalyst layer 12 opposite to the surface in contact with the electrolyte membrane 11. An anode separator 17 is laminated outside the anode diffusion layer 16.

  The cathode 25 includes the cathode catalyst layer 13 and the cathode diffusion layer 20. The cathode catalyst layer 13 is in contact with the surface of the electrolyte membrane 11 opposite to the surface with which the anode catalyst layer 12 is in contact. The cathode diffusion layer 20 includes a cathode water repellent layer 18 and a cathode porous substrate 19. The cathode water repellent layer 18 and the cathode porous substrate 19 are laminated in this order on the surface of the cathode catalyst layer 13 opposite to the surface in contact with the electrolyte membrane 11. On the outside of the cathode diffusion layer 20, a cathode side separator 21 is laminated.

  As described above, the laminate including the electrolyte membrane 11, the anode 23, the cathode 25, the anode side separator 17, and the cathode side separator 21 forms a basic configuration called a cell. In addition, the laminated body which consists of the anode catalyst layer 12 and the cathode catalyst layer 13 which pinches | interposes the electrolyte membrane 11 and the electrolyte membrane 11 bears the electric power generation of a fuel cell, and is called CCM (Catalyst Coated Membrane). In addition, a laminate composed of the CCM, the anode diffusion layer 16 and the cathode diffusion layer 20 is called a membrane electrode assembly (MEA). The anode diffusion layer 16 and the cathode diffusion layer 20 are responsible for uniform dispersion of the supplied fuel and oxidant and smooth discharge of water and carbon dioxide as products.

Further, in the fuel cell 10 of FIG. 1, the anode separator 17 has a fuel flow path 22 for supplying fuel to the MEA on the contact surface with the anode porous substrate 15. The fuel flow path 22 consists of a recessed part, for example. The cathode-side separator 21 has an oxidant channel (air channel) 24 for supplying an oxidant (air) to the MEA on the contact surface with the cathode porous substrate 19. The oxidant channel 24 is also composed of, for example, a recess.
Further, in the fuel cell 10, a gasket 26 is disposed between the anode separator 17 and the electrolyte membrane 11 so as to enclose the anode 23, and a cathode 25 is interposed between the cathode separator 21 and the electrolyte membrane 11. A gasket 27 is disposed so as to enclose the gas. Gaskets 26 and 27 prevent fuel and oxidant from leaking to the outside, respectively.
Note that the cell constituted by the MEA and the anode side separator 17 and the cathode side separator 21 arranged on both sides thereof is further provided with bolts, springs, etc. (not shown) with end plates 28 arranged on the outside of each separator. Is pressed and fastened.

Currently, as a technical problem to be solved in a direct oxidation fuel cell such as DMFC, a liquid fuel (methanol aqueous solution or the like) supplied from a fuel flow path passes through the anode 23 and the electrolyte membrane 11 and passes to the cathode 25. The phenomenon of reaching and oxidizing the cathode catalyst layer 13 can be mentioned. The above phenomenon is referred to as, for example, fuel crossover. In particular, DMFC is referred to as methanol crossover (MCO), which causes a decrease in fuel utilization efficiency. Such a phenomenon occurs because the liquid fuel used is often water-soluble, so that the liquid fuel easily penetrates into an electrolyte membrane having a property of easily containing water.
Furthermore, the fuel oxidation reaction at the cathode 25 competes with the oxidant (oxygen) reduction reaction that normally occurs at the cathode, thereby lowering the potential of the cathode 25. For this reason, the power generation voltage decreases, the power generation efficiency decreases, and the like.

  Therefore, in DMFC, in order to reduce MCO, electrolyte membranes in which the permeation amount of methanol is suppressed are actively developed. However, the electrolyte membrane currently in practical use conducts protons through the water present in the membrane, so the presence of water is indispensable in the electrolyte membrane. Moreover, methanol has a high affinity with water. Therefore, methanol cannot be sufficiently prevented from passing through the electrolyte membrane together with water.

  The movement of the liquid fuel in the electrolyte membrane is mainly caused by concentration diffusion. For this reason, it is known that the degree of fuel crossover largely depends on the fuel concentration difference between the anode 23 side surface and the cathode 25 side surface of the electrolyte membrane 11. The fuel concentration on the cathode 25 side surface of the electrolyte membrane 11 is considered to be negligibly low because the permeated fuel is rapidly oxidized at the cathode 25. Therefore, after all, the amount of fuel crossover largely depends on the fuel concentration on the surface of the electrolyte membrane 11 on the anode 23 side.

  In the anode 23, the diffusion speed of the liquid fuel supplied from the fuel flow path 22 is controlled by the diffusion resistance of the anode water repellent layer 14. Further, the fuel is consumed by an oxidation reaction in the anode catalyst layer 12. For this reason, it is generally considered that the fuel concentration on the anode 23 side surface of the electrolyte membrane 11 is extremely smaller than the fuel concentration in the fuel flow path 22.

However, considering the distribution of the fuel concentration in a plane parallel to the main surface of the electrolyte membrane 11, the concentration of the fuel present in the fuel flow path 22 is the largest at the inlet of the fuel flow path 22, and the fuel is It gradually decreases as it flows through the fuel flow path 22 and becomes the smallest at the outlet of the fuel flow path 22. That is, in the vicinity of the upstream side of the fuel flow path, the fuel concentration on the anode 23 side surface of the electrolyte membrane 11 becomes relatively large, and as a result, the amount of fuel crossover increases.
On the contrary, in the vicinity of the downstream of the fuel flow path, the concentration of the fuel existing inside the fuel flow path 22 is very small compared to the upstream of the fuel flow path. For this reason, it is necessary to improve the diffusibility of the fuel in the anode catalyst layer 12 and improve the fuel concentration around the anode catalyst, reduce the voltage drop due to the concentration overvoltage, and suppress the output drop.

  In response to the above technical problem, Patent Document 1 proposes changing the composition and thickness of the anode water repellent layer on the upstream side and the downstream side of the fuel flow path. Patent Document 1 describes that the configuration described above can reduce the fuel permeability on the upstream side of the fuel flow path and reduce the amount of methanol crossover.

  Although not related to DMFC, Patent Document 2 proposes changing the physical properties of the ionomer contained in the catalyst layer between the upstream side and the downstream side of the fuel gas. In Patent Document 2, an attempt is made to control the moisture retention of the electrode by decreasing the EW (equivalent weight per ion exchange group) of the ionomer on the upstream side and increasing it on the downstream side.

JP 2002-110191 A JP 2002-164057 A

  However, since the thickness of the water repellent layer is generally as thin as about 10 to 50 μm, it is difficult to control the permeability of liquid fuel such as methanol at the anode using only the water repellent layer. Specifically, as described above, since the thickness of the water repellent layer is thin, the difference in the fuel concentration generated between the flow path side surface and the catalyst layer side surface of the water repellent layer is small. The driving force for diffusing the liquid fuel is smaller as the concentration gradient is smaller. Therefore, even if the composition of the water repellent layer is changed between the upstream side and the downstream side of the fuel flow path as in Patent Document 1, the influence on the permeability of the liquid fuel is small. In particular, when the concentration of liquid fuel to be supplied is high, or when the operating temperature of the cell is high, the diffusion speed of the liquid fuel increases, so the permeability of the liquid fuel is controlled only by the water repellent layer. Is very difficult.

  Therefore, the present invention suppresses the phenomenon in which fuel supplied from the fuel flow path such as methanol crossover passes through the electrolyte membrane and is oxidized at the cathode, so that the fuel utilization efficiency, power generation voltage, power generation efficiency are reduced. An object of the present invention is to provide a fuel cell with excellent power generation performance.

  A direct oxidation fuel cell of the present invention includes a membrane-electrode assembly including an anode, a cathode, and an electrolyte membrane disposed therebetween, an anode separator in contact with the anode, and a cathode separator in contact with the cathode. It has at least one unit cell. The anode side separator has a fuel flow path for supplying fuel to the anode, and the cathode side separator has an oxidant flow path for supplying oxidant to the cathode. The anode includes an anode catalyst layer in contact with the electrolyte membrane and an anode diffusion layer in contact with the anode-side separator, and the anode catalyst layer includes an anode catalyst and a polymer electrolyte. The volume expansion coefficient of the polymer electrolyte is higher on the upstream side than the downstream side of the fuel flow path of the anode catalyst layer.

  In a preferred embodiment of the present invention, the volume expansion coefficient of the polymer electrolyte decreases stepwise from the upstream side to the downstream side of the fuel flow path. In another embodiment of the present invention, the volume expansion coefficient of the polymer electrolyte continuously decreases from the upstream side to the downstream side of the fuel flow path.

  It is preferable that a portion of the anode catalyst layer facing the upstream side of the fuel flow path is provided with a high swelling region in which the volume expansion coefficient of the polymer electrolyte is 20 to 40%. More preferably, the highly swelled region is provided in a region of the anode catalyst layer facing a portion having a length of 1/6 to 1/3 of the total length of the fuel channel upstream of the fuel channel.

  It is preferable that a portion of the anode catalyst layer facing the downstream side of the fuel flow path is provided with a low swelling region in which the volume expansion coefficient of the polymer electrolyte is 0 to 30%.

  More preferably, the highly swelled region contains a fluorine ionomer as a polymer electrolyte. The volume expansion coefficient of the fluorine ionomer is preferably 20 to 40%, and the proton conductivity is preferably 0.05 to 0.15 S / cm.

  More preferably, the low swelling region contains a hydrocarbon ionomer as a polymer electrolyte. The volume expansion coefficient of the hydrocarbon ionomer is preferably 0 to 30%, and the proton conductivity is preferably 0.01 to 0.1 S / cm.

  The fluorine ionomer preferably includes a copolymer of a perfluorosulfonic acid unit and a tetrafluoroethylene unit. The hydrocarbon ionomer preferably includes at least one selected from the group consisting of an engineering plastic having a sulfonic acid group introduced therein and an engineering plastic having a phosphonic acid group introduced therein.

  The amount of the polymer electrolyte contained in the anode catalyst layer preferably occupies 10 to 30% by weight of the anode catalyst layer.

The amount of the anode catalyst is preferably uniform throughout the anode catalyst layer. At this time, the amount of the anode catalyst is preferably 1 to 10 mg / cm ² .

  It is preferable that the thickness of the anode catalyst layer is uniform throughout the anode catalyst layer. At this time, the anode catalyst layer preferably has a thickness of 5 to 120 μm.

  According to the present invention, the type of polymer electrolyte contained in the anode catalyst layer is optimized between the portion of the anode catalyst layer facing the upstream portion of the fuel flow path and the portion facing the downstream portion. For this reason, in the part facing the upstream part of the anode catalyst layer, the fuel concentration at the interface between the anode catalyst layer and the electrolyte membrane can be reduced as compared with the prior art, and as a result, the fuel crossover can be reduced. It becomes possible. The fuel diffusibility can be improved at the portion facing the downstream portion of the anode catalyst layer. As a result, it is possible to reduce the concentration overvoltage and thus improve the power generation voltage. As described above, according to the present invention, it is possible to suppress a decrease in the fuel utilization efficiency of the direct oxidation fuel cell and a decrease in the generated voltage and the generated efficiency.

It is a longitudinal cross-sectional view which shows typically an example of a structure of the conventional polymer electrolyte fuel cell. 1 is a longitudinal sectional view schematically showing a direct oxidation fuel cell according to an embodiment of the present invention. It is a front view showing typically an anode catalyst layer contained in a direct oxidation fuel cell concerning one embodiment of the present invention. It is the schematic which shows an example of a structure of the spray type coating device used in order to form a catalyst layer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
The direct oxidation fuel cell according to the present invention includes a membrane-electrode assembly including an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, an anode separator in contact with the anode, and a cathode. It has at least 1 unit cell provided with the cathode side separator which touches. The anode side separator has a fuel flow path for supplying fuel to the anode, and the cathode side separator has an oxidant flow path for supplying oxidant to the cathode. The anode includes an anode catalyst layer in contact with the electrolyte membrane and an anode diffusion layer in contact with the anode-side separator. The present invention is characterized by the anode catalyst layer. Specifically, the anode catalyst layer includes an anode catalyst and a polymer electrolyte, and the volume expansion coefficient of the polymer electrolyte is larger on the upstream side than the downstream side of the fuel flow path of the anode catalyst layer.

  Hereinafter, the present invention will be described with reference to the drawings. FIG. 2 is a longitudinal sectional view schematically showing a fuel cell according to an embodiment of the present invention, and FIG. 3 is a front view schematically showing an example of an anode catalyst layer 32 included in the fuel cell 10 of FIG. The figure is shown. 2 and 3, the same components as those in FIG. 1 are denoted by the same reference numerals. In FIG. 3, the anode catalyst layer 32 and the electrolyte membrane 11 supporting the anode catalyst layer 32 are illustrated. In FIG. 3, the serpentine type fuel flow path 22 facing the anode catalyst layer 32 is also indicated by a dotted line.

  The fuel cell 30 of FIG. 2 includes an anode 31, a cathode 25, and an electrolyte membrane 11 disposed therebetween. The electrolyte membrane 11 has hydrogen ion conductivity. An anode side separator 17 is laminated on the surface of the anode 31 opposite to the surface in contact with the electrolyte membrane 11. A cathode-side separator 21 is laminated on the surface of the cathode 25 opposite to the surface in contact with the electrolyte membrane 11. Further, a gasket 26 is disposed between the anode separator 17 and the electrolyte membrane 11 so as to enclose the anode 31, and a cathode 25 is enclosed between the cathode separator 21 and the electrolyte membrane 11. In addition, a gasket 27 is arranged. Gaskets 26 and 27 prevent fuel and oxidant from leaking to the outside, respectively.

  The anode separator 17 is formed with a fuel flow path 22 for distributing fuel in a plane direction parallel to the main surface of the electrolyte membrane 11. The fuel flow path 22 is provided with at least one pair of fuel inlet and fuel outlet. Hereinafter, in order to simplify the description, the anode-side separator 17 has a fuel inlet 35 and a fuel outlet 36 one by one, and shows a mode in which fuel flows only in one direction from the fuel inlet 35 toward the fuel outlet 36. . In addition, this invention is not limited to the said form.

  The anode 31 includes an anode catalyst layer 32 in contact with the electrolyte membrane 11 and an anode diffusion layer 16 in contact with the anode side separator 17. The anode catalyst layer 32 includes an anode catalyst for promoting the reaction shown in the above reaction formula (1), and a polymer electrolyte for ensuring ion conductivity between the anode catalyst layer 32 and the electrolyte membrane 11.

  In the present invention, the volume expansion coefficient of the polymer electrolyte is larger on the upstream side than the downstream side of the fuel flow path of the anode catalyst layer 32. The volume expansion coefficient of the polymer electrolyte may be continuously decreased from the upstream side to the downstream side of the fuel flow path, or may be decreased stepwise. Especially, it is preferable that the volume expansion coefficient of a polymer electrolyte is changed in steps. In this case, the production process of the anode catalyst layer is simplified, and the packing density of the anode catalyst particles can be easily controlled. For example, the packing density of the anode catalyst particles is preferably changed in 2 to 10 stages, and more preferably in 2 to 5 stages.

In the present invention, the volume expansion coefficient of the polymer electrolyte to be used is changed in the surface direction of the anode based on the analysis of fuel reactivity and mass transfer distribution in the anode surface. That is, in the anode catalyst layer 32, the volume expansion coefficient of the polymer electrolyte contained in the anode catalyst layer is changed along the average fuel flow direction A.
Since the polymer electrolyte having improved proton conductivity has a large volume expansion when it comes into contact with a liquid fuel such as an aqueous methanol solution, the polymer having improved proton conductivity is added to the anode catalyst layer. When included, attention was paid to the relationship that the substantial porosity of the anode catalyst layer decreases. In the present invention, the optimum polymer electrolyte contained in the anode catalyst layer is selected according to the fuel flow direction by utilizing such a relationship.

  More specifically, the fuel concentration is relatively high on the upstream side of the fuel flow path. For this reason, in the part which opposes the upstream of the fuel flow path of an anode catalyst layer, it is calculated | required to advance an anode reaction rapidly and to consume a fuel. As a result, the fuel concentration at the interface between the anode catalyst layer and the electrolyte membrane can be reduced, thereby reducing the fuel crossover. For that purpose, a polymer electrolyte having a high proton conductivity is suitable as the polymer electrolyte contained on the upstream side of the anode catalyst layer. In addition, the polymer electrolyte having a high proton conductivity has a large volume expansion when in contact with the liquid fuel, and as a result, the porosity of the anode catalyst layer tends to be lowered. For this reason, in the portion of the anode catalyst layer containing the polymer electrolyte having high proton conductivity, the fuel diffusibility is also suppressed, and the function of lowering the fuel concentration at the interface between the anode catalyst layer and the electrolyte membrane is promoted. As the polymer electrolyte contained in the portion of the anode catalyst layer facing the upstream side of the fuel flow path, a fluorine ionomer is preferable.

  On the downstream side of the fuel flow path, the fuel concentration is relatively small. For this reason, in the part facing the downstream side of the fuel flow path of the anode catalyst layer, it is required to improve the fuel diffusibility by keeping the porosity high. As a result, the fuel concentration in the portion of the anode catalyst layer facing the downstream side of the fuel flow path can be improved, and the concentration overvoltage can be reduced. Therefore, as the polymer electrolyte contained in the portion of the anode catalyst layer that faces the downstream side of the fuel flow path, a polymer electrolyte that has a small volume expansion when in contact with the liquid fuel is obtained even if the proton conductivity is somewhat sacrificed. Is suitable. As such a polymer electrolyte, a hydrocarbon ionomer is preferable.

  The volume expansion coefficient of the fluorine ionomer is preferably 20 to 40%. A fluorine-based ionomer exhibiting excellent proton conductivity can secure a proton transport rate because the ionomer sufficiently retains moisture. In the current technology, obtaining high proton conductivity and obtaining a small volume expansion coefficient are in a trade-off relationship. Therefore, the volume expansion coefficient of the fluorine-based ionomer may be large. Furthermore, in the present invention, when the volume expansion coefficient of the fluorine ionomer is relatively large, the pore volume in the anode catalyst layer when the liquid fuel is supplied is easily reduced. For this reason, the use of a fluorinated ionomer having a relatively large volume expansion rate is advantageous for adjusting the diffusion rate of the liquid fuel upstream of the fuel flow path. However, it is necessary to appropriately select the amount of the fluorine ionomer and the porosity of the anode catalyst layer in consideration of the volume expansion coefficient of the fluorine ionomer to be used.

  The proton conductivity of the fluorine ionomer is preferably 0.05 to 0.15 S / cm. In order to advance the oxidation reaction of the liquid fuel efficiently on the upstream side of the fuel flow path, it is necessary to accelerate the proton transport rate by the ionomer. For this reason, high proton conductivity is required. If the oxidation reaction of the fuel is promoted, the fuel concentration at the catalyst layer / electrolyte membrane interface is also reduced as a result, leading to a reduction in the amount of fuel crossover.

  The ion exchange capacity per gram of the fluorine-based ionomer is preferably 0.9 to 1.3 meq / g. Fluorine ionomers are characterized by high proton conductivity even with a relatively small ion exchange capacity. However, in the current technology, in order to obtain the high proton conductivity as described above, the ion exchange capacity as described above is required.

  As represented by Nafion (trade name “Nafion (registered trademark)”, manufactured by DuPont), a fluorine-based ionomer includes a fluorinated main chain and an ion exchange group such as a sulfonic acid group in its molecular structure. Including side chains. Since the main chain portion exhibits water repellency and the side chain portion exhibits hydrophilicity, the fluorine-based ionomer forms a phase separation structure, and the hydrophilic phase cluster portion contains a large amount of water, so that relatively small ions are present. It is thought that even proton exchange capacity shows excellent proton conductivity. However, the fluorine ionomer easily expands in volume when the hydrophilic phase cluster part takes in water, and further, when it is immersed in an aqueous methanol solution, the volume expansion is further increased as compared with when it is immersed in water.

Examples of the fluorine ionomer include a copolymer (H ⁺ type) of a perfluorosulfonic acid unit and a tetrafluoroethylene unit. Examples of such a fluorine ionomer include Nafion (trade name “Nafion (registered trademark)”, manufactured by DuPont), Flemion (trade name “Flemion (registered trademark)”, manufactured by Asahi Glass Co., Ltd., Aciplex (product) Name "Aciplex (registered trademark)", manufactured by Asahi Kasei Corporation.

  The volume expansion coefficient of the hydrocarbon ionomer is preferably 0 to 30%. The smaller the volume expansion coefficient of the hydrocarbon-based ionomer contained on the downstream side of the fuel flow path of the anode catalyst layer, the better. In the current technology, even a hydrocarbon-based ionomer generally expands in volume. However, in order to maintain the diffusibility of liquid fuel downstream of the fuel flow path of the anode catalyst layer, the volume expansion is performed. The rate is preferably smaller than the volume expansion coefficient of the fluorinated ionomer.

  The proton conductivity of the hydrocarbon ionomer is preferably 0.01 to 0.1 S / cm. Similar to the case of the fluorine ionomer, the proton conductivity and the volume expansion coefficient are in a trade-off relationship also in the hydrocarbon ionomer. For this reason, the proton conductivity of hydrocarbon-based ionomers that place importance on a small volume expansion coefficient is smaller than the proton conductivity of fluorine-based ionomers.

  The ion exchange capacity per gram of hydrocarbon ionomer is preferably 1.0 to 1.5 meq / g. With the current technology, it is difficult to obtain sufficient proton conductivity for power generation reaction unless the ion exchange capacity of the hydrocarbon ionomer is increased compared to the ion exchange capacity of the fluorine ionomer. When compared with the same ion exchange capacity, the hydrocarbon ionomer generally has a smaller volume expansion coefficient than the fluorine ionomer. That is, even if the ion exchange capacity of the hydrocarbon ionomer is larger than the ion capacity of the fluorine ionomer, the volume expansion coefficient of the hydrocarbon ionomer can be made smaller than the volume expansion coefficient of the fluorine ionomer.

  In hydrocarbon ionomers represented by sulfonated polyetheretherketone (SPEEK), the sizes of the water-repellent phase and the hydrophilic phase are generally smaller than those of fluoropolymers and are easily observed. There is no hydrophilic phase cluster part of such a size. Therefore, the hydrocarbon ionomer has a smaller volume expansion than the fluorine ionomer when compared with the same ion exchange capacity, but has a proton conductivity smaller than that of the fluorine ionomer. However, in recent years, the molecular structural development of hydrocarbon ionomers has progressed and, as described in WO2008-149815, by copolymerizing three polymer blocks, the volume expansion is small and proton conduction is achieved. The development of highly functional hydrocarbon ionomers is progressing.

As the hydrocarbon ionomer, at least one selected from an engineering plastic having a sulfonic acid group introduced and an engineering plastic having a phosphonic acid group introduced can be used. Engineering plastics include, for example, polyetheretherketone, polysulfone, polyethersulfone, poly (arylene ether), polyimide, poly ((4-phenoxybenzoyl) -1,4-phenylene), polyphenylene sulfide, polyphenylquinoxalen. , Polymers such as polyphosphazene and polybenzimidazole. Furthermore, a copolymer obtained by copolymerizing a plurality of types of monomer units constituting the polymer can be used as an engineering plastic. The introduction of the sulfonic acid group or phosphonic acid group can be performed using a conventionally known technique.
Hydrocarbon ionomers include sulfoarylated polybenzimidazole, sulfoalkylated polybenzimidazole, phosphoalkylated polybenzimidazole, phosphonated poly (phenylene ether), polyvinyl sulfonic acid, polystyrene sulfonic acid, poly (α- Methylstyrene) sulfonic acid and the like can also be used.

  Proton conductivity can be measured by the AC impedance method. A solution containing a fluorine ionomer or a solution containing a hydrocarbon ionomer is cast on a glass plate to obtain a cast film of a fluorine ionomer or a cast film of a hydrocarbon ionomer. Gold wires are arranged at both ends of each cast film, and the gold wires are connected to an AC impedance measuring device. Measure proton conductivity by AC impedance method (measuring frequency: change frequency in the range of 100 kHz to 1 Hz, using the real axis intercept in the Nyquist plot as the impedance value) in a nitrogen atmosphere at normal temperature and 100% relative humidity. Can do.

  The volume expansion rate can be measured as follows. The fluorine ionomer cast film or the hydrocarbon ionomer cast film produced as described above was dried in a vacuum drier set at 100 ° C. for 12 hours. The dimensions of each cast film are measured with a vernier caliper or the like in a dry air atmosphere to determine the volume before immersion. Thereafter, each cast film is immersed in a 2M aqueous methanol solution at room temperature for 12 hours. After 12 hours, the dimensions of each cast film are measured again to determine the volume after immersion. The volume expansion coefficient is calculated using the volume before immersion of the 2M aqueous methanol solution and the volume after immersion. The volume expansion coefficient can be obtained by {[(volume after immersion) − (volume before immersion)] / (volume before immersion)} × 100.

  The ion exchange capacity can be measured by neutralization titration using 0.5M sodium hydroxide.

  The anode catalyst layer 32 preferably includes a highly swollen region in which the volume expansion coefficient of the polymer electrolyte is 20 to 40% at a portion of the anode catalyst layer 32 facing the upstream side of the fuel flow path 22. Furthermore, the anode catalyst layer 32 preferably includes a low swelling region in which the volume expansion coefficient of the polymer electrolyte is 0 to 30% in a portion of the anode catalyst layer 32 that faces the downstream side of the fuel flow path 22. This will be described with reference to FIG. FIG. 3 illustrates a case where the packing density of the anode catalyst particles is decreased stepwise.

The anode catalyst layer 32 in FIG. 3 includes a high swelling region (first region) 33 in which the volume expansion coefficient of the polymer electrolyte is 20 to 40% and a low swelling in which the volume expansion coefficient of the polymer electrolyte is 0 to 30%. A region (second region) 34. In FIG. 3, the overall flow direction of fuel from the upstream side to the downstream side of the fuel flow path 22 (an average direction in which the fuel concentration decreases) is represented by an arrow A. In the anode catalyst layer 32 shown in FIG. 3, the first region 33 is on the upstream side of the fuel flow path and faces a flow path portion that is half the total flow path length. The second region 34 is on the downstream side of the fuel flow path 22 and faces a flow path portion having a length that is half the total flow path length. That is, when the length of the side of the cathode catalyst layer 18 parallel to the arrow A from the upstream side to the downstream side of the fuel flow path 22 is L, in FIG. 3, the first region 33 is an upstream portion of the fuel flow path. And an area of the anode catalyst layer having a length of about L / 2 in the direction A (area occupying about 1/2 of the projected area of the anode catalyst layer). The second region 34 is located so as to face the downstream portion of the fuel flow path, and is a region of the anode catalyst layer having a length of about L / 2 in the direction A (about 1/2 of the projected area of the anode catalyst layer). Occupy area). It is preferable that the first region 33 is opposed to the channel portion of the fuel channel, preferably from 1/6 to 1/2 of the total channel length, from the fuel inlet 35.
In particular, the decrease in power generation performance due to fuel crossover is most remarkable when the total length of the fuel flow path is set to 1 from the end 32a of the anode catalyst layer 32 located on the upstream side of the fuel flow path. This is a portion corresponding to a length of 1/6 to 1/3 on the upstream side. Therefore, it is more preferable that the first region 33 of the anode catalyst layer 32 is opposed to a portion having a length of 1/6 to 1/3 of the entire length of the fuel flow path 22 on the upstream side of the fuel flow path 22. .
When the anode catalyst layer 32 includes the first region 33 and the second region 34 and the first region 33 occupies the above range, the second region 34 occupies the remaining part of the anode catalyst layer 32.

  Here, the projected area of the anode catalyst layer is the area of the anode catalyst layer as viewed from the normal direction with respect to the main surface of the cathode catalyst layer.

  In this case, the first region 33 can include a fluorine-based ionomer as a polymer electrolyte, and the second region 34 can include a hydrocarbon-based ionomer as a polymer electrolyte.

  1 type may be sufficient as the fluorine-type ionomer contained in the 1st area | region 33, and 2 or more types may be sufficient as it. Similarly, the hydrocarbon ionomer contained in the second region 34 may be one type or two or more types.

  The amount of ionomer contained in the first region 33 and the second region 34 is determined depending on the proton conductivity of the ionomer, the mixing dispersibility of the ionomer and catalyst particles, and the like. The amount of the fluorinated ionomer contained in the first region 33 is preferably 10 to 30% by weight of the first region 33. Similarly, the amount of the hydrocarbon-based ionomer contained in the second region 34 is preferably 10 to 30% by weight of the second region 34.

  The first region 33 may contain a small amount of a hydrocarbon ionomer in addition to the fluorine ionomer so that the volume expansion coefficient of the polymer electrolyte in the first region 33 is 20 to 40%. Similarly, the second region 34 may also contain a small amount of a fluorine ionomer in addition to the hydrocarbon ionomer so that the volume expansion coefficient of the polymer electrolyte in the second region 34 is 0 to 30%. . That is, the first region 33 and the second region 34 each contain a fluorine ionomer and a hydrocarbon ionomer, and in the first region 33, the content of the fluorine ionomer is larger than the content of the hydrocarbon ionomer, In the second region 34, the content of the hydrocarbon ionomer may be greater than the content of the fluorine ionomer.

  In this case, in the first ink for forming the first region 33 and the second ink for forming the second region 34, the fluorine-based ionomer and the hydrocarbon-based ionomer need not be mixed. For example, the first region 33 and the second region 34 may be formed by alternately applying an ink containing only a fluorine ionomer and an ink containing only a hydrocarbon ionomer. At this time, the concentration of the ionomer contained in each ink is appropriately adjusted according to the portion to be produced.

  Alternatively, in the thickness direction of the anode catalyst layer 32, each of the first region 33 and the second region 34 may be composed of two layers having different types of polymer electrolyte. In this case, in the first region 33, the content ratio of the fluorine ionomer per projected unit area is increased, and in the second region 34, the content ratio of the hydrocarbon ionomer per projected unit area is increased.

In addition, when the first region 33 and the second region 34 include a fluorine ionomer and a hydrocarbon ionomer, respectively, the physical properties of the fluorine ionomer and the hydrocarbon ionomer are determined between the first region 33 and the second region 34. , You may change. For example, an ionomer having a small weight per ion exchange group (EW) is mainly used as the fluorine ionomer contained in the first region 33, and an ionomer having a large EW is mainly used as the fluorine ionomer contained in the second region 34. Also good. Similarly, an ionomer having a small EW may be mainly used as the hydrocarbon ionomer contained in the first region 33, and an ionomer having a large EW may be mainly used as the hydrocarbon ionomer contained in the second region 34. With such a configuration, the effects of the present invention as described above can be obtained, the proton conductivity can be maximized in the first region 33, and the volume expansion of the ionomer can be reduced as much as possible in the second region 34. can do.
Note that the polymer electrolyte included in the first region 33 may include only a fluorine ionomer having a small EW, and the polymer electrolyte included in the second region 34 may include only a hydrocarbon ionomer having a large EW. . Also in this case, the effects as described above can be obtained.

  When each region includes a plurality of types of polymer electrolytes, the volume expansion coefficient of the polymer electrolyte in each region can be obtained from the volume expansion rate of each polymer electrolyte and the mass ratio of each polymer electrolyte. For example, when the predetermined region includes a fluorine ionomer having a volume expansion coefficient of SW1 and a hydrocarbon ionomer having a volume expansion coefficient of SW2, at a mass ratio of x: y, the volume expansion of the polymer electrolyte in the predetermined region The rate is represented by {SW1 × x / (x + y)} + {SW2 × y / (x + y)}. The volume expansion coefficient of each polymer electrolyte is determined as described above.

  Even when the first region 33 includes a fluorine ionomer and a hydrocarbon ionomer, the total amount of ionomers included in the first region 33 is 10 to 30% by weight of the first region 33 as described above. Is preferred. Similarly, when the second region 34 includes a fluorine ionomer and a hydrocarbon ionomer, the total amount of ionomer included in the second region 34 is preferably 10 to 30% by weight of the second region 34. .

In FIG. 3, the anode catalyst layer 32 is divided into a first region 33 in the upstream half and a second region 34 in the downstream half. The number of divisions of the anode catalyst layer is not limited to 2, and the anode catalyst layer may be divided into three or more along the average fuel flow direction (the direction of arrow A).
When the number of divisions is large, the content ratio of the fluorine ionomer and the hydrocarbon ionomer can be changed stepwise. Furthermore, the kind and ratio of the ionomer to be used may be gradually changed instead of clearly providing a boundary between the regions.

  For example, when a further third region is provided between the first region 33 and the second region 34, the volume expansion coefficient SWm of the polymer electrolyte in the third region is equal to the polymer electrolyte in the first region 33. The volume expansion coefficient SWu and the volume expansion coefficient SWd of the polymer electrolyte in the second region 34 are appropriately selected. For example, SWm may be selected such that the difference (SWu−SWm) and the difference (SWm−SWd) are substantially the same. Alternatively, the difference (SWu−SWm) may be selected to be larger than the difference (SWm−SWd), or the difference (SWm−SWd) may be selected to be larger than the difference (SWu−SWm). Also good. Moreover, when providing a some area | region between the 1st area | region 33 and the 2nd area | region 34, the volume expansion coefficient of the polymer electrolyte in each area | region is also selected suitably.

As described above, the volume expansion coefficient of the polymer electrolyte may be continuously changed from the upstream side to the downstream side of the fuel flow path. In this case, for example, the volume expansion coefficient of the polymer electrolyte is changed by continuously changing the mixing mass ratio of the fluorine ionomer and the hydrocarbon ionomer from the upstream side to the downstream side of the fuel flow path. Can be changed continuously.
Further, when the mixing ratio of the fluorine ionomer and the hydrocarbon ionomer is continuously changed, 1/6 to 1 of the total length of the fuel flow path 22 on the upstream side of the fuel flow path 22 of the anode catalyst layer 32. / 2, more preferably an average mixing mass of the fluorine-based ionomer and the hydrocarbon-based ionomer contained in a region (corresponding to the first region 33) facing the portion having a length of 1/6 to 1/3 The volume swelling ratio of the polymer electrolyte determined from the ratio is preferably 20 to 40%. Similarly, in the remaining region of the anode catalyst layer 32 (corresponding to the second region 34), the volume swelling rate of the polymer electrolyte obtained from the average mixing mass ratio of the fluorine-based ionomer and the hydrocarbon-based ionomer is 0. It is preferably ˜30%.

  Even when each region of the anode catalyst layer 32 contains a fluorine ionomer and a hydrocarbon ionomer, the amount of the polymer electrolyte contained in the anode catalyst layer 32 is preferably uniform throughout the anode catalyst layer.

  Examples of the anode catalyst included in the anode catalyst layer 32 include an alloy of platinum (Pt) and ruthenium (Ru), a mixture of Pt and ruthenium oxide, Pt, Ru, and other metal elements (for example, iridium (Ir)). Etc.) and the like. In the alloy of Pt and Ru, the atomic ratio of Pt and Ru is not limited to this, but is preferably 1: 1. The anode catalyst may be used as it is in a fine powder state. Alternatively, the anode catalyst may be supported on a powder having electronic conductivity such as carbon black.

The amount of the anode catalyst in the anode catalyst layer 32, as the amount of metal generally free of carrier, preferably in the range of 1-10 mg / cm ^2, in the range of 1 to 6 mg / cm ² Further preferred. Here, the amount of the anode catalyst refers to the amount of the anode catalyst contained in the portion per projected unit area of the anode catalyst layer, and the projected unit area of the anode catalyst layer refers to the main surface of the anode catalyst layer. On the other hand, it refers to the unit area (cm ² ) of the anode catalyst layer when viewed from the normal direction. For example, the amount of the anode catalyst can be obtained by dividing the total amount of the anode catalyst contained in the anode catalyst layer by the projected area of the anode catalyst.

  The amount of the anode catalyst contained in the anode catalyst layer is preferably uniform throughout the anode catalyst layer. As described above, the volume expansion coefficient of the polymer electrolyte contained in the portion facing the upstream side and the portion facing the downstream side of the fuel flow path of the anode catalyst layer is changed, so that the diffusion of fuel in the anode catalyst layer Sex is controlled. As a result, the fuel can be supplied uniformly over the entire anode catalyst layer. In this case, by making the amount of the anode catalyst uniform throughout the anode catalyst layer, power generation can be performed uniformly over the entire anode catalyst layer, and thus efficient power generation can be performed. As a result, the power generation characteristics and power generation efficiency can be further improved.

  The thickness of the anode catalyst layer 32 depends on the particle size of the catalyst particles to be used, the loading ratio of the catalyst particles on the carrier, the content of the polymer electrolyte, the porosity, and the like. The thickness of the anode catalyst layer 32 is preferably in the range of 5 to 120 μm, and more preferably in the range of 5 to 70 μm.

  The thickness of the anode catalyst layer 32 is preferably uniform throughout the anode catalyst layer. The components of the fuel cell and the stack are basically uniform in thickness, and the entire cell or the entire stack is fastened by applying uniform pressure in the thickness direction. For this reason, when the thickness of the anode catalyst layer changes, it is necessary to change the thickness of other parts of the MEA, for example, the diffusion layer and the electrolyte membrane, in order to absorb the change. This unnecessarily changes the balance of the MEA, which can be a factor of reducing the power generation characteristics as a whole.

  As described above, in the fuel cell of the present invention, on the upstream side of the fuel flow path of the anode catalyst layer, a polymer electrolyte such as a fluorine ionomer having a high proton conductivity but a large volume expansion when in contact with liquid fuel. And a polymer electrolyte such as a hydrocarbon-based ionomer having a small volume expansion when in contact with the liquid fuel, although the proton conductivity is not so high. A portion of the anode catalyst layer 32 on the upstream side of the fuel flow path contains a polymer electrolyte having a high proton conductivity, so that the anode reaction can be performed quickly. As a result, the fuel flow in the anode catalyst layer can be increased. In the portion on the upstream side of the road, the concentration of fuel at the interface between the anode catalyst layer 32 and the electrolyte membrane 11 can be reduced as compared with the prior art. Therefore, fuel crossover can be reduced. In the portion of the anode catalyst layer 32 on the downstream side of the fuel flow path, a polymer electrolyte having a small volume expansion coefficient is included in the portion, so that excellent fuel diffusibility can be maintained as compared with the prior art. Therefore, the concentration overvoltage of the electrode can be reduced.

Hereinafter, components other than the anode catalyst layer 32 will be described with reference to FIG. 2 again.
The cathode 25 has a cathode catalyst layer 13 in contact with the electrolyte membrane 11 and a cathode diffusion layer 20 in contact with the cathode-side separator 21. The cathode diffusion layer 20 includes a cathode water repellent layer 18 that contacts the cathode catalyst layer 13 and a cathode porous substrate 19 that contacts the cathode-side separator 21.

The cathode catalyst layer 13 includes a cathode catalyst for promoting the reaction shown in the above reaction formula (2), and a polymer electrolyte for securing ion conductivity between the cathode catalyst layer 13 and the electrolyte membrane 11. .
Examples of the cathode catalyst included in the cathode catalyst layer 13 include Pt simple substance and Pt alloy. Pt alloys include alloys of Pt and transition metals such as cobalt and iron. The Pt simple substance or Pt alloy may be used in the form of fine powder or may be supported on a carrier having electronic conductivity such as carbon black.
As the polymer electrolyte contained in the cathode catalyst layer 13, the materials exemplified as the polymer electrolyte contained in the anode catalyst layer 12 can be used.

  The cathode catalyst layer 13 can be produced, for example, as follows. Specifically, the cathode catalyst and the polymer electrolyte are dispersed in a suitable dispersion medium. An anode catalyst layer 13 can be obtained by applying the obtained ink to the electrolyte membrane 11 and drying it. Examples of the application means include a spray method and a squeegee method.

  The anode catalyst layer 32 including the first region 33 and the second region 34 as shown in FIG. 3 can also be produced basically in the same manner as the cathode catalyst layer 13. As an example, a method for producing the anode catalyst layer 32 using a spray method will be described below. In this case, the anode catalyst layer can be formed using a spray coating apparatus as shown in FIG. FIG. 4 is a side view schematically showing the configuration of the spray coating apparatus.

  First, a first ink is prepared by dispersing an anode catalyst and a fluorine-based ionomer in a suitable dispersion medium. Similarly, the second ink is prepared by dispersing an anode catalyst and a hydrocarbon ionomer in an appropriate dispersion medium.

4 includes a tank 71 that contains ink 72 and a spray gun 73 that discharges the ink 72.
In the tank 71, the ink 72 is stirred by a stirrer 74 and is always in a fluid state. The ink 72 is supplied to the spray gun 73 through the opening / closing valve 75 and is discharged from the spray gun 73 together with the jet gas. The ejected gas is supplied to the spray gun 73 via the gas pressure regulator 76 and the gas flow rate regulator 77. As the ejection gas, for example, nitrogen gas can be used. In the coating device 70, the surface temperature of the electrolyte membrane 11 is controlled by a heater 81 arranged so as to be in contact with the electrolyte membrane 11.
In the coating apparatus 70 of FIG. 4, the spray gun 73 is moved from an arbitrary position in two directions of an X axis parallel to the arrow X and a Y axis perpendicular to the X axis by an actuator 78 in a plane perpendicular to the paper surface. It is possible to move at any speed.

  The first ink is stored in the tank 71 of the spray type coating device 70. The first ink is spray applied by using a spray gun 73 to a place where the first region 33 of the electrolyte membrane 11 is disposed, and dried. At this time, masking 79 is applied to the areas other than the area of the electrolyte membrane 11 where the anode catalyst layer 32 is formed, and further, the masking 80 is applied to a place where the second area 34 is disposed on the electrolyte membrane 11. Keep it. Thus, the first region 33 can be formed.

  Next, the ink stored in the tank 71 is changed to the second ink, and the masking 80 is removed. Then, the second ink is spray-applied using a spray gun 73 to a place where the second region 34 of the electrolyte membrane 11 is disposed, and dried. In this way, the second region 34 can be formed.

  In this manner, a CCM in which the anode catalyst layer 32 is formed on one surface of the electrolyte membrane 11 and the cathode catalyst layer 13 is formed on the other surface can be formed.

  Alternatively, a spray-type coating device having two spray guns and tanks is prepared, the first ink is ejected from one set of spray guns, and the second ink is ejected from the other set of spray guns. The first region 33 and the second region 34 may be formed.

In addition, in the coating device 70 of FIG. 4, the ink 72 accommodated in the tank 71 can be discharged, moving the spray gun 73 to arbitrary positions. For example, if the type of ink 72 contained in the tank 71 (for example, the mixing ratio of fluorine ionomer and hydrocarbon ionomer) is changed sequentially, the anode catalyst comprising three or more parts on the electrolyte membrane 11 will be described. Layers can also be formed.
For example, the anode catalyst layer in which the volume expansion coefficient of the polymer electrolyte is continuously changed can be formed by continuously changing the type of the ink 72 stored in the tank 71.

  The anode catalyst layer 32 may be formed on a predetermined resin sheet. Specifically, the anode catalyst layer 32 can be obtained by applying the first ink and the second ink onto the resin sheet and drying. Similarly, the cathode catalyst layer 13 may also be formed on the resin sheet.

  Next, the anode catalyst layer and the cathode catalyst layer formed on the resin sheet are transferred to the electrolyte membrane 11 by hot pressing. The anode catalyst layer 32 is transferred to one surface of the electrolyte membrane 11, and the cathode catalyst layer 13 is transferred to the other surface. At this time, the anode catalyst layer 32 and the cathode catalyst layer 13 may be simultaneously transferred to the electrolyte membrane 11. Alternatively, after transferring one catalyst layer, the other catalyst layer may be transferred. Even in this way, a CCM can be formed.

  The constituent material of the electrolyte membrane 11 is not particularly limited as long as the electrolyte membrane 11 has ion conductivity. As such a material, for example, various polymer electrolyte materials known in the art can be used. The electrolyte membrane currently in circulation is mainly a proton conduction type electrolyte membrane.

Specific examples of the electrolyte membrane 11 include a fluorine-based polymer membrane. Specific examples of the fluorine-based polymer membrane include a polymer membrane containing a perfluorosulfonic acid polymer such as perfluorosulfonic acid / polytetrafluoroethylene copolymer (H ⁺ type). Specific examples of the membrane containing a perfluorosulfonic acid polymer include, for example, a Nafion membrane (trade name “Nafion (registered trademark)”, manufactured by DuPont).

  The electrolyte membrane 11 preferably further has an effect of reducing the crossover of the liquid fuel used in the fuel cell 30. As an electrolyte membrane having such an effect, in addition to the above-mentioned fluorine-based polymer membrane, for example, a membrane made of a hydrocarbon polymer containing no fluorine atom, such as sulfonated polyetherethersulfone (S-PEEK), an inorganic substance・ Organic composite membrane.

The anode diffusion layer 16 includes a porous substrate 15 that has been subjected to a water-repellent treatment, and a water-repellent layer 14 that is formed on the surface of the porous substrate 15 and is made of a highly water-repellent material. Similarly, the cathode diffusion layer 20 includes a porous substrate 19 that has been subjected to a water-repellent treatment, and a water-repellent layer 18 that is formed on the surface of the porous substrate 19 and is made of a highly water-repellent material.
Examples of the porous substrate used for the anode porous substrate 15 and the cathode porous substrate 19 include carbon paper made of carbon fiber, carbon cloth, carbon nonwoven fabric (carbon felt), a metal mesh having corrosion resistance, Examples include foam metal.

  Examples of the highly water-repellent material used for forming the anode water-repellent layer 14 and the cathode water-repellent layer 18 include fluorine-based polymers and fluorinated graphite. Examples of the fluorine-based polymer include polytetrafluoroethylene (PTFE).

  The anode diffusion layer 16 and the cathode diffusion layer 20 can be obtained as follows. First, for example, a highly water-repellent material such as a fluorine polymer and a conductive and porous aggregate such as carbon black (furnace black, acetylene black, etc.), graphite powder, porous metal powder, etc. are formed. The material that can be used and a suitable dispersion medium are mixed and stirred. The ink thus obtained is applied to the surface of a porous substrate that has been subjected to a water-repellent treatment and dried. Examples of the application means include a screen printing method and a squeegee method.

  The anode diffusion layer 16 and the cathode diffusion layer 20 thus obtained are joined to a laminate (CCM) of the anode catalyst layer 32, the electrolyte membrane 11 and the cathode catalyst layer 13 by hot pressing. At this time, the anode diffusion layer 16 is bonded to the anode catalyst layer 32, and the cathode diffusion layer 20 is bonded to the cathode catalyst layer 13. Thus, a membrane electrode assembly (MEA) in which the anode 23, the electrolyte membrane 11, and the cathode 25 are laminated in this order is obtained.

The anode side separator 17 and the cathode side separator 21 are made of a carbon material such as graphite, for example. The anode separator 17 is provided with a concave fuel flow path for supplying fuel (methanol aqueous solution or the like) to the anode 31 on the surface in contact with the anode 31. The cathode separator 21 is provided with a concave oxidant flow path for supplying an oxidant (air, oxygen, etc.) to the cathode 25 on the surface in contact with the cathode 25.
The fuel flow path 22 of the anode side separator 17 and the oxidant flow path 24 of the cathode side separator 21 can be formed, for example, by cutting the surface of the separator into a groove shape. The fuel flow path 22 and the oxidant flow path 24 can also be formed when the separator itself is formed (injection molding, compression molding, etc.).

Examples of the constituent material of the gaskets 26 and 27 include fluorine-based polymers such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), fluorine rubber, and ethylene-propylene-diene rubber. Synthetic rubbers such as (EPDM), silicone elastomers and the like can be mentioned.
Each of the gaskets 26 and 27 includes an opening having the same area as that of the MEA in order to accommodate a membrane electrode assembly (MEA) in a central portion of a sheet made of PTFE or the like. The gaskets 26 and 27 are disposed on the surface of the MEA so as to be in contact with the side surfaces of the anode catalyst layer 12 and the cathode catalyst layer 13, respectively.
Furthermore, the gaskets 26 and 27 pressurize the electrolyte membrane 11 in the thickness direction together with the separators 17 and 21.

A cell composed of the MEA and the anode-side separator 17 and the cathode-side separator 21 disposed on both sides of the MEA is sandwiched between two end plates 28 by a bolt or a spring (not shown). Pressurized and fastened. The two end plates 28 are disposed so as to be stacked on the anode side separator 17 and the cathode side separator 21, respectively.
The interface between the MEA and the pair of separators 17 and 21 has poor adhesion. However, the adhesiveness between the MEA and the pair of separators 17 and 21 can be enhanced by press-fastening the cell as described above, and as a result, between the MEA and the pair of separators 17 and 21. Contact resistance can be reduced.

  A plurality of cells may be stacked to form a cell stack. Also in this case, the cell stack is pressure-fastened by an end plate, a bolt, a spring or the like.

  As the fuel used in the direct oxidation fuel cell of the present invention, hydrocarbon liquids such as ethanol, dimethyl ether, formic acid, ethylene glycol and the like can be used in addition to methanol. Among these, it is preferable to use it as an aqueous solution having a methanol concentration of 1 mol / L to 8 mol / L. The methanol concentration of the aqueous methanol solution is more preferably 3 mol / L to 5 mol / L. Higher fuel concentrations lead to smaller and lighter fuel cell systems as a whole, but there is a risk of increased MCO. According to the present invention, since MCO can be reduced, an aqueous methanol solution having a higher methanol concentration than usual can be used. If the methanol concentration is less than 1 mol / L, it may be difficult to reduce the size and weight of the fuel cell system. If the methanol concentration exceeds 8 mol / L, the MCO may not be sufficiently reduced. By using the fuel having the above methanol concentration, in the anode catalyst layer of the present invention, it is possible to further ensure the supply amount of methanol on the downstream side of the fuel while reducing the MCO on the upstream side of the fuel.

  The fuel cell of the present invention is suitable for improving fuel utilization efficiency and further improving power generation performance such as power generation voltage and power generation efficiency.

  Next, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
In this example, a fuel cell as shown in FIG. 2 was produced. In this embodiment, the anode catalyst layer is composed of two regions, a first region and a second region, a fluorine ionomer is added as a polymer electrolyte to the first region, and a hydrocarbon ionomer is polymerized to the second region. Added as an electrolyte.

  As anode catalyst particles, conductive carbon particles having an average primary particle diameter of 30 nm to which platinum (Pt) -ruthenium (Ru) alloy (atomic ratio of 1: 1) was attached were used. The ratio of the weight of the platinum-ruthenium alloy to the total weight of the platinum-ruthenium alloy and the conductive carbon particles was 80% by weight.

  As the cathode catalyst particles, conductive carbon particles having an average primary particle diameter of 30 nm with platinum attached thereto were used. The ratio of the weight of platinum to the total weight of platinum and conductive carbon particles was 80% by weight.

The electrolyte membrane 11 has a 178 μm-thick fluoropolymer membrane (a film based on perfluorosulfonic acid / polytetrafluoroethylene copolymer (H ⁺ type), trade name “Nafion (registered trademark) 117”, DuPont) was used.

A perfluorosulfonic acid / polytetrafluoroethylene copolymer (H ⁺ type) was used as the fluorine ionomer.

A sulfonated polyether ether ketone was used as the hydrocarbon ionomer. A sulfonated polyetheretherketone was prepared as follows. 150 ml of concentrated sulfuric acid was placed in a reaction vessel equipped with a mechanical stirrer. While stirring, 5 g of polyether ether ketone (manufactured by Aldrich) was added to the concentrated sulfuric acid, and the resulting reaction solution was continuously stirred at room temperature for 10 hours.
Next, the stirred reaction solution was dropped into ion-exchanged water to precipitate the reaction product, filtered, and washed with ion-exchanged water until the filtrate became neutral.
The washed reaction product was dried for 12 hours in a vacuum drier set at 120 ° C. to obtain a sulfonated polyetheretherketone.
The obtained solid ionomer was dissolved in N, N-dimethylformamide (DMF) to obtain a solution-state ionomer. Thereafter, in order to facilitate the ink preparation and the catalyst layer preparation process, the ionomer in the solution state was mixed with a propanol aqueous solution, and the isopropanol aqueous solution containing the ionomer was stirred while applying ultrasonic waves.

  The physical properties of fluorine ionomer and hydrocarbon ionomer were evaluated. Specifically, the ion exchange capacity, proton conductivity, and volume expansion coefficient when immersed in an aqueous methanol solution of a fluorine ionomer and a hydrocarbon ionomer were measured.

  The ion exchange capacity was measured by neutralization titration using 0.5M sodium hydroxide.

  Proton conductivity was measured by the AC impedance method. A solution containing a fluorine ionomer and a solution containing a hydrocarbon ionomer were cast on separate glass plates to obtain a cast film of a fluorine ionomer and a cast film of a hydrocarbon ionomer. Gold wires were placed at both ends of each cast film, and the gold wires were connected to an AC impedance measuring device. Proton conductivity was measured by an AC impedance method (measurement frequency: changing frequency in the range of 100 kHz to 1 Hz, with the real axis intercept in the Nyquist plot as the impedance value) in a nitrogen atmosphere at room temperature and 100% relative humidity.

  The volume expansion coefficient was measured as follows. The fluorine ionomer cast membrane and the hydrocarbon ionomer cast membrane prepared as described above were dried in a vacuum drier set at 100 ° C. for 12 hours. The thickness, width, and length of each cast film was measured with a caliper in a dry air atmosphere to determine the volume before immersion. Thereafter, each cast film was immersed in a 2M aqueous methanol solution at room temperature for 12 hours. After 12 hours, the dimensions of each film were measured again to determine the volume after immersion. The volume expansion coefficient was calculated using the volume before immersion of the 2M aqueous methanol solution and the volume after immersion. The volume expansion rate was determined by {[(volume after immersion) − (volume before immersion)] / (volume before immersion)} × 100.

As a result, the ion exchange capacity of the sulfonated polyether ether ketone, which is a hydrocarbon ionomer, was 1.2 meq / g, the proton conductivity was 0.032 S / cm, and the volume expansion coefficient was 30%.
Nafion, which is a fluorine ionomer, had an ion exchange capacity of 1.0 meq / g, a proton conductivity of 0.097 S / cm, and a volume expansion coefficient of 45%.

A dispersion containing 10 g of the above anode catalyst powder and a perfluorosulfonic acid / polytetrafluoroethylene copolymer (H ⁺ type) (trade name: Nafion dispersion, “Nafion (registered trademark) 5 wt% solution”, DuPont 70 g) was mixed with an appropriate amount of water and stirred. Thereafter, the obtained mixture was defoamed to obtain a first ink containing fluorine-based ionomer and anode catalyst particles. In the first ink, the content of the fluorine ionomer contained in the solid content was set to 26% by weight of the solid content.

  10 g of the anode catalyst powder and a liquid containing the sulfonated polyetheretherketone obtained as described above were mixed and stirred. Thereafter, the obtained mixture was defoamed to obtain a second ink containing anode catalyst particles and a hydrocarbon ionomer. At this time, the content of the ionomer contained in the solid content of the second ink was set to 26 wt% of the solid content, as in the first ink.

  Using the first ink and the second ink thus obtained, a 60 mm × 60 mm square anode catalyst layer 32 was formed on one surface of the electrolyte membrane 11 using a spray method. Specifically, the first region 33 having a size of 20 × 60 mm was formed at a position facing the upstream portion of the fuel flow path on the electrolyte membrane 11. Next, a second region 34 having a size of 40 mm × 60 mm was formed at a position facing the downstream portion of the fuel flow path. The dimensions of each part were adjusted by masking.

Note that when the first ink and the second ink were sprayed, the electrolyte membrane 11 was fixed to the metal plate by suction under reduced pressure. The metal plate was provided with a heater for adjusting the surface temperature. Thus, by adjusting the surface temperature of the metal plate, the ink can be gradually dried during the application of the ink to the electrolyte membrane 11.
The surface temperature of the metal plate during ink application is 55 ° C. when the first region 33 containing the fluorine ionomer is formed, and 80 ° C. when the second region 34 containing the hydrocarbon ionomer is formed. did. This is because, since DMF having a high boiling point is used as the dispersion medium for the second ink containing the hydrocarbon ionomer, drying does not proceed rapidly at a low temperature. When a solvent having a lower boiling point is used as the dispersion medium for the second ink containing the hydrocarbon ionomer, it is not necessary to increase the drying temperature.

A cathode catalyst layer forming ink was prepared as follows.
10 g of the cathode catalyst powder and 100 g of a dispersion containing the perfluorosulfonic acid / polytetrafluoroethylene copolymer (H ⁺ type) (the above-mentioned trade name “Nafion (registered trademark) 5 wt% solution”) , Mixed and stirred with an appropriate amount of water. Thereafter, the obtained mixture was defoamed to obtain an ink for forming a cathode catalyst layer.

  The cathode catalyst layer forming ink obtained as described above was applied to the surface of the electrolyte membrane 11 opposite to the surface on which the anode catalyst layer 32 was formed, dried, and dried to a size of 60 mm × 60 mm. A cathode catalyst layer 13 was obtained.

  Thus, a CCM composed of the anode catalyst layer 32, the electrolyte membrane 11, and the cathode catalyst layer 13 was obtained. Finally, in order to completely remove DMF used as a solvent for the hydrocarbon ionomer, the obtained CCM was dried for 12 hours in a vacuum drier set at 130 ° C.

The amount of the PtRu alloy per unit area of the first region 33 and the second region 34 was 4 mg / cm ² for both the first region 33 and the second region 34. Moreover, the thickness of the 1st area | region 33 and the 2nd area | region 34 exists in the range of about 60-63 micrometers, and the thickness difference with a significant difference did not arise.

  The anode porous substrate 15 was obtained as follows. Water-repellent carbon paper (trade name “TGP-H-090”, thickness of about 300 μm, manufactured by Toray Industries, Inc.) diluted with polytetrafluoroethylene (PTFE) dispersion (trade name “D- 1 ", manufactured by Daikin Industries, Ltd.) for 1 minute. Thereafter, the carbon paper was dried in a hot air dryer set at 100 ° C. Next, the dried carbon paper was fired at 270 ° C. for 2 hours in an electric furnace. Thus, an anode porous substrate 15 having a PTFE content of 10% by weight was obtained.

  The cathode porous base material 19 is an anode porous substrate except that carbon cloth (trade name “AvCarb ™ 1071HCB”, manufactured by Ballard Material Products) is used instead of the carbon paper subjected to the water repellent treatment. A material 15 was produced in the same manner. In this way, a cathode porous substrate 19 having a PTFE content of 10% by weight was obtained.

By mixing and stirring the acetylene black powder and the PTFE dispersion (the above-mentioned trade name “D-1”), the PTFE content in the total solids is 10% by weight. A water repellent layer-forming ink having an acetylene black content of 90% by weight was obtained. The obtained ink for forming a water repellent layer was applied to one surface of the anode porous substrate 15 by a doctor blade method and dried in a thermostatic bath set at a temperature of 100 ° C. Next, the anode porous substrate 15 coated with the water repellent layer forming ink was baked in an electric furnace at 270 ° C. for 2 hours to remove the surfactant. Thus, the anode water repellent layer 14 was formed.
A cathode water repellent layer 18 was also formed on one surface of the cathode porous substrate 19 in the same manner as described above.

  The anode diffusion layer 16 composed of the anode porous substrate 15 and the anode water repellent layer 14 and the cathode diffusion layer 20 composed of the cathode porous substrate 19 and the cathode water repellent layer 18 both use a punching die. And formed into a 60 mm × 60 mm square.

  Next, the anode diffusion layer 16, the CCM, and the cathode diffusion layer 20 were laminated so that the anode water repellent layer 14 was in contact with the anode catalyst layer 32 and the cathode water repellent layer 18 was in contact with the cathode catalyst layer 13. The obtained laminated body was arrange | positioned at the hot press apparatus which set temperature to 140 degreeC. The laminate was pressurized at a pressure of 5 MPa for 1 minute to join the anode catalyst layer and the anode diffusion layer, and join the cathode catalyst layer and the cathode diffusion layer. Thus, a membrane electrode assembly (MEA) composed of the anode 31, the electrolyte membrane 11, and the cathode 25 was obtained.

A sheet of ethylene propylene diene rubber (EPDM) having a thickness of 0.25 mm was cut into a square of 120 mm × 120 mm. Further, the central portion of the sheet was cut out into a 162 mm × 62 mm square. In this way, two gaskets 26 and 27 were obtained.
The gasket 26 was disposed so that the anode 31 was disposed in the opening at the center. Similarly, the gasket 27 was disposed so that the cathode 25 was disposed in the opening at the center.

The anode-side separator 17 was produced by cutting the surface of a 2 mm thick graphite plate to form a fuel flow path 22 for supplying a methanol aqueous solution. Similarly, the cathode side separator 21 was produced by cutting the surface of a graphite plate having a thickness of 2 mm to form an oxidant channel 24 for supplying an oxidant. The anode separator 17 was laminated on the anode diffusion layer 16 so that the fuel flow path 22 was in contact with the anode diffusion layer 16. The cathode separator 21 was laminated on the cathode diffusion layer 20 so that the oxidant flow path 24 was in contact with the cathode diffusion layer 20.
The cross-sectional shapes of the fuel channel 22 and the oxidant channel 24 were 1 mm × 1 mm, respectively. In addition, the fuel flow path 22 and the oxidant flow path 24 are of a serpentine type that meanders uniformly on the surface of the anode 31 and the surface of the cathode 25, respectively.

  Then, the MEA sandwiched between the anode side separator 17 and the cathode side separator 21 was further sandwiched between a pair of end plates 28 made of a stainless steel plate having a thickness of 1 cm. Between the end plate 28 and the separator 17 and between the end plate 28 and the separator 21, a current collector plate made of a copper plate having a thickness of 2 mm, the surface of which is plated with gold, in order from each separator to the outside. And an insulating plate. In the following evaluation tests, the current collector plate was connected to an electronic load device. A pair of end plates 28 were fastened using bolts, nuts, and springs, and the MEA and separators 26 and 27 were pressurized. Thus, a single cell of a direct methanol fuel cell (DMFC) was obtained. In FIG. 2, the current collecting plate and the insulating plate are not shown. This also applies to FIG.

<< Comparative Example 1 >>
As Comparative Example 1, a fuel cell having a conventional structure as shown in FIG.
The anode catalyst layer 12 was a square of 60 mm × 60 mm, and the fluorine-based ionomer used in Example 1 was used as the polymer electrolyte contained in the anode catalyst layer 12. The anode catalyst layer 12 was produced in the same manner as the production method of the first region 33 of Example 1. The amount of catalyst contained in the anode catalyst layer 12 and the thickness of the anode catalyst layer 12 were the same as in Example 1.
A fuel cell (DMFC) of Comparative Example 1 was produced in the same manner as Example 1 except for the above.

<< Comparative Example 2 >>
The anode catalyst layer 12 was a square of 60 mm × 60 mm, and the hydrocarbon ionomer used in Example 1 was used in place of the fluorine ionomer as the polymer electrolyte contained in the anode catalyst layer 12. The anode catalyst layer 12 was produced in the same manner as the production method of the second region 34 of Example 1. The amount of catalyst contained in the anode catalyst layer 12 and the thickness of the anode catalyst layer 12 were the same as in Example 1.
A fuel cell (DMFC) of Comparative Example 2 was obtained in the same manner as Example 1 except for the above.

"Evaluation test"
For the fuel cell of Example 1 and the fuel cells of Comparative Examples 1 and 2, the methanol crossover amount during power generation and the power generation performance were evaluated, and the fuel utilization efficiency was calculated from the obtained results.

The power generation conditions of the fuel cell are as follows. A 4 mol / L aqueous methanol solution was used as a fuel and supplied to the anode using a tube pump at a flow rate of 0.3 cm ³ / min. Unhumidified air was supplied to the cathode while controlling the flow rate at 300 cm ³ / min by a mass flow controller. The temperature of the cell was controlled to 60 ° C. using a heating wire heater and a temperature controller. Thereafter, the fuel cell was connected to an electronic load device “PLZ164WA” (manufactured by Kikusui Electronics Co., Ltd.), and continuous power generation was performed while controlling the fuel cell to have a constant current density of 200 mA / cm ² .

A gas-liquid mixed fluid composed of an aqueous methanol solution and carbon dioxide in which unused fuel discharged from the anode side remained was caused to flow into a gas collection container filled with pure water. Thus, gas and liquid methanol were collected over 1 hour. At this time, the gas collection container was cooled in an ice water bath.
Thereafter, the amount of methanol in the gas collection container was measured by gas chromatography, and the mass balance of the anode (MCO amount) was determined by calculating the material balance of the anode. That is, the amount of MCO was obtained by subtracting the amount of methanol consumed at the electrode obtained from the amount of methanol discharged and collected and the amount of generated current from the amount of methanol supplied to the anode. As the amount of MCO, a numerical value converted into the amount of current that can be generated when an amount of methanol corresponding to the amount of MCO is electrode oxidized is used. The fuel utilization rate was calculated by the following formula.
Fuel utilization rate = (Generation current) / (Generation current + MCO amount converted to current)
The results are shown in Table 1.

  As is clear from Table 1, the fuel cell of Example 1 can obtain a higher power generation voltage than the fuel cell of Comparative Example 1. Furthermore, the fuel cell of Example 1 can obtain a higher fuel utilization rate and a higher power generation voltage than the fuel cell of Comparative Example 2.

  In the fuel cell of Comparative Example 1, the diffusibility of the fuel is not sufficient in the anode catalyst layer facing the downstream of the fuel where the fuel concentration decreases, and the concentration overvoltage increases. As a result, it is considered that the power generation voltage of the entire fuel cell has also decreased. On the other hand, in the fuel cell of Example 1, it is considered that this point was improved and a high power generation voltage was obtained.

In the fuel cell of Comparative Example 2, since the proton conductivity of the hydrocarbon ionomer used in the anode catalyst layer is small, it is considered that overvoltage due to proton conduction resistance increases in the entire anode catalyst layer. Furthermore, in the anode catalyst layer facing the upstream of the fuel with a high fuel concentration, the volume of the hydrocarbon ionomer does not expand due to the methanol aqueous solution as the fuel, so the porosity of the anode catalyst layer is kept large, and the diffusibility of the fuel Becomes higher. For this reason, it is considered that the fuel concentration at the interface between the anode catalyst layer and the electrolyte membrane is increased and the amount of methanol crossover is increased.
In addition, the fuel cell of Example 1 shows a power generation performance superior to that of the prior art while using a relatively generalized hydrocarbon ionomer called SPEEK. Recently, hydrocarbon ionomers with higher proton conductivity have been developed, and it can be estimated that the implementation effect of the present invention will be further enhanced by using such hydrocarbon ionomers with higher performance.

  As described above, the fuel cell of the present invention can obtain higher power generation performance and fuel utilization rate than the conventional fuel cell, and thus can obtain high energy conversion efficiency.

  The fuel cell of the present invention is useful as a power source in portable small electronic devices such as notebook personal computers, mobile phones, and personal digital assistants (PDAs). The fuel cell of the present invention can also be applied to uses such as a power source for electric scooters.

DESCRIPTION OF SYMBOLS 10 Fuel cell 11 Electrolyte membrane 12, 32 Anode catalyst layer 13 Cathode catalyst layer 14 Anode water repellent layer 15 Anode porous base material 16 Anode diffusion layer 17 Anode side separator 18 Cathode water repellent layer 19 Cathode porous substrate 20 Cathode diffusion layer 21 Cathode side separator 22 Fuel flow path 23, 31 Anode 24 Oxidant flow path 25 Cathode 26, 27 Gasket 28 End plate 33 1st area 34 2nd area 70 Spray type coating device 71 Tank 72 Ink 73 Spray gun 74 Stirrer 75 Open / close valve 76 Gas pressure regulator 77 Gas flow regulator 78 Actuator 79, 80 Masking 81 Heater

Claims (17)

At least one unit comprising a membrane-electrode assembly including an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode, an anode-side separator in contact with the anode, and a cathode-side separator in contact with the cathode Have cells,
The anode side separator has a fuel flow path for supplying fuel to the anode,
The cathode side separator has an oxidant flow path for supplying an oxidant to the cathode,
The anode includes an anode catalyst layer in contact with the electrolyte membrane, and an anode diffusion layer in contact with the anode separator,
The anode catalyst layer includes an anode catalyst and a polymer electrolyte,
The direct oxidation fuel cell, wherein the volumetric expansion rate of the polymer electrolyte is larger on the upstream side than the downstream side of the fuel flow path of the anode catalyst layer.   2. The direct oxidation fuel cell according to claim 1, wherein a volume expansion coefficient of the polymer electrolyte is gradually decreased from an upstream side to a downstream side of the fuel flow path.   The direct oxidation fuel cell according to claim 1, wherein the volume expansion coefficient of the polymer electrolyte continuously decreases from the upstream side to the downstream side of the fuel flow path.   The high swelling area | region where the volume expansion coefficient of the said polymer electrolyte is 20 to 40% is provided in the part which opposes the upstream of the said fuel flow path of the said anode catalyst layer. Direct oxidation fuel cell.   The high-swelling region is provided in a region of the anode catalyst layer facing a portion having a length of 1/6 to 1/3 of the entire length of the fuel flow channel on the upstream side of the fuel flow channel. 4. The direct oxidation fuel cell according to 4.   The low swelling area | region where the volume expansion coefficient of the said polymer electrolyte is 0 to 30% is provided in the part which opposes the downstream of the said fuel flow path of the said anode catalyst layer. Direct oxidation fuel cell.   6. The direct oxidation fuel cell according to claim 4, wherein a fluorine-based ionomer is contained as the polymer electrolyte in the highly swelled region.   The direct oxidation fuel cell according to claim 7, wherein the fluorine ionomer has a volume expansion coefficient of 20 to 40% and a proton conductivity of 0.05 to 0.15 S / cm.   The direct oxidation fuel cell according to claim 6, wherein a hydrocarbon-based ionomer is contained as the polymer electrolyte in the low swelling region.   The direct oxidation fuel cell according to claim 9, wherein the hydrocarbon ionomer has a volume expansion coefficient of 0 to 30% and a proton conductivity of 0.01 to 0.1 S / cm.   The direct oxidation fuel cell according to claim 7 or 8, wherein the fluorine-based ionomer includes a copolymer containing a perfluorosulfonic acid unit and a tetrafluoroethylene unit.   The direct oxidation according to claim 9 or 10, wherein the hydrocarbon ionomer includes at least one selected from the group consisting of an engineering plastic having a sulfonic acid group introduced therein and an engineering plastic having a phosphonic acid group introduced therein. Type fuel cell.   The direct oxidation fuel cell according to any one of claims 1 to 12, wherein the amount of the polymer electrolyte contained in the anode catalyst layer occupies 10 to 30% by weight of the anode catalyst layer.   The direct oxidation fuel cell according to claim 1, wherein the amount of the anode catalyst is uniform throughout the anode catalyst layer. The direct oxidation fuel cell according to claim 14, wherein the amount of the anode catalyst is 1 to 10 mg / cm ² .   The direct oxidation fuel cell according to claim 1, wherein the thickness of the anode catalyst layer is uniform throughout the anode catalyst layer.   The direct oxidation fuel cell according to claim 16, wherein the anode catalyst layer has a thickness of 5 to 120 μm.

Images