JP2006012449A - Membrane electrode junction body and solid polymer fuel cell using above - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a durability of a material structuring an electrode catalyst layer of a PEFC and provide a means capable of stably generating power for a long period in the PEFC. <P>SOLUTION: The membrane electrode junction body includes a polyelectrolyte membrane, a pair of electrode catalyst layers pinching the polyelectrolyte membrane and a pair of gas diffusion layers arranged to pinch the polyelectrolyte membrane and the electrode catalyst layers on a surface facing the polyelectrolyte membrane of the electrode catalyst layers. The electrode catalyst layers include a conductive carbon, a catalyst active material supported by the conductive carbon and a proton conductive polymer, and at least one of the electrode catalyst layers includes at least a conductive carbon (A), a conductive carbon (B) with a larger value of a lattice spacing (d<SB>002</SB>) than the conductive carbon (A) and a conductive carbon (C) with a larger value of a lattice spacing (d<SB>002</SB>) than the conductive carbon (B). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a membrane electrode assembly used for a polymer electrolyte fuel cell. Specifically, the present invention relates to a technique for improving the durability of the membrane electrode assembly.

  A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. Various fuel cells such as a polymer electrolyte fuel cell, a solid oxide fuel cell, a molten carbonate fuel cell, and a phosphoric acid fuel cell have been proposed as fuel cells. Among these, the polymer electrolyte fuel cell can be operated at a relatively low temperature, and thus is expected as a power source for moving bodies such as automobiles and is being developed.

  The polymer electrolyte fuel cell is a fuel cell using a proton conductive polymer electrolyte, also called a polymer electrolyte fuel cell or PEFC. In the following description, it is also referred to as PEFC. The PEFC has a structure in which an electrode catalyst layer (anode) to which a fuel gas containing hydrogen is supplied and an electrode catalyst layer (cathode) to which an oxidant containing oxygen is supplied are disposed on both sides of a proton conductive polymer electrolyte. Is basically included. The anode, polymer electrolyte membrane, and cathode are collectively referred to as a membrane electrode assembly (MEA).

  The electrode catalyst layer is generally porous, and usually has a catalyst active material that mediates an electrode reaction, a conductive carrier that supports the catalyst (for example, conductive carbon), and a proton conductive polymer. The reaction gas is supplied to the catalyst through the holes of the electrode catalyst layer, and water generated by the power generation reaction is discharged.

  Hydrogen contained in the fuel gas supplied to the anode side is oxidized by the catalyst existing in the electrode catalyst layer on the anode side, and protons and electrons are generated by the reaction shown in the following reaction formula (1).

  The produced protons pass through the proton conductive polymer constituting the electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the electrode catalyst layer on the cathode side. On the other hand, the electrons generated in the electrode catalyst layer on the anode side are the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer disposed on the surface of the electrode catalyst layer facing the polymer electrolyte membrane, the separator, and the outside. It reaches the cathode electrode catalyst layer via the circuit.

  Protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant supplied to the cathode-side electrode catalyst layer, and produce water by the reaction shown in the following reaction formula (2).

  Through the above series of reactions, the PEFC can supply electricity to the outside. In order to keep the performance of the PEFC stable for a long period of time, it is necessary to keep the constituent members of the PEFC stable. In particular, when the PEFC is used for an application having a long use period such as a vehicle, the PEFC should have high durability.

As a technique for improving the durability of PEFC, a technique for preventing deterioration of a conductive carrier in an electrode catalyst layer has been proposed. For example, including a first carbon-based component (conductive carrier) that hardly exhibits resistance to corrosion and a second carbon-based component (conductive carrier) having higher corrosion resistance than the first carbon-based component An anode for a fuel cell is disclosed (see Patent Document 1). The technique described in Document 1 delays corrosion of the second carbon-based component (conductive carrier) by preferentially corroding the first carbon-based component (conductive carrier) that is a sacrificial component. Thus, an object is to suppress a decrease in power generation performance at the anode.
Special table 2003-523056 gazette

  However, there are cases where the first carbon-based component, which is a sacrificial component, is completely corroded due to continuous operation over a long period of time or frequent repeated starting and stopping, and the function as the sacrificial component is lost. As a result, there was a problem that even the second carbon-based component having relatively high corrosion resistance was corroded and deteriorated, resulting in a decrease in power generation performance.

  Therefore, an object of the present invention is to provide means for improving the durability of the material constituting the electrode catalyst layer of PEFC and enabling stable power generation for a long time in PEFC.

The present invention provides a polymer electrolyte membrane, a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane, and a surface of the electrode catalyst layer facing the polymer electrolyte membrane, the polymer electrolyte membrane, A membrane electrode assembly having a pair of gas diffusion layers arranged so as to sandwich an electrode catalyst layer, wherein the electrode catalyst layer is a conductive carbon, a catalyst supported on the conductive carbon An active material and a proton conductive polymer are included, and at least one of the electrode catalyst layers is conductive carbon (A) and has a larger lattice spacing (d ₀₀₂ ) value than the conductive carbon (A). A membrane / electrode assembly including carbon (B) and conductive carbon (C) having a lattice spacing (d ₀₀₂ ) value larger than that of the conductive carbon (B).

  According to the present invention, deterioration of the conductive carbon contained in the electrode catalyst layer can be suppressed. As a result, the long-term stability of PEFC can be guaranteed.

  In PEFC, electric power is generated by the reaction in the electrode catalyst layer (anode and cathode). At this time, protons generated in the vicinity of the catalytic active material present in the electrode catalyst layer on the anode side reach the solid polymer electrolyte membrane via the proton conductive polymer dispersed in the electrode catalyst layer, and It passes through the solid polymer electrolyte membrane and moves to the electrode catalyst layer on the cathode side. Thereafter, it reaches the catalyst active material via the proton conductive polymer dispersed in the cathode-side electrode catalyst layer, and reacts with oxygen gas and electrons that have passed through the external circuit to generate water.

  As described above, in the fuel cell, water is generated along with the power generation reaction. If this water stays in the PEFC, the performance of the fuel cell may be deteriorated. In other words, the generated water may cause gas channel blockage in the separator and uneven water distribution in the electrode catalyst layer. As a result, the electrode catalyst layer is corroded and deteriorated, resulting in a decrease in PEFC battery performance.

  For example, when conductive carbon is used as the carrier for supporting the catalyst active material and platinum is used as the catalyst active material, the conductivity of the carrier is increased due to an increase in electrode potential accompanying fuel depletion that occurs during battery operation. Carbon corrodes by the reaction shown in the following reaction formula (3).

  When the conductive carbon is corroded, the porous structure of the electrode catalyst layer is destroyed, and the battery performance deteriorates due to a decrease in the diffusibility of the fuel gas and oxygen gas, and a decrease and interruption of the proton conduction path in the electrode catalyst layer. . Further, an increase in battery resistance due to a decrease in electronic conductivity also contributes to a decrease in battery performance. Furthermore, when the joining part of platinum and conductive carbon peels, the platinum particles are fused together, and the battery performance decreases when the surface area of the platinum particles decreases. Here, in order to prevent such a decrease in battery performance, it is preferable to take measures that can suppress the deterioration of the conductive carbon in the electrode catalyst layer.

  As a measure for suppressing deterioration of the conductive carbon in the electrode catalyst layer, there is a method of including a component that hardly exhibits corrosion resistance as a sacrificial component as described in Patent Document 1, but as described above. Such means may not sufficiently prevent the deterioration of the conductive carbon.

In contrast, in the present invention, the electrode catalyst layer includes at least three kinds of conductive carbons having different corrosion resistances, thereby balancing the durability and the catalyst performance of the electrode catalyst layer. The corrosion resistance means the resistance of the conductive carbon contained in the electrode catalyst layer against the phenomenon of deterioration damage due to a chemical reaction. Although details will be described later, in the present invention, as an index of the corrosion resistance of the conductive carbon, the lattice spacing (d ₀₀₂ ) of the conductive carbon measured by X-ray diffraction (XRD) (hereinafter simply referred to as “plane”). Also referred to as “interval”).

  Here, the influence of the surface spacing of the conductive carbon on the catalyst performance of the electrode catalyst layer and the corrosion resistance of the conductive carbon will be described.

  First, the smaller the plane spacing of the conductive carbon, the closer the shape of the conductive carbon is to graphite (plane spacing: about 3.36 mm), and the corrosion resistance is improved. This is probably because the corrosion resistance of carbon is related to the degree of graphitization in the structure. However, the smaller the interplanar spacing of the conductive carbon, the smaller the specific surface area of the conductive carbon and the lower the dispersibility of the supported catalyst particles. As a result, the catalyst particles are aggregated, the particle diameter is increased, and the catalyst performance is lowered.

  On the other hand, when the interplanar spacing of the conductive carbon is increased, the specific surface area of the conductive carbon is increased. As a result, the dispersibility of the catalyst particles is improved and the catalyst performance is also improved. However, as the surface spacing of the conductive carbon increases, the shape of the conductive carbon moves away from the graphite, and its corrosion resistance decreases.

  Thus, there is a trade-off relationship between the corrosion resistance of the conductive carbon and the catalyst performance in the electrode catalyst layer. As a result of various studies paying attention to this point, the present inventor found that the electrode catalyst layer can be balanced by including at least three kinds of conductive carbons having different corrosion resistances. The invention has been completed.

That is, the first of the present invention is a polymer electrolyte membrane, a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane, and a surface of the electrode catalyst layer facing the polymer electrolyte membrane, A membrane electrode assembly having a molecular electrolyte membrane and a pair of gas diffusion layers arranged so as to sandwich the electrode catalyst layer, wherein the electrode catalyst layer is formed of conductive carbon and conductive carbon. A catalyst active material that is supported; and a proton conductive polymer, wherein at least one of the electrode catalyst layers has at least a conductive carbon (A) and a lattice spacing (d ₀₀₂ ) value of the conductive carbon. (A) It is a membrane electrode assembly containing larger conductive carbon (B) and conductive carbon (C) having a larger lattice spacing (d ₀₀₂ ) value than the conductive carbon (B).

  Hereinafter, the membrane electrode assembly of the present invention (hereinafter also referred to as “MEA”) will be described in detail with reference to the drawings. In the present invention, materials used in conventional MEAs can be used in the same manner except that the form of conductive carbon contained in the electrode catalyst layer is defined. For this reason, although basic structures, such as a polymer electrolyte membrane and a gas diffusion layer (henceforth "GDL"), are demonstrated easily, these materials are not necessarily limited to the illustrated material and shape. .

  First, an outline of the basic configuration of the MEA will be described. FIG. 1 is a schematic cross-sectional view of one embodiment of the MEA of the present invention.

  A polymer electrolyte membrane 110 is disposed in the center of the MEA 10. On the anode side of the polymer electrolyte membrane 110, the electrode catalyst layer 120a and the GDL 130a are arranged in this order. On the other hand, the electrode catalyst layer 120c and the GDL 130c are also arranged in this order on the cathode side of the polymer electrolyte membrane 110.

In the MEA of the present invention, the electrode catalyst layers (120a, 120c) include conductive carbon, a catalyst active material supported on the conductive carbon, and a proton conductive polymer. Further, at least one of the electrode catalyst layers (120a, 120c) contains at least three types of conductive carbons having different values of the lattice spacing (d ₀₀₂ ) measured by the X-ray diffraction method. In addition, in this application, for convenience, three types of conductive carbons having different face spacings included in the electrode catalyst layer are divided into conductive carbon (A), conductive carbon (B) and conductive carbon ( C).

  Further, in the present application, “membrane electrode assembly (MEA)” means a polymer electrolyte membrane, a pair of electrode catalyst layers that sandwich the polymer electrolyte membrane, and a pair that sandwiches the polymer electrolyte membrane and the electrode catalyst layer. Means an aggregate having the GDL.

  When a PEFC is manufactured using the MEA, a pair of separators (not shown) are arranged outside the MEA 10 so as to sandwich the MEA 10. The separator has a gas flow path on the surface in contact with the GDL. In addition, various members can be installed as necessary. For example, a sealing material (not shown) for preventing leakage of gas supplied to the PEFC to the outside can be arranged.

  In the MEA 10 of the present invention, at least one of the electrode catalyst layers (120a, 120c) contains at least three kinds of conductive carbons having different face spacings. Both electrode catalyst layers (120a, 120c) may contain at least three types of conductive carbon.

  As described above, when at least three kinds of conductive carbons having different face spacings are included in the electrode catalyst layer, the deterioration of the conductive carbon due to the increase in electrode potential due to the start-stop and the fuel deficiency generated during battery operation as described above. First proceeds in the conductive carbon (C) which is inferior in corrosion resistance, that is, has a large interplanar spacing, and then proceeds in the order of the conductive carbon (B) and the conductive carbon (A). Therefore, deterioration of the conductive carbon (B) and the conductive carbon (A) having high corrosion resistance is suppressed, and as a result, the long-term stability of the PEFC can be guaranteed.

  Then, the member which comprises MEA is demonstrated in order.

  The polymer electrolyte membrane 110 is a polymer membrane having proton conductivity. Various materials have been proposed as materials constituting the polymer electrolyte membrane. For example, the film | membrane which consists of a perfluorocarbon polymer which has a sulfonic acid group is mentioned. As the polymer electrolyte membrane, a membrane synthesized by itself may be used, or a commercially available product may be used.

  The electrode catalyst layers (120a, 120c) are portions where electrode catalysts that mediate electrode reactions are disposed. In the present invention, the electrode catalyst layer includes conductive carbon, a catalyst active material supported on the conductive carbon, and a proton conductive polymer. The polymer electrolyte membrane is sandwiched between the electrode catalyst layers. That is, the electrode catalyst layer 120a / polymer electrolyte membrane 110 / electrode catalyst layer 120c are laminated in this order. In the present invention, “clamping” means a state in which a certain member is interposed between two other members. The contact area between the members is not particularly limited.

In the present invention, the conductive carbon contained in the electrode catalyst layer is conductive, and the generated electrons can move through the conductive carbon. Examples of the conductive carbon include various carbon blacks and activated carbon. The carbon black is obtained by thermally decomposing a hydrocarbon liquid or gas, and examples thereof include Vulcan ^™ , Ketjen Black ^™ , channel black, furnace black, thermal black, acetylene black, and the like. Activated carbon is obtained by carbonizing plant-based raw materials such as wood, sawdust, coconut husk and pulp waste liquid, and mineral-based raw materials such as coal, petroleum coke, and petroleum pitch, and further performing steam activation and chemical activation. . The conductive carbon is preferably composed of only carbon atoms, but impurities of about 2 to 3% by mass or less may be mixed therein.

As described above, in the present invention, at least one of the electrode catalyst layers contains at least three types of conductive carbon having different lattice spacings (d ₀₀₂ ). Here, “lattice plane spacing (d ₀₀₂ )” means the plane spacing of the hexagonal mesh plane based on the graphite structure of conductive carbon.

In the present invention, the lattice spacing (d ₀₀₂ ) is measured by the Gakushin method (Michio Inagaki, Carbon No. 36, 25-34 (1963)) using X-ray diffraction (XRD). If an accurate value can be measured, it may be replaced by other means.

  The face spacing of the three types of conductive carbons having different face spacings included in the electrode catalyst layer is not particularly limited. However, the plane spacing of the conductive carbon (A) having the smallest plane spacing is preferably less than 3.48 mm. When the plane spacing of the conductive carbon (A) is in such a range, the structure of the conductive carbon (A) is close to that of graphite and excellent in corrosion resistance. The plane spacing of the conductive carbon (C) having the largest plane spacing is preferably greater than 3.66 mm. When the surface spacing of the conductive carbon (C) is in such a range, the conductive carbon (C) is sacrificed and deteriorates in preference to the other conductive carbon. Can be effectively prevented. Furthermore, the plane spacing of the conductive carbon (B) having a plane spacing between them is preferably 3.48 to 3.66 mm. When the surface spacing of the conductive carbon (B) is in such a range, the specific surface area of the conductive carbon (B) becomes an appropriate value, and the dispersibility when the catalyst active material is supported is improved. sell.

  In the present invention, the three kinds of conductive carbons having different face spacings included in the electrode catalyst layer may be made of the same raw material or different raw materials. Moreover, a commercially available product may be used, and a material obtained by processing a commercially available product by itself may be used.

  In the case where the conductive carbon whose surface spacing is controlled is manufactured by itself, for example, a commercially available conductive carbon material may be processed by heat treatment. When the conductive carbon material is heat-treated, generally, as the processing temperature is increased, the surface spacing of the obtained conductive carbon is reduced, and the structure tends to approach graphite. That is, conductive carbon with higher corrosion resistance is produced by heat treatment at a higher temperature. Based on this tendency, in order to produce the conductive carbon (A), (B), and (C) contained in the electrode catalyst layer of the present invention, the raw material of the conductive carbon (C), the conductive carbon (B) The raw material and the conductive carbon (A) raw material may be heat-treated by increasing the processing temperature in this order.

  Specific conditions for producing the conductive carbon used in the present invention by heat-treating the conductive carbon material are not particularly limited, and can be appropriately determined based on the knowledge already obtained. For example, the treatment temperature is preferably 1000 ° C. or higher when the conductive carbon (A) is produced. Moreover, when manufacturing electroconductive carbon (B), Preferably it is 500-1000 degreeC. Furthermore, when manufacturing electroconductive carbon (C), Preferably it is less than 500 degreeC. Moreover, it is preferable that processing atmosphere is inert gas atmosphere, such as nitrogen gas, helium gas, and argon gas.

  Note that conductive carbon such as carbon black has a functional group such as a carboxyl group on its surface and is further oxidized to some extent in air even at room temperature. When the surface of the conductive carbon is oxidized, the supported catalyst active material particles may be detached during the operation of the fuel cell. By heat-treating the conductive carbon, the functional group present on the surface is removed, and the effect that the interface between the conductive carbon and the catalyst active material is chemically stabilized is also obtained.

  The catalytic active material is required to exhibit a catalytic action with respect to an oxidation reaction of hydrogen and / or a reduction reaction of oxygen. Examples of the catalyst active material include platinum, iridium, silver, palladium, ruthenium, rhodium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, copper and the like, and these And the like. From the viewpoint of catalytic activity, platinum, iridium, silver and palladium are preferably used. These catalyst active materials are contained in the electrode catalyst layer in a state of being supported on conductive carbon as a carrier as catalyst active material particles.

The particle diameter of the catalyst active material particles supported on the conductive carbon is generally about 1 to 30 nm, preferably 1.5 to 10 nm. From the viewpoint of ease of loading, it is preferably 1 nm or more, and from the viewpoint of catalyst utilization, it is preferably 20 nm or less. However, in some cases, the particle diameter may be out of this range. The mass of the catalyst active material per unit area of the electrode catalyst layer is usually about 0.01 to 5 mg / cm ² , preferably 0.1 to 1 mg / cm ² . If the mass of the catalyst active material is less than 0.01 mg / cm ² , the catalyst performance may be deteriorated. On the other hand, if the supported amount exceeds 5 mg / cm ² , an effect corresponding to the supported amount cannot be obtained. , The cost increases.

  The method for supporting the catalyst active material on the conductive carbon is not particularly limited, and a conventionally used method can be appropriately employed. For example, methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle method (microemulsion method) and the like can be used.

  Note that the combination of the catalyst active material and the conductive carbon when the catalyst active material is supported on the conductive carbon is not particularly limited. Based on the conventionally known knowledge about the corrosion resistance of the catalyst active material, the catalyst active material having high corrosion resistance is supported on the conductive carbon having a small face spacing and high corrosion resistance, and the catalyst activity having low corrosion resistance is provided on the conductive carbon having a large face spacing and low corrosion resistance. A substance may be carried or vice versa. From the viewpoint of suppressing a decrease in catalytic activity when the conductive carbon deteriorates, a catalytic active material having low corrosion resistance may be supported on the conductive carbon having a large interplanar spacing and low corrosion resistance.

  In the present invention, the catalyst active material may not be supported on all three types of conductive carbon contained in the electrode catalyst layer. That is, one or two of the three kinds of conductive carbon may not carry a catalyst active material. Moreover, when the conductive carbon which does not carry | support a catalyst active material is contained, it is preferable that the conductive carbon which does not carry a catalyst active material is conductive carbon with low corrosion resistance. That is, when there is only one kind of conductive carbon that does not support the catalyst active material, the conductive carbon that does not support the catalyst active material is preferably conductive carbon (C) having the largest interplanar spacing. In addition, when there are two types of conductive carbons that do not carry the catalyst active material, the conductive carbons that do not carry the catalyst active material are the conductive carbon (C) having the largest face spacing and the next largest face spacing. The conductive carbon (B) is preferable. When a large amount of the catalyst active material is supported by the conductive carbon having high corrosion resistance, a decrease in the catalyst activity when the conductive carbon is corroded can be suppressed. From the viewpoint of further improving the catalytic activity, it is preferable that the conductive carbon not supporting the catalytic active material is one kind. In other words, in the MEA of the present invention, the conductive carbon (A) and the conductive carbon (B) carry a catalyst active material, and the conductive carbon (C) does not carry a catalyst active material. It is preferable.

  In the MEA of the present invention, the structure of the electrode catalyst layer is particularly limited as long as it includes at least three kinds of conductive carbons (conductive carbons (A), (B), and (C)) having different face spacings. Alternatively, a uniform electrode catalyst layer may be used. However, preferably, the electrode catalyst layer containing conductive carbon is composed of two layers stacked in the direction in which the MEA components are stacked, and the two layers constituting the electrode catalyst layer are the polymer electrolyte. A layer containing the conductive carbon (B) disposed on the membrane side, and a layer containing the conductive carbon (A) and the conductive carbon (C) disposed on the gas diffusion layer side; Consists of.

  FIG. 2 is a schematic cross-sectional view showing a preferred embodiment as described above in the MEA of the present invention.

  The electrode catalyst layers (120a, 120c) are each composed of a first catalyst layer (121a, 121c) and a second catalyst layer (122a, 122c). The first catalyst layer 121a and the second catalyst layer 122a, and the first catalyst layer 121c and the second catalyst layer 122c are laminated in the direction in which the components of the MEA 10 are laminated. Furthermore, the first catalyst layers (121a, 121c) are disposed on the polymer electrolyte membrane 110 side and contain conductive carbon (B). On the other hand, the second catalyst layer (122a, 122c) is disposed on the gas diffusion layer (GDL) (130a, 130c) side, and includes conductive carbon (A) and conductive carbon (C).

  According to the form shown in FIG. 2, the first catalyst layer (121a, 121c) on the polymer electrolyte membrane 110 side contains conductive carbon (B) that can provide excellent catalytic activity. Thereby, improvement of battery performance is expected. On the other hand, in the second catalyst layer (122a, 122c) adjacent to the first catalyst layer (121a, 121c), the conductive carbon (A) having excellent corrosion resistance and the conductive carbon (C) that can function as a sacrificial component. )It is included. For this reason, in the second catalyst layer (122a, 122c), the conductive carbon (C) is preferentially deteriorated, so that the deterioration of the conductive carbon (A) is suppressed, and the deterioration of the entire MEA is prevented. sell. Also in the embodiment shown in FIG. 2, as described above, the conductive carbon (A) and the conductive carbon (B) carry the catalyst active material, and the conductive carbon (C) carries the catalyst active material. Preferably not.

  Although FIG. 2 shows a form in which the electrode catalyst layers on both the anode side and the cathode side are composed of two layers, it is not limited to such a form, and only one of them may be composed of two layers. Each electrode catalyst layer may be composed of three or more layers. In this case, the innermost layer adjacent to the polymer electrolyte membrane contains conductive carbon (B), and the outermost layer adjacent to the GDL is conductive. The conductive carbon (A) and the conductive carbon (C) are preferably contained. However, the present invention is not limited to such a form, and various improvements may be made.

  The electrode catalyst layer includes a proton conductive polymer. As the proton conductive polymer, the same polymer as the polymer electrolyte membrane can be used. By including a proton conductive polymer in the electrode catalyst layer, protons generated around the anode-side catalyst active material are transported to the polymer electrolyte membrane, and this proton is further transferred to the cathode-side catalyst active material. And can be transported.

  The electrode catalyst layer may contain other components. For example, a water repellent polymer such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer can be included in the electrode catalyst layer.

  The thickness of the electrode catalyst layer is not particularly limited, but is generally about 1 to 30 μm. If the thickness of the electrode catalyst layer is too thin, uniform film formation is difficult and sufficient functions may not be obtained. On the other hand, if it is too thick, water tends to stay in the catalyst layer, and there is a possibility that it cannot be drained efficiently. Furthermore, the gas diffusibility is lowered and the resistance of the catalyst layer is increased, which may result in failure to obtain good battery performance. As shown in FIG. 2, when the electrode catalyst layer consists of two layers, the ratio of the thickness of the first catalyst layer disposed on the polymer electrolyte membrane side to the thickness of the second catalyst layer disposed on the GDL side Although it does not restrict | limit in particular, Preferably it is about 0.1-9, More preferably, it is 0.8-4.5. If the first catalyst layer is too thin as compared with the second catalyst layer, the corrosion resistance is improved, but good battery performance may not be obtained. On the other hand, if the first catalyst layer is too thick compared to the second catalyst layer, good battery performance is easily obtained, but the proportion of the anti-corrosion characteristics in all electrode catalyst layers is small, and thus the durability is lowered. There is a fear.

  There are no particular limitations on the amount of conductive carbon, catalyst active material, and proton conductive polymer in the electrode catalyst layer. An appropriate blending amount may be determined based on the knowledge already obtained.

  In the present invention, the electrode catalyst layer contains at least three kinds of conductive carbons (conductive carbons (A), (B), and (C)) having different face spacings. The ratio of the blending amounts of these three types of conductive carbon is not particularly limited, and can be appropriately determined in consideration of desired characteristics and the like. Considering the balance between the corrosion resistance of the electrode catalyst layer and the catalyst performance, the mass ratio X of the conductive carbon (B) to the total amount of the conductive carbon (B) and the conductive carbon (A) is preferably 0.00. 3 ≦ X ≦ 0.9, and more preferably 0.4 ≦ X ≦ 0.85. Here, if X <0.3, the catalyst performance may be reduced. On the other hand, if X> 0.9, the corrosion resistance of the electrode catalyst layer may be reduced. The mass ratio Y of the conductive carbon (A) to the total amount of the conductive carbon (A) and the conductive carbon (C) is preferably 0.5 ≦ Y <1.0, more preferably 0.6 ≦ Y ≦ 0.9. If Y <0.5, the amount of the conductive carbon (C) having a small interplanar spacing and low corrosion resistance is relatively increased. As a result, the corrosion resistance of the electrode catalyst layer may be lowered as a whole. This is particularly noticeable in the embodiment shown in FIG.

  The concentration of the proton conductive polymer contained in the electrode catalyst layer preferably increases from the adjacent GDL to the polymer electrolyte membrane. That is, the concentration of the proton conductive polymer contained in the electrode catalyst layer increases as it approaches the polymer electrolyte membrane from the GDL. The method of increasing the concentration may be stepwise or continuous. In the case where the electrode catalyst layer is composed of two layers as in the embodiment shown in FIG. 2, the production is easy if the concentration of the proton conductive polymer is changed for each layer constituting the electrode catalyst layer. . As the concentration of the proton conducting polymer in the electrode catalyst layer increases, the proton transfer resistance decreases. For this reason, sufficient proton conductivity is ensured in the part close to the polymer electrolyte membrane by increasing the concentration of the proton conducting polymer. On the other hand, when the concentration of the proton conductive polymer is increased, gas diffusibility and drainage may be deteriorated. For this reason, in the part close | similar to GDL, it is good to reduce the density | concentration of a proton conductive polymer, and to ensure gas diffusibility and drainage.

  The gas diffusion layers (GDL) (130a, 130c) are generally made of a porous material, and the gas supplied to the fuel cell is dispersed by the porous GDL and supplied to the electrode catalyst layers (120a, 120c). The The GDL (130a, 130c) is disposed so that the polymer electrolyte membrane 110 and the electrode catalyst layers (120a, 120c) are sandwiched between the surfaces of the electrode catalyst layers (120a, 120c) facing the polymer electrolyte membrane 110. . That is, the GDL 130a is disposed on the surface of the electrode catalyst layer 120a opposite to the surface on which the polymer electrolyte membrane 110 is disposed. The GDL 130c is disposed on the surface of the electrode catalyst layer 120c opposite to the surface on which the polymer electrolyte membrane 110 is disposed. As a whole, the polymer electrolyte membrane 110 and the electrode catalyst layers (120a, 120c) are sandwiched between the GDL 130a and the GDL 130c. As a result, a laminate in which GDL 130a / electrode catalyst layer 120a / polymer electrolyte membrane 110 / electrode catalyst layer 120c / GDL 130c are arranged in this order is obtained.

  As a material used for GDL (130a, 130c), a sheet-like material made of carbon paper, carbon cloth, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. GDL is also required to have functions such as electron conductivity and water repellency. When GDL has excellent electron conductivity, efficient transport of electrons generated by the power generation reaction is achieved, and the performance of the fuel cell is improved. Moreover, if GDL has excellent water repellency, the generated water is efficiently discharged.

  In order to ensure high water repellency, a technique for water repellency treatment of a material constituting the GDL has also been proposed. For example, a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting GDL such as carbon paper and dried in the air or an inert gas such as nitrogen. Depending on the case, the hydrophilization treatment may be performed on the material constituting the GDL. After drying, a carbon layer formed of carbon black powder and PTFE may be disposed.

  Various improvements may be applied to the GDL (130a, 130c) for the purpose of improving performance. For example, GDL gas diffusibility and compression resistance may be improved by forming a layer composed of a fluororesin and carbon black on the surface of the carbon fiber woven fabric (for example, JP-A-10-261421). No. JP, 11-273688, A).

  The MEA production method of the present invention is not particularly limited, and a conventionally known method can be appropriately employed. As an example, first, conductive carbon (for example, conductive carbon (A) and conductive carbon (B) having a catalyst active material supported on a catalytic active material, a proton-conductive polymer, Is added to a solvent such as water or an alcohol-based solvent to prepare an electrode catalyst layer ink, which contains conductive carbon (for example, conductive carbon (C)) that does not carry a catalyst active material. The obtained electrode catalyst layer ink is applied to the anode side of the polymer electrolyte membrane 110 and dried to form the electrode catalyst layer 120a, in which case the application means is not particularly limited. Conventionally known means such as a die coater method, a screen printing method, a doctor blade method, a spray method, etc. can be used, and the electrode catalyst layer ink is also applied to the cathode side of the polymer electrolyte membrane 110. The electrode catalyst layer 120c is formed by drying, and when the MEA is manufactured, when forming a certain layer, a desired layer is formed on a predetermined sheet such as polytetrafluoroethylene (PTFE). Thereafter, the desired layer may be formed by transferring the layer to a surface on which the layer is desired and peeling the sheet.

The obtained laminate is sandwiched between two GDLs (130a, 130c) and hot pressed to produce the MEA of the present invention. At this time, the hot pressing is preferably performed at a temperature of 120 to 150 ° C. and a pressure of 5 to 50 kgf / cm ² with respect to the electrode surface. Thereby, the bondability between the polymer electrolyte membrane and the electrode catalyst layer can be improved.

  For example, the electrode catalyst layer ink is applied to both the anode-side and cathode-side GDLs (130a, 130c) and dried to produce two laminates. The MEA may be manufactured by sandwiching the electrolyte membrane 110.

  When manufacturing the MEA having the form shown in FIG. 2, the manufacturing method is not particularly limited, and various methods can be employed based on the method described above. If the anode side is described as an example, first, an electrode catalyst layer ink for forming the first catalyst layer 121a is applied on the polymer electrolyte membrane 110 and dried to form the first catalyst layer 121a. Subsequently, the second catalyst layer 122a and the GDL 130a are formed in this order by the same method. Similarly, on the cathode side, a first catalyst layer 121c, a second catalyst layer 122c, and a gas diffusion layer 130c are formed in this order on the polymer electrolyte membrane 110. Finally, hot pressing is performed as described above, and the MEA having the configuration shown in FIG. 2 can be manufactured. Note that the present invention is not limited to such a form. For example, the first catalyst layer (121a, 121c) is formed on the polymer electrolyte membrane 110, and the second catalyst layer (122a, 122c) is formed on the GDL (130a, 130c). ), The first catalyst layer and the second catalyst layer are adjacent to each other (121a and 122a are adjacent, 121c and 122c are adjacent), and hot pressed. MEAs can be manufactured.

  The MEA of the present invention is used for the production of PEFC. When manufacturing PEFC, a pair of separators are arranged so as to sandwich the MEA of the present invention. That is, the second of the present invention is a PEFC having the MEA of the present invention and a pair of separators arranged so as to sandwich the MEA. In addition, various members can be installed in the PEFC as necessary. For example, a gasket that prevents leakage of gas supplied to the PEFC to the outside can be arranged.

  The separator has a function of transmitting current generated by the MEA to the adjacent fuel cell. When the PEFC is arranged at the end of a stack composed of a large number of PEFCs, current is taken out from the separator arranged at the outermost part, or current flows into the separator arranged at the outermost part.

  The separator is disposed so as to sandwich the polymer electrolyte membrane, the electrode catalyst layer, and the GDL on the surface facing the GDL catalyst layer. That is, one separator is arrange | positioned on the surface on the opposite side to the surface where the electrode catalyst layer 120a of GDL130a is arrange | positioned. The other separator is disposed on the surface opposite to the surface on which the electrode catalyst layer 120c of the GDL 130c is disposed. As a whole, the polymer electrolyte membrane 110, the electrode catalyst layers (120a, 120c), and the GDL (130a, 130c) are sandwiched by two separators. As a result, a laminate (PEFC) in which separator / GDL 130a / electrode catalyst layer 120a / polymer electrolyte membrane 110 / electrode catalyst layer 120c / GDL 130c / separator is arranged in this order is obtained.

  A gas channel is formed on the GDL side surface of the separator, and a predetermined gas is supplied to the gas channel. The gas flowing through the gas flow path flows into the GDL, is diffused by the GDL, and is finally supplied to the MEA. The gas flow path is also used to discharge water generated along with the power generation reaction in the MEA to the outside. The water produced by the MEA is transported to the gas flow path of the separator via the GDL, and is discharged outside the PEFC through the gas flow path. The gas flow path is formed by irregularities that the separator has on the surface on the GDL side.

  The method for producing PEFC is not particularly limited. Known techniques and newly obtained knowledge can be referred to as appropriate. The PEFC of the present invention can be used for various applications. In particular, the PEFC of the present invention is useful for applications requiring durability over a long period of time, for example, a vehicle or a stationary power source. That is, the third aspect of the present invention is a vehicle equipped with the PEFC of the present invention.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following embodiment only illustrates one embodiment, and the technical scope of the present invention is not limited to the following form.

In the following examples, the lattice spacing (d) measured by the Gakushin method (Michio Inagaki, Carbon No. 36, 25-34 (1963)) using X-ray diffraction (XRD) as conductive carbon. _The following three types of carbon black having different values of ( ₀₀₂ ) were used.
Carbon black (A): carbon black obtained by heat-treating Vulcan XC72R (manufactured by Cabot) at 2700 ° C. (specific surface area: 70 m ² / g, lattice spacing (d ₀₀₂ ): 3.43 mm)
Carbon black (B): carbon black obtained by heat-treating Vulcan XC72R (manufactured by Cabot) at 800 ° C. (specific surface area: 220 m ² / g, lattice spacing (d ₀₀₂ ): 3.63 mm)
Carbon black (C): carbon black obtained by heat-treating Black Pearl 2000 (manufactured by Cabot) at 400 ° C. (specific surface area: 1500 m ² / g, lattice spacing (d ₀₀₂ ): 3.69 mm)
<Example 1>
By the method described below, an MEA having an electrode catalyst layer composed of two layers on both the anode side and the cathode side was produced.

  Carbon black (B) carrying platinum (Pt, average particle diameter 3 nm) as a catalyst active material was prepared. The mass ratio of platinum as the catalyst active material and carbon black (B) as the conductive carbon was 50:50. To this, a Nafion aqueous solution (5% by mass Nafion solution manufactured by Aldrich) having an ion exchange capacity of 1100 g / ew as a proton conductive polymer and ethylene glycol are added and mixed to form conductive carbon (carbon black (B)). Electrode catalyst layer ink A containing a catalyst active material and a proton conductive polymer was prepared.

On one side of a proton conductive polymer electrolyte membrane (DuPont, Nafion 112, film thickness: 50 μm), the amount of platinum supported is 0.30 mg / cm ² , the catalyst layer thickness is 5 μm, and the coating area is 50 × 50 mm. Then, the electrode catalyst layer ink A was applied by a die coater method. After coating, the coating film was air-dried, and an electrode catalyst layer (cathode side first catalyst layer) was formed on the cathode side of the proton conducting polymer electrolyte membrane. Using the same method, an electrode having a platinum loading of 0.30 mg / cm ² , a catalyst layer thickness of 8 μm, and a coating area of 50 × 50 mm on the opposite side (anode side) of the proton conductive polymer electrolyte membrane A catalyst layer (anode-side first catalyst layer) was formed. In each first catalyst layer formed as described above, the mass ratio of proton conductive polymer to conductive carbon (carbon black (B) supporting platinum) (mass of proton conductive polymer / conductive carbon). ) Was 0.85.

  As the gas diffusion layer of the electrode, a carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.) cut out to 55 × 55 mm was prepared on both the anode side and the cathode side. The carbon paper was subjected to water repellent treatment by immersing it in a solution obtained by diluting an aqueous dispersion of fluororesin (D1 manufactured by Daikin Industries, Ltd.) with pure water for 2 minutes and then drying at 60 ° C. for 10 minutes. The carbon paper after the water repellent treatment was impregnated with 25% by mass of tetrafluoroethylene particles.

  Subsequently, carbon black (A) carrying platinum (Pt, average particle diameter 3 nm) as a catalyst active material was prepared. The mass ratio of platinum as the catalyst active material and carbon black (A) as the conductive carbon was 50:50. Carbon black (C) which does not carry a catalyst active material, Nafion aqueous solution (5% by mass Nafion solution manufactured by Aldrich) having an ion exchange capacity of 1100 g / ew, which is a proton conductive polymer, and ethylene glycol In addition, an electrode catalyst layer ink B containing conductive carbon (carbon black (A) and carbon black (C)), a catalyst active material, and a proton conductive polymer was prepared by mixing.

On one side of the water-repellent treated carbon paper (cathode side) produced above, the platinum loading amount is 0.10 mg / cm ² , the catalyst layer thickness is 4 μm, and the carbon black (C) content is 0.05 mg / cm ² . Electrode catalyst layer ink B was applied by a spray method so as to be cm ² . After coating, the coating film was air-dried to obtain a gas diffusion substrate having an electrode catalyst layer (cathode side second catalyst layer) on one side. Using a similar method, the electrode catalyst layer ink B is applied to one side of the carbon paper (anode side) after the water repellent treatment, and a gas diffusion substrate having an electrode catalyst layer (anode side second catalyst layer) on one side is obtained. It was. In each of the second catalyst layers formed as described above, the mass ratio of proton conductive polymer to conductive carbon (carbon black (B) supporting platinum) (mass of proton conductive polymer / conductive carbon). ) Was 0.85.

Next, the laminated body in which the electrode catalyst layer is formed on both sides of the proton conductive polymer electrolyte membrane and the gas diffusion substrate are arranged so that the first catalyst layer and the second catalyst layer are adjacent to each other on the cathode side and the anode side. The MEA was manufactured by placing the film on the substrate and hot pressing it under conditions of 120 ° C. and 20 kgf / cm ² for 1 minute. About the produced MEA, the performance (initial cell voltage and cell voltage holding ratio) as a fuel cell was evaluated. The results are shown in Table 1. Table 1 shows the value of the mass ratio X of the conductive carbon (B) to the total amount of the conductive carbon (B) and the conductive carbon (A), and the conductive carbon (A) and the conductive carbon. The value of the mass ratio Y of the conductive carbon (A) to the total amount with the carbon (C) is also shown.

The initial cell voltage was evaluated by measuring the cell voltage when power was generated at a current density of 1.0 A / cm ² under conditions of atmospheric pressure and cell temperature of 70 ° C. Hydrogen gas was supplied as the fuel gas, and air was supplied as the oxidant. Both gases were humidified at 60 ° C. and then supplied to the cell.

  The cell voltage holding ratio was evaluated by the following procedure. After continuous power generation for 1 hour under the same conditions as those for evaluating the initial cell voltage, power generation was terminated. After power generation was completed, the cell was purged with nitrogen for 10 minutes for both the anode and cathode. The cell was left for 1 hour and continuously operated again under the same conditions. With this series of operations as conditions for starting and stopping, the cell voltage holding ratio of the cell voltage after repeating the starting and stopping 1000 times with respect to the initial cell voltage {(cell voltage after starting and stopping 1000 times / initial cell voltage) × 100 ( %)} Was calculated. The higher the cell voltage holding ratio, the better the durability.

<Example 2>
In both the anode side and cathode side first catalyst layers, the carbon black (B) content is 0.24 mg / cm ^2, and in both second catalyst layers, the carbon black (A) content is 0.16 mg. An MEA was produced in the same manner as in Example 1 except that the density was set to / cm ^2, and the performance as a fuel cell was evaluated. The results are shown in Table 1.

<Example 3>
In both the anode side and cathode side first catalyst layers, the carbon black (B) content is 0.20 mg / cm ^2, and in both second catalyst layers, the carbon black (A) content is 0.20 mg. An MEA was produced in the same manner as in Example 1 except that the density was set to / cm ^2, and the performance as a fuel cell was evaluated. The results are shown in Table 1.

<Example 4>
In both the anode side and cathode side first catalyst layers, the carbon black (B) content is 0.16 mg / cm ^2, and in both second catalyst layers, the carbon black (A) content is 0.24 mg. An MEA was produced in the same manner as in Example 1 except that the density was set to / cm ^2, and the performance as a fuel cell was evaluated. The results are shown in Table 1.

<Example 5>
In the first catalyst layer on both the anode side and the cathode side, the carbon black (B) content is 0.37 mg / cm ^2, and in both the second catalyst layers, the carbon black (A) content is 0.03 mg. An MEA was produced in the same manner as in Example 1 except that the density was set to / cm ^2, and the performance as a fuel cell was evaluated. The results are shown in Table 1.

<Example 6>
In both the anode side and cathode side first catalyst layers, the carbon black (B) content is 0.10 mg / cm ^2, and in both second catalyst layers, the carbon black (A) content is 0.30 mg. An MEA was produced in the same manner as in Example 1 except that the density was set to / cm ^2, and the performance as a fuel cell was evaluated. The results are shown in Table 1.

<Comparative Example 1>
In the first catalyst layer on both the anode side and the cathode side, the content of carbon black (B) was set to 0.40 mg / cm ^2, and both the second catalyst layers were not formed. The MEA was produced by the method described above, and the performance as a fuel cell was evaluated. The results are shown in Table 1.

<Comparative example 2>
The carbon black (B) content is 0.40 mg / cm ² in the first catalyst layer on both the anode side and the cathode side, and platinum and carbon black (A) are not contained in both the second catalyst layers. An MEA was produced by the same method as in Example 1 except that only carbon black (C) was contained at a content of 0.05 mg / cm ² , and the performance as a fuel cell was evaluated. The results are shown in Table 1.

  As can be seen from Table 1, the PEFC including the MEA of the present invention has a high cell voltage holding ratio. Therefore, it is excellent in durability over a long period of time.

It is a cross-sectional schematic diagram of one Embodiment of MEA of this invention. It is a cross-sectional schematic diagram of other embodiment of MEA of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Membrane electrode assembly, 110 ... Polymer electrolyte membrane, 120a ... Anode side electrode catalyst layer, 120c ... Cathode side electrode catalyst layer, 130a ... Anode side gas diffusion layer, 130c ... Cathode side gas diffusion layer

Claims (11)

A polymer electrolyte membrane;
A pair of electrode catalyst layers sandwiching the polymer electrolyte membrane;
A membrane electrode assembly comprising: a surface of the electrode catalyst layer facing the polymer electrolyte membrane; and a pair of gas diffusion layers disposed so as to sandwich the polymer electrolyte membrane and the electrode catalyst layer. There,
The electrode catalyst layer includes conductive carbon, a catalytic active material supported on the conductive carbon, and a proton conductive polymer,
At least one of the electrode catalyst layers includes at least conductive carbon (A), conductive carbon (B) having a lattice spacing (d ₀₀₂ ) value greater than the conductive carbon (A), and lattice spacing. A membrane electrode assembly comprising conductive carbon (C) having a value of (d ₀₀₂ ) greater than the conductive carbon (B).   The conductive carbon (A) and the conductive carbon (B) are loaded with the catalytic active material, and the conductive carbon (C) is not loaded with the catalytic active material. The membrane electrode assembly as described. The electrode catalyst layer containing conductive carbon consists of two layers laminated in the direction in which the constituent elements of the membrane electrode assembly are laminated,
The two layers constituting the electrode catalyst layer are disposed on the polymer electrolyte membrane side, the layer containing the conductive carbon (B), and the conductive layer disposed on the gas diffusion layer side. The membrane electrode assembly according to claim 1 or 2, comprising a layer containing carbon (A) and the conductive carbon (C). The value of the lattice spacing _{(d 002)} having the electrically conductive carbon (B) is a 3.48～3.66A, membrane electrode assembly according to any one of claims 1-3. The value of the lattice spacing _{(d 002)} having the electrically conductive carbon (A) is less than 3.48A, the membrane electrode assembly according to any one of claims 1 to 4. The value of the lattice spacing _{(d 002)} having the electrically conductive carbon (C) is, 3.66A larger, membrane electrode assembly according to any one of claims 1-5.   The membrane electrode assembly according to any one of claims 1 to 6, wherein the catalytic active material contains one or more metals selected from the group consisting of platinum, iridium, silver, and palladium. .   The mass ratio X of the conductive carbon (B) to the total amount of the conductive carbon (A) and the conductive carbon (B) is 0.3 ≦ X ≦ 0.9. The membrane electrode assembly according to any one of the above.   The mass ratio Y of the conductive carbon (A) to the total amount of the conductive carbon (A) and the conductive carbon (C) is 0.5 ≦ Y <1.0. The membrane electrode assembly according to any one of the above. The membrane electrode assembly according to any one of claims 1 to 9,
A solid polymer fuel cell comprising: a pair of separators disposed so as to sandwich the membrane electrode assembly.   A vehicle on which the polymer electrolyte fuel cell according to claim 10 is mounted.

Images