JP2010027360A - Polymer electrolyte membrane, and membrane electrode assembly using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means of suppressing occurrence of cross leak of a supplied gas and various problems accompanying this in a fuel cell. <P>SOLUTION: A polymer electrolyte membrane has a sheet-like substrate composed of a polymer electrolyte and an intermediate layer arranged parallel to the surface direction of the sheet-like substrate in the substrate. Then, this intermediate layer contains a hydrogen oxidation catalyst, a proton reduction catalyst, a polymer electrolyte and an electron conductor, and has a structure in which a hydrogen gas passage is formed in the thickness direction of the sheet-like substrate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte membrane and a membrane electrode assembly (MEA) using the polymer electrolyte membrane. In particular, the present invention relates to an improvement for suppressing a decrease in electromotive force of a fuel cell when used in a fuel cell.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. 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. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The PEFC generally has a structure in which an MEA is sandwiched between separators. The MEA has a structure in which the electrode catalyst layer is disposed so as to face both surfaces of the solid polymer electrolyte membrane, and the gas diffusion layer is sandwiched between the electrode catalyst layers.

In the PEFC having the MEA as described above, the following reaction formulas are applied to both electrode catalyst layers (the anode (hydrogen electrode) catalyst layer and the cathode (oxygen electrode) catalyst layer) sandwiching the solid polymer electrolyte membrane according to the polarity. The electrode reaction shown in FIG. First, hydrogen contained in the fuel gas supplied to the anode side is oxidized by the catalyst component in the anode catalyst layer to generate protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated proton is accompanied by a polymer electrolyte contained in the electrode catalyst layer (hereinafter also referred to as “ionomer”) and a solid polymer electrolyte membrane in contact with the electrode catalyst layer, accompanied by several water molecules. And reaches the cathode catalyst layer. Further, the electrons generated in the anode catalyst layer pass through the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer in contact with the side of the electrode catalyst layer different from the solid polymer electrolyte membrane, the separator, and the external circuit. To the cathode catalyst layer. The protons and electrons that have reached the cathode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O: Reaction 2 ). In PEFC, electricity can be taken out through the above-described electrochemical reaction.

  The performance required for the solid polymer electrolyte membrane (hereinafter also simply referred to as “electrolyte membrane”) constituting the PEFC is diverse. For example, the proton conductivity is excellent and the permeation of fuel and oxygen (cross leak, cross over) can be blocked.

  Here, the perfluorocarbon sulfonic acid polymer electrolyte membrane that is most commonly used as an electrolyte membrane has a problem in that the performance of blocking the above-described cross leak is not sufficient. When fuel or oxygen cross-leakage occurs in the electrolyte membrane, the electrode potential deviates from the equilibrium potential, resulting in a problem that output voltage and energy efficiency are lowered.

  As a technique for solving such a problem, a technique described in Patent Document 1 can be cited. Patent Document 1 discloses a technique in which an oxidation catalyst layer that oxidizes leaked hydrogen and a reduction catalyst layer that reduces leaked oxygen are arranged on an ion conductor such as an electrolyte membrane in a state of being separated from each other. ing. By adopting such a configuration, hydrogen and oxygen leaking from both poles are reacted in the oxidation catalyst layer and the reduction catalyst layer, respectively, and converted to water, thereby attempting to suppress performance degradation due to cross leakage.

According to the technique described in Patent Document 1 described above, it is considered possible to suppress to some extent the cross leak of hydrogen and oxygen itself and the problems caused by this. However, there is still a problem that the electromotive force obtained is not sufficient.
JP 2005-149939 A

  An object of the present invention is to provide means capable of suppressing the occurrence of cross-leakage of supplied gas and various problems associated therewith in a fuel cell.

  The inventors searched for a cause in which the electromotive force obtained in the technique described in Patent Document 1 is not sufficient despite taking countermeasures for preventing cross leaks. As a result, it was found that the proton transfer resistance in the electrolyte membrane was increased by providing the oxidation catalyst layer / reduction catalyst layer inside the electrolyte membrane. Further research was carried out under the hypothesis that the internal resistance of PEFC increased due to such an increase in proton transfer resistance, causing a decrease in electromotive force. As a result, it has been found that the proton transfer resistance in the electrolyte membrane can be reduced by configuring the electrolyte membrane as follows, and the present invention has been completed.

  That is, the polymer electrolyte membrane of the present invention for solving the above-mentioned problems is arranged in a sheet-like substrate made of a polymer electrolyte and in the sheet-like substrate in parallel with the surface direction of the sheet-like substrate. And an intermediate layer. The intermediate layer includes a hydrogen oxidation catalyst, a proton reduction catalyst, a polymer electrolyte, and an electronic conductor, and has a configuration in which a hydrogen gas flow path is formed in the thickness direction of the sheet-like substrate.

  According to the present invention, in a fuel cell, it is possible to suppress the occurrence of cross leaks of supplied gas and various problems associated therewith.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following forms. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

[MEA (membrane electrode assembly)]
FIG. 1 is a schematic cross-sectional view schematically showing a general overall structure of an MEA 100 according to an embodiment of the present invention. The MEA 100 of this embodiment can be used as a constituent element of a polymer electrolyte fuel cell (PEFC) described later, for example.

  As shown in FIG. 1, the MEA 100 of the present embodiment first includes a polymer electrolyte membrane 110 at the center thereof. The polymer electrolyte membrane 110 includes a sheet-like base material 111 made of a polymer electrolyte, and an intermediate layer 112 disposed in the sheet-like base material 111 in parallel with the surface direction of the sheet-like base material 111. Details of the intermediate layer 112 will be described later. Further, depending on the manufacturing method, the intermediate layer 112 and other parts constituting the polymer electrolyte membrane 110 may be separately prepared and prepared, and the polymer electrolyte membrane 110 may be manufactured by bonding them together. is there. Even in such a case, as long as the intermediate layer 112 and the sheet-like base material 111 are bonded via the polymer electrolyte, the “intermediate layer is disposed in the sheet-like base material”. .

  An anode catalyst layer 120 a is disposed on one surface of the polymer electrolyte membrane 110. On the other hand, the cathode catalyst layer 120 c is disposed on the other surface of the polymer electrolyte membrane 110. Further, these laminates are sandwiched between a pair of gas diffusion layers (anode-side gas diffusion layer 140a and cathode-side gas diffusion layer 140c). Hereinafter, although each member which comprises MEA of this embodiment is demonstrated in order, the technical scope of this invention is not restrict | limited only to the following form.

(Polymer electrolyte membrane)
The polymer electrolyte membrane 110 functions as a partition that physically separates the anode catalyst layer 120a and the cathode catalyst layer 120c, and prevents mixing of the fuel gas and the oxidant gas. The polymer electrolyte membrane 110 also has a function of selectively allowing protons generated in the anode catalyst layer 120a during the PEFC operation to permeate the cathode catalyst layer 120c along the thickness direction of the electrolyte membrane.

  As described above, the polymer electrolyte membrane 110 has the sheet-like substrate 111 made of a polymer electrolyte. As the sheet-like substrate 111, a polymer electrolyte membrane used in a conventional PEFC can be used as it is. There is no restriction | limiting in particular about the specific structure of the polymer electrolyte which comprises the sheet-like base material 111, A conventionally well-known material can be used suitably as a constituent material of the electrolyte membrane which comprises PEFC. Here, the polymer electrolyte constituting the sheet-like substrate 111 is roughly classified into a fluorine-based solid polymer electrolyte and a hydrocarbon-based solid polymer electrolyte according to the type of polymer electrolyte that is a constituent material.

  Examples of the fluorine-based solid polymer electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-perfluorocarbon sulfonic acid polymer Etc. From the viewpoint of power generation performance such as heat resistance and chemical stability, these fluorine-based solid polymer electrolytes are preferably used, and more preferably perfluorocarbon sulfonic acid polymers are used.

  Examples of the hydrocarbon solid polymer electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated. Examples include polyetheretherketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based solid polymer electrolytes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high.

  Materials other than the polymer electrolyte described above may be used as the polymer electrolyte. As such materials, for example, liquids, solids, and gel materials having high proton conductivity can be used, and solid acids such as phosphoric acid, sulfuric acid, antimonic acid, stannic acid, and heteropoly acid, phosphoric acid, and the like. Hydrocarbon polymer compound doped with a non-organic acid, organic / inorganic hybrid polymer partially substituted with proton conductive functional group, gel impregnated with phosphoric acid solution or sulfuric acid solution in polymer matrix And the like proton conductive material. A mixed conductor having both proton conductivity and electron conductivity can also be used as a polymer electrolyte. In addition, as for the various polymer electrolytes mentioned above, only 1 type may be used independently and 2 or more types may be used together.

  The ion exchange capacity of the polymer electrolyte is preferably 0.8 to 1.5 mmol / g, and more preferably 1.0 to 1.5 mmol / g, from the viewpoint of excellent ion conductivity. The “ion exchange capacity” of the polymer electrolyte means the number of moles of sulfonic acid groups per unit dry mass of the polymer electrolyte. The value of “ion exchange capacity” can be calculated by removing the dispersion medium of the polymer electrolyte dispersion by heat drying or the like to obtain a solid polymer electrolyte, and performing neutralization titration.

  The thickness of the sheet-like substrate 111 (distance from the end of the anode catalyst layer 120a to the end of the cathode catalyst layer 120c) is appropriately determined in consideration of the characteristics of the MEA and the polymer electrolyte, and is not particularly limited. However, the thickness of the sheet-like substrate 111 is preferably 5 to 300 μm, more preferably 5 to 200 μm, still more preferably 10 to 150 μm, and particularly preferably 15 to 50 μm. When the thickness of the sheet-like substrate 111 is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

  In the MEA 100 of the present embodiment, the polymer electrolyte membrane 110 is characterized in that the sheet-like base material 111 further includes an intermediate layer 112 arranged in parallel to the surface direction of the sheet-like base material 111. . Hereinafter, the “intermediate layer 112” which is a characteristic configuration of the present invention will be described in detail.

  In the form shown in FIG. 1, the intermediate layer 112 is composed of three layers. Specifically, the proton reduction layer 113a is disposed at one end of the intermediate layer 112 in the thickness direction (the end on the anode side in FIG. 1). The proton reduction layer 113a includes a proton reduction catalyst (for example, a carbon support on which platinum is supported) formed by supporting a catalyst component on a conductive support. The conductive carrier constituting the catalyst also functions as an electron conductor for imparting conductivity to the intermediate layer 112. The proton reduction layer 113a includes the same polymer electrolyte that constitutes the sheet-like substrate 111. However, the polymer electrolyte contained in the intermediate layer 112 may be different from the constituent material of the sheet-like substrate 111.

  On the other hand, a hydrogen oxide layer 113c is disposed on the other end in the thickness direction of the intermediate layer 112 (end on the cathode side in FIG. 1). The hydrogen oxidation layer 113c includes a hydrogen oxidation catalyst (for example, a carbon support on which platinum is supported) formed by supporting a catalyst component on a conductive support. The conductive carrier constituting the catalyst also functions as an electron conductor for imparting conductivity to the intermediate layer 112. Further, the hydrogen oxide layer 113 c includes the same polymer electrolyte that constitutes the sheet-like substrate 111. Specific forms of the proton reduction catalyst and the hydrogen oxidation catalyst will be described later.

  Furthermore, in the form shown in FIG. 1, a catalyst-free layer 113n that does not include a proton reduction catalyst and a hydrogen oxidation catalyst is interposed between the proton reduction layer 113c and the hydrogen oxidation layer 113a. This catalyst-free layer 113n includes a polymer electrolyte similar to that described above and an electron conductor for imparting conductivity to the intermediate layer 112. Details of the electron conductor will also be described later.

  Although not shown in FIG. 1, in the MEA of the present embodiment, a hydrogen gas flow path is formed in the intermediate layer 112 in the thickness direction of the sheet-like substrate. Thereby, the hydrogen gas that is the fuel gas supplied to the anode side can diffuse at least in the entire intermediate layer 112.

  Here, the operation of the MEA 100 of the present embodiment in the form shown in FIG. 1 will be described in comparison with the operation of a conventional MEA having no intermediate layer.

  First, the case of a conventional MEA in which the polymer electrolyte membrane has a form of a membrane composed only of an electrolyte such as a perfluorocarbon sulfonic acid polymer will be described. As described in the background art section, during the operation of PEFC, protons generated by the reaction in the anode catalyst layer move through the polymer electrolyte membrane with several water molecules, and the cathode catalyst layer. (Right virtual line (two-dot chain line) shown in FIG. 1). At this time, there is a movement resistance for protons moving through the polymer electrolyte membrane. A voltage drop (IR loss) occurs due to the proton transfer resistance. For this reason, the potential in the polymer electrolyte membrane 110 of the conventional MEA decreases as it goes from the anode side to the cathode side, as shown by the phantom line in FIG. As a result, the electromotive force of PEFC decreases as the potential in the membrane decreases.

  According to the MEA 100 of the present embodiment, such a decrease in electromotive force can be suppressed. The mechanism will be described below, but the technical scope of the present invention is not limited by the following mechanism.

  As described above, in the MEA including the polymer electrolyte membrane that does not have the intermediate layer 112 as in the present invention, the potential in the membrane shows a gradient as indicated by the phantom line in FIG. 1 due to proton transfer resistance. . On the other hand, in the MEA 100 of the present embodiment, since the electron conductor exists throughout the intermediate layer 112, the potentials at arbitrary portions of the intermediate layer 112 should all be equal. Specifically, when the PEFC including the MEA 100 of the present embodiment is operated (electrically connected to an external load), the potential in the intermediate layer 112 is indicated by a virtual line as shown by a thick line in FIG. It should be the average of the intramembrane potential in a conventional MEA.

As a result, a negative potential difference occurs between the anode side end portion of the intermediate layer 112 (that is, the proton reduction layer 113a) and the sheet-like base material 111 made of the polymer electrolyte (“HER” shown in FIG. 1). ). When a negative potential difference is generated in this way, in the proton reduction layer 113a, the generated potential difference (specifically, a potential difference corresponding to the difference between the virtual line and the thick line shown in FIG. 1) is used as a driving force in a direction to cancel the potential difference. The reaction proceeds. Specifically, in order to cancel the negative potential difference, a proton reduction reaction (hydrogen generation reaction (HER); 2H ⁺ + 2e ⁻ → H ₂ ) that is a reaction (reduction reaction) that consumes electrons proceeds.

On the other hand, at the cathode side end portion of the intermediate layer 112 (that is, the hydrogen oxide layer 113c), a positive potential difference is generated between the intermediate substrate 112 and the sheet-like substrate 111 (“HOR” shown in FIG. 1). When a positive potential difference is generated in this way, in the hydrogen oxide layer 113c, the generated potential difference (specifically, a potential difference corresponding to the difference between the virtual line and the thick line shown in FIG. 1) is used as a driving force in a direction to cancel the potential difference. The reaction proceeds. Specifically, in order to cancel out the positive potential difference, a hydrogen oxidation reaction (HOR; H ₂ → 2H ⁺ + 2e ⁻ ) that is a reaction that generates electrons (oxidation reaction) proceeds. Note that the proton reduction reaction and the hydrogen oxidation reaction are in a reverse reaction relationship with each other.

  As described above, when the proton reduction reaction proceeds in the proton reduction layer 113a and protons are consumed, and when the hydrogen oxidation reaction proceeds in the hydrogen oxidation layer 113c and protons are generated, a proton concentration gradient occurs. Specifically, in the intermediate layer 112, a proton concentration gradient from the hydrogen oxidation layer 113c toward the proton reduction layer 113a is generated (a broken line rising to the right in the intermediate layer 112 in FIG. 1). When such a proton concentration gradient occurs, protons move through the intermediate layer 112 using the concentration gradient as a driving force (a broken line pointing leftward in FIG. 1).

  Then, the proton movement caused by the original battery reaction (right virtual line shown in FIG. 1) and the proton movement (left broken line shown in FIG. 1) caused by the configuration of the present embodiment cancel each other. As a result, in the intermediate layer 112, no apparent proton transfer is observed. Therefore, no voltage drop (IR loss) due to proton movement resistance occurs in the intermediate layer 112. That is, according to the present embodiment, the potential inside the polymer electrolyte membrane 110 is represented by the solid line shown in FIG. 1 without receiving the conventional voltage drop represented by the phantom line shown in FIG. It is kept relatively high. As a result, the decrease in the electromotive force of PEFC due to the voltage drop (IR loss) in the polymer electrolyte membrane 110 can be suppressed.

  In addition, the movement of water from the anode to the cathode accompanying the movement of protons can also occur between the intermediate layer and the cathode. For this reason, compared with the conventional MEA which does not have an intermediate | middle layer, the water of an anode is hard to be consumed. As a result, there is also an advantage that problems such as a decrease in power generation performance and deterioration due to drying of the anode can be prevented. Further, the MEA of the present application having an intermediate layer contains a large amount of hydrogen gas as a fuel between the anode and the intermediate layer or in the intermediate layer itself. For this reason, compared with the conventional MEA which does not have an intermediate | middle layer, the fuel deficiency in an anode does not arise easily. As a result, the occurrence of problems such as deterioration due to fuel shortage can be prevented.

  Hereinafter, although the specific structure of the intermediate | middle layer 112 in MEA100 of this embodiment is demonstrated in detail, the technical scope of this invention is not limited only to the following form.

  The proton reduction catalyst contained in the proton reduction layer 113a is a catalyst that can promote a proton reduction reaction (hydrogen generation reaction (HER)) represented by the following reaction formula 1.

  On the other hand, the hydrogen oxidation catalyst included in the hydrogen oxidation layer 113c is a catalyst that can promote a hydrogen oxidation reaction (HOR) represented by the following reaction formula 2, which is the reverse reaction of the proton reduction reaction.

  The specific forms of the proton reduction catalyst and the hydrogen oxidation catalyst are not particularly limited as long as each reaction described above can be promoted. As an example, the proton reduction catalyst and the hydrogen oxidation catalyst may have a configuration in which a catalyst component is supported on a conductive carrier. This is the same configuration as the electrode catalyst used in the catalyst layer constituting PEFC.

  The conductive carrier that can constitute the proton reduction catalyst and the hydrogen oxidation catalyst is not particularly limited, and a conductive carrier conventionally used for an electrode catalyst of PEFC can be similarly employed. Any conductive carrier may be used as long as it has a specific surface area sufficient to support the catalyst component in a desired dispersed state and sufficient electron conductivity. In the composition of the conductive carrier, the main component is preferably carbon. Specific examples of the material for the conductive carrier include carbon black, activated carbon, coke, natural graphite, and artificial graphite. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, “consisting essentially of carbon atoms” means that contamination of about 2 to 3% by mass or less of impurities can be allowed.

The BET (Brunauer-Emmet-Teller) specific surface area of the conductive carrier is not particularly limited as long as it is a specific surface area sufficient to carry the catalyst component in a highly dispersed state. BET specific surface area of the conductive support is preferably 100~1500m ² / g, more preferably 600~1000m ² / g. When the specific surface area of the conductive support is within this range, the balance between the dispersibility of the catalyst component on the conductive support and the effective utilization rate of the catalyst component can be appropriately controlled.

  Although there is no restriction | limiting in particular also about the average particle diameter of an electroconductive support | carrier, Usually, it is 5-200 nm, Preferably it is about 10-100 nm. As the value of “average particle diameter of conductive carrier”, a value calculated by a primary particle diameter measurement method using a transmission electron microscope (TEM) is employed.

  The catalyst component that can constitute the proton reduction catalyst and the hydrogen oxidation catalyst can also be used without limitation as long as the above-described reactions can be promoted. Specific examples of the catalyst component include platinum, palladium, iridium, carbon, silver, gold, rhodium, ruthenium, tin, silicon, titanium, zirconium, aluminum, hafnium, tantalum, niobium, cerium, and alloys thereof. By using these components as catalyst components, proton reduction reaction (HER) and hydrogen oxidation reaction (HOR) can proceed efficiently. Of these, the catalyst component preferably contains at least platinum from the viewpoint of excellent catalytic activity, elution resistance, and the like. The composition of the alloy when the alloy is used as a catalyst component of the proton reduction catalyst and the hydrogen oxidation catalyst varies depending on the type of metal to be alloyed and the like, and can be appropriately selected by those skilled in the art. However, platinum is preferably about 30 to 90 atomic%, and the other metal to be alloyed is about 10 to 70 atomic%. Note that an “alloy” is a general term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. Here, the alloy composition can be specified by using an ICP emission analysis method.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as those of conventionally known catalyst components can be appropriately employed. However, the shape of the catalyst component is preferably granular. And the average particle diameter of a catalyst component particle becomes like this. Preferably it is 0.5-30 nm, More preferably, it is 1-20 nm. When the average particle diameter of the catalyst component particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. In the present invention, the value of the “average particle diameter of the catalyst component particles” is the crystal component diameter determined from the half-value width of the diffraction peak of the catalyst component particles in X-ray diffraction, or the catalyst component examined from the transmission electron microscope image. It can be calculated as the average value of the particle diameters.

  The ratio of the content of the conductive support and the catalyst component in the proton reduction catalyst or hydrogen oxidation catalyst is not particularly limited. However, the content (supported amount) of the catalyst component is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and further preferably 30 to 55% by mass with respect to the total mass of the catalyst. It is. A catalyst functions effectively as the content rate of a catalyst component is 5 mass% or more, and the effect of this invention can fully be exhibited. On the other hand, the catalyst component content of 70% by mass or less is preferable because aggregation of the catalyst components on the surface of the conductive support is suppressed and the catalyst components are supported in a highly dispersed state. In addition, as a value of the ratio of content mentioned above, the value measured by ICP emission spectrometry is adopted.

  There is no restriction | limiting in particular also about the polymer electrolyte which comprises the intermediate | middle layer 112, A conventionally well-known polymer electrolyte can be employ | adopted. Specifically, the polymer electrolyte constituting the sheet-like substrate 111 described above can be used as the constituent material of the intermediate layer 112 as well. Therefore, detailed description is omitted here. The polymer electrolyte constituting the intermediate layer 112 may be the same as or different from the polymer electrolyte constituting the sheet-like substrate 111, but is preferably the same. According to such a form, the polymer electrolyte membrane 110 can be easily manufactured. Further, when the polymer electrolyte membrane 110 is manufactured by laminating the sheet-like base material 111 and the intermediate layer 112 separately, the adhesion between the sheet-like base material 111 and the intermediate layer 112 is low. There is also an advantage that it can be improved.

  The intermediate layer 112 includes an electron conductor as described above. As a result, conductivity is imparted to the intermediate layer 112, and a potential difference serving as a driving force for advancing the HER and HOR described above can be generated. The electron conductor contained in the intermediate layer 112 is not particularly limited as long as it can impart conductivity to the intermediate layer 112. For example, in the proton reduction layer 113a and the hydrogen oxidation layer 113c shown in FIG. 1, it is preferable to use the conductive carrier constituting the proton reduction catalyst or the hydrogen oxidation catalyst as it is as the electron conductor contained in the intermediate layer 112. According to such a form, it is not necessary to add an electron conductor separately, which is preferable from the viewpoint of weight reduction and cost reduction. However, in some cases, an electron conductor may be added separately to the proton reduction layer 113a or the hydrogen oxide layer 113c.

  There is no particular limitation on the electron conductor that can be used in addition to the conductive carrier constituting the catalyst included in the proton reduction layer 113a and the hydrogen oxide layer 113c. Examples of electron conductors include carbon blacks such as acetylene black, ketjen black, and furnace black, carbon powders such as graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF). . The electron conductor is preferably a water retaining material. According to such a form, the water retention material as an electron conductor contained in the intermediate layer 112 can function as a water retention buffer. That is, when the PEFC take-out load is reduced or when the operation of the PEFC is stopped, the water retention material can hold the generated water (water vapor) in the cell. As a result, it is possible to respond smoothly when the take-out load increases again or when the PEFC operation is resumed, and it is possible to prevent a decrease in output. There is no restriction | limiting in particular about the specific form of the electronic conductor as a water retention material, The electron conductivity material which has water retention property can be used suitably. Examples include carbon materials such as ketjen black and acetylene black, metal oxides such as tin oxide, and carbon powder having hydrophilic functional groups (hydroxyl groups, carboxyl groups, and amino groups introduced on the surface).

  Note that the amount of proton movement indicated by the left-pointing broken line in FIG. 1 depends on the amount of protons generated by the HOR reaction in the hydrogen oxide layer 113c. The amount of protons generated by the HOR reaction depends on the amount of hydrogen gas that reaches the hydrogen oxide layer 113c due to cross leak from the anode side. Therefore, in order for the MEA 100 of the present embodiment to exhibit the mechanism described above, it is necessary that the hydrogen gas that is the fuel supplied to the anode side reaches the hydrogen oxide layer 113c by cross leak. For this reason, in the MEA of this embodiment, a hydrogen gas flow path is formed in the intermediate layer 112 in the thickness direction of the sheet-like substrate (not shown). Hydrogen gas has an overwhelmingly faster moving speed in the gas phase than moving the polymer electrolyte. For this reason, by providing the hydrogen gas flow path, the hydrogen gas, which is the fuel gas supplied to the anode side, can diffuse to at least the entire intermediate layer 112 and contribute to the progress of the mechanism described above. .

  There is no particular limitation on the specific form of the hydrogen gas flow path, and any form may be used as long as the hydrogen gas supplied to the anode side can reach the hydrogen oxide layer 113c by cross leak. As one form of providing the hydrogen gas flow path in the intermediate layer 112, a form of providing appropriate holes in the intermediate layer 112 is exemplified.

In relation to the hydrogen gas flow path formed in the intermediate layer 112, in a preferred form, the intermediate layer 112 has a predetermined pore structure. Specifically, the intermediate layer 112 has (1) the most frequent pore diameter in the range of 0.04 to 0.06 μm in the pore distribution by the mercury intrusion method, and (2) the most frequent pore diameter. It is preferable to have a pore structure in which the ratio of the full width at half maximum to the peak height is 0.045 μm (cm ³ g ⁻¹ ) or less. According to such a form, the hydrogen gas flow path is sufficiently ensured in the intermediate layer 112, and the effects of the present invention by the above-described mechanism can be effectively exhibited. In the following description, it is assumed that all the holes are cylindrical, the hole diameter is D, and the hole volume is V.

The mercury intrusion method is also called mercury porosimetry. Mercury, which does not react with most substances and does not wet, is pressed into solid vacancies under pressure, and pressed with the pressure applied at that time ( This is a method for measuring the size and volume of vacancies on the sample surface from the relationship between the volume of mercury that has entered. When a cell filled with a sample and mercury is continuously pressurized in a high-pressure vessel, mercury is sequentially injected from a large hole to a small hole. It can be theoretically calculated from the Washburn equation (D = −4σcos θ / P) how much pressure the mercury enters into the pores. Here, P is the applied pressure, D is the pore diameter, σ is the surface tension of mercury, and θ is the contact angle between mercury and the pore wall surface. By treating σ and θ as constants, the relationship between the pressure P applied from the Washburn equation and the hole diameter D is obtained, and the hole diameter and its volume distribution are derived by measuring the intrusion volume at that time. In the present application, the hole diameter is calculated assuming that the surface tension σ of mercury is 485 dyn cm ⁻¹ and the contact angle between mercury and the hole wall surface is 130 °.

A specific measuring method will be described. First, a portion corresponding to the intermediate layer 112 of the polymer electrolyte membrane 100 is taken out and put into a measuring cell. Next, the measurement cell is evacuated and then filled with mercury, the inside of the cell is continuously pressurized, and the mercury intrusion volume (W [cm ³ ]) in the process is detected by a capacitance detector. A value obtained by dividing the mercury intrusion volume (W [cm ³ ]) by the mass (g) of the charged intermediate layer 112 is the void volume V (cm ³ / g) of the intermediate layer.

  In the present invention, the pore distribution means a log differential pore volume distribution. In order to obtain the log differential pore volume distribution, first, the differential pore volume dV when the pore volume of the polymer electrolyte membrane obtained by the mercury intrusion method is set to V and the pore diameter is set to D is calculated. A value (dV / d (logD)) divided by a logarithmic difference value d (logD) of the hole diameter is obtained. Then, this dV / d (logD) may be plotted against the average pore diameter of each section. The differential hole volume dV refers to an increase in the hole volume between measurement points.

  FIG. 2 is a graph showing the pore distribution of the preferred pore structure that the intermediate layer 112 has. As shown in FIG. 2, the horizontal axis represents the hole diameter (logarithmic scale), and the left vertical axis represents the log differential hole volume. Here, the solid line is a graph with respect to the log differential integral void volume on the left vertical axis, and the broken line is a graph with respect to the accumulated void volume on the right vertical axis.

  As described above, in the preferred embodiment, in the hole structure of the intermediate layer 112, the most frequent hole diameter is in the range of 0.04 to 0.06 μm. This means that the maximum value of the log differential pore volume is in the range of the pore diameter of 0.04 to 0.06 μm. From the viewpoint of excellent hydrogen gas permeability, the most frequent pore diameter is preferably in the range of 0.02 to 0.07 μm, and more preferably in the range of 0.05 to 0.07 μm. .

And in the hole structure of the intermediate | middle layer 112, ratio of the half value width with respect to the peak height of the peak of a mode hole diameter is 0.045 micrometer (cm < ³ > g < ^-1 >) or less. In the following, “the ratio of the half-value width to the peak height of the peak of the mode pore diameter” is also simply referred to as “half-value width / peak height”. The peak of the most frequent pore diameter refers to a peak including the maximum value of the log differential pore volume. Peak height refers to the distance from the baseline to the peak top. Here, in the hole distribution of the intermediate layer, the value of the log differential hole volume when the hole diameter is 0.50 μm is defined as 0 cm ³ g ⁻¹ . This is because the value of the accumulated pore volume when the pore diameter is 0.50 μm is defined as 0 cm ³ g ⁻¹ . A line having a log differential pore volume value of 0 cm ³ g ⁻¹ is defined as a baseline. That is, in the present invention, the baseline is the horizontal axis of the log differential pore volume distribution graph. Therefore, the peak height corresponds to the value from the horizontal axis to the peak top, that is, the maximum value of the peak. The full width at half maximum is an index representing the extent of the spread of a certain peak, and refers to the peak width at half the height of the peak. The half width / peak height is preferably 0.044 μm / (cm ³ g ⁻¹ ) or less, and more preferably 0.043 μm / (cm ³ g ⁻¹ ) or less. If the full width at half maximum / peak height is 0.045 μm / (cm ³ g ⁻¹ ) or less, the uniformity of the pore structure is ensured, and the function of the hydrogen gas flow path can be sufficiently exhibited. The half-value width / peak height is theoretically a value exceeding 0 and is preferably as small as possible. However, in consideration of a practically manufacturable limit, it is preferably 0.010 μm / (cm ³ g ⁻¹ ). That's it.

  Further, from the viewpoint of excellent hydrogen gas permeability, the half width of the peak of the most frequent pore diameter in the pore distribution of the intermediate layer 112 by the mercury intrusion method is preferably 0.045 μm or less, and more preferably Is 0.043 μm or less, more preferably 0.042 μm or less. The half-value width is also theoretically a value exceeding 0 and is preferably as small as possible. However, in consideration of a practically manufacturable limit, it is preferably 0.010 μm or more, more preferably 0.019 μm or more. It is.

Furthermore, from the viewpoint of excellent hydrogen gas permeability, the total pore volume in the pore diameter range of 0.01 to 0.50 μm in the pore structure of the intermediate layer 112 is preferably 0.40 to 0.00. a 60cm ³ g ^-1, more preferably 0.47~0.60cm ³ g ^-1, more preferably from 0.49~0.56cm ³ g ^-1.

  In the present embodiment, it is only necessary that the above-described preferable hole structure exists in at least a part of the intermediate layer 112. In other words, in the intermediate layer, there may be a region having a pore structure that does not satisfy the numerical range described above in addition to a region having a pore structure that satisfies the numerical range described above. Further, the ratio of the region having the preferable pore structure described above is preferably 30 to 100% by volume, more preferably 40 to 100% by volume, and further preferably, based on the total volume of the intermediate layer. It is 50-100 volume%, Most preferably, it is 60-100 volume%, Most preferably, it is 100 volume% (whole).

  As another preferred embodiment, the porosity of the intermediate layer 112 is preferably within a predetermined range. Specifically, the porosity of the intermediate layer 112 is preferably 40 to 75%, more preferably 45 to 70%, and still more preferably 55 to 60%. If the porosity of the intermediate layer 112 is 40% or more, a sufficient hydrogen gas flow path is ensured in the intermediate layer 112, and the effects of the present invention by the mechanism described above can be effectively exhibited. On the other hand, if the porosity of the intermediate layer 112 is 75% or less, an increase in proton transfer resistance in the intermediate layer 112 can be prevented.

  In the MEA 100 of the form shown in FIG. 1, in the intermediate layer 112, a catalyst-free layer 113n containing no catalyst is interposed between the proton reduction layer 113a and the hydrogen oxide layer 113c. The proton reduction reaction (HER) and hydrogen oxidation reaction (HOR) described above are more likely to proceed as the potential difference between the potential of the intermediate layer 112 and the virtual potential increases. In other words, the proton reduction reaction (HER) is more likely to proceed closer to the anode, and the hydrogen oxidation reaction (HOR) is more likely to proceed closer to the cathode. Therefore, as shown in FIG. 1, if the proton reduction layer 113a and the hydrogen oxidation layer 113c are configured by disposing a catalyst at both ends of the intermediate layer 112, the reaction can be performed while minimizing the amount of expensive catalyst used. It is possible to proceed effectively. However, it is not limited only to such a form. For example, a form in which the catalyst is dispersed throughout the intermediate layer 112 can also be adopted.

  Further, in the MEA 100 of the form shown in FIG. 1, in the polymer electrolyte membrane 110, the intermediate layer 112 is disposed closer to the anode catalyst layer 120a. According to such a form, the following merits are obtained. That is, hydrogen gas as fuel leaks from the anode side, and air or oxygen gas as oxidant leaks from the cathode side. The potential of the intermediate layer 112 is determined by the partial pressure of these gases that have leaked. The proton reduction reaction (HER) or the fuel oxidation reaction occurs when the potential of the intermediate layer 112 is closer to the potential of the anode catalyst layer 120a. (HOR) proceeds smoothly. Therefore, according to such a form, the partial pressure of the fuel (hydrogen gas) in the intermediate layer 112 can be made relatively large, and as a result, the reaction of HER and HOR can proceed smoothly. The phrase “the intermediate layer is disposed closer to the anode catalyst layer in the polymer electrolyte membrane” means that the center plane in the thickness direction of the intermediate layer is closer to the anode catalyst layer than the center plane in the thickness direction of the polymer electrolyte membrane 110. It means that the intermediate layer is arranged so as to be located in However, it is not limited only to such a form. For example, the intermediate layer may be located at the center of the polymer electrolyte membrane, and in some cases, a configuration in which the intermediate layer is disposed near the cathode catalyst layer may be employed. The arrangement position of the intermediate layer in the polymer electrolyte membrane depends on the characteristics of the material constituting the sheet-like substrate 111 and the intermediate layer 112 of the polymer electrolyte membrane 110 and the properties of the gas used as the fuel and the oxidant. Just decide. In general, however, the distance between the catalyst layers (120a, 120c) is preferably as small as possible from the viewpoint of improving the output. From such a viewpoint, it can be said that the intermediate layer is preferably disposed in the center of the polymer electrolyte membrane.

  Further, in the MEA 100 in the form shown in FIG. 1, a portion other than the intermediate layer 112 in the sheet-like substrate 111 includes a short-circuit preventing material. By setting it as such a form, the electrical insulation of a catalyst layer (120a, 120c) and the intermediate | middle layer 112 can be ensured more reliably. As a result, it is possible to suppress the occurrence of problems such as a decrease in output due to a short circuit between the catalyst layers (120a, 120c) and deterioration of MEA. In addition, there is no restriction | limiting in particular about the specific form of a short circuit prevention material. As an example, resin materials such as polytetrafluoroethylene (PTFE; trade name Teflon (registered trademark)) and various fibril materials can be cited. These may be used alone or in combination of two or more.

  The thickness of the intermediate layer 112 is determined as appropriate in consideration of the characteristics of the constituent materials of the MEA and the intermediate layer, desired operational effects, and the like, and is not particularly limited. However, the thickness of the intermediate layer 112 is preferably 2 to 30 μm, more preferably 2 to 20 μm, still more preferably 3 to 10 μm, and particularly preferably 3 to 5 μm. When the thickness of the intermediate layer 112 is within such a range, the effects of the present invention can be sufficiently exerted. Moreover, as shown in FIG. 1, the preferable form of the thickness in the case where the catalyst non-containing layer 113n is interposed between the proton reduction layer 113a and the hydrogen oxidation layer 113c in the intermediate layer 112 is as follows. The thickness of the proton reduction layer 113a is preferably 1 to 15 μm, more preferably 1 to 5 μm. The thickness of the hydrogen oxide layer 113c is preferably 1 to 15 μm), more preferably 1 to 5 μm. When the thickness of the layer containing the catalyst is in such a range, the above-described HER and HOR reactions can be efficiently advanced while minimizing the amount of expensive catalyst used. Become.

  For the purpose of preventing gas leakage from the intermediate layer 112 to the outside, a gasket (not shown) may be disposed around the intermediate layer 112. Although the constituent material of such a gasket is not particularly limited, a resin material such as polyethylene naphthalate (PEN) can be used. A gasket for preventing gas leakage from a laminate (gas diffusion electrode) composed of an anode side gas diffusion layer / anode catalyst layer / polymer electrolyte membrane / cathode catalyst layer / cathode side gas diffusion layer (details will be described later) ) May have a function as a gasket around the intermediate layer. According to such a form, the number of parts constituting the PEFC can be reduced, which contributes to the weight reduction of the PEFC, which is preferable.

  Although the “intermediate layer” which is a characteristic configuration of the present invention has been described in detail above, other members constituting the MEA 100 will be briefly described below.

(Catalyst layer)
The catalyst layers (the anode catalyst layer 120a and the cathode catalyst layer 120c) are layers in which the cell reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer 120a, and the reduction reaction of oxygen proceeds in the cathode catalyst layer 120c. The catalyst layer includes an electrode catalyst and a polymer electrolyte. These specific modes are not particularly limited, and conventionally known knowledge can be appropriately referred to in the technical field of fuel cells. For example, as the electrode catalyst included in the catalyst layer, a catalyst similar to the above-described proton reduction catalyst or hydrogen oxidation catalyst can be used. Also, as the polymer electrolyte contained in the catalyst layer, the same polymer electrolyte as described above can be used as the constituent material of the sheet-like substrate constituting the polymer electrolyte membrane. Therefore, detailed description is omitted here.

  There is no restriction | limiting in particular about content of the polymer electrolyte in a catalyst layer. However, the mass ratio of the content of the polymer electrolyte to the content of the electroconductive carrier in the catalyst layer (the mass ratio of the polymer electrolyte / the electroconductive carrier) is preferably 0.5 to 2.0, more preferably. It is 0.6-1.5, More preferably, it is 0.8-1.3. When the mass ratio of the polymer electrolyte / conductive carrier is 0.8 or more, it is preferable from the viewpoint of suppressing the internal resistance value of the membrane electrode assembly. On the other hand, the polymer electrolyte / conductive support mass ratio is preferably 1.3 or less from the viewpoint of suppressing flooding. In addition, there is no restriction | limiting in particular about the thickness of a catalyst layer, A conventionally well-known knowledge can be referred suitably. For example, the thickness of each catalyst layer may be about 0.1 to 100 μm, preferably 1 to 30 μm, and more preferably 2 to 10 μm.

(Gas diffusion layer)
The gas diffusion layers (anode-side gas diffusion layer 140a, cathode-side gas diffusion layer 140c) have a function of promoting the diffusion of gas (fuel gas or oxidant gas) supplied through the separator flow path to the catalyst layer, and It functions as an electron conduction path.

  The material which comprises the base material of a gas diffusion layer (140a, 140c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer: MLP) composed of an aggregate of carbon particles containing a water repellent on the catalyst layer side of the base material. May be.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include the same water repellent as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles to the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in terms of mass ratio in consideration of the balance between water repellency and electron conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

(Production method)
The method for manufacturing the MEA 100 of the present embodiment is not particularly limited, and knowledge relating to a conventionally known manufacturing method in the technical field of MEA can be appropriately referred to.

  In order to manufacture the MEA 100 of this embodiment, first, the polymer electrolyte membrane 110 is manufactured. In order to manufacture the polymer electrolyte membrane 110, for example, as shown in FIG. 3A, various coating means such as a screen printing method are applied to the surface of a substrate 300 made of a resin such as polytetrafluoroethylene (PTFE). Then, the catalyst ink is applied using heat treatment, and heat treatment is performed as necessary to separately produce the anode catalyst layer 120a, the intermediate layer 112, and the cathode catalyst layer 120c. At this time, the catalyst ink may be prepared by adding a catalyst (an electrode catalyst for the catalyst layer, a catalyst that can function as a proton reduction catalyst or a hydrogen oxidation catalyst for the intermediate layer) and a polymer electrolyte to the solvent. . Examples of the solvent include water and propylene glycol. By applying a heat treatment after the coating, organic impurities contained in the catalyst ink can be removed. Although there is no restriction | limiting in the specific conditions of such heat processing, Usually, it is about 5 to 60 minutes at about 100-150 degreeC.

Although there is no restriction | limiting in the application quantity of the catalyst ink to the PTFE base material 200, What is necessary is just to adjust suitably according to the desired form about each layer finally obtained. In order to produce the catalyst layers (120a, 120c), the catalyst ink may be applied so that the supported amount of the catalyst component is about 0.1 to 0.5 mg / cm ² . Further, in order to produce the proton reduction layer 113a and the hydrogen oxide layer 113c in the intermediate layer 112, the catalyst ink is adjusted so as to be about 0.2 to 1.0 mg / cm ² with a relatively large amount of the catalyst component supported. May be applied.

  In addition, what is necessary is just to adjust content of each component which comprises the intermediate | middle layer 112, in order to form a desired hydrogen gas flow path in the intermediate | middle layer 112, and to provide the void | hole structure and porosity which were mentioned above preferably. Specifically, in order to increase the pores in the intermediate layer 112 or increase the porosity, the volume fraction of the polymer electrolyte, the catalyst, and the electron conductor in the constituent material of the intermediate layer 112 is decreased. The blending amount of these components may be relatively small. It is also conceivable to control the pulverization conditions of the catalyst ink used in the field where the catalyst is supported on the intermediate layer 112. For example, when the crushing strength is increased, the secondary particle size of the catalyst is reduced, and a more packed layer (having less porosity) can be formed.

  Subsequently, as shown in FIG. 3B, an electrolyte membrane 111 ′ constituting the sheet-like substrate 111 of the polymer electrolyte membrane 110 is prepared. Each surface of the electrolyte membrane 111 ′ is laminated so that the anode catalyst layer 120a and the intermediate layer 112 produced above are in contact with each other, and the PTEF base material is peeled and removed, whereby each surface of the electrolyte membrane 111 ′. Thus, a laminate in which the anode catalyst layer 120a and the intermediate layer 112 are transferred and formed is obtained. Similarly, a laminate in which the cathode catalyst layer 120c is transferred and formed on one side of the separately prepared electrolyte membrane 111 ″ is manufactured. In the above operations, the anode catalyst layer 120a and the cathode catalyst layer 120c are replaced. Also good.

  Next, as shown in FIG. 3 (c), the two laminates produced above are further laminated so that the exposed electrolyte membrane 111 '' and the exposed surface of the intermediate layer 112 are in contact with each other. There are no particular restrictions on the specific conditions of the heating / pressurizing treatment at this time, but usually at about 120 to 180 ° C. for about 5 to 60 minutes, about 0.5 to 5 MPa. In order to dispose a gasket around the intermediate layer 112, a material constituting the gasket (eg, PEN film 310) is disposed around the intermediate layer 112 when the two laminates are laminated. That's fine.

  According to the operation described above, a laminate in which the polymer electrolyte membrane 110 in which the intermediate layer 112 consisting of only one uniform layer is disposed in the sheet-like substrate 111 is sandwiched between the catalyst layers (120a, 120c) is obtained. can get. The laminated body thus obtained is further sandwiched between a pair of gas diffusion layers (140a, 140c) by a conventionally known method, whereby MEA 100 is obtained.

  In addition, as shown in FIG. 1, the manufacturing method of the polymer electrolyte membrane 110 which has the intermediate | middle layer 112 of the form by which the catalyst is arrange | positioned only at both ends is demonstrated easily below. In order to obtain such an electrolyte membrane 110, for example, the catalyst-free layer 113n in the intermediate layer 112 is formed by depositing an ink containing an electron conductor instead of the catalyst. Then, both surfaces of the catalyst-free layer 113n are sandwiched between a proton reduction layer 113a and a hydrogen oxide layer 113c obtained separately by film formation. By repeating such operations and sequentially laminating the layers shown in FIG. 1, the MEA 100 having the configuration shown in FIG. 1 can be manufactured.

  In addition, about the other form (catalyst manufacturing method etc.) relevant to the manufacturing method of MEA100, since the conventionally well-known knowledge regarding manufacture of PEFC can be referred suitably, detailed description is abbreviate | omitted here.

(Fuel cell)
The MEA 100 in the above-described form can be used for manufacturing a fuel cell. FIG. 4 is a schematic cross-sectional view schematically showing a general overall structure of a polymer electrolyte fuel cell (PEFC) 200 using the MEA 100 having the configuration shown in FIG. FIG. 4 shows a PEFC single cell.

  A polymer electrolyte fuel cell 200 shown in FIG. 4 has the MEA 100 of the form shown in FIG. In the polymer electrolyte fuel cell 200, the membrane electrode assembly 100 is sandwiched between a pair of separators including an anode side separator 150a and a cathode side separator 150c. Here, the anode side gas diffusion layer 140a side surface of the anode side separator 150a is provided with a fuel gas flow path 152a through which fuel gas flows during operation, and the coolant flows through the opposite surface during operation. A cooling flow path (not shown) is provided. On the other hand, an oxidant gas flow path 152c through which an oxidant gas flows during operation is provided on the cathode side gas diffusion layer 140c side surface of the cathode side separator 150c, and a coolant is provided on the opposite side surface during operation. A cooling flow path (not shown) through which is circulated is provided. A gasket 160 is disposed around the polymer electrolyte fuel cell 200 so as to surround the pair of gas diffusion electrodes.

  According to the PEFC 200 having the MEA 100 of the present invention as described above, a reduction in electromotive force associated with battery operation can be effectively suppressed.

  Hereinafter, although the member which comprises PEFC200 of the form shown in FIG. 4 is demonstrated easily, the technical scope of this invention is not restrict | limited only to the following form.

(Separator)
The separator has a function of electrically connecting cells in series when a plurality of single cells of a fuel cell such as PEFC are connected in series to form a fuel cell stack. The separator also functions as a partition wall that separates the fuel gas, the oxidant gas, and the coolant from each other. Therefore, as described above, each separator is provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

(gasket)
The gasket is disposed around the fuel cell so as to surround the pair of electrode catalyst layers and the gas diffusion layer, and has a function of preventing the gas supplied to the catalyst layer from leaking to the outside. A gas diffusion electrode refers to a joined body of a gas diffusion layer and an electrode catalyst layer. The material constituting the gasket is not particularly limited, but rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Examples thereof include fluorine polymer materials such as polyhexafluoropropylene and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. Moreover, there is no restriction | limiting in particular also in the thickness of a gasket, Preferably it is 50 micrometers-2 mm, More preferably, what is necessary is just to be about 100 micrometers-1 mm.

  As described above, the PEFC has been described as an example, but other examples of the fuel cell include an alkaline fuel cell, a direct methanol fuel cell, and a micro fuel cell, and can be applied to any cell.

(vehicle)
A vehicle equipped with the above-described fuel cell or fuel cell stack of the present invention is also included in the technical scope of the present invention. According to the fuel cell or fuel cell stack of the present invention, since a decrease in electromotive force accompanying the operation of the battery can be suppressed, the fuel cell and the fuel cell stack are suitable for vehicle applications that require high output over a long period of time.

<Production of CCM>
By the following method, a laminate (CCM) in which a polymer electrolyte membrane 110 in which an intermediate layer 112 consisting of only one uniform layer is disposed in a sheet-like substrate 111 is sandwiched between catalyst layers (120a, 120c). Catalyst Coated Membrane) was produced.

  First, an electrode catalyst powder (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and an ionomer dispersion (Nafion (registered trademark) DE2020CS, EW1000, manufactured by DuPont) are combined with a polymer electrolyte (ionomer) / conductive support (carbon support). So that the weight ratio of the mixture was 0.9. Next, a 50% by mass propylene glycol aqueous solution was added to this solution so that the solid content of the ink was 19% by mass to prepare a catalyst ink.

The catalyst ink prepared above was applied to each square of 50 mm square on each surface of three separately prepared PTFE substrates by screen printing. At this time, coating was performed so that the supported amount of platinum as a catalyst component was 0.35 mg / cm ^{2 on} the two substrates, and the supported amount of platinum was 0.70 mg / cm on the remaining one substrate. Application was performed so as to be cm ² . Next, these coating films were subjected to a heat treatment at 130 ° C. for 30 minutes to remove organic impurities. Thus, a PTEF base material on which two electrode catalyst layers (an anode catalyst layer and a cathode catalyst layer) and an intermediate layer were formed was obtained.

  Furthermore, the central part of a 72 mm square polymer electrolyte membrane (DuPont, Nafion (registered trademark) NRE211-CS, thickness 25 μm) separately prepared is sandwiched between the anode catalyst layer and the intermediate layer formed above, The PTFE base materials of both outermost layers were peeled off, and the anode catalyst layer and the intermediate layer were transferred to the respective surfaces of the polymer electrolyte membrane. On the other hand, a similar polymer electrolyte membrane was prepared separately, and the cathode catalyst layer was transferred to one side by the same method as described above. Thereafter, the periphery of the intermediate layer was surrounded by a polyethylene naphthalate (PEN) film (Q51, thickness 25 μm, manufactured by Teijin DuPont Films Ltd.) as a gasket. Next, the exposed surface of the polymer electrolyte membrane on which the cathode catalyst layer was formed and the exposed surface of the intermediate layer were joined so that the centers overlap, and the obtained joined body was subjected to hot press treatment. This completed the CCM. The hot press conditions were 150 ° C., 10 minutes, and 0.8 MPa. The structure of the produced CCM is as follows: anode catalyst layer (thickness 10 μm) / sheet-like substrate (electrolyte membrane) (Nafion® NRE211-CS, thickness 25 μm) / intermediate layer (thickness 20 μm) / It was a sheet-like substrate (electrolyte membrane) (Nafion (registered trademark) NRE211-CS, thickness 25 μm) / cathode catalyst layer (thickness 10 μm). Furthermore, the porosity of the intermediate layer was about 57%.

<Evaluation of battery performance>
A PEFC single cell was prepared by sandwiching both sides of the CCM produced above with a gas diffusion layer (SBC Carbon, 24BC) having a microporous layer and further sandwiching with a separator made of graphite carbon. Using this single cell, the battery performance was evaluated by the following method. In addition, as a comparative example, battery performance was evaluated using CCM (Nafion (registered trademark) NRE211-CS, thickness 25 μm (2 sheets)) having no intermediate layer.

  Specifically, hydrogen gas humidified to 100% RH was supplied to both electrodes, a direct current was passed in the range of the current density shown in FIG. 5, and the cell voltage drop was measured. At the time of evaluation, the cell temperature was 80 ° C.

The results of the battery performance evaluation are shown in FIG. From the results shown in FIG. 5, when the CCM having no intermediate layer was used, the cell voltage drop was 0.2 V or more at a current density of 0.8 A / cm ² . On the other hand, in the case of using the CCM of the example having the intermediate layer, it can be seen that the cell voltage drop is suppressed to less than 0.15 V even when the current density is 1.6 A / cm ² .

  From the above, according to the present invention, it is shown that the occurrence of problems such as a decrease in electromotive force due to gas cross leak in a fuel cell can be effectively suppressed.

1 is a schematic cross-sectional view schematically showing a general overall structure of an MEA according to an embodiment of the present invention. It is a graph showing the hole distribution of the preferable hole structure which an intermediate | middle layer has. It is process drawing which shows the typical manufacturing process of MEA by this invention. It is the cross-sectional schematic which represented typically the general whole structure of PEFC using MEA of the form shown in FIG. It is a graph which shows the result of the battery performance evaluation performed in the Example.

Explanation of symbols

100 membrane electrode assembly (MEA),
110 polymer electrolyte membrane,
111 sheet-like substrate,
111 ', 111 "electrolyte membrane,
112 middle layer,
113a proton reduction layer,
113c hydrogen oxide layer,
113n catalyst-free layer,
120a anode catalyst layer,
120c cathode catalyst layer,
140a anode side gas diffusion layer,
140c cathode side gas diffusion layer,
150a anode side separator,
150c cathode side separator,
152a fuel gas flow path,
152c oxidant gas flow path,
160 gasket,
200 Polymer electrolyte fuel cell (PEFC),
300 base material (PTFE base material),
310 PEN film,
HER proton reduction reaction,
HOR Hydrogen oxidation reaction.

Claims (11)

A sheet-like substrate made of a polymer electrolyte;
Hydrogen is provided in the sheet-like base material in the thickness direction of the sheet-like base material, including a hydrogen oxidation catalyst, a proton reduction catalyst, a polymer electrolyte, and an electron conductor, which are arranged in parallel to the surface direction of the sheet-like base material. An intermediate layer formed with a gas flow path;
A polymer electrolyte membrane. In the hole distribution by the mercury intrusion method of the intermediate layer, (1) the most frequent pore diameter is in the range of 0.04 to 0.06 μm, and (2) the peak height of the peak of the most frequent cavity diameter. 2. The polymer electrolyte membrane according to claim 1, wherein the half-value width ratio is 0.045 μm (cm ³ g ⁻¹ ) or less.   The polymer electrolyte membrane according to claim 1 or 2, wherein the porosity of the intermediate layer is 40 to 75%.   The polymer electrolyte membrane according to any one of claims 1 to 3, wherein a portion other than the intermediate layer in the sheet-like substrate contains a short-circuit preventing material.   The polymer electrolyte membrane according to any one of claims 1 to 4, wherein the electron conductor is a water retention material.   At least one of the hydrogen oxidation catalyst and the proton reduction catalyst is platinum, palladium, iridium, carbon, silver, gold, rhodium, ruthenium, tin, silicon, titanium, zirconium, aluminum, hafnium, tantalum, niobium, cerium, and these The polymer electrolyte membrane according to any one of claims 1 to 5, wherein a catalyst component selected from the group consisting of alloys is supported on a conductive carrier. The polymer electrolyte membrane according to any one of claims 1 to 6,
An anode catalyst layer that is disposed on one surface of the polymer electrolyte membrane and includes an electrode catalyst in which a catalyst component is supported on a conductive carrier and a polymer electrolyte;
A cathode catalyst layer that is disposed on the other surface of the polymer electrolyte membrane and includes an electrode catalyst in which a catalyst component is supported on a conductive carrier and a polymer electrolyte;
A pair of gas diffusion layers sandwiching a laminate composed of the polymer electrolyte membrane, the anode catalyst layer and the cathode catalyst layer;
A membrane electrode assembly. In the polymer electrolyte membrane, the intermediate layer is
A proton reduction layer including the proton reduction catalyst, disposed at one end in the thickness direction of the intermediate layer;
A hydrogen oxidation layer including the hydrogen oxidation catalyst, disposed at the other end in the thickness direction of the intermediate layer;
A catalyst-free layer that does not include the proton reduction catalyst and the hydrogen oxidation catalyst, interposed between the proton reduction layer and the hydrogen oxidation layer;
The membrane electrode assembly according to claim 7, comprising:   The membrane electrode assembly according to claim 7 or 8, wherein in the polymer electrolyte membrane, the intermediate layer is disposed closer to the anode catalyst layer. The membrane electrode assembly according to any one of claims 7 to 9,
A pair of separators sandwiching the membrane electrode assembly;
A fuel cell.   A vehicle equipped with the fuel cell according to claim 10.

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