Electrode catalyst layer, membrane electrode assembly, polymer electrolyte fuel cell, and method for manufacturing electrode catalyst layer

Abstract

To provide an electrode catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and a method for manufacturing an electrode catalyst layer that can increase proton conductivity under standard conditions and high-humidity conditions with a simple configuration.SOLUTION: An electrode catalyst layer includes a conductive support 21 supporting a catalyst material 22, a polymer electrolyte 23, and a fibrous material 24 that is an electron-conductive fiber. The fibrous material 24 has a surface with irregularities 25, and the depth peak of the distribution of the depth of the irregularities is 10 nm or more and 50 nm or less, the width peak of the distribution of the width of the irregularities is 100 nm or more and 300 nm or less, and the product of the depth peak and the width peak is 10,000 or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an electrode catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and a method for manufacturing an electrode catalyst layer. [Background technology]

[0002] Fuel cells are attracting attention as a type of battery that can contribute to solving environmental and energy problems. Fuel cells generate electricity by utilizing a chemical reaction between a fuel such as hydrogen and an oxidant such as oxygen. Among fuel cells, polymer electrolyte fuel cells are capable of operating at near room temperature, and are therefore expected to be used as home and automotive power sources. Therefore, research and development is underway to solve issues such as improving cell performance, including power generation characteristics and durability, and reducing manufacturing costs, in order to commercialize polymer electrolyte fuel cells.

[0003] A polymer electrolyte fuel cell comprises a membrane electrode assembly having an electrode catalyst layer that constitutes the anode (fuel electrode), an electrode catalyst layer that constitutes the cathode (air electrode), and a polymer electrolyte membrane sandwiched between these two electrode catalyst layers.

[0004] A fuel gas containing hydrogen is supplied to the fuel electrode, and an oxidant gas containing oxygen is supplied to the air electrode. Protons and electrons are generated from the fuel gas supplied to the fuel electrode due to the action of the catalyst contained in the electrode catalyst layer. The protons are conducted by the polymer electrolyte contained in the electrode catalyst layer and the polymer electrolyte membrane, and move through the polymer electrolyte membrane to the air electrode. The electrons are extracted from the fuel electrode to an external circuit, and move through the external circuit to the air electrode. At the air electrode, the oxidant gas reacts with the protons and electrons that have moved from the fuel electrode to produce water. This series of electrochemical reactions generates an electromotive force.

[0005] The electrode catalyst layer has pore-like voids that function as passages for various gases and generated water. To improve the reactivity of the electrochemical reaction, it is preferable that the voids in the electrode catalyst layer have an appropriate size and distribution. In order to form such voids well and improve the strength of the electrode catalyst layer, it has been proposed to include a fibrous material such as carbon fiber in the electrode catalyst layer.

[0006] In the series of electrochemical reactions described above, the proton conduction resistance is greater than the electron conduction resistance. In particular, when a fibrous material is contained in the electrode catalyst layer, the proton conductivity is likely to decrease. Therefore, in order to improve the reactivity and the battery performance, it is important to increase the efficiency of proton conduction. For example, Patent Document 1 describes a configuration in which the electrode catalyst layer contains carbon fiber carrying a proton-conductive material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-110181 Summary of the Invention [Problem to be solved by the invention]

[0008] In Patent Document 1, fullerenes with proton dissociative groups introduced therein are supported on carbon fibers as a proton-conducting material. However, the process of introducing such proton dissociative groups and supporting them on carbon fibers is complicated, which tends to increase manufacturing costs. Furthermore, the proton conductivity imparted to carbon fibers in Patent Document 1 is based on proton transport via the Grotthuss mechanism mediated by the proton dissociative groups. Therefore, there is a problem in that the effect of improving proton conductivity is small under high-humidity conditions. [Means for solving the problem]

[0009] The following describes various aspects of an electrode catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and a method for producing an electrode catalyst layer, which are intended to solve the above problems. [Aspect 1] An electrode catalyst layer comprising a conductive support supporting a catalyst substance, a polymer electrolyte, and a fibrous material that is an electron-conductive fiber, wherein the fibrous material has irregularities on its surface, the depth peak, which is the peak of the distribution of the depth of the irregularities, is 10 nm or more and 50 nm or less, the width peak, which is the peak of the distribution of the width of the irregularities, is 100 nm or more and 300 nm or less, and the product of the depth peak and the width peak is 10,000 or less.

[0010] According to the above-mentioned configuration, the polymer electrolyte is easily entangled with the fibrous material, which favorably forms proton conduction paths in the electrode catalyst layer and improves proton conductivity. Furthermore, because the proton conductivity is improved by controlling the distribution of the polymer electrolyte, a decrease in proton conductivity under high-humidity conditions is also suppressed.

[0011] Furthermore, compared to the case of introducing proton dissociative groups or supporting a proton-conductive material, the burden on the fibrous material required for processing can be reduced, which prevents increases in the manufacturing cost of the electrode catalyst layer and achieves the effect of improving proton conductivity with a simple configuration.

[0012] [Aspect 2] The electrode catalyst layer according to [Aspect 1], wherein the depth peak is 20 nm or more and 40 nm or less, and the width peak is 100 nm or more and 150 nm or less. According to the above-mentioned configuration, the polymer electrolyte is more easily entangled with the fibrous material, thereby further increasing the proton conductivity.

[0013] [Aspect 3] The electrode catalyst layer according to either [Aspect 1] or [Aspect 2], wherein the fibrous material is carbon fiber. [Aspect 4] The electrode catalyst layer according to any one of [Aspect 1] to [Aspect 3], wherein the fibrous material is a carbon nanofiber. According to each of the above configurations, the electrode catalyst layer can preferably obtain electron conductivity, and the effects of improving the strength of the electrode catalyst layer and suppressing the occurrence of cracks can also be preferably obtained.

[0014] [Aspect 5] The electrode catalyst layer according to any one of [Aspect 1] to [Aspect 4], wherein the average fiber diameter of the fibrous material is 50 nm or more and 400 nm or less. According to the above-mentioned configuration, voids are well formed in the electrode catalyst layer, which makes it possible to improve the power generation performance of the fuel cell.

[0015] [Aspect 6] The electrode catalyst layer according to any one of [Aspect 1] to [Aspect 5], wherein the average fiber length of the fibrous material is 1 μm or more and 50 μm or less.

[0016] The above-described configuration can increase the strength of the electrode catalyst layer, thereby suppressing the occurrence of cracks during the formation of the electrode catalyst layer. In addition, the formation of voids is favorable, which can improve the power generation performance of the fuel cell.

[0017] [Aspect 7] A membrane electrode assembly comprising a polymer electrolyte membrane and the electrode catalyst layer according to any one of [Aspect 1] to [Aspect 6], the electrode catalyst layer being in contact with a surface of the polymer electrolyte membrane.

[0018] According to the above configuration, a membrane electrode assembly having an electrode catalyst layer with enhanced proton conductivity even under high humidity conditions can be realized with a simple configuration. [Embodiment 8] [Embodiment 7] A polymer electrolyte fuel cell comprising the membrane electrode assembly according to embodiment 8 and a pair of separators sandwiching the membrane electrode assembly. According to the above configuration, an increase in manufacturing costs can be suppressed, and good power generation performance can be obtained under both standard conditions and high humidity conditions.

[0019] [Aspect 9] A method for producing an electrode catalyst layer, comprising: producing a catalyst ink containing a conductive support supporting a catalyst substance, a polymer electrolyte, and a fibrous material that is an electronically conductive fiber; and forming an electrode catalyst layer by drying a coating film formed from the catalyst ink, wherein the fibrous material has irregularities on its surface, a depth peak that is the peak of the depth distribution of the irregularities is 10 nm or more and 50 nm or less, a width peak that is the peak of the width distribution of the irregularities is 100 nm or more and 300 nm or less, and a peak product that is the product of the depth peak and the width peak is 10,000 or less.

[0020] According to the above-mentioned manufacturing method, in the obtained electrode catalyst layer, the polymer electrolyte is easily entangled with the fibrous material, thereby favorably forming proton conduction paths and improving proton conductivity. Furthermore, since the proton conductivity is improved by controlling the distribution of the polymer electrolyte, a decrease in proton conductivity under high-humidity conditions is also suppressed.

[0021] Furthermore, compared to the case of introducing proton dissociative groups or supporting a proton-conductive material, the burden on the fibrous material required for processing can be reduced, which prevents increases in the manufacturing cost of the electrode catalyst layer and achieves the effect of improving proton conductivity with a simple configuration.

[0022] [Aspect 10] A method for producing an electrode catalyst layer according to [Aspect 9], comprising forming the irregularities on the surface of an electron-conductive fiber by firing the fiber to form the fibrous material. According to the above-mentioned production method, a fibrous material having an uneven surface can be obtained in a simple manner. [Effects of the Invention]

[0023] According to the present disclosure, the proton conductivity of an electrode catalyst layer can be increased under standard conditions and high-humidity conditions with a simple configuration. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a cross-sectional structure of a membrane electrode assembly according to one embodiment. [Figure 2] FIG. 2 is a diagram showing the internal configuration of an electrode catalyst layer according to one embodiment. [Figure 3] FIG. 3 is a diagram showing a configuration in the vicinity of a conventional fibrous material. [Figure 4] FIG. 4 is a diagram showing the configuration around a fibrous material according to one embodiment. [Figure 5] FIG. 5 is an exploded perspective view showing the structure of a polymer electrolyte fuel cell according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] An embodiment of an electrode catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and a method for manufacturing an electrode catalyst layer will be described with reference to the drawings. [Configuration of membrane electrode assembly and electrode catalyst layer] As shown in FIG. 1, the membrane electrode assembly 10 includes a polymer electrolyte membrane 11 and a pair of electrode catalyst layers 12A and 12C.

[0026] The polymer electrolyte membrane 11 is sandwiched between the electrode catalyst layer 12A and the electrode catalyst layer 12C in the thickness direction. The electrode catalyst layer 12A is in contact with one of the two surfaces of the polymer electrolyte membrane 11, and the electrode catalyst layer 12C is in contact with the other of the two surfaces of the polymer electrolyte membrane 11.

[0027] The electrode catalyst layer 12A constitutes the fuel electrode, which is the anode of the polymer electrolyte fuel cell, and the electrode catalyst layer 12C constitutes the air electrode, which is the cathode of the polymer electrolyte fuel cell. When viewed from a position facing one surface of the polymer electrolyte membrane 11, the electrode catalyst layers 12A and 12C have substantially the same outer shape, and these outer shapes are smaller than the outer shape of the polymer electrolyte membrane 11. There are no particular limitations on the outer shapes of the electrode catalyst layers 12A and 12C and the polymer electrolyte membrane 11, and they may be, for example, rectangular.

[0028] The polymer electrolyte membrane 11 includes a polymer electrolyte. The polymer electrolyte used in the polymer electrolyte membrane 11 may be any polymer electrolyte having proton conductivity, such as a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte. As the fluorine-based polymer electrolyte, a polymer electrolyte having a tetrafluoroethylene skeleton may be used. An example of a fluorine-based polymer electrolyte is Nafion (registered trademark: manufactured by DuPont). Examples of hydrocarbon-based polymer electrolytes include sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene.

[0029] The electrode catalyst layers 12A and 12C contain a catalytic material, a conductive support, a polymer electrolyte, and a fibrous material. Fig. 2 shows a schematic diagram of the internal structure of the electrode catalyst layers 12A and 12C. As shown in Fig. 2, the electrode catalyst layers 12A and 12C contain a catalyst-supported support 20, which is a conductive support 21 supporting a catalytic material 22, a polymer electrolyte 23, and a fibrous material 24. In the electrode catalyst layers 12A and 12C, the polymer electrolyte 23 and the fibrous material 24 are positioned around the dispersed catalyst-supported support 20, and voids 26 are formed between these components.

[0030] The catalytic material 22 is in the form of fine particles. The material of the catalytic material 22 is, for example, a metal, an alloy, a metal oxide, a metal composite oxide, a metal carbide, etc. Examples of metals contained in the catalytic material 22 include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum.

[0031] The conductive support 21 may be any support that is conductive and not corroded by the catalyst. The conductive support 21 is preferably in the form of fine particles. For example, carbon materials such as carbon black, graphite, activated carbon, carbon nanotubes, carbon nanofibers, and fullerenes can be used as the conductive support 21.

[0032] The average particle size of the particulate conductive support 21 is preferably 10 nm or more and 1000 nm or less, and more preferably 10 nm or more and 100 nm or less. If the average particle size of the conductive support 21 is equal to or greater than the above-mentioned lower limit, the conductive support 21 will not be packed too densely inside the electrode catalyst layers 12A, 12C, and a decrease in gas diffusibility can be suppressed. If the average particle size of the conductive support 21 is equal to or less than the above-mentioned upper limit, the occurrence of cracks in the electrode catalyst layers 12A, 12C can be suppressed. The particle size of the conductive support 21 is a volume average diameter measured by a laser diffraction / scattering method.

[0033] The polymer electrolyte 23 may be any polymer electrolyte having proton conductivity, such as a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte. The polymer electrolytes exemplified as materials for the polymer electrolyte membrane 11 can be used as the polymer electrolyte 23.

[0034] The electrolyte constituting the polymer electrolyte membrane 11 and the polymer electrolyte 23 may be the same electrolyte or different electrolytes. If these polymer electrolytes are the same type of electrolyte or polymer electrolytes with similar thermal expansion coefficients, it is possible to reduce the interfacial resistance between the polymer electrolyte membrane 11 and the electrode catalyst layers 12A, 12C and to reduce the difference in dimensional change rate between the polymer electrolyte membrane 11 and the electrode catalyst layers 12A, 12C when humidity changes.

[0035] The fibrous material 24 is a fiber having electronic conductivity. Examples of electronically conductive fibers include carbon fibers and conductive polymer nanofibers. As the carbon fibers, carbon nanofibers, carbon nanotubes, carbon nanohorns, etc. can be used. In particular, it is preferable to use carbon nanofibers as the fibrous material 24 from the viewpoint of obtaining good conductivity and dispersibility.

[0036] The average fiber diameter of the fibrous material 24 is preferably 50 nm or more and 400 nm or less. If the average fiber diameter of the fibrous material 24 is within this range, the voids 26 in the electrode catalyst layers 12A, 12C are well formed, thereby improving the power generation performance of the fuel cell. Furthermore, the average fiber length of the fibrous material 24 is preferably 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 20 μm or less. If the average fiber length of the fibrous material 24 is within this range, the strength of the electrode catalyst layers 12A, 12C can be increased, thereby suppressing the occurrence of cracks during the formation of the electrode catalyst layers 12A, 12C. Furthermore, the voids 26 are well formed, thereby improving the power generation performance of the fuel cell.

[0037] The average fiber diameter and average fiber length of the fibrous material 24 are determined by observing the fibrous material 24 with a scanning electron microscope (SEM). The average fiber diameter is the average value of the diameters of 10 pieces of fibrous material 24 selected arbitrarily within the observation area of ​​the scanning electron microscope, and the average fiber length is the average value of the fiber lengths of 10 pieces of fibrous material 24 selected arbitrarily within the observation area.

[0038] In this embodiment, fibrous material 24 has an uneven surface. The function of fibrous material 24 having unevenness will be described with reference to Figures 3 and 4. Figures 3 and 4 are diagrams schematically showing the structure around the fibrous material, with Figure 3 showing an example of a conventional fibrous material 27 that does not have unevenness, and Figure 4 showing an example of a fibrous material 24 that has unevenness.

[0039] 3, the catalyst-supported carrier 20 has an uneven surface due to the support of the catalyst material 22, and therefore the polymer electrolyte 23 tends to remain near the surface of the catalyst-supported carrier 20 so that the polymer electrolyte 23 becomes entangled in the catalyst-supported carrier 20. On the other hand, the surface of the fibrous material 27 is flat, and therefore the polymer electrolyte 23 does not tend to remain near the surface of the fibrous material 27. As a result, the proton conduction path established by the polymer electrolyte 23 tends to be interrupted.

[0040] 4, when the fibrous material 24 has surface irregularities 25, the polymer electrolyte 23 tends to remain near the surface of the fibrous material 24 so that the polymer electrolyte 23 becomes entangled with the fibrous material 24. As a result, a proton conduction path is easily formed near the surface of the fibrous material 24 and the catalyst-supported carrier 20. In other words, the occurrence of uneven distribution of the polymer electrolyte 23 in the electrode catalyst layers 12A, 12C is suppressed, and therefore a proton conduction path is suitably formed.

[0041] This improves the proton conductivity of the electrode catalyst layers 12A, 12C. Furthermore, because the proton conductivity is improved by controlling the distribution of the polymer electrolyte 23 in this way, a decrease in proton conductivity under high humidity conditions is also suppressed.

[0042] Furthermore, when proton conductivity is increased by introducing proton dissociative groups into a fibrous material, the proton conductivity may decrease over time, or the proton dissociative groups may be deactivated over long-term use, resulting in a decrease in proton conductivity. In contrast, in this embodiment, the proton conductivity is increased by controlling the distribution of the polymer electrolyte 23 as described above, and therefore the decrease in proton conductivity over time or over long-term use is also suppressed.

[0043] Regarding the irregularities on the surface of the fibrous material 24, the depth peak Pd, which is the peak of the distribution of the depth of the irregularities, is 10 nm or more and 50 nm or less. Also, the width peak Pw, which is the peak of the distribution of the width of the irregularities, is 100 nm or more and 300 nm or less. And the peak product Pp, which is the product of the depth peak Pd and the width peak Pw, is 10,000 or less.

[0044] The depth and width of the irregularities are measured based on observation of the fibrous material 24 using a scanning electron microscope (SEM). Specifically, the maximum depth and maximum diameter of each recess that constitutes the irregularities are measured for each recess. Then, based on the measurement results for 100 recesses, a depth peak Pd is determined from the distribution of the maximum depths of the recesses, and a width peak Pw is determined from the distribution of the maximum diameters of the recesses.

[0045] Specifically, a histogram is created for the maximum depth of the recesses, with a class width of 10 nm. The lower limit of the class with the highest frequency is then designated as the depth peak Pd. For example, a depth peak Pd of 10 nm indicates that the number of data points in the class between 10 nm and 20 nm is the highest. Similarly, a histogram is created for the maximum diameter of the recesses, with a class width of 50 nm. The lower limit of the class with the highest frequency is then designated as the width peak Pw.

[0046] If the unevenness is too small, the polymer electrolyte 23 will not easily become entangled with the fibrous material 24, thereby reducing the effect of improving proton conductivity. On the other hand, if the unevenness is too large, the polymer electrolyte 23 will not easily become entangled with the fibrous material 24. Furthermore, the strength of the fibrous material 24 will decrease, reducing the effect of improving the strength of the electrode catalyst layers 12A, 12C and suppressing the occurrence of cracks.

[0047] The size of the unevenness is expressed by indices such as depth, width, and volume. If the peak depth Pd, peak width Pw, and peak product Pp of the unevenness are within the above ranges, the size of the unevenness is optimal, which appropriately enhances the proton conductivity of the electrode catalyst layers 12A and 12C, while also effectively improving the strength and suppressing the occurrence of cracks. This effectively improves the performance of the fuel cell. Furthermore, because the fibrous material 24 is an electronically conductive fiber, it is easier to achieve good electronic conductivity in the electrode catalyst layers 12A and 12C.

[0048] To enhance this effect, the depth peak Pd is preferably 20 nm or more and 40 nm or less, and the width peak Pw is preferably 100 nm or more and 150 nm or less.

[0049] The content of the fibrous material 24 in the electrode catalyst layers 12A, 12C is preferably 1% by mass or more and 30% by mass or less relative to the content of the conductive support 21. If the content of the fibrous material 24 is within the above range, the effects of improving the proton conductivity and strength described above can be suitably obtained. Furthermore, the content of the polymer electrolyte 23 in the electrode catalyst layers 12A, 12C is preferably 1% by mass or more and 100% by mass or less relative to the content of the conductive support 21, and more preferably 1% by mass or more and 30% by mass or less.

[0050] The electrode catalyst layers 12A, 12C may contain fibers other than the fibrous material 24, which is an electron-conductive fiber having an irregular surface. For example, the electrode catalyst layers 12A, 12C may contain fibers without irregularities or fibers with proton conductivity. The proton-conductive fiber is, for example, a fiber made of a polymer electrolyte. It is sufficient that at least one of the electrode catalyst layers 12A, 12C contains the fibrous material 24. To further improve the performance of the fuel cell, it is preferable that both of the electrode catalyst layers 12A, 12C contain the fibrous material 24.

[0051] [Polymer electrolyte fuel cell] The configuration of a polymer electrolyte fuel cell including the above-described membrane electrode assembly 10 will be described with reference to FIG.

[0052] 5, the polymer electrolyte fuel cell 30 includes a membrane electrode assembly 10, a pair of gas diffusion layers 31A and 31C, and a pair of separators 32A and 32C. The membrane electrode assembly 10 is sandwiched between the gas diffusion layer 31A and the gas diffusion layer 31C, with the gas diffusion layer 31A in contact with the electrode catalyst layer 12A, and the gas diffusion layer 31C in contact with the electrode catalyst layer 12C.

[0053] The gas diffusion layers 31A and 31C are layers for uniformly diffusing the supplied gas and have gas diffusibility and conductivity. The gas diffusion layers 31A and 31C include a porous material such as carbon cloth, carbon paper, or nonwoven fabric. The gas diffusion layer 31A, together with the electrode catalyst layer 12A, constitutes the fuel electrode, and the gas diffusion layer 31C, together with the electrode catalyst layer 12C, constitutes the air electrode.

[0054] The laminate of the membrane electrode assembly 10 and the gas diffusion layers 31A, 31C is sandwiched between separators 32A and 32C. The separators 32A, 32C are gas impermeable and electrically conductive. The separators 32A, 32C are made of, for example, a carbon-based or metal-based material.

[0055] Separator 32A faces gas diffusion layer 31A, and separator 32C faces gas diffusion layer 31C. Gas flow paths 33A are formed on the surface of separator 32A facing gas diffusion layer 31A, and cooling water flow paths 34A are formed on the surface opposite gas diffusion layer 31A. Similarly, gas flow paths 33C are formed on the surface of separator 32C facing gas diffusion layer 31C, and cooling water flow paths 34C are formed on the surface opposite gas diffusion layer 31C.

[0056] During operation of the polymer electrolyte fuel cell 30, a fuel gas such as hydrogen flows through the gas flow channel 33A of the separator 32A, and an oxidant gas such as oxygen flows through the gas flow channel 33C of the separator 32C. Cooling water flows through the cooling water flow channels 34A and 34C of the separators 32A and 32C. The fuel gas is supplied from the gas flow channel 33A to the fuel electrode, and the oxidant gas is supplied from the gas flow channel 33C to the air electrode, causing an electrochemical reaction to occur, generating an electromotive force between the fuel electrode and the air electrode. An organic fuel such as methanol may be supplied to the fuel electrode.

[0057] The polymer electrolyte fuel cell 30 may be used in the form of a single cell as shown in Fig. 5, or multiple polymer electrolyte fuel cells 30 may be stacked and connected in series to be used as a single fuel cell. The polymer electrolyte fuel cell 30 can be used by assembling it with a gas supply device, a cooling device, and other associated devices.

[0058] In addition to the above components, the polymer electrolyte fuel cell 30 may also include components such as gaskets to prevent gas leakage. The gaskets are arranged to surround the outer peripheries of the electrode catalyst layers 12A and 12C. The gas diffusion layer 31A and the separator 32A may be an integral structure, or the gas diffusion layer 31C and the separator 32C may be an integral structure. Alternatively, the gas diffusion layers 31A and 31C may be components that constitute the membrane electrode assembly 10.

[0059] [Method for manufacturing membrane electrode assembly] A method for manufacturing the membrane electrode assembly 10, including the method for manufacturing the electrode catalyst layers 12A and 12C, will now be described.

[0060] First, a catalyst ink is prepared as a coating liquid for forming the electrode catalyst layers 12 A and 12 C. The catalyst ink contains a catalyst-supporting carrier 20, a polymer electrolyte 23, a fibrous material 24, and a solvent.

[0061] The solvent functions as a dispersion medium for the catalyst ink. The solvent is not particularly limited as long as it does not corrode the catalyst-supported carrier 20, the polymer electrolyte 23, and the fibrous material 24, and can dissolve the polymer electrolyte 23 in a highly fluid state or disperse it as a fine gel. The solvent preferably contains a volatile organic solvent. Examples of the solvent include alcohols, ketone-based solvents, ether-based solvents, and other polar solvents. The solvent may be a mixed solvent or may contain water. The catalyst ink may contain a dispersant or a pore-forming agent, and may be subjected to a dispersion treatment.

[0062] The fibrous material 24 having irregularities is produced by baking electronically conductive fibers. The size of the irregularities can be controlled by adjusting the baking time and baking temperature. For example, the depth, width, and volume of the irregularities can be increased by extending the baking time. Also, the depth, width, and volume of the irregularities can be increased by increasing the baking temperature.

[0063] The catalyst ink is applied to a substrate to form a coating film, and the coating film is dried to form the electrode catalyst layers 12A, 12C. The catalyst ink can be applied by any known application method, such as a doctor blade method, a dipping method, a screen printing method, a die coating method, or a roll coating method.

[0064] The substrate may be, for example, a transfer substrate that is peeled off after transferring the electrode catalyst layers 12A, 12C to the polymer electrolyte membrane 11. The material of the transfer substrate may be, for example, a fluororesin or an organic polymer compound other than a fluororesin. The substrate for forming the electrode catalyst layers 12A, 12C may be the polymer electrolyte membrane 11 or the gas diffusion layers 31A, 31C.

[0065] When the substrate for forming the electrode catalyst layers 12A, 12C is a transfer substrate, the electrode catalyst layers 12A, 12C are bonded to the polymer electrolyte membrane 11 by thermocompression bonding, and then the transfer substrate is peeled off from the electrode catalyst layers 12A, 12C, thereby forming the membrane electrode assembly 10.

[0066] When the substrates for forming the electrode catalyst layers 12A, 12C are gas diffusion layers 31A, 31C, the electrode catalyst layers 12A, 12C supported by the gas diffusion layers 31A, 31C are joined to the polymer electrolyte membrane 11 by thermocompression bonding to form the membrane electrode assembly 10.

[0067] When the substrate for forming the electrode catalyst layers 12A, 12C is the polymer electrolyte membrane 11, the electrode catalyst layers 12A, 12C are formed directly on the surfaces of the polymer electrolyte membrane 11. In this way, the membrane electrode assembly 10 is formed.

[0068] [Example] The membrane electrode assembly and polymer electrolyte fuel cell provided with the above-described electrode catalyst layer will be described using specific examples and comparative examples.

[0069] (Examples / Comparative Examples) A platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used as the catalyst carrier, and calcined carbon nanofiber (VGCF®-H, manufactured by Showa Denko K.K.) was used as the fibrous material. The catalyst carrier, fibrous material, polymer electrolyte (Nafion® dispersion, manufactured by Wako Pure Chemical Industries, Ltd.), and dispersion media of water and 1-propanol were mixed. This mixture was dispersed in a planetary ball mill at 300 rpm for 60 minutes to produce a catalyst ink. During the dispersion process, 5 mm diameter zirconia balls were added to approximately one-third of the zirconia container.

[0070] In the catalyst ink, the mass of the polymer electrolyte was 100% by mass relative to the mass of the conductive support, and the mass of the fibrous material was 10% by mass relative to the mass of the conductive support. The catalyst ink was prepared so that the proportion of water in the dispersion medium was 50% by mass and the solids concentration of the catalyst ink was 10% by mass.

[0071] The catalyst ink was applied to one side of a polymer electrolyte membrane (Nafion (registered trademark) 211, manufactured by DuPont) with a platinum loading of 0.125 mg / cm. 2 A first coating film was formed by applying the catalyst ink using a slit die coater so that the thickness of the first coating film was 50 μm. The polymer electrolyte membrane on which the first coating film was formed was then dried in a hot air oven at 80°C for 5 minutes, and an electrode catalyst layer for the air electrode was formed from the first coating film. Next, a second coating film was formed by applying the catalyst ink to the other surface of the polymer electrolyte membrane using a slit die coater so that the thickness of the second coating film was 50 μm. The polymer electrolyte membrane on which the second coating film was formed was then dried on a hot plate at 80°C for 5 minutes, and an electrode catalyst layer for the fuel electrode was formed from the second coating film. This resulted in a membrane electrode assembly.

[0072] In the above manufacturing process, the calcination temperature of the carbon nanofibers was changed within the range of 750°C to 800°C, and the calcination time was changed within the range of 30 minutes to 120 minutes, thereby changing the size of the irregularities on the surface of the fibrous material, to obtain membrane electrode assemblies of Examples 1 to 8 and Comparative Examples 2 to 6. The calcination treatment was carried out in a nitrogen atmosphere using a calcination furnace. In Comparative Example 1, carbon nanofibers that had not been subjected to the calcination treatment were used as the fibrous material.

[0073] (Measurement of unevenness of fibrous materials) The depth and width of the irregularities of the fibrous material were measured by observing the fibrous material using a scanning electron microscope (FE-SEM Sigma500, manufactured by ZEISS). Specifically, the fibrous material adhered to a metal plate was used as the observation object, and for each fibrous material included in the field of view at an observation magnification of 20,000 times, the maximum depth and maximum diameter of the recesses constituting the surface irregularities were measured for each recess. Measurements were performed on multiple observation areas, and the maximum depth and maximum diameter of 100 recesses were measured for each example and each comparative example.

[0074] For each example and comparative example, a histogram was created based on the measurement results, with the maximum depth of the recesses in a 10 nm interval to determine the peak depth Pd of the irregularities, and a histogram was created based on the maximum diameter of the recesses in a 50 nm interval to determine the peak width Pw of the irregularities.The peak product Pp was then calculated by calculating the product of the peak depth Pd and the peak width Pw.

[0075] (Evaluation of power generation performance) In accordance with the "Cell Evaluation and Analysis Protocol" published by the New Energy and Industrial Technology Development Organization (NEDO), a JARI standard cell was used as the evaluation unit cell. The cell consisted of a gas diffusion layer, a gasket, and a separator on both sides of a membrane electrode assembly, and the assembly was clamped to a predetermined pressure. Then, for each example and comparative example, IV measurements were performed under both standard and high-humidity conditions. The standard conditions were those for IV measurements described in the "Cell Evaluation and Analysis Protocol." Under the high-humidity conditions, the relative humidity of both the anode and cathode was 100% RH.

[0076] In the evaluation of power generation performance, the current was 1.5A / cm 2 When the voltage was 0.64 V or higher, it was rated as particularly good (A); when it was 0.63 V or higher but less than 0.64 V, it was rated as good (B); when it was 0.60 V or higher but less than 0.63 V, it was rated as moderately poor (C); and when it was less than 0.60 V, it was rated as poor (D).

[0077] (Evaluation results) Table 1 shows the evaluation results of the peak depth Pd, peak width Pw, peak product Pp of the unevenness, and power generation performance for each example and each comparative example.

[0078] [Table 1]

[0079] As shown in Table 1, Examples 1 to 8, which satisfied the conditions of a depth peak Pd of 10 nm to 50 nm, a width peak Pw of 100 nm to 300 nm, and a peak product Pp of 10,000 or less, exhibited good or particularly good power generation performance under both standard and high-humidity conditions. Among these, Examples 4, 5, and 7, which had a depth peak Pd of 20 nm to 40 nm and a width peak Pw of 100 nm to 150 nm, exhibited particularly good power generation performance.

[0080] On the other hand, Comparative Example 1, in which the fibrous material had no irregularities, and Comparative Examples 2 to 6, in which at least one of the depth peak Pd, width peak Pw, and peak product Pp was outside the above range, had poor or slightly poor power generation performance.

[0081] Therefore, it is suggested that when the depth peak Pd, width peak Pw, and peak product Pp are within the above ranges, the proton conductivity can be suitably increased not only under standard conditions but also under high humidity conditions.

[0082] As explained above using the examples, the electrode catalyst layer, membrane electrode assembly, and polymer electrolyte fuel cell of the above-mentioned embodiment provide the following effects. (1) The fibrous material contained in the electrode catalyst layer has an uneven surface, and the depth peak Pd, width peak Pw, and peak product Pp are within the above-mentioned ranges. This makes it easier for the polymer electrolyte to become entangled with the fibrous material, favorably forming proton conduction paths in the electrode catalyst layer and improving proton conductivity. Furthermore, because proton conductivity is improved by controlling the distribution of the polymer electrolyte, a decrease in proton conductivity under high-humidity conditions is also suppressed. Therefore, the power generation performance of the fuel cell is improved.

[0083] (2) Because the fibrous material having an uneven surface can be formed by calcining electron-conductive fibers, the burden of processing the fibrous material can be reduced compared to when proton dissociative groups are introduced or proton-conductive materials are supported. This reduces the manufacturing cost of the electrode catalyst layer and achieves the effect of improving proton conductivity with a simple configuration.

[0084] (3) When the depth peak Pd is 20 nm or more and 40 nm or less and the width peak Pw is 100 nm or more and 150 nm or less, the polymer electrolyte is more easily entangled with the fibrous material, thereby further increasing the proton conductivity.

[0085] (4) When the fibrous material is carbon fiber, electronic conductivity is favorably obtained. Furthermore, the strength of the electrode catalyst layer is favorably improved and crack generation is suppressed. In particular, when the fibrous material is carbon nanofiber, these effects are enhanced.

[0086] (5) When the average fiber diameter of the fibrous material is 50 nm or more and 400 nm or less, pores in the electrode catalyst layer are well formed, which makes it possible to improve the power generation performance of the fuel cell. (6) When the average fiber length of the fibrous material is 1 μm or more and 50 μm or less, the strength of the electrode catalyst layer can be increased, which reduces the occurrence of cracks during the formation of the electrode catalyst layer. In addition, the formation of voids is favorable, which improves the power generation performance of the fuel cell. [Explanation of symbols]

[0087] 10...Membrane electrode assembly 11...Polymer electrolyte membrane 12A,12C…electrode catalyst layer 20...Catalyst support carrier 21...Conductive carrier 22...catalyst material 23...polymer electrolyte 24...Fibrous materials 30...Polymer fuel cell 32A, 32C...Separator

Claims

1. The electroconductive electrode includes a conductive support supporting a catalyst material, a polymer electrolyte, and a fibrous material that is an electron-conductive fiber, the fibrous material has an uneven surface; The depth peak, which is the peak of the distribution of the depth of the unevenness, is 10 nm or more and 50 nm or less, the width peak, which is the peak of the distribution of the width of the unevenness, is 100 nm or more and 300 nm or less, and the product of the depth peak and the width peak is 10,000 or less. Electrocatalyst layer.

2. The depth peak is 20 nm or more and 40 nm or less, and the width peak is 100 nm or more and 150 nm or less. The electrode catalyst layer according to claim 1 .

3. The fibrous material is carbon fiber. The electrode catalyst layer according to claim 1 .

4. The fibrous material is a carbon nanofiber. The electrode catalyst layer according to claim 1 .

5. The average fiber diameter of the fibrous material is 50 nm or more and 400 nm or less. The electrode catalyst layer according to claim 1 .

6. The average fiber length of the fibrous material is 1 μm or more and 50 μm or less. The electrode catalyst layer according to claim 1 .

7. a polymer electrolyte membrane; The electrode catalyst layer according to any one of claims 1 to 6, comprising: the electrode catalyst layer in contact with a surface of the polymer electrolyte membrane. Membrane electrode assembly.

8. The membrane electrode assembly according to claim 7; a pair of separators sandwiching the membrane electrode assembly therebetween; Polymer electrolyte fuel cell.

9. producing a catalyst ink containing a conductive support carrying a catalyst material, a polymer electrolyte, and a fibrous material that is an electron-conductive fiber; and drying a coating film formed from the catalyst ink to form an electrode catalyst layer, the fibrous material has an uneven surface; The depth peak, which is the peak of the distribution of the depth of the unevenness, is 10 nm or more and 50 nm or less, the width peak, which is the peak of the distribution of the width of the unevenness, is 100 nm or more and 300 nm or less, and the peak product, which is the product of the depth peak and the width peak, is 10,000 or less. A method for manufacturing an electrode catalyst layer.

10. and forming the fibrous material by forming the irregularities on the surface of the fiber by firing the electron conductive fiber. The method for producing an electrode catalyst layer according to claim 9 .

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