Catalyst electrode for fuel cell and solid polymer fuel battery having the same

Abstract

To provide a catalyst electrode for a fuel cell having an excellent output point performance, and a solid polymer fuel battery.SOLUTION: The catalyst electrode for a fuel cell includes: an electrode catalyst including a carrier and an active species carried by the carrier: and an ionomer. The pH in an aqueous solution of the electrode catalyst is in the range from 2.8 to 3.2. The distance between the active species and the ionomer is 2.09 at a maximum.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a catalyst electrode for a fuel cell and a polymer electrolyte fuel cell including the same. [Background technology]

[0002] Polymer electrolyte fuel cells, which generate electricity through an electrochemical reaction between fuel gas and oxidant gas, have been attracting attention as an energy source. Polymer electrolyte fuel cells can be operated at room temperature and have a high output density, so they are being actively researched as a form of fuel suitable for automotive applications.

[0003] In a solid polymer fuel cell, generally, a membrane electrode assembly ("fuel electrode-solid polymer electrolyte membrane-air electrode") (hereinafter also referred to as "MEA") is used, which is made by bonding catalyst electrodes (fuel electrode (anode catalyst layer) and air electrode (cathode catalyst layer)) consisting of catalyst layers to both sides of a solid polymer electrolyte membrane, which is an electrolyte membrane. In some cases, gas diffusion layers are further bonded to both sides of the MEA, which is called a membrane electrode gas diffusion layer assembly ("gas diffusion layer-MEA-gas diffusion layer") (hereinafter also referred to as "MEGA").

[0004] Each catalytic electrode is formed from a catalytic layer, which is a layer for carrying out an electrode reaction by an electrode catalyst contained in the catalytic layer. In order to advance the electrode reaction, a three-phase interface in which the electrolyte, the electrode catalyst, and the reactant gas coexist is necessary, so the catalytic layer is generally made of a layer containing the electrode catalyst and the electrolyte. The gas diffusion layer is a layer for supplying the reactant gas to the catalytic layer and transferring electrons thereto, and is made of a porous material having electronic conductivity.

[0005] Regarding catalyst electrodes used in such solid polymer fuel cells, for example, Patent Document 1 discloses a paste for forming an electrode catalyst layer in close contact with a solid polymer electrolyte membrane that selectively transmits hydrogen ions, the paste comprising catalyst-supported carbon dispersed in a polymer resin solution of the same quality as the solid polymer electrolyte membrane, and a basic functional group bonded to the surface aromatic ring of the catalyst-supported carbon.

[0006] Patent Document 2 discloses a fuel cell electrode comprising a solid polymer electrolyte membrane and a pair of electrodes having catalytic reaction layers sandwiching the solid polymer electrolyte membrane, the electrodes having a hydrogen ion diffusion layer on the surface of a catalyst particle or a support for the catalyst particle.

[0007] Patent Document 3 discloses a catalyst for a polymer electrolyte fuel cell, which is made of a supported catalyst formed by treating the carbon surface with a basic surface treatment agent.

[0008] Patent Document 4 discloses a catalyst for use in electrodes of polymer electrolyte fuel cells, which is formed by supporting metal particles on a carbon material, and is characterized in that the nitrogen adsorption specific surface area of ​​the carbon material, the ratio of the amount of basic functional groups to SBET, the ratio of the amount of acidic functional groups to SBET, and the ratio of the amount of basic functional groups B to the amount of acidic functional groups TA all have specific values. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 8-78021 [Patent Document 2] JP 2000-228204 A [Patent Document 3] JP 2002-373663 A [Patent Document 4] JP 2008-269850 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, the prior art only refers to the performance in the efficiency point region, and therefore does not refer to the power point region (material transport).

[0011] Therefore, an object of the present invention is to provide a catalyst electrode for a fuel cell having excellent power point performance, and a polymer electrolyte fuel cell including the same. [Means for solving the problem]

[0012] The power point performance of a catalyst electrode for a fuel cell requires both proton supply and gas diffusion performance, and also requires catalytic activity (efficiency point performance).

[0013] In a catalytic electrode, by making the catalytic surface of the electrode catalyst hydrophobic, an ionomer can be induced on the catalytic surface and a hydrogen ion channel can be formed near the carrier surface. As a result, proton transfer becomes favorable in the catalytic electrode, and the power point performance of the catalytic electrode is improved. However, in some fuel cells, the power point performance does not improve even if the hydrophobicity of the catalytic surface is increased.

[0014] This is thought to be because as the catalyst surface becomes more hydrophobic, ionomer is induced on the catalyst surface, which reduces the proton resistance, i.e., when proton transfer improves, the structure of the catalyst particles collapses, the gas diffusion performance decreases, and furthermore, the poisoning of active species by the ionomer is promoted, resulting in a decrease in catalytic activity. Therefore, the hydrophobicity of the electrode catalyst alone is insufficient to evaluate the output point performance of a fuel cell.

[0015] However, it has not been possible to measure the distance between the active species and the ionomer in the past. This is because, although a transmission electron microscope (TEM) is used for nano-sized structural analysis, the fluorine (F) in the ionomer is easily damaged by electron beams, and furthermore, the fluorine (F) in the ionomer is difficult to distinguish in contrast compared to the carbon (C) of the catalyst support, which is also a light element. Therefore, when measuring a catalyst electrode using TEM-EDX, the ionomer on the catalyst surface may be burned away, or it may be difficult to distinguish between the fluorine of the ionomer on the catalyst surface and the carbon of the catalyst support.

[0016] Therefore, the inventors have investigated various means for solving the above problems and have found that the water immersion pH, which is a surface property of the electrode catalyst, and the distance between the active species and the ionomer, which is obtained using advanced analytical technology using 3D-TEM, are highly correlated with the performance of the fuel cell catalyst electrode, thereby completing the present invention.

[0017] That is, the gist of the present invention is as follows. (1) A catalyst electrode for a fuel cell, comprising a support, an electrode catalyst containing an active species supported on the support, and an ionomer, The pH of the electrode catalyst when immersed in water is 2.8 to 3.2; The distance between the active species and the ionomer is 2.09 nm or less. Catalyst electrode for fuel cells. (2) A solid polymer electrolyte fuel cell comprising a membrane electrode assembly having an anode catalyst layer, a cathode catalyst layer, and a solid polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer, The anode catalyst layer and / or the cathode catalyst layer is the fuel cell catalyst electrode according to (1). Polymer electrolyte fuel cell. Effect of the Invention

[0018] The present invention provides a catalyst electrode for a fuel cell having excellent power point performance, and a polymer electrolyte fuel cell including the same. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating an example of a catalyst electrode for a fuel cell according to the present invention. [Diagram 2] Photographs showing an example of imaging and synthesis of a catalytic electrode by 3D-TEM. [Diagram 3] 1 is a graph showing the ratio of the accumulated number of active species particles to the active species-ionomer distance in the catalytic electrodes of Examples 1 to 4 and Comparative Example 1. [Figure 4] 1 is a graph showing the active species coverage and the active species-ionomer distance versus the pH of water immersion of the electrode catalyst in the catalyst electrodes of Examples 1 to 4 and Comparative Example 1. [Diagram 5] 1 is a graph showing (A) catalyst layer H+ resistance, (B) gas diffusion resistance, and (C) output point voltage versus active species-ionomer distance in the catalyst electrodes of Examples 1 to 4 and Comparative Example 1. [Figure 6] 1 is a graph showing (A) the water immersion pH, and (B) the output point voltage versus active species coverage in the catalytic electrodes of Examples 1 to 4 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity, and the actual dimensions and shapes are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the fuel cell catalyst electrode and the solid polymer electrolyte fuel cell including the same of the present invention are not limited to the following embodiments, and can be embodied in various forms with modifications and improvements that can be made by those skilled in the art within the scope of the gist of the present invention.

[0021] In the present invention, the support may be any support known in the art, and examples thereof include, but are not limited to, carbon materials such as carbon black, carbon nanotubes, and carbon nanofibers, and carbon compounds such as silicon carbide.

[0022] The average particle size of the carrier is not limited, but is usually 10 μm to 500 μm. Here, the average particle size of the carrier is usually the average value of the diameters of circles equivalent to the projected areas of 100 carrier particles measured by SEM, TEM, XRD, 3D-TEM, etc.

[0023] The BET specific surface area of ​​the support is not limited, but is usually 100 m 2 / g~2000m 2 / g.

[0024] Here, the BET specific surface area is a specific surface area determined by the BET method, and is known to those skilled in the art. The unit of the BET specific surface area is the area (m) per 1 g of the carrier. 2 / g).

[0025] When the support has the above average particle size and BET specific surface area, the performance of the fuel cell can be improved.

[0026] The active species supported on the carrier are the reactants at the MEA electrodes. Air electrode (cathode): O2+4H + +4e - →2H2O Fuel electrode (anode): 2H2→4H + +4e - The active species is not limited as long as it shows catalytic activity in the above-mentioned range, and metal catalysts known in the art can be used. As the active species, noble metals such as platinum, palladium, rhodium, gold, silver, osmium, iridium, etc. can be used, but are not limited thereto. The active species may also be an alloy of a noble metal, such as a platinum alloy, for example, an alloy of platinum with at least one selected from the group consisting of aluminum, chromium, manganese, iron, cobalt, nickel, gallium, zirconium, molybdenum, ruthenium, rhodium, palladium, vanadium, tungsten, rhenium, osmium, iridium, titanium, and lead.

[0027] The amount of the active species is not limited, but is usually 30% by mass to 70% by mass with respect to the total mass of the catalyst electrode for a fuel cell.

[0028] The average particle size of the active species is not limited, but is usually 2 nm to 10 nm. Here, the average particle size of the active species is usually the average value of the projected area circle equivalent diameters of 500 to 1000 particles of the active species measured by TEM, XRD, 3D-TEM, etc.

[0029] In the present invention, the active species is supported on the support to form an electrocatalyst comprising the support and the active species supported on the support.

[0030] The average particle size of the electrode catalyst is not limited, but is usually 10 μm to 500 μm. Here, the average particle size of the electrode catalyst is usually the average value of the projected area circle equivalent diameters of 100 particles measured by SEM, TEM, XRD, 3D-TEM, etc.

[0031] The water immersion pH of the electrode catalyst of the present invention is 2.8 to 3.2, and in one embodiment, 3.0 to 3.1.

[0032] Here, the water immersion pH of the electrode catalyst of the present invention can be measured as follows. 0.5 g of the electrode catalyst is added to 20 mL of ion-exchanged water and stirred for 1 hour, after which the suspension is measured with a pH meter (pH meter Navi 50 series F-21, manufactured by Horiba, Ltd.).

[0033] By setting the water immersion pH of the electrode catalyst within the above range, the distance between the active species and the ionomer in the catalyst electrode for a fuel cell can be adjusted to the range described below.

[0034] The ionomer can be any ionomer known in the art, and is not limited thereto.The ionomer can be the same as the electrolyte constituting the solid polymer electrolyte membrane described below, and can be, for example, a perfluorosulfonic acid resin material, such as Nafion (registered trademark), a sulfonated plastic electrolyte, such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfone, sulfonated polysulfide, sulfonated polyphenylene, or a sulfoalkylated plastic electrolyte, such as sulfoalkylated polyether ether ketone, sulfoalkylated polyether sulfone, sulfoalkylated polyether ether sulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, or sulfoalkylated polyphenylene.

[0035] More specifically, the ionomer is not particularly limited, but for example, perfluorocarbon sulfonic acid polymer, high oxygen permeable ionomer, etc. The ionomer may be used alone or in combination of two or more kinds.

[0036] Examples of perfluorocarbon sulfonic acid polymers include fluorine-containing ion exchange resins containing repeating units based on fluorinated sulfonyl vinyl ether monomers. Examples of perfluorocarbon sulfonic acid polymers include Nafion (registered trademark), Flemion (registered trademark), Aquivion (registered trademark), and Aciplex (registered trademark).

[0037] The highly oxygen-permeable ionomer refers to a polymeric compound that contains an acid group and a cyclic structure in its molecular structure. The highly oxygen-permeable ionomer has a high oxygen permeability coefficient because it contains a cyclic structure in its molecular structure. Therefore, when the highly oxygen-permeable ionomer is used as an ionomer, the oxygen transfer resistance at the interface with the catalyst becomes relatively small. In other words, the highly oxygen-permeable ionomer refers to an ionomer that has a higher oxygen permeability coefficient than perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark).

[0038] Examples of highly oxygen-permeable ionomers include (a) electrolyte polymers containing a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having perfluorosulfonic acid in the side chain, (b) electrolyte polymers containing a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having perfluoroimide in the side chain, and (c) electrolyte polymers containing a unit in which perfluorosulfonic acid is directly bonded to a perfluorocarbon having an aliphatic ring structure (see, for example, JP 2003-036856 A, WO 2012 / 088166 A, JP 2013-216811 A, and JP 2006-152249 A).

[0039] The equivalent weight (EW) of the ionomer is not limited, but is usually 500 g / mol to 1500 g / mol.

[0040] The content of the ionomer in the catalyst layer may be appropriately set depending on the amount of the support, and the I / C ratio (ionomer mass / carbon (support) mass) may be, for example, 0.3 to 1.3, in one embodiment, 0.4 to 1.1, and in one embodiment, 0.5 to 1.0.

[0041] In the fuel cell catalyst electrode of the present invention, the distance between the active species and the ionomer is 2.09 nm or less, in one embodiment it is less than 5.5 nm, and in another embodiment it is 1.50 nm or less. Note that the active species and the ionomer may be in contact with each other, in which case the distance between the active species and the ionomer is 0 nm.

[0042] Here, the distance between the active species and the ionomer means the distance up to which all active species particles that are not in contact with the ionomer in the electrode catalyst particle come into contact with the ionomer, i.e., the distance between the ionomer and the active species particle that is farthest from the ionomer in the electrode catalyst particle, and can be measured as follows.

[0043] First, a 3D image of the target fuel cell catalyst electrode is captured and synthesized using a 3D-TEM equipped with various detectors with different capture angles. In the obtained 3D image of the fuel cell catalyst electrode, carbon, active species, and ionomers are identified based on the difference in contrast. In the 3D image, the measurement area is 130 nm 3 For each of the active species (approximately 500 or more) in the sample, the shortest distance between the active species and the ionomer is measured, and the maximum distance among the shortest distances is regarded as the distance between the active species and the ionomer.

[0044] In the catalyst electrode for a fuel cell, by setting the distance between the active species and the ionomer within the above range, the output point performance of the catalyst electrode for a fuel cell is improved.

[0045] In the catalyst electrode for a fuel cell of the present invention, the proportion of active species and ionomer where the distance between them is 0 nm, i.e., the proportion of active species and ionomer in contact with each other (hereinafter also referred to as active species coverage), is not limited, but is usually 20% to 80% of the total number of active species particles, and in one embodiment, 38.4% to 79.4%.

[0046] In a catalyst electrode for a fuel cell, the output point performance of the catalyst electrode for a fuel cell is improved by having the distance between the active species and the ionomer within the above-mentioned range, i.e., short, and the coverage rate of the active species within the above-mentioned range, i.e., the active species and the ionomer come into contact at a specific ratio.

[0047] The catalyst electrode for a fuel cell of the present invention is shown in Fig. 1. In the present invention, the distance between the active species and the ionomer (active species-ionomer distance) shown in Fig. 1 is controlled to provide a catalyst electrode for a fuel cell with improved output point performance.

[0048] The fuel cell catalyst electrode of the present invention can be used as a catalyst electrode for a cathode catalyst layer and / or an anode catalyst layer in a fuel cell. The fuel cell catalyst electrode of the present invention is preferably used as a catalyst electrode for a cathode catalyst layer in a fuel cell. By using the fuel cell catalyst electrode of the present invention as a catalyst electrode for a cathode catalyst layer, output performance can be improved.

[0049] The catalyst electrode for fuel cells of the present invention can be manufactured by a method known in the art, except that the electrode catalyst and the ionomer are arranged so that the distance between the active species and the ionomer is 2.09 nm or less, that is, the active species are supported (the amount of support is controlled) so that the pH of the water immersion is in the above range, and the I / C is adjusted so that the distance between the active species and the ionomer is in the above range, using the carrier having a water immersion pH of 2.8 to 3.2 as the electrode catalyst, and the electrode catalyst and the ionomer are arranged so that the distance between the active species and the ionomer is 2.09 nm or less, that is, the active species are supported (the amount of support is controlled) so that the pH of the water immersion is in the above range, and the I / C is adjusted so that the distance between the active species and the ionomer is in the above range. For example, the method for manufacturing the catalyst electrode for fuel cells of the present invention is as follows.

[0050] (1) A support and an active species precursor, for example, when the active species is platinum, a dinitrodiamineplatinum nitrate solution, are suspended in a solvent, for example, pure water, to obtain a suspension.

[0051] (2) The active species precursor in the suspension obtained in (1) is reduced to a precious metal using a reducing agent, such as ethanol or sodium borohydride, usually at room temperature (about 20° C.) to 100° C. to obtain a dispersion.

[0052] (3) The dispersion obtained in (2) is filtered, and the resulting cake is dried usually at 80° C. to 120° C., usually for 1 hour to 12 hours, to obtain a powder.

[0053] (4) The powder obtained in (3) is calcined in an inert atmosphere, for example, a nitrogen or argon atmosphere, usually at 100° C. to 1200° C., usually for 1 hour to 8 hours, to obtain an electrode catalyst.

[0054] The calcination in (4) is carried out to improve the durability of the fuel cell catalyst electrode when used at high temperatures. If the electrode catalyst obtained in (4) contains impurities such as the metals added in (2), the electrode catalyst obtained in (4) can be added to a solution containing an acid or base to dissolve and remove the impurities.

[0055] Furthermore, when alloying precious metals in a fuel cell catalyst electrode, a solution containing the metal contained in the alloy, such as cobalt, in ionic form is added to the electrode catalyst, and the electrode catalyst is calcined (alloyed) to alloy platinum to platinum-cobalt, and finally an acid treatment is performed.

[0056] (5) The electrode catalyst and the ionomer are suspended in a solvent, such as pure water, with a suitable I / C to prepare a catalyst ink. In this case, ultrasonic dispersion or the like may be used to obtain a uniform catalyst ink.

[0057] (6) The catalyst ink obtained in (5) is sprayed and attached onto a peelable substrate, such as a Teflon sheet, to form a catalyst electrode precursor. For spraying and attachment, there are methods that utilize gravity, spray force, or electrostatic force.

[0058] (7) The catalyst electrode precursor on the substrate is dried to prepare a catalyst electrode on the substrate, and the catalyst electrode is peeled off from the substrate to obtain the catalyst electrode. Here, in (6) to (7), the catalyst ink is sprayed and adhered onto a substrate, and then dried and peeled off to obtain a catalyst electrode. However, the catalyst ink can also be directly sprayed and adhered onto the surface of a solid polymer electrolyte membrane, and then dried to prepare a catalyst electrode.

[0059] The present invention also relates to a fuel cell comprising the fuel cell catalyst electrode of the present invention, i.e., a solid polymer electrolyte fuel cell comprising a membrane electrode assembly having an anode catalyst layer, a cathode catalyst layer, and a solid polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer, in which the catalyst electrode of the anode catalyst layer and / or the cathode catalyst layer is the fuel cell catalyst electrode of the present invention.

[0060] Here, the solid polymer electrolyte membrane is preferably an electrolyte membrane having proton conductivity. As the electrolyte membrane having proton conductivity, an electrolyte membrane having proton conductivity known in the art can be used, and is not limited thereto, for example, a membrane formed from a fluorine resin having a sulfonic acid group (such as Nafion (manufactured by DuPont), Flemion (manufactured by AGC), and Aciplex (manufactured by Asahi Kasei)) which is an electrolyte can be used.

[0061] The thickness of the solid polymer electrolyte membrane is not limited, but is usually 5 μm to 50 μm in order to improve the proton conductivity function.

[0062] The anode catalyst layer serves as the fuel electrode, that is, the hydrogen electrode, and the cathode catalyst layer serves as the air electrode (oxygen electrode), and either or both of the catalyst layers are the catalyst electrodes for the fuel cell of the present invention.

[0063] When the anode catalyst layer or the cathode catalyst layer is not the catalyst electrode for the fuel cell of the present invention, the catalyst electrode may be any catalyst electrode known in the art.

[0064] The thickness of each catalyst layer is not limited, but is usually 1 μm to 20 μm in order to ensure the amount of catalyst necessary for power generation and to keep the proton resistance low.

[0065] The polymer electrolyte fuel cell of the present invention can be produced by a method known in the art.

[0066] The polymer electrolyte fuel cell of the present invention can be prepared, for example, as follows. (1) When the fuel cell catalyst electrode of the present invention is used as the air electrode and / or fuel electrode, and the fuel cell catalyst electrode of the present invention is not used as the air electrode and / or fuel electrode, a commercially available catalyst electrode is used. A layer assembly is obtained by placing a solid polymer electrolyte membrane in the center, placing an air electrode on one side, and placing a fuel electrode on the other side. In some cases, a diffusion layer, for example, a conductive porous sheet, such as a sheet made of a material having air or liquid permeability, such as carbon cloth or carbon paper, may be placed on the outside of each of the air electrode and the fuel electrode. (2) The layer assembly obtained in (1) in the form of (diffusion layer-) air electrode-solid polymer electrolyte membrane-fuel electrode (-diffusion layer) is pressed by hot pressing, usually at 100°C to 200°C, for example at 140°C, usually for 5 seconds to 600 seconds, for example for 300 seconds, to obtain a membrane electrode assembly or MEGA. (3) Separators that allow gas to flow are placed on both sides of the membrane electrode assembly or MEGA obtained in (2) to obtain a single cell. A plurality of such single cells are stacked to obtain a polymer electrolyte fuel cell.

[0067] The polymer electrolyte fuel cell of the present invention has excellent power point performance derived from the catalyst electrode for fuel cells of the present invention. EXAMPLES

[0068] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples.

[0069] 1. Manufacturing of membrane electrode assembly The membrane / electrode assemblies of Examples 1 to 4 and Comparative Example 1 were prepared according to the following methods.

[0070] [Example 1] (Supporting process) 1 g of heat-treated mesoporous carbon-1 (carbon soaked pH 10.4) was dispersed in 41.6 mL of pure water, to which was added an aqueous solution of dinitrodiamine platinum salt (see Patent No. 4315857, manufactured by Cataler Co., Ltd.) containing 0.72 g of platinum, and then 3.2 g of ethanol was further added and heated to reduce the platinum. In this way, platinum particles, which are catalytic metal particles, were supported on the support made of mesoporous carbon-1, and a platinum-supported catalyst was obtained. Next, cobalt was supported on the platinum catalyst, and a platinum-cobalt supported catalyst was obtained. Cobalt was supported in an amount such that the platinum:cobalt ratio in the final fuel cell electrode catalyst was 7:1 (molar ratio).

[0071] (Alloying process) The obtained platinum-cobalt supported catalyst was heated at 800°C under an argon atmosphere to alloy platinum and cobalt, thereby obtaining a powdered fuel cell electrode catalyst. The loading density of the platinum-cobalt alloy particles in the fuel cell electrode catalyst was 42% by mass. The loading density of platinum was calculated by (platinum mass / electrode catalyst mass) x 100 (mass%). The platinum mass was the mass of platinum supported on the fuel cell catalyst, determined by ICP spectroscopy.

[0072] (Preparation of catalyst ink) To 1 g of the fuel cell electrode catalyst powder, 8 g of ultrapure water and 6 g of ethanol were added and stirred, and then 0.52 g of ionomer was added. The mixture was then dispersed for 30 minutes using an ultrasonic disperser, and then dispersed for 15 minutes using a thin film swirling mixer (Filmix, manufactured by Primix Corporation) at 30 m / s to obtain a catalyst ink as a uniform slurry.

[0073] (Preparation of air electrode catalyst layer sheet) The catalyst ink was applied to a polytetrafluoroethylene sheet using an ink coater, and after application, the sheet was dried for 5 minutes in a blower dryer at 80°C to obtain an air electrode catalyst layer sheet in which an air electrode catalyst layer was formed on a polytetrafluoroethylene sheet. The air electrode catalyst layer had a platinum coverage of 0.2 mg / cm. 2 The I / C ratio (ionomer mass / carbon (support) mass) was 0.95.

[0074] (Preparation of fuel electrode catalyst layer sheet) 8 g of ultrapure water and 6 g of ethanol were added to 1 g of the platinum-supported carbon black powder (ketjen), and after stirring, 0.26 g of ionomer (Nafion) was added. Next, the mixture was dispersed for 30 minutes using an ultrasonic disperser, and then dispersed for 15 minutes at 30 m / s using a thin film swirling mixer (Filmix, manufactured by Primix Corporation), to obtain a catalyst ink as a uniform slurry. The catalyst ink was applied to a polytetrafluoroethylene sheet using an ink coater, and after application, the sheet was dried for 5 minutes in a blower dryer at 80° C. to obtain an anode catalyst layer sheet in which an anode catalyst layer was formed on a polytetrafluoroethylene sheet. The anode catalyst layer had a platinum coverage of 0.2 mg / cm. 2 and the I / C ratio (ionomer mass / carbon black (carrier) mass) was 0.5.

[0075] (Fabrication of membrane electrode assembly) The electrolyte membrane, a Teflon (registered trademark) sheet, was sandwiched between an air electrode catalyst layer sheet and an anode catalyst layer sheet, and hot-pressed to transfer the catalyst layers (air electrode catalyst layer and anode catalyst layer) to the Teflon (registered trademark). The polytetrafluoroethylene sheets were then peeled off to obtain a membrane electrode assembly (MEA).

[0076] [Example 2] The same procedure as in Example 1 was repeated except that in the supporting process, the heat-treated mesoporous carbon-1 was changed to heat-treated mesoporous carbon-2 (carbon immersion pH 10.0) and the I / C ratio (ionomer mass / carbon (support) mass) of the air electrode catalyst layer in the preparation of the air electrode catalyst layer sheet was changed to 1.05.

[0077] [Example 3] The same procedure as in Example 2 was carried out, except that in the supporting step, the heat-treated mesoporous carbon-2 was changed to heat-treated mesoporous carbon-3 (carbon soaked in water at pH 7.3).

[0078] [Example 4] The same procedure as in Example 2 was carried out, except that in the supporting step, the heat-treated mesoporous carbon-2 was changed to heat-treated mesoporous carbon-4 (carbon immersed in water at pH 6.5).

[0079] [Comparative Example 1] In Example 1, the heat-treated mesoporous carbon-1 in the supporting step was changed to heat-treated solid carbon-1 (carbon water immersion pH 5.64), and the platinum weight of the air electrode catalyst layer in the preparation of the air electrode catalyst layer sheet was 0.35 mg / cm 2 The same procedure as in Example 1 was carried out except that the I / C ratio (ionomer mass / carbon (carrier) mass) was set to 1.07.

[0080] The water immersion pH of the electrode catalyst was measured by putting 0.5 g of the electrode catalyst into 20 mL of ion-exchanged water, stirring for 1 hour, and measuring the resulting suspension with a pH meter (pH meter Navi 50 series F-21, manufactured by Horiba, Ltd.).

[0081] 2. Measurement of the distance between the active species and the ionomer (active species-ionomer distance) For the obtained Comparative Example 1 and Examples 1 to 4, the active species-ionomer distance was measured as follows.

[0082] 3D images of the air electrode catalyst layer sheet or the anode catalyst layer sheet, which are the fuel cell catalyst electrodes in the MEAs of Comparative Example 1 or Examples 1 to 4, were obtained by imaging and synthesizing using a 3D-TEM equipped with various detectors with different capture angles, as shown in FIG. 2. In the obtained 3D images of the fuel cell catalyst electrodes, carbon, active species, and ionomers were identified based on differences in contrast. In the 3D images, the measurement area was 130 nm 3 The shortest distance between the active species and the ionomer was measured for each of the active species (approximately 500 or more), and the maximum distance among the shortest distances was determined as the distance between the active species and the ionomer. The results are shown in Table 1 and Figures 3 and 4.

[0083] [Table 1]

[0084] From Table 1 and Figures 3 and 4, it was found that the more hydrophobic the surface (the higher the pH of water immersion), the shorter the distance between the active species and the ionomer tends to be. It was also found that when the pH of water immersion is 3.0 to 3.1, the coverage rate of the active species of the ionomer becomes relatively small, and the distance between the active species and the ionomer becomes shorter. On the other hand, it was found that when the pH of water immersion is 3.2, the coverage rate of the active species of the ionomer becomes high.

[0085] 3. Output point, gas diffusion resistance, and catalyst layer H + Resistance Evaluation Fuel cells were manufactured using the MEAs of Comparative Example 1 or Examples 1 to 4, and the performance of each fuel cell (output point, gas diffusion resistance, and catalyst layer H + The measurement methods for each performance were as follows:

[0086] How to measure the output point First, the MEA of Comparative Example 1 or Examples 1 to 4 was 2 The MEA was assembled into a rectangular cell for use in a fuel cell. Next, a diffusion layer and a current collector were placed on both sides of the MEA. Carbon paper (with a microporous layer) was used for the diffusion layer. A gold-plated steel sheet with an integrated circuit (flow path: linear flow path with a 0.4 mm pitch) was used for the current collector. Finally, using the obtained fuel cell, an output point voltage of 3.2 A / cm under humidified conditions (80% RH, cell temperature 60°C) was measured. 2 (mV) was evaluated. The power generation conditions were: H2 flow path: 500cc / min, air flow rate: 1000cc / min, back pressure: 1kg / cm 2 The measurement device used was an As-510-340 fuel cell power generation characteristic evaluation system (manufactured by NF Corporation).

[0087] -Method for measuring gas diffusion resistance For the MEAs of Comparative Example 1 or Examples 1 to 4, IV measurements were performed under conditions of 60°C, 80% RH, low oxygen concentration (oxygen concentration: 1%), and a measuring device (As-510-340 Fuel Cell Power Generation Characteristic Evaluation System (manufactured by NF Corporation)). The limiting current density was calculated from the obtained IV characteristics for each sample. That is, the limiting current density was calculated by dividing the value of the current (limiting current) in the portion of the IV characteristics where the current does not increase even if the voltage decreases, by the surface area of ​​the catalyst electrode layer. The gas diffusion resistance (unit: sec / m) was calculated by calculating the time required for one oxygen molecule to move 1 m based on the obtained limiting current density, temperature, humidity, and oxygen concentration.

[0088] ·Catalyst layer H + How to measure resistance For the MEAs of Comparative Example 1 or Examples 1 to 4, catalyst layer impedance measurement (60° C., 80% RH) was performed, and the catalyst layer H calculated from the real part of the catalyst layer impedance was + (Proton) resistance was sought. The results are shown in Table 2 and Figures 5 and 6.

[0089] [Table 2]

[0090] From Table 2 and Figure 5, it can be seen that the shorter the active species (Pt)-ionomer distance, the lower the gas diffusion performance is, but the catalyst layer H + It was found that the resistance (material transport) was improved, which resulted in improved output point performance. Furthermore, from Table 2 and Figure 6, it was found that when the water immersion pH was 2.8 to 3.2, the output performance improved, and further, when the coverage rate of the active species of the ionomer was high, the output performance tended to decrease.

Claims

1. A catalyst electrode for a fuel cell comprising an electrode catalyst including a support and an active species supported on the support, and an ionomer, The pH of the electrode catalyst immersion is 2.8 to 3.2; The distance between the active species and the ionomer is 2.09 nm or less. Catalyst electrode for fuel cells.

2. A solid polymer electrolyte fuel cell comprising a membrane electrode assembly having an anode catalyst layer, a cathode catalyst layer, and a solid polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer, The anode catalyst layer and / or the cathode catalyst layer is the catalyst electrode for a fuel cell according to claim 1. Polymer electrolyte fuel cell.

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