JP2005317467A - Electrode for fuel cell and mea for fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a fuel cell capable of showing high performance for a long period of time. <P>SOLUTION: In the electrode for a fuel cell including an electrode catalyst composed of conductive carrier carrying catalyst particles and a trap member, the trap member reduces the component of the catalyst particles eluted from the electrode catalyst to make it deposit on the surface of the trap member, thereby solving the problem. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell electrode, and more particularly to a fuel cell electrode having high durability.

  In recent years, in response to social demands and trends against the background of energy and environmental issues, polymer electrolyte 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. . The solid polymer fuel cell is characterized by using an electrolyte membrane made of a film-like solid polymer membrane.

  The polymer electrolyte fuel cell generally has a structure in which a membrane-electrode assembly (hereinafter also referred to as “MEA”) is sandwiched between separators. The MEA is formed by sandwiching an electrolyte membrane between fuel cell electrodes.

  Conventional polymer electrolyte fuel cells are used by forming a stack in which a plurality of MEAs are stacked in series through a separator so as to obtain a desired voltage or the like (for example, see Patent Document 1). ). The document 1 describes a method for comparing performance indications such as cell voltages in a stack and preventing operation in a state that causes a failure or danger of the fuel cell.

  In such a polymer electrolyte fuel cell, an electrode catalyst oxidizes the hydrogen gas of the fuel at the anode to convert it to protons, and at the cathode it reduces oxygen and combines it with protons that have passed through the electrolyte membrane to form water and chemical reaction Happens. The polymer electrolyte fuel cell directly obtains electric energy from the reaction energy obtained by the chemical reaction.

As an electrode catalyst, an electrode catalyst is used in which catalyst particles such as platinum or platinum alloy are made fine and supported on a carrier having a large specific surface area such as carbon black for both the cathode and the anode.
Japanese Translation of National Publication No. 05-502973

  However, in a conventional polymer electrolyte fuel cell, when the cathode becomes a noble potential environment (about 0.8 V or more) due to operating conditions, starting and stopping conditions, such as performing an air purge when the fuel cell is stopped, Since the electrochemical oxidation reaction of platinum occurs and the catalyst particles are eluted, the amount of the catalyst is reduced, which may reduce the battery life.

  On the other hand, when fuel shortage occurs in the anode, in order to maintain a desired current density, electrolysis of water and oxidation of the carrier may occur in place of the oxidation reaction of the fuel, and elution of catalyst particles may occur. was there.

  In the polymer electrolyte fuel cell, the life of the battery is a problem as well as the cost. The battery life is said to be 5000 hours for automobiles and 40,000 hours for home use, and it is required to maintain desired power generation performance over a long period of time.

  Accordingly, an object of the present invention is to provide a fuel cell electrode that can exhibit high performance over a long period of time.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be solved by including in the fuel cell electrode a trap material having an action of reducing and precipitating the catalyst particle component eluted from the electrode catalyst.

  That is, the present invention provides a fuel cell electrode comprising an electrode catalyst in which catalyst particles are supported on a conductive support and a trap material, wherein the trap material reduces catalyst particle components eluted from the electrode catalyst. Thus, the fuel cell electrode is deposited on the surface of the trap material.

  According to the trap material included in the fuel cell electrode of the present invention, the catalyst particle component eluted as the electrode reaction proceeds can be reduced and deposited on the surface of the trap material. The catalyst particles thus deposited can again exhibit catalytic action. Therefore, according to the present invention, it is possible to provide a fuel cell electrode capable of improving the utilization rate of catalyst particles and exhibiting high power generation performance over a long period of time, thereby further improving the performance of the fuel cell. Is possible.

  The first of the present invention is a fuel cell electrode comprising an electrode catalyst in which catalyst particles are supported on a conductive carrier and a trap material, wherein the trap material contains catalyst particle components eluted from the electrode catalyst. It is an electrode for a fuel cell that is reduced and deposited on the surface of the trap material.

  As described above, the catalyst particles of the electrode catalyst included in the fuel cell electrode may be eluted due to the operating conditions, starting and stopping conditions of the fuel cell. The catalyst particle component eluted from the electrode catalyst cannot participate in the electrode reaction. Therefore, the elution of catalyst particles is one of the causes of performance deterioration of the fuel cell electrode.

  In this invention, it discovered that the performance deterioration of an electrode could be suppressed by including the trap material which can precipitate the eluted catalyst particle component in the electrode for fuel cells. FIG. 1 illustrates an example of a trap material in which a reducing compound is adsorbed on the surface of a carbon support and is coated with an ion exchange polymer. When platinum or the like is used as catalyst particles in the electrode catalyst, elution of catalyst particle components such as platinum ions occurs in the electrode as the electrode reaction proceeds. Since the surface of the trap material shown in FIG. 1 is modified so that the catalyst particle component is captured and easily reduced by the reducing compound, the eluted platinum ions are reduced to form fine platinum particles by a chemical reaction. It can be deposited again on the carbon surface. The trap material not only has electronic conductivity by using carbon or the like as a carrier, but also has ion conductivity by being coated with an ion-exchange polymer. Therefore, the trap material having platinum particles deposited on the surface can act as a new electrode catalyst.

  By including such a trap material, it is possible to obtain a fuel cell electrode that can exhibit high power generation performance over a long period of time, has excellent durability, and has an improved utilization rate of catalyst particles such as platinum. .

  Hereinafter, the fuel cell electrode of the present invention will be described in detail in order.

  The fuel cell electrode of the present invention includes an electrode catalyst in which catalyst particles are supported on a conductive carrier, and a trap material.

  As the conductive carrier in the electrode catalyst, any conductive carrier may be used as long as it has a specific surface area sufficient for carrying the catalyst particles in a highly dispersed manner and has sufficient electronic conductivity as a current collector. Is preferably carbon. In the present invention, carbon refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Note that “substantially consisting of carbon atoms” means that contamination of about 2 to 3% by mass or less of impurities is allowed.

Specifically, BET specific surface area of ^{50 m} 2 / g or more, and preferably conductive carbon 250~1,600m ² / g. More specifically, ketjen black, black pearl, Vulcan XC72, and those obtained by graphitizing these may be used. In addition, the conductive carrier may be washed in advance with an alkaline solution such as sodium hydroxide, potassium hydroxide, or calcium hydroxide.

  In the present invention, the specific surface area of the conductive carrier is a value measured by a BET method using nitrogen.

  Next, the catalyst particles in the electrode catalyst are not particularly limited, but platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, etc. And their alloys, and the like. Such catalyst particles are preferably used because they exhibit high activity against various electrochemical reactions such as oxygen reduction reaction and hydrogen oxidation reaction.

  The smaller the particle size of the catalyst particles, the higher the catalytic activity obtained because the effective electrode area where the electrochemical reaction proceeds increases. However, in practice, if the catalyst particle diameter is too small, sintering or the like is likely to occur, and rather a phenomenon in which the catalytic activity decreases is observed. Therefore, the average particle diameter of the catalyst particles supported on the conductive support is preferably 1 to 30 nm, more preferably 1 to 10 nm, and particularly preferably 2 to 5 nm. Here, the “average particle diameter of the catalyst particles” refers to the average value of the particle diameter of the catalyst particles determined from the crystallite diameter or the transmission electron microscope image obtained from the half width of the diffraction peak of the catalyst particles in X-ray diffraction.

  The catalyst particles can be supported on the conductive support by a known method. The amount of catalyst particles supported on the conductive carrier is not particularly limited, but is preferably about 15 to 70% by mass. If it is less than 15% by mass, sufficient activity may not be obtained. Moreover, when it exceeds 70 mass%, it is difficult to disperse | distribute uniformly and it may become difficult to carry | support highly dispersed catalyst particles. The amount of catalyst particles supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  In the electrode of the present invention, the electrode catalyst is preferably coated with an ion exchange polymer. When the ion-exchange polymer acts as a binder polymer, the structure of the electrode can be maintained stably, and a high catalytic activity can be obtained by sufficiently securing the reaction site (three-phase interface) where the electrode reaction proceeds. .

  The ion-exchange polymer is not particularly limited and a known one can be used, but any member having at least high proton conductivity may be used. Specifically, a perfluorocarbon polymer having a sulfonic acid group such as NAFION (registered trademark of DuPont), a hydrocarbon polymer compound doped with an inorganic acid such as phosphoric acid, a part of which is proton conductive. Examples thereof include organic / inorganic hybrid polymers substituted with functional groups, proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution, and the like.

  Next, the trap material used for the fuel cell electrode of the present invention has a function of reducing the catalyst particle component eluted from the electrode catalyst and precipitating it on the surface of the trap material. In order to deposit catalyst particles without deteriorating the function of the fuel cell electrode, the trap material preferably has electron conductivity and ion conductivity.

  Specifically, the trap material has a reducing surface functional group on the carrier surface and is coated with an ion exchange polymer (1), and has a reducing compound on the carrier surface, and has an ion exchange property. Examples thereof include a trap material (2) coated with a polymer, a trap material (3) made of a material having a hydrogen storage property and coated with an ion-exchange polymer.

In the trap material (1), the surface functional group is not particularly limited as long as it has reducibility and is capable of reducing and depositing the eluted catalyst particle component. Examples thereof include a carboxyl group (—COOH), a phenol group (—OH), and a ketone group (> C═O). Such a surface functional group has a high ability to capture and reduce the catalyst particle component, so that the catalyst particles that have been reduced and deposited can be fixed on the support surface in a fine particle state. Among them, the carboxyl group is preferably used because a hydrogen ion (H ⁺ ) that easily dissociates at the terminal exists and the reduction performance of the catalyst particle component is high.

  Examples of the carrier include carbon carriers composed of simple carbon such as carbon black, acetylene black, furnace black, activated carbon, and amorphous carbon. In addition to these, carbon supports such as carbon nanotubes, fullerenes, carbon nanofibers, and graphite may be used. By using these carbons as a carrier, not only can a surface functional group be introduced to the carrier surface, but also electron conductivity can be imparted to the resulting trapping material (1).

Among those specifically recited as the carrier, in the case of using a spherical carrier, such as carbon black, BET specific surface area of ^{50 m} 2 / g or more, preferably to use one of 250~1,600m ² / g Good. By setting the specific surface area within the above range, it is possible to carry highly reduced and supported catalyst particles in a highly dispersed manner, and the trap material (1) can preferably act as an electrode catalyst.

  Further, when a fibrous carrier such as carbon nanotube is used, it is preferable to use one having an inner diameter of 100 nm or less, particularly 50 to 5 nm, and a length of 300 to 2000 nm, particularly 500 to 1000 nm. By setting the inner diameter and length within the above ranges, the catalyst particles can be supported on the surface of the carrier, and the trap material (1) can preferably act as an electrode catalyst.

  The method for introducing the surface functional group onto the support surface is not particularly limited, and various known techniques for oxidizing the support surface may be used. For example, the oxidation treatment is a liquid phase method using a strong oxidizing aqueous solution containing potassium permanganate, nitric acid, chlorate, persulfate, perborate, percarbonate, hydrogen peroxide, etc .; ozone, nitrogen oxide, Examples include a gas phase method using air, oxygen, etc .; a method using low temperature plasma. Among these, it is preferable to use an oxidation treatment by a liquid phase method because the carbon surface can be uniformly oxidized and a large number of carboxyl groups suitably used as surface functional groups can be introduced.

  Specifically, the oxidation treatment by the liquid phase method is performed by putting the carrier such as carbon into the strong oxidizing aqueous solution and stirring and mixing.

  After the carrier is added to the strong oxidizing aqueous solution, the carrier may be sufficiently dispersed in the solution by an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device, and these dispersing means may be appropriately combined. .

  Next, the carrier whose surface has been oxidized with the strong oxidizing aqueous solution is filtered and dried using a known means such as a separating means such as suction filtration, whereby the surface functional groups are obtained. An introduced carrier can be obtained. The drying method is not particularly limited as long as it is a known method such as vacuum drying, natural drying, rotary evaporator, drying by a blower dryer or the like. What is necessary is just to determine drying time etc. suitably according to the method to be used. Moreover, when the said support | carrier is a bulk form, you may grind | pulverize appropriately.

  The amount of the surface functional group introduced on the surface of the carrier may be appropriately determined so that the obtained electrode exhibits desired characteristics, but 1 to 10, preferably 3 to the primary particles of the carbon carrier. The number is preferably about 5. If the amount of the surface functional group is less than 1, the effect as expected may not be obtained, and if it exceeds 10, the affinity between the carbon support and water may be greatly changed. These can be controlled by appropriately adjusting the concentration of the strong oxidizing aqueous solution, the added amount of the carrier, the treatment temperature, the treatment time, and the like.

  In the present invention, the surface functional group introduced on the surface of the carrier is quantitatively analyzed using a temperature programmed desorption spectrum apparatus (TPD).

  The surface of the carrier into which the surface functional group has been introduced is preferably coated with an ion exchange polymer. Thereby, not only can ion conductivity be imparted to the trap material, but the structure of the obtained electrode can be stably maintained.

  The ion-exchange polymer is the same as that described in the above-mentioned electrode catalyst, and the description thereof is omitted here. The surface of the carrier is coated with an ion exchange polymer by mixing the carrier having a surface functional group introduced into a solution containing the ion exchange polymer.

  The solution containing the ion exchange polymer is not particularly limited, and examples thereof include those conventionally used for producing electrodes. Specifically, the ion-exchangeable polymer described in the above electrode catalyst is mixed and dispersed in a solvent such as water or an alcohol-based organic solvent.

  After dispersing and mixing in this manner, the trap material coated with the ion-exchange polymer can be obtained by filtering the carrier and drying it. The filtration and drying methods are not particularly limited and may be performed using known methods. When the obtained trap material is in a bulk form, it may be pulverized as appropriate. Note that the entire surface of the trap material may not be covered with the ion-exchange polymer, and it is sufficient that at least a part of the surface is covered with the ion-exchange polymer.

  Next, also with the trap material (2), the catalyst particle component eluted from the electrode catalyst can be reduced to deposit catalyst particles on the surface of the trap material. In the trap material (2), a reductive compound having a reducibility higher than the above-described surface functional group is adsorbed on the surface of the support by using a support having a high adsorbing power. With the reducing compound, it is possible to obtain a trap material (2) having higher ability to capture and reduce the eluted catalyst particle component.

  The reducing compound adsorbed on the surface of the carrier is not particularly limited as long as it has reducibility and is capable of reducing and depositing the eluted catalyst particle component. For example, sodium hypophosphite, sodium sulfite , Sodium thiosulfate, oxalic acid and the like. In these reducing compounds, reduction precipitation of the catalyst particle component easily occurs. Therefore, the collection efficiency of the catalyst particle component is high, and the catalyst particles that are reduced and precipitated can be fixed on the support surface in a fine particle state.

  Examples of the carrier include carbon carriers made of simple carbon such as carbon black, acetylene black, furnace black, activated carbon, and amorphous carbon, and carbon carriers such as carbon nanotubes, fullerenes, carbon nanofibers, and graphite. Of these, carbon black is preferably used in terms of surface area and conductivity. In addition to these, conductive metal oxides such as tungsten oxide, tin oxide and cerium oxide; carbides such as tungsten carbide, tantalum carbide and silicon carbide; nitrides such as titanium nitride and tantalum nitride are used as the carrier. be able to.

Among those specifically recited as the carrier, in the case of using a spherical carrier, such as carbon black, BET specific surface area of ^{50 m} 2 / g or more, preferably to use one of 250~1,600m ² / g Good. By setting the specific surface area within the above range, it is possible to carry the reduced-deposited catalyst particles in a highly dispersed manner, and the trap material (2) can preferably act as an electrode catalyst.

  Further, when a fibrous carrier such as carbon nanotube is used, it is preferable to use one having an inner diameter of 100 nm or less, particularly 50 to 5 nm, and a length of 300 to 2000 nm, particularly 500 to 1000 nm. By setting the inner diameter and length within the above ranges, the catalyst particles can be supported on the surface of the carrier, and the trap material (2) can preferably act as an electrode catalyst.

  The method for introducing the reducing compound onto the surface of the carrier is not particularly limited. For example, there is a method of impregnating the solution on the surface of the carrier by adding the carrier to the solution containing the reducing compound and stirring and mixing. Can be mentioned.

  Specific examples of the solution containing the reducing compound include those obtained by dissolving the reducing compound in water, alcohol, or a mixture thereof.

  After the carrier is added to the solution containing the reducing compound, the carrier impregnated with the solution is filtered and dried in the same manner as the trapping material (1) described above by stirring and mixing using an appropriate dispersing means. You can do it.

  The amount of the reducing compound introduced to the surface of the carrier may be appropriately determined so that the obtained electrode exhibits the desired characteristics, but is 5 to 30 wt%, preferably about 10 to 20 wt% with respect to the carrier. It is preferable to do this. If the amount of the reducing compound is less than 5 wt%, the effect as expected may not be obtained, and if it exceeds 30 wt%, the electrode reaction may be inhibited. These can be controlled by appropriately adjusting the concentration of the reducing compound in the solution, the amount of carrier added, the treatment temperature, the treatment time, and the like.

  In the present invention, quantitative analysis of the reducing compound introduced on the surface of the carrier is performed using inductively coupled plasma emission spectroscopy (ICP).

  Further, since the ion-exchangeable polymer and the coating method for coating the surface of the trap material (2) are the same as those described for the trap material (1) described above, detailed description thereof is omitted here.

  Next, also with the trap material (3), the catalyst particle component eluted from the electrode catalyst can be reduced to deposit catalyst particles on the surface of the trap material (3).

  Since hydrogen has reducibility, the catalyst particles can be reduced and deposited. Further, during operation of the fuel cell, hydrogen gas is supplied as the fuel gas. Therefore, if a material having hydrogen storage properties is used for the trap material, the supplied hydrogen gas can be stored in the trap material (3), and the catalyst particle components eluted thereby can be captured as fine catalyst particles. Reduction and precipitation can be performed on the surface of the trap material (3).

  In a fuel cell, hydrogen gas is supplied from the anode side and oxygen-containing gas is supplied from the cathode side, and these gases exhibit a characteristic of permeating the solid polymer electrolyte membrane, that is, a crossover phenomenon. In particular, since the polymer electrolyte membrane is wet, the amount of hydrogen gas permeated increases, and the hydrogen gas that has permeated from the anode side may react at the cathode, causing a reduction in efficiency.

  However, by using the trap material (3) made of a material having a hydrogen storage property for the cathode, it is possible to store the hydrogen that has permeated from the anode, and to prevent deterioration of the electrode catalyst due to such a crossover phenomenon. You can also.

Specifically, as materials having hydrogen storage properties, carbon materials such as carbon nanotubes, fullerenes, and carbon nanofibers; AB ₅ type alloys represented by LaNi ₅ ; Ti—Mn series, Ti—Cr series, Zr—Mn And AB ₂ type alloys of the system. Such a material is preferably used because it has not only hydrogen storage properties but also electron conductivity.

Among the materials specifically listed as the materials having hydrogen storage properties, when a spherical material such as an AB type ₅ alloy is used, the BET specific surface area is 50 m ² / g or more, preferably 250 to 1,600 m ² / It is good to use the thing of g. By setting the specific surface area within the above range, it is possible to carry the reduced-deposited catalyst particles in a highly dispersed manner, and the trap material (3) can preferably act as an electrode catalyst.

  Furthermore, when using fibrous things, such as a carbon nanotube, it is preferable to use a thing with an internal diameter of 100 nm or less, especially 50-5 nm, and length 300-2000 nm, especially 500-1000 nm. By setting the inner diameter and length within the above ranges, the catalyst particles can be supported on the surface, and the trap material (3) can preferably act as an electrode catalyst.

  The material having hydrogen storage properties is suitably used as a trap material by coating with an ion-exchange polymer. Since the ion-exchangeable polymer and the coating method for coating the material are the same as those described in the trap material (1) described above, detailed description thereof is omitted here.

  In the present invention, the specific surface area of the carrier used for the trap materials (1) and (2) and the hydrogen storage material used for the trap material (3) is a value measured by the BET method using nitrogen. And

  In the fuel cell electrode of the present invention, it is preferable that the size of the trap material and the size of the electrode catalyst are approximately the same considering the porosity, density, gas diffusibility, and the like of the obtained electrode. Thereby, the obtained trap material can be included in the electrode without affecting the electrode structure.

  The content of the trap material in the fuel cell electrode is 5 to 20 wt%, preferably 5 to 15 wt% with respect to the electrode catalyst. If the content is less than 5 wt%, the trap material may not be as effective as desired, and if it exceeds 20 wt%, the amount of the electrode catalyst may decrease and the electrode performance may decrease.

  The electrode for a fuel cell of the present invention has an electrode catalyst layer in which an electrode catalyst in which catalyst particles are highly dispersed and supported on a conductive carrier is highly dispersed, and the form containing the trap material described above is not particularly limited. For example, the trap material may be dispersed and mixed in the electrode catalyst layer.

  The fuel cell electrode having such a configuration will be described with reference to FIG. FIG. 2 shows a solid polymer electrolyte membrane in which a conventional fuel cell electrode composed of an electrode catalyst layer in which an electrode catalyst in which catalyst particles are supported on a conductive carrier are dispersed, a trap material and the electrode catalyst are mixed. 1 is a schematic cross-sectional view of a fuel cell MEA sandwiched between the electrode for a fuel cell of the present invention having an electrode catalyst layer. The electrode catalyst and trap material contained in each electrode catalyst layer are coated with an ion-exchange polymer.

  The fuel cell electrode of the present invention shown in FIG. 2 can reduce and deposit catalyst particle components eluted from the electrode catalyst on the surface of the trap material, and the finely divided catalyst particles thus deposited on the surface. Since the trap material having the above can exhibit an action as an electrode catalyst, it is excellent in the utilization rate and durability of the catalyst particles. Furthermore, since the trap material is coated with an ion-exchange polymer, the ion conductivity of the fuel cell electrode is improved, and a fuel cell electrode with high power generation performance is obtained.

  Such a fuel cell electrode is produced by further mixing a trapping material with the catalyst ink generally used in the conventional electrode production method. That is, a trap material is mixed with a catalyst ink containing an electrode catalyst, an ion-exchange polymer, water and / or an organic solvent, and the obtained mixed solution is applied onto a release sheet such as a Teflon (registered trademark) sheet. By drying, the fuel cell electrode of the present invention having the electrode catalyst layer shown in FIG. 2 is obtained.

  The trap material mixed with the catalyst ink may be added with a material not previously coated with an ion exchange polymer. That is, by using a mixed solution in which a catalyst ink is mixed with a carrier surface having a reducing surface functional group, an electrode catalyst layer is formed and a trap material (1) coated with an ion-exchange polymer is obtained. Can do. If this is carried out in the same manner for a material having a reducing compound on the support surface and a material having hydrogen storage properties, the trap material (2) and the trap material (3) can be obtained together with the formation of the electrode catalyst layer. Can do.

  However, since the coating state can be controlled, it is preferable to mix the trap material previously coated with the ion-exchange polymer with the catalyst ink.

  Further, the catalyst ink may contain a water-repellent polymer such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged.

  In order to apply and dry the mixed liquid of the catalyst ink and the trap material on the release sheet, it is not particularly limited, and any known technique may be used as appropriate to obtain a desired electrode catalyst layer.

  In addition to the release sheet, the catalyst ink is directly applied to a solid polymer electrolyte membrane, a gas diffusion layer or the like when the fuel cell electrode of the present invention is used for an MEA described later as a substrate on which the catalyst ink is applied. May be.

  The electrode for a fuel cell of the present invention may have a form in which a layer containing a trap material is formed on at least one surface of the electrode catalyst layer in addition to a form in which a trap material is mixed in the electrode catalyst layer shown in FIG. Even in such a form, the trap material can be contained in the fuel cell electrode. The fuel cell electrode having the above configuration will be described with reference to FIGS.

  FIG. 3 shows a conventional fuel cell electrode comprising a solid polymer electrolyte membrane, an electrode catalyst layer in which an electrode catalyst in which catalyst particles are supported on a conductive carrier is dispersed, and an electrode catalyst in which the electrode catalyst is dispersed. 1 is a schematic cross-sectional view of a fuel cell MEA sandwiched between a layer and a fuel cell electrode of the present invention having a layer containing a trap material on one side thereof. The electrode catalyst and trap material contained in each electrode catalyst layer are coated with an ion-exchangeable polymer.

  As in the fuel cell electrode of the present invention shown in FIG. 3, the catalyst particle component eluted from the electrode catalyst can be reduced and deposited on the surface of the trap material by forming a layer containing the trap material on one surface of the electrode catalyst layer. Can do. Since the layer containing the trapping material in which the catalyst particles are precipitated again in the form of fine particles can act as a new electrode catalyst layer, a fuel cell electrode excellent in the utilization rate and durability of the catalyst particles can be obtained. .

  When forming the fuel cell MEA using the fuel cell electrode, it is preferable to dispose the layer containing the trap material on the solid polymer electrolyte membrane side. As a result, the catalyst particle component can be prevented from diffusing into the solid polymer electrolyte membrane, and the power generation characteristics of the fuel cell MEA can be improved. Further, the eluted catalyst particle component may diffuse to the gas diffusion layer side together with water generated by the electrode reaction. Therefore, it is also a preferable embodiment to arrange the layer containing the trap material on the gas diffusion layer side of the electrode catalyst layer.

  Further, as shown in FIG. 4, in order to prevent the eluted catalyst particle component from diffusing into the solid polymer electrolyte membrane and the gas diffusion layer, a layer containing a trap material may be disposed on both sides of the electrode catalyst layer. Good.

  As shown in FIG. 3 and FIG. 4, in order to form a layer containing a trap material on at least one surface of the electrode catalyst layer, the ion-exchangeable polymer described in the above-mentioned electrode catalyst is mixed with water or an alcohol-based organic solvent. An ink in which a trap material is further mixed with an ion exchange polymer solution mixed and dispersed in a solvent such as the above may be used. By applying and drying the ink on at least one surface of the electrode catalyst layer, a fuel cell electrode having an electrode catalyst layer in which a layer containing a trap material is formed can be obtained.

  As a method for forming an electrode catalyst layer, a conventionally known method is to apply and dry a catalyst ink containing an electrode catalyst, an ion-exchange polymer, water and / or an organic solvent on a release sheet such as a Teflon (registered trademark) sheet. Technology can be used.

  Next, in order to apply the ink mixed with the trap material to the electrode catalyst layer, a conventional slurry application method such as a screen printing method, a deposition method, or a spray method may be used.

  The trap material to be added may be mixed with the ion-exchange polymer solution that is not previously coated with the ion-exchange polymer. That is, when forming the layer containing the trap material (1) described above, the carrier having the reducing surface functional group introduced therein is mixed with the ion exchange polymer solution, whereby the carrier is exchanged with the ion exchange polymer. And a layer containing the trap material (1) can be formed. The trap material (2) and the layer including the trap material (3) may be similarly formed using a carrier having a reducing compound on the surface and a material having hydrogen storage properties.

  Thereafter, the applied ink is dried, and the release sheet is peeled off, whereby a layer containing a trap material can be formed on one surface of the electrode catalyst layer. Although it does not specifically limit as a drying method, What is necessary is just to carry out for 30 minutes-about 6 hours by 20-80 degreeC by inert gas atmosphere, such as nitrogen atmosphere, argon, and helium.

  In order to form the layer containing the trap material on both surfaces of the electrode catalyst layer, the surface containing the release sheet of the electrode catalyst layer may be further coated and dried with ink containing the trap material.

  Moreover, the method of forming the layer containing an electrode catalyst layer and a trap material on a release sheet is not limited to the method described above. That is, a method of first forming a layer containing a trap material on a release sheet and then forming an electrode catalyst layer on the layer may be used. In addition, when the fuel cell electrode of the present invention is used as an MEA described later, a method of forming an electrode catalyst layer after forming a layer containing a trap material on a solid polymer electrolyte membrane, gas diffusion A method of forming a layer containing a trap material after forming an electrode catalyst layer on the layer may be used.

  The thickness of the layer containing the trap material may be appropriately determined so as to obtain a desired fuel cell electrode, but it is preferably 0.5 to 5 μm, and preferably 1 to 2 μm. If the thickness of the layer is less than 0.5 μm, the effect of the layer containing the trap material may not be obtained as desired. If the thickness exceeds 5 μm, the gas permeability, ion conductivity, etc. during electrode reaction will decrease. The power generation characteristics may be degraded.

  The second of the present invention is a fuel cell MEA using the fuel cell electrode described above. Since the fuel cell electrode of the present invention has the above-mentioned various characteristics, it can be suitably used for MEA. The MEA is obtained by sandwiching a solid polymer electrolyte membrane between two electrodes, that is, an anode and a cathode.

  By using the fuel cell electrode of the present invention, an MEA capable of exhibiting high power generation characteristics over a long period of time is obtained. In the conventional MEA, the catalyst particle component eluted from the electrode catalyst with the progress of the electrode reaction may diffuse into the solid polymer electrolyte membrane and be trapped at the ion exchange site of the solid polymer electrolyte membrane. This not only reduces the catalytic activity due to a decrease in the amount of the catalyst, but also reduces the ionic conductivity of the solid polymer electrolyte membrane, resulting in a decrease in power generation characteristics of the fuel cell MEA. However, if the fuel cell electrode of the present invention is used for MEA, the inclusion of a trap material suitably suppresses the decrease in the amount of catalyst and the elution of catalyst particle components into the solid polymer electrolyte membrane and gas diffusion layer. it can.

  In the MEA, the fuel cell electrode of the present invention can be used as a cathode and / or an anode. However, since elution of the catalyst particles is particularly likely to occur at the cathode, the fuel cell electrode is preferably used at least as the cathode. At this time, a conventional fuel cell electrode may be applied as the anode, and is not particularly limited.

  The solid polymer electrolyte membrane used in the MEA is not particularly limited, and examples thereof include those made of the same ion exchange polymer as listed in the description of the electrode catalyst described above. Further, commercially available polymer electrolyte membranes may be used, and examples thereof include NAFION manufactured by DuPont, FLEMION manufactured by Asahi Glass Co., and ACIPLEX manufactured by Asahi Kasei. In addition, fluoropolymer electrolytes such as ion exchange resins manufactured by Dow Chemical Co., ethylene-tetrafluoroethylene copolymer resin membranes, resin membranes based on trifluorostyrene, and hydrocarbons having sulfonic acid groups A resin film or the like may be used.

  The ion-exchangeable polymer used for the solid polymer electrolyte membrane, the electrode catalyst layer, and the layer containing the trap material may be the same or different, but considering each bondability, etc. It is desirable to use the same one.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 150 μm. From the viewpoint of strength during film formation and durability during operation of the fuel cell, it is preferably 5 μm or more, and from the viewpoint of output characteristics during operation of the fuel cell, it is preferably 300 μm or less.

  As a manufacturing method of MEA, when the above-mentioned fuel cell electrode is used as a cathode and a conventional fuel cell electrode is used as an anode, a solid polymer electrolyte membrane is sandwiched between these electrodes and then hot pressing is performed. Etc.

  Hot pressing is preferably performed at 100 to 200 ° C., preferably 110 to 170 ° C., with a pressing pressure of 1 to 5 MPa with respect to the electrode surface. Thereby, the bondability between the solid polymer electrolyte membrane and the catalyst layer can be enhanced.

  The MEA may be further sandwiched between gas diffusion layers. The gas diffusion layer is not particularly limited, and examples thereof include those based on 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. In order to increase water repellency and prevent flooding, the gas diffusion layer may be subjected to water repellency using a known means, or a layer of carbon particle aggregates may be formed on the gas diffusion layer. preferable.

  As a method of performing the water repellent treatment, for example, a method of performing water repellent treatment by immersing the gas diffusion layer in a dispersion of a water repellent polymer having fluorine or the like such as polytetrafluoroethylene and then drying by heating in an oven or the like. Is mentioned.

  As a method of forming a carbon particle aggregate layer on the gas diffusion layer, first, carbon particles such as carbon black, polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, etc. A slurry is prepared by dispersing a water-repellent polymer containing fluorine in a solvent such as water, alcohol solvents such as perfluorobenzene, dichloropentafluoropropane, methanol, ethanol and the like. Next, the slurry is applied on the gas diffusion layer and dried, or the slurry is once dried and pulverized to form a powder, which is then applied onto the gas diffusion layer. In the method, the gas diffusion layer on which the layer composed of the carbon particle aggregate is formed is preferably heat-treated at about 300 to 400 ° C. using a muffle furnace or a firing furnace.

  In the present invention, the fuel cell electrode and the fuel cell MEA described above are preferably used as a fuel cell. The fuel cell uses a fuel cell electrode including the trap material described above. Accordingly, the following description is merely an example of the other configurations, and other configurations that can be used for a conventionally known fuel cell may be similarly used for the fuel cell of the present invention.

  The type of fuel cell is not particularly limited as long as desired cell characteristics can be obtained, but it is used as a polymer electrolyte fuel cell (also simply referred to as “PEFC”) from the viewpoints of practicality and safety. Is preferred. The PEFC has a structure in which an MEA is sandwiched between separators.

  A known separator such as carbon paper or carbon cloth may be used as a separator for sandwiching the MEA. The separator has a function of separating air and fuel gas, and a flow groove may be formed in order to secure the flow path, and a conventionally known technique can be appropriately used. The thickness and size of the separator and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Furthermore, a stack in which a plurality of MEAs are stacked via a separator and connected in series may be formed so that a desired voltage or the like can be obtained by the PEFC. The shape of the PEFC is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  Since the fuel cell electrode of the present invention is excellent in power generation performance and durability, it can exhibit excellent characteristics over a long period of time. Therefore, the MEA and the fuel cell using such a fuel cell electrode can exhibit superior performance as compared with the conventional one. Therefore, the fuel cell system can be highly efficient, reduced in size, and reduced in weight, and is useful as a power source for moving bodies such as vehicles and a stationary power source.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples.

<Example 1>
1. Preparation of anode catalyst layer Platinum-supported carbon (TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum content 46.5 wt%), solid polymer electrolyte solution (NAFION solution DE520 manufactured by DuPont, electrolyte content 5 wt%), pure water 25 g, and Using a homogenizer for fine pulverization in a glass container in a water bath set so that isopropanol (special grade reagent manufactured by Kanto Chemical Co., Inc.) is held at 20 ° C. at a mass ratio of 1: 9: 2.5: 1. An anode catalyst layer ink was prepared by mixing and dispersing for 3 hours.

  Next, the anode catalyst layer ink prepared previously using a screen printer was applied to one side of a 0.2 mm thick Teflon (registered trademark) sheet (manufactured by Nichias, trade name Naflon), and 100% in an oven. After drying at 0 ° C. for 30 minutes, it was cut into a square of 5 cm on a side. In this way, an anode catalyst layer (10 μm) -formed Teflon (registered trademark) sheet was obtained.

2. Preparation of cathode catalyst layer 50 g of carbon black (VULCAN XC-72R manufactured by CABOT) was added to 500 ml of an aqueous potassium permanganate solution having a concentration of 1 mol / l, and the mixture was stirred and mixed at 60 ° C. for 3 hours to oxidize the carbon black surface. Processed. Thereafter, the carbon black was filtered, sufficiently washed with distilled water, dried at 80 ° C. for 3 hours in a vacuum dryer, and pulverized with a mixer to obtain oxidized carbon black.

  Next, this oxidized carbon black, platinum-supporting carbon (TEC10E50E, Tanaka Kikinzoku Kogyo Co., Ltd., platinum content 46.5 wt%), solid polymer electrolyte solution (NAFION solution DE520, DuPont NAFION solution 5 wt%), 25 g of pure water , And isopropanol (special grade reagent manufactured by Kanto Chemical Co., Ltd.) in a glass container in a water bath set to hold at 20 ° C. at a mass ratio of 0.1: 1: 12: 2.5: 1. The cathode catalyst layer ink was prepared by mixing and dispersing for 3 hours using a homogenizer for pulverization.

  The cathode catalyst layer ink prepared previously using a screen printer was applied to one side of a 0.2 mm thick Teflon (registered trademark) sheet (manufactured by Nichias Co., Ltd., trade name Naflon). After drying for a minute, it was cut into a square with a side of 5 cm. In this way, a cathode catalyst layer (10 μm) -formed Teflon (registered trademark) sheet in which the trap material was mixed was obtained.

3. Production of Membrane / Electrode Assembly A solid polymer electrolyte membrane (NAFION 111 manufactured by DuPont) having a square of 8 cm on a side and a thickness of 25 μm was prepared by using the previously prepared cathode catalyst layer-formed Teflon (registered trademark) sheet and anode catalyst layer-formed Teflon ( The Teflon (registered trademark) sheet is sandwiched by using the registered trademark sheet, and hot-pressed at 130 ° C. for 10 minutes at a pressure of 3 MPa per one side Teflon (registered trademark) sheet. By removing only the (trademark) sheet, each catalyst layer was transferred to the solid polymer electrolyte membrane to obtain a joined body. At this time, the transfer rate of each catalyst layer from the Teflon (registered trademark) sheet to the solid polymer electrolyte membrane was 100%, and the platinum weight per 1 cm ² of the single-sided catalyst layer area on the solid polymer electrolyte membrane was 0. 20 mg and the cathode were adjusted to 0.40 mg. Moreover, the schematic diagram sectional drawing of the obtained conjugate | zygote is shown in FIG.

4). Assembly of single cell for evaluation After immersing carbon paper (TGP-H-090 manufactured by Toray Industries Inc.) with a thickness of 270 μm in a polytetrafluoroethylene (PTFE) dispersion (polyflon D-1E manufactured by Daikin Industries, 60 wt%), PTFE was dispersed in carbon paper by drying at 80 ° C. for 1 hour in an oven. At this time, the PTFE content was 25 wt%. Carbon black containing 20 wt% PTFE was applied on the carbon paper. As a result, a water-repellent treated gas diffusion layer was obtained.

  Using these two water-repellent gas diffusion layers, the membrane / electrode assembly prepared above is sandwiched and sandwiched between graphite separators, and further sandwiched between gold-plated stainless steel collector plates Thus, an evaluation single cell was obtained.

5). Performance evaluation Hydrogen was supplied to the anode side as fuel, and air was supplied to the cathode side. The supply pressure of both gases is atmospheric pressure, hydrogen is 60 ° C, air is saturated and humidified at 60 ° C, the temperature of the fuel cell body is set to 70 ° C, the hydrogen utilization rate is 70%, and the air utilization rate is 40%. The operation was continued at a current density of 1 A / cm ² for 10 minutes. When power generation was stopped, the current density to be taken out was reduced to zero, and then the anode was purged with air to discharge hydrogen, and then the outlet side was opened to the atmosphere, and the cathode was similarly opened to the atmosphere. At this time, the temperature control of the fuel cell main body was not performed, and the stop time was 10 minutes. When power generation was stopped, the experimental environment was a room temperature of 20 to 25 ° C. and a humidity of 40 to 60% RH. When the operation was resumed after the stop, the gas was again introduced into the cell under the above conditions to generate power. The durability of the single cell was evaluated by repeating this operation-stop cycle.

  The single cell had a power generation start voltage of 0.6 V, a power generation voltage after 1000 cycle operation of 0.54 V, and the voltage drop rate was 10%.

<Example 2>
As shown below, a membrane / electrode assembly and an evaluation single cell were prepared in the same manner as in Example 1 except that a cathode catalyst layer having a layer containing a trap material formed on one side was used. Evaluation was performed. A schematic cross-sectional view of the produced membrane / electrode assembly is shown in FIG.
50 g of carbon black (VULCAN XC-72R manufactured by CABOT) was added to 500 ml of an aqueous potassium permanganate solution having a concentration of 1 mol / l, and the carbon black surface was oxidized by stirring and mixing at 60 ° C. for 3 hours. Thereafter, the carbon black was filtered, sufficiently washed with distilled water, dried at 80 ° C. for 3 hours in a vacuum dryer, and pulverized with a mixer to obtain oxidized carbon black.

  Next, this oxidized carbon black, solid polymer electrolyte solution (NAFION solution DE520 manufactured by DuPont, electrolyte content 5 wt%), 25 g of pure water, and isopropanol (special grade reagent manufactured by Kanto Chemical Co., Inc.) in a mass ratio of 1: 9. A trapping material ink was prepared by mixing and dispersing for 3 hours in a glass container in a water bath set to be kept at 20 ° C. at a ratio of 1: 1 using a homogenizer for fine grinding.

  Here, a cathode catalyst layer-formed Teflon (registered trademark) sheet was produced in the same manner as the anode catalyst layer of Example 1. On the cathode catalyst layer, the previously prepared trap material ink was applied using a screen printer, dried in an oven at 80 ° C. for 30 minutes, and then cut into a square having a side of 5 cm. As a result, a cathode catalyst layer (10 μm) and a layer containing a trap material (2 μm) were formed on the Teflon (registered trademark) sheet.

  The durability evaluation of the produced single cell was a power generation start voltage of 0.6 V, a power generation voltage after 1000 cycle operation of 0.577 V, and the voltage drop rate was 4%.

<Example 3>
As shown below, a membrane / electrode assembly and an evaluation single cell were prepared in the same manner as in Example 1 except that a cathode catalyst layer in which a layer containing a trap material was formed on both sides was used. Evaluation was performed. A schematic cross-sectional view of the produced membrane / electrode assembly is shown in FIG.

  First, the trap material ink prepared in Example 2 was applied on one side of a 0.2-mm-thick Teflon (registered trademark) sheet (manufactured by Nichias Co., Ltd., trade name Naflon) using a screen printer. For 30 minutes to form a layer containing a trap material on a Teflon (registered trademark) sheet.

  Next, the anode catalyst layer ink prepared in Example 1 was applied onto the layer containing the trap material using a screen printer and dried in an oven at 80 ° C. for 30 minutes to form a cathode catalyst layer.

  Further, the trap material ink prepared in Example 2 was again applied onto the cathode catalyst layer using a screen printer and dried in an oven at 80 ° C. for 30 minutes. In this manner, a Teflon (registered trademark) sheet on which each layer was formed was obtained in the order of a layer containing a trap material (2 μm) / a cathode catalyst layer (10 μm) / a layer containing a trap material (0.5 μm). Then, this was cut out into a square of 5 cm on a side.

  The durability evaluation of the produced single cell was a power generation start voltage of 0.596 V, a power generation voltage after 1000 cycle operation of 0.573 V, and the voltage drop rate was 3.8%.

<Comparative Example 1>
In Example 1, except that the produced anode catalyst layer was used for both the cathode and anode, a membrane / electrode assembly and an evaluation single cell were produced and evaluated in the same manner as in Example 1.

  The durability evaluation of the produced single cell was a power generation start voltage of 0.6 V, a power generation voltage after 1000 cycle operation of 0.51 V, and the voltage drop rate was 15%.

The schematic diagram at the time of carrying out reduction precipitation of the platinum ion eluted from the electrode catalyst on the trap material surface is shown. The schematic cross section of MEA for fuel cells using the electrode for fuel cells which has an electrode catalyst layer with which the trap material was mixed which is one suitable embodiment of this invention is shown. 1 is a schematic cross-sectional view of a fuel cell MEA using a fuel cell electrode in which a layer containing a trap material is formed on one surface of an electrode catalyst layer, which is a preferred embodiment of the present invention. 1 is a schematic cross-sectional view of a fuel cell MEA using a fuel cell electrode in which layers containing a trap material are formed on both sides of an electrode catalyst layer, which is a preferred embodiment of the present invention.

Claims (10)

A fuel cell electrode comprising an electrode catalyst in which catalyst particles are supported on a conductive carrier, and a trap material,
The fuel cell electrode, wherein the trap material is a material that reduces and deposits catalyst particle components eluted from the electrode catalyst on the surface of the trap material.   The fuel cell electrode according to claim 1, wherein the trap material has electron conductivity and ion conductivity.   3. The fuel cell electrode according to claim 1, wherein the trap material has a reducing surface functional group on the surface of the carrier and is coated with an ion exchange polymer.   The fuel cell electrode according to claim 1, wherein the trap material has a reducing compound on the surface of the carrier and is coated with an ion-exchange polymer.   3. The fuel cell electrode according to claim 1, wherein the trap material is a material having hydrogen storage properties coated with an ion-exchange polymer. 4.   The fuel cell electrode according to claim 1, wherein the trap material is uniformly dispersed in the electrode catalyst layer.   The electrode for a fuel cell according to any one of claims 1 to 6, further comprising a layer containing the trap material on at least one surface of the electrode catalyst layer. In a fuel cell MEA including a solid polymer electrolyte membrane, a pair of electrodes sandwiching the membrane, and a gas diffusion layer,
A fuel cell MEA, wherein at least one of the electrodes is a fuel cell electrode according to any one of claims 1 to 7.   The fuel cell MEA according to claim 8, wherein the fuel cell electrode according to claim 1 is used as a cathode.   A fuel cell using the fuel cell electrode according to any one of claims 1 to 7, or the fuel cell MEA according to claim 8 or 9.