JP6478677B2 - Fuel cell electrode - Google Patents

Description

  The present invention relates to a fuel cell electrode, a membrane electrode assembly having an electrode layer including the electrode, and a fuel cell including the membrane electrode assembly. More specifically, the present invention comprises a fuel cell electrode having high durability and capable of providing a high initial voltage, a membrane electrode assembly having an electrode layer including the electrode, and the membrane electrode assembly. The present invention relates to a fuel cell.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas has attracted attention as an energy source. As this fuel cell, there is a solid polymer fuel cell using a solid polymer membrane as an electrolyte membrane. In general, in such a polymer electrolyte fuel cell, a membrane electrode assembly (MEA) in which an electrode catalyst layer is bonded to both surfaces of an electrolyte membrane having proton conductivity is used.

  This membrane / electrode assembly is generally produced by applying electrode forming catalyst ink on both surfaces of an electrolyte membrane. The electrode forming catalyst ink includes catalyst particles such as platinum, a catalyst carrier (for example, carbon particles) for supporting the catalyst particles, and an ionomer having proton conductivity, which are dispersed in a dispersion medium.

  The electrochemical reaction in the fuel cell occurs at a so-called three-phase interface where the gas passing through the electrode layer, the ionomer, and the catalyst particles supported on the catalyst carrier are in contact with each other. The power generation performance can be improved by increasing the amount of catalyst particles at the three-phase interface and increasing the chance of gas contact with the catalyst particles. From this point of view, in Patent Document 1, in preparing the electrode forming catalyst ink, the power generation performance is improved by specifying the volume ratio of the catalyst particles and the ionomer covering the catalyst carrier.

  Furthermore, in Patent Document 2, studies are being made to improve the coverage of the catalyst carrier with ionomers. Here, the ionomer, which is a perfluorosulfonic acid resin, pays attention to the solubility parameter of the ionomer and the dispersion medium so that the catalyst carrier, which is carbon particles, can be coated in the dispersion medium containing water and alcohol. Yes.

  As a catalyst carrier, it has been known that carbon black having low crystallinity or high crystallinity is conventionally used.

  Patent Document 3 discloses a fuel cell electrode using a low crystalline carbon black, wherein the platinum-supported carbon is subjected to an acid treatment, and 0.7 mmol / g or more of an acid remains on the carbon support. . Thereby, the platinum-supporting carbon becomes hydrophilic, the water retention property of the electrode layer is improved, and the proton transfer resistance in the electrode layer is reduced, thereby improving the power generation performance.

  On the other hand, low crystalline carbon black has a problem that durability is inferior because carbon is electrochemically oxidized and disappears as carbon dioxide in a fuel cell operating environment.

Further, the high crystalline carbon black has higher durability than the low crystalline carbon black, but has a problem that the initial voltage is lowered. In Patent Document 4, as a problem of highly crystalline carbon black, since the specific surface area is low, the catalyst particles supported on the carbon carrier are aggregated to reduce the catalytic activity. In addition, when the specific surface area of the high crystalline carbon black exceeds 300 m ² / g, the oxidation resistance decreases, and the carbon support cannot be sufficiently covered with the electrolyte (corresponding to an ionomer), so it is used for the oxygen reduction reaction. It is disclosed that the number of catalyst particles that are not increased increases.

JP 2009-152112 A Japanese Patent Laid-Open No. 2014-060097 JP 2011-003492 A JP 2006-179463 A

  The present invention relates to an electrode for a fuel cell capable of giving a high initial voltage while using a highly durable and highly crystalline carbon black, a membrane electrode assembly having an electrode layer including the electrode, and the membrane electrode It aims at providing the fuel cell which comprises a zygote.

  As a result of intensive studies, the inventors have been able to maintain oxidation resistance even when the specific surface area is increased by using extremely high crystalline carbon black, and by increasing the specific surface area, agglomeration of catalyst particles can be achieved. I found out that it can be prevented. In addition, when a very high crystalline carbon black is used, the ionomer coverage is usually deteriorated. However, the present inventors have improved this significantly by a specific surface treatment, and thereby the durability is high and high. We have succeeded in developing a fuel cell electrode that can provide an initial voltage.

That is, the present invention includes the following aspects:
<< Aspect 1 >>
A fuel cell electrode comprising a catalyst carrier, platinum or platinum alloy catalyst particles carried on the catalyst carrier, and a proton conductive ionomer covering the catalyst carrier,
The catalyst support is a highly crystalline carbon black having a BET specific surface area of 300 to 700 m ² / g and a crystallite size L _c of 2.0 nm or more, and a catalytic acid amount is 0.55 mmol / g. Or more and less than 0.70 mmol / g,
Fuel cell electrode.
<< Aspect 2 >>
The electrode for fuel cells according to aspect 1, wherein the water immersion pH is 3.3 or less.
<< Aspect 3 >>
The electrode for a fuel cell according to aspect 1 or 2, wherein a covering ratio of the proton conductive ionomer to the catalyst carrier is 88% or more.
<< Aspect 4 >>
Any one of aspects 1 to 3, wherein the proton conductive ionomer is a hydrocarbon-based or fluorine-based polymer electrolyte having an acidic functional group such as a phosphoric acid group, a sulfonic acid group, or a phosphonic acid group in the side chain. The electrode for a fuel cell according to one item.
<< Aspect 5 >>
A membrane electrode assembly comprising electrode layers including the fuel cell electrode according to any one of aspects 1 to 4 on both surfaces of an electrolyte membrane having proton conductivity.
<< Aspect 6 >>
A fuel comprising the membrane electrode assembly according to aspect 5, the anode side gas flow path, the anode side gas diffusion layer, the anode side separator, the cathode side gas flow path, the cathode side gas diffusion layer, and the cathode side separator as a single cell. battery.

  According to the fuel cell electrode of the present invention, a high initial voltage can be applied while using highly durable and highly crystalline carbon black. Moreover, according to the fuel cell electrode of the present invention, the power generation performance of the fuel cell can be improved under various humidity conditions.

  Without being bound by theory, this is due to the improved ionomer coverage, which increased the three-phase interface between the gas passing through the electrode layer, the ionomer, and the catalyst particles supported on the catalyst support, and / or Alternatively, it is considered that the non-coated ionomer that causes the voids in the electrode layer to be blocked reduces the voids in the electrode layer to improve the material diffusibility.

The relationship between the amount of catalyst acid obtained in an Example and the ionomer coverage is shown. The relationship between the water immersion pH obtained in the Example and the ionomer coverage is shown. The relationship between the ionomer coverage in the low humidity condition obtained in the Example and an initial voltage is shown. The relationship between the ionomer coverage and the initial voltage under medium humidity conditions obtained in the examples is shown. The relationship between the ionomer coverage and the initial voltage under high humidity conditions obtained in the examples is shown. 1 illustrates one embodiment of a membrane electrode assembly and a fuel cell.

  Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist of the present invention.

<Fuel cell electrode>
The fuel cell electrode of the present invention includes a catalyst carrier, platinum or platinum alloy catalyst particles supported on the catalyst carrier, and a proton conductive ionomer covering the catalyst carrier. Here, this electrode has a catalytic acid amount of 0.55 mmol / g or more and less than 0.70 mmol / g.

  The amount of catalytic acid is a value measured by a back titration method. In the reverse titration method, 0.5 g of the electrode is suspended in 20 ml of 0.1N NaOH aqueous solution and then filtered; 0.05 ml of methyl orange is added to 5 ml of the filtrate, and titration is performed with 0.05 N HCl aqueous solution; The amount of catalyst acid is calculated from the difference between the amount of HCl input during titration and the amount of HCl consumed by the aqueous NaOH solution. This is preferably 0.58 mmol / g or more, 0.60 mmol / g or more, or 0.650 mmol / g or more, 1.0 mmol / g or less, 0.80 mmol / g or less, 0.75 mmol / g or less, Or it is less than 0.70 mmol / g. The inventors have found that when the amount of the catalyst acid is in such a specific range, the ionomer can coat the catalyst support with a high coverage even if the catalyst support is a very high crystalline carbon black. I found it. It has also been found that the improvement in water retention tends to improve the power generation performance during low humidification due to a decrease in proton transfer resistance in the catalyst layer.

  The water immersion pH of the fuel cell electrode of the present invention is preferably 3.3 or less. The water immersion pH is more preferably 3.3 or lower or 3.0 or lower, and is 2.0 or higher or 2.5 or higher. Here, the water immersion pH of the electrode is the pH of the suspension when 0.5 g of the electrode is suspended in 20 ml of pure water. Within such a range, even if the catalyst support is a very high crystalline carbon black, the ionomer can cover the catalyst support with a high coverage.

<Catalyst carrier>
The catalyst carrier used in the present invention is a highly crystalline carbon black having a BET specific surface area of 300 to 700 m ² / g and a crystallite size L _c of 2.0 nm or more. It has been found that such highly crystalline carbon black usually has hydrophobicity and decreases the ionomer coverage, but the ionomer coverage can be greatly improved by selecting the catalytic acid amount as described above. .

The BET specific surface area of the catalyst carrier is measured by calculating the specific surface area from the adsorption amount of N2 gas after 0.2 g of the catalyst carrier is heated at 150 ° C. for 2 hours in a vacuum atmosphere. The BET specific surface area of the catalyst carrier used in the present invention is more preferably in the range of 350 to 650 m ² / g, or 400 to 600 m ² / g. If it is such a range, the catalyst carrier which is highly crystalline carbon black can maintain durability, and the fuel cell electrode containing this can give a high initial voltage.

The crystallite size L _c indicates the thickness of the laminate-like crystals of carbon black, as determined by powder X-ray diffraction. The crystallite size _{L c} is at least 2.0 nm, preferably not less than or 2.5nm or 2.2 nm, also is below 20.0nm or less, or 15.0 nm. By being in such a range, high durability can be maintained.

  The coverage of the catalyst carrier with the ionomer is preferably 88% or more, 90% or more, or 92% or more. Here, the ionomer coverage of the catalyst support is measured as follows: the temperature of the single cell is set to 40 ° C., and the cathode side electrode is immersed in pure water or an aprotic conductive solvent (fluorine solvent). Then, humidified hydrogen that was passed through a bubbler heated to 45 ° C. was supplied to the anode side electrode at 1.0 L / min, and the potential was swept at 50 mV / s in the range of 50 mV to 1.0 V. The electric double layer is subtracted from the integral of the electric quantity of 0.1 to 0.4 V in the obtained cyclic voltammogram, and the electrochemically active surface area (ECSA) is calculated from the electric quantity. Then, the ionomer coverage is calculated from the percentage of ECSA when an aprotic conductive solvent is used relative to ECSA when pure water is used.

  The catalyst carrier used in the present invention is a carbon-based material such as carbon black or activated carbon, for example, in an inert atmosphere at 1 to 10 hours (particularly 3 to 8 hours), 1800 to 2500 ° C. (particularly 2000 to 2200 ° C.). It can be obtained by heat treatment. Such heat treatment can increase the crystallinity of the carbon material.

  However, the highly crystalline carbon black obtained in this way may have a low BET specific surface area. In this case, in a high temperature (for example, 80 ° C. to 100 ° C.), in an acid aqueous solution (for example, 1 to 10 N). The highly crystalline carbon black may be activated for several days in an inorganic acid aqueous solution) to increase the BET specific surface area. Alternatively, the BET specific surface area may be increased by heating to 200 to 600 ° C. and activating the highly crystalline carbon black in the air for 1 to 10 hours.

<Catalyst particles>
The catalyst particles used in the present invention are platinum or platinum alloy fine particles supported on a catalyst carrier.

  Platinum alloys include ruthenium (Ru), molybdenum (Mo), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), iron (Fe), nickel (Ni), titanium ( List alloys with at least one selected from Ti), tungsten (W), palladium (Pd), rhenium (Re), chromium (Cr), manganese (Mn), niobium (Nb), and tantalum (Ta). Can do.

  The average particle diameter of the catalyst particles is not particularly limited as long as the catalyst carrier can be supported. For example, when measured by powder X-ray diffraction, 1.0 to 10 nm, 1.5 to 8.0 nm, or 2.0 to 5. It can be 0 nm.

<Proton conductive ionomer>
Examples of the proton conductive ionomer used in the present invention include hydrocarbon-based or fluorine-based polymer electrolytes having an acidic functional group such as a phosphoric acid group, a sulfonic acid group, or a phosphonic acid group in the side chain. Generally, ionomers contain metal ions, but when used in the art, ionomers need not contain metal ions.

  As the hydrocarbon-based or fluorine-based polymer electrolyte, (i) a hydrocarbon-based polymer whose main chain is made of an aliphatic hydrocarbon, (ii) a main chain is made of an aliphatic hydrocarbon, and a part of the main chain or Examples include a polymer in which all hydrogen atoms are substituted with fluorine atoms, and (iii) a polymer in which the main chain has an aromatic ring. As the polymer electrolyte, either a polymer electrolyte having an acidic group or a polymer electrolyte having a basic group can be used. Examples of acidic groups include sulfonic acid groups, sulfonimide groups, carboxylic acid groups, phosphonic acid groups, phosphoric acid groups, and phenolic hydroxyl groups. Among these, a sulfonic acid group or a phosphonic acid group is preferable, and a sulfonic acid group is particularly preferable.

  Examples of such resins include resins described in JP2013-127865A, JP2011-238406A, and the like.

<Other ingredients>
The fuel cell electrode of the present invention may contain components other than the above components within a range not impairing the effects of the present invention.

<< Membrane electrode assembly and fuel cell >>
FIG. 1 shows a membrane electrode assembly (100) having an anode electrode layer (20) and a cathode electrode layer (30) including the fuel cell electrode on both surfaces of an electrolyte membrane (10) having proton conductivity. . FIG. 1 shows the membrane electrode assembly (10), anode side gas flow path (21), anode side gas diffusion layer (22), anode side separator (23), cathode side gas flow path (31), cathode side. Also shown is a fuel cell (200) comprising a gas diffusion layer (32) and a cathode separator (33) as a single cell.

  The electrolyte membrane (10) is a proton exchange membrane having a role of conducting protons from the anode electrode layer (20) to the cathode electrode layer (30). The electrolyte membrane (10) is composed of, for example, a hydrocarbon-based or fluorine-based polymer electrolyte having an acidic functional group such as a phosphoric acid group, a sulfonic acid group, or a phosphonic acid group in the side chain. Specific examples of such an electrolyte membrane 12 include NAFION (DuPont, trademark), FREMION (Asahi Glass Co., Ltd., trademark), ACIPLEX (Asahi Kasei Chemicals Corporation, trademark), and the like.

  The anode electrode layer (20) and the cathode electrode layer (30) are layers that function as electrodes in the fuel cell (200). Both the anode electrode layer (20) and the cathode electrode layer (30) include fuel cell electrodes.

  The gas diffusion layers (22, 32) are made of, for example, porous carbon having innumerable pores that allow reaction gas and water to pass through in the thickness direction. The gas diffusion layers (22, 32) have the ability to uniformly diffuse the reaction gas to the anode electrode layer (20) and the cathode electrode layer (30) and to suppress drying of the membrane electrode assembly (100). Examples of the gas diffusion layers (22, 32) include carbon-based porous bodies such as carbon paper, carbon cloth, carbon felt, carbonized polyimide, a mixture of carbon black and a fluororesin, and carbon non-woven fabric coated with fluorine. Etc. can be used.

  The separators (23, 33) are made of a material having electronic conductivity. Examples of such materials that can be used for the separators (23, 33) include carbon, resin-molded carbon, titanium, and stainless steel. On the surface of the anode separator (23) on the gas diffusion layer (22) side, an anode side gas flow path (21) for circulating hydrogen or the like as a fuel gas is formed. Similarly, a cathode side gas flow path (31) for circulating air (oxygen) or the like as an oxidant gas is formed on the surface of the cathode side separator (33) on the gas diffusion layer (32) side. .

  The present invention will be described more specifically with reference to the following examples, but is not limited thereto.

<< Preparation of electrode >>
<Example 1>
10 g of highly crystalline carbon black (BET specific surface area: 350 m ² / g, L _c = 2.2 nm) was dispersed in a 1.5 N nitric acid aqueous solution. The dispersion was heated to 100 ° C. and stirred uniformly for 45 hours to carry out activation treatment. Thereafter, the dispersion was allowed to cool and filtered to separate carbon black. The separated carbon black was repeatedly filtered and washed until the conductivity of the filtered waste liquid became 50 μm S / cm or less. 7 g of the washed carbon black is dispersed in 1 L of a 0.1 N nitric acid aqueous solution, and a dinitrodiamine Pt nitric acid solution containing 0.3 g of Pt with a platinum (Pt) loading rate of 30 wt%, and 20 g of 99.5% ethanol are added. In addition to this dispersion, it was thoroughly blended and heated at 90 ° C. for 3 hours.

  After the heating, this dispersion was repeatedly filtered and washed until the conductivity of the filtered waste liquid became 50 μm S / cm or less, and the resulting powder cake was dried by blowing at 80 ° C. for 15 hours. Next, this dry powder was heat-treated at 700 ° C. for 2 hours at a rate of temperature increase of 5 ° C./min in argon gas to obtain a Pt / C electrode.

  Further, this Pt / C electrode was dispersed in pure water 80 times the amount of carbon, and an aqueous cobalt nitrate (Co) solution was added dropwise so that the molar ratio of Pt: Co was 7: 1. Here, as the Ni nitrate aqueous solution, a commercially available Ni nitrate hexahydrate dissolved in pure water was used. After the addition, sodium borohydride diluted with pure water was added dropwise 6 times the Co molar amount. After stirring for about 15 hours, the filtration waste solution was repeatedly filtered and washed until the conductivity of the filtered waste liquid became 5 μm S / cm or less. The obtained powder cake was dried by air drying at 80 ° C. for 15 hours. After air drying, the dry powder was heat-treated at 800 ° C. to be alloyed to obtain a PtCo / C electrode.

  In order to perform the surface treatment of the PtCo / C electrode, the powder was dispersed in a 100-fold amount of 0.5N nitric acid aqueous solution, and the dispersion was heated to 90 ° C. and stirred for 45 hours. After completion of stirring, the dispersion was allowed to cool and filtered to separate the electrode. The separated PtCo / C electrode was repeatedly filtered and washed until the filtration waste liquid had a conductivity of 50 μm S / cm or less, and the resulting powder cake was dried by blowing air at 80 ° C. for 15 hours to obtain an electrode for Example 1. Got.

The catalytic acid amount of the electrode of Example 1 was 0.6 mmol / g, and the water immersion pH was 3.2. Furthermore, _{L c} of the catalyst carrier was 2.2 nm.

<Example 2>
The BET specific surface area of 250 meters ² / g, except _{that L c} is used highly crystalline carbon black is 2.5nm as a raw material in the same manner as in Example 1, to obtain an electrode for Example 2.

The catalyst acid amount of the electrode of Example 2 was 0.6 mmol / g, and the water immersion pH was 3.1. Furthermore, _{L c} of the catalyst carrier was 2.5 nm.

<Comparative example 1>
In Example 1, the activation condition after dispersing the highly crystalline carbon black in 1.5N nitric acid aqueous solution was changed from 100 ° C .: 45 hours of stirring to 80 ° C .: 0.5 hours of stirring. Except for this, an electrode for Comparative Example 1 was obtained in the same manner as Example 1.

The catalytic acid amount of the electrode of Comparative Example 1 was 0.40 mmol / g, and the water immersion pH was 4.2. Furthermore, _{L c} of the catalyst carrier was 2.2 nm.

<Comparative example 2>
In Example 1, except that the activation condition after dispersing the highly crystalline carbon black in 1.5N nitric acid aqueous solution was changed from 100 ° C .: stirring for 45 hours to 80 ° C .: stirring for 21 hours. In the same manner as in Example 1, an electrode for Comparative Example 2 was obtained.

The catalytic acid amount of the electrode of Comparative Example 2 was 0.50 mmol / g, and the water immersion pH was 4.2. Furthermore, _{L c} of the catalyst carrier was 2.2 nm.

<Comparative Example 3>
A comparison was made in the same manner as in Example 1 except that low crystalline carbon black having a BET specific surface area of 800 m ² / g and L _c of 1.9 nm was used as a raw material, and no activation treatment was performed. An electrode for Example 3 was obtained.

The catalytic acid amount of the electrode of Comparative Example 3 was 0.60 mmol / g, and the water immersion pH was 2.9. Further, L _c of the catalyst support was 1.9 nm.

<Comparative example 4>
A comparison was made in the same manner as in Example 1 except that low crystalline carbon black having a BET specific surface area of 790 m ² / g and L _c of 1.7 nm was used as a raw material, and no activation treatment was performed. An electrode for Example 4 was obtained.

The catalytic acid amount of the electrode of Comparative Example 4 was 0.60 mmol / g, and the water immersion pH was 3.1. Furthermore, _{L c} of the catalyst carrier was 1.7 nm.

<< Production of MEA >>
Ultrasonic dispersion of 1.2 g of the electrodes obtained as described above, 4 g of pure water, 4.74 g of a fluorine ionomer solution (ionomer concentration: 10 wt%), 8.8 g of 1-propanol, and 2.4 g of propylene glycol. did. The obtained electrode forming catalyst ink was applied to a Teflon sheet substrate with a doctor blade and dried at 80 ° C. for 15 hours. The obtained sheet was cut into 13 cm ² and thermocompression bonded to the electrolyte membrane to produce MEAs including the electrodes of Examples 1-2 and Comparative Examples 1-4.

<Evaluation>
<Ionomer coverage>
As a measure of how much the catalyst support of each electrode is covered with the ionomer, the ionomer coverage was determined as follows: First, the temperature of the single cell was set to 40 ° C., and the cathode side electrode was treated with pure water. Alternatively, humidified hydrogen that has been immersed in an aprotic conductive solvent and passed through a bubbler heated to 45 ° C. to the anode-side electrode is supplied at 1.0 L / min, and the potential is set at 50 mV / s in the range of 50 mV to 1.0 V. Sweep. The electrochemical active surface area (ECSA) was calculated from the amount of electricity by subtracting the electric double layer from the integral of the amount of electricity of 0.1 to 0.4 V in the obtained cyclic voltammogram. Then, the ionomer coverage was calculated by calculating the percentage of ECSA when using a non-proton conductive solvent with respect to ECSA when using pure water which is proton conductive.

<Initial voltage>
In order to compare the electrode performance in each humidified environment, the initial voltage was measured. The temperature of the single cell is set to 82 ° C. at low humidification (30% RH), 60 ° C. at high humidification (80% RH), 45 ° C. at over humidification (165% RH), and 55 ° C. to the cathode side electrode. Humidified air passed through a heated bubbler was supplied at 2.0 L / min, humidified hydrogen passed through a bubbler heated to 55 ° C. was supplied to the anode electrode at 0.5 L / min, and IV (current Voltage characteristics) were measured. After the current-voltage characteristics are stabilized, the initial voltage of each electrode is set to a voltage value of 1.2 A / cm ² in a low humidified environment, a voltage value of 2.5 A / cm ² in a highly humidified environment, and an overhumidified environment. Below, it compared with the voltage value in 2.0 A / cm < ² >.

<durability>
Under the same battery environment as the initial voltage measurement method, the IV characteristics were measured before and after holding at 1.3 V for 2 hours, and the ratio before and after this was used as an index of durability.

"result"
The results obtained by the above evaluation method are shown in Table 1.

  FIG. 1 shows the relationship between the amount of catalytic acid obtained by the above evaluation method and the ionomer coverage. Further, FIG. 2 shows the relationship between water immersion pH and ionomer coverage. Comparing only the highly crystalline carbon black, it can be seen that the ionomer coverage is improved when the acid catalyst amount is high or the water immersion pH is low.

  3 to 5 show the relationship between the ionomer coverage and the initial voltage under each humidity condition. By improving the ionomer coverage, the initial voltage could be improved under all conditions.

  Comparing Comparative Examples 1 and 2 with Comparative Examples 3 and 4, the electrode using low crystalline carbon black tends to have a higher initial voltage. However, by improving the ionomer coverage of highly crystalline carbon black, the electrodes of Examples 1 and 2 achieved a higher initial voltage than the electrodes using the low crystalline carbon black of Comparative Examples 3 and 4. Succeeded in doing.

  Furthermore, as shown in Table 1, it was confirmed that the electrodes of Examples 1 and 2 had higher durability than the electrodes using the low crystalline carbon black of Comparative Examples 3 and 4.

DESCRIPTION OF SYMBOLS 10 Electrolyte membrane 20 Anode electrode layer 21 Anode side gas flow path 22 Anode side gas diffusion layer 23 Anode side separator 30 Cathode electrode layer 31 Cathode side gas flow path 32 Cathode side gas diffusion layer 33 Cathode side separator 100 Membrane electrode assembly 200 Fuel battery

Claims (5)

A fuel cell electrode comprising a catalyst carrier, platinum or platinum alloy catalyst particles carried on the catalyst carrier, and a proton conductive ionomer covering the catalyst carrier,
The catalyst support is a highly crystalline carbon black having a BET specific surface area of 300 to 700 m ² / g and a crystallite size L _c of 2.0 nm or more ;
The coverage of the proton-conductive ionomer on the catalyst carrier is 88% or more, and the amount of catalyst acid is 0.55 mmol / g or more and less than 0.70 mmol / g,
Fuel cell electrode.   The electrode for fuel cells according to claim 1, wherein the water immersion pH is 3.3 or less. The proton conducting ionomers, phosphoric acid group in the side chain is a hydrocarbon or fluorinated polymer electrolyte having an acidic functional group such as sulfonic acid group or phosphonic acid group in the side chain, according to claim 1 or 2 Fuel cell electrode. The membrane electrode assembly which has an electrode layer containing the electrode for fuel cells as described in any one of Claims 1-3 on both surfaces of the electrolyte membrane which has proton conductivity. The membrane electrode assembly according to claim 4 , comprising the anode side gas flow path, the anode side gas diffusion layer, the anode side separator, the cathode side gas flow path, the cathode side gas diffusion layer, and the cathode side separator as a single cell. Fuel cell.

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