JP2006269368A - Electrode for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a fuel cell using a hydrocarbon system electrolyte material with oxidation resistance and a high cell performance. <P>SOLUTION: The electrode is provided with a hydrocarbon system electrolyte material with a vinyl system monomer as a component element, with an ion exchange capacity of 0.5 meq/g or more and 4.0 meq/g or less, and with an ion exchange capacity and/or molecular weight in the vicinity of electrode catalyst powder relatively lower than other parts. The above product can be simply realized by using two kinds of electrolyte and controlling a sequence of mixing/dispersion. As a result, the electrode catalyst powder can be well dispersed, and an action can well be improved. Further, stability is improved by adoption of an electrolyte material with a small ion-exchange capacity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell electrode employing a hydrocarbon-based electrolyte material.

  An electrode used in a fuel cell has an electrode catalyst powder composed of an electrode catalyst and a carrier carrying the electrode catalyst, and an electrolyte material for the electrode. Many electrolyte materials employing perfluoro-based electrolyte materials have been reported.

  The perfluoro-based electrolyte material is represented by Nafion (trademark), and is a material generally employed in fuel cells, and is a material excellent in oxidation resistance. In the fuel cell, when protons produced at the anode reach the cathode through the electrolyte membrane during the electrode reaction process, they are oxidized by oxygen supplied to the cathode to produce water. The hydroxyl radicals may diffuse and decompose fuel cell components.

  Further, due to the nature of the resin skeleton, a segment having a water repellent structure and a segment having a hydrophilic structure are mixed, and the water repellent layer and the hydrophilic layer have a phase separation structure. For this reason, the structure has a well-balanced function of water retention and gas diffusibility.

  However, although perfluoro-based electrolyte material has high performance when applied to a fuel cell, it is a material synthesized through a complicated process and has a high fluorine content, so the cost is very high. It is an obstacle to the spread of batteries.

  Therefore, with the aim of reducing costs, hydrocarbon-based electrolyte materials for fuel cell electrodes (in the present specification, replacement with fluorine is completely performed because the cost can be reduced by reducing fluorine. It is studied to adopt an electrolyte material that is not included in the "hydrocarbon electrolyte material" (Patent Documents 1 to 7).

Hydrocarbon electrolyte materials can generally be reduced in cost, but there is a tendency that sufficient performance cannot be exhibited as compared with perfluoro electrolyte materials. One reason for this is that the hydrophilic part and the water-repellent part of the hydrocarbon-based electrolyte material cannot sufficiently exhibit their functions in a well-balanced manner. In particular, since the function of the water repellent part is not sufficient, it is difficult to sufficiently exhibit proton conductivity. In addition, since the hydrocarbon-based electrolyte material has a smaller carbon-hydrogen bond energy than the carbon-fluorine bond energy, the oxidation resistance is not as good as that of the perfluoro-electrolyte material, and the oxidation resistance is fully exhibited. It is thought that it cannot be done.
Japanese Patent Laid-Open No. 5-36418 JP-A-6-203848 JP 2002-298855 A JP 2002-164055 A JP 2004-123794 A JP 11-502249 A JP 10-45193 A

  The present invention has been made in view of the above circumstances, and solves the problem of providing a fuel cell electrode mainly composed of a hydrocarbon-based electrolyte material that is excellent in oxidation resistance and can exhibit high performance, and a method for producing the same. It should be a challenge.

(1) As a result of intensive studies aimed at solving the above problems, the present inventors have completed the following invention. That is, the fuel cell electrode of the present invention includes a fuel cell having an electrode catalyst powder and an electrolyte material having a hydrocarbon electrolyte material having a vinyl monomer in which the electrode catalyst powder is dispersed as a constituent element. Electrode,
The electrolyte material has an ion exchange capacity of 0.5 meq / g or more and 4.0 meq / g or less, and the vicinity of the electrode catalyst powder is more ion exchange capacity and / or molecular weight than the part other than the vicinity of the electrode catalyst powder. Is relatively low. Here, it is preferable that the electrolyte material has a first electrolyte material disposed in the vicinity of the electrode catalyst powder and a second electrolyte material having a larger ion exchange capacity than the first electrolyte material.

  In order to fully exhibit the performance of the electrode catalyst, an attempt was made to finely disperse the carbon particles in the electrolyte material. In order to finely disperse the carbon particles, it is effective to employ an ionic electrolyte material having a surface active effect. Hydrocarbon electrolyte materials have good adsorptivity with carbon particles and have desirable properties as a dispersing agent.

  And in order to fully demonstrate the performance of an electrode catalyst, while dispersibility is improved, it is desirable to make the thickness of the electrolyte material which coats an electrode catalyst powder into the thickness which can permeate | transmit a gas. Therefore, in order to reduce the thickness of the electrolyte material adhering to the electrode catalyst powder, an electrolyte material (for example, the first electrolyte material) having a small molecular weight is employed as the electrolyte material disposed in the vicinity of the electrode catalyst powder.

  As a result, it became possible to disperse the electrode catalyst powder with very few hydrocarbon-based electrolyte materials, and it was possible to coat the carbon particles with an extremely thin electrolyte material. Therefore, as a result of being able to disperse the electrode catalyst powder in an extremely fine state, the action of the electrode catalyst can be sufficiently improved.

  However, the hydrocarbon-based electrolyte material does not have sufficient oxidation resistance and is decomposed by hydrogen peroxide generated in the electrode catalyst powder, and there is a concern that the durability is poor. Therefore, in order to improve the oxidation resistance, an electrolyte material having a small ion exchange capacity is employed as the first electrolyte material. Even if an electrolyte material having a small ion exchange capacity is used as the first electrolyte material arranged in the vicinity of the electrode catalyst powder, the effect on the performance is limited because the surface of the electrode catalyst powder is only covered very thinly. .

  And between the electrode catalyst powder coated with the 1st electrolyte material with good dispersibility, the 2nd electrolyte material which shows high proton conductivity is employ | adopted, and battery performance is ensured. Here, when the second electrolyte material is added in a colloidal form, the distribution of the electrolyte in the electrode catalyst can be localized. When the second electrolyte material is localized in the electrode catalyst, a proton conduction path is formed, and both good proton conductivity and gas diffusibility can be achieved.

  Accordingly, the electrode catalyst powder can be finely dispersed by coating relatively thinly with the first electrolyte material having good dispersibility and excellent oxidation resistance in the vicinity of the electrode catalyst powder. And battery performance is ensured by employ | adopting the material excellent in the electrical property as electrolyte, such as having a generally high ion exchange capacity as a 2nd electrolyte material.

  In order to improve dispersibility, a material having a relatively small molecular weight is employed as the first electrolyte material. In order to improve the oxidation resistance, a material having a relatively small ion exchange capacity is adopted. An extremely small amount is used in order to suppress the performance deterioration due to the low ion exchange capacity.

  As the second electrolyte material, an electrolyte material having a high ion exchange capacity is employed so that the battery performance can be sufficiently exhibited.

(2) The electrode for a fuel cell of the present invention includes the electrolyte material having a first electrolyte material and a second electrolyte material having a larger ion exchange capacity than the first electrolyte material,
What is manufactured with the manufacturing method which has the 1st dispersion | distribution process which disperse | distributes the said electrode catalyst powder in the said 1st electrolyte material, and the 2nd process of disperse | distributing a 2nd electrolyte material after this 1st dispersion | distribution process. desirable. Other properties are as described in the above (1).

  First, after the electrode catalyst powder is dispersed in the first electrolyte material having excellent dispersibility and oxidation resistance described above, the second electrolyte material is mixed and dispersed, so that the first electrolyte material The space between the coated electrocatalyst powders can be filled with the second electrolyte material. As a result, the fuel cell electrode described above can be realized.

  (3) As the first electrolyte material, specific preferred properties include an ion exchange capacity of 0.5 meq / g or more and 1.6 meq / g or less, and a molecular weight of 10,000 or more and 200,000 or less. In the above, it is desirable that (the first electrolyte material) / (the electrode catalyst powder) is mixed at a ratio of 0.05 to 0.40 on a mass basis.

  (4) Further, as the second electrolyte material, the second electrolyte material has an ion exchange capacity of 1.4 meq / g or more and 4.0 meq / g or less as a particularly preferable property, and is dispersed in the second step. It is desirable that the material is a colloid solution of 10 nm or more and 100 nm or less and (the second electrolyte material) / (the electrode catalyst powder) is 0.10 or more and 1.50 or less on a mass basis.

  (5) Here, it is desirable that the ion exchange capacity is improved by dispersing and containing a heteropoly acid typified by cattanguctenic acid or the like in the electrolyte material (particularly the first electrolyte material having a low ion exchange capacity). .

(6) The manufacturing method of the electrode for fuel cells of the present invention which solves the above-mentioned subject is a method for manufacturing the electrode for fuel cells according to any one of the above (1) to (5). The electrolyte material includes a first electrolyte material and a second electrolyte material having a larger ion exchange capacity than the first electrolyte material,
A first dispersion step of dispersing the electrode catalyst powder in the first electrolyte material;
And a second step of dispersing the second electrolyte material after the first dispersion step.

  Since the electrode for a fuel cell of the present invention has the above-described configuration, the electrode catalyst powder can be finely dispersed to fully exhibit the performance of the electrode catalyst powder, and the electrolyte material in the vicinity of the electrode catalyst powder can be oxidized. Deterioration due to can be suppressed. It has also succeeded in securing proton conductivity and gas diffusivity in the bulk, which greatly affects battery performance when a large current is passed. Therefore, since the fuel cell electrode manufactured by the manufacturing method of the present invention also has high performance, it is an excellent manufacturing method.

  The electrode for a fuel cell of this embodiment has an electrode catalyst powder and an electrolyte material in which the vicinity of the electrode catalyst powder has a relatively low ion exchange capacity and / or molecular weight. The fuel cell electrode can be used in various forms such as solid, gel, and liquid depending on the form of the electrolyte material employed. In general, an electrode for a fuel cell is dissolved or suspended in some solvent to form a paste, and then applied to the surface of an electrolyte membrane or the surface of a diffusion layer.

(Electrocatalyst powder)
The electrode catalyst powder is generally used as a catalyst-supported powder in which a catalyst is supported on a supported powder. As the catalyst, platinum, a noble metal catalyst obtained by alloying or mixing other elements (such as a noble metal such as ruthenium or palladium or a base metal such as copper) with platinum is used. Carbon powder or the like is used as the support powder. Platinum-supported carbon using carbon powder as the support powder and platinum as the catalyst is widely used. Platinum supported on platinum-supporting carbon may be alloyed with other elements, or may be used by mixing with other elements. The catalyst itself may be used as a powder without using the supported powder. In particular, it is desirable that the electrode catalyst powder employed in the fuel cell electrode of the present embodiment has a small particle size from the viewpoint of improving performance. For example, the secondary particle diameter of the electrode catalyst powder is preferably 1 μm or more and 100 μm or less before being dispersed in the medium (before the first dispersion step), and more preferably 10 μm or more and 80 μm or less. After being dispersed in the medium (after the second dispersion step), that is, the secondary particle diameter of the electrocatalyst powder in the produced electrode is preferably about 5 nm to 50 μm, more preferably about 40 nm to 10 μm, and more preferably 70 nm to 2 μm. Is more desirable.

(Electrolyte material)
The electrolyte material is a hydrocarbon electrolyte material having a vinyl monomer as a constituent element. Heteropolyacids such as silicotungstic acid can be mixed to improve ion exchange capacity. Moreover, antioxidants, such as hindered phenol and hindered amine, can also be mixed.

  The basic skeleton constituting the hydrocarbon electrolyte material is not limited. For example, an olefin polymer such as polyethylene or polypropylene; a structure in which a general vinyl polymer such as polystyrene is used as a basic skeleton and a functional group that imparts ion conductivity such as a sulfo group, a carboxy group, or a phosphate group is used. it can. In addition to a linear structure, the polymer can have a ladder-like structure, a three-dimensional network-like structure, etc. by adding an appropriate crosslinking agent. A hydrogen atom in the basic skeleton can be appropriately substituted with fluorine, chlorine or the like. Note that the cost is reduced by having hydrogen atoms that are not substituted with fluorine element or the like.

  The ion exchange capacity is 0.5 meq / g or more and 4.0 meq / g or less. The ion exchange capacity is lower in the vicinity of the electrode catalyst powder. A specific method for realizing such an inclination of the ion exchange capacity is not limited. For example, after preparing two or more electrolyte materials having different ion exchange capacities, the electrode catalyst powders are formed in ascending order of ion exchange capacity. By mixing and dispersing, the ion exchange capacity of the electrolyte material can be increased sequentially from the vicinity of the electrode catalyst powder.

  The ion exchange capacity was measured by substituting the ion exchange group for the test sample of the hydrocarbon-based electrolyte material with the H type, and then the mass of the test sample after the replacement with the dry H type based on the mass after dissolution. Dissolve in ethanol to a concentration of 3%, use phenolphthalein as an indicator, and titrate with 0.05 mol / L sodium hydroxide aqueous solution at the point where the color change of the solution is kept for several seconds. It is a value calculated according to the following formula based on the obtained value.

(Ion exchange capacity) (meq / g) = (0.05 × Titration volume (ml)) / (Dry mass of dissolved test sample (g))
First electrolyte material: In particular, as the first electrolyte material disposed in the vicinity of the electrode catalyst powder, it is preferable to employ a material having an ion exchange capacity in the range of 0.5 meq / g to 1.6 meq / g. Furthermore, it is desirable to adopt 0.7 meq / g or more and 1.2 meq / g or less. By setting it within this range, the stability in an oxidizing atmosphere in the fuel cell electrode is improved.

  And it is desirable to employ a molecular weight of 10,000 or more and 200,000 or less. Furthermore, 30,000 or more and 100,000 or less are more desirable. More preferably, it is 40,000 or more and 70,000 or less. By setting the molecular weight within this range, the first electrolyte material can be adhered thinly and uniformly to the surface of the electrode catalyst powder while maintaining the film forming property as a polymer material. The molecular weight is lower than that of the second electrolyte material.

  The amount of the first electrolyte material to be mixed is desirably (first electrolyte material) / (the electrode catalyst powder) of 0.05 or more and 0.40 or less on a mass basis. Furthermore, it is more desirable that it is 0.05 or more and 0.3 or less. The first electrolyte material is mainly added to finely disperse the electrode catalyst powder, and the addition amount is preferably small in order to ensure normal battery performance such as current density. Accordingly, the amount of the first electrolyte material added is set to a lower limit that is an amount necessary for dispersing the electrode catalyst powder and an upper limit that does not significantly affect proton conductivity.

  Second electrolyte material: As the second electrolyte material, it is preferable to employ a material having an ion exchange capacity of 1.4 meq / g or more and 4.0 meq / g or less. Furthermore, it is desirable to adopt 1.8 meq / g or more and 3 meq / g or less. By setting this range, proton conductivity in the fuel cell electrode can be ensured.

  And it is desirable to employ a molecular weight of 100,000 or more and 1,000,000 or less. By setting the molecular weight within this relatively high range, molecular continuity can be secured and high proton conductivity can be realized.

  The amount of the second electrolyte material to be mixed is desirably (second electrolyte material) / (the electrode catalyst powder) being 0.10 or more and 1.50 or less on a mass basis. Furthermore, it is more desirable that it is 0.20 or more and 1.2 or less. The second electrolyte material is added mainly to ensure proton conductivity in the fuel cell electrode, and it is preferable to add a larger amount than the first electrolyte material.

(Production method)
The fuel cell electrode can be produced by a first step of dispersing the electrode catalyst powder in the first electrolyte material and a second step of dispersing and mixing the second electrolyte material that is performed thereafter.

  First step: The surface of the electrode catalyst powder is coated with the first electrolyte material by mixing the electrode catalyst powder and the first electrolyte material with a ball mill, a roll or the like.

  Second step: Thereafter, the second electrolyte material is mixed and dispersed. Since the first electrolyte material is first brought into contact with the electrode catalyst powder, the surface of the electrode catalyst powder remains attached even if the second electrolyte material is mixed. The second electrolyte material is desirably mixed in a colloidal form. The particle size of the colloidal particles is preferably 10 nm or more and 100 nm or less. Furthermore, 20 nm or more and 80 nm or less are more desirable. When used as a colloidal solution, a phase separation structure can be realized in a hydrocarbon-based electrolyte material, so that a path involved in proton conduction is formed. The colloid can be formed by setting the molecular weight within the above range.

(Manufacture of hydrocarbon electrolyte materials)
A styrene polymer was selected as the base material for the hydrocarbon electrolyte material.

  Synthesis of polymers 1 to 3: Styrene polymer was synthesized by adding benzoyl peroxide (polymer 1: 0.6 g, polymer 2: 0.3 g, polymer 3: 0) to 200 mL of xylene heated to 90 ° C. in a nitrogen atmosphere. 2 g) of styrene in which 200 g was dissolved was added dropwise over 3 hours with stirring, and then heated (Polymer 1 and 2: 90 ° C., Polymer 3: 60 ° C.) for a predetermined time (Polymer 1 and 2: 1 hour, Polymer 3: 5 hours). Thereafter, the reaction solution cooled to room temperature was dropped into a large amount of methanol to precipitate a produced styrene polymer. The precipitate was collected by filtration and dried at 110 ° C. for 3 hours. When the molecular weight of the obtained styrene polymer was measured by GPC, Mw was 11700 for polymer 1, 54800 for polymer 2, and 124000 for polymer 3. The molecular weight was measured by GPC, and the weight average molecular weight was measured.

  Then, Mw 230000 (Aldrich, polystyrene [44, 114-7]) was adopted as the polymer 4, and Mw 350,000 (Aldrich, polystyrene [43, 010-2]) was adopted as the polymer 5.

  Sulfonation: Sulfo groups as ion exchange groups were introduced for polymers 1 to 5. For polymer 1, 150 g was dissolved in 500 mL of 1,2-dichloroethane. While this solution was heated to 60 ° C. and stirred, the amount of chlorosulfonic acid shown in the electrolytes 1 to 5 in Table 1 was added dropwise and held at 60 ° C. for 1 hour. The obtained chlorosulfonated styrene polymer of electrolytes 1-5 was washed with 1,2-dichloroethane and then ion-exchanged water in that order, and then left in ion-exchanged water for 1 hour at room temperature to hydrogenate the ion-exchange groups. did. Thereafter, it was vacuum dried to obtain a powdered sulfonated styrene polymer (corresponding to a hydrocarbon electrolyte material). The ion exchange capacities of the sulfonated styrene polymers of the obtained electrolytes 1 to 5 are also shown in Table 1. The ion exchange capacity was performed by the method described in the section of the embodiment described above. Polymers 2 to 5 were also sulfonated in the same manner as for polymer 1. The respective ion exchange capacities are shown in Table 2.

(Evaluation of oxidation resistance)
The oxidation resistance of each electrolyte derived from each polymer was evaluated. Evaluation of oxidation resistance was carried out by putting 56 mL of pure water in a 100 mL screw tube and keeping it at 60 ° C., and then dissolving or suspending 0.4 g of each electrolyte as a test sample. Thereafter, 16 mL of a Fe ²⁺ 10 ppm solution and 8 mL of a 30% by mass H ₂ O ₂ aqueous solution were added and stirred. This solution was in a state in which 0.4 g of electrolyte was put into 80 g of a test solution prepared to ₂ ppm of Fe ^{2+ and} 3% by mass of H ₂ O ₂ . Sampling was performed every 1 hour, 2 hours, 3 hours, and 4 hours, and the residue after filtration was separated and the molecular weight was measured by GPC. When the electrolyte material is decomposed by oxidation, the molecular weight is expected to decrease. The results for polymer 3 are shown in FIG.

  As is clear from FIG. 1, the oxidation resistance depends on the value of IEC (ion exchange capacity), and the smaller IEC (as it goes from electrolyte 1 to 5), the better the oxidation resistance. Similar results were obtained for polymers 1, 2, 4 and 5 with other molecular weight distributions.

(Evaluation of dispersibility of electrolyte solution)
Dispersibility was evaluated for each electrolyte derived from each polymer. Dispersibility was evaluated by preparing an electrolyte solution in which each electrolyte was dissolved in a water / ethanol (1/1) solution at a concentration of 10% by mass. The insoluble electrolyte was made into fine particles by an ultrasonic homogenizer so that the particle diameter was within the range of 10 nm to 100 nm. The particle size was measured with a dynamic light scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., Microtrac UPA-EX150).

  -Preparation of catalyst paste: 20 g of platinum-supported carbon (platinum content 50 mass%) as an electrode catalyst powder was added to 10 g of each electrolyte solution of each polymer (solvent water / ethanol (1/1), electrolyte concentration 10 mass%). In addition, a slurry was prepared.

  Thereafter, 60 g of ion-exchanged water and 60 g of ethanol were added to mix and disperse the platinum-supported carbon powder. Final mixing and dispersion was performed by dispersing for 1 hour with a high-speed homogenizer using 200 g of zirconia beads having a diameter of 2 mm to obtain catalyst pastes of the respective test examples. After mixing and dispersing, the particle size of the electrocatalyst powder in the catalyst paste was measured with a dynamic light scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., Microtrac UPA-EX150). Those having a particle diameter of 5 μm or more were measured with a laser diffraction particle size distribution meter. The results are shown in FIG.

  As is apparent from FIG. 2, it was found that the first electrolyte material contained during the dispersion operation can be made smaller in particle size after dispersion as the molecular weight is smaller, and is excellent in dispersibility. In particular, it was found that polymers 1 to 3 showed excellent dispersibility. And it turned out that the one where IEC is large is excellent in dispersibility. In particular, it was found that high dispersibility is exhibited when the IEC is 0.5 or more. Therefore, it was found that an electrolyte having a small molecular weight and a large IEC is suitable for the first electrolyte material.

  To the prepared catalyst paste (the electrode catalyst powder is dispersed in the first electrolyte material), a predetermined amount of the electrolyte solution of the combination shown in Table 3 and Table 4 (the added electrolyte is used as the second electrolyte material) is added. Then, the mixture was stirred and mixed to obtain a test catalyst paste for each test example corresponding to each electrolyte combination containing two types of electrolyte materials.

(Manufacture of membrane electrode assembly)
Each test catalyst paste was coated on a water-repellent carbon paper (thickness 180 μm, porosity 65%) to be a gas diffusion base material (diffusion layer) with a bar coater so that the amount of platinum supported was 1 mg / cm ² . . After coating, heating and drying were performed at 80 ° C. for 30 minutes to obtain a fuel cell electrode on which a catalyst layer was formed. An electrolyte membrane (Nafion 112, ion exchange capacity 0.909 meq / g) was sandwiched between two electrodes arranged in the direction of contact on the catalyst layer side, respectively, and bonded by hot pressing at 150 ° C. and 8 MPa for 3 minutes. The membrane electrode assembly for test of each test example using the test catalyst paste of the test example was obtained.

(Evaluation of battery performance)
The membrane electrode assembly for test of each test example was incorporated into a single cell for fuel cell evaluation and evaluated. The output voltage at current densities of 0.2 A / cm ² and 0.5 A / cm ² was measured. The operating conditions of the single cell for fuel cell evaluation are as follows. The fuel electrode side was pure hydrogen, the air electrode side was air, and the gas flow rate was adjusted so that the utilization rate of pure hydrogen was 90% and the utilization rate of air was 40%. The electrode area was 9 cm ² , the cell internal temperature was 75 ° C., and the humidifying condition was that water corresponding to 0.2 mol in terms of molar ratio was added to pure hydrogen and air. The results are shown in Table 3 and Table 4 together.

(About the first electrolyte material)
Since the test batteries of the respective test examples shown in Table 3 were evaluated by unifying the second electrolyte material, the results showed preferable properties as the first electrolyte material.

  First, comparing the test batteries of Test Examples 2 and 9 prepared under the same conditions except for the molecular weight of the first electrolyte material, it was found that Test Example 9 having a lower molecular weight can achieve higher battery performance than Test Example 2. This is because the electrode catalyst powder can be dispersed to a particle size of a few tenths by using a highly dispersible electrolyte material for the first electrolyte material (see FIG. 2). It became possible to pull out. Here, it is presumed that the battery performance of the test battery of Test Example 1, which is presumed to have a low molecular weight and excellent dispersibility of the electrode catalyst powder, is derived from the small IEC. That is, as described with reference to FIG. 2, when the IEC is small (particularly, it seems that there is a boundary line of about 0.5), the dispersibility of the electrode catalyst powder becomes insufficient (several times as much as Test Example 5). It is thought that this is due to the fact that a particle size of a certain degree is predicted from FIG. Accordingly, it has been found that the molecular weight of the first electrolyte material is less than 230,000, more desirably about 200,000 or less from the viewpoint of performance.

  Next, Comparative Examples 5 and 8 in which only IEC values are different will be compared. It was found that Test Example 8 having a larger IEC can exhibit higher battery performance. Therefore, it has been found that IEC is more than 0.33, more preferably about 0.5 or more.

  From the results of Test Examples 3 to 7, the S / C ratio {(mass of first electrolyte material) / (mass of electrode catalyst powder)} is more than 0.01, less than 0.5, and more preferably 0.05. As mentioned above, it turned out that it is desirable to set it as 0.4 or less. It was found that by adopting this lower limit, the electrode catalyst powder can be sufficiently dispersed, and by adopting this upper limit, sufficient proton conductivity can be obtained. In particular, a maximum value of battery performance was observed near 0.1. Moreover, it is high by adopting the 1st electrolyte material which shows S / C ratio in this range even if the value of IEC changes from the result of Test Examples 8-10 whose S / C ratio is in the above-mentioned range. It was found that the battery performance can be demonstrated.

  For the test batteries of Test Examples 3 and 4, the first electrolyte material and the second electrolyte material are preferable combinations and can be expected to have high durability, but sufficient battery performance cannot be obtained for the following reasons. Presumed to have been. That is, in the test battery of Test Example 4, although the electrode catalyst powder was sufficiently dispersed, the relative amount (S / C ratio) of the first electrolyte material was large, so that the first electrolyte material was proton (or electron). ) It is presumed that it was difficult to generate electricity at a large current density because the movement was hindered. In addition, the test battery of Test Example 3 has a relatively small amount of the first electrolyte material, and the proton conductivity by the first electrolyte material is high, but the electrode catalyst powder could not be sufficiently dispersed. Presumed to have been difficult.

(About the second electrolyte material)
Since the test battery of each test example shown in Table 4 was evaluated by unifying the first electrolyte material, the result showed that the preferred properties as the second electrolyte material were obtained.

  First, when the group of Test Examples 16 to 18 and the group of Test Examples 19 to 21 that are adjusted to the same conditions other than the molecular weight of the first electrolyte material are compared between the same IEC, Test Example 19 having a large molecular weight. It was found that the group of ~ 21 exhibited higher battery performance. Accordingly, it is desirable that the second electrolyte material has a high molecular weight. Specifically, since both polymers 3 and 4 can exhibit sufficient performance, a molecular weight of 100,000 or more is desirable.

  As the IEC value, it was found that the IEC in the second electrolyte material is desirably high because the battery performance improves as the IEC increases in the groups of Test Examples 16 to 18 and Test Examples 19 to 21. From the comparison between the test examples 16 to 18 and the test example 11, it was found that the value of IEC is desirably more than 0.55, more desirably 1.4 or more. S / C ratio {(mass of second electrolyte material) / (mass of electrode catalyst powder)} in the second electrolyte material is more than 0.05 and less than 1.6 from the results of the test batteries of Test Examples 12 to 15. It was found that 0.1 or more and 1.5 or less (1.4 or less) is more desirable.

  In addition, about the test battery of Test Examples 11-13, about the 1st electrolyte material and the 2nd electrolyte material, it can be expected to have high durability, but sufficient battery performance cannot be obtained for the following reasons. Presumed to have been. That is, it can be presumed that the test battery of Test Example 11 was difficult to achieve high battery performance because the proton conductivity of the second electrolyte material was insufficient (IEC 0.55 meq / g). In addition, it is presumed that it was difficult to obtain sufficient proton conductivity in the test batteries of Test Examples 12 and 13 because the added amount of the second electrolyte material was out of the appropriate range.

(Durability test)
A durability test was conducted by employing test batteries having combinations shown in Table 5 as the first electrolyte material and the second electrolyte material. The same conditions as described above were adopted for the structure and operating conditions of each test battery. Table 5 also shows the battery performance in the initial state. In addition, FIG. 3 shows changes with time in battery voltage at a current density of 0.2 A / cm ² .

  As a combination of the first electrolyte material and the second electrolyte material, the test battery adopting the conventional configuration in which both adopt the same electrolyte material has high initial performance, but has a high rate of deterioration. As in Test Examples 6 and 17, it was found that the use of an electrolyte material having a molecular weight and IEC smaller than that of the second electrolyte material as the first electrolyte material is excellent in durability. From comparison of the results of Test Examples 6 and 17, it was found that the higher the IEC of the first electrolyte material, the higher the initial battery performance, but the lower the IEC, the better the durability.

It is the graph shown about the IEC dependence of the oxidation resistance of electrolyte material. It is the graph which showed the molecular weight and IEC dependence of the electrocatalyst powder dispersibility of electrolyte material. It is the graph which showed the durability of the fuel cell by the difference in electrolyte material.

Claims (8)

An electrode catalyst powder;
An electrolyte material having a hydrocarbon electrolyte material comprising a vinyl monomer in which the electrode catalyst powder is dispersed, and a fuel cell electrode,
The electrolyte material has an ion exchange capacity of 0.5 meq / g or more and 4.0 meq / g or less, and the vicinity of the electrode catalyst powder is more ion exchange capacity and / or molecular weight than the part other than the vicinity of the electrode catalyst powder. Is a relatively low electrode for a fuel cell.   2. The fuel cell electrode according to claim 1, wherein the electrolyte material includes a first electrolyte material disposed in the vicinity of the electrode catalyst powder and a second electrolyte material having a larger ion exchange capacity than the first electrolyte material. The first electrolyte material is 0.5 meq / g or more and 1.6 meq / g or less, the molecular weight is 10,000 or more and 200,000 or less,
The electrode for a fuel cell according to claim 2, wherein (the first electrolyte material) / (the electrode catalyst powder) is 0.05 or more and 0.40 or less on a mass basis. The second electrolyte material is 1.4 meq / g or more and 4.0 meq / g or less,
The second electrolyte material dispersed in the second step is a colloidal solution of 10 nm or more and 100 nm or less,
The electrode for a fuel cell according to claim 3, wherein (second electrolyte material) / (the electrode catalyst powder) is 0.10 or more and 1.50 or less on a mass basis.   The fuel cell electrode according to any one of claims 1 to 4, comprising a heteropolyacid dispersed in the electrolyte material.   The electrolyte material according to claim 5, wherein the heteropolyacid is silicotungstic acid. The electrolyte material has a first electrolyte material and a second electrolyte material having a larger ion exchange capacity than the first electrolyte material,
A first dispersion step of dispersing the electrode catalyst powder and the first electrolyte material in a medium;
The fuel cell electrode according to any one of claims 1 to 6, which is manufactured by a manufacturing method including a second dispersion step of dispersing the second electrolyte material in the medium after the first dispersion step. A method for producing an electrode for a fuel cell according to any one of claims 1 to 6,
The electrolyte material has a first electrolyte material and a second electrolyte material having a larger ion exchange capacity than the first electrolyte material,
A first dispersion step of dispersing the electrode catalyst powder and the first electrolyte material in a medium;
And a second dispersion step of dispersing the second electrolyte material in the medium after the first dispersion step.

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