JP2006269357A - Electrolyte material, electrolyte solution, catalyst paste and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte material capable of exerting an antioxidant function over a long time and excelling in durability. <P>SOLUTION: This electrolyte material contains: a polymer electrolyte having ion exchange capacity of 0.5-6.0 meq/g and having, as a basic skeleton, a polymer formed by polymerizing a vinyl monomer; and a hindered amine-based light stabilization agent of which the content is 1-50 mass% based on the total mass. An oxidation inhibitor prevents deterioration of a polymer material by reacting with a produced radical. A sulfur-based or phenol-based oxidation inhibitor itself disclosed by a conventional technique is consumed by reacting with a radical causing oxidation. Accordingly, when the oxidation inhibitor is completely consumed by exerting a certain degree of antioxidant function, the antioxidant function can not be exerted any further. On the other hand, the hindered amine-based light stabilization agent can regenerate itself after reacting with the radical to extinguish the radical. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell having excellent durability, and an electrolyte material, an electrolyte solution, and a catalyst paste that contribute to the realization of such a fuel cell.

  Many electrolyte materials used in fuel cells that use perfluoro-based electrolyte materials typified by Nafion (trademark) have been reported, but perfluoro-based electrolyte materials have performance when applied to fuel cells. Although it is expensive, it is a material synthesized through a complicated process and a high fluorine content, the cost is very high, which is an obstacle to the spread of fuel cells (Patent Document 1).

  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 also being considered to include an electrolyte material that is not included in the "hydrocarbon electrolyte material").

  Hydrocarbon electrolyte materials can generally be reduced in cost, but there has been a tendency that sufficient performance cannot be exhibited as compared with perfluoro electrolyte materials. One reason for this is that the hydrocarbon-based electrolyte material has a lower carbon-hydrogen bond energy than the carbon-fluorine bond energy, so that the oxidation resistance is not as good as that of the perfluoro-electrolyte material. It is considered that the properties cannot be fully exhibited.

  Further, it is needless to say that even perfluoro-based electrolyte materials are not deteriorated by oxidation at all, and further improvement in oxidation resistance is required.

As a conventional technique developed for the purpose of improving the oxidation resistance of an electrolyte material, a sulfur-based antioxidant (Patent Document 2) and a phenol-based antioxidant (Patent Document 3) are mixed with the electrolyte material. A method is disclosed.
JP-A-3-208260 JP 2004-47936 A JP 2001-118591 A

  However, as a result of the study by the present inventors, even the techniques described in Patent Documents 2 and 3 sometimes have insufficient oxidation resistance.

  This invention is made | formed in view of such a situation, and makes it the subject which should be solved to provide the electrolyte material excellent in durability. Another object to be solved is to provide an electrolyte solution, a catalyst paste, and a fuel cell using an electrolyte material having excellent durability.

(1) As a result of intensive studies aimed at solving the above problems, the present inventors have come up with the following invention. That is, the electrolyte material of the present invention has a polymer electrolyte having an ion exchange capacity of 0.5 meq / g or more and 6.0 meq / g or less and a polymer formed by polymerizing a vinyl monomer as a basic skeleton. ,
A hindered amine light stabilizer having a content of 1% by mass or more and 50% by mass or less based on the total mass;
It is characterized by having.

  Degradation due to oxidation is caused by radicals generated by oxygen, light, heat, etc. attacking the polymer material constituting the electrolyte material. The antioxidant prevents the radicals from attacking and deteriorating the polymer material by reacting with the generated radicals.

  The sulfur-based antioxidants and phenol-based antioxidants disclosed in the prior art are consumed by themselves when they react with radicals that cause oxidation. Therefore, when the antioxidant function is exhibited to some extent, the content of the antioxidant is lowered, and the antioxidant function cannot be fully exhibited.

  On the other hand, the content of the hindered amine light stabilizer does not decrease so much even if it reacts with radicals. This is because the hindered amine light stabilizer reacts with the radical to extinguish the radical and then can regenerate itself. Therefore, the antioxidant function can be exhibited over a long period of time.

  It is presumed that the oxidation-reduction reaction always proceeds in the fuel cell, and a considerable amount of radicals are generated. When used in general applications where the absolute amount of radical generation is small, it is likely that there will be no significant difference in the use of any of sulfur, phenol, and hindered amines as the type of antioxidant. . However, high durability can be realized by employing a hindered amine light stabilizer that can maintain the antioxidant function for a long period in the fuel cell.

  (2) By employing such an electrolyte material, an electrolyte solution that can exhibit high durability can be provided. Moreover, the catalyst paste which can implement | achieve a highly durable catalyst can be provided by disperse | distributing an electrode catalyst powder to such electrolyte material. In the vicinity of the electrode catalyst powder, as the cell reaction proceeds, a radical is expected to be generated, so if a highly durable catalyst can be provided, the durability of the fuel cell can be greatly improved.

  In particular, by including a hindered amine light stabilizer on the cathode electrode side, higher durability can be realized. In the fuel cell, since the influence of durability reduction due to radicals is remarkable on the cathode electrode side, a highly durable fuel cell can be realized by including a hindered amine light stabilizer on the cathode electrode side.

  The electrolyte material of the present invention can maintain oxidation resistance for a long period of time by adding a hindered amine light stabilizer that is not consumed by itself when radicals disappear. Furthermore, it has become possible to provide a highly durable electrolyte solution, catalyst paste, and fuel cell by adopting such an electrolyte material having excellent oxidation resistance.

  The electrolyte material, electrolyte solution, catalyst paste, and fuel cell of the present invention will be described in detail below.

  (1) The electrolyte material of the present embodiment is a mixture having a polymer electrolyte and a hindered amine light stabilizer (hereinafter referred to as “HALS”). The mixing ratio of the polymer electrolyte and HALS is such that HALS is in the range of 1% by mass to 50% by mass based on the entire electrolyte material. By setting the HALS content within this range, sufficient oxidation resistance can be exhibited while maintaining sufficient proton conductivity. Furthermore, it is preferable that HALS is in the range of 5% by mass or more and 30% by mass or less based on the entire electrolyte material.

  The polymer electrolyte has an ion exchange capacity of 0.5 meq / g or more and 6.0 meq / g or less. By controlling within this range, sufficient proton conductivity can be obtained. Furthermore, it is desirable to set it to 0.6 meq / g or more and 3 meq / g or less.

  The polymer electrolyte has a basic skeleton formed by polymerizing a vinyl monomer, and an ion conductive group is introduced into the basic skeleton. This basic skeleton may be in a form bonded to another polymer material. For example, a plurality of polymer electrolytes having this basic skeleton can be assembled and bonded to other polymer materials as graft chains. Moreover, it is possible to crosslink with an appropriate crosslinking agent. The proton conductive group is not particularly limited. For example, general things, such as a sulfo group, a phosphoric acid group, and a carboxy group, are mentioned.

  As the vinyl polymer, a compound having high oxidation resistance is desirable. For example, styrene, ethylene, propylene, tetrafluoroethylene and the like can be employed as a single polymer or copolymer.

  The molecular weight of the polymer electrolyte is not particularly limited. The higher the molecular weight, the better the stability. However, if the molecular weight is too high, the handleability will be low. The molecular weight is desirably in the range of about 100,000 or more and 300,000 or less.

  HALS is not particularly limited. For example, 2,2,6,6-tetramethylpiperidyl; ester of 2,2,6,6-tetramethylpiperidyl introduced with OH group and (unsaturated) fatty acid (for example, CAS NO167078-06-0); Poly [(6-morpholino-S-triazine-2,4-diyl) [2,2,6,6-tetramethyl-4-piperidyl] imino] -hexamethylene [(2,2 , 6,6-tetramethyl-4-piperidyl) imino] (CAS NO82451-48-7); 1,6-hexanediamine, N, N′-bis (1,2,2,6,6-pentamethyl-4 -Piperidyl)-, polymers morpholine-2,4,6-trichloro-1,3,5-triazine (CAS NO 193098-40-7).

  In addition, these HALS exhibit a synergistic effect when used together with a phenol-based stabilizer (for example, fatty acid ester of 3,5-di-t-butyl-4-hydroxybenzoic acid (CAS No67845-93-6 etc.)). There is something to do.

  (2) By employing such an electrolyte material, an electrolyte solution that can exhibit high durability can be provided. Moreover, the catalyst paste which can implement | achieve a highly durable catalyst can be provided by disperse | distributing an electrode catalyst powder to such electrolyte material. In the vicinity of the electrode catalyst powder, as the cell reaction proceeds, a radical is expected to be generated, so if a highly durable catalyst can be provided, the durability of the fuel cell can be greatly improved.

  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 or 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.

  The fuel cell of the present invention employs an electrode containing HALS in one of the anode electrode and cathode electrode containing HALS. It is also possible to employ an electrode containing HALS in both electrodes. In particular, it is preferably employed for the cathode electrode. Other configurations of the fuel cell are not particularly limited, and a general configuration can be adopted. Of course, HALS can be contained in other electrolyte materials.

(Polymer electrolyte synthesis: Preparation of ion-conducting hydrocarbon electrolyte solution)
Under a nitrogen atmosphere, 200 mL of styrene in which 0.2 g of benzoyl peroxide was dissolved in 200 mL of xylene was added dropwise over 3 hours. After completion of dropping, the mixture was kept at 90 ° C. for 1 hour. Thereafter, the reaction solution cooled to room temperature was dropped into a large amount of methanol to precipitate a produced vinyl monomer polymer. The precipitate was collected by filtration and dried at 80 ° C. for 30 minutes to obtain a dry powdery styrene polymer. The molecular weight measured by GPC was Mw 270000.

  Next, 100 g of the above styrene polymer was dissolved in 500 mL of 1,2-dichloroethane in a 1000 mL flask. While heating at 60 ° C., 60 mL of chlorosulfonic acid was added dropwise, and the sulfo group was introduced into the styrene polymer by maintaining at 60 ° C. for 1 hour. The sulfonated styrene polymer obtained here was washed with 1,2-dichloroethane, further washed with ion-exchanged water, and the sulfo group introduced by immersing in ion-exchanged water for 1 hour at room temperature was hydrogenated. Thereafter, a powdered sulfonated styrene polymer was obtained by vacuum drying. The ion exchange capacity was 1.8 meq / g.

  10 g of the obtained sulfonated styrene polymer was dissolved in 190 g of ion exchange water / ethanol (1/1 volume ratio) to prepare an ion conductive hydrocarbon electrolyte solution (5% by mass).

(Preparation of HALS solution)
HALS solution A (sanduvor 3058) and HALS solution B (sanduvor 3051) were prepared by dissolving 10 g of commercially available HALS (sanduvor 3058, sanduvor 3051, manufactured by Client JAPAN) in 90 g of ethanol. By mixing the prepared HALS solution with the above-described polymer electrolyte, a material corresponding to the electrolyte material of the present invention is obtained, and by mixing the HALS solution with the above-mentioned ion-conducting hydrocarbon-based electrolyte solution, A material corresponding to the electrolyte solution is obtained.

(Evaluation of oxidation resistance)
8 g of the polymer electrolyte solution and 0.04 g of HALS solution A were mixed and stirred to obtain an electrolyte solution (Example 1). Also, 8 g of the polymer electrolyte solution and 0.04 g of HALS solution B were mixed and stirred to obtain an electrolyte solution (Example 2). Further, the polymer electrolyte solution as it was was evaluated without adding the HALS solution (Comparative Example).

  Each electrolyte solution was evaluated for oxidation resistance. Evaluation of oxidation resistance was performed by adding 56 mL of pure water into a 100 mL screw tube and maintaining the temperature at 60 ° C., and then adding each electrolyte solution in an amount corresponding to 0.4 g of the electrolyte material.

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 where 0.4 g of the electrolyte material 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, and 4 hours after immersion, and the residue after filtration was separated to measure mass, molecular weight (Mw), and EW. The mass of the dissolved material was also measured. When the electrolyte material is decomposed by oxidation, the residue is expected to decrease. The results are shown in Table 1. In particular, the dependence of the amount of non-dissolved substance (mass of the residue) on the immersion time is shown in FIG.

  As is clear from Table 1 and FIG. 1, the amount of the electrolyte material of Example 1 to which sanduvor 3058 was added as HALS most remained. Next, the amount of the electrolyte material remaining was large in the order of the electrolyte material of Example 2 to which sanduvor 3051 was added as HALS and the electrolyte material of the comparative example to which HALS was not added (corresponding to the polymer electrolyte in the present invention). Therefore, it became clear that high oxidation resistance can be realized by adding HALS. In particular, it was found that high oxidation resistance can be realized by using sanduvor 3058.

It is the graph which showed the result of having evaluated the oxidation resistance about the electrolyte material evaluated in the Example.

Claims (4)

A polymer electrolyte having an ion exchange capacity of 0.5 meq / g or more and 6.0 meq / g or less and a polymer formed by polymerizing a vinyl monomer as a basic skeleton;
A hindered amine light stabilizer having a content of 1% by mass or more and 50% by mass or less based on the total mass;
An electrolyte material characterized by comprising:   An electrolyte solution comprising the electrolyte material according to claim 1. An electrode catalyst powder;
A catalyst paste comprising the electrolyte material according to claim 1 in which the electrode catalyst powder is dispersed. An electrolyte membrane;
An anode electrode provided on one side of the electrolyte membrane;
A cathode electrode provided on the other side of the electrolyte membrane;
A fuel cell comprising:
At least one of the cathode electrode and the cathode electrode contains a hindered amine light stabilizer.

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