DE10347457B4 - Highly resistant polymer electrolyte composite - Google Patents

Abstract

worin x eine ganze Zahl von 0 bis 2, y eine ganze Zahl von 2 oder 3 ist und n/m Bereich von 1 bis 10 liegt,

worin n/m im Bereich von 0,1 bis 2 liegt, und einer Alkylphosphonsäure-haltigen Verbindung, wobei die Alkylphosphonsäure-haltige Verbindung wenigstens eine von Xylidylphosphonsäure und Benzylphosphonsäure umfasst.Highly resistant polymer electrolyte composite consisting of a mixture of a fluoropolymer electrolyte according to formula (1) or (2):

wherein x is an integer from 0 to 2, y is an integer of 2 or 3 and n / m is from 1 to 10,

wherein n / m is in the range of 0.1 to 2, and an alkylphosphonic acid-containing compound, wherein the alkylphosphonic acid-containing compound comprises at least one of xylidylphosphonic acid and benzylphosphonic acid.

Description

Field of the invention

The The invention relates to a highly resistant polymer electrolyte composite. More particularly, the invention relates to a highly resistant polymer electrolyte composite, the excellent resistance against oxidation and the like, and those for an electrolyte membrane, an electrode, etc. which are suitable for fuel cells, for the electrolysis of water, halogen halide electrolysis, salt electrolysis, for oxygen concentrators, Moisture sensors, gas sensors and the like are suitable.

State of the art

One Polymer electrolyte is a solid polymer material with an electrolyte-functional Group, such as a sulfonic acid group or the like, in the polymer chain. The polymer electrolyte binds is firmly attached to a particular ion or is selectively permeable to a positive one Ion or a negative ion. Therefore, the polymer electrolyte becomes too Particles, fibers or membranes shaped and used for various purposes, including of electrodialysis, diffusion dialysis, for battery membranes and the like.

A Fuel cell has z. B. a pair of electrodes, each on the surface a proton-conducting polymer electrolyte membrane are provided. Hydrogen gas by reforming a hydrocarbon with low molecular weight, such as methane, methanol or the like, is obtained as fuel gas to one of the electrodes (the fuel electrode) delivered while Oxygen gas or air as oxidant to the other electrode (the air electrode) is delivered. In this way, an electromotive Obtained power from the fuel cell. Water electrolysis is a Process in which by the electrolyzation of water by means of a polymer electrolyte membrane generates hydrogen and oxygen become.

in the Case of fuel cells or water electrolysis arises in the catalytic layer, which is at the boundary between the polymer electrolyte membrane and the electrodes is formed, peroxide. As it diffuses, it becomes converted the resulting peroxide into a peroxide radical and causes a reaction that the quality the polymer electrolyte membrane degrades. In the case of fuel cells or water electrolysis, it is therefore problematic to use an electrolyte membrane to use hydrocarbon type, since their oxidation resistance not enough. For this reason, in the field of fuel cells or water electrolysis generally a perfluorosulfonic acid membrane used, which has good proton conductivity and good oxidation resistance shows.

The Salt electrolysis is a process by which electrolysis a sodium chloride solution by means of a polymer electrolyte membrane sodium hydroxide, chlorine and Be generated hydrogen. Since the polymer electrolyte membrane of Action of chlorine and a solution, which is very hot and exposed to highly concentrated sodium hydroxide impossible, in this case, a hydrocarbon-type electrolyte membrane to use because of their durability across from Chlorine or hot, highly concentrated sodium hydroxide solutions is insufficient. Out This reason is for salt electrolysis generally a perfluorosulfonic acid membrane, the opposite Chlorine and hot, highly concentrated sodium hydroxide solutions, and in the surface partially Carboxylic acid groups introduced were to back diffusion to prevent the generated ions as a polymer electrolyte membrane used.

Fluorine electrolyte membranes, for example, perfluorosulfonic acid membranes, have a C-F bond and are therefore chemically very stable. Thus, fluoroelectrolyte membranes become not only as the above Polymer electrolyte membrane for Fuel cells, for used the electrolysis of water or salt electrolysis, but also as a polymer electrolyte membrane for the electrolysis of halo acids. Due to their proton conductivity Fluorolith membranes are widely used in the field of Humidity sensors, gas sensors, oxygen concentrators, etc. used.

In particular, fluorine electrolyte membranes, such as the perfluorosulfonic acid membrane known by the trade name Nafion ^® (manufacturer Du Pont Co., Ltd.), chemically very stable and thus are used as electrolyte membranes in question, which can be used under difficult conditions.

fluorine electrolytes However, they have the disadvantage that they difficult to manufacture and extremely expensive are.

In contrast, the electrolyte membranes of the hydrocarbon type have the advantage that they are opposed to fluorine electrolyte membranes such as Nafion ^® easy to manufacture and inexpensive. Nevertheless For example, in hydrocarbon type electrolyte membranes, there is a problem of low oxidation resistance as described above. This low oxidation resistance results from the fact that hydrocarbons generally have low resistance to radicals and that electrolytes with hydrocarbon skeletons can easily cause a deleterious reaction triggered by radicals (an oxidation reaction initiated by peroxide radicals).

With the aim of providing a long life polymer electrolyte whose oxidation resistance is at least equal to or excellent in oxidation resistance in practice, and which can be produced inexpensively, patents pertaining to a long life polymer electrolyte composed of a polymer electrolyte have been filed Polymer compound having a hydrocarbon moiety into which is introduced a functional phosphorus-containing group ( Japanese Patent Laid-Open Publication No. 2000-11755 and a polymer electrolyte composite obtained by mixing a polymer compound having an electrolyte-functional group and a hydrocarbon moiety with a phosphorus-containing compound ( Japanese Patent Laid-Open Publication No. 2000-11756 ).

However, when a hydrocarbon-type electrolyte is used in a fuel cell, the use of the high-resistance polymer electrolyte and the high-resistance polymer electrolyte composite material described in the aforementioned patent applications, namely in US Pat Japanese Patent Laid-Open Publication No. 2000-11755 and the Japanese Patent Laid-Open Publication No. 2000-11756 As electrode material (for anodes and cathodes), it is largely to prevent fuel gas (hydrogen or the like) or oxidizing gas (oxygen, air or the like) from coming into contact with the catalyst (platinum or the like) since the highly resistant polymer electrolyte and the highly resistant polymer electrolyte composite gas can largely deter. As a result, the performance of the fuel cell greatly deteriorates. As described so far, the idea of combining a hydrocarbon-type electrolyte with a phosphorus-containing functional group or a phosphorus-containing compound raises problems. As state of the art are also called the JP 1135410 A . DE 102 20818 A1 . WO 01/70858 A2 and WO 01/71839 A2 ,

task

object the invention is the life of a polymer electrolyte, the for a fuel cell or the like is used drastically to increase.

As a result from in-depth research, the inventors have developed a method with the oxidation resistance a fluoropolymer electrolyte which is chemically very stable per se is dramatically improved, and this is the object of this invention based.

The The invention relates to a highly resistant polymer electrolyte composite, the one polymer electrolyte and an alkylphosphonic acid-containing Includes connection according to claim 1. Preferred embodiments The invention can be found in the dependent claims 2 to 5.

fluoropolymers are chemically stable per se, because the bonds between carbon and fluorine are strong. Actually, it was considered unrealistic, activities to stabilize fluoropolymers. However, have the inventors gained the knowledge that the following phenomenon also in the case of fluoropolymers occurs. That is, when a hydrogen peroxide radical or the like is generated in a fluoropolymer, it decomposes Fluoropolymer gradually step for Step in ether units containing a fluoropolymer on a side chain contain. Once the decay process begins, a large amount of heat is generated because the binding energy between the atoms is at a high level. As a result, the thermal decomposition progresses rapidly.

In This invention is the alkylphosphonic acid-containing compound with the fluoropolymer electrolyte, whereby the alkylphosphonic acid-containing Compound not only catches the hydrogen peroxide radical that is produced in the fluoropolymer electrolyte, but also the decomposition radical, that while the decay of the fluoropolymer electrolyte is generated. So will the oxidation resistance of the fluoropolymer electrolyte significantly improved.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numbers are used to designate similar elements, and wherein:

1 Fig. 10 is a graph showing the behavior during SO ₂ generation in a fuel cell electrode;

2 Fig. 10 is a graph showing behavior during fluorocarbon generation in the fuel cell electrode;

3 Fig. 10 is a graph showing the initial IV characteristics of the fuel cell; and

4 Fig. 10 is a graph showing the change in the amount of gas leaked observed during the acceleration-resistance test of the fuel cell.

DETAILED DESCRIPTION

(Es sei darauf hingewiesen, daß in der obigen Formel ”x” eine ganze Zahl von 0 bis 2 darstellt, ”y” eine ganze Zahl von 2 oder 3 aufweist, und daß ”n/m” im Bereich von 1 bis 10 liegt.)

(Es sei darauf hingewiesen, daß in der obigen Formel ”n/m” im Bereich von 0,1 bis 2 liegt.)The fluoropolymer electrolyte of the invention is a polymer having a structure expressed by the formulas (1) or (2):

(It should be noted that in the above formula, "x" represents an integer of 0 to 2, "y" has an integer of 2 or 3, and "n / m" ranges from 1 to 10. )

(It should be noted that in the above formula, "n / m" ranges from 0.1 to 2.)

The polymers represented by the formula (1) are shown, "Nafion ^®", manufactured by Du Pont Co., Ltd. "Asiplex-S ^®", manufactured by Asahi Kasei Corporation, and the like are known. The Japanese Patent Laid-Open Publication No. 8-512358 discloses that a polymer represented by the formula (2) is used for a fuel cell. Of these polymers, a perfluoropolymer represented by the formula (1) is well suited to this invention because of its excellent stability when used in a fuel cell.

When Antioxidations, the fluoropolymer Elektrotyl composite of the Invention is used, serves at least one of xylidylphosphonic and Benzylphosphonic. additionally can as antioxidant a wide variety of known inhibitors for the Polymer compounding can be used. For example, a metal deactivator, a phenol compound, an amine compound, a sulfur compound etc. are called. As a concrete example of the metal deactivator can Be called diphenyloxamide.

As the phenol compound, a hindered phenol compound as well as hydroquinone p-cresol, BHT and the like. As concrete examples of the hindered phenol compound, 2,6-di-tert-butyl-4-methylphenol, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylene-bis (4 ethyl-6-tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-butylidenebis (3-methyl-6-tert-butylphenol), triethylene glycol bis- [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2 , 2-Thiodiethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionate, 3,5-di-tert-butyl Tert-butyl-4-hydroxybenzylphosphonate diethyl ester, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzylbenzene), isooctyl-3- (3,5-di-tert-butyl-4-hydroxybenzylbenzene); tert-butyl-4-hydroxyphenyl) propionate and the like.

When concrete examples of the amine compound can Phenyl-2-naphthylamine, phenothiazine, diphenylphenylenediamine, Naphthylamine, diphenylamine, which has one octyl group (4,4'-dioctyl-adiphenylamine) contains 4,4'-dicumyldiphenylamine, 6-Ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, 2,2,4-trimethyl-1,2-dihydroquinoline polymers and the like.

As specific examples of the sulfur compound, 2-mercaptobenzimidazole, 2,4-bis [(octylthio) methyl] -o-cresol, 2,4-bis (n-octylthio) -6- (4-hydroxy-3,5-di-tert -butylanilino) -1,3,5-triazine adk stab ^® AO-412S (manufacturer Asahi Denka Co., Ltd.) and the like are mentioned.

A concrete example of the phosphorus compound can be selected from a group consisting of triethyl phosphite, triethyl phosphate, triphenyl phosphine, triphenyl phosphine oxide, triphenyl phosphine sulfide, distearyl pentaerythrityl diphosphite, organic phosphite, diphenylisodecyl phosphite, diphenyl isooctyl phosphite, diisodecylphenyl phosphite, triphenyl phosphite and trisnonylphenyl phosphite. In addition, a concrete example of the phosphorus compound is preferably selected from the group consisting of conjugated organic phosphite, polyphosphite and tetrapentaerythritol. In addition, rod-adk ^® PER-4C (Manufacturer Asahi Denka Co., Ltd.), ADK STAB ^® 260 (manufactured by Asahi Denka Co., Ltd.), ADK STAB 522A ^® (manufacturer Asahi Denka Co., Ltd.) and the like to be named.

It can one or more of the antioxidants are used. One Polymer electrolyte composite normally contains 0.005 to 10% by weight of antioxidant and preferably 0.01 to 5% by weight Antioxidant.

The Method using a fluoropolymer electrolyte and an oxidation stabilizer are mixed with each other, subject to no restriction. The is called, You can act in different ways. For example, they can with the help of solutions doped or mixed with each other. When both the fluorine polymer electrolyte as well as the oxidation stabilizer are heat-meltable, they can be melted together by melting.

A Structure in which an oxidation stabilizer is homogeneous throughout Polymer electrolyte is distributed, by homogeneously mixing a Oxidation stabilizer can be obtained with a fluoropolymer electrolyte.

alternative it is also possible that the biggest parts of the polymer electrolyte exclusively from a fluoropolymer electrolyte exists, and that only the part of the polymer electrolyte which needs oxidation protection the fluoropolymer electrolyte / oxidation stabilizer mixture.

In an environment in which radicals are generated statistically distributed, for example, when heating a Polymer electrolyte membrane while in a peroxide solution it is beneficial to take over a structure in which an oxidation stabilizer is homogeneous with the fluoropolymer electrolyte mixed and thereby homogeneous throughout the polymer electrolyte membrane is dispersed.

on the other hand it is in an environment where a peroxide is in a catalyst layer at the membrane surface and in which the generated peroxide diffuses is converted to a peroxide radical, and this peroxide radical causes a deterioration reaction, as in the case of an electrolyte membrane for the Water electrolysis or for Fuel cells, not necessary that an oxidation stabilizer is distributed homogeneously in the membrane. In that case, it will be enough if only the surface section the membrane where the deterioration reaction caused by oxidation most violent, from a mixture of oxidation stabilizer and fluoropolymer electrolyte is prepared by doping the latter with the former.

Alternatively, a method in which a membrane molding, which consists of a mixture of Fluoropolymer electrolyte and oxidation stabilizer is introduced into the gap between an electrode and an electrolyte consisting only of fluoropolymer electrolyte, considered effective for maintaining the quality of an electrolyte membrane.

The mixing ratio between the phosphorus-containing compound and the fluoropolymer electrolyte membrane can according to the characteristics which are expected from the polymer electrolyte, d. H. the electrical conductivity, the oxidation resistance and the same.

The is called, the oxidation resistance is improved when the amount of the mixed oxidation stabilizer increases. Because many oxidation stabilizers, however, weakly acidic groups are, the electrical conductivity of the material decreases overall, when the mixed amount increases. Therefore, it is for uses, where only oxidation resistance Value is laid and for which does not have high electrical conductivity is necessary, appropriate, if the mixing ratio of the Oxidation stabilizer for polymer compound, which is a fluoropolymer electrolyte has increased.

If On the other hand, a high electrical conductivity as well as a high Oxidation resistance required are, as in the case of fuel cells or in the electrolysis of water, it is appropriate if the oxidation stabilizer and the fluoropolymer electrolyte, in the one sulfonic acid group introduced was mixed together in a predetermined ratio become. If high chlorine resistance, temperature resistance and durability against highly concentrated aqueous sodium hydroxide is required to prevent ion backdiffusion, As in the case of salt electrolysis, it is appropriate that the oxidation stabilizer and the fluoropolymer electrolyte into which a sulfonic acid group introduced were mixed together in a predetermined ratio become.

If the amount of einzumischenden oxidation stabilizer, however, under 0.1 mol% of all electrolyte-functional groups decreases, the improvement of the oxidation resistance not anymore. Therefore, it is necessary that the amount of the oxidation stabilizer, which is mixed in, at least 0.1 mol% of the total electrolyte-functional Makes up groups. Especially in the case of polymer electrolytes, which are used under difficult conditions, for example for fuel cells, for the Water electrolysis, salt electrolysis and the like, is the Amount of phosphorus-containing compound preferably in the range of 5 to 100 mol%.

As so far in detail described, the highly resistant Polymer electrolyte composite by mixing a fluoropolymer electrolyte with an oxidation stabilizer having a phosphonic acid group which the task has been to suppress an oxidative reaction obtained.

embodiment (not according to the invention)

(1) Production of a fuel cell electrode the polyvinylphosphonic acid is added

[Comparative Example]

By addition of 3.3 ml of an electrolytic solution (a commercial solution containing 5% Nafion ^® contains) and a predetermined amount of water to 1,100 mg carbon carrying 60% of platinum, and stirring was produced a homogenous dispersion solution. The dispersion solution was applied to an electrode sheet by means of a doctor blade. This sheet was dried under reduced pressure for 8 hours at a temperature of 80 ° C, whereby a fuel cell electrode sheet was obtained.

This is a commonly used fuel cell electrode (obtained by drying and solidifying a Nafion ^® dispersion solution of carbon, supporting the platinum). It should be noted that Pt: C: Nafion ^® = 60:40:28.

[Reference Example]

at the preparation of the dispersion solutions of the above comparative example, 160 mg of polyvinylphosphonic acid (manufacturer General Science Co., Ltd.) was added, whereby an electrode sheet with Antioxidant additive was obtained.

This is made by adding polyvinylphosphonic acid (PVPA) to the electrode of the above comparison obtained for example. It should be noted here that Pt: C: Nafion ^®: PVPA = 60: 40: 28: 14th

(2) Analysis of dispersion behavior by TG-MS

The amounts of gas generated from the anti-oxidant additive electrode sheets at particular temperatures were measured by TG-MS to determine the effect of polyvinylphosphonic acid (PVPA) addition on pyrolysis during an ambient temperature ramp at a rate of 10 ° C / min in a He atmosphere. Of the substances generated in this analysis, the behavior in the production of SO ₂ ( 1 ) and of fluorocarbon ( 2 ) Is shown as one produced by the decay of the Nafion ^® component.

SO ₂ , which in a temperature range in 1 is formed by oxidation of the sulfur adsorbed on the carbon by the oxygen adsorbed on the carbon. The SO _{2 produced in this way} has nothing to do with the decomposition of the Nafions ^® . The amount of SO ₂ that is produced by the decay of the Nafion ^®, increases at or above a temperature of 200 ° C. However, the amount of SO ₂ produced in this example is much smaller than the amount of SO ₂ produced in the comparative example.

What 2 In the comparative example, the generation of CF ₃ ⁺ and C ₂ F ₅ ⁺ in a temperature range of 250 ° C and above was observed. This generation of CF ₃ ⁺ and C ₂ F ₅ ⁺ is the result of Nafion ^® decay. On the other hand, no generation of C ₃ F ₅ ^{+ was} observed in the example, but only the production of CF ₃ ⁺

In addition, the CF ₃ ⁺ amount in the example is less than the CF ₃ ⁺ amount in the comparative example.

The analytical result above revealed that the addition of polyvinyl phosphonic acid (PVPA) greatly increased the stability to thermal degradation of the Nafion ^® in the electrode. Although this mechanism of decomposition suppression is not entirely clear, it can be concluded that a decay chain reaction has been halted by stabilizing a carbon residue after the release of a sulfonic acid group.

(3) exam the stability changes over time due to a battery test

[Top Properties]

3 represents the result of an IV test (current / voltage test) carried out under the following conditions: cell: 80 ° C, A-bubbler (anode): H ₂ , 275 cm ³ / min, K-bubbler (cathode ): air, 912 cm ³ / min, and both electrodes 2 Atü.

3 shows that although polyvinylphosphonic acid (PVPA) was added in the example, the gradient of the example and the gradient of the comparative example are substantially the same. In addition, the example and the comparative example are largely similar in their contact resistance between the membrane and the electrode. In addition, the example and the comparative example are similar in their current limit value and the discharge characteristics of the electrode. In general, the fact that the addition of polyvinylphosphonic acid (PVPA) shows that the limiting current remains essentially unchanged despite the increase in weight by a factor of 1.5 and the increase in volume by about a factor of 2 due to the addition of the polyvinylphosphonic acid (PVPA). does not degrade the derivative properties. In addition, shows 3 in that the tension in the example is lower overall than in the comparative example. It is believed that this is a consequence of the catalyst activity. However, the stress can be adjusted by reducing the amount of polyvinylphosphonic acid (PVPA) added.

The mentioned result of the test has revealed that the Addition of polyvinylphosphonic acid (PVPA) no change the fuel cell properties causes, in particular no change of resistance or current limit.

[Gas leak quantity in the acceleration resistance test]

Continuous operation was performed under the following conditions: cell: 80 ° C, A: humidified H ₂ gas, and C: humidified air, and under load conditions involving an open circuit. The result is in 4 shown.

4 shows that although the gas leakage amount of the comparative example is soon increased, the gas leakage amount of the example is still stable even after 250 hours. Although it was actually expected that an antioxidation effect would occur in the electrolyte of the electrode due to the addition of polyvinylphosphonic acid (PVPA), this is shown in FIG 4 shown result that the electrolyte membrane is also protected from deterioration. Although the reason for this phenomenon is not entirely clear, it is believed that peroxide radicals generated in the electrode or decomposition radicals are deactivated by the antioxidant and, as a result, possibly the diffusion of the radicals into the electrolyte membrane is suppressed.

By Combining a fluoropolymer electrolyte with an antioxidant will it be possible to suppress the generation of hydrogen peroxide radicals even if these radicals would be generated at high temperatures. As a result, the Life of the fluoropolymer electrolyte extended. Because the microphase separation between hydrophilic sections of the fluoropolymer and the antioxidant and hydrophobic portions of the fluoropolymer and the antioxidant to an increase the porosity leads, will also preventing the proton exchange material from introducing the catalyst into to coat the electrode. Thus, the performance of the fuel cell can be maintained.

Claims (5)

Highly resistant polymer electrolyte composite consisting of a mixture of a fluoropolymer electrolyte according to formula (1) or (2):

wherein x is an integer from 0 to 2, y is an integer of 2 or 3 and n / m is from 1 to 10,

wherein n / m is in the range of 0.1 to 2, and an alkylphosphonic acid-containing compound, wherein the alkylphosphonic acid-containing compound comprises at least one of xylidylphosphonic acid and benzylphosphonic acid. A polymer electrolyte composite according to claim 1, wherein the polymer electrolyte composite contains 0.005 to 10% by weight of the alkylphosphonic acid-containing ones Contains connection. A polymer electrolyte composite according to claim 2, wherein the polymer electrolyte composite contains 0.01 to 5% by weight of the alkylphosphonic acid Contains connection. Polymer electrolyte composite according to one of claims 1 to 3, wherein the blended amount of the alkylphosphonic acid-containing Compound 5 to 100 mol% of the total amount of the electrolyte-functional Makes up groups in the polymer electrolyte. Polymer electrolyte composite according to one of the preceding Anspürche, additionally at least one compound from the group of metal deactivator, phenolic compound, Amine compound and sulfur compound.