JP2000268834A - Proton conductive fuel cell - Google Patents

Abstract

(57) [Problem] To provide a novel proton-conducting fuel cell which is low in manufacturing cost, high in energy efficiency, easy to assemble, and can maintain its performance for a long period of time. The solid polymer electrolyte has a side chain of -O (C
A perfluorosulfonic acid membrane having a structure of F ₂ ) ₃ SO ₃ H is used. Further, a crosslinked polymer electrolyte having an imidic acid having the following structure is used as the electrode catalyst coating agent. Embedded image

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proton-conducting fuel cell used for electric vehicles and homes for cogeneration.

[0002]

2. Description of the Related Art Conventionally, a perfluorosulfonic acid membrane represented by the general formula (3) has been used as a solid polymer electrolyte that governs the performance of a proton conductive fuel cell.

Embedded image Of the above perfluorosulfonic acid membranes, those with q = 0 are q
It is disclosed in the following literature that a proton-conducting fuel cell using the same can reduce the internal electric resistance and increase the energy efficiency because the ion exchange capacity can be increased as compared with the case of = 1. (a) KEITH PRATER, "THE RENAISSANCE OF THE SOLID POL
YMER FUEL CELL "Jounal of Power Sources, 29 (1990) 239-
250 (b) EUROPIAN PATENT SPECIFICATION 0289869 B1

[0003] Another factor governing the performance of a proton-conducting fuel cell is an electrode catalyst coating material. For this purpose, high ion exchange of a perfluorosulfonic acid polymer represented by the formula (3) is required. The capacity portion is (lower aliphatic alcohol-
And water) is generally used. On the other hand, a crosslinked polymer electrolyte containing an imidic acid group represented by the general formula (4) can further increase the ion exchange capacity and reduce the overvoltage.
7969.

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[0004] However, these prior arts have the following disadvantages. (a) The ion exchange capacity can be increased by the above equation (3) q
The perfluorosulfonic acid membrane of = 0 is produced by copolymerizing tetrafluoroethylene and a perfluorovinyl ether monomer represented by the formula (5), forming a film, and then hydrolyzing it.

Embedded image CF ₂ ＣＦCFO (CF ₂ ) ₂ SO ₂ F (5)

As disclosed in US Pat. No. 4,358,412, the monomer of the above formula (5) is produced by the following reaction using chloropentafluoropropylene oxide, which is expensive.

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In this reaction, if hexafluoropropylene oxide which is inexpensive is used, for example, US Pat.
As described in US Pat. No. 3,560,568, US Pat. No. 4,329,435, no perfluorovinyl ether monomer is obtained, and a cyclic sulfone is formed during the vinylation step as described below.

Embedded image Therefore, a perfluorosulfonic acid membrane having q = 0 in the above formula (3) has to use chloropentafluoropropylene oxide, which is expensive in the production stage, and a proton conductive fuel cell using this membrane must be used. Manufacturing costs also increase.

(B) As described in US Pat. No. 3,560,568, the above-mentioned cyclization reaction occurs not only at the stage of monomer production but also at the time of copolymerization by the following mechanism depending on conditions, and the chain transfer occurs. May cause As a result, the molecular weight of the obtained copolymer is not sufficient, and the mechanical strength of the perfluorosulfonic acid membrane is lowered, so that the cell assembly and performance of the proton conductive fuel cell using the same are maintained for a long time. It becomes difficult. Since such a phenomenon is more likely to occur as the ratio of the perfluorovinyl ether monomer to tetrafluoroethylene is larger, using the monomer of the formula (5),
There is a limit in increasing the ion exchange capacity while maintaining mechanical strength.

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(C) The crosslinked polymer electrolyte represented by the above formula (4) can have a much larger ion exchange capacity than the perfluorosulfonic acid membrane of the formula (3). However, JP
As described in 1-7969,該Pa - so used for the production of FSO ₂ CF ₂ COF is the same material as the fluoroalkyl sulfonic acid membrane, CF structure of electron-withdrawing imidate groups as follows ₂ And only one unit, and the acidity of NH is not very strong. For this reason, there is a disadvantage that the effect of improving the electrical conductivity over the conventional method cannot be increased.

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[0009]

SUMMARY OF THE INVENTION The present invention provides a proton-conducting fuel cell which is low in manufacturing cost, high in energy efficiency, easy to assemble, and can maintain its performance for a long time. The purpose is to:

[0010]

In order to achieve the above object, a proton conductive fuel cell according to the present invention comprises, as a solid polymer electrolyte, a repeating unit of (A) and (B) represented by the formula (1) Is used.

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Further, as the electrode catalyst coating agent for the proton conductive fuel cell of the present invention, a crosslinked polymer electrolyte represented by the general formula (2) is preferable.

Embedded image The proton conductive fuel cell of the present invention has low manufacturing costs, high energy efficiency, easy cell assembly, and long-term performance. Further, an electrode catalyst garment goods CF ₂
Is used, the overvoltage can be reduced and the internal resistance can be reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the proton conducting fuel cell of the present invention, the solid polymer electrolyte comprises (A) represented by the formula (1) and
It is a perfluorosulfonic acid film composed of the repeating unit (B).

Embedded image Here, the ratio (A) / (B) of the number of repeating units is generally 1.
It is in the range of 5 to 10, preferably in the range of 2 to 7, and more preferably in the range of 2.5 to 6. The ion exchange capacity is represented by the following equation.

[Equation 1] Ion exchange capacity (meq / g dry resin) = 1,000 /
(100 (A) / (B) +328)

In the proton conductive fuel cell of the present invention, it is desirable to use a crosslinked polymer electrolyte represented by the general formula (2) as an electrode catalyst coating agent.

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As described in US Pat. No. 4,329,435, the perfluorosulfonic acid membrane used in the present invention is obtained by copolymerizing tetrafluoroethylene with a perfluorovinyl ether monomer represented by the formula (6). Then, after being formed into a film having a thickness of 10 to 300 μm, it is produced by hydrolysis. At the time of copolymerization, a third monomer such as chlorotrifluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether and the like can be added.

Embedded image _{CF 2 = CFO (CF 2)} 3 SO 2 F (6) above Pas - Furorobinirue - ether monomer, because (5) CF2 one unit greater than the monomer represented by the formula, The cyclization reaction does not occur during the copolymerization described above, and a high ion exchange capacity can be realized while maintaining the mechanical strength, and the energy efficiency of the proton conductive fuel cell can be improved. Further, since the mechanical strength of the membrane is large, the cell can be easily assembled and the performance can be maintained for a long period of time.

According to US Pat. No. 4,329,435, the above-mentioned perfluorovinyl ether monomer represented by the formula (6) is produced by the following reaction.

Embedded image In the case of the above perfluorovinyl ether monomer,
Since CF ₂ is one unit more than the monomer represented by the formula (5), even if hexafluoropropylene oxide, which is inexpensive, is used, no cyclization reaction occurs in the vinylation stage. Accordingly, a proton-conducting fuel cell using the perfluorosulfonic acid membrane represented by the formula (1) as a solid polymer electrolyte,
Manufacturing costs can be reduced.

In the present invention, the part of the copolymer represented by the formula (1), which cannot be molded into a film due to an excessively high ion exchange capacity, is dispersed in (lower aliphatic alcohol + water) to form an electrode catalyst. It can be used as a coating agent. However,
The crosslinked polymer electrolyte represented by the formula (2) is preferable because a much higher ion exchange capacity can be realized, the electric conductivity can be increased, and the overvoltage can be reduced. The cross-linked polymer electrolyte is the same raw material as that of the above-mentioned perfluorosulfonic acid membrane.
SO ₂ CF ₂ CF ₂ COF or ClSO ₂ CF ₂ CF ₂ SO ₂
It is produced from Cl by the same method as described in JP-A-11-7969 as follows. The substitution of H atoms for polyvalent metals is 2 to 30%.

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The crosslinked polymer electrolyte described above has a structure of an imido group containing two units of electron-withdrawing CF ₂ as shown below when compared with the crosslinked polymer electrolyte of the formula (4).
Has a strong acid strength and the effect of increasing electric conductivity is remarkable.

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FSO ₂ CF ₂ CF ₂ COF, which is a common raw material for the solid polymer electrolyte and the electrode catalyst coating agent used in the proton conductive fuel cell of the present invention, is produced by any of the following methods. Method described in USP 4,329,435

Embedded image C ₂ H ₅ SNa + CF ₂ CF ₂ + (CH ₃ O) ₂ CO ↓ C ₂ H ₅ SCF ₂ CF ₂ CO ₂ CH ₃ ↓ Cl ₂ ClSCF ₂ CF ₂ CO ₂ CH ₃ ↓ Cl ₂ / H ₂ O ClSO ₂ CF ₂ CF ₂ CO ₂ CH ₃ ↓ NaOH NaSO ₃ CF ₂ CF ₂ CO ₂ Na ↓ PCL ₅ / POCl ₃ ClSO ₂ CF ₂ CF ₂ COCl ↓ NaF / sulforane FSO ₂ CF ₂ CF ₂ COF

[0019]

Embedded image SO ₂ Q ₂ + CF ₂ CF ₂ + MCN ↓ QSO ₂ CF ₂ CF ₂ CN ↓ H ₂ SO ₄ or H ₃ PO ₄ QSO ₂ CF ₂ CF ₂ CO ₂ H ↓ SF ₄ / MF FSO ₂ CF ₂ CF ₂ COF (where Q is halogen, M is alkali metal ion)

[0020]

ASO ₂ M + CF ₂ CF ₂ + D ₂ CO ↓ ASO ₂ CF ₂ CF ₂ COD ↓ After alkali hydrolysis, acid addition HSO ₃ CF ₂ CF ₂ CO ₂ H ↓ SF ₄ FSO ₂ CF ₂ CF ₂ COF (here in a is OM, R, NR ₂ or NH _2, R is a C1 -C5 alkyl group or an allyl group, M is as defined above, D is halogen or oR) in the present invention, for use as a solid polymer electrolyte Par
As described in US Pat. No. 4,329,434, a fluorosulfonic acid film is produced by copolymerizing tetrafluoroethylene and a fluorinated vinyl ether represented by the formula (7), forming a film, and then hydrolyzing the film. Is also possible.

Embedded image CF ₂ ＣＦCFO (CF ₂ ) ₃ SO ₂ R (7) (where R is the same as above)

[0021]

Next, the present invention will be described in more detail with reference to Reference Examples and Examples, but the scope of the present invention is not limited thereto. <Reference Example 1> According to Example 1 of USP 4,329,435, FS
O ₂ CF ₂ CF ₂ COF was synthesized. This compound is
According to Example 2 on page 4,329,435, FSO ₂ (CF ₂ ) ₃ OCF (C
F ₃ ) COF was obtained. Further, Example 3 of USP 4,329,435
The compound is thermally decomposed over sodium carbonate to give a perfluorovinyl ether monomer: FSO ₂ (CF ₂ ) ₃ OC
F = CF ₂ was obtained.

Reference Example 2 FSO synthesized in Reference Example 1
₂ (CF ₂ ) ₃ OCF = CF ₂ was prepared in the same manner as in Example 4 of US Pat. Was copolymerized with tetrafluoroethylene under the conditions of a tetrafluoroethylene pressure of 5 atm and a polymerization temperature of 40 ° C. The obtained copolymer was molded into a film having a thickness of 100 μm, and then hydrolyzed with an alkali to obtain a perfluorosulfonic acid membrane having an ion exchange capacity of 1.2 (meq / g dry resin). Was.

Reference Example 3 FSO obtained in Reference Example 1
The ₂ CF ₂ CF ₂ COF, in the same manner as in Example 1 of JP-A-11-7969, a tetrahydrofuran as a solvent to obtain a polymer electrolyte is reacted with lithium bis (trimethylsilyl) amide. This polymer electrolyte was changed to H-form with sulfuric acid and further reacted with magnesium acetate to obtain a crosslinked polymer electrolyte in which about 10% of hydrogen atoms of imido groups were replaced with magnesium atoms.

<Example 1> A 5% by weight ethanol solution of the crosslinked polymer electrolyte obtained in Reference Example 3 was added to a 40% by weight platinum catalyst-supporting carbon, and the platinum catalyst and the crosslinked polymer electrolyte were mixed with each other. The paste was added so that the weight ratio was 2: 1 and uniformly dispersed to prepare a paste. The paste was applied on a sheet of polytetrafluoroethylene using a 200-mesh screen and then dried at 100 ° C. to obtain a catalyst sheet. The catalyst layers of the two catalyst sheets were opposed to each other, and between them, the perfluorosulfonic acid membrane obtained in Reference Example 2 was put into an H-type with hydrochloric acid at 150 ° C. and a pressure of 50 kg / c.
After hot pressing at m ² , the polytetrafluoroethylene sheets on both sides were peeled off to produce a membrane electrode assembly. On the other hand, a carbon cloth having a thickness of 400 microns was immersed in a dispersion of polytetrafluoroethylene, and then sintered at 340 ° C to prepare a catalyst layer support. The membrane electrode assembly and the catalyst layer support are laminated and assembled into a fuel cell single cell evaluation device. Using hydrogen gas as fuel and air as oxidant, a single cell characteristic test is performed at normal pressure and a cell temperature of 70 ° C. As a result, at a current density of 1.0 A / cm ² ,
The cell output voltage was 0.71V.

Example 2 A copolymer having a higher ion exchange capacity than that of Reference Example 2 was obtained by adjusting the copolymerization conditions, and was dispersed in a mixed solvent of (isopropyl alcohol and water). Using this in place of the ethanol solution of the crosslinked polymer electrolyte, the same operation as in Example 1 was carried out to prepare a catalyst sheet.
An evaluation cell was assembled using this catalyst sheet in the same manner as in Example 1, and a single cell evaluation was performed under the same conditions.
At a current density of 0 A / cm ² , the cell output voltage was 0.65V.

Comparative Example 1 In Example 1, a perfluorosulfonic acid membrane having an ion exchange capacity of 0.91 (m
eq / g dry resin), a Nafion membrane (manufactured by DuPont) having a thickness of 175 μm was used, and instead of the crosslinked polymer electrolyte, the Nafion polymer was replaced with (isopropyl alcohol +
Water) The same single-cell evaluation was performed using a solution dispersed in a mixed solvent, and the cell output voltage was 0.45 V at a current density of 1.0 A / cm ² .

[0027]

Proton conductivity type fuel cell of the present invention exhibits, path takes a specific value of the number of units of CF ₂ in the side chain 3 - for using the fluoroalkyl sulfonic acid membrane as a solid polymer electrolyte,
The manufacturing cost is low, the energy efficiency is high, and the cell can be easily assembled, and its performance can be maintained for a long time. Further, since the crosslinked polymer electrolyte used as the electrode catalyst coating agent has a structure of imidic acid having 2 units of CF ₂ , the acid strength of imidic acid is strong, and the effect of reducing overvoltage and reducing internal electric resistance is great.

Continued on the front page F-term (reference) 4F071 AA27 AA30 AA64 AA75 AA78 AE22 AH15 BC01 BC02 BC17 4J002 BD151 BP031 BQ001 EV176 EV236 GQ00 GQ02 5G301 CA30 CD01 5H026 AA06 BB04 CX05 EE19

Claims (2)

[Claims] 1. A proton conducting fuel cell in which a solid polymer electrolyte is a perfluorosulfonic acid membrane composed of repeating units (A) and (B) represented by the formula (1). 2. The proton conductive fuel cell according to claim 1, wherein the electrode catalyst coating agent is a crosslinked polymer electrolyte represented by the general formula (2).