WO2001006586A1 - Solid polymer electrolyte type fuel cell and method for manufacturing the same - Google Patents

Abstract

A solid polymer electrolyte type fuel cell having, as an electrolyte, a cation exchange resin film comprising a perfluorocarbon polymer having a sulfonic acid group which is reinforced with a woven fabric made from a fluorine-containing polymer, wherein warps and wefts independently have a denier number of 1.5 to 20 and a density of 1 to 120 /inch and a part where warps and wefts cross with each other has a thickness of 10 to 50 νm. Such reinforcement for the polymer allows the production of a thin film from the cation exchange resin having a high strength, which results in the achievement of a high output and excellent durability in a solid polymer electrolyte type fuel cell having the cation exchange resin as an electrolyte.

Description

 Specification

 TECHNICAL FIELD The present invention relates to a solid polymer electrolyte fuel cell and a method for producing the same.

 The present invention relates to a polymer electrolyte fuel cell and a method for manufacturing the same.

Background art

 In recent years, research on a solid polymer electrolyte fuel cell using a proton conductive polymer membrane as an electrolyte has been advanced. Solid polymer electrolyte fuel cells operate at low temperatures, have high output densities, and can be miniaturized, and are promising for applications such as power supplies for vehicles.

 As the electrolyte for a solid polymer electrolyte fuel cell, a 20- to 200-ni-thick, proton-conducting ion-exchange membrane is usually used. In particular, a perfluorocarbon polymer having a sulfonic acid group (hereinafter, referred to as a sulfone) is used. A positive ion-exchange membrane made of an acid-type perfluorocarbon polymer is widely studied because of its excellent basic characteristics.

 Methods for reducing the electrical resistance of the cation exchange membrane include increasing the sulfonic acid group concentration and decreasing the film thickness. However, when the sulfonic acid group concentration is significantly increased, problems such as a decrease in mechanical strength of the membrane, a creep of the membrane during long-term operation of the fuel cell, and a decrease in durability of the fuel cell occur. On the other hand, when the film thickness is reduced, the mechanical strength of the film is reduced, and when the film is bonded to the gas diffusion electrode, there are problems such as difficulty in processing and handling.

 As a method of solving the above problem, a composite cation exchange membrane comprising a film made of a sulfonic acid type perfluorocarbon polymer and a polytetrafluoroethylene (hereinafter referred to as PTFE) porous body has been proposed ( Mark. W. Barbrudge, AIC HE Journal, 38, 93 (1992)). However, with this method, although the film thickness can be reduced, the electric resistance of the film is not sufficiently reduced because the film contains porous PPTFE.

Further, Japanese Patent Application Laid-Open No. Hei 6-231780 proposes an ion exchange membrane for a fuel cell reinforced by a woven fabric using a thread made of a perfluorocarbon polymer. However, this woven fabric has a large fiber, and it has been difficult to put it into practical use as a membrane reinforcing body in a case where the thickness is set to 50 m to reduce the resistance of the ion exchange membrane. Disclosure of the invention

 Therefore, an object of the present invention is to provide a solid polymer electrolyte fuel cell having high output and excellent durability by having a cation exchange membrane having high strength even though it is thin.

 According to the present invention, the warp and the weft have a denier of 1.5 to 20 independently, a warp density and a weft density of 1 to 120 independently Z inches, and a thickness of an intersection of the warp and the weft. Wherein the electrolyte is a cation exchange membrane made of a perfluorocarbon polymer having a sulfonate group and reinforced with a fluorinated polymer woven fabric having a polymer content of 10 to 50. Provide batteries.

BEST MODE FOR CARRYING OUT THE INVENTION

 In the present invention, as the fluoropolymer constituting the fluoropolymer woven fabric, perfluoroolefins such as tetrafluoroethylene and hexafluoropropylene, black fluorotrifluoroethylene, perfluoroethylene, etc. Homopolymers or copolymers containing at least one polymerized unit based on a monomer such as (alkyl vinyl ether) are preferred. Specific examples include PTFE, tetrafluoroethylenenohexafluoropropylene copolymer (hereinafter referred to as FEP), and tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (hereinafter referred to as PFA). , Tetrafluoroethylenenoethylene copolymer (hereinafter referred to as ETFE), polychlorinated trifluoroethylene, tetrafluoroethylenenoperfluoro (2,2-dimethyl-1,3-dioxole) copolymer, polyperfluoro ( Buteryl vinyl) and the like. Among them, PTFE, FEP, PFA and ETFE are preferred. In the present invention, the fluorinated polymer is contained in the cation exchange membrane as a reinforcing material in the form of a woven fabric having a specific network structure. When this woven fabric is compared with the conventional PTFE porous body, the reinforcement ratio can be arbitrarily selected by adjusting the mesh structure. There are advantages such as a small increase in resistance and excellent dimensional stability.

In the present invention, the denier of the warp yarn and the weft yarn of the fluoropolymer woven fabric are each independently 1.5 to 20, preferably 3 to 15. If the denier of the warp or weft is less than 1.5, the reinforcing effect will be insufficient. Pinholes and cracks are easily generated in the exchange membrane. The density of the warp and the weft is independently 1 to 160 Z-inch, preferably 2.5 to 60 N-inch. If the density of the warp or weft is less than 1 yarn / inch, misalignment tends to occur and the reinforcing effect becomes insufficient. If it exceeds 160 noinches, the film will have high resistance. Further, the thickness of the intersection between the warp and the weft is 10 to 50 mm, preferably 10 to 30 zm. If it is less than 10 im, the warp and weft yarns are too thin, so that a sufficient reinforcing effect cannot be obtained. If it exceeds 50; tim, the thickness of the cation exchange membrane becomes too thick, and the membrane resistance cannot be lowered.

 As the warp and weft, either monofilament or multifilament can be used.In the case of multifilament, since the cross section of the yarn can be flattened, the rise in membrane resistance can be minimized even if the opening ratio of the woven fabric is reduced. It is preferred.

 The woven fabric is manufactured without twisting the yarn in the process of manufacturing the woven fabric (hereinafter, the untwisted yarn is referred to as untwisted yarn), so that the thickness of the intersection is 10 to 50 / m. Can be. In other words, a thread made of a fluoropolymer is produced by forming a slit into the film after forming the fluoropolymer into a film, and then stretching the thread, so that the thread has a flat shape (tape yarn) and a monofilament tape yarn. In the case of (1), the thickness direction of the yarn is the thickness direction of the woven fabric, and in the case of multifilament, the yarns are arranged side by side and become chewy, so that the thickness of the woven fabric at the intersection is in the above range.

 Further, the woven fabric is flattened by a flat plate press, a roll press or the like, and its thickness can be set to preferably 10 to 40 jum, more preferably 15 to 30 m. If the woven fabric is not flattened, the resistance of the cation exchange membrane reinforced with the woven fabric is unlikely to increase due to the reinforcement. However, if the thickness of the woven fabric is not less than 23 of the thickness of the cation exchange membrane, pinholes and cracks will occur in the cation exchange membrane, so it is better to use a non-flattened woven fabric. The resulting cation exchange membrane becomes thicker, resulting in a higher membrane resistance.

A method for producing a cation exchange membrane reinforced with a fluoropolymer woven fabric includes, for example, impregnating a woven fabric with a solution of a perfluorocarbon polymer having a sulfonic acid group or a dispersion thereof, and then drying and impregnating the fabric. Cast method, A method of laminating a film-like material made of a fluorocarbon polymer and a woven fabric and performing hot-melt pressing, and the like can be given. Examples of the hot melt press method include a batch method such as a flat plate press and a vacuum press and a continuous method such as a continuous roll press method. Then, the thickness of the cation exchange membrane is preferably 20 to 200 m, particularly preferably 30 to 80 m.

 Further, a film-like material made of a perfluorocarbon polymer having a sulfonic acid group and a woven fabric may be laminated, press-molded, and then stretched. In this case, since the woven fabric is also stretched, the denier numbers of the warp and the weft of the woven fabric after stretching are 1.5 to 20 independently, and the warp density and the weft density are independently 1 to 120. The thickness of the intersection between the warp and the weft may be 10 to 50 m per inch, and the woven fabric before stretching (at the time of lamination) may not have the above configuration. .

As the sulfonic acid type perfluorocarbon polymer used for the cation exchange membrane in the present invention, conventionally known polymers are widely used. For example, a sulfonic acid type perfluoro-mouthed carbon polymer can be obtained by subjecting a precursor made of a resin having a terminal of SO ₂ F (hereinafter, simply referred to as a precursor) to hydrolysis and acidification. In the present specification, the perfluorocarbon polymer may contain an oxygen atom having an ether bond or the like.

As the _{precursor, CF 2 = CF- (OCF 2} CFX) m -〇 _p - (CF _{2) n} - S_〇 Furuorobiniru compound represented by the ₂ F (wherein, X is a fluorine atom or a triflate Ruoromechiru group M is an integer of 0 to 3, n is an integer of 1 to 12, p is 0 or 1, and when n = 0, p = 0.) Polymerized units based on the above formula, tetrafluoroethylene, Copolymers containing polymer units based on perfluoroolefin, such as fluoropropylene, chlorotrifluoroethylene, or perfluoro (alkylbierether) are preferred. In particular, a copolymer containing a polymer unit based on the above fluorovinyl compound and a polymerized unit based on tetrafluoroethylene is preferable. Preferred examples of the above fluorovinyl compound include compounds represented by any of the following formulas: Is mentioned. In the following formula, Q represents an integer of 1 to 8, r represents an integer of 1 to 8, s represents an integer of 1 to 8, and t represents an integer of 1 to 5. CF ₂ = CFO (CF ₂ ) _q S0 ₂ F

CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _r S0 ₂ F

CF ₂ = CF (CF ₂ ) _s S0 ₂ F

CF ₂ = CF (OCF ₂ CF (CF ₃ )) _t O (CF ₂ ) ₂ S0 ₂ F Preferably, the resin is 0.5 to 2.0 meq dry resin, especially 0.7 to 1.6 meq Zg dry resin. When the ion exchange capacity is lower than this range, the electrical resistance of the membrane tends to increase, and when the ion exchange capacity is high, the mechanical strength of the membrane tends to decrease.

 A cation exchange membrane reinforced by a woven fabric is provided with a gas diffusion electrode in close contact with both sides by a generally known method, and a current collector is disposed outside the gas diffusion electrode to assemble a solid polymer electrolyte fuel cell.

 The above-mentioned gas diffusion electrode is usually made of a sheet-shaped porous body in which conductive carbon black powder carrying platinum catalyst particles or platinum alloy catalyst particles is held by a hydrophobic resin binder such as PTFE. Is preferred. The porous body may contain a perfluorocarbon polymer having a sulfonic acid group, and the polymer is preferably a perfluorocarbon polymer constituting a cation exchange membrane. The same polymer as the above-mentioned polymer is preferable. More preferably, the carbon black powder is coated with the above-mentioned perfluorocarbon polymer.

 It is preferable that the gas diffusion electrode and the cation exchange membrane are adhered to each other by a hot press method or the like. Further, as the current collector disposed outside the gas diffusion electrode, it is preferable to use a conductive carbon black plate or the like in which a groove serving as a passage for a fuel gas or an oxidizing gas is formed.

 Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

 Example 1 (Example)>

 [Preparation of cation exchange membrane]

In a 10-liter stainless steel pressure-resistant reaction vessel, 3.09 kg of 1, 1, 2- Charge 1,1,2,2-trifluoroethane and 13.5 g of a, a'-azobisisobutyronitrile, then 4.41 kg of CF ₂ = CF〇CF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ S〇 ₂ F was charged. After sufficient degassing, the temperature was increased to 70, and the pressure in the vessel was increased to 12.4 kg / cm ^{2 with} tetrafluoroethylene to initiate polymerization. Continue to introduce tetrafluoroethylene so that the pressure inside the vessel, which decreases as the polymerization proceeds, can be maintained.After 7.0 hours, the reaction is stopped, and the ion exchange capacity is 1.1 meq / g dry. a resin, to obtain a _{CF 2 = CFOCF 2 CF (CF} 3) O (CF 2) consisting of ₂ S_〇 ₂ based on F polymerized units and tetrafluoropropoxy O Roe Chile based on emissions polymerized units copolymer. The copolymer was extruded into a film at 220 to obtain a film having a thickness of 25 m.

 Next, a tape yarn made of PTFE with a thickness of 16.5 denier (10 m thick, 92 / zm wide cross section fiber) was used for both the warp and weft yarns. A woven fabric was produced using this yarn in an untwisted yarn state, and the intersection of the warp and weft yarns had a thickness of 20 m, and the warp and weft yarns had a density of 10 inches. The opening ratio of this woven fabric was 55%. Then, the woven fabric was sandwiched between the two films, and the film was pressed at 220 using a roll. This is hydrolyzed in an aqueous solution containing 30% by mass of dimethyl sulfoxide and 15% by mass of potassium hydroxide, then washed with water, immersed in 1 mo 1 ZL of hydrochloric acid, washed with water, and then fixed on four sides with a special jig. And dried at 60 for 1 hour to obtain a cation exchange membrane having a thickness of 50 / zm.

 [Strength measurement]

After the above cation exchange membrane was immersed in pure water of 90, the tensile strength of the membrane was measured by a tensile test method specified in JIS-K7127. That is, a cation exchange membrane was punched into a shape of a No. 3 test piece specified in J15-K7127, and the tensile strength was measured at 25 and a relative humidity of 50% at a test speed of 50 mm / min. The tensile strength was 1.38 kg / mm ² and the tensile elongation at break was 41%.

 After the cation exchange membrane was immersed in pure water of 90, the elemendorf tear load defined by JIS-K6732 was measured, and was 249 g.

[Measurement of membrane resistance] After immersing the cation exchange membrane in lmo 1ZL sulfuric acid at 25 for 24 hours, the AC specific resistance was measured. Specifically, a membrane with an effective membrane area of 1.87 cm ² was placed in an electrolyte made of lmo 1 / L sulfuric acid using a platinum electrode, and at 25, a Yokogawa Hewlett-Packard LCR meter was used. The AC specific resistance was measured. The AC specific resistance was 14.3 Ω · cm.

 [Fuel cell fabrication and performance evaluation]

Polymerized units based on tetrafluoroethylene ₂ = 2-0? ₂ 〇? A copolymer consisting of (CF ₃ ) O (CF ₂ ) ₂ S0 ₃ H based polymerized units (ion exchange capacity: 1.1 meq Z gram dry resin) and platinum-supported carbon in a mass ratio of 1: 3 A coating solution containing ethanol as a solvent was applied on a carbon cloth by a die coating method, and dried to form a gas diffusion electrode layer having a thickness of 10 / m and a platinum carrying amount of 0.5 mgZcm ² . The cation exchange membrane obtained above was sandwiched between the two gas diffusion electrodes, and pressed using a flat plate press to produce a membrane electrode assembly.

Titanium current collector on the outside of the membrane electrode assembly, the PTFE-made gas supply chamber to the outside, further a heating evening one placed on the outside, assembled fuel cells an effective membrane area of 9 cm ² further .

The temperature of the fuel cell was maintained at 80, and oxygen was supplied to the oxidizer electrode and hydrogen was supplied to the fuel electrode at 2 atm. When the terminal voltage was measured at a current density of lAZcm ² , the terminal voltage was 0.60 V.

Further, the above fuel cell was operated continuously at a current density of 1 A / cm ² at 80. The terminal voltage after 1000 hours was 0.59 V.

 <Example 2 (Comparative example)>

From the copolymer obtained in Example 1 and comprising a polymerized unit based on CF ₂ = CF〇CF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ S〇 ₂ F and a polymerized unit based on tetrafluoroethylene Using two films each having a thickness of 25 m and pressing the rolls in the same manner as in Example 1 except that the woven fabric was not sandwiched, an unreinforced cation exchange membrane having a thickness of 50 m was obtained.

Using this cation exchange membrane, strength, resistance and fuel cell characteristics were measured in the same manner as in Example 1. The tensile strength (width direction) is 1.8 kgZmm ² , Was 160%. In addition, when the Elmendorf tear load was measured in the same manner as in Example 1, it was 23 g, and the AC specific resistance was 12.6 Q * cm. A fuel cell was assembled using this cation exchange membrane in the same manner as in Example 1, and the characteristics were measured. As a result, the terminal voltage was 0.56 V at a current density of 1 A / cm ² .

Further, the above fuel cell was continuously operated at a current density of 1 A / cm ² at 80. After 1000 hours, the terminal voltage dropped to 0.42 V.

 Example 3 (Example)>

Example obtained in _{1, CF 2 = CFOCF 2 CF} (CF 3) O (CF 2) 2 S_〇 using styrenesulfonate from the ₂ F in based polymerized units and tetrafluoropropoxy O b ethylene based polymer units Extrusion was performed to obtain a film having a thickness of 60 m. Between these two films, 12 monofilaments of ethylene Z perfluoro (propyl vinyl ether) copolymer with a thickness of 5 denier for both warp and weft are stranded fibers (thickness 55 / zm, width 80m, fiber A 120 tm thick film was obtained by pressing a woven fabric made of 60 denier.

 The film was sandwiched between two amorphous polyethylene terephthalate films having a thickness of 200 iim as a stretching auxiliary film, and heated and roll-pressed with 8 O: to obtain a laminated film in which the stretching auxiliary film was laminated on both sides. The laminated film is biaxially stretched (area ratio: 4 times) twice in each axial direction (direction through the single screw extruder (MD direction) and direction perpendicular to the MD direction (TD direction)) at 85. Thus, a stretched film was obtained.

 After the auxiliary stretching film was peeled off from the stretched film, hydrolysis, treatment with hydrochloric acid and drying were performed in the same manner as in Example 1 to obtain a cation exchange membrane having a thickness of 30 / zm. In this cation exchange membrane, the woven fabric as the reinforcing material was also stretched, so that both the warp and the weft are equivalent to 15 denier, the intersection of the warp and the weft is 20 m thick, and the warp and the weft are the same. Both had a density of 12 inches.

When the strength of the above cation exchange membrane was measured in the same manner as in Example 1, the tensile strength was 1.7 kg / mm ² and the tensile elongation at break was 32%. The Elmendorf Tear Load was 310 g and the AC specific resistance was 10.5 Ω · cm.

A fuel cell was assembled using this cation exchange membrane in the same manner as in Example 1, and the characteristics were measured. As a result, the terminal voltage was 0.6 IV at a current density of 1 AZ cm ² . Further, the fuel cell was continuously operated at 80 and a current density of 1 AZ cm ² . The terminal voltage after 1000 hours was stable at 0.60 V. Industrial applicability

 Since the cation exchange membrane of the present invention has a high tear strength even if it is thin, it can be used with good durability even when used as a thin film in a fuel cell. Therefore, since the electric resistance of the cation exchange membrane can be reduced by reducing the film thickness, the solid polymer electrolyte fuel cell of the present invention having the cation exchange membrane as a solid polymer electrolyte can be used. High output and excellent durability.

Claims

The scope of the claims  1. The denier numbers of the warp and weft are independently 1.5 to 20, the warp density and the weft density are 1 to 120 inches independently, and the thickness of the intersection between the warp and the weft is 10 to A solid polymer electrolyte fuel cell characterized in that a cation exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group, which is reinforced with a 50-m fluoropolymer woven fabric, is used as an electrolyte.  2. The woven fabric is made of polytetrafluoroethylene, tetrafluoroethylene Z-perfluoro (alkyl vinyl ether) copolymer, tetrafluoroethylene hexafluoropropylene copolymer, or tetrafluoroethylene. 2. The solid polymer electrolyte fuel cell according to claim 1, comprising a ethylene copolymer. 3. The perfluorocarbon polymer is? ₂ = 〇? Polymerized units based on ₂ Binding F ₂ = CF- (〇_CF _{2 CFX) m -O p - (} CF 2) n - SO 3 H in based polymerization unit of (wherein, X is a fluorine atom or a triflate Ruo b methyl M is an integer from 0 to 3, n is an integer from 0 to 12, p is 0 or 1, and if n = 0, p = 0. 3. The solid polymer electrolyte fuel cell according to claim 1, which is a copolymer comprising:  4. The solid polymer electrolyte fuel cell according to claim 1, 2 or 3, wherein the cation exchange membrane has a thickness of 20 to 200 // m.  5. Denier numbers of warp and weft are 1.5 to 20 independently, and warp density and weft density are 1 to 120 independently, respectively, in membrane-like material made of perfluorocarbon polymer having sulfonic acid group. A cation-exchange membrane obtained by laminating and hot-melting a fluorine-based polymer woven fabric, which is a noinch and has a crossing point between the warp and the weft of 10 to 50 m; A solid polymer electrolyte fuel cell, wherein a gas diffusion electrode is disposed in close contact with both sides of the electrolyte.  6. The method for producing a solid polymer electrolyte fuel cell according to claim 5, wherein the thickness of the cation exchange membrane is 20 to 200 m by heat melting. 7. Laminate a membrane made of a perfluorocarbon polymer having a sulfonic acid group and a woven fabric, press-mold, stretch, and stretch the stretched woven fabric into warp and weft deniers. 1.5 to 20 independently, warp density and weft density independently 1 A method for manufacturing a solid polymer electrolyte fuel cell, wherein the thickness of the intersection of the warp and the weft is lo to 50 / zm.