Source: https://patents.google.com/patent/US20010026883A1/en
Timestamp: 2019-04-24 16:27:27+00:00

Document:
A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, which comprises forming into a membrane a mixture of a perfluorocarbon polymer having sulfonic acid groups or their precursors and a fluorocarbon polymer which can be fibrillated, laminating a support membrane for stretching to at least one side of the resulting membrane, and stretching the resulting laminated membrane under heating.
In the present invention, a precursor of a sulfonic acid group means a group which can be converted to sulfonic acid group (—SO 3H group) by e.g. hydrolysis, a treatment for converting to acid forms. As such an example, a —SO2F group, a —SO2Cl group, etc. may be mentioned.
A polymer containing polymer units derived from a perfluorovinyl compound having sulfonyl groups is usually produced by polymerizing a perfluorovinyl compound having —SO 2F group. While a perfluorovinyl compound having —SO2F groups can be polymerized by it self, it is usually copolymerized with e.g. a comonomer such as a perfluoroolefin or a perfluoro(alkylvinyl ether), as described above. As a perfluoroolefin to be used as a comonomer, usually, tetrafluoroethylene, hexafluoropropylen, etc. may be mentioned. Among them, tetrafluoroethylene is preferably employed.
As a perfluoro(alkylvinyl ether)to be used as a comonomer, a compound represented by CF 2═CF—(OCF2CFY)t—ORf is preferably mentioned. In the formula, Y is a fluorine atom or a trifluoromethyl group, t is an integer of from 0 to 3, Rf is a normal or a branched chain perfluoroalkyl group represented by CuF2u+1 (1≦u≦12).
As a preferred example of the compound represented by the formula: CF 2═CF—(OCF2CFY)t—O—Rf, the following compounds may be mentioned. In the formula, v is an integer of from 1 to 8, w is an integer of from 1 to 8 and x is an integer of from 1 to 3.
Further, instead of a perfluoroolefin and a perfluoro(alkylvinyl ether), as such a comonomer, a fluorine-containing monomer such as perfluoro(3-oxahepta-1,6-diene) may be copolymerized with a perfluorovinyl compound having —SO 2F.
When the electrolyte membrane in the present invention is comprised of a fibril-reinforced layer and a non-reinforced layer, such a fibril-reinforced layer may be produced in the same manner as in the fibril-reinforced membrane. Namely, by the step of preparing a precursor membrane of a fibril-reinforced membrane, a mixture of a sulfonic acid precursor type perfluorocarbon polymer and a fluorocarbon polymer which can be fibrillated may be formed into a membrane, and then, in the stretching step, the resulting membrane is stretched to obtain a fibril-reinforced film, from which a fibril 1 reinforced layer will be prepared. Besides the above step, in the step of preparing non-reinforced film, a sulfonic acid precursor type perfluorocarbon polymer is formed into a membrane, by which a non-reinforced layer will be prepared. Then, in the laminating step, the above fibril-reinforced membrane or the precursor membrane and the non-reinforced membrane are laminated to obtain an electrolyte membrane.
In a polymer electrolyte fuel cell obtained as described above, a hydrogen gas is supplied to its anode side and oxygen or air is supplied to its cathode side. At the anode, a reaction: H 2→2H+2e− occurs and at the cathode, a reaction: 1/2O2+2H+ +2e −→H2O occurs, whereby chemical energy is converted to electric energy.
9730 g of a powder of copolymer (ion exchange capacity: 1.1 meq/g dry resin, hereinafter referred to as copolymer A) consisting of polymer units derived from tetrafluoroethylene and polymer units derived from CF 2═CF—OCF2CF(CF3)O(CF2)2SO2F and 270 g of PTFE powder (trade name: Fluon CD-1, manufactured by Asahi Glass Co. Ltd.) were mixed and compounded by using a twin screw extruder to obtain 9500 g of pellets. A membrane having a thickness of 250 μm was obtained using the pellets through a single screw extruder. The resulting membrane was smoothed at a temperature of 220° C. by means of a heat-roll press and then was sandwiched between two amorphous polyethylene terephthalate films each having a thickness of 200 μm as support films for stretching, followed by a heat-roll press at 80° C. to obtain a membrane having its both sides laminated with the support films.
A fuel cell was assembled as follows. A coating liquid containing a copolymer (ion exchange capacity: 1.1 meq./g dry resin) consisting of polymer units derived from tetrafluoroethylene and polymer units derived from CF 2═CF—OCF2CF(CF3)O(CF2)2SO3H and platinum loaded carbon in a mass ratio of the copolymer/the carbon being 1/3 and using ethanol as a solvent was coated on a carbon cloth with a die-coating method, and dried to obtain a gas diffusion electrode layer to have a thickness of 10 μm and an amount of platinum loading of 0.5 mg/cm2.
Two sheets of the carbon cloth were disposed so that their gas diffusion layers face to inside, and the above fibril-reinforced membrane was sandwiched between them, followed by pressing by means of a smooth plate press machine to obtain a membrane-electrode assembly. A fuel cell having an effective membrane area of 25 cm 2 was assembled by disposing a separator made of carbon plate having grooves for gas passages formed by cutting in zigzags outside this membrane-electrode assembly, and disposing a heater further their outside.
While maintaining the temperature of the fuel cell at 80° C., air was supplied to the cathode, and hydrogen was supplied to the anode, respectively, under a pressure of 1.5 atom. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.62 V.
Further, the continuous operation of the above fuel cell was carried out at a temperature of 80° C. and at a current density of 1 A/cm 2. The terminal voltage after 1,000 hours was 0.62 V and thus no change was observed.
Using the above fibril-reinforced membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.61 V. The terminal voltage after 1,000 hours was 0.61 V and thus no change was observed.
Using the above fibril-reinforced membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.60 V. The terminal voltage after 1,000 hours was 0.60 V and thus no change was observed.
The obtained membrane was installed in a cell for a gas permeation equipment (effective gas permeation area: 3.3 cm 2) which was maintained at a temperature of 70° C. A humidified hydrogen gas (gas flow amount: 30 cm3/min.) of at the one side of the membrane and a humidified argon gas at the other side of the membrane were supplied respectively. The hydrogen gas which was permeated the membrane was detected by means of a gas-chromatography, and the hydrogen gas permeability of the membrane was measured. The amount of permeating gas was obtained at membrane are of 1 cm2, for a second and under a pressure difference of 1 Pa in the standard condition (0° C., 1 atom), and then converted to a value at a membrane thickness of 1 cm. The hydrogen gas permeability of the laminate-membrane at a temperature of 70° C. and at relative humidity of 95% was 6.9×10−12 cm3 (STP)·cm·cm−2·s−1·Pa−1.
Using the above fibril-reinforced membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.63 V. The terminal voltage after 1,000 hours was 0.63 V and thus no change was observed.
The pellets were prepared and then formed into a film to obtain a film having a thickness of 250 μm in the same manner as in Example 1 except that the amount of the powder of copolymer A was changed to 9,730 g and the amount of PTFE powder was changed to 270 g. The obtained film was laminated with a support film for stretching to obtain a laminated membrane in the same manner as in Example  4. This laminate-membrane was biaxially stretched at a temperature 85° C. with each stretch ratio of 2.5 (area stretch ratio: 6.3) in each direction (MD direction and TD direction), followed by removing the support film for stretching to obtain a fibril-reinforced membrane having a thickness of 40 μm.
The resulting laminate-membrane was evaluated in the same manner as in Example 4. The tear strength were 1.4 N/mm in MD direction and 9.5 N/mm in TD direction, respectively. The alternative current resistivity was 5 Ω·cm. Further, the hydrogen gas permeability of the laminate-membrane at a temperature of 70° C. and a relative humidity of 95% was 6.4×10 −12 cm3 (STP)·cm·cm·s−1·Pa−1.
Using the above laminate-membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.65 V. The terminal voltage after 1,000 hours was 0.65 V and thus no change was observed.
The resulting laminate-membrane was evaluated in the same manner as in Example 4. The tear strength were 8.8 N/mm in MD direction and 13 N/mm in TD direction, respectively. The alternative current resistivity was 6 Ω·cm. Further, the hydrogen gas permeability of the laminate-membrane at a temperature of 70° C. and a relative humidity of 95% was 6.2×10 −12 cm3 (STP)·cm·cm−2·s−1·Pa−1.
Using the above laminate-membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.64 V. The terminal voltage after 1,000 hours was 0.64 V and thus no change was observed.
The resulting laminate-membrane was evaluated in the same manner as in Example 4. The tear strength were 10 N/mm in MD direction and 17 N/mm in TD direction, respectively. The alternative current resistivity was 7 Ω·cm. Further, the hydrogen gas permeability of the laminate-membrane at a temperature of 70° C. and a relative humidity of 95% was 6.8×10 −12 cm 3 (STP)·cm·cm−2·s−1·Pa−1.
Using the above laminate-membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.62 V. The terminal voltage after 1,000 hours was 0.62 V and thus no change was observed.
The resulting fibril-reinforced membrane was evaluated in the same manner as in Example 1, and the number of fibrils having a fiber-diameter of 1 μm or less was 90% based on the total number of fibrils. Further, the tear strength of the fibril-reinforced membrane were 1.6 N/mm in MD direction and 10 N/mm in TD direction, respectively. The alternative current resistivity of the membrane was 5 Ω·cm. The hydrogen gas permeability was 12.6×10 −12 cm3 (STP)·cm·cm−2·s−1·Pa−1.
Using the above fibril-reinforced membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.54 V. The terminal voltage after 1,000 hours was 0.52 V.
Using the above fibril-reinforced membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.53 V. The terminal voltage after 1,000 hours was 0.53 V and thus no change was observed.
Using the above fibril-reinforced membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.57 V. The terminal voltage after 1,000 hours was 0.51 V.
The obtained membrane was evaluated in the same manner as in Example 1, and the tear strength were 0.4 N/mm in MD direction and 0.6 N/mm in TD direction, respectively. The alternative The alternative current resistivity of the film was 5 Ω·cm. The hydrogen gas permeability was 6.0×10 −12 cm3 (STP)·cm·cm−2·s−1·Pa−1.
Using the above membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.53 V. The terminal voltage after 1,000 hours was 0.50 V.
The obtained membrane was evaluated in the same manner as in Example 4, and the tear strength were 2.2 N/mm in MD direction and 7.3 N/mm in TD direction, respectively. The alternative current resistivity of the film was 6 ≠·cm. The hydrogen gas permeability at a temperature of 70° C. and a relative humidity of 95% was 6.2×10 −12 cm3 (STP)·cm·cm−2·s−1·Pa−1.
Using the above membrane, a fuel cell was assembled in the same manner as in Example 1 and the power generation performance was evaluated in the same manner as in Example 1. The terminal voltage was measured at a current density of 1 A/cm 2, and the terminal voltage was 0.67 V. The terminal voltage after 1,000 hours was 0.67 V and no change was observed.
1. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, which comprises forming into a membrane a mixture of a perfluorocarbon polymer having sulfonic acid groups or their precursors and a fluorocarbon polymer which can be fibrillated, laminating a support film for stretching to at least one side of the resulting laminated membrane, and stretching the laminate of the membrane and the support film under heating.
, wherein by carrying out the stretching under heating, the thickness of the membrane is made from 3 to 70 μm and the fluorocarbon polymer is fibrillated so that number of fibrils having a fibril fiber-diameter of at most 1 μm accounts for at least 70% of the total number of fibrils.
, wherein the mixture of the perfluorocarbon polymer having precursors of sulfonic acid groups and the fluorocarbon polymer is formed into a membrane and the precursors of sulfonic acid groups are hydrolyzed and converted to acid-forms, followed by the stretching under heating.
, wherein the support film for stretching is made of a polyethylene terephthalate or a polypropylene, and the stretching is carried out at a temperature of from 40 to 200° C.
, wherein the stretching is carried out by biaxial stretching.
a step of laminating the fibril-reinforced membrane or the precursor membrane and the non-reinforced membrane.
, wherein the step of laminating is carried out after the step of preparing a precursor membrane and the step of preparing a non-reinforced membrane, and then a support film for stretching is further laminated to at least one side of the resulting laminate of the precursor membrane and the non-reinforced membrane, followed by the step of stretching.
, wherein the membrane has a thickness of from 3 to 70 μm.
, wherein a support film for stretching is laminated to at least one side of the precursor membrane obtained by the step of preparing a precursor membrane, and the resulting laminate is stretched under heating, followed by the step of laminating the fibril-reinforced film and the non-reinforced membrane.
, wherein after the step of stretching, the fibril-reinforced membrane is hydrolyzed and converted from the precursors of sulfonic acid groups to sulfonic acid groups, and after the step of preparing a non-reinforced membrane, the non-reinforced membrane is hydrolyzed and converted from the precursors of sulfonic acid groups to sulfonic acid groups, and then the step of laminating is carried out by laminating the resulting fibril-reinforced membrane having slufonic acid groups and the resulting non-reinforced membrane having sulfonic acid groups.
a step of preparing a non-reinforced cation exchange layer by casting a solution containing a perfluorocarbon polymer having sulfonic acid groups onto at least one side of the membrane obtained from the acid-form converting step.
a laminating step of laminating the fibril-reinforced film obtained from the acid-form converting step and the non-reinforced cation exchange layer to prepare a laminate.
17. An electrolyte membrane for a polymer electrolyte fuel cell, which comprises a cation exchange membrane which is made of a perfluorocarbon polymer having sulfonic acid groups, reinforced with reinforcement made of a fibril-form fluorocarbon polymer and which has a thickness of from 3 to 70 μm, wherein number of fibrils of the reinforcement having a fibril-fiber diameter of at most 1 μm accounts for at least 70% of the total number of fibrils.
, wherein an amount of the reinforcement is from 0.5 to 15 mass % based on the total mass of the electrolyte membrane.
, wherein the reinforcement contains at least 80%, based on the total mass of the reinforcement, of polytetrafluoroethylene or a copolymer containing polymer units derived from tetrafluoroethylene in an amount of at least 95 mol %, based on of the copolymer.
, wherein the perfluorocarbon polymer is a copolymer having polymer units derived from CF2═CF2 and polymer units derived from CF2═CF(OCF2CFX)m—Op—(CF2)nSO3H, wherein X is a fluorine atom or a trifluoromethyl group; m is an integer of from 0 to 3; n is an integer of from 0 to 12; p is 0 or 1; if n is 0, p is 0.
21. An electrolyte membrane for a polymer electrolyte fuel cell, which is a laminate comprising at least two cation exchange layers made of a perfluorocarbon polymer having sulfonic acid groups, of which at least one layer is reinforced with reinforcement made of a fibril-form fluorocarbon polymer, and at least one layer is not substantially reinforced with any reinforcement.
, wherein the number of fibrils of the reinforcement having a fibril-fiber diameter of at most 1 μm accounts for at least 70% of the total number of fibrils.
27. A polymer electrolyte fuel cell comprising an electrolyte membrane and a gas diffusion electrode disposed on each side of the membrane, wherein the electrolyte membrane is made of a cation exchange membrane comprising a perfluorocarbon polymer having sulfonic acid groups, and reinforced with reinforcement made of a fibrilliform fluorocarbon polymer, and the membrane having a thickness of from 3 to 70 μm, and number of fibrils of the reinforcing material having a fibril-fiber diameter of at most 1 μm which accounts for at least 70% of the total number of fibrils.
28. A polymer electrolyte fuel cell comprising an electrolyte membrane and a gas diffusion electrode disposed on each side of the membrane, wherein the electrolyte membrane is made of a cation exchange membrane, and is a laminate comprising at least two cation exchange layers made of a perfluorocarbon polymer having sulfonic acid groups, of which at least one layer is reinforced with a reinforcement made of fibrilliform fluorocarbon polymer, and at least one layer is not substantially reinforced with any reinforcement.
, wherein the membrane has a thickness of from 3 to 70 μm, and number of fibrils of the reinforcement having a fibril-fiber diameter of at most 1 μm accounts for at least 70% of the total number of fibrils.

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