CA2068071A1 - Method for processing ion-exchange membrane, the ion-exchange membrane and fuel cells using same - Google Patents
Method for processing ion-exchange membrane, the ion-exchange membrane and fuel cells using sameInfo
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- CA2068071A1 CA2068071A1 CA 2068071 CA2068071A CA2068071A1 CA 2068071 A1 CA2068071 A1 CA 2068071A1 CA 2068071 CA2068071 CA 2068071 CA 2068071 A CA2068071 A CA 2068071A CA 2068071 A1 CA2068071 A1 CA 2068071A1
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- exchange membrane
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Abstract
ABSTRACT
Provided is a method for processing anion-exchange membrane which comprises immersing an ion-exchange membrane having a fluorine-containing polymer as matrix in a water-soluble organic solvent or an aqueous solution thereof to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof. The resulting ion-exchange membrane is improved in water content and is low in sheet resistance and ion-exchange membrane fuel cells in which said membrane used are excellent in discharge characteristics.
Provided is a method for processing anion-exchange membrane which comprises immersing an ion-exchange membrane having a fluorine-containing polymer as matrix in a water-soluble organic solvent or an aqueous solution thereof to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof. The resulting ion-exchange membrane is improved in water content and is low in sheet resistance and ion-exchange membrane fuel cells in which said membrane used are excellent in discharge characteristics.
Description
2~68~71 The present invention relates to a fuel cell in which a reducing agent such as pure hydrogen or hydrogen obtained by reforming methanol or fossil fuels is used as fuel and air or oxygen is used as an oxidizing agent and in particular to a method for processing an anion-exchange membrane used for fuel cells and the ion-exchange membrane.
In ion-exchange membrane fuel cells, sulfonic acid type cation exchange membranes comprising copolymers of perfluorovinyl ether and tetrafluoroethylene are generally used as electrolytes. For example, Japanese Patent Kokai (Laid-Open) Nos. Hei 3-184266, 3-182052 and 3-167752 have proposed ion-exchange membrane fuel cells which use NFION which is a perfluorocarbonsulfonic acid resin. The ion-exchange membrane is one of the main factors which govern output characteristics of cells and especially, sheet resistance greatly influences output characteristics.
However, in the conventional ion-exchange membrane fuel cells, commercially available membranes are used as they are and so, the thickness of the membranes is large and the sheet resistance is high and, as a result, the internal resistance of the cells increases and no sufficient output characteristics of cells can be , :
2a~07l 1 obtained.
SUMMARY OF THE INVENTION
The present invention solves the problems mentioned above and one of the objects of the present invention are to provide a method for processing an anion-exchange membrane for realizing ion-exchange fuel cells having a higher performance by lowering the sheet resistance of ion-exchange membxane, the ion-exchange membrane, and fuel cells in which the ion-exchange membrane is used.
For attaining the above objects, the present invention relates to a processing method which comprises immersing an ion-exchange membrane having a fluorine-containing polymer as a matrix in a water-soluble organic solvent or an aqueous solution thereof to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof.
The present invention further relates to an ion-exchange membrane fuel obtained by the above method which has a water content of 30-50% and an ion-exchange fuel cell in which the membrane is used.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph which shows a relation between the reduction ratio of thicXness and the sheet resistance of the ion-exchange membranes in the examples given below.
~ ~, ;
20~7~
1 Fig. 2 is a graph which shows a relation between the reduction ratio of thickness and the wat~r content of the ion-exchange membranes in the examples.
Fig. 3 is a graph which shows a relation be~ween the water content and the sheet resistance of the ion-exchange membranes in the examples.
Fig. 4 is a graph which shows a relation between the ethanol concentration and the reduction ratio of thickness of the ion-exchange membranes in the exam-ples.
Fig. 5 is a cross-sectional view of the ion-exchange membrane fuel cell used in the examples.
Fig. 6 is a voltage-current characteristic diagram of the ion-exchange membrane fuel cell used in the examples.
DESCRIPTION OF THE INVENTION
Examples of the water-soluble organic solvents used in the present invention include alcohols such as methanol, ethanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, methoxy ethanol and ethoxy ethanol and Xetones such as acetones and methyl ethyl ketone. These may be used each alone or in combination of two or more.
Furthermore, the water-soluble organic solvents may be used as an aqueous solution and in this case, the concentration thereof is preferably 20 vol% or more.
The ion exchange membranes having fluorine-- 2~68~7~
1 containing polymer as matrix are not limited and an example thereof is a membrane comprising a copolymer of perfluorovinyl ether and tetrafluoroethylene.
Temperature ~nd time for immersing and swelling the ion-exchange membrane in the water-soluble organic solvent are not critical, but preferably 10-40C and 1-3 minutes.
Rolling or stretching of the swollen membrane is carried out preferably at 120C or lower and at a rate of 30 cm/min.
Noreover, the reduction ratio of thickness of the membrane is preferably 50~ or less.
The thus obtained ion-exchange membrane prefer-ably has a water content of 30-50~.
When the ion-exchange membrane having a fluorine-containing polymer as a matrix is immersed in the water-soluble organic solvent or an aqueous solution thereof, the main chains of the polymer readily slip from each other and besides, ion clusters are formed. By subsequent rolling or stretching of the membrane in this state, it becomes possible to easily reduce the thickness of the ion-exchange membrane and freshly form ion clusters. ~hus, ion-exchange membrane of high water content and low sheet resistance can be obtained and output characteristics of cells can be improved.
The present invention will be illustrated by the following nonlimiting examples.
20~8~7~
l Example 1 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane com-prising a copolymer of perfluorovinyl ether an~l tetrafluoroethylene was immersed in ethanol and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at room temperature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 wt% hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated i.n an aqueous lN sulfuric acid solution at 70-80C for 1 hour to remove inorganic impurities and further convert the counter ions to a proton form. This ion-exchange membrane is called A.
Example 2 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane com-prising a copolymer of perflllorovinyl ether and tetrafluoroethylene was immersed in an aqueous 80 vol%
ethanol solution and swollen therewith. Thereafter, this membrane was rolled 3 times using rollers at room temper-ature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 wt% hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated in an aqueous lN
2~68~71 l sulfuric acid solution at 70-80C for l hour to remove inorganic impurities and ~urther convert the counter ions to a proton form. This ion-exchange membrane is called B~
Example 3 NAFION 117 manufactured by E.I. du Pont de nemours and Company as an ion-exchange membrane comprisiny a copol~mer of perfluorovinyl ether and tetrafluorovinylene was immersed in ethanol and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at 50C. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion~
exchange membrane was heat treated in an aqueous 5 wt%
hydrogen peroxide solution at 70-80C for 1 hour and thereafter heat treated in an aqueous lN sulfuric acid solution at 70-80C for 1 hour. This ion-exchange mambrane is called C.
Example 4 NAFION 117 manufac~ured by E.I. du Pont de Nemours and Company as an ion-exchange membrane com-prising a copolymer of perfluorovinyl ether and tetralfuoroethylene was immersed in acetone and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at room temperature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 -.
o ~ ~
1 wt~ hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated in a lN aqueous sulfuric acid solution at 70-80C for 1 hour to remove inorganic impurities and further convert the counter ions to a proton form. This ion-exchange mem-brane is called D.
Example 5 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion exchange membrane compris-ing a copol~mer of perfluorovinyl ether and tetrafluoro-ethylene was immersed in an aqueous 80 vol% acetone solution and swollen therewith. Thereafter, this membrane was rolled 3 times using rollers at room temperature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous S wt% hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated in an aqueous lN
sulfuric acid solution at 70-80C for 1 hour to remove inorganic impurities and further convert the counter ions to a proton form. This ion-exchange membrane is called E.
.
Example 6 ~AFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane comprising a copolymer of perfluorovinyl ether and 2 ~ 7 ~
1 tetrafluoroethylene was immersed in acetone and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at 50C. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 wt%hydrogen peroxide solution at 70-80C for 1 hour and thereafter heat treated in an aqueous lN sulfuric acid solution at 70-80C for 1 hour. This ion-exchange membrane is called F.
Comparative Example 1 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchanye membrane comprising a copolymer of perfluorovinyl ether and tetrafluoroethylene was heat treated in an aqueous 5 wt%
hydrogen peroxide solution at 70-80C for 1 hour and thereafter heat treated in an aqueous lN sulfuric acid solution at 70-80C for 1 hour. This ion-exchange membrane is called G.
Comparative Example 2 NAEION 115 (comprising the same materials as in NAFION 117 and having thinner thickness) manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane comprising a copolymer of perfluorovinyl ether and tetrafluoroethylene was heat treated in an a~ueous 5 wt% hydrogen peroxide solution at 70 80C for 1 hour and thereafter heat treated in an aqueous lN suluric acid 20~8~
l solution at 70-80C for 1 hour. This ion-exchange membrane is called H.
The above examples and comparative examples will be explained referring to the accompanying drawings.
S Fig. 1 shows a relation between the reduction ratio of thickness and the sheet resistance of the ion-exchange membranes of the above examples. The reduction ratio of thickness was obtained by the following formula.
Reduction ratio of thickness = (T-T')/T
T: Thickness of the NAFION membrane after heat-trea$ed with the given solutions (i.e., ion-exchange membrane G).
T': Thickness of the NAFION membrane after immersed in the water-soluble organic solvent or aqu~ous solution thereof and swollen therewith, then rolled or stretched and thereafter heat-treated with the given solutions (i.e., ion-exchange membranes A, B, C, D, E and F).
The sheet resistance was measured by four probe method in an a~ueous 1.5 M sulfuric acid solution at room temperature, 60C and 80C by providing an platinum electrodes and Hg/Hg2SO~ reference electrodes as in a conventional manner.
When the thickness of the membrane was reduced by several percent, the sheet resistance abruptly decreased and the sheet resistance linearly decreased 9 ~
.
. .
2~071 l when the reduction ratio of thickness was between 10-50%.
However, when the reduction ratio of thickness exceeded 50%, the membrane was broken and rolling was impossible.
Therefore, it can be seen that the effect of the present invention is obtained when rolling is carried out at a reduction ratio of thickness of 50% or less.
Fig. 2 shows a relation between the reduction ratio of thickness and the water content of the ion-exchange membranes of the above examples. The water content was measured by the following formula.
Water content = (Wwet - Wdry)/Wdry Wwet: Weight of the ion-exchange membrane when swollen with water of 60C.
Wdry: Weight of the dried ion-exchange membrane.
The water content increased nearly in propor-tion to the reduction ratio of thickness and the water content of the membrane of 50~ in reduction ratio, namely, the thinnest ion-exchange membrane in the present invention increased up to 50%.
Fig. 3 shows a relation between the water content and the sheet xesistance of the ion-exchange membranes of the above examples.
The sheet resistance decreased in proportion to increase of the water content. From this result 8 not only the reduction of thickness, but also increase of ~he water content can be considered to be causes for decrease of the sheet resistance. Increase of the water content ., ' ' .: , . .
2~8~7:~
1 and the accompanying decrease of sheet resistance are considered to occur ~ecause when the ion-exchange me~brane is immersed in the water-soluble organic solvent or aqueous solution thereof, khe main chains of the polymer which constitutes the membrane readily slips from each other and clusters which are passages of ions are formed and when the membrane in this state is rolled, the ion-exchange groups which have not contributed to the formation of clusters before rolling freshly form clusters.
On the other hand, the water content of the membrane which was minimum in reduction ratio of thick-ness, namely, which was not rolled after immersion in the water-so~uble organic solvent was 30%.
From the above results, it can be seen that the effect of the present invention is obtained for such ion-exchange membrane having a water content of 30-50%~
Fig. 4 shows a relation between the concentra-tion of the aqueous solution of ethanol or acetone and the maximum reduction ratio of thickness of the ion-exchange membrane. With decrease of the concentration, the swollen membrane became brittle and the reduction ratio of thickness decreased and when the concentration of the aqueous solution was less than 20 vol%, reduction of thickness was nok recogni~ed. Thus, it can be seen that the effect of the present invention is o~tained when the concentration o~ the aqueous solution is 20 vol% or higher.
.
~8~7~
1 The number of the rolling, thickness, water content, sheet resistance and gas permeation rate of the ion-exchange membranes of the above examples and compara-tive examples are shown in Table 1. The gas permeation rate was measured by a differential pressure method.
~ 12 -,, 2~6~7.1 _ ~ _ , N 1~ O ~
~ ~D l ~ O O O *~ X
_ d' N
oo I~ r~ o ~ ~
O . o ~ O l ~1 ~ _l l a~ t~l _l ~1 X X
~ ~ O O O ~ N
_____ . ~ ~
C~ ~ ~ ~ Cp ~;P
O ~ . ~O ~ ~ ~4 ~
~r o O O l'X
O ~1 O _ U~ . ~ OD ~D ~ ~h 1~1 C~ ~) O O O O X 5~ ..
CO O O~ O ~1 ~
O . O ~ ~ lS~ ~
~ ~D ~ ~ ~1 O O ~ X
_~ O O ~ U~ ~
__ . ~b a5 U~ ~ ~t O ~1 ~1 O . tD r~ C`~ ~ ~4 E~ ~ ~ N ~` O O O X X
O O O ~D ~
- - - ~ ~
O ~ O~ In ~1 ~ ~
~ co ~ ~r o o o X X
- ~---- ~ ~
O . ~ ~D ~ l ~D C~ ~ O ~ O ~ X
- - o o o ~
~ s~ c~ c~
;
O ~ 0~ ~D CO
o 4~ ~ a~ 'a q) ~ o ~ ~ ~ o ~ ~ s~ ~ ~ ~
~ R .4 ~`
ri ~ ~ ~ ~ a) ~ a ~q o ~ ~ ~ ~ ~ ~ a) ~ ~.
E~ 13 z; - 3 C~ ~_ ~ ~ o m s~`~
.,, ' ::
.
2~68~7~
1 The ion-exchange membranes A-F of the above examples decreased in both the thickness and sheet resistance and increased in water content and gas permeation rate as compared with the ion-exchange membrane G of the comparative example. Although the ion-exchange membranes A and D differed in the swelling solvent, namely, ethanol and acetone, they were the same in the number of rolling and were nearly the same in thickness, water content, resistance and gas permeation rate. Furthermore, the ion-exchange membranes A and D
were nearly the same in thickness as the ion-exchange membrane H of Comparative Example 1, but were higher i~
water content and lower in sheet resistance. ~he ion-exchange membranes C and F decreased in both the thick-ness and the sheet resistance and improved in watercontent as compared with the ion-exchange membranes A and D which were the same as the former in the number of rolling.
~rom the fact that fluorine-containing polymers have an oxygen-nitrogen selectivity ~ in the air of about 2 and the ion-exchange membranes A-F of the present invention had ~ of 1.8, 2.1, 2.4, 1.8, 2.1 and 2.3, respectively, it can be seen that no physical holes were made by rolling in these ion-exchange membranes.
Further, if the gas permeation rate of ion-exchange membrane is large in ion-exchange membrane fuel cells, hydrogen and oxygen which permeate the ion-exchange membrane (namely, cross-leak3 directly react on catalyst ,. , ~ ~ .;, ..
, - 2~6~7~
1 to cause deterioration of cell performance. The ion-exchange membranes A-F of the above examples increased in gas permeation rate, but the rate was such that caused no deterioration of cell performance.
In the above Examples 3 and 6, rolling was carried out at 50C, but the similar rasults were obtained by rolling at 120C or lower. When the ion-exchange membranes were rolled at higher than 120C, the membranes dried owing to the rapid evaporation of the organic solvent and thickness of the membranes was not reduced by the rolling. Thus, it can be seen that the effect of the present invention is obtained by the rolling at 120C or lower. Furthermore, the rolling was conducted at a rate of 14 cm/min in the above examples, but the similar results were obtained at a rolling rate of 30 cm/min or lower. When the ion-exchange membranes were rolled at a rate of higher than 30 cm/min, the membranes could not be uniformly rolled and were broken.
Thus, it can be seen that the effect of the present invention is obtained when a rolling rate of 30 cm/min or lower is employed.
Next, each of the ion-exchange membranes of the above examples and comparative examples and electrodes were hot pressed at 120 150C under 20-60 kg/cm2 to form an assembly of an anode, an ion-exchange membrane and a cathode. A single cell of ion-exchange membrane fuel cell as shown in Fig. 5 was fabricated using the result-ing assembly. In Fig. 5, 10 denotes the ion-exchange - 15 _ 2 ~
1 membrane and 11 and 12 denote the anode and the cathode, respectively. Both the electrodes were made by adding a solid polymer electrolyte to carbon powders which carried a platinum catalyst. The amount of platinum was 0.01-0.5 mg/cm2 and the amount of the solid polymer electrolyte added was 0.1-3.0 mg/cm2 per area for both the elec-trodes. hydrogen gas humidified at 90C was fed to the anode side and oxygen gas humidified at 80C was fed to the cathode side and discharge test of the cell was conducted.
Fig. 6 shows voltage-current characteristic curves of the ion-exchange membrane fuel cells in which the ion-exchange membranes of the abo~e examples and comparative examples were used. The fuel cells in which ion-exchange membranes A-F of the present invention were used showed cell voltages of 0.67 V, 0.64 V, 0.69 V, 0.67 V, 0.64 V and 0.69 V at 200 mA/cm2, xespectivelyO On the other hand, the fuel cells in which ion-exchange memb-ranes G and H of the comparative examples were used showed cell voltages of 0.53 V and 0.56 V at 200 mA/cm2, respectively.
In the above examples, NAFION was used as ion-exchange membrane, but the similar results were obtained also when other ion-exchange membranes comprising copolymers of perfluorovinyl ether and tetrafluoroethy-lene were used. Further, in the above examples, ion-exchange membranes were rolled in biaxial direction, but the similar results were obtained by rolling in monoaxial ~, 2 ~ 7 ~
1 direction. Moreover, ethanol and acetone were used as water-soluble organic solvents for swelling of ion~
exchange membranes, but the similar results were obtained by using at least one of water-soluble organic solvents such as methanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, methoxy ethanol, ethoxy ethanol, methyl ethyl ketone and the like.
In the above examples, hydrogen-oxygen fuel cell was taken up as one example of ion-exchange membrane fuel cells, but the present invention can also be applied to fuel cells which use hydrogen obtained by re~orming methanol, natural gas, naphtha, or the like as fuels and fuel cells which use air as an oxidizing agent.
As explained above, according to the present invention, an ion-exchange membrane is immersed in a water-soluble organic sol~ent ~r an aqueous solution thereof and is swollen ~herewith and is rolled or stretched in such a state that main chains of polymer easily slip from each other and ion clusters are formed, whereby the thickness of the membrane can be easily reduced and an ion-exchange membrane of high water content and low theet resistance can be obtained. Thus, ion-exchange membrane fuel cells which exhibit higher discharge characteristics can be realized.
In ion-exchange membrane fuel cells, sulfonic acid type cation exchange membranes comprising copolymers of perfluorovinyl ether and tetrafluoroethylene are generally used as electrolytes. For example, Japanese Patent Kokai (Laid-Open) Nos. Hei 3-184266, 3-182052 and 3-167752 have proposed ion-exchange membrane fuel cells which use NFION which is a perfluorocarbonsulfonic acid resin. The ion-exchange membrane is one of the main factors which govern output characteristics of cells and especially, sheet resistance greatly influences output characteristics.
However, in the conventional ion-exchange membrane fuel cells, commercially available membranes are used as they are and so, the thickness of the membranes is large and the sheet resistance is high and, as a result, the internal resistance of the cells increases and no sufficient output characteristics of cells can be , :
2a~07l 1 obtained.
SUMMARY OF THE INVENTION
The present invention solves the problems mentioned above and one of the objects of the present invention are to provide a method for processing an anion-exchange membrane for realizing ion-exchange fuel cells having a higher performance by lowering the sheet resistance of ion-exchange membxane, the ion-exchange membrane, and fuel cells in which the ion-exchange membrane is used.
For attaining the above objects, the present invention relates to a processing method which comprises immersing an ion-exchange membrane having a fluorine-containing polymer as a matrix in a water-soluble organic solvent or an aqueous solution thereof to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof.
The present invention further relates to an ion-exchange membrane fuel obtained by the above method which has a water content of 30-50% and an ion-exchange fuel cell in which the membrane is used.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph which shows a relation between the reduction ratio of thicXness and the sheet resistance of the ion-exchange membranes in the examples given below.
~ ~, ;
20~7~
1 Fig. 2 is a graph which shows a relation between the reduction ratio of thickness and the wat~r content of the ion-exchange membranes in the examples.
Fig. 3 is a graph which shows a relation be~ween the water content and the sheet resistance of the ion-exchange membranes in the examples.
Fig. 4 is a graph which shows a relation between the ethanol concentration and the reduction ratio of thickness of the ion-exchange membranes in the exam-ples.
Fig. 5 is a cross-sectional view of the ion-exchange membrane fuel cell used in the examples.
Fig. 6 is a voltage-current characteristic diagram of the ion-exchange membrane fuel cell used in the examples.
DESCRIPTION OF THE INVENTION
Examples of the water-soluble organic solvents used in the present invention include alcohols such as methanol, ethanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, methoxy ethanol and ethoxy ethanol and Xetones such as acetones and methyl ethyl ketone. These may be used each alone or in combination of two or more.
Furthermore, the water-soluble organic solvents may be used as an aqueous solution and in this case, the concentration thereof is preferably 20 vol% or more.
The ion exchange membranes having fluorine-- 2~68~7~
1 containing polymer as matrix are not limited and an example thereof is a membrane comprising a copolymer of perfluorovinyl ether and tetrafluoroethylene.
Temperature ~nd time for immersing and swelling the ion-exchange membrane in the water-soluble organic solvent are not critical, but preferably 10-40C and 1-3 minutes.
Rolling or stretching of the swollen membrane is carried out preferably at 120C or lower and at a rate of 30 cm/min.
Noreover, the reduction ratio of thickness of the membrane is preferably 50~ or less.
The thus obtained ion-exchange membrane prefer-ably has a water content of 30-50~.
When the ion-exchange membrane having a fluorine-containing polymer as a matrix is immersed in the water-soluble organic solvent or an aqueous solution thereof, the main chains of the polymer readily slip from each other and besides, ion clusters are formed. By subsequent rolling or stretching of the membrane in this state, it becomes possible to easily reduce the thickness of the ion-exchange membrane and freshly form ion clusters. ~hus, ion-exchange membrane of high water content and low sheet resistance can be obtained and output characteristics of cells can be improved.
The present invention will be illustrated by the following nonlimiting examples.
20~8~7~
l Example 1 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane com-prising a copolymer of perfluorovinyl ether an~l tetrafluoroethylene was immersed in ethanol and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at room temperature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 wt% hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated i.n an aqueous lN sulfuric acid solution at 70-80C for 1 hour to remove inorganic impurities and further convert the counter ions to a proton form. This ion-exchange membrane is called A.
Example 2 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane com-prising a copolymer of perflllorovinyl ether and tetrafluoroethylene was immersed in an aqueous 80 vol%
ethanol solution and swollen therewith. Thereafter, this membrane was rolled 3 times using rollers at room temper-ature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 wt% hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated in an aqueous lN
2~68~71 l sulfuric acid solution at 70-80C for l hour to remove inorganic impurities and ~urther convert the counter ions to a proton form. This ion-exchange membrane is called B~
Example 3 NAFION 117 manufactured by E.I. du Pont de nemours and Company as an ion-exchange membrane comprisiny a copol~mer of perfluorovinyl ether and tetrafluorovinylene was immersed in ethanol and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at 50C. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion~
exchange membrane was heat treated in an aqueous 5 wt%
hydrogen peroxide solution at 70-80C for 1 hour and thereafter heat treated in an aqueous lN sulfuric acid solution at 70-80C for 1 hour. This ion-exchange mambrane is called C.
Example 4 NAFION 117 manufac~ured by E.I. du Pont de Nemours and Company as an ion-exchange membrane com-prising a copolymer of perfluorovinyl ether and tetralfuoroethylene was immersed in acetone and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at room temperature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 -.
o ~ ~
1 wt~ hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated in a lN aqueous sulfuric acid solution at 70-80C for 1 hour to remove inorganic impurities and further convert the counter ions to a proton form. This ion-exchange mem-brane is called D.
Example 5 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion exchange membrane compris-ing a copol~mer of perfluorovinyl ether and tetrafluoro-ethylene was immersed in an aqueous 80 vol% acetone solution and swollen therewith. Thereafter, this membrane was rolled 3 times using rollers at room temperature. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous S wt% hydrogen peroxide solution at 70-80C for 1 hour to remove organic impurities and thereafter heat treated in an aqueous lN
sulfuric acid solution at 70-80C for 1 hour to remove inorganic impurities and further convert the counter ions to a proton form. This ion-exchange membrane is called E.
.
Example 6 ~AFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane comprising a copolymer of perfluorovinyl ether and 2 ~ 7 ~
1 tetrafluoroethylene was immersed in acetone and swollen therewith. Thereafter, this membrane was rolled 2 times using rollers at 50C. The direction of the rolling was biaxial and rolling rate was 14 cm/min. This ion-exchange membrane was heat treated in an aqueous 5 wt%hydrogen peroxide solution at 70-80C for 1 hour and thereafter heat treated in an aqueous lN sulfuric acid solution at 70-80C for 1 hour. This ion-exchange membrane is called F.
Comparative Example 1 NAFION 117 manufactured by E.I. du Pont de Nemours and Company as an ion-exchanye membrane comprising a copolymer of perfluorovinyl ether and tetrafluoroethylene was heat treated in an aqueous 5 wt%
hydrogen peroxide solution at 70-80C for 1 hour and thereafter heat treated in an aqueous lN sulfuric acid solution at 70-80C for 1 hour. This ion-exchange membrane is called G.
Comparative Example 2 NAEION 115 (comprising the same materials as in NAFION 117 and having thinner thickness) manufactured by E.I. du Pont de Nemours and Company as an ion-exchange membrane comprising a copolymer of perfluorovinyl ether and tetrafluoroethylene was heat treated in an a~ueous 5 wt% hydrogen peroxide solution at 70 80C for 1 hour and thereafter heat treated in an aqueous lN suluric acid 20~8~
l solution at 70-80C for 1 hour. This ion-exchange membrane is called H.
The above examples and comparative examples will be explained referring to the accompanying drawings.
S Fig. 1 shows a relation between the reduction ratio of thickness and the sheet resistance of the ion-exchange membranes of the above examples. The reduction ratio of thickness was obtained by the following formula.
Reduction ratio of thickness = (T-T')/T
T: Thickness of the NAFION membrane after heat-trea$ed with the given solutions (i.e., ion-exchange membrane G).
T': Thickness of the NAFION membrane after immersed in the water-soluble organic solvent or aqu~ous solution thereof and swollen therewith, then rolled or stretched and thereafter heat-treated with the given solutions (i.e., ion-exchange membranes A, B, C, D, E and F).
The sheet resistance was measured by four probe method in an a~ueous 1.5 M sulfuric acid solution at room temperature, 60C and 80C by providing an platinum electrodes and Hg/Hg2SO~ reference electrodes as in a conventional manner.
When the thickness of the membrane was reduced by several percent, the sheet resistance abruptly decreased and the sheet resistance linearly decreased 9 ~
.
. .
2~071 l when the reduction ratio of thickness was between 10-50%.
However, when the reduction ratio of thickness exceeded 50%, the membrane was broken and rolling was impossible.
Therefore, it can be seen that the effect of the present invention is obtained when rolling is carried out at a reduction ratio of thickness of 50% or less.
Fig. 2 shows a relation between the reduction ratio of thickness and the water content of the ion-exchange membranes of the above examples. The water content was measured by the following formula.
Water content = (Wwet - Wdry)/Wdry Wwet: Weight of the ion-exchange membrane when swollen with water of 60C.
Wdry: Weight of the dried ion-exchange membrane.
The water content increased nearly in propor-tion to the reduction ratio of thickness and the water content of the membrane of 50~ in reduction ratio, namely, the thinnest ion-exchange membrane in the present invention increased up to 50%.
Fig. 3 shows a relation between the water content and the sheet xesistance of the ion-exchange membranes of the above examples.
The sheet resistance decreased in proportion to increase of the water content. From this result 8 not only the reduction of thickness, but also increase of ~he water content can be considered to be causes for decrease of the sheet resistance. Increase of the water content ., ' ' .: , . .
2~8~7:~
1 and the accompanying decrease of sheet resistance are considered to occur ~ecause when the ion-exchange me~brane is immersed in the water-soluble organic solvent or aqueous solution thereof, khe main chains of the polymer which constitutes the membrane readily slips from each other and clusters which are passages of ions are formed and when the membrane in this state is rolled, the ion-exchange groups which have not contributed to the formation of clusters before rolling freshly form clusters.
On the other hand, the water content of the membrane which was minimum in reduction ratio of thick-ness, namely, which was not rolled after immersion in the water-so~uble organic solvent was 30%.
From the above results, it can be seen that the effect of the present invention is obtained for such ion-exchange membrane having a water content of 30-50%~
Fig. 4 shows a relation between the concentra-tion of the aqueous solution of ethanol or acetone and the maximum reduction ratio of thickness of the ion-exchange membrane. With decrease of the concentration, the swollen membrane became brittle and the reduction ratio of thickness decreased and when the concentration of the aqueous solution was less than 20 vol%, reduction of thickness was nok recogni~ed. Thus, it can be seen that the effect of the present invention is o~tained when the concentration o~ the aqueous solution is 20 vol% or higher.
.
~8~7~
1 The number of the rolling, thickness, water content, sheet resistance and gas permeation rate of the ion-exchange membranes of the above examples and compara-tive examples are shown in Table 1. The gas permeation rate was measured by a differential pressure method.
~ 12 -,, 2~6~7.1 _ ~ _ , N 1~ O ~
~ ~D l ~ O O O *~ X
_ d' N
oo I~ r~ o ~ ~
O . o ~ O l ~1 ~ _l l a~ t~l _l ~1 X X
~ ~ O O O ~ N
_____ . ~ ~
C~ ~ ~ ~ Cp ~;P
O ~ . ~O ~ ~ ~4 ~
~r o O O l'X
O ~1 O _ U~ . ~ OD ~D ~ ~h 1~1 C~ ~) O O O O X 5~ ..
CO O O~ O ~1 ~
O . O ~ ~ lS~ ~
~ ~D ~ ~ ~1 O O ~ X
_~ O O ~ U~ ~
__ . ~b a5 U~ ~ ~t O ~1 ~1 O . tD r~ C`~ ~ ~4 E~ ~ ~ N ~` O O O X X
O O O ~D ~
- - - ~ ~
O ~ O~ In ~1 ~ ~
~ co ~ ~r o o o X X
- ~---- ~ ~
O . ~ ~D ~ l ~D C~ ~ O ~ O ~ X
- - o o o ~
~ s~ c~ c~
;
O ~ 0~ ~D CO
o 4~ ~ a~ 'a q) ~ o ~ ~ ~ o ~ ~ s~ ~ ~ ~
~ R .4 ~`
ri ~ ~ ~ ~ a) ~ a ~q o ~ ~ ~ ~ ~ ~ a) ~ ~.
E~ 13 z; - 3 C~ ~_ ~ ~ o m s~`~
.,, ' ::
.
2~68~7~
1 The ion-exchange membranes A-F of the above examples decreased in both the thickness and sheet resistance and increased in water content and gas permeation rate as compared with the ion-exchange membrane G of the comparative example. Although the ion-exchange membranes A and D differed in the swelling solvent, namely, ethanol and acetone, they were the same in the number of rolling and were nearly the same in thickness, water content, resistance and gas permeation rate. Furthermore, the ion-exchange membranes A and D
were nearly the same in thickness as the ion-exchange membrane H of Comparative Example 1, but were higher i~
water content and lower in sheet resistance. ~he ion-exchange membranes C and F decreased in both the thick-ness and the sheet resistance and improved in watercontent as compared with the ion-exchange membranes A and D which were the same as the former in the number of rolling.
~rom the fact that fluorine-containing polymers have an oxygen-nitrogen selectivity ~ in the air of about 2 and the ion-exchange membranes A-F of the present invention had ~ of 1.8, 2.1, 2.4, 1.8, 2.1 and 2.3, respectively, it can be seen that no physical holes were made by rolling in these ion-exchange membranes.
Further, if the gas permeation rate of ion-exchange membrane is large in ion-exchange membrane fuel cells, hydrogen and oxygen which permeate the ion-exchange membrane (namely, cross-leak3 directly react on catalyst ,. , ~ ~ .;, ..
, - 2~6~7~
1 to cause deterioration of cell performance. The ion-exchange membranes A-F of the above examples increased in gas permeation rate, but the rate was such that caused no deterioration of cell performance.
In the above Examples 3 and 6, rolling was carried out at 50C, but the similar rasults were obtained by rolling at 120C or lower. When the ion-exchange membranes were rolled at higher than 120C, the membranes dried owing to the rapid evaporation of the organic solvent and thickness of the membranes was not reduced by the rolling. Thus, it can be seen that the effect of the present invention is obtained by the rolling at 120C or lower. Furthermore, the rolling was conducted at a rate of 14 cm/min in the above examples, but the similar results were obtained at a rolling rate of 30 cm/min or lower. When the ion-exchange membranes were rolled at a rate of higher than 30 cm/min, the membranes could not be uniformly rolled and were broken.
Thus, it can be seen that the effect of the present invention is obtained when a rolling rate of 30 cm/min or lower is employed.
Next, each of the ion-exchange membranes of the above examples and comparative examples and electrodes were hot pressed at 120 150C under 20-60 kg/cm2 to form an assembly of an anode, an ion-exchange membrane and a cathode. A single cell of ion-exchange membrane fuel cell as shown in Fig. 5 was fabricated using the result-ing assembly. In Fig. 5, 10 denotes the ion-exchange - 15 _ 2 ~
1 membrane and 11 and 12 denote the anode and the cathode, respectively. Both the electrodes were made by adding a solid polymer electrolyte to carbon powders which carried a platinum catalyst. The amount of platinum was 0.01-0.5 mg/cm2 and the amount of the solid polymer electrolyte added was 0.1-3.0 mg/cm2 per area for both the elec-trodes. hydrogen gas humidified at 90C was fed to the anode side and oxygen gas humidified at 80C was fed to the cathode side and discharge test of the cell was conducted.
Fig. 6 shows voltage-current characteristic curves of the ion-exchange membrane fuel cells in which the ion-exchange membranes of the abo~e examples and comparative examples were used. The fuel cells in which ion-exchange membranes A-F of the present invention were used showed cell voltages of 0.67 V, 0.64 V, 0.69 V, 0.67 V, 0.64 V and 0.69 V at 200 mA/cm2, xespectivelyO On the other hand, the fuel cells in which ion-exchange memb-ranes G and H of the comparative examples were used showed cell voltages of 0.53 V and 0.56 V at 200 mA/cm2, respectively.
In the above examples, NAFION was used as ion-exchange membrane, but the similar results were obtained also when other ion-exchange membranes comprising copolymers of perfluorovinyl ether and tetrafluoroethy-lene were used. Further, in the above examples, ion-exchange membranes were rolled in biaxial direction, but the similar results were obtained by rolling in monoaxial ~, 2 ~ 7 ~
1 direction. Moreover, ethanol and acetone were used as water-soluble organic solvents for swelling of ion~
exchange membranes, but the similar results were obtained by using at least one of water-soluble organic solvents such as methanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, methoxy ethanol, ethoxy ethanol, methyl ethyl ketone and the like.
In the above examples, hydrogen-oxygen fuel cell was taken up as one example of ion-exchange membrane fuel cells, but the present invention can also be applied to fuel cells which use hydrogen obtained by re~orming methanol, natural gas, naphtha, or the like as fuels and fuel cells which use air as an oxidizing agent.
As explained above, according to the present invention, an ion-exchange membrane is immersed in a water-soluble organic sol~ent ~r an aqueous solution thereof and is swollen ~herewith and is rolled or stretched in such a state that main chains of polymer easily slip from each other and ion clusters are formed, whereby the thickness of the membrane can be easily reduced and an ion-exchange membrane of high water content and low theet resistance can be obtained. Thus, ion-exchange membrane fuel cells which exhibit higher discharge characteristics can be realized.
Claims (13)
1. A method for processing an ion-exchange membrane which comprises immersing an ion-exchange membrane having a fluorine-containing polymer as a matrix in a water soluble organic solvent to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof.
2. A method according to claim 1, wherein the water-soluble solvent is at least one solvent selected from the group consisting of alcohols and ketones.
3. A method according to claim 2, wherein the alcohols are selected from the group consisting of methanol, ethanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, methoxy ethanol and ethoxy ethanol.
4. A method according to claim 2, wherein the ketones are selected from the group consisting of acetone and methyl ethyl ketone.
5. A method according to claim 1, wherein the water-soluble organic solvent is used as an aqueous solution.
6. A method according to claim 5, wherein concen-tration of the water-soluble organic solvent in the aqueous solution is 20 vol% of more.
7. A method according to claim 1, wherein the rolling or stretching is carried out at 120°C or lower.
8. A method according to claim 1, wherein the rolling and stretching is carried out at a rate of 30 cm/min or lower.
9. A method according to claim 1, wherein the reduction ratio of thickness of the ion-exchange membrane is 50% or less.
10. A method according to claim 1, wherein the ion-exchange membrane comprises a copolymer of perfluoro-vinyl ether and tetrafluoroethylene.
11. An ion-exchange membrane which has a water content of 30-50% and which is produced by immersing an ion-exchange membrane having a fluorine-containing polymer as a matrix in a water-soluble organic solvent or an aqueous solution thereof to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof.
12. An ion-exchange membrane according to claim 11, wherein the ion-exchange membrane comprises a copolymer of perfluorovinyl ether and tetrafluoroethylene.
13. An ion-exchange membrane fuel cell in which is used an ion-exchange membrane which has a water content of 30-50% and which is produced by immersing an ion-exchange membrane having a fluorine-containing polymer as a matrix in a water-soluble organic solvent or an aqueous solution thereof to swell the membrane and then, rolling or stretching the membrane to reduce the thickness thereof.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP04-003540 | 1992-01-13 | ||
| JP354092 | 1992-01-13 | ||
| JP04-057686 | 1992-03-16 | ||
| JP4057686A JPH05255522A (en) | 1992-01-13 | 1992-03-16 | Method of processing ion-exchange membrane, ion-exchange membrane, and fuel cell employing the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2068071A1 true CA2068071A1 (en) | 1993-07-14 |
Family
ID=26337146
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2068071 Abandoned CA2068071A1 (en) | 1992-01-13 | 1992-05-06 | Method for processing ion-exchange membrane, the ion-exchange membrane and fuel cells using same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2068071A1 (en) |
-
1992
- 1992-05-06 CA CA 2068071 patent/CA2068071A1/en not_active Abandoned
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