Polymer electrolyte membrane and membrane-electrode assembly for polymer electrolyte fuel cell

Abstract

A polymer electrolyte membrane which comprises a polymer electrolyte having sulfonic acid groups, and contains any one of the following (a) to (c): (a) cerium ions and an organic compound (X) capable of forming an inclusion compound with cerium ions; (b) an inclusion compound (Y) comprising the organic compound (X) including cerium ions; and (c) at least one of cerium ions and the organic compound (X), and the inclusion compound (Y).

Claims

1. A polymer electrolyte membrane which comprises a polymer electrolyte having sulfonic acid groups, and contains at least one of the following (a), (b), (c1), (c2) and (c3): (a) cerium ions and an organic compound (X) capable of forming an inclusion compound with cerium ions, wherein the organic compound (X) is a calixerene, crown ether or cyclodextrin, (b) an inclusion compound (Y) comprising the organic compound (X) and cerium ions, (c1) cerium ions and the inclusion compound (Y), (c2) the organic compound (X) and the inclusion compound (Y), and (c3) cerium ions, the organic compound (X) and the inclusion compound (Y).

2. The polymer electrolyte membrane according to claim 1, wherein the organic compound (X) is a crown ether.

3. The polymer electrolyte membrane according to claim 2, Wherein the crown ether is at least one crown ether selected from the group consisting of 15-crown-5, 18-crown-6 and an organic compound having such a structure in its molecule.

4. The polymer electrolyte membrane according to claim 1, which contains cerium ions and the organic compound (X) (provided that the inclusion compound (Y) is regarded as a mixture of them) in a total amount of from 0.5 to 80 mass %.

5. The polymer electrolyte membrane according to claim 2, which contains cerium ions and the organic compound (X) (provided that the inclusion compound (Y) is regarded as a mixture of them) in a total amount of from 0.5 to 80 mass %.

6. The polymer electrolyte membrane according to claim 3, which contains cerium ions and the organic compound (X) (provided that the inclusion compound (Y) is regarded as a mixture of them) in a total amount of from 0.5 to 80 mass %.

7. The polymer electrolyte membrane according to claim 1, which contains the organic compound (X) in a ratio of from 0.2 to 1.2 mole per mole of the cerium ions (provided that the inclusion compound (Y) is regarded as a mixture of them).

8. The polymer electrolyte membrane according to claim 2, which contains the organic compound (X) in a ratio of from 0.2 to 1.2 mole per mole of the cerium ions (provided that the inclusion compound (Y) is regarded as a mixture of them).

9. The polymer electrolyte membrane according to claim 3, which contains the organic compound (X) in a ratio of from 0.2 to 1.2 mole per mole of the cerium ions (provided that the inclusion compound (Y) is regarded as a mixture of them).

10. The polymer electrolyte membrane according to claim 4, which contains the organic compound (X) in a ratio of from 0.2 to 1.2 mole per mole of the cerium ions (provided that the inclusion compound (Y) is regarded as a mixture of them).

11. The poly er electrolyte membrane according to claim 5, which contains the organic compound (X) in a ratio of from 0.2 to 1.2 mole per mole of the cerium ions (provided that the inclusion compound (Y) is regarded as a mixture of them).

12. The polymer electrolyte membrane according to claim 6, which contains the organic compound (X) in a ratio of from 0.2 to 1.2 mole per mole of the cerium ions (provided that the inclusion compound (Y) is regarded as a mixture of them).

13. The polymer electrolyte membrane according to claim 1, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

14. The polymer electrolyte membrane according to claim 2, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

15. The polymer electrolyte membrane according to claim 3, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

16. The poly er electrolyte membrane according to claim 4, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

17. The polymer electrolyte membrane according to claim 5, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

18. The polymer electrolyte membrane according to claim 6, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

19. The polymer electrolyte membrane according to claim 7, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

20. The polymer electrolyte membrane according to claim 8, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

21. The polymer electrolyte membrane according to claim 9, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

22. The polymer electrolyte membrane according to claim 10, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

23. The polymer electrolyte membrane according to claim 11, wherein the polymer electrolyte is a sulfonic acid group-containing perfluorocarbon polymer.

24. A membrane-electrode assembly for a fuel cell, which comprises a layer of a polymer electrolyte membrane Which comprises a polymer electrolyte having sulfonic acid groups and contains at least one of the following (a), (b), (c1), (c2) and (c3), and a catalyst layer containing a catalyst, an electrically conductive material and an ion exchange resin, provided on both sides of the polymer electrolyte membrane: (a) cerium ions and an organic compound (X) capable of forming an inclusion compound with cerium ions, wherein the organic compound (X) is a calixerene, crown ether or cyclodextrin, (b) an inclusion compound comprising the organic compound (X) and cerium ions, (c1) cerium ions and the inclusion compound (Y), (c2) the organic compound (X) and the inclusion compound (Y), and (c3) cerium ions, the organic compound (X) and the inclusion compound (Y).

25. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the organic compound (X) is a crown ether.

26. The membrane-electrode assembly for a fuel cell according to claim 25, wherein the crown ether is at least one crown ether selected from the group consisting of 15-crown-5, 18-crown-6 and an organic compound having such a structure in its molecule.

27. The membrane-electrode assembly for a fuel cell according to claim 24, which further has a gas diffusion layer outside the both catalyst layers.

28. The membrane-electrode assembly for a fuel cell according to claim 25, which further has a gas diffusion layer outside the both catalyst layers.

29. The membrane-electrode assembly for a fuel cell according to claim 26, which further has a gas diffusion layer outside the both catalyst layers.

30. The polymer electrolyte membrane according to claim 1, which comprises (a).

31. The polymer electrolyte membrane according to claim 1, which comprises (b).

32. The polymer electrolyte membrane according to claim 1, which comprises (c1).

33. The polymer electrolyte membrane according to claim 1, which comprises (c2).

34. The polymer electrolyte membrane according to claim 1, which comprises (c3).

35. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the polymer electrolyte membrane comprises (a).

36. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the polymer electrolyte membrane comprises (b).

37. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the polymer electrolyte membrane comprises (c1).

38. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the polymer electrolyte membrane comprises (c2).

39. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the polymer electrolyte membrane comprises (c3).

40. The polymer electrolyte membrane according to claim 1, wherein the inclusion compound (Y) is trivalent or tetravalent.

41. The membrane-electrode assembly for a fuel cell according to claim 24, wherein the inclusion compound (Y) is trivalent or tetravalent.

Description

EXAMPLE 1

(1) 300 g of a perfluorocarbon polymer having sulfonic acid groups (ion exchange capacity: 1.1 meq/g dry resin), 420 g of ethanol and 280 g of water were charged in a 2 L autoclave, sealed hermetically and stirred by a double helical blade at 105 C. for 6 hours to obtain a uniform liquid (hereinafter referred to as solution A). The solid content concentration of solution A was 30 mass %.

(2) 100 g of solution A and 1.00 g of cerium carbonate hydrate (Ce.sub.2(CO.sub.3).sub.3.8H.sub.2O) were charged into a 300 ml round-bottomed flask made of glass and stirred at room temperature for 8 hours by a meniscus blade made of PTFE. Bubbles due to generation of CO.sub.2 were generated from the start of stirring, and uniform transparent liquid composition C was finally obtained.

(3) The above composition C was applied to a 100 m ETFE sheet (AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited) by cast coating with a die coater, preliminarily dried at 80 C. for 10 minutes and dried at 120 C. for 10 minutes and further annealed at 150 C. for 30 minutes to obtain a polymer electrolyte membrane having a thickness of 50 m.

(4) From this electrolyte membrane, a membrane having a size of 5 cm5 cm was cut out and left to stand in dry nitrogen for 16 hours, and then the membrane was ashed and subjected to measurement by ICP spectrometry to quantitatively analyze the amount of cerium in the polymer electrolyte membrane for confirmation and as a result, the amount of cerium was 1.5% which corresponds to the addition amount of cerium carbonate hydrate based on the mass of the membrane.

(5) Then, as a crown ether, 0.87 g of 18-crown-6 manufactured by SIGMA ALDRICH Japan K.K. was added to the above liquid composition C, followed by stirring at room temperature for 24 hours to obtain uniform transparent liquid composition D. The solid content concentration of the obtained liquid composition D was 30.9 mass %.

(6) The above composition D was applied to a 100 m ETFE sheet (AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited) by cast coating with a die coater, preliminarily dried at 80 C. for 10 minutes and dried at 120 C. for 10 minutes and further annealed at 150 C. for 30 minutes to obtain a polymer electrolyte membrane having a thickness of 50 m.

(7) Here, since the content of 0.87 g of 18-crown-6 added to prepare the above-described liquid composition D in the membrane corresponds to 2.8% based on the mass of the membrane, it was found that 1.5% of cerium and 2.8% of 18-crown-6, i.e. totally 4.3% of them are contained based on the mass of the membrane.

(8) Then, 5.1 g of distilled water was mixed with 1.0 g of a carbon black powder having platinum fine particles supported on a carbon black carrier (specific surface area: 800 m.sup.2/g) (amount of platinum fine particles supported: 50%, manufactured by N.E. CHEMCAT CORPORATION). With this liquid mixture, 5.6 g of a liquid having a perfluorocarbon polymer having sulfonic acid groups (ion exchange capacity: 1.1 meq/g dry resin) dispersed in ethanol, having a solid content concentration of 9 mass %, was mixed. This mixture was homogenized by using a homogenizer (Polytron, tradename, manufactured by Kinematica Company) to prepare coating fluid E for forming a catalyst layer.

(9) This coating fluid E was applied on a substrate film made of polypropylene with a bar coater, and dried in a dryer at 80 C. for 30 minutes to prepare a catalyst layer. The amount of platinum per unit area contained in the catalyst layer was calculated by measuring the mass of the substrate film alone before formation of a catalyst layer and the mass of the substrate film after formation of the catalyst layer and as a result, it was 0.5 mg/cm.sup.2.

(10) Then, using the above-described polymer electrolyte membrane containing cerium and 18-crown-6, the above catalyst layers formed on the substrate film were disposed on both sides of the membrane and transferred by hot press method to obtain a membrane-catalyst layer assembly having an anode catalyst layer and a cathode catalyst layer bonded to both sides of the polymer electrolyte membrane. The electrode area was 16 cm.sup.2.

(11) This membrane-catalyst layer assembly was interposed between two gas diffusion layers made of carbon cloth having a thickness of 350 m to prepare a membrane-electrode assembly, which was assembled into a cell for power generation, and an open circuit voltage test (OCV test) was carried out as an accelerated test. In the test, hydrogen (utilization ratio: 70%) and air (utilization ratio: 40%) corresponding to a current density of 0.2 A/cm.sup.2 were supplied under ambient pressure to the anode and to the cathode, respectively, the cell temperature was set at 90 C., the dew point of the anode gas was set at 60 C. and the dew point of the cathode gas was set at 60 C., the cell was operated for 100 hours in an open circuit state without generation of electric power, and a voltage change was measured during the period. Furthermore, by supplying hydrogen to the anode and nitrogen to the cathode, amounts of hydrogen gas having leaked from the anode to the cathode through the membrane were analyzed before and after the test, thereby to check the degree of degradation of the membrane. The results are shown in Table 1.

(12) Then, a membrane-electrode assembly was prepared and assembled into a cell for power generation in the same manner as above, and a durability test under operation conditions under low humidification was carried out. The test conditions were as follows. Hydrogen (utilization ratio: 70%)/air (utilization ratio: 40%) was supplied under ambient pressure at a cell temperature of 80 C. and at a current density of 0.2 A/cm.sup.2, and the polymer electrolyte fuel cell was evaluated as to the initial property and durability. Hydrogen and air were so humidified and supplied into the cell that the dew point on the anode side was 80 C. and that the dew point on the cathode side was 50 C., respectively, whereupon the cell voltage at the initial stage of the operation and the relation between the elapsed time after the initiation of the operation and the cell voltage were measured. The results are shown in Table 2. In addition, the cell voltage at the initial stage of the operation and the relation between the elapsed time after the initiation of the operation and the cell voltage were also measured in the same manner as above under the above cell evaluation conditions except that the dew point on the cathode side was changed to 80 C. The results are shown in Table 3.

(13) Then, a membrane-electrode assembly was prepared and assembled into a cell for power generation in the same manner, and a durability test under operation conditions under low humidification at 120 C. was carried out. The test conditions were as follows. The anode and the cathode were pressurized under 200 kPa, hydrogen (utilization ratio: 50%)/air (utilization ratio: 50%) was supplied at a cell temperature of 120 C. and at a current density of 0.2 A/cm.sup.2, and the polymer electrolyte fuel cell was evaluated as to the initial property and durability. Hydrogen and air were so humidified and supplied into the cell that the dew point on the anode side was 100 C. and that the dew point on the cathode side was 100 C., respectively, whereupon the cell voltage at the initial stage of the operation and the relation between the elapsed time after the initiation of the operation and the cell voltage were measured. The results are shown in Table 4.

EXAMPLE 2

(14) Using uniform transparent liquid composition C prepared in the same manner as in Example 1, 0.73 g of 15-crown-5 manufactured by SIGMA ALDRICH Japan K.K. as a crown ether in an equimolar amount to cerium in the cerium carbonate hydrate was added to the above uniform transparent liquid composition C, followed by stirring at room temperature for 24 hours to obtain uniform transparent liquid composition F. Then, in the same manner as in Example 1, it was found that the total mass of cerium and 15-crown-5 was 3.9% based on the membrane.

(15) Then, a polymer electrolyte membrane having a thickness of 50 m was prepared in the same manner as in Example 1 except that the above liquid composition F was used, and electrode layers were bonded to the membrane in the same manner as in Example 1 to prepare a membrane-electrode assembly, and the same evaluations as in Example 1 were carried out. The results are shown in Tables 1 to 4.

EXAMPLE 3

(16) As a polymer electrolyte membrane, an ion exchange membrane having a thickness of 50 m, made of a perfluorocarbon polymer having sulfonic acid groups (ion exchange capacity: 1.1 meq/g dry resin) in a size of 5 cm5 cm (area: 25 cm.sup.2) was used. The weight of the entire membrane after left to stand in dry nitrogen for 16 hours was measured in dry nitrogen and was 0.251 g. The amount of sulfonic acid groups in the membrane is determined in accordance with the following formula:

(17) 0.2511.1 (1.1 meq/g dry resin)=0.276 (meq).

(18) Then, 24.0 mg of cerium(III) nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O) was dissolved in 500 ml of distilled water so that cerium ions (trivalent) in an amount corresponding to 60% of the amount of sulfonic acid groups in the membrane were contained, and the above ion exchange membrane was immersed in the solution, followed by stirring with a stirrer at room temperature for 40 hours so that part of sulfonic acid groups in the ion exchange membrane were ion-exchanged with cerium ions. The cerium(III) nitrate solution before and after the immersion was analyzed by ion chromatography and as a result, the ion exchange rate of the ion exchange membrane with cerium ions (the ratio of SO.sub.3.sup. groups exchanged with cerium ions to the total number of SO.sub.3.sup. groups originally present in the membrane) was found to be 58%. The cerium content in the membrane was 2.94 mass %. The membrane was immersed in a 1 mol/L phosphoric acid aqueous solution at room temperature for 60 hours and as a result, precipitation of cerium phosphate in the membrane was confirmed by X-ray diffraction. Then, using the membrane, electrode layers were bonded to the membrane in the same manner as in Example 1 to prepare a membrane-electrode assembly, and the same evaluations as in Example 1 were carried out. The results are shown in Tables 1 to 4.

EXAMPLE 4

(19) 100 g of solution A and 0.87 g of 18-crown-6 manufactured by SIGMA ALDRICH Japan K.K. were charged into a 300 ml round-bottomed flask made of glass and stirred at room temperature for 24 hours by a meniscus blade made of PTFE to obtain uniform transparent liquid composition F. The obtained composition F was applied to a 100 m ETFE sheet (AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited) by cast coating with a die coater, preliminarily dried at 80 C. for 10 minutes and dried at 120 C. for 10 minutes and further annealed at 150 C. for 30 minutes to obtain a polymer electrolyte membrane having a thickness of 50 m.

(20) Then, using the membrane, electrode layers were bonded to the membrane in the same manner as in Example 1 to prepare a membrane-electrode assembly, and the same evaluations as in Example 1 were carried out. The results are shown in Tables 1 to 4.

EXAMPLE 5

(21) Using, as a polymer electrolyte membrane, the same ion exchange membrane as used in Example 3 without any treatment, a membrane-electrode assembly was prepared in the same manner as in Example 1. With respect to the membrane-electrode assembly, the same evaluations as in Example 1 were carried out. The results are shown in Tables 1 to 4.

(22) TABLE-US-00001 TABLE 1 Open circuit voltage (V) Hydrogen leak (ppm) Initial After 100 hrs Initial After 100 hrs Example 1 0.99 0.98 700 720 Example 2 0.99 0.99 700 710 Example 3 0.98 0.90 730 4000 Example 4 0.93 0.60 900 25000 Example 5 0.94 0.51 1000 40000

(23) TABLE-US-00002 TABLE 2 Initial output Durability/output voltage (V) voltage (V) After 500 hrs After 2000 hrs Example 1 0.77 0.77 0.76 Example 2 0.77 0.76 0.76 Example 3 0.73 0.72 0.70 Example 4 0.73 0.62 0.55 Example 5 0.73 0.58 0.50

(24) TABLE-US-00003 TABLE 3 Initial output Durability/output voltage (V) voltage (V) After 500 hrs After 2000 hrs Example 1 0.78 0.78 0.78 Example 2 0.78 0.78 0.77 Example 3 0.75 0.73 0.72 Example 4 0.74 0.70 0.64 Example 5 0.72 0.60 0.55

(25) TABLE-US-00004 TABLE 4 Initial output Durability/output voltage (V) voltage (V) After 500 hrs After 2000 hrs Example 1 0.77 0.73 0.68 Example 2 0.77 0.74 0.69 Example 3 0.68 0.62 Power generation impossible Example 4 0.73 Power Power generation generation impossible impossible Example 5 0.73 Power Power generation generation impossible impossible

(26) It was confirmed from the above results of Examples and Comparative Examples that the open circuit voltage test (OCV test) under high temperature and low humidification conditions as an acceleration test resulted in deterioration of the conventional electrolyte membranes and increase of hydrogen leak due to hydrogen peroxide or peroxide radials formed on the anode and the cathode, but exhibited the dramatically excellent durability of the electrolyte membrane of the present invention.

(27) The electrolyte membrane of the present invention is very excellent in durability against hydrogen peroxide or peroxide radicals formed by power generation of a fuel cell. Accordingly, a polymer electrolyte fuel cell provided with a membrane-electrode assembly having the electrolyte membrane of the present invention has durability over a long period of time either in power generation under low humidification and in power generation under high humidification.

(28) The entire disclosure of Japanese Patent Application No. 2006-316308 filed on Nov. 22, 2006 including specification, claims and summary is incorporated herein by reference in its entirety.