Method for manufacturing membrane electrode assembly for hydrogen fuel cell using two types of binders, and membrane electrode assembly manufactured by the method

Abstract

A method of manufacturing a membrane electrode assembly for hydrogen fuel cells includes mixing an electrode binder with a catalyst, followed by dispersing and thermal treatment, to prepare an electrode slurry, coating release paper with the electrode slurry to produce an electrode, and bonding the release paper-coated electrode to an electrolyte membrane, followed by thermal treatment, to perform electrode-membrane bonding.

Claims

1. A method of manufacturing a membrane electrode assembly for hydrogen fuel cells comprising steps of: mixing an electrode binder comprising a first ionomer and a second ionomer with a catalyst, drying a resultant mixture performing a first thermal treatment to the resultant mixture to prepare an electrode slurry; coating the electrode slurry on release paper to produce electrodes; placing the electrode electrodes in contact with an electrolyte membrane; and performing a second thermal treatment to the electrode and the electrolyte membrane to bond them; wherein the first ionomer has a higher -transition temperature than that of the second ionomer, the first thermal treatment is carried out at a temperature between the -transition temperature of the first ionomer and the -transition temperature of the second ionomer in presence of the first ionomer and the second ionomer for 30 minutes to 2 hours, and the second thermal treatment is carried out at a temperature not less than the -transition temperature of the first ionomer.

2. The method according to claim 1, wherein the first ionomer or the second ionomer includes a perfluorosulfonic acid (PFSA)-based ionomer.

3. The method according to claim 1, wherein the -transition temperature of the first ionomer having is higher than 140 C.

4. The method according to claim 1, wherein the -transition temperature of the second ionomer is lower than 120 C.

5. The method according to claim 3, wherein the thermal treatment in the step of preparing the electrode slurry is carried out at 130 C.

6. The method according to claim 3, wherein thermal treatment in the step of the electrode-membrane bonding is carried out at 150 C.

7. A membrane electrode assembly for hydrogen fuel cells manufactured by the method according to claim 1.

8. A hydrogen fuel cell comprising the membrane electrode assembly according to claim 7.

9. A method of manufacturing a membrane electrode assembly for hydrogen fuel cells comprising steps of: mixing an electrode binder with a catalyst, followed by dispersing, drying and thermal treatment, to prepare an electrode slurry; coating the electrode slurry on release paper to produce electrodes; and placing the electrodes in contact with an electrolyte membrane, followed by thermal treatment, to bond the electrodes and the electrolyte membrane, wherein the electrode binder comprises a first ionomer and a second ionomer in an amount which is 20% to 40% of a total amount of the first and second ionomers with respect to a total weight of the electrode slurry, an -transition temperature of the first ionomer is higher than an -transition temperature of the second ionomer, the thermal treatment in the step of preparing an electrode slurry is carried out at a temperature between the -transition temperature of the first ionomer and the -transition temperature of the second ionomer for 30 minutes to 2 hours, and the thermal treatment in the step of bonding the electrodes and the electrolyte membrane is carried out at a temperature not less than the -transition temperature of the first ionomer.

10. The method according to claim 9, wherein the thermal treatment in the step of bonding the electrodes and the electrolyte membrane is carried out at a temperature of 150 C. so that the second ionomer is crystallized by the thermal treatment in the step of bonding.

11. The method according to claim 9, wherein the -transition temperature of the first ionomer is higher than 140 C.

12. The method according to claim 9, wherein the first ionomer or the second ionomer includes a perfluorosulfonic acid (PFSA)-based ionomer.

13. The method according to claim 9, wherein the -transition temperature of the second ionomer is lower than 120 C.

14. The method according to claim 9, wherein the thermal treatment in the step of preparing the electrode slurry is carried out at 130 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

(2) FIG. 1 is an image showing two types of ionomer binders having different -transition temperatures applied to a catalyst/support according to one embodiment of the present disclosure.

(3) FIG. 2 is a flow chart of a method of manufacturing a membrane electrode assembly for hydrogen fuel cells.

DETAILED DESCRIPTION

(4) Hereinafter, reference will be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention to the exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. In the following description of the present disclosure, detailed descriptions of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present disclosure.

(5) The present disclosure provides a method of manufacturing a membrane electrode assembly for hydrogen fuel cells which includes: mixing an electrode binder with a catalyst, followed by dispersing and thermal treatment, to prepare an electrode slurry S10; coating release paper with the electrode slurry to produce an electrode S20; and bonding the release paper-coated electrode to an electrolyte membrane, followed by thermal treatment, to conduct electrode-membrane bonding S30, wherein the electrode binder includes two types of ionomers having different -transition temperature (T), the thermal treatment in the step of preparing the electrode slurry is carried out at a temperature between a T of an ionomer having a relatively high T and a T of an ionomer having a relatively low T, among the ionomers having different Ts, and the thermal treatment in the step of the electrode-membrane bonding is carried out at a temperature not less than the T of the ionomer having the relatively high T, among the ionomers having different Ts.

(6) Hereinafter, a method of manufacturing a membrane electrode assembly for hydrogen fuel cells according to an embodiment will be described in more detail.

(7) According to a conventional method, when a temperature not lower than an electrode binder T is applied after uniformly coating the catalyst/support, the structure of the catalyst-support-binder becomes robust, but crystallinity of the binder is provided under the condition that the morphology of the binder is changed, thus causing a problem of lowering interfacial bonding strength upon bonding of the electrode-membrane. In addition, it is necessary that the temperature at which the electrode is bonded to the membrane by decal (release transfer) is not higher than the T of the electrolyte membrane so that the crystallinity of the electrolyte membrane can be maintained. At this time, a temperature which is higher than T of an electrode binder should be applied in order to improve ease of electrode-membrane bonding and interfacial bonding strength. Moreover, thermal treatment involved in the post-process after the electrode-membrane bonding is conducted at a temperature not less than T of the electrolyte membrane and the electrode binder in order to improve interfacial bonding strength. However, in the process of manufacturing an electrode, the crystallinity of the binder is already improved. For this reason, there is a limitation on improving interfacial bonding strength.

(8) Accordingly, the present inventors found from testing that electrode-membrane bonding can be facilitated, mechanical robustness can be maintained due to improved interfacial bonding strength of the membrane electrode assembly, and deterioration in performance can be retarded by using different two types of ionomers having different Ts in the process of manufacturing a membrane electrode assembly for hydrogen fuel cells, thereby completing the present disclosure.

(9) Regarding the method of manufacturing a membrane electrode assembly for hydrogen fuel cells according to one embodiment of the present disclosure, an electrode binder includes two types of ionomers having different Ts, and the thermal treatment in the step of preparing the electrode slurry is carried out at a temperature between a T of an ionomer having a relatively high T and a T of an ionomer having a relatively low T, among the ionomers having different Ts, and the thermal treatment in the process of the electrode-membrane bonding is carried out at a temperature not less than the T of the ionomer having the relatively high T, among the ionomers having different Ts.

(10) In a conventional method, in the process of preparing an electrode slurry (catalyst+support+binder), catalyst/support was coated at a temperature not less than the electrode binder T. At this time, crystallinity of the binder is created under the condition that the morphology of the binder is changed, thus causing a problem of lowering interfacial bonding strength, upon bonding of the electrode-membrane, which is disadvantageous under freezing and thawing environments.

(11) In an attempt to solve these problems, there is a method of improving binding strength by changing the roughness of the bonding surface to a level of several nanometers in order to produce an electrode with excellent interfacial bonding strength. However, this method has a drawback of considerably poor applicability to mass-production.

(12) According to one embodiment of the present disclosure, it is possible to provide a method of manufacturing a membrane electrode assembly for hydrogen fuel cells which can ensure robustness and ease of electrode-membrane bonding as well as improve interfacial bonding strength by using ionomers having different thermal properties (T) as electrode binders.

(13) Meanwhile, the ionomer may be a fluorine-based ionomer, preferably a perfluorosulfonic acid (PFSA)-based ionomer.

(14) In generally, the T of a PFSA-based ionomer is determined by the length of a side-chain attached to a main chain and, as the length of the side-chain increases, the T decreases. In addition, the amount of side-chain attached to the main chains well as the length of side-chain determines equivalent EW) which also affects a T.

(15) According to the present invention, specifically, a mixture of PFSA ionomers having different T is applied as the electrode binder, the thermal treatment in the step of preparing the electrode slurry is carried out at a temperature between a T of an ionomer having a relatively high T and a T of an ionomer having a relatively low T, among the ionomers having different Ts, and the thermal treatment in the process of electrode-membrane bonding is carried out at a temperature not less than the T of the ionomer having the relatively high T, among the ionomers having different Ts.

(16) FIG. 1 is an image showing two types of ionomer binders having different Ts applied to a catalyst/support according to one embodiment of the present disclosure.

(17) The ionomer having a relatively high T, among the ionomers having different Ts, acquires crystallinity by thermal treatment in the process of preparing an electrode slurry. At this time, the ionomer having a relatively high T functions to strongly bind the catalyst-support-binder structure.

(18) Meanwhile, the ionomer having a relatively low T is crystallized by thermal treatment in the process of electrode-membrane bonding. Such an ionomer functions to improve interfacial bonding strength upon catalyst-support coating and electrode-membrane bonding.

(19) The T of the ionomer having a relatively high T, among the ionomers having different Ts, may be higher than 140 C.

(20) In addition, the T of the ionomer having a relatively low T, among the ionomers having different Ts, may be lower than 120 C.

(21) When both the ionomer having a T lower than 120 C. and the ionomer having a T higher than 140 C. are used, thermal treatment in the step of preparing the electrode slurry is preferably performed at 130 C.

(22) In addition, when both the ionomer having a T lower than 120 C. and the ionomer having a T higher than 140 C. are used, thermal treatment in the process of electrode-membrane bonding is preferably performed at 150 C.

(23) As described above, the ionomer having a relatively high T, among the ionomers having different Ts acquires crystallinity by thermal treatment in the step of preparing the electrode slurry. Accordingly, the ionomer having a relatively high T functions to strongly bind the catalyst-support-binder structure. Meanwhile, the ionomer having a relatively low T is crystallized by thermal treatment in the step of electrode-membrane bonding. Accordingly, such an ionomer performs functions to improve interfacial bonding strength upon catalyst-support coating and electrode-membrane bonding.

(24) As a result, by using two types of ionomers and controlling thermal treatment temperature, the bonding structure of the catalyst-support-binder can be reinforced so that robustness of the electrode can be ensured, the low-crystallinity ionomer contained in the electrode binder has relatively strong bonding strength so that the ease of electrode-membrane bonding can be improved, and interfacial bonding strength of the membrane electrode assembly is enhanced so that mechanical robustness can be maintained and deterioration in performance can be delayed.

(25) Meanwhile, the same effects as described above can be obtained although replacing two types of ionomers having different Ts with a thermoplastic ionomer and a thermosetting ionomer, respectively.

(26) According to another embodiment of the present disclosure, provided are a membrane electrode assembly for hydrogen fuel cells produced by the method described above, and a hydrogen fuel cell including the same.

(27) Meanwhile, a decal process, rather than direct coating, may be used for bonding to an electrode electrolyte membrane using a certain ionomer having a T lower than 120 C. (DuPont Corp., Nafion, T: 105115 C.) and a certain ionomer having a T higher than 140 C. (Solvay Corp., Aquivion, T: about 140 C., ionomer based on hydrocarbon such as sulfonated polyetheretherketone or sulfonated polysulfone, T: 140250 C.).

(28) To produce an electrode, a platinum catalyst supported on carbon is mixed with two types of ionomers, followed by homogeneously dispersing. At this time, the total amount of ionomer is 20 to 40% (on a weight basis) with respect to the total weight of the dispersion. This dispersion is referred to as an electrode slurry and thermal treatment is incorporated in order to induce suitable bonding of the incorporated ionomer to the surface of the platinum catalyst supported on carbon and improve the molecular structural crystallinity of the ionomer. After the electrode slurry is completely dried, thermal treatment is conducted at a thermal treatment temperature of 130 C. for 30 minutes to 2 hours, so that the ionomer having a T lower than 120 C. can be sufficiently affected by the thermal treatment and the ionomer having a T higher than 140 C. can maintain the crystallinity. The electrode cake subjected to drying and thermal treatment is dispersed in an organic solvent (mix solution containing at least one solvent of water, ethanol and propanol), and a release film (PEN, PET, PI or the like) is directly coated with the electrode slurry thus formed and then dried, to produce a transferable electrode.

(29) The electrode thus produced is transferred from release paper to the electrolyte membrane to produce a membrane-electrode assembly. In this case, the electrode is bonded to the electrolyte membrane at a pressure of 80 to 150 kgf and at 80 to 110 C. The ionomer having a T higher than 140 C. which did not undergo increase in crystallinity during initial thermal treatment (120 C.) is soft and thus provides an effect of improving interface bonding strength, as compared to the case of incorporating an ionomer with improved crystallinity. In order to further improve interfacial bonding strength between the electrode and the electrolyte membrane after the membrane-electrode bonding, thermal treatment is performed at 150 to 180 C. for 30 seconds to 5 minutes. At this time, by using a temperature higher than Ts of the two types of ionomers, rubber-like property is imparted to the ionomer and, upon cooling, high crystallinity is imparted thereto, so that the interface bonding strength of the membrane-electrode as well as the mechanical robustness of the electrode can be improved.

(30) As apparent from the foregoing, the membrane electrode assembly for hydrogen fuel cells manufactured by the method according to the present disclosure has a reinforced bonding structure of catalyst-support-binder, thus being effective in ensuring robustness and ease of electrode-membrane bonding, maintaining mechanical robustness based on improved interfacial bonding strength of electrode-membrane assembly and delaying deterioration in performance.

(31) The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.