Ionomer for Fuel Cell Capable of Self-Assembly and Method of Preparing the Same

Abstract

An embodiment ionomer for a fuel cell includes a copolymer having no carbon-oxygen bond, wherein the copolymer includes hydrophilic moieties disposed at both ends, wherein each hydrophilic moiety includes a styrene unit and a proton conductive functional group, and a hydrophobic moiety interposed between the hydrophilic moieties, wherein the hydrophobic moiety includes an ethylene-based unit, a butylene-based unit, an isoprene-based unit, or any combination thereof.

Claims

1. An ionomer for a fuel cell, the ionomer comprising: a copolymer having no carbon-oxygen bond, wherein the copolymer comprises: hydrophilic moieties disposed at both ends, wherein each hydrophilic moiety comprises a styrene unit and a proton conductive functional group; and a hydrophobic moiety interposed between the hydrophilic moieties, wherein the hydrophobic moiety comprises an ethylene-based unit, a butylene-based unit, an isoprene-based unit, or any combination thereof.

2. The ionomer according to claim 1, wherein the copolymer has a micelle structure, wherein the hydrophobic moiety is located inside of the micelle structure and the hydrophilic moieties are located outside of the micelle structure.

3. The ionomer according to claim 1, wherein the proton conductive functional group comprises a sulfonic acid group.

4. The ionomer according to claim 1, wherein the copolymer comprises a compound represented by ##STR00009## wherein x.sub.1=x?a, x.sub.2=x?(1?a), a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein x.sub.1=x?(1?a), x.sub.2=x?a, a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein y is a number from 10 to 1,000; wherein z is a number from 10 to 1,000; and wherein n is a number from 2 to 12.

5. A method of forming the fuel cell comprising the ionomer of claim 1, the method comprising: providing an electrolyte membrane; disposing a cathode on a first surface of the electrolyte membrane; and disposing an anode on a second surface of the electrolyte membrane; and wherein the electrolyte membrane, the cathode, or the anode comprises the ionomer.

6. The method according to claim 5, wherein the copolymer has a micelle structure, wherein the hydrophobic moiety is located inside of the micelle structure and the hydrophilic moieties are located outside of the micelle structure.

7. The method according to claim 5, wherein the proton conductive functional group comprises a sulfonic acid group.

8. The method according to claim 5, wherein the copolymer comprises a compound represented by ##STR00010## wherein x.sub.1=x?a, x.sub.2=x?(1?a), a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein x.sub.1=x?(1?a), x.sub.2=x?a, a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein y is a number from 10 to 1,000; wherein z is a number from 10 to 1,000; and wherein n is a number from 2 to 12.

9. A fuel cell comprising: an electrolyte membrane; a cathode disposed on a first surface of the electrolyte membrane; and an anode disposed on a second surface of the electrolyte membrane; and wherein the electrolyte membrane, the cathode, or the anode comprises an ionomer comprising a copolymer having no carbon-oxygen bond, wherein the copolymer comprises: hydrophilic moieties disposed at both ends, wherein each hydrophilic moiety comprises a styrene unit and a proton conductive functional group; and a hydrophobic moiety interposed between the hydrophilic moieties, wherein the hydrophobic moiety comprises an ethylene-based unit, a butylene-based unit, an isoprene-based unit, or any combination thereof.

10. The fuel cell according to claim 9, wherein the copolymer has a micelle structure, wherein the hydrophobic moiety is located inside of the micelle structure and the hydrophilic moieties are located outside of the micelle structure.

11. The fuel cell according to claim 9, wherein the proton conductive functional group comprises a sulfonic acid group.

12. The fuel cell according to claim 9, wherein the copolymer comprises a compound represented by ##STR00011## wherein x.sub.1=x?a, x.sub.2=x?(1?a), a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein x.sub.1=x?(1?a), x.sub.2=x?a, a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein y is a number from 10 to 1,000; wherein z is a number from 10 to 1,000; and wherein n is a number from 2 to 12.

13. A method for preparing an ionomer for a fuel cell, the method comprising: reacting a starting material comprising chloromethylated styrene ethylene-butylene styrene (CMSEBS) and a monomer having a sulfonic acid-protecting group to obtain an intermediate material represented by ##STR00012## and removing the sulfonic acid-protecting group from the intermediate material to obtain the ionomer represented by ##STR00013## wherein x.sub.1=x?a, x.sub.2=x?(1?a), a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein x.sub.1=x?(1?a), x.sub.2=x?a, a is a number from 0.1 to 0.9, and x is a number from 10 to 1,000; wherein y is a number from 10 to 1,000; wherein z is a number from 10 to 1,000; and wherein n is a number from 2 to 12.

14. The method according to claim 13, wherein the monomer having the sulfonic acid-protecting group comprises a compound represented by ##STR00014##

15. The method according to claim 13, wherein the starting material further comprises copper halide and 2,2-bipyridine.

16. The method according to claim 13, wherein the starting material further comprises copper halide and 2,2-bipyridine in a mole ratio of 1:1 to 1:3.

17. The method according to claim 13, wherein the intermediate material is obtained by reacting the starting material at a temperature of 50? C. to 150? C. for 1 hour to 48 hours.

18. The method according to claim 13, wherein the ionomer is obtained by removing the sulfonic acid-protecting group by heat-treating the intermediate material at a temperature of 100? C. to 200? C. for 1 hour to 4 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other features of embodiments 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 hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

[0023] FIG. 1 shows self-assembly of an ionomer according to embodiments of the present disclosure;

[0024] FIG. 2A shows a membrane according to Example 1 (n=2);

[0025] FIG. 2B shows a membrane according to Example 2 (n=5);

[0026] FIG. 2C shows a membrane according to Example 3 (n=7);

[0027] FIG. 3 shows an electrolyte membrane according to Example 2 (n=5);

[0028] FIG. 4 shows proton conductivity of the electrolyte membranes according to Examples 1, 2 and 4, and Nation 211;

[0029] FIG. 5 shows self-assembly behavior of the ionomer according to Example 2;

[0030] FIG. 6A shows the microstructures and self-assembly behaviors of the electrolyte membranes according to Examples 1, 2 and 4 before heat treatment; and

[0031] FIG. 6B shows the microstructures and self-assembly behaviors of the electrolyte membranes according to Examples 1 to 4 after heat treatment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0032] The embodiments described above, and other embodiments, features and advantages, will be clearly understood from the following preferred embodiments with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments, and will be embodied in different forms. The embodiments are suggested only to offer a thorough and complete understanding of the disclosed contents and to sufficiently inform those skilled in the art of the technical concept of the present disclosure.

[0033] Like reference numbers refer to like elements throughout the description of the figures. In the drawings, the sizes of structures are exaggerated for clarity. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be construed as being limited by these terms, and are used only to distinguish one element from another. For example, within the scope defined by the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. Singular forms are intended to include plural forms as well, unless the context clearly indicates otherwise.

[0034] It will be further understood that the terms comprises, has and the like, when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, components or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof. In addition, it will be understood that, when an element such as a layer, film, region or substrate is referred to as being on another element, it can be directly on the other element, or an intervening element may also be present. It will also be understood that, when an element such as a layer, film, region or substrate is referred to as being under another element, it can be directly under the other element or an intervening element may also be present.

[0035] Unless the context clearly indicates otherwise, all numbers, figures and/or expressions that represent ingredients, reaction conditions, polymer compositions and amounts of mixtures used in the specification are approximations that reflect various uncertainties of measurement occurring inherently in obtaining these figures, among other things. For this reason, it should be understood that, in all cases, the term about should be understood to modify all numbers, figures and/or expressions. In addition, when numeric ranges are disclosed in the description, these ranges are continuous and include all numbers from the minimum to the maximum including the maximum within the ranges unless otherwise defined. Furthermore, when a range refers to integers, it includes all integers from the minimum to the maximum including the maximum within the range, unless otherwise defined.

[0036] The ionomer for a fuel cell according to embodiments of the present disclosure may include a hydrocarbon-based copolymer having no carbon-oxygen bond.

[0037] The copolymer may include hydrophilic moieties disposed at both ends and a hydrophobic moiety disposed therebetween. Based on this configuration, the ionomer may undergo self-assembly.

[0038] FIG. 1 shows self-assembly of the ionomer according to embodiments of the present disclosure. Since the ionomer includes the hydrophilic moieties (A) and the hydrophobic moiety (B), it may have a micelle structure in which the hydrophobic moiety (B) is located inside and each hydrophilic moiety (A) is located outside. The micelle structure is not limited to FIG. 1 and the hydrophilic moiety (A) may be located inside and the hydrophobic moiety (B) may be located outside depending on the polarity and type of the solvent.

[0039] The hydrophilic moiety may include a styrene unit.

[0040] The hydrophilic moiety may include a proton conductive functional group. The proton conductive functional group may include at least one selected from the group consisting of a carboxyl group, a phosphoric acid group, a sulfonic group, and a combination thereof, and may preferably include a sulfonic acid group.

[0041] The hydrophobic moiety may include at least one selected from the group consisting of an ethylene-based unit, a butylene-based unit, an isoprene-based unit, and a combination thereof.

[0042] The copolymer may include a compound represented by the following Formula 1.

##STR00004##

wherein x.sub.1=x?a, x.sub.2=x?(1?a), a is a number from 0.1 to 0.9, x is a number from 10 to 1,000, x is the number of moles of the hydrophilic moiety located at one end of the copolymer, and a is a ratio of units substituted with a sulfonic acid group to such a hydrophilic moiety.

[0043] In Formula 1, x.sub.1=x?(1?a), x.sub.2=x?a, a is a number from 0.1 to 0.9, x is a number from 10 to 1,000, x is the number of moles of the hydrophilic moiety disposed at the other end of the copolymer, and a is a ratio of units substituted with a sulfonic acid group to such a hydrophilic moiety.

[0044] In Formula 1, y is a number from 10 to 1,000 and z is a number from 10 to 1,000.

[0045] In Formula 1, n is a number from 2 to 12. n indicates a graft degree and may mean the number of moles of monomers having a sulfonic acid-protecting group reacted with one halogen group.

[0046] The fuel cell according to embodiments of the present disclosure may include an electrolyte membrane, a cathode disposed on one surface of the electrolyte membrane, and an anode disposed on the other surface of the electrolyte membrane. At least one of the electrolyte membrane, cathode, and anode may include the ionomer.

[0047] A method for preparing an ionomer for a fuel cell according to embodiments of the present disclosure includes reacting a starting material including chloromethylated styrene ethylene-butylene styrene (CMSEBS) and a monomer having a sulfonic acid-protecting group to obtain an intermediate material and removing the sulfonic acid-protecting group from the intermediate material to obtain an ionomer represented by Formula 1.

[0048] The CMSEBS may be a compound represented by the following Formula 1b.

##STR00005##

[0049] In Formula 1b, x.sub.1, x.sub.2, x.sub.1, x.sub.2, y and z are as defined in Formula 1.

[0050] The preparation method of the CMSEBS is not particularly limited. For example, SEBS represented by Formula 1c is dissolved in chlorobenzene, paraformaldehyde is added thereto and the temperature is elevated to about 55? C. The CMSEBS may be obtained by adding chlorotrimethylsilane and tin (IV) chloride to the resulting product, followed by reacting at about 80? C.

##STR00006##

[0051] In Formula 1c, x, x, y and z are as defined in Formula 1.

[0052] The monomer having a sulfonic acid-protecting group may include a compound represented by the following Formula 2.

##STR00007##

[0053] In the monomer, the sulfonic acid-protecting group may be a neopentyl group.

[0054] The starting material may further include copper halide and 2,2-bipyridine. The copper halide is not particularly limited, but may include copper chloride (CuCl).

[0055] The starting material may include the copper halide and the 2,2-bipyridine in a mole ratio of 1:1 to 1:3.

[0056] n in Formula 1 may be adjusted by appropriately changing the ratio between the monomer having the sulfonic acid-protecting group, the copper halide, and the 2,2-bipyridine in the starting material.

[0057] The intermediate material represented by Formula la may be obtained by reacting the starting material at 50? C. to 150? C. for 1 hour to 48 hours.

##STR00008##

[0058] In Formula 1a, x.sub.1, x.sub.2, x.sub.1, x.sub.2, y and z are as defined in Formula 1.

[0059] The ionomer according to embodiments of the present disclosure may be obtained by removing the sulfonic acid-protecting group from the intermediate material.

[0060] The removal of the sulfonic acid-protecting group may be carried out by heat treatment or hydrolysis of the intermediate material and is preferably carried out by heat treatment. Specifically, the ionomer according to embodiments of the present disclosure may be obtained by removing the sulfonic acid-protecting group through heat treatment of the intermediate material at 100? C. to 200? C. for 1 hour to 4 hours.

[0061] In this case, the intermediate material may be dissolved in a solvent to obtain a solution, the solution may be coated on a substrate to prepare a membrane having a predetermined shape, and then the membrane may be heat treated to remove the sulfonic acid-protecting group.

PREPARATION EXAMPLES 1 TO 4

[0062] 1 g of CMSEBS was dissolved in 15 mL of toluene, and then neopentyl styrene sulfonate, copper chloride (CuCl), and 2,2-bipyridine were added to the solution, followed by purging with nitrogen gas for about 30 minutes to prepare a starting material. The copper chloride and 2,2-bipyridine were added at a mole ratio of 1:1.5.

[0063] The starting material was allowed to react at 100? C. for 24 hours to synthesize intermediate materials in which n is 2 (Preparation Example 1), 5 (Preparation Example 2), 7 (Preparation Example 3), and 12 (Preparation Example 4).

[0064] Each intermediate material was precipitated in an excess of isopropyl alcohol. The result was repeatedly washed twice or more to remove residues such as copper chloride and then dried in an oven at about 50? C. to obtain an intermediate material.

EXAMPLES 1 to 4

[0065] 0.3 g of the intermediate materials according to Preparation Examples 1 to 4 were weighed and each was dissolved in 3 mL of toluene to obtain a solution.

[0066] The solution was applied to a substrate to produce a membrane having a predetermined shape and the membrane was then dried in an oven at 50? C. The membrane-formed substrate was immersed in a water bath to separate the membrane.

[0067] FIG. 2A shows the membrane according to Example 1(n=2). FIG. 2B shows the membrane according to Example 2 (n=5). FIG. 2C shows the membrane according to Example 3 (n=7). As the value of n decreases, flexibility increases, but physical properties such as strength are lowered.

[0068] Each of the membranes was placed in a furnace, heat-treated at about 150? C. for about 2 hours to remove the sulfonic acid-protecting group and washed to prepare an electrolyte membrane including the ionomer according to embodiments of the present disclosure.

[0069] FIG. 3 shows the electrolyte membrane according to Example 2 (n=5).

[0070] FIG. 4 shows proton conductivity of the electrolyte membranes according to Examples 1, 2 and 4 and Nation 211. The proton conductivity is shown as a function of relative humidity at 80? C. in an in-plane direction. The proton conductivity is shown in Table 1 below.

TABLE-US-00001 TABLE 1 Proton conductivity [mS/cm] Item Relative humidity 50% Relative humidity 90% Nafion 211 40.9 175.5 Example 1 (n = 2) 1.2 19.2 Example 2 (n = 5) 10.1 120.5 Example 4 (n = 12) 20.0 317

[0071] Under high humidity conditions (90% relative humidity), Example 4 has higher proton conductivity than Nation 211. In addition, it can be seen that the proton conductivity improves as the degree of grafting increases.

[0072] FIG. 5 shows the self-assembly behavior of the ionomer according to Example 2. The ionomer was added to toluene and tetrahydrofuran, and the result was analyzed by scanning electron microscopy. It can be seen that the ionomer has a micelle structure in a solvent.

[0073] FIG. 6A shows self-assembly behaviors of the electrolyte membranes according to Examples 1, 2 and 4 before heat treatment. FIG. 6B shows the microstructures and self-assembly behaviors of the electrolyte membranes according to Examples 1 to 4 after heat treatment. Each result was analyzed by small angle x-ray scattering (SAXS). Styrene ethylene-butylene styrene (SEBS) was also analyzed as a Comparative Example.

[0074] In SEBS, a SAXS peak having a cylindrical structure is observed. Comparing FIG. 6A with FIG. 6B, dissociation of the neopentyl group occurs during the heat treatment process, and an ordered structure is formed. It can be seen that, in Example 1 (n=2) and Example 2 (n =5), the 2.sup.nd peak is observed and a shift to a lamellar structure occurs.

[0075] As is apparent from the foregoing, according to embodiments of the present disclosure, it is possible to obtain an ionomer for a fuel cell capable of self-assembly and a method of preparing the same.

[0076] The effects of embodiments of the present disclosure are not limited to those mentioned above. It should be understood that the effects of embodiments of the present disclosure include all effects that can be inferred from the foregoing description of embodiments of the present disclosure.

[0077] 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.