ELECTROLYTE MEMBRANE FOR MEMBRANE-ELECTRODE ASSEMBLY INCLUDING SELF-ASSEMBLED BLOCK COPOLYMER

Abstract

Disclosed is an electrolyte membrane for a membrane-electrode assembly including a block copolymer composed of a hydrophilic domain and a hydrophobic domain.

Claims

1. An electrolyte membrane for a membrane-electrode assembly comprising: an admixture comprising: (a) an ionomer; and (b) a block copolymer comprising a hydrophilic domain and a hydrophobic domain.

2. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein the hydrophilic domain comprises a cation conductivity repeat unit.

3. The electrolyte membrane for the membrane-electrode assembly of claim 2, wherein the cation conductivity repeat unit comprises one or more repeat units having Formula 1-1 to Formula 1-5 below, ##STR00013## wherein n ranges from 1 to 100,000.

4. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein the hydrophobic domain comprises an antioxidation repeat unit.

5. The electrolyte membrane for the membrane-electrode assembly of claim 4, wherein the antioxidation repeat unit comprises one or more repeat units having Formula 2-1 to Formula 2-10 below, ##STR00014## ##STR00015## wherein m ranges from 1 to 100,000.

6. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein a ratio between the number of repeat units (n) of the hydrophilic domain and the number of repeat units (m) of the hydrophobic domain is about 20:80 to 70:30.

7. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein the block copolymer has the number average molecular weight (Mn) of about 25,000 or less.

8. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein the block copolymer is formed in a micelle comprising a core part and a shell part surrounding the core part, and wherein the core part comprises the hydrophobic domain, and the shell part comprises: the hydrophilic domain.

9. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein the block copolymer has the particle radius of about 4 nm to 6 nm.

10. The electrolyte membrane for the membrane-electrode assembly of claim 1, wherein the additives of about 1 part by weight to 10 parts by weight based on 100 parts by weight of the ionomer are comprised.

11. A membrane-electrode assembly comprising: an electrolyte membrane of claim 1; and a pair of electrodes located on both surfaces of the electrolyte membrane.

12. A fuel cell comprising: the membrane-electrode assembly of claim 11.

13. A water electrolysis device comprising: the membrane-electrode assembly of claim 11.

14. A vehicle comprising a membrane-electrode assembly of claim 11.

15. A vehicle comprising a fuel cell of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and other features of the present invention will now be described in detail with reference to certain exemplary examples thereof illustrated in the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present invention, and wherein:

[0037] FIG. 1 shows an exemplary block copolymer according to an exemplary embodiment of the present invention.

[0038] FIG. 2 shows the state where the block copolymer according to the present invention is self-assembled in a micelle form.

[0039] FIG. 3 shows the antioxidation evaluation result according to an Experimental Example 2.

[0040] It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the disclosure. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in section by the particular intended application and use environment.

[0041] In the figures, reference numbers refer to the same or equivalent sections of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

[0042] As described above, objects, other objects, features, and advantages according to the present invention will be readily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the Examples described herein and may also be embodied in other forms. Rather, the Examples introduced herein are provided so that the invention may be made thorough and complete, and the spirit according to the present invention may be sufficiently conveyed to those skilled in the art.

[0043] Similar reference numerals are used for similar components while describing each drawing. In the accompanying drawings, the dimensions of the structures are illustrated to be enlarged larger than the actual one for clarity of the present disclosure. The terms “first,” “second,” and the like may be used to illustrate various components, but the components should not be limited by the terms. The terms are used only to differentiate one element from another. For example, a first component may be referred to as a second component, and similarly, the second component may also be referred to as the first component without departing from the scope of the present disclosure. The singular forms may include plural forms unless the contexts clearly indicate the opposite.

[0044] In this specification, it should be understood that terms such as “comprise” or “have” are intended to indicate that there is a feature, a number, a step, an operation, a component, a part, or a combination thereof described on the specification, and do not exclude the possibility of the presence or the addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof in advance. Further, when a portion such as a layer, a film, an area, or a plate is said to be “on” another portion, this includes not only the case where the portion is “directly above” another portion but also the case where other portions are interposed therebetween. Conversely, when a portion such as a layer, a film, an area, or a plate is said to be “under” another portion, this includes not only the case where the portion is “directly under” another portion but also the case where other portions are interposed therebetween.

[0045] Unless otherwise indicated, all numbers, values, and/or expressions referring to quantities of ingredients, reaction conditions, polymer compositions, and formulations used herein are to be understood as modified in all instances by the term “about” as such numbers are inherently approximations that are reflective of, among other things, the various uncertainties of measurement encountered in obtaining such values. Further, unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

[0046] Further, where a numerical range is disclosed herein, such a range is continuous, and includes unless otherwise indicated, every value from the minimum value to and including the maximum value of such range. Still further, where such a range refers to integers, unless otherwise indicated, every integer from the minimum value to and including the maximum value is included. For example, the range of “5 to 10” will be understood to include any subranges, such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual values of 5, 6, 7, 8, 9 and 10, and will also be understood to include any value between valid integers within the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, and the like. Also, for example, the range of “10% to 30%” will be understood to include subranges, such as 10% to 15%, 12% to 18%, 20% to 30%, etc., as well as all integers including values of 10%, 11%, 12%, 13% and the like up to 30%, and will also be understood to include any value between valid integers within the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

[0047] It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

[0048] An electrolyte membrane for a membrane-electrode assembly may include an ionomer and an additive dispersed to the ionomer.

[0049] The ionomer as used herein may transfer protons within the electrolyte membrane.

[0050] The ionomer may include a perfluorinated sulfonic acid polymer having a functional group capable of transferring the protons such as nafion.

[0051] The additive may include a block copolymer illustrated in FIG. 1. The block copolymer may include a hydrophilic domain (A) and a hydrophobic domain (B).

[0052] The hydrophilic domain (A) may include a cation conductivity repeat unit.

[0053] The cation conductivity repeat unit is a repeat unit including a functional group such as a sulfonic acid group capable of transferring the proton, and may include one or more of the repeat units having Formula 1-1 to Formula 1-5 below.

##STR00005##

n ranges from 1 to 100,000.

[0054] The block copolymer including the hydrophilic domain (A) may provide the new movement path of the proton other than the ionomer within the electrolyte membrane, thereby largely improving the photon conductivity of the electrolyte membrane.

[0055] The hydrophobic domain (B) may include the antioxidation repeat unit.

[0056] The antioxidation repeat unit may have a partial structure capable of converting the hydroxyl radical into hydroxide through the reaction paths of Reaction Formula 1 and Reaction Formula 2 below, or decomposing hydrogen peroxide.

##STR00006##

[0057] The antioxidation repeat unit may include one or more repeat units expressed by Formula 2-1 to Formula 2-10 below.

##STR00007## ##STR00008##

[0058] A rate between the number of repeat units (n) of the hydrophilic domain and the number of repeat units (m) of the hydrophobic domain (n:m) may be of about 20:80 to 70:30. When the rate of the number of repeat units (m) of the hydrophobic domain is greater than about 80, the particle radius of the block copolymer may become too large, such that the proton conductivity may not be improved.

[0059] Further, the block copolymer may have a number average molecular weight (Mn) of about 25,000 or less, about 10,000 or less, or about 8,000 or less. The lower limit of the number average molecular weight (Mn) is not specially limited. When the number average molecular weight of the block copolymer is greater than about 25,000, the particle radius of the block copolymer may become large, such that the proton conductivity may not be improved.

[0060] The electrolyte membrane exists in the humidified state, and the block copolymer includes all of the hydrophilic domain and the hydrophobic domain in one molecule. For example, as illustrated in FIG. 2, the block copolymer is self-assembled within the electrolyte membrane to form the micelle form including a core part 10 and a shell part 20 surrounding the core part 10.

[0061] The block copolymer may have the particle radius of about 4 nm to 6 nm. In the present specification, the “particle radius” refers to the linear distance from the center point of the micelle cell to the surface of the shell part in the state where the block copolymer is self-assembled in the micelle form. Further, the particle radius refers to the particle radius when the block copolymer is in the hydrated state. For example, according to a cluster-network model which is a fine molecular structure of the hydrated nafion, the absorbed water of the sulfonic acid group (—SO.sub.3.sup.−) forms a cluster of the spherical form having the diameter of about 4 nm, and the movement path of the proton is known as the narrow channel having 1 nm in width connecting the consecutive clusters. Therefore, to increase the proton conductivity, the particle radius of the block copolymer may be of about 4 nm to 6 nm, or particularly about 4 nm to 5 nm.

[0062] The electrolyte membrane may include the additive of 1 part by weight to 10 parts by weight based on 100 parts by weight of the ionomer. When the content of the additive is less than about 1 part by weight, the degree of improving the proton conductivity and the antioxidation may be insufficient, and when the content of the additive is greater than about 10 parts by weight, the amount thereof may be excessive, thereby rather lowering the proton conductivity of the electrolyte membrane.

Example

[0063] Exemplary embodiments of the present invention will be described in more detail through the exemplary examples below. The exemplary embodiment below is merely illustrative for helping to understand the present disclosure, and the scope of the present invention is not limited thereto.

Manufacturing Example 1 to Manufacturing Example 3

[0064] The block copolymer was manufactured in the following method.

[0065] As a monomer of the hydrophobic domain, 2,2,6,6-Tetramethyl-4-piperidinyl methacrylate expressed by Formula 3 below was used as a hydrophobic monomer.

##STR00009##

[0066] As a monomer of the hydrophilic domain, sodium 4-vinylbenzenesulfonate expressed by Formula 4 below was used as a hydrophilic monomer.

##STR00010##

[0067] The block copolymer was synthesized by a reversible addition-fragmentation chain transfer (RAFT) below.

[0068] First, the hydrophobic monomer of 10 g (0.04 moles), 2,2′-azobis(2-methylpropionitrile) (AIBN) of 0.146 g (0.8 moles) and 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid of 1.117 g (0.01 moles) were input into anhydrous toluene of 20 mL, the dissolved oxygen was removed, and then the argon purging was performed. After the 5-hour reaction at a temperature of about 55 to 75° C., the polymerization was completed after cooling. After the reactant was precipitated in a hexane solvent, a sediment was obtained by the centrifugation, and dried in a decompression oven for a day to obtain an intermediate expressed by Formula 5 below.

##STR00011##

[0069] The intermediate of 0.02 moles, the hydrophilic monomer, and AIBN of 0.146 g (0.8 moles) were input into the solvent of mixing water with methanol. At this time, the samples in which the input amount of the hydrophilic monomer was adjusted to 0.01 moles (Manufacturing Example 1), 0.02 moles (Manufacturing Example 2), and 0.04 moles (Manufacturing Example 3) were manufactured, respectively.

[0070] After each sample was reacted for 5 hours at a temperature of about 55 to 75° C., the polymerization was completed by the cooling. After the reactant was precipitated into the hexane solvent, the precipitate was obtained by the centrifugation, and dried for a day in the depression oven, such that the copolymer was obtained.

[0071] The copolymer of 5 g, and meta-chloroperoxybenzoic acid (mCPBA) of 17.25 g (0.1 moles) were input into dichloromethane of 50 mL, and agitated for 12 hours at room temperature, such that the copolymer was oxidized. After the reactant was precipitated in the hexane solvent, the precipitate was obtained by the centrifugation, and dried for a day in the depression oven, such that the block copolymer according to an exemplary embodiment of the present invention expressed by Formula 6 below was obtained.

##STR00012##

[0072] The physical properties for the block copolymers of the Manufacturing Example 1, the Manufacturing Example 2, and the Manufacturing Example 3 were measured. The result is expressed in Table 1 below.

TABLE-US-00001 TABLE 1 Number average Particle Items m/n.sup.1) molecular weight .sup.2) radius [nm] Manufacturing 43/57 6,000 2.3 Example 1 Manufacturing 31/69 8,000 3.4 Example 2 Manufacturing 73/27 23,000 5.2 Example 3 .sup.1)The rate (m/n) of the number of repeat units (n) of the hydrophilic domain and the number of repeat units (m) of the hydrophobic domain, measured by .sup.1H—NMR .sup.2) Measured by DOSY-NMR 3) Measured by a dynamic light scattering (DLS)

Example 1 to Example 4 and Comparative Example

[0073] Nafion solution was prepared. Mixtures were manufactured by adding the block copolymer of the Manufacturing Example 1 by 1 part by weight (Example 1), 3 parts by weight (Example 2), 5 parts by weight (Example 3), and 10 parts by weight (Example 4) based on 100 parts by weight of the nafion (ionomer) included in the nafion solution, respectively.

[0074] The electrolyte membrane was manufactured by applying each mixture on a release paper, and drying and thermally treating the mixture.

[0075] The electrolyte membrane was manufactured with only the nafion solution without adding the block copolymer, and set as the Comparative Example.

Experimental Example 1—Proton Conductivity Measurement

[0076] The proton conductivity of the electrolyte membranes according to the Example 1 to the Example 4 and the Comparative Example are measured in an in-plane in the condition of 80° C. and the relative humidity of 50%. The result is expressed by Table 2 below.

TABLE-US-00002 TABLE 2 Content of block Thickness of Proton Items copolymer electrolyte membrane conductivity Comparative  0 part by weight 28 um 45.1 mS/cm Example Example 1  1 part by weight 24 um 46.5 mS/cm Example 2  3 parts by weight 28 um 48.6 mS/cm Example 3  5 parts by weight 26 um 51.4 mS/cm Example 4 10 parts by weight 31 um 38.2 mS/cm

[0077] As shown in Table 2, the Example 3 shows the highest proton conductivity, and this is a value increased by about 6 mS/cm compared to the Comparative Example.

Experimental Example 2—Antioxidation Evaluation

[0078] The antioxidation was evaluated by measuring the changes in the fluorine ion emission according to the times of the electrolyte membranes according to the Example 1 to the Example 4 and the Comparative Example. The result is illustrated in FIG. 3.

[0079] As shown in FIG. 3, the Example 1 to the Example 4 show the remarkably low fluorine ion emission compared to the Comparative Example, such that it may be seen that when the block copolymer according to an exemplary embodiment of the present invention is input as an additive, the chemical durability of the electrolyte membrane may be largely improved.

[0080] As described above, the Experimental Examples and the Examples according to various exemplary embodiments of the present invention have been described in detail, and the scope of the present invention is not limited to the aforementioned Experimental Examples and the Examples, and various forms modified and improved by those skilled in the art using the basic concept of the present invention defined by the claims are also included in the scope of the present invention.