KR102699314B1 - Polymer electrolyte membrane with high water content and ion conductivity - Google Patents

Abstract

The present invention relates to a polymer electrolyte membrane having a high water content and ionic conductivity. Specifically, by mixing ionomer resins having different equivalent weights, i.e., asymmetric ionomer resins, to provide an ionomer membrane, the ionomer membrane has a water content and ionic conductivity that are more improved than those of a single ionomer membrane having the same monomer weight.

Description

Polymer electrolyte membrane with high water content and ion conductivity

The present invention relates to a polymer electrolyte membrane having high moisture content and ionic conductivity.

Energy conversion devices utilizing hydrogen are based on cation-conducting polymer electrolytes, and among them, the polymer electrolyte must have a high water content for conducting cations and be able to maintain them. Based on this, it plays the role of a separator that separates the cathode and anode of polymer electrolyte fuel cells and polymer electrolyte water electrolysis.

Perfluorinated polymer electrolyte membranes are based on PTFE polymers and contain ion-conducting sulfonic acid groups, and the polymer electrolyte is used as an ion exchange passage and gas permeation barrier between the cathode and the anode. It has a great influence on the performance of actual fuel cells and water electrolysis devices, and the development of polymer electrolyte membranes with high water content and ion conductivity is essential for improving the performance of electrode assemblies for fuel cells and water electrolysis, and much research is being conducted to achieve this.

However, in the case of conventional polymer electrolyte membranes, when an ionomer resin having a low equivalent weight is used, the moisture content and ionic conductivity are relatively high but the durability is low. On the other hand, when a membrane is manufactured using an ionomer resin having a high equivalent weight, the moisture content and ionic conductivity may be low.

Although the water content and ionic conductivity can be improved by adding additional inorganic substances or hydrophilic polymers, side reactions may occur due to the additives, and the durability of the ionomer membrane may decrease when used for a long period of time.

In order to solve the above-mentioned problems, the present invention aims to provide an ionomer membrane having excellent moisture content and ion conductivity without including additional inorganic substances or polymer resins.

The present invention provides an ionomer membrane comprising two or more kinds of perfluorinated ionomer resins having different equivalent weights, wherein the two kinds of perfluorinated ionomer resins satisfy the following formula 1.

[Formula 1]

(The above HEW is the equivalent weight of the perfluorocarbon ionomer resin with the highest equivalent weight, and LEW is the equivalent weight of the perfluorocarbon ionomer resin with the lowest equivalent weight.)

According to one aspect of the present invention, the ionomer membrane may include two or more types of perfluorinated ionomer resins having different equivalent weights in a weight ratio of 2:8 to 8:2.

According to one aspect of the present invention, the molecular weights of two or more types of perfluorinated ionomer resins having different equivalent weights may be 500 to 1000 g/eq or 600 to 1500 g/eq, respectively.

According to one aspect of the present invention, the perfluorinated ionomer resin may include one represented by the following chemical formula 1.

[Chemical Formula 1]

(In the above chemical formula 1, X is a covalent bond or -O-, and Rf _1, Rf ₂ and R _f3 are independently -(CF ₂ ) _n -, -(CF(CF ₃ )) _n -, or -(C(CF ₃ ) ₂ ) _n -, m is from 1 to 30, and n is from 1 to 5.)

The present invention comprises the steps of: preparing a mixed dispersion by mixing two or more kinds of perfluorinated ionomer dispersions having different equivalent weights; obtaining a mixed powder by evaporating a solvent from the mixed dispersion; pulverizing the obtained mixed powder; preparing a mixed organic solution by dissolving the mixed powder in an organic solvent; preparing an ionomer membrane from the mixed organic solution, and activating it with an acid solution; wherein the two kinds of perfluorinated ionomer resins may satisfy the following formula 1.

[Formula 1]

(The above HEW is the equivalent weight of the perfluorocarbon ionomer resin with the highest equivalent weight, and LEW is the equivalent weight of the perfluorocarbon ionomer resin with the lowest equivalent weight.)

According to one aspect of the present invention, the evaporation may be performed at a temperature of 40 to 100°C.

According to one aspect of the present invention, the organic solvent may include one or a mixed solution of two or more selected from dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and acetone.

According to one aspect of the present invention, the concentration of the perfluorinated ionomer resin in the mixed organic solution may be 1 to 90 wt%.

According to one aspect of the present invention, the mixed organic solution may be manufactured into an ionomer membrane and may further include an annealing process.

According to one aspect of the present invention, the annealing process may be performed at 100 to 150° C.

According to one aspect of the present invention, the acid aqueous solution may include one or more mixed aqueous solutions selected from a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution, and a nitric acid aqueous solution.

According to one aspect of the present invention, the concentration of the acid aqueous solution may be 0.1 to 10 mol/L.

According to one aspect of the present invention, a perfluorinated ionomer resin having different equivalents is represented by the following chemical formula 1, and A may be any one selected from the following chemical formulas 2 to 3.

[Chemical Formula 1]

(In the above chemical formula 1, X is a covalent bond or -O-, and Rf _1, Rf ₂ and R _f3 are independently -(CF ₂ ) _n -, -(CF(CF ₃ )) _n -, or -(C(CF ₃ ) ₂ ) _n -, 1 to 30, and n is 1 to 5.)

The present invention can produce an ionomer membrane having very excellent ion conductivity without including additional inorganic substances or polymer resins.

In addition, a polymer electrolyte membrane manufactured by a method for manufacturing a polymer electrolyte membrane according to one aspect of the present invention has a high water content and ionic conductivity, and thus, high performance can be expected based on low resistance in a hydrogen-based energy conversion device in the future.

Figure 1 is a graph showing the moisture content of ionomer membranes of examples and comparative examples.
Figure 2 is a graph showing the ionic conductivity of ionomer membranes of examples and comparative examples.

The present invention will be described in more detail below through specific examples or embodiments including the attached drawings. However, the following specific examples or embodiments are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of this invention is only for the purpose of effectively describing particular embodiments and is not intended to be limiting of the invention.

Additionally, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly dictates otherwise.

Additionally, when a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

The problem with conventional ionomer membranes is that when a high equivalent weight ionomer is used, the membrane has low moisture content and ionic conductivity, and when a low equivalent weight ionomer is used, the membrane has low durability. Therefore, these problems were improved by adding additional additives.

However, as the additional additives are added, the cost increases, and when the ionomer membrane is used for a long period of time, side reactions such as precipitation may occur, and durability may also be reduced.

Accordingly, the present invention solves the above problem by providing an ionomer membrane including two or more types of perfluorinated ionomer resins having different equivalent weights.

The ionomer membrane of the present invention provides an ionomer membrane by mixing ionomer resins having different equivalent weights, i.e., asymmetric ionomer resins, thereby providing an ionomer membrane having a moisture content and ionic conductivity that is more improved than a single ionomer membrane of the same monomer weight, although the exact reason is unknown. This is a remarkable effect that occurs simply by mixing asymmetric ionomer resins without adding conventional additives such as hydrophilic polymers and inorganic substances.

In addition, the two or more types of perfluorinated ionomer resins having different equivalents may satisfy the following formula 1, and specifically, may satisfy the following formula 2, but is not limited thereto.

[Formula 1]

[Formula 2]

The above HEW is the equivalent weight of the perfluorocarbon ionomer resin having the highest equivalent weight, and LEW is the equivalent weight of the perfluorocarbon ionomer resin having the lowest equivalent weight.

By providing an ionomer membrane by mixing two or more types of perfluorinated ionomer resins satisfying the ranges of the above formulas 1 and 2, it can have a moisture content and ionic conductivity that are better than those of a conventional single type of ionomer membrane.

According to one embodiment of the present invention, the mixing weight of two or more kinds of perfluorinated ionomer resins having different equivalent weights included in the ionomer membrane is not limited thereto as long as it can satisfy a desired average equivalent weight of the ionomer resin. For example, in the case of two kinds of perfluorinated ionomer resins having different equivalent weights, the mixing weight ratio may be 1:99 to 99:1, specifically, 2:8 to 8:2, but is not limited thereto. As a more specific example, in order to satisfy an equivalent weight of 1000 g/eq, an ionomer resin having an equivalent weight of 1100 g/eq and an ionomer resin having an equivalent weight of 720 g/eq may be mixed at a weight ratio of 7.5:2.5.

As described above, it can be confirmed that the moisture content and ionic conductivity of a single type of ionomer resin and the mixed ionomer resin of two or more types of the present invention are significantly different even though the average monomer amounts are similar.

In addition, the equivalent weight of two or more kinds of perfluorinated ionomer resins having different equivalent weights according to one embodiment of the present invention may be 500 to 1,000 g/eq or 600 to 1,500 g/eq, respectively, but is not limited thereto.

According to one aspect of the present invention, the perfluorinated ionomer resin may be represented by the following chemical formula 1.

[Chemical Formula 1]

In the above chemical formula 1, X is a covalent bond or -O-, and Rf _1, Rf ₂ and R _f3 is independently -(CF ₂ ) _n -, -(CF(CF ₃ )) _n -, or -(C(CF ₃ ) ₂ ) _n -, m is from 1 to 30, and n is from 1 to 5.

According to one aspect of the present invention, the perfluorinated ionomer resin may be a commercially available ionomer resin, and specifically, commercial ionomers such as Nafion and Aquibion may be used, but are not limited thereto.

The present invention can provide a method for producing an ionomer membrane, comprising: a step of mixing two or more perfluorinated ionomer dispersions having different equivalent weights to produce a mixed dispersion; a step of obtaining a mixed powder by evaporating a solvent from the mixed dispersion; a step of pulverizing the obtained powder; a step of preparing a mixed organic solution by dissolving the mixed powder in an organic solvent; a step of producing the mixed organic solution into an ionomer membrane and activating it with an acidic solution.

The above perfluorinated ionomer dispersions can be mixed to provide a mixed dispersion. The solvent of the above perfluorinated ionomer dispersion can be water, a mixed aqueous solution of water and alcohol, but is not limited thereto. The solvent of the above mixed perfluorinated ionomer dispersion can be evaporated to obtain a mixed powder. The evaporation method can be a general drying method, can be thermal drying in an oven, can be drying using a rotary evaporator, etc., but is not limited thereto.

The above evaporation may be evaporated at 40 to 100°C, and specifically dried at 50 to 80°C, and specifically dried at 50 to 70°C, but is not limited thereto.

The above organic solvent may be one or a mixed solution of two or more selected from dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and acetone. However, the present invention is not limited thereto, and may be freely selected from organic solvents generally known in the art.

In addition, according to one embodiment of the present invention, the concentration of the perfluorinated ionomer resin in the mixed organic solution may be 1 to 90 wt%, specifically 10 to 50 wt%, specifically 10 to 30 wt%, but is not limited thereto.

In addition, when manufacturing the above mixed organic solution into an ionomer membrane, it may be manufactured by introducing a casting method or a doctor blade, but is not limited thereto if it is a conventional method for manufacturing the ionomer membrane.

The above-mentioned manufactured ionomer film may include an annealing process. The annealing process may be performed at 100 to 150° C., and specifically, may be performed at 110 to 130° C., but is not limited thereto.

In order to acidify the sulfonic acid group of the above-mentioned manufactured ionomer membrane, it can be immersed in an acidic solution. The acidic solution may be an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution, an aqueous nitric acid solution, etc., and specifically, an aqueous hydrochloric acid solution may be used, but is not limited thereto.

The concentration of the above acid solution may be 0.1 to 10 mol/L, specifically 0.5 to 5 mol/L, specifically 1 to 3 mol/L, but is not limited thereto.

In addition, the above two types of perfluorinated ionomer resins may satisfy the following equation 1, but since the above description has been previously explained, it is omitted here.

[Formula 1]

The above HEW is the number average molecular weight of a perfluorinated ionomer resin having a high number average molecular weight, and LEW is the number average molecular weight of a perfluorinated ionomer resin having a low number average molecular weight.

According to one aspect of the present invention, a perfluorinated ionomer resin having different equivalents is represented by the following chemical formula 1, and A may be any one selected from the following chemical formulas 2 to 3, but since this has also been described above, a detailed description thereof will be omitted.

[Chemical Formula 1]

In the above chemical formula 1, X is a covalent bond or -O-, and Rf _1, Rf ₂ and R _f3 is independently -(CF ₂ ) _n -, -(CF(CF ₃ )) _n -, or -(C(CF ₃ ) ₂ ) _n -, m is from 1 to 30, and n is from 1 to 5.

The ionomer membrane comprising two or more ionomer resins having different equivalent weights of the present invention has better moisture content and ionic conductivity than an ionomer membrane manufactured with a single ionomer having the same equivalent weight. In particular, the above effect is an effect achieved by mixing asymmetric ionomer resins without adding additional additives, and is a heterogeneous effect that has not been confirmed in the past.

The present invention will be described in more detail based on the following examples and comparative examples. However, the following examples and comparative examples are only examples for describing the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

[Equivalent weight (EW measurement)

In the case of ionomer resins, the equivalent weight and ion exchange capacity are inversely proportional. That is, the lower the equivalent weight of the ionomer resin, the higher the ion exchange capacity. Therefore, the ion exchange capacity of the examples of the present invention was measured and compared with the ion exchange capacity of a single ionomer resin to determine the average equivalent weight.

The dried ionomer membrane was cut into a size of 3 cm × 4 cm, immersed in 200 mL of a 1.0 M HCl aqueous solution for 24 hours, taken out, and re-dried to perform a pretreatment. Thereafter, the 3 cm × 4 cm ionomer membrane that had been pretreated was immersed in 200 mL of a 1.0 M NaCl aqueous solution for 24 hours. After 24 hours, the immersed ionomer membrane was removed from the NaCl aqueous solution, and the 200 mL of 1.0 M NaCl aqueous solution in which the ionomer membrane was immersed was titrated with a 0.01 M NaOH aqueous solution using an automatic titrator (848 Titrino plus, Metrohom). The ion exchange capacity (IEC) was calculated by substituting the volume and concentration of the NaOH aqueous solution used in the measurement under the above conditions into the IEC calculation formula below. The IEC titration solution weight and dry membrane weight are listed in Table 1 below.

IEC calculation formula

ceremony.

: Concentration for NaOH solution (mol/L)

: Titrated volume of NaOH solution(L) for the samples

: Titrated volume of NaOH solution(L) for the blank

: Dry membrane weight (g)

: Total volume of NaCl/Sampling volume of NaCl for titration

[Water Uptake Measurement]

The moisture content was measured by drying the membrane manufactured above at 80°C and swelling it in deionized water until it reached equilibrium, and calculating the moisture content according to the following mathematical formula 1, and the results are shown in Table 2 below.

[Mathematical formula 1]

Moisture content (%) = (W _wet - W _dry ) / W _dry x 100

(In the above mathematical expression 1, W _dry : weight of the membrane before swelling (g), W _wet : weight of the membrane after swelling (g))

[Ionic Conductivity Measurement]

The proton conductivity of the membrane was measured using a potentiostat (SP-150, Bio-Logic Science Instruments, France) with an AC voltage supply in the scan range of 100 kHz to 1 Hz with an amplitude of 10 mV. The ohmic resistance (R) was derived from the high-frequency resistance of the impedance. The proton conductivity was measured by the following equation. The measured ionic conductivities are listed in Table 3 below.

[ceremony]

* Here, l is the distance between the electrodes, R is the membrane resistance, and S is the membrane cross-sectional area.

[Example 1]

Nafion D1021 (EW1100) aqueous solution and Aquibion D72-25BS (EW720) aqueous solution were mixed at a weight ratio of 7:3 based on the solid content, and the mixed aqueous solution was evaporated in an oven at 60°C for 24 hours to obtain a solid perfluorinated ionomer resin.

100 parts by weight of the solid perfluorinated ionomer resin obtained above was added to 500 parts by weight of anhydrous DMAc and stirred to prepare a perfluorinated ionomer resin solution. The perfluorinated ionomer resin solution was coated on a glass plate by controlling the thickness using a Dr. blade knife.

The above-mentioned coated plate was heated at 120°C for 24 hours and annealed in an oven at 190°C for 3 hours to produce a membrane. The above-mentioned manufactured membrane was removed from the glass plate by immersing it in deionized water, and the residual solvent was removed. In addition, the membrane was immersed in a 1 mol/L HCl aqueous solution at room temperature for 24 hours to acidify the sulfonic acid groups. Thereafter, the manufactured membrane was washed several times with deionized water.

[Example 2]

The same procedure was followed as in Example 1, except that instead of the perfluorinated ionomer mixture solution in which the Nafion D1021 (EW1100) aqueous solution and the Aquibion D72-25BS (EW720) aqueous solution were mixed in a weight ratio of 7:3 based on the solid content, a perfluorinated ionomer mixture solution in which the Aquibion D98-25BS (EW980) and Aquibion D72-25BS (EW720) aqueous solutions were mixed in a weight ratio of 5.5:4.5 based on the solid content was used.

[Comparative Example 1]

The same procedure was followed as in Example 1, except that an Aquibion D98-25BS (EW980) aqueous solution was used instead of the perfluorocarbon ionomer mixed aqueous solution.

[Comparative Example 2]

The same procedure was followed as in Example 1, except that an Aquibion D83-24B (EW830) aqueous solution was used instead of the perfluorocarbon ionomer mixed aqueous solution.

: 0.01 M-NaOH
(mL) Dry membrane
(g)
(mL) -
(mL) Example 1 11.2447 0.1 0.9420 10.3027 Example 2 12.7264 0.1 0.9420 11.7844 Comparative Example 1 10.9269 0.1 0.7540 10.1729 Comparative Example 2 12.2374 0.1 0.7540 11.4834

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Average EW 980 830 980 830 temperature Function rate (%) 25℃ 24.81 31.25 21.14 21.82 30℃ 27.04 39.44 26.48 29.83 50℃ 40.25 65.97 30.88 34.81 70℃ 48.52 71.94 34.08 38.95 90℃ 53.09 76.39 36.93 42.26 100℃ 55.31 81.25 39.55 46.41

* EW is equivalent weight and the unit is g/eq.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 25℃ 0.0848 0.1285 0.0818 0.1107 30℃ 0.1054 0.157 0.0914 0.1366 50℃ 0.1491 0.2203 0.1285 0.1854 70℃ 0.1909 0.2733 0.1633 0.2492 90℃ 0.2447 0.3206 0.1881 0.2953 100℃ 0.2475 0.3383 0.2023 0.305

As described in Table 1 above, Example 1 and Comparative Example 1 have similar NaOH titration amounts, and Example 2 and Comparative Example 2 have similar NaOH titration amounts, which suggests that the average equivalents of Example 1 and Comparative Example 1 are similar, and that the average equivalents of Example 2 and Comparative Example 2 are also similar.

Example 1 and Comparative Example 1 were manufactured with the same equivalent weight, with an average equivalent weight of 980 g/eq, and Example 2 and Comparative Example 2 were manufactured with the same average equivalent weight of 830 g/eq.

As described in Table 2 and Fig. 1, when comparing the water content per equivalent at the same level, it can be confirmed that all examples have higher water content than the comparative examples. In particular, in the case of Example 2 and Comparative Example 2, although they are ionomer membranes having the same equivalent weight of 830 g/eq, it can be confirmed that the water content differs by approximately 1.5 times or more.

In addition, when comparing the ion conductivity with reference to Table 3 and Figure 2, the examples were measured to be better than the comparative examples.

In conclusion, the present invention shows that the moisture content and ionic conductivity of an ionomer membrane can be dramatically improved simply by mixing ionomer resins having different equivalent weights without adding additional additives.

Although the present invention has been described with reference to specific matters, limited examples, and drawings, these have been provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art will appreciate that various modifications and variations may be made from this description.

Therefore, the idea of the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims described below as well as the claims are included in the scope of the idea of the present invention.

Claims (13)

delete delete delete delete A step of preparing a mixed dispersion by mixing each dispersion containing two types of perfluorinated ionomer resins having different equivalent weights;
A step of evaporating the solvent from the above mixed dispersion to obtain a mixed powder;
A step of grinding the obtained mixed powder;
A step of preparing a mixed organic solution by dissolving the above mixed powder in an organic solvent;
A step of manufacturing the above mixed organic solution into an ionomer membrane and activating it with an acid aqueous solution; wherein the two types of perfluorinated ionomer resins satisfy the following formula 2,
The weight ratio of two types of perfluorinated ionomer resins having different equivalent weights included in the above ionomer membrane is 2:8 to 8:2,
A method for producing an ionomer membrane, wherein the equivalent weights of two types of perfluorinated ionomer resins having different equivalent weights are each 500 to 1000 g/eq or 600 to 1500 g/eq.
[Formula 2]

The above HEW is the equivalent weight of the perfluorocarbon ionomer resin having the highest equivalent weight, and LEW is the equivalent weight of the perfluorocarbon ionomer resin having the lowest equivalent weight. In paragraph 5,
A method for manufacturing an ionomer membrane, wherein the above evaporation is performed at a temperature of 40 to 100°C. In paragraph 5,
A method for producing an ionomer membrane, wherein the organic solvent is one or a mixed solution of two or more selected from dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and acetone. In paragraph 5,
A method for producing an ionomer membrane, wherein the concentration of the perfluorinated ionomer resin in the above mixed organic solution is 1 to 90 wt%. In paragraph 5,
A method for producing an ionomer membrane, comprising producing the above mixed organic solution into an ionomer membrane and further comprising an annealing process. In Article 9,
A method for manufacturing an ionomer membrane, wherein the above annealing process is performed at 100 to 150°C. In paragraph 5,
A method for manufacturing an ionomer membrane, wherein the above acid solution is one or a mixed solution of two or more selected from a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution.
In Article 11,
A method for producing an ionomer membrane, wherein the concentration of the above acid solution is 0.1 to 10 mol/L.
In paragraph 5,
A method for producing an ionomer membrane, wherein the perfluorinated ionomer resin is represented by the following chemical formula 1.
[Chemical Formula 1]

In the above chemical formula 1, X is a covalent bond or -O-, and Rf _1, Rf ₂ and R _f3 is independently -(CF ₂ ) _n -, -(CF(CF ₃ )) _n -, or -(C(CF ₃ ) ₂ ) _n -, m is from 1 to 30, and n is from 1 to 5.