KR101824531B1 - Method for preparing covalently cross-linked membrane by changing ionic cross-linking to covalent cross-linking and covalently cross-linked membrane prepared thereby - Google Patents

Abstract

A polymer having an amino group such as a PBI derivative containing electron rich aromatic rings and the like and a sulfonated polymer such as a sulfonated polyether sulfone or the like are blended to prepare an ion crosslinked membrane or a sulfonated PBI Ion crosslinked membranes are prepared from the derivatives and thermally cured to prepare covalently crosslinked membranes. The cured crosslinked film thus thermally cured can exhibit mechanical properties such as an improved tensile strength as compared with an ionically crosslinked film which is not thermally cured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a covalently crosslinked membrane by converting an ionic crosslink to a covalently crosslinked membrane and a method for preparing the covalently crosslinked membrane using the covalently crosslinked membrane membrane prepared thereby.

The present invention relates to a method for producing a covalent crosslinked membrane by converting ionic crosslinks into covalent crosslinks through thermal curing, a covalent bonding membrane such as a polybenzimidazole-based membrane prepared by the method, and a high-temperature polyelectrolyte fuel cell using the same Device.

High Temperature Polymer electrolyte fuel cells (HT PEMFC) are fuel cells that operate at about 150-200 ° C. They mainly use phosphoric acid-doped polybenzimidazole (PBI) membranes as electrolyte membranes. Phosphorus-doped PBI membranes are commercially available. For example, BASF or Power Systems of Denmark sells PBI-based membranes and membrane electrode assemblies for high temperature polyelectrolyte fuel cells.

In such high temperature polyelectrolyte fuel cells, ionic conductivity and performance strongly depend on phosphorus absorption (PA uptake).

However, because phosphoric acid plasticizes the polymer, increased phosphoric acid uptake leads to increased phosphoric acid absorption, resulting in mechanical, such as tensile strength, young modulus or creep compliance, and creep resistance. Thereby reducing stability.

One way to stabilize the phosphate-doped PBI membrane is to crosslink the membrane. Such crosslinking can be done by the addition of a double or multifunctional compound or polymer that reacts with the amine group of the PBI. Alpha-dibromosilene or alpha, alpha-dichlorosilane, or 1,3-dibromopropane or epoxide or polyvinyl chloride into the casting solution (Non-Patent Document 1).

However, the problem with using amine groups of PBI in this way is that the methyl groups are cleaved from the imidazolium group in the presence of anions at about 180-220 占 (non-patent document 2). Thus, cross-linking the nitrogen atoms (N-CH ₂ ) of PBI can experience degradation in long-term operation at elevated operating temperatures (150-200 ° C) of the fuel cell.

Can be crosslinked by attaching -CH ₂ - (N-Ph) -CH ₂ - to the 4 and / or 7 position of meta-PBI using benzoxazine. In this structure, the cross-linking group has an amine bond in the CH ₂ group, which can be protonated at the corresponding amine bond and can be fully degraded at the fuel cell operating temperature (Non-Patent Document 3).

On the other hand, difurfuryloxy-p-xylene may be used in a Diels-Alder reaction with a PBI derivative containing a pendant styrene group (Non-Patent Document 4). However, this process can not be applied to all PBI derivatives, and in the case of the Diel-Adler reaction system, cleavage of the chemical bond at the temperature rise may occur. For example, cyclopentadiene is formed when the dicyclopentadiene is heated to 170 ° C in a retro-Diel-Adler reaction.

Non-Patent Document 1: ChemSus Chem 2013, 6: 275-282. Non-Patent Document 2: Polymer Degradation and Stability 97 (2012) 264-272 Non-Patent Document 3: Macromolecules 2012, 45, 14381446 Non-Patent Document 4: J. Mater. Chem., 2012, 22, 20696 Non-Patent Document 5: Fuel Cells, 2014, 14, 7-15 Non-Patent Document 6: J. Mater. Chem., 2012, 22, 11185-11195 Non-Patent Document 7: FUEL CELLS 13, 2013, No. 5, 832-842

Embodiments of the present invention, in one aspect, provide a method for producing a covalent crosslinked membrane by converting an ionic crosslink to a covalent crosslink, which can prevent deterioration during long-term operation and improve the mechanical properties of the membrane, To provide a covalent bonding film.

In exemplary embodiments of the present invention, a covalently crosslinked membrane obtained by thermally curing an ionically crosslinked membrane, wherein the covalent crosslinking site is a sulfone bond ). ≪ / RTI >

Exemplary embodiments of the present invention also provide an element comprising the covalent crosslinked membrane.

Exemplary embodiments of the present invention also provide a method of manufacturing a covalent crosslinked membrane by heating and thermally curing an ionically crosslinked membrane.

According to embodiments of the present invention, in one aspect, deterioration during operation can be prevented, the mechanical properties of the film can be improved, and the lifetime of the film can be improved.

FIG. 1 shows a conceptual diagram for preparing a covalent crosslinked membrane by heating an ionically crosslinked membrane to thermoset in the exemplary embodiments of the present invention.
2 is a graph of phosphoric acid absorption and tensile strength results in an embodiment of the present invention.
Figure 3 shows the polarization curve of a film in an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail.

In this specification, an aromatic sulfone bond means an aromatic ring connected to at least one side of a sulfone bond (-SO ₂ -). For example, the aromatic sulfone linkage is R-SO ₂ -Ar. Wherein Ar is an aromatic ring and R can be Ar (aromatic ring), alkyl, or fluoroalkyl.

As used herein, the residual solvent is a solvent remaining after thermal curing of the covalent bonding film, and includes water, an acid, and an organic solvent.

A polymer having an amino group such as a PBI derivative containing electron rich aromatic rings and the like and a sulfonated polymer such as a sulfonated polyether sulfone or the like are blended to prepare an ion crosslinked membrane or a sulfonated PBI Or a derivative thereof, and thermally cures the same to prepare a covalently crosslinked membrane.

The method using the blend uses two different polymers, and the method using the sulfonated PBI or a derivative thereof uses one homogenous material. However, in both methods, the sulfonic acid group is bonded to the nitrogen atom of the imidazole And is ion-crosslinked. This is heated to obtain a covalent crosslink.

The reaction in which the ionic bond is converted into the covalent bond is unexpected. That is, the sulfonic acid group has a small number of sulfonic acid groups which are not decomposed due to acid base interaction (Reaction 1) with the amino group of PBI.

[Reaction Scheme 1]

In other words, the interaction between nitrogen and SO ₃ H lowers the reactivity of sulfonic acid groups. Nevertheless, as described above, it is surprising that ion crosslinking is converted into shared crosslinking. In addition, the covalent cross-linking is also mechanically distinctive in that covalent cross-linking occurs due to sulfone bond.

The sulfone bond can be formed, for example, by the following reaction formula.

[Reaction Scheme 2]

RSO ₃ H + Ar-> R-SO ₂ -Ar, where Ar is an aromatic ring and R can be Ar, alkyl or fluoroalkyl.

In a non-limiting example, the sulfone linkage can be, for example, Ar-SO ₂ -Ar, as shown in the following scheme.

[Reaction Scheme 3]

Since the thermosetting covalent crosslinked membrane exhibits mechanical properties such as improved tensile strength and the like compared with the ionic crosslinked membrane not thermally cured, it is possible to use a fuel cell such as a high temperature polymer fuel cell or a redox flow cell flow battery or an electrolyzer.

In exemplary embodiments of the present invention, a covalently crosslinked membrane obtained by thermally curing an ionically crosslinked membrane, wherein the covalent crosslinking site is a sulfone bond ). ≪ / RTI > Such sulfone crosslinking is more stable than crosslinking involving nitrogen atoms.

In one exemplary embodiment, an ionic crosslinking membrane comprising at least one sulfonated polymer and at least one amino group containing polymer is a covalent crosslinked membrane obtained by thermosetting, wherein the covalent crosslinking site is a sulfonated sulfone bond).

In an exemplary embodiment, the amino group-containing polymer is not particularly limited, but may be an imidazole-based polymer such as PBI or a derivative thereof. For example, in a non-limiting example, meta-PBI, para-PBI, O-PBI, PBI-OO, PBI-HFA, PBI-OH, PBI containing pyridine or mixtures thereof or copolymers thereof. O-PBI or PBI-OO is more preferred because it provides an electron rich aromatic ring for the cross-linking reaction.

In one exemplary embodiment, the sulfonated polymer (or sulfonic acid containing polymer) may be a sulfonated hydrocarbon based membrane such as, for example, SPAES 40 or 50, or a perfluorinated polymer such as Nafion.

In one exemplary embodiment, the ionic crosslinking membrane comprising a sulfonated PBI or a derivative thereof is a covalent crosslinked membrane obtained by thermosetting, and the covalent crosslinking site is a sulfone bond. Thereby providing a bonding film.

In an exemplary embodiment, the sulfone linkage may be an aromatic sulfone linkage R-SO ₂ -Ar. Where Ar is an aromatic ring and R can be Ar (aromatic ring), alkyl, or fluoroalkyl (e.g., CF ₂ ).

In an exemplary embodiment, the sulfonated PBI derivative may be sulfonated PBI-OO, sulfonated O-PBI, sulfonated meta-PBI, etc., and may be, for example, a compound represented by the following formula , But is not limited thereto.

[Chemical Formula 1]

(2)

(3)

In the exemplary embodiment, PBI-OO is more electronegative than meta-PBI, etc., as described above, so that reaction with the sulfonated polymer is more likely to occur, which is desirable.

In one exemplary embodiment, in ion crosslinked materials prior to thermal cure (i.e., blends of one or more sulfonated polymers and one or more amino group containing polymers, or sulfonated PBI or derivatives thereof), the sulfonic acid group SO ₃ H / C = NC molar ratio SO ₃ H / C = NC can be, for example, 0 <SO ₃ H / C = NC <0.5, preferably 0 <SO ₃ H / C = be an NC <0.1 and, more preferably is _{0 <SO 3 H / C =} NC <0.05.

Exemplary embodiments of the present invention also provide an element comprising the covalent crosslinked membrane. Such a device may be a fuel cell such as a high temperature polymer fuel cell, a redox flow battery, or an electrolyzer.

Exemplary embodiments of the present invention also provide a method of making a covalent crosslinked membrane by heating an ionically crosslinked membrane to heat cure.

FIG. 1 shows a conceptual diagram for preparing a covalent crosslinked membrane by heating an ionically crosslinked membrane to thermoset in the exemplary embodiments of the present invention.

As shown in Figure 1, in an exemplary embodiment, an ionically crosslinked membrane comprising one or more sulfonated polymers and one or more amino group containing polymers (PBI in Figure 1) is heated to heat And a cured crosslinked membrane can be prepared.

In an exemplary embodiment, a covalent crosslinked membrane can be prepared by heating an ionically crosslinked membrane comprising a sulfonated PBI derivative to thermally cure.

In an exemplary embodiment, the heating temperature is 180-400 占 폚. If the temperature is lower than 180 ° C., the reaction may not occur. If the temperature is higher than 400 ° C., the backbone deterioration may occur in some polymers.

In an exemplary embodiment, the heating can be performed in a gaseous atmosphere, wherein the gas can be, for example, an inert gas or air.

In an exemplary embodiment, the heating time may be 10 seconds to 30 hours, preferably 25-250 minutes. If it is less than 10 seconds, crosslinking may not occur effectively, and if it exceeds 30 hours, the process time may become too long and the technical value may be decreased.

In one exemplary embodiment, the membrane may absorb up to 30 wt% water before heating, and an acid such as phosphoric acid or sulfuric acid, or an organic solvent such as DMAc, DMSO, NMP, sulfolane, MSA, %. &Lt; / RTI &gt;

However, if the solvent is excessively absorbed, the film may be softened and the solvent may be suddenly discharged to form pores or cracks in the film. In this regard, in a non-limiting example, water in the solvent may preferably comprise less than 10 wt%, more preferably less than 5 wt%. An acid or an organic solvent or a mixture thereof may preferably be contained in an amount of less than 10 wt%, more preferably less than 5 wt%.

In connection with this, trace solvents can plasticize the polymer and thus enable more effective crosslinking by lowering the curing temperature and / or the processing time.

In a non-limiting example, the membrane may contain about 1 mole of organic solvent (e. G., DMAc) as a residual solvent per repeat unit, unless the PBI membrane is dried and over-washed. The PBI membrane may also contain water as residual solvent, for example, up to about 20 wt% under humidified conditions. In addition, in the following Experimental Example, it was confirmed that mostly commercial PBI-OO contained methane sulfonic acid (MSA) as a residual solvent.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the embodiments of the present invention. It should be understood, however, that such embodiments are not to be construed as limiting the scope of the invention, and that various modifications are possible within the scope of the invention.

Example  And Comparative Example

(PBI-OO) and PBI-OO (PBI-OO), which are PBI derivatives containing electron rich aromatic rings, Polymer blends were prepared using a sulfonated polyether sulfone (SPAES50), a sulfonated polymer known to exhibit thermal cross-linking behavior with thermal stability.

Then, the polymer blend was cast to prepare a membrane to obtain ionically cross-linked membranes. Cross-linking reactions were performed using thermal curing for covalently cross-linking.

The blend film obtained by weight ratio of 95: 5 (PBI-OO: SPAES50) was compared with a thermally cured, non-thermally cured film. For thermal curing, the film was placed in an oven furnace into which nitrogen was introduced, heated to 320 ° C, allowed to stand for 30 minutes, and then cooled.

The tensile strength and fuel cell performance of the membranes were investigated and compared with the uncured membranes. The thermally cured membrane had nearly twice the phosphate uptake (PA uptake) (see Table 1 below).

Also, a single cell test was performed at 160 캜 by supplying hydrogen and air. After 24 hours of activation, the polarization curve was measured.

Phosphoric acid absorption and mechanical properties tests were performed as follows.

Phosphoric acid uptake: The sample (4 × 1 cm ² ) was immersed in 85% phosphoric acid to perform phosphoric acid doping of the membrane. Phosphoric acid doping conditions are shown in Table 1 below. Phosphorus absorption was determined by gravimetric measurements before and after doping. The weight gain due to phosphoric acid absorption was calculated as the difference between initial weight (w _i ) (drying at 60 ° C under vacuum) and doped sample weight (w _PA ) as follows.

[Equation 1]

On the other hand, for mechanical properties testing, the maximum tensile strength, Young's modulus, and elongation at break of the phosphate-doped membrane were determined from force displacement curves measured with a Cometech QC-508E instrument.

For each material, at least five samples obtained from the same membrane were used and the average value was calculated. The sample size is 4 × 1 cm ² and the elongation speed is 10 mm min ^-1 .

Table 1 below shows heat treatment conditions and the like, and Table 2 shows properties and performance evaluation results.

Sample Polymer blend composition
PBI-OO: SES PBI-OO purification
Reprecipitation in water
(xg PBI-OO, yg NMP, z ml water) Membrane Casting Petri dish / glass plate Oven heating / metal plate Heating conditions (temperature, gas, time) PA doping conditions One 100 6, 54, 2000 Petri dish - Heat treatment
none 80 ℃
/ 48 h 2 100 6, 54, 2000 Petri dish - Heat treatment
none 30 ℃
/ 48 h 3 100 6, 54, 2000 Petri dish Metal plate 300 ° C / Ar / 2.5 h 90 ° C
/ 48 h 4 100 6, 54, 2000 Petri dish Oven 300 ° C / N ₂ / 2.5 h 90 ° C
/ 48 h 5 100 6, 54, 2000 Petri dish Oven 300 ° C / N ₂ / 2.5 h 80 ℃
/ 48 h 6 100 6, 54, 2000 Petri dish Oven 320 ° C / N ₂ / 2.5 h 80 ℃
/ 24 h 7 97.5: 2.5 6, 54, 2000 Petri dish Oven 290 ° C / N ₂ / 2.5 h 80 ℃
/ 48 h 8 95: 5 6, 54, 2000 Petri dish - No heat treatment 80 ℃
/ 24 h 9 95: 5 6, 54, 2000 Petri dish Oven 280 ° C / N ₂ / 2.5 h 90 ° C
/ 48 h 10 95: 5 6, 54, 2000 Petri dish Oven 280 ° C / N ₂ / 2.5 h 90 ° C
/ 48 h 11 95: 5 6, 54, 2000 Petri dish Oven 280 ° C / N ₂ / 2.5 h 80 ℃
/ 48 h 12 95: 5 6, 54, 2000 Petri dish Oven 320 ° C / N ₂ / 0.5 h 80 ℃
/ 24 h 13 90:10 6, 54, 2000 Petri dish - No heat treatment 80 ℃
/ 24 h 14 90:10 6, 54, 2000 Petri dish Oven 260 ° C / N ₂ / 2.5 h 90 ° C
/ 48 h 15 90:10 6, 54, 2000 Petri dish Oven 260 ° C / N ₂ / 2.5 h 90 ° C
/ 48 h 16 90:10 6, 54, 2000 Petri dish Oven 260 ° C / N ₂ / 2.5 h 80 ℃
/ 48 h 17 90:10 6, 54, 2000 Petri dish Oven 320 ° C / N ₂ / 2.5 h 80 ℃
/ 24 h 18 90:10 6, 54, 2000 Glass plate Oven 320 ° C / N ₂ / 2.5 h 80 ℃
/ 24 h 19 80:20 6, 54, 2000 Petri dish Oven 220 ° C / N ₂ / 2.5 h 90 ° C
/ 48 h

Sample Phosphate absorption (wt%) The tensile strength
(MPa) Youngmamu Russ
(MPa) Elongation at break (%) Performance evaluation
Indices One Excessive swelling - - - - 2 361 ± 17 5.93 ± 1.3 78.14 ± 12 102 ± 21 4.3 3 582 ± 118 2.32 ± 0.3 75.23 ± 9 8 ± 2 2.7 4 903 ± 357 2.96 ± 0.8 29.27 ± 9 52 ± 35 5.3 5 649 ± 142 4.68 ± 2.3 65.03 ± 19 65 ± 26 6.1 6 505 ± 30 6.4 ± 2.4 84.02 ± 23 28 ± 7 6.5 7 459 ± 39 5.35 0.90 104.27 ± 36 39 ± 6 4.9 8 419 ± 65 3.4 ± 0.6 85.49 ± 11 15 ± 7 2.8 9 329 ± 10 10.05 ± 3 151.40 ± 8 55 ± 25 6.6 10 325 ± 19 8.57 ± 1.7 168.40 ± 10 30 ± 21 5.6 11 494 ± 26 4.97 ± 0.84 75.94 + 4 33 ± 30 4.9 12 445 ± 3 8.6 ± 0.7 70.06 ± 13 20 ± 2 7.7 13 380 ± 32 4.33 ± 0.83 57.03 ± 15 60 ± 16 3.3 14 385 ± 10 9.10 ± 0.24 73.65 ± 19 113 ± 6 7.0 15 400 ± 33 5.84 ± 1.74 95.16 ± 34 36 ± 27 4.7 16 400 ± 29 5.86 ± 0.94 99.48 ± 28 62 ± 30 4.7 17 454 ± 57 7.7 ± 1.8 85.25 ± 19 15 ± 9 7.0 18 394 ± 7 5.4 ± 0.8 102.56 ± 12 29 ± 15 4.3 19 313 ± 31 7.13 + - 0.24 106.16 ± 49 44 ± 24 4.5

* Performance evaluation index = (phosphoric acid absorption) x (tensile strength) x 2/1000

<3.5: Poor

<5: Medium

5>: Excellent

On the other hand, in the case of meta-PBI (MW = 37 kDa, fully doped) of the following formula 4, phosphoric acid absorption is about 400% and tensile strength is about 6-7 MPa (Non-Patent Document 5). In this case, the performance evaluation index is 4.8-5.6.

[Chemical Formula 4]

Further, in the case of a meta-PBI having a phosphoric acid absorption of 360% and a tensile strength of 5.8 (Non-Patent Document 6), the performance evaluation index is 4.2.

In the case of the prior art (Non-Patent Document 7) in which BTBP-PBI of the following Chemical Formula 5 is doped at various levels, the phosphoric acid absorption and tensile strength performance evaluation indexes are shown in Table 3 below.

[Chemical Formula 5]

Phosphate absorption (wt%) Tensile Strength (Mpa) Performance evaluation index 0 111 - 74 46 6.9 113 27 6.0 133 15 3.9 201 3 1.3

2 is a graph of phosphorus absorption and tensile strength (logarithmic) results in Table 2 according to an embodiment of the present invention.

In FIG. 2, all of the squares are excellent in that the performance evaluation index is greater than 5. The triangle has a good performance index of 3.5-5, and the rhombus has a performance evaluation index of less than 3.5.

It can be seen from FIG. 2 that the film (rhombus) treated between the blend film and the metal plate obtained without heat treatment has a poor relationship between phosphoric acid absorption and tensile strength. On the other hand, the heat treatment showed an excellent performance evaluation index.

On the other hand, the fuel cell test was performed on the sample 12 having the highest performance evaluation index.

Figure 3 shows the polarization curve of a sample 12 film in an embodiment of the present invention.

The thickness of the sample 12 film after doping was 130 占 퐉. The polarization curve was measured at 160 DEG C and the cell area was 7.84 cm &lt; ^{2 &} gt ;. It was not humidified and was measured after activation at 160 ° C and 0.2 A cm ^-2 for 24 hours.

As can be seen from FIG. 3, it can be seen that the power density is good when the thickness of the film is taken into consideration.

Claims (16)

A covalently crosslinked membrane obtained by thermally curing an ionically crosslinked membrane,
Wherein the covalent crosslinking site is a sulfone bond (- SO ₂ -).
The method according to claim 1,
Wherein said ionic crosslinking membrane comprises at least one sulfonated polymer and at least one amino group containing polymer.
3. The method of claim 2,
Wherein the amino group-containing polymer is a PBI-based polymer.
The method of claim 3,
The PBI polymer is one or a mixture or copolymer selected from the group consisting of meta-PBI, para-PBI, O-PBI, PBI-OO, PBI-HFA, PBI- &Lt; / RTI &gt;
3. The method of claim 2,
Wherein the sulfonated polymer is a sulfonated hydrocarbon-based membrane or a perfluorinated polymer.
The method according to claim 1,
&Lt; / RTI &gt; wherein the ionic crosslinking membrane comprises a sulfonated PBI derivative.
The method according to claim 1,
The molar ratio (SO ₃ H / C = NC) of the sulfonic acid group SO ₃ H and C = NC in the ion-crosslinked material before thermosetting is 0 <SO ₃ H / C = NC <0.5 Shared cross-linking membrane.
A device comprising the covalent crosslinked membrane of any of claims 1 to 7.
9. The method of claim 8,
Wherein the device is a fuel cell, a redox flow cell or an electrolytic device.
Characterized in that a covalent crosslinking site is a sulfone bond (- SO ₂ -), and the covalent crosslinking site is a sulfone bond (- SO ₂ -). .
11. The method of claim 10,
The method comprises the steps of: preparing an ionic crosslinked membrane comprising at least one sulfonated polymer and at least one amino group containing polymer;
And heating the ionically crosslinked membrane to thermally cure the membrane to form a covalent crosslinked membrane.
11. The method of claim 10,
The method comprises the steps of: preparing an ionically crosslinked membrane comprising a sulfonated PBI derivative; And
And heating the ionically crosslinked membrane to thermally cure the membrane to form a covalent crosslinked membrane.
11. The method of claim 10,
Wherein the heating temperature is 180 to 400 占 폚.
14. The method of claim 13,
Wherein the heating time is from 10 seconds to 30 hours.
11. The method of claim 10,
Characterized in that the membrane is allowed to absorb up to 30 wt% of the water before heating, or to absorb up to 20 wt% of the acid or organic solvent or mixture thereof.
11. The method of claim 10,
Wherein the covalent cross-linking membrane comprises a trace solvent.

Images