KR20160087727A - Zirconium-based sulfonic metal-organic framework and its manufauring process - Google Patents

Abstract

The present invention relates to a sulfonic acid group-induced zirconium-based metal-organic framework and a manufacturing method thereof. The sulfonic acid group-induced zirconium-based metal-organic framework is represented by chemical formula 1, [Zr_6O_4(OH)_4(C_8H_4O_10S_2)_6]m, has excellent proton conductivity, and exhibits long-term stability with respect to the proton conductivity.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconium-based sulfonic acid metal-organic skeleton and a method for producing the same,

The present invention relates to a zirconium-based metal-organic skeleton having a sulfonic acid group having excellent proton conductivity and exhibiting long-term stability against the proton conductivity and a method for producing the same.

The environmental problems of serious greenhouse gas emissions from the burning of carbon-based fuels as well as the increasing global demand for energy due to rapid industrialization trigger the need for alternative energy technologies.

Among these alternative energy technologies, fuel cells are electrochemical devices that convert chemical energy directly into electrical energy. Proton exchange membrane fuel cells (PEMFCs) are considered to be the most promising systems for transportation transport applications. It generates water, heat and electricity by discharging very little environmental pollutants through oxidation-reduction reaction of hydrogen which is fuel and oxygen which is oxidizing agent. This reaction occurs when an oxidized proton in the cathode diffuses through the electrolyte membrane to the anode and meets with electrons moved through an external circuit.

A well-developed PEMFC consists of a perfluorinated polymer membrane (e.g., Nafion) containing a sulfonic acid group at the end, which exhibits a proton conductivity as high as 0.10 S / cm under wet conditions. Materials such as polysulfone, polybenzimidazole, polyimide, and polyaryl ether ketone have been studied as substitutes for Nafion, but these aromatic-based polymers must be functionalized as sulfonic acid groups to achieve efficient proton conduction .

The metal-organic skeleton (MOF) is a porous crystalline solid with a very large surface area. MOF is being studied extensively for potential applications in various fields such as gas storage and separation, heterogeneous catalysts, luminescence sensors, and the like. A notable characteristic of the metal-organic skeleton is that it can control the uniformity of pores in the structure, the ability to control the size of such pores, and the properties of the pore surface. These features can be an advantage in developing thin film materials with proton conductivity of PEMFCs because multiple proton acceptors and acceptors can be arranged in the conduction path of the skeleton.

Conductivity of the material is mainly determined by proton mobility and concentration. To increase the number of protons in the skeleton, the skeleton and internal space of the MOF can be controlled using two different strategies. The first strategy is to incorporate guest molecules (eg, triazole, imidazole, histamine, ammonium cations, or hydronium ions) in the structure. A molecule embedded in a structure establishes a proton conduction path by forming a hydrogen bond between the molecules or forming a hydrogen bond with an existing water molecule in the structure. Another method is to synthesize a metal-organic skeleton by introducing an acidic functional group into an organic linker. In this case, the proton conductivity depends on the pKa of the functional group present in the organic linker. Due to the acidic group covalently linked to the organic linker of the skeleton, the proton can be provided more stably in the proton conduction pathway than the acidic molecules contained in the intracellular cavity in the hydrated condition.

Strong acids (sulfuric acid, phosphoric acid or trifluoromethanesulfonic acid) easily dissociate proton to increase proton ion conductivity. Most of the acidic molecules are located in the cavity of the MOF for proton conduction, and a group that can cause such high conductivity in the skeleton based on the presence of the sulfonic acid at the terminal end of the Nafion with the highest proton conductivity . The introduction of sulfonic acid groups that are not coordinated to the skeleton tends to interact with metal ions, making them proton accessible and prone to conduction. Post-synthetic transformation methods can be used to control the properties of the skeleton in a variety of applications.

In this sense, an unknown system for proton conduction MOF is required to make sulfonic acid groups bound to the skeleton.

Korea Patent Publication No. 10-2009-008487

Korea Chem. Eng. Res., 51 (4), 470-475 (2013)

It is an object of the present invention to provide a zirconium-based metal-organic skeleton having sulfonic acid groups which have excellent proton conductivity and exhibit long-term stability against the proton conductivity.

Another object of the present invention is to provide a method for preparing a zirconium-based metal-organic skeleton having the sulfonic acid group introduced therein.

The zirconium-based metal-organic skeleton incorporating the three-dimensional porous sulfonic acid group of the present invention for achieving the above object is represented by the following Chemical Formula 1;

[Chemical Formula 1]

[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₁₀ S ₂ ) ₆ ] m

The metal-organic skeleton is a three-dimensional structure in which 1,4-dimethyl-2,5-benzenesulfonic acid is bonded to Zr ₆ O ₄ (OH) ₄ , and m is an integer of 0 to 100.

The zirconium-based metal-organic skeleton may have a proton conductivity of 1.0 X 10 ^-2 to 1.0 X 10 ^-1 S / cm under 80 and 90% relative humidity (RH).

The BET surface area of the zirconium-based metal-organic skeleton may be 30 to 100 m ² / g.

In order to achieve the above other objects, the present invention provides a process for preparing a zirconium-based metal-organic skeleton by introducing a sulfonic acid group of the present invention represented by the following formula (1) By adding an acidic solution;

[Chemical Formula 1]

[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₁₀ S ₂ ) ₆ ] m

(2)

[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₄ S ₂ ) ₆ ] m

The metal-organic skeleton represented by the formula (1) is a three-dimensional structure in which 1,4-dimethyl-2,5-benzenesulfonic acid is bonded to Zr ₆ O ₄ (OH) ₄ , Lt; / RTI >

The oxidizing agent may be a 20 to 50% hydrogen peroxide solution.

The compound of formula (2) may be prepared by mixing a compound of the following formula (3), zirconium tetrachloride (ZrCl ₄ ) and acetic acid, followed by irradiation with microwave;

(3)

C ₈ S ₂ O ₄ H _{6 .}

The output of the microwave may be between 50 and 300 W and the pressure may be between 80 and 200 psi.

The 3-dimensional porous zirconium-based metal-organic skeleton having the sulfonic acid group of the present invention has a proton conductivity higher than that of the conventional metal-organic skeleton and shows a long-term stability against the proton conductivity.

In addition, since the structure is maintained even in boiling water, it can be applied to a hydrogen fuel cell.

FIG. 1A is a PXRD spectrum of a simulated spectrum, a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7, prepared according to a comparative example, prepared according to an embodiment of the present invention. FIG.
FIG. 1B is a PXRD spectrum showing the stability to water of the compound of Formula 4 prepared according to an embodiment of the present invention over time. FIG.
(B) 1 hour, (c) 2 hours, (d) 3 hours, and (d) 3 hours at room temperature with H ₂ O ₂ , (e) 4 hours, (f) 6 hours, (g) 24 hours, and (h) 48 hours.
FIG. 3A is a survey scan XPS spectrum of S 2p for a compound of Formula 4 and a compound of Formula 5 prepared according to an embodiment of the present invention. FIG.
FIG. 3B is a narrow scan XPS spectrum of S 2p for the compound of Formula 4 and the compound of Formula 5. FIG.
4 is an FT-IR spectrum of the compound of Formula 4, the compound of Formula 5, and the compound of Formula 7 prepared according to the Comparative Example, which is prepared according to an embodiment of the present invention.
FIG. 5 is TGA data of a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7, prepared according to an embodiment of the present invention.
Figure 6 is a PXRD pattern of a compound of formula 5 showing stability to water.
7 is a SEM photograph of a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7 prepared according to an embodiment of the present invention.
FIG. 8 is a graph showing the relationship between N _{2 of the} compound of Formula 4, the compound of Formula 5, and the compound of Formula 7 prepared according to the present invention, Adsorption isotherm.
Figure 9a is the water adsorption and desorption isotherms of the compound of formula 7 (black), the compound of formula 5 (blue), and the compound of formula 4 (red) at 25 ° C.
FIG. 9B is an impedance spectrum during heating and cooling circulation of the compound of Formula 4 under 90% relative humidity. FIG.
9c is a graph showing the activation energies during heating and cooling cycles of the compound of Formula 4 under 90% relative humidity.
FIG. 9d is a graph showing the log-scale hydrogen ion conductivity during heating and cooling cycles of the compound of Formula 4 under 90% relative humidity. FIG.
10 is a PXRD spectrum of a compound represented by the formula (4), a compound represented by the formula (5), and a compound represented by the formula (7) prepared according to the comparative example after adsorption of water molecules.
Figure 11a is a Nyquist plot for a compound of Formula 7 at 90% relative humidity and 25-80 占 폚.
11b is an Arrhenius plot for bulk conductivity versus resistance of a compound of Formula 7 at 90% relative humidity conditions.
Figure 12a is a Nyquist plot for a compound of Formula 5 at 90% relative humidity and 25-80 占 폚.
Figure 12b is an Arrhenius plot of the compound of Formula 5 at 90% relative humidity conditions.
13 is a PXRD graph for post-impedance measurement of a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7 prepared according to an embodiment of the present invention.
14 is a graph showing the hydrogen ion conductivity according to the relative humidity of the compound of Formula 4 at 25 ° C.
15 is a PXRD graph for post-impedance measurement of the compound of Formula 4;

The present invention relates to a zirconium-based metal-organic skeleton having a sulfonic acid group having excellent proton conductivity and exhibiting long-term stability against the proton conductivity and a method for producing the same.

Hereinafter, the present invention will be described in detail.

The zirconium-based metal-organic skeleton incorporating the three-dimensional porous sulfonic acid group of the present invention is represented by the following formula (1), and has a proton conductivity higher than that of the sulfonic acid group introduced therein and exhibits long-term stability against the proton conductivity.

[Chemical Formula 1]

[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₁₀ S ₂ ) ₆ ] m

The metal-organic skeleton has a structure in which eight oxygen atoms are coordinated to each of six zirconium metal atoms, four oxygen atoms are provided from a carboxy ligand, and the remainder are oxygen atoms provided from bridging oxygen atoms and oxygen of a hydroxy molecule will be. This unit structure is expanded to form two types of cages, octahedron and tetrahedron, and these cages are connected to each other to form a three-dimensional structure. And m is an integer of 0 to 100.

Specifically, the compound of Formula 1 is UiO-66 (University of Oslo) type, and 1,4-dimethyl-2,5-benzenesulfonic acid is bonded to Zr ₆ O ₄ (OH) ₄ .

The UiO-66 structure is a material that forms a three-dimensional structure having zirconium as a central metal and having an internal void space by binding an organic ligand.

The compound of Formula 1 has a proton conductivity of 1.0 X 10 ^-2 to 1.0 X 10 ^-1 S / cm, preferably 5.0 X 10 ^-2 to 9.0 X 10 ^-2 S / cm, at 80 and 90% relative humidity ; The BET surface area is 30 to 100 m ² / g, preferably 30 to 40 m ² / g.

The crystal structure of the compound of Formula 1 is as follows.

[modelling]

In the crystal structure, zirconium is green with several sides, oxygen is a red dot, and carbon is represented by a line.

Further, the compound of the formula (1) is synthesized according to the synthesis process of the following Reaction Scheme 1.

[Reaction Scheme 1]

_{C 8 S 2 O 4 H 6} -> [Zr 6 O 4 (OH) 4 (C 8 H 4 O 4 S 2) 6] m -> [Zr 6 O 4 (OH) 4 (C 8 H 4 O 10 S ₂ ) ₆ ] m

[Chemical Formula 3] < EMI ID =

Specifically, the above-mentioned formulas (1) to (3) can be represented by the following formulas (4) to (6), respectively. For example, a zirconium metal is bonded to eight oxygen atoms, and m ₁ to m ₄ are the same or different from 0 to 100.

[Chemical Formula 4] < EMI ID =

(ZrCl ₄ ) and acetic acid as a reaction modifier are added to a compound of the formula (1) in a DMF solvent, and the mixture is stirred for 1 to 3 hours and then irradiated with a microwave to obtain a compound of the formula The carboxyl group of the compound is dehydrogenated and a compound of formula (2), which is functionalized with a thiol (-SH) functional group, is combined with zirconium which is a metal ion.

(2) is treated with an oxidizing agent to oxidize the thiol (-SH) functional group of the compound of formula (2) to a sulfonic acid (-SO ₃ H) functional group, and then a dilute acid solution is added thereto, Min. ≪ / RTI > Examples of the oxidizing agent include hydrogen peroxide or nitric acid, and the dilute acid solution includes sulfuric acid or hydrochloric acid.

The output of the microwave used in the preparation of the compound of Formula 2 is 50 to 300 W, preferably 100 to 150 W. When the output of the microwave is less than the lower limit value, a UiO-66 type structure can not be formed, and when the output is higher than the upper limit value, side reactions may occur.

Also, the microwave pressure is 80 to 200 psi, preferably 100 to 150 psi. When the pressure of the microwave is less than the lower limit value, skeletons having different structures may be formed, and in the case of exceeding the upper limit value, side reactions may occur.

In the present invention, the UiO-66 type structure may not be formed when a chemical mechanical synthesis method or an ultrasonic synthesis method other than the microwave synthesis method is used in the production of the compound of formula (2).

The oxidizing agent used in the preparation of the compound of formula (1) is a dilute oxidizing agent solution at a concentration of 20 to 50%, preferably 30 to 40%. When the concentration of the oxidizing agent is less than the lower limit, the oxidation reaction is not completely performed and it may take a longer time to convert the thiol into the sulfonic acid anion. If the concentration exceeds the upper limit, the compound structure of the formula have.

Further, the dilute acid solution is an acid solution having a concentration of 0.01 to 0.09 M, preferably 0.02 to 0.04 M. When the concentration of the sulfuric acid solution is out of the above range, it is not sufficiently acidified or the stability of the structure is reduced.

The structure of these compounds can be confirmed by PXRD, XPS, FT-IR and the like.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

<Examples>

Synthesis Example 1. Synthesis of Compound (4)

1-1. Synthesis of Compound Represented by Formula 3

[Reaction Scheme 2]

 (3)

Dihydroxyterephthalic acid diethyl ester (10 g, 39.00 mmol) and DABCO (18 g, 157 mmol) were completely dissolved in DMA (100 mL) under a nitrogen atmosphere, And cooled. To this is added dimethylthiocarbamoyl chloride (19 g, 157 mmol) dissolved in 50 mL of DMA dropwise. The mixture was stirred at room temperature for 16 hours, and the resulting white precipitate was filtered, washed with a large amount of water, and dried under vacuum to synthesize 2,5-bis (dimethylthiocarbamoyloxy) terephthalic acid diethyl ester. The synthesized 2,5-bis (dimethylthiocarbamoyloxy) terephthalic acid diethyl ester was heated in a temperature range of 220 to 230 ° C for 1 hour in a nitrogen atmosphere, and the resulting brownish compound was cooled to 70 ° C and ethanol was added . The pale brown crystals obtained by cooling to room temperature are filtered to obtain 2,5-bis (dimethylthiocarbamoylsulfanyl) terephthalic acid diethyl ester. The above-mentioned 2,5-bis (dimethylthiocarbamoylsulfanyl) terephthalic acid diethyl ester compound (1.3 g, 3.03 mmol) was placed in a 1.3 M KOH solution prepared by mixing 1: 1 volume ratio of ethanol and water, And the resulting reaction was cooled in an ice bath. To this was added HCl solution (15 mL) to obtain a yellow compound of formula (III).

1-2. Synthesis of Compound Represented by Formula 2

[Reaction Scheme 3]

[Chemical Formula 6]

To a solution of the compound of formula 6 (96 mg, 0.41 mmol) in DMF (8 mL) was added ZrCl ₄ (95 mg, 0.41 mmol) and acetic acid (5.5 mL, 95.7 mmol) dissolved in DMF And the mixture was stirred for 2 hours. The pale clear yellow solution (2 mL) was transferred to a 10 mL Pyrex cell and sealed with polytetrafluoroethylene (PTFE). The mixture was irradiated with a microwave irradiator (CEM Discover, 100 W, 140 psi) at 120 ° C for 40 minutes. The resulting solid was collected by a centrifuge, washed with DMF and dichloromethane, and the resulting pale yellow precipitate was dried in air to obtain the compound of Formula 5 (yield: 72%).

Chemical elemental analysis (%) calcd for [Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₄ S ₂ ) ₆ ] 1.4 (DMF) 22 (H ₂ O): N 0.77, C 24.61, H 3.24, S 15.10; Found: N 0.46, C 24.35, H 2.84, S 15.44.

1-2. Synthesis of Compound Represented by Formula 1

[Reaction Scheme 4]

[Chemical Formula 5]

The compound of Formula 5 (0.2 g) was dissolved in 30% H ₂ O ₂ (20 mL). The solid suspension was stirred at room temperature for 1 hour, and was recovered by centrifugation and suspended in 0.02 MH ₂ SO ₄ solution (20 mL) for 30 minutes so that the solid was completely acidified with the sulfonate group. The resulting solid was collected by centrifugation and washed several times with water, and the resulting pale yellow precipitate was dried in air to obtain the compound of Formula 4 (yield: 90%).

Chemical elemental analysis (%) calcd for [Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₁₀ S ₂ ) ₆ ] 30 (H ₂ O) : C 18.21, H 2.80, S 12.16; found: C 18.33, H 2.90, S 12.13.

< Comparative Example >

Synthetic example  2. A compound represented by the formula (7)

2-1. Synthesis of Compound Represented by Formula 7

[Reaction Scheme 5]

                              (7)

An aqueous solution of zirconium chloride (ZrCl ₄ ) (1.70 mg, 7.27 mmol) dissolved in 0.4 g (21.8 mmol) of water (H ₂ O) is added to a solution of terephthalic acid (1.21 g, 7.27 mmol) in 375 mL of DMF. The clear mixed solution is transferred into a 500 mL vessel and reacted in an oven preheated to 120 ° C for 24 hours. The obtained white compound was filtered and washed with a large amount of DMF to obtain a compound represented by the formula (7).

< Test Example >

A sulfonic acid functional group was introduced into a UiO-66 type skeleton known to have excellent water and chemical stability to synthesize a compound of formula (4). The compound of formula (4) is obtained by in situ oxidation of a thiol group in a compound of formula (5) functionalized with a thiol functional group. This compound, in which sulfonic acid is present in the skeleton as a covalent bond, is stable under boiling water conditions near 100 ° C. and proton conductivity is 8.4 × 10 ^-2 S / cm at 80 ° C. and 90% relative humidity. The proton conductivity values were much higher than those of the compound of formula (7) which was not functionalized with the skeleton and showed long-term stability against proton conductivity. In particular, the proton conductivity values surpass the record of the values of the metal-organic skeleton-based proton conducting materials known to date and are comparable to those of Nafion.

Test Example  One. PXRD  Measure

FIG. 1A is a PXRD spectrum of a simulated spectrum, a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7 prepared according to an embodiment of the present invention, and FIG. The PXRD spectrum showing the stability to water according to the time of the compound of Formula 4 prepared according to the embodiment.

In addition, Figure 2 is a [Formula 5] the compound at room temperature with H ₂ O ₂ (a) before treatment made in accordance with an embodiment of the invention, the process (b) 1 sigan, (c) 2 sigan, (d) 3 hours, (e) 4 hours, (f) 6 hours, (g) 24 hours, (h) 48 hours.

As shown in FIG. 1 and FIG. 2, it was confirmed that the compounds of formula 4, the compound of formula 5 and the compound of formula 7 were structurally matched (FIG. 1A) in order to oxidize a ₃ H-functionalized material with a thiol (-SH) is soaked in hydrogen peroxide (H ₂ O ₂₎ it must be stable in solution [formula 5] 30% hydrogen peroxide at room temperature, the compound (H ₂ O ₂₎ solution time To investigate the stability of the compound of the formula (5) to the oxidizing agent. The compound of formula (5) retained its structure for 48 hours (FIG. 2), and based on the stability test and other supporting data ( vide infra ), the time for which the thiol group H ₂ O ₂ for a period of time.

The sulfonic anion group was treated with 0.02 M sulfuric acid (H ₂ SO ₄ ) solution for 30 minutes in order to protonate the sulfonic acid anion group into sulfonic acid. The PXRD pattern of the compound showed that the compound had the same structure as the compound of Formula 7 (FIG. 1A).

In addition, it was confirmed that no phase change was observed even when immersed in water for 30 days, and thus the stability to water was excellent (Fig. 1B).

Test Example  2. Structural Analysis

FIG. 3A is a survey scan XPS spectrum of S 2p for a compound of Formula 4 and a compound of Formula 5 prepared according to an embodiment of the present invention, and FIG. 3B is a survey scan XPS spectrum of a compound of Formula 4 and a compound of Formula 5 ] &Lt; / RTI &gt; compound.

4 is an FT-IR spectrum of the compound of Formula 4, the compound of Formula 5, and the compound of Formula 7 prepared in accordance with the present invention.

5 is TGA data of the compound of the formula (4), the compound of the formula (5) and the compound of the formula (7) prepared according to the comparative example prepared according to the embodiment of the present invention.

Also, Figure 6 is a PXRD pattern of a compound of formula 5 showing stability to water.

7 is a SEM photograph of a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7 prepared according to an embodiment of the present invention.

As shown in FIGS. 3 to 6, the oxidation state of sulfur contained in each of the [Formula 4] and [Formula 5] compounds can be evaluated from x-ray photoelectron spectroscopy (XPS) This is because the functional group when the acid group is oxidized to change the combination of S 2p _2/3 the energy that appears in the -SO ₃ H can check by being blue shift than the binding energy of the S -SH. [Chemical Formula 5] S 2p _2/3 binding energy in the compound (163.4eV) is lower than [Chemical Formula 4] compound (167.8eV), which describes the oxidation of sulfur (FIG. 3b).

Infrared (IR) spectra of the compound of formula (4), the compound of formula (5) and the compound of formula (7) were obtained to confirm the presence of -SH and -SO ₃ H functional groups (FIG. In the IR spectrum of the compound of Formula 5, it shows a peak at 2570 cm ^-1 , which is consistent with the stretching frequency of the freely present thiol group and is absent from the spectrum of the compound of Formula 7. By comparison, in the IR spectrum of the compound of Formula 4, the thiol peak completely disappeared and the band of 1238 cm ^-1 and 1183 cm ^-1 appeared. The band is a symmetric asymmetric stretching frequency of S = O. An additional peak at 661 cm ^-1 represents the SO stretching vibration and the newly observed peak in the IR spectrum of this compound means the presence of the -SO ₃ H group and was further confirmed by elemental analysis . Therefore, the thiol group of the compound of formula (5) is H ₂ O ₂ It was completely converted to sulfonic acid group through oxidation and continuous acid treatment.

The thermogravimetric (TG) analysis of the compound of Formula 7 also shows that initial weight loss occurs up to 150 ° C and skeletal degradation begins at 500 ° C due to removal of solvent molecules present on the surface. The weight reduction in the compound means 1.4 DMF molecules and 22 H ₂ O molecules in the temperature range of 30-320 ° C. and the removal of water molecules (30 H ₂ O) from the compound is 30 -200 &lt; 0 &gt; C. The functionalized structure is thermally stable up to 400 占 폚.

MOF as a water-mediated proton conductor must have stability to water. Therefore, in order to examine the water stability of each of the compound of formula 4 and the compound of formula 5, it is immersed in water at 100 ° C, boiled for about 30 days, (Fig. 1B and Fig. 6). Even under these harsh conditions, the compounds of formula (IV) and compounds of formula (V) showed structural integrity for over 30 days, indicating excellent stability to water.

In addition, through the scanning electron microscope (SEM), the particle size and shape of the compound of formula (7) can be confirmed to differ from the compound of formula (4) and the compound of formula (5) because the synthesis method is different.

Test Example  3. Nitrogen gas adsorption

FIG. 8 is a graph showing the relationship between N _{2 of the} compound of Formula 4, the compound of Formula 5, and the compound of Formula 7 prepared according to the present invention, Adsorption isotherm.

As shown in FIG. 8, the permanent porosity of the materials can be determined by N ₂ gas adsorption measured at a temperature of 77 K. Prior to the gas adsorption experiment, the compound of formula 7 was immersed in methanol for 3 days, After the solvent is exchanged with methanol, it is treated at 250 ° C under vacuum for 2 hours. The solvent-exchange process of the compound of formula (4) and the compound of formula (5) is carried out in acetone for 3 days and then treated at 150 ° C. and 120 ° C., respectively.

At 77 K, the adsorption isotherm of N ₂ represents a typical type-1 form of the graph of the material with micro-sized pores. A sudden increase in the value seen near 1 bar can be explained by adsorption between particles. The Brunauer-Emmett-Teller (BET) surface area calculated through N ₂ gas adsorption was 897 m ² / g for the compound of formula 7, 308 m ² / g for the compound of formula 5, 35 m &lt; ² &gt; / g. The order of the BET surface area size appears in the order of the degree of steric hindrance that occurs as the size of the -H, -SH, -SO ₃ H functional groups present in the cavities of each material increases.

Test Example  4. Water molecule adsorption

9a shows the water adsorption and desorption isotherms of the compound of formula 7 (black), the compound of formula 5 (blue) and the compound of formula 4 (red) at 25 ° C, FIG. 9C is a graph showing the activation energy during compound heating and cooling circulation under 90% relative humidity, and FIG. 9D is a graph showing the activation energy during 90% relative humidity at 90% relative humidity [ 4 is a graph showing the log-scale hydrogen ion conductivity during heating and cooling circulation of the compound. The filled and unfilled figures in FIG. 9A indicate adsorption and desorption, respectively.

10 is a PXRD spectrum of a compound of the formula (4), a compound of the formula (5), and a compound of the formula (7) prepared according to the comparative example after adsorption of water molecules.

In a water-borne system, the skeleton must adsorb water molecules well to create a water-network of stable hydrogen bonds along the hydrogen ion transport path. With respect to this point, the water adsorption and desorption isotherms of the compound of Formula 4, the compound of Formula 5, and the compound of Formula 7 were measured (FIG. 9A).

The isotherm of the compound showed a faster increase in adsorption in the low pressure region (P / Po < 0.3) and a larger hysteresis than the other samples. This characteristic signal indicates that a substance having sulfonic acid functional groups has a higher affinity for water than other substances having -H and -SH functional groups. This hydrophilicity plays a key role in the effective transfer of hydrogen ions.

In addition, the skeletal structure of the compound of formula (4), the compound of formula (5), and the compound of formula (7) was maintained after the water adsorption experiment when compared with the skeleton before the adsorption experiment (FIG.

Test Example  5. Hydrogen ion (Proton) Conductivity measurement

Figure 11a is a Nyquist plot for a compound of Formula 7 at 90% relative humidity and 25-80 ° C, and Figure 11b is a graph of Nyquist plot for bulk resistance against resistance of a compound at 90% relative humidity conditions. It is a Renius plot.

Figure 12a is a Nyquist plot for a compound of Formula 5 at 90% relative humidity and 25-80 ° C, and Figure 12b is an Arrhenius plot of a compound of Formula 5 at 90% relative humidity.

13 is a PXRD graph for post-impedance measurement of a compound of Formula 4, a compound of Formula 5, and a compound of Formula 7 prepared according to an embodiment of the present invention.

In order to measure the hydrogen ion conductivities of the compounds represented by Chemical Formulas [4], [Chemical Formula 5] and [Chemical Formula 7], pellet-shaped samples were measured at a relative humidity of 90% The AC impedance spectrum was measured. Conductivity values were calculated by fitting the experimentally obtained impedance spectrum to the presented equivalent circuit.

As shown in FIGS. 11 and 12, the two semicircles shown in the compound of formula (5) and the compound of formula (7) obtained at 90% relative humidity and at different temperature conditions are well separated in the impedance graph appear. This seems to be attributed to bulk resistance and inter-particle resistance, possibly with electrode contact (Figs. 11A, 12A).

At 25 캜, 90% relative humidity, the bulk conductivity of the compound of Formula 7 is 3.5 x ^10-7 S / cm; It increases to 4.3 x ^10-6 S / cm at 80 ℃ and 90% relative humidity condition. Under the same conditions, the value of the compound of Formula 5 is much higher than that of the compound of Formula 7 (6.3 x 10 ^-6 S / cm at 25 ° C and 2.5 x 10 ^-5 S / cm at 80 ° C).

Since the proton donating ability of the functional groups existing in the water-network forming the hydrogen bond is governed by pKa, this property is more preferable because the -SH functional groups of the compound represented by formula (5) It comes from being acidic. Surprisingly, the conductivity of the compound of Formula 4 is 1.4 x 10 &lt; ^-2 &gt; S / cm at 25 DEG C and 90% relative humidity and has four orders of magnitude larger values compared to the compound of Formula 7. Increasing the temperature to 80 DEG C leads to a more pronounced increase in the conductivity value to 8.4 x 10 &lt; ^-2 &gt; S / cm (Fig. 9B).

This notable conductivity value is due to the presence of strong Bronsted acid sites (-SO ₃ H) in the organic linker. These acidic functional groups help the water to be well absorbed into the confined space and allow the organization of hydrophilic regions thereby forming an efficient hydrogen ion transport pathway. This is similar to that seen in Nafion.

The super proton conductivity of the compound is the most superior among the MOF materials that have been reported so far in hydrogen ion conductivity. For example, the introduction of strong acids such as H ₂ SO ₄ , H ₃ PO ₄ , Toluenesulfonicacid, and TfOH (trifuluoromethanesulfonicacid) into the empty space of the skeleton using an acid-stable solid MIL- The conductivity value was increased to 8x10 &lt; ^-2 & gt ^; S / cm at 60 DEG C and 15% relative humidity. One of the interesting experimental results is that the hydrogen ion conductivity of water-mediated and anhydrous conditions is found in the same skeleton (for example, {[(Me ₂ NH ₂ ) ₃ (SO ₄ )] ₂ [Zn ₂ (oxalate) ₃ ]} _n ).

These high hydrogen ion conductivity materials are different from the [Formula 4] compounds containing strong acid functional groups covalently bonded to organic linkers because they have guest molecules that enable conduction. The compound of formula (4) is a water-mediated proton conduction pathway in which strongly acidic units capable of providing a large amount of hydrogen ion are present in the metal-organic skeleton as a covalent bond, which is represented by Nafion To have the corresponding highest conductivity value. Structural stability after the conductivity measurements of all the samples was confirmed by measuring PXRD (Fig. 13), confirming that the structure was not changed.

Test Example  6. Measurement of activation energy

The activation energies obtained from Arrhenius plots are (E _a ) values of 0.43 eV (compounds of formula 7), 0.23 eV (of compounds 5) and 0.32 eV (of formula 4) Respectively. These results suggest that the functionalization inside the pore forms a proper gap between hydrogen donor and acceptor. The determined activation energy (E _a ) values of functionalized solids are similar to those of Nafion (0.22 eV), uranium phosphate (0.32 eV), and many other conductive MOFs reported. The range of the activation energy of the compound of the formula 5 and the compound of the formula 4 corresponds to the conventional Grotthuss mechanism in which the functional groups are diffused through the water channel and hydrogen is supplied by the hydrogen ion leaching process.

Test Example  7. Hydrogen ion  Correlation between conductivity and humidity

14 is a graph showing the hydrogen ion conductivity according to the relative humidity of the compound of Formula 4 at 25 ° C.

As shown in FIG. 14, to clarify the correlation between the conductivity and humidity, the hydrogen ion conductivity was measured while applying various relative humidity at 25 ° C. to the compound of Chemical Formula 4, and the points corresponding to the data were plotted on a straight line graph Respectively.

Hydrogen ionic conductivity increases slowly in the low relative humidity range and increases abruptly above 50% relative humidity. This tendency suggests that hydrogen ion conduction is highly dependent on the content of water molecules contained in the conduction pathway and supports the fact that hydrogen ion conductivity occurs through the Grotthuss mechanism. This tendency was similar for H ⁺ @ Ni ₂ (dobdc) (H ₂ O) ₂ , which exhibited a steep increase in conductivity when the relative humidity was above 75%.

Test Example  8. Hydrogen ion  Correlation between conductivity and temperature

15 is a PXRD graph for post-impedance measurement of the compound of Formula 4;

Temperature-dependent changes in hydrogen ion conductivity were observed under two heating-cooling cycles at 90% relative humidity. Hydrogen ion conductivity increased with increasing temperature and decreased together during cooling. The difference between the heating and cooling profiles is noticeable, which is expected to be related to the degree of hydration of the sample itself, since the sample lacked sufficient time to reabsorb water molecules during the cooling process. This difference is further increased at low temperatures, probably due to the slow adsorption-desorption rate of water molecules into the conduction path.

Conductivity patterns required for fuel cell applications are predictable because the first and second heating, first cooling, and second cooling lines are nearly identical for two repeated heating-cooling cycles. Furthermore, it was confirmed that the structure was maintained well by the PXRD measurement after the conductivity measurement during the heating-cooling circulation process (FIG. 15).

[Chemical Formula 4] In order to confirm the long-term stability of the compound, the conductivity was measured in an environment maintained at 25 ° C and 90% relative humidity. Conductivity did not change until nearly 96 hours, suggesting that it is structurally stable during conductivity measurements.

As a result, a compound represented by Formula 5 that is functionalized with a thiol functional group is synthesized through a microwave reaction. The thiol functional groups are completely oxidized and acidified by treatment with a solution of H ₂ O ₂ and H ₂ SO ₄ to obtain a compound of Formula 4 .

Successfully, the -SO ₃ H functional groups were covalently bound to the backbone of the MOF, and their efficient hydrogen ion delivery enabled much greater hydrogen ion conduction. The skeleton of the compound of Formula 4 was confirmed to maintain its structure even in the state of boiling water essential to the hydrogen fuel cell technology mediated by water.

In addition, the conductivity value of 8.4 x 10 ^-2 S / cm observed at 80 ° C and 90% relative humidity is the best value among the MOFs with hydrogen ion conductivity reported so far and comparable to that of Nafion. These results will provide a promising pathway to maximize the hydrogen ion conductivity of MOF materials.

Physical measurement

The elemental analysis for C, H and N was measured at Sogang University elemental analysis center and the thermogravimetric analysis was carried out using a Scinco TGA N-1000 at a ramp rate of 10 ° C / min under nitrogen flow (50 mL / min) .

PXRD diffraction analysis was performed using a Rigaku Ultima III diffractometer [CuKa (λ = 1.5406)] at a scan rate of 2 ° / min and a step size of 0.02 ° and infrared spectra were measured using a Bomen MB 104 FT-IR spectrometer KBr pellets.

The XPS spectrum was also measured at the KIST analysis center using PHI 5000 VersaProbe equipped with Al Kα monochromatic X-ray emission source (1486.7 eV).

Adsorption measurement

Gas adsorption isotherms were measured using a BEL Belsorp mini II gas adsorber to a gas pressure of 1 atm. High purity N ₂ (99.999%) and CO ₂ (99.999%) were used for adsorption experiments.

Gas isotherms were measured at 77 K (N ₂ ), 273 K (CO ₂ ), and 298 K (CO ₂ ) and water adsorption experiments were carried out at 25 ° C using the Micrometrics ASAP2020 apparatus.

Impedance Analysis

AC impedance data was obtained using pellets (0.6 cm in diameter), and the thickness of the pellets was 0.10-0.14 cm.

The measurement is performed using a Solartron SI 1260 Impedance / Gain-Phase analyzer with a Pt pressurized electrode and a 1287 Dielectric Interface, with an AC voltage amplitude of 100 mV and a frequency range of 3 MHz to 0.1 Hz.

Claims (8)

A three-dimensional porous zirconium-based metal-organic skeleton having a sulfonic acid group represented by the following formula (1);
[Chemical Formula 1]
[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₁₀ S ₂ ) ₆ ] m
The metal-organic skeleton is a three-dimensional structure in which 1,4-dimethyl-2,5-benzenesulfonic acid is bonded to Zr ₆ O ₄ (OH) ₄ ,
M is an integer of 0 to 100; The zirconium-based metal-organic skeleton according to claim 1, wherein the zirconium-based metal-organic skeleton has a proton conductivity of 1.0 X 10 ^-2 to 1.0 X 10 ^-1 S / cm at 80 ° C and 90% relative humidity. Based metal - organic skeleton. The zirconium-based metal-organic skeleton according to claim 1, wherein the zeta-based metal-organic skeleton has a BET surface area of 30 to 100 m ² / g. A process for producing a zirconium-based metal-organic skeleton by introducing a sulfonic acid group represented by the following formula (1), which is prepared by treating a compound of the following formula (2) with an oxidizing agent and then adding a dilute acid solution thereto;
[Chemical Formula 1]
[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₁₀ S ₂ ) ₆ ] m
(2)
[Zr ₆ O ₄ (OH) ₄ (C ₈ H ₄ O ₄ S ₂ ) ₆ ] m
The metal-organic skeleton represented by the formula (1) is a three-dimensional structure in which 1,4-dimethyl-2,5-benzenesulfonic acid is bonded to Zr ₆ O ₄ (OH) ₄ ,
M is an integer of 0 to 100; 5. The process for producing a zirconium-based metal-organic skeleton according to claim 4, wherein the oxidizing agent is 20 to 50% hydrogen peroxide solution. The zirconium-based compound according to claim 4, wherein the compound of formula (2) is prepared by mixing a compound of formula (3), zirconium tetrachloride (ZrCl ₄ ) and acetic acid, A method for producing a metal-organic skeleton;
(3)
C ₈ S ₂ O ₄ H _6.  7. The method of claim 6, wherein the output of the microwave is 50 to 300W.  7. The method of claim 6, wherein the pressure of the microwave is 80 to 200 psi.

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