RU2787343C1 - Proton-exchange membrane based on organometallic framework structure hkust-1 - Google Patents

Abstract

FIELD: electrolytic materials.

SUBSTANCE: invention relates to an electrolytic material for carrying out the transfer of positively charged hydrogen ions between the electrodes of a hydrogen fuel cell. A proton-exchange composite membrane SPES/HKUST-1 for solid polymer fuel cells with a thickness of 48-52 µm is proposed. The membrane contains an HKUST-1 organometallic frame structure doped with a sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES), in the following ratio, wt.%: HKUST-1 - 4.5-5.5, SPES - 94.5-95.5.

EFFECT: production of a proton-exchange membrane, which, due to its high ionic conductivity and exchange capacity, provides an increase in the efficiency of power generation by fuel cells, while significantly reducing carbon monoxide emissions, which has a positive effect on the environment.

1 cl, 4 dwg, 2 tbl

Description

The invention relates to the field of chemistry and chemical technology, namely, it is an electrolytic material for carrying out the transfer of positively charged hydrogen ions between the electrodes of a hydrogen fuel cell. Thus, this material is a structural element of a hydrogen fuel cell.

The technical result is the manufacture of a proton-exchange membrane based on the HKUST-1 organometallic frame structure, which will be used in hydrogen fuel cells to carry out the transfer of positively charged hydrogen ions between electrodes and generate electricity. The use of a proton-exchange membrane based on the HKUST-1 metal-organic framework structure improves the efficiency of power generation by fuel cells due to high ionic conductivity and exchange capacity. Increasing the efficiency of power generation by hydrogen fuel cells is necessary to expand the range of applications of this type of power source. Since hydrogen fuel cells are an environmentally friendly way to generate electricity, expanding the scope helps to reduce carbon monoxide emissions and has a positive impact on the environment.

NAFION and its modifications can be distinguished as analogues of proton-exchange membranes used in hydrogen fuel cells. The original NAFION membranes were patented in 1964 by "Fluorocarbon vinyl ether polymers" under patent US3282875A, but various modifications of NAFION are still relevant today, for example, "Perfluorinated sulfonic resin/sulfonation SiO 2Molecular sieve compound proton exchange membrane and preparation method thereof" under the patent CN101938002B, Modified nafion proton exchange membrane, preparation method of proton exchange membrane, direct methanol fuel cell electrode membrane and preparation method of membrane electrode patent CN112885982A.

NAFION proton exchange membranes, due to their superacid groups, provide high conductivity and high oxidation stability, which allows high performance and durability in hydrogen fuel cells. However, NAFION also has disadvantages such as low thermomechanical stability, high oxygen permeability, and membrane degradation in real devices. These shortcomings necessitate the search for other ionomers based on other polymer chains. The use of NAFION is limited, for example, in the automotive industry. The thickness of NAFION membranes cannot be lower than approximately 100 microns so as not to compromise the mechanical stability of the membrane.

All prior art or commercially available fuel cell membranes have substantially no gas permeability (Gurley number >10,000). In addition, these membranes, especially if they have a large thickness, are difficult to recover after dehydration. Up to now, this is an unresolved problem that hinders the operation of fuel cells.

In addition, in order to prevent poisoning of electrodes containing platinum, very pure hydrogen (99%) is used for prior art fuel cells. In fact, if reformed hydrogen containing CO is used, the platinum is rapidly poisoned. In accordance with the prior art, hydrogen produced in the reforming process must be purified from CO before being used in fuel cells.

The thickness of proton exchange membranes affects a number of parameters such as gas permeability, charge transfer rate, and recovery from dehydration. Accordingly, the smaller the thickness of the membrane used, the higher these indicators, which means that the use of thinner membranes will also have a positive effect on the efficiency of the hydrogen fuel cell. However, the low thickness of the membrane can adversely affect its mechanical stability, which will lead to destruction during operation. The developed membranes have a thickness of approximately 40 ± 10 μm, which is significantly lower than analogues. At the same time, the mechanical properties of these membranes ensure the operability of these membranes in fuel cells even if HKUST-1 metal-organic frame structures are added.

In the claimed development, all the disadvantages are compensated by the use of a sulphonated multiblock copolymer of polysulfone and polyphenylsulfone, which have a higher thermomechanical stability, provide a higher specific power of a hydrogen fuel cell, and the addition of an organometallic frame structure also increases this indicator without harm to thermomechanical properties.

Brief description of illustrations:

Fig. 1. Specific power curves of the SPES@HKUST-1 membrane at 50 - (1), 60 - (2), 70 - (3) and 80 - (4)°C and 100% relative humidity.

Fig. Fig. 2. Proton conductivity of synthesized membranes based on HKUST-1 loaded with HKUST-1 5 - (1), 10 - (2) and 20 - (3) wt. % depending on temperature at 90% relative humidity.

Fig. 3 Photograph of the obtained proton-exchange membrane based on the organometallic framework structure HKUST-1.

Fig. 4 Structure of the organometallic framework structure HKUST-1, where 1) trimesic acid, 2) organometallic framework structure HKUST-1, 3) a cluster of copper atoms.

A proton exchange membrane based on HKUST-1 and a sulfonated polysulfone-polyphenylsulfone multiblock copolymer is more hydrophilic than its counterparts, which provides a fast recovery rate after dehydration. The thickness of the membranes immediately after synthesis is 38.8 micrometers and was determined using a thickness gauge under the following standard conditions:

Standard pressure 105 Pa

Standard temperature 20°C

Relative humidity 30%

Organometallic frameworks (MOFs) are a unique class of crystalline porous materials where metal centers are connected to each other by organic linkers. This class of materials can have a large pore size, high surface area, and the possibility of functionalization, additional guest molecules, changing or adding unique properties, all this due to the high variability of the structural elements used.

The use of organometallic framework structures for the manufacture of proton-exchange membranes is primarily due to their high specific surface area and large number of pores. There are only a small number of articles by research groups using organometallic framework structures exclusively for the modification of already known proton-exchange films, all of which have been published within the last 10 years [3–5].

The material that is supposed to be implemented in proton-exchange membranes is HKUST-1. Metal-organic framework structure HKUST-1 is a nanoporous crystalline material consisting of clusters of Cu II copper atoms and a 1,3,5-benzene tricarboxylate (BTC) linker. This structure has a high specific surface area of 1500-2100 m2/g and a large pore size, which opens up the possibility of storing a large number of water molecules inside this material, which has a positive effect on the water absorption of the ion-exchange capacity of proton-exchange membranes.

The novelty of the development lies in the combination of a multiblock copolymer of polysulfone and polyphenylsulfone SPES with an organometallic framework structure HKUST-1. Since the HKUST-1 used is crystalline, it is possible to create a film with the necessary requirements for use in hydrogen fuel cells by using a polymeric substance that also has the ability to transport charged ions. Ionomers based on multiblock polycondensates are best suited for this purpose, namely, a sulfonated multiblock copolymer of polysulfone and polyphenylsulfone. Combining these two nanostructured materials creates a proton exchange membrane with high ionic conductivity due to increased water absorption, which provides the presence of the HKUST-1 metal-organic framework and all the necessary properties for hydrogen fuel cell applications. All this thanks to the sulphonated multiblock copolymer of polysulfone and polyphenylsulfone.

The technology for creating a proton-exchange membrane based on the organometallic framework structure HKUST-1 consists in doping the sulphonated multiblock copolymer of polysulfone and polyphenylsulfone SPES with crystallites of the organometallic framework structure HKUST-1 distributed over the membrane volume. The metal-organic framework structures used as an additive increase the water absorption of these membranes from 22% to 42% at a temperature of 30°C and from 31% to 74% at a temperature of 60°C close to the operating temperature of a hydrogen fuel cell, the ion exchange capacity of the multiblock polyethersulfone increases with 1.62 to 1.93 (meq H+ g-1). The membrane was tested under operating conditions on an Autolab PGStat30 potentiostat with an FRA module.

Test conditions:

Temperature range from 50 to 80°С;

Relative humidity 100%;

The frequency range used was 10 kHz to 1 Hz;

The amplitude of the sinusoidal signal was 10 mV;

Humidified hydrogen (HHE, anode) and nitrogen (cathode) were continuously supplied to the cell at a rate of 200 ml/min;

In FIG. Figure 1 shows the curves of polarization (A) and power density (B) obtained as a result of testing the developed membrane based on HKUST-1 depending on temperature. The conducted studies have shown that the highest current density is achieved at the operating temperature of the hydrogen fuel cell of 70 and 80°C, where the maximum power density of about ~900 mW/cm ² is reached at a current density of about 2400 mA/cm ² .

If we compare the obtained results with the results obtained using commercial NAFION membranes under the same experimental conditions Tab. 1, it can be answered that the specific power when using a proton-exchange membrane based on the HKUST-1 metal-organic frame structure is higher than the presented analogues, which confirms the possibility of effective use of the developed material in hydrogen fuel cells.

Table 1. Comparison table for power density of proton exchange membranes according to thickness

Membrane name Thickness (µm) Specific power (mW/cm ² ) SPES@HKUST-1 38 933 SPES [2] 59 403 Nafion 112 [2] 51 729 Nafion 117 [2] 178 310

1. Synthesis of the organometallic framework structure HKUST-1.

For the synthesis of 100 g of the organometallic framework structure HKUST-1 ([Cu3(TMA)2(H2O)3]n)

1) Copper nitrate CuH ₆ N ₂ O ₉ is taken in the amount of 133.32 g, trimesic acid TMA-H ₃ in the amount of 64.23 g in accordance with the stoichiometric equality 1.8: 1 of the reaction of copper atoms and trimesic acid to form the crystal structure of HKUST- 1.

2) Separately, the precursors are dissolved in 12 ml of 50% ethanol solution to dissociate the starting products.

3) The resulting water-alcohol solutions are mixed in a single glass. As a result of mixing, a homogeneous solution of the reactants is formed.

4) The resulting mixture is heated in a laboratory microwave oven for 1 hour at a temperature of 100°C to activate the processes of dissociation and the formation of HKUST-1 crystallites.

5) Crystallites of the HKUST-1 blue organometallic framework are separated from the supernatant by centrifugation.

6) The resulting blue powder is washed in 50 ml of distilled water in order to purify HKUST-1 from unreacted precursors.

7) The resulting powder is placed in an oven at a temperature of 60°C for 24 hours to remove guest solvent molecules from the pores of the structure [1].

2. Synthesis of a proton-exchange membrane based on the organometallic framework structure HKUST-1.

1) Take the sulfonated multiblock copolymer of polysulfone and polyphenylsulfone SPES in the amount of 0.19 g. The amount of justified required thickness (30-50 micrometers) of the resulting membrane for further optimal use in hydrogen fuel cells and ensure the transport of hydrogen ions between the electrodes.

2) Dissolve in 6 ml of dimethylformamide to create a homogeneous medium [2].

3) Crystallites of the organometallic framework structure HKUST-1 are added to the resulting solution in an amount of 0.01 g for the optimal ratio of the membrane to the used organometallic framework structure HKUST-1.

4) The resulting mixture is stirred until a homogeneous state, then transferred to a Petri dish in order to evenly distribute the crystallites throughout the volume.

5) The resulting mixture in a Petri dish is dried at a temperature of 60°C in a vacuum oven for 48 hours to bake and remove the solvent.

6) Then the resulting membrane is treated with 1 M HCl solution at 60°C for 24 hours, as a result of which sodium ions Na + are replaced by H + protons, which brings the proton exchange membrane into working condition.

The best ratio of SPES to HKUST-1 was determined in the course of optimizing the procedure for the synthesis of proton-exchange membranes based on the organometallic framework structure of HKUST-1. For this, three membranes with a mass equivalent of 5%, 10%, and 20% of the HKUST-1 organometallic framework structure were fabricated. The efficiency of using a metal-organic framework structure was evaluated using impedance spectroscopy, since ionic conductivity is a key parameter since membranes must have high proton conductivity in order to achieve high performance fuel cells.

In FIG. Figure 2 shows the evolution of the proton conductivity of the synthesized membranes with HKUST-1 loadings of 5, 10, and 20 wt %. % under the following conditions:

Temperature 40-90°С in steps of 10°С

Relative humidity 90%

Frequency range from 10 ^-1 Hz to 1 MHz

Voltage amplitude 0.01 V

Tab. Fig. 2. Comparison of the conductivity and specific power indices of proton-exchange membranes with the addition of HKUST-1 and their analogues at various temperatures and relative humidity of 90%.

Sample number Content
SPES, wt.%
94.5-95.5 The content of HKUST-1, wt.%
4.5-5.5 Membrane thickness, µm
48-52 Ionic
conductivity, mSm * cm ^-1 . Specific power of the SPES@HKUST-1 membrane, mW*cm ^-2 50°C 60°С 70°С 80°С 90°С 50°С 60°С 70°C 80°C SPES@4.5%HKUST-1 95.5 4.5 48 7.21 16.2 31.6 53.8 63.1 290 742 910 929 SPES@5%HKUST-1 95% five 50 7.26 16.7 32.1 54.4 63.5 301 746 918 933 SPES@5.5%HKUST-1 94.5 5.5 52 7.23 16.5 32.2 54.9 63.4 296 748 917 933 SPES one hundred% 0% 59 9.23 16.1 27.3 31.3 15.8 251 340 394 403 Nafion 112 [2] - - 51 - - - - - - - 729 - Nafion 117 [2] - - 178 - - - - - - - 310 -

A specific example of the application of this membrane is the use as a structural element of a hydrogen fuel cell, namely as an electrolytic material between the anode and cathode for the transfer of positively charged hydrogen ions. The possibility of using the developed proton-exchange membranes based on HKUST-1 organometallic framework structures in hydrogen fuel cells and their ionic conductivity were proved above.

In FIG. Figure 4 shows the structure of the HKUST-1 organometallic framework structure, consisting of an organic trimesic acid linker and clusters of copper atoms derived from copper acetate, which are combined into a three-dimensional porous material.

Sources of information:

1. Chui, S.S.-Y., et al., A Chemically Functionalizable Nanoporous Material [Cu₃(TMA)₂(H₂O )₃]_<i>n</i>. Science, 1999. 283(5405): p. 1148-1150.

2. Ureña, N., et al., Multiblock copolymers of sulfonated PSU/PPSU Poly(ether sulfone)s as solid electrolytes for proton exchange membrane fuel cells. Electrochimica Acta, 2019. 302.

3. Talukdar, K. and S.-J. Choi, Tuning of Nafion® by HKUST-1 as coordination network to enhance proton conductivity for fuel cell applications. Journal of Nanoparticle Research, 2016. 18.

4. Horike, S., D. Umeyama, and S. Kitagawa, Ion conductivity and transport by porous coordination polymers and metal-organic frameworks. Accounts of chemical research, 2013. 46 11: p. 2376-84.

5. Patel, H., et al., Superacidity in Nafion/MOF Hybrid Membranes Retains Water at Low Humidity to Enhance Proton Conduction for Fuel Cells. ACS Applied Materials & Interfaces, 2016. 8.

Claims (2)

Proton-exchange composite membrane SPES/HKUST-1 for solid polymer fuel cells, containing an organometallic frame structure HKUST-1 doped with a sulfonated multiblock copolymer of polysulfone and polyphenylsulfone SPES in the following ratio, wt.%: HKUST-1 4.5 – 5.5 SPES 94.5 – 95.5 thick 48-52 µm

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