Ion-conducting membrane with high temperature yellowing resistance and method of making same

Abstract

The application relates to an ion-conducting membrane with high-temperature yellowing resistance and a preparation method thereof, and belongs to the technical field of high-temperature stable ion-exchange membranes. The ion-conducting membrane takes perfluorosulfonic acid resin as a base film, the counter ion of ion activation sites of the ion-conducting membrane is an organic cation, the ion exchange site activation number accounts for 60-100%, and the ion exchange capacity of the perfluorosulfonic acid resin is 0.9-1.3 mmol / g. The preparation method comprises the following steps: melt extrusion flow casting to form a base film, hydrolyzing and ionizing in an organic ammonium alkaline aqueous solution, and acidizing and replacing into a protonated form. Through counter ion optimization and ionization degree control, the yellowing phenomenon of the membrane body at high temperature is significantly inhibited, the initial decomposition temperature is increased to 289-352 DEG C, the yellowing index (YI) is reduced to 2.4-4.7, and meanwhile, the proton conductivity is kept as 45-79 mS / cm. The application has the advantages of simple process, adaptation to continuous production, and solution to the problem of easy high-temperature yellowing of traditional perfluorosulfonic acid membranes.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature stable ion exchange membrane technology, specifically relating to a perfluorosulfonic acid ion conduction membrane with high-temperature resistance to yellowing and its preparation method. Background Technology

[0002] Perfluorosulfonic acid (PFSA) ion-conducting membranes are core components of energy devices such as fuel cells, water electrolysis for hydrogen production, and flow batteries. The synergistic improvement of their high-temperature stability and proton conductivity has long been a key technological focus in this field. While traditional PFSA membranes possess excellent proton conductivity, they generally require operation at relatively low temperatures (60-80°C) and high humidity (>40% RH). Research has found that increasing the operating temperature offers several advantages, such as improved fuel cell efficiency, simplified thermal management, accelerated reaction kinetics, and enhanced catalyst poisoning resistance. However, high-temperature environments are prone to dehydration, leading to a significant decrease in proton conductivity, accompanied by severe "high-temperature yellowing," where the membrane color gradually deepens from colorless and transparent to brown or dark brown. Yellowing not only directly reflects a decline in membrane material durability but also indicates irreversible degradation of the microstructure, such as ion cluster network collapse and polymer chain rearrangement, further exacerbating the decline in proton conductivity. Therefore, improving the yellowing resistance of PFSA ion-conducting membranes is essentially a key pathway to enhancing their high-temperature stability.

[0003] The mechanism of "high-temperature yellowing" of perfluorosulfonic acid ion-conducting membranes has not been clearly elucidated in published literature. Related research indicates that after the perfluorosulfonic acid ion-conducting polymer transforms from a salt form to an acid form, its ion exchange sites are activated, and it immediately begins to react with its surrounding environment. Water vapor in the air is absorbed and reacts with the surface sulfonic acid groups. Under the catalytic effect of the superacidic sites of the perfluorosulfonic acid ion-conducting polymer, reactive organic gas components in the surrounding air may undergo chemical changes. These organic gases can combine to form larger compounds. Over time, these organic residues form deposits on the perfluorosulfonic acid ion-conducting polymer, causing the original color of the ion-conducting membrane to gradually change from colorless and transparent to yellow, then to brown, or even darker. Alternatively, under long-term high-temperature environments, the perfluorosulfonic acid ion-conducting membrane may undergo chemical degradation, with the sulfonic acid groups decomposing to produce carbonyl groups and other chromophores, thus causing the membrane's apparent color to gradually yellow. On the other hand, the membrane loses free and bound water, leading to a decrease in the mobility of polymer chain segments, rearrangement, and a reduction in free volume. This process is accompanied by an increase in the glass transition temperature (Tg) and the collapse of the hydrophilic ion cluster network, ultimately leading to a densification of the membrane structure. This densification may further affect the expression of color.

[0004] The apparent changes of perfluorosulfonic acid ion-conducting membranes are a direct characteristic of their microscopic morphological structure changes. Improving the yellowing resistance of perfluorosulfonic acid ion-conducting membranes is essentially about improving the temperature resistance of the ion-conducting membrane and suppressing microscopic changes caused by high temperatures to maintain the intrinsic properties of the ion-conducting membrane.

[0005] Patent CN115954510A discloses a yellowing-resistant hot melt adhesive membrane for hydrogen fuel cells and its preparation method. This membrane uses an organic-inorganic framework compound as its core, forming a nitrogen-containing heterocyclic cross-linked structure through in-situ polymerization of a porous inorganic coordination matrix and pyrrole monomers, providing a proton transport channel. It is supplemented with an organosilicon dispersant, nanofillers, and coupling agents, with the remainder being a fluorine-modified, durable casting solution, significantly improving aging resistance. While this patent combines high proton conductivity, mechanical strength, and yellowing resistance, the membrane preparation process described in this patent is complex, involving numerous small-molecule fillers. Furthermore, the patent does not directly demonstrate the improvement in color change related to yellowing resistance, but rather indirectly reflects it through properties such as tensile strength, elongation at break, and proton conductivity. Therefore, we cannot clearly determine the extent of the improvement in yellowing resistance, and there are significant differences between the main materials of the patent and this invention.

[0006] Patent CN118748263A discloses a high-temperature resistant ion exchange membrane for hydrogen fuel cells and its preparation method. It uses perfluorosulfonic acid resin as a matrix and improves the high-temperature proton conduction stability of the membrane material by introducing a self-made phosphated MOF (metal-organic framework material). The phosphated MOF is combined with the metal framework support through a liquid-phase conversion process, using chelation to anchor the phosphorus-containing structure, forming a stable hydrogen bond network, enhancing proton transfer efficiency, and suppressing the loss of proton conduction medium at high temperatures (120–160℃), thereby improving the energy efficiency of the fuel cell. Although this patent focuses on improving high-temperature stability and proton conduction performance, it does not involve research or optimization of the ion exchange membrane's resistance to yellowing. Similarly, patents CN115991821B and CN115991828B, in order to improve the performance of ion exchange membranes at high temperatures, both disclose a proton exchange membrane containing phosphate structural units and its preparation method. This method involves a precursor polymer formed by the ternary copolymerization of fluoroolefin / fluoroolefin ether, perfluoroethylene phosphonate monomer, and perfluorovinyl ether sulfonyl fluoride monomer. After hydrolysis and acidification, a perfluorosulfonic acid resin with both phosphonic acid and sulfonic acid groups is obtained. The introduction of phosphate structural units enhances the stability of the ion exchange membrane. However, neither patent mentions the yellowing resistance of the ion exchange membrane.

[0007] Patents CN102828198A, CN213388920U, and CN118767700A all disclose ion-exchange membranes and the tetramethylammonium ion mentioned in this invention. Patent CN102828198A discloses a method for preparing high-purity quaternary ammonium alkali by electrolyzing organic ammonium salts using a perfluorinated ion-exchange membrane in chlor-alkali production. The perfluorinated ion-exchange membranes used in the patent (such as DF988, F8020, and N2030 types) are commercially available products. These membranes belong to the perfluorosulfonic acid-perfluorocarboxylic acid composite ion-exchange membranes used in the chlor-alkali industry. Their characteristic is that the anode side is a perfluorosulfonic acid layer, and the cathode side is a perfluorocarboxylic acid layer, with the counterion still being a traditional alkali metal cation. Patent CN213388920U discloses an electronic-grade tetramethylammonium hydroxide production apparatus. This apparatus only uses an ion-exchange membrane, with almost no information provided about the membrane itself. Patent CN118767700A discloses a method for preparing perfluorinated cation exchange membranes for electrodialysis, which addresses the problems of membrane deformation, warping, and wrinkling caused by uneven hot air distribution or differences in natural drying speeds in traditional drying processes. The core innovation lies in introducing a multi-step drying device with anti-deformation features, combining multi-stage drying, hot air oscillation, and membrane tensioning technology to ensure membrane flatness and performance stability. However, this patent does not address improvements in the temperature resistance, yellowing resistance, or maintenance of high proton conductivity of the perfluorinated ion exchange membrane.

[0008] Therefore, previous studies have mainly focused on indicators such as proton conduction efficiency, high temperature stability and mechanical properties, while systematic research on resistance to yellowing is still lacking. This invention provides a new path to solve this technical bottleneck through counterion optimization and ionization degree control. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of traditional perfluorosulfonic acid ion-conducting membranes in terms of high-temperature yellowing resistance and the deficiencies in their preparation methods. It provides an ion-conducting membrane with high yellowing resistance and its preparation method, achieving the proton conductivity of traditional ion-conducting membranes while significantly reducing the yellowing index and improving the yellowing resistance of the membrane.

[0010] This invention discloses an ion-conducting membrane with high-temperature yellowing resistance, comprising a base membrane of perfluorosulfonic acid resin. The counterions at the ion activation sites of this perfluorosulfonic acid ion-conducting membrane are organic cations, and the activated ion exchange sites account for 60% to 100% of the total. When the activated ion exchange sites are below 60%, the number of ion exchange sites is relatively small, resulting in relatively high ion conduction resistance and a significant decrease in proton conductivity. The ionized base membrane is then protonated through acidification.

[0011] The activation number of ion exchange sites is calculated as follows: The ionized base membrane sample is immersed in a 95℃ hydrochloric acid solution, with the acid solution changed every 1-2 hours, for a total of 10 changes. The sample is then washed several times with deionized water until neutral. The sample is placed in a 100mL volumetric flask, and 50mL of 0.1mol / L NaOH solution is added to bring the volume to a stop. 25mL of the solution is placed in a beaker, and deionized water is added to ensure the electrode is submerged. Automatic potentiometric titration is performed using 0.1mol / L hydrochloric acid solution. The formula for calculating IEC (mmol / g) is:

[0012]

[0013] in,

[0014] C NaOH —Concentration of NaOH solution, mol / L

[0015] V NaOH —Volume of NaOH solution, mL

[0016] C HCl —Concentration of hydrochloric acid solution, mol / L

[0017] V HCl —Volume of hydrochloric acid solution consumed, mL

[0018] m—mass of the ion-exchange membrane precursor sample, in g

[0019] ρ—Bulk density of the ion-exchange membrane resin, g / cm³ 3

[0020] The ion exchange capacity of the perfluorosulfonic acid ion-conducting membranes in each embodiment and comparative example was obtained by the above method, and then the number of activated ion exchange sites was obtained by comparing it with the ion exchange capacity of the original perfluorosulfonic acid resin.

[0021] The ion exchange capacity of perfluorosulfonic acid resin is 0.9~1.3 mmol / g. When the ion exchange capacity is below 0.9 mmol / g, the proton conductivity of the perfluorosulfonic acid ion-conducting membrane is relatively low and the resistance is relatively high. When the ion exchange capacity is above 1.3 mmol / g, the water absorption rate and swelling rate of the perfluorosulfonic acid ion-conducting membrane are too high. Even at a low ion exchange site activation ratio, its shrinkage after high-temperature treatment is too large, its dimensional stability is insufficient, its yellowing degree is relatively large, and its temperature resistance is poor.

[0022] The organic cation refers to an organic ammonium ion used as the counterion in ionization. The alkaline aqueous solution is selected from tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), or tetrabutylammonium hydroxide (TBAH) organic aliphatic ammonium ion alkaline solutions, with tetramethylammonium hydroxide (TMAH) aqueous solution being preferred. The mass fraction of the solution is 5-25%.

[0023] The perfluorosulfonic acid resin used is a currently disclosed perfluorosulfonic acid resin material, preferably a perfluorosulfonic acid resin obtained by copolymerization of tetrafluoroethylene and perfluorosulfonyl vinyl ether.

[0024] The thickness of the perfluorosulfonic acid resin-based membrane is 120~200μm. When the thickness of the base membrane is less than 120μm, the mechanical strength of the ion-conducting membrane decreases significantly; when the thickness of the base membrane is greater than 200μm, the resistance of the ion-conducting membrane increases significantly, and it is difficult to improve its proton conductivity even at a high ion exchange site activation ratio.

[0025] The protonation of the ionized base membrane is achieved by replacing organic ammonium ions with hydrogen ions using an acidic solution, wherein the acidic solution is a common acid solution such as sulfuric acid or hydrochloric acid. The concentration of the acidic solution is 2.0~4.0 mol / L, preferably 3.0 mol / L.

[0026] The present invention discloses a method for preparing an ion-conducting membrane with high-temperature yellowing resistance, comprising the following preparation steps:

[0027] (1) After drying the perfluorosulfonic acid resin, the perfluorosulfonic acid resin is melt-extruded and cast by a screw extruder to obtain a perfluorosulfonic acid-based film;

[0028] (2) The perfluorosulfonic acid-based membrane obtained in step (1) is hydrolyzed in an organic ammonium alkaline aqueous solution at a temperature of 70-95℃ for 60-120 min to ionize it;

[0029] (3) Thoroughly clean the ionized base membrane with pure water, and then use an inorganic acid with a molar concentration of 2.0~4.0 mol / L to replace it at 25~30℃ for 24 hours to protonate it, thus obtaining the desired perfluorosulfonic acid ion-conducting membrane.

[0030] In step (1), the perfluorosulfonic acid ion exchange resin may contain short or long branches.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The high-temperature resistant yellowing ion-conducting membrane prepared in this invention uses large-volume organic ammonium ions (such as TMA⁺) with hydrophobic alkyl chains to replace traditional alkali metal ions (such as Na⁺, K⁺). By optimizing the selection of counterions, the large-volume molecular structure and the hydrophobic properties of the outer periphery are used to suppress water absorption and swelling. The steric hindrance effect delays the collapse of the ion cluster structure network caused by high temperature, improves the temperature resistance of the ion membrane, and reduces the yellowing resistance index.

[0033] (2) Based on the ion exchange capacity of the perfluorosulfonic acid-based membrane, this invention selects a perfluorosulfonic acid resin with an appropriate IEC to prepare a high-temperature resistant yellowing ion-conducting membrane. By adjusting the ionization degree of the sulfonyl fluoride group to above 60%, a yellowing-resistant membrane with low membrane resistance and high proton conductivity can be obtained;

[0034] (3) The high-temperature resistant yellowing ion-conducting membrane prepared by the present invention does not require complex coating or doping processes. Its performance is improved by optimizing the selection of counterions and controlling the degree of ionization, which is suitable for continuous production. Attached Figure Description

[0035] Figure 1 It is a counterion with TMA + The diagram illustrates the ionization and protonation reaction process, for example.

[0036] Figure 2 This is a performance comparison chart between the embodiment and the comparative example. Detailed Implementation

[0037] The present invention will now be described in detail through examples.

[0038] Example 1

[0039] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 0.90 mmol / g.

[0040] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have TMA⁺ ions as the counterions, and the activation rate of ion exchange sites is 100%.

[0041] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 16 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 200 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 25% TMAH aqueous solution and hydrolyzed at 70℃ for 120 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 4 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0042] Performance testing:

[0043] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 289°C.

[0044] The thermal stability of a material can also be macroscopically reflected by the color change after heat treatment. The perfluorosulfonic acid ion-conducting membrane was removed from pure water, its surface was wiped clean with filter paper, and then dried at 110℃ for 3 hours. The yellowness index (YI) of different samples was then tested using a benchtop colorimeter with an L*, a*, b* three-color system. Here, L represents the lightness axis, with 0 representing black and 100 representing white; a is the red-green axis, with positive values ​​for red, negative values ​​for green, and 0 for neutral; and b is the yellow-blue axis, with positive values ​​for yellow, negative values ​​for blue, and 0 for neutral. The test conditions were calculated according to ASTM E313 YI under a D65 light source at a 10° viewing angle. The yellowness index YI was 4.5.

[0045] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25℃. The test environment was pure water at 25℃. A polysulfone insulating frame was placed on each side of the membrane sample as an end plate, with a square hole (2.0 cm × 2.0 cm) on each end plate to serve as the effective test area of ​​the membrane and to ensure that the membrane placed within it maintains the same temperature and humidity as the environment. A non-conductive plastic film of the same size was placed inside one end plate as a sample support. A gold-plated sheet and gold-plated electrode wire were embedded at both ends of this end plate as conductive materials, connected to the electrochemical impedance spectroscopy instrument for testing. The proton conductivity was 63 mS / cm.

[0046] Comparative Example 1

[0047] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 0.90 mmol / g.

[0048] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have K⁺ ions as the counterion, and the activation rate of ion exchange sites is 100%.

[0049] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 16 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 200 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 25% TMAH aqueous solution and hydrolyzed at 70℃ for 120 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 4 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0050] Performance testing:

[0051] The perfluorosulfonic acid ion-conducting membrane prepared above was removed from pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 75°C.

[0052] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI was measured to be 5.4 using a benchtop colorimeter combined with the L*, a*, b* three-color system.

[0053] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 71 mS / cm.

[0054] Example 2

[0055] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.3 mmol / g.

[0056] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have TMA⁺ ions as the counterions, and the activation rate of ion exchange sites is 60%.

[0057] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set to 9 rpm, resulting in a perfluorosulfonic acid precursor membrane with a thickness of 120 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 5% TMAH aqueous solution and hydrolyzed at 95℃ for 60 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 2 mol / L hydrochloric acid aqueous solution and ion-exchanged at 25~30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0058] Performance testing:

[0059] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 313°C.

[0060] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI measured using a benchtop colorimeter with the L*, a*, b* three-color system was 2.6.

[0061] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 47 mS / cm.

[0062] Comparative Example 2

[0063] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.3 mmol / g.

[0064] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have Na⁺ ions as the counterion, and the activation rate of ion exchange sites is 60%.

[0065] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set to 9 rpm, resulting in a perfluorosulfonic acid precursor membrane with a thickness of 120 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 5% TMAH aqueous solution and hydrolyzed at 70℃ for 60 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 2 mol / L hydrochloric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0066] Performance testing:

[0067] The perfluorosulfonic acid ion-conducting membrane prepared above was removed from pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 63°C.

[0068] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI was measured to be 5.1 using a benchtop colorimeter combined with the L*, a*, b* three-color system.

[0069] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 49 mS / cm.

[0070] Example 3

[0071] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.0 mmol / g.

[0072] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have TMA⁺ ions as the counterions, and the activation rate of ion exchange sites accounts for 76%.

[0073] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 11 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 140 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 15% TMAH aqueous solution and hydrolyzed at 80℃ for 90 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 3 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0074] Performance testing:

[0075] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 309°C.

[0076] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI measured using a benchtop colorimeter with the L*, a*, b* three-color system was 2.4.

[0077] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 45 mS / cm.

[0078] Example 4

[0079] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.0 mmol / g.

[0080] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have TMA⁺ ions as the counterions, and the activation rate of ion exchange sites is 100%.

[0081] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 11 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 140 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 15% TMAH aqueous solution and hydrolyzed at 95℃ for 120 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 3 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0082] Performance testing:

[0083] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed by thermogravimetric analysis. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 301°C.

[0084] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI measured using a benchtop colorimeter with the L*, a*, b* three-color system was 4.6.

[0085] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 70 mS / cm.

[0086] Comparative Example 3

[0087] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.0 mmol / g.

[0088] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have Na⁺ ions as the counterion, and the activation rate of ion exchange sites is 100%.

[0089] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 11 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 140 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 15% TMAH aqueous solution and hydrolyzed at 80℃ for 90 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 3 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0090] Performance testing:

[0091] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 31°C.

[0092] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110°C for 3 hours, the yellowness index YI measured using a benchtop colorimeter with the L*, a*, b* three-color system was 6.1.

[0093] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 78 mS / cm.

[0094] Example 5

[0095] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.0 mmol / g.

[0096] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have TEA⁺ ions as the counterions, and the activation rate of ion exchange sites is 100%.

[0097] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 11 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 140 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 25% TMAH aqueous solution and hydrolyzed at 95℃ for 120 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 3 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0098] Performance testing:

[0099] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 335°C.

[0100] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI was measured to be 3.4 using a benchtop colorimeter combined with the L*, a*, b* three-color system.

[0101] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 55 mS / cm.

[0102] Example 6

[0103] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.0 mmol / g.

[0104] The ion activation site counterion of the perfluorosulfonic acid ion-conducting membrane is TBA⁺ ion, and the activation rate of ion exchange sites is 100%.

[0105] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set at 11 rpm to obtain a perfluorosulfonic acid precursor membrane with a thickness of 140 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 25% TMAH aqueous solution and hydrolyzed at 95℃ for 120 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 3 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0106] Performance testing:

[0107] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 352°C.

[0108] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI measured using a benchtop colorimeter with the L*, a*, b* three-color system was 2.9.

[0109] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 47 mS / cm.

[0110] Example 7

[0111] The aforementioned perfluorinated ion-conducting membrane with high-temperature resistance and yellowing resistance is composed of a perfluorosulfonic acid ion exchange resin as the base membrane. The perfluorosulfonic acid resin has an ion exchange capacity of 1.3 mmol / g.

[0112] The ion activation sites of the perfluorosulfonic acid ion-conducting membrane have TMA⁺ ions as the counterions, and the activation rate of ion exchange sites is 100%.

[0113] The specific preparation method involves drying the above-mentioned perfluorosulfonic acid ion exchange resin at high temperature, then melt-extruding and casting it using a single-screw extruder to obtain a perfluorosulfonic acid-based membrane. The extrusion temperature is controlled at 280℃, and the screw speed is set to 9 rpm, resulting in a perfluorosulfonic acid precursor membrane with a thickness of 120 μm. The perfluorosulfonic acid precursor membrane is then immersed in a 25% TMAH aqueous solution and hydrolyzed at 95℃ for 120 min to complete the ionization of the precursor membrane. The ionized membrane is thoroughly washed with pure water, then immersed in a 3 mol / L sulfuric acid aqueous solution and ion-exchanged at 25-30℃ for 24 h to obtain the desired perfluorosulfonic acid ion-conducting membrane, which is then placed in pure water for performance testing.

[0114] Performance testing:

[0115] The perfluorosulfonic acid ion-conducting membrane prepared above was taken out of pure water, and the surface of the ion-conducting membrane was wiped clean with filter paper. The thermal stability of the perfluorosulfonic acid ion-conducting membrane was analyzed using a thermogravimetric analyzer. The temperature was increased from 25°C to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. The initial decomposition temperature was the temperature at which the weight loss was 5%. The decomposition temperature of the sample in this embodiment was 298°C.

[0116] The perfluorosulfonic acid ion-conducting membrane was removed from pure water, and the surface of the membrane was wiped clean with filter paper. After drying at 110℃ for 3 hours, the yellowness index YI measured using a benchtop colorimeter with the L*, a*, b* three-color system was 4.7.

[0117] The proton conductivity in the planar direction of the ion-exchange membrane was determined using electrochemical impedance spectroscopy (EIS) at 25°C. The test environment was pure water at 25°C. The proton conductivity was 79 mS / cm.

Claims

1. An ion-conducting membrane with resistance to high-temperature yellowing, characterized in that: (1) Using perfluorosulfonic acid resin as the base membrane, wherein the ion exchange capacity (IEC) of the perfluorosulfonic acid resin is 0.9~1.3 mmol / g; (2) The counterion of the ion activation site of the base membrane is an organic cation, and the organic cation is an organic aliphatic ammonium ion; (3) The activation rate of ion exchange sites is 60%~100%; (4) The thickness of the base film is 120~200 μm.

2. The ion-conducting membrane according to claim 1, characterized in that, The organic cation is tetramethylammonium ion (TMA⁺), tetraethylammonium ion (TEA⁺), or tetrabutylammonium ion (TBA⁺).

3. The ion-conducting membrane according to claim 1, characterized in that, The perfluorosulfonic acid resin is copolymerized from tetrafluoroethylene and perfluorosulfonyl vinyl ether.

4. A method for preparing an ion-conducting membrane as described in any one of claims 1-3, characterized in that, The process includes the following steps: (1) After drying the perfluorosulfonic acid resin, it is melt-extruded and cast using a screw extruder to form a base film; (2) The base film obtained in step (1) is immersed in an organic ammonium alkaline aqueous solution with a mass fraction of 5%~25% and hydrolyzed at 70~95℃ for 60~120 minutes to ionize; (3) The ionized base film is washed with pure water and then immersed in an inorganic acid solution of 2.0~4.0 mol / L and protonated at 25~30℃ for 24 hours to obtain the ion-conducting membrane.

5. The method according to claim 4, characterized in that, The organic ammonium alkaline aqueous solution is a tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), or tetrabutylammonium hydroxide (TBAH) solution.

6. The method according to claim 4, characterized in that, The inorganic acid solution is a sulfuric acid or hydrochloric acid solution.

7. The method according to claim 6, characterized in that, The concentration of the inorganic acid solution is 3.0 mol / L.

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