Preparation method and application of organic phosphonic acid in-situ doped polybenzimidazole gel proton membrane
By combining the sol-gel method with organophosphonic acid doping, polybenzimidazole gel proton exchange membranes were prepared, which solved the problems of low proton conductivity and insufficient mechanical strength, and improved the stability and performance of high-temperature proton exchange membrane fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-10
- Publication Date
- 2026-06-05
AI Technical Summary
Existing polybenzimidazole proton exchange membranes have low proton conductivity and insufficient mechanical strength at high temperatures, and phosphoric acid is easily lost, affecting the long-term stability and performance of high-temperature proton exchange membrane fuel cells.
The sol-gel method combined with organophosphonic acid doping was used to form a three-dimensional network porous gel membrane by adding organophosphonic acid as an additive to the polyphosphoric acid system. The strong hydrogen bond network and cross-linking points formed by the phosphonic acid groups and PBI molecules were utilized to improve proton conduction efficiency and mechanical strength.
It significantly improved the proton conductivity and mechanical strength of the proton exchange membrane, solved the problem of phosphoric acid loss, and achieved long-term stability and performance improvement of high-temperature proton exchange membrane fuel cells.
Smart Images
Figure CN122145854A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer proton exchange membrane technology, specifically relating to a method for preparing and applying an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane. The application areas include fuel cells, flow batteries, water electrolysis for hydrogen production, wastewater treatment, and gas separation. Background Technology
[0002] Polybenzimidazole (PBI) is the preferred matrix material for high-temperature proton exchange membranes (HT-PEMFCs) due to its excellent thermal stability, chemical stability, and mechanical strength. HT-PEMFCs, as a next-generation fuel cell, can operate at 120–200 °C without humidification, tolerate trace amounts of CO, reduce fuel purification costs, and improve waste heat utilization, making them suitable for demanding applications such as vehicle power and distributed generation. Their core performance directly depends on the quality of the high-temperature proton exchange membrane. Pure PBI membranes have extremely low proton conductivity (only 10 Ω·cm at room temperature). -8 -10 -7 The current efficiency (S / cm) is insufficient for fuel cell operation, necessitating proton carrier modification. The mainstream approach in current technology is to prepare phosphoric acid foamed PBI membranes (i.e., concentrated phosphoric acid-doped PBI membranes). However, phosphoric acid foamed PBI membranes have a core defect: phosphoric acid and PBI are only bonded through weak hydrogen bonds, making them prone to dissolution and loss during long-term high-temperature operation. This leads to a significant decrease in membrane proton conductivity and deterioration of mechanical properties, severely restricting the long-term stability of HT-PEMFCs.
[0003] To address the aforementioned phosphoric acid loss problem, researchers began exploring the preparation of PBI-based composite membranes using the sol-gel method. The sol-gel method is a wet chemical process where precursors undergo hydrolysis and condensation in solution to form a three-dimensional network gel structure. In this process, polyphosphoric acid not only acts as a reaction medium but also transforms into phosphoric acid during subsequent hydrolysis and remains in situ within the gel network, thus achieving molecular-level dispersion and anchoring of phosphoric acid. Compared to traditional dense solid PBI membranes, gel membranes possess a unique porous, three-dimensional cross-linked network structure. Their pores provide continuous channels for proton conduction, and the pore size and porosity can be adjusted by regulating the gelation conditions. This process offers significant advantages: it achieves uniform dispersion of phosphoric acid within the membrane, improving proton conduction efficiency; simultaneously, the physical binding effect of the gel network on phosphoric acid effectively mitigates its loss; furthermore, the process is carried out at lower temperatures, avoiding the degradation of PBI molecular chains caused by high-temperature processing.
[0004] However, PBI gel membranes prepared by the simple sol-gel method still face two major challenges: First, the absolute number of proton carriers (phosphate) in the gel network structure is still limited by the precursor formulation and process, resulting in limited improvement in proton conduction capacity; Second, the PBI molecular chains in the gel membrane are mainly connected by physical entanglement and a small number of hydrogen bonds, and their mechanical strength is usually lower than that of dense solid membranes, which may lead to structural collapse or damage during long-term operation or assembly.
[0005] To address the shortcomings of the aforementioned gel membranes, organophosphonic acids (OPA) have been introduced into the sol-gel preparation system. OPA molecules contain multiple phosphonic acid groups, which not only serve as efficient proton carriers but also form strong and numerous hydrogen bonds, and even partial coordination interactions, with the imidazole groups of PBI molecules. This allows for the construction of continuous and stable proton conduction channels within the gel network. More importantly, OPA can act as "crosslinking points" or "reinforcing agents," forming stronger interactions with PBI chains, effectively enhancing the mechanical properties of the gel network and compensating for the insufficient strength of pure gel membranes.
[0006] Therefore, combining organophosphonic acids with the sol-gel method to prepare organophosphonic acid-doped PBI gel proton exchange membranes is expected to synergistically leverage the structural regulation advantages of gel membranes (high porosity, uniform dispersion, and phosphate retention) with the proton conduction enhancement and structural strengthening advantages of organophosphonic acids. This would overcome the bottleneck of PBI-based high-temperature proton exchange membranes in simultaneously achieving high conductivity, high mechanical strength, and long-term stability, becoming a key technological direction for promoting the commercial application of HT-PEMFCs. Furthermore, composite membranes prepared based on this strategy have also shown good application potential in flow batteries, water electrolysis for hydrogen production, wastewater treatment, and gas separation.
[0007] Based on this, this patent application is filed. Summary of the Invention
[0008] To address the issues of easy phosphoric acid loss and insufficient mechanical stability in traditional phosphoric acid-doped polybenzimidazole (PBI) proton exchange membranes, as well as the limited proton conductivity and low mechanical strength of existing PBI gel membranes prepared by the simple sol-gel method, this invention aims to provide a method for preparing and applying organophosphonic acid-doped polybenzimidazole gel proton exchange membranes. This method introduces organophosphonic acid in situ during the sol-gel preparation of PBI, constructing a composite gel proton exchange membrane that combines high proton conductivity, excellent mechanical strength, and good structural stability, potentially solving or at least significantly optimizing the aforementioned deficiencies in existing technologies.
[0009] The gel proton exchange membrane of this invention is prepared using a sol-gel process. Specifically, while synthesizing PBI by adding condensation monomers to a polyphosphoric acid system for solution condensation polymerization, one or more organophosphonic acids are added as additives to synthesize a uniform organophosphonic acid-doped polybenzimidazole membrane solution (sol state). This membrane solution is then poured hot onto a smooth surface and coated or cast to form a wet film, which is then placed in a controlled temperature and humidity environment. In this environment, the polyphosphoric acid in the system gradually hydrolyzes, the temperature decreases, promoting the sol to gel transformation, and finally solidifying into a membrane. Unlike traditional dense solid PBI membranes, this method yields a gel membrane with a three-dimensional network porous structure. Within this gel membrane, organophosphonic acids play multiple key roles: First, the abundant phosphonic acid groups in their molecules can act as efficient proton carriers, significantly increasing the number of mobile protons within the membrane; second, these phosphonic acid groups can form a broad and robust hydrogen bond network with the imidazole groups on the PBI molecular chain, constructing a continuous and stable proton conduction channel and greatly improving proton conduction efficiency; third, as "molecular cross-linking points," organophosphonic acids, through their interaction with multiple PBI molecular chains, effectively enhance the structural integrity of the gel network, thereby compensating for the shortcomings of insufficient mechanical strength in traditional gel membranes and achieving a synergistic improvement in proton conduction performance and mechanical properties.
[0010] The organophosphonic acid-doped polybenzimidazole gel proton exchange membrane prepared by the above method not only inherits the advantages of uniform phosphoric acid distribution and high retention rate of sol-gel membranes, but also achieves significantly enhanced proton conductivity and mechanical strength due to the introduction of organophosphonic acid. This proton exchange membrane exhibits excellent overall performance and has broad application prospects in various fields such as high-temperature proton exchange membrane fuel cells, flow batteries, water electrolysis for hydrogen production, wastewater treatment, and gas separation.
[0011] To achieve the first objective of this invention, the technical solution adopted by this invention is as follows: A method for preparing an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, the method specifically comprising the following steps: ① In the process of synthesizing polybenzimidazole by adding polycondensation monomers to the polyphosphoric acid system through solution polycondensation reaction, one or more "organophosphonic acids" are used as additives to synthesize an organophosphonic acid-doped polybenzimidazole solution, which is called "membrane solution". ② Pour the “membrane liquid” while it is still hot onto a “smooth surface” and use a scraper with a limited height to scrape or cast it to obtain a “wet film” of organophosphonic acid-doped polybenzimidazole gel proton exchange membrane. ③ After the “wet film” is placed in a constant temperature and humidity environment for a period of time, the “wet film” gradually solidifies as the polyphosphoric acid in the system hydrolyzes and the temperature decreases. After wiping the acidic liquid on the surface, an organophosphonic acid in-situ doped polybenzimidazole gel proton membrane is obtained.
[0012] Furthermore, in the above technical solution, the "polybenzimidazole" mentioned in step ① comprises one or a mixture of several of the following structures:
[0013] Furthermore, in the above technical solution, within the polyphosphoric acid system described in step ①, the actual mass ratio of polybenzimidazole to polyphosphoric acid is 1~20:99~80.
[0014] Furthermore, in the above technical solution, the polyphosphoric acid system described in step ① includes one or a mixture of several types of solvent "polyphosphoric acid": general-purpose type with 83% and 84% phosphorus pentoxide (P2O5) content and high degree of polymerization type with 105% / 115% / 116% H3PO4 equivalent.
[0015] Furthermore, in the above technical solution, phosphorus pentoxide (P2O5) can be added to the polyphosphoric acid system in step ① in an appropriate amount, with its mass being 0% to 30% of the mass of polyphosphoric acid.
[0016] Furthermore, in the above technical solution, the temperature of the solution polycondensation reaction in step ① is 150 ℃ ~ 250 ℃.
[0017] Furthermore, in the above technical solution, the solution condensation reaction time in step ① is 0.5 h ~ 20 h.
[0018] Furthermore, in the above technical solution, the "organophosphonic acid" mentioned in step ① comprises: (1-hydroxyethylidene) diphosphonic acid (CAS#: 2809-21-4), nitrotri(methylenephosphonic acid) (CAS#: 6419-19-8), ethylenediaminetetramethylenephosphonic acid (CAS#: 1429-50-1), diethylenetriaminepentamethylenephosphonic acid (CAS#: 15827-60-8), 2-phosphonobutane-1,2,4-tricarboxylic acid (CAS#: 37971-36-1), phytic acid (CAS#: 83-86-3), and one or a mixture of several of them in the form of hydrates, lithium salts, sodium salts, potassium salts, and ammonium salts.
[0019] Furthermore, in the above technical solution, the mass of "organophosphonic acid" added in step ① is 0.1 to 2 times the actual mass of polybenzimidazole produced.
[0020] Furthermore, in the above technical solution, the timing of adding the "organophosphonic acid" to the system in step ① is any moment from 0 min before the start of the reaction to 5 min before the end of the reaction.
[0021] Furthermore, in the above technical solution, the temperature of the "membrane liquid" poured while hot in step ② is 150 ℃ ~ 250 ℃.
[0022] Furthermore, in the above technical solution, the material of the contact surface between the "smooth plane" and the "film liquid" in step ② is one or a mixture of several of the following: glass, quartz, corundum, artificial ceramic tile, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PVC (polyvinyl chloride), PMMA (acrylic sheet), PTFE (Teflon), stainless steel, titanium alloy, and aluminum alloy.
[0023] Furthermore, in the above technical solution, the contact surface between the "smooth plane" and the "film liquid" mentioned in step ② can be selected as appropriate to add release silicone oil and determine the weight of release silicone oil added.
[0024] Furthermore, in the above technical solution, the height limit of the scraper mentioned in step ② is 100 μm ~ 2000 μm.
[0025] Furthermore, in the above technical solution, the speed limit for scraping or casting in step ② is 0.03 m / min. -1 ~ 50 m min -1 .
[0026] Furthermore, in the above technical solution, the constant temperature and humidity environment mentioned in step ③ is any combination of the following values: temperature: 20℃ ~ 100℃, humidity: 20%RH ~ 100%RH.
[0027] Furthermore, in the above technical solution, the "wet film" mentioned in step ③ is placed in a constant temperature and humidity environment for a period of 1 h to 168 h.
[0028] Furthermore, in the above technical solution, the thickness of the organophosphonic acid in-situ doped polybenzimidazole gel proton membrane obtained in step ③ is 50 μm ~ 1000 μm.
[0029] The second objective of this invention is to provide an application of the above-described organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, which can be used in fuel cells, flow batteries, water electrolysis for hydrogen production, wastewater treatment, gas separation and other fields.
[0030] The mechanism involved in this invention is as follows: ① The present invention discloses a method for preparing and applying an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, which involves adding a polycondensation monomer to a polyphosphoric acid system for polycondensation, and the reaction formula is shown below:
[0031] ② The gelation process completely opens up the molecular chains of different PBI molecules, and the gel proton exchange membrane can obtain higher phosphoric acid absorption and retention rates than the traditional phosphoric acid-soaked proton exchange membrane, which can improve the electrochemical performance of the proton exchange membrane.
[0032] ③ Organophosphonic acids contain multiple phosphonic acid groups, which not only serve as efficient proton carriers to supplement the number of protons, but also form a strong hydrogen bond network with the imidazole groups of PBI molecules, constructing a continuous and stable proton conduction channel. Simultaneously, the interaction between organophosphonic acids and PBI imidazoles forms a strong cross-linking structure, effectively preventing a decrease in gel membrane strength. Combining organophosphonic acids with the sol-gel method to prepare PBI composite membranes can synergistically leverage the advantages of gel membrane structure regulation and the efficient proton conduction and cross-linking advantages of organophosphonic acids, thus overcoming the performance bottleneck of PBI-based high-temperature proton exchange membranes.
[0033] The present invention relates to a method for preparing and applying an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, which has the following advantages compared with existing related technologies: ① The present invention uses a gelation process to prepare proton exchange membranes, which can obtain higher phosphoric acid absorption and retention rates, and improve the electrochemical performance of proton exchange membranes.
[0034] ② The present invention uses organophosphonic acid as an additive to obtain a gel proton membrane with higher mechanical strength and proton conductivity.
[0035] ③ The organophosphonic acid in-situ doped polybenzimidazole gel proton exchange membrane prepared by the present invention has a wide range of applications and has a very broad application prospect in fuel cells, flow batteries, water electrolysis for hydrogen production, sewage treatment, gas separation and other fields. Attached Figure Description
[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0037] Figure 1 Examples of organophosphonic acid-doped polybenzimidazole gel proton membranes prepared in Examples 1-3 of this invention; Figure 2 Stress-strain curves of organophosphonic acid-doped polybenzimidazole gel proton membranes prepared in Examples 1-3 of this invention and comparative examples; Figure 3 The graphs show the conductivity changes of the organophosphonic acid-doped polybenzimidazole gel proton membranes prepared in Examples 1-3 of this invention and the comparative examples applied to hydrogen fuel cells at different temperatures. Figure 4 The graph shows the power density curves of the organophosphonic acid-doped polybenzimidazole gel proton membranes prepared in Examples 2 and 3 of this invention at 160°C when applied to hydrogen fuel cells. Detailed Implementation
[0038] This invention discloses a method for preparing and applying an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane. The preparation process includes the following steps: ① During the synthesis of polybenzimidazole by adding condensation monomers to a polyphosphoric acid system via solution polycondensation reaction, one or more organophosphonic acids are used as additives to synthesize an organophosphonic acid-doped polybenzimidazole solution, referred to as a "membrane solution"; ② The "membrane solution" is poured onto a "smooth surface" while hot, and then coated or cast using a height-limited scraper to obtain a "wet film" of the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane; ③ After the "wet film" is placed in a constant temperature and humidity environment for a period of time, the "wet film" gradually solidifies as the polyphosphoric acid in the system hydrolyzes and the temperature decreases. After wiping away the acidic liquid on the surface, an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane is obtained. The method of this invention is simple to operate and has lower cost. The synthesized organophosphonic acid in-situ doped polybenzimidazole gel proton exchange membrane has higher mechanical and electrochemical properties, and has a very broad application prospect in fuel cells, flow batteries, water electrolysis for hydrogen production, sewage treatment, gas separation and other fields.
[0039] All pharmaceuticals, raw materials, and equipment used in this invention can be purchased directly from the market or are commonly used in the industry. The values in the embodiments of this invention were obtained using conventional rounding methods. The amount of each solid sample added in the embodiments of this invention takes into account the purity reference provided by the original manufacturer.
[0040] Example 1 This embodiment describes a method for preparing an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, comprising the following steps: ① Weigh 21.4 g (0.1 mol) 3,3-diaminobenzidine (CAS#: 91-95-2), 16.6 g (0.1 mol) isophthalic acid (CAS#: 121-91-5), and 19 g (0.5 times the mass of PBI monomer) ethylenediaminetetramethylenephosphonic acid (CAS#: 1429-50-1), and mix them evenly in a beaker. This mixture is called "mixed raw materials".
[0041] ② Weigh 500 g of polyphosphoric acid and 50 g of phosphorus pentoxide, place them in a three-necked flask and mix them. Under the protection of nitrogen, heat the three-necked flask to 200 °C and add the "mixed raw materials" to carry out the reaction. Adjust the speed of the top stirrer to 200 and the reaction time to 4 h.
[0042] ③ When the reaction is complete, the viscosity increases. Pour the hot "film solution" directly onto a smooth PET sheet. At this point, the temperature of the "film solution" is slightly below 200℃. Adjust the doctor blade height of the coating machine to 400 μm and the coating speed limit to 10 m / min. -1 After uniformly coating the "membrane solution", a "wet membrane" of organophosphonic acid-doped polybenzimidazole gel proton exchange membrane is obtained.
[0043] ④ Place the wet film along with the PET sheet in a constant temperature and humidity chamber. Set the environment to 60℃ and 55%RH for 48 hours. At this time, the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane has fully cured. After wiping the liquid off the surface of the gel proton exchange membrane with filter paper, measure the thickness of the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane with a micrometer: 155 μm.
[0044] Example 2 This embodiment describes a method for preparing an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, comprising the following steps: ① Weigh 21.4 g (0.1 mol) 3,3-diaminobenzidine (CAS#: 91-95-2), 16.6 g (0.1 mol) terephthalic acid (CAS#: 100-21-0), and 38 g (1 times the mass of PBI monomer) nitrilotri(methylenephosphonic acid) (CAS#: 6419-19-8), and mix them evenly in a beaker. This mixture is called the "mixed raw materials".
[0045] ② Weigh 500 g of polyphosphoric acid. Under the protection of nitrogen, heat the three-necked flask to 200 °C and add the "mixed raw materials" to carry out the reaction. Adjust the speed of the top stirrer to 200 and the reaction time to 4 h.
[0046] ③ When the reaction is complete, the viscosity increases. Pour the hot "film solution" directly onto a smooth PET sheet. At this point, the temperature of the "film solution" is slightly below 200℃. Adjust the doctor blade height to 400 μm and the coating speed to 10 m / min. -1 After uniformly coating the "membrane solution", a "wet membrane" of organophosphonic acid-doped polybenzimidazole gel proton exchange membrane is obtained.
[0047] ④ Place the wet film along with the PET sheet in a constant temperature and humidity chamber. Set the environment to 60℃ and 55%RH for 48 hours. At this time, the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane has fully cured. After wiping the liquid off the surface of the gel proton exchange membrane with filter paper, measure the thickness of the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane with a micrometer: 158 μm.
[0048] Example 3 This embodiment describes a method for preparing an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, comprising the following steps: ① Weigh 21.4 g (0.1 mol) of 3,3-diaminobenzidine (CAS#: 91-95-2) and 16.6 g (0.1 mol) of terephthalic acid (CAS#: 100-21-0), place them in a beaker and mix them evenly. This mixture is called "mixed raw materials".
[0049] ② Weigh 500 g of polyphosphoric acid and 50 g of phosphorus pentoxide, place them in a three-necked flask and mix them. Under the protection of nitrogen, heat the three-necked flask to 200 °C and add the "mixed raw materials" to carry out the reaction. Adjust the speed of the top stirrer to 200 and the reaction time to 4 h.
[0050] ③ After 3 hours and 40 minutes of reaction, the viscosity increased. At this point, 19 g (0.5 times the mass of PBI monomer) of (1-hydroxyethylidene) diphosphonic acid (CAS#: 2809-21-4) was added to the system, and the reaction continued for another 20 minutes. After the reaction was completed, the "film solution" was poured onto a smooth glass plate while still hot. At this point, the temperature of the "film solution" was slightly below 200 ℃. The doctor blade height was adjusted to 400 μm, and the doctor blade speed was limited to 10 m / min. -1 After uniformly coating the "membrane solution", a "wet membrane" of organophosphonic acid-doped polybenzimidazole gel proton exchange membrane is obtained.
[0051] ④ Place the wet membrane along with the glass plate in a constant temperature and humidity chamber. Set the environment to 60℃ and 55%RH for 48 hours. At this time, the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane has fully solidified. After wiping the liquid off the surface of the gel proton exchange membrane with filter paper, measure the thickness of the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane with a micrometer: 156 μm.
[0052] Comparative example: To more intuitively demonstrate the advantages of the present invention, a comparative example is provided below: a method for preparing an undoped organophosphonic acid polybenzimidazole gel proton exchange membrane, comprising the following steps: ① Weigh 21.4 g (0.1 mol) of 3,3-diaminobenzidine (CAS#: 91-95-2) and 16.6 g (0.1 mol) of terephthalic acid (CAS#: 100-21-0), place them in a beaker and mix them evenly. This mixture is called "mixed raw materials".
[0053] ② Weigh 500 g of polyphosphoric acid and 50 g of phosphorus pentoxide, place them in a three-necked flask and mix them. Under the protection of nitrogen, heat the three-necked flask to 200 °C and add the "mixed raw materials" to carry out the reaction. Adjust the speed of the top stirrer to 200 and the reaction time to 4 h.
[0054] ③ After 4 hours of reaction, the reaction is complete. While still hot, pour the "film solution" onto a smooth glass plate. At this point, the temperature of the "film solution" is slightly below 200 °C. Adjust the doctor blade height to 400 μm and the coating speed to 10 m / min. -1 After uniformly coating the "membrane solution", a "wet membrane" of undoped organophosphonic acid polybenzimidazole gel proton exchange membrane is obtained.
[0055] ④ Place the wet membrane along with the glass plate in a constant temperature and humidity chamber. Set the environment to 60℃ and 55%RH for 48 hours. At this point, the undoped organophosphonic acid polybenzimidazole gel proton exchange membrane has fully cured. After wiping the liquid off the surface of the gel proton exchange membrane with filter paper, measure the thickness of the undoped organophosphonic acid polybenzimidazole gel proton exchange membrane with a micrometer: 154 μm.
[0056] Performance testing: (I) The specific testing methods for mechanical properties are as follows: ① Under constant temperature and humidity conditions of 25℃±2℃ and 50%±5%, rapidly measure the sample thickness. The thickness and width of each sample should be measured at three points within the gauge length, and the average value should be taken. The accuracy of thickness measurement is ±0.2%, and the accuracy of width measurement is ±0.5%. ② Place the sample in the tensile testing machine fixture, aligning the longitudinal axis of the sample with the line connecting the centers of the upper and lower fixtures, and clamp it tightly. The pressure value of the pneumatic fixture is set to 5.3 MPa; ③ The tensile speed of the tensile testing machine is set to 100 mm min⁻¹; ④ After the sample breaks, read the corresponding load value. If the sample breaks outside the mark, the test is invalid.
[0057] Based on the measured tensile curve, the required load and corresponding membrane thickness and width are read, and the maximum tensile strength of the membrane is calculated according to the formula.
[0058] P=F / (bd) In the formula: P – Maximum tensile strength of the membrane, measured in megapascals (MPa); F – Maximum load, in Newtons (N); b—Sample width, in millimeters (mm); d — Sample thickness, in millimeters (mm).
[0059] Take 3 samples as a group and calculate the average value as the test result.
[0060] (II) The specific test method for the proton conductivity of hydrogen fuel cells is as follows: The proton conductivity testing method involved in this invention refers to Section 3.5 "Proton Conductivity Testing" in GB / T 20042.3-2009, and the detailed testing method is as follows: A film of a certain size was cut as a sample. The thickness of the sample was measured using a thickness gauge at a temperature of 25℃±2℃ and a relative humidity of 50±5%. The average value of three points was taken as the calculated thickness d. The sample was fixed in a conductivity measuring fixture, and the bolts were tightened with a torque wrench to a torque of 3 Nm. The conductivity measuring fixture was then placed in constant temperature and humidity environments for 30 minutes at each temperature and humidity condition before testing. The impedance spectrum of the sample was measured using an electrochemical impedance spectroscopy instrument at a frequency range of 1 Hz to 2 × 10⁶ Hz and a disturbance voltage of 10 mV. The impedance value (R) of the sample was read from the intersection of the high-frequency part of the spectral line with the real axis in the measured impedance spectrum. The proton conductivity of the sample was calculated using the following formula: σ = a / (R bd) In the formula: σ—Proton conductivity of the sample, in millisiemens per centimeter (mS cm⁻¹); a — Distance between the two electrodes, in centimeters (cm); R—Measurement impedance of the sample, in kiloohms (kΩ); b — the effective length of the membrane in the direction perpendicular to the electrode, in centimeters (cm); d — The thickness of the sample, in centimeters (cm).
[0061] Take 3 samples as a group and calculate the average value as the test result.
[0062] (III) The specific method for testing the power density of high-temperature proton exchange membrane fuel cells is as follows: ① Test preparation: A single cell was assembled from an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane with an area of 4 cm². 2 Both the cathode and anode used Pt / C catalysts with a loading of 0.6 mg / cm³. 2 The gas diffusion layer is made of carbon paper with a thickness of 200 μm, and the sealing element is made of high-temperature resistant polyimide sheet. Before the test, the single cell is placed on the test bench and preheated to 160°C to maintain an unhumidified environment.
[0063] ② Gas supply: Pure oxygen is introduced into the cathode (gas flow rate 0.5 mL / min).-1 Hydrogen gas is introduced into the anode (gas flow rate 0.5 mL / min). -1 This ensures that the gas fully contacts the electrode surface, and that neither the cathode nor anode gases are pressurized or humidified.
[0064] ③ Performance Testing: Using a fuel cell testing system, under constant temperature and gas supply conditions, the current density was changed by adjusting the external circuit load (test range 0–2500 mA cm⁻¹). -2 Record the battery voltage corresponding to different current densities; calculate the power density corresponding to each current density according to the formula P=U×I / S (where P is the power density, U is the battery voltage, I is the current, and S is the effective area of the electrode), and plot the "power density-current density" polarization curve.
[0065] ④ Data Processing: The maximum power density in the polarization curve is taken as the peak power density of the battery. Simultaneously, the stable power density under rated current density is recorded as the core indicator for evaluating the proton exchange membrane's compatibility. During the test, temperature fluctuations must be maintained ≤±2℃, and gas flow rate fluctuations ≤0.05 mL / min. -1 To ensure data repeatability, each sample should be tested at least three times, and the average value should be taken as the final result.
[0066] Test Result Analysis Figure 1 The images shown are examples of organophosphonic acid-doped polybenzimidazole gel proton exchange membranes prepared in Examples 1-3 of this invention, demonstrating the successful synthesis of organophosphonic acid-doped polybenzimidazole gel proton exchange membranes.
[0067] Figure 2 This figure shows the stress-strain curves of the organophosphonic acid-doped polybenzimidazole gel proton membranes prepared in Examples 1-3 of this invention and the comparative examples. The figure demonstrates that the organophosphonic acid-doped polybenzimidazole gel proton membrane prepared in Example 1 has a mechanical strength of 2.54 MPa and an elongation at break of nearly 90%, meeting the requirements for use; the organophosphonic acid-doped polybenzimidazole gel proton membrane prepared in Example 2 has a mechanical strength of 3.07 MPa and an elongation at break of nearly 95%, meeting the requirements for use; the organophosphonic acid-doped polybenzimidazole gel proton membrane prepared in Example 3 has a mechanical strength of 3.05 MPa and an elongation at break of nearly 100%, all meeting the requirements for use; in contrast, the mechanical strength of the undoped organophosphonic acid-doped polybenzimidazole gel proton membrane in the comparative example is only 1.37 MPa, and the elongation at break is only 78%, which is relatively low in the industry.
[0068] Figure 3This figure shows the conductivity variations of the organophosphonic acid-doped polybenzimidazole gel proton exchange membranes prepared in Examples 1-3 of this invention and in comparative examples, applied to hydrogen fuel cells at different temperatures. The figure illustrates that the optimal temperature conductivity of the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane prepared in Example 1 is 164.8 mS / cm. -1 The optimal temperature conductivity of the organophosphonic acid-doped polybenzimidazole gel proton membrane prepared in Example 2 of this invention is 170.1 mS cm⁻¹, which is at a relatively high level in the industry. The optimal temperature conductivity of the organophosphonic acid-doped polybenzimidazole gel proton membrane prepared in Example 3 of this invention is 181.6 mS cm⁻¹. -1 This represents a high level within the industry; in comparison, the optimal temperature conductivity of a comparative example of an undoped organophosphonic acid polybenzimidazole gel proton membrane is only 143.6 mS / cm. -1 This is at a relatively low level within the industry.
[0069] Figure 4 This figure shows the power density curves of the organophosphonic acid-doped polybenzimidazole gel proton exchange membranes prepared in Examples 2 and 3 of this invention when applied to hydrogen fuel cells at 160°C. The figure demonstrates that the maximum power density of the organophosphonic acid-doped polybenzimidazole gel proton exchange membrane prepared in Example 2 of this invention is 591 mW / cm². -2 This has reached a high level within the industry; the maximum power density of the organophosphonic acid-doped polybenzimidazole gel proton membrane prepared in Example 3 of this invention is 860 mW cm⁻¹. -2 This has reached a relatively high level within the industry.
Claims
1. A method for preparing and applying an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane, characterized in that, Includes the following steps: S1 In the process of synthesizing polybenzimidazole by adding polycondensation monomers to the polyphosphoric acid system through solution polycondensation reaction, one or more "organophosphonic acids" are used as additives to synthesize an organophosphonic acid-doped polybenzimidazole solution, which is called "membrane solution". S2 The "membrane liquid" is poured onto a "smooth surface" while it is still hot, and a scraper with a limited height is used to scrape or cast the liquid to obtain a "wet film" of organophosphonic acid-doped polybenzimidazole gel proton exchange membrane. After the S3 "wet film" is placed in a constant temperature and humidity environment for a period of time, the "wet film" gradually solidifies as the polyphosphoric acid in the system hydrolyzes and the temperature decreases. After wiping the acidic liquid on the surface, an organophosphonic acid-doped polybenzimidazole gel proton exchange membrane is obtained.
2. The preparation method according to claim 1, characterized in that, The "polybenzimidazole" mentioned in step S1 comprises one or a mixture of the following structures:
3. The preparation method according to claim 1, characterized in that, In the polyphosphoric acid system described in step S1, the actual mass ratio of polybenzimidazole to polyphosphoric acid is 1~20:99~80.
4. The preparation method according to claim 1, characterized in that, The "organophosphonic acid" mentioned in step S1 includes: (1-hydroxyethylidene) diphosphonic acid (CAS#: 2809-21-4), nitrotri(methylenephosphonic acid) (CAS#: 6419-19-8), ethylenediaminetetramethylenephosphonic acid (CAS#: 1429-50-1), diethylenetriaminepentamethylenephosphonic acid (CAS#: 15827-60-8), 2-phosphonobutane-1,2,4-tricarboxylic acid (CAS#: 37971-36-1), phytic acid (CAS#: 83-86-3), and one or a mixture of several of them in the form of hydrates, lithium salts, sodium salts, potassium salts, or ammonium salts.
5. The preparation method according to claim 1, characterized in that, The mass of "organophosphonic acid" added in step S1 is 0.1 to 2 times the actual mass of polybenzimidazole produced.
6. The preparation method according to claim 1, characterized in that, The material of the contact surface between the "smooth plane" and the "film liquid" in step S2 is one or a mixture of several of the following: glass, quartz, corundum, artificial ceramic tile, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PVC (polyvinyl chloride), PMMA (acrylic sheet), PTFE (Teflon), stainless steel, titanium alloy, and aluminum alloy.
7. The preparation method according to claim 1, characterized in that, The height limit of the scraper mentioned in step S2 is 100um ~ 2000um.
8. The preparation method according to claim 1, characterized in that, The constant temperature and humidity environment mentioned in step S3 is any combination of the following values: temperature: 20℃ ~ 100℃, humidity: 20%RH ~ 100%RH.
9. The preparation method according to claim 1, characterized in that, The "wet film" mentioned in step S3 is placed in a constant temperature and humidity environment for a period of 1 h to 168 h.
10. The organophosphonic acid-doped polybenzimidazole gel proton exchange membrane according to any one of claims 1-10 is applied in the fields of fuel cells, flow batteries, water electrolysis for hydrogen production, wastewater treatment, and gas separation.