Phosphonized polyborosiloxane proton exchange membrane and application thereof

Abstract

The invention discloses a phosphorylated polyborosiloxane proton exchange membrane and application thereof, and belongs to the field of proton exchange membranes. The preparation method comprises the following steps: firstly preparing phosphorylated polyborosiloxane, grafting a phosphonic acid group to a polysiloxane main chain to ensure the stability of a proton carrier, and then blending with chitosan to form a hydrogen bond with phosphonic acid in the phosphorylated polyborosiloxane and unreacted free phosphoric acid. Compared with a method of doping or utilizing a metal organic framework for stabilization, the method provided by the invention fundamentally solves the problem that phosphoric acid is easy to lose by utilizing chemical bonds to graft phosphoric acid from the structure. Experimental results show that the phosphorylated polyborosiloxane proton exchange membrane provided by the invention has excellent thermal stability, the mass loss at 200 DEG C is lower than 10%, the high-temperature proton conductivity can reach 40-100 mS / cm, a single cell test shows that the open-circuit voltage is 0.2-1.0 V, the maximum power density reaches 200-800 mW / cm, and the phosphorylated polyborosiloxane proton exchange membrane shows good high-temperature low-humidity application performance.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membranes, and particularly to a phosphine-modified polyboronsiloxane proton exchange membrane and its applications. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) offer significant advantages such as zero emissions, low start-up temperature, rapid start-up, and high energy efficiency. As a key factor in battery performance and lifespan, the proton exchange membrane (PEM) must possess effective proton migration and conduction channels and prevent cross-permeation between hydrogen at the cathode and oxygen at the anode. In commercial applications, DuPont's Nafion® membranes dominate the market. Their molecular structure contains abundant sulfonic acid groups, giving these proton exchange membranes excellent proton conductivity. However, in practical applications, sulfonic acid-based proton exchange membranes are prone to internal moisture evaporation at high temperatures, leading to sulfonate group loss and reduced proton conductivity, which to some extent limits their application and development.

[0003] To address the issue of sulfonate group detachment from traditional proton exchange membranes under high temperature and low humidity conditions, researchers have introduced phosphoric acid (phosphonic acid) as a proton conduction medium. Phosphoric acid (phosphonic acid) exhibits chemical stability and high electrical conductivity under high temperature and low humidity conditions. Currently, the application technology of phosphoric acid in proton exchange membranes covers various methods such as crosslinking, doping, and grafting (Wang L, et al. Effects of branching structures on the properties of phosphoric acid-doped polybenzimidazole as a membrane material for high-temperature proton exchange membrane fuel cells. International Journal of Hydrogen Energy, 2018, 43(34): 16694-16703.)(Cui C, et al. Highly proton-conductive and low swelling polymeric membranes achieved by hydrophiliccovalent cross-linking. Journal of colloid and interface science, 2024, 672664-674.). The proton exchange membrane with phosphoric acid as the proton carrier not only exhibits high proton conductivity, but also shows good stability under high temperature and low humidity conditions, effectively solving the problem of performance degradation of traditional perfluorosulfonic acid membranes at high temperatures.

[0004] Existing technology, Chinese patent application CN120149469A, discloses a high-temperature proton exchange membrane based on a metal-organic framework-supported phosphoric acid MIL-101(Cr)@PBI gel-type mixed matrix. A suspension of the metal-organic framework MIL-101(Cr) and water is added to a polybenzimidazole solution to form a gel mixture, which is then coated onto a membrane. Although the cage structure formed by the organometallic framework greatly improves the stability of phosphoric acid molecules in the system, the proton carrier still exists in a free manner in the system, and its dispersion uniformity and long-term durability must be considered. Summary of the Invention

[0005] The purpose of this invention is to provide a phosphide polyborosiloxane proton exchange membrane and its application. The phosphide polyborosiloxane proton exchange membrane provided by this invention grafts phosphonic acid groups into the main chain, and the prepared proton exchange membrane has excellent thermal stability and is suitable for high-temperature proton exchange membranes.

[0006] The technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a phosphine-modified polyborosiloxane proton exchange membrane, comprising the following steps: Step S1: Under a nitrogen atmosphere, heat and stir the silane coupling agent to remove moisture and oxygen from the silane coupling agent; then, under stirring, add dropwise a phosphonic acid functionalized mixed solution of phosphoric acid or organophosphonic acid and formaldehyde; then, under a nitrogen atmosphere, heat to 40~120℃ and stir under reflux for 4~24 h to obtain phosphosiloxane; the reaction is carried out with phosphoric acid or organophosphonic acid and silane coupling agent at a functional group molar ratio of (0.2~2.4):1.

[0007] Step S2: Add concentrated hydrochloric acid to the obtained phosphosiloxane and stir and reflux at 50~120℃ for 4~24 h to obtain phosphopolysiloxane.

[0008] Step S3: Add boric acid or borate ester to the obtained phosphopolysiloxane. The feed ratio of boric acid or borate ester to phosphopolysiloxane is (0.5~1.5):1. The reaction is carried out by heating to 60~140℃ and stirring for 4-24 h to obtain phosphopolyborosilicate.

[0009] Step S4: Add chitosan and an aqueous acetic acid solution to the prepared phosphopolyborosiloxane, dissolve and stir at room temperature to form a blend solution; cast the blend solution into a mold, then heat to 40~100℃ and dry for 4~12 h to obtain a phosphopolyborosiloxane / chitosan composite proton exchange membrane; the blending ratio of chitosan to phosphopolyborosiloxane is (0.02~0.2):1.

[0010] Furthermore, the silane coupling agent is selected from one or more of 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, and methacryloxysilane.

[0011] Furthermore, the organophosphonic acid is selected from one or more of aminotrimethylene phosphate, diethylenetriaminepenta-methylenephosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetra-methylenephosphonic acid.

[0012] Preferably, in step S1, phosphoric acid or organophosphonic acid reacts with a silane coupling agent at a molar ratio of 2:1 for the functional groups.

[0013] Preferably, in step S1, the molar ratio of phosphoric acid to formaldehyde is 1:1.

[0014] Preferably, in step S3, the feed ratio of boric acid and phosphopolysiloxane is 1:1 according to the reaction functional groups. Further, in step S4, the weight-average molecular weight of chitosan is 100~300000 g / mol.

[0015] Preferably, in step S4, the blending ratio of chitosan to phosphopolyborosilicate is 0.15:1.

[0016] Secondly, the present invention provides an application of the above-mentioned phosphine-modified polyboronsiloxane proton exchange membrane, which is used in a proton exchange membrane fuel cell.

[0017] The beneficial effects of this invention are as follows: This invention provides a phosphide polyborosiloxane proton exchange membrane and its application. First, phosphide polyborosiloxane is prepared, and phosphonic acid groups are grafted onto the polysiloxane backbone to ensure the stability of the proton carrier. Then, it is blended with chitosan, forming hydrogen bonds with the phosphonic acid and unreacted free phosphoric acid in the phosphide polyborosiloxane. Compared with doping or stabilization using metal-organic frameworks, this invention starts from the structure and uses chemical bonds to graft phosphoric acid, fundamentally solving the problem of easy phosphoric acid loss. Experimental results show that the phosphide polyborosiloxane proton exchange membrane provided by this invention has excellent thermal stability, with a mass loss of less than 10% at 200℃, a high-temperature proton conductivity of 40-100 mS / cm, a single-cell test showing an open-circuit voltage of 0.2-1.0 V, and a maximum power density of 200-800 mW / cm², demonstrating good performance in high-temperature and low-humidity applications. Attached Figure Description

[0018] Figure 1 The diagram shown is a schematic diagram of the device connection when performing step S1 of the present invention.

[0019] Figure 2 The diagram shown is a schematic of the equipment connection after the reflux device of the present invention is installed.

[0020] Figure 3 The figure shows the reaction formula for preparing phosphine-modified polysiloxanes using the silane coupling agent of the present invention.

[0021] Figure 4 The figure shows the reaction formula for the formation of phosphopolyborosilicate by reacting phosphopolysiloxane with boric acid according to the present invention.

[0022] Figure 5 The figure shown is a GPC result diagram of the present invention.

[0023] Figure 6 The image shows the proton exchange membrane prepared in Example 1 of the present invention.

[0024] Figure 7The image shown is an infrared test result of the composite proton exchange membrane prepared in Example 1 of this invention, 3-aminopropyldiethoxysilane, phosphine-modified polysiloxane, and the composite proton exchange membrane after high temperature testing at 140°C.

[0025] Figure 8 The image shown is a scanning electron microscope (SEM) image of the surface and cross-sectional morphology of the membrane sample prepared in Example 1 of this invention.

[0026] Figure 9 The figure shown is a characterization diagram of phosphorus distribution in the cross section of the membrane sample prepared in Example 1 of the present invention.

[0027] Figure 10 The figure shown is a diagram of the proton conductivity of the composite membrane of the present invention.

[0028] Figure 11 The product shown is Nafion. TM Figures showing the single-cell performance test results of the 117 membrane and the composite membrane in this invention at 40℃, 90℃, and 140℃, respectively.

[0029] Figure 12 The image shown is a scanning electron microscope image of the composite membrane prepared in experimental group 1.3 of this invention.

[0030] Figure 13 The product obtained in experimental group 2.3 of this invention is shown.

[0031] Figure labeling: 1. Heat-collecting constant temperature magnetic stirrer, 2. Oil bath, 3. Three-necked flask, 4. Condenser, 5. Beaker containing water, 6. Stirring bar. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the following examples, unless otherwise specified, the raw materials used are commercially available products. Among them, the silane coupling agent, phosphoric acid and organophosphonic acid, boric acid and borate ester were all purchased from the China Titan Science Exploration Platform.

[0034] Example 1: This invention provides a phosphide polyborosiloxane proton exchange membrane, which is obtained by the following method.

[0035] The preparation equipment used in this embodiment of the invention includes a heat-collecting, constant-temperature magnetic stirrer 1, model DF-101S. This instrument achieves liquid mixing by driving a stir bar 6 with a magnetic rotor. The integrated heating system supports water bath and oil bath modes, and can simultaneously complete stirring and constant temperature control. The heat-collecting, constant-temperature magnetic stirrer 1 integrates an oil bath 2; the oil bath 2 contains an oil bath. In this embodiment of the invention, the container used for the reaction is a three-necked flask 3, which is fixed inside the oil bath 2 by a support. In addition, a condenser 4 and a beaker 5 containing water are also used in the preparation process of this invention. The specific preparation process of this invention describes the specific usage of the equipment in detail below.

[0036] The preparation method provided in Example 1 of this invention includes the following steps.

[0037] Step S1: Under a nitrogen atmosphere, the silane coupling agent is heated and stirred to remove moisture and oxygen. Then, under stirring, a phosphonic acid functionalized mixture of phosphoric acid or organophosphonic acid and formaldehyde is added dropwise. Next, under a nitrogen atmosphere, the mixture is heated to 40–120°C and refluxed with stirring for 4–24 h to obtain phosphosiloxane. Nitrogen gas is not introduced into subsequent processes after step S1.

[0038] In this invention, the silane coupling agent can be one or more selected from 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, and methacryloxysilane. In this embodiment, the silane coupling agent used is 3-aminopropyldiethoxysilane; the amount used is 3 g.

[0039] In this invention, the organophosphonic acid can be one or more of aminotrimethylene phosphate, diethylenetriaminepentamethylenephosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetramethylenephosphonic acid.

[0040] In this invention, phosphoric acid or organophosphonic acid reacts with a silane coupling agent at a functional group molar ratio of (0.2~2.4):1; in this embodiment, the ratio is 2:1.

[0041] In this embodiment, a phosphonic acid functionalized mixed solution is prepared by mixing phosphoric acid and formaldehyde; specifically, 3.62 g of concentrated phosphoric acid with a concentration of 85% and 0.941 g of formaldehyde are used to prepare the mixed solution, and the molar ratio of phosphoric acid to formaldehyde is 1:1.

[0042] In this embodiment, the heating reaction temperature is 70°C, and the reaction is carried out under stirring and reflux for 12 hours.

[0043] The specific operation method of step S1 in this embodiment is as follows. Figure 1The diagram shows the equipment connection during step S1 of this invention. A three-necked flask 3 is fixed inside an oil bath 2 using a support. The left opening of the three-necked flask 3 is sealed with a rubber stopper with a tubing connected to a nitrogen cylinder. The nitrogen cylinder supplies nitrogen to the three-necked flask 3. A stir bar 6 is placed inside the three-necked flask 3 to stir the reactants. Then, 3 g of 3-aminopropyldiethoxysilane is added to the three-necked flask 3, and the right opening is sealed with a rubber stopper. The middle opening is sealed with a rubber stopper with a tubing, the end of which is inserted into a beaker 5 containing water.

[0044] After the equipment is assembled, the heat-collecting constant temperature magnetic stirrer 1 is started for heating, and the heating temperature is set to 70°C; nitrogen gas is introduced into the three-necked flask 3 by opening the nitrogen cylinder valve, and the gas flow rate is 0.5 L / min; under the nitrogen atmosphere, the stir bar 6 is driven to rotate by the magnetic rotor for stirring; in this embodiment, the stirring time is 30 min; then heating is stopped and the flask is cooled to room temperature.

[0045] After the three-necked flask 3 has cooled to room temperature, install a reflux device (i.e., condenser 4) on the opening in the middle of the three-necked flask 3. Figure 2 The diagram shown is a schematic of the equipment connection after the reflux device of this invention is installed. (As shown...) Figure 2 As shown, the bottom opening of the inner tube of the condenser 4 is connected to the middle opening of the three-necked flask 3, and the top opening of the inner tube of the condenser 4 is sealed by a rubber stopper with a conduit. The end of the conduit is inserted into a beaker 5 containing water. Circulating cooling water is introduced into the outer tube of the condenser 4 to cool the inner tube.

[0046] After the equipment is assembled, the heat-collecting constant temperature magnetic stirrer 1 is started again for heating, and the heating temperature is set to 70℃; nitrogen gas is introduced into the three-necked flask 3 by opening the nitrogen cylinder valve, and the gas flow rate is 0.5 L / min; under the nitrogen atmosphere, the stir bar 6 is driven by the magnetic rotor for stirring; the right opening of the three-necked flask 3 is opened, and the mixed solution of phosphoric acid and formaldehyde is added dropwise to the three-necked flask 3; then the mixture is stirred and refluxed for 12 h to obtain phosphine siloxane.

[0047] like Figure 3 The figure shows the reaction formula for preparing phosphine-modified polysiloxanes using the silane coupling agent of the present invention. Figure 3 In Figures 1 and 2, the chemical reaction equations for the steps described above in this invention are shown. During this reaction, the feed ratio of phosphoric acid to the silane coupling agent is 2:1 according to the functional group ratio. In the reaction of this invention, after stirring and refluxing at 70°C for 12 h under a nitrogen atmosphere, phosphonic acid groups are grafted onto the amino groups of the siloxane. The nitrogen atmosphere is maintained to prevent oxidation side reactions. As shown in the figure, one or two phosphonic acid groups can be grafted onto one amino group.

[0048] In this invention, 3-aminopropyldiethoxysilane is heated and stirred under a nitrogen atmosphere primarily to remove moisture and oxygen from the reagents. The 3-aminopropyldiethoxysilane molecule contains a hydrolyzable alkoxy group (Si-OC2H5), which spontaneously hydrolyzes in the presence of moisture to generate silanols (Si-OH). If 3-aminopropyldiethoxysilane hydrolyzes to silanol, it becomes difficult to prepare the polyborosiloxane network in subsequent steps.

[0049] In this invention, deoxygenation is mainly to prevent the occurrence of oxidation side reactions: on the one hand, formaldehyde is easily oxidized to formic acid or carbon dioxide in the presence of oxygen, which will lead to raw material loss, reduce its effective concentration for reaction with 3-aminopropyldiethoxysilane and phosphonic acid, and affect the grafting rate of phosphonic acid groups; on the other hand, oxygen will participate in the oxidation reaction of amino groups in 3-aminopropyldiethoxysilane to generate nitroso groups, reduce the effective concentration of siloxane, reduce the yield, and increase impurities.

[0050] In this invention, the mixed solution of phosphoric acid and formaldehyde is added to the flask dropwise for the following reasons. First, dropwise addition prevents excessively high local concentrations, avoiding intermolecular self-polymerization of formaldehyde to form paraformaldehyde, or cross-condensation with the silane coupling agent to form a network structure instead of the target product. Second, dropwise addition maintains a stable pH of the solution, ensuring reaction selectivity. If added all at once, the pH of the system would drop rapidly, and the siloxane would easily undergo hydrolysis and condensation reactions under acidic conditions.

[0051] Step S2: Add concentrated hydrochloric acid to the obtained phosphosiloxane and stir and reflux at 50~120℃ for 4~24 h to obtain phosphopolysiloxane.

[0052] In this embodiment, phosphopolysiloxane was prepared by stirring and refluxing at 70°C for 12 h.

[0053] In step S2 of this invention, the concentrated hydrochloric acid has a pH of 2 and is added in an amount of 10 mL.

[0054] The reaction principle of step S2 of this invention is as follows: Under acidic conditions, phosphine-modified siloxanes undergo condensation polymerization to form phosphine-modified polysiloxanes, such as... Figure 3 As shown in step 3. In this invention, concentrated hydrochloric acid provides the acidic conditions; the amount added should not be too small, otherwise the reaction will be interrupted. The reflux device should still be maintained to reduce the loss of concentrated hydrochloric acid during the reaction.

[0055] Step S3: Add boric acid or borate ester to the obtained phosphopolysiloxane. The feed ratio of boric acid or borate ester to phosphopolysiloxane is (0.5~1.5):1. The reaction is carried out by heating to 60~140℃ and stirring for 4-24 h to obtain phosphopolyborosilicate.

[0056] In this invention, the borate ester is selected from one or more of trimethyl borate, triethyl borate, and trimethoxyboroxane.

[0057] In this embodiment, boric acid was used, and the amount of boric acid added was 48 mg. The feed ratio of boric acid and phosphopolysiloxane was 1:1 according to the reaction functional groups. The mixture was heated to 120°C and stirred for 5 h to obtain phosphopolyborosiloxane.

[0058] Figure 4 The diagram shows the reaction formula for the formation of phosphopolyborosilicates from the reaction of phosphopolysiloxanes with boric acid according to the present invention. Boric acid contains three hydroxyl groups, all of which can react with the terminal hydroxyl or terminal ethoxy groups of the phosphopolysiloxanes to generate polyborosilicates (ternary structure) with boric acid as the crosslinking point, connecting the linear phosphopolysiloxane chains into a network structure. Binary and monomeric structures may also exist.

[0059] Crosslinking phosphosiloxanes with boric acid allows the polysiloxanes to function without relying on a polymer matrix, which significantly increases the content of proton carriers in the system and avoids compatibility issues between the polymer matrix and the phosphosiloxanes.

[0060] In this invention, the boric acid feed ratio is 1:1 according to the functional groups. The main point is that the hydroxyl groups of boric acid are equivalent to the terminal hydroxyl or ethoxy groups of the phosphopolysiloxane. Therefore, it is necessary to determine the molecular weight of the phosphopolysiloxane, which is characterized using gel permeation chromatography (GPC). The specific operation method is as follows: 3-5 mg of sample is dissolved in 1 mL of sodium nitrate aqueous solution. After dissolution, it is allowed to stand for 1 hour, filtered through a 0.22 mm polyvinylidene fluoride filter membrane, and then tested. The test is carried out in H2O solution at 40℃ with an elution rate of 1.0 mL / min using a Waters-E2695 GPC system equipped with a refractive index detector. The apparent molecular weight is determined on a single PL aquagel-OH MIXED-M column using linear polyethylene glycol (PEG) as a standard. The molecular weight of the phosphopolysiloxane is determined to be 2605 g / mol, and the terminal group equivalent is 7.68 × 10⁻⁶ g / mol. -4 mol / g. For example... Figure 5 The figure shown is a GPC result diagram of the present invention.

[0061] In step S3 of this invention, the reaction temperature must not exceed 150°C; otherwise, boric acid will cause the phosphopolysiloxane to undergo random breakage, reducing its molecular weight.

[0062] Step S4: Add chitosan and acetic acid aqueous solution to the obtained phosphopolyborosiloxane, dissolve and stir at room temperature to form a blend solution; cast the blend solution into a mold, then heat to 40~100℃ and dry for 4~12 h to obtain phosphopolyborosiloxane / chitosan composite proton exchange membrane.

[0063] In this invention, the weight-average molecular weight of chitosan is 100~300000 g / mol. Preferably, the chitosan is selected from one or more of the following weight-average molecular weights: 1000, 5000, 10000, 100000, 200000, and 300000. The blending ratio of chitosan to phosphobutyl polyborosiloxane is (0.02~0.2):1.

[0064] In this embodiment, 35.8 mg of chitosan (molecular weight 10000 g / mol) with a mass concentration of 0.5~5 wt% was added to phosphoborosilicate, along with 20 mL of an aqueous solution containing 2% acetic acid (mass fraction). The mixture was dissolved and stirred at room temperature (25°C) for 3 h to form a blend solution. The blend solution was then cast into a petri dish (9 cm in diameter) and dried in an oven at 60°C for 12 h to finally obtain the phosphoborosilicate / chitosan composite proton exchange membrane.

[0065] In this embodiment, a petri dish is used as the mold, and the size of the dish determines the thickness of the final product. In this embodiment, with this dosage, a proton exchange membrane with a thickness of approximately 0.5 mm can be prepared in the petri dish. Figure 6 The image shows the proton exchange membrane prepared in Example 1 of the present invention.

[0066] In this invention, the temperature used for solvent removal in the oven should not be too high, otherwise the solvent evaporation rate will be too fast, affecting the morphology of the film.

[0067] In this invention, chitosan is a natural alkaline polyelectrolyte material with advantages such as simple film-forming process and low cost. The cyclic structure in its molecule ensures the mechanical and thermal properties of the membrane. The abundant amino and hydroxyl groups not only endow it with good film-forming properties but also allow it to form ionic cross-linking structures and continuous hydrogen bond networks with phosphate and phosphonic acid groups, enhancing membrane stability and promoting proton conduction. Phospholated polyborosiloxanes and chitosan are cosoluble in aqueous acetic acid solution. However, the amount of acetic acid solution should not be excessive, otherwise the solvent removal process will be too long, reducing efficiency.

[0068] Furthermore, this invention employs a PerkinElmer Spectrum 3 Fourier Transform Infrared Spectrometer (FTIR) to characterize the microstructure of the film sample using FTIR spectroscopy. The measurement range is 400-4000 cm⁻¹. -1 .

[0069] like Figure 7 The image shown is an infrared test result of the composite proton exchange membrane prepared in Example 1 of this invention, 3-aminopropyldiethoxysilane, phosphine-modified polysiloxane, and the composite proton exchange membrane after high temperature testing at 140°C.

[0070] from Figure 7As can be seen from this, 3-aminopropyldiethoxysilane 1083 cm -1 The characteristic peak of the Si-O bond transforms into the 1100 cm⁻¹ peak in the spectrum of phosphine-modified polysiloxanes. -1 The asymmetric stretching vibration peaks of Si-O-Si on the left and right indicate that the Si-OC2H5 in 3-aminopropyldiethoxysilane underwent hydrolysis and condensation to form a long-chain Si-O-Si polysiloxane. (3400 cm⁻¹) -1 The characteristic peak of the amino group in 3-aminopropyldiethoxysilane is located nearby. After the phosphination reaction, it almost disappears in the spectrum of phosphinated polysiloxane, confirming the successful grafting of the phosphonic acid group. After the phosphination reaction, the peak at 1014 cm⁻¹... -1 946 cm -1 The presence of a characteristic peak for CP at 3100-3600 cm⁻¹ confirms that phosphoric acid has been successfully grafted into the composite membrane. -1 The broad peaks are multiple broad peaks formed by the overlapping of the stretching vibration absorption peaks of the chitosan hydroxyl groups and the stretching vibration absorption peaks of the amino groups. After high-temperature characterization, the infrared spectrum of the composite film was re-examined, and the characteristic peak of CP (1014 cm⁻¹) was still found to be retained. -1 946 cm -1 This confirms the stability of the proton carrier.

[0071] Furthermore, this invention employs a Thermo Scientific Apreo 2C field emission scanning electron microscope to observe the surface and cross-sectional morphology of the film sample. Before testing, the sample was cut into rectangles and dried at 100°C, with the cross-section subjected to liquid nitrogen quenching.

[0072] like Figure 8 The image shown is a scanning electron microscope (SEM) image of the surface and cross-sectional morphology of the membrane sample prepared in Example 1 of this invention. Figure 8 a is a scanning electron microscope image of the surface morphology. Figure 8 b is a scanning electron microscope image of the cross-sectional morphology. As can be seen from the image, the composite film prepared by this invention is uniform, dense, and free from phase separation.

[0073] Furthermore, this invention employs the EDS analysis system of an ULTIM Max 65 energy dispersive spectrometer to characterize the phosphorus distribution across the membrane cross-section. For example... Figure 9 The figure shown is a characterization diagram of phosphorus distribution in the cross-section of the membrane sample prepared in Example 1 of this invention. The analysis revealed that the phosphorus element is uniformly distributed in the membrane, a characteristic that ensures the uniformity of proton conduction sites.

[0074] Furthermore, this invention employs an electrochemical workstation to determine the proton conductivity of the membrane using the AC impedance method. The test parameters are: frequency range 1 Hz-1 MHz, AC amplitude 10 MV. Under conditions without external humidification, the resistance (R) was measured at 20℃, 60℃, 100℃, and 140℃, respectively.

[0075] In an impedance spectrum, the intersection of the linear portion of the curve with the horizontal axis represents the membrane resistance R. The conductivity of the proton exchange membrane is calculated using the following formula:

[0076] Where: s is the conductivity of the proton exchange membrane, in S / cm; L is the membrane thickness, in cm; A is the test area of ​​the membrane, in cm². 2 R represents the impedance of the membrane obtained from the test, in units of... .

[0077] like Figure 10 The diagram shows the proton conductivity of the composite membrane of this invention. At room temperature, the proton conductivity is 32 mS / cm; under anhydrous conditions at 140°C, the proton conductivity is 63 mS / cm. At high temperatures, the self-dissociation rate of phosphonic acid increases, and the flexibility of the molecular chain also increases with rising temperature. The probability of collisions between phosphonic acid groups increases, and a dense hydrogen bond network is formed between the phosphonic acid groups and chitosan, maintaining a high proton conductivity.

[0078] Furthermore, the present invention utilizes the proton exchange membrane prepared in Example 1 to fabricate a membrane electrode assembly (MEA) for a fuel cell.

[0079] The fabrication method of the membrane electrode assembly (MEA) for a fuel cell is as follows.

[0080] The catalysts used for the anode and cathode were Pt-Ru / C (30%, total Pt-Ru mass fraction, Pt:Ru molar ratio 1:1) and Pt / C (10%, Pt mass fraction), respectively. A suitable amount of 5% Nafion emulsion and 20% ethylene glycol were added and mixed thoroughly at room temperature to prepare a catalyst slurry. Subsequently, the catalyst slurry was uniformly coated onto carbon paper (TGPh-120, manufactured by Toray Industries, Japan), ensuring that the catalyst loading at the anode and cathode reached 4 mg / cm³. 2The coated sample is clamped between the two electrodes to form the membrane electrode assembly (MEA), without the need for hot pressing. All MEAs have a uniform effective size of 20 mm × 20 mm. Single-cell assembly requires ensuring the MEA is correctly clamped between the two bipolar plates to form a sealed gas flow channel, clamping tightly to guarantee good electrical contact and sealing. The MEA is fixed in a hydrogen-oxygen fuel mold with dimensions of 70 × 60 × 20 mm and an effective area of ​​25 × 25 mm. After the MEA is attached to the bipolar plates, end plates are added on both sides to apply appropriate force, ensuring good electrical contact between the MEA and the plates. Sealing material is placed at the edges to prevent hydrogen and oxygen leakage and their mixing inside the cell. During assembly, ensure good sealing and contact while minimizing excessive local stress.

[0081] The prepared composite membrane was assembled into a single-cell unit. The performance of the single-cell unit was tested using an electrochemical workstation at temperatures of 40℃, 90℃, and 140℃.

[0082] The relationships between current density and potential, and between current density and power density of the battery were precisely determined using LSV (linear sweep voltammetry) experiments. During the experiment, hydrogen gas was introduced into the anode at a constant flow rate of 0.2 L / min, while the cathode was kept in open air. This also characterized the performance of the commercial Nafion battery. TM The single-cell performance of the 117 membrane and the composite membrane of this invention at 40°C, 90°C, and 140°C, respectively, is as follows: Figure 11 The product shown is Nafion. TM Figures showing the single-cell performance test results of the 117 membrane and the composite membrane in this invention at 40℃, 90℃, and 140℃, respectively.

[0083] from Figure 11 As can be seen from this, Nafion TM The 117 membrane exhibits excellent battery power at low temperatures, reaching 335.9 mW / cm² at 40°C and 664.7 mW / cm² at 90°C. 2 While exhibiting excellent low-temperature battery performance, the membrane ruptured after the 90°C test and could no longer be used. Therefore, the Nafion™ 117 membrane cannot be used in high-temperature environments, consistent with its product specification's usage temperature of 30~80°C. The composite membrane in this invention maintains high battery power even at high temperatures, achieving a maximum power density of 420.2 mW / cm² under anhydrous conditions at 140°C, demonstrating excellent high-temperature battery performance and meeting the requirements for proton exchange membrane use under high temperature and low humidity conditions.

[0084] Furthermore, this invention conducted single-variable experimental studies on the key conditions in the method.

[0085] Experiment 1: Effect of phosphoric acid feed ratio on the performance of the product of this invention.

[0086] In this invention, the ratio of phosphoric acid to silane coupling agent is crucial. Phosphoric acid, as a proton carrier, determines the proton conductivity of the proton exchange membrane and the performance of a single cell. This experiment uses a single-variable method, changing only the amount of phosphoric acid, to study its effect on the membrane proton conductivity and determine the optimal amount.

[0087] In this experiment, the independent variable was the amount of phosphoric acid used, with four levels: 1.81 g (50% of Example 1), 2.72 g (75% of Example 1), 3.62 g (the amount used in Example 1), and 4.53 g (125% of Example 1). The amounts of other reagents and the process conditions were completely consistent with those in Example 1.

[0088] The samples prepared in this experiment and their properties are shown in Table 1 below:

[0089] Experimental results show that the optimal feed ratio of phosphoric acid or organophosphonic acid in this invention is 2:1, based on the molar ratio of the reacting functional groups. After reaction, phosphoric acid or organophosphonic acid is grafted onto the siloxane molecular chain. Under the optimal ratio, the higher the feed ratio of phosphoric acid or organophosphonic acid, the higher the phosphonic acid group content, and the higher the membrane conductivity and battery power (e.g., experimental groups 1.1 and 1.2). When the feed ratio is higher than the optimal ratio, increasing the content will not increase the proton conductivity and battery power of the composite membrane (e.g., experimental group 1.3), but will instead lead to phosphonic acid aggregation and membrane inhomogeneity. Figure 12 The image shown is a scanning electron microscope image of the composite membrane prepared in experimental group 1.3 of this invention.

[0090] Experiment 2: Effect of boric acid feeding ratio on the performance of the product of this invention.

[0091] In this invention, the molar ratio of boric acid or borate esters to phosphopolysiloxane is also crucial. Boric acid, as a chemical crosslinking agent, determines the film-forming performance of the proton exchange membrane. This experiment uses a single-variable method, changing only the amount of boric acid, to study its effect on film-forming performance and determine the optimal dosage.

[0092] In this experiment, the independent variable was the amount of boric acid used, with four levels: 24 mg (50% of the amount used in Example 1), 48 mg (the amount used in Example 1), 72 mg (150% of the amount used in Example 1), and 96 mg (200% of the amount used in Example 1). The amounts of other reagents and the process conditions were completely consistent with those in Example 1.

[0093] The samples prepared in this experiment and their properties are shown in Table 2 below:

[0094] The experimental results indicate that the optimal feed ratio of boric acid or borate ester is 1:1 based on the molar ratio of the reacting functional groups. After reaction, boric acid or borate ester forms a cross-linked polyborosiloxane. A low feed ratio of boric acid or borate ester results in insufficient cross-linking (e.g., experimental group 2.1), leading to the disruption of the proton conduction pathway; an excessively high feed ratio results in over-cross-linking (e.g., experimental group 2.3), causing the prepared membrane to become brittle or even fail to form a membrane. Figure 13 And it hinders proton migration (as in experimental group 2.3). Figure 13 The product obtained in experimental group 2.3 of this invention is shown.

[0095] Experiment 3: The effect of chitosan blending ratio on product performance.

[0096] In this invention, phosphopropyl polysiloxane is used as the matrix material, and chitosan is used to construct the hydrogen bond network in the system. Therefore, its dosage has a significant impact on film formation and proton conductivity. This experiment uses a single-variable method, changing only the amount of chitosan, to study its effect on the proton conductivity of the film and determine the optimal amount of chitosan.

[0097] In this experiment, the independent variable was the amount of chitosan used, with four levels: 11.8 mg (33.3% of Example 1), 23.7 mg (66.7% of Example 1), 35.8 mg (the amount used in Example 1), and 60.3 mg (167% of Example 1). The amounts of other reagents and the process conditions were completely consistent with those in Example 1.

[0098] The samples prepared in this experiment and their properties are shown in Table 3 below:

[0099] Experimental results show that the optimal addition ratio of chitosan to phosphobromosiloxane is 0.15:1 by mass. The hydroxyl and amino groups of chitosan form hydrogen bonds with the hydroxyl groups of phosphonic acid groups in the system, constructing a hydrogen bond network as a proton conduction pathway. Insufficient chitosan (experimental group 3.1) leads to discontinuous proton conduction pathways and low proton conductivity; excessive chitosan makes film formation difficult (experimental group 3.3).

[0100] It is understood that this invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this invention are within the protection scope of this invention.

Claims

1. A phosphine-modified polyborosiloxane proton exchange membrane, characterized in that, Includes the following steps: Step S1: Under a nitrogen atmosphere, heat and stir the silane coupling agent to remove moisture and oxygen from it; then, under stirring, add a phosphonic acid functionalized mixed solution of phosphoric acid or organophosphonic acid and formaldehyde dropwise; next, under a nitrogen atmosphere, heat to 40~120℃ and stir under reflux for 4~24 h to obtain phosphosiloxane; the reaction is carried out with phosphoric acid or organophosphonic acid and silane coupling agent at a functional group molar ratio of (0.2~2.4):

1. Step S2: Add concentrated hydrochloric acid to the obtained phosphosiloxane and stir and reflux at 50~120℃ for 4~24 h to obtain phosphopolysiloxane. Step S3: Add boric acid or borate ester to the obtained phosphopolysiloxane. The feed ratio of boric acid or borate ester to phosphopolysiloxane is (0.5~1.5):

1. The reaction is carried out by heating to 60~140℃ and stirring for 4-24 h to obtain phosphopolyborosiloxane. Step S4: Add chitosan and an aqueous acetic acid solution to the prepared phosphopolyborosiloxane, dissolve and stir at room temperature to form a blend solution; cast the blend solution into a mold, then heat to 40~100℃ and dry for 4~12 h to obtain a phosphopolyborosiloxane / chitosan composite proton exchange membrane; the blending ratio of chitosan to phosphopolyborosiloxane is (0.02~0.2):

1.

2. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, The silane coupling agent is selected from one or more of 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, and methacryloxysilane.

3. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, The organophosphonic acid is selected from one or more of aminotrimethylene phosphate, diethylenetriaminepenta-phosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetra-methylenephosphonic acid.

4. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, In step S1, phosphoric acid or organophosphonic acid reacts with a silane coupling agent at a molar ratio of 2:1 for the functional groups.

5. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, In step S1, the molar ratio of phosphoric acid to formaldehyde is 1:

1.

6. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, In step S3, the feed ratio of boric acid and phosphine-modified polysiloxane is 1:1 according to the reaction functional groups.

7. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, In step S4, the weight-average molecular weight of chitosan is 100~300000 g / mol.

8. The phosphine-modified polyborosiloxane proton exchange membrane according to claim 1, characterized in that, In step S4, the blending ratio of chitosan to phosphopolyborosiloxane is 0.15:

1.

9. An application of the phosphide polyborosiloxane proton exchange membrane according to any one of claims 1-8, characterized in that, Proton exchange membranes are used in proton exchange membrane fuel cells.

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