A reinforcing layer for a proton exchange membrane with a wide temperature range and a manufacturing method thereof

Abstract

The application discloses a reinforcing layer for a wide-temperature-range proton exchange membrane and a manufacturing method thereof, which comprises an ePTFE layer, nanofiber layers respectively formed on two sides of the ePTFE layer, and phytic acid adsorbed in the nanofiber layers; the phytic acid modified polymer nanofiber layer and the ePTFE layer are combined to form the reinforcing layer for the wide-temperature-range proton exchange membrane. The ePTFE layer has strong strength and stability, and can enhance the strength of the proton exchange membrane; the polymer layer which can be spun and has proton conduction capacity or has proton conduction capacity after post-modification is deposited on the ePTFE layer through the electrospinning technology, so that the proton conduction rate of the proton exchange membrane can be effectively improved; the reinforcing layer formed has high strength and high proton conduction capacity; and the proton exchange membrane prepared from the reinforcing layer can meet the use requirements in a high-temperature and low-humidity environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of proton exchange membrane, in particular to a reinforcing layer for wide-temperature-range proton exchange membrane and a manufacturing method thereof. BACKGROUND

[0002] As one of the key components of fuel cells, the proton exchange membrane has the functions of blocking the anode and cathode reactants and transferring protons. According to the Grotthuss and transport two proton transfer mechanisms, the proton exchange membrane has a low hydration number under high-temperature and low-humidity conditions, and the activation energy of proton transfer is large, so the proton transfer is difficult, and the proton conductivity is low. The perfluorosulfonic acid resin with proton transfer ability has a low glass transition temperature, and will creep at high temperatures, resulting in a decrease in mechanical strength, a decrease in chemical stability, an increase in gas permeability, and an inability to meet the use requirements.

[0003] At present, in order to meet the use requirements in high-temperature environments, the commercial proton exchange membrane is generally composed of a resin with high proton conduction capacity and a reinforcing layer. The commonly used reinforcing layer is expanded polytetrafluoroethylene, which mainly plays a role in improving the mechanical strength and dimensional stability of the membrane in the proton exchange membrane. However, since the expanded polytetrafluoroethylene does not have proton conduction capacity, its introduction into the proton exchange membrane is equivalent to diluting the concentration of proton transfer groups, resulting in a significant decrease in the proton conduction capacity of the proton exchange membrane. Therefore, it is crucial to design a reinforcing layer with proton conduction capacity that can ensure the mechanical stability of the proton exchange membrane while also improving the proton conductivity of the proton exchange membrane, and a new technical solution needs to be sought to solve the above problems. SUMMARY

[0004] The purpose of the present application is to solve the problems existing in the prior art, and the ePTFE layer is modified by adding a polymer nanofiber layer.

[0005] The nanofiber layer is formed on both sides of the ePTFE layer, and the nanofiber layer has phytic acid adsorbed therein.

[0006] The phytic acid-modified polymer nanofiber layer and the ePTFE layer form the reinforcing layer for the wide-temperature-range proton exchange membrane.

[0007] As a further description of the above technical solution, the polymer nanofiber layer is formed by directly depositing the polymer on the ePTFE layer using an electrospinning technique.

[0008] As a further description of the above technical solution, the thickness of the ePTFE layer is 2-6 microns, and the thickness of the polymer layer is 2-3 microns.

[0009] As a further description of the above technical solution: the polymer is any one of polybenzimidazole, sulfonated polybenzimidazole or polyimide.

[0010] A method for manufacturing a reinforcing layer for a proton exchange membrane with a wide temperature range, specifically comprising the following steps:

[0011] S1, configure the spinning solution with a concentration of 15-25%;

[0012] S2, paste the 2-6 micron thick ePTFE to the receiver of the electrospinning machine, then add the spinning solution to the spinning needle tube of the electrospinning machine, start electrospinning on one side of the ePTFE, and control the thickness of the fiber felt by controlling the spinning time and the injection speed;

[0013] S3, take off the ePTFE with single-side electrospinning, and perform the same operation on the other side to obtain the double-sided nanofiber ePTFE reinforcing layer;

[0014] S4, heat-press the double-sided nanofiber ePTFE reinforcing layer under the condition of 120-150℃ and 0.5-1MPa to form the reinforcing layer, and control the thickness of the reinforcing layer to be 6-12 microns.

[0015] As a further description of the above technical solution: in step S4, the heat-pressed nanofiber ePTFE reinforcing layer is soaked in a 10wt%-25wt% phytic acid solution at a temperature of 25-60℃, the phytic acid is adsorbed in the nanofiber through the hydrogen bond interaction between the N on the imidazole in the nanofiber main chain and the phosphate group on the phytic acid, and after soaking in the phytic acid solution for a predetermined time, the residual phytic acid on the surface of the reinforcing layer is washed away with deionized water. The modified reinforcing layer is dried for standby.

[0016] As a further description of the above technical solution: in step S1, the method for forming the spinning solution in step S1 comprises:

[0017] The molecular weight of the polymer powder is 30000-60000, and the solvent is added;

[0018] Under the condition of heating and stirring reflux at a preset temperature, the spinning solution with a concentration of 15-25% is configured and formed;

[0019] The spinning solution is filtered while hot to remove impurities and collected for standby;

[0020] The solvent uses one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

[0021] As a further description of the above technical solution: in steps S2 and S3, the electrostatic spinning machine should be wrapped with aluminum foil in advance, the spinning voltage of the electrostatic spinning machine is controlled at 12kV-18kV, the distance between the needle head of the spinning needle tube and the receiver is controlled at 10cm-18cm, the push injection speed is 0.1mm / min, and the spinning is performed on the surface of the ePTFE layer for 20-60 minutes.

[0022] A wide-temperature-range proton exchange membrane comprises:

[0023] The reinforcing layer is made by the method;

[0024] Perfluorosulfonic acid resin layers are respectively formed on two sides of the reinforcing layer.

[0025] As a further description of the above technical solution: in the forming of the perfluorosulfonic acid resin layer on the reinforcing layer, a perfluorosulfonic acid resin solution is poured onto the surface of a release film, then scraped with a scraper, the modified reinforcing layer fixed by a frame is quickly placed on the wet film, after the reinforcing layer is completely wetted, the perfluorosulfonic acid resin solution is poured onto the surface of the film, then dried to make the solvent completely volatilize and the resin solidify, and finally the prepared proton exchange membrane is annealed in a vacuum oven to obtain the proton exchange membrane.

[0026] The above technical solution has the following advantages or beneficial effects:

[0027] 1、The ePTFE layer has strong strength and stability, which can enhance the strength of the proton exchange membrane, the polymer layer which can be spun and has proton conduction capacity or has proton conduction capacity after modification is deposited on the ePTFE layer by electrospinning technology, so that the proton exchange membrane can effectively improve the proton conduction rate, and the formed reinforcing layer has high strength and high proton conduction capacity, and the prepared proton exchange membrane can meet the use requirements in high-temperature and low-humidity environment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of an existing proton exchange membrane;

[0029] Figure 2 It is a structural schematic diagram of a reinforcing layer in an embodiment of the present application;

[0030] Figure 3 It is a structural schematic diagram of a reinforcing layer forming a proton exchange membrane in an embodiment of the present application;

[0031] Figure 4 It is Figure 2 It is an electron microscope image of the ePTFE layer in the reinforcing layer;

[0032] Figure 5 It is Figure 2The electron microscope image of the polymer layer in the reinforcing layer;

[0033] Figure 6 The proton conductivity graph under different temperature and humidity;

[0034] Figure 7 The mechanical strength graph under different temperature;

[0035] Figure 8 The single cell performance graph of different membranes under high temperature and low humidity conditions.

[0036] Legend:

[0037] 1, ePTFE layer; 2, nanofiber layer. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] Embodiment one:

[0040] Please refer to Figures 1-3 As shown in the figure, the present application provides an embodiment: a reinforcing layer for a wide-temperature-range proton exchange membrane, comprising: an ePTFE layer 1; a nanofiber layer 2 formed on both sides of the ePTFE layer 1, the nanofiber layer 2 having phytic acid adsorbed therein; the phytic acid-modified polymer nanofiber layer 2 and the ePTFE layer 1 are combined to form a reinforcing layer for a wide-temperature-range proton exchange membrane, the polymer nanofiber layer 2 is deposited on the ePTFE layer 2 by using electrospinning technology, the thickness of the ePTFE layer is 2-6 microns, the thickness of the polymer layer is 2-3 microns, and the polymer is any one of polybenzimidazole, sulfonated polybenzimidazole or polyimide.

[0041] In this embodiment, the ePTFE layer 1 has strong strength and stability to enhance the strength of the proton exchange membrane, the polymer layer 2 which can be spun and has proton conduction capacity or has proton conduction capacity after modification is deposited on the ePTFE layer 1 by using electrospinning technology, so that the proton conduction rate of the proton exchange membrane can be effectively improved, and the reinforcing layer with high strength and high proton conduction capacity is formed, and the proton exchange membrane prepared therefrom can meet the use requirements in high temperature and low humidity environment.

[0042] Since the perfluorosulfonic acid resin with proton transfer ability will creep at high temperature, resulting in reduced mechanical strength, poor chemical stability, increased gas permeability, and inability to meet the use requirements, commercialized proton exchange membranes are generally composed of two parts: a resin with high proton conductivity and a reinforcing layer. The performance of the proton exchange membrane is directly related to the two components. The commonly used reinforcing layer is expanded polytetrafluoroethylene (ePTFE layer), which mainly plays a role in improving the mechanical strength and dimensional stability of the membrane inside the proton exchange membrane. However, since the ePTFE layer does not have proton conductivity, its introduction into the proton exchange membrane is equivalent to diluting the concentration of proton transfer groups, resulting in a significant decrease in the proton conductivity of the proton exchange membrane.

[0043] Polymer electrospinning refers to the process of polymer jetting, stretching, and phase separation solidification into fibers under the action of high-voltage electric field. There have been many reports on the use of nanofiber mats prepared by electrospinning technology as a reinforcing layer to support proton exchange membranes. Due to the inherent characteristics of polymers and the basic requirements of electrospinning for polymers, not all polymers are suitable for electrospinning. The use of nanofiber mats prepared by electrospinning technology using polymers that can be spun and have proton conductivity or have proton conductivity after modification can effectively improve the proton conductivity of the proton exchange membrane. However, the fiber mat prepared by electrospinning technology cannot improve the mechanical stability of the proton exchange membrane due to its low mechanical strength. The mechanical strength of the proton exchange membrane prepared with the fiber mat as a reinforcing layer will be lower than that of the proton exchange membrane with an ePTFE layer as a reinforcing layer, and its low strength poses a risk of damage during the preparation of the membrane electrode and the operation of the fuel cell.

[0044] The method of using electrospinning as a proton membrane reinforcing layer is currently limited to scientific research and academic research, and has not been mass-produced. It usually only focuses on whether the conductivity of the proton exchange membrane has been improved, without considering the strength problem in engineering; the commercial proton membrane uses the ePTFE layer as a reinforcing layer as a mature technical solution, which has met the past use requirements below 95°C and does not need to be further developed; however, since the current increase in fuel cell operating temperature is an inevitable trend, it also puts forward higher requirements for the proton membrane. The use of ePTFE layer alone cannot meet the use requirements, so the reinforcing layer needs to be modified.

[0045] Example Two:

[0046] A method for making a reinforcing layer for a wide-temperature-range proton exchange membrane, specifically comprising the following steps:

[0047] S1, put the polybenzimidazole powder with different molecular weight into one or more solvents of N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and heat and stir under the condition of reflux at 150℃, to configure a spinning solution with a concentration of 15-25%, the molecular weight of the PBI powder is 30000-60000, select one or more molecular weights, filter the impurities during the preparation of the PBI spinning solution, and collect it for standby. S2, paste the ePTFE layer with a thickness of 2-6 microns on the receiver of the electrospinning machine, then add the spinning solution into the spinning needle tube of the electrospinning machine, start electrospinning on one side of the ePTFE layer, and control the thickness of the fiber felt by controlling the spinning time and the injection speed; S3, take down the ePTFE layer with single-side electrospinning completed, and perform the same operation on the other side to obtain the double-sided nanofiber ePTFE layer reinforcement layer; S4, heat-press the double-sided nanofiber ePTFE layer reinforcement layer under the condition of 120-150℃ and 0.5-1 MPa to form the reinforcement layer, and control the thickness of the reinforcement layer to be 6-12 microns.

[0048] Specifically, the electrospinning machine should be wrapped with aluminum foil in advance, the spinning voltage of the electrospinning machine is controlled to be 12kV-18kV, the distance between the needle head of the spinning needle tube and the receiver is controlled to be 10cm-18cm, and the injection speed is 0.1mm / min, and the spinning is performed on the surface of the ePTFE layer for 20-60 minutes.

[0049] By using the ePTFE layer as the reinforcement layer of the electrospun nanofiber felt, a proton exchange membrane reinforcement layer with high conductivity and high mechanical strength is constructed, and the proton exchange membrane prepared by using the reinforcement layer developed in the present patent has more excellent performance, especially the performance is improved more obviously under the working condition of high temperature and low humidity, and the working temperature requirement of the fuel cell is met.

[0050] As shown in Figure 4 and Figure 5 , in step S4, the nanofiber ePTFE reinforcement layer after heat pressing is soaked in a 10wt%-25wt% phytic acid solution, the soaking temperature is 25℃-60℃, the phytic acid is adsorbed in the nanofiber by using the hydrogen bond interaction between the N on the imidazole in the main chain of the nanofiber and the phosphate group on the phytic acid, and after soaking in the phytic acid solution for a predetermined time, the phytic acid remaining on the surface of the reinforcement layer is washed away with deionized water, and the modified reinforcement layer is dried for standby.

[0051] Specifically, the phytic acid modification of the reinforcement layer contains a large amount of phosphate on the phytic acid molecule, so that the phosphate on the reinforcement layer can form a hydrogen bond interaction with water molecules, and the hydrogen bond between the phytic acid modified reinforcement layer and water molecules improves the water retention of the reinforcement layer.

[0052] Currently, the proton membrane of the commercialized proton membrane manufacturer usually does not add water-retaining materials, so that under the condition of high temperature and low humidity, the proton transfer activation energy of the proton membrane is increased due to water deficiency, the proton conductivity is decreased, and only the use demand of <95 DEG C in the past can be met. At present, the working temperature of the fuel cell is increased, which is an inevitable trend, which also puts forward higher requirements for the proton membrane. The pure use of ePTFE layer cannot meet the use demand. The modified reinforcing layer introduced in the application can improve the water-retaining capacity of the proton membrane due to the hydrogen bond interaction. Even under the condition of high temperature and low humidity, the hydrogen bond network constructed by a large number of water molecules in the membrane can also be obtained, the proton transfer activation energy is reduced, and the modified reinforcing layer has good water-retaining property and the ability of promoting proton conduction, which can meet the use demand of <105 DEG C.

[0053] The deposition of PBI on the ePTFE layer by electrospinning technology can avoid the loss of phytic acid, and improve the water-retaining property and the ability of promoting proton conduction of the modified reinforcing layer. Because the N atom on the imidazole ring in PBI and the phosphoric acid group have hydrogen bond interaction, the loss of phytic acid can be avoided.

[0054] Meanwhile, the PBI polymer layer is in the form of nanofiber, the surface is smooth, and there is no obvious stringing. The smooth surface and uniform diameter of the PBI polymer layer can make the mechanical strength of the fiber mat have anisotropy, and the surface without obvious stringing can make the reinforcing layer as a microporous membrane, which will not affect the porosity of the microporous membrane.

[0055] As shown in Figure 2 and Figure 3 , the perfluorosulfonic acid resin solution is poured on the surface of the release film, then scraped by a scraper, the wet film thickness is controlled to be 120 microns, the modified reinforcing layer fixed by the frame is quickly placed on the wet film, after the reinforcing layer is completely wetted, the perfluorosulfonic acid resin solution with a thickness of 80 microns is poured on the surface of the film, then dried at 60 DEG C for 12h, so that the solvent is completely volatilized, and the resin is solidified. The prepared proton exchange membrane is annealed in a vacuum oven at 130 DEG C for 1h, and finally a high-strength and high-proton-conductivity proton exchange membrane with wide temperature adaptability is obtained.

[0056] Example three:

[0057] All prepared samples used perfluorosulfonic acid resin (PFSA) with an EW value of 800 as the matrix. The proton exchange membrane prepared with an ePTFE layer as the reinforcing layer was named ePTFE-PFSA; the proton exchange membrane prepared with a reinforcing layer combining PBI and an ePTFE layer (prepared in this invention) was named PBI-PFSA; and the proton exchange membrane with only PBI as the reinforcing layer was named NF-PBI-PFSA. All prepared samples were tested and evaluated.

[0058] like Figure 6 As shown, the proton conductivity of the samples was tested under different temperature and humidity conditions. At 80℃ and 105℃, the proton conductivity of PBI-PFSA was higher than that of ePTFE-PFS under all humidity conditions. This is mainly because the reinforcing layer of the PBI-PFSA proton exchange membrane, after being treated with phytic acid, also possesses proton conductivity; while the ePTFE layer lacks proton conductivity, leading to a decrease in the proton conductivity of the proton exchange membrane prepared from it. At 105℃ and 30% RH, PBI-PFSA also exhibited a high proton conductivity of 0.032 S / cm, far exceeding that of proton exchange membranes with traditional ePTFE layers as the reinforcing layer. Therefore, the PBI-PFSA proton exchange membrane, exhibiting high proton conductivity under high temperature and low humidity conditions, also meets the potential for application in high-temperature conditions.

[0059] Example 4:

[0060] like Figure 7 The mechanical properties of three membranes—one with PBI as the reinforcing layer, one with an ePTFE layer as the reinforcing layer, and one with a PBI reinforcing layer containing an ePTFE layer—are shown. The proton exchange membrane containing only PBI, without an ePTFE layer in the reinforcing layer, exhibits lower mechanical strength and elongation at break. Uneven stress exists in the proton exchange membrane during assembly and battery operation; lower strength may lead to membrane breakage and battery failure. In contrast, the proton exchange membrane produced using the reinforcing layer prepared in this invention exhibits better mechanical strength and elongation at break.

[0061] Example 5:

[0062] The table below shows the water absorption and swelling rates of different samples. PBI-PFSA exhibits similar dimensional stability to ePTFE-PFSA, but its water absorption rate is higher. This is mainly because the phytic acid-modified reinforcing layer can form more hydrogen bonds with water molecules, which helps to improve the membrane's water absorption and retention.

[0063]

[0064] Example 6:

[0065] like Figure 8As shown, the polarization curve of the single cell assembled by the proton exchange membrane is given.

[0066] Finally, it should be noted that the above only for the preferred embodiments of the present application, and is not intended to limit the present application, although the foregoing embodiments of the present application has been described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement, within the spirit and principles of the present application, any modification, equivalent replacement, improvement, etc., should be included within the scope of the present application.

Claims

1. A method for fabricating a reinforcing layer for a wide-temperature-range proton exchange membrane, characterized in that, The enhancement layer includes: ePTFE layer; Polymer nanofiber layers are formed on both sides of the ePTFE layer, and phytic acid is adsorbed in the polymer nanofiber layers. The phytic acid-modified polymer nanofiber layer is combined with the ePTFE layer to form the reinforcing layer for the wide-temperature-range proton exchange membrane; The polymer nanofiber layer is formed by directly depositing the polymer onto the ePTFE layer using electrospinning technology. The manufacturing method specifically includes the following steps: S1, a polymer spinning solution with a concentration of 15% to 25% is prepared, wherein the polymer is polybenzimidazole; S2, attach 2-6 micrometer thick ePTFE to the receiver of the electrospinning machine, then add the spinning solution into the spinning needle of the electrospinning machine, and start electrospinning on one side of the ePTFE. The fiber layer thickness is controlled by controlling the spinning time and the injection speed. S3, remove the ePTFE completed by single-sided electrospinning, and perform the same operation on the other side to obtain an ePTFE reinforced layer with polymer nanofiber layers on both sides; S4, the ePTFE reinforcement layer is hot-pressed at 120-150℃ and 0.5-1MPa to form a reinforcement layer, and the thickness of the reinforcement layer is controlled at 6-12 micrometers; In step S1, the method for forming the spinning solution includes: Polymer powder with a molecular weight of 30,000 to 60,000 is added to a solvent; Under the conditions of heating, stirring and reflux at a preset temperature, a spinning solution with a concentration of 15-25% is prepared. Filter the spinning solution while it is still hot to remove impurities, and collect it for later use; The solvent is one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide. In steps S2 and S3, the electrospinning machine is wrapped with aluminum foil in advance, the spinning voltage of the electrospinning machine is controlled at 12kV to 18kV, the distance between the needle tip of the spinning needle tube and the receiver is controlled at 10cm to 18cm, the injection speed is 0.1mm / min, and spinning is carried out on the surface of the ePTFE layer for 20 to 60 minutes. In step S4, the hot-pressed reinforcing layer is immersed in a 10wt% to 25wt% phytic acid solution at a temperature of 25℃ to 60℃. After immersion in the phytic acid solution for a predetermined time, the residual phytic acid on the surface of the reinforcing layer is washed away with deionized water, and the modified reinforcing layer is dried for later use.

2. A wide-temperature-range proton exchange membrane, characterized in that, include: The reinforcing layer is made by the method of claim 1; Perfluorosulfonic acid resin layers are formed on both sides of the reinforcing layer.

3. The wide-temperature-range proton exchange membrane according to claim 2, characterized in that: The process of forming the perfluorosulfonic acid resin layer in the reinforcing layer includes: pouring a perfluorosulfonic acid resin solution onto the surface of the release membrane, then scraping it with a scraper, quickly placing the modified reinforcing layer, which is fixed by the frame, onto the wet membrane, pouring the perfluorosulfonic acid resin solution onto the surface of the wetted reinforcing layer after the reinforcing layer is completely wetted, drying it to allow the solvent to completely evaporate and the resin to cure, and then annealing the prepared proton exchange membrane in a vacuum oven to finally obtain the proton exchange membrane.

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