A proton exchange membrane and a preparation process thereof

Abstract

The present application relates to a kind of proton exchange membrane and its preparation process, including first exchange layer, intermediate layer and second exchange layer, the three-dimensional network structure of intermediate layer is connected by intermediate layer fiber, is formed around, the average diameter D of intermediate layer fiber is 60-400nm;The average spacing d of adjacent two intermediate layer fibers is 80-450nm, under the synergistic effect of intermediate layer fiber with suitable diameter and suitable spacing, the pore structure with suitable pore size in the interior of proton exchange membrane intermediate layer, on the one hand, the dimensional stability of proton exchange membrane is significantly improved, the service life of proton exchange membrane is extended, on the other hand, the proton conductivity of proton exchange membrane in actual use has not reduced, even slightly improved.The preparation process provided by the present application can conveniently, quickly and effectively prepare the above-mentioned proton exchange membrane.

Description

Technical Field

[0001] This invention relates to the technical field of proton exchange membrane fuel cells, and in particular to a proton exchange membrane and its preparation process. Background Technology

[0002] With the worsening of environmental problems and the depletion of fossil fuels, people have begun to explore sustainable energy technologies. Fuel cells can directly convert chemical energy into electrical energy, offering advantages such as high energy conversion efficiency and environmental friendliness. Fuel cells are mainly classified into proton exchange membrane fuel cells (PEMFC), alkaline fuel cells, phosphoric acid fuel cells, and solid oxide fuel cells.

[0003] Proton exchange membrane fuel cells (PEMFCs) offer advantages such as high efficiency, low-temperature operation, ease of operation, and safety and reliability, and are widely used in electric vehicles and military fields. The proton exchange membrane, as the core component of a PEMFC, is often referred to as the "chip" of the fuel cell. Globally, proton exchange membranes have achieved mass production.

[0004] For example, Japanese patent application JP2006260811A (application filed by Asahi Glass Co., Ltd.) discloses an electrolyte membrane for a solid polymer electrolyte fuel cell, which is made of a polymer compound with sulfonic acid groups (a perfluorocarbon polymer with sulfonic acid groups). Perfluorocarbon polymers with sulfonic acid groups (perfluorosulfonic acid resins) are good proton conductors, and the fact that the proton exchange membrane (electrolyte membrane) is made of perfluorosulfonic acid resin means that the proton exchange membrane has good proton conductivity. However, with the development of proton exchange membranes, they have gradually become thinner (from tens of micrometers to tens of micrometers). This is because a reduction in the thickness of the proton exchange membrane reduces the internal resistance of the proton exchange membrane fuel cell, further improving the working efficiency of the fuel cell. However, the reduction in the thickness of the proton exchange membrane undoubtedly affects its durability, especially since mechanical damage and chemical degradation can occur during long-term operation.

[0005] To ensure the high durability of thin-film proton exchange membranes, a series of reinforced composite membranes have been researched. Currently, proton exchange membranes are gradually shifting from pure perfluorosulfonic acid resin materials to composite materials using expanded polytetrafluoroethylene (e-PTFE) membranes as reinforcing materials. This type of composite membrane improves the mechanical strength and stability of the membrane while maintaining battery performance. Furthermore, the membrane can be made very thin, reducing internal resistance and the amount of perfluorosulfonic acid material used.

[0006] For example, Chinese invention patent document CN1134288C (applied by W.L. Gore and Tongren Co., Ltd.) discloses a composite membrane comprising an expanded polytetrafluoroethylene membrane with a porous microstructure of polymer fibers; and an ion exchange material filling the entire membrane, the ion exchange material including (but not limited to) perfluorosulfonic acid resin, wherein the Gurley number of the impregnated expanded polytetrafluoroethylene membrane is greater than 10,000 seconds, wherein the ion exchange material substantially fills the membrane so that the internal volume of the membrane is substantially closed.

[0007] In the aforementioned composite membrane (proton exchange membrane), the polytetrafluoroethylene (PTFE) membrane serves as the reinforcing microporous medium. Since PTFE (e-PTFE) membranes cannot conduct protons, the micropores of the PTFE membrane are filled with perfluorosulfonic acid material, which forms the proton transport channels. It is generally believed that increasing the content of perfluorosulfonic acid resin is beneficial for increasing proton conductivity; that is, the more perfluorosulfonic acid resin (the higher the content of sulfonic acid groups) filling the PTFE membrane, the higher the proton conductivity of the proton exchange membrane (composite membrane). Therefore, in the aforementioned patent, the ion exchange material essentially fills the membrane, and the internal volume of the proton exchange membrane is essentially closed (sealed).

[0008] However, the aforementioned composite membranes also have certain shortcomings. For example, when the proton exchange membrane is working normally, it inevitably absorbs a certain amount of water (the movement of hydrogen ions within the membrane is actually in the form of hydrated protons), and the swelling of the ion exchange material (perfluorosulfonic acid resin) upon water absorption is an inevitable phenomenon. A high packing density of ion exchange material also means that the deformation of the proton exchange membrane during water absorption and swelling is relatively large. During the continuous switching between hygroscopic swelling and dry shrinkage states (for example, every time a hydrogen fuel cell vehicle starts and stops, the proton exchange membrane in the hydrogen fuel cell undergoes a cycle of drying shrinkage to hygroscopic swelling, and then back to drying shrinkage), the deformation of the proton exchange membrane is relatively large, increasing the likelihood of membrane damage.

[0009] To address the aforementioned issues, researchers have adopted the following approach: using expanded polytetrafluoroethylene (PTFE) membranes with superior mechanical properties to ensure higher dimensional stability of the proton exchange membrane. For example, Chinese invention patent document CN100372883C (applied by Gore Inc.) discloses an ion-conducting membrane with high hardness and dimensional stability. This ion-conducting membrane is a composite membrane, specifically comprising: an expanded polytetrafluoroethylene (PTFE) membrane (specifically disclosed in US patent application US5814405A) and an ion-exchange resin impregnated with the membrane. The impregnated PTFE membrane exhibits a Gurley number greater than 10,000 seconds, measured using a Gurley density meter according to ASTM 0726-58. The ion-exchange material essentially permeates the membrane, effectively sealing the internal cavities. The internal microstructure of this expanded PTFE membrane is primarily composed of interwoven fibrillated nodules, which are substantially parallel and highly stretched, with a diameter-to-width ratio equal to or greater than 25:1. Because expanded polytetrafluoroethylene (PTFE) membranes (porous base membranes) have highly elongated fiber nodes interconnected by proto-fibers, they possess a relatively rough yet highly uniform microstructure, resulting in very high strength. It is precisely this high-strength porous base membrane that enables ion-conducting membranes (composite membranes) to exhibit high stability and high hardness.

[0010] However, in the above-mentioned composite membrane, the ion exchange material basically permeates the membrane, which essentially closes the cavities inside the membrane. The high filling degree of the ion exchange material also means that the ion conduction membrane (proton exchange membrane) has better water absorption and swelling properties. The above method has limited effect on improving the problem of relatively weak dimensional stability of proton exchange membrane.

[0011] In summary, the preparation of a proton exchange membrane that combines high proton conductivity and high dimensional stability is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0012] To address the shortcomings of existing technologies, the present invention aims to provide a proton exchange membrane and its preparation process, which combines high proton conductivity and high dimensional stability with a long service life.

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] In a first aspect, this application provides a proton exchange membrane, which adopts the following technical solution:

[0015] A proton exchange membrane includes a main body comprising a first exchange layer, an intermediate layer, and a second exchange layer. The first exchange layer has a dense first outer surface, and the second exchange layer has a dense second outer surface. The first and second exchange layers comprise ion exchange materials. The intermediate layer comprises a porous base membrane and ion exchange materials filled within the porous base membrane. The first, intermediate, and second exchange layers are integrally connected via the ion exchange materials. In a dry state, the thickness H of the proton exchange membrane is not higher than 25 μm. The three-dimensional network structure of the intermediate layer is formed by interconnecting and surrounding intermediate layer fibers. The intermediate layer fibers comprise porous base membrane fibers and ion exchange materials attached to the porous base membrane fibers. The average diameter D of the intermediate layer fibers is 60-400 nm, and the average spacing d between two adjacent intermediate layer fibers is 80-450 nm.

[0016] By adopting the above technical solution, in the membrane structure of the proton exchange membrane provided by this invention, it can be clearly seen along the membrane thickness direction that the membrane comprises a three-layer structure, namely a first exchange layer, an intermediate layer, and a second exchange layer. In this application, the first and second exchange layers can be composed solely of ion exchange materials, or, depending on actual needs, the first and second exchange layers can also include other substances, such as peroxide catalysts. Furthermore, both the first and second outer surfaces are dense, which ensures the high selective permeability of the proton exchange membrane (only H₂). + It provides a channel for proton transfer and also ensures the high gas barrier properties of the proton exchange membrane (isolating the fuel at the anode from the oxidant at the cathode, preventing short circuits in the proton exchange membrane fuel cell).

[0017] In this application, the intermediate layer includes a porous base membrane and an ion exchange material filled inside the porous base membrane. The porous base membrane material can be expanded polytetrafluoroethylene (e-PTFE), or it can be polyvinylidene fluoride, polychlorotrifluoroethylene, polyimide, polybenzimidazole, polyethersulfone, or nonwoven fabric. This ensures that the thin-film proton exchange membrane (thickness not exceeding 25 μm) has high mechanical strength. Simultaneously, since the porous base membrane cannot conduct protons, the interior of the porous base membrane must be filled with ion exchange material (forming pathways for proton conduction in the membrane thickness direction through continuously distributed ion exchange material). Furthermore, since the ion exchange material cannot be suspended within the pore structure of the porous base membrane, it must be attached to the base membrane fibers. It is generally believed that increasing the ion exchange material content is beneficial to increasing proton conductivity; that is, the more ion exchange material filled in the porous base membrane, the higher the proton conductivity of the proton exchange membrane (this is also the reason why the aforementioned Gore patent uses perfluorosulfonic acid resin to completely fill the pore structure in the PTFE layer). However, fully filled proton exchange membranes contain a relatively large amount of ion exchange material. Therefore, when fully filled proton exchange membranes absorb water and swell, the deformation generated is relatively large, and their dimensional stability is relatively low.

[0018] To effectively improve the dimensional stability of the proton exchange membrane, firstly, the intermediate layer of the proton exchange membrane in this application has intermediate layer fibers of suitable thickness (average diameter D of 60-400 nm, preferably 60-350 nm). The average diameter of the intermediate layer fibers is not too small (D not less than 60 nm), indicating that the fiber diameter of the porous base membrane in the intermediate layer is not too small. This gives the intermediate layer relatively good mechanical properties (good self-supporting properties), so that the overall deformation of the proton exchange membrane is relatively small when it absorbs water and swells. At the same time, the average diameter of the intermediate layer fibers is not too large (D not greater than 400 nm), indicating that the ion exchange material attached to the porous base membrane fibers is not very thick. The appropriate amount of intermediate layer fibers attached to the porous base membrane fibers further ensures that the overall deformation of the proton exchange membrane is relatively small when it absorbs water and swells.

[0019] Meanwhile, the intermediate layer fibers include porous base membrane fibers and ion exchange material attached to the porous base membrane fibers. The intermediate layer fibers are interconnected, surrounding each other to form a three-dimensional network structure. That is, the intermediate layer includes a solid skeleton structure formed by the intermediate layer fibers (solid fibers), and porous structures are formed between the intermediate layer fibers (solid fibers). Furthermore, the porous structure has a suitable average pore size (a suitable average spacing d between two adjacent intermediate layer fibers, with an average spacing d of 80-450 nm). Compared to a fully filled proton exchange membrane (the membrane in the aforementioned Gore patent), the intermediate layer of an incompletely filled proton exchange membrane (a proton exchange membrane with a porous intermediate layer) contains relatively less ion exchange material. Therefore, the overall deformation caused by water absorption and swelling of the proton exchange membrane is relatively small. Moreover, this porous structure provides a certain swelling space for the ion exchange material; that is, some of the ion exchange material from the first and second exchange layers can swell into the porous structure inside the intermediate layer, ensuring that the deformation caused by water absorption and swelling of the proton exchange membrane is relatively small. Therefore, the pore size of the pore structure cannot be too small (e.g., less than 80 nm). Too small a pore size means there is insufficient space for the ion exchange material to swell within the interlayer, resulting in a relatively large deformation of the proton exchange membrane. Conversely, the pore size cannot be too large (e.g., greater than 450 nm). Too large a pore size means the interlayer is too porous, leading to poor overall mechanical properties and a relatively large deformation of the proton exchange membrane. In other words, the dimensional stability of the proton exchange membrane is affected by two factors: the mechanical properties of the interlayer (self-supporting properties) and the overall deformation of the proton exchange membrane before and after swelling. If the volume change of the proton exchange membrane before and after swelling is too large, the dimensional stability of the proton exchange membrane will be poor.

[0020] The intermediate layer possesses a pore structure with appropriate pore size. Through the synergistic effect of intermediate layer fibers of suitable diameter and spacing, this pore structure ensures that the intermediate layer has a suitable pore size. On one hand, this pore structure provides sufficient swelling space for the ion exchange materials on both sides of the intermediate layer, ensuring that the deformation of the proton exchange membrane is controlled within a small range. On the other hand, the presence of this pore structure does not cause significant loss to the mechanical properties of the intermediate layer; the intermediate layer still possesses high mechanical strength, further ensuring that the deformation of the proton exchange membrane is controlled within a small range. Under the combined effect of these two factors, the deformation of the proton exchange membrane will not approach the damage threshold (the maximum deformation that the proton exchange membrane can withstand before damage occurs). In other words, the proton exchange membrane has high dimensional stability and a longer service life.

[0021] It is generally believed that, compared to a fully filled proton exchange membrane, an incompletely filled proton exchange membrane has a relatively lower proton conductivity due to the relatively less ion exchange material contained in its intermediate layer. However, the inventors of this application have discovered that when the average diameter D of the intermediate layer fibers of the proton exchange membrane is 60-400 nm and the average distance d between two adjacent intermediate layer fibers is 80-450 nm, the proton exchange membrane actually has a better proton conductivity, which is quite unexpected.

[0022] This may be because a fully filled proton exchange membrane (PEM) contains a relatively large amount of ion exchange material, requiring a significant amount of moisture to be adequately wetted. Therefore, when using a PEM in a fuel cell, the fuel gas and oxidant gas at the cathode and anode need to maintain high humidity during actual operation to ensure proper wetting of the PEM. However, substantial humidification of the fuel gas can also lead to the accumulation of a certain amount of gaseous and / or liquid water at the electrode interface, gas diffusion layer pores, and bipolar plate channels. This gaseous water affects the diffusion coefficients of the fuel gas and oxidant gas at the cathode and anode, altering their flow and diffusion. Furthermore, excessive gaseous water dilutes the concentration of the reactant gases, reducing the electrochemical reaction rate and consequently decreasing the fuel cell's internal resistance. Meanwhile, liquid water clogs the pores of the gas diffusion layer and the bipolar plate channels, causing insufficient supply, uneven dispersion, and pressure unevenness of the reactant gas. This increases the mass transfer resistance of the reactant gas diffusion to the catalytic interface. Furthermore, the dissolution and diffusion of the reactant gas in liquid water leads to increased mass transfer losses, which also increases the internal resistance of the fuel cell. In other words, for a single proton exchange membrane, a high-filling ion exchange material does indeed mean a relatively high proton conductivity (theoretical value) for the proton exchange membrane itself. However, for the fuel cell as a whole, a high-filling proton exchange membrane may increase the internal resistance of the fuel cell, thus reducing the actual proton conductivity (actual value) of the proton exchange membrane during actual use.

[0023] For incompletely filled proton exchange membranes, firstly, the average diameter of the intermediate layer fibers is not too small (D not less than 60nm), which also indicates that the ion exchange material attached to the porous base membrane fibers of the intermediate layer is not too little, ensuring the most basic proton conduction capacity of the proton exchange membrane.

[0024] Secondly, the intermediate layer possesses a pore structure with a suitable pore size (a suitable average spacing d between two adjacent intermediate layer fibers, with an average spacing d of 80-450 nm, preferably 80-400 nm). This pore structure reduces the permeation resistance of water through the proton exchange membrane to a certain extent, and also has a certain water storage and retention function, improving the uniformity of water distribution and ensuring relatively good wetting throughout the proton exchange membrane. It also ensures that the water inside the proton exchange membrane does not easily evaporate. The pore structure with a suitable pore size within the intermediate layer ensures that, in actual operation of the fuel cell, only a low level of humidification of the gas at the cathode and anode is required to completely wet the proton exchange membrane. Because the humidification of the gas at both the cathode and anode is relatively low, the accumulation of gaseous and liquid water at the electrode interfaces, gas diffusion layer pores, and bipolar plate channels of the proton exchange membrane fuel cell is significantly reduced. This means that the internal resistance of the fuel cell not only does not increase but actually decreases. Consequently, the proton conductivity of the proton exchange membrane not only does not decrease but even increases during actual use. This contradicts the common belief that the more ion exchange material filled within the porous base membrane of the proton exchange membrane, the higher its proton conductivity.

[0025] Specifically, the pore size of the internal pore structure of the interlayer cannot be too small (average spacing d less than 80 nm). If the pore size is too small, it indicates that the internal structure of the interlayer is still relatively dense, and the water retention capacity of the internal pore structure is relatively low. The amount of gaseous and liquid water accumulated at the electrode interface, gas diffusion layer pores, and bipolar plate flow channels of the proton exchange membrane fuel cell is still relatively large, resulting in a relatively low proton conductivity in actual use. In other words, while the pore size of the internal pore structure of the interlayer is relatively small, the amount of ion exchange material filling the interlayer is relatively large. For the single proton exchange membrane itself, its internal resistance is indeed lower, but in terms of mass transfer efficiency... In actual use, the accumulation of gaseous and liquid water in the proton exchange membrane fuel cell can actually increase the overall internal resistance, leading to a decrease in the proton conductivity. While the pore size of the intermediate layer cannot be too large (average spacing d greater than 450 nm), the presence of pores also means the existence of several "open circuits" within the membrane. If the pore size is too large, it means too many "open circuits," resulting in a still relatively low proton conductivity. Understandably, the intermediate layer's pore structure's ability to store and retain water prevents the proton exchange membrane from becoming excessively dry when not in use. Excessive dryness would cause the membrane to shrink excessively, also leading to damage.

[0026] The synergistic effect of intermediate layer fibers with appropriate diameter and spacing ensures that the intermediate layer of the proton exchange membrane has a pore structure with appropriate pore size. This ensures that in actual operation, fuel gas and catalyst gas only need to be slightly humidified to completely wet the proton exchange membrane. Only a small amount of water vapor and liquid accumulates at the electrode interface, gas diffusion layer pores, and bipolar plate channels of the proton exchange membrane fuel cell, significantly improving the proton conductivity of the proton exchange membrane in actual use, and also significantly improving the output power of the fuel cell in actual use.

[0027] The phrase "the first exchange layer, the intermediate layer, and the second exchange layer are integrally connected by ion exchange materials" in this application means that the ion exchange materials in the first exchange layer, the intermediate layer, and the second exchange layer are "continuous". The first exchange layer, the intermediate layer, and the second exchange layer are integrally formed without the need for additional adhesives or the like to connect them to each other. Unless torn by external force, the first exchange layer, the intermediate layer, and the second exchange layer cannot be separated from each other.

[0028] In this application, the "average diameter D of the intermediate layer fibers" and the "average spacing d of the intermediate layer fibers" are measured as follows: On a cross-sectional electron microscope image of the membrane at 5000x magnification, the boundary between the intermediate layer and the first exchange layer is taken as the 0% position of the intermediate layer, and the boundary between the intermediate layer and the second exchange layer is taken as the 100% position of the intermediate layer. Four reference lines perpendicular to the membrane thickness direction are drawn at the 20%, 40%, 60%, and 80% positions of the intermediate layer. The length of the reference lines is 10 μm. The average diameter D is the arithmetic mean of the lengths of the overlapping areas of all intermediate layer fibers and the reference lines on each reference line; the average spacing d is the arithmetic mean of the lengths of the non-overlapping areas between all adjacent intermediate layer fibers on each reference line. For example, refer to the appendix to the specification. Figure 4 After characterizing the morphology of the membrane cross-section using scanning electron microscopy, an electron microscope image of the membrane cross-section at a magnification of 5000x was obtained. Four baseline lines (straight lines) perpendicular to the membrane thickness direction were drawn at positions of 20%, 40%, 60%, and 80% of the membrane's intermediate layer cross-section, and recorded as X. 20 X 40 X 60 X 80 The four baselines are 10 μm long, with X... 40 For example, measure the length of the region where the baseline coincides with the intermediate layer fiber, and record it as L1, L2, ... L 21 The arithmetic mean of the lengths of all overlapping regions is used to characterize the average diameter of the fibers in the membrane at the horizontal plane where the baseline is located. This average diameter ΔX 40 For: (L1+L2....+L 21 ) / 21, the average diameter D of the intermediate layer fibers is: (△X 20 +△X40 +△X 60 +△X 80 4. The average spacing d of the intermediate layer fibers was also measured in the manner described above. It is understood that, since positions representing 20%, 40%, 60%, and 80% of the intermediate layer cross-section of the proton exchange layer are used, the measurement of the average diameter D and average spacing d of the intermediate layer fibers will not be affected in the membrane electron microscopy images, regardless of which side of the intermediate layer is the first exchange layer. The average diameter of the fiber nodes, as discussed later, can also be measured in the manner described above.

[0029] In this application, "dense" refers to a membrane image taken at 50,000x magnification using a scanning electron microscope (SEM), where the pore area ratio of the first and second outer surfaces is no greater than 5%. This means either no pore structure is observable, or only a very small number of pores are observable, or the membrane is essentially impermeable to air, with a Gurley number greater than 10,000 seconds. It is understandable that observation of the first and second outer surfaces of the proton exchange membrane may sometimes reveal several disordered cracks. These disordered cracks may be caused by the electron beam bombarding the first and second outer surfaces during nanometer-resolution image analysis using the SEM. Therefore, the disordered cracks on the first and second outer surfaces should not be considered pore structures; the first and second outer surfaces of the membrane remain dense.

[0030] The term "ion exchange material" in this application includes, but is not limited to, the following compounds and combinations thereof: perfluorosulfonic acid polymers, perfluorocarboxylic acid polymers, perfluorophosphonic acid polymers, styrene-type ion exchange polymers, fluorostyrene-type ion exchange polymers, polyaryletherketone ion exchange polymers, polysulfone ion exchange polymers, bis(fluoroalkylsulfonyl)imides, (fluoroalkylsulfonyl)(fluorosulfonyl)imides, polyvinyl alcohol, polyethylene oxide, divinylbenzene, metal salts with or without polymers, and mixtures thereof. The ion exchange material is preferably a perfluorosulfonic acid resin.

[0031] In this application, "dry state" refers to the state of the proton exchange membrane after drying at constant temperature and humidity (30℃, 25%RH) for 2 hours. When measuring the thickness of the proton exchange membrane and the thickness of the interlayer, the proton exchange membrane is first dried at constant temperature and humidity (30℃, 25%RH) for 2 hours, and then the cross-section of the membrane is characterized using a scanning electron microscope to obtain the corresponding SEM image. The thickness of the proton exchange membrane and the thickness of the interlayer are then measured using appropriate computer software or manually. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0032] Optionally, the ratio of the average spacing d between two adjacent intermediate layer fibers to the average diameter D of the intermediate layer fibers is 0.5-2.

[0033] By adopting the above technical solution, the average spacing d of the intermediate layer fibers of the proton exchange membrane has a suitable ratio with the average diameter D of the intermediate layer fibers, which further ensures that the proton exchange membrane as a whole has high proton conductivity and high dimensional stability.

[0034] If the ratio of the two is too large (d / D > 2), it means that the average spacing d of the intermediate layer fibers is relatively large and / or the average diameter D of the intermediate layer fibers is relatively small. This indicates that the pore size of the intermediate layer's pore structure is relatively large or the number of pores is relatively excessive, while the diameter of the intermediate layer fibers is relatively small or the number of fibers is relatively small. A relatively large or excessive number of pores indicates relatively many breaks in the intermediate layer and relatively little ion exchange material, resulting in relatively low overall proton conductivity of the proton exchange membrane. A relatively small or insufficient number of intermediate layer fibers indicates relatively insufficient overall mechanical properties of the intermediate layer and relatively low overall dimensional stability of the proton exchange membrane. Furthermore, relatively small intermediate layer fibers also indicate, to some extent, relatively little ion exchange material attached to the porous base membrane fibers, and a relatively insufficient number of intermediate layer fibers also indicates, to some extent, insufficient internal supply of H+. + The relatively small number of protons conducting means that the proton conductivity of the proton exchange membrane is also relatively low.

[0035] If the ratio of the two is too small (d / D < 0.5), it means that the average spacing d of the intermediate layer fibers is relatively small and / or the average diameter D of the intermediate layer fibers is relatively large. This indicates that the pore size of the intermediate layer is relatively small or the number of pores is relatively small, while the diameter of the intermediate layer fibers is relatively large or the number of fibers is relatively large. Both of these indicate that the interior of the intermediate layer is relatively dense, and the intermediate layer is filled with a relatively large amount of ion exchange material. The proton exchange membrane as a whole contains a relatively large amount of ion exchange material, and the degree of swelling of the ion exchange material after absorbing water is relatively large. The overall dimensional stability of the proton exchange membrane is relatively insufficient. The relatively large amount of ion exchange material contained in the proton exchange membrane also indicates that a large amount of water is required to completely wet the proton exchange membrane during actual operation. In other words, during actual operation, the amount of gaseous water and liquid water accumulating at the electrode interface, gas diffusion layer pores, and bipolar plate flow channels of the proton exchange membrane fuel cell is still relatively large, and its proton conductivity is still relatively low.

[0036] In summary, the intermediate layer of the proton exchange membrane has intermediate layer fibers of appropriate diameter and an appropriate spacing between adjacent intermediate layer fibers (the intermediate layer has a pore structure of appropriate pore size). Furthermore, the average spacing d of the intermediate layer fibers of the proton exchange membrane has an appropriate ratio to the average diameter D of the intermediate layer fibers, which further ensures that the proton exchange membrane as a whole has high proton conductivity and high dimensional stability.

[0037] Optionally, the average density of the intermediate layer fibers is 10-40 fibers / 10μm.

[0038] By adopting the above technical solution, the intermediate layer as a whole has an appropriate density of intermediate layer fibers, and furthermore, the intermediate layer fibers have an appropriate average diameter D. Under the combined effect of the two, the intermediate layer as a whole has relatively good mechanical properties, which ensures the high dimensional stability of the proton exchange membrane.

[0039] Meanwhile, the presence of a suitable number of intermediate layer fibers on the baseline also indicates the presence of a suitable number of pore structures on the baseline. Combined with the fact that the pore structures have suitable pore sizes (adjacent intermediate layer fibers have suitable average spacing d), this suggests that the intermediate layer contains pore structures with suitable pore sizes and quantities. These pore structures provide sufficient swelling space for the ion exchange material. The intermediate layer has sufficient swelling space and good mechanical properties. The combined effect of these two factors significantly improves the overall dimensional stability of the proton exchange membrane.

[0040] Furthermore, the pore structure with appropriate density and pore size greatly reduces the permeation resistance when water permeates the proton exchange membrane, improves the uniformity of water distribution inside the intermediate layer, and allows the proton exchange membrane to be fully wetted with only a small amount of water. In actual operation, the amount of gaseous water and liquid water accumulating at the electrode interface, gas diffusion layer pores, and bipolar plate flow channels of the proton exchange membrane fuel cell is still relatively small, and the proton exchange membrane has high proton conductivity.

[0041] Understandably, the average density of the intermediate layer fibers is obtained as follows: On a cross-sectional electron microscope image of the membrane at 5000x magnification, the boundary between the intermediate layer and the first exchange layer is taken as the 0% position of the intermediate layer, and the boundary between the intermediate layer and the second exchange layer is taken as the 100% position of the intermediate layer. Four baselines perpendicular to the membrane thickness direction are drawn at the 20%, 40%, 60%, and 80% positions of the intermediate layer, and recorded as L. 20 L 40 L 60 L 80 The four baselines are 10 μm long, with L 40 For example, the number of areas where the baseline coincides with the intermediate layer fibers is recorded, which is the number of intermediate layer fibers on the baseline, and is recorded as L.40-中间层纤维 Record L as described above. 20-中间层纤维 L 60-中间层纤维 L 80-中间层纤维 The average density of the intermediate layer fibers is (L 20-中间层纤维 +L 40-中间层纤维 +L 60-中间层纤维 +L 80-中间层纤维 ) / 4. The average density of the primary fibers and the average density of the secondary fibers mentioned later can be measured using the above method.

[0042] Optionally, the intermediate layer fiber includes a plurality of main fibers, the diameter of the main fibers being not less than 1.5D, and the average density of the main fibers being 1-10 fibers / 10μm.

[0043] By adopting the above technical solution, the diameter of the main fiber is not less than 1.5D. On the one hand, the relatively large diameter of the main fiber further ensures that the intermediate layer as a whole has good mechanical properties, thereby ensuring the high dimensional stability of the proton exchange membrane as a whole. On the other hand, the relatively large diameter of the main fiber also indicates that a relatively large amount of ion exchange material is attached to the main fiber. An appropriate number of main fibers ensures that the ion exchange membrane as a whole has a relatively high proton conductivity.

[0044] Furthermore, the relatively large-diameter main fibers also need a suitable density. If the density of the main fibers is not too low (not less than 1 fiber / 10μm), the overall mechanical properties of the intermediate layer will be relatively low, the improvement in the overall dimensional stability of the proton exchange membrane will be insignificant, and the lack of main fibers with a large amount of attached ion exchange material will result in an insignificant improvement in the overall proton conductivity of the proton exchange membrane. Of course, the density of the main fibers cannot be too high (not more than 10 fibers / 10μm). Firstly, the main fibers are relatively thick, which means that the ion exchange material closer to the porous base membrane fibers is more difficult to wet. If the density of the main fibers is too high, it means that more water is needed to completely wet the ion exchange material of the main fibers. As mentioned above, too much water will result in a large amount of gaseous and liquid water accumulating at the electrode interface, gas diffusion layer pores, and bipolar plate flow channels of the proton exchange membrane fuel cell during actual operation, and its proton conductivity will still be low. Therefore, an excessive number of main fibers... Excessive ion exchange material on the main fibers may result in a limited increase in the proton conductivity of the proton exchange membrane and consequently, a limited increase in the output power of the proton exchange membrane fuel cell. Furthermore, a higher density of ion exchange material on the main fibers leads to greater swelling of the ion exchange material after the proton exchange membrane absorbs water and swells. If the density of the main fibers is too high, the swollen ion exchange material will occupy more space in the pore structure of the intermediate layer, causing the ion exchange material in the first and second exchange layers to swell only in the direction away from the intermediate layer, resulting in a limited improvement in the overall dimensional stability of the proton exchange membrane.

[0045] In summary, the intermediate layer has an appropriate density of intermediate layer fibers and an appropriate density of main fibers. Furthermore, the intermediate layer has a pore structure with an appropriate pore size. The combined effect of these three factors ensures that the proton exchange membrane has high proton conductivity and high dimensional stability.

[0046] Optionally, the intermediate layer fiber includes several secondary fibers, the diameter of which is no greater than 0.7D and the average density of which is 5-20 fibers / 10μm.

[0047] By adopting the above technical solution, the intermediate layer also includes a suitable number and diameter of secondary fibers, further ensuring the high dimensional stability and high proton conductivity of the proton exchange membrane as a whole. Compared with the main fibers, the secondary fibers have a significantly higher density. The relatively dense fine fibers make the overall three-dimensional network structure of the intermediate layer relatively dense, and its three-dimensional network structure has relatively high integrity. That is, there are relatively more pathways for proton conduction in the intermediate layer. Even if some pathways are "broken," it will not have a significant impact on the proton conduction rate of the proton exchange membrane. Therefore, the density of secondary fibers cannot be too small (not less than 5 fibers / 10μm). If the density of secondary fibers is too small, there will be relatively fewer pathways for proton conduction in the intermediate layer, and the improvement in the proton conductivity of the proton exchange membrane will not be significant.

[0048] Of course, the density of secondary fibers cannot be too high (no more than 20 fibers / 10μm). The diameter of secondary fibers is relatively small, and the mechanical properties of secondary fibers are relatively low. If the density of secondary fibers is too high, it also means that the probability of secondary fibers being damaged is high during the dimensional changes of the proton exchange membrane as it continuously absorbs water and swells, dehydrates and dries, and then absorbs water and swells again. Once a large number of secondary fibers are damaged, the number of branches in the intermediate layer used for proton conduction will decrease, the overall proton conductivity of the proton exchange membrane will be low, and the number of broken secondary fibers will have a certain impact on the mechanical properties of the intermediate layer, and the overall dimensional stability of the proton exchange membrane will also be low.

[0049] Optionally, in the dry state, the thickness h of the intermediate layer is 2-10 μm, and the ratio of the thickness h of the intermediate layer to the thickness H of the proton exchange membrane is 0.3-0.6.

[0050] By adopting the above technical solution, the intermediate layer has intermediate layer fibers with appropriate diameter and density, and the intermediate layer has a pore structure with appropriate pore size. Furthermore, the intermediate layer has an appropriate thickness. Under the combined effect of these three factors, the proton exchange membrane as a whole is further guaranteed to have high proton conductivity and high dimensional stability.

[0051] If the interlayer is relatively thin (less than 2 μm and / or h:H < 0.3), the relatively thin thickness means that the overall mechanical properties of the interlayer are relatively low, and the number of pore structures inside the interlayer is relatively limited. Under the combined influence of these two factors, the improvement in the dimensional stability of the proton exchange membrane is relatively limited. If the interlayer is relatively thick (greater than 10 μm and / or h:H > 0.6), the relatively thick interlayer certainly means that it has higher mechanical properties. However, the relatively thick interlayer also often means that the overall proton exchange membrane has a higher thickness, the overall internal resistance of the proton exchange membrane is relatively large, and the improvement in the proton conductivity of the proton exchange membrane is relatively limited.

[0052] Of course, some researchers are currently studying proton exchange membranes with thicker interlayers. For example, by using a thicker porous base membrane as the interlayer and employing higher-quality ion exchange materials (with lower Ew values), the proton exchange membrane can maintain relatively high dimensional stability without significantly increasing its thickness, thus ensuring high proton conductivity. However, these proton exchange membranes also have certain drawbacks. Using higher-quality ion exchange materials (with higher ion exchange group content) often means better water absorption and swelling properties, which has limited effect on improving the dimensional stability of the proton exchange membrane. Furthermore, higher-quality ion exchange materials also mean higher costs in actual production.

[0053] Optionally, the ratio of the thickness h of the intermediate layer to the sum of the thicknesses of the first exchange layer and the second exchange layer is 0.3-1.

[0054] By adopting the above technical solution, the thickness h of the intermediate layer has a suitable ratio with the sum of the thicknesses of the first exchange layer and the second exchange layer, which further ensures the high dimensional stability and high proton conductivity of the sub-exchange membrane as a whole.

[0055] If the ratio of the two is too large (e.g., greater than 1), it means that the thickness of the intermediate layer is relatively thick, while the sum of the thicknesses of the first and second exchange layers is relatively thin. This indicates that there are relatively too many pore structures inside the intermediate layer. Admittedly, this means that there is relatively ample space inside the intermediate layer for the first and second exchange layers on both sides of the intermediate layer to swell. However, the relatively excessive pore structure in the intermediate layer also means that there are relatively many proton conduction "breaks" inside the intermediate layer, and the number of proton exchange membranes may still be low.

[0056] If the ratio of the two is too small (e.g., less than 0.3), it means that the thickness of the intermediate layer is relatively thin, while the sum of the thicknesses of the first and second exchange layers is relatively too thick. On the one hand, the support performance of the intermediate layer for the first and second exchange layers may be relatively low. On the other hand, there are relatively few pore structures inside the intermediate layer for the swelling of the first and second exchange layers on both sides of the intermediate layer. Under the influence of these two factors, the dimensional stability of the proton exchange membrane may still be low.

[0057] Optionally, the intermediate layer has a plurality of fiber nodes, each fiber node being formed by stacking and fusing a plurality of intermediate layer fibers, and the average diameter of the fiber nodes is 500-800 nm.

[0058] Optionally, the average density of the fiber nodes is 1-5 per 10 μm. 2 .

[0059] By adopting the above technical solution, the intermediate layer has fiber nodes of appropriate diameter and density. The fiber nodes have a certain reinforcing effect on the overall mechanical properties of the intermediate layer, further ensuring the high dimensional stability and high proton conductivity of the proton exchange membrane.

[0060] The diameter of the fiber nodes should not be too small or too few (e.g., less than 500 nm and / or less than 1 per 10 μm). 2 This ensures that the fiber nodes provide sufficient reinforcement to the intermediate layer, further ensuring that the deformation of the proton exchange membrane during water absorption and swelling does not exceed the damage threshold, thus giving the proton exchange membrane high dimensional stability.

[0061] The diameter of the fiber nodes will not be too large or too numerous (e.g., greater than 800 nm and / or less than 1 per 10 μm). 2 While excessively coarse fiber nodes mean stronger reinforcement of the interlayer as a whole, they can also create significant resistance to the filling of ion exchange material in the interlayer. Furthermore, excessively coarse fiber nodes can cause some loss of space in the pore structure inside the interlayer. As a result, the amount of ion exchange material filling the interlayer may be relatively small, leading to a lower proton conductivity of the proton exchange membrane.

[0062] Understandably, when measuring the density of fiber nodes, one can first characterize the cross-section of the proton exchange membrane using a scanning electron microscope to obtain the corresponding SEM image, and then select a certain area, such as 10 μm. 2(5μm x 2μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the number of all fiber knots in this area and record it as A1. Then select different areas and repeat the above measurement operation, recording them as A2, A3, A4, and A5. The density of fiber knots is (A1+A2+A3+A4+A5) / 5. Those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0063] Optionally, the ratio of the thickness of the first exchange layer to the thickness of the second exchange layer is 0.8-1.5, and the equivalent weight Ew of the ion exchange material is not higher than 1600.

[0064] By adopting the above technical solution, with the proton exchange membrane and intermediate layer having suitable thicknesses, and the thickness of the intermediate layer and the proton exchange membrane having an appropriate ratio, and the first and second exchange layers having essentially the same thickness, it is evident that the first and second exchange layers of the proton exchange membrane have suitable thicknesses. This ensures that the dimensional deformation of the first and second exchange layers after water absorption and swelling will not be excessive. Simultaneously, the intermediate layer possesses a suitable number and volume of pores, which provide sufficient swelling space for the ion exchange materials of the first and second exchange layers, further guaranteeing the dimensional stability of the proton exchange membrane. Furthermore, the suitable thickness of the first and second exchange layers indicates that the overall proton exchange membrane has a suitable thickness, its internal resistance will not be excessively high, and the overall proton conductivity of the proton exchange membrane is high.

[0065] In this application, the ion exchange material has a suitable equivalent weight (Ew not higher than 1600), which further ensures the proton conduction capacity of the proton exchange membrane. The equivalent weight Ew of the ion exchange material is the number of grams of polymer per mole of ionic acid functional group. For example, if the ion exchange material is a perfluorosulfonic acid resin (nafion), then the ionic acid functional group is a sulfonic acid group. Ew not higher than 1600 means that the mass of perfluorosulfonic acid resin containing 1 mol of sulfonic acid groups does not exceed 1600g.

[0066] Secondly, this application provides a process for preparing a proton exchange membrane, which adopts the following technical solution:

[0067] S1. Preparation of ion exchange resin solution, the ion exchange resin solution includes the following raw materials: ion exchange material and solvent, the solid content of the ion exchange resin solution is 5-30%, and the temperature T1 of the ion exchange resin solution is 30-40℃;

[0068] S2. Coating: The ion exchange resin solution is coated onto one side of the carrier, and a porous base membrane is placed over the ion exchange resin solution, with the lower layer of the porous base membrane in contact with the ion exchange resin solution. Subsequently, the ion exchange resin solution is coated onto the porous base membrane. During the coating process, the ambient temperature T2 is 5-15℃ higher than the ion exchange resin solution temperature T1, causing the ion exchange resin solution to penetrate into the porous base membrane, forming a primary migration and obtaining a composite membrane. The composite membrane is then subjected to a cooling treatment. During the cooling treatment, the ambient temperature T3 is 10-20℃ lower than the ion exchange resin solution temperature T1, causing the ion exchange material to migrate a secondary migration to both sides of the membrane surface.

[0069] S3. Drying: Dry the composite membrane to obtain a proton exchange membrane.

[0070] By adopting the above technical solution, the first step in preparing the proton exchange membrane is the preparation of the ion exchange resin solution. This application controls the ion exchange resin solution to have a suitable solid content (solid content refers to the mass ratio of the ion exchange material in the ion exchange resin solution), and simultaneously controls the temperature T1 of the ion exchange resin solution to 30-40℃. The relatively high temperature (not lower than 30℃) and suitable solid content ensure that the ion exchange resin solution has suitable viscosity and fluidity, facilitating subsequent coating work. Of course, the temperature of the ion exchange resin solution T1 cannot be too high (not higher than 40℃). If the temperature of the ion exchange resin solution T1 is too high, since the preparation process of the ion exchange resin solution requires a relatively long time, and if the temperature of the ion exchange resin solution T1 is too high, and the ambient temperature T2 further increases in the subsequent coating step, it may cause solvent evaporation of the ion exchange resin solution (the solvent generally contains alcohol), which may affect the solid content of the ion exchange resin solution.

[0071] The second step of this application is the coating step. During the coating process, the ambient temperature T2 is 5-15°C higher than the temperature of the ion exchange resin solution. Affected by the ambient temperature T2, the temperature of the ion exchange resin solution is further increased. After the temperature rises, the viscosity of the ion exchange resin solution is further reduced and the fluidity is further improved. The ion exchange resin solution is more likely to penetrate into the porous base membrane. That is, the ion exchange material resin is more likely to migrate into the porous base membrane in one step. After one migration, the ion exchange resin solution is basically completely filled into the pore structure of the intermediate layer.

[0072] During the coating process, the ambient temperature T2 should not be too low (it needs to be at least 5°C higher than the ion exchange resin solution). If it is less than 5°C, the ion exchange resin solution will not be significantly heated, and its fluidity will not be fully guaranteed. The ion exchange resin may not be able to completely fill the pore structure inside the porous base membrane. Of course, the ambient temperature T2 should not be too high. If the ambient temperature T2 is too high (more than 15°C higher than the ion exchange resin solution), the solvent in the ion exchange resin solution may evaporate, which will increase the viscosity of the ion exchange resin solution. The fluidity of the ion exchange resin solution will not be fully guaranteed, which may result in the ion exchange resin not being able to completely fill the pore structure inside the porous base membrane.

[0073] After the ion exchange resin solution completes its first migration, the composite membrane is cooled. During the cooling process, the ambient temperature T3 is 10-20℃ lower than the ion exchange resin solution temperature T1. Since the ambient temperature T2 is 5-15℃ higher than the ion exchange resin solution temperature T1 during the coating process, the temperature difference between ambient temperature T2 and ambient temperature T3 is relatively large (15-35℃). Under the sudden temperature change in a short period of time, the ion exchange resin solution inside the composite membrane migrates to both sides of the composite membrane, which is the secondary migration of the ion exchange material. This results in the intermediate layer of the final proton exchange membrane having a pore structure with a suitable pore size.

[0074] This is likely because, under a sudden drop in temperature, the overall temperature of the composite membrane decreases to some extent. The temperature drop of the ion exchange resin solution on both sides of the composite membrane (especially on the surface) is significantly greater than that of the ion exchange resin solution inside the membrane. In other words, the temperature of the ion exchange resin solution inside the membrane is relatively higher, while the temperature of the ion exchange resin solution on both sides is relatively lower. Generally, the surface tension of a solution decreases with increasing temperature. This means that the surface tension of the ion exchange resin solution inside the composite membrane is relatively low, while the surface tension of the ion exchange resin solution on both sides is relatively high. The relatively higher surface tension of the ion exchange resin solution on both sides of the membrane exerts a certain pulling force on the relatively lower surface tension of the ion exchange resin solution inside the membrane, causing the ion exchange resin solution inside the membrane to migrate towards both sides. This secondary migration of the ion exchange resin solution inside the membrane results in the formation of a suitable number and size of pores within the final proton exchange membrane.

[0075] Understandably, during the cooling process, the temperature drop cannot be too small. The ambient temperature T3 needs to be at least 10°C lower than that of the ion exchange resin solution. If it is lower than 10°C, the temperature drop of the ion exchange resin solutions on both sides of the composite membrane will not be significant. The traction force of the ion exchange resin solutions on both sides of the composite membrane on the ion exchange resin solution inside the composite membrane will be too small, resulting in too few or too small pores in the middle layer of the final proton exchange membrane. Consequently, the high proton conductivity and high dimensional stability of the final proton exchange membrane cannot be fully guaranteed. Of course, the ambient temperature T3 cannot be too low. If it is below 20℃, the temperature difference between the ion exchange resin solutions on both sides of the composite membrane and the ion exchange resin solution inside the composite membrane will be too large. This will result in excessive traction between the ion exchange resin solutions on both sides of the composite membrane and the ion exchange resin solution inside the composite membrane, leading to an excessively large and numerous pore structure in the intermediate layer of the final proton exchange membrane. Furthermore, due to the low ambient temperature, the viscosity of the ion exchange resin solutions on both sides of the intermediate layer may be relatively high, making it difficult for the ion exchange resin solution inside the intermediate layer to migrate to the sides. Consequently, the high proton conductivity and high dimensional stability of the final proton exchange membrane cannot be fully guaranteed. However, during the secondary migration process of the composite membrane, the ambient temperature T3 drops sharply. In a low-temperature environment, the solvent of the ion exchange materials on both sides of the composite membrane will not evaporate significantly, resulting in the solid content of the ion exchange resin solutions on both sides of the composite membrane being essentially the same as that inside the composite membrane. In other words, the solid content will have little impact on the surface tension of the ion exchange resin solutions on both sides and inside the composite membrane.

[0076] In summary, this application controls the solid content and initial temperature T1 of the ion exchange resin solution to ensure that the ion exchange resin solution has suitable viscosity and fluidity, guaranteeing that the ion exchange material can relatively fully penetrate into the porous base membrane, thereby ensuring that the final proton exchange membrane has suitable proton conductivity. Furthermore, this application employs a coating process of heating followed by cooling. During the heating process, the ion exchange resin solution further ensures that the porous base membrane's pore structure is completely filled. During the cooling process, by controlling the surface tension of the ion exchange resin solutions on both sides of the composite membrane and the surface tension of the ion exchange resin solutions inside the composite membrane, the traction force of the high surface tension solution on the low surface tension solution causes the ion exchange material inside the composite membrane to migrate to both sides, thereby ensuring that the proton exchange membrane has a suitable number and volume of pores, further guaranteeing that the final proton exchange membrane has suitable proton conductivity and dimensional stability.

[0077] Optionally, in step S2, the temperature difference between ambient temperature T2 and ambient temperature T3 is 20-30℃.

[0078] By adopting the above technical solution, in step S2, there is a suitable temperature difference between the heating ambient temperature and the cooling ambient temperature, which further ensures that the intermediate layer of the finally formed proton exchange membrane has a suitable pore size and a suitable number of pores.

[0079] If the temperature difference between the two is too small (the temperature difference between ambient temperature T2 and ambient temperature T3 is less than 20℃), the traction force of the ion exchange resin solution on both sides of the composite membrane on the ion exchange resin solution inside the composite membrane will be relatively small. This will result in the pore structure inside the middle layer of the final proton exchange membrane being too small and too few, and the high proton conductivity and high dimensional stability of the final proton exchange membrane cannot be fully guaranteed.

[0080] If the temperature difference between the two is too large (the temperature difference between ambient temperature T2 and ambient temperature T3 is greater than 30℃), the ion exchange resin solution on both sides of the composite membrane will exert a relatively large traction force on the ion exchange resin solution inside the composite membrane. This will result in an excessively large and numerous pore structure inside the intermediate layer of the final proton exchange membrane, leading to too many "breaks" in proton conduction. Furthermore, the overall mechanical properties of the intermediate layer will be relatively insufficient, and the high proton conductivity and high dimensional stability of the final proton exchange membrane cannot be fully guaranteed.

[0081] Optionally, between steps S1 and S2, a pretreatment step is further included, wherein the porous base membrane is placed in ethanol gas for 5-20 seconds for pretreatment, and the temperature of the porous base membrane is 20-40°C lower than that of the ethanol gas.

[0082] By adopting the above technical solution, the porous base membrane is pretreated in ethanol gas before being coated with the ion exchange resin solution. Since the temperature of the porous base membrane is 20-40°C lower than that of the ethanol gas, some of the ethanol gas can condense inside the porous base membrane. After the ion exchange resin solution is coated on both sides of the porous base membrane, the ion exchange resin solution that has penetrated into the porous base membrane mixes with the ethanol inside the porous base membrane, reducing the solid content of the ion exchange resin solution inside the porous base membrane to a certain extent. In other words, the ion exchange resin solution inside the composite membrane has a low solid content and relatively low surface tension, while the ion exchange resin solution on both sides of the composite membrane has a high solid content and relatively high surface tension. Combined with the cooling step after S2 coating, this further widens the surface tension difference between the ion exchange resin solutions inside and on both sides of the composite membrane, making it easier for the ion exchange resin solution inside the composite membrane to migrate to both sides, ensuring that the middle layer of the final proton exchange membrane has a pore structure with suitable pore size and quantity.

[0083] To ensure that the intermediate layer of the final proton exchange membrane has a pore structure with suitable pore size and quantity, the ethanol content condensed inside the porous base membrane cannot be too low. Specifically, the pretreatment time cannot be too short (less than 5 seconds) and / or the temperature difference between the porous base membrane and the ethanol gas cannot be too small (less than 20°C). If the ethanol content is too low, the surface tension difference between the ion exchange resin solutions inside and on both sides of the composite membrane will be relatively small, potentially resulting in a relatively small and insufficient pore structure inside the intermediate layer of the final proton exchange membrane. This would compromise the high dimensional stability and high proton conductivity of the proton exchange membrane. Of course, the ethanol content inside the porous base membrane cannot be... Too much ethanol content can lead to excessive dilution of the ion exchange resin solution that has permeated into the porous membrane. This results in an excessively low solid content in the ion exchange resin solution inside the composite membrane, leading to a large difference in surface tension between the ion exchange resin solutions inside and on both sides of the composite membrane. Consequently, a large amount of ion exchange resin solution migrates inside the composite membrane, resulting in an excessively large and numerous pore structure in the intermediate layer of the final proton exchange membrane. Consequently, the high dimensional stability and high proton conductivity of the proton exchange membrane cannot be guaranteed.

[0084] Optionally, the porous base membrane is PTFE, the average pore size of the porous base membrane is 0.15-0.4 μm, the thickness of the porous base membrane is 2-9 μm, and the basis weight of the porous base membrane is 3-8 g / m³. 2 .

[0085] By adopting the above technical solution, polytetrafluoroethylene (PTFE) is a typical perfluorinated polymer. Its macromolecule contains only carbon and fluorine atoms. The CF bond energy is much higher than that of the CH and CC bonds. The F atoms form a tight protective layer outside the CC main chain backbone, which gives the polymer excellent chemical stability. Except for molten alkali metals, chlorine trifluoride and liquid fluorine, it can withstand almost all other chemical reagents. At the same time, it also has excellent thermal stability, anti-pollution, electrical insulation and anti-aging properties. It is non-toxic to the human body and is an ideal porous membrane material.

[0086] Meanwhile, the morphology of the porous base membrane directly affects the overall morphology of the intermediate layer. By controlling the selection of the porous base membrane, when the porous base membrane has a suitable thickness and a suitable basis weight, the final proton exchange membrane can be further guaranteed to have high proton conductivity and high dimensional stability. This is likely because the basis weight and density (density of PTFE) of the porous base membrane are known, and the per unit area (1m³) can be calculated. 2The theoretical volume of the porous membrane (if the porous membrane is a completely dense object without any pore structure, the size of the three-dimensional space occupied by the porous membrane). Meanwhile, since the actual thickness of the porous membrane is known, the volume per unit area (1m²) can be obtained by calculation. 2 The actual volume of the support layer is the difference between the actual volume and the theoretical volume, which represents the volume of the pore structure within the porous base membrane. The presence of a suitable pore structure within the porous base membrane indicates that it has appropriate pore sizes to accommodate the ion exchange material. Combined with the secondary migration of the ion exchange material in step S2, the presence of pores of suitable size and quantity within the intermediate layer results in relatively low water mass transfer resistance, ensuring that the final proton exchange membrane possesses high proton conductivity.

[0087] Meanwhile, the presence of pores of appropriate volume within the porous base membrane also implies that the porous base membrane has an appropriate amount and density of fibers. The porous base membrane possesses sufficient mechanical properties, which, combined with the secondary migration of the ion exchange material in step S2, results in a pore structure with appropriate pore size and quantity within the intermediate layer, further ensuring the high dimensional stability of the proton exchange membrane.

[0088] Optionally, in step S1, the solvent comprises deionized water and an alcohol solvent, wherein the mass ratio of deionized water to alcohol solvent is 0.2-1, and the alcohol solvent is at least one of ethanol, propanol, and isopropanol.

[0089] A specific solvent system further ensures that the ion exchange material has a suitable viscosity, thereby further ensuring the penetration of the ion exchange resin solution into the intermediate layer. Secondly, a specific solvent volume combined with specific pretreatment steps makes it easier to control the change in the solid content of the ion exchange resin solution, thereby further controlling the surface tension gradient of the ion exchange resin on both sides of the porous base membrane and the surface tension gradient of the ion exchange resin inside the porous base membrane, further controlling the migration of the ion exchange material, and thus further ensuring that the final proton exchange membrane has a suitable number and volume of pores.

[0090] This application provides the following beneficial effects: the proton exchange membrane and its preparation process provided in this application exhibit high proton conductivity and high dimensional stability under both normal humidity conditions and special conditions such as high humidity, high temperature and low humidity. Furthermore, the preparation method provided by this invention allows for the convenient, rapid, and effective preparation of the aforementioned proton exchange membrane. Attached Figure Description

[0091] Figure 1 This is a schematic diagram of the cross-section of the proton exchange membrane prepared in Example 1 using a scanning electron microscope (SEM), with a magnification of 5000×.

[0092] Figure 2 This is a schematic diagram of the cross-section of the proton exchange membrane prepared in Comparative Example 2 using a scanning electron microscope (SEM), with a magnification of 5000×.

[0093] Figure 3 This is a schematic diagram showing the measurement of the average diameter D of the intermediate layer fibers in this application;

[0094] Figure 4 for Figure 3 ZhongX 40 Enlarged diagram of the location;

[0095] Figure 5 The image shows the polarization curve of the proton exchange membrane prepared in Example 1 during actual use. Detailed Implementation

[0096] Example 1

[0097] This application discloses a proton exchange membrane, which is prepared using the following process steps:

[0098] S1. Preparation of ion exchange resin solution: The ion exchange resin solution includes the following raw materials: ion exchange material and solvent; the ion exchange material is specifically perfluorosulfonic acid resin, and the solvent is deionized water and alcohol solvent, with a mass ratio of deionized water to alcohol solvent of 0.6; the alcohol solvent is ethanol; the solid content of the ion exchange resin solution is 19.1 wt%, the Ew of the perfluorosulfonic acid resin is 1098, and the temperature T1 of the ion exchange resin solution is 35℃.

[0099] Pretreatment: A suitable porous base membrane was selected and pretreated in ethanol gas for 12 seconds. The temperature of the porous base membrane was 30°C lower than that of the ethanol gas. The porous base membrane was a PTFE membrane with an average pore size of 0.22 μm, a thickness of 9.37 μm, and a basis weight of 6.9 g / m³. 2 ;

[0100] S2, Coating: The ion exchange resin solution is coated onto one side of the carrier, and a porous base membrane is placed over the ion exchange resin solution, with the lower layer of the porous base membrane in contact with the ion exchange resin solution. Then, the ion exchange resin solution is coated onto the top of the porous base membrane. During the coating process, the ambient temperature T2 is 45℃ (the temperature difference between T2 and T1 is 10℃). The ion exchange resin solution permeates into the porous base membrane, forming a primary migration, resulting in a composite membrane. Subsequently, the composite membrane is cooled. During the cooling process, the ambient temperature T3 is 20℃ (the temperature difference between T3 and T1 is 15℃, and the temperature difference between T3 and T2 is 25℃). The ion exchange material inside the porous base membrane migrates a secondary time to both sides of the porous base membrane.

[0101] S3. Drying: Place the composite membrane in an environment of 150℃ to dry. After drying, the composite membrane is obtained as a proton exchange membrane.

[0102] Examples 2-7

[0103] The difference between Examples 2-7 and Example 1 is that the process parameters for each step are different, as detailed in Table 1.

[0104] Comparative Example 1

[0105] The difference between Comparative Example 1 and Example 1 is that the process parameters for each step are different, as detailed in Table 1.

[0106] Table 1. Process parameters for each embodiment and Comparative Example 1

[0107]

[0108]

[0109] It is particularly important to note that:

[0110] Example 2 does not include an ethanol gas pretreatment step; the ethanol pretreatment time in Example 4 is relatively long, the temperature difference between the porous membrane and the ethanol gas is relatively large, and the temperature difference between T2 and T3 is relatively small; in Comparative Example 1, the temperatures of T1, T2, and T3 are the same.

[0111] Comparative Example 3

[0112] The proton exchange membrane of Comparative Example 3 was prepared using the following process steps:

[0113] S1. Preparation of ion exchange resin solution; The ion exchange resin solution includes the following raw materials: ion exchange material and solvent; The ion exchange material is specifically perfluorosulfonic acid resin, and the solvent is deionized water and an alcohol solvent, with a mass ratio of deionized water to alcohol solvent of 0.6; The alcohol solvent is ethanol; The solid content in the ion exchange resin solution is 19.7 wt%; The Ew of the ion exchange material is 795; The temperature T1 of the ion exchange resin solution is 35℃;

[0114] S2. Coating: The ion exchange resin solution is coated onto one side of the support, and the porous base membrane is then coated over the ion exchange resin solution. Subsequently, the ion exchange resin solution is coated over the porous base membrane to obtain the composite membrane. The porous base membrane is a PTFE membrane with an average pore size of 0.24 μm, a thickness of 8.86 μm, and a basis weight of 6.4 g / m³. 2 ;

[0115] S3. High-temperature drying: The raw membrane is dried at 150°C to obtain a proton exchange membrane.

[0116] S4. Repeat the above steps of coating in S2 and drying at high temperature in S3 until the proton exchange membrane is basically transparent. Then it can be considered that the support layer of the proton exchange membrane has been completely filled.

[0117] The detection methods are as follows:

[0118] Proton conductivity test: The proton exchange membranes prepared in each example and comparative example were used to fabricate proton exchange membrane fuel cells. The current density of the fuel cell was measured to be 1.5 A / cm² when the fuel cell temperature was 80°C. 2 At that time, the voltage of the fuel cell is used to characterize the proton conductivity of the proton exchange membrane. Under the same current density, if the proton conductivity (transfer H) of proton exchange membrane A is higher... + If the proton velocity (of type A proton exchange membrane) is lower than that of type B proton exchange membrane, then the characteristic result is that the voltage of the fuel cell made with type A proton exchange membrane is lower than that of the fuel cell made with type B proton exchange membrane. During the test, the relative humidity of the fuel gas and oxidant gas at the cathode and anode was 40% RH, and the pressure of the fuel gas and oxidant gas at the cathode and anode was 150 kPa.

[0119] Dimensional stability test: The dimensional stability of the proton exchange membrane was characterized by the swelling value D (thickness change of the proton exchange membrane in the dry and wetted states). Proton exchange membranes prepared in each embodiment and comparative example were used. First, the thickness of the proton exchange membrane in the dry state was measured and recorded as H. 干 Then, the thickness of the proton exchange membranes prepared in each embodiment and comparative example when fully wetted was measured and recorded as H. 润 Swelling value D = (H) 润 -H 干 ) / H 干 .

[0120] The thickness of the proton exchange membrane in the dry state specifically refers to the thickness of the proton exchange membrane after drying at a constant temperature and humidity (30℃, 25%RH) for 2 hours; the thickness of the proton exchange membrane in the fully wetted state specifically refers to the thickness of the proton exchange membrane after soaking in a 25℃ water bath for 10 minutes (at this point, the proton exchange membrane can be considered to have completely absorbed water and swelled).

[0121] Ew: The proton exchange membranes prepared in each example and comparative example were used as samples for ion exchange equivalent (EW) testing. The detection method was in accordance with GB / T 20042.3—2022.

[0122] The morphological and performance parameters of the proton exchange membranes prepared in each embodiment and comparative example are detailed in Tables 2 and 3:

[0123] Table 2 Morphological parameters of the intermediate layer of the proton exchange membrane

[0124]

[0125]

[0126] Table 3. Morphological and performance parameters of the proton exchange membrane as a whole.

[0127]

[0128] in conclusion:

[0129] By comparing Example 1 and Comparative Example 1, it is easy to see that the Ew of the ion exchange material in Comparative Example 1 is smaller than that in Example 1, and the overall thickness of the proton exchange membranes in Comparative Example 1 and Example 1 is basically similar. The expected result is that the proton conductivity of Comparative Example 1 is higher than that of Example 1. However, in actual use, the voltage of the fuel cell in Comparative Example 1 is much lower than that in Example 1, that is, the proton conductivity of Comparative Example 1 is much lower than that in Example 1. This may be because the average spacing d of the fibers in the intermediate layer of the proton exchange membrane in Comparative Example 1 is smaller, and the content of the ion exchange material (perfluorosulfonic acid resin) filled inside the intermediate layer is larger. In actual use of the fuel cell, the fuel gas and oxidant gas at the cathode and anode need to have high humidity to ensure that the proton exchange membrane can be well wetted. However, significant humidification of the fuel gas leads to the accumulation of a certain amount of gaseous and / or liquid water at the electrode interface, gas diffusion layer pores, and bipolar plate channels. This gaseous water affects the diffusion coefficients of the fuel gas and oxidant gas at the cathode and anode, altering their flow and diffusion. Furthermore, excessive gaseous water dilutes the reactant gas concentration, reducing the electrochemical reaction rate and consequently lowering the fuel cell's electrochemical reaction rate—that is, it actually "reduces" the proton conductivity of the proton exchange membrane. Simultaneously, liquid water clogs the gas diffusion layer pores and bipolar plate channels, causing insufficient reactant gas supply, uneven dispersion, and pressure unevenness, increasing the mass transfer resistance of the reactant gas diffusing to the catalytic interface. Moreover, the dissolution and diffusion of reactant gases in liquid water leads to increased mass transfer losses, similarly "reducing" the proton conductivity of the proton exchange membrane.

[0130] The average spacing d of the intermediate layer fibers in the proton exchange membrane of Example 1 is relatively suitable, indicating that the proton exchange membrane of Example 1 has a more ideal pore structure. This pore structure has a certain water storage and retention function, allowing the proton exchange membrane to be completely wetted in a low humidity environment, greatly improving the problem of gaseous and liquid water accumulation. As a result, the proton exchange membrane actually has a higher proton conductivity in practical use. At the same time, it is precisely because of the existence of this pore structure that the pore structure provides a certain space for the ion exchange materials on both sides of the intermediate layer to swell inward. This makes the swelling degree D of Example 1 much smaller than that of Comparative Example 1, that is, the dimensional stability of the proton exchange membrane of Example 1 is much higher than that of Comparative Example 1.

[0131] In Comparative Example 2, the average spacing d between the fibers is relatively large. The expected result is that the intermediate layer of the proton exchange membrane in Comparative Example 2 has more and larger pore structures for the ion exchange material to swell, resulting in relatively high dimensional stability. However, the swelling value of Comparative Example 2 is much higher than that of the other embodiments. This may be because the number of fibers in the intermediate layer of the Comparative Example 2 is relatively small, while the average spacing d between the fibers is relatively large, leading to relatively weak self-supporting performance of the intermediate layer of the proton exchange membrane in Comparative Example 2, and consequently, relatively poor dimensional stability.

[0132] By comparing Example 4 and Comparative Example 3, it is easy to see that the Ew of the ion exchange material in Comparative Example 3 is greater than that in Example 4, the thickness of the proton exchange membrane in Comparative Example 3 is less than that in Example 4, and the thickness of the intermediate layer of the proton exchange membrane in Comparative Example 3 is greater than that in Example 4. It is expected that the dimensional stability of the proton exchange membrane in Comparative Example 3 should be less than that of the proton exchange membrane in Example 4. This may be because the proton exchange membrane in Comparative Example 3 is completely filled, and its intermediate layer does not contain a porous structure, while the intermediate layer of the incompletely filled proton exchange membrane in Example 4 has a certain amount of porous structure. On the one hand, the relatively small amount of ion exchange material in Example 4 results in relatively less deformation caused by the overall water absorption and swelling of the proton exchange membrane in Example 4. On the other hand, the porous structure inside the intermediate layer of Example 4 provides a certain swelling space for the ion exchange material. That is, a portion of the ion exchange material in the first and second exchange layers of Example 4 can swell into the porous structure inside the intermediate layer. With the combined effect of these two aspects, the degree of swelling generated when the proton exchange membrane of Example 4 absorbs water and swells is much lower than that of Comparative Example 3. That is, the dimensional stability of Example 4 is much higher than that of Comparative Example 3.

[0133] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A proton exchange membrane, comprising a main body, characterized in that, The main body includes a first exchange layer, an intermediate layer, and a second exchange layer. The first exchange layer has a dense first outer surface, and the second exchange layer has a dense second outer surface. The first exchange layer and the second exchange layer include ion exchange materials. The intermediate layer includes a porous base membrane and ion exchange materials filled inside the porous base membrane. The first exchange layer, the intermediate layer, and the second exchange layer are integrally connected through the ion exchange materials. In a dry state, the thickness H of the proton exchange membrane is no greater than 25 μm; The three-dimensional network structure of the intermediate layer is formed by interconnecting and surrounding each other through intermediate layer fibers, which include porous base membrane fibers and ion exchange materials attached to the porous base membrane fibers. The average diameter D of the intermediate layer fiber is 60-400 nm; The average spacing d between two adjacent intermediate layer fibers is 80-450 nm; The average diameter D of the intermediate layer fibers and the average spacing d of the intermediate layer fibers are measured in the following manner: On a cross-sectional electron microscope image of the membrane at 5000x magnification, the boundary between the intermediate layer and the first exchange layer is taken as the 0% position of the intermediate layer, and the boundary between the intermediate layer and the second exchange layer is taken as the 100% position of the intermediate layer. Four reference lines perpendicular to the membrane thickness direction are drawn at the 20%, 40%, 60%, and 80% positions of the intermediate layer. The length of the reference lines is 10 μm. The average diameter D is the arithmetic mean of the lengths of the overlapping areas of all intermediate layer fibers and the reference lines on each reference line. The average spacing d is the arithmetic mean of the lengths of the non-overlapping areas between all adjacent intermediate layer fibers on each reference line.

2. The proton exchange membrane according to claim 1, characterized in that: The ratio of the average spacing d between two adjacent intermediate layer fibers to the average diameter D of the intermediate layer fibers is 0.5-2.

3. A proton exchange membrane according to claim 1, characterized in that: The average density of the intermediate layer fibers is 10-40 fibers / 10μm.

4. A proton exchange membrane according to claim 1, characterized in that: The intermediate layer fiber includes several main fibers, the diameter of which is not less than 1.5D, and the average density of which is 1-10 fibers / 10μm.

5. A proton exchange membrane according to claim 4, characterized in that: The intermediate layer fiber includes several secondary fibers, the diameter of which is no greater than 0.7D, and the average density of which is 5-20 fibers / 10μm.

6. A proton exchange membrane according to claim 1, characterized in that: In the dry state, the thickness h of the intermediate layer is 2-10 μm, and the ratio of the thickness h of the intermediate layer to the thickness H of the proton exchange membrane is 0.3-0.

6.

7. A proton exchange membrane according to claim 1, characterized in that: The ratio of the thickness h of the intermediate layer to the sum of the thicknesses of the first and second exchange layers is 0.3-1.

8. A proton exchange membrane according to claim 1, characterized in that: The intermediate layer has several fiber nodes, each of which is formed by stacking and fusing several intermediate layer fibers, and the average diameter of the fiber nodes is 500-800 nm.

9. A proton exchange membrane according to claim 8, characterized in that: Along the length of each of the aforementioned baselines, the average density of the fiber nodes is 1-5 per 10 μm. 2 .

10. A proton exchange membrane according to claim 1, characterized in that: In a dry state, the ratio of the thickness of the first exchange layer to the thickness of the second exchange layer is 0.8-1.5, and the equivalent weight Ew of the ion exchange material is not higher than 1600.

11. A process for preparing a proton exchange membrane as described in any one of claims 1-10, characterized in that, The process includes the following steps: S1. Preparation of ion exchange resin solution, the ion exchange resin solution includes the following raw materials: ion exchange material and solvent, the solid content of the ion exchange resin solution is 5-30%, and the temperature T1 of the ion exchange resin solution is 30-40℃. S2, Coating: The ion exchange resin solution is coated onto one side of the carrier, and the porous base membrane is placed on top of the ion exchange resin solution, with the lower layer of the porous base membrane in contact with the ion exchange resin solution. Then, the ion exchange resin solution is coated onto the top of the porous base membrane. During the coating process, the ambient temperature T2 is higher than the ion exchange resin solution temperature T15-15℃, and the ion exchange resin solution permeates into the porous base membrane, forming a primary migration to obtain a composite membrane. The composite membrane is then subjected to a cooling treatment. During the cooling treatment, the ambient temperature T3 is lower than the ion exchange resin solution temperature T110-20℃, and the ion exchange material inside the porous base membrane migrates to the two sides of the porous base membrane a second time. S3. Drying: Dry the composite membrane to obtain a proton exchange membrane.

12. The preparation process of a proton exchange membrane according to claim 11, characterized in that: In step S2, the temperature difference between ambient temperature T2 and ambient temperature T3 is 20-30℃.

13. The preparation process of a proton exchange membrane according to claim 11, characterized in that: Between steps S1 and S2, a pretreatment step is also included, in which the porous base membrane is placed in ethanol gas for 5-20 seconds for pretreatment, and the temperature of the porous base membrane is 20-40°C lower than that of the ethanol gas.

14. The preparation process of a proton exchange membrane according to claim 11, characterized in that: The porous base membrane is made of PTFE, with an average pore size of 0.15-0.4 μm, a thickness of 3-15 μm, and a basis weight of 3-10 g / m³. 2 .

15. The preparation process of a proton exchange membrane according to claim 11, characterized in that: In step S1, the solvent comprises deionized water and an alcohol solvent, wherein the mass ratio of deionized water to alcohol solvent is 0.2-1; the alcohol solvent is at least one of ethanol, propanol, and isopropanol.

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