A proton exchange membrane and a method for preparing the same

Abstract

The present application relates to a kind of proton exchange membrane and its preparation method, including first exchange layer, intermediate layer and second exchange layer, intermediate layer includes support layer, ion exchange material filled in support layer and water hole, equivalent weight Ew of ion exchange material is not higher than 1600, the thickness H of proton exchange membrane in dry state 干 Not higher than 17 μm, the compactness I of proton exchange membrane is 0.15-0.65, the mass m of support layer per unit area in dry state P 2-10 g;The thickness h of support layer in dry state p 2-8 μm.The existence of water hole reduces water permeation resistance, reduces the difficulty of proton membrane forming proton transport channel, reduces the possibility of water flooding under high humidity condition, the possibility of proton transport channel circuit breaking under high temperature and low humidity condition, ensures high proton conductivity;In addition, the existence of water hole provides ion exchange material swelling deformation space, thereby improving the dimensional stability of proton membrane.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more specifically to a proton exchange membrane and its preparation method. Background Technology

[0002] 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 (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 resins 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). The lower the thickness of the proton exchange membrane, the shorter the proton transport path, i.e., the lower the internal resistance of the proton exchange membrane. However, a thinner proton exchange membrane also means relatively poor mechanical strength and durability, and mechanical damage may occur during long-term operation.

[0005] In order to ensure that proton exchange membranes with low thickness still have high durability, a series of reinforced composite membranes have been studied. At present, proton exchange membranes have gradually shifted from pure perfluorosulfonic acid resin material to composite materials with expanded polytetrafluoroethylene (e-PTFE) membrane as the reinforcing material.

[0006] For example, Chinese invention patent document CN1134288C (application 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] For example, Chinese invention patent application CN101273487A (applied by W.L. Gore and Tongren Co., Ltd.) discloses a solid polymer electrolyte membrane comprising a composite membrane mainly composed of the following components: (a) at least one expandable PTFE membrane having a porous microstructure of polymer fibrils, and (b) at least one ion exchange material filling all the porous microstructures of the expandable PTFE membrane, such that the internal volume of the expandable PTFE membrane is substantially closed.

[0008] Both of the aforementioned patent documents describe composite membranes for proton exchange membranes. The PTFE membrane acts as a reinforcing element, ensuring that the thin-film proton exchange membrane also possesses high mechanical strength, thereby reducing the probability of mechanical damage. Furthermore, a thin-film proton exchange membrane often implies lower internal resistance; therefore, fuel cells employing thin-film proton exchange membranes typically exhibit better electrical performance.

[0009] However, thin-film proton exchange membranes also have certain limitations. For example, the high proton conductivity and high dimensional stability of the aforementioned proton exchange membranes cannot be simultaneously achieved. This is because PTFE material itself lacks proton conductivity. Therefore, after introducing a proton exchange membrane into a PTFE membrane, the PTFE membrane must be filled with perfluorosulfonic acid resin (an ion exchange material) to ensure the proton conductivity of the proton exchange membrane. It is generally believed that increasing the content of perfluorosulfonic acid resin is beneficial to increasing proton conductivity; that is, the more perfluorosulfonic acid resin filled into the PTFE membrane (the higher the content of sulfonic acid groups), the higher the proton conductivity of the proton exchange membrane. Currently, the proton exchange membrane manufacturing process generally adopts methods similar to those in the aforementioned patent documents, ensuring that the ion exchange material completely fills the PTFE layer and using perfluorosulfonic acid resin with stronger proton conductivity to ensure that the proton exchange membrane has high mechanical strength and high proton conductivity.

[0010] However, while completely filling the PTFE layer with perfluorosulfonic acid resin (an ion exchange material) ensures high proton conductivity of the proton exchange membrane, it also leads to certain deficiencies in the dimensional stability of the membrane. This is because, during proton transport, the protons are hydrated protons (H3O2). + The proton exchange membrane (PEM) moves in a specific form, meaning that it inevitably absorbs a certain amount of water (wetting) during operation. 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 proton exchange membrane undergoes relatively large deformation during water absorption and swelling. The repeated deformation during the water absorption, swelling, dehydration, and drying process makes the PEM more susceptible to damage.

[0011] To address the aforementioned issue of poor dimensional stability in proton exchange membranes, some researchers have opted for the following approach: appropriately increasing the thickness of the PTFE membrane and using a higher-quality perfluorosulfonic acid resin (with a relatively higher sulfonic acid group content). However, a higher-quality perfluorosulfonic acid resin often also implies better water absorption and swelling properties in the proton exchange membrane, limiting the effectiveness of this approach in improving the relatively weak dimensional stability of the proton exchange membrane.

[0012] 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

[0013] To address the shortcomings of existing technologies, the present invention aims to provide a proton exchange membrane and its preparation method, which combines high proton conductivity and high dimensional stability with a long service life.

[0014] To achieve the above objectives, the present invention provides the following technical solution:

[0015] In a first aspect, this application provides a proton exchange membrane, which adopts the following technical solution:

[0016] A proton exchange membrane 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. Both the first and second exchange layers are made of ion exchange material. The intermediate layer includes a support layer, ion exchange material partially filled within the support layer, and water-retaining pores located inside the support layer. The thickness H of the proton exchange membrane in its dry state is... 干 Not higher than 17μm;

[0017] The density coefficient I of the proton exchange membrane is 0.15-0.65, and the density coefficient I is calculated by the following formula: I=m n / (m n +m P ), where m n When dry, fill in a unit area (1m²) 2 The mass of the ion exchange material within the support layer of a proton exchange membrane, expressed in g; m P Under dry conditions, per unit area (1m²) 2 The mass of the support layer of a proton exchange membrane, expressed in g; m n The following formula is used to calculate: m n =M0-(m P +ρ n V n), where M0 is the density of a unit area (m²) under dry conditions. 2 The mass of the proton exchange membrane is expressed in g; ρ n The density of the ion exchange material in its dry state, expressed in g / m³. 3 V n The volume of the first and second exchange layers in a proton exchange membrane under dry conditions is expressed in m³. 3 ;

[0018] In a dry state, the mass m of the support layer per unit area of ​​the proton exchange membrane P The thickness of the support layer in its dry state is 2-10g; p The size ranges from 2 to 9 μm, and the unit area mentioned above is 1 m². 2 .

[0019] 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 a proton exchange membrane fuel cell (PEMFC), on the one hand, the proton exchange membrane needs to act as a selectively permeable membrane, allowing only protons (H+) to pass through. + On the one hand, the proton exchange membrane provides a channel for proton transfer (ensuring good proton conductivity). On the other hand, it also needs to act as a diaphragm, separating the fuel at the anode from the oxidant at the cathode (ensuring low gas permeability). Therefore, the first and second exchange layers of the proton exchange membrane in this application are both made of ion exchange materials, and both surfaces of the membrane (first outer surface and second outer surface) are dense. In this application, a support layer is introduced between the first and second exchange layers to ensure that the thin-film proton exchange membrane (thickness not exceeding 17 μm) has high mechanical strength and reduces the probability of mechanical damage during use. Since the support layer cannot conduct protons, it must be filled with ion exchange material (forming a proton conduction pathway in the membrane thickness direction through continuously distributed ion exchange material). 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 support layer, 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).

[0020] However, the inventors of this application unexpectedly discovered during the preparation of the proton exchange membrane that when the ion exchange material in the support layer did not completely fill the pore structure within the support layer (density coefficient I is 0.15-0.65), several pore structures (water-retaining pores) existed within the support layer, and in the dry state of the proton exchange membrane, the density per unit area (1m²) was significantly reduced. 2 The mass m of the support layer of the proton exchange membrane. P It weighs 2-10g and has a thickness of h.p Unexpectedly, at a size of 2-9 μm, proton exchange membranes exhibit better proton conductivity and higher dimensional stability.

[0021] This may be because, during the proton exchange membrane's transport of protons, the protons are in the form of hydrated protons (H3O). + The proton conductivity of a proton exchange membrane (PEM) is closely related to its water content. Therefore, in actual operation, the fuel gas and oxidant gas at both the cathode and anode of a proton exchange membrane fuel cell need to be humidified to ensure sufficient wetting of the PEM, thereby ensuring high proton conductivity and good output power of the fuel cell.

[0022] However, if the proton exchange membrane (PEM) in a fuel cell is a fully filled PEM (the pore structure of the PEM support layer is completely filled with ion exchange material), on the one hand, the relatively large amount of ion exchange material in the PEM requires a significant amount of water for proper wetting; on the other hand, because the PEM is completely dense, the water mass transfer resistance during water permeation is relatively high, thus requiring more water mass transfer driving force. Therefore, in actual operation, the fuel gas and oxidant gas at the cathode and anode of a PEM fuel cell need to have high humidity to ensure good wetting of the PEM. However, significant humidification of the fuel gas can also lead to water accumulation on the surface of the PEM, which increases the proton mass transfer resistance, causing flooding of the fuel cell. Ultimately, this results in an increase in the internal resistance of the fuel cell and a decrease in output power.

[0023] If the proton exchange membrane in the fuel cell uses the partially filled proton exchange membrane provided in this application, the support layer of the proton exchange membrane in this application has a suitable content of ion exchange material (density coefficient I is 0.15-0.65) and contains several water-retaining pores. First, compared with a fully filled proton exchange membrane, the support layer of the proton exchange membrane provided in this application contains relatively less ion exchange material, indicating that the proton exchange membrane only needs relatively little water to be fully wetted. Furthermore, since there are several water-retaining pores inside the support layer, the presence of these pores can reduce the permeation resistance when water permeates the proton exchange membrane to a certain extent, and the water-retaining pores have a certain water-retaining function, the water in the pores can further ensure good wetting of the proton exchange membrane. Under the combined effect of a suitable filling amount and suitable water-retaining pores, it is ensured that in actual operation of the fuel cell, the gas at the cathode and anode only needs a low degree of humidification to completely wet the proton exchange membrane. Because the gas humidification at both the anode and cathode is relatively low, fuel cells are less prone to flooding, further ensuring their output power. Therefore, to ensure an appropriate number and volume of water-retaining pores within the support layer, the filling amount of ion exchange material in the support layer cannot be too high; that is, the density coefficient of the support layer cannot be too high (I not exceeding 0.65). Of course, to ensure the proton exchange membrane's basic proton conductivity, the density coefficient of the ion exchange material in the support layer cannot be too low (I not less than 0.15).

[0024] It should be noted that the specific compaction coefficient I is for a support layer with a specific morphology. The support layer provided in this application has a compaction coefficient I per unit (1m). 2 Within a given area, the support layer should have a suitable mass of 2-10g and a suitable thickness of 2-9μm, with a suitable mass m P and a suitable thickness h p This indicates that the support layer possesses a suitable volumetric pore structure. A suitable volumetric pore structure within the support layer, combined with an appropriate amount of ion exchange material, is necessary to ensure that the proton exchange membrane has appropriately sized water-holding pores and maintains its basic proton conductivity. It is understandable that, due to the mass m of the support layer… P It is known that the area per unit area (1m²) can be obtained through calculation. 2 In a proton exchange membrane, the theoretical volume of the support layer (if the support layer is a completely dense object without any porous structure, the size of the three-dimensional space occupied by the support layer). Meanwhile, due to the actual thickness h of the support layer... p It is known that the area per unit area (1m²) can be obtained by calculation. 2 The actual volume of the support layer is calculated, and the difference between the actual volume and the theoretical volume is the volume of the pore structure within the support layer. Therefore, a suitable mass m... P and a suitable thickness hp This indicates that the support layer has a suitable volumetric porosity structure.

[0025] If each unit area (1m 2 The mass m of the support layer P Too small and thickness h p Too high (m) P <2g and h p >8μm), indicating that the support layer is too porous overall, with an excessive number and volume of pores. Even with a certain amount of ion exchange material, the support layer may still contain a large number of large water-holding pores. While these pores can reduce the water permeation resistance of the proton exchange membrane and ensure sufficient water storage, their presence also often indicates several "breaks" in the membrane. An excessive number and large size of these pores means too many "breaks" in the membrane, resulting in low proton conductivity. If the per unit area (1m²) is... 2 The mass m of the support layer P Too large and thickness h p Too low (m) P >10g and h p <2μm), indicating that the support layer is too dense overall, and there is not enough space within the support layer for the ion exchange material to fill, so the proton conductivity of the proton exchange membrane cannot be guaranteed. Even if the support layer is filled with a sufficient amount of ion exchange material, the proton exchange membrane may already be close to a completely filled state, meaning that there are not enough water-holding pores of sufficient volume inside the proton exchange membrane support layer, and the water permeation resistance of the proton exchange membrane is still high, and its proton conductivity is still low.

[0026] Furthermore, in certain special scenarios, such as high-temperature and low-humidity environments, the incompletely filled proton exchange membrane of this application also exhibits higher proton conductivity compared to a fully filled proton exchange membrane. This may be because, in high-temperature and low-humidity environments, it is difficult for the proton exchange membrane to be fully wetted. However, since the support layer of the proton exchange membrane provided in this application contains a certain number of water-retaining pores, these pores endow the proton exchange membrane with a certain water-retaining and water-preserving function, reducing water permeation resistance and improving the uniformity of water distribution. This ensures that the proton exchange membrane is relatively well wetted throughout, while also ensuring that the water inside the proton exchange membrane does not easily evaporate. This guarantees that the proton exchange membrane of this application can maintain a high proton conductivity even under high-temperature and low-humidity conditions, thereby ensuring the battery output power. For a fully filled proton exchange membrane, on the one hand, the support layer contains a large amount of ion exchange material, which means the proton exchange membrane requires a lot of water to be fully wetted. However, due to the relatively dry air environment, the proton exchange membrane, which has a high water requirement, cannot obtain enough water, making it difficult to be fully wetted. On the other hand, because the support layer of the proton exchange membrane lacks a porous structure with water retention and storage functions, in a relatively dry and high-temperature environment, the water permeation resistance is high and the water evaporates more easily, making it difficult to fully wet the proton exchange membrane. This results in a low actual proton conductivity of the proton exchange membrane, which in turn leads to a low battery output power.

[0027] If the density coefficient I is too large (greater than 0.65), it means that there is too much ion exchange material and too few pores inside the support layer, resulting in a relatively low overall water retention capacity of the proton exchange membrane, making it difficult for the proton exchange membrane to be fully wetted in high-temperature and low-humidity environments. If the density coefficient I is too small (less than 0.15), it means that there is too little ion exchange material inside the support layer, which fails to guarantee the most basic proton conduction capacity of the proton exchange membrane. In this application, the most basic proton conduction capacity of the proton exchange membrane is guaranteed by controlling the content of ion exchange material in the support layer (I > 0.15). At the same time, the thickness of the proton exchange membrane in this application does not exceed 17 μm. The thin-film proton exchange membrane has a low internal resistance. With the combined effect of the appropriate thickness and filling amount of the proton exchange membrane, the proton conduction capacity of the proton exchange membrane itself is further guaranteed, thereby further guaranteeing the output power of the fuel cell.

[0028] Furthermore, the inventors of this application unexpectedly discovered that the lifespan of the incompletely filled proton exchange membrane provided in this application is significantly longer than that of the fully filled proton exchange membrane. This may be because, firstly, per unit area (1m²) 2The proton exchange membrane possesses a support layer with suitable mass, thickness, and density, which endows the proton exchange membrane with appropriate mechanical properties. Secondly, during operation, the proton exchange membrane inevitably absorbs a certain amount of water (wetting), and swelling of the ion exchange material is an inevitable phenomenon. The incompletely filled proton exchange membrane provided in this application has water-retaining pores within its support layer. This porous structure provides a certain swelling space for the ion exchange material; that is, some ion exchange material can swell into the support layer, ensuring that the deformation generated during water absorption and swelling of the proton exchange membrane is relatively small. Therefore, the thickness of the proton exchange membrane in this application does not exceed 17 μm, and the thickness of the support layer is h. p The thickness is 2-9 μm, and the fill factor of the support layer in this application is no higher than 0.65. This ensures that the support layer has a suitable water retention effect while also guaranteeing sufficient deformation space within the support layer. Through the synergistic effect of these three factors, the deformation of the proton exchange membrane is further controlled within a small range, preventing it from approaching the damage threshold. This results in high dimensional stability of the proton exchange membrane, thus ensuring a longer service life. The damage threshold is the maximum deformation that the proton exchange membrane can withstand before damage occurs.

[0029] The compactness coefficient I in this application is calculated using the following formula: I=m n / (m n +m P ), where m n Under dry conditions, per unit area (1m²) 2 The mass of ion exchange material filling the porous structure of the support layer of a proton exchange membrane, expressed in g; m P Under dry conditions, per unit area (1m²) 2 The mass of the support layer of the proton exchange membrane is expressed in grams (g); in this application, m P 2-10g, m P This is achieved by selecting a proton exchange membrane of a certain area, for example, 2625 mm². 2 (25mm x 75mm) or 3750mm 2 (50mm x 75mm), the specific area size depends on the actual situation. The proton exchange membrane is placed in a hydrothermal reactor and immersed in a methanol-water solution (methanol to water ratio 4:1) at 180℃ for 24 hours. After this immersion, the methanol-water solution is considered to have completely dissolved the ion exchange material of the proton exchange membrane (at this point, only the support layer remains). The support layer is then removed, dried, and its mass is measured. Through conversion, the area per unit area (1m²) can be obtained. 2 The mass of the support layer in the proton exchange membrane. (m) n The following formula is used to calculate: mn =M0-(m P +ρ n V n ), where M0 is the dry condition, per unit area (1m²) 2 The mass of the proton exchange membrane after drying at constant temperature and humidity (30℃, 25%RH) for 2 hours is expressed in g; ρ n The density of the ion exchange material in its dry state, expressed in g / m³. 3 V n The volume of the first and second exchange layers in a proton exchange membrane under dry conditions is expressed in m³. 3 The first and second exchange layers are “dense”. “Dense” specifically means that the pore area ratio inside the first and second exchange layers is no more than 5%, that is, there are two situations: the pore structure cannot be observed or a very small number of pore structures can be observed, or the membrane is basically unable to permeate air and its Gurley number is greater than 10,000 seconds.

[0030] In this invention, "dense" refers to a membrane where, when photographed under a scanning electron microscope at 50,000x magnification, 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 understood that when observing the first and second outer surfaces of the proton exchange membrane, some disordered cracks may sometimes be found. These disordered cracks may be caused by the electron beam bombarding the first and second outer surfaces during nanometer-resolution image analysis using the scanning electron microscope. Therefore, the disordered cracks on the first and second outer surfaces should not be considered as pore structures; the first and second outer surfaces of the membrane remain dense.

[0031] 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.

[0032] The materials of the support layer include two types of substances: fluorinated materials or non-fluorinated materials. Fluorinated materials may include, but are not limited to, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or polychlorotrifluoroethylene (PCTFE); non-fluorinated materials may include, but are not limited to, polyimide (PI), polybenzimidazole (PBI), or polyethersulfone (PES), with polytetrafluoroethylene (PTFE) being the preferred material.

[0033] When measuring the thickness of the proton exchange membrane and the support layer, the proton exchange membrane is first dried at a constant temperature and humidity (30℃, 25%RH) for 2 hours, and then the cross-section of the membrane is characterized by a scanning electron microscope to obtain the corresponding SEM image. The thickness of the proton exchange membrane and the thickness of the support layer are then measured by appropriate computer software or manually. Of course, those skilled in the art can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0034] Optionally, the swelling value D of the proton exchange membrane is 0.2-1.5, and the swelling value D is calculated by the following formula: D=(H 润 -H 干 ) / H 干 , where H 润 The thickness of a proton exchange membrane in a saturated wetted state after absorbing water and swelling is expressed in μm.

[0035] By adopting the above technical solution, the swelling value D of the proton exchange membrane reflects the thickness change of the proton exchange membrane in the dry and wet states, and to a certain extent, also reflects the overall volume change of the proton exchange membrane. In this application, the proton exchange membrane has a suitable swelling value D (0.2-1.5), which further illustrates that the proton exchange membrane of this application has a small deformation during swelling and dehydration. With a small deformation, the proton exchange membrane is less prone to mechanical damage (or the probability of mechanical damage is very small), thereby ensuring a significantly improved service life of the proton exchange membrane of this application. In addition, the suitable swelling value also further illustrates that the support layer used in this application has a suitable thickness and density, making the deformation of the proton membrane itself relatively small. At the same time, the introduction of water storage pores further reduces the deformation of the proton exchange membrane. Of course, in order to ensure the proton conduction capacity of the proton exchange membrane, it is still necessary to ensure that the support layer has an appropriate content of ion exchange material, and to ensure that the number and volume of water storage pores in the support layer are not excessive (the number of open circuits is not excessive). Therefore, the proton exchange membrane needs to ensure a basic degree of swelling. The proton exchange membrane has a suitable degree of swelling, thereby ensuring that the proton exchange membrane has high dimensional stability and high proton conductivity. It is understood that in this application, H_wetting refers to the thickness of the proton exchange membrane after being soaked in a water bath at 25°C for 10 minutes (at this point, it can be considered that the proton exchange membrane has completely absorbed water and swelled, that is, the proton exchange membrane is in a saturated wetted state).

[0036] If the swelling value is too large (greater than 1.5), it indicates that the proton exchange membrane (PEM) deforms relatively significantly before and after wetting. During the continuous swelling and dehydration process, the local stress of the PEM increases, leading to a higher probability of mechanical damage and a reduced lifespan. Furthermore, excessive deformation can also cause electrode deformation in the PEM fuel cell, resulting in decreased battery performance. If the swelling value is too small (less than 0.2), it indicates that the space reserved for the first and second exchange layers to swell into the support layer is too large, or that the ion exchange material's Ew is too large. This suggests that the amount of ion exchange material filled in the support layer may be relatively insufficient, resulting in a relatively low proton conductivity of the PEM. Consequently, the output power of the PEM fuel cell cannot be guaranteed.

[0037] In summary, a suitable density coefficient I ensures that the swelling value D of the proton exchange membrane is not too low. Furthermore, the combined effect of a suitable density coefficient I and a suitable mass and thickness of the support layer per unit area ensures that the swelling value D of the proton exchange membrane is not too high. This ensures that the proton exchange membrane has high proton conductivity and high dimensional stability (lifespan).

[0038] Optionally, the thickness h of the support layer in the dry state p The thickness H of the proton exchange membrane in the dry state 干 The ratio is 0.3-0.6.

[0039] By adopting the above technical solution, the thickness h of the support layer in the dry state is [value missing]. p Thickness H of the proton exchange membrane 干 The ratio between them is appropriate, the thickness of the proton exchange membrane does not exceed 17 μm, and the support layer has an appropriate thickness (h). p The thickness is 2-8 μm, indicating that the ratio between the support layer and the ion exchange layer (first exchange layer and second exchange layer) is appropriate for the proton exchange membrane. This further shows that after the proton exchange membrane absorbs water and swells, the deformation of the proton exchange membrane will not be too high compared with the dry membrane state, which further ensures the dimensional stability of the proton exchange membrane.

[0040] If the ratio of the two is too large (h) p :H 干A value greater than 0.6 indicates that the thickness of the support layer is relatively too high, while the overall thickness of the proton exchange membrane (i.e., the overall thickness of the first and second exchange layers is too small). This means that the content of ion exchange material in the proton exchange membrane is relatively low, especially in the support layer. While this implies higher dimensional stability, the low content of ion exchange material also reduces the proton conductivity of the proton exchange membrane, leading to a decrease in the output power of the fuel cell. Furthermore, some researchers are currently studying proton exchange membranes with thicker support layers. For example, while preparing proton exchange membranes with even thicker support layers, they are using ion exchange materials with lower Ew values. Although the amount of ion exchange material in the proton exchange membrane is relatively low, the low Ew value of the ion exchange material still ensures a relatively high proton conductivity. However, the above-mentioned proton exchange membranes also have certain shortcomings. Using higher-quality ion exchange materials (relatively higher content of ion exchange groups) often means better water absorption and swelling properties, which has limited effect on improving the dimensional stability of the proton exchange membrane. At the same time, higher quality ion exchange materials also mean higher costs in the actual production process.

[0041] If the ratio of the two is too small (h) p :H 干 A value <0.3 indicates that the thickness of the support layer is relatively too small, while the overall thickness of the proton exchange membrane is too large (i.e., the overall thickness of the first and second exchange layers is too large). A small support layer thickness means relatively limited space within it for the ion exchange material to swell, while a large overall thickness of the first and second exchange layers means relatively large swelling amplitudes. Large swelling amplitudes of the ion exchange material, coupled with limited space within the support layer for swelling, mean a relatively high degree of deformation of the proton exchange membrane and poor dimensional stability.

[0042] Optionally, the water content Q of the proton exchange membrane under saturated wettability is 0.1-0.45, preferably 0.15-0.45. The water content Q is calculated by the following formula: Q=(M1-M0) / M0, where M1 is the mass of the proton exchange membrane per unit area under saturated wettability, and its unit is g.

[0043] M1 represents the saturated wetted state, per unit area (1m²) 2 The mass of the proton exchange membrane; M0 is the mass per unit area (m²) under dry conditions. 2 The mass of the proton exchange membrane is M1 - M0, and the difference between them (M1 - M0) is the mass of the membrane per unit area (m²) under saturated wetted conditions. 2The water content (water content) of a proton exchange membrane has a significant impact on its conductivity. Higher water content results in higher proton conductivity and a decrease in membrane resistance, meaning the proton conductivity of the proton exchange membrane increases.

[0044] Of course, the water content of the proton exchange membrane (PEM) should not be too high (e.g., above 0.45%). If the water content is too high, it indicates either an excessive amount of ion exchange material used for water absorption or too much water in the pores (too many pores, too large a volume). If the excessive ion exchange material content causes the PEM to swell after absorbing water, the overall deformation will be too high, making it prone to damage during continuous swelling and dehydration. Furthermore, a high water content in the PEM also means a high water content inside the fuel cell, which can easily lead to flooding and reduced output power. If the excessive water in the pores prevents them from conducting protons, there will be more "open circuits" in the PEM, resulting in lower proton conductivity.

[0045] At the same time, the water content of the proton exchange membrane should not be too low (e.g., below 0.1). If the water content in the proton exchange membrane is too low, it means that the Ew of the ion exchange material in the proton exchange membrane is too high and / or the content of the ion exchange material in the proton exchange membrane is too low. In either case, the overall proton conductivity of the proton exchange membrane will be too low, which will lead to a reduction in the output power of the proton exchange membrane.

[0046] In summary, the appropriate water content of the proton exchange membrane indicates that it possesses suitable ion exchange materials, thus ensuring high proton conductivity in practical applications. Furthermore, the presence of a suitable number of water-retaining pores within the support layer further guarantees the water content of the proton exchange membrane, and these pores provide the ion exchange materials with sufficient swelling space, enabling the proton exchange membrane to maintain high dimensional stability.

[0047] Optionally, the thickness of the first exchange layer and the second exchange layer are substantially the same, and the equivalent weight Ew of the ion exchange material is not higher than 1600.

[0048] By adopting the above technical solution, the thicknesses of the first exchange layer and the second exchange layer are basically the same. Specifically, the difference in thickness between the first exchange layer and the second exchange layer is not higher than 1.5 μm, preferably not higher than 1 μm, and more preferably not higher than 0.8 μm.

[0049] With the proton exchange membrane and support layer having appropriate thicknesses, and the thickness ratio between the proton exchange membrane and support layer being appropriate, the thicknesses of the first and second exchange layers are basically the same. This indicates that the first and second exchange layers of the proton exchange membrane have appropriate thicknesses, and the degree of dimensional deformation after the first and second exchange layers absorb water and swell will not be too high. At the same time, the support layer has an appropriate number of water-retaining pores. These water-retaining pores reserve a certain swelling space for the ion exchange materials of the first and second exchange layers, further ensuring the dimensional stability of the proton exchange membrane.

[0050] In this application, the high proton conductivity of the proton exchange membrane is further ensured by controlling the equivalent weight Ew of the ion exchange material to be no higher than 1600g. In this application, the equivalent weight Ew of the ion exchange material is the number of grams of polymer per mole of ionic acid functional groups. 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.

[0051] Optionally, the intermediate layer includes intermediate layer fibers, which are interconnected to form a three-dimensional network structure of the intermediate layer, and the SEM average diameter of the intermediate layer fibers is 30-200 nm.

[0052] By adopting the above technical solution, the intermediate layer is composed of intermediate layer fibers with a suitable average diameter (thickness). The diameter of the intermediate layer fibers consists of two parts: the support layer fibers and the ion exchange material attached to the support layer fibers.

[0053] If the diameter of the intermediate layer fibers is too fine (e.g., less than 30 nm), it indicates that the support layer fibers are too fine and / or the content of ion exchange material attached to the support layer fibers is too low. If the support layer fibers are too fine, the overall mechanical properties of the intermediate layer are relatively low, which leads to lower dimensional stability of the proton exchange membrane. If the support layer fibers have too little ion exchange material attached, the overall proton conductivity of the proton exchange membrane is low.

[0054] If the diameter of the intermediate layer fiber is too large (e.g., greater than 200 nm), it indicates that the support layer fiber is too large and / or there is too much ion exchange material attached to the support layer fiber. If the intermediate layer fiber itself is too large, it means that the number of intermediate layer fibers is relatively small. Even if each intermediate layer fiber is attached with ion exchange material, the number of "pathways" for proton conduction inside the intermediate layer is relatively small, and the overall proton conductivity of the proton exchange membrane is low. If there is too much ion exchange material attached to the intermediate layer fiber, it means that the deformation of the proton exchange membrane when it absorbs water and swells is relatively large, and the dimensional stability of the proton exchange membrane is not high.

[0055] In summary, per unit area (1m²)2 The intermediate layer of the proton exchange membrane has suitable mass and thickness, with intermediate layer fibers of suitable coarseness and a filling amount with a suitable density coefficient, which further ensures that the proton exchange membrane as a whole has high dimensional stability and high proton conductivity.

[0056] Understandably, when measuring the diameter of the intermediate layer fibers, the cross-section of the proton exchange membrane can first be characterized using a scanning electron microscope (SEM) to obtain the corresponding SEM image, and a certain area, such as 100 μm, can be selected. 2 (10μm x 10μm) or 25μm 2 (5μm by 5μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the diameter of all intermediate layer fibers in this area, and then calculate their average value to obtain the average diameter of the intermediate layer fibers in this cross section. Those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0057] Optionally, the SEM average diameter of the intermediate layer fibers is related to the thickness h of the support layer in its dry state. p The ratio is 5-50 nm / μm, preferably 7-35 nm / μm.

[0058] By adopting the above technical solution, the SEM average diameter of the intermediate layer fiber and the thickness h of the support layer in the dry state are compared. p The ratio between the two should be appropriate. If the ratio is too small, it means that the support layer fibers are relatively thin and there is relatively little ion exchange material attached to the support layer fibers, resulting in relatively weak ion conduction capacity. At the same time, the support layer is relatively thick, which means that the "path" for proton conduction in the proton exchange membrane is relatively long and the internal resistance of the proton exchange membrane is high. Under the combined effect of the two, the proton conductivity of the proton exchange membrane is low.

[0059] If the ratio of the two is too large, it indicates that the intermediate layer fibers are relatively thick and the support layer is relatively thin. If the support layer fibers are thick, given that the mass and thickness of the intermediate layer per unit area (and the mass and volume of the solid part are fixed), this means that the number of intermediate layer fibers is relatively small, resulting in fewer "pathways" for proton conduction within the intermediate layer and a lower overall proton conductivity of the proton exchange membrane. If there is a relatively large amount of ion exchange material attached to the support layer fibers and the support layer is thin, it means that the deformation of the proton exchange membrane during water absorption and swelling is relatively large, resulting in low dimensional stability of the proton exchange membrane.

[0060] In summary, per unit area (1m²) 2The proton exchange membrane has an intermediate layer with suitable mass and thickness, contains intermediate layer fibers of suitable coarseness, and has a filling amount with a suitable density coefficient. Furthermore, the SEM average diameter of the intermediate layer fibers is similar to the thickness h of the support layer in the dry state. p The appropriate ratio between these features, combined with the aforementioned characteristics, further ensures that the proton exchange membrane as a whole possesses high dimensional stability and high proton conductivity.

[0061] Optionally, the intermediate layer has several nodes, each node being formed by stacking and fusing several intermediate layer fibers, and the SEM average diameter of the nodes is 100-600 nm.

[0062] By adopting the above technical solution, the intermediate layer contains several nodes, which reinforce the overall mechanical properties of the intermediate layer. The diameter of the nodes is not too small (e.g., less than 100 nm), thus ensuring the reinforcing effect of the nodes on the intermediate layer and further ensuring that the deformation of the proton exchange membrane during water absorption and swelling does not exceed the damage threshold, thereby giving the proton exchange membrane high dimensional stability and ensuring a better service life. At the same time, the diameter of the nodes is not too large (e.g., greater than 500 nm). Although larger nodes mean a stronger reinforcing effect on the intermediate layer, they will create relatively large resistance to the ion exchange material when filling the intermediate layer, and will also cause some loss of pore space inside the intermediate layer. Under the combined effect of these two factors, the amount of ion exchange material inside the intermediate layer may be relatively small, resulting in a lower proton conductivity of the proton exchange membrane.

[0063] In summary, per unit area (1m²) 2 The intermediate layer of the proton exchange membrane (PEM) possesses a certain mass and thickness, with appropriately sized intermediate layer fibers and nodes, ensuring sufficient self-supporting performance and preventing excessive overall deformation. It also ensures sufficient space for the ion exchange material to fill the intermediate layer, and even after the ion exchange material fills the intermediate layer, it still contains a suitable number and volume of water-retaining pores. The introduction of these pores further reduces the deformation of the PEM, keeping it within a small range and preventing it from exceeding the damage threshold. This results in high dimensional stability and a longer service life for the PEM. The damage threshold is the maximum deformation the PEM can withstand before damage occurs. Furthermore, the introduction of water-retaining pores increases the proton conductivity of the PEM.

[0064] Optionally, the ratio of the SEM average diameter of the intermediate layer fiber to the SEM average diameter of the node is 0.2-0.4 nm / nm.

[0065] By adopting the above technical solution, a suitable ratio is achieved between the diameters of the intermediate layer fibers and the nodes. If the ratio is too small, it means that the intermediate layer fibers are relatively too thick and the nodes are relatively too thin, resulting in insufficient reinforcement of the intermediate layer fibers (intermediate layer) by the nodes. If the ratio is too large, it means that the intermediate layer fibers are relatively too thin and the nodes are relatively too thick, leading to insufficient mechanical properties of the intermediate layer even with its reinforcement effect. The intermediate layer possesses appropriately sized intermediate layer fibers and nodes, with a suitable ratio between the fibers and nodes, further ensuring appropriate mechanical strength. Combined with the intermediate layer being filled with a suitable amount of ion exchange material (with a certain number and volume of water-retaining pores), this further ensures that the proton exchange membrane has high dimensional stability and high proton conductivity.

[0066] Optionally, the porosity of the intermediate layer cross-section is 8%-30%.

[0067] The intermediate layer has a suitable pore area ratio, further confirming the appropriate filling amount of ion exchange material inside the intermediate layer. The water-retaining pores with a suitable pore area ratio endow the proton exchange membrane with certain water storage and retention functions, reducing water permeation resistance and improving the uniformity of water distribution. This ensures relatively good wetting throughout the proton exchange membrane, guaranteeing complete wetting even with low water content (the fuel cell will not experience flooding under normal humidity and high humidity conditions; and the proton membrane can be fully wetted even in high temperature and low humidity environments). In other words, the intermediate layer has water-retaining pores with a suitable pore area ratio, enabling the proton exchange membrane to maintain high proton conductivity under various operating conditions (normal and extreme conditions).

[0068] Due to the per unit area (1m 2 The proton exchange membrane possesses an intermediate layer with suitable mass, thickness, and density, which endows the proton exchange membrane with appropriate mechanical properties. At the same time, the cross-section of the intermediate layer has a suitable pore area. This pore structure provides a certain swelling space for the ion exchange material. Under the combined effect of these two factors, some ion exchange material can swell into the intermediate layer, ensuring that the deformation generated when the proton exchange membrane absorbs water and swells is relatively small, that is, the proton exchange membrane has high dimensional stability.

[0069] Secondly, this application provides a process for preparing a proton exchange membrane, which adopts the following technical solution:

[0070] S1. Preparation of ion exchange resin solution; the ion exchange resin solution comprises the following raw materials: ion exchange material and solvent; the solid content of the ion exchange resin solution is 5-30%, preferably 8-28%.

[0071] S2, Coating; The ion exchange resin solution is coated onto one side of the carrier, and the support layer is placed over the ion exchange resin solution, with the lower layer of the support layer in contact with the ion exchange resin solution. Then, the ion exchange resin solution is coated over the support layer to obtain a composite membrane; the ion exchange resin solution permeates into the interior of the support layer, forming a primary migration.

[0072] S3. Pretreatment: Dry the composite membrane at a temperature 15-25°C higher than the temperature of the ion exchange resin solution. The pretreatment time is 5-25 minutes. After pretreatment, a raw membrane is obtained. During the pretreatment process, the ion exchange material migrates to both sides of the membrane surface for a second time.

[0073] S4. High-temperature drying: The raw membrane is dried at 120-160℃ to obtain a proton exchange membrane.

[0074] When preparing a proton exchange membrane, the first step is to prepare the ion exchange resin solution. This application controls the ion exchange resin solution to have a suitable solid content (the solid content refers to the mass ratio of the ion exchange material in the ion exchange resin solution) so that the ion exchange resin solution has a suitable viscosity and fluidity, which facilitates the subsequent coating and drying steps.

[0075] The second step of this application is a coating step. After coating, there is an ion exchange resin solution of a certain thickness on both sides of the support layer. Further, the ion exchange resin solution with suitable viscosity and fluidity penetrates into the interior of the support layer and fills the pore structure inside the support layer. That is, the ion exchange resin solution migrates into the pore structure inside the support layer in one step.

[0076] The third step of this application is a pretreatment step. During the drying process of the composite membrane in an environment of 25-45℃, the solvent of the ion exchange resin solution (especially the solvent on both sides of the composite membrane) will evaporate to a certain extent. The solid content is higher closer to the two sides of the composite membrane. That is, the solid content (concentration) gradient of the ion exchange resin solution on both sides of the support layer and inside the support layer becomes larger. It is generally believed that the solute in the solution will diffuse from high concentration to low concentration, that is, the ion exchange material will diffuse from both sides of the support layer to inside the support layer. However, the inventors of this application have found that in actual production, the ion exchange material inside the support layer will migrate to both sides of the support layer instead, so that the proton exchange membrane in the final form has a certain number and volume of pore structures (water storage pores), which is quite unexpected.

[0077] This is likely because after the solvent portion of the ion exchange resin solution on both sides of the support layer evaporates, the solid content of the ion exchange resin solution on both sides of the support layer increases, leading to a greater surface tension. Compared to the ion exchange resin solution on both sides of the support layer, the surface tension of the ion exchange resin solution inside the support layer is relatively small. The ion exchange resin solution on both sides of the support layer exerts a certain pulling force on the ion exchange solution inside the support layer, causing the ion exchange material inside the support layer to migrate to both sides. This pulling force has a greater impact on the ion exchange material than the concentration gradient, ultimately leading to the migration of the ion exchange material inside the support layer to the surfaces on both sides. In other words, during the pretreatment process, the ion exchange material in the ion exchange resin solution migrates a second time to the surfaces on both sides of the support layer, resulting in a certain number and volume of pores inside the final proton exchange membrane.

[0078] Furthermore, for ion exchange materials that are fluorinated organic materials, during the pretreatment process, the fluorinated organic matter migrates to both sides of the support layer when heated. After the ion material inside the support layer migrates, it ensures that the final proton exchange membrane has an appropriate number and space of water-retaining pores.

[0079] To ensure adequate migration of the ion exchange material within the support layer, the pretreatment temperature and time must be appropriate. If the pretreatment temperature is too low or the time too short (below 30°C, below 5 minutes), the solvent in the ion exchange resin solution may not evaporate sufficiently, resulting in insufficient driving force and time for the ion exchange material to migrate. This leads to an insufficient number and size of water-retaining pores within the final proton exchange membrane, resulting in low proton conductivity and dimensional stability. Conversely, if the pretreatment temperature is too high or the time too long (above 45°C, above 25 minutes), excessive migration of the ion exchange material may occur, resulting in an excessive number and size of water-retaining pores within the final proton exchange membrane, excessive "open circuits," and low proton conductivity.

[0080] After a pretreatment process at a suitable temperature and time, the ion exchange material inside the support layer has migrated to a suitable degree. The next step is to place the green membrane in a high-temperature environment of 120-160℃ to dry it. Admittedly, higher temperatures will lead to a higher migration rate of the ion exchange material. However, in a high-temperature environment of 120-160℃, the ion exchange material will dry and solidify in a relatively short time. At this time, the ion material inside the support layer will not migrate excessively.

[0081] In summary, this application controls the solid content of the ion exchange resin solution to ensure it has suitable viscosity and fluidity, guaranteeing that the ion exchange material can sufficiently penetrate into the support layer, thereby ensuring that the final proton exchange membrane possesses appropriate proton conductivity. Furthermore, this application employs a low-temperature pretreatment step followed by a high-temperature drying step to allow an appropriate amount of ion exchange material to migrate to both sides of the support layer, ensuring that the proton exchange membrane has a suitable number and volume of pores (water-retaining pores), further guaranteeing that the final proton exchange membrane possesses suitable proton conductivity and dimensional stability.

[0082] Optionally, step S2 specifically involves coating an ion exchange resin solution onto one side of the carrier, covering the ion exchange resin solution with a stretched support layer, and after the lower layer of the support layer contacts the ion exchange resin solution for 2-10 seconds, coating the support layer with the ion exchange resin solution to obtain a composite membrane; the stretching range of the support layer is 10-30%.

[0083] By adopting the above technical solution, the support layer is stretched by 10-30% before being covered by the ion exchange resin solution. The inventors of this application unexpectedly discovered that stretching the support layer by 10-30% before being covered by the ion exchange resin solution can further ensure that the proton exchange membrane has a suitable number and volume of pore structures (water storage pores).

[0084] This may be because the inventors of this application discovered that as the support layer is stretched, the holes in the support layer first expand slightly, but as the stretching of the support layer gradually increases, the hole structure in the support layer actually decreases to a certain extent.

[0085] In this application, before the support layer is covered with the ion exchange resin solution, the support layer is stretched by more than 10%, resulting in a relatively smaller pore size compared to a conventionally tensioned support layer. After the support layer is covered with the ion exchange resin solution, the solution essentially fills the pores inside the support layer. As the support layer slowly recovers its deformation, the pores gradually enlarge, creating additional unfilled space within the support layer. Simultaneously, since the upper layer of the support layer is not covered with the ion exchange resin solution, air enters from the upper layer into the support layer. This air entry further prevents the ion exchange resin solution from filling the extra space, thus ensuring that the final proton exchange membrane has a suitable number and volume of pores (water-retaining pores). Furthermore, because the ion exchange resin solution has suitable viscosity and solids content, the ion exchange material is less likely to permeate into the pores (water-retaining pores) after the support layer has been covered with the solution.

[0086] The combined effect of the stretching step and the low-temperature pretreatment step (ion exchange material migration) further ensures that the proton exchange membrane has a suitable number and volume of pore structures (water storage pores). Of course, in order to ensure that the support layer is not overstretched and damaged, and to ensure that the number and volume of water storage pores inside the final proton exchange membrane are not too many, the stretching range of the support layer cannot be too large (greater than 30%).

[0087] Optionally, in step S2, the thickness of the ion exchange resin solution above the support layer is greater than the thickness of the ion exchange resin solution below the support layer.

[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 support 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 of the ion exchange resin on both sides of the base membrane and the surface tension gradient of the ion exchange resin inside the base membrane to further control the migration of the ion exchange material, thus further ensuring that the final proton exchange membrane has a suitable number and volume of pore structures (water-retaining pores).

[0090] This application provides the following beneficial effects: the proton exchange membrane and its preparation method 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 Example 3 using a scanning electron microscope (SEM), with a magnification of 5000×.

[0093] Figure 3 This is a schematic diagram of the cross-section of the proton exchange membrane prepared in Comparative Example 1 using a scanning electron microscope (SEM), with a magnification of 5000×. Detailed Implementation Example 1

[0094] This application discloses a proton exchange membrane, which is prepared using the following process steps:

[0095] S1. Raw material preparation; The raw materials include ion exchange resin solution and support layer. 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 support layer is a PTFE membrane; The solid content of the ion exchange resin solution is 18.2 wt%, and the Ew of the ion exchange material is 1124 g.

[0096] S2, Coating; The ion exchange resin solution is coated onto one side of the carrier, and the support layer is placed over the ion exchange resin solution. The lower layer of the support layer is in contact with the ion exchange resin solution for 6 seconds, and then the ion exchange resin solution is coated over the support layer to obtain the composite membrane; Before the support layer is placed over the ion exchange resin solution, the support layer is stretched by 20%.

[0097] S3. Pretreatment: Place the composite membrane in an environment with a temperature of 30℃ for pre-drying for 12 minutes. After pre-drying, the raw membrane is obtained.

[0098] S4. High-temperature drying: The raw membrane is dried at 140℃ to obtain a proton exchange membrane.

[0099] Examples 2-7

[0100] The difference between Examples 2-7 and Example 1 lies in the solid content of the ion exchange resin solution and the various process parameters, as detailed in Table 1.

[0101] Table 1. Solid content and process parameters of ion exchange resin solutions in each embodiment.

[0102] Solids content / wt% Ion exchange material Ew / g Stretching amplitude / % Air section residence time / s Pre-drying temperature / °C Pre-drying time / min High temperature drying temperature / °C Example 1 18.2 1124 20 6 35 12 140 Example 2 8.9 835 35 12 43 7 145 Example 3 25.4 1305 / / 30 20 148 Example 4 20.2 651 15 4 36 8 125 Example 5 15.3 985 25 7 33 14 130 Example 6 17.9 1640 10 2 25 11 55 Example 7 27.2 742 30 10 45 5 160

[0103] Comparative Example 1:

[0104] The proton exchange membrane of Comparative Example 1 was prepared using the following process steps:

[0105] 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, the solvent is deionized water and alcohol solvent, the mass ratio of deionized water to alcohol solvent is 0.6; the alcohol solvent is ethanol; the support layer is a PTFE membrane; the solid content in the ion exchange resin solution is 18.7 wt%; the Ew of the ion exchange material is 1153 g;

[0106] S2. Coating: The ion exchange resin solution is coated onto one side of the carrier, and the support layer is covered over the ion exchange resin solution. Then, the ion exchange resin solution is coated over the support layer to obtain a composite membrane.

[0107] S3. High-temperature drying: The raw membrane is dried at 170℃ to obtain a proton exchange membrane.

[0108] 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.

[0109] Comparative Example 2:

[0110] The proton exchange membrane of Comparative Example 2 was prepared using the following process steps:

[0111] 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, the solvent is deionized water and alcohol solvent, the mass ratio of deionized water to alcohol solvent is 0.6; the alcohol solvent is ethanol; the support layer is a PTFE membrane; the solid content in the ion exchange resin solution is 17.6 wt%; the Ew of the ion exchange material is 512 g;

[0112] S2. One-time coating and drying: The ion exchange resin solution is coated onto one side of the carrier to obtain the first composite membrane. Then, the first composite membrane is dried at 165°C to obtain the raw membrane.

[0113] S3. Secondary coating and drying: The ion exchange resin solution is coated onto the other side of the carrier to obtain a second composite membrane. The second composite membrane is then dried at 165°C to obtain a proton exchange membrane.

[0114] 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.

[0115] Performance testing and data

[0116] The detection methods are as follows:

[0117] Proton conductivity: The proton exchange membranes prepared in each example and comparative example were used as samples for proton conductivity testing. The testing method was in accordance with GB / T 20042.3—2022.

[0118] 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.

[0119] The morphological and performance parameters of the proton exchange membranes prepared in each embodiment and comparative example are detailed in Tables 2 and 3:

[0120] Table 2. Morphological and performance parameters of proton exchange membranes

[0121]

[0122] Remark:

[0123] Proton conductivity ① is the proton conductivity of the proton exchange membrane at 25℃ and 40%RH.

[0124] Proton conductivity ② is the proton conductivity of the proton exchange membrane in a scenario of 80℃ and 30%RH.

[0125] Table 3. Cross-sectional morphology parameters of the inner support layer of the proton exchange membrane

[0126] Average diameter of interlayer fibers / nm Average diameter of intermediate layer fibers and h p Ratio Average diameter of nodes / nm Ratio of interlayer fiber and node diameters Support layer cross-sectional hole area rate / % Example 1 109.1 24.80 317.3 0.34 19.4 Example 2 57.3 7.96 188.1 0.30 28.2 Example 3 153.5 47.97 488.2 0.31 9.3 Example 4 63.1 21.76 299.8 0.21 9.9 Example 5 88.4 16.68 346.1 0.26 14.5 Example 6 33.5 15.95 121.9 0.27 18.8 Example 7 188.1 21.13 484.5 0.39 26.3 Comparative Example 1 / / / / / Comparative Example 2 / / / / 1.2

[0127] in conclusion:

[0128] 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, and the amount of ion exchange material filling the support layer of Comparative Example 1 is much higher than that in Example 1. The expected effect is that the proton conductivity of Comparative Example 1 is higher than that of Example 1. However, under specific operating conditions (high temperature and low humidity), the proton conductivity of Comparative Example 1 is much lower than that of Example 1. This may be because the support layer of the proton exchange membrane provided in Example 1 has a certain number of water-retaining pores. These pores give the proton exchange membrane a certain water-retaining and water-holding function, reducing water permeation resistance, improving the uniformity of water distribution, and ensuring relatively good wetting throughout the proton exchange membrane. They also ensure that the water inside the proton exchange membrane does not easily evaporate, thus ensuring that the proton exchange membrane of Example 1 also has a high proton conductivity under high temperature and low humidity conditions. As for the (fully filled) proton exchange membrane provided in Comparative Example 1, on the one hand, its support layer contains a large amount of ion exchange material, which means that the proton exchange membrane requires a lot of water to be fully wetted. However, due to the relatively dry air environment, the proton exchange membrane with high water requirements cannot obtain sufficient water, making it difficult to be fully wetted. On the other hand, because the support layer of this proton exchange membrane lacks a porous structure with water retention and storage functions, in a relatively dry and high-temperature environment, the water permeation resistance is large and the water evaporates more easily, making it difficult for the proton exchange membrane to be fully wetted. This results in a low actual proton conductivity of the proton exchange membrane, which in turn leads to a low battery output power.

[0129] By comparing Example 1 and Comparative Example 2, it was found that the thickness of the proton exchange membrane in Comparative Example 2 was basically similar to that of the proton exchange membrane in Example 1, while the thickness of the support layer of the proton exchange membrane in Comparative Example 2 was much greater than that in Example 1. The expected effect was that the dimensional stability of Comparative Example 2 was higher than that of Example 1. However, in actual use, the dimensional stability of Comparative Example 2 was much lower than that of Example 1. This may be because the proton exchange membrane inevitably absorbs a certain amount of water (wetting) during operation, and the swelling of ion exchange materials is an inevitable phenomenon. The support layer of the proton exchange membrane in Example 1 has certain water-retaining pores. This pore structure provides a certain swelling space for the ion exchange material, that is, some ion exchange material can swell into the support layer, ensuring that the deformation generated when the proton exchange membrane absorbs water and swells is relatively small, thus possessing higher dimensional stability.

[0130] 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. Both the first exchange layer and the second exchange layer are made of ion exchange material. The intermediate layer includes a support layer, ion exchange material partially filled in the support layer and water storage pores located inside the support layer. The thickness H of the proton exchange membrane in the dry state 干 Not higher than 17μm; The density coefficient I of the proton exchange membrane is 0.15-0.65, and the density coefficient I is calculated by the following formula: I=m n / (m n +m P ), where m n This refers to the mass of ion exchange material per unit area in the intermediate layer under dry conditions, expressed in g; m P The mass of the support layer per unit area in a dry state is expressed in grams. m n The following formula is used to calculate: m n =M0-(m P +ρ n V n ), where M0 is the mass of the proton exchange membrane per unit area under dry conditions, and its unit is g; ρ n The density of the ion exchange material in its dry state, expressed in g / m³. 3 V n The volume of the first and second exchange layers per unit area in the proton exchange membrane under dry conditions is expressed in m³. 3 ; In a dry state, the mass m of the support layer per unit area P 2-10g; thickness h of the support layer in the dry state p The range is 2-9 μm, and the unit area mentioned above is 1 m². 2 ; The thickness of the first exchange layer and the second exchange layer are basically the same, and the equivalent weight Ew of the ion exchange material is not higher than 1600. The intermediate layer includes intermediate layer fibers, which are interconnected to form a three-dimensional network structure of the intermediate layer. The average SEM diameter of the intermediate layer fibers is 30-200 nm. The intermediate layer has several nodes, each node being formed by stacking and fusing several intermediate layer fibers together, and the average SEM diameter of the nodes is 100-600nm.

2. The proton exchange membrane according to claim 1, characterized in that: The swelling value D of the proton exchange membrane is 0.2-1.5, and the swelling value D is calculated by the following formula: D=(H 润 -H 干 ) / H 干 , where H 润 The thickness of a proton exchange membrane in a saturated wetted state after absorbing water and swelling is expressed in μm.

3. A proton exchange membrane according to claim 1, characterized in that: The thickness h of the support layer in the dry state p The thickness H of the proton exchange membrane in the dry state 干 The ratio is 0.3-0.

6.

4. A proton exchange membrane according to claim 1, characterized in that: The water content Q of the proton exchange membrane under saturated wetted state is 0.1-0.

45. The water content Q is calculated by the following formula: Q=(M1-M0) / M0, where M1 is the mass of the proton exchange membrane per unit area under saturated wetted state, and its unit is g.

5. A proton exchange membrane according to claim 1, characterized in that: The SEM average diameter of the intermediate layer fibers and the thickness h of the support layer in its dry state are related. p The ratio is 5-50 nm / μm.

6. A proton exchange membrane according to claim 1, characterized in that: The ratio of the average SEM diameter of the intermediate layer fiber to the average SEM diameter of the node is 0.2-0.

4.

7. A proton exchange membrane according to claim 1, characterized in that: The porosity of the intermediate layer cross-section is 8%-30%.

8. A process for preparing a proton exchange membrane as described in any one of claims 1-7, characterized in that, The process includes the following steps: S1. Preparation of ion exchange resin solution; the ion exchange resin solution comprises the following raw materials: ion exchange material and solvent; the solid content of the ion exchange resin solution is 5-30%. S2, coating; An ion exchange resin solution is coated onto one side of a carrier, and a support layer is placed over the ion exchange resin solution. Then, an ion exchange resin solution is coated over the support layer to obtain a composite membrane. The ion exchange resin solution permeates into the support layer, forming a primary migration. S3. Drying; Dry the composite membrane to obtain a proton exchange membrane; Drying specifically includes pre-drying and high-temperature drying. During the pre-drying process, the ambient temperature is 30-50℃ and the pre-drying time is 5-25min. The ion exchange material migrates to both sides of the membrane surface for a second time. During the high-temperature drying process, the ambient temperature is 120-160℃.

9. The preparation process of a proton exchange membrane according to claim 8, characterized in that, Specifically, step S2 involves coating an ion exchange resin solution onto one side of the carrier, covering the ion exchange resin solution with a stretched support layer, and after the lower layer of the support layer contacts the ion exchange resin solution for 2-10 seconds, coating the support layer with the ion exchange resin solution again to obtain a composite membrane; the stretching range of the support layer is 10-30%.

10. The preparation process of a proton exchange membrane according to claim 8, characterized in that, In step S2, the thickness of the ion exchange resin solution above the support layer is greater than the thickness of the ion exchange resin solution below the support layer.

11. The preparation process of a proton exchange membrane according to claim 8, 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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