Method for preparing a water management membrane for electrochemical hydrogen compressors and use thereof

Abstract

The application belongs to the technical field of gas diffusion layer preparation, and particularly relates to a preparation method of a water management film for an electrochemical hydrogen compressor and application thereof. The method solves the dual challenges of anode side film dehydration and mechanical durability in an EHC under low humidity conditions. After laser drilling treatment, N element-containing groups modified on the surface of the hole wall can form hydrogen bonds with water molecules and promote water adsorption, thereby realizing stable film hydration and reducing the in-plane resistance. The method is simple and convenient to operate, has strong practicability, and the prepared water management film for the electrochemical hydrogen compressor can effectively improve the performance and mechanical strength of the EHC under extreme humidity conditions after being assembled into the EHC.

Description

Technical Field

[0001] This invention belongs to the field of gas diffusion layer preparation technology, specifically relating to a method for preparing a water management membrane for an electrochemical hydrogen compressor and its application. Background Technology

[0002] Electrochemical hydrogen compressors (EHCs) have gained widespread attention in recent years for their ability to achieve highly efficient static compression of high-purity hydrogen without moving mechanical parts, particularly in distributed hydrogen supply and storage equipment. However, the practical operation of EHCs still faces significant structural and water management challenges, severely limiting their performance and long-term reliability.

[0003] Under common operating conditions such as low humidity, high humidity intake, or high pressure compression, significant moisture distribution imbalances can easily occur inside membrane electrode assemblies (MEAs): dehydration of the anode-side membrane leads to a decrease in proton conductivity and a weakening of local membrane mechanical strength; long-term supply of humidifying gas to the anode side causes water vapor accumulation, which can easily block the active sites of the catalyst layer; while flooding of the cathode side hinders hydrogen diffusion and induces local concentration polarization. Both factors contribute to performance degradation and operational instability. Furthermore, under high-pressure output (5-100 MPa or higher), the risk of pressure instability of the internal porous structure increases significantly.

[0004] Existing gas diffusion layers (GDLs) are typically made of carbon paper, whose mechanical strength decreases significantly in high-pressure hydrogen environments, making them prone to crushing, delamination, or debris shedding. Under stress, the GDL may also become partially embedded within the catalyst layer, or even puncture the ion exchange membrane, causing irreversible damage. The microporous layer (MPL), a crucial component of the GDL, is often prepared using brushing, scraping, or spraying processes. Due to its dense and brittle structure, it is highly susceptible to collapse under high pressure, leading to blockage of existing pores, decreased gas permeability, and localized mass transfer obstruction. The collapse of carbon nanotubes in the carbon paper and the MPL also alters the hydrophobic / hydrophilic balance, exacerbating the coupling problem between cathode water accumulation and anode dehydration, further worsening water management within the MEA.

[0005] On the other hand, traditional MPLs have high surface roughness and are prone to microcracks, resulting in high interfacial contact resistance between the MPL and the catalyst layer. To reduce this resistance, a large clamping force is usually applied during MEA assembly. However, under high-pressure EHC operation, this clamping method further amplifies the risk of mechanical damage to the MPL and GDL, limits the disassembly of the membrane electrode and the reuse of components, and increases system maintenance costs.

[0006] In summary, existing EHC membrane electrode structures generally suffer from technical bottlenecks such as "GDL fragility under high pressure, MPL easy collapse and pore blockage, difficulty in water management inside MEA and poor recyclability." There is an urgent need to develop a membrane electrode configuration that combines reliable structural stability and excellent water management performance to improve the performance, durability and maintainability of EHC. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments.

[0008] As one aspect of the present invention, the present invention provides a method for preparing a water management membrane for an electrochemical hydrogen compressor, which includes the following steps:

[0009] Step 1: Preparation of oxidized multi-walled carbon nanotubes;

[0010] Step 2: Disperse the oxidized multi-walled carbon nanotubes, carbon nanofibers, and polyvinylidene fluoride obtained in Step 1 in a solvent to form a uniform slurry;

[0011] Step 3: The slurry obtained in Step 2 is vacuum filtered or hot-pressed and sintered to obtain a base film;

[0012] Step 4: Perform laser perforation on the basement membrane obtained in Step 3 to form through or non-through channels on the basement membrane.

[0013] As a preferred embodiment of the preparation method described in this invention, in step 4, before laser drilling, a precursor material containing doped elements is first coated on the surface of the base film. During laser treatment, the laser penetrates the precursor material and forms a channel on the surface of the base film, while the doped elements in the precursor material are introduced into the channel wall. After the treatment is completed, the residual precursor material is removed.

[0014] As a preferred embodiment of the preparation method described in this invention, the sintering is carried out at a temperature of 130-160 ℃ for a time of 20-60 min.

[0015] As a preferred embodiment of the preparation method described in this invention, the precursor material is a nitrogen-containing, sulfur-containing, or phosphorus-containing polymer film or powder coating.

[0016] As a preferred embodiment of the preparation method described in this invention, the precursor material is a polyimide film, a urea coating, a melamine coating, a dicyandiamide coating, a polyacrylonitrile film, a thiourea coating, or an ammonium phosphate coating.

[0017] As a preferred embodiment of the preparation method described in this invention, in step 1, the preparation method of oxidized multi-walled carbon nanotubes is as follows: multi-walled carbon nanotubes are dispersed in nitric acid solution and oxidized by reflux heating under oil bath conditions for 6-24 hours and heating temperature of 100-140 ℃.

[0018] In a preferred embodiment of the preparation method described in this invention, the slurry in step 2 contains 5%-20% polyvinylidene fluoride based on the total mass of oxidized multi-walled carbon nanotubes, carbon nanofibers, and polyvinylidene fluoride.

[0019] The mass fraction of oxidized multi-walled carbon nanotubes is 70-85%.

[0020] The mass fraction of carbon nanofibers is 5-20%.

[0021] As a preferred embodiment of the preparation method described in this invention, the parameters for laser drilling in step 4 are: laser power 5-11 W, scanning speed 50-250 mm / s, number of scans 1-2, and pattern spacing 0.5-2 mm.

[0022] In a preferred embodiment of the preparation method described in this invention, in step 2, the solvent of the slurry is water, and the total solid content of the slurry is 0.3-1 mg / mL.

[0023] The present invention also provides the application of the water management membrane prepared by the method described above in the electrochemical hydrogen compressor in the electrochemical hydrogen compressor. The water management membrane is used to assemble on the anode side of the electrochemical hydrogen compressor and is disposed between the anode gas diffusion layer and the proton exchange membrane.

[0024] The beneficial effects of this invention are as follows: This invention constructs a self-supporting, hydrophilic water management membrane with high mechanical toughness based on a PVDF and O-MWCNT (oxidized multi-walled carbon nanotube) composite architecture, addressing the dual challenges of anolyte dehydration and mechanical durability in EHCs under low humidity conditions. In this invention, molecular-level interactions, especially the hydrogen bonds between PVDF molecular chains and O-MWCNTs, support the structural integrity of the MPL and enhance its water-holding capacity. After laser drilling, the nitrogen-containing groups modified on the pore wall surface can form hydrogen bonds with water molecules and promote water adsorption, thereby achieving stable membrane water bonding and reducing in-plane resistivity. The method of this invention is simple and convenient to operate, highly practical, and the electrochemical hydrogen compressor using the prepared water management membrane, when assembled into an EHC, can effectively improve performance and mechanical strength under extreme humidity conditions. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:

[0026] Figure 1 The Fourier transform infrared (FTIR), Raman, and TGA test results are for O-MWCNT.

[0027] Figure 2 The water contact angle of O-MWCNT with different oxidation times and the water absorption of different types of water management membranes were studied.

[0028] Figure 3 Performance testing of water management membrane samples with different PVDF contents.

[0029] Figure 4 Electrochemical performance analysis of O-MWCNT samples with different oxidation degrees.

[0030] Figure 5 The electrochemical performance of different types of gas diffusion layers was studied.

[0031] Figure 6 Physical properties characterization of the water management membrane after durability testing.

[0032] Figure 7 The tensile test results are for Example 2 (before laser treatment) and Comparative Example 1.

[0033] Figure 8 This is a cycle stability test and scale-up experiment for Example 2 (before laser treatment).

[0034] Figure 9 The XPS and FTIT spectra of Example 2 (after laser treatment) and the N-containing film before and after laser treatment are shown.

[0035] Figure 10 The images show the physical sample of Example 2 (after laser treatment) and the water absorption of different types of samples.

[0036] Figure 11 The performance of Example 2 (after laser treatment) and Comparative Example 6 samples were tested.

[0037] Figure 12 The polarization curves of the sample from Example 2 (after laser treatment) and the commercial gas diffusion layer were obtained under 100% humidity conditions.

[0038] Figure 13 Performance tests were conducted on samples from Comparative Example 7 and Example 2 (after laser treatment) under 50% humidity conditions. Detailed Implementation

[0039] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0040] Example 1:

[0041] Preparation steps of O-MWCNT: Weigh 100 mg of multi-walled carbon nanotubes (MWCNT, Nanjing Xianfeng Nano, purity 95%, 100288, length less than 10 μm, average diameter 50 nm), disperse in a nitric acid solution with a volume ratio of nitric acid to ultrapure water of 1:1, and ultrasonically disperse the suspension for 2 h to ensure uniform dispersion of MWCNTs. Subsequently, the mixture was refluxed in an oil bath at 120 ℃ for 6 h, 12 h, or 24 h, respectively. After heat treatment, the reaction solution was cooled to room temperature, and the solid product was recovered by vacuum filtration. The filtrate was repeatedly washed with ultrapure water until it was neutral to remove residual acid. The filtrate was vacuum dried overnight at 60 ℃ to obtain samples with different degrees of surface modification, which were designated as multi-walled carbon nanotubes (O-MWCNT, oxidation 6 h), multi-walled carbon nanotubes (O-MWCNT, oxidation 12 h), and multi-walled carbon nanotubes (O-MWCNT, oxidation 24 h), respectively.

[0042] Example 2:

[0043] Preparation steps of water management membrane for electrochemical hydrogen compressor: 15.88 mg of multi-walled carbon nanotubes (O-MWCNT, oxidized for 24 h) and 2.27 mg of CNFs (carbon nanofibers, Nanjing Xianfeng Nano, 95% purity, 100221, average diameter 50-200 nm, length 1-15 μm) prepared in Example 1 were dispersed in an aqueous solution containing 2.02 mg of PVDF (polyvinylidene fluoride, Solef® 9007). Ultrapure water was added to make the total solid content of the slurry 0.5 mg / mL. The mixture was ultrasonically sonicated for 3 h at 40 W output power using a probe-type ultrasonic transducer (SCIENTZ-750F, Xinzhi, China) to ensure thorough dispersion of the components. The resulting suspension was then vacuum filtered (0.01 MPa) through a mixed cellulose ester filter membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense film. The film was then thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 °C overnight, the film was heat-treated at 150 °C for 30 min, and the resulting film thickness was 30 μm, which was recorded as "Example 2 (before laser treatment)".

[0044] The glass plate was cleaned with ultrapure water, and the surface of the glass was wiped clean with a lint-free cloth. Polyimide powder (Matrimid 5218, Suxingrui) was dissolved in DMF (HLDDMF-500ml, Tianjin Fuyu) solvent to make the polyimide mass fraction 5%. A thin film was coated with a coater at a distance of 50 μm from the glass plate. The glass plate was placed in an oven and heated to 80 ℃ for 10 min for heat setting, followed by heat treatment at 180 ℃ for 30 min to obtain a nitrogen-containing film (polyimide film, thickness of 40 μm).

[0045] Subsequently, a nitrogen-containing film was applied to the surface of Example 2 (before laser treatment). In an air atmosphere, the laser power was adjusted to 7 W, the pattern spacing to 1 mm, the scanning speed to 101.6 mm / s, and the number of scans to 1. Laser drilling was performed, and the laser penetrated the nitrogen-containing film to form conical channels on the surface of the underlying base film. At the same time, nitrogen from the nitrogen-containing film was doped into the channel walls. After the treatment was completed, the nitrogen-containing film on the surface was peeled off and removed to obtain an electrochemical hydrogen compressor water management membrane (thickness of 30 μm), which was designated as "Example 2 (after laser treatment)".

[0046] Comparative Example 1:

[0047] Preparation steps of water management membrane containing O-MWCNT and Nafion: Take 15.88 mg of multi-walled carbon nanotubes (oxidized for 24 h) and 2.27 mg of CNFs (Nanjing Xianfeng Nano, purity 95%, 100221, diameter 50-200 nm, length 1-15 μm) prepared in Example 1 and disperse them in an aqueous solution containing 10.08 mg of Nafion (D2020, 20 wt%) (or a corresponding proportion of Aquivion (D79-25BS, 2 wt%) and 3M (5 wt%)). Add ultrapure water to make the total solids content of the slurry 0.5 mg·mL. -1 The membrane was homogenized using a probe-type ultrasonic scanner (SCIENTZ-750F, Xinzhi, China) at 40 W output power for 3 h to ensure thorough dispersion of all components. The resulting suspension was then vacuum-filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense membrane. The membrane was then thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 °C overnight, the membrane was heat-treated at 150 °C for 30 min. The resulting membrane is designated as Comparative Example 1.

[0048] Comparative Example 2:

[0049] Preparation steps of water management membrane containing O-MWCNTs and PTFE: 15.88 mg of multi-walled carbon nanotubes (oxidized for 24 h) and 2.27 mg of CNFs (Nanjing Xianfeng Nano, purity 95%, 100221, diameter 50-200 nm, length 1-15 μm) prepared in Example 1 were dispersed in an aqueous solution containing 3.36 mg PTFE (60 wt%). Ultrapure water was added to make the total solids content of the slurry 0.5 mg·mL⁻¹. -1 The membrane was homogenized using a probe-type ultrasonic scanner (SCIENTZ-750F, Xinzhi, China) at 40 W output power for 3 h to ensure thorough dispersion of all components. The resulting suspension was then vacuum-filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense membrane. The membrane was then thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 °C overnight, the membrane was heat-treated at 200 °C for 30 min. The resulting membrane is designated as Comparative Example 2.

[0050] Comparative Example 3:

[0051] Preparation steps of water management membranes containing O-MWCNTs with different oxidation degrees: 15.88 mg of multi-walled carbon nanotubes (oxidized for 12 h) and 2.27 mg of multi-walled carbon nanotubes (oxidized for 6 h) prepared in Example 1, and 2.27 mg of CNFs (Nanjing Xianfeng Nano, 95% purity, 100221, diameter 50-200 nm, length 1-15 μm) were dispersed in an aqueous solution containing 2.02 mg of PVDF (Solef® 9007). Ultrapure water was added to make the total solids content of the slurry 0.5 mg·mL⁻¹. -1 The components were homogenized by ultrasonication using a probe-type ultrasonic transducer (SCIENTZ-750F, Xinzhi, China) at 40 W output power for 3 h to ensure thorough dispersion. The resulting suspension was then vacuum-filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense membrane. The membrane was then thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 ℃ overnight, the membrane was heat-treated at 150 ℃ for 30 min. The resulting membranes were designated as Comparative Example 3 (oxidation for 12 h) and Comparative Example 3 (oxidation for 6 h), respectively.

[0052] Comparative Example 4:

[0053] Preparation steps of water management membranes with different PVDF contents: 15.88 mg of multi-walled carbon nanotubes (oxidized for 24 h) and 2.27 mg of CNFs (Nanjing Xianfeng Nano, 95% purity, 100221, diameter 50-200 nm, length 1-15 μm) prepared in Example 1 were dispersed in aqueous solutions containing 2.02, 3.20, and 4.54 mg of PVDF (Solef® 9007), respectively. Ultrapure water was added to make the total solids content of the slurry 0.5 mg·mL. -1 The components were homogenized by ultrasonication using a probe-type ultrasonic transducer (SCIENTZ-750F, Xinzhi, China) at 40 W output power for 3 h to ensure thorough dispersion. The resulting suspension was then vacuum-filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense membrane. The membrane was then thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 °C overnight, the membrane was heat-treated at 125 °C for 30 min. The resulting membranes were designated as Comparative Example 4 (10% content), Comparative Example 4 (15% content), and Comparative Example 4 (20% content).

[0054] Comparative Example 5:

[0055] Example 2 (before laser treatment): 53.9 mg of multi-walled carbon nanotubes (oxidized for 24 h) and 7.7 mg of CNFs (Nanjing Xianfeng Nano, 95% purity, 100221, diameter 50-200 nm, length 1-15 μm) prepared in Example 1 were dispersed in an aqueous solution containing 15.4 mg of PVDF. Ultrapure water was added to bring the total solids content of the slurry to 0.5 mg·mL⁻¹. The mixture was homogenized using a probe-type ultrasonic scanner (SCIENTZ-750F, Xinzhi, China) at 40 W output power for 3 h to ensure thorough dispersion of all components. The resulting suspension was then vacuum filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense film. The film was thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 °C overnight, the membrane was heat-treated at 125 °C for 30 min to obtain the scaled-up sample.

[0056] Comparative Example 6:

[0057] Sample preparation steps with modified laser parameter settings: 15.88 mg of multi-walled carbon nanotubes (oxidized for 24 h) prepared in Example 1 and 2.27 mg of CNFs (Nanjing Xianfeng Nano, 95% purity, 100221, diameter 50-200 nm, length 1-15 μm) were dispersed in an aqueous solution containing 2.02 mg of PVDF (Solef® 9007). Ultrapure water was added to bring the total solids content of the slurry to 0.5 mg·mL.-1 The membrane was homogenized using a probe-type ultrasonic scanner (SCIENTZ-750F, Xinzhi, China) at 40 W output power for 3 hours to ensure thorough dispersion of all components. The resulting suspension was then vacuum-filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense membrane. The membrane was then thoroughly rinsed with ultrapure water to remove residual solutes. After vacuum drying at 60 °C overnight, the membrane was heat-treated at 150 °C for 30 min. The glass plate was cleaned with ultrapure water, and the surface was wiped dry with a lint-free cloth. Polyimide powder (Matrimid 5218, Suxingrui) was dissolved in DMF (HLDDMF-500ml, Tianjin Fuyu) to achieve a polyimide mass fraction of 5%. A thin film was coated using a coater at a distance of 50 μm from the glass plate. The glass plate was then placed in an oven and heated to 80 °C for 10 min for heat setting, followed by heat treatment at 180 °C for 30 min to obtain a nitrogen-containing membrane. This nitrogen-containing membrane was then applied to the surface of the heat-treated filter membrane. In an air atmosphere, the laser power was adjusted to 11 W, the pattern spacing to 1 mm, the scanning speed to 50.8 mm / s, and the number of scans to 2. The resulting membrane was designated as Comparative Example 6.

[0058] Comparative Example 7:

[0059] Sample preparation steps using different nitrogen-containing precursors: 15.88 mg of multi-walled carbon nanotubes (oxidized for 24 h) prepared in Example 1 and 2.27 mg of CNFs (Nanjing Xianfeng Nano, 95% purity, 100221, diameter 50-200 nm, length 1-15 μm) were dispersed in an aqueous solution containing 2.02 mg of PVDF (Solef® 9007). Ultrapure water was added to bring the total solids content of the slurry to 0.5 mg·mL. -1 The components were homogenized by ultrasonication at 40 W output power for 3 h using a probe-type ultrasonic transducer (SCIENTZ-750F, Xinzhi, China) to ensure sufficient dispersion. The resulting suspension was then vacuum filtered (0.01 MPa) through a mixed cellulose ester membrane with a nominal pore size of 0.45 μm to obtain a uniform and dense film. The film was thoroughly rinsed with ultrapure water to remove residual solutes and vacuum dried overnight at 60 °C, followed by heat treatment at 150 °C for 30 min. Other nitrogen-containing precursors, such as urea (Shanghai, Aladdin, China, U141075), were uniformly coated onto the surface of the heat-treated membrane to achieve a precursor membrane thickness of 50 μm. Laser treatment was then performed in air at a laser power of 7 W, a pattern spacing of 1 mm, a scanning speed of 203.2 mm / s, and one scan, resulting in a laser-drilled precursor sample, designated as Comparative Example 7.

[0060] Furthermore, the precursor powder can be other nitrogen-, sulfur-, or phosphorus-containing compound powders. Specifically, the nitrogen-containing precursor powder can be selected from melamine, urea, dicyandiamide, polyacrylonitrile, or imidazole compounds; the sulfur-containing precursor powder can be selected from thiourea, thioacetamide, thiourea, or thiophene compounds; and the phosphorus-containing precursor powder can be selected from ammonium phosphate, ammonium dihydrogen phosphate, triphenyl phosphate, or phytic acid. The membrane material can be a polymer membrane or composite membrane pre-introduced with nitrogen-, sulfur-, or phosphorus-containing functional groups. Specifically, the nitrogen-containing membrane material can be selected from polyamide membranes, polyacrylonitrile membranes, polypyrrole membranes, polyaniline membranes, or nitrogen-doped polyvinylidene fluoride composite membranes; the sulfur-containing membrane material can be selected from sulfonated polyetheretherketone membranes, polyphenylene sulfide membranes, sulfonated polystyrene membranes, or sulfur-containing copolymer membranes; and the phosphorus-containing membrane material can be selected from phosphoric acid-doped polybenzimidazole membranes, polymer membranes containing phosphonic acid groups, or phytic acid-modified polymer composite membranes. The aforementioned membrane material can be directly applied to the substrate surface, and channels can be constructed on the membrane surface using laser treatment.

[0061] Material characterization: Figure 1 The results show the FTIR spectrum of O-MWCNT and the TGA test results.

[0062] All O-MWCNT samples were at 3445 cm⁻¹ -1 With 1634 cm -1 Characteristic absorption bands appeared at all points, corresponding to the stretching vibrations of O–H and C=O, respectively, indicating the presence of hydroxyl and carboxyl groups; and the intensity of these peaks increased with prolonged oxidation time, indicating an increase in the content of oxygen-containing functional groups. Further Raman spectroscopy was used to assess oxidation-induced structural changes. Figure 1 (b) shows that the intensity ratio of peak D to peak G (I D / I G The increase from 0.62 to 1.04 indicates that more structural defects were introduced into the carbon framework, generating more potential active sites. (TGA results) Figure 1 (c) indicates that all samples exhibited significant weight loss at 250–350 °C, primarily due to the thermal decomposition of oxygen-containing functional groups; furthermore, the weight loss increased with oxidation time, demonstrating the enhanced functionalization. In summary, these characterization results confirm the successful introduction of numerous oxygen-containing functional groups onto the O-MWCNT surface. When introduced into the water management membrane, these functional groups can form extensive hydrogen bonds with water molecules, significantly improving the water retention capacity of the membrane under low humidity conditions. This molecular-level design provides a powerful strategy for maintaining membrane hydration, thus laying a solid foundation for the stable and efficient performance of the EHC under various operating conditions.

[0063] Figure 2 (a) Water contact angle of O-MWCNTs with different oxidation times and (b) Water absorption of water management membranes prepared with different binders and different oxidation times of O-MWCNTs.

[0064] With prolonged oxidation time of O-MWCNTs, the water contact angle decreased significantly, especially after 24 hours when the contact angle reached 0°. This indicates that the surface hydrophilicity of carbon nanotubes significantly increases with increasing oxidation degree. Water absorption tests after the water management membrane was prepared showed that the increased hydrophilicity of O-MWCNTs due to high oxidation degree manifested as enhanced membrane water absorption. Furthermore, when hydrophilic ionomers such as Nafion (or Aquivion and 3M) were used as binders, the prepared water management membrane exhibited stronger water absorption capacity than that of Example 2 (before laser treatment). Conversely, using strongly hydrophobic binders such as PTFE weakened the water absorption performance of the water management membrane.

[0065] Figure 3 Performance testing of membrane electrodes prepared for water management membranes with different PVDF contents at 50% RH: (a) Polarization curve (b) 0.25 A·cm -2 Electrochemical impedance spectroscopy.

[0066] To optimize the binder ratio, samples with PVDF contents of 10%, 15%, and 20% were prepared and their EHC performance was tested at 50% RH. The test conditions were: 0.5 slpm hydrogen gas flow through the cathode and a back pressure of 2 bar. The membrane electrode containing 10% PVDF achieved a maximum current density of 4.65 A·cm⁻¹ at 0.5 V. -2 However, when the PVDF content increased to 15% and 20%, the polarization performance decreased to some extent. According to... Figure 3 (b) The EIS test results show that as the PVDF content increases, the ohmic impedance of the membrane electrode decreases from 56.8 mΩ·cm. 2 Increased to 68.3 mΩ·cm 2 This indicates that the electrical insulation properties of PVDF increase the contact resistance between the water management membrane and other components.

[0067] Figure 4 Electrochemical performance analysis of samples containing O-MWCNTs with different oxidation degrees: (a) Polarization curves; (b) Current density at 0.5 V; (c) 0.25 A·cm⁻¹ -2 Electrochemical impedance spectroscopy.

[0068] Figure 4 The polarization performance results in (a) and (b) show that the battery polarization performance improves with the increased oxidation degree of the incorporated O-MWCNTs. Figure 4(c) The EIS results show that the ohmic impedance of the membrane electrode after incorporating O-MWCNTs oxidized for 24 h was significantly reduced. This is because the improved water retention capacity of the membrane electrode effectively alleviated membrane dehydration in low humidity environments, thus reducing the internal resistance of the membrane. As the oxidation degree of O-MWCNTs decreased, the ohmic impedance increased significantly. Therefore, a higher oxidation degree of O-MWCNTs is beneficial for EHC operation under low humidity conditions.

[0069] Figure 5 The polarization curves (a) and (b) of the film electrodes of commercial samples, Comparative Example 1, and Example 2 (before laser treatment) at 50% RH are shown in Figure 2. -2 (c) Comparison of ohmic impedance and mass transfer impedance in electrochemical impedance spectroscopy at 0.3V. (d) Hydrogen compression performance at 0.3V.

[0070] Figure 5 (a) Polarization curves of MEAs using three different GDLs under 50% RH conditions are presented. The electrochemical performance across the entire voltage range is in the order of Comparative Example 1 ≥ Example 2 (before laser treatment) > Commercial Sample. At 0.3 V, the corresponding current densities are 3.20, 3.00, and 2.05 A·cm⁻¹, respectively. -2 The performance difference is mainly attributed to the superior hydrophilicity of Comparative Example 1 and Example 2 (before laser treatment): they can effectively retain water under low humidity inlet conditions, thereby promoting full hydration of the PEM and significantly improving the electrochemical performance of the EHC. Compared with Example 2 (before laser treatment), Comparative Example 1 has stronger hydrophilicity, enabling it to store more water in a short time, further improving membrane hydration and performance, and thus slightly improving polarization performance.

[0071] EIS analysis ( Figure 5 (b) and (c) reveal the ohmic impedance and mass transfer impedance of different samples. Comparative Example 1 and Example 2 (before laser treatment) achieved better interfacial contact during MEA preparation due to their smoother surface morphology and self-supporting structure; simultaneously, their hydrophilic properties improved the hydration level of PEM. These synergistic effects jointly contributed to a significant reduction in ohmic impedance: the ohmic impedance of the commercial sample was 71.5 mΩ·cm. 2 The values ​​of Comparative Example 1 and Example 2 (before laser treatment) decreased to 52.8 mΩ·cm, respectively. 2 With 55.8 mΩ·cm 2 Regarding mass transfer impedance, the value for the commercial sample is 0.62 mΩ·cm. 2 In contrast, Comparative Example 1 and Example 2 (before laser treatment) showed a significant reduction to 0.42 mΩ·cm. 2 With 0.32 mΩ·cm 2This improvement can be attributed to the independently constructed water management membrane: its dense and ordered pore network provides ample gas transport channels without hindering gas diffusion within the GDL, thereby effectively reducing mass transfer resistance. As... Figure 5 As shown in (d), the actual compression performance at 0.3 V follows the same trend as the electrochemical performance: within the same test duration, the cathode-side output pressure is in the order of Comparative Example 1 ≥ Example 2 (before laser treatment) > Commercial Sample. It is noteworthy that the EHCs using Comparative Example 1 and Example 2 (before laser treatment) can achieve an output pressure of 1 MPa within 100 s, and the performance between Comparative Example 1 and Example 2 (before laser treatment) is almost identical, with no significant difference.

[0072] Figure 6 For the durability test of the water management membrane, (a) fracture morphology of Comparative Example 1 after the test and (b) corresponding SEM micrographs, (c) surface SEM morphology of Example 2 (before laser treatment) after the durability test and (d) appearance morphology.

[0073] Although the two water management membrane variants share the same crosslinked network, their mechanical behaviors differ significantly due to differences in binder chemistry. After repeated cycling at 50% RH, Comparative Example 1 exhibited severe mechanical degradation, including macroscopic cracking, delamination with the GDB, and localized adhesion to the CCM. Figure 6 (a)). SEM imaging ( Figure 6 (b) further revealed microstructural damage. Similar structural damage was also observed when using ionomers like Aquivion and 3M as binders. In contrast, Example 2 (before laser treatment) maintained excellent structural integrity throughout the test. Figure 6 (c) and (d)), SEM analysis confirmed that its microstructure was not damaged. The above results highlight the key role of binder selection in determining the mechanical durability of water management membranes: compared with hydrophilic but weakly rigid ionomers such as Nafion, PVDF provides stronger structural robustness and long-term durability.

[0074] Figure 7 The tensile test results are shown in (a) Example 2 (before laser treatment) and (b) Comparative Example 1.

[0075] Example 2 (before laser treatment) has a maximum tensile strength of 63.5 MPa, which is much higher than Comparative Example 1 by about 2 MPa. This further confirms the key role of binder selection in determining the mechanical durability of water management membranes: compared with Nafion, PVDF provides stronger structural robustness and long-term durability.

[0076] Figure 8The polarization curves of (a) Example 2 (before laser treatment) after repeated testing under 50% RH conditions, and (b) electrochemical impedance spectroscopy, (c) bulk resistance and surface resistance, and (d) polarization curves of the magnified sample.

[0077] Electrochemical stability was also evaluated during multiple EHC operating cycles. For example... Figure 8 As shown in (a), the polarization curve of Example 2 (before laser treatment) remained stable under 50% RH conditions, and the differences between tests were negligible. Electrochemical impedance spectroscopy (EIS) Figure 8 (b) The performance degradation is minimal; the volume resistivity measured after testing remains consistently low (~2.7 mΩ·cm). 2 The in-plane resistivity also remained at ~53.2 mΩ·cm. Figure 8 (c)). These results indicate that the structure and electronic properties of Example 2 (before laser treatment) remain essentially unchanged after long-term use.

[0078] It is worth emphasizing that the preparation process of water management membranes is scalable. Vacuum filtration / hot pressing can achieve the preparation of large-area membranes while maintaining structural uniformity and functional performance. Comparative tests of scaled-up samples yielded completely consistent normalized polarization curves. Figure 8 (d) indicates that performance was not affected during scale-up. These results establish the advantages of Example 2 (before laser treatment) in terms of mechanical toughness, electrochemical stability, and manufacturing scalability.

[0079] Figure 9 (a) FTIR spectra of N / S / P elemental films and defective graphene products after laser perforation treatment; (b) N 1s XPS spectra of Example 2 (after laser treatment).

[0080] like Figure 9 As shown in (a), the characteristic peaks of N appear at 1780 and 1720 cm⁻¹. -1 At this location, they were classified as asymmetric and symmetric stretching vibrations at C=O, respectively, at 1380 cm. -1 The peak at 720 cm⁻¹ was identified as a CN vibration. -1 The peak at 1099 cm⁻¹ was identified as a bending vibration of C=O. After laser drilling, the nitrogen-containing film exhibited a new characteristic peak, corresponding to 1099 cm⁻¹. -1 COC stretching vibration at 1626 cm -1 The C=O stretching vibration at the point and the NH stretching vibration or OH vibration caused by absorbed water molecules (3000-3500 cm⁻¹) -1 ). N 1s XPS spectral analysis results ( Figure 9(b) shows that after laser drilling, the nitrogen element in the nitrogen-containing membrane was modified onto the pore wall surface in the form of pyridyl-N (398.7 eV), pyrrole-N (399.5 eV), graphyl-N (400.3 eV) and oxide-N (401.3 eV), which can form hydrogen bonds with water molecules and promote water adsorption.

[0081] Figure 10 (a) Physical image of sample from Example 2 (after laser treatment) and (b) Water absorption of different types of samples.

[0082] like Figure 10 As shown in (a), by controlling reasonable laser parameters, a sample with a pore size of 500 μm and a pore spacing of 1 mm was successfully prepared, and the surface showed no structural damage or mechanical degradation, continuing the advantage of mechanical toughness of the sample in Example 2 (before laser treatment). Furthermore, since pyridyl-N and pyrrole-N can form hydrogen bonds with water molecules, promoting water adsorption, the water absorption test results under the same conditions ( Figure 10 (b) shows that the sample of Example 2 (after laser treatment) has a stronger hydrophilic effect.

[0083] Figure 11 (a) Polarization curves of Comparative Example 6 and Example 2 (after laser treatment) at 50%RH; (b) Electrochemical impedance spectroscopy.

[0084] like Figure 11 As shown in (a), the electrochemical performance across the entire voltage range was in the following order: Example 2 (after laser treatment) > Comparative Example 6 > Example 2 (before laser treatment). At 0.3 V, the corresponding current densities were 3.46, 3.10, and 3.00 A·cm⁻¹, respectively. -2 The performance difference is mainly attributed to the excellent hydrophilicity resulting from the wall modification: due to the nitrogen modification of the wall, pyridyl-N and pyrrole-N can form hydrogen bonds with water. The presence of these bound waters further enhances the hydrophilicity and water retention properties of the water management membrane, thereby promoting the full hydration of the PEM and significantly improving the electrochemical performance of the EHC. Compared with Example 2 (after laser treatment), Comparative Example 6 has lower performance due to the lack of nitrogen modification, but thanks to the presence of tapered channels, some water can be transported to the membrane, slightly increasing the degree of hydration. Therefore, its electrochemical performance is slightly higher than that of Example 2 (before laser treatment).

[0085] EIS analysis ( Figure 11 (b) revealed the ohmic impedance of different samples. Example 2 (after laser treatment) enhanced the hydration effect of PEM due to its more hydrophilic and water-retaining structural features and elemental modification, thus leading to a significant reduction in ohmic impedance: the ohmic impedance of Example 2 (before laser treatment) was 55.8 mΩ·cm. 2Meanwhile, the Ω·cm of Example 2 (after laser treatment) and Comparative Example 6 decreased to 42.8 mΩ·cm. 2 With 53.1 mΩ·cm 2 This improvement can be attributed to the unique structure and elemental modification of Example 2 (after laser treatment): the tapered channels created by laser drilling can transport some water to the PEM membrane without hindering gas diffusion. At the same time, thanks to the N element modification on the wall, water molecules can more easily bind to it through hydrogen bonds, which further improves the overall hydrophilicity and water retention properties, thereby reducing the ohmic impedance.

[0086] Figure 12 The polarization curves of the sample from Example 2 (after laser treatment) and the commercial gas diffusion layer were obtained under 100% humidity conditions.

[0087] like Figure 12 As shown, across the entire voltage range, the electrochemical performance of the Example 2 (laser-treated) sample was significantly higher than that of the commercial sample, with corresponding current densities of 4.02 and 2.90 A·cm⁻¹ at 0.3 V, respectively. -2 The reason for such a significant performance difference is that under high humidity conditions, if there is too much water on the anode side, the water enriched on the catalyst side will spontaneously condense into liquid water. Thanks to the presence of the conical channels, this liquid water will be transported from the catalyst layer to the flow field plate side under the drive of capillary force, thus avoiding water flooding on the anode side under high current and high humidity conditions.

[0088] Figure 13 Polarization curves of Comparative Example 7 and Example 2 (after laser treatment) were obtained under 50% humidity conditions.

[0089] like Figure 13 As shown, the sample from Example 2 (after laser treatment) exhibited superior electrochemical performance across the entire voltage range, with current densities of 3.46 and 3.25 A·cm⁻¹ at 0.3 V, respectively. -2 Although urea, as a high-nitrogen precursor, can be modified with nitrogen-containing groups on its surface under laser induction, it is prone to decomposition and release of nitrogen-containing volatiles under laser irradiation. The degree of nitrogen retention in the final solid phase is closely related to the laser parameters and the ambient atmosphere. In contrast, nitrogen-containing polymer films such as polyimide inherently possess nitrogen in their molecular framework, resulting in more stable nitrogen retention and better reproducibility. Therefore, samples prepared using nitrogen-containing films as precursors exhibit better hydration retention and electrochemical performance.

[0090] In summary, we developed a self-supporting, highly hydrophilic, and mechanically tough water management membrane based on a PVDF-O-MWCNT composite architecture, incorporating a unique conical pore structure and elemental modifications. This membrane addresses the dual challenges of anolyte dehydration and mechanical durability in EHC under low humidity conditions. Molecular-level interactions—particularly hydrogen bonds between PVDF molecular chains and O-MWCNTs, and hydrogen bonds between nitrogen-containing groups and water molecules—support the structural integrity of the water management membrane and enhance its water-holding capacity, thereby achieving stable membrane water coalescence and reducing in-plane resistivity. Simultaneously, thanks to the conical pore structure, anolyte flooding caused by high humidity is avoided under capillary action. Furthermore, the fabrication process is scalable, maintaining electrochemical performance and stable mechanical strength even when samples are scaled up.

[0091] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a water management membrane for an electrochemical hydrogen compressor, characterized in that, Includes the following steps: Step 1: Preparation of oxidized multi-walled carbon nanotubes; Step 2: Disperse the oxidized multi-walled carbon nanotubes, carbon nanofibers, and polyvinylidene fluoride obtained in Step 1 in a solvent to form a uniform slurry; Step 3: The slurry obtained in Step 2 is vacuum filtered or hot-pressed and sintered to obtain a base film; Step 4: Perform laser perforation on the basement membrane obtained in Step 3 to form through or non-through channels on the basement membrane.

2. The preparation method according to claim 1, characterized in that, In step 4, before laser drilling, a precursor material containing doped elements is first coated on the surface of the base film. During laser treatment, the laser penetrates the precursor material and forms a channel on the surface of the base film, while the doped elements in the precursor material are introduced into the channel wall. After the treatment is completed, the residual precursor material is removed.

3. The preparation method according to claim 2, characterized in that, The sintering process is carried out at a temperature of 130-160 ℃ for 20-60 min.

4. The preparation method according to claim 2 or 3, characterized in that, The precursor material is a polymer film or powder coating containing nitrogen, sulfur, or phosphorus.

5. The preparation method according to claim 4, characterized in that, The precursor material is a polyimide film, urea coating, melamine coating, dicyandiamide coating, polyacrylonitrile film, thiourea coating, or ammonium phosphate coating.

6. The preparation method according to claim 1, characterized in that, In step 1, the preparation method of oxidized multi-walled carbon nanotubes is as follows: multi-walled carbon nanotubes are dispersed in nitric acid solution and oxidized by reflux heating under oil bath conditions for 6-24 hours and heating temperature of 100-140 ℃.

7. The preparation method according to claim 1, characterized in that, In the slurry of step 2, based on the total mass of oxidized multi-walled carbon nanotubes, carbon nanofibers and polyvinylidene fluoride, the mass fraction of polyvinylidene fluoride is 5%-20%; The mass fraction of oxidized multi-walled carbon nanotubes is 70-85%. The mass fraction of carbon nanofibers is 5-20%.

8. The preparation method according to claim 1, characterized in that, In step 4, the parameters for laser drilling are: laser power 5-11 W, scanning speed 50-250 mm / s, number of scans 1-2, and pattern spacing 0.5-2 mm.

9. The preparation method according to claim 1, characterized in that, In step 2, the solvent of the slurry is water, and the total solids content of the slurry is 0.3-1 mg / mL.

10. The application of the water management membrane prepared by the method for preparing a water management membrane for an electrochemical hydrogen compressor according to claim 1 in an electrochemical hydrogen compressor, characterized in that, The water management membrane is used to assemble on the anode side of the electrochemical hydrogen compressor, and is disposed between the anode gas diffusion layer and the proton exchange membrane.

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