An intelligent gas diffusion layer with reversible deformation response function and a preparation method and application thereof

Abstract

This invention discloses a smart gas diffusion layer with reversible deformation response, its preparation method, and its application. The gas diffusion layer includes a conductive substrate and a microporous layer disposed on the conductive substrate. A smart responsive material is composited in the microporous layer and / or the conductive substrate. The smart responsive material is selected from at least one of shape memory polymers, thermosensitive hydrogels, or humidity-responsive hydrogels, and has the characteristic of reversibly changing volume with changes in temperature and / or humidity. Under high temperature and low humidity conditions, the smart responsive material shrinks, reducing porosity and increasing hydrophobicity, thus achieving water retention; under low temperature and high humidity conditions, the smart responsive material expands, increasing porosity and increasing hydrophilicity, thus achieving water drainage. This invention also provides its preparation method and its application in dynamically controlling water management in proton exchange membrane fuel cells. This smart gas diffusion layer achieves adaptive water management under all operating conditions, significantly improving the voltage stability and durability of the fuel cell.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, specifically to a smart gas diffusion layer (GDL) for proton exchange membrane fuel cells (PEMFC), and more particularly to a gas diffusion layer with reversible deformation response that can adaptively adjust the pore structure and surface wettability according to changes in internal temperature and humidity of the cell, as well as its preparation method and application. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is a highly efficient and clean power generation device that directly converts chemical energy into electrical energy. One of its core components is the gas diffusion layer (GDL). Located between the flow field plate and the catalyst layer, the GDL primarily performs three functions: electron conduction, reactant gas diffusion, and product water removal. An ideal GDL needs to achieve dynamic water balance under different operating conditions: it must prevent the membrane electrode from decreasing its proton conductivity due to water shortage, while also avoiding the accumulation of liquid water that clogs the pores and hinders reactant gas transport.

[0003] Currently, commercially available gas diffusion layers (GDLs) typically use hydrophobically treated carbon fiber paper or carbon fiber cloth as the supporting substrate, with a micro-porous layer (MPL) containing polytetrafluoroethylene (PTFE) and conductive carbon black coated on its surface. To improve water management performance, researchers have proposed various structural optimization strategies. For example, CN102456891B discloses a gas diffusion layer with a gradient pore structure. By controlling the spraying pressure, the microporous layer components are distributed in a concentration gradient along the thickness direction, forming a transition pore layer between the macroporous support layer and the microporous layer. This structure exhibits good permeability and water retention in low-humidity or alkaline fuel cells. However, such gradient pore structures remain fixed after fabrication, and their physical parameters such as pore distribution and wettability cannot adaptively adjust to dynamic changes in temperature, humidity, or current density during battery operation.

[0004] Similarly, some researchers have proposed using a layered coating process to construct multilayer microporous structures from conductive carbon black, multi-walled carbon nanotubes, and graphite sheets, utilizing the intrinsic pore size differences of the different carbon materials to achieve a gradient transition from small to large pore size. Experiments show that this gradient microporous layer can improve the battery's output stability under high current densities. However, this approach is still a static design; once each layer solidifies, its porosity characteristics are locked, making it unable to respond to fluctuations in actual operating conditions.

[0005] Furthermore, studies have verified the comprehensive advantages of bilayer gradient MPLs over homogeneous MPLs in terms of air permeability, breakthrough pressure, and conductivity, and pointed out that they help alleviate flooding problems under high power conditions. Nevertheless, such structures are essentially still pre-defined optimizations, lacking the ability to sense and respond to environmental variables.

[0006] In particular, research on smart materials in the field of fuel cells is still in its early stages, and there is a lack of precise design for the function of the gas diffusion layer. A key scientific question is how to enable the physical properties of the gas diffusion layer (GDL), such as porosity and wettability, to be autonomously and reversibly adjusted according to the actual operating conditions such as temperature and humidity inside the cell. Ideally, smart responsive materials should be able to respond individually or synergistically to changes in the operating temperature or water concentration inside the cell, depending on their specific type. For example, thermotropic materials mainly respond to temperature signals, while humidity-sensitive materials mainly respond to humidity changes, thereby achieving dynamic and precise control of water management strategies.

[0007] In summary, while existing technologies have improved the mass transfer and drainage performance of GDLs to some extent through gradient pore structures and multi-scale carbon material combinations, their physicochemical properties remain fixed after manufacturing, representing a static and passive water management strategy. Faced with the demands of fuel cells under complex dynamic conditions such as start-up, variable loads, and high / low humidity, such GDLs struggle to balance the conflicting goals of water retention and drainage, becoming a key bottleneck restricting the dynamic response capability, low-temperature start-up performance, and long-term durability of PEMFCs. Summary of the Invention

[0008] The purpose of this invention is to overcome the technical defects of existing gas diffusion layers, such as fixed structure, passive water management capabilities, and inability to adapt to the dynamic operating conditions of fuel cells, and to provide an intelligent gas diffusion layer with reversible deformation response function, its preparation method, and its application.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A smart gas diffusion layer with reversible deformation response function includes a conductive substrate (2) and a microporous layer (3) disposed on the conductive substrate (2), wherein the microporous layer (3) and / or the conductive substrate (2) are composited with a smart response material; the smart response material is selected from at least one of shape memory polymer, thermosensitive hydrogel or humidity-responsive hydrogel; the smart response material has the property of reversibly changing volume with temperature and / or humidity.

[0011] Furthermore, the shape memory polymer is a thermotropic shape memory polymer with a shape transition temperature of 60°C to 85°C.

[0012] Furthermore, the thermosensitive hydrogel is poly(N-isopropylacrylamide) or its derivative, and its lower critical dissolution temperature is 30 ℃ to 35 ℃.

[0013] Furthermore, the smart response material is dispersed in the microporous layer (3) in the form of microspheres, nanoparticles or fibers, and the particle size of the microspheres or particles is 0.5 μm to 20 μm.

[0014] Furthermore, the conductive substrate (2) is composed of carbon fiber paper or carbon fiber cloth, and the smart response material is co-woven with carbon fiber in fiber form to form a composite conductive substrate (2).

[0015] Furthermore, the microporous layer (3) comprises the following components: conductive carbon material, accounting for 70-90 wt% of the total mass of the microporous layer (3); the smart response material, accounting for 1-20 wt% of the total mass of the microporous layer (3); and fluoropolymer binder, accounting for 5-10 wt% of the total mass of the microporous layer (3).

[0016] Furthermore, when the internal temperature of the fuel cell is higher than the response threshold of the smart response material, the smart response material is in a contracted state, the porosity of the gas diffusion layer is 30-45%, and the contact angle is 90-120°; when the temperature is lower than the response threshold, the smart response material is in an expanded state, the porosity of the gas diffusion layer is 45-60%, and the contact angle is 30-60°.

[0017] The present invention also provides a method for preparing the above-mentioned intelligent gas diffusion layer, comprising the following steps: S1, mixing the precursor or preform of the intelligent response material with conductive carbon material, pore-forming agent and binder to prepare a uniform slurry; S2, coating the slurry onto the surface of the conductive substrate (2); S3, curing the slurry by heat treatment, ultraviolet curing or solvent evaporation, and forming the intelligent response material into a three-dimensional network structure with reversible response capability, thereby obtaining the microporous layer (3).

[0018] Furthermore, when the smart responsive material is shape memory polymer microspheres, it also includes a programming process after curing: heating the coated substrate to a temperature higher than the shape transition temperature, applying a pressure of 0.1-0.5 MPa to deform the microspheres into a temporary expanded shape, and then cooling and solidifying them.

[0019] The present invention also provides a membrane electrode, comprising a proton exchange membrane (5), an anode catalyst layer and a cathode catalyst layer (4) respectively disposed on both sides of the proton exchange membrane (5), and the aforementioned smart gas diffusion layer disposed on the outside of the anode catalyst layer and / or the cathode catalyst layer (4).

[0020] The present invention also provides a proton exchange membrane fuel cell comprising the above-described membrane electrode.

[0021] The present invention also provides the application of the above-mentioned intelligent gas diffusion layer in proton exchange membrane fuel cells for dynamic water management.

[0022] The intelligent gas diffusion layer provided by this invention has the following beneficial effects: By composite intelligent responsive materials in the microporous layer and / or conductive substrate, the gas diffusion layer is transformed from a static structure into a dynamic functional component. It can automatically and reversibly adjust the pore structure and surface wettability according to the internal temperature and / or humidity signals of the battery. Under low humidity conditions, it shrinks to retain water to prevent the proton exchange membrane from drying out, and under high humidity conditions, it expands to drain water to prevent the electrodes from being flooded. This significantly broadens the efficient and stable operating window of the fuel cell and improves the performance, start-up speed and durability under varying operating conditions. At the same time, since the gas diffusion layer itself has self-adjusting capabilities, it can reduce the dependence on external humidification and thermal management systems, which helps to simplify the structure of the fuel cell system and reduce costs. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the layered structure of the intelligent gas diffusion layer provided in an embodiment of the present invention.

[0024] In the figure: 1. Flow field plate; 2. Conductive substrate; 3. Microporous layer; 4. Catalytic layer; 5. Proton exchange membrane. Detailed Implementation

[0025] To make the technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the scope of protection of the present invention.

[0026] like Figure 1 As shown, the intelligent gas diffusion layer provided by this invention includes, from bottom to top, a flow field plate 1, a conductive substrate 2, a microporous layer 3, a catalyst layer 4, and a proton exchange membrane 5. The conductive substrate 2 is selected from carbon fiber paper or carbon fiber cloth, with a thickness of 100-300 μm and a porosity of 60%-80%, and is hydrophobically treated (e.g., impregnated with PTFE, content 5-30 wt%). The microporous layer 3 is coated on the side of the conductive substrate 2 facing the catalyst layer 4, with a thickness of 20-100 μm, and is composed of conductive carbon material, intelligent responsive material, and a fluoropolymer binder. The conductive carbon material is selected from one or more of acetylene black, Vulcan XC-72 carbon black, graphite powder, multi-walled carbon nanotubes, or graphene, accounting for 70-90 wt% of the total mass of the microporous layer 3. The smart responsive material is selected from at least one of thermotropic shape memory polymer microspheres, thermosensitive poly(N-isopropylacrylamide) hydrogel microspheres, or humidity-responsive polyacrylic acid hydrogels, accounting for 1-20 wt% of the total mass of the microporous layer 3, preferably 5-15 wt%. The binder is a fluoropolymer emulsion, preferably a polytetrafluoroethylene emulsion, with a solid content of 5-10 wt%. The solvent is an alcohol / water mixture (such as isopropanol:water = 7:3, v / v) or N-methylpyrrolidone, used to adjust the rheological properties of the slurry.

[0027] The smart responsive material is uniformly dispersed in the microporous layer 3 in the form of microspheres with a particle size of 0.5-20 μm. When a shape memory polymer is used, its permanent shape is a contracted state, and its temporary shape is an expanded state, which is fixed in the initial structure of the microporous layer 3 through a programming process. When poly(N-isopropylacrylamide) is used, its lower critical solution temperature is 30-35℃. Below the lower critical solution temperature, it absorbs water and swells to become hydrophilic, and above the lower critical solution temperature, it dehydrates and collapses to become hydrophobic.

[0028] The reversible response mechanism of the intelligent gas diffusion layer is as follows: When the fuel cell is under high temperature and low humidity conditions (e.g., 70-85℃, anode / cathode relative humidity <40%), if a shape memory polymer is used, when the ambient temperature reaches or exceeds the shape transition temperature, the shape memory polymer microspheres recover from the expanded temporary shape to the contracted permanent shape, resulting in a reduction in local pore volume, pore size, and tortuosity. Simultaneously, the surface hydrophobicity is enhanced, effectively suppressing excessive water vapor loss through the gas diffusion layer and maintaining sufficient hydration of the proton exchange membrane 5. If poly(N-isopropylacrylamide) is used, when the temperature is above the lower critical dissolution temperature, the hydrogel segments change from hydrophilic to hydrophobic, undergoing a volume phase change and shrinking, similarly reducing porosity and enhancing hydrophobicity, thus achieving water retention. When the fuel cell is under low temperature and high humidity or high current density conditions, the intelligent response material absorbs water and expands, increasing porosity, expanding the average pore size, and enhancing hydrophilicity. This promotes the discharge of liquid water from the catalyst layer 4 towards the flow field plate 1, preventing the three-phase interface from being blocked by liquid water and alleviating flooding. The process is completely reversible, and the response time is in the range of seconds to minutes, allowing for real-time matching of changes in battery operating conditions.

[0029] Example 1: Smart Gas Diffusion Layer Based on Thermotropic Shape Memory Polymer Microspheres

[0030] (1) Material preparation: The conductive substrate 2 is Toray TGP-H-060 carbon paper (thickness 190 μm, porosity 78%); the shape memory polymer microspheres are thermotropic polyurethane-based shape memory polymers with a shape transition temperature of 75 ℃ and an average particle size of 5 μm; the conductive carbon black is Vulcan XC-72; the binder is 60 wt% PTFE emulsion; the pore-forming agent is ammonium bicarbonate powder with an average particle size of 5-10 μm; the solvent is isopropanol:deionized water with a volume ratio of 7:3.

[0031] (2) Slurry preparation: shape memory polymer microspheres (10 g), Vulcan XC-72 (85 g), PTFE emulsion (corresponding to a solid content of 5 g), and ammonium bicarbonate pore-forming agent (8.5 g, the amount of which is 10 wt% of the mass of conductive carbon black) were added to 200 g of solvent, ultrasonically dispersed for 30 min, and then ball-milled for 2 h to obtain a uniform slurry with a solid content of about 20 wt%.

[0032] (3) Coating, programming and curing process:

[0033] (a) The slurry was applied to the surface of PTFE-hydrophobically treated carbon paper (PTFE content 20 wt%) with a doctor blade gap of 80 μm and dried at room temperature for 4 h to allow most of the solvent to evaporate and form a pre-cured coating.

[0034] (b) The dried sample was then placed in a thermocompression apparatus and heated to 85 °C (a temperature higher than the shape transition temperature of the SMP microspheres). It was held at a pressure of 0.3 MPa for 10 minutes. Under these conditions, the SMP microspheres softened upon heating and were compressed and deformed under external force, forming a pre-defined expanded temporary shape. Subsequently, the sample was cooled to room temperature (below Ttrans) while maintaining pressure, freezing the molecular chain segment movement of the SMP microspheres and thus fixing the expanded temporary shape.

[0035] (c) The programmed sample was then heat-treated at 350 °C for 30 min. This process is crucial for forming the final microporous layer structure and realizing the intelligent response function. The specific mechanism is as follows: 1) Morphological changes of SMP microspheres during sintering: In the initial stage of heating in the sintering furnace, when the ambient temperature exceeds the Ttrans (75 °C) of SMP, the SMP microspheres programmed to be in an expanded state begin to activate due to their shape memory effect, tending to recover to their intrinsic contracted state permanent shape. At this time, the microspheres will undergo a certain degree of volume shrinkage and morphological change. 2) Final morphological state of SMP microspheres after sintering: After sintering, the SMP microspheres do not recover to their completely free contracted dense state, but are frozen in a constrained intermediate morphology between the programmed expanded state and the intrinsic contracted state. 3) Mechanical locking mechanism of PTFE network: The core of achieving the above morphology lies in the synchronous curing process of PTFE. At the same time as the SMP microspheres begin to shrink, the PTFE emulsion melts, flows, and gradually encapsulates the SMP microspheres, then fibroses and forms a strong, continuous three-dimensional network skeleton. After cooling and solidification, this rigid PTFE network provides strong spatial constraint and mechanical locking for the internal SMP microspheres, effectively inhibiting further shrinkage of the SMP microspheres and stabilizing their morphology near the expanded state. Therefore, after sintering, the SMP microspheres exhibit a pre-set expanded state mechanically locked by the PTFE network at room temperature. This is the initial stable structure of the intelligent gas diffusion layer at the normal operating temperature of the fuel cell (usually lower than the Ttrans of SMP). 4) The pore-forming agent ammonium bicarbonate decomposes upon heating to generate ammonia, carbon dioxide, and water vapor (NH4HCO3→NH3↑+CO2↑+H2O↑). After the gas escapes, it generates uniformly distributed micron-sized channels in the microporous layer, thereby increasing the initial porosity and gas diffusion channels, forming a stable porous structure.

[0036] (4) Performance testing: The obtained gas diffusion layer was used on the cathode side to assemble a single cell (active area 5 cm²). The test conditions are as follows: Condition A (dry heat): 70℃, H2 / Air, anode / cathode humidity 50% RH, back pressure 28 psig. Condition B (wet cooling high load): 60℃, cathode 100% RH, current density 0.2→2.0 A / cm² step load.

[0037] Results: Under operating condition A, the current density at 0.8 V reached 1.35 A / cm², a 12% improvement compared to Comparative Example 1. Under operating condition B, the voltage decayed by only 8 mV after 30 min at 2.0 A / cm², while Comparative Example 1 showed a decay of 25 mV. Electrochemical impedance spectroscopy showed high-frequency resistance fluctuations of less than 3%, indicating stable membrane hydration.

[0038] Example 2: Smart Gas Diffusion Layer Based on PNIPAM Thermosensitive Hydrogel Microspheres

[0039] (1) Material preparation:

[0040] The smart responsive material is thermosensitive poly(N-isopropylacrylamide) PNIPAM microspheres with an average particle size of 3 μm. To ensure thermosensitivity, these PNIPAM microspheres are not subjected to any high-temperature carbonization treatment; the conductive carbon material uses a composite conductive agent of highly conductive carbon nanotubes and carbon black to construct a highly conductive network, compensating for the non-conductive nature of the PNIPAM microspheres. Specifically, the composition is as follows: multi-walled carbon nanotubes with a purity >95%, a length of 10-20 μm, a diameter of 8-15 nm, and a mass percentage of 20-30% are physically mixed with Vulcan XC-72 carbon black with a mass percentage of 70-80%; the binder is a low-temperature curable polyvinylidene fluoride-hexafluoroacrylic acid copolymer (PVDF-HFP) emulsion with a solid content of 20 wt%, which can form a film and provide adhesion at temperatures below 100°C, avoiding damage to the temperature sensitivity of PNIPAM at high temperatures; the solvent is a mixture of N-methylpyrrolidone (NMP) and deionized water in a volume ratio of 7:3, used to disperse PNIPAM microspheres and composite conductive agents; the conductive substrate is Toray TGP-H-060 carbon paper with a thickness of 190 μm, which is impregnated with a PTFE emulsion with a content of 20 wt%.

[0041] (2) Slurry preparation

[0042] The mass ratio of PNIPAM microspheres, composite conductive agent (MWCNTs / XC-72), and PVDF-HFP was 8:87:5. Each component was accurately weighed. The PNIPAM microspheres, composite conductive agent, and PVDF-HFP emulsion were added to a mixed solvent and emulsified at 5000 rpm for 10 min, followed by ultrasonic treatment for 1 h to obtain a uniform and stable slurry. This slurry was then coated onto a pre-treated carbon paper surface using a doctor blade with a gap of 70 μm, and pre-leveled at room temperature for 10 min. The coated sample was placed in an 80 °C oven and dried for 4 h to completely remove the solvent and allow the PVDF-HFP polymer chains to fully fuse and form a film. To further improve the mechanical strength and dimensional stability of the microporous layer, the sample was annealed at 120 °C for 2 hours under vacuum (this temperature is far below the thermal decomposition initiation temperature of PNIPAM, ensuring the complete preservation of its thermosensitive chemical structure).

[0043] (3) Verification and testing methods for temperature-sensitive function

[0044] To confirm that the temperature-sensitive function of the PNIPAM microspheres is retained after the low-temperature process, the prepared smart gas diffusion layer sample was characterized as follows:

[0045] Contact angle testing: The seated drop method was used on a contact angle measuring instrument equipped with a precision temperature control stage. The sample was placed on the temperature control stage, and after the temperature stabilized, 5 μL of deionized water was added using a microsyringe. Ten seconds after the droplet contacted the surface, the left and right contact angles were measured and the average value was taken. At least 5 points were measured at different locations for each sample, and the results are given in the form of mean ± standard deviation.

[0046] Test results: At 30 °C (below the LCST of PNIPAM), the contact angle of the sample surface was (45±3)°, exhibiting hydrophilicity; at 40 °C (above the LCST of PNIPAM), the contact angle of the sample surface increased to (105±4)°, exhibiting hydrophobicity. This change in contact angle showed good reversibility during heating and cooling cycles, confirming that PNIPAM microspheres still possess significant temperature-sensitive wettability regulation function in microporous layers prepared by low-temperature processes.

[0047] (4) Performance testing of proton exchange membrane fuel cells

[0048] The prepared gas diffusion layer was used for testing on the cathode side of a single cell (active area 5 cm²). Low-temperature start-up performance: Start-up was performed at 0 °C, followed by heating to 60 °C. Thanks to the hydrophilic expansion state of the PNIPAM microporous layer at low temperatures, which facilitates product water drainage and avoids catalyst layer flooding and channel ice blockage, the time required for the battery voltage to reach 0.6 V was shortened by approximately 35% compared to Comparative Example 1 (commercial GDL). High-humidity performance: Polarization curves were tested under saturated humidification conditions with a battery temperature of 60 °C and a cathode inlet gas relative humidity of 100%. Thanks to the hydrophobic contraction state of the PNIPAM microporous layer at high temperatures, which optimizes the gas transport channels, the maximum power density reached 1.28 W / cm², an improvement of approximately 9.4% compared to Comparative Example 1. Dynamic response and durability: After variable load cycling tests (current density changing stepwise between 0.5 A / cm² and 1.8 A / cm², 100 cycles), the battery performance retention rate was higher than 94%, demonstrating its excellent dynamic water management capability and structural stability.

[0049] Example 3: Shape memory polymer and PNIPAM composite dual-response smart gas diffusion layer

[0050] (1) Design concept: combining high-temperature water retention (shape memory polymer) and low-temperature drainage (poly(N-isopropylacrylamide)) dual mechanisms.

[0051] (2) Formulation: Shape memory polymer microspheres (5 g) + poly(N-isopropylacrylamide) microspheres (5 g) + carbon black (80 g) + PTFE (5 g) + solvent.

[0052] (3) Preparation: First program the shape memory polymer (85℃, 0.3 MPa), then sinter and solidify.

[0053] (4) Results: It exhibits excellent stability over a wide temperature range (40–80℃). After 100 cycles of variable load (0.5–1.8 A / cm²), the performance retention rate is >95%. After 500 h of durability testing, the voltage decay rate is <5%, which is significantly better than that of a single-response system.

[0054] Porosity testing methods and results

[0055] To verify the function of the intelligent gas diffusion layer with reversible adjustable pore structure of the present invention and to support the limitation on the porosity range in the claims, the porosity of the samples prepared in Examples 1-3 above was tested.

[0056] 1. Test Method: Porosity was measured using mercury porosimetry. The gas diffusion layer sample (approximately 1 cm²) was equilibrated in a constant temperature and humidity chamber at a set temperature for 2 hours to allow the smart response material to reach the corresponding equilibrium state (expanded or contracted state). Subsequently, the sample was rapidly transferred to the constant temperature sample cell of the mercury porosimeter, and the test was completed at the appropriate temperature. The porosity of the sample was measured at temperatures below the smart response material's response threshold (corresponding to the expanded state) and above the response threshold (corresponding to the contracted state).

[0057] 2. Test Results

[0058] (1) Example 1 (based on shape memory polymer microspheres): The expanded state was tested at 60 °C (below the shape transition temperature of 75 °C), and the contracted state was tested at 85 °C (above the shape transition temperature). The test results showed that the porosity of the expanded state (60 °C) was 52±2%, and the porosity of the contracted state (85 °C) was 38±2%.

[0059] Example 2 (based on PNIPAM thermosensitive hydrogel microspheres): The expanded state was tested at 30 °C (below the lower critical solution temperature ~32 °C), and the contracted state was tested at 40 °C (above the lower critical solution temperature). Test results: The porosity of the expanded state (30 °C) was 48±3%, and the porosity of the contracted state (40 °C) was 35±2%.

[0060] Example 3 (Shape Memory Polymer and PNIPAM Composite): Tests were conducted at 40 °C (above the LCST of PNIPAM but below the Ttrans of SMP, where PNIPAM shrinks and SMP is in a programmed expansion state) and 70 °C (above the response thresholds of both, where both PNIPAM and SMP are in a shrinking state). Test results: The porosity at 40 °C was 50 ± 2%, reflecting the combined effect of PNIPAM shrinkage and SMP expansion. The porosity at 70 °C was 33 ± 2%, reflecting the superimposed effect of the shrinkage of both materials.

[0061] 3. Conclusion

[0062] The porosity test data above fully demonstrates that the intelligent gas diffusion layer prepared in this invention can reversibly and significantly adjust its porosity within the range defined in claim 7 according to temperature changes. This dynamic adjustment characteristic of the structure is the fundamental reason for its ability to achieve adaptive water management and improve fuel cell performance.

[0063] Comparative Example 1: Commercial gas diffusion layer (Toray TGP-H-060 + standard microporous layer)

[0064] The microporous layer is composed of Vulcan XC-72 + PTFE (1:1), with a coating amount of 1.6 mg / cm². No smart response materials are present. Under the same testing conditions, the current density at 0.8 V in dry heat is only 1.21 A / cm²; under high humidity conditions (2.0 A / cm²), significant voltage oscillations occur after 10 minutes; the maximum power density is 1.17 W / cm².

[0065] Comparative Example 2: Gradient Pore Structure Gas Diffusion Layer

[0066] A gradient microporous layer (with inner fine pores of approximately 40 nm and outer coarse pores of approximately 200 nm) was prepared using a three-layer spraying method, but no responsive material was found. Although its performance was slightly better than Comparative Example 1 (maximum power 1.20 W / cm²) under steady-state high humidity, the voltage fluctuated drastically under variable load or alternating wet and dry conditions, making dynamic self-adaptation impossible.

[0067] Performance Comparison Summary Table (Cathode Side Application, 70℃, H2 / Air)

[0068]

[0069] As shown in the table above, Examples 1-3 containing smart responsive materials significantly outperformed Comparative Examples 1 and 2 without smart responsive materials in all performance indicators, especially in voltage decay and variable load cycle retention under high humidity and high current conditions. This fully demonstrates the effectiveness of smart responsive materials in imparting dynamic adaptive water management capabilities to the gas diffusion layer. Among them, Example 3 (a dual-response system of shape memory polymer and poly(N-isopropylacrylamide) composite) showed the best performance, possessing the dual advantages of high-temperature water retention and low-temperature drainage.

[0070] The foregoing descriptions have outlined some exemplary embodiments of the present invention. It is understood that these embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. All other embodiments obtained by those skilled in the art based on the foregoing embodiments without inventive effort fall within the scope of protection claimed by the present invention.

Claims

1. A smart gas diffusion layer with reversible deformation response function, characterized in that, It includes a conductive substrate (2) and a microporous layer (3) disposed on the conductive substrate (2), wherein the microporous layer (3) and / or the conductive substrate (2) are composited with a smart responsive material; the smart responsive material is selected from at least one of shape memory polymer, thermosensitive hydrogel or humidity responsive hydrogel; the smart responsive material has the property of reversibly changing volume with temperature and / or humidity.

2. The intelligent gas diffusion layer according to claim 1, characterized in that, The shape memory polymer is a thermotropic shape memory polymer with a shape transition temperature of 60 ℃ to 85 ℃.

3. The intelligent gas diffusion layer according to claim 1, characterized in that, The thermosensitive hydrogel is poly(N-isopropylacrylamide) or its derivative, and its lower critical dissolution temperature is 30 ℃ to 35 ℃.

4. The intelligent gas diffusion layer according to claim 1, characterized in that, The smart response material is dispersed in the microporous layer (3) in the form of microspheres, nanoparticles or fibers, and the particle size of the microspheres or particles is from 0.5 μm to 20 μm.

5. The intelligent gas diffusion layer according to claim 1, characterized in that, The conductive substrate (2) is made of carbon fiber paper or carbon fiber cloth, and the smart response material is woven together with carbon fiber in the form of fibers to form a composite conductive substrate (2).

6. The intelligent gas diffusion layer according to claim 1, characterized in that, The microporous layer (3) comprises the following components: conductive carbon material, accounting for 70-90 wt% of the total mass of the microporous layer (3); the smart response material, accounting for 1-20 wt% of the total mass of the microporous layer (3); and fluoropolymer binder, accounting for 5-10 wt% of the total mass of the microporous layer (3).

7. The intelligent gas diffusion layer according to claim 1, characterized in that, When the internal temperature of the fuel cell is higher than the response threshold of the smart response material, the smart response material is in a contracted state, the porosity of the gas diffusion layer is 30-45%, and the contact angle is 90-120°; when the temperature is lower than the response threshold, the smart response material is in an expanded state, the porosity of the gas diffusion layer is 45%-60%, and the contact angle is 30%-60°.

8. A method for preparing a smart gas diffusion layer as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Mix the precursor or preform of the smart response material with conductive carbon material, pore-forming agent and binder to prepare a uniform slurry; S2. Coat the slurry onto the surface of the conductive substrate (2); S3. Cure the slurry by heat treatment, ultraviolet curing or solvent evaporation, and make the smart response material form a three-dimensional network structure with reversible response capability, thereby obtaining the microporous layer (3).

9. The preparation method according to claim 8, characterized in that, When the smart response material is shape memory polymer microspheres, the process also includes programming after curing: heating the coated substrate to a temperature higher than the shape transition temperature, applying a pressure of 0.1-0.5 MPa to deform the microspheres into a temporary expanded shape, and then cooling and solidifying them.

10. A membrane electrode, characterized in that, It includes a proton exchange membrane (5), an anode catalyst layer and a cathode catalyst layer (4) respectively disposed on both sides of the proton exchange membrane (5), and a smart gas diffusion layer as described in any one of claims 1 to 7 disposed on the outside of the anode catalyst layer and / or the cathode catalyst layer (4).

11. A proton exchange membrane fuel cell, characterized in that, It includes the membrane electrode as described in claim 10.

12. The application of the intelligent gas diffusion layer as described in any one of claims 1 to 7 in the dynamic control of water management in a proton exchange membrane fuel cell.

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