Gas diffusion layer assembly for a fuel cell and method of selecting

Abstract

This invention provides a gas diffusion layer assembly and selection method for a fuel cell. The gas diffusion layer assembly includes a rigid gas diffusion layer for the cathode and a flexible gas diffusion layer for the anode. In the fuel cell stack assembly state, the porosity of the rigid gas diffusion layer exhibits abrupt changes along its thickness direction. The porosity of the region between the first side and the abrupt interface is greater than the porosity of the region between the second side and the abrupt interface, and the porosity change on both sides of the abrupt interface accounts for more than 80% of the total porosity change of the rigid gas diffusion layer along its thickness direction. The porosity of the flexible gas diffusion layer decreases continuously and uniformly from the third side to the fourth side along its thickness direction. This invention employs a differentiated gas diffusion layer design for the anode and cathode, solving four core problems: membrane water loss, anode water blockage, low stack density, and tolerance absorption.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and more specifically, to a gas diffusion layer assembly for a fuel cell and a selection method thereof. Background Technology

[0002] As a highly efficient and clean energy conversion device, fuel cells have broad application prospects in the field of new energy. The gas diffusion layer, as one of the core components of fuel cells, plays a key role in gas transmission, water management, electronic conduction and mechanical support. Its performance directly determines the output efficiency, stability and service life of fuel cells.

[0003] As fuel cell technology develops towards higher temperatures, longer lifespans, and adaptability to various operating conditions, the selection and design of existing gas diffusion layers and component configurations are gradually revealing numerous technical bottlenecks, making it difficult to meet the needs of practical applications.

[0004] First, membrane dehydration is a significant issue under high-temperature conditions: Current fuel cells are trending towards higher operating temperatures, leading to increased cooling water outlet temperatures and a faster rate of liquid water evaporation inside the cell. Since the outlet pressure is lower than the inlet pressure, water evaporation at the outlet is more intense, making the proton exchange membranes at the cathode outlet and anode inlet areas prone to dehydration and drying. The proton conductivity of the proton exchange membrane depends on its wettability; membrane dehydration significantly reduces conductivity, and in severe cases, can cause membrane rupture, drastically shortening its lifespan.

[0005] Second, anodic water shut-off and catalyst corrosion under low current density conditions: at less than 0.2 A / cm² 2 In low-current-density idling conditions, the hydrogen intake is positively correlated with the current density, resulting in a significant reduction in hydrogen supply. Because the reverse diffusion of water from the cathode to the anode exceeds the electroosmotic drag of water from the anode to the cathode, water accumulates on the anode side, causing blockage. This blockage hinders hydrogen from entering the gas diffusion layer, leading to "hydrogen starvation." Consequently, the fuel cell is forced to consume carbon in the catalyst layer during power generation, causing catalyst corrosion and failure, thus affecting the reliability of the battery operation.

[0006] Third, uneven air intake distribution in the fuel cell stack leads to the "low individual cell" problem: Fuel cell stacks are typically composed of hundreds of tightly assembled individual cells, and the uniformity of air intake distribution directly affects the overall performance of the stack. Because air viscosity is greater than hydrogen, the flow resistance at the cathode air end is more significantly affected by the individual cell structure. Existing gas diffusion layers lack targeted structural design, resulting in inconsistent air intake for each individual cell. Some individual cells experience low output power due to insufficient air intake (i.e., "low individual cell" power), severely limiting the overall power generation efficiency of the stack.

[0007] Fourth, insufficient capacity to absorb thermal expansion and contraction tolerances: Single-cell plates are mostly made of metal. During fuel cell start-up, shutdown, and operation, temperature changes cause thermal expansion and contraction of the plates, with cumulative dimensional changes reaching up to 80mm (for a 400-cell stack, the average change per plate is approximately 0.2mm). Existing stacks have fixed structural dimensions after assembly, and the gas diffusion layer lacks elastic adjustment capabilities, failing to absorb these dimensional changes. This results in uneven stress on individual cells, easily leading to component deformation or poor contact, affecting the stack's structural stability and lifespan.

[0008] In summary, the selection and design of gas diffusion layers in existing technologies mostly adopt a single structural type, without considering the differences in working environment and performance requirements of fuel cell anode and cathode. They lack systematic component configuration schemes and scientific selection methods, making it difficult to simultaneously solve the multi-dimensional problems mentioned above, such as high-temperature membrane water loss, low-current water blockage, uneven air intake, and thermal expansion and contraction tolerance absorption. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is that existing fuel cells use a single-structure gas diffusion layer and lack differentiated selection design for anode and cathode, which easily leads to problems such as membrane water loss under high-temperature conditions, anode water blockage and catalyst corrosion under low current density, uneven gas intake in the stack causing single low temperature and insufficient absorption of thermal expansion and contraction tolerances.

[0010] To address the above problems, a first aspect of the present invention provides a gas diffusion layer assembly for a fuel cell, comprising:

[0011] A rigid gas diffusion layer for the cathode has a first side and a second side on both sides along its thickness direction. The first side is in contact with the cathode catalyst layer, and the second side is in contact with the cathode flow channel.

[0012] A flexible gas diffusion layer for the anode has a third side and a fourth side on both sides along its thickness direction, the third side being in contact with the anode catalyst layer and the fourth side being in contact with the anode flow channel.

[0013] In the assembled state of the fuel cell stack, the porosity of the rigid gas diffusion layer has an abrupt interface along its thickness direction. The porosity of the region between the first side and the abrupt interface is greater than that between the second side and the abrupt interface. Moreover, the porosity change on both sides of the abrupt interface accounts for more than 80% of the total porosity change of the rigid gas diffusion layer along its thickness direction. The porosity of the flexible gas diffusion layer decreases continuously and uniformly from the third side to the fourth side along its thickness direction.

[0014] This invention employs a differentiated gas diffusion layer design for the anode and cathode. The cathode uses a rigid gas diffusion layer, which, in its assembled state, exhibits abrupt interface changes that significantly reduce the porosity on the flow channel side. This prevents liquid water from evaporating into the flow channel under high-temperature conditions at the cathode, thus avoiding dehydration and drying of the proton exchange membrane. The anode uses a flexible gas diffusion layer, which, in its assembled state, has a continuous and uniform porosity distribution, providing a smooth discharge channel for liquid water and avoiding water blockage issues at low current densities. Simultaneously, the rigid diffusion layer is less susceptible to pressure encroachment on the flow channel, ensuring uniform gas distribution in the fuel cell stack. The elastic properties of the flexible diffusion layer provide structural space to absorb tolerance changes caused by thermal expansion and contraction of the metal plates, thereby solving four core problems: membrane dehydration, anode water blockage, low current density in the fuel cell stack, and tolerance absorption.

[0015] In a preferred or optional embodiment, the porosity of the first side of the rigid gas diffusion layer is 0.70-0.80, the porosity of the second side is 0.40-0.50, and the porosity of the flexible gas diffusion layer continuously varies from 0.7-0.8 to 0.45-0.55 from the third side to the fourth side.

[0016] By precisely limiting the porosity range of the anode and cathode gas diffusion layers, the porosity variation of the rigid gas diffusion layer is ensured to meet the cathode water retention requirements. This not only preserves sufficient channels for oxygen transport but also retains liquid water through the low porosity of the flow channel side. The porosity gradient of the flexible gas diffusion layer is matched with the anode drainage logic to avoid hydrogen escape due to excessive porosity or poor drainage due to excessively low porosity. This precise porosity control enables efficient and reliable water-gas balance management.

[0017] In a preferred or optional embodiment, the tortuosity of the first side of the rigid gas diffusion layer is 2.5-3.5, the tortuosity of the second side is 4.0-5.0, and it increases abruptly near the second side. The tortuosity of the flexible gas diffusion layer changes continuously from 2.0-3.0 to 3.5-4.5 from the third side to the fourth side.

[0018] The abrupt increase in the tortuosity of the rigid gas diffusion layer and the continuous change in the tortuosity of the flexible diffusion layer are adapted to the mass transfer requirements of the anode and cathode respectively: the high tortuosity on the cathode flow channel side further enhances the liquid water retention capacity, and the abrupt change in porosity strengthens the water retention effect, avoiding the decrease in proton conductivity caused by membrane water loss; the continuously changing tortuosity on the anode can reduce the liquid water migration resistance, while ensuring hydrogen transport efficiency, thus balancing mass transfer efficiency and reaction stability.

[0019] In a preferred or optional embodiment, the normal permeability of the rigid gas diffusion layer is 10-15 × 10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 30-70×10 -12 m 3 / (Pa·s), the normal permeability of the flexible gas diffusion layer is 3000-5000×10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 60-90×10 -12 m 3 / (Pa·s).

[0020] By limiting the normal and in-plane permeability parameters of the anode and cathode gas diffusion layers, a precise match between gas transport and water management is achieved: the low normal permeability of the cathode rigid diffusion layer can suppress water vapor escape and realize its water retention function; the high normal permeability of the anode flexible diffusion layer accelerates the discharge of liquid water; the limitation of in-plane permeability ensures the uniform distribution of reactant gases in the electrode plane, balances the requirements of lateral gas diffusion and anti-cross-ridge mass transfer, and helps to avoid the "single low" phenomenon caused by uneven gas intake.

[0021] In a preferred or optional embodiment, the rigid gas diffusion layer has a flexural modulus of 6.0-8.0 GPa and an elastic recovery of 7.0-10.0 μm under a pressure change of 1.7 MPa to 0.6 MPa; the flexible gas diffusion layer has a flexural modulus of 9.0-11.0 GPa and an elastic recovery of 10.0-13.0 μm under a pressure change of 1.7 MPa to 0.6 MPa.

[0022] The mechanical properties of the rigid gas diffusion layer ensure its structural stability after assembly under pressure, preventing excessive deformation that could encroach on the flow channel and maintain unobstructed air intake. The high elastic recovery capability of the flexible gas diffusion layer can effectively absorb the dimensional changes caused by the thermal expansion and contraction of the metal plates during the operation of the fuel cell stack, alleviate the problem of uneven stress on a single cell, and extend the service life of the fuel cell stack.

[0023] In a preferred or optional embodiment, the density of the rigid gas diffusion layer is 420-450 mg / cm³. 3 The thickness is 150-170 μm; the density of the flexible gas diffusion layer is 360-380 mg / cm³. 3 The thickness is 140-160μm.

[0024] The density and thickness parameters of the rigid gas diffusion layer are matched with its rigid structural design to ensure the formation of a stable porosity abrupt change interface after pressure, providing structural support for cathode water retention and gas intake uniformity; the lightweight and adaptable thickness design of the flexible gas diffusion layer ensures both flexibility and elastic recovery capability, while adapting to the overall assembly space requirements of the fuel cell stack.

[0025] In a preferred or optional embodiment, the electronic resistance of the rigid gas diffusion layer is 5.5-9.0 mΩ·cm. 2Under conditions of 80% relative humidity, the oxygen diffusion rate of the rigid gas diffusion layer is 16-22 mm / s; under conditions of 165% relative humidity, the oxygen diffusion rate of the rigid gas diffusion layer is 11-15 mm / s; the electronic resistance of the flexible gas diffusion layer is 8.0-9.5 mΩ·cm. 2 Under a relative humidity of 80%, the oxygen diffusion rate of the flexible gas diffusion layer is 18-24 mm / s, and under a relative humidity of 165%, the oxygen diffusion rate of the flexible gas diffusion layer is 12-16 mm / s.

[0026] By limiting the electronic resistance and oxygen diffusion rate parameters of the anode and cathode gas diffusion layers, the electrical conduction and mass transfer efficiency are balanced: the low resistance of the rigid diffusion layer reduces electronic conduction loss, and the oxygen diffusion rate under different humidity conditions is adapted to the oxygen demand of the cathode, avoiding the decrease in reaction efficiency caused by insufficient mass transfer; the resistance parameters of the flexible diffusion layer are adapted to the hydrogen oxidation reaction of the anode, and the higher oxygen diffusion rate can help alleviate the local oxygen deficiency problem. At the same time, combined with its drainage characteristics, it further reduces the risk of catalyst layer corrosion.

[0027] A second aspect of the present invention provides a method for selecting a gas diffusion layer assembly for a fuel cell, comprising the following steps:

[0028] Determine the target operating parameters of the fuel cell, including high temperature operating conditions and / or low current density idling operating conditions.

[0029] Based on the target operating parameters, a rigid gas diffusion layer is selected for the cathode, and a flexible gas diffusion layer is selected for the anode.

[0030] Based on the tortuosity and compressibility distribution model, the liquid water saturation distribution along the thickness direction of the gas diffusion layer is calculated using the following formula to verify the selection effect:

[0031]

[0032] in, Represents current density, Represents the water purification transfer coefficient. Represents the molar mass of water. Represents the velocity of the flowing fluid. Represents Faraday's constant. Represents surface tension. Represents the contact angle between the liquid and solid phases. Represents absolute penetration rate. Represents porosity. Represents the coordinate position along the thickness direction of the gas diffusion layer. This represents the saturation level of liquid water.

[0033] This invention provides a scientific selection method that first determines the operating conditions and then matches rigid / flexible properties, and then uses a specific water distribution calculation formula for quantitative verification. This method specifically addresses the problems of membrane water loss and water blockage at low current densities under high-temperature conditions, avoiding performance shortcomings caused by blind selection. Through formula simulation, the water distribution state can be predicted in advance, ensuring the effectiveness of cathode water retention and anode drainage. It systematically guides designers to select the optimal gas diffusion layer combination for specific application scenarios, thereby ensuring that the fuel cell system can achieve reliable, efficient and long-life operation under various complex operating conditions.

[0034] In a preferred or optional embodiment, the high-temperature operating condition is an operating condition where the fuel cell coolant outlet temperature is greater than or equal to 95°C, and the low current density idling condition is an operating condition where the fuel cell output current density is less than or equal to 0.2 A / cm². 2 Operating conditions.

[0035] By clearly defining the specific thresholds for high-temperature operating conditions and low-current-density idling operating conditions, the selection method becomes more targeted, focusing on the key operating conditions in which fuel cells are most prone to membrane dehydration and blockage, ensuring that the selected gas diffusion layer can fully play its role in water retention and drainage in core operating scenarios, and improving the stability of the fuel cell stack under extreme operating conditions.

[0036] In a preferred or optional embodiment, in the tortuosity and compression ratio distribution model, tortuosity With compression ratio Satisfying the relation: .

[0037] By establishing a correlation formula between tortuosity and compressibility, key theoretical support is provided for the calculation model. The establishment of this universal relationship enables simulation predictions to better reflect the mass transfer characteristics of different gas diffusion layers under real pressure conditions, greatly improving the accuracy and reliability of selection verification.

[0038] In summary, this invention systematically solves the four core challenges that fuel cells have long faced by proposing a differentiated design that uses a rigid gas diffusion layer for the cathode and a flexible gas diffusion layer for the anode. The beneficial effects are summarized as follows:

[0039] (1) The abrupt change in porosity of the cathode rigid gas diffusion layer after the stack assembly under pressure effectively prevents the water generated under high temperature conditions from evaporating too quickly to the flow channel side, keeping the liquid water near the proton exchange membrane, fundamentally avoiding the risk of decreased proton conductivity and rupture caused by membrane dehydration and drying; at the same time, the continuous and uniformly decreasing pore structure of the anode flexible gas diffusion layer provides a smooth discharge channel for the liquid water that diffuses back to the anode under low current density idling conditions, effectively eliminating the problem of hydrogen transmission obstruction caused by anode water blockage, thereby preventing catalyst layer corrosion caused by hydrogen starvation.

[0040] (2) Due to its high flexural modulus, the rigid gas diffusion layer on the cathode side can maintain structural stability after being compressed, avoiding excessive deformation that encroaches on the flow channel space, thereby ensuring the consistency of air intake for hundreds of single cells in the stack and effectively solving the problem of low single-cell pressure caused by uneven flow resistance; while the excellent elastic recovery capability of the flexible gas diffusion layer on the anode side can actively absorb the dimensional changes caused by thermal expansion and contraction of metal plates during the start-up, shutdown and operation of the stack, alleviate mechanical stress, and significantly improve the structural reliability and lifespan of the stack under long-term thermal cycling.

[0041] (3) By limiting the combination of parameters such as low normal permeability and high tortuosity on the cathode side and high normal permeability and gradual tortuosity on the anode side, not only is the mass transfer path of oxygen and hydrogen optimized, but the phase change and migration behavior of water is also more precisely controlled. This collaborative design based on multi-dimensional parameters such as porosity, permeability and mechanical properties enables the technical solution to adapt to a wide range of operating conditions from high temperature to idle speed.

[0042] (4) It provides a complete and quantifiable selection methodology. Its established model of the relationship between tortuosity and compressibility and the calculation formula of liquid water saturation distribution elevate the selection process from empirical judgment to theoretical prediction, enabling designers to accurately match the optimal combination of anode and cathode gas diffusion layers for specific application scenarios, thereby achieving a leapfrog improvement in the overall performance of fuel cell systems in terms of reliability, efficiency and lifespan. Attached Figure Description

[0043] Figure 1 This is a flowchart of the gas diffusion layer selection method in a specific embodiment of the present invention.

[0044] Figure 2 This is a water distribution diagram along the thickness direction of the cathode rigid gas diffusion layer in Embodiment 1 of the present invention.

[0045] Figure 3 This is a water distribution diagram along the thickness direction of the anode flexible gas diffusion layer in Embodiment 1 of the present invention.

[0046] Figure 4 This is a water distribution diagram along the thickness direction of the cathode rigid gas diffusion layer in Embodiment 2 of the present invention.

[0047] Figure 5 This is a water distribution diagram along the thickness direction of the anode flexible gas diffusion layer in Embodiment 2 of the present invention. Detailed Implementation

[0048] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0049] The present invention provides a gas diffusion layer assembly and selection method for a fuel cell, with the core objective of solving four major problems: high-temperature membrane water loss, low current density anode water blockage, uneven gas intake in the fuel cell stack, and thermal expansion and contraction tolerance absorption. Figure 1 As shown, the selection method specifically includes the following steps:

[0050] S1. Operating Condition Analysis and Parameter Setting

[0051] Based on the actual operating requirements of the fuel cell, target operating parameters are set. In a specific embodiment, the target operating parameters include high-temperature operating conditions and low-current-density idling operating conditions. The high-temperature operating condition is defined as a coolant outlet temperature ≥ 95°C, and the low-current-density idling operating condition is defined as an output current density ≤ 0.2A / cm². 2 .

[0052] S2. Diffusion Layer Selection and Parameter Definition

[0053] Based on the target operating parameters, a core selection strategy is established: a rigid gas diffusion layer is selected for the cathode, and a flexible gas diffusion layer is selected for the anode. Furthermore, the microstructures of the rigid and flexible gas diffusion layers in the fuel cell stack assembly state are parameterized to address the correlation between theoretical selection and actual physical conditions. Unless otherwise specified, the "fuel cell stack assembly state" referred to in this paper means that the gas diffusion layer is under continuous pressure within the range of 1.0-2.0 MPa under the action of endplate preload and operating pressure.

[0054] In a specific embodiment, for the cathode rigid gas diffusion layer, its structure under pressure is defined as a two-region model with abrupt interface. The two sides of the cathode rigid gas diffusion layer along the thickness direction are a first side contacting the cathode catalyst layer and a second side contacting the cathode flow channel, respectively. Near the first side, the porosity is set to 0.70-0.80, and the tortuosity to 2.5-3.5; near the crushed area of ​​the second side, the porosity is set to 0.40-0.50, and the tortuosity to 4.0-5.0. The porosity change on both sides of the abrupt interface is limited to more than 80% of the total. For the anode flexible gas diffusion layer, its structure is defined as a single-region model with continuously and uniformly decreasing porosity. The porosity continuously changes from 0.7-0.8 on the third side to 0.45-0.55 on the fourth side. The term "continuous change" here means that the rate of change of porosity along the thickness direction is basically constant, and the tortuosity correspondingly changes continuously from 2.0-3.0 to 3.5-4.5.

[0055] S3. Water Distribution Simulation Calculation and Selection Verification

[0056] Based on tortuosity With compression ratio Related formula: , construct a distribution model.

[0057] Based on the above tortuosity and compressibility distribution models, the formula for calculating the liquid water saturation distribution is obtained:

[0058]

[0059] in, Represents current density, Represents the water purification transfer coefficient. Represents the molar mass of water. Represents the velocity of the flowing fluid. Represents Faraday's constant. Represents surface tension. Represents the contact angle between the liquid and solid phases. Represents absolute penetration rate. Represents porosity. Represents the coordinate position along the thickness direction of the gas diffusion layer. This represents the saturation level of liquid water.

[0060] The simulation was conducted using the MATLAB platform, simultaneously verifying the mass transfer effect of water retention on the cathode side and smooth migration of water from the anode side to the flow channel side. If the simulation results showed that the membrane water loss rate exceeded the standard, there was a risk of water blockage, or the air intake uniformity was insufficient, the porosity gradient, tortuosity value, or permeability parameter were adjusted, and the calculation was iterated again until all performance indicators met the preset targets, and the final parameter combination was output.

[0061] After successful simulation verification, the macroscopic performance parameters of the final selected gas diffusion layer component are confirmed to ensure its mechanical and mass transfer functions. In a specific embodiment, under fuel cell stack assembly conditions, the cathode rigid gas diffusion layer must meet the following requirement: normal permeability 10⁻¹⁵ × 10⁻¹⁰. -6 m / (Pa·s), in-plane air permeability is 30-70×10 -12 m 3 / (Pa·s); flexural modulus is 6.0-8.0 GPa, elastic recovery under pressure changes from 1.7 MPa to 0.6 MPa is 7.0-10.0 μm; density is 420-450 mg / cm³. 3 The thickness is 150-170 μm; the electronic resistance is 5.5-9.0 mΩ·cm. 2 Under conditions of 80% relative humidity, the oxygen diffusion rate is 16-22 mm / s; under conditions of 165% relative humidity, the oxygen diffusion rate is 11-15 mm / s. The anode flexible gas diffusion layer must meet the following requirement: normal air permeability 3000-5000 × 10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 60-90×10 -12 m 3 / (Pa·s); flexural modulus is 9.0-11.0 GPa, elastic recovery under pressure changes from 1.7 MPa to 0.6 MPa is 10.0-13.0 μm; density is 360-380 mg / cm³. 3 The thickness is 140-160 μm; the electronic resistance is 8.0-9.5 mΩ·cm. 2 Under conditions of 80% relative humidity, the oxygen diffusion rate is 18-24 mm / s; under conditions of 165% relative humidity, the oxygen diffusion rate is 12-16 mm / s. These parameters collectively ensure the synergistic optimization of the gas diffusion layer component in terms of microstructure, mass transport, mechanical properties, and electrochemical characteristics.

[0062] The gas diffusion layer assembly obtained by the above selection method has a rigid cathode side and a flexible anode side. The rigid cathode gas diffusion layer forms a porosity abrupt change interface after assembly and pressure. Its low porosity and high tortuosity on the flow channel side effectively prevent water vapor escape at high temperatures, retaining liquid water near the membrane electrode for self-humidification. The continuous porosity gradient of the flexible anode gas diffusion layer establishes an efficient drainage path for liquid water. Combined with its high elastic recovery, it solves the anode water blockage problem under low current density and absorbs thermal stress from the fuel cell stack. The high structural stability of the rigid cathode layer ensures consistent gas intake across the fuel cell stack, avoiding single-low current phenomena; the elastic properties of the flexible anode layer solve the tolerance absorption problem.

[0063] The specific implementation of this invention, through a systematic selection process, parameterized microstructure models, and quantitative water distribution simulation verification, achieves a leap from empirical selection to scientific design of gas diffusion layer components. This method precisely matches the distinct water and gas management requirements of the anode and cathode, fundamentally and collaboratively solving four core problems: membrane dehydration, anode water blockage, low fuel cell stack performance, and thermal expansion and contraction. It provides core component selection support for improving the performance, durability, and reliability of fuel cells under complex operating conditions such as high power density, high temperature, and variable load.

[0064] The technical effects of the present invention will be illustrated below with reference to specific embodiments.

[0065] Example 1

[0066] The gas diffusion layer assembly in this embodiment is designed for the continuous operation of fuel cell systems under high load and high temperature environments. Specifically, the target operating conditions are defined as: a stable coolant outlet temperature of 105°C and an output current density of 1.0 A / cm². 2 Under these conditions, the core issues to be addressed are high-temperature water loss in the membrane electrode, insufficient efficiency in anode-side water management, and coordination of internal thermal stress in the fuel cell stack.

[0067] Based on the above operating conditions, the following selection strategy is adopted: a rigid gas diffusion layer is selected for the cathode to enhance water retention, and a flexible gas diffusion layer is selected for the anode to optimize drainage. Specific parameter definitions are as follows:

[0068] Cathode Rigid Gas Diffusion Layer: In the assembled state of the fuel cell stack, it forms a significant abrupt interface along its thickness. The first side near the cathode catalyst layer has a porosity of 0.78 and a tortuosity of 3.0; the second side near the cathode flow channel, due to compression and breakage, has a porosity that decreases to 0.43 and a tortuosity that increases to 4.8. The normal permeability is 12.5 × 10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 45×10 -12 m 3 / (Pa·s); flexural modulus is 7.2 GPa, elastic recovery under pressure changes from 1.7 MPa to 0.6 MPa is 8.8 μm; density is 430 mg / cm³. 3 The thickness is 160 μm; the electronic resistance is 7.0 mΩ·cm. 2 The oxygen diffusion rate is 19 mm / s at a relative humidity of 80% and 13 mm / s at a relative humidity of 165%.

[0069] Anode flexible gas diffusion layer: In the assembled state of the fuel cell stack, its porosity continuously and uniformly decreases from 0.80 on the third side in contact with the anode catalyst layer to 0.52 on the fourth side in contact with the anode flow channel, with the tortuosity correspondingly changing from 2.8 to 4.2. The normal permeability is 4200 × 10⁻⁶.-6 m / (Pa·s), in-plane air permeability is 75×10 -12 m 3 / (Pa·s); flexural modulus is 9.8 GPa, elastic recovery under pressure changes from 1.7 MPa to 0.6 MPa is 12.0 μm; density is 370 mg / cm³. 3 The thickness is 150 μm; the electronic resistance is 8.5 mΩ·cm. 2 Under a relative humidity of 80%, the oxygen diffusion rate is 22 mm / s, and under a relative humidity of 165%, the oxygen diffusion rate is 14 mm / s.

[0070] To verify the effectiveness of the selection, a water distribution simulation was performed using the MATLAB platform. The battery was divided into 15 segments along the flow channel, from Seg1 to Seg15, and the liquid water saturation distribution calculation formula was applied:

[0071]

[0072] The key parameter is set as follows: water purification transfer coefficient. =0.5, contact angle =110°, porosity With absolute penetration Assign values ​​to partitions according to the above definition.

[0073] The simulation results for the cathode rigid gas diffusion layer and the anode flexible gas diffusion layer are as follows: Figure 2 and Figure 3 As shown in the figure, the horizontal axis represents the coordinate position along the thickness direction of the gas diffusion layer, ranging from 0 to 1. 0 represents the side of the gas diffusion layer in contact with the catalyst layer, and 1 represents the side of the gas diffusion layer in contact with the flow channel. The vertical axis represents the liquid water saturation. It can be seen that the liquid water saturation of the rigid gas diffusion layer at the cathode is significantly higher than that at the flow channel side (x>0.7) in the region near the catalyst layer (x<0.7), confirming that the rigid gas diffusion layer successfully retains water near the membrane, preventing high-temperature evaporation and drying. The flexible gas diffusion layer at the anode drains smoothly near the catalyst layer, with low water saturation. Near the flow channel side, the porosity decreases, and more water accumulates on one side of the flow channel.

[0074] This embodiment, through systematic selection and simulation verification, confirms the effectiveness of the gas diffusion layer component under high-temperature conditions: the cathode rigid gas diffusion layer, through its low permeability and high tortuosity structure, successfully retains water on the membrane electrode side, avoiding performance degradation at high temperatures.

[0075] Example 2

[0076] The gas diffusion layer assembly in this embodiment is designed for fuel cell systems operating under low load and idling conditions. Specifically, the target operating conditions are defined as: a stable coolant outlet temperature of 95°C and an output current density of 0.2 A / cm². 2 Under these conditions, the key challenge is to address the water blockage and hydrogen starvation issues on the anode side caused by low hydrogen flow and water back-diffusion accumulation, while simultaneously ensuring that the cathode side maintains a suitable humidity level at a moderate temperature to prevent localized membrane drying.

[0077] Based on the above operating conditions, the selection strategy is as follows: The anode side requires enhanced drainage capacity, therefore a highly permeable flexible gas diffusion layer is selected; the cathode side, operating at a relatively mild temperature, needs a balance between water retention and oxygen transport, therefore a rigid gas diffusion layer is selected. Specific parameter definitions are as follows:

[0078] Cathode Rigid Gas Diffusion Layer: In the assembled state of the fuel cell stack, a significant abrupt interface forms in its thickness direction. The first side near the cathode catalyst layer has a porosity of 0.76 and a tortuosity of 2.8; the second side near the cathode flow channel, due to compression and breakage, has a porosity that decreases to 0.46 and a tortuosity that increases to 4.3. The normal permeability is 13.5 × 10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 50×10 -12 m 3 / (Pa·s); flexural modulus is 6.5 GPa, elastic recovery under pressure changes from 1.7 MPa to 0.6 MPa is 8.0 μm; density is 435 mg / cm³. 3 The thickness is 155 μm; the electronic resistance is 7.8 mΩ·cm. 2 Under a relative humidity of 80%, the oxygen diffusion rate is 18 mm / s, and under a relative humidity of 165%, the oxygen diffusion rate is 12.5 mm / s.

[0079] Anode flexible gas diffusion layer: In the assembled state of the fuel cell stack, its porosity continuously and uniformly decreases from 0.77 on the third side in contact with the anode catalyst layer to 0.48 on the fourth side in contact with the anode flow channel, with the tortuosity correspondingly changing from 2.9 to 4.0. The normal permeability is 3800 × 10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 80×10 -12 m 3 / (Pa·s); flexural modulus is 10.5 GPa; elastic recovery under pressure changes from 1.7 MPa to 0.6 MPa is 12.5 μm; density is 365 mg / cm³. 3 The thickness is 145 μm; the electronic resistance is 8.8 mΩ·cm. 2 Under a relative humidity of 80%, the oxygen diffusion rate is 23 mm / s, and under a relative humidity of 165%, the oxygen diffusion rate is 15.5 mm / s.

[0080] To verify the effectiveness of the selected model under idling conditions, a water distribution simulation was performed using the MATLAB platform. The simulation conditions were set as follows: outlet temperature 95°C and current density 0.2 A / cm². 2 A segmented battery model (Seg1-Seg15) was adopted, and the formula for calculating the liquid water saturation distribution was substituted into it.

[0081] The simulation results for the cathode rigid gas diffusion layer and the anode flexible gas diffusion layer are as follows: Figure 4 and Figure 5 As shown, the liquid water saturation distribution of the cathode rigid gas diffusion layer is relatively balanced. Thanks to its moderate rigidity, it can form a certain resistance on the flow channel side to prevent water loss too quickly, and also ensure the effective transfer of oxygen to the catalyst layer. The liquid water saturation of the anode flexible gas diffusion layer shows an increasing curve from the catalyst layer to the flow channel, and the drainage on the catalyst layer side is smooth.

[0082] This embodiment, through systematic selection and simulation verification, confirms the effectiveness of the gas diffusion layer component under idling conditions: the high normal permeability and continuous pore gradient of the anode flexible gas diffusion layer ensure efficient drainage and prevent hydrogen starvation.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas diffusion layer assembly for a fuel cell, characterized in that, include: A rigid gas diffusion layer for the cathode has a first side and a second side on both sides along its thickness direction. The first side is in contact with the cathode catalyst layer, and the second side is in contact with the cathode flow channel. A flexible gas diffusion layer for the anode has a third side and a fourth side on both sides along its thickness direction, the third side being in contact with the anode catalyst layer and the fourth side being in contact with the anode flow channel. The porosity of the first side of the rigid gas diffusion layer is 0.70-0.80, the porosity of the second side is 0.40-0.50, and the porosity of the flexible gas diffusion layer continuously changes from 0.7-0.8 to 0.45-0.55 from the third side to the fourth side. In the assembled state of the fuel cell stack, the porosity of the rigid gas diffusion layer has an abrupt interface along its thickness direction. The porosity of the region between the first side and the abrupt interface is greater than that between the second side and the abrupt interface. Moreover, the porosity change on both sides of the abrupt interface accounts for more than 80% of the total porosity change of the rigid gas diffusion layer along its thickness direction. The porosity of the flexible gas diffusion layer decreases continuously and uniformly from the third side to the fourth side along its thickness direction.

2. The gas diffusion layer assembly of the fuel cell according to claim 1, characterized in that, The tortuosity of the first side of the rigid gas diffusion layer is 2.5-3.5, and the tortuosity of the second side is 4.0-5.0, with an abrupt increase near the second side. The tortuosity of the flexible gas diffusion layer changes continuously from 2.0-3.0 to 3.5-4.5 from the third side to the fourth side.

3. The gas diffusion layer assembly of the fuel cell according to claim 1, characterized in that, The normal permeability of the rigid gas diffusion layer is 10⁻¹⁵ × 10⁻¹⁰. -6 m / (Pa·s), in-plane air permeability is 30-70×10 -12 m 3 / (Pa·s), the normal permeability of the flexible gas diffusion layer is 3000-5000×10⁻⁶. -6 m / (Pa·s), in-plane air permeability is 60-90×10 -12 m 3 / (Pa·s).

4. The gas diffusion layer assembly of the fuel cell according to claim 1, characterized in that, The rigid gas diffusion layer has a flexural modulus of 6.0-8.0 GPa and an elastic recovery of 7.0-10.0 μm under a pressure change of 1.7 MPa to 0.6 MPa; the flexible gas diffusion layer has a flexural modulus of 9.0-11.0 GPa and an elastic recovery of 10.0-13.0 μm under a pressure change of 1.7 MPa to 0.6 MPa.

5. The gas diffusion layer assembly of the fuel cell according to claim 1, characterized in that, The density of the rigid gas diffusion layer is 420-450 mg / cm³. 3 The thickness is 150-170 μm; the density of the flexible gas diffusion layer is 360-380 mg / cm³. 3 The thickness is 140-160μm.

6. The gas diffusion layer assembly of the fuel cell according to claim 1, characterized in that, The electronic resistance of the rigid gas diffusion layer is 5.5-9.0 mΩ·cm. 2 Under conditions of 80% relative humidity, the oxygen diffusion rate of the rigid gas diffusion layer is 16-22 mm / s; under conditions of 165% relative humidity, the oxygen diffusion rate of the rigid gas diffusion layer is 11-15 mm / s; the electronic resistance of the flexible gas diffusion layer is 8.0-9.5 mΩ·cm. 2 Under a relative humidity of 80%, the oxygen diffusion rate of the flexible gas diffusion layer is 18-24 mm / s, and under a relative humidity of 165%, the oxygen diffusion rate of the flexible gas diffusion layer is 12-16 mm / s.

7. A method for selecting a gas diffusion layer assembly for a fuel cell as described in any one of claims 1-6, characterized in that, Includes the following steps: Determine the target operating parameters of the fuel cell, including high temperature operating conditions and / or low current density idling operating conditions. Based on the target operating parameters, a rigid gas diffusion layer is selected for the cathode, and a flexible gas diffusion layer is selected for the anode. The rigid gas diffusion layer has a first side that contacts the cathode catalyst layer and a second side that contacts the cathode flow channel on both sides along its thickness direction. The flexible gas diffusion layer has a third side that contacts the anode catalyst layer and a fourth side that contacts the anode flow channel on both sides along its thickness direction. In the stack assembly state, the porosity of the rigid gas diffusion layer has an abrupt interface along its thickness direction. The porosity of the region between the first side and the abrupt interface is greater than the porosity of the region between the second side and the abrupt interface. Moreover, the porosity change on both sides of the abrupt interface accounts for more than 80% of the total porosity change of the rigid gas diffusion layer along its thickness direction. The porosity of the flexible gas diffusion layer decreases continuously and uniformly from the third side to the fourth side along its thickness direction. Based on the tortuosity and compressibility distribution model, the liquid water saturation distribution along the thickness direction of the gas diffusion layer is calculated using the following formula to verify the selection effect: in, Represents current density, Represents the water purification transfer coefficient. Represents the molar mass of water. Represents the velocity of the flowing fluid. Represents Faraday's constant. Represents surface tension. Represents the contact angle between the liquid and solid phases. Represents absolute penetration rate. Represents porosity. Represents the coordinate position along the thickness direction of the gas diffusion layer. This represents the saturation level of liquid water.

8. The selection method according to claim 7, characterized in that, Among the target operating parameters, the high-temperature operating condition refers to the operating condition where the fuel cell coolant outlet temperature is greater than or equal to 95°C, and the low current density idling condition refers to the fuel cell output current density being less than or equal to 0.2 A / cm². 2 Operating conditions.

9. The selection method according to claim 7, characterized in that, In the tortuosity and compression ratio distribution model, tortuosity With compression ratio Satisfying the relation: .

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