Integral gas diffusion layer with hydrophilic and hydrophobic structure, its preparation method and application

Abstract

This invention discloses an integrated gas diffusion layer with hydrophilic and hydrophobic structures, its preparation method, and its application, belonging to the field of fuel cell technology. The integrated gas diffusion layer structure comprises a hydrophilic layer and a hydrophobic layer. The hydrophilic layer is a planar layer, and the hydrophobic layer is a hybrid layer with ridge I and groove I. There is no transition layer between the hydrophilic and hydrophobic layers. The hydrophilic layer is located between the hydrophobic layer and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer is located between the fuel cell bipolar plate and the hydrophilic layer. The integrated gas diffusion layer is prepared by sequentially coating the hydrophobic layer slurry and the hydrophilic layer slurry into a mold with ridge II and groove II, and finally demolding to obtain the final product. This integrated gas diffusion layer is used as a gas diffusion layer in proton exchange membrane fuel cells. The hydrophobic layer has a larger contact angle, which is beneficial for gas transport and the discharge of generated water. The hydrophilic layer separates water through capillary action, reducing mass transfer resistance and improving membrane electrode performance.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, its preparation method, and its application. Background Technology

[0002] The gas diffusion layer (GDL) is a crucial component of the membrane electrode assembly (MEA) in a proton exchange membrane fuel cell (PEMFC). Its performance directly affects the MEA's performance, thus influencing the overall efficiency of the fuel cell. The GDL plays several key roles in the fuel cell: first, it provides support for the catalyst layer, maintaining the stability of the electrode structure; second, it ensures the transport channels for gas, electrons, and water, providing the necessary conditions for the electrode reactions; third, it is responsible for transporting reactants, namely fuel and catalyst; and finally, it ensures good electrical conductivity between the bipolar plates and the catalyst layer. During the power generation process of the fuel cell, the hydrogen oxidation reaction at the anode produces protons and electrons. Electrons are transported to the cathode through an external circuit, while protons reach the cathode through the proton exchange membrane. At the cathode, oxygen combines with electrons and protons to form water. In this process, the GDL needs to rapidly drain the generated water to prevent flooding of the catalyst layer, thereby avoiding disruption to the continuous reaction of the fuel cell.

[0003] Currently, the development of hydrogen fuel cells largely focuses on reducing membrane electrode thickness while increasing battery power density. However, traditional gas diffusion layers are quite thick and have high manufacturing costs, making the development of an integrated gas diffusion layer of significant research value. Existing technologies, while including integrated gas diffusion layers for PEMFC membrane electrodes, suffer from the following problems: 1) This method requires first impregnating carbon fiber base paper with resin and then performing high-temperature carbonization to obtain carbonized carbon fiber paper; then preparing a microporous layer slurry and coating it onto the surface of the carbonized carbon fiber paper, followed by drying and high-temperature graphitization to obtain the integrated gas diffusion layer. This method requires first performing high-temperature carbonization on the carbon fiber base paper, then directly coating it with a microporous layer, followed by high-temperature graphitization, increasing the manufacturing cost of the gas diffusion layer and prolonging the processing time. Additionally, the added hydrophobic agent decomposes at high temperatures, resulting in poor hydrophobicity. 2) A proposed approach is to use an independent microporous layer, premixing carbon nanotubes, hydrophobic agents, and carbon materials, and then using filtration to form a film from the slurry to create an integrated gas diffusion layer. The methods, material selection, preparation processes, and final effects differ from those of this invention. 3) The gas diffusion layer near the bipolar plate needs to drain water and guide gas, so it needs to be more hydrophobic, while the side near the catalyst layer needs to be more hydrophilic to release capillary water generated during the electrochemical reaction. However, current integrated gas diffusion layers mainly focus on structural formation and ignore the changes in hydrophilicity and hydrophobicity of the diffusion layer. 4) Existing integrated gas diffusion layers generally use a substrate bonded to them due to their poor support, while the flow field structure of the bipolar plate is still retained. This results in interfacial resistance between the substrate layer and the microporous layer, which affects the mass transfer effect. 5) In terms of preparation process, the integrated gas diffusion layer is prepared by filtration and then matched with the required single cell structure by etching the flow field. The process is relatively complex and requires additional equipment costs. Summary of the Invention

[0004] In order to solve the above-mentioned technical problems, one of the objectives of this invention is to provide an integrated gas diffusion layer with a hydrophilic and hydrophobic structure having a flow field structure and a planar structure.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is: an integrated gas diffusion layer with a hydrophilic and hydrophobic structure, comprising a hydrophilic layer and a hydrophobic layer, wherein the hydrophilic layer is a planar layer, the hydrophobic layer is a hybrid layer with ridge I and groove I, there is no transition layer between the hydrophilic layer and the hydrophobic layer, the hydrophilic layer is located between the hydrophobic layer and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer is located between the fuel cell bipolar plate and the hydrophilic layer.

[0006] Furthermore, the thickness of the hydrophilic layer is 10μm-50μm, the thickness of the hydrophobic layer is 500μm-1000μm, and the ratio of the thickness of the hydrophilic layer to the thickness of the hydrophobic layer is 1:15-1:75; the width of ridge I is 200μm-500μm, and the width of groove I is 200μm-500μm.

[0007] A second objective of this invention is to provide a method for preparing an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, the method comprising the following steps:

[0008] Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry separately;

[0009] Step 2: Apply the hydrophobic slurry to the mold with ridge II and groove II, control the coating thickness and fill the groove II with the hydrophobic slurry, and then dry it; after cooling, remove the hydrophobic slurry on the upper part of ridge II and the upper part of groove II to obtain a hydrophobic layer with ridge I and groove I.

[0010] Step 3: Apply the hydrophilic slurry onto the hydrophobic layer treated in Step 2, control the coating thickness, and dry it to obtain the hydrophilic layer;

[0011] Step 4: Place the sample processed in Step 3, along with the mold, into a high-temperature furnace for high-temperature heat treatment, and then cool.

[0012] Step 5: Demold the sample after step 4 to obtain the integrated gas diffusion layer with hydrophilic and hydrophobic structure.

[0013] Furthermore, the hydrophilic layer slurry is made by mixing a hydrophobic agent, a solvent, a dispersant and conductive carbon black; by mass ratio, hydrophobic agent: solvent: dispersant: conductive carbon black = (10-15): (100-150): (30-60): (6-12).

[0014] Furthermore, the hydrophobic slurry is made by mixing a hydrophobic agent, a solvent, a dispersant and conductive carbon black, with the following mass ratio: hydrophobic agent: solvent: dispersant: conductive carbon black = (25-30): (100-150): (30-60): (6-12).

[0015] Furthermore, the hydrophobic agent includes one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and ethylene-tetrafluoroethylene copolymer (ETFE);

[0016] The solvent is deionized water;

[0017] The dispersant is a surfactant;

[0018] The conductive carbon black includes one or more of Cabot XC carbon black, acetylene black, graphite, carbon nanotubes, and carbon nanofibers.

[0019] Furthermore, the surfactant is a nonionic surfactant; the nonionic surfactant includes polyethylene glycol or alkylolamide; the polyethylene glycol includes polyethylene glycol phenyl ether.

[0020] Furthermore, in step 2, the drying temperature is 80℃-120℃ and the drying time is 5min-10min; in step 3, the drying temperature is 80℃-120℃ and the drying time is 5min-10min.

[0021] Furthermore, in step 4, the high-temperature heat treatment temperature is 350℃-400℃, and the time is 1h-2h.

[0022] A third objective of this invention is to provide an application of an integrated diffusion layer with a hydrophilic and hydrophobic structure, which is used in the gas diffusion layer of a proton exchange membrane fuel cell.

[0023] The beneficial effects of this invention are:

[0024] The integrated gas diffusion layer provided by this invention forms a flow field structure by fabricating a hydrophobic layer with ridges I and grooves I, resulting in a larger contact angle that is more conducive to gas transport and the discharge of generated water. Meanwhile, the hydrophilic layer in contact with the catalyst layer more easily separates the gaseous or liquid water generated in the catalyst layer through capillary action, thereby reducing mass transfer resistance and improving membrane electrode performance. In the integrated gas diffusion layer prepared by this invention, the hydrophobic and hydrophilic layers have clearly distinct functions: the hydrophobic layer is used for gas supply and liquid water discharge, while the hydrophilic layer is used for the precipitation of generated water. Because this invention contains a low amount of hydrophobic agent and lacks the interfacial resistance of hydrophobic carbon paper and microporous layers, the entire diffusion layer has a low internal resistance, resulting in higher output performance of the fuel cell membrane electrode. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure provided in an embodiment of the present invention.

[0027] Figure 2 This is provided by the embodiments of the present invention. Figure 1 A magnified view of the main scene.

[0028] Figure 3 This is a schematic diagram of the glass plate mold structure provided in an embodiment of the present invention.

[0029] Figure 4 This is provided by the embodiments of the present invention. Figure 3 A magnified view of the main scene.

[0030] Figure 5 These are polarization curve performance diagrams provided in Embodiments 1-3 and Comparative Example 1 of the present invention; wherein, A is the polarization curve performance diagram of Embodiment 1, B is the polarization curve performance diagram of Embodiment 2, C is the polarization curve performance diagram of Embodiment 3, and D is the polarization curve performance diagram of Comparative Example 1. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] In a first aspect, the present invention provides an integral gas diffusion layer having a hydrophilic and hydrophobic structure, the integral gas diffusion layer comprising a hydrophilic layer and a hydrophobic layer, the hydrophilic layer being a planar layer, the hydrophobic layer being a hybrid layer with ridges I and grooves I, there being no transition layer between the hydrophilic layer and the hydrophobic layer, the hydrophilic layer being located between the hydrophobic layer and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer being located between the fuel cell bipolar plate and the hydrophilic layer.

[0033] This invention prepares an integrated gas diffusion layer with hydrophilic and hydrophobic structures. The hydrophilic layer is made into a planar structure, which directly contacts the catalyst layer during practical applications, effectively absorbing generated water and reducing interfacial resistance. The hydrophobic layer is made into a hybrid layer with ridges I and grooves I to form a flow field structure, which has a larger contact angle and is more conducive to gas transport and the discharge of generated water. In actual use, the side containing the flow field structure will directly contact the electrode plate, while the hydrophilic layer structure contacts the catalyst layer of the membrane electrode, replacing the flow field structure in the original bipolar plate. This results in a lower cross-sectional resistance, lower ohmic loss, and better performance during fuel cell assembly. There is no transition layer between the hydrophilic and hydrophobic layers, thus eliminating the interfacial resistance of the hydrophobic carbon paper and microporous layer. The entire diffusion layer has a low internal resistance, which also leads to higher output performance of the fuel cell membrane electrode.

[0034] In some feasible implementations, the thickness of the hydrophilic layer is 10μm-50μm, the thickness of the hydrophobic layer is 500μm-1000μm, and the ratio of hydrophilic layer thickness to hydrophobic layer thickness is 1:15-1:75; the width of ridge I is 200μm-500μm, and the width of groove I is 200μm-500μm.

[0035] Specifically, a hydrophilic layer thickness of 10μm-50μm facilitates the precipitation of generated water and reduces the bulk resistance. During fuel cell operation, there are low-electrical-density and high-electrical-density operating conditions. In typical low-electrical-density conditions, insufficient water generation occurs, and the proton exchange membrane requires a certain level of humidity to improve proton conductivity. Therefore, the diffusion layer also needs a certain water retention capacity. A thinner hydrophilic layer can easily result in low water content, high internal resistance, and low fuel cell performance under low electrical-density conditions. Conversely, an excessively thick hydrophilic layer, under high electrical-density conditions, causes water to concentrate within the microporous layer, making it difficult to drain and resulting in mass transfer difficulties and flooding. Regarding the hydrophobic layer, this invention is an integrated gas diffusion layer, replacing the traditional electrode and diffusion layer structure. The hydrophobic layer acts as the flow field structure, thus requiring a certain thickness and strength. If the hydrophobic layer is too thin, it is prone to poor sealing during encapsulation, requiring excessive assembly force for encapsulation. However, excessive assembly pressure will cause severe compression of the gas diffusion layer, collapse of the pore structure, and failure of the diffusion layer's gas guiding and drainage functions. On the other hand, an excessively thick hydrophobic layer will greatly increase the mass transfer resistance and the bulk resistance of the gas diffusion layer, increasing the ohmic loss and mass transfer loss during fuel cell operation, resulting in poor battery performance. Therefore, the preferred hydrophobic layer thickness in this invention is 500μm-1000μm. Correspondingly, the width range of ridge I and trench I affects the drainage and reaction zone characteristics. Based on the verified electrode structure, although excessively thin ridge I and trench I may seem to increase the effective reaction zone, the demand for reaction gas increases under high electrical density, especially for the cathode, which requires a large amount of gas. Excessively narrow width will increase the gas mass transfer resistance and easily cause the diffusion layer structure to collapse. On the other hand, excessively high width, although it increases the flow field intensity, also affects the gas intake and output performance. Therefore, the width of ridge I is preferably 200μm-500μm and the width of trench I are preferably 200μm-500μm.

[0036] A second aspect of the present invention provides a method for preparing an integral gas diffusion layer having a hydrophilic-hydrophobic structure, the method comprising the following steps:

[0037] Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry separately;

[0038] Step 2: Apply the hydrophobic slurry to the mold with ridge II and groove II, control the coating thickness and fill the groove II with hydrophobic slurry, and then dry it; after cooling, remove the hydrophobic slurry on the top of ridge II and groove II of the mold to obtain a hydrophobic layer with ridge I and groove I.

[0039] Step 3: Apply the hydrophilic layer slurry onto the hydrophobic layer treated in Step 2, control the coating thickness, and dry it to obtain the hydrophilic layer;

[0040] Step 4: Place the sample processed in Step 3, along with the mold, into a high-temperature furnace for high-temperature heat treatment, and then cool.

[0041] Step 5: Demold the sample after step 4 to obtain an integrated gas diffusion layer with a hydrophilic and hydrophobic structure.

[0042] Unlike traditional integrated gas diffusion layers, which are prepared by filtration to obtain a microporous layer and then matched with conventional hydrophobic carbon paper for application, the integrated gas diffusion layer prepared in this invention uses a special mold with ridges II and grooves II. Two slurries are sequentially coated onto the pre-designed mold. Grooves II of the mold correspond to the ridges I of the hydrophobic layer, and ridges II correspond to the grooves I of the hydrophobic layer. Finally, after sintering to obtain a certain degree of support, the mold is demolded. The entire preparation process is simpler and has lower production costs. Furthermore, the integrated gas diffusion layer prepared in this invention, with its flow field structure, eliminates the need for a separate flow field structure for the bipolar plate. During bipolar plate processing, there is no need to consider coating peeling due to pre-coating and subsequent stamping, which affects durability, nor is there a need to consider coating unevenness due to pre-stamping and subsequent coating, which affects conductivity. This results in lower bipolar plate production costs and promotes the industrialization of fuel cells.

[0043] In some feasible embodiments, in step 1, the hydrophilic layer slurry is prepared by mixing a hydrophobic agent, a solvent, a dispersant, and conductive carbon black; by mass ratio, the hydrophobic agent: solvent: dispersant: conductive carbon black = (10-15): (100-150): (30-60): (6-12). In step 1, the hydrophobic layer slurry is prepared by mixing a hydrophobic agent, a solvent, a dispersant, and conductive carbon black, by mass ratio, the hydrophobic agent: solvent: dispersant: conductive carbon black = (25-30): (100-150): (30-60): (6-12).

[0044] Specifically, the diffusion layer is mainly composed of carbon materials, which plays a role in establishing the microporous structure. The hydrophobic agent not only acts as a hydrophobic transport agent but also serves as a binder for the microporous layer. Traditional diffusion layers consist of a carbon substrate and a microporous layer; the substrate has a macroporous structure, while the microporous layer has a microporous structure. At the transition point, abrupt changes in pore size can easily occur, leading to water accumulation and significant mass transfer polarization. However, this situation does not occur with the same raw materials. Because the hydrophilic and hydrophobic layers of this invention use the same raw materials, the pore size range remains consistent in both layers, resulting in a more gradual gas transport and water vapor expulsion process without sudden performance abrupt changes.

[0045] In some feasible embodiments, the hydrophobic agent comprises one or a mixture of several of polytetrafluoroethylene, polyvinylidene fluoride, and ethylene-tetrafluoroethylene copolymer; the solvent is deionized water; the dispersant is a surfactant; the surfactant is preferably a nonionic surfactant, including polyethylene glycol or alkylolamides, most preferably polyethylene glycol phenyl ether; the conductive carbon black comprises one or a mixture of several of Cabot XC carbon black, acetylene black, graphite, carbon nanotubes, and carbon nanofibers.

[0046] Specifically, for the hydrophobic agent, one or more of polytetrafluoroethylene, polyvinylidene fluoride, and ethylene-tetrafluoroethylene copolymer are preferred. These materials possess high chemical stability and can withstand almost all strong acids, strong alkalis, strong oxidants, and organic solvents. As a commonly used hydrophobic material in the industry, it exhibits high hydrophobicity after sintering and also acts as a binder. For the solvent, since it replaces the traditional carbon substrate, the integrated gas diffusion layer of this invention requires a large amount of microporous material. This invention uses deionized water as the solvent, which, compared to the traditional ethanol-based solution, not only addresses environmental and safety concerns but also reduces production costs. Because the operating conditions of fuel cells are relatively harsh, free ions can affect the proton exchange membrane and catalyst, impacting their durability and reliability. Through experimental comparison, we found that using nonionic surfactants as dispersants helps improve the durability of the membrane electrode assembly (MEA). The most preferred dispersant is polyethylene glycol phenyl ether. For conductive carbon black, one or more of XC carbon black, acetylene black, graphite, carbon nanotubes and carbon nanofibers can be selected. Due to their high degree of graphitization, the bulk resistance of the gas diffusion layer is low. As for carbon nanotubes and carbon nanofibers, they can effectively construct large and small pore structures and improve the cracking caused by water-based slurries, thereby improving the durability of the diffusion layer.

[0047] In some feasible implementations, in step 2, the drying temperature is 80℃-120℃, and the drying time is 5 min-10 min. In step 3, the drying temperature is 80℃-120℃, and the drying time is 5 min-10 min.

[0048] The present invention performs drying in two steps because the wet thickness and dry thickness of the slurry vary depending on the solid content. The hydrophobic layer is dried first. After the hydrophobic layer shrinks, the thickness of the hydrophobic layer can be better controlled due to the influence of the mold depth. At the same time, the hydrophobic layer also plays a supporting role for the hydrophilic layer to be coated.

[0049] In some feasible implementations, in step 4, the high-temperature heat treatment temperature is 350℃-400℃ and the time is 1h-2h.

[0050] A third aspect of the present invention provides an application of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, which is applied to the gas diffusion layer of a proton exchange membrane fuel cell.

[0051] The integrated gas diffusion layer provided by this invention forms a flow field structure by fabricating a hydrophobic layer with ridges I and grooves I, resulting in a larger contact angle that is more conducive to gas transport and the discharge of generated water. Meanwhile, the hydrophilic layer in contact with the catalyst layer more easily separates the gaseous or liquid water generated in the catalyst layer through capillary action, thereby reducing mass transfer resistance. Furthermore, due to the absence of interfacial resistance from the hydrophobic carbon paper and microporous layer, the entire diffusion layer has low internal resistance, thus improving the output performance of the fuel cell membrane electrode assembly.

[0052] Example 1: An integral gas diffusion layer with a hydrophilic-hydrophobic structure

[0053] (a) Structure

[0054] like Figure 1 and Figure 2 As shown, an integrated gas diffusion layer with a hydrophilic and hydrophobic structure includes a hydrophilic layer 10 and a hydrophobic layer 20; wherein, the hydrophilic layer 10 is a planar layer, the hydrophobic layer 20 is a hybrid layer with ridges I 21 and grooves I 22, there is no transition layer between the hydrophilic layer 10 and the hydrophobic layer 20, the hydrophilic layer 10 is located between the hydrophobic layer 20 and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0055] In this embodiment, the overall thickness of the integrated gas diffusion layer is 510 μm, the thickness a of the hydrophilic layer 10 is 10 μm, the thickness b of the hydrophobic layer 20 is 500 μm, the width c of the ridge I 21 is 200 μm, and the width d of the trench I 22 is 200 μm.

[0056] (II) Preparation method

[0057] Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry

[0058] Preparation of hydrophilic layer slurry: Weigh 10g of polytetrafluoroethylene, 100g of deionized water, 30g of polyethylene glycol phenyl ether, and 6g of Cabot XC carbon black, and disperse them using a high-speed dispersion disc for 1 hour.

[0059] Preparation of hydrophobic layer slurry: Weigh 25g of polytetrafluoroethylene, 100g of deionized water, 30g of polyethylene glycol phenyl ether, and 6g of Cabot XC carbon black, and disperse them using a high-speed dispersion disc for 1 hour.

[0060] Step 2: Preparation of the hydrophobic layer

[0061] like Figure 3 and Figure 4 As shown, the glass plate mold structure has several ridges II 31 on the base plate 30, and grooves II 32 are formed between adjacent ridges II 31. The height h of the ridge II 31 is 500 μm, the width e of the ridge II is 200 μm, and the width f of the groove II 32 is 200 μm.

[0062] The glass plate mold is placed on the coating machine platform, and the hydrophobic slurry is evenly coated onto the glass plate mold. The coating thickness is controlled, and the groove II 32 is filled with the hydrophobic slurry. After coating, the glass plate mold is transferred to an oven for drying. The oven temperature is set to 80℃, and the drying time is 5-10 minutes. After drying, the mold is removed and cooled. The hydrophobic slurry on the ridge II 31 and the upper part of the groove II 32 is removed. The ridge II 31 part of the glass plate mold forms the hydrophobic groove I 22, and the groove II 32 part of the glass plate mold forms the hydrophobic ridge I 21, thus obtaining a hydrophobic layer 20 with ridge I 21 and groove I 22 on the glass plate mold.

[0063] Step 3: Preparation of the hydrophilic layer

[0064] After cooling, the glass plate mold is placed on the coating machine platform, and the hydrophilic layer slurry is evenly coated onto the surface of the glass plate mold, that is, the hydrophilic layer slurry is coated onto the hydrophobic layer 20 after step 2. The coating thickness is controlled. After coating, the glass plate mold is transferred to the oven for drying. The oven temperature is set to 80℃ and the drying time is 5min-10min.

[0065] Step 4: High-temperature treatment

[0066] The sample processed in step 3, along with the glass plate mold, was placed in a high-temperature furnace for high-temperature treatment at 350°C for 2 hours.

[0067] Step 5: Demolding

[0068] The sample processed in step 4 was demolded to obtain an integrated gas diffusion layer with a hydrophilic and hydrophobic structure.

[0069] Example 2: An integral gas diffusion layer with a hydrophilic-hydrophobic structure

[0070] (a) Structure

[0071] like Figure 1 and Figure 2 As shown, an integrated gas diffusion layer with a hydrophilic and hydrophobic structure includes a hydrophilic layer 10 and a hydrophobic layer 20; wherein, the hydrophilic layer 10 is a planar layer, the hydrophobic layer 20 is a hybrid layer with ridges I 21 and grooves I 22, there is no transition layer between the hydrophilic layer 10 and the hydrophobic layer 20, the hydrophilic layer 10 is located between the hydrophobic layer 20 and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0072] In this embodiment, the overall thickness of the integrated gas diffusion layer is 780 μm, the thickness a of the hydrophilic layer 10 is 30 μm, the thickness b of the hydrophobic layer 20 is 750 μm, the width c of the ridge I 21 is 350 μm, and the width d of the trench I 22 is 350 μm.

[0073] (II) Preparation method

[0074] Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry

[0075] Preparation of hydrophilic layer slurry: Weigh 12.5g of polytetrafluoroethylene, 125g of deionized water, 45g of polyethylene glycol phenyl ether, and 9g of Cabot XC carbon black, and disperse them using a high-speed dispersion disc for 1 hour.

[0076] Preparation of hydrophobic layer slurry: Weigh 27.5g of polytetrafluoroethylene, 125g of deionized water, 45g of polyethylene glycol phenyl ether, and 9g of Cabot XC carbon black, and disperse them using a high-speed dispersion disc for 1 hour.

[0077] Step 2: Preparation of the hydrophobic layer

[0078] like Figure 3 and Figure 4 As shown, the glass plate mold structure has several ridges II 31 on the base plate 30, and grooves II 32 are formed between adjacent ridges II 31. The height h of the ridge II 31 is 750μm, the width e of the ridge II is 350μm, and the width f of the groove II 32 is 350μm.

[0079] The glass plate mold is placed on the coating machine platform, and the hydrophobic slurry is evenly coated onto the glass plate mold. The coating thickness is controlled, and the groove II 32 is filled with the hydrophobic slurry. After coating, the glass plate mold is transferred to an oven for drying. The oven temperature is set to 80℃, and the drying time is 5-10 minutes. After drying, the mold is removed and cooled. The hydrophobic slurry on the ridge II 31 and the upper part of the groove II 32 is removed. The ridge II 31 part of the glass plate mold forms the hydrophobic groove I 22, and the groove II 32 part of the glass plate mold forms the hydrophobic ridge I 21, thus obtaining a hydrophobic layer 20 with ridge I 21 and groove I 22 on the glass plate mold.

[0080] Step 3: Preparation of the hydrophilic layer

[0081] After cooling, the glass plate mold is placed on the coating machine platform, and the hydrophilic layer slurry is evenly coated onto the surface of the glass plate mold, that is, the hydrophilic layer slurry is coated onto the hydrophobic layer 20 after step 2. The coating thickness is controlled. After coating, the glass plate mold is transferred to the oven for drying. The oven temperature is set to 80℃ and the drying time is 5min-10min.

[0082] Step 4: High-temperature treatment

[0083] The sample processed in step 3, along with the glass plate mold, was placed in a high-temperature furnace for high-temperature treatment at 350°C for 2 hours.

[0084] Step 5: Demolding

[0085] The sample processed in step 4 was demolded to obtain an integrated gas diffusion layer with a hydrophilic and hydrophobic structure.

[0086] Example 3: An integral gas diffusion layer with a hydrophilic-hydrophobic structure

[0087] (a) Structure

[0088] like Figure 1 and Figure 2 As shown, an integrated gas diffusion layer with a hydrophilic and hydrophobic structure includes a hydrophilic layer 10 and a hydrophobic layer 20; wherein, the hydrophilic layer 10 is a planar layer, the hydrophobic layer 20 is a hybrid layer with ridges I 21 and grooves I 22, there is no transition layer between the hydrophilic layer 10 and the hydrophobic layer 20, the hydrophilic layer 10 is located between the hydrophobic layer 20 and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0089] In this embodiment, the overall thickness of the integrated gas diffusion layer is 1050 μm, the thickness a of the hydrophilic layer 10 is 50 μm, the thickness b of the hydrophobic layer 20 is 1000 μm, the width c of the ridge I 21 is 500 μm, and the width d of the trench I 22 is 500 μm.

[0090] (II) Preparation method

[0091] Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry

[0092] Preparation of hydrophilic layer slurry: Weigh 15g of polytetrafluoroethylene, 150g of deionized water, 60g of polyethylene glycol phenyl ether, and 12g of Cabot XC carbon black, and disperse them using a high-speed dispersion disc for 1 hour.

[0093] Preparation of hydrophobic layer slurry: Weigh 30g of polytetrafluoroethylene, 150g of deionized water, 60g of polyethylene glycol phenyl ether, and 12g of Cabot XC carbon black, and disperse them using a high-speed dispersion disc for 1 hour.

[0094] Step 2: Preparation of the hydrophobic layer

[0095] like Figure 3 As shown, the glass plate mold structure has several ridges II 31 on the base plate 30, and grooves II 32 are formed between adjacent ridges II 31. The height h of the ridge II 31 is 1000μm, the width e of the ridge II is 500μm, and the width f of the groove II 32 is 500μm.

[0096] The glass plate mold is placed on the coating machine platform, and the hydrophobic slurry is evenly coated onto the glass plate mold. The coating thickness is controlled, and the groove II 32 is filled with the hydrophobic slurry. After coating, the glass plate mold is transferred to an oven for drying. The oven temperature is set to 80℃, and the drying time is 5-10 minutes. After drying, the mold is removed and cooled. The hydrophobic slurry on the ridge II 31 and the upper part of the groove II 32 is removed. The ridge II 31 part of the glass plate mold forms the hydrophobic groove I 22, and the groove II 32 part of the glass plate mold forms the hydrophobic ridge I 21, thus obtaining a hydrophobic layer 20 with ridge I 21 and groove I 22 on the glass plate mold.

[0097] Step 3: Preparation of the hydrophilic layer

[0098] After cooling, the glass plate mold is placed on the coating machine platform, and the hydrophilic layer slurry is evenly coated onto the surface of the glass plate mold, that is, the hydrophilic layer slurry is coated onto the hydrophobic layer 20 after step 2. The coating thickness is controlled. After coating, the glass plate mold is transferred to the oven for drying. The oven temperature is set to 80℃ and the drying time is 5min-10min.

[0099] Step 4: High-temperature treatment

[0100] The sample processed in step 3, along with the glass plate mold, was placed in a high-temperature furnace for high-temperature treatment at 350°C for 2 hours.

[0101] Step 5: Demolding

[0102] The sample processed in step 4 was demolded to obtain an integrated gas diffusion layer with a hydrophilic and hydrophobic structure.

[0103] Comparative Example 1

[0104] The traditional combination of microporous layer and carbon paper was used. 15g of polytetrafluoroethylene, 150g of deionized water, 60g of polyethylene glycol phenyl ether, and 12g of Cabot XC carbon black were weighed and dispersed in a high-speed dispersion disk for 1 hour to obtain a microporous layer slurry for later use.

[0105] Commercial carbon paper of a certain size was cut and immersed in an aqueous solution containing PTFE for 3 minutes. Then it was drained and dried at 100°C for 10 minutes. Finally, it was placed in a high-temperature furnace and sintered at 350°C for 2 hours to obtain hydrophobic carbon paper.

[0106] The prepared microporous layer slurry was coated onto the surface of carbon paper, dried at 100°C, and then subjected to high-temperature heat treatment at 350°C for 2 hours to obtain a gas diffusion layer with a thickness of 180μm.

[0107] Example 4 Performance Testing

[0108] The monolithic gas diffusion layers prepared in Examples 1, 2, and 3, and the conventional gas diffusion layer prepared in Comparative Example 1, were subjected to polarization curve performance and electrical performance experiments. The results are as follows: Figure 5 See Table 1.

[0109] Depend on Figure 5 As can be seen from Figure A, the monolithic gas diffusion layer prepared in Example 1 exhibits higher performance, with polarization curve performance at a current density of 2.5 A / cm². 2 The voltage was 0.623V.

[0110] Depend on Figure 5 As can be seen from B, the integrated gas diffusion layer prepared in Example 2, when the current density is greater than 2A / cm², 2 Subsequently, under high electrical density conditions, no severe mass transfer polarization occurred, exhibiting low mass transfer resistance and high electrochemical performance. The polarization curve performance was observed at a current density of 2.5 A / cm². 2 The voltage is 0.625V.

[0111] Depend on Figure 5As can be seen from Figure C, the monolithic gas diffusion layer prepared in Example 3 exhibits relatively smooth mass transfer with increasing current density. Even with an increase in the overall diffusion layer thickness, it still maintains low internal resistance and mass transfer resistance, resulting in high electrochemical performance. The polarization curve performance is shown at a current density of 2.5 A / cm². 2 The voltage was 0.614V.

[0112] Depend on Figure 5 As can be seen in Figure D, the traditional gas diffusion layer prepared in Comparative Example 1 has a high bulk resistance due to the PTFE hydrophobic treatment of the carbon paper. After the microporous layer forms a gas-density diffusion layer (GDL) with the carbon paper, during fuel cell assembly, the flow field of the bipolar plate comes into contact with the carbon paper, and the microporous layer comes into contact with the catalyst layer, resulting in a large interfacial resistance. Moreover, there is a structural transformation between large and small pores between the carbon paper and the microporous layer, making it easier for water generated in the reaction to accumulate, thus easily leading to flooding and a decrease in battery performance. Figure 5 As shown in Figure D, due to the presence of alternating pores between the substrate and the microporous layer, the electrical density increases with increasing electrical density above 2 A / cm. 2 Under these conditions, battery performance deteriorates significantly, mass transfer polarization is severe, and the polarization curve performance is poor at a current density of 2.5 A / cm². 2 The voltage is less than 0.5V.

[0113] Table 1. Performance comparison of the integrated gas diffusion layer in Examples 1-3 and the conventional gas diffusion layer in Comparative Example 1.

[0114]

[0115] As shown in Table 1, after adjusting the thickness of different hydrophilic and hydrophobic layers, the minimum thickness of the monolithic gas diffusion layer is 510 μm, and the maximum thickness is 1050 μm. However, since they are all made of the same material, their bulk resistivity is low, remaining at 7 mΩ·cm under 1 MPa testing conditions. 2 The resistance of the substrate material (carbon paper) after hydrophobic treatment and the interfacial resistance between the coated microporous layer and the substrate is approximately 15.3 mΩ·cm. However, for Comparative Example 1, the bulk resistance of the substrate material (carbon paper) after hydrophobic treatment and the interfacial resistance between the coated microporous layer and the substrate is 15.3 mΩ·cm under a 1 MPa test condition. 2 This represents a doubling of the performance compared to the present invention, significantly improving its ohmic loss. Secondly, the integrated diffusion layer prepared based on the present invention, because the hydrophilic and hydrophobic layers are made of the same material and there are no abrupt pores, results in better mass transfer performance of the membrane electrode under high dielectric density, at 2.5 A / cm². 2 Under operating conditions, the voltage performance can still be greater than 0.6V, which will effectively improve the ultimate power of the fuel cell. However, for traditional gas diffusion layers, due to severe mass transfer polarization, the voltage performance is limited to 2.5A / cm². 2 Under operating conditions, due to water flooding, the battery performance rapidly declines to less than 0.5V.

[0116] Example 5: Thickness Selection of an Integrated Gas Diffusion Layer with Hydrophilic / Hydrophobic Structure

[0117] (a) Structure

[0118] like Figure 1 and Figure 2 As shown, an integrated gas diffusion layer with a hydrophilic and hydrophobic structure includes a hydrophilic layer 10 and a hydrophobic layer 20; wherein, the hydrophilic layer 10 is a planar layer, the hydrophobic layer 20 is a hybrid layer with ridges I 21 and grooves I 22, there is no transition layer between the hydrophilic layer 10 and the hydrophobic layer 20, the hydrophilic layer 10 is located between the hydrophobic layer 20 and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0119] (1) Fix the thickness a of the hydrophilic layer 10 to 30 μm, adjust the thickness b of the hydrophobic layer 20 to 400 μm, 500 μm, 750 μm, 1000 μm and 1200 μm respectively, the width c of the ridge I 21 is 350 μm, and the width d of the groove I 22 is 350 μm.

[0120] (2) Fix the thickness b of the hydrophobic layer 20 to 750 μm, adjust the thickness a of the hydrophilic layer 10 to 5 μm, 10 μm, 35 μm, 50 μm and 60 μm respectively, the width c of ridge I 21 is 350 μm, and the width d of groove I 22 is 350 μm.

[0121] (II) Preparation method

[0122] Similar to Example 2, integral gas diffusion layers with different hydrophilic and hydrophobic layer thickness ratios were obtained. Performance test results are shown in Table 2.

[0123] Table 2 Performance of integrated gas diffusion layers with hydrophilic and hydrophobic layers of different thicknesses

[0124]

[0125] As shown in Table 2, when the thickness of the hydrophilic layer is kept consistent, adjusting the thickness of the hydrophobic layer will result in a greater resistance to gas flow as the hydrophobic layer controls the height of the entire flow field. This can easily lead to a gas shortage, especially when the electrical density is high, where mass transfer polarization will be more pronounced. Furthermore, the hydrophobic layer contains a significant amount of hydrophobic agent, which increases the internal resistance of the material itself. Under high electrical density, the internal resistance loss will be substantial. When the thickness of the hydrophobic layer is constant, i.e., the height of the flow field is constant, adjusting the thickness of the hydrophilic layer will produce a large amount of gaseous water during the fuel cell reaction. The gaseous water condenses into liquid water through the capillary action of the microporous layer and is then discharged from the fuel cell by the flow field and the action of the reactant gas. The hydrophilic layer is directly attached to the catalyst layer, and the thickness of this part directly affects the discharge of water generated during the reaction. When the thickness of the hydrophilic layer is relatively thin, the water retention performance under low electrical density cannot be guaranteed, the proton exchange membrane is always in a dry state, the conductivity is relatively poor, and the electrochemical performance is extremely poor, with a performance of only 0.4V. As the thickness of the hydrophilic layer increases, although the internal resistance does not change significantly, when the thickness of the hydrophilic layer is greater than 50μm, the water generated is difficult to discharge under high current conditions. Excessive water generated accumulates in the hydrophilic layer, causing flooding under high electrical density. To balance flow field strength and drainage performance, the thickness of the hydrophobic layer is maintained at 500μm-1000μm, and the thickness of the hydrophilic layer is maintained at 10μm-50μm. The ratio of hydrophilic layer thickness to hydrophobic layer thickness is 1:15-1:75, which is more suitable, and the electrochemical performance is relatively close.

[0126] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. An integral gas diffusion layer with a hydrophilic-hydrophobic structure, characterized in that: The integrated gas diffusion layer comprises a hydrophilic layer and a hydrophobic layer. The hydrophilic layer is a planar layer, and the hydrophobic layer is a hybrid layer with ridge I and groove I. There is no transition layer between the hydrophilic layer and the hydrophobic layer. The hydrophilic layer is located between the hydrophobic layer and the fuel cell membrane electrode catalytic layer, and the hydrophobic layer is located between the fuel cell bipolar plate and the hydrophilic layer. The method for preparing the integrated gas diffusion layer with hydrophilic and hydrophobic structures includes the following steps: Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry separately; Step 2: Apply the hydrophobic slurry to the mold with ridges II and grooves II, control the coating thickness and fill the grooves II with the hydrophobic slurry, and then dry it; After cooling, the hydrophobic slurry on the upper part of ridge II and the upper part of groove II is removed to obtain a hydrophobic layer with ridge I and groove I; Step 3: Apply the hydrophilic slurry onto the hydrophobic layer treated in Step 2, control the coating thickness, and dry it to obtain the hydrophilic layer; Step 4: Place the sample processed in Step 3, along with the mold, into a high-temperature furnace for high-temperature heat treatment, and then cool. Step 5: Demold the sample after step 4 to obtain the integrated gas diffusion layer with hydrophilic and hydrophobic structure.

2. The integrated gas diffusion layer with a hydrophilic-hydrophobic structure according to claim 1, characterized in that: The thickness of the hydrophilic layer is 10μm-50μm, the thickness of the hydrophobic layer is 500μm-1000μm, and the ratio of the thickness of the hydrophilic layer to the thickness of the hydrophobic layer is 1:15-1:75; the width of ridge I is 200μm-500μm, and the width of groove I is 200μm-500μm.

3. The method for preparing an integrated gas diffusion layer with a hydrophilic-hydrophobic structure as described in claim 1, characterized in that: The hydrophilic layer slurry is made by mixing a hydrophobic agent, a solvent, a dispersant and conductive carbon black; by mass ratio, hydrophobic agent: solvent: dispersant: conductive carbon black = (10-15): (100-150): (30-60): (6-12).

4. The method for preparing an integrated gas diffusion layer with a hydrophilic-hydrophobic structure as described in claim 1, characterized in that: The hydrophobic slurry is made by mixing a hydrophobic agent, a solvent, a dispersant and conductive carbon black, with the following mass ratio: hydrophobic agent: solvent: dispersant: conductive carbon black = (25-30): (100-150): (30-60): (6-12).

5. The preparation method according to claim 3 or 4, characterized in that: The hydrophobic agent includes one or more of polytetrafluoroethylene, polyvinylidene fluoride and ethylene-tetrafluoroethylene copolymer; The solvent is deionized water; The dispersant is a surfactant; The conductive carbon black includes one or more of Cabot XC carbon black, acetylene black, graphite, carbon nanotubes, and carbon nanofibers.

6. The preparation method according to claim 5, characterized in that: The surfactant is a nonionic surfactant; the nonionic surfactant includes polyethylene glycol or alkyl alcohol amide; the polyethylene glycol includes polyethylene glycol phenyl ether.

7. The preparation method according to claim 3 or 4, characterized in that: In step 2, the drying temperature is 80℃-120℃ and the drying time is 5min-10min. In step 3, the drying temperature is 80℃-120℃ and the drying time is 5min-10min.

8. The preparation method according to claim 3 or 4, characterized in that: In step 4, the high-temperature heat treatment temperature is 350℃-400℃, and the time is 1h-2h.

9. An application of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, characterized in that: The integrated gas diffusion layer according to any one of claims 1-2 or the integrated gas diffusion layer prepared by the preparation method according to any one of claims 3-8 is used as a gas diffusion layer for a proton exchange membrane fuel cell.

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