Integrated gas diffusion layer with hydrophilic and hydrophobic structure as well as preparation method and application of integrated gas diffusion layer

Abstract

The invention discloses an integrated gas diffusion layer with a hydrophilic and hydrophobic structure and a preparation method and application thereof, and belongs to the technical field of fuel cells. The integrated gas diffusion layer structure comprises a hydrophilic layer and a hydrophobic layer, the hydrophilic layer is a planar layer, the hydrophobic layer is a mixed layer with ridges I and grooves I, no transition layer exists between the hydrophilic layer and the hydrophobic layer, the hydrophilic layer is located between the hydrophobic layer and a fuel cell membrane electrode catalyst layer, and the hydrophobic layer is located between a fuel cell bipolar plate and the hydrophilic layer. The preparation method of the integrated gas diffusion layer comprises the following steps: sequentially blade-coating hydrophobic layer slurry and hydrophilic layer slurry into a mold with a ridge II and a groove II, and finally demolding to obtain the integrated gas diffusion layer. The integrated gas diffusion layer is used for the gas diffusion layer of the proton exchange membrane fuel cell, the hydrophobic layer has a larger contact angle, gas transmission and discharge of generated water are facilitated, the hydrophilic layer separates out the water through capillary action, the mass transfer resistance is reduced, and the performance of a membrane electrode is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and particularly relates to an integral gas diffusion layer with a hydrophilic-hydrophobic structure, a preparation method thereof, and an application thereof. Background Art

[0002] The gas diffusion layer (GDL) is an important component of the membrane electrode assembly (MEA) in a proton exchange membrane fuel cell (PEMFC). Its performance is directly related to the performance of the membrane electrode, and thus affects the efficiency of the entire cell unit. The GDL plays several key roles in the fuel cell: First, it provides support for the catalyst layer and maintains the stability of the electrode structure; Second, it ensures the transmission channels for gases, electrons, and water, providing the necessary conditions for the electrode reaction; Third, it is responsible for transporting reactants, namely fuel and catalyst; Finally, it ensures good electrical conductivity between the bipolar plate and the catalyst layer. During the power generation process of the fuel cell, the hydrogen oxidation reaction at the anode generates protons and electrons. The electrons are transmitted to the cathode through the external circuit, while the protons reach the cathode through the proton exchange membrane. At the cathode, oxygen combines with electrons and protons to form water. During this process, the GDL needs to quickly discharge the generated water to prevent flooding of the catalyst layer, thus avoiding affecting the continuous reaction of the cell.

[0003] At present, the development of hydrogen fuel cells mostly aims at reducing the thickness of the membrane electrode while increasing the power density of the cell. Since the traditional gas diffusion layer has a relatively high thickness and high preparation cost, the development of an integrated gas diffusion layer is of great research significance. In the prior art, although there is also an integrated gas diffusion layer for PEMFC membrane electrodes, the problems are as follows: 1) It is necessary to first impregnate the carbon fiber base paper with resin and perform high-temperature carbonization treatment to obtain carbonized carbon fiber paper; then prepare the microporous layer slurry and coat the microporous layer slurry on the surface of the carbonized carbon fiber paper, and after drying and high-temperature graphitization treatment, an integrated gas diffusion layer is obtained. This method requires high-temperature carbonization and carbon addition treatment of the carbon fiber base paper first, directly coat the microporous layer, and then perform high-temperature graphitization treatment, which increases the preparation cost of the gas diffusion layer, prolongs the treatment time, and at the same time the added hydrophobic agent will decompose at high temperature and has poor hydrophobicity. 2) An independent microporous layer is proposed, and carbon nanotubes, hydrophobic agents, carbon materials, etc. are premixed, and the slurry is formed into a film by suction filtration to form an integrated gas diffusion layer. There are differences between it and the present invention in terms of method, material selection, preparation process, and final effect. 3) The gas diffusion layer needs to drain and conduct gas on the side close to the bipolar plate, so it needs to have higher hydrophobicity, while on the side close to the catalytic layer, it needs to have higher hydrophilicity to precipitate the capillary water generated during the electrochemical reaction process. However, the current integrated gas diffusion layer mainly focuses on the structural formation and ignores the change of the hydrophilicity and hydrophobicity of the diffusion layer; 4) Since the existing integrated gas diffusion layer has poor support, it is generally used in combination with a substrate. The flow field structure of the bipolar plate still remains, which will cause an interfacial resistance between the substrate layer and the microporous layer, and instead affect the mass transfer effect; 5) In the preparation process, the integrated gas diffusion layer is prepared by suction 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 existing technical problems, one of the objectives of the present invention is to provide an integrated gas diffusion layer with a hydrophilic-hydrophobic structure having a flow field structure and a planar structure.

[0005] To achieve the above-mentioned invention objective, the technical solution adopted by the present invention is: an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, comprising a hydrophilic layer and a hydrophobic layer. The hydrophilic layer is a planar layer, and the hydrophobic layer is a mixed layer with ridges Ⅰ and grooves 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] Further, the thickness of the hydrophilic layer is 10 μm - 50 μm, the thickness of the hydrophobic layer is 500 μm - 1000 μm, 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 the ridge I is 200 μm - 500 μm, and the width of the groove I is 200 μm - 500 μm.

[0007] The second object of the present invention is to provide a preparation method of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, and the preparation method includes the following steps: Step 1: Prepare a hydrophilic layer slurry and a hydrophobic layer slurry respectively; Step 2: Coat the hydrophobic layer slurry into a mold with a ridge II and a groove II, control the coating thickness and fill the groove II with the hydrophobic layer slurry, and then dry it; after cooling, remove the hydrophobic layer slurry on the upper part of the ridge II and the upper part of the groove II to obtain a hydrophobic layer with a ridge I and a groove I; Step 3: Coat the hydrophilic layer slurry onto the hydrophobic layer treated in Step 2, control the coating thickness, and dry it to obtain a hydrophilic layer; Step 4: Put the sample treated in Step 3 together with the mold into a high-temperature furnace for high-temperature heat treatment, and then cool it; Step 5: Demold the sample treated in Step 4 to obtain the integrated gas diffusion layer with a hydrophilic-hydrophobic structure.

[0008] Further, the hydrophilic layer slurry is made by mixing a water repellent, a solvent, a dispersant, and conductive carbon black; by mass ratio, water repellent: solvent: dispersant: conductive carbon black = (10 - 15): (100 - 150): (30 - 60): (6 - 12).

[0009] Further, the hydrophobic layer slurry is made by mixing a water repellent, a solvent, a dispersant, and conductive carbon black, and by mass ratio, water repellent: solvent: dispersant: conductive carbon black = (25 - 30): (100 - 150): (30 - 60): (6 - 12).

[0010] Further, the water repellent includes one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and ethylene-tetrafluoroethylene copolymer (ETFE); 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.

[0011] Further, the surfactant is a non-ionic surfactant; the non-ionic surfactant includes polyethylene glycols or alkylolamides; the polyethylene glycols include polyethylene glycol phenyl ether.

[0012] Further, in step 2, the drying temperature is 80°C - 120°C and the drying time is 5 min - 10 min; in step 3, the drying temperature is 80°C - 120°C and the drying time is 5 min - 10 min.

[0013] Further, in step 4, the high-temperature heat treatment temperature is 350°C - 400°C and the time is 1 h - 2 h.

[0014] The third object of the present invention is to provide an application of an integrated diffusion layer with a hydrophilic-hydrophobic structure, and apply it to the gas diffusion layer of a proton exchange membrane fuel cell.

[0015] The beneficial effects of the present invention are as follows: The integrated gas diffusion layer provided by the present invention forms a flow field structure by making the hydrophobic layer into a mixed layer with ridges I and grooves I, which has a larger contact angle, is more conducive to gas transmission and the discharge of generated water. The hydrophilic layer of the contact catalytic layer can more easily analyze the gaseous water or liquid water generated by the catalytic layer through capillary action, thereby reducing the mass transfer resistance and improving the performance of the membrane electrode. For the integrated gas diffusion layer prepared by the present invention, the functions of the hydrophobic layer and the hydrophilic layer are more distinct. The hydrophobic layer is used for gas supply and the discharge of liquid water, and the hydrophilic layer is used for analyzing the generated water. Due to the low hydrophobic agent content and the absence of the interfacial resistance between the hydrophobic carbon paper and the microporous layer in the present invention, the entire diffusion layer has a lower internal resistance in the body, and the output performance of the fuel cell membrane electrode is higher. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0017] Figure 1 It is a schematic structural diagram of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure provided by an embodiment of the present invention.

[0018] Figure 2 It is provided by an embodiment of the present invention Figure 1 The main view enlarged drawing.

[0019] Figure 3 It is a schematic structural diagram of a glass plate mold provided by an embodiment of the present invention.

[0020] Figure 4 is the enlarged front view provided by the embodiment of the present invention Figure 3 .

[0021] Figure 5 is the polarization curve performance diagram provided by 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 manners

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] In the first aspect of the embodiment of the present invention, an integrated gas diffusion layer with a hydrophilic-hydrophobic structure is provided. The integrated gas diffusion layer includes a hydrophilic layer and a hydrophobic layer. The hydrophilic layer is a planar layer, and the hydrophobic layer is a mixed layer with ridges I and grooves 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.

[0024] The integrated gas diffusion layer with a hydrophilic-hydrophobic structure is prepared in the present invention. The hydrophilic layer is made into a planar structure and directly contacts the catalytic layer during actual application, playing a role in sucking out the generated water and reducing the interface resistance. The hydrophobic layer is made into a mixed 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 transmission and the discharge of generated water. During actual use, the side with the flow field structure will directly contact the bipolar plate, while the hydrophilic layer structure contacts the catalytic layer of the membrane electrode, replacing the flow field structure in the original bipolar plate. In this way, when the fuel cell is assembled, it has a lower cross-sectional resistance, lower ohmic loss, and better performance. There is no transition layer between the hydrophilic layer and the hydrophobic layer, so there is no interface resistance between the hydrophobic carbon paper and the microporous layer. The entire diffusion layer has a lower internal resistance, which also makes the output performance of the fuel cell membrane electrode higher.

[0025] In some feasible implementation manners, 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 the ridge I is 200μm - 500μm, and the width of the groove I is 200μm - 500μm.

[0026] Specifically, a hydrophilic layer thickness of 10 μm - 50 μm contributes to the precipitation of generated water and the reduction of bulk resistance. During the operation of a fuel cell, there are low-current-density conditions and high-current-density conditions. In general low-current-density conditions, due to insufficient generated water and the need for a certain humid environment for the proton exchange membrane to improve proton conductivity, the diffusion layer also requires a certain water retention capacity. For a relatively thin hydrophilic layer, the water content at low current density is likely to be low, the internal resistance is large, and the performance of the fuel cell is low. For an overly thick hydrophilic layer, water accumulates in the microporous layer and is not easily discharged under high current density, resulting in difficult mass transfer under high current density and the phenomenon of flooding. For the hydrophobic layer, the present invention is an integrated gas diffusion layer that replaces the traditional bipolar plate and diffusion layer structure. The hydrophobic layer acts as a flow field structure, so it requires a certain thickness and strength. For a too-thin hydrophobic layer, during encapsulation, the sealing performance is likely to be poor, and only a too-high assembly force can be used for encapsulation. However, a too-high assembly pressure will cause severe compression of the gas diffusion layer, collapse of the pore structure, and failure of the gas conduction and water drainage functions of the diffusion layer. An overly thick hydrophobic layer greatly increases 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, and resulting in poor battery performance. Therefore, the present invention preferably has a hydrophobic layer thickness of 500 μm - 1000 μm. For the corresponding Ridge I and Groove I, their width ranges affect the drainage and reaction zone characteristics. Combining with the verified bipolar plate structure, for too-thin Ridge I and Groove I, although it seemingly increases the effective reaction zone, under high current density, the demand for reaction gas increases, especially for the cathode, which requires a large amount of gas consumption. A too-narrow width will increase the gas mass transfer resistance and easily cause collapse of the diffusion layer structure. While a too-high width, although it improves the strength of the flow field, also affects the intake air volume and the output performance. Therefore, the present invention preferably has a width of Ridge I of 200 μm - 500 μm and a width of Groove I of 200 μm - 500 μm.

[0027] In the second aspect of the embodiments of the present invention, a preparation method of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure is provided. The preparation method includes the following steps: Step 1: Prepare hydrophilic layer slurry and hydrophobic layer slurry respectively; Step 2: Coat the hydrophobic layer slurry into a mold with Ridge II and Groove II, control the coating thickness and make Groove II filled with the hydrophobic layer slurry, and then perform drying; after cooling, remove the hydrophobic layer slurry on the upper parts of Ridge II and Groove II of the mold to obtain a hydrophobic layer with Ridge I and Groove I; Step 3: Coat the hydrophilic layer slurry onto the hydrophobic layer processed in Step 2, control the coating thickness, and perform drying to obtain a hydrophilic layer; Step 4: Put the sample processed in Step 3 together with the mold into a high-temperature furnace for high-temperature heat treatment, and then cool down; Step 5: Demold the sample processed in Step 4 to obtain an integral gas diffusion layer with a hydrophilic-hydrophobic structure.

[0028] Different from the traditional integral gas diffusion layer which is prepared by a suction filtration method to obtain a microporous layer, and then matches with a traditional hydrophobic carbon paper for application. The integral gas diffusion layer prepared by the present invention, through a special mold with ridges II and grooves II, only needs to scrape two slurries into the preset mold successively. The grooves II of the mold correspond to form the ridges I of the hydrophobic layer, and the ridges II of the mold correspond to form the grooves I of the hydrophobic layer. Finally, after sintering the material to obtain a certain support, demolding is carried out. The whole preparation process is relatively simple and the production cost is lower. For the integral gas diffusion layer prepared by the present invention, after including the flow field structure, the bipolar plate no longer needs the flow field structure. During the processing of the bipolar plate, it is not necessary to consider the influence of coating shedding on durability caused by coating first and then stamping, nor to consider the uneven coating caused by stamping first and then coating, which affects the conductivity, making the production cost of the bipolar plate lower and promoting the industrial development of fuel cells.

[0029] In some feasible embodiments, in Step 1, 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). In Step 1, the hydrophobic 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 = (25 - 30):(100 - 150):(30 - 60):(6 - 12).

[0030] Specifically, the diffusion layer is mainly based on carbon materials as the main body, which plays a role in establishing a microporous structure. For the hydrophobic agent, it not only plays a hydrophobic role in transmission, but also plays a role in bonding the microporous layer. For the traditional diffusion layer, there is a carbon substrate and a microporous layer. The substrate has a macroporous structure and the microporous layer has a microporous structure. At the alternating part, there is an obvious pore size mutation, accumulating some water and obvious mass transfer polarization. For the same raw materials, this situation will not occur. Since the hydrophilic layer and the hydrophobic layer of the present invention use the same raw materials, the pore size range of both the hydrophilic layer and the hydrophobic layer remains the same, and the gas transmission and water-vapor discharge conditions are relatively mild, without sudden performance mutations.

[0031] In some feasible embodiments, the hydrophobic agent includes 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 non-ionic surfactant, including polyethylene glycols or alkylolamides, and most preferably polyethylene glycol phenyl ether; the conductive carbon black includes one or a mixture of several of Cabot XC carbon black, acetylene black, graphite, carbon nanotubes, and carbon nanofibers.

[0032] Specifically, for the hydrophobic agent, one or several of polytetrafluoroethylene, polyvinylidene fluoride, and ethylene-tetrafluoroethylene copolymer are preferred. They have high chemical stability and can withstand almost all strong acids, strong bases, strong oxidants, and organic solvents. As a commonly used hydrophobic material in the industry, after sintering, it has high hydrophobicity and also plays a bonding role. For the solvent, since it replaces the traditional carbon substrate, a large amount of microporous materials are required for the integrated gas diffusion layer of the present invention. The solvent used in the present invention is deionized water. Compared with the traditional ethanol-based solvent solution, it not only solves the environmental protection and safety impacts but also reduces the production cost. Since the operating conditions of fuel cells are relatively harsh, free ions will affect the proton membrane and catalyst, affecting their durability and reliability. Through experimental comparison, we found that selecting a non-ionic surfactant as the dispersant helps to improve the durability of the membrane electrode, and the most preferred dispersant is polyethylene glycol phenyl ether. For the conductive carbon black, one or several of XC carbon black, acetylene black, graphite, carbon nanotubes, and carbon nanofibers are selected. Due to their high degree of graphitization, the bulk resistance of the gas diffusion layer is relatively low. For carbon nanotubes and carbon nanofibers, they can effectively construct large and small pore structures and improve the crack situation caused by aqueous slurries, thereby improving the durability of the diffusion layer.

[0033] In some feasible embodiments, in step 2, the drying temperature is 80°C - 120°C, and the drying time is 5 min - 10 min. In step 3, the drying temperature is 80°C - 120°C, and the drying time is 5 min - 10 min.

[0034] The present invention dries in two steps because for the slurry, its wet thickness and dry thickness vary due to the solid content. First, drying the hydrophobic layer, after the hydrophobic layer shrinks, due to the influence of the mold depth, the thickness of the hydrophobic layer can be better controlled. At the same time, for the hydrophilic layer to be coated, the hydrophobic layer plays a supporting role at this time.

[0035] In some feasible embodiments, in step 4, the high-temperature heat treatment temperature is 350°C - 400°C, and the time is 1 h - 2 h.

[0036] In the third aspect of the embodiments of the present invention, an application of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure is provided, and it is applied to the gas diffusion layer of a proton exchange membrane fuel cell.

[0037] For the integrated gas diffusion layer provided by the present invention, the hydrophobic layer is made into a mixed 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 transmission and the discharge of generated water. For the hydrophilic layer of the contact catalytic layer, it is easier to analyze water through capillary action for the gaseous water or liquid water generated by the catalytic layer, thereby reducing the mass transfer resistance. In addition, due to the absence of the interface resistance between the hydrophobic carbon paper and the microporous layer, the entire diffusion layer has a lower internal resistance, thereby improving the output performance of the fuel cell membrane electrode.

[0038] Example 1 An integrated gas diffusion layer with a hydrophilic-hydrophobic structure (I) Structure As Figure 1 and Figure 2 shown, an integrated gas diffusion layer with a hydrophilic-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 mixed 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 catalytic layer of the fuel cell membrane electrode, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0039] 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 groove Ⅰ 22 is 200 μm.

[0040] (II) Preparation method Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry Preparation of the hydrophilic layer slurry: Weigh 10 g of polytetrafluoroethylene, 100 g of deionized water, 30 g of polyglycol phenyl ether, and 6 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk for standby; Preparation of the hydrophobic layer slurry: Weigh 25 g of polytetrafluoroethylene, 100 g of deionized water, 30 g of polyglycol phenyl ether, and 6 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk for standby; Step 2: Preparation of the hydrophobic layer As Figure 3 and Figure 4 shown, the structure of the glass plate mold is that there are several ridges Ⅱ 31 on the bottom 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.

[0041] Place the glass plate mold on the doctor blade coater platform, evenly coat the hydrophobic layer slurry into the glass plate mold, control the coating thickness and fill the groove Ⅱ 32 with the hydrophobic layer slurry. After coating, transfer the glass plate mold to an oven for drying. Set the oven temperature to 80 °C and the drying duration to 5 min - 10 min. After drying is completed, take it out. After cooling, remove the hydrophobic layer slurry on the upper part of the ridge Ⅱ 31 and the groove Ⅱ 32. The groove Ⅰ 22 of the hydrophobic layer is formed in the ridge Ⅱ 31 part of the glass plate mold, and the ridge Ⅰ 21 of the hydrophobic layer is formed in the groove Ⅱ 32 part of the glass plate mold, so as to obtain the hydrophobic layer 20 with the ridge Ⅰ 21 and the groove Ⅰ 22 on the glass plate mold.

[0042] Step 3: Preparation of the hydrophilic layer Continue to place the cooled glass plate mold on the doctor blade coater platform, evenly coat the hydrophilic layer slurry on the surface of the glass plate mold, that is, coat the hydrophilic layer slurry on the hydrophobic layer 20 treated in Step 2, control the wet coating thickness. After coating, transfer the glass plate mold to an oven for drying. Set the oven temperature to 80 °C and the drying duration to 5 min - 10 min.

[0043] Step 4: High-temperature treatment Place the sample treated in Step 3 together with the glass plate mold as a whole in a high-temperature furnace for high-temperature treatment at 350 °C for 2 h.

[0044] Step 5: Demolding Demold the sample treated in Step 4 to obtain an integrated gas diffusion layer with a hydrophilic-hydrophobic structure.

[0045] Example 2 An integrated gas diffusion layer with a hydrophilic-hydrophobic structure (I) Structure As Figure 1 and Figure 2 shown, an integrated gas diffusion layer with a hydrophilic-hydrophobic structure includes a hydrophilic layer 10 and a hydrophobic layer 20; among them, the hydrophilic layer 10 is a planar layer, the hydrophobic layer 20 is a mixed layer with a ridge Ⅰ 21 and a groove 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 catalyst layer, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0046] 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 groove Ⅰ 22 is 350 μm.

[0047] (II)Preparation method Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry Preparation of the hydrophilic layer slurry: Weigh 12.5 g of polytetrafluoroethylene, 125 g of deionized water, 45 g of poly(ethylene glycol) phenyl ether, and 9 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk for standby; Preparation of the hydrophobic layer slurry: Weigh 27.5 g of polytetrafluoroethylene, 125 g of deionized water, 45 g of poly(ethylene glycol) phenyl ether, and 9 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk for standby; Step 2: Preparation of the hydrophobic layer As Figure 3 and Figure 4 shown, the glass plate mold structure is that there are several ridges II 31 on the bottom plate 30, and grooves II 32 are formed between adjacent ridges II 31. The height h of the ridge II 31 is 750 μm, the width e of the ridge II is 350 μm, and the width f of the groove II 32 is 350 μm.

[0048] Place the glass plate mold on the doctor blade coater platform, evenly coat the hydrophobic layer slurry into the glass plate mold, control the coating thickness and make the groove II 32 filled with the hydrophobic layer slurry. After coating, transfer the glass plate mold to the oven for drying, set the oven temperature to 80 °C, and the drying duration is 5 min - 10 min. After drying, take it out, and after cooling, remove the hydrophobic layer slurry on the upper part of the ridge II 31 and the groove II 32. The ridge II 31 part of the glass plate mold forms the groove I 22 of the hydrophobic layer, and the groove II 32 part of the glass plate mold forms the ridge I 21 of the hydrophobic layer, so as to obtain a hydrophobic layer 20 with the ridge I 21 and the groove I 22 on the glass plate mold.

[0049] Step 3: Preparation of the hydrophilic layer Place the cooled glass plate mold on the doctor blade coater platform continuously, and evenly coat the hydrophilic layer slurry on the surface of the glass plate mold, that is, coat the hydrophilic layer slurry on the hydrophobic layer 20 processed in Step 2, control the wet coating thickness. After coating, transfer the glass plate mold to the oven for drying treatment, set the oven temperature to 80 °C, and the drying duration is 5 min - 10 min.

[0050] Step 4: High-temperature treatment Place the sample processed in Step 3 together with the glass plate mold as a whole in a high-temperature furnace for high-temperature treatment at 350 °C for 2 h.

[0051] Step 5: Demolding Demold the sample processed in Step 4 to obtain an integrated gas diffusion layer with a hydrophilic-hydrophobic structure.

[0052] Example 3 An integrated gas diffusion layer with hydrophilic-hydrophobic structure (I) Structure As Figure 1 and Figure 2 shown, an integrated gas diffusion layer with hydrophilic-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 mixed 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 catalyst layer, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0053] 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 groove I 22 is 500 μm.

[0054] (II) Preparation method Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry Preparation of the hydrophilic layer slurry: Weigh 15 g of polytetrafluoroethylene, 150 g of deionized water, 60 g of polyethylene glycol phenyl ether, and 12 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk for standby; Preparation of the hydrophobic layer slurry: Weigh 30 g of polytetrafluoroethylene, 150 g of deionized water, 60 g of polyethylene glycol phenyl ether, and 12 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk for standby; Step 2: Preparation of the hydrophobic layer As Figure 3 shown, the structure of the glass plate mold is that there are several ridges II 31 on the bottom plate 30, and grooves II 32 are formed between adjacent ridges II 31. The height h of the ridge II 31 is 1000 μm, the width e of the ridge II is 500 μm, and the width f of the groove II 32 is 500 μm.

[0055] Place the glass plate mold on the scraper coating machine platform, evenly coat the hydrophobic layer slurry into the glass plate mold, control the coating thickness and make the groove II 32 filled with the hydrophobic layer slurry. After coating, transfer the glass plate mold to the oven for drying, set the oven temperature to 80 °C, and the drying time is 5 min - 10 min. After drying, take it out, and after cooling, remove the hydrophobic layer slurry on the upper parts of the ridge II 31 and the groove II 32. The groove I 22 of the hydrophobic layer is formed on the ridge II 31 part of the glass plate mold, and the ridge I 21 of the hydrophobic layer is formed on the groove II 32 part of the glass plate mold, so as to obtain the hydrophobic layer 20 with ridges I 21 and grooves I 22 on the glass plate mold.

[0056] Step 3: Preparation of the hydrophilic layer Continue to place the cooled glass plate mold on the scraper platform, and evenly coat the hydrophilic layer slurry onto the surface of the glass plate mold, that is, coat the hydrophilic layer slurry onto the hydrophobic layer 20 treated in Step 2. Control the wet coating thickness. After coating, transfer the glass plate mold to an oven for drying. The oven temperature is set at 80 °C, and the drying duration is 5 min - 10 min.

[0057] Step 4: High-temperature treatment Place the sample treated in Step 3 together with the glass plate mold as a whole in a high-temperature furnace for high-temperature treatment at 350 °C for 2 h.

[0058] Step 5: Demolding Demold the sample treated in Step 4 to obtain an integrated gas diffusion layer with a hydrophilic-hydrophobic structure.

[0059] Comparative Example 1 For the combination of traditional microporous layer and carbon paper, weigh 15 g of polytetrafluoroethylene, 150 g of deionized water, 60 g of polyethylene glycol phenyl ether, and 12 g of Cabot XC carbon black respectively, and disperse them for 1 h using a high-speed dispersion disk to obtain the microporous layer slurry for standby.

[0060] Cut commercial carbon paper to a certain size, immerse it in an aqueous solution containing PTFE for 3 min, then drain and dry it at 100 °C for 10 min, and then put it into a high-temperature furnace for high-temperature sintering at 350 °C for 2 h to obtain a hydrophobic carbon paper.

[0061] Coat the prepared microporous layer slurry onto the surface of the carbon paper, dry it at 100 °C, and then perform high-temperature heat treatment at 350 °C for 2 h to obtain a gas diffusion layer with a thickness of 180 μm.

[0062] Example 4 Performance test Perform polarization curve performance and electrical performance experiments on the integrated gas diffusion layers prepared in Example 1, Example 2, and Example 3 and the traditional gas diffusion layer prepared in Comparative Example 1. The results are as Figure 5 and Table 1.

[0063] As Figure 5 shown in A, the integrated gas diffusion layer prepared in Example 1 has higher performance, and the voltage of the polarization curve performance is 0.623 V at a current density of 2.5 A / cm 2 ².

[0064] As Figure 5 shown in B, for the integrated gas diffusion layer prepared in Example 2, when the current density is greater than 2 A / cm 2Afterwards, under high current density conditions, there was no serious mass transfer polarization, with relatively low mass transfer resistance, high electrochemical performance, and the polarization curve performance showed a voltage of 0.625 V at a current density of 2.5 A / cm 2 at this time.

[0065] As can be seen from Figure 5 C in, for the integrated gas diffusion layer prepared in Example 3, as the current density increased, the mass transfer was relatively gentle. Even though the overall diffusion layer thickness increased, it still had relatively low internal resistance and mass transfer resistance, high electrochemical performance, and the polarization curve performance showed a voltage of 0.614 V at a current density of 2.5 A / cm 2 at this time.

[0066] As can be seen from Figure 5 D in, for the traditional gas diffusion layer prepared in Comparative Example 1, because the carbon paper was treated with PTFE for hydrophobicity, the bulk resistance was relatively high. After the microporous layer and the carbon paper formed the GDL, when the fuel cell was assembled, the flow field of the bipolar plate contacted the carbon paper, and after the microporous layer contacted the catalytic layer, there was a large interfacial resistance. Moreover, there was a structural transformation between large and small pores between the carbon paper and the microporous layer, and the water generated by the reaction was more likely to accumulate, thus easily forming flooding and causing a decline in battery performance. As Figure 5 shown in D in, due to the alternating pores between the substrate and the microporous layer, as the current density increased, when it was higher than 2 A / cm 2 , the battery performance decreased significantly, the mass transfer polarization was serious, and the polarization curve performance showed a voltage < 0.5 V at a current density of 2.5 A / cm 2 at this time.

[0067] Table 1 Comparison of the performance of the integrated gas diffusion layers of Examples 1 - 3 and the traditional gas diffusion layer of Comparative Example 1

[0068] As can be seen from Table 1, after adjusting the thicknesses of different hydrophilic and hydrophobic layers, the minimum thickness of the integrated gas diffusion layer was 510 μm and the maximum thickness was 1050 μm. However, since they were all made of the same material, their bulk resistance was relatively low, maintaining at about 7 mΩ·cm 2 under the test condition of 1 Mpa. For Comparative Example 1, there was an interfacial resistance between the hydrophobic substrate material (carbon paper) and the coated microporous layer and the substrate. Its bulk resistance was 15.3 mΩ·cm 2 under the test condition of 1 Mpa, which was doubled compared to the present invention and would greatly increase its ohmic loss. Secondly, for the integrated diffusion layer prepared based on the present invention, since the hydrophilic layer and the hydrophobic layer were made of the same material and there were no abrupt pores, the membrane electrode had a good mass transfer effect under high current density, and at 2.5 A / cm 2Under the operating conditions, the voltage performance can still be greater than 0.6V, which will effectively improve the limiting power of the fuel cell. For traditional gas diffusion layers, due to severe mass transfer polarization, at 2.5 A / cm 2 Under the operating conditions, due to the phenomenon of flooding, the battery performance rapidly decreases to less than 0.5V.

[0069] Example 5 Thickness Selection of an Integral Gas Diffusion Layer with Hydrophilic-Hydrophobic Structure (I) Structure As Figure 1 and Figure 2 shown, an integral gas diffusion layer with a hydrophilic-hydrophobic structure includes a hydrophilic layer 10 and a hydrophobic layer 20; among them, the hydrophilic layer 10 is a planar layer, and the hydrophobic layer 20 is a mixed 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 catalytic layer of the fuel cell membrane electrode, and the hydrophobic layer 20 is located between the fuel cell bipolar plate and the hydrophilic layer 10.

[0070] (1) Fix the thickness a of the hydrophilic layer 10 at 30μm, and adjust the thickness b of the hydrophobic layer 20 to be 400μm, 500μm, 750μm, 1000μm, and 1200μm respectively. The width c of the ridge I 21 is 350μm, and the width d of the groove I 22 is 350μm.

[0071] (2) Fix the thickness b of the hydrophobic layer 20 at 750μm, and adjust the thickness a of the hydrophilic layer 10 to be 5μm, 10μm, 35μm, 50μm, and 60μm respectively. The width c of the ridge I 21 is 350μm, and the width d of the groove I 22 is 350μm.

[0072] (II) Preparation Method Same as Example 2, integral gas diffusion layers with different thickness ratios of the hydrophilic layer and the hydrophobic layer are obtained. The performance test results are shown in Table 2.

[0073] Table 2 Performance of Integral Gas Diffusion Layers with Different Thickness Hydrophilic Layers and Different Thickness Hydrophobic Layers

[0074] As shown in Table 2, when the thickness of the hydrophilic layer is kept constant and the thickness of the hydrophobic layer is adjusted, since the hydrophobic layer controls the height of the entire flow field, the thinner the thickness, the greater the resistance when the gas flows, which is likely to cause an under-gas state. Especially in the case of a relatively large current density, the mass transfer polarization will be more obvious. Moreover, there are still a relatively large amount of hydrophobic agents in the hydrophobic layer, and the addition of the hydrophobic agents leads to a relatively large internal resistance of the material itself. At a high current density, the internal resistance loss will be relatively large. When the thickness of the hydrophobic layer is fixed, that is, when the height of the flow field is fixed, and the thickness of the hydrophilic layer is adjusted, a large amount of gaseous water will be generated during the reaction of the fuel cell. The gaseous water condenses into liquid water through the capillary action of the microporous layer and is discharged from the fuel cell by the action of the flow field and the reaction gas. Since the hydrophilic layer is directly attached to the catalytic layer, the thickness of this part directly affects the water discharge situation during the reaction. When the thickness of the hydrophilic layer is relatively thin, the water retention performance at a low current density cannot be guaranteed, and the proton exchange membrane is always in a dry state, with poor conductivity and extremely poor electrochemical performance, and the performance is only 0.4V. As the thickness of the hydrophilic layer increases, although the internal resistance does not change significantly, but when the thickness of the hydrophilic layer is greater than 50μm, under a large current state, the generated water is difficult to discharge, and too much generated water accumulates in the hydrophilic layer, resulting in a flooding phenomenon at a high current density. Considering both the flow field strength and the drainage performance, it is more appropriate that the thickness of the hydrophobic layer is maintained at 500μm - 1000μm, the thickness of the hydrophilic layer is maintained at 10μm - 50μm, and the ratio of the thickness of the hydrophilic layer to the thickness of the hydrophobic layer is 1:15 - 1:75, and the electrochemical performances are relatively close.

[0075] It is easy for those skilled in the art to understand that, on the premise of no conflict, the above advantageous ways can be freely combined and superimposed. The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only the preferred implementation manner of the present application. It should be noted that for those of ordinary skill in the art in the technical field of the present application, without departing from the technical principle of the present application, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. An integrated gas diffusion layer with a hydrophilic-hydrophobic structure, characterized in that: The integrated gas diffusion layer includes a hydrophilic layer and a hydrophobic layer. The hydrophilic layer is a planar layer, and the hydrophobic layer is a mixed layer with ridges Ⅰ and grooves 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 catalyst layer, and the hydrophobic layer is located between the fuel cell bipolar plate and the hydrophilic layer.

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, and the thickness of the hydrophobic layer is 500μm - 1000μm, and the thickness ratio of the hydrophilic layer to the hydrophobic layer is 1:15 - 1:75; the width of the ridges Ⅰ is 200μm - 500μm, and the width of the grooves Ⅰ is 200μm - 500μm.

3. A preparation method of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure, characterized in that: For the integrated gas diffusion layer according to claim 1 or 2, the preparation method comprises the following steps: Step 1: Prepare the hydrophilic layer slurry and the hydrophobic layer slurry respectively. Step 2: Coat the hydrophobic layer slurry into a mold with ridges Ⅱ and grooves Ⅱ, control the coating thickness to make the grooves Ⅱ filled with the hydrophobic layer slurry, and then dry it. After cooling, remove the hydrophobic layer slurry on the upper parts of the ridges Ⅱ and the grooves Ⅱ to obtain a hydrophobic layer with ridges Ⅰ and grooves Ⅰ. Step 3: Coat the hydrophilic layer slurry onto the hydrophobic layer processed in Step 2, control the coating thickness, and dry it to obtain the hydrophilic layer. Step 4: Put the sample processed in Step 3 together with the mold into a high-temperature furnace for high-temperature heat treatment, and then cool it. Step 5: Demold the sample processed in Step 4 to obtain the integrated gas diffusion layer with a hydrophilic-hydrophobic structure.

4. The preparation method of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure according to claim 3, characterized in that: The hydrophilic layer slurry is made by mixing a water repellent, a solvent, a dispersant, and conductive carbon black; by mass ratio, water repellent: solvent: dispersant: conductive carbon black = (10 - 15):(100 - 150):(30 - 60):(6 - 12).

5. The preparation method of an integral gas diffusion layer with a hydrophilic-hydrophobic structure according to claim 3, characterized in that: The hydrophobic layer slurry is made by mixing a water repellent, a solvent, a dispersant, and conductive carbon black; by mass ratio, water repellent: solvent: dispersant: conductive carbon black = (25 - 30):(100 - 150):(30 - 60):(6 - 12).

6. For the preparation method of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure according to claim 4 or 5, it is characterized in that: The water repellent 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.

7. The preparation method of an integrally formed gas diffusion layer with a hydrophilic-hydrophobic structure according to claim 6, characterized in that: The surfactant is a non-ionic surfactant; the non-ionic surfactant includes polyethylene glycols or alkylolamides; the polyethylene glycols include polyethylene glycol phenyl ether.

8. For the preparation method of an integrated gas diffusion layer with a hydrophilic-hydrophobic structure according to any one of claims 3 - 5, it is 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.

9. The preparation method of an integral gas diffusion layer with a hydrophilic-hydrophobic structure according to any one of claims 3-5, characterized in that: In the step 4, the high-temperature heat treatment temperature is 350°C - 400°C, and the time is 1h - 2h.

10. Application of an integrally formed gas diffusion layer with a hydrophilic-hydrophobic structure, characterized in that: The integrated gas diffusion layer according to claim 1 or 2, which is used as the gas diffusion layer of a proton exchange membrane fuel cell.

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