Microporous layer slurry, gas diffusion layer and preparation method thereof, hydrogen fuel cell

Abstract

The present application discloses a microporous layer slurry, a gas diffusion layer, a preparation method thereof, and a hydrogen fuel cell. The microporous layer slurry comprises the following components, measured by weight: 1 to 50 parts of hydrophobically modified coconut shell activated carbon, 1 to 50 parts of a conductive agent, 1 to 50 parts of a first hydrophobic agent, 0.1 to 50 parts of a dispersing aid, and 10 to 150 parts of a solvent. The microporous layer slurry described herein can improve the pore structure of the gas diffusion layer, increase the transmission path of the reactant gas, and facilitate the rapid and effective diffusion of more reactant gas to the catalyst layer for reaction, thereby improving transmission efficiency. It can also enhance the hydrophobicity of the microporous layer, which not only maintains the humidity of the reactant gas but also promptly discharges the liquid water produced by the cathode reaction, thereby reducing mass transfer polarization and improving the performance of the fuel cell.

Description

Technical Field

[0001] The present application relates to the field of hydrogen fuel cell technology, and in particular to a microporous layer slurry and a preparation method thereof, a gas diffusion layer and a preparation method thereof, and a hydrogen fuel cell. Background Art

[0002] Hydrogen is the lightest, cleanest, and most efficient fuel, possessing many unique properties. In fuel cells, hydrogen's chemical energy can be efficiently converted into electrical energy. Consequently, researchers have invested significant effort in developing efficient hydrogen fuel cells to meet future applications in transportation, stationary power generation, portable power systems, and more. Hydrogen fuel cells currently include alkaline hydrogen fuel cells (AFC), proton exchange membrane hydrogen fuel cells (PEMFC), hydrogen phosphate fuel cells (PAFC), molten carbonate hydrogen fuel cells (MCFC), and solid oxide hydrogen fuel cells (SOFC). Among these, the performance of proton exchange membrane hydrogen fuel cells is particularly satisfactory.

[0003] Gas diffusion layers (GDLs) are one of the most core materials in proton exchange membrane hydrogen fuel cells. Their primary functions include transferring reactant gases, removing liquid water produced by the reaction, conducting electrons, and supporting the catalyst layer and proton exchange membrane. Therefore, the overall performance requirements for GDLs are very high. First, the GDL must be a good conductor with low resistivity and strong electron conductivity. Second, the GDL must possess a uniform porous medium structure and good air permeability. The GDL is a key factor in determining the overall performance of a fuel cell. Currently, commonly used GDLs are made from carbon fiber. A base paper is prepared through a wet or dry process, and the GDL substrate is prepared through carbonization and graphitization. To further improve performance, a microporous layer (MPL) is often applied to the base paper to increase the smoothness of the diffusion layer, reduce contact resistance, and improve the pore structure of the diffusion layer.

[0004] In proton exchange membrane hydrogen fuel cells, on the one hand, a certain amount of water must be retained in the electrode to ensure the wettability of the membrane and reduce the membrane resistance. To this end, the reaction gas containing water vapor must be able to quickly diffuse through the pores of the gas diffusion layer to the catalyst layer for reaction; on the other hand, the liquid water produced by the cathode reaction must also be discharged in time through the pores of the gas diffusion layer, otherwise the excess water will occupy the gas transmission channel and cover the catalyst surface, increasing the transmission resistance of the reaction gas and causing the electrode "flooding" phenomenon. Therefore, an excellent gas diffusion layer should have a suitable porosity, pore size and reasonable pore size distribution to ensure the uniform and rapid passage of the reaction gas, and the water in the electrode should reach a balance between ensuring sufficient wetting of the membrane and avoiding "flooding" of the electrode. Usually, people prepare MPL by physically mixing carbon powder and hydrophobic agent, and control the formation of pore size through the gaps between carbon powder particles.

[0005] In some prior arts, the pore size of the gas diffusion layer is improved by adding porous carbon powder with a surface-modified coral shape, starfish shape, tree shape, or protruding shape structure to the microporous layer, thereby improving its gas transmission capacity. In other prior arts, carbon materials with different pore structures, binders, and conductive agents are mixed and ground, and a self-supporting carbon film is prepared by rolling and sheeting. The self-supporting carbon film is stacked and assembled according to the pore size to prepare a gas diffusion layer with a gradient pore distribution. However, most porous carbons have problems such as poor pore structure, high ash content, and many impurities, which will affect the overall performance of the gas diffusion layer. In addition, porous carbon has a strong adsorption effect on water, which will lead to a decrease in the humidity of the reaction gas. At the same time, the adsorbed water molecules will enter the pores of the porous carbon, thereby blocking the gas transmission channel, and ultimately reducing the overall performance of the fuel cell. Summary of the Invention

[0006] The purpose of this application is to provide a microporous layer slurry, a gas diffusion layer and a preparation method thereof, and a hydrogen fuel cell to overcome the defects of the prior art.

[0007] To achieve the above objectives, this application provides the following technical solutions.

[0008] In a first aspect, the present application provides a microporous layer slurry comprising the following components in parts by weight: 1 to 50 parts of hydrophobically modified coconut shell activated carbon, 1 to 50 parts of a conductive agent, 1 to 50 parts of a first hydrophobic agent, 0.1 to 50 parts of a dispersing aid, and 10 to 150 parts of a solvent.

[0009] This application adds ash-free, porous coconut shell activated carbon to the microporous layer slurry, which not only increases gas pathways and improves the gas transmission efficiency of the gas diffusion layer, but also avoids the effects of impurities. The coconut shell activated carbon is also hydrophobicized to avoid the problem of decreased fuel cell performance due to water absorption. Therefore, the microporous layer slurry provided by this application can enable the gas diffusion layer to have good gas transmission capacity, reduce mass transfer polarization, and ensure good fuel cell performance.

[0010] In a preferred embodiment, the microporous layer slurry comprises the following components in parts by weight: 5 to 10 parts of hydrophobically modified coconut shell activated carbon, 5 to 15 parts of a conductive agent, 5 to 10 parts of a first hydrophobic agent, 5 to 10 parts of a dispersing aid, and 10 to 150 parts of a solvent.

[0011] More preferably, the microporous layer slurry comprises the following components in parts by weight: 5 to 10 parts of hydrophobically modified coconut shell activated carbon, 9 to 11 parts of conductive agent, 6 to 9 parts of first hydrophobic agent, 5 to 8 parts of dispersing aid, and 10 to 150 parts of solvent.

[0012] More preferably, the microporous layer slurry comprises the following components in parts by weight: 5 to 10 parts of hydrophobically modified coconut shell activated carbon, 10 parts of a conductive agent, 6 to 9 parts of a first hydrophobic agent, 5 to 8 parts of a dispersing aid, and 10 to 150 parts of a solvent.

[0013] Particularly preferably, the microporous layer slurry comprises the following components in parts by weight: 5 to 10 parts of hydrophobically modified coconut shell activated carbon, 10 parts of a conductive agent, 7 to 8 parts of a first hydrophobic agent, 6 to 8 parts of a dispersing aid, and 10 to 150 parts of a solvent.

[0014] In a preferred embodiment, the hydrophobically modified coconut shell activated carbon is organosilane-modified coconut shell activated carbon. Organosilane modification can effectively improve the hydrophobicity of coconut shell activated carbon, thereby effectively avoiding the negative impact caused by water absorption by the microporous layer.

[0015] Preferably, the organosilane comprises trimethylchlorosilane (TMCS) and / or fluorinated silane. Experimental results show that the contact angle of coconut shell activated carbon can reach above 118° after modification with trimethylchlorosilane (TMCS) or fluorinated silane.

[0016] More preferably, since the carbon chain of the fluorine-containing compound has ultra-high chemical stability and extremely low surface free energy, the fluorine-containing silane has higher hydrophobicity than trimethylchlorosilane.

[0017] Perfluoroalkyl groups are particularly preferred because they have the best hydrophobicity compared to other fluorinated silanes. Experimental results have shown that the contact angle of coconut shell activated carbon modified with (trifluoromethyl)trimethylsilane can reach up to 148°, achieving a superhydrophobic effect.

[0018] In a preferred embodiment, the conductive agent includes at least one of Vulcan XC-72 carbon black, Ketjen black, acetylene black, Black pearls conductive carbon black, carbon nanotubes, and graphene powder. More preferably, the conductive agent is Vulcan XC-72 carbon black.

[0019] In a preferred embodiment, the first hydrophobic agent includes at least one of polytetrafluoroethylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, polyvinylidene fluoride, and polychlorotrifluoroethylene. More preferably, the first hydrophobic agent includes polytetrafluoroethylene.

[0020] In a preferred embodiment, the dispersing aid includes TEGO 760w (Tego wetting and dispersing agent 760W), TEGO 755w (Tego wetting and dispersing agent 755W), Solsperse W210 (Lubrizol, Solsperse TM W210 aqueous dispersant), Solsperse W205 (Lubrizol, Solsperse TM W205 aqueous polymer dispersant). More preferably, the dispersing aid is TEGO 760w.

[0021] In a preferred embodiment, the solvent comprises at least one of water, ethanol, ethylene glycol, isopropyl alcohol, and n-propyl alcohol. More preferably, the solvent is a mixed solvent of one of ethanol, ethylene glycol, isopropyl alcohol, and n-propyl alcohol and water. Even more preferably, the solvent is a mixed solvent of ethanol and water.

[0022] In a second aspect, the present application provides a method for preparing the aforementioned microporous layer slurry, comprising: uniformly mixing, by weight, hydrophobically modified coconut shell activated carbon, a conductive agent, a first hydrophobizing agent, a dispersing aid, and a solvent to obtain the microporous layer slurry. The microporous layer slurry preparation method of the present application utilizes readily available raw materials and is simple to operate, making it well-suited for industrial production.

[0023] Traditional methods for hydrophobic modification include alkali modification, plasma vapor deposition, and heat treatment. However, these methods have harsh processing conditions, high costs, and can also cause pore collapse in the activated carbon. Therefore, this application uses a chemical grafting modification method to hydrophobically modify coconut shell activated carbon.

[0024] In a preferred embodiment, the preparation method of the hydrophobically modified coconut shell activated carbon comprises: hydrophobically modifying the coconut shell activated carbon using organosilane.

[0025] Preferably, the ratio of the mass of the coconut shell activated carbon to the volume of the organosilane (also referred to as the mass-to-volume ratio) is (5-10) g:(1-6) mL.

[0026] Preferably, the hydrophobic modification is carried out at ambient temperature for 5 to 24 hours with stirring and reflux. The ambient temperature is determined according to the environment in which the hydrophobic modification process is carried out, for example, the ambient temperature can be 10°C, 15°C, 20°C, 30°C, 35°C, etc.

[0027] More preferably, after the hydrophobic modification, the obtained hydrophobically modified coconut shell activated carbon is washed alternately multiple times with ethanol and deionized water.

[0028] More preferably, the hydrophobically modified coconut shell activated carbon is further dried, and the drying temperature is 100° C. to 120° C., and the drying time is 10 hours to 12 hours.

[0029] In a specific embodiment, the method for hydrophobically modifying coconut shell activated carbon using organosilane may include: providing a toluene suspension of coconut shell activated carbon; adding organosilane to the toluene suspension of coconut shell activated carbon for hydrophobic modification; removing toluene to obtain hydrophobically modified coconut shell activated carbon, and washing and drying the hydrophobically modified coconut shell activated carbon.

[0030] In a specific embodiment, the toluene suspension of coconut shell activated carbon can be prepared by the following method: crushing and screening the raw material of coconut shell activated carbon to obtain the target particle size, and drying it in an oven to obtain coconut shell activated carbon particles; adding the coconut shell activated carbon particles to a toluene solution and stirring to obtain the toluene suspension of coconut shell activated carbon.

[0031] In another specific embodiment, the method for hydrophobic modification of coconut shell activated carbon using organosilane may include: crushing and screening the raw material of coconut shell activated carbon to obtain a target particle size, and drying it in an oven to obtain coconut shell activated carbon particles; and soaking the coconut shell activated carbon particles in a toluene solution of organosilane for hydrophobic modification.

[0032] In some preferred embodiments, the viscosity of the microporous layer slurry prepared by the microporous layer slurry preparation method is 200 cP to 1100 cP.

[0033] In a third aspect, the present application provides a gas diffusion layer, comprising: a hydrophobic substrate layer; and a microporous layer located on the hydrophobic substrate layer, wherein the microporous layer is made of the above-mentioned microporous layer slurry.

[0034] By adding coconut shell activated carbon to the microporous layer slurry, the pore structure of the gas diffusion layer can be effectively improved and the gas path can be increased. Experimental verification shows that compared with no coconut shell activated carbon, whether adding un-hydrophobically modified coconut shell activated carbon or adding hydrophobically modified coconut shell activated carbon, the porosity and air permeability of the gas diffusion layer are significantly improved, with the porosity reaching 70% to 90% and the air permeability reaching 50L / m 2 ·S~60L / m 2 Furthermore, compared with the addition of unhydrophobically modified coconut shell activated carbon, the addition of hydrophobically modified coconut shell activated carbon can avoid the pore blockage problem caused by water absorption under high humidity, allowing the reaction gas with a certain humidity to diffuse smoothly through the pores.

[0035] In a preferred embodiment, the hydrophobic substrate layer is hydrophobically modified carbon fiber paper or hydrophobically modified carbon fiber cloth.

[0036] In a fourth aspect, the present application provides a method for preparing the above-mentioned gas diffusion layer, which comprises: coating the above-mentioned microporous layer slurry on a hydrophobic substrate layer and drying it to form a microporous layer; and sintering the hydrophobic substrate layer and the microporous layer to obtain the gas diffusion layer.

[0037] In some preferred embodiments, the drying temperature is 80° C. to 100° C., and the drying time is 10 min to 15 min.

[0038] In some preferred embodiments, the sintering temperature is 300° C. to 400° C., and the sintering time is 1 hour to 8 hours.

[0039] In some specific embodiments, when coating the microporous layer slurry on the hydrophobic substrate layer, spray coating, blade coating or slit coating is adopted.

[0040] In some preferred embodiments, the method for preparing the hydrophobic substrate layer comprises: coating a second hydrophobic agent on a substrate, and sequentially performing drying and sintering.

[0041] More preferably, the substrate is porous carbon fiber paper or porous carbon fiber cloth.

[0042] Preferably, the second hydrophobic agent is at least one selected from polytetrafluoroethylene emulsion, tetrafluoroethylene and hexafluoropropylene copolymer emulsion, polyvinylidene fluoride emulsion, and polychlorotrifluoroethylene suspension.

[0043] More preferably, the mass percentage of the second hydrophobic agent in the hydrophobic substrate layer is 1% to 50%.

[0044] Preferably, when preparing the hydrophobic substrate layer, the drying temperature is 80° C. to 100° C., and the drying time is 10 min to 15 min.

[0045] Preferably, when preparing the hydrophobic substrate layer, the sintering temperature is 300° C. to 400° C., and the sintering time is 1 hour to 8 hours.

[0046] In some specific embodiments, the second hydrophobic agent is coated on the substrate by spraying, blade coating or dipping.

[0047] In some specific embodiments, the method for preparing the hydrophobic substrate layer includes: first performing the following operations one or more times: immersing the substrate in an emulsion or suspension containing a second hydrophobic agent, standing for a target time, and then taking it out and drying it; and then sintering to form the hydrophobic substrate layer.

[0048] In a fifth aspect, the present application provides a hydrogen fuel cell comprising the above-mentioned gas diffusion layer.

[0049] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0050] The microporous layer slurry of the present application includes a specific proportion of hydrophobically modified coconut shell activated carbon, a conductive agent, a first hydrophobic agent, a dispersing aid and a solvent. The microporous layer slurry can improve the pore structure of the gas diffusion layer, increase the transmission path of the reaction gas, and facilitate more reaction gases to diffuse quickly and effectively to the catalyst layer for reaction, thereby improving the transmission efficiency; at the same time, it can also effectively improve the hydrophobicity of the microporous layer, which can not only maintain the humidity of the reaction gas, but also discharge the liquid water produced by the cathode reaction in time, thereby reducing the mass transfer polarization phenomenon and improving the performance of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The following figures describe in detail exemplary embodiments disclosed in this application. Identical reference numerals denote similar structures in several views of the drawings. Those skilled in the art will appreciate that these embodiments are non-limiting, exemplary embodiments, and that the drawings are for illustration and description purposes only and are not intended to limit the scope of this application. Other embodiments may also achieve the same inventive intent as described in this application. It should be understood that the drawings are not drawn to scale. Among them:

[0052] Figure 1 The infrared spectra of the hydrophobically modified coconut shell activated carbon and the unhydrophobically modified coconut shell activated carbon prepared in Example 1 of the present application are shown;

[0053] Figure 2Schematic diagrams of contact angles of the hydrophobically modified coconut shell activated carbons prepared in Examples 1, 2, and 5, and the unhydrophobically modified coconut shell activated carbon of Comparative Example 1, wherein (A) is a schematic diagram of the contact angle of the unhydrophobically modified coconut shell activated carbon of Comparative Example 1, (B) is a schematic diagram of the contact angle of the hydrophobically modified coconut shell activated carbon prepared in Example 5, (C) is a schematic diagram of the contact angle of the hydrophobically modified coconut shell activated carbon prepared in Example 1, and (D) is a schematic diagram of the contact angle of the hydrophobically modified coconut shell activated carbon prepared in Example 2;

[0054] Figure 3 Schematic diagram of electrochemical performance test results of proton exchange membrane fuel cells assembled using the GDLs prepared in Examples 6 to 10 and Comparative Examples 3 to 4. DETAILED DESCRIPTION

[0055] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content of this application. Various local modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but is intended to be of the widest scope consistent with the claims.

[0056] Unless otherwise specified, all reagents and raw materials used can be purchased from commercial sources. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or according to the product specifications.

[0057] Coconut shell activated carbon was purchased from Tianneng Carbon; Vulcan XC-72 carbon black was purchased from Cabot Corporation, USA; PTFE emulsion was purchased from Daikin Fluorochemical; TEGO 760w was purchased from Yingchuang, Germany; TMCS was purchased from Macklin Reagent; porous carbon paper was purchased from Toray, Japan;

[0058] The viscosity test was performed using a rotational viscometer (Shanghai Lichen Instrument Technology Co., Ltd., NDJ-8S) under the following conditions: temperature 25 ± 5 °C, rotor No. 3, and rotation speed 30 rpm.

[0059] In order to analyze the chemical structure and composition of the samples, FTIR spectroscopy was performed on the samples using a Brugg Tensor27, Bruker, Germany. Before recording the spectrum, all samples were dried to remove the influence of moisture. The spectrum acquisition range was set at 4000–400 cm -1 , this range covers a wide range of chemical bond vibrations from high-frequency OH stretching vibrations to low-frequency skeleton vibrations.

[0060] The electrochemical performance test was carried out using the Dalian Ruige fuel cell test platform.

[0061] Microporous Layer Slurry Example

[0062] Example 1

[0063] This embodiment provides a microporous layer slurry, which includes the following components: 5g of hydrophobically modified coconut shell activated carbon, 10g of Vulcan XC-72 carbon black, 7g of PTFE emulsion, 6g of TEGO 760w, and 72g of a mixed solvent of water and ethanol, wherein the mass ratio of water to ethanol is 1:1.

[0064] The preparation method of the microporous layer slurry of this embodiment includes the following steps:

[0065] (1) Hydrophobic modification of coconut shell activated carbon

[0066] Weigh 5g of 30x60 mesh coconut shell activated carbon, crush it in a ball mill, and sieve it to obtain particles 100nm in size. Soak the coconut shell activated carbon in 200mL of toluene solution and stir for 10 minutes to obtain a toluene suspension of coconut shell activated carbon. Add 1mL of (trifluoromethyl)trimethylsilane, stir and reflux for 8 hours, and remove excess toluene by rotary evaporation. Wash the suspension three times with ethanol and then deionized water, alternating between each. Dry it in a vacuum at 110°C for 12 hours before use.

[0067] Figure 1 The infrared spectra of unmodified coconut shell activated carbon (Origin) and hydrophobically modified coconut shell activated carbon (Modified) are shown in Figure 1. Comparing the infrared curves of the two, we can see that the hydrophobically modified coconut shell activated carbon has a high IR value at 1206.7 cm -1 An obvious CF peak appeared at , which indicated that (trifluoromethyl)trimethylsilane was successfully grafted onto coconut shell activated carbon.

[0068] (2) Preparation of microporous layer slurry

[0069] Hydrophobically modified coconut shell activated carbon, Vulcan XC-72 carbon black, PTFE emulsion, and TEGO 760w were added to a mixed solvent of water and ethanol according to a mass ratio, and mixed evenly using a homogenizer to obtain a microporous layer slurry. The viscosity of the microporous layer slurry was measured to be 1000 cP.

[0070] Example 2

[0071] This embodiment provides a microporous layer slurry, which includes the following components: 5g of hydrophobically modified coconut shell activated carbon, 10g of Vulcan XC-72 carbon black, 7g of PTFE emulsion, 6g of TEGO 760w, and 72g of a mixed solvent of water and ethanol, wherein the mass ratio of water to ethanol is 1:1.

[0072] The preparation method of the microporous layer slurry of this embodiment includes the following steps:

[0073] (1) Hydrophobic modification of coconut shell activated carbon

[0074] Weigh 5g of 30x60 mesh coconut shell activated carbon, crush it in a ball mill, and sieve it to obtain particles 100nm in size. Soak the coconut shell activated carbon in 200mL of toluene solution and stir for 10 minutes to obtain a toluene suspension of coconut shell activated carbon. Add 3mL of (trifluoromethyl)trimethylsilane, stir and reflux for 8 hours, and remove excess toluene by rotary evaporation. Wash the suspension three times with ethanol and then distilled water, alternating between each. Dry it in a vacuum at 110°C for 12 hours before use.

[0075] (2) Preparation of microporous layer slurry

[0076] Hydrophobically modified coconut shell activated carbon, Vulcan XC-72 carbon black, PTFE emulsion, and TEGO 760w were added to a mixed solvent of water and ethanol according to a mass ratio, and mixed evenly using a homogenizer to obtain a microporous layer slurry. The viscosity of the microporous layer slurry was measured to be 1000 cP.

[0077] Example 3

[0078] This embodiment provides a microporous layer slurry, which includes the following components: 8g of hydrophobically modified coconut shell activated carbon, 10g of Vulcan XC-72 carbon black, 9g of PTFE emulsion, 6g of TEGO 760w, and 87g of a mixed solvent of water and ethanol, wherein the mass ratio of water to ethanol is 1:1.

[0079] The preparation method of the microporous layer slurry of this embodiment includes the following steps:

[0080] (1) Hydrophobic modification of coconut shell activated carbon

[0081] Weigh 8g of 30x60 mesh coconut shell activated carbon, crush it in a ball mill, and sieve it to obtain particles 100nm in size. Soak the coconut shell activated carbon in 200mL of toluene solution and stir for 10 minutes to obtain a toluene suspension of coconut shell activated carbon. Add 4.8mL of (trifluoromethyl)trimethylsilane, stir and reflux for 8 hours, and remove excess toluene by rotary evaporation. Then, wash the suspension three times with ethanol and then distilled water, alternating between each. Then, vacuum dry it at 110°C for 12 hours before use.

[0082] (2) Preparation of microporous layer slurry

[0083] Hydrophobically modified coconut shell activated carbon, Vulcan XC-72 carbon black, PTFE emulsion, and TEGO 760w were added to a mixed solvent of water and ethanol according to a mass ratio, and mixed evenly using a homogenizer to obtain a microporous layer slurry. The viscosity of the microporous layer slurry was measured to be 1000 cP.

[0084] Example 4

[0085] This embodiment provides a microporous layer slurry, which includes the following components: 10g of hydrophobically modified coconut shell activated carbon, 10g of Vulcan XC-72 carbon black, 10g of PTFE emulsion, 6g of TEGO 760w, and 98g of a mixed solvent of water and ethanol, wherein the mass ratio of water to ethanol is 1:1.

[0086] The preparation method of the microporous layer slurry of this embodiment includes the following steps:

[0087] (1) Hydrophobic modification of coconut shell activated carbon

[0088] Weigh 10g of 30x60 mesh coconut shell activated carbon, crush it in a ball mill, and sieve it to obtain particles 100nm in size. Soak the coconut shell activated carbon in 200mL of toluene solution and stir for 10 minutes to obtain a toluene suspension of coconut shell activated carbon. Add 6mL of (trifluoromethyl)trimethylsilane, stir and reflux for 8 hours, and remove excess toluene by rotary evaporation. Wash the suspension three times with ethanol and then distilled water, alternating between each. Dry it in a vacuum at 110°C for 12 hours before use.

[0089] (2) Preparation of microporous layer slurry

[0090] Hydrophobically modified coconut shell activated carbon, Vulcan XC-72 carbon black, PTFE emulsion, and TEGO 760w were added to a mixed solvent of water and ethanol according to a mass ratio, and mixed evenly using a homogenizer to obtain a microporous layer slurry. The viscosity of the microporous layer slurry was measured to be 1000 cP.

[0091] Example 5

[0092] This embodiment provides a microporous layer slurry, which includes the following components: 5g of hydrophobically modified coconut shell activated carbon, 10g of Vulcan XC-72 carbon black, 7g of PTFE emulsion, 6g of TEGO 760w, and 72g of a mixed solvent of water and ethanol, wherein the mass ratio of water to ethanol is 1:1.

[0093] The preparation method of the microporous layer slurry of this embodiment includes the following steps:

[0094] (1) Hydrophobic modification of coconut shell activated carbon

[0095] Weigh 5 g of 30×60 mesh coconut shell activated carbon, crush it in a ball mill, and sieve it to obtain 100 nm particles. This particle size was then immersed in 100 mL of a 6% (volume fraction) TMCS solution in toluene, stirred, and refluxed for 24 hours. The mixture was then washed three times with ethanol and then distilled water, alternating between washes, to remove excess TMCS. The mixture was then vacuum-dried at 110°C for 12 hours before use.

[0096] (2) Preparation of microporous layer slurry

[0097] Hydrophobically modified coconut shell activated carbon, Vulcan XC-72 carbon black, PTFE emulsion, and TEGO 760w were added to a mixed solvent of water and ethanol according to a mass ratio, and mixed evenly using a homogenizer to obtain a microporous layer slurry. The viscosity of the microporous layer slurry was measured to be 200 cP.

[0098] Comparative Example 1

[0099] This comparative example provides a microporous layer slurry, which differs from the microporous layer slurry of Example 1 only in that coconut shell activated carbon without hydrophobic modification is used.

[0100] The only difference between the preparation method of the microporous layer slurry of this comparative example and the preparation method of Example 1 is that the coconut shell activated carbon is not subjected to hydrophobic modification. The viscosity of the microporous layer slurry prepared in this comparative example is 200 cP.

[0101] Comparative Example 2

[0102] This comparative example provides a microporous layer slurry without adding coconut shell activated carbon, and includes the following components: 10g of Vulcan XC-72 carbon black, 5g of PTFE emulsion, 6g of TEGO 760w, and 46g of a mixed solvent of water and ethanol, wherein the mass ratio of water to ethanol is 1:1.

[0103] The preparation method of the microporous layer slurry of this comparative example comprises the following steps:

[0104] Vulcan XC-72 carbon black, PTFE emulsion, and TEGO 760w were added to a mixed solvent of water and ethanol according to a mass ratio, and mixed evenly using a homogenizer to obtain a microporous layer slurry. The viscosity of the microporous layer slurry was measured to be 1000 cP.

[0105] Contact angle test

[0106] The hydrophobicity of a material surface can be characterized by measuring the contact angle between the material and water. When the contact angle is less than 90°, the material is hydrophilic, and when the contact angle is greater than 90°, the material is hydrophobic.

[0107] Figure 2The contact angles of the hydrophobically modified coconut shell activated carbons prepared in Examples 1, 2 and 5 and the non-hydrophobically modified coconut shell activated carbon of Comparative Example 1 are shown. Figure 2 As shown in Figure (A), the contact angle of coconut shell activated carbon without hydrophobic modification is 64°, showing typical hydrophilic properties. This hydrophilicity will cause it to easily absorb water, thereby blocking the internal pores, which seriously affects the passage of gas. At the same time, water absorption will also destroy the water balance inside the entire battery, ultimately leading to a decrease in battery performance. Figure 2 As shown in Figure (B), after TMCS treatment, hydrophobic methyl (-CH3) groups are introduced on the surface and inside the pores of coconut shell activated carbon, so the contact angle reaches 118° and the material begins to become hydrophobic. Figure 2 As shown in Figures (C) and (D), when treated with (trifluoromethyl)trimethylsilane, CF bonds with extremely low surface energy are introduced on the surface of coconut shell activated carbon, making the material more hydrophobic and reaching a contact angle of 130°. As the amount of (trifluoromethyl)trimethylsilane increases, more CF bonds are grafted onto the surface, further increasing the hydrophobicity and reaching a contact angle of 148°. The coconut shell activated carbon changes from hydrophilic to superhydrophobic, thus effectively avoiding the negative effects of water absorption.

[0108] Gas Diffusion Layer Embodiment

[0109] Example 6

[0110] This embodiment provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Example 1.

[0111] The method for preparing the gas diffusion layer of this embodiment comprises the following steps:

[0112] (1) Preparation of hydrophobic substrate layer

[0113] A porous carbon paper measuring 200 mm × 150 mm × 0.2 mm was impregnated with a 1% PTFE emulsion. After standing for 10 minutes, the paper was removed and dried at 100°C. This step was repeated three times to obtain a porous carbon paper containing 5% PTFE. The paper was then sintered at 350°C for 1 hour to obtain a hydrophobic substrate layer.

[0114] (2) Preparation of microporous layer

[0115] The microporous layer slurry of Example 1 was evenly coated on the hydrophobic substrate layer by slit coating, baked at 90° C. for 10 minutes, and then sintered at 350° C. for 2 hours. The thickness of the microporous layer was measured by a thickness gauge and was 50 μm.

[0116] Example 7

[0117] This embodiment provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Example 2.

[0118] The method for preparing the gas diffusion layer of this embodiment comprises the following steps:

[0119] (1) Preparation of hydrophobic substrate layer: same as Example 6.

[0120] (2) Preparation of microporous layer: The only difference from Example 6 is that the microporous layer slurry of Example 2 is used.

[0121] Example 8

[0122] This embodiment provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Example 3.

[0123] The method for preparing the gas diffusion layer of this embodiment comprises the following steps:

[0124] (1) Preparation of hydrophobic substrate layer: same as Example 6.

[0125] (2) Preparation of microporous layer: The only difference from Example 6 is that the microporous layer slurry of Example 3 is used.

[0126] Example 9

[0127] This embodiment provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Example 4.

[0128] The method for preparing the gas diffusion layer of this embodiment comprises the following steps:

[0129] (1) Preparation of hydrophobic substrate layer: same as Example 6.

[0130] (2) Preparation of microporous layer: The only difference from Example 6 is that the microporous layer slurry of Example 4 is used.

[0131] Example 10

[0132] This embodiment provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Example 5.

[0133] The method for preparing the gas diffusion layer of this embodiment comprises the following steps:

[0134] (1) Preparation of hydrophobic substrate layer

[0135] A porous carbon paper measuring 200 mm x 150 mm x 0.2 mm was impregnated with a 2% PTFE emulsion. After standing for 10 minutes, the paper was removed and dried at 100°C. This step was repeated three times to obtain a carbon paper with a 15% PTFE content. The paper was then sintered at 350°C for 1 hour to form a hydrophobic substrate layer.

[0136] (2) Preparation of microporous layer

[0137] The microporous layer slurry of Example 5 was evenly coated on the hydrophobic substrate layer by a slit coating method, baked at 90° C. for 10 minutes, and then sintered at 350° C. for 2 hours. The thickness of the microporous layer was 50 μm.

[0138] Comparative Example 3

[0139] This comparative example provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Comparative Example 1.

[0140] The method for preparing the gas diffusion layer of this embodiment comprises the following steps:

[0141] (1) Preparation of hydrophobic substrate layer: same as Example 6.

[0142] (2) Preparation of microporous layer: The only difference from Example 6 is that the microporous layer slurry of Comparative Example 1 is used.

[0143] Comparative Example 4

[0144] This comparative example provides a gas diffusion layer, which includes a hydrophobic substrate layer and a microporous layer located on the hydrophobic substrate layer, and the microporous layer is made of the microporous layer slurry of Comparative Example 2.

[0145] The preparation method of the gas diffusion layer of this comparative example comprises the following steps:

[0146] (1) Preparation of hydrophobic substrate layer

[0147] A porous carbon paper measuring 200 mm × 150 mm × 0.2 mm was impregnated with a 2% PTFE emulsion. After standing for 10 minutes, the paper was removed and dried at 100°C. This step was repeated three times to obtain a porous carbon paper containing 15% PTFE. The paper was then sintered at 350°C for 1 hour to obtain a hydrophobic substrate layer.

[0148] (2) Preparation of microporous layer

[0149] The microporous layer slurry of Comparative Example 2 was evenly coated on the hydrophobic substrate layer by a slit coating method, baked at 90° C. for 10 minutes, and then sintered at 350° C. for 2 hours. The thickness of the microporous layer was 50 μm.

[0150] GDL air permeability test

[0151] Air permeability and porosity are two important indicators reflecting the air permeability of GDL. The air permeability and porosity of the GDL prepared in the above examples and comparative examples will be tested below.

[0152] The air permeability of GDL is tested using Shanghai Luozhong Technology's RT-5300 air permeability tester. Under a specified pressure difference, the volume of air per unit area flowing through the GDL per unit time is measured in L / m -2 s.

[0153] The porosity of the GDL was measured using an American AutoPore IV 9500 fully automatic mercury intrusion instrument. The porosity of the GDL was obtained by multiplying the ratio of the pore volume measured by mercury intrusion to the total volume of the sample by 100%.

[0154] Table 1 GDL air permeability test results

[0155]

[0156] As shown in Table 1, compared to Comparative Example 4, the addition of hydrophobically modified coconut shell activated carbon or unmodified coconut shell activated carbon to the GDLs in Examples 6-10 and Comparative Example 3 significantly improved the air permeability and porosity of the GDLs. Furthermore, a comparison of the results of Comparative Example 3, Examples 6 and 7, and Example 10 shows that, when the mass of the added coconut shell activated carbon is the same, changes in other factors do not significantly affect the air permeability and porosity of the GDLs. This demonstrates that the addition of coconut shell activated carbon plays a crucial role in the pore structure of the GDLs. Furthermore, after hydrophobic modification, the organosilane used for modification occupies a small portion of the pore volume of the original coconut shell activated carbon, resulting in a slight decrease in the porosity and air permeability of Examples 6, 7, and Example 10 compared to Comparative Example 3. Furthermore, Examples 8 and 9 show that the air permeability and porosity of the GDLs increase with increasing amounts of hydrophobically modified coconut shell activated carbon.

[0157] It should be noted that the air permeability and porosity can reflect the effect of the addition of coconut shell activated carbon on the pore structure of GDL, but cannot reflect the effect on the performance of the fuel cell when operating under a certain humidity environment. 2The proton exchange membrane fuel cell uses the American Gore proton exchange membrane and the Japanese TANAKA platinum carbon catalyst. The electrochemical performance of the fuel cell was tested under the same conditions: the relative humidity of the cathode and anode inlets was 30%, and the battery temperature was 80℃. The test results are as follows: Figure 3 Typically, the operating voltage of a fuel cell is 0.65 V, so Table 2 lists the current density of the fuel cell at 0.65 V. A higher current density at the same operating voltage indicates higher power and better fuel cell performance.

[0158] Table 2 Current density of fuel cell at 0.65V operating voltage

[0159]

[0160] like Figure 3 As shown, a comparison of the results of Comparative Examples 3 and 4 shows that, after adding unmodified coconut shell activated carbon, at low current densities, the hydrophilic coconut shell activated carbon absorbs moisture from the passing reactant gases, causing a water shortage within the fuel cell, which is detrimental to the cell's catalytic reaction. As the reaction proceeds, at high current densities, the large amount of liquid water generated by the reaction enters the coconut shell activated carbon, clogging its pores and preventing effective discharge, causing flooding of the fuel cell. Therefore, compared to Comparative Example 4, the cell performance of Comparative Example 3, which added unmodified coconut shell activated carbon, was significantly reduced.

[0161] In Example 10, hydrophobic treatment of the hydrophilic coconut shell activated carbon improved its hydrophobicity, resulting in a slight improvement in battery performance. Furthermore, the test results of Examples 6 and 7 show that as the hydrophobicity of the coconut shell activated carbon improves, its adsorption of moisture carried by the reactant gases decreases. Its rich internal pore structure increases gas pathways, allowing more moist reactant gases to enter the battery's catalyst layer for reaction. At the same time, water produced by the reaction can also be smoothly discharged through the pores, improving the water balance within the battery, resulting in a significant improvement in battery performance.

[0162] However, it should be noted that in Example 8, although the proportion of hydrophobic coconut shell activated carbon increased, the porosity of the GDL increased, and therefore water was discharged smoothly at high current density, at low current density, excessive drainage would cause the membrane to overdry, which also affected the smooth progress of the reaction. Therefore, the performance of Example 8 at low current density was basically the same as that of Example 7, and even the current density at 0.65V was slightly reduced, while the performance was improved at high current density. In Example 9, as the hydrophobic coconut shell activated carbon was further increased, the phenomenon of battery water shortage became more serious, and the battery performance began to decline at low current density, which was not conducive to improving battery performance. However, the battery performance was still significantly better than Comparative Examples 3 and 4 without the addition of hydrophobic coconut shell activated carbon.

[0163] The above description of the embodiments is intended to facilitate understanding and application of the present application by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without expending any creative effort. Therefore, the present application is not limited to the embodiments described herein, and improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope and spirit of this application are within the scope of this application.

Claims

1. A gas diffusion layer, characterized in that: include: a hydrophobic substrate layer; a microporous layer located on the hydrophobic substrate layer, wherein the microporous layer is made of a microporous layer slurry; The microporous layer slurry comprises the following components in parts by weight: 5 to 10 parts of hydrophobically modified coconut shell activated carbon, 5 to 15 parts of conductive agent, 5 to 10 parts of first hydrophobic agent, 5 to 10 parts of dispersing aid, and 10 to 150 parts of solvent; The hydrophobically modified coconut shell activated carbon is coconut shell activated carbon modified by organosilane, wherein the organosilane comprises trimethylchlorosilane and / or fluorine-containing silane; The ratio of the mass of the coconut shell activated carbon to the volume of the organosilane is (5-10) g: (1-6) mL; The conductive agent includes at least one of Vulcan XC-72 carbon black, Ketjen black, acetylene black, Black pearls conductive carbon black, carbon nanotubes, and graphene powder; The first hydrophobic agent includes at least one of polytetrafluoroethylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, polyvinylidene fluoride, and polychlorotrifluoroethylene; The porosity of the gas diffusion layer is 70% to 90%, and the air permeability is 50 L / m 2 ·S~60L / m 2 ·S.

2. The gas diffusion layer according to claim 1, characterized in that The dispersing aid includes at least one of TEGO 760w, TEGO755w, Solsperse W210, and Solsperse W205; And / or, the solvent includes at least one of water, ethanol, ethylene glycol, isopropanol, and n-propanol.

3. The gas diffusion layer according to claim 1 or 2, characterized in that The preparation method of the microporous layer slurry comprises: uniformly mixing hydrophobically modified coconut shell activated carbon, a conductive agent, a first hydrophobic agent, a dispersing aid and a solvent according to parts by weight to obtain the microporous layer slurry.

4. The gas diffusion layer according to claim 3, characterized in that The preparation method of the hydrophobically modified coconut shell activated carbon meets at least one of the following conditions: (1) The temperature during hydrophobic modification is ambient temperature, the time is 5 hours to 24 hours, and stirring and refluxing are performed; (2) After hydrophobic modification, the hydrophobically modified coconut shell activated carbon was washed alternately with ethanol and deionized water for multiple times; (3) The hydrophobically modified coconut shell activated carbon was also dried at a temperature of 100°C to 120°C and a drying time of 10 hours to 12 hours.

5. The gas diffusion layer according to claim 1, characterized in that The hydrophobic substrate layer is hydrophobically modified carbon fiber paper or hydrophobically modified carbon fiber cloth.

6. A method for preparing a gas diffusion layer according to any one of claims 1 to 5, characterized in that: include: coating the microporous layer slurry on the hydrophobic substrate layer and drying it to form a microporous layer; The hydrophobic substrate layer and the microporous layer are sintered to obtain the gas diffusion layer.

7. The method for preparing a gas diffusion layer according to claim 6, characterized in that: After coating the microporous layer slurry on the hydrophobic substrate layer, the drying temperature is 80°C to 100°C and the drying time is 10min to 15min; And / or, the hydrophobic substrate layer and the microporous layer are sintered at a temperature of 300° C. to 400° C. and for a time of 1 hour to 8 hours.

8. The method for preparing a gas diffusion layer according to claim 6, wherein: The preparation method of the hydrophobic substrate layer comprises: coating a second hydrophobic agent on a substrate, and sequentially performing drying and sintering.

9. The method for preparing a gas diffusion layer according to claim 8, characterized in that: The second hydrophobic agent includes at least one of polytetrafluoroethylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, polyvinylidene fluoride, and polychlorotrifluoroethylene; And / or, the mass percentage of the second hydrophobic agent in the hydrophobic substrate layer is 1% to 50%.

10. A hydrogen fuel cell, characterized in that: The gas diffusion layer comprises the gas diffusion layer according to any one of claims 1 to 5.

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