A gas diffusion layer comprising a gradient hydrophilic resin microporous layer and a preparation method thereof

Abstract

The invention belongs to the technical field of fuel cells, and discloses a gas diffusion layer including a gradient hydrophilic resin microporous layer and a preparation method thereof, wherein the preparation method comprises the following steps: 1) soaking a substrate in a PTFE emulsion, taking it out and drying it to obtain a substrate layer; 2) mixing carbon powder, water, an alcohol solvent, a PTFE emulsion and a pore-forming agent evenly to form a slurry, and then coating it on one side of the substrate layer, drying and sintering it to form a homogeneous microporous layer on the substrate layer to obtain a gas diffusion layer including a homogeneous microporous layer; 3) fixing the gas diffusion layer including a homogeneous microporous layer by a clamp, making the homogeneous microporous layer contact Nafion solution or Nafion / PTFE composite emulsion, and making the substrate layer contact water or low-concentration PTFE emulsion at the same time, and drying after the contact is terminated to obtain a gas diffusion layer including a gradient hydrophilic resin microporous layer. The invention optimizes the water management capacity of the gas diffusion layer and improves the performance, stability and safety of the fuel cell at high current density.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cells, and in particular relates to a gas diffusion layer comprising a gradient hydrophilic resin microporous layer and a preparation method thereof. Background Art

[0002] As people pay more and more attention to energy consumption and environmental issues, the demand for environmentally friendly and sustainable energy solutions has become imperative. Proton exchange membrane fuel cells (PEMFCs) convert hydrogen energy into electrical energy and have attracted worldwide attention due to their high efficiency, high energy density and environmental friendliness.

[0003] The components of proton exchange membrane fuel cells mainly include membrane electrode (MEA) and bipolar plates, which together carry important functions such as electrochemical reaction and gas transmission. The core component membrane electrode consists of gas diffusion layer (GDL) on the anode side and cathode side, catalyst layer (CL) and proton exchange membrane (PEM). When the proton exchange membrane fuel cell is working, the reaction gas passes through the bipolar plate, gas diffusion layer and then reaches the three-phase interface of the catalyst layer to participate in electrochemical reactions, such as hydrogen oxidation reaction (HOR) at the anode and oxygen reduction reaction (ORR) at the cathode, and then the water produced by the electrochemical reaction is discharged to the flow channel.

[0004] The gas diffusion layer plays a vital role in the operation of proton exchange membrane fuel cells, including mechanical support, reaction gas diffusion, product water diffusion and transmission, electrical and thermal conductivity, etc., which directly affects the performance of the fuel cell. However, when the existing gas diffusion layer is operated for a longer time or at a higher current density, a large amount of water generated by electrochemistry cannot be discharged in time, and "flooding" is prone to occur. The water that cannot be discharged in time blocks the transmission path of oxygen or hydrogen to the catalyst layer, causing insufficient gas supply and a series of stability problems, resulting in fuel cell performance degradation and potential safety hazards. Summary of the invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies in the prior art and provide a gas diffusion layer comprising a gradient hydrophilic resin microporous layer and a preparation method thereof, thereby optimizing the water management capability of the gas diffusion layer and improving the performance, stability and safety of the fuel cell at high current density.

[0006] In order to solve the technical problem proposed by the present invention, the present invention provides a method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer, comprising the following steps:

[0007] 1) Soak the substrate in PTFE emulsion, take it out and dry it to obtain a base layer;

[0008] 2) carbon powder, water, alcohol solvent, PTFE emulsion and pore-forming agent are uniformly mixed to form a slurry, which is then coated on one side of the substrate layer, dried and sintered to form a homogeneous microporous layer on the substrate layer, thereby obtaining a gas diffusion layer including a homogeneous microporous layer;

[0009] 3) Fixing the gas diffusion layer including the homogeneous microporous layer by a fixture, making the homogeneous microporous layer contact with the Nafion solution or the Nafion / PTFE composite emulsion, and making the substrate layer contact with water or a low-concentration PTFE emulsion, and drying after the contact is terminated to obtain a gas diffusion layer including the gradient hydrophilic resin microporous layer.

[0010] In the above scheme, the substrate is a composite of one or more carbon fiber paper, carbon fiber woven cloth, and non-woven fabric, with a thickness of 100-500 μm and a porosity of 70-90%.

[0011] In the above scheme, the mass concentration of the PTFE emulsion in step 1) is 5-30%.

[0012] In the above scheme, the soaking time in step 1) is 1 to 5 minutes.

[0013] In the above scheme, the drying temperature in step 1) is 90-150°C.

[0014] In the above solution, the carbon powder is one or more of carbon black, acetylene black, carbon nanotubes, and graphite powder.

[0015] In the above scheme, the alcohol solvent is one or more of isopropanol, n-propanol and ethanol.

[0016] In the above scheme, the mass concentration of the PTFE emulsion in step 2) is 30-60%.

[0017] In the above scheme, the pore-forming agent is one or more of ammonium chloride, ammonium carbonate, and ammonium bicarbonate.

[0018] In the above scheme, the mass ratio of the carbon powder, water, alcohol solvent, PTFE in the PTFE emulsion, and pore-forming agent in step 2) is 100: (400-1000): (200-600): (10-40): (20-150).

[0019] In the above scheme, the drying temperature in step 2) is 90-150°C.

[0020] In the above scheme, the sintering temperature is 250-350° C., and the sintering time is 1-5 hours.

[0021] In the above solution, the thickness of the homogeneous microporous layer is 20-100 μm.

[0022] In the above scheme, the mass concentration of the Nafion solution is 5~20%.

[0023] In the above scheme, in the Nafion / PTFE composite emulsion, the sum of the mass concentrations of Nafion and PTFE is 5-35%, and the rest is water.

[0024] In the above scheme, in the Nafion / PTFE composite emulsion, the mass ratio of Nafion to PTFE is (0.5~3):1.

[0025] In the above scheme, the mass concentration of the low concentration PTFE emulsion in step 3) is 5-10%.

[0026] In the above scheme, the contact time is 30 to 120 minutes.

[0027] In the above scheme, the drying temperature in step 3) is 90-150°C.

[0028] The present invention also provides a gas diffusion layer comprising a gradient hydrophilic resin microporous layer, which is prepared by the above method.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The present invention allows the homogeneous microporous layer surface to contact with a Nafion solution or a Nafion / PTFE composite emulsion containing a hydrophilic group, and the substrate layer to contact with water or a low-concentration PTFE emulsion. Under the action of the concentration difference, the Nafion diffuses into the microporous layer, so that the Nafion forms a gradient distribution in the microporous layer, and a gas diffusion layer including a gradient hydrophilic resin microporous layer is obtained. Compared with a conventional gas diffusion layer, the drainage capacity of the gas diffusion layer is significantly improved, and the uniform distribution of reactants (H2 / O2) and water in the catalyst layer is promoted, thereby improving the performance, stability and safety of the fuel cell at a high current density.

[0031] 2) The preparation process of the gas diffusion layer of the present invention is simple, low-cost, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the principle of forming a gradient hydrophilic resin microporous layer according to an embodiment of the present invention.

[0033] Figure 2 A clamp used in an embodiment of the present invention.

[0034] Figure 3 Polarization curve test results of fuel cells prepared with gas diffusion layers of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of the present invention.

[0035] Figure 4Impedance test results of fuel cells prepared with gas diffusion layers of Example 1, Example 2 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0036] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0037] Example 1

[0038] A method for preparing a gas diffusion layer comprising a gradient hydrophilic resin comprises the following steps:

[0039] 1) Select carbon fiber paper with a thickness of 180 μm and a porosity of 86% as the substrate, soak the substrate in a PTFE emulsion with a mass concentration of 5% for 1 min, take it out and dry it at 90°C to obtain a base layer;

[0040] 2) acetylene black, deionized water, isopropanol, PTFE emulsion with a mass concentration of 60% and ammonium chloride are uniformly mixed to form a slurry, wherein the mass ratio of acetylene black, deionized water, isopropanol, PTFE in the PTFE emulsion and ammonium chloride is 100:800:300:10:20, the slurry is coated on one side of the substrate layer, dried at 90° C., and sintered at 300° C. for 1 hour to form a 30 μm thick homogeneous microporous layer on the substrate layer, thereby obtaining a gas diffusion layer including a homogeneous microporous layer;

[0041] 3) By Figure 2 The clamp shown fixes and seals the gas diffusion layer including the homogeneous microporous layer, and then injects Nafion / PTFE composite emulsion (the sum of Nafion+PTFE mass concentration is 30% and the mass ratio of Nafion:PTFE is 2:1) and deionized water into the homogeneous microporous layer side and the substrate layer side respectively, so that the homogeneous microporous layer surface contacts the Nafion / PTFE composite emulsion and the substrate layer surface contacts the water. After contacting for 90 minutes, the gas diffusion layer is taken out and dried at 90°C to obtain a gas diffusion layer including a gradient hydrophilic resin microporous layer.

[0042] Example 2

[0043] A method for preparing a gas diffusion layer comprising a gradient hydrophilic resin comprises the following steps:

[0044] 1) Select carbon fiber paper with a thickness of 200 μm and a porosity of 78% as the substrate, soak the substrate in a PTFE emulsion with a mass concentration of 30% for 5 minutes, take it out and dry it at 150°C to obtain a base layer;

[0045] 2) carbon black, deionized water, ethanol, PTFE emulsion with a mass concentration of 30% and ammonium bicarbonate are uniformly mixed to form a slurry, wherein the mass ratio of carbon black, deionized water, ethanol, PTFE in the PTFE emulsion and ammonium bicarbonate is 100:500:600:40:100, the slurry is coated on one side of the substrate layer, dried at 150° C., and sintered at 350° C. for 5 hours to form a homogeneous microporous layer with a thickness of 80 μm on the substrate layer, thereby obtaining a gas diffusion layer including a homogeneous microporous layer;

[0046] 3) By Figure 2 The clamp shown fixes and seals the gas diffusion layer including the homogeneous microporous layer, and then injects a Nafion solution with a mass concentration of 5% and a PTFE emulsion with a mass concentration of 10% into the homogeneous microporous layer side and the substrate layer side, respectively, so that the homogeneous microporous layer surface contacts the Nafion solution, and the substrate layer contacts the PTFE emulsion at the same time. After contacting for 120 minutes, the layer is taken out and dried at 150°C to obtain a gas diffusion layer including a gradient hydrophilic resin microporous layer.

[0047] Example 3

[0048] A method for preparing a gas diffusion layer comprising a gradient hydrophilic resin comprises the following steps:

[0049] 1) Select carbon fiber paper with a thickness of 300 μm and a porosity of 74% as the substrate, soak the substrate in a PTFE emulsion with a mass concentration of 20% for 3 minutes, take it out and dry it at 120°C to obtain a base layer;

[0050] 2) carbon black, deionized water, ethanol, PTFE emulsion with a mass concentration of 30% and ammonium bicarbonate are uniformly mixed to form a slurry, wherein the mass ratio of carbon black, deionized water, ethanol, PTFE in the PTFE emulsion and ammonium bicarbonate is 100:600:400:30:50, the slurry is coated on one side of the substrate layer, dried at 120° C., and sintered at 320° C. for 2 h to form a 40 μm thick homogeneous microporous layer on the substrate layer, thereby obtaining a gas diffusion layer including a homogeneous microporous layer;

[0051] 3) By Figure 2 The clamp shown fixes and seals the gas diffusion layer including the homogeneous microporous layer, and then injects Nafion / PTFE composite emulsion (the sum of Nafion+PTFE mass concentration is 10% and the Nafion:PTFE mass ratio is 1:1) and PTFE emulsion with a mass concentration of 8% into the homogeneous microporous layer side and the substrate layer side respectively, so that the homogeneous microporous layer surface contacts the Nafion / PTFE composite emulsion, and the substrate layer contacts the PTFE emulsion at the same time. After contacting for 100 minutes, the layer is taken out and dried at 120°C to obtain a gas diffusion layer including a gradient hydrophilic resin microporous layer.

[0052] Example 4

[0053] A method for preparing a gas diffusion layer comprising a gradient hydrophilic resin comprises the following steps:

[0054] 1) Select carbon fiber paper with a thickness of 200 μm and a porosity of 78% as the substrate, soak the substrate in a PTFE emulsion with a mass concentration of 30% for 5 minutes, take it out and dry it at 150°C to obtain a base layer;

[0055] 2) carbon black, deionized water, ethanol, PTFE emulsion with a mass concentration of 30% and ammonium bicarbonate are uniformly mixed to form a slurry, wherein the mass ratio of carbon black, deionized water, ethanol, PTFE in the PTFE emulsion and ammonium bicarbonate is 100:800:500:40:100, the slurry is coated on one side of the substrate layer, dried at 150° C., and sintered at 350° C. for 5 hours to form a homogeneous microporous layer with a thickness of 80 μm on the substrate layer, thereby obtaining a gas diffusion layer including a homogeneous microporous layer;

[0056] 3) By Figure 2 The clamp shown fixes and seals the gas diffusion layer including the homogeneous microporous layer, and then injects a Nafion solution with a mass concentration of 20% and a PTFE emulsion with a mass concentration of 10% into the homogeneous microporous layer side and the substrate layer side, respectively, so that the homogeneous microporous layer surface contacts the Nafion solution, and the substrate layer contacts the PTFE emulsion at the same time. After contacting for 120 minutes, the layer is taken out and dried at 150°C to obtain a gas diffusion layer including a gradient hydrophilic resin microporous layer.

[0057] Comparative Example 1

[0058] The difference between Comparative Example 1 and Example 1 is that the operation of step 3) is not performed, and the gas diffusion layer including the homogeneous microporous layer obtained in step 2) is used as the final product.

[0059] Comparative Example 2

[0060] The difference between Comparative Example 2 and Example 2 is that the process of step 3) is:

[0061] A Nafion solution with a mass concentration of 5% is directly coated on the homogeneous microporous layer of the gas diffusion layer including the homogeneous microporous layer, and dried at 90° C. to obtain a gas diffusion layer containing Nafion on the surface of the microporous layer.

[0062] The gas diffusion layers prepared in the examples and comparative examples were used as cathode gas diffusion layers to assemble membrane electrodes for testing, and other assembly conditions remained the same. Battery assembly information: The battery active area is 5×5 cm 2 The anode and cathode catalyst loadings were 0.1 and 0.3 mg / cm 2The plate is a graphite plate with a multi-channel serpentine flow field. The test conditions include: battery temperature 80°C, anode and cathode excess coefficients 1.0 and 2.0 respectively, anode and cathode inlet pressures controlled at 160 KPa and 150 KPa respectively, and cathode and cathode humidity of 80%. Figure 3 The polarization curve data shown. Impedance test at 1500 mA·cm −2 The test amplitude is 5%, the frequency range is 10K Hz~0.1 Hz, and the following is obtained: Figure 4 Impedance data shown.

[0063] like Figure 3 As shown, the performance of the fuel cell using the gas diffusion layer prepared in Example 1 and Example 2 is significantly better than that of the comparative example. The examples show better performance at high current density. −2 At the current density, the performance is improved by about 60 mV.

[0064] Figure 4 Indicates that each battery is at 1500 mA·cm −2 According to the impedance analysis below, when the embodiment and the comparative example have similar ohmic internal resistance, the embodiment has a smaller mass transfer resistance. This data further illustrates that the embodiment has a better water management capability.

[0065] Table 1 lists the microporous layer contact angle, air permeability and liquid water penetration pressure of each gas diffusion layer. It can be seen from the data that the embodiment has a smaller surface contact angle, reduced air permeability, and reduced liquid water penetration pressure, which once again shows that the embodiment is more conducive to the discharge of liquid water.

[0066] Table 1 Physical properties of gas diffusion layer

[0067]

[0068] The above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above descriptions. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims

1. A method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer, characterized in that: The following steps are involved: 1) Soak the substrate in PTFE emulsion, take it out and dry it to obtain a base layer; 2) carbon powder, water, alcohol solvent, PTFE emulsion and pore-forming agent are uniformly mixed to form a slurry, which is then coated on one side of the substrate layer, dried and sintered to form a homogeneous microporous layer on the substrate layer, thereby obtaining a gas diffusion layer including a homogeneous microporous layer; 3) Fixing the gas diffusion layer including the homogeneous microporous layer by a fixture, so that the homogeneous microporous layer surface contacts the Nafion solution or the Nafion / PTFE composite emulsion, and the substrate layer contacts water or a low-concentration PTFE emulsion; wherein the mass concentration of the Nafion solution is 5-25%; in the Nafion / PTFE composite emulsion, the sum of the mass concentrations of Nafion and PTFE is 5-35%, and the mass ratio of Nafion to PTFE is (0.5-3):1; the mass concentration of the low-concentration PTFE emulsion is 5-10%; drying is performed after the contact is terminated to obtain a gas diffusion layer including a gradient hydrophilic resin microporous layer.

2. The method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer according to claim 1, characterized in that: The contact time in step 3) is 30-120 minutes; the drying temperature in steps 1) to 3) is 90-150°C.

3. The method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer according to claim 1, characterized in that: The carbon powder is one or more of carbon black, carbon nanotubes, and graphite powder; the alcohol solvent is one or more of isopropanol, n-propanol, and ethanol; and the pore-forming agent is one or more of ammonium chloride, ammonium carbonate, and ammonium bicarbonate.

4. The method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer according to claim 1, characterized in that: In step 2), the mass concentration of the PTFE emulsion is 30-60%, and the mass ratio of the carbon powder, water, alcohol solvent, PTFE in the PTFE emulsion, and pore-forming agent is 100: (400-1000): (200-600): (10-40): (20-150).

5. The method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer according to claim 1, characterized in that: The sintering temperature is 250-350° C., and the sintering time is 1-5 hours. The thickness of the homogeneous microporous layer is 20-100 μm.

6. The method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer according to claim 1, characterized in that: The substrate is a composite of one or more carbon fiber paper, carbon fiber woven cloth, and non-woven cloth, with a thickness of 100-500 μm and a porosity of 70-90%.

7. The method for preparing a gas diffusion layer comprising a gradient hydrophilic resin microporous layer according to claim 1, characterized in that: In step 1), the mass concentration of the PTFE emulsion is 5-30%, and the immersion time is 1-5 min.

8. A gas diffusion layer comprising a gradient hydrophilic resin microporous layer prepared by the method according to any one of claims 1 to 7.

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