Membrane electrode with gradient catalyst layer on cathode side and preparation method of membrane electrode

Abstract

The invention relates to a membrane electrode of a gradient catalyst layer on a cathode side and a preparation method of the membrane electrode. The method comprises the following steps: providing a proton exchange membrane and an anode catalyst layer; providing first catalyst layer slurry, and coating the surface of the proton exchange membrane with the catalyst layer slurry to obtain a first catalyst layer; second catalyst layer slurry is provided, the second catalyst layer slurry is spun onto the first catalyst layer through an electrostatic spinning technology, a second catalyst layer is obtained after drying, and the first catalyst layer and the second catalyst layer form a double-layer gradient cathode catalyst layer; and carrying out hot-pressing transfer printing on the double-layer gradient cathode catalyst layer and the anode catalyst layer so as to combine the double-layer gradient cathode catalyst layer and the anode catalyst layer on the proton exchange membrane to obtain the membrane electrode. The catalyst layer obtained through the electrostatic spinning process and spinning is higher in porosity and better in pore structure uniformity, so that the cathode gradient catalyst layer with pores in an increasing trend is formed, water-gas mass transfer of a fuel cell in a high-current density area is facilitated, and the cell performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a membrane electrode with a gradient catalytic layer on the cathode side and a preparation method thereof. Background Art

[0002] Proton exchange membrane fuel cell (PEMFC) is an energy device that can directly convert hydrogen energy into electrical energy. It has broad application prospects in new energy vehicles, backup power supplies and other fields due to its high energy conversion efficiency, low operating temperature and environmental friendliness.

[0003] As one of the important components of the membrane electrode, the core component of the fuel cell, the catalyst layer provides a transmission channel in the electrochemical reaction, allowing the reactants to reach the triple phase point through the pore structure to participate in the chemical reaction and discharge the product water out of the catalyst layer. Its water vapor management ability determines the performance of the battery. Insufficient water in the catalyst layer will cause the ionomer proton conductivity to decrease, resulting in an increase in the battery's internal resistance and voltage loss. Excessive water will block the reactant transmission channel, thereby limiting the transport of hydrogen and oxygen and aggravating the concentration polarization of the battery. Therefore, improving the rationality of the pore distribution structure of the catalyst layer, thereby promoting water vapor diffusion under high current density of the battery and reducing material transmission resistance, will help improve battery performance.

[0004] The traditional PEMFC cathode catalyst layer is mostly a single layer, and its porosity and pore distribution are relatively simple. In order to improve the porosity of the catalyst layer, CN1964111A publicly proposed adding solvents with different boiling points to the catalyst slurry, and controlling the escape velocity of solvents with different boiling points in the catalyst layer by programmed temperature drying, thereby adjusting the porosity. However, these formed pores are irregular and can only provide channels for water vapor transmission, but cannot effectively guide water discharge. In addition, there are many uncertain factors in the solvent volatilization process, and it is difficult to ensure the consistency of the membrane electrode. CN113066999A publicly proposed adding ammonium salt pore formers to the catalyst slurry, spraying or coating the catalyst slurry on the substrate, and removing the solvent and ammonium salt pore formers in the slurry by heating and forming to obtain a porous membrane electrode. However, since the pore former is still present in the membrane electrode, and the PEMFC is very sensitive to impurities, trace amounts of impurity residues will also affect the performance or life of the battery. Summary of the invention

[0005] To this end, the present invention provides a membrane electrode with a gradient catalytic layer on the cathode side and a preparation method thereof, wherein the second catalytic layer is spun onto the first catalytic layer through an electrostatic spinning process, and the spun catalytic layer has a higher porosity and a better pore structure uniformity, thereby forming a cathode gradient catalytic layer with an increasing porosity, which is beneficial to the water vapor mass transfer of the fuel cell in the high current density region and improves the battery performance.

[0006] In order to solve the above technical problems, the present invention provides a membrane electrode with a gradient catalytic layer on the cathode side, comprising a proton exchange membrane and an anode catalytic layer and a cathode catalytic layer respectively arranged on the two side surfaces of the proton exchange membrane; wherein the cathode catalytic layer comprises a first catalytic layer and a second catalytic layer sequentially arranged along the surface of the proton exchange membrane.

[0007] In one embodiment of the present invention, the ratio of resin in the slurry to carbon in the catalyst (I / C) in the first catalytic layer is 0.7-1, and the platinum loading is 0.1 mg / cm 2 -0.25mg / cm 2 ;

[0008] In one embodiment of the present invention, the ratio of resin in the slurry to carbon in the catalyst (I / C) in the second catalytic layer is 0.5-0.7, and the platinum loading is 0.05 mg / cm 2 -0.1mg / cm 2 .

[0009] The present invention also provides a method for preparing a membrane electrode having a gradient catalytic layer on the cathode side, comprising:

[0010] Providing a proton exchange membrane and an anode catalyst layer;

[0011] Providing a first catalytic layer slurry, and coating the catalytic layer slurry on the surface of the proton exchange membrane to obtain a first catalytic layer;

[0012] Providing a second catalytic layer slurry, spinning the second catalytic layer slurry onto the first catalytic layer through an electrostatic spinning process, and obtaining a second catalytic layer after drying, wherein the first catalytic layer and the second catalytic layer constitute a double-layer gradient cathode catalytic layer;

[0013] The double-layer gradient cathode catalyst layer and the anode catalyst layer are hot-pressed and transferred to be combined on the proton exchange membrane to obtain a membrane electrode.

[0014] In one embodiment of the present invention, the catalyst layer slurry is coated on the surface of the proton exchange membrane to obtain a first catalyst layer, comprising:

[0015] The catalyst layer slurry is coated on the surface of the proton exchange membrane by using coating methods including scraping, spraying and slit coating.

[0016] In one embodiment of the present invention, the electrospinning process includes: an applied voltage of 10-30 kV, a flow rate of the spinning slurry of 1.0-1.8 mL / h, a solidification distance of 5-20 cm, and a spinning time of 2-5 h.

[0017] In one embodiment of the present invention, the second catalytic layer is dried at 40-80° C. to obtain a double-layer gradient cathode catalytic layer.

[0018] In one embodiment of the present invention, the first catalytic layer slurry and the second catalytic layer slurry both include a catalyst, a resin and a solvent; the second catalytic layer slurry also includes a high molecular polymer with a mass fraction of 5%-25%, and the high molecular polymer includes one or more of polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polyvinyl pyrrolidone, polycaprolactone, and polyvinyl butyral;

[0019] In the first catalytic layer slurry and the second catalytic layer slurry:

[0020] The catalyst comprises one or more of a platinum-carbon catalyst having a platinum content of 45-70%, a platinum-cobalt alloy catalyst having a platinum content of 40-70%, and a platinum-cobalt-manganese catalyst having a platinum content of 30-50%.

[0021] The resin includes one or more of DuPont Nafion solution, Aquivion D72-25BS resin solution and Aquivion D79-25BS resin solution.

[0022] The solvent includes one or more of water, n-propanol, isopropanol, N,N-dimethylacetamide, and N,N-dimethylpyrrolidone.

[0023] In one embodiment of the present invention, the method for preparing the first catalytic layer slurry comprises:

[0024] Add the catalyst and resin into the solvent and disperse them by ultrasonic for 0.5h-2h to obtain a uniform first catalyst layer slurry;

[0025] The preparation method of the second catalytic layer slurry comprises:

[0026] The catalyst and resin are added to the solvent, ultrasonically dispersed for 0.5h-2h to obtain a uniform dispersion, the high molecular polymer solution is added to the dispersion, and mechanically stirred for 1-3h at room temperature of 20℃-25℃ to obtain a uniformly dispersed second catalyst layer slurry.

[0027] In one embodiment of the present invention, the double-layer gradient cathode catalyst layer and the anode catalyst layer are subjected to hot pressing transfer, comprising:

[0028] The hot pressing transfer is carried out at 140℃-180℃ and 1-5MPa pressure.

[0029] The above technical solution of the present invention has the following advantages compared with the prior art:

[0030] The present invention discloses a membrane electrode with a gradient catalytic layer on the cathode side and a preparation method thereof. The second catalytic layer of the membrane electrode is prepared by electrostatic spinning technology. Compared with the conventional catalytic layer, a high molecular polymer is added to the catalyst slurry as a condition for electrostatic spinning. The prepared second catalytic layer is in a fiber arrangement state. The perfluorosulfonic acid resin is used as a fiber skeleton to maintain the stability of the catalytic layer, and the catalyst and the high molecular polymer are coated on the fiber skeleton. The catalytic layer in fiber arrangement has a higher porosity and a more uniform pore distribution, thereby forming a gradient distribution of increasing pores in the thickness direction of the catalytic layer.

[0031] The present invention utilizes the hydrophobic properties of fibrous sulfonic acid resin to promote the discharge of water under high current density; at the same time, the first catalyst layer has a certain water retention, thereby ensuring the wettability of the membrane and the entire catalyst layer under low current or low humidity conditions. Through the synergistic effect of pore gradient and hydrophobicity gradient, the effective discharge of water under high current density is promoted, thereby reducing the battery mass transfer polarization and improving the battery performance. In addition, by changing the content and molecular weight of the catalyst layer slurry component, a double-layer gradient membrane electrode with different porosities can be obtained to adapt to different humidity environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0033] Figure 1 It is a schematic diagram of the structure of the membrane electrode with a gradient catalytic layer on the cathode side of the present invention.

[0034] Figure 2 It is a comparison chart of polarization curve performance between Example 1 and Comparative Example 1 described in the present invention.

[0035] Figure 3 It is a comparison chart of polarization curve performance between Example 2 and Comparative Example 2 described in the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0037] In the present invention, "several" means one or more, "multiple" means more than two, "greater than", "less than", "exceed" and the like are understood to exclude the number itself; "above", "below", "within" and the like are understood to include the number itself. In the description of the present invention, if there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0038] Reference Figure 1 As shown, a membrane electrode with a gradient catalytic layer on the cathode side includes a proton exchange membrane and an anode catalytic layer and a cathode catalytic layer respectively arranged on the two side surfaces of the proton exchange membrane; wherein the cathode catalytic layer includes a first catalytic layer and a second catalytic layer sequentially arranged along the surface of the proton exchange membrane.

[0039] Specifically, the ratio of resin in the slurry to carbon in the catalyst (I / C) in the first catalytic layer is 0.7-1, and the platinum loading is 0.1 mg / cm 2 -0.25mg / cm 2 ;

[0040] Specifically, the ratio of resin in the slurry to carbon in the catalyst (I / C) in the second catalytic layer is 0.5-0.7, and the platinum loading is 0.05 mg / cm 2 -0.1mg / cm 2 .

[0041] The above-mentioned method for preparing a membrane electrode with a gradient catalytic layer on the cathode side comprises:

[0042] S1, providing a proton exchange membrane and an anode catalyst layer;

[0043] S2, providing a first catalyst layer slurry, coating the catalyst layer slurry on the surface of the proton exchange membrane, and drying to obtain a first catalyst layer;

[0044] S3, providing a second catalytic layer slurry, spinning the second catalytic layer slurry onto the first catalytic layer through an electrostatic spinning process, and obtaining a second catalytic layer after drying, wherein the first catalytic layer and the second catalytic layer constitute a double-layer gradient cathode catalytic layer;

[0045] S4. Perform hot-pressing transfer printing on the double-layer gradient cathode catalyst layer and the anode catalyst layer to combine them on the proton exchange membrane to obtain a membrane electrode.

[0046] Specifically, the catalyst layer slurry is coated on the surface of the proton exchange membrane to obtain a first catalyst layer, comprising:

[0047] The catalyst layer slurry is coated on the surface of the proton exchange membrane by using coating methods including scraping, spraying and slit coating.

[0048] Specifically, the electrospinning process includes: an applied voltage of 10-30 kV, a flow rate of the spinning slurry of 1.0-1.8 mL / h, a solidification distance of 5-20 cm, and a spinning time of 2-5 h.

[0049] Specifically, after the second catalytic layer is dried at 40-80° C., a double-layer gradient cathode catalytic layer is obtained.

[0050] Specifically, the first catalytic layer slurry and the second catalytic layer slurry both include a catalyst, a resin and a solvent; the second catalytic layer slurry also includes a high molecular polymer with a mass fraction of 5%-25%, and the high molecular polymer includes one or more of polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polyvinyl pyrrolidone, polycaprolactone, and polyvinyl butyral;

[0051] In the first catalytic layer slurry and the second catalytic layer slurry:

[0052] The catalyst comprises one or more of a platinum-carbon catalyst having a platinum content of 45-70%, a platinum-cobalt alloy catalyst having a platinum content of 40-70%, and a platinum-cobalt-manganese catalyst having a platinum content of 30-50%.

[0053] The resin includes perfluorosulfonic acid resin, including one or more of DuPont Nafion solution, Aquivion D72-25BS resin solution and Aquivion D79-25BS resin solution.

[0054] The solvent includes one or more of water, n-propanol, isopropanol, N,N-dimethylacetamide, and N,N-dimethylpyrrolidone.

[0055] Specifically, the preparation method of the first catalytic layer slurry includes:

[0056] Add the catalyst and resin into the solvent and disperse them by ultrasonic for 0.5h-2h to obtain a uniform first catalyst layer slurry;

[0057] Specifically, the preparation method of the second catalytic layer slurry includes:

[0058] The catalyst and resin are added to the solvent, ultrasonically dispersed for 0.5h-2h to obtain a uniform dispersion, the high molecular polymer solution is added to the dispersion, and mechanically stirred for 1-3h at room temperature of 20℃-25℃ to obtain a uniformly dispersed second catalyst layer slurry.

[0059] Specifically, hot pressing transfer is performed on the double-layer gradient cathode catalyst layer and the anode catalyst layer, comprising:

[0060] The hot pressing transfer is carried out at 140℃-180℃ and 1-5MPa pressure.

[0061] Example 1

[0062] A method for preparing a membrane electrode having a gradient catalytic layer on the cathode side, comprising:

[0063] S1, weighing 2g of 47wt% Pt / C catalyst and 22g of D520 resin solution, and mixing with 70g of water and ultrasonically dispersing to obtain a first catalyst layer slurry, and coating the first catalyst layer slurry on an 8μm proton exchange membrane to obtain a first catalyst layer with a Pt loading of 0.25mg / cm2;

[0064] S2, weighing 2g of 47wt% Pt / C catalyst and 11g of D520 resin solution, and mixing with 78g of water to obtain a dispersion after ultrasonic dispersion, adding 1.1g of 25wt% polycaprolactone solution to the dispersion and mechanically stirring for 2h to obtain a uniformly mixed second catalytic layer slurry, electrospinning the second catalytic layer slurry onto the first catalytic layer, the applied voltage is 10kV, the flow rate of the spinning slurry is 1.0mL / h, the curing distance is 5cm, the spinning time is 5h, the Pt loading is 0.05mg / cm2, and drying is performed at 50°C to obtain a double-layer gradient catalytic layer;

[0065] S3. The gradient cathode catalyst layer and the anode are hot-pressed and transferred at 140° C. and 2 MPa pressure to obtain a membrane electrode.

[0066] Example 2

[0067] A method for preparing a membrane electrode having a gradient catalytic layer on the cathode side, comprising:

[0068] S1, weighing 2.1g 70wt% Pt / Co catalyst and 2.2g D2020 resin solution, and mixing with 107g water and ultrasonically dispersing to obtain a first catalyst layer slurry, spraying the first catalyst layer slurry on an 8μm proton exchange membrane to obtain a first catalyst layer with a Pt loading of 0.10mg / cm2;

[0069] S2, weigh 3.1g 40wt% Pt / Co catalyst and 5.2g Aquivion D72-25BS resin solution, and 120g n-propanol to mix and ultrasonically disperse to obtain a dispersion, add 11.1g 5wt% polyvinyl butyral solution to the dispersion and mechanically stir for 2h to obtain a uniformly mixed second catalyst layer slurry, electrospin the second catalyst layer slurry onto the first catalyst layer, the applied voltage is 30kV, the flow rate of the spinning slurry is 1.8mL / h, the curing distance is 20cm, the spinning time is 2h, the Pt loading is 0.10mg / cm2, and it is dried at 80°C to obtain a double-layer gradient catalyst layer. The gradient cathode catalyst layer and the anode catalyst layer obtained in step (2) are hot-pressed and transferred at 140°C and 2MPa pressure to obtain a membrane electrode.

[0070] Comparative Example 1

[0071] In this comparative example, a conventional membrane electrode is prepared. Except that the second catalytic layer is not provided, the remaining steps of this comparative example are the same as those of Example 1.

[0072] Comparative Example 2

[0073] This comparative example uses electrostatic spinning to prepare a membrane electrode. Except that the first catalytic layer is not provided, the remaining steps of this comparative example are the same as those of Example 2.

[0074] Figure 2 is a comparison diagram of polarization curve performance between Example 1 and Comparative Example 1; Figure 3 2 is a comparison chart of polarization curve performance between Example 2 and Comparative Example 2. Figure 2 , Figure 3 It can be seen that the performance of each embodiment is significantly better than that of the corresponding comparison example, especially under high current density, the ohmic loss of the embodiment is significantly smaller than that of the comparison example. This is because the second catalytic layer formed by electrospinning forms more multi-level channels, and the pore increasing gradient structure formed with the first catalytic layer is beneficial to water vapor mass transfer. Compared with a single catalytic layer, the three-phase interface of the reaction is optimized to prevent local flooding.

[0075] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A membrane electrode having a gradient catalytic layer on the cathode side, characterized in that: It comprises a proton exchange membrane and an anode catalyst layer and a cathode catalyst layer respectively arranged on the two side surfaces of the proton exchange membrane; wherein the cathode catalyst layer comprises a first catalyst layer and a second catalyst layer sequentially arranged along the surface of the proton exchange membrane.

2. A membrane electrode with a gradient catalytic layer on the cathode side according to claim 1, characterized in that: The ratio of resin in the slurry to carbon in the catalyst in the first catalytic layer is 0.7-1, and the platinum loading is 0.1 mg / cm 2 -0.25mg / cm 2 .

3. The membrane electrode with a gradient catalytic layer on the cathode side according to claim 1, characterized in that: The ratio of resin in the slurry to carbon in the catalyst in the second catalytic layer is 0.5-0.7, and the platinum loading is 0.05 mg / cm 2 -0.1mg / cm 2 .

4. A method for preparing a membrane electrode having a gradient catalytic layer on the cathode side according to any one of claims 1 to 3, characterized in that: include: Providing a proton exchange membrane and an anode catalyst layer; Providing a first catalytic layer slurry, and coating the catalytic layer slurry on the surface of the proton exchange membrane to obtain a first catalytic layer; Providing a second catalytic layer slurry, spinning the second catalytic layer slurry onto the first catalytic layer through an electrostatic spinning process, and obtaining a second catalytic layer after drying, wherein the first catalytic layer and the second catalytic layer constitute a double-layer gradient cathode catalytic layer; The double-layer gradient cathode catalyst layer and the anode catalyst layer are hot-pressed and transferred to be combined on the proton exchange membrane to obtain a membrane electrode.

5. The method for preparing a membrane electrode with a gradient catalytic layer on the cathode side according to claim 4, characterized in that: The catalyst layer slurry is coated on the surface of the proton exchange membrane to obtain a first catalyst layer, comprising: The catalyst layer slurry is coated on the surface of the proton exchange membrane by using coating methods including scraping, spraying and slit coating.

6. The method for preparing a membrane electrode with a gradient catalytic layer on the cathode side according to claim 4, characterized in that: The electrostatic spinning process includes: an applied voltage of 10-30 kV, a flow rate of a spinning slurry of 1.0-1.8 mL / h, a solidification distance of 5-20 cm, and a spinning time of 2-5 h.

7. The method for preparing a membrane electrode with a gradient catalytic layer on the cathode side according to claim 4, characterized in that: After the second catalytic layer is dried at 40-80° C., a double-layer gradient cathode catalytic layer is obtained.

8. The method for preparing a membrane electrode with a gradient catalytic layer on the cathode side according to claim 4, characterized in that: The first catalytic layer slurry and the second catalytic layer slurry both include a catalyst, a resin and a solvent; the second catalytic layer slurry also includes a high molecular polymer with a mass fraction of 5%-25%, and the high molecular polymer includes one or more of polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polyvinyl pyrrolidone, polycaprolactone, and polyvinyl butyral; In the first catalytic layer slurry and the second catalytic layer slurry: The catalyst comprises one or more of a platinum-carbon catalyst having a platinum content of 45-70%, a platinum-cobalt alloy catalyst having a platinum content of 40-70%, and a platinum-cobalt-manganese catalyst having a platinum content of 30-50%. The resin includes one or more of DuPont Nafion solution, Aquivion D72-25BS resin solution and Aquivion D79-25BS resin solution; The solvent includes one or more of water, n-propanol, isopropanol, N,N-dimethylacetamide, and N,N-dimethylpyrrolidone.

9. The method for preparing a membrane electrode with a gradient catalytic layer on the cathode side according to claim 8, characterized in that: The preparation method of the first catalytic layer slurry comprises: Add the catalyst and resin into the solvent and disperse them by ultrasonic for 0.5h-2h to obtain a uniform first catalyst layer slurry; The preparation method of the second catalytic layer slurry comprises: The catalyst and resin are added to the solvent, ultrasonically dispersed for 0.5h-2h to obtain a uniform dispersion, the high molecular polymer solution is added to the dispersion, and mechanically stirred for 1-3h at room temperature of 20℃-25℃ to obtain a uniformly dispersed second catalyst layer slurry.

10. The method for preparing a membrane electrode having a gradient catalytic layer on the cathode side according to claim 4, characterized in that: The double-layer gradient cathode catalyst layer and the anode catalyst layer are subjected to hot pressing transfer, comprising: The hot pressing transfer is carried out at 140℃-180℃ and 1-5MPa pressure.

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