A catalyst coated film with a multi-layer catalytic layer structure, its preparation method and application

Abstract

The present invention belongs to the field of fuel cells, and particularly relates to a catalyst coated membrane with a multi-layer catalyst layer structure, a preparation method thereof, and an application. In the present invention, the CCM containing the first catalyst layer is first heat-treated to stabilize the structure of the catalyst layer, and then the second and above catalyst layer structures are constructed by slit coating, so as to obtain a catalyst coated membrane with a multi-layer catalyst layer structure and excellent electrical properties. In the preparation method of the present invention, slit coating has less limitation on the properties of the slurry and high coating efficiency. Moreover, the method of the present invention has less limitation on the thickness of the catalyst layer in the catalyst coated membrane, which is more conducive to designing and preparing an ideal catalyst layer structure.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and particularly relates to a catalyst coated membrane with a multi-layer catalyst layer structure, a preparation method thereof, and an application thereof. Background Art

[0002] The membrane electrode is the core component of a fuel cell. The performance and durability of the membrane electrode largely depend on the structure of the catalyst layer of the catalyst coated membrane (CCM) in the membrane electrode. The usual CCM has a three-layer structure, with a proton exchange membrane in the middle, and an anode catalyst layer and a cathode catalyst layer on both sides of the proton exchange membrane respectively. Designing the structure of the membrane electrode catalyst layer, especially the cathode catalyst layer, to be stratified or gradient can optimize the mass transfer process in the catalyst layer. There are many literatures disclosing the design of a multi-layer catalyst layer structure or a gradient distribution catalyst layer design, such as CN108063267A, CN103367768A, and CN103165915A. Constructing a multi-layer catalyst layer structure in the membrane electrode, especially in the cathode of the membrane electrode, has many benefits. For example, it can improve the performance of the membrane electrode, improve the mass transfer ability, and reduce the Pt loading in the membrane electrode, etc. However, it is also noted that the preparation method of the usual double-layer catalyst layer structure or multi-layer catalyst layer structure is to directly spray layers on the proton membrane, or spray two layers on polytetrafluoroethylene (PTFE) and then transfer them to the proton exchange membrane. The preparation of a multi-layer structure catalyst layer by spraying is slow and inefficient, and is not suitable for large-scale applications. In addition, the spraying technology has relatively high requirements for the particle size, viscosity, and solid content of the slurry. Usually, a smaller catalyst particle size, lower viscosity, and solid content are required to effectively spray. And the properties of the slurry (such as particle size, viscosity, etc.) have a decisive effect on the formed catalyst layer structure. Therefore, the spraying technology has great limitations on the structure design of the catalyst layer. In addition, when using the continuous spraying method, the spraying process of the subsequent layer usually affects the structure of the previous layer, which is not conducive to designing independent two-layer catalyst layers.

[0003] The preparation of the catalytic layer by slit coating on a thin film has the advantages of fast coating speed, precise control, continuous production, and good coating effect, and has been widely used in the fields of lithium batteries and fuel cells. In the field of lithium batteries, it is common to coat multiple layers of electrodes by slit coating. For example, CN110911669A discloses a method for preparing a positive electrode with a multi-layer composite structure, and a composite positive electrode is obtained by the method of layer-by-layer coating of multiple slurries. However, it should be noted that although the preparation of the multi-layer structure of the fuel cell membrane electrode catalytic layer is similar in form to the preparation of the above-mentioned lithium battery positive electrode composite structure, the actual difficulties to be overcome are completely different. In the field of fuel cells, the slit coating method is mostly limited to direct coating on both sides of the proton exchange membrane only once, that is, there is only one catalytic layer on each of the cathode and anode. There are still many limitations in the only slit coating technology for preparing multi-layer catalytic layers. For example, the patent document with the application number 2020065524.4 discloses a crack-free catalytic layer coating method, and a multi-layer catalytic layer is coated by the method of slit coating and lamination coating, requiring that the thickness of each layer is less than 10 μm, and the thickness of the catalytic layer decreases layer by layer from the inside to the outside (from the side of the proton membrane to the side of the gas diffusion layer). Although this method can prepare some multi-layer catalytic layer structures, it is helpless for the catalytic layer structure with a thickness of each layer > 10 μm and the outer layer thickness greater than the inner layer thickness.

[0004] There are several reasons for the limitation of the technology of preparing multi-layer catalytic layers by slit coating in the field of fuel cells. First of all, the substrate for coating the fuel cell membrane electrode is generally a perfluorosulfonic acid resin proton exchange membrane. This polymer membrane will undergo obvious swelling after absorbing water and alcohol (that is, dimensional changes will occur in the thickness, length, and width directions); while the positive electrode current collector of a lithium battery usually uses a metal foil, such as aluminum foil, and this material is relatively stable and does not have a swelling problem. Secondly, the binder used in the catalytic layer of the fuel cell is also perfluorosulfonic acid resin, and the structure of this resin is the same as that of the resin used in the proton exchange membrane. Therefore, obvious deformation will occur when encountering alcohol and water; PVDF is used as the binder in the slurry of lithium batteries, and this substance is insoluble in alcohol and water, so it is generally not affected by alcohol and water. Therefore, when preparing the multi-layer catalytic layer structure of the fuel cell membrane electrode, it is not possible to simply coat the first layer first, dry it, and then coat the second layer. Such an operation will cause swelling of the proton membrane and swelling of the resin in the first catalytic layer and secondary dispersion by the solvent in the slurry of the second layer coating. In this way, when coating the second catalytic layer, the original first catalytic layer will be deformed and peeled off, and a bilayer or multi-layer structure with good performance cannot be formed. Summary of the Invention

[0005] Aiming at the problems involved in the above-mentioned prior art that are not conducive to designing a good catalytic layer with an independent two-layer or multi-layer structure, the present invention will provide a catalyst coating film with a multi-layer catalytic layer structure, a preparation method thereof, and an application.

[0006] To achieve the above object, the specific technical solutions include the following:

[0007] A method for preparing a catalyst coated membrane with a multi-layer catalytic layer structure, comprising the following steps:

[0008] (1) Prepare catalyst slurry A and catalyst slurry B;

[0009] (2) Coat the catalyst slurry A described in step (1) on one side of the proton exchange membrane, and after drying, use it as the first cathode catalytic layer to obtain a catalyst coated membrane with the first cathode catalytic layer;

[0010] (3) Heat-treat the catalyst coated membrane with the first cathode catalytic layer described in step (2);

[0011] (4) On the first cathode catalytic layer of the catalyst coated membrane after heat-treatment in step (3), coat at least one layer of cathode catalytic layer with the catalyst slurry B described in step (1) as the raw material to obtain a catalyst coated membrane containing multiple cathode catalytic layers; the coating in step (4) is in the form of slot coating;

[0012] (5) Coat at least one layer of anode catalytic layer on the side of the catalyst coated membrane containing multiple cathode catalytic layers described in step (4) without a catalytic layer to obtain a catalyst coated membrane with a multi-layer catalytic layer structure.

[0013] Research has found that when using the slot die coating method to construct a multi-layer catalytic layer structure, the reason why the thickness of the second catalytic layer cannot be too thick or greater than the first layer is that the coating slurry solvent damages the existing catalytic layer. Further research has found that heat-treating (heating or hot pressing) the first catalytic layer on the proton membrane and stabilizing the catalytic layer and the proton membrane can effectively improve the solvent tolerance of the catalytic layer.

[0014] When the membrane electrode without heat treatment is immersed in an alcohol-containing solvent, the catalytic layer is very likely to peel off from the proton membrane, while the membrane electrode after heat treatment can stably exist when immersed in an alcohol-containing solvent.

[0015] Therefore, we have invented a method for preparing a CCM with a multi-layer catalytic layer structure by using the slot die coating method, as well as its membrane electrode and fuel cell. By first heat-treating the CCM coated with the first catalytic layer to stabilize the structure of the catalytic layer, and then using slot coating to construct the second and above catalytic layer structures. On the one hand, during the heat-treatment process, it mainly affects the morphology of the perfluorosulfonic acid resin in the catalytic layer and the proton exchange membrane, making the ionic clusters of the perfluorosulfonic acid resin more closely and regularly arranged, and reducing the swelling stress of the membrane; on the other hand, in the absence of heat treatment, the perfluorosulfonic acid resin in the catalytic layer can move in an environment with a solvent, while after heat treatment, the sulfonic acid resin is not easily mobile in the solvent, which is more conducive to the direct combination of the catalytic layers.

[0016] As a preferred embodiment of the present invention, the conditions for the heat treatment in step (3) are as follows: temperature 130°C to 210°C, time 1 s to 300 s, pressure 0 to 0.5 MPa.

[0017] As a further preferred embodiment of the present invention, the conditions for the heat treatment in step (3) are as follows: temperature 150°C, time 10 s, pressure 0.3 MPa.

[0018] As a preferred embodiment of the present invention, the temperature of the heat treatment needs to be greater than 130°C.

[0019] As a preferred embodiment of the present invention, the material of the proton exchange membrane in step (1) includes perfluorosulfonic acid resin.

[0020] As a preferred embodiment of the present invention, for samples with an EW value of the perfluorosulfonic acid resin used in the catalytic layer ≤ 850, the preferred heat treatment temperature is 150°C - 200°C; for samples with an EW value of the perfluorosulfonic acid resin used in the catalytic layer of 850 - 1000, the preferred heat treatment temperature is 140 - 200°C, and for samples with an EW value of the perfluorosulfonic acid resin used in the catalytic layer ≥ 1000, the preferred heat treatment temperature is 130 - 200°C; the time of the heat treatment needs to be more than 1 s when the temperature of the catalytic layer reaches the specified temperature.

[0021] As a preferred embodiment of the present invention, the coating in step (1) includes at least one of ultrasonic spraying, electrostatic spraying, doctor blade coating, slot coating, and screen printing.

[0022] As a further preferred embodiment of the present invention, the coating method in step (1) is slot coating.

[0023] The second layer and above on the catalyst coated film of the multi-layer cathode catalytic layer are completed by the slot coating method, and the first layer can be the slot coating or other coating methods, preferably the slot coating method.

[0024] As a preferred embodiment of the present invention, the catalyst slurry A in step (1) includes the following components: catalyst, perfluorosulfonic acid resin, solvent; the catalyst slurry B in step (1) includes the following components: catalyst, perfluorosulfonic acid resin, solvent, wherein the solvent contains an organic solvent accounting for 5 wt% - 70 wt% of the total mass of the solvent, and further preferably, the solvent contains an organic solvent accounting for 15 wt% - 40 wt% of the total mass of the solvent.

[0025] As a preferred embodiment of the present invention, the organic solvent includes ethanol.

[0026] As a preferred embodiment of the present invention, in the catalyst slurry A in step (1), the solvent contains an organic solvent accounting for 5 wt% - 70 wt% of the total mass of the solvent, and the solvent contains an organic solvent accounting for 15 wt% - 40 wt% of the total mass of the solvent.

[0027] As a preferred embodiment of the present invention, the catalyst in the catalyst slurry A and the catalyst slurry B in step (1) includes at least one of Pt / C, PtM / C, Fe-N-C, and Co-N-C, where M in PtM / C is at least one of Co, Ni, Cu, Au, Ag, Ir, Ru, Cr, and Fe.

[0028] As a further preferred embodiment of the present invention, the catalyst in the catalyst slurry A in step (1) is Pt / C or PtM / C, and the catalyst in the catalyst slurry B is Pt / C.

[0029] As a preferred embodiment of the present invention, in the catalyst-coated film containing a multi-layer cathode catalyst layer in step (3), the thickness of each cathode catalyst layer is 0.1 - 30 μm, and the loading of the active substance in each cathode catalyst layer is 10 - 500 μg / cm 2 。

[0030] As a further preferred embodiment of the present invention, in the catalyst-coated film containing a multi-layer cathode catalyst layer in step (3), the thickness of each cathode catalyst layer is 1 - 15 μm, and the loading of the active substance in each cathode catalyst layer is 100 - 300 μg / cm 2 。

[0031] Here, each cathode catalyst layer includes the cathode first catalyst layer in the above step (1) and the cathode catalyst layer in step (4).

[0032] The active substance here refers to a substance with catalytic activity, such as at least one of Pt, Co, Ni, Cu, Au, Ag, Ir, Ru, Cr, and Fe.

[0033] In the catalyst-coated film with a two-layer or multi-layer structure, there is a difference in at least one property among the pore structure, ionomer type and content, catalyst type and content, surfactant content and type, additive content and type, platinum loading, catalyst layer thickness, catalyst layer roughness, and surface hydrophobicity of the catalyst layers in different layers.

[0034] When constructing the double-layer catalyst layer structure of the cathode or anode, it can be that one side of the double-layer structure is continuously prepared and then the other side is coated; or the catalyst layers on both sides of the cathode and anode can be prepared first, and then the second catalyst layer is coated on one side or both sides of the catalyst layers.

[0035] When the active substance in the catalyst layer is Pt, one layer of the multi-layer catalyst layer can be a functional layer without Pt.

[0036] The application of the catalyst coated film with the multi-layer catalyst layer structure in the membrane electrode and fuel cell, and the catalyst coated film with the multi-layer catalyst layer structure can endow the membrane electrode and fuel cell with better electrical properties.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Compared with the traditional spraying method for constructing a double-layer or multi-layer catalyst layer structure, the preparation method of the present invention has the advantages of fast coating speed and high efficiency, which is conducive to large-scale production.

[0039] (2) In the preparation method of the present invention, the slit coating has less restriction on the properties of the slurry, and the slurry used is less limited by the coating equipment, which is more conducive to designing and preparing an ideal catalyst layer structure.

[0040] (3) The preparation method of the present invention has no limitation on the thickness of the catalyst layer in the catalyst coated film with the multi-layer catalyst layer structure. The thickness of the first layer can be less than that of the second layer, or the thickness of the first layer can be greater than that of the second layer, and the thickness of both catalyst layers can be > 10 μm.

[0041] (4) The catalyst coated film with the multi-layer catalyst layer structure prepared by the present invention has good electrical properties and can maintain good electrical properties even under the condition of high current density. Description of the Drawings

[0042] Figure 1 Surface morphology diagrams of the double-layer cathode catalyst layers prepared in Examples 1 to 3 and Comparative Example 1.

[0043] Figure 2 Cross-sectional morphology diagrams of the double-layer cathode catalyst layers prepared in Examples 1 to 3 and Comparative Example 1.

[0044] Figure 3 Polarization curve diagrams of the membrane electrodes prepared in Example 1, Example 3 and Comparative Example 2. Detailed Embodiments

[0045] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below through specific comparative examples and examples.

[0046] Example 1

[0047] S1: Weigh 5.1 g of Tec10E50E 50wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 12.8 g of 20wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst into the stirred water, stir for 5 min, then add the perfluorosulfonic acid resin dispersion (EW is 790) and stir for 2 min, then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser, the rotation speed of the disperser is 3000 rpm, the dispersion time is 30 min, then collect the dispersed catalyst slurry for defoaming treatment to obtain catalyst slurry A for coating the first catalytic layer of the proton exchange membrane. Weigh 5.1 g of Tec10E50E-HT 50wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 8 g of 20wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst into the stirred water, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser, the rotation speed of the disperser is 3000 rpm, the dispersion time is 30 min, then collect the dispersed catalyst slurry for defoaming treatment to obtain catalyst slurry B for coating the second catalytic layer.

[0048] S2: Coat the catalyst slurry A prepared in S1 on one side of the perfluorosulfonic acid resin proton exchange membrane (EW is 900) by the slit coating method and dry it at 80 °C to obtain a semi-CCM (catalyst coated membrane) containing the first cathode catalytic layer, where the Pt loading of the catalytic layer is 100 μg / cm 2 , and the thickness is 3.5 μm.

[0049] S3: Hot press the semi-CCM prepared in S2 at 150 °C for 10 s, the hot press pressure is 0.3 MPa, to perform the stabilization treatment of the catalytic layer structure.

[0050] S4: Above the first cathode catalytic layer of the semi-CCM after the catalytic layer structure stabilization treatment, coat the second cathode catalytic layer with the catalyst slurry B prepared in S1 by the slit coating method, and the Pt loading of this catalytic layer is 250 μg / cm 2 , and the thickness is 8 μm.

[0051] S5: Coat the anode catalyst slurry on the side of the proton exchange membrane in S4 where no catalytic layer is coated, with a Pt loading of 100 μg / cm 2 to form a CCM, and further assemble to form a membrane electrode and a fuel cell.

[0052] Example 2

[0053] S1: Weigh 5.1 g of Tec10E50E 50wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 12.8 g of 20wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst into the stirred water, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue stirring for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser with a rotational speed of 3000 rpm and a dispersion time of 30 min, and then collect the dispersed catalyst slurry for degassing treatment to obtain catalyst slurry A for coating the first catalytic layer of the proton exchange membrane. Weigh 5.1 g of Tec10E50E-HT 50wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 8 g of 20wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst into the stirred water, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue stirring for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser with a rotational speed of 3000 rpm and a dispersion time of 30 min, and then collect the dispersed catalyst slurry for degassing treatment to obtain catalyst slurry B for coating the second catalytic layer.

[0054] S2: Coating the catalyst slurry A prepared in S1 on one side of the perfluorosulfonic acid resin proton exchange membrane by the slot coating method and drying at 80 °C to obtain a semi-CCM containing the first cathode catalytic layer, where the Pt loading of the catalytic layer is 300 μg / cm 2 , and the thickness is 11 μm;

[0055] S3: Hot press the semi-CCM prepared in S2 at 150 °C for 10 s with a hot press pressure of 0.3 MPa for the stabilization treatment of the catalytic layer structure.

[0056] S4: Above the first cathode catalytic layer of the semi-CCM after the catalytic layer structure stabilization treatment, coat the second cathode catalytic layer with the catalyst slurry B prepared in S1 by the slot coating method, and the Pt loading of this catalytic layer is 50 μg / cm 2 , and the thickness is 1 μm.

[0057] S5: Coat the catalyst slurry B on the side of the proton exchange membrane in S5 where the catalytic layer is not coated, with a Pt loading of 100 μg / cm 2 to form a CCM, and further assemble to form a membrane electrode and a fuel cell.

[0058] Example 3

[0059] S1: Weigh 5.1 g of Tec10E50E 50wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 12.8 g of 20wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst to the water under stirring, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser, the rotation speed of the disperser is 3000 rpm, and the dispersion time is 30 min. Then collect the dispersed catalyst slurry for degassing treatment to obtain catalyst slurry A for coating the first catalytic layer of the proton exchange membrane. Weigh 5.1 g of Tec10E50E-HT 50wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 8 g of 20wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst to the water under stirring, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser, the rotation speed of the disperser is 3000 rpm, and the dispersion time is 30 min. Then collect the dispersed catalyst slurry for degassing treatment to obtain catalyst slurry B for coating the second catalytic layer.

[0060] S2: Coating the catalyst slurry A prepared in S1 on one side of the perfluorosulfonic acid resin proton exchange membrane by the slit coating method and drying at 80 °C to obtain a semi-CCM containing the first cathode catalytic layer, where the Pt loading of the catalytic layer is 100 μg / cm 2 , and the thickness is 3.5 μm.

[0061] S3: Hot press the semi-CCM prepared in S2 at 210 °C for 10 s, the hot press pressure is 0.1 MPa, to perform the stabilization treatment of the catalytic layer structure.

[0062] S4: Above the first cathode catalytic layer of the semi-CCM after the catalytic layer structure stabilization treatment, coat the second cathode catalytic layer with the catalyst slurry B prepared in S1 by the slit coating method. The Pt loading of this catalytic layer is 250 μg / cm 2 , and the thickness is 8 μm.

[0063] S5: Coat the anode catalyst slurry on the side of the proton exchange membrane in S4 where no catalytic layer is coated, with a Pt loading of 100 μg / cm 2 to form a CCM, and further assemble to form a membrane electrode and a fuel cell.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that it does not go through the S3 process (hot pressing stabilization treatment) of Example 1.

[0066] S1: Weigh 5.1 g of Tec10E50E 50 wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 12.8 g of 20 wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst to the water under stirring, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; disperse the slurry through a Beads mill disperser with a rotation speed of 3000 rpm and a dispersion time of 30 min, and then collect the dispersed catalyst slurry for defoaming treatment to obtain catalyst slurry A for coating the first catalytic layer of the proton exchange membrane. Weigh 5.1 g of Tec10E50E-HT 50 wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 8 g of 20 wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst to the water under stirring, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; disperse the slurry through a Beads mill disperser with a rotation speed of 3000 rpm and a dispersion time of 30 min, and then collect the dispersed catalyst slurry for defoaming treatment to obtain catalyst slurry B for coating the second catalytic layer.

[0067] S2: Coating the catalyst slurry A prepared in S1 on one side of the perfluorosulfonic acid resin proton exchange membrane by the slit coating method and drying it at 80 °C to obtain a semi-CCM containing the first cathode catalytic layer, where the Pt loading of the catalytic layer is 100 μg / cm 2 , and the thickness is 3.5 μm.

[0068] S3: On top of the first cathode catalytic layer of the semi-CCM prepared in step S2, coat the second cathode catalytic layer with the catalyst slurry B prepared in S1 by the slit coating method, and the Pt loading of this catalytic layer is 250 μg / cm 2 , and the thickness is 8 μm.

[0069] S4: Coat the anode catalyst slurry with a Pt loading of 100 μg / cm 2 on the side of the proton exchange membrane in S3 that is not coated with the catalytic layer to form a CCM, and further assemble it to form a membrane electrode and a fuel cell.

[0070] Comparative Example 2

[0071] S1: Weigh 5.1 g of Tec10E50E 50 wt% Pt / C catalyst produced by Tanaka Kikinzoku Kogyo K.K. (TKK) of Japan, 12.8 g of 20 wt% perfluorosulfonic acid resin dispersion, 7.2 g of ethanol, and 39.0 g of ultrapure water. Slowly add the Pt / C catalyst into the stirred water, stir for 5 min, then add the perfluorosulfonic acid resin dispersion and stir for 2 min, and then add ethanol and continue to stir for 2 min to complete the pre-dispersion of the slurry; Disperse the slurry through a Beads mill disperser, the rotation speed of the disperser is 3000 rpm, the dispersion time is 30 min, and then collect the dispersed catalyst slurry for defoaming treatment to obtain catalyst slurry A coated with a proton exchange membrane.

[0072] S2: Coating the catalyst slurry A prepared in S1 on one side of the proton exchange membrane by the slit coating method and drying at 80 °C, where the Pt loading of the catalytic layer is 350 μg / cm 2 , and the thickness is 13 μm;

[0073] S3: Coating the anode catalyst slurry (the same as that in Example 1) on the side of the proton exchange membrane in S2 where the catalytic layer is not coated, with a loading of 100 μg / cm 2 to form CCM, and further assembling to form a membrane electrode and a fuel cell.

[0074] It can be seen from Figure 1 that by adopting the solutions of the present invention (Examples 1 to 3), regardless of whether the thickness of the first-layer cathode catalytic layer is greater or smaller than that of the second-layer cathode catalytic layer, the surface morphology of the finally formed double-layer structure cathode catalytic layer is intact, without cracks and defects. For the double-layer structure cathode catalytic layer prepared by the comparative example 1 without heat pressing stabilization treatment, due to the movement of perfluorosulfonic acid resin in the catalytic layer in an environment with solvent and the swelling stress of the membrane, obvious cracking has occurred in its catalytic layer. The process of heat pressing stabilization treatment mainly affects the morphology of perfluorosulfonic acid resin in the catalytic layer and the proton exchange membrane, making the ionic clusters of perfluorosulfonic acid resin more closely and regularly arranged, reducing the swelling stress of the membrane, making the sulfonic acid resin not easily move in the solvent, and finally the formed double-layer cathode catalytic layer is more intact, without cracks and defects.

[0075] Further, it can be seen from Figure 2 that for the double-layer structure catalytic layer prepared by the comparative example 1, it is separated from the proton membrane, and there is a phenomenon of warping in the catalytic layer. The double-layer cathode catalytic layer structure prepared by the solution of the present invention is tightly combined with the proton membrane, without the phenomenon of separation between the proton membrane and the catalytic layer.

[0076] It can be seen from Figure 3As can be seen, the membrane electrode prepared by the solution of the present invention has electrochemical performance far superior to that of the membrane electrode of Comparative Example 2, especially at high current densities. It was also found that when the treatment temperature was too high (210 °C), although no obvious changes were found on the surface and cross-section of the catalyst layer, the performance of the membrane electrode would be slightly reduced, which might be due to the structural change of the perfluorosulfonic acid resin at high temperatures.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a catalyst coated film with a multi-layer catalyst layer structure, characterized in that, It includes the following steps: (1) Prepare catalyst slurry A and catalyst slurry B; the catalyst slurry A includes the following components: catalyst, perfluorosulfonic acid resin, solvent, and the catalyst slurry B includes the following components: catalyst, perfluorosulfonic acid resin, solvent; (2) Coat the catalyst slurry A obtained in step (1) on one side of the proton exchange membrane, and after drying, use it as the first cathode catalytic layer to obtain a catalyst-coated membrane with the first cathode catalytic layer; the material of the proton exchange membrane includes perfluorosulfonic acid resin; (3) Heat-treat the catalyst-coated membrane with the first cathode catalytic layer obtained in step (2); the conditions for the heat treatment are: temperature 130°C - 210°C, time 1 s - 300 s, pressure 0 - 0.5 MPa; (4) On the first cathode catalytic layer of the catalyst-coated membrane after heat treatment in step (3), coat at least one layer of cathode catalytic layer using the catalyst slurry B obtained in step (1) as the raw material to obtain a catalyst-coated membrane containing multiple layers of cathode catalytic layers; the coating in step (4) is in the form of slot coating; (5) Coat at least one layer of anode catalytic layer on the side without a catalytic layer of the catalyst-coated membrane containing multiple layers of cathode catalytic layers obtained in step (4) to obtain a catalyst-coated membrane with a multi-layer catalytic layer structure.

2. The preparation method according to claim 1, characterized in that, The conditions for the heat treatment in step (3) are: temperature 150°C, time 10 s, pressure 0.3 MPa.

3. The preparation method according to claim 1 or 2, characterized in that, The coating in step (2) includes at least one of ultrasonic spraying, electrostatic spraying, doctor blade coating, slot coating, and screen printing.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The solvent contains an organic solvent accounting for 5 wt% - 70 wt% of the total mass of the solvent.

5. The preparation method according to claim 4, characterized in that, The catalyst in the catalyst slurry A and catalyst slurry B in step (1) includes at least one of Pt / C, PtM / C, Fe-N-C, Co-N-C, where M in PtM / C is at least one of Co, Ni, Cu, Au, Ag, Ir, Ru, Cr, Fe.

6. The preparation method according to any one of claims 1 to 3, characterized in that, In the catalyst coated film with multiple cathode catalyst layers described in step (4), the thickness of each cathode catalyst layer is 0.1 - 30 μm, and the loading of the active substance in each cathode catalyst layer is 10 - 500 μg / cm 2 .

7. A catalyst-coated membrane with a multi-layer catalytic layer structure prepared by the preparation method according to any one of claims 1 - 6.

8. Application of the catalyst-coated membrane with the multi-layer catalytic layer structure according to claim 7 in a membrane electrode and a fuel cell.

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