Carbon nanotube composite anti-poisoning cathode catalytic layer, preparation method and application thereof

Abstract

The application provides a carbon nanotube composite anti-poisoning cathode catalytic layer and a preparation method and application thereof. The cathode catalytic layer comprises a three-dimensional porous framework formed by carbon nanotube composites interwoven and jointed with each other, the carbon nanotube composite comprises multi-walled carbon nanotubes and an ionomer, the ionomer is uniformly dispersed on the outer wall of the multi-walled carbon nanotubes; a catalyst is distributed on the surface and inside of the three-dimensional porous framework; the tube diameter of the multi-walled carbon nanotubes is 40nm-80nm; the porosity of the catalytic layer is 50.4%-59.3%, and more than 95wt% of the ionomer contained is combined on the carbon nanotubes. The cathode catalytic layer of the application adopts large-diameter carbon nanotubes combined with ionomers, can significantly improve the proton conduction and oxygen transmission capacity of the cathode catalytic layer and reduce the poisoning effect of the ionomer on the catalyst, and enhance the effective efficiency and activity of the catalyst. In addition, the proton conduction capacity and operating power of the fuel cell under a high-temperature environment are enhanced.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a carbon nanotube composite anti-poisoning cathode catalyst layer, its preparation method, and its application. Background Technology

[0002] The catalyst layer is a core component of a proton exchange membrane fuel cell (PEMFC). Its composition and structure directly determine the fuel cell's performance and significantly impact its stability, reliability, and durability. Ionomers, an indispensable part of the cathode catalyst layer, act as both a binder and a proton transport carrier, playing a crucial role in constructing an efficient three-phase interface. However, due to the strong adsorption of metal catalysts by ionomers, a serious poisoning problem exists at the active sites of the metal catalyst within the cathode catalyst layer. Traditional cathode catalyst layer preparation methods involve uniformly dispersing the catalyst and ionomer in a solvent to form a homogeneous catalyst slurry, which is then directly coated or transferred onto the proton exchange membrane and dried to obtain the cathode catalyst layer. In this method, the ionomer densely covers the catalyst surface, resulting in a high sulfonic acid group coverage, irreversibly poisoning a large number of active sites. For example, the paper "Overcoming the Limitation of Ionomers on Mass Transport and Pt Activity to Achieve High-Performing Membrane Electrode Assembly" mentions that the sulfonic acid group coverage of active sites is generally 25-30%, which significantly reduces the kinetic activity of the oxygen reduction reaction. Furthermore, oxygen molecules must diffuse through the dense ionomer layer to reach the reaction site, resulting in extremely high oxygen mass transfer resistance, which severely limits performance at high current densities.

[0003] High-temperature operation (100~120℃) of proton exchange membrane fuel cells (PEMFCs) is a globally recognized development direction in the field. High-temperature operation can effectively improve catalyst reactivity, impurity (such as CO) tolerance, and oxygen global diffusion characteristics. Furthermore, it simplifies hydrothermal management, reduces costs, and increases operating efficiency. However, high-temperature operation places the fuel cell under low-humidity conditions. The ionomers that dominate proton conduction are highly dependent on the aqueous environment for proton transport, resulting in insufficient proton conduction capacity of the current catalyst layer, making it difficult to meet the requirements for high current density. Summary of the Invention

[0004] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0005] A first aspect of the present invention provides a carbon nanotube composite anti-poisoning cathode catalyst layer, comprising:

[0006] A three-dimensional porous framework is formed by interweaving and overlapping carbon nanotube composite materials, wherein the carbon nanotube composite materials include multi-walled carbon nanotubes and ionomers, and the ionomers are uniformly dispersed on the outer wall of the multi-walled carbon nanotubes.

[0007] The catalyst is distributed on the surface and inside the three-dimensional porous framework;

[0008] Furthermore, the diameter of the multi-walled carbon nanotube is 40 nm to 80 nm, the porosity of the cathode catalyst layer is 50.4% to 59.3%, and more than 95 wt% of the ionomers contained in the cathode catalyst layer are bonded to the carbon nanotube.

[0009] The carbon nanotube composite anti-poisoning cathode catalyst layer of the present invention can significantly improve the proton conduction and oxygen transport capabilities of the cathode catalyst layer and reduce the poisoning effect of ionomers on the catalyst.

[0010] In some embodiments, the mass ratio of ionomer to multi-walled carbon nanotubes in the carbon nanotube composite material is 0.8~1.2:1.

[0011] In some embodiments, the thickness of the ionomer on the surface of the multi-walled carbon nanotube composite material is 4 nm to 10 nm.

[0012] If too much ionomer is used, it will lead to the formation of a thicker and denser ionomer layer on the carbon nanotubes. This will cause the outer ionomers to fall off due to weak bonding, thus covering the catalyst and causing poisoning. Through systematic research, this invention has found that when the mass ratio of ionomer to multi-walled carbon nanotubes is 0.8~1.2:1 and the thickness of the ionomer on the surface of the multi-walled carbon nanotubes is 4nm~10nm, the coverage of sulfonic acid groups at the active sites in the catalyst layer is low, while also exhibiting excellent proton conduction and oxygen transport characteristics.

[0013] In some embodiments, the diameter of the multi-walled carbon nanotubes is 40 nm to 60 nm.

[0014] In some embodiments, the length of the multi-walled carbon nanotubes is 0.5 μm to 5 μm. If the length of the carbon nanotubes is too short, it is not conducive to long-range proton conduction; if the length of the carbon nanotubes is too long, they are prone to aggregation, resulting in uneven distribution of carbon nanotubes within the catalyst layer.

[0015] In some embodiments, the outer wall of the multi-walled carbon nanotubes is modified with functional groups, which are capable of chemically bonding with the ionomer. The functional groups may include at least one of amino, carboxyl, and hydroxyl groups.

[0016] In some embodiments, the mass ratio of carbon nanotube composite material to catalyst in the cathode catalyst layer is (0.2~0.8):1.

[0017] The catalyst can be any known catalyst in the field of fuel cells. In some embodiments, the catalyst includes a support and a catalytically active material supported on the support. The support can be, for example, a carbon support, and the catalytically active material can be, for example, platinum and / or platinum alloys. Platinum alloys can be, for example, Pt-Fe, Pt-Co, etc.

[0018] In a typical embodiment, the catalyst comprises a Pt / C catalyst. The platinum loading in the Pt / C catalyst can be 20 wt% to 60 wt%.

[0019] The ionomer can be a known ionomer in the field of fuel cells, which typically poisons the catalytically active material on the catalyst.

[0020] In some embodiments, the ionomer includes a perfluorosulfonic acid resin.

[0021] In some embodiments, the oxygen transport resistance of the carbon nanotube composite anti-poisoning cathode catalyst layer is 41.3 s / m to 64.5 s / m.

[0022] In some embodiments, the proton conduction impedance of the carbon nanotube composite anti-poisoning cathode catalyst layer is 0.0425~0.0503Ω×cm. 2 .

[0023] In some embodiments, the coverage of sulfonic acid groups at the active sites in the carbon nanotube composite anti-poisoning cathode catalytic layer is 14.4% to 17.9%.

[0024] In some embodiments, the catalyst mass activity of the carbon nanotube composite anti-poisoning cathode catalytic layer is 0.18 A / mg. pt ~0.31A / mg pt .

[0025] The carbon nanotube composite anti-poisoning cathode catalyst layer provided by this invention incorporates ionomers bonded to large-diameter (40nm~80nm) multi-walled carbon nanotubes, forming a linear carbon nanotube composite material with strong ionomer anchoring, thus reducing the strong adsorption of ionomers on the catalyst surface. Using large-diameter carbon nanotubes maximizes the utilization of the outer wall of the carbon nanotubes, providing sufficient loading space for the ionomers, improving the binding rate between the carbon nanotubes and the ionomers, and achieving a concentration of over 95wt% of the ionomers on the carbon nanotubes. This significantly reduces the ionomer content on the catalyst surface, noticeably decreases the coverage of sulfonic acid groups at active sites, and significantly improves the activity of the membrane electrode.

[0026] Meanwhile, the carbon nanotube composite anti-poisoning cathode catalytic layer provided by this invention also possesses excellent proton conduction properties. Long-range proton conduction requires the use of ionomers. In the catalytic layer of this invention, ionomers are continuously bonded to the outer wall of the carbon nanotubes to form a continuous proton conduction path. Proton conduction directly relies on the carbon nanotube composite material. Protons can be accessed within the area accessible to the carbon nanotube composite material, thus achieving a more efficient proton conduction path.

[0027] Traditional catalyst layers without carbon nanotubes have low porosity due to the accumulation of catalyst particles. This invention utilizes large-diameter carbon nanotubes (40nm-80nm) to form a more porous catalyst layer structure, increasing its porosity. The multiple interconnected pores within the three-dimensional porous framework formed by the linear carbon nanotube composite material create three-dimensional fluid mass transfer channels, which is more conducive to accelerating the transport of reactant gases and product water. Simultaneously, the interior of the large-diameter carbon nanotubes also serves as a natural gas transport path, further enhancing the oxygen transport rate.

[0028] A second aspect of the present invention provides a method for preparing the carbon nanotube composite anti-poisoning cathode catalyst layer as described in any of the above technical solutions, comprising:

[0029] Multi-walled carbon nanotubes and ionomers are dispersed in a first solvent to form a mixture, and the mass ratio of ionomers to multi-walled carbon nanotubes in the mixture is controlled to be 0.8~1.2:1. The mixture is stirred continuously at 80~140℃ for more than 1 hour, and then dried to obtain a carbon nanotube composite material.

[0030] The carbon nanotube composite material and the catalyst are dispersed in a second solvent to prepare a slurry, and the slurry is used to form the carbon nanotube composite anti-poisoning cathode catalyst layer.

[0031] The above preparation method enables the ionomer to form a stable composite structure with carbon nanotubes, and ensures that the ionomer is uniformly and continuously bonded to the multi-walled carbon nanotubes. By optimizing the preparation process and using large-diameter carbon nanotubes with a diameter of 40nm~80nm, it is possible to achieve "almost complete distribution of ionomers on the carbon nanotubes" (more than 95wt% of the ionomers contained in the cathode catalyst layer are bonded to the carbon nanotubes), rather than only partially bonded. By controlling the ionomers to bind to the carbon nanotubes as much as possible, the poisoning of the catalyst can be further reduced, and the continuous arrangement of ionomers on the carbon nanotubes can accelerate proton conduction and reduce oxygen transport resistance.

[0032] In some embodiments, the solid content of the mixture is 0.4wt% to 1.2wt%.

[0033] In some embodiments, the mixture contains 0.2wt% to 0.6wt% of multi-walled carbon nanotubes and 0.2wt% to 0.6wt% of ionomers.

[0034] In some embodiments, the ionomer can be prepared as an ionomer solution with a mass fraction of 10% to 30%, and then uniformly mixed with the carbon nanotubes and the first solvent to form the mixture.

[0035] In some embodiments, the mixture is continuously stirred for 1 to 5 hours at a stirring rate of 200 to 600 rpm.

[0036] In some embodiments, the first solvent comprises water and alcohol, with a water-to-alcohol mass ratio of 0.8 to 1.2:1.

[0037] In some embodiments, the second solvent comprises water and alcohol, wherein the mass ratio of water to alcohol is 0.2 to 0.5:1.

[0038] In some embodiments, the alcohol includes ethanol and / or isopropanol.

[0039] In some embodiments, the solid content of the slurry is 0.7wt% to 0.9wt%.

[0040] A third aspect of the present invention provides a fuel cell membrane electrode structure, comprising a proton exchange membrane, a gas diffusion layer, and an anode catalyst layer and a cathode catalyst layer formed on both sides of the proton exchange membrane, wherein the cathode catalyst layer comprises the carbon nanotube composite anti-poisoning cathode catalyst layer described in any of the above technical solutions.

[0041] In some embodiments, the thickness of the proton exchange membrane is 5 μm to 10 μm.

[0042] In some embodiments, the loading of the cathode catalyst layer on the proton exchange membrane satisfies the following condition: the loading of the catalytically active material on the catalyst is 0.1 mg / cm³. 2 ~0.2mg / cm 2 .

[0043] The method for preparing the fuel cell membrane electrode structure can be based on the method for preparing the carbon nanotube composite anti-poisoning cathode catalyst layer described in the second aspect of the present invention. The slurry is coated onto the proton exchange membrane to form the carbon nanotube composite anti-poisoning cathode catalyst layer on the proton exchange membrane, thereby obtaining the fuel cell membrane electrode structure.

[0044] A fourth aspect of the present invention provides a fuel cell comprising the fuel cell membrane electrode structure described in any of the technical solutions.

[0045] Compared with existing technologies, the present invention has at least the following beneficial effects: The present invention combines ionomers with large-diameter multi-walled carbon nanotubes (40nm~80nm) to form a linear carbon nanotube composite material. The high-porosity cathode catalyst layer formed by their overlapping has both excellent proton conductivity and oxygen transport properties; it can also reduce the poisoning effect of ionomers on the catalyst, thereby increasing both catalyst efficiency and activity. In some embodiments of the present invention, the porosity of the catalyst layer can reach 50.4%~59.3%, the sulfonic acid group coverage can be reduced to 14.4%~17.9%, and the proton conductivity resistance can reach 0.0425~0.0503Ω×cm in tests at a normal temperature (80℃). 2 The oxygen transport resistance can reach 41.3 s / m to 64.5 s / m, and the membrane electrode mass activity can reach 0.18 to 0.31 A / mg. pt In high-temperature (120℃) tests, the proton conduction impedance was 0.0874~0.1014 Ω×cm. 2 . Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the structure of the catalyst layer obtained in Example 1 of the present invention;

[0048] Figure 2 These are TEM images and corresponding EDS images of the carbon nanotube composite material prepared in Example 1.

[0049] Figure 3 The images shown are TEM images and corresponding EDS images of the cathode catalyst layer prepared in Example 1.

[0050] Figure 4 The images show the TEM image and corresponding EDS image of the cathode catalyst layer prepared in Comparative Example 1. Detailed Implementation

[0051] The invention will be more fully understood through the following detailed description, which should be read in conjunction with the accompanying drawings. Detailed embodiments of the invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as intended to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0052] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art, as are the testing methods used.

[0053] Example 1

[0054] This embodiment provides a membrane electrode structure based on a carbon nanotube composite anti-poisoning cathode catalytic layer and its preparation method. Figure 1 This is a flowchart of the preparation process in this embodiment, which specifically includes the following steps:

[0055] (1) Take 40 mg of hydroxyl multi-walled carbon nanotube powder (the diameter of the multi-walled carbon nanotube is 40 nm to 60 nm and the length is 1 to 2 micrometers) and 160 mg of perfluorosulfonic acid resin solution with a mass fraction of 25%, disperse them in a water-alcohol solvent (containing 5 g of water and 5 g of isopropanol) to obtain a mixture.

[0056] (2) The above mixture was stirred at 120°C for 2 hours at a stirring speed of 400 rpm, and then dried in a vacuum environment to obtain a powdered carbon nanotube composite material.

[0057] (3) Disperse 80 mg of the carbon nanotube composite material prepared above and 160 mg of commercial platinum carbon catalyst (of which the loading of Pt is 50 wt%) in a water-alcohol solvent (containing 6 g water and 24 g isopropanol), and sonicate to obtain a uniformly mixed cathode catalyst slurry.

[0058] (4) The above-mentioned catalyst slurry is sprayed onto a proton exchange membrane with a thickness of 8 micrometers using a spraying process to form a cathode catalyst layer, and its loading is controlled at 0.1 mg / cm³. 2 .

[0059] Example 2

[0060] Example 2 is basically the same as Example 1, except that the diameter of the hydroxyl multiwalled carbon nanotubes used in Example 2 is 60nm~80nm. The rest is the same as in Example 1, and will not be repeated here.

[0061] Example 3

[0062] Example 3 is basically the same as Example 1, except that step (2) of Example 3 includes: stirring the above mixture at 80°C for 5 hours at a stirring speed of 200 rpm, and then drying it to obtain a powdered carbon nanotube composite material. The rest is the same as in Example 1, and will not be repeated here.

[0063] Example 4

[0064] Example 4 is basically the same as Example 1, except that step (2) of Example 4 includes: stirring the above mixture at 140°C for 1 hour at a stirring speed of 600 rpm, and then drying it to obtain a powdered carbon nanotube composite material. The rest is the same as in Example 1, and will not be repeated here.

[0065] Example 5

[0066] Example 5 is basically the same as Example 1, except that the amount of hydroxyl multiwalled carbon nanotubes used in step (1) of Example 5 is 32 mg. The rest is the same as in Example 1, and will not be repeated here.

[0067] Example 6

[0068] Example 6 is basically the same as Example 1, except that the amount of hydroxyl multiwalled carbon nanotubes used in step (1) of Example 6 is 48 mg. The rest is the same as in Example 1, and will not be repeated here.

[0069] Example 7

[0070] Example 7 is basically the same as Example 1, except that in step (3) of Example 7, 32 mg of carbon nanotube composite material and 160 mg of commercial platinum carbon catalyst are used to prepare a slurry. The rest is the same as in Example 1, and will not be repeated here.

[0071] Example 8

[0072] Example 8 is basically the same as Example 1, except that in step (3) of Example 8, 128 mg of carbon nanotube composite material and 160 mg of commercial platinum carbon catalyst are used to prepare a slurry. The rest is the same as in Example 1, and will not be repeated here.

[0073] Example 9

[0074] Example 9 is basically the same as Example 1, except that Example 9 uses multi-walled carbon nanotubes without hydroxyl modification on the outer wall. The rest is the same as Example 1, and will not be repeated here.

[0075] Comparative Example 1

[0076] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 1 uses small-diameter (5nm~15nm) hydroxyl multi-walled carbon nanotubes. The rest of the procedures are the same as in Example 1, and will not be repeated here.

[0077] Comparative Example 2

[0078] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not pre-prepare carbon nanotube composite materials. Instead, it directly mixes the same amount of hydroxyl multi-walled carbon nanotubes (with a diameter of 5 nm to 15 nm), perfluorosulfonic acid resin, and platinum-carbon catalyst and sonicates them to prepare a cathode catalyst slurry. The rest is the same as in Example 1 and will not be repeated here.

[0079] The membrane electrode performance of the cathode catalyst layers formed on the proton exchange membranes prepared in the above embodiments and comparative examples was tested according to the method described in "Overcoming the Limitation of Ionomers on Mass Transport and Pt Activity to Achieve High-Performing Membrane Electrode Assembly". The sulfonic acid group coverage was determined using a CO adsorption-dissolution experiment, where θ = 2q. red / q oxi q red With q oxi These represent the reduction charge and oxidation charge during the CO adsorption and desorption processes, respectively.

[0080] The test results are summarized in Table 1.

[0081] Table 1. Porosity, sulfonic acid group coverage, and performance test results of the cathode catalyst layers in the examples and comparative examples.

[0082] Figure 2 These are TEM images and corresponding EDS images of the carbon nanotube composite material prepared in Example 1, showing the distribution of perfluorosulfonic acid resin ionomers reacted with fluorine. Figure 2 It can be seen that the distribution area of ​​the ionomer completely overlaps with that of the carbon nanotubes, indicating that in the prepared carbon nanotube composite material, the ionomers are stably bonded along the carbon nanotubes, and the ionomers are continuously distributed on the outer wall of the multi-walled carbon nanotubes, forming a continuous proton conduction path.

[0083] The diameter of the carbon nanotubes used is quite important. If the diameter of the carbon nanotubes is small, on the one hand, the porosity of the catalyst layer will be small, which will increase the difficulty of oxygen transport. The porosity of the catalyst layer prepared in Example 1 of this invention is 57.1%, while the porosity of the catalyst layer prepared in Comparative Example 1 is 48.7%. On the other hand, it is not conducive to the adhesion of ionomers. Figure 3 , Figure 4 The images shown are, in order, TEM and EDS images of the cathode catalyst layers prepared in Example 1 and Comparative Example 1. Comparing Example 1 and Comparative Example 1, it was found that in Comparative Example 1, which used a catalyst layer with small-diameter (5nm~15nm) multi-walled carbon nanotubes, the fluorine signal was stronger on the platinum-carbon surface and weaker in the carbon nanotube region. This indicates that the small-diameter carbon nanotubes can only bind a portion of the ionomers, and under these conditions, the platinum-carbon particles still face a significant poisoning problem. In Example 1, which used a catalyst layer with large-diameter multi-walled carbon nanotubes, the fluorine signal was mainly present in the carbon nanotube region, with only a small amount of ionomers on the surface of the platinum-carbon particles, thus minimizing the poisoning of platinum. Comparing Example 1 and Example 2, it was found that the proton conduction impedance of Example 2 increased slightly. This may be due to the less continuous distribution of ionomers on the carbon nanotubes compared to Example 1, but the catalyst layer performance of Example 2 is still relatively good. If the carbon nanotube diameter is too large, such as greater than 80nm, the discontinuous distribution of ionomers on the carbon nanotubes may become more severe, which will be detrimental to proton conduction.

[0084] This invention enables ionomers to uniformly and continuously bond to the outer wall of large-diameter multi-walled carbon nanotubes. Its advantage lies in the fact that the large-diameter multi-walled carbon nanotube framework allows for the widespread distribution of ionomers within the catalytic layer, thereby achieving rapid long-range proton conduction. Stirring a mixture of ionomers and carbon nanotubes at a mass ratio of 0.8–1.2:1 at 80–140°C for at least 1 hour achieves the aforementioned bonding method and ensures stable bonding, with over 95 wt% of the ionomers bonded to the carbon nanotubes. Specific effects are evident. Figure 2 Compared to ultrasonic mixing, the vigorous physical stirring employed in this invention more effectively disperses the polymer ionomers uniformly in the solution phase, thereby achieving a stable bond with carbon nanotubes through physical adsorption and chemical bonding. Ultrasonic mixing, however, cannot form a stable and uniform bond, easily leading to some ionomers detaching from the carbon nanotubes or failing to adhere successfully. Furthermore, as shown in Comparative Example 2, if the carbon nanotube composite material is not prepared beforehand, and the cathode catalyst layer is obtained by directly ultrasonically mixing hydroxyl multi-walled carbon nanotubes, perfluorosulfonic acid resin, and platinum-carbon catalyst, the same problem exists, stemming from the inability to uniformly distribute more ionomers on the carbon nanotubes.

[0085] The mass ratio of carbon nanotubes and ionomers in a mixture significantly affects the bonding effect. Both excessively low and excessively high mass ratios of ionomers and carbon nanotubes lead to performance degradation. This is because the amounts of ionomers and carbon nanotubes need to be precisely balanced. If the mass ratio is too high, the carbon nanotubes cannot completely adsorb the ionomers, and excess ionomers will adhere to the platinum-carbon catalyst. If the mass ratio is too low, the proton conduction channels will be difficult to maintain continuity. Our systematic research has found that when the mass ratio of ionomers to carbon nanotubes is within the range of 0.8 to 1.2:1, the ionomers can be continuously distributed on the carbon nanotubes without excessive poisoning, resulting in excellent overall performance of the cathode catalyst layer.

[0086] Comparing Examples 1 and 9 reveals that carbon nanotubes without functional group modification suffer some performance loss. This is because the hydroxyl groups modified on the outer wall of multi-walled carbon nanotubes can form bonds with the sulfonic acid groups of the ionomer, making the ionomer more stably bound to the outer wall of the carbon nanotube. However, if the outer wall of the carbon nanotube is unmodified with functional groups, physical bonding alone reduces the ionomer binding rate, making it difficult for the ionomer to form a continuous axial distribution on the carbon nanotube, thus affecting proton conduction and platinum poisoning. Besides hydroxyl groups, carbon nanotubes modified with functional groups such as amino and carboxyl groups on the outer wall can also achieve comparable results, as they can all form stable bonds through hydrogen bonding.

[0087] As shown in Table 1, compared with the comparative example, the cathode catalyst layer prepared by this invention not only exhibits excellent performance within the conventional operating temperature range (80℃), but also shows a significant performance improvement at high temperatures (120℃). At 120℃, the peak power density of the examples is 0.81~0.95 W / cm². 2 The peak power density of the comparative example is 0.71~0.73 W / cm³. 2 The high-temperature proton conduction impedance of the embodiment is 0.0874~0.1014Ω×cm. 2 The comparative high-temperature proton conduction impedance is 0.1239~0.1457 Ω×cm. 2 This is because the presence of a three-dimensional porous framework improves the internal structure and proton conduction of the catalyst layer, thus each embodiment exhibits superior high-temperature performance compared to conventional catalyst layers.

[0088] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0089] In summary, the carbon nanotube composite anti-poisoning cathode catalyst layer provided by this invention incorporates ionomers onto the carbon nanotubes to form a carbon nanotube composite material, achieving physical barrier between the ionomers and the catalyst. This reduces the poisoning effect of the ionomers on the catalyst, improving catalyst efficiency and activity. Furthermore, the continuous distribution of ionomers on the carbon nanotubes constructs a continuous proton conduction pathway, and the use of large-diameter carbon nanotubes enables the formation of a more "fluffy" three-dimensional porous framework, simultaneously enhancing the proton conduction and oxygen transport capabilities of the cathode catalyst layer.

[0090] All aspects, embodiments, features, and examples of this invention should be considered illustrative and used to explain and illustrate the invention, but not to limit the invention. The scope of the invention is defined only by the claims.

[0091] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.

Claims

1. A carbon nanotube composite anti-poisoning cathode catalytic layer, characterized in that, include: A three-dimensional porous framework is formed by interweaving and overlapping carbon nanotube composite materials, wherein the carbon nanotube composite materials include multi-walled carbon nanotubes and ionomers, and the ionomers are uniformly dispersed on the outer wall of the multi-walled carbon nanotubes. The catalyst is distributed on the surface of the three-dimensional porous framework; Furthermore, the diameter of the multi-walled carbon nanotube is 40 nm to 80 nm, the porosity of the cathode catalyst layer is 50.4% to 59.3%, and more than 95 wt% of the ionomers contained in the cathode catalyst layer are bonded to the carbon nanotube.

2. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The oxygen transport resistance of the cathode catalyst layer is 41.3 s / m to 64.5 s / m; and / or, the proton conduction impedance of the cathode catalyst layer is 0.0425 Ω × cm. 2 ~0.0503Ω×cm 2 .

3. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The coverage of sulfonic acid groups at the active sites in the cathode catalyst layer is 14.4% to 17.9%.

4. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The catalyst activity of the cathode catalyst layer is 0.18 A / mg. pt ~0.31A / mg pt .

5. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The diameter of the multi-walled carbon nanotube is 40 nm to 60 nm; and / or the length of the multi-walled carbon nanotube is 0.5 μm to 5 μm.

6. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The mass ratio of ionomer to multi-walled carbon nanotubes in the carbon nanotube composite material is 0.8~1.2:1, and / or the thickness of the ionomer on the surface of the multi-walled carbon nanotubes in the carbon nanotube composite material is 4nm~10nm.

7. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The outer wall of the multi-walled carbon nanotube is modified with functional groups, which can chemically bond with the ionomer.

8. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 7, characterized in that: The functional group includes at least one of amino, carboxyl, and hydroxyl groups.

9. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The mass ratio of carbon nanotube composite material to catalyst in the cathode catalyst layer is 0.2~0.8:

1.

10. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The catalyst includes a support and a catalytically active substance supported on the support.

11. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 10, characterized in that: The catalyst includes a Pt / C catalyst, wherein the Pt content in the Pt / C catalyst is 20wt%~60wt%.

12. The carbon nanotube composite anti-poisoning cathode catalytic layer according to claim 1, characterized in that: The ionomer includes perfluorosulfonic acid resin.

13. The method for preparing the carbon nanotube composite anti-poisoning cathode catalyst layer according to any one of claims 1-12, characterized in that, include: Multi-walled carbon nanotubes and ionomers are dispersed in a first solvent to form a mixture, and the mass ratio of ionomers to multi-walled carbon nanotubes in the mixture is controlled to be 0.8~1.2:

1. The mixture is stirred continuously at 80~140℃ for more than 1 hour, and then dried to obtain a carbon nanotube composite material. The carbon nanotube composite material and the catalyst are dispersed in a second solvent to prepare a slurry, and the slurry is used to form the carbon nanotube composite anti-poisoning cathode catalyst layer.

14. The preparation method according to claim 13, characterized in that: The solid content of the mixture is 0.4wt% to 1.2wt%.

15. The preparation method according to claim 13, characterized in that: The mixture is stirred continuously for 1 to 5 hours at a stirring rate of 200 to 600 rpm.

16. The preparation method according to claim 13, characterized in that: The first solvent comprises water and alcohol, with a water-to-alcohol mass ratio of 0.8 to 1.2:

1.

17. The preparation method according to claim 13, characterized in that: The second solvent comprises water and alcohol, with a water-to-alcohol mass ratio of 0.2 to 0.5:

1.

18. The preparation method according to claim 16 or 17, characterized in that: The alcohols include ethanol and / or isopropanol.

19. The preparation method according to claim 13, characterized in that: The solid content of the slurry is 0.7wt%~0.9wt%.

20. A membrane electrode structure for a fuel cell, characterized in that, It includes a proton exchange membrane, a gas diffusion layer, and an anode catalyst layer and a cathode catalyst layer formed on both sides of the proton exchange membrane, wherein the cathode catalyst layer includes the carbon nanotube composite anti-poisoning cathode catalyst layer as described in any one of claims 1-12.

Images