Preparation method of nitrogen-doped carbon-coated ionomer catalyst and application of nitrogen-doped carbon-coated ionomer catalyst in fuel cell

Abstract

The invention discloses a preparation method of a nitrogen-doped carbon-coated ionomer catalyst and application of the catalyst in a fuel cell, and the catalyst is prepared by the following steps: weighing a nitrogen source substance, a carbon source and an isopropanol solvent, mixing, reacting and drying to obtain a nitrogen-doped carbon NC mixed powder material; weighing the NC mixed powder material, a Nafion ionomer and an isopropanol solvent, and dispersing to obtain an NC-coated Nafion ionomer solution; weighing a Pt / C catalyst, the NC-coated Nafion ionomer solution, deionized water and an isopropanol solvent, and dispersing to obtain a nitrogen-doped carbon-coated ionomer catalyst; according to the application, the catalyst is sprayed on the two sides of a proton exchange membrane to form a catalyst coating membrane CCM; and performing hot press molding on the CCM and the diffusion layer to form the membrane electrode for the fuel cell. Through the mode, the local proton transfer resistance under high current density can be reduced, and the durability of the membrane electrode under the high current density condition is remarkably improved; by enhancing the oxygen mass transfer efficiency, the membrane electrode can still maintain high-performance operation at low potential, and the working window of the fuel cell is widened.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and particularly to a preparation method of a nitrogen-doped carbon-coated ionomer catalyst and its application in fuel cells. Background Art

[0002] As the core carrier of clean energy, fuel cell vehicles have become an important application direction. The membrane electrode assembly (MEA) is the core component of a fuel cell, and the durability of the catalyst layer directly determines the performance and lifespan of the MEA.

[0003] Currently, high specific surface area (HSA) carbon carriers (such as mesoporous size 5 - 14 nm) have become the mainstream materials due to their high Pt loading capacity (about 75%), but they are prone to performance degradation due to the increased local proton transport resistance at high current densities. Specifically, under high current density conditions, water cannot effectively transfer protons to the Pt active sites; the micropores of traditional carbon carriers are insufficiently filled, resulting in limited proton transport efficiency; and oxygen mass transfer is insufficient at low potentials, leading to a sudden drop in performance.

[0004] In the prior art, although mass transfer has been improved by optimizing the carbon carrier structure or ionomer distribution, it is difficult to simultaneously achieve high durability and low potential stability. Therefore, it is urgent to develop a preparation method for a membrane electrode assembly with both high activity and durability. Summary of the Invention

[0005] The main technical problem to be solved by the present invention is to provide a preparation method of a nitrogen-doped carbon-coated ionomer catalyst and its application in fuel cells, which can improve the stability of the carbon carrier through nitrogen doping, optimize the proton and oxygen mass transfer paths by combining with the NC@Nafion ionomer layer, and significantly improve the durability and performance of the membrane electrode assembly.

[0006] To solve the above technical problem, one technical solution adopted by the present invention is: to provide a preparation method of a nitrogen-doped carbon-coated ionomer catalyst, comprising the following steps: (1) Weigh a nitrogen source material and a carbon source according to a mass ratio, add an isopropanol solvent, and react at 100 - 150 °C for 3 - 5 h. After the reaction is completed, dry to obtain a nitrogen-doped carbon NC mixed powder material; (2) Weigh the NC mixed powder material and Nafion ionomer according to a mass ratio, add an isopropanol solvent, and disperse by shear or high-speed stirring for 15 - 30 min to obtain an NC@Nafion ionomer solution; (3) Weigh a Pt / C catalyst, the NC@Nafion ionomer solution, deionized water, and an isopropanol solvent, and disperse by high-speed shear or ball milling for 15 - 20 min to obtain a nitrogen-doped carbon-coated ionomer catalyst.

[0007] In a preferred embodiment of the present invention, the mass ratio of the nitrogen source material to the carbon source in step (1) is 3-5:8-10, wherein the nitrogen source material includes thiourea, urea or N-sulfonyl aniline; the carbon source is XC-72 carbon powder, ECP300 carbon powder or EC600 carbon powder.

[0008] In a preferred embodiment of the present invention, the drying in step (1) includes subjecting the solution to heat treatment in an oven at 400-600 °C, or freeze-drying in a freeze dryer at -25 °C to -40 °C.

[0009] In a preferred embodiment of the present invention, the mass ratio of the NC mixed powder material to the Nafion ionomer in step (2) is 8-10:2-4, wherein the Nafion ionomer is Dupont520, Dupont1020 or Dupont2020.

[0010] In a preferred embodiment of the present invention, the mass ratio of the Pt / C catalyst, the NC@Nafion ionomer solution, deionized water and isopropanol in step (3) is 0.1-0.2:4-6:7-10:7-10.

[0011] In a preferred embodiment of the present invention, the Pt / C catalyst in step (3) includes 40% Pt / C catalyst, 50% Pt / C catalyst or 60% Pt / C catalyst.

[0012] To solve the above technical problems, another technical solution adopted by the present invention is: to provide an application of a nitrogen-doped carbon-coated ionomer catalyst in a fuel cell, spraying the nitrogen-doped carbon-coated ionomer catalyst on both sides of a proton exchange membrane, with the Pt loading of the cathode catalyst being 0.3-0.4 mg / cm 2 , and the Pt loading of the anode catalyst being 0.05-0.1 mg / cm 2 , to form a catalyst-coated membrane CCM; then thermocompression molding the CCM with a diffusion layer to form a membrane electrode for a fuel cell.

[0013] In a preferred embodiment of the present invention, the diffusion layer is Toray TGL-R045, TGL-R055, SGL22BB, 28BC, 36BB, 39BB, etc.

[0014] In a preferred embodiment of the present invention, the proton exchange membrane is Gore 765.08 membrane, Gore788.12 membrane or Gore775.15 membrane.

[0015] The beneficial effects of the present invention are as follows: The nitrogen-doped carbon (NC) material of the present invention optimizes the electronic structure of the carbon support, enhances the anchoring ability of the Pt catalyst, and effectively inhibits the corrosion of the carbon support and the aggregation of Pt particles; the NC@Nafion ionomer layer reduces the local proton transport resistance at high current densities through microporous filling (2.77 - 5.3 mol m -3 ) and mesoporous size regulation, significantly improving the durability of the membrane electrode under high current density conditions.

[0016] The present invention can improve the oxygen mass transfer performance at low potentials. The NC@Nafion ionomer layer provides a continuous proton transport channel at low potentials, optimizes the oxygen mass transfer path, and avoids the sudden performance drop of traditional membrane electrodes due to insufficient oxygen mass transfer at low potentials; by enhancing the oxygen mass transfer efficiency, the membrane electrode can still maintain high-performance operation at low potentials, broadening the working window of the fuel cell.

[0017] The present invention can maintain the high performance of the membrane electrode. After 0 - 5000 cycles and 0 - 30000 cycles of durability tests, the voltage decay rate of the membrane electrode is less than 5%, and the oxygen mass transfer resistance is reduced by 30%, verifying its long-term stability; the membrane electrode prepared by the method of the present invention has high activity, high durability, and low potential stability, and is suitable for the commercial application of high-performance fuel cells. Detailed Embodiments

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated in the present solution can be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the present invention provided in the solution is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0020] It should be noted that similar reference numerals and letters denote similar items in the following solution. Therefore, once an item is defined in one solution, it does not need to be further defined and explained in subsequent solutions.

[0021] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "front" and "rear" is based on the orientation or positional relationship shown in the solution, or the orientation or positional relationship in which the inventive product is habitually placed during use. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention. In addition, terms such as "first" and "second" are only used for differential description and cannot be construed as indicating or implying relative importance.

[0022] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "arrangement" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] In the present invention, unless otherwise clearly specified and defined, the first feature being above or below the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being above, over, and on the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being below, under, and beneath the second feature includes the first feature being directly below and obliquely below the second feature, or simply indicating that the horizontal height of the first feature is lower than that of the second feature.

[0024] Embodiments of the present invention include: Embodiment 1:

[0025] A preparation method of a nitrogen-doped carbon-coated ionomer catalyst, comprising the following steps: Weigh 5 g of urea and 10 g of XC-72 carbon powder, place them in a 500 mL reaction kettle, add 100 mL of isopropanol solvent, and mix thoroughly at 100 °C for 3 h. After the reaction is completed, place the liquid after the reaction in an oven at 600 °C for drying to obtain the dried NC mixed powder.

[0026] Weigh 8 g of the NC mixed powder and 2 g of DuPont D520 ionomer, place them in a 100 mL beaker, add 50 mL of isopropanol as the solvent, and disperse them in a high-speed shearing manner for 15 min. After standing, obtain the NC@Nafion ionomer solution.

[0027] Weigh 0.2 g of 40% Pt / C catalyst, 5 g of NC@Nafion ionomer solution, 8 g of deionized water, and 8 g of isopropanol, and disperse them for 15 min using high-speed shearing to obtain a nitrogen-doped carbon-coated ionomer catalyst.

[0028] The preparation method of the nitrogen-doped carbon-coated ionomer catalyst for use in a fuel cell is as follows: the dispersed catalyst is placed in a sprayer and sprayed on a Gore 788.12 membrane. The anode catalyst Pt loading is 0.1 mg / cm 2 The cathode catalyst Pt loading is 0.3 mg / cm 2 , forming a catalyst coating membrane CCM, bonding the CCM to TGL-R055 to obtain a membrane electrode for a fuel cell, and installing the membrane electrode on a fuel cell test system to prepare for testing. Embodiment 2:

[0029] A method for preparing a nitrogen-doped carbon-coated ionomer catalyst comprises the following steps: (1) Weigh 5 g of thiourea and 9 g of EC-300J carbon powder, place them in a 500 mL reactor, add 80 mL of isopropanol solvent, and mix them at 120 °C for 4 h. After the reaction is completed, place the liquid after the reaction in an oven at 600 °C to dry it to obtain a dried NC mixed powder.

[0030] (2) Weigh 9 g of NC mixed powder and 4 g of DuPont 2020 ionomer, place them in a 100 mL beaker, add 80 mL of isopropanol as solvent, disperse them under high-speed shear for 20 min, and let them stand to obtain the NC@Nafion ionomer solution.

[0031] (3) Weigh 0.2 g of 50% Pt / C catalyst, 6 g of NC@Nafion ionomer solution, 10 g of deionized water, and 9 g of isopropanol, and disperse them for 20 min using high-speed shear to obtain a nitrogen-doped carbon-coated ionomer catalyst.

[0032] The preparation method of the nitrogen-doped carbon-coated ionomer catalyst for use in a fuel cell is as follows: the catalyst solution is placed in a sprayer and sprayed on a Gore 765.08 membrane, with an anode catalyst loading of 0.05 mg / cm 2 , the cathode catalyst loading is 0.3 mg / cm 2 , forming a catalyst coating membrane CCM; bonding the CCM and TGL-R045 to obtain the final membrane electrode, and installing the membrane electrode on the fuel cell test system to prepare for testing. Embodiment 3:

[0033] A method for preparing a nitrogen-doped carbon-coated ionomer catalyst comprises the following steps: (1) Weigh 4 g of N-sulfonyl aniline and 8 g of ECP-600JD toner, place them in a 500 mL reactor, add 70 mL of isopropanol solvent, and mix thoroughly at 150 °C for 5 h. After the reaction is completed, dry the liquid after the reaction in an oven at 600 °C to obtain the dried NC mixed powder.

[0034] (2) Weigh 10 g of the NC mixed powder and 3 g of DuPont D1020 ionomer, place them in a 100 mL beaker, add 80 mL of isopropanol as the solvent, and disperse them for 15 min under high-speed shearing. After standing, obtain the NC@Nafion ionomer solution.

[0035] (3) Weigh 0.2 g of 50% Pt / C catalyst, 5 g of NC@Nafion ionomer solution, 9 g of deionized water, and 7 g of isopropanol, and disperse them by high-speed shearing for 15 min to obtain the nitrogen-doped carbon-coated ionomer catalyst.

[0036] The preparation method when applying the nitrogen-doped carbon-coated ionomer catalyst in a fuel cell is as follows: Place the catalyst solution in a spraying machine and spray it on the GORE 775.15 membrane. The anode catalyst loading is 0.08 mg / cm 2 , and the cathode catalyst loading is 0.4 mg / cm 2 , to form the catalyst-coated membrane CCM. Then laminate the CCM with SGL 22BB to obtain the final membrane electrode, and install the membrane electrode on the fuel cell test system for preparation of testing.

[0037] Comparative Example 1: Cut a Gore 788.12 membrane as the proton exchange membrane. Weigh 0.2 g of 40% Pt / C catalyst, 5 g of Dupnt 520 solution, 8 mL of ethylene glycol, and 8 mL of deionized water, and mix them by high-speed shearing for 15 min. Then spray the anode and cathode slurries on both sides of the proton exchange membrane respectively. The anode Pt loading is controlled at 0.1 mg / cm 2 , and the cathode Pt loading is controlled at 0.3 mg / cm 2 , to obtain the CCM.

[0038] Laminate the sprayed CCM with TGL-R055 to obtain the final membrane electrode, and install the membrane electrode on the fuel cell test system for preparation of testing.

[0039] The polarization test conditions in the fuel cell test systems of Examples 1-3 and Comparative Example 1 were as follows: starting from the open circuit potential and scanning to 0.55 V, running for 3 min at each current, anodic stoichiometry of 1.2, and cathodic stoichiometry of 2.5. Anodic humidity was 100% RH, cathodic humidity was 100% RH, hydrogen back pressure was 200 kPa, air back pressure was 200 kPa, anodic temperature was 80 °C, cathodic temperature was 80 °C, and single cell temperature was 80 °C.

[0040] The durability test conditions in the fuel cell test systems of Examples 1-3 and Comparative Example 1 were as follows: the temperature of the single fuel cell was set at 80 °C, and H2 with a relative humidity of 100% was supplied to the anode and cathode at a flow rate of 100 mL min -1 respectively, and N2 with a relative humidity of 100% was supplied at a flow rate of 40 mL min -1 respectively. The square wave cycle was carried out by alternating between 0.6 V and 0.95 V for 30,000 cycles, with each step lasting 3 s and the rise time being about 0.5 s or shorter. The triangular wave scanning cycle was carried out between 1.0 V and 1.5 V at a speed of 500 mV / s for 5,000 cycles.

[0041] After cycling 0, 2,000, and 5,000 cycles at a triangular wave potential of 1-1.5 V, a polarization test was carried out to obtain the final data, as shown in Table 1: Table 1 Comparison data table of current densities at 0.65 V after 0, 2,000, and 5,000 cycles of the 1-1.5 V triangular wave accelerated carrier durability test for Examples 1-3 and Comparative Example 1 Number of cycles <![CDATA[Example 1 / A / cm 2 > <![CDATA[Example 2 / A / cm 2 > <![CDATA[Example 3 / A / cm 2 > <![CDATA[Comparative Example 1 / A / cm 2 > 0 2.22 2.27 2.32 2.12 2000 2.12 2.08 2.12 1.87 5000 1.94 1.89 2.02 1.42 After cycling 0, 10,000, and 30,000 cycles at a square wave potential of 0.6-0.95 V, a polarization test was carried out to obtain the final data, as shown in Table 2: Table 2 Comparison data table of current densities at 0.65 V after 0, 10,000, and 30,000 cycles of the 0.6-0.95 V square wave accelerated Pt durability test for Examples 1-3 and Comparative Example 1 Number of cycles <![CDATA[Example 1 / A / cm 2 > <![CDATA[Example 2 / A / cm 2 > <![CDATA[Example 3 / A / cm 2 > <![CDATA[Comparative Example 1 / A / cm 2 <!-- 4 -->]]> 0 2.21 2.23 2.18 2.05 10000 2.18 2.14 2.03 1.62 30000 1.62 1.72 1.78 0.98 From the test data in Table 1 and Table 2, it can be analyzed that for the examples with the addition of the NC@Nafion layer as a protective layer, after 5,000 cycles of aging, the performance degradation was 13%, and after 30,000 cycles of aging, the performance degradation was 23%. This was because the protective layer avoided the adsorption of oxygen-containing groups on Pt, avoided the agglomeration of Pt, and reduced the corrosion of the carbon carrier. Similarly, for the comparative example, after 5,000 cycles of aging, the performance degradation was 34%, and after 30,000 cycles of aging, the performance degradation was 53%. The performance comparison showed obvious differences.

[0042] The nitrogen-doped carbon (NC) material of the present invention enhances the anchoring ability of the Pt catalyst by optimizing the electronic structure of the carbon support, effectively inhibits the corrosion of the carbon support and the aggregation of Pt particles; the NC@Nafion ionomer layer reduces the local proton transport resistance at high current densities through microporous filling (2.77 - 5.3 mol m -3 ), and mesoporous size regulation, significantly improving the durability of the membrane electrode under high current density conditions.

[0043] The present invention can improve the oxygen mass transfer performance at low potentials. The NC@Nafion ionomer layer provides a continuous proton transport channel at low potentials, optimizes the oxygen mass transfer path, and avoids the sudden drop in performance caused by insufficient oxygen mass transfer in traditional membrane electrodes at low potentials; by enhancing the oxygen mass transfer efficiency, the membrane electrode can still maintain high-performance operation at low potentials, broadening the working window of the fuel cell.

[0044] The present invention can maintain the high performance of the membrane electrode. After 0 - 5000 cycles and 0 - 30000 cycles of durability tests, the voltage decay rate of the membrane electrode is less than 5%, and the oxygen mass transfer resistance is reduced by 30%, verifying its long-term stability; the membrane electrode prepared by the method of the present invention has high activity, high durability and low potential stability, and is suitable for the commercial application of high-performance fuel cells.

[0045] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon-coated ionomer catalyst, characterized in that: The following steps are involved: (1) Weighing a nitrogen source and a carbon source according to a mass ratio, adding isopropanol solvent, reacting at 100-150° C. for 3-5 hours, and drying after the reaction to obtain a nitrogen-doped carbon NC mixed powder material; (2) Weigh the NC mixed powder material and Nafion ionomer according to the mass ratio, add isopropanol solvent, and disperse by shearing or high-speed stirring for 15-30 minutes to obtain NC@Nafion ionomer solution; (3) Pt / C catalyst, NC@Nafion ionomer solution, deionized water and isopropanol solvent are weighed in proportion by mass, and dispersed for 15-20 min by high-speed shearing or ball milling to obtain a nitrogen-doped carbon-coated ionomer catalyst.

2. The method for preparing the nitrogen-doped carbon-coated ionomer catalyst according to claim 1, characterized in that: The mass ratio of the nitrogen source to the carbon source in step (1) is 3-5:8-10, wherein the nitrogen source comprises thiourea, urea or N-sulfonylanilide; and the carbon source comprises XC-72 carbon powder, EC-300J carbon powder or ECP-600JD carbon powder.

3. The method for preparing the nitrogen-doped carbon-coated ionomer catalyst according to claim 1, characterized in that: The drying of step (1) comprises placing the solution in an oven at 400-600°C for heat treatment, or placing the solution in a freeze dryer at -25°C to -40°C for freeze drying.

4. The method for preparing the nitrogen-doped carbon-coated ionomer catalyst according to claim 1, characterized in that: In step (2), the mass ratio of the NC mixed powder material to the Nafion ionomer is 8-10:2-4, wherein the Nafion ionomer is Dupont D520, D1020 or D2020.

5. The method for preparing the nitrogen-doped carbon-coated ionomer catalyst according to claim 1, characterized in that: In step (3), the mass ratio of the Pt / C catalyst, NC@Nafion ionomer solution, deionized water and isopropanol is 0.1-0.2:4-6:7-10:7-10.

6. The method for preparing the nitrogen-doped carbon-coated ionomer catalyst according to claim 1, characterized in that: The Pt / C catalyst in step (3) includes a 40% Pt / C catalyst, a 50% Pt / C catalyst or a 60% Pt / C catalyst.

7. Application of a nitrogen-doped carbon-coated ionomer catalyst in a fuel cell, characterized in that: The nitrogen-doped carbon-coated ionomer catalyst according to any one of claims 1 to 6 is sprayed on both sides of the proton exchange membrane, and the Pt loading of the cathode catalyst is 0.3-0.4 mg / cm 2 The Pt loading of the anode catalyst is 0.05-0.1 mg / cm 2 , forming a catalyst coating membrane CCM; then the CCM and the diffusion layer are hot-pressed to form a membrane electrode for a fuel cell.

8. The use according to claim 7, characterized in that: The diffusion layer is Toray TGL-R045, TGL-R055, SGL 22BB, 28BC, 36BB or 39BB.

9. The use according to claim 7, characterized in that: The proton exchange membrane is Gore 765.08 membrane, Gore 788.12 membrane or Gore 775.15 membrane.