Ionomer of catalyst layer of proton exchange membrane fuel cell and preparation method of ionomer

Abstract

The invention provides an ionomer of a catalyst layer of a proton exchange membrane fuel cell as well as a preparation method and application of the ionomer. The ionomer is directly generated on the surface of a catalyst through an in-situ polymerization technology, a sulfonated styrene monomer (0.5-2.0 mol / L) and an azodiisobutyronitrile initiator (0.1-0.5 wt%) react for 2-6 hours under the conditions of 80-120 DEG C and 0.5-2 MPa, and the networked ionomer with an oriented structure is formed by controlling the polymerization reaction rate and orientation. Ion clusters in the ionomer network are in 75%-95% directional arrangement, and a graded distribution multistage pore channel structure is constructed and comprises micropores (2-10 nm), mesopores (10-50 nm) and macropores (50-200 nm). The thickness of the prepared catalyst layer is 5-15 [mu] m, the ionomer content is 15-30 wt%, the electrochemical active area reaches 80-120 m < 2 > / Pt, the proton conductivity is 0.05-0.15 S / cm, and the current density under the working voltage of 0.6 V reaches 1.2-1.8 A / cm < 2 >. And the performance degradation does not exceed 10% after a 1000-hour cycle test. Accurate regulation and control of an ionomer-catalyst interface are realized through an in-situ directional polymerization technology, the proton conduction efficiency and the three-phase reaction interface activity are effectively improved, and meanwhile, a multi-scale mass transfer channel is optimized, so that the activity, the stability and the durability of the fuel cell are comprehensively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to an ionomer for a catalyst layer of a proton exchange membrane fuel cell, a preparation method thereof, and a proton exchange membrane fuel cell using the ionomer. Through in-situ directional polymerization technology, the present invention realizes precise control of the ionomer-catalyst interface, thereby effectively improving the proton conduction efficiency and the activity of the three-phase reaction interface. At the same time, the present invention also optimizes the multi-scale mass transfer channels, so that the fuel cell is comprehensively improved in terms of activity, stability and durability. Background Art

[0002] A proton exchange membrane fuel cell (PEMFC) is an efficient and clean energy conversion device. In the catalyst layer, the distribution and structure of the ionomer are crucial for the performance of the battery. In the prior art, the ionomer is usually introduced into the catalyst layer by simple mixing or impregnation methods, and it is difficult to achieve uniform distribution and directional arrangement.

[0003] For example, US Patent No. US8202669 discloses a method for preparing a catalyst layer by solution impregnation. Although this method is simple and feasible and can introduce the ionomer, it is difficult to precisely control its distribution and structure, and it is impossible to achieve uniform distribution and directional arrangement of the ionomer, resulting in a large number of disordered structures in the catalyst layer, which affects the electrochemical active area and mass transfer performance. Specifically, in the catalyst layer prepared by this method, the non-uniformity of the ionomer distribution reaches 30%, the electrochemical active area is only 60 m 2 / g Pt, and the proton conductivity is 0.03 S / cm.

[0004] Japanese Patent JP2015233012A proposes a design method for a porous structure catalyst layer, and forms a hierarchical pore structure by regulating the solvent evaporation rate during the film-forming process. However, this method has some limitations: it is difficult to optimize the ionomer distribution and pore structure at the same time, and it is impossible to fully exert the performance potential of the catalyst layer; the controllable range of the porosity of the prepared catalyst layer is only 40-60%, and the proton conductivity is 0.06 S / cm; the directional arrangement of ion clusters cannot be achieved, and the orientation degree of ion clusters is only 50%. These problems result in non-uniform distribution of the ionomer in the catalyst layer, affecting the electrochemical active area and mass transfer performance, and at the same time, it is difficult to optimize the pore structure of the catalyst layer, restricting the transport efficiency of reactants and products.

[0005] The main problems existing in the prior art include:

[0006] 1. The non-uniform distribution of the ionomer affects the electrochemical active area;

[0007] 2. It is difficult to achieve the directional arrangement of ion clusters, restricting the proton conduction efficiency;

[0008] 3. The pore structure is unreasonable, affecting the transport of reactants and products;

[0009] 4. It is difficult to precisely control the distribution and structure of the ionomer at the nanoscale.

[0010] With the development of fuel cell technology, there is an urgent need to develop a new technical solution to precisely control the distribution and structure of the ionomer at the nanoscale, while optimizing the pore structure of the catalyst layer to improve the performance and durability of the fuel cell. This requires integrating multidisciplinary knowledge such as polymer chemistry, electrochemistry, and materials science to achieve cross-field technological integration and innovation. Summary of the Invention

[0011] The present invention aims to solve the following problems existing in the existing preparation technology of PEMFC catalyst layers:

[0012] 1. The ionomer distribution is uneven, affecting the catalyst utilization rate and the electrochemically active area;

[0013] 2. The arrangement of ion clusters is disordered, reducing the proton conduction efficiency;

[0014] 3. The pore structure is unreasonable, restricting the transport efficiency of reactants and products;

[0015] 4. The performance and durability of the catalyst layer are insufficient, restricting the overall performance of the fuel cell.

[0016] To solve the above technical problems, the present invention provides an ionomer for a proton exchange membrane fuel cell catalyst layer and a preparation method thereof. The core innovation of this technical solution is to directly generate an ionomer network with a directional structure on the catalyst surface through in-situ polymerization technology, while forming a hierarchical pore structure with a gradient structure.

[0017] Specifically, the technical solution of the present invention includes the following key features:

[0018] 1. In-situ polymerization technology:

[0019] Sulfonated styrene monomer is used for in-situ free radical polymerization to directly generate an ionomer network on the catalyst surface. The polymerization reaction is carried out in a high-pressure reactor at a temperature of 80 - 120 °C, a pressure of 0.5 - 2 MPa, and a reaction time of 2 - 6 hours. By adjusting the monomer concentration (0.5 - 2.0 mol / L), the initiator dosage (azobisisobutyronitrile, 0.1 - 0.5 wt%), and the reaction temperature, the rate and orientation of the polymerization reaction are precisely controlled.

[0020] 2. Directional structure ionomer network:

[0021] By controlling the polymerization kinetics, the directional arrangement of ion clusters is achieved. The degree of orientation of the ion clusters reaches 75%-95%, as determined by small-angle X-ray scattering. This oriented structure forms continuous proton conduction channels, significantly improving the proton conduction efficiency.

[0022] 3. Gradient structure multi-level pores:

[0023] The catalyst layer forms a gradient structure of micropores (2-10 nm), mesopores (10-50 nm), and macropores (50-200 nm). The micropores are mainly formed by the voids between polymer chains, which are beneficial for proton conduction; the mesopores and macropores are formed by the voids between polymer aggregates, improving the transport of reactants and products. By adjusting the reaction temperature, pressure, and monomer concentration, the proportion of pores of different sizes can be controlled.

[0024] 4. Real-time monitoring and dynamic regulation:

[0025] The gel permeation chromatography (GPC) technique is used to monitor the degree of polymerization in real time, and a quantitative relationship model between the degree of polymerization and reaction parameters is established. The degree of polymerization is sampled and measured every 30 minutes, and the reaction conditions are dynamically adjusted according to the measurement results. When the degree of polymerization is lower than 5000, the monomer concentration is increased by 0.1 mol / L or the reaction temperature is increased by 2 °C; when the degree of polymerization is higher than 10000, the monomer concentration is decreased by 0.1 mol / L or the reaction temperature is decreased by 2 °C.

[0026] 5. Preparation of the catalyst layer

[0027] The catalyst containing the oriented structure ionomer is mixed with deionized water to form a slurry, which is coated on the gas diffusion layer, and the thickness is controlled to be 5-15 μm. It is dried at 80 °C for 2 hours to obtain a catalyst layer with an optimized structure. The content of the ionomer is 15-30 wt% of the total weight of the catalyst layer.

[0028] Through the above technical solutions, the present invention realizes the uniform distribution and directional arrangement of the ionomer in the catalyst layer, and at the same time forms a multi-level pore structure conducive to mass transfer, thus significantly improving the performance and durability of the fuel cell.

[0029] The present invention realizes the uniform distribution and directional arrangement of the ionomer on the catalyst surface through in-situ polymerization technology, and at the same time forms a multi-level pore with a gradient structure, having the following significant advantages:

[0030] 1. Improving the degree of orientation of ion clusters:

[0031] The degree of orientation of the ion clusters reaches 75%-95%, which is 25%-45% higher than that of the traditional method (50%). This highly oriented structure forms continuous proton conduction channels, significantly improving the proton conduction performance. The proton conductivity reaches 0.05-0.15 S / cm, which is 67%-400% higher than that of the traditional method (0.03 S / cm).

[0032] 2. Increase the electrochemically active area:

[0033] The electrochemically active area of the catalyst layer reaches 80 - 120 m 2 / g Pt, which is 33% - 100% higher than the prior art (60 m 2 / g Pt). This improvement effectively increases the catalyst utilization rate, reduces the amount of precious metal used, and lowers the cost.

[0034] 3. Optimize the pore structure:

[0035] A gradient structure of micropores (2 - 10 nm), mesopores (10 - 50 nm), and macropores (50 - 200 nm) is formed, significantly improving the transport efficiency of reactants and products. This hierarchical pore structure optimizes gas diffusion and water management while ensuring proton conduction.

[0036] 4. Improve the performance of the fuel cell:

[0037] At a working voltage of 0.6 V, the current density reaches 1.2 - 1.8 A / cm 2 , which is 50% - 125% higher than the prior art (0.8 A / cm 2 ), significantly enhancing the power density. This performance improvement directly translates into an increase in the efficiency of the fuel cell system, estimated to be 10% - 20%.

[0038] 5. Improve durability:

[0039] The optimized three-phase interface structure and water management ability contribute to extending the service life of the fuel cell. Preliminary accelerated aging tests show that the performance of the catalyst layer of the present invention decays by no more than 10% after 1000 hours of cycling tests, significantly higher than that of traditional catalyst layers (performance decay of 20% - 30%).

[0040] 6. Reduce costs:

[0041] By increasing the catalyst utilization rate and extending the service life, the present invention can significantly reduce the unit power cost of the fuel cell. Preliminary estimates show that the unit power cost can be reduced by 15% - 25%.

[0042] These advantages make the present invention have important application value in improving the performance of PEMFCs, reducing costs, and extending the service life, providing a new technical path for the further development and commercial application of fuel cell technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the ionomer network structure of the present invention.

[0044] Figure 2Schematic diagram of the hierarchical pore structure of the catalyst layer of the present invention.

[0045] Figure 3 Flow chart of the preparation method of the ionomer of the present invention. Detailed implementation manners

[0046] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0047] Example 1: Preparation of ionomer

[0048] 1. Disperse 10 g of Pt / C catalyst in 100 mL of N,N-dimethylformamide (DMF) solution containing 1.5 mol / L sulfonated styrene monomer.

[0049] 2. Add 0.1 g of azobisisobutyronitrile (AIBN) as an initiator.

[0050] 3. Transfer the mixture to a high-pressure reactor and carry out in-situ free radical polymerization reaction at 100 °C and 1.5 MPa pressure with a stirring speed of 350 rpm for 4 hours.

[0051] 4. Monitor the degree of polymerization in real time by GPC and sample and measure it every 30 minutes. When the degree of polymerization is lower than 5000, increase the monomer concentration by 0.1 mol / L; when the degree of polymerization is higher than 10000, lower the reaction temperature by 2 °C.

[0052] 5. After the reaction is completed, cool the product to room temperature, filter, wash it with deionized water and ethanol, and dry it in vacuum at 60 °C for 12 hours to obtain a catalyst containing ionomer with a directional structure.

[0053] Example 2: Preparation of catalyst layer

[0054] 1. Mix the catalyst prepared in Example 1 with deionized water at a mass ratio of 1:5 and ultrasonically disperse it for 30 minutes to make a slurry.

[0055] 2. Use an automatic coater to uniformly coat the slurry on the carbon paper gas diffusion layer, and control the wet film thickness to be 50 μm.

[0056] 3. Dry it at 80 °C for 2 hours to obtain a catalyst layer with a dry film thickness of 10 μm.

[0057] Example 3: Preparation of membrane electrode assembly

[0058] 1. Place the anode catalyst layer and the cathode catalyst layer prepared in Example 2 on both sides of the Nafion 212 proton exchange membrane respectively.

[0059] 2. Hot press at 130 °C and 2 MPa for 5 minutes to obtain a membrane electrode assembly with an effective area of 25 cm 2 .

[0060] Example 4: Fuel cell performance test

[0061] 1. Assemble the membrane electrode assembly prepared in Example 3 into a single cell test device.

[0062] 2. Under the conditions of 80 °C and 100% relative humidity, introduce H2 / O2 gas (flow rates are 200 / 500 sccm respectively) for performance testing.

[0063] 3. Determine the electrochemically active area to be 95 m 2 / g Pt by cyclic voltammetry.

[0064] 4. Measure the proton conductivity to be 0.12 S / cm using the alternating current impedance method.

[0065] 5. At a working voltage of 0.6 V, the current density reaches 1.6 A / cm 2 .

[0066] Example 5: Durability test

[0067] 1. Use the test device of Example 4 to conduct potential cycling tests in the voltage range of 0.6 - 0.9 V.

[0068] 2. Each cycle lasts for 30 seconds, and a total of 1000 hours of testing is carried out.

[0069] 3. The test results show that after 1000 hours, the electrochemically active area of the catalyst layer decreases by 8%, and the current density at 0.6 V decreases by 9%.

[0070] Through the above examples, the present invention successfully prepared an ionomer network with a directional structure, realizing the directional arrangement of ion clusters and the formation of a hierarchical pore structure. Compared with the prior art, the present invention significantly improves the electrochemically active area and proton conduction performance of the catalyst layer, while improving the mass transfer characteristics, thereby greatly enhancing the overall performance and durability of the fuel cell.

[0071] The present invention realizes the directional growth of the ionomer network and the formation of a hierarchical pore structure by precisely controlling the polymerization kinetics. This unique structural design not only improves the electrochemically active area and proton conduction performance of the catalyst layer, but also significantly improves the transport efficiency of reactants and products. Combining with the experimental data, it can be seen that the catalyst layer prepared by the present invention has achieved significant improvements in various key performance indicators, providing a new technical path for improving the power density and durability of PEMFCs.

[0072] The technical solution of the present invention integrates multidisciplinary knowledge such as polymer chemistry, electrochemistry, and materials science, and realizes structural control at the nanoscale through in-situ polymerization technology. This synergistic mechanism of cross-field technology integration provides new ideas for the design and optimization of fuel cell catalyst layers, and is expected to promote the development of fuel cell technology towards higher performance and lower cost.

Claims

1. An ionomer for a proton exchange membrane fuel cell catalyst layer, characterized in that: The ionomer is directly generated on the catalyst surface by in-situ polymerization technology; the ionomer forms a network with a directional structure; the ion clusters in the ionomer network are arranged in a directional manner; the catalyst layer has multi-level pores with a gradient structure; wherein the in-situ polymerization technology includes using functionalized monomers for in-situ free radical polymerization, and forming the directional structure by controlling the rate and orientation of the polymerization reaction; the temperature of the in-situ free radical polymerization is 80-120°C, the pressure is 0.5-2MPa, and the reaction time is 2-6 hours.

2. The ionomer according to claim 1, characterized in that The orientation degree of the ion clusters is 75% to 95%, wherein the orientation degree is determined by small angle X-ray scattering.

3. The ionomer according to claim 1, characterized in that The multi-level pores of the gradient structure include micropores, mesopores and macropores; the pore size of the micropores is 2-10nm, the pore size of the mesopores is 10-50nm, and the pore size of the macropores is 50-200nm; wherein the pore size distribution is determined by nitrogen adsorption-desorption isotherms.

4. The ionomer according to claim 1, characterized in that The electrochemical active area of ​​the catalyst layer is 80-120 m 2 / g Pt, measured by cyclic voltammetry at 25°C and 100% relative humidity.

5. The ionomer according to claim 1, characterized in that The proton conductivity of the catalyst layer is 0.05-0.15 S / cm, and the measurement conditions are 25° C. and 100% relative humidity.

6. A method for preparing the ionomer according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: dispersing the catalyst in a solution containing a functionalized monomer, wherein the concentration of the functionalized monomer is 0.5-2.0 mol / L; Step 2: adding an initiator to the solution and performing an in-situ free radical polymerization reaction at a temperature of 80-120° C.; Step 3: Control the rate and orientation of the polymerization reaction by adjusting the monomer concentration, the amount of initiator and the reaction temperature to form an ionomer network with a directional structure; Step 4: Adjust the reaction conditions to form a multi-level channel with a gradient structure.

7. The method according to claim 6, characterized in that The functionalized monomer includes a vinyl monomer containing a sulfonic acid group.

8. The method according to claim 6, characterized in that The pressure of the in-situ free radical polymerization reaction is 0.5-2 MPa; the time of the in-situ free radical polymerization reaction is 2-6 hours; and the stirring speed of the reaction is 200-500 rpm.

9. The method according to claim 6, characterized in that In step three, the rate and orientation of the polymerization reaction are controlled by real-time monitoring of the degree of polymerization and dynamic adjustment of reaction parameters; when the degree of polymerization is lower than 5000, the monomer concentration is increased or the reaction temperature is increased; when the degree of polymerization is higher than 10000, the monomer concentration is reduced or the reaction temperature is lowered.

10. A proton exchange membrane fuel cell using the ionomer according to any one of claims 1 to 5, characterized in that: The invention comprises an anode, a cathode and a proton exchange membrane arranged between the anode and the cathode; the anode and the cathode both comprise a catalyst layer; the catalyst layer contains the ionomer; wherein the content of the ionomer is 15-30wt% of the total weight of the catalyst layer, and the thickness of the catalyst layer is 5-15μm; the current density of the proton exchange membrane fuel cell at an operating voltage of 0.6V is 1.2-1.8A / cm 2 , measured by constant potential test at 80°C and 100% relative humidity.

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