A fuel cell membrane electrode having a gradient structure and a method for preparing the same

Abstract

The present application relates to the technical field of fuel cells, and particularly relates to a fuel cell membrane electrode with a gradient structure and a preparation method thereof, which has an integrated gradient structure from a micro-porous layer of a gas diffusion layer to a catalytic layer of the membrane electrode, can effectively improve the utilization rate of the catalyst, improve the water vapor transmission process of the membrane electrode, realize integrated preparation of the catalytic layer and the micro-porous layer, and the catalyst concentration, the ionomer concentration, the hydrophobic agent concentration and the pore distribution all present a gradient structure along the direction away from the proton exchange membrane from the catalytic layer of the membrane electrode to the micro-porous layer of the gas diffusion layer, the gradient structure can effectively improve the utilization rate of the catalyst, improve the water vapor transmission process of the membrane electrode, the pore size distribution is more conducive to the gas-liquid two-phase mass transfer, and is conducive to the improvement of the performance and stability of the battery in a high current density interval.

Description

Technical Field

[0001] This invention relates to the technical field of combustion batteries, and in particular to a fuel cell membrane electrode with a gradient structure and its preparation method. Background Technology

[0002] The membrane electrode assembly (MEA) is the core component of a proton exchange membrane fuel cell (PEMFC). It serves as the site for multiphase mass transport and electrochemical reactions, involving three-phase interfacial reactions and complex mass and heat transfer processes, directly determining the performance, lifespan, and cost of the PEMFC. The MEA structure mainly consists of a gas diffusion layer, a catalyst layer, and a proton exchange membrane. The gas diffusion layer typically comprises carbon paper / carbon cloth and a microporous layer supported on it. An MEA consisting of the cathode gas diffusion layer, cathode catalyst layer, proton exchange membrane, anode catalyst layer, and anode gas diffusion layer is often referred to as a "five-in-one" MEA, while one that includes the microporous layer is called a "seven-in-one" MEA. As the most crucial component of a fuel cell, improving the performance and lifespan of the MEA and reducing its cost are of paramount importance, accelerating the large-scale commercialization of PEMFCs. Therefore, developing MEAs with simpler fabrication processes, more stable performance, and lower costs is a major research direction.

[0003] However, the pore structure formed by traditional PEMFC electrodes is disordered, has low porosity, and contains many closed pores, which is not conducive to the diffusion of gas and liquid water. In a proton exchange membrane fuel cell, hydrogen reacts at the anode to generate protons. These protons are then transferred through the proton exchange membrane and ionomers (such as Nafion) in the catalyst layer to the catalyst surface at the cathode, where they combine with oxygen to form water. Therefore, ionomers need to be doped into the catalyst layer. However, these ionomers hinder oxygen diffusion, resulting in a lower oxygen concentration on the catalyst surface and a slower reaction. Summary of the Invention

[0004] To address the technical deficiencies mentioned in the background section, one objective of this invention is to provide a fuel cell membrane electrode with a gradient structure. From the catalytic layer to the microporous layer of the gas diffusion layer, the membrane electrode has an integrated gradient structure, which can effectively improve the utilization rate of the catalyst, enhance the water-gas transport process of the membrane electrode, and improve the electrochemical performance and stability of the membrane electrode.

[0005] A fuel cell membrane electrode assembly with a gradient structure includes a proton exchange membrane. One side of the proton exchange membrane is provided with a cathode diffusion catalyst layer for cathode gas diffusion catalysis; the other side is provided with an anode diffusion catalyst layer for anode gas diffusion catalysis. The cathode diffusion catalyst layer includes a first cathode layer made of a first slurry, a second cathode layer made of a second slurry, and a third cathode layer made of a third slurry. The anode diffusion catalyst layer includes a first anode layer made of a first slurry, a second anode layer made of a second slurry, and a third anode layer made of a third slurry.

[0006] The first slurry, the second slurry, and the third slurry each include a catalyst, an ionomer, a pore-forming agent, and a hydrophobic agent. The concentrations of the ionomer and the catalyst decrease sequentially from the first slurry to the third slurry, while the concentrations of the pore-forming agent and the hydrophobic agent increase sequentially from the first slurry to the third slurry.

[0007] Preferably, the catalyst is one or any combination of Pt, Pt / C, PtRu, PtRu / C, PtFe / C, PtCo / C, PtNi / C, PtAu / C, PtPd / C, PtPb / C, and PtMn / C, and except for Pt used alone as a catalyst, the Pt loading in the other catalysts is 0wt%-70wt%.

[0008] Preferably, the ionomer is a long-chain perfluorosulfonic acid polymer, a short-chain perfluorosulfonic acid polymer, or any mixture of long-chain and short-chain perfluorosulfonic acid polymers, and the solution concentration of the ionomer used is 5wt%-20wt%.

[0009] Preferably, the pore-forming agent is ammonium bicarbonate or ammonium carbonate, or any combination of both.

[0010] Preferably, the hydrophobic agent is one or any combination of polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE).

[0011] Preferably, the first slurry, the second slurry, and the third slurry also contain organic solvents and ultrapure water. The organic solvents can be one or a mixture of several of ethanol, isopropanol, n-propanol, n-butanol, etc.

[0012] The first slurry contains 1 wt% to 50 wt% of catalyst, 1 wt% to 80 wt% of organic solvent, 10 wt% to 90 wt% of ultrapure water, and 0.8 to 2 times the catalyst content.

[0013] The second slurry contains 1 wt% to 50 wt% catalyst, 1 wt% to 80 wt% organic solvent, 10 wt% to 90 wt% ultrapure water, 0.8 to 2 times the catalyst content, 1 wt% to 30 wt% hydrophobic agent, and 0.1 wt% to 2 wt% pore-forming agent. The catalyst and ionomer contents in the second slurry are both lower than those in the first slurry.

[0014] The third slurry contains 1wt% to 50wt% catalyst, 1wt% to 80wt% organic solvent, 10wt% to 90wt% ultrapure water, 1wt% to 30wt% hydrophobic agent, and 0.1wt% to 2wt% pore-forming agent. The hydrophobic agent and pore-forming agent contents in the third slurry are higher than those in the second slurry.

[0015] Preferably, the target Pt loading in the cathode diffusion catalyst layer and the anodic diffusion catalyst layer is 0.01 mg / cm³. 2 ~0.5mg / cm 2 Carbon loading is 1 mg / cm³ 2 ~6mg / cm 2 .

[0016] A second objective of this invention is to provide a method for preparing a fuel cell membrane electrode assembly (MEA) with a gradient structure. This method achieves the integrated preparation of the catalyst layer and the microporous layer. Furthermore, from the catalyst layer to the microporous layer of the gas diffusion layer, the catalyst concentration, ionomer concentration, hydrophobic agent concentration, and pore distribution all exhibit a gradient structure away from the proton exchange membrane. This gradient structure effectively improves catalyst utilization, enhances the water-gas transport process of the MEA, and its pore size distribution is more conducive to gas-liquid two-phase mass transfer, thus improving the performance and stability of the battery in the high current density range. In addition, this preparation method is simple and easy to implement, facilitating large-scale production.

[0017] A method for fabricating a fuel cell membrane electrode with a gradient structure, applicable to the aforementioned fuel cell membrane electrode with a gradient structure, includes the following steps:

[0018] S1. Pre-preparation of the first slurry: Weigh the catalyst, ultrapure water and organic solvent according to a certain metering ratio, then add them to a glass container in sequence, disperse them evenly, add a certain amount of ionomer solution, disperse them evenly again, and set aside for use;

[0019] S2. Pre-preparation of the second slurry: Weigh the catalyst, ultrapure water and organic solvent according to a certain measurement ratio, and then add them to a glass container in sequence. After uniform dispersion, add a certain amount of ionomer solution, hydrophobic agent and pore-forming agent in sequence, and then disperse them evenly again. Set aside for use.

[0020] S3. Pre-preparation of the third slurry: Weigh the catalyst, ultrapure water and organic solvent according to a certain measurement ratio, and then add them to a glass container in sequence. After uniform dispersion, add a certain amount of hydrophobic agent and pore-forming agent in sequence, and then disperse them evenly again. Set aside for use.

[0021] S4. Preparation of integrated gradient structure electrode layer: The first slurry, the second slurry and the third slurry are sequentially coated onto both sides of the proton exchange membrane to achieve the target Pt loading and carbon loading. Then, the pore-forming agent is removed by hot pressing to form a cathode diffusion catalyst layer and an anode diffusion catalyst layer with a gradient structure, thus obtaining the desired CCM.

[0022] S5. Carbon paper without microporous layers is fixed to the surface of the cathode diffusion catalyst layer and anode diffusion catalyst layer of the CCM obtained in S4 by hot pressing, to obtain a fuel cell membrane electrode with a gradient structure.

[0023] Preferably, the dispersion method used for the first slurry, the second slurry, and the third slurry can be one or a mixture of several of shear dispersion, homogeneous dispersion, ball milling dispersion, and sand milling dispersion.

[0024] The method used to prepare the cathode diffusion catalyst layer and the anode diffusion catalyst layer can be any one of spraying, screen printing, direct coating, transfer printing and slot coating.

[0025] Preferably, the substrate material used to prepare the cathode diffusion catalyst layer and the anode diffusion catalyst layer by means of transfer printing is any one of polytetrafluoroethylene (PTFE) film, polyester (PET) film, polyimide high temperature film, Nafion film, perfluorosulfonic acid composite film, carbon paper, and carbon cloth.

[0026] In summary, the present invention has the following beneficial effects:

[0027] A fuel cell membrane electrode assembly (MEA) with a gradient structure and its fabrication method are disclosed. Both the cathode and anode are fabricated using the same method and exhibit similar gradient pore structures. In the gradient pore structure proposed in this invention, the microporous layer from the catalyst layer to the gas diffusion layer of the MEA has an integrated structure. Furthermore, the Pt / C catalyst concentration, Nafion ionomer concentration, PTFE concentration, and pore distribution all exhibit a gradient structure away from the proton exchange membrane. According to the proton transport law, the ionomer in the catalyst layer needs to transfer more protons closer to the proton exchange membrane, while the catalyst layer closer to the carbon paper side does not require as many. Proton conductivity; similarly, the catalyst layer near the proton exchange membrane needs a relatively small porosity to ensure a sufficiently low contact resistance between the catalyst layer and the proton exchange membrane, while the side near the carbon paper needs sufficient porosity to ensure the entry of reactant gases and the exit of products; simultaneously, since water is produced by the electrochemical reaction on the cathode side, the catalyst layer near the carbon paper should have a good hydrophobic porous structure to facilitate water exit. Based on this principle, the concentration of ionomers, porosity, and the concentration of the hydrophobic medium PTFE at different locations in the catalyst layer can be optimized to ensure the proton conductivity of the catalyst layer while improving the transport capacity of oxygen and water, thereby increasing the reaction rate. Specifically, this manifests as follows:

[0028] 1. The concentrations of Pt / C catalyst and Nafion ionomer gradually decrease with the direction away from the proton exchange membrane. The gradient structure of Pt / C catalyst and Nafion ionomer concentrations helps to improve the utilization rate of Pt / C catalyst, thereby improving the electrochemical performance of membrane electrode.

[0029] 2. The PTFE concentration gradually increases with the direction away from the proton exchange membrane. The gradient distribution of PTFE concentration is conducive to the formation of continuous and orderly water transport channels, which improves the water management capability of the membrane electrode and thus improves the electrochemical performance of the membrane electrode under high current density.

[0030] 3. The pore distribution gradually increases with distance from the proton exchange membrane. This gradient pore distribution facilitates the formation of continuous gas and water transport channels, enhancing the mass transfer capacity of the membrane electrode assembly (MEA) and reducing mass transfer impedance. The gradient-structured fuel cell MEA proposed in this paper effectively improves catalyst utilization and enhances the gas-water transport process. Its pore size distribution is more conducive to gas-liquid two-phase mass transfer, contributing to improved battery performance and stability in high current density ranges.

[0031] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below. Attached Figure Description

[0032] Figure 1 This is a polarization curve diagram of the present invention. Detailed Implementation

[0033] To make the content of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0034] It should be noted that material C in the following embodiments can be one or any combination of carbon black, acetylene black, graphite, carbon fiber, carbon nanotubes, and graphene.

[0035] Example 1

[0036] (1) Pre-preparation of the first slurry: A mixed solution was prepared according to the mass ratio of catalyst:water:isopropanol = 1:70:30. First, 1g of HISPEC9100 catalyst was weighed, 70g of ultrapure water was added, and after shaking, 30g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 6.9g of D520-Nafion ionomer solution was added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the first slurry. The D520-Nafion ionomer solution was a 5% Nafion solution.

[0037] (2) Pre-preparation of the second slurry: A mixed solution was prepared according to the mass ratio of catalyst: carbon powder: water: isopropanol = 0.5:0.5:35:15. First, 0.5g of HISPEC9100 catalyst and 0.5g of VC-72R superconducting carbon powder were weighed, 35g of ultrapure water was added, and after shaking, 15g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 3.45g of D520-Nafion ionomer solution and 0.05g of 20% PTFE emulsion were added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the second slurry.

[0038] (3) Pre-preparation of the third slurry: A mixed solution was prepared according to the mass ratio of carbon powder: water: isopropanol = 1:80:20. First, 1g of VC-72R superconducting carbon powder was weighed, 80g of ultrapure water was added, and after shaking, 20g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Next, 0.2g of 20% PTFE emulsion was added to the above dispersion, and then sheared and dispersed for another 20min to obtain the third slurry.

[0039] (4) Preparation of integrated gradient structure electrode layer: The first slurry is first sprayed onto one side of the proton exchange membrane using ultrasonic spraying. The drying temperature is 80℃, and the coating is continued until the target Pt loading of 0.2 mg / cm³ is achieved. 2 Replace with a second slurry and spray, drying at 80℃, until the target total Pt loading of 0.3 mg / cm³ is achieved.2 Finally, replace with the third slurry for spraying, drying at 80℃, and continue spraying until the target carbon loading of 3 mg / cm³ is achieved. 2 Thus, a gradient-structured cathode diffusion catalyst layer was obtained; subsequently, an anodic diffusion catalyst layer was sprayed onto the other side of the proton exchange membrane, first using a first slurry, drying at 80℃, until the target Pt loading of 0.07 mg / cm³ was achieved. 2 Replace with a second slurry and spray, drying at 80℃, until the target total Pt loading of 0.1 mg / cm³ is achieved. 2 Finally, replace with the third slurry for spraying, drying at 80℃, and continue spraying until the target carbon loading of 3 mg / cm³ is achieved. 2 This yields a gradient-structured anodic diffusion catalyst layer. Consequently, a CCM with gradient-structured cathodic diffusion catalyst layer and anodic diffusion catalyst layer is obtained.

[0040] (5) SGL-29AA non-porous carbon paper is fixed to the surface of the cathode diffusion catalyst layer and anode diffusion catalyst layer of the CCM obtained in step (4) by hot pressing to obtain a fuel cell membrane electrode with a gradient structure. Example 1 is obtained.

[0041] Example 2

[0042] (1) Pre-preparation of the first slurry: A mixed solution was prepared according to the mass ratio of catalyst:water:isopropanol = 1:10:3. First, 1g of HISPEC9100 catalyst was weighed, 10g of ultrapure water was added, and after shaking, 3g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 6.9g of D520-Nafion ionomer solution was added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the first slurry. The D520-Nafion ionomer solution was a 5% Nafion solution.

[0043] (2) Pre-preparation of the second slurry: A mixed solution was prepared according to the mass ratio of catalyst: toner: water: isopropanol = 0.5:0.5:10:5. First, 0.5g of HISPEC9100 catalyst and 0.5g of Denka-DB250 toner were weighed, 10g of ultrapure water was added, and the mixture was shaken well. Then, 5g of isopropanol was added, and the mixture was sheared and dispersed for 20min using a shearing machine. Then, 3.45g of D520-Nafion ionomer solution and 0.02g of 20% PTFE emulsion were added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the second slurry.

[0044] (3) Pre-preparation of the third slurry: A mixed solution was prepared according to the mass ratio of toner:water:isopropanol = 1:13:8. First, 1g of Denka-DB250 toner was weighed, 13g of ultrapure water was added, and after shaking, 8g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Next, 0.2g of 20% PTFE emulsion and 0.1g of ammonium bicarbonate were added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the third slurry.

[0045] (4) Fabrication of integrated gradient structure electrode layer: The third paste was first screen-printed onto the PTFE substrate using a screen printing method, and then dried at 60°C. After drying, the target Pt loading of 0.3 mg / cm³ was achieved. 2 The second paste was used for screen printing, and dried at 60°C. The target total Pt loading was 0.4 mg / cm³. 2 Finally, replace the first ink paste for screen printing, dry at 60℃, and apply a final coat to achieve the target carbon loading of 4 mg / cm³. 2 Thus, a gradient-structured cathode diffusion catalyst layer was obtained; subsequently, a third paste was screen-printed onto a PTFE substrate, and dried at 60°C, achieving a target Pt loading of 0.05 mg / cm³. 2 The second paste was used for screen printing, and dried at 60°C. The target total Pt loading was 0.1 mg / cm³. 2 Finally, replace the first ink paste for screen printing, dry at 60℃, and apply a final coat to achieve the target carbon loading of 4 mg / cm³. 2 Thus, a gradient-structured anodic diffusion catalyst layer is obtained. Then, the anodic diffusion catalyst layer and the cathodic diffusion catalyst layer are transferred to both sides of the proton exchange membrane at 150°C by a transfer method, thereby obtaining a CCM with a gradient-structured cathodic diffusion catalyst layer and an anodic diffusion catalyst layer.

[0046] (5) SGL-29AA non-porous carbon paper is fixed to the surface of the cathode diffusion catalyst layer and anode diffusion catalyst layer of the CCM obtained in step (4) by hot pressing to obtain a fuel cell membrane electrode with a gradient structure. Example 2 is obtained.

[0047] Example 3

[0048] (1) Pre-preparation of the first slurry: A mixed solution was prepared according to the mass ratio of catalyst:water:isopropanol = 1:12:1. First, 1g of HISPEC9100 catalyst was weighed, 12g of ultrapure water was added, and after shaking, 1g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 1.68g of D2020-Nafion ionomer solution was added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the first slurry. The D2020-Nafion ionomer solution was a Nafion solution with a mass concentration of 20%.

[0049] (2) Pre-preparation of the second slurry: A mixed solution was prepared according to the mass ratio of catalyst: carbon powder: water: isopropanol = 0.5:0.5:10:5. First, 0.5g of HISPEC9100 catalyst and 0.5g of carbon fiber were weighed, 10g of ultrapure water was added, and after shaking, 5g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 0.84g of D2020-Nafion ionomer solution, 0.02g of 20% PTFE emulsion and 0.05g of ammonium bicarbonate were added to the above dispersion. The mixture was then sheared and dispersed for another 20min to obtain the second slurry.

[0050] (3) Pre-preparation of the third slurry: A mixed solution was prepared according to the mass ratio of carbon powder: water: isopropanol = 1:13:8. First, 1g of carbon fiber was weighed, 13g of ultrapure water was added, and after shaking, 8g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 0.2g of 20% PTFE emulsion and 0.1g of ammonium bicarbonate were added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the third slurry.

[0051] (4) Preparation of integrated gradient structure electrode layer: The third slurry was first applied to the PTFE substrate by a blade coating method and dried at 60°C. After drying, the target Pt loading of 0.3 mg / cm³ was achieved. 2 The second slurry was applied and dried at 60°C. The target total Pt loading was 0.4 mg / cm³. 2 Finally, replace the first slurry and apply it, drying at 60°C. The final coat should be applied until the target carbon loading of 4 mg / cm³ is achieved. 2 Thus, a gradient-structured cathode diffusion catalyst layer 1 was obtained; subsequently, a third slurry was applied to the PTFE substrate by coating, and then dried at 60°C to achieve the target Pt loading of 0.05 mg / cm³. 2 The second slurry was applied and dried at 60°C. The target total Pt loading was 0.1 mg / cm³. 2 Finally, replace the first slurry and apply it, drying at 60°C. The final coat should be applied until the target carbon loading of 4 mg / cm³ is achieved.2 Thus, a gradient-structured anodic diffusion catalyst layer is obtained. Then, the anodic diffusion catalyst layer and the cathodic diffusion catalyst layer are transferred to both sides of the proton exchange membrane at 150°C by a transfer method, thereby obtaining a CCM with a gradient-structured cathodic diffusion catalyst layer and an anodic diffusion catalyst layer.

[0052] (5) SGL-29AA non-porous carbon paper is fixed to the surface of the cathode diffusion catalyst layer and anode diffusion catalyst layer of the CCM obtained in step (4) by hot pressing to obtain a fuel cell membrane electrode with a gradient structure. Example 3 is obtained.

[0053] Example 4

[0054] (1) Pre-preparation of the first slurry: A mixed solution was prepared according to the mass ratio of catalyst:water:ethanol = 1:12:1. First, 1g of PtRu / C catalyst was weighed, 12g of ultrapure water was added, and after shaking, 1g of ethanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 1.68g of D2020-Nafion ionomer solution was added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the first slurry. The D2020-Nafion ionomer solution was a Nafion solution with a mass concentration of 20%.

[0055] (2) Pre-preparation of the second slurry: A mixed solution was prepared according to the mass ratio of catalyst: carbon powder: water: ethanol = 0.5:0.5:10:5. First, 0.5g of PtRu / C catalyst and 0.5g of carbon powder (graphene and VC-72R carbon powder were mixed in a mass ratio of 1:1) were weighed, 10g of ultrapure water was added, and after shaking, 5g of isopropanol was added. Then, the mixture was sheared and dispersed for 20min. Then, 0.84g of D2020-Nafion ionomer solution, 0.02g of 20% PTFE emulsion and 0.05g of ammonium bicarbonate were added to the above dispersion. The mixture was then sheared and dispersed for another 20min to obtain the second slurry.

[0056] (3) Pre-preparation of the third slurry: A mixed solution was prepared according to the mass ratio of toner:water:n-propanol = 1:15:4. First, 1g of toner (graphene and VC-72R toner mixed in a mass ratio of 1:1) was weighed, 15g of ultrapure water was added, and after shaking well, 4g of isopropanol was added. Then, the mixture was sheared and dispersed for 30min using a shearing machine. Then, 0.2g of 20% PTFE emulsion and 0.1g of ammonium bicarbonate were added to the above dispersion, and the mixture was sheared and dispersed for another 20min to obtain the third slurry.

[0057] (4) Preparation of integrated gradient structure electrode layer: The third slurry was first applied to the PTFE substrate by a blade coating method and dried at 60°C. After drying, the target Pt loading was achieved to be 0.1 mg / cm³. 2The second slurry was applied and dried at 60°C. The target total Pt loading was 0.2 mg / cm³. 2 Finally, replace the first slurry and apply it, drying at 60°C. The final coat should be applied until the target carbon loading of 3 mg / cm³ is achieved. 2 Thus, a gradient-structured cathode diffusion catalyst layer was obtained; subsequently, a third slurry was applied to the PTFE substrate by coating, and then dried at 60°C, achieving a target Pt loading of 0.01 mg / cm³. 2 The second slurry was then applied and dried at 60°C. The target total Pt loading was 0.05 mg / cm³. 2 Finally, replace the first slurry and apply it, drying at 60°C. The final coat should be applied until the target carbon loading of 3 mg / cm³ is achieved. 2 Thus, a gradient-structured anodic diffusion catalyst layer is obtained. Then, the anodic diffusion catalyst layer and the cathodic diffusion catalyst layer are transferred to both sides of the proton exchange membrane at 150°C by a transfer method, thereby obtaining a CCM with a gradient-structured cathodic diffusion catalyst layer and an anodic diffusion catalyst layer.

[0058] (5) SGL-29AA non-porous carbon paper is fixed to the surface of the cathode diffusion catalyst layer and anode diffusion catalyst layer of the CCM obtained in step (4) by hot pressing to obtain a fuel cell membrane electrode with a gradient structure. Example 4 is obtained.

[0059] Comparison Example 1

[0060] (1) Preparation of catalyst slurry: A mixed solution was prepared according to the mass ratio of catalyst:water:ethanol = 1:12:1. First, 1g of Pt / C catalyst was weighed, 12g of ultrapure water was added, and after shaking, 1g of ethanol was added. Then, the mixture was sheared and dispersed for 20min using a shearing machine. Then, 1.68g of D2020-Nafion ionomer solution was added to the above dispersion, and then sheared and dispersed for another 20min.

[0061] (2) Membrane electrode preparation: The catalyst slurry was first coated onto the PTFE substrate by a blade coating method and then dried at 60°C. After drying, the target Pt loading of 0.1 mg / cm³ was achieved. 2 Thus, the anode catalyst layer was obtained; subsequently, the catalyst slurry was coated onto the PTFE substrate by a blade coating method and dried at 60°C. After drying, the target Pt loading of 0.4 mg / cm³ was achieved. 2 Thus, the cathode catalyst layer was obtained. Then, the anode catalyst layer and the cathode catalyst layer were transferred to both sides of the proton exchange membrane at 150°C by a transfer method, thereby obtaining the comparative example CCM.

[0062] (3) The SGL-29BC gas diffusion layer is fixed to the surface of the cathode catalyst layer and anode catalyst layer of the CCM obtained in step (2) by hot pressing, to obtain Comparative Example 1.

[0063] Performance comparison of contrasting examples:

[0064] Membrane electrode testing methods:

[0065] The single cells were assembled and activated according to GB / T20042.5-2009 standard, and the corresponding polarization curve tests were performed. The test conditions were as follows: the cell temperature was 80℃, the anode was hydrogen gas with a stoichiometric ratio of 1.5, the cathode was air gas with a stoichiometric ratio of 2.5, the back pressure was 150kPa, and the relative humidity was 100%RH. After the cell was activated and its steady-state performance was stable, the load was gradually reduced to open circuit, and the polarization curve tests were performed. After each load current was applied, the voltage was recorded after the voltage stabilized.

[0066] Conclusion: As the current density increases, the voltages of Examples 1 to 3 are all greater than those of Comparative Example 1, and the power densities of Examples 1 to 3 are all greater than those of Comparative Example 1. In other words, at the same voltage, the technical solution adopted in this invention can achieve higher current and power densities, thereby enabling the fuel cell to have a greater output power. The voltage and power density of Example 4 are lower than those of Comparative Example 1, mainly because an alloy catalyst is used, and it is an ultra-low Pt loading membrane electrode, but it also exhibits superior electrochemical performance at 2.0 A / cm². 2 The power density is greater than 1.15 W / cm². 2 Therefore, the technical solution in this case is also applicable to the preparation of other alloy catalyst membrane electrodes and ultra-low platinum membrane electrodes.

[0067] The embodiments described above are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and modifications made by those skilled in the art based on the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for fabricating a fuel cell membrane electrode with a gradient structure, comprising a proton exchange membrane, characterized in that: The proton exchange membrane has a cathode diffusion catalytic layer for cathode gas diffusion catalysis on one side and an anode diffusion catalytic layer for anode gas diffusion catalysis on the other side. The cathode diffusion catalytic layer includes a first cathode layer made of a first slurry, a second cathode layer made of a second slurry, and a third cathode layer made of a third slurry. The anode diffusion catalytic layer includes a first anode layer made of a first slurry, a second anode layer made of a second slurry, and a third anode layer made of a third slurry. The first slurry, the second slurry, and the third slurry all contain a catalyst; the first slurry contains a catalyst and an ionomer, but does not contain a hydrophobic agent or a pore-forming agent; the second slurry contains a catalyst, an ionomer, a hydrophobic agent, and a pore-forming agent; the third slurry contains a catalyst, a hydrophobic agent, and a pore-forming agent, but does not contain an ionomer; in the first slurry, the concentration of the ionomer and the catalyst decreases sequentially from the first slurry to the third slurry, while the concentration of the pore-forming agent and the hydrophobic agent increases sequentially from the first slurry to the third slurry, wherein the hydrophobic agent is a polytetrafluoroethylene emulsion; The preparation method includes the following specific steps. S1. Pre-preparation of the first slurry: Weigh the catalyst, ultrapure water and organic solvent according to a certain metering ratio, then add them to a glass container in sequence, disperse them evenly, add a certain amount of ionomer solution, disperse them evenly again, and set aside for use; S2. Pre-preparation of the second slurry: Weigh the catalyst, ultrapure water and organic solvent according to a certain measurement ratio, and then add them to a glass container in sequence. After uniform dispersion, add a certain amount of ionomer solution, hydrophobic agent and pore-forming agent in sequence, and then disperse them evenly again. Set aside for use. S3. Pre-preparation of the third slurry: Weigh the catalyst, ultrapure water and organic solvent according to a certain measurement ratio, and then add them to a glass container in sequence. After uniform dispersion, add a certain amount of hydrophobic agent and pore-forming agent in sequence, and then disperse them evenly again. Set aside for use. S4. Preparation of integrated gradient structure electrode layer: The first slurry, the second slurry and the third slurry are sequentially coated onto both sides of the proton exchange membrane to achieve the target Pt loading and carbon loading. Then, the pore-forming agent is removed by hot pressing to form a cathode diffusion catalyst layer and an anode diffusion catalyst layer with a gradient structure, thus obtaining the desired CCM. S5. Carbon paper without microporous layers is fixed to the surface of the cathode diffusion catalyst layer and anode diffusion catalyst layer of the CCM obtained in S4 by hot pressing, to obtain a fuel cell membrane electrode with a gradient structure.

2. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 1, characterized in that: The dispersion method used for the first slurry, the second slurry, and the third slurry is one or a mixture of several of the following: shear dispersion, homogeneous dispersion, ball milling dispersion, and sand milling dispersion. The cathode diffusion catalyst layer and the anode diffusion catalyst layer are prepared by any one of the following methods: spraying, screen printing, direct coating, transfer printing, and slot coating.

3. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 2, characterized in that: The substrate material used to prepare the cathode diffusion catalyst layer and the anode diffusion catalyst layer by the transfer method is any one of polytetrafluoroethylene (PTFE) film, polyester (PET) film, polyimide high temperature film, Nafion film, perfluorosulfonic acid composite film, carbon paper, and carbon cloth.

4. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 1, characterized in that: The catalyst is one or any combination of Pt, Pt / C, PtRu, PtRu / C, PtFe / C, PtCo / C, PtNi / C, PtAu / C, PtPd / C, PtPb / C, and PtMn / C. Except for Pt alone, the Pt loading in the other catalysts does not exceed 70 wt%.

5. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 1, characterized in that: The ionomer is a long-chain perfluorosulfonic acid polymer, a short-chain perfluorosulfonic acid polymer, or any mixture of long-chain and short-chain perfluorosulfonic acid polymers, and the concentration of the solution of the ionomer used is 5wt%-20wt%.

6. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 1, characterized in that: The pore-forming agent is ammonium bicarbonate or ammonium carbonate, or any combination of both.

7. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 1, characterized in that: The first slurry, the second slurry, and the third slurry also contain organic solvents and ultrapure water. The organic solvents are one or a mixture of several of ethanol, isopropanol, n-propanol, and n-butanol. The first slurry contains 1wt% to 50wt% catalyst, 1wt% to 80wt% organic solvent, 10wt% to 90wt% ultrapure water, and 0.8 to 2 times the catalyst content. The second slurry contains 1wt% to 50wt% catalyst, 1wt% to 80wt% organic solvent, 10wt% to 90wt% ultrapure water, 0.8 to 2 times the catalyst content, 1wt% to 30wt% hydrophobic agent, and 0.1wt% to 2wt% pore-forming agent. The catalyst and ionomer contents in the second slurry are lower than those in the first slurry. The third slurry contains a catalyst content of 1wt%~50wt%, an organic solvent content of 1wt%~80wt%, an ultrapure water content of 10wt%~90wt%, a hydrophobic agent content of 1wt%~30wt%, and a pore-forming agent content of 0.1wt%~2wt%. The hydrophobic agent and pore-forming agent content in the third slurry are higher than those in the second slurry.

8. The method for preparing a fuel cell membrane electrode with a gradient structure according to claim 1, characterized in that: The target Pt loading in the cathode diffusion catalyst layer and the anodic diffusion catalyst layer is 0.01 mg / cm³. 2 ~0.5mg / cm 2 Carbon loading is 1 mg / cm³ 2 ~6mg / cm 2 .

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