Catalytic layer for fuel cell and fuel cell

Abstract

The present invention discloses a method for preparing a catalytic layer for a fuel cell, comprising the following steps: preparing a pore-forming agent solution, wherein the pore-forming agent solution comprises a perfluorosulfonic acid resin, a first solvent, and a pore-forming agent; spraying the pore-forming agent solution onto both sides of a proton exchange membrane according to a network path to form a network of protruding pore-forming agent layers; coating the pore-forming agent layer with a catalyst slurry to form a catalyst layer; and first drying at 30-50°C and then drying at 100-150°C to obtain the catalytic layer for a fuel cell. The present invention also provides a catalytic layer for a fuel cell and a fuel cell. The preparation method provided by the present invention, by pre-spraying a layer of pore-forming agent slurry, not only solves the membrane swelling problem, but also enables the catalyst layer to form regular cracks, can alleviate the volume change problem during repeated charge and discharge, and improve the durability of the fuel cell membrane electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a catalyst layer for a fuel cell and a fuel cell. Background Art

[0002] The fuel cell stack is the heart of the fuel cell system, and the core component is the membrane electrode assembly (MEA). The MEA is responsible for the multiphase transport of substances within the fuel cell (liquid water, hydrogen, oxygen, protons, and electrons), converting the chemical energy of hydrogen into electrical energy through electrochemical reactions. The performance and cost of the MEA affect the performance, lifespan, and cost of proton exchange membrane fuel cells.

[0003] Slurry coating is the first step in preparing MEA. During the slurry coating process, a liquid slurry containing solvents, active substances, membrane solutions and other additives is directly coated onto the proton exchange membrane, and then dried to form a solid catalytic layer. However, these membrane electrodes exhibit poor performance due to the following reasons. 1) The electrodes prepared by the conventional slurry coating method are relatively dense. This structure makes it difficult for the reaction gas to reach the entire electrode to realize the utilization of all catalytic sites at a higher current density, especially hindering the transmission of oxygen, resulting in higher mass transfer polarization. 2) In the dense catalytic layer, the cathode flooding problem will prevent the supply of reaction gas, increase mass transfer polarization, and cause the voltage to drop rapidly at high current density. 3) During repeated charge and discharge, the surface of the catalyst layer will undergo significant volume expansion and contraction, resulting in uncontrolled cracking of the electrode, causing the catalyst layer to peel off, and significantly reducing the durability of the fuel cell. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a catalytic layer for a fuel cell. By pre-spraying a layer of pore-forming agent slurry, not only the membrane swelling problem is solved, but also regular cracks can be formed in the catalytic layer, which can alleviate the volume change problem during repeated charging and discharging and improve the durability of the fuel cell membrane electrode.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention provides a method for preparing a catalytic layer for a fuel cell, comprising the following steps:

[0007] preparing a pore-forming agent solution, wherein the pore-forming agent solution comprises a perfluorosulfonic acid resin, a first solvent and a pore-forming agent;

[0008] spraying the pore-forming agent solution onto both sides of the proton exchange membrane along a network path to form a network-shaped convex pore-forming agent layer;

[0009] coating a catalyst slurry on the pore-forming agent layer to form a catalyst layer; and

[0010] The catalyst layer for fuel cell is obtained by first drying at 30-50° C. and then drying at 100-150° C.

[0011] Furthermore, the first solvent is a mixed solvent formed by mixing water and low-boiling-point alcohols, and the low-boiling-point alcohols are one or more of n-propanol, isopropanol, ethanol, and methanol;

[0012] And / or, the pore-forming agent is one or more of ammonium bicarbonate, ammonium carbonate or ammonium oxalate.

[0013] Furthermore, the proton exchange membrane is a perfluorosulfonic acid proton exchange membrane with a thickness of 12-18 μm;

[0014] And / or, in the mesh path, the spacing between the transverse path and the longitudinal path is independently 5-10 mm.

[0015] Furthermore, the catalyst slurry includes perfluorosulfonic acid resin, a second solvent and a catalyst.

[0016] Furthermore, the catalyst is a carbon-supported Pt catalyst or a carbon-supported Pt alloy catalyst; the Pt content in the carbon-supported Pt catalyst or the carbon-supported Pt alloy catalyst is 40-80 wt%.

[0017] Furthermore, the second solvent is a mixed solvent formed by mixing water and low-boiling-point alcohols, and the low-boiling-point alcohols are one or more of n-propanol, isopropanol, ethanol, and methanol.

[0018] Furthermore, the solid content of the perfluorosulfonic acid resin is 5-20 wt%.

[0019] Furthermore, the solid content of the catalyst slurry is 5-20 wt%.

[0020] A second aspect of the present invention provides a catalyst layer for a fuel cell, comprising a proton exchange membrane and catalyst layers located on both sides of the proton exchange membrane, wherein the catalyst layer has a network of regular cracks.

[0021] A third aspect of the present invention provides a fuel cell comprising a catalytic layer prepared by the above method or the above catalytic layer.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Before coating the catalyst slurry on the proton exchange membrane, the present invention pre-sprays a layer of pore-forming agent, thereby reducing the area of ​​direct contact between the catalyst slurry and the proton exchange membrane and avoiding the problem of membrane shrinkage or swelling caused by direct coating of the catalyst slurry on the proton exchange membrane.

[0024] 2. The preparation method provided by the present invention can form a regular and orderly crack structure on the catalytic layer. The crack structure of the catalytic layer is loose, which enables oxygen to reach the interior of the catalytic layer smoothly and reduces mass transfer polarization.

[0025] 3. The preparation method provided by the present invention forms a regular and orderly crack structure on the catalytic layer. The existence of the cracks in the catalytic layer can allow the water generated inside the catalytic layer to be discharged smoothly, avoiding "flooding".

[0026] 4. The catalyst layer for fuel cells provided by the present invention solves the problem of volume expansion and contraction of the catalyst layer surface during repeated charging and discharging. The regular and orderly crack structure can alleviate the volume change problem and improve the durability of the fuel cell membrane electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1 is a comparison of polarization curves of MEA of Example 1 and Comparative Example 1;

[0028] Figure 2 The polarization curves of the MEAs of Example 1 and Comparative Example 1 are compared after 100 relative humidity (RH) cycles. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] As described in the background technology, current fuel cell membrane electrodes generally adopt a conventional slurry coating method, that is, directly coating the catalyst slurry on the proton exchange membrane. This method can easily cause membrane shrinkage or swelling problems. In addition, the electrodes prepared by this method are relatively dense, resulting in higher mass transfer polarization and the problem of cathode "flooding"; and during repeated charging and discharging, the surface of the catalyst layer will undergo significant volume expansion and contraction, causing uncontrolled cracking of the electrode, causing the catalyst layer to peel off, and significantly reducing the durability of the fuel cell. At present, some researchers have tried to introduce cracks in the catalyst layer, but irregular cracks will cause uneven mechanical stress on the surface of the catalyst layer, ultimately leading to membrane failure at the cracks, which directly affects the durability of the fuel cell.

[0032] In order to solve the above technical problems, the present invention provides a method for preparing a catalytic layer for a fuel cell, comprising the following steps:

[0033] preparing a pore-forming agent solution, wherein the pore-forming agent solution comprises a perfluorosulfonic acid resin, a first solvent and a pore-forming agent;

[0034] spraying the pore-forming agent solution onto both sides of the proton exchange membrane along a network path to form a network-shaped convex pore-forming agent layer;

[0035] coating a catalyst slurry on the pore-forming agent layer to form a catalyst layer; and

[0036] The catalyst layer for fuel cell is obtained by first drying at 30-50° C. and then drying at 100-150° C.

[0037] In the present invention, before applying the catalyst slurry to the proton exchange membrane, a layer of pore-forming agent solution is first applied to form a mesh-like, protruding pore-forming agent layer on the proton exchange membrane. This reduces the area of ​​direct contact between the catalyst slurry and the proton exchange membrane when the catalyst slurry is subsequently applied, thus avoiding the problem of membrane shrinkage or swelling caused by direct application of the catalyst slurry to the proton exchange membrane. In addition, in the present invention, the pore-forming agent solution is sprayed onto the proton exchange membrane through a mesh path to form a mesh-like, protruding pore-forming agent layer. During the subsequent drying process, the presence of surface tension causes a mesh-like, regular cracks to form on the surface of the catalyst layer. Compared to irregular cracks, this catalyst layer containing regular cracks can alleviate the problem of volume change during charging and discharging, thereby improving the durability of the fuel cell membrane electrode.

[0038] In the present invention, the pore-forming agent solution is prepared by dispersing and mixing a perfluorosulfonic acid resin, a first solvent, and a pore-forming agent. The first solvent is a mixed solvent formed by mixing water and a low-boiling-point alcohol, wherein the low-boiling-point alcohol includes, but is not limited to, one or more of n-propanol, isopropanol, ethanol, and methanol; and the pore-forming agent includes, but is not limited to, one or more of ammonium bicarbonate, ammonium carbonate, or ammonium oxalate.

[0039] In the present invention, the proton exchange membrane is preferably a perfluorosulfonic acid proton exchange membrane with a thickness of 12-18 μm. When spraying the pore-forming agent solution, the nozzle height is preferably set to 10-30 mm. Spraying is performed according to a predetermined reticular path, wherein the spacing between the transverse and longitudinal paths in the reticular path is independently 5-10 mm. For example, the spacing can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, etc. The spraying can be repeated multiple times until a reticular, raised pore-forming agent layer is formed on the proton exchange membrane.

[0040] In the present invention, the catalyst slurry includes a perfluorosulfonic acid resin, a second solvent, and a catalyst. The second solvent is a mixed solvent formed by mixing water and a low-boiling-point alcohol, wherein the low-boiling-point alcohol is one or more of n-propanol, isopropanol, ethanol, and methanol. The solid content of the perfluorosulfonic acid resin is 5-20wt%, for example, 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 15wt%, 16wt%, 18wt%, 20wt%, etc. The catalyst is a carbon-supported Pt catalyst or a carbon-supported Pt alloy catalyst; the Pt content of the carbon-supported Pt catalyst or the carbon-supported Pt alloy catalyst is 40-80wt%, for example, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, etc. Preferably, the solid content of the catalyst slurry is 5-20wt%, for example, it can be 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 15wt%, 16wt%, 18wt%, 20wt%, etc.

[0041] In the present invention, the catalyst slurry is prepared by the following steps: mixing a perfluorosulfonic acid resin and a second solvent, dispersing them uniformly to obtain a perfluorosulfonic acid resin solution; then adding a catalyst to the perfluorosulfonic acid resin solution, mixing them uniformly to obtain a catalyst slurry.

[0042] In the present invention, after the catalyst layer is coated, a gradient temperature drying system is performed. The temperature of the first drying step is 30-50°C, for example, 30°C, 32°C, 35°C, 36°C, 38°C, 40°C, 42°C, 44°C, 45°C, 46°C, 48°C, 50°C, etc. The temperature of the second drying step is 100-150°C, for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, etc. Specifically, the temperature is first raised to 30-50°C for drying. The purpose of this step is to dry the catalyst layer. During the drying process, due to the network-like protrusion structure of the pore-forming agent layer, the surface tension causes a network of regular cracks to form on the surface of the catalyst layer. The temperature is then raised to 100-150°C. The purpose of this drying step is to volatilize the pore-forming agent from the cracks, thereby removing the pore-forming agent.

[0043] On the basis of the above-mentioned catalytic layer, the present invention further provides a fuel cell comprising the above-mentioned catalytic layer.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0045] Example 1

[0046] This embodiment provides a method for preparing a membrane electrode, and the specific steps are as follows:

[0047] (1) Weigh 10 g of a 20% Nafion resin solution, 40 g of isopropyl alcohol, and 1 g of ammonium bicarbonate, mix them together, and disperse them ultrasonically at 35 kHz for 10 min while controlling the temperature below 20° C. to obtain a pore-forming agent solution.

[0048] (2) Place a 12 μm perfluorosulfonic acid proton exchange membrane on the adsorption platform of an ultrasonic spraying apparatus and flatten the proton exchange membrane. Set a mesh spray path, set the horizontal and vertical path spacing to 8 mm, and set the nozzle height to 15 mm. Repeat the mesh spray path on both sides of the proton exchange membrane to form a mesh-like raised pore-forming agent layer.

[0049] (3) Take 10g of 20% Nafion resin solution, add 60g of isopropanol, stir for 30min, rotate at 500rpm, and control the temperature at 15°C to obtain a pre-dispersed membrane solution. Weigh 10g of 70% Pt content carbon-supported platinum catalyst, add 60g of deionized water, and stir with a glass rod for 2min to obtain a catalyst solution. Mix the catalyst solution and the pre-dispersed membrane solution to form a slurry. Shear the slurry for 2h at a rotation speed of 12000rpm and control the temperature at 15°C to obtain a catalyst slurry.

[0050] (4) Use a sheet coater to evenly coat the catalyst slurry prepared in step (3) on both sides of the proton exchange membrane, and control the cathode platinum loading to 0.4 mg / cm 2 , the anode platinum loading is 0.1 mg / cm 2 The temperature of the heating platform of the sheet coating machine was first set to 30°C, dried for 2 minutes, then raised to 100°C and dried for 5 minutes.

[0051] (5) A gas diffusion layer is added to both sides of the proton membrane coated with the catalytic layer and packaged to obtain membrane electrode sample 1.

[0052] Comparative Example 1

[0053] This comparative example provides a method for preparing a membrane electrode, and the specific steps are as follows:

[0054] (1) Weigh 10 g of a 20% Nafion resin solution, 40 g of isopropyl alcohol, and 1 g of ammonium bicarbonate, mix them together, and disperse them ultrasonically at 35 kHz for 10 min while controlling the temperature below 20° C. to obtain a pore-forming agent solution.

[0055] (2) Place a 12 μm perfluorosulfonic acid proton exchange membrane on the adsorption platform of an ultrasonic spraying instrument to flatly adsorb the proton exchange membrane. Spray both sides of the proton exchange membrane to form a flat pore-forming agent layer.

[0056] (3) Take 10g of 20% Nafion resin solution, add 60g of isopropanol, stir for 30min, rotate at 500rpm, and control the temperature at 15°C to obtain a pre-dispersed membrane solution. Weigh 10g of 70% Pt content carbon-supported platinum catalyst, add 60g of deionized water, and stir with a glass rod for 2min to obtain a catalyst solution. Mix the catalyst solution and the pre-dispersed membrane solution to form a slurry. Shear the slurry for 2h at a rotation speed of 12000rpm and control the temperature at 15°C to obtain a catalyst slurry.

[0057] (4) Use a sheet coater to evenly coat the catalyst slurry prepared in step (3) on both sides of the proton exchange membrane, and control the cathode platinum loading to 0.4 mg / cm 2 , the anode platinum loading is 0.1 mg / cm 2 The temperature of the heating platform of the sheet coating machine was first set to 30°C, dried for 2 minutes, then raised to 100°C and dried for 5 minutes.

[0058] (5) A gas diffusion layer is added to both sides of the proton membrane coated with the catalytic layer and packaged to obtain membrane electrode sample 2.

[0059] Electrochemical performance test

[0060] See Figure 1 Compared to the membrane electrode 2 in Comparative Example 1, the membrane electrode 1 obtained in Example 1 of the present invention exhibited higher voltage at high current densities. The voltage difference became more pronounced with increasing current density. This is primarily due to the loose structure of the catalyst layer with regular cracks, which allows oxygen to reach the interior of the catalyst layer smoothly and reduces mass transfer polarization. The presence of regular cracks in the catalyst layer facilitates the drainage of liquid water at high current densities, preventing flooding.

[0061] See Figure 2 After 100 relative humidity (RH) cycles, the voltage difference between the membrane electrode 1 obtained in Example 1 of the present invention and the membrane electrode 2 in Comparative Example 1 became even greater, indicating that the membrane electrode 1 obtained in Example 1 has better durability. This is because the regular and orderly crack structure in the membrane electrode 1 obtained in Example 1 can alleviate the volume change caused by humidity changes, thereby improving the durability of the fuel cell membrane electrode.

[0062] In summary, the present invention provides a method for preparing a catalyst layer for fuel cells. By pre-spraying a layer of pore-forming agent slurry, the membrane swelling problem is resolved. Furthermore, the introduction of regular cracks significantly increases the overall porosity, reduces mass transfer polarization at high current densities, and avoids the "flooding" problem. Furthermore, the regular, ordered crack structure mitigates volume changes during repeated charge and discharge, improving the durability of the fuel cell membrane electrode.

[0063] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a catalyst layer for a fuel cell, characterized in that: The following steps are involved: preparing a pore-forming agent solution, wherein the pore-forming agent solution comprises a perfluorosulfonic acid resin, a first solvent and a pore-forming agent; spraying the pore-forming agent solution onto both sides of the proton exchange membrane along a network path to form a network-shaped convex pore-forming agent layer; coating a catalyst slurry on the pore-forming agent layer to form a catalyst layer; as well as The catalyst layer for fuel cell is obtained by first drying at 30-50° C. and then drying at 100-150° C. to remove the pore-forming agent; the catalyst layer has regular network cracks.

2. The method for preparing a catalyst layer for a fuel cell according to claim 1, characterized in that: The first solvent is a mixed solvent formed by mixing water and low-boiling-point alcohols, and the low-boiling-point alcohols are one or more of n-propanol, isopropanol, ethanol, and methanol; And / or, the pore-forming agent is one or more of ammonium bicarbonate, ammonium carbonate or ammonium oxalate.

3. The method for preparing a catalyst layer for a fuel cell according to claim 1, wherein: The proton exchange membrane is a perfluorosulfonic acid proton exchange membrane with a thickness of 12-18 μm; And / or, in the mesh path, the spacing between the transverse path and the longitudinal path is independently 5-10 mm.

4. The method for preparing a catalyst layer for a fuel cell according to claim 1, wherein: The catalyst slurry includes perfluorosulfonic acid resin, a second solvent and a catalyst.

5. The method for preparing a catalyst layer for a fuel cell according to claim 4, characterized in that: The catalyst is a carbon-supported Pt catalyst or a carbon-supported Pt alloy catalyst; the Pt content in the carbon-supported Pt catalyst or the carbon-supported Pt alloy catalyst is 40-80 wt%.

6. The method for preparing a catalyst layer for a fuel cell according to claim 4, characterized in that: The second solvent is a mixed solvent formed by mixing water and low-boiling-point alcohols, and the low-boiling-point alcohols are one or more of n-propanol, isopropanol, ethanol, and methanol.

7. The method for preparing a catalyst layer for a fuel cell according to claim 4, characterized in that: The solid content of the perfluorosulfonic acid resin is 5-20 wt%.

8. The method for preparing a catalyst layer for a fuel cell according to claim 1, characterized in that: The solid content of the catalyst slurry is 5-20 wt%.

9. A catalyst layer for a fuel cell, comprising a proton exchange membrane and catalyst layers located on both sides of the proton exchange membrane, characterized in that: The catalytic layer is a catalytic layer prepared by the method according to any one of claims 1 to 8, and has a network of regular cracks.

10. A fuel cell, characterized in that: The catalytic layer comprises a catalytic layer prepared by the method according to any one of claims 1 to 8 or a catalytic layer according to claim 9.

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