A method for preparing a membrane electrode

Abstract

The present invention discloses a method for preparing a membrane electrode. First, a catalyst slurry is coated or sprayed on a substrate and dried to form a film, thereby obtaining a substrate covered with a catalyst membrane. The substrate covered with the catalyst membrane is then placed in a substrate stripping agent to separate the catalyst membrane from the substrate, thereby obtaining a catalyst membrane. The catalyst membrane is then placed in water, and another electrolyte membrane is taken. The electrolyte membrane is placed in the water below the catalyst membrane and the catalyst membrane is lifted up from the bottom to the top. The catalyst membrane adheres to the electrolyte membrane under the surface tension of the water. Finally, a layer of catalyst membrane is attached to the other side of the electrolyte membrane by lifting it up from the bottom of the water, thereby obtaining a membrane electrode that can be used for fuel cell assembly. The present invention provides a separate catalyst layer preparation method and a gentle assembly method. This allows the catalyst layer and electrolyte membrane of the present invention to be assembled and peeled off as needed, thereby improving assembly flexibility.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, relates to an accessory of a fuel cell, and specifically relates to a method for preparing a membrane electrode using a new technology. Background Art

[0002] Energy and environmental issues are major challenges facing human society today. The widespread use of fossil fuels has not only caused serious greenhouse effects and environmental pollution problems, but its limited reserves have also led to energy crises and regional conflicts. In recent years, "energy / matter conversion" based on electrochemical reactions has received widespread attention, including fuel cells, water electrolysis, carbon dioxide electrolysis, etc., which are expected to establish a new social energy structure system based on renewable energy, thereby getting rid of dependence on fossil energy. In order to improve the energy density and space utilization of the above-mentioned devices, polymer electrolytes are widely used, such as Nafion that can conduct cations and QAPPT (quaternary ammonium polyaryl piperidine copolymer) that can conduct anions. Usually, the core of this type of device adopts a symmetrical "five-in-one" structure, called a membrane electrode, such as Figure 1 As shown, the electrolyte membrane is flanked by catalytic layers for electrochemical reactions, while gaseous reactants or products are conducted through the outer gas diffusion layer. The catalytic layer is very thin, typically only tens of microns thick, or even just a few microns at low loadings, and has poor mechanical strength. Therefore, the catalytic layer must be coated onto the membrane or gas diffusion layer, and sometimes hot pressing is required to form an integrated membrane electrode structure. This can lead to several problems: First, the catalytic layer is manufactured using a dry process, but actual operating conditions are wet with water. In this case, the membrane swells more than the catalytic layer, causing mechanical damage to the catalytic layer due to traction on the membrane. Second, when studying the membrane electrode, such as the cause of performance degradation after stability testing, it is impossible to analyze each component individually. Third, if a component develops a problem, such as performance degradation caused by prolonged operation, the entire membrane electrode must be replaced, rather than just the problematic component, resulting in a waste of resources.

[0003] Prior art CN113745538A is a method for manufacturing a fuel cell membrane electrode, which includes: coating a catalyst slurry on a transfer substrate and drying it, forming a catalytic layer on the surface of the transfer substrate, coating a swelling agent on the dried catalytic layer, and tightly fitting the surface of the catalytic layer to the proton exchange membrane. After hot pressing, the transfer substrate is peeled off to form a membrane electrode. The present invention does not require adding a special coating layer to adjust the adhesion between the transfer substrate, the catalytic layer, and the PEM. The present invention coats the catalytic layer with a swelling agent before transfer. During transfer, the swelling agent penetrates into the molecular chains of the proton exchange membrane of the catalytic layer, weakening the secondary bonds between the resin molecules and increasing the mobility of the molecular chains, thereby allowing the PEM to partially fuse with the ionomer in the catalytic layer, thereby increasing the adhesion between the catalytic layer and the PEM. The increase in adhesion can lower the threshold of the transfer conditions. However, this technology requires clamping and transferring the catalyst layer. However, the catalyst layer is very thin, making it difficult to perform mechanical operations such as clamping and transferring. In addition, this technology uses a transfer method to peel off the substrate, which has extremely high requirements for the substrate material. Therefore, the yield rate is not high and the production cost is greatly reduced. Therefore, a new technology is needed to be able to transfer the catalyst layer and the proton exchange membrane with high quality. Summary of the Invention

[0004] The present invention aims to provide a novel membrane electrode fabrication method that allows for the separation of the membrane, catalyst layer, and gas diffusion layer. This method avoids structural damage to the catalyst layer caused by inconsistent swelling between the membrane and catalyst layer, and also facilitates separate study and replacement of the various components.

[0005] The present invention first applies a catalyst slurry to a substrate, then places it in a solution capable of etching the substrate to remove the catalytic layer. This catalytic layer can remain stable in aqueous solution without damage. The membrane is then placed in water, and after it has fully swelled, the catalytic layer is "lifted" from below. At this point, due to the surface tension of water, the catalytic layer adheres to the membrane to form a membrane electrode, allowing device assembly to proceed. If the catalytic layer swells significantly in a certain solvent, the substrate coated with the catalytic layer can also be placed directly in the solvent, and the dimensional changes of the catalytic layer can be used to remove it from the substrate.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A method for preparing a membrane electrode comprises the following steps:

[0008] Step 1: coating the catalyst slurry on the substrate and drying it to form a film to obtain a substrate covered with a catalyst film;

[0009] Step 2: placing the substrate covered with the catalyst film in a substrate stripping agent to separate the catalyst film from the substrate to obtain the catalyst film;

[0010] Step 3: Place the catalyst membrane in water, take another electrolyte membrane, place the electrolyte membrane in the water below the catalyst membrane, and lift the catalyst membrane from bottom to top. The catalyst membrane adheres to the electrolyte membrane under the action of the surface tension of water.

[0011] Step 4: Using the same method as step 3, a catalyst membrane is attached to the other side of the electrolyte membrane by scooping it up from under the catalyst membrane in water to obtain a membrane electrode that can be used for fuel cell assembly.

[0012] Furthermore, in step 1, the catalyst slurry preparation method is as follows: the catalyst, electrolyte solution and dispersant are mixed together, and the catalyst slurry is obtained after ultrasonic dispersion.

[0013] Furthermore, the catalyst includes Pt / C catalyst, Ru / C catalyst, PtRu / C catalyst, Cu catalyst, Ag catalyst, and Au catalyst.

[0014] Furthermore, the electrolyte solution is a QAPPT solution or a Nafion solution.

[0015] Furthermore, the dispersant is ethanol, isopropanol, or n-propanol.

[0016] Furthermore, the substrate is aluminum foil, copper foil, silver foil, PTFE, SPEEK or a glass plate, and the substrate should be smooth and flat and have a fully clean surface.

[0017] Furthermore, in step 1, after drying and film formation, the thickness of the catalyst film is 5 microns to 80 microns.

[0018] Furthermore, in step 2, the substrate stripping agent includes a swelling stripping type swelling agent and a substrate etching type etching solution. Swelling stripping or etching stripping needs to be selected according to the type of substrate material. When the substrate can be etched, etching solution is used for etching. When the substrate cannot be etched, swelling agent swelling stripping is selected; the swelling agent includes water, ethanol, potassium hydroxide solution, and sodium hydroxide solution. The etching solution includes potassium hydroxide solution, sodium hydroxide solution, sodium carbonate solution, and potassium carbonate solution.

[0019] Furthermore, in step 3 and step 4, the catalyst membrane is placed in water by replacing the substrate stripping agent with water.

[0020] Furthermore, in step 3 and step 4, the scooping process is carried out manually or by mechanical equipment.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. Unlike traditional CCM preparation technology, the preparation method of the present invention can separate the membrane and the catalyst layer and assemble them after both are fully swollen. This effectively avoids damage to the catalyst layer structure caused by inconsistent swelling of the two.

[0023] 2. After the test, the membrane electrode is re-immersed in water to separate the membrane and the catalyst layer, so that different components can be studied and analyzed separately;

[0024] 3. If a component undergoes a major change, it can be replaced separately, and the other components can be reused, thus reducing resource waste;

[0025] 4. The operating conditions are a mild environment such as normal temperature aqueous solution or alcohol solution, avoiding the influence of low temperature or high temperature on the polymer;

[0026] 5. The separation of the catalyst layer from the substrate is simple and fast. The separation relies on the slight difference in dimensional changes between the catalyst layer and the substrate in water or alcohol environment and the rapid corrosion of the substrate in the etchant, which has almost no effect on the catalyst layer structure.

[0027] 6. The catalytic layer and the membrane are re-bonded by the surface tension of water. The membrane and the catalytic layer can be tightly and smoothly attached without the need for hot pressing or other operations, thus reducing damage to the catalytic layer structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 .Schematic diagram of membrane electrode structure.

[0029] Figure 2 .Catalytic layer sprayed on aluminum foil.

[0030] Figure 3 .Catalytic layer suspended in water.

[0031] Figure 4 .Battery polarization curve and power density.

[0032] Reference numerals: 1 - electrolyte membrane, 2 - first catalytic layer, 3 - first gas diffusion layer, 4 - second catalytic layer, 5 - second gas diffusion layer. DETAILED DESCRIPTION

[0033] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0034] Example 1:

[0035] Weigh 60mg of a 60% commercial Pt / C catalyst, add 750μL of QAPPT solution (solvent: dimethyl sulfoxide, concentration: 20mg / mL, purchased from EVE Fuel Cell Co., Ltd.) as the electrolyte solution, add 10mL of isopropyl alcohol as the dispersant, and ultrasonicate for 1 hour to uniformly disperse the catalyst slurry, which serves as the precursor ink. The precursor ink is sprayed onto an aluminum foil substrate at 70°C and dried to form a film to obtain a catalyst layer. The catalyst layer has a size of 2cm×2cm, as shown in the following figure. Figure 2 shown.

[0036] The aluminum foil was placed in a beaker containing 500 mL of 1 M KOH solution (as a swelling agent). The catalyst film was peeled off from the aluminum foil. The aluminum foil was fished out and the catalyst film floated in the solution in the beaker. The beaker was then placed in an oven and heated at 60 ° C for 24 h to obtain a counter ion of OH. - The catalyst layer (catalyst membrane) is fully washed with deionized water to remove excess KOH, thus obtaining a catalyst membrane suspended in water ( Figure 3 ). This catalytic layer (catalyst membrane) can be used as the cathode or anode of a fuel cell.

[0037] A 4 cm × 4 cm QAPPT membrane was used as the electrolyte membrane (thickness 25 μm, purchased from Yiwei Fuel Cell Co., Ltd.), which was placed in 1 M KOH and heated at 60 ° C for 24 h. The excess KOH was then washed thoroughly with deionized water to obtain a counter ion of OH. - The QAPPT membrane is placed in water below the catalyst membrane, then lifted upwards and positioned so that the catalyst membrane is centered. The catalyst membrane is then attached to the electrolyte membrane. The catalyst membrane is attached to the other side of the electrolyte membrane using the same method, ensuring that the catalyst layers on both sides are aligned. This creates a membrane electrode suitable for fuel cell assembly.

[0038] The battery test was carried out with a flow rate of 1000mL / min of hydrogen into the anode and 1000mL / min of oxygen into the cathode. The back pressure of both the cathode and cathode was 0.2MPa and the battery operating temperature was 80℃. The polarization curve and power density curve of the battery are shown in Figure 2. Figure 4 As shown, the maximum current density can exceed 4A / cm 2 , the maximum power density can reach 1.6W / cm 2 .

[0039] Example 2:

[0040] The difference from Example 1 is that the precursor ink is sprayed onto a plastic film and then placed in ethanol. The catalytic layer swells significantly in ethanol and can be peeled off the plastic film. After washing with water, ion exchange is performed. The remaining steps are the same as in Example 1.

[0041] Example 3:

[0042] The difference from Example 1 is that the precursor ink is sprayed onto a glass plate and then placed in water. The catalyst layer swells slightly in the water and can be peeled off the glass plate, allowing ion exchange to proceed without washing. The remaining steps are the same as in Example 1.

[0043] Example 4:

[0044] The difference from Example 1 is that the electrolyte membrane can be sprayed with a catalyst membrane on one side first, and then placed in 1M KOH and heated at 60 ° C for 24 hours, and then fully washed with deionized water to remove excess KOH, so as to obtain a counter ion of OH. - The remaining steps are the same as those in Example 1.

[0045] The above embodiments are intended to illustrate the present invention only and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be encompassed by the scope of the claims of the present invention.

Claims

1. A method for preparing a membrane electrode, characterized in that: The following steps are involved: Step 1: coating or spraying the catalyst slurry on the substrate and drying it to form a film to obtain a substrate covered with a catalyst film; Step 2: placing the substrate covered with the catalyst film in a substrate stripping agent to separate the catalyst film from the substrate to obtain the catalyst film; Step 3: Place the catalyst membrane in water, take another electrolyte membrane, place the electrolyte membrane in the water below the catalyst membrane, and lift the catalyst membrane from bottom to top. The catalyst membrane adheres to the electrolyte membrane under the action of the surface tension of water. The electrolyte membrane is a QAPPT membrane. Step 4: Using the same method as step 3, a catalyst membrane is attached to the other side of the electrolyte membrane by scooping it up from under the catalyst membrane in water to obtain a membrane electrode that can be used for fuel cell assembly; In step 3 and step 4, the catalyst film is placed in water by replacing the substrate stripping agent with water.

2. The method for preparing a membrane electrode according to claim 1, characterized in that: In step 1, the catalyst slurry is prepared by mixing the catalyst, electrolyte solution and dispersant together, and obtaining the catalyst slurry by ultrasonic dispersion.

3. The method for preparing a membrane electrode according to claim 2, wherein: The catalyst includes a Pt / C catalyst, a Ru / C catalyst, a PtRu / C catalyst, a Cu catalyst, an Ag catalyst, and an Au catalyst.

4. The method for preparing a membrane electrode according to claim 2, wherein: The electrolyte solution is a QAPPT solution or a Nafion solution.

5. The method for preparing a membrane electrode according to claim 2, wherein: The dispersant is ethanol, isopropanol, or n-propanol.

6. The method for preparing a membrane electrode according to claim 2, wherein: The substrate is aluminum foil, copper foil, silver foil, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK) or a glass plate with a smooth and flat surface. The substrate should be smooth and flat and the surface should be fully clean.

7. The method for preparing a membrane electrode according to claim 2, wherein: In step 1, after drying and film formation, the thickness of the catalyst film is 5 microns to 80 microns.

8. The method for preparing a membrane electrode according to claim 2, wherein: In step 2, the substrate stripping agent includes a swelling stripping type swelling agent and a substrate etching type etching solution, the swelling agent includes water, ethanol, potassium hydroxide solution, and sodium hydroxide solution, and the etching solution includes potassium hydroxide solution, sodium hydroxide solution, sodium carbonate solution, and potassium carbonate solution.

9. The method for preparing a membrane electrode according to claim 2, wherein: In step 3 and step 4, the scooping process is carried out manually or with mechanical equipment.

Images