Membrane electrode suitable for low humidity conditions and preparation method thereof
By coating the catalyst surface with ionic liquid and mixing it with ionomer, a membrane electrode was prepared, which solved the problem of proton transport and oxygen mass transfer under low humidity conditions, achieved efficient proton conduction and oxygen transfer, and improved the performance and durability of fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI JIAOTONG UNIV
- Filing Date
- 2024-10-16
- Publication Date
- 2026-05-12
AI Technical Summary
Under low humidity conditions, the proton transport channels of the membrane electrode are blocked, and the change in the distribution of hydrophilic and hydrophobic waters in the ionomer of the catalyst layer leads to an increase in oxygen mass transfer resistance. Existing covalent organic framework materials may dissolve during long-term operation, resulting in a decrease in the water retention capacity of the membrane electrode and a weakening of proton transport performance.
The catalyst surface is coated with ionic liquid, and the catalyst is formed by rotary evaporation and cleaning. After being mixed with ionomer, the catalyst is sprayed to prepare a cathode catalyst layer and hot-pressed onto both sides of the proton exchange membrane to form a microstructure in which the ionic liquid and ionomer interact, thereby optimizing proton transport and oxygen mass transfer.
Ensuring efficient proton transport under low humidity conditions, improving oxygen mass transfer, enhancing the durability of the membrane electrode and battery performance, increasing peak power by approximately 37% to 54%, and reducing membrane electrode costs.
Smart Images
Figure CN119517998B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of fuel cell technology, and more specifically to a membrane electrode suitable for low humidity conditions and its preparation method. Background Technology
[0002] Proton exchange membrane fuel cells (PEMFCs) are the primary form of hydrogen energy utilization. They convert the chemical energy stored in hydrogen into electrical energy through electrochemical methods, offering advantages such as high energy conversion efficiency, zero pollution, and fast dynamic response. Currently, the main application of fuel cells is in new energy vehicles, thus requiring them to cope with diverse operating conditions, especially low-humidity operating conditions.
[0003] However, proton transport within the catalytic layer of the membrane electrode is highly dependent on the proton transport channels constructed by the hydration of the ionomer. Therefore, under low humidity conditions, the hydration degree of the ionomer decreases, which leads to the interruption of the proton transport channels. At the same time, low water content will cause changes in the distribution of hydrophilic and hydrophobic water regions within the ionomer of the catalytic layer, which is not conducive to oxygen passing through the ionomer membrane to reach the catalytic active sites and increases the local oxygen mass transfer resistance.
[0004] Patent ZL201910585539.0 discloses a method for preparing a membrane electrode assembly (MEA) to improve the low-humidity operation performance of a proton exchange membrane fuel cell (PEMFC). By adding appropriate amounts of covalent organic framework materials to the cathode and anode catalyst layers, the MEA of the PEMFC gains a certain degree of self-humidification capability, enabling stable operation of the fuel cell under low humidity conditions. Simultaneously, due to this self-humidification capability, the proton transfer efficiency within the cell is significantly improved, and the current density and power density of the cell are also enhanced. However, this technology utilizes covalent organic framework materials to give the MEA a certain water retention capacity, thereby aiding proton conduction, rather than providing a new proton transport channel. Furthermore, this technology directly adds triazine-based covalent organic framework materials to the catalyst layer slurry to directly prepare the catalyst layer. During long-term operation, the triazine-based covalent organic framework materials may dissolve in the product water and be carried away from the catalyst layer, leading to a decrease in the water retention capacity of the MEA and a weakening of proton transport performance. Summary of the Invention
[0005] The purpose of this invention is to overcome the defects of the prior art and provide a membrane electrode and its preparation method suitable for low humidity conditions, so as to ensure proton transport and enhance local oxygen mass transfer.
[0006] The objective of this invention can be achieved through the following technical solution: a method for preparing a membrane electrode suitable for low humidity conditions, comprising the following steps:
[0007] (1) Dissolve the ionic liquid in ultrapure water and disperse it evenly to obtain an aqueous solution of the ionic liquid;
[0008] (2) Mix the aqueous solution of ionic liquid obtained in step (1) with the catalyst evenly, coat the catalyst surface with ionic liquid, and clean and dry the coated catalyst to obtain the catalyst coated with ionic liquid.
[0009] (3) The catalyst coated with ionic liquid obtained in step (2) is mixed evenly with ionomer and dispersion solvent to prepare catalyst slurry and then sprayed to prepare cathode catalyst layer;
[0010] (4) The cathode catalyst layer and anode catalyst layer obtained in step (3) are hot-pressed onto both sides of the proton exchange membrane to prepare the membrane electrode.
[0011] Furthermore, the ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIM][NTF2]).
[0012] Furthermore, the mass ratio of the ionic liquid to ultrapure water in step (1) is 1:200-1:1000.
[0013] Furthermore, the mixing method of the ionic liquid and ultrapure water in step (1) is to add the ionic liquid to the ultrapure water; ultrapure water cannot be added to the ionic liquid. (Adding the ionic liquid first and then adding water may cause local aggregation of the ionic liquid, affecting the dissolution rate and dissolution effect).
[0014] The dispersion method is magnetic stirring, and the dispersion time is 1-5 hours.
[0015] Furthermore, the mass ratio of the catalyst to the ionic liquid aqueous solution in step (2) is 1:100-1:5000.
[0016] Furthermore, the coating method in step (2) is rotary evaporation, which specifically includes two stages. In the first stage, the rotation speed is 60-80 rpm, the water bath temperature is 50℃-60℃, and the time is 1-10 h. If the rotation speed is too low, the temperature distribution inside the flask will be uneven; if the rotation speed is too high, the liquid will vibrate. If the water temperature is too low, the heating effect will not be achieved, and the evaporation rate will be slow; if the water temperature is too high, the liquid will easily boil over. If the time is too short, the liquid evaporation cannot be guaranteed; if the time is too long, the preparation efficiency will be too low. In the second stage, the rotation speed is 80-100 rpm, the water bath temperature is 60℃-80℃, and the time is 1-10 h. The higher rotation speed, temperature, and sufficient time enhance the interaction between the ionic liquid and the catalyst and carbon support surface, ensuring the coating effect of the ionic liquid on the catalyst.
[0017] In the above technical solution, the purpose of cleaning and drying in step (2) is that after rotary evaporation, there will be an excess of ionic liquid physically mixed with the catalyst, but it will not be coated on the surface of the catalyst. Therefore, it is necessary to clean off this excess of ionic liquid.
[0018] Further, the catalyst in step (2) is one or more of the following: a carbon-supported platinum catalyst, a carbon-supported platinum alloy catalyst, a core-shell catalyst, and a non-precious metal catalyst; the ionomer is a perfluorosulfonic acid ionomer; and the dispersion solvent is one or more of deionized water, isopropanol, and ethanol. The mass ratio of the catalyst, ionomer, and dispersion solvent is 1:(1-5):(100-500).
[0019] Furthermore, the mixing method described in step (3) is ultrasonic dispersion, and the dispersion time is 10-60 min;
[0020] The spraying method is electrostatic spraying or ultrasonic spraying.
[0021] Furthermore, in step (4), the hot pressing temperature is 120-150℃ and the hot pressing time is 1-10min. The purpose is to: (1) ensure that the anode and cathode catalyst layers are attached to both sides of the proton exchange membrane, and (2) use heating to enhance the interaction between the ionomers and ionic liquids in the catalyst layer, thereby improving the durability of the catalyst layer structure and membrane electrode performance.
[0022] The present invention also provides a membrane electrode suitable for low humidity conditions, which is prepared by the above method.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] 1. Ionic liquids, as salts that are liquid at room temperature, possess advantages such as high ionic conductivity, high oxygen solubility, low vapor pressure, and good thermal and chemical stability. This invention selects a suitable ionic liquid to modify the catalyst surface. The ionic liquid can replace water in forming a hydrogen bond network within the ionomer. The ionic liquid also helps the sulfonic acid groups on the side chains of the ionomer to dissociate, forming SO3. - As a proton transfer site (because the ionic liquid used in this invention is a proton-type ionic liquid that can dissociate into anions and cations), it can conduct protons even in the absence of water, ensuring proton transport; at the same time, the interaction between the ionomer and the ionic liquid can optimize the microstructure inside the ionomer film and enhance the local mass transfer of oxygen.
[0025] The membrane electrode prepared by this invention can ensure efficient proton transport within the catalyst layer under low humidity conditions, enabling wide-range operation; it also enhances oxygen mass transfer, improving battery performance at high current densities. Notably, this study also found that modifying the catalyst with ionic liquids can reduce the amount of ionomer used, thereby reducing the cost of the membrane electrode to some extent.
[0026] 2. The present invention first coats the catalyst surface with an ionic liquid and then prepares a catalyst layer. The resulting structure is: the catalyst surface is first coated with an ionic liquid layer, and then coated with an ionomer layer. This can strengthen the interaction between the ionic liquid and the catalyst, prevent the ionic liquid from detaching from the catalyst layer during long-term operation, and at the same time, the interaction between the ionomer and the ionic liquid can optimize the microstructure inside the ionomer film, especially to prevent the formation of a dense layer of ionomer on the catalyst surface (a dense layer would seriously hinder oxygen mass transfer), and enhance local oxygen mass transfer.
[0027] 3. The membrane electrode prepared by this invention has a peak power that is about 37% higher than that prepared by conventional processes under 100% relative humidity conditions; and a peak power that is about 54% higher than that prepared by conventional processes under unhumidified cathode conditions. Attached Figure Description
[0028] Figure 1 This is a graph showing the test performance of Example 1 under high humidity conditions;
[0029] Figure 2 This is a graph showing the test performance of Example 1 under low humidity conditions;
[0030] Figure 3 This is a graph showing the test performance of Comparative Example 1 under high humidity conditions.
[0031] Figure 4 This is a graph showing the test performance of Comparative Example 1 under low humidity conditions.
[0032] Figure 5 This is a graph showing the test performance of Comparative Example 2 under high humidity conditions.
[0033] Figure 6 The graph shows the test performance of Comparative Example 2 under low humidity conditions. Detailed Implementation
[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.
[0035] Unless otherwise specified, all raw materials and equipment used in this invention are commonly used commercially available materials and equipment in the field.
[0036] Example 1
[0037] This embodiment provides a membrane electrode suitable for low humidity conditions and its preparation method, including the following steps:
[0038] 1. Dissolve 0.1 mg of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in 49.9 mg of ultrapure water and disperse evenly to obtain an aqueous solution of ionic liquid. The dispersion method was magnetic stirring, and the dispersion time was 3 h.
[0039] 2. The aqueous solution of the ionic liquid obtained in the previous step was mixed with 0.2 mg of commercial carbon-supported platinum catalyst. The ionic liquid was coated on the surface of the catalyst by rotary evaporation. The rotary evaporation was divided into two stages. The first stage was carried out at a rotation speed of 70 rpm, a water bath temperature of 60 ℃, and a time of 3 h. The second stage was carried out at a rotation speed of 90 rpm, a water bath temperature of 70 ℃, and a time of 3 h.
[0040] 3. The coated catalyst is cleaned and dried to obtain the catalyst coated with ionic liquid;
[0041] 4. The catalyst coated with ionic liquid is mixed with perfluorosulfonic acid ionomer and dispersion solvent at a mass ratio of 1:2:280. The dispersion solvent is composed of deionized water and ethanol at a mass ratio of 80:200. The catalyst slurry is prepared by ultrasonic dispersion for 20 minutes. Then, the cathode catalyst layer is prepared by spraying using electrostatic spraying, which is commonly used in the preparation of existing membrane electrodes.
[0042] 5. Hot-press the cathode catalyst layer and a commercially available anode catalyst layer onto both sides of the proton exchange membrane to prepare the membrane electrode. The hot-pressing temperature is 130℃ and the hot-pressing time is 5min.
[0043] High humidity test conditions for membrane electrode performance: Hydrogen / air were introduced into the anode / cathode respectively; operating temperature was 80℃; operating pressure was 150kPa; and the relative humidity of both anode and cathode was 100%. Test results are as follows: Figure 1 As shown, from Figure 1 It can be seen that the battery performance is good in both the low current density region and the high current density region, with a peak power reaching 598mW / cm². 2 .
[0044] Low-humidity test conditions for membrane electrode performance: Hydrogen / air were introduced into the anode / cathode respectively; operating temperature was 80℃; operating pressure was 150 kPa; anode relative humidity was 100%; and cathode relative humidity was 0%. Test results are as follows: Figure 2 As shown, from Figure 2 It can be seen that the fuel cell performance does not decrease significantly under the condition of no cathode humidification, indicating that the ionic liquid can help the effective transport of protons within the catalyst layer, and the peak power reaches 500mW / cm². 2 .
[0045] Comparative Example 1
[0046] This comparative example provides a conventional membrane electrode and its preparation method, including the following steps:
[0047] 1. A commercial carbon-supported platinum catalyst, perfluorosulfonic acid ionomer, and dispersion solvent were mixed evenly at a mass ratio of 1:2:280 to prepare a catalyst slurry. The mixing method was ultrasonic dispersion, and the dispersion time was 20 min. Then, a catalyst layer was prepared by spraying. The spraying method was the same as that in Example 1, using electrostatic spraying.
[0048] 2. The catalyst layer is hot-pressed onto both sides of the proton exchange membrane to prepare the membrane electrode. The hot-pressing temperature is 130℃ and the hot-pressing time is 5min.
[0049] High humidity test conditions for membrane electrode performance: Hydrogen / air were introduced into the anode / cathode respectively; operating temperature was 80℃; operating pressure was 150kPa; and the relative humidity of both anode and cathode was 100%. Test results are as follows: Figure 3 As shown, from Figure 3 It can be seen that the peak power is only 437mW / cm². 2 The membrane electrode prepared based on the ionic liquid modified catalyst in Example 1 is lower than that prepared in Example 1.
[0050] Low-humidity test conditions for membrane electrode performance: Hydrogen / air were introduced into the anode / cathode respectively; operating temperature was 80℃; operating pressure was 150 kPa; anode relative humidity was 100%; and cathode relative humidity was 0%. Test results are as follows: Figure 4 As shown, from Figure 4 It can be seen that the performance of the fuel cell drops significantly after the humidity decreases, indicating that proton transport within the catalyst layer is limited, and the peak power is only 325 mW / cm². 2 The membrane electrode prepared based on the ionic liquid modified catalyst in Example 1 is lower than that prepared in Example 1.
[0051] Comparative Example 2
[0052] This embodiment provides a membrane electrode suitable for low humidity conditions and its preparation method, including the following steps:
[0053] 1. Dissolve 0.1 mg of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in 49.9 mg of ultrapure water and disperse evenly to obtain an aqueous solution of ionic liquid. The dispersion method is magnetic stirring and the dispersion time is 3 h.
[0054] 2. The aqueous solution of the ionic liquid obtained in the previous step was mixed with 0.2 mg of commercial carbon-supported platinum catalyst. The ionic liquid was coated on the surface of the catalyst by rotary evaporation. The rotary evaporation was divided into two stages. The first stage was carried out at a rotation speed of 70 rpm, a water bath temperature of 60 ℃, and a time of 3 h. The second stage was carried out at a rotation speed of 90 rpm, a water bath temperature of 70 ℃, and a time of 3 h.
[0055] 3. The coated catalyst is cleaned and dried to obtain the catalyst coated with ionic liquid;
[0056] 4. Mix the ionic liquid-coated catalyst with perfluorosulfonic acid ionomer and dispersion solvent evenly to prepare a catalyst slurry. The mixing method is ultrasonic dispersion, and the dispersion time is 20 min. Then, the cathode catalyst layer is prepared by electrostatic spraying.
[0057] 5. The cathode catalyst layer and the conventional anode catalyst layer are hot-pressed onto both sides of the proton exchange membrane to prepare the membrane electrode. The hot-pressing temperature is 130℃ and the hot-pressing time is 5min.
[0058] High humidity test conditions for membrane electrode performance: Hydrogen / air were introduced into the anode / cathode respectively; operating temperature was 80℃; operating pressure was 150kPa; and the relative humidity of both anode and cathode was 100%. Test results are as follows: Figure 5 As shown, from Figure 5 It can be seen that the battery performance drops significantly in the low current density region, indicating that the selected ionic liquid not only fails to help conduct protons but also poisons the catalytic active sites, reducing fuel cell performance, with a peak power of only 215 mW / cm². 2 .
[0059] Low-humidity test conditions for membrane electrode performance: Hydrogen / air were introduced into the anode / cathode respectively; operating temperature was 80℃; operating pressure was 150 kPa; anode relative humidity was 100%; and cathode relative humidity was 0%. Test results are as follows: Figure 6 As shown, from Figure 6 It can be seen that the battery performance drops significantly in the low current density region, indicating that the selected ionic liquid not only fails to help conduct protons but also poisons the catalytic active sites, reducing fuel cell performance, with a peak power of only 182 mW / cm². 2 .
[0060] Comparing the performance test results of Example 1 and Comparative Example 1, it can be seen that the membrane electrode prepared based on the ionic liquid-modified catalyst performs better than the membrane electrode prepared using commercial catalysts under both high and low humidity conditions. This indicates that the ionic liquid can not only help water transport within the catalyst layer, but also improve the oxygen reduction activity of the catalyst to a certain extent. The only difference between Comparative Example 2 and Example 1 is the type of ionic liquid. From the performance test results, it can be seen that the performance of Comparative Example 2 is much lower than that of Example 1 and also lower than that of Comparative Example 2. This indicates that an unsuitable ionic liquid not only cannot help conduct protons, but also poisons the catalytic active sites and reduces the performance of the fuel cell. Therefore, it is necessary to select a suitable ionic liquid.
[0061] Example 2
[0062] The mass ratio of ionic liquid to ultrapure water was 1:450, and the rest was the same as in Example 1.
[0063] Example 3
[0064] The mass ratio of ionic liquid to ultrapure water was 1:550, and the rest was the same as in Example 1.
[0065] Comparative Example 3
[0066] The mass ratio of ionic liquid to ultrapure water was 1:200, and the rest was the same as in Example 1.
[0067] Comparative Example 4
[0068] The mass ratio of the sub-liquid to ultrapure water was 1:1000, and the rest was the same as in Example 1.
[0069] The performance of the membrane electrodes of each embodiment and comparative example was tested using the same method as in Example 1, and the results are shown in the table below:
[0070]
[0071] The mass ratio of ionic liquid to ultrapure water is crucial, affecting the ionic liquid loading on the catalyst surface after modification, and consequently influencing the catalyst layer structure. Excessive ionic liquid leads to an overly high solid content within the catalyst layer, restricting oxygen gas phase diffusion, causing significant concentration polarization losses, and reducing fuel cell performance. Conversely, insufficient ionic liquid hinders proton conduction, making it unsuitable for low-humidity operating conditions. Therefore, selecting an appropriate ionic liquid content is essential.
Claims
1. A method for preparing a membrane electrode suitable for low humidity conditions, characterized in that, Includes the following steps: (1) Dissolve the ionic liquid in ultrapure water and disperse it evenly to obtain an aqueous solution of the ionic liquid; the ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIM][NTF2]), and the mass ratio of the ionic liquid to ultrapure water is 1:450-1:
550. (2) The aqueous solution of ionic liquid obtained in step (1) is mixed evenly with the catalyst. The ionic liquid is coated on the surface of the catalyst through a two-stage rotary evaporation process. The coated catalyst is then cleaned and dried to obtain the catalyst coated with ionic liquid. The two-stage rotary evaporation process is as follows: the rotation speed of the first stage is 60 rpm-80 rpm, the water bath temperature is 50℃-60℃, and the time is 1h-10h; the rotation speed of the second stage is 80 rpm-100 rpm, the water bath temperature is 60℃-80℃, and the time is 1h-10h. (3) The catalyst coated with ionic liquid obtained in step (2) is mixed evenly with ionomer and dispersion solvent to prepare catalyst slurry and then sprayed to prepare cathode catalyst layer; (4) The cathode catalyst layer and anode catalyst layer obtained in step (3) are hot-pressed onto both sides of the proton exchange membrane to prepare the membrane electrode.
2. The method for preparing a membrane electrode suitable for low humidity conditions according to claim 1, characterized in that, The mixing method of ionic liquid and ultrapure water in step (1) is to add ionic liquid to ultrapure water; The dispersion method is magnetic stirring, and the dispersion time is 1-5 hours.
3. The method for preparing a membrane electrode suitable for low humidity conditions according to claim 1, characterized in that, The mass ratio of the catalyst to the ionic liquid aqueous solution in step (2) is 1:100-1:5000.
4. The method for preparing a membrane electrode suitable for low humidity conditions according to claim 1, characterized in that, The catalyst mentioned in step (2) is one or more of the following: carbon-supported platinum catalyst, carbon-supported platinum alloy catalyst, core-shell catalyst, and non-precious metal catalyst; the ionomer is a perfluorosulfonic acid ionomer; and the dispersion solvent is one or more of the following: deionized water, isopropanol, and ethanol.
5. The method for preparing a membrane electrode suitable for low humidity conditions according to claim 1, characterized in that, The mixing method described in step (3) is ultrasonic dispersion, and the dispersion time is 10-60 min; The spraying method is electrostatic spraying or ultrasonic spraying.
6. The method for preparing a membrane electrode suitable for low humidity conditions according to claim 1, characterized in that, In step (4), the hot pressing temperature is 120-150 ℃ and the hot pressing time is 1-10 min.
7. A membrane electrode suitable for low humidity conditions, characterized in that, It is prepared by any one of the methods of claims 1-6.