A method for preparing a membrane electrode with a gradient distribution of ionic liquid along the inlet and outlet directions

Abstract

The present invention discloses a method for preparing a membrane electrode in which ionic liquid is distributed in a gradient along the inlet and outlet directions. The prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid are sprayed on both sides of the proton exchange membrane by using ultrasonic spraying equipment. Then, by controlling the number of ultrasonic spraying, the gradient distribution area to be sprayed is sprayed at different times, so that the ionic liquid is distributed in a gradient along the flow direction of hydrogen on the anode surface of the membrane electrode and oxygen on the cathode area. The position where the gas flows into the membrane electrode is the inlet direction, and the position where the gas flows out of the membrane electrode is the outlet direction, forming a membrane electrode catalyst layer in which the ionic liquid is distributed in a gradient along the gas flow direction. The present invention improves the proton transmission performance and electron transmission performance of the membrane electrode and increases the durability of the membrane electrode, minimizes the problem of water flooding, gas shortage and reverse polarity in the gas outlet area of ​​the membrane electrode, effectively improves the proton transmission performance and oxygen transmission performance of the membrane electrode, and effectively reduces the mass transfer polarization and ohmic polarization of the membrane electrode.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cells, and in particular relates to a method for preparing a membrane electrode in which ionic liquid is distributed in a gradient along an inlet and outlet direction. Background Art

[0002] As a key core component of a fuel cell stack, the membrane electrode plays a decisive role in the energy output of the fuel cell stack and is the direct place for energy conversion. Multiple physical and chemical processes such as electrochemical reaction, material transfer, and electrical conduction and heat transfer are carried out simultaneously inside the membrane electrode. The membrane electrode must have efficient material transfer, efficient electrochemical reaction, and excellent electrical conduction and heat transfer processes to achieve efficient conversion of electrochemical energy into electrical energy. In actual operation, the membrane electrode faces the phenomenon of water flooding and gas shortage. Water flooding will block the gas transmission channel of the membrane electrode, leading to problems such as gas shortage at the anode or cathode of the membrane electrode. At the same time, gas shortage caused by water flooding will bring a serious problem: the membrane electrode will be reversed, generating a high potential at the anode. The high potential will seriously corrode the carbon carrier of the membrane electrode, resulting in a sharp decline in the electrochemical performance and durability of the membrane electrode. The gas is evenly distributed to the membrane electrode reaction area along the bipolar plate flow field from the membrane electrode inlet. At the same time, the excess water generated inside the membrane electrode is discharged from the membrane electrode along with the gas. This will cause the membrane electrode to contain a large amount of liquid water in the outlet area, making it easy for the membrane electrode outlet area to be flooded and reverse polarity to occur. Material transfer is blocked, resulting in problems such as poor electrochemical uniformity of the membrane electrode and a sharp drop in durability.

[0003] At present, some existing literatures have proposed relevant solutions based on solving the problem of membrane electrode flooding, gas shortage and polarity reversal, such as:

[0004] 1. Patent application CN202010448071.3 discloses an anti-reversal electrode membrane electrode for fuel cells and a preparation method thereof. The anti-reversal electrode membrane electrode is prepared by mixing and coating a suspension of an anti-reversal active substance and a catalyst ink and then drying. The suspension of the anti-reversal active substance is composed of an anti-reversal active substance and a solvent. The pH of the suspension of the anti-reversal active substance is 6-7. The anti-reversal active substance is a nanomaterial catalyst containing a single substance of iridium or ruthenium, a single substance oxide containing iridium or ruthenium, or a single substance hydroxide containing iridium or ruthenium. The mass fraction of the anti-reversal active substance in the anti-reversal electrode membrane electrode is 1% to 15%. While ensuring the anti-reversal capability of the membrane electrode, the method can further reduce the amount of precious metal active substances added and reduce costs. During the preparation process, the anti-reversal active substance can be added together with other additives in the membrane electrode without adding an additional coating process, which is suitable for the preparation of large-area membrane electrodes. However, this method solves the problem by adding an anti-reverse polarity catalyst composed of non-conductive substances that cannot transport protons and gases to the anode. Excessive addition will lead to severe ohmic polarization and mass transfer polarization of the membrane electrode.

[0005] 2. Patent application CN202111012268.3 discloses a method for treating the anti-reverse pole of a membrane electrode in a fuel cell stack, wherein an anti-reverse pole catalyst is added to the platinum-carbon catalyst of the membrane electrode to obtain a mixed catalyst, and the mixed catalyst is used as a catalyst on the hydrogen side of the membrane electrode. The method uniformly mixes the anti-reverse pole catalyst into the platinum-carbon catalyst, and the obtained mixed catalyst is used as a catalyst layer on the hydrogen side of the membrane electrode. When the reverse pole occurs, the anti-reverse pole catalyst can preferentially act on the electrolysis of water, thereby avoiding oxidation damage to the carbon carrier or carbon diffusion material on the platinum-carbon catalyst, solving the problems of irreversible and attenuated performance after the membrane electrode reverses, and ensuring the normal operation of the fuel cell and the fuel cell stack, as well as its working efficiency and reliable stability of the system. However, the method is to add an anti-reverse pole catalyst to the platinum-carbon catalyst of the membrane electrode, and the anti-reverse pole catalyst is one or both of iridium oxide or ruthenium oxide. Iridium oxide or ruthenium oxide is non-conductive, cannot transmit protons, and cannot transmit gas substances. Excessive addition will cause serious ohmic polarization and mass transfer polarization of the membrane electrode.

[0006] The above existing patent documents mainly add an anti-reverse polarity catalyst to the anode so that the membrane electrode first catalyzes the decomposition of water when the reverse polarity occurs, thereby avoiding corrosion of the membrane electrode carbon carrier.

[0007] However, although the addition of anti-reversal catalysts can alleviate the problem of carbon carrier corrosion of membrane electrodes under high potential conditions to a certain extent, effectively improve the durability of membrane electrodes, and play an important role in the comprehensive electrochemical performance of membrane electrodes, anti-reversal catalysts are mainly composed of non-conductive substances that cannot transport protons and gases, and cannot alleviate the flooding problem. Excessive addition will lead to severe ohmic polarization and mass transfer polarization of the membrane electrode. At the same time, the proton-conducting substances in the catalytic layer are generally non-conductive substances, which will also increase the ohmic polarization of the membrane electrode. Therefore, the above solutions have obvious deficiencies in solving the problem of flooding, gas-deficient reversal of membrane electrodes, and further optimization is needed to enable the membrane electrode to have excellent electron, gas and proton transport properties, while enabling the membrane electrode to have excellent durability and electrochemical performance. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a membrane electrode in which an ionic liquid is distributed in a gradient along the inlet and outlet directions. Based on the existing technology, the present invention improves the comprehensive performance of the membrane electrode by using a design in which hydrophobic and oxygen-philic proton-type ionic liquids are distributed in a gradient along the inlet and outlet directions of the membrane electrode, and minimizes the problem of water flooding, gas shortage and reverse polarity in the gas outlet area of ​​the membrane electrode, while effectively improving the proton transmission performance and oxygen transmission performance of the membrane electrode, further improving the electrochemical performance and durability of the membrane electrode, and effectively reducing the problems of mass transfer polarization and ohmic polarization of the membrane electrode.

[0009] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0010] A method for preparing a membrane electrode in which ionic liquid is distributed in a gradient along the inlet and outlet directions, wherein the membrane electrode ionic liquid is designed in a gradient along the inlet and outlet directions, including a gradient design of the ionic liquid along the inlet and outlet directions on the anode surface of the membrane electrode and a gradient design of the ionic liquid along the inlet and outlet directions on the cathode surface of the membrane electrode; the gradient design along the inlet and outlet directions means that the ionic liquid is distributed in a gradient along the flow direction of hydrogen on the anode surface of the membrane electrode and oxygen on the cathode surface, the position where the gas flows into the membrane electrode is the inlet direction, and the position where the gas flows out of the membrane electrode is the outlet direction.

[0011] Furthermore, the ionic liquid has 3 to 5 gradients in the plane direction of the anode catalyst layer, the first gradient is close to the gas inlet, and the last gradient is close to the gas outlet. The mass fraction of the first gradient is 1wt% to 5wt%, and the mass fraction of the last gradient is 40wt% to 50wt%, and the difference between two adjacent gradient values ​​is equal.

[0012] Furthermore, the ionic liquid has 3 to 5 gradients in the plane direction of the cathode catalyst layer, the first gradient is close to the gas inlet, and the last gradient is close to the gas outlet. The mass fraction of the first gradient is 1wt% to 5wt%, and the mass fraction of the last gradient is 40wt% to 50wt%, and the difference between two adjacent gradient values ​​is equal.

[0013] Furthermore, the ionic liquid is an oxophilic and hydrophobic protic ionic liquid, which is one of [MTBD][NTf2] and [MTBD][PF6].

[0014] Furthermore, the ionic liquid is uniformly sprayed into the anode catalyst layer and the cathode catalyst layer by ultrasonic spraying equipment.

[0015] Furthermore, the anode catalyst layer is composed of an anode Pt-based catalyst, an anti-reverse polarity catalyst, and an ionic liquid, wherein the Pt-based catalyst and the anti-reverse polarity catalyst are uniformly distributed in the anode catalyst layer.

[0016] Furthermore, the anti-reversal catalyst is an oxygen evolution catalyst, selected from one or more of IrO2, RuO2, Ir alloy catalyst, and Ru alloy catalyst.

[0017] Furthermore, the cathode catalyst layer is composed of an anode Pt-based catalyst and an ionic liquid, wherein the Pt-based catalyst is uniformly distributed in the cathode catalyst layer.

[0018] Furthermore, the anode Pt-based catalyst and the cathode Pt-based catalyst are both selected from one or more of a Pt / C catalyst, a Pt alloy catalyst, a non-Pt-based noble metal catalyst, and a non-noble metal catalyst, and the uniform distribution concentration of the anode Pt-based catalyst is 0.02 to 0.15 mgPt / cm 2 Cathode, cathode Pt-based catalyst uniformly distributed concentration of 0.1 ~ 0.4mgPt / cm 2 .

[0019] Furthermore, a method for preparing a membrane electrode with a gradient distribution of ionic liquid along the inlet and outlet directions as described above specifically comprises the following steps:

[0020] (1) Preparation of anode catalyst slurry: placing an anode Pt-based catalyst, an anti-reverse polarity catalyst, and an isopropanol solution in a glass bottle, and uniformly dispersing them by ultrasonication to obtain an anode catalyst slurry;

[0021] (2) Preparation of cathode catalyst slurry: Placing the cathode Pt-based catalyst and isopropanol solution in a glass bottle and uniformly dispersing them by ultrasonication to obtain cathode catalyst slurry;

[0022] (3) Preparation of ionic liquid: Weigh the ionic liquid and isopropanol solution in a glass bottle, and uniformly disperse them by ultrasonication to obtain the ionic liquid; the mass percentages of the ionic liquid [MTBD][NTf2] and the isopropanol solution are 5-10 wt % and 70-90 wt %, respectively;

[0023] (4) Preparation of the catalyst layer: Use ultrasonic spraying equipment to spray the prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid on both sides of the proton exchange membrane, and then control the number of ultrasonic spraying to spray the gradient distribution area that needs to be sprayed for different times, so that different areas of the catalyst layer have ionic liquids with different loading amounts, and the ionic liquids are distributed in a gradient along the flow direction of hydrogen on the anode surface of the membrane electrode and oxygen on the cathode surface. The position where the gas flows into the membrane electrode is the inlet direction, and the position where the gas flows out of the membrane electrode is the outlet direction, forming a membrane electrode with a gradient distribution of ionic liquid distributed along the gas flow direction, forming a uniform membrane electrode cathode catalyst layer and a membrane electrode anode catalyst layer, respectively.

[0024] Furthermore, in steps (1), (2) and (3), the ultrasonic dispersion time is 28 to 33 minutes;

[0025] Since the present invention adopts the above technical solution, it has the following beneficial effects:

[0026] (1) In order to further improve the comprehensive performance of the membrane electrode, alleviate the problem of membrane electrode flooding, improve the proton transport performance and electron transport performance of the membrane electrode, and increase the durability of the membrane electrode, the present invention, based on the existing technology, uses a design in which hydrophobic and oxygen-philic proton-type ionic liquids are distributed in a gradient along the inlet and outlet directions of the membrane electrode to minimize the problem of water flooding, gas shortage and reverse polarity in the gas outlet area of ​​the membrane electrode, while effectively improving the proton transport performance and oxygen transport performance of the membrane electrode, further improving the electrochemical performance and durability of the membrane electrode, and effectively reducing the problems of mass transfer polarization and ohmic polarization of the membrane electrode.

[0027] (2) Since the proton-conducting Nafion solution does not have electronic conductivity and oxygen affinity, and is hydrophilic, excessive addition will lead to serious ohmic polarization and mass transfer polarization problems of the membrane electrode. The present invention innovates on the existing solution to the problem of oxidation corrosion of the carbon carrier of the catalyst layer caused by water flooding and gas shortage in the membrane electrode, removes the proton-conducting additive Nafion solution added when preparing the traditional membrane electrode catalyst layer, and replaces it with a proton-type ionic liquid that has oxygen affinity, hydrophobicity and high-efficiency proton conductivity. Therefore, the present invention uses a proton-type ionic liquid with oxygen affinity, hydrophobicity and high-efficiency proton conductivity to be distributed in a gradient along the inlet and outlet directions of the membrane electrode, which can effectively avoid the problem of water flooding and gas shortage in the outlet area of ​​the membrane electrode, and can greatly improve the proton transfer performance, oxygen transfer performance and durability of the membrane electrode. At the same time, it can also effectively reduce the problems of mass transfer polarization and ohmic polarization of the membrane electrode, so that the membrane electrode has excellent electrochemical performance, greatly improves the comprehensive electrochemical performance of the membrane electrode, and has a non-negligible impact on the improvement of the comprehensive performance of the membrane electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the examples of the present invention or the prior art, the drawings required in the implementation examples or the prior art description are briefly introduced below. Obviously, the drawings in the following description are only some examples of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without inventiveness:

[0029] Figure 1 Polarization curves of membrane electrodes of five different samples of Examples 1 to 4 of the present application and Comparative Example;

[0030] Figure 2 The electrochemical impedance spectra of five different sample membrane electrodes of Examples 1 to 4 of the present application and the comparative example are shown;

[0031] Figure 3 This is a polarization curve diagram before and after the durability test of Example 1 of the present application;

[0032] Figure 4 This is a polarization curve diagram before and after the durability test of the comparative example of this application. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are further described in detail below, but the present invention is not limited to these embodiments, and any improvement or substitution based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0034] Example 1

[0035] A method for preparing a membrane electrode in which an ionic liquid is distributed in a gradient along an inlet and outlet direction, comprising the following steps:

[0036] (1) Preparation of anode catalyst slurry: IrO2, Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain anode catalyst slurry;

[0037] The mass percentages of the IrO2, Pt / C and isopropanol solution are 0.2wt%, 9.8wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0038] (2) Preparation of cathode catalyst slurry: Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain cathode catalyst slurry;

[0039] The mass percentages of the Pt / C and isopropanol solutions are 10wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0040] (3) Preparation of ionic liquid: Weigh the ionic liquid [MTBD][NTf2] and isopropanol solution in a glass bottle and disperse them evenly by ultrasonication to obtain the ionic liquid;

[0041] The mass percentages of the ionic liquid [MTBD] [NTf2] and the isopropanol solution are 5wt% and 70wt% respectively; the ultrasonic dispersion time is 30min;

[0042] (4) Preparation of Catalytic Layer: The prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid were sprayed on both sides of the proton exchange membrane using ultrasonic spraying equipment to form a uniform membrane electrode cathode catalyst layer and membrane electrode anode catalyst layer, respectively, so that the Pt loading of the membrane electrode cathode and anode was 0.3 mg / cm 2 and 0.1mg / cm 2 The anode ionic liquid loading is 0.007 mg / cm 2Then, by controlling the number of ultrasonic spraying, the gradient distribution area that needs to be sprayed is sprayed for different times, so that different areas of the catalyst layer have ionic liquids with different loading amounts, forming an ionic liquid gradient distribution membrane electrode distributed along the gas flow direction; the ionic liquid distribution of the anode and cathode of the membrane electrode includes three gradient distributions, with mass percentages of 5wt%, 25wt% and 45wt%, respectively, among which the mass percentage of IrO2 in the anode catalyst layer is always 2wt%, even if the ionic liquid loading amounts of the first gradient area, the second gradient area and the third gradient area of ​​the anode catalyst layer of the membrane electrode are 0.011mg / cm 2 , 0.068mg / cm 2 and 0.170mg / cm 2 The ionic liquid loading in the first gradient region, the second gradient region and the third gradient region of the membrane electrode cathode catalyst layer is 0.032 mg / cm 2 , 0.2mg / cm 2 and 0.491mg / cm 2 .

[0043] Example 2

[0044] A method for preparing a membrane electrode in which an ionic liquid is distributed in a gradient along an inlet and outlet direction, comprising the following steps:

[0045] (1) Preparation of anode catalyst slurry: IrO2, Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain anode catalyst slurry;

[0046] The mass percentages of the IrO2, Pt / C and isopropanol solution are 0.2wt%, 9.8wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0047] (2) Preparation of cathode catalyst slurry: Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain cathode catalyst slurry;

[0048] The mass percentages of the Pt / C and isopropanol solutions are 10wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0049] (3) Preparation of ionic liquid: Weigh the ionic liquid [MTBD][NTf2] and isopropanol solution in a glass bottle and disperse them evenly by ultrasonication to obtain the ionic liquid;

[0050] The mass percentages of the ionic liquid [MTBD] [NTf2] and the isopropanol solution are 10wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0051] (4) Preparation of Catalytic Layer: The prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid were sprayed on both sides of the proton exchange membrane using ultrasonic spraying equipment to form a uniform membrane electrode cathode catalyst layer and membrane electrode anode catalyst layer, respectively, so that the Pt loading of the membrane electrode cathode and anode was 0.3 mg / cm 2 and 0.1mg / cm 2 The anode ionic liquid loading is 0.007 mg / cm 2 Then, by controlling the number of ultrasonic spraying, the gradient distribution area that needs to be sprayed is sprayed for different times, so that different areas of the catalyst layer have ionic liquids with different loading amounts, forming an ionic liquid gradient distribution membrane electrode distributed along the gas flow direction; the ionic liquid distribution of the anode and cathode of the membrane electrode includes four gradient distributions, with mass percentages of 5wt%, 20wt%, 35wt% and 50wt%, respectively, among which the mass percentage of IrO2 in the anode catalyst layer is always 2wt%, even if the ionic liquid loading amounts of the first gradient area, the second gradient area, the third gradient area and the fourth gradient area of ​​the anode catalyst layer of the membrane electrode are 0.011mg / cm 2 , 0.051mg / cm 2 , 0.111mg / cm 2 and 0.208mg / cm 2 The ionic liquid loading in the first gradient region, the second gradient region and the third gradient region of the membrane electrode cathode catalyst layer is 0.032 mg / cm 2 , 0.15mg / cm 2 , 0.323mg / cm 2 and 0.6mg / cm 2 .

[0052] Example 3

[0053] A method for preparing a membrane electrode in which an ionic liquid is distributed in a gradient along an inlet and outlet direction, comprising the following steps:

[0054] (1) Preparation of anode catalyst slurry: IrO2, Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain anode catalyst slurry;

[0055] The mass percentages of the IrO2, Pt / C and isopropanol solution are 0.2wt%, 9.8wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0056] (2) Preparation of cathode catalyst slurry: Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain cathode catalyst slurry;

[0057] The mass percentages of the Pt / C and isopropanol solutions are 10wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0058] (3) Preparation of ionic liquid: Weigh the ionic liquid [MTBD][NTf2] and isopropanol solution in a glass bottle and disperse them evenly by ultrasonication to obtain the ionic liquid;

[0059] The mass percentages of the ionic liquid [MTBD] [NTf2] and the isopropanol solution are 6wt% and 75wt% respectively; the ultrasonic dispersion time is 30min;

[0060] (4) Preparation of Catalytic Layer: The prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid were sprayed on both sides of the proton exchange membrane using ultrasonic spraying equipment to form a uniform membrane electrode cathode catalyst layer and membrane electrode anode catalyst layer, respectively, so that the Pt loading of the membrane electrode cathode and anode was 0.3 mg / cm 2 and 0.1mg / cm 2 The anode ionic liquid loading is 0.007 mg / cm 2 ; Then, by controlling the number of ultrasonic spraying, the gradient distribution area that needs to be sprayed is sprayed for different times, so that different areas of the catalyst layer have ionic liquids with different loading amounts, forming an ionic liquid gradient distribution membrane electrode distributed along the gas flow direction; the ionic liquid distribution of the anode and cathode of the membrane electrode includes five gradient distributions, and the mass percentages are 5wt%, 15wt%, 25wt%, 35wt%, and 45wt%, respectively, among which the mass percentage of IrO2 in the anode catalyst layer is always 2wt%, even if the ionic liquid loading amounts of the first gradient area, the second gradient area, the third gradient area, the fourth gradient area, and the fifth gradient area of ​​the anode catalyst layer of the membrane electrode are 0.011mg / cm 2 , 0.036mg / cm 2 , 0.068mg / cm 2 , 0.111mg / cm 2 and 0.170mg / cm 2 The ionic liquid loading in the first gradient region, the second gradient region and the third gradient region of the membrane electrode cathode catalyst layer is 0.032 mg / cm 2 , 0.106mg / cm 2 , 0.2mg / cm 2 , 0.323mg / cm 2 and 0.491mg / cm 2 .

[0061] Example 4

[0062] A method for preparing a membrane electrode in which an ionic liquid is distributed in a gradient along an inlet and outlet direction, comprising the following steps:

[0063] (1) Preparation of anode catalyst slurry: RuO2, PtCo, and isopropanol solution are placed in a glass bottle and dispersed evenly by ultrasonication to obtain an anode catalyst slurry;

[0064] The mass percentages of the RuO2, PtCo and isopropanol solution are 0.2wt%, 9.8wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0065] (2) Preparation of cathode catalyst slurry: PtCo and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain cathode catalyst slurry;

[0066] The mass percentages of the PtCo and isopropanol solution are 10wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0067] (3) Preparation of ionic liquid: Weigh the ionic liquid [MTBD] [PF6] and isopropanol solution in a glass bottle and disperse them evenly by ultrasonication to obtain the ionic liquid;

[0068] The mass percentages of the ionic liquid [MTBD][PF6] and the isopropanol solution are 9wt% and 85wt% respectively; the ultrasonic dispersion time is 30min;

[0069] (4) Preparation of Catalytic Layer: Use ultrasonic spraying equipment to spray the prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid on both sides of the proton exchange membrane to form a uniform membrane electrode cathode catalyst layer and membrane electrode anode catalyst layer respectively; the Pt loading of the membrane electrode cathode and anode is 0.3 mg / cm 2 and 0.1mg / cm 2 The anode ionic liquid loading is 0.007 mg / cm 2 ; Then, by controlling the number of ultrasonic spraying, the gradient distribution area that needs to be sprayed is sprayed for different times, so that different areas of the catalyst layer have ionic liquids with different loading amounts, forming an ionic liquid gradient distribution membrane electrode distributed along the gas flow direction; the ionic liquid distribution of the anode and cathode of the membrane electrode includes five gradient distributions, and the mass percentages are 5wt%, 15wt%, 25wt%, 35wt%, and 45wt%, respectively, among which the mass percentage of RuO2 in the anode catalyst layer is always 2wt%, even if the ionic liquid loading amounts of the first gradient area, the second gradient area, the third gradient area, the fourth gradient area, and the fifth gradient area of ​​the anode catalyst layer of the membrane electrode are 0.011mg / cm 2 , 0.036mg / cm 2 , 0.068mg / cm2 , 0.111mg / cm 2 and 0.170mg / cm 2 The ionic liquid loading in the first gradient region, the second gradient region and the third gradient region of the membrane electrode cathode catalyst layer is 0.032 mg / cm 2 , 0.106mg / cm 2 , 0.2mg / cm 2 , 0.323mg / cm 2 and 0.491mg / cm 2 .

[0070] Comparative Example 1

[0071] A method for preparing a membrane electrode in which an ionic liquid is distributed non-gradiently along an inlet and outlet direction, comprising the following steps:

[0072] (1) Preparation of anode catalyst slurry: IrO2, Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain anode catalyst slurry;

[0073] The mass percentages of the IrO2, Pt / C and isopropanol solution are 0.2wt%, 9.8wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0074] (2) Preparation of cathode catalyst slurry: Pt / C and isopropanol solution were placed in a glass bottle and dispersed evenly by ultrasonication to obtain cathode catalyst slurry;

[0075] The mass percentages of the Pt / C and isopropanol solutions are 10wt% and 90wt% respectively; the ultrasonic dispersion time is 30min;

[0076] (3) Preparation of ionic liquid: Weigh the ionic liquid [MTBD][NTf2] and isopropanol solution in a glass bottle and disperse them evenly by ultrasonication to obtain the ionic liquid;

[0077] The mass percentages of the ionic liquid [MTBD] [NTf2] and the isopropanol solution are 5wt% and 70wt% respectively; the ultrasonic dispersion time is 30min;

[0078] (4) Preparation of catalyst layer: using ultrasonic spraying equipment to spray the prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid on both sides of the proton exchange membrane to form a uniform membrane electrode cathode catalyst layer and membrane electrode anode catalyst layer respectively;

[0079] The mass percentages of the anode Pt-based catalyst, ionic liquid and IrO2 in the membrane electrode anode catalyst layer are 58wt%, 40wt% and 2wt%, respectively, so that the anode Pt loading and ionic liquid loading are 0.1mg / cm 2 、0.138mg / cm 2 and 0.007mg / cm 2 The mass percentages of the cathode Pt-based catalyst and the ionic liquid in the cathode catalyst layer of the membrane electrode are 60wt% and 40wt%, respectively, so that the cathode Pt loading and the ionic liquid are 0.3mg / cm 2 and 0.4mg / cm 2 .

[0080] In order to further illustrate that the present invention can achieve the technical effect, the following experiments are performed:

[0081] 1. Membrane electrode performance test

[0082] 1. Membrane electrode electrochemical performance test

[0083] Electrochemical performance tests were conducted using the membrane electrodes prepared in Examples 1 to 4 and Comparative Example 1. During the polarization curve test, the battery operating temperature was 80°C, the gas humidity was 100%, and the cathode and anode stoichiometric ratios were 2 and 1.5, respectively. The results are shown in FIG. Figure 1 As shown in Table 1. As can be seen from the figure, the gradient distribution of ionic liquid along the inlet and outlet directions of the membrane electrode can greatly improve the electrochemical performance of the membrane electrode. This is because the hydrophobic ionic liquid can greatly discharge excess water in the outlet area and reduce the frequency of flooding.

[0084] The electrochemical impedance of each membrane electrode prepared in Examples 1 to 4 and Comparative Example 1 was tested in situ at a relative humidity of 100% and 0.65 V. The impedance is as follows: Figure 2 As shown in Table 1. The electrochemical impedance value of the membrane electrode corresponding to the non-gradient distribution comparative example 1 is larger than that of the membrane electrode of the gradient examples 1 to 4. This is because the ionic liquid is electronically insulating, and the total content of the ionic liquid corresponding to the non-gradient distribution comparative example 1 is greater than that of the gradient examples 1 to 4, resulting in a decrease in the electronic conductivity of the membrane electrode, thereby increasing the impedance value of the membrane electrode.

[0085] 2. Membrane electrode durability test

[0086] The membrane electrodes prepared in Examples 1 to 4 and Comparative Example 1 were used for durability test: the battery operating temperature was 80°C, the gas humidity was 100%, the cathode and anode stoichiometric ratios were 2 and 1.5 respectively, and the constant potential 0.5V test was performed for 200h. Then the polarization curves before and after the membrane electrode durability test were compared. The test results are shown in FIG. Figure 3 , Figure 4 And as shown in Table 1.

[0087] As can be seen from the figure, after 200h durability test, the power density of the membrane electrode of the gradient distribution embodiment of the present application at a voltage of 0.65V was reduced by 42mW, while the power density of the membrane electrode of the comparison example 1 with non-gradient distribution was reduced by 92mW, and the performance declined faster. This is because the gradient membrane electrode can reduce the frequency of water flooding, gas deficiency and reversal in the outlet area of ​​the membrane electrode, thereby better protecting the membrane electrode and improving the durability of the membrane electrode.

[0088] Table 1 Electrochemical parameter values ​​of different membrane electrodes

[0089]

[0090] In summary, the present invention innovates on the existing solution to the problem of oxidation corrosion of the carbon carrier of the catalyst layer caused by water flooding and gas shortage in the membrane electrode, removes the proton conductive additive Nafion solution added when preparing the traditional membrane electrode catalyst layer, and replaces it with a proton type ionic liquid that has oxygen affinity, hydrophobicity and high-efficiency proton conductivity. Therefore, the present invention uses a proton type ionic liquid with oxygen affinity, hydrophobicity and high-efficiency proton conductivity to be distributed in a gradient along the inlet and outlet directions of the membrane electrode, which can effectively avoid the problem of water flooding and gas shortage in the outlet area of ​​the membrane electrode, and can greatly improve the proton transfer performance, oxygen transfer performance and durability of the membrane electrode. At the same time, it can also effectively reduce the problems of mass transfer polarization and ohmic polarization of the membrane electrode, so that the membrane electrode has excellent electrochemical performance, greatly improves the comprehensive electrochemical performance of the membrane electrode, and has a non-negligible impact on the improvement of the comprehensive performance of the membrane electrode.

[0091] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from all points of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the equivalent meaning and scope of the claims be included within the scope of protection of the present invention.

Claims

1. A method for preparing a membrane electrode in which an ionic liquid is distributed in a gradient along the inlet and outlet directions, characterized in that: The gradient design of the membrane electrode ionic liquid along the inlet and outlet directions includes a gradient design of the ionic liquid along the inlet and outlet directions of the membrane electrode anode surface and a gradient design of the ionic liquid along the inlet and outlet directions of the membrane electrode cathode surface; the gradient design along the inlet and outlet directions means that the ionic liquid is distributed in a gradient along the flow direction of hydrogen on the anode surface of the membrane electrode and oxygen on the cathode surface, the position where the gas flows into the membrane electrode is the inlet direction, and the position where the gas flows out of the membrane electrode is the outlet direction; The ionic liquid has 3 to 5 gradients in the plane direction of the anode catalyst layer, the first gradient is close to the gas inlet, the last gradient is close to the gas outlet, the mass fraction of the first gradient is 1wt% to 5wt%, the mass fraction of the last gradient is 40wt% to 50wt%, and the difference between two adjacent gradient values ​​is equal; The ionic liquid has 3 to 5 gradients in the plane direction of the cathode catalyst layer, the first gradient is close to the gas inlet, the last gradient is close to the gas outlet, the mass fraction of the first gradient is 1wt% to 5wt%, the mass fraction of the last gradient is 40wt% to 50wt%, and the difference between two adjacent gradient values ​​is equal; The ionic liquid is an oxophilic and hydrophobic protonic ionic liquid, and is one of [MTBD][NTf2] and [MTBD][PF6].

2. The method for preparing a membrane electrode having a gradient distribution of ionic liquid along the inlet and outlet directions according to claim 1, characterized in that: The ionic liquid is uniformly sprayed into the anode catalyst layer and the cathode catalyst layer by ultrasonic spraying equipment.

3. The method for preparing a membrane electrode having a gradient distribution of ionic liquid along the inlet and outlet directions according to claim 1, characterized in that: The anode catalyst layer is composed of an anode Pt-based catalyst, an anti-reverse polarity catalyst, and an ionic liquid, wherein the Pt-based catalyst and the anti-reverse polarity catalyst are uniformly distributed in the anode catalyst layer.

4. The method for preparing a membrane electrode having a gradient distribution of ionic liquid along the inlet and outlet directions according to claim 3, characterized in that: The anti-reverse polarity catalyst is an oxygen evolution catalyst, which is selected from one or more of IrO2, RuO2, Ir alloy catalyst, and Ru alloy catalyst.

5. The method for preparing a membrane electrode having an ionic liquid gradient distribution along the inlet and outlet directions according to claim 1, characterized in that: The cathode catalyst layer is composed of a cathode Pt-based catalyst and an ionic liquid, wherein the Pt-based catalyst is evenly distributed in the cathode catalyst layer.

6. The method for preparing a membrane electrode having a gradient distribution of ionic liquid along the inlet and outlet directions according to claim 3, characterized in that: The anode Pt-based catalyst is selected from one or more of a Pt / C catalyst, a Pt alloy catalyst, a non-Pt-based noble metal catalyst, and a non-noble metal catalyst. The uniform distribution concentration of the anode Pt-based catalyst is 0.02-0.15 mgPt / cm 2 .

7. The method for preparing a membrane electrode having an ionic liquid gradient distribution along the inlet and outlet directions according to claim 5, characterized in that: The cathode Pt-based catalyst is selected from one or more of a Pt / C catalyst, a Pt alloy catalyst, a non-Pt-based noble metal catalyst, and a non-noble metal catalyst. The cathode Pt-based catalyst is uniformly distributed at a concentration of 0.1 to 0.4 mg Pt / cm 2 .

8. A method for preparing a membrane electrode having an ionic liquid gradiently distributed along the inlet and outlet directions as claimed in any one of claims 1 to 7, characterized in that: The specific steps include: (1) Preparation of anode catalyst slurry: placing an anode Pt-based catalyst, an anti-reverse polarity catalyst, and an isopropanol solution in a glass bottle, and uniformly dispersing them by ultrasonication to obtain an anode catalyst slurry; (2) Preparation of cathode catalyst slurry: Placing the cathode Pt-based catalyst and isopropanol solution in a glass bottle and uniformly dispersing them by ultrasonication to obtain cathode catalyst slurry; (3) Preparation of ionic liquid: Weigh the ionic liquid and isopropanol solution in a glass bottle, and uniformly disperse them by ultrasonication to obtain the ionic liquid; the mass percentages of the ionic liquid [MTBD][NTf2] and the isopropanol solution are 5-10 wt % and 70-90 wt %, respectively; (4) Preparation of the catalyst layer: Use ultrasonic spraying equipment to spray the prepared anode catalyst slurry, cathode catalyst slurry and ionic liquid on both sides of the proton exchange membrane, and then control the number of ultrasonic spraying to spray the gradient distribution area that needs to be sprayed for different times, so that different areas of the catalyst layer have ionic liquids with different loading amounts, and the ionic liquids are distributed in a gradient along the flow direction of hydrogen on the anode surface of the membrane electrode and oxygen on the cathode surface. The position where the gas flows into the membrane electrode is the inlet direction, and the position where the gas flows out of the membrane electrode is the outlet direction, forming a membrane electrode with a gradient distribution of ionic liquid distributed along the gas flow direction, forming a uniform membrane electrode cathode catalyst layer and a membrane electrode anode catalyst layer, respectively.

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