Membrane electrode of Merry type pore structure cathode catalyst layer as well as preparation method and application of membrane electrode

Abstract

The invention relates to a membrane electrode of a Merry type pore structure cathode catalyst layer and a preparation method and application thereof. The proton exchange membrane comprises a proton exchange membrane, and an anode catalyst layer and a cathode catalyst layer which are respectively arranged on two side surfaces of the proton exchange membrane, wherein the cathode catalyst layer comprises a cathode inner catalyst layer and a cathode outer catalyst layer which are sequentially arranged along the surface of the proton exchange membrane; the cathode catalyst layer has a micropore-mesopore-macropore structure, the micropore size is 0.1-2 nm, the mesopore size is 2-50 nm, and the macropore size is 50-7000 nm; and the diameters and proportions of the macropores, the micropores and the mesopores conform to the Merry's law. The Merry type pore structure cathode catalyst layer can obviously improve the material transmission efficiency, so that the catalytic efficiency is improved, meanwhile, the addition of a pore-forming agent or other substances is avoided, the problem of poisoning of a membrane electrode caused by introduction of impurity ions is solved, and the service life of the membrane electrode is prolonged. And the problems of low transmission efficiency and performance reduction under a low-humidity working condition caused by a single pore structure of a traditional catalyst layer are solved.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, and particularly relates to a membrane electrode of a Murray-type porous cathode catalyst layer, its preparation method and application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have attracted much attention in the clean energy field due to their advantages such as high specific energy, environmental friendliness, and rapid start-up at low temperatures. The membrane electrode assembly (MEA), as its core power generation component, directly affects the cell's power density and energy distribution efficiency.

[0003] Currently, traditional catalyst layers are often monolayer structures, with relatively simple structures and uniform composition. However, reactants are not uniformly distributed during operation, so not all active sites can exert catalytic activity. Especially under high electrical density, the monolayer pore structure hinders oxygen transport, limiting the oxygen reduction reaction. Furthermore, decreased humidity during fuel cell operation leads to a decrease in the proton conductivity of the proton exchange membrane and an increase in internal resistance, thus degrading battery performance. Currently, from the perspective of the catalyst layer, there are two solutions to this problem: 1. Adding hydrophilic substances such as inorganic metal oxides to the catalyst layer to improve its hydrophilicity. However, the addition of hydrophilic substances often causes problems such as increased resistance and decreased catalytic activity. 2. Using pore-forming agents such as calcium carbonate to improve the pore structure of the catalyst layer to increase active sites and enhance its catalytic activity. However, subsequent pore-forming agent removal steps, such as acid washing and alkali washing, can damage the catalyst layer, and residual impurity ions can also affect the membrane electrode life. Summary of the Invention

[0004] To overcome the above problems, the present invention provides a membrane electrode with a Murray-type porous cathode catalytic layer, its preparation method and application.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a membrane electrode with a Murray-type porous cathode catalytic layer, comprising a proton exchange membrane and an anode catalytic layer and a cathode catalytic layer respectively disposed on two sides of the proton exchange membrane; wherein the cathode catalytic layer comprises an inner cathode catalytic layer and an outer cathode catalytic layer disposed sequentially along the surface of the proton exchange membrane; The cathode catalyst layer has a micropore-mesopore-macropore structure, wherein the micropores are 0.1-2 nm, the mesopores are 2-50 nm, and the macropores are 50-7000 nm. The diameters and proportions of the macropores, micropores, and mesopores conform to Murray's Law.

[0006] In this invention, the diameters of macropores, mesopores, and micropores satisfy the condition that the square of the diameter of a macropore is approximately equal to the sum of the squares of the diameters of the mesopores it cross-links with, and the square of the diameter of a mesopore is approximately equal to the sum of the squares of the diameters of the micropores it cross-links with, which conforms to the Murray Law.

[0007] In one or more embodiments, the ratio (I / C) of the resin in the slurry within the cathode inner catalyst layer to the carbon in the low specific surface area platinum-carbon catalyst is 0.8~1.1, and the platinum loading is 0.1 mg / cm³. 2 ~0.3mg / cm 2 The preferred platinum loading is 0.2 mg / cm³. 2 ~0.25mg / cm 2 ; The ratio (I / C) of the resin in the slurry of the cathode outer catalyst layer to the carbon in the high specific surface area platinum-carbon catalyst is 0.6~0.9, and the platinum loading is 0.1 mg / cm³. 2 ~0.3mg / cm 2 The preferred platinum loading is 0.05 mg / cm³. 2 ~0.1mg / cm 2 .

[0008] Furthermore, the total platinum loading in the cathode catalyst layer, which consists of the inner and outer catalyst layers, is preferably 0.3 mg / cm³. 2 .

[0009] Furthermore, the catalyst used in the anode catalyst layer is a commercial Pt / C catalyst with a platinum loading of 0.05–0.1 mg / cm³. 2 .

[0010] In a second aspect, the present invention also provides a method for preparing a membrane electrode with a Murray-type porous cathode catalytic layer as described in the above-described technical solution, comprising: Provides proton exchange membranes and anode catalyst layers; A cathode inner catalyst layer slurry is provided, and the cathode inner catalyst layer slurry is coated on the surface of the proton exchange membrane and dried by gradient heating to obtain the cathode inner catalyst layer. A cathode outer catalyst layer slurry is provided, and the cathode outer catalyst layer slurry is coated on the surface of the cathode inner catalyst layer. The slurry is then dried by gradient heating to obtain the cathode outer catalyst layer. The cathode inner catalyst layer and the cathode outer catalyst layer constitute a Murray-type porous cathode catalyst layer. The Murray-type porous cathode catalytic layer and the anode catalytic layer are hot-pressed and transferred to the proton exchange membrane to obtain a membrane electrode.

[0011] In one or more embodiments, the cathode inner catalyst layer slurry comprises a low specific surface area platinum-carbon catalyst, resin, deionized water, and organic solvent; The cathode outer catalyst layer slurry includes a high specific surface area platinum-carbon catalyst, resin, deionized water, and organic solvent; The resin includes one or more of DuPont Nafion solution, Aquivion D72-25BS resin solution and Aquivion D79-25BS resin solution; The organic solvent includes one or more of n-propanol, isopropanol, ethanol, glycerol, and 1,2-propanediol; The ratio (I / C) of the resin in the slurry within the inner catalyst layer of the cathode to the carbon in the low specific surface area platinum-carbon catalyst is 0.8~1.1, and the mass ratio of the deionized water to the organic solvent is (5~9):(1~5). The ratio (I / C) of the resin in the slurry of the cathode outer catalyst layer to the carbon in the high specific surface area platinum carbon catalyst is 0.6~0.9, and the mass ratio of the deionized water and the organic solvent is (5~9):(1~5).

[0012] In one or more embodiments, the method for preparing the cathode inner catalyst layer slurry includes: Deionized water was slowly added to the low specific surface area platinum-carbon catalyst. After ultrasonic stirring for 5-10 minutes, resin solution and organic solvent were added in sequence, mixed evenly, and ultrasonically stirred for 1 hour. Then, the mixture was transferred to a ball mill jar and ball-milled for 12 hours to obtain the slurry of the inner catalyst layer of the cathode. The preparation methods of the cathode outer catalyst layer slurry include: Deionized water was slowly added to the high specific surface area platinum-carbon catalyst. After ultrasonic stirring for 5-10 minutes, resin solution and organic solvent were added in sequence, mixed evenly, and ultrasonically stirred for 1 hour. Then, the mixture was transferred to a ball mill jar and ball-milled for 12 hours to obtain the cathode outer catalyst layer slurry.

[0013] In one or more embodiments, the zirconium beads used in the ball mill have a diameter of 5 mm to 10 mm and a filling volume of 30-35% of the total volume.

[0014] In one or more embodiments, the method for preparing the platinum-carbon catalyst includes: The carbon support was dispersed in a solvent, a platinum source solution was added, and the mixture was ultrasonically and sheared to disperse it evenly. Alkali solution was added dropwise until the pH of the solution was 13. The mixed solution was placed in a microwave oven for reaction. After cooling, acid solution was added dropwise until the pH of the solution was 1. The product was filtered and washed until neutral, and then vacuum dried to obtain the platinum-carbon catalyst. The platinum content of the platinum-carbon catalyst is 50% to 70%. When the platinum-carbon catalyst is a low specific surface area platinum-carbon catalyst, it includes Lion EC300J, Cabot VXC-72R or Cabot FCX800; When the platinum-carbon catalyst is a high specific surface area platinum-carbon catalyst, the carbon support includes mesoporous carbon, Lion EC600JD, or Cabot BP2000.

[0015] In one or more embodiments, the platinum source comprises any one or a combination of at least two of chloroplatinic acid, platinum chloride, platinum acetylacetonate, or organic platinum salts; the mass fraction of the platinum source solution is 2%-5%. The alkaline solution is a sodium hydroxide solution or a sodium carbonate solution, and the mass fraction of the alkaline solution is 5% to 15%. The solvent is ethylene glycol or methanol; The ratio of carbon support to solvent is 0.3-300:150-7500; The acid solution is a hydrochloric acid, nitric acid, or sulfuric acid solution, and the mass fraction of the acid solution is 5% to 15%. The ultrasonic time is 30-40 minutes, the shearing speed is 2000-5000 rpm, and the shearing time is 1-1.5 hours. The microwave duration is 80s~120s, and the power is 800W~1000W.

[0016] In one or more embodiments, the coating method is any one of scraping, spraying, or slot coating; The platinum loading of the cathode inner catalyst layer slurry coated on the surface of the proton exchange membrane is 0.1 mg / cm². 2 ~0.3mg / cm 2 ; The platinum loading of the outer catalyst layer slurry coated on the inner catalyst layer surface of the cathode is 0.1 mg / cm². 2 ~0.3mg / cm 2 ; The gradient temperature drying process is divided into two stages. The first stage drying temperature is 40°C. o C~70 o C, the drying time is 10-20 minutes, and the second stage drying temperature is 90 degrees Celsius. o C~130 o C, drying time is 20min~30min; In 130 o C~160 o Heat transfer is performed at 0.2MPa~1MPa.

[0017] Furthermore, the platinum loading in the inner catalyst layer of the cathode is preferably 0.2 mg / cm³. 2 ~0.25mg / cm 2 ; The platinum loading of the outer catalyst layer of the cathode is preferably 0.05 mg / cm³. 2 ~0.1mg / cm2 ; The total platinum loading in the cathode catalyst layer, which consists of an inner cathode catalyst layer and an outer cathode catalyst layer, is preferably 0.3 mg / cm³. 2 .

[0018] In a third aspect, the present invention also provides the application of the membrane electrode of the Murray-type porous cathode catalyst layer described in the first aspect or the membrane electrode of the Murray-type porous cathode catalyst layer prepared by the preparation method described in the second aspect in a proton exchange membrane fuel cell.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) Based on the general Murray theorem, the present invention designs and optimizes the pore structure of the catalyst layer, and combines the characteristics of the platinum-carbon catalyst itself to design and prepare a membrane electrode with a Murray-type pore catalyst layer. On the side close to the proton exchange membrane, the inner catalytic layer of the cathode is prepared by using a low specific surface area platinum-carbon catalyst and the outer catalytic layer of the cathode is prepared by using a high specific surface area platinum-carbon catalyst. The pore size structure of the cathode catalyst layer increases from the inside to the outside and also exhibits the characteristics of the Murray-type pore structure. The micropore-mesopore-macropore three-level structure designed based on Murray's law can effectively shorten the transport path of substances from the outside to the inside of the substances, reduce the transport time and resistance, and significantly improve the transport efficiency, thereby improving the catalytic efficiency. The outer macropores allow the reactants to quickly reach the three-phase point through the pore structure to participate in the chemical reaction, improving the electrochemical performance. The mesopores at the middle junction play a transition role and improve the transport efficiency. The inner micropores ensure that the catalyst layer can still maintain wettability even under low humidity conditions, preventing problems such as increased membrane resistance and performance degradation caused by low humidity. At the same time, it avoids the addition of pore-forming agents or other substances, which not only solves the problem of poisoning of membrane electrodes caused by the introduction of impurity ions, but also improves the problems of low transport efficiency and performance degradation under low humidity conditions caused by the single pore structure of traditional catalyst layers.

[0020] (2) In the preparation method of the present invention, firstly, different carbon supports are screened and platinum-carbon catalysts with different specific surface areas and pore structures are prepared according to the characteristics of the carbon supports; secondly, considering that the reaction rate of the catalytic reaction is different at different positions of the catalyst layer, the inner catalyst layer slurry is selected with a higher I / C to reduce the interfacial resistance and ensure that the proton transport proceeds quickly, while the outer catalyst layer slurry is selected with a lower I / C to slow down the oxygen transport resistance; finally, the thickness of the catalyst layer is controlled by the platinum loading, thereby controlling the porosity, pore volume and specific surface area of ​​the inner and outer layers, ensuring that a three-level structure of micropore-mesopore-macropore is prepared, and realizing the Murray-type pore structure of the cathode catalyst layer.

[0021] (3) The present invention enables oxygen to be delivered more evenly to the surface of platinum-carbon catalyst particles through the design of the Murray-type porous catalyst layer, thereby maximizing the utilization efficiency of Pt / C catalyst, which helps to reduce Pt loading and lower battery cost.

[0022] (4) In this invention, different platinum carbon catalysts with different characteristics can be used to customize the catalyst layer structure with different porosities to adapt to different humidity environments. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 This is a schematic diagram of the membrane electrode structure of the Murray-type porous cathode catalyst layer of the present invention; Figure 2 This is a conceptual schematic diagram of the cathode catalyst layer with a Murray-type pore structure according to the present invention; Figure 3 This is the micro-mesoporous pore structure distribution curve of the Murray-type porous cathode catalytic layer membrane electrode obtained by nitrogen adsorption method in Example 2. Figure 4 This is the meso-macropore structure distribution curve of the Murray-type porous cathode catalytic layer film electrode obtained by mercury porosimetry in Example 2. Figure 5 The BET test diagrams of the cathode catalyst layers provided in Example 2, Comparative Example 1, and Comparative Example 2 are shown. Figure 6 This is a SEM cross-sectional view of the membrane electrode of the Murray-type porous cathode catalyst layer provided in Example 2. Figure 7 This is a Pt elemental distribution diagram of the membrane electrode of the Murray-type porous cathode catalytic layer provided in Example 2; Figure 8 This is a diagram showing the number of pores in the Murray-type porous cathode catalyst layer provided in Example 2. Figure 9 SEM cross-sectional view of the membrane electrode provided for Comparative Example 3; Figure 10 SEM cross-sectional view of the membrane electrode provided for Comparative Example 4; Figure 11 The pore size distribution curve of the membrane electrode provided for this Comparative Example 5; Figure 12 The membrane electrodes of Examples 2, 3, 4, and 5 were subjected to a temperature of 70°C. o Polarization curves under C-100%RH conditions; Figure 13 The membrane electrodes provided for Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 were subjected to a temperature of 40°C. o Polarization curves under C-20%RH conditions. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] Explanation of related terms CCM: refers to the catalyst / proton exchange membrane module, which is prepared by coating fuel cell catalysts on both sides of the proton exchange membrane surface. It is the site where the fuel cell performs a chemical reaction to convert chemical energy into electrical energy.

[0028] CCL: Cathode catalyst layer.

[0029] PEM: Proton Exchange Membrane (PEM).

[0030] GDL: The gas diffusion layer plays an important role in fuel cells by supporting the catalyst layer, collecting current, conducting gas, and expelling water, a product of the reaction. Commonly used gas diffusion layer materials are carbon materials such as carbon fiber paper and carbon fiber woven fabric.

[0031] Murray's Law states that for hierarchical porous materials, the sum of the squares or cubes of the radii of different levels of pores is equal. During material transport, the hierarchical structure that conforms to Murray's Law has the least resistance, while the resistance increases the further it deviates from Murray's Law.

[0032] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0033] Example 1 Preparation of a low specific surface area platinum-carbon catalyst: Weigh 3g of Lion EC300J and add 5L of ethylene glycol as a dispersant. Stir for 30min and then sonicate for 30min to uniformly disperse and emulsify the carbon support in ethylene glycol. Add 400g of chloroplatinic acid solution (mass fraction of 5%) and place it in an ultrasonic shearing machine. First, sonicate for 30min, then shear at 3000rpm for 1h. Add 1M NaOH solution dropwise to make the pH value 13. Place the mixed solution in a microwave oven for reaction at a microwave power of 900W for 80s. After cooling, add 10% hydrochloric acid dropwise until the pH of the solution is 1. Filter and wash the product until the filtrate is neutral. After vacuum drying, a low specific surface area Pt / C catalyst with a Pt loading of 60% is obtained.

[0034] Preparation of a high specific surface area platinum-carbon catalyst: Weigh 3g of mesoporous carbon and add 5L of ethylene glycol as a dispersant. Stir for 30min and then sonicate for 30min to ensure uniform dispersion and emulsification of the carbon support in ethylene glycol. Add 400g of chloroplatinic acid solution (mass fraction of 5%) and place it in an ultrasonic shearing machine. First, sonicate for 30min, then shear at 3000rpm for 1h. Add 1M NaOH solution dropwise to adjust the pH to 13. Place the mixed solution in a microwave oven for reaction at 900W for 80s. After cooling, add 10% hydrochloric acid dropwise until the pH of the solution is 1. Filter and wash the product until the filtrate is neutral. After vacuum drying, a high specific surface area Pt / C catalyst with a Pt loading of 60% is obtained.

[0035] The following examples and comparative examples use the low specific surface area platinum-carbon catalyst and the high specific surface area platinum-carbon catalyst prepared in Example 1.

[0036] Example 2 Fabrication of a membrane electrode with a Murray-type porous cathode catalytic layer: 25.38g of deionized water was slowly added to 5g of low specific surface area Pt / C catalyst. After ultrasonic stirring for 5min, 17g of Nafion 10% membrane solution, 5.44g of n-propanol and 5.44g of 1,2-propanediol were added in sequence to prepare a catalyst slurry. The catalyst slurry was stirred and ultrasonicated for 1h and ball-milled for 12h to obtain the inner catalyst layer slurry of the cathode. 38.25g of deionized water was slowly added to 5g of high specific surface area Pt / C catalyst. After ultrasonic stirring for 5min, 17g of Nafion 10% membrane solution and 6.75g of 1,2-propanediol were added in sequence to prepare a catalyst slurry. The catalyst slurry was stirred and ultrasonicated for 1h and ball-milled for 12h to obtain the cathode outer catalyst layer slurry. The proton exchange membrane was adsorbed onto the vacuum adsorption stage, and the slurry of the inner catalyst layer of the cathode was coated on the surface of the proton exchange membrane until the Pt loading was 0.225 mg / cm³. 2The first stage of drying temperature is 50 degrees Celsius. o C, the drying time is 15 minutes, and the second stage drying temperature is 90 degrees Celsius. o C. The drying time is 25 min. After drying, the inner catalyst layer of the cathode is obtained. The outer catalyst layer slurry is then sprayed onto the surface of the inner catalyst layer until the total Pt loading of the cathode is 0.3 mg / cm³. 2 The first stage of drying temperature is 50 degrees Celsius. o C, the drying time is 15 minutes, and the second stage drying temperature is 90 degrees Celsius. o C, the drying time is 25 min, and after drying, the Murray-type porous cathode catalyst layer CCL-1 is obtained; The catalyst used in the anode catalyst layer is a commercial Pt / C catalyst, with an anode loading of 0.05 mg / cm³. 2 The Murray-type porous cathode catalyst layer and the anode were hot-pressed together at 140°C and 1 MPa pressure to obtain the membrane electrode CCM-1.

[0037] Example 3 Fabrication of a membrane electrode with a Murray-type porous cathode catalytic layer: 25.12g of deionized water was slowly added to 5g of low specific surface area Pt / C catalyst. After ultrasonic stirring for 5min, 18g of Nafion 10% membrane solution, 3.14g of n-propanol and 3.14g of 1,2-propanediol were added in sequence to prepare a catalyst slurry. The catalyst slurry was stirred and ultrasonicated for 1h and ball-milled for 12h to obtain the inner catalyst layer slurry of the cathode. 38.25g of deionized water was slowly added to 5g of high specific surface area Pt / C catalyst. After ultrasonic stirring for 5min, 17g of Nafion 10% membrane solution and 6.75g of 1,2-propanediol were added in sequence to prepare a catalyst slurry. The catalyst slurry was stirred and ultrasonicated for 1h and ball-milled for 12h to obtain the cathode outer catalyst layer slurry. The proton exchange membrane was adsorbed onto the vacuum adsorption stage, and the slurry of the inner catalyst layer of the cathode was coated on the surface of the proton exchange membrane until the Pt loading was 0.225 mg / cm³. 2 The first stage of drying temperature is 50 degrees Celsius. o C, the drying time is 15 minutes, and the second stage drying temperature is 90 degrees Celsius. o C. The drying time is 25 min. After drying, the inner catalyst layer of the cathode is obtained. The outer catalyst layer slurry is then coated onto the surface of the inner catalyst layer until the total Pt loading of the cathode is 0.3 mg / cm³. 2 The first stage of drying temperature is 50 degrees Celsius. o C, the drying time is 15 minutes, and the second stage drying temperature is 90 degrees Celsius. o C, the drying time is 25 min, and after drying, a Murray-type porous cathode catalyst layer is obtained; The catalyst used in the anode catalyst layer is a commercial Pt / C catalyst, with an anode loading of 0.05 mg / cm³. 2 The Murray-type porous cathode catalyst layer and the anode were hot-pressed together at 140°C and 1 MPa pressure to obtain the membrane electrode.

[0038] Figure 3 This is the micro-mesoporous pore structure distribution curve of the Murray-type porous cathode catalytic layer membrane electrode obtained by nitrogen adsorption method in Example 2. Figure 4 This is a mesopore-macropore pore structure distribution curve of the Murray-type porous cathode catalytic layer membrane electrode, measured by mercury porosimetry, as provided in Example 2. The data shows that CCM-1 contains macropores with an average diameter of 87 nm, mesopores of 6.8 nm, and micropores of 0.4 nm.

[0039] Figure 6 This is a SEM cross-sectional view of the membrane electrode of the Murray-type porous cathode catalyst layer provided in Example 2. Figure 7 The Pt elemental distribution diagram is shown for the membrane electrode of the Murray-type porous cathode catalytic layer provided in Example 2. Figure 8 This is a diagram showing the number of pores in the Murray-type porous cathode catalyst layer provided in Example 2. Figure 6 , Figure 7 It can be seen that the cathode catalyst layer thickness is approximately 13 μm. The catalyst layer near the PEM side is denser, with smaller pores and a higher concentration of Pt; the catalyst layer near the GDL side is looser, with larger pores and a lower concentration of Pt. Figure 8 A counting analysis of the pore structure revealed approximately 260 mesopores cross-linked with macropores and approximately 290 micropores cross-linked with mesopores. 43.5 2 ≈3.4 2 *140, 3.4 2 ≈0.2 2 *290, which proves that the pore structure of this catalyst layer conforms to the characteristics of Murray's theorem.

[0040] In addition, since the pore size and number of pores in a material affect its specific surface area, different cathode catalyst layers were prepared to better understand the physical parameters of the catalyst layer, and the specific surface area information of the catalyst layer was tested and compared.

[0041] Comparative Example 1 Comparative Example 1 used an inner catalyst layer slurry to prepare a cathode with a loading of 0.225 mg / cm². 2 Cathode catalyst layer CCL-2; Comparative Example 2 Comparative Example 2 used an external catalyst layer slurry to prepare a cathode with a loading of 0.075 mg / cm². 2 Cathode catalyst layer CCL-3.

[0042] Figure 5 Table 1 shows the BET test results of the cathode catalyst layers provided in Example 2, Comparative Example 1, and Comparative Example 2; Table 1 shows the BET data results of the cathode catalyst layers provided in Example 2, Comparative Example 1, and Comparative Example 2. Figure 5 As can be seen from Table 1, the specific surface area of ​​CCL-1 is the sum of the specific surface areas of CCL-2 and CCL-3, and the specific surface areas of CCL-2 and CCL-3 are approximately equal, which further confirms that the pore structure of the prepared catalyst layer conforms to the Murray theorem.

[0043] Table 1 BET data for different cathode catalyst layers

[0044] Comparative Example 3 Compared to Example 2, the cathode loading prepared using the cathode inner catalyst layer slurry was 0.3 mg / cm². 2 The catalyst layer and the remaining steps are the same as in Example 2, to obtain the membrane electrode CCM-2.

[0045] Figure 9 The cross-sectional morphology of the non-Murray porous membrane electrode CCM-2 provided in Comparative Example 3 shows that the cathode catalyst layer does not exhibit delamination, and the pores are relatively uniform and dense.

[0046] Comparative Example 4 Compared to Example 2, the cathode loading was 0.3 mg / cm² prepared using an external catalyst layer slurry. 2 The catalyst layer and the remaining steps are the same as in Example 2, to obtain the membrane electrode CCM-3.

[0047] Figure 10 The cross-sectional morphology of the non-Murray porous membrane electrode CCM-3 provided in Comparative Example 4 shows that the cathode catalyst layer does not exhibit delamination and has a relatively large pore size.

[0048] Comparative Example 5 Compared to Example 2, the Pt loading of the cathode inner catalyst layer slurry in this comparative example is 0.15 mg / cm³. 2 The Pt loading of the cathode outer catalyst layer slurry is 0.15 mg / cm³. 2 The remaining steps are the same as in Example 2, and the membrane electrode CCM-4 is obtained.

[0049] Figure 11 The pore size distribution curve of the non-Murray porous membrane electrode CCM-4 provided in Comparative Example 5 is compared with that of this example. Figure 4 As can be seen, compared with the Murray-type porous membrane electrode, its pore size distribution curve is significantly different, with a significant increase in the proportion of macropores and a decrease in the number of micropores, and no peak in the 50-1000nm range.

[0050] Figure 12The membrane electrodes of Examples 2, 3, 4, and 5 were subjected to a temperature of 70°C. o Polarization curves under C-100%RH conditions; Figure 13 The membrane electrodes provided for Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 were subjected to a temperature of 40°C. o Polarization curves under C-20%RH conditions. From... Figure 12 and Figure 13 It can be seen that at 70 o Under C-100%RH conditions, CCM-1, CCM-2, CCM-3, and CCM-4 at 2A / cm 2 The corresponding performance values ​​are 0.663V, 0.652V, 0.643V, and 0.657V respectively; while at 40 o Under C-20%RH conditions, CCM-1, CCM-2, CCM-3, and CCM-4 at 2A / cm 2 The corresponding performance values ​​are 0.609V, 0.506V, 0.439V, and 0.441V, respectively. This comparison shows that the Murray porous catalyst layer design not only improves the single-cell performance of the membrane electrode under high humidity conditions but also reduces the membrane electrode's dependence on humidity.

[0051] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A membrane electrode with a Murray-type porous cathode catalytic layer, characterized in that, It includes a proton exchange membrane and an anode catalyst layer and a cathode catalyst layer respectively disposed on both sides of the proton exchange membrane; wherein, the cathode catalyst layer includes an inner cathode catalyst layer and an outer cathode catalyst layer disposed sequentially along the surface of the proton exchange membrane; The cathode catalyst layer has a micropore-mesopore-macropore structure, wherein the micropores are 0.1-2 nm, the mesopores are 2-50 nm, and the macropores are 50-7000 nm. The diameters and proportions of the macropores, micropores, and mesopores conform to Murray's Law.

2. The membrane electrode of the Murray-type porous cathode catalytic layer as described in claim 1, characterized in that, The ratio (I / C) of the resin in the slurry within the cathode inner catalyst layer to the carbon in the low specific surface area platinum-carbon catalyst is 0.8~1.1, and the platinum loading is 0.1 mg / cm³. 2 ~0.3mg / cm 2 The preferred platinum loading is 0.2 mg / cm³. 2 ~0.25mg / cm 2 ; The ratio (I / C) of the resin in the slurry of the cathode outer catalyst layer to the carbon in the high specific surface area platinum-carbon catalyst is 0.6~0.9, and the platinum loading is 0.1 mg / cm³. 2 ~0.3mg / cm 2 The preferred platinum loading is 0.05 mg / cm³. 2 ~0.1mg / cm 2 .

3. A method for preparing a membrane electrode with a Murray-type porous cathode catalytic layer as described in any one of claims 1-2, characterized in that, include: Provides proton exchange membranes and anode catalyst layers; A cathode inner catalyst layer slurry is provided, and the cathode inner catalyst layer slurry is coated on the surface of the proton exchange membrane and dried by gradient heating to obtain the cathode inner catalyst layer. A cathode outer catalyst layer slurry is provided, and the cathode outer catalyst layer slurry is coated on the surface of the cathode inner catalyst layer. The slurry is then dried by gradient heating to obtain the cathode outer catalyst layer. The cathode inner catalyst layer and the cathode outer catalyst layer constitute a Murray-type porous cathode catalyst layer. The Murray-type porous cathode catalytic layer and the anode catalytic layer are hot-pressed and transferred to the proton exchange membrane to obtain a membrane electrode.

4. The preparation method according to claim 3, characterized in that, The cathode inner catalyst layer slurry includes a low specific surface area platinum-carbon catalyst, resin, deionized water, and organic solvent; The cathode outer catalyst layer slurry includes a high specific surface area platinum-carbon catalyst, resin, deionized water, and organic solvent; The resin includes one or more of DuPont Nafion solution, Aquivion D72-25BS resin solution and Aquivion D79-25BS resin solution; The organic solvent includes one or more of n-propanol, isopropanol, ethanol, glycerol, and 1,2-propanediol; The ratio (I / C) of the resin in the slurry within the inner catalyst layer of the cathode to the carbon in the low specific surface area platinum-carbon catalyst is 0.8~1.1, and the mass ratio of the deionized water to the organic solvent is (5~9):(1~5). The ratio (I / C) of the resin in the slurry of the cathode outer catalyst layer to the carbon in the high specific surface area platinum carbon catalyst is 0.6~0.9, and the mass ratio of the deionized water and the organic solvent is (5~9):(1~5).

5. The preparation method according to claim 4, characterized in that, The preparation methods of the cathode inner catalyst layer slurry include: Deionized water was slowly added to the low specific surface area platinum-carbon catalyst. After ultrasonic stirring for 5-10 minutes, resin solution and organic solvent were added in sequence, mixed evenly, and ultrasonically stirred for 1 hour. Then, the mixture was transferred to a ball mill jar and ball-milled for 12 hours to obtain the slurry of the inner catalyst layer of the cathode. The preparation methods of the cathode outer catalyst layer slurry include: Deionized water was slowly added to the high specific surface area platinum-carbon catalyst. After ultrasonic stirring for 5-10 minutes, resin solution and organic solvent were added in sequence, mixed evenly, and ultrasonically stirred for 1 hour. Then, the mixture was transferred to a ball mill jar and ball-milled for 12 hours to obtain the cathode outer catalyst layer slurry.

6. The preparation method according to claim 5, characterized in that, The zirconium beads used in the ball mill have a diameter of 5mm to 10mm and a filling volume of 30-35% of the total volume.

7. The preparation method according to claim 4, characterized in that, The preparation method of the platinum-carbon catalyst includes: The carbon support was dispersed in a solvent, a platinum source solution was added, and the mixture was ultrasonically and sheared to disperse it evenly. Alkali solution was added dropwise until the pH of the solution was 12-13. The mixture was placed in a microwave oven for reaction. After cooling, acid solution was added dropwise until the pH of the solution was 1-2. The product was filtered and washed until neutral, and then vacuum dried to obtain the platinum-carbon catalyst. When the platinum-carbon catalyst is a low specific surface area platinum-carbon catalyst, it includes Lion EC300J, Cabot VXC-72R or Cabot FCX800; When the platinum-carbon catalyst is a high specific surface area platinum-carbon catalyst, the carbon includes mesoporous carbon, Lion EC600JD, or Cabot BP2000.

8. The preparation method according to claim 7, characterized in that, The platinum source includes any one or a combination of at least two of chloroplatinic acid, platinum chloride, platinum acetylacetonate, or organic platinum salts; the mass fraction of the platinum source solution is 2%-5%; The alkaline solution is a sodium hydroxide solution or a sodium carbonate solution, and the mass fraction of the alkaline solution is 5% to 15%. The solvent is ethylene glycol or methanol; The ratio of carbon support to solvent is 0.3-300:150-750; The acid solution is a hydrochloric acid, nitric acid, or sulfuric acid solution, and the mass fraction of the acid solution is 5% to 15%. The ultrasonic time is 30-40 minutes, the shearing speed is 2000-5000 rpm, and the shearing time is 1-1.5 hours. The microwave duration is 80s~120s, and the power is 800W~1000W.

9. The preparation method according to claim 3, characterized in that, The coating method is any one of scraping, spraying, or slot coating; The platinum loading of the cathode inner catalyst layer slurry coated on the surface of the proton exchange membrane is 0.1 mg / cm². 2 ~0.3mg / cm 2 ; The platinum loading of the outer catalyst layer slurry coated on the inner catalyst layer surface of the cathode is 0.1 mg / cm². 2 ~0.3mg / cm 2 ; The gradient temperature drying process is divided into two stages. The first stage drying temperature is 40°C. o C~70 o C, the drying time is 10-20 minutes, and the second stage drying temperature is 90 degrees Celsius. o C~130 o C, drying time is 20min~30min; In 130 o C~160 o Heat transfer is performed at 0.2MPa~1MPa.

10. The application of the membrane electrode of the Murray-type porous cathode catalyst layer according to claim 1 or 2, or the membrane electrode of the Murray-type porous cathode catalyst layer prepared by the preparation method according to any one of claims 3 to 9, in a proton exchange membrane fuel cell.

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