Membrane electrode catalyst layer and preparation method and application thereof

Abstract

The invention provides a membrane electrode catalyst layer and a preparation method and application thereof, and belongs to the technical field of proton exchange membrane fuel cells. The content and particle size of the noble metal in the catalyst layer of the membrane electrode are continuously distributed in the thickness direction of the catalyst layer, so that the utilization rate of the noble metal can be fully improved, the entry of reaction raw materials and the discharge of products are effectively promoted, the efficiency of the catalyst layer and the durability of the noble metal are improved, and the dosage of the noble metal is effectively reduced; meanwhile, good catalytic performance is kept; the manufacturing cost of the catalyst layer is reduced, and industrial application of the catalyst layer is facilitated.

Description

A membrane electrode catalytic layer, its preparation method and application Technical Field

[0001] This disclosure relates to the field of proton exchange membrane fuel cell technology, specifically to a membrane electrode catalytic layer, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) possess advantages such as high energy density, high conversion efficiency, and environmental friendliness, and have been widely promoted and demonstrated in transportation and other fields in recent years. However, high cost remains a bottleneck for the large-scale commercialization of PEMFCs. It is estimated that, with an annual production of 500,000 fuel cell stacks, platinum-based catalysts will account for 42% of the stack cost. Therefore, improving the utilization rate of platinum-based catalysts and reducing the amount of platinum used in the membrane electrode assembly (MEA) to promote the mass application of fuel cells is urgently needed.

[0003] The membrane electrode assembly (MEA) is a core component of a fuel cell, serving as its "active center," "lifespan center," and "cost center." The catalyst layer, composed of catalysts and ion exchange resins, is the site of electrochemical reactions. Conventional MEA fabrication processes include catalyst preparation, catalyst slurry preparation, coating, and encapsulation, typically resulting in a MEA with noble metals randomly distributed within the catalyst layer. This process is crucial regardless of the hydrogenation reaction occurring at the anode (2H₂→4H₂). + +4e - ), or the oxygen reduction reaction (O2 + 4H) that occurs at the cathode. + +4e - The reaction →2H₂O involves proton transport, and the conduction of protons in the catalyst layer and proton exchange membrane requires the assistance of sulfonate groups or liquid water, making it a rate-determining step in the electrochemical reaction. For the cathode catalyst layer, protons transferred from the anode via the proton exchange membrane reach the cathode catalyst layer and are reduced to water upon contact with the platinum-based catalyst and oxygen. Therefore, the platinum-based catalyst near the proton exchange membrane has a higher utilization rate. Consequently, in the direction perpendicular to the cathode catalyst layer, the noble metal loading exhibits a gradient distribution that gradually decreases from the side closest to the proton exchange membrane outwards, effectively improving Pt utilization.

[0004] Existing techniques for preparing membrane electrodes with gradient noble metal distribution typically involve layered coating. Chinese patent CN108063267B, by altering at least one condition in the composition, content, and mixing process of the catalyst slurry, employs a cone-spraying mode of electrostatic spraying to sequentially form a multilayered catalyst layer with progressively varying porosity. PCT patent PCT / US2010 / 042451 discloses a catalyst layer with gradient porosity and catalyst density, achieved by depositing different catalyst slurries on multiple layers of Buck paper to achieve gradient changes in pore size and catalyst nanoparticle distribution. However, the noble metal concentration in the membrane electrode prepared by the aforementioned layered coating method is not continuously distributed. Therefore, how to prepare a membrane electrode with a continuously distributed noble metal concentration is a pressing problem that needs to be solved. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a membrane electrode catalytic layer, its preparation method and application.

[0006] To achieve the above objectives, the technical solution adopted in this disclosure is as follows: In a first aspect, a membrane electrode catalytic layer is provided, wherein the catalytic layer includes a first surface and a second surface along its thickness direction;

[0007] The catalyst layer includes a support material and noble metal particles distributed in the support material. The content and particle size of the noble metal particles decrease continuously from the first surface to the second surface. The decrease in the content of noble metal particles at the second surface is ≥50%, and the decrease in the particle size of noble metal particles at the second surface is ≥30%.

[0008] The average content of the precious metal particles is 0.01-0.2 mg / cm³. 2 The average particle size of the precious metal particles is 1-5 nm.

[0009] Secondly, a method for preparing the aforementioned membrane electrode catalytic layer is provided, comprising the following steps:

[0010] The carbon carrier is mixed evenly with the binder and solvent to obtain a carbon slurry;

[0011] The carbon slurry is applied to the surface of the substrate material, and then dried and / or calcined to obtain a first carbon layer.

[0012] The first carbon layer is pretreated with a gas at a temperature of 30-450℃ to obtain a second carbon layer; wherein the gas is one of ozone, plasma nitrogen, plasma ammonia and plasma oxygen, the gas flow rate is 0.5-2L / min, and the pretreatment temperature is 30-450℃.

[0013] Noble metal particles are deposited onto the second carbon layer using atomic layer deposition.

[0014] An ion exchange resin is applied to obtain the membrane electrode catalytic layer.

[0015] Thirdly, a membrane electrode is provided, comprising a cathode catalytic layer, an anode catalytic layer, a cathode gas diffusion layer, an anode gas diffusion layer, and a proton exchange membrane disposed between the cathode catalytic layer and the anode catalytic layer;

[0016] Wherein, at least one of the cathode catalyst layer or the anode catalyst layer includes the membrane electrode catalyst layer;

[0017] The cathode gas diffusion layer and the cathode catalyst layer away from the proton exchange membrane are in surface contact; the anode gas diffusion layer and the anode catalyst layer away from the proton exchange membrane are in surface contact.

[0018] Fourthly, a fuel cell is provided, the fuel cell including the membrane electrode assembly described above.

[0019] Compared with the prior art, the beneficial effects of this disclosure are as follows: the content and particle size of noble metals in the membrane electrode catalytic layer of this disclosure are distributed in a continuous gradient in the thickness direction of the catalytic layer, which can fully improve the utilization rate of noble metals, effectively promote the entry of reaction raw materials and the discharge of products, improve the efficiency and durability of the catalytic layer and the noble metals, and effectively reduce the amount of noble metals used while maintaining good catalytic performance; reduce the manufacturing cost of the catalytic layer and facilitate the industrial application of the catalytic layer. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the structure of the membrane electrode of this disclosure, wherein 100: proton exchange membrane, 200: cathode catalytic layer, 400: anode catalytic layer, 201 and 401 are noble metal nanoparticles, 300: cathode gas diffusion layer, and 500: anode gas diffusion layer.

[0021] Figure 2 is a schematic diagram of the preparation process of the membrane electrode of this disclosure. Detailed Implementation

[0022] To facilitate understanding of this disclosure, a more complete description will be provided below. However, this disclosure may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0023] As used in this article:

[0024] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0025] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0026] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0027] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0028] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0029] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0030] In a first aspect, a membrane electrode catalytic layer is provided, the catalytic layer including a first surface and a second surface along its thickness direction, the first surface being close to a proton exchange membrane;

[0031] The catalyst layer includes a support material and noble metal particles distributed in the support material. The content and particle size of the noble metal particles decrease continuously from the first surface to the second surface. The decrease in the content of noble metal particles at the second surface is ≥50%, and the decrease in the particle size of noble metal particles at the second surface is ≥30%.

[0032] The average content of the precious metal particles is 0.01-0.2 mg / cm³. 2 The average particle size of the precious metal particles is 1-5 nm.

[0033] The content and particle size of noble metal particles in the membrane electrode catalytic layer of this disclosure are distributed in a continuous gradient along the thickness direction of the catalytic layer. This can fully improve the utilization rate of noble metals, effectively promote the entry of reaction raw materials and the discharge of products, improve the efficiency and durability of the catalytic layer, and effectively reduce the amount of noble metals used while maintaining good catalytic performance. It also reduces the manufacturing cost of the catalytic layer and facilitates its industrial application.

[0034] In different embodiments, the reduction in the content of noble metal particles at the second surface is 50-95%, for example, but not limited to 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%.

[0035] In different embodiments, the reduction in particle size of the noble metal particles on the second surface is 30-95%, for example, but not limited to 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%.

[0036] In different embodiments, the average content of precious metal particles can be, but is not limited to, 0.01 mg / cm³. 2 0.03 mg / cm 2 0.05 mg / cm 2 0.08 mg / cm 2 0.1 mg / cm 2 0.12 mg / cm 2 0.14 mg / cm 2 0.16 mg / cm 2 0.18 mg / cm 2 0.2 mg / cm 2 .

[0037] In different embodiments, the average particle size of the noble metal particles can be, but is not limited to, 1nm, 1.2nm, 1.5nm, 1.7nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.3nm, 4.5nm, 4.8nm, or 5nm.

[0038] Specifically, scanning electron microscopy and energy dispersive spectroscopy were used to test the cross-section of the catalyst layer, and the content of noble metal particles was represented by the signal value (au) of noble metal in the thickness direction of the catalyst layer.

[0039] The decrease in the content of precious metal particles at the second surface was calculated using the following formula:

[0040] The decrease in the content of precious metal particles at the second surface = (precious metal signal value (au) at the first surface - precious metal signal value (au) at the second surface) / precious metal signal value (au) at the first surface * 100%.

[0041] Samples were taken from the first and second surfaces of the catalyst layer for transmission electron microscopy (TEM) testing, and the particle size of the noble metal particles was statistically analyzed.

[0042] The reduction in the particle size of the noble metal particles at the second surface is calculated using the following formula:

[0043] The reduction in the particle size of the precious metal particles on the second surface = (the particle size of the precious metal particles on the first surface - the particle size of the precious metal particles on the second surface) / the particle size of the precious metal particles on the first surface * 100%.

[0044] The average content of precious metal particles refers to the mass of precious metal per unit area in the entire catalyst layer, expressed in mg / cm³. 2 The testing method is inductively coupled plasma-emission spectroscopy (ICP-OES);

[0045] The average particle size of precious metal particles refers to the average particle size of precious metal particles in the entire catalyst layer. The test method is as follows: the entire catalyst layer is uniformly dispersed into a slurry, and then a sample is taken for transmission electron microscopy (TEM) testing, and the particle size of the precious metal particles is counted.

[0046] In some embodiments, the precious metal is at least one of platinum, iridium, ruthenium, and palladium.

[0047] In some embodiments, the support material is a carbon support material, and the catalyst layer further includes a binder and an ion exchange resin.

[0048] In some embodiments, the carbon support is at least one of conductive carbon black, activated carbon, and carbon nanotubes.

[0049] Specifically, the specific surface area of ​​the carbon support is 200-1500 m². 2 / g, for example, can be but is not limited to 200m 2 / g、300m 2 / g、400m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g.

[0050] Specifically, with the catalyst layer comprising 100% by mass, the carbon support comprises 50-90% by mass.

[0051] In some embodiments, the adhesive is at least one of polytetrafluoroethylene and polyvinylidene fluoride.

[0052] The binder disclosed herein is non-polar and hydrophobic. On the one hand, the non-polar binder can prevent the polar functional groups in the polar binder from interacting with the noble metal precursor, which would cause the noble metal precursor to preferentially combine with the polar functional groups of the binder, resulting in the agglomeration and growth of noble metal particles during atomic layer deposition. On the other hand, in the catalyst layer, the hydrophobic binder can form hydrophobic channels to avoid water flooding under fuel cell operating conditions.

[0053] Specifically, based on the mass percentage of the catalyst layer being 100%, the mass of the binder is 5-30%, for example, but not limited to 5%, 7%, 10%, 12%, 15%, 17%, 20%, 23%, 25%, 28%, 30%, preferably 10-20%.

[0054] In some embodiments, the ion exchange resin is at least one of a cation exchange resin and anion exchange resin.

[0055] More preferably, the ion exchange resin is a perfluorosulfonic acid resin.

[0056] Secondly, a method for preparing the aforementioned membrane electrode catalytic layer is provided, comprising the following steps:

[0057] The carbon carrier is mixed evenly with the binder and solvent to obtain a carbon slurry;

[0058] The carbon slurry is applied to the surface of the substrate material, and then dried and / or calcined to obtain a first carbon layer.

[0059] The first carbon layer is pretreated with a gas at a temperature of 30-450℃ to obtain a second carbon layer; wherein the gas is one of ozone, plasma nitrogen, plasma ammonia, and plasma oxygen, the gas flow rate is 0.5-2L / min, and the pretreatment temperature is 30-450℃.

[0060] Noble metal particles are deposited onto the second carbon layer using atomic layer deposition.

[0061] An ion exchange resin is applied to obtain the membrane electrode catalytic layer.

[0062] This disclosure involves pretreatment to form free or bound oxygen- or nitrogen-containing functional groups on a first carbon layer. The second carbon layer includes opposing first and second surfaces. The first surface is bonded to the substrate material, and the second surface is located away from the substrate material. By controlling the temperature and flow rate of the pretreatment, the content of oxygen- or nitrogen-containing functional groups on the first and second surfaces is controlled, resulting in a continuous decrease in the number of oxygen- or nitrogen-containing functional groups from the second surface to the first surface. During atomic layer deposition pulse adsorption, the oxygen- or nitrogen-containing functional groups act as active sites, connecting the support and noble metal particles. Furthermore, the bound oxygen- or nitrogen-containing functional groups enhance the stability of the bond between the noble metal particles and the support. Driven by a concentration gradient, the noble metal precursor diffuses from the second surface of the second carbon layer to the first surface, and undergoes chemical adsorption with the active sites on the first and second surfaces and inside the second carbon layer. As a result, the noble metal particles are partially adsorbed in the pores of the second carbon layer, and the noble metal particles tend to have a continuous gradient distribution in terms of particle size and content. This application controls the content and particle size reduction of noble metal particles at the second surface in the catalyst layer, as well as the average content and average particle size of noble metal particles in the catalyst layer, by controlling the content of oxygen- or nitrogen-containing functional groups on the first and second surfaces, and the process conditions of atomic layer deposition, such as the number of cycles, temperature, and pressure.

[0063] In different embodiments, the carbon slurry further includes a pore-forming agent. Adding a pore-forming agent to the carbon slurry can increase the porosity of the second carbon layer, thereby increasing the diffusion rate of the noble metal precursor in the second carbon layer.

[0064] Specifically, the pore-forming agent may be, but is limited to, ammonium oxalate, lithium carbonate, ammonium chloride, ammonium carbonate and ammonium bicarbonate, and methylcellulose.

[0065] In different embodiments, the gas flow rate may be, but is not limited to, 0.5 L / min, 0.7 L / min, 1 L / min, 1.2 L / min, 1.5 L / min, 1.8 L / min, or 2 L / min.

[0066] In different implementations, the pretreatment temperature can be, but is not limited to, 30°C, 50°C, 70°C, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 420°C, or 450°C.

[0067] Specifically, increasing the pretreatment temperature allows for the incorporation of more oxygen- or nitrogen-containing functional groups, while increasing the gas flow rate enables a more uniform longitudinal distribution of functional groups in the second carbon layer.

[0068] Specifically, the types and contents of functional groups on the first or second surface can be tested by infrared spectroscopy.

[0069] Specifically, the membrane electrode catalytic layer includes a second carbon layer and noble metal particles distributed on the surface and pores of the second carbon layer.

[0070] The thickness of the second carbon layer is 1-20 μm; the thickness of the noble metal layer composed of noble metal particles distributed on the surface and in the pores of the second carbon layer is less than the thickness of the second carbon layer.

[0071] In some embodiments, the substrate material is one of carbon fiber paper, carbon fiber cloth, polytetrafluoroethylene film, polyvinylidene fluoride film, polyimide film, polyetheretherketone film, and polyethylene naphthalate film.

[0072] Specifically, the thickness of the substrate material is 100-1000μm, for example, but not limited to 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, and 1000μm.

[0073] The substrate material disclosed herein can withstand the processing temperature of atomic layer deposition and the calcination temperature.

[0074] In some embodiments, the calcination temperature is 120-350°C, for example, but not limited to 120°C, 150°C, 200°C, 250°C, 300°C, and 350°C.

[0075] In some embodiments, the step of depositing noble metal particles onto the second carbon layer by atomic layer deposition is as follows: a noble metal precursor is adsorbed onto the surface and interior of the second carbon layer through the second surface of the second carbon layer, then excess noble metal precursor and byproducts are removed, followed by the introduction of a reaction gas to carry out the reaction, and finally excess reactants and byproducts are removed; wherein, the temperature of atomic layer deposition is 150-300℃ and the pressure is 10Pa-0.2MPa.

[0076] This disclosure further improves the continuous distribution of noble metals in the catalyst layer by controlling the number of atomic layer deposition cycles. During the atomic layer deposition cycle, the noble metal particles deposited in the previous deposition will occupy part of the pores in the second carbon layer, which will increase the resistance of the noble metal precursor to the interior of the second carbon layer. The noble metal precursor tends to be adsorbed at the active sites on the surface of the second carbon layer away from the substrate material and gradually accumulates, improving the continuous distribution of the noble metal precursor in the catalyst layer. Then, under the action of the reaction gas, noble metal particles with a continuous gradient distribution of particle size and content are generated.

[0077] In different embodiments, the temperature for atomic layer deposition can be 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, or 300°C.

[0078] In different implementations, the pressure for atomic layer deposition is 10 Pa, 100 Pa, 300 Pa, 500 Pa, 1 kPa, 2 kPa, 5 kPa, 10 kPa, 50 kPa, 100 kPa, or 200 kPa.

[0079] This disclosure achieves control over the atomic layer deposition process parameters, thereby maintaining the range of noble metal particles with an average content of 0.01-0.2 mg / cm³. 2 The average particle size is 1-5 nm. For example, by controlling the pressure and time of the precursor pulse, the distribution of the precursor from the first surface to the second surface of the second carbon layer can be regulated, thereby controlling the longitudinal gradient distribution of noble metals in the catalyst layer. The average content and average particle size of noble metals can be regulated by controlling the number of cycles; increasing the number of cycles will increase both the average content and average particle size of noble metals.

[0080] In some embodiments, the noble metal precursor is an organoplatinum compound; and / or, the reactant gas is oxygen or ozone.

[0081] Specifically, the organoplatinum compound is one of (trimethyl)methylcyclopentadiene platinum, trimethylcyclopentadiene platinum, and acetylacetonate platinum.

[0082] This disclosure removes excess precious metal precursors, excess reactants, and byproducts by means of carrier gas purging. The carrier gas can be nitrogen, argon, or other gases.

[0083] In some embodiments, the ion exchange resin can be applied by dip coating or spray coating.

[0084] As shown in Figure 1, in a third aspect, a membrane electrode is provided, comprising a cathode catalytic layer (200), an anode catalytic layer (400), a cathode gas diffusion layer (300), an anode gas diffusion layer (500), and a proton exchange membrane (100) disposed between the cathode catalytic layer and the anode catalytic layer;

[0085] Wherein, at least one of the cathode catalyst layer or the anode catalyst layer includes the membrane electrode catalyst layer;

[0086] The cathode gas diffusion layer and the cathode catalyst layer away from the proton exchange membrane are in surface contact; the anode gas diffusion layer and the anode catalyst layer away from the proton exchange membrane are in surface contact.

[0087] The present disclosure does not impose specific limitations on the preparation method of the membrane electrode. Those skilled in the art can prepare the membrane electrode using known methods, such as transfer bonding or direct bonding.

[0088] Specifically, the transfer and bonding steps are as follows:

[0089] A catalytic layer is formed on a transfer substrate, and then hot-pressed onto a proton exchange membrane coated with a noble metal catalyst. The transfer substrate is removed, and then the membrane electrode is formed by pressing it with a gas diffusion layer.

[0090] As shown in Figure 2, the specific steps for direct pressing are as follows:

[0091] An anode catalyst layer is formed on the anode gas diffusion layer to obtain the first component;

[0092] A cathode catalyst layer is formed on the cathode gas diffusion layer to obtain the second component;

[0093] A proton exchange membrane, a first component, and a second component are pressed together to form a membrane electrode, wherein the proton exchange membrane is located between the cathode catalytic layer and the anode catalytic layer.

[0094] Fourthly, a fuel cell is provided, the fuel cell including the membrane electrode assembly described above.

[0095] To further illustrate the present invention, the membrane electrode catalytic layer, membrane electrode, and fuel cell provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0096] The materials used in the embodiments and comparative examples will now be described, but are not limited to the following materials:

[0097] Perfluorosulfonic acid resin: DuPont Nafion D2020.

[0098] The thickness of the catalyst layer in the following examples and comparative examples is the same, which is 8 μm.

[0099] Example 1

[0100] This embodiment provides a method for preparing a membrane electrode, including the following steps:

[0101] Pulping: Pulping with a specific surface area of ​​800 m² 2 / g of conductive carbon black, polytetrafluoroethylene emulsion, and isopropanol / water mixed solvent are placed in a container and mixed evenly to obtain carbon slurry, wherein the mass of polytetrafluoroethylene is 15% of the solid mass.

[0102] Preparation of the first carbon layer: The carbon slurry is sprayed onto the surface of the polyimide film, dried, and then calcined at 300°C for 1 hour to obtain the first carbon layer, wherein the carbon loading is 0.2 mg / cm³. 2 ;

[0103] Preparation of the second carbon layer: The polyimide film containing the first carbon layer is placed in an atomic layer deposition apparatus, oxygen is introduced and the ozone generator is turned on for pretreatment to obtain a second carbon layer with non-uniformly distributed oxygen-containing functional groups. The oxygen flow rate is 1 L / min and the oxygen temperature is 30 °C. After the pretreatment is completed, the ozone generator is turned off.

[0104] Atomic layer deposition: using (trimethyl)methylcyclopentadiene platinum alloy as the noble metal precursor and oxygen as the working gas; the steps of a single atomic layer deposition are as follows:

[0105] (1) Degassing: The polyimide film containing the second carbon layer is placed in an atomic layer deposition equipment, vacuumed to ≤10Pa and heated to 200℃ for degassing treatment;

[0106] (2) Adsorption of precious metal precursors: The atomic layer deposition equipment is heated to 280°C, and then the gas outlet of the reaction chamber is closed. Under the guidance of nitrogen, the precious metal precursors are introduced into the reaction chamber at a flow rate of 20 sccm for pulse adsorption. After the pressure in the reaction chamber rises to 50 Pa, the gas inlet is closed and held for 60 s.

[0107] (3) Carrier gas purging: Nitrogen gas is introduced at a flow rate of 20 sccm and purged for 120 s to remove the noble metal precursors that have not undergone chemical adsorption.

[0108] (4) Working gas pulse: Close the gas outlet of the reaction chamber, introduce oxygen at a flow rate of 20 sccm, and close the inlet after the pressure in the reaction chamber rises to 100 Pa, and maintain this for 60 s;

[0109] (5) Carrier gas purging: Nitrogen gas is introduced at a flow rate of 20 sccm and purged for 120 s to remove excess reactants and byproducts.

[0110] The atomic layer deposition cycle consisted of 10 cycles. After deposition, the resulting product was completely immersed in a 5 wt% perfluorosulfonic acid resin solution for 2 hours at room temperature. After drying, the membrane electrode catalytic layer was obtained. The average content of noble metal particles in the membrane electrode catalytic layer was 0.12 mg / cm³. 2 The average particle size of the precious metal particles is 1.9 nm; the content of precious metal particles at the second surface decreases by 54%; and the particle size of the precious metal particles at the second surface decreases by 42%.

[0111] Preparation of catalyst-coated membrane: The membrane electrode catalytic layer is hot-pressed with a proton exchange membrane pre-coated with a platinum-based catalyst on one side, and the membrane electrode catalytic layer is transferred to the other side of the proton exchange membrane as the cathode catalytic layer to obtain the catalyst-coated membrane;

[0112] Preparation of membrane electrode: Two gas diffusion layers of type SGL 22BB were placed on both sides of the catalyst-coated membrane as the cathode gas diffusion layer and the anode gas diffusion layer, and then pressed together to obtain the membrane electrode.

[0113] Example 2

[0114] This embodiment provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Example 1 only in the temperature of the reaction gas. In this embodiment, the temperature of the oxygen reaction gas is 250°C, and the average content of noble metals in the catalyst layer of the resulting membrane electrode is 0.05 mg / cm³. 2 The average particle size of the precious metal is 1.2 nm; the content of the precious metal at the second surface decreases by 78%; and the particle size of the precious metal at the second surface decreases by 35%.

[0115] Example 3

[0116] This embodiment provides a method for preparing a membrane electrode, which differs from the method in Example 1 only in the type of reactant gas and the atomic layer deposition temperature. In this embodiment, ozone is used as the reactant gas, and the atomic layer deposition temperature is 150°C. The average content of noble metal particles in the resulting membrane electrode catalyst layer is 0.18 mg / cm³. 2 The average particle size of the precious metal particles is 2.2 nm; the content of precious metal particles on the second surface decreases by 62%; and the particle size of the precious metal particles on the second surface decreases by 68%.

[0117] Example 4

[0118] This embodiment provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Embodiment 1 only in that the steps for preparing the second carbon layer are different. In this embodiment, the steps for preparing the second carbon layer are as follows: a polyimide membrane containing a first carbon layer is placed in an atomic layer deposition apparatus, nitrogen gas is introduced and a plasma generator is turned on for pretreatment to obtain a second carbon layer with non-uniformly distributed nitrogen functional groups. The flow rate of nitrogen gas is 1 L / min and the pretreatment temperature is 450 °C.

[0119] The average content of noble metal particles in the obtained membrane electrode catalytic layer is 0.10 mg / cm³. 2 The average particle size of the precious metal particles is 1.8 nm; the content of precious metal particles on the second surface decreases by 57%; and the particle size of the precious metal particles on the second surface decreases by 40%.

[0120] Example 5

[0121] This embodiment provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Example 1 only in the atomic layer deposition process conditions and the number of deposition cycles. In this embodiment, the atomic layer deposition steps are as follows: using (trimethyl)methylcyclopentadiene platinum as the noble metal precursor and oxygen as the working gas; the single atomic layer deposition steps are as follows:

[0122] (1) Degassing: The polyimide film containing the second carbon layer is placed in an atomic layer deposition equipment, vacuumed to ≤10Pa and heated to 200℃ for degassing treatment;

[0123] (2) Adsorption of precious metal precursors: The atomic layer deposition equipment is heated to 280°C, and then the gas outlet of the reaction chamber is closed. Under the guidance of nitrogen, the precious metal precursors are introduced into the reaction chamber at a flow rate of 20 sccm for pulse adsorption. After the pressure in the reaction chamber rises to 100 Pa, the gas inlet is closed and held for 10 s.

[0124] (3) Carrier gas purging: Nitrogen gas is introduced at a flow rate of 20 sccm and purged for 10 s to remove the noble metal precursors that have not undergone chemical adsorption.

[0125] (4) Working gas pulse: Close the gas outlet of the reaction chamber, introduce oxygen at a flow rate of 20 sccm, and close the inlet after the pressure in the reaction chamber rises to 100 Pa, and keep it for 10 s;

[0126] (5) Carrier gas purging: Nitrogen gas is introduced at a flow rate of 20 sccm and purged for 10 s to remove excess reactants and byproducts.

[0127] The atomic layer deposition cycle was 30 cycles. After deposition, the resulting product was completely immersed in a 5 wt% perfluorosulfonic acid resin solution for 2 hours at room temperature, then removed and dried to obtain the membrane electrode catalytic layer. The average content of noble metal particles in the membrane electrode catalytic layer was 0.08 mg / cm³. 2 The average particle size of the precious metal particles is 1.6 nm; the content of precious metal particles at the second surface decreases by 75%; and the particle size of the precious metal particles at the second surface decreases by 48%.

[0128] Example 6

[0129] This embodiment provides a method for preparing a membrane electrode, including the following steps:

[0130] Pulping: Pulping with a specific surface area of ​​800 m² 2 / g of conductive carbon black, polytetrafluoroethylene emulsion, and isopropanol / water mixed solvent are placed in a container and mixed evenly to obtain carbon slurry, wherein the mass of polytetrafluoroethylene is 15% of the solid mass.

[0131] Preparation of the first carbon layer: The carbon slurry is sprayed onto the surface of the gas diffusion layer, dried, and then calcined at 300°C for 1 hour to obtain the first carbon layer, wherein the carbon loading is 0.2 mg / cm³. 2 Among them, the gas diffusion layer is a gas diffusion layer of model SGL 22BB;

[0132] Preparation of the second carbon layer: The gas diffusion layer containing the first carbon layer is placed in an atomic layer deposition device, oxygen is introduced and an ozone generator is turned on for pretreatment to obtain a second carbon layer with non-uniform distribution of oxygen-containing functional groups. The oxygen flow rate is 1 L / min and the oxygen temperature is 30 °C.

[0133] Atomic layer deposition: using (trimethyl)methylcyclopentadiene platinum alloy as the noble metal precursor and oxygen as the working gas; the steps of a single atomic layer deposition are as follows:

[0134] (1) Degassing: The gas diffusion layer containing the second carbon layer is placed in an atomic layer deposition equipment, vacuumed to ≤10Pa and heated to 200℃ for degassing treatment;

[0135] (2) Adsorption of precious metal precursors: The atomic layer deposition equipment is heated to 280°C, and then the gas outlet of the reaction chamber is closed. Under the guidance of nitrogen, the precious metal precursors are introduced into the reaction chamber at a flow rate of 20 sccm for pulse adsorption. After the pressure in the reaction chamber rises to 100 Pa, the gas inlet is closed and held for 60 s.

[0136] (3) Carrier gas purging: Nitrogen gas is introduced at a flow rate of 20 sccm and purged for 120 s to remove the noble metal precursors that have not undergone chemical adsorption.

[0137] (4) Working gas pulse: Close the gas outlet of the reaction chamber, introduce oxygen at a flow rate of 20 sccm, and close the inlet after the pressure in the reaction chamber rises to 100 Pa, and maintain this for 60 s;

[0138] (5) Carrier gas purging: Nitrogen gas is introduced at a flow rate of 20 sccm and purged for 120 s to remove excess reactants and byproducts.

[0139] The atomic layer deposition cycle consisted of 10 cycles. After deposition, the resulting product was completely immersed in a 5 wt% perfluorosulfonic acid resin solution for 2 hours at room temperature. After drying, the membrane electrode catalytic layer was obtained. The average content of noble metal particles in the membrane electrode catalytic layer was 0.12 mg / cm³. 2 The average particle size of the precious metal particles is 1.8 nm; the content of precious metal particles at the second surface decreases by 50%; and the particle size of the precious metal particles at the second surface decreases by 43%.

[0140] Preparation of membrane electrode: The above-mentioned membrane electrode catalytic layer is placed on both sides of the proton exchange membrane and pressed together to obtain the membrane electrode.

[0141] Comparative Example 1

[0142] This comparative example provides a method for preparing a membrane electrode, including the following steps:

[0143] Slurry preparation: The TEC10E50E catalyst (46.5% Pt / C), a 20% perfluorosulfonic acid resin solution, and an isopropanol / water mixed solvent are mixed evenly to obtain a catalyst slurry, wherein the mass of the perfluorosulfonic acid resin is 30% of the solid mass.

[0144] Preparation of the cathode catalyst layer: The catalyst slurry was sprayed onto the surface of the polyimide film and dried to form the cathode catalyst layer, wherein the Pt loading was 0.2 mg / cm³. 2 ;

[0145] Preparation of the anodic catalyst layer: The catalyst slurry is sprayed onto the surface of the polyimide film and dried to form the anodic catalyst layer, wherein the Pt loading is 0.05 mg / cm³. 2 ;

[0146] Preparation of catalyst-coated film: The cathode catalyst layer, the anode catalyst layer and the proton exchange membrane are prepared by hot pressing transfer to obtain the catalyst-coated film;

[0147] Preparation of membrane electrode: Two gas diffusion layers of type SGL 22BB were placed on both sides of the catalyst-coated membrane as the cathode gas diffusion layer and the anode gas diffusion layer, respectively, and then pressed together to obtain the membrane electrode.

[0148] Comparative Example 2

[0149] This comparative example provides a method for preparing a membrane electrode, including the following steps:

[0150] Slurry preparation: The TEC10E30E catalyst (30% Pt / C), a 20% perfluorosulfonic acid resin solution, and an isopropanol / water mixed solvent are mixed evenly to obtain catalyst slurry A, wherein the mass of the perfluorosulfonic acid resin is 10% of the solid mass.

[0151] The TEC10E50E catalyst (46.5% Pt / C), a 20% perfluorosulfonic acid resin solution, and an isopropanol / water mixed solvent were mixed evenly to obtain catalyst slurry B, wherein the mass of the perfluorosulfonic acid resin was 20% of the solid mass.

[0152] Hispec9100 catalyst (60% Pt / C), a 20% perfluorosulfonic acid resin solution, and an isopropanol / water mixed solvent were mixed evenly to obtain catalyst slurry C, wherein the mass of the perfluorosulfonic acid resin was 30% of the solid mass.

[0153] Preparation of the cathode catalyst layer: Catalyst slurry A was sprayed onto the surface of a polyimide film, and after drying, cathode catalyst layer A was formed with a Pt loading of 0.03 mg / cm³. 2 Catalyst slurry B is sprayed onto the surface of cathode catalyst layer A, and after drying, cathode catalyst layer B is formed with a Pt loading of 0.05 mg / cm³. 2 Catalyst slurry C was sprayed onto the surface of the cathode catalyst layer B, and after drying, the cathode catalyst layer C was formed with a Pt loading of 0.12 mg / cm³. 2 The total Pt loading of the cathode catalyst layer is 0.2 mg / cm³. 2 ;

[0154] Preparation of the anodic catalyst layer: Catalyst slurry B was sprayed onto the surface of a polyimide film, and after drying, an anodic catalyst layer was formed, wherein the Pt loading was 0.05 mg / cm³. 2 ;

[0155] Preparation of catalyst-coated film: The cathode catalyst layer, the anode catalyst layer and the proton exchange membrane are prepared by hot pressing transfer to obtain the catalyst-coated film;

[0156] Preparation of membrane electrode: Two gas diffusion layers of type SGL 22BB were placed on both sides of the catalyst-coated membrane as the cathode gas diffusion layer and the anode gas diffusion layer, respectively, and then pressed together to obtain the membrane electrode.

[0157] Comparative Example 3

[0158] This comparative example provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Example 1 only in that: the method for preparing the membrane electrode in this comparative example does not include the step of preparing a second carbon layer, that is, the method for preparing the membrane electrode in this comparative example does not include pretreatment of the first carbon layer; the average content of noble metal particles in the catalytic layer of the membrane electrode is 0.05 mg / cm³. 2 The average particle size of the precious metal particles is 6.5 nm; the content of precious metal particles on the second surface decreases by 22%; and the particle size of the precious metal particles on the second surface decreases by 16%.

[0159] Comparative Example 4

[0160] This comparative example provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Example 1 only in that the atomic layer deposition temperature is different. In this comparative example, the atomic layer deposition temperature is 140°C, and no noble metal signal was detected in the catalyst layer of the resulting membrane electrode.

[0161] Comparative Example 5

[0162] This comparative example provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Example 1 only in the atomic layer deposition temperature. In this comparative example, the atomic layer deposition temperature is 350°C, and the average content of noble metal particles in the resulting membrane electrode catalyst layer is 0.82 mg / cm³. 2 The average particle size of the precious metal particles is 15.1 nm; the content of precious metal particles on the second surface decreases by 62%; and the particle size of the precious metal particles on the second surface decreases by 78%.

[0163] Comparative Example 6

[0164] This comparative example provides a method for preparing a membrane electrode, which differs from the method for preparing the membrane electrode in Example 1 only in the number of atomic layer deposition cycles. In this example, the number of atomic layer deposition cycles is 30, and the average content of noble metal particles in the resulting membrane electrode catalyst layer is 0.58 mg / cm³. 2 The average particle size of the precious metal particles is 5.4 nm; the content of precious metal particles on the second surface decreases by 38%; and the particle size of the precious metal particles on the second surface decreases by 54%.

[0165] Performance testing

[0166] Precious metal content: The content of precious metals on the cross-section of the catalyst layer was qualitatively and quantitatively analyzed by scanning electron microscopy and energy dispersive spectroscopy; the total content of precious metal particles was quantitatively analyzed by ICP-OES.

[0167] Particle size of precious metals: The particle size of precious metals was obtained by taking samples from the first and second surfaces of the catalyst layer and performing transmission electron microscopy (TEM) tests, and statistical analysis was performed.

[0168] Electrochemical performance: The membrane electrodes (effective area of ​​5cm*5cm) obtained in each example and comparative example were placed in a test fixture with a three-serpentine flow field (with sealing gasket). A torque wrench was used to gradually apply a force of 5Nm to lock the fixture to obtain a single cell. IV polarization curves and accelerated durability tests were performed using a Scribner 850 fuel cell test bench.

[0169] The IV polarization curve test conditions were as follows: temperature: 80℃; relative humidity of cathode / anode gas: 50% / 50%; back pressure of cathode / anode: 150kPa / 150kPa (gauge pressure); anode gas: 99.999% high-purity hydrogen, stoichiometric ratio 1.5; cathode gas: compressed air, stoichiometric ratio 2.5.

[0170] The accelerated endurance test conditions were as follows: square wave cycling at 0.6V / 0.95V, 3s / 3s, 30,000 cycles; temperature: 80℃; relative humidity of cathode / anode gas: 100% / 100%; back pressure of cathode / anode: 0kPa / 0kPa (gauge pressure); anode gas: 99.999% high-purity hydrogen, 0.2NL / min; cathode gas: 99.999% high-purity nitrogen, 0.075NL / min.

[0171] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this disclosure and not to limit the scope of protection of this disclosure. Although this disclosure has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this disclosure without departing from the substance and scope of the technical solutions of this disclosure.

Claims

1. A membrane electrode catalytic layer, characterized in that, The catalyst layer includes a first surface and a second surface along its thickness direction; the catalyst layer includes a support material and noble metal particles distributed in the support material, wherein the content and particle size of the noble metal particles continuously decrease from the first surface to the second surface, with the content of noble metal particles at the second surface decreasing by ≥50%; the particle size of noble metal particles at the second surface decreasing by ≥30%; and the average content of the noble metal particles is 0.01-0.2 mg / cm³. 2 The average particle size of the precious metal particles is 1-5 nm.

2. The membrane electrode catalytic layer as described in claim 1, characterized in that, The precious metal is at least one of platinum, iridium, ruthenium, and palladium.

3. The membrane electrode catalytic layer as described in claim 1, characterized in that, The carrier material is a carbon carrier material, and the catalyst layer also includes a binder and an ion exchange resin.

4. The membrane electrode catalytic layer as described in claim 3, characterized in that, The carbon support is at least one of conductive carbon black, activated carbon, and carbon nanotubes; and / or, the binder is at least one of polytetrafluoroethylene and polyvinylidene fluoride; and / or, the ion exchange resin is at least one of cation exchange resin and anion exchange resin.

5. The method for preparing the membrane electrode catalytic layer according to any one of claims 3-4, characterized in that, The process includes the following steps: uniformly mixing a carbon support with a binder and a solvent to obtain a carbon slurry; applying the carbon slurry to the surface of a substrate material, and drying and / or calcining it to obtain a first carbon layer; pretreating the first carbon layer with a gas to obtain a second carbon layer; wherein the gas is at least one of ozone, plasma nitrogen, plasma ammonia, and plasma oxygen, the gas flow rate is 0.5-2 L / min, and the pretreatment temperature is 30-450℃; depositing noble metal particles onto the second carbon layer using atomic layer deposition; and applying an ion exchange resin to obtain the membrane electrode catalytic layer.

6. The method for preparing the membrane electrode catalytic layer as described in claim 5, characterized in that, The substrate material is one of carbon fiber paper, carbon fiber cloth, polytetrafluoroethylene film, polyvinylidene fluoride film, polyimide film, polyetheretherketone film, and polyethylene naphthalate film.

7. The method for preparing the membrane electrode catalytic layer as described in claim 5, characterized in that, The steps for depositing noble metal particles onto the second carbon layer using atomic layer deposition are as follows: a noble metal precursor is adsorbed onto the surface and interior of the second carbon layer through the second surface of the second carbon layer, followed by the introduction of a reaction gas to carry out the reaction, and finally the removal of excess reactants and byproducts; wherein, the temperature of atomic layer deposition is 120-300℃ and the pressure is 10Pa-0.2MPa.

8. The method for preparing the membrane electrode catalytic layer as described in claim 7, characterized in that, The noble metal precursor is an organoplatinum compound; and / or, the reactant gas is oxygen or ozone.

9. A membrane electrode, characterized in that, The device includes a cathode catalytic layer, an anode catalytic layer, a cathode gas diffusion layer, and a proton exchange membrane disposed between the cathode catalytic layer and the anode catalytic layer; wherein at least one of the cathode catalytic layer or the anode catalytic layer includes a membrane electrode catalytic layer as described in any one of claims 1-4; the cathode gas diffusion layer is in contact with the surface of the cathode catalytic layer away from the proton exchange membrane; and the anode gas diffusion layer is in contact with the surface of the anode catalytic layer away from the proton exchange membrane.

10. A fuel cell, characterized in that, The fuel cell includes the membrane electrode assembly as described in claim 9.

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