Air-cooled fuel cell catalyst layer with high efficient proton transport network and method of making same

Abstract

This invention relates to an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network and its preparation method. It addresses the problems of poor battery performance and low stability under low humidity conditions in existing air-cooled fuel cell catalyst layers. The first catalyst layer of this invention consists of a platinum catalyst supported on a nanoscale conductive oxide and an ionomer; the second catalyst layer consists of a platinum-carbon catalyst supported on modified mesoporous carbon, an ionomer, and a hydrophilic conductive additive. The platinum-carbon catalyst is prepared by modifying the mesoporous carbon through mixed acid hydrophilization and laser fluorination hydrophobic treatment, followed by pressure-assisted capillary effect-based confined deposition of platinum nanoparticles within the pores. The single-cell output performance of this catalyst layer under low humidity conditions is 0.734 V@500 mA / cm². 2 The output performance of the air-cooled short reactor is 0.729 V@500 mA / cm³. 2 It can be used in the field of air-cooled fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen fuel cell technology, specifically relating to a high-performance, high-durability catalyst layer structure suitable for air-cooled proton exchange membrane fuel cells and its preparation method. Background Technology

[0002] Air-cooled proton exchange membrane fuel cells (AC-PEMFCs) have shown broad application prospects in small backup power supplies, drones, and portable power generation devices due to their advantages such as simple structure, compact system, rapid start-up, and no need for complex external humidification systems. However, AC-PEMFCs typically rely on self-humidification or low-humidification conditions for operation, and their cathode catalyst layers still face a series of severe challenges under actual operating conditions, seriously limiting the overall performance and long-term operational stability of the battery. Specifically, the water management mechanism has an inherent contradiction: due to the forced convection caused by air cooling, the water molecules generated in the reaction are easily evaporated and lost, making it difficult to effectively maintain the humidity level inside the membrane electrode assembly. This leads to localized drying of the proton exchange membrane and catalyst layer, resulting in a sharp decrease in proton conductivity and a significant degradation in battery performance. Meanwhile, a difficult conflict arises between oxygen mass transfer resistance and proton conduction requirements: increasing the ionomer content to improve water retention often clogs the gas-phase pores in the catalyst layer, hindering oxygen transport to the three-phase reaction interface; conversely, reducing the ionomer content, while improving gas permeability, leads to discontinuity in the proton conduction network, increased resistance, and decreased catalyst utilization efficiency. Furthermore, under low humidity conditions, the contact interface between the catalyst layer and the proton exchange membrane is prone to forming poor proton transport channels, significantly increasing interfacial impedance and further reducing the battery's output efficiency and dynamic response.

[0003] Currently, most catalyst layers in this field employ a single-component homogeneous structure. The material properties and functional distribution of these layers cannot synergistically address the three mutually constraining key requirements of water retention, proton conductivity, and gas diffusion. Although some studies have attempted to optimize the catalyst layer through gradient design, such as constructing a gradient distribution of catalyst loading along the thickness direction, these strategies primarily focus on macroscopic platinum distribution control. Systematic and in-depth research is still lacking on the fine-tuning of the hydrophilic and hydrophobic properties of the catalyst support material itself, the gradient design of ionomer spatial distribution, and the synergistic mechanism between catalyst position and proton transport pathway within the support's pore structure. Therefore, it is impossible to fundamentally achieve efficient and balanced management of water, gas, and protons in the membrane electrode assembly. Summary of the Invention

[0004] This invention aims to solve the technical problems of poor battery performance and low stability caused by water management difficulties, mass transfer contradictions, and high catalyst-membrane interface impedance in existing air-cooled fuel cell catalyst layers under low humidity conditions. The water management difficulties manifest as easy evaporation of reaction-generated water, leading to dryness of the membrane and catalyst layer and a sharp decrease in proton conductivity. The mass transfer contradiction refers to the fact that while increasing the ionomer content can retain water, it blocks oxygen transport channels, while reducing the ionomer content results in discontinuity in the proton conduction network. Therefore, this invention provides an air-cooled fuel cell catalyst layer with a highly efficient proton transport network and its preparation method.

[0005] The air-cooled fuel cell catalyst layer with a high-efficiency proton transport network of the present invention is composed of a first catalyst layer and a second catalyst layer forming a gradient structure;

[0006] The first catalyst layer is in contact with the proton exchange membrane, and the first catalyst layer is composed of nanoscale conductive oxides / M x O y The composition consists of a platinum catalyst supported by a first ionomer; the nanoscale conductive metal oxide / M x O y Ti4O7, CoO x MnO x NiO, WO3, or SnO2; the first ionomer is a low equivalent molecular weight ionomer, and in the first catalyst layer, the mass ratio of the first ionomer to the nanoscale conductive metal oxide is I / M x O y The value is 1.0~1.2;

[0007] The second catalyst layer is in contact with the gas diffusion layer. The second catalyst layer consists of a platinum-carbon catalyst supported on modified mesoporous carbon, a second ionomer, and a hydrophilic conductive additive. The modified mesoporous carbon is prepared through a cyclic process of mixed acid hydrophilization treatment and laser fluorination hydrophobic treatment. The pores of the modified mesoporous carbon are rich in hydrophilic functional groups, while the outer surface is a superhydrophobic layer with a micro-nano hierarchical structure. Platinum nanoparticles are loaded into the pores of the modified mesoporous carbon through a pressure-assisted capillary confinement process, with a confinement rate of not less than 90%. The second ionomer is a high equivalent molecular weight ionomer, and the mass ratio (I / C) of the second ionomer to the modified mesoporous carbon is 0.6~0.8. The amount of hydrophilic conductive additive added is 3%~8% of the mass of the platinum-carbon catalyst supported on mesoporous carbon.

[0008] Furthermore, the low equivalent molecular weight ionomer in the first catalyst layer is a perfluorosulfonic acid resin with an equivalent molecular weight (EW value) in the range of 600~700 g / mol.

[0009] Furthermore, the high equivalent molecular weight ionomer in the second catalyst layer is a perfluorosulfonic acid ionomer with an equivalent molecular weight (EW value) in the range of 900~1000 g / mol.

[0010] Furthermore, the hydrophilic conductive additive in the second catalyst layer is a carbon nanotube coated with polyaniline, polypyrrole or their copolymers, with a coating rate of 18% to 25% by mass; or it is a carbon nanofiber modified with poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS).

[0011] The above-mentioned method for preparing the catalyst layer of an air-cooled fuel cell with a high-efficiency proton transport network is carried out according to the following steps:

[0012] I. Precise Construction of Hydrophilic and Hydrophobic Microregions on Carbon Carriers Based on Laser Surface Engineering:

[0013] (1) Hydrophilic treatment with mixed acid: Take the mesoporous carbon support and place it in a three-necked flask containing a mixed acid solution of concentrated H2SO4 and concentrated HNO3. Place the three-necked flask in an oil bath at 50~85 ℃, stir mechanically and reflux for 4~6 hours. After the reaction is completed, cool naturally to room temperature, transfer the mixture to a centrifuge tube and centrifuge to separate the mixture, and discard the supernatant. Wash the precipitate repeatedly with ultrapure water and centrifuge until the pH of the supernatant after centrifugation is 6~7. Then vacuum dry the precipitate to obtain the acid-treated mesoporous carbon support.

[0014] (2) Fluorinated atmosphere laser hydrophobication treatment: The acid-treated mesoporous carbon support is evenly spread on a tray and transferred to a closed laser treatment reaction chamber filled with F2 / Ar mixed gas. A near-infrared fiber laser with a wavelength of 600~1064 nm is used at a power density of 8~10 J / cm³. 2 Under these conditions, the carbon support surface is scanned 2-5 times; after stopping the laser scanning, a protective atmosphere is continued until the reaction chamber cools to room temperature, and the material is removed under this protective atmosphere, completing the fluorinated atmosphere laser hydrophobication treatment; in the fluorinated atmosphere, the laser energy can promote the reconstruction of the surface structure of the carbon material and react with active fluorine species, generating superhydrophobic groups such as CF bonds in situ in the irradiated area, by precisely controlling the laser power density to 8-10 J / cm². 2 By scanning 2 to 5 times, a superhydrophobic functional layer with a micro-nano composite structure can be constructed on the outer surface of the carbon support. The static water contact angle can reach more than 150°. Since the laser energy cannot penetrate the pores inside the support, hydrophilic functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH) can be completely preserved, thus forming a precise gradient distribution of "inner hydrophilic and outer superhydrophobic".

[0015] (3) Repeat the cycle of mixed acid hydrophilization treatment and fluorinated atmosphere laser hydrophobic treatment, repeating the cycle 2 to 4 times to obtain a gradient mesoporous carbon support; hydrophilic and hydrophobic micro-regions are precisely constructed in the carbon support.

[0016] II. Pore-confined deposition of platinum nanoparticles based on pressure-assisted capillary effect:

[0017] (1) The gradient mesoporous carbon support was added to ethylene glycol at a mass concentration of 0.5~2 mg / mL and crushed under nitrogen protection using a high-shear emulsifier to obtain a uniform and stable suspension. Then, the suspension was placed in a vacuum reactor and degassed for 20~30 minutes under a vacuum of -0.090~-0.098 MPa. The degassed treatment thoroughly removed the pores of the support and the air bubbles in the solution, which significantly enhanced the capillary flow capacity of the precursor into the pores in the subsequent solution.

[0018] (2) Add a chloroplatinic acid (H2PtCl6·6H2O) ethylene glycol solution equivalent to 55%~65% of the carrier mass of platinum to the suspension. Seal the vacuum reactor and, under nitrogen protection, heat the reactor to 150~160 ℃ using a microwave reactor. Then, apply a constant pressure of 1.0~2.0 MPa to the reactor and maintain the reaction at this pressure for 2~3 minutes. After the reaction was completed, the mixture was cooled to room temperature and depressurized to atmospheric pressure. The pH of the product was adjusted to 1-2 with dilute nitric acid solution and stirred for 12 hours. The product was washed with deionized water until neutral and then vacuum dried to obtain a platinum-carbon catalyst supported on modified mesoporous carbon. During this process, the external pressure and the capillary force generated by the hydrophilic micropores inside the modified carbon support synergistically drove the platinum precursor solution to permeate efficiently and accumulate in the pores. Subsequently, ethylene glycol rapidly reduced the platinum ions in the pores to metallic platinum nanoparticles in situ under high temperature and high pressure. The high pressure environment not only greatly promoted the mass transfer of the precursor to the deep pores, but also effectively inhibited the random nucleation and growth of platinum particles on the outer surface of the pores, realizing the spatially selective deposition of platinum species.

[0019] III. Catalytic Layer Ink Formulation and Gradient Coating:

[0020] (1) Preparation of the first catalyst layer ink: Weigh out nanoscale conductive metal oxide M x O y A platinum catalyst supported on a substrate is then reacted with a first ionomer and a nanoscale conductive metal oxide M. x O y mass ratio (I / M) x O y Weigh out the first ionomer at a ratio of 1.0 to 1.2, wherein the nanoscale conductive metal oxide / M x O y Ti4O7, CoOx MnO x NiO, WO3 or SnO2, the first ionomer is a low equivalent molecular weight ionomer; then the platinum catalyst with nano-sized conductive oxide as support and the first ionomer are added to a mixed solvent of isopropanol and water, first mechanically stirred, and then transferred to an ice-water bath for ultrasonic dispersion by probe to form a first catalyst layer ink with a solid mass content of 1.5%~2%.

[0021] (2) Preparation of the second catalyst layer ink: Weigh the platinum-carbon catalyst with modified mesoporous carbon as the support, the second ionomer, and the hydrophilic conductive additive, and add them to a mixed solvent of isopropanol and water. First, stir mechanically, and then transfer to an ice-water bath for ultrasonic dispersion to form a stable second catalyst layer ink; wherein the second ionomer is a high equivalent molecular weight ionomer, and the mass ratio (I / C) of the second ionomer to the modified mesoporous carbon is 0.6~0.8; the amount of hydrophilic conductive additive added is 3%~8% of the mass of the platinum-carbon catalyst with modified mesoporous carbon as the support;

[0022] (3) Gradient coating:

[0023] The proton exchange membrane was fixed on a heated platform of an ultrasonic sprayer at a temperature of 75-90 ℃; first, the first catalytic layer ink was sprayed, and multiple thin layers were sprayed until the platinum loading reached 0.09-0.11 mg / cm³. 2 The thickness of the first catalyst layer after drying is 2~3μm; after the surface of the first layer is semi-dry, the second catalyst layer ink is sprayed at the same temperature, and multiple thin layers are sprayed until the platinum loading reaches 0.29~0.31 mg / cm³. 2 The thickness of the second catalyst layer after drying is 8~10 μm, thus obtaining the catalyst layer / membrane module;

[0024] (4) Hot pressing:

[0025] The catalyst layer / membrane assembly is aligned and stacked with the hydrophobic carbon paper gas diffusion layer, placed in a hot press, and hot-pressed for 3 to 8 minutes at a temperature of 130~140 ℃ and a pressure of 0.8~1.2 MPa. Then, it is held under pressure and naturally cooled to room temperature to obtain an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network, namely the membrane electrode assembly (MEA).

[0026] Furthermore, the mixed acid solution mentioned in step one (1) is prepared by mixing concentrated H2SO4 with a mass percentage concentration of 95%~98% and concentrated HNO3 with a mass percentage concentration of 63%~65% in a volume ratio of 3:1.

[0027] Furthermore, the mechanical stirring described in step one (1) is performed at a stirring speed of 200~300 rpm.

[0028] Furthermore, the centrifugation described in step one (1) is performed at a speed of 8000~10000 rpm for 5~10 minutes.

[0029] Furthermore, the vacuum drying described in step one (1) is carried out in a vacuum oven at a temperature of 60~80 ℃ for 10~12 hours.

[0030] Furthermore, the F2 / Ar mixture mentioned in step one (2) is a mixture of F2 and Ar gas, wherein the volume percentage of F2 in the mixture is 4%~6%.

[0031] Furthermore, in step two (1), the high-shear emulsifier operates at a speed of 8000~10000 rpm, and the crushing process takes 30~60 minutes.

[0032] Furthermore, the platinum catalyst supported on a nanoscale conductive metal oxide as described in step three (1) is a 20 wt.% Pt / Ti4O7 catalyst, wherein the Ti4O7 support has a particle size of 50~100 nm and a BET specific surface area of ​​25~50 m². 2 / g.

[0033] Furthermore, the low equivalent molecular weight ionomer mentioned in step three (1) is a perfluorosulfonic acid ionomer solution with a solid percentage of 20%~25% and an equivalent molecular weight (EW) of 700 g / mol.

[0034] Furthermore, the mixed solvent of isopropanol and water mentioned in step three (1) is prepared by mixing isopropanol and water at a volume ratio of (2.5~3.5):1.

[0035] The mechanical stirring described in steps (1) and (2) is to stir at a speed of 12,000 to 15,000 rpm for 20 to 30 minutes.

[0036] Furthermore, the ultrasonic dispersion of the probe described in steps (1) and (2) is a process of working for 2 seconds, followed by a 2-second interval, with a total dispersion time of 25 to 30 minutes.

[0037] Furthermore, the high equivalent molecular weight ionomer mentioned in step three (2) is a perfluorosulfonic acid ionomer solution with a solid content of 4%~6% and an equivalent molecular weight EW of 900~1000 g / mol.

[0038] Furthermore, in the mixed solvent of isopropanol and water described in step three (2), the volume ratio of isopropanol to water is (3.5~4.5):1.

[0039] Furthermore, in step three (3), the ink delivery rate for the first catalyst layer is 0.1 mL / min, the spraying distance is 5 cm, and the platform moving speed is 10 mm / s.

[0040] Furthermore, in step three (3), the second catalyst layer is sprayed with an ink delivery rate of 0.15 mL / min, a spraying distance of 5 cm, and a platform moving speed of 8 mm / s.

[0041] Furthermore, the operation in step two (2) can be replaced by the following operation:

[0042] (2) Add chloroplatinic acid (H2PtCl6·6H2O) ethylene glycol solution equivalent to 55~65% of the carrier mass of platinum to the suspension, place the mixture in a microwave reactor, irradiate and heat to 180~200 ℃ at a microwave power of 500 W and hold for 60~90 seconds to carry out the reaction, and then cool rapidly to obtain a platinum carbon catalyst with modified mesoporous carbon as the support. This method can also realize the confined deposition of platinum nanoparticles in carbon pores.

[0043] Furthermore, the operation in step three (3) can be replaced by the following operation:

[0044] The proton exchange membrane was fixed on a heating platform of a high-precision micro-metering coating machine at a temperature of 75–90 °C. First, the first catalytic layer ink was coated at a coating speed of 0.5–2.0 m / min and a slit gap of 100–200 μm. After coating, the platinum loading reached 0.09–0.11 mg / cm³. 2 The thickness of the first catalyst layer after drying is 2-3 μm. After the surface of the first layer is semi-dry, the second catalyst layer ink is applied at the same temperature at a coating speed of 0.5-2.0 m / min and a slit gap of 100-200 μm. After coating, the platinum loading reaches 0.29-0.31 mg / cm³. 2 The second catalyst layer, after drying, has a thickness of 8–10 μm, resulting in a catalyst layer / membrane module. A high-precision micro-metering coating machine is employed to meet the requirements of large-scale continuous preparation.

[0045] The catalyst layer design of this invention achieves performance breakthroughs through the following mechanism:

[0046] (1) Synergistic effect of laser-induced hydrophilic-hydrophobic Janus structure and pressure-assisted pore confinement: Through a cyclic process of "mixed acid hydrophilic modification - laser fluorination / graphitization hydrophobic treatment", the outer surface of the carbon support is selectively processed by pulsed laser in a fluorinated atmosphere to precisely construct a superhydrophobic surface with a micro-nano hierarchical structure, which greatly promotes the diffusion of reactive gases and the discharge of liquid water; while the pores inside the support are not irradiated by laser, the hydrophilic functional groups (-COOH, -OH) are retained, and water molecules are strongly adsorbed through capillary action to form a local high-humidity environment. Combined with the pressure-assisted capillary confinement process, the platinum precursor is driven to preferentially permeate and be reduced into the hydrophilic pores under high temperature and high pressure, achieving an ultra-high pore confinement rate (>90%) of platinum nanoparticles. This structure not only significantly shortens the proton transport path and reduces the dependence on the ionomer network, but also effectively protects the platinum particles inside the pores by the carbon wall, inhibiting migration and aggregation and improving catalytic stability.

[0047] (2) Bilayer functional gradient design and media transport regulation: The first catalyst layer adopts M with high conductivity and high hydrophilicity. x O y (e.g., Ti4O7) support with high I / M x O y The low EW ionomer (1.0~1.2) significantly enhances proton conduction efficiency and water retention at the proton exchange membrane interface, preventing interface drying. The second catalyst layer employs the aforementioned laser-modified carbon support, a standard ionomer with a low I / C ratio (0.6~0.8), and hydrophilic conductive additives (such as PANI-CNTs). While maintaining effective proton conduction, it significantly optimizes the gas transport channel by utilizing the superhydrophobic properties of the surface, achieving the dual effect of "unobstructed gas phase and liquid phase management".

[0048] (3) Multi-level transport channels and structural stability optimization: The hydrophilic conductive polymer added to the second catalyst layer coats CNTs, constructing a through-pore network that effectively bridges the pores between the catalyst layer and the gas diffusion layer, avoiding abrupt mass transfer changes at the interface and improving the uniformity of gas diffusion and the continuity of electron conduction. The laser-constructed micro-nano composite hydrophobic structure has good mechanical and chemical stability, further enhancing the durability of the catalyst layer under dry and wet cycling conditions.

[0049] The catalyst layer prepared in this invention has the characteristics of reasonable structure, high proton transport efficiency, low gas diffusion resistance, and excellent water management capability. It is particularly suitable for air-cooled fuel cells operating under self-humidification or low humidity conditions, and can significantly improve their output performance and operational stability. The single-cell output performance of this catalyst layer under low humidity conditions is 0.734 V@500 mA / cm². 2 The output performance of the air-cooled short reactor is 0.729 V@500 mA / cm³. 2It has broad prospects in applications such as portable power supplies and drones. Attached Figure Description

[0050] Figure 1 The surface water contact angle photographs of the first and second catalyst layers prepared in step three (3) of Example 1, the second catalyst layer of Comparative Example 2, and the catalyst layer of Comparative Example 1 are taken.

[0051] Figure 2 The images show secondary electron transmission analysis of platinum-supported sites of the platinum-carbon catalyst prepared in step two of Example 1 and Comparative Example 3.

[0052] Figure 3 This is a diagram showing the proportion of platinum-supported sites in the platinum-carbon catalyst prepared in step two of Example 1 and the platinum-carbon catalyst prepared in step two of Comparative Example 3.

[0053] Figure 4 The film electrode polarization curves of Example 1 and Comparative Example 1 under low humidity are shown.

[0054] Figure 5 This is a voltage comparison graph at the rated current density point for Example 1 and Comparative Example 1 of the air-cooled fuel cell stack. Detailed Implementation

[0055] The beneficial effects of the present invention will be verified using the following examples.

[0056] Example 1: The preparation method of the air-cooled fuel cell catalyst layer with a high-efficiency proton transport network in this example is carried out according to the following steps:

[0057] I. Precise Construction of Hydrophilic and Hydrophobic Microregions on Carbon Carriers Based on Laser Surface Engineering:

[0058] (1) Hydrophilic treatment with mixed acid: 1.0 g of Toyo Carbon MH-18 mesoporous carbon support was placed in a three-necked flask containing a mixed acid solution of concentrated H2SO4 and concentrated HNO3. The three-necked flask was placed in an oil bath at 80±2 ℃ and mechanically stirred at 200 rpm and refluxed for 6 hours. After the reaction was completed, the mixture was naturally cooled to room temperature. The mixture was transferred to a centrifuge tube and centrifuged at 10000 rpm for 5 minutes. The supernatant was discarded. The precipitate was washed with ultrapure water and centrifuged until the pH of the supernatant after centrifugation was 7. The precipitate was then placed in a vacuum oven at 80 ℃ and dried for 12 hours to obtain the acid-treated mesoporous carbon support. The mixed acid solution was prepared by mixing concentrated H2SO4 with a mass percentage concentration of 95%~98% and concentrated HNO3 with a mass percentage concentration of 63%~65% in a volume ratio of 3:1.

[0059] (2) Fluorinated atmosphere laser hydrophobication treatment: The acid-treated mesoporous carbon support was evenly spread on a tray and transferred to a closed laser treatment reaction chamber filled with F2 / Ar mixed gas. A near-infrared fiber laser with a wavelength of 1064 nm was used at a power density of 9 J / cm³. 2 The carbon support surface was scanned three times under the following conditions: after stopping the laser scanning, protective Ar gas was continuously introduced into the reaction chamber until it cooled to room temperature. The sample was then removed under the protective atmosphere to complete the laser hydrophobication treatment in the fluorination atmosphere. The F2 / Ar mixture was a mixture of F2 and Ar gas, with F2 accounting for 5% of the volume of the mixture.

[0060] (3) Repeat the mixed acid hydrophilization treatment and fluorinated atmosphere laser hydrophobic treatment cycle three times to obtain a gradient mesoporous carbon support.

[0061] II. Pore-confined deposition of platinum nanoparticles based on pressure-assisted capillary effect:

[0062] (1) 200 mg gradient mesoporous carbon support was added to 100 mL of ethylene glycol and crushed for 30 minutes at 10,000 rpm under nitrogen protection using a high shear emulsifier to obtain a uniform and stable suspension. Then, the suspension was placed in a vacuum reactor and degassed for 20 minutes under a vacuum of -0.095 MPa.

[0063] (2) Add chloroplatinic acid (H2PtCl6·6H2O) ethylene glycol solution equivalent to 60% of the carrier mass of platinum to the suspension, seal the vacuum reactor, and heat the reactor to 150 °C under nitrogen protection using a microwave reactor. Then apply a constant pressure of 1.5 MPa to the reactor and maintain the reaction at this pressure for 3 hours. After the reaction is completed, cool the system to room temperature and slowly depressurize. Adjust the pH to 2 with 0.1 M dilute nitric acid solution. Stir with a magnetic stirrer at 200 rpm for 12 hours. After the final product is washed with deionized water until neutral, dry it in a vacuum oven at 60 °C for 12 hours to obtain a platinum carbon catalyst with modified mesoporous carbon as the support.

[0064] III. Catalytic Layer Ink Formulation and Gradient Coating:

[0065] (1) Preparation of the first catalyst layer ink: Weigh 125 mg of 20 wt.% Pt / Ti4O7 catalyst, and weigh the first ionomer according to the mass ratio of the first ionomer to Ti4O7 (I / Ti4O7) of 1.0. The first ionomer is a perfluorosulfonic acid ionomer with an equivalent molecular weight (EW) of 700 g / mol. Then add 20 wt.% Pt / Ti4O7 catalyst and the first ionomer to 20 mL of a mixed solvent of isopropanol and water with a volume ratio of 3:1. Stir at high speed of 15000 rpm for 30 minutes, and then transfer to an ice-water bath for ultrasonic dispersion. The ultrasonic dispersion is carried out by working for 2 seconds and then resting for 2 seconds. The total dispersion time is 30 minutes to form a uniform first catalyst layer ink.

[0066] (2) Preparation of the second catalyst layer ink: Weigh 250 mg of platinum carbon catalyst with modified mesoporous carbon as support, and weigh the second ionomer with a mass ratio (I / C) of 0.7 between the second ionomer and the modified mesoporous carbon. The second ionomer is a perfluorosulfonic acid ionomer with an EW of 1000 g / mol. Weigh 15 mg of polyaniline-coated carbon nanotubes (PANI-CNTs). Add the platinum carbon catalyst with modified mesoporous carbon as support, the second ionomer and the polyaniline-coated carbon nanotubes to a mixed solvent of 20 mL isopropanol and water in a volume ratio of 4:1. Stir at high speed of 15000 rpm for 30 minutes. Then transfer to an ice-water bath for ultrasonic dispersion with a probe. The ultrasonic dispersion with the probe is carried out by working for 2 seconds and then resting for 2 seconds. The total dispersion time is 30 minutes to form a stable second catalyst layer ink.

[0067] (3) Gradient coating:

[0068] The Nafion® 211 proton exchange membrane was fixed on a heated platform of an ultrasonic sprayer at 75 °C. First, the first catalytic layer ink was sprayed at a delivery rate of 0.1 mL / min, a spraying distance of 5 cm, and a platform movement speed of 10 mm / s. Multiple thin-layer sprayings were performed until the platinum loading reached 0.1 mg / cm². 2 A first catalyst layer was obtained, with a dry film thickness of approximately 2-3 μm. After the surface of the first layer was semi-dry, a second catalyst layer ink was applied at the same temperature. The ink delivery rate was 0.15 mL / min, the spraying distance was 5 cm, and the platform moving speed was 8 mm / s. Multiple thin-layer coatings were applied until the platinum loading reached 0.3 mg / cm². 2 A second catalyst layer is obtained, and the dry film formed by this second catalyst layer has a thickness of about 8~10 μm, thus obtaining the catalyst layer / membrane module;

[0069] (4) Hot pressing:

[0070] The catalyst layer / membrane assembly is aligned and stacked with the hydrophobic carbon paper gas diffusion layer, placed in a hot press, and hot-pressed for 3 minutes at a temperature of 130 ℃ and a pressure of 0.8 MPa. Then, it is held under pressure and naturally cooled to room temperature to obtain an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network, which is the membrane electrode assembly (MEA).

[0071] Comparative Example 1: This comparative example describes the preparation of a conventional monolayer homogeneous catalytic membrane electrode. The specific method is as follows:

[0072] I. Preparation of Catalytic Layer Slurry: Weigh 125 mg of 40 wt.% Pt / C commercial catalyst (JM Company), and weigh a perfluorosulfonic acid ionomer solution with EW=1000 g / mol according to the mass ratio of ionomer to carbon (I / C) of 0.8. Add the 40 wt.% Pt / C commercial catalyst and perfluorosulfonic acid ionomer solution to 20 mL of a mixed solvent with a volume ratio of isopropanol to water of 3:1, and ultrasonically disperse for 30 minutes to obtain a uniform catalytic layer ink.

[0073] II. Spray Coating and Forming: The Nafion® 211 proton exchange membrane was fixed on a heated platform of an ultrasonic sprayer at 75 ℃. Catalytic layer ink was sprayed onto both sides of the proton exchange membrane. The ink delivery rate was 0.1 mL / min, the spraying distance was 5 cm, and the platform moving speed was 10 mm / s. Multiple thin layers were sprayed onto both sides of the membrane, with a platinum loading of 0.2 mg / cm². 2 To obtain the catalyst layer / membrane module;

[0074] 3. Hot pressing: Align and stack the catalyst layer / membrane module with the hydrophobic carbon paper gas diffusion layer, place it in a hot press, and hot press for 3 minutes at a temperature of 130 ℃ and a pressure of 0.8 MPa. Then, hold the pressure and let it cool naturally to room temperature to obtain a traditional single-layer homogeneous catalyst layer membrane electrode.

[0075] Comparative Example 2: This comparative example describes the preparation of a membrane electrode without laser fluorination modification. However, this membrane electrode still employs pressure-assisted confined deposition and a double-layer gradient coating method. The specific preparation method is as follows:

[0076] I. Carbon Support Modification: Hydrophilic Treatment with Mixed Acid: 1.0 g of Toyo Carbon MH-18 mesoporous carbon support was placed in a three-necked flask containing a mixed acid solution of concentrated H2SO4 and concentrated HNO3. The flask was placed in an oil bath at 80±2 ℃ and mechanically stirred at 200 rpm under reflux for 6 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The mixture was then transferred to a centrifuge tube and centrifuged at 10000 rpm for 5 minutes. The supernatant was discarded. The precipitate was washed with ultrapure water and centrifuged until the pH of the supernatant was 7. The precipitate was then dried in a vacuum oven at 80 ℃ for 12 hours to obtain the acid-treated mesoporous carbon support. The mixed acid solution was prepared by mixing 98% concentrated H2SO4 and 63% concentrated HNO3 at a volume ratio of 3:1.

[0077] II. Platinum loading: This step is the same as step two in Example 1;

[0078] III. Preparation and coating of catalytic layer ink: This step is the same as step three in Example 1; a membrane electrode without laser fluorination modification is obtained.

[0079] Comparative Example 3: This comparative example describes the preparation of a membrane electrode without pressure-assisted confinement. However, this electrode still utilizes laser fluorination modification and a double-layer gradient coating to prepare the membrane electrode. The specific preparation method is as follows:

[0080] I. Carbon support modification: This step is the same as step one in Example 1, to obtain a gradient mesoporous carbon support;

[0081] II. Platinum Loading: The conventional atmospheric pressure ethylene glycol reduction method is used, and the specific steps are as follows:

[0082] (1) 200 mg gradient mesoporous carbon support was added to 100 mL of ethylene glycol and crushed for 30 minutes at 10,000 rpm under nitrogen protection using a high shear emulsifier to obtain a uniform and stable suspension. Then, the suspension was placed in a vacuum reactor and degassed for 20 minutes under a vacuum of -0.095 MPa.

[0083] (2) Add chloroplatinic acid (H2PtCl6·6H2O) ethylene glycol solution equivalent to 60% of the carrier mass of platinum to the suspension, seal the vacuum reactor, and heat the reactor to 150 °C under nitrogen protection using a microwave reactor and react for 3 hours. After the reaction is completed, cool the system to room temperature and slowly depressurize it. Adjust the pH to 2 with 0.1 M dilute nitric acid solution, stir at 200 rpm for 12 hours, and wash the final product with deionized water until neutral. Then dry it in a vacuum oven at 60 °C for 12 hours to obtain a platinum carbon catalyst with modified mesoporous carbon as the support.

[0084] III. Preparation and coating of catalytic layer ink: This step is the same as step three in Example 1; a membrane electrode without pressure-assisted confinement is obtained.

[0085] The surface hydrophilicity and hydrophobicity of the first and second catalyst layers prepared in step three (3) of Example 1, the second catalyst layer of Comparative Example 2, and the catalyst layer of Comparative Example 1 were tested, and the resulting water contact angle photographs are shown below. Figure 1 As shown, from Figure 1 As can be seen, the first catalyst layer in Example 1, employing a hydrophilic Pt / Ti4O7 catalyst and a high ionomer / carbon ratio (I / C ratio), exhibits an excellent water retention capacity with a surface water contact angle of 129.7°. The second catalyst layer, through a "mixed acid hydrophilization-fluorinated atmosphere laser hydrophobication" treatment of the carbon support, achieves a contact angle of 151.9°, demonstrating highly hydrophobic properties. These results confirm that Example 1 successfully constructed a continuous gradient structure from hydrophilic to superhydrophobic within the catalyst layer, extending from the proton exchange membrane side to the gas diffusion layer side. This structure effectively coordinates the water management behavior of the membrane electrode under air-cooled self-humidification conditions, thereby ensuring its high-performance and stable output. In contrast, the second catalyst layer in Comparative Example 2, lacking fluorinated atmosphere laser hydrophobication treatment, has a contact angle of 138.4°, a smaller hydrophilic-hydrophobic gradient, and a weakened water-gas control capability. In Comparative Example 1, since no hydrophilic or hydrophobic functionalization design was carried out on the catalyst layer, its contact angle was 144.9°, exhibiting intermediate hydrophobic characteristics. It lacked clear directional water management capabilities and could not achieve efficient proton conduction and gas transport simultaneously under low humidity conditions.

[0086] The platinum-carbon catalyst with modified mesoporous carbon as the support prepared in step two of Example 1 and the platinum-carbon catalyst prepared in step two of Comparative Example 3 were subjected to secondary electron transmission analysis of platinum-supported sites. The secondary electron transmission analysis diagrams of the platinum-supported sites of the catalysts are shown in the figure below. Figure 2 As shown, the proportion of platinum sites outside the catalyst pores is as follows: Figure 3 As shown, Figure 2 and Figure 3The results show that Example 1, employing a pressure-assisted confined deposition strategy, achieved a 92% distribution of platinum nanoparticles within the pores of the support, demonstrating a significant spatial confinement effect. In contrast, Comparative Example 3, without pressure assistance and relying solely on atmospheric pressure reduction, showed a 75% distribution of platinum particles within the pores, with a considerable portion of platinum active sites exposed outside the pores. These results demonstrate that a pressure-assisted strategy can effectively promote the migration and enrichment of platinum precursors into the deep pores of the support and suppress their random deposition on the pore surface, thereby achieving highly efficient intrapore confinement of platinum nanoparticles. This highly confined structure not only increases the three-phase contact efficiency between platinum particles and protons and reactants but also helps alleviate platinum migration and aggregation under operating conditions, improving catalyst stability. In contrast, Comparative Example 3, lacking external pressure drive, relied mainly on capillary spontaneous flow of the precursor, resulting in limited confinement. Some platinum particles located outside the pores were easily covered by ionomers or sintered, leading to reduced availability and durability of active sites.

[0087] On the Qunyi 850e membrane electrode testing system, the hydrogen-air polarization performance of the membrane electrode samples was evaluated according to GB / T20042.5-2009: Proton Exchange Membrane Fuel Cells Part 5: Membrane Electrode Test Methods. All membrane electrodes were subjected to four consecutive test cycles at an operating temperature of 80 ℃, an outlet back pressure of 50 kPa, an anode / cathode gas flow rate of 0.5 L / min, and a relative humidity of 20% in a hydrogen / air atmosphere, following the procedure below:

[0088] (i) Maintain a constant voltage of 0.8 V for 2 minutes;

[0089] (ii) Switch to a constant voltage of 0.7 V and maintain it for 6 minutes;

[0090] (iii) Adjust to a constant voltage of 0.6 V and maintain it for 2 minutes;

[0091] (iv) From 0 mA / cm 2 Current density is scanned in a stepwise manner from the point of origin to 3000 mA / cm². 2 Each current density point was maintained stably for 4 minutes.

[0092] The membrane electrode polarization curves of Example 1 and Comparative Example 1 under low humidity conditions are shown in the figure below. Figure 4 As shown, from Figure 4 As can be seen, under low-humidity hydrogen-air testing conditions, the membrane electrode prepared in Example 1 exhibits a higher peak power density compared to the membrane electrode prepared by the conventional method in Comparative Example 1. Simultaneously, the membrane electrode of Example 1 effectively alleviates the performance degradation problem caused by water loss in the membrane electrode, and its operational stability is significantly improved. Specifically, the membrane electrode of Example 1 achieves a peak power density of 500 mA / cm² under low humidity conditions. 2The voltage at the current density can reach 0.734 V, while the voltage of the membrane electrode prepared by the conventional method in Comparative Example 1 is only 0.677 V under the same conditions, representing a performance improvement of 57 mV.

[0093] The membrane electrode prepared in Example 1 and the membrane electrode prepared in Comparative Example 1 were compared at the rated current density point of the air-cooled stack. After checking the stack's airtightness, the air-cooled stack was activated by multiple constant current charge-discharge activations. After the voltage stabilized, the voltage of the air-cooled stack at 500 mA / cm² was recorded. 2 The voltage values ​​of each element at the current density were calculated, and the average value was then compared. A comparison graph of the voltages at the rated current density points for the air-cooled fuel cell stack of Example 1 and Comparative Example 1 is shown below. Figure 5 As shown, from Figure 5 It can be seen that at 500 mA / cm 2 At the rated operating point, the average voltage of the membrane electrode prepared in Example 1 reached 0.729 V, while the average voltage of the air-cooled stack prepared using a conventional membrane electrode catalytic layer in Comparative Example 1 was 0.652 V, representing a voltage increase of 77 mV and a relative performance improvement of 11.8%. The results indicate that the gradient catalytic layer structure constructed in Example 1 can significantly improve the output voltage and overall performance of the air-cooled stack under rated operating conditions.

[0094] This invention constructs a gradient catalytic layer with "inner hydrophilicity and outer hydrophobicity" Janus structure by sequentially subjecting a carbon support to mixed acid hydrophilic treatment and laser fluorination hydrophobic modification, combined with a pressure-assisted confined deposition of platinum within the pores. This significantly improves the water retention capacity and gas transport efficiency of the membrane electrode under low humidity conditions, while effectively promoting proton conduction and catalytic activity at the reaction interface. It achieves efficient synergistic management of water, gas, and protons, enabling synergistic optimization of the performance and durability of air-cooled fuel cells, and can promote the commercial application of air-cooled proton exchange membrane fuel cells.

Claims

1. An air-cooled fuel cell catalyst layer with a high-efficiency proton transport network, characterized in that, The catalyst layer consists of a first catalyst layer and a second catalyst layer that form a gradient structure; The first catalyst layer is in contact with the proton exchange membrane, and the first catalyst layer is composed of nanoscale conductive oxide M. x O y The composition consists of a platinum catalyst supported by a first ionomer; the nanoscale conductive oxide M x O y Ti4O7, CoO x MnO x NiO, WO3, or SnO2; the first ionomer is a low equivalent molecular weight ionomer, and in the first catalyst layer, the mass ratio of the first ionomer to the nanoscale conductive oxide is 1.0~1.2; The second catalyst layer is in contact with the gas diffusion layer. The second catalyst layer consists of a platinum-carbon catalyst supported on modified mesoporous carbon, a second ionomer, and a hydrophilic conductive additive. The modified mesoporous carbon is prepared through a cyclic process of mixed acid hydrophilization treatment and laser fluorination hydrophobic treatment. The pores of the modified mesoporous carbon are rich in hydrophilic functional groups, while the outer surface is a superhydrophobic layer with a micro-nano hierarchical structure. Platinum nanoparticles are loaded into the pores of the modified mesoporous carbon through a pressure-assisted capillary confinement process, with a confinement rate of not less than 90%. The second ionomer is a high equivalent molecular weight ionomer, and the mass ratio of the second ionomer to the modified mesoporous carbon is 0.6~0.

8. The amount of hydrophilic conductive additive added is 3%~8% of the mass of the platinum-carbon catalyst supported on the modified mesoporous carbon.

2. The air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 1, characterized in that, The low equivalent molecular weight ionomer in the first catalyst layer is a perfluorosulfonic acid resin with an equivalent molecular weight range of 600-700 g / mol.

3. The air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 1 or 2, characterized in that, The high equivalent molecular weight ionomer in the second catalyst layer is a perfluorosulfonic acid ionomer with an equivalent molecular weight range of 900~1000 g / mol.

4. The air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 1 or 2, characterized in that, The hydrophilic conductive additive in the second catalyst layer is a carbon nanotube coated with polyaniline, polypyrrole or their copolymers, with a coating rate of 18% to 25% by mass; or it is a carbon nanofiber modified with poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate.

5. The method for preparing an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network as described in claim 1, characterized in that, This method is performed in the following steps: I. Precise Construction of Hydrophilic and Hydrophobic Microregions on Carbon Carriers Based on Laser Surface Engineering: (1) Hydrophilic treatment with mixed acid: Take the mesoporous carbon support and place it in a three-necked flask containing a mixed acid solution of concentrated H2SO4 and concentrated HNO3. Place the three-necked flask in an oil bath at 50~85 ℃, stir mechanically and reflux for 4~6 hours. After the reaction is completed, cool naturally to room temperature, transfer the mixture to a centrifuge tube and centrifuge to separate the mixture, and discard the supernatant. Wash the precipitate repeatedly with ultrapure water and centrifuge until the pH of the supernatant after centrifugation is 6~7. Then vacuum dry the precipitate to obtain the acid-treated mesoporous carbon support. (2) Fluorinated atmosphere laser hydrophobication treatment: The acid-treated mesoporous carbon support is evenly spread on a tray and transferred to a closed laser treatment reaction chamber filled with F2 / Ar mixed gas. A near-infrared fiber laser with a wavelength of 600~1064 nm is used at a power density of 8~10 J / cm³. 2 Under the conditions of scanning the carbon support surface 2 to 5 times; after stopping the laser scanning, continue to introduce the protective atmosphere until the reaction chamber cools to room temperature, and take it out under the protective atmosphere to complete the fluorination atmosphere laser hydrophobication treatment; (3) Repeat the cycle of mixed acid hydrophilization treatment and fluorinated atmosphere laser hydrophobic treatment, repeating the cycle 2 to 4 times to obtain a gradient mesoporous carbon support. II. Pore-confined deposition of platinum nanoparticles based on pressure-assisted capillary effect: (1) The gradient mesoporous carbon support is added to ethylene glycol at a mass concentration of 0.5~2 mg / mL. The mixture is crushed by a high-shear emulsifier under nitrogen protection to obtain a uniform and stable suspension. Then, the suspension is placed in a vacuum reactor and degassed for 20~30 minutes under a vacuum of -0.090~-0.098 MPa. (2) Add ethylene glycol chloroplatinic acid solution equivalent to 55%~65% of the carrier mass of platinum to the suspension, seal the vacuum reactor, and heat the reactor to 150~160 ℃ under nitrogen protection using a microwave reactor. Then apply a constant pressure of 1.0~2.0 MPa to the reactor and maintain the reaction at this pressure for 2~3 h. After the reaction is completed, cool to room temperature and release the pressure to atmospheric pressure. Adjust the pH of the product to 1~2 with dilute nitric acid solution and stir for 12 hours. After washing the product with deionized water until neutral, dry it under vacuum to obtain a platinum carbon catalyst with modified mesoporous carbon as the support. III. Catalytic Layer Ink Formulation and Gradient Coating: (1) Preparation of the first catalytic layer ink: Weigh out nano-sized conductive oxide M x O y A platinum catalyst supported on a substrate is then reacted with a first ionomer and a nanoscale conductive oxide M. x O y mass ratio I / M x O y Weigh out 1.0~1.2 of the first ionomer, wherein the nanoscale conductive oxide M... x O y Ti4O7, CoO x MnO x NiO, WO3, or SnO2, the first ionomer is a low equivalent molecular weight ionomer; then, nano-sized conductive oxide M x O y The platinum catalyst, supported by a platinum catalyst, and the first ionomer were added to a mixed solvent of isopropanol and water. The mixture was first mechanically stirred and then transferred to an ice-water bath for ultrasonic dispersion to form a first catalytic layer ink with a solid mass content of 1.5% to 2%. (2) Preparation of the second catalyst layer ink: Weigh the platinum-carbon catalyst with modified mesoporous carbon as the support, the second ionomer, and the hydrophilic conductive additive, and add them to a mixed solvent of isopropanol and water. First, mechanically stir, and then transfer to an ice-water bath for ultrasonic dispersion to form a stable second catalyst layer ink; wherein the second ionomer is a high equivalent molecular weight ionomer, and the mass ratio of the second ionomer to the modified mesoporous carbon (I / C) is 0.6~0.8; the amount of hydrophilic conductive additive added is 3%~8% of the mass of the platinum-carbon catalyst with modified mesoporous carbon as the support; (3) Gradient coating: The proton exchange membrane was fixed on a heated platform of an ultrasonic sprayer at a temperature of 75-90 ℃; first, the first catalytic layer ink was sprayed, and multiple thin layers were sprayed until the platinum loading reached 0.09-0.11 mg / cm³. 2 After the first layer is semi-dry, the second catalytic layer ink is sprayed at the same temperature, and multiple thin layers are sprayed until the platinum loading reaches 0.29~0.31 mg / cm³. 2 To obtain the catalyst layer / membrane module; (4) Hot pressing: The catalyst layer / membrane module is aligned and stacked with the hydrophobic carbon paper gas diffusion layer, placed in a hot press, and hot-pressed for 3 to 8 minutes at a temperature of 130~140 ℃ and a pressure of 0.8~1.2 MPa. Then, it is held under pressure and naturally cooled to room temperature to obtain an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network, namely the membrane electrode.

6. The method for preparing an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 5, characterized in that, The mechanical stirring described in step one (1) has a stirring speed of 200~300 rpm.

7. A method for preparing an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 5 or 6, characterized in that, The centrifugation described in step one (1) is performed at a speed of 8000~10000 rpm for 5~10 minutes.

8. A method for preparing an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 5 or 6, characterized in that, In step two (1), the high-shear emulsifier operates at a speed of 8000~10000 rpm, and the crushing process takes 30~60 minutes.

9. A method for preparing an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 5 or 6, characterized in that, The operation in step two (2) can be replaced by the following operation: (2) Add ethylene glycol chloroplatinic acid solution equivalent to 55-65% of the carrier mass of platinum to the suspension, place the mixture in a microwave reactor, irradiate and heat to 180-200 °C at a microwave power of 500 W and hold for 60-90 seconds to carry out the reaction, and then cool rapidly to obtain a platinum carbon catalyst with modified mesoporous carbon as the support.

10. A method for preparing an air-cooled fuel cell catalyst layer with a high-efficiency proton transport network according to claim 5 or 6, characterized in that, The operation in step 3 (3) can be replaced by the following operation: (3) The proton exchange membrane was fixed on a heating platform of a high-precision micro-metering coating machine at a temperature of 75~90 ℃; the first catalytic layer ink was coated first at a coating speed of 0.5~2.0 m / min and a slit gap of 100~200 μm. After coating, the platinum loading reached 0.09~0.11 mg / cm³. 2 After the first layer surface is semi-dry, the second catalytic layer ink is applied at the same temperature at a coating speed of 0.5–2.0 m / min and a slit gap of 100–200 μm. The resulting platinum loading reaches 0.29–0.31 mg / cm³. 2 The catalyst layer / membrane module is obtained.

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