Gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode

Abstract

The invention relates to the technical field of new energy materials, and discloses a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode. The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode comprises an exchange membrane, an anode catalyst layer, a cathode catalyst layer and a gas diffusion layer, wherein the anode catalyst layer and the cathode catalyst layer have gradient pore size distribution from the exchange membrane side to the gas diffusion layer side; wherein the interiors of the anode catalyst layer and the cathode catalyst layer are provided with three-dimensional interpenetrating network structures. According to the invention, the utilization rate of the catalyst is improved by 30-50%, the mass transfer resistance is reduced by 40-60%, the interface contact is improved, the controllability of the preparation process is improved, the structural stability is enhanced, the power density of the direct ammonia fuel cell reaches 250-300mW / cm < 2 >, the performance retention rate after 5000 cycles can reach 85% or more, and the method has remarkable technical advantages and application prospects.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and more specifically, to a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode. Background Technology

[0002] With the increasing severity of the global energy crisis and environmental pollution, the development of clean and efficient energy conversion and storage technologies has become a current research hotspot. Hydrogen energy, as a clean energy carrier, boasts advantages such as high energy density and zero pollution; however, its storage and transportation face significant challenges. Ammonia (NH3), as a carbon-free hydrogen carrier molecule, possesses advantages such as high energy density, high liquefaction temperature (-33℃, 0.1MPa), and ease of storage and transportation, making it considered an ideal hydrogen energy carrier. Direct ammonia fuel cells (DAFCs) are electrochemical devices that use ammonia as fuel, directly converting the chemical energy in ammonia molecules into electrical energy through an electrochemical reaction. Compared to traditional hydrogen fuel cells, DAFCs can utilize the existing global ammonia production and distribution network, reducing the cost and technical barriers to large-scale applications, and avoiding the difficulties of hydrogen storage and transportation, thus possessing broad application prospects.

[0003] The membrane electrode assembly (MEA) is the core component of a DAFC (Dissolved Acoustic Fuel Cell), forming the basic unit of a fuel cell together with the bipolar plates. The MEA mainly consists of a proton exchange membrane / anion exchange membrane (depending on the fuel cell type), an anode catalyst layer (the region where ammonia oxidation occurs), a cathode catalyst layer (the region where oxygen reduction occurs), and a gas diffusion layer (providing reactant transport channels). In a DAFC, ammonia oxidation (AOR) occurs at the anode, a multi-step process involving the breaking of NH bonds, the formation of NN bonds, and the release of dinitrogen. Due to the complexity of the reaction pathway, AOR suffers from slow kinetics, uncontrollability, and instability, severely limiting the performance and commercial application of DAFCs.

[0004] Currently, MEA (Membrane Electrode) preparation technology has undergone three generations of development. The first generation, the gas diffusion electrode method (GDE), involves directly coating a well-dispersed catalyst slurry onto a pretreated porous diffusion layer, and then hot-pressing this gas diffusion electrode and the proton exchange membrane (PEM) into a membrane electrode assembly. The advantages of GDE-type MEAs are their relatively simple and mature preparation process, which facilitates the formation of pores within the MEA and protects the PEM from deformation. However, due to the catalyst utilization rate being less than 20%, the cost of the MEA is increased, and the GDE structure MEA preparation process is currently mainly used in laboratories. The second generation, the catalyst coating membrane method (CCM), involves directly coating the catalyst onto the PEM, and then hot-pressing the cathode and anolyte gas diffusion layers onto both sides of the catalyst-coated PEM to form a thin, three-in-one membrane electrode assembly of approximately 10 μm thickness. The catalyst and PEM bond well, preventing delamination and improving the catalyst utilization rate in the catalyst layer, resulting in good overall performance. CCM technology is widely adopted and is currently the mainstream commercial MEA preparation method. Third-generation ordered membrane electrodes (MEAs) construct ordered structures within the membrane electrode, including nanoarray structures or other ordered structures of various shapes. These ordered structures can be ordered proton transport structures, ordered electron transport structures, ordered catalytic layer structures, or ordered mass transport structures. These structures can provide ordered proton, electron, or mass transport channels, reduce transport resistance, maximize the three-phase interface of chemical reactions, improve the stability of the electrode structure, and thus greatly extend the battery's lifespan.

[0005] However, existing DAFC membrane electrodes still suffer from the following problems: 1) Low catalyst utilization: In traditional disordered MEAs, the catalyst distribution is uneven and the three-phase interface is limited, resulting in low catalyst utilization, typically not exceeding 30%, leading to waste of precious metal resources and increased costs. 2) High mass transfer resistance: In existing MEA structures, the transport paths of reactants and products are complex and have high resistance, especially at high current densities, where mass transfer limitation becomes the main factor restricting battery performance. 3) Poor interfacial contact: Poor interfacial contact between the catalyst layer and the membrane, and between the catalyst layer and the gas diffusion layer, leads to increased interfacial resistance, affecting battery performance and lifespan. 4) Uncontrollable preparation process: Traditional preparation processes such as coating and spraying make it difficult to accurately control the distribution and loading of the catalyst, resulting in poor product consistency and hindering large-scale production. 5) Poor structural stability: During long-term operation, the catalyst layer structure is prone to changes, leading to a reduction in the three-phase interface and a decline in battery performance.

[0006] Therefore, there is an urgent need to develop a novel DAFC membrane electrode structure and its preparation method to solve the problems of low catalyst utilization, high mass transfer resistance, poor interfacial contact, uncontrollable preparation process and poor structural stability in the existing technology, so as to improve the performance and commercial application prospects of DAFC. Summary of the Invention

[0007] The purpose of this invention is to provide a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode to solve the problems of low catalyst utilization, high mass transfer resistance, poor interface contact, uncontrollable preparation process and poor structural stability in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention: A gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode includes: an exchange membrane, an anode catalyst layer, a cathode catalyst layer, and a gas diffusion layer; The anode catalyst layer and the cathode catalyst layer have a gradient pore size distribution from the exchange membrane side to the gas diffusion layer side, including: The microporous structure near the exchange membrane has a pore size of 1–5 μm; The intermediate region has a mesoporous structure with a pore size of 5–20 μm; The macroporous structure near the gas diffusion layer has a pore size of 20–50 μm. The anode catalyst layer and the cathode catalyst layer have a three-dimensional interpenetrating network structure, including: The catalyst network forms a continuous electron conduction channel; An ion conduction network forms a continuous ion conduction channel; A gas transport network forms a continuous gas transport channel.

[0009] Furthermore, the exchange membrane is a proton exchange membrane or anion exchange membrane.

[0010] Furthermore, the anolyte catalyst in the anolyte catalyst layer is a platinum-based catalyst, an iridium-based catalyst, a ruthenium-based catalyst, or an alloy thereof, and the anolyte catalyst loading is 0.1–1.0 mg / cm³. 2 .

[0011] Furthermore, the cathode catalyst in the cathode catalyst layer is a platinum-based catalyst, a silver-based catalyst, a palladium-based catalyst, or an alloy thereof, and the cathode catalyst loading is 0.1–1.0 mg / cm³. 2 .

[0012] Furthermore, the ion-conducting network is composed of an ion-conducting polymer, which is one or more of perfluorosulfonic acid ion exchange resin, polybenzimidazole, polyether ether ketone, polysulfone, and quaternized polyarylether.

[0013] Furthermore, a transition layer is provided between the exchange membrane and the anode catalyst layer to improve interfacial contact and compatibility; The thickness of the transition layer is 1 to 10 μm, and it is composed of the ion-conducting polymer and the anode catalyst. The content of the anode catalyst gradually increases from 10% to 70% from the exchange membrane side to the anode catalyst layer side, and the content of the ion-conducting polymer gradually decreases from 30% to 90% from the exchange membrane side to the anode catalyst layer side.

[0014] Furthermore, the cathode catalytic layer and the gas diffusion layer have a gradient hydrophobic design to optimize water management; The gradient hydrophobicity design specifically involves increasing hydrophobicity from the cathode catalytic layer side to the gas diffusion layer side, wherein the contact angle on the cathode catalytic layer side is 60–90° and the contact angle on the gas diffusion layer side is 120–150°.

[0015] The second technical solution of the present invention: The above-mentioned method for preparing a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode includes the following steps: (1) Functional treatment of the exchange membrane surface The exchange membrane is placed in a functionalizing reagent and its surface is functionalized to introduce functional groups on the surface of the exchange membrane as anchors for catalyst growth. (2) Preparation of transition layer After surface functionalization treatment in step 1, a mixed solution containing ion-conducting polymer and anode catalyst precursor is deposited on the surface of the exchange membrane using a precision deposition technique to form a transition layer. (3) Precise deposition of catalyst precursor Using improved inkjet printing or ultrasonic atomization technology, ink containing anodic catalyst precursor and cathode catalyst precursor is precisely deposited sequentially on the surface of the transition layer obtained in step 2, thereby achieving precise deposition of catalyst precursor; (4) In-situ reduction / growth The exchange membrane with the catalyst precursor deposited in step 3 is placed in a reducing agent and reduced in situ, so that the catalyst precursor grows at a preset position to form an anode catalyst layer and a cathode catalyst layer that are tightly bonded to the exchange membrane. (5) Gradient aperture structure formation A template method was used to form porous structures with gradient pore size distribution in the anode and cathode catalyst layers; (6) Construction of three-dimensional interpenetrating network By controlling the proportions and distributions of catalyst, ion-conducting polymer, and pore-forming agent, a three-dimensional interpenetrating structure of catalyst network, ion-conducting network, and gas transport network was constructed. (7) Gradient hydrophobicity treatment The surface of the cathode catalyst layer is subjected to a gradient hydrophobicity treatment, so that its hydrophobicity gradually increases from the exchange membrane side to the gas diffusion layer side. (8) Assembly of gas diffusion layer The treated gas diffusion layer and the catalyst layer after the treatment in step 7 are assembled by hot pressing to form a complete membrane electrode.

[0016] Further, in step (1), the functionalizing reagent is specifically an organic solution containing carboxyl, sulfonic acid, amino, or hydroxyl groups.

[0017] Furthermore, in step (1), the surface functionalization treatment is carried out at a temperature of 30 to 80°C for a time of 0.5 to 5 hours.

[0018] Further, in step (2), the anode catalyst precursor is specifically one or more of the soluble salts or complexes of platinum, iridium, and ruthenium.

[0019] Further, in step (3), the cathode catalyst precursor is specifically one or more of the soluble salts or complexes of platinum, silver, and palladium.

[0020] Furthermore, in step (3), the inkjet printing uses a piezoelectric inkjet printhead with an ink droplet volume of 1 to 100 pL and a printing accuracy of ±5 μm.

[0021] Furthermore, in step (3), the ultrasonic frequency of the ultrasonic atomization technology is 1 to 3 MHz, and the atomization rate is 0.1 to 5 mL / min.

[0022] Further, in step (4), the reducing agent is specifically one or more of sodium borohydride, hydrogen, formic acid, ascorbic acid and ethylene glycol.

[0023] Furthermore, in step (4), the in-situ reduction temperature is 30-100℃ and the time is 0.5-5h.

[0024] Furthermore, in step (5), the template is a polystyrene microsphere, a silica microsphere, or a carbon nanomaterial.

[0025] Furthermore, in step (7), the gradient hydrophobic treatment is performed by fluorination or hydrophobic polymer impregnation, and the treatment depth gradually increases from the exchange membrane side to the gas diffusion layer side.

[0026] Furthermore, in step (8), the hot pressing temperature is 120-180°C, the pressure is 0.5-5 MPa, and the time is 1-10 min.

[0027] The third technical solution of this invention: The above-mentioned gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode assembly is used as a membrane electrode assembly in direct ammonia fuel cells.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) Improve catalyst utilization: By using a gradient porous three-dimensional interpenetrating network structure, the three-phase interface is maximized, which improves the catalyst utilization by 30-50%, reduces the amount of precious metal catalyst, and reduces costs. 2) Reduced mass transfer resistance: The gradient pore size distribution optimizes the transport path of reactants and products, reducing mass transfer resistance by 40-60% and improving performance under high current density. 3) Improved interfacial contact: The transition layer and gradient hydrophobic design improve the interfacial contact between the catalyst layer and the exchange membrane, and between the catalyst layer and the gas diffusion layer, thereby reducing interfacial resistance and improving battery performance and lifespan. 4) Improved controllability of the preparation process: The in-situ growth and precise deposition composite process enables precise positioning and loading control of the catalyst, improves product consistency, and is suitable for large-scale production; 5) Enhanced structural stability: The three-dimensional interpenetrating network structure enhances the mechanical stability of the catalyst layer, extends battery life, and maintains a performance retention rate of over 85% after 5000 cycles. 6) Improved battery performance: Combining the above advantages, the membrane electrode of this invention can enable the power density of DAFC to reach 250-300 mW / cm². 2 It improves efficiency by 25-35% compared to traditional membrane electrodes. Attached Figure Description

[0029] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is an electron microscope image of the gradient aperture structure of the membrane electrode in Embodiment 1 of the present invention; Figure 2 This is a diagram showing the hydrophobicity of the gas diffusion layer of the membrane electrode in Embodiment 1 of the present invention; Figure 3 The diagram shows the power density of the direct ammonia fuel cell assembled with membrane electrode assembly in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0031] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0033] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0034] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0035] Example 1 1. Functional treatment of exchange membrane surface Fumasep FAAM-15 anion exchange membrane (average thickness 15 μm) was placed in 0.5 M sulfonic acid functionalizing reagent for surface functionalization treatment (temperature 50 °C, time 2 h) to introduce sulfonic acid functionalization groups as anchor sites for catalyst growth; after the surface functionalization treatment, it was washed with deionized water 3 times, 10 min each time, and then dried at 60 °C for 1 h. 2. Preparation of transition layer Prepare a mixed solution containing 5 wt% Nafion solution and 0.01 M chloroplatinic acid (H2PtCl6); deposit the above mixed solution on the surface of the exchange membrane after surface functionalization treatment in step 1 using ultrasonic atomization technology (frequency 2 MHz, atomization rate 1 mL / min) to form a transition layer with a thickness of 5 μm; after deposition, dry at 80 °C for 30 min; 3. Precise deposition of catalyst precursors A mixed solution containing 0.05M chloroplatinic acid and 0.005M cobalt chloride was prepared as the anode catalyst precursor ink, and a solution containing 0.05M chloroplatinic acid was prepared as the cathode catalyst precursor ink. Using a piezoelectric inkjet printhead (droplet volume 50 pL, printing accuracy ±3 μm), the inks containing the anode and cathode catalyst precursors were sequentially and precisely deposited onto the surface of the transition layer obtained in step 2, achieving precise deposition of the catalyst precursors. The loading of both the anode and cathode catalysts was controlled at 0.4 mg / cm³. 2 ; 4. In-situ reduction / growth The exchange membrane with the catalyst precursor deposited in step 3 was placed in a 0.1M sodium borohydride (NaBH4) solution and reduced in situ (temperature 60℃, time 2h) to allow the catalyst precursor to grow at the preset position, forming an anode catalyst layer and a cathode catalyst layer that are tightly bonded to the exchange membrane. After the reduction was completed, it was washed with deionized water 3 times for 10min each time, and then dried at 60℃ for 2h. 5. Gradient aperture structure formation Three polystyrene microsphere suspensions with different particle sizes were prepared: 2 μm (for the side near the exchange membrane), 10 μm (for the middle region), and 30 μm (for the side near the gas diffusion layer). A layer-by-layer impregnation method was used: the catalyst layer was first impregnated in the 2 μm microsphere suspension, dried, then impregnated in the 10 μm microsphere suspension, and finally impregnated in the 30 μm microsphere suspension. The impregnation depth decreased layer by layer, forming a gradient distribution. After impregnation, the mixture was heat-treated at 350 °C for 1 h to remove the polystyrene microspheres, forming a porous structure with a gradient pore size distribution. 6. Construction of 3D Interpenetrating Networks A mixed solution containing 20 wt.% Nafion solution and 10 wt.% carbon nanotubes was prepared and uniformly coated onto a porous catalyst layer using a spraying method. A partitioned program control strategy was adopted to regulate the ratio and spatial distribution of Nafion and carbon nanotubes, which specifically included the following three steps: (1) Spraying on the membrane side: First, spray the catalyst layer area close to the exchange membrane. This area requires strong ion conduction ability. Therefore, a spraying solution with a mass ratio of Nafion to carbon nanotubes of 2:1 is used. Fine spraying is carried out under low pressure (0.1MPa) and low speed (nozzle movement speed of about 1mm / s) to control the thickness of the membrane surface adhesion layer to about 2μm, forming a dense and uniform ion conduction layer. (2) Spraying the intermediate area: The intermediate layer area is then sprayed with a spraying liquid with a mass ratio of Nafion to carbon nanotubes of 1:1. The spraying pressure is adjusted to 0.2MPa and the nozzle speed is adjusted to 2mm / s to control the coating thickness at 2μm, ensuring a balanced distribution of ion and electron channels, and at the same time having a certain degree of pore connectivity, which is beneficial to the mass transfer of reactants. (3) Spraying the gas diffusion layer side area: Finally, spray the area close to the gas diffusion layer. This area should have higher electronic conductivity and gas permeability. Therefore, a spraying liquid with a mass ratio of Nafion to carbon nanotubes of 1:2 is used. Spraying is carried out under high pressure (0.3MPa) and high speed (nozzle speed 3mm / s) to make the carbon nanotubes more densely distributed, enhance the continuity of the electrode electronic channel, and form some microporous structures in this area to assist gas emission. By controlling the ratio and distribution of Nafion and carbon nanotubes, a three-dimensional interpenetrating structure of catalyst network, ion conduction network and gas transport network was constructed. After coating, it needs to be heat-treated at 120℃ for 1 hour. 7. Gradient hydrophobicity treatment Polytetrafluoroethylene (PTFE) emulsions of different concentrations were prepared: 5 wt.% (for the side near the exchange membrane), 15 wt.% (for the middle region), and 25 wt.% (for the side near the gas diffusion layer). A layer-by-layer impregnation method was used to control the impregnation depth, forming a gradient structure with gradually increasing hydrophobicity from the exchange membrane side to the gas diffusion layer side. After impregnation, heat treatment was carried out at 150℃ for 30 min. 8. Assembly of the gas diffusion layer Carbon paper (TGP-H-060, Toray) was selected as the gas diffusion layer and assembled with the catalyst layer after step 7 by hot pressing. The hot pressing conditions were 140℃, 2MPa, and 3min to form a complete membrane electrode.

[0036] Performance testing: The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode prepared in Example 1 was assembled into a single cell, and its performance was tested under the following conditions: Fuel: 7M ammonia solution, flow rate 2mL / min Oxidizing agent: pure oxygen, flow rate 100 mL / min Operating temperature: 80℃ Working pressure: normal pressure The test results are shown in Table 1: Table 1 Performance Test Results

[0037] Example 2 Influence of different gradient parameters on the performance of membrane electrode assemblies in gradient porous three-dimensional interpenetrating networks for direct ammonia fuel cells The preparation method is basically the same as in Example 1, except that different pore size distribution parameters are used in the gradient pore size structure formation step, as follows: Sample A: Uniform pore size distribution, all pores are 10 μm; Sample B: Bilayer pore size distribution, with a pore size of 5 μm near the exchange membrane and a pore size of 20 μm near the gas diffusion layer; Sample C (i.e. Example 1): Three-layer gradient pore size distribution, with a pore size of 2 μm near the exchange membrane, a pore size of 10 μm in the middle region, and a pore size of 30 μm near the gas diffusion layer; Sample D: Five-layer gradient pore size distribution, with pore sizes of 1 μm, 3 μm, 10 μm, 20 μm, and 40 μm from the exchange membrane side to the gas diffusion layer side; The performance test conditions are the same as in Example 1, and the test results are shown in Table 2: Table 2 Performance Test Results

[0038] As shown in Table 2, the performance of the membrane electrode gradually improves with the increase of the number of gradient layers. However, the improvement from three-layer gradient to five-layer gradient is relatively small. Considering the complexity of the fabrication process and cost factors, the three-layer gradient structure is a more ideal choice.

[0039] Example 3 The Influence of Precision Deposition and In-situ Reduction / Growth Composite Processes on the Membrane Electrode Performance of Gradient Porous 3D Interpenetrating Network Direct Ammonia Fuel Cells The preparation method is basically the same as in Example 1, except that different process parameters are used for the precise deposition of the catalyst precursor and the in-situ reduction / growth steps, as detailed below: Process A: Traditional coating method, which involves directly coating the catalyst slurry onto the exchange membrane; Process B: Simple inkjet printing, using inkjet printing technology to deposit catalyst ink, without in-situ reduction steps; Process C: Simple in-situ growth, using an impregnation method to impregnate the catalyst precursor onto the exchange membrane, followed by in-situ reduction; Process D (i.e. Example 1): In-situ growth and precision deposition composite process; The performance test conditions are the same as in Example 1, and the test results are shown in Table 3: Table 3 Performance Test Results

[0040] As shown in Table 3, the in-situ growth and precision deposition composite process outperforms other processes in all performance indicators, especially in terms of catalyst utilization and interfacial bonding.

[0041] Example 4 The Influence of Different Catalyst Systems on the Membrane Electrode Performance of Gradient Porous Three-Dimensional Interpenetrating Network Direct Ammonia Fuel Cells The preparation method is basically the same as in Example 1, except that a different catalyst system is used in the precise deposition step of the catalyst precursor, as detailed below: Catalyst A: Pure Pt catalyst (both anode and cathode are Pt) Catalyst B: Pt-Co catalyst (anode is Pt-Co, cathode is Pt) Catalyst C: Pt-Ir catalyst (Pt-Ir at the anode, Pt at the cathode) Catalyst D: Pt-Ru catalyst (anode is Pt-Ru, cathode is Pt) The performance test conditions are the same as in Example 1, and the test results are shown in Table 4: Table 4 Performance Test Results

[0042] As shown in Table 4, the Pt-Ir catalyst (catalyst C) performs best in all performance indicators, especially in terms of the ammonia oxidation initiation potential, which is mainly due to the excellent ammonia oxidation catalytic activity of Ir. However, considering the high cost of Ir, the Pt-Co catalyst (catalyst B) is more cost-effective.

[0043] Example 5 Based on Examples 2-4, a three-layer gradient pore size distribution, in-situ growth and precise deposition composite process and Pt-Ir catalyst system were selected as the optimal parameter combination to prepare gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode, and the specific preparation method was the same as in Example 1. The prepared membrane electrode was assembled into a DAFC single cell and stack, and its performance was tested under different conditions: 1. Performance testing at different temperatures The performance of DAFC single cells was tested at four temperature points: 60℃, 70℃, 80℃, and 90℃. The performance test results are shown in Table 5. Table 5 Performance Test Results

[0044] 2. Performance testing at different ammonia concentrations The performance of DAFC single cells was tested at four ammonia concentration points: 0.5M, 1M, 2M, and 5M. The performance test results are shown in Table 6. Table 6 Performance Test Results

[0045] Comparative Example 1 Traditional disordered structure MEA (gas diffusion electrode method) The disordered MEA structure was prepared using the traditional gas diffusion electrode method, and the specific steps are as follows: 1. Catalyst slurry preparation Pt-Ir / C catalyst (20wt% Pt, 4wt% Ir), Nafion solution (5wt%) and isopropanol were mixed in a mass ratio of 3:1:20 and ultrasonically dispersed for 30 min to prepare catalyst slurry. 2. Preparation of gas diffusion electrode The catalyst slurry was directly coated onto carbon paper (TGP-H-060, Toray), with the catalyst loading controlled at 0.4 mg / cm³. 2 The gas diffusion electrode was prepared by drying at 80℃ for 1 hour. 3. Membrane electrode assembly The anode and cathode gas diffusion electrodes were assembled with the Fumasep FAAM-15 anion exchange membrane by hot pressing. The hot pressing conditions were 140℃, 2MPa, and 3min to form a complete membrane electrode.

[0046] The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0047] Comparative Example 2 Single-aperture ordered structure MEA The single-pore ordered MEA structure was prepared using a template method. The specific steps are as follows: 1. Catalyst slurry preparation Pt-Ir / C catalyst (20wt% Pt, 4wt% Ir), Nafion solution (5wt%), polystyrene microspheres (10μm in diameter) and isopropanol were mixed in a mass ratio of 3:1:2:20 and ultrasonically dispersed for 30 min to prepare a catalyst slurry containing a template. 2. Catalyst layer preparation The catalyst slurry was directly coated onto a Fumasep FAAM-15 anion exchange membrane, with the catalyst loading controlled at 0.4 mg / cm³. 2 Dry at 80℃ for 1 hour; 3. Template Removal The exchange membrane coated with the catalyst layer was heat-treated at 350℃ for 1 hour to remove the polystyrene microspheres and form an ordered porous structure with a single pore size. 4. Membrane electrode assembly The prepared exchange membrane was assembled with carbon paper (TGP-H-060, Toray) by hot pressing. The hot pressing conditions were 140℃, 2MPa, and 3min to form a complete membrane electrode. The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0048] Comparative Example 3 MEA prepared by conventional coating method The MEA was prepared using a traditional coating method, and the specific steps are as follows: 1. Catalyst slurry preparation Pt-Ir / C catalyst (20wt% Pt, 4wt% Ir), Nafion solution (5wt%) and isopropanol were mixed in a mass ratio of 3:1:20 and ultrasonically dispersed for 30 min to prepare catalyst slurry. 2. Catalyst layer preparation The catalyst slurry was directly coated onto a Fumasep FAAM-15 anion exchange membrane, with the catalyst loading controlled at 0.4 mg / cm³. 2 Dry at 80℃ for 1 hour; 3. Membrane electrode assembly The prepared exchange membrane was assembled with carbon paper (TGP-H-060, Toray) by hot pressing. The hot pressing conditions were 140℃, 2MPa, and 3min to form a complete membrane electrode. The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0049] Comparative Example 4 MEA prepared by inkjet printing alone The specific steps for fabricating MEAs using simple inkjet printing technology are as follows: 1. Preparation of catalyst ink Pt-Ir / C catalyst (20wt%Pt, 4wt%Ir), Nafion solution (5wt%), ethylene glycol and deionized water were mixed in a mass ratio of 3:1:10:10 and ultrasonically dispersed for 30 min to prepare catalyst ink. 2. Catalyst layer preparation Catalyst ink was precisely deposited on a Fumasep FAAM-15 anion exchange membrane using a piezoelectric inkjet printhead (droplet volume 50 pL, printing accuracy ±3 μm), with the catalyst loading controlled at 0.4 mg / cm³. 2 Dry at 80℃ for 1 hour; 3. Membrane electrode assembly The prepared exchange membrane was assembled with carbon paper (TGP-H-060, Toray) by hot pressing. The hot pressing conditions were 140℃, 2MPa, and 3min to form a complete membrane electrode. The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0050] Comparative Example 5 MEA prepared by simple in-situ growth MEAs were prepared using a simple in-situ growth technique, and the specific steps are as follows: 1. Membrane surface functionalization treatment Fumasep FAAM-15 anion exchange membrane (average thickness 15 μm) was placed in 0.5 M sulfonic acid functionalizing reagent for surface functionalization treatment (temperature 50 °C, time 2 h) to introduce sulfonic acid functionalization groups as anchor sites for catalyst growth; after the surface functionalization treatment, it was washed with deionized water 3 times, 10 min each time, and then dried at 60 °C for 1 h. 2. Catalyst precursor impregnation The treated exchange membrane was immersed in a mixed solution containing 0.05M chloroplatinic acid and 0.01M iridium chloride for 12 hours at room temperature. 3. In-situ reduction / growth An exchange membrane impregnated with a catalyst precursor was placed in a 0.1 M sodium borohydride solution at 60 °C for 2 h to carry out an in-situ reduction reaction. 4. Membrane electrode assembly The prepared exchange membrane was assembled with carbon paper (TGP-H-060, Toray) by hot pressing. The hot pressing conditions were 140℃, 2MPa, and 3min to form a complete membrane electrode. The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0051] Table 7 Performance Test Results

[0052] As shown in Table 7, the gradient porous three-dimensional interpenetrating network membrane electrode of the present invention is significantly superior to the comparative examples in all performance indicators. Compared with the traditional GDE method (Comparative Example 1), the maximum power density of the present invention is increased by 72.2%, the catalyst utilization rate is increased by 125%, and the performance retention rate after 5000 cycles is increased by 38.5%. Compared with the single-pore ordered structure (Comparative Example 2), the maximum power density of the present invention is increased by 47.6%, the catalyst utilization rate is increased by 60.7%, and the performance retention rate after 5000 cycles is increased by 25%. Compared with the traditional coating method (Comparative Example 3), simple inkjet printing (Comparative Example 4), and simple in-situ growth (Comparative Example 5), the present invention also shows significant advantages.

[0053] These results fully demonstrate the significant effect of the gradient porous three-dimensional interpenetrating network structure and the in-situ growth and precise deposition composite process of the present invention on improving the performance of DAFC, especially in key indicators such as catalyst utilization, long-term stability and interfacial bonding.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode, characterized in that, include: Exchange membrane, anode catalyst layer, cathode catalyst layer, and gas diffusion layer; The anode catalyst layer and the cathode catalyst layer have a gradient pore size distribution from the exchange membrane side to the gas diffusion layer side, including: The microporous structure near the exchange membrane has a pore size of 1–5 μm; The intermediate region has a mesoporous structure with a pore size of 5–20 μm; The macroporous structure near the gas diffusion layer has a pore size of 20–50 μm. The anode catalyst layer and the cathode catalyst layer have a three-dimensional interpenetrating network structure, including: The catalyst network forms a continuous electron conduction channel; An ion conduction network forms a continuous ion conduction channel; A gas transport network forms a continuous gas transport channel.

2. The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode according to claim 1, characterized in that, The exchange membrane is a proton exchange membrane or an anion exchange membrane; The anolyte catalyst in the anolyte catalyst layer is a platinum-based catalyst, an iridium-based catalyst, a ruthenium-based catalyst, or an alloy thereof, and the anolyte catalyst loading is 0.1–1.0 mg / cm³. 2 ; The cathode catalyst in the cathode catalyst layer is a platinum-based catalyst, a silver-based catalyst, a palladium-based catalyst, or an alloy thereof, and the cathode catalyst loading is 0.1–1.0 mg / cm³. 2 .

3. The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode according to claim 1, characterized in that, The ion conduction network is composed of an ion conduction polymer, which is one or more of perfluorosulfonic acid ion exchange resin, polybenzimidazole, polyether ether ketone, polysulfone, and quaternized polyarylether.

4. The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode according to claim 1, characterized in that, A transition layer is provided between the exchange membrane and the anode catalyst layer to improve interfacial contact and compatibility; The thickness of the transition layer is 1 to 10 μm, and it is composed of the ion-conducting polymer and the anode catalyst. The content of the anode catalyst gradually increases from 10% to 70% from the exchange membrane side to the anode catalyst layer side, and the content of the ion-conducting polymer gradually decreases from 30% to 90% from the exchange membrane side to the anode catalyst layer side.

5. The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode according to claim 1, characterized in that, Furthermore, the cathode catalytic layer and the gas diffusion layer have a gradient hydrophobic design to optimize water management; The gradient hydrophobicity design specifically involves increasing hydrophobicity from the cathode catalytic layer side to the gas diffusion layer side, wherein the contact angle on the cathode catalytic layer side is 60–90° and the contact angle on the gas diffusion layer side is 120–150°.

6. A method for preparing a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Functional treatment of the exchange membrane surface The exchange membrane is placed in a functionalizing reagent and its surface is functionalized to introduce functional groups on the surface of the exchange membrane as anchors for catalyst growth. (2) Preparation of transition layer After surface functionalization treatment in step 1, a mixed solution containing ion-conducting polymer and anode catalyst precursor is deposited on the surface of the exchange membrane using a precision deposition technique to form a transition layer. (3) Precise deposition of catalyst precursor Using improved inkjet printing or ultrasonic atomization technology, ink containing anodic catalyst precursor and cathode catalyst precursor is precisely deposited sequentially on the surface of the transition layer obtained in step 2, thereby achieving precise deposition of catalyst precursor; (4) In-situ reduction / growth The exchange membrane with the catalyst precursor deposited in step 3 is placed in a reducing agent and reduced in situ, so that the catalyst precursor grows at a preset position to form an anode catalyst layer and a cathode catalyst layer that are tightly bonded to the exchange membrane. (5) Gradient aperture structure formation A template method was used to form porous structures with gradient pore size distribution in the anode and cathode catalyst layers; (6) Construction of three-dimensional interpenetrating network By controlling the proportions and distributions of catalyst, ion-conducting polymer, and pore-forming agent, a three-dimensional interpenetrating structure of catalyst network, ion-conducting network, and gas transport network was constructed. (7) Gradient hydrophobicity treatment The surface of the cathode catalyst layer is subjected to a gradient hydrophobicity treatment, so that its hydrophobicity gradually increases from the exchange membrane side to the gas diffusion layer side. (8) Assembly of gas diffusion layer The treated gas diffusion layer and the catalyst layer after the treatment in step 7 are assembled by hot pressing to form a complete membrane electrode.

7. The preparation method according to claim 6, characterized in that, In step (1), the functionalizing agent is specifically an organic solution containing carboxyl, sulfonic acid, amino, or hydroxyl groups; the surface functionalization treatment is performed at a temperature of 30–80°C for 0.5–5 hours. In step (2), the anode catalyst precursor is specifically one or more of the following: soluble salts or complexes of platinum, iridium, and ruthenium; In step (3), the cathode catalyst precursor is specifically one or more of the soluble salts or complexes of platinum, silver, and palladium; the inkjet printing uses a piezoelectric inkjet printhead with a droplet volume of 1 to 100 pL and a printing accuracy of ±5 μm; the ultrasonic atomization technology has an ultrasonic frequency of 1 to 3 MHz and an atomization rate of 0.1 to 5 mL / min. In step (4), the reducing agent is specifically one or more of sodium borohydride, hydrogen, formic acid, ascorbic acid and ethylene glycol; the in-situ reduction temperature is 30-100℃ and the time is 0.5-5h. In step (5), the template is polystyrene microspheres, silica microspheres, or carbon nanomaterials; In step (7), the gradient hydrophobic treatment is performed by fluorination or hydrophobic polymer impregnation, and the treatment depth gradually increases from the exchange membrane side to the gas diffusion layer side. In step (8), the hot pressing temperature is 120-180℃, the pressure is 0.5-5MPa, and the time is 1-10min.

8. The application of a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode assembly as described in any one of claims 1 to 5 in a direct ammonia fuel cell.

Images