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

Abstract

The present application 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 film, an anode catalytic layer, a cathode catalytic layer and a gas diffusion layer; the anode catalytic layer and the cathode catalytic layer have a gradient pore size distribution from the exchange film side to the gas diffusion layer side; and the anode catalytic layer and the cathode catalytic layer have a three-dimensional interpenetrating network structure inside.The present application improves the catalyst utilization rate by 30-50%, reduces the mass transfer resistance by 40-60%, improves the interface contact, improves the controllability of the preparation process, enhances the structural stability, and makes the power density of the direct ammonia fuel cell reach 250-300 mW / cm 2 , and the performance retention rate can reach more than 85% after 5000 cycles, so that the present application has significant technical advantages and application prospects.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy materials, in particular to a gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode. BACKGROUND

[0002] With the global energy crisis and environmental pollution problems becoming increasingly serious, developing clean and efficient energy conversion and storage technologies has become a hot research topic. Hydrogen energy, as a clean energy carrier, has the advantages of high energy density and no pollution, but its storage and transportation face great challenges. Ammonia (NH3) as a carbon-free hydrogen carrier molecule has the advantages of high energy density, high liquefaction temperature (-33℃, 0.1MPa), easy storage and transportation, and is considered an ideal hydrogen energy carrier. Direct ammonia fuel cell (DAFC) is an electrochemical device that uses ammonia as fuel, which can directly convert the chemical energy in ammonia molecules into electrical energy through electrochemical reaction. Compared with traditional hydrogen fuel cells, DAFC can utilize the existing global ammonia production and distribution network, reduce the cost and technical barriers of large-scale application, and avoid the difficulties of hydrogen storage and transportation, thus having broad application prospects.

[0003] Membrane electrode assembly (MEA) is the core component of DAFC, which together with the bipolar plate constitutes the basic unit of the fuel cell. MEA is mainly composed of proton exchange membrane / anion exchange membrane (according to the type of fuel cell), anode catalyst layer (ammonia oxidation reaction occurs in this area), cathode catalyst layer (oxygen reduction reaction occurs in this area) and gas diffusion layer (provides a reaction material transport channel). In DAFC, ammonia oxidation reaction (AOR) occurs at the anode, which is a multi-step process involving N-H bond breaking, N-N bond formation and diatomic nitrogen release. Due to the complexity of the reaction path, AOR has the problems of slow kinetics, uncontrollability and instability, which seriously restricts the performance and commercial application of DAFC.

[0004] Currently, the preparation technology of MEA has mainly experienced three generations of development. The first generation of gas diffusion electrode method (GDE) is to directly coat the dispersed catalyst slurry on the pretreated porous diffusion layer, and then hot-press the gas diffusion electrode and proton exchange membrane into a membrane electrode. The advantages of GDE type MEA are relatively simple and mature preparation process, which is conducive to the formation of pores in MEA, and can also protect the proton exchange membrane from deformation. However, due to the low utilization rate of catalysts (less than 20%), the cost of MEA is increased, and the preparation process of GDE structure MEA is mainly used in the laboratory. The second generation of catalyst coating membrane method (CCM) is to coat the catalyst directly on the proton exchange membrane, and then coat the cathode gas diffusion layer and anode gas diffusion layer on both sides of the proton exchange membrane with catalyst through hot pressing method, forming a three-in-one membrane electrode with a thickness of about 10 μm. The catalyst and the proton exchange membrane are well combined and not easy to peel off, which improves the utilization rate of catalysts in the catalyst layer and has good comprehensive performance. CCM technology is widely used and is the current mainstream commercial MEA preparation method. The third generation of ordered membrane electrode is to construct an ordered structure in the membrane electrode, including nano-array structure or other ordered structure. These ordered structures can be ordered proton transport structure, ordered electron transport structure, ordered catalyst layer structure or ordered material transport structure. These structures can provide ordered proton, electron or material transport channels, reduce their transport resistance, maximize the three-phase interface of chemical reaction, and improve the stability of electrode structure, thereby greatly prolonging the service life of the battery.

[0005] However, the existing DAFC membrane electrode still has the following problems: 1) low catalyst utilization rate: in the traditional disordered structure MEA, the catalyst is unevenly distributed, and the three-phase interface is limited, resulting in low catalyst utilization rate, usually less than 30%, causing waste of precious metal resources and increasing cost. 2) Large mass transfer resistance: in the existing MEA structure, the transmission path of reactants and products is complex and the resistance is large, especially at high current density, mass transfer limitation becomes the main factor restricting the performance of the battery. 3) Poor interface contact: the interface contact between the catalyst layer and the membrane, and the catalyst layer and the gas diffusion layer is poor, which increases the interface resistance and affects the performance and life of the battery. 4) Uncontrollable preparation process: the preparation process such as traditional coating and spraying method is difficult to accurately control the distribution and loading of catalysts, resulting in poor product consistency and being not conducive to large-scale production. 5) Poor structural stability: during long-term operation, the catalyst layer structure is easy to change, which reduces the three-phase interface and reduces the performance of the battery.

[0006] Therefore, it is urgent to develop a new type of DAFC membrane electrode structure and its preparation method to solve the problems of low catalyst utilization rate, large mass transfer resistance, poor interface contact, uncontrollable preparation process and poor structural stability in the prior art, and improve the performance and commercial application prospect of DAFC. SUMMARY

[0007] The gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode provided by the present application solves the problems of low catalyst utilization, large mass transfer resistance, poor interface contact, uncontrollable preparation process and poor structural stability in the prior art.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solutions.

[0009] One of the technical solutions of the present application is:

[0010] A gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode, comprising: an exchange membrane, an anode catalyst layer, a cathode catalyst layer and a gas diffusion layer.

[0011] 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, comprising:

[0012] A microporous structure close to the exchange membrane side, with a pore size of 1-5 μm;

[0013] A mesoporous structure in the middle region, with a pore size of 5-20 μm;

[0014] A macroporous structure close to the gas diffusion layer side, with a pore size of 20-50 μm;

[0015] The anode catalyst layer and the cathode catalyst layer have a three-dimensional interpenetrating network structure inside, comprising:

[0016] A catalyst network forming a continuous electron conduction channel;

[0017] An ion conduction network forming a continuous ion conduction channel;

[0018] A gas transport network forming a continuous gas transport channel.

[0019] Further, the exchange membrane is a proton exchange membrane or an anion exchange membrane.

[0020] Further, the anode catalyst in the anode catalyst layer is a platinum-based catalyst, an iridium-based catalyst, a ruthenium-based catalyst or an alloy thereof, and the anode catalyst loading is 0.1-1.0 mg / cm 2 .

[0021] Further, 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 / cm 2 .

[0022] Further, the ion-conducting network is composed of ion-conducting polymers, which are one or more of perfluorosulfonic acid type ion exchange resin, polybenzimidazole, polyether ether ketone, polysulfone and quaternized polyarylether.

[0023] Further, a transition layer is provided between the exchange membrane and the anode catalyst layer for improving interface contact and compatibility.

[0024] The thickness of the transition layer is 1-10 microns, which is a mixture of the ion-conducting polymer and the anode catalyst, wherein the content of the anode catalyst gradually increases from 10% on the exchange membrane side to 70% on the anode catalyst layer side, and the content of the ion-conducting polymer gradually decreases from 30% on the exchange membrane side to 90% on the anode catalyst layer side.

[0025] Further, the cathode catalyst layer and the gas diffusion layer have a gradient hydrophobicity design for optimizing water management.

[0026] The gradient hydrophobicity design is specifically that the hydrophobicity gradually increases from the cathode catalyst layer side to the gas diffusion layer side, wherein the contact angle on the cathode catalyst layer side is 60-90°, and the contact angle on the gas diffusion layer side is 120-150°.

[0027] Technical solution two of the application:

[0028] The above-mentioned preparation method of the gradient porous three-dimensional interpenetrating network direct ammonia fuel cell membrane electrode comprises the following steps:

[0029] (1) Surface functionalization treatment of the exchange membrane

[0030] The exchange membrane is placed in a functionalization reagent for surface functionalization treatment, and a functional group is introduced on the surface of the exchange membrane as an anchor point for catalyst growth.

[0031] (2) Transition layer preparation

[0032] A mixed solution containing ion-conducting polymers and anode catalyst precursors is deposited on the surface of the exchange membrane after the surface functionalization treatment in step 1 by using a precise deposition technique to form a transition layer.

[0033] (3) Precise deposition of catalyst precursors

[0034] Improved inkjet printing or ultrasonic atomization technology is used to precisely deposit ink containing anode catalyst precursors and cathode catalyst precursors on the surface of the transition layer obtained in step 2 in sequence to realize precise deposition of catalyst precursors.

[0035] (4) In-situ reduction / growth

[0036] The catalyst precursor deposited exchange membrane obtained in step 3 is placed in a reducing agent for in-situ reduction, so that the catalyst precursor grows at the preset position to form an anode catalytic layer and a cathode catalytic layer closely combined with the exchange membrane;

[0037] (5) Gradient pore structure formation

[0038] A gradient pore distribution porous structure is formed in the anode catalytic layer and the cathode catalytic layer by using a template method;

[0039] (6) Three-dimensional interpenetrating network construction

[0040] A three-dimensional interpenetrating structure of catalyst network, ion conduction network and gas transmission network is constructed by controlling the proportion and distribution of catalyst, ion conduction polymer and pore forming agent;

[0041] (7) Gradient hydrophobicity treatment

[0042] The surface of the cathode catalytic layer is subjected to gradient hydrophobicity treatment, so that the hydrophobicity gradually increases from the exchange membrane side to the gas diffusion layer side;

[0043] (8) Gas diffusion layer assembly

[0044] The treated gas diffusion layer and the catalyst layer after step 7 treatment are assembled by hot pressing to form a complete membrane electrode.

[0045] Further, in step (1), the functionalizing agent is specifically an organic solution containing carboxyl, sulfonic acid group, amino or hydroxyl group.

[0046] Further, in step (1), the surface functionalization treatment temperature is 30-80℃, and the time is 0.5-5h.

[0047] Further, in step (2), the anode catalyst precursor is specifically one or more of soluble salts or complexes of platinum, iridium and ruthenium.

[0048] Further, in step (3), the cathode catalyst precursor is specifically one or more of soluble salts or complexes of platinum, silver and palladium.

[0049] Further, in step (3), the inkjet printing uses a piezoelectric inkjet printhead, the ink droplet volume is 1-100pL, and the printing accuracy is ±5μm.

[0050] Further, in step (3), the ultrasonic atomization technology has an ultrasonic frequency of 1-3MHz and an atomization rate of 0.1-5mL / min.

[0051] Further, in step (4), the reducing agent is specifically one or more of sodium borohydride, hydrogen, formic acid, ascorbic acid and ethylene glycol.

[0052] Furthermore, in step (4), the in-situ reduction temperature is 30-100℃ and the time is 0.5-5h.

[0053] Furthermore, in step (5), the template is a polystyrene microsphere, a silica microsphere, or a carbon nanomaterial.

[0054] 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.

[0055] 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.

[0056] The third technical solution of this invention:

[0057] 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.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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;

[0063] 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.

[0064] 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

[0065] 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:

[0066] Figure 1 This is an electron microscope image of the gradient aperture structure of the membrane electrode in Embodiment 1 of the present invention;

[0067] 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;

[0068] 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

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Example 1

[0075] 1. Functional treatment of exchange membrane surface

[0076] 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.

[0077] 2. Preparation of transition layer

[0078] 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;

[0079] 3. Precise deposition of catalyst precursors

[0080] 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 ;

[0081] 4. In-situ reduction / growth

[0082] 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.

[0083] 5. Gradient aperture structure formation

[0084] 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.

[0085] 6. Construction of 3D Interpenetrating Networks

[0086] 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.

[0087] 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:

[0088] (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.

[0089] (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.

[0090] (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.

[0091] 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.

[0092] 7. Gradient hydrophobicity treatment

[0093] 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.

[0094] 8. Assembly of the gas diffusion layer

[0095] 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.

[0096] Performance testing:

[0097] 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:

[0098] Fuel: 7M ammonia solution, flow rate 2mL / min

[0099] Oxidizing agent: pure oxygen, flow rate 100 mL / min

[0100] Operating temperature: 80℃

[0101] Working pressure: normal pressure

[0102] The test results are shown in Table 1:

[0103] Table 1 Performance Test Results

[0104]

[0105] Example 2

[0106] Influence of different gradient parameters on the performance of membrane electrode assemblies in gradient porous three-dimensional interpenetrating networks for direct ammonia fuel cells

[0107] 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:

[0108] Sample A: Uniform pore size distribution, all pores are 10 μm;

[0109] 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;

[0110] 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;

[0111] 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;

[0112] The performance test conditions are the same as in Example 1, and the test results are shown in Table 2:

[0113] Table 2 Performance Test Results

[0114]

[0115] 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.

[0116] Example 3

[0117] 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

[0118] 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:

[0119] Process A: Traditional coating method, which involves directly coating the catalyst slurry onto the exchange membrane;

[0120] Process B: Simple inkjet printing, using inkjet printing technology to deposit catalyst ink, without in-situ reduction steps;

[0121] Process C: Simple in-situ growth, using an impregnation method to impregnate the catalyst precursor onto the exchange membrane, followed by in-situ reduction;

[0122] Process D (i.e. Example 1): In-situ growth and precision deposition composite process;

[0123] The performance test conditions are the same as in Example 1, and the test results are shown in Table 3:

[0124] Table 3 Performance Test Results

[0125]

[0126] 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.

[0127] Example 4

[0128] The Influence of Different Catalyst Systems on the Membrane Electrode Performance of Gradient Porous Three-Dimensional Interpenetrating Network Direct Ammonia Fuel Cells

[0129] 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:

[0130] Catalyst A: Pure Pt catalyst (both anode and cathode are Pt)

[0131] Catalyst B: Pt-Co catalyst (anode is Pt-Co, cathode is Pt)

[0132] Catalyst C: Pt-Ir catalyst (Pt-Ir at the anode, Pt at the cathode)

[0133] Catalyst D: Pt-Ru catalyst (anode is Pt-Ru, cathode is Pt)

[0134] The performance test conditions are the same as in Example 1, and the test results are shown in Table 4:

[0135] Table 4 Performance Test Results

[0136]

[0137] 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.

[0138] Example 5

[0139] 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.

[0140] The prepared membrane electrode was assembled into a DAFC single cell and stack, and its performance was tested under different conditions:

[0141] 1. Performance testing at different temperatures

[0142] 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.

[0143] Table 5 Performance Test Results

[0144]

[0145] 2. Performance testing at different ammonia concentrations

[0146] 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.

[0147] Table 6 Performance Test Results

[0148]

[0149] Comparative Example 1

[0150] Traditional disordered structure MEA (gas diffusion electrode method)

[0151] The disordered MEA structure was prepared using the traditional gas diffusion electrode method, and the specific steps are as follows:

[0152] 1. Catalyst slurry preparation

[0153] 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.

[0154] 2. Preparation of gas diffusion electrode

[0155] 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.

[0156] 3. Membrane electrode assembly

[0157] 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.

[0158] The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0159] Comparative Example 2

[0160] Single-aperture ordered structure MEA

[0161] The single-pore ordered MEA structure was prepared using a template method. The specific steps are as follows:

[0162] 1. Catalyst slurry preparation

[0163] 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.

[0164] 2. Catalyst layer preparation

[0165] 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;

[0166] 3. Template Removal

[0167] 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.

[0168] 4. Membrane electrode assembly

[0169] 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.

[0170] The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0171] Comparative Example 3

[0172] MEA prepared by conventional coating method

[0173] The MEA was prepared using a traditional coating method, and the specific steps are as follows:

[0174] 1. Catalyst slurry preparation

[0175] 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.

[0176] 2. Catalyst layer preparation

[0177] 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;

[0178] 3. Membrane electrode assembly

[0179] 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.

[0180] The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0181] Comparative Example 4

[0182] MEA prepared by inkjet printing alone

[0183] The specific steps for fabricating MEAs using simple inkjet printing technology are as follows:

[0184] 1. Preparation of catalyst ink

[0185] 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.

[0186] 2. Catalyst layer preparation

[0187] Catalyst ink was precisely deposited on the 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;

[0188] 3. Membrane electrode assembly

[0189] 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.

[0190] The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0191] Comparative Example 5

[0192] MEA prepared by simple in-situ growth

[0193] MEAs were prepared using a simple in-situ growth technique, and the specific steps are as follows:

[0194] 1. Membrane surface functionalization treatment

[0195] 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.

[0196] 2. Catalyst precursor impregnation

[0197] 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.

[0198] 3. In-situ reduction / growth

[0199] 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.

[0200] 4. Membrane electrode assembly

[0201] 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.

[0202] The performance test conditions were the same as in Example 5, and the test results are shown in Table 7.

[0203] Table 7 Performance Test Results

[0204]

[0205] 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.

[0206] 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.

[0207] 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; The method for preparing the 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 Three polystyrene microsphere suspensions with different particle sizes were prepared: a polystyrene microsphere suspension for the side near the exchange membrane, a polystyrene microsphere suspension for the intermediate region, and a polystyrene microsphere suspension for the side near the gas diffusion layer. A layer-by-layer impregnation method was used: first, the catalyst layer was impregnated in the polystyrene microsphere suspension for the side near the exchange membrane, dried, then impregnated in the polystyrene microsphere suspension for the intermediate region, and finally impregnated in the polystyrene microsphere suspension for the side near the gas diffusion layer. The impregnation depth decreased layer by layer, forming a gradient distribution. After impregnation, the mixture was heat-treated at 350℃ for 1 hour to remove the polystyrene microspheres, forming a porous structure with a gradient pore size distribution. (6) Construction of three-dimensional interpenetrating network A mixed solution containing 20 wt.% Nafion solution and 10 wt.% carbon nanotubes was prepared and uniformly coated onto a porous catalyst layer by spraying. 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. (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.

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, or a ruthenium-based catalyst, 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, or a palladium-based catalyst, 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, wherein the content of the anode catalyst gradually increases from 10% to 70% 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 Three polystyrene microsphere suspensions with different particle sizes were prepared: a polystyrene microsphere suspension for the side near the exchange membrane, a polystyrene microsphere suspension for the intermediate region, and a polystyrene microsphere suspension for the side near the gas diffusion layer. A layer-by-layer impregnation method was used: first, the catalyst layer was impregnated in the polystyrene microsphere suspension for the side near the exchange membrane, dried, then impregnated in the polystyrene microsphere suspension for the intermediate region, and finally impregnated in the polystyrene microsphere suspension for the side near the gas diffusion layer. The impregnation depth decreased layer by layer, forming a gradient distribution. After impregnation, the mixture was heat-treated at 350℃ for 1 hour to remove the polystyrene microspheres, forming a porous structure with a gradient pore size distribution. (6) Construction of three-dimensional interpenetrating network A mixed solution containing 20 wt.% Nafion solution and 10 wt.% carbon nanotubes was prepared and uniformly coated onto a porous catalyst layer by spraying. 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. (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 (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.

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