Gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material and preparation method thereof

Abstract

The invention discloses a gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material and a preparation method thereof, and belongs to the field of hydrogen fuel cell catalytic materials. The catalyst is prepared by taking an AB2 type superlattice PtCoFeCr alloy as an active core (Co: Fe: Cr = 3: 1: 0.2), forming a periodic strain field through [111] crystal face orientation regulation and control, combining a nitrogen-doped carbon nanotube (N content is 8.5 at%) carrier and adopting a pulsed laser deposition-microwave annealing combined technology and a supercritical CO2 fluid loading process. The ORR mass activity reaches 6.2 A / mgPt at 0.9 V and is improved by 17 times compared with that of commercial Pt / C, and the activity is attenuated by lt after 30,000 times of circulation; the single-stack platinum dosage is 7.2 mg / kW, the large-scale cost is 380 yuan / g, the cost bottleneck of a hydrogen energy automobile catalyst can be broken through, and the method is suitable for the field of new energy automobiles.

Description

Technical Field

[0001] This invention belongs to the technical field of high-efficiency catalytic materials for hydrogen fuel cells, specifically a gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method. This technology significantly enhances the catalytic activity and durability of the oxygen reduction reaction (ORR) by utilizing an atomic-level gradient doping strategy (PtCoFeCr alloy), periodic lattice strain field control, and synergistic optimization of the nitrogen-doped carbon nanotube support. To address core issues in proton exchange membrane fuel cell (PEMFC) cathode materials, including low platinum utilization (commercial Pt / C only 0.35 A / mgPt), lifetime degradation due to metal dissolution (>40% after 30,000 cycles), and high scale-up production costs (commercial Pt / C reaches 1,200 yuan / gram), a superlattice structure design combined with a low-temperature epitaxial growth process (pulsed laser deposition-microwave annealing) and a supercritical CO2 fluid dispersion process was proposed. This technology reduces the platinum loading to 7.2 mg / kW (compared to 18.5 mg / kW with conventional solutions), increases activity by 17 times (6.2 A / mgPt at 0.9V), and reduces the scale-up cost to 380 yuan / gram. This technology has broad applications in automotive hydrogen fuel cells (especially high-power stacks for heavy trucks), stationary power generation systems, and hydrogen production from water electrolysis, providing an innovative solution to overcome material cost and performance bottlenecks in the hydrogen energy industry. Background Art

[0002] As a key clean energy technology for achieving the "dual carbon" goals, hydrogen fuel cells rely heavily on breakthroughs in cathode oxygen reduction reaction (ORR) catalysts for their core performance and cost. Currently, the development of cathode materials for proton exchange membrane fuel cells (PEMFCs) faces multiple technical challenges, severely hindering the large-scale deployment of hydrogen vehicles.

[0003] Commercial Pt / C catalysts, the current mainstream choice, have inherent defects that are difficult to overcome: under the critical operating condition of 0.9V vs. RHE, the ORR mass activity is only 0.35 A / mgPt, which cannot meet the high current density requirements of high-power fuel cells such as heavy trucks. At the same time, its platinum utilization rate is less than 20%, resulting in a single-stack platinum dosage of up to 18.5 mg / kW. Combined with a large-scale production cost of 1,200 yuan / gram, the purchase cost of hydrogen vehicles far exceeds that of traditional fuel vehicles. The more prominent problem lies in durability. After 30,000 cycle tests, the activity of commercial Pt / C has decayed by more than 40%, and the dissolution rate of metallic platinum is as high as 0.9 μg / cm 2 / 10,000 times, which is far from the 80,000-hour life requirement of the vehicle fuel cell, greatly increasing the user's subsequent maintenance costs.

[0004] To address the above issues, the industry has tried a variety of technical approaches, but all have significant limitations. Regarding platinum-based alloy catalysts, Toyota's Pt-Co octahedral alloy has increased its activity to 1.2 A / mgPt by regulating lattice strain. However, this relies on expensive molecular beam epitaxy technology, resulting in a large-scale production cost exceeding 2,000 yuan / gram. Furthermore, the activity decays by 35% after 30,000 cycles, and the dissolution rate of metallic Co is 0.4 μg / cm 2 While non-precious metal catalysts such as Fe-NC are inexpensive, their ORR mass activity is less than 0.1 A / mgPt, and their activity decays by more than 70% after 10,000 cycles, making them inadequate for practical applications.

[0005] Superlattice structure design is considered a potential solution for simultaneously improving activity and stability, but its development is limited by three major technical bottlenecks: First, structural regulation is difficult. The PtNi superlattice developed by KAIST in South Korea completely failed after 5,000 cycles because it could not suppress the dissolution of metal ions. Second, the preparation process is complex. The atomic layer deposition (ALD) technology used by the Argonne National Laboratory in the United States has a yield of less than 5%, making it difficult to achieve large-scale production. Third, the carrier synergy effect is missing. The specific surface area of ​​traditional carbon black carriers is only 240 m 2 / g, conductivity 0.4×10 3 S / cm and lack of strong interaction with superlattice particles, leading to severe particle agglomeration and further exacerbating performance degradation. Furthermore, the nitrogen source and doping method of nitrogen-doped carbon supports are not rational, with pyridinic nitrogen content generally below 5 at%, which cannot effectively increase the density of ORR active sites and makes it difficult to control the surface adsorption energy of the catalyst through electronic effects.

[0006] The carrier preparation process also has its pain points. Traditionally, the highly corrosive HF etching template is used, which not only produces highly toxic wastewater and high processing costs, but also damages the integrity of the carbon skeleton, resulting in a corrosion rate exceeding 30% in acidic conditions. Existing carbon materials lack adequate surface functional groups, resulting in weak anchoring with metal particles, further reducing the catalyst's cyclic stability. Therefore, achieving comprehensive breakthroughs in catalyst activity, durability, and cost through precise superlattice structure design, coordinated carrier optimization, and innovative low-cost preparation processes has become a core issue in promoting the commercial application of hydrogen fuel cells. Summary of the Invention

[0007] In order to better explain the present invention, exemplary embodiments of the present invention will be described in more detail below. Although exemplary embodiments of the present invention are shown below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to enable the scope of the present invention to be fully conveyed to those skilled in the art. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0008] The present invention provides a gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and a preparation method thereof. This process achieves a breakthrough improvement in catalyst activity and durability through the synergistic effect of three core technologies: structural regulation of the nitrogen-doped carrier (S1), atomic-level superlattice construction (S2), and supercritical fluid dispersion (S3). Specific technical features are as follows: S1, preparation of nitrogen-doped carbon nanotube (N-CNT) support; S2, epitaxial growth of superlattice platinum-cobalt alloy; S3, supercritical CO2 fluid is evenly dispersed; S4. Membrane electrode integration and performance verification.

[0009] Furthermore, in S1, the preparation of the nitrogen-doped carbon nanotube (N-CNT) support further includes the following steps: S1-1, precursor design; S1-2, template synthesis; The specific steps for preparing nitrogen-doped carbon nanotube (N-CNT) carriers are as follows: S1-1. Precursor design: A dual-template system was constructed using a [BMIM][TFSI] ionic liquid as a soft template (thermal decomposition temperature >400°C) combined with a silica hard template (mass ratio 1:3). Gradient nitrogen doping was achieved using a urea-melamine composite nitrogen source (mass ratio 1:2). Urea was pre-decomposed at 150°C to produce an NH3-pre-nitrided carbon skeleton. 0.5wt% FeCl3 was added as a graphitization promoter, and the microwave pyrolysis temperature was lowered to 750°C.

[0010] S1-2, Template Synthesis: After pyrolysis under pulsed microwave irradiation (2 seconds on / 1 second off), the specific surface area reached 850 m 2 / g, pore size distribution of 12-18nm, and pyridinic nitrogen content of 9.2at%. The template was then removed using a 5wt% NH4HF2 solution etched at 60°C for 6 hours, leaving a surface -COOH fraction ≥18%. The oxygen vacancy concentration was then increased by 15% via Ar / O2 low-temperature plasma activation.

[0011] Furthermore, in S2, the epitaxial growth of the superlattice platinum-cobalt alloy further includes the following steps: S2-1, pulsed laser deposition (PLD) regulation; S2-2, gradient microwave annealing ordering.

[0012] The specific steps of epitaxial growth of superlattice platinum-cobalt alloy are as follows: S2-1. Pulsed Laser Deposition (PLD) Control: In vacuum ≤5×10 -6 Under Torr conditions, Pt is deposited alternately 50 Co 45 The Fe5 prefabricated alloy target and the Cr single element target were used, and the thickness of each layer was controlled to ±0.1nm. 5% CO gas was introduced into the chamber to combine with 3.5 J / cm 2 Laser energy density (wavelength 248nm) induces preferential growth of crystal planes with an orientation degree of >95%. Real-time monitoring of superlattice diffraction fringes (period 2.71Å) via reflection high-energy electron diffraction (RHEED) triggers interlayer switching, reducing interface defect rates by 30%.

[0013] S2-2, Gradient microwave annealing ordering: A three-stage gradient annealing process is used: Atomic diffusion activation: 2.45 GHz microwave irradiation at 400-500°C for 30 seconds; Short-range order formation: 500-650℃ dual-frequency alternating radiation (2.45GHz+5.8GHz) for 60 seconds; Long-range structural locking: 5.8 GHz directional radiation at 650-700°C for 30 seconds. Annealing atmosphere is a CO / H2 / Ar mixture (volume ratio 1:4:95) with a CO partial pressure of 0.01 atm to suppress surface reconstruction. After annealing, the lattice constant accuracy reaches ±0.01 Å.

[0014] Furthermore, in S3, the uniform dispersion of the supercritical CO2 fluid further comprises the following steps: S3-1, dynamic pressure dispersion and in-situ reduction; S3-2, post-processing and stability enhancement.

[0015] The supercritical CO2 fluid is evenly dispersed. The specific steps are as follows: S3-1. Dynamic pressure dispersion and in-situ reduction: The precursor was placed in a supercritical CO2 fluid (50°C, 10-15 MPa periodic pressure fluctuation, frequency 0.1 Hz), and 5 vol% ethanol co-solvent was added to improve the solubility of the platinum precursor. 0.5% H2 was introduced to achieve Pt 2+ →Pt 0In-situ reduction, platinum utilization rate reaches 82%, particle size distribution D90≤8%. Simultaneously using cavitation effect to break the tendency of particle aggregation, anchoring density increased to 4.5 particles / nm 2 .

[0016] S3-2, Post-processing and stability enhancement: Ar / O2 low-temperature plasma (100W, 5min) was used to remove surface organic matter and increase the oxygen vacancy concentration by 15%. Sodium dodecyl sulfate (SDS) was introduced in supercritical CO2 to self-assemble into a nano-protective layer, which was then microwave annealed at 250°C for 2 hours to reduce the surface defect activity. After storage for 6 months, the activity decayed by <0.5%.

[0017] Furthermore, in S4, membrane electrode integration and performance verification further includes the following steps: S4-1, catalytic layer construction; S4-2. Electrochemical performance test.

[0018] Membrane electrode integration and performance verification, the specific steps are as follows: S4-1. Construction of catalytic layer: Short side chain perfluorosulfonic acid resin (EW=670) was used as the ionomer, and a slurry was prepared with a mixed solvent of water / ethylene glycol / n-propanol (volume ratio 6:3:1) and sprayed onto the surface of the proton membrane. The catalyst loading was 0.15 mg / cm 2 , the thickness of the three-phase interface is compressed to 15nm.

[0019] S4-2. Electrochemical performance test: In the rotating disk electrode test, the ORR mass activity reached 6.2 A / mgPt at 0.9V vs. RHE, with a Tafel slope of 29mV / dec; after the accelerated endurance test (0.6-1.0V, 30,000 cycles), the activity decay was <5%, and the platinum dissolution rate was <0.01μg / km. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the preparation process of gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material; from Figure 1As can be seen, the figure shows the complete preparation process of gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode materials, which specifically includes four core process stages and key sub-steps in each stage: First, the preparation of N-CNT carriers, including precursor design (using dual templates and urea-melamine gradient nitrogen source to configure raw materials) and template synthesis (carriers are obtained by pulsed microwave radiation pyrolysis, NH4HF2 etching and Ar / O2 low-temperature plasma activation); second, the epitaxial growth of superlattice platinum-cobalt alloys, covering pulsed laser deposition (PLD) regulation (alternating deposition of PtCoF under vacuum environment); The first is the uniform dispersion of supercritical CO2 fluid, including dispersion and reduction (using supercritical CO2 dynamic pressure dispersion and H2 in-situ reduction to achieve active core loading) and post-treatment (forming a protective layer through plasma cleaning and SDS self-assembly); the fourth is membrane electrode integration and performance verification, involving the construction of a catalytic layer (using a specific ionomer and a mixed solvent to prepare and spray the catalytic layer) and performance testing (verifying the electrochemical performance and operating adaptability of the membrane electrode). The flowchart clearly shows the full process logic from support synthesis, active core construction, load binding to final integration verification. The synergistic effect of the sub-steps in each stage ensures the high performance and preparability of the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material.

[0021] The gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite catalyst and its preparation method disclosed in the present invention have significant advantages in the field of hydrogen fuel cell catalytic materials.

[0022] 1. This catalyst uses an AB2-type superlattice PtCoFeCr alloy as its active core.

[111] crystal plane orientation is manipulated to form a periodic strain field. Combined with nitrogen-doped carbon nanotubes as a support, it is prepared using a pulsed laser deposition-microwave annealing technique and a supercritical CO2 fluid loading process. Its performance far exceeds that of conventional catalysts. Its ORR mass activity reaches 6.2 A / mgPt@0.9V, a 17-fold increase over commercial Pt / C. After 30,000 cycles, its activity decay is less than 5%, effectively solving the problems of low activity and poor stability of conventional catalysts.

[0023] 2. In terms of cost and resource utilization, the platinum consumption per stack is only 7.2mg / kW, which is 61% less than the traditional solution. The scale cost is reduced to 380 yuan / gram, which is only 32% of commercial Pt / C, breaking through the cost bottleneck of hydrogen vehicle catalysts. The specific surface area of ​​the nitrogen-doped carbon nanotube carrier reaches 850±15m 2 / g, and the pyridinic nitrogen content is ≥9.2at%, which improves the catalytic active site density and conductivity.

[0024] 3. The supercritical CO2 fluid loading process reduces organic solvents by 96%, making it more environmentally friendly. After H2 regeneration, the spent catalyst has an activity recovery rate of ≥92%, and a platinum recovery rate of ≥99.5%, aligning with green production principles. Furthermore, this catalyst is adaptable to multiple scenarios, with a cold start time of ≤28 seconds at -30°C, a high-temperature decay of <3% / 1,000 hours at 160°C, and reverse polarity resistance of >500 hours, providing strong support for the development of the hydrogen energy industry.

[0025] Through the collaborative innovation of superlattice structure design, gradient doping strategy and green preparation process, this invention simultaneously achieves the quadruple breakthrough of "high activity, high stability, low cost and easy mass production" of the catalyst. Its technical indicators comprehensively surpass the existing commercial and literature-reported catalyst systems, and it has significant industrial application value and scientific innovation significance. DETAILED DESCRIPTION

[0026] In order to better explain the present invention, exemplary embodiments of the present invention will be described in more detail below. Although exemplary embodiments of the present invention are shown below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0027] The gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method are described in detail with reference to the following examples: Example 1: Preparation of Gradient Nitrogen-Doped Carbon Nanotube (N-CNT) Support S1. Precursor configuration: Weigh 10 g of [BMIM][TFSI] ionic liquid (soft template) and 30 g of SiO2 nanoparticles (hard template, average particle size 50 nm), add 5 g of urea-melamine composite nitrogen source (mass ratio 1:2) and 0.05 g of FeCl3, grind in an agate mortar for 30 min until uniformly mixed, and transfer to a polytetrafluoroethylene reactor.

[0028] S2. Dual template synthesis: The reactor was placed in a pulsed microwave reactor with the following parameters: power 800 W, pulse mode 2 seconds on / 1 second off, temperature raised to 750°C and maintained for 30 minutes. After the reaction was complete, the mixture was cooled to room temperature and the black product was collected.

[0029] S3, template etching and activation: The product was added to a 5wt% NH4HF2 solution (solid-to-liquid ratio of 1:20) and stirred in a 60°C water bath for 6 hours. The mixture was filtered and washed with deionized water until the filtrate had a pH of 7. The solid was then placed in a low-temperature plasma treatment apparatus and treated with an Ar / O2 mixture (9:1 by volume) at 100W for 5 minutes to obtain an N-CNT substrate.

[0030] Table 1 Comparison of carrier structure performance.

[0031] The nitrogen content of the carrier was determined to be 8.5 at%, including 9.2 at% pyridinic nitrogen by X-ray photoelectron spectroscopy (XPS); the specific surface area was determined to be 852 m 2 / g, pore size distribution 14-16nm; X-ray diffraction (XRD) shows the degree of graphitization ID / IG=0.23.

[0032] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method are combined with gradient nitrogen doping through a dual-template method (ionic liquid + SiO2), and the specific surface area of ​​the carrier reaches 850 m 2 / g (traditional carbon black is only 240 m 2 / g), with a pyridinic nitrogen content of up to 9.2 at%. The presence of pyridinic nitrogen not only increases the density of ORR active sites but also enhances the catalyst's conductivity by regulating the electronic structure of the carbon skeleton. Compared to a graphene support from KAIST in South Korea (with 5.2 at% pyridinic nitrogen), the active site density is further increased by 74%.

[0033] More optimally, the gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method utilize NH4HF2 instead of highly corrosive HF for template etching, reducing wastewater toxicity by 90%. Furthermore, 18% of the carboxyl groups (-COOH) remain on the carrier surface after etching, enhancing the anchoring effect with the alloy particles. After low-temperature plasma activation, the oxygen vacancy density reaches 1.5×10 15 / cm 2 By capturing free electrons through oxygen vacancies, carbon corrosion is suppressed (the corrosion rate is only 2% after 30,000 cycles), and the stability of the carrier in an acidic environment is significantly improved.

[0034] Example 2: Epitaxial Growth of Superlattice PtCoFeCr Alloy S1. Pulsed Laser Deposition (PLD): The N-CNT carrier was fixed on the target stage of the PLD vacuum chamber, and the background vacuum was pumped to 3×10 -6 Torr. Alternate sputtering Pt 50 Co 45A prefabricated Fe5 alloy target (99.95% purity) and a Cr target (99.99% purity) were used. The laser frequency was set at 5 Hz, and the deposition time per layer was controlled to be 12 seconds for the PtCoFe layer (0.8 nm thickness) and 3 seconds for the Cr layer (0.2 nm thickness), with 30 cycles. A 5% CO / Ar mixture was continuously introduced during the deposition process at a flow rate of 20 sccm.

[0035] S2, gradient microwave annealing: The deposited sample was transferred to a microwave annealing furnace and subjected to three stages of treatment: 400-500°C (heating rate 5°C / min), 2.45 GHz microwave radiation for 30 seconds; 500-650℃, 2.45GHz and 5.8GHz dual-frequency alternating radiation (30 seconds each); 650-700℃, 5.8GHz directional radiation for 30 seconds.

[0036] The annealing atmosphere was CO / H2 / Ar (volume ratio 1:4:95) and the pressure was 0.1 MPa.

[0037] Table 2 Key indicators of superlattice alloys High-resolution transmission electron microscopy (HRTEM) showed that the

[111] crystal plane orientation was 96% and the lattice constant was 3.85Å (deviation 0.008Å); energy-dispersive X-ray spectroscopy (EDS) mapping confirmed that the surface Fe / Cr ratio was 1:1.3, which was consistent with the gradient distribution characteristics.

[0038] More optimally, the gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method, the gradient doping of Fe / Cr (Co:Fe=3:1 in the core → 1:1.3 on the surface) inhibits the dissolution of Co by lattice distortion (the dissolution rate is only 0.04 μg / cm 2 10,000 times). The reduced local electron density of Co optimizes the center position of the Pt d-band, resulting in an ORR mass activity of 6.2 A / mgPt at 0.9V, 17 times that of commercial Pt / C. Real-time reflection high-energy electron diffraction (RHEED) monitoring technology controls the lattice constant accuracy to ±0.01Å, reducing the interface defect rate by 30%, surpassing the ±0.05Å achieved by molecular beam epitaxy.

[0039] The optimized, gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method utilize a three-stage gradient microwave annealing process (400-700°C) combined with a CO / H2 / Ar mixed atmosphere. This process accelerates atomic migration through the selective heating effect of microwaves, reducing energy consumption by 65% ​​compared to traditional molecular beam epitaxy (≥1000°C). A CO partial pressure of 0.01 atm suppresses surface reconstruction, resulting in an orientation degree of >95% for the alloy particles after annealing and a batch-to-batch consistency (CpK) of ≥1.45.

[0040] The optimized gradient-doped superlattice structure of a platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method utilizes a periodic strain field design oriented in the crystal plane. This compressive strain reduces the Pt-Pt bond spacing (0.272 to 0.265 nm), weakening the adsorption energy of oxygen intermediates and improving reaction kinetics. After accelerated endurance testing, the mass activity decay was less than 5%, breaking through the lifespan bottleneck of Toyota's Pt-Co alloy caused by Co dissolution.

[0041] Example 3: Supercritical CO2 fluid dispersion process S1. Precursor dispersion: Take 0.5g N-CNT carrier and 0.1g H2PtCl6·6H2O and dissolve them in a supercritical reactor. Add 5vol% ethanol (co-solvent), introduce CO2 to 12MPa, and dynamically adjust the pressure at 0.1Hz frequency (10-15MPa cycle) at 50℃ for 30 minutes.

[0042] S2. In-situ reduction and post-processing: A 5% H2 / Ar mixture (10 sccm) was introduced for reduction at 12 MPa for 2 hours. The CO2 was released after cooling to room temperature. The product was dispersed in a 0.1 wt% SDS solution, sonicated for 10 minutes, and microwave annealed at 250°C for 2 hours to obtain the target catalyst.

[0043] Table 3 Environmental benefits of supercritical process Transmission electron microscopy (TEM) statistics show that the average particle size is 4.2nm, D90=7.8nm, and the anchoring density is 4.7 particles / nm 2 ; Inductively coupled plasma optical emission spectroscopy (ICP-OES) measured the platinum loading to be 20 wt%.

[0044] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method, dynamic pressure regulation (10-15 MPa, 0.1 Hz) combined with the cavitation effect of supercritical CO2, can increase the solubility of the platinum precursor by 3 times, with a particle size distribution D90 ≤ 8% (conventional process ≤ 12%) and an anchoring density of 4.5 particles / nm. 2. H2 in situ reduction technology to Pt 0 The proportion is increased to ≥99%, avoiding the residual pollution of traditional chemical reducing agents.

[0045] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method, supercritical CO 2 Replaces organic solvents (dosage reduced by 96%), COD value of wastewater is <50 mg / L.

[0046] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material and its preparation method, the nano-protective layer formed by self-assembly of sodium dodecyl sulfate (SDS), can form a stable hydrophobic interface after microwave annealing at 250°C, and the activity decay is <0.5% after storage for 6 months.

[0047] Example 4: Membrane Electrode Performance Verification Assemble 50cm 2 Single cell, test conditions: 80°C, 100% RH, H2 / air stoichiometry = 1.2 / 2.0. Single stack power density 1.8W / cm 2 , platinum dosage is 7.2mg / kW, and voltage attenuation is < 2% after 500 hours of continuous operation.

[0048] Table 4 Performance of membrane electrode under extreme working conditions More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material and its preparation method compress the catalytic layer thickness to 15 nm and use short side chain perfluorosulfonic acid resin (EW=670) to optimize proton transport at the three-phase interface.

[0049] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material and its preparation method have a dynamic response speed of 0.8 seconds (industry benchmark 2.5 seconds), a cold start time of 28 seconds at -30°C, and an anti-reverse polarity ability of >500 hours (traditional catalysts <50 hours), and are suitable for frequent start-stop scenarios of heavy trucks.

[0050] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method can reduce the platinum loading to 0.15 mg / cm 2 The platinum usage per stack is only 7.2 mg / kW (compared to 18.5 mg / kW for conventional solutions). After accelerated endurance testing (30,000 cycles), activity decay was <5%, and platinum dissolution rate was <0.01 μg / km.

[0051] Example 5: Industrial production verification A digital twin system is used to link three pulsed laser deposition instruments (PLD, cavity volume 50L), a continuous microwave annealing furnace (power 10kW, conveyor belt speed 0.5m / min) and a supercritical CO2 fluid load production line (pressure 15MPa, processing capacity 2L / h). The single batch feed quantity is: 5kg of N-CNT carrier and 1.2kg of PtCoFeCr alloy target. The supporting raw material delivery accuracy is controlled at ±0.1kg.

[0052] The PLD laser energy density (3.5±0.2J / cm 2 The matching relationship between the annealing temperature (650±10°C) and the microwave annealing temperature (650±10°C) stabilizes the superlattice orientation at over 95%, with batch-to-batch activity variation ≤3%. A single batch production cycle is 8 hours, with a production capacity of 0.5 kg (based on finished catalyst).

[0053] The cost of raw materials accounts for 62% (of which Pt accounts for 45%), the energy consumption cost is 120kWh / kg (microwave annealing accounts for 70%), labor and equipment depreciation accounts for 26%, and the comprehensive cost is 380±15 yuan / gram.

[0054] Table 5 Economic analysis of mass production More optimally, the gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method utilize a digital twin system to optimize PLD-microwave annealing parameters, increasing single-batch production capacity to 0.5 kg (molecular beam epitaxy to 0.005 kg), with an overall cost of 380 yuan / gram (commercial Pt / C is 1,200 yuan / gram). Microwave annealing energy consumption is reduced to 120 kWh / g (compared to 580 kWh / g for conventional processes), reducing carbon emissions by 67%.

[0055] Optimally, the gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method restore 92% of spent catalyst activity through H2 regeneration, achieving a platinum recovery rate of 99.5%. Using supercritical CO2-assisted stripping technology, the particle size distribution of the regenerated catalyst deviates by less than 5% from the initial product, achieving closed-loop resource utilization.

[0056] Example 6: Multi-scenario application verification Scenario 1: High-temperature PEMFC Test conditions: -30°C cold start test (environmental chamber temperature -30±1°C, H2 pressure 0.1MPa); 160°C high temperature operating conditions (no humidification, H2 / air stoichiometry = 1.5 / 3.0).

[0057] Performance data: Cold start time 28±2 seconds (Toyota Mirai catalyst: 45 seconds), startup voltage fluctuation ≤50mV; after 1000 hours of continuous operation at 160°C, ORR mass activity maintained at 5.1A / mgPt (initial 5.3A / mgPt), with a decay rate of 1.9% / 1,000 hours.

[0058] Scenario 2: Hydrogen production by water electrolysis Test system: alkaline electrolytic cell (1 mol / L KOH), current density 10 mA / cm 2 , temperature 60℃.

[0059] Performance data: overpotential 28±1mV (commercial Pt / C is 35mV), energy consumption reduced to 4.2kWh / Nm 3 (Traditional process 4.8kWh / Nm 3 ), after 500 hours of continuous operation, the overpotential increase is < 5mV.

[0060] Scenario 3: Anti-reverse polarity performance Test method: Proton exchange membrane fuel cell single cell (50cm 2 ), simulate the reverse polarity condition (current density -0.5A / cm 2 , lasting 1 hour), and repeat the test 500 times.

[0061] Results: Battery voltage decay rate < 8%, N-CNT carrier corrosion rate 2.1% (conventional carbon black carrier is 25%), active core dissolution amount < 0.01μg / cm 2 .

[0062] Table 6 Multi-scenario performance verification The performance of this catalyst is better than commercial Pt / C and Toyota Pt-Co alloy in extreme temperature, long-term operation and reverse polarity scenarios, and is adapted to the core equipment needs of the entire hydrogen energy industry chain.

[0063] More optimally, the gradient-doped superlattice structured platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method achieve stability at 160°C for 1000 hours with a decay rate of <3% (ASTM F3354). The nitrogen-doped carrier enhances electron conduction efficiency through π electron resonance. The overpotential for hydrogen production from water electrolysis is reduced to 28 mV@10mA / cm 2 (Commercial Pt / C is 35mV), suitable for wind, solar and storage integrated green hydrogen systems.

[0064] More optimally, the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite positive electrode material and its preparation method have an anti-reverse polarity capability of >500 hours (industry benchmark <50 hours). The electronic "buffer layer" formed by Fe / Cr gradient doping inhibits the oxidative corrosion of the carbon carrier under reverse polarity conditions, making it suitable for high power density fuel cells (4.8 kW / L).

[0065] As verified by the above examples, the gradient-doped superlattice platinum-cobalt alloy / nitrogen-doped carbon nanotube composite catalyst proposed in the present invention has achieved breakthroughs in core indicators such as activity (6.2 A / mgPt), stability (attenuation <5% after 30,000 cycles), cost (380 yuan / g) and environmental protection (96% reduction in organic solvents). It is suitable for all scenarios such as hydrogen fuel cells and hydrogen production by electrolysis of water, and provides a mass-producible solution for the industrialization of hydrogen energy.

[0066] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A gradient doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite cathode material and its preparation method, characterized in that include: The active core is an AB2-type superlattice PtCoFeCr alloy, in which the molar ratio of Co, Fe, and Cr is 3:1:0.2, and the gradient distribution ratio of Fe to Cr on the surface is 1:1.3; The carrier is nitrogen-doped carbon nanotubes (N-CNTs), the nitrogen content of the carrier is 8.5at%, of which the pyridinic nitrogen content is ≥9.2at%, and the specific surface area is 850±15m 2 / g; The active core forms a periodic strain field through [111] crystal plane orientation control, and its lattice constant accuracy is ±0.01Å; The anchoring density between the active core and the carrier is ≥4.5 particles / nm 2 , the particle size distribution of the active core is D90≤8nm; The catalyst has an oxygen reduction reaction (ORR) mass activity of ≥6.2A / mgPt at 0.9V vs. RHE, and its activity decay is <5% after 30,000 cycles. The platinum consumption per stack is ≤7.2mg / kW, and the large-scale production cost is ≤380 yuan / gram.

2. The catalyst according to claim 1, characterized in that The active core of the AB2 superlattice PtCoFeCr alloy is formed into a crystal plane orientation by pulsed laser deposition. During the formation process, PtCoFe prefabricated alloy and Cr target are alternately deposited, and the thickness of each layer is controlled to be ±0.1nm, and the vacuum is ≤5×10 -6 The laser was operated under 300-1000 Torr conditions, with 5% CO gas introduced into the chamber and a laser energy density of 3.5 J / cm 2 , with a wavelength of 248nm.

3. The catalyst according to claim 1, characterized in that The pore size distribution of the nitrogen-doped carbon nanotube (N-CNT) carrier is 12-18 nm, and the oxygen vacancy density reaches 1.5×10 15 / cm 2 , and the proportion of carboxyl groups (-COOH) retained on the surface is ≥18%.

4. The catalyst according to claim 1, characterized in that In a cold start scenario at -30°C, the catalyst's startup time is ≤28 seconds; under high-temperature conditions of 160°C, the activity decay rate is <3% / thousand hours; its reverse polarity resistance is >500 hours, and its dynamic response speed is ≤0.8 seconds (10%-90% load change).

5. A method for preparing the gradient-doped superlattice structure platinum-cobalt alloy / nitrogen-doped carbon nanotube composite catalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, using a dual template method (ionic liquid soft template + SiO2 hard template) combined with a urea-melamine gradient nitrogen source and pulsed microwave irradiation (750℃) to synthesize N-CNT supports; S2, superlattice epitaxial growth was achieved by alternating deposition of PtCoFe pre-alloy and Cr target by pulsed laser deposition (PLD), combined with three-stage gradient microwave annealing (400-700°C); S3, using supercritical CO2 fluid dynamic pressure dispersion (10-15MPa, frequency 0.1Hz) combined with H2 in situ reduction to achieve uniform loading of active components; S4. A short side chain perfluorosulfonic acid resin (EW=670) was used to construct the catalytic layer, and the spraying solvent was water / ethylene glycol / n-propanol (volume ratio 6:3:1).

6. The method according to claim 5, characterized in that In step S1, the ionic liquid soft template is [BMIM][TFSI], whose thermal decomposition temperature is greater than 400°C, and the mass ratio of the ionic liquid soft template to the SiO2 hard template is 1:3; the mass ratio of the urea-melamine composite nitrogen source is 1:2, and 0.5wt% FeCl3 is added as a graphitization promoter; pulsed microwave radiation adopts a 2-second on / 1-second off mode, and after thermal decomposition, the template is removed by etching with a 5wt% NH4HF2 solution at 60°C for 6 hours, and then the oxygen vacancy concentration is increased by 15% by Ar / O2 low-temperature plasma activation.

7. The method according to claim 5, characterized in that In step S2, the three-stage gradient microwave annealing is specifically as follows: Atomic diffusion activation was performed by 2.45 GHz microwave irradiation for 30 seconds at 400-500 °C; 500-650℃ dual-frequency alternating radiation (2.45GHz+5.8GHz) for 60 seconds to form short-range order; 5.8GHz directional radiation at 650-700℃ for 30 seconds to lock the long-range structure; The annealing atmosphere was a mixture of CO / H2 / Ar (volume ratio 1:4:95) with a CO partial pressure of 0.01 atm.

8. The method according to claim 5, characterized in that In step S3, supercritical CO2 fluid dispersion was carried out at 50°C, 5 vol% ethanol co-solvent was added, and H2 was in situ reduced to make Pt 2+ Converted to Pt 0 , and the platinum utilization rate is ≥78%; after dispersion, sodium dodecyl sulfate (SDS) is used for self-assembly to form a nano protective layer, and then microwave annealing is performed at 250°C for 2 hours.

9. The method according to claim 5, characterized in that In step S4, the catalyst loading of the catalytic layer is 0.15 mg / cm 2 , the thickness of the three-phase interface is compressed to 15nm.

10. The method according to claim 5, characterized in that The method also includes a step of regenerating the spent catalyst: after the spent catalyst is regenerated with H2, the activity recovery rate is ≥92%, the platinum recovery rate is ≥99.5%, and the particle size distribution of the regenerated catalyst deviates from that of the initial product by <5%.

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