Efficient electrochemical ammonia preparation material based on MOF (Metal Organic Framework) derived monatomic catalyst and preparation method of efficient electrochemical ammonia preparation material

Abstract

The invention discloses a bimetallic monatomic catalyst derived on the basis of a metal organic framework (MOF) and an efficient preparation method for electrochemical ammonia preparation of the bimetallic monatomic catalyst, and belongs to the crossing field of new energy materials and green chemical industry. Aiming at the technical bottlenecks of low nitrogen adsorption capacity, insufficient hydrogen evolution side reaction inhibition rate, poor dynamic response stability and the like in the traditional electrochemical nitrogen reduction reaction (NRR), a Zn / Co bimetal MOF precursor is innovatively designed, Fe ion gradient phosphorization and asymmetric coordination engineering are combined, and a femtosecond laser-plasma gradient activation composite process is adopted, so that the nitrogen adsorption capacity of the nitrogen-rich nitrogen reduction reaction is improved. The catalytic performance is obviously improved. The technology has high activity, stability and economical efficiency, provides a breakthrough solution for large-scale production of green ammonia, and particularly has an important application prospect in deep and far sea wind power absorption and low-carbon transformation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the cross field of new energy materials and green chemical industry, and specifically relates to a single-atom catalyst (SACs) based on metal-organic framework (MOF) and its high-efficiency electrochemical nitrogen reduction reaction (NRR) for synthesizing green ammonia under renewable energy driving. The technology solves the bottleneck problems of traditional catalysts in nitrogen adsorption capacity, hydrogen evolution side reaction inhibition and dynamic response to wind and light fluctuation power supply scenarios through innovative bimetallic synergy and asymmetric coordination engineering, combined with femtosecond laser-plasma gradient activation process, and provides core material support with high activity (faraday efficiency > 89%), high selectivity (HER inhibition rate > 95%) and strong stability (salt spray life > 2000 hours) for large-scale production of green ammonia, and the unit energy consumption can be reduced to the commercialization critical level of 20 kWh / kg-NH3. BACKGROUND

[0002] The electrochemical synthesis of ammonia technology currently faces three major bottlenecks, which seriously restrict its industrialization process. In terms of active sites and mass transfer efficiency, the active site density of traditional transition metal catalysts (such as Fe, Mo-based) is less than 1.5 atoms / nm 2 , and the unreasonable pore structure leads to a nitrogen adsorption capacity generally lower than 20 mmol / g, and the faraday efficiency has been hovering at 58%-63% for a long time; although the MOF-based single-atom catalyst realizes more than 90% atomic dispersion through micropore confinement effect, the single-metal site (such as Fe-N4) has limited ability to coordinate and regulate the dissociation and hydrogenation path of N≡N bond (bond energy 942kJ・mol -1 ), and it is difficult to break through the industrial current density threshold of 500mA / cm 2 . At the same time, the conventional gas diffusion layer has a porosity of less than 30%, resulting in a mass transfer efficiency loss of more than 35%, further limiting the reaction kinetics process. The serious interference of hydrogen evolution side reaction (HER) is another key obstacle. The low H adsorption free energy (ΔG_H) on the catalyst surface, such as ΔG_H*=-0.15 eV of Fe-based materials, will trigger uncontrollable proton reduction, resulting in a current loss of 40%-60%. Although the edge modification of sulfide catalysts (such as MoS2) improves the HER inhibition rate, the selectivity is still less than 60%; in recent years, the asymmetric coordination engineering (such as Fe-N3P) introduced P / S heteroatoms to make the d-band center downshift by 0.2-0.25 eV, and ΔG_H* up to + 0.12 eV, but still faces the optimization problems of coordination structure stability and large-scale preparation process. The problem of poor dynamic response and wind-solar fluctuation adaptability is also prominent. Fluctuations of ±30% in renewable energy power can cause imbalance in catalyst interface charge distribution, and a decrease in activity of more than 25% when current suddenly changes, with a recovery time of more than 30 seconds. MXene conductive substrate has a high electrical conductivity of >10 3 S / cm, but its salt spray life is less than 500 hours due to its sensitivity to oxidation, which cannot meet the needs of deep-sea floating wind power scenarios. In addition, existing systems lack adaptive control algorithms, resulting in ammonia production rate fluctuations of more than 20% and unit energy consumption of >35 kWh / kg-NH3, which is significantly higher than the commercial critical value of 25 kWh / kg-NH3. In the prior art, MOF-based single-atom catalysts achieve atomic dispersion through micropore confinement effects, but single-metal sites (such as Fe-N4) have insufficient control over the dissociation path of N≡N bonds (bond energy 942 kJ·mol -1 ) and lack large-scale preparation processes. In addition, femtosecond laser technology is only used for surface modification and has not been reported in the application of dynamic response regulation of catalysts.

[0003] In view of the above, technical breakthroughs focus on two directions: one is the design of double-metal coordination and asymmetric coordination, which improves the nitrogen adsorption capacity to 35 mmol / g by combining Zn / Co double-metal MOF-derived porous carbon skeleton (specific surface area >600 m 2 / g) with Fe-N3P / Co-N4 double active sites, breaks through 89% faradic efficiency, and simultaneously improves electrical conductivity (1.8×10 3 S / cm) and dynamic response stability (recovery time <10 seconds) through femtosecond laser (pulse width 100 fs) and plasma gradient activation processes (nitrogen vacancy concentration 12.5%); the other is system integration innovation, which matches wind and solar power fluctuations in real time through a 5-20 kHz adjustable magnetic pulse regulation module, reduces unit energy consumption to 20 kWh / kg-NH3, and reduces the levelized cost of ammonia (LCOA) to 320 US dollars / ton, which is much lower than the traditional process of 550 US dollars / ton. SUMMARY

[0004] In order to better explain the present application, the exemplary embodiments of the present application will be described in more detail below. Although the exemplary embodiments of the present application are shown below, it should be understood that the present application can be implemented in various forms and should not be limited by the described embodiments. On the contrary, these embodiments are provided to enable a clearer, more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0005] The catalyst of the application is prepared by Fe ion gradient phosphorization and asymmetric coordination engineering of Zn / Co bimetallic MOF precursor to form Fe-N3P / Co-N4 bireactive sites, and by femtosecond laser-plasma gradient activation compounding process. Its technical features include: 1. Bimetallic synergistic architecture: Zn / Co molar ratio 3:1, precursor BET specific surface area 820±30 m² / g, micropore ratio ≥92%, with 0.34 nm micropores and 2.1 nm mesopores, nitrogen adsorption capacity 35 mmol / g (traditional ZIF-67 only 18 mmol / g).

[0006] 2. Asymmetric coordination verification: Fe-P bond length 2.18±0.05 Å, Co-N bond length 1.92±0.03 Å (EXAFS fitting), d-band center downshift 0.2-0.25 eV, DFT calculation N≡N dissociation energy reduced to 0.89 eV.

[0007] 3. Composite activation process: femtosecond laser (1030 nm, 3.5 J / cm 2 ) induced sulfur vacancy (Raman shift 402 cm -1 ), conductivity increased to 1.8×10 3 S / cm; plasma controlled nitrogen vacancy concentration 12.5%, salt spray life >2000 hours The application provides a high-efficiency electrochemical ammonia production material based on MOF-derived single-atom catalyst and a preparation method thereof. The specific synthesis steps of the catalyst are as follows: S1, bimetallic MOF precursor synthesis; S2, Fe ion exchange and gradient phosphorization; S3, femtosecond laser-plasma composite activation.

[0008] Further, in S1, the bimetallic MOF precursor synthesis further includes the following steps: S1-1, preparation of precursor solution; S1-2, crystallization and post-treatment.

[0009] The specific steps of bimetallic MOF precursor synthesis are as follows: S1-1, preparation of precursor solution: Dissolve zinc nitrate (Zn(NO3)2·6H2O, 2 mmol) and cobalt nitrate (Co(NO3)2·6H2O, 0.67 mmol) in a methanol / water mixed solvent (volume ratio 9:1), and dissolve 2-methylimidazole (8 mmol, 1.312 g) in 40 mL of methanol, and use an ultrasonic cleaning instrument (power 200 W, frequency 40 kHz) to ultrasonically treat for 10 minutes until complete dissolution.

[0010] S1-2, Crystallization and post-treatment: The metal salt solution was added dropwise into the ligand solution using a peristaltic pump at a flow rate of 5 mL / min, placed in a constant temperature water bath (accuracy ±0.1°C) at 25°C, and stirred using a magnetic stirrer (800 rpm) for 24 hours. A white precipitate was generated, which was then separated by centrifugation (10,000 rpm, 10 minutes, 4°C). After separation, the precipitate was washed with methanol and ethanol three times each, and then transferred to a vacuum drying oven (pressure <10 kPa) for drying at 60°C for 12 hours. White Zn / Co bimetallic MOF powder was obtained (yield 92%).

[0011] Further, in S2, Fe ion exchange and gradient phosphatization further include the following steps: S2-1, Fe loading; S2-2, Gradient pyrolysis.

[0012] The specific steps of Fe ion exchange and gradient phosphatization are as follows: S2-1, Fe loading: 1 g of Zn / Co-MOF was immersed in 50 mL of 0.1 M Fe(NO3)3 anhydrous ethanol solution, placed in a nitrogen glove box (O2<0.1 ppm), and shaken using a constant temperature shaker (speed 120 rpm, 25°C) for 24 hours. Then, the mixture was centrifuged (8,000 rpm, 5 minutes) and washed with anhydrous ethanol three times, and then dried at 60°C for 6 hours under vacuum.

[0013] S2-2, Gradient pyrolysis: The Fe-loaded MOF was mixed with triphenylphosphine (mass ratio 1:0.5), and placed in a tube furnace for processing according to the following procedure: Pre-treatment stage: Ar gas (purity 99.999%) flow rate 50 sccm, from room temperature to 300°C at a rate of 5°C / min, and held for 1 hour; Activation stage: the flow rate was increased to 100 sccm, and the temperature was increased to 900°C at a rate of 2°C / min, and held for 6 hours.

[0014] Further, in S3, femtosecond laser-plasma combined activation further includes the following steps: S3-1, femtosecond laser treatment; S3-2, plasma activation.

[0015] The specific steps of femtosecond laser-plasma combined activation are as follows: S3-1, femtosecond laser treatment: Femtosecond laser treatment was performed using a Yb:KGW femtosecond laser (Pharos, Light Conversion), with the following preparation parameters: Wavelength 1030 nm, pulse width 100 fs, pulse energy 1 mJ, repetition rate 1 kHz; Energy density 3.5 J / cm 2 (Scanning speed 5 mm / s, spot diameter 200 μm, Hilbert curve filling path).

[0016] S3-2, Plasma activation: Plasma activation treatment was performed using a PlasmaPro 100 ICP etching system (Oxford Instruments) in an Ar / N2 mixed gas (volume ratio 4:1, total flow rate 100 sccm) environment at 200 W for 30 minutes to regulate the nitrogen vacancy concentration to 12.5%. Advantages of the present application

[0017] 1. Breakthrough improvement in catalytic performance: (1) Dual active site synergistic catalytic mechanism: Based on the design of Fe-N3P / Co-N4 dual active sites derived from Zn / Co bimetallic MOF, the nitrogen activation path was significantly optimized through asymmetric coordination engineering (EXAFS verified Fe-P bond length 2.18 Å, Co-N bond length 1.92 Å): Faraday efficiency reached 89% (0.3 V vs. RHE), bimetallic synergistic effect (Co-N4 dominated adsorption ΔE_ads=-0.78 eV, Fe-N3P optimized dissociation, DFT calculation N≡N dissociation energy reduced to 0.89 eV) solved the problem of single dissociation path of traditional single metal sites, which was 53% higher than traditional Fe-based catalysts (58%).

[0018] Nitrogen adsorption capacity increased to 35 mmol / g (BET test, 77 K), attributed to 0.34 nm micropore sieving effect and 20 nm mesopore accelerating H + Transport (molecular dynamics simulation showed that the mass transfer efficiency was improved by 3.2 times); Current density breakthrough 520 mA / cm 2 Combined with the synergistic effect of molten electrolyte (KOH-CsOH) and LaNiO3 additive (particle size 50 nm), the unit energy consumption of 20 kWh / kg-NH3 (international benchmark 35 kWh / kg-NH3) was achieved.

[0019] (2) Hydrogen evolution side reaction (HER) inhibition: Through Fe-N3P asymmetric coordination regulation of H adsorption free energy (ΔG_H from-0.15 eV to +0.12 eV), HER inhibition rate > 95% (linear sweep voltammetry test), current density loss rate < 5% (potentiostatic electrolysis verification), better than the edge modification scheme of sulfide.

[0020] 2. Dynamic response and long-term stability innovation (1) Wind and light fluctuation scene adaptability: Dynamic response time < 10 seconds (traditional > 30 seconds), integrated magnetic pulse control module (5-20 kHz adjustable), real-time matching of ±30% power fluctuation, ammonia yield fluctuation rate < 5%; Conductivity optimization: femtosecond laser (1030 nm, energy density 3.5 J / cm 2 Induced sulfur vacancies (Raman shift from 384→402 cm -1 ) and plasma fluoride reduction technology (XPS verified F - Content decreased by 72%, conductivity reached 1.8×10 3 S / cm; Salt spray life > 2000 hours (ISO 9227 C5-M level certification), suitable for deep sea wind power scene (wave height > 10m, salt spray concentration ≥5 mg / m 3 ).

[0021] (2) Anti-poisoning and cycle stability: 2000 hours continuous operation activity retention rate > 95% (HAADF-STEM verified Fe / Co dispersion > 98%), gradient pore size design combined with nitrogen vacancies (12.5%, XPS quantification) optimization, CO poisoning resistance increased by 3 times (compared with traditional Fe-N4 catalyst); Catalyst recovery rate > 95% (Fe / Co recovered by acid leaching, ICP-MS verified metal loss rate < 2%), waste liquid heavy metal residue < 0.1 ppm.

[0022] 3. Energy consumption optimization and scale economy (1) Energy efficiency is significantly improved: Levelized cost of production (LCOA) is reduced to 320 dollars / ton (traditional SMR-HB process 550 dollars / ton), wind and light consumption rate > 96%, suitable for northwest China / deep sea wind power scene (LCOE < 0.03 USD / kWh); Roll-to-roll femtosecond laser scanning process capacity 200 kg / day (galvanometer precision ±5μm), mass production cost < 85 dollars / kg (traditional plasma process > 120 dollars / kg), zero addition of noble metals (no Pt, Ir), material cost reduced by 62%.

[0023] (2) System flexibility and compatibility: compatible with alkaline electrolytic cell (efficiency > 78%) and PEM electrolytic cell (efficiency > 82%) mixed integration, support super capacitor-lithium hybrid energy storage module (response time < 50 ms), suitable for 10 MW to GW level projects.

[0024] 4. Environmental benefits and sustainable development (1) Low carbon emissions throughout the life cycle Carbon intensity <0.1 tCO2 / tNH3 (traditional SMR process 1.6 tCO2 / tNH3), in line with ISO 14067 standards (system boundary covers raw material extraction, preparation, operation and disposal stages), and synergistic reduction of pollutants: SOx emissions are zero, NOx emission intensity <5 mg / kWh (traditional process >50 mg / kWh); (2) Solid waste resource utilization: waste carbon skeleton for dye wastewater treatment (methylene blue adsorption capacity >450 mg / g), and waste electrolyte conversion into building material additives (resource utilization rate >80%).

[0025] (3) Ecological friendliness verification: electrolyte without toxic additives such as cyanide and sulfide, and wastewater discharge toxicity to aquatic organisms reduced by >90% (verified by zebrafish survival rate experiment); compared with traditional ammonia synthesis process, the contribution rate of nitrogen and phosphorus loss to water eutrophication is reduced by >70%. DETAILED DESCRIPTION

[0026] In order to better explain the present application, the exemplary embodiments of the present application will be described in more detail below. Although the exemplary embodiments of the present application are shown below, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described. Rather, these embodiments are provided so that the present application can be more clearly, thoroughly and completely understood, and so that the scope of the present application can be accurately conveyed to those skilled in the art.

[0027] Example 1: Optimization of synthesis of bimetallic MOF precursor 1. Precursor solution gradient preparation: Three groups of solutions were prepared with Zn / Co molar ratios of 3:1, 2:1 and 1:1, respectively: Group 1: Zinc nitrate 3.0 mmol + Cobalt nitrate 1.0 mmol; Group 2: Zinc nitrate 2.0 mmol + Cobalt nitrate 1.0 mmol; Group 3: Zinc nitrate 1.0 mmol + Cobalt nitrate 1.0 mmol.

[0028] Dissolved in a methanol / water mixed solvent (volume ratio 7:3 to 9:1, HPLC grade, impurities <0.1 ppm), and ultrasonically treated (200 W, 40 kHz) for 15 minutes.

[0029] 2. Crystallization and post-treatment: Constant temperature magnetic stirring (800 rpm, 25±0.5℃) for 24 hours, and centrifugal separation (10,000 rpm, 4℃); Washing with methanol, ethanol, respectively, 3 times, vacuum drying (60℃, 12 hours, pressure <10 kPa).

[0030] Table 1 Comparison of key performance parameters of gradient Zn / Co bimetallic MOF precursor More optimally, the high-efficiency electrochemical ammonia production material based on MOF-derived single-atom catalyst and preparation method, by gradient control of Zn / Co ratio (optimal 3:1), the BET specific surface area of MOF precursor reaches 820±30 m 2 / g, 93% higher than traditional ZIF-67, the two-stage structure of 92% micropore ratio combined with 2.1 nm mesopore significantly enhances nitrogen adsorption capacity (35 mmol / g vs. traditional 18 mmol / g) and mass transfer efficiency (3.2 times higher).

[0031] More optimally, the high-efficiency electrochemical ammonia production material based on MOF-derived single-atom catalyst and preparation method, the MOF yield in the synthesis step reaches 92% (traditional process is usually 80-85%), combined with precise crystallization control of gradient Zn / Co ratio (3:1) (25±0.5℃ constant temperature stirring, centrifugal separation parameters ±0.1% error), the specific surface area deviation between batches is only ±30 m 2 / g, significantly better than the ±50 m 2 / g fluctuation of traditional ZIF-67, ensuring the repeatability of large-scale production.

[0032] More optimally, the high-efficiency electrochemical ammonia production material based on MOF-derived single-atom catalyst and preparation method, the crystallinity reaches 95.3% (traditional 88-92%), the structural integrity is better maintained during high-temperature pyrolysis, avoiding the collapse of active sites, providing a stable substrate for subsequent phosphidation.

[0033] Example 2: Gradient phosphidation process optimization: 1. Fe loading: Dip 1 g of Zn / Co-MOF in 50 mL of 0.1 M Fe(NO3)3 ethanol solution, place it in a nitrogen glove box (O2<0.1 ppm), use a constant temperature oscillator (speed 120 rpm, 25℃) to oscillate for 24 hours, then centrifugal separation (8,000 rpm, 5 minutes), wash with anhydrous ethanol 3 times, 60℃ vacuum drying for 6 hours.

[0034] 2. Gradient pyrolysis: Mix the Fe-loaded MOF with triphenylphosphine (mass ratio 1:0.5), place it in a tube furnace, and process according to the following program: Pre-treatment stage: Ar gas (purity 99.999%) flow rate 50 sccm, from room temperature to 300℃ at 5℃ / min, and keep for 1 hour; Activation stage: the flow rate is increased to 100 sccm, Group 1: increase the temperature to 800℃ at 2℃ / min, and keep for 6 hours; Group 2: increase the temperature to 900℃ at 2℃ / min, and keep for 6 hours; Group 3: increase the temperature to 1000℃ at 2℃ / min, and keep for 6 hours.

[0035] Table 2 Comparison of catalyst performance at different pyrolysis temperatures More preferably, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the Fe-N3P / Co-N4 dual-site design optimizes the nitrogen dissociation path through asymmetric coordination, the Faraday efficiency reaches 89% (traditional 58%), DFT calculation shows that the N≡N dissociation energy is reduced to 0.89 eV, and the active site density is increased to 4.8 atoms / nm 2 (Traditional 1.2 atoms / nm 2 ).

[0036] More preferably, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the H adsorption free energy ΔG_H* is regulated to +0.12 eV (Fe-based traditional -0.15 eV), the hydrogen evolution side reaction inhibition rate is >95%, and the current density loss rate is <5% (traditional >40%), which significantly improves the electrochemical selectivity.

[0037] More preferably, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the temperature is increased in stages (pre-treatment 300℃+activation 900℃) combined with Ar gas flow regulation (50→100 sccm), which avoids active site agglomeration at high temperature, and after phosphorization, the BET specific surface area reaches 620±20 m 2 / g, which is 46% higher than that of traditional Fe-N4 (425±25 m 2 / g), and there is no grain coarsening phenomenon.

[0038] Example 3: Femtosecond laser-plasma combined activation 1. Femtosecond laser treatment: a femtosecond laser with a wavelength of 1030 nm and a pulse width of 100 fs is used, and the catalyst surface is scanned by a Hilbert curve filling path to induce sulfur vacancy formation and improve conductivity; 2. Plasma activation: in an Ar / N2 mixed gas environment, the nitrogen vacancy concentration is regulated to 12.5% by 200 W power plasma treatment for 30 minutes.

[0039] Table 3 Comparison table of femtosecond laser-plasma complex activation effect More preferably, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the femtosecond laser (1030 nm, 3.5 J / cm 2 ) induced sulfur vacancy concentration to increase by 52.4% (to 12.5%), the conductivity from 1.2 x 10 3 S / cm to 1.8 x 10 3 S / cm, the dynamic response time is shortened to <8 seconds (traditional >30 seconds), and it is suitable for rapid fluctuations in wind and light power.

[0040] More preferably, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the salt spray life breaks through 2000 hours, which is better than the traditional process of 500 hours, and meets the deep sea high humidity and high salt spray scene requirements.

[0041] More preferably, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the femtosecond laser adopts a Hilbert curve filling path (spot diameter 200 μm, overlap rate ≥98%), combined with a galvanometer precision of ±5 μm, to realize a sulfur vacancy distribution uniformity deviation of <2%, and the surface roughness is reduced from the traditional pyrolysis method of 120 nm to 15 nm, ensuring uniform exposure of active sites.

[0042] Example 4: Wind and light fluctuation scene dynamic response test (system level verification) 1. Electrolytic cell construction: Positive catalyst loading: 1.5-2.5 mg / cm 2 (gradual distribution); Molten electrolyte: KOH-CsOH (molar ratio 2:1-4:1), adding 0.5-1.5 wt% LaNiO3 nanoparticles (particle size 30-70 nm, BET specific surface area >80 m 2 / g).

[0043] 2. Dynamic simulation Photovoltaic simulator: AM 1.5G standard, irradiance fluctuation ±10%; Wind power simulation module: IEC 61400-21 standard, turbulence intensity >15%; Magnetic pulse regulation module: frequency adjustable 5-20 kHz, response delay <10 ms.

[0044] Table 4 Comparison table of dynamic response and system performance More optimally, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method integrates a 5-20 kHz magnetic pulse regulation module, with an ammonia yield fluctuation rate of <5% (traditional 25.7%), real-time matching of ±30% wind and light power fluctuations, and a unit energy consumption reduced to 20 kWh / kg-NH3.

[0045] More optimally, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the KOH-CsOH electrolyte cooperates with the LaNiO3 additive (particle size 50 nm) to reduce the reaction impedance, the electrolyte cycle number reaches 1500 times (traditional 300 times), and supports large-scale continuous operation.

[0046] Example 5: Roll-to-roll continuous production process (industrialization verification) 1. Roll-to-roll laser processing: Air floatation conveying belt speed: 8-12 m / min (PID closed loop control, accuracy ±0.1 m / min); Galvanometer system: accuracy ±3-5 μm (Hexagon laser interferometer calibration), spot overlap rate ≥98%; Real-time quality inspection: online Raman spectrometer (785 nm laser) monitors sulfur vacancy concentration deviation <2%.

[0047] 2. Metal recovery process: Acid leaching solution formula: 1-5 M HNO3 + 0.1-0.5 M citric acid; Solid-liquid ratio: 1:10-1:15 (ultrasonic assisted, 40 kHz); Recovery rate verification: ICP-MS detects Fe / Co ≥96.5%, and waste liquid heavy metal residue <0.08 ppm.

[0048] Table 5 Comparison of technical indicators of roll-to-roll production process More optimally, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the femtosecond laser scanning process realizes a daily production capacity of 200 kg (traditional 80 kg), the galvanometer accuracy ±5 μm ensures the sulfur vacancy concentration deviation <2%, the acid leaching method has a metal recovery rate >96.5% (traditional 89%), and the waste liquid heavy metal residue <0.08 ppm.

[0049] More optimally, the MOF-derived single-atom catalyst-based efficient electrochemical ammonia production material and preparation method, the precious metal zero addition strategy reduces the material cost by 62%, the mass production cost is <85 dollars / kg (traditional process >120 dollars / kg), and the equipment investment cost is reduced by 45.3%.

[0050] Example 6: Life cycle environmental assessment (ecological verification) 1. Carbon footprint analysis: According to ISO 14067 standards, covering raw material mining (zinc mine, cobalt mine), catalyst production, electrolysis operation and waste disposal stage; 2. Ecotoxicity test: Electrolytic wastewater is treated by activated carbon adsorption (empty speed 2-4 h⁻¹), and acute toxicity experiment of zebra fish is carried out according to OECD 203 standard (96 hours LC 50 >100 mg / L).

[0051] Table 6 Comparison table of life cycle environmental benefits More preferably, the one kind of MOF derivative single atom catalyst based efficient electrochemical ammonia production material and preparation method, carbon emission intensity is only 0.09 tCO2 / tNH3 (traditional SMR process 1.6 tCO2 / tNH3), reduces 94.4% greenhouse gas emissions; waste carbon skeleton is used for dye wastewater treatment (adsorption capacity > 450 mg / g), and solid waste resource utilization rate > 80%.

[0052] More preferably, the one kind of MOF derivative single atom catalyst based efficient electrochemical ammonia production material and preparation method, zebra fish survival rate of electrolytic wastewater > 98% (traditional 65%), no cyanide / sulfide residue, meet ISO 14067 standards, life cycle pollution control covers raw material mining to waste stage.

[0053] Table 7 Comparison table of technical advantages based on MOF derivative single atom catalyst More preferably, the one kind of MOF derivative single atom catalyst based efficient electrochemical ammonia production material and preparation method, realizes 89% faradic efficiency at 0.3 V vs. RHE, and current density is as high as 520 mA / cm 2 , breaks through the bottleneck of traditional Fe-based catalyst (FE 58-63%, current density < 300 mA / cm 2 ) and MoS2-based catalyst (FE ≤ 60%, current density < 350 mA / cm 2 ).

[0054] More preferably, the one kind of MOF derivative single atom catalyst based efficient electrochemical ammonia production material and preparation method, significantly optimizes nitrogen dissociation path through double active sites (EXAFS verifies bond length and d-band center downshift), DFT calculation shows that N≡N dissociation energy is reduced from traditional 942 kJ / mol to 0.89 eV; by asymmetric coordination engineering, P heteroatom is introduced to regulate H adsorption free energy (ΔG_H from-0.15 eV to +0.12 eV), HER inhibition rate > 95%, far more than traditional Fe-based catalyst (< 60%).

[0055] The present application breaks through in catalytic activity (FE>89%), selectivity (HER inhibition rate>95%), stability (salt spray life>2000 hours) and cost (mass production cost<85 dollars / kg) through the system innovation of bimetallic MOF derivative design, asymmetric coordination engineering and composite activation process, and provides an efficient, low-carbon and adaptable solution for large-scale green ammonia production.

[0056] It will be obvious to a person skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments and can be implemented in other concrete forms without departing from the spirit or essential characteristics of the application. The foregoing embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A bimetallic single-atom catalyst derived from a MOF, characterized by: The Zn / Co bimetallic MOF precursor was subjected to Fe ion gradient phosphating and asymmetric coordination engineering to form Fe-N3P / Co-N4 dual active sites, which were then treated by a femtosecond laser-plasma gradient activation composite process. The molar ratio of Zn to Co was 3:1, and the BET specific surface area of ​​the catalyst was 620 m 2 / g, micropore ratio ≥92%, nitrogen adsorption capacity ≥35 mmol / g, electrical conductivity ≥1.8×10 3 S / cm, dynamic response time <10 seconds, salt spray life >2000 hours.

2. The catalyst according to claim 1, characterized in that: The coordination structure of the Fe-N3P / Co-N4 dual active site was verified by EXAFS, where the Fe-P bond length was 2.18±0.05 Å, the Co-N bond length was 1.92±0.03 Å, and the d-band center was shifted down by 0.2-0.25 eV compared to the single metal site.

3. The preparation method according to claim 1, wherein: The Fe ion gradient phosphating process specifically includes: S2-1, Fe loading: Zn / Co-MOF was immersed in 0.1M Fe(NO3)3 ethanol solution and shaken in a nitrogen glove box with an O2 concentration of <0.1 ppm for 24 h at a shaking speed of 120 rpm; S2-2, gradient pyrolysis: mixed with triphenylphosphine in a mass ratio of 1:0.5, heated to 300°C at 5°C / min and kept warm for 1 hour in the pretreatment stage, heated to 900°C at 2°C / min and kept warm for 6 hours in the activation stage, and the Ar gas flow rate was increased from 50 sccm to 100 sccm.

4. The femtosecond laser processing process according to claim 1, characterized in that: The laser was powered by a Yb:KGW femtosecond laser with a wavelength of 1030 nm, a pulse width of 100 fs, a pulse energy of 1 mJ, and an energy density of 3.5 J / cm 2 , the scanning speed is 5 mm / s, the spot diameter is 200 μm, the Hilbert curve is used to fill the path and the spot overlap rate is ≥98%.

5. The plasma activation process according to claim 1, wherein: The activation parameters are Ar / N2 mixed gas volume ratio 4:1, total flow rate 100 sccm, power 200 W, processing time 30 minutes, and the nitrogen vacancy concentration is controlled to be 12.5%.

6. Use of the catalyst according to claim 1 in an electrochemical nitrogen reduction reaction, characterized in that: A molten electrolyte containing KOH-CsOH (molar ratio 2:1-4:1) and 0.5-1.5 wt% LaNiO3 nanoparticles (particle size 30-70 nm) was used to achieve a Faradaic efficiency ≥89% and a current density ≥520 mA / cm at 0.3 V vs. RHE. 2 , unit energy consumption ≤ 20 kWh / kg-NH3, electrolyte cycle times ≥ 1500 times.

7. The use according to claim 6, characterized in that: The integrated 5-20 kHz magnetic pulse control module has a trigger delay of less than 10 ms, and can match the ±30% wind and solar power fluctuations in real time, making the ammonia yield fluctuation less than 5%, and the electrolyzer cathode catalyst gradient loading is 1.5-2.5 mg / cm 2 .

8. The large-scale preparation system of the catalyst according to claim 1, characterized in that: A roll-to-roll femtosecond laser scanning device is used, including an air-floating conveyor belt (speed 8-12 m / min±0.1 m / min), a galvanometer system (accuracy ±5 μm) and an online Raman quality inspection module (wavelength 785 nm, detection sulfur vacancy concentration deviation <2%), to achieve a daily production capacity of ≥200±10 kg and a mass production cost of <85±5 US dollars / kg.

9. The catalyst recovery method according to claim 1, wherein: A mixed acid leaching solution of 1-5 M HNO3 and 0.1-0.5 M citric acid was used, with a solid-liquid ratio of 1:10-1:15, an ultrasonic-assisted frequency of 40±5 kHz, an Fe / Co recovery rate ≥96.5±0.5%, and heavy metal residues in the waste liquid <0.08±0.01 ppm.

10. The application scenario of the catalyst according to claim 1, characterized in that: Suitable for deep-sea floating wind power scenarios with wave heights > 10 m and salt spray concentrations ≥ 5 mg / m 3 , integrating magnetic pulse module and supercapacitor-lithium battery hybrid energy storage system (response time <50 ms) to ensure ammonia yield fluctuation rate <5%.