Preparation method of selective oxygen removal electrode and application of the electrode in electrocatalytic synthesis of ammonia

Abstract

This invention discloses a method for preparing a selective deoxygenation electrode and its application in electrocatalytic ammonia synthesis, belonging to the field of new energy materials. Addressing the problems of low NO mass transfer efficiency and catalytic selectivity limited by oxygen reduction reactions due to competitive adsorption of O2 molecules in industrial waste gas when low concentrations of nitrogen oxides (NO) coexist with air (N2, O2), this invention constructs a functional carbon layer with specific size defects and surface charge distribution. Utilizing the molecular sieve effect of its micropores, it selectively retains O2 molecules while preferentially anchoring NO at the defect sites of the carbon layer, achieving efficient NO / O2 sieving and targeted catalytic conversion. This electrode achieves efficient, highly selective, and highly stable electrocatalytic ammonia synthesis in a low-concentration NO mixture. This method is simple and rapid, can be extended to other catalytic scenarios requiring selective sieving, significantly improves catalytic performance, and has promising application prospects.

Description

Technical Field

[0001] This invention relates to a method for preparing a selective deoxygenation electrode, which can be used for the electrocatalytic synthesis of ammonia from low concentrations of nitrogen oxides, and belongs to the fields of materials science and electrocatalysis. Background Technology

[0002] Ammonia (NH3), as a core raw material for nitrogen fertilizer production, chemical synthesis, and clean energy carriers, is crucial for ensuring food security and promoting energy transition through efficient and low-carbon production technologies. Since the development of the Haber-Bosch process (HBP) in the early 20th century, global ammonia production has exceeded 180 million tons per year. However, its technological limitations have become increasingly apparent: this process relies on fossil fuels (natural gas, coal) to produce hydrogen through steam reforming (SMR), and its high-temperature (400–500°C) and high-pressure (15–25 MPa) reaction conditions result in the synthetic ammonia industry contributing over 300 million tons of carbon emissions globally. To overcome the carbon emission and energy dependence bottlenecks of the Haber-Bosch process, electrocatalytic reduction reactions have attracted widespread attention due to their advantages of directly utilizing renewable energy electricity and operating at ambient temperature and pressure. Early research focused on electrocatalytic nitrogen reduction (NRR), but the extremely high N≡N bond energy (941 kJ / mol) and extremely low water solubility of nitrogen molecules lead to slow reaction kinetics and intense competition with the hydrogen evolution reaction (HER). In contrast, electrocatalytic reduction (NO3-) using nitrogen oxides such as nitrate (NO3-) or nitric oxide (NO) as nitrogen sources... X RR exhibits significant advantages, with its molecular bond energy (N=O: 204 kJ / mol) being significantly lower than that of the nitrogen-nitrogen triple bond. Furthermore, its high molecular polarity and fast mass transfer rate make it more readily enriched on the electrode surface in electrolytes. Current research suggests that optimized catalyst materials can be used in pure NO... X The system can achieve a Faraday efficiency of >90%, and the ammonia synthesis rate can reach mg / h. -1 level.

[0003] This process (NO) X Electrocatalytic oxidation (ERO) can be applied to the catalytic conversion of industrial waste gases (such as coal-fired flue gas, steel smelting exhaust gas, and diesel vehicle exhaust). Industrial waste gases typically contain large amounts of low-concentration NO (50–1,500 ppm), and their uncontrolled emissions not only exacerbate smog and acid rain problems but also waste nitrogen resources. Statistics show that my country's annual industrial NO emissions exceed 10 million tons. If this NO is converted into ammonia using electrocatalytic technology, it can replace a large amount of traditional synthetic ammonia production capacity, achieving both pollution control and resource recycling benefits. However, NO… X The practical industrial application of oxygen reduction reaction (RR) is limited by the competitive oxygen reduction reaction (ORR). This is in contrast to pure NO produced in the laboratory. XThe catalytic systems differ, and NO in industrial waste gas often coexists with air components such as O2 and N2. Furthermore, the O2 content (~20%) in the air components is much higher than the NO content (~0.1%), posing a significant challenge to electrocatalytic ammonia synthesis. The competitive adsorption of O2 molecules and NO at active sites on the catalyst surface significantly weakens NO mass transfer efficiency. Simultaneously, the O2 reduction reaction (ORR: O2 + 4H+ + 4e- → 2H2O) competes with NO reduction, drastically reducing and inhibiting the selectivity of ammonia synthesis. Traditional catalysts lack the ability to dynamically sieve multiple gas molecules. Therefore, developing a selective deoxygenation electrode that combines molecular sieving, enhanced dynamic mass transfer, and high stability is the core breakthrough for achieving efficient electrocatalytic ammonia production from oxygen-containing industrial waste gas. This can overcome the technical bottleneck of ammonia synthesis in low-concentration, high-oxygen-content waste gas, propelling electrocatalytic ammonia synthesis from the laboratory to industrial applications. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a selective deoxygenation electrode and its application in the electrocatalytic reduction of ammonia from low-concentration nitrogen oxides. By introducing functional carbon with controllable defects into a traditional electrocatalytic electrode structure, its sieving effect is utilized to achieve selective separation of NO and O2 molecules, thereby increasing the reaction rate of NO at the catalytic site and successfully establishing a gaseous pollutant sieving-catalytic synergistic system. This electrode structure design exhibits excellent ammonia synthesis catalytic performance in a gas flow environment where low-concentration NO (0.5%) and high-concentration oxygen (20%) coexist, showing broad application potential in the fields of gas separation and catalytic coupling technology, especially suitable for directed synthesis systems under complex gas source environments. This method is simple and rapid, with a significant improvement in catalytic effect, and has good application prospects.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a selective deoxygenation electrode, the method comprising the following steps:

[0006] 1) Conductive graphite is activated by plasma to form a plasma-activated carbon precursor;

[0007] 2) The plasma-activated carbon precursor is oxidized using a wet chemical method to form an oxide carbon precursor;

[0008] 3) The carbon oxide precursor is heated and reduced to form defective functional carbon;

[0009] 4) Defective functional carbon is printed on carbon paper to obtain a selective deoxygenation electrode precursor;

[0010] 5) Copper catalyst is sprayed onto the selective deoxygenation electrode precursor to obtain the selective deoxygenation electrode.

[0011] Preferably, the plasma activation process uses dielectric barrier discharge plasma with a plasma power of 30-50W, an argon atmosphere, and a processing time of 8-12 minutes.

[0012] Preferably, the plasma power is 40W and the processing time is 10min;

[0013] Preferably, the wet chemical oxidation method is as follows: 200 mL of hydrogen peroxide solution is added to 5 g of plasma-activated carbon precursor. The mass concentration of the hydrogen peroxide solution is 5% to 20%. After stirring for 24 h, the mixture is filtered, washed, and dried under vacuum at 80 °C.

[0014] Preferably, the mass concentration of the hydrogen peroxide solution can be 10%.

[0015] Preferably, the heating and reduction process is performed by a tubular furnace under Ar atmosphere with a heating rate of 5°C / min, a holding time of 300°C, and a holding duration of 2 hours to obtain defective functional carbon.

[0016] Preferably, the printing process involves dissolving 6 mg of defective functional carbon in 1 mL of ethanol, sonicating for 10 min to form a uniform suspension, and then printing it onto the surface of carbon paper. The loading amount is 3 mg cm⁻¹. -2 It was prepared as a selective deoxygenation electrode precursor.

[0017] Preferably, the spraying process is as follows: 6 mg of commercial copper nanoparticles are dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, and 50 μL of commercial Nafion ionomer is added. After ultrasonic dispersion for 30 min, a suspension is formed and sprayed onto the CP / FCL surface. The spraying loading is 2 mg / cm³. -2 The final selective deoxygenation electrode was used for the electrocatalytic reduction of low-concentration NO gas to synthesize ammonia.

[0018] Secondly, the present invention also provides a selective deoxygenation electrode prepared based on the method described above.

[0019] Thirdly, the present invention also provides an application of the selective deoxygenation electrode prepared based on the method in the electrocatalytic conversion of low-concentration nitrogen oxides (NO concentration <1,000 ppm) into ammonia.

[0020] The advantages of this invention are:

[0021] (1) The method is simple. The selective deoxygenation electrode preparation method provided by the present invention is simple, with compact operation steps, and is easy to operate. It does not require large-scale equipment, the raw materials are readily available, and it is conducive to large-scale production.

[0022] (2) Excellent catalytic performance. The selective deoxygenation electrode provided by this invention can maintain a Faradaic efficiency of over 80% in the electrocatalytic reduction of ammonia with a NO component supply of less than 0.5%, effectively suppressing the competitive adsorption of O2. It is of great significance for the industrial promotion of high-efficiency and high-activity electrocatalytic ammonia synthesis.

[0023] (3) Strong scalability. The selective deoxygenation electrode provided by this invention can be extended to the development of electrocatalytic electrode materials for other mixed gas components. By appropriately controlling the defect size and charge arrangement of functional carbon, selective sieving of complex component gases can be achieved, and it has broad application prospects in the conversion of low-concentration NO, low-concentration CO2, low-concentration SO2, etc. Attached Figure Description

[0024] Figure 1 This is a layered scanning electron microscope image of a selective oxygen desiccant electrode;

[0025] Figure 2 This is a cross-sectional scanning electron microscope image of a selective oxygen desiccant electrode;

[0026] Figure 3 This is a comparison of the Raman spectra of functional carbon powder and ordinary conductive graphite in a selective deoxygenation electrode.

[0027] Figure 4 This is a comparison chart of the catalytic efficiency of selective deoxygenation electrode and ordinary electrode;

[0028] Figure 5 This is a comparison chart of the stability of selective deoxygenation electrodes and ordinary electrodes;

[0029] Figure 6 This is a comparison chart of the catalytic efficiency of selective deoxygenation electrodes prepared by different processes. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] Example 1:

[0032] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma and treated at a discharge power of 40W for 10min. It was then added to 200mL of 10% hydrogen peroxide solution and stirred for 24h, followed by filtration. Residual hydrogen peroxide was washed off with deionized water and dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (1mL ethanol containing 6mg of solid powder), sonicated for 10min, and then printed onto carbon paper with a loading of 3mg / cm³. -2Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode was prepared.

[0033] The electrode structure was characterized layer by layer using scanning electron microscopy. The characterization process was as follows: characterizing carbon paper, characterizing carbon paper-loaded functional toner, and characterizing carbon paper-loaded functional toner + commercial copper nanoparticles. Figure 1 As shown, the functional toner has a size of about 1 micrometer. After loading copper powder, the surface functional toner is completely covered and sandwiched in the middle layer between the carbon paper and the copper powder.

[0034] Example 2:

[0035] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma and treated at a discharge power of 40W for 10min. It was then added to 200mL of 10% hydrogen peroxide solution and stirred for 24h, followed by filtration. Residual hydrogen peroxide was washed off with deionized water and dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (1mL ethanol containing 6mg of solid powder), sonicated for 10min, and then printed onto carbon paper with a loading of 3mg / cm³. -2 Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode was prepared.

[0036] The cross-section of the electrode was characterized using scanning electron microscopy, such as... Figure 2 As shown, the thickness of the functional toner layer and the copper powder layer is approximately 10 micrometers, and the functional toner exists stably between the copper powder layer and the carbon paper.

[0037] Example 3:

[0038] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma at a discharge power of 40W for 10 min. It was then added to 200mL of 10% hydrogen peroxide solution and stirred for 24 h. After filtration, the surface residual hydrogen peroxide was washed away with deionized water and dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2 h to obtain functional carbon powder. Raman spectroscopy was used to characterize the functional carbon powder and commercial conductive graphite. Figure 3As shown, the ratio of the D peak to the G peak of the functional toner is significantly higher than that of commercial conductive graphite, proving that its surface has pore defects of a specific size.

[0039] Example 4:

[0040] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma and treated at a discharge power of 40W for 10min. It was then added to 200mL of 10% hydrogen peroxide solution and stirred for 24h, followed by filtration. Residual hydrogen peroxide was washed off with deionized water and dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (1mL ethanol containing 6mg of solid powder), sonicated for 10min, and then printed onto carbon paper with a loading of 3mg / cm³. -2 Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode was prepared.

[0041] Commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed onto carbon paper with a loading of 2 mg / cm³. -2 Ordinary electrodes were prepared.

[0042] Using a typical membrane electrode system as the reaction system and 1,000 ppm NO + air as the reaction gas, the electrocatalytic ammonia synthesis performance of the electrode at different potentials was evaluated using an electrochemical workstation. Figure 4 As shown,

[0043] Example 5:

[0044] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma and treated at a discharge power of 40W for 10min. It was then added to 200mL of 10% hydrogen peroxide solution and stirred for 24h, followed by filtration. Residual hydrogen peroxide was washed off with deionized water and dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (1mL ethanol containing 6mg of solid powder), sonicated for 10min, and then printed onto carbon paper with a loading of 3mg / cm³. -2Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode was prepared.

[0045] Commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed onto carbon paper with a loading of 2 mg / cm³. -2 Ordinary electrodes were prepared.

[0046] Using a typical membrane electrode system as the reaction system, and employing 1,000 ppm NO + air as the reaction gas, the long-term stability of the electrode was evaluated using a DC power supply. Figure 5 As shown, in the range of 20–100 mA cm -2 Under various operating conditions, the selective deoxygenation electrode maintains good catalytic performance, with the highest ammonia synthesis Faradaic efficiency exceeding 80%, while the highest ammonia synthesis Faradaic efficiency of the ordinary electrode does not exceed 50%.

[0047] Example 6:

[0048] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma at a discharge power of 30W for 8 min. It was then added to 200mL of 5% hydrogen peroxide solution and stirred for 24h, filtered, and washed with deionized water to remove residual hydrogen peroxide. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (6mg solid powder per mL of ethanol), sonicated for 10 min, and then printed onto carbon paper with a loading of 3mg / cm³. -2 Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode with process parameters A was obtained.

[0049] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma and treated at a discharge power of 40W for 10min. It was then added to 200mL of 10% hydrogen peroxide solution and stirred for 24h, followed by filtration. Residual hydrogen peroxide was washed off with deionized water and dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (1mL ethanol containing 6mg of solid powder), sonicated for 10min, and then printed onto carbon paper with a loading of 3mg / cm³. -2 Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode with process parameters B was prepared.

[0050] 5g of commercial conductive graphite was activated using Ar atmosphere dielectric barrier discharge plasma and treated at a discharge power of 50W for 12min. It was then added to 200mL of 20% hydrogen peroxide solution and stirred for 24h, followed by filtration. Residual hydrogen peroxide was washed away with deionized water, and the graphite was dried at 80℃ under vacuum. After drying, it was placed in an Ar atmosphere tube furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 2h. Subsequently, it was dissolved in an ethanol solution (1mL ethanol containing 6mg of solid powder), sonicated for 10min, and then printed onto carbon paper with a loading of 3mg / cm³. -2 Finally, commercial copper nanoparticles were dissolved in a solvent (6 mg of commercial copper nanoparticles dissolved in a mixed solution of 750 μL isopropanol and 250 μL deionized water, with 50 μL of commercial Nafion ionomer added), and after ultrasonic dispersion for 30 min, they were sprayed with a loading of 2 mg / cm³. -2 A selective deoxygenation electrode with C process parameters was prepared.

[0051] Using a typical membrane electrode system as the reaction system and 1,000 ppm NO + air as the reaction gas, the electrocatalytic ammonia synthesis performance of different electrodes was evaluated using an electrochemical workstation. Figure 6 As shown, the selective deoxygenation electrodes prepared by the three process parameters all maintain a synthetic ammonia faradaic efficiency of over 50%, among which process parameter B has the highest synthetic ammonia faradaic efficiency, thus process parameter B is the preferred option.

[0052] Experimental results

[0053] Through the exploration of operating conditions and performance comparison of the above embodiments, the selective deoxygenation electrode, due to the specific size defects on its surface, effectively enhances the activity of electrocatalytic ammonia synthesis reaction under low-concentration NO feed. It can achieve ammonia synthesis Faradaic efficiency of more than 80% at a NO concentration of only about 1,000 ppm, demonstrating excellent catalytic performance and promising application prospects.

[0054] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a selective deoxygenation electrode, characterized in that, The method includes the following steps: 1) Conductive graphite is activated by plasma to form a plasma-activated carbon precursor; the plasma activation process uses dielectric barrier discharge plasma with a plasma power of 30~50 W, an argon atmosphere, and a processing time of 8~12 min. 2) The plasma-activated carbon precursor is oxidized by a wet chemical method to form an oxidized carbon precursor. The wet chemical oxidation method is as follows: 200 mL of hydrogen peroxide solution is added to 5 g of plasma-activated carbon precursor. The mass concentration of hydrogen peroxide solution is 5%~20%. After stirring for 24 h, the mixture is filtered, washed, and dried under vacuum at 80°C. 3) The carbon oxide precursor is heated and reduced to form defective functional carbon; the heating and reduction process is to heat the carbon oxide precursor to 300°C in Ar atmosphere at a heating rate of 5°C / min and hold it for 2 h to obtain defective functional carbon. 4) Defective functional carbon is printed on carbon paper to obtain a selective deoxygenation electrode precursor; 5) Copper catalyst is sprayed onto the selective deoxygenation electrode precursor to obtain the selective deoxygenation electrode.

2. The method for preparing a selective deoxygenation electrode according to claim 1, characterized in that, The printing process is: 6 mg of defective functional carbon is dissolved in 1 mL of ethanol, ultrasonic for 10 min to form a uniform suspension and printed on the surface of carbon paper, the loading capacity is controlled to be 3 mg cm -2 , and prepared as a selective oxygen removal electrode precursor.

3. The method for preparing a selective deoxygenation electrode according to claim 1, characterized in that, The spraying process is as follows: 6 mg of copper nanoparticles are dissolved in a mixed solution of 750 µL isopropanol and 250 µL deionized water, and 50 µL of Nafion ionomer is added. After ultrasonic dispersion for 30 min, a suspension is formed and sprayed onto the CP / FCL surface, controlling the Cu loading to be 2 mg / cm³. -2 A selective deoxygenation electrode was obtained.

4. A selective deoxygenation electrode prepared according to any one of claims 1 to 3.

5. The application of a selective deoxygenation electrode prepared according to any one of claims 1 to 3 in the electrocatalytic conversion of low-concentration nitrogen oxides (NO concentration <1,000 ppm) into ammonia.

Images