A method for preparing nanowires with enhanced gas turnover and electrocatalytic synthesis of ammonia

Abstract

The application discloses a kind of nano-wire preparation methods and electrocatalytic synthesis of ammonia application of reinforced gas turnover.Nitrate reduction synthesis ammonia process hydrogen micro-bubble generated by local hydrogen evolution reaction prevents active site from contacting electrolyte, thereby causing reaction kinetics slow, low current density, high overpotential and other problems.To solve this problem, the application forms cationophilic site on the surface of transition metal nano-wire by embedding phosphorus strategy, modulates local cation enrichment to improve micro-bubble interfacial tension, strengthens local bubble turnover, forms high-activity catalytic site on the surface of nano-wire, improves the performance of electrocatalytic nitrate reduction reaction, realizes high current density, high selectivity, long-time stable ammonia synthesis.The synthesis method is simple and fast, and has strong expandability, and by improving the substrate condition, the nano-wire structure with reinforced gas turnover can be formed on different transition metals, the catalytic effect is significantly improved, and the method can be applied to various solid-liquid two-phase electrocatalytic reactions, and has good application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing nanowires that enhance gas circulation and their application in electrocatalytic ammonia synthesis, belonging to the fields of materials science and electrocatalysis. Background Technology

[0002] Ammonia is an indispensable chemical in agriculture and industry. Currently, the global ammonia synthesis industry mainly relies on the Haber-Bosch process. This process, which has been the standard method for ammonia production since the early 20th century, synthesizes ammonia from nitrogen and hydrogen under high temperature (approximately 500°C) and high pressure (approximately 20-30 MPa) conditions. However, the high-purity hydrogen source for this process typically depends on the steam reforming (SMR) process of natural gas, generating significant carbon dioxide emissions. The extraction and transportation of natural gas resources also introduce environmental and economic uncertainties. The high temperature and high pressure conditions of the Haber-Bosch process also consume large amounts of fossil fuels, resulting in the ammonia synthesis industry consuming approximately 2% of the Earth's energy annually and emitting over 300 million tons of carbon dioxide, placing enormous pressure on the environment and further exacerbating global climate change. Furthermore, due to the economies of scale of the Haber-Bosch process, most ammonia production facilities are large and centralized, limiting the flexibility and decentralization of ammonia production, making it unsuitable for geographically remote areas or regions lacking industrial infrastructure.

[0003] With the continuous development of renewable energy technologies, electrocatalytic nitrogen reduction (NRR) ammonia synthesis can be carried out at ambient temperature and pressure, offering advantages such as rapid start-up, flexible operation, and clean, pollution-free processes, and is considered a potential clean ammonia synthesis route. However, the high bond energy and low solubility of nitrogen molecules result in strong competitive hydrogen evolution reactions in the electrocatalytic nitrogen reduction system, hindering improvements in ammonia yield and Faradaic efficiency. Electrocatalytic nitrate reduction (NO3RR), utilizing nitrate as a nitrogen source, features a more active N=O bond (204 kJ / mol) than nitrogen, making it easier to achieve high Faradaic efficiency and high ammonia yield in the electrocatalytic system. Furthermore, considering that nitrate in the environment can lead to nitrogen cycle imbalances in water bodies, affecting the structure and function of aquatic ecosystems, ammonia synthesis via nitrate reduction not only achieves green and clean chemical production but also contributes to resource recycling and pollution control.

[0004] As the most significant competing reaction for nitrate electrocatalysis, the hydrogen evolution reaction (HEP) generates microbubbles that create a gas layer at the catalyst-electrolyte interface, hindering the active reaction sites and thus reducing the reactivity of ammonia synthesis. Although some studies have reported catalysts with near-100% Faraday efficiency under ideal conditions, factors such as power fluctuations, temperature changes, and reactant consumption in real industrial environments can cause the reaction to deviate from optimal conditions, making it difficult to completely avoid competitive HEP reactions in ammonia synthesis under industrial environments. Therefore, industrial-grade ammonia synthesis catalysts with high interfacial gas turnover rates, good stability, and high electrocatalytic performance urgently need to be developed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing nanowires with enhanced gas circulation and its application in the electrocatalytic reduction of nitrate to ammonia. This method addresses the problems of slow reaction kinetics, low current density, and high overpotential caused by hydrogen microbubbles generated during the local hydrogen evolution reaction in the ammonia reduction process, which hinder the contact between active sites and electrolytes. By employing a phosphorus intercalation strategy to form cationic sites on the surface of transition metal nanowires, local cation enrichment is modulated to improve the interfacial tension of microbubbles, enhance local bubble circulation, and form highly active catalytic sites on the nanowire surface. This improves the performance of the electrocatalytic nitrate reduction reaction, achieving high current density, high selectivity, and long-term stable ammonia synthesis.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, the present invention provides a method for preparing nanowires with enhanced gas circulation, the method comprising the following steps:

[0007] 1) Thoroughly clean and dry the transition metal substrate;

[0008] 2) Metal oxide nanowire precursors are prepared by oxidizing and etching the surface of a transition metal substrate using a strong oxidizing agent.

[0009] 3) Phosphate the metal oxide nanowire precursor obtained in step 2) to obtain a phosphorus-embedded metal oxide nanowire precursor.

[0010] 4) Electroreducing the phosphorus-intercalated metal oxide nanowire precursor obtained in step 2) yields nanowires with enhanced gas circulation.

[0011] Furthermore, the transition metal substrate is one of foamed copper, foamed nickel, or foamed iron.

[0012] Furthermore, the cleaning method is as follows: soaking in 0.05M HCl for 10 minutes, and rinsing repeatedly with deionized water and anhydrous ethanol at 30°C; the drying method is vacuum drying in an oven at 60°C for 10 hours.

[0013] Furthermore, the strong oxidizing agent is 1M NaOH + 0.1M (NH4)2S2O8, and the dosage is per 1cm³. 2 The transition metal substrate requires 10 mL of strong oxidant.

[0014] Furthermore, the phosphating treatment involves placing sodium hypophosphite upstream of a tubular furnace at a dosage of 1 cm³. 2 0.3 g of transition metal substrate is required, and a metal oxide nanowire precursor is placed downstream. The mixture is then in an argon atmosphere at 1 °C for 1 min. -1 After heating to 240℃ at a certain rate, maintain the temperature for 1-3 hours.

[0015] Furthermore, the electroreduction process involves reducing the electrode in a 1M KOH electrolyte environment in a single-cell three-electrode system for 2 hours using a constant current method, with a current of 150mA applied to the electrode per square centimeter.

[0016] Secondly, the present invention provides a nanowire for enhancing gas circulation.

[0017] Thirdly, the present invention provides a catalyst application for the electrocatalytic reduction of nitrate to ammonia reaction, using nanowires that enhance gas circulation.

[0018] This invention involves thoroughly cleaning and drying a transition metal substrate, then using a strong oxidizing agent to perform oxidation etching on the surface of the transition metal substrate to obtain a metal oxide nanowire precursor. The obtained metal oxide nanowire precursor is then subjected to phosphating treatment to obtain a phosphorus-embedded metal oxide nanowire precursor. Finally, the obtained phosphorus-embedded metal oxide nanowire precursor is electro-reduced to obtain nanowires with enhanced gas circulation, which can be used in the field of electrocatalytic nitrate reduction to achieve efficient and stable ammonia synthesis.

[0019] The advantages of this invention are:

[0020] (1) Simple method. The method for preparing nanowires with enhanced gas circulation provided by the present invention has simple operation steps, short preparation process, simple and easy-to-operate synthesis process, strong electrocatalytic activity and high selectivity, etc. It does not require large-scale equipment, the raw materials are readily available, and it is conducive to large-scale production.

[0021] (2) Excellent catalytic performance. The nanowires with enhanced gas circulation provided by this invention maintain a Faradaic efficiency of over 95% in the electrocatalytic reduction of nitrate to ammonia, achieving a 600 mA cm⁻¹ at a potential of -0.5 V vs. RHE. -2 The above-mentioned ammonia synthesis current density is of great significance for the industrial promotion of high-efficiency and high-activity electrocatalytic ammonia synthesis.

[0022] (3) High scalability. The method for preparing nanowires with enhanced gas circulation provided by this invention can be extended to the development of other two-phase reaction catalysts. By implementing an appropriate phosphorus doping strategy on the surface of the nanowires, the hydrogen micro- and nano-bubbles can be modulated, weakening the obstruction of hydrogen bubbles to the active centers and improving the activity of solid-liquid two-phase reactions. By improving the substrate conditions, nanowire structures with enhanced gas circulation can be formed on different transition metals, resulting in a significant improvement in catalytic effect and broad application prospects. Attached Figure Description

[0023] Figure 1 This is a transmission electron microscope image of nanowires that enhance gas circulation;

[0024] Figure 2 This is a comparison of X-ray diffraction patterns between nanowires with enhanced gas circulation and ordinary nanowires.

[0025] Figure 3 This is a comparison of the X-ray photoelectron spectra of nanowires with enhanced gas circulation and ordinary nanowires.

[0026] Figure 4 This is a Faraday efficiency diagram of enhanced gas circulation nanowires and ordinary nanowires at different potentials.

[0027] Figure 5 This is a current density diagram of enhanced gas circulation nanowires and ordinary nanowires at different potentials.

[0028] Figure 6 The graph shows the current density versus Faraday efficiency of nanowires with enhanced gas circulation at -0.2V vs. RHE potentials with different phosphorus doping levels.

[0029] Figure 7 This is a graph showing the ammonia synthesis rate of metal-based nanowires with enhanced gas circulation at -0.2V vs. RHE potential. 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] Take 1×1cm 2 Copper foam was first soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Next, the copper foam was immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes. After removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and placed downstream of a tube furnace. 0.3g of sodium hypophosphite was placed upstream of the tube furnace, and the furnace was heated at 1°C for 1 minute under an argon atmosphere. -1The temperature was raised to 240℃ at a certain rate and held for 1.5 hours; after natural cooling, it was subjected to a 150mA cm-wave electrolysis in a 1M KOH electrolyte environment in a single-cell three-electrode system. -2 Nanowires with enhanced gas circulation were prepared by reduction under a constant current for 2 hours. The microstructure of the obtained nanowires with enhanced gas circulation was characterized by transmission electron microscopy, such as... Figure 1 As shown, the nanowires that enhance gas circulation exhibit a typical nanowire structure with a diameter of approximately 20-30 nm.

[0033] Example 2:

[0034] Take 1×1cm 2 Copper foam was first soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Next, the copper foam was immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes. After removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and placed downstream of a tube furnace. 0.3g of sodium hypophosphite was placed upstream of the tube furnace, and the furnace was heated at 1°C for 1 minute under an argon atmosphere. -1 The temperature was raised to 240℃ at a certain rate and held for 1.5 hours; after natural cooling, it was subjected to a 150mA cm-wave electrolysis in a 1M KOH electrolyte environment in a single-cell three-electrode system. -2 Nanowires with enhanced gas circulation were prepared by reduction under a constant current for 2 hours. The phase composition of the obtained nanowires with enhanced gas circulation was characterized by X-ray diffraction, as shown in the figure. Figure 2 As shown, the nanowires that enhance gas circulation are mainly composed of Cu, and there are no obvious X-ray diffraction peaks of CuP compounds or P particles, proving that P is dispersed and embedded inside Cu.

[0035] Example 3:

[0036] Take 1×1cm 2 Copper foam was first soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Next, the copper foam was immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes. After removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and placed downstream of a tube furnace. 0.3g of sodium hypophosphite was placed upstream of the tube furnace, and the furnace was heated at 1°C for 1 minute under an argon atmosphere. -1 The temperature was raised to 240℃ at a certain rate and held for 1.5 hours; after natural cooling, it was subjected to a 150mA cm-wave electrolysis in a 1M KOH electrolyte environment in a single-cell three-electrode system. -2 Nanowires with enhanced gas circulation were prepared by reduction under a constant current for 2 hours. The valence states of surface species in the obtained nanowires with enhanced gas circulation were characterized by X-ray photoelectron spectroscopy, such as... Figure 3 As shown, the Cu on the surface has a valence of 0 and is in a metallic state.

[0037] Example 4:

[0038] Take 1×1cm 2 Copper foam was first soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Next, the copper foam was immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes. After removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and placed downstream of a tube furnace. 0.3g of sodium hypophosphite was placed upstream of the tube furnace, and the furnace was heated at 1°C for 1 minute under an argon atmosphere. -1 The temperature was raised to 240℃ at a certain rate and held for 1.5 hours; after natural cooling, it was subjected to a 150mA cm-wave electrolysis in a 1M KOH electrolyte environment in a single-cell three-electrode system. -2 Nanowires with enhanced gas circulation were obtained by reducing them under a constant current for 2 hours.

[0039] Take 1×1cm 2 Copper foam was soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Copper foam was then immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes; after removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and then subjected to a 150mA cm-wave electrolysis in a single-cell three-electrode system with 1M KOH electrolyte. -2 Ordinary nanowires were prepared by reducing them under a constant current for 2 hours.

[0040] The performance of two materials in nitrate reduction to ammonia synthesis was evaluated in an H-type electrolytic cell. Different cathode potentials were applied to the system, and after holding for 30 minutes, the Faraday efficiency and partial current density at the corresponding potentials were measured. Figure 4 As shown, the nanowires with enhanced gas circulation exhibit higher Faraday efficiency than ordinary nanowires at all potentials from -0.5 to 0 V vs. RHE, reaching a maximum Faraday efficiency (96.76%) at -0.2 V vs. RHE. Figure 5 As shown, the nanowires with enhanced gas circulation exhibit a higher ammonia synthesis current density than ordinary nanowires at all potentials from -0.5 to 0 V vs. RHE, reaching -644.35 mA cm⁻¹ at -0.5 V vs. RHE. -2 .

[0041] Example 5:

[0042] Take 1×1cm 2Copper foam was first soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Next, the copper foam was immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes. After removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and placed downstream of a tube furnace. 0.3g of sodium hypophosphite was placed upstream of the tube furnace, and the furnace was heated at 1°C for 1 minute under an argon atmosphere. -1 The temperature was raised to 240℃ at a constant heating rate and held for 1 hour; after natural cooling, it was then subjected to a 150mA cm-wave electrolysis in a 1M KOH electrolyte environment within a single-cell three-electrode system. -2 Nanowires with enhanced gas circulation were prepared by reduction under a constant current for 2 hours. Using the same method, nanowires with enhanced gas circulation and different phosphorus doping degrees were prepared by changing the temperature holding time to 1.5, 2, 2.5, and 3 hours: P 1.5 P2, P 2.5 , P3.

[0043] The performance of several materials in nitrate reduction to ammonia synthesis was evaluated in an H-type electrolytic cell. A cathode potential of -0.2V vs. RHE was applied to the system, and after 30 minutes, the Faraday efficiency and ammonia yield at the corresponding potential were measured. Figure 6 As shown, P was kept at a temperature of 1.5 hours during the phosphating process. 1.5 The sample exhibited the highest ammonia synthesis rate, reaching 13.95 mg / h. -1 cm -2 The Faraday efficiency was 96.76%; the P-type phosphorus phosphorus was maintained at a temperature of 2.5 hours during the phosphating process. 2.5 The sample exhibited the highest Faraday efficiency, reaching 97.31%, with an ammonia synthesis rate of 10.32 mg / h. -1 cm -2 In contrast, P 1.5 The ammonia synthesis rate of the sample was much higher than that of P. 2.5 The samples are similar in efficiency to the Faraday efficiencies, therefore P 1.5 The sample represents the preferred design.

[0044] Example 6:

[0045] Take 1×1cm 2 Copper foam was first soaked in 0.05M HCl for 10 minutes, then repeatedly rinsed with deionized water and anhydrous ethanol at 30°C to remove surface impurities, and then vacuum dried in an oven at 60°C for 10 hours. Next, the copper foam was immersed in a solution of 1M NaOH + 0.1M (NH4)2S2O8 for 30 minutes. After removal, it was repeatedly rinsed with deionized water and anhydrous ethanol at 30°C, dried again, and placed downstream of a tube furnace. 0.3g of sodium hypophosphite was placed upstream of the tube furnace, and the furnace was heated at 1°C for 1 minute under an argon atmosphere.-1 The temperature was raised to 240℃ at a certain rate and held for 1.5 hours; after natural cooling, it was subjected to a 150mA cm-wave electrolysis in a 1M KOH electrolyte environment in a single-cell three-electrode system. -2 Nanowires with enhanced gas circulation (Cu) were prepared by reduction under a constant current for 2 hours. Using the same method, nanowires with enhanced gas circulation based on different metals were prepared by changing the initial materials to nickel foam, iron foam, and titanium foam: Ni, Fe, and Ti.

[0046] The performance of several materials in nitrate reduction to ammonia synthesis was evaluated in an H-type electrolytic cell. A cathode potential of -0.2V vs. RHE was applied to the system, and after 30 minutes, the Faraday efficiency and ammonia yield at the corresponding potential were measured. Figure 7 As shown, Cu nanowires with enhanced gas circulation, fabricated using copper foam as a transition metal substrate, exhibited a better ammonia synthesis rate than both Ni and Fe, thus Cu is the preferred option.

[0047] Experimental results

[0048] Through the exploration of operating conditions and performance comparison of the above embodiments, the nanowires that enhance gas circulation effectively enhance the activity of electrocatalytic ammonia synthesis reaction due to the phosphorus intercalation strategy on the surface. They can synthesize ammonia efficiently with a Faraday efficiency of over 95% under fluctuating operating conditions, demonstrating excellent catalytic performance and promising prospects for industrial application.

[0049] 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. The application of a nanowire that enhances gas circulation as a catalyst in the electrocatalytic reduction of nitrate to ammonia, characterized in that, The method for preparing the nanowires with enhanced gas circulation includes the following steps: 1) Thoroughly clean and dry the transition metal substrate; the transition metal substrate is copper foam; 2) Metal oxide nanowire precursors are prepared by oxidizing and etching the surface of a transition metal substrate using a strong oxidizing agent. 3) The metal oxide nanowire precursor obtained in step 2) is subjected to phosphating treatment to obtain phosphorus-embedded metal oxide nanowire precursor; the phosphating treatment is performed by placing sodium hypophosphite upstream of a tube furnace, with an amount of sodium hypophosphite per 1 cm³. 2 0.3 g of transition metal substrate is required, and a metal oxide nanowire precursor is placed downstream. The mixture is then in an argon atmosphere at 1 °C for [time missing]. -1 After heating to 240 °C at a rising rate, hold for 1-3 hours; 4) Electroreducing the phosphorus-intercalated metal oxide nanowire precursor obtained in step 2) to obtain nanowires with enhanced gas circulation.

2. The application of the nanowire for enhancing gas circulation as described in claim 1 as a catalyst in the electrocatalytic reduction of nitrate to ammonia reaction, characterized in that, The cleaning method is as follows: soaking in 0.05 M HCl for 10 min, and rinsing repeatedly with deionized water and anhydrous ethanol at 30 °C; the drying method is vacuum drying in an oven at 60 °C for 10 hours.

3. The application of the nanowire for enhancing gas circulation as described in claim 1 as a catalyst in the electrocatalytic reduction of nitrate to ammonia reaction, characterized in that, The strong oxidizing agent is 1 M NaOH + 0.1 M (NH4)2S2O8, and the dosage is per 1 cm³. 2 The transition metal substrate requires 10 mL of strong oxidant.

4. The application of the nanowire for enhancing gas circulation as described in claim 1 as a catalyst in the electrocatalytic reduction of nitrate to ammonia reaction, characterized in that, The electroreduction process involves reducing the electrode in a single-cell three-electrode system using a constant current method for 2 hours in a 1 M KOH electrolyte environment, with a current of 150 mA applied to the electrode per square centimeter.

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