Bifunctional Cu-Co / NF series catalyst and preparation method thereof

Abstract

The invention relates to the technical field of electro-catalysis, and provides a bifunctional Cu-Co / NF series catalyst and a preparation method thereof. The preparation method comprises the following steps: dissolving cobalt nitrate and urea serving as reaction raw materials, adding a foamed nickel substrate, carrying out primary hydrothermal reaction, and washing and drying to obtain a first precursor; dissolving copper nitrate and urea serving as reaction raw materials, adding the first precursor to carry out a second hydrothermal reaction, and washing and drying to obtain a second precursor; and calcining the second precursor to obtain the bifunctional Cu-Co / NF series catalyst. Effective construction of bimetal active sites is achieved, the anode has the excellent performance of converting hydrazine into nitrogen through oxidation, a nitrogen circulation closed-loop system is successfully constructed through a synergistic mechanism of coupling cathode nitrate reduction with anode hydrazine oxidation, bidirectional nitrogen neutralization of nitrate pollutant resource utilization and nitrogen-containing waste liquid harmless treatment is achieved, and the nitrogen-containing waste liquid harmless treatment effect is achieved. A secondary hydrothermal method is adopted to effectively avoid the segregation phenomenon generated in the hydrothermal growth process due to the physicochemical property difference of copper ions and cobalt ions.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and particularly relates to a bifunctional Cu-Co / NF tandem catalyst and a preparation method thereof. Background Art

[0002] Agricultural activities and industrial wastewater discharges have led to a significant increase in the concentration of nitrate (NO3 - ) in water bodies, seriously disrupting the balance of the natural nitrogen cycle and posing a threat to human health. Specifically, excessive NO3 - in water bodies can trigger eutrophication, resulting in a decrease in dissolved oxygen content and an explosive proliferation of harmful algae. From the perspective of human health, long-term ingestion of drinking water with a high concentration of NO3 - may increase the risk of cancer and may cause diseases such as methemoglobinemia (commonly known as "blue baby disease"). Based on these health risks, the World Health Organization (WHO) has limited the maximum allowable concentration of NO3 - in drinking water to 50 mg L -1 .

[0003] Ammonia (NH3), as a key chemical widely used in agriculture, industry, and national defense, is also regarded as a highly potential carbon-free energy carrier. Compared with hydrogen (H2), NO3 - has significant advantages: it can be liquefied under relatively mild conditions of -10 °C and 5.6 MPa, and its volumetric energy density reaches 4.32 kW h L -1 , about twice that of H2, which makes it more advantageous in terms of safe storage and transportation. Since the content of nitrogen (N2) in the earth's atmosphere is as high as 78%, current industrial ammonia production still mainly relies on the traditional Haber-Bosch Process. This century-old production process not only consumes huge amounts of energy (about 2% of the global energy consumption), but also is accompanied by serious environmental problems - about 400 million tons of carbon dioxide emissions are generated annually, and this figure is still rising. Electrocatalytic nitrogen reduction reaction (NRR) provides a promising technical path for the green synthesis of ammonia. However, this technology faces significant challenges in practical applications: due to the extremely low solubility of nitrogen in aqueous solutions and the need to overcome an energy barrier as high as 941 kJ mol -1 for the cleavage of the N≡N triple bond, the current ammonia production rate and Faradic efficiency (FE) of NRR are still at relatively low levels. In contrast, nitrate ions not only have excellent water solubility, but their N=O bond energy (204 kJ mol -1) is also significantly lower than the N≡N bond energy. Therefore, considering the dual perspectives of energy efficiency and environmental protection, the electrochemical conversion of nitrate into high-value-added product ammonia not only helps alleviate the imbalance of the global nitrogen cycle but also creates considerable economic benefits, providing a practical industrial approach for sustainable ammonia production. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a bifunctional Cu-Co / NF tandem catalyst and its preparation method, aiming to solve the problems mentioned in the background art.

[0005] In the first aspect, the present invention provides a preparation method of a bifunctional Cu-Co / NF tandem catalyst. Using cobalt nitrate and urea as reaction raw materials, after dissolution, the pretreated nickel foam substrate is added for the first hydrothermal reaction, and after washing and drying, the first precursor is obtained; using copper nitrate and urea as reaction raw materials, after dissolution, the first precursor is added for the second hydrothermal reaction, and after washing and drying, the second precursor is obtained; the second precursor is calcined to obtain the bifunctional Cu-Co / NF tandem catalyst.

[0006] Furthermore, it specifically includes the following steps:

[0007] Step S1: Immerse the nickel foam substrate successively in hydrochloric acid, absolute ethanol, and deionized water, perform ultrasonic cleaning respectively, and then vacuum dry to obtain the pretreated nickel foam substrate;

[0008] Step S2: Dissolve cobalt nitrate and urea in deionized water, continuously stir until fully dissolved, and then immerse the pretreated nickel foam substrate; carry out a hydrothermal reaction at 100 - 140 °C under sealed conditions for 10 - 15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then alternately wash with deionized water and absolute ethanol, and then vacuum dry to obtain the Co / NF precursor;

[0009] Step S3: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; carry out a hydrothermal reaction at 100 - 140 °C under sealed conditions for 10 - 15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then alternately wash with deionized water and absolute ethanol, and then vacuum dry to obtain the Cu-Co / NF precursor;

[0010] Step S4: Place the Cu-Co / NF precursor in a porcelain boat, program the temperature to 300 - 350 °C at a heating rate of 2 °C / min under the protection of an inert gas, and keep it warm for 2 - 3 hours for pyrolysis treatment to finally obtain the bifunctional Cu-Co / NF tandem catalyst.

[0011] Further, step S1 is specifically as follows: Immerse the nickel foam substrate in 2-3M hydrochloric acid, absolute ethanol, and deionized water in sequence, perform ultrasonic cleaning for 15 minutes respectively, and then dry it in a vacuum drying oven at 60°C.

[0012] Further, in step S2, cobalt nitrate: urea: deionized water = 4 mmol: 10 mmol: 30 mL.

[0013] Further, step S3 is specifically as follows: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; in a sealed stainless steel autoclave with a polytetrafluoroethylene liner, carry out a hydrothermal reaction at 120°C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, wash it alternately with deionized water and absolute ethanol three times respectively, and finally dry it under vacuum conditions at 60°C for 12 hours to obtain the Co / NF precursor.

[0014] Further, in step S3, copper nitrate: urea: deionized water = 2 mmol: 10 mmol: 30 mL.

[0015] Further, step S3 is specifically as follows: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; in a sealed stainless steel autoclave with a polytetrafluoroethylene liner, carry out a hydrothermal reaction at 120°C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, wash it alternately with deionized water and absolute ethanol three times respectively, and finally dry it under vacuum conditions at 60°C for 12 hours to obtain the Cu-Co / NF precursor.

[0016] Further, place the Cu-Co / NF precursor in a porcelain boat, program the temperature to 350°C at a heating rate of 2°C / min under argon protection, and keep it at this temperature for 2 hours for pyrolysis treatment to finally obtain the Co-Cu / NF tandem catalyst.

[0017] In the second aspect, the present invention also provides a bifunctional Cu-Co / NF tandem catalyst, which has a hierarchical structure of nanoneedle clusters composed of a cobalt source and nanosheet stacks composed of a copper source, forming a tandem structure.

[0018] In the third aspect, the present invention also provides the application of the bifunctional Cu-Co / NF tandem catalyst in electrocatalytic nitrate reduction to ammonia and hydrazine oxidation.

[0019] The present invention has the following beneficial effects:

[0020] (1) The prepared bifunctional Cu-Co / NF tandem catalyst can "turn waste into treasure" for nitrate at the cathode. Under normal temperature and pressure conditions, sustainable clean electric energy is used to convert nitrate into high-value ammonia, and it shows excellent ammonia Faraday efficiency and yield. In the wide potential range of -0.24 to -0.74 V vs. RHE, its Faraday efficiency remains above 90%, and the ammonia production Faraday efficiency reaches 97.01 ± 0.026% at -0.74 V vs. RHE. In addition, the bifunctional Cu-Co / NF tandem catalyst has excellent performance for the oxidation of hydrazine to nitrogen at the anode. Through the synergistic mechanism of coupling nitrate reduction at the cathode with hydrazine oxidation at the anode, a nitrogen cycle closed-loop system is successfully constructed, realizing the two-way nitrogen neutralization of resource utilization of nitrate pollutants and harmless treatment of nitrogen-containing waste liquid.

[0021] (2) The method of secondary hydrothermal effectively avoids the segregation phenomenon of copper ions and cobalt ions during the hydrothermal growth process due to their different physical and chemical properties, ensuring the uniformity of catalytic active sites, thereby significantly improving the overall performance of the catalyst. The catalyst prepared by this method has nanoneedle clusters composed of cobalt sources and nanoplate stacks composed of copper sources, which not only provide rich active sites for nitrate reduction at the cathode and hydrazine oxidation reaction at the anode, but also promote electron transfer, and at the same time show excellent stability and environmental friendliness.

[0022] (3) The secondary hydrothermal method also realizes the controllable growth of copper sites through the hetero-structure assisted strategy; the cobalt transition layer deposited during the first hydrothermal process constructs a hetero-interface, which can effectively reduce the formation energy barrier of copper sites, thereby promoting the uniform epitaxial growth of copper sites at the hetero-interface. Through secondary hydrothermal treatment, the hetero-interface induces the formation of a tandem nanostructure, which optimizes the adsorption energy of reaction intermediates through the interface electron effect, and at the same time the three-dimensional porous structure provides rich mass transfer channels, making the catalyst show more excellent catalytic performance for nitrate reduction at the cathode and hydrazine oxidation reaction at the anode. Description of the Drawings

[0023] By referring to the following drawings, the exemplary embodiments of the present invention can be more completely understood:

[0024] Figure 1 Scanning electron microscope image of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention.

[0025] Figure 2 Scanning electron microscope image of Cu / NF prepared in Comparative Example 3 of the present invention.

[0026] Figure 3 Scanning electron microscope image of the bifunctional Cu-Co / NF tandem catalyst prepared in Comparative Example 1 of the present invention.

[0027] Figure 4Element (Co) distribution image of the Cu-Co / NF catalyst prepared in Comparative Example 1 of the present invention.

[0028] Figure 5 Element (Cu) distribution image of the Cu-Co / NF catalyst prepared in Comparative Example 1 of the present invention.

[0029] Figure 6 LSV (NITRR) test result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention and the Co-Cu / NF catalyst prepared in Comparative Example 1.

[0030] Figure 7 LSV (NITRR) test result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention, Co / NF prepared in Comparative Example 2, and Cu / NF catalyst prepared in Comparative Example 3.

[0031] Figure 8 Faraday efficiency (NITRR) test result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention.

[0032] Figure 9 Ammonia yield (NITRR) result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention.

[0033] Figure 10 Scanning electron microscope image of the Co / NF catalyst prepared in Comparative Example 2 of the present invention.

[0034] Figure 11 LSV (HzOR) test result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention at different hydrazine hydrate concentrations.

[0035] Figure 12 LSV (HzOR) comparative test result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention with / without 0.3 M hydrazine hydrate.

[0036] Figure 13 For the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention at 100 mA cm -2 (HzOR) potential displacement graph at a current density of.

[0037] Figure 14 LSV (HzOR) test result graph of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 of the present invention, Co / NF catalyst prepared in Comparative Example 2, and Cu / NF catalyst prepared in Comparative Example 3. Detailed implementation manners

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0040] The embodiment of the present invention provides a method for preparing a bifunctional Cu-Co / NF tandem catalyst. Using cobalt nitrate and urea as reaction raw materials, after dissolution, the pretreated nickel foam substrate is added for the first hydrothermal reaction, and the first precursor is obtained after washing and drying; using copper nitrate and urea as reaction raw materials, after dissolution, the first precursor is added for the second hydrothermal reaction, and the second precursor is obtained after washing and drying; the second precursor is calcined to obtain the bifunctional Cu-Co / NF tandem catalyst.

[0041] In some embodiments, it specifically includes the following steps:

[0042] Step S1: Immerse the nickel foam substrate in hydrochloric acid, absolute ethanol and deionized water in sequence, perform ultrasonic cleaning respectively, and then vacuum dry to obtain the pretreated nickel foam substrate;

[0043] Step S2: Dissolve cobalt nitrate and urea in deionized water, continuously stir until fully dissolved, and then immerse the pretreated nickel foam substrate; perform a hydrothermal reaction at 100 - 140 °C under sealed conditions for 10 - 15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash alternately with deionized water and absolute ethanol, and then vacuum dry to obtain the Co / NF precursor;

[0044] Step S3: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; perform a hydrothermal reaction at 100 - 140 °C under sealed conditions for 10 - 15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash alternately with deionized water and absolute ethanol, and then vacuum dry to obtain the Cu-Co / NF precursor;

[0045] Step S4: Place the Cu-Co / NF precursor in a porcelain boat, program the temperature to 300 - 350 °C at a heating rate of 2 °C / min under the protection of an inert gas, and keep the temperature for 2 - 3 hours for pyrolysis treatment to finally obtain the bifunctional Cu-Co / NF tandem catalyst.

[0046] In some embodiments, step S1 is specifically as follows: Immerse the nickel foam substrate successively in 2 - 3M hydrochloric acid, absolute ethanol, and deionized water, perform ultrasonic cleaning for 15 minutes respectively, and then dry it in a vacuum drying oven at 60°C.

[0047] In some embodiments, in step S2, cobalt nitrate: urea: deionized water = 4 mmol: 10 mmol: 30 mL.

[0048] In some embodiments, step S3 is specifically as follows: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; in a sealed stainless - steel autoclave with a polytetrafluoroethylene lining, carry out a hydrothermal reaction at 120°C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, wash it alternately with deionized water and absolute ethanol three times respectively, and finally dry it under vacuum conditions at 60°C for 12 hours to obtain the Co / NF precursor.

[0049] In some embodiments, in step S3, copper nitrate: urea: deionized water = 2 mmol: 10 mmol: 30 mL.

[0050] In some embodiments, step S3 is specifically as follows: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; in a sealed stainless - steel autoclave with a polytetrafluoroethylene lining, carry out a hydrothermal reaction at 120°C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, wash it alternately with deionized water and absolute ethanol three times respectively, and finally dry it under vacuum conditions at 60°C for 12 hours to obtain the Cu - Co / NF precursor.

[0051] In some embodiments, place the Cu - Co / NF precursor in a porcelain boat, program - heat it to 350°C at a heating rate of 2°C / min under argon protection, and keep it at this temperature for 2 hours for pyrolysis treatment to finally obtain the Co - Cu / NF tandem catalyst.

[0052] In some embodiments, the present invention also provides a bifunctional Cu - Co / NF tandem catalyst, which has a hierarchical structure of nanoneedle clusters composed of a cobalt source and nanoplate stacks composed of a copper source, forming a tandem structure.

[0053] In some embodiments, the present invention provides the application of the bifunctional Cu - Co / NF tandem catalyst in electrocatalytic nitrate reduction to ammonia and hydrazine oxidation.

[0054] Example 1:

[0055] (1) Immerse the nickel foam substrate successively in 2M hydrochloric acid, absolute ethanol, and deionized water, and perform ultrasonic cleaning for 15 min respectively. Subsequently, dry it in a vacuum drying oven at 60 °C to obtain the pretreated nickel foam substrate;

[0056] (2) Dissolve 4 mmol of cobalt nitrate and 10 mmol of urea in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner, and immerse the pretreated nickel foam substrate. After sealing the stainless-steel autoclave, carry out a hydrothermal reaction at 120 °C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash it alternately with deionized water and absolute ethanol three times, and finally dry it under vacuum conditions at 60 °C for 12 hours to obtain the Co / NF precursor;

[0057] (3) Dissolve 2 mmol of copper nitrate and 10 mmol of urea in a certain proportion of copper nitrate and urea dissolved in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner, and immerse the Co / NF precursor. After sealing the stainless-steel autoclave, react at a constant temperature of 120 °C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash it alternately with deionized water and absolute ethanol three times, and finally dry it in a vacuum environment at 60 °C for 12 hours to obtain the Cu-Co / NF precursor;

[0058] (4) Place the Cu-Co / NF precursor in a porcelain boat, and program the temperature to rise to 350 °C at a heating rate of 2 °C / min under nitrogen protection, and keep it at this temperature for 2 hours for pyrolysis treatment to finally obtain the bifunctional Cu-Co / NF tandem catalyst.

[0059] Example 2:

[0060] (1) Immerse the nickel foam substrate successively in 3M hydrochloric acid, absolute ethanol, and deionized water, and perform ultrasonic cleaning for 15 min respectively. Subsequently, dry it in a vacuum drying oven at 60 °C to obtain the pretreated nickel foam substrate;

[0061] (2) Dissolve 4 mmol of cobalt nitrate and 10 mmol of urea in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner, and immerse the pretreated nickel foam substrate. After sealing the stainless-steel autoclave, carry out a hydrothermal reaction at 100 °C for 15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash it alternately with deionized water and absolute ethanol three times, and finally dry it under vacuum conditions at 60 °C for 12 hours to obtain the Co / NF precursor;

[0062] (3) Dissolve 2 mmol of copper nitrate and 10 mmol of urea in 30 mL of deionized water. A certain proportion of copper nitrate and urea is dissolved in deionized water, and continuously stir for 1 hour to fully dissolve it. Then transfer it to a stainless-steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and immerse the Co / NF precursor; after sealing the stainless-steel high-pressure reaction kettle, react at a constant temperature of 100 °C for 15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash it alternately with deionized water and absolute ethanol three times, and finally dry it in a vacuum environment at 60 °C for 12 hours to obtain the Cu-Co / NF precursor;

[0063] (4) Place the Cu-Co / NF precursor in a porcelain boat, and program the temperature to rise to 300 °C at a rate of 2 °C / min under nitrogen protection, and keep it at this temperature for 3 hours for pyrolysis treatment to finally obtain the bifunctional Cu-Co / NF tandem catalyst.

[0064] Example 3:

[0065] (1) Immerse the nickel foam substrate in 2 M hydrochloric acid, absolute ethanol, and deionized water in sequence, and perform ultrasonic cleaning for 15 min respectively. Then dry it in a vacuum drying oven at 60 °C to obtain the pretreated nickel foam substrate;

[0066] (2) Dissolve 4 mmol of cobalt nitrate and 10 mmol of urea in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless-steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and immerse the pretreated nickel foam substrate; after sealing the stainless-steel high-pressure reaction kettle, carry out a hydrothermal reaction at 140 °C for 10 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash it alternately with deionized water and absolute ethanol three times, and finally dry it under vacuum conditions at 60 °C for 12 hours to obtain the Co / NF precursor;

[0067] (3) Dissolve 2 mmol of copper nitrate and 10 mmol of urea in 30 mL of deionized water. A certain proportion of copper nitrate and urea is dissolved in deionized water, and continuously stir for 1 hour to fully dissolve it. Then transfer it to a stainless-steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and immerse the Co / NF precursor; after sealing the stainless-steel high-pressure reaction kettle, react at a constant temperature of 140 °C for 10 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, then wash it alternately with deionized water and absolute ethanol three times, and finally dry it in a vacuum environment at 60 °C for 12 hours to obtain the Cu-Co / NF precursor;

[0068] (4) Place the dried Cu-Co / NF precursor in a porcelain boat, and program the temperature to 320 °C at a heating rate of 2 °C / min under nitrogen protection, and keep it at this temperature for 2 hours for pyrolysis treatment to finally obtain a bifunctional Cu-Co / NF tandem catalyst.

[0069] Comparative Example 1:

[0070] (1) Immerse the nickel foam substrate in 2 M hydrochloric acid, anhydrous ethanol, and deionized water in sequence, and perform ultrasonic cleaning for 15 min respectively, and then dry it in a 60 °C vacuum drying oven to obtain a pretreated nickel foam substrate;

[0071] (2) Dissolve 4 mmol of cobalt nitrate, 2 mmol of copper nitrate, and 10 mmol of urea in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless steel autoclave with a polytetrafluoroethylene liner, and immerse the pretreated nickel foam substrate; after sealing the stainless steel autoclave, react at a constant temperature of 120 °C for 12 hours. After the reaction is completed, wait for the reaction system to cool to room temperature naturally, then wash it alternately with deionized water and anhydrous ethanol three times, and finally dry it in a 60 °C vacuum environment for 12 hours to obtain a Cu-Co / NF precursor;

[0072] (3) Place the dried Cu-Co / NF precursor in a porcelain boat, and program the temperature to 350 °C at a heating rate of 2 °C / min under argon protection, and keep it at this temperature for 2 hours for pyrolysis treatment to finally obtain a Cu-Co / NF catalyst (one-step hydrothermal).

[0073] Comparative Example 2:

[0074] (1) Immerse the nickel foam substrate in 2 M hydrochloric acid, anhydrous ethanol, and deionized water in sequence, and perform ultrasonic cleaning for 15 min respectively, and then dry it in a 60 °C vacuum drying oven to obtain a pretreated nickel foam substrate;

[0075] (2) Dissolve 4 mmol of cobalt nitrate and 10 mmol of urea in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless steel autoclave with a polytetrafluoroethylene liner, and immerse the pretreated nickel foam substrate; after sealing the stainless steel autoclave, perform a 12-hour hydrothermal reaction at 120 °C. After the reaction is completed, wait for the reaction system to cool to room temperature naturally, then wash it alternately with deionized water and anhydrous ethanol three times, and finally dry it in a 60 °C vacuum condition for 12 hours to obtain a Co / NF precursor;

[0076] (3) Place the Co / NF precursor in a porcelain boat, and program the temperature to 340 °C at a heating rate of 2 °C / min under argon protection, and hold at this temperature for 2 hours for pyrolysis treatment to finally obtain the Co / NF catalyst.

[0077] Comparative Example 3:

[0078] (1) Immerse the nickel foam substrate successively in 2 M hydrochloric acid, absolute ethanol and deionized water, and perform ultrasonic cleaning for 15 min respectively, and then dry it in a vacuum drying oven at 60 °C to obtain the pretreated nickel foam substrate;

[0079] (2) Dissolve 2 mmol of copper nitrate and 10 mmol of urea in 30 mL of deionized water, continuously stir for 1 hour to fully dissolve it, then transfer it to a stainless steel autoclave with a polytetrafluoroethylene liner, and immerse the pretreated nickel foam substrate; after sealing the stainless steel autoclave, react at a constant temperature of 120 °C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Wash the obtained Cu / NF precursor alternately with deionized water and absolute ethanol three times, and finally dry it in a vacuum environment at 60 °C for 12 hours to obtain the Cu / NF precursor;

[0080] (3) Place the dried Cu / NF precursor in a porcelain boat, and program the temperature to 350 °C at a heating rate of 2 °C / min under argon protection, and hold at this temperature for 2 hours for pyrolysis treatment to finally obtain the Cu / NF catalyst.

[0081] The scanning electron microscope image of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 is as Figure 1 shown. It can be seen that the bifunctional Cu-Co / NF tandem catalyst has nano-needle clusters composed of cobalt source and nano-sheet stacks composed of copper source. These two unique morphological structures of the sites not only provide rich active sites for the nitrate reduction reaction, but also promote electron transport, and at the same time exhibit excellent stability and environmental friendliness. Example 1 uses the secondary hydrothermal method to effectively avoid the segregation phenomenon of copper ions and cobalt ions due to the differences in physical and chemical properties during the hydrothermal growth process, ensuring the uniformity of catalytic active sites, thereby significantly improving the overall performance of the catalyst.

[0082] In addition, the scanning electron microscope image of the Cu / NF catalyst prepared in Comparative Example 3 is as Figure 2 shown. It can be seen that it is not easy for copper sites to adsorb-nucleate-grow on the surface of nickel foam; thermodynamically, due to the standard reduction potential of copper (Cu 2+ / Cu: +0.34 V vs SHE) is much lower than that of nickel (Ni 2+ / Ni: -0.25 V), which causes the preferential self-dissolution of nickel foam during the hydrothermal reaction, and the mass transfer efficiency of the hydrothermal system is low kinetically, making it difficult for copper ions to break through the oxide layer (NiO / Ni(OH)2) formed by the dissolution of the nickel foam surface to achieve effective adsorption. However, the secondary hydrothermal method used in Example 1 achieved the controllable growth of copper sites through a hetero-structure assisted strategy. The cobalt transition layer deposited during the first hydrothermal process constructed a hetero-interface, which effectively reduced the formation energy barrier of copper sites, thus promoting the uniform epitaxial growth of copper sites at the hetero-interface.

[0083] The scanning electron microscope images of the Co-Cu / NF catalyst prepared in Comparative Example 1 are as Figure 3 shown. It can be seen that although the one-step hydrothermal method can form a uniform nano-villous structure, due to the lack of hetero-interface induction, the copper and cobalt elements exhibit the characteristics of a uniform solid solution, and a hetero-structure with site differences cannot be formed. At the same time, the element distribution images of the Co-Cu / NF catalyst prepared in Comparative Example 1 are as Figure 4 and Figure 5 shown. The result analysis shows that: although the copper element in the catalyst synthesized by the one-step hydrothermal method is evenly distributed on the nickel foam substrate, its surface density is significantly lower than that of the cobalt element; combined with the morphological characteristics of the nano-villous structure, this may be due to the solid solution segregation phenomenon of copper and cobalt elements during the hydrothermal process, resulting in copper sites being wrapped by high-density cobalt sites.

[0084] Electrochemical performance test of the cathodic nitrate reduction reaction:

[0085] All electrochemical tests of the nitrate reduction reaction were carried out at room temperature using a CHI 760E electrochemical workstation with a standard three-electrode system. The tests were carried out in an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane, with a graphite rod as the counter electrode, a HgO / Hg electrode as the reference electrode, and the prepared catalyst material as the working electrode. The electrocatalytic nitrate performance test was carried out in 0.1 M KOH electrolyte with and without 0.1 M KNO3. Before use, argon was introduced to remove the dissolved oxygen in the electrolyte. The linear sweep voltammetry (LSV) was used to systematically study the electrochemical activity of the catalyst, and the scanning rate was 10 mV s -1 .

[0087] The LSV test results of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 and the Co-Cu / NF catalyst prepared in Comparative Example 1 are as Figure 6As shown, the electrochemistry performance test data indicate that: compared with Comparative Example 1 (one-step hydrothermal method), the catalyst prepared by the secondary hydrothermal method used in Example 1 exhibits more excellent catalytic performance for nitrate reduction. This performance improvement can be attributed to the tandem nanostructure induced by the heterointerface, which optimizes the adsorption energy of reaction intermediates through the interfacial electron effect, while the three-dimensional porous structure provides abundant mass transfer channels.

[0088] The LSV test results of the Co / NF prepared in Comparative Example 2, the Cu / NF catalyst prepared in Comparative Example 3, and the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 are as Figure 7 shown. The results show that the increase in current density reflects the enhancement of the electrocatalytic activity of the catalyst for nitrate reduction; in an electrolyte of 0.1 M KOH, the current response is mainly generated by the hydrogen evolution reaction. With the addition of nitrate, the increase in current density indicates an improvement in the electrocatalytic activity of the catalyst for nitrate reduction. It is worth noting that compared with the non-tandem catalysts (Cu / NF or Co / NF catalysts), the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 exhibits a more positive onset potential and a higher current density, indicating that this catalyst has more excellent catalytic performance for nitrate reduction.

[0089] The electrochemistry performance test results of the nitrate reduction reaction for Example 1 and Comparative Examples 1-3 are shown in Table 1. It can be seen that compared with Comparative Examples 1-3, the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 exhibits higher performance, providing a potential and efficient catalyst for the nitrate reduction reaction.

[0090] Table 1 Electrochemistry performance test results of nitrate reduction reaction

[0091]

[0092] To deeply study the selectivity of the catalyst for electrochemical reduction of nitrate to ammonia, the nitrate reduction reaction performance of the bifunctional Cu-Co / NF tandem catalyst at different applied potentials was systematically analyzed by combining chronoamperometry and colorimetry. The Faraday efficiency of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 is as Figure 8 shown. It can be seen that the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 exhibits excellent Faraday efficiency within the tested potential range, always remaining above 90%; at a relatively low potential of -0.24 V vs. RHE, the Faraday efficiency of ammonia reaches a maximum of 96.77 ± 1.50%, especially at a potential of -0.74 V vs. RHE, the Faraday efficiency of ammonia reaches a maximum of 97.01 ± 0.026%. In addition, the ammonia yield of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 is as Figure 9As shown, it can be seen that with the increase of the applied voltage, the ammonia production rate increases significantly. When the applied voltage is -0.74 V vs. RHE, the ammonia production rate reaches 11.06 ± 0.0030 mg h -1 cm -2 , demonstrating its efficient ammonia production performance at higher potentials.

[0093] Scanning electron microscope images of the bifunctional Cu-Co / NF tandem catalyst (Example 1), Cu / NF catalyst (Comparative Example 3), and Co / NF catalyst (Comparative Example 2) are as Figure 1 、 Figure 2 and Figure 10 shown. By comparison, it can be clearly seen that the successful growth of copper-cobalt sites, combined with Figure 7 the current response, this tandem synergistic effect of copper-cobalt sites significantly improves the electrocatalytic activity of the catalyst, further verifying the excellent performance of the Co-Cu / NF tandem catalyst in the nitrate reduction reaction.

[0094] Anodic hydrazine oxidation reaction performance test:

[0095] The current NITRR system lacks a mechanism for constructing anodic-cathodic cooperative optimization. The traditional oxygen evolution reaction (OER) consumes up to 90% of the input energy but only produces oxygen with low economic value (about $25 per ton), resulting in the ammonia synthesis cost of NITRR (> $1000 per ton NH3) far exceeding that of the Haber-Bosch process ($560 per ton NH3). Developing an anodic oxidation reaction with high added value and thermodynamic advantages to replace the traditional oxygen evolution reaction has become a key strategy to reduce the reaction overpotential and energy consumption.

[0096] The electrocatalytic activity of the hydrazine oxidation reaction (HzOR) of the bifunctional Cu-Co / NF tandem catalyst electrode prepared in Example 1 was evaluated by the LSV system. When a trace amount of hydrazine hydrate (N2H4·H2O) was introduced into a 1 M KOH electrolyte, the corresponding current density increased significantly, which fully demonstrated that the bifunctional Cu-Co / NF tandem catalyst has excellent catalytic activity for HzOR.

[0097] The results of the influence of different hydrazine hydrate concentrations (0 - 0.5 M) on the catalytic performance of the bifunctional Cu-Co / NF tandem catalyst prepared in this Example 1 are as Figure 11 shown. The results show that in the concentration range of 0.1 - 0.3 M, the HzOR current density is positively correlated with the hydrazine hydrate concentration; when the concentration exceeds 0.3 M, the current response enters the plateau region, indicating that the surface reaction of the catalyst has reached the mass transfer control stage.

[0098] To illustrate the significant advantages of the hydrazine oxidation reaction at the electrocatalytic level, the LSV comparative test results of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 with / without 0.3 M hydrazine hydrate are shown as Figure 12 follows; the potential shift of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1 at a current density of 100 mA cm -2 is shown as Figure 13 follows. The results show that when the current density reaches 100 mA cm-2, the HzOR overpotential of the bifunctional Cu-Co / NF tandem catalyst electrode prepared in Example 1 is only 0.13 V vs. RHE, which is significantly negatively shifted by 1.592 V vs. RHE compared to the OER overpotential (1.7268 V vs. RHE) of the same electrode. This characteristic provides a key theoretical basis for the development of hydrazine oxidation-assisted energy-saving electrolysis technology. This huge potential difference indicates that by replacing the traditional OER reaction with the hydrazine oxidation path, the energy barrier limitation of the alkaline electrolysis system can be effectively broken through.

[0099] Although NF has a certain HzOR response, it is almost negligible compared with Cu-Co / NF, which indicates that the catalytic activity of the bifunctional Cu-Co / NF tandem catalyst electrocatalyst mainly comes from the copper-cobalt dual active sites. The LSV test results of the bifunctional Cu-Co / NF tandem catalyst prepared in Example 1, the Co / NF catalyst prepared in Comparative Example 2, and the Cu / NF catalyst prepared in Comparative Example 3 are shown as Figure 14 follows. The results show that compared with the Co / NF catalyst (Comparative Example 2) and the Cu / NF catalyst (Comparative Example 3), the bifunctional Cu-Co / NF tandem catalyst (Example 1) shows a more negative initial oxidation potential in terms of HzOR activity, proving that the tandem structure formed by secondary hydrothermal treatment is the reason for its high activity.

[0100] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Preparation method of bifunctional Cu-Co / NF tandem catalyst, characterized in that: Using cobalt nitrate and urea as reaction raw materials, after dissolution, the pretreated nickel foam substrate is added for the first hydrothermal reaction, and after washing and drying, the first precursor is obtained; Using copper nitrate and urea as reaction raw materials, after dissolution, the first precursor is added for the second hydrothermal reaction, and after washing and drying, the second precursor is obtained; The second precursor is calcined to obtain a bifunctional Cu-Co / NF tandem catalyst.

2. The preparation method according to claim 1, characterized in that: Specifically, it includes the following steps: Step S1: The nickel foam substrate is successively immersed in hydrochloric acid, absolute ethanol and deionized water, and ultrasonic cleaning is carried out respectively, and then vacuum dried to obtain the pretreated nickel foam substrate; Step S2: Dissolve cobalt nitrate and urea in deionized water, continuously stir until fully dissolved, and then immerse the pretreated nickel foam substrate; Carry out a hydrothermal reaction at 100-140 °C under sealed conditions for 10-15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, and then alternately wash with deionized water and absolute ethanol, and then vacuum dry to obtain the Co / NF precursor; Step S3: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; Carry out a hydrothermal reaction at 100-140 °C under sealed conditions for 10-15 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, and then alternately wash with deionized water and absolute ethanol, and then vacuum dry to obtain the Cu-Co / NF precursor; Step S4: Place the Cu-Co / NF precursor in a porcelain boat, and program the temperature to 300-350 °C at a heating rate of 2 °C / min under the protection of an inert gas, and keep the temperature for 2-3 hours for pyrolysis treatment to finally obtain the bifunctional Cu-Co / NF tandem catalyst.

3. The preparation method according to claim 2, characterized in that: Specifically, step S1 is: The nickel foam substrate is successively immersed in 2-3M hydrochloric acid, absolute ethanol and deionized water, and ultrasonic cleaning is carried out for 15 minutes respectively, and then dried in a 60 °C vacuum drying oven.

4. The preparation method according to claim 3, characterized in that: In step S2, cobalt nitrate:urea:deionized water = 4 mmol:10 mmol:30 mL.

5. The preparation method according to claim 4, characterized in that: Specifically, step S3 is: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; In a sealed stainless steel autoclave with a polytetrafluoroethylene lining, carry out a hydrothermal reaction at 120 °C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, alternately wash with deionized water and absolute ethanol three times, and finally dry under vacuum at 60 °C for 12 hours to obtain the Co / NF precursor.

6. The preparation method according to claim 5, characterized in that: In step S3, copper nitrate:urea:deionized water = 2 mmol:10 mmol:30 mL.

7. The preparation method according to claim 6, characterized in that: Step S3 specifically is as follows: Dissolve copper nitrate and urea in deionized water, continuously stir until completely dissolved, and then immerse the Co / NF precursor; in a sealed stainless-steel autoclave with a polytetrafluoroethylene liner, carry out a hydrothermal reaction at 120 °C for 12 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature, wash it three times alternately with deionized water and absolute ethanol, and finally dry it under vacuum at 60 °C for 12 hours to obtain the Cu-Co / NF precursor.

8. The preparation method according to claim 7, characterized in that: Step S6 specifically is as follows: Place the Cu-Co / NF precursor in a porcelain boat, program the temperature to rise at a rate of 2 °C / min under argon protection to 350 °C, and hold it at this temperature for 2 hours for pyrolysis treatment to finally obtain the Co-Cu / NF tandem catalyst.

9. Bifunctional Cu-Co / NF tandem catalyst, the bifunctional Cu-Co / NF tandem catalyst is prepared by the preparation method according to any one of claims 1 to 8, characterized in that: It has a hierarchical structure composed of nanoneedle clusters with a cobalt source composition and nanoplate stacks with a copper source composition, forming a tandem structure.

10. Application of the bifunctional Cu-Co / NF tandem catalyst in electrocatalytic nitrate reduction to ammonia and hydrazine oxidation.

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