Preparation method and application of plasma-modified multi-scale defect copper-nickel electrocatalyst

Abstract

The present invention discloses a method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst and its application. The conventional electrocatalyst carrier commercial foam is subjected to an electrodeposition treatment to obtain a foam copper-supported nickel oxide catalyst (NiO@Cu foam), which is then subjected to low-temperature plasma modification to form a foam copper-supported nickel oxide catalyst (NTP‑NiO@Cu) with a multi-scale defect structure on the surface as an electrocatalytic cathode electrode material. The method is simple and fast, the parameters are easy to control, the economy is good, and it has good electrocatalytic nitrate reduction to ammonia synthesis performance. In the acid-base decoupled electrocatalytic nitrate reduction to ammonia synthesis system, it has better electrochemical performance, ammonia synthesis rate, and selectivity than traditional catalysts or electrocatalytic systems.

Description

Technical Field

[0001] The invention relates to the fields of electrocatalysis and materials science, and in particular to a preparation method of a plasma-modified multi-scale defect copper-nickel electrocatalyst and its application. Background Art

[0002] Ammonia (NH3) is one of the most basic chemicals and raw materials for industry and agriculture today. However, the traditional Haber-Bosch process (HBP) is industrially produced through the reaction of nitrogen (N2) and hydrogen (H2) (N2+3H2→2NH3). However, the HBP under high temperature and high pressure (450-500℃, 20-30 MPa) conditions consumes 3-5% of the world's natural gas and emits more than 300 million tons of carbon dioxide (CO2) each year. At the same time, nitrate in groundwater is an increasing and widespread pollutant. The pollution caused by the excessive discharge of large amounts of nitrate-containing wastewater and waste has caused serious nitrate pollution in groundwater.

[0003] In order to solve the problem of nitrate wastewater treatment and efficient ammonia synthesis at the same time, the electrocatalytic nitrate reduction reaction (ENRR) is considered to be one of the most promising technologies for collecting NH3. It has mild reaction conditions at room temperature and pressure, and can utilize intermittent renewable electricity. However, the current technological development is greatly limited by the extremely low selectivity of ammonia synthesis and the NH3 yield. For example, the general Faradaic efficiency (FE) of traditional ENRR is mostly less than 15%, and it is severely competed by the hydrogen evolution reaction in the electrolyte. In addition, based on the proportional relationship of the adsorption energy of intermediates revealed by theoretical calculations, the theoretical calculations of common transition metal catalysts in ENRR further point out the dilemma of achieving high activity and high selectivity at the same time.

[0004] The acid-base decoupled electrocatalytic nitrate reduction system can efficiently synthesize ammonia. Its cathode's inhibition of hydrogen evolution is combined with the anode's promotion of electrochemical reactions. The bipolar membrane promotes the intermediate ion exchange. The different directions of the bipolar membrane determine the different properties of the electrocatalytic system, which can achieve the purpose of extending the service life or efficient production. However, the selection of electrode materials still has an important influence on the reaction rate. Electrocatalysts such as metal materials, metal oxide materials, and carbon-based materials are widely used in the study of nitrate electrocatalytic reduction to synthesize ammonia, but the rate and selectivity of nitrate reduction to synthesize ammonia are still limited. For traditional carbon material-based catalysts, their polytetrafluoroethylene (PTFE) materials limit the increase in current density, so commercial and industrial applications are strictly limited, and it is difficult to increase the current density to a higher order. At present, the research on electrode materials for electrocatalysis focuses on metal supports, especially copper-based supports, which have the advantages of good conductivity, low price, and good ammonia synthesis performance. Theoretical calculations have proved that the transition metal Cu is located at the top of the ENRR reaction volcano diagram and has the highest activity of the transition metal catalyst for synthesizing NH3. However, the catalytic performance of conventional copper foam materials is low. For this reason, recent studies have mostly used copper foam as a carrier, and have enhanced the possibility of rich atomic-scale regulation by heteroatom doping. The changes in the local metal environment and ligand effect have significantly increased the rate of electrochemical synthesis of ammonia by nitrate. Metal doping has been carried out on traditional copper-based catalysts. Studies have shown that Ni and Cu alloys enhance the d-band center of the catalyst in the process of nitrate reduction to synthesize ammonia, regulate the adsorption energy of intermediate products, and are conducive to the dissociation and adsorption of reaction molecules. However, doping, modulation and other methods are difficult to effectively adhere to traditional copper foam materials. The treated smooth copper foam surface is difficult to form a large number of doping sites as electrocatalytic active centers. Therefore, problems such as catalyst shedding and catalyst failure greatly shorten the life of the electrocatalytic system. Therefore, there is a lack of methods to effectively improve the adhesion of copper foam materials and significantly increase the defect sites on the surface of copper foam. This urgently requires the exploration of an energy-saving, fast, and controllable method for the preparation of electrodes for nitrate electrocatalytic reduction to synthesize ammonia. Summary of the invention

[0005] The purpose of the present invention is to propose a method for synthesizing a copper-nickel electrocatalyst modified by low-temperature plasma and its application in ammonia synthesis based on the limitations of the performance of the electrodes in the existing electrocatalytic ammonia synthesis reaction, so as to solve the problems of low ammonia yield and poor selectivity in the existing electrocatalytic ammonia synthesis process and the shortcomings of complex electrocatalyst synthesis, cumbersome steps, and poor economy. The modified design method simplifies the catalyst synthesis cost, improves the ammonia synthesis rate and stability, and has the characteristics of simple synthesis process, high electrocatalytic efficiency, and good economy.

[0006] The object of the present invention is achieved through the following technical scheme: A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst comprises the following steps:

[0007] 1) washing the copper foam material with a strong acid solution to remove surface oxide impurities, then rinsing with deionized water, and drying in a vacuum to obtain a copper foam carrier of the electrocatalyst for standby use;

[0008] 2) using the pure copper foam carrier prepared in step 1) to prepare a nickel oxide-supported copper foam catalyst precursor by a voltammetric cyclic electrodeposition method in a three-electrode system;

[0009] 3) placing the nickel oxide-loaded copper foam catalyst precursor obtained in step 2) in a low-temperature plasma generator, evacuating the environment in the low-temperature plasma generator and bombarding it with argon plasma to form a multi-defect structure on the surface of the nickel oxide-loaded copper foam catalyst precursor, thereby obtaining a multi-scale defect copper-nickel electrocatalyst.

[0010] Furthermore, the strong acid solution is 2-4 mol / L hydrochloric acid (HCl).

[0011] Furthermore, the copper foam material is commercial copper foam or self-prepared copper foam.

[0012] Furthermore, the three-electrode system consists of a working electrode, a counter electrode, and a reference electrode, wherein the working electrode is a foam copper carrier, the counter electrode is a graphite rod C, and the reference electrode is a silver / silver chloride Ag / AgCl electrode.

[0013] Furthermore, the electrolyte environment of the electrodeposition method is a deionized aqueous solution of nickel nitrate.

[0014] Furthermore, the electrodeposition method adopts cyclic voltammetry, and performs 4-10 cycles of cyclic voltammetry scanning between -1.1V and -0.1V (reference electrode is Ag / AgCl), with a scanning rate of 0.01-0.05mV / s.

[0015] Furthermore, the low-temperature plasma generator is dielectric barrier plasma DBD, radio frequency inductively coupled plasma ICP or sliding arc jet plasma, the gas source is Ar, the plasma working power is 100-300W, and the plasma generation time is 3min-5min.

[0016] Furthermore, the multi-defect structure is composed of multi-scale defects: the nickel oxide-loaded copper foam catalyst precursor is bombarded with plasma to create a micrometer-level defect surface on the surface, and defect active sites rich in oxygen vacancies are constructed on the surface of the nickel oxide.

[0017] The present invention also provides an application of a multi-scale defect copper-nickel electrocatalyst in an acid-base decoupled electrocatalytic nitrate reduction reaction to synthesize ammonia.

[0018] Furthermore, in the acid-base decoupled electrocatalytic nitrate reduction to synthesize ammonia reaction, the cathode uses an alkaline electrolyte, which is a 0.1M-10M KOH solution, and the anode uses an acidic electrolyte, which is a 0.05M-1M H2SO4 solution; the middle is separated by a bipolar membrane, which is composed of an anion membrane and a cation membrane, and is divided into forward bias and reverse bias according to different directions. In the forward bias mode, it is a production mode to achieve higher yield and current density; in the reverse voltage transformation mode, it is a long-term working mode to extend the service life.

[0019] The advantages of the present invention are:

[0020] (1) High catalytic performance. The multi-defective copper foam carrier formed under plasma bombardment is used to form a surface nickel oxide layer by electrodeposition, which is used for efficient nitrate reduction to synthesize ammonia electrocatalytic reaction, greatly improving the reaction rate and selectivity. The high current density is conducive to industrial application.

[0021] (2) Environmentally friendly. Catalyst synthesis does not involve high temperature and high pressure. The low-energy RF induction plasma and electrodeposition synthesis method at room temperature and pressure are green, environmentally friendly, energy-saving and efficient compared with traditional catalyst synthesis methods such as hydrothermal method, firing method and rotary evaporation method.

[0022] (3) Strong adjustability. Under this method, various reaction parameters, including plasma power, plasma bombardment time, electrodeposition type, electrodeposition time, cyclic voltammetry voltage window, electrodeposition electrolyte ratio, etc., can be flexibly adjusted. In the plasma-electrochemical coupled synthesis catalyst system, the operating conditions can be flexibly changed according to the target disposal amount, target product morphology and other conditions to obtain the target results;

[0023] (4) The method is simple. The two-step plasma-electrodeposition catalyst synthesis method is easy to master and takes a short time.

[0024] (5) Good economic efficiency. The synthesis conditions without high temperature and high pressure greatly reduce the energy consumption, and the application of non-precious metals has a positive effect on large-scale promotion;

[0025] The ammonia catalytic electrode prepared by the present invention can obtain higher electrocatalytic ammonia synthesis performance and stability without using traditional precious metals, which is of great significance for obtaining efficient ammonia catalytic electrodes at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a schematic diagram of a low-temperature plasma treatment precursor, in which: 13 is a reaction generator housing, 14 is a low-temperature plasma generator, 15 is a nickel oxide-loaded foam copper catalyst precursor, 16 is a generator gas inlet, and 17 is a generator gas outlet;

[0027] Figure 2 Schematic diagram of electrodeposition loading of nickel oxide, in which: 1 is an electrochemical workstation, 2 is a working electrode holder, 3 is a reference electrode holder, 4 is a counter electrode holder, 6 is a working electrode, 7 is a reference electrode, and 8 is a counter electrode;

[0028] Figure 3 It is a schematic diagram of synthesizing ammonia by electrocatalysis, in which: 1 is an electrochemical workstation, 2 is a working electrode clip, 3 is a reference electrode clip, 4 is a counter electrode clip, 5 is an electrolytic cell, 6 is a working electrode, 7 is a reference electrode, 8 is a counter electrode, 9 is an electrolytic cell gas inlet, 10 is an electrolytic cell gas outlet, 11 is a multi-scale defective copper-nickel electrocatalyst, and 12 is a bipolar membrane;

[0029] Figure 4 Electron microscope images of the surface structure of copper foam before and after plasma treatment;

[0030] Figure 5 Electron paramagnetic resonance spectra before and after plasma treatment;

[0031] Figure 6 is a comparison of the current density of different catalysts;

[0032] Figure 7 is a comparison of the current density of different catalysts;

[0033] Figure 8 It is a comparison of the electrochemically active specific surface areas of different catalysts. DETAILED DESCRIPTION

[0034] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0035] The present invention provides a method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst, comprising the following steps:

[0036] 1) The commercial copper foam or the self-prepared copper foam material is washed with 2-4 mol / L hydrochloric acid HCl solution, and ultrasonically washed for 10-15 min during the acid washing and water washing process to remove the surface oxide impurities, and then the surface acid is rinsed with deionized water, and maintained at 50° C. for 2 h-4 h in a vacuum environment to fully remove the surface moisture and prevent oxidation, so as to obtain the copper foam carrier of the electrocatalyst for use;

[0037] 2) If Figure 2As shown, the pure foam copper carrier prepared in step 1) is used to prepare a foam copper catalyst precursor supported by nickel oxide by a voltammetric cyclic electrodeposition method in a three-electrode system with an electrolyte environment of a deionized aqueous solution of nickel nitrate, and 4-10 cycles of cyclic voltammetric scanning are performed between -1.1V and -0.1V (the reference electrode is Ag / AgCl), and the scanning rate is 0.01-0.05mV / s; the three-electrode system is composed of a working electrode 6, a counter electrode 8, and a reference electrode 7, the counter electrode 8 is a graphite rod C, and the reference electrode 7 is a silver / silver chloride Ag / AgCl electrode. The three-electrode system is connected to an electrochemical workstation 1, and the electrochemical workstation 1 includes a working electrode clamp 2, a reference electrode clamp 3, and a counter electrode clamp 4, which are respectively connected to the working electrode 6, the reference electrode 7, and the counter electrode 8.

[0038] 3) If Figure 1 As shown, the nickel oxide-loaded copper foam catalyst precursor 15 obtained in step 2) is placed in the middle of the low-temperature plasma generator 14 to ensure that the surface is fully and evenly treated. The outside of the low-temperature plasma generator 14 is provided with a reaction generator cover 13, and the vacuum condition is 7×10 -2 Pa or less; the low-temperature plasma generator 14 is a dielectric barrier plasma DBD, a radio frequency inductively coupled plasma ICP or a sliding arc jet plasma, the gas source is Ar, the plasma working power is 100-300W, and the plasma generation time is 3min-5min; the generator gas outlet 17 of the low-temperature plasma generator 14 is connected to a vacuum pump, and after the environment is evacuated, argon plasma bombardment is introduced through the generator gas inlet 16 to form a multi-defect structure on the surface of the nickel oxide-loaded foam copper catalyst precursor, and a multi-scale defect copper-nickel electrocatalyst is prepared. The multi-defect structure is composed of multi-scale defects: the nickel oxide-loaded foam copper catalyst precursor is bombarded by plasma to create a micron-level defect surface on the surface, and defect active sites rich in oxygen vacancies are constructed on the surface of the nickel oxide.

[0039] The present invention also provides an application of a multi-scale defective copper-nickel electrocatalyst in an acid-base decoupled electrocatalytic nitrate reduction reaction to synthesize ammonia. Figure 3As shown, in the acid-base decoupled electrocatalytic nitrate reduction reaction for synthesizing ammonia, the electrolytic cell 5 has an electrolytic cell gas inlet 9 and an electrolytic cell gas outlet 10. The cathode of the electrolytic cell 5 uses an alkaline electrolyte, which is a 0.1M-10M KOH solution. The multi-scale defective copper-nickel electrocatalyst 11 is clamped on the working electrode. The anode of the electrolytic cell 5 uses an acidic electrolyte, which is a 0.05M-1M H2SO4 solution; the bipolar membrane 12 is separated in the middle, and the bipolar membrane 12 is composed of an anion membrane and a cation membrane. It is divided into forward bias and reverse bias according to different directions. In the forward bias mode, it is a production mode to achieve higher yield and current density; in the reverse voltage conversion mode, it is a long-term working mode to extend the service life. The rate of product generation is determined by the ammonia concentration in the electrolyte, and the selectivity is calculated by the Faraday efficiency.

[0040] Embodiment 1:

[0041] Step 1: Cut a piece of copper foam with a thickness of 1mm and a size of 1cm×3cm. Soak the copper foam material with 4mol / L hydrochloric acid and thoroughly rinse it with ultrasound for 10min to remove oxide impurities and contaminants on the surface of the copper foam. Then rinse the surface acid with deionized water and ultrasonicate for 10min to fully remove the residual hydrochloric acid. Dry it in a vacuum oven at 50℃ for 4h to remove surface moisture;

[0042] Step 2: Place the pure copper foam material substrate obtained in step 1 into the radio frequency inductively coupled plasma generator, keep the copper foam in the middle area of ​​the plasma reactor, and evacuate the internal pressure to less than 7×10 -2 Pa, then open the Ar gas source for sufficient purge, evacuate again and purge again, repeat 2-3 times to ensure an oxygen-free environment to prevent the formation of oxidized structures;

[0043] Step 3: Prepare nickel oxide-supported multi-defective copper foam catalyst by electrodeposition in a three-electrode system, such as Figure 2 As shown. Use copper foam as the working electrode, and clamp the copper foam material with a platinum electrode clamp; graphite rod as the counter electrode; silver / silver chloride as the reference electrode. The electrolyte is 50ml of 0.5mol / L nickel nitrate aqueous solution (deionized water). The electrodeposition adopts cyclic voltammetry scanning method, and the scanning voltage range is selected between -1.1V vs AgCl and -0.1V vs AgCl working voltage. The number of scanning circles is 4 scanning circles, and the scanning rate is set to 0.01mV / s; after the electrodeposition is completed, the copper foam loaded with nickel oxide is taken out, and the residual nickel nitrate solution on the surface is rinsed with deionized water. It is left to dry naturally in the air and can be used as a precursor;

[0044] Step 4: Under the conditions of step 3, the surface of the copper foam is bombarded with low-temperature plasma from an Ar gas source at a power of 300 W and a treatment time of 5 min. Figure 1 After the process is completed, the copper foam material is promptly taken out to form a copper foam with a multi-defect structure loaded with nickel oxide;

[0045] Step 5: Use the catalyst in an acid-base decoupling system to efficiently electrocatalyze nitrate reduction to synthesize ammonia, such as Figure 3 As shown, the cathode liquid uses 1M KOH, the anode liquid uses 0.5M H2SO4, and the orientation of the middle bipolar membrane is cathode-cation membrane-anion membrane-anode.

[0046] Embodiment 2:

[0047] Step 1: Cut a piece of copper foam with a thickness of 1mm and a size of 1cm×3cm. Soak the copper foam material with 4mol / L hydrochloric acid and thoroughly rinse it with ultrasound for 10min to remove oxide impurities and contaminants on the surface of the copper foam. Then rinse the surface acid with deionized water and ultrasonicate for 10min to fully remove the residual hydrochloric acid. Dry it in a vacuum oven at 50℃ for 4h to remove surface moisture;

[0048] Step 2: Prepare nickel oxide-supported multi-defective copper foam catalyst by electrodeposition in a three-electrode system, such as Figure 2 As shown. Use copper foam as the working electrode, and clamp the copper foam material with a platinum electrode clamp; graphite rod as the counter electrode; silver / silver chloride as the reference electrode. The electrolyte is 50ml of 0.5mol / L nickel nitrate aqueous solution (deionized water). The electrodeposition adopts cyclic voltammetry scanning method, and the scanning voltage range is selected between -1.1V vs AgCl and -0.1V vs AgCl working voltage. The number of scanning circles is 4 circles, and the scanning rate is set to 0.01mV / s; after the electrodeposition is completed, the copper foam loaded with nickel oxide is taken out, and the residual nickel nitrate solution on the surface is rinsed with deionized water. It is left in the air to dry naturally and can be used as a working electrode;

[0049] Step 3: The catalyst is used in an acid-base decoupling system for efficient electrocatalytic reduction of nitrate to synthesize ammonia. The cathode liquid uses 1 M KOH, the anode liquid uses 0.5 M H2SO4, and the orientation of the intermediate bipolar membrane is cathode-cation membrane-anion membrane-anode.

[0050] Embodiment 3:

[0051] Step 1: Cut a piece of copper foam with a thickness of 1mm and a size of 1cm×3cm. Soak the copper foam material with 4mol / L hydrochloric acid and thoroughly rinse it with ultrasound for 10min to remove oxide impurities and contaminants on the surface of the copper foam. Then rinse the surface acid with deionized water and ultrasonicate for 10min to fully remove the residual hydrochloric acid. Dry it in a vacuum oven at 50℃ for 4h to remove surface moisture;

[0052] Step 2: The catalyst is used in an acid-base decoupling system for efficient electrocatalytic reduction of nitrate to synthesize ammonia. The cathode liquid uses 1 M KOH, the anode liquid uses 0.5 M H2SO4, and the orientation of the intermediate bipolar membrane is cathode-cation membrane-anion membrane-anode.

[0053] Experimental example

[0054] 1. Microstructure testing

[0055] like Figure 4 As shown in the figure, the left side is the foam copper without plasma treatment, and the right side is the foam copper material after plasma treatment; under an electron microscope, it can be seen that the foam copper after plasma treatment has significant defects.

[0056] like Figure 5 As shown, in the electron paramagnetic resonance spectrum, it can be seen that abundant oxygen vacancies appear at g=2.001 after plasma treatment.

[0057] 2. Electrochemical performance test

[0058] The electrocatalyst prepared by the present invention is used in the reaction of electrocatalytic nitrate reduction, wherein the reaction system is in an H-type electrolytic cell, 50 ml of 1M KOH solution is added to the anode, 50 ml of 1M KOH / 0.1M KNO3 mixed solution is added to the cathode, wherein KNO3 is used as a nitrate source, and the two electrodes are separated by a Nafion proton exchange membrane. The working electrode is clamped with a platinum sheet electrode clamp to clamp the prepared catalyst, and the immersion area in the electrolyte is controlled to be 1 cm×cm, the reference electrode is a saturated silver / silver chloride electrode, and the counter electrode is a 1.5 cm×1 cm platinum sheet electrode; the electrochemical test is performed using a Chenhua Chi760 workstation, the working electrode clamp is connected to the working electrode of the reaction cell, the reference electrode clamp is connected to the reference electrode, and the counter electrode clamp is connected to the counter electrode; before the electrochemical reaction, Ar is continuously introduced into the cathode at a rate of 30 sccm and maintained for more than 20 minutes, and when the electrochemical reaction is performed, Ar is also continuously introduced to remove the influence of air on the reaction.

[0059] (1) Current density test

[0060] Figure 6The current density curve of the linear voltammetry (LSV) scan of the electrocatalysts prepared in Examples 1-3 of the present invention as working electrodes. The scanning interval is 0.2 to -0.6 V vs RHE. The experimental results show that the nickel oxide-loaded copper foam has a significant increase in current density compared with the pure copper foam, and the nickel oxide-loaded copper foam after plasma treatment has a significant increase in current density compared with the ordinary nickel oxide-loaded copper foam, which proves that low-temperature plasma treatment improves the electrochemical activity of the catalyst;

[0061] (2) Yield test

[0062] The electrocatalysts prepared in Examples 1-3 of the present invention were used as working electrodes to measure the yield using a constant potential method. The working potential was set to -1 V, -1.2 V, -1.4 V, -1.6 V, -1.8 V, and -2.0 V. The power was continuously turned on for 1 h. After the reaction was completed, the electrolyte was collected to measure the ammonia concentration and calculate the Faraday efficiency. The formula for the electrocatalytic yield was:

[0063] (ammonia concentration × electrolyte volume) / (electrocatalytic reaction time × catalyst area)

[0064] The formula for Faraday efficiency is:

[0065] The test results of (actual number of moles of ammonia generated × number of reaction electrons × Faraday constant) / (electrocatalytic reaction time × electrocatalytic reaction current) are shown in the following table:

[0066]

[0067]

[0068]

[0069] The analysis of yield and Faraday efficiency shows that the adhesion of nickel oxide can increase the ammonia synthesis performance. The Faraday efficiency is increased from 7-35% to 34-59%, and the maximum yield reaches 18.91 mg / h cm 2 The performance of the copper-nickel catalyst treated with plasma was greatly improved compared with that without plasma treatment. The Faradaic efficiency was increased from 34-59% to more than 98%, and the highest yield reached 50mg / h cm 2 This indicates that the preparation method can be used to obtain a highly efficient and stable electrocatalytic nitrate reduction catalyst for ammonia synthesis.

[0070] (3) Tafel slope test

[0071] Figure 7The Tafel slope (Tafel) scanning diagram of the electrocatalysts prepared in Examples 1-3 of the present invention as working electrodes. The smaller Tafel slope reflects a greater current density growth trend. The experimental results show that the nickel oxide-loaded copper foam after plasma treatment has the lowest Tafel slope (115.06mV dec-1), which reflects the improvement of the electrochemical activity of the catalyst by low-temperature plasma treatment;

[0072] (4) Electrochemically active specific surface area test

[0073] Figure 8 The electrochemically active specific surface area of ​​the electrocatalysts prepared in Examples 1-3 of the present invention as working electrodes was measured. The double electrical layer method was used for testing. The cyclic voltammetry curves of the three catalysts in the non-Faraday region were tested and calculated. The results showed that the catalyst loaded with nickel oxide had a higher electrochemically active specific surface area than the foamed copper, and the electrochemical specific surface area of ​​the foamed copper catalyst loaded with nickel oxide was further improved after plasma treatment, which reflects the improvement of catalyst performance and electrochemical activity by plasma treatment;

[0074] Experimental results

[0075] Through the working condition exploration and performance comparison of the above examples, the nickel oxide-loaded copper foam catalyst treated with plasma has better electrochemical activity, and under the experimental conditions of electrocatalytic nitrate reduction to synthesize ammonia when the working voltage is -1.8V vs AgCl working voltage, it achieves the best effect explored so far, maintaining a Faradaic efficiency of more than 98%. + The yield was 47.85 mg / h cm 2 Compared with the current synthetic ammonia effect, it has achieved a significant improvement, and in the future it is expected to achieve higher synthesis effects through further improvements in the catalyst structure.

[0076] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst, characterized in that: The following steps are involved: 1) The copper foam material is washed with a strong acid solution to remove surface oxide impurities, then rinsed with deionized water, and dried in a vacuum to obtain a copper foam carrier for electrocatalyst for use; 2) using the pure copper foam carrier prepared in step 1) to prepare a nickel oxide-supported copper foam catalyst precursor by a voltammetric cyclic electrodeposition method in a three-electrode system; 3) placing the nickel oxide-loaded copper foam catalyst precursor obtained in step 2) in a low-temperature plasma generator, wherein the low-temperature plasma generator is a dielectric barrier plasma DBD, a radio frequency inductively coupled plasma ICP or a sliding arc jet plasma, the gas source is Ar, the plasma working power is 100-300W, and the plasma generation time is 3min-5min; after evacuating the environment in the low-temperature plasma generator, argon plasma bombardment is performed to form a multi-defect structure on the surface of the nickel oxide-loaded copper foam catalyst precursor, thereby obtaining a multi-scale defect copper-nickel electrocatalyst.

2. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst according to claim 1, characterized in that: The strong acid solution is 2-4 mol / L hydrochloric acid HCl.

3. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst according to claim 1, characterized in that: The foam copper material is commercial foam copper or self-prepared foam copper.

4. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst according to claim 1, characterized in that: The three-electrode system consists of a working electrode, a counter electrode and a reference electrode, wherein the working electrode is a foam copper carrier, the counter electrode is a graphite rod C, and the reference electrode is a silver / silver chloride Ag / AgCl electrode.

5. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst according to claim 1, characterized in that: The electrolyte environment of the electrodeposition method is a deionized aqueous solution of nickel nitrate.

6. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst according to claim 1, characterized in that: The electrodeposition method adopts cyclic voltammetry, the reference electrode is Ag / AgCl, 4-10 cycles of cyclic voltammetry scanning are performed between -1.1V and -0.1V, and the scanning rate is 0.01-0.05mV / s.

7. A method for preparing a plasma-modified multi-scale defect copper-nickel electrocatalyst according to claim 1, characterized in that: The multi-defect structure is composed of multi-scale defects: the nickel oxide-loaded copper foam catalyst precursor is bombarded with plasma to create a micron-level defect surface, and defect active sites rich in oxygen vacancies are constructed on the surface of the nickel oxide.

8. Use of a multi-scale defect copper-nickel electrocatalyst prepared by the method according to any one of claims 1 to 7 in an acid-base decoupled electrocatalytic nitrate reduction reaction to synthesize ammonia.

9. The use according to claim 8, characterized in that: In the acid-base decoupled electrocatalytic nitrate reduction reaction to synthesize ammonia, the cathode uses an alkaline electrolyte, which is a 0.1M-10M KOH solution, and the anode uses an acidic electrolyte, which is a 0.05M-1M H2SO4 solution; the middle is separated by a bipolar membrane, which is composed of an anion membrane and a cation membrane. The bipolar membrane is divided into forward bias and reverse bias according to different directions. The forward bias mode is the production mode to achieve higher yield and current density; The reverse transformer mode is a long-term working mode, which prolongs the service life.

Images