Preparation method of a bimetallic site single-atom catalyst and its application in electrocatalytic ammonia oxidation total denitrification reaction

Abstract

The present invention discloses a preparation method of a bimetallic-site single-atom catalyst and its application in the electrocatalytic ammonia oxidation total denitrification reaction. The preparation method of the catalyst is as follows: pyrolyze citrate under an inert atmosphere, wash it successively with an acid solution and water, and then dry it to obtain an ordered porous carbon support; mix and grind the ordered porous carbon support, metal salt M1, metal salt M2 and glucose to obtain a mixed material; then mix the mixed material with a nitrogen source and grind it again to obtain a precursor; place the obtained precursor under an inert atmosphere for pyrolysis, and grind it after cooling to obtain the bimetallic-site single-atom catalyst. The electrode prepared by the bimetallic-site single-atom catalyst disclosed in the present invention has extremely high electrocatalytic ammonia oxidation performance and product selectivity, and can achieve the total denitrification effect. In addition, the catalyst material is simple and reliable to prepare, has high cost-effectiveness, and is easy to realize large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic ammonia oxidation, and in particular to a preparation method of a bimetallic site single-atom catalyst and its application in the electrocatalytic ammonia oxidation total denitrification reaction. Background Art

[0002] As one of the important components of the global biogeochemical cycle, the nitrogen cycle balance plays an important role in maintaining a good ecological environment. The discharge of a large amount of nitrogen-containing substances such as ammonia in industrial wastewater, domestic sewage and agricultural non-point sources causes the imbalance of the nitrogen cycle, which is one of the main reasons for water eutrophication and water body black odor, bringing an unignorable negative impact on the balance of the ecosystem and human health. Traditional methods for treating ammonia nitrogen in wastewater mainly include biological nitrification / denitrification technology, breakpoint chlorination method, air stripping method, etc. However, these methods generally take a long time, are not easy to operate, and have problems such as harsh required conditions and easy secondary pollution. The direct electrocatalytic ammonia oxidation technology has become a method with broad application prospects due to its advantages such as simple operation, high cost-effectiveness, and environmental friendliness. In addition, ammonia can also be directly used as an ideal carbon-free fuel for direct ammonia fuel cells, and its high calorific value and low price make it have natural advantages. Therefore, the electrocatalytic ammonia oxidation technology can not only effectively degrade ammonia nitrogen pollution, but also "turn waste into treasure", either produce clean hydrogen energy, or be directly used in fuel cells to supply energy. Based on the above advantages, the field of electrocatalytic ammonia oxidation has received extensive attention in recent years.

[0003] So far, many nano-catalysts constructed from noble metals (such as platinum and palladium), transition metals (such as nickel, copper, iron, cobalt, manganese and zinc), etc. have been reported for electrochemical ammonia oxidation, aiming to promote the reaction at a lower overpotential. For example, the "Preparation method of a heteroatom-doped nickel-copper bimetallic high-efficiency ammonia catalytic electrode" disclosed in Chinese patent document CN202111073952.2. This invention prepared a heteroatom-doped nickel-copper bimetallic ammonia catalytic electrode with highly dispersed nano-spherical particles on the electrode substrate through a hydrothermal-low temperature annealing-electrochemical reconstruction strategy, which can greatly reduce the electrode preparation cost and optimize the ammonia catalytic oxidation performance of the ammonia catalytic electrode.

[0004] However, generally, there are two mechanisms for the ammonia oxidation reaction (AOR). One is the O-S mechanism: *NH 3 gradually dehydrogenates to form N species, and then dimerizes to N 2 , during which *N is extremely easy to peroxidize to form toxic by-products such as NO 2 - and NO 3 - ; the other is the G-M mechanism: *NH 3 dehydrogenates to *NH 2 *NHx and *NH y Dimerization to form *N 2 H x+y , and then dehydrogenated to form N 2 Existing nanoscale metal catalysts are composed of nanoparticles and sub-nano clusters of various sizes, with multiple active sites such as different crystal faces and vertices. It is difficult to ensure that the sites of diverse expression are *N 2 H x+y The formation of this hydrazine analogue, and thus the AOR reaction generally proceeds according to the OS mechanism, induces too many side reactions. Therefore, when the existing nanoscale metal catalysts are used for electrocatalytic ammonia oxidation reaction, the nitrogen selectivity and Faraday efficiency are low, and NO 2 − 、NO 3 − A large number of toxic by-products are generated, and the effect of complete denitrification cannot be achieved. Summary of the invention

[0005] The present invention aims to overcome the problems of low nitrogen selectivity and Faraday efficiency when nano-scale metal catalysts are used in the electrocatalytic ammonia oxidation reaction in the prior art, and the low NO 2 − 、NO 3 − The invention provides a method for preparing a bimetallic site single atom catalyst and its application in the electrocatalytic ammonia oxidation full denitrification reaction, and prepares a bimetallic site single atom catalyst with good AOR activity, which can efficiently and selectively catalyze the oxidation of ammonia into the ideal final product N 2 , effectively inhibiting NO 2 − , NO 3 − Toxic by-products such as nitrogen oxides are eliminated, thus achieving the effect of complete denitrification.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a bimetallic site single atom catalyst comprises the following steps:

[0008] (1) pyrolyzing citrate under an inert atmosphere, washing with an acid solution and water in sequence, and drying to obtain an ordered porous carbon support;

[0009] (2) mixing and grinding the ordered porous carbon support, the metal salt M1, the metal salt M2 and glucose to obtain a mixed material; then mixing the mixed material with a nitrogen source and grinding again to obtain a precursor;

[0010] (3) Pyrolyze the precursor obtained in step (2) under an inert atmosphere, and grind it after cooling to obtain the bimetallic site single-atom catalyst.

[0011] In the present invention, the citrate is first pyrolyzed to obtain an ordered porous carbon support (PC). The citrate is an organic acid salt formed by the complexation of citrate ions and metal cations. When carbonized under an inert atmosphere, metal ions can act as unique activators to etch and create pores in the carbon material, forming an amorphous three-dimensional porous carbon structure, which provides abundant sites for the subsequent anchoring of atoms. Then, the obtained PC is mixed and ground with two metal salts, glucose, and a nitrogen source, and pyrolyzed at a high temperature. Glucose helps the chelation between the metal salts, nitrogen source, and PC during grinding, so that metal atoms and nitrogen atoms can coordinate to form a special bimetallic atomic site structure under high-temperature pyrolysis.

[0012] The bimetallic site single-atom catalyst prepared by the present invention has the distribution characteristics of highly dispersed atoms. This uniform site allows the catalyst to achieve extremely high nitrogen selectivity, facilitating the ammonia oxidation reaction to proceed according to the G-M mechanism: the electronic interaction between the two metals optimizes the internal electronic structure well to improve its adsorption capacity for intermediates, which is conducive to each of the adjacent bimetallic sites adsorbing an ammonia molecule on the surface, and then deprotonating to generate *N with a stable N-N bond. 2 H x+y and further dehydrogenate to form N 2 effectively inhibits the generation of toxic by-products such as NO 2 − and NO 3 − etc., achieving the effect of complete denitrification. Using the catalyst prepared by the present invention, high electrocatalytic ammonia oxidation activity and nitrogen selectivity can be obtained on the basis of ensuring cost-effectiveness, which provides a strong guarantee for the development of electrocatalytic treatment technology for ammonia-nitrogen wastewater.

[0013] Preferably, the citrate described in step (1) is selected from one or more of trisodium citrate, potassium citrate, potassium dihydrogen citrate, and sodium dihydrogen citrate; the acid solution is selected from one of sulfuric acid, hydrochloric acid, and nitric acid; the concentration of the acid solution is 1.0 - 8.0 mol / L; washing with the acid solution can remove potassium / sodium cations in the porous carbon skeleton, causing certain defects in the carbon skeleton. This appropriate undercoordinated structure helps the subsequent embedding and fixation of active metal atoms.

[0014] Preferably, the pyrolysis temperature in step (1) is 700 - 900 °C, and the pyrolysis time is 0.5 - 3 h.

[0015] Preferably, the metal salt M1 in step (2) is selected from one of nickel sulfate, nickel chloride, nickel bromide, nickel nitrate, nickel acetate and their hydrates; the metal salt M2 is selected from one of sulfates, chlorides, nitrates, acetates of copper, iron, cobalt, manganese and zinc and their hydrates; the nitrogen source is selected from one or more of dicyandiamide, melamine, urea and thiourea.

[0016] Preferably, in the mixed material in step (2), the molar ratio of metal ions in metal salt M1 and metal salt M2 is 1:0.5 - 5; the ratio of the addition amounts of the ordered porous carbon support, metal ions in metal salt M1 and glucose is 0.06 g:0.3 - 0.5 mmol:1.2 - 1.5 g; the mass ratio of the mixed material to the nitrogen source in the precursor is 1:5 - 10.

[0017] Preferably, the pyrolysis temperature in step (3) is 600 - 1000 °C, and the pyrolysis time is 1 - 3 h.

[0018] The present invention also provides an electrocatalytic ammonia oxidation electrode, including a conductive substrate and a bimetallic site single-atom catalyst prepared by the above method and loaded on the conductive substrate.

[0019] Preferably, the loading amount of the bimetallic site single-atom catalyst on the conductive substrate is 1 - 2 mg / cm 2 .

[0020] Preferably, the conductive substrate is selected from one of carbon paper, carbon fiber paper, carbon cloth, carbon fiber cloth, nickel foam, copper foam, boron-doped diamond film, conductive glass and titanium plate.

[0021] The present invention also provides an application of the above electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction. The reaction method is: placing the electrocatalytic ammonia oxidation electrode and the counter electrode in a solution containing ammonia nitrogen, connecting the electrocatalytic ammonia oxidation electrode and the counter electrode, and performing an electrochemical reaction.

[0022] Preferably, the counter electrode is a platinum electrode.

[0023] Therefore, the present invention has the following beneficial effects:

[0024] (1) The prepared bimetallic site single-atom catalyst has an atomic utilization rate of nearly 100%, and the active sites are fully exposed; compared with electrocatalysts at the nanoscale, it has extremely high product selectivity in the electrocatalytic ammonia oxidation reaction, and can efficiently and selectively catalyze the ammonia oxidation into the ideal final product N 2 , effectively inhibiting NO 2 − , NO 3 −The generation of toxic by-products such as... is achieved to reach the effect of complete denitrification;

[0025] (2)The preparation of the bimetallic site single-atom catalyst material in the present invention is simple, easy to operate and environmentally friendly, and has broad application prospects;

[0026] (3)On the basis of ensuring cost-effectiveness, the catalyst prepared in the present invention can obtain high electrocatalytic ammonia oxidation activity and nitrogen selectivity, which provides a strong guarantee for the development of electrocatalytic treatment technology for ammonia-nitrogen wastewater. Brief Description of the Drawings

[0027] Figure 1 is the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the NiCu 3 -N-C bimetallic site single-atom catalyst prepared in Example 1 of the present invention.

[0028] Figure 2 is the linear sweep voltammetry (LSV) test spectrum of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of the present invention.

[0029] Figure 3 is the NiCu prepared in Example 1 of the present invention 3 -N-C bimetallic site single-atom catalyst for the ammonia-nitrogen degradation curve and nitrogen selectivity comparison effect diagram of simulated wastewater with different initial ammonia-nitrogen concentrations.

[0030] Figure 4 is the NiCu prepared in Example 1 of the present invention 3 -N-C bimetallic site single-atom catalyst and the denitrification utility, Faraday efficiency and energy consumption diagram of the nanoscale catalysts in Comparative Examples 3 and 4.

[0031] Figure 5 is the linear sweep voltammetry (LSV) test spectrum of the NiCu 3 -N-C bimetallic site single-atom catalyst prepared in Example 1 and Comparative Example 5 of the present invention.

[0032] Figure 6 is the linear sweep voltammetry (LSV) test spectrum of the NiCu 3 -N-C bimetallic site single-atom catalyst prepared in Example 1 and Comparative Example 6 of the present invention.

[0033] Figure 7 is the linear sweep voltammetry (LSV) test spectrum of the NiCu 3 -N-C bimetallic site single-atom catalyst prepared in Example 1 and Comparative Example 7 of the present invention. Detailed Embodiments

[0034] The present invention will be further described in detail through specific embodiments as follows: The following embodiments are implemented on the premise of the technical solution of the present invention, and the specific implementation methods and processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0035] Example 1:

[0036] A preparation method of a nickel-copper bimetallic site single-atom catalyst, the steps are as follows:

[0037] (1) Weigh 10 g of trisodium citrate, place it in a muffle furnace under a nitrogen (N 2 ) atmosphere and pyrolyze it at 800 °C for 1 hour to obtain a black solid product; wash it with a 5 mol / L dilute sulfuric acid solution to remove inorganic impurities; then wash it with water and dry it to obtain an ordered porous carbon support (PC);

[0038] (2) Mix 0.06 g of PC, 0.085 g of nickel sulfate, 0.225 g of copper sulfate and 1.328 g of glucose, grind and weigh them, and mix them with melamine in a mass ratio of 1:5, and grind again to obtain a precursor;

[0039] (3) Place the precursor in a muffle furnace under a N 2 atmosphere and calcine it at 800 °C for 2 hours. After cooling, take out the obtained product and grind it to obtain a nickel-copper bimetallic site single-atom catalyst (NiCu 3 -N-C DSAC).

[0040] A method for preparing an electrocatalytic ammonia oxidation electrode is as follows: Weigh 0.01 g of NiCu 3 -N-C DSAC sample, add it to a dispersion composed of 1000 μL of absolute ethanol, 1000 μL of water, and 40 μL of 5 wt.% Nafion membrane solution, ultrasonically mix it evenly and then coat it on a carbon paper (CP) substrate (coating amount 1.5 mg / cm 2 ); after drying, obtain the electrocatalytic ammonia oxidation electrode, denoted as NiCu 3 -N-C / CP.

[0041] The high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of NiCu 3 -N-C DSAC shows ( Figure 1 ) that the support is a nitrogen-rich doped ordered porous carbon skeleton, and there are a large number of bright spots related to Ni and Cu atoms on its surface, confirming the characteristics of highly dispersed atoms. This is the bonding effect of metal-nitrogen coordination that creates the isolated state of metal atoms. In addition, the adjacent bright atomic bright spots in the surrounding circle also confirm the existence of bimetallic atomic sites.

[0042] Example 2:

[0043] A preparation method of a nickel-iron bimetallic site single-atom catalyst, the steps are as follows:

[0044] (1) Weigh 10 g of trisodium citrate and place it in a muffle furnace under a nitrogen (N 2 ) atmosphere and pyrolyze it at a constant temperature of 800 °C for 1 hour to obtain a black solid product; wash it with a 3 mol / L dilute hydrochloric acid solution to remove inorganic impurities; then wash it with water and dry it to obtain an ordered porous carbon support (PC);

[0045] (2) Mix 0.06 g of PC, 0.085 g of nickel sulfate, 0.065 g of iron sulfate and 1.328 g of glucose, grind and weigh, and mix it with melamine in a mass ratio of 1:8, and grind it again to obtain a precursor;

[0046] (3) Place the precursor in a muffle furnace under a N 2 atmosphere and calcine it at a constant temperature of 900 °C for 2 hours. After cooling, take out the obtained product and grind it to obtain a nickel-iron bimetallic site single-atom catalyst (NiFe-N-C DSAC).

[0047] A preparation method of an electrocatalytic ammonia oxidation electrode is as follows: Weigh 0.01 g of the NiFe-N-C DSAC sample and add it to a dispersion composed of 1200 μL of absolute ethanol, 800 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat it on a carbon cloth (CF) substrate (coating amount 2.0 mg / cm 2 ); after drying, obtain the electrocatalytic ammonia oxidation electrode, denoted as NiFe-N-C / CF.

[0048] Example 3:

[0049] A preparation method of a nickel-cobalt bimetallic site single-atom catalyst, the steps are as follows:

[0050] (1) Weigh 8 g of sodium citrate and place it in a muffle furnace under an argon (Ar) atmosphere and pyrolyze it at a constant temperature of 800 °C for 1 hour to obtain a black solid product; wash it with a 6 mol / L dilute nitric acid solution to remove inorganic impurities; then wash it with water and dry it to obtain an ordered porous carbon support (PC);

[0051] (2) Mix 0.06 g of PC, 0.088 g of nickel nitrate, 0.088 g of cobalt nitrate and 1.328 g of glucose, grind and weigh, and mix it with urea in a mass ratio of 1:5, and grind it again to obtain a precursor;

[0052] (3) Place the precursor in a muffle furnace under an Ar atmosphere and calcine it at a constant temperature of 950 °C for 2 hours. After cooling, take out the obtained product and grind it to obtain a nickel-cobalt dual-metal site single-atom catalyst (NiCo-N-C DSAC).

[0053] An electrocatalytic ammonia oxidation electrode, and its preparation method is as follows: Weigh 0.01 g of NiCo-N-C DSAC sample and add it to a dispersion composed of 800 μL of absolute ethanol, 1200 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat it on a conductive glass (ITO) substrate (coating amount 1.0 mg / cm 2 ); After drying, obtain the electrocatalytic ammonia oxidation electrode, denoted as NiCo-N-C / ITO.

[0054] Example 4:

[0055] A preparation method of a nickel-zinc dual-metal site single-atom catalyst, the steps are as follows:

[0056] (1) Weigh 10 g of sodium dihydrogen citrate, place it in a muffle furnace under a nitrogen (N 2 ) atmosphere and pyrolyze it at a constant temperature of 800 °C for 1 hour to obtain a black solid product; Wash it with a 4 mol / L dilute sulfuric acid solution to remove inorganic impurities; Then wash it with water and dry it to obtain an ordered porous carbon support (PC);

[0057] (2) Mix 0.06 g of PC, 0.088 g of nickel nitrate, 0.070 g of zinc nitrate, and 1.328 g of glucose, grind and weigh them, and mix them with dicyandiamide in a mass ratio of 1:10, and grind again to obtain a precursor;

[0058] (3) Place the precursor in a muffle furnace under an N 2 atmosphere and calcine it at a constant temperature of 950 °C for 2 hours. After cooling, take out the obtained product and grind it to obtain a nickel-zinc dual-metal site single-atom catalyst (NiZn-N-C DSAC).

[0059] An electrocatalytic ammonia oxidation electrode, and its preparation method is as follows: Weigh 0.01 g of NiZn-N-C DSAC sample and add it to a dispersion composed of 1000 μL of absolute ethanol, 1000 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat it on a titanium plate (TB) substrate (coating amount 1.5 mg / cm 2 ); After drying, obtain the electrocatalytic ammonia oxidation electrode, denoted as NiZn-N-C / TB.

[0060] Example 5:

[0061] A preparation method of a nickel-manganese bimetallic site single-atom catalyst, the steps are as follows:

[0062] (1) Weigh 10 g of sodium dihydrogen citrate, place it in a muffle furnace under a nitrogen (N 2 ) atmosphere, pyrolyze it at a constant temperature of 800 °C for 1 hour to obtain a black solid product; wash it with a 5 mol / L dilute sulfuric acid solution to remove inorganic impurities; then wash it with water and dry it to obtain an ordered porous carbon support (PC);

[0063] (2) Mix 0.06 g of PC, 0.069 g of nickel acetate, 0.068 g of manganese acetate and 1.328 g of glucose, grind and weigh them, and mix them with thiourea in a mass ratio of 1:5, and grind again to obtain a precursor;

[0064] (3) Place the precursor in a muffle furnace under a N 2 atmosphere, calcine it at a constant temperature of 700 °C for 2 hours, take out the obtained product after cooling, and grind it to obtain a nickel-manganese bimetallic site single-atom catalyst (NiMn-N-C DSAC);.

[0065] An electrocatalytic ammonia oxidation electrode, its preparation method is: weigh 0.01 g of NiMn-N-C DSAC sample, add it to a dispersion composed of 800 μL of absolute ethanol, 1200 μL of water, and 40 μL of 5 wt.% Nafion membrane solution, ultrasonically mix it evenly and then coat it on a conductive glass (ITO) substrate (coating amount 1.8 mg / cm 2 ); after drying, obtain the electrocatalytic ammonia oxidation electrode, denoted as NiMn-N-C / ITO.

[0066] Comparative Example 1 (Ni-N-C single-atom catalyst):

[0067] A nickel single-atom catalyst (Ni-N-C SAC), in the preparation process, copper sulfate is not added in step (2), and the remaining steps and the preparation method of the electrocatalytic ammonia oxidation electrode are the same as those in Example 1.

[0068] Comparative Example 2 (Cu-N-C single-atom catalyst):

[0069] A nickel single-atom catalyst (Cu-N-C SAC), in the preparation process, nickel sulfate is not added in step (2), and the remaining steps and the preparation method of the electrocatalytic ammonia oxidation electrode are the same as those in Example 1.

[0070] Comparative Example 3 (nanoscale catalyst Ni 1 Cu 3 -S-T / CP):

[0071] A nanoscale nickel-copper bimetallic catalytic electrode, the preparation method is the same as that of Ni in Example 1 of Patent CN202111073952.2 1 Cu 3 -S-T / CP catalytic electrode.

[0072] Comparative Example 4 (nanoscale catalyst Ni 1 Cu 1 Co 0.5 -S-T / CP):

[0073] A nanoscale nickel-copper bimetallic catalytic electrode, the preparation method is: Fix the pretreated carbon paper (CP, 1×1 cm 2 ) in the electrode clip as the working electrode of the three-electrode system, and a platinum wire and Hg / HgO are used as the counter electrode and reference electrode respectively. Electrodeposit CP for 120 s at a deposition voltage of -1.3 V, and then further prepare the Ni 1 Cu 1 Co 0.5 -S-T / CP catalytic electrode by alkaline electrochemical tuning with the help of a cyclic voltammetry curve scanned 30 cycles in 1 M NaOH solution. The composition of the deposition electrolyte includes NiNO 3 ·6H 2 O (0.40 mmol), CuNO 3 ·3H 2 O (0.4 mmol), CoNO 3 ·6 H 2 O (0.20 mmol), urea (5.00 mmol) and thiourea (4.00 mmol).

[0074] Comparative Example 5 (using carbon nanotubes as the carrier):

[0075] A preparation method of a nickel-copper bimetallic site single-atom catalyst, the steps are:

[0076] (1) Mix 0.06 g of carbon nanotubes (CNT), 0.085 g of nickel sulfate, 0.225 g of copper sulfate and 1.328 g of glucose, grind and weigh, and mix with melamine in a mass ratio of 1:5, and grind again to obtain the precursor;

[0077] (2) Place the precursor in a muffle furnace under N 2 atmosphere and calcine at 800 °C for 2 hours, take out the obtained product after cooling, and grind to obtain the nickel-copper bimetallic site single-atom catalyst;

[0078] The preparation method of the electrocatalytic ammonia oxidation electrode is the same as that in Example 1.

[0079] Comparative Example 6 (the carrier is not pickled with acid):

[0080] In the preparation process of the nickel-copper bimetallic site single-atom catalyst of Comparative Example 6, the black solid product obtained in step (1) was not washed with dilute sulfuric acid solution, and the remaining steps and the preparation method of the electrocatalytic ammonia oxidation electrode were the same as those in Example 1.

[0081] Comparative Example 7 (without adding glucose):

[0082] In the preparation process of the nickel-copper bimetallic site single-atom catalyst of Comparative Example 7, glucose was not added in step (2), and the remaining steps and the preparation method of the electrocatalytic ammonia oxidation electrode were the same as those in Example 1.

[0083] The application performance of the electrocatalytic ammonia oxidation electrodes prepared in the above examples and comparative examples in the electrocatalytic ammonia oxidation total denitrification reaction was investigated. The method was as follows: In a CHI 604E electrochemical workstation, using NiCu 3 -N-C / CP as the working electrode, a platinum wire as the counter electrode, and a mercury / mercuric oxide electrode as the reference electrode, the electrochemical activity test of the catalyst was carried out by linear sweep voltammetry in a solution of 1 M NaOH + 0.2 M NH 4 Cl. Then, with an operating potential of 0.6 V vs. Hg / HgO, electrocatalytic ammonia oxidation treatment was carried out for 5 hours respectively in simulated wastewater with ammonia nitrogen concentrations of 350, 700, and 1400 mg / L to explore the treatment capacity of the catalyst per unit time. The results are as Figures 2 - 4 shown.

[0084] Figure 2 The LSV test results in 3 show that compared with the Ni-N-C (Comparative Example 1) and Cu-N-C (Comparative Example 2) single-atom catalysts, the NiCu 2 -N-C DSAC prepared by the method of the present invention in Example 1 has significantly improved electrochemical activity, obtaining a maximum AOR current density of 90 mA / cm 2 ², the lowest onset potential (1.210 V vs. RHE @5 mA / cm -1 ²), and the maximum turnover frequency (TOF: 3.64 s -1 ⁻¹).

[0085] As shown in Figure 3 a, in terms of cost-effectiveness within 5 hours, the electrocatalytic ammonia oxidation efficiency is the best when the initial concentration is 700 mg / L. Continuing to increase the initial concentration, its utilization efficiency will not increase but decrease, because the atomic sites are saturated per unit time. At this time, the catalyst obtained an ammonia nitrogen removal rate of 98.74% and a Faraday efficiency of 85.27%, achieving efficient electrocatalytic ammonia oxidation. At the same time, its nitrogen selectivity is as high as 97.87%, almost achieving the effect of total denitrification (Figure 3 b).

[0086] Finally, given an operating potential of 0.6 V vs. Hg / HgO, electrocatalytic ammonia oxidation treatment was carried out for 6 hours in actual ammonia nitrogen wastewater with a concentration of approximately 616 mg / L. It can be seen from Figure 4 that compared with Ni 1 Cu 3 -S-T / CP (Comparative Example 3) and Ni 1 Cu 1 Co 0.5 -S-T / CP (Comparative Example 4), two kinds of nanoscale catalysts, the atomic-scale NiCu 3 -N-C DSAC exhibits excellent electrocatalytic ammonia oxidation performance. In the electrocatalytic ammonia oxidation system of this catalyst, the ammonia nitrogen removal rate is as high as 99.72%, obtaining a Faraday efficiency of 86.60% and an energy consumption of 0.05 kW·h kg -1 N. It is worth noting that compared with the nanoscale catalyst, while electrocatalytic ammonia oxidation to nitrogen gas, the nitrate content in the electrolysis system of NiCu 3 -N-C DSAC also decreases significantly. This is attributed to, on the one hand, the electrochemical reduction of nitrate at the cathode, and on the anode side, the highly selective ammonia oxidation process greatly inhibits or even avoids the generation of nitrate. In short, NiCu 3 -N-C DSAC and the electrolysis device constructed therefrom are expected to achieve the full denitrification effect of ammonia nitrogen wastewater.

[0087] It can be seen from Figure 5 that compared with carbon nanotubes (CNT) as a porous carbon skeleton carrier (Comparative Example 5), the porous carbon PC fired with citrate in Example 1 can provide better and more anchoring sites for bimetallic atoms, so the catalyst constructed by the latter shows nearly twice as high electrocatalytic ammonia oxidation activity as the former.

[0088] It can be seen from Figure 6 that compared with PC before pickling (Comparative Example 6), the catalyst constructed by PC after pickling shows significantly higher electrocatalytic ammonia oxidation activity. Because the pickling step will remove the original metal cations "potassium" or "sodium", causing certain defects in the carbon skeleton, and this appropriate undercoordinated structure helps the subsequent embedding and fixation of active metal atoms.

[0089] It can be seen from Figure 7It can be seen that after adding glucose, the electrocatalytic ammonia oxidation activity of the constructed catalyst is significantly higher than that of the catalyst prepared without adding glucose (Comparative Example 7). This is because glucose can well promote the chelation between PC, metal salt and nitrogen source during grinding, so as to improve the uniform dispersion of active metal atoms and nitrogen atoms in the porous carbon skeleton during high-temperature pyrolysis, which helps to form the structure of bimetallic sites.

Claims

1. Application of an electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction, Characterized in that, The reaction method is: placing the electrocatalytic ammonia oxidation electrode and the counter electrode in a solution containing ammonia nitrogen, connecting the electrocatalytic ammonia oxidation electrode and the counter electrode, and carrying out an electrochemical reaction; The electrocatalytic ammonia oxidation electrode includes a conductive substrate and a bimetallic site single-atom catalyst supported on the conductive substrate; The preparation method of the bimetallic site single-atom catalyst includes the following steps: (1) Pyrolyzing the citrate under an inert atmosphere, washing successively with an acid solution and water, and drying to obtain an ordered porous carbon support; (2) Mixing and grinding the ordered porous carbon support, metal salt M1, metal salt M2 and glucose to obtain a mixed material; then mixing the mixed material with a nitrogen source and grinding again to obtain a precursor; metal salt M1 is selected from one of nickel sulfate, nickel chloride, nickel bromide, nickel nitrate, nickel acetate and their hydrates; metal salt M2 is selected from one of copper sulfate, copper chloride, copper nitrate, copper acetate and their hydrates; (3) Pyrolyzing the precursor obtained in step (2) under an inert atmosphere, cooling and grinding to obtain a bimetallic site single-atom catalyst.

2. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 1, Characterized in that, In step (1), the citrate is selected from one or more of trisodium citrate, potassium citrate, potassium dihydrogen citrate, and sodium dihydrogen citrate; the acid solution is selected from one of sulfuric acid, hydrochloric acid, and nitric acid; the concentration of the acid solution is 1.0 - 8.0 mol / L.

3. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 1 or 2, Characterized in that, In step (1), the pyrolysis temperature is 700 - 900 °C, and the pyrolysis time is 0.5 - 3 h.

4. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 1, Characterized in that, In step (2), the nitrogen source is selected from one or more of dicyandiamide, melamine, urea, and thiourea.

5. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 1, Characterized in that, The loading amount of the bimetallic site single-atom catalyst on the conductive substrate is 1-2 mg / cm 2 .

6. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 4, Characterized in that, In the mixed material in step (2), the molar ratio of metal ions in metal salt M1 and metal salt M2 is 1:0.5 - 5; the addition ratio of the ordered porous carbon support, metal ions in metal salt M1, and glucose is 0.06 g:0.3 - 0.5 mmol:1.2 - 1.5 g; the mass ratio of the mixed material and the nitrogen source in the precursor is 1:5 - 10.

7. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 1, Characterized in that, In step (3), the pyrolysis temperature is 600 - 1000 °C, and the pyrolysis time is 1 - 3 h.

8. The application of the electrocatalytic ammonia oxidation electrode in the electrocatalytic ammonia oxidation total denitrification reaction according to claim 1, Characterized in that, The described conductive substrate is selected from one of carbon paper, carbon cloth, nickel foam, copper foam, boron-doped diamond film, conductive glass and titanium plate.

9. The application of the electrocatalytic ammonia oxidation electrode according to claim 1 in the electrocatalytic ammonia oxidation total denitrification reaction, characterized in that, the counter electrode is a platinum electrode.

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