Method for preparing ammonia by reducing nitrate using bimetallic phosphide three-dimensional self-supporting electrocatalyst

Abstract

The present invention discloses a method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst. The method uses the bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode to electrochemically reduce nitrate. The bimetallic phosphide three-dimensional self-supporting electrocatalyst used is based on a three-dimensional substrate material, on which nickel-cobalt bimetallic phosphide is in situ deposited. In the nickel-cobalt bimetallic phosphide, the nickel exists in the form of Ni 3+ , the existing forms of cobalt include Co 3+ and Co 2+ Phosphorus exists in the form of phosphorus oxides and ionic phosphorus. The method of the present invention has the advantages of simple process, convenient operation, low energy consumption, low cost, mild reaction conditions, good removal effect, high ammonia selectivity, no generation of toxic and harmful substances, and environmental friendliness. It can not only efficiently reduce nitrates, but also convert more nitrates into ammonia, with high use value and good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental functional materials, and specifically relates to a method for preparing ammonia by reducing nitrates using a bimetallic phosphide three-dimensional self-supporting electrocatalyst. Background Art

[0002] At present, conventional methods of removing NO3 from water are - Methods include physical, biological, and chemical methods, but these methods still have some defects in practical application. For example, physical methods are prone to secondary pollution during practical application, thus limiting their practical application, such as concentrate produced by membrane filtration, saturated adsorbent produced by adsorption process, etc.; chemical methods are prone to secondary pollution during the reduction of NO3 - A large amount of chemicals need to be added during the process, which is costly and environmentally unfriendly. In practical applications, biological methods have the defect of unstable denitrification performance, that is, they are easily affected by operating conditions such as pH, temperature, C / N ratio, etc.

[0003] Electrochemical reduction of nitrates is considered to be a very promising method. This method can convert nitrates or nitrites into nitrogen or ammonia, wherein nitrates or nitrites are converted into recyclable and high-value ammonia, thereby turning waste into treasure, which is of great significance. However, the existing methods for electrochemical reduction of nitrates still find it difficult to reduce more nitrates or nitrites to ammonia, that is, they still have defects such as low nitrate removal rate and low ammonia selectivity. The reason may be that the existing electrocatalysts for electrochemical reduction of nitrates still have defects such as low specific surface area, small number of active sites, and poor catalytic activity, making it difficult to effectively reduce nitrates, which is not conducive to improving the nitrate removal effect. At the same time, the existing electrocatalysts easily promote the generation of hydrogen, which is not conducive to conversion into ammonia, resulting in low ammonia selectivity. In addition, when existing metal-based electrocatalysts are used to reduce nitrate wastewater, they also have defects such as poor stability and easy dissolution of metals. They not only easily cause secondary pollution, but also are not conducive to the reuse of catalysts, making it difficult to reduce preparation costs. Therefore, obtaining a metal-based electrocatalyst with rich pore size, high specific surface area, high catalytic activity, good stability, high repeatability, good applicability, no secondary pollution, and green environmental protection is of great significance for achieving efficient electroreduction of nitrate and synthesis of ammonia. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a method for reducing nitrate to prepare ammonia using a bimetallic phosphide three-dimensional self-supporting electrocatalyst with good nitrate removal effect and high ammonia selectivity.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst, wherein the method uses the bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode to electrochemically reduce nitrate; the bimetallic phosphide three-dimensional self-supporting electrocatalyst is based on a three-dimensional substrate material, on which a nickel-cobalt bimetallic phosphide is in situ deposited, wherein the nickel in the nickel-cobalt bimetallic phosphide is in the form of Ni 3+ , the existing forms of cobalt include Co 3+ and Co 2+ The forms of phosphorus include phosphorus oxide and ionic phosphorus.

[0007] The above method is further preferred, wherein the atomic ratio of nickel, cobalt and phosphorus in the three-dimensional self-supporting bimetallic phosphide electrocatalyst is 33.12:16.3:50.58; and the nickel-cobalt bimetallic phosphide has a spherical structure.

[0008] The above method is further preferred, and the preparation method of the bimetallic phosphide three-dimensional self-supporting electrocatalyst includes the following steps: immersing the three-dimensional substrate material in an electrodeposition solution for electrodeposition treatment to obtain a bimetallic phosphide three-dimensional self-supporting electrocatalyst; the electrodeposition solution contains nickel, cobalt, and phosphorus.

[0009] The above method is further preferred, wherein the three-dimensional substrate material is a metal-based three-dimensional porous material, including at least one of nickel foam, copper foam, cobalt foam and iron foam, and the electrodeposition solution is prepared by dissolving nickel salt, cobalt salt and phosphate in water; the molar ratio of nickel element, cobalt element and phosphorus element in the electrodeposition solution is 1:1:8-15, the nickel salt is at least one of NiCl2, nickel nitrate and nickel sulfate, the cobalt salt is at least one of CoCl2, cobalt nitrate and cobalt sulfate, and the phosphate is at least one of NaH2PO4 and sodium hypophosphite; during the electrodeposition process, the three-dimensional substrate material is used as the working electrode, the platinum sheet electrode is used as the counter electrode, and the saturated Ag / AgCl electrode is used as the reference electrode; during the electrodeposition process, the deposition potential is controlled to be -0.9V vs.AgCl to -1.1V vs.AgCl, and the electrodeposition time is 10min to 30min.

[0010] In the above method, it is further preferred that the electrodeposition treatment time is 15 minutes to 25 minutes.

[0011] The above method is further preferred, wherein the three-dimensional base material further includes the following treatment before use: washing the three-dimensional base material with hydrochloric acid, acetone, anhydrous ethanol and water in sequence, each washing for 15 minutes to 30 minutes, soaking the washed three-dimensional base material in a nickel salt solution for 4 hours, washing the soaked three-dimensional base material with water and anhydrous ethanol in sequence, and drying; the mass fraction of the hydrochloric acid is 5%, the concentration of the nickel salt solution is 0.1 mM, the nickel salt solution is a nickel chloride solution, the drying is carried out under vacuum conditions, the drying temperature is 60°C, and the drying time is 6 hours.

[0012] The above method is further preferred, in which nitrate wastewater is electrochemically reduced using a bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode, comprising the following steps: using a bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode and an Ir-Ru / Ti electrode as an anode, placing them in nitrate wastewater to carry out an electro-reduction catalytic reaction, thereby completing the removal of nitrate and producing ammonia.

[0013] The above method is further preferred, in which the applied current density is controlled to be 1 mA / cm during the electro-reduction catalytic reaction. 2 ~5mA / cm 2 The electro-reduction catalytic reaction time is 5h, and the electro-reduction catalytic reaction is carried out under stirring conditions, and the stirring speed is 400rpm.

[0014] The above method is further preferred, wherein the electro-reduction catalytic reaction process further includes adding an electrolyte to the nitrate wastewater so that the concentration of the electrolyte in the solution is 0.05M, and the electrolyte is sodium sulfate.

[0015] The above method is further preferred, wherein the initial concentration of nitrate in the nitrate wastewater is 25 mg·N / L to 100 mg·N / L, the nitrate in the nitrate wastewater is at least one of sodium nitrate and potassium nitrate, and the pH value of the nitrate wastewater is 3 to 11.

[0016] Compared with the prior art, the advantages of the present invention are:

[0017] (1) The present invention discloses a method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst, wherein the bimetallic phosphide three-dimensional self-supporting electrocatalyst is used as a cathode to electrochemically reduce nitrate, wherein the bimetallic phosphide three-dimensional self-supporting electrocatalyst is based on nickel foam, on which nickel-cobalt bimetallic phosphide is in situ deposited, and in the nickel-cobalt bimetallic phosphide, the nickel exists in the form of Ni 3+ , the existing forms of cobalt include Co 3+ and Co 2+, the existence forms of phosphorus include phosphorus oxide and ionic phosphorus. In the present invention, the bimetallic phosphide three-dimensional self-supporting electrocatalyst used is based on nickel foam, and nickel-cobalt bimetallic phosphide is in situ deposited on the nickel foam, wherein the nickel foam is a three-dimensional porous material, so the nickel-cobalt bimetallic phosphide is in situ deposited on the three-dimensional porous material so that the composite material has a rich pore structure and has a higher specific surface area and more active sites. At the same time, the cobalt, nickel and phosphorus in the nickel-cobalt bimetallic phosphide have a synergistic promotion effect, so that the catalyst has higher catalytic activity, better stability, and is more environmentally friendly. It can be seen that the bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention has the advantages of rich pore structure, high specific surface area, a large number of active sites, high catalytic activity, good stability, good applicability, no secondary pollution, and environmental protection. It is a new type of electrocatalyst with excellent performance and good application prospects. When it is used as a cathode for electrochemical reduction of nitrate, after power is applied, electrons are transferred from the partially positively charged metal Ni and Co (δ + ) is transferred to the partially negatively charged P (δ - ), phosphorus acts as a site for capturing positive charges during electrocatalysis, while positively charged Ni and Co act as sites for adsorbing NO3 - The site, namely NO3 - (ads) first adsorbed on the positively charged Ni and Co sites. On this basis, the bimetallic phosphide three-dimensional self-supporting electrocatalyst reduced nitrate to synthesize ammonia through two reaction mechanisms: direct reduction and indirect reduction. Specifically: in the direct reduction mechanism, on the one hand, the nickel-cobalt bimetallic phosphide mainly acts as an electron shuttle rather than a reducing agent, through Co 2+ →Co 3+ →Co 2+ The redox process reduces the nitrate adsorbed on the metal Ni and Co sites. On the other hand, the adjacent negatively charged phosphorus sites anchor the protons in the water molecules (H + ), and the activated protons tend to form more stable NH bonds and destroy N=O bonds, so as H + With the successive addition of electrons, NO3 - At the same time, the electron transfer between metal Ni, Co and P is conducive to reducing internal resistance, enhancing electron transfer, and increasing the reaction rate, thereby promoting the conversion of more nitrates into ammonia. In the indirect reduction mechanism, the bimetallic phosphide three-dimensional self-supporting electrocatalyst can activate the production of more atomic H * As an active substance for reducing nitrate, its presence can also promote the reduction of nitrate. It can be seen that the bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention is not only effective for the reduction of nitrate and H +The bimetallic phosphide three-dimensional self-supporting electrocatalyst exhibits excellent adsorption and synergistic reduction properties, and can also induce the production of atomic hydrogen (H*), an active substance for reducing nitrates. This can further enhance catalytic activity without the addition of additional additives. Through the combination of direct and indirect reduction reaction mechanisms, the bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention can efficiently remove nitrates from water and synthesize more ammonia. Furthermore, the present method for reducing nitrates to produce ammonia using the bimetallic phosphide three-dimensional self-supporting electrocatalyst offers advantages such as a simple process, convenient operation, low energy consumption, low cost, mild reaction conditions, excellent removal efficiency, high ammonia selectivity, no production of toxic and hazardous substances, and environmental friendliness. It not only efficiently reduces nitrates but also converts more nitrates into ammonia, offering high utility value and promising application prospects.

[0018] (2) In the present invention, the bimetallic phosphide three-dimensional self-supporting electrocatalyst used is based on a three-dimensional porous nickel foam. By electroplating, the nickel-cobalt bimetallic phosphide is deposited and loaded on the nickel foam substrate, thereby obtaining a self-supporting material without adding a binder. At the same time, by optimizing the time of electroplating treatment, the number of reaction active sites of the nickel-cobalt bimetallic phosphide three-dimensional self-supporting electrocatalyst can be further optimized, thereby enhancing the hydrogenation and deoxidation ability of the catalyst. The bimetallic phosphide three-dimensional self-supporting electrocatalyst thus prepared has higher catalytic activity and selectivity for ammonia. Under the joint action of Ni, Co and P, it can more thoroughly degrade nitrate and obtain more product ammonia. At the same time, the preparation method of the present invention also has the advantages of simple process, convenient operation, low energy consumption, no generation of toxic and harmful substances, and environmental friendliness. It is suitable for large-scale preparation and is conducive to industrial application.

[0019] (3) In the present invention, by optimizing the molar ratio of nickel, cobalt and phosphorus in the electroplating solution to 1:1:8-15, the bimetallic phosphide three-dimensional self-supporting electrocatalyst has higher catalytic activity and selectivity for ammonia. In particular, when the molar ratio of nickel, cobalt and phosphorus in the electroplating solution is 1:1:12, the prepared bimetallic phosphide three-dimensional self-supporting electrocatalyst can efficiently remove nitrate from wastewater and has better selectivity for ammonia. In addition, when the content of phosphorus in the electroplating solution is too small (such as the molar ratio of nickel, cobalt and phosphorus is 1:1:5) or too large (such as the molar ratio of nickel, cobalt and phosphorus is 1:1:20), it is impossible to prepare an electrocatalyst with high catalytic activity and good selectivity for ammonia. As a result, it is difficult to effectively remove nitrate from wastewater, and the selectivity for ammonia is still poor. At the same time, in the present invention, the deposition potential during the electrodeposition treatment is also optimized to be -0.9V vs.AgCl to -1.1V vs.AgCl. Under these conditions, it is also beneficial to prepare an electrocatalyst with higher catalytic activity and selectivity for ammonia, thereby being able to more efficiently remove nitrates from wastewater and having better selectivity for ammonia. Among them, the deposition potential is -1.0 V vs.AgCl, and the performance of the prepared electrocatalyst is optimal. In particular, when the deposition potential during the electrodeposition treatment is -0.8V vs.AgCl or -1.2V vs.AgCl, it is not conducive to the preparation of electrocatalysts with excellent performance.

[0020] (4) In the present invention, the current density during the electro-reduction catalytic reaction is optimized to be 1 mA / cm 2 ~5mA / cm 2 , which can achieve efficient removal of nitrate and synthetic ammonia, that is, the nitrate removal rate can be as high as 97.68% and the ammonia selectivity can be as high as 95.44% (that is, the ammonia productivity). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0022] Figure 1 This is a SEM image of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 of the present invention.

[0023] Figure 2 1 and 2 are XRD patterns of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), NiP / NF, and nickel foam (NF) prepared in Example 1 of the present invention.

[0024] Figure 3These are the SEM-Mapping and SAED patterns of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 of the present invention.

[0025] Figure 4 These are XPS graphs of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 of the present invention before and after use.

[0026] Figure 5 These are the EIS Nerquist plots of the bimetallic phosphide three-dimensional self-supporting electrocatalysts (NiCoP / NF, NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, and NiCoP / NF-30) prepared in Example 1 of the present invention.

[0027] Figure 6 This is a diagram showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), NiP / NF, CoP / NF, NiCo / NF and nickel foam (NF) prepared in Example 1 of the present invention on the removal of nitrate and the synthesis of ammonia.

[0028] Figure 7 This is a diagram showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalysts (NiCoP / NF, NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, NiCoP / NF-30) prepared in Example 1 of the present invention on the removal of nitrate and the synthesis of ammonia.

[0029] Figure 8 This is a diagram showing the effect of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) in Example 2 of the present invention on the removal of nitrate with different initial concentrations and the synthesis of ammonia.

[0030] Figure 9 Graph showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) on nitrate removal and ammonia synthesis at different current densities in Example 3 of the present invention.

[0031] Figure 10 Graph showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) on nitrate removal and ammonia synthesis under different pH conditions in Example 4 of the present invention.

[0032] Figure 11 This is a diagram of the cyclic degradation of nitrate by the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) in Example 5 of the present invention.

[0033] Figure 12This is a diagram showing the effect of reducing nitrate to synthesize ammonia using the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) in Example 5 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby. The materials and instruments used in the following examples are all commercially available.

[0035] Example 1:

[0036] A method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention, specifically electrochemically reducing sodium nitrate wastewater using the bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode, comprises the following steps:

[0037] Bimetallic phosphide three-dimensional self-supporting electrocatalysts (NiCoP / NF, NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, NiCoP / NF-30), NiP / NF, CoP / NF, NiCo / NF, and nickel foam (NF) were used as cathodes, and Ir-Ru / Ti electrodes were used as anodes (the effective area of the Ir-Ru / Ti electrode was 1×4 cm). 2 ), were inserted together into an H-type electrolytic cell separated by a Nafion 117 membrane. 80 mL of sodium nitrate wastewater containing Na2SO4 with an initial pH of 7 was added to the cathode and anode chambers of the H-type electrolytic cell. The initial concentration of sodium nitrate in the wastewater was 50 mg·N / L and the concentration of Na2SO4 was 0.05 M. Under stirring at a speed of 400 rpm and a flow rate of 2 mA / cm 2 The electro-reduction catalytic reaction was carried out under a constant current of for 5 hours to complete the degradation of sodium nitrate in the wastewater and obtain ammonia.

[0038] In this embodiment, the preparation method of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) includes the following steps:

[0039] (1) A piece of nickel foam (NF, 2 cm × 2.5 cm × 0.2 cm) was cut from the nickel foam sheet and ultrasonically washed with 5% hydrochloric acid, acetone, anhydrous ethanol and deionized water for 20 min each to completely remove impurities and oxide layer. Then, the washed nickel foam was immersed in 0.1 mM NiCl2·6H2O solution for 4 h to activate the nickel foam. Finally, the immersed nickel foam sheet was washed with deionized water and anhydrous ethanol three times each and dried at 60 °C under vacuum for 6 h to obtain activated nickel foam.

[0040] (2) 50 mM NiCl2 solution, 50 mM CoCl2 solution and 0.6 M NaH2PO4 solution were mixed so that the molar ratio of Ni, Co and P in the mixed solution was 1:1:12, and then ultrasonically treated for 20 min to obtain a uniform pink transparent solution, namely the electrodeposition solution.

[0041] (3) The active nickel foam obtained in step (1) was used as a working electrode, a platinum electrode was used as a counter electrode, and a saturated Ag / AgCl electrode was used as a reference electrode. The electrodes were immersed in a three-electrode electrolytic cell containing the electrodeposition solution obtained in step (2). The electrodeposition reaction was carried out at a constant potential of -1.0 V vs. Ag / AgCl for 20 min. The reaction product was taken out, rinsed with deionized water and anhydrous ethanol several times, and dried in a vacuum drying oven to obtain a bimetallic phosphide three-dimensional self-supporting electrocatalyst, which was recorded as NiCoP / NF.

[0042] In this embodiment, the prepared bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) is based on nickel foam, on which nickel-cobalt bimetallic phosphide is in situ deposited. The nickel element in the nickel-cobalt bimetallic phosphide exists in the form of Ni 3+ , the existing forms of cobalt include Co 3+ and Co 2+ The phosphorus element exists in the form of phosphorus oxide and ionic phosphorus; the atomic ratio of nickel, cobalt, and phosphorus in the electrocatalyst is 33.12:16.3:50.58. The nickel-cobalt bimetallic phosphide of the present invention is a spherical structure with a rough surface.

[0043] In this embodiment, the preparation method of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, NiCoP / NF-30) used is basically the same as the preparation method of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), with the only difference being that in step (3), the electrodeposition reaction time corresponding to the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, NiCoP / NF-30) is 10 min, 15 min, 25 min, and 30 min, respectively.

[0044] In this embodiment, the preparation method of NiP / NF is basically the same as the preparation method of bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), with the only difference being that in step (2), CoCl2·6H2O is not added to the electrodeposition solution.

[0045] In this embodiment, the preparation method of CoP / NF is basically the same as the preparation method of bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), with the only difference being that in step (2), NiCl2·6H2O is not added to the electrodeposition solution.

[0046] In this embodiment, the preparation method of NiCo / NF is basically the same as the preparation method of bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), with the only difference being that in step (2), NaH2PO4·2H2O is not added to the electrodeposition solution.

[0047] Table 1 Differences in the three-dimensional self-supporting electrocatalysts with different components prepared in Example 1

[0048]

[0049] Figure 1 This is a SEM image of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 of the present invention. Figure 1 It can be seen that the nickel-cobalt bimetallic phosphide in the bimetallic phosphide self-supporting electrocatalyst prepared in the present invention is an accumulated spherical structure with a rough surface.

[0050] Figure 2 The XRD patterns of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), NiP / NF and nickel foam (NF) prepared in Example 1 of the present invention are shown in FIG. Figure 2 It can be seen that the bimetallic phosphide three-dimensional self-supporting electrocatalyst prepared by the present invention, bimetallic phosphide (NiCoP) is successfully deposited on nickel foam.

[0051] Figure 3 The SEM-Mapping and SAED patterns of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 of the present invention are shown. Figure 3 It can be seen that the bimetallic phosphide three-dimensional self-supporting electrocatalyst prepared by the present invention was successfully synthesized, and the material has an amorphous structure.

[0052] Figure 4 The XPS graphs of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 of the present invention before and after use. Figure 4 It can be seen that the XPS spectrum shows the presence of Ni, Co, and P signals, which means the successful conversion of NiCoP. The Co2p XPS spectrum shows the presence of Co 3+ and Co 2+ , after the reaction, Co 3+ / Co 2+The ratio increases, and high-valent cobalt has a stronger reducing ability, which indicates that the material is conducive to electron transfer, that is, NO3RR occurs in the reaction system. The Ni 2p XPS spectrum shows that there is Ni 3+ , after the reaction, all peaks have a slight negative shift, which indicates that Ni 3+ Transformed into Ni 2+ From the P 2p spectrum, two main peaks can be observed, which can be considered to be reduced phosphorus in the form of metal phosphate (PM (Ni, Co)) and can match with high-valent phosphorus (PO). After the reaction, the PO signal peak weakened and the PM signal peak strengthened. It is worth noting that the binding energy of PM (Ni, Co) (129.18 eV) is slightly lower than the binding energy of phosphorus atoms (130.0 eV), which indicates that the electrons from the partially positively charged (δ + ) transition metals Ni and Co are partially negatively charged (δ - ), therefore, phosphorus can serve as a proton-capturing site during electrocatalysis.

[0053] Figure 5 The EIS Nerquist plots of the bimetallic phosphide three-dimensional self-supporting electrocatalysts (NiCoP / NF, NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, and NiCoP / NF-30) prepared in Example 1 of the present invention are shown in FIG. Figure 5 It can be seen that the arc radius in the figure corresponds to the limiting process of electron transfer. Obviously, the arc radius of NiCoP / NF is the smallest, which is more conducive to electron transfer.

[0054] During the electro-reduction catalytic reaction, 1.5 mL of sample was taken out from the solution at regular intervals, filtered with a 0.22 μm membrane, and tested with a UV-visible spectrophotometer to determine the nitrate removal rate R(NO3 - ), the generation rate of nitrite S(NO2 - ), ammonia generation rate S(NH4 + ), nitrogen generation rate S(N2), and further calculated energy consumption (EC), Faraday efficiency (FE) and ammonia yield (NH3 yield), the results are shown in Table 2, Figure 6-7 shown.

[0055] Table 2 Treatment results of nitrate by catalyst

[0056]

[0057] Figure 6This is a diagram showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF), NiP / NF, CoP / NF, NiCo / NF and nickel foam (NF) prepared in Example 1 of the present invention on the removal of nitrate and the synthesis of ammonia. Figure 6 The nitrate removal rate is R(NO3 - ), the generation rate of nitrite is S(NO2 - ), the ammonia generation rate is S(NH4 + ), the nitrogen generation rate is S(N2), the energy consumption is EC, the Faraday efficiency is FE, and the ammonia yield is NH3 yield. Figure 6 It can be seen that the removal rate of nitrate (R(NO3 - )) is 97.6761%, while the removal rate of nitrate by nickel foam (NF) (R(NO3 - )) was 6.1402%, far lower than the nitrate removal rate of NiCoP / NF, indicating that the bimetallic phosphide (NiCoP) supported on nickel foam effectively degrades nitrate. Compared with NiP / NF and CoP / NF, the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) of the present invention exhibits the best performance in terms of nitrate removal, nitrite byproduct formation, ammonia selectivity and yield, and Faradaic efficiency. This is due to the following: firstly, the synergistic effect between the two metals in the bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention enhances electrocatalytic performance, thereby facilitating the highly selective and energy-efficient production of the target product, ammonia. Secondly, the performance of the phosphorus-containing bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) is significantly superior to that of the phosphorus-free NiCo / NF, demonstrating that the non-metallic element phosphorus plays a crucial role in the catalytic reaction of this material.

[0058] Figure 7 This is a diagram showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalysts (NiCoP / NF, NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, NiCoP / NF-30) prepared in Example 1 of the present invention on the removal of nitrate and the synthesis of ammonia. Figure 7 The nitrate removal rate is R(NO3 - ), the generation rate of nitrite is S(NO2 - ), the ammonia generation rate is S(NH4 + ), the nitrogen generation rate is S(N2), the energy consumption is EC, the Faraday efficiency is FE, and the ammonia yield is NH3 yield. Figure 7It can be seen that among the bimetallic phosphide three-dimensional self-supporting electrocatalysts with different deposition times (NiCoP / NF, NiCoP / NF-10, NiCoP / NF-15, NiCoP / NF-25, and NiCoP / NF-30), NiCoP / NF has the highest nitrate removal rate. At the same time, the ammonia generation rate is all above 90%, indicating that the bimetallic phosphide three-dimensional self-supporting electrocatalysts of the present invention have high selectivity for ammonia. In particular, the ammonia yield of NiCoP / NF is 75.28 μg h -1 cm -2 , with a Faradaic efficiency of 57.6549%. NiCoP / NF exhibits the highest ammonia yield and Faradaic efficiency. Therefore, in the preparation method of the present invention, when the electrodeposition treatment time is 15 to 25 minutes, the prepared three-dimensional self-supporting bimetallic phosphide electrocatalyst can effectively reduce nitrates and improve selectivity for ammonia. In particular, the best treatment effect is achieved when the electrodeposition treatment time is 20 minutes.

[0059] Example 2:

[0060] A method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention, specifically electrochemically reducing sodium nitrate wastewater using the bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode, comprises the following steps:

[0061] The bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 was used as the cathode, and the Ir-Ru / Ti electrode was used as the anode (the effective area of the Ir-Ru / Ti electrode was 1×4 cm 2 ), were inserted together into an H-type electrolytic cell separated by a Nafion 117 membrane. Four 80 mL portions of sodium nitrate wastewater containing Na2SO4 (the concentration of Na2SO4 in the wastewater was 0.05 M) with an initial pH value of 7 were added to the cathode chamber and the anode chamber of the H-type electrolytic cell, respectively. The initial concentrations of sodium nitrate in these four wastewaters were 25 mg·N / L, 50 mg·N / L, 75 mg·N / L, and 100 mg·N / L, respectively. The mixture was stirred at a speed of 400 rpm and a flow rate of 2 mA / cm 2 The electro-reduction catalytic reaction was carried out under a constant current of for 5 hours to complete the degradation of sodium nitrate in the wastewater and obtain ammonia.

[0062] During the electro-reduction catalytic reaction, 1.5 mL of sample was taken from the solution at regular intervals, filtered through a 0.22 μm membrane, and tested using a UV-visible spectrophotometer to determine the catalyst's nitrate removal rate, nitrite generation rate, ammonia generation rate, nitrogen generation rate, energy consumption, Faradaic efficiency, and ammonia yield. The results are shown in Table 3.

[0063] Table 3 Treatment results of catalyst for nitrate

[0064]

[0065] Figure 8 This is a diagram showing the effect of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) in Example 2 of the present invention on the removal of nitrate with different initial concentrations and the synthesis of ammonia. Figure 8 The nitrate removal rate is R(NO3 - ), the generation rate of nitrite is S(NO2 - ), the ammonia generation rate is S(NH4 + ), the nitrogen generation rate is S(N2), the energy consumption is EC, the Faraday efficiency is FE, and the ammonia yield is NH3 yield. Figure 8 It can be seen that after 5 hours of electrolysis, when the initial concentration of nitrate in the wastewater is 25 mg·N / L, 50 mg·N / L, 75 mg·N / L, and 100 mg·N / L, the removal rate of nitrate (R(NO3 - )) were 100%, 97.6761%, 84.6653%, and 57.7682%, respectively. It can be seen that the higher the initial nitrate concentration in the wastewater, the lower the nitrate removal rate. Therefore, under the influence of the electrolysis time and current density, the bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention is more suitable for medium- and low-concentration nitrate wastewater. If the power consumption is increased, the catalyst can be used to remove high-concentration nitrate. In particular, under the conditions of a large range of nitrate concentrations and low energy consumption, the electrocatalyst's selectivity for ammonia (i.e., ammonia productivity) remains high (at least 93.8299%), and the amount of the more toxic intermediate product nitrite remains at a very low level (less than 0.085 mg·N / L). Furthermore, under the same conditions, when the electrolyte without nitrate was electrolyzed, almost no ammonia was detected, proving that the ammonia nitrogen produced by the electroreduction catalytic reaction comes entirely from the nitrate nitrogen in the electrolyte.

[0066] Example 3:

[0067] A method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention, specifically electrochemically reducing sodium nitrate wastewater using the bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode, comprises the following steps:

[0068] The bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 was used as the cathode, and the Ir-Ru / Ti electrode was used as the anode (the effective area of the Ir-Ru / Ti electrode was 1×4 cm 2), were inserted into an H-type electrolytic cell separated by a Nafion 117 membrane. 80 mL of sodium nitrate wastewater containing Na2SO4 and an initial pH value of 7 was added to the cathode and anode chambers of the H-type electrolytic cell. The initial concentration of sodium nitrate in the wastewater was 50 mg·N / L and the concentration of Na2SO4 was 0.05 M. Under stirring at a speed of 400 rpm, the concentrations of 1 mA / cm 2 , 2 mA / cm 2 , 3 mA / cm 2 , 4 mA / cm 2 , 5 mA / cm 2 The electro-reduction catalytic reaction was carried out at a constant current density of for 5 hours, completing the degradation of sodium nitrate in the wastewater and obtaining ammonia.

[0069] During the electro-reduction catalytic reaction, 1.5 mL of sample was taken from the solution at regular intervals, filtered through a 0.22 μm membrane, and tested using a UV-visible spectrophotometer to determine the catalyst's nitrate removal rate, nitrite generation rate, ammonia generation rate, nitrogen generation rate, energy consumption, Faraday efficiency, and ammonia yield. The results are shown in Table 4.

[0070] Table 4 Treatment results of catalyst for nitrate

[0071]

[0072] Figure 9 Graph showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) on nitrate removal and ammonia synthesis at different current densities in Example 3 of the present invention. Figure 9 The nitrate removal rate is R(NO3 - ), the generation rate of nitrite is S(NO2 - ), the ammonia generation rate is S(NH4 + ), the nitrogen generation rate is S(N2), the energy consumption is EC, the Faraday efficiency is FE, and the ammonia yield is NH3 yield. Figure 9 It can be seen that as the current density increases from 1 mA / cm 2 Increase to 5 mA / cm 2 , the nitrate removal efficiency of NiCoP / NF was significantly improved; in particular, when the current density was increased from 1 mA / cm 2 Increased to 2 mA / cm 2 When NiCoP / NF is used to treat nitrate (NO3 - -N) removal rate increased from 45.9131% to 97.6761%, and the ammonia (NH4 +-N) selectivity (i.e., ammonia production rate) increased significantly from 81.6986% to 95.4437%. 2 When the current density is 2 mA / cm, the nitrate in the wastewater is completely removed. The improvement of the nitrate removal rate can be explained by Faraday's law, that is, the change of the substance on the electrode surface is proportional to the number of electrons it accepts, that is, the higher the current density, the higher the energy consumption. 2 Under these conditions, the lowest energy consumption is 0.098684 KWh / g N. Taking into account the factors such as nitrate removal rate, ammonia generation rate (i.e., ammonia selectivity), energy consumption, ammonia yield, and Faraday efficiency, when the current density is 2 mA / cm 2 It is more suitable for actual production operation and can be used for subsequent experimental exploration.

[0073] Example 4:

[0074] A method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention, specifically electrochemically reducing sodium nitrate wastewater using the bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode, comprises the following steps:

[0075] The bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 was used as the cathode, and the Ir-Ru / Ti electrode was used as the anode (the effective area of the Ir-Ru / Ti electrode was 1×4 cm 2 ), were inserted together into an H-type electrolytic cell separated by a Nafion 117 membrane. 80 mL of sodium nitrate wastewater containing Na2SO4 was added to the cathode and anode chambers of the H-type electrolytic cell. The initial concentration of sodium nitrate in the wastewater was 50 mg·N / L and the concentration of Na2SO4 was 0.05 M. The pH values of the wastewater were adjusted to 3, 5, 7, 9, and 11, respectively. The reaction mixture was stirred at a speed of 400 rpm and a flow rate of 2 mA / cm 2 The electro-reduction catalytic reaction was carried out under a constant current of for 5 hours to complete the degradation of sodium nitrate in the wastewater and obtain ammonia.

[0076] During the electro-reduction catalytic reaction, 1.5 mL of sample was taken from the solution at regular intervals, filtered through a 0.22 μm membrane, and tested using a UV-visible spectrophotometer to determine the catalyst's nitrate removal rate, nitrite generation rate, ammonia generation rate, nitrogen generation rate, energy consumption, Faraday efficiency, and ammonia yield. The results are shown in Table 5.

[0077] Table 5 Treatment results of nitrate by catalyst

[0078]

[0079] Figure 10 Graph showing the effects of the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) on nitrate removal and ammonia synthesis under different pH conditions in Example 4 of the present invention. Figure 10 The nitrate removal rate is R(NO3 - ), the generation rate of nitrite is S(NO2 - ), the ammonia generation rate is S(NH4 + ), the nitrogen generation rate is S(N2), the energy consumption is EC, the Faraday efficiency is FE, and the ammonia yield is NH3 yield. Figure 10 It can be seen that when the pH of the wastewater is 11, the removal rate of nitrate by NiCoP / NF is 75.47%, and its NO3 - The reduction efficiency decreased slightly; when the wastewater pH ranged from 3 to 9, the NiCoP / NF achieved a nitrate removal rate exceeding 86.9%. Specifically, compared with initial wastewater pH values of 3 and 5, NiCoP / NF demonstrated higher nitrate removal rates, ammonia selectivity (i.e., ammonia productivity), and Faradaic efficiency at initial pH values of 7 and 9. Furthermore, the ammonia selectivity (i.e., ammonia productivity) remained consistently greater than 95.4% in both neutral and alkaline environments. Furthermore, energy consumption remained low throughout the entire process, below 0.16 kWh / g N. In summary, the bimetallic phosphide three-dimensional self-supporting electrocatalyst employed in this invention is adaptable to a wide pH range, particularly in neutral and weakly alkaline environments.

[0080] Example 5:

[0081] The reusability of a bimetallic phosphide three-dimensional self-supporting electrocatalyst in reducing nitrate was investigated. Specifically, sodium nitrate wastewater was electrochemically reduced using the bimetallic phosphide three-dimensional self-supporting electrocatalyst as the cathode, including the following steps:

[0082] (1) The bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared in Example 1 was used as the cathode and the Ir-Ru / Ti electrode was used as the anode (the effective area of the Ir-Ru / Ti electrode was 1×4 cm 2 ), were inserted into an H-type electrolytic cell separated by a Nafion117 membrane. 80 mL of sodium nitrate wastewater containing Na2SO4 with an initial pH of 7 was added to the cathode and anode chambers of the H-type electrolytic cell. The initial concentration of sodium nitrate in the wastewater was 50 mg·N / L and the concentration of Na2SO4 was 0.05 M. Under stirring at a speed of 400 rpm and a flow rate of 2 mA / cm 2 The electro-reduction catalytic reaction is carried out under a constant current of 5 h to degrade sodium nitrate in the wastewater and obtain ammonia, completing one cycle.

[0083] (2) After completing one cycle, the bimetallic phosphide three-dimensional self-supporting electrocatalyst in step (1) is separated from the above reaction system, rinsed three times with ultrapure water and dried to obtain a regenerated bimetallic phosphide three-dimensional self-supporting electrocatalyst.

[0084] (3) Repeat steps (1) and (2) for a total of 6 cycles to complete the degradation of sodium nitrate in the wastewater and obtain ammonia.

[0085] During the electro-reduction catalytic reaction, 1.5 mL of sample was removed from the solution at regular intervals, filtered through a 0.22 μm membrane, and tested using a UV-visible spectrophotometer to determine the catalyst's nitrate removal rate, nitrite generation rate, ammonia generation rate, nitrogen generation rate, energy consumption, Faradaic efficiency, and ammonia yield.

[0086] Figure 11 This is a diagram of the cyclic degradation of nitrate by the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) in Example 5 of the present invention. Figure 12 This is a diagram showing the effect of reducing nitrate to synthesize ammonia using the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) in Example 5 of the present invention. Figure 12 The rate of ammonia production is S(NH4 + ), Faradaic efficiency is FE, ammonia yield is NH3 yield. Figure 11 and Figure 12 As can be seen, the bimetallic phosphide three-dimensional self-supporting electrocatalyst (NiCoP / NF) prepared by the present invention maintained a nitrate removal rate consistently exceeding 84% over six treatment cycles; the ammonia selectivity (i.e., ammonia productivity) remained consistently high at over 92%; nitrite accumulation was not observed during the electroreduction catalytic reaction and was virtually absent afterward; and neither the ammonia yield nor the Faradaic efficiency showed significant changes. Furthermore, testing the concentrations of metallic Ni and Co in the electrolyte after the reaction revealed that both were below the instrument's detection limit, indicating virtually no metal dissolution. These results demonstrate that the bimetallic phosphide three-dimensional self-supporting electrocatalyst employed in the present invention, as an electrode material, offers advantages such as stability and environmental friendliness, providing excellent electrocatalytic performance for long-term operation.

[0087] Based on the above results, it can be seen that the bimetallic phosphide three-dimensional self-supporting electrocatalyst used in the present invention has the advantages of rich pore structure, high specific surface area, large number of active sites, high catalytic activity, good stability, good applicability, no secondary pollution, and green environmental protection. It is a new type of electrocatalyst with excellent performance and good application prospects. When it is used as a cathode for electrochemical reduction of nitrate, it not only reduces nitrate and H +The bimetallic phosphide three-dimensional self-supporting electrocatalyst exhibits excellent adsorption and synergistic reduction properties, and can also induce the production of atomic hydrogen (H*), an active substance for reducing nitrates. This can further enhance catalytic activity without the addition of additional additives. Through the combination of direct and indirect reduction reaction mechanisms, the bimetallic phosphide three-dimensional self-supporting electrocatalyst of the present invention can efficiently remove nitrates from water and synthesize more ammonia. Furthermore, the present method for reducing nitrates to produce ammonia using the bimetallic phosphide three-dimensional self-supporting electrocatalyst offers advantages such as a simple process, convenient operation, low energy consumption, low cost, mild reaction conditions, excellent removal efficiency, high ammonia selectivity, no production of toxic and hazardous substances, and environmental friendliness. It not only efficiently reduces nitrates but also converts more nitrates into ammonia, offering high utility value and promising application prospects.

[0088] The above description is only a preferred embodiment of the present invention and does not constitute any formal limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for producing ammonia by reducing nitrate using a three-dimensional self-supporting bimetallic phosphide electrocatalyst, characterized in that: The method uses a bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode to perform electrochemical reduction treatment on nitrate; The bimetallic phosphide three-dimensional self-supporting electrocatalyst is based on a three-dimensional substrate material, on which nickel-cobalt bimetallic phosphide is in situ deposited. In the nickel-cobalt bimetallic phosphide, the nickel exists in the form of Ni 3+ , the existing forms of cobalt include Co 3+ and Co 2+ , the forms of phosphorus include phosphorus oxide and ionic phosphorus; The preparation method of the bimetallic phosphide three-dimensional self-supporting electrocatalyst comprises the following steps: immersing a three-dimensional substrate material in an electroplating solution for electroplating treatment to obtain the bimetallic phosphide three-dimensional self-supporting electrocatalyst; the electroplating solution contains nickel, cobalt, and phosphorus; the molar ratio of nickel, cobalt, and phosphorus in the electroplating solution is 1:1:8-15; and the electroplating treatment time is 10 minutes to 30 minutes.

2. The method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 1, characterized in that: The atomic ratio of nickel, cobalt and phosphorus in the three-dimensional self-supporting bimetallic phosphide electrocatalyst is 33.12:16.3:50.58; the nickel-cobalt bimetallic phosphide has a spherical structure.

3. The method for producing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 2, characterized in that: The three-dimensional substrate material includes at least one of foamed nickel, foamed copper, foamed cobalt, and foamed iron; the electrodeposition solution is prepared by dissolving a nickel salt, a cobalt salt, and a phosphate in water; the nickel salt is at least one of NiCl2, nickel nitrate, and nickel sulfate; the cobalt salt is at least one of CoCl2, cobalt nitrate, and cobalt sulfate; and the phosphate is at least one of NaH2PO4 and sodium hypophosphite; during the electrodeposition process, the three-dimensional substrate material is used as a working electrode, a platinum sheet electrode is used as a counter electrode, and a saturated Ag / AgCl electrode is used as a reference electrode; and during the electrodeposition process, the deposition potential is controlled to be -0.9V vs.AgCl to -1.1V vs.AgCl.

4. The method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 3, characterized in that: The time of the electrodeposition treatment is 15 minutes to 25 minutes.

5. The method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 4, characterized in that: The three-dimensional base material also includes the following treatment before use: washing the three-dimensional base material with hydrochloric acid, acetone, anhydrous ethanol and water in sequence, each washing for 15 minutes to 30 minutes, soaking the washed three-dimensional base material in a nickel salt solution for 4 hours, washing the soaked three-dimensional base material with water and anhydrous ethanol in sequence, and drying; the mass fraction of the hydrochloric acid is 5%, the concentration of the nickel salt solution is 0.1mM, the nickel salt solution is a nickel chloride solution, the drying is carried out under vacuum conditions, the drying temperature is 60°C, and the drying time is 6 hours.

6. The method for producing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to any one of claims 1 to 5, characterized in that: The electrochemical reduction treatment of nitrate wastewater is carried out using a bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode, comprising the following steps: using a bimetallic phosphide three-dimensional self-supporting electrocatalyst as a cathode and an Ir-Ru / Ti electrode as an anode, placing them in nitrate wastewater for an electroreduction catalytic reaction to complete the removal of nitrate and produce ammonia.

7. The method for producing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 6, characterized in that: During the electro-reduction catalytic reaction, the applied current density was controlled to be 1 mA / cm 2 ~5mA / cm 2 ; The electro-reduction catalytic reaction was carried out for 5 hours under stirring conditions at a stirring speed of 400 rpm.

8. The method for preparing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 7, characterized in that: The electro-reduction catalytic reaction process further includes adding an electrolyte to the nitrate wastewater to make the concentration of the electrolyte in the solution be 0.05M, and the electrolyte is sodium sulfate.

9. The method for producing ammonia by reducing nitrate using a bimetallic phosphide three-dimensional self-supporting electrocatalyst according to claim 8, characterized in that: The initial concentration of nitrate in the nitrate wastewater is 25 mg·N / L to 100 mg·N / L, the nitrate in the nitrate wastewater is at least one of sodium nitrate and potassium nitrate, and the pH value of the nitrate wastewater is 3 to 11.

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