A Cu-MOF-derived mixed-valence Cu-Cu x O / C catalysts, their preparation methods, and applications

Abstract

The application belongs to the field of catalytic chemistry, and particularly relates to a Cu-Cu x O / C catalyst and a preparation method thereof, the catalyst is composed of a carrier carbon and an active component of copper and copper oxide with mixed valence, KBr is added as an inducer during Cu-MOF nucleation and growth, and the obtained sample is pyrolyzed at low temperature in a nitrogen atmosphere to obtain Cu-Cu x O / C. The prepared Cu-MOF derived mixed valence Cu-Cu x O / C catalyst can efficiently catalyze the electro-reduction of nitrate to ammonia.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemistry technology, specifically relating to Cu-MOF-derived mixed-valence Cu-Cu x O / C catalysts, their preparation methods, and applications. Background Technology

[0002] Electrocatalytic denitrification is a green and energy-saving artificial ammonia production technology under environmental conditions. However, the conversion of N2 to NH3 requires a high dissociation energy (approximately 941 kJ / mol). -1 Nitrates (NO3) and N2 have very low solubility in aqueous solutions. - The dissociation energy of the NO bond in ) is relatively low (approximately 204 kJ / mol). -1 Furthermore, nitrogen oxides are a serious source of pollution, entering surface waters in the form of nitrates, causing eutrophication and red tides in coastal areas. Therefore, electrochemical nitrate reduction reactions can not only synthesize valuable NH3 but also alleviate environmental pollution. Currently, under strongly acidic conditions, Cu exhibits higher NO3RR exchange current density and yield; and Cu-based catalysts have advantages such as low cost, weak hydrogen evolution capacity, high conductivity, and the highest kinetics for the electrocatalytic reduction of nitrates to nitrites. However, Cu is prone to electrocatalytic passivation and gradual deactivation in alkaline environments, mainly due to the decomposition of copper hydrides (CuH, CuH2) generated at high cathode potentials, which inhibits electrocatalytic performance.

[0003] Currently, copper oxides are promising electrocatalysts for NO3RR. Copper oxide, with its diverse surface and bulk compositions, plays a crucial role in catalysis, existing in two stable crystalline phases: copper oxide (CuO) and cuprous oxide (Cu2O). Copper oxide is low-cost and possesses optimal physical and chemical properties, exhibiting structural stability, high thermal conductivity, environmental friendliness, non-toxicity, and good optical and electrical properties. Cuprous oxide (Cu2O) possesses excellent electron-donating characteristics and a tunable electronic structure, along with properties similar to noble metal electrodes (H2 splitting and H adsorption), making it suitable for nitrate reduction reactions.

[0004] Previous studies have shown that copper oxide forms the *NOH intermediate more readily than Cu. During nitrate reduction, due to electrostatic interactions, the positively charged CuO surface can adsorb more NO3-. - Furthermore, the built-in electric field promotes interfacial carrier transport, enhances conductivity, and attracts NO3. - Accumulation around the electrocatalyst optimizes the adsorption of reactants and intermediates by the catalyst, accelerating the nitrate electroreduction kinetics. Electron transfer from Cu2O to Cu at the interface inhibits HER, and the *NH2O→*NH2OH conversion is more likely to occur on the Cu2O surface, thereby improving the catalytic activity and selectivity of NO3RR.

[0005] Therefore, developing an effective preparation method to prepare carbon-supported copper and copper oxide composite catalysts is of great significance. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the above-mentioned problems and those existing in the prior art, the present invention is proposed.

[0008] Therefore, this invention provides a Cu-MOF-derived mixed-valence Cu-Cu x O / C catalyst, its preparation method, and its application. This Cu-Cu... x The spatial confinement of Cu within the metal-organic framework in the O / C catalyst restricts the position and size of Cu, maintaining a uniform and highly dispersed state during the reaction. By adding the inorganic salt KBr, the particle morphology and size of Cu-MOF nanocrystals can be controlled, and the occurrence morphology of Cu in the derivatives can be adjusted. The resulting Cu-MOFs can be derivatized into porous carbon-supported Cu and its oxides through low-temperature pyrolysis, giving full play to their synergistic advantages in electrocatalytic NO3RR, thus exhibiting good electrocatalytic nitrate reduction reaction activity and stability.

[0009] The objective of this invention is achieved through the following technical solution: a Cu-MOF-derived mixed-valence Cu-Cu x O / C catalyst, consisting of a carbon support and Cu in mixed valence states, Cu X Composed of O nanoparticles; Cu and Cu in mixed valence states. X O nanoparticles are loaded on a porous carbon support; Cu, C, and O elements are uniformly distributed in the catalyst.

[0010] As described in this invention, a Cu-MOF-derived mixed-valence Cu-Cu x A preferred embodiment of the method for preparing an O / C catalyst includes the following steps:

[0011] (1) The organic ligand and triethylamine were ultrasonically mixed evenly, then dissolved in a mixed solvent of ethanol and water after rotary evaporation and drying to form an organic ligand-TEA solution.

[0012] (4) Dissolve potassium bromide and hexadecyltrimethylammonium bromide in an ethanol-water solution to obtain a hexadecyltrimethylammonium bromide-potassium bromide solution;

[0013] (5) Add Cu to the mixed solution obtained by mixing the organic ligand-TEA solution and the hexadecyltrimethylammonium bromide-potassium bromide solution. 2+ The solution, after ultrasonic reaction at room temperature, forms a blue turbid solution; the precipitate is collected by centrifugation, washed, and dried. The resulting sample is then pyrolyzed at a low temperature of 250–350 °C in a nitrogen atmosphere at a rate of 2 °C / min to obtain MOF-derived Cu-Cu. x O / C catalyst.

[0014] In a preferred embodiment of the preparation method described in this invention, the molar ratio of the organic ligand to triethylamine is 1:2.16. The organic ligand includes, but is not limited to, aromatic carboxylic acids and imidazoles. The aromatic carboxylic acids include pyromellitic acid, terephthalic acid, isophthalic acid, and phthalic acid, etc., and the imidazoles include 2-methylimidazole, etc.

[0015] As a preferred embodiment of the preparation method described in this invention, the ultrasonic mixing is performed for 30 to 90 minutes to achieve uniform mixing, followed by rotary evaporation and vacuum drying at 60 to 100°C.

[0016] In a preferred embodiment of the preparation method described in this invention, the mixed solvent of ethanol and water is a mixed solution of ethanol and water with a volume ratio of 1:1 to 9.

[0017] In a preferred embodiment of the preparation method described in this invention, the potassium bromide and hexadecyltrimethylammonium bromide are dissolved in an ethanol-water solution, and the molar ratio of potassium bromide to hexadecyltrimethylammonium bromide is 1-5:0.25; the volume ratio of the 50 mL ethanol-water solution is 1:1.

[0018] As a preferred embodiment of the preparation method described in this invention, the mixed solution and Cu 2+ The solution undergoes an ultrasonic reaction at room temperature, Cu 2+ Solutions include, but are not limited to, CuSO4 solution, CuNO3 solution, CuCl2 solution, and Cu(acac)2 solution, wherein Cu 2+ The molar ratio of organic ligand to KBr in the mixed solution is 9:2.4:1-5; preferably, Cu 2+ The molar ratio of organic ligand to KBr in the mixed solution is 9:2.4:3.

[0019] As a preferred embodiment of the preparation method described in this invention, the centrifugation collection, washing and drying are performed by centrifuging at 10,000 rpm for 3 to 5 minutes, washing three times with deionized water and ethanol respectively, and then vacuum drying at 70 to 100°C.

[0020] As a preferred embodiment of the preparation method described in this invention, the low-temperature pyrolysis is to calcine at 250-350°C for 30 minutes under a N2 atmosphere at a heating rate of 2-5°C / min.

[0021] This invention also provides Cu-MOF-derived mixed-valence Cu-Cu x The application of O / C catalysts in the electrochemical catalytic reduction of nitrates to ammonia, specifically, in the mixed-valence Cu-Cu catalysts derived from supported Cu-MOF. x The O / C catalyst uses carbon paper as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode, forming a traditional three-electrode system for use at room temperature; the electrolyte is 1M KOH and 0.1M KNO3, and the process is carried out under magnetic stirring at a rate of 10 mV / s. -1 A linear sweep voltammetric plot was obtained at a scan rate from -0.8 to -1.0 V vs. Ag / AgCl, and a 1-hour chronoamperometry test was performed at a given potential to evaluate the yield and Faraday efficiency of NH3.

[0022] The beneficial effects of this invention are:

[0023] Traditional approaches typically involve electrochemical reduction to achieve a multiphase coexistence of transition metal Cu and its oxides. This invention utilizes a two-step process of direct precipitation and low-temperature pyrolysis to achieve the simultaneous presence of Cu and CuO on a porous carbon-supported catalyst. After low-temperature pyrolysis of the Cu-MOF, copper oxide is present in the catalyst, and the distribution of Cu, C, and O elements is uniform. Furthermore, an appropriate amount of KBr is added as an inducer during Cu-MOF nucleation and growth to regulate the catalyst composition, thereby optimizing charge transfer and electrolyte ion diffusion rates. This invention constructs a MOF-derived porous carbon material-supported copper and copper oxide composite catalyst through morphology control and valence state optimization. This facilitates the synergistic effects of the catalyst in the electrocatalytic NO3RR process, optimizes the material structure, increases the number of active sites, expands the capacitance, promotes charge migration in the electrode material, and enhances catalytic activity.

[0024] The preparation process of this invention is simple and the conditions are mild, providing a new approach for designing efficient and convenient electrode materials for the synthesis of ammonia by nitrate reduction. Attached image description:

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0026] Figure 1The above are XRD patterns of the catalysts in the comparative examples and Examples 1, 2 and 3 of this invention.

[0027] Figure 2 SEM images of the comparative catalyst (a) and the catalyst (b) of Example 2 described in this invention;

[0028] Figure 3 XPS plots of the catalysts in the comparative examples and Examples 1, 2 and 3 of this invention;

[0029] Figure 4 The LSV diagrams are for the catalysts of the comparative example and Example 2 described in this invention;

[0030] Figure 5 This is a comparison of ammonia production at -1.0V versus RHE between the comparative examples and catalysts of Examples 1, 2 and 3 described in this invention. Detailed Implementation

[0031] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0034] The concentration of hexadecyltrimethylammonium bromide (CTAB) used in the embodiments of the present invention is 25 mM; the concentration of CuSO4 solution used in the embodiments of the present invention is 0.1 M; and the ethanol used is anhydrous ethanol, ≥99.7%.

[0035] Example 1:

[0036] 2.1 g H3BTC (0.01 mol) was dissolved in 10 mL of triethylamine solution (30 wt%, 21.6 mmol), sonicated for 30 min to mix evenly, rotary evaporated, and vacuum dried at 70 °C to obtain BTC triethylamine salt. Then the salt was dissolved in 50 mL of ethanol and 200 mL of deionized water to form BTC-TEA solution.

[0037] 9.11 g of hexadecyltrimethylammonium bromide (CTAB, 25 mmol) and 0.29 g of KBr (0.1 mol) were dissolved in 50 mL of ethanol-water solution (1:1, v / v). Then, 9 mL of CuSO4 solution (0.1 M) and 6 mL of BTC-TEA solution were added. The mixture was sonicated at room temperature for 5 min, forming a blue turbid solution. The resulting blue precipitate was centrifuged at 10,000 rpm for 5 min, washed three times with water and twice with ethanol, and then dried under vacuum at 70 °C overnight. The sample was ground into powder, placed in a porcelain boat, and calcined in a tube furnace at a rate of 2 °C / min to 310 °C for 30 min under N2 atmosphere to finally obtain MOF-derived Cu-Cu. x O / C-0.1 catalyst.

[0038] Example 2:

[0039] 2.1 g H3BTC (0.01 mol) was dissolved in 10 mL of triethylamine solution (30 wt%), sonicated for 30 min to mix evenly, rotary evaporated, and vacuum dried at 70 °C to obtain BTC triethylamine salt. Then the salt was dissolved in 50 mL of ethanol and 200 mL of deionized water to form BTC-TEA solution.

[0040] 9.11 g of hexadecyltrimethylammonium bromide (CTAB, 25 mmol) and 0.89 g of KBr (0.3 mol) were dissolved in 50 mL of ethanol-water solution (1:1, v / v). Then, 9 mL of CuSO4 solution (0.1 M) and 6 mL of BTC-TEA solution were added. The mixture was sonicated at room temperature for 5 min, forming a blue turbid solution. The resulting gray solution was centrifuged at 10,000 rpm for 5 min, washed three times with water and twice with ethanol, and then vacuum dried overnight at 70 °C. The sample was ground into powder, placed in a porcelain boat, and calcined in a tube furnace at a rate of 2 °C / min to 310 °C for 30 min under N2 atmosphere to finally obtain MOF-derived Cu-Cu. x O / C-0.3 catalyst.

[0041] Example 3:

[0042] 2.1 g H3BTC (0.01 mol) was dissolved in 10 mL of triethylamine solution (30 wt%), sonicated for 30 min to mix evenly, rotary evaporated, and vacuum dried at 70 °C to obtain BTC triethylamine salt. Then the salt was dissolved in 50 mL of ethanol and 200 mL of deionized water to form BTC-TEA solution.

[0043] 9.11 g of hexadecyltrimethylammonium bromide (CTAB, 25 mmol) and 1.49 g of KBr (0.5 mol) were dissolved in 50 mL of ethanol-water solution (1:1, v / v). Then, 9 mL of CuSO4 solution (0.1 M) and 6 mL of BTC-TEA solution were added. The mixture was sonicated at room temperature for 5 min, forming a blue turbid solution. The resulting gray solution was centrifuged at 10,000 rpm for 5 min, washed three times with water and twice with ethanol, and then vacuum dried overnight at 70 °C. The sample was ground into powder, placed in a porcelain boat, and calcined in a tube furnace at a rate of 2 °C / min to 310 °C for 30 min under N2 atmosphere to finally obtain MOF-derived Cu-Cu. x O / C-0.5 catalyst.

[0044] Comparative example:

[0045] 2.1 g H3BTC (0.01 mol) was dissolved in 10 mL of triethylamine solution (30 wt%), sonicated for 30 min to mix evenly, rotary evaporated, and vacuum dried at 70 °C to obtain BTC triethylamine salt. Then the salt was dissolved in 50 mL of ethanol and 200 mL of deionized water to form BTC-TEA solution.

[0046] 9.11 g of hexadecyltrimethylammonium bromide (CTAB, 25 mmol) was dissolved in 50 mL of ethanol-water solution (1:1, v / v), followed by the addition of 9 mL of CuSO4 solution (0.1 M) and 6 mL of BTC-TEA solution. The mixture was sonicated at room temperature for 5 min, resulting in a blue turbid solution. The resulting gray solution was centrifuged at 10,000 rpm for 5 min, washed three times with water and twice with ethanol, and then dried under vacuum at 70 °C overnight. The sample was ground into powder, placed in a porcelain boat, and calcined in a tube furnace at a rate of 2 °C / min to 310 °C for 30 min under N2 atmosphere to finally obtain MOF-derived Cu-Cu. x O / C catalyst.

[0047] The catalysts prepared in Examples 1-3 and the comparative examples were characterized. Figure 1 Cu-Cu x O / C, Cu-Cu x O / C-0.1 and Cu-Cu x O / C-0.5 and Cu-Cu x The XRD pattern of the O / C-0.3 catalyst clearly shows the Cu-Cu in Examples 1 and 3. x O / C-0.1 and Cu-Cu x O / C-0.5 catalyst and Cu-Cu from Example 2 xThe XRD pattern of the O / C-0.3 catalyst is similar to that of the comparative Cu-Cu catalyst. x The XRD patterns of the O / C catalysts partially overlap. The peaks appearing at 27.1° for all four samples are diffraction peaks of carbon, indicating that BTC-TEA retains carbon after low-temperature pyrolysis under nitrogen and exhibits good crystallinity, further demonstrating the successful preparation of porous carbon materials. In addition, the comparative Cu-Cu... x The characteristic peaks of the O / C catalyst at 32.5°, 35.5°, 38.6°, 48.8°, and 61.6° are highly consistent with those of CuO (JCPDS 45-0937), and the characteristic peaks at 29.5°, 36.5°, 42.3°, and 61.6° are consistent with those of CuO. 2+1 The peaks at 43.3°, 50.4°, and 74.1° are consistent with those of O (JCPDS 05-0667), and belong to the characteristic diffraction peaks of Cu (JCPDS 04-0836); Cu-Cu x O / C-0.1, Cu-Cu x O / C-0.3 and Cu-Cu x The O / C-0.5 catalyst exhibits characteristic peaks at 36.3° and 42.4° similar to those of Cu. 2+1 The peaks at 43.3°, 50.4°, and 74.1° are consistent with those of O (JCPDS 05-0667), and the characteristic peaks at these peaks belong to those of Cu (JCPDS 04-0836), indicating the presence of Cu and copper oxide in the catalyst after low-temperature pyrolysis of Cu-MOF. This is likely due to the presence of oxygen in the organic ligands. Comparative example: Cu-Cu x The presence of CuO phase in the O / C catalyst may be due to incomplete pyrolysis, resulting in CuO not being fully converted into Cu. 2+1 O, Cu-Cu synthesized by adding KBr x O / C-0.1, Cu-Cu x O / C-0.3 and Cu-Cu x The O / C-0.5 sample does not contain pure CuO, possibly because KBr promotes the conversion of CuO to Cu. 2+1 O conversion further indicates that the addition of KBr during Cu-MOF growth can regulate the crystal phase composition of the catalyst.

[0048] Figure 2 (a) is Cu-Cu x SEM characterization of the O / C material indicates that the catalyst is a gel-like, flower-like catalyst composed of stacked small particles. (b) Cu-Cu x SEM characterization of the O / C-0.3 catalyst showed that the catalyst consists of layered carbon-encapsulated nanoparticles.

[0049] Figure 3 Cu-Cux O / C, Cu-Cu x O / C-0.1, Cu-Cu x O / C-0.3 and Cu-Cu x XPS characterization of the O / C-0.5 catalyst revealed that the dominant oxygen type was Cu-O, accounting for 89.3% of the total O types, indicating the presence of Cu-O bonds in the catalyst. The peak areas corresponding to Cu-O and CO bonds were minimized when 0.3 M of KBr was added. This demonstrates that the method disclosed in this invention can prepare Cu-based catalysts with mixed valence states, and the valence state changes can be controlled by adjusting the amount of KBr added.

[0050] Application Example 1:

[0051] Cu-Cu x O / C, Cu-Cu x O / C-0.1, Cu-Cu x O / C-0.3 and Cu-Cu x O / C-0.5 catalyst material is used in electrochemical nitrate reduction reaction.

[0052] The performance of the nitrate reduction reaction was evaluated on a CHI760E electrochemical workstation equipped with a 50 mL sealed H-shaped electrochemical electrolytic cell separated by a Nafion 115 membrane. A conventional three-electrode system was used at room temperature, with carbon paper loaded with the catalyst directly used as the working electrode, and Ag / AgCl (saturated KCl) and platinum wire used as the reference and counter electrodes, respectively. The electrolyte was 1 M KOH and 0.1 M KNO3, and the reaction was carried out under magnetic stirring (800 rpm) at a rate of 10 mV / s. -1 The scan rate was adjusted from -0.2 to -1.0 V vs. Ag / AgCl to obtain linear sweep voltammetry (LSV), and a 1-hour chronoamperometry test was performed at a given potential to evaluate the yield and Faraday efficiency of NH3.

[0053] Table 1 - Electrocatalytic reduction performance of various materials for ammonia production from nitrate at 1.0V vs. RHE voltage.

[0054]

[0055] Figure 4 Cu-Cu x O / C and Cu-Cu x The LSV of the O / C-0.3 catalyst indicates that the addition of NO3... - Previously, the HER catalytic current of both catalysts in 1M KOH solution started at approximately -0.4V, and the current density increased with the addition of 0.1M NO3. - The potentials increased significantly, shifting positively to -0.1V. Relatively speaking, Cu-Cu...x The current density of O / C-0.3 is higher than that of other catalysts.

[0056] Figure 5 To compare several Cu-Cu x The NO3RR activity of the O / C catalyst at -1.0V indicates that Cu-Cu x The O / C-0.3 catalyst exhibits the highest NH3 yield and NH3 Faradaic efficiency, with an NH3 yield of approximately 17.64 mg. NH3 h -1 cm -2 The NH3 Faraday efficiency is approximately 79.9%. This indicates that the component with high catalytic activity for nitrate reduction is Cu. 0 / Cu + Mutually.

[0057] Depend on Figure 4 , 5 As shown in Table 1, Cu-MOF-derived mixed-valence Cu-Cu alloys can be successfully prepared with the addition of KBr at concentrations ranging from 0.1 to 0.5 M. X O / C catalysts are used, but their effects vary. Specifically, when the concentration of the added inducing agent KBr is 0.3M, the prepared Cu-Cu... x The O / C-0.3 catalyst exhibited optimal nitrate reduction activity. This is likely because the optimal concentration of the added inducing agent KBr was 0.3 M. A MOF-derived porous carbon material-supported copper and copper oxide composite catalyst was constructed through morphology control and valence state optimization. Adding an appropriate amount of KBr during Cu-MOF nucleation and growth adjusted the catalyst composition, optimized the material structure, increased the number of active sites, and promoted charge migration in the electrode material, thereby improving nitrate reduction activity.

[0058] The spatial confinement of Cu within the metal-organic framework restricts its position and size, maintaining a uniform and highly dispersed state during the reaction. Furthermore, the addition of inorganic salt KBr controls the particle morphology and size of Cu-MOF nanocrystals, adjusting the occurrence morphology of Cu in the derivatives. This allows the obtained Cu-MOFs to be pyrolyzed at low temperatures to yield porous carbon-supported Cu and its oxides, leveraging their synergistic advantages in electrocatalytic NO3RR. Consequently, Cu exhibits excellent electrocatalytic nitrate reduction activity and stability, demonstrating potential for industrial applications.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A Cu-MOF-derived mixed-valence Cu-Cu x O / C catalyst, characterized in that The Cu-MOF-derived mixed-valence Cu-Cu x The O / C catalyst consists of a carbon support and Cu in mixed valence states. x Composed of O nanoparticles; Cu and Cu in mixed valence states. x O nanoparticles are supported on a porous carbon support; Cu, C, and O elements are uniformly distributed in the catalyst; The Cu-MOF-derived mixed-valence Cu-Cu x The preparation method of the O / C catalyst includes the following steps: (1) Mix 0.01 mol H3BTC and 10 mL of 30 wt% triethylamine solution by ultrasonication, evaporate by rotary evaporation and dry, and then dissolve in a mixed solvent of 50 mL ethanol and 200 mL water to form BTC-TEA solution. (2) Dissolve potassium bromide and hexadecyltrimethylammonium bromide in an ethanol-water solution to obtain a hexadecyltrimethylammonium bromide-potassium bromide solution; the mass of hexadecyltrimethylammonium bromide is 9.11 g, and the mass of potassium bromide is 0.89 g or 1.49 g; the volume of the ethanol-water solution is 50 mL; (3) In the hexadecyltrimethylammonium bromide-potassium bromide solution obtained in step (2), add 9 mL of 0.1 mol / L CuSO4 solution and 6 mL of BTC-TEA solution. After ultrasonic reaction at room temperature, a blue turbid solution is formed. The precipitate is collected by centrifugation, washed, and dried. The obtained sample is then pyrolyzed at a low temperature of 250~350 ℃ in a nitrogen atmosphere at a rate of 2 ℃ / min to obtain MOF-derived Cu-Cu. x O / C catalyst.

2. The Cu-MOF-derived mixed-valence Cu-Cu as described in claim 1 x The method for preparing the O / C catalyst is characterized by, Includes the following steps: (1) Mix 0.01 mol H3BTC and 10 mL of 30 wt% triethylamine solution by ultrasonication, evaporate by rotary evaporation and dry, and then dissolve in a mixed solvent of 50 mL ethanol and 200 mL water to form BTC-TEA solution. (2) Dissolve potassium bromide and hexadecyltrimethylammonium bromide in an ethanol-water solution to obtain a hexadecyltrimethylammonium bromide-potassium bromide solution; the mass of hexadecyltrimethylammonium bromide is 9.11 g, and the mass of potassium bromide is 0.89 g or 1.49 g; the volume of the ethanol-water solution is 50 mL; (3) In the hexadecyltrimethylammonium bromide-potassium bromide solution obtained in step (2), add 9 mL of 0.1 mol / L CuSO4 solution and 6 mL of BTC-TEA solution. After ultrasonic reaction at room temperature, a blue turbid solution is formed. The precipitate is collected by centrifugation, washed, and dried. The obtained sample is then pyrolyzed at a low temperature of 250~350 ℃ in a nitrogen atmosphere at a rate of 2 ℃ / min to obtain MOF-derived Cu-Cu. x O / C catalyst.

3. The Cu-MOF-derived mixed-valence Cu-Cu as described in claim 1 x The application of O / C catalysts is characterized by... The Cu-MOF-derived mixed-valence Cu-Cu x Application of O / C catalysts in the electrochemical catalytic reduction of nitrates to produce ammonia.

4. The Cu-MOF-derived mixed-valence Cu-Cu according to claim 3 x The application of O / C catalysts is characterized by... Cu-Cu derived from supported Cu-MOF x The O / C catalyst uses carbon paper as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode, forming a traditional three-electrode system for use at room temperature. The electrolyte is 1 M KOH and 0.1 M KNO3, and the process is carried out under magnetic stirring at a rate of 10 mV s⁻¹. -1 A linear sweep voltammogram was obtained by scanning at a rate from -0.8 to -1.0 V vs. Ag / AgCl, and a 1-hour chronoamperometry test was performed at a given potential to evaluate the yield and Faraday efficiency of NH3.

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