1. A preparation method of a Cu-C-N metal organic frame electrocatalyst for reducing nitrate into ammonia is characterized by comprising the following preparation steps:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution;

(3) adding the second solution into the first solution to form a suspension by ultrasonic treatment, transferring the suspension into a reaction kettle, reacting at a constant temperature for a period of time, and cooling to room temperature to obtain a dark blue precipitate;

(4) washing the collected dark blue precipitate with absolute ethyl alcohol, performing centrifugal separation, and drying under a vacuum condition to obtain a precursor;

(5) and calcining the precursor under vacuum protection to obtain a final product.

2. The method of claim 1, wherein in step (1), the concentration of 2-methylimidazole in the first solution is 10-20mmol/L, and the addition is performed by adding methanol to 2-methylimidazole.

3. The method of claim 1 or 2, wherein in step (2), the concentration of zinc nitrate hexahydrate in the second solution is 3-10mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added to the vessel in this order.

4. The method of claim 1, wherein in step (2), the concentration of copper acetylacetonate in the second solution is 1-1.5 mmol/L.

5. The method for preparing a Cu-C-N metal-organic framework electrocatalyst for nitrate reduction to ammonia according to claim 1 or 4, wherein in step (3), the ratio of the volume of the second solution added to the volume of the first solution is 1: 1.8-2.2.

6. The method for preparing a Cu-C-N metal-organic framework electrocatalyst for nitrate reduction to ammonia according to claim 1, wherein in step (3), the sonication time is 10-20 min.

7. The method for preparing a Cu-C-N metal-organic framework electrocatalyst for nitrate reduction to ammonia according to claim 1, wherein in step (3), the isothermal reaction conditions are: the heating temperature is 100-200 ℃, and the reaction time is 4-8 h.

8. The method for preparing a Cu-C-N metal-organic framework electrocatalyst for nitrate reduction to ammonia according to claim 1, wherein in step (4), the centrifugal rotation speed of the centrifugal separation is 3000-8000 r/min.

9. The method for preparing a Cu-C-N metal-organic framework electrocatalyst for nitrate reduction to ammonia according to claim 1 or 8, wherein in step (4), the vacuum drying temperature is 65-75 ℃ and the drying time is 2-2.5 h.

10. The method for preparing a Cu-C-N metal-organic framework electrocatalyst for nitrate reduction to ammonia according to claim 9, wherein in step (5), the calcination temperature is 800-950 ℃ and the calcination time is 2.8-3.2 h.

Background

Haber-boschThe process enables large scale production of ammonia with typical yields of less than 200mmol gcat for this industrial Nitrogen Reduction Reaction (NRR)^-1h^-1. This process is energy intensive because it is carried out at high temperatures of 400-. However, these reaction rates and bias current densities are typically less than 10mmol gcat, respectively^-1h^-1And 1mA cm^-2The N.ident.N bond cleavage of nitrogen requires 941kJ/mol, whereas the energy for decomposition of nitrate into the deoxygenated state is much lower, only 204 kJ/mol. From an energy perspective, it is of great interest to explore the electrocatalytic nitrate reduction reaction (NITRR) as a promising tool for low temperature ammonia synthesis. The NITRR occurs at a solid-liquid interface, and the reaction energy barrier is lower than that of the solid-liquid interface. It also has an advantage in selectivity, since the kinetics of the nitro group can optimize the competing Hydrogen Evolution Reaction (HER). In addition, nitrate is very abundant in the natural environment due to the use of nitrogen-containing fertilizers and pesticides worldwide. It is known that nitrate in drinking water can cause diseases such as methemoglobinemia and non-hodgkin's lymphoma; electrocatalysis of nitrate to ammonia potentially solves energy and environmental problems.

The electrocatalytic process of nitrate nitrogen conversion to ammonia involves 9 protons and 8 electrons (NO)₃ ^-+9H⁺+8e^-→NH₃+3H₂O), nitrogen oxyanions and dinitrogen are inevitably produced in the process, which are undesirable by-products. For conventional metal-based catalysts, better selectivity of nitrate to ammonia can only be obtained at low overpotentials and low current densities, while hydrogen evolution is still dominant at high overpotentials, further exploiting the potential of nitro groups in ammonia synthesis depends on creating more efficient electrocatalysts.

The invention discloses a patent No. CN202011032642.1 with the patent name of 'a catalyst for electrocatalytic reduction of nitrate and a preparation method and application thereof', relates to the technical field of catalyst preparation, in particular to a preparation method of a catalyst for electrocatalytic reduction of nitrate, which comprises the following steps: forming a nickel oxide layer on the surface of the foamed nickel by using the foamed nickel as a substrate to obtain a compound; and depositing ruthenium nano particles on the compound by adopting a ruthenium trichloride solution and an electrochemical cyclic voltammetry to obtain the Ni-Ru composite catalyst. The invention provides a preparation method of a catalyst for electrocatalytic reduction of nitrate, which has the advantages of simple preparation method process, low Ru loading amount of the catalyst and low catalyst cost. It is disadvantageous in that the catalytic efficiency thereof is to be improved.

Disclosure of Invention

The invention aims to overcome the problem of low catalytic efficiency of the existing catalyst for converting nitrate into ammonia, and provides a preparation method of a Cu-C-N metal organic framework electrocatalyst for reducing nitrate into ammonia, and the prepared Cu-C-N metal organic framework structure nano material electrocatalyst has high one-dimensional structure, rich micropores and larger specific surface area due to the core/shell structure nano particles, so that the electrocatalyst can generate higher electrocatalytic activity in an electrochemical workstation and has wide application prospect in the field of electrocatalysis; the synthesis method has the characteristics of simple process, low energy consumption, mild conditions, good product appearance and the like, and is suitable for large-scale production and application.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a Cu-C-N metal organic framework electrocatalyst for reducing nitrate into ammonia comprises the following preparation steps: (1) dissolving 2-methylimidazole in a methanol solution to form a first solution;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution;

(3) adding the second solution into the first solution to form a suspension by ultrasonic treatment, transferring the suspension into a reaction kettle, reacting at a constant temperature for a period of time, and cooling to room temperature to obtain a dark blue precipitate;

(4) washing the collected dark blue precipitate with absolute ethyl alcohol, performing centrifugal separation, and drying under a vacuum condition to obtain a precursor;

(5) and calcining the precursor under vacuum protection to obtain a final product.

In the step (1) and the step (2), methanol is used for dissolving, 2-methylimidazole, zinc nitrate hexahydrate and copper acetylacetonate form an inorganic compound containing a specific copper atom as a precursor, the precursor is wrapped by an imidazole zeolite framework (ZIF-8) before pyrolysis, and in the ZIF-8 synthesis process, monoatomic copper is wrapped in a cavity of the ZIF-8 in situ to form a Cu @ ZIF-8 hybrid structure. During the subsequent pyrolysis treatment, copper acetylacetonate in the cavity is decomposed into Cu clusters, whereas the separation of the ZIF-8 cavity prevents the Cu clusters from being aggregated well, whereas ZIF-8 is converted into N-doped carbon by evaporation of Zn under high temperature calcination. Therefore, the single atom is anchored on N-doped carbon (namely Cu-C-N), and the catalyst with high catalytic activity and high catalytic efficiency is finally prepared.

Preferably, in the step (1), the concentration of 2-methylimidazole in the first solution is 10 to 20mmol/L, and the adding sequence is that methanol is added to 2-methylimidazole.

Preferably, in the step (2), the concentration of the zinc nitrate hexahydrate in the second solution is 3-10mmol/L, and the zinc nitrate hexahydrate, the copper acetylacetonate and the methanol are added into the container in sequence.

The reason for adopting the above-mentioned addition sequence is: this sequence favors the formation of a dodecahedral morphology, and for nitrate adsorption.

Preferably, in the step (2), the concentration of copper acetylacetonate in the second solution is 1 to 1.5 mmol/L.

Preferably, in the step (3), the volume ratio of the second solution to the first solution is 1: 1.8-2.2.

Preferably, in the step (3), the ultrasonic treatment time is 10-20 min.

Preferably, in the step (3), the isothermal reaction conditions are as follows: the heating temperature is 100-200 ℃, and the reaction time is 4-8 h.

Preferably, in the step (4), the centrifugal speed of the centrifugal separation is 3000-8000 r/min.

Preferably, in the step (4), the vacuum drying temperature is 65-75 ℃, and the drying time is 2-2.5 h.

Preferably, in the step (5), the calcining temperature is 800-950 ℃, and the calcining time is 2.8-3.2 h.

Under vacuum conditions, pyridine nitrogen species are favored for the formation, while the pyridine nitrogen species favor the adsorption and reduction of nitrate. Therefore, the invention has the following beneficial effects:

the invention has the following beneficial effects:

(1) the Cu-C-N metal organic framework electrocatalyst is applied to the catalysis of reducing ammonia by nitrate for the first time, a better effect is obtained, and the ammonia production activity reaches 246440.3ug^-1.h^-1The Faraday efficiency is close to 100%;

(2) in the process of synthesizing the Cu-C-N metal organic framework electrocatalyst, the preparation and the addition sequence of the first solution and the second solution define and prepare the dodecahedral structure which has uniform and regular surface appearance, unique electronic structure and larger specific surface area and single metal atom;

(3) the catalyst particles prepared by the invention have high one-dimensional structure, rich micropores and larger specific surface area, so that the catalyst particles can generate higher electrocatalytic activity in an electrochemical workstation, and have wide application prospect in the field of electrocatalysis.

Drawings

FIG. 1 is an electron microscope image of the Cu-C-N metal organic framework material prepared in example 1.

FIG. 2 is an electron microscope image of the Cu-C-N metal organic framework material electrocatalyst prepared in example 2.

FIG. 3 is an electron microscope image of the Cu-C-N metal organic framework material electrocatalyst prepared in comparative example 1.

FIG. 4 is the XRD pattern of the Cu-C-N metal organic framework material electrocatalyst prepared in example 1.

FIG. 5 is a vacuum scan of the Cu-C-N metal organic framework material electrocatalyst prepared in example 1 after calcination is complete.

FIG. 6 is a graph showing the reduction activity of Cu-C-N metal-organic framework material electrocatalyst on potassium nitrate and Faraday efficiency prepared in example 1.

Detailed Description

The invention is further described with reference to specific embodiments.

General examples

A method of preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in methanol solution to form a first solution with the concentration of 2-methylimidazole of 10-20mmol/L, wherein the adding sequence is that methanol is added into 2-methylimidazole;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 3-10mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into the container in sequence; the concentration of copper acetylacetonate in the second solution is 1-1.5 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 10-20min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 100-200 ℃ for 4-8 h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 1.8-2.2;

(4) cleaning the collected dark blue precipitate by absolute ethyl alcohol, performing centrifugal separation at 3000-8000 r/min, and drying at 65-75 ℃ for 2-2.5 h under a vacuum condition to obtain a precursor;

(5) and calcining the precursor for 2.8-3.2h at 800-950 ℃ under vacuum protection to obtain a final product.

Example 1

A method of preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution having a concentration of 15mmol/L of 2-methylimidazole by adding methanol to 2-methylimidazole in the order of addition;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 6mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into a container in sequence; the concentration of copper acetylacetonate in the second solution is 1.2 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 15min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 150 ℃ for 6h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2;

(4) washing the collected dark blue precipitate with absolute ethanol, centrifuging at 5000r/min, and drying at 70 deg.C under vacuum for 2.2h to obtain precursor;

(5) and calcining the precursor for 3h at 900 ℃ under vacuum protection to obtain a final product.

Example 2

A method of preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution of 2-methylimidazole with a concentration of 10mmol/L, the order of addition being that methanol is added to 2-methylimidazole;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 3mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into a container in sequence; the concentration of copper acetylacetonate in the second solution is 1.5 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 10min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 200 ℃ for 4h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 1.8;

(4) washing the collected dark blue precipitate with absolute ethyl alcohol, centrifuging at 3000r/min, and drying at 75 ℃ for 2h under a vacuum condition to obtain a precursor;

(5) and calcining the precursor at 800 ℃ for 3.2h under vacuum protection to obtain a final product.

Example 3

A method of preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution having a concentration of 20mmol/L of 2-methylimidazole by adding methanol to 2-methylimidazole in the order of addition;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 10mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into a container in sequence; the concentration of copper acetylacetonate in the second solution is 1.5 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 20min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 200 ℃ for 4h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2.2;

(4) cleaning the collected dark blue precipitate with absolute ethanol, centrifuging at 8000r/min, and drying at 75 deg.C under vacuum for 2h to obtain precursor;

(5) and calcining the precursor for 2.8h at 950 ℃ under vacuum protection to obtain a final product.

Comparative example 1 (differing from example 1 in that the calcination temperature of step (5) was reduced from 900 ℃ to 700 ℃) a process for preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution having a concentration of 15mmol/L of 2-methylimidazole by adding methanol to 2-methylimidazole in the order of addition;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 6mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into a container in sequence; the concentration of copper acetylacetonate in the second solution is 1.2 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 15min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 150 ℃ for 6h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2;

(4) washing the collected dark blue precipitate with absolute ethanol, centrifuging at 5000r/min, and drying at 70 deg.C under vacuum for 2.2h to obtain precursor;

(5) and calcining the precursor for 3h at 700 ℃ under vacuum protection to obtain a final product.

Comparative example 2 (differing from example 1 in that the calcination of step (5) was carried out under a nitrogen atmosphere.) a method for preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution having a concentration of 15mmol/L of 2-methylimidazole by adding methanol to 2-methylimidazole in the order of addition;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 6mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into a container in sequence; the concentration of copper acetylacetonate in the second solution is 1.2 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 15min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 150 ℃ for 6h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2;

(4) washing the collected dark blue precipitate with absolute ethanol, centrifuging at 5000r/min, and drying at 70 deg.C under vacuum for 2.2h to obtain precursor;

(5) and calcining the precursor at 900 ℃ for 3h under the protection of nitrogen to obtain a final product.

Comparative example 3 (differing from example 1 in that 2-methylimidazole is sequentially added to methanol in step (1)) a method of preparing a Cu-C-N metal-organic framework electrocatalyst for nitric acid reduction to ammonia comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution of 2-methylimidazole with a concentration of 15mmol/L, the order of addition being that 2-methylimidazole is added to methanol;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 6mmol/L, and the zinc nitrate hexahydrate, copper acetylacetonate and methanol are added into a container in sequence; the concentration of copper acetylacetonate in the second solution is 1.2 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 15min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 150 ℃ for 6h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2;

(4) washing the collected dark blue precipitate with absolute ethanol, centrifuging at 5000r/min, and drying at 70 deg.C under vacuum for 2.2h to obtain precursor;

(5) and calcining the precursor for 3h at 900 ℃ under vacuum protection to obtain a final product.

Comparative example 4 (different from example 1 in that the order of addition to the vessel in step (2) was copper acetylacetonate, zinc nitrate hexahydrate, methanol.)

A method of preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution having a concentration of 15mmol/L of 2-methylimidazole by adding methanol to 2-methylimidazole in the order of addition;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 6mmol/L, and the zinc nitrate hexahydrate and the methanol are added into a container in the sequence of copper acetylacetonate, zinc nitrate hexahydrate and methanol; the concentration of copper acetylacetonate in the second solution is 1.2 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 15min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 150 ℃ for 6h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2;

(4) washing the collected dark blue precipitate with absolute ethanol, centrifuging at 5000r/min, and drying at 70 deg.C under vacuum for 2.2h to obtain precursor;

(5) and calcining the precursor for 3h at 900 ℃ under vacuum protection to obtain a final product.

Comparative example 5 (different from example 1 in that the order of addition to the vessel in step (2) was methanol, zinc nitrate hexahydrate, copper acetylacetonate.)

A method of preparing a Cu-C-N metal-organic framework electrocatalyst for the reduction of nitric acid to ammonia, comprising the preparation steps of:

(1) dissolving 2-methylimidazole in a methanol solution to form a first solution having a concentration of 15mmol/L of 2-methylimidazole by adding methanol to 2-methylimidazole in the order of addition;

(2) dissolving zinc nitrate hexahydrate and copper acetylacetonate in a methanol solution to form a second solution; the concentration of the zinc nitrate hexahydrate in the second solution is 6mmol/L, and the adding sequence of the zinc nitrate hexahydrate and the copper acetylacetonate into the container is methanol, zinc nitrate hexahydrate and copper acetylacetonate; the concentration of copper acetylacetonate in the second solution is 1.2 mmol/L;

(3) adding the second solution into the first solution, performing ultrasonic treatment for 15min to form a suspension, transferring the suspension into a reaction kettle, performing constant-temperature reaction at 150 ℃ for 6h, and cooling to room temperature to obtain a dark blue precipitate; the volume ratio of the second solution to the first solution is 1: 2;

(4) washing the collected dark blue precipitate with absolute ethanol, centrifuging at 5000r/min, and drying at 70 deg.C under vacuum for 2.2h to obtain precursor;

(5) and calcining the precursor for 3h at 900 ℃ under vacuum protection to obtain a final product.

The final products of the above examples and comparative examples were weighed to obtain 4mg, and 750u of deionized water, 200u of isopropyl alcohol and 50u of naphthol were added to prepare a catalyst solution, and 30u of the catalyst solution was dropped onto 1cm by 1cm of carbon paper to measure the reduction activity.

Electrocatalytic test method:

the prepared Cu-C-N metal organic framework is subjected to a nitric acid reduction catalytic activity test, and the test method comprises the following steps:

the test adopts a three-electrode system, carbon paper is clamped by an electrode clamp to be used as a working electrode, a silver/silver chloride electrode is used as a reference electrode, a platinum net is used as a counter electrode, 1mol/L potassium hydroxide and 1mol/L potassium nitrate mixed solution is used as an electrolyte solution, an electrochemical workstation is used for providing a power supply, the applied voltage range is-0.2 to-1.0 v, and the test duration is 1 hour.

And (3) performance characterization:

SEM test is carried out on the Cu-C-N metal organic framework material electro-catalysts prepared in the embodiments 1-2 and the comparative example 1 to observe the appearance; XRD test is carried out on the Cu-C-N cubic block structure nano material electro-catalyst prepared in the examples 1-2 and the comparative example 1 of the invention; the electrochemical tests for nitric acid reduction were performed on the Cu-C-N metal organic framework material electrocatalysts prepared in examples 1-2 of the present invention and comparative example 1.

TABLE 1 Process and Performance parameters for Cu-C-N Metal organic framework electrocatalyst materials

Item	Catalyst and process for preparing same	Calcination temperature (. degree.C.)	Voltage of	Activity (ug. mg)-1.h-1)	Faraday efficiency (%)
						Example 1	Cu-C-N	900°	-1V	246440.3	95.48
Example 2	Cu-C-N	800°	-1V	205887.4	89.4
						Example 3	Cu-C-N	950°	-1V	213398.5	87.8
Comparative example 1	Cu-C-N	700°	-1V	104495.0	79.1
						Comparative example 2	Cu-C-N	900°	-1V	237753.1	90.11
Comparative example 3	Cu-C-N	900°	-1V	213376.4	91.28
						Comparative example 4	Cu-C-N	900°	-1V	201189.7	90.79
Comparative example 5	Cu-C-N	900°	-1V	209981.1	90.62

Comparative example 1 differs from example 1 in that the calcination temperature of step (5) is reduced from 900 ℃ to 700 ℃; the temperature has a certain influence on the evaporation of Zn, and Zn has a certain influence on the formation of monoatomic Cu. The degree of Cu-C-N graphitization at 900 ℃ is higher, which is beneficial to nitrate reduction.

Comparative example 2 differs from example 1 in that the calcination of step (5) is carried out under a nitrogen atmosphere; vacuum conditions to form pyridine nitrogen species are more favorable for nitrate reduction.

Comparative example 3 differs from example 1 in that 2-methylimidazole is added to methanol in the order of addition in step (1); the order of addition is favorable for imidazole zeolite framework formation, and the regular surface structure is favorable for nitrate adsorption.

Comparative example 4 differs from example 1 in that the order of addition of the vessels in step (2) is copper acetylacetonate, zinc nitrate hexahydrate, methanol; the order of addition is favorable for imidazole zeolite framework formation, and the regular surface structure is favorable for nitrate adsorption.

Comparative example 5 differs from example 1 in that the order of addition to the vessel in step (2) is methanol, zinc nitrate hexahydrate, copper acetylacetonate; the order of addition is favorable for imidazole zeolite framework formation, and the regular surface structure is favorable for nitrate adsorption.

The following problems are illustrated by FIGS. 1-6:

as can be seen from FIG. 1, the Cu-C-N metal-organic framework material electrocatalysts prepared in example 1 of the present invention are mostly present in the form of blocks and have uniform sizes, and are tested by electrochemical workstations using 1M KOH and 1M KNO₃In the electrolyte, the measured nitric acid reduction rate is good. As can be seen from FIG. 3, the Cu-C-N MOM electrocatalyst prepared in example 2 of the present invention is mostly present in a block state and has non-uniform size, and is tested by the electrochemical workstationIn 1M KOH and 1M KNO₃In the electrolyte, the measured nitric acid reduction rate is better.

As can be seen from FIG. 3, the Cu-C-N metal-organic framework material electrocatalysts prepared by comparative example 1 of the present invention are mostly present in a bulk state and are not uniform in size, and were tested by electrochemical workstation at 1M KOH and 1M KNO₃In the electrolyte, the measured reduction rate of the nitric acid is poor; as can be seen from fig. 4, the XRD pattern of Cu — C — N prepared by the present invention shows no Cu atom clusters, indicating the success of the catalyst preparation of monoatomic Cu. As is clear from FIG. 5, the 900 ℃ vacuum scanning chart shows that most of the Cu-C-N metal-organic framework material electrocatalysts exist in a block state and have uniform sizes, and as is clear from FIG. 6, the Cu-C-N activity at 900 ℃ is the highest in the present invention as shown by the nitric acid reduction activity and the Faraday efficiency chart.

It can be seen from the data of the examples and comparative examples that the above requirements can be satisfied in all aspects only by the scheme within the scope of the claims of the present invention, an optimized scheme can be obtained, a Cu-C-N metal organic framework electrocatalyst with high catalytic activity can be obtained, and the material utilization and recovery rate can be maximized by each process parameter. The change of the mixture ratio, the replacement/addition/subtraction of raw materials or the change of the feeding sequence can bring corresponding negative effects.

The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.