CN111477889A - A single-atom iron-nitrogen co-doped carbon electrocatalyst and its preparation method and application - Google Patents

Abstract

The invention relates to the technical field of electrocatalysts, and discloses a single-atom iron-nitrogen co-doped carbon electrocatalyst and a preparation method and application thereof. In the pores of the metal-organic framework ZIF-8 with a mesoporous structure, the catalyst includes micropores with a pore diameter of less than 3 nm, and mesopores with a diameter of 3-5 nm and 29-32 nm; adding iron phthalocyanine to the imidazole solution; (2) adding a solution of zinc nitrate, and mixing to obtain an iron phthalocyanine composite material encapsulated by ZIF-8; (3) calcining and pickling the composite material to obtain the electro-optical material of the present invention. catalyst. The macroscopic morphology of the catalyst is regular dodecahedron, which is regular and reproducible. When applied, the electrolyte can transfer mass through the abundant mesoporous structure in the catalyst, realizing high selectivity, high activity and low electrocatalytic CO2 to _CO preparation. overpotential.

Description

A single-atom iron-nitrogen co-doped carbon electrocatalyst and its preparation method and application

technical field

The invention relates to the technical field of electrocatalysts, in particular to a single-atom iron-nitrogen co-doped carbon electrocatalyst and a preparation method and application thereof.

Background technique

Traditional biological and chemical wastewater treatment technologies mainly oxidize organic pollutants in wastewater into _CO2 emissions, which not only waste the chemical energy stored in wastewater, but also emit a large amount of greenhouse gases. _{Bioelectrochemical} system is one of the most promising technologies for converting chemical energy in wastewater into electrical energy in recent years, and is widely used in wastewater treatment. a specific reduction reaction.

Among many reduction reactions, electrocatalytic _CO2 reduction reaction can reduce _CO2 generated from wastewater treatment and convert it into high value-added chemical fuels, such as methane, formic acid, CO, etc., which can realize _CO2 emission reduction and resource recovery at the same time. use. Therefore, the coupling of the electrocatalytic CO ₂ reduction reaction and the bioelectrochemical system can convert the chemical energy in the wastewater into electrical energy and apply it to reduce the CO ₂ generated from the wastewater treatment, realizing the simultaneous recovery of energy and resources.

However, limited by the metabolic rate of microorganisms and the low concentration of organic pollutants in wastewater, it is difficult for the electrons generated at the anode of this coupled system to drive the high-energy barrier electrocatalytic _CO2 reduction reaction at the cathode. Therefore, the development and application of this coupled system is limited by the low activity, low selectivity, and high overpotential of the electrocatalytic _CO2 reduction reaction.

In previous reports, scholars have devoted themselves to the study of gold, silver and other noble metal catalysts for highly selective electrocatalytic _CO reduction to CO under low overpotential conditions, however, their high price and low reserves limit their wide practical applications . In recent years, the chemical bonding of single-atom metal and non-metal heteroatoms to co-doped nanocarbon-based materials has become a research hotspot. Due to their unique physicochemical properties and atomic-level distribution, this type of catalyst has the potential to electrocatalyze _CO2 reduction. of high activity. In addition, the interaction force between atomic-scale metals and non-metallic heteroatom-doped carbon supports can change the electronic structure of metal catalysts, thereby improving the stability of catalysts and reducing their overpotentials.

For example, publication number CN110067003A discloses a metal single-atom doped graphene material and its preparation method and application. The method uses ammonium chloride, glucose, dicyandiamide and metal salt as raw materials and uses freeze-drying and high-temperature calcination. , Synthesized metal single-atom doped graphene material, which is used in electrocatalytic _CO reduction to prepare CO, with high reducibility and activity; researchers can choose different synthesis methods and precursors to obtain higher selectivity, overpotential Lower catalytic material.

CN108899556A discloses a method for preparing carbon-nitrogen-based single-atom iron catalyst assisted by ball milling. The method adopts a one-pot method to encapsulate iron porphyrin in the pores of metal organic framework in the form of single molecule through mechanical ball milling to form a host-guest structure. After high-temperature pyrolysis, the metal-organic framework guest forms a nitrogen-doped porous carbon support and maintains its original porous structure, and the iron porphyrin molecule forms a single-atom Fe-Nx structure and is fixed in the porous structure. However, the intercalation effect of iron single atoms and metal organic frameworks in the catalyst prepared by ball milling is not good, and the selectivity of the catalyst is not high and the activity is insufficient.

Therefore, in order to match the above-mentioned coupling system of bioelectrochemical technology and electrocatalytic _CO reduction, the development of catalysts with high activity and high selectivity, especially low overpotential electrocatalytic _CO reduction catalysts, still needs to be further studied and solved. question.

SUMMARY OF THE INVENTION

The present invention aims to provide a single-atom iron-nitrogen co-doped carbon electrocatalyst, which wraps iron in a metal-organic framework in the form of iron single-atom-nitrogen coordination. The mesoporous structure can promote the mass transfer of the electrolyte, so that the catalyst has the advantages of high selectivity, low overpotential, and high catalytic activity when it is applied to electrocatalytic _CO reduction to prepare CO.

For achieving the above object, the technical scheme adopted in the present invention is:

A single-atom iron-nitrogen co-doped carbon electrocatalyst, iron is wrapped in the pores of a metal-organic framework ZIF-8 containing micropores and/or mesoporous structures in the form of single-atom iron-nitrogen coordination; It includes micropores with a pore size below 3 nm, mesopores with 3-5 nm and 29-32 nm.

The preparation method provided by the invention is a molecular confinement coupled high temperature calcination method, the iron phthalocyanine molecules are confined in the cavity of the metal organic framework ZIF-8 compound, and then calcined at high temperature in an inert gas, the iron phthalocyanine molecules and the ZIF-8 skeleton are Carbonization, the iron-nitrogen bond of iron phthalocyanine itself is anchored in the ZIF-8-derived nanocarbon support, and additionally, excess metallic iron will agglomerate at high temperature to form mesopore-sized iron oxide, while zinc will sublime at high temperature The formation of micropores, through pickling and etching of iron oxide and residual zinc, can form mesoporous and microporous structures, respectively, which is beneficial to expose more active sites, and obtain three-dimensional nitrogen doping grades with micropore-mesoporous structure. Porous carbon anchors monatomic iron materials. The material has a high specific surface area, can attach more active sites, and the rich mesoporous structure can promote the mass transfer of the electrolyte, thereby achieving high selectivity, high activity and low overcatalyzed electrocatalytic CO to _CO preparation potential.

The catalyst has a BET specific surface area of 500-1100 m ² g ^-1 , and a pore volume of 0.36-0.97 cm ³ g ^-1 .

The present invention also provides the preparation method of the single-atom iron-nitrogen co-doped carbon electrocatalyst, comprising the following steps:

(1) adding iron phthalocyanine to the methanol solution of 2-methylimidazole, and dissolving to obtain a mixed solution;

(2) adding the methanol solution of zinc nitrate to the mixed solution, and obtaining ZIF-8/iron phthalocyanine composite material after stirring;

(3) calcining and pickling the ZIF-8/iron phthalocyanine composite material in step (2) under nitrogen atmosphere to obtain the single-atom iron-nitrogen co-doped carbon electrocatalyst.

The molar ratio of the 2-methylimidazole to the zinc nitrate is 7.5-8.5:1, which can ensure that the ligand 2-methylimidazole is excessive and can effectively combine with the zinc ion to generate the ZIF-8 precursor.

In the methanol solution of 2-methylimidazole, the concentration of 2-methylimidazole is 0.75-0.85 mol/L; in the methanol solution of zinc nitrate, the concentration of zinc nitrate is 0.09-0.11 mol/L.

Preferably, the molar ratio of the 2-methylimidazole to zinc nitrate is 8:1. Since each zinc ion in the ZIF-8 structure will be combined with four 2-methylimidazole molecules, the The amount will determine the particle size of ZIF-8. Choosing the molar ratio of 2-methylimidazole to zinc nitrate to be 8:1 can effectively control the particle size of ZIF-8 to 60-70nm, which is convenient for mesoporous and microporous structures. simultaneously exist.

The addition amount of the iron phthalocyanine is 0.2 to 1.2 g/L. If the addition amount is too small, the amount of metal iron will be insufficient, and the number of active sites will be too small, and the addition amount will lead to the formation of metal iron particles or iron carbide. The formation of , which reduces the amount of monoatomic iron, also leads to a decrease in the number of active sites.

In step (2), the stirring temperature is 15-30° C., and the stirring time is 20-30 h. The preparation process of ZIF-8 does not require heating or low temperature, and can be realized at room temperature, and the iron phthalocyanine is fully and uniformly encapsulated into ZIF-8. In the pores of 8, the size of ZIF-8 nucleation has a certain relationship with the stirring time. The stirring time is 20-30 h, and the particle size of ZIF-8 within this range is about 60-70 nm.

Preferably, in step (2), the stirring temperature is 20-25° C., and the stirring time is 20-25 h.

In step (3), the calcination temperature is 700-1050°C, the heating rate is 2-10°C min ^-1 , and the calcination time is 2-4h; 0.5-1.0M sulfuric acid is used for pickling, and the pickling time is 20-30h.

Among them, the calcination temperature directly affects the type and content of nitrogen and the coordination form of iron and nitrogen in the single-atom iron-nitrogen co-doped carbon electrocatalyst. By controlling the calcination temperature, the content of iron-nitrogen bonds is in the total nitrogen content. The increase of the percentage of , can bring better catalytic activity, higher selectivity and lower overpotential. The calcination temperature is in the range of 700-1050℃, which can ensure the carbonization of the precursor is uniform and sufficient. The iron-nitrogen bond of the iron phthalocyanine itself breaks through the limitation of the original macrocyclic molecule and is embedded in the framework of the carbonized ZIF-8. 0.5~1.0M sulfuric acid etching for 10~30h can ensure the removal of iron oxide and residual metal zinc in the calcined product, thereby increasing the micropore and mesoporous structure of the catalyst, which is beneficial to the increase of the number of active sites and the reaction process. The mass transfer of _CO2 as well as the electrolyte improves the stability of the single-atom iron-nitrogen coordination structure, and finally achieves high activity and low overpotential of the catalyst.

Preferably, in step (3), the calcination temperature is 900-1050°C, and the catalyst obtained at this calcination temperature has better pore size distribution and higher catalytic activity.

Further preferably, the calcination temperature is 950-1000°C, and the prepared single-atom iron-nitrogen co-doped carbon electrocatalyst has a BET specific surface area of about 1011 m ² g ^-1 .

Further preferably, the mol ratio of 2-methylimidazole in step (1) and zinc nitrate in step (2) is 8:1, the concentration of 2-methylimidazole is 0.8mol/L, and the concentration of zinc nitrate is 0.1mol /L, the addition amount of iron phthalocyanine is 0.3g/L, the stirring temperature in step (2) is 25°C, the stirring time is 24h, the calcination temperature is 1000°C, the calcination time is 3h, and the sulfuric acid in step (3) The concentration is 0.5M, and the pickling time is 24h.

The present invention also provides the application of the single-atom iron-nitrogen co-doped carbon electrocatalyst in electrocatalytic CO ₂ reduction to prepare CO, and the carbon paper supporting the single-atom iron-nitrogen co-doped carbon electrocatalyst is used as the work Electrodes, saturated silver/silver chloride electrode as reference electrode, platinum column as counter electrode, potassium bicarbonate solution as electrolyte, electrocatalytic _CO reduction through a three-electrode system. The Faradaic efficiency of its reduction to prepare CO is very high, up to about 96%, which shows that the catalyst has high catalytic activity.

The present invention also provides the application of the single-atom iron-nitrogen co-doped carbon electrocatalyst in electrocatalytic CO ₂ reduction to prepare CO in a bioelectrochemical system. Carbon paper is used as the cathode material of microbial electrolysis cell (MEC), and under the drive of microbial fuel cell (MFC), the electrocatalytic CO ₂ reduction reaction to prepare CO occurs. The whole electrocatalytic process is stable and efficient, and does not require external energy input. Using the energy in wastewater to drive electrocatalytic _CO reduction to prepare CO under the action of catalyst, the output current is up to 1.54±0.05mA, and the rate of CO production is up to 33.66±0.58mmol g ^-1 _cat h ^-1 . Compared with the prior art, the present invention has the following beneficial effects:

(1) The catalyst of the present invention wraps iron in the pores of the metal-organic framework ZIF-8 in the form of single-atom iron-nitrogen coordination, and utilizes calcination and pickling processes to remove iron oxide and zinc, so as to manufacture and classify the metal-organic framework. The microporous and mesoporous structure enables the electrolyte to transfer mass through the abundant mesoporous structure when the catalyst is applied, thereby realizing the high selectivity, high activity and low overpotential of electrocatalytic CO to _CO production.

(2) The preparation method of the single-atom iron-nitrogen co-doped carbon electrocatalyst provided by the present invention is easy to operate, the macroscopic morphology of the catalyst is regular dodecahedron, the regularity and repeatability are good, the raw materials are cheap and easy to obtain, and it is easy for industrial production .

(3) The single-atom iron-nitrogen co-doped carbon electrocatalyst provided by the present invention has good catalytic stability in neutral electrolyte, and can realize high-efficiency electrocatalytic _CO reduction to prepare CO under normal temperature conditions, and the initial voltage is as low as -0.2V (relative to the standard reversible hydrogen electrode), the Tafel slope is as low as 92mV dec ^-1 , and when the applied voltage is -0.5V (relative to the standard reversible hydrogen electrode), the Faradaic efficiency of CO reaches the highest 96%.

(4) The single-atom iron-nitrogen co-doped carbon electrocatalyst provided by the present invention is applied to electrocatalytic CO ₂ reduction to prepare CO in a bioelectrochemical system, the electrocatalytic process is stable and efficient, no external energy input is required, and the effect is good.

Description of drawings

1 is a TEM image of a single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention;

2 is an AC-STEM image of a single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention;

3 is a BET diagram of a single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention;

4 is a pore size distribution diagram of a single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention;

5 is the XPS spectrum of the single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention;

6 is a Faradaic efficiency diagram of the electrocatalytic _CO reduction of the single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention to prepare CO;

7 is a graph of the output current and output voltage of the single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 of the present invention in the electrocatalytic CO ₂ reduction to prepare CO in a bioelectrochemical system.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. Those skilled in the art can make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, and all should be included within the protection scope of the present invention.

Example 1

(1) 32 mmol of 2-methylimidazole and 24 mg of iron phthalocyanine (FePc) were added to 40 mL of methanol, and stirred magnetically for 10 min to uniformly mix to obtain a mixed solution; 4 mmol of zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ ·6H ₂₀ ) was added to 40 mL of methanol, magnetically stirred for 10 min until uniformly mixed to obtain a methanol solution of zinc nitrate;

(2) The methanol solution of zinc nitrate was added to the mixed solution, and after magnetic stirring at room temperature for 24 h, centrifuged and washed three times with methanol and deionized water, respectively, and vacuum dried at 70 °C for 12 h to obtain the metal organic framework ZIF-8 package. The iron phthalocyanine composite material;

(3) The prepared composite material was calcined at 1000 ℃ under nitrogen atmosphere, the heating rate was 5 ℃ min ^-1 , and the calcination time was 3 h, and the calcined product was monoatomic iron-nitrogen co-doped carbon containing iron oxide and metallic zinc. Electrocatalyst: Wash the calcined product with 0.5M dilute sulfuric acid for 24h to remove iron oxide and residual metal zinc, filter and dry to obtain a single-atom iron-nitrogen co-doped carbon electrocatalyst.

The morphology of the prepared single-atom iron-nitrogen co-doped carbon electrocatalyst was observed by transmission scanning electron microscopy (TEM) and spherical aberration-corrected scanning transmission electron microscopy (AC-STEM). The results are shown in Figures 1 and 2. 1 It can be seen that the single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in this example has abundant mesoporous and microporous structures, showing a hierarchical microporous-mesoporous structure; In atomic iron-nitrogen co-doped carbon electrocatalysts, iron exists in the material in the form of single atoms.

The nitrogen adsorption and desorption curve of the prepared catalyst is shown in Fig. 3, its BET specific surface area is 1011 m ² g ^-1 , and its pore volume is 0.97 cm ³ g ^-1 . The pore size distribution is shown in Figure 4. It can be seen that the catalyst includes micropores with a pore size below 3 nm, mesopores with a pore size of 3-5 nm and 29-32 nm. Among the mesopores of 29-32nm, the mesopores of 31.2nm are the most, and a catalyst containing a large number of micropores and mesopores at the same time was successfully obtained; the X-ray photoelectron spectroscopy (XPS) was observed. The results are as follows As shown in FIG. 5 , it can be seen that the existing form of iron and nitrogen elements in the prepared catalyst is an iron-nitrogen coordination structure.

Example 2-4

According to the preparation method of Example 1, the calcination temperature in step (3) was changed to 700° C., 800° C. and 900° C., respectively, and the remaining steps remained unchanged. The BET specific surface areas of the obtained catalyst were 469 m ² g ⁻¹ and 693 m ² g ^-1 and 775 m ² g ^-1 , the pore volumes are 0.36 cm ³ g ^-1 , 0.50 cm ³ g ^-1 and 0.69 cm ³ g ^-1 , respectively, and the pore size distribution is the same as that of the catalyst in Example 1, including the low pore size Micropores at 3nm, mesopores at 3-5nm and 29-32nm.

Examples 5-7

According to the preparation method of Example 1, the addition amount of iron phthalocyanine in step (1) was changed to 8 mg, 16 mg and 48 mg respectively, and the remaining steps remained unchanged.

Application example 1 Single-atom iron-nitrogen co-doped carbon electrocatalyst applied to electrocatalytic _CO reduction test

Step (1): Take 5 mg of the single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 and add it to a mixed solution of a perfluorosulfonic acid type polymer solution (Nafion) (0.5 wt %) and 450 μL of absolute ethanol , then ultrasonic for 2h and magnetic stirring for 2h to form a uniform catalyst suspension;

Step (2): select 100 μL of the catalyst suspension in step (1) to drop on 1×1 cm ² of carbon paper, and dry it under an infrared lamp to obtain a catalyst working electrode with a loading of 1.0 mg cm ⁻² ;

Step (3): The catalyst-supported carbon paper obtained in step (2) is used as the working electrode, the saturated silver/silver chloride electrode is used as the reference electrode, the platinum column is used as the counter electrode, and the 0.5M potassium bicarbonate solution is used as the electrolyte. The electrode system electrocatalyzed the reduction of _CO2 . Under different applied voltages, the exhaust gas samples were selected every 20min and entered into the gas chromatography to analyze the content of CO, and through calculation, the Faradaic efficiency of CO was obtained.

As shown in Figure 6, the single-atom iron-nitrogen co-doped carbon electrocatalyst prepared in Example 1 has the highest Faradaic efficiency of about 96% in electrocatalytic _CO reduction to prepare CO.

Application example 2 Single-atom iron-nitrogen co-doped carbon electrocatalyst in bioelectrochemical system

Step (1): The electrochemically active bacteria (ShewanellaoneidensisMR-1) domesticated by acetate as an organic matter were inoculated in a microbial fuel cell (MFC) and a microbial electrolysis cell (MEC), and the open circuit voltage of the MFC was 6 months after stable operation. 680mV.

Step (2): In step (1), the cathode and anode electrode materials of the MFC device are composed of carbon felt (6×3×1 cm) and carbon brush; the anolyte of the MFC is composed of phosphate buffer solution (6g L ^-1 disodium hydrogen phosphate, 3g L ^-1 potassium dihydrogen phosphate, 1g L ^-1 ammonium chloride and 0.5g L ^-1 sodium chloride), 5mL L ^-1 vitamin solution, 12.5mL L- ¹ mineral solution and 15mM L ^- 1 ¹ acetate composition; MFC catholyte is composed of 16.64g potassium ferricyanide added 1L phosphate buffer solution; MFC cathode and anode chambers are separated by proton exchange membrane.

Step (3): In step (1), the anode electrode material and anolyte of the MEC device are the same as those of the MFC device; the cathode material of the MEC is 1× prepared by supporting the single-atom iron-nitrogen co-doped carbon electrocatalyst of Example 1. 1cm ² carbon paper, the catholyte is 0.5M potassium bicarbonate solution;

Step (4): use MFC as the driving energy, MEC as the driven device, and connect an external auxiliary resistor with a resistance value of 20Ω in series at the same time, measure the current in the entire MFC-MEC coupling system, and use a multimeter to measure the voltage in the coupling system;

The single-atom iron-nitrogen co-doped carbon electrocatalyst at the cathode of the MEC in this coupled device enables the electrocatalytic _CO reduction to CO reaction driven by the MFC. As shown in Figure 7, the single-atom iron-nitrogen co-doped carbon electrocatalyst applied to the MFC-MEC coupling device showed an output voltage of 1.14±0.02 V, an output current of 1.54±0.05 mA, and a CO production rate of 33.66±0.58 mmol g ^{− 1} _cat h ^-1 .

Application examples 3 to 5

According to the steps of Application Example 1, the atomic iron-nitrogen co-doped carbon electrocatalysts prepared in Examples 2 to 4 were respectively used as cathode materials, and their electrocatalytic CO ₂ reduction performance was tested, and the Faradaic efficiency of electrocatalytic CO ₂ reduction to CO was tested. The highest were around 58%, 82% and 89%, respectively. It can be seen that in the process of catalyst preparation, the calcination temperature has a great influence on its catalytic activity. When the calcination temperature is above 800°C, the catalytic activity of the catalyst is better.

Application examples 6 to 8

According to the steps of Application Example 1, the atomic iron-nitrogen co-doped carbon electrocatalysts prepared in Examples 5 to 7 were respectively used as cathode materials, and their electrocatalytic CO ₂ reduction performance was tested, and the Faradaic efficiency of electrocatalytic CO ₂ reduction to CO was tested. The highest were around 92%, 93% and 94%, respectively.

Claims (10)

1. a monoatomic iron-nitrogen co-doped carbon electrocatalyst, is characterized in that, iron is wrapped in the hole of the metal organic framework ZIF-8 containing micropore and/or mesoporous structure with monoatomic iron-nitrogen coordination form The catalyst includes micropores with pore diameters below 3 nm, mesopores of 3-5 nm and 29-32 nm. 2 . The single-atom iron-nitrogen co-doped carbon electrocatalyst according to claim 1 , wherein the catalyst has a BET specific surface area of 500-1100 m ² g ^-1 and a pore volume of 0.36-0.97 cm ³ g ^-1 . 3. the preparation method of monoatomic iron-nitrogen co-doped carbon electrocatalyst according to claim 1 and 2, is characterized in that, comprises the steps: (1) adding iron phthalocyanine to the methanol solution of 2-methylimidazole, and dissolving to obtain a mixed solution; (2) adding the methanol solution of zinc nitrate to the mixed solution, and after mixing, centrifuging, washing and drying to obtain the ZIF-8 encapsulated iron phthalocyanine composite material; (3) calcining and pickling the ZIF-8/iron phthalocyanine composite material in step (2) under nitrogen atmosphere to obtain the single-atom iron-nitrogen co-doped carbon electrocatalyst. 4. the preparation method of monoatomic iron-nitrogen co-doped carbon electrocatalyst according to claim 3, is characterized in that, in step (1), the mol ratio of 2-methylimidazole and zinc nitrate in step (2) is 7.5 to 8.5:1. 5. the preparation method of monoatomic iron-nitrogen co-doped carbon electrocatalyst according to claim 3, is characterized in that, in the methanol solution of described 2-methylimidazole, the molar concentration of 2-methylimidazole is 0.75 ～0.85mol/L; in the methanol solution of zinc nitrate, the molar concentration of zinc nitrate is 0.09～0.11mol/L. 6. The preparation method of monoatomic iron-nitrogen co-doped carbon electrocatalyst according to claim 3, wherein in step (1), the mass concentration of iron phthalocyanine in the mixed solution after adding iron phthalocyanine is 0.2～1.2g/L. 7 . The method for preparing a monoatomic iron-nitrogen co-doped carbon electrocatalyst according to claim 3 , wherein, in step (2), the stirring temperature is 15-30° C., and the stirring time is 20-30 h. 8 . 8 . The method for preparing a monoatomic iron-nitrogen co-doped carbon electrocatalyst according to claim 3 , wherein in step (3), the calcination temperature is 700-1050° C., and the heating rate is 2-10° C. min. 8 . ^-1 , the calcination time is 2~4h; the pickling time is 0.5~1.0M sulfuric acid, and the pickling time is 10~30h. 9 . The application of the single-atom iron-nitrogen co-doped carbon electrocatalyst according to claim 1 or 2 in electrocatalytic CO ₂ reduction to prepare CO. 10 . 10. Application of the single-atom iron-nitrogen co-doped carbon electrocatalyst according to claim 1 or ₂ in electrocatalytic CO reduction to prepare CO in a bioelectrochemical system.

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