Asymmetric metal monatomic electrocatalyst and application thereof in electrochemical production of hydrogen peroxide

Abstract

The invention belongs to the technical field of electrocatalyst preparation, and particularly relates to an asymmetric metal monatomic electrocatalyst and application thereof in electrochemical production of hydrogen peroxide. The asymmetric monatomic metal catalyst is MBmNn, m is more than or equal to 0 and less than or equal to 4, n is more than or equal to 0 and less than or equal to 4, m + n is less than or equal to 4, m and n are integers, and M is one of nickel, copper, cobalt and iron. The mass fraction of monatomic metal in the asymmetric metal monatomic electrocatalyst is 0.5-3.5%, and the mass fraction of boron is 0.3-7%. The asymmetric metal monatomic electrocatalyst provided by the invention is high in ORR activity, high in selectivity of catalyzing two electrons of H2O2, high in Faraday efficiency and simple in preparation method, and has good electrocatalytic performance and electrochemical stability.

Description

Technical Field

[0001] The invention relates to the technical field of electrode preparation, and in particular to an asymmetric metal single-atom electrocatalyst and its application in electrochemical production of hydrogen peroxide. Background Art

[0002] Hydrogen peroxide (H2O2) is an environmentally friendly chemical reagent that can be used as both an oxidant and a reductant. It is widely used in many industrial fields, such as organic synthesis, wastewater treatment, bleaching and disinfection. At present, the industrial production of H2O2 mainly relies on the anthraquinone redox process. However, this process has the problems of high cost, high energy consumption and the generation of organic waste. Therefore, the development of more economical, efficient and environmentally friendly H2O2 production technology has become a research hotspot. In recent years, electrocatalysis, photocatalysis and enzyme-based processes have been widely explored. Among them, the electrocatalytic two-electron oxygen reduction reaction (2e - ORR) as a green method for producing H2O2 has shown good selectivity and activity. Compared with the traditional anthraquinone process, this method operates under ambient conditions and is not only more environmentally friendly, but also provides a viable alternative for achieving sustainable H2O2 production.

[0003] In the research of electrocatalytic H2O2 production, the development of electrocatalysts with high activity and selectivity still faces great challenges. Precious metal-based nano-alloy catalysts show good application potential because they can optimize and selectively regulate their binding energy during the alloying process. However, their high cost makes their economic feasibility questionable. In contrast, non-precious metal-based transition metal catalysts (such as metal nanoparticles, metal oxides, metal selenides, etc.) have been widely tried, but they often fail to achieve the desired effect due to the catalytic decomposition of H2O2 during the reaction. Carbon-based materials are also considered promising candidates, but their complex surface chemical properties (such as ether, hydroxyl, carbonyl, carboxyl, quinone and other functional groups and the presence of other main group elements) make the reaction mechanism difficult to clarify and limit the possibility of further optimizing their activity. Single atom catalysts (SACs), especially those with M-N4 or M-N5 structures, have shown great potential in the photoelectric activation of molecular oxygen to produce H2O2. This type of catalyst can effectively decipher the structure-performance relationship of electrocatalysts through atomic-level structural regulation, thereby gaining a deeper understanding of the reaction mechanism. Studies have shown that compared with pyridine coordination, pyrrole-coordinated active centers are more inclined to selectively generate H2O2 through the 2e-pathway. Summary of the invention

[0004] It should be pointed out that although the traditional symmetric MN4 configuration shows high efficiency in the oxygen reduction process, its symmetry leads to a weak local electric field, making it difficult to effectively activate molecular oxygen. In order to enhance the external electric field, constructing an asymmetric coordination microenvironment with high polarity is a potential feasible strategy. Ideally, by doping non-metallic heteroatoms (such as sulfur, phosphorus, boron, etc.), the local environment of the carbon substrate can be regulated to enhance its polarity. Among them, since boron and nitrogen have similar atomic radii, boron doping usually partially replaces N atoms in the covalent substrate and directly coordinates with metal atoms, thereby changing the configuration of the catalyst. Because the electronegativity of boron and carbon is significantly different, this change can significantly increase the intensity of the local electric field and provide additional driving force for the reaction system. Through this asymmetric structure, the activation process of molecular oxygen and the proton-coupled electron transfer process of OOH can be promoted at a lower energy barrier, and H2O2 can be further selectively generated.

[0005] In order to solve the technical problem that the two-electron selectivity of most oxygen reduction reactions of nickel single-atom electrocatalysts in the prior art is low, and it is difficult to achieve selective regulation from four electrons to two electrons, resulting in low hydrogen peroxide yield and unable to meet the demand for efficient production of hydrogen peroxide in practical applications, the present invention provides an asymmetric single-atom metal catalyst and its application in electrochemical production of hydrogen peroxide. The present invention constructs a NiB2N2 single-atom catalyst by regulating the microenvironment of the single-atom Ni site through the first shell coordination of B and N. The prepared NiB2N2 catalyst exhibits excellent ORR activity and efficient 2e-H2O2 selectivity in an alkaline environment. In the solid electrolyte electrolytic cell test, the catalyst achieved a Faraday efficiency of up to 90%, showing excellent electrocatalytic performance.

[0006] The first object of the present invention is to provide a method for preparing an asymmetric metal single-atom electrocatalyst, comprising the following steps:

[0007] (1) mixing a zinc precursor and a metal precursor in a solvent to obtain a solution A; dissolving a nitrogen source in a solvent to obtain a solution B; mixing the solution A and the solution B to perform a heating reaction to obtain a metal nitrogen precursor;

[0008] (2) The metal nitrogen precursor and the boron source are mixed and ball-milled, and heated and calcined in an inert atmosphere. The calcined material is acidified in an acid solution to obtain an asymmetric metal single atom electrocatalyst.

[0009] In some embodiments of the present invention, in step (1), the zinc precursor is selected from one or more of zinc nitrate, zinc acetate, and zinc sulfate;

[0010] The metal in the metal precursor is one of nickel, copper, cobalt and iron; further, nickel is preferred.

[0011] The salt in the metal precursor is selected from one or more of nitrates, sulfates and chlorides.

[0012] In some embodiments of the present invention, in step (1), the nitrogen source is selected from one or more of dimethylimidazole, acetonitrile, and urea;

[0013] The metal nitrogen precursor includes one or more of zeolite imidazolate metal, zeolite imidazolate zinc, and zeolite imidazolate metal / zinc.

[0014] In some embodiments of the present invention, the mass ratio of the metal precursor to the boron source is (1-10): (1-10).

[0015] In some embodiments of the present invention, in step (1), the mass ratio of the zinc precursor, the metal precursor and the nitrogen source is 10:(0.1-3):(100-500).

[0016] In some embodiments of the present invention, in step (1), the temperature of the heating reaction is 25-60° C., and the reaction time is 8-24 hours. After the heating reaction, the product is dried by vacuum drying for 10-24 hours.

[0017] In some embodiments of the present invention, in step (2), the boron source is selected from boric acid and / or borate.

[0018] In some embodiments of the present invention, in step (2), the conditions for heating and calcining are: heating temperature is 700°C to 900°C, constant temperature time is 1-6h, and heating rate is 1 to 10°C·min -1 ;

[0019] The inert gas in the inert atmosphere is selected from argon and / or nitrogen.

[0020] Furthermore, the heating and calcining is carried out by heating in a tubular furnace.

[0021] In some embodiments of the present invention, in step (2), the acid is selected from one or more of sulfuric acid, hydrochloric acid, and nitric acid; the present invention removes non-single-atom metal clusters by acid washing, thereby forming a metal single-atom catalyst.

[0022] The temperature of the acidification treatment is 20-90°C, and the time of the acidification treatment is 4-12h;

[0023] The concentration of the acid solution is 0.1-6.0 mol / L.

[0024] In some embodiments of the present invention, in step (2), after the acidification treatment, drying is also included, and the drying method is vacuum drying; the drying time is 10-24 hours.

[0025] The second object of the present invention is to provide an asymmetric single-atom metal catalyst prepared by the preparation method, wherein the asymmetric single-atom metal catalyst is MB m N n , wherein 0≤m≤4, 0≤n≤4, m+n≤4, m and n are integers, and M is one of nickel, cobalt, copper, and iron. Exemplarily, m is 0, 1, 2, or 3, and n is 0, 1, 2, or 3. Preferably, MB m N n They are MB2N2, MBN3, MB3N1, MB2N2, etc., except MB4 and MN4, where m and n are not 0 at the same time.

[0026] Furthermore, the metal loading in the asymmetric metal single-atom electrocatalyst is 0.5-3.5wt%; the boron loading is 0.3-7wt%.

[0027] The third object of the present invention is to provide the asymmetric metal single-atom electrocatalyst in the field of electrochemical selective production of hydrogen peroxide and electrochemical water pollution control.

[0028] The above technical solution of the present invention has the following advantages compared with the prior art:

[0029] 1. The present invention provides an asymmetric metal single-atom electrocatalyst, wherein the mass fraction of the single-atom metal in the asymmetric metal single-atom electrocatalyst is 0.5-3.5%. The asymmetric metal single-atom electrocatalyst provided by the present invention has high ORR activity, high two-electron selectivity for catalyzing the production of H2O2, high Faraday efficiency, simple preparation method, and good electrocatalytic performance and electrochemical stability.

[0030] 2. Compared with the traditional nickel-nitrogen catalyst, the asymmetric metal single-atom electrocatalyst provided by the present invention has a 2e - The oxygen reduction selectivity was increased from 30% to 90%, achieving a transition from a four-electron to a two-electron oxygen reduction process.

[0031] 3. The asymmetric metal single atom electrocatalyst provided by the present invention, wherein boron and nitrogen have similar atomic radii, but their electronegativity is significantly different, and boron doping usually partially replaces N atoms in the covalent substrate and directly coordinates with metal atoms, thereby changing the configuration of the catalyst. This change can significantly increase the intensity of the local electric field and provide additional driving force for the reaction system. Through this asymmetric structure, the activation process of molecular oxygen and the proton-coupled electron transfer process of OOH can be promoted at a lower energy barrier, and H2O2 can be further selectively generated.

[0032] 4. The present invention provides a method for preparing the above-mentioned asymmetric metal single-atom electrocatalyst, comprising the following steps: (1) mixing, reacting and drying nitrogen-containing heterocyclic organic matter, zinc precursor, sodium carbonate, nickel precursor and methanol to obtain a nickel-nitrogen precursor; (2) ball-milling the nickel-nitrogen precursor and boric acid mixture, calcining, acidifying and drying to obtain a nickel single-atom electrocatalyst. The acidification treatment can remove elemental nickel and nickel oxide, thereby improving the two-electron selectivity in the oxygen reduction process.

[0033] 5. The present invention also provides an asymmetric metal single atom electrocatalyst or a nickel single atom electrocatalyst prepared by the preparation method for use in hydrogen peroxide production. The electrocatalyst provided by the present invention meets the needs of economical, flexible and sustainable hydrogen peroxide production and enables its implementation in remote communities and regions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0035] Figure 1 This is a spherical aberration electron microscope image of the catalyst prepared by the present invention.

[0036] Figure 2 It is a two-electron oxygen reduction selectivity diagram of the catalyst rotating disk test prepared in the examples of the present invention and the comparative examples. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0038] Example 1

[0039] This embodiment provides an asymmetric nickel single-atom electrocatalyst, wherein the mass fraction of single-atom nickel in the nickel single-atom electrocatalyst is 3.00±0.2% and the boron content is 2.00±0.2%. The preparation method specifically includes the following steps:

[0040] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Ni(NO3)2·6H2O (2.093 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain a NiZn-ZIF-8 precursor.

[0041] (2) 500 mg of dried NiZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1 The samples were heated to 700°C at a heating rate of , kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a forced air drying oven at 60°C to obtain NiB2N2 catalysts.

[0042] Example 2

[0043] This embodiment provides a nickel single-atom electrocatalyst, in which the mass fraction of single-atom nickel in the nickel single-atom electrocatalyst is 3.00±0.2% and the mass fraction of boron is 0.7%. The preparation method specifically includes the following steps:

[0044] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Ni(NO3)2·6H2O (2.093 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain a NiZn-ZIF-8 precursor.

[0045] (2) 500 mg of dried NiZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1The samples were heated to 800°C at a heating rate of , kept at a constant temperature for 2 hours in an argon atmosphere, and then naturally cooled to room temperature. The obtained material was acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a 60°C forced air drying oven to obtain the nickel single atom electrocatalyst NiBN3 catalyst.

[0046] Example 3

[0047] This embodiment provides a nickel single-atom electrocatalyst, in which the mass fraction of single-atom nickel is 3.00±0.2% and the mass fraction of boron is 0.2%. The preparation method specifically includes the following steps:

[0048] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Ni(NO3)2·6H2O (2.093 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain a NiZn-ZIF-8 precursor.

[0049] (2) 500 mg of dried NiZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1 The samples were heated to 900°C at a heating rate of , kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a forced air drying oven at 60°C to obtain NiN3-B catalyst.

[0050] Example 4

[0051] This embodiment provides a cobalt single-atom electrocatalyst, in which the mass fraction of single-atom cobalt is 3.00±0.2% and the mass fraction of boron is 0.6%. The preparation method specifically includes the following steps:

[0052] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Co(NO3)2·6H2O (2.095 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain CoZn-ZIF-8 precursor.

[0053] (2) 500 mg of the dried CoZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1 The samples were heated to 700°C at a heating rate of , kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a forced air drying oven at 60°C to obtain the cobalt single atom electrocatalyst CoB2N2 catalyst.

[0054] Example 5

[0055] This embodiment provides an iron single-atom electrocatalyst, in which the mass fraction of single-atom iron in the iron single-atom electrocatalyst is 3.00±0.2% and the mass fraction of boron is 2.0%. The preparation method specifically includes the following steps:

[0056] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Fe(NO3)2·9H2O (2.909 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 h. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight under vacuum at 60°C to obtain a FeZn-ZIF-8 precursor.

[0057] (2) 500 mg of the dried FeZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1The samples were heated to 700°C at a heating rate of , kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a forced air drying oven at 60°C to obtain FeB2N2 catalysts.

[0058] Example 6

[0059] This embodiment provides a copper single-atom electrocatalyst, in which the mass fraction of single-atom copper is 3.00±0.2% and the mass fraction of boron is 0.5%. The preparation method specifically includes the following steps:

[0060] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Cu(NO3)2·3H2O (1.739 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 h. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight under vacuum at 60°C to obtain a CuZn-ZIF-8 precursor.

[0061] (2) 1000 mg of dried CuZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1 The samples were heated to 700°C at a heating rate of , kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a forced air drying oven at 60°C to obtain CuB2N2 catalyst.

[0062] Comparative Example 1 (Compared with Example 1, without acidification treatment)

[0063] This comparative example provides a nickel nanoparticle electrocatalyst, wherein the nickel mass fraction of the nickel nanoparticle electrocatalyst is 3.00±0.2%, and the boron mass fraction is 0.5%. The preparation method specifically comprises the following steps:

[0064] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Ni(NO3)2·6H2O (2.093 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain a NiZn-ZIF-8 precursor.

[0065] (2) 500 mg of dried NiZn-ZIF-8 precursor was mixed with 50 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1 The samples were heated to 700, 800, and 900°C at a heating rate of , and kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained material was filtered and washed with deionized water until neutral, and dried in a 60°C forced air drying oven to obtain a NiB2N2 catalyst.

[0066] Comparative Example 2 (Compared with Example 1, the mass ratio of the nickel nitrogen precursor to the boron source is not within the protection range)

[0067] This comparative example provides a nickel single-atom electrocatalyst, in which the mass fraction of single-atom nickel in the nickel single-atom electrocatalyst is 3.00±0.2% and the mass fraction of boron is 1.7%. The preparation method specifically comprises the following steps:

[0068] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Ni(NO3)2·6H2O (2.093 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain a NiZn-ZIF-8 precursor.

[0069] (2) 500 mg of dried NiZn-ZIF-8 precursor was mixed with 25 mg of boric acid and ball-milled for 1 h. The mixed powder was then transferred to a ceramic boat and placed in a tube furnace. -1The samples were heated to 800°C at a heating rate of , kept at a constant temperature for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a forced air drying oven at 60°C to obtain NiB3N1 catalyst.

[0070] Comparative Example 3

[0071] This comparative example provides a nickel single-atom electrocatalyst, in which the mass fraction of single-atom nickel in the nickel single-atom electrocatalyst is 3.00±0.2%, and the preparation method specifically comprises the following steps:

[0072] (1) Zn(NO3)2·6H2O (21.419 g, 72 mmol) and Ni(NO3)2·6H2O (2.093 g, 7.2 mmol) were dissolved in 100 mL of methanol and stirred for 15 min under ultrasound to form a transparent solution A. Dimethylimidazole (23.644 g, 288 mmol) was then ultrasonically dissolved in 100 mL of methanol, which was recorded as solution B. Solution A was then slowly added dropwise to solution B and heated at 60°C for 12 hours. After the reaction, the product was separated by centrifugation, washed three times with DMF and twice with methanol, and dried overnight in vacuum at 60°C to obtain a NiZn-ZIF-8 precursor.

[0073] (2) Transfer 500 mg of the dried NiZn-ZIF-8 precursor to a ceramic boat and place it in a tube furnace at 5 °C min -1 The samples were heated to 700°C at a heating rate of , kept at a constant temperature for 2 hours in an argon atmosphere, and then naturally cooled to room temperature. The obtained materials were acid-washed in 3M H2SO4 at 80°C for 4 hours, then filtered and washed with deionized water until neutral, and dried in a 60°C forced air drying oven to obtain the nickel single atom electrocatalyst NiN4 catalyst.

[0074] Test Example 1

[0075] The electrodes prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance tests, and the content of the performance tests was the yield of hydrogen peroxide. The specific test method is as follows:

[0076] Selective test method of hydrogen peroxide: Grind the electrodes prepared in Examples 1-6 and Comparative Examples 1-3, then add 0.4 mL of 0.05% naphthol solution to a container containing 2 mg of catalyst powder, ultrasonically disperse for 10 minutes, measure 10 microliters of the mixed solution with a pipette, drip it on the surface of the rotating disk electrode, and then conduct electrochemical testing after natural drying at room temperature. The counter electrode is a platinum wire, the reference electrode is a saturated calomel electrode, and the electrolyte solution is 0.1M KOH. The rotating disk electrode test was performed using an electrochemical workstation. Before the electrochemical test, oxygen was continuously introduced into the electrolyte solution for 20 to 30 minutes, and the oxygen flow rate was 100.0 mL / min. After oxygen saturation, a rotating disk linear scanning voltammetric curve test was performed. The test results are shown in Table 1 below:

[0077] Table 1

[0078] Selectivity of hydrogen peroxide Example 1 92 Example 2 70 Example 3 65 Example 4 72 Example 5 64 Example 6 61 Comparative Example 1 12 Comparative Example 2 34 Comparative Example 3 58

[0079] Conclusion: The electrodes prepared in Examples 1-6 and Comparative Examples 1-3 were respectively subjected to rotating disk electrode tests, and then the two-electron selectivities were calculated to be between 90% and 55%. The selectivity of the optimal sample Example 1 can reach 90%, and its two-electron selectivities are much higher than those of nickel-carbon-based catalysts.

[0080] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing an asymmetric metal single atom electrocatalyst, characterized in that: The following steps are involved: (1) mixing a zinc precursor and a metal precursor in a solvent to obtain a solution A; dissolving a nitrogen source in a solvent to obtain a solution B; mixing the solution A and the solution B to perform a heating reaction to obtain a metal nitrogen precursor; (2) The metal nitrogen precursor and the boron source are mixed and ball-milled, and heated and calcined in an inert atmosphere. The calcined material is acidified in an acid solution to obtain an asymmetric metal single atom electrocatalyst.

2. The preparation method according to claim 1, characterized in that: In step (1), the zinc precursor is selected from one or more of zinc nitrate, zinc acetate, and zinc sulfate; The metal in the metal precursor is one of nickel, copper, cobalt and iron; The salt in the metal precursor is selected from one or more of nitrates, sulfates and chlorides.

3. The preparation method according to claim 1, characterized in that: In step (1), the nitrogen source is selected from one or more of dimethylimidazole, acetonitrile and urea; The temperature of the heating reaction is 25-60°C, and the reaction time is 8-24h.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the nickel precursor to the boron source is (1-10): (1-10).

5. The preparation method according to claim 1, characterized in that: In step (2), the boron source is selected from boric acid and / or borate.

6. The preparation method according to claim 1, characterized in that: In step (2), the conditions for heating and calcining are: heating temperature is 700℃~900℃, constant temperature time is 1-6h, and heating rate is 1~10℃·min -1 ; The inert gas in the inert atmosphere is selected from argon and / or nitrogen.

7. The preparation method according to claim 1, characterized in that: In step (2), the acid is selected from one or more of sulfuric acid, hydrochloric acid, and nitric acid; The temperature of the acidification treatment is 20-90°C, and the time of the acidification treatment is 4-12h; The concentration of the acid solution is 0.1-6.0 mol / L.

8. An asymmetric metal single atom electrocatalyst, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7, the asymmetric metal single atom electrocatalyst is MB m N n , wherein 0≤m≤4, 0≤n≤4, m+n≤4, m and n are integers, and M is one of nickel, copper, cobalt, and iron.

9. The asymmetric metal single atom electrocatalyst according to claim 8, characterized in that: The metal loading in the asymmetric metal single-atom electrocatalyst is 0.5-3.5 wt %; the boron loading is 0.3-7 wt %.

10. Use of the asymmetric metal single atom electrocatalyst according to claim 9 in electrochemical selective production of hydrogen peroxide and electrochemical water pollution control.

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