Boron coordination chromium monatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrochemical synthesis of hydrogen peroxide, in particular to a boron coordination chromium monatomic catalyst and a preparation method and application thereof. The preparation method comprises the following steps: mixing zinc nitrate, soluble chromium salt, hexadecyl trimethyl ammonium bromide and an aqueous solution of 2-methylimidazole, and filtering to obtain Cr salt-ZIF-L; the Cr salt-ZIF-L solution, boron salt and triethylamine are subjected to mixing treatment, and Cr salt-ZIF-L-B salt is obtained; the Cr salt-ZIF-L-B salt is subjected to carbonization treatment, and the boron coordination chromium monatomic catalyst is obtained. According to the preparation method, the selectivity and stability of electrocatalytic synthesis of hydrogen peroxide are improved, meanwhile, efficient hydrogen peroxide production under high current density is achieved through the prepared boron coordination chromium monatomic catalyst, and a new way is provided for industrial application of electrochemical synthesis of hydrogen peroxide.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemically synthesizing hydrogen peroxide, and specifically relates to a boron-coordinated chromium single-atom catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen peroxide, i.e., H2O2, is an indispensable oxidant in today's chemical industry, especially in the paper industry. In recent years, electrocatalytic two-electron oxygen reduction reaction for synthesizing hydrogen peroxide has become a very promising alternative method in terms of energy efficiency, production cost, and environmental friendliness. At the same time, distributed electrochemical H2O2 synthesis can also address the challenges in the storage and transportation of high-concentration H2O2. Although electrochemically producing H2O2 has many advantages, its practical application still faces challenges. Acidic or alkaline electrolytes can cause H2O2 degradation or equipment corrosion. At the same time, the steps for removing alkaline or acidic electrolytes can lead to wastewater discharge and increased costs. A neutral electrolyte environment can effectively avoid the above problems.

[0003] However, in a neutral electrolyte environment, under high current density conditions, there are still problems of poor selectivity and stability in the synthesis of H2O2. Therefore, there is an urgent need to precisely design highly stable catalysts that can effectively electrosynthesize H2O2 at industrial current density in neutral electrolytes. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a boron-coordinated chromium single-atom catalyst, a preparation method thereof, and an application thereof. The present invention uses zinc nitrate, soluble chromium salt, cetyltrimethylammonium bromide, and 2-methylimidazole as raw materials. An aqueous solution of zinc nitrate, soluble chromium salt, cetyltrimethylammonium bromide, and 2-methylimidazole is mixed. During the mixing process, zinc ions and chromium ions coordinate with the nitrogen atoms of 2-methylimidazole to form metal-organic complexes. At the same time, cetyltrimethylammonium bromide is arranged orderly on the surface of the metal-organic complexes to form a layered structure, obtaining Cr salt-ZIF-L. Subsequently, the Cr salt-ZIF-L solution, boron salt, and triethylamine are mixed and treated, and under the catalytic action of triethylamine, the boron salt reacts on Cr salt-ZIF-L to obtain Cr salt-ZIF-L-B salt. Finally, the Cr salt-ZIF-L-B salt is carbonized to obtain a boron-coordinated chromium single-atom catalyst. The present invention regulates the electronic structure of chromium single-atom sites by introducing boron, promotes the adsorption of O2, optimizes its adsorption of the intermediate -OOH, improves the selectivity and stability of hydrogen peroxide in the electrocatalytic reaction process, and overcomes the problems of poor selectivity and stability in the synthesis of H2O2 in neutral electrolytes in the existing technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The first object of the present invention is to provide a preparation method of a boron-coordinated chromium single-atom catalyst, comprising the following steps:

[0007] S1. Mix an aqueous solution of zinc nitrate, soluble chromium salt, cetyltrimethylammonium bromide and organic ligand. The organic ligand is 2-methylimidazole. During the mixing process, zinc nitrate and chromium ions coordinate with the nitrogen atoms of 2-methylimidazole together to form a metal-organic complex. At the same time, cetyltrimethylammonium bromide is arranged orderly on the surface of the metal-organic complex to form a layered structure, obtaining Cr salt-ZIF-L. Among them, the role of zinc nitrate is to form a ZIF structure. Among them, zinc nitrate and 2-methylimidazole form a metal-organic complex; the role of cetyltrimethylammonium bromide is a morphology regulator and mesoporous template agent.

[0008] S2. Using the Cr salt-ZIF-L solution and boron salt as raw materials, under the catalytic action of triethylamine, the boron salt reacts on the Cr salt-ZIF-L to obtain Cr salt-ZIF-L-B salt; among them, the Cr salt-ZIF-L-B salt is a complex, and there is no positional relationship between the boron atom, chromium atom, zinc atom and carbon atom in the Cr salt-ZIF-L-B salt.

[0009] S3. Carbonize the Cr salt-ZIF-L-B salt to obtain a boron-coordinated chromium single-atom catalyst.

[0010] Preferably, the mass ratio of zinc nitrate, soluble chromium salt to cetyltrimethylammonium bromide is 5-10:100-500:0.1-0.3.

[0011] Preferably, the mass ratio of soluble chromium salt to 2-methylimidazole is 1-5:60-110.

[0012] Preferably, the mass-volume ratio of Cr salt-ZIF-L, boron salt to triethylamine is 1mg-5mg:1mg-5mg:0.5mL-3mL.

[0013] Preferably, the conditions for carbonization treatment are: in an inert atmosphere, carbonize at 700°C-1100°C for 1h-3h; among them, within this temperature range, it can ensure the Cr metal atomic-level active sites in the boron-coordinated chromium single-atom catalyst, thereby improving the selectivity of hydrogen peroxide in the electrocatalytic reaction process.

[0014] Preferably, the heating rate for carbonization treatment is 5°C / min-15°C / min.

[0015] Preferably, the soluble chromium salt is selected from chromium acetate, chromium nitrate, chromium acetylacetonate or chromium chloride.

[0016] Preferably, the boron source is selected from boric acid, 1,4-benzenediboronic acid or benzeneboronic acid.

[0017] The second object of the present invention is to provide a boron-coordinated chromium single-atom catalyst prepared by the above preparation method.

[0018] Preferably, in the boron-coordinated chromium single-atom catalyst, the mass of Cr element accounts for 0.5% to 5% of the mass of the boron-coordinated chromium single-atom catalyst.

[0019] Preferably, the boron-coordinated chromium single-atom catalyst has a cubic structure.

[0020] The third object of the present invention is to provide the application of the above boron-coordinated chromium single-atom catalyst in the preparation of an electrocatalytic synthesis hydrogen peroxide catalyst.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention provides a preparation method of a boron-coordinated chromium single-atom catalyst. An aqueous solution of zinc nitrate, soluble chromium salt, cetyltrimethylammonium bromide and 2-methylimidazole is mixed to obtain Cr salt-ZIF-L; the Cr salt-ZIF-L solution, boron salt and triethylamine are mixed and processed. During the mixing process, after drying, Cr salt-ZIF-L-B salt is obtained; the Cr salt-ZIF-L-B salt is carbonized to obtain a boron-coordinated chromium single-atom catalyst. The transition metal single-atom catalyst on the heteroatom-doped carbon substrate has a customizable electronic structure and the maximum atomic utilization efficiency. The present invention regulates the electronic structure of the metal atom sites by introducing boron atoms, promotes the adsorption of O2, optimizes its adsorption of the intermediate -OOH, and realizes the efficient electrochemical preparation of hydrogen peroxide.

[0023] 2. In the present invention, carbonization treatment is carried out at 700 °C to 1100 °C, which can ensure the Cr metal atomic active sites in the Cr single-atom catalyst, thereby improving the selectivity of hydrogen peroxide in the electrocatalytic reaction process.

[0024] 3. The boron-coordinated chromium single-atom catalyst prepared by the present invention by impregnation combined with carbonization method can electro-synthesize hydrogen peroxide in a neutral electrolyte. The present invention greatly improves the activity, selectivity and stability of electro-synthesizing hydrogen peroxide in a neutral electrolyte by modifying the coordination environment of Cr single atoms with B. The selectivity exceeds 90% in the range of 0 to 0.4 Cr, and high-efficiency stability is maintained. After working for 100 h, its current density remains basically unchanged. At the same time, at a high current density of 500 mA / cm 2 the Faraday efficiency is still 89%, greatly improving the selectivity and production capacity of hydrogen peroxide, and providing a new way for the industrialization of electro-synthesizing hydrogen peroxide.

[0025] 4. The boron-coordinated chromium single-atom catalyst prepared by the present invention can electro-synthesize hydrogen peroxide in a neutral electrolyte. Description of the Drawings

[0026] Figure 1 It is the X-ray diffraction pattern of the boron-coordinated chromium single-atom catalyst prepared in Example 1.

[0027] Figure 2 It is the aberration-corrected electron microscopy image of the boron-coordinated chromium single-atom catalyst prepared in Example 1.

[0028] Figure 3 It is the linear sweep voltammetry graph of the boron-coordinated chromium single-atom catalyst prepared in Example 1.

[0029] Figure 4 It is the graph of the electron transfer number and hydrogen peroxide selectivity of the boron-coordinated chromium single-atom catalyst prepared in Example 1.

[0030] Figure 5 It is the graph of the reaction stability test results of the boron-coordinated chromium single-atom catalyst prepared in Example 1. Detailed implementation manners

[0031] Next, the technical solutions of the present invention will be clearly and completely described in combination with the data in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0032] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods.

[0033] In the prior art, although electrocatalytic two-electron oxygen reduction reaction for hydrogen peroxide synthesis shows great potential in terms of energy efficiency and environmental friendliness, in a neutral electrolyte environment, especially under high current density conditions, the synthesis of H2O2 still faces problems of poor selectivity and stability, which limits its industrial application. At the same time, traditional catalysts often cannot meet the requirements of high activity, high selectivity, and long-term stability under neutral conditions.

[0034] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for preparing a boron-coordinated chromium single-atom catalyst, comprising the following steps: mixing zinc nitrate, soluble chromium salt, cetyltrimethylammonium bromide and 2-methylimidazole solution, during the mixing process, zinc nitrate and chromium ions coordinate with the nitrogen atoms of 2-methylimidazole to form a metal-organic complex, and at the same time, cetyltrimethylammonium bromide is orderly arranged on the surface of the metal-organic complex to form a layered metal-organic framework structure, obtaining Cr salt-ZIF-L; using the Cr salt-ZIF-L solution and boron salt as raw materials, under the catalytic action of triethylamine, the boron source reacts on the Cr salt-ZIF-L to obtain Cr salt-ZIF-L-B salt; carbonizing the Cr salt-ZIF-L-B salt to obtain the boron-coordinated chromium single-atom catalyst.

[0035] In view of the problem that the existing catalysts in the prior art have insufficient activity under neutral conditions, the present invention regulates the electronic structure of metal chromium atomic sites by introducing boron, promotes the adsorption of O2, optimizes its adsorption capacity for intermediates, and thus improves the activity of the boron-coordinated chromium single-atom catalyst. At the same time, the present invention constructs the structure of the boron-coordinated chromium single-atom catalyst and uses carbonization treatment to ensure the stable existence of Cr metal atomic-level active sites, solves the problem of poor stability of the existing catalysts, and realizes efficient and stable electro-synthesis of hydrogen peroxide.

[0036] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will specifically describe the technical solution of the present invention with reference to specific embodiments:

[0037] Example 1

[0038] A method for preparing a boron-coordinated chromium single-atom catalyst, comprising the following steps:

[0039] S1. Mix 700 mg of zinc nitrate, 30 mg of chromium chloride, 20 mg of cetyltrimethylammonium bromide and 30 mL of water, stir evenly to obtain a first mixed solution; add 900 mg of 2-methylimidazole to 130 mL of water, stir evenly to obtain a second mixed solution; add the second mixed solution to the first mixed solution, stir thoroughly for 5 h, then filter, and vacuum dry at 70 °C for 6 h to obtain Cr salt-ZIF-L.

[0040] S2. Dissolve 300 mg of Cr salt-ZIF-L in 70 mL of methanol, sequentially add 300 mg of 1,4-benzenediboronic acid and 1 mL of triethylamine, stir evenly, filter, and dry to obtain Cr salt-ZIF-L-B salt.

[0041] S3. Under a nitrogen atmosphere, heat the Cr salt-ZIF-L-B salt at a heating rate of 10 °C / min to 950 °C, and maintain carbonization at this temperature for 2 h. Then, cool it naturally to obtain a boron-coordinated chromium single-atom catalyst, denoted as CrN4B / NC-950.

[0042] Example 2

[0043] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as that of Example 1, except that heating from 10 °C / min to 950 °C in S2 is replaced by heating from 5 °C / min to 700 °C to obtain a boron-coordinated chromium single-atom catalyst, denoted as CrNB / NC-700.

[0044] Example 3

[0045] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as that of Example 1, except that heating from 10 °C / min to 950 °C in S2 is replaced by heating from 5 °C / min to 800 °C to obtain a boron-coordinated chromium single-atom catalyst, denoted as CrNB / NC-800.

[0046] Example 4

[0047] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as that of Example 1, except that heating from 10 °C / min to 950 °C in S2 is replaced by heating from 5 °C / min to 1000 °C to obtain a boron-coordinated chromium single-atom catalyst, denoted as CrNB / NC-1000.

[0048] Example 5

[0049] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as that of Example 1, except that heating from 10 °C / min to 950 °C in S2 is replaced by heating from 5 °C / min to 1100 °C to obtain a boron-coordinated chromium single-atom catalyst, denoted as CrNB / NC-1100.

[0050] Example 6

[0051] A preparation method of a boron-coordinated chromium single-atom catalyst includes the following steps:

[0052] S1. Mix 500 mg of zinc nitrate, 10 mg of chromium nitrate, 10 mg of cetyltrimethylammonium bromide, and 20 mL of water, and stir evenly to obtain a first mixed solution; add 600 mg of 2-methylimidazole to 100 mL of water, and stir evenly to obtain a second mixed solution; add the second mixed solution to the first mixed solution, stir well for 4 h, then filter, and vacuum dry at 50 °C for 6 h to obtain Cr salt-ZIF-L.

[0053] S2. Dissolve 100 mg of Cr salt-ZIF-L in 50 mL of methanol, sequentially add 100 mg of phenylboronic acid and 0.5 mL of triethylamine, stir evenly, filter, and dry to obtain Cr salt-ZIF-L-B salt.

[0054] S3. Under a nitrogen atmosphere, heat the Cr salt-ZIF-L-B salt to 900 °C at a heating rate of 5 °C / min and maintain carbonization at this temperature for 2 h, then cool naturally to obtain the boron-coordinated chromium single-atom catalyst.

[0055] Example 7

[0056] A preparation method of a boron-coordinated chromium single-atom catalyst includes the following steps:

[0057] S1. Mix 600 mg of zinc nitrate, 8 mg of chromium acetate, 20 mg of cetyltrimethylammonium bromide, and 30 mL of water, stir evenly to obtain the first mixed solution; add 800 mg of 2-methylimidazole to 110 mL of water, stir evenly to obtain the second mixed solution; add the second mixed solution to the first mixed solution, stir well for 5 h, then filter and vacuum dry at 60 °C for 6 h to obtain Cr salt-ZIF-L.

[0058] S2. Dissolve 200 mg of Cr salt-ZIF-L in 70 mL of methanol, sequentially add 300 mg of boric acid and 1 mL of triethylamine, stir evenly, filter, and dry to obtain Cr salt-ZIF-L-B salt.

[0059] S3. Under a nitrogen atmosphere, heat the Cr salt-ZIF-L-B salt to 1000 °C at a heating rate of 15 °C / min and maintain carbonization at this temperature for 2 h, then cool naturally to obtain the boron-coordinated chromium single-atom catalyst.

[0060] Example 8

[0061] A preparation method of a boron-coordinated chromium single-atom catalyst includes the following steps:

[0062] S1. Mix 800 mg of zinc nitrate, 10 mg of chromium acetylacetonate, 30 mg of cetyltrimethylammonium bromide, and 40 mL of water, stir evenly to obtain the first mixed solution; add 1000 mg of 2-methylimidazole to 100 mL of water, stir evenly to obtain the second mixed solution; add the second mixed solution to the first mixed solution, stir well for 6 h, then filter and vacuum dry at 60 °C for 6 h to obtain Cr salt-ZIF-L.

[0063] S2. Dissolve 400 mg of Cr salt-ZIF-L in 80 mL of methanol. Sequentially add 300 mg of phenylboronic acid and 1.5 mL of triethylamine, stir evenly, filter, and dry to obtain Cr salt-ZIF-L-B salt.

[0064] S3. Under a nitrogen atmosphere, heat Cr salt-ZIF-L-B salt at a heating rate of 10 °C / min to 950 °C and maintain carbonization at this temperature for 2 h. Then, cool naturally to obtain the boron-coordinated chromium single-atom catalyst.

[0065] Example 9

[0066] A preparation method of a boron-coordinated chromium single-atom catalyst, comprising the following steps:

[0067] S1. Mix 1000 mg of zinc nitrate, 50 mg of chromium chloride, 30 mg of cetyltrimethylammonium bromide, and 40 mL of water, stir evenly to obtain a first mixed solution; add 1100 mg of 2-methylimidazole to 150 mL of water, stir evenly to obtain a second mixed solution; add the second mixed solution to the first mixed solution, fully stir for 6 h, then filter and vacuum dry at 80 °C for 6 h to obtain Cr salt-ZIF-L.

[0068] S2. Dissolve 500 mg of Cr salt-ZIF-L in 100 mL of methanol. Sequentially add 500 mg of boric acid and 3 mL of triethylamine, stir evenly, filter, and dry to obtain Cr salt-ZIF-L-B salt.

[0069] S3. Under a nitrogen atmosphere, heat Cr salt-ZIF-L-B salt at a heating rate of 15 °C / min to 1100 °C and maintain carbonization at this temperature for 2 h. Then, cool naturally to obtain the boron-coordinated chromium single-atom catalyst.

[0070] Comparative Example 1

[0071] A preparation method of a catalyst of boron and nitrogen co-doped carbon material is the same as that of Example 1, except that in S1, the dosage of chromium chloride is replaced by 0 to obtain the catalyst of boron and nitrogen co-doped carbon material, denoted as BNC catalyst.

[0072] Comparative Example 2

[0073] A preparation method of a chromium single-atom catalyst is the same as that of Example 1, except that in S1, the dosage of 1,4-benzenediboronic acid is replaced by 0 to obtain the chromium single-atom catalyst, denoted as CrN4 / NC catalyst.

[0074] Comparative Example 3

[0075] A preparation method of a carbon material catalyst is the same as the preparation method of Example 1, except that in S1, the dosage of chromium chloride is replaced by 0 mg, and the dosage of 1,4-benzenediboronic acid is replaced by 0 mg, obtaining a carbon material catalyst, denoted as NC catalyst.

[0076] Comparative Example 4

[0077] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as the preparation method of Example 1, except that in S1, chromium chloride is replaced by chromium nitrate, obtaining a boron-coordinated chromium single-atom catalyst, denoted as Cr a N4B / NC catalyst.

[0078] Comparative Example 5

[0079] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as the preparation method of Example 1, except that in S1, chromium chloride is replaced by chromium acetylacetonate, obtaining a boron-coordinated chromium single-atom catalyst, denoted as Cr b N4B / NC catalyst.

[0080] Comparative Example 6

[0081] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as the preparation method of Example 1, except that in S1, chromium chloride is replaced by chromium acetate, obtaining a boron-coordinated chromium single-atom catalyst, denoted as Cr c N4B / NC catalyst.

[0082] Comparative Example 7

[0083] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as the preparation method of Example 1, except that in S2, 1,4-benzenediboronic acid is replaced by boric acid, obtaining a boron-coordinated chromium single-atom catalyst, denoted as CrN4B a / NC catalyst.

[0084] Comparative Example 8

[0085] A preparation method of a boron-coordinated chromium single-atom catalyst is the same as the preparation method of Example 1, except that in S2, 1,4-benzenediboronic acid is replaced by benzeneboronic acid, obtaining a boron-coordinated chromium single-atom catalyst, denoted as CrN4B b / NC catalyst.

[0086] Observation Figure 1 It is concluded that there are no obvious diffraction peaks attributed to metallic Cr in the XRD pattern, which means that the contained metallic Cr in the boron-coordinated chromium single-atom catalyst does not form a particulate structure.

[0087] Observation Figure 2It is concluded that the TEM image shows no obvious particles in the boron-coordinated chromium single-atom catalyst, which means that in the boron-coordinated chromium single-atom catalyst of Example 1, metallic chromium does not exist in the form of particles. Instead, metallic chromium atoms are atomically dispersed in the carbon support.

[0088] Observation Figure 3 It is concluded that the boron-coordinated chromium single-atom catalyst of Example 1 shows a ring current of 0.17 mA and a disk current density of 3.18 mA / cm at a potential of 0.0 V vs RHE under the condition of a 0.5 mol / L Na2SO4 neutral electrolyte. 2 。

[0089] Observation Figure 4 It is concluded that by using Figure 3 the ring current and disk current density data provided in, the selectivity of hydrogen peroxide (H2O2) and the number of electron transfers at different potentials were calculated. The results show that in the potential range of 0.0 V vs RHE to 0.4 V vs RHE, the average selectivity of H2O2 of the boron-coordinated chromium single-atom catalyst of Example 1 is as high as 96.6%, and the average number of electron transfers is close to 2.07, indicating that the boron-coordinated chromium single-atom catalyst mainly promotes the two-electron transfer process in this potential range.

[0090] For the boron-coordinated chromium single-atom catalyst of the present invention, in the voltage range of 0.0 V vs RHE to 0.4 V vs RHE, the average selectivity of hydrogen peroxide is 84% to 100%. This boron-coordinated chromium single-atom catalyst can efficiently promote the two-electron oxygen reduction reaction (2e-ORR) path, thereby effectively synthesizing hydrogen peroxide.

[0091] It is Figure 5 concluded that the current density of the boron-coordinated chromium single-atom catalyst of Example 1 remains basically unchanged after working for 100 h, indicating that the stability of the boron-coordinated chromium single-atom catalyst is very good.

[0092] For the electro-synthesis of H2O2 in a flow electrolytic cell, the boron-coordinated chromium single-atom catalysts prepared in Examples 1 to 5 were used for the electro-synthesis of H2O2. The comparison results of the H2O2 selectivity are shown in Table 1.

[0093] Table 1 Comparison table of the selectivity of the boron-coordinated chromium single-atom catalysts of Examples 1 to 5 for the electro-catalytic synthesis of H2O2

[0094] Example Sample Name <![CDATA[Selectivity of H2O2 (%)]]> Test Solution Example 2 CrNB / NC-700 83 <![CDATA[0.5mol / L Na2SO4 solution]]> Example 3 CrNB / NC-800 87 <![CDATA[0.5 mol / L Na2SO4 solution]]> Example 1 <![CDATA[CrN4B / NC-950]]> 98 <![CDATA[0.5mol / L Na2SO4 solution]]> Example 4 CrNB / NC-1000 79 <![CDATA[0.5 mol / L Na2SO4 solution]]> Example 5 CrNB / NC-1100 74 <![CDATA[0.5 mol / L Na2SO4 solution]]>

[0095] It can be seen from Table 1 that the boron-coordinated chromium single-atom catalyst has a higher H2O2 selectivity at 950 °C, showing better performance in the electro-synthesis of H2O2. This is attributed to the fact that the metal element in the boron-coordinated chromium single-atom catalyst is dispersed in single atoms, but too high a temperature will lead to the formation of particles, thereby affecting the activity.

[0096] Table 2 Comparison table of half-wave potentials of the boron-coordinated chromium single-atom catalyst in Example 1, the BNC catalyst in Comparative Example 1, the chromium single-atom catalyst in Comparative Example 2, and the NC catalyst in Comparative Example 3

[0097] <![CDATA[Selectivity of H2O2 (%)]]> Test Solution Example 1 98 <![CDATA[0.5mol / L Na2SO4 solution]]> Comparative Example 1 64 <![CDATA[0.5 mol / L Na2SO4 solution]]> Comparative Example 2 41 <![CDATA[0.5mol / L Na2SO4 solution]]> Comparative Example 3 40 <![CDATA[0.5mol / L Na2SO4 solution]]>

[0098] It can be seen from Table 2 that the H2O2 selectivity of the boron-coordinated chromium single-atom catalyst in Example 1 of the present invention is much higher than that of the chromium single-atom catalyst without B modification.

[0099] The Faraday efficiency of the boron-coordinated chromium single-atom catalyst in Test Example 1 at different current densities was measured, and the results are shown in Table 3.

[0100] Table 3 Faraday efficiency table of the boron-coordinated chromium single-atom catalyst in Example 1 at different current densities

[0101]

[0102] It can be seen from Table 3 that the CrN4B / NC-950 catalyst exhibits excellent Faraday efficiency at different current densities. Among them, at a current density as high as 600 mA / cm 2 , its Faraday efficiency is still 88.7%. This indicates that an excellent boron-coordinated chromium single-atom catalyst prepared by the present invention is used for the electro-synthesis of hydrogen peroxide.

[0103] The comparison results of the half-wave potentials of the boron-coordinated chromium single-atom catalyst in Example 1 and the boron-coordinated chromium single-atom catalysts in Comparative Examples 4 to 8 are shown in Table 4.

[0104] Table 4 Comparison table of half-wave potentials of the boron-coordinated chromium single-atom catalyst in Example 1 and the boron-coordinated chromium single-atom catalysts prepared in Comparative Examples 4 to 8

[0105] Catalyst <![CDATA[H2O2 selectivity (%)]]> Test Solution Example 1 98 <![CDATA[0.5mol / L Na2SO4 solution]]> Comparative Example 4 93.4 <![CDATA[0.5 mol / L Na2SO4 solution]]> Comparative Example 5 91.2 <![CDATA[0.5mol / L Na2SO4 solution]]> Comparative Example 6 93.3 <![CDATA[0.5mol / L Na2SO4 solution]]> Comparative Example 7 90.9 <![CDATA[0.5mol / L Na2SO4 solution]]> Comparative Example 8 92.9 <![CDATA[0.5mol / L Na2SO4 solution]]>

[0106] It can be seen from Table 4 that the types of metal salts and boron salts in the raw materials of the boron-coordinated chromium single-atom catalyst in Example 1 of the present invention have little effect on the H2O2 selectivity.

[0107] It should be noted that when the present invention involves a numerical range, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods adopted are the same as those in the embodiments, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

Claims

1. A preparation method of a boron-coordinated chromium single-atom catalyst, characterized in that, It includes the following steps: Mix zinc nitrate, soluble chromium salt, cetyltrimethylammonium bromide and 2-methylimidazole solution. During the mixing process, zinc nitrate and chromium ions coordinate with the nitrogen atoms of 2-methylimidazole together and form a metal-organic complex. At the same time, cetyltrimethylammonium bromide arranges orderly on the surface of the metal-organic complex to form a layered metal-organic framework structure, obtaining Cr salt-ZIF-L; Using the Cr salt-ZIF-L solution and boron source as raw materials, under the catalytic action of triethylamine, the boron source reacts on Cr salt-ZIF-L to obtain Cr salt-ZIF-L-B salt; Carry out carbonization treatment on the Cr salt-ZIF-L-B salt to obtain a boron-coordinated chromium single-atom catalyst.

2. The preparation method of the boron-coordinated chromium single-atom catalyst according to claim 1, wherein The mass ratio of zinc nitrate, soluble chromium salt to cetyltrimethylammonium bromide is 5-10:100-500:0.1-0.

3.

3. The preparation method of the boron-coordinated chromium single-atom catalyst according to claim 1, wherein, The mass ratio of soluble chromium salt to 2-methylimidazole is 1-5:60-110.

4. The preparation method of the boron-coordinated chromium single-atom catalyst according to claim 1, characterized in that, The mass ratio of Cr salt-ZIF-L to boron source is 1-5:1-5.

5. The preparation method of the boron-coordinated chromium single-atom catalyst according to claim 1, wherein The boron source is selected from boric acid, 1,4-benzenediboronic acid or phenylboronic acid.

6. The preparation method of the boron-coordinated chromium single-atom catalyst according to claim 1, characterized in that, The conditions for carbonization treatment are: in an inert atmosphere, carbonize at 700°C - 1100°C for 1h - 3h.

7. A boron-coordinated chromium single-atom catalyst prepared by the preparation method according to any one of claims 1-6.

8. The boron-coordinated chromium single-atom catalyst according to claim 7, wherein In the boron-coordinated chromium single-atom catalyst, the mass of Cr element accounts for 0.5% - 5% of the mass of the boron-coordinated chromium single-atom catalyst.

9. The boron-coordinated chromium single-atom catalyst according to claim 7, characterized in that, The boron-coordinated chromium single-atom catalyst has a cubic structure.

10. Use of the boron-coordinated chromium single-atom catalyst according to claim 7 in the preparation of an electrocatalytic synthesis hydrogen peroxide catalyst.

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