Preparation method of alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst and application of electro-synthetic hydrogen peroxide

Abstract

The application belongs to the technical field of chemical catalysis, and particularly relates to a preparation method of an alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst and an application of the catalyst in electro-synthesizing hydrogen peroxide. A cobalt-containing compound is used as a metal source, mixed with a nitrogen-containing organic matter and carbon material, and then subjected to rotary evaporation, grinding, inert atmosphere high-temperature pyrolysis, and finally, surface defect construction through strong acid pickling. Finally, the Co-N-C / X catalyst is obtained through stirring adsorption of an alkali metal salt solution, suction filtration and drying. In the application, the alkali metal cation is physically adsorbed and anchored on the surface interface of the Co-N-C catalyst, rather than being dissolved in the solution, which not only optimizes the electronic structure of the Co active site and the adsorption energy of the OOH intermediate, but also avoids the difficulty in separating the alkali metal from the product. When the catalyst is used in the electro-catalytic oxygen reduction reaction, the selectivity of H2O2 is as high as 98%, and the preparation process is simple, low in cost and scalable, thereby solving the problems of high energy consumption, serious pollution and insufficient selectivity of existing catalysts in the traditional method.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, specifically a method for preparing an alkali metal cation-modified cobalt-nitrogen-carbon single-atom catalyst (Co-NC / X, where X is an alkali metal element) and its application in the electrosynthesis of hydrogen peroxide. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important modern industrial product, is widely used in semiconductor device manufacturing, medical applications, environmental protection, and the production of high-value-added chemicals. However, the traditional anthraquinone process for preparing hydrogen peroxide is hampered by high energy consumption, high pollution, and high transportation risks, failing to meet the demands of green chemistry and severely limiting the application potential of H2O2 at its source. Therefore, seeking a green, in-situ, and efficient method for preparing H2O2 is of great significance.

[0003] An innovative solution for the green synthesis of H2O2 is provided by using single-atom catalysts (SACs) to drive the electrocatalytic oxygen reduction reaction (ORR). This process can utilize green electricity to reduce oxygen (O2) to H2O2, meeting the requirements of green and in-situ preparation. SACs have become a popular catalyst in the field due to their advantages such as high atom utilization, high catalytic activity, and high stability. Co-NC single-atom catalysts (Co-SACs) have attracted widespread attention due to their suitable intermediate (*OOH) adsorption energy, O2 end adsorption (Pauling type) mode, and low cost (Chem., 2025, 11, 102393; Angew. Chem. Int. Ed., 2023, 62, e202304754; J. Am. Chem. Soc. 2025, 147, 22322-22328).

[0004] Conventional control strategies mainly focus on controlling the coordination structure of Co-NC catalysts or employing doping strategies to achieve 2e- ... -Significant improvements in ORR performance. Chen et al. prepared a Co-N5-C catalyst with axial nitrogen (N) coordination on a hierarchically porous carbon substrate using a sacrificial template method. The axial N ligand can effectively regulate the d-band center of the Co active site, resulting in a more suitable adsorption energy for *OOH compared to the traditional planar symmetric Co-N4 coordination structure (App. Catal. B: Environ., 2023, 338, 123078). Gao et al. successfully prepared a Co-NC catalyst with an asymmetric coordination structure (Co-N5) using phenylporphyrin cobalt by utilizing the thermal stability differences of different cobalt precursors. The analysis results showed that this asymmetric Co-N5 is more conducive to O2 activation and can further optimize the adsorption energy of the material for *OOH (Angew. Chem., Int. Ed., 2025, 64, e202418713).

[0005] However, the catalytic performance achieved through modification of Co-NC catalysts still falls short of practical industrial applications. Recent studies have found that alkali metal cations at the solution interface significantly improve ORR performance. For example, Liu et al. discovered that alkali metal cations can form a "shielding layer" on the surface of the cathode catalyst to compress protons at the catalyst / electrolyte interface, preventing further reduction of hydrogen peroxide and thus effectively improving the Faraday efficiency of H2O2 (Nat. Commun., 2022, 13, 2880). However, the addition of alkali metal cations to the solution makes separation from the product H2O2 difficult, resulting in a complex system and high separation costs.

[0006] Patent CN116676620A discloses a Co single-atom catalyst and its preparation method, as well as a method for preparing hydrogen peroxide. Although it is a Co single-atom catalyst used for the electrosynthesis of hydrogen peroxide, it relies on the co-impregnation of zinc nitrate and cobalt nitrate. The single-atom dispersed structure is formed through the evaporation of Zn salt during pyrolysis, and the coordination environment is regulated by Zn salt. This method cannot solve the problem of separation when additives are added to the solution. Patent CN117599761A discloses an alkali metal-doped carbon-based adsorbent, its preparation method, and its application. This adsorbent uses an alkali metal-doped carbon-based adsorbent, which forms an adsorbent material through the coordination self-assembly of alkali metal and cyclodextrin. However, it lacks cobalt-nitrogen-carbon single-atom catalytic active sites and cannot achieve the electrocatalytic oxygen reduction reaction (ORR) to produce hydrogen peroxide.

[0007] In summary, existing research has found that adding alkali metal cations to the solution can improve the Faradaic efficiency of hydrogen peroxide. However, the alkali metal cations are difficult to separate from the product hydrogen peroxide, leading to system complexity and increased separation costs, which limits its practical application. Furthermore, existing modification methods for Co-NC catalysts mostly rely on special precursors or complex processes, making large-scale production difficult and further hindering technology promotion. Therefore, developing a simple, low-cost, highly selective Co-NC catalyst modification method that requires no additional separation steps is crucial to overcoming the technical bottlenecks in the electrosynthesis of hydrogen peroxide. Summary of the Invention

[0008] To address the aforementioned challenges, the present invention aims to provide a method for preparing an alkali metal cation-modified cobalt-nitrogen-carbon single-atom catalyst (Co-NC / X, where X is an alkali metal element) and its application in the electrosynthesis of hydrogen peroxide. By modifying the surface of Co-SACs with alkali metal cations (X), the Co-SACs physically adsorb specific alkali metal ions, significantly improving the 2e- content of the Co-SACs. - ORR's ability to produce H2O2.

[0009] The technical solution of this invention is as follows:

[0010] A method for preparing an alkali metal cation-modified cobalt-nitrogen-carbon single-atom catalyst includes the following steps:

[0011] (1) Using a cobalt-containing compound as a metal source, the metal source dispersion was ultrasonically dispersed in an organic solvent to obtain a metal source dispersion;

[0012] (2) Add nitrogen-containing organic matter and carbon material to the metal source dispersion in step (1), and stir to disperse evenly to obtain a suspension;

[0013] (3) The suspension from step (2) was evaporated in a water bath to obtain a mixed powder, which was then ground evenly.

[0014] (4) The powder ground in step (3) is pyrolyzed at 850-1000℃ for 2-5 hours in an inert gas atmosphere;

[0015] (5) Add the pyrolysis product from step (4) into the acid solution and perform oil bath stirring and acid washing;

[0016] (6) The acid washing suspension from step (5) was filtered, and the filter cake was dried in an oven to obtain the Co-NC catalyst.

[0017] (7) Add the Co-NC catalyst to the alkali metal salt solution and stir to disperse it evenly;

[0018] (8) The suspension from step (7) is filtered, and the filter cake is dried in an oven to obtain the Co-NC / X catalyst, where X is an alkali metal element.

[0019] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, in step (1), the metal source is cobalt phthalocyanine, cobalt nitrate, cobalt chloride or cobalt sulfate, and the organic solvent is common organic solvents such as N,N-dimethylformamide, dichloromethane, ethanol, isopropanol or chloroform; the ratio of metal source to organic solvent is 3-24 mg: 5-25 mL, and the ultrasonic dispersion time is 5-8 min.

[0020] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, in step (2), the nitrogen-containing organic compound is one or more of dicyandiamide, amine, quaternary ammonium salt, quaternary ammonium base, nitro compound, nitrile, and isocyanate, and the carbon material is carbon black, graphene, carbon nanotubes, C 60 One or more of the following: nitrogen-containing organic matter added at a rate of 400–800 mg, carbon material added at a rate of 200–600 mg, stirring at room temperature, and stirring for 4–12 hours.

[0021] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, the temperature of water bath rotary evaporation in step (3) is 70-120℃.

[0022] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, in step (4), the high-temperature pyrolysis adopts the inert atmosphere high-temperature calcination technology, and the inert gas is argon or nitrogen.

[0023] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, in step (5), the acid solution is one or more of nitric acid, sulfuric acid, and perchloric acid; the concentration of the acid solution is 9-12 mol / L, the volume of the nitric acid solution is 100-150 mL, the oil bath temperature is 80-100℃, the washing time is 8-12 h, the reflux operation is carried out using a spherical condenser, and the condensate is room temperature water.

[0024] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, in steps (6) and (8), the drying temperature is 50-70℃, the drying time is 8-16h, and the drying oven used is an electric heating blast drying oven.

[0025] In the preparation method of the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, in step (7), the alkali metal salt solution is an aqueous or organic solution containing various alkali metal elements; the concentration of the alkali metal salt solution is 1-1.5 mol / L, the volume of the alkali metal salt solution is 15-20 mL, the stirring temperature is 10-50℃, and the stirring time is 8-16 h.

[0026] The method for preparing the alkali metal cation modified cobalt-nitrogen-carbon single-atom catalyst, wherein X in the Co-NC / X catalyst is selected from one or more of lithium, sodium, potassium, rubidium, and cesium.

[0027] The alkali metal cation-modified cobalt-nitrogen-carbon single-atom catalyst described herein is used in the electrocatalytic oxygen reduction reaction to synthesize hydrogen peroxide, and the selectivity of hydrogen peroxide in the electrocatalytic oxygen reduction reaction is not less than 90%.

[0028] The design concept of this invention is:

[0029] Traditional anthraquinone methods for hydrogen peroxide production suffer from high energy consumption, high pollution, and high transportation risks, failing to meet the demands of green chemistry. Existing electrocatalytic ORR (Organic Reduction) hydrogen peroxide production technologies suffer from insufficient catalyst selectivity, hindering efficient directional conversion. While adding alkali metal cations to the solution can improve the Faradaic efficiency of hydrogen peroxide production in current research, it presents technical challenges such as difficulty in separating the alkali metal from the product, system complexity, and high separation costs. The core innovation of this invention lies in adsorbing and anchoring electrocatalytically active alkali metal cations from the electrolyte onto the surface of a Co-NC single-atom catalyst. By treating the Co-NC catalyst with strong acid, abundant surface defects and oxygen-containing functional groups are constructed, enhancing the catalyst's adsorption capacity for alkali metal cations. This brings the alkali metal cations closer to the catalytically active center of Co, forming a local microenvironment and achieving higher performance improvement, while avoiding excessive addition of alkali metal cations that could hinder product separation. This design utilizes alkali metal cations to regulate the electronic structure of the Co active site and the adsorption energy of the *OOH intermediate, promoting the 2e- ... - The ORR reaction pathway avoids the separation problem caused by the dissolution of alkali metal cations in solution, achieving the dual goals of improving catalytic performance and simplifying the process.

[0030] Experiments have confirmed that the preparation method of the single-atom cobalt-nitrogen-carbon / X (Co-NC / X) composite catalyst provided by this invention has the following advantages:

[0031] (1) Compared with the previously reported Co-SACs modification schemes, the present invention provides a technique for surface and interface alkali metal cation modification, which constructs an alkali metal cation microenvironment near the active site of the electrocatalyst, greatly improving the electrocatalytic performance.

[0032] (2) Compared with the previously reported Co-SACs modification schemes, the route of the present invention has the advantages of low cost and large-scale production. By treating the Co-NC catalyst with strong acid, rich surface defects and oxygen-containing functional groups are constructed, which can anchor high loading of alkali metal cations on the surface. The alkali metal cations are firmly adsorbed through the catalyst surface defects and oxygen-containing functional groups, and there is no shedding phenomenon during the catalytic reaction. The catalyst has good long-term operational stability.

[0033] (3) Compared with previously reported Co-SACs modification schemes, the catalyst preparation process of this invention is simple, mild, and highly tunable. Alkali metal cations can be modified by stirring and adsorption, and the low preparation cost meets the needs of large-scale industrial production. In this preparation method, the carbon composition, alkali metal element, and nitrogen content can all be efficiently adjusted by changing the experimental feed amount, achieving controllable adjustment of catalyst properties.

[0034] (4) This invention focuses on the preparation of Co-NC and Co-NC / X catalysts and their application in the electrosynthesis of H2O2. The Co-NC / X catalyst is modified with alkali metal cations to optimize the electronic structure of the Co active site and the adsorption energy of the *OOH intermediate, making the ORR reaction more inclined towards 2e - The Co-NC / X catalyst demonstrated excellent H2O2 selectivity of 98% in the electrocatalytic ORR experiment, far exceeding the catalytic performance of existing Co-NC catalysts. Attached Figure Description

[0035] Figure 1 (a) and (b) are scanning electron microscope (SEM) images of the Co-NC catalyst, and (c) and (d) are SEM images of the Co-NC / Cs catalyst.

[0036] Figure 2 (a) and (b) are transmission electron microscopy (TEM) images of the Co-NC catalyst, and (c) and (d) are TEM images of the Co-NC / Cs catalyst.

[0037] Figure 3 Transmission electron microscopy (SEI mode imaging) and elemental distribution diagrams of C, O, N, and Co for Co-NC catalysts.

[0038] Figure 4 Transmission electron microscopy (SEI mode imaging) of Co-NC / Cs catalyst and elemental distribution diagrams of C, O, N, Co, and Cs.

[0039] Figure 5 (a) and (b) are the X-ray diffraction (XRD) patterns of the Co-NC catalyst and the Co-NC / Cs catalyst, respectively. In the figures, the horizontal axis 2theta represents the diffraction angle (degree), and the vertical axis Intensity represents the relative intensity (au).

[0040] Figure 6 (a) shows the 2e-ion concentration before and after Cs ion adsorption on the Co-NC catalyst. - The ORR H2O2 generation performance graph shows that the horizontal axis, Potential, represents the potential relative to the reversible hydrogen electrode (V vs. RHE), and the vertical axis represents the upper I... RingThe lower part represents the loop current (mA), and the lower part represents the current density (mA / cm²). -2 (b) shows two catalysts, 2e - The ORR H2O2 selectivity curves are shown, with Potential on the x-axis representing the potential relative to the reversible hydrogen electrode (V vs. RHE) and H2O2 Selectivity on the y-axis representing the hydrogen peroxide selectivity (%). (c) shows the ORR reaction pathway curves for the two catalysts, with Potential on the x-axis representing the potential relative to the reversible hydrogen electrode (V vs. RHE) and n on the y-axis representing the number of electrons transferred.

[0041] Figure 7 (a) The 2e-ion concentrations before and after Cs ion adsorption on the Co-NC catalyst (Co-NC, Co-NC / Cs (0.5M CsCl), Co-NC / Cs (1M CsCl), Co-NC / Cs (2M CsCl)) - The ORR H2O2 generation performance graph shows that the horizontal axis, Potential, represents the potential relative to the reversible hydrogen electrode (V vs. RHE), and the vertical axis represents the upper I... Ring The lower part represents the loop current (mA), and the lower part represents the current density (mA / cm²). -2 (b) shows four catalysts 2e - The ORR H2O2 selectivity curves are shown, with Potential on the x-axis representing the potential relative to the reversible hydrogen electrode (V vs. RHE) and H2O2 Selectivity on the y-axis representing the hydrogen peroxide selectivity (%). (c) shows the ORR reaction pathway curves for four catalysts, with Potential on the x-axis representing the potential relative to the reversible hydrogen electrode (V vs. RHE) and n on the y-axis representing the number of electrons transferred.

[0042] Figure 8 (a) The 2e-ion adsorption of Cs ions on Co-NC catalysts before and after treatment with different molar amounts of nitric acid (Co-NC, Co-NC / Cs(9M HNO3), Co-NC / Cs(12M HNO3)) - The ORR H2O2 generation performance graph shows that the horizontal axis, Potential, represents the potential relative to the reversible hydrogen electrode (V vs. RHE), and the vertical axis represents the upper I... Ring The lower part represents the loop current (mA), and the upper part represents the current density (mA / cm²). -2 (b) shows three catalysts 2e -The ORR H2O2 selectivity curves are shown, with Potential on the x-axis representing the potential relative to the reversible hydrogen electrode (V vs. RHE) and H2O2 Selectivity on the y-axis representing the hydrogen peroxide selectivity (%). (c) shows the ORR reaction pathway curves for the three catalysts, with Potential on the x-axis representing the potential relative to the reversible hydrogen electrode (V vs. RHE) and n on the y-axis representing the number of electrons transferred. Detailed Implementation

[0043] In its specific implementation, this invention proposes a method for preparing a single-atom cobalt-nitrogen-carbon / alkali metal cation (Co-NC / X) composite catalyst and its application in the electrosynthesis of hydrogen peroxide, comprising the following steps:

[0044] (1) Using the corresponding Co compound as the metal source, weigh an appropriate amount and ultrasonically disperse it in a certain amount of organic solvent;

[0045] In step (1), the metal source includes, but is not limited to, cobalt phthalocyanine (CoPc), cobalt nitrate, cobalt chloride, cobalt sulfate and other cobalt-containing compounds, and the organic solvent includes, but is not limited to, common organic solvents such as N,N-dimethylformamide (DMF), dichloromethane, ethanol, isopropanol, chloroform, etc.; 3-24 mg of metal source is added to 5-25 mL of organic solvent and ultrasonically dispersed for 5-8 min.

[0046] (2) Weigh an appropriate amount of nitrogen-containing organic matter and carbon material, dissolve them in step (1), and stir to disperse them evenly to obtain a suspension;

[0047] In step (2), nitrogen-containing organic compounds include, but are not limited to, amines, dicyandiamide, azo compounds, quaternary ammonium salts, quaternary ammonium bases, nitro compounds, nitriles, isocyanates, and other nitrogen-containing organic compounds. Carbon materials include, but are not limited to, carbon black, graphene, carbon nanotubes, and C. 60 Common carbon carriers such as nitrogen-containing organic matter are added at a rate of 400–800 mg, carbon material at a rate of 200–600 mg, stirring at room temperature, and stirring for 4–12 hours.

[0048] (3) The resulting suspension was rotary evaporated to obtain a mixed powder, which was then thoroughly ground;

[0049] In step (3), rotary evaporation is carried out using a water bath for heating, and the rotary evaporation temperature is 70-120℃.

[0050] (4) The powder after grinding in step (3) is pyrolyzed at high temperature in an inert gas atmosphere;

[0051] In step (4), the high-temperature pyrolysis adopts the inert atmosphere high-temperature calcination technology. The inert gas includes, but is not limited to, inert gases such as argon and nitrogen. The pyrolysis temperature is 850-1000℃ and the pyrolysis time is 2-5h.

[0052] (5) The product after pyrolysis in step (4) is stirred and acid-washed in an acidic solution in an oil bath;

[0053] In step (5), the acid solution includes, but is not limited to, common acids such as nitric acid, sulfuric acid, and perchloric acid; the concentration of the acid solution is 9-12 mol / L, the volume of the nitric acid solution is 100-150 mL, the oil bath temperature is 80-100℃, the washing time is 10 h, and a spherical condenser is required for reflux operation, and the condensate is room temperature water.

[0054] (6) The suspension from step (5) was filtered and dried in an oven to obtain the Co-NC catalyst;

[0055] (7) Weigh a certain amount of Co-NC catalyst and stir it in an alkali metal salt solution to disperse it evenly;

[0056] In step (7), the alkali metal salt solution includes various aqueous and organic solutions containing alkali metal elements; the concentration of the alkali metal salt solution is 1 to 1.5 mol / L, the volume of the alkali metal salt solution is 15 to 20 mL, the stirring temperature is 10 to 50 °C, and the stirring time is 12 h.

[0057] (8) The suspension from step (7) was filtered and dried to obtain the Co-NC / X catalyst.

[0058] In steps (6) and (8), the drying temperature is 50-70℃, the drying time is 12h, and the drying oven used is a conventional electric heating blast drying oven.

[0059] In order to provide a clear and complete description of the technical solution, technical effects, and application of electrosynthesized hydrogen peroxide of the present invention, the following description is provided in conjunction with specific embodiments.

[0060] Example 1

[0061] In this embodiment, a cobalt-nitrogen-carbon / cesium (Co-NC / Cs) catalyst was prepared by pyrolysis synthesis with coupling defect anchoring, as follows:

[0062] 9 mg of CoPc was weighed and dissolved in 15 mL of DMF. The solution was sonicated for 5 min to ensure complete dispersion of CoPc. 600 mg of dicyandiamide and 200 mg of Ketjen black were weighed and added to the dispersion. The mixture was stirred at room temperature for 4 h to obtain a suspension. The resulting suspension was rotary evaporated in an 80 °C water bath to obtain a solid powder, which was then thoroughly ground. The powder was calcined at 850 °C for 2 h under a nitrogen atmosphere. After natural cooling, it was washed in a 9 M nitric acid solution in an oil bath at 80 °C for 10 h to remove metal nanoparticles generated during pyrolysis. The resulting product was then filtered and dried to obtain the Co-NC catalyst.

[0063] 100 mg of Co-NC catalyst was weighed and dissolved in a 1 M cesium sulfate (15 mL, Cs2SO4) solution and stirred at room temperature for 12 h. The solution was then filtered and dried to obtain the Co-NC / Cs catalyst.

[0064] like Figure 1 As shown in (a) and (b), the scanning electron microscope (SEM) images of the Co-NC catalyst clearly show a large number of nanoscale spherical particles stacked into irregular blocky materials, which is the conventional morphology of Ketjen Black particles. Figure 1 (c) and (d) are SEM images of the Co-NC / Cs catalyst, which are similar to those of the Co-NC catalyst.

[0065] like Figure 2 (a) and (b) are transmission electron microscopy (TEM) images of the Co-NC catalyst. Figure 2 (a) Clearly shows the internal structure and stacking pattern of the spherical particles. Figure 2 (b) The clearly visible lattice fringes of graphite indicate that the carbon component in the material is highly graphitized. For example... Figure 2 As shown in (c) and (d), the TEM images of the Co-NC / Cs catalyst are similar to those of the Co-NC catalyst. Figure 3 As shown in the transmission electron microscope (TEM) image of the Co-NC catalyst, the distribution outlines of C, O, and N elements highly coincide with the shape of the material, which is consistent with the material's composition. Co, however, is randomly distributed in a dotted pattern and is scarce, indicating that the Co metal nanoparticles formed during the pyrolysis process were completely removed during acid washing. The random, sporadic distribution of Co is also consistent with the distribution of single-atom active sites in traditional single-atom catalysts. Figure 4 As shown in the transmission electron microscope (TEM) diagram of the Co-NC / Cs catalyst, the distribution of C, O, N, and Co elements is similar to that of the Co-NC catalyst, but a certain amount of randomly distributed Cs elements are clearly present in the material, proving that the material has successfully adsorbed Cs ions.

[0066] like Figure 5 As shown in (a) and (b), the X-ray diffraction (XRD) patterns of the Co-NC catalyst and the Co-NC / Cs catalyst, respectively, both exhibit a relatively sharp peak at approximately 26°, which is attributed to the (002) crystal plane of graphitic carbon. Furthermore, the XRD patterns show no diffraction peaks associated with metal nanoparticles, indicating the absence of metal nanoparticles within the material, consistent with the TEM results.

[0067] To demonstrate that the Co-NC catalyst can significantly improve 2e after physical adsorption of Cs ions. - The selectivity of ORR was assessed by testing the material properties using a rotating disk electrode. For example... Figure 6 As shown in (a), the 2e- ... - The ORR (Orbital Electrode Reaction) performance graph for H2O2 generation shows that the ring current of the Co-NC / Cs catalyst is significantly higher than that of the Co-NC catalyst, while the disk current density is similar. The stronger ring electrode signal indicates a significantly increased H2O2 content generated during the reaction. Figure 6 As shown in (b) and (c), the test data of the rotating disk were further analyzed. Figure 6 (b) shows two catalysts 2e - The selectivity of H2O2 generated by ORR is significantly higher than that of the Co-NC / Cs catalyst, which exceeds 90% in most potential ranges. This indicates that the selectivity of H2O2 production by the Co-NC catalyst is significantly improved after modification. Figure 6 (c) The ORR reaction pathways of the two catalysts were analyzed. The figure shows that the number of transferred electrons of the Co-NC / Cs catalyst is close to 2, while that of the Co-NC catalyst is close to 3. This indicates that after adsorbing Cs ions, the material tends to carry out the 2-electron reaction pathway when performing the ORR reaction, which provides an explanation for the significant improvement in H2O2 selectivity of the material.

[0068] Example 2

[0069] In this embodiment, a cobalt-nitrogen-carbon / cesium (Co-NC / Cs) catalyst was prepared by pyrolysis synthesis with coupling defect anchoring. The steps were the same as in Example 1, except that cesium sulfate (Cs2SO4) was replaced with cesium chloride (CsCl), and the concentration of CsCl was changed. By adjusting the concentration of the salt solution in the external environment, the adsorption capacity of alkali metal ions was controlled.

[0070] like Figure 7 As shown in (a), (b), and (c), the rotating disk test results for the three groups of materials indicate that all three groups of materials possess good 2e properties. - ORR performance. Based on the test results, the Co-NC catalysts treated with different concentrations of CsCl (0.5M, 1M, and 2M) showed little difference in performance, with similar ring current and disk current signals, all exhibiting H2O2 selectivity exceeding 80%, and the ORR reaction pathways all closely approximating 2e⁻. - path.

[0071] Example 3

[0072] In this embodiment, a cobalt-nitrogen-carbon / cesium (Co-NC / Cs) catalyst was prepared by pyrolysis synthesis coupled with defect anchoring. The steps were the same as in Example 1, except that the concentration of nitric acid during acid washing was changed. By adjusting the density of defect sites on the surface of the carbon material inside the material, the adsorption amount of alkali metal cations was controlled.

[0073] like Figure 8 As shown in (a), (b), and (c), the rotating disk test results for the three groups of materials indicate that, after the acid concentration is adjusted, the material's 2e - The performance of ORR in preparing H2O2 shows significant differences. Figure 8 In (a), the material treated with 9M nitric acid showed a significantly stronger ring current signal than the sample treated with 12M nitric acid, while the disk current density was similar, indicating that the 2e- ... - The path clearly accounts for a larger proportion. Figure 8 (b) Sample 2e treated with 9M nitric acid. - ORR exhibits significantly superior performance in preparing H2O2, demonstrating selectivity exceeding 90% in the potential range of -0.2 to 0.3 V (vs. RHE). Figure 8 (c) also shows that the number of electrons transferred during the ORR process is closer to 2 after treatment with a suitable concentration of nitric acid (molar concentration of 9M).

[0074] The above experimental and test results fully demonstrate that this invention provides a simple, low-cost, and efficient method for preparing high-performance 2e - The ORR single-atom catalyst method, which optimizes the properties of the Co metal site through simple physical adsorption of Cs ions, significantly improves the selectivity for H2O2 production in electrocatalytic ORR. In the electrocatalytic oxygen reduction reaction, the electrolyte can be acidic, basic, or neutral, and the reaction temperature is room temperature. The H2O2 selectivity remains above 90%, even reaching 98%. The electron transfer number is close to 2, typically in the range of 1.9–2.1, indicating that the reaction mainly follows the 2e-electron transition law. - The oxygen reduction pathway directs the generation of H2O2.

[0075] The embodiments described above are some embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments disclosed in the present invention without creative effort should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an alkali metal cation-modified cobalt-nitrogen-carbon single-atom catalyst, characterized in that, Includes the following steps: (1) Using a cobalt-containing compound as a metal source, the metal source dispersion was ultrasonically dispersed in an organic solvent to obtain a metal source dispersion; (2) Add nitrogen-containing organic matter and carbon material to the metal source dispersion of step (1), and stir to disperse evenly to obtain a suspension; the nitrogen-containing organic matter is one or more of dicyandiamide, quaternary ammonium salt, quaternary ammonium base, nitro compound, nitrile, and isocyanate, and the carbon material is carbon black, graphene, carbon nanotubes, and C 60 One or more of the following; (3) The suspension from step (2) is evaporated in a water bath to obtain a mixed powder, which is then ground evenly; (4) The powder ground in step (3) is pyrolyzed at 850~1000℃ for 2~5 hours in an inert gas atmosphere; (5) Add the pyrolysis product from step (4) into the acid solution and perform oil bath stirring and acid washing; (6) The acid washing suspension from step (5) is filtered, and the filter cake is dried in an oven to obtain the Co-NC catalyst; (7) Add the Co-NC catalyst to the alkali metal salt solution and stir to disperse it evenly. The alkali metal salt solution is an aqueous or organic salt solution containing one or more of lithium, sodium, potassium, rubidium and cesium. (8) The suspension from step (7) is filtered, and the filter cake is dried in an oven to obtain the Co-NC / X catalyst, wherein X is selected from one or more of lithium, sodium, potassium, rubidium and cesium.

2. The preparation method according to claim 1, characterized in that, In step (1), the metal source is cobalt phthalocyanine, cobalt nitrate, cobalt chloride or cobalt sulfate, and the organic solvent is N,N-dimethylformamide, dichloromethane, ethanol, isopropanol or chloroform; the ratio of metal source to organic solvent is 3~24mg:5~25mL, and the ultrasonic dispersion time is 5~8min.

3. The preparation method according to claim 2, characterized in that, In step (2), the amount of nitrogen-containing organic matter added is 400~800 mg, the amount of carbon material added is 200~600 mg, the stirring temperature is room temperature, and the stirring time is 4 h~12 h.

4. The preparation method according to claim 3, characterized in that, In step (3), the temperature of the water bath rotary evaporation is 70~120℃.

5. The preparation method according to claim 4, characterized in that, In step (4), the high-temperature pyrolysis adopts the inert atmosphere high-temperature calcination technology, and the inert gas is argon or nitrogen.

6. The preparation method according to claim 5, characterized in that, In step (5), the acid solution is nitric acid. The concentration of the nitric acid solution is 9~12 mol / L, the volume of the nitric acid solution is 100~150 mL, the oil bath temperature is 80~100℃, the washing time is 8~12 h, and a spherical condenser is used for reflux operation. The condensate is room temperature water.

7. The preparation method according to claim 6, characterized in that, In steps (6) and (8), the drying temperature is 50~70℃, the drying time is 8~16h, and the drying box used is an electric heating blast drying box.

8. The preparation method according to claim 7, characterized in that, In step (7), the concentration of the alkali metal salt solution is 1~1.5mol / L, the volume of the alkali metal salt solution is 15~20mL, the stirring temperature is 10~50℃, and the stirring time is 8~16h.

9. The application of an alkali metal cation-modified cobalt-nitrogen-carbon single-atom catalyst prepared by the method according to any one of claims 1 to 8 in the synthesis of hydrogen peroxide by electrocatalytic oxygen reduction reaction, wherein the selectivity of hydrogen peroxide in the electrocatalytic oxygen reduction reaction is not less than 90%.

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