Oxygen-coordinated cobalt monatomic catalyst, preparation method and application thereof

Abstract

The application provides an oxygen-coordinated cobalt monatomic catalyst, a preparation method and application thereof. The oxygen-coordinated cobalt monatomic catalyst is composed of a porous carbon skeleton, cobalt monatomic and oxygen atoms. The specific surface area of the porous carbon skeleton is 100-3000 m 2 / g, the mass content of the cobalt monatomic is 0.01%-10%, and the mass content of the oxygen atoms is 1%-15%. The catalyst anchors the cobalt metal center by using an oxygen-rich metal organic framework, and forms Co-O-C after carbonization. In the oxygen-coordinated cobalt monatomic catalyst, the oxygen-coordinated structure can adjust the electronic structure of the central metal cobalt to promote the transfer of active sites, provide the optimal adsorption energy of the intermediate OOH, and thus improve the selectivity of 2e ‑ ORR.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to an oxygen-coordinated cobalt single-atom catalyst, its preparation method, and its application. Background Technology

[0002] Oxygen, as an abundant natural resource, is reduced to oxygen by two electrons via electrocatalysis (2e- ... - ORR (Organic Oxygen Reduction) can efficiently produce hydrogen peroxide (H2O2). H2O2, as a green oxidant, has wide applications in many fields. Single-atom-site carbon-based catalysts show great potential in two-electron oxygen reduction reactions due to their high atom utilization and tunable structural characteristics.

[0003] Numerous studies have shown that by constructing Co-N x -C sites can significantly improve the activity and selectivity of catalysts (Angew. Chem. Int. Ed., 2020, 60, 4448–4463). Compared with nitrogen coordination, oxygen coordination can promote the transfer of active sites by modulating the electronic structure of the central cobalt metal, providing optimal intermediate adsorption energy, thereby improving 2e-C activity. - The selectivity of ORR (J. Am. Chem. Soc., 2021, 143, 7819–7827). Currently, the synthesis methods for oxygen-cobalt single-atom catalysts mainly rely on traditional methods such as wet chemical impregnation or carbonization fixation, which have limitations such as cumbersome steps, limited substrate availability, and limited controllability (Energy Environ. Sci., 2024, 17, 1950–1960). Therefore, it is necessary to develop new synthetic strategies to overcome the shortcomings of existing technologies and provide high-performance catalysts.

[0004] With the pursuit of sustainable energy, electrocatalysis technology, combined with green energy sources such as solar and wind power, provides an effective way to reduce carbon emissions and improve energy efficiency. However, the intermittency and variability of green energy pose challenges to the stability and reliability of electrocatalytic systems. Electrocatalytic systems need to possess high flexibility and adaptability to cope with fluctuations in green electricity and achieve effective coupling with green energy sources such as photovoltaic systems. Testing and evaluation methods for catalysts / systems under non-steady-state power input are powerful tools for promoting the efficient utilization of green electricity, but related research is currently relatively scarce. Summary of the Invention

[0005] To address the aforementioned problems and limitations of existing technologies, one objective of this invention is to provide an oxygen-coordinated cobalt single-atom catalyst that utilizes a bottom-up synthesis method to introduce cobalt into a three-dimensional framework self-assembled from terephthalic acid and zinc, retaining the Co–O–C coordination structure after carbonization.

[0006] A second objective of this invention is to design an electrochemical testing method simulating operating conditions to evaluate the performance of electrocatalytic oxygen reduction to hydrogen peroxide. This involves simulating start-up, shutdown, and fluctuating operating conditions to evaluate catalyst stability, catalyst Faradaic efficiency, and the cumulative Faradaic efficiency of the system.

[0007] In a first aspect, the present invention provides an oxygen-coordinated cobalt single-atom catalyst. According to embodiments of the present invention, the oxygen-coordinated cobalt single-atom catalyst is composed of a porous carbon framework, cobalt single atoms, and oxygen atoms, wherein the specific surface area of ​​the porous carbon framework is 100–3000 m². 2 / g, wherein the mass content of the cobalt single atom is 0.01%–10%, and the mass content of the oxygen atom is 1%–15%. This catalyst utilizes an oxygen-rich metal-organic framework to anchor the cobalt metal center, forming Co–O–C through carbonization. In this oxygen-coordinated cobalt single-atom catalyst, the oxygen coordination structure can modulate the electronic structure of the central cobalt metal to promote the transfer of active sites, providing optimal adsorption energy for the intermediate *OOH, thereby improving 2e… - ORR selectivity.

[0008] In another aspect, the present invention also provides a method for preparing an oxygen-coordinated cobalt single-atom catalyst. According to an embodiment of the present invention, the method includes:

[0009] 1) Dissolve cobalt salt and zinc salt in an organic solution to obtain solution A;

[0010] 2) Dissolve terephthalic acid in an organic solution to obtain solution B;

[0011] 3) Mix the solutions A and B with triethylamine to obtain a metal-organic framework material containing oxygen coordination;

[0012] 4) The oxygen-coordinated metal-organic framework material is washed and dried to obtain the precursor;

[0013] 5) The precursor is subjected to a carbonization reaction to obtain a powdered catalyst;

[0014] 6) The powdered catalyst was subjected to reflux heating to obtain an oxygen-coordinated cobalt single-atom catalyst. Using a bottom-up synthesis method, cobalt was introduced into a three-dimensional framework self-assembled from terephthalic acid and zinc, and the Co–O coordination structure was retained after carbonization.

[0015] According to embodiments of the present invention, the above method may further include at least one of the following additional technical features:

[0016] According to an embodiment of the present invention, the organic solvents in steps 1) and 2) are the same.

[0017] According to embodiments of the present invention, the organic solution is selected from one or more of N,N-dimethylformamide, water, ethanol, and methanol.

[0018] According to an embodiment of the present invention, the molar ratio of terephthalic acid, zinc salt, and cobalt salt is 1:(0.1-1):(0.01-0.5).

[0019] According to an embodiment of the present invention, the molar ratio of terephthalic acid, zinc salt, and cobalt salt is 1:1:(0.01-0.1).

[0020] According to an embodiment of the present invention, the volume ratio of N,N-dimethylformamide, water, and ethanol is (1:0.05)-(0.1:0.05)-0.1.

[0021] According to embodiments of the present invention, the cobalt salt and zinc salt are one or both of nitrate or chloride salts.

[0022] According to an embodiment of the present invention, the mixing process is carried out by ultrasonic aging.

[0023] According to an embodiment of the present invention, the ultrasonic aging time is 1 to 10 hours.

[0024] According to an embodiment of the present invention, the temperature of the ultrasonic aging is 20–45°C.

[0025] According to an embodiment of the present invention, the drying temperature is not lower than 70°C.

[0026] According to an embodiment of the present invention, the drying process is carried out in a vacuum environment.

[0027] According to an embodiment of the present invention, the drying process takes 8 to 12 hours.

[0028] According to an embodiment of the present invention, the carbonization process is carried out under an argon atmosphere.

[0029] According to an embodiment of the present invention, the heating rate of the carbonization treatment is 2 to 5 °C / min.

[0030] According to an embodiment of the present invention, the carbonization temperature is 800–1000°C.

[0031] According to an embodiment of the present invention, the carbonization treatment time is 1 to 5 hours.

[0032] According to an embodiment of the present invention, the carbonization treatment time is 3 hours.

[0033] According to an embodiment of the present invention, the heating reflux treatment is carried out in an acidic solution.

[0034] According to an embodiment of the present invention, the concentration of the acidic solution is 0.1 to 3 mol / L.

[0035] According to an embodiment of the present invention, the concentration of the acidic solution is 1 mol / L.

[0036] According to an embodiment of the present invention, the temperature of the heating reflux treatment is 40 to 100°C.

[0037] According to an embodiment of the present invention, the temperature of the heating reflux treatment is 60-80°C.

[0038] According to an embodiment of the present invention, the heating reflux treatment time is 2 to 24 hours.

[0039] In another aspect, the present invention provides a method for preparing an oxygen-coordinated cobalt single-atom catalyst. According to an embodiment of the present invention, the method includes the following steps:

[0040] (1) Dissolve cobalt salt and zinc salt in an organic solution to obtain solution A, and dissolve terephthalic acid in the same organic solution to obtain solution B;

[0041] (2) Mix the clear solution A and solution B obtained in step (1), add triethylamine dropwise, and then use ultrasonic aging to make it uniformly dispersed. After centrifugation, separate the metal-organic framework material containing oxygen coordination.

[0042] (3) The precursor is obtained by washing and drying the metal-organic framework material from step (2);

[0043] (4) The precursor from step (3) is carbonized at high temperature under an inert atmosphere to remove zinc and obtain a powdered catalyst.

[0044] (5) The powdered catalyst from step (4) is heated and refluxed in an acidic solution to remove excess cobalt particles, and finally oxygen-coordinated cobalt single-atom catalyst is obtained.

[0045] According to embodiments of the present invention, the above method may further include at least one of the following additional technical features:

[0046] According to an embodiment of the present invention, the molar ratio of terephthalic acid, zinc salt, and cobalt salt is 1:1:(0.01-0.1).

[0047] According to embodiments of the present invention, the organic solution components include one or more of N,N-dimethylformamide, water, and ethanol.

[0048] According to an embodiment of the present invention, the volume ratio of N,N-dimethylformamide, water, and ethanol is (1:0.05)-(0.1:0.05)-0.1.

[0049] According to an embodiment of the present invention, triethylamine is added dropwise to allow the metal to coordinate with the oxygen in terephthalic acid to form a metal-organic framework carrier. The ultrasonic aging time is 5 to 10 hours, and the liquid temperature is maintained at 20 to 35°C.

[0050] According to an embodiment of the present invention, the high-temperature carbonization heating rate is 2-5℃ / min, the temperature range is 800-950℃, and the carbonization time range is 3h.

[0051] According to an embodiment of the present invention, the concentration of the acidic solution is 1 mol / L.

[0052] According to an embodiment of the present invention, the heating reflux temperature is controlled at 60-80°C, and the reflux time is 2-12 hours.

[0053] In another aspect of the invention, the invention proposes the application of the oxygen-coordinated cobalt single-atom catalyst described above or the oxygen-coordinated cobalt single-atom catalyst prepared according to the method described above in the electrocatalytic reduction of oxygen to prepare hydrogen peroxide.

[0054] According to embodiments of the present invention, the above application may further include at least one of the following additional technical features:

[0055] According to an embodiment of the present invention, the electrocatalytic reduction of oxygen to prepare hydrogen peroxide is carried out in an acidic medium.

[0056] According to an embodiment of the present invention, the acidic medium is one of perchloric acid, sulfuric acid, or hydrochloric acid.

[0057] According to an embodiment of the present invention, the concentration of the acidic medium is 0.01 to 1 mol / L.

[0058] According to an embodiment of the present invention, the concentration of the acidic medium is 0.1 mol / L.

[0059] According to an embodiment of the present invention, the acidic medium is 0.1 mol / L perchloric acid.

[0060] According to an embodiment of the present invention, the electrocatalytic reduction of oxygen to prepare hydrogen peroxide is carried out in a flowing electrolyzer.

[0061] According to an embodiment of the present invention, the flowing electrolytic cell utilizes one of constant current electrolysis, constant voltage electrolysis, or new energy simulation working condition electrolysis.

[0062] According to an embodiment of the present invention, the simulated operating conditions in the application are one or more of start-stop and fluctuating operating conditions.

[0063] According to an embodiment of the present invention, the current density in the simulated operating condition is 10–500 mA / cm². 2The start-stop interval is 0.01 to 20 hours / time; the fluctuating operating condition is to alternate electrolysis at 5 to 20% and 120 to 150% of the rated current density, with a fluctuation frequency of 0.01 to 20 hours / time.

[0064] In another aspect, the present invention also proposes a test for the electrocatalytic reduction of oxygen to prepare hydrogen peroxide. According to an embodiment of the present invention, the test includes using carbon paper as a gas diffusion layer, loading an oxygen-cobalt single-atom catalyst, and performing constant-current electrolysis in a flow electrolyzer using a simulated electrochemical testing method. The evaluation methods include cumulative Faradaic efficiency, catalyst Faradaic efficiency, and electrode stability.

[0065] According to embodiments of the present invention, the above test may further include at least one of the following additional technical features:

[0066] According to an embodiment of the present invention, the electrode area is 1 cm². 2 The controlled current density is 50–100 mA / cm². 2 .

[0067] According to an embodiment of the present invention, the operating condition simulation electrochemical testing method includes start-up, shutdown, and fluctuating operating conditions.

[0068] According to an embodiment of the present invention, the start-stop condition involves intermittently stopping the constant current electrolysis process, followed by resuming constant current electrolysis, with a current density of 50–100 mA / cm². 2 The start-stop interval is 0.5 to 20 hours per time.

[0069] According to an embodiment of the present invention, the current density is 50–80 mA / cm². 2 The Faraday efficiency is ≥90%, and the start-stop interval is 0.5 to 10 hours / time.

[0070] According to an embodiment of the present invention, the fluctuation condition is electrolysis within a test current range of 10-20% to 120-150%, with a fluctuation frequency of 0.1-2 hours / cycle; preferably, the test current range is 20% to 120%, and the fluctuation frequency is 0.5-1 hour / cycle.

[0071] According to an embodiment of the present invention, the cumulative Faraday efficiency is the Faraday test after a simulated operating condition test, and the catalyst Faraday efficiency is the Faraday test of the catalyst at the end of the test or during the interval.

[0072] According to embodiments of the present invention, a method for preparing an oxygen-coordinated cobalt single-atom catalyst is provided. The method comprises: dissolving cobalt salt and zinc salt in a mixed solution of N,N-dimethylformamide, water, and ethanol, obtaining solution A; dissolving terephthalic acid in the same mixed solution to obtain solution B; mixing clarified solutions A and B, adding triethylamine dropwise, and aging the mixture ultrasonically to achieve uniform dispersion; centrifuging to separate the oxygen-coordinated metal-organic framework material; washing and drying the metal-organic framework material to obtain a precursor; carbonizing the dried precursor at high temperature under an inert atmosphere to remove zinc, obtaining a powdered catalyst; and heating the powdered catalyst under reflux in an acidic solution to remove excess cobalt particles, finally obtaining the oxygen-coordinated cobalt single-atom catalyst. The catalyst prepared by this invention is applied to the electrocatalytic reduction of oxygen to produce hydrogen peroxide. In a rotating ring disk test, the hydrogen peroxide selectivity is ≥90% within a potential range of 0.2–0.5 V vs. RHE. Using carbon paper as the gas diffusion layer, oxygen-cobalt single-atom catalysts were loaded and subjected to constant current electrolysis in a flow electrolyzer under simulated start-up, shutdown, and fluctuating electrolysis conditions. The evaluation methods included cumulative Faradaic efficiency, catalyst Faradaic efficiency, and electrode stability. The cumulative Faradaic efficiency was ≥90%@5h, the catalyst Faradaic efficiency was ≥90%, the electrode stability was ≥200h, and the catalyst Faradaic efficiency decay was ≤20%.

[0073] According to embodiments of the present invention, the beneficial effects of the present invention include at least one of the following:

[0074] (1) This invention utilizes an oxygen-rich metal-organic framework to anchor a cobalt metal center, forming Co–O–C through carbonization. In this oxygen-coordinated cobalt single-atom catalyst, the oxygen coordination structure can regulate the electronic structure of the central cobalt metal to promote the transfer of active sites, providing optimal adsorption energy for the intermediate *OOH, thereby increasing 2e - ORR selectivity.

[0075] (2) The oxygen-coordinated cobalt single-atom catalyst provided by the present invention contains trace amounts of cobalt single atoms. Compared with pure carbon-based catalysts, it not only brings a significant improvement in activity and stability, but also reduces the risk of metal dissolution. It can effectively solve the problems of poor catalyst stability and low efficiency under acidic conditions, and is suitable for application scenarios with high purity requirements.

[0076] (3) In the application of electrocatalytic oxygen reduction to prepare hydrogen peroxide, the catalyst of the present invention simulates start-stop and fluctuating electrolysis conditions to perform constant current electrolysis. The flexibility and adaptability of the catalyst / system are evaluated by cumulative Faraday efficiency, catalyst Faraday efficiency and electrode stability, providing theoretical and technical support for the coupling of green energy such as photovoltaic systems with electrocatalytic systems. Attached Figure Description

[0077] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood in conjunction with the following description of the embodiments in conjunction with the accompanying drawings, wherein:

[0078] Figure 1 This is a structural diagram of a metal-organic framework material precursor.

[0079] Figure 2 Aberration-corrected high-angle annular dark-field scanning transmission microscope (AC-HAADF-STEM) image of the oxygen-coordinated cobalt single-atom catalyst prepared in Example 1;

[0080] Figure 3 The graph is a simulation test curve of the fluctuating operating conditions in Example 7. Detailed Implementation

[0081] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0082] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0083] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0084] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0085] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0086] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0087] Example 1:

[0088] Preparation of oxygen-coordinated cobalt single-atom catalyst: Cobalt and zinc salts were dissolved in a mixed solution of N,N-dimethylformamide, water, and ethanol to obtain solution A. Terephthalic acid was dissolved in the same mixed solution to obtain solution B, wherein the molar ratio of terephthalic acid, zinc salt, and cobalt salt was 1:1:0.01. Solution A and solution B were clarified and mixed, and triethylamine was added dropwise. After ultrasonic aging for 8 hours to achieve uniform dispersion, the oxygen-coordinated metal-organic framework material was separated by centrifugation. The metal-organic framework material was washed and dried at 80 °C to obtain a precursor. The dried precursor was carbonized at high temperature under an inert atmosphere with a heating rate of 2 °C / min, a carbonization temperature of 950 °C, and a carbonization time of 3 hours to obtain a powdered catalyst. The powdered catalyst was heated in 1 mol / L HCl at 80 °C under reflux for 2 hours to remove excess cobalt particles. After washing and drying, the oxygen-coordinated cobalt single-atom catalyst was obtained. In the rotating ring disk test, the hydrogen peroxide selectivity was ≥90% within the potential range of 0.1–0.5 V vs. RHE.

[0089] Example 2:

[0090] Preparation of oxygen-coordinated cobalt single-atom catalyst: Cobalt and zinc salts were dissolved in a mixed solution of N,N-dimethylformamide, water, and ethanol to obtain solution A. Terephthalic acid was dissolved in the same mixed solution to obtain solution B, wherein the molar ratio of terephthalic acid, zinc salt, and cobalt salt was 1:1:0.1. Solution A and solution B were clarified and mixed, and triethylamine was added dropwise. After ultrasonic aging for 4 hours to achieve uniform dispersion, the oxygen-coordinated metal-organic framework material was separated by centrifugation. The metal-organic framework material was washed and dried at 80 °C to obtain a precursor. The dried precursor was carbonized at high temperature under an inert atmosphere with a heating rate of 2 °C / min, a carbonization temperature of 800 °C, and a carbonization time of 3 hours to obtain a powdered catalyst. The powdered catalyst was heated in 1 mol / L HCl at 80 °C under reflux for 2 hours to remove excess cobalt particles. After washing and drying, the oxygen-coordinated cobalt single-atom catalyst was obtained. In the rotating ring disk test, the hydrogen peroxide selectivity was ≥90% within the potential range of 0.2–0.5 V vs. RHE.

[0091] Example 3:

[0092] Preparation of oxygen-coordinated cobalt single-atom catalyst: Cobalt and zinc salts were dissolved in a mixed solution of N,N-dimethylformamide, water, and ethanol to obtain solution A. Terephthalic acid was dissolved in the same mixed solution to obtain solution B. The molar ratio of terephthalic acid, zinc salt, and cobalt salt was 1:1:0.5. Solution A and solution B were clarified and mixed. Triethylamine was added dropwise, and the mixture was ultrasonically aged for 1 hour to achieve uniform dispersion. The oxygen-coordinated metal-organic framework material was then separated by centrifugation. The metal-organic framework material was washed and dried at 80 °C to obtain a precursor. The dried precursor was carbonized at high temperature under an inert atmosphere at a heating rate of 2 °C / min, a carbonization temperature of 950 °C, and a carbonization time of 3 hours to obtain a powdered catalyst. The powdered catalyst was heated in 1 mol / L HCl at 80 °C under reflux for 12 hours to remove excess cobalt particles. After washing and drying, the oxygen-coordinated cobalt single-atom catalyst was obtained. In the rotating ring disk test, the hydrogen peroxide selectivity was ≥85% in the potential range of 0.1–0.6 V vs. RHE.

[0093] Example 4:

[0094] Start-stop simulation test: The oxygen-cobalt single-atom catalyst prepared in this invention was applied to the electrocatalytic reduction of oxygen to produce hydrogen peroxide. Carbon paper was used as the gas diffusion layer, supporting the oxygen-cobalt single-atom catalyst, with an electrode area of ​​1 cm². 2 The current density is controlled at 10 mA / cm². 2Electrolysis was performed at constant current in a flowing electrolytic cell, with a start-stop interval of 1 hour per cycle and a total start-stop interval of 20 hours. The cumulative Faradaic efficiency of the system was ≥94%@1h, and the catalyst Faradaic efficiency was ≥95%. After 50 cycles, the electrode stability was ≥100h, and the catalyst Faradaic efficiency decay was ≤10%.

[0095] Example 5:

[0096] Start-stop simulation test: The oxygen-cobalt single-atom catalyst prepared in this invention was applied to the electrocatalytic reduction of oxygen to produce hydrogen peroxide. Carbon paper was used as the gas diffusion layer, supporting the oxygen-cobalt single-atom catalyst, with an electrode area of ​​1 cm². 2 The current density is controlled at 50 mA / cm². 2 Constant current electrolysis was performed in a flowing electrolytic cell, with a start-stop interval of 10 hours per cycle and a total start-stop time of 20 hours. The cumulative Faradaic efficiency of the system was ≥90% @ 1 hour, and the catalyst Faradaic efficiency was ≥90%. Electrode stability was ≥200 hours, and the catalyst Faradaic efficiency decay was ≤20%.

[0097] Example 6:

[0098] Fluctuation condition simulation test: The oxygen-cobalt single-atom catalyst prepared in this invention was applied to the electrocatalytic reduction of oxygen to produce hydrogen peroxide. Carbon paper was used as the gas diffusion layer, supporting the oxygen-cobalt single-atom catalyst, with an electrode area of ​​1 cm². 2 The constant current density is controlled at 20 mA / cm². 2 Electrolysis was performed in a flowing electrolytic cell with fluctuations ranging from 10% to 150%, at a frequency of 0.5 h / cycle, for a total of 10 cycles. The cumulative Faradaic efficiency of the system was ≥94%@10h, and the catalyst Faradaic efficiency was ≥95%. After 10 cycles, the electrode stability was ≥100h, and the catalyst Faradaic efficiency decay was ≤5%.

[0099] Example 7:

[0100] Fluctuation condition simulation test: The oxygen-cobalt single-atom catalyst prepared in this invention was applied to the electrocatalytic reduction of oxygen to produce hydrogen peroxide. Carbon paper was used as the gas diffusion layer, supporting the oxygen-cobalt single-atom catalyst, with an electrode area of ​​1 cm². 2 The constant current density is controlled at 50 mA / cm². 2 Electrolysis was performed in a flowing electrolytic cell with fluctuations ranging from 20% to 120%, at a frequency of 1 hour per cycle, for a total of 10 cycles. The cumulative Faradaic efficiency of the system was ≥94% over 20 hours, and the catalyst Faradaic efficiency was ≥80%. After 10 cycles, the electrode stability was ≥200 hours, and the catalyst Faradaic efficiency decay was ≤10%.

[0101] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0102] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. The use of oxygen-cobalt single-atom catalysts in the electrocatalytic reduction of oxygen to hydrogen peroxide, characterized in that, The oxygen-coordinated cobalt single-atom catalyst is composed of a porous carbon framework, cobalt single atoms, and oxygen atoms, wherein the specific surface area of ​​the porous carbon framework is 100~3000 m². 2 / g, wherein the mass content of cobalt single atoms is 0.01% to 10%, and the mass content of oxygen atoms is 1% to 15%; The method for preparing the oxygen-cobalt single-atom catalyst includes: 1) Dissolve cobalt salt and zinc salt in a mixed solvent of organic solvent and water to obtain solution A, wherein the organic solvent is selected from N,N-dimethylformamide and ethanol, and the volume ratio of N,N-dimethylformamide, water and ethanol is (1-0.05):(0.1-0.05):0.1; 2) Dissolve terephthalic acid in a mixture of organic solvent and water to obtain solution B; the organic solvent used in steps 1) and 2) is the same; 3) The solutions A and B are mixed with triethylamine to obtain an oxygen-coordinated metal-organic framework material; the molar ratio of terephthalic acid, zinc salt, and cobalt salt is 1:(0.1-1):(0.01-0.5); the mixing treatment is carried out by ultrasonic aging; the ultrasonic aging time is 1-10 h; the ultrasonic aging temperature is 20-45℃; 4) The oxygen-coordinated metal-organic framework material is washed and dried to obtain a precursor. The drying temperature is not lower than 70°C. The drying is carried out in a vacuum environment. The drying time is 8 to 12 hours. 5) The precursor is subjected to a carbonization reaction to obtain a powdered catalyst; the carbonization treatment is carried out under an argon atmosphere; the heating rate of the carbonization treatment is 2-5℃ / min; the temperature of the carbonization treatment is 800-1000℃; and the time of the carbonization treatment is 1-5 h. 6) The powdered catalyst is subjected to reflux heating to obtain an oxygen-coordinated cobalt single-atom catalyst. The reflux heating is carried out in an acidic solution with a concentration of 0.1–3 mol / L; the reflux heating temperature is 40–100°C; and the reflux heating time is 2–24 h. In the application of the oxygen-coordinated cobalt single-atom catalyst in the electrocatalytic reduction of oxygen to produce hydrogen peroxide, The electrocatalytic reduction of oxygen to produce hydrogen peroxide is carried out in an acidic medium; the acidic medium is one of perchloric acid, sulfuric acid, or hydrochloric acid; the concentration of the acidic medium is 0.01~1 mol / L. In the rotating ring disk test, the hydrogen peroxide selectivity was ≥90% within a potential range of 0.2 ~ 0.5 V vs. RHE. Using carbon paper as a gas diffusion layer, the oxygen-coordinated cobalt single-atom catalyst is loaded onto it. Electrolysis is performed in a flowing electrolyzer under simulated start-up, shutdown, and fluctuating electrolysis conditions, either constant current electrolysis, constant voltage electrolysis, or new energy simulated electrolysis. The current density under the simulated conditions is 10~500 mA / cm². 2 The start-stop interval is 0.01~20 h / time; the fluctuating operating condition is to alternate electrolysis at 5~20% and 120~150% of the rated current density, with a fluctuation frequency of 0.01~20 h / time, cumulative Faradaic efficiency ≥90%@5 h, catalyst Faradaic efficiency ≥90%, electrode stability ≥200h, and catalyst Faradaic efficiency decay ≤20%.

2. The use according to claim 1, characterized in that, The cobalt salt and zinc salt are one or both of nitrate or chloride salts.

Images