A carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide and a preparation method and application thereof

Abstract

The application provides a carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide, the carbon-based gallium monatomic material is composed of carbon atoms, oxygen atoms and gallium atoms, does not contain gallium oxide form, has a Ga-O-C structure, and the three atoms are uniformly distributed; the gallium atoms and the oxygen atoms are bonded in the form of a covalent bond, and the oxygen atoms are bonded with the carbon atoms; the gallium atoms are uniformly dispersed on the carbon-based base material in the form of monatomic atoms. The carbon-based gallium monatomic material provided by the technical scheme of the application is used for electrocatalytic oxygen reduction synthesis of hydrogen peroxide, only C, O and Ga three elements are present in the prepared carbon-based gallium monatomic material, and the three elements are uniformly distributed in the form of monatomic atoms and are free of agglomeration and crystallization, the carbon-based gallium monatomic material has high conductivity of carbon material, overcomes the defects that a homogeneous catalyst is unstable and is prone to agglomeration, and simultaneously, compared with other heterogeneous catalysts in the prior art, the catalytic selectivity has good controllability and the catalytic selectivity is greater than 90%.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, and in particular, relates to a carbon-based gallium single-atom material for electrocatalytic oxygen reduction to synthesize hydrogen peroxide, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2), one of the world's 100 most important chemicals, is environmentally friendly and has a wide range of applications. The demand for H2O2 is constantly increasing. Currently, the most common industrial process is the anthraquinone process, but this complex process suffers from drawbacks such as high equipment requirements, large energy demands, and numerous byproducts, and it is particularly polluting to the environment. Furthermore, the produced H2O2 is a strong oxidant and explosive, requiring strict storage and transportation procedures. In contrast, the electrochemical oxygen reduction (ORR) method, which directly produces H2O2, is an ideal alternative. The ORR method for preparing hydrogen peroxide not only effectively solves the problems existing in the anthraquinone process and direct synthesis, but also makes full use of renewable energy sources such as wind and solar power, thereby effectively alleviating drinking water problems in remote areas.

[0003] In the ORR process, the reaction pathway is divided into 4e - The process generates H2O or through 2e - The path generates H2O2, so the reaction is relatively simple, and then through 2e... - The ORR process for preparing H2O2 utilizes small-scale electrochemical equipment. The reactant is O2, and the product is H2O2; even if there are byproducts, they are still H2O. Therefore, it is non-toxic and harmless to the environment, and the prepared H2O2 can be used immediately, making it an ideal method for H2O2 preparation. Generally, ORR performance is stronger under alkaline conditions than under acidic conditions. The overpotential is smaller under alkaline conditions, with most of the electrical energy being converted into chemical energy in H2O2. Under alkaline conditions, O2 combines with a proton in H2O to form the *OOH intermediate, and then combines with another proton in H2O to form H2O2. This avoids the competitive hydrogen evolution reaction (HER) that occurs under acidic conditions due to the large number of protons adsorbed at active sites. Furthermore, acidic conditions place higher demands on the structural stability and corrosion resistance of the catalyst. Under alkaline conditions, 2e... - The H2O2 generated by ORR can be used for bleaching in the pulp and paper industry, so there is a wealth of research on it under alkaline conditions.

[0004] On the other hand, the efficiency of the direct two-electron oxygen electrochemical method for preparing H2O2 largely depends on the availability of an excellent catalyst. Existing technologies have explored the use of noble metals and their alloys, single atoms, carbon-based materials, and metal oxides as catalysts for H2O2 preparation. For example, Chinese invention patent CN115369427A discloses a molecular hybrid single-atom catalyst for the electrocatalytic oxygen reduction synthesis of hydrogen peroxide, its preparation method, and its application. This catalyst uses carbon materials as a support and 3d transition metal porphyrin / phthalocyanine as the active center, and the resulting catalyst exhibits a hydrogen peroxide synthesis selectivity of over 90% under alkaline conditions. However, the catalyst synthesis in this patent requires pretreatment of the carbon materials, making the entire preparation process complex and demanding, hindering its widespread application.

[0005] Qihao Yang and others Nat. Commun In 2020, on November 11, 5478, theoretical simulations demonstrated that atomically dispersed Lewis acid sites (MO, M = Al, Ga) have the potential to enhance the electrochemical preparation of H2O2 from oxygen-containing carbon (OC) materials. OC(M) materials with atomically dispersed Lewis acid sites were prepared through pyrolysis and alkaline washing, and it was concluded that OC(Al) possesses the optimal 2e... - ORR catalytic performance. However, using this technical solution, the OC(M) carbon-based material contains a large amount of M oxide. In view of this, the present invention improves upon the above-mentioned prior art by providing a carbon-based gallium single-atom material as a catalyst for the electrocatalytic oxygen reduction synthesis of hydrogen peroxide. Compared with the prior art, the electrocatalytic material provided by the present invention has atomically dispersed Lewis acid sites. It is a carbon-based gallium single-atom material with a Ga-OC structure composed entirely of carbon atoms, oxygen atoms, and gallium atoms, and does not contain gallium oxide, thus improving gallium utilization.

[0006] On the other hand, H2O2 undergoes a self-decomposition reaction to produce H2O and O2. As a diprotic weak acid (pKa = 11.7), its decomposition rate is even faster under alkaline conditions, and the decomposition rate increases with increasing H2O2 concentration. Therefore, under alkaline conditions... - In practical applications of ORR (Organic Oxygen Retention Ration) for H2O2 production, it is less effective at higher concentrations. Intuitively, the Faraday efficiency of the system decreases significantly, greatly impacting practical applications. Therefore, how to store peroxide (O2) is crucial. 2- This is therefore of particular importance.

[0007] It has the advantages of simple synthesis process and high selectivity. At the same time, the storage of hydrogen peroxide prepared by this method was studied, which can completely solve the problem of hydrogen peroxide self-decomposition, facilitate the long-term preservation of peroxide ions, and facilitate transportation, thus solving the high cost transportation problem caused by the explosiveness of high concentration H2O2. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention discloses a carbon-based gallium single-atom material for electrocatalytic oxygen reduction to synthesize hydrogen peroxide, its preparation method, and its application, which has the advantages of simple preparation method and high selectivity.

[0009] To achieve the above-mentioned technical objectives, the present invention provides the following technical solutions:

[0010] A carbon-based gallium single-atom material for electrocatalytic oxygen reduction to synthesize hydrogen peroxide, wherein the carbon-based gallium single-atom material is composed of carbon atoms, oxygen atoms and gallium atoms, has a Ga-OC structure, and the three types of atoms are uniformly distributed; wherein, carbon atoms and oxygen atoms constitute the substrate material, and gallium atoms are uniformly dispersed on the carbon-based substrate material in the form of single atoms; gallium atoms and oxygen atoms are bonded in the form of covalent bonds, and oxygen atoms are then bonded to carbon atoms, so that gallium atoms are anchored on the substrate material.

[0011] Preferably, the atomic distribution density is arranged from high to low as carbon atoms-oxygen atoms-gallium atoms; the gallium atom loading is 1.0~2.5wt%.

[0012] To achieve another objective, the present invention also provides a method for preparing the above-mentioned carbon-based gallium single-atom material, specifically comprising uniformly dispersing a gallium source in a carbon source / template agent mixed solution to obtain a precursor material, and calcining it by a stepwise calcination method to obtain the carbon-based gallium single-atom material.

[0013] Preferably, the gallium source includes any one or a combination of gallium chloride and gallium acetylacetonate; and / or, the template agent includes any one or a combination of sodium chloride and potassium chloride; and the carbon source includes any one or a combination of tannic acid and glucose.

[0014] Preferably, the stepwise calcination method includes a combination of low-temperature calcination and high-temperature calcination, in which the precursor material is sequentially subjected to low-temperature calcination, washing, drying, and instantaneous high-temperature calcination steps to obtain the carbon-based gallium single-atom material.

[0015] The low-temperature calcination step gradually removes the anions coordinated with gallium ions and covalently bonds the exposed gallium atoms with oxygen atoms, anchoring gallium single atoms onto the substrate material. This avoids the problem of gallium atom aggregation caused by the rapid removal of anions during high-temperature processing. The washing step removes weakly bonded or unanchored free gallium atoms and the template agent. The instantaneous high-temperature calcination step pyrolyzes the carbon source into oxygen-containing carbon material, thereby further strengthening the bonding strength between gallium atoms and oxygen atoms, resulting in the Ga-OC structured carbon-based gallium single-atom material.

[0016] The washing step is used to remove weakly bonded gallium atoms and the template agent; the instantaneous heating and high-temperature calcination step pyrolyzes the carbon source into an oxygen-containing carbon material, and further strengthens the bonding ability between gallium and oxygen atoms, to obtain the carbon-based gallium single-atom material with a Ga-OC structure.

[0017] Preferably, the low-temperature calcination process includes heating to 200~350℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and calcining for 3~5 hours.

[0018] Preferably, the high-temperature calcination is a rapid heating method, including heating to 600-1600°C at a heating rate of 120-320°C / s under a nitrogen atmosphere, and calcining for 5-600s.

[0019] In some preferred embodiments, the specific steps of the above-mentioned method for preparing carbon-based gallium single-atom materials include:

[0020] S1. Stir and mix the carbon source and template agent evenly to obtain a carbon source / template agent mixed solution;

[0021] S2. The gallium source is uniformly dispersed into the carbon source / template agent mixed solution and dried to obtain the precursor material;

[0022] S3. The precursor material is calcined using a stepwise calcination method to obtain the carbon-based gallium single-atom material.

[0023] The carbon-based gallium single-atom material provided by the above technical solution, or the carbon-based gallium single-atom material prepared therefrom, can be used as an electrocatalyst for the preparation of hydrogen peroxide. In particular, this catalyst exhibits good catalytic selectivity, greater than 90%, under alkaline conditions.

[0024] Meanwhile, this invention also provides a method for storing hydrogen peroxide. Hydrogen peroxide prepared by the present invention using carbon-based gallium single-atom material as an electrocatalyst for the two-electron oxygen reduction reaction is passed through the cathode and directly introduced into a saturated barium hydroxide solution. The white solid appearing in the solution is collected, washed twice with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 80°C to obtain white barium peroxide solid. The mass did not change after 7 days of storage, indicating that converting hydrogen peroxide into solid barium peroxide allows for excellent storage of peroxide ions, avoiding the problem of long-term storage due to the self-decomposition of hydrogen peroxide. In particular, the solid state is easier to transport, solving the high-cost transportation problem caused by the explosiveness of high-concentration H2O2.

[0025] Technical effects of the present invention:

[0026] 1. The carbon-based gallium single-atom material provided by the technical solution of the present invention is used for electrocatalytic oxygen reduction to synthesize hydrogen peroxide. The prepared carbon-based gallium single-atom material contains only three elements: C, O, and Ga. It is uniformly distributed as single atoms without agglomeration or crystallization. It also has the high conductivity of carbon materials, overcoming the defects of homogeneous catalysts such as instability and easy agglomeration. At the same time, compared with other heterogeneous catalysts in the prior art, it has good controllability of catalytic selectivity and the catalytic selectivity is greater than 90%.

[0027] 2. The carbon-based gallium single-atom material provided by the technical solution of this invention has the advantages of simple preparation method and wide range of selectable carbon sources. Combined with stepwise calcination method, gallium atoms and oxygen atoms are covalently bonded under low temperature conditions, and then carbon atoms are bonded to oxygen atoms by instantaneous heating. This changes the electron cloud structure by changing the bonding coordination of gallium atoms with surrounding oxygen and carbon atoms. The outer electrons of gallium will transfer to oxygen and carbon, thereby optimizing the adsorption / desorption strength of the *OOH intermediate on the carbon active site and improving the overall catalyst performance of the material.

[0028] 3. In the carbon-based gallium single-atom material provided by the technical solution of the present invention, gallium atoms exist in the form of single atoms, which can fully expose each gallium atom and make each gallium atom connected to OC, so that the utilization rate of gallium atoms reaches 100%; at the same time, the gallium single atoms have a high loading, making the carbon-based gallium single-atom material a heterogeneous catalyst with high selectivity and high efficiency, exhibiting good performance in the two-electron oxygen reduction reaction to generate hydrogen peroxide.

[0029] 4. By adopting the technical solution of the present invention, the generated hydrogen peroxide is directly introduced into the barium hydroxide solution, and the two react to generate solid barium peroxide. The peroxide ions are stably stored in the form of solid barium peroxide, which effectively avoids the problem of the concentration continuously decreasing due to the decomposition of hydrogen peroxide itself, greatly extends the storage time of peroxide ions, and solves the problem of high cost transportation caused by the explosiveness of high concentration H2O2. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is the XRD pattern of Ga-OC, a carbon-based gallium single-atom material, in Embodiment 1 of the present invention.

[0032] Figure 2 This is a transmission electron microscope (TEM) image of Ga-OC, a carbon-based gallium single-atom material, in Embodiment 1 of the present invention.

[0033] Figure 3 This is an aberration-corrected transmission electron microscope (AC-TEM) image of Ga-OC, a carbon-based gallium single-atom material, in Example 1 of this invention.

[0034] Figure 4a This is the full HAADF mapping diagram of the carbon-based gallium single-atom material Ga-OC in Embodiment 1 of the present invention.

[0035] Figure 4b This is the HAADF-Mapping diagram of carbon in the carbon-based gallium single-atom material Ga-OC in Embodiment 1 of the present invention.

[0036] Figure 4c This is the HAADF-Mapping diagram of oxygen in the carbon-based gallium single-atom material Ga-OC in Embodiment 1 of the present invention.

[0037] Figure 4d This is the HAADF-Mapping diagram of gallium element in Ga-OC, a carbon-based gallium single-atom material, in Embodiment 1 of the present invention.

[0038] Figure 5 These are current curves of carbon-based gallium single-atom materials Ga-OC, AC-Ga-OC, and GLC-Ga-OC in 0.1M NaOH (pH=13) in Examples 1, 4, and 5 of this invention.

[0039] Figure 6 This is a selectivity diagram of carbon-based gallium single-atom materials Ga-OC, AC-Ga-OC, and GLC-Ga-OC in 0.1M NaOH (pH=13) in Examples 1, 4, and 5 of this invention.

[0040] Figure 7 This is a stability diagram of the carbon-based gallium single-atom materials Ga-OC and GLC-Ga-OC in 0.1M NaOH (pH=13) in Examples 1 and 5 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0042] This invention provides a carbon-based gallium single-atom material for electrocatalytic oxygen reduction to synthesize hydrogen peroxide. The carbon-based gallium single-atom material is composed of carbon atoms, oxygen atoms, and gallium atoms, has a Ga-OC structure, and the three types of atoms are uniformly distributed. Gallium atoms are bonded to oxygen atoms by covalent bonds, and oxygen atoms are then bonded to carbon atoms. Gallium atoms are uniformly dispersed in single-atom form on a carbon-based substrate material. The atomic distribution density is arranged from high to low as carbon atoms-oxygen atoms-gallium atoms. The gallium atom loading is 1.0~2.5wt%.

[0043] In some preferred embodiments, the preparation method includes: S1. stirring and mixing a carbon source and a template agent to obtain a carbon source / template agent mixed solution; S2. uniformly dispersing a gallium source into the carbon source / template agent mixed solution and drying it to obtain a precursor material; S3. calcining the precursor material using a stepwise calcination method to obtain a carbon-based gallium single-atom material.

[0044] In some preferred embodiments, the molar ratio of carbon source to template agent is 1:20~80.

[0045] In some preferred embodiments, the molar ratio of gallium source to carbon source is 1:1.25~3.75.

[0046] In some preferred embodiments, the stepwise calcination method includes a combination of low-temperature calcination and high-temperature calcination, wherein the precursor material is sequentially subjected to low-temperature calcination-washing-drying-instantaneous high-temperature calcination steps to obtain carbon-based gallium single-atom material;

[0047] In the low-temperature calcination step, anions coordinated with gallium ions are gradually removed to expose gallium atoms. Simultaneously, the exposed gallium atoms covalently bond with oxygen atoms, anchoring gallium single atoms onto the substrate material. The washing step is used to remove free gallium atoms with weak bonding or those that have not been anchored onto the substrate material, as well as the template agent. In the instantaneous high-temperature calcination step, the carbon source is pyrolyzed into an oxygen-containing carbon material, further enhancing the bonding performance between gallium atoms and oxygen atoms, resulting in the carbon-based gallium single-atom material with a Ga-OC structure.

[0048] In some preferred embodiments, the low-temperature calcination process includes heating to 200~350°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcining for 3~5 hours.

[0049] In some preferred embodiments, high-temperature calcination is a rapid heating method, including heating to 600-1600°C at a heating rate of 120-320°C / s under a nitrogen atmosphere, and calcining for 5-600s.

[0050] The technical solution of the present invention will be described in detail below through specific embodiments.

[0051] Example 1

[0052] This embodiment provides a carbon-based gallium single-atom material, the preparation method of which specifically includes the following steps:

[0053] (1) Synthesis of precursor materials

[0054] Take a 50mL beaker and add 20mL of deionized water. Then add 1.2mmol of tannic acid as a carbon source and 4.0g (0.053mol) of potassium chloride as a template agent to the deionized water. Add a rotor to the beaker and place it on a magnetic stirrer. Stir at 25℃ until completely dissolved to obtain a carbon source / template agent mixed solution.

[0055] 0.7 mmol of anhydrous gallium chloride was added to the carbon source / template agent mixture as a gallium source. After stirring for 0.5 h, the mixture was placed in an ultrasonic cleaner and sonicated for 1 h until the solution was evenly dispersed. The solution was then transferred to a rotary evaporator and dried to obtain the precursor material.

[0056] (2) Preparation of carbon-based gallium single-atom materials

[0057] This step employs a stepwise calcination method involving low-temperature calcination followed by high-temperature calcination to prepare carbon-based gallium single-atom materials. Specific methods include:

[0058] The precursor material obtained in step (1) was placed in a quartz ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 300°C and calcined for 3.5 hours at a heating rate of 5°C / min. After naturally cooling to room temperature, a blackish-gray powder was obtained.

[0059] The blackish-gray powder was taken out and washed. The obtained blackish-gray powder was placed in a mortar and ground thoroughly. It was then washed three times in 50 mL of deionized water and 50 mL of anhydrous ethanol, and then dried in an oven at 60 °C to obtain an intermediate. The purpose of washing was to remove the free gallium atoms that could not be anchored on the substrate material, and at the same time remove the template agent.

[0060] The dried intermediate sample was placed in a Joule heating device, and after being purged with nitrogen atmosphere, the temperature was raised to 1000℃ for 5 seconds and calcined for 120 seconds. After calcination, carbon-based gallium single-atom material (Ga-OC) was obtained. The gallium single-atom loading in the carbon-based gallium single-atom material sample was measured to be ~1.6 wt% using ICP.

[0061] Example 2

[0062] This embodiment provides a carbon-based gallium single-atom material, the preparation method of which specifically includes the following steps:

[0063] (1) Synthesis of precursor materials

[0064] Add 20 mL of deionized water to a 50 mL beaker, add 1.40 mmol of tannic acid as a carbon source and 2.5 g (0.03 mol) of potassium chloride as a template agent. Add a rotor to the beaker and place it on a magnetic stirrer. Stir at 25 °C until completely dissolved to obtain a carbon source / template agent mixed solution.

[0065] 0.8 mmol of anhydrous gallium chloride was used as the gallium source and added to the carbon source / template agent mixed solution. After stirring for 0.5 h, the solution was placed in an ultrasonic cleaner and sonicated for 2 h until it was evenly dispersed. The solution was then transferred to a rotary evaporator and dried to obtain the precursor material.

[0066] (2) Preparation of carbon-based gallium single-atom materials

[0067] This step employs a stepwise calcination method to prepare carbon-based gallium single-atom materials. Specific methods include:

[0068] The precursor material prepared in step (1) was placed in a quartz ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 350°C and calcined for 4.5 h at a heating rate of 5°C / min. After that, the temperature was naturally cooled to room temperature to obtain a blackish-gray powder.

[0069] The obtained blackish-gray powder was taken out and washed. The blackish-gray powder was then placed in a mortar and ground thoroughly. It was washed three times in 50 mL of deionized water and 50 mL of anhydrous ethanol, and then placed in an oven and dried at 60 °C to obtain an intermediate. In this step, the purpose of washing is to remove the free gallium ions that have not been anchored on the substrate, and at the same time remove the template agent.

[0070] The dried sample was placed in a Joule heating device, and after being purged with nitrogen atmosphere, the temperature was raised to 600°C in 5 seconds and calcined for 600 seconds for rapid heating and calcination. After calcination, carbon-based gallium single-atom material (Ga-OC) was obtained. ICP measurement of the sample showed that the gallium single-atom loading was about 2.1 wt%.

[0071] Example 3

[0072] This embodiment provides a carbon-based gallium single-atom material, the preparation method of which specifically includes the following steps:

[0073] (1) Synthesis of precursor materials

[0074] Add 20 mL of deionized water to a 50 mL beaker, add 1.1 mmol of tannic acid as a carbon source and 3.0 g (0.04 mol) of potassium chloride as a template agent. Add a rotor to the beaker and place it on a magnetic stirrer. Stir at 25 °C until completely dissolved to obtain a carbon source / template agent mixed solution.

[0075] 0.4 mmol of anhydrous gallium chloride was added to the carbon source / template agent mixture as a gallium source. After stirring for 0.5 h, the mixture was placed in an ultrasonic cleaner and sonicated for 1.5 h until the solution was evenly dispersed. The solution was then transferred to a rotary evaporator and dried to obtain the precursor material.

[0076] (2) Preparation of carbon-based gallium single-atom materials

[0077] This step employs a stepwise calcination method to prepare carbon-based gallium single-atom materials. Specific methods include:

[0078] The precursor material prepared in step (1) was placed in a quartz ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 250°C and calcined for 3 hours at a heating rate of 5°C / min. After that, the temperature was naturally cooled to room temperature to obtain a blackish-gray powder.

[0079] The obtained blackish-gray powder was taken out and washed. The blackish-gray powder was then placed in a mortar and ground thoroughly. It was washed three times in 50 mL of deionized water and 50 mL of anhydrous ethanol, and then placed in an oven and dried at 80 °C to obtain an intermediate. The purpose of washing here is to remove the free gallium ions that have not been anchored on the substrate, and at the same time remove the template agent.

[0080] The dried intermediate sample was placed in a Joule heating device, and after being purged with nitrogen atmosphere, the temperature was raised to 1600℃ for 5 seconds and calcined for 5 seconds for rapid heating calcination. After calcination, carbon-based gallium single-atom material (Ga-OC) was obtained. ICP measurement of the sample showed that the gallium single-atom loading was about 1.20 wt%.

[0081] Example 4

[0082] This embodiment provides a carbon-based gallium single-atom material, the preparation method of which specifically includes the following steps:

[0083] (1) Synthesis of precursor materials

[0084] Add 20 mL of deionized water to a 50 mL beaker, add 1.2 mmol of tannic acid as a carbon source and 5.0 g (0.067 mol) of potassium chloride as a template agent. Add a rotor to the beaker and place it on a magnetic stirrer. Stir at 25 °C until completely dissolved to obtain a carbon source / template agent mixed solution.

[0085] 0.7 mmol of gallium acetylacetonate was added to the carbon source / template mixture as a gallium source. After stirring for 0.5 h, the mixture was placed in an ultrasonic cleaner and sonicated for 1 h until the solution was evenly dispersed. The solution was then transferred to a rotary evaporator and dried to obtain the precursor material.

[0086] (2) Preparation of carbon-based gallium single-atom materials

[0087] This step employs a stepwise calcination method to prepare carbon-based gallium single-atom materials. Specific methods include:

[0088] The precursor material prepared in step (1) was placed in a quartz ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200°C and calcined for 3.5 h at a heating rate of 5°C / min. After natural cooling to room temperature, a blackish-gray powder was obtained.

[0089] The dark gray powder was removed and ground thoroughly in a mortar. It was then washed three times with 50 mL of deionized water and 50 mL of anhydrous ethanol, and finally dried in an oven at 70°C to obtain the intermediate. The purpose of this washing was to remove free gallium ions that failed to anchor on the substrate, as well as the template agent.

[0090] The dried intermediate sample was placed in a Joule heating device, and after being purged with nitrogen atmosphere, the temperature was raised to 800℃ in 5 seconds and calcined for 240 seconds for rapid heating and calcination. After calcination, carbon-based gallium single-atom material (hereinafter referred to as AC-Ga-OC) was obtained. ICP measurement of the sample showed that the gallium single-atom loading was about 1.69 wt%.

[0091] Example 5

[0092] This embodiment provides a carbon-based gallium single-atom material, the preparation method of which specifically includes the following steps:

[0093] (1) Synthesis of precursor materials

[0094] Add 20 mL of deionized water to a 50 mL beaker, along with 1.2 mmol of glucose as a carbon source and 4.5 g (0.06 mol) of potassium chloride as a template agent. Place a rotor in the beaker and put it on a magnetic stirrer. Stir at 25 °C until completely dissolved to obtain a carbon source / template agent mixed solution. Add 0.7 mmol of anhydrous gallium chloride as a gallium source to the carbon source / template agent mixed solution. Continue stirring for 0.5 h, then place it in an ultrasonic cleaner and sonicate for 1.5 h until the solution is evenly dispersed. Transfer it to a rotary evaporator and dry to obtain the precursor material.

[0095] (2) Preparation of carbon-based gallium single-atom materials

[0096] This step employs a stepwise calcination method to prepare carbon-based gallium single-atom materials. Specific methods include:

[0097] The precursor material prepared in step (1) was placed in a quartz ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 350°C and calcined for 3 h at a heating rate of 5°C / min. After natural cooling to room temperature, a blackish-gray powder was obtained.

[0098] The resulting dark gray powder was taken out and ground thoroughly in a mortar. It was then washed three times with 50 mL of deionized water and 50 mL of anhydrous ethanol, and finally dried in an oven at 90 °C to obtain the intermediate. The purpose of this washing was to remove the weakly bonded gallium atoms and the template agent.

[0099] The dried intermediate sample was placed in a Joule heating device, and after being purged with nitrogen atmosphere, the temperature was raised to 1200℃ in 5 seconds and calcined for 90 seconds for rapid heating and calcination. After calcination, carbon-based gallium single-atom material (hereinafter referred to as GLC-Ga-OC) was obtained. ICP measurement of the sample showed that the gallium single-atom loading was about 1.42 wt%.

[0100] To compare the electrocatalytic performance and electrochemical stability of the carbon-based gallium single-atom materials prepared in each example, the electrocatalytic oxygen reduction performance of the carbon-based gallium single-atom materials prepared in Examples 1, 4, and 5 was tested. The specific test steps are as follows:

[0101] On a rotating ring-disk electrode system, 3 mg of the synthesized carbon-based gallium single-atom material was dispersed in a mixed solution of 950 μL anhydrous ethanol and 50 μL of 5% Nafion and sonicated for 2 h until the catalyst was uniformly dispersed to obtain ink.

[0102] Using a pipette, 6 μL of ink was dropped onto the surface of the ring-disk electrode. The ring-disk electrode, carbon rod, and mercury / mercury oxide electrode were used as the working electrode, counter electrode, and reference electrode in the three-electrode system, respectively. After assembling the three electrodes, performance tests were performed. The electrolyte used was 0.1 M NaOH saturated with O2. The rotation speed of the ring-disk electrode was set to 1600 rpm, the scan rate was set to 5 mV / s, and the scan range was 0-1 V (vs. RHE).

[0103] Results analysis:

[0104] See Figure 1 The image shows the X-ray diffraction (XRD) pattern of the carbon-based gallium single-atom material prepared in Example 1. In the XRD image, only peaks around 25° and 43° C were observed, and no other crystalline peaks were observed, proving that gallium atoms in the material did not agglomerate or crystallize. Furthermore, the XRD results of Examples 2-5 are similar to those of Example 1, indicating that the technical solutions of Examples 1-5 can be used to prepare carbon-based gallium single-atom materials with the same structure.

[0105] See Figure 2 This is a transmission electron microscope (TEM) image of the carbon-based gallium single-atom material prepared in Example 1. Figure 2 As shown, no aggregated particles or lattice fringes caused by crystallization were observed in the high-resolution TEM mode, proving that gallium atoms are distributed in single-atom form on the carbon-based substrate and do not contain gallium oxide morphology. The TEM results of Examples 2-5 are similar to those of Example 1, indicating that the technical solutions of Examples 1-5 can be used to prepare carbon-based gallium single-atom materials with the same microstructure.

[0106] See Figure 3 The image shown is an aberration-corrected transmission electron microscope (AC-TEM) image of the carbon-based gallium single-atom material prepared in Example 1. Figure 3 As shown, many bright white dots, i.e., gallium atoms, can be seen on the carbon substrate. The gallium atoms are distributed very uniformly and there is no aggregation. The atomic distribution in the AC-TEM results of Examples 2-5 is similar to that of Example 1, indicating that the technical solutions of Examples 1-5 can be used to prepare carbon-based gallium single-atom materials with the same atomic distribution.

[0107] See Figures 4a-4d The elemental mapping of the carbon-based gallium single-atom material prepared in Example 1 was performed using high-angle annular dark-field imaging transmission electron microscopy (HAADF-STEM). Figures 4a-4dAs shown, the carbon-based gallium single-atom material is composed of three atoms: C, O, and Ga. C has the highest density as the substrate, followed by O, and then Ga. The distribution of the three atoms is very uniform, without aggregation. The introduction of Ga single atoms causes the electron cloud of Ga to shift towards O, reducing the electronegativity of O. Consequently, the attraction of O to the electron cloud of C decreases, resulting in a higher electron cloud density at the active sites of C. This effectively reduces the desorption difficulty of the *OOH intermediate on C, thereby improving its catalytic performance and contributing to the efficient preparation of hydrogen peroxide. The mapping results of Examples 2-5 are similar to those of Example 1, indicating that the technical solutions of Examples 1-5 can prepare carbon-based gallium single-atom materials with a uniform distribution of C, O, and Ga atoms. Furthermore, since the gallium atoms are completely dispersed at the atomic level, each gallium atom can be bonded to C, resulting in 100% utilization of gallium atoms, which helps to improve the selectivity and catalytic performance of the catalyst.

[0108] See Figures 5-6 The carbon-based gallium single-atom materials Ga-OC, AC-Ga-OC, and GLC-Ga-OC prepared in Examples 1, 4, and 5 were subjected to ring disk tests in 0.1M NaOH (pH=13). The results are as follows. Figures 5-6 As shown, using gallium chloride and gallium acetylacetonate as gallium sources has little effect on the electron oxygen reduction reaction activity of the materials. However, the activity of carbon-based gallium single-atom materials obtained by carbonization using tannic acid as a carbon source is better than that of carbon-based gallium single-atom materials obtained by using glucose as a carbon source. Clearly, in terms of selectivity, the Ga-OC material prepared in Example 1 and the AC-Ga-OC material prepared in Example 4 have higher selectivity than the GLC-Ga-OC material prepared in Example 5. Between 0.65V and 0.22V, Ga-OC exhibits a selectivity of over 90%, which is approximately 10% higher than that of GLC-Ga-OC.

[0109] See Figure 7 Regarding electrochemical stability, at a voltage of 0.2V (vs. RHE), the stability of Example 1 was 32h, while that of Example 5 was 14h. Clearly, the electrochemical stability of the Ga-OC material prepared using Example 1 is higher than that of the GLC-Ga-OC prepared using Example 5.

[0110] Example 6

[0111] Furthermore, in order to study the actual electrocatalytic hydrogen peroxide production performance of the prepared carbon-based gallium single-atom material, the carbon-based gallium single-atom material (Ga-OC material) prepared in Example 1 was loaded into a flow-cell electrolyzer for electrocatalytic oxygen reduction performance testing. The specific steps are as follows:

[0112] Take 8 mg of the carbon-based gallium single-atom material prepared in Example 1 and disperse it in a mixed solution of 1450 μL deionized water, 490 μL anhydrous ethanol and 60 μL Nafion with a mass fraction of 5%. Sonicate for 2 h until the catalyst is uniformly dispersed to obtain ink containing Ga-OC material.

[0113] Assemble a Flow-Cell electrolyzer, which consists of a cathode, an anode, and a diaphragm. A circular piece of carbon paper with a radius of 1.5 cm is drop-coated with ink containing Ga-OC material at a loading of 1 mg / cm³. 2 Carbon paper coated with Ga-OC, NiFe-LDH, and Grade-60 were used as the cathode, anode, and diaphragm, respectively.

[0114] After assembling the Flow-Cell, the cathode gas flow rate was fixed at 60 mL / min, and the anolyte liquid flow rate was 2 mL / min using 0.1 M NaOH solution. A constant current mode was set, with the current set to the maximum value of 400 mA for the electrochemical workstation, and the running time was 60 min. The liquid (H2O2) flowing out of the cathode outlet was collected.

[0115] The collected H2O2 liquid was titrated to determine the concentration of H2O2 generated. 1 mL of the solution flowing from the outlet was added to 49 mL of deionized water and mixed thoroughly. 2 mL of this solution was then added to titanium sulfate titrant. The concentration was determined to be 1782 ppm based on the change in absorbance measured using a UV spectrophotometer.

[0116] This invention also investigated the storage of H2O2 prepared by the above-mentioned technical solution. Specifically, the collected liquid was placed in a reagent bottle and stored for seven days. The H2O2 concentration was then titrated again. 1 mL of the solution flowing from the outlet was added to 49 mL of deionized water, and after thorough mixing, 2 mL of this solution was added to titanium sulfate titrant. The concentration was determined to be 798 ppm based on the change in absorbance measured by an ultraviolet spectrophotometer. This indicates that the concentration of H2O2 decreased by 55.2% due to self-decomposition within seven days.

[0117] Example 7

[0118] Furthermore, the present invention also provides a method for storing H2O2.

[0119] Take 8 mg of the carbon-based gallium single-atom material prepared in Example 1 and disperse it in a mixed solution of 1450 μL deionized water, 490 μL anhydrous ethanol and 60 μL Nafion with a mass fraction of 5%. Sonicate for 2 h until the catalyst is uniformly dispersed to obtain ink containing Ga-OC material.

[0120] Assemble a Flow-Cell electrolyzer, which consists of a cathode, an anode, and a diaphragm. A circular piece of carbon paper with a radius of 1.5 cm is drop-coated with ink containing Ga-OC material at a loading of 1 mg / cm³. 2 Carbon paper coated with Ga-OC, NiFe-LDH, and Grade-60 were used as the cathode, anode, and diaphragm, respectively.

[0121] After assembling the Flow-Cell, the cathode gas flow rate was fixed at 60 mL / min, and the anolyte liquid flow rate was 2 mL / min using 0.1 M NaOH solution. A constant current mode was set, with the current set to the maximum value of 400 mA for the electrochemical workstation, and the running time was 60 min. The liquid (H2O2) flowing out of the cathode outlet was collected.

[0122] H2O2 flowing from the cathode was passed into a saturated barium hydroxide solution. The white solid that appeared in the barium hydroxide solution was collected, washed twice with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 80°C to obtain barium peroxide white solid with a mass of 1.04 g. After 7 days of storage, its mass remained unchanged at 1.04 g, indicating that the prepared peroxide ions were well stored.

[0123] Results analysis:

[0124] Analysis of hydrogen peroxide storage in Example 6: After loading Ga-OC material into a flow-cell electrolyzer, with a fixed current I = 400 mA and electrolyte flow rate v = 2 mL / min, the theoretical H2O2 concentration was calculated to be 2114 ppm based on the running time t = 60 min, Faraday's law Q = nzF, and the charge formula Q = it. However, titration revealed that the actual concentration was 1782 ppm, indicating a Faraday efficiency of 84.3%. After 7 days of liquid storage, 55.2% of the generated H2O2 degraded, leaving a concentration of only 798 ppm.

[0125] In Example 7, the H2O2 solution flowing out of the outlet was passed into a saturated barium hydroxide solution to generate barium peroxide to store peroxide ions. As a relatively stable peroxide, barium peroxide did not show significant changes in mass after 7 days, proving that the peroxide ions were well stored.

[0126] Clearly, converting hydrogen peroxide into solid barium peroxide for storage can effectively avoid the problem of continuously decreasing concentration caused by the decomposition of hydrogen peroxide itself, and greatly extend the storage time of peroxide ions.

[0127] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide, characterized in that, The carbon-based gallium monatomic material is composed of carbon atoms, oxygen atoms and gallium atoms, does not contain gallium oxide, has a Ga-O-C structure, and the three atoms are uniformly distributed; The carbon atoms and the oxygen atoms form a base material, and the gallium atoms are uniformly dispersed on the base material in the form of monatomic atoms; The oxygen atoms and the carbon atoms are bonded, and the gallium atoms and the oxygen atoms are covalently bonded, so that the gallium atoms are anchored on the base material; The atomic distribution density of the carbon-based gallium monatomic material is arranged in descending order as follows: carbon atoms, oxygen atoms, and gallium atoms; The loading amount of the gallium atoms is 1.4-2.1wt%; The preparation method of the carbon-based gallium monatomic material comprises uniformly dispersing a gallium source into a carbon source / template agent mixed solution to obtain a precursor material, and calcining the precursor material by a step-by-step calcination method to obtain the carbon-based gallium monatomic material. The template agent is selected from any one or a combination of two of sodium chloride and potassium chloride. The carbon source is selected from any one or a combination of two of tannic acid or glucose. The step-by-step calcination method comprises a method combining low-temperature calcination and high-temperature calcination, and the precursor material sequentially undergoes the steps of low-temperature calcination, washing, drying, and instantaneous high-temperature calcination to obtain the carbon-based gallium monatomic material. The low-temperature calcination process comprises heating to 200-350℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and calcining for 3-5h. The high-temperature calcination is a rapid heating method, which comprises heating to 600-1600℃ at a heating rate of 120-320℃ / s under a nitrogen atmosphere, and calcining for 5-600s.

2. A method for the preparation of carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide according to claim 1, characterized by, The preparation method of the carbon-based gallium monatomic material comprises uniformly dispersing a gallium source into a carbon source / template agent mixed solution to obtain a precursor material, and calcining the precursor material by a step-by-step calcination method to obtain the carbon-based gallium monatomic material. The template agent is selected from any one or a combination of two of sodium chloride and potassium chloride. The carbon source is selected from any one or a combination of two of tannic acid or glucose. The step-by-step calcination method comprises a method combining low-temperature calcination and high-temperature calcination, and the precursor material sequentially undergoes the steps of low-temperature calcination, washing, drying, and instantaneous high-temperature calcination to obtain the carbon-based gallium monatomic material. The low-temperature calcination process comprises heating to 200-350℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and calcining for 3-5h. The high-temperature calcination is a rapid heating method, which comprises heating to 600-1600℃ at a heating rate of 120-320℃ / s under a nitrogen atmosphere, and calcining for 5-600s.

3. The method for preparing carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide according to claim 2, characterized in that, The gallium source comprises any one or a combination of two of gallium chloride and gallium acetylacetonate.

4. The method for preparing carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide according to claim 2, characterized in that, In the low-temperature calcination step, anions coordinated with gallium ions are gradually removed to expose gallium atoms, and the exposed gallium atoms are covalently bonded with oxygen atoms to anchor the gallium monatomic atoms on the base material; the washing step is used to remove free gallium atoms that are not anchored on the base material and the template agent; in the instantaneous high-temperature calcination step, the instantaneous increase in temperature causes the carbon source to pyrolyze into oxygen-containing carbon material, strengthens the bonding strength between the gallium atoms and the oxygen atoms, and obtains the carbon-based gallium monatomic material with a Ga-O-C structure.

5. The method for preparing carbon-based gallium monatomic material for electrocatalytic oxygen reduction synthesis of hydrogen peroxide according to any one of claims 2-4, characterized in that, dispersing a gallium source into a carbon source / template agent mixed solution to obtain a precursor material, comprising the following steps: S1. uniformly mixing a carbon source and a template agent by stirring to obtain a carbon source / template agent mixed solution; S2. uniformly dispersing a gallium source into the carbon source / template agent mixed solution and drying to obtain a precursor material.

6. The carbon-based gallium monatomic material of claim 1, or the carbon-based gallium monatomic material prepared by the method of any one of claims 2-5, for use as a catalyst in the preparation of hydrogen peroxide by a two-electron electrochemical oxygen reduction reaction.

7. A catalyst for electrocatalytic oxygen reduction to produce hydrogen peroxide, characterized by, The carbon-based gallium monatomic material of claim 1, or the carbon-based gallium monatomic material prepared by the method of any one of claims 2-5.

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