Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide and preparation and application thereof

Abstract

The invention discloses a Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide. The Fe3N-porous carbon composite material is prepared from a porous carbon carrier and an iron precursor through a two-step heat treatment reaction, the porous carbon carrier is a graded porous carbon nanosheet HPC formed by ball milling treatment and high-temperature carbonization at 700-900 DEG C under the action of a NaCl-KCl composite salt template by taking an industrial byproduct pitch as a carbon source; the two-step heat treatment comprises a first step of completing decomposition of an iron precursor and preliminary anchoring of iron ions on the porous carbon support at 300-400 DEG C and a second step of completing generation of Fe3N nanoparticles on the porous carbon support at 700-900 DEG C. The Fe3N-porous carbon composite material has the characteristics that the d-band center of Fe moves downwards and the binding energy of a C = O peak is positively shifted, and has high activity, high selectivity and high stability, so that the composite material shows extremely high H2O2 electrocatalytic synthesis performance, and the composite material is simple in preparation process, low in cost and beneficial to large-scale production and application.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic synthesis of hydrogen peroxide, specifically to a catalyst for catalyzing the two-electron oxygen reduction reaction to synthesize hydrogen peroxide—Fe3N-porous carbon composite material, and the preparation method and application of the composite material. Background Technology

[0002] Hydrogen peroxide (H2O2), as the cleanest oxidant, is experiencing rapid growth in demand due to the increasing emphasis on green and sustainable development. Its applications are no longer limited to traditional industrial processes such as pulp bleaching, textile printing and dyeing, and bulk chemical synthesis, but are rapidly expanding into high-end manufacturing, deep environmental governance, and high-value-added consumer sectors. This evolution in demand from "traditional bulk" to "high-precision and innovative" applications places new demands on the supply model of H2O2, requiring high purity and distributed supply. Currently, global industrial production of H2O2 is almost entirely monopolized by the anthraquinone process (AO process), a typical centralized, capital-intensive petrochemical route characterized by high energy consumption and heavy pollution. To overcome the shortcomings of the AO process, industry and academia are actively developing alternative routes, including those based on the two-electron oxygen reduction reaction (2e...). - The electrochemical synthesis method of ORR (Organic Renewable Energy) uses water, oxygen, and renewable electricity as raw materials to achieve green and distributed production of H2O2 at ambient temperature and pressure, making it a promising alternative route. However, this technology is still in the experimental stage, and its large-scale application is limited by the lack of catalysts that simultaneously possess high activity, high selectivity, and low cost.

[0003] Carbon-based materials have been extensively studied due to their low cost, high specific surface area, and tunable electronic structure. Their performance can be modulated through heteroatom doping and defect engineering, but single modification strategies have limited effectiveness. Transition metal nitrides (such as Fe3N) have attracted attention in the field of electrocatalysis due to their good conductivity and tunable electronic structure; however, pure Fe3N nanoparticles are prone to aggregation, leading to a reduction in active sites. Existing technologies combine iron nitrides (Fe3N) with carbon materials for applications in the oxygen evolution reaction (OER) or zinc-air batteries (4e2+). - ORR), due to 4e - ORR and 2e - Different reaction objectives in ORR necessitate different optimization approaches for the catalyst. Specifically, 4e... - ORR needs to be completely reduced, aiming to gain 4 electrons from O2 and completely reduce it to OH. - Therefore, ideal Fe sites tend to have higher d-band centers to facilitate stronger interactions with oxygen species (*O, *OH), driving the dissociation of the OO bond; while 2e -ORR is a selective reduction catalyst that aims for O2 to gain only two electrons to generate H2O2. Therefore, it is crucial to protect the O2 / O2 bond from breaking. Catalyst optimization focuses on the appropriate adsorption of the key intermediate *OOH, ensuring both stability and easy release. This involves shifting the d-band center of Fe downwards to weaken the adsorption of *OOH and prevent excessive dissociation. Thus, simultaneously improving activity, selectivity, and stability through interfacial electronic structure modulation and microstructure design is essential to satisfying the 2e2 bond requirement. - The technical problems that urgently need to be solved in ORR catalysis. Summary of the Invention

[0004] This invention targets the two-electron oxygen reduction reaction (2e... - To address the shortcomings of catalysts used in the ORR (Organic Reactive Catalysis) synthesis of H2O2, such as insufficient activity, selectivity, and stability, a high-performance, low-cost Fe3N-porous carbon composite material is provided. This material establishes a two-site synergistic catalytic system by constructing strong electronic interactions between Fe3N nanoparticles and heteroatoms (N, O) activated carbon atoms. Combined with a hierarchical porous nanosheet structure, this optimizes the control of the adsorption energy of the *OOH intermediate, thereby significantly improving the 2e- ... - The performance of ORR in controlling H2O2.

[0005] To achieve the above objectives, the present invention provides a Fe3N-porous carbon composite material for the electrocatalytic synthesis of hydrogen peroxide, which is prepared by a two-step heat treatment reaction of a porous carbon support and an iron precursor. The porous carbon support is a hierarchical porous carbon nanosheet (HPC) formed by ball milling and high-temperature carbonization at 700-900℃ under the action of a NaCl-KCl composite salt template, using industrial by-product pitch as the carbon source. The two-step heat treatment includes a first step at 300-400℃ to complete the decomposition of the iron precursor and the preliminary anchoring of iron ions on the porous carbon support, and a second step at 700-900℃ to complete the generation of Fe3N nanoparticles on the porous carbon support.

[0006] This invention uses a NaCl-KCl composite salt as a template, which is ball-milled with industrial by-product asphalt and then carbonized at high temperature. At high temperature (~650°C), the mixed salt melts to form a liquid phase, forcing the molten asphalt to carbonize and spread into ultrathin, wrinkled nanosheets. After washing away the salt, a porous carbon support with a unique hierarchical (microporous + mesoporous) porous structure remains. Then, the porous carbon support and an iron precursor undergo a two-step heat treatment: first at 300~400°C, then at 700~900°C. The gentle first heat treatment allows the iron precursor to be uniformly dispersed and initially anchored. The second heat treatment, at a precise temperature, forms small and uniform Fe3N nanoparticles (~10⁻⁶). (nm), and ensure that they are firmly bonded to the carbon support; finally, the loosely attached and easily agglomerated large iron-nitride particles are washed away by strong acid reflux washing, while the carbon surface is slightly oxidized to create more selective active sites such as C=O, and to open up the blocked pores, so as to obtain Fe3N-porous carbon composite material with high activity, high selectivity and high stability, exhibiting extremely high H2O2 electrosynthesis performance.

[0007] As a limitation of the above technical solution, the mass ratio of carbon source to composite salt template used in the preparation of porous carbon support is 1:2 to 1:5; the mass ratio of NaCl to KCl in composite salt is 1:3 to 3:1; preferably, industrial by-product asphalt includes petroleum asphalt and coal tar pitch.

[0008] Petroleum asphalt, coal tar pitch and other industrial by-product asphalt are not only extremely low in cost, but are also "soft" carbon sources rich in polycyclic aromatic hydrocarbons. They can be molded into nanosheets by molten salt templates, and their chemical composition is conducive to reaction with iron precursors and can withstand acid washing treatment.

[0009] As a limitation of the above technical solution, the preparation of porous carbon supports includes the following steps: The carbon source is mixed with NaCl and KCl, and then grinding balls and grinding solvent are added. The mixture is repeatedly ball-milled. After drying, the product is subjected to high-temperature carbonization at 700~900℃ for 2~3 h under an Ar atmosphere. After cooling, the composite salt template is washed off and dried to obtain hierarchical porous carbon nanosheets (HPC), which are porous carbon supports. Preferably, the ratio of carbon source, composite salt template, grinding balls and grinding solvent is 0.3~0.5g:1.0~1.5g:15~30g:5~8mL. The grinding solvent is ethanol or isopropanol.

[0010] As a limitation of the above technical solution, the repeated ball milling process involves ball milling at a frequency of 30-45Hz in a planetary ball mill for 30-40 minutes, stopping for 10-15 minutes, and repeating the cycle 4-6 times.

[0011] As a limitation of the above technical solution, the iron precursor is selected from ferric chloride, ferric nitrate, and ferric sulfate.

[0012] As a limitation of the above technical solution, the preparation of Fe3N-porous carbon composite material includes the following steps: After dissolving the iron precursor, HPC was added and impregnated at room temperature for 6-8 hours, followed by evaporation, drying, and grinding. A two-step heat treatment was then performed under an Ar atmosphere: first, the iron precursor was held at 300-400℃ for 2-3 hours to decompose and initially anchor it with carbon-nitrogen; then, it was held at 700-900℃ for 2-3 hours to generate Fe3N nanoparticles on the porous carbon support, yielding the initial composite material Fe3N NPs@HPC. Finally, a strong acid reflux cleaning treatment was performed to obtain the Fe3N-porous carbon composite material Fe3N@HPC. Preferably, the ratio of iron precursor to HPC was 0.05-0.12 g:0.05-0.15 g, and the iron precursor was dissolved in water to prepare a solution with a concentration of 0.005-0.01 mol / L.

[0013] Improve the preparation conditions of porous carbon support and Fe3N-porous carbon composite material, and further optimize the structure and properties of the composite material.

[0014] As a limitation of the above technical solution, the surface of Fe3N-porous carbon composite material contains C=O and CO functional groups, and the binding energy of the C=O peak is positively shifted, and the d-band center of Fe in Fe3N nanoparticles shifts down to between -1.10 and -1.25 eV.

[0015] As a limitation of the above technical solution, the average size of Fe3N nanoparticles is 5~15 nm, preferably 8~12 nm.

[0016] The Fe3N-porous carbon composite material consists of highly dispersed ε-Fe3N nanoparticles anchored on heteroatom (N, O)-doped carbon nanosheets with a hierarchical porous structure. The composite surface contains abundant C=O and CO functional groups. Due to interfacial electron transfer between Fe3N and the carbon support, the binding energy of the C=O peak shifts positively (approximately +0.7 eV) compared to the pure carbon support. The d-band center of Fe in the Fe3N nanoparticles shifts downward to between -1.10 eV and -1.25 eV due to interfacial interactions, thus significantly improving the binding energy of 2e- electrons. - The selectivity of the ORR reaction.

[0017] The preparation method of Fe3N-porous carbon composite material as described above includes the following steps: a. Preparation of porous carbon support: Industrial by-product pitch, NaCl and KCl are mixed, and grinding balls and grinding solvent are added. The mixture is subjected to repeated ball milling. The resulting product is dried and placed in a tube furnace. Under an Ar atmosphere, the temperature is increased to 700-900℃ at 5-8℃ / min and held for 2-3 h. Then, it is cooled and washed with deionized water to remove the composite salt template NaCl-KCl. The product is then dried at 60-80℃ to obtain hierarchical porous carbon nanosheets (HPC), which is the porous carbon support. Preferably, the repeated ball milling is performed in a planetary ball mill at a frequency of 30-45Hz for 30-40 min, followed by a 10-15 min stop, for 4-6 cycles. b. Preparation of Fe3N-porous carbon composite material: Iron precursor was dissolved in water, HPC was added, and impregnated at room temperature for 6-8 h; then evaporated and dried, ground and placed in a ceramic boat, and subjected to two-step heat treatment under Ar atmosphere: first, the temperature was increased to 300-400°C at 2-5 °C / min and held for 2-3 h, then increased to 700-900°C at 5-8 °C / min and held for 2-3 h, and after cooling, the initial composite material Fe3N NPs@HPC was obtained; c. Acid washing treatment: The initial composite material Fe3N NPs@HPC obtained in step b is subjected to reflux washing treatment with strong acid, cooled, washed with a large amount of deionized water until neutral, and dried at 60~80℃ to obtain the final product Fe3N-porous carbon composite material Fe3N@HPC; preferably, the strong acid is a 4 mol / L HNO3 solution, the reflux temperature is 120~130℃, and the time is 6~8h.

[0018] The preparation of Fe3N-porous carbon composite material of the present invention involves forming a porous carbon carrier by ball milling carbon source and a specific double salt (NaCl-KCl) template, and then obtaining the final composite material through impregnation-two-step heat treatment-acid washing process. The process is simple, low-cost, and conducive to large-scale production.

[0019] As mentioned above, the application of Fe3N-porous carbon composite material is to use Fe3N-porous carbon composite material to catalyze the two-electron oxygen reduction reaction to synthesize hydrogen peroxide. Preferably, Fe3N-porous carbon composite material is used as a catalyst to make electrode material for electrocatalytic reaction. Specifically, Fe3N-porous carbon composite material can be made into catalyst ink and then made into electrode material for electrolysis reaction.

[0020] Fe3N-porous carbon composite material, as a catalyst for electrode materials, can catalyze the two-electron oxygen reduction reaction to synthesize hydrogen peroxide, resulting in high H2O2 yield, high Faraday efficiency and long-term stability.

[0021] In summary, the Fe3N-porous carbon composite material of the present invention has the following significant advantages: (1) High performance: Fe3N-porous carbon composite material exhibits extremely high electrocatalytic synthesis performance of H2O2. In an H-type electrolytic cell with 0.1 mol / L KOH solution at a potential of 0.5 V (vs. RHE), the yield of H2O2 can reach 1600 mmol·g. cat -1 ·h -1 The Faraday efficiency exceeds 87%; its performance is even better in a flow cell (flowing tank) with 1 mol / L KOH solution.

[0022] (2) Synergistic effect of high selectivity and high activity: A dual-active-site synergistic system was constructed by interfacial electron transfer between Fe3N and the carbon support, with Fe sites and neighboring heteroatoms (N, O) activating carbon atoms. This interaction optimized the d-band center of Fe (shifting down to approximately -1.18 eV), placing the adsorption energy for the key intermediate *OOH in the optimal range, effectively suppressing the breaking of the OO bond (4e) while ensuring high activity. - (Path), thus achieving high selectivity.

[0023] (3) Excellent stability: The hierarchical porous carbon nanosheet structure provides a stable carrier and a fast mass transfer channel. The Fe3N nanoparticles are firmly anchored, so that the composite material can run continuously in the flow cell for 120 hours without significant performance degradation, and has the potential for industrial application.

[0024] (4) Low cost and scalability: Using inexpensive industrial by-product asphalt as a carbon source, and employing scalable dual-salt template method and impregnation-pyrolysis method, the process is simple, low cost, and more suitable for large-scale production and application. Attached Figure Description

[0025] Figure 1 The figures show the electrocatalytic performance and stability test results of the two Fe3N-porous carbon composite materials in Examples 1 and 2.

[0026] Figure 2 The figures show the electrocatalytic performance and stability test results of the two Fe3N-porous carbon composite materials in Examples 1 and 3.

[0027] Figure 3 The microstructure characterization and elemental composition analysis diagrams are for the Fe3N@HPC material in Example 1 and the Fe3N NPs@HPC material in Comparative Example 1.

[0028] Figure 4 The chemical composition and structure analysis diagrams are shown for the Fe3N@HPC material of Example 1, the Fe3N NPs@HPC material of Comparative Example 1, the HPC material of Comparative Example 2, and the Fe3N@AC material of Comparative Example 3.

[0029] Figure 5The graph shows the electrocatalytic performance results of Fe3N@HPC material in Example 1, Fe3N NPs@HPC material in Comparative Example 1, HPC material in Comparative Example 2, and Fe3N@AC material in Comparative Example 3.

[0030] Figure 6 The graphs show the yield, Faraday efficiency, and stability test results of H2O2 synthesis catalytically synthesized from Fe3N@HPC material in Example 1, Fe3N NPs@HPC material in Comparative Example 1, HPC material in Comparative Example 2, and Fe3N@AC material in Comparative Example 3.

[0031] Figure 7 The diagram shows the electrocatalytic performance and structural analysis of the Fe3N@HPC material in the flow cell in Example 1.

[0032] Figure 8 The figures show the electrocatalytic performance, structural analysis diagrams, and stability test results of the Fe3N@HPC material in Example 1, the Fe3N@HPC-NaCl material in Comparative Example 4, and the Fe3N@HPC-KCl material in Comparative Example 5.

[0033] Figure 9 The graph shows the electrocatalytic performance results of Fe3N@HPC material in Example 1 and Fe3N@Gr material in Comparative Example 6. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental methods described below are conventional methods; the raw materials or test materials used are typical products purchased from the market, unless otherwise specified. In the quantitative experiments of the following examples and comparative examples, three replicate experiments were conducted, and the results were averaged.

[0036] The electrocatalytic performance of the materials in the examples and comparative examples was determined by preparing each material as an electrode material for the electrolysis reaction and conducting electrolysis experiments in an H-cell and a flow cell.

[0037] First, the materials to be tested were prepared into catalyst inks: each material was thoroughly ground in a mortar (about 30 min), and then 2.5 mg of each material was added to the sample tubes with 980 μL of anhydrous ethanol and 20 μL of 5% (mass fraction) Nafion membrane solution, respectively. After sealing, the tubes were sonicated in an ultrasonic machine for 30 min until the ink was uniformly dispersed, thus obtaining catalyst inks for different materials.

[0038] The Nafion membrane used is the Nafion 117 membrane. Before use, it is pretreated by treating it with 5% (mass fraction) H2O2, deionized water and 5% H2SO4 at 80 °C for 1 h each. Then the membrane is repeatedly rinsed with deionized water and finally stored in deionized water for later use.

[0039] The electrolysis experiment for the H-cell test is as follows: (1) Pretreatment of hydrophobic carbon paper: The surface of the Toray hydrophobic carbon paper was cleaned by ultrasonic treatment with methanol, ethanol and water for 20 min each, and then dried in an oven at 60 ℃ for later use.

[0040] (2) Preparation of working electrode of H-type electrolytic cell: 40 μL of catalyst ink was evenly dropped onto the treated carbon paper (1×1.5 cm), and tested after natural air drying.

[0041] (3) Assembly of H-type electrolytic cell: Add 50 mL of electrolyte (0.1 mol / L KOH) to the cathode and anode chambers respectively, and test the three-electrode system on the Chenhua workstation. The three-electrode system is composed as follows: the working electrode is the electrode prepared in step (2), the counter electrode is a platinum wire, and the reference electrode is a saturated calomel electrode.

[0042] (4) Oxygen is delivered through a hose into the electrolyte in the cathode chamber until it is saturated, and oxygen is continuously supplied until the end of the experiment.

[0043] The electrolysis experiment for the flow cell test is as follows: (1) Cathode of the flowing electrolytic cell: Take 40 μL of catalyst ink and drop it evenly onto the treated carbon paper (the pretreatment of hydrophobic carbon paper is the same as above), and its effective working area is 1 cm. 2 After air drying, the samples were tested.

[0044] (2) Anode of the flowing electrolytic cell: The foamed nickel (thickness: 0.5 mm) was ultrasonically cleaned for 15 min each with 0.1 mol / L HCl, deionized water and anhydrous ethanol, and then dried in an oven at 60 ℃ for later use.

[0045] (3) Assembly of the flow electrolyzer: The electrodes from steps (1) and (2) are used as the anode and cathode, respectively, and are assembled with the Nafion 117 membrane to form a flow electrolyzer. The electrolyte for the anode and cathode is 250 mL (1 mol / L KOH).

[0046] (4) Oxygen is transported by a hose. It is first introduced into the electrolyte until it is saturated, and the oxygen is continuously supplied until the end of the experiment. Then, the electrolyte is transported to the cathode chamber of the flow cell for circulation by a pump.

[0047] The yield of hydrogen peroxide in the electrolyte was determined to evaluate the electrocatalytic performance of the materials in each example and comparative example. The hydrogen peroxide yield was detected using cerium sulfate titration-UV-Vis spectrophotometry, and the specific procedures are as follows: (1) Dissolve cerium sulfate in dilute sulfuric acid of a certain concentration to prepare a Ce(SO4)2 stock solution of a specific concentration.

[0048] (2) A series of standard solutions with known Ce(IV) concentrations were prepared by quantitatively diluting the stock solution; the absorbance of each standard solution at 320 nm was measured using a UV-Vis spectrophotometer, and the absorbance (A) was plotted against the Ce(IV) concentration (C) to obtain a linear calibration curve.

[0049] (3) At the predetermined time point during the electrolysis reaction, accurately transfer 100 µL of electrolyte sample and quickly add it to a centrifuge tube or cuvette containing 3.0 mL of Ce(SO4)2 stock solution. Vortex thoroughly to mix, and react at room temperature for 10 minutes to ensure that H2O2 and Ce are properly combined. 4+ Fully functional.

[0050] (4) Using a UV-Vis spectrophotometer, the Ce concentration at 320 nm before and after the reaction was determined by UV-Vis spectrophotometry. 4+ The change in concentration is used to obtain the concentration of H2O2 through quantitative calculation.

[0051] Example

[0052] Preparation of Fe3N-porous carbon composite materials for use as 2e - Electrode catalyst for the electrochemical synthesis of H2O2 using ORR.

[0053] Example 1 The Fe3N-porous carbon composite material Fe3N@HPC was prepared using petroleum asphalt as the carbon source and ferric chloride as the iron precursor. The specific operation steps are as follows: a. Preparation of porous carbon support: Weigh 0.3 g petroleum asphalt, 0.54 g NaCl and 0.66 g KCl, mix them, then add 15 g ZrO2 grinding balls and 5 mL ethanol. Ball mill in a planetary ball mill at a frequency of 30 Hz for 30 min, stop for 10 min, and repeat 4 times. Collect the product, dry it and place it in a tube furnace. Heat the furnace to 800℃ at 5℃ / min under Ar gas flow and keep it at that temperature for 2 h. Then cool it, wash it with deionized water to remove the salt template NaCl-KCl, and dry it at 80℃ to obtain hierarchical porous carbon nanosheets (HPC), which are the porous carbon supports used as supports in subsequent steps. In the above operation, the asphalt is fully pulverized by the high-energy mechanical force of ball milling and mixed with the composite salt template NaCl-KCl at the nanoscale to ensure that the molten asphalt can uniformly coat the salt particles during subsequent pyrolysis, thus obtaining a uniform pore structure and a basis for reproducibility. b. Formation and loading of Fe3N nanoparticles on porous carbon support: 81 mg FeCl3·6H2O was dissolved in 40 mL of deionized water, 100 mg HPC was added, and the mixture was impregnated at room temperature for 6 h; then it was evaporated and dried at 100 °C, ground, and placed in a ceramic boat. It was then subjected to a two-step heat treatment under an Ar gas flow: first, the temperature was increased to 360 °C at 2 °C / min and held for 2 h, then the temperature was increased to 700 °C at 5 °C / min and held for 2 h. After cooling, the initial composite material Fe3N NPs@HPC was obtained. c. Acid washing treatment: The initial composite material Fe3NNPs@HPC obtained in step b was refluxed at 120℃ for 6 h using a 4 mol / L HNO3 solution, then cooled, washed with a large amount of deionized water until neutral, and then dried in an oven at 60℃ for 6~8 h to obtain the final product Fe3N-porous carbon composite material Fe3N@HPC.

[0054] Example 2 The Fe3N-porous carbon composite material Fe3N@HPC was prepared using petroleum asphalt as the carbon source and ferric nitrate as the iron precursor. The specific operation steps are as follows: a. Preparation of porous carbon support: Weigh 0.3 g petroleum asphalt, 0.54 g NaCl and 0.66 g KCl, mix them, then add 15 g ZrO2 grinding balls and 5 mL ethanol. Ball mill in a planetary ball mill at a frequency of 30 Hz for 30 min, stop for 10 min, and repeat 4 times. Collect the product, dry it and place it in a tube furnace. Heat the furnace to 700℃ at 5℃ / min under Ar gas flow and keep it at that temperature for 2 h. Then cool it, wash it with deionized water to remove the salt template NaCl-KCl, and dry it at 80℃ to obtain hierarchical porous carbon nanosheets (HPC), which are the porous carbon support used as the support in subsequent steps. b. Preparation of Fe3N-porous carbon composite material: 121 mg Fe(NO3)3·9H2O was dissolved in 40 mL of deionized water, 100 mg HPC was added, and the mixture was impregnated at room temperature for 6 h; then it was evaporated and dried at 100 °C, ground, and placed in a ceramic boat. It was then subjected to a two-step heat treatment under an Ar gas flow: first, the temperature was increased to 350 °C at 2 °C / min and held for 2 h, then the temperature was increased to 700 °C at 5 °C / min and held for 2 h. After cooling, the initial composite material Fe3N NPs@HPC was obtained. c. Acid washing treatment: The initial composite material Fe3NNPs@HPC obtained in step b was refluxed at 120℃ for 6 h using a 4 mol / L HNO3 solution, cooled, washed with a large amount of deionized water until neutral, and dried at 60℃ for 6~8 h to obtain the final product Fe3N-porous carbon composite material Fe3N@HPC.

[0055] Example 3 Fe3N-porous carbon composite material Fe3N@HPC was prepared using coal tar pitch as a carbon source and ferric chloride as an iron precursor. The specific operation steps are as follows: a. Preparation of porous carbon materials: Weigh 0.3 g of coal tar pitch material, 1.04 g of NaCl and 0.46 g of KCl, mix them, and then add 20 g of grinding balls ZrO2 and 7 mL of ethanol (or use isopropanol as the grinding solvent). Ball mill the mixture in a planetary ball mill at a frequency of 30 Hz for 35 min, stop for 15 min, and repeat 5 times. Collect the product, dry it, and place it in a tube furnace. Heat the furnace to 900℃ at 7℃ / min under an Ar gas flow and keep it at that temperature for 3 h. Then cool it, wash it with deionized water to remove the salt template NaCl-KCl, and dry it at 70℃ to obtain hierarchical porous carbon nanosheets (HPC), which are the porous carbon supports used as carriers in subsequent steps. b. Preparation of Fe3N-porous carbon composite material: 100 mg FeCl3·6H2O was dissolved in 40 mL of deionized water, 115 mg HPC was added, and the mixture was impregnated at room temperature for 8 h; then it was evaporated and dried at 100 °C, ground, and placed in a ceramic boat; a two-step heat treatment was carried out under Ar gas flow, namely, firstly, the temperature was increased to 360 °C at 4 °C / min and held for 2 h, and then increased to 700 °C at 5 °C / min and held for 3 h. After cooling, the initial composite material Fe3N NPs@HPC was obtained. c. Acid washing treatment: The initial composite material Fe3NNPs@HPC obtained in step b was refluxed at 125℃ for 8 h using a 4 mol / L HNO3 solution, cooled, washed with a large amount of deionized water until neutral, and dried at 60℃ for 6~8 h to obtain the final product Fe3N-porous carbon composite material Fe3N@HPC.

[0056] The electrocatalytic performance of the Fe3N-porous carbon composite materials in Examples 1-3 was determined, see [see details]. Figure 1 , 2 As shown.

[0057] Figure 1a shows the electrochemical test results of the two Fe3N-porous carbon composite materials in Examples 1 and 2 in O2-saturated 0.1 mol / L KOH solution. It can be seen that Example 2 and Example 1 have similar current densities within the same voltage range of 0~1 V (vs. RHE), i.e., similar 2e-1. - ORR catalytic performance. Figure 2 b shows the stability test results of the two Fe3N-porous carbon composite materials from Examples 1 and 2 in O2-saturated 0.1 mol / L KOH solution in the H-cell. Example 2 showed a current density decrease of only 1.7% within 10 h, similar to the 1.4% decrease in Example 1. This demonstrates that the selection of iron precursors is not limited to a single source and can be extended to other common iron salts, showcasing the flexibility and universality of this synthesis method in iron source selection, and providing more raw material selection options for practical large-scale preparation.

[0058] Figure 2 a shows the electrochemical test results of the two Fe3N-porous carbon composite materials in Examples 1 and 3 in O2-saturated 0.1 mol / L KOH solution. It can be seen that Example 3 and Example 1 have similar current densities in the same voltage range of 0~1 V (vs. RHE), that is, they have similar 2e⁻ORR catalytic performance. Figure 2 b shows the stability test results of the two Fe3N-porous carbon composite materials from Examples 1 and 3 in O2-saturated 0.1 mol / L KOH solution in the H-cell. The current density of Example 3 decreased by only 1.992% within 10 h, which is similar to the 1.4% decrease in Example 1. This demonstrates that industrial by-product pitch, such as petroleum pitch and coal tar pitch, can be used as a carbon source to prepare catalyst materials with excellent electrocatalytic performance. This greatly broadens the selection range of low-cost carbon sources and enhances the flexibility of the technical route and the feasibility of large-scale production.

[0059] Comparative Example Using different materials as 2e - The electrode catalyst for the electrochemical synthesis of H2O2 by ORR is compared with the Fe3N-porous carbon composite material of Example 1.

[0060] Comparative Example 1 Untreated Fe3N NPs@HPC composite material.

[0061] Fe3N NPs@HPC material was prepared according to steps a and b of Example 1, namely 0.3 g petroleum asphalt, 0.54 g NaCl, 0.66 g KCl, 15 g ZrO2 grinding balls, and 5 mL ethanol. The mixture was ball-milled in a planetary ball mill at 30 Hz for 30 min, with a 10 min stop, for 4 cycles. After drying, the product was placed in a tube furnace and heated to 800 °C at 5 °C / min under an Ar gas flow, held for 2 h, cooled, washed with deionized water to remove the salt template, and dried at 80 °C to obtain hierarchical porous carbon nanosheets (HPC). 81 mg FeCl3·6H2O was dissolved in 40 mL of deionized water, and 100 mg HPC was added. The mixture was impregnated at room temperature for 6 h, then evaporated and dried at 100 °C. After grinding, the material was placed in a ceramic boat and heated to 360 °C at 2 °C / min under an Ar gas flow, held for 2 h, then heated to 700 °C at 5 °C / min, held for 2 h. h, after cooling, the initial composite material Fe3N NPs@HPC is obtained, without subsequent acid washing.

[0062] Comparative Example 2 The porous carbon material HPC was prepared according to step a of Example 1, without iron loading and subsequent heat treatment.

[0063] Comparative Example 3 The Fe3N@AC composite material prepared using a salt-free template is specifically prepared as follows: 0.3 g of petroleum asphalt was placed in a ceramic boat and heated to 800 °C at 5 °C / min under an Ar atmosphere, and held for 2 h to obtain blocky asphalt-derived carbon AC. Then, 81 mg of FeCl3·6H2O was dissolved in 40 mL of deionized water, 100 mg of AC was added, and the mixture was impregnated at room temperature for 6 h. After that, it was evaporated and dried at 100 °C, ground, and placed in a ceramic boat. Under an Ar gas flow, the temperature was first increased to 360 °C at 2 °C / min and held for 2 h; then increased to 700 °C at 5 °C / min and held for 2 h. The resulting sample was then refluxed with 4 mol / L HNO3 solution at 120 °C for 6 h, and finally washed with deionized water until neutral. The sample was then dried in an oven at 60 °C for 6-8 h to obtain the Fe3N@AC composite material.

[0064] Comparative Example 4 The composite material Fe3N@HPC-NaCl prepared using NaCl single salt template was prepared in almost the same way as in Example 1, except that KCl was replaced with an equal mass of NaCl, i.e., the amount of NaCl added was 1.2g.

[0065] Comparative Example 5 The composite material Fe3N@HPC-KCl prepared using KCl as a single salt template was prepared in almost the same way as in Example 1, except that NaCl was replaced with an equal mass of KCl, i.e., the amount of KCl added was 1.2g.

[0066] Comparative Example 6 The composite material Fe3N@Gr prepared using graphene as the carbon source was prepared in almost the same way as in Example 1, except that the carbon source petroleum asphalt (0.3 g) was replaced with an equal mass of graphene to obtain the final product Fe3N@Gr (Gr represents graphene) material.

[0067] Structural characterization and performance testing 1. The microstructure and elemental composition of the Fe3N@HPC material in Example 1 were characterized, such as... Figure 3 As shown.

[0068] Figure 3 a is a SEM image of the Fe3N NPs@HPC material in Comparative Example 1, which shows a large number of white particles on its surface, which are Fe-related particles; Figure 3 Images b and 3c are SEM and TEM images of the Fe3N@HPC material in Example 1, respectively. The material exhibits a wrinkled, lamellar structure, and no white particles were observed, indicating that the acid washing treatment effectively removed unstable Fe-related particles from the surface. SEM and TEM characterization provide a deeper understanding of the material's microstructure and structural features, allowing for a direct observation of the catalyst size and the distribution of particles on the carbon support surface.

[0069] Figure 3 Images d~3e are HRTEM images of the Fe3N@HPC material from Example 1. They show Fe3N nanoparticles with an average diameter of approximately 10 nm distributed on a carbon substrate, surrounded by a disordered layer of graphitized carbon. Figure 3 No large-sized nanoparticles were observed in the carbon nanosheet structure of d, indicating that no severe metal agglomeration occurred during pyrolysis. These highly dispersed small-sized Fe3N nanoparticles are beneficial to improving the catalytic activity of the sites. This shows that the unique carbon layer structure not only effectively inhibits the high-temperature agglomeration of nanoparticles, but also promotes rapid charge transfer.

[0070] Figure 3 f is the IFFT image of Fe3N@HPC material in Example 1. Observe the lattice fringes of the nanoparticles in the image. The crystal plane with a spacing of 0.208 nm corresponds to the (111) plane of Fe3N, and the crystal plane with a spacing of 0.217 nm corresponds to the (002) plane of Fe3N. Figure 3 g is the elemental mapping diagram of the Fe3N@HPC material in Example 1, showing a uniform distribution of C, O, Fe, and N elements. (Summary) Figure 3 f and Figure 3 g proved the successful loading of Fe element in pitch carbon material, and the distribution characteristics of Fe and N elements in carbon material show that Fe and N coexist, and the content of Fe element is more than that of N element, which further indicates that Fe atoms and N atoms form Fe3N nanoparticles.

[0071] 2. Compare the chemical composition and structure of the Fe3N@HPC material in Example 1 with those of Comparative Example 1 (Fe3N NPs@HPC material), Comparative Example 2 (HPC material), and Comparative Example 3 (Fe3N@AC material), as follows: Figure 4 As shown.

[0072] The success of Fe3N synthesis can be determined by analyzing the crystal structure and phase composition of the material sample using XRD. Figure 4 a shows the XRD patterns of the materials in Example 1 and Comparative Examples 1-3. The characteristic peaks appearing near 2θ≈26° in all samples correspond to broad diffraction peaks of the carbon (002) crystal plane. In Comparative Example 1, the characteristic peaks near 43.7°, 41.2°, and 38.1° correspond to Fe3N crystals (PDF#83-0878), indicating that Fe element successfully combines with the N element in the pitch carbon material itself. However, Example 1 only showed weak peaks in these regions, possibly because the aggregated Fe3N particles were washed away during acid treatment, resulting in weaker peak intensity. Figure 3 The Fe3N lattice can still be observed in the TEM image, indicating that Fe3N nanoparticles are still present in Example 1.

[0073] Figure 4 b shows the Raman spectra of the materials in Example 1 and Comparative Examples 1-3. It can be seen that all materials exhibit Raman spectra at 1350 cm⁻¹. -1 and 1590 cm -1 Two distinct characteristic peaks appeared at each location, corresponding to the D and G bands of the carbon material, respectively. Among them, I... D / I G The ratio represents the degree of defect and disorder of the carbon material; the larger the ratio, the more defects and the higher the structural disorder; the lower the ratio, the higher the degree of graphitization and the fewer defects. Examples 1 (Fe3N@HPC), Comparative Example 1 (Fe3N NPs@HPC), Comparative Example 2 (HPC), and Comparative Example 3 (Fe3N@AC) show the following I values: D / I G The values ​​were 0.98, 1.07, 0.75, and 0.84, respectively. It can be seen that the ball-milled sample had a higher Ig content. D / I G This is because the ball milling process increases the amount of sp. 3The carbon content introduces structural defects into the pitch carbon, possibly due to the localized heat generated by the mechanical stress of ball milling breaking the C=C bonds. In the electrocatalytic preparation of H₂O₂, carbon defects on the electrode material surface can serve as active sites for the reaction, and are a key factor affecting the H₂O₂ yield.

[0074] XPS spectra can be used to analyze the elemental composition and corresponding chemical valence states of catalysts. Figure 4 c shows the XPS spectra of the materials in Example 1 and Comparative Example 2. The appearance of the Fe-N peak in Example 1 indicates that the Fe3N component was successfully introduced.

[0075] Infrared spectroscopy revealed that different catalysts have many oxygen-containing functional groups on their surfaces and exhibit different characteristic absorption peaks. Figure 4 Figure d shows the infrared spectra of the materials in Example 1 and Comparative Examples 1-3. The sample in Example 1 and Comparative Examples 1 and 2 exhibits higher intensity characteristic peaks of oxygen-containing functional groups, indicating that the carbon nanosheet structure obtained by ball milling contains more oxygen-containing functional groups on its surface, providing more active sites. Furthermore, the Fe3N@HPC treated with HNO3 shows higher intensity peaks at 1360 cm⁻¹. -1 and 1735cm -1 The surrounding area exhibits distinct C-OH and C=O characteristic peaks, indicating that this strongly oxidizing functional group facilitates the reduction of O2.

[0076] 3. Compare the electrocatalytic performance of Fe3N@HPC material in Example 1 with that of Fe3N NPs@HPC material in Comparative Example 1, HPC material in Comparative Example 2, and Fe3N@AC material in Comparative Example 3. Figures 5-7 As shown.

[0077] LSV curves (cyclic voltammetry curves) show the current density performance of materials in the 0~1 V (vs. RHE) potential range, and can directly reflect the electrocatalytic performance of electrode materials. Figure 5 Figure a shows the LSV curves of the materials in Example 1 and Comparative Examples 1-3. Example 1 exhibits the highest current density within the same voltage range of 0-1 V (vs. RHE), indicating that this material possesses significant ORR catalytic activity. Electrochemical impedance spectroscopy (EIS) can reflect the kinetic rate of the catalyst reaction process, where R... ct This represents the interfacial charge transfer resistance. Figure 5 b shows the Nyquist plots of the materials in Example 1 and Comparative Examples 1-3. Compared with the charge transfer resistance of Comparative Example 1 (480.1 Ω), Comparative Example 2 (526.1 Ω), and Comparative Example 3 (424 Ω), the charge transfer resistance of Example 1 is the smallest (85.31 Ω), indicating that its charge transfer capability and reaction kinetics are the best.

[0078] Hydrogen peroxide yield can directly reflect the performance of a catalyst. Figure 6 a is a graph showing the yield of H2O2 synthesized by the materials in Example 1 and Comparative Examples 1-3 under catalytic conditions of 0.5 V (vs. RHE), indicating the H2O2 yield of Example 1 at 0.5 V (vs. RHE) (1621 mmol·g). cat -1 ·h -1 The concentration was significantly higher than that of control group 1 (1283.88 mmol·g). cat -1 ·h -1 Comparative Example 2 (877.64 mmol g) cat -1 h -1 ) and Comparative Example 3 (262.83 mmol·g cat -1 ·h -1 ), indicating that Example 1 (Fe3N@HPC) has 2e - ORR has superior catalytic activity. Figure 6 Figure b shows the yield and Faradaic efficiency of the material in Example 1 for the catalytic synthesis of H2O2 under different voltage conditions. It indicates that the Fe3N@HPC material achieves the highest Faradaic efficiency (87.7%) at 0.5V (vs. RHE), and the highest yield (3377.96 mmol·g) at 0.3V (vs. RHE). cat -1 ·h -1 It combines high selectivity and high yield. Figure 6 c shows the stability curves of the materials in Example 1 and Comparative Examples 1-3 in O2-saturated 0.1 mol / L KOH solution at a potential of 0.5 V (vs. RHE) for 10 h. It shows that the current density decay rate of Example 1 (1.4%) is much lower than that of Comparative Example 1 (22%), Comparative Example 2 (31%) and Comparative Example 3 (56%), proving that its electrochemical stability is better.

[0079] The electrocatalytic performance of the material in Example 1 was measured in a flow cell. Figure 7 a is a schematic diagram of the flow channel structure. Figure 7 Figure b shows the H2O2 yield and Faraday efficiency of Example 1 under different voltages in the flow cell. The results show that the Fe3N@HPC material achieved the highest H2O2 yield (4158 mmol·g) at 0.3 V (vs. RHE). cat -1 ·h -1 It achieves a peak Faraday efficiency of 79.5% at 0.5 V (vs. RHE), demonstrating its high selectivity and high yield. Figure 7c shows the stability results of Example 1 tested at 0 V (vs. RHE) for 120 h, indicating that the Fe3N@HPC material maintains a stability of approximately 60 mA·cm⁻¹. -2 It can operate continuously for 120 hours at a current density without significant current decay, demonstrating high stability.

[0080] The functional groups contained in the material were determined using in-situ ATR-SEIRAS spectroscopy. Figure 7 d and 7e are the in-situ ATR-SEIRAS spectra of the materials in Example 1 (Fe3N@HPC) and Comparative Example 2 (HPC), respectively. Example 1 shows a more obvious *OOH characteristic peak intensity than Comparative Example 2, indicating that it has better *OOH adsorption capacity. Meanwhile, at 1380 cm⁻¹... -1 The faint characteristic peaks observed nearby originate from the adsorption of *H2O2 (HOOH) on the catalyst surface. ad The OOH stretching pattern in the image confirms the continuous generation of H2O2 in the reaction system, thus demonstrating that Fe3N@HPC exhibits good 2e-ion generation properties. - ORR selectivity. Comparative Example 2 at 1175 cm -1 and 1480 cm -1 The characteristic peaks nearby correspond to OOH ad and O 2,ad But at 1380 cm -1 No HOOH was detected nearby. ad The characteristic peaks indicate that the OO bonds of the *OOH intermediate may break on the surface of HPC materials, rather than through 2e-phase synthesis. - H₂O₂ is generated through the pathway. HOOH exists in Fe₃N@HPC materials. ad Characteristic peaks demonstrate that the introduction of Fe3N improves the selectivity of H2O2 electrosynthesis; further comparison reveals that the OOH corresponding to Fe3N@HPC... ad The characteristic peak shifts positively compared to HPC, indicating that the Fe3N component weakens the interaction between the catalyst and the intermediate *OOH. This moderate adsorption strength facilitates the timely desorption of the reaction intermediate, thereby promoting the conversion of *OOH to the 2e- of H2O2. - Reaction pathway.

[0081] 4. Compare the electrocatalytic performance of Fe3N@HPC material in Example 1 with that of Fe3N@HPC-NaCl material in Comparative Example 4 and Fe3N@HPC-KCl material in Comparative Example 5. Figure 8 As shown.

[0082] Figure 8Figure a shows the electrochemical test results of the materials in Example 1 and Comparative Examples 4 and 5 in O2-saturated 0.1 mol / L KOH solution. It illustrates the number of electrons transferred by different materials at different voltages, allowing for a direct observation of whether the reaction proceeds (2e⁻). - ORR path. The results show that the material prepared using the composite salt NaCl-KC template in Example 1 exhibits an electron transfer number close to 2, the highest current density, and the best stability, significantly outperforming the single salt template. Analysis suggests that the nanosheet structure of the mixed salt template has a large specific surface area, abundant oxygen-containing functional groups, sufficient conductivity and active sites, and 2e... - ORR exhibits high selectivity. However, a single NaCl template (Comparative Example 4) has numerous defects, poor conductivity, and a large current density decay; a single KCl template (Comparative Example 5) has excessive graphitization, few active sites, and an electron transfer number bias towards 4e. - The path leads to reduced selectivity and poor stability of H2O2.

[0083] Figure 8 b shows the Raman spectra of the materials in Example 1 and Comparative Examples 4 and 5, illustrating the different materials' I... D / I G Ratio, I in Comparative Example 4 D / I G The ratio is the largest, indicating the highest degree of defect, with its 2e - The ORR performance was also low, possibly because the material's poor conductivity at this point was unfavorable for the electrocatalytic reaction; while the I in Comparative Example 5... D / I G The smallest ratio indicates a higher degree of graphitization, which accelerates the electron transfer rate and is detrimental to 2e. - ORR reaction process. Example 1 has a more suitable I... D / I G The ratio is favorable for electrocatalytic reactions.

[0084] Figure 8 c shows the LSV curves of the materials in Example 1 and Comparative Examples 4 and 5, demonstrating that Example 1 has the highest current density and excellent catalytic performance within the same voltage range of 0~1 V (vs. RHE).

[0085] Figure 8 d represents the stability results of the materials in Example 1 and Comparative Examples 4 and 5 at 0.5 V (vs. RHE) for 10 h. It shows that the current density of Example 1 decreased by only 1.4% within 10 h, which is much lower than that of Comparative Examples 4 and 5, and has the best stability.

[0086] The mechanism analysis of salt template is as follows.

[0087] The high melting point (801℃) of NaCl causes it to remain solid throughout the pyrolysis process, which is the key factor leading to its performance bottleneck. Solid NaCl particles act as a hard template, although they can etch abundant pores and defects (I... D / I G While the current density is as high as 1.01, it cannot promote the fusion and rearrangement of precursors at the molecular / nanoscale, demonstrating the limitations of hard templates. Furthermore, it exhibits problems of hindered mass transfer and poor conductivity; that is, the carbon source generated by pitch pyrolysis experiences poor mass transfer between solid templates, making it difficult to form a continuous, highly ordered graphitized conductive network. This results in poor conductivity and low electron transport rate in the generated carbon material. This not only limits the current density but also exacerbates current decay during operation.

[0088] KCl's low melting point (770℃) causes it to melt prematurely, losing its core template function and directly leading to uncontrolled and selective changes in material structure. Specifically, the premature loss of its "skeleton" function, melting into a liquid phase in the early stages of pyrolysis, eliminates its ability to provide rigid template support and create pores, resulting in uneven pore structures and a relatively low specific surface area in the formed carbon structure. Liquid-phase KCl provides an environment similar to molten salt carbonization, greatly promoting the graphitization (Ig) of carbon materials. D / I G (as low as 0.84), but it also reduces edge defects and oxygen-containing functional groups, etc. 2e - The number of ORR active sites can lead to either excessive graphitization or insufficient active sites. Highly graphitized carbon surfaces exhibit enhanced chemical inertness, making them more prone to catalyzing the complete four-electron reduction of O2 to H2O, selectively oxidizing to the 4-electron atom. - Path offset. As a result, the selectivity of H2O2 is significantly reduced, the structure is unstable, and the overall performance deteriorates.

[0089] The mixed salt template combines the advantages of NaCl and KCl while avoiding their respective shortcomings, achieving comprehensive optimization of material structure and performance, specifically in terms of structure and conductivity, defects and active sites, and selective regulation.

[0090] Structure and conductivity: NaCl (high melting point) and KCl (low melting point) form a "temperature gradient template" during pyrolysis. At the carbonization temperature, KCl melts to form a liquid phase, promoting uniform coating of the asphalt and reorganization of the carbon skeleton, ensuring good conductivity. At the same time, the unmelted NaCl solid particles act as a rigid skeleton, preventing excessive fusion and collapse of the structure caused by the KCl liquid phase. Together, they construct a three-dimensional hierarchical porous structure with a large specific surface area, uniform pore structure, and good conductive network.

[0091] Defects and Active Sites: NaCl templates introduce numerous defects, while KCl templates promote graphitization. The combination of these two elements achieves a balance between defect density and conductivity. The hybrid template not only provides abundant oxygen-containing functional groups and active sites but also ensures efficient electron conduction to these sites, facilitating 2e... - The ORR path creates an ideal environment.

[0092] Selective regulation: This optimized structure (large specific surface area, moderate defects, and high conductivity) is conducive to the adsorption of O2 and the stability of the *OOH intermediate, while inhibiting further breaking of the OO bond, thereby significantly improving the selectivity of H2O2.

[0093] The electrocatalytic performance of the Fe3N@HPC material in Example 1 and the Fe3N@Gr material in Comparative Example 6 are compared. Figure 9 As shown.

[0094] Figure 9 The electrochemical test results of the materials in Example 1 and Comparative Example 6 in O2-saturated, 0.1 mol / L KOH solution demonstrate the crucial role of nitrogen (N) in the carbon substrate. The substrate of Example 1 was petroleum pitch carbon, rich in N, while the substrate of Comparative Example 6 was graphene, which contains no N. Figure 9 The LSV curves show that the electrochemical performance of Example 1 is superior to that of Comparative Example 6; that is, within the same voltage range of 0–1 V (vs. RHE), Example 1 exhibits the highest current density. This is because the nitrogen element maintains the 2e⁻ content by forming Fe₃N active sites, regulating the electronic structure of the carbon substrate, and introducing defects. - ORR exhibits high selectivity and stability. The absence of nitrogen (in comparative example 6, graphene) in the carbon source disrupts this synergistic effect, leading to a decrease in the number of electrons transferred by the catalyst under the same conditions, thus resulting in a decrease in current.

[0095] In summary, the Fe3N-porous carbon composite material of this invention possesses a specific composite structure of "Fe3N nanoparticles + hierarchical porous heteroatom-doped carbon nanosheets." Its Fe d-band center exhibits a downward shift, the C=O peak binding energy is positively shifted, and its microstructure displays a nanosheet structure with 5-15 nm dispersed particles and hierarchical pores of "micropores + mesopores." This achieves a coexistence of high activity, high selectivity, and high stability, thus demonstrating extremely high H2O2 electrosynthesis performance. The preparation of this Fe3N-porous carbon composite material uses petroleum asphalt as the carbon source, employs a specific dual-salt (NaCl-KCl) template, and combines ball milling to prepare a porous carbon support. The composite material is then obtained through an impregnation-two-step heat treatment-acid washing process. This process is simple, low-cost, and conducive to large-scale production. The application of the Fe3N-porous carbon composite material of this invention in the electrocatalysis of H2O2... -The ORR reaction for synthesizing H2O2, especially in the application of alkaline flowing electrolyzers, has achieved high H2O2 yields (>4000 mmol·g). cat -1 ·h -1 Performance parameters such as stability over long periods (>120 h) demonstrate significant technological advancements.

[0096] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A Fe3N-porous carbon composite material for the electrocatalytic synthesis of hydrogen peroxide, characterized in that: The Fe3N-porous carbon composite material is prepared by a two-step heat treatment reaction of a porous carbon support and an iron precursor. The porous carbon support is a hierarchical porous carbon nanosheet (HPC) formed by ball milling and high-temperature carbonization at 700-900℃ under the action of NaCl-KCl composite salt template, using industrial by-product pitch as the carbon source. The two-step heat treatment includes the first step of decomposing the iron precursor and initially anchoring iron ions on the porous carbon support at 300-400℃, and the second step of generating Fe3N nanoparticles on the porous carbon support at 700-900℃.

2. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 1, characterized in that: The carbon source used to prepare the porous carbon support and the composite salt template are used in a mass ratio of 1:2 to 1:5; the NaCl and KCl in the composite salt are used in a mass ratio of 1:3 to 3:1; preferably, industrial by-product asphalt includes petroleum asphalt and coal tar pitch.

3. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 1, characterized in that, The preparation of porous carbon supports includes the following steps: The carbon source is mixed with NaCl and KCl, and then grinding balls and grinding solvent are added. The mixture is repeatedly ball-milled. After drying, the product is subjected to high-temperature carbonization at 700~900℃ for 2~3 h under an Ar atmosphere. After cooling, the composite salt template is washed off and dried to obtain hierarchical porous carbon nanosheets (HPC), which are porous carbon supports. Preferably, the ratio of carbon source, composite salt template, grinding balls and grinding solvent is 0.3~0.5g:1.0~1.5g:15~30g:5~8mL. The grinding solvent is ethanol or isopropanol.

4. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 3, characterized in that: Repeated ball milling involves milling in a planetary ball mill at a frequency of 30-45 Hz for 30-40 minutes, stopping for 10-15 minutes, and repeating the cycle 4-6 times.

5. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 1, characterized in that: The iron precursor is selected from ferric chloride, ferric nitrate, and ferric sulfate.

6. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 1, characterized in that: The preparation of Fe3N-porous carbon composite materials includes the following steps: After dissolving the iron precursor, HPC was added and impregnated at room temperature for 6-8 hours, followed by evaporation, drying, and grinding. A two-step heat treatment was then performed under an Ar atmosphere: first, the iron precursor was held at 300-400℃ for 2-3 hours to decompose and initially anchor it with carbon-nitrogen; then, it was held at 700-900℃ for 2-3 hours to generate Fe3N nanoparticles on the porous carbon support, yielding the initial composite material Fe3N NPs@HPC. Finally, a strong acid reflux cleaning treatment was performed to obtain the Fe3N-porous carbon composite material Fe3N@HPC. Preferably, the ratio of iron precursor to HPC was 0.05-0.12 g:0.05-0.15 g, and the iron precursor was dissolved in water to prepare a solution with a concentration of 0.005-0.01 mol / L.

7. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 6, characterized in that: The surface of the Fe3N-porous carbon composite material contains C=O and CO functional groups, and the binding energy of the C=O peak is positively shifted. The d-band center of Fe in Fe3N nanoparticles shifts downward to between -1.10 and -1.25 eV.

8. The Fe3N-porous carbon composite material for electrocatalytic synthesis of hydrogen peroxide according to claim 6, characterized in that: The average size of Fe3N nanoparticles is 5~15 nm, preferably 8~12 nm.

9. The method for preparing the Fe3N-porous carbon composite material according to any one of claims 1 to 8, characterized in that, The following steps are included: a. Preparation of porous carbon support: Industrial by-product pitch, NaCl and KCl are mixed, and grinding balls and grinding solvent are added. The mixture is subjected to repeated ball milling. The resulting product is dried and placed in a tube furnace. Under an Ar atmosphere, the temperature is increased to 700-900℃ at 5-8℃ / min and held for 2-3 h. Then, it is cooled and washed with deionized water to remove the composite salt template NaCl-KCl. The product is then dried at 60-80℃ to obtain hierarchical porous carbon nanosheets (HPC), which is the porous carbon support. Preferably, the repeated ball milling is performed in a planetary ball mill at a frequency of 30-45Hz for 30-40 min, followed by a 10-15 min stop, for 4-6 cycles. b. Preparation of Fe3N-porous carbon composite material: The iron precursor was dissolved in water, HPC was added, and the mixture was impregnated at room temperature for 6-8 hours; then evaporated and dried, ground, and placed in a ceramic boat. Two-step heat treatment was carried out under Ar atmosphere: first, the temperature was increased to 300-400°C at 2-5 °C / min and held for 2-3 hours, then increased to 700-900°C at 5-8 °C / min and held for 2-3 hours. After cooling, the initial composite material Fe3N NPs@HPC was obtained. c. Acid washing treatment: The initial composite material Fe3N NPs@HPC obtained in step b is subjected to reflux washing treatment with strong acid, cooled, washed with a large amount of deionized water until neutral, and dried at 60~80℃ to obtain the final product Fe3N-porous carbon composite material Fe3N@HPC; preferably, the strong acid is a 4 mol / L HNO3 solution, the reflux temperature is 120~130℃, and the time is 6~8 h.

10. The application of the Fe3N-porous carbon composite material according to any one of claims 1 to 8, characterized in that: The synthesis of hydrogen peroxide is achieved by catalyzing the two-electron oxygen reduction reaction using Fe3N-porous carbon composite materials. Preferably, Fe3N-porous carbon composite materials are used as the electrode material for the electrocatalytic reaction.

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