Iron-nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material, preparation method and application thereof

Abstract

The present application relates to the technical field of zinc-air battery catalyst, in particular to iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material and its preparation method and application. The present application introduces nitrogen source, soluble iron salt, pore-forming agent and template agent into medium temperature coal pitch, and sequentially carries out heat treatment, acid washing and carbon dioxide activation treatment, to prepare iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material. The iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material obtained by the method of the present application does not introduce impurities, does not have structural defects, uniformly dopes nitrogen and has ideal pore structure, overcoming the problems of poor conductivity, limited number of active sites and low catalytic activity of the nitrogen-doped carbon material in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of zinc-air battery catalysts, in particular to iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material and its preparation method and application. BACKGROUND

[0002] In recent years, with the increasing demand for sustainable energy, zinc-air batteries have attracted widespread attention due to their high energy density, low cost and environmental friendliness. However, one of the key challenges in the practical application of zinc-air batteries is how to improve the catalytic efficiency of the oxygen reduction reaction. For this reason, researchers have devoted to developing catalytic materials with high activity, good stability and high conductivity to improve the overall performance of zinc-air batteries.

[0003] Nitrogen-doped carbon materials have been widely studied in the field of electrochemical catalysis in recent years due to their unique electrochemical properties and structural characteristics. Nitrogen doping can improve the catalytic activity of carbon materials by adjusting the electronic structure, while providing abundant active sites. However, existing nitrogen-doped carbon materials still have some obvious technical defects in practical application. Specifically, the nitrogen-doped carbon materials obtained by existing technical methods have the following shortcomings: first, the problem of conductivity - the impurities and structural defects introduced by some preparation methods can reduce the conductivity of nitrogen-doped carbon materials, limiting their efficiency in electrochemical reactions; second, the lack of availability of active sites - the distribution of nitrogen in nitrogen-doped carbon materials is often uneven, resulting in limited number of effective active sites; finally, the non-ideal pore structure limits the transmission rate of reactants and the progress of catalytic reactions. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the present application provides an iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material and its preparation method and application. The present application introduces a nitrogen source, a soluble iron salt, a pore-forming agent and a template agent into medium-temperature coal pitch, and then undergoes heat treatment, acid washing and carbon dioxide activation treatment to prepare an iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material. The iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material obtained by the method of the present application does not introduce impurities, has no structural defects, has uniform nitrogen doping and has an ideal pore structure, overcoming the problems of poor conductivity, limited number of active sites and low catalytic activity of existing nitrogen-doped carbon materials.

[0005] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0006] The preparation method of the iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material comprises the following steps:

[0007] The medium temperature coal tar pitch is dissolved in a solvent, and then is uniformly mixed with melamine, a soluble iron salt, a soluble zinc salt and nano silicon dioxide, to obtain a mixture with synergistic catalytic effect, in which the medium temperature coal tar pitch is used as a carbon source, the melamine is used as a nitrogen source, the nano silicon dioxide is used as a template agent, the soluble zinc salt is used as a pore-forming agent, and the soluble iron salt is used as an iron source.

[0008] The selected solvent is selected from ethanol, an ethanol aqueous solution or limonene, and in the ethanol aqueous solution, ethanol and water are mixed in any ratio.

[0009] The high-temperature coal tar pitch, the medium-temperature coal tar pitch and the low-temperature coal tar pitch are classified according to different heating temperatures in a coal tar refining process, the high-temperature coal tar pitch is obtained at a heating temperature exceeding 350 DEG C, the medium-temperature coal tar pitch is obtained at a heating temperature of 250 DEG C to 350 DEG C, and the low-temperature coal tar pitch is obtained at a heating temperature of 150 DEG C to 250 DEG C, and the viscosity and hardness of the medium-temperature coal tar pitch are between those of the high-temperature coal tar pitch and the low-temperature coal tar pitch. The medium-temperature coal tar pitch has good processability, good carbonization performance, controllable pore structure and compatibility with nitrogen sources and metal salts, and thus is selected as the best carbon source material in the present application. The low-temperature coal tar pitch or the high-temperature coal tar pitch has deficiencies in these aspects and cannot meet the requirements of the modified coal tar pitch-based hierarchical porous carbon material with iron and nitrogen co-doping in the present application.

[0010] The melamine has a high nitrogen content, a moderate decomposition temperature and can form various nitrogen chemical environments, and more importantly, the melamine can be coordinated with iron ions in the soluble iron salt, so that the melamine is uniformly dispersed, and then the modified coal tar pitch-based hierarchical porous carbon material with iron and nitrogen co-doping is obtained, in which the nitrogen is uniformly doped.

[0011] The melting and volatilization characteristics of the soluble zinc salt play an important role in pore formation, the soluble zinc salt is selected from ZnCl2 or zinc acetate, and the soluble zinc salt does not immediately melt when mixed, the melting process occurs in the heat treatment stage, and in the heat treatment process, the soluble zinc salt melts at a temperature of 290 DEG C, promotes the uniform dispersion of other components, and volatilizes at high temperature to generate gas, thereby promoting the formation of pores through diffusion and gas escape, so as to form pores in the modified coal tar pitch-based hierarchical porous carbon material with iron and nitrogen co-doping; the melting and volatilization of the zinc salt can also regulate the pore size and distribution through ion diffusion, so that the pores of the modified coal tar pitch-based hierarchical porous carbon material with iron and nitrogen co-doping are more uniform.

[0012] In the present application, the formation of pores mainly depends on the joint action of the template agent and the soluble zinc salt, the melting and pore-forming properties of the soluble zinc salt are utilized to promote the uniform dispersion of each raw material in the mixture, and the nano-silica as a hard template helps to build the micro-pore structure of the carbon material by being uniformly distributed in the mixture. After high-temperature heat treatment, the nano-silica is removed by acid washing, leaving a hierarchical porous carbon material, which significantly improves the specific surface area and porosity, and combines with the pores generated by the heat treatment of the soluble zinc salt to form a porous structure, thereby enhancing the electrochemical performance of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material.

[0013] The mixture is first heat treated under a protective atmosphere to carbonize the medium-temperature coal tar pitch to form a carbon matrix, decompose the melamine to achieve nitrogen doping, reduce the soluble iron salt to form catalytically active sites, and form an internal porous structure through the volatilization of the soluble zinc salt, thereby obtaining an iron and nitrogen doped porous carbon material.

[0014] The iron and nitrogen doped porous carbon material is subjected to acid washing with hydrofluoric acid at a volume fraction of 5% to 10% to etch the nano-silica and form mesopores, and then subjected to water washing, when the pH value of the washing liquid is 6 to 7, the acidic components in the iron and nitrogen doped porous carbon material have been completely removed, thereby obtaining an iron and nitrogen doped porous carbon material precursor.

[0015] The iron and nitrogen doped porous carbon material precursor is subjected to carbon dioxide activation treatment to react carbon dioxide with carbon to obtain micropores, and under the action of the pore-forming agent, the soluble zinc salt, the micropores and the mesopores obtained by etching the nano-silica are connected, thereby increasing the specific surface area and optimizing the pore structure, improving the electrical conductivity and catalytic activity, and obtaining an iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material.

[0016] Preferably, the mass ratio of the medium-temperature coal tar pitch, the melamine and the nano-silica is 4 to 8: 2 to 4: 0.05 to 0.2. The mass ratio of the medium-temperature coal tar pitch, the melamine and the nano-silica is obtained through optimization screening, the purpose is to ensure that the electrical conductivity, the catalytic activity and the pore structure of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material achieve the best effect. If it is not within this ratio range, it will lead to uneven pore generation, decreased electrical conductivity, insufficient catalytic active sites or unstable structure.

[0017] Preferably, the molar ratio of the soluble zinc salt to the medium-temperature coal tar pitch is 45 to 55: 1, and the molar ratio of the soluble iron salt to the medium-temperature coal tar pitch is 1: 0.35 to 0.45. Too low an amount of the soluble zinc salt will result in insufficient pores, affecting the specific surface area of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material; too high an amount of the soluble iron salt will lead to agglomeration of iron nanoparticles, reducing the catalytic performance of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material.

[0018] Preferably, the heat treatment is carried out at 800-1000 DEG C for 0.5-2 hours in an inert atmosphere.

[0019] Preferably, the carbon dioxide activation treatment is carried out by increasing the temperature to 700-900 DEG C, when the temperature reaches the maximum, a mixed gas of carbon dioxide and nitrogen is introduced, and the activation treatment is carried out for 0.5-2 hours in an inert atmosphere.

[0020] Preferably, the volume ratio of carbon dioxide to nitrogen is 0.75-2.3:1, and the volume ratio of carbon dioxide to nitrogen is calculated according to 0.6:0.8 to 0.7:0.3.

[0021] The application also protects the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material prepared by the above preparation method.

[0022] The application also protects the application of the above iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material in preparing a zinc-air battery cathode catalyst.

[0023] Compared with the prior art, the application has the beneficial effects that:

[0024] 1. The application mixes medium-temperature coal tar pitch with a nitrogen source melamine, a soluble iron salt, a pore-forming agent soluble zinc salt and a template nano-silicon dioxide, and then sequentially carries out heat treatment, acid washing and carbon dioxide activation treatment to prepare a high-performance iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material, denoted as Fe-NHPC material. First, the medium-temperature coal tar pitch is mixed with the nitrogen source, the soluble iron salt, the pore-forming agent and the template agent, and is uniformly dispersed by a solvent, and then high-temperature heat treatment is carried out in an inert atmosphere to carbonize the medium-temperature coal tar pitch and form a stable carbon matrix structure, and in this process, the nitrogen source decomposes and releases nitrogen atoms to realize nitrogen doping in the carbon matrix; at the same time, the soluble iron salt is reduced to iron oxide or metal nanoparticles at high temperature to enhance the electrocatalytic activity of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material.

[0025] In the present application, melamine is used as a nitrogen source. Melamine can not only form coordination with zinc ions of soluble zinc salt and iron ions of soluble iron salt, but also can coordinate and combine with pyrolyzed medium-temperature coal pitch, obtaining carbon-nitrogen-iron coordination structure. At this time, the template silica is uniformly distributed in the carbon-nitrogen-iron coordination structure, and the uniformly distributed soluble zinc salt forms pores in the iron-nitrogen doped porous carbon material by diffusion and gas escape during the pyrolysis process. The iron-nitrogen doped porous carbon material precursor is obtained by etching nanosilica to form mesopores using hydrofluoric acid. The iron-nitrogen doped porous carbon material precursor is subjected to carbon dioxide activation treatment. At this time, carbon dioxide reacts with carbon to obtain micropores, and the micropores and mesopores are connected under the action of the pore-forming agent, soluble zinc salt, to obtain iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material.

[0026] After removing nanosilica by acid washing, the present application forms a hierarchical porous structure, which significantly improves the specific surface area and porosity of the iron-nitrogen doped porous carbon material precursor, making the transport of reactants and products more efficient. Subsequently, the pore structure is further optimized by carbon dioxide activation treatment, increasing the active sites and conductivity of the iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material, and improving its performance in electrochemical reactions. Finally, the co-doping of iron and nitrogen significantly improves the catalytic activity of the iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material in the oxygen reduction reaction by changing the electronic structure and physical properties of the carbon material, providing an efficient cathode material for zinc-air batteries.

[0027] The present application optimizes the synergistic effect of doping elements and pore structure, so that the prepared iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material exhibits excellent electrochemical performance, overcoming the shortcomings of traditional nitrogen-doped carbon materials in terms of conductivity, active sites and catalytic activity, and is suitable for large-scale application in zinc-air battery electrochemical energy storage devices. The iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material as a cathode catalyst in zinc-air batteries exhibits excellent performance, overcoming the defects of the prior art and providing a new possibility for the development of high-performance batteries.

[0028] 2、The preparation method of the present application is not only simple and easy to operate, but also uses inexpensive raw materials, reducing production costs and providing an economical and efficient solution suitable for large-scale application. In addition, compared with the prior art nitrogen-doped carbon material, the present application also solves the problem of poor stability of the existing nitrogen-doped carbon material, ensuring the structural stability and catalytic effect of the iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material in actual use, which helps to realize large-scale application.

[0029] 3、The application provides a strategy for melting medium-temperature coal pitch by inorganic salt soluble iron salt, specifically, the soluble iron salt can be melted at high temperature, and in the molten state, the soluble iron salt can fully contact and mix with the medium-temperature coal pitch, so that the medium-temperature coal pitch is more uniformly distributed in the carbonization process. The molten soluble zinc salt can not only help the raw materials to be well dispersed under high temperature conditions, but also generate gas through its volatility in the subsequent heat treatment process, and then form a pore structure, so that the formed pore structure realizes the penetration of mesopores and micropores, and therefore the melting process of ZnCl2 helps to regulate the pore structure of the carbon material, increase the specific surface area, and finally enhance the electrochemical performance of the iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material. In addition, in combination with melamine as a nitrogen source, a method for preparing a nitrogen-doped hierarchical porous carbon material with high nitrogen content is provided, by optimizing the combination of carbon source, nitrogen source and metal salt, and under suitable heat treatment conditions, an iron-nitrogen co-doped modified coal pitch-based hierarchical porous carbon material with high conductivity, rich active sites and ideal pore structure is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Raman spectrum of the Fe-NHPC material of the embodiment 1 of the application.

[0031] Figure 2 X-ray photoelectron spectrogram of the Fe-NHPC material of the embodiment 1 of the application.

[0032] Figure 3 N1s spectrogram of the Fe-NHPC material of the embodiment 1 of the application.

[0033] Figure 4 X-ray diffraction pattern of the Fe-NHPC material of the embodiment 1 of the application.

[0034] Figure 5 Cyclic voltammetry test diagram of the Fe-NHPC material of the embodiment 1 of the application.

[0035] Figure 6 Linear sweep voltammetry test diagram of the Fe-NHPC material of the embodiment 1 of the application.

[0036] Figure 7 Open-circuit voltage, discharge voltage and energy density diagram of the Fe-NHPC material of the embodiment 1 of the application as a cathode for assembling a zinc-air battery.

[0037] Figure 8 Current density-voltage-power density curve diagram of the zinc-air battery assembled by using the Fe-NHPC material of the embodiment 1 of the application as a cathode.

[0038] Figure 9The constant current discharge curve of the zinc-air battery assembled by using the Fe-NHPC material of embodiment 1 of the present application as the cathode is shown in the figure. DETAILED DESCRIPTION

[0039] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application. The experimental methods described in the embodiments of the present application are conventional methods unless otherwise specified.

[0040] In view of the technical defects of poor electrical conductivity, insufficient availability of active sites and unsatisfactory pore structure of the nitrogen-doped carbon material in the prior art, the present application designs the structure of the nitrogen-doped carbon material, specifically: the present application effectively overcomes the problems of introduction of impurities, structural defects and uneven nitrogen doping in the prior art by optimizing the selection of raw materials and the preparation process. By using pure raw materials and reasonable heat treatment process, the introduction of impurities is avoided; the use of zinc salt and silica template ensures the uniformity and stability of the pore structure, and reduces the structural defects; melamine as a nitrogen source coordinates with iron salt, which can realize uniform doping of nitrogen during carbonization, thereby improving the electrocatalytic performance of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material. Therefore, the present application realizes high structural integrity and uniformity of doping in the preparation of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material, provides abundant active sites, and has excellent electrical conductivity.

[0041] The medium temperature coal tar of the present application is purchased from Hebei Luma Energy Technology Co., Ltd., and the technical solutions of the present application are studied by using the following examples, and the specific research methods and results are shown as follows:

[0042] Example 1

[0043] The preparation method of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material comprises the following steps:

[0044] S1, 6g of medium temperature coal tar is dissolved in 15mL of ethanol, then 3g of melamine, 0.6mol of ZnCl2, 5.0mmol of FeCl3 and 0.1g of nano-silicon dioxide are added, mixed and stirred for 30min to obtain a mixture. The average molecular weight of the medium temperature coal tar is between 200g / mol and 1000g / mol, which depends on the type of coal and processing conditions, and a reasonable estimate is selected as the basis for calculation, and 500g / mol is used as the basis for calculation in the present application, and the amount of substance of 6g of medium temperature coal tar is 0.012mol.

[0045] S2, the mixture is dried to constant weight, 1.5 g is taken and placed in a large boat, nitrogen is introduced, heated at 900℃ for 1h, the heating rate is 5℃ / min, the cooling rate is 20℃ / min, and an iron and nitrogen doped porous carbon material is obtained.

[0046] S3, the iron and nitrogen doped porous carbon material is pickled in hydrofluoric acid with a volume fraction of 5%, the nano-silicon dioxide is etched to form mesopores, then deionized water is used to wash to neutral, and then dried at 80℃ to obtain an iron and nitrogen doped porous carbon material precursor.

[0047] S4, the iron and nitrogen doped porous carbon material precursor is placed in a large boat, nitrogen is introduced, heated to 800℃ at a heating rate of 5℃ / min, when the temperature reaches 800℃, a mixed gas is introduced, the mixed gas is composed of carbon dioxide and nitrogen with a volume ratio of 0.6:0.8, and the activation treatment is carried out for 1h, after activation, stop introducing carbon dioxide, and cool to room temperature at a cooling rate of 20℃ / min, to obtain an iron and nitrogen co-doped modified coal pitch-based hierarchical porous carbon material, denoted as Fe-NHPC material.

[0048] Example 2

[0049] A method for preparing an iron and nitrogen co-doped modified coal pitch-based hierarchical porous carbon material, comprising the following steps:

[0050] S1, 4g of medium temperature coal pitch is dissolved in 15mL of ethanol, then 2g of melamine, 0.36mol of ZnCl2, 3.6mmol of FeCl3 and 0.05g of nano-silicon dioxide are added, mixed and stirred for 30min to obtain a mixture.

[0051] S2, the mixture is dried to constant weight, 1.5 g is taken and placed in a large boat, nitrogen is introduced, heated at 800℃ for 2h, the heating rate is 5℃ / min, the cooling rate is 20℃ / min, and an iron and nitrogen doped porous carbon material is obtained.

[0052] S3, the iron and nitrogen doped porous carbon material is pickled in hydrofluoric acid with a volume fraction of 8%, the nano-silicon dioxide is etched to form mesopores, then deionized water is used to wash to neutral, and then dried at 80℃ to obtain an iron and nitrogen doped porous carbon material precursor.

[0053] S4, the iron and nitrogen doped porous carbon material precursor is placed in a large boat, nitrogen is introduced, heated to 900℃ at a heating rate of 5℃ / min, when the temperature reaches 900℃, a mixed gas is introduced, the mixed gas is composed of carbon dioxide and nitrogen with a volume ratio of 0.7:0.3, and the activation treatment is carried out for 0.5h, after activation, stop introducing carbon dioxide, and cool to room temperature at a cooling rate of 20℃ / min, to obtain an iron and nitrogen co-doped modified coal pitch-based hierarchical porous carbon material.

[0054] Example 3

[0055] A preparation method of the modified coal-tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen comprises the following steps:

[0056] S1, 8g of medium-temperature coal-tar pitch was dissolved in 15mL of ethanol, then 4g of melamine, 0.88mol of ZnCl2, 5.6mmol of FeCl3 and 0.2g of nano-silicon dioxide were added thereto, mixed and stirred for 30min to obtain a mixture.

[0057] S2, the mixture was dried to constant weight, 1.5g of which was taken into a large boat, nitrogen was introduced, heated at 1000℃ for 0.5h, the heating rate was 5℃ / min, and the cooling rate was 20℃ / min, to obtain the iron and nitrogen doped porous carbon material.

[0058] S3, the iron and nitrogen doped porous carbon material was pickled in 10% hydrogen fluoride acid by volume fraction to etch off the nano-silicon dioxide, form mesopores, then washed with deionized water to neutral, and dried at 80℃ to obtain the iron and nitrogen doped porous carbon material precursor.

[0059] S4, the iron and nitrogen doped porous carbon material precursor was placed in a large boat, nitrogen was introduced, heated to 700℃ at a heating rate of 5℃ / min, when the temperature reached 700℃, a mixed gas was introduced, the mixed gas was composed of carbon dioxide and nitrogen with a volume ratio of 0.7:0.3, and the activation treatment was carried out for 2h, after activation, the introduction of carbon dioxide was stopped, and the temperature was lowered to room temperature at a cooling rate of 20℃ / min, to obtain the modified coal-tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen.

[0060] In order to evaluate the structure and morphology of the prepared Fe-NHPC material, the following characterization was carried out:

[0061] (1) Raman spectrum analysis: the Fe-NHPC material obtained in Example 1 was subjected to Raman spectrum analysis using a Renishaw InVia Raman spectrometer. As shown in Figure 1 , the D band and the G band were observed, the D band was about 1350cm -1 , the G band was about 1580cm -1 , and the I D / I G ratio indicated that the Fe-NHPC material had a high defect density, which was beneficial to the formation of catalytic active sites.

[0062] (2) X-ray photoelectron spectroscopy analysis: XPS analysis was carried out using a Thermo Fisher Scientific ESCALAB 250Xi XPS instrument, and the results showed that the surface of the Fe-NHPC material of Example 1 contained C1s, N 1s and O1s elements.Figure 2 The most obvious is the C1s peak, indicating that carbon is the main component of the Fe-NHPC material. In addition, N 1s and O1s signals are clearly visible, indicating that nitrogen and oxygen are successfully doped in the Fe-NHPC material. It is worth noting that the presence of nitrogen element is of great significance to enhance the electrocatalytic activity, which provides a good foundation for the application of Fe-NHPC material in oxygen reduction reaction.

[0063] As Figure 3 shown, the N1s spectrum of the Fe-NHPC material of Example 1 shows different types of nitrogen chemical environment, including pyridine nitrogen N-Q, pyrrole nitrogen N-5 and graphite nitrogen N-6 peaks. The presence of these nitrogen species confirms the successful doping of nitrogen element, and in different chemical states, nitrogen element can enhance the catalytic performance of carbon material by changing its electronic structure. Pyridine nitrogen and pyrrole nitrogen are particularly helpful to enhance the electrocatalytic activity of Fe-NHPC material, because they can provide effective reaction sites and promote the adsorption and reduction of oxygen molecules. The introduction of graphite nitrogen improves the conductivity of Fe-NHPC material, which is conducive to the rapid transfer of electrons. This diversified nitrogen doping structure provides important support for the high-efficiency catalytic performance of Fe-NHPC material.

[0064] (3) X-ray diffraction analysis: In the XRD analysis using Bruker D8 Advance X-ray diffractometer, as Figure 4 shown, the Fe-NHPC material of Example 1 shows obvious amorphous carbon characteristics, i.e. there are broad diffuse peaks near about 25° and 43°, indicating the presence of disordered carbon structure in the Fe-NHPC material. In addition, several weaker diffraction peaks can be observed between 20° and 30°, which may correspond to the crystalline phases of iron carbide and iron oxide, showing that part of the iron salt is converted into iron compounds during the heat treatment process. The presence of these iron-based compounds in the Fe-NHPC material not only improves the conductivity, but also provides additional catalytic active sites for the oxygen reduction reaction. The obvious iron carbide and iron oxide peaks in the Fe-NHPC material indicate that it has significant advantages in structure and function.

[0065] Through Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction analysis, the Fe-NHPC material exhibits excellent structural characteristics and realizes effective nitrogen doping. The structural characteristics provide strong support for its excellent electrocatalytic performance in zinc-air batteries, further proving the wide application prospect of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material prepared by the present application in high-performance zinc-air batteries.

[0066] To evaluate the electrocatalytic performance of the prepared Fe-NHPC material in zinc-air batteries, the following tests were conducted:

[0067] (1) Electrode preparation: The Fe-NHPC material prepared in Example 1 was mixed with conductive carbon black and polytetrafluoroethylene at a mass ratio of 85:10:5, and ethanol was added to stir into a uniform slurry. The slurry was uniformly coated on a foamed nickel electrode, dried, and then pressed into an electrode sheet as the working electrode.

[0068] (2) Electrochemical testing: The test was performed on a CHI760E electrochemical workstation using a three-electrode system. The electrolyte used in the test was a 0.1 mol / L KOH solution. The Ag / AgCl electrode was used as the reference electrode, and the platinum electrode was used as the counter electrode to form a three-electrode system with the working electrode.

[0069] (3) Cyclic voltammetry test: In the cyclic voltammetry test, the potential range was from 0.2 V vs. RHE to 1.0 V vs. RHE, and the scan rate was 10 mV / s. The oxygen reduction reaction activity of the Fe-NHPC material was evaluated. The evaluation method of the oxygen reduction reaction activity was as follows: first, nitrogen was introduced into the three-electrode system to remove the oxygen in the electrolyte; then, the three-electrode system was used for testing; subsequently, oxygen was introduced to saturation, and the three-electrode system was used for testing; by comparing the results of the two tests, the electrocatalytic performance of the Fe-NHPC material was obtained. From Figure 5 it can be observed that there is a significant difference in the cyclic voltammetry curves under nitrogen and oxygen environments. Compared with the nitrogen environment, the current density in the oxygen environment increases significantly, which indicates that the Fe-NHPC material has high electrocatalytic activity in the oxygen environment and can effectively catalyze the oxygen reduction reaction. This activity shows the excellent performance of the Fe-NHPC material in actual electrochemical applications, especially in zinc-air battery energy conversion devices.

[0070] (4) Linear sweep voltammetry test: Linear sweep voltammetry test was performed on a rotating disk electrode. The potential range was from 0.0 V vs. RHE to 1.2 V vs. RHE, and the scan rate was 10 mV / s with a rotation speed of 1600 rpm. The oxygen reduction reaction performance was evaluated. Figure 6 In the oxygen environment, the Fe-NHPC material exhibits a significant change in current density, especially a significant current rise near 0.8 V, which indicates that the Fe-NHPC material has high catalytic activity in this potential range. The Fe-NHPC material exhibits a high initial potential and half-wave potential, which indicates that it has excellent electrocatalytic activity in the oxygen reduction reaction and is suitable for zinc-air battery electrochemical devices. By optimizing the structure and doping process of the Fe-NHPC material, the Fe-NHPC material exhibits excellent performance in electrocatalytic performance and stability, which can meet the demand for high-efficiency catalysts in zinc-air batteries.

[0071] (5) Zinc-air battery assembly and testing: Zinc-air batteries were assembled using a two-electrode system, with zinc metal serving as the zinc anode, responsible for providing electrons and undergoing oxidation reactions to generate zinc ions. The air cathode used a conductive carbon material containing Fe-NHPC material, which was prepared according to the following steps: Fe-NHPC material, conductive agent carbon black, binder polyvinylidene fluoride, and solvent N-methyl pyrrolidone were mixed uniformly to obtain a slurry, with a mass ratio of Fe-NHPC material, conductive agent carbon black, and binder polyvinylidene fluoride of 8:1:1. The slurry was uniformly coated on carbon cloth using a spin coating method to ensure uniform distribution of the slurry on the surface of the carbon cloth. The coated carbon cloth was then compacted and dried to increase its density and mechanical strength, and then cut to size. The resulting material was responsible for absorbing oxygen from the air and undergoing oxygen reduction reactions. Zinc-air batteries were assembled using zinc anodes, air cathodes, polytetrafluoroethylene separators, and 0.1 mol / L KOH solution for testing.

[0072] The zinc anode and air cathode work together to complete the electrochemical reaction process through the flow of electrons, achieving electrical energy output. The Fe-NHPC material as a cathode catalyst significantly improves the catalytic performance of the oxygen reduction reaction, enabling the system to have high energy density and good electrochemical stability. In the assembly and testing of zinc-air batteries, Fe-NHPC material was used as a cathode catalyst, and zinc sheets were used as anodes for electrochemical testing. The tests focused on the cycle stability, open-circuit voltage, discharge voltage, and energy density of the zinc-air battery.

[0073] Figure 7 The results showed that the zinc-air battery using Fe-NHPC material as the cathode exhibited stable discharge voltage during a cycle test lasting up to 160 h, with a voltage of 1.2 V to 2.6 V, demonstrating excellent cycle stability. In addition, the zinc-air battery exhibited high open-circuit voltage and excellent discharge platform, indicating that the Fe-NHPC material could effectively improve the performance and stability of the zinc-air battery. The Fe-NHPC material exhibited high energy density and excellent voltage retention capability, demonstrating its good potential as a high-efficiency zinc-air battery cathode material. Its excellent electrochemical performance is attributed to the structural optimization of the Fe-NHPC material and the synergistic effect of iron and nitrogen co-doping, making it have a significant advantage in the application of zinc-air batteries.

[0074] In the performance testing of zinc-air batteries, the current density-voltage and power density curves of the Fe-NHPC material as a cathode catalyst showed that it had excellent electrochemical performance. Figure 8 As can be seen, as the current density increased, the voltage of the zinc-air battery gradually decreased, showing typical discharge characteristics of a zinc-air battery. At a current density of about 300 mA / cm 2At this time, the zinc-air battery still maintains a high voltage, indicating that the Fe-NHPC material has good electrochemical stability. In addition, the peak of the power density curve appears around 100 mW / cm 2 This indicates that the Fe-NHPC material can still output significant power at higher current densities. This shows that the Fe-NHPC material can provide efficient electrocatalytic activity and stable electrical energy output for zinc-air batteries, suitable for high-power demand application scenarios.

[0075] In the constant current discharge test, the Fe-NHPC material maintains stable voltage output for a long time, further verifying its excellent electrochemical performance, as shown in Figure 9 The figure shows that the zinc-air battery voltage remains around 1.4 V for 80 min of test time, with almost no significant decay, indicating that the Fe-NHPC material has good stability and durability during long-term discharge. This performance stability is very important for the practical application of zinc-air batteries, meaning that the Fe-NHPC material can maintain efficient energy conversion and provide sustained and stable power output under actual operating conditions. This excellent performance feature makes the Fe-NHPC material have broad prospects and potential for application in zinc-air batteries.

[0076] The electrocatalytic performance test shows that the Fe-NHPC material has significant application potential as a zinc-air battery catalyst. This further proves that the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material prepared by the present application has broad application prospects in high-performance zinc-air batteries.

[0077] Obviously, those skilled in the art can make various modifications and changes to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and changes of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and changes. The above-described embodiments are only preferred embodiments of the present application, and the scope of protection is not limited thereto.

Claims

1. A method for preparing iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon materials, characterized in that, Includes the following steps: After dissolving medium-temperature coal tar pitch in a solvent, it is mixed evenly with melamine, soluble iron salt, soluble zinc salt and nano silica. The medium-temperature coal tar pitch is used as the carbon source, melamine as the nitrogen source, soluble zinc salt as the pore-forming agent and nano silica as the template agent to obtain a mixture. The mixture is first heat-treated under a protective atmosphere to carbonize the medium-temperature coal tar pitch to form a carbon matrix, decompose melamine to achieve nitrogen doping, reduce soluble iron salt to generate catalytic active sites, and form an internal porous structure through the volatilization and diffusion of soluble zinc salt, thus obtaining an iron-nitrogen doped porous carbon material. The iron-nitrogen-doped porous carbon material was acid-washed with hydrofluoric acid to etch away the template agent nano-silica, forming mesopores, and thus obtaining the iron-nitrogen-doped porous carbon material precursor. The precursor of iron-nitrogen-doped porous carbon material was activated by carbon dioxide. The carbon dioxide reacted with carbon to generate micropores. Under the action of the porous structure, the micropores and mesopores were connected to obtain iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material. The molar ratio of soluble iron salt to medium-temperature coal tar pitch is 1:0.35~0.

45.

2. The method for preparing iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 1, characterized in that, The mass ratio of medium-temperature coal tar pitch, melamine, and nano-silica is 4~8:2~4:0.05~0.

2.

3. The method for preparing iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 1, characterized in that, The molar ratio of soluble zinc salt to medium-temperature coal tar pitch is 45~55:

1.

4. The method for preparing the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 1, characterized in that, The heat treatment conditions are: under an inert atmosphere, at 800℃~1000℃ for 0.5h~2h.

5. The method for preparing iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 1, characterized in that, The conditions for carbon dioxide activation treatment are as follows: under an inert atmosphere, the temperature is raised to 700℃~900℃. When the temperature reaches its maximum value, a mixture of carbon dioxide and nitrogen is introduced, and the activation treatment is carried out for 0.5h~2h.

6. The method for preparing the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 5, characterized in that, The volume ratio of carbon dioxide to nitrogen is 0.75 to 2.3:

1.

7. The method for preparing iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 1, characterized in that, After the mesopores are formed, the material is washed with deionized water until the pH of the washing solution is neutral, thus obtaining the iron-nitrogen-doped porous carbon material precursor.

8. A modified coal tar pitch-based hierarchical porous carbon material with iron and nitrogen co-doped structure, prepared by the method according to any one of claims 1 to 7.

9. The application of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material as described in claim 8 in the preparation of a zinc-air battery cathode.

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