Iron-nitrogen co-doped modified coal pitch-based graded porous carbon material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of zinc air battery catalysts, in particular to an iron-nitrogen co-doped modified coal pitch-based graded porous carbon material as well as a preparation method and application thereof. A nitrogen source, soluble iron salt, a pore-foaming agent and a template agent are introduced into medium-temperature coal pitch, and heat treatment, acid pickling and carbon dioxide activation treatment are sequentially performed to prepare the iron-nitrogen co-doped modified coal pitch-based graded porous carbon material. According to the iron-nitrogen co-doped modified coal pitch-based graded porous carbon material obtained by adopting the method, impurities are not introduced, structural defects do not exist, nitrogen is uniformly doped, an ideal pore structure is achieved, and the problems that a nitrogen-doped carbon material in the prior art is poor in conductivity, limited in number of active sites and low in catalytic activity are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of zinc-air battery catalysts, and particularly relates to an iron and nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the continuous growth of the demand for sustainable energy, zinc-air batteries have received extensive attention due to their high energy density, low cost, and environmental friendliness. However, a key challenge faced by zinc-air batteries in practical applications is how to improve the catalytic efficiency of their oxygen reduction reaction. For this purpose, researchers are committed to developing catalytic materials with high activity, good stability, and high conductivity to improve the overall performance of zinc-air batteries.

[0003] Due to their unique electrochemical properties and structural characteristics, nitrogen-doped carbon materials have been widely studied in the field of electrochemical catalysis in recent years. Nitrogen doping can improve the catalytic activity of carbon materials by regulating the electronic structure and provide abundant active sites. However, there are still some obvious technical defects in existing nitrogen-doped carbon materials in practical applications. Specifically, the nitrogen-doped carbon materials obtained by existing technical methods have the following deficiencies: First, the conductivity problem - impurities and structural defects introduced by some preparation methods will reduce the conductivity of nitrogen-doped carbon materials, limiting their efficiency in electrochemical reactions; Second, the availability of active sites is insufficient - the distribution of nitrogen in nitrogen-doped carbon materials is often uneven, resulting in a limited number of effective active sites; Finally, the unsatisfactory pore structure restricts the transport rate of reactants and the progress of catalytic reactions. Summary of the Invention

[0004] In view of the above deficiencies in the prior art, the present invention provides an iron and nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material, a preparation method thereof, and an application thereof. The present invention prepares an iron and nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material by introducing a nitrogen source, a soluble iron salt, a pore-forming agent, and a templating agent into medium-temperature coal-tar pitch, and successively performing heat treatment, pickling, and carbon dioxide activation treatment. The iron and nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material obtained by the method of the present invention 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 existing in the nitrogen-doped carbon materials of the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of an iron and nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material, comprising the following steps:

[0007] 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. Using medium-temperature coal tar pitch as the carbon source, melamine as the nitrogen source, nano-silica as the templating agent, soluble zinc salt as the pore-forming agent, and soluble iron salt as the iron source, a mixture with a synergistic catalytic effect is obtained. In the synergistic catalytic effect, through the screening of raw materials, a carbon material with iron-nitrogen co-doping and a hierarchical porous structure is obtained, which has a higher catalytic performance than the individual effects.

[0008] Among them, the selected solvent is selected from ethanol, aqueous ethanol solution, or limonene. In the aqueous ethanol solution, ethanol and water are mixed in any proportion.

[0009] Among them, high-temperature coal tar pitch, medium-temperature coal tar pitch, and low-temperature coal tar pitch are classified according to different heating temperatures in the coal tar refining process. High-temperature coal tar pitch is obtained when the heating temperature exceeds 350 °C, medium-temperature coal tar pitch is obtained when the heating temperature is 250 °C to 350 °C, and low-temperature coal tar pitch is obtained when the heating temperature is 150 °C to 250 °C. The viscosity and hardness of medium-temperature coal tar pitch are between those of high-temperature coal tar pitch and low-temperature coal tar pitch. Medium-temperature coal tar pitch has good processability, good carbonization performance, controllability of pore structure, and compatibility with nitrogen source and metal salts. Therefore, it is selected as the best carbon source material in the present invention; low-temperature coal tar pitch or high-temperature coal tar pitch has deficiencies in these aspects and cannot meet the requirements of the present invention for the performance of iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon materials.

[0010] Melamine has a high nitrogen content, a moderate decomposition temperature, and can form a variety of nitrogen chemical environments. More importantly, melamine can coordinate with iron ions in the soluble iron salt, making melamine evenly dispersed, and then making nitrogen evenly doped in the obtained iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material.

[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. When mixed, the soluble zinc salt does not melt immediately, and the melting process occurs in the heat treatment stage. During the heat treatment process, the soluble zinc salt melts at a temperature reaching the melting point of 290 °C, promoting the uniform dispersion of other components, and volatilizes at high temperature to generate gas, promoting the formation of pores through diffusion and gas escape, thereby forming pores inside the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material; the melting and volatilization of the zinc salt can also regulate the pore size and distribution through ion diffusion, making the pores of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material more uniform.

[0012] In the present invention, the formation of pores mainly depends on the combined action of a templating agent and a soluble zinc salt. By utilizing the melting and pore-forming characteristics of the soluble zinc salt, the uniform dispersion of each raw material in the mixture is promoted. Nano-silica serves as a hard template and helps to construct the microscopic pore structure of the carbon material by being uniformly distributed in the mixture. After high-temperature heat treatment, the nano-silica is removed by pickling, leaving a hierarchically porous carbon material, which significantly increases 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 hierarchically 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 melamine to achieve nitrogen doping, reduce the soluble iron salt to form catalytic active sites, and form an internal porous structure through the volatilization of the soluble zinc salt, obtaining an iron and nitrogen-doped porous carbon material.

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

[0015] The precursor of the iron and nitrogen-doped porous carbon material 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 forms pores, enabling the micropores and the mesopores obtained by etching the nano-silica to communicate. By increasing the specific surface area and optimizing the pore structure, the conductivity and catalytic activity are improved, obtaining an iron and nitrogen co-doped modified coal-tar pitch-based hierarchically porous carbon material.

[0016] Preferably, the mass ratio of the medium-temperature coal-tar pitch, melamine, and nano-silica is 4 to 8: 2 to 4: 0.05 to 0.2. The mass ratio of the medium-temperature coal-tar pitch, melamine, and nano-silica is obtained through optimization and screening, aiming to ensure that the conductivity, catalytic activity, and pore structure of the iron and nitrogen co-doped modified coal-tar pitch-based hierarchically porous carbon material reach the best effects. If it is not within this ratio range, it will lead to uneven pore generation, decreased 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 hierarchically porous carbon material; too high an amount of the soluble iron salt will cause agglomeration of iron nanoparticles, reducing the catalytic performance of the iron and nitrogen co-doped modified coal-tar pitch-based hierarchically porous carbon material.

[0018] Preferably, the heat treatment conditions are as follows: under an inert atmosphere, treat at 800 °C to 1000 °C for 0.5 h to 2 h.

[0019] Preferably, the carbon dioxide activation treatment conditions are as follows: under an inert atmosphere, raise the temperature to 700 °C to 900 °C. When the temperature reaches the maximum value, introduce a mixed gas of carbon dioxide and nitrogen, and carry out the activation treatment for 0.5 h to 2 h.

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

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

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

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. In the present invention, medium-temperature coal tar pitch is mixed with nitrogen source melamine, soluble iron salt, pore-forming agent soluble zinc salt, and template agent nano-silica, and then successively subjected to heat treatment, pickling, and carbon dioxide activation treatment to prepare a high-performance iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material, denoted as Fe-NHPC material. First, medium-temperature coal tar pitch is used as the carbon source, uniformly mixed with the nitrogen source, soluble iron salt, pore-forming agent, and template agent, and evenly dispersed through a solvent. Then, high-temperature heat treatment is carried out under an inert atmosphere to promote the carbonization of medium-temperature coal tar pitch and form a stable carbon matrix structure. During this process, the nitrogen source decomposes to release nitrogen atoms, realizing 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, enhancing the electrocatalytic activity of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material.

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

[0026] After removing the nano-silica by pickling in the present invention, a hierarchical porous structure is formed, which significantly improves the specific surface area and porosity of the precursor of the iron-nitrogen-doped porous carbon material, making the transport of reactants and products more efficient; subsequently, the pore structure is further optimized by carbon dioxide activation treatment to increase the active sites and conductivity of the modified coal tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen, and improve its performance in electrochemical reactions. Finally, co-doping with iron and nitrogen is adopted to significantly improve the catalytic activity of the modified coal tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen 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] By optimizing the synergistic effect of the doping elements and the pore structure in the present invention, the prepared modified coal tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen exhibits excellent electrochemical performance, overcomes the deficiencies 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 modified coal tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen exhibits excellent performance as a cathode catalyst in zinc-air batteries, overcomes the defects of the prior art, and provides new possibilities for the development of high-performance batteries.

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

[0029] 3. The present invention proposes a strategy for melting medium-temperature coal tar pitch with inorganic soluble iron salts. Specifically, the soluble iron salts will melt at high temperatures. In the molten state, the soluble iron salts can come into full contact and mixing with the medium-temperature coal tar pitch, promoting a more uniform distribution of the medium-temperature coal tar pitch during the carbonization process. The molten soluble zinc salts can not only help the raw materials achieve good dispersion under high-temperature conditions but also generate gases through their volatility during the subsequent heat treatment process, thereby forming a pore structure. The formed pore structure enables the penetration of mesopores and micropores. Therefore, the melting process of ZnCl2 helps to regulate the pore structure of the carbon material, increase the specific surface area, and ultimately enhance the electrochemical performance of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material. Additionally, a method for preparing a nitrogen-doped hierarchical porous carbon material with a high nitrogen content by combining melamine as a nitrogen source is proposed. By optimizing the combination of the carbon source, nitrogen source, and metal salt and under suitable heat treatment conditions, an iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material with high conductivity, abundant active sites, and an ideal pore structure is prepared. Description of the Drawings

[0030] Figure 1 It is the Raman spectrum of the Fe-NHPC material of Example 1 of the present invention.

[0031] Figure 2 It is the X-ray photoelectron spectrum of the Fe-NHPC material of Example 1 of the present invention.

[0032] Figure 3 It is the N1s spectrum of the Fe-NHPC material of Example 1 of the present invention.

[0033] Figure 4 It is the X-ray diffraction pattern of the Fe-NHPC material of Example 1 of the present invention.

[0034] Figure 5 It is the cyclic voltammetry test chart of the Fe-NHPC material of Example 1 of the present invention.

[0035] Figure 6 It is the linear sweep voltammetry test chart of the Fe-NHPC material of Example 1 of the present invention.

[0036] Figure 7 It is the open-circuit voltage, discharge voltage, and energy density chart of the zinc-air battery assembled with the Fe-NHPC material of Example 1 of the present invention as the cathode.

[0037] Figure 8 It is the current density-voltage-power density curve chart of the zinc-air battery assembled with the Fe-NHPC material of Example 1 of the present invention as the cathode.

[0038] Figure 9It is the constant current discharge curve of a zinc-air battery assembled with the Fe-NHPC material of Embodiment 1 of the present invention as the cathode. Detailed Description of the Invention

[0039] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the protection scope of the present invention is not limited by the specific embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0040] Considering the technical defects of poor conductivity, insufficient availability of active sites, and unsatisfactory pore structure in the existing nitrogen-doped carbon materials, the present invention has carried out the structural design of nitrogen-doped carbon materials, specifically: by optimizing the raw material selection and preparation process, the present invention effectively overcomes the problems of introducing impurities, structural defects, and uneven nitrogen doping in the prior art. By using pure raw materials and reasonable heat treatment processes, the introduction of impurities is avoided; the use of zinc salts and silica templating agents ensures the uniformity and stability of the pore structure and reduces structural defects; melamine as a nitrogen source coordinates with iron salts, enabling uniform doping of nitrogen during the carbonization process, thereby improving the electrocatalytic performance of the iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material. Therefore, the present invention achieves high structural integrity and doping uniformity in the preparation of iron-nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon materials, provides abundant active sites, and has excellent electrical conductivity.

[0041] The medium-temperature coal tar pitch of the present invention is purchased from Hebei Lumao Energy Technology Co., Ltd. The following uses examples to study the technical solutions of the present invention. The specific research methods and results are as follows:

[0042] Example 1

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

[0044] S1. Dissolve 6 g of medium-temperature coal tar pitch in 15 mL of ethanol, then add 3 g of melamine, 0.6 mol of ZnCl2, 5.0 mmol of FeCl3, and 0.1 g of nano-silica thereto, and mix and stir for 30 min to obtain a mixture. The average molecular weight of the medium-temperature coal tar pitch is between 200 g / mol and 1000 g / mol, specifically depending on the type of coal and processing conditions. A reasonable estimated value is selected as the calculation basis. In the present invention, 500 g / mol is used as the calculation basis, and the amount of substance of 6 g of medium-temperature coal tar pitch is 0.012 mol.

[0045] S2. Dry the mixture to a constant weight, take 1.5 g and place it in a large ark. Introduce nitrogen, heat it at 900 °C for 1 h, with a heating rate of 5 °C / min and a cooling rate of 20 °C / min to obtain an iron and nitrogen co-doped porous carbon material.

[0046] S3. Pickle the iron and nitrogen co-doped porous carbon material in hydrofluoric acid with a volume fraction of 5% to etch away the nano-silica and form mesopores. Then wash it with deionized water until neutral, and then dry it at 80 °C to obtain a precursor of the iron and nitrogen co-doped porous carbon material.

[0047] S4. Place the precursor of the iron and nitrogen co-doped porous carbon material in a large ark. Introduce nitrogen and heat it at a heating rate of 5 °C / min to 800 °C. When the temperature reaches 800 °C, introduce a mixed gas composed of carbon dioxide and nitrogen with a volume ratio of 0.6:0.8 for 1 h of activation treatment. After activation, stop introducing carbon dioxide and cool it to room temperature at a cooling rate of 20 °C / min to obtain a modified coal tar pitch-based hierarchically porous carbon material co-doped with iron and nitrogen, denoted as Fe-NHPC material.

[0048] Example 2

[0049] A preparation method of a modified coal tar pitch-based hierarchically porous carbon material co-doped with iron and nitrogen, comprising the following steps:

[0050] S1. Dissolve 4 g of medium-temperature coal tar pitch in 15 mL of ethanol, then add 2 g of melamine, 0.36 mol of ZnCl2, 3.6 mmol of FeCl3 and 0.05 g of nano-silica thereto, and mix and stir for 30 min to obtain a mixture.

[0051] S2. Dry the mixture to a constant weight, take 1.5 g and place it in a large ark. Introduce nitrogen, heat it at 800 °C for 2 h, with a heating rate of 5 °C / min and a cooling rate of 20 °C / min to obtain an iron and nitrogen co-doped porous carbon material.

[0052] S3. Pickle the iron and nitrogen co-doped porous carbon material in hydrofluoric acid with a volume fraction of 8% to etch away the nano-silica and form mesopores. Then wash it with deionized water until neutral, and then dry it at 80 °C to obtain a precursor of the iron and nitrogen co-doped porous carbon material.

[0053] S4. Place the precursor of the iron and nitrogen co-doped porous carbon material in a large ark. Introduce nitrogen and heat it at a heating rate of 5 °C / min to 900 °C. When the temperature reaches 900 °C, introduce a mixed gas composed of carbon dioxide and nitrogen with a volume ratio of 0.7:0.3 for 0.5 h of activation treatment. After activation, stop introducing carbon dioxide and cool it to room temperature at a cooling rate of 20 °C / min to obtain a modified coal tar pitch-based hierarchically porous carbon material co-doped with iron and nitrogen.

[0054] Example 3

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

[0056] S1. Dissolve 8 g of medium-temperature coal-tar pitch in 15 mL of ethanol, then add 4 g of melamine, 0.88 mol of ZnCl2, 5.6 mmol of FeCl3 and 0.2 g of nano-silica thereto, and mix and stir for 30 min to obtain a mixture.

[0057] S2. Dry the mixture to constant weight, take 1.5 g and place it in a large square boat, introduce nitrogen, heat it at 1000 °C for 0.5 h, with a heating rate of 5 °C / min and a cooling rate of 20 °C / min, to obtain an iron-nitrogen doped porous carbon material.

[0058] S3. Pickle the iron-nitrogen doped porous carbon material in hydrofluoric acid with a volume fraction of 10%, etch away the nano-silica to form mesopores, then wash it with deionized water until neutral, and then dry it at 80 °C to obtain a precursor of the iron-nitrogen doped porous carbon material.

[0059] S4. Place the precursor of the iron-nitrogen doped porous carbon material in a large square boat, introduce nitrogen, heat it to 700 °C at a heating rate of 5 °C / min. When the temperature reaches 700 °C, introduce a mixed gas, which is composed of carbon dioxide and nitrogen with a volume ratio of 0.7:0.3, and carry out an activation treatment for 2 h. After activation, stop introducing carbon dioxide, and cool it to room temperature at a cooling rate of 20 °C / min to obtain an iron-nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material.

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

[0061] (1) Raman spectroscopy analysis: Use a Renishaw InVia Raman spectrometer to perform Raman spectroscopy analysis on the Fe-NHPC material obtained in Example 1. As Figure 1 shown, both the D band and the G band were observed. The D band is about 1350 cm -1 , and the G band is about 1580 cm -1 , and the I D / I G ratio indicates that the Fe-NHPC material has a high defect density, which is beneficial to the formation of catalytic active sites.

[0062] (2) X-ray photoelectron spectroscopy analysis: Use a Thermo Fisher Scientific ESCALAB 250Xi XPS instrument to perform XPS analysis. The results show that the surface of the Fe-NHPC material in Example 1 contains C1s, N 1s and O1s elements.Figure 2 The most obvious one is the C1s peak, indicating that carbon is the main component of the Fe-NHPC material. In addition, the N 1s and O1s signals are clearly visible, indicating the successful doping of nitrogen and oxygen in the Fe-NHPC material. It is worth noting that the presence of nitrogen element is of great significance for enhancing the electrocatalytic activity, which provides a good basis for the application of Fe-NHPC material in the 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 environments, specifically including pyridine nitrogen N-Q, pyrrole nitrogen N-5, and graphitic nitrogen N-6 peaks. The presence of these nitrogen species confirms the successful doping of nitrogen element, and in different chemical states, the nitrogen element can enhance its catalytic performance by changing the electronic structure of the carbon material. Pyridine nitrogen and pyrrole nitrogen are particularly helpful in enhancing the electrocatalytic activity of the Fe-NHPC material because they can provide effective reaction sites and promote the adsorption and reduction reaction of oxygen molecules. The introduction of graphitic nitrogen improves the conductivity of the Fe-NHPC material, which is beneficial to the rapid transfer of electrons. This diverse nitrogen-doped structure provides important support for the high-efficiency catalytic performance of the Fe-NHPC material.

[0064] (3) X-ray diffraction analysis: In the XRD analysis using a Bruker D8 Advance X-ray diffractometer, as Figure 4 shown, the Fe-NHPC material of Example 1 shows obvious amorphous carbon characteristics, that is, broad diffuse peaks appear near about 25° and 43°, indicating the existence of a disordered carbon structure in the Fe-NHPC material. In addition, several weak diffraction peaks can be observed between 20° and 30°. These peaks may correspond to the crystal 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 it in the oxygen reduction reaction. The obvious iron carbide peaks and iron oxide peaks in the Fe-NHPC material indicate its 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 demonstrating the broad application prospects of the iron-nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material prepared by the present invention 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 carried out:

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

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

[0069] (3) Cyclic voltammetry testing: In the cyclic voltammetry testing, within the potential range of 0.2 V vs. RHE to 1.0 V vs. RHE, measurements were carried out at a scanning rate of 10 mV / s to evaluate the oxygen reduction reaction activity of the Fe-NHPC material. The evaluation method for the oxygen reduction reaction activity was as follows: First, nitrogen was introduced into the three-electrode system to exhaust the oxygen in the electrolyte, and testing was carried out using the three-electrode system; subsequently, oxygen was introduced until saturation, and testing was carried out using the three-electrode system; by comparing the results of these two tests, the electrocatalytic performance of the Fe-NHPC material was obtained. It can be observed from Figure 5 that there are significant differences in the cyclic voltammetry curves under nitrogen and oxygen environments respectively. Compared with the nitrogen environment, the current density under the oxygen environment increased significantly, indicating that the Fe-NHPC material has high electrocatalytic activity in the oxygen environment and can effectively catalyze the oxygen reduction reaction. This activity demonstrates the excellent performance of the Fe-NHPC material in practical electrochemical applications, especially in zinc-air battery energy conversion devices.

[0070] (4) Linear sweep voltammetry testing: Linear sweep voltammetry testing was carried out on a rotating disk electrode. Within the potential range of 0.0 V vs. RHE to 1.2 V vs. RHE, measurements were carried out at a scanning rate of 10 mV / s and a rotation speed of 1600 rpm to evaluate its oxygen reduction reaction performance. Figure 6 It is shown in that under the oxygen environment, the Fe-NHPC material exhibits a significant change in current density, especially an obvious current increase near 0.8 V, indicating that the Fe-NHPC material has high catalytic activity within this potential range. The Fe-NHPC material exhibits a high onset potential and half-wave potential, indicating its excellent electrocatalytic activity in the oxygen reduction reaction and being suitable for zinc-air battery electrochemical devices. By optimizing the structure and doping process of the Fe-NHPC material, the Fe-NHPC material shows excellent performance in electrocatalytic performance and stability, and can meet the requirements of zinc-air batteries for efficient catalysts.

[0071] (5) Zinc-air battery assembly and testing: A zinc-air battery was assembled using a two-electrode system. The zinc anode is composed of zinc metal, which is responsible for providing electrons and undergoing an oxidation reaction to generate zinc ions. The air cathode uses a conductive carbon material containing Fe-NHPC material. The conductive carbon material containing Fe-NHPC material was prepared according to the following steps: Mix the Fe-NHPC material, conductive agent carbon black, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone evenly to obtain a slurry. The mass ratio of the Fe-NHPC material, conductive agent carbon black, and binder polyvinylidene fluoride is 8:1:1. Coat the slurry evenly on the carbon cloth using the spin coating method to ensure that the slurry is evenly distributed on the surface of the carbon cloth. Compact and dry the coated carbon cloth to increase density and mechanical strength, and then cut it. It is responsible for inhaling oxygen in the air and undergoing an oxygen reduction reaction. A zinc-air battery was assembled using a zinc anode, air cathode, polytetrafluoroethylene separator, and 0.1 mol / L KOH solution for testing.

[0072] The zinc anode and the air cathode work together to complete the electrochemical reaction process through the flow of electrons, realizing the output of electrical energy. As a cathode catalyst, the Fe-NHPC material significantly improves the catalytic performance of the oxygen reduction reaction, making this system have a high energy density and good electrochemical stability. In the assembly and testing of the zinc-air battery, the Fe-NHPC material was used as the cathode catalyst, and the zinc sheet was used as the anode 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 the Fe-NHPC material as the cathode exhibited a stable discharge voltage during a 160-hour cycle test, with a voltage of 1.2 V to 2.6 V, showing excellent cycle stability. In addition, the zinc-air battery showed a relatively high open-circuit voltage and a good discharge platform, indicating that the Fe-NHPC material can effectively improve the performance and stability of the zinc-air battery. The Fe-NHPC material demonstrated a relatively high energy density and excellent voltage retention ability, showing its good potential as a cathode material for high-performance zinc-air batteries. Its excellent electrochemical performance benefits from the structural optimization of the Fe-NHPC material and the synergistic effect of iron-nitrogen co-doping, giving it significant advantages in the application of zinc-air batteries.

[0074] In the performance test of the zinc-air battery, the current density-voltage and power density curves of the Fe-NHPC material as the cathode catalyst showed its excellent electrochemical performance. Figure 8 It can be seen that as the current density increases, the voltage of the zinc-air battery gradually decreases, showing the typical discharge characteristics of a zinc-air battery. When the current density reaches about 300 mA / cm 2When the zinc-air battery still maintains a relatively high voltage, it indicates that the Fe-NHPC material has good electrochemical stability. In addition, the peak of the power density curve appears at around 100 mW / cm 2 or so, indicating that the Fe-NHPC material can still output significant power at a relatively high current density. This shows that the Fe-NHPC material can provide efficient electrocatalytic activity and stable electrical energy output for zinc-air batteries, and is suitable for application scenarios with high power requirements.

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

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

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

Claims

1. Preparation method of iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material, characterized in that, It 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. Using medium-temperature coal tar pitch as the carbon source, melamine as the nitrogen source, soluble zinc salt as the pore-forming agent, and nano-silica as the template agent, a mixture is obtained. 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 the soluble iron salt to generate catalytic active sites, and form an internal porous structure through the volatilization and diffusion of the soluble zinc salt, obtaining an iron-nitrogen doped porous carbon material. The iron-nitrogen doped porous carbon material is pickled with hydrofluoric acid to etch away the template agent nano-silica to form mesopores, obtaining a precursor of the iron-nitrogen doped porous carbon material. The precursor of the iron-nitrogen doped porous carbon material is subjected to carbon dioxide activation treatment. Carbon dioxide reacts with carbon to form micropores, and under the action of the porous structure, the micropores and mesopores are connected to obtain a modified coal tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen.

2. The preparation method of the iron and nitrogen co-doped modified coal tar pitch-based hierarchically porous carbon material according to 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 preparation method of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material according to claim 1, characterized in that, The molar ratio of soluble zinc salt to medium-temperature coal tar pitch is 45-55:

1.

4. The preparation method of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material according to claim 1, characterized in that, The molar ratio of soluble iron salt to medium-temperature coal tar pitch is 1:0.35-0.

45.

5. The preparation method of the iron and nitrogen co-doped modified coal-tar pitch-based hierarchically porous carbon material according to claim 1, characterized in that, The conditions for heat treatment are: under an inert atmosphere, treat at 800°C - 1000°C for 0.5h - 2h.

6. The preparation method of the iron and nitrogen co-doped modified coal-tar pitch-based hierarchical porous carbon material according to claim 1, characterized in that, The conditions for carbon dioxide activation treatment are: under an inert atmosphere, raise the temperature to 700°C - 900°C. When the temperature reaches the maximum value, introduce a mixed gas of carbon dioxide and nitrogen, and carry out activation treatment for 0.5h - 2h.

7. The preparation method of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material according to claim 6, characterized in that, The volume ratio of carbon dioxide to nitrogen is 0.75 - 2.3:

1.

8. The preparation method of the iron and nitrogen co-doped modified coal tar pitch-based hierarchical porous carbon material according to claim 1, characterized in that, After forming mesopores, wash with deionized water until the pH value of the washing liquid is neutral to obtain a precursor of the iron-nitrogen doped porous carbon material.

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

10. An application of the modified coal tar pitch-based hierarchical porous carbon material co-doped with iron and nitrogen according to claim 9 in the preparation of a cathode of a zinc-air battery.

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