Preparation method of nitrogen and phosphorus co-doped three-dimensional porous carbon material

Abstract

The present invention discloses a preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material, comprising the following steps: pretreating aniline; preparing an aniline phytate micelle solution; preparing an oxidant solution; respectively cooling the prepared solutions for standby; rapidly dropping the cooled oxidant solution into the cooled aniline phytate micelle solution, and continuously reacting for a period of time under low-temperature conditions to obtain a polyaniline hydrogel; collecting the obtained sample using a dialysis bag with a molecular weight cut-off of 8000-14000, and repeatedly washing with deionized water, with a total of three dialysis washes, each dialysis for one day; vacuum freeze-drying the sample obtained from the dialysis bag to obtain a polyaniline aerogel; pyrolyzing the polyaniline aerogel in a reducing atmosphere of a mixed gas of argon and hydrogen using a rapid heating furnace to obtain the nitrogen and phosphorus co-doped three-dimensional porous carbon material. The present invention can prepare a nitrogen and phosphorus co-doped three-dimensional porous carbon material with regular structure and multi-level pores.

Description

Technical Field

[0001] The present invention relates to the technical field of sol-gel, and particularly relates to a preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material. Background Art

[0002] With the development of industrialized society and the rapid growth of the population, the problems of fossil fuel depletion and environmental pollution are becoming more and more serious. The production and utilization of new energy have become urgent issues to be developed in modern life. The theoretical energy density of a lithium-air battery can reach 11700 Wh / kg, and it is expected to be applied to a new energy storage system with high energy density. The lithium-air battery uses O 2 loaded on the cathode as the active substance: during discharge, oxygen undergoes a reduction reaction (ORR, oxygen reduction reaction) to form lithium oxide. During charging, lithium oxide is oxidized to generate oxygen, and an oxygen evolution reaction (OER, oxygen evolution reaction) occurs. Therefore, the structural design, element composition, and their bonding states of the cathode material are crucial for achieving a high-performance lithium-air battery.

[0003] Three-dimensional network carbon materials have advantages such as good electrical conductivity, low density, rich spatial configurations, easy surface composite modification, low price, and abundant sources, and are currently widely used in lithium-air batteries. However, due to problems such as the easy accumulation of a large amount of reaction products such as lithium oxide and lithium peroxide during charge and discharge, which can block channels, cover active centers, resulting in too high charge / discharge overpotential, and reducing cycle stability, etc., it severely restricts the practical application of three-dimensional network carbon materials. To improve the stability of three-dimensional network carbon materials, doping heteroatoms such as nitrogen and phosphorus to promote the catalytic decomposition of oxidation products is a low-cost and effective method. Gas deposition method, ball milling method, polymerization-pyrolysis or sol-gel-pyrolysis method have been successively used at home and abroad to add heteroatoms such as nitrogen and phosphorus to three-dimensional carbon materials. Among them, the sol-gel-pyrolysis method is most conducive to uniformly in-situ doping nitrogen and phosphorus into the entire carbon substrate and has become the focus of research. In the prior art, there are still the following problems: the internal structure controllability of porous materials is poor, the cracking reaction process of nitrogen and phosphorus elements is easy to lose, and the bonding state is difficult to regulate, so that the ORR and OER performances of the products cannot be balanced. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material, which can prepare a nitrogen and phosphorus co-doped three-dimensional porous carbon material with regular structure, multi-level pores, uniform distribution of doped atoms, and optimized chemical structure.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material, comprising the following steps:

[0007] (1) Pretreat aniline: perform vacuum distillation purification with a vacuum pump, remove the fore fraction obtained at 60 - 80 °C, and collect the main fraction at 90 - 110 °C;

[0008] (2) Prepare an aniline phytate micelle solution: transfer the pretreated aniline into a container. After preparing phytate into an aqueous solution, mix the aniline and the phytate aqueous solution, then make up the volume to 2 mL with deionized water and mix evenly. Ultrasonic for half an hour until the solution is clear to form an aniline phytate micelle solution;

[0009] (3) Prepare an oxidant solution: weigh an oxidant and add it to deionized water, and form an oxidant solution after magnetic stirring;

[0010] (4) Cool the solutions prepared in step (2) and step (3) respectively for standby;

[0011] (5) Rapidly drop the cooled oxidant solution into the cooled aniline phytate micelle solution, and continue to react for a period of time under low temperature conditions to obtain a polyaniline hydrogel;

[0012] (6) Use a dialysis bag with a molecular weight cut-off of 8000 - 14000 to collect the obtained sample, and wash it repeatedly with deionized water. Dialyze and wash three times in total, with each dialysis for one day;

[0013] (7) Vacuum freeze-dry the sample obtained from the dialysis bag overnight at -60 °C to obtain a polyaniline aerogel;

[0014] (8) Use a rapid heating furnace to pyrolyze the polyaniline aerogel for a period of time under a reducing atmosphere of a mixed gas of argon and hydrogen at a certain temperature to obtain the nitrogen and phosphorus co-doped three-dimensional porous carbon material.

[0015] Preferably, in step (2), phytate is prepared into an aqueous solution of 1 mmol.

[0016] Preferably, in step (2), the molar ratio of aniline to phytate is 1 - 7:1.

[0017] Preferably, in step (3), the oxidant is ammonium persulfate. Magnetic stir to make it fully dissolve in 1 mL of deionized water to form an oxidant solution. The addition amount of ammonium persulfate is 0.25 - 1.75 mol / L, and the molar ratio of ammonium persulfate to aniline is 0.9 - 1.1:1.

[0018] Preferably, in step (4), the aniline phytate micelle solution and the oxidant solution are respectively cooled to 4 °C.

[0019] Preferably, the oxidant solution in step (5) is rapidly added to the aniline phytate micelle solution at a rate of 1 drop / second, and after thorough mixing, the reaction is carried out at 4 °C for 2-8 h.

[0020] Preferably, in step (8), the pyrolysis temperature is 900-1100 °C and the time is 2 h.

[0021] Preferably, in step (8), the volume fraction of hydrogen in the argon-hydrogen mixed gas reducing atmosphere is 10%.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) The present invention adopts the sol-gel pyrolysis method, selects aniline with high chemical activity as the precursor (providing carbon and nitrogen), mixes it with the cross-linking agent phytic acid (providing phosphorus), and then adds an initiator to carry out a polymerization reaction to form a gel with a three-dimensional network structure. Subsequently, through pyrolysis and carbonization, a nitrogen and phosphorus co-doped three-dimensional porous carbon material with regular structure, large specific surface area, and hierarchical pores is obtained. The doped nitrogen and phosphorus atoms are evenly distributed, the chemical structure is optimized, and the internal pore structure of the material is highly cross-linked, effectively increasing the specific surface area of the catalyst and improving the catalytic activity. The catalyst exhibits excellent catalytic oxygen evolution and oxygen reduction performance, high energy conversion efficiency, large current density, and good stability.

[0024] 2) The prepared nitrogen and phosphorus co-doped three-dimensional porous carbon material has high oxygen reduction and oxygen evolution bifunctional catalytic performance. It can be directly used as a cathode material in lithium-air batteries or as a substrate to support micro-scale catalytic materials in the field of electrocatalysis. The doped nitrogen and phosphorus atoms provide active sites for the reversible catalytic degradation of metal oxides, which can effectively prevent the pores on the surface of the three-dimensional porous carbon from being blocked, resulting in excessive overpotential, low cycle stability, or even complete inactivation.

[0025] 3) The present invention uniformly dopes two elements, nitrogen and phosphorus, on the three-dimensional network porous carbon substrate through the sol-gel pyrolysis method. This material has the characteristics of highly cross-linked hierarchical network pores and optimized binding states of nitrogen and phosphorus elements. It can not only provide rich oxygen adsorption / desorption sites and electrical / ionic transport channels, but also have more voids for accommodating lithium oxides. Moreover, due to the uniform distribution and optimized binding state of nitrogen and phosphorus, it has more catalytic sites for lithium compounds, showing good bifunctional catalytic characteristics and high cycle stability.

[0026] 4) By changing the ratios of precursors and crosslinkers and the concentration of oxidants in the chemical polymerization reaction of the sol-gel method, regulating the polymerization reaction time, and comprehensively controlling the above conditions according to the micelle template reaction mechanism, the structure of the obtained polyaniline is regulated. By continuously adjusting the molar ratio between aniline as the precursor of carbon and nitrogen sources and phytic acid as the crosslinker of phosphorus source in this polymerization reaction, as well as the oxidant concentration and polymerization reaction time to reach appropriate values respectively, a three-dimensional polyaniline with ideal good conductivity and a fiber structure of reticular crosslinking can be rapidly obtained.

[0027] 5) By adjusting the pyrolysis temperature and under the protection of a reducing argon-hydrogen (hydrogen volume fraction is 10%) atmosphere, when the decomposition rate of phosphate groups and the degradation rate of aniline are effectively controlled to reach appropriate values, the loss of nitrogen and phosphorus functional atoms can be reduced and their binding states can be optimized, and the carbon substrate is deeply graphitized.

[0028] 6) The nitrogen and phosphorus co-doped three-dimensional porous carbon material structure obtained by the sol-gel - pyrolysis method of the present invention has the characteristics of simple process, low cost, safety, reliability and no pollution, and is suitable for large-scale production, so it has great commercial prospects. Description of the Drawings

[0029] Figure 1 Scanning electron microscope images and corresponding physical photos of the polymerization reaction time process of the three-dimensional reticular porous polyaniline hydrogel prepared in Example 1 of the present invention;

[0030] Figure 2 Infrared spectrum of the three-dimensional reticular porous polyaniline aerogel prepared in Example 1 of the present invention;

[0031] Figure 3 Thermogravimetric analysis of the three-dimensional reticular porous polyaniline aerogel prepared in Example 1 of the present invention;

[0032] Figure 4 Scanning electron microscope images of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 of the present invention at different magnifications;

[0033] Figure 5 Transmission electron microscope images and elemental surface scan images of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 of the present invention;

[0034] Figure 6 X-ray photoelectron spectroscopy analysis of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 of the present invention, where Figure a is the full spectrum, Figure b is the XPS spectrum of nitrogen element, and Figure c is the XPS spectrum of phosphorus element;

[0035] Figure 7 Cyclic voltammetry scan of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 of the present invention;

[0036] Figure 8 Electrocatalytic performance graph of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 of the present invention: (a) Rotating cycle test curves at different rotation speeds; (b) Corresponding Koutechy-Levich curves; (c) Transfer electron number graph; (d) Catalytic oxygen evolution polarization curve;

[0037] Figure 9 Electrocatalytic stability graph of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 of the present invention.

[0038] Figure 10 Scanning electron microscope image of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 2 of the present invention;

[0039] Figure 11 Scanning electron microscope image of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 3 of the present invention;

[0040] Figure 12 Scanning electron microscope image of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 4 of the present invention. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] Example 1

[0043] A preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material, the specific steps are as follows:

[0044] (1) Aniline was purified by vacuum distillation using a vacuum pump, and the pre-fraction obtained at 60 - 80 °C was removed, and the main fraction at 90 - 110 °C was collected;

[0045] (2) Preparation of an aniline phytate micelle solution: The aniline pretreated in step (1) was mixed with phytic acid in a molar ratio of 5:1: Among them, 458 μL of aniline was taken, and after phytic acid was made into a 1 mmol solution, 921 μL was taken, and then it was made up to 2 mL with deionized water and mixed evenly, and ultrasonicated for half an hour to form a light yellow clear liquid to form an aniline phytate micelle solution;

[0046] (3) Preparation of an oxidant solution: Weigh 0.2860 g of ammonium persulfate and add it to a beaker containing 1 mL of deionized water, and form an oxidant solution after magnetic stirring;

[0047] (4) Cool the solutions prepared in steps (2) and (3) to 4 °C respectively for standby;

[0048] (5) Subsequently, quickly drop the cooled solution prepared in step (3) into the solution prepared in step (2), and continue the reaction at 4 °C for 2 h to obtain polyaniline hydrogel;

[0049] (6) Use a dialysis bag with a molecular weight cut-off of 8000 - 14000 to collect the obtained sample, and repeatedly wash it with deionized water. Dialyze and wash three times in total, with each dialysis lasting for one day;

[0050] (7) Vacuum freeze-dry the sample obtained from the dialysis bag at -60 °C overnight to obtain polyaniline aerogel;

[0051] (8) Use a rapid heating furnace to pyrolyze the polyaniline aerogel in a reducing atmosphere of argon-hydrogen mixture (hydrogen volume fraction is 10%) at 1000 °C for 2 h to obtain the nitrogen-phosphorus co-doped three-dimensional porous carbon material.

[0052] Figure 1 Shows the change of the polymerization process with time in Example 1. Figure 1 a shows that at 2 min, aniline just starts to polymerize, and the microscopic morphology shows the appearance of granular protrusions. It can be seen from the corresponding reaction physical picture in the upper right corner that a blue-black suspension appears above the container. At 4 min ( Figure 1 b) The granular protrusions further grow into the main chain of polyaniline hydrogel, and at the same time, multiple rod-shaped side chains are generated in different directions on the main chain; the corresponding physical picture shows that the blue-black turbidity has spread to four-fifths. It shows that at 4 minutes, most of the aniline has undergone polymerization reaction. At 8 min ( Figure 1 c), the microscopic morphology shows that the polyaniline fibrous polymer chains further grow and crosslink together. Large pores are surrounded between the polyaniline main chains, and micropores are formed inside the side chains. Polyaniline initially shows a three-dimensional network morphology with a hierarchical pore structure; the corresponding physical picture shows that the blue-black product has filled the entire container at 8 minutes, indicating that the polymerization reaction has been basically completed. At 2 h ( Figure 1 d), further multi-directional side chain polymerization occurs on the basis of the three-dimensional network skeleton, making the polyaniline fibers further crosslink. The microscopic morphology presents a three-dimensional network morphology with regular structure and multi-level pore structure, and its basic skeleton is composed of fibrous polymer chains with a diameter of about 200 nm. The reaction physical results show that when the container is inverted, the blue-black turbid part does not collapse, indicating that a gel has been formed.

[0053] In Example 1, the molar ratio of aniline to phytic acid was 5:1, and anilinium phytate formed columnar micelles in an aqueous solution. After quickly dropping the oxidant, a polymerization reaction occurred rapidly with the columnar micelles as the template. First, the main chain of a polyaniline fibrous chain structure was formed, and then new short rod-like polymer chains grew on the main chain. The main chain and the side chains were cross-linked with each other to form a three-dimensional network structure with hierarchical pores. According to the microscopic morphology of the samples at different time periods and the results of physical monitoring and analysis, Example 1 can quickly obtain a highly cross-linked three-dimensional network polyaniline with a hierarchical pore structure within 2 hours.

[0054] Figure 2 The infrared spectrum of the polyaniline prepared in Example 1 is shown. In the figure, PANi is the abbreviation of polyaniline. In this infrared spectrum, the characteristic peaks at 1567 cm -1 and 1485 cm -1 are respectively the stretching vibration peaks of the C═C double bond in the quinoid and benzenoid structures of PANi, and the ratio of their peak intensities indicates that the product formed is polyaniline with an intermediate redox degree; the peaks at 1302 cm -1 and 1224 cm -1 are respectively the stretching vibration peaks of aniline protonation and C-N bonds, indicating the presence of the conductive structure of polyaniline, emeraldine; the vibration peak at 1140 cm -1 is the stretching vibration peak of the -NH+═ structure formed after the protonation of polyaniline phytic acid. The characteristic bands at 1060 cm -1 , 943 cm -1 , and 875 cm -1 prove the presence of phytic acid. The infrared spectrum shows that the polymer in Example 1 is composed of polyaniline with good conductivity and phytic acid. The protonation of phytic acid is crucial for the formation and stability of the PANi cross-linked network structure.

[0055] Figure 3 The polyaniline aerogel prepared in Example 1 has multiple weight loss segments. Among them, the weight loss within 100 °C comes from the free water in polyaniline; the minor weight loss from 200 °C to 310 °C comes from the adsorbed bound water; the continuous weight loss from 310 °C to 800 °C mainly comes from the thermal decomposition of phytic acid groups and the degradation of the polyaniline structure; and the slow weight loss after 800 °C comes from the decarboxylation reaction and deep graphitization. The thermogravimetric analysis results show that the temperature for obtaining nitrogen and phosphorus doped porous carbon by pyrolyzing polyaniline can be selected between 900 - 1100 °C.

[0056] Figure 4SEM scanning images at different magnifications of the carbon material obtained by high-temperature pyrolysis of the polyaniline prepared in Example 1 show that after high-temperature pyrolysis, the fibrous polymer chains of the polyaniline aerogel have undergone a certain degree of shrinkage, but the skeleton structure has not changed significantly. A very small part has agglomerated after high-temperature pyrolysis. The diameter of the fibrous polyaniline aerogel after carbonization obtained by pyrolysis at 1000 °C in Example 1 is approximately 100 nm, and there are multiple levels of pores on the product: macropores mainly composed of the main chains of the pyrolyzed polymer chains and micropores formed between the side chains. Compared with the products obtained at other pyrolysis temperatures, the product obtained at 1000 °C has less agglomeration and denser pores, which will contribute a larger specific surface area to the catalyst.

[0057] Figure 5 This is the transmission electron microscopy image of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1. Different-sized white regions can be seen in the figure, corresponding to pores of different sizes in the product. For example, the one pointed by the arrow belongs to the mesoporous structure. The high-magnification transmission electron microscopy image shows a growth mode in which the side chains grow in multiple directions and cross-link with each other. The elemental surface distribution map shows that carbon is the substrate, phosphorus is uniformly distributed on the entire carbon substrate, and nitrogen is sporadically dotted on the entire carbon substrate, indicating that a nitrogen and phosphorus uniformly doped three-dimensional porous carbon material is formed after high-temperature pyrolysis.

[0058] Figure 6 This is the X-ray photoelectron spectroscopy analysis image of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1. The XPS analysis results show that the pyrolysis product is composed of four elements: P, C, N, and O. In the figure, N1 (398.6 eV), N2 (400.5 eV), N3 (401.3 eV), and N4 (402.0 eV) represent pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, and nitrogen cation radicals, respectively. Compared with the pyrolysis products at other temperatures, the graphitization of the product obtained by pyrolysis at 1000 °C is almost complete; the content of pyrrole nitrogen N2 in the N element is the lowest (since pyrrole nitrogen does not have oxygen reduction activity, the lower the content, the better); the P-C intensity is the highest and the P-O content is the lowest, indicating that most phosphorus has changed from the P-O form in the original phosphate group to the P-C form combined with carbon.

[0059] Figure 7 This is the cyclic voltammogram of the nitrogen and phosphorus co-doped three-dimensional porous carbon material (NPMC-1000) prepared in Example 1 in a 0.1 mol / L KOH electrolyte. Under the condition of oxygen saturation, the cathode current density shows an obvious increasing trend, and an obvious oxygen reduction peak appears near 0.72 V, proving that the catalyst has catalytic activity for oxygen. No obvious redox peak appears under the condition of nitrogen saturation, indicating the self-stability of the catalyst.

[0060] In contrast, the oxygen reduction peak of NPMC-1000 is more obvious than that of the pyrolysis product at 1100 °C and the peak position is slightly higher, showing stronger oxygen catalytic activity; there is no obvious oxygen reduction peak in the pyrolysis product at 900 °C.

[0061] Figure 8 The electrocatalytic performance of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 is shown, and it is tested on a RRDE-3A type rotating ring-disk electrode device. An Ag / AgCl electrode is used as the reference electrode, a graphite sheet is used as the counter electrode, and the electrolyte is 0.1 mol / L KOH. Figure 8 a shows that at a rotation speed of 1600 rpm, the initial potential of oxygen reduction of NPMC-1000 is around 820 mV, and the limiting current density is 6.3 mA·cm -2 . The limiting current density of NPMC-1000 is increased by 50% compared with the pyrolysis product at 1100 °C and by 110% compared with the pyrolysis product at 900 °C.

[0062] The Koutechy-Levich curve of NPMC-1000 ( Figure 8 b) and the number of electron transfers calculated according to the K-L equation ( Figure 8 c). The results show that 3.50 - 3.89 electrons participate in the oxygen reduction, indicating that the oxygen reduction reaction of NPMC-1000 is a four-electron reaction mechanism and has a high energy conversion efficiency. Figure 8 d The results of oxygen evolution catalysis show that at a current density of 10 mA·cm -2 , the oxygen evolution potential of NPMC-1000 is 1.82 V. While the oxygen evolution catalytic curves of the pyrolysis products at other temperatures do not reach a current density of 5 mA·cm within the test voltage range of 1.4 V to 2.0 V -2 . The oxygen reduction (ORR) and oxygen evolution (OER) catalytic performances of NPMC-1000 are both strong, which may be caused by the lowest content of pyrrole nitrogen and the most generated phosphorus-carbon P-C in this product.

[0063] Figure 9 The stability of the catalytic performance of the nitrogen and phosphorus co-doped three-dimensional porous carbon material prepared in Example 1 is shown, and it is tested by chronoamperometry. A voltage value reaching its limiting current density is applied to the catalyst, that is, a voltage of 0.4 V is applied at a rotation speed of 900 rpm. NPMC-1000 undergoes a constant voltage test for 40000 s, and the current magnitude still remains at 96.6% of the initial current value.

[0064] In addition, the onset potential of the nitrogen and phosphorus porous carbon NPC-1000 obtained by the polymerization-pyrolysis method is about 10 mV higher than that of NPMC-1000, and the limiting current density is about 43.2% lower; after 40,000 s of cycling, its stability can be maintained at about 94.5%. Generally speaking, the oxygen reduction and catalytic oxygen evolution performances of NPMC-1000 obtained by the sol-gel pyrolysis method are superior to those of NPC-1000 obtained by the polymerization-pyrolysis method.

[0065] Example 2

[0066] A preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material comprises the following specific steps:

[0067] (1) Aniline is purified by vacuum distillation using a vacuum pump, the pre-fraction obtained at 60 - 80 °C is removed, and the main fraction at 90 - 110 °C is collected;

[0068] (2) Prepare an aniline phytate micelle solution: Mix the aniline pretreated in step (1) with phytic acid in a molar ratio of 1:1, where the aniline is 92 μL; after preparing a 1 mmol solution of phytic acid, take 921 μL, then make up the volume to 2 mL with deionized water and mix evenly, and ultrasonicate for half an hour until a clear liquid is formed to obtain an aniline phytate micelle solution;

[0069] (3) Prepare an oxidant solution: Weigh 0.0572 g of ammonium persulfate and add it to a beaker containing 1 mL of deionized water, and form an oxidant solution after magnetic stirring;

[0070] (4) Cool the solutions prepared in steps (2) and (3) to 4 °C respectively for standby;

[0071] (5) Then quickly add the solution prepared in step (3) after cooling dropwise to the solution prepared in step (2), and continue to react at 4 °C for 8 h;

[0072] (6) Use a dialysis bag with a molecular weight cut-off of 8000 - 14000 to collect the obtained sample, and wash it repeatedly with deionized water, and dialyze and wash three times in total, with each dialysis lasting for one day; freeze-dry the sample obtained from the dialysis bag under vacuum at -60 °C overnight to obtain a polyaniline aerogel;

[0073] (7) Pyrolyze the polyaniline at 1000 °C for 2 hours in a reducing atmosphere of argon-hydrogen mixture (the volume ratio of hydrogen is 10%) using a rapid heating furnace to obtain a nitrogen and phosphorus co-doped carbon material.

[0074] Figure 10It is the SEM morphology diagram of the nitrogen and phosphorus co-doped three-dimensional porous carbon material in Example 2. As can be seen from the figure, larger spherical substances are piled up together, and an interconnected network-like porous carbon structure is not formed. In this example, the molar ratio of aniline to phytic acid is 1:1. The concentration of aniline is relatively low, and spherical micelles are formed after binding with phytic acid. The polyaniline formed by polymerization using this as a template has a spherical structure, and the corresponding physical object does not form a gel either. Due to the low molar ratio of aniline to phytic acid in this example, a three-dimensional network structure cannot be obtained after pyrolysis.

[0075] Example 3

[0076] A preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material comprises the following specific steps:

[0077] (1) Aniline is purified by vacuum distillation using a vacuum pump, the pre-fraction obtained at 60 - 80 °C is removed, and the main fraction at 90 - 110 °C is collected;

[0078] (2) Prepare an aniline phytate micelle solution: Mix the aniline pretreated in step (1) with phytic acid in a molar ratio of 3:1, where the aniline is 275 μL; after preparing a 1 mmol solution of phytic acid, take 921 μL, then make up the volume to 2 mL with deionized water and mix evenly, and ultrasonicate for half an hour until a clear liquid is formed to obtain an aniline phytate micelle solution;

[0079] (3) Prepare an oxidant solution: Weigh 0.1716 g of ammonium persulfate and add it to a beaker containing 1 mL of deionized water, and form an oxidant solution after magnetic stirring;

[0080] (4) Cool the solutions prepared in steps (2) and (3) to 4 °C respectively for standby;

[0081] (5) Then quickly add the solution prepared in step (3) after cooling dropwise to the solution prepared in step (2), and continue to react at 4 °C for 4 h;

[0082] (6) Use a dialysis bag with a molecular weight cut-off of 8000 - 14000 to collect the obtained sample, and wash it repeatedly with deionized water, for a total of three dialysis washes, with each dialysis lasting for one day; freeze-dry the sample obtained from the dialysis bag under vacuum at -60 °C overnight to obtain polyaniline aerogel;

[0083] (7) Use a rapid heating furnace to pyrolyze polyaniline for 2 hours under a reducing atmosphere of argon-hydrogen mixture (the volume fraction of hydrogen is 10%) at a temperature of 1000 °C to obtain a nitrogen and phosphorus co-doped carbon material.

[0084] Figure 11It is the SEM morphology diagram of the nitrogen and phosphorus co-doped porous carbon in Example 3. In this example, the molar ratio of aniline to phytic acid is 3:1. As the relative content ratio of aniline to phytic acid increases, the micelles formed by aniline phytate in the aqueous solution gradually change from spherical to columnar. The polymerization using spherical micelles as templates gradually decreases, and at the same time, the polymerization of columnar micelles appears. However, the finally formed polyaniline product has poor cross-linking property, and no structure with interconnected hierarchical pores is formed after pyrolysis. In addition, the polymerization reaction rate of aniline in this example is relatively slow, and the amount of gel formed is relatively small. Generally speaking, the ratio of each substance in this example needs to be further optimized.

[0085] Example 4

[0086] A preparation method of a nitrogen and phosphorus co-doped three-dimensional porous carbon material, the specific steps are as follows:

[0087] (1) Purify aniline by vacuum distillation using a vacuum pump, remove the fore fraction obtained at 60 - 80 °C, and collect the main fraction at 90 - 110 °C;

[0088] (2) Prepare an aniline phytate micelle solution: Mix the aniline pretreated in step (1) with phytic acid in a molar ratio of 7:1, where aniline is 641 μL; after preparing a 1 mmol solution of phytic acid, take 921 μL. Then, make up the volume to 2 mL with deionized water and mix evenly. Ultrasonic for half an hour until the solution turns milky white to form an aniline phytate micelle solution;

[0089] (3) Prepare an oxidant solution: Weigh 0.4004 g of ammonium persulfate and add it to a beaker containing 1 mL of deionized water, and form an oxidant solution after magnetic stirring;

[0090] (4) Cool the solutions prepared in steps (2) and (3) to 4 °C respectively for standby;

[0091] (5) Then quickly drip the solution prepared in step (3) after cooling into the solution prepared in step (2), and continue to react at 4 °C for 4 h;

[0092] (6) Use a dialysis bag with a molecular weight cut-off of 8000 - 14000 to collect the obtained sample, and wash it repeatedly with deionized water. Dialyze and wash three times in total, with each dialysis for one day; Freeze-dry the sample obtained from the dialysis bag under vacuum at -60 °C overnight to obtain a polyaniline aerogel;

[0093] (7) Use a rapid heating furnace to pyrolyze polyaniline for 2 hours under a reducing atmosphere of argon-hydrogen mixture (the volume fraction of hydrogen is 10%) at a temperature of 1000 °C to obtain a nitrogen and phosphorus co-doped carbon material.

[0094] Figure 12It is the scanning electron microscope morphology diagram of the nitrogen and phosphorus co-doped porous carbon in Example 4. The sample of this example shows a fibrous long-chain structure, with only a small number of positions cross-linked and no network structure formed. Since the molar ratio of aniline to phytic acid in this example is 7:1 and the aniline concentration is too high, some aniline cannot combine with phytic acid to form water-soluble aniline phytate, and this part of aniline cannot participate in the reaction. Although the columnar micelles are still used as templates during polymerization, the undissolved aniline destroys the multi-directional chain growth of polyaniline during the polymerization reaction, and the reaction proceeds in the gaps of the suspension. Therefore, a network-crosslinked porous structure cannot be formed under this condition.

[0095] The above content is only an example and illustration of the structure of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution. As long as they do not deviate from the structure of the present invention or exceed the scope defined by this claim book, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing nitrogen and phosphorus co-doped three-dimensional porous carbon material, It is characterized in that It consists of the following steps: (1) pre-treating aniline: purifying by vacuum distillation using a vacuum pump, removing the front fraction obtained at 60-80° C., and collecting the main fraction at 90-110° C.; (2) preparing an aniline phytate micelle solution: pipetting the pretreated aniline into a container, preparing phytic acid into an aqueous solution, mixing the aniline and phytic acid aqueous solutions, then making up to volume with deionized water and mixing evenly, and ultrasonicating for half an hour until the solution is clear, thereby forming an aniline phytate micelle solution; (3) preparing an oxidant solution: weighing an oxidant and adding it to deionized water, and stirring the solution magnetically to form an oxidant solution; (4) cooling the solutions prepared in step (2) and step (3) respectively for standby use; (5) rapidly dropping the cooled oxidant solution into the cooled aniline phytate micelle solution, and continuing the reaction for a period of time under low temperature conditions to obtain a polyaniline hydrogel; (6) Collect the obtained sample using a dialysis bag with a molecular weight cutoff of 8000-14000, and wash it repeatedly with deionized water for a total of three times, each dialysis lasting one day; (7) freezing and drying the sample obtained from the dialysis bag at -60°C overnight in a vacuum oven to obtain a polyaniline aerogel; (8) Using a rapid heating furnace, thermally cracking the polyaniline aerogel in an argon-hydrogen mixed gas reducing atmosphere at a certain temperature for a period of time, wherein the volume proportion of hydrogen in the argon-hydrogen mixed gas reducing atmosphere is 10%, the thermal cracking temperature is 900-1100° C., and the time is 2 h, thereby obtaining the nitrogen-phosphorus co-doped three-dimensional porous carbon material.

2. The method for preparing a nitrogen-phosphorus co-doped three-dimensional porous carbon material according to claim 1, Features: In the step (2), phytic acid is prepared into a 1 mmol aqueous solution.

3. The method for preparing a nitrogen-phosphorus co-doped three-dimensional porous carbon material according to claim 1, Features: In the step (2), the molar ratio of aniline to phytic acid is 1-7:

1.

4. The method for preparing a nitrogen-phosphorus co-doped three-dimensional porous carbon material according to claim 1, Features: In the step (3), the oxidant is ammonium persulfate, which is fully dissolved in 1 mL of deionized water by magnetic stirring to form an oxidant solution. The amount of ammonium persulfate added is 0.25-1.75 mol / L, and the molar ratio of ammonium persulfate to aniline is 0.9-1.1:

1.

5. The method for preparing a nitrogen-phosphorus co-doped three-dimensional porous carbon material according to claim 1, Features: In the step (4), the aniline phytate micelle solution and the oxidant solution are cooled to 4° C. respectively.

6. The method for preparing a nitrogen-phosphorus co-doped three-dimensional porous carbon material according to claim 1, Features: In the step (5), the oxidant solution is rapidly added to the aniline phytate micelle solution at a rate of 1 drop / second, and after being fully mixed, the mixture is reacted at 4° C. for 2-8 hours.

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