CN111573666B

CN111573666B - Optimization method for carbon source molecular layer of porous carbon material of supercapacitor

Info

Publication number: CN111573666B
Application number: CN202010315951.3A
Authority: CN
Inventors: 樊星; 张晓云; 余果; 魏贤勇
Original assignee: Shandong University of Science and Technology
Current assignee: Shandong University of Science and Technology
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2022-07-01
Anticipated expiration: 2040-04-21
Also published as: CN111573666A

Abstract

The invention discloses an optimization method for a carbon source molecular layer of a porous carbon material of a supercapacitor, which specifically comprises the following steps: the method comprises the steps of obtaining various carbon source precursors through pretreatment, analyzing the composition of the carbon source precursors by mass spectrometry, preparing the porous carbon material by adopting the carbon source precursors under the optimal experimental conditions, characterizing the morphology and the electrochemical performance of the prepared porous carbon material, and constructing the relationship between the molecular composition and the structure of the carbon source and the morphology and the electrochemical performance of the porous carbon material based on the characterization results. Through the research on the carbon source molecular level, the relationship between the carbon source and the material morphology structure is established and the influence on the material electrochemical performance is further clarified. By constructing the relation between the carbon source and the electrochemical formation of the carbon material, the feasibility guidance is provided for the optimization of the carbon source raw material and the optimization modification of the preparation process of the carbon material.

Description

Optimization method for carbon source molecular layer of porous carbon material of supercapacitor

Technical Field

The invention relates to the technical field of material preparation of energy storage equipment, in particular to an optimization method for a carbon source molecular level of a porous carbon material of a supercapacitor.

Background

With the rapid development of economy, the demand of human beings for energy greatly surpasses the reserves of the currently known fossil energy, and the development of novel energy is imperative. New energy sources that people have started to use today include solar, nuclear, tidal and wind energy, etc. However, the utilization efficiency of the pollution-free and sustainable energy sources in China can not achieve ideal effects all the time. In order to effectively solve the problem of utilization and storage of sustainable energy, development of novel efficient energy storage devices has gradually attracted attention. When various energy storage devices are researched, the super capacitor stands out and becomes one of the most potential energy storage devices. The super capacitor has excellent electrochemical performance, and has the excellent characteristics of high power density, high energy density, long cycle life, quick charge and discharge, instantaneous heavy current discharge, no environmental pollution and the like. Due to the excellent performance, the super capacitor becomes a better choice for the auxiliary energy source and the rapid power supply device of the electric automobile. The super capacitor mainly comprises four parts, namely an electrode, electrolyte, a current collector and a diaphragm, wherein the electrode material is one of the most critical factors influencing the performance and the production cost of the super capacitor. Research and development of high-performance low-cost electrode materials are important contents of research and development work of supercapacitors. The porous carbon material is mostly used as the electrode material of the super capacitor because the porous carbon material has a developed pore structure, so that the sufficient contact area is increased in the charge and discharge process, and the specific capacitance and the energy density of the double electric layer capacitor can be improved. However, the performance of the porous carbon material is affected by many factors, such as calcination temperature, calcination time, the amount of the template, the amount of the activator, and the like. At present, most of researches are conducted to explore the influence of the factors on the performance of the supercapacitor so as to guide the preparation of the porous carbon material. However, the most important internal factor affecting the performance of the porous carbon material is that the composition of a carbon source is only studied, so that blindness exists in the selection of raw materials in the preparation process of the supercapacitor.

Disclosure of Invention

In order to solve the defects of the existing research, the invention aims to provide an optimization method aiming at the carbon source molecular level of the porous carbon material of the supercapacitor. By the method, the relationship between the molecular composition and structure of the carbon source and the morphology structure and electrochemical performance of the porous carbon material is explored, the basis for selecting the raw material of the supercapacitor is provided, and the material selection of the porous carbon material is guided in a targeted manner. The blindness of raw material selection in the prior art is solved.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for optimizing a carbon source molecular layer of a porous carbon material of a supercapacitor comprises the following steps:

(1) obtaining various carbon source precursors through pretreatment;

(2) analyzing the composition of the carbon source precursor by adopting a mass spectrum, specifically, analyzing by adopting a GC/MS and a quadrupole/electrostatic field orbit trap high-resolution mass spectrometer to obtain the composition of the carbon source precursor;

(3) preparing a porous carbon material by adopting the carbon source precursor in the step (1) under the optimal experimental conditions;

(4) performing morphology and electrochemical performance characterization on the prepared porous carbon material;

(5) and (4) constructing the relationship between the molecular composition and the structure of the carbon source and the morphology structure and the electrochemical performance of the porous carbon material based on the characterization results of the step (2) and the step (4).

Specifically, in the step (4), a Scanning Electron Microscope (SEM) and a projection electron microscope (TEM) are adopted to characterize the apparent morphology of the porous carbon material; the phase composition of the porous carbon material is analyzed by adopting X-ray diffraction (XRD), the information such as the element composition, the chemical state, the molecular structure and the like of the porous carbon material is analyzed by adopting X-ray photoelectron spectroscopy (XPS), and the specific surface area and the like of the porous carbon material are analyzed by adopting nitrogen physical adsorption and desorption.

Compared with the prior art, the invention has the beneficial effects that:

introducing high-resolution mass spectrum, and establishing a corresponding relation between the carbon source molecular composition and the morphology structure and the electrochemical performance of the porous carbon material through the research on the carbon source molecular composition and structure, thereby providing a basis for the directional selection and optimization of the future carbon source.

Drawings

Fig. 1 is a flowchart of an optimization method for a carbon source molecular layer of a supercapacitor porous carbon material according to the present invention.

FIG. 2 shows SP obtained by GC/MS in example 1_RHXThe relative content distribution diagram of each component in the composition.

FIG. 3 is the electrochemical performance of HPC-RHx as described in example 1, where a) is HPC-RH_XCyclic voltammogram curves in a three-electrode system, b) HPC-RH_XConstant current charge-discharge curve in a three-electrode system, c) HPC-RH_XAc impedance curve under three-electrode system.

FIG. 4 shows SP obtained by GC/MS in example 2_WSXThe relative content distribution diagram of each component in the composition.

FIG. 5 shows SP obtained by GC/MS in example 2_WSXBar graph of the content of N compound.

FIG. 6 shows the electrochemical performance of HPC-WSx in example 2, where a) is the cyclic voltammetry curve of HPC-WSx in a three-electrode system, b) is the galvanostatic charging and discharging curve of HPC-WSx in a three-electrode system, and c) is HPC-WS_XAc impedance curve under three-electrode system.

Detailed Description

For the purpose of enhancing the understanding of the present invention, the present invention will be further explained with reference to the accompanying drawings and examples, which are only for the purpose of explaining the present invention and do not limit the scope of the present invention.

An optimization method aiming at a carbon source molecular layer of a porous carbon material of a super capacitor,

example 1

(1) Pretreatment of raw materials

Selecting Yunnan brown coal and rice hull as raw materials, pulverizing brown coal to below 200 meshes by a pulverizer, pulverizing rice hull to below 80 meshes by a pulverizer, drying in a vacuum drying oven at 80 ℃ for 24h, and storing in a dryer for later use as hot-melt raw materials.

(2) Hot melt experiment

As shown in figure 1, 6.0g of coal and rice hulls with different mass ratios are weighed, and the mass ratio of the coal to the rice hulls is 1:0,3:1,1:1,1:3 and 0: 1. 6.0g of hot-melt raw material is placed in a 250mL high-pressure kettle, 60mL of absolute ethyl alcohol is added as a hot-melt solvent, the high-pressure kettle is symmetrically screwed, and then N is used₂Replacing air in the autoclave body, continuously charging and discharging air for three times to replace air, and charging 1MPa N into the autoclave₂And checking the airtightness of the device. The autoclave is placed on a heating furnace, a control panel is opened, the reaction temperature is set to be 300 ℃, and the reaction time is 2 hours. After the reaction is finished, cooling to room temperature, taking out the reaction mixture to a suction filtration device for suction filtration, and obtaining filtrate and hot melt residue. Carrying out ultrasonic extraction on the hot-melt residue for multiple times by using absolute ethyl alcohol, and filtering until the color of the filtrate becomes light or colorless. Combining the filtrates, concentrating with rotary evaporator, and bottling at 40 deg.CAnd drying in an air drying box for later use. Obtaining 5 samples SP_RHx、SP_RH1/4、SP_RH1/2、SP_RH3/4And SP_RH1The carbon source precursor is used as a raw material for preparing the porous carbon material.

(3) Mass spectrometry analysis of molecular structure and composition of porous carbon material

For SP_RH0、SP_RH1/4、SP_RH1/2、SP_RH3/4And SP_RH1Both GC/MS (7890/5975) from Agilent Inc. and quadrupole/electrostatic field Orbitrap Mass spectrometer (Orbitrap MS) from Thermo Fisher Inc. were used for analysis. Two mass spectrum analysis methods are adopted, so that the data can be more perfect, and the data reliability is enhanced. Mass spectrometry data as shown in fig. 2 and table 1, mass spectrometry analysis shows that the ratio of the oxygen-containing compound to the nitrogen-containing compound in the carbon source is high, the rice hull content is increased from 0 to 3/4, the nitrogen-containing compound is increased, the unsaturation degree is basically in a reduction trend, and the nitrogen-containing compound is reduced and the unsaturation degree is increased when the rice hull reaches 1. The reason is that when the rice hulls are separately hot-dissolved, nitrogen in the rice hulls is unstable and volatile, and when the rice hulls are hot-dissolved in a different proportion from coal, polymerization reaction occurs in the hot-dissolving process, and the retention rate of nitrogen is improved along with the increase of the content of the rice hulls.

TABLE 1

(4) Preparation method and condition optimization of porous carbon material

The carbon source precursor is used as the carbon source to explore the optimal conditions for preparing the material. Weighing 1.0g of carbon source precursor obtained under the condition that the mass ratio of coal to rice hull is 1:0, adding nano zinc oxide with a certain proportion into a mortar, wherein the particle size of the nano zinc oxide is about 30nm, a certain amount of mesoporous structures can be brought to the material, fully grinding the material to be completely and uniformly mixed, adding KOH with a certain proportion, further grinding the material, and uniformly mixing the material. Spreading the ground mixture in a porcelain boat with N₂The calcination is carried out in a tube furnace for the purpose of protecting the gas. The temperature of the tube furnace is raised by taking the room temperature as the initial temperature and taking the temperature of 5 ℃ as the temperatureAnd (3) raising the temperature to 300 ℃ at the heating rate of min, standing at 300 ℃ for 30min, continuing raising the temperature to the activation temperature at the heating rate of 5 ℃/min, activating for a period of time, washing to be neutral by using 6M HCl and deionized water, and drying in a vacuum drying oven at 80 ℃ for 24h to obtain the porous carbon material taking the coal and rice hull co-thermal solution as a carbon source precursor. In the process, conditions are optimized by adjusting the proportion (1:1,1:2,1:3,1:4) of template agent nano zinc oxide, the alkali-carbon ratio (1:1,1:2,1:3,1:4) and the activation temperature (500 ℃,600 ℃,700 ℃,800 ℃). Obtaining 16 porous carbon material samples in the condition optimization process, and finally determining the optimal conditions by comparing the electrochemical performance difference of the materials obtained under different preparation conditions: the template ratio is 1:3, the alkali-carbon ratio is 1:3, the activation time is 2h, the activation temperature is 700 ℃, and the retention time is 30 min.

(5) Carbon source optimization and carbon material modification under optimal conditions

And optimizing the carbon source and modifying the carbon material under the determined optimal conditions. Respectively weighing SP_RH0、SP_RH1/4、SP_RH1/2、SP_RH3/4、SP_RH11.0g of co-thermal solvent is put in a mortar, 3.0g of nano zinc oxide is weighed as a template agent, 3.0g of KOH is weighed as an activating agent, the three are fully ground and uniformly mixed by an agate mortar, then the ground mixture is flatly paved in a porcelain boat, and N is used₂The calcination is carried out in a tube furnace for the purpose of protecting the gas. The temperature rise program of the tubular furnace is that the room temperature is taken as the initial temperature, the temperature is raised to 300 ℃ at the temperature rise rate of 5 ℃/min, the temperature is maintained at 300 ℃ for carbonization for 30min, and then the temperature is raised to 700 ℃ at the temperature rise rate of 5 ℃/min. Carbonizing at 700 ℃ for 2h, washing with 6M HCl and deionized water to be neutral, and drying in a vacuum drying oven at 80 ℃ for 24h to obtain the porous carbon material taking the coal and rice hull co-thermal solution as a carbon source precursor, which is named as HPC-RHx, wherein x is 0, 1/4,1/2,3/4 and 1 and represents the mass proportion of the rice hulls in the raw materials.

(6) Characterization of morphology and structure of porous carbon material

A series of morphologies of the porous carbon materials (HPC-RHx, X ═ 0, 1/4,1/2,3/4, and 1) were performed using a Scanning Electron Microscope (SEM), a projection electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen physical adsorption and desorption, and the likeAnd characterization of the structure. Specific data are shown in table 2, and the results show that: HPC-RH_3/4Has the highest specific surface area of 2214m²(ii) in terms of/g. The micropores are dominant, and are accompanied by partial mesopores and a small amount of macropores, the average pore diameter is about 2.50nm, the rice hull content is increased from 0 to 3/4, the specific surface area is gradually increased, the rice hull content is reduced from 3/4 to 1, and the specific surface area is approximately opposite to the change result of the unsaturation degree in the raw material, which is due to the fact that the unsaturation degree of the compound is reduced along with the increase of the proportion of rice hulls in the carbon source, and a large amount of pores are generated due to the volatilization of gas during the roasting process more easily, and the specific surface area is increased.

TABLE 2

(7) Electrochemical performance testing of supercapacitors

Mixing the prepared porous carbon material powder with acetylene black and polytetrafluoroethylene according to the weight ratio of 8: 1:1, adding a proper amount of absolute ethyl alcohol, performing ultrasonic treatment at room temperature for 10min, and then manually and uniformly coating the mixture on foamed nickel with the thickness of 1cm multiplied by 0.25cm, wherein the mass of the porous carbon material coated on the foamed nickel is about 0.01 g. And then drying the electrode plate in a vacuum drying oven at 80 ℃ for 24 hours to obtain the electrode plate. The obtained electrode plate is clamped on an electrode clamp to be used as a negative electrode, a platinum electrode is used as a positive electrode, a mercury-mercury oxide electrode is used as a reference electrode, and a three-electrode super capacitor is assembled to perform cyclic voltammetry, constant current charge and discharge and alternating current impedance tests (figure 3). The two-electrode cyclic voltammetry test is that two electrode plates with equal mass are respectively clamped on an electrode clamp to be used as a positive electrode and a negative electrode, and constant current charging and discharging is to assemble electrode materials into a button cell for testing. The electrochemical performance of the obtained 4 porous carbon materials was tested, and as shown in FIG. 2, the porous carbon material with the best electrochemical performance was HPC-RH_3/4The specific capacitance is 352F/g, and the result of the optimum specific surface area and the highest nitrogen content is oneThus, the method can be used for the treatment of the tumor. This is because the increase of nitrogen content improves the conductivity and wettability of the material, and improves the electrochemical properties.

(8) The relationship between the molecular composition and structure of the constructed carbon source and the morphology and electrochemical properties of the porous carbon material

The content of oxygen and nitrogen in the carbon source has an influence on the specific surface area and the electrochemical performance of the porous carbon material, the content of nitrogen in the carbon source has a positive influence on the improvement of the electrochemical performance of the porous carbon material, and the lower the unsaturation degree of the carbon source is, the positive influence is generated on the specific surface area of the porous carbon material, so that the positive influence is generated on the electrochemical performance of the porous carbon material. Therefore, the nitrogen content in the raw materials is high, and the unsaturation degree is low, so that the supercapacitor material with better performance can be prepared.

Example 2

(1) Pretreatment of raw materials

Selecting Yunnan brown coal and wheat straw as raw materials, pulverizing the brown coal to below 200 meshes by a pulverizer, pulverizing the wheat straw to below 80 meshes by the pulverizer, drying for 24h at 80 ℃ in a vacuum drying oven, and storing in a dryer for later use as a hot-melt raw material.

(2) Hot melt test

The mass ratio of the coal to the wheat straw is 1:0,3:1,1:1,1:3 and 0: 1. 6.0g of hot-melt raw material is placed in a 250mL autoclave, 60mL of absolute ethanol is added, the autoclave is symmetrically tightened, and then N is used₂Replacing air in the autoclave body, continuously charging and discharging air for three times to replace air, and charging 1MPa N into the autoclave₂And checking the airtightness of the device. The autoclave is placed on a heating furnace, a control panel is opened, the reaction temperature is set to be 300 ℃, and the reaction time is 2 hours. After the reaction is finished, cooling to room temperature, taking out the reaction mixture to a suction filtration device for suction filtration, and obtaining filtrate and hot melt residue. Carrying out ultrasonic extraction on the hot-melt residue for multiple times by using absolute ethyl alcohol, and filtering until the color of the filtrate becomes light or colorless. Combining the filtrates collected for many times, concentrating by a rotary evaporator, filling into weighed sample bottles, and drying in a vacuum drying oven at 40 ℃ for later use. Obtaining 5 samples SP_ws0、SP_ws1/4、SP_ws1/2、SP_ws3/4、SP_ws1As porous carbon materialThe raw material for the material preparation is used as a precursor of a carbon source.

For SP_ws0、SP_ws1/4、SP_ws1/2、SP_ws3/4、SP_ws1Both GC/MS (7890/5975) from Agilent Inc. and quadrupole/electrostatic field Orbitrap Mass spectrometer (Orbitrap MS) from Thermo Fisher Inc. were used for analysis. Mass spectral data as shown in fig. 4, fig. 5 and table 3, it was found by mass spectrometry that: the content of the wheat straws is from 1/4 to 1, the total nitrogen content in the raw materials is gradually increased, the content of N in the ring is gradually reduced, and the content of oxygen-containing compounds and nitrogen-containing compounds in the carbon source is higher; the wheat straw content is from 1/4 to 3/4, the degree of unsaturation gradually decreases, and when the degree of unsaturation reaches 1, the degree of unsaturation increases.

TABLE 3

(4) Carbon source optimization and carbon material modification under optimal conditions

Weighing 1.0g of co-thermal solution obtained by coal and wheat straw in different proportions in a mortar, weighing 3.0g of nano zinc oxide as a template agent and 3.0g of KOH as an activating agent, fully grinding and uniformly mixing the three by using an agate mortar, then flatly paving the ground mixture in a porcelain boat, and taking N₂The calcination is carried out in a tube furnace for the purpose of protecting the gas. The temperature rise program of the tubular furnace is that the room temperature is taken as the initial temperature, the temperature is raised to 300 ℃ at the temperature rise rate of 5 ℃/min, the temperature is kept at 300 ℃ for carbonization for 30min, and then the temperature is raised to 700 ℃ at the temperature rise rate of 5 ℃/min. Carbonizing at 700 ℃ for 2h, washing with 6M HCl and deionized water to be neutral, and drying in a vacuum drying oven at 80 ℃ for 24h to obtain the porous carbon material taking the coal and wheat straw co-thermal solution as a carbon source precursor, wherein the porous carbon material is named as HPC-WSx, and x is 0, 1/4,1/2,3/4 and 1 and represents the mass ratio of the rice hulls in the raw materials.

(5) Characterization of morphology and structure of porous carbon material

Using Scanning Electron Microscope (SEM), projection electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectricityA series of morphologies and structures were characterized for the prepared HPC-WSx, x 0, 1/4,1/2,3/4 and 1, porous carbon materials by sub-spectra (XPS), nitrogen physical adsorption and desorption, and the like. Specific data are shown in table 4, and the results show that: HPC-WS_1/4The optimal specific surface area is 2343m2/g, the surface micropores of the porous material are dominant, and the average pore size distribution is about 2-3 nm. The straw content was 1/2 to 1, and the change in specific surface area was approximately opposite to the result of the change in unsaturation degree, which is consistent with the conclusion in example 1. The increase in the specific surface area at 1/4 f may be caused by a higher N content in the ring.

TABLE 4

(6) Electrochemical performance testing of supercapacitors

Mixing the prepared porous carbon material powder with acetylene black and polytetrafluoroethylene according to the weight ratio of 8: 1:1, adding a proper amount of absolute ethyl alcohol, performing ultrasonic treatment at room temperature for 10min, and then manually and uniformly coating the mixture on foamed nickel with the thickness of 1cm multiplied by 0.25cm, wherein the mass of the porous carbon material coated on the foamed nickel is about 0.01 g. And then drying the electrode plate in a vacuum drying oven at 80 ℃ for 24 hours to obtain the electrode plate. The obtained electrode slice is clamped on an electrode clamp to be used as a negative electrode, a platinum electrode is used as a positive electrode, and a mercury-mercury oxide electrode is used as a reference electrode to assemble a three-electrode super capacitor for cyclic volt-ampere, constant-current charge-discharge and alternating-current impedance test. The two-electrode cyclic voltammetry test is that two electrode plates with equal mass are respectively clamped on an electrode clamp to be used as a positive electrode and a negative electrode, and constant current charging and discharging is to assemble electrode materials into a button cell for testing. The test results are shown in FIG. 6. As shown in the figure, the optimal porous carbon material is HPC-WS_1/4The specific capacitance is 384F/g, and the content of N in the ring in the raw material is the highest and the content of total nitrogen is the lowest. It can be concluded that the existence of nitrogen also affects the performance of the electrode material, and the nitrogen in the ring is due toIt is present in the ring, is not easy to volatilize during carbonization roasting and is more remained in the material. Therefore, the content of the intra-ring N in the raw materials has a positive influence on the electrochemical performance of the porous carbon material.

(8) Constructing the relationship between the molecular composition and structure of the carbon source and the morphology and electrochemical properties of the porous carbon material

The electrochemical performance of the porous carbon material is positively influenced by the high specific surface area of the carbon source and the high N content in the ring, the specific surface area is greatly influenced by factors such as the degree of unsaturation, and the performance of the porous carbon material is caused by comprehensive influence of various factors.

The embodiments of the present invention are disclosed as the preferred embodiments, but not limited thereto, and those skilled in the art can easily understand the spirit of the present invention and make various extensions and changes without departing from the spirit of the present invention.

Claims

1. A preparation method of a porous carbon material of a super capacitor is characterized by comprising the following steps:

(1) selecting Yunnan brown coal and rice hull as raw materials, pulverizing brown coal to below 200 meshes with a pulverizer, pulverizing rice hull to below 80 meshes with a pulverizer, and drying in a vacuum drying oven for 80 meshes^oDrying for 24h under C, and storing in a drier for use as hot melt raw material;

(2) weighing 6.0g of coal and rice hull together, wherein the mass ratio of the coal to the rice hull is 1:3, putting 6.0g of hot-melt raw material into a 250mL high-pressure kettle, adding 60mL of absolute ethyl alcohol as a hot-melt solvent, symmetrically screwing the high-pressure kettle, and then using N to₂Replacing air in the autoclave body, continuously charging and discharging air for three times to replace air, and charging 1MPa N into the autoclave₂Checking the airtightness of the device, placing the autoclave on a heating furnace, opening a control panel, and setting the reaction temperature to 300^oC, reacting for 2 hours, cooling to room temperature after the reaction is finished, taking out a reaction mixture, performing suction filtration in a suction filtration device to obtain filtrate and hot melt residues, performing ultrasonic extraction on the hot melt residues for multiple times by using absolute ethyl alcohol, filtering until the color of the filtrate is lightened or colorless, and adding a solvent to the filtrateThe filtrates collected in the second time are combined together, concentrated by a rotary evaporator and filled in a weighed sample bottle 40^oC, drying in a vacuum drying oven for later use to obtain a sample SP_RH3/4；

(3) Weighing SP_RH3/41.0g of the mixture is put in a mortar, 3.0g of nano zinc oxide is weighed as a template agent, 3.0g of KOH is weighed as an activating agent, the three are fully ground and uniformly mixed by an agate mortar, then the ground mixture is flatly paved in a porcelain boat, and N is used₂Roasting in a tubular furnace for protecting gas, wherein the temperature rise procedure of the tubular furnace is that room temperature is used as initial temperature and 5 is used^oThe temperature rise rate of C/min is up to 300^oC, at 300^oStaying and carbonizing for 30min under C, and continuing to use 5^oThe temperature rises to 700 ℃ at the temperature rising rate of C/min^oC, at 700^oCarbonizing for 2h under C, washing with 6M HCl and deionized water to neutrality, and drying at 80 deg.C^oAnd C, drying in a vacuum drying oven for 24 hours to obtain the porous carbon material taking the coal and rice hull co-thermal solution as a carbon source precursor.