CN111153403B

CN111153403B - Alginate-based porous carbon and preparation method and application thereof

Info

Publication number: CN111153403B
Application number: CN202010018786.5A
Authority: CN
Inventors: 韩奎华; 李明; 齐建荟; 牛胜利; 王梅梅; 滕召才; 赵建立
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2020-01-08
Filing date: 2020-01-08
Publication date: 2022-01-14
Anticipated expiration: 2040-01-08
Also published as: CN111153403A

Abstract

The invention relates to alginate-based porous carbon and a preparation method and application thereof. The method comprises the following specific steps: putting alginate or calcium modified alginate precursor into a tube furnace, introducing protective gas, and heating for carbonization; washing and drying the carbonized product, and then impregnating the carbonized product with a chemical activating agent solution; and heating under a protective atmosphere after impregnation for activation, and washing after activation to obtain the alginate-based porous carbon. The obtained porous carbon has uniform and consistent appearance, rich pores, large specific surface area and reasonable distribution of micropores, mesopores and macropores. The super capacitor electrode prepared by the method has excellent performance and good circulation stability.

Description

Alginate-based porous carbon and preparation method and application thereof

Technical Field

The invention belongs to the technical field of porous carbon materials and electrochemical capacitors, and particularly relates to alginate-based porous carbon and a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The carbon-based super capacitor has the characteristics of ultra-long cycle life, rapid charge and discharge process, good rate characteristic, higher energy density and power density and the like, and has wide application prospect in various energy storage devices. When the porous carbon is used as an electrode material of a supercapacitor, charge and discharge are mainly performed by using an electric double layer. The larger the effective specific surface area provided by the porous carbon is, the larger the capacitance of the super capacitor prepared by taking the porous carbon as an electrode material is, and therefore, the charge capacity of the super capacitor is effectively improved by increasing the specific surface area of the porous carbon.

Chemical activation has proven to be a very effective method for preparing ultra-high surface area porous carbon so far, but since the process of chemically activating pore-forming is mainly to develop the pore structure by etching the surface of the carbon material, the pores generated by activating pore-forming are mainly micropores. Although the capacitance of the porous carbon is mainly generated by micropores therein, to fully utilize the microporous structure, it is necessary to construct a rational spatial structure of macropores, mesopores and micropores, and it is difficult to achieve this object only by using an activating agent.

Patent CN103771408A discloses a preparation method of seaweed-based activated carbon for a supercapacitor, which utilizes polyvalent metal cations to perform cross-linking pretreatment on the surface of seaweed to prepare activated carbon with an optimized macroporous-mesoporous-microporous structure. The method directly uses metal cations to treat the seaweed which belongs to raw materials with more complex components, and has the problems of incomplete reaction, low efficiency, uneven structure distribution of obtained products and the like.

Disclosure of Invention

In view of the problems in the prior art, the present invention aims to provide an alginate-based porous carbon, a preparation method and an application thereof.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a preparation method of alginate-based porous carbon comprises the following specific steps:

putting the precursor into a tube furnace, introducing protective gas, heating and carbonizing;

washing and drying the carbonized product, and then impregnating the carbonized product with a chemical activating agent solution;

and heating under a protective atmosphere after impregnation for activation, and washing after activation to obtain the alginate-based porous carbon.

According to the preparation method, the alginate-based porous carbon is prepared, elements such as oxygen, hydrogen and the like in a precursor are removed through a carbonization reaction to obtain a carbonization sample rich in carbon elements, then, a chemical activating agent is used for etching the surface of the carbonization sample to carry out an activation reaction under an inert atmosphere and a heating condition to develop the pore structure of the carbonization sample, and further, the porous carbon material which is rich in pores, high in specific surface area and excellent in pore channel capacitance characteristics is obtained.

In some embodiments, the precursor is an alginate or a calcium-modified alginate. Preferably, when the precursor is alginate, the alginate comprises one of sodium alginate, potassium alginate and calcium alginate. When the precursor is only alginate, the porous carbon obtained by the preparation method of alginate-based porous carbon has excellent pore capacitance characteristics and benefits from a developed microporous structure. According to the method, carbon elements are enriched through a carbonization reaction and a microstructure of a carbon material is constructed, the distribution of an activating agent on the surface of a carbonized sample is optimized, the effect of etching the activating agent to develop the pore structure of the carbon material is further promoted, the distribution of the microporous structure of the porous carbon is improved under the dual effects of carbonization and activation, and the proportion of the microporous pore volume to the total pore volume is high.

In some embodiments of the invention, the calcium-modified alginate is prepared by: the method comprises the following specific steps: respectively dissolving soluble alginate and soluble calcium salt in water to obtain alginate solution and calcium salt water solution;

adding the calcium salt solution into the alginate solution, stirring and mixing under the heating condition, and obtaining a solid product, namely the calcium-modified alginate precursor.

According to the invention, the precursor obtained by using calcium modified alginate has rich pore structure and higher specific surface area through the preparation method of the porous carbon, the pore distribution of the porous carbon is improved by optimizing the microstructure of the carbon material, and reasonable spatial structures of macropores, mesopores and micropores are constructed while more microporous structures are provided, so that the microporous structure of the porous carbon can be more fully utilized.

In the invention, soluble calcium salt and alginate are added and mixed to obtain the precursor modified by calcium, and a calcium carbonate template is not formed in the process like the prior art. The proportion of each component in the precursor is adjusted by controlling the mass ratio of alginate to calcium salt, so as to further regulate and control the microstructure of the carbonized product, and then the pore structure of porous carbon is controlled by adjusting the mass ratio of the carbonized product to the activating agent, wherein the porous carbon is a final product; unlike the prior art, the content and concentration of carbonate are adjusted to control the pore structure of the porous carbon, and then the porous carbon is used as a carrier to load other components.

In some preferred embodiments of the invention, the soluble alginate is at least one of sodium alginate, potassium alginate, magnesium alginate and lithium alginate.

In some preferred embodiments of the invention, the soluble calcium salt includes, without limitation, one or more of calcium lactate, calcium chloride, calcium nitrate, calcium dihydrogen phosphate, calcium bicarbonate, calcium hydrogen sulfate, calcium hydrogen sulfite, calcium hypochlorite, calcium bromide, calcium iodide, calcium chlorate, calcium perchlorate, calcium permanganate; further preferably, the soluble calcium salt is calcium lactate.

In some preferred embodiments of the present invention, the mass ratio of the soluble alginate to the deionized water in the alginate solution is 1:40 to 1: 100; further preferably, the mass ratio is 1: 60.

In some preferred embodiments of the invention, the mass ratio of the soluble calcium salt to the deionized water in the calcium salt solution is 1: 25-1: 100; further preferred mass ratio is 1: 50.

In some preferred embodiments of the present invention, the mass ratio of alginate to soluble calcium salt is 1:1 to 12: 1. Compared with other existing modification methods, the method for preparing the porous carbon by using the calcium-modified alginate has the advantages that the pore size distribution of the porous carbon is prepared, the structures of macropores, mesopores and micropores are optimized, the microporous structure of the porous carbon can be fully utilized, the capacitance of the carbon-based supercapacitor is mainly generated by utilizing micropores, and the method has the effect of improving the capacitance of the carbon-based supercapacitor. The different components of the calcium-modified alginate precursor are uniformly distributed in the precursor, the microstructure of the carbon material is optimized by utilizing the different functions of the different components in the carbonization process, and the carbon material can be controlled to form different microstructures by adjusting the proportion of the components in the precursor; unlike the prior art in which calcium salt reacts with carbonate to form calcium carbonate, the carbon material forms a spherical structure by utilizing the template effect of the calcium carbonate in the carbonization process.

In some preferred embodiments of the invention, the calcium-modified alginate is dried, then crushed and sieved, and the mesh number of the sieving is 20-300 meshes; further preferably, 80 mesh.

In some embodiments, the activator solution is a saturated aqueous solution of the activator, the activator being KOH, NaOH, K₂CO₃，H₃PO₄，ZnCl₂One or more of; further preferably, KOH is used as the chemical activator. The activating agent is attached to the surface of a carbonized sample in the dipping process, then the activating agent and the carbonized sample are subjected to an activating reaction under the conditions of inert atmosphere and heating, the activating agent is used for etching the surface structure of the carbonized sample and developing the pore structure of a carbon material, so that the specific surface area and the pore volume of the porous carbon are improved, and the porous carbon has higher micropore volume due to the fact that pores formed in the activating process are mainly micropores, the quality of the activating agent attached to the unit area of the carbonized sample can be influenced by different mass ratios of the activating agent to the carbonized sample, different etching effects can be generated by different attached activating agent amounts, and the porous carbon with different pore volumes and specific surface areas can be obtained. The activation process is combined with the calcium modified alginate process to further improve the pore size distribution of the porous carbon.

In some embodiments, the impregnation ratio of the carbonized product to the activating agent is 1:1 to 1:5, preferably 1: 4. The impregnation ratio is the mass ratio of the impregnation to the solute in the liquid used for impregnation.

In some embodiments, the activation process comprises performing low-temperature activation at 300-400 ℃ for 30-50 min, and performing high-temperature activation at 700-900 ℃ for 60-140 min; preferably, the low-temperature activation temperature is 350 ℃ and the time is 30min, and the high-temperature activation temperature is 800 ℃ and the time is 120 min. The low-temperature activation and the high-temperature activation have different functions, the low-temperature activation is mainly a process in which an activator directly reacts with a carbon material, a new pore structure formed in the process can provide more active sites for the activator, the high-temperature activation is a process in which the activator fully exerts an etching effect to develop the pore structure, the formation of the etching effect of the activator not only comprises the direct reaction of the activator and the carbon material, but also comprises the high-temperature characteristic of the activator, such as potassium vapor diffusing between carbon layers at high temperature to form the pore structure.

In some embodiments, the temperature for heat carbonization is 500-; further preferably 600 ℃.

In some embodiments, the heating rate is 1-20 ℃/min; further preferably, the temperature increase rate is 5 ℃/min.

In some embodiments, the protective gas is one or a combination of several of inert gases such as nitrogen, helium, argon and the like, and the flow rate of the protective gas is 0.1-2L/min; more preferably, the shielding gas is nitrogen, and the flow rate of the shielding gas is 0.6L/min.

In some embodiments, the washing process is acid washing and then water washing, the acid washing reagent is one or a combination of aqueous solutions of hydrochloric acid, nitric acid and hydrofluoric acid, and the concentration of the acid washing reagent is 1 wt% to 60 wt%; preferably, the acid washing reagent is hydrochloric acid, and the concentration is 1-20 wt%. The purpose of acid washing in the present invention is to reduce the content of impurity components in the final product, and acid washing is a process for improving the quality of the product, and is not a process which is necessary to perform acid washing in the prior art, and acid reacts with a calcium carbonate template to remove calcium carbonate.

In some embodiments, the temperature of the acid washing is 30-100 ℃ and the acid washing time is 120-300 min.

In a second aspect, the porous carbon obtained by the above preparation method. The microstructure of the porous carbon obtained by the invention is changed along with the change of the mass ratio of alginate to calcium salt, a three-dimensional communicated or flaky thin-layer non-spherical cavity structure can be formed, a calcium carbonate template is formed by utilizing the calcium salt in the prior art, and then the template is removed, so that the microstructure of the porous carbon obtained is a regular spherical structure. Therefore, the preparation method and the technical scheme of the invention are totally different from those in the prior art in the whole view.

In a third aspect, the above porous carbon is used as an electrode material in the field of capacitors.

In a fourth aspect, a preparation method of a supercapacitor is provided, wherein an electrode material is prepared by mixing the porous carbon, a conductive agent acetylene black and a binder, the electrode material is pressed to obtain an electrode sheet, and the electrode sheet and an electrolyte are assembled to obtain the supercapacitor.

Preferably, the binder is PTFE, the mass ratio of the porous carbon to the conductive agent acetylene black to the binder PTFE is 7-9: 1: 1.

the invention has the beneficial effects that:

(1) the raw materials used in the process of the invention are cheap and easily available. The alginate can be extracted from the seaweed widely existing in the nature, the seaweed resource is rich, and the existing extraction technology is mature, which is beneficial to the large-scale production.

(2) The method for regulating and controlling the microstructure of the alginate-based porous carbon is simple, effective and convenient to operate. By controlling the mass ratio of alginate to calcium salt in the precursor, porous carbon materials with different microstructures can be obtained after carbonization. After the carbonized sample is subjected to chemical activation treatment, porous carbon with different microstructures (such as a three-dimensional communicated cavity structure or a sheet thin layer structure) and large specific surface area and high micropore volume ratio can be obtained.

(3) The porous carbon super capacitor prepared by the invention has good electrochemical performance. The alginate-based porous carbon supercapacitor works by utilizing the principle of a double electric layer, the reversibility of the charging and discharging process is very good, and the cycle performance is ultrahigh. The super capacitor has larger capacitance due to the characteristics of developed pore structure, reasonable macroporous-mesoporous-microporous three-dimensional distribution structure and high microporous pore volume ratio.

(4) The method for improving the quality of the porous carbon is simple and easy to implement and has obvious effect. After carbonization, the carbonized product is acid-washed, so that impurities such as metal compounds can be removed, and the positions where the activating agents are attached can be increased, so that the activating reaction is more sufficient. After activation, the activated product is subjected to acid washing to remove impurities such as redundant activating agents, so that the ash content in the porous carbon can be reduced, the porosity can be improved, and the pore-forming effect can be optimized.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a scanning electron microscope photograph of the porous carbon prepared in example 4.

Fig. 2 shows a nitrogen adsorption and desorption curve of the porous carbon prepared in example 4.

FIG. 3 is a scanning electron microscope photograph of the porous carbon prepared in example 5.

FIG. 4 is a graph showing the pore size distribution of micropores of the porous carbon prepared in example 5.

FIG. 5 is a scanning electron microscope photograph of the porous carbon prepared in example 6.

FIG. 6 is an X-ray diffraction chart of the porous carbon prepared in example 6.

FIG. 7 shows the cyclic voltammogram of the supercapacitor prepared in example 7 at a scan rate of 200 mV/s.

FIG. 8 shows the long cycle performance curve of the supercapacitor made in example 8.

FIG. 9 is a scanning electron microscope photograph of the porous carbon prepared in example 9.

Fig. 10 shows a nitrogen adsorption and desorption curve of the porous carbon prepared in example 9.

FIG. 11 is a scanning electron microscope photograph of the porous carbon prepared in example 10.

Fig. 12 shows a nitrogen adsorption and desorption curve of the porous carbon prepared in example 10.

FIG. 13 shows the constant current charge and discharge curve of the supercapacitor made in example 13 at a current density of 1A/g.

FIG. 14 shows the cyclic voltammogram of the supercapacitor prepared in example 13 at a scan rate of 20 mV/s.

Fig. 15 shows the rate performance curve of the supercapacitor made in example 14.

FIG. 16 shows the long cycle performance curve of the supercapacitor made in example 14.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise. The invention will be further illustrated by the following examples

Example 1:

the embodiment relates to a preparation method of a calcium-modified soluble alginate-based porous carbon precursor, which comprises the following steps:

step one, dissolving 50g of sodium alginate in 3000ml of deionized water, and fully stirring by using an electric stirrer to obtain a sodium alginate aqueous solution.

And step two, dissolving 36g of calcium lactate in 1000ml of deionized water, and manually stirring to obtain a calcium lactate aqueous solution.

Step three, under the conditions that the solution obtained in the step one is stirred electrically at the speed of 2000r/min in a thermostatic water bath at the temperature of 50 ℃, the solution obtained in the step two is slowly added into the solution obtained in the step one, and the solution is kept stirred electrically and heated for 6 hours;

and step four, fully drying and crushing the product obtained in the step three, and sieving the product by using a sieve of 80 meshes to obtain the calcium modified soluble alginate-based porous carbon precursor for the supercapacitor.

Example 2:

And step two, dissolving 18g of calcium lactate in 1000ml of deionized water, and manually stirring to obtain a calcium lactate aqueous solution.

Example 3:

And step two, dissolving 6g of calcium lactate in 1000ml of deionized water, and manually stirring to obtain a calcium lactate aqueous solution.

Example 4:

the present example relates to a method for preparing calcium-modified soluble alginate-based porous carbon, comprising the steps of:

step one, 20g of the precursor prepared in example 1 was weighed, placed in a tube furnace, heated to 600 ℃ at a heating rate of 5 ℃/min, and held at this temperature for 2 h. Nitrogen was used as a shielding gas and the rate of introduction was 1L/min.

And step two, firstly, washing the product obtained in the step one with 20 wt% hydrochloric acid at 80 ℃, then washing the product with deionized water at 80 ℃ to be neutral, and drying the product for 12 hours at 105 ℃.

Step three, weighing 3g of the product obtained in the step two, mixing the product with KOH according to the mass ratio of 1:4, and soaking the product for 5 hours at the temperature of 80 ℃.

And step four, putting the product obtained in the step three into a muffle furnace, raising the temperature to 350 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 30min, and then raising the temperature to 800 ℃ and keeping the temperature for 120 min. The nitrogen gas was introduced at a rate of 0.6L/min.

And step five, washing the product obtained in the step four by using 20 wt% hydrochloric acid at 80 ℃ until the product is neutral, and then washing the product by using deionized water until the product is neutral. And drying the obtained product at 105 ℃ for 12h to obtain the calcium modified soluble alginate-based porous carbon.

FIG. 1 is a scanning electron microscope photograph showing the porous carbon having a loose porous structure, FIG. 2 is a nitrogen adsorption/desorption curve of the porous carbon, and the specific surface area calculated by the BET method is 2732.2m²G, total pore volume of 1.753cm³(ii)/g, the average pore size of mesopores was 3.8nm, the average pore size of micropores was 0.64nm, and the ratio of the specific surface area of mesopores to the specific surface area of micropores was 0.62.

Example 5:

step one, 20g of the precursor prepared in example 2 was weighed, placed in a tube furnace, heated to 600 ℃ at a heating rate of 5 ℃/min, and held at this temperature for 2 h. Nitrogen was used as a shielding gas and the rate of introduction was 1L/min.

Fig. 3 is a scanning electron microscope image of the porous carbon, and the porous carbon prepared by the invention has a three-dimensional communicated porous structure obtained from fig. 3, and the pore channels present the characteristics of reasonable distribution of macropores, mesopores and micropores. The pore size distribution curve of the micropores of the porous carbon is shown in FIG. 4, and it can be seen from FIG. 4 that the pore size distribution of the micropores of the porous carbon prepared by the present invention is relatively concentrated. The implementation effect is as follows: the porous carbon has a specific surface area of 2776.6m calculated by BET method²Per g, total pore volume of 1.723cm³(ii)/g, the average pore size of mesopores was 3.4nm, the average pore size of micropores was 0.64nm, and the ratio of the specific surface area of mesopores to the specific surface area of micropores was 0.94.

Example 6:

step one, 20g of the precursor prepared in example 3 was weighed, placed in a tube furnace, heated to 600 ℃ at a heating rate of 5 ℃/min and held at this temperature for 2 h. Nitrogen was used as a shielding gas and the rate of introduction was 1L/min.

Fig. 5 is a scanning electron microscope image of the porous carbon, and it can be seen from fig. 5 that the porous carbon of the present invention has a relatively uniformly distributed cavity structure inside. Fig. 6 shows an X-ray diffraction pattern of the porous carbon, and it can be obtained from fig. 6 that the porous carbon prepared according to the present invention exhibits characteristics of amorphous carbon. The implementation effect is as follows: the porous carbon has a specific surface area of 2563.5m calculated by BET method²Per g, total pore volume of 1.489cm³(ii)/g, the average pore size of mesopores was 3.4nm, the average pore size of micropores was 0.63nm, and the ratio of the specific surface area of mesopores to the specific surface area of micropores was 0.38.

Example 7:

the embodiment relates to application of porous carbon in an electrode material of an aqueous electrochemical capacitor, which comprises the following steps:

the electrode material for a supercapacitor was prepared by mixing the porous carbon obtained in example 1, acetylene black as a conductive agent, and PTFE as a binder in a mass ratio of 8:1: 1. And (3) coating the electrode material on foamed nickel, drying for 12h at 80 ℃ in vacuum, and pressing for 1min at the pressure of 12MPa by using a tablet press to obtain the electrode sheet. Then 2 electrode sheets and 6mol/L KOH electrolyte are assembled into the super capacitor. Electrochemical performance tests were then performed on the electrochemical workstation. FIG. 7 shows the cyclic voltammogram of the supercapacitor at a scan rate of 200 mV/s. The rectangular shape presented in fig. 7 indicates that the electrochemical capacitor prepared from the porous carbon of the present invention has good charge transport properties.

Example 8:

the electrode material for a supercapacitor was prepared by mixing the porous carbon obtained in example 2 with acetylene black as a conductive agent and PTFE as a binder in a mass ratio of 8:1: 1. And (3) coating the electrode material on foamed nickel, drying for 12h at 80 ℃ in vacuum, and pressing for 1min at the pressure of 12MPa by using a tablet press to obtain the electrode sheet. Then 2 electrode sheets and 6mol/L KOH electrolyte are assembled into the super capacitor. Electrochemical performance tests were then performed on the electrochemical workstation. The long cycle performance curve of the supercapacitor is shown in fig. 8. As can be seen from FIG. 8, the super capacitor of the present invention has a high capacity retention rate, and has a high capacitance value even when the super capacitor is cycled to the range of 4000-.

Example 9:

the embodiment relates to a preparation method of porous carbon for a sodium alginate-based supercapacitor, which comprises the following steps:

step one, weighing 20g of sodium alginate, placing the sodium alginate in a tube furnace, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, and keeping the temperature for 2 h. Nitrogen was used as a shielding gas at a gas rate of 1L/min.

And step two, firstly, washing the product obtained in the step one with 2mol/L hydrochloric acid at 80 ℃ for 2h, then washing the product with 80 ℃ deionized water to be neutral, and drying the product at 105 ℃ for 12 h.

Step four, putting the mixture obtained in the step three into a muffle furnace, raising the temperature to 350 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 30min, and then raising the temperature to 800 ℃ and keeping the temperature for 120 min. The nitrogen gas was introduced at a rate of 0.6L/min.

And step five, washing the product obtained in the step four by using 2mol/L hydrochloric acid at 80 ℃, and then washing the product by using deionized water until the product is neutral. Drying the obtained product at 105 ℃ for 12h to obtain the alginate-based porous carbon.

FIG. 9 shows the porous structureScanning electron microscopy of the carbon from figure 9 it can be seen that the surface of the porous carbon of the present invention exhibits well-etched features. FIG. 10 shows a nitrogen adsorption/desorption curve of the porous carbon, which is obtained from FIG. 10 and has a specific surface area of 2226.3m calculated by the BET method²G, pore volume of 1.28cm³(ii)/g, the average micropore diameter is 0.62nm, the average mesopore diameter is 3.36nm, and the proportion of micropore volume to total pore volume is 0.8.

Example 10:

the example relates to a preparation method of porous carbon for an alginate-based supercapacitor, which comprises the following steps:

step one, weighing 20g of calcium alginate, placing the calcium alginate in a tube furnace, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, and keeping the temperature for 2 h. Nitrogen was used as a shielding gas at a gas rate of 1L/min.

Fig. 11 is a scanning electron microscope image of the porous carbon, and as can be obtained from fig. 11, the porous carbon has a porous structure in which micropores and mesopores are distributed on a macroporous structure. It can be seen that there is a significant difference in microstructure compared to the porous carbon prepared from calcium-modified alginate (see fig. 3 and 5), which is mainly due to the difference in the microstructure of the carbonized sample formed due to the difference in the components in the precursor. FIG. 12 shows a nitrogen adsorption/desorption curve of the porous carbon, which can be obtained from FIG. 12, and the product obtained by the methodThe specific surface area is 2203.8m calculated by the BET method²G, pore volume of 1.24cm³(ii)/g, the average micropore diameter is 0.61nm, the average mesopore diameter is 3.71nm, and the proportion of the micropore volume to the total pore volume is 0.8.

Example 11:

Step three, weighing 3g of the product obtained in the step two, mixing the product with KOH according to the mass ratio of 1:3, and soaking the product for 5 hours at the temperature of 80 ℃.

The implementation effect is as follows: the product has a specific surface area of 1830.0m calculated by a BET method²G, pore volume of 1.20cm³(ii)/g, the average micropore diameter is 0.61nm, the average mesopore diameter is 4.45nm, and the proportion of the micropore volume to the total pore volume is 0.7.

Example 12:

The implementation effect is as follows: the product has a specific surface area of 1807.2m calculated by a BET method²G, pore volume of 1.18cm³(ii)/g, the average micropore diameter is 0.60nm, the average mesopore diameter is 4.82nm, and the proportion of micropore volume to total pore volume is 0.7.

Example 13:

the electrode material for a supercapacitor prepared by mixing the porous carbon prepared in example 9 with the conductive agent and the binder in a mass ratio of 8:1:1 was subjected to a constant current charge-discharge test using 6mol/L KOH as an electrolyte, and the specific capacitance value reached 312.9F/g when the current density was 0.1A/g, and reached 232F/g when the current density was 10A/g. FIG. 13 shows the constant current charging and discharging curve of the super capacitor at a current density of 1A/g, from FIG. 13, the specific capacitance value of 274.1F/g at a current density of 1A/g can be obtained, and the cyclic voltammetry curve of the super capacitor at a scanning rate of 20mV/s shown in FIG. 14 shows that the super capacitor of the present invention has ideal double layer effect as shown by the rectangular shape presented in FIG. 14.

Example 14

An electrode material for a supercapacitor prepared by mixing the porous carbon prepared in the example 10 with a conductive agent and a binder in a mass ratio of 8:1:1, and performing a constant current charge-discharge test by using 6mol/L KOH as an electrolyte, wherein a rate performance curve of the supercapacitor shown in fig. 15 can be obtained from fig. 15, and the specific capacitance value reaches 304.3F/g when the current density is 0.1A/g, can still reach 220.5F/g when the current density is 10A/g, and reaches 125F/g when the current density is 50A/g, which indicates that the supercapacitor has a better rate performance. Fig. 16 shows a long cycle performance curve of the supercapacitor, and it can be seen from fig. 16 that the capacity retention rate reaches 90% or more when the number of cycles is 10000.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for regulating and controlling the pore structure of alginate-based porous carbon is characterized in that: the method comprises the following specific steps:

heating under protective atmosphere after dipping for activation, and washing after activation to obtain alginate-based porous carbon;

the precursor is calcium-modified alginate;

the preparation method of the calcium modified alginate comprises the following steps:

the method comprises the following specific steps: respectively dissolving soluble alginate and soluble calcium salt in water to obtain alginate solution and calcium salt water solution;

adding a calcium salt solution into an alginate solution, and stirring under a heating condition to obtain a solid product, namely a calcium-modified alginate precursor;

the mass ratio of soluble alginate to deionized water in the alginate solution is 1: 40-1: 100;

the mass ratio of soluble calcium salt to deionized water in the calcium salt solution is 1: 25-1: 100;

the mass ratio of the alginate to the soluble calcium salt is 1: 1-12: 1;

by controlling the mixing mass ratio of the alginate to the calcium salt, the porous carbon material with different pore structures can be obtained after carbonization; the pore structure is a structure with three-dimensional distribution of macropores, mesopores and micropores.

2. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the soluble alginate is at least one of sodium alginate, potassium alginate, magnesium alginate and lithium alginate.

3. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: soluble calcium salts include, but are not limited to, one or more of calcium lactate, calcium chloride, calcium nitrate, calcium dihydrogen phosphate, calcium bicarbonate, calcium bisulfate, calcium bisulfite, calcium hypochlorite, calcium bromide, calcium iodide, calcium chlorate, calcium perchlorate, and calcium permanganate.

4. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: and drying the calcium-modified alginate, and then crushing and screening, wherein the screening mesh number is 20-300 meshes.

5. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the activator solution is saturated aqueous solution of activator, the activator is KOH, NaOH, K₂CO₃，H₃PO₄，ZnCl₂One or more of (a).

6. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the impregnation ratio of the carbonized product to the activating agent is 1: 1-1: 5.

7. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the activation process comprises the steps of firstly carrying out low-temperature activation and then carrying out high-temperature activation, wherein the low-temperature activation temperature is 300-400 ℃, the time is 30-50 min, the high-temperature activation temperature is 700-900 ℃, and the time is 60-140 min.

8. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 7, wherein: the low-temperature activation temperature is 350 ℃ and the time is 30min, and the high-temperature activation temperature is 800 ℃ and the time is 120 min.

9. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the temperature of heating carbonization is 500-900 ℃; the heating rate is 1-20 ℃/min.

10. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the protective gas is one or combination of several of nitrogen, helium and argon inert gases, and the flow rate of the protective gas is 0.1-2L/min.

11. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 1, wherein: the washing process is acid washing and then water washing, the acid washing reagent is one or the combination of a plurality of aqueous solutions of hydrochloric acid, nitric acid and hydrofluoric acid, and the concentration of the acid washing reagent is 1 wt% -60 wt%.

12. The method of modulating the pore structure of alginate-based porous carbon as claimed in claim 11, wherein: the pickling temperature is 30-100 ℃, and the pickling time is 120-300 min.