Method for preparing biomass porous carbon for supercapacitor based on Cistanche deserticola and its application

Abstract

The present invention discloses a method for preparing biomass porous carbon for supercapacitors based on Cistanche deserticola residue and its application, belonging to the field of energy. The present invention uses Cistanche deserticola residue as a carbon source and KOH as an activator, adopts a low-temperature pre-activation and high-temperature carbonization method to prepare supercapacitor electrode materials, and characterizes the prepared materials using SEM, BET and other characterization methods. The material has a large number of microporous structures and a specific surface area of ​​2767.2m 2 g ‑1 The above materials were applied to supercapacitor research and the experiment found that at 6 mol L ‑1 In KOH electrolyte, when the current density is 1Ag ‑1 When the specific capacitance reaches 360.26F g ‑1 , even at 100A g ‑1 It can also maintain 193.1F g ‑1 , the capacitance retention rate reached 53.1%.

Description

Technical Field

[0001] The present invention belongs to the field of energy, and in particular relates to a method for preparing biomass porous carbon for supercapacitors based on Cistanche deserticola and application thereof. Background Art

[0002] Carbon-based supercapacitors are one of the most promising energy storage devices due to their high power density, fast charge and discharge rates, good rate performance, and long cycle life. Based on the charge storage mechanism, supercapacitors based on pure carbonaceous electrode materials are called electrochemical double-layer capacitors (EDLCs), which store energy through the physical adsorption-desorption of electrolyte ions at the electrode and electrolyte interface. High specific surface area is an effective strategy to improve the energy storage performance of carbon materials. Carbon materials derived from biomass are considered to be important candidates for electrochemical double-layer capacitor (EDLC) electrode materials. As one of the most abundant renewable resources on Earth, biomass has the advantages of abundant reserves, unique natural structure, low cost, non-toxicity, and environmental friendliness. The abundance of carbon elements, tunable pore structure, and high specific surface area give these biomass-based electrode materials great potential as high-performance carbon-based supercapacitor electrode materials.

[0003] Traditional Chinese medicine (TCM), a special type of biomass, plays an important role in people's lives. It is reported that over 30 million tons of TCM residues are produced annually. However, only a small portion of these residues is recycled as feed and fertilizer, while the majority is still disposed of in traditional ways: by stacking, incineration, or landfill, causing environmental pollution. If TCM residues can be reutilized and treated harmlessly, it would not only protect the environment but also improve resource utilization.

[0004] Cistanche deserticola is a traditional Chinese medicinal herb with both medicinal and edible properties. Its main chemical components are phenylethanoid glycosides, iridoid ether terpenes and their glycosides, sugars, proteins, and amino acids. Companies produce over 200 million bottles of Cistanche deserticola oral liquid annually, requiring 2,300 tons of raw Cistanche deserticola. This production, combined with a large amount of Cistanche deserticola residue, has caused significant environmental pollution. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing biomass porous carbon for supercapacitors based on Cistanche deserticola and its application.

[0006] To achieve the above objectives, the first aspect of the present invention is to provide a method for preparing biomass porous carbon for supercapacitors based on Cistanche deserticola, the technical solution of which comprises the following steps:

[0007] (1) Crush the Cistanche deserticola residue into fine particles and dry them;

[0008] (2) Cistanche deserticola powder was heated under nitrogen flow (5℃min-1 ) for 2 h;

[0009] (3) Mix the activated Cistanche deserticola with KOH (weight ratio 1:3) and ball mill;

[0010] (4) under the protection of inert gas, carbonizing the mixture after ball milling in step (3) at high temperature and cooling it to room temperature to obtain a product;

[0011] (5) The product is repeatedly rinsed with hydrochloric acid solution, then washed with distilled water until neutral, and dried to obtain biomass porous carbon for supercapacitors.

[0012] Furthermore, in step (1), the fine particles have a mesh size of 100 mesh.

[0013] Furthermore, in step (1), the drying temperature is 105°C.

[0014] Furthermore, in step (2), the Cistanche deserticola is pre-activated at 300-400°C for 2h.

[0015] Furthermore, in step (3), the mass ratio of the Cistanche deserticola to KOH is 1:3.

[0016] Furthermore, in step (5), the drying temperature is 80°C.

[0017] Furthermore, the inert gas is nitrogen.

[0018] Furthermore, the high-temperature carbonization is carried out for 2 hours.

[0019] Furthermore, the heating rate is 5°C / min.

[0020] This invention uses Cistanche deserticola residue as a carbon source and KOH as an activator, employing low-temperature preactivation and high-temperature carbonization to prepare an aqueous supercapacitor electrode material with excellent performance. This method utilizes waste raw materials, a simple preparation process, and the resulting porous carbon material has a high specific surface area. As an electrode material, it exhibits a stable structure, high capacity, and stability, achieving resourceful utilization of traditional Chinese medicine residue.

[0021] Therefore, the present invention adopts Cistanche deserticola residue and simple synthesis technology to prepare electrode materials with high specific capacitance and high stability. The preparation process is simple and the cost is low. It not only opens up a new way to convert waste biomass into high-value-added products, but also provides an important solution for reducing environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0023] Figure 1 These are SEM images of Example 1 of the present invention under a 50x microscope and a 10x microscope;

[0024] Figure 2 These are SEM images of Example 2 and Example 3 of the present invention under a 10x microscope;

[0025] Figure 3 This is a SEM image of Comparative Example 1 of the present invention under a 5x microscope;

[0026] Figure 4 This is a SEM image of Comparative Example 2 of the present invention under a 5x microscope;

[0027] Figure 5 are adsorption / desorption isotherms and pore size distribution diagrams of Examples 1, 2, and 3 of the present invention and Comparative Examples 1 and 2;

[0028] Figure 6 1 is the cyclic voltammogram of Examples 1, 2, and 3 of the present invention and Comparative Examples 1 and 2;

[0029] Figure 7 1 is the cyclic voltammogram of Example 1 at different scan rates;

[0030] Figure 8 1 is a constant current charge and discharge diagram of Examples 1, 2, 3 and Comparative Examples 1 and 2;

[0031] Figure 9 1 is a constant current charge and discharge diagram of Example 1 at different current densities;

[0032] Figure 10 is the cyclic stability diagram of Example 1. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0034] Example 1

[0035] (1) Wash the Cistanche deserticola residue, dry it, grind it into fine particles, filter it through a 100-mesh filter, and dry it in an oven at 105°C overnight. The Cistanche deserticola residue described in this embodiment is collected from the residue after extraction from a traditional Chinese medicine factory, or the residue after extraction by boiling it in water three times;

[0036] (2) placing the Cistanche deserticola powder pre-treated in step (1) in a tubular furnace for pre-carbonization under nitrogen flow at a temperature of 350° C. for 2 h at a heating rate of 5° C. / min;

[0037] (3) The pre-carbonized product of step (2) was mixed with KOH (weight ratio 1:3) and ball milled

[0038] (4) using a tubular furnace, carbonizing the mixture after ball milling in step (3) under nitrogen protection at a temperature of 800°C for 2 h at a heating rate of 5°C / min, and then naturally cooling to room temperature;

[0039] (5) The product obtained in step (4) was treated with 1 mol L -1 The product was washed with HCl and deionized water until neutral and dried at 80°C to obtain the product CHC-350-800-3.

[0040] Example 2

[0041] (1) The product of step (1) in Example 1 was pre-carbonized in a tube furnace under nitrogen protection at a temperature of 300°C for 2 h and a heating rate of 5°C / min; the conditions of the remaining steps remained unchanged to obtain the product CHC-300-800-3.

[0042] Example 3

[0043] (1) The product of step (1) in Example 1 was pre-carbonized in a tube furnace under nitrogen protection at a temperature of 400°C for 2 hours at a heating rate of 5°C / min; the remaining steps remained unchanged to obtain the product CHC-400-800-3.

[0044] Comparative Example 1

[0045] The product of step (2) in Example 1 was directly processed according to the methods of steps (4) and (5) in Example 1. This comparative example did not undergo KOH activation treatment to obtain the product CHC-350-800-0.

[0046] Comparative Example 2

[0047] The product of step (1) in Example 1 was mixed with KOH (weight ratio 3:1) and ball-milled to obtain a mixture, and the operation was continued according to the methods of steps (4) and (5) in Example 1. This comparative example did not undergo pre-carbonization treatment to obtain the product CHC-800-3.

[0048] Microscopic characterization:

[0049] Figure 1 For Example 1 (CHC-350-800-3), Figure 2The scanning electron microscope images of Example 2 (CHC-300-800-3) and Example 3 (CHC-400-800-3) show that the combined effects of potassium hydroxide and pre-carbonization completely changed the surface and internal structure of the samples of Examples 1-3. The samples exhibit irregular carbon flakes of varying thicknesses, a rich porous structure, and a loose and fluffy surface.

[0050] Figure 3 This is a scanning electron microscope image of comparative example 1 (CHC-350-800-0). It can be seen from the figure that without potassium hydroxide activation, comparative example 1 has a smooth flaky surface, a compact overall structure, and a sparse pore size.

[0051] Figure 4 This is a scanning electron microscope image of Comparative Example 2 (CHC-800-3). Without pre-carbonization, some holes appear in the material. This is the result of direct reaction of potassium hydroxide and indirect reaction of byproducts with carbon. However, compared to Example 1, the material remains compact and has fewer holes.

[0052] The results show that the combined effect of pre-carbonization and potassium hydroxide has an important influence on the morphology of the obtained porous carbon, which can significantly enhance its surface area and porosity.

[0053] Figure 5 The adsorption / desorption isotherms and pore size distribution diagrams of Example 1 (CHC-350-800-3), Example 2 (CHC-300-800-3), Example 3 (CHC-400-800-3), Comparative Example 1 (CHC-350-800-0), and Comparative Example 2 (CHC-800-3) are shown in Table 1. The specific surface area and pore size data are shown in Table 1.

[0054]

[0055] Table 1 Specific surface area and pore size distribution of five samples

[0056] from Figure 5 As can be seen from Table 1, in Comparative Example 1, when only pre-carbonization was performed without potassium hydroxide activation, the specific surface area of ​​the sample was very low, only 307.9 m 2 g -1 In comparative example 2, only potassium hydroxide activation was used without pre-carbonization, and the specific surface area increased to 1241.5 m 2 g -1 This is due to the direct reaction of potassium hydroxide and the indirect reaction between the by-products and carbon. In contrast, Examples 1-3 have higher N2 adsorption capacity, showing the type I isotherm characteristics of microporous materials. The distribution range of specific surface area is 2269.7~2767.2m 2 g -1, the pore volume range is 1.12~1.43cm 3 g -1 . It shows that pre-carbonization and potassium hydroxide activation have significant advantages in increasing the specific surface area. This is because during the pre-carbonization process, volatile substances can more easily penetrate the sample and volatilize, so a small microporous structure of a certain scale is initially formed in the sample. During the secondary carbonization process, the activator is in complete contact with the carbon material, corroding the material, forming a pore structure, and corroding the tiny structure formed during the pre-carbonization process. Therefore, we conducted a series of experiments at three different pre-carbonization temperatures to screen out the optimal synthesis conditions. As can be seen from Table 1, compared with Examples 2 and 3, the specific surface area of ​​Example 1 (2767.2m 2 / g) and total pore volume (1.4252 cm 3 / g) are the highest. This is because when the pre-carbonization temperature is set to 300℃, the pre-carbonization process is not complete enough. At 400℃, the layered structure cannot withstand such a high temperature and breaks into fragments. The results of scanning electron microscopy also confirmed this result. The above results show that potassium hydroxide activation and appropriate pre-carbonization temperature are conducive to the formation of porous carbon with high specific surface area. A large specific surface area and the presence of micropores are conducive to exposing more active sites and improving the specific capacitance value of the material, because the larger the specific surface area, the more opportunities for electrolyte ions to contact the material, and the presence of micropores is conducive to the migration of electrolyte ions to form an electrochemical double layer.

[0057] Electrochemical performance test:

[0058] Figure 6 The cyclic voltammograms of Example 1 (CHC-350-800-3), Example 2 (CHC-300-800-3), Example 3 (CHC-400-800-3), Comparative Example 1 (CHC-350-800-0), and Comparative Example 2 (CHC-800-3) in a three-electrode system (electrolyte: 6 M KOH) are shown. As can be seen from the figure, the CV plots exhibit a nearly rectangular shape, indicating that the specific capacitance is primarily due to the electric double layer capacitance (EDLC), with Example 1 having the largest rectangular area.

[0059] Figure 7 1 is the cyclic voltammogram of Example 1 at different scan rates. It can be seen that at a high scan rate of 400 mV / s, the curve is still approximately a symmetrical rectangle, indicating that the electrode exhibits ideal electrochemical capacitance behavior.

[0060] Figure 8The constant current charge-discharge graphs (electrolyte: 6M KOH) are shown for Example 1 (CHC-350-800-3), Example 2 (CHC-300-800-3), Example 3 (CHC-400-800-3), Comparative Example 1 (CHC-350-800-0), and Comparative Example 2 (CHC-800-3). The curves exhibit a typical triangular shape, indicating good double-layer capacitance performance. The capacitance values ​​of the five materials are shown in Table 2, with Example 1 having the largest capacitance value.

[0061] Figure 9 1 is a constant current charge-discharge diagram of Example 1 at different current densities. The GCD curve of this material can maintain its shape well, indicating that it has good rate stability. By calculation, at 1A / g, the specific capacitance is 360.26F / g, and when the current density is increased to 100A / g, the specific capacitance value can still be 191.3F / g, and its capacitance retention rate is as high as 53.1%. This shows that this material still has a higher specific capacitance under large current density and has a higher capacitance retention ability.

[0062]

[0063] Table 2 Capacitance values ​​of five samples at different current densities

[0064] Figure 10 The cycling stability of Example 1. The electrode material of Example 1 has good long-term stability and high Coulombic efficiency. -1 In the case of 10,000 charge-discharge cycles, the capacitance of the electrode was maintained at 91.38%.

[0065] Although the present invention has been described with reference to several specific embodiments, it should be understood that the invention is not limited to the specific embodiments disclosed, and the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for preparing biomass porous carbon for supercapacitors based on Cistanche deserticola residue, characterized in that The following steps are involved: (1) Wash the Cistanche deserticola residue, dry it, and grind it into small particles to make Cistanche deserticola powder; (2) Heat the Cistanche deserticola powder at a rate of 5°C min -1 Pre-carbonize under nitrogen flow for 2 h at 300-400 °C; (3) mixing the Cistanche deserticola powder treated in step (2) with KOH in a weight ratio of 1:3 and ball milling to obtain a mixture; (4) Under the protection of inert gas, the mixture of step (3) was carbonized at high temperature and cooled to room temperature. The obtained product was treated with 1 mol L -1 The mixture was washed with HCl and deionized water until neutral, and then dried at 80°C overnight to obtain biomass porous carbon for supercapacitors. In step (1), the mesh size of the Cistanche deserticola powder is 100 mesh; In step (1), the drying temperature is 105°C; The inert gas in step (4) is nitrogen; The high temperature carbonization in step (4) is carried out at 800°C for 2 hours.

2. A biomass porous carbon for supercapacitor prepared by the method according to claim 1.

3. An application of the biomass porous carbon for supercapacitors as claimed in claim 2, characterized in that: The biomass porous carbon for supercapacitors is used as a supercapacitor electrode material.

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