A nitrogen-containing manganese-oxygen enzymatic wood-derived carbonaceous electrode material, and a preparation method and application thereof

Abstract

The application discloses a kind of nitrogen-containing manganese oxygen enzymatic wood-derived carbon electrode materials and preparation method and application thereof, it is related to supercapacitor electrode material technical field.The preparation method includes: wood is treated with enzyme, and enzyme-treated wood is obtained;Enzymatic wood is soaked in urea solution or melamine solution, hydrothermal reaction, drying, and nitrogen-doped enzymatic wood is obtained;The nitrogen-doped enzymatic wood is soaked in potassium permanganate solution, and after drying, pre-carbonization and carbonization are sequentially carried out, and the nitrogen-containing manganese oxygen enzymatic wood-derived carbon electrode material is obtained.The application first prepares carbon material base by enzyme treatment wood, then simultaneously loads nitrogen atom, manganese atom and oxygen atom, increases the wettability of material to electrolyte, avoids the cavity effect caused by poor contact between material and electrolyte to reduce effective specific surface area, to improve the pore structure, specific surface area, specific capacitance, conductivity and energy density of supercapacitor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of supercapacitor electrode materials, in particular to a nitrogen-containing manganese oxide enzyme-degraded wood-derived carbon electrode material and a preparation method and application thereof. BACKGROUND

[0002] Supercapacitors, as a kind of energy storage device that can be quickly charged and discharged, have always been characterized by high power density and ultra-long cycle stability, while the lower energy density and higher cost limit its application scenarios. Therefore, it is necessary to reduce the production cost and improve the energy density. In order to reduce the cost and realize sustainable development, researchers have increasingly paid attention to the use of environmentally friendly wood-derived carbon materials to prepare supercapacitor electrodes. Wood, as a widely available renewable resource, provides high specific surface area and abundant pores for derived carbon materials due to its natural three-dimensional pore structure, and the integrated structure enables it to be used as a self-supporting thick electrode without the need for adhesives. In addition, the mature wood processing technology also significantly reduces the production cost of the material. Whether it is physical method or acid-base method to activate wood, or use carbon nanotubes, graphene oxide, MXene and other high-conductivity materials to construct composite electrode materials with wood, or use fungi to treat wood. All of these are to design an electrode structure with good pore distribution and improve the electrical conductivity of the material to reduce the internal resistance and achieve fast ion transfer.

[0003] However, these methods have more or less some defects, acid-base treatment method is efficient but easy to corrode processing equipment, MXene, carbon nanotube, graphene oxide and other high-conductivity materials are easy to form self-stacking, causing material waste, and may cause the shedding of the loaded material during rapid cycling. Although the biological treatment method has the advantage of environmental friendliness in the modification of biomass carbon materials, its long production cycle, complex operation process and strict culture conditions limit its large-scale commercial application. Therefore, it is urgent to develop a new wood modification technology for preparing supercapacitor electrode materials - such a technology not only needs to effectively optimize the pore structure of wood and reduce environmental risks, but also should have a reasonable production cycle, high energy density and excellent cycle stability. SUMMARY

[0004] The purpose of the present application is to provide a nitrogen-containing manganese oxide enzyme-degraded wood-derived carbon electrode material and a preparation method and application thereof to solve the problems existing in the prior art.

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

[0006] One of the technical solutions of the present application: a preparation method of a nitrogen-containing manganese oxide enzyme-degraded wood-derived carbon electrode material, comprising the following steps:

[0007] The wood is subjected to enzyme treatment to obtain enzymatic hydrolysis wood; the enzymatic hydrolysis wood is soaked in a urea solution or a melamine solution, subjected to hydrothermal reaction, dried to obtain nitrogen-doped enzymatic hydrolysis wood; the nitrogen-doped enzymatic hydrolysis wood is soaked in a potassium permanganate solution, dried, and then subjected to pre-carbonization and carbonization in sequence to obtain the nitrogen-containing manganese-oxygen enzymatic hydrolysis wood-derived carbonaceous electrode material.

[0008] The present application first prepares a carbon material substrate by enzyme treatment of wood, and then simultaneously loads nitrogen atoms, manganese atoms and oxygen atoms, increases the wettability of the material to the electrolyte, avoids poor contact between the material and the electrolyte to form a cavity effect to reduce the effective specific surface area, and improves the pore structure, specific surface area, specific capacitance, conductivity and energy density of the supercapacitor. Specifically, by using the high specificity and catalytic nature of enzyme chemical reaction, part of cellulose, hemicellulose or lignin in wood is effectively hydrolyzed in a directional manner under mild and environmentally friendly treatment conditions, while the 3D structure of wood is retained to construct more ion transmission channels. Between the channels with low bending degree, a hierarchical interconnected porous structure with rich mesopores and micropores is formed, which is very advantageous for use as a thick electrode of a supercapacitor with high specific surface area and volumetric energy density. The introduction of nitrogen elements using urea or melamine can increase the number of hydrophilic functional groups on the material surface, improve the surface wettability, increase the accessibility of the electrolyte, and prevent the occurrence of a cavity between the electrode material and the electrolyte to reduce the effective surface area of the electrode material. And by loading MnO on the surface of the biomass material through pyrolysis of potassium permanganate at high temperature to enhance the conductivity of the material, the ion transmission rate is significantly increased.

[0009] The present application is a convenient, effective and fast method for preparing biomass carbon materials by enzyme-assisted conversion of cellulose biomass materials and loading of appropriate amounts of active substances, which can effectively produce low-cost, high-porosity and high-specific-surface-area carbonaceous electrode materials, and further improve the specific surface area, specific capacitance, conductivity and energy density.

[0010] Further, the step of enzyme treatment comprises: adding enzymes and pretreated wood in acetic acid-sodium acetate buffer, and culturing at 45-55℃ for 20-30h.

[0011] Further, the enzymes include cellulase, hemicellulase or laccase (which can degrade lignin).

[0012] Wood is mainly composed of three elements, namely cellulose, hemicellulose and lignin, and the three enzymes are selected for enzyme treatment to directionally strip the three elements of wood to improve the performance of wood.

[0013] Further, the mass ratio of the enzymes to the pretreated wood is 1:5-10.

[0014] Further, the preparation step of the acetic acid-sodium acetate buffer solution comprises: adjusting the pH value of the sodium acetate solution to 4.5-5.5 by using acetic acid to obtain the acetic acid-sodium acetate buffer solution.

[0015] Different enzymes have their optimum temperature and pH value, and the enzyme activity will greatly decrease or even directly inactivate when the temperature or pH value is higher or lower than this interval, so configuring a buffer solution with a suitable pH value before treatment can ensure that the enzyme treatment is effective and efficient. Common cellulase is acid cellulase produced by Trichoderma reesei, hemicellulase is acid hemicellulase from Aspergillus niger, and laccase is laccase from white rot fungi, and the intersection of their optimum temperature and pH value is pH value 4.5-5.5 and temperature 45-55℃, and the enzyme hydrolysis efficiency will greatly decrease when the temperature or pH value is higher or lower than this range.

[0016] Further, the concentration of the sodium acetate solution is 0.2-0.3 mol / L.

[0017] Further, the mass ratio of the acetic acid-sodium acetate buffer solution to the enzyme is 1000:3-10.

[0018] Optionally, after the culture is completed, the method further comprises a step of rinsing to remove residual enzyme and buffer solution.

[0019] Further, the concentration of the urea solution is 0.1-0.5 mol / L.

[0020] Further, the concentration of the melamine solution is 0.1-0.5 mol / L.

[0021] Further, the temperature of the hydrothermal reaction is 85-105℃, and the time is 4-8h.

[0022] Further, the concentration of the potassium permanganate solution is 0.05-0.15 mol / L, and the soaking treatment time in the potassium permanganate solution is 1-3h.

[0023] Further, the temperature of the pre-carbonization is 400-600℃, and the time is 1.5-3h.

[0024] Further, the temperature of the carbonization is 750-850℃, and the time is 1.5-2.5h.

[0025] Pre-carbonization before carbonization can avoid the bending of the enzyme hydrolysis wood-derived carbonaceous electrode material due to the too fast heating rate, which causes the material to be unable to be assembled or broken during the assembly process when preparing the electrode material.

[0026] Further, the pretreatment comprises: cutting, cleaning and drying the wood.

[0027] Further, the cutting is specifically cutting the wood into wood pieces with a thickness of 1-3 mm along the natural growth direction.

[0028] Further, the cleaning includes: after being immersed in water for 6-12 h, using a large amount of water to wash to remove the dust and water-soluble impurities on the surface of the wood.

[0029] Optionally, the wood includes but is not limited to Paulownia wood, fir wood, larch, Chinese toon, elm or cypress.

[0030] Optionally, the pre-carbonization temperature rising rate is 3-8 ℃ / min, and the carbonization temperature rising rate is 3-5 ℃ / min.

[0031] Optionally, after the carbonization, the method further includes the steps of cleaning and drying.

[0032] Optionally, the drying temperature is 50-70 ℃.

[0033] The second technical scheme of the present application is a nitrogen-containing manganese-oxygen enzyme-decomposed wood-derived carbon electrode material prepared by the above preparation method.

[0034] The third technical scheme of the present application is an application of the above nitrogen-containing manganese-oxygen enzyme-decomposed wood-derived carbon electrode material in preparing a super capacitor.

[0035] The present application discloses the following technical effects:

[0036] (1) The present application uses enzymes (cellulase, hemicellulase or laccase) to treat wood as a carbon base. The green enzymatic reaction optimizes the pore structure of the wood under mild conditions, while retaining the basic skeleton of the wood and significantly increasing the specific surface area of the material, thereby increasing the specific capacitance of the electrode material and providing more attachable sites for nitrogen, manganese and oxygen atoms.

[0037] (2) The present application improves the functional group composition of the surface of the enzyme-decomposed wood-derived carbon material by loading nitrogen elements. The hydrothermal method can uniformly and effectively load a large amount of nitrogen elements on the carbon material, greatly improving the wettability of the material surface and being beneficial to the subsequent loading of manganese and oxygen.

[0038] (3) The present application soaks potassium permanganate on uncarbonized wood, carbonizes and activates, loads manganese and oxygen elements while carbonizing the wood, and the in-situ generated manganese and oxygen atoms can be more firmly attached to the carbon skeleton, effectively avoiding the decrease of the material cycle stability caused by the falling of the loaded materials.

[0039] (4) The preparation process of the present application is simple, the raw materials are abundant, and the raw materials and processing activation cost are low, having the advantages of low cost, green and fast. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments will be briefly introduced. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative work based on these drawings.

[0041] Figure 1 Scanning electron microscope images of the Paulownia wood without any treatment in Example 1 ((a)-(b)), scanning electron microscope images of the enzymatic wood ((c)-(d)), scanning electron microscope images of the finally prepared carbonaceous electrode material ((e)-(h)), and element mapping images of the finally prepared carbonaceous electrode material ((i)-(l)).

[0042] Figure 2 Actual photos of the carbonaceous electrode materials prepared in Example 1 (left) and Comparative Example 9 (right).

[0043] Figure 3 XPS (N 1s) spectrum of the carbonaceous electrode material prepared in Example 1.

[0044] Figure 4 XPS (N 1s) spectrum of the carbonaceous electrode material prepared in Example 2.

[0045] Figure 5 XPS (Mn 2p) spectrum of the carbonaceous electrode material prepared in Example 1.

[0046] Figure 6 XPS (Mn 2p) spectrum of the carbonaceous electrode material prepared in Example 2.

[0047] Figure 7 XPS (O 1s) spectrum of the carbonaceous electrode material prepared in Example 1.

[0048] Figure 8 XPS (O 1s) spectrum of the carbonaceous electrode material prepared in Example 2.

[0049] Figure 9 XRD spectrum of the carbonaceous electrode materials prepared in Example 1, Example 2 and Comparative Example 1.

[0050] Figure 10 Raman spectrum of the carbonaceous electrode materials prepared in Example 1, Example 2 and Comparative Example 1.

[0051] Figure 11 Pore size distribution graph of the carbonaceous electrode materials prepared in Example 1 and Comparative Example 1.

[0052] Figure 12Pore size distribution of the carbonaceous electrode material prepared for Example 2 and Comparative Example 1.

[0053] Figure 13 Cyclic voltammogram of the alkaline supercapacitor assembled using the carbonaceous electrode material prepared for Example 1.

[0054] Figure 14 Galvanostatic charge-discharge plot of the alkaline supercapacitor assembled using the carbonaceous electrode material prepared for Example 1.

[0055] Figure 15 Cyclic voltammogram of the neutral supercapacitor assembled using the carbonaceous electrode material prepared for Example 1.

[0056] Figure 16 Galvanostatic charge-discharge plot of the neutral supercapacitor assembled using the carbonaceous electrode material prepared for Example 1. DETAILED DESCRIPTION

[0057] Various illustrative embodiments of the present application are now described in detail below. The description made herein is not to be construed as limiting the present application, but rather merely as describing certain aspects, features, and embodiments of the present application.

[0058] It should be understood that the terms used herein are merely descriptive, but that the application should not be construed as being limited thereto. In addition, with respect to numerical ranges recited in the present application, it is contemplated that every numerical value, including any intermediate value and any other stated value, within that range is specifically and explicitly disclosed. Each stated value within any stated range and any other stated value, and any smaller range that falls within the larger stated range, are all specifically and explicitly disclosed. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0059] Unless otherwise defined, 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 application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not construed as an admission that it is prior art with respect to the present application.

[0060] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof, and it is to be understood that all such modifications and variations warrant the patentable subject matter under the patent laws. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only. It is to be understood that the application is not limited in any way by the specific details of that specification.

[0061] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0062] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0063] In the following embodiments and comparative examples of the present invention, room temperature refers specifically to 20-30°C.

[0064] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of this invention are commercially available products. Paulownia wood was sourced from Heze, Shandong; Chinese fir from Sanming, Fujian; larch from Tonghua, Jilin; Chinese toon and elm from Shijiazhuang, Hebei; and cypress from Yichang, Hubei. Cellulase (derived from *Trichoderma reesei*, enzyme activity 10000 U / g) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; anhydrous zinc acetate (purity 99.99%), anhydrous cobalt acetate (purity 98%), laccase (derived from *Trametes versicolor*, enzyme activity 0.5 U / mg), hemicellulase (derived from *Aspergillus niger*, enzyme activity 5 U / mg), and pectinase (derived from *Aspergillus niger*, enzyme activity 30000 U / g) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; potassium permanganate (KMnO4, Sodium acetate (CH3COONa, 99%) and urea (CO(NH2)2, 99%), potassium hydroxide (KOH, 85%), and acetic acid (CH3COOH, 99%) were purchased from China National Pharmaceutical Group Co., Ltd.; all chemicals and reagents were used as is upon receipt without further purification, and deionized water was used as the solvent for preparing solutions.

[0065] Example 1

[0066] A method for preparing a nitrogen-, manganese-, and oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material, comprising the following steps:

[0067] (1) Cut the paulownia wood into 20mm×20mm×2mm wood chips along the natural growth direction, soak them in deionized water for 6 hours, and then rinse them with a large amount of deionized water to remove floating dust and water-soluble impurities on the surface of the wood chips. Then, vacuum dry the wood at 60℃ for 24 hours to obtain the pretreated wood.

[0068] (2) A 0.22 mol / L sodium acetate solution was prepared, and the pH value was adjusted to 4.6 using acetic acid to obtain an acetic acid-sodium acetate buffer solution. The prepared buffer solution, cellulase, and pretreated wood (the pretreated wood was dried Paulownia wood chips, the mass ratio of cellulase to Paulownia wood chips was 1:6, and the mass ratio of the buffer solution to cellulase was 1000:5, wherein the cellulase was 0.1 g, and the Paulownia wood chips were completely immersed in the buffer solution) were added to a flask, which was sealed with plastic wrap and incubated at 50°C for 24 h. Subsequently, the Paulownia wood chips were washed with a large amount of deionized water to remove the residual enzyme and buffer solution, and the enzyme-treated wood (i.e., the enzymatic wood) was obtained.

[0069] (3) The enzymatic wood was immersed in a 0.1 mol / L urea solution, and then placed in a hydrothermal reactor at 95°C for 6 h. Subsequently, the sample was vacuum dried at 60°C for 24 h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was immersed in a 0.1 mol / L KMnO4 solution for 1.5 h, vacuum dried at 60°C for 24 h, and then placed in a tube furnace under a nitrogen atmosphere. The temperature was increased to 500°C at a rate of 5°C / min, and the sample was held at this temperature for 2 h for pre-carbonization. Subsequently, the temperature was increased to 800°C at a rate of 5°C / min, and the sample was held at this temperature for 2 h for carbonization. After removal, the residual KMnO4 was washed away using a large amount of deionized water, and the sample was vacuum dried at 60°C for 24 h to obtain a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material.

[0070] Example 2

[0071] A method for preparing a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material, the steps of which are as follows:

[0072] (1) The Paulownia wood was cut into wood chips with a size of 20 mm x 20 mm x 2 mm along the natural growth direction. The wood chips were immersed in deionized water for 10 h, and then washed with a large amount of deionized water to remove surface dust and water-soluble impurities. Subsequently, the wood was vacuum dried at 65°C for 24 h to obtain pretreated wood.

[0073] (2) A 0.25 mol / L sodium acetate solution was prepared, and the pH value was adjusted to 5.0 using acetic acid to obtain an acetic acid-sodium acetate buffer solution. The prepared buffer solution, laccase, and pretreated wood (i.e., dried Paulownia wood chips, the mass ratio of laccase to Paulownia wood chips was 1:6, and the mass ratio of the buffer solution to laccase was 1000:5, wherein the laccase was 0.1 g, and the Paulownia wood chips were completely immersed in the buffer solution) were added to a flask, which was sealed with plastic wrap and incubated at 60°C for 24 h. Subsequently, the Paulownia wood chips were washed with a large amount of deionized water to remove the residual enzyme and buffer solution, and the enzyme-treated wood (i.e., the enzymatic wood) was obtained.

[0074] (3) The enzymatic wood was soaked in 0.2 mol / L urea solution, and then placed in a hydrothermal reactor at 90°C for 8 h, and then vacuum dried at 60°C for 24 h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was soaked in 0.15 mol / L KMnO4 solution for 1.5 h, vacuum dried at 60°C for 24 h again, and then placed in a tube furnace under a nitrogen atmosphere, heated to 600°C at a heating rate of 3°C / min, and held for 2.5 h for pre-carbonization, and then heated to 800°C at a heating rate of 3°C / min and held for 1.5 h for carbonization. After taking out, the residual KMnO4 was washed away with a large amount of deionized water, vacuum dried at 60°C for 24 h, and then a nitrogen-containing manganese oxide-containing enzymatic wood-derived carbonaceous electrode material was obtained.

[0075] Example 3

[0076] A method for preparing a nitrogen-containing manganese oxide-containing enzymatic wood-derived carbonaceous electrode material, the steps are as follows:

[0077] (1) The Chinese fir was cut into wood chips of 20 mm x 20 mm x 1.5 mm along the natural growth direction, soaked in deionized water for 6 h, and then washed with a large amount of deionized water to remove dust and water-soluble impurities on the surface of the wood chips, and then vacuum dried at 60°C for 24 h to obtain pretreated wood.

[0078] (2) A 0.3 mol / L sodium acetate solution was prepared, and the pH value was adjusted to 4.6 with acetic acid to obtain an acetic acid-sodium acetate buffer solution. The prepared buffer solution, cellulase and pretreated wood (i.e. dried Chinese fir chips, the mass ratio of cellulase to Chinese fir chips was 1:8, and the mass ratio of buffer solution to cellulase was 1000:7, wherein the cellulase was 0.1 g, and the Chinese fir chips were completely immersed in the buffer solution) were added to a conical flask, sealed with plastic wrap, and incubated at 50°C for 24 h. Then the Chinese fir chips were washed with a large amount of deionized water to remove residual enzymes and buffer solution, and then an enzyme-treated wood (i.e. enzymatic wood) was obtained.

[0079] (3) The enzymatic wood was soaked in 0.4 mol / L urea solution, and then placed in a hydrothermal reactor at 105°C for 5 h, and then vacuum dried at 60°C for 24 h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was soaked in 0.08 mol / L KMnO4 solution for 1 h, vacuum dried at 60°C for 24 h again, and then placed in a tube furnace under a nitrogen atmosphere, heated to 550°C at a heating rate of 5°C / min, and held for 2 h for pre-carbonization, and then heated to 750°C at a heating rate of 5°C / min and held for 2.5 h for carbonization. After taking out, the residual KMnO4 was washed away with a large amount of deionized water, vacuum dried at 60°C for 24 h, and then a nitrogen-containing manganese oxide-containing enzymatic wood-derived carbonaceous electrode material was obtained.

[0080] Example 4

[0081] A method for preparing a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material, comprising the following steps:

[0082] (1) Cutting the larch along the natural growth direction into wood pieces of 30 mm x 30 mm x 3 mm, immersing in deionized water for 6 h, then washing with a large amount of deionized water to remove the dust and water-soluble impurities on the surface of the wood pieces, and then vacuum drying the wood at 55°C for 24 h to obtain pretreated wood.

[0083] (2) Preparing an acetic acid-sodium acetate buffer by configuring a 0.2 mol / L sodium acetate solution and adjusting the pH value of the solution to 4.6 with acetic acid, and then preparing the buffer, cellulase and pretreated wood (i.e. dried larch wood pieces, the mass ratio of cellulase to larch wood pieces is 1:7, and the mass ratio of buffer to cellulase is 1000:10, wherein the cellulase is 0.1 g, and the larch wood pieces are completely immersed in the buffer) in a flask, sealing with plastic wrap and culturing at 50°C for 24 h. Then washing the larch wood pieces with a large amount of deionized water to remove the residual enzyme and buffer, to obtain enzyme-treated wood (i.e. enzymatic wood).

[0084] (3) Immersing the enzymatic wood in a 0.1 mol / L urea solution, then placing it in a hydrothermal reactor at 85°C for 8 h of hydrothermal reaction, and then vacuum drying at 55°C for 24 h to obtain nitrogen-doped enzymatic wood. Immersing the nitrogen-doped enzymatic wood in a 0.15 mol / L KMnO4 solution for 3 h, vacuum drying at 55°C for 24 h again, and then placing it in a tube furnace under a nitrogen atmosphere, heating to 400°C at a heating rate of 8°C / min, holding for 1.5 h of pre-carbonization, and then heating to 800°C at a heating rate of 5°C / min, holding for 2.5 h of carbonization. After taking out, washing the residual KMnO4 with a large amount of deionized water, and vacuum drying at 55°C for 24 h, a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material is obtained.

[0085] Example 5

[0086] A method for preparing a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material, comprising the following steps:

[0087] (1) Cutting the Japanese toona along the natural growth direction into wood pieces of 15 mm x 15 mm x 0.2 mm, immersing in deionized water for 10 h, then washing with a large amount of deionized water to remove the dust and water-soluble impurities on the surface of the wood pieces, and then vacuum drying the wood at 70°C for 24 h to obtain pretreated wood.

[0088] (2) A 0.28 mol / L sodium acetate solution was prepared and the pH value was adjusted to 4.6 using acetic acid to obtain an acetic acid-sodium acetate buffer solution. The prepared buffer solution, cellulase and pretreated wood (i.e. dried Chinese toon wood chips, the mass ratio of cellulase to Chinese toon wood chips was 1:10, and the mass ratio of buffer solution to cellulase was 1000:3, wherein the cellulase was 0.1 g, and the Chinese toon wood chips were completely immersed in the buffer solution) were added to a flask, which was sealed with plastic wrap and incubated at 50°C for 24 h. Subsequently, the Chinese toon wood chips were washed with a large amount of deionized water to remove the residual enzyme and buffer solution, thereby obtaining enzyme-treated wood (i.e. enzymatic wood).

[0089] (3) The enzymatic wood was immersed in a 0.5 mol / L melamine solution, and then placed in a hydrothermal reactor at 105°C for 8 h. Subsequently, the sample was vacuum dried at 70°C for 24 h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was immersed in a 0.15 mol / L KMnO4 solution for 3 h, and then vacuum dried at 70°C for 24 h. The sample was placed in a tube furnace and heated to 400°C at a heating rate of 8°C / min under a nitrogen atmosphere for 1.5 h. Subsequently, the sample was heated to 790°C at a heating rate of 3°C / min and maintained for 1.5 h. After removal, the residual KMnO4 was washed away using a large amount of deionized water, and the sample was vacuum dried at 70°C for 24 h to obtain a nitrogen-containing manganese-oxygen enzymatic wood-derived carbon electrode material.

[0090] Example 6

[0091] A method for preparing a nitrogen-containing manganese-oxygen enzymatic wood-derived carbon electrode material, comprising the following steps:

[0092] (1) Chinese toon was cut into wood chips with a size of 20 mm x 20 mm x 2.5 mm along the natural growth direction. The wood chips were immersed in deionized water for 6 h, and then washed with a large amount of deionized water to remove surface dust and water-soluble impurities. Subsequently, the wood was vacuum dried at 65°C for 24 h to obtain pretreated wood.

[0093] (2) A 0.2 mol / L sodium acetate solution was prepared and the pH value was adjusted to 4.8 using acetic acid to obtain an acetic acid-sodium acetate buffer solution. The prepared buffer solution, hemicellulase and pretreated wood (i.e. dried Chinese toon wood chips, the mass ratio of hemicellulase to Chinese toon wood chips was 1:5, and the mass ratio of buffer solution to hemicellulase was 1000:5, wherein the hemicellulase was 0.1 g, and the Chinese toon wood chips were completely immersed in the buffer solution) were added to a flask, which was sealed with plastic wrap and incubated at 45°C for 24 h. Subsequently, the Chinese toon wood chips were washed with a large amount of deionized water to remove the residual enzyme and buffer solution, thereby obtaining enzyme-treated wood (i.e. enzymatic wood).

[0094] (3) The enzymatic wood was soaked in 0.1 mol / L urea solution, and then placed in a hydrothermal reactor at 85°C for 7h, and then vacuum dried at 65°C for 24h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was soaked in 0.12 mol / L KMnO4 solution for 1.5h, vacuum dried at 65°C for 24h again, and then placed in a tube furnace under nitrogen atmosphere, heated to 500°C at a heating rate of 5°C / min, and held for 2h for pre-carbonization, and then heated to 800°C at a heating rate of 3°C / min, and held for 2h for carbonization. After taking out, a large amount of deionized water was used to wash away the residual KMnO4, and vacuum dried at 65°C for 24h to obtain nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material.

[0095] Example 7

[0096] A method for preparing a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material, the steps are as follows:

[0097] (1) Elm was cut into wood chips of 15mm x 15mm x 1mm along the natural growth direction, soaked in deionized water for 6h, and then washed with a large amount of deionized water to remove dust and water-soluble impurities on the surface of the wood chips, and then the wood was vacuum dried at 60°C for 24h to obtain pretreated wood.

[0098] (2) A 0.22 mol / L sodium acetate solution was prepared, and the pH value was adjusted to 5.2 using acetic acid to obtain an acetic acid-sodium acetate buffer solution. A conical flask was added with the prepared buffer solution, hemicellulase and pretreated wood (i.e. dried elm chips, the mass ratio of hemicellulase to elm chips was 1:7, and the mass ratio of buffer solution to hemicellulase was 1000:3.5, wherein the hemicellulase was 0.1g, and the elm chips were completely immersed in the buffer solution), and the conical flask was sealed with plastic wrap and incubated at 45°C for 24h. Then the elm chips were washed with a large amount of deionized water to remove residual enzymes and buffer solution to obtain enzyme-treated wood (i.e. enzymatic wood).

[0099] (3) The enzymatic wood was soaked in 0.1 mol / L urea solution, and then placed in a hydrothermal reactor at 95°C for 6h, and then vacuum dried at 60°C for 24h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was soaked in 0.1 mol / L KMnO4 solution for 1.5h, vacuum dried at 60°C for 24h again, and then placed in a tube furnace under nitrogen atmosphere, heated to 500°C at a heating rate of 5°C / min, and held for 2h for pre-carbonization, and then heated to 800°C at a heating rate of 3°C / min, and held for 2h for carbonization. After taking out, a large amount of deionized water was used to wash away the residual KMnO4, and vacuum dried at 60°C for 24h to obtain nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material.

[0100] Example 8

[0101] A method for preparing a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material, comprising the following steps:

[0102] (1) Cypress was cut along the natural growth direction into wood chips with a size of 30 mm x 30 mm x 1.5 mm, and then immersed in deionized water for 6 h. The wood chips were then washed with a large amount of deionized water to remove the dust and water-soluble impurities on the surface of the wood chips, and then dried at 60°C under vacuum for 24 h to obtain pretreated wood.

[0103] (2) A 0.25 mol / L sodium acetate solution was prepared, and the pH value of the solution was adjusted to 4.6 using acetic acid to obtain an acetic acid-sodium acetate buffer solution. The prepared buffer solution, laccase and pretreated wood (i.e. dried cypress wood chips, the mass ratio of laccase to cypress wood chips was 1:10, and the mass ratio of buffer solution to laccase was 1000:5, wherein the laccase was 0.1 g, and the cypress wood chips were completely immersed in the buffer solution) were added into a flask, which was then sealed with plastic wrap and incubated at 55°C for 24 h. Then the cypress wood chips were washed with a large amount of deionized water to remove the residual enzyme and buffer solution, and the enzyme-treated wood (i.e. enzymatic wood) was obtained.

[0104] (3) The enzymatic wood was immersed in a 0.4 mol / L urea solution, and then placed in a hydrothermal reactor at 100°C for 5 h. The sample was then dried at 60°C under vacuum for 24 h to obtain nitrogen-doped enzymatic wood. The nitrogen-doped enzymatic wood was immersed in a 0.15 mol / L KMnO4 solution for 1 h, and then dried at 60°C under vacuum for 24 h. The sample was then placed in a tube furnace and heated to 420°C at a heating rate of 3°C / min under a nitrogen atmosphere, and then held at 420°C for 2.5 h. The sample was then heated to 850°C at a heating rate of 5°C / min, and then held at 850°C for 2 h. The sample was then removed and washed with a large amount of deionized water to remove the residual KMnO4. The sample was then dried at 60°C under vacuum for 24 h to obtain a nitrogen-manganese-oxygen-containing enzymatic wood-derived carbonaceous electrode material.

[0105] Example 9

[0106] The same as Example 1, except that in step (3), the urea solution was replaced with an equimolar concentration of a melamine solution.

[0107] Comparative Example 1

[0108] This comparative example was a blank control of Example 1. In step (2), no cellulase was added to the buffer solution. In step (3), both the urea solution and the potassium permanganate solution were replaced with deionized water. The other conditions were the same as those in Example 1.

[0109] Comparative Example 2

[0110] The same as Example 1, except that in step (2), the cellulase was replaced with an equal amount of pectinase.

[0111] Comparative Example 3

[0112] The same as Example 1, except that no cellulase was added in the buffer in step (2).

[0113] Comparative Example 4

[0114] The same as Example 1, except that the potassium permanganate solution was replaced by deionized water in step (3).

[0115] Comparative Example 5

[0116] The same as Example 1, except that the urea solution was replaced by deionized water in step (3).

[0117] Comparative Example 6

[0118] The same as Example 1, except that both the urea solution and the potassium permanganate solution were replaced by deionized water in step (3).

[0119] Comparative Example 7

[0120] The same as Example 1, except that the potassium permanganate solution was replaced by an equimolar cobalt acetate solution in step (3).

[0121] Comparative Example 8

[0122] The same as Example 1, except that the potassium permanganate solution was replaced by an equimolar zinc acetate solution in step (3).

[0123] Comparative Example 9

[0124] The same as Example 1, except that no pre-carbonization was performed in the carbonization process in step (3), and the temperature was directly increased to 800°C at a rate of 5°C / min, and then carbonized for 2h.

[0125] Test Example 1

[0126] Characterization data:

[0127] Figure 1 Scanning electron microscope images of the Paulownia wood without any treatment in Example 1 ((a)-(b)), the enzymatic wood ((c)-(d)), the nitrogen and manganese oxide-containing enzymatic wood-derived carbonaceous electrode material finally prepared ((e)-(h)), and the element mapping of the nitrogen and manganese oxide-containing enzymatic wood-derived carbonaceous electrode material finally prepared ((i)-(l)).

[0128] Figure 2 Actual photos of the carbonaceous electrode materials prepared in Example 1 (left) and Comparative Example 9 (right).

[0129] From Figure 1As can be seen in the scanning electron microscope images in FIGS. 1A-1B, untreated Paulownia wood has a loose structure, large pore size, thin and smooth cell wall, making it lighter than most wood materials, but also resulting in a low specific surface area. Figure 1 After cellulase treatment, the Paulownia wood in FIGS. 2A-2B becomes more rough, with slight collapse of the pore structure, partial stacking inside the pores, and complex three-dimensional networks formed by the collapsed and broken fiber tissues, greatly increasing the number of mesopores and micropores, and thus increasing the specific surface area. Figure 1 After cellulase treatment, the Paulownia wood in FIGS. 2A-2B becomes more rough, with slight collapse of the pore structure, partial stacking inside the pores, and complex three-dimensional networks formed by the collapsed and broken fiber tissues, greatly increasing the number of mesopores and micropores, and thus increasing the specific surface area. Figure 1 After cellulase treatment, the Paulownia wood in FIGS. 2A-2B becomes more rough, with slight collapse of the pore structure, partial stacking inside the pores, and complex three-dimensional networks formed by the collapsed and broken fiber tissues, greatly increasing the number of mesopores and micropores, and thus increasing the specific surface area. Figure 1 As can be seen in the element mapping images in FIGS. 3A-3D, the manganese element is uniformly loaded, while the carbon, oxygen, and nitrogen elements are also present. Figure 1 As can be seen in the element mapping images in FIGS. 3A-3D, the manganese element is uniformly loaded, while the carbon, oxygen, and nitrogen elements are also present. Figure 2 The carbonaceous electrode physical images in FIGS. 4A-4B show the difference between pre-carbonization and direct carbonization. Pre-carbonization allows the carbon material to gradually adapt to the high-temperature carbonization process, greatly reducing the curvature change of the material during the subsequent carbonization process. The direct carbonization method causes the carbon material to undergo severe bending deformation, making it almost impossible to serve as a self-supporting integrated electrode material.

[0130] Other characterization data is as follows:

[0131] Figure 3 and Figure 4 are XPS (N 1s) spectra of the carbonaceous electrode materials prepared in Example 1 and Example 2, respectively.

[0132] Figure 5 and Figure 6 are XPS (Mn 2p) spectra of the carbonaceous electrode materials prepared in Example 1 and Example 2, respectively.

[0133] Figure 7 and Figure 8 are XPS (O 1s) spectra of the carbonaceous electrode materials prepared in Example 1 and Example 2, respectively.

[0134] Figure 9 is an XRD spectrum of the carbonaceous electrode materials prepared in Example 1, Example 2, and Comparative Example 1.

[0135] Figure 10 is a Raman spectrum of the carbonaceous electrode materials prepared in Example 1, Example 2, and Comparative Example 1.

[0136] XPS (N 1s) spectra showed four nitrogen configurations of the doped nitrogen-containing functional groups: pyridine nitrogen (397.9 eV), pyrrole nitrogen (399.7 eV), graphite nitrogen (401.8 eV) and oxidized nitrogen (406.4 eV); XPS (Mn 2p) spectra clearly showed the presence of Mn, which could be fitted into double peaks at 642.1 eV (Mn 2p 3 / 2 ) and 653.9 eV (Mn 2p 1 / 2 ), with a binding energy interval of 11.8 eV, and an obvious satellite peak at 646 eV, which was highly consistent with the Mn 2+ species, indicating that the Mn element introduced by potassium permanganate was in the form of basic oxide MnO, which was confirmed by the XRD pattern (MnO, PDF #07-0230). XPS (O 1s) spectra showed that the types of doped oxygen-containing functional groups were 531.6 eV (C=O) and 533.7 eV (C-O-C). The Raman spectra again verified the introduction of MnO in the stretching vibration of Mn-O bond at a Raman shift of 650 cm -1 . The introduction of a large number of nitrogen- and oxygen-containing functional groups significantly improved the wettability of the material, which was conducive to promoting the interface contact between the electrode and the electrolyte, reducing the internal resistance, avoiding the formation of bubbles or cavities due to poor contact, and thus increasing the effective reaction area, which was conducive to improving the electrochemical performance of the material.

[0137] In addition, the contents of carbon (C), oxygen (O), nitrogen (N) and manganese (Mn) elements in the carbonaceous electrode materials prepared in each example are shown in Table 1

[0138] Table 1 Element contents of carbonaceous electrode materials prepared in Examples 1-9

[0139]

[0140] Test Example 2

[0141] Pore structure and specific surface area

[0142] Figure 11 and Figure 12 are the pore size distribution diagrams of the carbonaceous electrode materials prepared in Example 1 and Comparative Example 1, and Example 2 and Comparative Example 1, respectively. It can be seen that the pore structures of Examples 1 and 2, especially the number of micropores (pore size less than 2 nm) and small mesopores (pore size of 2-5 nm), are significantly increased compared with Comparative Example 1, indicating that enzymatic hydrolysis can greatly increase the number of micropores of the material, thereby increasing the specific surface area of the material, and the loading of nitrogen, manganese and oxygen does not block the micropore structure generated by enzyme treatment. Figure 11 and Figure 12 It can also be seen from the comparison that laccase and cellulase show similar pore-forming mechanisms, both of which generate a large number of micropores and small mesopores.

[0143] The specific surface area of the carbonaceous electrode materials prepared in each example and comparative example is shown in Table 2.

[0144] Table 2 Specific surface area of the carbonaceous electrode materials prepared in each example and comparative example

[0145]

[0146] As can be seen from Table 2, the specific surface area of the enzyme-wood-derived carbonaceous electrode material prepared in Example 1 is significantly increased compared with Comparative Example 1 (without enzyme treatment and loading of nitrogen, manganese and oxygen), which is due to the directional degradation of enzymes to wood structure and the synergistic effect in the loading process of nitrogen, oxygen and manganese, proving that the method can effectively increase the specific surface area of the material.

[0147] Test Example 3

[0148] The carbonaceous electrode materials prepared in each example and comparative example were used to assemble supercapacitors, and the electrochemical performance of the supercapacitors was tested in a two-electrode system. The assembly steps of the supercapacitors were as follows: two pieces of carbonaceous electrode materials of the same size were polished to 10 mm x 10 mm x 1 mm to serve as the positive and negative electrodes of the supercapacitors, filter paper was used as a separator, and 6M potassium hydroxide (KOH) solution or 1M anhydrous sodium sulfate (Na2SO4) solution was used as an electrolyte to obtain supercapacitors of different properties. The thickness of the entire supercapacitor device included the thickness of two electrodes (2 mm) and the thickness of a piece of filter paper (0.02 mm).

[0149] Figure 13 The cyclic voltammogram of the alkaline supercapacitor assembled using the carbonaceous electrode material prepared in Example 1 (with 6M KOH as the electrolyte).

[0150] Figure 14 The galvanostatic charge-discharge curve of the alkaline supercapacitor assembled using the carbonaceous electrode material prepared in Example 1 (with 6M KOH as the electrolyte).

[0151] Figure 15 The cyclic voltammogram of the neutral supercapacitor assembled using the carbonaceous electrode material prepared in Example 1 (with 1M Na2SO4 as the electrolyte).

[0152] Figure 16 The galvanostatic charge-discharge curve of the neutral supercapacitor assembled using the carbonaceous electrode material prepared in Example 1 (with 1M Na2SO4 as the electrolyte).

[0153] From the above test results, it can be seen that the carbonaceous electrode material prepared in Example 1 has a specific surface area of 1, 200 m2 / g, which is significantly higher than that of Comparative Example 1 (without enzyme treatment and loading of nitrogen, manganese and oxygen), and the specific surface area of the carbonaceous electrode material prepared in Example 1 is also significantly higher than that of Comparative Example 2 (without enzyme treatment, but with loading of nitrogen, manganese and oxygen), which proves that the method can effectively increase the specific surface area of the material. Figure 13 and Figure 15It can be seen that all the cyclic voltammograms of the neutral supercapacitor show a quasi-rectangular shape, exhibiting excellent double-layer capacitance behavior and ideal capacitance characteristics. The cyclic voltammograms at different scan rates all show a quasi-rectangular shape, and as the scan rate increases, the gradually moving high interference impedance produces a larger integral area. The alkaline electrolyte has extremely high ionic conductivity, which is mainly due to the high mobility of OH - . This significantly reduces the ion transport resistance and improves the specific capacitance of the material. In addition, OH - directly participates in the rapid oxidation-reduction reaction of the MnO surface, resulting in polarization and distortion at high scan rates (50 mV / s). Figure 14 and Figure 16 It can be seen that the carbonaceous electrode material prepared in Example 1 has an area specific capacitance of 4.7269 mF / cm 2 at a current density of 1 mA / cm 2 in a 6M KOH electrolyte, and an area specific capacitance of 2.9031 F / cm 2 at a current density of 1 mA / cm 2 in a 1M Na2SO4 electrolyte. The charging and discharging processes of the constant current charge-discharge curves at different current densities in the two systems both show an approximately symmetrical shape, exhibiting good charge-discharge reversibility.

[0154] In addition, the area specific capacitances of the carbonaceous electrode materials prepared in the examples and comparative examples at a current density of 1 mA / cm 2 in different electrolytes are shown in Table 3, and the energy density and power density at a current density of 1 mA / cm 2 in a 6M KOH electrolyte are shown in Table 4. Compared with Comparative Examples 1-8, the specific capacitance and energy density of Example 1 are significantly improved. This is due to the introduction of abundant pores and more exposed oxygen-containing functional groups by cellulase treatment, which increases ion accessibility and active sites. At the same time, the high conductivity of the porous carbon skeleton, the improved wettability of N-doping, and the synergistic conductivity effect between MnO nanoparticles and the carbon matrix further improve the charge storage capacity of the material. Meanwhile, the examples treated with hemicellulase and laccase also exhibit similar performance, and the performance difference between the examples is mainly due to the different pore structures and specific surface areas of different woods.

[0155] Table 3 Area specific capacitances of carbonaceous electrode materials prepared in Examples 1-9 and Comparative Examples 1-8 at a current density of 1 mA / cm 2 in different electrolytes

[0156]

[0157] Table 4 Energy density and power density at 1 mA / cm2for carbonaceous electrode materials prepared in Examples 1-9 and Comparative Examples 1-8 in 6 M KOH electrolyte 2 Energy density and power density at current densities

[0158]

[0159] The above embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for preparing a nitrogen-, manganese-, oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material, characterized in that, Includes the following steps: Wood is enzymatically treated to obtain enzymatically hydrolyzed wood; the enzymatically hydrolyzed wood is soaked in urea solution or melamine solution, subjected to hydrothermal reaction, and dried to obtain nitrogen-doped enzymatically hydrolyzed wood; the nitrogen-doped enzymatically hydrolyzed wood is soaked in potassium permanganate solution, dried, and then subjected to pre-carbonization and carbonization in sequence to obtain the nitrogen-manganese-oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material. The enzyme treatment steps include: adding the enzyme and pretreated wood to an acetate-sodium acetate buffer solution and culturing at 45-55℃ for 20-30 hours; The enzymes include cellulase, hemicellulase, or laccase; The pre-carbonization temperature is 400-600℃, and the time is 1.5-3h; The carbonization temperature is 750-850℃, and the time is 1.5-2.5h; The pretreatment includes: cutting, cleaning and drying the wood; The cutting process specifically involves cutting the wood into pieces with a thickness of 1-3 mm along its natural growth direction.

2. The method for preparing the nitrogen-, manganese-, oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material as described in claim 1, characterized in that, The mass ratio of the enzyme to the pretreated wood is 1:5-10; And / or, the preparation steps of the acetate-sodium acetate buffer solution include: adjusting the pH of the sodium acetate solution to 4.5-5.5 using acetic acid to obtain the acetate-sodium acetate buffer solution.

3. The method for preparing the nitrogen-, manganese-, oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material as described in claim 1, characterized in that, The concentration of the urea solution is 0.1-0.5 mol / L; Alternatively, the concentration of the melamine solution is 0.1-0.5 mol / L; And / or, the hydrothermal reaction is carried out at a temperature of 85-105°C for a time of 4-8 hours.

4. The method for preparing the nitrogen-, manganese-, oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material as described in claim 1, characterized in that, The concentration of the potassium permanganate solution is 0.05-0.15 mol / L, and the soaking time in the potassium permanganate solution is 1-3 hours.

5. A nitrogen-, manganese-, oxygen-containing enzymatically hydrolyzed wood-derived carbon electrode material prepared by the preparation method according to any one of claims 1-4.

6. The application of the nitrogen-manganese-oxygen-containing enzymatically hydrolyzed wood-derived carbonaceous electrode material as described in claim 5 in the preparation of supercapacitors.

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