Preparation method of porous capacitor material rich in heteroatom doping and porous capacitor material

Abstract

The invention discloses a preparation method of a porous capacitor material rich in heteroatom doping. The preparation method comprises the following steps: uniformly mixing lignocellulose biomass and microalgae, and then carrying out a co-pyrolysis carbonization reaction; and carrying out activation and plasma doping modification on the co-pyrolysis biochar prepared by the co-pyrolysis carbonization reaction. According to the method disclosed by the invention, the microalgae can fully realize self-doping of a nitrogen element, and the lignocellulosic biomass provides a rich carbon-based framework, so that the prepared biochar contains more void structures and nitrogen-containing functional groups; meanwhile, the lignocellulose biomass and microalgae co-pyrolysis charcoal are further subjected to low-temperature plasma doping modification, so that the amount of heteroions introduced to the surface of the co-pyrolysis charcoal is synergistically increased, a certain defect structure is further formed on the surface, and an oxidation-reduction reaction is facilitated; the co-pyrolysis biochar modified by microalgae and NH3 has the lowest contact resistance and the most excellent double-electric-layer capacitance characteristic, and the specific capacitance reaches up to 216 F / g.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of capacitor materials, and particularly relates to a preparation method of a porous capacitor material doped with heteroatoms and the porous capacitor material. BACKGROUND

[0002] In today's era of rapid industrial development, the research and application of sustainable energy and green technology have become a hot spot in the global scientific research field. As a new type of energy storage device, supercapacitors have high power density, fast charging and discharging, long cycle life, environmental friendliness and other excellent characteristics, and have broad application prospects in electric vehicles, electronic devices, industrial power supplies and many other fields.

[0003] Supercapacitors are mainly composed of electrodes, electrolytes, separators and current collectors, among which the electrode active material is the most important part in the energy storage process of supercapacitors, and determines a series of evaluation indexes such as specific capacity, cycle life, charging and discharging speed of supercapacitors.

[0004] Biomass is rich in carbon elements, widely sourced and low in price, and is the most potential precursor of carbon materials for preparing carbon materials. Through thermochemical means, it can obtain carbon materials with high specific surface area and rich pore structure, which can be applied to supercapacitor electrode materials. Guo et al. used sawdust as raw material to prepare carbon-based electrode materials by KOH impregnation coupled with pyrolysis activation process, and the specific capacity was 120 F / g at a current density of 1 A / g. At present, the electrochemical performance of carbon-based electrode materials directly prepared from biomass is generally low, which limits its industrial application.

[0005] Furthermore, the introduction of heteroatoms (such as nitrogen, phosphorus, and sulfur) into carbon materials can increase the migration rate of electrolyte ions, facilitating charge storage. Redox reactions of heteroatoms can also enhance charge storage capacity. For example, heteroatom doping (e.g., nitrogen doping) not only enhances the redox capacity and pseudocapacitance of carbon-based materials but also improves their hydrophilicity and double-layer capacitance. Therefore, nitrogen doping of biomass-based carbon materials is an effective means of improving their supercapacitor performance. Traditional nitrogen-doped carbon materials are prepared thermochemically using biomass as a substrate and nitrogen-containing chemicals or gases such as melamine, urea, and ammonia as a nitrogen source. Rustamaji et al. prepared nitrogen-doped carbon materials using hydrothermal carbonization of oil palm shells as a raw material and urea as a nitrogen source via CaCl2 activation. Compared to carbon materials obtained by direct hydrothermal carbonization, these materials showed a surface nitrogen atom content approximately threefold higher (approximately 8 at%) and a specific capacitance increase of 70 F / g. Li et al. used ammonia as a carrier gas and nitrogen source, and bamboo strips as raw materials to prepare nitrogen-doped carbon materials using a one-step pyrolysis-activation method. The nitrogen content was as high as 7.55 at%, and the specific capacitance was increased by 14.3% at a current density of 1 A / g. Although urea, melamine, ammonia, etc. as nitrogen sources can improve the nitrogen content and capacitance performance of carbon materials to a certain extent, melamine, urea, and ammonia are expensive and come from fossil energy, resulting in high nitrogen doping costs and difficulties in practical application. Therefore, using clean, cheap, and readily available nitrogen sources to dope carbon materials with nitrogen is of great significance for obtaining high-performance supercapacitor carbon-based electrode materials. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the main purpose of the present invention is to provide a method for preparing a porous capacitor material rich in heteroatom doping, which effectively solves the problem of low carbon nitrogen content generated by using a single lignocellulosic biomass or the increase in cost caused by the introduction of a large amount of nitrogen-doping chemical reagents by co-pyrolysis of microalgae and lignocellulosic biomass; on the other hand, heteroatoms are further introduced on the surface of the co-pyrolysis biochar by low-temperature plasma modification technology, while obtaining biomass with excellent specific surface area and rich pore structure, further introducing heteroatoms on the surface of the biomass, effectively alleviating the problem of heteroatom loss during the biochar activation process, and then obtaining a biochar material with excellent specific surface area, rich pore structure and heteroatom doping amount, and then obtaining a high-performance porous capacitor material rich in heteroatom doping.

[0007] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a heteroatom-rich porous capacitor material comprises the following steps: The lignocellulosic biomass and microalgae are mixed evenly and then subjected to a co-pyrolysis carbonization reaction to obtain co-pyrolysis biochar.

[0008] wherein the mass ratio of lignocellulosic biomass and microalgae is (0.5-6):(0.5-3).

[0009] In some embodiments, the co-pyrolysis carbonization reaction is specifically carried out under an inert atmosphere at a pyrolysis temperature of 300-500 ℃ for 0.5-1.5 h.

[0010] In some embodiments, the co-pyrolysis biochar obtained by the co-pyrolysis carbonization reaction is further activated and modified by plasma doping.

[0011] In some embodiments, the activation is specifically carried out by stirring and dispersing the co-pyrolysis biochar and an activating agent in a water solution at a mass ratio of 1:(2-5), drying, and then activating the obtained solid mixture of hydrochar and activating agent in an inert atmosphere, and cooling and washing to obtain the activated co-pyrolysis biochar.

[0012] In some embodiments, the activating agent includes, but is not limited to, one or more of potassium hydroxide, potassium carbonate, and zinc chloride.

[0013] In some embodiments, the process conditions for the activation are as follows: under an inert atmosphere, the flow rate of inert gas is 50-150 mL / min, the temperature is raised to 600-1000 ℃ at a rate of 5-15 ℃ / min, and the temperature is maintained for 1-3 h.

[0014] In some embodiments, the plasma modification is specifically carried out by doping the activated co-pyrolysis biochar in a doping gas atmosphere of NH3 / Ar (V NH3 :V Ar =1:(2-6), H2S / Ar (V H2S :V Ar =1:(2-6), and N2 / Ar (V N2 :V Ar =1:(5-12) to obtain a porous capacitive material rich in heteroatom doping.

[0015] In some embodiments, the process parameters for the plasma modification are as follows: the frequency of the plasma modification device is set to 5-15 kHz, the input voltage is 30-80 V, and the doping gas atmosphere is introduced at a flow rate of 50-150 mL / min at normal temperature and pressure.

[0016] In some embodiments, the doping gas atmosphere includes, but is not limited to, one or more of NH3 / Ar, H2S / Ar, and N2 / Ar.

[0017] In some specific embodiments, the lignocellulosic biomass and the microalgae subjected to the co-pyrolysis carbonization are sequentially subjected to crushing, screening, washing and drying treatments.

[0018] In some specific embodiments, the lignocellulosic biomass includes, but is not limited to, one or more of straw, wood, fruit shell, bagasse, and bamboo.

[0019] As the same inventive concept, the present application also discloses a porous capacitive material.

[0020] Compared with the prior art, the present application has at least the following advantages: 1) The preparation method of the present application provides a porous capacitive material rich in heteroatom doping, in which the microalgae can fully realize self-doping of nitrogen elements, and the lignocellulosic biomass provides a rich carbon-based skeleton, so that the prepared biochar contains more void structures and nitrogen-containing functional groups; the nitrogen element content on the surface of the co-pyrolysis biochar is 4.42 %, which is much higher than that of the biochar pyrolyzed from the lignocellulosic biomass alone (0.13 %). In addition, the co-pyrolysis biochar after activation has high specific surface area, developed hierarchical pore structure and high nitrogen content, and has high specific capacitance (151 F / g). The preparation method reduces the use of traditional chemical reagents, reduces a large amount of cost investment, and is environmentally friendly; 2) The present application further modifies the co-pyrolysis biochar of the lignocellulosic biomass and the microalgae by low-temperature plasma doping, further introduces heteroatoms on the surface of the co-pyrolysis biochar, cooperatively increases the amount of heteroatoms doped on the surface of the biochar, effectively alleviates the problem of loss of heteroatoms in the activation process of the biochar; at the same time, the number of mesopores of the co-pyrolysis biochar and the degree of disorder of the carbon skeleton are improved. The effective introduction of heteroatoms further improves the wettability of the co-pyrolysis biochar and reduces the ion transfer resistance. After the plasma modification, the co-pyrolysis biochar further forms certain defect structures on the surface, which is beneficial to the occurrence of oxidation-reduction reactions, so that the pseudo capacitance of the modified co-pyrolysis biochar is further improved; the co-pyrolysis biochar modified by NH3 has the highest heteroatom content, specific surface area and mesopore abundance, resulting in the lowest contact resistance and the best double-layer capacitance characteristics, and the specific capacitance is as high as 216 F / g. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the specific embodiments of the present application, the drawings required to be used in the specific embodiments or the prior art description will be briefly introduced below.

[0022] Figure 1 The process flow chart of the porous capacitive material rich in heteroatom doping provided by the present application; Figure 2 The Fourier infrared spectrum analysis diagram of the co-pyrolysis biochar in Example 1 of the present application; Figure 3 XPS survey spectrum of co-pyrolysis biochar in Example 1 of the present application; Figure 4 Pore size distribution of porous capacitive material in Example 2 of the present application; Figure 5 Electrical performance test chart of porous capacitive material in Example 2 of the present application; Figure 6 Electrical performance test chart of porous capacitive material after NH3 / Ar plasma treatment in Example 3 of the present application; Figure 7 Electrical performance test chart of porous capacitive material after H2S / Ar plasma treatment in Example 4 of the present application; Figure 8 Electrical performance test chart of porous capacitive material after N2 / Ar plasma treatment in Example 5 of the present application; Figure 9 SEM chart of co-pyrolysis biochar after activation prepared in Example 2 of the present application, and porous capacitive material prepared in Examples 3-5 of the present application; Figure 10 Contact angle test chart of co-pyrolysis biochar after activation prepared in Example 2 of the present application, and porous capacitive material prepared in Examples 3-5 of the present application; Figure 11 EDS spectrum analysis chart of co-pyrolysis biochar after activation prepared in Example 2 of the present application, and porous capacitive material prepared in Examples 3-5 of the present application. DETAILED DESCRIPTION

[0023] The present application will be further described with reference to the following figures and examples, which are illustrative only and should not be construed as limiting the scope of the present application.

[0024] When expressing a quantity, concentration or other value or parameter either as a range, a preferred range, or a range preferred for use in a particular embodiment, it is intended to convey that the particular value or parameter can vary from the lower to the upper range limit, or anywhere within the range, and that the range is merely preferred for use in that particular embodiment. Unless otherwise stated, the numerical ranges listed herein are inclusive of the recited endpoint and all integer and fraction values within the range.

[0025] All percentages, parts, ratios, etc. herein are by weight, unless otherwise indicated.

[0026] The materials, methods, and examples herein are illustrative only and, except as specifically stated, are not intended to be limiting.

[0027] In the following examples, the lignocellulose is pine sawdust, and the microalgae is Nannochloropsis.

[0028] The test methods used in the following examples include: The electrical properties of the porous capacitive material are embodied by testing the main properties of each test sample respectively. The main properties tested in this application include morphology characterization, nitrogen content, and specific capacitance, etc.

[0029] 1) Morphology characterization test; The specific surface and pore structure test is performed by using a full-automatic multi-station specific surface and pore size analyzer device, by nitrogen adsorption-desorption method, and according to the method specified in GB / T 7702.20-2008.

[0030] 2) Nitrogen content test The element composition analysis test is performed on the sample by using an elemental analyzer device, and according to the method in GB / T 31391-2015. 3) Specific capacitance test The constant current charge-discharge test is performed on the sample by using an electrochemical workstation device, and according to the method in GB / T 34870.1-2017. 20 mg of activated biochar is mixed with polyvinylidene fluoride and acetylene black at a ratio of 8:1:1, 2 ml of N-methyl pyrrolidone solution is added dropwise to prepare a slurry, the slurry is uniformly mixed by magnetic stirring for 12 h, and then uniformly sprayed on the nickel foam for electrochemical performance test.

[0031] Example 1 The present embodiment provides a preparation method of a heteroatom-doped porous capacitive material, which comprises the following steps: Step S1, the microalgae and pine sawdust are crushed and sieved through a 100 mesh screen, washed clean with deionized water, dried in a vacuum drying oven at 60°C for 24 h, and then reserved; Step S2, 8 g of microalgae and 8 g of pine sawdust treated in step S1 are placed in a mortar and stirred for 0.5 h to uniformly mix, then transferred to a tube furnace, reacted at 400°C for 1 h under a nitrogen atmosphere, and a co-pyrolysis biochar is obtained. The specific surface area and nitrogen content of the co-pyrolysis biochar prepared in this embodiment are tested, and the results are that the carbon content in the co-pyrolysis biochar is 61.56%, the surface nitrogen content is 4.42%, which is 34 times higher than that of the single pine sawdust pyrolysis biochar, and the specific surface area is 1.03 m 2 / g.

[0032] The Fourier infrared spectrum analysis of the co-pyrolysis biochar prepared in this embodiment is also performed, and the results are shown in Figure 2 From the figure, according to the peak intensity of the pine sawdust and Nannochloropsis, the peak intensity of the co-pyrolysis biochar is 3420 cm−1 At this point, the overall strength of the co-pyrolysis biochar decreases, representing the occurrence of deamination and dehydration reactions; 2970-2850 cm −1 representing the stretching of C-H bonds in aromatic and aliphatic, respectively, indicating that more C=O in pine sawdust is fixed in the biochar through the Maillard reaction, resulting in an increase in the intensity of the C=O stretching vibration peak.

[0033] In addition, the co-pyrolysis biochar prepared in the present application was subjected to XPS full spectrum analysis, and the results are shown in Figure 3 As can be seen from the figure, the addition of Nannochloropsis significantly promotes the fixation of N atoms in the biochar. In addition, after co-pyrolysis of pine sawdust and Nannochloropsis, the nitrogen-containing functional groups in the biochar are mainly protein-N, pyridine-N, pyrrole-N and quaternary-N. Among them, part of the pyridine-N and pyrrole-N is directly converted from the amino acids in Nannochloropsis, and the other part is due to the Maillard reaction and cyclization reaction of amino acids with carbonyl groups on pine charcoal to generate nitrogen-containing heterocyclic compounds, and further through dehydration and decarboxylation reactions to form pyridine-N and pyrrole-N.

[0034] Example 2 The present embodiment provides a preparation method of a porous capacitive material doped with heteroatoms, comprising the following steps: Step S1, after crushing and sieving the microalgae and pine sawdust through a 100 mesh screen, washing them clean with deionized water, drying them in a vacuum drying oven at 60°C for 24h, and then preparing them for use; Step S2, after stirring and uniformly mixing 8g of microalgae and 8g of straw treated in step S1 in a mortar for 0.5h, transferring them to a tube furnace, and reacting them under a nitrogen atmosphere at 400°C for 1h, co-pyrolysis biochar is obtained; Step S3, after uniformly stirring and dispersing the co-pyrolysis biochar obtained in step S2 and the activating agent KOH in a mass ratio of 1:3 in an aqueous solution, drying them at a temperature of 105°C for 12h, and then transferring the obtained hydrothermal carbon and KOH solid mixture to a tube furnace, heating them to 800°C at a nitrogen flow rate of 100 mL / min and a heating rate of 10°C / min, and keeping them at 800°C for 2h, after the activation is completed, washing them with 1mol / L hydrochloric acid and deionized water, and drying them at 105°C for 12h to obtain the co-pyrolysis biochar after activation (referred to as PS / NS-A).

[0035] The present application tests the physicochemical properties and electrochemical performance of the co-pyrolysis biochar prepared, and the pore size distribution diagram of the co-pyrolysis biochar is shown in Figure 4 As can be seen from the figure, there are both microporous and mesoporous structures, and the specific surface area is 1736.05m 2 / g, which is much higher than the specific surface area (1.03m 2(g); the nitrogen element content was 1.96%, which was increased by 66.1% compared with the KOH activated pine sawdust pyrolysis biochar; the electrochemical performance test results are shown in Figure 5 The specific capacitance reached 151 F / g at a current density of 0.5 A / g.

[0036] Example 3 The present embodiment provides a preparation method of a porous capacitive material doped with heteroatoms, comprising the following steps: Step S1, after the microalgae and pine sawdust are crushed, they are sieved with a 100 mesh screen, washed clean with deionized water, and then dried in a vacuum drying box at 60°C for 24h for standby.

[0037] Step S2, 8g of microalgae and 8g of straw treated in step S1 are placed in a mortar and stirred for 0.5h to uniformly mix, then transferred to a tube furnace, reacted at 400°C for 1h under a nitrogen atmosphere, and co-pyrolysis biochar is obtained; Step S3, the co-pyrolysis biochar obtained in step S2 and the activating agent KOH are uniformly dispersed in an aqueous solution at a mass ratio of 1:3, then dried at 105°C for 12h, and then the obtained hydrothermal carbon and KOH solid mixture is transferred to a tube furnace, heated to 800°C at a nitrogen flow rate of 100 mL / min at a rate of 10°C / min, and kept for 2h; after activation, washed with 1mol / L hydrochloric acid and deionized water, and dried at 105°C for 12h to obtain activated co-pyrolysis biochar.

[0038] Step S4, the activated co-pyrolysis biochar obtained in step S3 is placed in a low-temperature plasma modification device, set to a frequency of 9 kHz and an input voltage of 50V, and treated at room temperature and atmospheric pressure in an NH3 / Ar (V NH3 :V Ar =1:4) atmosphere at a flow rate of 100 mL / min to obtain a porous capacitive material doped with heteroatoms (referred to as PS / NS-NH3).

[0039] The prepared porous capacitive material is tested for physical and chemical properties and electrochemical performance, as shown in Figure 6 The nitrogen element content of the co-pyrolysis biochar treated by NH3 plasma is 3.65%, and the specific capacitance reaches 216 F / g at a current density of 0.5 A / g; Example 4 The present embodiment provides a preparation method of a porous capacitive material doped with heteroatoms, which is basically the same as example 3, except that in step S4, the doping atmosphere is H2S / Ar, specifically: Step S4: The activated co-pyrolysis biochar obtained in step S3 is placed in a low-temperature plasma modification device, and the frequency and input voltage are set to 9 kHz and 50 V, respectively. The plasma is heated at a flow rate of 100 mL / min with H2S / Ar (V H2S:VAr =1:4) atmosphere to obtain heteroatom-rich porous capacitor materials (abbreviated as PS / NS-H2S).

[0040] Its S1, S2 and S3 are the same as those in Example 3; The physical and chemical properties and electrochemical performance of the prepared porous capacitor material were tested in this example. Figure 7 As shown in the figure, the sulfur content of the co-pyrolysis biochar after H2S plasma treatment is 1.36%, and the specific capacitance reaches 192.3F / g at a current density of 0.5A / g.

[0041] Example 5 This embodiment provides a method for preparing a heteroatom-rich porous capacitor material, comprising the following steps: This embodiment provides a method for preparing a heteroatom-rich porous capacitor material, which is basically the same as that of Example 3, except that in step S4, the doping atmosphere is N2 / Ar. Specifically: Step S4: The activated co-pyrolysis biochar obtained in step S3 is placed in a low-temperature plasma modification device, with a frequency of 9 kHz and an input voltage of 50 V. At room temperature and pressure, a N2 / Ar (V N2 :V Ar =1:9) atmosphere to obtain heteroatom-rich doped porous capacitor materials (abbreviated as PS / NS-N2).

[0042] Its S1, S2 and S3 are the same as those in Example 3; The physical and chemical properties and electrochemical performance of the prepared porous capacitor material were tested in this example. Figure 8 As shown in the figure, the nitrogen content of the co-pyrolysis biochar after N2 plasma treatment is 2.89%, and the specific capacitance reaches 175.3F / g at a current density of 0.5A / g.

[0043] From the test results of Examples 3, 4 and 5, it can be seen that the electrochemical properties of the co-pyrolysis biochar after plasma treatment are higher than those of the co-pyrolysis biochar without plasma treatment.

[0044] This application is for Example 2 ( Figure 9 a), Examples 3-5 (respectively Figure 9 The contact angle of the prepared porous capacitor materials was tested. Figure 9As shown in the figure, after the activated co-pyrolysis biochar is modified by NH3 and N2 plasma, the morphology does not change obviously, and still has rich pore structure. In addition, the pore diameter of the carbon material obtained by H2S modification is obviously larger, indicating that the sulfur-containing plasma modification is more serious in damaging the pore structure.

[0045] The present application tests the contact angle of Example 2 and the activated co-pyrolysis biochar after plasma modification, and the contact angle test of the activated co-pyrolysis biochar after plasma modification is as follows Figure 10 As shown in the figure, the contact angle of the activated co-pyrolysis biochar after plasma modification in NH3, H2S and N2 atmosphere is reduced from 91° to 76°, 81° and 85° respectively, and the change of the contact angle is closely related to the content of heteroatoms. Among them, the N atom content of PS / NS-NH3 is as high as 3.65 at%, and the wettability is the best. The wettability improvement effect of PS / NS-H2S and PS / NS-N2 is limited due to the relatively low content of heteroatoms S and N; the significant improvement of wettability improves the accessibility of electrolyte ions, which is beneficial to the formation of double layer.

[0046] The present application tests the contact angle of Example 2 ( Figure 11 a), Example 3-5 (respectively Figure 11 b, 11c and 11d) to prepare the porous capacitive material, and the results are shown in Figure 11 and the following table: Surface element composition of activated biochar modified by plasma under different atmosphere From Figure 11 and the data in the table, after the activated biochar is treated by plasma under different atmosphere, the heteroatoms are uniformly distributed on the surface of the biochar, which is beneficial to the modification of the activated biochar as electrode material to fully play its electrochemical performance. The N atom content of the activated biochar PS / NS-NH3 modified by NH3 plasma increases from 1.96 at% to 3.65 at%, indicating that ammonia is excited into nitrogen-containing groups by high-voltage electric excitation and effectively introduced into the surface of the carbon material. In addition, the S atom content of the carbon material obtained by H2S modification increases from 0.27 at% to 2.97 at%, and the N atom content of the co-pyrolysis activated biochar modified by N2 increases to 2.89 at%. Compared with PS / NS-N2, PS / NS-NH3 has higher surface nitrogen atom content.

[0047] Comparative Example 1 This comparative example provides a preparation method of a porous capacitive material doped with heteroatoms, which is basically the same as Example 1, except that the microalgae is not added, but the microalgae is replaced by pine sawdust, which specifically includes the following steps: Step S1, pine sawdust was crushed and sieved with a 100 mesh screen, washed with deionized water, and dried in a vacuum drying oven at 60°C for 24h before use; Step S2, 16 g of pine sawdust treated in step S1 was placed in a mortar and stirred for 0.5 h to mix uniformly, then transferred to a tube furnace, reacted at 400°C for 1 h under a nitrogen atmosphere, and pine sawdust pyrolysis biochar was obtained.

[0048] The specific surface area and nitrogen content of the co-pyrolysis biochar prepared in this example were tested, and the results were that the carbon content in the co-pyrolysis biochar was 75.55%, the surface nitrogen content was 0.13%, and the specific surface area was 4.79m 2 / g.

[0049] Comparative Example 2 The present comparative example provides a preparation method of a porous capacitive material rich in heteroatom doping, which is basically the same as example 1, except that pine sawdust is not added, but is replaced by microalgae, which specifically includes the following steps: Step S1, the microalgae was crushed and sieved with a 100 mesh screen, washed with deionized water, and dried in a vacuum drying oven at 60°C for 24h before use; Step S2, 16 g of microalgae treated in step S1 was placed in a mortar and stirred for 0.5 h to mix uniformly, then transferred to a tube furnace, reacted at 400°C for 1 h under a nitrogen atmosphere, and pine sawdust pyrolysis biochar was obtained.

[0050] The specific surface area and nitrogen content of the co-pyrolysis biochar prepared in this example were tested, and the results were that the carbon content in the co-pyrolysis biochar was 44.27%, the surface nitrogen content was 6.12%, and the specific surface area was 0.69m 2 / g.

[0051] Comparative Example 3 The present comparative example provides a preparation method of a porous capacitive material rich in heteroatom doping, which is basically the same as example 2, except that microalgae is not added, but is replaced by pine sawdust, which specifically includes the following steps: Step S1, the pine sawdust was crushed and sieved with a 100 mesh screen, washed with deionized water, and dried in a vacuum drying oven at 60°C for 24h before use; Step S2, 16 g of pine sawdust treated in step S1 was placed in a mortar and stirred for 0.5 h to mix uniformly, then transferred to a tube furnace, reacted at 400°C for 1 h under a nitrogen atmosphere, and pine sawdust pyrolysis biochar was obtained. Step S3, the pyrolysis biochar obtained in step S2 and the activating agent KOH were stirred and dispersed uniformly in an aqueous solution at a mass ratio of 1:3, and then dried at 105°C for 12 hours. The obtained hydrothermal carbon and KOH solid mixture was transferred to a tube furnace, heated to 800°C at a nitrogen flow rate of 100 mL / min and a heating rate of 10°C / min, and kept for 2 hours. After activation, the activated pyrolysis biochar was obtained by washing with 1 mol / L hydrochloric acid and deionized water, and drying at 105°C for 12 hours.

[0052] The prepared pyrolysis biochar was tested for physical and chemical properties, and the results were as follows: the nitrogen content of the biochar was 0.17%, and the specific surface area was 1830.98 m 2 / g.

[0053] Comparative Example 4 This comparative example provides a method for preparing a porous capacitive material doped with heteroatoms, which is basically the same as comparative example 3, except that the pyrolysis biochar obtained after activation in comparative example 3 is subjected to plasma activation treatment, specifically: Step S4, the activated co-pyrolysis biochar obtained in comparative example 3 was placed in a low-temperature plasma modification device, and set to a frequency of 9 kHz and an input voltage of 50V. It was treated under the condition of normal temperature and pressure, with a flow rate of 100 mL / min of NH3 / Ar (V NH3 :V Ar =1:4) atmosphere, to obtain a porous capacitive material doped with heteroatoms.

[0054] The prepared porous capacitive material was tested for physical and chemical properties and electrochemical performance. The nitrogen content of the co-pyrolysis biochar after NH3 plasma treatment was 1.48%, and the specific capacitance reached 118 / F / g at a current density of 0.5A / g. This is mainly because the lack of co-pyrolysis process results in a significantly lower content of heteroatoms in the biochar after plasma treatment, which reduces the wettability and conductivity, and weakens the redox reaction characteristics and pseudo-capacitance characteristics, ultimately leading to a significant decrease in capacitive performance.

[0055] The above examples are only used to illustrate the technical solutions of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not change the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and description of the present application.

Claims

1. A method for preparing a heteroatom-rich porous capacitor material, characterized in that: The steps include: 1) The lignocellulosic biomass and microalgae are mixed uniformly and then subjected to a co-pyrolysis carbonization reaction to obtain co-pyrolysis biochar; 2) The co-pyrolysis biochar prepared by the co-pyrolysis carbonization reaction is activated and modified by plasma doping.

2. The method for preparing heteroatom-rich doped porous capacitor material according to claim 1, characterized in that: The activation is specifically as follows: the co-pyrolysis biochar and the activator are stirred and dispersed uniformly in an aqueous solution, and then dried; the obtained solid mixture of hydrothermal biochar and the activator is activated in an inert atmosphere; and after cooling and washing, the activated co-pyrolysis biochar is obtained.

3. The method for preparing a heteroatom-rich porous capacitor material according to claim 2, wherein: The activator includes but is not limited to one or more of potassium hydroxide, potassium carbonate and zinc chloride.

4. The method for preparing heteroatom-rich porous capacitor materials according to claim 3, wherein: The activation process conditions are as follows: under an inert atmosphere, the flow rate of the inert gas is 50-150 mL / min, the temperature is increased to 600-1000°C at a rate of 5-15°C / min, and the temperature is kept at this temperature for 1-3 hours.

5. The method for preparing heteroatom-rich doped porous capacitor material according to claim 1, characterized in that: The plasma doping modification specifically includes: subjecting the activated co-pyrolyzed biochar to plasma modification in a doping atmosphere to obtain a heteroatom-rich porous capacitor material.

6. The method for preparing a heteroatom-rich porous capacitor material according to claim 5, characterized in that: The doping atmosphere includes but is not limited to one or more of NH3 / Ar, H2S / Ar, and N2 / Ar.

7. The method for preparing a heteroatom-rich doped porous capacitor material according to claim 1, wherein: The method also includes sequentially crushing, screening, washing and drying the lignocellulosic biomass and microalgae to be co-pyrolyzed and carbonized.

8. The method for preparing heteroatom-rich doped porous capacitor material according to claim 7, characterized in that: The lignocellulosic biomass includes but is not limited to one or more of straw, wood, fruit shell, bagasse, and bamboo.

9. A porous capacitor material prepared according to the preparation method according to any one of claims 1 to 8.

Images