Preparation Method and Application of a Doped Activated Carbon Electrode Material for Supercapacitors

Abstract

The present invention provides a preparation method of a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance. The method is as follows: After cutting banana peels into pieces, they are dried and ground to obtain a sample to be processed; the sample to be processed and KOH are mixed, deionized water a is added and mixed, followed by magnetic stirring, standing, filtration. After drying the filter cake, it is heated to 700 °C at a heating rate of 10 °C / min and treated at a constant temperature for 2 h. After successively undergoing pickling, deionized water washing, and drying, activated carbon particles are obtained; the activated carbon particles are mixed with urea, deionized water b is added, and after shaking and mixing, they are allowed to stand, filtered. The filter cake is washed with deionized water until the pH is 7.0, dried, and then heated by microwave and cooled. An application is also provided. Due to its good pore structure and the stable combination of hybrid functional groups with the activated carbon substrate, the present invention shows good capacitance among similar heterocyclic atom-doped activated carbon materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercapacitor electrode materials, and particularly relates to a preparation method and application of a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance. Background Art

[0002] As the main raw material of commercial electrode materials, the conductivity and specific capacitance of activated carbon have an important impact on the overall electrochemical performance of electrode materials. Based on the conductivity of activated carbon, how to further enhance conductivity, reduce internal resistance, and at the same time increase the specific surface area utilization rate and unit capacitance of activated carbon are the main problems. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a preparation method and application of a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance in view of the above-mentioned deficiencies of the prior art. Due to its good pore structure and stable combination of hybrid functional groups with the activated carbon substrate, the doped activated carbon supercapacitor electrode material shows good capacitance among similar heterocyclic atom-doped activated carbon materials.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: a preparation method of a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance, and the method is as follows:

[0005] S1. After cutting the banana peel into pieces, drying and grinding, a sample to be processed is obtained;

[0006] S2. After mixing the sample to be processed obtained in S1 with KOH and adding deionized water a, magnetically stirring for 2 h, standing for 12 h, filtering, drying the filter cake, heating to 700 °C at a heating rate of 10 °C / min, performing constant temperature treatment for 2 h, then successively performing pickling with 2 M hydrochloric acid, washing with deionized water at 60 °C until the pH is 6.5 - 7.0, and drying to obtain activated carbon particles;

[0007] S3. After mixing the activated carbon particles obtained in S2 with urea, adding deionized water b, oscillating and mixing for 8 h and then standing, filtering, washing the filter cake with deionized water until the pH is 7.0, drying, performing microwave heating, and cooling to obtain a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance.

[0008] Preferably, the drying condition in S1 is 105 °C for 24 h.

[0009] Preferably, the drying condition in S2 is 105 °C for 12 h.

[0010] Preferably, the dosage ratio of the sample to be processed, KOH and deionized pure water a in S2 is 30 g:60 g:500 mL.

[0011] Preferably, the dosage ratio of the activated carbon particles, urea, and deionized water b in S3 is 2 g : (2 - 8) g : 50 mL.

[0012] Preferably, the drying conditions in S3 are 105 °C for 4 h.

[0013] Preferably, the microwave heating conditions in S3 are: 800 W for 1 min.

[0014] Preferably, the specific surface area of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance in S3 is 901.38 m 2 / g - 942.66 m 2 / g.

[0015] The present invention also provides an application of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance prepared by the above preparation method, and the doped activated carbon supercapacitor electrode material with high specific surface area capacitance is used as the electrode material of a supercapacitor.

[0016] The present invention has the following advantages compared with the prior art:

[0017] 1. In the selection of raw materials of the present invention, banana peel (agricultural waste) rich in heterocyclic atoms and potassium element is selected as the raw material to realize waste utilization. Also, during the carbonization and activation processes, self - hybridization and in - situ pore formation of activated carbon are carried out to obtain a mesoporous wall - embedded microporous and high - pore - density structure and multiple active sites, improving the electrochemical performance.

[0018] 2. The present invention combines chemical hybridization and microwave heating. On the basis of strengthening and consolidating the chemical bond combination between the hybrid functional groups and activated carbon, residual gases in the microporous structure of activated carbon are removed, etc., so as to achieve the purpose of stabilizing the material and structure and removing excess impurities.

[0019] 3. The entire experimental design of the present invention integrates three advantages: banana peel rich in heterocyclic atoms and potassium, one - step carbonization and activation, and microwave stabilization of materials. As a result, the obtained doped activated carbon has a more excellent specific surface area capacitance and internal resistance. Due to its excellent pore structure and the stable combination of hybrid functional groups with the activated carbon substrate, the prepared doped activated carbon shows outstanding capacitance among similar heterocyclic - atom - doped activated carbon materials.

[0020] The present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a comparison chart of specific capacitance vs. specific surface area between the optimal electrode of the present invention and doped activated carbon electrodes reported in other literatures.

[0022] Figure 2 SEM images of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance of the present invention at different magnification ratios.

[0023] Figure 3 Fourier transform infrared spectrum, X-ray powder diffraction, X-ray photoelectron spectroscopy and diagrams of different element contents of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance of the present invention.

[0024] Figure 4 Cyclic voltammetry, constant current charge and discharge and calculated specific capacitance diagrams of the doped activated carbon supercapacitor electrode with high specific surface area capacitance of the present invention.

[0025] Figure 5 Diagram of the influence of the doped element content on the specific capacitance of the electrode.

[0026] Figure 6 AC impedance spectrum and calculated internal resistance diagram of the doped activated carbon supercapacitor electrode with high specific surface area capacitance of the present invention. Detailed implementation manners

[0027] Example 1

[0028] Preparation method of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance in this example. The method is as follows:

[0029] S1. After cutting the banana peel into pieces, it is dried at 105 °C for 24 h and then ground to obtain the sample to be processed; the banana peel is rich in heteroatoms.

[0030] S2. After mixing 30 g of the sample to be processed obtained in S1 and 60 g of KOH, adding 500 mL of deionized water a and mixing, magnetically stirring for 2 h, standing for 12 h, filtering, drying the filter cake at 105 °C for 12 h, and then using the molten salt method, heating to 700 °C at a heating rate of 10 °C / min, and performing constant temperature treatment for 2 h to achieve the purpose of carbonization and activation. Then, it is successively pickled with 2M hydrochloric acid, washed with deionized water at 60 °C until the pH is 6.5, and dried at 105 °C for 12 h to obtain activated carbon particles.

[0031] S3. Mix the activated carbon particles obtained in S2 (2 g) with 2 g of urea, add 50 mL of deionized water b, shake and mix for 8 h, then let it stand. After filtration, wash the filter cake with deionized water until the pH reaches 7.0, dry it at 105 °C for 4 h, then heat it by microwave, and after cooling, obtain a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance (named C1N1); through doping by soaking in urea solution, on the basis of etching the activated carbon, the heterocyclic atom functional groups are initially combined with the activated carbon matrix. The etching effect can further change the pore structure size and volume, and the heterocyclic atom functional groups can introduce redox reactions to increase the total capacitance. Then, the microwave heating method is used to fix the combination of the functional groups on the surface of the activated carbon and the matrix material in a short time.

[0032] Alkaline urea has an etching effect on the structure of porous activated carbon, further increasing the specific surface area. At the same time, the heterocyclic atom functional groups can provide more active sites, higher conductivity and lower charge transfer resistance, thereby reducing the internal resistance.

[0033] In this example, activated carbon is prepared by the first-step molten salt method, the urea solution soaking doping method and the microwave heating method. The prepared doped activated carbon material shows excellent capacitance among similar heterocyclic atom-doped activated carbon materials due to the stable combination of its excellent pore structure and nitrogen-containing hybrid functional groups (where pyrimidine nitrogen can provide active sites, pyrrole nitrogen can increase the mobility of ions, and tetravalent nitrogen or graphitic nitrogen can assist redox reactions) with the activated carbon substrate (providing a porous structural scaffold, a conductive matrix and defect binding sites).

[0034] Example 2

[0035] The preparation method of the doped activated carbon supercapacitor electrode material with a high specific surface area capacitance in this example is as follows:

[0036] S1. Cut the banana peel into pieces, dry it at 105 °C for 24 h, and then grind it to obtain a sample to be processed;

[0037] S2. Mix 30 g of the sample to be processed obtained in S1 with 60 g of KOH, add 500 mL of deionized water a and mix. After magnetic stirring for 2 h, let it stand for 12 h, filter, dry the filter cake at 105 °C for 12 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 2 h, and then successively carry out pickling with 2 M hydrochloric acid and washing with deionized water at 60 °C until the pH reaches 7.0, and dry it at 105 °C for 12 h to obtain activated carbon particles;

[0038] S3. Mix the activated carbon particles obtained in S2 (2 g) with urea (4 g), add 50 mL of deionized water b, shake and mix for 8 h, then let it stand. After filtration, wash the filter cake with deionized water until the pH reaches 7.0, dry it at 105 °C for 4 h, then heat it by microwave, and after cooling, obtain a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance (named C1N2).

[0039] Example 3

[0040] The preparation method of the doped activated carbon supercapacitor electrode material with a high specific surface area capacitance in this example is as follows:

[0041] S1. Cut the banana peel into pieces, dry it at 105 °C for 24 h, and then grind it to obtain a sample to be processed.

[0042] S2. Mix the sample to be processed obtained in S1 (30 g) with KOH (60 g), add 500 mL of deionized water a, mix them by magnetic stirring for 2 h, then let it stand for 12 h, filter, dry the filter cake at 105 °C for 12 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 2 h, and then successively carry out pickling with 2 M hydrochloric acid, wash it with deionized water at 60 °C until the pH reaches 7.0, and dry it at 105 °C for 12 h to obtain activated carbon particles.

[0043] S3. Mix the activated carbon particles obtained in S2 (2 g) with urea (6 g), add 50 mL of deionized water b, shake and mix for 8 h, then let it stand. After filtration, wash the filter cake with deionized water until the pH reaches 7.0, dry it at 105 °C for 4 h, then heat it by microwave, and after cooling, obtain a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance (named C1N3).

[0044] Example 4

[0045] The preparation method of the doped activated carbon supercapacitor electrode material with a high specific surface area capacitance in this example is as follows:

[0046] S1. Cut the banana peel into pieces, dry it at 105 °C for 24 h, and then grind it to obtain a sample to be processed.

[0047] S2. Mix the sample to be processed obtained in S1 (30 g) with KOH (60 g), add 500 mL of deionized water a, mix them by magnetic stirring for 2 h, then let it stand for 12 h, filter, dry the filter cake at 105 °C for 12 h, then heat it to 700 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 2 h, and then successively carry out pickling with 2 M hydrochloric acid, wash it with deionized water at 60 °C until the pH reaches 7.0, and dry it at 105 °C for 12 h to obtain activated carbon particles.

[0048] S3. Mix the activated carbon particles obtained in S2 (2 g) with urea (8 g), add 50 mL of deionized water b, shake and mix for 8 h, then let it stand. After filtration, wash the filter cake with deionized water until the pH reaches 7.0, dry it at 105 °C for 4 h, then heat it by microwave, and after cooling, obtain a doped activated carbon supercapacitor electrode material with a high specific surface area capacitance (named C1N4).

[0049] Comparative Example 1

[0050] The preparation method of the activated carbon particles in this comparative example is the same as steps S1 - S2 of Example 1. The prepared activated carbon particles are named C1N0).

[0051] Figure 1 It is a comparison chart of the specific capacitance vs. specific surface area of the best electrode of the present invention and the electrodes reported in other literatures (○@2 mV / s, △@1 mA / g, ◇0.5 A / g). Among them, ○ represents the electrode specific capacitance calculated by cyclic voltammetry (CV) at a scan rate of 2 mV / s, and △ and ◇ represent the electrode specific capacitance calculated by galvanostatic charge - discharge test (GCD) at current densities of 1 mA / g and 0.5 A / g. It can be seen from this figure that among the doped activated carbons with a specific surface area similar to that of the doped banana peel activated carbon of the present invention and the doped activated carbons with a supersaturated specific surface area reported in other literatures, under the same test conditions, the C1N3 with the best performance of the present invention has a specific capacitance at least close to twice that of other doped activated carbon electrodes.

[0052] It can be seen from this that the high - electrochemical - activity specific surface capacitance of the present invention: has a higher (about twice) specific capacitance below the saturated specific surface area (1000 m 2 / g).

[0053] Figure 2 It is the low - magnification and high - magnification scanning electron microscope images of the activated carbon of the present invention before doping and at different doping coefficients. Among them, 7(d) is the undoped activated carbon C1N0, and 7(e - h) are the doped activated carbons C1N1, C1N2, C1N3, and C1N4 respectively. It can be seen from the figure that the undoped activated carbon 7(d and d1) has spatial mesopores and some micropores connected by continuous strips. After urea doping treatment, as the urea concentration increases, its micro - corrosion effect etches out a high - density small - micropore group on the pore wall. When C:N = 1:3, the small micropores are interconnected. However, when the urea concentration reaches C:N = 1:4, the urea concentration is too high, resulting in an overly thin etched pore wall and causing the pore structure to collapse and pulverize.

[0054] It can be seen from this that the doped activated carbon supercapacitor electrode active material with a high specific surface area capacitance of the present invention has a three - dimensionally connected mesoporous - wall - embedded micropore - group structure, which can maximize the active surface area of the electrode and greatly improve the infiltration of the electrolyte into the surface micropores.

[0055] Figure 3 For the Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) of the doped banana-derived activated carbon of the present invention and their diagrams of different element contents. As can be seen from the figures, FTIR ( Figure 3 a) The results show that in a limited oxygen atmosphere, the activated carbon prepared from banana peel has carbon-oxygen single bonds, carbon-oxygen double bonds, and hydroxyl groups. After doping, the activated carbon has rich single bonds and double bonds formed by nitrogen element and carbon, and nitrogen and oxygen coexist. XRD ( Figure 3 b) The results show that doping makes the activated carbon have a higher layered graphite structure and has a typical graphite crystal structure of (002) plane. This layered structure is more regular. XPS ( Figure 3 c) The results show that the doped activated carbon has rich oxygen element content and a certain nitrogen element content. Through the quantitative analysis of the XPS results, it is found that after the urea concentration increases, the nitrogen element content in the activated carbon increases, gradually replacing the oxygen element, and the carbon content increases during the doping process. The results show that the prepared activated carbon in the doped activated carbon has a good layered structure and rich O and N hybrid elements.

[0056] It can be seen therefrom that the doped banana-derived activated carbon of the present invention has rich carbon-oxygen, carbon-nitrogen and nitrogen-oxygen bonds, also has a graphite-like layered graphite carbon structure, and also has rich oxygen and nitrogen elements and their functional groups, which can improve the conductivity of the doped activated carbon material of the present invention and increase the electrode specific capacitance.

[0057] Figure 4 For the cyclic voltammetry (4a), galvanostatic charge-discharge (4b) of the doped activated carbon supercapacitor electrode with high specific surface area capacitance of the present invention and its calculated specific capacitance diagrams (4c and 4d). As can be seen from the figures, the specific capacitance of the doped activated carbon increases significantly, but the specific capacitance of C1N4 with too high urea concentration drops significantly, which is consistent with the observed microstructure trend.

[0058] It can be seen therefrom that the calculated specific capacitance of the optimal electrode (C1N3) of the present invention is 537 F·g -1 (cyclic voltammetry method, 2 mV·s -1 ) and 1020 F·g -1 (galvanostatic charge-discharge method, 1 A·g -1 ).

[0059] Figure 5 For the diagram of the influence of the doped element content on the electrode specific capacitance of the present invention, where Figure 6 (a) is the relationship between the pseudocapacitance and the element content of the pure activated carbon and the doped activated carbon electrodes, where the element content is the quantitative analysis result of XPS, and the pseudocapacitance is the percentage content of the specific capacitance calculated by cyclic voltammetry in the total capacitance. By Figure 5(a) It can be seen that the pseudocapacitance increases with the increase of nitrogen and decreases with the decrease of oxygen element, indicating that nitrogen element has a stronger ability to provide pseudocapacitance through redox reactions than oxygen element. Figure 5 (b) It is the content analysis of different N-containing functional groups in each activated carbon. Among them, N-5 is pyrimidine nitrogen, which can provide active sites; N-6 is pyrrole nitrogen, which can increase the mobility of ions; N-O is nitrogen oxide, which is a suspended oxygen structure and has no obvious effect on capacitance; N-Q is tetravalent nitrogen or graphitic nitrogen, which can assist redox reactions and improve pseudocapacitance. Among them, N-5 and N-6 can provide electrons, and N-Q can provide electrons or accept protons. Therefore, the presence of these three kinds of nitrogen can achieve the effects of reducing reaction resistance and increasing conductivity. The specific capacitance is more sensitive to the increase of N element content than O element, and by increasing N-5 and N-6 that help increase active sites and N-Q that assist redox reactions, the internal resistance can be reduced and the specific capacitance can be increased.

[0060] It can be seen from this that with the increase of the doping source concentration, the contents of N-5 and N-6, which are beneficial to reducing resistance and providing higher pseudocapacitance, increase, thereby improving the pseudocapacitance. Combining with the N-Q functional group, this doping can further improve its electrochemical performance.

[0061] Figure 6 This is the AC impedance spectrum and calculated internal resistance diagram of the doped activated carbon supercapacitor electrode with high specific surface area capacitance of the present invention. It can be seen from the figure that the specific surface areas of C1N0, C1N1, C1N2, C1N3 and C1N4 are 900.55, 921.07, 942.66, 901.38 and 936.83 m 2 / g respectively. The advantage of the present invention in specific surface area can greatly increase the electrochemical active surface area and achieve the effect of increasing the capacitance of the activated carbon electrode.

[0062] The electrode materials of the doped activated carbon supercapacitor with high specific surface area capacitance prepared in Examples 1 to 4 can be used as the electrode materials of supercapacitors.

[0063] Due to its good pore structure and the stable combination of hybrid functional groups with the activated carbon substrate, the electrode material of the doped activated carbon supercapacitor with high specific surface area capacitance prepared by the present invention shows excellent capacitance among similar heterocyclic atom-doped activated carbon materials.

[0064] The present invention uses banana peel-derived doped activated carbon as the electrode material of supercapacitors. Essentially, it utilizes the high conductivity and surface area of activated carbon (physical adsorption and desorption process), as well as the doped heterocyclic atoms to assist ion transfer and participate in redox reactions to provide higher conductivity and higher capacitance. Other banana peel-derived porous carbons are essentially the matrix materials of catalysts, forming composite electrodes with surface modifiers to catalyze the oxidation reaction of methanol in fuel cells.

[0065] The present invention introduces heteroatoms N (2.74%) and O (16.8%) with high contents, and utilizes their physical and chemical properties to achieve the purpose of increasing active sites, reducing internal resistance and increasing the capacitance of the activated carbon electrode.

[0066] When C1N0, C1N1, C1N2, C1N3 and C1N4 are used for the supercapacitor electrode, the electrolyte is 6M KOH, the counter electrode is a platinum wire, and the reference electrode is Ag / AgCl. Using the constant current charge-discharge test method at 1 A·g -1 −1, their capacitances are 674, 902, 795, 1020 and 469 F·g -1 −1 respectively; using the cyclic voltammetry method at 2 mV / s, their capacitances are 365, 407, 377, 537 and 333 F·g -1 −1 respectively. Their calculated internal resistances are 23, 16.6, 15.8, 13.3 and 19.9 Ω / 2.4 g (calculated by the impedance method).

[0067] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes and equivalent changes made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. Application of a doped activated carbon supercapacitor electrode material with high specific surface area capacitance, Characterized in that, The doped activated carbon supercapacitor electrode material with high specific surface area is used as the electrode material for supercapacitors; using the constant current charge-discharge test method at 1 A∙g -1 The capacitance is 469 F∙g -1 ~1020 F∙g -1 ; Using cyclic voltammetry measurement method at 2 mV / s, the capacitance is 333 F∙g -1 ~537 F∙g -1 ; The preparation method of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance is as follows: S1. After cutting the banana peel into pieces, drying and grinding, a sample to be treated is obtained; S2. After mixing the sample to be treated obtained in S1 with KOH and adding deionized water a, magnetically stirring for 2 h, standing for 12 h, filtering, drying the filter cake, heating to 700 °C at a heating rate of 10 °C / min, performing constant temperature treatment for 2 h, then successively performing pickling with 2 M hydrochloric acid and washing with deionized water at 60 °C until the pH is 6.5 - 7.0, and drying to obtain activated carbon particles; the dosage ratio of the sample to be treated, KOH and deionized water a in S2 is 30 g:60 g:500 mL; S3. After mixing the activated carbon particles obtained in S2 with urea, adding deionized water b, oscillating and mixing for 8 h and then standing, filtering, washing the filter cake with deionized water until the pH is 7.0, drying, performing microwave heating, and cooling to obtain a doped activated carbon supercapacitor electrode material with high specific surface area capacitance; the dosage ratio of the activated carbon particles, urea and deionized water b in S3 is 2 g:(2 - 8) g:50 mL; the conditions of the microwave heating in S3 are: 800 W, 1 min; the specific surface area of the doped activated carbon supercapacitor electrode material with high specific surface area capacitance in S3 is 901.38 m² / g - 942.66 m² / g.

2. The application of a doped activated carbon supercapacitor electrode material with high specific surface area capacitance according to claim 1, Characterized in that, The drying condition in S1 is 105 °C, 24 h.

3. The application of a doped activated carbon supercapacitor electrode material with high specific surface area capacitance according to claim 1, Characterized in that, The drying condition in S2 is 105 °C, 12 h.

4. The application of a doped activated carbon supercapacitor electrode material with high specific surface area capacitance according to claim 1, Characterized in that, The drying condition in S3 is 105 °C, 4 h.

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