Method for preparing nitrogen-rich super-capacitor carbon material through wet sludge activation and nitrogen fixation
Through in-situ alkali-heat microwave activation and phosphate dynamic nitrogen-etching technology, the problems of high energy consumption, single pore structure and low nitrogen doping content of carbon materials for wet sludge preparation are solved, and the construction of multi-stage pore structure and stable nitrogen doping is achieved, which improves electrochemical energy storage performance and process economy.
Patent Information
- Application Number
- CN202510574396.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-06
- Publication Date
- 2025-06-20
AI Technical Summary
The prior art has high energy consumption, a single pore structure and a low nitrogen doping content when preparing carbon materials in wet sludge, resulting in poor electrochemical energy storage performance.
Through in-situ alkali-heat microwave activation of wet sludge, microwave excitation reaction between alkali and biomass ash is used to reduce drying energy consumption and pre-construct a macroporous-mesporous structure. Combined with the phosphoric acid dynamic nitrogen fixation-etching technology, micropores are formed during the pyrolysis process and P-N-C coordination structure is constructed to fix the nitrogen component.
The construction of a multi-stage pore structure has been realized, which significantly improves the ion transmission efficiency and charge storage capacity of the electrolyte, improves the stability and retention rate of nitrogen doping, and reduces process energy consumption.
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Figure CN120172406A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the cross - technical field of solid waste resource utilization and new energy materials, and particularly relates to a method for preparing nitrogen - rich supercapacitor carbon materials by activating and nitrogen - fixing wet sludge. Background Art
[0002] With the accelerating progress of urbanization, the annual output of urban sludge shows a continuous growth trend, and its safe disposal has become a major challenge threatening the safety of the ecological environment. The current mainstream landfill and incineration disposal methods are facing increasingly severe environmental pressures and technical bottlenecks. The technical path of pyrolyzing sludge into supercapacitor carbon materials has become a research hotspot in the field of environmental functional materials because of its dual value of both solid waste resource utilization and new energy electrode material development. However, there are still significant defects in the key process links of the existing technical system.
[0003] First of all, in terms of pore structure regulation, the preparation of traditional sludge pyrolysis carbon materials mostly uses a single chemical activation method. Taking the typical KOH activation process as an example, although it has a relatively high specific surface area, the single - pore system dominated by micropores in the obtained materials leads to the obstruction of electrolyte ion transport kinetics. Although recent research has tried to introduce template agents such as nano - metal salts, silica, and metal oxides to construct mesoporous structures, there are still disadvantages such as increased process complexity, risk of secondary pollution, and limited technical economy.
[0004] In terms of nitrogen element fixation, sludge, as a natural nitrogen - rich biomass, should inherently have the advantage of preparing nitrogen - doped carbon materials. However, during the conventional high - temperature pyrolysis process, the volatilization loss rate of organic nitrogen components can reach more than 60%. Although the existing urea - assisted nitrogen - fixation technology can increase the nitrogen content, it has defects such as poor nitrogen - doping stability and easy decomposition at high temperatures, which seriously restricts the electrochemical energy storage performance of the materials.
[0005] Furthermore, in terms of controlling the energy consumption of pretreatment, wet sludge (with a water content > 60%) needs to be dried before pyrolysis conversion. Traditional thermal drying technology has high energy consumption, significantly increasing the overall process cost.
[0006] The above - mentioned technical pain points together expose the systematic deficiencies of the existing technical system in key links such as multi - level pore construction, nitrogen - doping stability regulation, energy consumption optimization, and process integration. How to achieve the coordinated optimization of pore engineering, element doping, and energy - saving processes has become the core technical problem restricting the industrialization of sludge - based supercapacitor carbon materials. Summary of the Invention
[0007] Aiming at the existing technical problems above, the purpose of the present invention is to provide a method for preparing nitrogen - rich supercapacitor carbon materials by activating and nitrogen - fixing wet sludge, so as to solve the problems of high energy consumption, single voids, and low nitrogen - doping content in the preparation of carbon materials from wet sludge.
[0008] To achieve the above object, the present invention is realized through the following technical solutions:
[0009] A method for preparing nitrogen-rich supercapacitor carbon materials by activating and nitrogen-fixing wet sludge. First, through in-situ alkali-thermal microwave activation of wet sludge, using the microwave-excited reaction of alkali with SiO2 in biomass ash, on the one hand, the drying energy consumption is reduced; on the other hand, macropore-mesopore prefabrication is realized in-situ. Secondly, coupling with the dynamic nitrogen-fixing and etching technology of phosphoric acid, micropores are formed by gas etching during pyrolysis, and at the same time, PO4 3- and pyridine nitrogen are used to construct a P-N-C coordination structure to fix more nitrogen components in the carbon; specifically, it includes the following steps:
[0010] S1. Mix the wet sludge and the composite alkali activator evenly, and carry out alkali-thermal activation drying under microwave conditions to obtain a composite alkali-thermal microwave activation product; the composite alkali activator is selected from a mixture of one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and biomass ash, and the biomass ash needs to meet the requirement that the Fe2O3 content > 0.2%; through the microwave synergistic effect of the composite alkali activator and biomass ash, pores are pre-constructed in the low-temperature activation stage;
[0011] S2. Mix the composite alkali-thermal microwave activation product obtained in step S1 and the KH2PO4 nitrogen-fixing agent evenly, and then place them in a pyrolysis furnace for in-situ reaction for pyrolysis phosphorus etching. Keep it at 600 - 800 °C for 1 hour under the protection of inert gas to obtain a pyrolysis product with a micropore-mesopore-macropore through-hole system;
[0012] S3. Take out the pyrolysis product obtained in step S2, wash it and dry it to obtain the supercapacitor carbon material.
[0013] Preferably, the water content of the wet sludge is 60% - 85%.
[0014] Preferably, in S1, the temperature during the alkali-thermal activation drying process under microwave conditions is controlled at 80 - 100 °C, the microwave power is 300 - 500 W, the working frequency is 2.45 GHz, and the time is 5 hours.
[0015] Preferably, in S1, the mass ratio of alkali to biomass ash in the composite alkali activator is 5:5 - 7:3.
[0016] Preferably, in S1, the mass ratio of the wet sludge to the composite alkali activator is 30:1 - 30:5.
[0017] Preferably, in S1, the content of the KH2PO4 nitrogen-fixing agent is 10 wt%.
[0018] Preferably, the washing process uses deionized water or distilled water and is washed until the washing liquid is neutral.
[0019] The supercapacitor carbon material prepared by the method described above.
[0020] Application of the supercapacitor carbon material described above as an electrode material in a supercapacitor.
[0021] Compared with the prior art, the present invention has the following beneficial effects:
[0022] The present invention shows multi-dimensional innovative breakthroughs compared with the prior art, and systematic optimization has been achieved in key process links. Through the microwave synergistic effect of the composite alkali activator and biomass ash, the dependence on traditional templating agents has been broken through. Pores are pre-constructed innovatively in the low-temperature activation stage, and a through-system of micropores-mesopores-macropores is realized in combination with pyrolytic phosphorus etching. The hierarchical pore structure not only significantly improves the ion transport efficiency of the electrolyte, but also enhances the charge storage capacity through the pore channel synergy effect.
[0023] In terms of nitrogen element fixation, the phosphoric acid nitrogen fixation technology is used to form a stable nitrogen-doped configuration through in-situ reactions during pyrolysis, effectively suppressing the volatilization of nitrogen components in a high-temperature environment, and significantly improving the nitrogen retention rate and structural stability compared with traditional external nitrogen doping processes.
[0024] In terms of process energy consumption control, the innovative alkali-thermal microwave synergistic drying mechanism is adopted to directly activate and treat wet sludge with high moisture content, reducing the energy consumption of pretreatment while avoiding the high energy consumption of traditional thermal drying, forming a more economical technical path.
[0025] In addition, using urban sludge as a raw material, converting traditional disposal problems into advantages in the preparation of functional materials, the prepared supercapacitor carbon material has an excellent specific surface area and a high nitrogen element doping amount, effectively improving its electrochemical performance as an electrode material in the field of supercapacitors. The high-value conversion of "solid waste - material" is realized, providing a conversion path with both environmental and economic benefits for the resource utilization of urban solid waste. Description of the Drawings
[0026] Figure 1 XPS spectral peak fitting for the supercapacitor carbon material;
[0027] Figure 2 SEM image of the supercapacitor carbon material;
[0028] Figure 3 Specific capacitance diagram of the supercapacitor carbon material;
[0029] Figure 4 Cyclic voltammetry curves of the supercapacitor carbon material at different scanning rates;
[0030] Figure 5 Galvanostatic charge-discharge curves of the supercapacitor carbon material at different current densities. Detailed Description of the Invention
[0031] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.
[0032] The urban wet sludge used in the following embodiments of the present invention is taken from the Dengjiacun Wastewater Treatment Plant in Xi'an. After being retrieved, all the sludge is put into self-sealing bags and stored in a 4°C refrigerator.
[0033] Example 1
[0034] (1) Take a part of urban sludge incineration ash (with a Fe2O3 content of 3.1%) and mix it with KOH at a mass ratio of 1:1 to obtain a composite alkali activator. Mix the urban wet sludge with this composite alkali activator evenly at a mass ratio of 30:1.
[0035] (2) Place the mixture in a microwave reactor with a working frequency of 2.45 GHz, set the microwave power to 400 W, control the reaction temperature to be stable at 90 ± 2°C, and continuously process for 5 hours. The water content of the activated product is less than 3%.
[0036] (3) Take 90 g of the above-activated product and mix it with 10 g of KH2PO4 in a ball mill for 30 minutes. Place the mixture in a tube furnace, use nitrogen as the protective gas with a flow rate of 50 mL / min, heat it to 700°C at a rate of 5°C / min and hold for 1 hour, and let the pyrolysis product cool naturally to room temperature.
[0037] (4) Place the pyrolysis product in deionized water and perform ultrasonic-assisted washing with a power of 300 W and a frequency of 40 kHz until the pH of the filtrate is 7.0. Dry it in an oven at 105°C for 12 hours and then grind it to finally obtain a black porous carbon material.
[0038] Example 2
[0039] (1) Mix the urban sludge with the composite activator at a mass ratio of 30:2. The composite activator is selected as a mixture of Na2CO3 and rice husk incineration ash (with a Fe2O3 content of 0.8%) at a ratio of 1.5:1.
[0040] (2) Place the mixture in a microwave reactor. In a 2.45 GHz microwave field, set the power to 350 W, control the reaction temperature to be 95 ± 3°C, and the treatment time to be 5 hours. The water content of the activated product is less than 5%.
[0041] (3) Mix the above activation product with 10 wt% KH₂PO₄, and under the protection of argon at 50 mL / min, heat it to 650 °C at a rate of 8 °C / min and hold for 1 hour, then the pyrolysis product is naturally cooled to room temperature.
[0042] (4) Place the pyrolysis product in deionized water, wash and filter it repeatedly until the pH of the filtrate is 7.0. Dry it in an oven at 105 °C for 12 hours and then grind it to obtain the black porous carbon material, and finally obtain the black porous carbon material.
[0043] Example 3
[0044] (1) Take urban sludge and a composite alkali activator and mix them at a mass ratio of 30:3. The composite activator is composed of K₂CO₃ and urban sludge incineration ash (with a Fe₂O₃ content of 3.1%) mixed at a ratio of 2:1.
[0045] (2) Place the mixture in a microwave reactor, control the temperature at 98 ± 2 °C under a microwave power of 500 W and process for 5 hours, and the water content of the activation product is less than 2%.
[0046] (3) Take the above activation product and mix it with 10 wt% KH₂PO₄, and under the protection of nitrogen at 50 mL / min, heat it to 800 °C at a rate of 10 °C / min and pyrolyze for 1 hour.
[0047] (4) Continuously wash the pyrolysis product with water for 2 hours using a Soxhlet extractor, dry it at 105 °C and then grind it to obtain the final product.
[0048] Effect verification
[0049] The method for preparing a supercapacitor electrode using the supercapacitor carbon material prepared in this example includes:
[0050] Mix the supercapacitor carbon material, conductive acetylene black and PTFE binder in ethanol at a mass fraction of 16:3:1 and ultrasonicate for a period of time to obtain a slurry. After drying the slurry, press it into an electrode material thin sheet with a diameter of 10 mm; press the nickel foam into a nickel foam thin sheet with a diameter of 15 mm, cut a nickel strip with a length of 150 mm, and place the electrode material thin sheet and the nickel strip between two nickel foam thin sheets and press them together into a supercapacitor electrode using a press.
[0051] Combined with the testing of relevant supercapacitor electrode materials, taking the carbon material obtained in Example 1 as an example for testing,
[0052] See Figure 1 , from Figure 1 it can be seen that the content of graphite-N in the prepared supercapacitor carbon material is about 59.67% of the total N content, which is beneficial to improving the conductivity of the material.
[0053] See Figure 2 , fromFigure 2 It can be seen that the prepared supercapacitor carbon material has significant multi-level porous characteristics.
[0054] See Figure 3 , from Figure 3 It can be seen that the specific capacitance of the prepared supercapacitor carbon material in 6 mol / L KOH electrolyte at a current density of 1 A / g is 317.6 F / g.
[0055] See Figure 4 , from Figure 4 It can be seen that the cyclic voltammetry curves of the prepared supercapacitor carbon material show a quasi-rectangular shape at different current densities, indicating that the storage mechanism is dominated by the electric double layer capacitance behavior. The curves have good symmetry, indicating excellent electrochemical reversibility.
[0056] See Figure 5 , from Figure 5 It can be seen that the CV curves of the prepared supercapacitor carbon material at different current densities have good symmetry, the charge and discharge times are consistent, and there is no obvious voltage drop.
[0057] The above examples show that by regulating the composition of the composite base activator, microwave parameters and the ratio of the nitrogen-fixing agent, a supercapacitor carbon material with hierarchical pores and stable nitrogen doping can be stably prepared, verifying the feasibility and technical advantages of the present invention.
Claims
1. A method for preparing nitrogen-rich supercapacitor carbon material by activating nitrogen fixation in wet sludge, characterized in that: The following steps are involved: S1. The wet sludge is fully and evenly mixed with a composite alkali activator, and alkali heat activation and drying are performed under microwave conditions to obtain a composite alkali heat microwave activation product; the composite alkali activator is selected from a mixture of one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and biomass ash, wherein the biomass ash must satisfy the requirement of Fe2O3 content>0.2%; through the microwave synergistic effect of the composite alkali activator and the biomass ash, pores are pre-constructed in the low-temperature activation stage; S2. The composite alkali thermal microwave activation product obtained in step S1 is fully mixed with the nitrogen fixer KH2PO4 and then placed in a pyrolysis furnace for in-situ reaction to perform pyrolysis phosphorus etching, and maintained at 600-800°C for 1 hour under the protection of an inert gas to obtain a microporous-mesoporous-macroporous through-system pyrolysis product; S3. The pyrolysis product obtained in step S2 is taken out, washed and dried to obtain a supercapacitor carbon material.
2. The method according to claim 1, characterized in that The moisture content of the wet sludge is 60%-85%.
3. The method according to claim 1, characterized in that In S1, the alkali heat activation drying process under microwave conditions is carried out at a controlled temperature of 80-100° C., a microwave power of 300-500 W, an operating frequency of 2.45 GHz, and a time of 5 hours.
4. The method according to claim 1, characterized in that: In S1, the mass ratio of alkali to biomass ash in the composite alkali activator is 5:5-7:
3.
5. The method according to claim 1, characterized in that: In S1, the mass ratio of the wet sludge to the composite alkali activator is 30:1-30:
5.
6. The method according to claim 1, characterized in that In S1, the content of KH2PO4 nitrogen fixer is 10wt%.
7. The preparation method according to claim 1, characterized in that: The washing process uses deionized water or distilled water until the washing liquid is neutral.
8. A supercapacitor carbon material, characterized in that: The supercapacitor carbon material is prepared by the method according to any one of claims 1 to 7.
9. A supercapacitor, characterized in that: The supercapacitor carbon material according to claim 8 is used.