A supercapacitor carbon material prepared by coupling hydrochloric acid with ultrasonic secondary activation of municipal sludge, and its preparation method and application

Abstract

The present invention discloses a supercapacitor carbon material prepared by hydrochloric acid coupling ultrasonic secondary activation of urban sludge, and its preparation method and application. In the present invention, urban sludge is hydrolyzed in subcritical water, and then solid-liquid separation is carried out to obtain an aqueous phase rich in urban sludge organic matter; the aqueous phase rich in urban sludge organic matter is subjected to hydrothermal co-carbonization with glucose to obtain hydrothermal carbon; the hydrothermal carbon is mixed with potassium hydroxide and activated in a high-temperature inert atmosphere; then the activated hydrothermal carbon is subjected to secondary activation under the coupling action of hydrochloric acid and ultrasonic waves, and finally a supercapacitor carbon material can be obtained. The electrode made of this supercapacitor carbon has a specific capacitance of 420.90 F / g at a current density of 1 A / g in a 6 mol / L KOH electrolyte under a three-electrode system. When the current density is 1 A / g and the power density is 1000 W / kg, the energy density is 47.67 Wh / kg. At a high current density of 10 A / g, the capacitance retention rate after 30,000 cycles of charge and discharge still remains at 106.61%, showing excellent capacitance retention rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of supercapacitor carbon materials, and particularly relates to a supercapacitor carbon material prepared by secondary activation of urban sludge by hydrochloric acid coupling ultrasonic waves, and a preparation method and application thereof. Background Art

[0002] A supercapacitor, also known as an electrochemical capacitor, as a new type of energy storage device, has a higher energy storage capacity and a higher power density than traditional capacitors, and has characteristics such as a high power density, fast charge and discharge speed, and long cycle life. And supercapacitors are widely used in fields such as backup power supplies and power sources for hybrid electric vehicles. A supercapacitor is composed of an electrode material, an electrolyte, a separator, a current collector, and a packaging material. In the preparation of supercapacitors, the key link is the preparation of the electrode material, and among them, carbon-based materials are in the majority. Compared with materials such as graphene and transition metal oxides, porous carbon materials have many excellent properties such as light weight, large specific surface area, good stability, high temperature resistance, acid and alkali resistance, and non-toxicity, and have received extensive attention from the industry and academia in recent years.

[0003] The supercapacitor electrode prepared from porous carbon materials is a type of electric double layer supercapacitor, which mainly stores charges through ions enriched on the electrode. Low specific capacitance, poor conductivity, and low energy density are the aspects that need to be improved for electric double layer capacitors. Existing research has shown that urban sludge contains a large amount of organic substances and a large amount of elements such as nitrogen and phosphorus. By doping nitrogen into the carbon material, the addition of nitrogen-containing functional groups can introduce a pseudocapacitance reaction, and at the same time increase the surface polarity of the porous carbon material, making the wettability of the ion channels increase, which can greatly improve the electrochemical performance of the material. Therefore, reasonably using sludge as a nitrogen source to prepare a nitrogen-containing carbon material for preparing a supercapacitor electrode can effectively improve the material performance. CN111508726A discloses a preparation method of dendritic fiber-shaped hollow nitrogen-doped carbon nanocages for supercapacitors, with a specific capacitance as high as 350 F / g at 0.1 A / g, but the specific surface area is small and the operation process is complicated. CN116206906A discloses a preparation method of a high-temperature carbonized nitrogen-doped core-shell structured activated carbon composite electrode, and an electrode material with a specific capacitance as high as 389 F / g at 0.1 A / g is obtained, but the operation amount is small and the reaction time is long.

[0004] The common way of hydrothermal carbon activation is mainly to fully mix the activators (such as potassium hydroxide, phosphoric acid, etc.). During the high-temperature pyrolysis process, the activator (KOH) decomposes into metal cations and hydroxyl anions. The activator and hydrothermal carbon form a solvate complex, and the metal cations are attracted to the carbon hydroxyl surface, followed by the activation process. The positively charged solvate complex inserts into the carbon structure of the porous carbon. These reactions result in the formation of micropores or mesopores on the synthesized porous carbon. However, after activation, part of the potassium hydroxide remains in the activated carbon material, and it is impossible to effectively remove the activator remaining in the pores by directly rinsing with deionized water. Especially compared with the hydrothermal carbon prepared from urban sludge, the hydrothermal carbon prepared by directly hydrothermal carbonizing pure sugar sources contains more impurities such as ash. If not removed in time and effectively, it will block the pores of the activated carbon material and cannot maximize the activation efficiency of this activation method. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a supercapacitor carbon material prepared by hydrochloric acid-coupled ultrasonic secondary activation of urban sludge, its preparation method and application, so as to solve the technical problems of the supercapacitor electrode material prepared by the existing technology, such as small specific surface area, small specific capacitance, serious attenuation of specific capacitance after multiple cycles, and complicated operation process.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention discloses a method for preparing a supercapacitor carbon material by hydrochloric acid-coupled ultrasonic secondary activation of urban sludge, comprising the following steps:

[0008] 1) Preparation of urban sludge-based hydrothermal carbon

[0009] Hydrolyze and pre-treat urban sludge in subcritical water to obtain an urban sludge hydrolysis solution. Mix the urban sludge hydrolysis solution, deionized water and glucose, and then carry out hydrothermal carbonization treatment. Separate the carbonization product to obtain urban sludge-based hydrothermal carbon;

[0010] 2) Primary activation of urban sludge-based hydrothermal carbon

[0011] Mix urban sludge-based hydrothermal carbon and potassium hydroxide and grind them, and then carry out high-temperature activation treatment under an inert atmosphere to obtain a mixture of primary-activated hydrothermal carbon and potassium hydroxide;

[0012] 3) Secondary activation of urban sludge-based hydrothermal carbon

[0013] Add the mixture of primary-activated hydrothermal carbon and potassium hydroxide to a hydrochloric acid solution, carry out ultrasonic treatment, and then carry out static settlement, solid-liquid separation, washing and drying and grinding treatment to obtain a supercapacitor carbon material.

[0014] Preferably, in step 1), the hydrolysis pretreatment conditions are as follows: in an air atmosphere, the temperature of subcritical water is 200-250 °C, the stirring rate is 1000-1500 revolutions per minute, and the treatment time is 1-2 hours.

[0015] More preferably, the temperature of subcritical water is 225-235 °C, the stirring rate is 1000-1200 revolutions per minute, the treatment time is 1-1.2 hours, and the sludge hydrolysis yield is 48.21%-48.94%.

[0016] Preferably, in step 1), the mass ratio of the sludge hydrolysis liquid, deionized water and glucose during the hydrothermal carbonization process is (2-14):(1-14):1.

[0017] The hydrothermal carbonization conditions are as follows: in an air atmosphere, at 200-280 °C, for 0.8-2 hours, and the stirring rate during the reaction process is 90-150 revolutions per minute.

[0018] More preferably, the hydrothermal carbonization conditions are as follows: in an air atmosphere, at 235-245 °C, for 0.8-1.2 hours, and the stirring rate during the reaction process is 90-110 revolutions per minute.

[0019] Preferably, in step 2), the mass ratio of the hydrochar from municipal sludge and potassium hydroxide in the primary activation is 1:(1-3); the high-temperature activation treatment temperature is 700-900 °C, and the treatment time is 0.8-2 hours.

[0020] More preferably, the mass ratio of the hydrochar from municipal sludge and potassium hydroxide in the primary activation is 1:(2.9-3.1); the high-temperature activation treatment temperature is 790-810 °C, and the treatment time is 0.8-1.2 hours.

[0021] Preferably, in step 3), the dosage ratio of the mixture of the hydrochar from the primary activation and potassium hydroxide to the hydrochloric acid solution is 1:(210-280); the concentration of the hydrochloric acid solution is 1 mol / L.

[0022] Preferably, in step 3), the temperature of the ultrasonic treatment is 25-35 °C, the ultrasonic treatment time is 25-35 minutes; the standing time is more than 12 hours.

[0023] The present invention also discloses a supercapacitor carbon material prepared by the above method.

[0024] The present invention also discloses the application of the above supercapacitor carbon material in the preparation of supercapacitor electrodes.

[0025] The present invention also discloses a supercapacitor electrode made of the above supercapacitor carbon material.

[0026] Preferably, in a three - electrode system, in a 6 mol / L KOH aqueous electrolyte, the specific capacitance value is 353 - 420 F / g at a current density of 1 A / g; when the current density is 1 A / g and the power density is 1000 W / kg, the energy density is 43.14 - 47.67 Wh / kg, and the specific capacitance retention rate is not less than 106.61% after 30000 continuous charge - discharge cycles at a high current density of 10 A / g.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The preparation method of the supercapacitor carbon material prepared by hydrochloric acid - coupled ultrasonic secondary activation of urban sludge disclosed in the present invention uses the hydrolyzed extract of urban sludge as a raw material for preparing the supercapacitor carbon material. First, the Maillard reaction between amino acids and glucose produced by the hydrolysis of urban sludge protein is utilized to strengthen the conversion of urban sludge protein, and nitrogen in the urban sludge protein is maximally converted into the product - hydrothermal carbon. Then, potassium hydroxide is used to assist in pore formation to increase the specific surface area, enhance the ion transport rate, and increase active sites while improving the electrochemical performance of the supercapacitor electrode material. Then, the activated sample is treated with hydrochloric acid to make the pore - forming process of the nitrogen - containing carbon material more complete, effectively removing residual alkaline substances and ash, minimizing the influence of inorganic ash on the electrical conductivity of the material. At the same time, ultrasonic treatment is used in the secondary activation process. Ultrasonic waves can accumulate energy through cavitation, and then the cavitation bubbles collapse instantaneously to release energy sharply, breaking the chemical bonds of reactants, breaking through the interface limitations of the multiphase system, and strengthening heat and mass transfer. At the same time, the shock waves and micro - jets generated by cavitation can continuously clean and strip impurities adsorbed on the surface of the carbon material; it can cause strong intermolecular collisions and aggregations, resulting in significant changes in the structure, composition, and reaction activity of the carbon material, thereby enhancing the catalytic effect. Therefore, the method for improving the electrochemical performance of hydrothermal carbon based on urban sludge by hydrochloric acid - coupled ultrasonic secondary activation disclosed in the present invention has technical advantages such as simple operation, low cost, and low energy consumption, and is an economical and efficient method for improving the electrochemical performance of carbon materials based on urban sludge. Description of the Drawings

[0029] Figure 1 SEM image of the supercapacitor carbon material prepared in Example 1;

[0030] Figure 2 Contact angle image of the supercapacitor electrode sheet prepared in Example 1;

[0031] Figure 3 Nitrogen adsorption / desorption curve of the supercapacitor carbon material prepared in Example 1;

[0032] Figure 4Pore size distribution diagram of the supercapacitor carbon material prepared in Example 1;

[0033] Figure 5 Cyclic voltammetry curves of the supercapacitor carbon material prepared in Example 1 at different scanning rates;

[0034] Figure 6 Galvanostatic charge-discharge curves of the supercapacitor carbon material prepared in Example 1 at different current densities;

[0035] Figure 7 Capacitance retention rate diagram of the supercapacitor carbon material prepared in Example 1 after 30,000 cycles;

[0036] Figure 8 Specific capacitance diagram of the supercapacitor carbon material prepared in Example 1. Detailed implementation manners

[0037] In order to enable those skilled in the art of the present technology to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0039] The present invention will be further described in detail below with reference to the accompanying drawings:

[0040] The municipal sludge used in the following embodiments of the present invention is taken from Xi'an Chuangye Water Service Co., Ltd. After the retrieved sludge is all packed into self-sealing bags and placed in a 4°C refrigerator for storage.

[0041] Example 1

[0042] A method for preparing a supercapacitor carbon material by hydrochloric acid coupling ultrasonic secondary activation of municipal sludge, comprising the following steps:

[0043] Step 1: Preparation of hydrothermal carbon from municipal sludge

[0044] 1) Mix 40 g of municipal sludge and 140 mL of deionized water, then add the mixture into a 200 mL autoclave and seal it. Place the autoclave in a salt bath and react at 230 °C for 1 hour with a rotation speed of 1000 r / min. After the reaction, wait for the autoclave to cool down, then separate the mixture in the autoclave through a Buchner funnel. Collect the liquid phase and store it in a 4 °C refrigerator. The hydrolysis rate of sludge organic matter at this stage is 48.89%.

[0045] 2) Weigh 5 g of glucose, mix 14 mL of sludge filtrate and 56 mL of deionized water, then add the mixture into a high-pressure reaction kettle and seal it. Heat it to 240 °C in a heating jacket and react for 1 hour with a rotation speed of 100 r / min. After the reaction, wait for the autoclave to cool down, then separate the mixture in the autoclave through a Buchner funnel. Place the separated solid product in an oven for 12 hours and then grind it to obtain hydrothermal carbon from municipal sludge. The yield of hydrothermal carbon from municipal sludge is 47.2%.

[0046] Step 2: Primary activation of hydrothermal carbon from municipal sludge

[0047] 1) Mix 0.6 g of the hydrothermal carbon from municipal sludge prepared above and potassium hydroxide in a ratio of 1:3, then grind the mixture. Put the ground mixture into a corundum boat.

[0048] 2) Under the protection of inert gas, heat the mixture obtained in step 1) to 800 °C at a heating rate of 10 °C / min and hold for 1 hour. After cooling to room temperature, take it out to obtain a nitrogen-containing activated carbon material (i.e., the mixture of primary-activated hydrothermal carbon and potassium hydroxide).

[0049] Step 3: Secondary activation of hydrothermal carbon from municipal sludge

[0050] 1) Pour the nitrogen-containing activated carbon material prepared above into 70 mL of hydrochloric acid with a concentration of 1 mol / L at a temperature of 30 °C, perform ultrasonic treatment for 30 minutes, and let it stand for more than 12 hours.

[0051] 2) Wash the carbon material obtained in step 1) to neutral, dry it, and grind it to obtain a supercapacitor carbon material. The yield of the secondary-activated hydrothermal carbon material is 50.2%.

[0052] The method for preparing a supercapacitor electrode using the supercapacitor carbon material prepared by the method of this example is as follows:

[0053] Mix the supercapacitor carbon material, conductive acetylene black, and PTFE binder according to a mass fraction of 16:3:1 in ethanol and ultrasonicate for a period of time to obtain a slurry. After drying the slurry, press it into a thin electrode material sheet with a diameter of 10 mm; press the nickel foam into a thin nickel foam sheet with a diameter of 15 mm, cut a nickel strip with a length of 150 mm, and place the thin electrode material sheet and the nickel strip between two thin nickel foam sheets and use a tablet press to press them into a supercapacitor electrode.

[0054] Combined with the tests of relevant supercapacitor electrode materials, under this condition, the specific capacitance of the electrode material in 6 mol / L KOH electrolyte at a current density of 1 A / g is 353.45 F / g, and the energy density is 43.14 Wh / kg at a current density of 1 A / g and a power density of 1000 W / kg.

[0055] See Figure 1 , from Figure 1 It can be seen that the nano-porous structure of the supercapacitor carbon material prepared by using hydrochloric acid ultrasonic activation of sludge in combination with glucose carbonization in Example 1 has more micropores.

[0056] See Figure 2 , from Figure 2 It can be seen that the contact angle of the supercapacitor carbon material prepared by using hydrochloric acid ultrasonic activation of sludge in combination with glucose carbonization in Example 1.

[0057] See Figure 3 , from Figure 3 It can be seen that the nitrogen adsorption / desorption curve of the supercapacitor carbon material prepared by using hydrochloric acid ultrasonic activation of sludge in combination with glucose carbonization in Example 1 shows an obvious type I, indicating that it has obvious microporous structure characteristics, and its BET specific surface area is 2162.74 m 2 / g.

[0058] See Figure 4 , from Figure 4 It can be seen that the pore size distribution curve of the supercapacitor carbon material prepared by using hydrochloric acid ultrasonic activation of sludge in combination with glucose carbonization in Example 1 is mainly concentrated in micropores below 2 nm.

[0059] See Figure 5 , from Figure 5 It can be seen that in Example 1, the supercapacitor carbon material prepared by using hydrochloric acid ultrasonic activation of sludge in combination with glucose carbonization in Example 2 shows symmetry up and down at different current densities, presenting a quasi-rectangular pattern.

[0060] See Figure 6 , from Figure 6It can be seen that for the CV curves of Example 2 of the supercapacitor carbon material prepared by the synergistic carbonization of hydrochloric acid-ultrasonic-activated sludge and glucose in Example 1, the curves have good symmetry, the charge and discharge times are consistent, and there is no obvious voltage drop.

[0061] See Figure 7 , from Figure 7 It can be seen that for the 30,000-cycle charge and discharge curve of Example 2 of the supercapacitor carbon material prepared by the synergistic carbonization of hydrochloric acid-ultrasonic-activated sludge and glucose in Example 1 at a current density of 10 A / g, the capacitance retention rate remains at 106.61%, indicating that the electrode material has good cycle stability.

[0062] See Figure 8 , from Figure 8 It can be seen that for the specific capacitance curve of the supercapacitor carbon material prepared by the synergistic carbonization of hydrochloric acid-ultrasonic-activated sludge and glucose in Example 1 under two-electrode testing.

[0063] Example 2

[0064] A method for preparing supercapacitor carbon materials by secondary activation of urban sludge with hydrochloric acid coupled with ultrasonic waves, comprising the following steps:

[0065] Step 1: Preparation of hydrothermal carbon based on urban sludge

[0066] 1) Mix 40 g of urban sludge and 140 mL of deionized water and add them to a 200 mL autoclave, then seal it; place the autoclave in a salt bath and react at 225 °C for 1.1 hours with a rotation speed of 1200 r / min. After the reaction is completed, wait for the autoclave to cool, then separate the mixture in the autoclave through a Buchner funnel, collect the liquid phase and store it in a 4 °C refrigerator. The hydrolysis rate of sludge organic matter at this stage is 48.21%.

[0067] 2) Weigh 5 g of glucose, mix 35 mL of sludge filtrate and 35 mL of deionized water and add them to the autoclave, then seal it; heat it to 245 °C in a heating jacket and react for 1.1 hours with a rotation speed of 95 r / min. After the reaction is completed, wait for the autoclave to cool, then separate the mixture in the autoclave through a Buchner funnel, and place the separated solid product in an oven for 12 hours and then grind it to obtain hydrothermal carbon based on urban sludge, and the yield of hydrothermal carbon based on urban sludge is 49.4%.

[0068] Step 2: Primary activation of hydrothermal carbon based on urban sludge

[0069] 1) Mix 0.6 g of the above-prepared hydrothermal carbon based on urban sludge and potassium hydroxide in a ratio of 1:2.9 and grind them, then put the ground mixture into a corundum boat;

[0070] 2) Under the protection of inert gas, the mixture obtained in step 1) is heated to 800 °C at a heating rate of 10 °C / min and held for 1 hour, then taken out after cooling to room temperature to obtain a nitrogen-containing activated carbon material (i.e., a mixture of primary activated hydrothermal carbon and potassium hydroxide).

[0071] Step 3: Secondary activation of urban sludge-based hydrothermal carbon

[0072] 1) Pour the above-prepared nitrogen-containing activated carbon material into 70 mL of hydrochloric acid with a concentration of 1 mol / L at a temperature of 35 °C, perform ultrasonic treatment for 32 minutes, and let it stand for more than 12 hours;

[0073] 2) Rinse the carbon material obtained in step 1) to neutral, dry it, and grind it to obtain a supercapacitor carbon material. The yield of the secondary-activated hydrothermal carbon material is 47.2%.

[0074] The method for preparing a supercapacitor electrode using the supercapacitor carbon material prepared by the above method of this example is as follows:

[0075] Mix the supercapacitor carbon material, conductive acetylene black, and PTFE binder in ethanol at a mass fraction of 16:3:1 and perform ultrasonic treatment 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 use a tablet press to press them into a supercapacitor electrode.

[0076] Combined with the tests of relevant supercapacitor electrode materials, under these conditions, the specific capacitance of the electrode material in a 6 mol / L KOH electrolyte at a current density of 1 A / g is 420.90 F / g, and the energy density is 47.57 Wh / kg at a current density of 1 A / g and a power density of 1000 W / kg.

[0077] Example 3

[0078] A method for preparing a supercapacitor carbon material by hydrochloric acid coupling ultrasonic secondary activation of urban sludge, comprising the following steps:

[0079] Step 1: Preparation of urban sludge-based hydrothermal carbon

[0080] 1) Mix 40 g of urban sludge and 140 mL of deionized water, then add them to a 200 mL high-pressure reactor and seal it; place the reactor in a salt bath and react at 228 °C for 1.1 hours at a rotation speed of 1500 r / min. After the reaction is completed and the reactor is cooled, separate the mixture in the reactor through a Buchner funnel, collect the liquid phase and store it in a 4 °C refrigerator. The hydrolysis rate of sludge organic matter at this stage is 48.66%.

[0081] 2) Weigh 5 g of glucose, mix 49 mL of sludge filtrate and 21 mL of deionized water, add the mixture to a high-pressure reactor, and seal it. Heat it to 235 °C in a heating jacket and react for 1.1 hours at a rotation speed of 90 r / min. After the reaction is completed and the reactor has cooled down, separate the mixture in the reactor through a Buchner funnel. Place the separated solid product in an oven for 12 hours and then grind it to obtain hydrothermal carbon based on municipal sludge, with a yield of 53.4% of the hydrothermal carbon based on municipal sludge.

[0082] Step 2: Primary activation of hydrothermal carbon based on municipal sludge

[0083] 1) Mix 0.6 g of the hydrothermal carbon based on municipal sludge prepared above and potassium hydroxide in a ratio of 1:3.1, grind the mixture, and place the ground mixture into a corundum boat.

[0084] 2) Under the protection of an inert gas, heat the mixture obtained in step 1) to 800 °C at a heating rate of 10 °C / min and hold for 1 hour. After cooling to room temperature, take it out to obtain a nitrogen-containing activated carbon material (i.e., a mixture of primary-activated hydrothermal carbon and potassium hydroxide).

[0085] Step 3: Secondary activation of hydrothermal carbon based on municipal sludge

[0086] 1) Pour the nitrogen-containing activated carbon material prepared above into 70 mL of hydrochloric acid with a concentration of 1 mol / L at a temperature of 30 °C, perform ultrasonic treatment for 28 minutes, and let it stand for more than 12 hours.

[0087] 2) Rinse the carbon material obtained in step 1) to neutral, dry it, and grind it to obtain a supercapacitor carbon material, with a yield of 46.5% of the secondary-activated hydrothermal carbon material.

[0088] The method for preparing a supercapacitor electrode using the supercapacitor carbon material prepared by the method of this example is as follows: Mix the supercapacitor carbon material, conductive acetylene black, and PTFE binder in ethanol at a mass fraction of 16:3:1 and perform ultrasonic treatment 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 use a tablet press to press them into a supercapacitor electrode.

[0089] Combined with the testing of relevant supercapacitor electrode materials, under this condition, the specific capacitance of the electrode material in a 6 mol / L KOH electrolyte at a current density of 1 A / g is 373.65 F / g, and the energy density is 46.21 Wh / kg at a current density of 1 A / g and a power density of 1000 W / kg.

[0090] Example 4

[0091] A method for preparing supercapacitor carbon materials by coupling hydrochloric acid and ultrasonic waves for secondary activation of urban sludge, comprising the following steps:

[0092] Step 1: Preparation of hydrothermal carbon based on urban sludge

[0093] 1) Mix 40 g of urban sludge and 140 mL of deionized water, then add the mixture into a 200 mL autoclave and seal it. Place the autoclave in a salt bath and react at 235 °C for 1 hour with a rotation speed of 1100 r / min. After the reaction ends and the autoclave cools down, separate the mixture in the autoclave through a Buchner funnel, collect the liquid phase and store it in a refrigerator at 4 °C. The hydrolysis rate of sludge organic matter at this stage is 48.94%.

[0094] 2) Weigh 5 g of glucose, mix 70 mL of sludge filtrate and 0 mL of deionized water, then add the mixture into a high-pressure reaction kettle and seal it. Heat it to 238 °C in a heating jacket and react for 1.2 hours with a rotation speed of 110 r / min. After the reaction ends and the autoclave cools down, separate the mixture in the autoclave through a Buchner funnel, place the separated solid product in an oven for 12 hours and then grind it to obtain hydrothermal carbon based on urban sludge. The yield of hydrothermal carbon based on urban sludge is 54.2%.

[0095] Step 2: Primary activation of hydrothermal carbon based on urban sludge

[0096] 1) Mix 0.6 g of the above-prepared hydrothermal carbon based on urban sludge and potassium hydroxide in a ratio of 1:3 and grind them. Put the ground mixture into a corundum boat.

[0097] 2) Under the protection of an inert gas, heat the mixture obtained in step 1) to 800 °C at a heating rate of 10 °C / min and hold for 1 hour. After cooling to room temperature, take it out to obtain a nitrogen-containing activated carbon material (i.e., a mixture of primary-activated hydrothermal carbon and potassium hydroxide).

[0098] Step 3: Secondary activation of hydrothermal carbon based on urban sludge

[0099] 1) Pour the above-prepared nitrogen-containing activated carbon material into 70 mL of hydrochloric acid with a concentration of 1 mol / L at a temperature of 31 °C, perform ultrasonic treatment for 28 minutes, and let it stand for more than 12 hours.

[0100] 2) Wash the carbon material obtained in step 1) until it is neutral, dry it, and grind it to obtain supercapacitor carbon materials. The yield of the secondary-activated hydrothermal carbon material is 46.3%.

[0101] The method for preparing a supercapacitor electrode from the supercapacitor carbon material prepared by the above method of this embodiment is as follows: Mix the supercapacitor carbon material, conductive acetylene black, and PTFE binder according to a mass fraction of 16:3:1 in ethanol 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 use a tablet press to press them into a supercapacitor electrode.

[0102] Combined with the testing of relevant supercapacitor electrode materials, under this condition, the specific capacitance of the electrode material in 6 mol / L KOH electrolyte at a current density of 1 A / g is 360.35 F / g, and the energy density is 44.03 Wh / kg at a current density of 1 A / g and a power density of 1000 W / kg.

[0103] Comparative Example 1

[0104] Different from Example 1, in the process of preparing the supercapacitor carbon material, the secondary activation of the urban sludge-based hydrothermal carbon in step 3 was not carried out, and the material after primary activation was directly used to prepare the supercapacitor electrode. After testing, its corresponding specific capacitance is 298.65 F / g.

[0105] Comparative Example 2

[0106] Different from Example 2, in the process of preparing the supercapacitor carbon material, the secondary activation of the urban sludge-based hydrothermal carbon in step 3 was not carried out, and the material after primary activation was directly used to prepare the supercapacitor electrode. After testing, its corresponding specific capacitance is 297.60 F / g.

[0107] Comparative Example 3

[0108] Different from Example 3, in the process of preparing the supercapacitor carbon material, the secondary activation of the urban sludge-based hydrothermal carbon in step 3 was not carried out, and the material after primary activation was directly used to prepare the supercapacitor electrode. After testing, its corresponding specific capacitance is 224.55 F / g.

[0109] Comparative Example 4

[0110] Different from Example 4, in the process of preparing the supercapacitor carbon material, the secondary activation of the urban sludge-based hydrothermal carbon in step 3 was not carried out, and the material after primary activation was directly used to prepare the supercapacitor electrode. After testing, its corresponding specific capacitance is 204.50 F / g.

[0111] In summary, the present invention uses sludge filtrate as a raw material to assist in the hydrothermal carbonization of glucose to obtain a nitrogen-containing carbon material, and performs activation and subsequent treatment to obtain a supercapacitor electrode material with excellent performance. The advantages of the present invention are as follows:

[0112] 1. The supercapacitor electrode material prepared by the technology of the present invention uses urban sludge as a raw material. While providing nitrogen elements to improve its electrochemical performance, the material has a rich microporous structure. In a 6 mol / L KOH electrolyte, the specific capacitance at a current density of 1 A / g is 420.90 F / g. At a current density of 1 A / g and a power density of 1000 W / kg, the energy density is 47.67 Wh / kg. At a high current density of 10 A / g, the capacitance retention rate after 30,000 cycles of charge and discharge still remains at 106.61%, showing excellent capacitance retention.

[0113] 2. The present invention adopts the hydrothermal carbonization treatment technology. The advantage of this technology is that the water content of the sample does not affect the hydrothermal carbonization process, and the nitrogen elements in the sludge filtrate are transferred to the material to the greatest extent, maximizing the utilization rate of nitrogen-containing substances in the sludge.

[0114] 3. To minimize the ash content and residual alkali in the nitrogen-containing carbon material as much as possible, hydrochloric acid is used for rinsing. While meeting the above conditions, the pore formation of the material is made more sufficient.

[0115] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A method for preparing supercapacitor carbon materials by coupling hydrochloric acid and ultrasonic waves for secondary activation of municipal sludge, characterized in that, it comprises the following steps: 1) Preparation of hydrothermal carbon based on municipal sludge The municipal sludge is subjected to hydrolysis pretreatment in subcritical water to obtain a municipal sludge hydrolysis solution. The municipal sludge hydrolysis solution, deionized water and glucose are mixed and then subjected to hydrothermal carbonization treatment. The carbonization product is separated to obtain hydrothermal carbon based on municipal sludge; wherein, the mass ratio of the municipal sludge hydrolysis solution, deionized water and glucose during the hydrothermal carbonization treatment is (2~14):(1~14):1; 2) Primary activation of hydrothermal carbon based on municipal sludge The hydrothermal carbon based on municipal sludge and potassium hydroxide are mixed and ground, and then subjected to high-temperature activation treatment in an inert atmosphere to obtain a mixture of primary-activated hydrothermal carbon and potassium hydroxide; 3) Secondary activation of hydrothermal carbon based on municipal sludge The mixture of primary-activated hydrothermal carbon and potassium hydroxide is added to a hydrochloric acid solution, subjected to ultrasonic treatment, and then subjected to standing, solid-liquid separation, washing and drying and grinding treatments to obtain supercapacitor carbon materials; In step 3), the dosage ratio of the mixture of primary-activated hydrothermal carbon and potassium hydroxide to the hydrochloric acid solution is 1:(210~280), and the concentration of the hydrochloric acid solution is 1 mol / L; the temperature of the ultrasonic treatment is 25~35°C, and the ultrasonic treatment time is 25~35 minutes.

2. The method for preparing supercapacitor carbon materials by coupling hydrochloric acid and ultrasonic waves for secondary activation of municipal sludge according to claim 1, characterized in that, in step 1), the hydrolysis pretreatment conditions are: in an air atmosphere, the temperature of the subcritical water is 200~250°C, the stirring rate is 1000 - 1500 revolutions per minute, and the treatment time is 1~2 hours.

3. The method for preparing supercapacitor carbon materials by coupling hydrochloric acid and ultrasonic waves for secondary activation of municipal sludge according to claim 1, characterized in that, in step 1), the hydrothermal carbonization treatment conditions are: in an air atmosphere, at 200~280°C, for 0.8~2 hours, and the stirring rate during the reaction is 90~150 revolutions per minute.

4. The method for preparing supercapacitor carbon materials by coupling hydrochloric acid and ultrasonic waves for secondary activation of municipal sludge according to claim 1, characterized in that, in step 2), the mass ratio of the hydrothermal carbon based on municipal sludge and potassium hydroxide in the primary activation is 1:(1~3); the high-temperature activation treatment temperature is 700~900°C, and the treatment time is 0.8~2 hours.

5. The method for preparing supercapacitor carbon materials by coupling hydrochloric acid and ultrasonic waves for secondary activation of municipal sludge according to claim 1, characterized in that, in step 3), the standing time is more than 12 hours.

6. Supercapacitor carbon materials prepared by the method according to any one of claims 1~5.

7. Application of the supercapacitor carbon materials according to claim 6 in the preparation of supercapacitor electrodes.

8. A supercapacitor electrode, characterized in that, Made of the supercapacitor carbon material according to claim 6, characterized in that, under a three-electrode system, in a 6 mol / L KOH aqueous electrolyte, the specific capacitance value is 353-420 F / g at a current density of 1 A / g; when the current density is 1 A / g and the power density is 1000 W / kg, the energy density is 43.14-47.67 Wh / kg, and the specific capacitance retention rate is not less than 106.61% after continuous charge and discharge cycling 30,000 times at a high current density of 10 A / g.

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