Method for preparing porous activated carbon based on pulse electrochemical activation, porous activated carbon and application

Abstract

The invention discloses a method for preparing porous activated carbon based on pulse electrochemical activation, the porous activated carbon and application, and the method comprises the following steps: preparing a working electrode plate from carbon powder, and placing the working electrode plate in an electrolyte for pulse electrochemical square wave circulation treatment, wherein the electrolyte is an aqueous solution containing sulfuric acid, persulfate, sulfate and a cationic surfactant, stripping, cleaning and drying to obtain the porous activated carbon. According to the preparation method, the carbon powder is prepared into the working electrode plate, and the working electrode plate is subjected to pulse electrochemical square wave circulation treatment in the electrolyte containing the sulfuric acid, the persulfate, the sulfate and the cationic surface active agent, so that the porous activated carbon with large specific surface area, high electro-adsorption capacity and good conductivity can be prepared; when being used as a raw material for preparing a capacitive deionization electrode, the composite material shows good conductivity, high desalination capacity and high desalination rate, can be widely used for electro-adsorption desalination, and is high in use value and good in application prospect.

Description

Technical Field

[0001] This invention belongs to the field of capacitive deionization technology, and relates to a method for preparing porous activated carbon based on pulsed electrochemical activation, as well as the porous activated carbon and its applications. Background Technology

[0002] Capacitive deionization (CDI) technology, as a cutting-edge green and low-carbon water treatment method, requires its core electrode material to simultaneously meet the requirements of "high specific surface area (≥600 m²)". 2 To significantly improve wastewater treatment performance, two key indicators are required: "high surface area (≥5 S / cm, providing ample adsorption sites)" and "high conductivity (≥5 S / cm, reducing energy consumption)". Currently, commercial CDI electrodes mostly use biomass-based activated carbon (such as coconut shell activated carbon) as raw material, although its specific surface area can reach 800~1000 m². 2 While the surface area is large, the conductivity is usually below 0.5 S / cm. It is evident that existing CDI electrodes cannot simultaneously meet the requirements of large specific surface area and high conductivity, which greatly limits the widespread use of CDI technology.

[0003] The preparation of high-performance porous carbon materials using electrochemical activation methods offers advantages such as mild reaction conditions and controllable electrochemical properties of the products, making it a current research hotspot in this field. However, existing electrochemical activation methods mainly employ a constant voltage mode, lacking control over the reaction process. This can easily lead to side reactions and over-etching, making it difficult to balance the dual requirements of efficient pore formation and improved conductivity. Therefore, developing a more advanced and controllable electrochemical activation strategy is crucial.

[0004] Furthermore, with the widespread application of lithium-ion batteries in new energy vehicles, energy storage, and other fields, over one million tons of waste lithium-ion batteries are generated globally each year in recent years. Among these, graphite electrodes account for approximately 15% to 20% of the mass of lithium-ion batteries. However, waste lithium-ion battery recycling focuses on the extraction of valuable metals (lithium, cobalt, and nickel) from the cathode, while graphite electrodes are often treated as solid waste and disposed of through landfill or incineration. In particular, during the disposal process, not only may residual pollutants such as lithium and fluorine in the graphite seep into the soil, but large amounts of CO2 are also emitted, resulting in a waste of carbon resources and environmental risks.

[0005] Currently, existing technologies for recycling graphite from waste lithium-ion batteries mainly fall into two categories: The first is high-temperature thermal treatment, requiring temperatures above 2500 °C. While this can rearrange graphite atoms and restore some electrochemical performance, it is energy-intensive and easily forms amorphous carbon on the graphite surface, resulting in a 30%–50% decrease in conductivity after regeneration. The second is wet treatment of the graphite electrodes using strong acids / bases, such as oxidation with HNO3. Although this method can create pores, the graphite framework is easily over-corroded, reducing its electrochemical performance. Data shows that even with a specific surface area of ​​600 m², treatment of waste graphite electrodes with strong acids / bases can reduce their electrochemical performance. 2 The conductivity is less than 1 S / cm at a given g. This indicates that current technologies for regenerating graphite from waste lithium-ion batteries still cannot simultaneously meet the requirements of large specific surface area and high conductivity in the resulting electrode material. In particular, the carbon content of graphite electrodes from waste lithium-ion batteries typically exceeds 80%. As an ideal alternative to biomass-based activated carbon, converting it into CDI electrode material could achieve high-value utilization of waste.

[0006] For the reasons stated above, this invention is proposed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing porous activated carbon based on pulsed electrochemical activation, as well as porous activated carbon and its applications.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0009] A method for preparing porous activated carbon based on pulsed electrochemical activation includes the following steps: S1. Make working electrode sheets from carbon powder; S2. The working electrode obtained in step S1 is placed in an electrolyte for pulsed electrochemical square wave cycling treatment; the electrolyte is an aqueous solution containing sulfuric acid, persulfate, sulfate and cationic surfactant; S3. After the activated carbon on the working electrode sheet is treated with pulsed electrochemical square wave cycling in step S2, it is peeled off, cleaned, and dried to obtain porous activated carbon.

[0010] In a further improvement to the above method, step S2 includes an alternating oxidation and reduction phases in the pulsed electrochemical square wave cyclic treatment; the number of cycles for the oxidation and reduction phases is 10 to 80.

[0011] In a further improvement to the above method, the voltage of the oxidation stage is +2 V to +4 V; the duration of a single oxidation stage is 40 seconds to 90 seconds; the voltage of the reduction stage is -4 V to -6 V; and the duration of a single reduction stage is 80 seconds to 150 seconds.

[0012] In a further improvement to the above method, the voltage of the oxidation stage is +2.5 V to +3.5 V; the duration of a single oxidation stage is 40 to 60 seconds; the voltage of the reduction stage is -4.5 V to -5.5 V; and the duration of a single reduction stage is 80 to 120 seconds.

[0013] In a further improvement to the above method, in step S2, the electrolyte contains 0.05M to 0.5M sulfuric acid, 0.05M to 0.3M persulfate, 0.1M to 0.5M sulfate, and 0.005M to 0.05M cationic surfactant; the persulfate is (NH4)2S2O8 or K2S2O8; the sulfate is Na2SO4 or K2SO4; and the cationic surfactant is hexadecyltrimethylammonium bromide (CTAB) and / or dodecyltrimethylammonium bromide (DTAB).

[0014] In a further improvement to the above method, step S1 involves the following steps in the preparation of the working electrode sheet: The toner, binder A, and dispersant A are mixed and ultrasonically dispersed to obtain a slurry; The slurry is coated onto the surface of the substrate electrode and dried at 60℃~120℃ for 2 hours~8 hours to obtain the working electrode sheet.

[0015] In a further improvement to the above method, the mass ratio of the toner to binder A is 90-97:10-3.

[0016] In a further improvement to the above method, the mass of the dispersant A is 1 to 10 times the total mass of the toner and binder A.

[0017] In a further improvement to the above method, the carbon powder includes at least one of graphite powder and biomass-based activated carbon.

[0018] A further improvement to the above method, wherein the graphite powder is prepared from the graphite electrodes of waste lithium-ion batteries, includes the following steps: The graphite electrodes obtained from the dismantling of waste lithium-ion batteries are immersed in an H2SO4 solution with a concentration of 1 mol / L to 5 mol / L and treated at 25℃ to 30℃ for 6 to 24 hours to complete the delithiation. After that, they are dried at 60℃ to 120℃ for 1 to 4 hours and ground to 100 mesh to 300 mesh to obtain graphite powder.

[0019] In a further improvement to the above method, the adhesive A is at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0020] In a further improvement to the above method, the dispersant A is at least one of acetone, pure water, and N-methylpyrrolidone.

[0021] In a further improvement to the above method, the substrate electrode is one of a titanium plate, a stainless steel sheet, or carbon cloth. More preferably, the substrate electrode is a titanium plate, which possesses good conductivity, mechanical strength, and electrochemical stability, making it suitable for pulsed electrochemical activation processes.

[0022] In a further improvement to the above method, in step S3, the cleaning process involves sequentially cleaning the stripped activated carbon with anhydrous ethanol and deionized water until the conductivity of the effluent is below 10 μS / cm.

[0023] In a further improvement to the above method, in step S3, the drying temperature is 60℃~120℃; and the drying time is 2 hours~4 hours.

[0024] As a general technical concept, the present invention also provides a porous activated carbon, which is prepared by the above-described method.

[0025] The aforementioned porous activated carbon is further improved by having a specific surface area ≥ 600 m². 2 / g, conductivity ≥5S / cm.

[0026] As a general technical concept, the present invention also provides an application of the above-mentioned porous activated carbon as a raw material in the preparation of capacitor deionization electrodes.

[0027] The above-mentioned application, in a further improvement, involves preparing the capacitive deionization electrode by coating porous activated carbon, binder B, conductive agent, and dispersant B onto a current collector, including the following steps: Slurry preparation: Mix porous activated carbon, conductive agent and binder B, add dispersant B, and stir to form a uniform slurry; Electrode forming: The slurry is coated onto the current collector and dried at 60℃~120℃ for 1 hour~6 hours to obtain a capacitor deionization electrode.

[0028] In the above application, a further improvement is made where the mass ratio of the porous activated carbon, binder B, and conductive agent is 80-90:10-5:10-5.

[0029] In the above-described application, a further improvement is made where the mass of the dispersant B is 2 to 10 times the total mass of the porous activated carbon, binder B, and conductive agent.

[0030] In the above-described application, a further improvement is made, wherein the adhesive B is at least one of polyvinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber.

[0031] In a further improvement to the above application, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and acetylene black.

[0032] In the above-described application, a further improvement is made, wherein the dispersant B is at least one of acetone, pure water, and N-methylpyrrolidone.

[0033] In the above-described application, a further improvement is made, wherein the current collector is one of titanium plate, stainless steel sheet, or carbon cloth.

[0034] Compared with the prior art, the advantages of the present invention are as follows: (1) To address the shortcomings of existing activated carbons in possessing large specific surface area, high electroadsorption capacity, and good conductivity, this invention provides a method for preparing porous activated carbon based on pulsed electrochemical activation. This method involves fabricating carbon powder into working electrode sheets and subjecting them to pulsed electrochemical square wave cycling treatment in an electrolyte containing sulfuric acid, persulfate, sulfate, and cationic surfactants. During this process, the dynamic cycling and synergistic effect of the oxidation and reduction stages under pulsed electric field regulation is utilized. Through stepwise and precise physicochemical reactions, the multidimensional properties of the carbon material are simultaneously optimized, resulting in porous activated carbon with large specific surface area, high electroadsorption capacity, and good conductivity. Specifically, in the positive pulse (oxidation) stage, the applied high potential drives the persulfate ions (S2O8) in the electrolyte... 2- Electrochemical activation occurs, producing strongly oxidizing sulfate free radicals (SO4). - The hydrogen evolution reaction (H+) violently attacks the carbon skeleton and selectively oxidizes carbon atoms into CO2 and oxygen-containing functional groups, thereby constructing a rich porous structure within the graphite matrix. Simultaneously, the water system undergoes an oxygen evolution reaction at a high potential, and the generated oxygen is confined between the graphite layers to form nanobubbles, generating significant expansion pressure. This physically peels off and expands the graphite sheets, synergistically enhancing the material's specific surface area and pore volume in conjunction with chemical etching. In the subsequent negative pulse (reduction) phase, the mechanism shifts to repairing and improving the material's conductivity and stability: the hydrogen radicals (H+) generated by the hydrogen evolution reaction... With its high reactivity, it preferentially etches high-energy amorphous carbon regions, removes structural defects, and, in conjunction with exogenous electrons, reduces some unstable oxygen-containing functional groups, effectively repairing and purifying sp. 2The carbon conductive network significantly improves conductivity. Simultaneously, cationic surfactants are directionally adsorbed onto the carbon material surface under negative potential, their hydrophilic ends enhancing the wettability of the electrode / electrolyte interface, while the hydrophobic long chains prevent the graphite sheets from re-stacking through steric hindrance, ensuring the maintenance of the porous structure and efficient ion transport. The porous activated carbon prepared by the method of this invention possesses advantages such as large specific surface area, high electroadsorption capacity, and good conductivity. When used as a raw material to prepare capacitive deionization electrodes, it exhibits excellent conductivity, high desalination capacity, and rapid desalination rate, making it widely applicable for electroadsorption desalination with high practical value and promising application prospects.

[0035] (2) In the method for preparing porous activated carbon based on pulse electrochemical activation of the present invention, the essence of the whole process lies in the precise control of pulse voltage, action time and cycle period, so that the two thermodynamically contradictory processes of "oxidation to create pores" and "reduction to repair" can achieve cyclical alternation and dynamic balance in kinetics, and finally achieve synergistic optimization and precise control of the pore structure and conductivity of activated carbon.

[0036] (3) In the method for preparing porous activated carbon based on pulse electrochemical activation of the present invention, the carbon powder used can be derived from graphite electrodes of waste lithium-ion batteries. This provides a green and effective way to realize the high-value recycling and resource utilization of graphite electrodes from waste lithium-ion batteries. In addition, in the present invention, when preparing porous activated carbon using graphite powder, a pore structure suitable for CDI technology can be directionally constructed without significantly damaging the conductive structure of the graphite body. This enables the high-value resource utilization of waste graphite resources and solves the problems of low utilization rate of waste graphite electrodes, high process energy consumption, and environmental pollution in the existing lithium-ion battery recycling process. Attached Figure Description

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0038] Figure 1 This is a process flow diagram of the preparation of porous activated carbon based on pulsed electrochemical activation in Example 1 of the present invention.

[0039] Figure 2 This is a SEM image of the porous activated carbon prepared in Example 1 of the present invention.

[0040] Figure 3 The image shows a SEM image of the porous activated carbon prepared in Comparative Example 1.

[0041] Figure 4 This is a SEM image of the porous activated carbon (graphite powder) prepared in Comparative Example 3.

[0042] Figure 5 XPS images of the porous activated carbon prepared in Examples 1-2 and Comparative Examples 1-3 of this invention.

[0043] Figure 6 This is a comparison chart showing the specific capacitance of the capacitive deionized electrodes prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention, calculated under different CV scan rate curves. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0045] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0046] To address the shortcomings of existing activated carbons, such as difficulty in simultaneously achieving large specific surface area, high electroadsorption capacity, and good conductivity, this invention provides a method for preparing porous activated carbon based on pulsed electrochemical activation. This method involves fabricating carbon powder into working electrode sheets and subjecting them to pulsed electrochemical square wave cyclic treatment in an electrolyte containing sulfuric acid, persulfate, sulfate, and cationic surfactants. During this process, the dynamic cycle and synergistic effect of the oxidation and reduction stages under the control of a pulsed electric field are utilized. Through stepwise and precise physicochemical reactions, the multidimensional properties of the carbon material are simultaneously optimized. Specifically, in the positive pulse (oxidation) stage, the applied high potential drives the persulfate ions (S₂O₈) in the electrolyte... 2- Electrochemical activation occurs, producing strongly oxidizing sulfate free radicals (SO4). - The hydrogen evolution reaction (H+) violently attacks the carbon skeleton and selectively oxidizes carbon atoms into CO2 and oxygen-containing functional groups, thereby constructing a rich porous structure within the graphite matrix. Simultaneously, the water system undergoes an oxygen evolution reaction at a high potential, and the generated oxygen is confined between the graphite layers to form nanobubbles, generating significant expansion pressure. This physically peels off and expands the graphite sheets, synergistically enhancing the material's specific surface area and pore volume in conjunction with chemical etching. In the subsequent negative pulse (reduction) phase, the mechanism shifts to repairing and improving the material's conductivity and stability: the hydrogen radicals (H+) generated by the hydrogen evolution reaction... With its high reactivity, it preferentially etches high-energy amorphous carbon regions, removes structural defects, and, in conjunction with exogenous electrons, reduces some unstable oxygen-containing functional groups, effectively repairing and purifying sp. 2The carbon conductive network significantly improves conductivity. Simultaneously, cationic surfactants are directionally adsorbed onto the carbon material surface under negative potential, their hydrophilic ends enhancing the wettability of the electrode / electrolyte interface, while the hydrophobic long chains prevent the graphite sheets from re-stacking through steric hindrance, ensuring the maintenance of the porous structure and efficient ion transport. The porous activated carbon prepared by the method of this invention possesses advantages such as large specific surface area, high electroadsorption capacity, and good conductivity. When used as a raw material to prepare capacitive deionization electrodes, it exhibits excellent conductivity, high desalination capacity, and rapid desalination rate, significantly improving the desalination performance of CDI devices. It can be widely used in electroadsorption desalination, demonstrating high practical value and promising application prospects.

[0047] The method for preparing porous activated carbon based on pulsed electrochemical activation according to the present invention will be explained in detail below with reference to the accompanying drawings and embodiments: Example 1 A method for preparing porous activated carbon based on pulsed electrochemical activation is shown in the following process flow diagram. Figure 1 As shown, it includes the following steps: S1. The carbon powder is made into a working electrode sheet, specifically as follows: Waste graphite electrodes taken from lithium-ion batteries were immersed in a 2 mol / L H2SO4 solution for 12 hours, then washed with anhydrous ethanol and pure water until neutral, and then dried at 80°C for 12 hours. The resulting graphite powder was then ground through a 200-mesh sieve.

[0048] The obtained graphite powder was mixed with polyvinylidene fluoride (PVDF) at a mass ratio of 95:5, and N-methylpyrrolidone was added in 5 times the total mass of the mixture. The mixture was ultrasonically treated to form a uniform slurry, which was then coated on the surface of a titanium plate and dried at 100°C for 6 hours to produce a graphite electrode sheet.

[0049] S2. The working electrode sheet and the titanium mesh counter electrode obtained in step S1 are placed in an electrolyte for pulsed electrochemical square wave cycling treatment. The electrolyte is an aqueous solution containing 0.1 M sulfuric acid, 0.2 M persulfate ((NH4)2S2O8), 0.3 M sulfate (Na2SO4), and 0.01 M cationic surfactant (hexadecyltrimethylammonium bromide CTAB).

[0050] In step S2, the pulsed electrochemical square wave cyclic treatment includes alternating oxidation and reduction phases, with each oxidation and reduction phase being repeated 15 times.

[0051] The voltage for the oxidation phase is +3 V (relative to the counter electrode), and the duration of a single oxidation phase is 60 seconds.

[0052] The voltage during the reduction phase is -5 V (relative to the counter electrode), and the duration of a single reduction phase is 120 seconds.

[0053] S3. After the pulsed electrochemical square wave cycle treatment in step S2, the activated carbon is peeled off from the working electrode plate. The peeled activated carbon is cleaned with anhydrous ethanol and deionized water until the conductivity of the effluent is lower than 10 μS / cm. The cleaned activated carbon is dried at 60℃ for 6 hours to obtain porous activated carbon.

[0054] In this embodiment, the specific surface area of ​​the prepared porous activated carbon is ≥600m². 2 / g, conductivity ≥5S / cm.

[0055] In this embodiment, the prepared porous activated carbon is used as a raw material to prepare the capacitor deion electrode, including the following steps: Slurry preparation: Mix 4g of porous activated carbon, 0.5g of conductive agent (conductive carbon black) and 0.5g of binder B (PVDF), add 25 mL of dispersant B (N-methylpyrrolidone), and stir at 500 r / min for 4 hours to form a uniform slurry.

[0056] Electrode forming: The slurry is coated onto the titanium plate current collector with a loading of 8 mg / cm². 2 The capacitor deionization electrode was prepared by drying at 80°C for 2 hours.

[0057] Example 2 A method for preparing porous activated carbon based on pulsed electrochemical activation is shown in the following process flow diagram. Figure 1 As shown, it includes the following steps: S1. The carbon powder is made into a working electrode sheet, specifically as follows: Waste graphite electrodes taken from lithium-ion batteries were immersed in a 2 mol / L H2SO4 solution for 12 hours, then washed with anhydrous ethanol and pure water until neutral, and then dried at 80°C for 12 hours. The resulting graphite powder was then ground through a 300-mesh sieve.

[0058] The obtained graphite powder was mixed with binder A (which was obtained by mixing carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 1:1) at a mass ratio of 95:5. Water was added in a volume of 5 times the total mass of the mixture. The mixture was ultrasonically treated to form a uniform slurry, which was then coated onto the surface of carbon cloth and dried at 100°C for 6 hours to produce a graphite electrode sheet.

[0059] S2. The working electrode sheet and the titanium mesh counter electrode obtained in step S1 are placed in an electrolyte for pulsed electrochemical square wave cycling treatment. The electrolyte is an aqueous solution containing 0.1 M sulfuric acid, 0.2 M persulfate (K2S2O8), 0.4 M sulfate (K2SO4), and 0.01 M cationic surfactant (dodecyltrimethylammonium bromide DTAB).

[0060] In step S2, the pulsed electrochemical square wave cyclic treatment includes alternating oxidation and reduction phases, with the oxidation and reduction phases being cycled 30 times.

[0061] The voltage during the oxidation phase is +3.5 V (relative to the counter electrode), and the duration of a single oxidation phase is 50 seconds.

[0062] The voltage during the reduction phase is -5.5 V (relative to the counter electrode), and the duration of a single reduction phase is 100 seconds.

[0063] S3. After the pulsed electrochemical square wave cycle treatment in step S2, the activated carbon is peeled off from the working electrode plate. The peeled activated carbon is cleaned with anhydrous ethanol and deionized water until the conductivity of the effluent is lower than 10 μS / cm. The cleaned activated carbon is dried at 60℃ for 6 hours to obtain porous activated carbon.

[0064] In this embodiment, the specific surface area of ​​the prepared porous activated carbon is ≥600m². 2 / g, conductivity ≥5S / cm.

[0065] In this embodiment, the prepared porous activated carbon is used as a raw material to prepare the capacitor deion electrode, including the following steps: Slurry preparation: Porous activated carbon, conductive agent (carbon nanotubes) and binder B (PVDF) are mixed in a mass ratio of 85:5:5. 25 mL of dispersant B (N-methylpyrrolidone) is added and the mixture is stirred at 500 r / min for 4 hours to form a uniform slurry.

[0066] Electrode forming: The slurry is coated onto the carbon cloth current collector with a loading of 10 mg / cm². 2 The capacitor deionization electrode was prepared by drying at 75°C for 3 hours.

[0067] Comparative Example 1 A method for preparing porous activated carbon is basically the same as that in Example 1, except that: in Comparative Example 1, the pulse mode is cancelled, and a constant potential of +3 V is applied for 900 seconds during the oxidation stage (the total amount of charge is equivalent to that in the oxidation stage of Example 1), without performing a reduction stage.

[0068] Comparative Example 2 A method for preparing porous activated carbon is basically the same as that in Example 1, except that in Comparative Example 2, the pulse mode is cancelled, and a constant potential of -5 V is applied for 1800 seconds during the reduction stage (the total amount of charge treated is equivalent to that in the reduction stage of Example 1), without performing an oxidation stage treatment.

[0069] Comparative Example 3 A method for preparing a capacitive deionization electrode is basically the same as that in Example 1, except that in Comparative Example 3, the graphite powder in step S1 is used instead of the porous activated carbon in Example 1, and other conditions are the same.

[0070] Test method: Conductivity was measured using the four-probe method: 5 g of sample was accurately weighed and pressed into a standard disc of Φ20 mm × 2 mm under a pressure of 10 MPa. Test conditions: DC constant current source output 10.00 mA, probe spacing 1 mm, 5 sets of voltage data were collected and the arithmetic mean was taken. The volumetric conductivity was calculated according to σ = 1 / ρ (unit: S / cm, ASTM F390 standard).

[0071] Desalination performance testing: The testing system consisted of a self-made CDI module, a peristaltic pump, and a conductivity meter. The working electrode was a 5cm × 5cm titanium plate (active material loading of 8 mg / cm²). 2 The test procedure is as follows: 50 mL of a 0.75 mol / L NaCl solution is circulated at a flow rate of 10 mL / min; a constant voltage of 1.5 V is applied for adsorption until the rate of change in solution conductivity is less than 0.5% / min for 5 consecutive minutes, which is considered as complete adsorption; the solution conductivity κ is measured using a conductivity meter (accuracy ±1%), and the real-time concentration is calculated using Ct=κ / Λ (Λ is the molar conductivity of NaCl). The adsorption capacity is calculated using the following formula: Γ (mg / g) = (C0 - C t ) × V × M × 1000 / m, where: C0 = 0.75 mol / L (initial concentration), C t Let t be the concentration (mol / L), V = 0.05 L (total solution volume), M = 58.44 g / mol (molar mass of NaCl), and m = 0.2 g (mass of active substance).

[0072] Cyclic voltammetry (CV): A three-electrode system was used in 1 M NaCl electrolyte, with scan rates of 5, 10, 20, 50, and 100 mV / s within a voltage window of -0.5 to 0.5 V (vs. SCE). The specific capacitance was calculated as: C = (∫IdV) / (ν × ΔV × m), where ∫IdV is the integral area of ​​the voltammetry curve, ν is the scan rate, ΔV is the voltage window width, and m is the mass of the active material.

[0073] Constant current charge-discharge test (GCD): In 1 M NaCl electrolyte, the electrodes were tested at current densities of 0.5, 1, 2, 4, and 5 A / g within a voltage range of -0.6 to 0.6 V (vs. SCE). The specific capacitance was calculated as: C = (I × Δt) / (ΔV × m), where I is the discharge current, Δt is the discharge time, ΔV is the discharge voltage window (IR drop needs to be deducted), and m is the mass of the active material.

[0074] Specific surface area and pore structure analysis: Characterization was performed using the nitrogen adsorption-desorption isotherm (BET method). Before testing, the samples needed to be vacuum degassed at 120℃ for more than 6 hours to completely remove surface physical adsorbates.

[0075] Surface elemental analysis: X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental composition and chemical state of the material surface. An Al Kα (1486.6 eV) monochromatic X-ray source was used, with the binding energy calibrated at C 1s (284.8 eV).

[0076] Material morphology characterization: The microstructure of the material was observed using scanning electron microscopy (SEM).

[0077] like Figure 1 The diagram shown is a schematic of the process flow for converting waste lithium-ion battery graphite electrodes into porous activated carbon using the pulse electrochemical activation method provided by this invention.

[0078] like Figures 2 to 5 As shown, the graphite electrode of the lithium-ion battery underwent a significant oxidation reaction after pulsed electrochemical treatment. SEM characterization results showed that a rich and uniform porous structure was successfully constructed on the treated graphite surface. XPS analysis indicated that, compared with Comparative Example 3 (original graphite), the carbon-to-oxygen ratio (C / O ratio) on the material surface was significantly reduced after pulsed electrochemical activation, indicating that a large number of oxygen-containing functional groups were introduced, effectively improving the wettability and chemical activity of the material surface. A comparison of XPS results between Example 1 and Comparative Example 1 showed that the carbon-to-oxygen ratio of the sample treated with pulsed electrochemical treatment was significantly increased compared to the pure oxidized sample, reflecting a certain degree of recovery in graphitization and repair of the conductive structure. These results confirm that pulsed electrochemical treatment, while constructing a porous structure, achieves a synergistic improvement in the controllable oxidation modification and conductivity of the graphite surface.

[0079] Table 1. Comparison data of porous activated carbon performance between Examples 1-2 and Comparative Examples 1-3

[0080] As shown in Table 1, the pulsed electrochemical activation method developed in this invention has achieved significant results in the conversion of waste graphite. Performance comparisons indicate that the porous activated carbon prepared in Example 1 possesses both high electrical conductivity (5.9 S / cm) and high specific surface area (782.8 m²). 2 Its specific capacitance reached 96.5 F / g, more than 18 times that of Comparative Example 3 (original graphite), demonstrating excellent overall performance. Comparative Example 1, which underwent a single oxidation treatment, had the highest specific surface area (806.2 m² / g). 2 However, the conductivity decreased significantly to 0.8 S / cm, and the specific capacitance was only 72.8 F / g; Comparative Example 2, which used a single reduction treatment, maintained a conductivity of 8.8 S / cm, but the specific surface area did not show a significant increase (88.2 m² / g). 2 The specific capacitance was only 11.9 F / g. This significant difference highlights the limitations of existing single-processing methods: simple oxidation, while creating pores, severely damages the conductive structure; simple reduction, while beneficial for maintaining conductivity, cannot effectively construct porous structures. The innovative value of this invention lies in achieving a synergistic effect of oxidation pore creation and reduction repair through precisely controlled pulsed electrochemical cycling, successfully breaking the traditional performance paradox of "high specific surface area inevitably accompanied by low conductivity" in porous carbon materials, and providing a new path for the preparation of high-performance CDI electrode materials. In addition, although the conductivity (5.3 S / cm) and specific capacitance (87.3 F / g) of Example 2 were slightly lower than those of Example 1 by adjusting the grinding fineness, binder type, and activation parameters, they were still significantly better than all comparative examples, indicating that the method has good parameter adaptability and adjustability, further proving the robustness and application potential of the technical route. Specific capacitance data calculated from CV curves at different scan rates ( Figure 6 This further confirms the superiority of pulsed electrochemical methods in improving the electrochemical performance of materials.

[0081] Table 2 Comparative data on the electroadsorption performance of capacitive deionization electrodes in Examples 1-2 and Comparative Examples 1-3

[0082] Table 2 data further confirms the superiority of the material of this invention and its great potential in CDI applications from two key dimensions: practical application effectiveness (electroadsorption capacity) and application efficiency (average adsorption rate). Electroadsorption capacity, as the core indicator for measuring the desalination capacity of CDI, directly reflects the total amount of salt ions adsorbed by the material. The data above show that Example 1 exhibits the highest adsorption capacity (15.95 mg / g), which is 173% higher than the original graphite in Comparative Example 3 (5.85 mg / g). This directly corresponds to its ultra-high specific capacitance (96.5 F / g), proving that its good electrochemical performance can be efficiently converted into actual desalination capacity. Although Example 2 (13.33 mg / g) is slightly lower than Example 1, it is still significantly better than all comparative examples, reflecting the robustness and tunability of this technical route. Although Comparative Example 1 (10.41 mg / g) has the highest specific surface area, its adsorption capacity is severely limited due to its low conductivity. Comparative Example 2 (6.32 mg / g) shows a negligible increase in capacity due to the lack of sufficient pore space. Regarding adsorption rates, Example 1 (1.38 mg / g·min) was 5.5 times faster than the original graphite, thanks to the synergistic effect of its excellent conductive network and well-developed pore structure, which ensured rapid electron transport and ion diffusion. Example 2 (1.19 mg / g·min) also exhibited excellent kinetic performance. In contrast, Comparative Example 1 (0.61 mg / g·min) showed slow ion migration due to its low conductivity, with a rate only 37% of that of Example 1. Comparative Example 2 (0.48 mg / g·min) had the lowest rate due to insufficient pores. These results clearly demonstrate that only by achieving a synergistic improvement in both specific surface area and high conductivity through pulsed electrochemical activation can the superior comprehensive performance of high adsorption capacity and high adsorption rate be obtained simultaneously.

[0083] As can be seen from the above results, the porous activated carbon prepared by the method of the present invention has the advantages of large specific surface area, high electro-adsorption capacity and good conductivity. When used as a raw material to prepare capacitive deion electrodes, it exhibits good conductivity, high desalination capacity and fast desalination rate, which can significantly improve the desalination performance of CDI devices. It can be widely used for electro-adsorption desalination, has high application value and good application prospects.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing porous activated carbon based on pulsed electrochemical activation, characterized in that, Includes the following steps: S1. Make working electrode sheets from carbon powder; S2. The working electrode obtained in step S1 is placed in an electrolyte for pulsed electrochemical square wave cycling treatment; the electrolyte is an aqueous solution containing sulfuric acid, persulfate, sulfate and cationic surfactant; S3. After the activated carbon on the working electrode sheet is treated with pulsed electrochemical square wave cycling in step S2, it is peeled off, cleaned, and dried to obtain porous activated carbon.

2. The method according to claim 1, characterized in that, In step S2, the pulsed electrochemical square wave cyclic treatment includes alternating oxidation and reduction phases; the oxidation and reduction phases are repeated 10 to 80 times.

3. The method according to claim 2, characterized in that, The voltage of the oxidation stage is +2 V to +4 V; the duration of a single oxidation stage is 40 to 90 seconds; the voltage of the reduction stage is -4 V to -6 V; the duration of a single reduction stage is 80 to 150 seconds.

4. The method according to claim 3, characterized in that, The voltage of the oxidation stage is +2.5 V to +3.5 V; the duration of a single oxidation stage is 40 to 60 seconds; the voltage of the reduction stage is -4.5 V to -5.5 V; the duration of a single reduction stage is 80 to 120 seconds.

5. The method according to claim 1, characterized in that, In step S2, the electrolyte contains 0.05M to 0.5M sulfuric acid, 0.05M to 0.3M persulfate, 0.1M to 0.5M sulfate, and 0.005M to 0.05M cationic surfactant; the persulfate is (NH4)2S2O8 or K2S2O8; the sulfate is Na2SO4 or K2SO4; and the cationic surfactant is hexadecyltrimethylammonium bromide and / or dodecyltrimethylammonium bromide.

6. The method according to any one of claims 1 to 5, characterized in that, In step S1, the preparation method of the working electrode sheet includes the following steps: mixing carbon powder, binder A, and dispersant A, ultrasonically dispersing to obtain a slurry; coating the slurry onto the surface of the substrate electrode, and drying to obtain the working electrode sheet; the mass ratio of carbon powder to binder A is 90-97:10-3; the mass of dispersant A is 1 to 10 times the total mass of carbon powder and binder A; the carbon powder includes at least one of graphite powder and biomass-based activated carbon; the graphite powder is prepared from the graphite electrode of a waste lithium-ion battery; the binder A is at least one of polyvinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber; the dispersant A is at least one of acetone, pure water, and N-methylpyrrolidone; the substrate electrode is one of titanium plate, stainless steel sheet, and carbon cloth. In step S3, the cleaning process involves sequentially cleaning the stripped activated carbon with anhydrous ethanol and deionized water until the conductivity of the effluent is below 10 μS / cm.

7. A porous activated carbon, characterized in that, The porous activated carbon is prepared by the method according to any one of claims 1 to 6.

8. The porous activated carbon according to claim 7, characterized in that, The specific surface area of ​​the porous activated carbon is ≥600m². 2 / g, conductivity ≥5S / cm.

9. The use of porous activated carbon as described in claim 7 or 8 as a raw material in the preparation of capacitor deionization electrodes.

10. The application according to claim 9, characterized in that, The capacitive deionization electrode is prepared by coating porous activated carbon, binder B, conductive agent, and dispersant B onto a current collector. The mass ratio of the porous activated carbon, binder B, and conductive agent is 80-90:10-5:10-5. The mass of the dispersant B is 2 to 10 times the total mass of the porous activated carbon, binder B, and conductive agent. The binder B is at least one of polyvinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber. The conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and acetylene black. The dispersant B is at least one of acetone, pure water, and N-methylpyrrolidone. The current collector is one of titanium plate, stainless steel sheet, and carbon cloth.

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