High-specific-surface-area porous carbon based on coal gasification carbon residue, preparation method and application

Abstract

The invention discloses high-specific-surface-area porous carbon based on coal gasification carbon residues and a preparation method and application thereof.The method comprises the steps that coal gasification residues serve as raw materials and are treated to obtain a carbon-rich precursor, and the carbon-rich precursor is carbonized to obtain a coal gasification residue-based hard carbon matrix; then, the hard carbon matrix is in contact with a modified solution containing hydrogen peroxide, synergistic pore-forming agents such as an inorganic gas generating type pore-forming agent, an organic small molecule pore-forming agent and a soft and hard template pore-forming agent can be further added into the modified solution, and selective oxidation etching and gas-phase pore-forming are carried out under the conditions of controlled temperature, time and pH; a multi-scale micropore and mesopore structure is formed; and washing, drying and re-carbonizing or thermally annealing to obtain the coal gasification slag-based hard carbon material with high specific surface area. Compared with unmodified hard carbon, the method has the advantages that the specific surface area can be obviously increased, micropores and mesopores are synergistically developed, electrolyte infiltration and an ion transmission channel are obviously improved, and controllable construction of a multistage pore channel can be realized on the premise of ensuring relatively high yield and structural stability.

Description

Technical Field

[0001] This invention relates to the field of coal chemical solid waste resource utilization and carbon material preparation technology, specifically to a high specific surface area porous carbon based on coal gasification residue, its preparation method and application, which can significantly improve its specific surface area and pore structure development, and can be applied to electrochemical energy storage and adsorption separation. Background Technology

[0002] Coal gasification is a core component of modern coal chemical engineering and syngas production, widely used in coal-to-oil, coal-to-methanol, coal-to-natural gas, and downstream fine chemical production. With the construction and operation of various large-scale coal gasification plants, a considerable amount of coal gasification slag is generated annually, including dry slag, wet slag, and coarse slag after roughing. Coal gasification slag typically contains 20–90% by mass of inorganic ash and 5–60% by mass of carbonaceous components. Its mineral phases are complex, mainly including silica, alumina, calcium oxide, iron oxide, and small amounts of oxides or silicates of alkali metals and alkaline earth metals. If coal gasification slag is simply stockpiled for a long period, it not only occupies a large amount of land resources but may also cause environmental risks such as dust dispersion, acid rain leaching of heavy metals and soluble salts, posing a potential threat to the surrounding ecosystem and groundwater safety. Existing research and engineering practices regarding the resource utilization of coal gasification slag mainly focus on low-value applications such as building material admixtures, road filling materials, and soil conditioners. For example, coal gasification slag is used as cement or concrete admixtures, brick and tile sintering aggregates, or roadbed fillers. In recent years, utilizing residual carbon in coal gasification slag to prepare high-value-added carbon materials has gradually become a research hotspot. For instance, hard carbon materials are prepared from coal gasification slag through deashing and heat treatment for use as anodes in lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, or as porous adsorbent materials. However, because coal gasification slag undergoes complex thermal processes under high temperature, high pressure, and strong oxidizing or reducing environments during gasification, its residual carbon skeleton is usually quite dense and exhibits characteristics such as mineral encapsulation, numerous closed pores, and a mixture of disordered and ordered carbon. This results in a generally low specific surface area for hard carbon obtained through direct carbonization, typically less than 100 square meters per gram. The poorly ventilated pores limit electrolyte wetting and ion transport, hindering high-performance applications in batteries and supercapacitors.

[0003] To improve the specific surface area and pore volume of carbon materials, traditional methods mainly employ two categories: chemical activation and physical activation. In terms of chemical activation, activators such as potassium hydroxide, sodium hydroxide, potassium carbonate, and zinc chloride react with the carbon framework at 700–900 degrees Celsius, generating a large number of micropores and achieving a specific surface area of ​​1000 square meters per gram or even higher. Some studies have also attempted to introduce phosphates or ammonium salts into phosphorus- or nitrogen-containing precursor systems to achieve simultaneous pore formation and heteroatom doping.

[0004] This type of chemical activation route has significant drawbacks: Firstly, it requires a large amount of strong alkali or corrosive salts, necessitating repeated water washing after activation to remove residual salts, resulting in large quantities of high-salt wastewater, high treatment costs, and a heavy environmental impact. Secondly, strong alkalis are highly corrosive to furnace tubes, linings, and post-treatment equipment at high temperatures, placing high demands on engineering materials. Furthermore, the activation process window is narrow; improper activator dosage or temperature control can easily lead to over-etching of the carbon skeleton, significantly reducing yield and mechanical strength, which is particularly detrimental to the high ash content and brittle structure of coal gasification slag-based hard carbon. Physical activation methods commonly include steam activation, carbon dioxide activation, and limited oxidation in air or oxygen-containing atmospheres. These methods slowly erode the carbon skeleton through gas-solid reactions, forming a certain amount of micropores and mesopores, with relatively lower environmental burden and weaker corrosivity, making them more suitable for engineering scale-up. However, for coal gasification slag-based hard carbon with a dense initial structure, high ash content, and pores largely blocked by minerals, relying solely on steam or carbon dioxide activation often requires long activation times and high activation temperatures to achieve a significant increase in specific surface area. This not only leads to high energy consumption, but may also cause uneven local ablation of the skeleton, with excessive etching of the outer layer of carbon particles while the interior remains dense, making it difficult to achieve uniform and controllable multi-scale porous structure construction.

[0005] In addition, some literature attempts to prepare porous carbon materials using template methods. For example, silica, calcium carbonate particles, or soft template surfactants are introduced into the precursor system, and a porous structure is formed through carbonization and subsequent template removal steps. Alternatively, acid washing and strong oxidizing agents are used to improve the functional group type and pore structure of the carbon material surface. For example, concentrated nitric acid, mixed acid, or potassium permanganate systems are used to oxidize the carbon material surface to introduce oxygen-containing functional groups and expand the pores to a certain extent. However, such strong oxidizing systems also have problems such as strong corrosivity, high by-product salts, and poor operational safety. Moreover, they are not specifically targeted at high-ash coal gasification slag-based hard carbon, which can easily cause uncontrolled dissolution and structural damage of the mineral and carbon phases.

[0006] Hydrogen peroxide is a common green oxidant whose decomposition products are mainly water and oxygen. Under appropriate concentration, temperature, and pH conditions, it can mildly and selectively oxidize and etch the active sites on the surface of carbon materials. A few studies have attempted to use hydrogen peroxide to modify the surface of activated carbon or biomass-based carbon materials, introducing oxygen-containing functional groups to improve hydrophilicity or adsorption performance. However, among existing publicly available technologies, there are very few reports on systematic processes for controlling the construction of hierarchical pore structures using hydrogen peroxide in combination with synergistic pore-forming agents (including inorganic gas-generating pore-forming agents, organic small-molecule pore-forming agents, and soft and hard template pore-forming agents) after deashing and carbonization to obtain hard carbon from coal gasification slag as a carbon source. There is also a lack of complete technical solutions designed specifically for the structural characteristics of coal gasification slag-based hard carbon. The few known hydrogen peroxide modification methods are mostly single oxidation treatments, with limited ability to control pore size distribution, making it difficult to achieve a good balance between the ratio of micropores to mesopores, the increase in specific surface area and yield, and mechanical stability.

[0007] In summary, existing technologies still face the following pressing technical challenges in the high-value utilization of coal gasification slag-based hard carbon:

[0008] First, although traditional strong alkali or strong oxidant activation can increase the specific surface area to a certain extent, it is highly corrosive, has a large environmental load, and a narrow process window, which is not conducive to industrial scale-up. Moreover, it can easily cause excessive etching and structural damage to the skeleton of high-ash coal gasification slag-based hard carbon.

[0009] Second, single physical activation or mild oxidation methods are insufficient to fully open the dense carbon skeleton and the pores encapsulated by minerals, resulting in limited improvement in specific surface area. The pore structure is mostly a single micropore or uneven pore size distribution, making it difficult to achieve both high capacity and high rate performance.

[0010] Third, there is a lack of a green synergistic pore-forming system of "hydrogen peroxide and synergistic pore-forming agent" specifically designed for the hard carbon characteristics of coal gasification slag. A complete process route that can significantly improve specific surface area and multi-level pore structure while taking into account yield, mechanical stability and environmental friendliness has not yet been formed.

[0011] Therefore, it is necessary to develop a modification method that uses coal gasification slag as raw material, hydrogen peroxide as the main oxidant, and inorganic gas generating agents, organic small molecules, and soft and hard templates as synergistic pore-forming agents to achieve the controllable construction of multi-scale pore structures and significant improvement of specific surface area of ​​coal gasification slag-based hard carbon under mild conditions, thereby providing a new technical path for the high-value utilization of coal gasification slag carbon resources. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of existing coal gasification slag-based hard carbon, such as low specific surface area, insufficient pore structure development, and strong corrosiveness and high environmental impact of traditional strong alkali activation. This invention proposes a modification method that uses hydrogen peroxide as the main oxidant and combines it with a synergistic pore-forming agent to construct a multi-scale pore structure. Under the premise of ensuring high yield and structural stability, this method significantly increases the specific surface area of ​​hard carbon and optimizes the ratio of micropores to mesopores, thereby improving its comprehensive performance in electrochemical energy storage and adsorption separation.

[0013] To achieve the above objectives, the present invention provides a method for preparing high specific surface area porous carbon based on coal gasification residue, comprising the following steps:

[0014] (1) Raw material pretreatment: The coal gasification slag is crushed and screened to obtain coal gasification slag powder with a particle size of 10 to 500 micrometers;

[0015] (2) Deashing and carbonization: The coal gasification slag powder is added to an acidic solution and / or an alkaline solution for deashing treatment to remove some inorganic mineral components. It is then filtered until neutral and dried to obtain a carbon-rich precursor.

[0016] (3) Carbonization to obtain hard carbon matrix: The carbon-rich precursor is heated to 700-1400 ℃ at a heating rate of 1-15 ℃ per minute under an inert atmosphere and held for 0.5-6 hours. After cooling, coal gasification slag-based hard carbon matrix is ​​obtained.

[0017] (4) Hydrogen peroxide modification and synergistic pore formation: The coal gasification slag-based hard carbon matrix is ​​contacted with a modification solution containing hydrogen peroxide, wherein the modification solution contains hydrogen peroxide and one or more synergistic pore-forming agents; wherein the mass fraction of hydrogen peroxide is 1 to 50% by mass, the amount of synergistic pore-forming agent added is 0.1 to 50% by mass of the hard carbon, the solid-liquid mass ratio is 1:(3 to 100), and the reaction is carried out at 20 to 100 °C for 0.1 to 12 hours to selectively oxidize and etch the disordered carbon phase on the surface and inside of the hard carbon and / or create pores in the gas phase.

[0018] (5) Washing and drying: Separate the solid product obtained in step (4), wash it with deionized water and / or dilute acid and dilute alkali solutions until neutral, and then dry it to obtain porous carbon with high specific surface area.

[0019] Furthermore, the synergistic pore-forming agent is selected from one or more of the following classes:

[0020] a) Inorganic gas-generating pore-forming agents: any one or more of carbonates, bicarbonates, and ammonium salts, including but not limited to sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate, ammonium phosphate, and ammonium diphosphate.

[0021] b) Inorganic oxidizing pore-forming agents: any one or more of persulfates, nitrites, nitrates and their complex salts.

[0022] c) Phosphorus-containing pore-forming agents: any one or more of phosphoric acid, metaphosphoric acid, polyphosphoric acid, phosphates or ammonium salts.

[0023] d) Organic small molecule pore-forming agents: nitrogen- or oxygen-containing organic compounds that can thermally decompose to generate gas or carbon skeletons.

[0024] e) Soft and hard template pore-forming agents: any one or more of surfactants, block copolymers, organosilicon, and inorganic oxide particles, including but not limited to sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, Pluronic block copolymers, silica gel or nanoparticles, and alumina particles.

[0025] Further, the acidic solution used in step (2) is selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid and mixtures of two or more thereof, with a concentration of 0.1 to 5.0 mol per liter; the alkaline solution is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and mixtures thereof, with a concentration of 0.1 to 4.0 mol per liter, a deashing temperature of 25 to 95 °C, and a deashing time of 0.5 to 8 hours.

[0026] Furthermore, the inert atmosphere in step (3) is selected from nitrogen, argon and their mixtures, the carbonization temperature is preferably 900-1250 ℃, more preferably 950-1200 ℃, and the holding time is preferably 1-4 hours.

[0027] Furthermore, in step (4), the pH of the modified solution is adjusted to 1-13, and mechanical stirring and / or ultrasonic oscillation and / or circulating spraying are used during the modification process to improve the wetting and mass transfer efficiency of hydrogen peroxide and synergistic pore-forming agent on hard carbon particles.

[0028] Furthermore, the synergistic pore-forming agent preferably comprises at least one inorganic gas-generating pore-forming agent and at least one organic small molecule pore-forming agent, so as to form a multi-scale pore structure through synergistic gas evolution and organic framework pyrolysis while etching with hydrogen peroxide.

[0029] Furthermore, the synergistic pore-forming agent and hydrogen peroxide are added in the following manner:

[0030] The simultaneous addition method involves dissolving or dispersing hydrogen peroxide and the synergistic pore-forming agent simultaneously in the same modification solution; and / or the stepwise addition method involves pre-modifying with hydrogen peroxide solution first, followed by secondary impregnation and / or heat treatment with synergistic pore-forming agent solution; or impregnating with synergistic pore-forming agent and drying, followed by oxidation etching in a system containing hydrogen peroxide. Different addition methods can be used individually or in combination.

[0031] Furthermore, after step (4) and before step (5), the following steps are also included:

[0032] The recarbonization or heat treatment step involves recarbonizing or heat annealing the wet or dry hard carbon modified with hydrogen peroxide and synergistic pore-forming agent at 500–1100 °C for 0.1–4 hours under an inert atmosphere to further stabilize the pore structure and regulate the content and type of oxygen-containing functional groups on the surface.

[0033] Furthermore, the coal gasification slag includes dry slag, wet slag, or coarse coal gasification slag separated by flotation, magnetic separation, or heavy media separation, with an ash content of 20-90% by mass and a fixed carbon content of 5-60% by mass.

[0034] This invention also provides a high specific surface area coal gasification slag-based hard carbon material, prepared using the method described in this invention, and possessing at least two of the following characteristics:

[0035] a) Specific surface area of ​​150–800 square meters per gram;

[0036] b) The volume fraction of micropores with a pore size of less than 2 nanometers is 20% to 80% of the total pore volume;

[0037] c) The volume fraction of mesopores with pore sizes in the range of 2–50 nm is 10–70% of the total pore volume;

[0038] d) The electrolyte wetting contact angle is less than 60 degrees;

[0039] e) The capacity retention rate is not less than 80% after 100 cycles at a current density of 100 mA / g in a sodium-ion half-cell;

[0040] The oxygen-containing functional groups in this material exist in the form of carbon-oxygen single bonds, carbon-oxygen double bonds, and / or carboxyl groups.

[0041] The present invention also provides an electrochemical energy storage electrode material, the electrode material comprising an active substance, a conductive agent, and a binder, wherein the conductive agent is selected from carbon black, conductive graphite, carbon nanotubes, graphene, and combinations thereof; the binder is selected from polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylate, and combinations thereof; characterized in that the active substance is a high specific surface area coal gasification slag-based hard carbon material as described in the present invention.

[0042] The present invention also provides an electrochemical energy storage device, wherein the electrochemical energy storage device is selected from one or more of lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, lithium-ion capacitors, and supercapacitors, characterized in that the negative electrode and / or positive electrode of the electrochemical energy storage device is a high specific surface area coal gasification slag-based hard carbon material as described in the present invention.

[0043] The present invention also provides an application of high specific surface area coal gasification slag-based hard carbon material in the field of adsorption and separation, the application including the adsorption and removal of small organic molecules, heavy metal ions, dye molecules, volatile organic compounds and / or carbon dioxide.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] First, the process is mild and environmentally friendly. Hydrogen peroxide is the main oxidant, and the synergistic pore-forming agents are mostly low-toxicity or controllable emission substances, avoiding the use of large amounts of strong alkaline salts and significantly reducing equipment corrosion and the pressure of high-salt wastewater discharge.

[0046] Second, the specific surface area is significantly increased and adjustable. Through the synergistic pore-forming effect of hydrogen peroxide and synergistic pore-forming agents, the specific surface area of ​​coal gasification slag-based hard carbon can be increased from less than 100 square meters per gram to 150-800 square meters per gram. Furthermore, the ratio of micropores to mesopores can be directionally adjusted by regulating process parameters to meet the needs of different energy storage and adsorption applications.

[0047] Third, the hierarchical pore structure can be constructed in a controllable manner. By using a combination of inorganic gas-generating pore-forming agents, organic small molecule pore-forming agents, and soft and hard template pore-forming agents, a hierarchical pore network consisting of micropores, mesopores, and some larger pore diameter channels can be constructed in a hard carbon framework, taking into account both high specific capacity and high rate performance.

[0048] Fourth, the structure is stable and the yield is high. By reasonably controlling the dosage of the synergistic pore-forming agent, the concentration of hydrogen peroxide, and the reaction time, and by combining it with appropriate recarburization or thermal annealing steps, structural collapse caused by excessive etching can be avoided, achieving a better trade-off between increasing specific surface area and mechanical and structural stability, while maintaining a high material yield.

[0049] Fifth, it is suitable for industrial scale-up. This invention uses coal gasification slag as raw material, which is widely available and inexpensive. The process steps are relatively simple and can be integrated with existing coal gasification slag pretreatment and carbonization processes. It has good prospects for industrial application and promotion and helps to promote the green and low-carbon development of the coal gasification industry.

[0050] Instruction manual illustrations

[0051] Figure 1 To implement Case 1, SEM images of carbon materials were obtained.

[0052] Figure 2 To implement Case 2, SEM images of carbon materials were obtained. Detailed Implementation

[0053] The following specific embodiments are used to further illustrate the present invention, but do not constitute a limitation on the scope of protection of the present invention. Those skilled in the art can adjust the specific conditions without departing from the spirit and essence of the present invention. Unless otherwise stated, the raw materials are all from conventional industrial sources or analytical grade reagents, the water is deionized water, and the specific surface area is calculated using the 77 Kelvin nitrogen adsorption-desorption test according to the Bronner-Emmett-Teller method.

[0054] 1. General Deashing and Carbonization Procedures

[0055] General step S0, raw material pretreatment: The dried coal gasification slag from a coal gasification unit is mechanically crushed and sieved to obtain powder with a particle size in the range of 10-500 micrometers. Under typical conditions, it can pass through a 200-mesh sieve, approximately 75 micrometers. The undersize material is used as raw material for subsequent processing.

[0056] General step S1, deashing and carbon enrichment: Take a certain amount of coal gasification slag powder, for example, 100 grams, and add it to an acidic solution and / or alkaline solution. Stir and react at a set temperature to remove soluble and some insoluble inorganic minerals. After the reaction is complete, filter and wash with deionized water until the pH of the filtrate is about 7. Dry at 105 degrees Celsius for 8-12 hours to obtain a carbon-rich precursor.

[0057] General step S2, carbonization to obtain hard carbon precursor: The carbon-rich precursor is placed in a tube furnace or box furnace and heated to 700-1400 degrees Celsius at a heating rate of 1-15 degrees Celsius per minute under nitrogen or argon protection, held at that temperature for 0.5-6 hours, and then cooled to room temperature to obtain coal gasification slag-based hard carbon precursor.

[0058] Unless otherwise specified, the following embodiments are based on the general steps described above.

[0059] Example 1: Basic Example Using Only Hydrogen Peroxide Modification

[0060] This embodiment does not include a synergistic pore-forming agent and is used to illustrate the simplest solution of the present invention.

[0061] 1. Deashing and Carbonization

[0062] Following general procedure S0, the coal gasification slag is crushed and passed through a 200-mesh sieve to obtain coal gasification slag powder with a particle size of approximately 75 micrometers. 100 grams of this powder is weighed and added to 1 liter of hydrochloric acid solution with a concentration of 2.0 mol / L. The mixture is stirred in an 80°C water bath for 2 hours to remove soluble inorganic minerals such as calcium and iron. After the reaction is complete, the mixture is filtered and washed with deionized water until the pH of the filtrate is approximately 7. Subsequently, it is dried at 105°C for 12 hours to obtain a carbon-rich precursor.

[0063] The aforementioned carbon-rich precursor was placed in a tubular furnace and heated to 1100°C at a rate of 5°C per minute under nitrogen protection, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain coal gasification slag-based hard carbon matrix A. The specific surface area of ​​hard carbon A was determined to be approximately 80 square meters per gram by a 77 Kelvin nitrogen adsorption test.

[0064] 2. Hydrogen peroxide wet modification

[0065] Weigh 10 g of hard carbon A and add it to 300 mL of a 30% (w / w) hydrogen peroxide solution, with a solid-liquid mass ratio of approximately 1:30. Pre-disperse the solution magnetically at room temperature for 10 minutes. Then, heat the system to 70°C and maintain the reaction under magnetic stirring for 4 hours, controlling the reaction temperature to not exceed 75°C, allowing a small amount of gas to escape.

[0066] 3. Washing and Drying

[0067] After the reaction was complete, the system was cooled to room temperature, and the solid and liquid were separated by vacuum filtration. The filter cake was first washed with deionized water until there was no obvious hydrogen peroxide odor. If necessary, it was slightly neutralized with a small amount of 0.01 mol / L sodium hydroxide solution, and then washed with deionized water until the pH of the filtrate was approximately 7. Subsequently, it was dried at 105 degrees Celsius for 12 hours to obtain hydrogen peroxide modified hard carbon B.

[0068] IV. Performance

[0069] Hard carbon B, after nitrogen adsorption-desorption testing at 77 Kelvin, has a specific surface area of ​​approximately 280 m² / g, about 3.5 times that of hard carbon A. Pore size distribution analysis shows that hard carbon B has a higher proportion of micropores, while also exhibiting a certain amount of mesopores, resulting in a significant increase in overall pore volume. When hard carbon B was used as the anode material for sodium-ion batteries, formulated into electrode sheets and assembled into coin half-cells, the first-cycle reversible capacity at a current density of 100 mA / g was approximately 320 mAh / g, significantly higher than the approximately 240 mAh / g of hard carbon A, demonstrating good cycle performance.

[0070] The SEM morphology of the material is as follows: Figure 1 As shown, a large number of voids can be observed on the surface of the carbon material.

[0071] Example 2: Simultaneous modification of inorganic gas-generating synergistic pore-forming agents ammonium bicarbonate and hydrogen peroxide

[0072] This embodiment uses an inorganic gas-generating pore-forming agent, which releases carbon dioxide and ammonia through the decomposition of ammonium bicarbonate, and works in synergy with the oxidative etching of hydrogen peroxide to create pores.

[0073] 1. Deashing and Carbonization

[0074] Following the general steps S0, S1, and S2, under the same conditions as in Example 1, hard carbon precursor A′ was obtained. The specific surface area of ​​hard carbon A′ was approximately 85 square meters per gram.

[0075] Second, hydrogen peroxide and ammonium bicarbonate are used in a synergistic pore-forming method, with simultaneous addition.

[0076] Weigh 10 g of hard carbon A′ and add it to 500 mL of hydrogen peroxide solution with a mass fraction of 20%, the solid-liquid mass ratio is approximately 1:50, and mechanically stir until homogeneous at room temperature. Then add 2 g of ammonium bicarbonate, the amount of synergistic pore-forming agent added is 20% of the mass of hard carbon.

[0077] The reaction system was heated to 60 degrees Celsius and maintained under mechanical stirring for 6 hours. During the reaction, ammonium bicarbonate underwent thermal decomposition, generating carbon dioxide and ammonia. The gas release helped form pores in the carbon framework. At the same time, hydrogen peroxide gently oxidized and etched the disordered carbon phase on the hard carbon surface. The two worked together to form a multi-scale porous structure inside the hard carbon.

[0078] 3. Washing and Drying

[0079] After the reaction was completed and cooled to room temperature, the solid and liquid were separated by filtration. The filter cake was first washed with warm water to remove residual ammonium salts and carbonate ions, and then washed with deionized water until the pH of the filtrate was close to neutral. It was then dried at 105 degrees Celsius for 12 hours to obtain hard carbon C modified by the synergistic effect of hydrogen peroxide and ammonium bicarbonate.

[0080] IV. Performance

[0081] Nitrogen adsorption tests showed that the specific surface area of ​​hard carbon C was approximately 320 m² / g, significantly higher than that of hard carbon A′. Pore size distribution analysis indicated a significant increase in the volume fraction of mesopores, which is beneficial for electrolyte wetting and ion migration within the pores. When hard carbon C was used as the anode material for sodium-ion batteries, the first-cycle reversible capacity was approximately 330 mAh / g at a current density of 100 mA / g; even at a high current density of 1 A / g, it maintained a capacity exceeding 200 mAh / g, demonstrating excellent rate performance.

[0082] The SEM morphology of the material is as follows: Figure 2 As shown, a large number of voids can be observed on the surface of the carbon material.

[0083] Example 3: Organic small molecule synergistic pore-forming agents urea and sucrose modified with hydrogen peroxide and then recarbonized.

[0084] This embodiment uses an organic small molecule pore-forming agent and includes a recarbonization step.

[0085] 1. Deashing and Carbonization

[0086] The carbon-rich precursor of the coal gasification slag was prepared according to general steps S0 and S1. During the carbonization stage, the precursor was placed in a tubular furnace and heated to 1000 degrees Celsius at a rate of 3 degrees Celsius per minute under a nitrogen atmosphere, held at that temperature for 3 hours, and then cooled to obtain hard carbon matrix A″. The specific surface area of ​​hard carbon A″ was approximately 70 square meters per gram.

[0087] Second, hydrogen peroxide is synergistically modified with urea and sucrose, and added simultaneously.

[0088] Weigh 10 g of hard carbon A″ and add it to 400 mL of hydrogen peroxide solution with a mass fraction of 15%. Add 3 g of urea and 2 g of sucrose to the solution and dissolve them completely to obtain a transparent mixed modified solution. At this point, the total amount of synergistic pore-forming agent added is 50% of the mass of hard carbon.

[0089] The mixture was heated to 50 degrees Celsius and reacted for 4 hours under magnetic stirring. During the reaction, hydrogen peroxide oxidized and etched the hard carbon surface, and the small organic molecules underwent pyrolysis in the subsequent heat treatment stage, thereby further forming microporous and mesoporous structures in conjunction with hydrogen peroxide modification.

[0090] 3. Filtration and preliminary drying

[0091] After the reaction was completed and cooled to room temperature, the mixture was filtered and separated. The filter cake was briefly washed with deionized water to remove some soluble byproducts and residual small molecules. Then, it was dried under vacuum at 60 degrees Celsius for 8 hours to obtain a modified hard carbon precursor containing a small amount of residual organic synergistic pore-forming agent.

[0092] Fourth, recarbonization and heat treatment

[0093] The modified hard carbon precursor was placed in a tube furnace and heated to 800°C at a rate of 5°C per minute under nitrogen protection, and held at this temperature for 1.5 hours. This allowed for the complete pyrolysis of residual urea and sucrose, generating gas and partially converting it into an amorphous carbon framework. Simultaneously, the newly formed pore structure was stabilized, and some oxygen-containing functional groups on the surface were partially removed. After natural cooling to room temperature, the sample was removed to obtain modified hard carbon D.

[0094] 5. Performance

[0095] The specific surface area of ​​hard carbon D is approximately 360 square meters per gram, significantly higher than that of the parent hard carbon A″ and hard carbon C in Example 2. Pore size distribution results show that hard carbon D has a relatively high micropore volume fraction and a moderate mesopore volume fraction, forming a more optimized micropore and mesopore synergistic structure.

[0096] X-ray photoelectron spectroscopy analysis revealed that the surface of hard carbon D contains a certain amount of oxygen-containing functional groups, such as carbon-oxygen single bonds and carbon-oxygen double bonds, with an oxygen-to-carbon atomic ratio of approximately 0.06. This is beneficial for the wettability of the electrolyte on the carbon material surface and for interfacial stability. When hard carbon D was used as an anode material for sodium-ion batteries, tests under suitable electrolyte systems and voltage windows showed that its initial coulombic efficiency and long-term cycle stability were superior to those of uncarbonized samples, making it suitable for energy storage applications with high cycle life requirements.

[0097] Example 4: A synergistic pore-forming system of soft and hard templates, consisting of hexadecyltrimethylammonium bromide and silica template modified with hydrogen peroxide.

[0098] This embodiment uses a soft and hard template pore-forming agent, and uses surfactants and inorganic hard templates to jointly construct a multi-level porous structure.

[0099] 1. Deashing and Carbonization

[0100] The coal gasification slag was deashed according to general steps S0 and S1 to obtain a carbon-rich precursor. The precursor was placed in a tubular furnace and heated to 1200 degrees Celsius at a heating rate of 10 degrees Celsius per minute under argon protection, held at that temperature for 1 hour, and then cooled to obtain hard carbon matrix A‴. The specific surface area of ​​hard carbon A‴ is approximately 75 square meters per gram.

[0101] 2. Impregnation with hexadecyltrimethylammonium bromide and silica template

[0102] Prepare 500 mL of an aqueous solution containing 0.05 mol / L hexadecyltrimethylammonium bromide and 5% by mass silica, wherein the average particle size of the silica is approximately 20 nm.

[0103] Ten grams of hard carbon A‴ were added to the above solution, and the mixture was mechanically stirred at 40°C for 2 hours. This allowed hexadecyltrimethylammonium bromide molecules to self-assemble on the surface or within the pores of the carbon material, while silica particles entered the spaces between the carbon particles and their internal pores. After stirring, the solid was separated by filtration and dried at 60°C for 10 hours to obtain an impregnated hard carbon precursor containing a surfactant and a silica template.

[0104] 3. Hydrogen peroxide modification

[0105] The impregnated hard carbon precursor was added to 400 mL of a 25% (w / w) hydrogen peroxide solution. A suitable amount of dilute hydrochloric acid was added to adjust the pH to approximately 3. The solution was magnetically stirred at room temperature for 30 minutes to ensure thorough impregnation of the precursor. The system was then heated to 70°C and reacted for 3 hours. During the reaction, hydrogen peroxide gently oxidized and etched the carbon framework under acidic conditions. Hexadecyltrimethylammonium bromide acted as a soft template to assist in the formation of ordered or quasi-ordered mesoporous structures, while silica particles acted as hard templates, supporting the structure within the pores.

[0106] IV. Template Removal and Post-processing

[0107] After cooling the reaction system to room temperature, filtration was performed. First, the filter cake was washed with a large amount of deionized water to remove hexadecyltrimethylammonium bromide. Then, the washed solid was immersed in a 0.5 mol / L hydrofluoric acid solution for 1–2 hours to dissolve and remove the silica hard template. During the hydrofluoric acid immersion process, corrosion-resistant equipment should be used and strict safety precautions should be taken.

[0108] After template removal, the sample was washed with plenty of deionized water until the pH of the filtrate was close to neutral and free of fluoride ions. Finally, it was dried at 105 degrees Celsius for 12 hours to obtain modified hard carbon E with pore-forming effect of soft and hard templates and hydrogen peroxide.

[0109] 5. Performance

[0110] Hard carbon E has a specific surface area of ​​approximately 400 m² / g. Its nitrogen adsorption-desorption isotherm exhibits significant microporous and mesoporous adsorption characteristics, with high pore volume. The pore size distribution shows a large volume fraction of both micropores and mesopores, forming a hierarchical porous structure. When used as an anode material in sodium-ion batteries, hard carbon E maintains a high discharge capacity even at a high current density of 2 A / g, demonstrating excellent rate performance. In supercapacitor tests, hard carbon E exhibits a large specific capacitance and good rate characteristics, indicating that the hierarchical porous structure facilitates rapid ion transport in the electrolyte.

[0111] Example 5: A modification method combining synergistic pore-forming agent pre-impregnation with secondary hydrogen peroxide modification and high-temperature annealing.

[0112] This embodiment adopts a step-by-step addition method and includes a reheat treatment step.

[0113] 1. Deashing and Carbonization

[0114] A carbon-rich precursor from coal gasification slag was obtained following general steps S0 and S1. The precursor was placed in a tubular furnace and heated to 950°C at a rate of 4°C per minute under a nitrogen atmosphere, held at that temperature for 2 hours, and then cooled to obtain a hard carbon matrix. Hard carbon Its specific surface area is approximately 90 square meters per gram.

[0115] Second, pre-impregnation with synergistic pore-forming agent.

[0116] Prepare 400 mL of an aqueous solution containing 0.5 mol / L urea and 0.5 mol / L ammonium bicarbonate. Add 10 g of hard carbon... Add the above solution and mechanically stir for 1 hour at room temperature to allow urea and ammonium bicarbonate to fully wet the surface and internal pores of the hard carbon, and then let it stand for 1 hour for adsorption.

[0117] After completion, the solid and liquid were separated by filtration, and the filter cake was dried at 80 degrees Celsius for 8 hours to obtain a hard carbon precursor pre-impregnated with a synergistic pore-forming agent.

[0118] Third, initial heat treatment and pore-forming pre-activation.

[0119] The pre-impregnated hard carbon precursor was placed in a tube furnace and heated to 700°C at a rate of 5°C per minute under a nitrogen protective atmosphere, and held at that temperature for 1 hour. During this process, urea and ammonium bicarbonate undergo thermal decomposition, generating gases that cause a certain degree of expansion and reconstruction of the carbon skeleton, forming a primary porous structure, thus obtaining a pre-activated intermediate. -1.

[0120] IV. Secondary modification with hydrogen peroxide

[0121] Weigh 10 grams of the pre-activated intermediate. -1. Add 300 mL of a 10% (w / w) hydrogen peroxide solution. Adjust the pH of the solution to approximately 9 using a small amount of ammonia, and then magnetically stir the reaction at 50°C for 5 hours. An alkaline environment facilitates the participation of hydrogen peroxide in surface oxidation as peroxide ions and free radicals, further expanding and connecting the micropores and mesopores based on the primary pore structure.

[0122] 5. High-temperature annealing and recarbonization

[0123] After the reaction was complete, the system was cooled to room temperature, and the solid was separated by filtration. The filter cake was thoroughly washed with deionized water until the pH of the filtrate was close to neutral. The sample was then pre-dried at 60 degrees Celsius.

[0124] The dried sample was placed in a tube furnace and heated to 900°C at a rate of 8°C per minute under argon protection, held at that temperature for 1 hour, and then subjected to heat treatment again to stabilize the pore structure and control the content of oxygen-containing functional groups on the surface. After natural cooling to room temperature, modified hard carbon F was obtained.

[0125] 6. Performance

[0126] Hard carbon F, as tested by nitrogen adsorption, has a specific surface area of ​​approximately 380 m² / g, with a moderate ratio of micropores to mesopores and a relatively continuous pore size distribution, which is beneficial for balancing high specific capacity and high rate performance. In sodium-ion half-cell testing, after 100 cycles at a current density of 100 mA / g, hard carbon F retains no less than 85% of its capacity, exhibiting slow capacity decay under high rate conditions, demonstrating excellent cycle stability and rate characteristics.

[0127] Comparative Example 1: Hard carbon sample without modification by hydrogen peroxide and synergistic pore-forming agent

[0128] 1. Deashing and Carbonization

[0129] The coal gasification slag was deashed according to general steps S0 and S1 to obtain a carbon-rich precursor. The carbon-rich precursor was placed in a tube furnace and heated to 1100 degrees Celsius at a heating rate of 5 degrees Celsius per minute under nitrogen protection, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain a hard carbon sample A0.

[0130] II. Post-processing

[0131] Hard carbon A0 was not treated with any hydrogen peroxide or synergistic pore-forming agents; it was simply crushed and dried and used directly as a control sample.

[0132] Third, performance

[0133] Hard carbon A0 has a specific surface area of ​​approximately 80 m² / g, a low pore volume, and a pore size distribution mainly consisting of a small number of micropores. When hard carbon A0 was tested as a negative electrode material for sodium-ion batteries, its reversible capacity and rate performance were significantly lower than the modified samples in Examples 1 to 5, and its cycle performance was also poor. This comparative example demonstrates that it is difficult to obtain coal gasification slag-based hard carbon with a high specific surface area through conventional deashing and carbonization alone. The hydrogen peroxide and synergistic pore-forming agent modification steps proposed in this invention play a crucial role in improving specific surface area and performance.

[0134] Comparative Example 2: Using only the synergistic pore-forming agent, without hydrogen peroxide modification.

[0135] 1. Deashing and Carbonization

[0136] Hard carbon matrix A″ was obtained under the deashing and carbonization conditions of Example 3, with a specific surface area of ​​approximately 70 square meters per gram.

[0137] Second, pore-forming is achieved using urea and sucrose, without the use of hydrogen peroxide.

[0138] Weigh 10 g of hard carbon A″ and add it to 400 mL of aqueous solution. Add 3 g of urea and 2 g of sucrose to the aqueous solution and dissolve them completely. Mechanically stir at room temperature for 2 hours to ensure sufficient contact between the hard carbon particles and the small organic molecules. Then filter and separate the components. Dry the filter cake at 60 degrees Celsius for 8 hours to obtain the organic pore-forming precursor.

[0139] III. Heat Treatment

[0140] The above-mentioned organic pore-forming precursor was placed in a tube furnace and heated to 800 degrees Celsius at a heating rate of 5 degrees Celsius per minute under a nitrogen atmosphere. The temperature was held for 1.5 hours and then cooled to room temperature to obtain a hard carbon sample D0 that had only undergone pore-forming treatment with urea and sucrose.

[0141] IV. Performance

[0142] The specific surface area of ​​hard carbon D0 is approximately 200 square meters per gram, which is significantly higher than that of unmodified hard carbon A″, but still significantly lower than that of hard carbon D obtained in Example 3 by synergistic pore formation with urea and sucrose and hydrogen peroxide and subsequent recarbonization, which is approximately 360 square meters per gram.

[0143] In sodium-ion battery testing, although hard carbon D0 exhibited a higher capacity than the unmodified sample A″, its rate performance and cycle stability were inferior to those of hard carbon D. This comparative example demonstrates that while the use of organic synergistic pore-forming agents alone can increase the specific surface area to some extent, the pore structure is more developed and the performance is superior when synergistically combined with hydrogen peroxide. The hydrogen peroxide and synergistic pore-forming agent combination system proposed in this invention has significant advantages.

[0144] Comparative Example 3: Excessive concentration of hydrogen peroxide and high dose of synergistic pore-forming agent caused over-etching.

[0145] 1. Deashing and Carbonization

[0146] Hard carbon matrix A′ was obtained under the deashing and carbonization conditions of Example 2, with a specific surface area of ​​approximately 85 square meters per gram.

[0147] Second, the use of excessively high concentrations of hydrogen peroxide and high doses of ammonium bicarbonate.

[0148] Weigh 10 g of hard carbon A′ and add it to 300 mL of a 50% (w / w) hydrogen peroxide solution, with a solid-liquid mass ratio of approximately 1:30. Add 5 g of ammonium bicarbonate to the system, corresponding to a synergistic pore-forming agent dosage of 50% (w / w) of the hard carbon mass. After stirring at room temperature for 10 minutes, heat the system to 80°C and react for 10 hours under mechanical stirring.

[0149] During the reaction, a large amount of gas is rapidly released, and the hard carbon particles suffer severe mass loss and surface erosion.

[0150] 3. Washing and Drying

[0151] After cooling the reaction system to room temperature, it was filtered, washed with water to remove residual inorganic salts, and washed until the pH of the filtrate was close to neutral. Then it was dried at 105 degrees Celsius to obtain the hard carbon sample H0.

[0152] IV. Performance

[0153] The specific surface area of ​​hard carbon H0 is approximately 310 m² / g, nominally similar to or slightly higher than that of hard carbon in Examples 2 and 3. However, the overall material yield is significantly reduced, some particle structures collapse, and mechanical strength decreases markedly. Electrochemical cycling tests show that hard carbon H0 exhibits significant capacity decay in the first few cycles, severe electrode pulverization, and intensified polarization. This comparative example illustrates that while a high specific surface area may be achieved in a short time when the hydrogen peroxide concentration and synergistic pore-forming agent dosage are too high and the reaction time is too long, it leads to excessive etching and structural damage, which is detrimental to practical applications.

[0154] Compared with the hydrogen peroxide concentration of 10-30% by mass, the amount of synergistic pore-forming agent, and the reasonable reaction time used in the embodiments of the present invention, the results of Comparative Example 3 further verify that the process window proposed in the present invention achieves a reasonable balance between specific surface area, yield, and structural stability.

[0155] The above description of the examples and comparative examples shows that by modifying coal gasification slag-based hard carbon with hydrogen peroxide and different types of synergistic pore-forming agents within a reasonable range of process parameters, the specific surface area of ​​hard carbon can be significantly increased and a multi-scale pore structure can be constructed, thereby improving its comprehensive performance in electrochemical energy storage and adsorption separation, while avoiding the serious equipment corrosion and environmental burden caused by traditional strong alkali activation, and realizing the high-value utilization of coal gasification slag carbon resources.

Claims

1. A method for preparing high specific surface area porous carbon based on coal gasification residue, characterized in that, Includes the following steps: (1) Raw material pretreatment: The coal gasification slag is crushed and screened to obtain coal gasification slag powder with a particle size of 10 to 500 micrometers; (2) Deashing and carbonization: The coal gasification slag powder is added to an acidic solution and / or an alkaline solution for deashing treatment to remove some inorganic mineral components. It is then filtered until neutral and dried to obtain a carbon-rich precursor. (3) Carbonization to obtain hard carbon matrix: The carbon-rich precursor is heated to 700-1400 ℃ at a heating rate of 1-15 ℃ per minute under an inert atmosphere and held for 0.5-6 hours. After cooling, coal gasification slag-based hard carbon matrix is ​​obtained. (4) Hydrogen peroxide modification and synergistic pore formation: The coal gasification slag-based hard carbon matrix is ​​contacted with a modification solution containing hydrogen peroxide, wherein the modification solution contains hydrogen peroxide and one or more synergistic pore-forming agents; wherein the mass fraction of hydrogen peroxide is 1 to 50% by mass, the amount of synergistic pore-forming agent added is 0.1 to 50% by mass of the hard carbon, the solid-liquid mass ratio is 1:(3 to 100), and the reaction is carried out at 20 to 100 °C for 0.1 to 12 hours to selectively oxidize and etch the disordered carbon phase on the surface and inside of the hard carbon and / or create pores in the gas phase; (5) Washing and drying: Separate the solid product obtained in step (4), wash it with deionized water and / or dilute acid and dilute alkali solutions until neutral, and then dry it to obtain porous carbon with high specific surface area.

2. The method according to claim 1, characterized in that, The synergistic pore-forming agent is selected from one or more of the following classes: a) Inorganic gas-generating pore-forming agents: including any one or more of carbonates, bicarbonates, and ammonium salts; b) Inorganic oxidizing pore-forming agents: including any one or more of persulfates, nitrites, nitrates and their complex salts; c) Phosphorus-containing pore-forming agents: including any one or more of phosphoric acid, metaphosphoric acid, polyphosphoric acid, phosphates, and ammonium salts; d) Organic small molecule pore-forming agents: nitrogen- or oxygen-containing organic compounds that can thermally decompose to generate gas or carbon skeletons; e) Soft and hard template pore-forming agents: including any one or more of surfactants, block copolymers, organosilicon, and inorganic oxide particles.

3. The method according to claim 2, characterized in that: The inorganic gas-generating pore-forming agent includes any one or more of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate, ammonium phosphate, and ammonium diphosphate. The soft and hard template pore-forming agent includes any one or more of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, Pluronic block copolymer, silica gel or nanoparticles, and alumina particles. The synergistic pore-forming agent comprises at least one inorganic gas-generating pore-forming agent and at least one organic small molecule pore-forming agent, so as to form a multi-scale pore structure through synergistic gas evolution and organic framework pyrolysis while etching with hydrogen peroxide.

4. The method according to claim 1, characterized in that: The acidic solution used in step (2) is selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid and mixtures of two or more thereof, with a concentration of 0.1 to 5.0 mol per liter; the alkaline solution is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and mixtures thereof, with a concentration of 0.1 to 4.0 mol per liter, a deashing temperature of 25 to 95 ℃, and a deashing time of 0.5 to 8 hours; In step (3), the inert atmosphere is selected from nitrogen, argon and their mixtures, the carbonization temperature is 900-1250 ℃, and the holding time is 1-4 hours; In step (4), the pH of the modified solution is adjusted to 1-13. During the modification process, mechanical stirring and / or ultrasonic oscillation and / or circulating spraying are used to improve the wetting and mass transfer efficiency of hydrogen peroxide and synergistic pore-forming agent on hard carbon particles.

5. The method according to any one of claims 1 to 4, characterized in that, The synergistic pore-forming agent and hydrogen peroxide are added in the following manner: The methods of simultaneous addition involve dissolving or dispersing hydrogen peroxide and a synergistic pore-forming agent in the same modification solution; and / or stepwise addition involves pre-modifying the solution with hydrogen peroxide, followed by secondary impregnation and / or heat treatment with a synergistic pore-forming agent solution; or impregnating the solution with a synergistic pore-forming agent followed by drying, and then performing oxidation etching in a system containing hydrogen peroxide. These different addition methods may include using them alone or in combination.

6. The method according to any one of claims 1 to 6, characterized in that, After step (4) and before step (5), the following steps are also included: The recarbonization or heat treatment step involves recarbonizing or heat annealing the wet or dry hard carbon modified with hydrogen peroxide and synergistic pore-forming agent at 500–1100 °C for 0.1–4 hours under an inert atmosphere to further stabilize the pore structure and regulate the content and type of oxygen-containing functional groups on the surface. The coal gasification slag includes dry slag, wet slag, or coarse coal gasification slag separated by flotation, magnetic separation, or heavy media separation, with an ash content of 20-90% by mass and a fixed carbon content of 5-60% by mass.

7. A high specific surface area coal gasification slag-based hard carbon material, characterized in that, Prepared by the method according to any one of claims 1 to 6, and having at least two of the following characteristics: a) Specific surface area of ​​150–800 square meters per gram; b) The volume fraction of micropores with a pore size of less than 2 nanometers is 20% to 80% of the total pore volume; c) The volume fraction of mesopores with pore sizes in the range of 2–50 nm is 10–70% of the total pore volume; d) The electrolyte wetting contact angle is less than 60 degrees; e) After cycling 100 times at a current density of 100 mA / g in a sodium-ion half-cell, the capacity retention is not less than 80%; The oxygen-containing functional groups of the high specific surface area coal gasification slag-based hard carbon material exist in the form of carbon-oxygen single bonds, carbon-oxygen double bonds and / or carboxyl groups.

8. An electrochemical energy storage electrode material, the electrode material comprising an active substance, a conductive agent, and a binder, wherein the conductive agent is selected from carbon black, conductive graphite, carbon nanotubes, graphene, and combinations thereof; the binder is selected from polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylate, and combinations thereof; characterized in that, The active material is a high specific surface area coal gasification slag-based hard carbon material as described in claim 7.

9. An electrochemical energy storage device, wherein the electrochemical energy storage device is selected from one or more of lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, lithium-ion capacitors, and supercapacitors, characterized in that, The negative electrode and / or positive electrode of the electrochemical energy storage device is a high specific surface area coal gasification slag-based hard carbon material as described in claim 7.

10. The application of a high specific surface area coal gasification slag-based hard carbon material according to claim 7 in the field of adsorption and separation, characterized in that, The applications include the adsorption and removal of small organic molecules, heavy metal ions, dye molecules, volatile organic compounds and / or carbon dioxide.

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