A porous silicon carbide, a porous silicon carbide@G composite material, and a preparation method and application thereof

Abstract

The present application relates to a kind of porous silicon carbide, porous silicon carbide@G composite material and its preparation method and application, belong to the technical field of semiconductor materials.The preparation method of porous silicon carbide uses silicon carbide as anode, Pt is cathode, potassium hydroxide aqueous solution is electrolyte, control potassium hydroxide aqueous solution temperature, using two-step constant voltage constant current etching, while carrying out solution electrochemical corrosion on the surface of silicon carbide, carry out depth vapor assisted diffusion layer corrosion, obtain porous silicon carbide.The present application also obtains porous silicon carbide@G composite material by using porous silicon carbide as substrate, and in-situ graphitization is carried out on the surface of silicon carbide substrate.The present application uses potassium hydroxide to replace HF when preparing porous silicon carbide, and steam is used to improve the uniformity and etching efficiency of silicon carbide etching.The uniform mesoporous structure in the porous silicon carbide prepared after etching provides high specific surface area and optimized ion transmission path.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor materials, and particularly relates to a porous silicon carbide, a porous silicon carbide@G composite material, and a preparation method and application thereof. BACKGROUND

[0002] Silicon carbide (SiC) as the third generation of wide band gap semiconductor material has high thermal conductivity, high mechanical strength, excellent chemical stability and high temperature stability, and shows broad application prospects in high temperature, high frequency and high power electronic devices and energy storage fields. However, intrinsic silicon carbide has poor electrical conductivity and low specific surface area, which limits its application in electrochemical energy storage devices (such as supercapacitors). In order to improve the electrochemical performance of silicon carbide, researchers usually build a porous structure to increase the specific surface area and improve the ion transmission path, and introduce carbon material composite to enhance the electrical conductivity.

[0003] At present, the preparation methods of porous silicon carbide mainly include anodic oxidation etching method, chemical vapor deposition (CVD) method and template method. Among them, the electrochemical etching method is widely studied due to its simple process and strong controllability. The traditional electrochemical etching usually uses hydrofluoric acid (HF) based electrolyte, which can prepare a porous structure, but has problems such as poor etching uniformity, easy to produce cracks, and environmental unfriendliness. In addition, the "cap layer" formed in the HF etching process will hinder the penetration of the electrolyte, reducing the effective specific surface area and electrochemical performance of the electrode.

[0004] In recent years, etching silicon carbide with alkaline solution (such as potassium hydroxide) has gradually attracted attention. Alkaline etching can avoid the safety and environmental problems of HF to some extent, and realize the processing of micron-level structure through the anisotropic corrosion of each crystal plane of silicon carbide. For example, patents CN113550012A and CN118326516A disclose a device and equipment for etching silicon carbide wafer with alkaline vapor, which are mainly used for defect characterization of silicon carbide wafer. The wafer is etched by generating vapor through heating alkaline solution, but this method focuses on the appearance of macroscopic defects, rather than the construction of nano-level porous structure, and the corrosion temperature is high and the time is long, which makes it difficult to realize the controllable growth of mesoporous structure.

[0005] Patent CN103646868A proposes a method for preparing porous silicon by hydrothermal-vapor etching, which involves vapor etching, but the object is silicon material, the etching solution is acidic (HF+HNO3), and the obtained is mainly micron-level pores, and the application field is light emitting material, which has essential differences in structure, function and application scene from the nano-level mesoporous silicon carbide electrode material to be realized in the present application.

[0006] The closest existing technology is the 4H-silicon carbide nanochannel array (NCAs) electrode prepared by a two-step anodic oxidation method proposed by Li et al. (Mater. Horiz., 2018, 5, 883). This method successfully prepared highly ordered silicon carbide nanochannel structures by optimizing the etching solution formulation and process parameters, resulting in a significantly improved specific surface area, excellent electrochemical performance, and extremely high cycling stability over a wide temperature range. However, this method still relies on HF-based electrolytes, posing environmental and safety risks, and the "cap layer" problem still needs to be overcome during the etching process, making the process complex and difficult to reproduce.

[0007] In summary, current methods for preparing porous silicon carbide wafers still use HF etching, which results in problems such as uneven etching, low etching efficiency, environmentally unfriendly reagents, and poor structural stability of the prepared porous wafers. These are all issues that urgently need to be addressed. Summary of the Invention

[0008] To address the problems of uneven etching, low etching efficiency, and environmentally unfriendly reagents in existing porous silicon carbide wafer fabrication methods, this invention provides a porous silicon carbide, a porous silicon carbide@G composite material, its preparation method, and its applications to solve these problems. This invention employs a potassium hydroxide vapor-assisted electrochemical etching method to construct a uniform mesoporous structure on the silicon carbide surface, and further grows graphene in situ to form an integrated electrode. This invention solves the problems of uneven etching, low efficiency, environmental unfriendliness, and poor structural stability in existing technologies, providing a new approach for the development of high-performance silicon carbide-based high-temperature energy storage devices.

[0009] The technical solution of this invention is as follows:

[0010] In a first aspect, the present invention provides a method for preparing porous silicon carbide, comprising the following steps: using silicon carbide as the anode, Pt as the cathode, and potassium hydroxide aqueous solution as the electrolyte, controlling the temperature of the potassium hydroxide aqueous solution, and employing a two-step constant voltage and constant current etching process, performing deep vapor-assisted diffusion layer etching on the surface of silicon carbide while simultaneously performing solution electrochemical etching, thereby obtaining porous silicon carbide.

[0011] Furthermore, the specific steps include:

[0012] (1) Steam electrochemical corrosion

[0013] Electrolyte: Potassium hydroxide aqueous solution;

[0014] Electrode configuration: silicon carbide wafer as anode, Pt as cathode, with a spacing of 3~5 cm;

[0015] Corrosion conditions: constant voltage 32 V, current density 1.0–3.0 A / cm² 2The potassium hydroxide aqueous solution is at a temperature of 100℃~104℃, the reaction time is 3~5 minutes, and the heating platform is at 120℃~140℃.

[0016] Steam-assisted etching: An electrochemical diffusion layer is formed on the sample surface, which induces the etching solution to climb upwards, achieving differential etching between the upper and lower parts of the liquid surface and forming a gradient mesoporous structure.

[0017] (2) Deep regulation

[0018] Reduce the current and continue the reaction for 10-30 minutes to extend the pore depth to more than 1 μm, thus obtaining porous silicon carbide.

[0019] Furthermore, before performing steam electrochemical corrosion, the silicon carbide wafer is pretreated by immersing it in a 1:1 mixture of 40% HF aqueous solution and ethanol for 2 to 10 minutes to remove the surface oxide layer.

[0020] Furthermore, the concentration of the potassium hydroxide aqueous solution is 10 wt%.

[0021] Furthermore, in step (2), the current is reduced to 0.1-0.3 A / cm. 2 .

[0022] Secondly, the present invention provides a porous silicon carbide prepared by the above method.

[0023] Thirdly, the present invention provides a method for preparing porous silicon carbide@G composite material, wherein porous silicon carbide obtained by the above method is used as a substrate, and in-situ graphitization is performed on the surface of the silicon carbide substrate to obtain porous silicon carbide@G composite material.

[0024] Specifically, the following steps are included:

[0025] Porous silicon carbide was placed in an Ar / H2 atmosphere tube furnace, and pyrolyzed at 1200℃~1220℃ for 30 minutes using the porous silicon carbide itself as the carbon source to achieve in-situ graphitization of the silicon carbide surface and form silicon carbide@G composite material.

[0026] Fourthly, the present invention provides a porous silicon carbide@G composite material prepared by the above method.

[0027] Fifthly, the present invention provides an application of the above-mentioned porous silicon carbide@G composite material in a high-temperature supercapacitor.

[0028] Furthermore, in high-temperature supercapacitors, porous silicon carbide@G composite material is used as the electrode, and EMImNTf2 (1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imide) ionic liquid is used as the electrolyte to assemble a two-electrode supercapacitor.

[0029] The beneficial effects of this invention are as follows:

[0030] In the preparation of porous silicon carbide, this invention uses potassium hydroxide instead of HF to avoid the use of toxic reagents; simultaneously, steam-assisted etching is used to improve the uniformity and etching efficiency of silicon carbide etching. The uniform mesoporous structure in the porous silicon carbide prepared after etching provides a high specific surface area and optimized ion transport pathways.

[0031] Traditional graphene preparation involves growing graphene on metal substrates such as copper using CVD (chemical vapor deposition) and then transferring it to the desired substrate. Existing methods suffer from several drawbacks: damage to the transfer film and poor, unstable bonding between the transfer substrate and graphene. The method presented in this invention, however, involves in-situ pyrolytic growth of graphene on a porous silicon carbide surface. This eliminates the need for transfer, and the substrate and graphene are covalently bonded, preserving the structural integrity and interfacial conductivity of the porous silicon carbide@G composite material. Testing shows that the porous silicon carbide@G composite material prepared by this invention maintains high power density and cycle stability at 150°C, outperforming existing silicon carbide-based electrode materials. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the electrochemical etching system for preparing porous silicon carbide according to the present invention; in the figure, 1-etching silicon carbide wafer, 2-platinum electrode, 3-heating stage, 4-DC power supply.

[0034] Figure 2 This is a SEM image of the porous silicon carbide prepared in Example 1 of the present invention.

[0035] Figure 3 The image shows the Raman spectrum of the porous silicon carbide@G composite material prepared in Example 1 of this invention.

[0036] Figure 4 The image shows the CV curve of the porous silicon carbide@G composite material prepared in Example 1 of this invention under three-electrode testing.

[0037] Figure 5 The XPS spectrum of the porous silicon carbide@G composite material C1s prepared in Example 1 of this invention is shown.

[0038] Figure 6 This is a SEM image of porous silicon carbide prepared by steam electrochemical etching using a 20% potassium hydroxide aqueous solution in Example 2.

[0039] Figure 7 For Comparative Example 1, a current density of 3.5~4 A / cm was used. 2 SEM image of porous silicon carbide prepared by steam electrochemical etching.

[0040] Figure 8 This is a SEM image of porous silicon carbide prepared by electrochemical etching using potassium hydroxide aqueous solution at 75°C in Comparative Example 2.

[0041] Figure 9 SEM image of the porous silicon carbide@G composite material prepared at 1350℃ in Comparative Example 3.

[0042] Figure 10 This is a SEM image of the porous silicon carbide prepared by etching with HF aqueous solution in Comparative Example 4.

[0043] Figure 11 This is a SEM image of the porous silicon carbide prepared by etching with potassium hydroxide aqueous solution in Comparative Example 5. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0045] Example 1

[0046] A method for preparing porous silicon carbide@G composite material, the specific steps of which are as follows:

[0047] (1) Pretreatment of silicon carbide wafers

[0048] The silicon carbide wafer is a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer is immersed in a 1:1 mixture of 40% HF aqueous solution and ethanol for 5 minutes to remove the surface oxide layer.

[0049] (2) Steam electrochemical corrosion

[0050] Electrolyte: Prepare a 10% potassium hydroxide aqueous solution;

[0051] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0052] Corrosion conditions: constant voltage 32 V, current density 2.5~3.0 A / cm² 2 The solution temperature was 102 °C, and the reaction time was 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm), achieving differential etching above and below the liquid surface and forming a gradient mesoporous structure.

[0053] (3) Deep regulation

[0054] Reduce the current to 0.2 A / cm 2 The reaction was continued for another 10 minutes to further extend the pore depth to over 1 μm, obtaining porous silicon carbide. The prepared porous silicon carbide was subjected to SEM testing; the obtained SEM images are detailed below. Figure 2 .

[0055] (4) Pyrolysis growth of graphene

[0056] Porous silicon carbide was placed in an Ar / H2 atmosphere tube furnace and pyrolyzed at 1200℃~1220℃ for 30 minutes using the porous silicon carbide itself as the carbon source to achieve in-situ graphitization of the silicon carbide surface, forming a porous silicon carbide@G composite material. The prepared porous silicon carbide@G composite material was subjected to Raman spectroscopy, three-electrode spectroscopy, and XPS spectroscopy. The Raman spectra are detailed below. Figure 3 For details of the CV curves for the three-electrode test, please refer to [link / reference needed]. Figure 4 For XPS spectra, please refer to [link / reference]. Figure 5 .

[0057] from Figure 3 The Raman spectrum shows a strong D peak around 1300 nm, indicating that the grown graphene has high defect activity, which is beneficial for participating in electrochemical reactions. Furthermore, the peaks at 1580 and 2700 cm⁻¹ are also significant. -2 The good shape of the G peak and 2D peak indicates that the graphene structure is complete and uniformly covered.

[0058] from Figure 4 The three-electrode test results show that the peak value and closed curve area of ​​the CV curve after graphene growth are much higher than those of the porous silicon carbide etched before growth, indicating that the capacitance performance of the electrode is significantly improved after graphene growth.

[0059] from Figure 5The XPS energy spectrum shows that, in addition to the C-Si and CC bonds present in the silicon carbide crystal itself, XPS exhibits strong C=C bonds and weak CO bonds, indicating that the graphene is uniformly covered and has a good morphology.

[0060] Example 2

[0061] Investigating the effect of potassium hydroxide aqueous solution concentration on the preparation of porous silicon carbide@G composite materials

[0062] The same preparation method as in Example 1 was used, except that 2% and 20% potassium hydroxide aqueous solutions by mass fraction were used as the electrolyte, respectively. The specific steps are as follows:

[0063] (1) Pretreatment of silicon carbide wafers

[0064] The silicon carbide wafer was prepared using a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer was immersed in an HF:ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0065] (2) Steam electrochemical corrosion

[0066] Electrolyte A: Prepare a 2% (w / w) potassium hydroxide aqueous solution.

[0067] Electrolyte B: Prepare a 20% potassium hydroxide aqueous solution;

[0068] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0069] Corrosion conditions: constant voltage 32 V, current density 2.5~3.0 A / cm² 2 Both electrolyte A and electrolyte B solutions were controlled at 102 °C and reacted for 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm).

[0070] (3) Deep regulation

[0071] Reduce the current to 0.2 A / cm 2 Continue the reaction for 10 minutes to obtain porous silicon carbide.

[0072] (4) Graphene growth by pyrolysis

[0073] The porous silicon carbide prepared in step (3) was placed in an Ar / H2 atmosphere tube furnace and pyrolyzed at 1200℃~1220℃ for 30 minutes with the porous silicon carbide itself as the carbon source to achieve in-situ graphitization of the silicon carbide surface and form a porous silicon carbide@G composite material.

[0074] Test Example 1

[0075] Porous silicon carbide obtained by etching with a 20% potassium hydroxide aqueous solution was subjected to SEM testing. See attached SEM image for details. Figure 6 Under otherwise identical corrosion conditions, the effect of different concentrations of potassium hydroxide on the porous morphology is relatively small at low concentrations. However, at lower concentrations, the mesoporous areas are smaller and the mesoporous depth is shallower, meaning that there are fewer areas where graphene can grow after pyrolysis. When the potassium hydroxide concentration is too high, the corrosion surface will be covered with a mixture of potassium hydroxide and oxides, thus blocking further etching.

[0076] The porous silicon carbide@G composite self-supporting sheets (1×1 cm) prepared in Examples 1 and 2 were respectively used. 2 Using EMImNTf2 ionic liquid as the electrolyte and EMImNTf2 as the electrode, a two-electrode supercapacitor was assembled and electrochemically tested at 25℃~150℃. The sheet capacitance is the primary performance indicator for supercapacitors. Tests showed that the sheet capacitance of the porous silicon carbide@G composite material prepared in Example 1 reached 10 mF / cm². 2 In Example 2, the surface capacitance of the porous silicon carbide@G composite material obtained after etching with a 2% potassium hydroxide aqueous solution was only 1.3 mF / cm. 2 .

[0077] Comparative Example 1

[0078] Investigating the effect of current density on the preparation of porous silicon carbide@G composite materials

[0079] The same preparation method as in Example 1 was used, except that a current density of 1.5~2 A / cm was used. 2 and 3.5~4·A / cm 2 The electrolysis is carried out under the specified conditions. The specific steps are as follows:

[0080] (1) Pretreatment of silicon carbide wafers

[0081] The silicon carbide wafer was prepared using a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer was immersed in an HF:ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0082] (2) Steam electrochemical corrosion

[0083] Electrolyte: Prepare a 10% potassium hydroxide aqueous solution;

[0084] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0085] Corrosion conditions:

[0086] Condition A: Constant voltage 32 V, current density 1.5~2 A / cm² 2 The solution temperature was 102 °C, and the reaction time was 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm).

[0087] Condition B: Constant voltage 32 V, current density 3.5~4 A / cm² 2 The solution temperature was 102 °C, and the reaction time was 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm).

[0088] (3) Deep regulation

[0089] Reduce the current to 0.2 A / cm 2 Continue the reaction for 10 minutes to obtain porous silicon carbide.

[0090] (4) Pyrolysis growth of graphene

[0091] The porous silicon carbide prepared in step (3) was placed in an Ar / H2 atmosphere tube furnace and pyrolyzed at 1200℃~1220℃ for 30 minutes with the porous silicon carbide itself as the carbon source to achieve in-situ graphitization of the silicon carbide surface and form a porous silicon carbide@G composite material.

[0092] Test Example 2

[0093] With a current density of 3.5~4 A / cm 2 The porous silicon carbide obtained after etching was subjected to SEM testing. See the attached SEM images for details. Figure 7 .

[0094] Depend on Figure 7 It can be seen that at a current density of 3.5~4 A / cm 2 The corrosion was quite severe, destroying the nanoscale porous morphology of silicon carbide. Simultaneously, due to the reduced specific surface area and crystal quality, the electrochemical performance was far inferior to that of normally corroded wafers; the sheet capacitance of the porous silicon carbide@G composite material was 0.3 mF / cm². 2 .

[0095] When the current density is 1.5~2 A / cm 2 At the same time, similar to low-temperature corrosion, the corrosion effect is relatively weak, and the resulting structure has poor electrochemical performance.

[0096] Comparative Example 2

[0097] Investigating the effect of vapor etching parameters on the preparation of porous silicon carbide@G composite materials

[0098] The same preparation method as in Example 1 was used, except that potassium hydroxide aqueous solutions at 75°C and 25°C were used as electrolytes, respectively.

[0099] The specific steps are as follows:

[0100] (1) Pretreatment of silicon carbide wafers

[0101] The silicon carbide wafer was prepared using a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer was immersed in an HF:ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0102] (2) Steam electrochemical corrosion

[0103] Electrolyte: Prepare a 10% potassium hydroxide aqueous solution;

[0104] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0105] Corrosion condition A: constant voltage 32 V, current density 2.5~3.0 A / cm² 2 The solution temperature was 75 °C, and the reaction time was 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm).

[0106] Corrosion condition B: constant voltage 32 V, current density 2.5~3.0 A / cm² 2 The solution temperature was 25 °C, and the reaction time was 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm).

[0107] (3) Deep regulation

[0108] Reduce the current to 0.2 A / cm 2 Continue the reaction for 10 minutes to obtain porous silicon carbide.

[0109] (4) Graphene growth by pyrolysis

[0110] The porous silicon carbide prepared in step (3) was placed in an Ar / H2 atmosphere tube furnace and pyrolyzed at 1200℃~1220℃ for 30 minutes with the porous silicon carbide itself as the carbon source to achieve in-situ graphitization of the silicon carbide surface and form a porous silicon carbide@G composite material.

[0111] Test Example 3

[0112] Porous silicon carbide prepared by electrochemical etching with potassium hydroxide aqueous solution at 75℃ was subjected to SEM testing. See attached image for details. Figure 8 .

[0113] At room temperature, etching fails to form a mild silicon dioxide oxide layer due to weak activation of the silicon carbide surface, resulting in a very weak etching effect under otherwise identical conditions, with almost no formation of nanoscale mesopores. At 75°C, a porous etching structure exists, but it is weak. Furthermore, the electrochemical performance is weak; the sheet capacitance of the porous silicon carbide@G composite material prepared by electrochemical etching at 25°C is measured to be 0.02 mF / cm². 2 The sheet capacitance of the porous silicon carbide@G composite material prepared by electrochemical etching at 75℃ was measured to be 0.1 mF / cm. 2 .

[0114] Comparative Example 3

[0115] Investigating the effect of graphene growth temperature on the preparation of porous silicon carbide@G composite materials

[0116] The same preparation method as in Example 1 was used, except that graphene was grown by pyrolysis at 1100°C and 1350°C, respectively.

[0117] The specific steps are as follows:

[0118] (1) Pretreatment of silicon carbide wafers

[0119] The silicon carbide wafer was prepared using a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer was immersed in an HF:ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0120] (2) Steam electrochemical corrosion

[0121] Electrolyte: Prepare a 10% potassium hydroxide aqueous solution;

[0122] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0123] Corrosion conditions: constant voltage 32 V, current density 2.5~3.0 A / cm² 2 The solution temperature was 75 °C, and the reaction time was 5 minutes. The vapor formed an electrochemical diffusion layer on the sample surface, which induced the corrosion liquid to climb upward and etch on the liquid surface (below the liquid surface: 1~4 μm; above the liquid surface: 300 nm~1 μm).

[0124] (3) Deep regulation

[0125] Reduce the current to 0.2 A / cm 2 Continue the reaction for 10 minutes to further extend the pore depth to more than 1 μm and obtain porous silicon carbide.

[0126] (4) Graphene growth by pyrolysis

[0127] The porous silicon carbide prepared in step (3) was placed in an Ar / H2 atmosphere tube furnace and pyrolyzed at 1100℃ and 1350℃ for 30 minutes respectively to achieve in-situ graphitization of the silicon carbide surface and form a porous silicon carbide@G composite material.

[0128] Test Example 4

[0129] The porous silicon carbide@G composite material prepared at 1350℃ was subjected to SEM testing. See attached SEM images for details. Figure 9 .

[0130] At lower growth temperatures, the Si in silicon carbide cannot volatilize through pyrolysis, making it difficult for the C component that makes up graphene to reconstruct on the surface. Therefore, graphene cannot form, and no graphene peak is observed in Raman spectroscopy. When the growth temperature is increased to 1350℃, the pyrolysis of the Si component becomes more intense. This results in a higher concentration of carbon in the reaction environment, forming a thicker layer of graphene that covers the porous silicon carbide structure. However, the porous structure is also damaged by pyrolysis, leading to a surface capacitance of only 3 mF / cm² for the prepared porous silicon carbide@G composite material. 2 .

[0131] Comparative Example 4

[0132] The etching process using HF as the etchant involves the following steps:

[0133] (1) Pretreatment of silicon carbide wafers

[0134] The silicon carbide wafer was prepared using a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer was immersed in an HF:ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0135] (2) Electrochemical corrosion

[0136] Electrolyte: Prepare a saturated aqueous solution of ammonium bifluoride;

[0137] Corrosion conditions: constant voltage 32V, current density 2.5~3.0 A / cm² 2 , room temperature, 1min;

[0138] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0139] (3) Secondary corrosion

[0140] Electrolyte: Prepare a solution of ethanol: hydrofluoric acid: hydrogen peroxide = 6:3:1;

[0141] Corrosion conditions: constant current 0.2 A / cm 2 Corrosion for 5 minutes.

[0142] The porous silicon carbide prepared in Comparative Example 4 was subjected to SEM testing, and the obtained SEM images are detailed below. Figure 10 .like Figure 10 As shown, the porous silicon carbide prepared by HF etching exhibits poor microstructure uniformity and unsatisfactory pore morphology, with a sheet capacitance of 0.005 mF / cm. 2 .

[0143] Comparative Example 5

[0144] The etching process uses potassium hydroxide as the etchant, and the specific steps are as follows:

[0145] (1) Pretreatment of silicon carbide wafers

[0146] The silicon carbide wafer was prepared using a self-made heavily doped N-type 4H-silicon carbide single crystal with a resistivity of 7~8 mΩ·cm and a thickness of 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer was immersed in an HF:ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0147] (2) Electrochemical corrosion

[0148] Electrolyte: Prepare a 10% potassium hydroxide aqueous solution;

[0149] Corrosion conditions: constant current 32V, current density 2.5~3.0 A / cm² 2 , room temperature, 1min;

[0150] Electrode configuration: Silicon carbide pretreated in step (1) is used as the anode and Pt is used as the cathode, with a spacing of 5 cm;

[0151] (3) Secondary corrosion

[0152] Electrolyte: Prepare a solution of ethanol: hydrofluoric acid: hydrogen peroxide = 6:3:1;

[0153] Corrosion conditions: 5 minutes of corrosion.

[0154] The porous silicon carbide prepared in Comparative Example 5 was subjected to SEM testing, and the obtained SEM images are detailed below. Figure 11 .like Figure 11 As shown, porous silicon carbide prepared by etching with potassium hydroxide aqueous solution alone can be seen to have micron-sized macropores but no nano-sized microstructures. Therefore, the improvement in surface area and capacitance is very small.

[0155] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preparing porous silicon carbide, characterized in that, Includes the following steps: (1) Steam electrochemical corrosion Electrolyte: 10 wt% potassium hydroxide aqueous solution; Electrode configuration: silicon carbide wafer as anode, Pt as cathode, with a spacing of 3~5 cm; Corrosion conditions: constant voltage 32 V, current density 2.5~3.0 A / cm² 2 The potassium hydroxide aqueous solution is at a temperature of 100℃~104℃, the reaction time is 3~5 minutes, and the heating platform is at 120℃~140℃. (2) Deep regulation Reduce the current to 0.1~0.3 A / cm 2 Continue the reaction for 10-30 minutes to extend the pore depth to more than 1 μm and obtain porous silicon carbide.

2. The method for preparing porous silicon carbide as described in claim 1, characterized in that, Before performing steam electrochemical etching, the silicon carbide wafers are pretreated by immersing them in a 1:1 HF:ethanol solution for 2 to 10 minutes.

3. A porous silicon carbide, characterized in that, The porous silicon carbide is obtained by the preparation method described in claim 1.

4. A method for preparing a porous silicon carbide@G composite material, characterized in that, Using the porous silicon carbide described in claim 3 as a substrate, in-situ graphitization is performed on the surface of the silicon carbide substrate at 1200℃~1220℃ to obtain a porous silicon carbide@G composite material.

5. A porous silicon carbide@G composite material, characterized in that, The porous silicon carbide@G composite material was obtained using the preparation method described in claim 4.

6. The application of the porous silicon carbide@G composite material as described in claim 5 in a high-temperature supercapacitor.

7. The application as described in claim 6, characterized in that, In high-temperature supercapacitors, porous silicon carbide@G composite material is used as the electrode and EMImNTf2 ionic liquid is used as the electrolyte to assemble a two-electrode supercapacitor.

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