Porous silicon carbide, porous silicon carbide (at) G composite material and preparation method and application thereof

Abstract

The invention relates to porous silicon carbide, a porous silicon carbide (at) G composite material and a preparation method and application thereof, and belongs to the technical field of semiconductor materials. According to the preparation method of the porous silicon carbide, silicon carbide is taken as an anode, Pt is taken as a cathode, a potassium hydroxide aqueous solution is taken as an electrolyte, the temperature of the potassium hydroxide aqueous solution is controlled, two-step constant-voltage constant-current etching is adopted, and deep steam-assisted diffusion layer corrosion is performed while solution electrochemical corrosion is performed on the surface of the silicon carbide, so that the porous silicon carbide is obtained. Porous silicon carbide is used as a substrate, in-situ graphitization is carried out on the surface of the silicon carbide substrate, and the porous silicon carbide (at) G composite material is obtained. When the porous silicon carbide is prepared, HF is replaced by potassium hydroxide, and meanwhile, the etching uniformity and etching efficiency of the silicon carbide are improved under the assistance of steam. A uniform mesoporous structure in the porous silicon carbide prepared after etching provides a high specific surface area and optimizes an 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 prior art is the 4H-SiC nanochannel array (NCAs) electrode prepared by a two-step anodization method proposed by Li et al. (Mater. Horiz., 2018, 5, 883). By optimizing the etching solution formula and process parameters, highly ordered SiC nanochannel structures are successfully prepared, which have significantly improved specific surface area, excellent electrochemical performance, and extremely high cycle stability in a wide temperature range. However, this method still relies on HF-based electrolyte, which poses environmental and safety risks, and the etching process still needs to overcome the "cap layer" problem, which has high process complexity and is difficult to reproduce.

[0007] In summary, the existing preparation of porous silicon carbide wafer still uses HF for etching, and the prepared porous silicon carbide wafer has problems such as uneven etching, low etching efficiency, environmental unfriendly reagents, and poor structure stability of the prepared porous wafer, which are urgent problems to be solved. SUMMARY

[0008] In view of the problems of uneven etching, low etching efficiency, and environmental unfriendly reagents in the existing preparation of porous silicon carbide wafer, the present application provides a porous silicon carbide, a porous silicon carbide@G composite material, and a preparation method and application thereof to solve the above problems. The present application uses a potassium hydroxide vapor assisted electrochemical etching method to construct a uniform mesoporous structure on the surface of silicon carbide, and further grows graphene through in-situ pyrolysis to form an integrated electrode. The present application solves the problems of uneven etching, low efficiency, environmental unfriendliness, and poor structure stability in the prior art, and provides a new idea for the development of high-performance silicon carbide-based high-temperature energy storage devices.

[0009] The technical scheme of the present application is as follows: In a first aspect, the present application provides a method for preparing a porous silicon carbide, comprising the following steps: using silicon carbide as an anode, Pt as a cathode, and a potassium hydroxide aqueous solution as an electrolyte, controlling the temperature of the potassium hydroxide aqueous solution, and using a two-step constant voltage and constant current etching to etch the surface of the silicon carbide while performing a depth vapor assisted diffusion layer etching to obtain a porous silicon carbide.

[0010] Further, the method specifically comprises the following steps: (1) Vapor electrochemical etching Electrolyte: potassium hydroxide aqueous solution; Electrode configuration: silicon carbide wafer as anode, Pt as cathode, and spacing of 3-5 cm; Etching conditions: constant voltage of 32 V, current density of 1.0-3.0 A / cm 2 , potassium hydroxide aqueous solution temperature of 100℃-104℃, reaction time of 3-5 minutes, and heating table temperature of 120℃-140℃; Steam assisted: form electrochemical diffusion layer on the surface of the sample, induce the corrosion liquid to climb up, realize the difference etching between the upper and lower liquid surface, and form gradient mesoporous structure.

[0011] (2) Depth control Reduce the current, continue the reaction for 10-30 minutes, extend the depth of the channel to more than 1 μm, and obtain porous silicon carbide.

[0012] Further, before the steam electrochemical corrosion is performed, the silicon carbide wafer is pretreated by immersing in a mixed solution of 40% HF aqueous solution: ethanol = 1:1 for 2-10 minutes to remove the surface oxide layer.

[0013] Further, the concentration of the potassium hydroxide aqueous solution is 10 wt%.

[0014] Further, in the step (2), the current is reduced to 0.1-0.3 A / cm 2 .

[0015] In a second aspect, the application provides a porous silicon carbide prepared by the above method.

[0016] In a third aspect, the application provides a preparation method of a porous silicon carbide@G composite material, wherein the porous silicon carbide is obtained by the above method, and in-situ graphitization is performed on the surface of the silicon carbide substrate to obtain the porous silicon carbide@G composite material.

[0017] Specifically, the following steps are included: The porous silicon carbide is placed in an Ar / H2 atmosphere tube furnace, and the porous silicon carbide itself is used as a carbon source to pyrolyze at 1200-1220℃ for 30 minutes to realize in-situ graphitization of the surface of the silicon carbide and form the silicon carbide@G composite material.

[0018] In a fourth aspect, the application provides a porous silicon carbide@G composite material prepared by the above method.

[0019] In a fifth aspect, the application provides an application of the above porous silicon carbide@G composite material in a high-temperature supercapacitor.

[0020] Further, in the high-temperature supercapacitor, the porous silicon carbide@G composite material is used as an electrode, and EMImNTf2 (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide) ionic liquid is used as an electrolyte to assemble a two-electrode supercapacitor.

[0021] The application has the following beneficial effects: The present application uses potassium hydroxide instead of HF when preparing porous silicon carbide, avoiding the use of toxic reagents; and uses steam to improve the uniformity and etching efficiency of silicon carbide etching.

[0022] The traditional preparation of graphene is to grow on a metal substrate such as copper using CVD (chemical vapor deposition method), and then to be transferred to the required substrate. The existing method can cause damage to the transferred film on the one hand, and the bonding effect between the transferred substrate and graphene is poor and unstable on the other hand. The preparation method provided by the present application grows graphene in situ on the surface of porous silicon carbide, without the need for transfer and with covalent bonding between the substrate and graphene, maintaining the structural integrity of the porous silicon carbide@G composite material and the interface conductivity. Through testing, the porous silicon carbide@G composite material prepared by the present application still maintains high power density and cycle stability at 150 DEG C, which is superior to existing silicon carbide-based electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0024] Figure 1 The figure is an electrochemical etching system for preparing porous silicon carbide of the present application; in the figure, 1 is an etched silicon carbide wafer, 2 is a platinum electrode, 3 is a heating table, and 4 is a direct current power supply.

[0025] Figure 2 The figure is a SEM test graph of the porous silicon carbide prepared in Example 1 of the present application.

[0026] Figure 3 The figure is a Raman spectrum graph of the porous silicon carbide@G composite material prepared in Example 1 of the present application.

[0027] Figure 4 The figure is a CV curve graph of the porous silicon carbide@G composite material prepared in Example 1 of the present application in a three-electrode test.

[0028] Figure 5 The figure is an XPS energy spectrum graph of C1s of the porous silicon carbide@G composite material prepared in Example 1 of the present application.

[0029] Figure 6 The figure is a SEM test graph of the porous silicon carbide prepared by using a 20% mass fraction potassium hydroxide aqueous solution and then steam electrochemical etching in Example 2.

[0030] Figure 7For the comparative example 1, the current density used is 3.5~4·A / cm 2 SEM test diagram of porous silicon carbide prepared by steam electrochemical corrosion.

[0031] Figure 8 SEM test diagram of porous silicon carbide prepared by electrochemical corrosion using 75℃ potassium hydroxide aqueous solution in the comparative example 2.

[0032] Figure 9 SEM test diagram of porous silicon carbide@G composite material prepared using 1350℃ conditions in the comparative example 3.

[0033] Figure 10 SEM test diagram of porous silicon carbide prepared by etching using HF aqueous solution in the comparative example 4.

[0034] Figure 11 SEM test diagram of porous silicon carbide prepared by etching using potassium hydroxide aqueous solution method in the comparative example 5. DETAILED DESCRIPTION

[0035] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0036] Embodiment 1 A preparation method of a porous silicon carbide@G composite material, the specific steps are as follows: (1) Silicon carbide wafer pretreatment The silicon carbide wafer adopts self-made heavily doped N-type 4H-silicon carbide single crystal, the resistivity is 7~8 mΩ·cm, and the thickness is 520 μm. The preparation method of the heavily doped N-type 4H-silicon carbide single crystal is disclosed in the patent CN202411763136.8. The silicon carbide wafer is soaked in a mixed solution of 40% HF aqueous solution: ethanol = 1:1 for 5 minutes to remove the surface oxide layer.

[0037] (2) Steam electrochemical corrosion Electrolyte: prepare 10% potassium hydroxide aqueous solution; Electrode configuration: use the silicon carbide pretreated in step (1) as an anode, Pt as a cathode, and the distance is 5 cm; Corrosion conditions: constant voltage 32 V, current density 2.5~3.0·A / cm 2, solution temperature 102 ℃, reaction 5 minutes; the steam formed an electrochemical diffusion layer on the surface of the sample, inducing the corrosion liquid to climb up and etch on the liquid surface (under the liquid surface: 1-4 μm; on the liquid surface: 300 nm-1 μm), realizing the differential etching of the upper and lower liquid surfaces, and forming a gradient mesoporous structure.

[0038] (3) Depth regulation Lower the current to 0.2 A / cm 2 , continue to react for 10 minutes, further extend the depth of the channel to more than 1 μm, and obtain porous silicon carbide. The SEM image obtained by testing the prepared porous silicon carbide is shown in Figure 2 .

[0039] (4) Pyrolysis growth of graphene Place the porous silicon carbide in an Ar / H2 atmosphere tube furnace, use the porous silicon carbide itself as a carbon source, pyrolyze at 1200-1220 ℃ for 30 minutes, realize in-situ graphitization of the silicon carbide surface, and form a porous silicon carbide@G composite material. The prepared porous silicon carbide@G composite material is respectively subjected to Raman spectrum analysis, three-electrode test, and XPS energy spectrum test. The Raman spectrum is shown in Figure 3 ; the CV curve of the three-electrode test is shown in Figure 4 ; and the XPS energy spectrum is shown in Figure 5 .

[0040] From the Raman spectrum of Figure 3 , it can be seen that there is a strong D peak around 1300 peak position, which means that the defect activity of the grown graphene is high, which is beneficial to participate in the electrochemical reaction, and the G peak at 1580 and 2700 cm -2 and the 2D peak shape are good, indicating that the structure of the graphene is complete and uniformly covered.

[0041] From the three-electrode test of Figure 4 , it can be seen that the CV curve peak value and the closed curve area of the porous silicon carbide etched after the growth of graphene are much higher than those before the growth of graphene, representing that the capacitance performance of the electrode after the growth of graphene has been significantly improved.

[0042] From the XPS energy spectrum of Figure 5 , it can be seen that in addition to the C-Si bond and C-C bond existing in the silicon carbide crystal itself, a high-intensity C=C bond and a weak C-O bond appear in the XPS, indicating that the graphene is uniformly covered and has a good morphology.

[0043] Example 2 Investigation of the influence of the concentration of potassium hydroxide aqueous solution on the preparation of porous silicon carbide@G composite material Using the same preparation method as Example 1, the difference is that the mass fraction of 2% and 20% potassium hydroxide aqueous solution is used as electrolyte respectively. The specific steps are as follows: (1) Silicon carbide wafer pretreatment The silicon carbide wafer is self-made heavy-doped N-type 4H-silicon carbide single crystal, resistivity 7~8 mΩ·cm, thickness 520 μm, the preparation method of heavy-doped N-type 4H-silicon carbide single crystal is disclosed in patent CN202411763136.8. The silicon carbide wafer is immersed in HF: ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0044] (2) Steam electrochemical etching Electrolyte A: prepare a mass fraction of 2% potassium hydroxide aqueous solution Electrolyte B: prepare a mass fraction of 20% potassium hydroxide aqueous solution Electrode configuration: the silicon carbide pretreated in step (1) is used as anode, Pt is used as cathode, and the distance is 5 cm Etching conditions: constant voltage 32 V, current density 2.5~3.0·A / cm 2 , the solution of electrolyte A and electrolyte B is controlled at 102 ℃, and the reaction is 5 minutes; the steam forms an electrochemical diffusion layer on the surface of the sample, induces the etching liquid to climb up and etch on the liquid surface (1~4 μm under the liquid surface; 300 nm~1 μm above the liquid surface).

[0045] (3) Depth control Reduce the current to 0.2 A / cm 2 , continue to react for 10 minutes to obtain porous silicon carbide.

[0046] (4) Pyrolysis growth of graphene The porous silicon carbide prepared in step (3) is placed in an Ar / H2 atmosphere tube furnace, and the porous silicon carbide itself is used as a carbon source to pyrolyze at 1200℃~1220℃ for 30 minutes to realize in-situ graphitization on the surface of silicon carbide and form porous silicon carbide@G composite material.

[0047] Test Example 1 The porous silicon carbide obtained after etching with a mass fraction of 20% potassium hydroxide aqueous solution is tested by SEM, and the SEM diagram obtained is shown in Figure 6 . Under the same etching conditions, the influence of different concentrations of potassium hydroxide at low concentration on the porous morphology is small, but the mesoporous area etched at low concentration is small and the mesoporous depth is shallow, that is, the area that can grow graphene after pyrolysis is less, and when the concentration of potassium hydroxide is too high, the etched surface will be covered with a mixture of potassium hydroxide and oxide, thereby blocking further etching.

[0048] The self-supporting sheets (1×1 cm 2 ) of the porous silicon carbide@G composite material prepared in Example 1 and Example 2 were used as electrodes, and EMImNTf2 ionic liquid was used as electrolyte to assemble a two-electrode supercapacitor, which was subjected to electrochemical test at 25℃-150℃. The surface capacitance of the supercapacitor was used as the evaluation index of electrochemical performance. After test, the surface capacitance of the porous silicon carbide@G composite material prepared in Example 1 reached 10 mF / cm 2 , while the surface capacitance of the porous silicon carbide@G composite material obtained after corrosion by 2% potassium hydroxide aqueous solution in Example 2 was only 1.3 mF / cm 2 .

[0049] Comparative Example 1 Influence of current density on preparation of porous silicon carbide@G composite material The same preparation method as in Example 1 was used, except that the electrolysis conditions were 1.5-2·A / cm 2 and 3.5-4·A / cm 2 , respectively. The specific steps were as follows: (1) Pretreatment of silicon carbide wafer The silicon carbide wafer was 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 a HF:ethanol=1:1 solution for 5 minutes to remove the surface oxide layer.

[0050] (2) Vapor electrochemical corrosion Electrolyte: 10% potassium hydroxide aqueous solution; Electrode configuration: the pretreated silicon carbide in step (1) was used as anode, and Pt was used as cathode with a distance of 5 cm; Corrosion conditions: Condition A: constant voltage 32 V, current density 1.5-2·A / cm 2 , solution temperature 102℃, reaction time 5 minutes; vapor formed an electrochemical diffusion layer on the surface of the sample, inducing the corrosion solution to climb up and etch on the liquid surface (1-4 μm below the liquid surface; 300 nm-1 μm above the liquid surface).

[0051] Condition B: constant voltage 32 V, current density 3.5-4·A / cm 2 , solution temperature 102℃, reaction time 5 minutes; vapor formed an electrochemical diffusion layer on the surface of the sample, inducing the corrosion solution to climb up and etch on the liquid surface (1-4 μm below the liquid surface; 300 nm-1 μm above the liquid surface).

[0052] (3) Depth regulation Lower the current to 0.2 A / cm 2 , continue to react for 10 minutes to obtain porous silicon carbide.

[0053] (4) Pyrolysis growth of graphene The porous silicon carbide prepared in step (3) is placed in an Ar / H2 atmosphere tube furnace, and the porous silicon carbide itself is used as a carbon source. Pyrolysis is carried out at 1200°C-1220°C for 30 minutes to realize in-situ graphitization of the surface of the porous silicon carbide and form a porous silicon carbide@G composite material.

[0054] Test Example 2 The current density is 3.5-4·A / cm 2 After etching, the porous silicon carbide obtained is subjected to SEM testing, and the SEM diagram obtained is shown in Figure 7 .

[0055] From Figure 7 It can be seen that the etching is more intense at a current density of 3.5-4·A / cm 2 , the nano-scale porous morphology of silicon carbide is destroyed, and at the same time, due to the decrease in specific surface area and the decrease in crystal quality, the electrochemical test performance is also far lower than that of the normal etched wafer, and the surface capacitance of the porous silicon carbide@G composite material is 0.3 mF / cm 2 .

[0056] When the current density is 1.5-2·A / cm 2 , the etching effect is relatively weak, and the electrochemical performance of the obtained structure is also poor.

[0057] Comparative Example 2 Influence of steam etching parameters on the preparation of a porous silicon carbide@G composite material The same preparation method as in Example 1 is used, except that a 75°C and 25°C potassium hydroxide aqueous solution is used as the electrolyte, respectively.

[0058] The specific steps are as follows: (1) Silicon carbide wafer pretreatment 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 an HF:ethanol=1:1 solution for 5 minutes to remove the surface oxide layer.

[0059] (2) Steam electrochemical etching Electrolyte: prepare a 10% potassium hydroxide aqueous solution by mass fraction; Electrode configuration: SiC as anode, Pt as cathode, 5 cm apart Corrosion condition A: constant voltage 32 V, current density 2.5~3.0·A / cm 2 , solution temperature 75 ℃, reaction for 5 minutes; vapor forms an electrochemical diffusion layer on the surface of the sample, inducing the corrosion solution to climb up and etch on the liquid surface (under the liquid surface: 1~4 μm; on the liquid surface: 300 nm~1 μm).

[0060] Corrosion condition B: constant voltage 32 V, current density 2.5~3.0·A / cm 2 , solution temperature 25 ℃, reaction for 5 minutes; vapor forms an electrochemical diffusion layer on the surface of the sample, inducing the corrosion solution to climb up and etch on the liquid surface (under the liquid surface: 1~4 μm; on the liquid surface: 300 nm~1 μm).

[0061] (3) Depth control Lower the current to 0.2 A / cm 2 , continue to react for 10 minutes to obtain porous silicon carbide.

[0062] (4) Pyrolysis of graphene Put the porous silicon carbide prepared in step (3) into an Ar / H2 atmosphere tube furnace, use the porous silicon carbide itself as a carbon source, pyrolyze at 1200 ℃~1220 ℃ for 30 minutes, realize in-situ graphitization of the surface of the silicon carbide, and form a porous silicon carbide@G composite material.

[0063] Test Example 3 The porous silicon carbide prepared by electrochemical corrosion of a 75 ℃ potassium hydroxide aqueous solution was subjected to SEM testing, and the obtained SEM image is shown in Figure 8 .

[0064] When etching at room temperature, due to weak activation of the surface of the silicon carbide, a mild silicon dioxide oxidation layer cannot be formed for etching reaction, and under the same other conditions, the corrosion effect obtained is very weak, and almost no nano-sized mesoporous structure is formed. At 75 ℃, there is a porous etching structure, but it is relatively weak. And the electrochemical performance is weak, the surface capacitance test of the porous silicon carbide@G composite material prepared by electrochemical corrosion at 25 ℃ is 0.02 mF / cm 2 , and the surface capacitance test of the porous silicon carbide@G composite material prepared by electrochemical corrosion at 75 ℃ is 0.1 mF / cm 2 .

[0065] Comparative Example 3 Investigate the effect of graphene growth temperature on the preparation of porous silicon carbide@G composite material Using the same preparation method as in Example 1, except that the graphene was grown by pyrolysis at 1100°C and 1350°C, respectively.

[0066] The specific steps are as follows: (1) Silicon carbide wafer pretreatment 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 HF:ethanol=1:1 solution for 5 minutes to remove the surface oxide layer.

[0067] (2) Steam electrochemical etching Electrolyte: prepare a 10% potassium hydroxide aqueous solution by mass fraction; Electrode configuration: use the pretreated silicon carbide in step (1) as the anode and Pt as the cathode with a distance of 5 cm; Etching conditions: constant voltage 32 V, current density 2.5-3.0 A / cm 2 , solution temperature 75°C, reaction time 5 minutes; the steam forms an electrochemical diffusion layer on the sample surface, inducing the etching solution to climb up and etch on the liquid surface (1-4 μm below the liquid surface; 300 nm-1 μm above the liquid surface).

[0068] (3) Depth control Reduce the current to 0.2 A / cm 2 , continue to react for 10 minutes to further extend the pore depth to more than 1 μm, and obtain porous silicon carbide.

[0069] (4) Pyrolysis growth of graphene Place the porous silicon carbide prepared in step (3) in an Ar / H2 atmosphere tube furnace, use the porous silicon carbide itself as a carbon source, and pyrolyze at 1100°C and 1350°C, respectively, for 30 minutes to realize in-situ graphitization of the silicon carbide surface and form porous silicon carbide@G composite materials.

[0070] Test Example 4 The porous silicon carbide@G composite material prepared at 1350°C was subjected to SEM testing, and the obtained SEM images are shown in Figure 9 .

[0071] When the growth temperature is low, the Si in the silicon carbide cannot be volatilized by pyrolysis, so the C component of graphene is also difficult to restructure on the surface, and therefore graphene cannot be formed, and there is no graphene peak in the Raman test. When the growth temperature is increased to 1350°C, the pyrolysis of the Si component is more intense. Therefore, there is more carbon component in the reaction environment, forming a thicker graphene and covering the porous structure of the silicon carbide, and at the same time the porous structure is also damaged by pyrolysis, and the surface capacitance of the prepared porous silicon carbide@G composite material is only 3 mF / cm 2 .

[0072] Comparative Example 4 HF is used as an etchant for etching, and the specific steps are as follows: (1) Pretreatment of silicon carbide wafer 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 HF:ethanol=1:1 solution for 5 minutes to remove the surface oxide layer.

[0073] (2) Electrochemical etching Electrolyte: saturated ammonium hydrogen fluoride aqueous solution is prepared; Etching conditions: constant voltage 32V, current density 2.5-3.0·A / cm 2 , room temperature, 1 min; Electrode configuration: the pretreated silicon carbide in step (1) is used as the anode, and Pt is used as the cathode with a distance of 5 cm; (3) Secondary etching Electrolyte: a solution of ethanol:hydrofluoric acid:hydrogen peroxide=6:3:1 is prepared; Etching conditions: constant current 0.2 A / cm 2 , etching for 5 min.

[0074] The porous silicon carbide prepared in Comparative Example 4 is subjected to SEM test, and the obtained SEM image is shown in Figure 10 . As shown in Figure 10 , the micro-uniformity of the porous silicon carbide prepared by HF etching is poor, and the pore size morphology is not ideal, and the surface capacitance test is 0.005 mF / cm 2 .

[0075] Comparative Example 5 Potassium hydroxide is used as an etchant for etching, and the specific steps are as follows: (1) Pretreatment of silicon carbide wafer The silicon carbide wafer is made of self-prepared 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 soaked in a HF: ethanol = 1:1 solution for 5 minutes to remove the surface oxide layer.

[0076] (2) Electrochemical etching Electrolyte: prepare a 10% potassium hydroxide aqueous solution by mass fraction; Etching conditions: constant current 32V, current density 2.5-3.0·A / cm 2 , room temperature, 1 min; Electrode configuration: the silicon carbide pretreated in step (1) is used as the anode, and Pt is used as the cathode, with a distance of 5 cm; (3) Secondary etching Electrolyte: prepare a solution of ethanol: hydrofluoric acid: hydrogen peroxide = 6:3:1; Etching conditions: etching for 5 min.

[0077] The porous silicon carbide prepared in Comparative Example 5 is subjected to SEM test, and the obtained SEM image is shown in Figure 11 . As shown in Figure 11 , the porous silicon carbide prepared by simply using potassium hydroxide aqueous solution for etching can be seen to be etched into micron-sized large pores, without nanoscale microstructure, so the improvement effect on the specific surface area and the capacitance is small.

[0078] Although the present application has been described in detail with reference to the preferred embodiments, the present application is not limited thereto. Various equivalent modifications or replacements can be made to the embodiments of the present application by those skilled in the art without departing from the spirit and essence of the present application, and these modifications or replacements shall be within the scope of the present application. Any person skilled in the art within the technical scope disclosed in the present application can easily think of changes or replacements, which shall be covered within the protection scope of the present application.

Claims

1. A method for producing porous silicon carbide, characterized by, Comprising the following steps: The porous silicon carbide is obtained by two-step constant voltage and constant current etching with silicon carbide as anode, Pt as cathode, and aqueous potassium hydroxide solution as electrolyte, controlling the temperature of the aqueous potassium hydroxide solution, and carrying out deep vapor-assisted diffusion layer etching while electrochemically etching the surface of the silicon carbide.

2. The method for preparing porous silicon carbide as described in claim 1, characterized in that, Specifically comprising the following steps: (1) Vapor electrochemical etching Electrolyte: aqueous potassium hydroxide solution; Electrode configuration: silicon carbide wafer as anode, Pt as cathode, and the distance between them is 3-5 cm; Corrosion condition: constant voltage 32 V, current density 1.0~3.0 A / cm 2 The temperature of the potassium hydroxide aqueous solution is 100~104℃, the reaction time is 3~5 minutes, and the heating platform is 120~140℃. (2) Deep regulation Lower the current and continue the reaction for 10-30 minutes to extend the depth of the pores to more than 1 μm, and obtain the porous silicon carbide.

3. The method for preparing porous silicon carbide as described in claim 2, characterized in that, Before the vapor electrochemical etching, the silicon carbide wafer is pretreated by immersing it in a HF:ethanol=1:1 solution for 2-10 minutes.

4. The method for preparing porous silicon carbide as described in claim 2, characterized in that, The concentration of the aqueous potassium hydroxide solution is 10 wt%.

5. The method for preparing porous silicon carbide as described in claim 2, characterized in that, In the step (2), the current is reduced to 0.1-0.3 A / cm 2 .

6. A porous silicon carbide characterized by, The porous silicon carbide is obtained by the preparation method of claim 1.

7. A method for preparing a porous silicon carbide@G composite material, characterized in that, The porous silicon carbide@G composite material is obtained by in-situ graphitization of the porous silicon carbide of claim 6 at 1200-1220℃ on the surface of the silicon carbide substrate.

8. A porous silicon carbide@G composite material, characterized in that, The porous silicon carbide@G composite material is obtained by the preparation method of claim 7.

9. The porous silicon carbide@G composite material of claim 8 is used in high-temperature supercapacitors.

10. The use according to claim 9, wherein the compound is ###0002### In the high-temperature supercapacitor, the 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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