Biomass carbon material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biomass carbon materials, in particular to a biomass carbon material and a preparation method and application thereof.The preparation method comprises the following steps that biomass serves as a carbon source, the biomass is pretreated, and pretreated biomass powder is obtained; the preparation method comprises the following steps: mixing pretreated biomass powder with a metal catalyst, and carrying out pyrolysis-electrolysis in a CaCl2-NaCl molten salt system in a nitrogen atmosphere to obtain the biomass carbon material. Natural poplar leaves are used as a biomass carbon source, the CaCl2-NaCl molten salt system is used as an electrolyte, and the carbon material is prepared through a molten salt assisted thermal-electric field; the pyrolysis temperature, the electrolysis voltage and the electrolysis time are optimized, and the problems that in a traditional carbon material preparation method, the carbon yield is low, the operation steps are complex, and the preparation cost is high are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass carbon materials, and particularly relates to a biomass carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, a large amount of waste biomass resources are generated every year. In the Northeast region, the agricultural economy is dominated by large-scale planting industries. The annual output of major grain crops such as corn and rice accounts for more than 28% of the total national output. Affected by seasonal sandstorm weather, local windbreak and sand-fixation tree species such as poplar are widely planted to improve the ecological environment. At present, the resource utilization of biomass wastes such as crop straws, rice husks, and forest tree leaves in this region still mainly relies on direct combustion for heating.

[0003] Although this method realizes energy recovery to a certain extent, pollutants such as particulate matter and sulfur oxides released during the combustion process pose a significant threat to the regional air quality. In traditional methods for preparing carbon materials, there are problems such as low carbon yield, complex operation steps, and high preparation costs. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a biomass carbon material, a preparation method thereof, and an application thereof. The present invention uses natural poplar leaves as the biomass carbon source and a CaCl2-NaCl molten salt system as the electrolyte, and prepares the carbon material by molten salt-assisted thermal-electric two fields, optimizing the pyrolysis temperature, electrolysis voltage, and electrolysis time, and solving the problems of low carbon yield, complex operation steps, and high preparation costs in traditional methods for preparing carbon materials.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A preparation method of a biomass carbon material, comprising the following steps:

[0007] Using biomass as the carbon source, pre-treating the biomass to obtain pre-treated biomass powder.

[0008] Mixing the pre-treated biomass powder with a metal catalyst, and performing pyrolysis-electrolysis in a CaCl2-NaCl molten salt system under a protective atmosphere to obtain a biomass carbon material, wherein the pyrolysis temperature is 550°C to 600°C, the electrolysis voltage is 2.8V, and the electrolysis time is 2h to 4h.

[0009] By optimizing the pyrolysis temperature, electrolysis voltage, and electrolysis time, the pyrolysis temperature can regulate the degree of pyrolysis and graphitization of the material, which has a regulatory effect on the microscopic structural characteristics of the product. The electrolysis voltage affects the structural evolution process of the material by regulating the energy input. The electrolysis time significantly affects its charge storage performance by regulating the pore structure, carbon skeleton order, and surface active site distribution of the material. The material prepared by the thermo-electric dual-field composite action of the present invention exhibits a significant porous structure, with dense and interlaced pore channels. The porous structure not only increases the specific surface area of the material but also provides favorable conditions for the insertion and extraction of charges. The carbon material prepared by the method of the present invention has a high carbon yield, simple operation steps, and low cost.

[0010] In a preferred embodiment of the present invention, the biomass is poplar leaves.

[0011] In a preferred embodiment of the present invention, in the CaCl2-NaCl molten salt system, the molar ratio of CaCl2 to NaCl is 0.25 - 0.55:0.45 - 0.75, and the sum of the molar ratios is 1.

[0012] In a preferred embodiment of the present invention, the pyrolysis time is 0.5 h - 5 h.

[0013] In a preferred embodiment of the present invention, the mass ratio of biomass to metal catalyst is 2 - 20:1.

[0014] In a preferred embodiment of the present invention, the metal catalyst is Ni.

[0015] The second object of the present invention is to provide a biomass carbon material prepared by the preparation method described in any one of the above.

[0016] The third object of the present invention is to provide an application of the biomass carbon material described above in a supercapacitor.

[0017] In a preferred embodiment of the present invention, the working electrode of the supercapacitor is the biomass carbon material.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] Based on the problems of low carbon yield, complex operation steps and high preparation cost in the traditional method for preparing carbon materials, the present invention proposes a method for preparing a biomass carbon material. Using biomass as the carbon source and a CaCl2-NaCl molten salt system as the electrolyte, pyrolysis-electrolysis is carried out under a nitrogen atmosphere to obtain the biomass carbon material. By optimizing the pyrolysis temperature, electrolysis voltage and electrolysis time, the pyrolysis temperature can regulate the degree of pyrolysis and graphitization of the material, and has a regulating effect on the microscopic structural characteristics of the product. The electrolysis voltage affects the structural evolution process of the material by regulating the energy input. The electrolysis time significantly affects its charge storage performance by regulating the pore structure, carbon skeleton order degree and surface active site distribution of the material. The material prepared by the present invention through the combined action of thermal-electric dual fields presents a significant porous structure, with dense and interlaced pore channels. The porous structure not only increases the specific surface area of the material, but also provides favorable conditions for the insertion and extraction of charges. The carbon material prepared by the method of the present invention has a high carbon yield, simple operation steps and low cost. Description of the Drawings

[0020] Figure 1 It is the morphology of poplar leaves before and after pretreatment of the present invention. a is before treatment, and b is after treatment.

[0021] Figure 2 It is the SEM diagram of P-NPEC materials prepared at different pyrolysis temperatures of the present invention. Among them, a and b are P-NPEC-550-2.8-2, c and d are P-NPEC-600-2.8-2, e and f are P-NPEC-650-2.8-2, and g and h are P-NPEC-700-2.8-2.

[0022] Figure 3 It is the XRD pattern of P-NPEC materials prepared at different pyrolysis temperatures of the present invention.

[0023] Figure 4 It is the Raman diagram of P-NPEC materials obtained at different pyrolysis temperatures of the present invention.

[0024] Figure 5 It is the electrochemical characteristics of P-NPEC materials synthesized at different electrolysis voltages of the present invention. a is the CV curve at a scan rate of 20 mVs -1 and b is the GCD curve at 0.5 Ag -1 and c is the EIS spectrum, and d is the specific capacitance.

[0025] Figure 6 It is the SEM diagram of P-NPEC materials obtained at different electrolysis voltages of the present invention. a is P-NPEC-550-2.6-2, b is P-NPEC-550-2.8-2, c is P-NPEC-550-3.0-2, and d is P-NPEC-550-3.2-2.

[0026] Figure 7 XRD patterns of the P-NPEC materials prepared at different electrolysis voltages of the present invention.

[0027] Figure 8 Raman graphs of the P-NPEC materials prepared at different electrolysis voltages of the present invention.

[0028] Figure 9 Electrochemical characteristics of the P-NPEC materials synthesized at different electrolysis voltages of the present invention. Among them, a is the CV curve at a scan rate of 20 mV s -1 and b is the GCD curve at 0.5 Ag -1 , c is the EIS spectrum, and d is the specific capacitance.

[0029] Figure 10 SEM images of the P-NPEC materials obtained at different electrolysis times of the present invention. Among them, a and b are P-NPEC-550-2.8-2, c and d are P-NPEC-550-2.8-4, e and f are P-NPEC-550-2.8-6, and g and h are P-NPEC-550-2.8-8.

[0030] Figure 11 XRD graphs of the P-NPEC materials obtained at different electrolysis times of the present invention.

[0031] Figure 12 Raman graphs of the P-NPEC materials obtained at different electrolysis times of the present invention.

[0032] Figure 13 Electrochemical characteristics of the P-NPEC materials synthesized at different electrolysis times of the present invention. Among them, a is the CV curve at a scan rate of 20 mV s -1 and b is the GCD curve at 0.5 Ag -1 , c is the EIS spectrum, and d is the specific capacitance.

[0033] Figure 14 SEM images of P and P products treated in different ways of the present invention.

[0034] Figure 15 N2 adsorption-desorption isotherms of P and P products treated in different ways of the present invention at 77 K.

[0035] Figure 16 Electrochemical characteristics of P and P products treated in different ways of the present invention. a is the CV at a scan rate of 20 mV s -1 and b is the GCD at 0.5 Ag -1 .

[0036] Figure 17Among them, a - c are TEM images of the present invention's P-NPEC-550-2.8-4 at different magnifications.

[0037] Figure 18 is the TG curve of the present invention's P-NPEC-550-2.8-4.

[0038] Figure 19 shows the electrochemical characteristics of the present invention's P-NPEC-550-2.8-4 material. Among them, a is the CV curve at different scanning rates, b is the GCD curve at different current densities, c is the EIS spectrum, and d is the cycle life test.

[0039] Figure 20 is for different products of the present invention at 0.5Ag -1 specific capacitance. Detailed implementation manners

[0040] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described with the help of preferred embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0041] It should be noted that all the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods.

[0042] Embodiment 1

[0043] A preparation method of poplar leaf carbon material, comprising the following steps:

[0044] Perform simple pretreatment on poplar leaves: clean, soak, dry for 48h, and ball mill for 2h to obtain pretreated poplar leaves.

[0045] Mix CaCl2 and NaCl in a molar ratio of 0.55:0.45 to prepare a CaCl2-NaCl molten salt system. Using the CaCl2-NaCl molten salt electrolyte system, with galvanized iron as the cathode, mix 0.1g of poplar leaves (P) and 0.01g of Ni powder and press them into a tablet as the anode, and carry out pyrolysis-electrolysis in an N2 atmosphere. Among them, the pyrolysis temperature is 550°C, the pyrolysis time is 2h, the electrolysis voltage is 2.8V, and the electrolysis time is 4h to obtain poplar leaf carbon material, denoted as P-NPEC-550-2.8-4.

[0046] Example 2

[0047] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 550 °C, the pyrolysis time is 2 h, the electrolysis voltage is 2.8 V, and the electrolysis time is 2 h, to obtain poplar leaf carbon material, denoted as P-NPEC-550-2.8-2.

[0048] Example 3

[0049] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 600 °C, the pyrolysis time is 2 h, the electrolysis voltage is 2.8 V, and the electrolysis time is 2 h, to obtain poplar leaf carbon material, denoted as P-NPEC-600-2.8-2.

[0050] Example 4

[0051] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 650 °C, the pyrolysis time is 2 h, the electrolysis voltage is 2.8 V, and the electrolysis time is 2 h, to obtain poplar leaf carbon material, denoted as P-NPEC-650-2.8-2.

[0052] Example 5

[0053] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 700 °C, the pyrolysis time is 2 h, the electrolysis voltage is 2.8 V, and the electrolysis time is 2 h, to obtain poplar leaf carbon material, denoted as P-NPEC-700-2.8-2.

[0054] Example 6

[0055] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 550 °C, the pyrolysis time is 2 h, the electrolysis voltage is 3.2 V, and the electrolysis time is 2 h, to obtain poplar leaf carbon material, denoted as P-NPEC-550-3.2-2.

[0056] Example 7

[0057] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 550 °C, the pyrolysis time is 2 h, the electrolysis voltage is 2.6 V, and the electrolysis time is 2 h, to obtain poplar leaf carbon material, denoted as P-NPEC-550-2.6-2.

[0058] Example 8

[0059] The preparation method is the same as that of Example 1, except that the pyrolysis temperature is 550 °C, the pyrolysis time is 2 h, the electrolysis voltage is 2.8 V, and the electrolysis time is 4 h, to obtain poplar leaf carbon material, denoted as P-NPEC-550-3.0-2.

[0060] Example 9

[0061] The preparation method is the same as that in Example 1, except that the pyrolysis temperature is 550°C, the pyrolysis time is 2 hours, the electrolysis voltage is 2.8 V, and the electrolysis time is 6 hours to obtain a poplar leaf carbon material, which is recorded as P-NPEC-550-2.8-6.

[0062] Example 10

[0063] The preparation method is the same as that in Example 1, except that the pyrolysis temperature is 550°C, the pyrolysis time is 2h, the electrolysis voltage is 2.8V, and the electrolysis time is 8h to obtain a poplar leaf carbon material, which is recorded as P-NPEC-550-2.8-8.

[0064] Results Analysis

[0065] Effect of pyrolysis temperature on carbon materials

[0066] SEM was used to analyze the effect of different synthesis temperatures on the morphology of P-NPEC materials. Figure 1 The morphology of the poplar leaves before and after pretreatment of the present invention, a is before treatment, b is after treatment, Figure 2 Figures a and b are SEM images of P-NPEC-550-2.8-2 material synthesized at 550°C at 5000 times and 50000 times magnification, respectively. Figure 2 As can be seen in Figure a, the material presents a scattered hollow skeleton structure with a large number of gaps between the skeletons and some small block structures with a diameter of no more than 5 μm. Figure 2 A local enlarged view of the dotted box area in a ( Figure 2 In b), it was further found that the hollow skeleton was interwoven with rod-like structures with a diameter of about 200 nm. These rod-like structures were characterized by bending and interlacing, forming a complex multi-level pore network. Figure 2 Figures c and d are SEM images of P-NPEC-600-2.8-2 synthesized at 600°C. Figure 2 As shown in (c), the surface of the material is relatively rough, but no obvious porous features are observed. Figure 2 d found that there are a small number of pore structures on the surface of the material. Figure 2 Figures e and f show the SEM images of the P-NPEC-650-2.8-2 sample prepared at 650°C. From the images, it can be seen that with the increase of pyrolysis temperature, the pore structure characteristics of the material completely disappear and transform into a thick layered structure, but the layered structure has some wrinkles, but the inner wall is smooth and has no holes. Figure 2Figures g and h show SEM images of the NPEC-700-2.8-2 sample prepared at 700 °C. As the pyrolysis temperature increases, the pore structure characteristics of the material completely disappear and transform into a thin-layered structure. Although there are certain wrinkles on the surface of the layered structure, its inner wall is smooth and no obvious pore structure is observed.

[0067] In summary, when the temperature is 550 °C, the product shows a hollow structure intertwined with rod-like structures. The reason for the formation of this structure is that the pyrolysis process using P as the raw material is relatively mild, and the volatile components (such as CO, CO2, H2O, etc.) generated by the decomposition of organic matter are slowly released, forming gas diffusion channels, resulting in the formation of a hollow framework structure. The formation of the rod-like structure is due to the catalytic effect of metallic Ni, which may guide the formation of nanorods by catalyzing carbon deposition or acting as a template. As the temperature rises to 600 °C, the pyrolysis reaction rate increases significantly. The rapid decomposition of organic matter leads to the violent release of gas, and the gas accumulation in local areas forms an instantaneous high pressure, breaking through the weak areas that are not fully carbonized, forming curved large pores and a rough layered structure. When the temperature continues to rise to 650 °C, a smooth and wrinkled layered structure is formed. Due to the complete escape of volatile components at high temperature and the reduction of residual impurities, the inner wall tends to be smooth due to the rearrangement of the carbon structure. When the temperature reaches 700 °C, a thin-layered wrinkled structure is formed because the high temperature causes the further loss of the structure in the material, the further growth of carbon microcrystals, the reduction of the interlayer spacing, and the tendency towards a graphite-like structure, showing a thinner and more uniform layered morphology.

[0068] To further reveal the crystal structure characteristics of the product, XRD analysis was performed on the P-NPEC materials synthesized at different pyrolysis temperatures, and the results are as Figure 3As shown in the figure. The XRD patterns show that typical characteristic diffraction peaks of carbon materials appear at 2θ = 26.5°, 42.6°, and 44.4° for all samples, corresponding to the (002), (101), and (100) crystal planes of the graphite structure, respectively. The diffraction peaks corresponding to all crystal planes show a systematic left shift phenomenon, which can be attributed to the increase in the unit cell parameters caused by the doping of Ni and Fe elements during the synthesis process, resulting in a corresponding increase in the interplanar spacing. By comparing the diffraction patterns under different pyrolysis temperature conditions, it can be found that as the pyrolysis temperature increases from 550 °C to 700 °C, the diffraction peaks of the P-NPEC material gradually show a trend of narrowing and sharpening, indicating that the structural order of the material gradually increases and the graphitization degree is significantly enhanced. It can be found that the sample P-NPEC-550-2.8-2 prepared at 550 °C shows the widest diffraction peak at the (002) crystal plane, indicating that its internal structure has a high degree of disorder, which may be related to the complex hierarchical pore network existing in the material. As the pyrolysis temperature increases to 700 °C, the sample NPEC-700-2.8-2 shows a characteristic diffraction peak at 2θ = 26.5° (002), and its full width at half maximum is significantly reduced, indicating that the graphitization degree of the material is significantly improved. This phenomenon can be attributed to the fact that high temperature can induce the rearrangement of carbon atoms and the growth of graphite crystallites.

[0069] To more deeply evaluate the graphitization degree of the P-NPEC material, the characteristics of the P-NPEC materials synthesized under different pyrolysis temperature conditions were further studied by Raman spectroscopy. As Figure 4 shown, all samples show characteristic double peaks at 1350 cm -1 (D band) and 1580 cm -1 (G band), corresponding to the structural defects in the sp 2 hybridization domain and the in-plane vibration of the ordered graphite lattice in the carbon material, respectively. The ratios of ID / IG corresponding to P-NPEC-550-2.8-2 and P-NPEC-700-2.8-2 are 0.901 and 0.722. The results show that the material synthesized at 550 °C has a higher degree of structural disorder. This conclusion is consistent with the data results in the XRD analysis.

[0070] To explore the electrochemical properties of the P-NPEC materials synthesized under different pyrolysis temperature conditions, the electrochemical performance of a three-electrode system supercapacitor with each sample as the working electrode was measured. Cyclic voltammetry tests ( Figure 5 a in the figure) show that at a scan rate of 20 mV s -1 , the P-NPEC-550-2.8-2 electrode shows the largest closed integral area of the CV curve, revealing its optimal charge storage ability in the pyrolysis temperature range of 550 - 700 °C. Galvanostatic charge-discharge tests ( Figure 5 b in the figure) show that at 0.5 Ag-1 At the current density, the P-NPEC-550-2.8-2 electrode has the longest discharge time. Through the calculation data of specific capacitance ( Figure 5 in d), it is further confirmed that the specific capacitance value shows a gradually decreasing trend with the increase of temperature. The specific capacitances of P-NPEC-550-2.8-2, P-NPEC-600-2.8-2, P-NPEC-650-2.8-2, and P-NPEC-700-2.8-2 are 164, 154, 150, and 100 F g -1 , respectively, which is in good agreement with the CV analysis results. Through electrochemical impedance spectroscopy analysis ( Figure 5 in c), it is found that P-NPEC-550-2.8-2 exhibits the smallest charge transfer resistance (Rct = 0.0940 Ω), significantly lower than that of NPEC-600-2.8-2 (0.145 Ω), NPEC-650-2.8-2 (0.2591 Ω), and NPEC-700-2.8-2 (0.526 Ω). This result indicates that low temperature (550 °C) can effectively improve the conductivity and charge transfer kinetics of the material, which shows a strong correlation with the change trend of specific capacitance.

[0071] Under the pyrolysis condition of 550 °C, the material forms a typical hierarchical pore network system. SEM images ( Figure 2 in a and b) show that the three-dimensional hollow skeletons are cross-linked with each other, and there are a large number of voids between the skeletons. XRD ( Figure 3 ) shows a broadened diffraction peak at 26°, combined with the high value of ID / IG = 0.901 in the Raman spectrum ( Figure 4 ), which confirms that the material has a highly disordered carbon skeleton structure. This structural feature provides efficient ion transport channels through the hollow skeleton and enhances the charge adsorption ability through structural defect sites, thereby endowing the material with significant energy storage advantages. Therefore, this sample obtains a relatively high specific capacitance of 164 F g -1 at a current density of 0.5 A g -1 . When the temperature rises to 600 °C ( Figure 2 in c and d), the material undergoes a structural reorganization phenomenon. The surface roughness of the material increases, and a small amount of pore structure appears. Although the macropores can reduce the ion transport resistance, the pore structure is less, and the XRD pattern shows an increase in the internal order degree, ultimately resulting in a decrease in the specific capacitance. When the temperature reaches 650 °C, the material shows a tendency of partial graphitization (the diffraction of the 002 crystal plane in the XRD pattern is enhanced), and the structure gradually becomes a smooth and wrinkled layered structure ( Figure 2In (e) and (f), although the structural ordering leads to a sharp reduction in specific surface area and ionic active sites, the secondary ion channels provided by the wrinkled structure maintain part of the capacitance performance, with a decrease of less than 1% compared to the sample at 600 °C. When the temperature reaches 700 °C, the high-temperature treatment accelerates the graphitization process, the disorder of the material decreases (the Raman ID / IG value decreases), and the pores collapse to form a dense structure. These changes together lead to hindered ion transport and the attenuation of the electric double layer capacitance. The experimental results show that the pyrolysis temperature affects the charge storage performance by regulating the microstructure and crystal order of the material. Among them, the preparation condition of 550 °C can be used as the optimized parameter for the preparation of P-NPEC materials.

[0072] Effect of electrolysis voltage on carbon materials

[0073] As Figure 6 Figure shows the SEM images of P-NPEC materials synthesized under different electrolysis voltage conditions. As Figure 6 As shown in (a), the P-NPEC-550-2.6-2 sample synthesized under the electrolysis condition of 2.6 V shows a large blocky structure in its morphology through SEM characterization. It can be further confirmed by the high-magnification SEM image that the surface of the blocky structure has obvious roughness and is accompanied by some small pores. However, due to the thick overall structure of the blocky structure, the pores are very shallow. This is mainly attributed to the local selective etching effect under a lower electric field strength. As the voltage increases to 2.8 V, the P-NPEC-550-2.8-2 sample synthesized under this electrolysis condition undergoes significant structural dissociation, forming a rod-like network skeleton with an average diameter of about 200 nm. This structure has typical hollow characteristics and a hierarchical pore system ( Figure 6 as shown in (b)). As Figure 6 As shown in (c), for the P-NPEC-550-3.0-2 material synthesized under the electrolysis condition of 3.0 V, the rod-like network skeleton collapses, and the material undergoes structural collapse and reorganization to form a lamellar structure, while large pores are generated. When the electrolysis voltage increases to 3.2 V ( Figure 6 as shown in (d)), the material further breaks into a blocky structure, and its surface structure shows a thin-layer wrinkled structure, accompanied by the generation of pores and an increase in surface roughness.

[0074] The experimental results show that the electrolysis voltage exhibits a significant gradient effect on the microstructure regulation of P-NPEC materials. Under the condition of a low voltage of 2.6 V, the restricted electrochemical driving force causes the anodic oxidation etching to be limited to the material surface, thus forming a dense blocky structure. When the voltage rises to 2.8 V, the electric field energy intensity increases, triggering the topological reconstruction of the carbon skeleton, and the blocky structure will be dissociated into a hollow rod-like network with a diameter of 200 nm. When the voltage is further increased to 3.0 V, the dipole-dipole interaction induced by the strong electric field drives the carbon layer to preferentially orient along the (002) crystal plane, forming a layer-stacked lamellar structure. At the same time, the O2 bubbles generated by the oxygen evolution reaction act as a dynamic template to generate macropores. When the voltage reaches 3.2 V, the electrochemical polarization causes the sp 3 / sp 2 hybrid state transition, promoting the generation of thin-layered folded structures.

[0075] Figure 7 The XRD diffraction patterns of P-NPEC materials prepared at different electrolysis voltages are shown. All samples exhibit typical characteristic diffraction peaks of carbon materials at 2θ = 26.5°, 42.6°, and 44.4°, which are attributed to the (002), (101), and (100) crystal planes of the graphite structure, respectively. The overall peaks shift to the left, especially for P-NPEC-550-3.0-2 and P-NPEC-550-3.2-2, and the shifting angles are more obvious. The reason is that the doping of Ni / Fe elements leads to an increase in the unit cell parameters, thereby causing a corresponding increase in the interplanar spacing. And the enhanced metal ion mobility at high voltages (≥3.0 V) increases the Fe / Ni doping concentration, resulting in an intensified shift. In addition, the full width at half maximum and the peak shape evolution of the (002) diffraction peak reveal the key regulatory effect of voltage on the microstructure of the material. For the P-NPEC-550-2.8-2 sample (2.8 V), the (002) peak shows significant broadening and weak peak intensity, indicating a high degree of disorder in its crystal structure. When the voltage rises to 3.0 V (P-NPEC-550-3.0-2), the (002) peak becomes significantly higher and narrower, confirming that the increase in electrolysis voltage promotes the ordered arrangement of the carbon layer. When the voltage is further increased to 3.2 V (P-NPEC-550-3.2-2), the (002) continues to sharpen, and the material gradually forms a graphite-like microcrystalline structure.

[0076] To further investigate the graphitization degree of P-NPEC materials, the characteristics of P-NPEC materials synthesized under different electrolysis voltage conditions were further studied by Raman spectroscopy. As Figure 8 shown, all samples exhibit characteristic double peaks at 1350 cm -1 (D band) and 1580 cm -1 (G band), corresponding to sp 2Structural defects in the hybrid domain and in-plane vibrations of the ordered graphite lattice. The ratios of ID / IG corresponding to P-NPEC-550-2.8-2 and P-NPEC-550-3.2-2 are 0.901 and 0.755, respectively. This result indicates that the material synthesized under the condition of 2.8 V has a higher degree of structural disorder, which is highly consistent with the conclusion of the broadening of the (002) peak and the decrease in the crystallite size in the XRD analysis ( Figure 7 ). This non-linear variation behavior of the voltage-dependent graphitization degree can be attributed to the competitive regulation mechanism of the electric field strength on the pyrolysis-reorganization kinetics of the carbon precursor.

[0077] To investigate the electrochemical properties of the P-NPEC materials synthesized under different electrolysis voltages, the electrochemical performance of a three-electrode system supercapacitor with each sample as the working electrode was measured. The cyclic voltammetry test ( Figure 9 a) shows that at a scan rate of 20 mV s -1 , the P-NPEC-550-2.8-2 electrode exhibits the largest closed integral area of the CV curve, revealing its optimal charge storage capacity in the electrolysis voltage range of 2.6 - 3.2 V. The galvanostatic charge-discharge test ( Figure 9 b) shows that at a current density of 0.5 A g -1 , the P-NPEC-550-2.8-2 electrode has the longest discharge time. The calculation data of the specific capacitance ( Figure 9 d) further confirms that the specific capacitance value first increases and then decreases with the increase of the electrolysis voltage: the specific capacitances of P-NPEC-550-2.6-2, P-NPEC-550-2.8-2, P-NPEC-550-3.0-2, and P-NPEC-550-3.2-2 are 128, 164, 158, and 151 F g-1, respectively, which is in good agreement with the CV analysis results.

[0078] Through electrochemical impedance spectroscopy analysis ( Figure 9 c), it is found that P-NPEC-550-2.8-2 exhibits the smallest charge transfer resistance (Rct = 0.0940 Ω), which is significantly lower than that of P-NPEC-550-2.6-2 (0.3638 Ω), P-NPEC-550-3.0-2 (0.1292 Ω), and P-NPEC-550-3.2-2 (0.1584 Ω). This result indicates that a moderate electrolysis voltage (2.8 V) can effectively improve the conductivity and charge transfer kinetics of the material, which shows a strong correlation with the change trend of the specific capacitance.

[0079] Combined with the microscopic structure characterization ( Figures 6 - 8 ), a structure-property relationship can be established: when the electrolysis voltage is 2.6 V, the material presents a dense blocky structure with insufficient pore development ( Figure 6In a), it leads to restricted ion transport; SEM image at 2.8 V ( Figure 6 In b), combined with XRD ( Figure 7 ) and Raman ( Figure 8 ) analysis shows that the highly disordered carbon skeleton, in cooperation with the interconnected pore channels, jointly promotes the ion adsorption / desorption process, significantly enhancing the electric double-layer capacitance; when the voltage exceeds 3.0 V, the material shows a tendency of partial graphitization (enhanced diffraction of the 002 crystal plane in the XRD pattern), and the rod-shaped hollow intertwined skeleton disappears ( Figure 6 In c)), resulting in a reduction in the effective specific surface area and hindrance to the ion transport path. When the voltage continues to increase to 3.2 V, the material morphologically shows a wrinkled thin-layer structure, with a decrease in internal disorder (decrease in the Raman ID / IG value), inhibiting the ion adsorption sites and further hindering ion transport. The experimental results show that the electrolysis voltage affects the charge storage performance by regulating the microstructure and crystal order of the material. Among them, the preparation condition of 2.8 V achieves the optimal balance among pore development, structural disorder degree, and conductivity, and can be used as the optimized parameter for the preparation of P-NPEC materials.

[0080] Effect of electrolysis time on carbon materials

[0081] The morphology of P-NPEC materials prepared at different electrolysis times was characterized by SEM to explore the influence law of electrolysis time on the microstructure of the materials. Figure 10 As shown in a and b, they are the images of electrolysis for 2 h. The material presents a rod-shaped intertwined hollow network structure. This three-dimensional porous structure is beneficial to the penetration of the electrolyte and ion transport. Figure 10 c and d show the SEM images of the P-NPEC-550-2.8-4 sample prepared under the condition of electrolysis for 4 h. The morphology of the sample P-NPEC-550-2.8-4 changes significantly. The material changes from a rod-shaped structure to a thin-layer structure, and obvious wrinkles appear on the surface. In addition, the high-magnification image ( Figure 10 In d) shows that a hierarchical pore structure is formed inside the material, in which macropores, mesopores, and small pores intersect with each other, forming a high-density porous network. This structural feature is beneficial to increasing the specific surface area and active sites of the material. Figure 10 e and f show the SEM images of the P-NPEC-550-2.8-6 sample prepared under the condition of electrolysis for 6 h. As the electrolysis time is further extended to 6 h, the morphology of the sample P-NPEC-550-2.8-6 continues to evolve. Although the material still maintains a thin-layer structure, part of the structure is lost, and the pore structure is significantly simplified, only retaining the macropore structure. At the same time, the surface of the layered structure becomes more compact, and the roughness is significantly reduced. When the electrolysis time reaches 8 h ( Figure 10In (g) and (h), the morphology of sample P-NPEC-550-2.8-8 underwent a fundamental transformation. The overall material presented a flaky structure with a smooth surface and no pore structure, but clusters of particles could be observed attached to the surface. This structural change might lead to a significant reduction in the specific surface area and active sites of the material.

[0082] The above results indicate that the electrolysis time has a significant impact on the microstructure of P-NPEC materials. When the electrolysis time was 2 h, the combined effects of gas volatilization under the thermal field and the promotion of the directional rearrangement of carbon atoms by the electric field catalyzed by metallic Ni formed a rod-like intertwined hollow network structure. When the electrolysis time was extended to 4 h, significant structural reorganization occurred in the material, forming a structure mainly composed of thin layers and supplemented by a hierarchical pore structure. The generation of the hierarchical pore structure originated from the electrochemical activity difference in the sp 2 / sp 3 hybrid region in the carbon matrix, resulting in selective etching to form a macroporous (>50 nm) skeleton support and a mesoporous (2 - 50 nm) wall structure. When the time continued to increase to 8 h, under the action of the thermoelectric coupling field, in-plane reorganization of the carbon layer continued to occur, forming a continuous two-dimensional sheet structure through edge fusion. As the electrolysis time increased, the material gradually transformed from a three-dimensional porous network structure to a two-dimensional flaky structure, accompanied by the simplification of the pore structure and the reduction of surface roughness.

[0083] To further reveal the crystal structure characteristics of the products, XRD analysis was performed on the P-NPEC materials synthesized at different electrolysis times, and the results are as Figure 11 shown. The XRD patterns showed that typical characteristic diffraction peaks of carbon materials appeared at 2θ = 26.5°, 42.6°, and 44.4° for all samples, corresponding to the (002), (101), and (100) crystal planes of the graphite structure, respectively. However, it was not intuitive to determine which of the sample P-NPEC-5502.8-2 with an electrolysis time of 2 h and the sample P-NPEC-550-2.8-4 with an electrolysis time of 4 h was more disordered. They were basically similar and further Raman analysis was needed to determine their internal graphitization degree. As the electrolysis time was extended to 8 h, a sharp (002) characteristic diffraction peak appeared near 2θ = 26.5° for sample P-NPEC-550-2.8-8, and its full width at half maximum decreased significantly, indicating a significant improvement in the graphitization degree of the material. This phenomenon can be attributed to the combined action of the thermal field and the electric field during the long-term electrolysis process, which promoted the rearrangement of carbon atoms and the growth of graphite microcrystals. In addition, the sharpening of the (002) crystal plane diffraction peak also reflected the improvement in the regularity and crystallinity of the layered structure of the material. These results further confirmed the significant impact of the electrolysis time on the microstructure and graphitization degree of the material.

[0084] To further investigate the graphitization degree of the P-NPEC material, the characteristics of the P-NPEC materials synthesized under different electrolysis time conditions were further studied by Raman spectroscopy. As Figure 12 shown, all samples presented characteristic double peaks at 1350 cm -1 (D band) and 1580 cm -1 (G band), corresponding to the structural defects in the sp 2 hybridization domain and the in-plane vibration of the ordered graphite lattice in the carbon material, respectively. The ratios of ID / IG corresponding to P-NPEC-550-2.8-2 and P-NPEC-550-2.8-4 were 0.901 and 0.824. This result indicates that the material synthesized under the condition of 2 h electrolysis has a higher degree of structural disorder.

[0085] To explore the electrochemical properties of the P-NPEC materials synthesized under different electrolysis time conditions, the electrochemical performance of a three-electrode system supercapacitor with each sample as the working electrode was measured. Cyclic voltammetry tests ( Figure 13 a in) showed that at a scan rate of 20 mV s -1 , the P-NPEC-550-2.8-4 electrode exhibited the largest closed integral area of the CV curve, revealing its optimal charge storage capacity within the electrolysis time range of 2 - 8 h. Galvanostatic charge-discharge tests ( Figure 13 b in) showed that at a current density of 0.5 A g -1 , the P-NPEC-550-2.8-4 electrode had the longest discharge time. Further confirmation by the specific capacitance calculation data ( Figure 13 d in) showed that the specific capacitance value first increased and then decreased with the increase of electrolysis time: the specific capacitances of P-NPEC-550-2.8-2, P-NPEC-550-2.8-4, P-NPEC-550-2.8-6, and P-NPEC-550-2.8-8 were 164, 177, 156, and 118 F g -1 , respectively, which was in good agreement with the CV analysis results.

[0086] Through electrochemical impedance spectroscopy analysis ( Figure 13 c in), it was found that P-NPEC-550-2.8-4 exhibited the smallest charge transfer resistance (Rct = 0.0560 Ω), significantly lower than that of P-NPEC-550-2.6-2 (0.0940 Ω), P-NPEC-550-2.8-6 (0.1355 Ω), and P-NPEC-550-2.8-8 (0.4041 Ω). This result indicates that a moderate electrolysis time (4 h) can effectively improve the conductivity and charge transfer kinetics of the material, which shows a strong correlation with the change trend of specific capacitance.

[0087] Combined with the microstructure characterization (Figures 10 - 12 )The structure-activity relationship can be established: The experimental results show that the electrolysis time has a significant impact on the material structure and electrochemical performance. When the electrolysis time is 2 h, the material presents a highly disordered carbon skeleton structure ( Figure 10 in a)), and this structural feature provides sufficient space for the ion adsorption / desorption process, thus showing a high specific capacitance. When the electrolysis time is extended to 4 h, the SEM characterization ( Figure 10 in b)) combined with XRD ( Figure 11 ) and Raman ( Figure 12 ) analyses show that although the internal structure of the sample electrolyzed for 2 h has a higher degree of disorder, the sample electrolyzed for 4 h (P-NPEC-550-2.8-4) presents a wrinkled lamellar structure and hierarchical pore characteristics. This unique structure is conducive to ion transport, so it also shows a high specific capacitance. This phenomenon indicates that the specific capacitance performance of the material is not completely determined by the degree of disorder. When the electrolysis time exceeds 6 h, the material begins to show a tendency of partial graphitization, which is reflected in the enhancement of the diffraction peak of the 002 crystal plane in the XRD pattern. Although the material still maintains a thin lamellar structure, some structures are lost, the pore structure is significantly simplified, and only the macropore structure is retained ( Figure 10 in c)), resulting in a decrease in the effective specific surface area and hindrance to the ion transport path. When the electrolysis time is further extended to 8 h, the material morphology transforms into a smooth lamellar structure, which is not conducive to ion transport. At the same time, the diffraction peak of the 002 crystal plane in the XRD pattern continues to increase ( Figure 11 ), indicating that the internal structure of the material tends to be ordered, which inhibits the formation of ion adsorption sites and leads to a further reduction in the ion transport efficiency. In summary, the specific capacitance performance of the material is affected by various factors, including morphological characteristics and the degree of internal structure disorder, etc. Based on comprehensive characterization data, the sample P-NPEC-550-2.8-4 with an electrolysis time of 4 h exhibits the optimal structural characteristics and electrochemical performance, which can be used as the optimization parameter for the preparation of P-NPEC materials.

[0088] Comparative experiment analysis and characterization of the best product

[0089] Table 1 shows the percentage of C, H, O, N, and S elements of P, the product P-NPC after pyrolysis of P in a pure thermal field at 550℃ for 6 hours, and the product (P-NPEC-550-2.8-4) after pyrolysis of P in a thermal field at 550℃ for 2 hours and then applying a 2.8V electric field at the same temperature for 4 hours. According to the experimental data, the carbon content of P, P-NPC, and P-NPEC-550-2.8-4 showed an increasing trend, which were 41.3%, 51.12%, and 73.35%, respectively; while the oxygen content decreased in turn, which were 41.68%, 23.49%, and 15.41%, respectively; and the hydrogen content was 5.316%, 3.0484%, and 2.975%, respectively. These results show that under the combined action of the thermoelectric dual field, P underwent a more thorough dehydrogenation and deoxidation process, thereby obtaining a carbon material with higher purity.

[0090] Table 1 Elemental analysis data

[0091]

[0092]

[0093] Figure 14 The SEM images of three samples, P, P-NPC and P-NPEC-550-2.8-4, are shown. Figure 13 Figures a and b are SEM images of P, showing that the overall structure is a stacked thick layer with a dense surface and no pore structure. Figure 14 Figures c and d show the microscopic morphology of P-NPC materials, indicating that after 6 h of pure pyrolysis, the overall structure of P-NPC was broken into block structures with a diameter of less than 10 μm. The surface was relatively rough, but there was still no obvious pore structure. Figure 14 Figures d and e are SEM images of the P-NPEC-550-2.8-4 material, which was prepared by the thermoelectric dual field composite effect. The image shows that the material exhibits a wrinkled layered structure and multi-level pore characteristics. This shows that compared with the pure thermal field, the thermoelectric composite field has a more significant effect on the raw material and can induce the formation of a thin layer structure and a porous structure. The wrinkles of the layered structure increase the specific surface area of ​​the material, while the porous structure provides favorable conditions for the embedding and extraction of charges, which may improve its electrochemical performance.

[0094] Figure 15 The N2 adsorption-desorption isotherms of P and its products treated by different methods at 77 K are shown. Combined with the data analysis in Table 2, the curve of P is not closed and SBET is close to 0, indicating that it is a non-porous material. This result is consistent with Figure 14The SEM images of a and b are consistent, that is, P shows a stacked thick-layer structure with a dense surface and no pore structure. The N2 adsorption-desorption isotherm of P-NPC belongs to type IV, and a hysteresis loop appears when P / P0 = 0.4, indicating the presence of mesoporous structure in the material. According to the data in Table 2, the SBET of P-NPC is 64.1 m 2 g -1 , which is significantly increased compared to the raw material P. The SBET of P-NPEC-550-2.8-4 is 285.9 m 2 g -1 , and the pore volume is 0.461 cm 3 g -1 . From Figure 15 it can be seen that the N2 adsorption-desorption isotherm of P-NPEC-550-2.8-4 shows the composite characteristics of type I and type IV: the rapid adsorption behavior in the low-pressure region (P / P0 = 0 - 0.1) indicates the dominant distribution of microporous structure; the gradual increase in adsorption amount in the middle-pressure region reflects the enrichment of mesoporous structure; while the sudden increase in adsorption amount in the high-pressure region is attributed to the presence of macroporous structure. The significant H3-type hysteresis loop in the desorption curve further verifies the extensive distribution of mesoporous structure. Combining Figure 14 the SEM image analysis of e and f in, macroporous structures with micrometer-sized dimensions can be clearly observed on the material surface, which highly coincides with the characteristics of the high-pressure region of the isotherm. This hierarchical microporous-mesoporous-macroporous synergistic system provides key structural support for the functional design of materials in the fields of adsorption, catalysis, and energy storage.

[0095] Table 2 Overview of N2 adsorption-desorption data of P and products of P treated by different methods

[0096] Item <![CDATA[S BET > Pore Volume Average pore size P 4.7 0.003 2.50 P-NPC 64.1 0.174 11.05 P-NPEC-550-2.8-4 285.9 0.461 5.20

[0097] To further confirm the advantages of preparing carbon materials by the thermal-electric composite field, the electrochemical performance of a three-electrode system supercapacitor with each sample as the working electrode was measured. Figure 16 shows the CV curves and GCD curves of P and products of its different treatment methods. The CV test results ( Figure 16 a) in show that at a scan rate of 20 mV s -1 , the closed integral area of the CV curve of the P-NPEC-550-2.8-4 electrode is the largest, indicating that the material prepared by the thermoelectric two-field composite method has more excellent charge storage ability compared with the pure pyrolysis method. The GCD test results ( Figure 16 b) in further show that at a current density of 0.5 A g -1 , the discharge time of the P-NPEC-550-2.8-4 electrode is significantly longer than that of other samples. By calculation, the specific capacitance values of P, P-NPC, and P-NPEC-550-2.8-4 are 11, 31, and 177 F g-1 In addition, the specific capacitance of the P-NPEC-550-2.8-4 material prepared by the thermal-electric dual field composite method is 5.7 times that of the material prepared by the pure thermal field. This result fully proves that the thermal-electric dual field composite method can significantly improve the electrochemical properties of carbon materials, providing an important basis for its application in supercapacitors and other fields.

[0098] In order to further explore the microstructural characteristics of P-NPEC-550-2.8-4, the present invention uses transmission electron microscopy (TEM) to characterize and analyze it. Figure 17 As shown in a, the TEM image shows a thin layer structure. Figure 14 The SEM characterization results in e and f confirm each other, confirming that P-NPEC-550-2.8-4 is mainly in the form of thin layers, supplemented by a multi-level pore structure. Figure 17 Figure b shows the microstructure features at a higher resolution. It was observed that the sample as a whole showed obvious lattice fringes, with a lattice spacing of 0.34nm, which is exactly the lattice spacing of carbon materials. The material has obvious order, which is a structural feature consistent with the Figure 11 XRD patterns and Figure 12 The Raman spectrum analysis results confirm each other. Combining the above characterization results, it can be determined that NPEC-550-2.8-4 material has typical thin layer-porous characteristics.

[0099] The thermal stability of P-NPEC-550-2.8-4 sample in air atmosphere was tested by thermogravimetric analyzer. Figure 18 The weight loss range is mainly divided into three stages: the first stage of temperature loss range is 0-100℃, and the weight loss is mainly attributed to the volatilization of adsorbed water in the material, and the mass loss is small, which is consistent with the typical behavior of porous carbon materials in low temperature areas. The second stage is the low-temperature oxidation stage (100-350℃), and the oxygen-containing functional groups on the surface of amorphous carbon (such as CO, C=O, etc.) undergo oxidative decomposition, resulting in a mass loss of about 5%. This phenomenon is consistent with the thermal degradation behavior of amorphous carbon materials in an oxidizing atmosphere; the weight loss range of the third stage is 400-500℃. In this temperature range, the carbon skeleton undergoes a violent oxidation reaction to generate CO2, resulting in a sharp increase in weight loss, and the weight loss rate reaches about 77%. This significant weight loss behavior further confirms that the main component of the sample is amorphous carbon. Thermogravimetric analysis showed that the final residual ash content was about 17%. Compared with the NPEC-550-2.8-4 sample (ash content of about 7%), the ash content increase of P-based carbon materials was mainly due to the characteristics of its biomass raw materials: P that has not been industrially purified contains a higher concentration of metal ions (K + , Ca 2+etc.) and silicate components, and the inorganic impurity content of AL has been significantly reduced by chemical treatment. The above thermogravimetric analysis results are highly consistent with the elemental analysis data in Table 1, indicating that the sample has a high carbon content and its thermal degradation behavior conforms to the typical characteristics of amorphous carbon. Combining the thermogravimetric analysis and elemental analysis results, it can be confirmed that the P-NPEC-550-2.8-4 sample is also an amorphous carbon material.

[0100] Further, the electrochemical performance of the best synthesized sample P-NPEC-550-2.8-4 was analyzed. CV tests were carried out on it at different scanning rates of 20, 40, 60, 80, 100 mV s -1 and the corresponding curves are shown in Figure 19 a respectively. Ideal electric double layer capacitance behavior was observed during the charge and discharge process. Even at a high scanning rate of 100 mV s -1 , it still maintains its original shape, indicating good electrochemical stability and reversibility. Similarly, Figure 19 b shows its GCD curves at different current densities. The specific capacitances corresponding to 0.1, 0.2, 0.5, 1, 2, 5, 10 A g -1 are 270, 212, 177, 155, 139, 122.5, 110 F g -1 respectively. This excellent capacitance behavior can be attributed to the unique structural features of the material: ① The interlayer space formed by the three-dimensional wrinkled thin layer structure provides effective active sites for charge storage; ② High-resolution TEM analysis shows that there are characteristic lattice fringes of 0.34 nm inside the material (corresponding to the (002) crystal plane of graphitized carbon), constructing a continuous ion transport channel; combined with the hierarchical pore system (synergistic distribution of micropores-mesopores-macropores) revealed by SEM characterization, it jointly optimizes the electrolyte infiltration efficiency and ion migration kinetics. This structural synergistic effect significantly improves the reversibility of charge adsorption / desorption, thereby endowing the material with excellent electrochemical performance. Figure 19 c shows its EIS impedance spectrum. Rs and Rct have values of 0.6132 Ω and 0.0560 Ω respectively, indicating good conductivity and low charge transfer resistance. The steep line in the low-frequency region represents typical EDLC behavior and high ability of fast ion migration. In addition, the capacitance stability of P-NPEC-550-2.8-4 was tested. After 5000 cycles at a current density of 5 A g -1 in a three-electrode system, the capacitance retention rate reached 99.5%, reflecting good cycle stability ( Figure 19 d).

[0101] Substituting the mass of raw material P, the mass of product P-NPEC-550-2.8-4 and the corresponding elemental analysis carbon content into the formula, we can obtain:

[0102]

[0103] Optimized experiment

[0104] Table 3 Optimized experimental design table

[0105]

[0106] To determine the optimal synthesis parameters of the P-NPEC material, on the basis of the preliminary condition screening in the present invention, the experimental parameter range is further narrowed down to systematically explore the synthesis conditions for the optimal electrochemical performance. The experimental results show that there is a significant negative correlation between the pyrolysis temperature and the specific capacitance of the material, that is, as the temperature increases, the specific capacitance shows a monotonic decreasing trend. Therefore, 550 °C is determined as the optimal pyrolysis temperature. In contrast, the influence of the electrolysis voltage and the electrolysis time on the specific capacitance shows a non-linear relationship of first increasing and then decreasing, indicating that there is an optimal value range for these two parameters. Therefore, more refined condition optimization is required for them.

[0107] To quantitatively evaluate the electrochemical performance of the materials under different synthesis conditions, the present invention carried out GCD tests on each sample at a constant current density of 0.5 A g-1. The specific data are shown in Table 3. By comparing and analyzing the GCD test results and combining with Figure 20 the intuitive display, the optimal synthesis condition combination can be clearly obtained: pyrolysis temperature 550 °C, electrolysis voltage 2.8 V, electrolysis time 4 h. The sample P-NPEC-550-2.8-4 prepared under this condition shows the most excellent electrochemical performance. This result is consistent with the trend of the previous experiments, confirming the rationality and reliability of the parameter optimization.

[0108] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the adopted step methods are the same as those in the embodiments, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0109] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a biomass carbon material, characterized in that: The following steps are involved: Using biomass as a carbon source, pretreating the biomass to obtain pretreated biomass powder; The pretreated biomass powder is mixed with a metal catalyst, and pyrolyzed and electrolyzed in a CaCl2-NaCl molten salt system under a protective atmosphere to obtain a biomass carbon material; Among them, the pyrolysis temperature is 550°C to 600°C, the electrolysis voltage is 2.8V, and the electrolysis time is 2h to 4h.

2. The method for preparing biomass carbon material according to claim 1, characterized in that: In the CaCl2-NaCl molten salt system, the molar ratio of CaCl2 and NaCl is 0.25-0.55:0.45-0.75, and the sum of the molar ratios is 1.

3. The method for preparing biomass carbon material according to claim 1, characterized in that: The pyrolysis time is 0.5h~5h.

4. The method for preparing biomass carbon material according to claim 1, characterized in that: The mass ratio of biomass to metal catalyst is 2 to 20:

1.

5. The method for preparing biomass carbon material according to claim 1, characterized in that: The metal catalyst is Ni.

6. The method for preparing biomass carbon material according to claim 1, characterized in that: The biomass is poplar leaves.

7. A biomass carbon material obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the biomass carbon material according to claim 7 in a supercapacitor.

9. The use according to claim 8, characterized in that: The working electrode of the supercapacitor is the biomass carbon material.

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