Tar-based nitrogen-doped graphene oxide and preparation method and application thereof

Abstract

The application discloses tar-based nitrogen-doped graphene oxide and a preparation method and application thereof. The preparation method comprises the following steps: 1) uniformly mixing pine nut shell tar powder, nano magnesium oxide and KOH according to a mass ratio of 1:(6-8):(1-2) to prepare a precursor; 2) placing the precursor into a tube furnace to perform carbonization under a nitrogen atmosphere, adopting two-stage heating, the first stage is to heat from room temperature to 300 DEG C and keep the temperature, the second stage is to heat to 900 DEG C, after keeping the temperature, cooling to room temperature; 3) drying the obtained solid product after acid pickling. The tar-based nitrogen-doped graphene oxide prepared by the application exhibits a good graphene structure, a large specific surface area, and rich pore structure and total pore volume. Meanwhile, the thin-layer graphene structure and the number of graphene layers are directly observed by HRTEM. In addition, the tar-based nitrogen-doped graphene oxide has a good double-layer capacitance and is an excellent supercapacitor material.

Description

Technical Field

[0001] This invention belongs to the field of graphene material preparation, specifically relating to a tar-based nitrogen-doped graphene oxide, its preparation method, and its application. Background Technology

[0002] With the increasing energy consumption and environmental pollution, there is an urgent need to develop new electrochemical storage technologies. Currently, supercapacitors (SCs) are widely recognized as an attractive and promising general-purpose power system for energy storage applications, possessing numerous advantages such as long lifespan, excellent power density, and superior reversibility. During energy storage, the ion transport performance of the electrodes depends on the structure of the electrode materials themselves; therefore, the electrode materials play a crucial role in the overall performance of supercapacitors.

[0003] Carbon materials possess ideal properties for supercapacitors, such as a large specific surface area (SSA), easy acquisition of excellent adsorption capacity, and chemical stability. Graphene oxide, a type of graphene, is a novel material for supercapacitors. It also features short ion transport paths, abundant exposed active sites, and excellent electron transport capabilities. Furthermore, good conductivity is crucial for the capacitance of carbon materials, ensuring high rate capability and high power density. Graphene oxide exhibits satisfactory properties such as good conductivity, a large theoretical surface area, and excellent stability. Moreover, its preparation is relatively simple and cost-effective compared to other graphene-based materials.

[0004] Biomass tar is a byproduct of biomass pyrolysis or carbonization. It is primarily composed of various hydrocarbons and oxygen-containing compounds, with aromatics and polycyclic aromatic hydrocarbons making up the majority. This substance has a smaller molecular structure than ordinary biomass and contains a certain amount of nitrogen. Furthermore, compared to ordinary solid biomass, biomass tar is an ideal material for synthesizing high-value-added carbon sources due to its high activity, thermoplasticity, thermal polymerization, oxygen enrichment, and naturally high carbon content. Biomass tar has the potential to serve as a sustainable raw material for various functional carbon materials, including carbon quantum dots, aerogels, and graphene-like materials. Summary of the Invention

[0005] In view of this, the present invention uses pine nut shell tar as raw material, and nano-magnesium oxide and KOH as template agent and activator, respectively, to rapidly and efficiently prepare a nitrogen-doped graphene oxide with high specific surface area using a one-step two-stage heating method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing tar-based nitrogen-doped graphene oxide, characterized by comprising the following steps:

[0008] 1) Mix pine nut shell tar powder, nano magnesium oxide and KOH in a mass ratio of 1:(6-8):(1-2) to prepare a precursor;

[0009] 2) The precursor is placed in a tube furnace for carbonization in a nitrogen atmosphere. Two-stage heating is used. In the first stage, the temperature is raised from room temperature to 250-350℃ and held. In the second stage, the temperature is raised to 850-950℃ and held. After holding, the temperature is cooled to room temperature.

[0010] 3) The obtained solid product is acid washed and then dried.

[0011] Preferably, the preparation method of pine nut shell tar powder is as follows: carbonize pine nut shells at 400-500℃ for 1 hour, remove moisture from the obtained bio-oil, dry it, and then grind it thoroughly through a 60-80 mesh sieve.

[0012] Preferably, the mass ratio of pine nut shell tar powder, nano magnesium oxide and KOH is 1:6:2.

[0013] Preferably, the heating rate in both stages of heating in step 2) is 2-5℃·min. -1 The first stage of heat preservation time is 20-40 minutes, and the second stage of heat preservation time is 0.5-1.5 hours.

[0014] Preferably, in step 3), the template and impurities are removed by acid washing with 1-2M HCl, and then dried in an oven at 105-120℃ after filtration.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The tar-based nitrogen-doped graphene oxide material prepared in this invention has a three-dimensional (3D) interconnected porous layered structure with a clear pore structure and a large specific surface area and pore volume. Its XPS full spectrum clearly shows the presence of the three main elements, C, N, and O, while Raman results show clear 2D peaks, indicating the formation of a graphene oxide structure. HRTEM images clearly show the graphene structure and the number of layers; approximately five layers are stacked with a spacing of 1.46 nm, and the calculated distance between adjacent layers is approximately 0.365 nm, consistent with the characteristics of graphene. The formation of a three-dimensional interconnected structure not only facilitates faster ion transport in the electrolyte but also effectively reduces the diffusion resistance of electrolyte ions. Attached Figure Description

[0017] Figure 1 TG and DTG diagrams of precursors with different tar powder:MgO:KOH ratios are shown, where (a) is the TG diagram of precursors with different magnesium oxide ratios, (b) is the DTG diagram of precursors with different magnesium oxide ratios, (c) is the TG diagram of precursors with different KOH ratios, and (d) is the DTG diagram of precursors with different KOH ratios.

[0018] Figure 2 (a) N2 adsorption-desorption isotherms for each PTNCs sample, (b) Pore size distribution curves for each PTNCs sample.

[0019] Figure 3 The images show the microstructures of various PTNCs samples. (a)-(g) are FESEM images of PTNC3-18-6-900, PTNC3-12-6-900, PTNC3-24-6-900, PTNC3-18-3-900, PTNC3-18-12-900, PTNC3-18-6-800, and PTNC3-18-6-700, respectively. (h) and (i) are HRTEM images of PTNC3-18-6-900, and (j)-(m) are EDS images of PTNC3-18-6-900.

[0020] Figure 4 The X-ray electron spectrum of PTNC3-18-6-900 is shown in the following figures: (a) total XPS spectrum; (b) O1s high-resolution spectrum; (c) C1s high-resolution spectrum; and (d) N1s high-resolution spectrum.

[0021] Figure 5 XRD patterns of various PTNCs samples under different conditions.

[0022] Figure 6 (a) Raman plot of each PTNCs sample, (b) magnified Raman plot of each PTNCs sample.

[0023] Figure 7 The electrochemical performance curves of each PTNCs sample under the three-electrode system are shown in Figure 1. (a) CV curves of each sample at a scan rate of 20 mV / s, and (b) CV curves of each sample at a scan rate of 0.5 A g. -1 (c) GCD curve of current density, (d) rate characteristic curve of each sample, (e) Nyquist curve of each sample, (f) CV curve of PTNC3-18-6-900 at different scan rates, (g) GCD curve of PTNC3-18-6-900 at different current densities, (h) cycle performance curve of PTNC3-18-6-900, (i) relationship between log(i) and log(v) of PTNC3-18-6-900 at different scan rates, and (v) contribution ratio of pseudocapacitance and double layer capacitance of PTNC3-18-6-900 at different scan rates.

[0024] Figure 8Electrochemical performance curves of the symmetric supercapacitor assembled for PTNC3-18-6-900 under two electrodes, including (a) CV curve, (b) GCD curve, (c) cycle performance curve, and (d) Ragone relationship. Detailed Implementation

[0025] Embodiments of the present invention are described below. Examples of these embodiments are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0026] Example 1

[0027] The pine nut shells used in this experiment were from Northeast China's red pine nuts, containing 33.96% cellulose, 15.22% hemicellulose, and 38.42% lignin. Pine nut shell tar was obtained by placing the pine nut shells, after impurity removal, crushing, and drying, in a tube furnace and carbonizing them at 500℃ for 1 hour under a nitrogen atmosphere. The resulting bio-oil was separated by centrifugation to remove the upper layer of moisture. The lower layer of tar was then dried in an oven for 6 hours. After drying, it was thoroughly ground and passed through an 80-mesh sieve for storage and later use.

[0028] Table 1 lists the basic analysis of pine nut shell tar, which contains a high carbon content of 69.1%, likely closely related to the carbon yield during pyrolysis. The analysis also revealed that pine nut shell tar contains phenols, hydrocarbons, aldehydes, alcohols, ketones, furans, acids, and nitrogen-containing substances, with contents of 39.05%, 25.85%, 0.61%, 0.38%, 2.70%, 3.82%, 1.23%, and 5.50%, respectively. The high content of aromatic compounds in pine nut shell tar is beneficial for carbonization to obtain solid products, thus increasing carbon yield, improving product quality, and enhancing material properties. Furthermore, the presence of various hydrocarbons and oxygen-containing compounds results in the carbon products containing a variety of functional groups.

[0029] Table 1. Basic Properties of Pine Nut Shell Tar

[0030]

[0031]

[0032] The nano-magnesium oxide template agent used in this experiment is a white solid powder with a particle size of 100 nanometers, no flowability, and a density of 1.26 g / cm³. 3 It has a melting point of 2852℃ and a purity of ≥99.9%.

[0033] A tar-based nitrogen-doped graphene oxide material is prepared as follows:

[0034] 1) Weigh tar powder (3g), nano magnesium oxide white powder (12g, 18g, 24g) and KOH powder (3g, 6g, 12g) using a weighing balance, put the three into a mortar, grind and mix them thoroughly to prepare the precursor;

[0035] 2) Place the mixed precursor into a quartz boat, then place the quartz boat into the quartz tube inside the tube furnace. Before heating the furnace, inject nitrogen gas to purge the air inside the furnace and maintain this for 20 minutes to ensure that all air is purged. Then set the nitrogen flow rate to 20 mL / min. -1 The heating program for the tubular furnace is set up using a two-stage heating method. The initial heating temperature is room temperature (20°C), and the heating rate is 5°C / min. -1 Heat to 300℃ and hold for 30 minutes. Then heat to the set carbonization temperature (700℃, 800℃, 900℃) at the same heating rate. Hold at the constant temperature for 1 hour and then cool to room temperature.

[0036] 3) The obtained solid product was acid washed with 2M HCl to remove the template and impurities, filtered, and then dried in an oven at 105℃ for later use.

[0037] In this embodiment, precursor samples were prepared in five different ratios: tar powder:MgO:KOH = 3:12:6, 3:18:6, 3:18:3, 3:24:6, and 3:18:12. The common name for the carbon material product is PTNCs, and different samples are named PTNC-xyzt (Pinenut Shell Tar Based Nitrogen Endopeptinated Porous Carbon), where x, y, and z are the proportions of tar powder, MgO, and KOH added, respectively, and t represents the carbonization temperature of the tube furnace, including 700℃, 800℃, and 900℃.

[0038] 1. Thermogravimetric analysis

[0039] Thermogravimetric analysis was performed on precursors of five different proportions. Figure 1 (a) and (b) are the TG and DTG graphs for tar powder:MgO:KOH = 3:12:6, 3:18:6, and 3:24:6. It can be seen that reactions occurred between the materials as the temperature increased. Analysis revealed that the sample with ratio 3:12:6 showed the largest decrease, while the sample with ratio 3:24:6 showed the smallest decrease. This may be because magnesium oxide has a relatively high melting point, melting only after 2852℃. Figure 1(b) It can be seen that peaks were observed in the 200-400℃ and 700-900℃ regions for all three precursor ratios. In the 700-900℃ region, the reaction intensity showed a trend of first decreasing and then increasing with the increase of the template agent. This is because the dispersion effect of magnesium oxide may not be significant in the initial stage of its increase. With further increase, the oil powder becomes more dispersed, which makes the activation reaction between KOH and the oil powder easier to occur. Figure 1 (c) and (d) are the TG and DTG graphs of the precursors with the ratios of tar powder:MgO:KOH = 3:18:3, 3:18:6, and 3:18:12. The mass loss rate of the precursor increases with the increase of the KOH addition ratio, which may be because the activator intensifies the entire reaction process. (Combined with...) Figure 1 A comprehensive analysis of the DTG plots (b) and (d) reveals a significant downward trend in the DTG of different precursor ratios between 200℃ and 400℃. This is likely due to the melting of the tar powder, which encapsulates the magnesium oxide, accompanied by the volatilization of some ash impurities. Interestingly, there is also a significant decrease in the DTG between 700℃ and 900℃, with distinct peaks for each precursor in these two ranges. This indicates drastic changes in the precursors within these ranges, possibly related to chemical reactions between the three precursor mixtures. Therefore, this invention sets the carbonization temperature of the precursors in a two-stage heating process. The target temperature for the first stage is set at 300℃ to ensure sufficient melting and encapsulation of the MgO template agent by the tar powder. The target temperature range for the second stage is set between 700℃ and 900℃ to guarantee a complete reaction throughout the process.

[0040] 2. Aperture characteristic analysis

[0041] A suitable carbonization temperature ensures sufficient chemical activation reaction and appropriate pore size structure, while the appropriate template ratio and activator are crucial conditions for achieving the desired porosity and pore size distribution. To evaluate the structural characteristics of PTNCs, N2 adsorption-desorption isotherms and corresponding pore size measurements were performed. The results are summarized in […]. Figure 2 The corresponding physical properties are described in Table 2. Figure 2 (a) It can be seen that the adsorption capacity of PTNC3-18-6-900 is the highest among all the tested samples, and there are a large number of micropores and mesopores. Figure 2 (b) The pore size distribution diagram reveals the layered porous structure of PTNCs. Analysis and comparison show that PTNC3-18-6-900 has the largest specific surface area among the seven samples. Furthermore, PTNC3-18-6-900 has a specific surface area of ​​3492.55 μm. 2The specific surface area is high, and a large specific surface area can provide abundant active sites for ion storage. Compared with PTNC3-18-6-900, the other samples have lower specific surface area and total pore volume (Vt).

[0042] Table 2. Pore structure parameters of PTNCs

[0043]

[0044] 3. Morphological and compositional analysis

[0045] The microstructure of the prepared carbon samples (PTNCs) was characterized by FESEM as follows: Figure 3 As shown in the figure, all seven samples formed a three-dimensionally interconnected porous structure. Figure 3 As shown in (a), the pore structure of PTNC3-18-6-900 is very clear, and the surface pore structure is relatively smooth, exhibiting a sheet-like structure after the template has been removed. Figure 3 (b) It can be seen that the porous structure of PTNC3-12-6-900 is more tightly connected, but compared with the structure of PTNC3-18-6-900, its structure is not smooth enough, and the porous structure is not continuous and clear enough. This may be because the amount of template agent magnesium oxide added is insufficient, resulting in the incomplete formation of the porous structure. Further analysis... Figure 3 (c) The structure of PTNC 3-24-6-900 shows that its surface morphology is much rougher than that of (a) and (b). This may be because the excessive addition of magnesium oxide will cause accumulation, thus affecting the formation of the sample structure. In addition, PTNCs also exhibit a distinct lamellar structure, with the lamellars interpenetrating and stacking to form a porous structure.

[0046] Through observation Figure 3 The electron micrographs (a), (d), and (e) lead to the conclusion that gases such as carbon monoxide produced by the decomposition of KOH also promote the formation of micropores. However, excessive KOH may lead to further etching of the pores, resulting in micropore enlargement, macropore collapse, and pore merging.

[0047] Similarly, comparison Figure 3 The scanning electron microscope (SEM) images (a), (f), and (g) show that lower carbonization temperatures prevent sufficient reaction between KOH and oil powder, resulting in an uneven pore structure. At a carbonization temperature of 900℃, the activator achieves its optimal effect, exhibiting the best pore structure. Compared to other samples, PTNC3-18-6-900 exhibits a more regular structure and a clear graphene structure, which is expected to demonstrate better performance in subsequent electrochemical tests.

[0048] from Figure 3 As can be seen in (h), the structure of PTNC3-18-6-900 is a 3D graphene structure formed by multiple layers of graphene stacked together, which is consistent with the previous FESEM image. Figure 3 The layered structure clearly visible in (i) shows stacked edges, with a spacing of 1.46 nm between the five stacked layers. Calculations show that the distance between adjacent layers is approximately 0.365 nm, consistent with the structural characteristics of graphene. This not only facilitates faster ion transport in the electrolyte but also effectively reduces the diffusion resistance of electrolyte ions.

[0049] Figure 4 (a) The XPS full spectrum of PTNC3-18-6-900 clearly shows the presence of the three main elements, C, N and O. Figure 7 (b)-(d) demonstrate that oxygen, carbon, and nitrogen exist in various chemical combinations within the material, which directly impacts its electrical conductivity and electrochemical reactivity. The atomic content of nitrogen was also calculated to be 3.28 at.% and the oxygen content to be 11.56 at.%, consistent with previous energy dispersive spectroscopy (EDS) analysis results.

[0050] 4. Structural Analysis

[0051] from Figure 5 As can be seen from the XRD pattern, the test sample can be roughly divided into three characteristic peak positions. The first peak is (001) at around 17°, which proves the presence of C-C atomic bonds in the material, and the addition of nitrogen causes the peak to shift to the right. The peaks PTNC3-18-6 and PTNC3-24-6 are quite prominent, because the increased template ratio enhances the exfoliation effect on the carbon material, resulting in a graphene structure. The second diffraction peak is (002), located at around 25°. Its presence indicates that the material has a layered crystal structure, and the crystal structure is relatively ordered. The interlayer spacing corresponding to the peak at approximately 25° is about 0.355 nm, which is larger than the typical interlayer spacing of graphene (0.34 nm). This is attributed to the presence of oxygen-containing functional groups in graphene oxide, which increase the interlayer distance of graphene. The peaks PTNC3-18-6 and PTNC3-24-6 are relatively sharp, indicating that the structures of these two materials are relatively ordered. A broad peak (100) appeared in PTGs near 42.6°, which proves that the crystal sheets of graphite are arranged very uniformly.

[0052] Figure 6 (a) shows the Raman spectra of PTNC samples prepared under various conditions. Figure 6(a) It was found that increasing temperature increases the graphitization degree of PTNCs, and the graphitization degree first increases and then decreases with increasing amounts of KOH or MgO. Meanwhile, PTNCs at 2700 cm⁻¹... -1 2D peaks appeared on both sides. The thickness of the graphene sheet is related to the ratio of the intensity of the 2D and G peaks. 2D / I G Relatedly, these PTNCs are also multilayered graphene materials. As the number of layers increases, I... 2D / I G The p-value decreased from 2.1 ± 0.2 for single-layer graphene to 0.8 ± 0.1 for five-layer graphene. The p-values ​​of PTNC3-18-6-900 and PTNC3-24-6-900 were calculated experimentally from this invention. 2D / I G The values ​​are 0.849 and 0.58, respectively, indicating a multilayered graphene structure, which is consistent with the TEM analysis results.

[0053] Figure 6 (b) is a magnified image of the Raman G peak of PTNCs. The magnified image shows two shoulder peaks at the G peaks of PTNC3-18-6-900 and PTNC3-24-6-900. The appearance of these shoulder peaks indicates elemental doping in the graphene structure, leading to further defects in the material structure. Simultaneously, the G band peak shifts to the left. Since the pine nut shell tar used contains a certain amount of nitrogen, the sample should be a nitrogen-doped graphene oxide structure, consistent with the XRD and XPS analyses.

[0054] 5. Electrochemical performance analysis

[0055] To investigate the electrochemical performance of PTNCs as electrode materials, electrochemical performance tests were conducted in 6MKOH electrolyte. A three-electrode system (CV, GCD, and EIS) was used to test the electrochemical performance of seven tar-based materials, and the specific capacitance of each tar-based carbon material was calculated using formulas. Figure 7 As shown in (a), the CV curves of each sample were obtained at a scan rate of 20 mV / s in the range of -1.1 to -0.1 V. The CV curves of all PTNCs are symmetrical and resemble rectangles, which effectively proves that PTNCs have good double-layer capacitance characteristics. At the same time, according to the CV curves of different samples, the size of the area enclosed by the curves represents the specific capacitance. It is worth noting that the CV curve area of ​​PTNC3-18-6-900 is the largest, indicating that it has the highest specific capacitance.

[0056] Figure 7 (b) shows the values ​​of each sample at 0.5A g. -1The GCD curves of the current density show that each sample exhibits a symmetrical triangular shape, indicating that the prepared material possesses good EDLC properties, excellent conductivity, good electrochemical stability, and good charge-discharge reversibility. The charge-discharge times show that PTNC3-18-6-900 has the longest discharge time, suggesting that the electrode should have a correspondingly high specific capacitance.

[0057] like Figure 7 (c) shows the rate characteristic curves of the seven samples calculated according to the formula. It can be seen from the figure that the PTNC3-18-6-900 has the highest capacitance retention rate of 80.92% at a current density of 40 A g. -1 This indicates that PTNC3-18-6-900 has excellent rate performance.

[0058] To investigate the electrochemical performance of the samples from a kinetic perspective, constant potential alternating impedance spectroscopy was performed on each sample, with a test frequency range of 10 Hz. -2 Hz-10 5 Hz, amplitude 5mV. For example... Figure 7 (d) shows the Nyquist curves for each PTNC sample, reflecting data such as charge transfer resistance (Rct), series equivalent resistance (Rs), and Warburg resistance (Rw). The graph reveals that the Rs value of PTNC3-18-6-900 is approximately 0.45, significantly lower than the values ​​of other samples, indicating a smaller equivalent resistance. PTNC3-18-6-900 also exhibits the smallest Rct, suggesting easier charge and electrolyte ion transfer within it. Furthermore, in the low-frequency region, the slope of the curve represents the Warburg resistance (Rw), reflecting the diffusion impedance of the electrode material; PTNC3-18-6-900 shows the smallest Rw. In conclusion, PTNC3-18-6-900 exhibits the smallest Rct, Rs, and Rw, thus demonstrating the best electrochemical performance.

[0059] Subsequently, to further analyze the optimal material, PTNC3-18-6-900 was individually tested, including CV testing at scan rates of 5–100 mV / s and current densities of 0.5–10 A g. -1 GCD testing, and at a current density of 5A g -1 Under the test conditions, a cyclic stability test of 10,000 cycles was conducted. Figure 7(e) shows the CV curves of PTNC3-18-6-900 at different scan rates. As can be seen from the figure, the area enclosed by the CV curve gradually increases as the scan rate increases from 5 mV / s to 100 mV / s. This is because a higher scan rate leads to a faster change in electrode potential, resulting in a larger double-layer current and consequently, a larger response current. Meanwhile, compared to the graphene supercapacitors listed in Table 3, PTNC3-18-6-900 demonstrates its unique advantages. Figure 7 (f) shows the GCD curves of sample PTNC3-18-6-900 measured at different current densities. As can be seen from the figure, the curves at both high and low current densities exhibit a symmetrical triangular shape, indicating that the prepared material demonstrates excellent charge-discharge performance. Analysis of the charge-discharge time reveals its outstanding specific capacitance. Furthermore, PTNC3-18-6-900 exhibits a very small voltage drop, indicating low internal resistance. All of these factors combined demonstrate that PTNC3-18-6-900 possesses excellent EDLC performance. Subsequently, PTNC3-18-6-900 underwent cycle stability testing. Figure 7 (g) is sample PTNC3-18-6-900 at 5A g -1 The cycle performance curves measured at the specified current density show that after 10,000 charge-discharge cycles, the specific capacity still retains 98.2%, which is precisely the advantage of PTNC3-18-6-900 compared to other energy storage materials. This also demonstrates that the material prepared in this chapter possesses excellent reversibility and is a promising material for electrode fabrication.

[0060] Table 3. Structure and electrochemical properties of other nitrogen-doped graphene oxide electrode materials

[0061]

[0062] To investigate the contribution of nitrogen (N) to the electrochemical properties of supercapacitors, this invention calculates the double-layer capacitance and pseudocapacitance components of the supercapacitor. The Dunn analysis method is used to perform kinetic calculations on the electrochemical processes of the PTNC3-18-6-900 supercapacitor. Figure 7As shown in (h)-(i), the value of constant b can be calculated by fitting the logarithm of peak current density and scan rate, which reflects the electrochemical kinetic process. The calculated values ​​for reduction and oxidation processes are 0.985 and 0.978, respectively, both close to 1. This indicates that the double-layer capacitance dominates the electrochemical test process, while a small amount of pseudocapacitance also occurs. Furthermore, as the scan rate increases, the contribution of the double-layer capacitance increases from 98.81% to 99.42%. This is because a higher scan rate can promote rapid charge transport and rapid ion diffusion, thereby increasing the effective utilization rate of the electrode surface area and improving the contribution of the double-layer capacitance.

[0063] Based on the three-electrode test results, this invention assembles PTNC3-18-6-900 into a symmetrical supercapacitor to verify its practical application value. Two-electrode tests are conducted using 1 mol / L Na2SO4 solution as the electrolyte solution to evaluate its potential in practical applications.

[0064] The testing conditions for the assembled supercapacitor are closer to those of real-world applications. Figure 8 (a) shows the CV curves of the symmetrical supercapacitor PTNC3-18-6-900 at different scan rates. As can be seen from the figure, the area enclosed by the CV curves gradually increases with increasing scan rate. The CV curves from 0 to 1.8V all exhibit a rectangular shape without obvious polarization, indicating that the supercapacitor assembled from this material can withstand a wide potential window. Therefore, the potential window of 0–1.8V was subsequently selected to examine the CV curves at different scan rates, and further tests were conducted on the supercapacitor. Figure 8 (b) is a current density of 0.5-10Ag -1 The GCD curves of PTNC3-18-6-900 show a symmetrical triangular shape with no significant pressure drop, which fully demonstrates that PTNC3-18-6-900 has good rate capability. Its good performance may be attributed to its good mesoporosity and interconnected pore structure.

[0065] To further examine the cycling performance of the supercapacitor, a cycling test was conducted on it, such as... Figure 8 (c) shows the cycling performance curve of the symmetrical supercapacitor, with a test current density of 5 A g. -1 It can be observed that after the capacitor has been cycled 10,000 times, the curves of the first five cycles are almost unchanged in shape compared with the curves of the last five cycles, showing good cycle stability. The capacitance retention rate of PTNC3-18-900 is 95.7%. Figure 8(d) shows the energy density of PTNC3-18-6-900 at different power densities. When the power density is 450 W / kg, PTNC3-18-900 exhibits an energy density of 21.59 Wh / kg, demonstrating excellent performance compared to other existing similar materials. This is not only due to the very large specific surface area of ​​PTNC3-18-6-900, but also closely related to its well-developed pore structure. These factors combined contribute to the stable performance of this charge-discharge material.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing tar-based nitrogen-doped graphene oxide, characterized in that, Includes the following steps: 1) Mix pine nut shell tar powder, nano magnesium oxide and KOH in a mass ratio of 1:6:2 to prepare a precursor; 2) The precursor is placed in a tube furnace for carbonization in a nitrogen atmosphere. Two-stage heating is used. In the first stage, the temperature is raised from room temperature to 250-350℃ and held. In the second stage, the temperature is raised to 850-950℃ and held. After holding, the temperature is cooled to room temperature. 3) The obtained solid product is acid washed and then dried.

2. The method for preparing tar-based nitrogen-doped graphene oxide according to claim 1, characterized in that, The preparation method of pine nut shell tar powder is as follows: carbonize pine nut shells at 400-500℃ for 0.5-1h, remove water from the obtained bio-oil, dry it, and then grind it thoroughly through a 60-80 mesh sieve.

3. The method for preparing tar-based nitrogen-doped graphene oxide according to claim 1, characterized in that, In step 2), the heating rate for both stages is 2-5℃·min. -1 The first stage of heat preservation time is 20-40 minutes, and the second stage of heat preservation time is 0.5-1.5 hours.

4. The method for preparing tar-based nitrogen-doped graphene oxide according to claim 1, characterized in that, In step 3), the template and impurities are removed by acid washing with 1-2M HCl, and then dried in an oven at 100-120℃ after filtration.

5. Tar-based nitrogen-doped graphene oxide prepared by the preparation method according to any one of claims 1-4.

6. The application of the tar-based nitrogen-doped graphene oxide according to claim 5 in the preparation of supercapacitor electrodes.

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