CN109994319B

CN109994319B - Nitrogen-sulfur co-doped biomass derived carbon material and synthesis method and application thereof

Info

Publication number: CN109994319B
Application number: CN201910287591.8A
Authority: CN
Inventors: 李强; 彭程; 韩军建; 王嘉琪
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2019-04-11
Filing date: 2019-04-11
Publication date: 2020-11-27
Anticipated expiration: 2039-04-11
Also published as: CN109994319A

Abstract

The invention discloses a nitrogen and sulfur co-doped biomass derived carbon material and a synthesis method and application thereof, wherein the biomass derived carbon material is prepared by taking a biological waste winter bamboo shoot shell as a carbon source and a nitrogen source and performing ball milling to obtain powdery biomass particles; then, EDOT is used as a sulfur source, and the PEDOT is polymerized on the surfaces of the biomass particles by using an in-situ growth method; and finally, carrying out one-step carbonization and activation on the obtained compound to obtain the nitrogen and sulfur co-doped biomass derived carbon material. The synthetic method is simple, the obtained product has uniform appearance and large specific surface area, the advantages of the biomass material are combined, and the pseudo-capacitance reaction of the heteroatom is introduced, so that the product has better performance when being used as an electrode material of a super capacitor.

Description

Nitrogen-sulfur co-doped biomass derived carbon material and synthesis method and application thereof

Technical Field

The invention belongs to the field of supercapacitors and the field of nano material synthesis, and particularly relates to a nitrogen and sulfur co-doped biomass derived carbon material and a synthesis method thereof.

Background

The super capacitor is used as a novel energy storage device combining the advantages of a traditional capacitor and a secondary battery, can provide energy density higher than that of the traditional capacitor, has more excellent power density and cycle life compared with the secondary battery, and is expected to be widely applied to the fields of energy conversion, aerospace systems, communication engineering, microelectronic devices and the like. From the viewpoint of energy storage mechanism, the super capacitor mainly has: an electric double layer capacitor using a carbon-related material as an electrode, which stores energy by means of charge separation at the surface of the electrode/electrolyte; the pseudo capacitor uses polymer and metal oxide as electrodes and stores energy by means of the Faraday reaction of the electrodes in electrolyte. However, the ultracapacitor has a low energy density (5 Wh kg)^-1) This is a challenging issue for the development of the supercapacitor industry.

The research of the electrode material is a key factor for improving the electrochemical performance of the super capacitor. For carbon-based electrode materials, the electrochemical performance of the material is affected by the high specific surface area, the layered porous structure and the introduction of impurity atoms. And the heteroatom is introduced into the carbon-based material, so that the surface structure of the carbon atom can be effectively improved, and the electrochemical performance of the carbon-based material is further improved. Therefore, the introduction of impurity atoms into the carbon material has important significance for developing high-performance advanced electrode materials and the practical application of future supercapacitors.

The biomass is used as a raw material, has the advantages of rich raw materials, low price, large specific surface area and the like, and is widely applied to microwave absorption, sewage treatment, catalyst carriers and electrochemical electrode materials. In addition, the biomass nanoporous carbon is renewable, environmentally friendly and non-toxic in source. These advantages make them one of the carbon-based materials that is being used as an emphasis in the development and synthesis of hybrid electrode materials.

Disclosure of Invention

In order to avoid the problems in the prior art, the invention provides a nitrogen and sulfur co-doped biomass derived carbon material and a synthesis method and application thereof, and aims to solve the technical problem that the biomass derived carbon rich in heteroatoms is obtained by mixing a biomass precursor with other heteroatom-containing precursors, so that the biomass derived carbon has better performance when being used as an electrode material of a supercapacitor.

In order to realize the purpose of the invention, the following technical scheme is adopted:

the invention discloses a method for synthesizing a nitrogen-sulfur co-doped biomass derived carbon material, which takes a biological waste winter bamboo shoot shell as a carbon source and a nitrogen source, and obtains powdery biomass particles through ball milling; then, EDOT is used as a sulfur source, and the PEDOT is polymerized on the surfaces of the biomass particles by using an in-situ growth method; and finally, carrying out one-step carbonization and activation on the obtained compound to obtain the nitrogen and sulfur co-doped biomass derived carbon material. The method specifically comprises the following steps:

(1) slicing winter bamboo shoot shells, cleaning, drying, then putting into a ball mill, and grinding into powder to obtain powdery small bamboo shoot shell particles, and recording the powdery small bamboo shoot shell particles as Raw-C;

(2) under the condition of ice-water bath, adding 4g of Raw-C into 400mL of 1mol/L diluted hydrochloric acid, and stirring for 0.1-1 h; then adding 0.02mol of EDOT, and continuously stirring for 0.5-1 h; then, 40mL of aqueous solution containing 0.04mol of APS is added dropwise by using a burette, and stirring is continued for 12 hours;

performing suction filtration on the obtained product by using deionized water, and drying to obtain a composite carbon precursor, which is recorded as PEDOT @ Raw-C;

(3) adding 1g of PEDOT @ Raw-C and 1g of KOH into a proper amount of deionized water, mixing, and performing magnetic stirring drying at 80 ℃ until water is completely evaporated; then placing the obtained mixture in a tubular furnace, heating to 500-700 ℃ in a nitrogen environment, and carbonizing and activating for 2 hours at constant temperature; and washing the obtained product to be neutral by using deionized water, thus obtaining the target product nitrogen and sulfur co-doped biomass derived carbon material.

Further, in the step (1), the cleaning is ultrasonic cleaning for 20min by using deionized water, acetone and ethanol in sequence.

Further, in the step (1), the rotation speed of the grinding is 450rap/min, and the time is 8-10 h.

The invention also discloses a nitrogen and sulfur co-doped biomass derived carbon material synthesized by the synthesis method and application thereof, and the nitrogen and sulfur co-doped biomass derived carbon material is used as an electrode material of a super capacitor.

The invention has the beneficial effects that:

1. the synthetic method is simple, the obtained product has uniform appearance and large specific surface area, the advantages of the biomass material are combined, and the pseudo-capacitance reaction of the heteroatom is introduced, so that the product has better performance when being used as an electrode material of a super capacitor.

2. The invention takes EDOT as a sulfur source, overcomes the defect that the biomass does not have S doping, introduces a large amount of doping atoms and obviously improves the specific capacitance.

Drawings

FIG. 1 is an SEM image of each sample obtained in example 1, wherein (a) to (d) correspond to samples AC-600, PC-500, PC-600 and PC-700, respectively.

FIGS. 2(a) to (e) are graphs showing elemental distributions of the sample PC-600 obtained in example 1.

FIG. 3 shows the results obtained in example 1Product N₂Adsorption and desorption isotherms (fig. 3(a)) and pore size distribution (fig. 3 (b)).

Fig. 4 shows an XRD spectrum (fig. 4(a)) and a raman spectrum (fig. 4(b)) of each sample obtained in example 1.

FIG. 5 is a schematic representation at 1M H₂SO₄The electrochemical performance of each sample of example 1 was determined in (1), wherein: (a) the CV curve of each sample at 10mV s-1; (b) constant current charge and discharge curves of each sample at 1A g-1; (c) the mass specific capacitance is calculated according to the discharge curves under different current densities; (d) the nyquist plot shows the high frequency range.

FIG. 6 is a graph of the samples obtained in example 1 at different scan rates (0.01-0.2V s)^-1) CV curve of time.

FIG. 7 is a schematic representation at 1M H₂SO₄The GCD curves of the samples obtained in example 1 at different current densities, wherein (a) to (d) correspond to samples AC-600, PC-500, PC-600 and PC-700, respectively.

FIG. 8(a) is a graph showing that the current density of the sample PC-600 obtained in example 1 is 5A g^-1Electrolyte 1M H₂SO₄(ii) the cycle stability after 10000 cycles, and (b) is a charge-discharge curve of the first and last cycles.

Fig. 9 is a Ragone diagram of sample PC-600 obtained in example 1 (fig. 9(a)) and a power supply diagram for an LED lamp based on a super capacitor assembled therefrom (fig. 9 (b)).

Detailed Description

The following examples of the present invention are described in detail, and the present invention is implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific procedures are given, but the scope of the present invention is not limited to the following example 1.

Example 1

The nitrogen and sulfur co-doped biomass derived carbon material is synthesized by the following steps:

(1) slicing winter bamboo shoot shells, sequentially using deionized water, acetone and ethanol to perform ultrasonic cleaning for 20min respectively, drying in a 60 ℃ blast drying oven, then putting into a ball mill to be ground into powder (the grinding speed is 450rap/min, the grinding time is 8h), and obtaining powdery bamboo shoot shell small particles which are recorded as Raw-C;

(2) under the condition of ice-water bath, adding 4g of Raw-C into 400mL of 1mol/L diluted hydrochloric acid, and stirring for 10 min; then adding 0.02mol of EDOT, and continuing stirring for 30 min; then, 40mL of aqueous solution containing 0.04mol of APS is added dropwise by using a burette, and stirring is continued for 12 hours;

(3) adding 1g of PEDOT @ Raw-C and 1g of KOH into 20mL of deionized water, mixing, and performing magnetic stirring drying at 80 ℃ until the water is completely evaporated; then placing the obtained mixture in a tube furnace, heating to 500 deg.C, 600 deg.C, 700 deg.C under nitrogen environment, and heating at a rate of 10 deg.C for 10min^-1Gas flow rate of 100mL min^-1Carbonizing and activating for 2 hours at constant temperature; and washing the obtained product to be neutral by using deionized water, thus obtaining the target product nitrogen and sulfur co-doped biomass derived carbon material. The products obtained at 500 deg.C, 600 deg.C and 700 deg.C were respectively designated as PC-500, PC-600 and PC-700.

For comparison, the PEDOT-free material Raw-C was directly activated in the same manner as in step (3) at a carbonization activation temperature of 600 ℃ and the resulting material was designated as AC-600.

The above samples obtained in this example were subjected to the following verification and analysis.

1. SEM analysis

FIGS. 1(a) to (d) are SEM images of samples AC-600, PC-500, PC-600 and PC-700 obtained in this example in this order. The porous structure is one of the key factors affecting the electrochemical performance of the supercapacitor, and it can be seen from fig. 1 that all the activated samples have certain pore structures. It can be observed from the SEM image at the same magnification that PC-500 and PC-700 have a smaller macro pore size and a large number of irregular platelets. The macro-pore diameters of the AC-600 and the PC-600 are large in quantity and relatively uniform in distribution, and the large number of irregular sheets is avoided. The electrochemical performance of the supercapacitor is affected differently by different pore diameter structures of the layered porous carbon structure, the specific surface area of the material can be improved by the micropores, the electric double layer capacitance is enhanced, a passage is provided for ion transmission by the mesoporous channels, and the formation of the macropores is beneficial to buffering and storing ions and effectively shortening the diffusion distance of the ions. PC-600 exhibits a large number of relatively small pore size distributions (circled in the figure) compared to AC-600.

To further confirm the successful introduction of N, S element in this example, EDS images of sample PC-600 were taken and the results are shown in FIGS. 2(a) - (e). The distribution of the N, S, C, O elements is evident from the figure.

2. Pore size structure and distribution thereof

The pore size structure of the carbon material plays a key role in the formation of the electric double layer, and therefore, in order to further analyze the pore size structure and the distribution thereof, the present example performed a desorption test using nitrogen. N of all samples₂Adsorption and desorption isotherms and pore size distributions are shown in figure 3. As shown in fig. 3(a), the nitrogen adsorption-desorption isotherms of all the samples showed type I/IV isotherm characteristics corresponding to the microporous and mesoporous structures. Pore size characteristics of all samples were subjected to pore size distribution analysis using the Density Functional Theory (DFT) method, as shown in fig. 3(b), it can be seen that all samples exhibited different degrees of micropores and mesopores, the micropores being mainly concentrated at 1-2 nm. The contribution of pore size per fraction to surface area and pore volume is given in table 1. The specific surface area and pore volume of each sample increased with increasing pyrolysis temperature due to the increasing chemical activation at high temperature. It is noted that with the introduction of S atoms, the specific surface areas of AC-600 and PC-600 are 765 and 1032 respectively at the same temperature, the specific surface area of the material is increased to some extent, and the pore volume is also increased. The results show that the PEDOT used has the following effects: 1. the pore diameter is favorably formed; 2. impurity atom S is introduced.

TABLE 1

In the table: s_BETIs a specific surface area; s_microIs the surface area of the micropores; s_meso/macroSurface area for mesopores and macropores; v_TTotal pore volume; v_microIs the micropore volume; v_meso/macroThe volumes of mesopores and macropores.

3. XRD and Raman measurement

Fig. 4(a) shows XRD patterns of all samples. The two broad diffraction peaks at 23 ° and 43 ° correspond to the (002) diffraction of amorphous carbon and the (100) diffraction of graphitized carbon, respectively. The strength of the low angle region is greatly enhanced, indicating a rich channel in the material, which is consistent with the pore size distribution of the AC-600, PC-500, PC-600 and PC-700 obtained. The broad and weak peaks at 23 ° and the insignificant peak appearing at 43 ° indicate that all samples were dominated by amorphous structure carbon. The degree of defects in the samples was further analyzed by raman. FIG. 4(b) shows the Raman spectra of all samples, from which it is observed at 1338 and 1589cm^-1Two different peaks at (a), which correspond to the D and G bands, respectively. The D band is related to the degree of structural disorder, and the G band is related to the order of graphitization. Intensity ratio of D and G bands (I)_D/I_G) May be used to reflect the degree of graphitization of the carbon material. I of AC-600, PC-500, PC-600 and PC-700_D/I_GThe ratios were 0.93, 0.89, 1.01 and 1.12, respectively. With increasing temperature (PC-500, PC-600 and PC-700) and introduction of impurity atoms (AC-600 and PC-600), I_D/I_GIncreasing, which implies that both the introduction of impurity atoms and the increase in temperature lead to more defects and disorder of the material.

4. XPS test analysis

The content of elements in each sample was measured by X-ray photoelectron spectroscopy, and the C, N, O and S element contents of all samples from the XPS result are shown in table 2. As the processing temperature increases, the doping atom content of the sample may decrease. In contrast, there is some increase in carbon content. For the two samples AC-600 and PC-600, the ratio of N and S contents was 13.5 and 1.7, respectively, and it can be seen from Table 2 that the N atom content in AC-600 is much higher than that in PC-600, while the mass specific capacitance (C) is_g(F g^-1) But less than PC-600. The results show that, due to the introduction of the S atom, between the atomsAnd the electrochemical performance of the material can be improved by the synergistic effect. This is consistent with the results of the electrochemical tests. In addition, the increase in temperature affects the content of dopant atoms as well as the pore size structure.

TABLE 2

5. Electrochemical performance test

Under the test item, the electrochemical performance of the material is tested at 1M H₂SO₄The method is carried out in an electrolyte, and the related electrochemical test characterization methods comprise the following steps: cyclic voltammetry, constant current charge and discharge, and electrochemical impedance spectroscopy.

FIG. 5 is a schematic representation at 1M H₂SO₄The electrochemical properties of AC-600, PC-500, PC-600 and PC-700 determined in (1), wherein: (a) for each sample at 0.01V s^-1The lower CV curve; (b) for each sample at 1Ag^-1A lower constant current charge-discharge curve; (c) the mass specific capacitance is calculated according to the discharge curves under different current densities; (d) the nyquist plot shows the high frequency range. The system for testing adopts a double-electrode testing system, and the electrolyte is 1M H₂SO₄And the working voltage window is 0-1V.

FIG. 5(a) shows that AC-600, PC-500, PC-600 and PC-700 are scanning at a scan rate of 0.01V s^-1As is apparent from the figure, the CV curves of all the samples have a rectangular shape. In addition, sample PC-600 has the largest CV curve profile area relative to the other samples at the same scan rate, indicating that PC-600 has a large specific capacitance and good rate performance. Meanwhile, it was suggested that PC-600 had a significant improvement in electrochemical performance as compared with the remaining samples due to the successful introduction of a heteroatom such as N, S. AC-600, PC-500, PC-600 and PC-700 electrodes at different scan rates (0.01-0.2V s)^-1) The CV curve at time is shown in fig. 6. As the scan rate increased, all CV curves were rectangular-like in shape, indicating good electric double layer capacitance characteristics.

FIG. 5(b) shows Ag at a current density of 0.5^-1GCD profile for each sample. Also, figure 7 shows the GCD plot for each sample at different current densities. The curve shape approximating an isosceles triangle indicates that the doped electrode has typical double layer capacitance characteristics, which is consistent with the results of the CV curve. There was no significant difference in charge time and discharge time, indicating that it had excellent coulombic efficiency. The specific capacitance of the supercapacitor device based on each sample was calculated at a current density of 0.5Ag^-1The specific capacitances of the AC-600, PC-500, PC-600 and PC-700 samples were, respectively: 283F g^-1，182F g^-1，303F g^-1，263F g^-1. Figure 5(c) shows the specific capacitance of each sample at different current densities derived from the GCD curve. It can be seen that the PC-600 maintains a larger specific capacitance at the same current density. Even at high current densities (20 Ag)^-1) Next, PC-600 can still provide 203F g^-1Indicating that it has excellent rate performance. In particular, the specific capacitance of PC-600 was improved compared to AC-600, indicating that the introduction of S atoms can further increase the specific capacitance. In addition, the present example also examined that the current density was 5Ag^-1In the process, the test result is shown in fig. 8 based on the cycle stability of the PC-600 symmetric supercapacitor device, and the result shows that the PC-600 symmetric supercapacitor device has good cycle stability, after 10,000 charging and discharging, the initial capacitance retention rate is 87%, and the coulomb efficiency is 95%.

FIG. 5(d) shows electrochemical impedance spectra of AC-600, PC-500, PC-600 and PC-700. The intercept of the nyquist plot with the real axis illustrates the equivalent series resistance (Rs) of the electrode. Rs for all electrode materials was low, and the equivalent series resistances of AC-600, PC-500, PC-600, and PC-700 were 1.3 Ω, 1.1 Ω, 1.2 Ω, and 1.2 Ω, respectively. The approximate vertical lines in the low frequency region indicate that the prepared material has ideal capacitive behavior. Compared with AC-600, PC-600 is more tilted in the low frequency range, indicating that the introduction of S impurity atoms has some effect on its capacitive performance.

It is known that carbon is contained in an organic electrolyte as compared with an aqueous electrolyteA symmetric electrochemical double layer capacitor device will result in higher energy density due to a larger operating voltage window. To further explore the electrochemical behavior in organic electrolytes, a solution using 1M EMIMPF was prepared₆A symmetric supercapacitor device of a coin cell device, which is an electrolyte, was used to evaluate the electrochemical performance of a PC-600 based symmetric supercapacitor. Fig. 9(a) is a Ragone diagram of a PC-600 based symmetric supercapacitor device. The results show that the electrode material is in 1M EMIMPF₆In the electrolyte, the power density is 468.75W kg^-1When it is used, the energy density is 30.6Wh kg^-1. Even though the power density is 16375W kg^-1This fabricated symmetrical supercapacitor still had 13.42Wh kg^-1The energy density of (1). The energy density and power density of the symmetrical supercapacitor based on the PC-600 are superior to those of other recently reported N, S co-doped carbon materials. Currently, the energy density of commercial activated carbon electrodes is less than 7. The N, S co-doped biomass activated carbon material prepared by the method has wide prospect in the practical application of the super capacitor.

To further illustrate the practical application of the N, S co-doped biomass activated carbon material prepared in this work, this example used a symmetrical supercapacitor device fabricated to illuminate an LED, as shown in fig. 9 (b). More importantly, the PC-600 based symmetric device can power fourteen yellow LEDs for 30 seconds after only 2 seconds of charging.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A synthetic method of a nitrogen and sulfur co-doped biomass derived carbon material is characterized by comprising the following steps: taking the biological waste winter bamboo shoot shells as a carbon source and a nitrogen source, and performing ball milling to obtain powdery biomass particles; then, EDOT is used as a sulfur source, and the PEDOT is polymerized on the surfaces of the biomass particles by using an in-situ growth method; finally, performing one-step carbonization and activation on the obtained compound to obtain a nitrogen and sulfur co-doped biomass derived carbon material; the method comprises the following steps:

2. The method of synthesis according to claim 1, characterized in that: in the step (1), the cleaning is ultrasonic cleaning for 20min by sequentially using deionized water, acetone and ethanol.

3. The method of synthesis according to claim 1, characterized in that: in the step (1), the rotation speed of grinding is 450rap/min, and the time is 8-10 h.

4. A nitrogen and sulfur co-doped biomass derived carbon material synthesized by the synthesis method according to any one of claims 1 to 3.

5. The use of the nitrogen and sulfur co-doped biomass-derived carbon material as claimed in claim 4, wherein: the material is used as an electrode material of a super capacitor.