CN110589823A - A pomelo peel porous carbon material and its preparation method and application - Google Patents

Abstract

The invention discloses a pomelo peel porous carbon material and its preparation method and application, and relates to an electrode material. The carbon material contains a certain amount of nitrogen, which can increase the hydrophilicity of the electrode material, so that it can be easily mixed with an aqueous electrolyte. Form the electric double layer capacitance well and improve the specific capacitance of the electrode material. The preparation method of the carbon material comprises the following steps: 1) Put the pomelo peel in a tube furnace, first pass nitrogen gas for 20 to 40 minutes, then raise the temperature to 440 to 460 degrees Celsius at a rate of 1 to 3 degrees Celsius/min, and carbonize for 1 to 40 minutes. Cool naturally after 3 hours to obtain carbonized pomelo peel; 2) Mix carbonized pomelo peel and KOH at a mass ratio of 1:1 to 4, grind, put into a tube furnace and pass nitrogen gas for 20 to 40 minutes, and then use 1 to 3 Raise the temperature to 790-810°C at the rate of ℃/min, cool naturally after activation for 1-3 hours, and obtain activated pomelo peel; 3) Adjust the pH of the activated pomelo peel to 10, centrifuge, filter under reduced pressure, wash, and put it into blast drying drying in the box to obtain the pomelo peel porous carbon material.

Description

A pomelo peel porous carbon material and its preparation method and application

technical field

The invention relates to an electrode material, in particular to a pomelo peel porous carbon material and a preparation method and application thereof.

Background technique

With the advancement of science and technology, the development of social economy and the rapid growth of population, the consumption of energy is also increasing. The depletion of non-renewable resources urgently requires renewable resources to play their role as substitutes, and at the same time requires the sustainable development of non-renewable resources. , effective use, and give full play to its potential. The existing traditional energy system can no longer meet the needs of the development of modern industry, agriculture, forestry, etc. Fuel and coal resources are not only non-renewable, but also produce a large amount of harmful substances such as CO ₂ and SO ₂ in the process of use and consumption. to serious environmental pollution. This has prompted people to pay more attention to establishing a new and efficient energy supply system to ensure sustainable economic growth and at the same time be beneficial to protect the environment.

Among them, the development of new energy and renewable clean energy is the most effective way to solve this problem at present, and it is one of the key technologies that must be solved in the 21st century. New energy materials are to realize the development and utilization of new energy and support its development. base and core.

The battery industry is an important part of the new energy application field, because electric energy, as the ultimate form of energy utilization, has become an indispensable source of human production and social development. The first thing people think of in the development of power sources is lithium-ion batteries with high energy density, but when lithium batteries are used as power sources, there is an obvious disadvantage that the power density is so small that it cannot meet the needs of high-power discharge. become the main obstacle restricting its development. Therefore, supercapacitors capable of fast charging and discharging have become a new research hotspot, but the charge storage density of supercapacitors is too low to make them unable to supply power for a long time, which limits their application prospects as power sources.

A supercapacitor is a device between a traditional capacitor and a rechargeable battery. It has the characteristics of fast charge and discharge, environmental friendliness, high power density, long cycle life, no pollution and wide operating temperature range. At present, metal oxides, conductive polymers, activated carbon materials and many doped composite materials are mainly used as electrode materials. Activated carbon has a long history of research on capacitors as electrode materials, and the technology is the most mature, but its production process is complicated, the production cycle is long, and the capacity is generally relatively low, which limits the application of supercapacitors.

Contents of the invention

The present invention aims to provide a pomelo peel porous carbon material and its preparation method and application. The carbon material contains a certain amount of nitrogen, which can increase the hydrophilicity of the electrode material, so that it can be well formed with the aqueous electrolyte Electric double layer capacitance, improve the specific capacitance of the electrode material.

In order to achieve the above object, the technical solution provided by the present invention is as follows: a method for preparing pomelo peel porous carbon material, comprising the following steps:

1) Put the pomelo peel in a tube furnace, first pass nitrogen gas for 20 to 40 minutes, then raise the temperature to 440 to 460°C at a rate of 1 to 3°C/min, carbonize for 1 to 3 hours, and then cool naturally to obtain carbonized grapefruit peel;

2) Mix the carbonized pomelo peel and KOH at a mass ratio of 1:1~4, grind them, put them into a tube furnace and pass in nitrogen gas for 20~40min, and then raise the temperature to 790~810℃ at a rate of 1~3°C/min. ℃, after activation for 1 to 3 hours, cool naturally to obtain activated pomelo peel;

3) Adjust the pH of the activated pomelo peel to 10, centrifuge, filter under reduced pressure, wash, dry in a blast drying oven, and obtain a porous carbon material from pomelo peel.

The feeding time of nitrogen in the step 1) is 30 minutes, and the carbonization time is 2 hours.

The heating rate in the step 1) is 2°C/min, and the target temperature is 450°C.

Grinding in the step 2) adopts an agate mortar.

The feeding time of nitrogen in the step 2) is 30min, and the activation time is 2h.

The reagent used to adjust the pH in the step 3) is KOH.

In the step 3), the centrifugal speed is 7000r/min, and the centrifugal time is 5min.

The washing solvent in the step 3) is HCl and deionized water.

The drying temperature in step 3) is 80°C.

A pomelo peel porous carbon material prepared by the method described in any one of claims 1-9.

A pomelo peel porous carbon material as claimed in claim 9 is applied to electrode fabrication and assembly, namely:

Firstly, nickel foam is washed with deionized water and ethanol ultrasonically, dried and weighed, then the prepared sample is mixed with polyvinylidene fluoride and acetylene black at a mass ratio of 0.85:0.05:0.15, and N-methylpyrrolidone is added After mixing, apply it on 2×1cm foamed nickel, then place it in a vacuum oven and dry it at 80°C for about 6 hours, press it on a desktop electric tablet machine with a pressure of 10MPa, weigh the mass of foamed nickel again, twice 85% of the mass difference is the active substance mass. A three-electrode system is composed of nickel foam coated with active material as the working electrode, nickel foam as the counter electrode, and HgO/Hg electrode as the reference electrode. It is immersed in 6MKOH for 3 hours, and the electrolytic cell is filled with N for 10min before the test ₂ to exhaust O ₂ .

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

The preparation processes of graphene and carbon nanotubes are relatively complicated. At present, regarding the preparation of graphene, there are mainly physical methods (mechanical exfoliation method, explosion method, epitaxial method, etc.) and chemical methods (electrochemical method, chemical vapor deposition method, graphite intercalation method, graphite oxide method, etc.) recovery, etc.). Regarding the preparation of carbon nanotubes, the literature mainly includes catalytic pyrolysis, flame method, template method, arc discharge method, condensed phase electrolysis method and laser evaporation method. No matter which method is used, the preparation process is relatively complicated, and some conditions are difficult to accurately control, resulting in poor repeatability of some physicochemical characteristics of the product.

Most carbonaceous materials have poor hydrophilicity, which reduces the electric double layer capacitance formed by carbonaceous materials in electrode materials to a certain extent. However, carbon materials containing heteroatoms (such as N, S, B, etc.), especially N-containing elements, have aroused the attention of many researchers because they enhance the charge asymmetry and induce structural deformation, which improves the electron transfer ability of the material itself. interest.

The invention provides a method with simple operation and easy control. Pomelo is a kind of common fruit in China, pomelo skin accounts for 44%-55% of whole pomelo mass, but pomelo is not well utilized after being eaten. Because it has a large amount of fluffy fiber structure and pectin, if it is activated to prepare porous carbon materials, it will provide many hydrophilic groups for the material. Therefore, in this study, grapefruit peels were used as raw materials to prepare cathode materials for supercapacitors, which are expected to be applied on a large scale.

In the present invention, grapefruit peels are used as raw materials, first carbonized at 450°C for 2 hours, and then KOH is used as an activator under the condition of a carbon-to-alkaline ratio of 1:1, and calcined at 800°C for 2 hours to obtain a supercapacitor cathode material with high specific capacitance. Its specific capacitance reaches 357.6F/g, and the specific capacitance retention rate reaches over 90% after 3000 cycles. The preparation method is simple, the raw materials are readily available and cheap, and the prepared material has excellent performance, which can not only solve the problem of low recycling rate of pomelo peel, but also prepare a material with high electrochemical performance.

Description of drawings

Fig. 1 is the production flowchart of pomelo peel porous carbon material;

Fig. 2 is the cyclic voltammetry curve diagram of different proportions of activated samples at a scan rate of 5mV/s;

Figure 3 is the constant current charge and discharge curves of different samples at a current density of 0.5A/g;

Figure 4 is a representative cyclic voltammetry curve of the PH1 sample at a scan rate of 5-100 mV/s;

Figure 5 is the constant current charge and discharge curve of the PH1 sample at a current density of 0.5 to 5A/g;

Figure 6 is a graph of the cycle life of the PH1 sample at a current density of 1A/g;

Fig. 7 is a scanning electron microscope image of pomelo peel; (a) a scanning electron microscope image of unactivated grapefruit peel, (b) a scanning electron microscope image of a PH1 sample.

Detailed ways

The present invention further describes the above claims in detail through the following specific examples, but does not constitute any limitation to the present invention.

Example 1

To prepare grapefruit peel charcoal:

Put 5g of pomelo peel in a porcelain boat, put nitrogen in the tube furnace for 30min, then raise the temperature to 450℃ at a rate of 2℃/min under the protection of nitrogen, carbonize for 2 hours and then cool naturally to obtain carbonization grapefruit peel. Mix the carbonized pomelo peel and KOH in a certain mass ratio (m (carbonized pomelo peel): m(KOH)=1:1, 1:2, 1:3, 1:4) and name them PH1, PH2 , PH3, PH4. Then each sample was ground in an agate mortar and then placed in a tube furnace and fed with nitrogen for 30 minutes. Under the protection of nitrogen, the temperature was raised to 800 degrees Celsius at a rate of 2 degrees Celsius/min, activated for 2 hours and then cooled naturally. . Add 6M KOH to the activated material and adjust the pH to about 10 (because the alkali will corrode the porcelain boat, so add the lye to dissolve the corroded porcelain boat inner wall material mixed in the material), and put it in the centrifuge with Centrifuge at a speed of 7000r/min for 5min, then filter under reduced pressure, wash with deionized water first, then wash with 1M HCl until the pH is about 7, and then wash with deionized water to remove Cl ^- and K ⁺ . Finally, the activated material was dried in a blast drying oven at 80°C.

Perform performance tests on the above samples, see Figure 2-7 for details, in which:

Figure 2 is the cyclic voltammetry curves of porous carbon materials activated by KOH at different mass ratios at 5mV/s. From the figure, it can be found that the curves of the four samples are similar to rectangles, and at the same time exhibit excellent electrochemical performance. In addition, it can be seen that the rectangular area of the PH1 (m (carbonized grapefruit peel): m (KOH) = 1:1) material is the largest, indicating that the mass specific capacitance of the material is also larger

As shown in Figure 3, it is the constant current charge and discharge curves of different samples at 0.5A/g. At this time, the charge and discharge time of the PH1 sample is still longer than that of the other three samples, and the curves of each sample are well presented. A linear relationship is established, and the charging and discharging curves and the time axis form an approximate isosceles triangle, which reflects the excellent symmetry of the material during charging and discharging. According to the data in Figure 3, the mass specific capacitance of the four materials can be calculated using formula (1). The calculation results are shown in Table 1. The mass specific capacitance of the PH1 sample reached 357.6 F/g. As the amount of alkali increases, the mass specific capacitance decreases continuously.

The further cyclic voltammetry test of the PH1 sample is shown in Figure 4. Figure 4 is the cyclic voltammetry curve of the PH1 sample at a scan rate of 5-100mV/s. The figure shows that before the scan rate of 80mV/s, the PH1 sample The curves all present a relatively regular rectangular shape, and when the scanning rate is greater than 80mV/s, the material is slightly polarized.

Figure 5 is the charge and discharge curves of PH1 samples at different current densities. In the figure, under different current densities, the curves still have a good linear relationship and a symmetrical triangular shape, and the curves change suddenly near the inflection point of charging and discharging at high currents. Smaller, which means that even in high current charging and discharging, the polarization phenomenon is very small.

Figure 6 is a graph of the cycle life of the PH1 sample at a current density of 1A/g. After 3,000 cycles, the material can still maintain more than 90% of the specific capacitance. In addition, when charging and discharging less than 500 times, the specific capacitance will first decrease slightly, and then increase, even exceeding the initial specific capacitance.

Fig. 7(a) is a scanning electron microscope image (SEM) of pomelo peel without alkali activation, and Fig. 7(b) is an SEM image of PH1 sample. By comparison, it can be found that the surface of the pomelo peel has a layered structure when it is not activated, but the layered structure of the activated grapefruit peel is still retained, as shown in the red circle in Figure 7. In addition, the activated material also has many nano-spheres with a diameter of about 30nm, as shown in the yellow dotted circle in Figure 7(b), there are many holes between the balls, which is very conducive to the insertion and de-intercalation of electrolyte ions.

Table 2 shows the test results of the C, O, and N element contents of the material by the desktop electron microscope and energy spectrum integrated machine. Comparing the O content/C content of the two materials, it can be found that the O content of the PH1 sample increases significantly, which means that more oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups may be introduced on the surface of the material, which can improve the hydrophilicity of the material properties, thereby improving the adsorption and wettability of the electrode material and the electrolyte, and finally improving the specific capacitance of the material.

Example 2

Electrode fabrication and assembly:

Firstly, nickel foam is washed with deionized water and ethanol ultrasonically, dried and weighed, then the prepared sample is mixed with polyvinylidene fluoride and acetylene black at a mass ratio of 0.85:0.05:0.15, and N-methylpyrrolidone is added After mixing, apply it on 2×1cm foamed nickel, then place it in a vacuum oven and dry it at 80°C for about 6 hours, press it on a desktop electric tablet machine with a pressure of 10MPa, weigh the mass of foamed nickel again, twice 85% of the mass difference is the active substance mass. A three-electrode system is composed of nickel foam coated with active material as the working electrode, nickel foam as the counter electrode, and HgO/Hg electrode as the reference electrode. It is immersed in 6MKOH for 3 hours, and the electrolytic cell is filled with N for 10min before the test ₂ to exhaust O ₂ .

Claims (10)

1. A preparation method of a shaddock peel porous carbon material is characterized by comprising the following steps:

1) placing the shaddock peel in a tubular furnace, introducing nitrogen for 20-40 min, heating to 440-460 ℃ at the speed of 1-3 ℃/min, carbonizing for 1-3 h, and naturally cooling to obtain carbonized shaddock peel;

2) mixing carbonized shaddock peel and KOH according to the mass ratio of 1: 1-4, grinding, putting into a tubular furnace, introducing nitrogen for 20-40 min, heating to 790-810 ℃ at the speed of 1-3 ℃/min, activating for 1-3 h, and naturally cooling to obtain activated shaddock peel;

3) and (3) adjusting the pH value of the activated shaddock peel to 10, centrifuging, performing vacuum filtration, washing, and drying in a forced air drying oven to obtain the shaddock peel porous carbon material.

2. The preparation method of the shaddock peel porous carbon material as claimed in claim 1, wherein the nitrogen gas is introduced for 30min and the carbonization time is 2h in the step 1).

3. The method for preparing the shaddock peel porous carbon material as recited in claim 1, wherein the temperature increase rate in the step 1) is 2 ℃/min, and the target temperature is 450 ℃.

4. The method for preparing the shaddock peel porous carbon material as claimed in claim 1, wherein the grinding in step 2) is performed using an agate mortar.

5. The preparation method of the shaddock peel porous carbon material as claimed in claim 1, wherein the nitrogen gas is introduced for 30min and the activation time is 2h in the step 2).

6. The method for preparing the shaddock peel porous carbon material as recited in claim 1, wherein the agent for adjusting the pH in the step 3) is KOH, and the washing solvent is HCl and deionized water.

7. The method for preparing the shaddock peel porous carbon material as recited in claim 6, wherein the centrifugation speed in the step 3) is 7000r/min and the centrifugation time is 5 min.

8. The method for preparing the shaddock peel porous carbon material as recited in claim 7, wherein the drying temperature in the step 3) is 80 ℃.

9. A porous carbon material of shaddock peel, characterized by being produced by the method of any one of claims 1 to 9.

10. The shaddock peel porous carbon material as claimed in claim 9, applied to electrode fabrication and assembly.