CN111341569A - Green controllable preparation method of nitrogen-doped graphene-based iron oxide supercapacitor material - Google Patents

Abstract

The invention discloses a green controllable preparation method of a nitrogen-doped graphene-based iron oxide supercapacitor material, which is characterized in that iron oxide and amino acid which are good in environment and rich in resources are utilized, GO is used as a precursor, a one-step hydrothermal method is used for preparing the nitrogen-doped graphene-based iron oxide composite material, the iron oxide is controllable in shape due to complexation of the amino acid and iron salt, and the prepared electrode material which can be used for a supercapacitor is superior to most reported iron oxide-based heteroatom-doped graphene materials.

Description

Green and controllable preparation method of nitrogen-doped graphene-based iron oxide supercapacitor materials

technical field

The invention relates to the field of novel energy storage materials, and more particularly, to a green and controllable preparation method of a high-performance nitrogen-doped graphene-based iron oxide supercapacitor material.

Background technique

Today's world economy is growing rapidly, the demand for energy is increasing, and the problem of energy shortage is becoming more and more serious. Therefore, the development of various types of renewable green and clean energy, such as supercapacitors, has a positive effect on alleviating energy shortages and reducing environmental pollution.

The performance of supercapacitors depends to a large extent on the electrode material. Therefore, the development of an inexpensive, environmentally friendly and high-capacity electrode material has become the focus of current research. The carbon material with dual capacitance characteristics has the characteristics of excellent electrical conductivity, large specific surface area and stable structure, so it can be used as the carrier of the composite material. Combining it with transition metal oxide can improve the electrical conductivity of the material and reduce the oxidation of nano-transition metal. Through the synergistic effect with pseudocapacitive materials, the advantages of the two can be complementary and synergistic.

Among them, the research on nitrogen-doped graphene-based iron oxide composites has become a research hotspot. Taking advantage of the low price, environmental friendliness, and high pseudocapacitance of iron oxide, combined with the excellent electrical conductivity, large surface area and stability of nitrogen-doped graphene, the two are combined to prepare high specific capacity, high energy density and high stability. Supercapacitor electrode material. In the past hydrothermal preparation of nitrogen-doped graphene, most of the commonly used nitrogen sources (hydrazine hydrate, pyrrole, ammonia water) are toxic, and their morphology is uncontrollable in the process of hydrothermal composite preparation of iron oxide.

SUMMARY OF THE INVENTION

Aiming at the deficiencies in the prior art, the object of the present invention is to provide a green and controllable preparation method of nitrogen-doped graphene-based iron oxide supercapacitor material that solves the above problems, and a green, environmentally friendly amino acid is used as a nitrogen source, and amino acid is simultaneously The complexation with iron salt makes the morphology of iron oxide controllable, and the electrode material of the prepared supercapacitor has high specific capacity and excellent conductivity.

For achieving the above object, the present invention provides the following technical solutions:

A green and controllable preparation method of nitrogen-doped graphene-based iron oxide supercapacitor material, comprising the following steps:

1) After the amino acid is dissolved in water, add iron salt, and continue stirring for 0.5-10 hours; mix the amino acid-coordinated iron salt solution with the graphene oxide aqueous solution with a concentration of 0.5-20 mg/mL, keep stirring, the quality of amino acid and GO The ratio is 1:5 to 5:1, and the mass ratio of iron salt to GO is 1:2 to 20:1;

2) Put the mixed solution into the reaction kettle, and treat it in an oven at a high temperature of 100 to 250 °C for 2 to 24 hours. During this process, the heating rate is controlled at 2 to 10 °C/min;

3) After the reaction kettle is naturally cooled, the obtained hydrogel or black powder is taken out and washed repeatedly with ethanol and distilled water to obtain nitrogen-doped graphene-based iron oxide material.

Further, the amino acids in step 1) refer to glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine One of acid, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine and histidine and its derivatives.

Still further, the amino acid in step 1) is an acidic amino acid. Acidic amino acids are aspartic acid or glutamic acid.

Further, the iron salt in step 1) is one of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric citrate, ferric acetylacetonate, and ferrocene.

Further, in step 1), the graphene oxide aqueous solution is prepared by first preparing graphene oxide from natural flake graphite by Hummer's method, and then dissolving it in water.

Further, step 1) the amino acid-coordinated iron salt solution is added dropwise to the graphene oxide aqueous solution.

In a further improvement scheme, the filling degree of the reactor in step 2) is less than or equal to 80%.

Beneficial effects of the present invention:

In view of the lack of green preparation technology for high-performance supercapacitor electrode materials, the use of iron oxide and amino acids with good environment and abundant resources, using GO as a precursor, prepared electrode materials that can be used for supercapacitors, which is superior to most of the reported oxidation Fe-based heteroatom-doped graphene material (151-618 F g ^-1 ), especially under the preparation conditions of Example 1, the Fe ₂ O ₃ nanoparticles are in the form of a shuttle, and the overall composite sample is loose and cross-linked. The coupled structure, at a small current density of 1 A g ^-1 , the specific capacitance value of the material can reach 1060 F g ^-1 . Combining the high specific capacity of iron oxide and the excellent conductivity of nitrogen-doped graphene, the material has good supercapacitive performance.

Description of drawings

Fig. 1 is the XRD pattern of FeO-NG-A in embodiment 1;

Fig. 2 is the SEM morphology photograph of FeO-NG-A in embodiment 1;

Fig. 3 is the XPS figure of N in FeO-NG-A in embodiment 1;

4 is a cross-current charge-discharge diagram of FeO-NG-A in Example 1;

Fig. 5 is the SEM morphology photograph of FeO-NG-N in embodiment 2;

Fig. 6 is the thermogravimetric topography diagram of FeO-NG-N in embodiment 2;

7 is a cross-current charge-discharge diagram of FeO-NG-N in Example 2;

Fig. 8 is the SEM morphology photograph of FeO-NG-B in Example 3;

Fig. 9 is the Raman diagram of FeO-NG-B in embodiment 3;

Figure 10 is a cross-current charge-discharge diagram of FeO-NG-B in Example 3;

Fig. 11 is the scanning electron microscope picture of FeO-NG-A1 in embodiment 4;

Figure 12 is a cross-current charge-discharge diagram of FeO-NG-A1 in Example 4;

Fig. 13 is the scanning electron microscope picture of FeO-NG-B1 in embodiment 5;

14 is a cross-current charge-discharge diagram of FeO-NG-B1 in Example 5. FIG.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings, but it should be pointed out that the implementation of the present invention is not limited to the following embodiments.

Example 1

Using glutamic acid as the nitrogen source, 30 mg of GO was dissolved in 10 mL of deionized water to prepare a GO solution, dispersed by ultrasonic, and stirred uniformly for 2 h to form a GO suspension; FeCl ₃ 6H ₂ O (100 mg) and glutamic acid ( Acidic amino acid, 81 mg) was dissolved in 5 mL of deionized water and stirred continuously for 2 h to form a Fe-glutamic acid complex solution. After that, the above solution was added dropwise to the continuously stirred GO suspension and stirred uniformly to form a mixed solution. Then the mixture was sealed in a 25 mL high temperature and high pressure reactor, and placed in a constant temperature blast drying oven at 160 °C for constant temperature reaction for 12 h, with a heating rate of 5 °C/min. After the heat preservation, the reaction kettle was naturally cooled to room temperature. Subsequently, the obtained black hydrogel was washed with deionized water to obtain iron oxide/nitrogen-doped graphene ( _Fe2O3 /NG), and this sample was named _FeO -NG-A. The XRD pattern of FeO-NG-A (Fig. 1) shows that the diffraction peaks of the composite are consistent with a-Fe ₂ O ₃ (JCP DS no. 33-0664), confirming the existence of a-Fe ₂ O ₃ . From the SEM results (Fig. 2), it can be seen that the Fe ₂ O ₃ nanoparticles are in the shape of a fusiform, about 200 nm long and 100 nm wide (Fig. 2 left). right). The XPS results showed that the doped nitrogens were mainly pyridine nitrogen, pyrrolic nitrogen and graphitized nitrogen (Fig. 3). At a small current density of 1 A g ^-1 , the specific capacitance value of the material is 1060 F g ^-1 . (Figure 4).

Example 2

Using alanine (neutral amino acid) as the nitrogen source, changing the mass of the amino acid to 162 mg, and the same method as in Example 1, Fe ₂ O ₃ /NG was prepared, and the sample was named FeO-NG-N. The XRD pattern of FeO-NG-N is similar to _FeO -NG-A, confirming the presence of a- _Fe2O3 in the composite. From the SEM results (Fig. 5), it can be seen that the morphology of Fe ₂ O ₃ nanoparticles is nearly cubic and the overall sample is agglomerated (Fig. 5 left), NG in the composite is agglomerated (Fig. 5 right), and there is no cross-linked porous structure. Thermogravimetric results showed an iron oxide content of 43% (Figure 6). At a current density of 1 A g ^-1 , the material has a specific capacitance value of 860 F g ^-1 (Fig. 7).

Example 3

Using histidine (basic amino acid) as the nitrogen source, changing the hydrothermal temperature to 120 ^o C, and adjusting the same method as in Example 1 to prepare Fe ₂ O ₃ /NG, this sample was named FeO-NG-B. The XRD pattern of FeO-NG-B is similar to _FeO -NG-A, confirming the presence of a- _Fe2O3 in the composite. From the SEM results (Fig. 8), it can be seen that the morphology of Fe ₂ O ₃ nanoparticles is nearly cubic and the whole sample is agglomerated (Fig. 8 left), and NG in the composite is seriously agglomerated (Fig. 8 right). Fig.9 Raman spectrum shows A _1g symmetry vibration (about 219 cm ^-1 ) and E _g symmetry vibration (about 285 cm ^-1 ) of Fe ₂ O ₃ , and D peak of carbon material (about 1350 cm ^-1 ) also appears and the G peak of the degree of order (about 1580 cm ⁻¹ ), illustrating the presence _{of Fe2O3} and graphene in the composites. At a current density of 1 A g ^-1 , the material has a specific capacitance value of 770 F g ^-1 (Fig. 10).

Example 4

Use glutamic acid as nitrogen source (acidic amino acid) as nitrogen source, change the amount of FeCl ₃ 6H ₂ O to be 1 g, and adjust and prepare Fe ₂ O ₃ /NG in the same way as in Example 1, and name this sample as FeO- NG-A1. It can be seen from the SEM results that Fe ₂ O ₃ in the composite is seriously agglomerated (Fig. 11) and separated from nitrogen-doped graphene, which may be due to the excessive addition of FeCl ₃ •6H ₂ O. Capacitance performance tests show that the material has a specific capacitance value of 590 F g ^{-1 at a current density of 1 A g -1 (} Figure 12). The capacitance of the material is relatively small, which is related to the excessive addition of FeCl ₃ •6H ₂ O, and the Fe ₂ O ₃ in the composite is seriously agglomerated and separated from the nitrogen-doped graphene, which reduces the conductivity of the material and reduces the composite's performance. Capacitive performance.

Example 5

Using histidine (basic amino acid) as the nitrogen source, changing the hydrothermal temperature to 270 ^o C, and adjusting the same method as in Example 1 to prepare Fe ₂ O ₃ /NG, this sample was named FeO-NG-B1. From the SEM results, it can be seen that the nitrogen-doped graphene in the composite is seriously agglomerated (Fig. 13), and Fe ₂ O ₃ is wrapped by the agglomerated graphene, which may be caused by the excessive addition of hydrothermal temperature. The reduction degree of graphene oxide increases, the oxygen-containing functional groups decrease, and the repulsive force between the lamellae decreases. Capacitance performance tests show that the material has a specific capacitance value of 569 F g ^{-1 at a current density of 1 A g -1 (} Figure 14). The capacitance of the material is relatively small, which is related to the excessive hydrothermal temperature, and the reduction degree of nitrogen-doped graphene increases at high temperature, and the agglomeration is serious, which reduces the capacitance performance of the composite.

Comparative ratio:

Wang (J. Phys. Chem. C 2014, 118, 31, 17231-17239.) et al. used ammonia water as a nitrogen source to prepare random Fe ₂ O ₃ nitrogen-doped graphene composites. See loose porous structure, the specific capacitance of the composite is 618 F g ^-1 (0.5A g ^-1 ). Ren (Journal of Alloys and Compounds, 2014, 604, 87-93.) et al. prepared 20–100 nm Fe ₂ O ₃ particle nitrogen-doped graphene composites using hydrazine hydrate and urea as nitrogen sources, and nitrogen-doped graphite There is no loose porous structure in the olefin, and the specific capacity of the composite is 260.1 F g ^-1 (2 A g ^-1 ).

The above examples 1-3 show that the composites of Fe ₂ O ₃ and nitrogen-doped graphene with different morphologies can be prepared by changing the feeding ratio and the reaction temperature. The nitrogen in the material exists in the form of pyridine nitrogen, pyrrolic nitrogen and graphitized nitrogen, and the nitrogen in the material exists in the form of pyridine nitrogen, pyrrolic nitrogen and graphitized nitrogen, and the content of iron oxide can reach 43%. In Example 1, Example 2 and Example 3, composite materials with different doping ratios and different electrochemical properties can be obtained. The capacitance performance of the material is better than that of most reported iron oxide-based heteroatom-doped graphene materials (151-618 F g ^-1 ). The amount of nitrogen source added in Example 4 and the hydrothermal temperature in Example 5 exceeded the limited conditions of the present invention, and the morphology and specific capacitance of the prepared products were obviously poor. In the comparative example, the performance of materials prepared by using ammonia water, hydrazine hydrate and urea as nitrogen sources is worse.

Furthermore, amino acids with different acidity will affect the morphology of iron oxide and graphene structure, which may be due to the different complexation of amino acids with different acidity and Fe ions, and the different electrostatic interactions between GO. The three amino acids each have a different isoelectric point (pI) due to the difference in the R-group attached to the alpha carbon (glutamic acid (acidic), alanine (neutral), and histidine (basic). The isoelectric points of 3.22, 6.02 and 7.59). The pH value of the mixture solution before and after the reaction is about 5.1. Obviously, the pH of the mixed solution is higher than the isoelectric point of glutamic acid (pI value of 3.22), but lower than that of alanine (pI value of 6.02) and histidine (pI value of 6.02). 7.59). Therefore, in solution glutamic acid is negatively charged and the other two amino acids are positively charged. The electrostatic repulsion between negatively charged aspartic acid and negatively charged GO prevents the agglomeration between graphene sheets during hydrothermal reaction, forming FeO-NG-A composite with loose porous three-dimensional network structure Material. However, the negatively charged GO was attracted by the electrostatic interaction of positively charged glycine or lysine, which weakened the electrostatic repulsion and narrowed the distance of the monolayer, finally resulting in FeO-NG-N and FeO-NG- Agglomeration of composite materials such as B.

At the same time, there is coordination-chelation of Fe ³⁺ and amino acids, and during the hydrothermal synthesis, the formed chelate is hydrolyzed to form FeOOH, which is further converted into Fe ₂ O ₃ nuclei, and then mainly the polymerization of nanocrystals and recrystallization to form _{Fe2O3 nanoparticles} with different morphologies. In the FeO-NG-A sample, the R group of the acidic amino acid contains a carbon-oxygen double bond (C=O) and is negatively charged (pH>pI) in the reaction solution, and the negatively charged glutamic acid promotes the The formation of Fe ₂ O ₃ nuclei may be due to acidic amino acids changing the growth rate of different crystal planes of Fe ₂ O ₃ nuclei, thereby changing the crystal planes to aggregate into initial nanocrystals, and finally assemble to form a fusiform Fe ₂ O ₃ Nanoparticles. In FeO-NG-N and FeO-NG-B samples, alanine and histidine are positively charged. During the formation of these _two complexes, amino acid coordination-chelation also changed the growth rate of different crystal faces _{of Fe2O3} , and finally formed approximately cubic _Fe2O3 nanoparticles.

Therefore, in Example 1, the capacitance performance of the material obtained by complexation with an acidic amino acid is the best, which can reach 1060 F g ^-1 .

Claims (8)

1. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material is characterized by comprising the following steps of: the method comprises the following steps:

1) dissolving amino acid in water, adding iron salt, and continuously stirring for 0.5-10 hours; mixing an amino acid coordinated iron salt solution with a graphene oxide aqueous solution with the concentration of 0.5-20 mg/mL, and keeping stirring, wherein the mass ratio of amino acid to GO is 1: 5-5: 1, and the mass ratio of iron salt to GO is 1: 2-20: 1;

2) putting the mixed solution into a reaction kettle, and carrying out high-temperature treatment in an oven at 100-250 ℃ for 2-24 hours, wherein the temperature rise speed is controlled at 2-10 ℃/min in the process;

3) and naturally cooling the reaction kettle, taking out the prepared hydrogel or black powder, and repeatedly washing the hydrogel or black powder with ethanol and distilled water to obtain the nitrogen-doped graphene-based iron oxide material.

2. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 1, which is characterized by comprising the following steps: the amino acid in the step 1) refers to one of glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine and histidine and derivatives thereof.

3. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 1, which is characterized by comprising the following steps: the amino acid in step 1) is an acidic amino acid.

4. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 3, characterized by comprising the following steps: the acidic amino acid is aspartic acid or glutamic acid.

5. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 1, which is characterized by comprising the following steps: in the step 1), the ferric salt is one of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric citrate, ferric acetylacetonate and ferrocene.

6. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 1, which is characterized by comprising the following steps: the graphene oxide aqueous solution in the step 1) is prepared by firstly preparing graphene oxide from natural crystalline flake graphite by a Hummer's method and then dissolving the graphene oxide in water.

7. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 1, which is characterized by comprising the following steps: step 1), dropwise adding an amino acid coordinated iron salt solution into a graphene oxide aqueous solution.

8. The green controllable preparation method of the nitrogen-doped graphene-based iron oxide supercapacitor material according to claim 1, which is characterized by comprising the following steps: the filling degree of the reaction kettle in the step 2) is less than or equal to 80 percent.

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