CN111210997B

CN111210997B - M for super capacitornOmPreparation method of @ BCCNFs composite material

Info

Publication number: CN111210997B
Application number: CN202010090185.5A
Authority: CN
Inventors: 王崇太; 华英杰; 刘嘉豪; 舒澜清; 马杭
Original assignee: Hainan Normal University
Current assignee: Hainan Normal University
Priority date: 2020-02-13
Filing date: 2020-02-13
Publication date: 2022-05-03
Anticipated expiration: 2040-02-13
Also published as: CN111210997A

Abstract

The invention discloses a super capacitor M_nO_mA process for preparing the composite material ' @ ' BCCNFs ' from the natural coconut water in Hainan province as nutritive liquid includes such steps as preparing the product of static metabolism fermentation of acetobacter xylinum, and directly coating the transition metal oxide (M) dispersed in nutritive liquid_nO_m) Colloidal particles, forming a gel (M) of bacterial cellulose-coated transition metal oxide colloidal particles_nO_m@ BC). The gel is subjected to freeze drying and high-temperature annealing treatment to obtain the composite material (M) with the coating structure of the bacterial cellulose carbon nanofiber-coated transition metal oxide nanoparticles_nO_m@ BCCNFs) and is applied in the field of supercapacitors.

Description

M for super capacitornOmPreparation method of @ BCCNFs composite material

Technical Field

The invention belongs to the technical field of materials, relates to a super capacitor electrode material, and particularly relates to a bacterial cellulose carbon material prepared by using natural coconut water as a nutrient solution.

Background

The super capacitor can be divided into two types according to different energy storage modes, one type is an Electric Double Layer Capacitor (EDLCs), and the super capacitor realizes energy storage through electric charges and an electric double layer formed on the surface of an electrode by electrolyte ions; the other type is a pseudo-capacitance capacitor which realizes energy storage through oxidation-reduction reaction of electroactive substances on the surface of an electrode. The electric quantity or electric energy stored by the pseudo capacitor is far larger than that of the electric double layer capacitor. At present, commercial super capacitors are mainly EDLCs capacitors, and the energy density of the capacitors is relatively low, so that the capacitors cannot meet the increasing production and living needs. Therefore, the development of a supercapacitor with high energy density is urgently required. To improve the energy density of the super capacitor, the key is to improve the specific capacitance of the electrode material and the working voltage of the device.

The electrode material of the super capacitor is mainly carbon material, metal oxide, conductive polymer and the like. The carbon material is an ideal electrode material of the double-electric-layer capacitor and has been widely applied to the super capacitor due to the advantages of good conductivity, large specific surface area, abundant sources, low cost and the like. Commonly used carbon materials include activated carbon, activated carbon fibers, carbon fibrils, carbon aerogels, carbon honeycombs, and the like. However, the theoretical specific capacitance of the carbon material is low, and the carbon material is often applied to asymmetric and hybrid supercapacitors.

The metal oxide stores electric energy (pseudo capacitance) through oxidation-reduction reaction, and the theoretical specific capacitance is higher. A commonly used metal oxide is Co₃O₄、NiO、MnO₂、CuO、Fe₂O₃And the like. However, metal oxides have poor conductivity and often need to be compounded with materials having good conductivity, such as carbon materials, to improve conductivity.

Bacterial Cellulose (BC) is a natural high molecular compound having a three-dimensional network space structure cross-linked with each other, and can be produced in large quantities by microbial fermentation. The bacterial cellulose carbon material obtained after carbonization of bacterial cellulose has the characteristics of porosity, high specific surface area, good electric conductivity, low density and the like.

Disclosure of Invention

The invention provides a method for preparing transition metal oxide M by microorganism in-situ fermentation technology_nO_mThe nanoparticles are wrapped in bacterial cellulose, and then the BCCNFs @ M is prepared by program temperature control carbonization_nO_mA composite material.

In order to achieve the purpose, the technical scheme of the invention is as follows: novel BCCNFs @ M_nO_mThe preparation method of the composite material comprises the steps of taking natural coconut water as nutrient solution, and directly coating transition metal oxide (M) dispersed in the nutrient solution by a product generated by static metabolic fermentation of acetobacter xylinum_nO_m) Colloidal particles, forming a gel (M) of bacterial cellulose-coated transition metal oxide colloidal particles_nO_m@ BC), the gel is subjected to freeze drying and high-temperature annealing treatment to obtain the novel (M) coating structure of the bacterial cellulose carbon nanofiber-coated transition metal oxide nano particle_nO_m@ BCCNFs).

The specific reaction step is coconut waterThe culture medium is cultured at 30 deg.C statically, and M dispersed in the culture solution is directly coated by bacterial cellulose three-dimensional network structure generated by microbial fermentation_nO_mNanoparticles to give M_nO_m@ BC primary product. The product is frozen and dried, and then carbonized at a certain heating rate and a set temperature to finally obtain the bacterial cellulose carbon nanofiber composite material M with a three-dimensional network structure_nO_m@BCCNFs。

Another object of the present invention is to provide M_nO_mApplication of the @ BCCNFs composite material in a supercapacitor.

The invention has the following beneficial effects:

(1) the most common coconut water in Hainan is used as a liquid culture medium, and the natural fermentation process of microorganisms is used for directly performing M_nO_mGrowing bacterial cellulose on the surface of the nano particle in situ, and preparing M by program temperature control carbonization_nO_m@ BCCNFs composite material. The preparation method of the material is an innovation, and the used raw materials are environment-friendly and non-toxic, so that a new idea is provided for commercial production.

(2) Using M_nO_mThe @ BCCNFs composite material has stronger circulation stability as a supercapacitor electrode material, and meanwhile, the specific capacitance is also obviously improved.

Drawings

FIG. 1 is a scanning electron micrograph of a material prepared according to the present invention; wherein: (a) BCCNFs; (b) (c) Fe₃O₄@ BCCNFs composite;

FIG. 2 is Fe₃O₄The element analysis and distribution diagram of the @ BCCNFs composite material; wherein: (d) selecting a region; (e-g) are mapping graphs respectively representing the distribution of Fe, O and C elements; (h) fe₃O₄EDS energy spectrogram of @ BCCNFs composite material;

FIG. 3 is Fe₃O₄An electrode physical diagram of the @ BCCNFs composite material;

FIG. 4 is a plot of cyclic voltammetry of materials prepared in accordance with the present invention; wherein: (A) fe₃O₄@ BCCNFs composite material at different sweeping speedsCyclic voltammogram under; (B) fe₃O₄Cyclic voltammogram of @ BCCNFs composite material and pure BCCNFs at a sweep rate of 20 mV/s;

FIG. 5 is a constant current charge-discharge curve diagram of the material prepared by the present invention; wherein: (A) fe₃O₄The constant current charge-discharge curve diagram of the @ BCCNFs composite material under different current densities; (B) fe₃O₄A constant current charge-discharge curve chart of the @ BCCNFs composite material and pure BCCNFs at the current density of 1A/g;

FIG. 6 shows the charge-discharge cycle stability and AC impedance spectrum of the material prepared according to the present invention; wherein: (A) fe₃O₄@ BCCNFs composite material is in the range of 2 A.g^-1Cycling stability under current density conditions; (B) fe₃O₄The alternating current impedance spectrogram of the @ BCCNFs composite material and the pure BCCNFs;

FIG. 7 shows MnO₂Scanning electron microscope picture of @ BCCNFs composite material; wherein: (a) (b) MnO₂@ BCCNFs; (c) EDS element analysis;

FIG. 8 shows MnO₂BCCNFs and MnO₂XRD spectrogram of @ BCCNFs;

FIG. 9 shows MnO₂The cyclic voltammetry curve (A) and the charge-discharge curve (B) of the @ BCCNFs composite material.

Detailed Description

One, Fe₃O₄Preparation of @ BCCNFs electrode

1. Culture of acetic acid bacteria

Collecting acetic acid bacteria culture medium (containing polyprotein 5g, yeast extract 5g, glucose 5g, mannitol 5g, and MgSO 5g₄O₇H₂O1 g and pH 6.6-7.0)21g into 1000mL of distilled water, autoclaving at 121 deg.C for 15min to obtain acetic acid bacteria culture solution, and cooling to room temperature. Under aseptic operation, the acetobacter xylinum strain is inoculated into the culture solution, and cultured for 7 days at 30 ℃ to obtain a mother solution of acetobacter xylinum which is propagated and grown in a large quantity.

2.Fe₃O₄Preparation of @ BCCNFs electrode material

0.8g FeCl was weighed₃.6H₂Adding O into 4mL of distilled water, dissolving, adding 20mL of boiling water dropwise, and standing for 2minNaturally cooling to obtain ferric hydroxide colloid.

Purchasing fresh green coconut on the market, and carrying out suction filtration to obtain coconut water. Placing 0.6mL ferric hydroxide colloid and 30 mL purified coconut water in a culture bottle, sterilizing at 121 deg.C for 15min, inoculating 5mL Acetobacter xylinum mother liquor into the culture bottle under aseptic condition, and culturing in 30 deg.C incubator for seven days to obtain Fe₃O₄@ BC bacterial cellulosic material. Taking out the material, repeatedly washing with deionized water, soaking in deionized water for two days, and freeze drying for 24 hr. Freeze-drying the obtained Fe₃O₄@ BC bacterial cellulose Material at 2 ℃. min under Nitrogen atmosphere^-1The temperature is raised to 500 ℃ at a speed, and then the temperature is kept for 1 h; then at 5 ℃ for min^-1The temperature is raised to 700 ℃, and then the temperature is kept for 2 hours, thus obtaining the Bacterial Cellulose Carbon Nanofiber (BCCNFs) coated Fe₃O₄Composite carbon material Fe₃O₄@ BCCNFs. Preparation method of pure BCCNFs material and Fe₃O₄@ BCCNFs, except that no iron hydroxide colloid is added during the preparation process.

3.Fe₃O₄Preparation of @ BCCNFs electrode

Taking the grinded Fe₃O₄Mixing the @ BCCNFs composite material, acetylene black and PTFE emulsion with a proper amount of absolute ethyl alcohol according to a mass ratio of 80:15:5, grinding into a film with the size of 1cm multiplied by 1cm, attaching the film to a foamed nickel current collector, tabletting by using a powder tabletting machine under the pressure of 4MPa, and drying in a vacuum drying oven at 60 ℃ for 24 hours.

II, Fe₃O₄Characterization of the @ BCCNFs electrode

Fe prepared by the invention₃O₄The @ BCCNFs electrode is uniform and dense, and the microstructure is shown in FIG. 1. FIG. 1(a) is a scanning electron microscope image of pure bacterial cellulose carbon nanofibers obtained by using coconut water as a liquid medium, performing static fermentation culture, performing freeze drying, calcining at 500 ℃ for 1 hour under nitrogen atmosphere, and continuously heating to 700 ℃ for calcining for 2 hours. FIG. 1(b) and (c) shows the bacterial cellulose carbon nanofiber composite obtained by adding ferric hydroxide colloid into a culture medium, fermenting and calcining by acetobacter xylinumScanning electron micrographs of the material. The diameter of the bacterial cellulose carbon nano-fiber is 10-20nm, the bacterial cellulose carbon nano-fiber and the bacterial cellulose carbon nano-fiber are mutually crosslinked to form a three-dimensional network structure, and the diameter of the bacterial cellulose carbon nano-fiber is 200-300nm of Fe₃O₄The particles are encapsulated in a fibrous network.

The elemental distributions of FIG. 2(e-g) and the EDS spectroscopy analysis of (h) demonstrate that the composite material is composed primarily of Fe, O, C elements. Dehydrating ferric hydroxide colloid at high temperature to generate ferric oxide, calcining bacterial cellulose carbon nanofiber at high temperature under nitrogen atmosphere to form graphite carbon, and reacting graphite carbon with ferric oxide to finally obtain Fe₃O₄The @ BCCNFs composite material has the following reaction formula:

the ferric hydroxide colloid particles can stably exist in the culture solution for a long time, so that the problem that the metal oxide particles are easy to settle in the microbial culture process can be avoided, and the metal oxide particles can be completely coated by the bacterial cellulose. FIG. 3 is a graph showing the use of Fe₃O₄An electrode picture made of the @ BCCNFs composite material. III, Fe₃O₄Electrochemical performance of @ BCCNFs composite material

Fig. 4, 5 and 6 are electrochemical performance test results of the prepared materials. The test procedure used a 3-electrode system. Fe₃O₄The @ BCCNFs composite material and the pure BCCNFs electrode are respectively a working electrode, a platinum sheet is a counter electrode, a saturated calomel electrode is a reference electrode, a potential window is-1-0V, and the electrolyte is 6 mol. L^-1KOH solution. FIG. 4(A) shows Fe₃O₄The cyclic voltammetry scans of the @ BCCNFs at different sweep rates are similar to rectangles, and the areas of the cyclic voltammetry scans are increased along with the increase of the sweep rate, but the shapes of the cyclic voltammetry scans are basically kept unchanged, so that the cyclic voltammetry scans show typical capacitance characteristics. Thus, Fe₃O₄@ BCCNFs andpure bccnf is a capacitive type material like fig. 4 (B). FIG. 5(A) shows Fe₃O₄@ BCCNFs constant current charge-discharge curves at different current densities. According to the constant current charging and discharging curve and the following formula

Wherein I is a current (A), Δ t is a discharge time(s), m is a mass (g) of the electrode active material, and Δ V is a potential window (V) of charge and discharge. Calculating to obtain Fe₃O₄@ BCCNFs composites at 1, 2 and 5A · g^-1Specific capacitances at current densities of 215.3, 123.6 and 97.2 Fg^-1. Under the same conditions (1A · g)^-1) The specific capacitance of BCCNFs is only 130.4F g^-1(FIG. 5B). It can be seen that BCCNFs and Fe₃O₄After recombination, the specific capacitance is from 130.4 F.g^-1Increased to 215.3 F.g^-1(1A·g^-1) The effect is obvious by increasing 65 percent, which is Fe₃O₄The pseudocapacitance contribution of (a).

The cycling stability is another important index for measuring the performance of the electrode material of the supercapacitor. FIG. 6(A) is Fe₃O₄@ BCCNFs electrode material is 2 A.g^-1The specific capacitance change curve of 500 charge-discharge cycles at the current density of (2). As can be seen from the figure, after 500 times of charge and discharge, Fe₃O₄The specific capacitance of the @ BCCNFs electrode material still keeps 99.4% of the initial value, and the good stability is shown. Electrochemical impedance spectroscopy measurement shows that Fe₃O₄The interface electron transfer resistance of the @ BCCNFs electrode is small, about 0.215 Ω (fig. 6 (B)), and the charge and discharge process is controlled by the diffusion of electrolyte ions.

Applying the above method to MnO₂Nanoparticles, likewise giving MnO₂@ BCCNFs composite, as shown in FIG. 7. FIG. 8 shows the results of XRD measurements, which also demonstrates that the material produced is MnO₂@ BCCNFs. The cyclic voltammetry test result shows that MnO₂@ BCCNFs electrode Cyclic voltammogram and Fe at different sweep rates₃O₄In a quasi-rectangular shape like @ BCCNFs (FIG. 9 (A)), indicating MnO₂@ BCCNFs also belong to capacitive materials. The specific capacitance values of the materials obtained by calculation based on the constant current charging and discharging curves (FIG. 9 (B)) and the above formula (1) are shown in Table 1. As can be seen from the table, (1A. g) under the same conditions^-1)，MnO₂Specific capacitance of @ BCCNFs composite material (206.6F g)^-1) And pure BCCNFs (130.4F g)^-1) Compared with the prior art, the method is also obviously improved. Thus, the method of the invention for preparing bacterial cellulose carbon nanofiber composites for energy storage applications can be extended to all transition metal oxides M_nO_m。

TABLE 1 MnO₂Specific capacitance value of @ BCCNFs composite material under different current densities

Claims

1. M for super capacitor_nO_mThe preparation method of the @ BCCNFs composite material is characterized by comprising the following steps of: taking natural coconut water as nutrient solution, and directly coating transition metal oxide M dispersed in the nutrient solution by product generated by static metabolic fermentation of acetobacter xylinum_nO_mColloidal particles, forming a gel M of bacterial cellulose-coated transition metal oxide colloidal particles_nO_m@ BC, the gel is subjected to freeze drying and high-temperature annealing treatment to obtain a coating structure M of the bacterial cellulose carbon nanofiber-coated transition metal oxide nano particles_nO_m@ BCCNFs composite; the M is_nO_mIs Fe₃O₄Or MnO₂。