KR101418864B1

KR101418864B1 - Carbon nanoplates using silk proteins and the manufacturing method

Info

Publication number: KR101418864B1
Application number: KR1020120100349A
Authority: KR
Inventors: 진형준; 윤영수
Original assignee: 인하대학교 산학협력단
Priority date: 2012-09-11
Filing date: 2012-09-11
Publication date: 2014-07-17
Also published as: KR20140044965A

Abstract

The present invention relates to a carbon nanoplate produced by using a silk protein and a method for producing the same. More particularly, the present invention relates to a carbon nanoplate prepared by mixing a regenerated silk fibroin solution obtained by dissolving sericin-removed regenerated silk fibroin in a silk protein and an alkaline activator To a carbon nanoplate that can be used for a supercapacitor electrode that can improve the low energy density of a super capacitor by carbonizing the film, and a manufacturing method thereof.
According to the present invention, since the activation of the regenerated silk fibroin and the alkali activating agent caused by the activation of the alkali activating agent during the carbonization process of the film, the large surface area of the H-CMNs is generated and the micropores It has a structural advantage and a pore distribution which is favorable for bilayer formation. In addition, the increase in intrinsic capacitance due to the superior electrical characteristics and the pseudop capacitive action due to the many hetero atoms bonded to the carbon material and the polarity improves the energy density while maintaining the high power density and cycle stability of the supercapacitor You have a useful effect.

Description

TECHNICAL FIELD [0001] The present invention relates to carbon nanoparticles prepared by using silk protein,

The present invention relates to a carbon nanoplate produced by using a silk protein and a method for producing the same. More particularly, the present invention relates to a carbon nanoplate prepared by mixing a regenerated silk fibroin solution obtained by dissolving sericin-removed regenerated silk fibroin in a silk protein and an alkaline activator To a carbon nanoplate that can be used for a supercapacitor electrode that can improve the low energy density of a super capacitor by carbonizing the film, and a manufacturing method thereof.

Supercapacitors, also known as electrochemical capacitors or supercapacitors, have received much attention due to their high power, excellent reversibility, and long cycle life. Supercapacitors replace or supplement batteries in a variety of energy storage applications, such as uninterruptible power supplies used in electric vehicles, mobile phones, and computers, because of their ability to discharge and absorb high power (10 kW / kg) for short periods of time It has played an important role. However, since the energy density (about 5Wh / kg) of the super capacitor is lower than that of the battery, there is a limitation in use in the above-mentioned fields. Therefore, it is necessary to develop a supercapacitor with improved energy density while maintaining high power density and periodic stability .

In order to improve the low energy density of the super capacitor, Korean Patent Registration No. 10-0894481 (an electrode for a supercapacitor composed of a metal oxide accumulated in ultrafine carbon fibers and a manufacturing method thereof) is characterized in that a super-fine carbon having a high specific surface area and a high electric conductivity There is provided an electrode for a supercapacitor and a method of manufacturing the same, which can maintain a high specific capacity even at a high rate of charge / discharge by electrochemically accumulating a metal oxide thin film capable of oxidation / reduction reaction on the substrate, Japanese Patent Application No. 10-1079317 (a method for producing a graphene electrode for a supercapacitor and a graphene electrode for a supercapacitor produced thereby) is a method for producing a graphene electrode for a capacitor, which comprises graphene powder, conductive material, molasses, polytetrafluoroethylene, A graphite electrode for a supercapacitor that has a higher specific capacity than conventional activated carbon by using a mixture Of the present invention.

Super capacitors are defined in two categories according to the energy storage mechanism. First, electric double-layer capacitors (EDLC) generate capacitance from the static charge accumulated at the interface between the electrode and the electrolyte. The electrode material of such an electric double layer capacitor requires large surface area and pore size of ion size . Second, as a pseudo capacitor, a rapid and reversible Faraday process occurs due to electroactive species, and metal oxides such as RuO ₂ or MnO ₂ and electroconductive polymers have been used to increase intrinsic capacitance through a pseudo-capacitive redox reaction. However, due to low cycle stability, low electrical conductivity, and high cost, practical use of pseudop capacitors is limited. Thus, the present inventors have sought to develop EDLC-based materials with a pseudosaccharide effect.

The maximum power density of the supercapacitor is given by P _max = V _i ² / (4R) where V _i is the initial voltage and R is the equivalent series resistance (ESR) value. The resistance of these electrodes is a major factor in determining the output of the supercapacitor. In addition, given the maximum storage energy (energy storage) is the CV _i ^2/2 where C means the capacitance. Therefore, maximizing the capacitance of the electrode is a key factor for improving the energy density.

Silk produced from cocoons of Bombyx mori is one of nature's most abundant polymers. The silk is made up of sericin, a protein that binds and coats the fiber proteins fibroin and fibroin. The silk protein usually means fibroin. Silk fibroin is made of recycled silk fibroin, which is a new material through dissolution of water-soluble sericin. The cast film obtained by swelling several layers of regenerated silk fibroin has a thickness of 100 nm or less per layer. These results show that carbonization of recycled silk fibroin can produce new carbon-based nanoplates.

It is an object of the present invention to provide novel carbon-based microporous nanoplates (H-CMNs) containing a large number of heteroatoms through the activation process using regenerated silk fibroin carbonization and an alkaline activator, Based material having a pseudopotential effect that can be utilized for electrodes of supercapacitors that have superior electrochemical performance with high energy and power density, unlike super capacitors with limited capillary capacitances.

In order to achieve the above object, the present invention is characterized in that an alkaline activator is added to an aqueous solution of regenerated silk fibroin in which regenerated silk fibroin from which sericin has been removed from a silk protein is dissolved to form a film, and the film is carbonized Carbon nanoplate.

The regenerated silk fibroin aqueous solution is prepared by dissolving regenerated silk fibroin in a mixed solution of LiBr, LiSCN (lithium thiocyanate) or N-methylmorpholine N-oxide, CaCl ₂ / H ₂ O / ethanol or Ca (NO ₃ ) ₂ / .

The alkaline activator may be one selected from the group consisting of KOH, NaOH, and LiOH.

The formed film is characterized in that the weight ratio of the regenerated silk fibroin and the alkaline activator is 0.1 to 10.

The film is characterized by carbonization at 400 to 2500 ° C for 1 to 24 hours.

Further, the present invention provides a method for producing regenerated silk fibroin, comprising the steps of: (1) removing sericin, which is a protein having adhesive and coating functions, from silk extracted from a cocoon of silkworm (Bombyx mori) (2) dissolving the regenerated silk fibroin prepared in the step (1) to prepare a regenerated silk fibroin aqueous solution; (3) adding an alkaline activator to the aqueous solution of regenerated silk fibroin prepared in the step (2) to produce a film; And (4) carbonizing the film produced by the step (3); The present invention also provides a method for producing a carbon nanoplate.

In the step (1), the regenerated silk fibroin is produced by heat-treating the silkworm cocoons in boiling Na ₂ CO ₃ aqueous solution for 20 to 30 minutes to remove sericin and refining.

The 2 reproduction silk fibroin aqueous solution in step is playing a silk fibroin in 15 to 25 ℃ LiBr, LiSCN (lithium thiocyanate ) or N-methylmorpholine N-oxide _{solution, CaCl 2 / H 2 O /} ethanol or Ca (NO ₃₎ ₂ / methanol mixed solution and dialyzed in water for 24 to 96 hours.

The aqueous solution of the regenerated silk fibroin prepared in the step (2) is characterized by a concentration of 0.01 to 23 wt%.

In the step (3), one kind selected from alkaline activators including KOH, NaOH, and LiOH is added to the aqueous solution of regenerated silk fibroin, and the mixture is stirred for 20 to 40 minutes and cast, To 200 < 0 > C for 24 to 80 hours.

In the step (3), the weight ratio of the regenerated silk fibroin and the alkaline activator is 0.1-10.

In the step (4), the film is carbonized at 400 to 2500 ° C for 1 to 24 hours.

According to the present invention, since the activation of the regenerated silk fibroin and the alkali activating agent caused by the activation of the alkali activating agent during the carbonization process of the film, the large surface area of the H-CMNs is generated and the micropores It has a structural advantage and a pore distribution which is favorable for bilayer formation. In addition, the increase in intrinsic capacitance due to the superior electrical characteristics and the pseudop capacitive action due to the many hetero atoms bonded to the carbon material and the polarity improves the energy density while maintaining the high power density and cycle stability of the supercapacitor You have a useful effect.

FIG. 1 (a) shows the production process of H-CMNs, (b) FE-TEM image of H-CMNs observed on a porous carbon grid, and (c) FE of H-CMNs observed on alumina template membranes -SEM image.
FIG. 2 shows a schematic model in which a silk fibroin of a silkworm forms a lamellar-like layer by self-assembly in water, and a shows an SEM image of a regenerated silk fibroin film heat-treated at 200.degree.
FIG. 3 shows the spectrum of the regenerated silk fibroin film by Fourier transform infrared spectroscopy (FT-IR), the red line shows the film not heat-treated, and the green line shows the film heat-treated at 200 ° C.
Figure 4 shows a TEM image of a carbon-based nanoplate peeled from a carbonized regenerated silk fibroin film.
FIG. 5 (a) is a surface precision photograph of the H-CMNs observed through an atomic force microscope (AFM), b is a graph in which the contents in a white dotted line are enlarged in a photograph, c is a Raman spectrum of H-CMNs, d Shows the nitrogen adsorption-desorption isotherm curves and pore distribution of H-CMNs with a 1: 1 weight ratio of regenerated silk fibroin and KOH and e shows the distribution of micropores of H-CMNs with a 1: 1 weight ratio of regenerated silk fibroin and KOH .
Figure 6 shows the nitrogen adsorption-desorption isotherms of H-CMNs with a weight ratio of regenerated silk fibroin to KOH of (a) 1: 0.5 (b) 1: 0.8 (c) 1:
Figure 7 shows the pore distribution of H-CMNs with a weight ratio of regenerated silk fibroin to KOH of (a) 1: 0.5 (b) 1: 0.8 (c) 1: 2.
Figure 8 shows the micropore distribution of H-CMNs with a weight ratio of regenerated silk fibroin to KOH of (a) 1: 0.5 (b) 1: 0.8 (c) 1:
9 (a) to 9 (c) show measurement results of X-ray photoelectron spectroscopy (XPS) of H-CMNs, d shows results of measurement by X-ray diffractometer (XRD) of H- The voltage (IV) curve and f show the resistance ( rho (T)) obtained from the current-voltage (IV) curve with temperature. e shows the AFM image of H-CMNs with a scale bar of 2 μm and a sample size of 3778 nm × 1000 nm × 35 nm, and the graph inserted in f shows a jump in two-dimensional various positions (Two-dimensional variable range hopping).
FIG. 10 shows two-dimensional variable range hopping at various positions measured by the 4-probe method. The image inserted in a shows the optical microscope image of the sample.
FIG. 11A is a cyclic voltammogram of BM-BF ₄ / AN electrolyte of H-CMNs, and b is a cyclic volt-ampere diagram of a 1 molar aqueous sulfuric acid electrolyte of H-CMNs C is the Nyquist plot in the frequency range of 100 kHz to 0.1 Hz of the H-CMNs and d is the non-accumulating capacity according to the various current densities measured in the organic and aqueous electrolytes specific capacitance. The black squares in c and d represent the BMIM BF ₄ / AN electrolyte and the red circle represents 1 mole of sulfuric acid aqueous electrolyte. The plot inserted in d represents the capacitance retention according to the number of cycles.
12 shows the energy density and power density of H-CMNs based on a supercapacitor of BMIM BF ₄ / AN electrolyte (black squares) and 1 mol of sulfuric acid aqueous electrolyte (red circle) Lt; / RTI >

Hereinafter, the present invention will be described in detail.

The novel carbon-based microporous nano-plates comprising a number of heteroatoms made through the carbonization process of the regenerated silk fibroin-alkaline activator film in the present invention are referred to as H-CMNs.

The present invention provides a carbon nanoplate characterized in that an alkaline activator is added to an aqueous solution of regenerated silk fibroin in which regenerated silk fibroin having sericin removed from silk protein is dissolved to form a film, and the film is carbonized.

The regenerated silk fibroin aqueous solution is prepared by dissolving regenerated silk fibroin in an aqueous solution of LiBr, LiSCN (lithium thiocyanate) or N-methylmorpholine N-oxide, CaCl ₂ / H ₂ O / ethanol or Ca (NO ₃ ) ₂ / methanol And the amount of regenerated silk fibroin which can be dissolved when the concentration of the solvent for dissolving the regenerated silk fibroin is low, so that the concentration of the solvent is preferably 1 to 10.0M. In addition, the mixing ratio of CaCl ₂ / H ₂ O / ethanol is preferably 1: 8: 2 M.

The alkaline activator is preferably one selected from the group consisting of KOH, NaOH, and LiOH.

The formed film has an optimum effect when the weight ratio of the regenerated silk fibroin and the alkaline activator is 0.1 to 10, preferably 0.5 to 3. The weight ratio of the alkaline activator to the regenerated silk fibroin used for activation affects the intrinsic surface area of H-CMNs. When the weight ratio of regenerated silk fibroin to alkaline activator is 1, the highest surface area is obtained. As the amount of activator increases, the ratio of micropores to heavy metals increases. However, too much of the activator has a negative effect on the formation of micropores.

Activation by an alkaline activator that produces a rough surface results in more surface area and needle-like micropores than in the activation method by steam. This is an important factor that has many advantages in charge accumulation, and these micropores and rough surfaces have the effect of reducing the phenomenon of restacking the nanoparticles and thus having a wide electrochemical interface between the electrodes and the electrolyte.

The film is preferably carbonized at 400 to 2500 ° C, preferably 800 to 900 ° C, for 1 to 24 hours, preferably 2 to 4 hours.

In the step (1), the regenerated silk fibroin can be prepared by heat treating the silkworm cocoons in boiling Na ₂ CO ₃ aqueous solution for 20 to 30 minutes to remove sericin and refining.

The 2 reproduction silk fibroin aqueous solution in step is playing a silk fibroin in 15 to 25 ℃ LiBr, LiSCN (lithium thiocyanate ) or N-methylmorpholine N-oxide _{solution, CaCl 2 / H 2 O /} ethanol or Ca (NO ₃₎ ₂ / methanol mixed solution, and dialyzed in water for 24 to 96 hours. When the concentration of the solvent for dissolving the regenerated silk fibroin is low, the amount of regenerated silk fibroin that can be dissolved decreases, 1 to 10.0M. In addition, the mixing ratio of CaCl ₂ / H ₂ O / ethanol is preferably 1: 8: 2 M.

The regenerated silk fibroin aqueous solution prepared in the step (2) has an optimum concentration of 0.01 to 23 wt%, preferably 7 to 8 wt%.

In the step (3), one kind selected from alkaline activators including KOH, NaOH, and LiOH is added to the aqueous solution of regenerated silk fibroin, and the mixture is stirred for 20 to 40 minutes and cast, To < RTI ID = 0.0 > 200 C < / RTI > for 24 to 80 hours.

In the step (3), the optimum effect is obtained when the weight ratio of the regenerated silk fibroin and the alkaline activator is 0.1 to 10, preferably 0.5 to 3.

In the step (4), the film is preferably carbonized at 400 to 2500 ° C, preferably 800 to 900 ° C for 1 to 24 hours, preferably 2 to 4 hours.

The energy density (133 Wh / kg) of the new carbon-based microporous nanoplates (H-CMNs) containing many heteroatoms according to the present invention is comparable to that of lithium-ion batteries and the output density (217 kW / kg) It is several times higher than the battery. These results are due to the excellent electrical properties and high capacitance of H-CMNs, and the capacitor cells using H-CMNs are very stable even in repetitive cycles. In addition, H-CMNs have excellent electrochemical performance, such as an intrinsic capacitance of 264 F / g in aqueous electrolyte and a stable life after 10,000 cycles or more, and a high electrical conductivity value of 1.15 × 10 ⁴ S / m at 300K. This high electrical conductivity indicates that the H-CMNs are good current collectors with low contact resistance.

There are several reasons why the capacitance of H-CMNs is excellent. First, H-CMNs have a large number of open micropores 5 to 8 Å in diameter on the surface, and these properties are very effective for bilayer formation. Second, electroactive heteroatoms such as 5.1 wt% nitrogen and 10.7 wt% oxygen cause pseudocapacitor behavior and improve the polarity of H-CMNs. The functional groups on the surface created by the heteroatoms are usefully used to form excellent performance electrodes with excellent supercapacitance due to faradaic reaction and improved wettability due to the increase of hydrophilic polarity sites. Third, the large surface area of 2553.3 m ² / g of H-CMNs, rough surface, and microporous structure prevents restacking of the nanoplate and is advantageous for forming a contact surface in the electrolyte, increasing the electrochemical interface .

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

Examples. Preparation of H-CMNs

The silkworm silk fibroin was prepared by boiling the silkworm silkworm in an aqueous solution of sodium carbonate (OCI company, 99%, 0.02M) for 30 minutes, then washing the sericin with adhesive and coating function several times with water. The reconstituted silk fibroin was dissolved in an aqueous solution of 9.3 M lithium bromide (Sigma-Aldrich, ≥99%) at room temperature to prepare a 20 wt% aqueous solution of regenerated silk fibroin. Slide-a-Lyzer dialysis cassettes (Pierce, MWCO 3500) And the solution was dialyzed in water for 48 hours so that the concentration of the aqueous solution of the final regenerated silk fibroin was 7.0 to 8.0 wt%.

Various amounts of KOH (4, 6.4, 8 and 16 g) were added to the prepared aqueous solution of 100 g of regenerated silk fibroin and stirred for 30 minutes before casting into a Teflon dish. The cast solution was dried at 120 DEG C for 3 days to prepare a regenerated silk fibroin-KOH film.

The thus-prepared regenerated silk fibroin-KOH film was heated at a rate of 5 ° C / min from room temperature to 800 ° C at an injection rate of 200 ml / min in an argon atmosphere, and then carbonized at a constant temperature for 3 hours to produce H-CMNs. The carbonized H-CMNs were washed several times with distilled water and ethanol (OCI company, 99.9%) and then dried in a vacuum oven at 30 ° C to produce H-CMNs having a thickness of less than 100 nm and a lateral size of 5 μm or more, Used in examples.

Experimental Example 1. Characterization of H-CMNs

(TEM, CM200, Philips, USA), scanning electron microscope (FESEM, S-4300, Hitachi, Japan) equipped with energy dispersive X-ray and atomic force microscope (AFM, Digital Instrument Nanoscope IVA) was used. The porosity characteristics of H-CMNs were analyzed by nitrogen adsorption-desorption isotherm at -196 ° C obtained with a surface area and porosity analyzer (ASAP 2020, Micromeritics, USA). BET surface area (S _BET ) was measured by Barrett-Johner-Halendar theory.

The X-ray diffraction (XRD, Rigaku DMAX 2500) analysis of H-CMNs was carried out using copper Kα radiation (frequency λ = 0.154 nm) at 40 kV, 100 mA and EA1112 (CE instrument, Italy) And X-ray photoelectron spectroscopy (XPS, PHI 5700 ESCA) analysis was performed under the condition of monochromated aluminum Kα radiation (hv = 1486.6 eV). A commercially available cantilever, NSG-10 (NT-MDT, Russia), was used in the semi-contact mode of an atomic force microscope (AFM).

In Raman spectroscopy, a 473 nm (2.62 eV) continuous wave linear polarization laser, a 50 μm pinhole, and a 600 grrooves / mm diffraction grating were used and a low power laser (<300 μW) was used for nondestructive measurement.

As a result, as shown in FIG. 1, shiny carbon pieces obtained by carbonization of the cast recycled silk fibroin and H-CMNs having a flat nanoplate structure were confirmed. The H-CMNs prepared by this example contain many heteroatoms, such as nitrogen and oxygen, with a thickness less than 100 nm and a lateral dimension of greater than 5 micrometers.

In addition, the carbon-based nanoplates (H-CNs) into which the heteroatoms were introduced were peeled off from the carbon pieces by ultrasonic treatment in an organic solvent such as N-methylpyrrolidone, and the H-CMNs were removed from the cast regenerated silk fibroin- Carbonization process. The major difference between H-CNs and H-CMNs appears to be the result of this KOH treatment, which suggests that the KOH reaction takes place between the ₆ KOH + C ↔ 2 K + 3 H ₂ + ₂ K ₂ CO ₃ reaction followed by the decomposition of K ₂ CO ₃ Carbon and K / K ₂ CO ₃ / CO ₂ .

As shown in FIGS. 2 and 3, the cast regenerated silk fibroin film having an amorphous irregular coil structure is subjected to thermal annealing at 200 DEG C exceeding the glass transition temperature to form a beta -sheet crystalline form The lamella structure of the lamella was analyzed. The secondary structure of the regenerated silk fibroin film subjected to thermal annealing at 200 ° C was confirmed by FTIR-ATR.

H-CMNs formed more surface area and needle-like micropores than the activation method by vapor by KOH-activated method of producing rough surface. This is an important factor that has many advantages in charge accumulation. The BET (Brunauer-Emmett-Teller) specific surface area of H-CMNs is 2557.3m ² / g, which is similar to the theoretical surface area of pure graphene sheet. The surface area of H-CNs is 30m ² / I did. As shown in Figure 5-c, the D, G and 2D peaks were at 1361, 1600 and 2746 cm ^-1 , respectively. These D / G ratios (~ 1) and 2D / G ratios (~0.17) are similar to the typical values of graphene oxide nanoplates. The nitrogen adsorption-desorption isotherm curve in FIG. 5-d shows the structure of the type-I micropores defined by IUPAC, and the diameter of the formed micropores was 4 nm or less and most of the medium holes had a diameter of several nanometers. Particularly, as shown in FIG. 5-e, most of the micropores had a size of 5 to 8 Å which is effective for bilayer formation. These micropores and rough surfaces appear to cause the nanoplate to have a broad electrochemical interface between the electrode and the electrolyte, reducing restacking effects.

In the XPS C 1s spectrum of the H-CMNs of FIG. 9, a pronounced peak of C (O) O at 285.8 eV and a pronounced peak of C (O) O at 284.6 eV were found at C-O, C-N and 288.7 eV. Nitrogen atoms in H-CMNs are mostly formed by pyrrolic / pyridine groups, which appear as N 1s peaks appearing at the center of 400.0 eV. These peaks are the pyridine groups of the pentagonal rings at the edge of the graphene sheet It is found in nitrogen. In addition, the distinct peaks of 531.5 eV and 533.5 eV found in the O 1s spectrum appear to be present in a variety of functional groups including oxygen atoms present in the carbonyl group and other oxygen. It is believed that the functional groups on the surface generated by these heteroatoms are advantageous as an excellent electrode having excellent supercapacitance due to faradaic reaction and improved wettability due to increase of hydrophilic polarity sites.

The 2-theta values found in the vicinity of 22.5 ° and 43.8 ° in FIG. 9-d represent a hexagonal structure aligned with the layered carbon structure, respectively. The 2-theta value appears to be due to 100 planes resulting from the formation of aligned hexagonal carbon structures. In addition, a large increase in intensity at low-angle scatter appears to coincide with the presence of high-density micropores.

Experimental Example 2. Electrical Characterization of H-CMNs

The electrodes were patterned with VEGA MM5150 (with 30 keV filament, Tescan) electron beam lithography machine and deposited by ZZS550-2 / D e-gun evaporator (Maestech). The temperature-dependent current-voltage characteristics were measured using a semiconductor characterization instrument (4200-SCS, Keithley) and a Janis cryogenic system using a 2-probe method. Temperature resistance was measured at a current of 220 at Keithley's 182 nm Probe method using a voltmeter. The atomic force microscope (AFM) was a SPA-400 model of Seiko instrument.

A source-drain voltage of 500mV was used for the current-effect measurement, and H-CMNs were dispersed in ethanol and deposited on 300nm SiO2 / p-doped silicon wafers to obtain temperature-dependent resistance. Electrodes were made through standard electron beam lithography, evaporation of Ti / Au (5/50 nm), and lift off processes. The electrical properties of H-CMNs were measured after storage at room temperature in a vacuum overnight (over 12 hours).

As a result, the current-voltage (IV) characteristics measured by the conventional two-probe method from 20K to 300K as shown in Figs. 9E and 9F were symmetrical and linear in all the temperature ranges, ( ρ ( T )) increased with decreasing temperature, which seems to be due to the localized charge carriers of H-CMNs.

Variable-range hopping (VRH) at various locations is one of the conduction mechanisms of localized charge carriers. In a VRH model at various locations, the resistance ( ρ) has a relationship between temperature T and ρ = ρ ₀ exp (T ₀ / T) ^{1 / (D + 1)} , T ₀ is the localized energy- And D means dimension. The resistivity is proportional to T ^-1/3 in a two-dimensional system and the plot of ln ρ vs T ^-1/3 is proportional to 20K to 180K, which indicates that H-CMNs have a two-dimensional characteristic . As shown in Fig. 10, this behavior was also the same in the 4-probe method.

Also, it should be noted that the resistance at 300 K is 8.7 m? / Cm (the conductivity is 1.15 x 10 ⁴ S / m). These values are similar to those of high doping silicon and are lower than the metal oxide or graphene oxide used in supercapacitor cells. This high electrical conductivity indicates that the H-CMNs are good current collectors with low contact resistance.

Experimental Example 3. Electrochemical Characterization of H-CMNs

Previous polar cell structures were used to measure the performance of H-CMNs used as supercapacitor electrodes. 5 wt% of polytetrafluoroethylene (PTFE, Sigma-Aldrich, 60 wt% dispersion in H ₂ O) was used as a binder in the aqueous electrolyte and H-CMNs and PTFE were mixed in a paste bowl using a mortar , And a sheet having a constant thickness of 40 to 50 mu m was formed using a roller. The sheet thus formed was made into a circular electrode having a diameter of 1 cm by using a punch. In the non-aqueous electrolyte, the H-CMNs were mixed with 5 wt% poly-vinylidene fluoride to form a paste state, and the electrode was pressed in a thick slurry to an aluminum collector coated with conductive carbon made. Each electrode had a diameter of 1 cm and a thickness of 100 [mu] m, and the pair of electrodes had a weight of 2.5 to 3.0 mg after drying overnight at 100 [deg.] C. 1 mol of sulfuric acid aqueous solution (OCI company, 95%) was used as the aqueous electrolyte and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF _4, SigmaAldrich) was dissolved in acetonitrile (AN) at a ratio of 1: 1. A pair of electrodes and a porous polypropylene separator were sandwiched between (Whatman GF / D) stainless steel cells to assemble the previous polar cell. The entire process of assembling the cell was done in a glove box in an argon atmosphere, keeping oxygen and moisture below 1 ppm, respectively.

The electrochemical data were measured by circulating voltammetry, large time potential difference method and electrochemical impedance spectroscopy. Capacitance, energy density, and power density were measured by a constant current method. At a current range of 0.1 to 70 A / g, the potential between the electrodes was swept between the cutoff values (0-1 V for the aqueous electrolyte and 0-3.5 V for the non-aqueous electrolyte). 2.5 A / g was used for cycle testing in water and non-aqueous electrolytes.

As a result, as shown in FIG. 11, a typical rectangular capacitor behavior characteristic was observed at various voltage scanning rates of 0 to 3.5 V. In a 1 molar aqueous sulfuric acid electrolyte, a circulating voltage- In addition. These properties appear as a combination of electrical double layer formation and redox reaction and appear to be due to the action of heteroatoms present in the material.

In addition, the equivalent series resistance of the H-CMNs estimated at 448 Hz in the BMIM BF ₄ / AN electrolyte is 0.62 Ω, which is a much smaller value than 6.2 Ω measured in one molar aqueous sulfuric acid electrolyte, It is considered that the difference in series resistance occurs due to the ion resistance due to the movement of the electrolyte ion.

On the other hand, the curve in the electrolyte of 1 mol of sulfuric acid aqueous solution shows a semicircular shape in the high frequency region, which is indicated by the surface characteristics of the porous electrode and coincides with the charge transfer resistance of the induced current. Therefore, it was confirmed that the pseudo-capacitor behavior of heteroatoms such as nitrogen and oxygen occurred through the semicircular shape shown in the 1 molar aqueous sulfuric acid electrolyte, and the results were consistent with the circulating voltage-current chart shown in FIG.

The imaginary part of the impedance plot in the low frequency region showed the capacitance behavior. For an electric double-layer capacitor, the impedance plot should theoretically be vertical and parallel to the imaginary axis. Impedance plots in the BMIM BF ₄ / AN electrolyte follow the capacitance behavior, but not in the 1 molar aqueous sulfuric acid electrolyte. The intrinsic capacitance exhibited by the discharge curves of H-CMNs at a constant current of 0.1 A / g in an aqueous solution of sulfuric acid aqueous solution was 264 F / g, and the capacitance remained above 100 F / g even at 70 A / g, The intrinsic capacitance of H-CMNs when discharged under the condition of BMIM BF ₄ / AN electrolyte, 3.5 V operating voltage and 0.8 A / g constant current was 168 F / g (FIG. 11-d).

As shown in the graph in FIG. 11-d, the capacitance was 3.5% in the BMIM BF ₄ / AN electrolyte and 1 mol of sulfuric acid in the BMIM BF ₄ / AN electrolyte compared to the initial capacitance even after repeating 10000 constant current charging / discharging at a current density of 2.5 A / And 6.8% in aqueous electrolyte, confirming excellent cycle stability of H-CMNs.

Having described specific portions of the present invention in detail, it will be apparent to those skilled in the art that this specific description is only a preferred embodiment and that the scope of the present invention is not limited thereby. It will be obvious. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims

(1) removing sericin, which is a bonding and coating functioning protein, from silk extracted from a cocoon of silkworm (Bombyx mori) to prepare refined regenerated silk fibroin;
(2) The regenerated silk fibroin prepared in the step (1) is dissolved in a solvent LiBr, lithium thiocyanate (LiSCN) or N-methylmorpholine N-oxide aqueous solution having a concentration of 1 to 10 M at 15 to 25 ° C, CaCl ₂ / H ₂ O / ethanol or Ca (NO ₃ ) ₂ / methanol mixed solution to prepare an aqueous solution of regenerated silk fibroin;
(3) adding an alkaline activator selected from the group consisting of KOH, NaOH, and LiOH to the aqueous solution of regenerated silk fibroin prepared in the step (2) to produce a film; And
(4) carbonizing the film produced by the step (3) at 400 to 2500 ° C for 1 to 24 hours; Wherein the carbon nanofibers are produced by a method comprising the steps of:

The method according to claim 1,
In the step (1), the regenerated silk fibroin is prepared by heat treating the silkworm cocoons in a boiling Na ₂ CO ₃ aqueous solution for 20 to 30 minutes to remove sericin and refining the silk fibroin.

The method according to claim 1,
Wherein the aqueous solution of the regenerated silk fibroin prepared in the step (2) has a concentration of 0.01 to 23 wt%.

The method according to claim 1,
Wherein the weight ratio of the regenerated silk fibroin to the alkaline activator is 0.1 to 10 in the step (3).

The method according to claim 1,
In the step (3), the film is prepared by adding an alkaline activator to an aqueous solution of regenerated silk fibroin, stirring for 20 to 40 minutes and casting, and then drying the cast solution at 60 to 200 DEG C for 24 to 80 hours Wherein the carbon nanofibers are formed on the surface of the carbon nanofibers.

A supercapacitor employing the carbon nanoplate produced by the method of any one of claims 1 to 5.

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