KR101540357B1 - Au/metal oxide or hydroxide complex for supercapacitor and method for preparing same - Google Patents
Au/metal oxide or hydroxide complex for supercapacitor and method for preparing same Download PDFInfo
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Abstract
The present invention relates to a gold / metal oxide or hydroxide complex for a supercapacitor and a method for producing the same, and more particularly, to a metal oxide or hydroxide of a three-dimensional (3D) structure and a gold The gold / metal oxide or hydroxide complex of the present invention, including Au nanoparticles, provides excellent electrochemical performance such as an improved capacity value, an excellent discharge capacity ratio behavior, and excellent cycle stability, and thus is useful for manufacturing electrodes for supercapacitors .
Description
The present invention relates to a gold / metal oxide or hydroxide complex which can be used for the production of electrodes of a supercapacitor and a method for producing the same.
Supercapacitors are semi-permanent, and are a promising device for energy storage due to their high power density and fast charge and discharge rates. In the case of electrical double-layer capacitors (EDLCs), the charge stores the energy accumulated by the electrostatic force between the surface of the carbon-based electrode and the electrolyte, whereas the pseudocapacitor has a reversible redox oxidation near the electrode surface, such as by the EDLC- The ionic charge is stored by the reaction. For this reason, pseudo-capacitors typically have a high specific capacitance that can store more energy than an energy electric double-layer capacitor. The electrode material used in the pseudo capacitor is a metal oxide or a metal hydroxide semiconductor because a reversible surface oxidation-reduction reaction between an oxide and an electrolyte can be easily performed from various metal oxides. Of the various pseudo-capacitor materials, RuO 2 is considered to be the most useful because of its excellent electrochemical properties such as high capacity, wide potential range, high proton conductivity, and high reversible redox reactivity. However, due to high cost and environmental concerns, it is difficult to commercialize RuO 2 as a supercapacitor material. Accordingly, finding a substitute for RuO 2 with similar electrochemical properties has become an important issue in the field of super capacitors. Of the various transition metal oxides / hydroxides, Ni (OH) 2 is not only inexpensive, environmentally friendly, but also provides a very high theoretical capacity (2,358 F / g) However, although Ni (OH) 2 has a high theoretical specific capacity, it has a problem that it is difficult to achieve the theoretical capacity because of low conductivity, and there is a problem that the cycle stability is low. One example of such a phenomenon is that after 300 cycles, the cost amount is reduced to about half of the initial value.
Recent studies on superconductors using Ni (OH) 2 due to the above problems have been conducted to combine with highly conductive carbon materials to improve the poor electrical conductivity of Ni (OH) 2 . For example, the Wei Group (see T. Wei et al., Adv . Fun. Mater 2012 , 22 , 2632-2641) has proposed a method for producing graphene / Ni (OH) 2 - based super capacitor. The specific capacity of Ni (OH) 2 containing 21 wt% graphene was increased from about 1,600 F / g to 1,735 F / g at a scan rate of 1 mV / s and was increased to 30 % Or more capacity value was maintained. Graphene with good conductivity provides an easy channel for fast electron transport and Ni (OH) 2 with Faraday behavior provides high specific capacity. It is meaningful to bond with graphene to improve the conductivity and stability of Ni (OH) 2 because it is cost effective and effective. However, the discharge capacity ratio is still low, and the process of manufacturing graphene having excellent performance is complicated.
As its alternative, a cyano group, (lit. [YY Xia et al., J Electrochem Soc 2006, 153, A743-A748] Reference) The carbon nanotubes (CNT) having a further increased ratio capacitance and excellent cycle performance / Ni ( OH) 2 system super capacitor. The specific capacity of Ni (OH) 2 containing 50 wt% MWNT increased from 218 F / g to 310 F / g at a current density of 0.1 A / g and retained 95% or more capacity after 2,000 cycles. CNTs with large surface area and good conductivity not only increase energy capacity but also improve the excellent cycle stability of EDLC. However, in order to improve the overall capacitor performance, a large amount of CNTs are combined with Ni (OH) 2 , resulting in a low specific capacitance value.
Another possible way to improve the conductivity of low-conductivity Ni (OH) 2 is to incorporate metals with high conductivity into the pseudo-capacitor material. Very recently, the Chen group (see MW Chen et al., Nat Nanotechnol 2011 , 6 , 232-236) has shown that the cost of the nanoporous gold / MnO 2 hybrid structure is greatly increased up to 1,145 F / g without any additive And excellent cyclic stability. The main reason for the remarkable improvement in capacitance value is the existence of a three-dimensional conductive network of nanoporous gold prepared by dealloying a specific composition of Au (Ag 65 Au 35 ). The high conductivity and degenerative gold network enabled the electrons generated from oxidation / reduction of MnO 2 to be effectively transported to the current collector. Although the report clearly demonstrates the effectiveness and importance of 3D gold nanostructures, the manufacturing process is very complex and not practical in practice.
Accordingly, an object of the present invention is to provide a metal oxide or hydroxide-based complex which can provide an improved capacity value, excellent discharge capacity ratio behavior and excellent cycle stability when applied to an electrode of a supercapacitor, and a method for simply and economically producing the complex .
In order to achieve the above object,
Metal oxide or hydroxide complex comprising a metal oxide or hydroxide in a three-dimensional (3D) structure, and gold (Au) nanoparticles deposited in a form dispersed on the surface of the metal oxide or hydroxide.
In addition,
(1) preparing a three-dimensional (3D) structure metal oxide or hydroxide by hydrothermal synthesis; And
(2) mixing the metal oxide or hydroxide, the gold precursor, and the reducing agent in a solvent to prepare a gold / metal oxide or hydroxide composite.
The gold / metal oxide or hydroxide complex according to the present invention facilitates transport of electrons or charges by creating a three-dimensional conductive network through gold / semiconductor contact due to the presence of gold nanoparticles on the surface of the metal oxide or hydroxide semiconductor An excellent electrochemical performance such as an improved capacity value, an excellent discharge capacity ratio behavior and an excellent cycle stability can be usefully used for manufacturing an electrode for a supercapacitor.
Figure 1 of Examples 1 and 2 each prepared nickel hydroxide (Ni (OH) 2), and gold / nickel hydroxide (Au / Ni (OH) 2 ) injection of the complex electron microscope (SEM) (a, b) and transmitted in Electron Microscopy (TEM) (c, d) As a photograph, a and c are for Ni (OH) 2 and b and d are for Au / Ni (OH) 2 complex.
2 is an X-ray diffraction (XRD) pattern of Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2, respectively.
Figure 3 is the first embodiment and each of the produced Ni (OH) 2 In the second and the nitrogen of the Au / Ni (OH) 2 complex (N 2) adsorption / desorption as an isothermal loop (a: Ni (OH) 2 , b: Au / Ni (OH) 2 complex), and the degree of insertion shows the BJH (Barret-Joyner-Halenda) pore size distribution curve in each structure.
4 is a cyclic current-voltage diagram (a, b) and a constant current discharge curve (c, d) of a Ni (OH) 2 and Au / Ni (OH) 2 composite prepared in Examples 1 and 2, c is for Ni (OH) 2 , b and d are for Au / Ni (OH) 2 complexes.
Figure 5 shows the specific capacities (a, b) at 5 to 20 A / g at different current densities of the Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2, As a cycle retention curve (c, d), a and c are for Ni (OH) 2 and b and d are for Au / Ni (OH) 2 complexes.
FIG. 6 is a Nyquist plot of the Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2, respectively, and the degree of insertion is the equivalent used for data fitting Circuit and near-electrochemical impedance spectroscopy (EIS) imaging in the high frequency region. Measurements were performed in the frequency range of 100 kHz to 0.1 Hz under 1 M KOH electrolyte and open circuit voltage conditions.
FIG. 7 is a graph showing the change in specific capacitance value according to the content of gold nanoparticles, which was performed in Example 3. FIG.
As Figure 8 showing the ohmic contacts (ohmic contact) between the gold nanoparticles and the Ni (OH) 2 semiconductor, (a) is a schematic diagram showing a band matching between Au and Ni (OH) 2, (b) Ni (OH) 2 Pellet and Au / Ni (OH) 2 pellets.
9 is a SEM image of NiO, CuO, MnO 2 , Au / NiO, Au / CuO and Au / MnO 2 prepared in Examples 4 to 6, MnO 2 , (b) Au / NiO, (d) Au / CuO, and (f) Au / MnO 2 .
An XRD pattern of Figure 10 in Example 4, each manufactured to 6 NiO, CuO, MnO 2, Au / NiO, Au / CuO and Au / MnO 2, (a) NiO , and Au / NiO, (b) CuO and It is for the Au / CuO, and (c) MnO 2 and Au / MnO 2.
11 is a cyclic current-voltage diagram at a scan rate of 50 mV / s of NiO, CuO, MnO 2 , Au / NiO, Au / CuO and Au / MnO 2 prepared in Examples 4 to 6, NiO and Au / NiO, (b) CuO and Au / CuO, and (c) MnO 2 and Au / MnO 2 .
The gold / metal oxide or hydroxide complex according to the present invention comprises a metal oxide or hydroxide of a three-dimensional (3D) structure and gold (Au) nanoparticles deposited in the form of being dispersed on the surface of the metal oxide or hydroxide .
Further, according to the present invention, the gold / metal oxide or hydroxide complex
(1) preparing a three-dimensional (3D) structure metal oxide or hydroxide by hydrothermal synthesis; And
(2) mixing the metal oxide or hydroxide, the gold precursor, and the reducing agent in a solvent to prepare a gold / metal oxide or hydroxide composite.
The metal oxide or hydroxide has a flower-like three-dimensional (3D) structure, preferably Ni (OH) 2 , NiO, CuO, MnO 2 or a mixture thereof.
The gold (Au) nanoparticles deposited in the form of dispersed on the surface of the metal oxide or hydroxide may have an average particle size of 10 to 100 nm, preferably 20 to 50 nm, more preferably 25 to 40 nm, May be present in an amount of from 0.1 to 15% by weight, preferably from 0.1 to 10% by weight, more preferably from 0.3 to 1.0% by weight, based on the weight.
Deposition of gold nanoparticles on the surface of metal oxides or hydroxides can result in surface areas and pore volumes of the gold / metal oxide or hydroxide complexes obtained after deposition compared to pure metal oxides or hydroxides, due to the presence of heavy gold nanoparticles . However, the pore size of the composite is greater than that of the pure metal oxide or hydroxide, which facilitates the transport of charge within the electrolyte.
The gold / metal oxide or hydroxide complex of the present invention may have a surface area of 50 to 500 m 2 / g, a pore size of 5 to 20 nm and a pore volume of 0.2 to 1.0 cm 3 / g.
Specifically, a metal oxide or hydroxide precursor and an alkaline compound (e.g., hexamethylenetetramine (HMTA), sodium hydroxide, ammonium hydroxide, etc.) in a 3D structure are prepared by hydrothermal synthesis, To 120 < 0 > C for 1 to 12 hours, followed by drying. The precursors of metal oxides or hydroxides may be those commonly used in hydrothermal synthesis reactions, such as metal containing nitrates, sulfates, and the like.
The metal oxide or hydroxide thus prepared is mixed with a gold precursor and a reducing agent, reacted in a solvent, and then dried to produce the desired complex.
The gold precursor may be at least one selected from the group consisting of chloroauric acid and gold nitrate, and the reducing agent may be at least one selected from the group consisting of tin sodium citrate and sodium borohydride. The solvent may be at least one selected from the group consisting of water, ethanol, isopropanol, and methanol. The gold precursor used may be used in an amount that satisfies the weight range of gold nanoparticles relative to the total weight of the composite.
The reaction of the metal oxide or hydroxide with the gold precursor may be performed at a temperature of 80 to 120 ° C for 30 minutes to 12 hours. By such a colloid deposition method, partial deposition of the gold nanoparticles on the surface of metal oxide or hydroxide can be achieved very easily.
The gold / metal oxide or hydroxide complex according to the present invention thus produced overcomes the problem of instability and low conductivity of pure metal oxides or hydroxides by forming a 3D conductive network through gold / semiconductor contact, And provides an excellent electrochemical performance such as an improved capacity value, an excellent discharge capacity ratio behavior, and excellent cycle stability, and thus can be usefully used in the manufacture of electrodes for supercapacitors.
Accordingly, the present invention provides a supercapacitor comprising the gold / metal oxide or hydroxide complex.
Hereinafter, the present invention will be described in more detail with reference to preferred embodiments for better understanding of the present invention. However, the following examples are intended to illustrate the present invention, but the scope of the present invention is not limited to or by the following examples.
Compound used
All compounds such as nickel nitrate hexahydrate (Sigma-Aldrich,> 99%), hexamethylenetetramine (HMTA) (Sigma-Aldrich,> 99%), Respectively.
Example 1
Ni (OH) 2 Synthesis of
For the synthesis of Ni (OH) 2 in 3D structure, 300 mM nickel nitrate solution (40 ml) and 300 mM hexamethylenetetramine (HMTA) (40 ml) were mixed well and mixed with 120 ml of Teflon-lined stainless steel And transferred to an autoclave. The autoclave was then heated at 100 < 0 > C for 4 hours. The final product was thoroughly washed with deionized water and ethanol and filtered. The synthesized powder was dried under vacuum at 80 캜 for 12 hours to obtain a Ni (OH) 2 powder having a 3D structure.
Example 2
Au / Ni (OH) 2 Synthesis of
The deposition of gold nanoparticles was performed using colloid deposition. Specifically, 0.3 g of Ni (OH) 2 was mixed with 30 mM of chloroauric acid, dissolved in distilled water, and 1 wt% of citric acid dissolved in water was added thereto. The mixture was heated at 100 < 0 > C for 30 minutes and then naturally cooled as with the substrate. The resulting solution was dried at 80 DEG C for 6 hours.
Character rating
The synthesized structure was evaluated at an acceleration voltage of 200 kV using FE-SEM (SEM, FEI / USA Nanonova 230) and high resolution transmission electron microscope (FETEM, JEOL TEM 2100). The crystallinity of the sample was checked using a Bruker D8 Advance system using Cu Ka radiation ([lambda] = 1.5406 A) at a scan rate of 2 [deg.] / Min and a range of 20 [deg.] To 80 [ The specific surface area, pore size and pore volume were analyzed by the Belsorp max system (Bel Japan) using the Brunauer-Emmett-Teller (BET) method.
Electrochemical measurement
Ni (OH) 2 or Au / Ni (OH) 2 (85 wt%), acetylene black (10 wt%) as an electroactive material and polyvinylidene difluoride (PVDF, 5 wt% A mixture for working electrode was prepared. Then 20 mg of the mixture was applied to a Ni foam and dried at 150 ° C under atmospheric pressure for 2 hours. The electrochemical performance of the nanostructured Au / Ni (OH) 2 was measured using a Pt foil as the counter electrode and a KOH solution (1M) as the electrolyte. The constant current charge-discharge and circulating current-voltage were measured using a computer controlled electrochemical interface (biological VMP3) at room temperature, 0.2 V to 0.6 V. Electrochemical impedance spectroscopy (EIS) was analyzed over the 100 kHz to 0.1 Hz frequency range using potentiostat (
Scanning electron microscope (SEM) (a, b) and transmission electron microscope (SEM) of the nickel hydroxide (Ni (OH) 2 ) and gold / nickel hydroxide (Au / Ni (OH) 2 ) composites prepared in Examples 1 and 2 TEM) (c, d) photographs are shown in Fig. a and c are for Ni (OH) 2 , and b and d are for Au / Ni (OH) 2 complexes.
As shown in Fig. 1 (a), the synthesized Ni (OH) 2 has an interconnected 3D structure, which is effective for transporting inter-domain electrons or electrolyte ions of the particles. Figure 1 b and d represents a Au / Ni (OH) 2 structure after the deposition of gold nanoparticles Ni (OH) 2 to the top. In FIG. 1 (b), the SEM image shows that gold nanoparticles of 25-40 nm in diameter are slightly randomly distributed on the 3D-Ni (OH) 2 surface. However, TEM image gives (Fig. 1 d), revealed that the gold nano-particles are firmly adhered to the surface without distortion or aggregation of the Ni (OH) 2 Ni (OH ) 2. The interplanograms of Figures 1 (c) and (d) show the clear edge spacing of Ni (OH) 2 and Au / Ni (OH) 2 measured by TEM images, respectively. 1 (c) corresponds to the (101) plane of? -Ni (OH) 2 , and the interval of 0.23 nm in the inset of FIG. Indicating the presence of cotton.
The X-ray diffraction (XRD) patterns of the Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2 are shown in FIG.
In Figure 2, the pattern of the Ni (OH) 2 are (001), (006), (002) Ni (OH) having a pack position at 2θ = 12.1 o, 23.6 o, 24.8 o corresponding to the surface 2 (JCPDS, 02-1112). ≪ / RTI > The peak at 2θ = 33.4 ° and 59.8 ° can be indexed to the (101) face of α-Ni (OH) 2 with different degree of water molecule insertion in the crystal (? -Ni (OH) 2 0.75H 2 O and? -3Ni (OH) 2 .2H 2 O, respectively). The XRD pattern demonstrates that the prepared sample is of high purity since? -Ni (OH) 2 is a mixture of two types and there is no additional peak. Ni (OH), and gold particles of nano size is very small amount compared to the second, since the peak position, and Ni (OH) 2 of the peak position of the gold nanoparticles is superimposed gold in the XRD pattern of the Au / Ni (OH) 2 conjugate It is difficult to distinguish the peaks. However, the peak is very sharp at 2θ = 38.24 ° and 44.2 ° (Au: JCPDS card 071-4073), and the successful deposition of gold nanoparticles from TEM images and the formation of Au / Ni (OH) 2 complexes are clearly supported .
Examples 1 and 2 each prepared Ni (OH) 2 and the nitrogen of the Au / Ni (OH) 2 complex (N 2) adsorption / desorption isotherms loop at (a: Ni (OH) 2, b: Au / Ni ( OH) 2 complex) is shown in FIG. 3, and the insertion degree shows a BJH (Barret-Joyner-Halenda) pore size distribution curve in each structure. Further, the measured values of surface area, pore size and pore volume of each of the Ni (OH) 2 and Au / Ni (OH) 2 composites are shown in Table 1 below.
As shown in FIG. 3 and Table 1, surface properties such as nitrogen adsorption / desorption isotherms, surface area, pore volume, and pore size of Ni (OH) 2 were measured before and after gold deposition. The IV-type isotherm and the H3 hysteresis loop indicate that mesopores are fairly open. During the Au deposition process, some Au nanoparticles experimentally attach to the inside of the pores of Ni (OH) 2 , often occluding small pores. As a result, the nitrogen adsorption / desorption amount of FIG. 3 is reduced, which is a cause of the general tendency to decrease the surface area and pore volume of the sample after gold deposition as shown in Table 1. [ In addition, relatively heavy Au NPs increase the total weight of Au / Ni (OH) 2 to reduce the surface area from 179.92 to 130.32 m 2 / g. Interestingly, however, the pore size of Au / Ni (OH) 2 is larger than that of pure Ni (OH) 2 , which would be advantageous for easy transport of charge within the electrolyte. This seems to occur when the surface of Ni (OH) 2 is partially decomposed in an acidic chlorochloric acid solution during the deposition process of Au nanoparticles.
Despite the problem of reduced surface area, there are two reasons for choosing Au nanoparticles among many metal particles with improved conductivity performance. First, Au nanoparticles have been reported to catalytically improve electrochemical activity and to broaden the electrochemical reaction region (dislocation). Au has such a characteristic because Au nanoparticles having high d-band energy can strongly adsorb O and OH species and exhibit high electrochemical characteristics in an alkaline electrolyte. The second reason is that Au nanoparticles allow for the creation of metal-semiconductor contacts, which can potentially increase the electrical conductivity of Ni (OH) 2 . According to a given combination of metal and semiconductor, the resistance of the composite can be increased or decreased. The large discrepancy between the Fermi energy of the metal and the semiconductor energy gap causes low conductive rectification contact. On the other hand, the proper arrangement of the bandgap between metal and semiconductor forms a low resistive ohmic contact (see FIG. 8). In order to achieve a low resistance ohmic contact at the interface between the P-type semiconductor material (Ni (OH) 2 in this case) and the metal, the work function of the metal should be similar to or greater than the sum of the band gap energy and electron affinity of the semiconductor . Since the bandgap and electron affinity of Ni (OH) 2 are about 3.5 eV and 1.47 eV, respectively, the work function of the metal for the appropriate bandgap energy arrangement should be slightly greater than 5 eV, To give an ability to produce efficient metal / semiconductor contact, thereby improving the conductivity of Ni (OH) 2 . Here we Although Ni (OH) 2 is even if it is not completely covered with the Au nanoparticle, Au / Ni (OH) 2 in part, conductive Ni (OH) 2 in the virtual through the high-conductive metal / semiconductor contact through the network 3D It can be hypothesized that it can form a current collector, which greatly increases the overall electrical conductivity of Ni (OH) 2 .
(A, b) and constant current discharge curves (c, d) of the Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2 are shown in FIG. a and c are for Ni (OH) 2 , and b and d are for Au / Ni (OH) 2 complexes.
Figures 4a and 4b show cyclic current-voltage performance results of the Ni (OH) 2 and Au / Ni (OH) 2 composites obtained at different scan rates of 1 mV / s to 50 mV / s. The specific capacities calculated at 1 mV / s from the CV curves of Ni (OH) 2 and Au / Ni (OH) 2 are 1,093 F / g and 1,660 F / g, respectively. In both samples, a representative anode peak (E o ) due to oxidation of? -Ni (OH) 2 to? -NiOOH and a cathode reduction peak (E R ) due to its reverse reaction were detected, It is a typical feature. It can clearly be seen that Au / Ni (OH) 2 shows higher capacity and higher corresponding E o and E R current density values than pure Ni (OH) 2 at the same scan rate. The potential difference (E O -E R ) between the anode and cathode peaks provides useful information on the reversibility of the redox reaction, which is an indirect indication of the discharge capacity ratio and long-term stability. Au / Ni (OH) 2 with a value of about 10% lower (E O -E R ) suggests a higher capacity as well as a more reversible reaction and better electrochemical performance.
The reduction potential (E R ), the oxidation potential (E O ), and the potential difference (E O - E R ) values for Ni (OH) 2 and Au / Ni (OH) 2 at a scan rate of 20 mV / Respectively.
The longer discharge times in Figures 4c and 4d indicate better charge storage performance of the supercapacitor. At a current density of 1 A / g, 2 A / g, 5 A / g, 10 A / g and 20 A / g, relatively low specific capacities of Ni (OH) 2 of 1,363 F / g, 1,130 F the values of Au / Ni (OH) 2 were 1,927 F / g, 1,765 F / g, 1,506 F / g, and 1,450 F / g, respectively, as compared to 912 F / g, 851 F / / g, and 1,274 F / g, respectively. By simply depositing Au nanoparticles, the specific capacitance value increased to about 1.5 times. Although there was a reduction of about 25% in the specific surface area of the Au / Ni (OH) 2 composite, there was no significant effect on the capacitance value, as shown in Fig. This is believed to be due to the increased conductivity of Au / Ni (OH) 2 with the 3D conductive path and due to the sufficient compensation due to the improved catalytic effect. More ions on the highly conductive surface of Au / Ni (OH) 2 reduce the "dead surface" part and participate in the redox reaction by the support of the catalytic Au nanoparticles to quickly and reversibly dissociate the electrolytic dissociation reaction . However, it should be noted that as shown in Figure 7, the highest Au / Ni (OH) 2 with the highest Au nanoparticle area density does not have to represent the highest capacity. The optimum gold density for the best capacity was only 0.3 wt% in Au / Ni (OH) 2 , unexpectedly. It is believed that this is due to a balance between the improvement in conductivity by Au nanoparticles and the number of useful active sites for redox reactions provided by Ni (OH) 2 .
Capacity (a, b) at different current densities of 1 to 20 A / g of the Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2, respectively, The curve (c, d) is shown in Fig. a and c are for Ni (OH) 2 , and b and d are for Au / Ni (OH) 2 complexes.
Generally, the discharge capacity ratio of a pure Ni (OH) 2 electrode is very low due to the slow response of Ni (OH) 2 with low electrical conductivity. For example, as shown by pure Ni (OH) 2 , which decreases 52% at a current density of 20 A / g, the capacity decreases very rapidly with increasing current density (FIG. However, under the same conditions, the specific capacity value of Au / Ni (OH) 2 has been shown to be reduced by only 35%, which strongly supports the positive effect of improved conductivity on capacity retention at high density currents ).
In addition, Ni (OH) more greatly improved Au / Ni (OH) 2 the cycle stability than 2 was also observed. 5 (c), Au / Ni (OH) 2 had a value of 80% in the same cycle, while the capacity retention rate of Ni (OH) 2 after 5,000 cycles was reduced to 30% ), Which appears to be due to the binding of electrochemically stable and conductive Au nanoparticles, leading to a faster and more reversible redox reaction as evidenced by the low potential difference (E O -E R , Table 2 above). Approach of the present invention is a highly promising together the conventional method and different from each other, and the goal to improve the conductivity and stability by combining the EDLC characteristics, was ensure a sufficient capacity via the pseudo capacitor material for the Ni (OH) 2 The discharge capacity ratio and stability were further improved without any loss of pseudo capacity by slight deformation. From these results it can be concluded that the low discharge capacity ratio, long term stability and low capacitance value of Ni (OH) 2 have been successfully solved by simply depositing a small amount of Au nanoparticles, which has excellent electrochemical catalytic activity and conductivity .
The Nyquist plots of Ni (OH) 2 and Au / Ni (OH) 2 composites prepared in Examples 1 and 2 are shown in FIG. The degree of insertion is the equivalent circuit used for data fitting and the proximate electrochemical impedance spectroscopy (EIS) image in the high frequency domain. Measurements were performed in the frequency range of 100 kHz to 0.1 Hz under 1 M KOH electrolyte and open circuit voltage conditions.
As shown in FIG. 6, the change in the internal electrode resistance or interface resistance between the electrodes and the electrolyte in the device was shown in a specific operating frequency range. The starting point on the real axis (R s ) in the high frequency region reflects the intrinsic resistance and electrical contact resistance of the electrode material. The diameter of the semicircle R ct in the intermediate frequency domain represents the interface charge transfer resistance. Information on ion diffusion at the electrode can be obtained from the long tail in the low frequency region. Relatively lower R s value of 11.6 Ω of Au / Ni (OH) 2 is Au / Ni (OH) 2 electrode is a lower contact than the second electrode pure Ni (OH) resistance and a more pure Ni (OH) 12.3 Ω 2 Indicating that it has better conductivity, which is clear evidence of improved conductivity of Au / Ni (OH) 2 . This is believed to be due to the generation of 3D-network current collectors, which ultimately facilitates transport of electrons. In addition, by depositing Au nanoparticles on the Ni (OH) 2 phase, the diameter of the semicircle in the intermediate frequency range is greatly reduced to 6.1 Ω to 1.9 Ω because Au / Ni (OH) 2 is deposited between the electrolyte and the electrode Thereby providing a path for more effective charge transfer. Ni for introducing the Au nanoparticles on the (OH) 2 is to produce a Ni (OH) low-resistance Au / Ni (OH) 2 on the second surface contact. This increases the overall electronic conductivity of the 3D electrode and thereby reduces the conductivity difference between the active material and the electrolyte, as shown by the much smaller diameter of the semicircle of Au / Ni (OH) 2 in the intermediate frequency region, Bringing movement resistance. In addition, a slightly larger vertical line characteristic of Au / Ni (OH) 2 , that is, a typical shape of an ideal supercapacitor in the low frequency region, indicates that Au nanoparticles improve the capacitance characteristics of the 3D- Prove that.
The above results indicate that simply depositing Au nanoparticles on a low-conductivity Ni (OH) 2 phase not only improves the conductivity of the electrode but also significantly improves reversibility and stability. As a result, excellent electrochemical capacitive performance was achieved while maintaining a high capacitance value of the pseudo capacitor.
Example 3
Optimization of Au nanoparticle content
The content of Au nanoparticles was controlled by fixing the concentration of metal hydroxide and changing the concentration of the gold precursor solution, and was measured by an inductively coupled plasma-mass spectrometer (ICP / MS). Ni (OH) 2 was prepared in the same manner as in Examples 1 and 2, except that the amount of gold nanoparticles to be deposited was changed as shown in Table 3 by controlling the amount of chloroauric acid used as a gold precursor. 2
As can be seen from FIG. 7 and Table 3 above, the optimized ratio of Au nanoparticles to the total weight of the composite was 0.3 wt.%, Indicating a capacity value of 1,927 F / g at a scan rate of 1 A / g.
Examples 4 to 6
(1) NiO, CuO and MnO 2 Synthesis of
For the synthesis of each of the 3D structures of NiO, CuO and MnO 2 , the mixture solutions A, B and C of the compositions shown in Table 4 below were respectively prepared and transferred to a stainless steel autoclave thinly lined with 120 ml of Teflon. The autoclave was then heated at 120 占 폚 for 4 hours. The final product was thoroughly washed with deionized water and ethanol and filtered. The synthesized powder was dried under vacuum at 80 캜 for 12 hours and finally annealed at 500 캜 for 2 hours to obtain powders of NiO, CuO and MnO 2 of 3D structure.
(2) Au / NiO , Au / CuO And Au / MnO 2 Synthesis of
Ni (OH) 2 instead of on and is, The same procedure as in Example 2 except for using the, NiO, CuO and MnO 2, respectively prepared in (1) Au / NiO, Au / CuO and Au / MnO 2 were synthesized.
SEM photographs of NiO, CuO, MnO 2 , Au / NiO, Au / CuO and Au / MnO 2 prepared in Examples 4 to 6 are shown in FIG. (a) NiO, (c) CuO and (e) MnO 2 , (b) Au / NiO, (d) Au / CuO and (f) Au / MnO 2 .
XRD patterns of NiO, CuO, MnO 2 , Au / NiO, Au / CuO and Au / MnO 2 prepared in Examples 4 to 6, respectively, are shown in FIG. (a) NiO and Au / NiO, (b) CuO and Au / CuO, and (c) MnO 2 and Au / MnO 2 .
The cyclic current-voltage diagrams of NiO, CuO, MnO 2 , Au / NiO, Au / CuO and Au / MnO 2 prepared in Examples 4 to 6 at a scan rate of 50 mV / s are shown in FIG. (a) NiO and Au / NiO, (b) CuO and Au / CuO, and (c) MnO 2 and Au / MnO 2 .
Claims (12)
Wherein the gold nanoparticles have an average particle diameter of 10 to 100 nm.
Wherein the composite comprises the gold nanoparticles in an amount of from 0.1 to 15% by weight based on the total weight of the composite.
Wherein the complex comprises the gold nanoparticles in an amount of 0.1 to 10 wt% based on the total weight of the composite.
Wherein the gold / metal oxide or hydroxide complex has a surface area of 50 to 500 m 2 / g, a pore size of 5 to 20 nm and a pore volume of 0.2 to 1.0 cm 3 / g. .
(2) A process for producing a gold / metal oxide or hydroxide complex according to claim 1, which comprises mixing the metal oxide or hydroxide, a gold precursor and a reducing agent in a solvent.
Metal oxide or hydroxide complex in the step (1), wherein the precursor of the metal oxide or hydroxide and the alkaline compound are reacted at a temperature of 90 to 120 캜 in water to produce a metal oxide or hydroxide of a three- ≪ / RTI >
Wherein the gold precursor of step (2) is at least one selected from the group consisting of chloroauric acid and gold nitrate.
Wherein the reaction of step (2) is carried out at a temperature of 80 to 120 占 폚.
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| KR101716867B1 (en) | 2015-11-20 | 2017-03-16 | 울산과학기술원 | Electrode for supercapacitor and preparation method thereof |
| KR20200030295A (en) | 2018-09-12 | 2020-03-20 | 연세대학교 산학협력단 | Nanoporous transition metal alloy and manufacturing the same |
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| KR20200030295A (en) | 2018-09-12 | 2020-03-20 | 연세대학교 산학협력단 | Nanoporous transition metal alloy and manufacturing the same |
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