WO2022228137A1 - 一种石墨烯/MnO电极、其制备方法及高能量密度超级电容器 - Google Patents

一种石墨烯/MnO电极、其制备方法及高能量密度超级电容器 Download PDF

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WO2022228137A1
WO2022228137A1 PCT/CN2022/086742 CN2022086742W WO2022228137A1 WO 2022228137 A1 WO2022228137 A1 WO 2022228137A1 CN 2022086742 W CN2022086742 W CN 2022086742W WO 2022228137 A1 WO2022228137 A1 WO 2022228137A1
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mno
graphene
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frgo
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林瀚
贾宝华
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伊诺福科光学技术有限公司
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    • H—ELECTRICITY
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    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
    • H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for electrodes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/02—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof using combined reduction-oxidation reactions, e.g. redox arrangement or solion
    • H—ELECTRICITY
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    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/46—Metal oxides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors

Definitions

  • the present invention requires the priority of a Chinese patent application with an application number of 202110460094.0 and an application title of "a graphene/MnO electrode, its preparation method and a high energy density supercapacitor" submitted to the China Patent Office on April 27, 2021, Its entire contents are incorporated herein by reference.
  • the invention belongs to the technical field of energy storage, and in particular relates to a graphene/MnO electrode, a preparation method thereof and a high energy density supercapacitor.
  • Supercapacitors are electrochemical capacitors that have a much higher capacitance value than other capacitors.
  • Supercapacitors are widely used in energy storage and energy supply due to their high energy density, fast charge/discharge capability, long life of over one million charge cycles, and ability to operate in a wide temperature range from -40°C to 70°C . Since the production and disposal of batteries can adversely affect environmental pollution and human health, the environmentally friendly materials in supercapacitors and their low maintenance costs have promoted the development of supercapacitors in recent years.
  • supercapacitors are superior to batteries because they can provide higher power density (up to 45kW kg -1 ) and longer cycle life (one million cycles). Nevertheless, the energy density of supercapacitors is about an order of magnitude lower than that of batteries, which limits the use of supercapacitors in practical applications.
  • the specific capacitance mainly depends on the electrode properties. In the process of developing carbon-based supercapacitors, the overall capacitance and energy density of pure carbon-based electrodes are still relatively low.
  • graphene is considered to be the most promising electrode material with excellent electrical conductivity and high theoretical surface area
  • the theoretical limit of specific capacitance is 550F g-1. Therefore, different strategies have been employed to improve the capacitance of carbon-based electrodes, and one promising approach is to introduce pseudocapacitance by adding manganese oxides (MnOx) due to their high theoretical capacitance and their abundance Earth and non-toxic properties.
  • MnOx manganese oxides
  • the object of the present invention is to provide a graphene/MnO electrode, its preparation method and high energy density supercapacitor, the graphene/MnO electrode prepared in the present invention shows up to 1706F ⁇ g - 1 at 0.2A ⁇ g-1 1 ultra-high capacitance.
  • the invention provides a preparation method of graphene/MnO electrode, comprising the following steps:
  • the mass ratio of the MnO 2 nano-needles to the graphene oxide is 1: (0.5-12);
  • the MnO 2 nano-needles are first ultrasonically mixed with water to obtain a MnO 2 nano-needle colloid, and then mixed with a graphene oxide solution to obtain a mixed solution.
  • the MnO 2 nanoneedles have a diameter of 10-30 nm and a length of 200-400 nm.
  • the mass ratio of the MnO 2 to graphene oxide is 1:(0.8-1.2).
  • the mixed solution is formed into a membrane by a vacuum filtration method, and the pore size of the filter membrane used in the vacuum filtration is 0.02-0.03 ⁇ m.
  • the power of the flash reduction is 600-700Ws.
  • the graphene oxide in the film generates a sufficient amount of reducing gas to convert MnO 2 into MnO x during the flash reduction process, 1 ⁇ x ⁇ 2.
  • the MnO nanoneedles are prepared according to the following steps:
  • the divalent manganese salt is heated to reflux in an organic solvent, potassium permanganate is added, and after stirring the reaction, the precipitate is collected, washed, and dried to obtain MnO2 nano-needles.
  • the present invention provides a graphene/MnO electrode prepared by the above-mentioned preparation method.
  • the graphene/MnO electrode includes reduced graphene oxide and MnO x nanoneedles distributed between the reduced graphene oxide layers, 1 ⁇ x ⁇ 2.
  • the mass fraction of the MnO x nanoneedles is 27-92 wt %.
  • the present invention provides a high-energy-density supercapacitor comprising the graphene/MnO electrode described above and a water-based electrolyte.
  • the invention provides a method for preparing a graphene/MnO electrode, comprising the following steps: A) forming a mixed solution comprising MnO nano-needles and graphene oxide; the mass ratio of the MnO nano-needles and graphene oxide is 1 : (0.5-12); B) forming the mixed solution into a film; C) performing flash reduction on the film to obtain a graphene/MnO electrode.
  • the present invention proposes a low-cost, one-step flash reduction process to prepare high-performance graphene/MnO x electrodes by rationally designing reaction conditions. This facile method enables the fabrication of high-quality porous graphene networks and the simultaneous efficient synthesis of intercalated pseudocapacitively active MnO nanomaterials. Ultra-high capacitance (up to 1706 F ⁇ g ⁇ 1 ) beyond the theoretical limit of pure graphene and MnO x was demonstrated using the fabricated electrodes.
  • Figure 1 is a schematic diagram of the co-reduction process of GO/ MnO2 by reducing gas under (a) insufficient and (b) sufficient conditions, respectively;
  • Figure 3 is (a) Scanning Electron Microscope (SEM) image of MnO2 nanoneedles; (b) and (c) SEM images of 6M6G at different magnifications; (d) Elemental distribution of 6M6G (CK ⁇ 1, OK ⁇ 1 and MnK ⁇ 1) Images, scale bar is 20 ⁇ m; (e) transmission electron microscopy (TEM) image of 6M6G, inset shows the corresponding selected area electron diffraction (SAED) pattern of 6M6G; (f) high resolution transmission electron microscopy (HRTEM) image of 6M6G;
  • SEM Scanning Electron Microscope
  • SAED selected area electron diffraction
  • HRTEM high resolution transmission electron microscopy
  • Figure 4 (a) XRD patterns of all reduced samples; (b) XPS analysis of the C1s peak of 6M6G, (c) Mn3s peak of 6M6G, and (d) Mn2p peak of 6M6G; (e) comparison of each of the C1s peaks Carbon oxide bond ratio (left) and CC bond ratio (right) of the samples; (f) Comparison of the ratio of Mn 2+ to Mn 4+ for each sample (left) by peak separation of Mn 2p peaks and Mn 3s peaks (right);
  • Figure 5 (a) CV curves at 10 mV s -1 and (b) CCD curves at 1 A g -1 for frGO, 0.5M6G, 3M6G, 6M6G and 6M3G; (c) 6M6G electrode at 1 mV s -1 CV curves at scan rates up to 20mV s -1 ; (d) Capacitance comparison between frGO, 0.5M6G, 3M6G, 6M6G and 6M3G calculated from the CCD curves, the inset shows the three-electrode cell used for this work Schematic diagram of the electrochemical measurements of ; (e) Nyquist plots of frGO, 0.5M6G, 3M6G, 6M6G and 6M3G, the inset shows the high frequency region; (f) 6M6G under the fast charge-discharge cycle of 5A g -1 Cycle retention, the inset shows a comparison of the CCD curves for the first and 1500th cycles;
  • Figure 7 (a) CV curves of frGO//6M6G asymmetric SC devices at different scan rates; (b) Nyquist plots of frGO//6M6G asymmetric SC devices, the inset shows the high frequency of the Nyquist plot Area and fitted equivalent circuit; (c) specific capacitance of frGO//6M6G, inset illustrating the configuration of asymmetric SC devices; (d) frGO//6M6G repeatedly charged at a large current density of 2 A g -1 / Cycling stability under discharge, inset shows that frGO//6M6G is able to light up LED cells; (e) Ragone diagram of frGO//6M6G;
  • FIG. 1 Gas chromatograph (GC) with thermal conductivity detector (TCD) and flame ionization detector (FID), flash reduction of GO compared with glove box atmosphere;
  • GC gas chromatograph
  • TCD thermal conductivity detector
  • FID flame ionization detector
  • Figure 9 SEM images of (a) frGO, (b) 0.5M6G, (c) 3M6G and (d) 6M6G samples.
  • the scale bar is 2 ⁇ m;
  • Figure 10 (a) TEM images of 0.5M6G and (b) 6M6G samples and corresponding histograms of the width distribution of MnO nanoparticles in (c) 0.5M6G and (d) 6M6G;
  • FIG 11 shows the thermogravimetric analysis (TGA) data of frGO, MnO 2 and frGO/MnOx samples
  • Figure 13 shows the XRD patterns of GO, 0.5M6GO, 3M6GO, 6M6GO and 6M3GO;
  • Fig. 14 XPS analysis of (a) GO and frGO, (b) 0.5M6GO and 0.5M6G, (c) 3M6GO and 3M6G, (d) 6M3GO and 6M3G and (e) carbon bond ratio (C-C)% and carbon oxygen ratio;
  • Figure 15 XPS analysis of wide scan spectra of (a) GO and frGO, (b) 0.5M6GO and 0.5M6G, (c) 3M6GO and 3M6G and (d) 6M3GO and 6M3G;
  • Figure 17 is the Raman spectrum of pure acicular nano-MnO 2 , indicating that pure ⁇ -MnO 2 was successfully synthesized
  • Figure 19 compares the total electrode capacitance of 3M6G and 6M6G electrodes at a current density of 0.2 A ⁇ g -1 , the capacitance contribution of frGO and the capacitance contribution of MnO x ;
  • FIG. 20 CCD curves of frGO//6M6G asymmetric supercapacitor devices at current densities (based on the total mass of frGO and 6M6G electrodes) between 1.5 A g -1 and 15 A g -1 ;
  • Fig. 21 Bode plot (impedance phase versus frequency) of the frGO//6M6G asymmetric supercapacitor device, the relaxation time is estimated to be 0.89s.
  • the invention provides a preparation method of a graphene/MnO electrode, comprising the following steps:
  • the mass ratio of the MnO 2 to the graphene oxide is 1: (0.5 ⁇ 12);
  • the present invention reports for the first time a green and simple co-reduction method that can produce high-performance graphene/MnO electrodes in milliseconds via an ultrafast flash reduction process.
  • reducing gases CO and H 2
  • the best reduction conditions can be achieved.
  • the results show that the as-produced frGO/MnO electrode exhibits an ultracapacitance as high as 1706F ⁇ g -1 at 0.2A ⁇ g-1, which even exceeds the theoretical limit of pristine graphene electrode and pure MnO electrode.
  • MnO 2 nano-needles are first synthesized according to the following method.
  • the MnO 2 nano-needles refer to needle-shaped MnO 2 nanoparticles.
  • the diameter of the MnO 2 nanoneedles is 10-30 nm, more preferably 15-20 nm; the length is preferably 200-400 nm, more preferably 300-350 nm.
  • the divalent manganese salt is heated to reflux in an organic solvent, potassium permanganate is added, and after stirring the reaction, the precipitate is collected, washed, and dried to obtain MnO2 nano-needles.
  • the divalent manganese salt is preferably manganese chloride, such as MnCl 2 ⁇ 4H 2 O
  • the organic solvent is preferably an alcohol solvent, such as isopropanol.
  • the temperature of the heating under reflux is preferably 80 to 85°C, and more preferably 82 to 83°C.
  • the mass ratio of the potassium permanganate to manganese chloride is preferably 1:(1-2), more preferably 1:(1.5-1.8).
  • the heating and refluxing and the reaction are all carried out under stirring conditions. After 10 to 15 minutes, cooling to room temperature, collecting the resulting black precipitate, centrifuging, washing with DI water, and finally drying at 60° C. for about 8 hours to obtain MnO 2 Nanoneedles.
  • the source of the graphene oxide is not particularly limited, and can be prepared by an improved Hummer method.
  • a certain mass of MnO 2 nano-needles is preferably added into deionized water and subjected to ultrasonic treatment to form a hydrate-stable colloid.
  • nano-MnO 2 colloid is mixed with graphene oxide (GO) solution and ultrasonically treated for 15-20 min to obtain a mixture.
  • GO graphene oxide
  • the mass ratio of the MnO 2 nanoneedles to graphene oxide is 1:(0.5-12), preferably 1:(0.8-1.2), and most preferably 1:1.
  • the mixture was vacuum filtered through a polyethersulfone (PES) membrane with a nominal pore size of 0.03 ⁇ m. Films were formed, dried at 60°C and carefully peeled off to form freestanding films.
  • PES polyethersulfone
  • the formed films were flash-reduced using a flash device to obtain graphene/MnO electrodes.
  • the flash device is preferably an Einstein (E640) flash device, and the flash power is preferably 600-700Ws, more preferably 640-650Ws.
  • E640 Einstein
  • the flash reduction has an effective photothermal effect
  • the irradiation of the intense flash pulse triggers the violent reduction and exfoliation of graphene oxide (GO) films
  • the high-power flash pulse triggers the rapid dissociation of oxygen-containing functional groups (OCFGs) due to the instantaneous high temperature and CO. , CO 2 and H 2 O, and other gaseous products, which lead to a local pressure rise, which builds up a porous 3D graphene network.
  • OCFGs oxygen-containing functional groups
  • the present invention also provides a high-energy-density supercapacitor comprising a graphene/MnO electrode and a water-based electrolyte.
  • the present invention has no special restrictions on the type and amount of the water-based electrolyte, and the water-based electrolyte commonly used in the field can be used.
  • MnCl2 ⁇ 4H2O manganese(II) chloride
  • GO solution (2 mg ⁇ ml ⁇ 1 in water) was prepared by a modified Hummer method and purchased from SupraG Energy Pty Ltd.
  • the feeding ratio of the GO/ MnO film was controlled by adjusting the volume and concentration of the MnO nanoneedle colloid and the GO solution.
  • Each GO/ MnO2 sample is labeled as xMyGO to indicate that each fabricated film contains x mg of MnO2 nanoneedles and y mg of GO flakes. After flash reduction, the corresponding reduced membranes were labeled as xMyG.
  • pure GO film, 0.5M6GO film, 3M6GO film, 6M6GO film and 6M3GO film were prepared respectively.
  • pure reduced graphene oxide film, 0.5M6G film, 3M6G film, 6M6G film and 6M3G film were obtained respectively. .
  • This processing environment can be controlled by adjusting the feeding ratio of GO and MnO nanoneedles during film fabrication.
  • two reaction schemes in the flash reduction process can be realized by controlling the feed ratio: (1) When GO reduction provides a sufficient amount of reducing gas and remains in the frGO network, the co-reduction process can produce frGO/ Electrodes that fully reduce MnO to MnO are expected, whereas ( 2 ) in an environment with insufficient reducing gas, only a fraction of MnO can be reduced to MnO, although the same efficient reduction of GO can be achieved. This results in partial reduction to frGO/MnO 2 /MnO films.
  • the reasons for the insufficient reduction gas may be: firstly, the amount of gas released from GO decreases during the flash reduction process, or these gases escape rapidly from the interstices of the GO film. Therefore, the key to ensure the efficient production of frGO/MnO electrodes is considered to be the generation of a large amount of reducing gas through the flash reduction process, followed by successful capture of the reducing gas in the frGO network.
  • the initial amounts of GO and MnO in this model were set according to the feed mass of pure GO films, 0.5M6GO, 3M6GO, 6M6GO and 6M3GO samples, where xMyGO indicates that the film contains x mg MnO and y mg GO. After flash reduction, the xMyGO membrane was labeled as xMyG accordingly. Temperature changes for different reaction scenarios were measured using a laser thermometer (Fig. 2a) and were also taken into account in the simulation model. It can be observed that almost all samples show a peak temperature around 700°C within a few milliseconds of the fast irradiation.
  • the peak temperature of the 6M6GO film is only about 470 °C, which is still higher than the temperature required to remove OCFG, and enables high-quality GO reduction at a high heating rate of about 6 ⁇ 10 6 °C ⁇ min -1 .
  • Figure 2b demonstrates that the pressure changes in the aforementioned GO/ MnO samples are caused by the immediate heating and decomposition of OCFG.
  • the amount of GO in the free-standing film is less, thereby limiting the generation of reducing gas, resulting in a much lower pressure in 6M3GO, the pressure is still more than 2 orders of magnitude higher than the pressure required to exfoliate the frGO layer and create a porous film .
  • a numerical simulation model of the flash reduction of GO/ MnO2 was calculated using COMSOL Multiphysics 5.5, which is consistent with the experimental setup.
  • the chemical reactions were simulated based on an 0D model with constant volume, where the reactions within the entire free-standing GO/MnO 2 (GO) film were considered to be homogeneous in all directions. Calculate the volume of the reaction model based on the volume of each filter membrane.
  • the flash reduction of GO can be described as the following irreversible reaction (6):
  • the x:y ratio during the thermal decomposition of GO has been determined to be approximately 1:2. According to our measured thermal profiles, the GO thin films suffered a sudden increase in temperature due to the photothermal effect upon exposure to a flash lamp, and a local pressure was rapidly built up due to the release of gas. In such a high temperature and high pressure environment, the following reversible reactions (7)-(9) may occur:
  • reaction rate r(aA+bB ⁇ product) of the reaction can be described as:
  • reaction rate constant [A(B)] is the concentration
  • a(b) is the reaction order.
  • the reaction rate constant for each reaction can be further defined according to the Arrhenius expression:
  • A is the forward frequency factor
  • E a is the activation energy
  • T is the temperature
  • R is the gas constant.
  • a list of parameters (A, E a and n) used in this simulation model can be found in Table 1, while T used in this model was measured directly from a laser thermometer. The reversible reaction rates were further corrected with equilibrium constants.
  • the diffusion of reducing gas after flashing was evaluated using the Knudsen diffusion model.
  • the Knudsen diffusion flux (J K ) characterizes the molar flow rate of the diffusing gas and is calculated as follows (12):
  • n is the molar concentration
  • ⁇ P is the pressure difference between the interior of the frGO network and ambient pressure
  • T is the temperature
  • l is the length of the frGO flakes
  • R is the gas constant.
  • D KA represents the Knudsen diffusivity of the reducing gas, which can be obtained from (Equation (13)):
  • d represents the gap between adjacent frGO layers and M A is the molar mass of a single reducing gas.
  • x0 is the time at which JK reaches a maximum value
  • ⁇ represents the standard deviation
  • the total amount of H or CO escaping from the frGO network after the flash can be calculated. Therefore, the reducing gas remaining in the frGO network after its rapid escape by Knudsen diffusion can be deduced by subtracting the escaped gas concentration from the total reducing gas produced by the flash radiation, which The volatile gas can be directly derived from the numerical model.
  • H2 has a higher diffusive flux due to its much smaller molar mass than CO ( Figure 2c and d).
  • GO, 0.5M6GO and 3M6GO showed higher fluxes than 6M6GO due to higher temperature and pressure within the system, while the calculated flux of 6M3GO was evident due to the much smaller amount of reducing gas lower.
  • reducing gas the total amount of H and CO required to achieve complete reduction of MnO nanoneedles for each sample (blue bars) based on the MnO feed mass per film, and Comparing this with the ideal case, the amount of residual gas should be greater than the amount of gas required to completely convert MnO to MnO .
  • Thermogravimetric analysis (TGA) of all reduced films was performed by a TGA Q500 analyzer under N2 flow from 40 °C to 800 °C at a heating rate of 10 °C min ⁇ 1 .
  • the temperature change during the reduction process was measured by an Optris laser thermometer.
  • the porous microstructure was revealed in scanning electron microscope (SEM) images taken on the FEI Helios NanoLab 600 Dual Beam FIB-SEM.
  • TEM transmission electron microscopy
  • the xMyG samples were sonicated in isopropanol solvent for 3 minutes.
  • the sonicated samples were drop cast on porous carbon TEM grids and dried at room temperature.
  • the morphology and selected area diffraction (SAED) patterns of the xMyG samples were obtained using TEM (1010 and 2100F).
  • the lattice fringes of 6M6G were observed using a high-resolution TEM (HRTEM-JEOL 2100F).
  • X-ray photoelectron spectroscopy (XPS) studies were performed on an AXIS Ultra spectrometer with a monochromatic AlK ⁇ X-ray source.
  • Raman spectra were acquired with the NTEGRA SPECTRA II AFM-Raman SNOM system.
  • GC gas chromatography
  • TCD thermal conductivity detector
  • FID flame ionization detector
  • the densely packed GO sheets rapidly expanded and formed a 3D sponge-like frGO network with numerous pores and cracks formed due to the reduction and exfoliation of GO (Fig. 3b).
  • the MnO2 nanoneedles in xMyG other than 0.5M6G (Fig. 3a) maintained the nanoneedle shape after reduction and crossed each other and formed a uniform and porous capping layer on the frGO nanosheets (Fig. 3b,c and Fig. 3a). 3d, Fig. 9, Fig. 10).
  • the uniform distribution of C, O and Mn elements in the 6M6G films after flash reduction can also be seen from the energy dispersive X-ray spectroscopy (EDS) elemental map in Figure 3d.
  • EDS energy dispersive X-ray spectroscopy
  • This unique morphology indicates a high level of surface exposure of the pseudocapacitive active material and good adhesion on the frGO network.
  • the reduced MnO2 nanoneedles deposited on the frGO network also provide a fine porous structure for graphene-based films, as they can act as "spacers" between frGO layers, further enlarging the interlayer spacing.
  • TEM transmission electron microscope
  • Fig. 3e The successful reduction of ⁇ - MnO to pure MnO was also observed in the transmission electron microscope (TEM) image in Fig. 3e, where the MnO nanoneedles were uniformly distributed on the frGO flakes.
  • SAED selected area electron diffraction
  • Fig. 3e shows distinct diffraction rings corresponding to the MnO (111), (200) and (220) lattice planes, which confirms that the MnO nanometers in 6M6G during this flash reduction process Needle formation.
  • Figure 3f the crystal structure of MnO nanoneedles was also investigated in high-resolution transmission electron microscopy (HRTEM) images, where clear (111) and (200) lattice fringes were found in MnO nanoneedles.
  • HRTEM transmission electron microscopy
  • HRTEM images also show the existence of folded graphene layers between the amorphous frGO regions and the crystalline MnO regions, which indicates a strong bond between MnO nanoneedles and frGO sheets, which is beneficial for electron transport and cycling when used as supercapacitor electrodes stability.
  • X-ray photoelectron spectroscopy (XPS) analysis showed an increase in C/O ratio ( Figures 14, 15 and Table 2) and a decrease in oxygen-to-oxygen content in all samples after reduction, indicating that OCFGs dissociated efficiently in all samples.
  • XPS X-ray photoelectron spectroscopy
  • FIG. 4c shows the Mn3s spectrum of the 6M6G film, in which doublets at 83.7 eV and 89.7 eV were identified.
  • the peak spacing ( ⁇ E) in the Mn3s spectrum is generated by the parallel spin coupling between the 3s core level electrons and the 3d valence band electrons, which can directly determine the oxidation state of Mn.
  • ⁇ E(Mn3s) of Mn 2+ and Mn 4+ are assigned as 6.0 and 4.7 eV, respectively.
  • the ⁇ E(Mn3s) for 0.5M6G and 6M6G was calculated to be 6.0 eV, while the ⁇ E(Mn3s) for 3M6G and 6M3G were 5.4 and 5.3 eV, respectively. Consistent with the results of XRD, complete reduction from MnO2 to MnO can be observed in 0.5M6G and 6M6G films, while only partial reduction to MnO2 /MnO is observed in 3M6G and 6M3G films.
  • the Mn2p1/2 spectrum of 6M6G (Fig.
  • PVDF polyvinylidene fluoride
  • Cyclic voltammetry (CV), cyclic charge-discharge (CCD) and electrochemical impedance spectroscopy (EIS) measurements were performed using a Biologic VMP-300 potentiostat/galvanostat.
  • CV Cyclic voltammetry
  • CCD cyclic charge-discharge
  • EIS electrochemical impedance spectroscopy
  • I/m is the current density (A ⁇ g ⁇ 1 ) applied to the working electrode
  • ⁇ t(s) is the discharge time
  • ⁇ V(V) is the voltage window during the discharge.
  • I/M is the current density (A ⁇ g ⁇ 1 ) applied to the supercapacitor based on the mass of the two electrodes
  • ⁇ t(s) is the discharge time
  • ⁇ V(V) is the voltage window treatment during discharge.
  • the energy density (E cell , Wh ⁇ kg -1 ) and power density (P cell , W ⁇ kg -1 ) of frGO//6M6G were calculated according to the following formulas:
  • Figure 5c shows the CV curves of 6M6G at different scan rates. It can be observed that more than one pair of redox peaks appear at a low scan rate of 1 mV ⁇ s ⁇ 1 . This suggests that 6M6G undergoes a two-step redox reaction at a slow scan rate, not limited to the redox reaction between Mn 2+ and Mn 3+ during charge/discharge, which can be described as follows:
  • 6M6G With further oxidation/reduction of Mn 4+ , 6M6G can be expected to exhibit excellent capacitance values during slow charge/discharge cycles.
  • the internal resistance of the 6M6G electrode is also lower than other samples, which is demonstrated in the Nyquist plot in Fig. 5e. This can be explained from the uniform dispersion of MnO nanoneedles, which can enlarge the interlayer distance of the frGO network and facilitate ion diffusion within the frGO/MnO electrode.
  • the capacitance of 6M6G calculated from the CCD curve at a current density of 0.2 A ⁇ g -1 was as high as 1706 F ⁇ g -1 , and still remained at 108 F ⁇ g -1 at an ultra - high current density of 20 A ⁇ g -1 1 ( Figure 5d).
  • the maximum capacitance of 3M6G is 843F ⁇ g -1 , while other electrodes can hardly reach capacitance values higher than 300F ⁇ g -1 .
  • the impaired capacitive performance of 0.5M6G may be due to the relatively small amount of MnO incorporated into the frGO network.
  • the relatively low capacitive performance of 0.5M6G can also be explained by the aggregation of MnO nanoparticles, which is represented by the increase in the average particle width in the TEM images (shown in Fig. 10).
  • the aggregation of MnO species in 0.5M6G may be caused by the higher temperature and pressure during the reduction of 0.5M6GO, which loosens the attachment between MnO species and frGO flakes. Therefore, the internal resistance is observed to be high and the capacitance is limited due to insufficient charge transport. As a result, the capacitive performance of the 0.5M6G film was significantly affected, although the complete conversion to frGO/MnO was achieved therein.
  • Equation (17) can be rearranged as:
  • k 1 and k 2 can be determined from each given voltage The slope and y-intercept of the lower linear fit line are obtained. Thereafter, for each voltage in the CV curve, the capacitance contributed by the capacitive control process is calculated from k 1 ⁇ and plotted accordingly, as shown in Figure 18. The capacitance contribution (%) of the capacitance control process is determined based on the integration of the separate capacitance control curves.
  • the capacitance of the diffusion-controlled process is attributed to ion intercalation and solid-state Faradaic redox reactions, while the capacitance-controlled reaction establishes electrochemical double-layer capacitance (EDLC).
  • EDLC electrochemical double-layer capacitance
  • Figure 6c summarizes and compares the capacitance and diffusion contributions of the 3M6G and 6M6G electrodes at scan rates from 1 to 10 mV s, where the 6M6G electrode shows higher capacitive contributions than 3M6G at all scan rates (also shown in Fig. 18). Since the kinetics of capacitively controlled reactions are generally faster, the higher capacitive contributions in the 6M6G electrodes suggest that they are able to maintain higher capacitances at high current densities compared to 3M6G. This trend is consistent with the capacitance results shown in Fig. 5d.
  • MnO in 6M6G The specific capacitance contributed by MnO in 6M6G is consistently higher than that of MnO 2 /MnO in 3M6G even at the ultra-high current density of 20 A ⁇ g ⁇ 1 . This can be attributed to the complete conversion of MnO to MnO in 6M6G, which improves the electrochemical performance.
  • the excellent capacitive performance of 6M6G is also attributed to the high-quality frGO network.
  • the conductive porous frGO network not only provides highly conductive channels for electron transport and ion diffusion, but also contributes additional EDLC to the composite electrode. Therefore, ultrahigh capacitance values exceeding the theoretical limit of pure MnO can be obtained by the fully reduced 6M6G electrode.
  • the mechanically strong frGO network also acts as a backbone to tightly support the MnO nanoneedles and prevent them from failing during repeated charge/discharge cycles. For 6M6G, the capacitance can still maintain more than 81% of its original value under 1500 ultrafast charge/discharge cycles of 5A g -1 .
  • FIG. 7a shows the CV curves of the assembled frGO//6M6G asymmetric SC device under a large voltage window of 1.6 V.
  • the broadened voltage window in aqueous electrolytes can be explained by the different electrochemical reactions of anode and cathode materials under different voltage windows. Clear redox peaks can be identified in the CV curve (Fig. 7a) and the CCD curve (Fig. 20), which confirms the existence of pseudocapacitance caused by MnO.
  • a high energy density of 26.8Wh ⁇ kg -1 can be achieved at a high power density of 1198W ⁇ kg -1 .
  • the assembled supercapacitor device can maintain a good energy density performance of 10.9 Wh kg -1 even at an ultra-high power density of 15696 W ⁇ kg -1 , which is better than many reported graphene- and MnOx -based supercapacitor devices. Both are superior.
  • high-capacity frGO/MnO electrodes were produced by a facile and facile flash reduction process under the condition of sufficient reducing gas. Such a process can simultaneously achieve high-quality GO reduction and complete conversion from MnO to MnO within milliseconds.
  • the resulting MnO nanoneedles were homogeneously immobilized on the conductive and porous frGO network. This unique structure enables electrodes with extraordinary capacitance (1706F ⁇ g -1 /current density 0.2A g -1 ), which exceeds the theoretical limit of MnO and pristine graphene.

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Abstract

本发明提供了一种石墨烯/MnO电极的制备方法，包括以下步骤：A)形成包含MnO 2纳米针和氧化石墨烯的混合液；所述MnO 2纳米针与氧化石墨烯的质量比为1：(0.5～12)；B)将所述混合溶液形成膜；C)对所述膜进行闪光还原，得到石墨烯/MnO电极。本发明通过合理设计反应条件，提出了一种低成本，一步法闪光还原工艺来制备高性能石墨烯/MnOx电极。这种简单的方法可以制造高质量的多孔石墨烯网络，并且可以同时有效地合成嵌入赝电容活性MnO x纳米材料。使用所制造的电极证明了超出纯石墨烯和MnO x的理论极限的超高电容(高达1706F·g -1)。本发明还提供了一种石墨烯/MnO电极及高能量密度超级电容器。

Description

一种石墨烯/MnO电极、其制备方法及高能量密度超级电容器
本发明要求于2021年4月27日提交中国专利局、申请号为202110460094.0、申请名称为“一种石墨烯/MnO电极、其制备方法及高能量密度超级电容器”的中国专利申请的优先权，其全部内容通过引用结合在本发明中。
技术领域
本发明属于能量存储技术领域，尤其涉及一种石墨烯/MnO电极、其制备方法及高能量密度超级电容器。
背景技术
超级电容器(也称为“超级电容器”或“双电层电容器”)是电化学电容器，其电容值远高于其他电容器。由于其高能量密度，快速充电/放电能力，超过一百万次充电循环的长寿命以及在-40℃至70℃的宽温度范围内工作的能力，超级电容器被广泛用于储能和能源供应。由于电池的生产和处置会对环境污染和人体健康造成不利影响，近年来，超级电容器中的环保材料及其低维护成本促进了超级电容器的发展。此外，超级电容器比电池优越，因为它们可以提供更高的功率密度(最高45kW kg -1)和更长的循环寿命(一百万次循环)。尽管如此，超级电容器的能量密度比电池的能量密度低约一个数量级，这限制了超级电容器在实际应用中的使用。
超级电容器的能量密度(E)由E＝1/2CV 2给出，它与比电容(C)和工作电压窗口(V)的平方成正比。比电容主要取决于电极性能。在开发基于碳的超级电容的过程中，纯碳基电极的总电容和能量密度仍然相对较低。在碳基电极中，尽管石墨烯被认为是最有前途的电极材料，具有出色的导电性和较高的理论表面积，但比电容的理论极限为550F g-1。因此，已经采用了不同的策略来改善碳基电极的电容，其中一种有前途的方法是通过添加锰氧化物(MnOx)来引入赝电容，这是因为它们具有较高的理论电容以及其丰富的地球和无毒性质。
一氧化锰(MnO)的理论电容(～1,350F g-1)比经过广泛研究的二氧化锰(MnO2)电极(1,110F g-1)更高，表明其有可能进一步提高二氧化锰的电容。碳基电极。2013年，廖等他提出通过水热法将垂直取向的石墨烯@MnO纳米片制备为高性能超级电容电极，并将电极的比电容提高到790F g-1。后来，还研究了其他制造方法，例如对MnO纳米颗粒的自组装进行碳涂层，在碳纳米纤维上直接静电纺丝以及将MnO热等离子体沉积在多孔碳材料上以合成MnO/碳电极。然而，尽管已经合成了纳米MnO并将其沉积在碳基电极中，但是该过程相对复杂并且通常需要多个步骤。因为纳米MnO在合成过程中遭受颗粒的团聚，这导致表面活性位点的损失并因此降低了电化学活性。结果，所报道的MnO/碳电极的电容通常小于800F·g -1，这远低于理论极限(仅达到约60％)。因此，通过一种容易且简单的方法来生产高电容超级电容电极，将MnO均匀地锚固在碳网络上仍然具有挑战性。
发明内容
本发明的目的在于提供一种石墨烯/MnO电极、其制备方法及高能量密度超级电容器，本发明中制备得到的石墨烯/MnO电极在0.2A·g -1时显示出高达1706F·g -1的超高电容。
本发明提供一种石墨烯/MnO电极的制备方法，包括以下步骤：
A)形成包含MnO 2纳米针和氧化石墨烯的混合液；
所述MnO 2纳米针与氧化石墨烯的质量比为1：(0.5～12)；
B)将所述混合溶液形成膜；
C)对所述膜进行闪光还原，得到石墨烯/MnO电极。
优选的，所述先将MnO 2纳米针与水超声混合，得到MnO 2纳米针胶体，再与氧化石墨烯溶液混合，得到混合溶液。
优选的，所述MnO 2纳米针的直径为10～30nm，长度为200～400nm。
优选的，所述MnO 2与氧化石墨烯的质量比为1：(0.8～1.2)。
优选的，所述混合溶液通过真空过滤法形成膜，所述真空过滤使用的过滤膜孔径为0.02～0.03μm。
优选的，所述闪光还原的功率为600～700Ws。
优选的，所述膜中的氧化石墨烯在闪光还原过程中产生足量的还原性气体使MnO 2转化为MnO x，1≤x＜2。
优选的，所述MnO 2纳米针按照以下步骤制备：
将二价锰盐在有机溶剂中加热回流，加入高锰酸钾，搅拌反应后，收集沉淀物，洗涤，干燥后得到MnO 2纳米针。
本发明提供一种如上文所述的制备方法制备得到的石墨烯/MnO电极。
优选的，所述石墨烯/MnO电极包括还原氧化石墨烯和分布在还原氧化石墨烯层间的MnO x纳米针，1≤x＜2。
优选的，所述MnO x纳米针的质量分数为27～92wt％。
本发明提供一种高能量密度超级电容器，包括上文所述的石墨烯/MnO电极和水基电解液。
本发明提供了一种石墨烯/MnO电极的制备方法，包括以下步骤：A)形成包含MnO 2纳米针和氧化石墨烯的混合液；所述MnO 2纳米针与氧化石墨烯的质量比为1：(0.5～12)；B)将所述混合溶液形成膜；C)对所述膜进行闪光还原，得到石墨烯/MnO电极。本发明通过合理设计反应条件，提出了一种低成本，一步法闪光还原工艺来制备高性能石墨烯/MnO x电极。这种简单的方法可以制造高质量的多孔石墨烯网络，并且可以同时有效地合成嵌入赝电容活性MnO x纳米材料。使用所制造的电极证明了超出纯石墨烯和MnO x的理论极限的超高电容(高达1706F·g -1)。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据提供的附图获得其他的附图。
图1为通过还原气体分别在(a)不足和(b)足够的情况进行GO/MnO 2共还原过程的示意图；
图2为独立的GO，0.5M6GO，3M6GO，6M6GO和6M3GO薄膜的温度(a)和压力(b)随时间变化的曲线；上述样品的(c)H 2和(d)CO气体的克努森扩散通量随时间变化的曲线；(e)比较产生的还原气体，该气体完全还原MnO 2所需的量，并且在上述样品在克努森扩散后仍保留的；
图3为(a)MnO 2纳米针的扫描电子显微镜(SEM)图像；(b)和(c)为不同放大倍数下6M6G的SEM图像；(d)6M6G的元素分布(CKα1，OKα1和MnKα1)图像，比例尺为20μm；(e)6M6G的透射电子显微镜(TEM)图像，插图显示了6M6G的相应选择区域电子衍射(SAED)模式；(f)6M6G的高分辨率透射电子显微镜(HRTEM)图像；
图4(a)所有还原样本的XRD图谱；(b)对6M6G的C1s峰进行XPS分析，(c)6M6G的Mn3s峰，以及(d)6M6G的Mn2p峰；(e)比较C1s峰中每个样品的碳氧化物键比(左)和C-C键比(右)；(f)比较每个样品的Mn 2+与Mn 4+的比率(左)通过Mn 2p峰与和Mn 3s峰的峰分离(右)；
图5(a)对于frGO，0.5M6G，3M6G，6M6G和6M3G，在10mV s -1的CV曲线和(b)在1A·g -1的CCD曲线；(c)6M6G电极在1mV·s -1至20mV·s -1的扫描速率下的CV曲线；(d) 根据CCD曲线计算的frGO，0.5M6G，3M6G，6M6G和6M3G之间的电容比较，插图显示了用于这项工作的三电极电池的电化学测量示意图；(e)frGO，0.5M6G，3M6G，6M6G和6M3G的奈奎斯特图，插图显示了高频区域；(f)6M6G在5A·g -1的快速充放电循环下的循环保持率，插图显示了第一个和第1500个循环的CCD曲线比较；
图6(a)3M6G和(b)6M6G在1mV·s -1扫描速率下的电容分离分析结果；(c)根据电容分离分析，在3M6G和6M6G不同扫描速率下的归一化电容贡献率；(d)仅基于MnO 2/MnO和MnO含量的贡献，在3M6G和6M6G不同电流密度下的比电容，插图显示了3M6G和6M6G膜中MnO 2/MnO和MnO含量的重量比；
图7(a)不同扫描速率下frGO//6M6G不对称SC器件的CV曲线；(b)frGO//6M6G非对称SC器件的奈奎斯特图，插图显示了奈奎斯特图的高频区域和拟合的等效电路；(c)frGO//6M6G的比电容，插图说明了非对称SC器件的配置；(d)frGO//6M6G在2A·g -1的大电流密度下反复充电/放电下的循环稳定性，插图显示frGO//6M6G能够点亮LED单元；(e)frGO//6M6G的Ragone图；
图8气相色谱仪(GC)带有热导检测器(TCD)和火焰离子化检测器(FID)，与手套箱气氛相比，GO的闪光还原情况；
图9(a)frGO，(b)0.5M6G，(c)3M6G和(d)6M6G样品的SEM图像。比例尺为2μm；
图10(a)0.5M6G和(b)6M6G样品的TEM图像以及(c)0.5M6G和(d)6M6G中MnO纳米颗粒宽度分布的相应直方图；
图11为frGO，MnO 2和frGO/MnOx样品的热重分析(TGA)数据；
图12与标准α-MnO 2JCPDS PDF 44-0141相比，针状纳米MnO 2的XRD图谱；
图13为GO，0.5M6GO，3M6GO，6M6GO和6M3GO的XRD图谱；
图14 XPS分析(a)GO和frGO，(b)0.5M6GO和0.5M6G，(c)3M6GO和3M6G，(d)6M3GO和6M3G以及(e)碳键比(C-C)％与碳氧比；
图15对(a)GO和frGO，(b)0.5M6GO和0.5M6G，(c)3M6GO和3M6G和(d)6M3GO和6M3G的宽扫描光谱XPS分析；
图16(a)MnO 2，(b)0.5M6G，(c)3M6G和(d)6M3G的Mn3s的XPS光谱分析；
图17为纯针状纳米MnO 2的拉曼光谱，表明成功合成了纯α-MnO 2；
图18 3M6G在扫描速率为(a)2mV·s -1，(b)5mV·s -1，(c)10mV·s -1和6M6G在扫描速率为(d)2mV·s -1，(e)5mV·s -1，(f)10mV·s -1时的电容分离分析结果；
图19为比较3M6G和6M6G电极在电流密度为0.2A·g -1时的总电极电容，frGO的电容贡献和MnO x的电容贡献；
图20在电流密度(基于frGO和6M6G电极的总质量)在1.5A g -1和15A g -1之间的情况下，frGO//6M6G非对称超级电容器件的CCD曲线；
图21 frGO//6M6G非对称超级电容器件的波特图(阻抗相位与频率的关系)，松弛时间估计为0.89s。
具体实施方式
本发明提供了一种石墨烯/MnO电极的制备方法，包括以下步骤：
A)形成包含MnO 2纳米针和氧化石墨烯的混合溶液；
所述MnO 2与氧化石墨烯的质量比为1：(0.5～12)；
B)将所述混合溶液形成膜；
C)对所述膜进行闪光还原，得到石墨烯/MnO电极。
本发明首次报告了一种绿色且简单的共还原方法，该方法可在几毫秒内通过超快闪光还原工艺生产高性能石墨烯/MnO电极。在生产高质量多孔石墨烯材料的过程中，我们利用 GO闪光还原产生的还原气体(CO和H 2)将预沉积的MnO 2纳米针完全转变为MnO，而不会发生团聚。通过合理控制原料比，可以达到最佳的还原条件。结果表明，所生产的frGO/MnO电极在0.2A·g -1时显示出高达1706F·g -1的超常电容，甚至超过了原始石墨烯电极和纯MnO电极的理论极限。
本发明首先按照以下方法合成MnO 2纳米针，在本发明中，所述MnO 2纳米针指的是针状的MnO 2纳米颗粒。
优选的，所述MnO 2纳米针的直径为10～30nm，更优选为15～20nm；长度优选为200～400nm，更优选为300～350nm。
将二价锰盐在有机溶剂中加热回流，加入高锰酸钾，搅拌反应后，收集沉淀物，洗涤，干燥后得到MnO 2纳米针。
在本发明中，所述二价锰盐优选为氯化锰，如MnCl 2·4H 2O，所述有机溶剂优选为醇溶剂，比如异丙醇。所述加热回流的温度优选为80～85℃，更优选为82～83℃。
在本发明中，所述高锰酸钾与氯化锰的质量比优选为1：(1～2)，更优选为1：(1.5～1.8)。
所述加热回流和反应均在搅拌的条件下进行，10～15min之后，冷却至室温，收集产生的黑色沉淀物，离心，用DI水洗涤，最后在60℃下干燥约8小时，得到MnO 2纳米针。
在本发明中，所述氧化石墨烯的来源没有特殊的限制，可采用改良的Hummer方法制备。
本发明优选先将一定质量的MnO 2纳米针加入去离子水中并进行超声处理，形成水合物稳定的胶体。
然后将纳米MnO 2胶体与氧化石墨烯(GO)溶液混合并超声处理15～20min，得到混合物。
在本发明中，所述MnO 2纳米针与氧化石墨烯的质量比为1：(0.5～12)，优选为1：(0.8～1.2)，最优选为1：1。
将混合物以真空过滤法通过标称孔径为0.03μm的聚醚砜(PES)膜过滤。形成膜，在60℃下干燥并小心地剥离以形成独立膜。
使用闪光装置对所形成的膜进行闪光还原，得到石墨烯/MnO电极。
在本发明中，所述闪光装置优选为Einstein(E640)闪光装置，所述闪光功率优选为600～700Ws，更优选为640～650Ws。
所述闪光还原具有有效的光热效应，强闪光脉冲的照射引发氧化石墨烯(GO)膜的剧烈还原和剥落，大功率闪光脉冲触发了含氧官能团的快速离解(OCFGs)是由于瞬时高温和CO，CO 2和H 2O等气态产物的爆发而引起的，这些气态产物导致局部压力上升，从而建立了多孔3D石墨烯网络。从而使高导电性和多孔性的快速还原氧化石墨烯(frGO)电极具有出色的电化学性能。大量一氧化碳(CO)，二氧化碳(CO 2)，水蒸气(H 2O)和氢(H 2)之类的气体从GO的还原过程中释放出来，再加上快速辐照后GO膜内的瞬间温度升高，提供了理想的环境用于将MnO 2还原为MnO。
本发明还提供了一种如上述制备方法制备得到的石墨烯/MnO电极，所述石墨烯/MnO电极包括石墨烯和掺杂在石墨烯层间的MnO x纳米针，1≤x＜2，优选的，x＝1，即全部的MnO 2都被还原形成MnO。
本发明还提供了一种高能量密度超级电容器，包括石墨烯/MnO电极和水基电解液。
本发明对水基电解液的种类和用量没有特殊限制，采用本领域常用的水基电解液即可。
实施例1
将0.18g氯化锰(II)(MnCl2·4H2O)添加到50mL异丙醇中，然后在剧烈搅拌下于83℃回流，然后将5mL高锰酸钾(KMnO 4)水溶液(0.02g·mL -1)快速添加到沸腾溶液中。搅拌10分钟然后冷却至室温后，收集立即产生的黑色沉淀物，离心，用DI水洗涤，最后 在60℃下干燥约8小时，得到MnO 2纳米针。
然后将一定质量的MnO 2纳米针加入去离子水中并进行超声处理，形成水合物稳定的胶体。
GO溶液(2mg·ml -1水溶液)是通过改良的Hummer方法制备的，购自SupraG Energy PtyLtd。
将15毫升0.2毫克mL -1纳米MnO 2胶体与3毫升2mg·ml -1的GO溶液混合并超声处理15分钟。然后将混合物通过真空过滤法通过标称孔径为0.03μm的聚醚砜(PES)膜过滤。随后将膜在60℃下干燥并小心地剥离以形成独立膜3M6GO膜(每个独立膜3mg MnO 2和6mg GO)。
闪光还原的过程均在Einstein(E640)闪光装置的充氮手套箱内进行，功率为640Ws，经闪光还原后，得到3M6G膜。
通过调节MnO 2纳米针胶体和GO溶液的体积和浓度来控制GO/MnO 2膜的进料比。每个GO/MnO 2样品都标记为xMyGO，以表明每个制作的薄膜均包含x mg的MnO 2纳米针和y mg的GO薄片。闪光还原后，将相应的还原膜标记为xMyG。
按照上述方法，分别制备得到纯GO膜，0.5M6GO膜，3M6GO膜，6M6GO膜和6M3GO膜，经过闪光还原后，分别得到纯还原氧化石墨烯膜，0.5M6G膜，3M6G膜，6M6G膜和6M3G膜。
由于石墨烯片之间局部温度和压力的瞬时升高，所产生的气体在闪光还原后不久就通过石墨烯网络的间隙迅速逸出，从而在该反应中几乎没有留下CO和H 2。因此，还原过程中frGO网络中滞留的还原气体量在提供合适的还原环境以确保高MnO 2转化率方面起着关键作用。
进料比的控制以及对还原的影响
可以通过调节制膜过程中GO和MnO 2纳米针的进料比例来控制这种加工环境。如图1所示，通过控制进料比可以实现闪光还原过程中的两种反应方案：(1)当GO还原提供足够量的还原气体并保留在frGO网络中时，共还原过程可产生frGO/期望将MnO 2完全还原为MnO的电极，而(2)在还原气体不足的环境中，尽管可以实现GO的相同有效还原，但只有一部分MnO 2可以还原为MnO。这导致部分还原为frGO/MnO 2/MnO膜。还原气体不足的原因可能是：首先在闪光还原过程中从GO释放的气体量减少，或者是这些气体从GO膜的间隙中快速逸出。因此，确保有效生产frGO/MnO电极的关键被认为是通过闪光还原过程产生大量还原气体，然后在frGO网络中成功捕获还原气体。
为了揭示进料比对共还原性能的影响，我们使用COMSOL Multiphysics 5.5建立了包含关键化学反应的数值模型，以模拟还原气体的产生。在该闪光减少过程中考虑了四个关键的化学反应(反应(2)-(5))：
GO→frGO+CO+CO 2+H 2O      (2)
Figure PCTCN2022086742-appb-000001
Figure PCTCN2022086742-appb-000002
Figure PCTCN2022086742-appb-000003
根据纯GO膜，0.5M6GO，3M6GO，6M6GO和6M3GO样品的进料质量设置该模型中GO和MnO 2的初始量，其中xMyGO表示膜包含x mg MnO 2和y mg GO。闪光还原后，将xMyGO膜相应地标记为xMyG。使用激光温度计测量了不同反应场景的温度变化(图2a)，并在模拟模型中也进行了考虑。可以观察到，这在快速照射后几毫秒内几乎所有样品 均显示出在700℃左右的峰值温度。然而6M6GO薄膜的峰值温度仅约为470℃，但仍高于去除OCFG所需的温度，并能够以约6×10 6℃·min -1的高加热速率实现高质量的GO还原。图2b证明了上述GO/MnO 2样品中的压力变化是由OCFG的即时加热和分解引起的。尽管独立膜中的GO量较少，从而限制了还原性气体的产生，从而导致6M3GO中的压力低得多，但其压力仍比剥落frGO层并产生多孔膜所需的压力高2个数量级以上。在frGO层之间保留的巨大压力会导致气体通过间隙快速从frGO网络中逸出。在这种情况下，我们基于气体动力学理论研究了克努森扩散通量(J K)，以显示每单位面积从frGO网络逸出的气体的摩尔流量。
使用COMSOL Multiphysics 5.5计算了GO/MnO 2闪光还原的数值模拟模型，该模型与实验设置一致。化学反应是基于具有恒定体积的0D模型进行模拟的，其中整个独立式GO/MnO 2(GO)膜内的反应被认为在所有方向上都是均匀的。基于每个过滤膜的体积计算反应模型的体积。GO的闪光还原可描述为以下不可逆反应(6)：
GO→frGO+CO+CO 2+zH 2O     (6)
已确定GO热分解期间的x：y比约为1：2。根据我们测得的热曲线，GO薄膜由于在闪光灯下曝光时的光热效应而承受了温度的突然升高，并且由于气体的释放而迅速建立了局部压力。在这样的高温高压环境下，可能会发生以下可逆反应(7)-(9)：
Figure PCTCN2022086742-appb-000004
Figure PCTCN2022086742-appb-000005
Figure PCTCN2022086742-appb-000006
根据反应动力学定义，反应的正向反应速率r(aA+bB→product)可描述为：
r＝k[A] a[B] b      (10)
其中k表示反应速率常数，[A(B)]是浓度，a(b)是反应顺序。每个反应的反应速率常数可以根据Arrhenius表达式进一步定义：
Figure PCTCN2022086742-appb-000007
其中A是正向频率因子，E a代表活化能，T代表温度，R是气体常数。在表1中可以找到此仿真模型中使用的参数(A，E a和n)的列表，而该模型中使用的T是直接从激光温度计测量的。用平衡常数进一步校正可逆反应速率。
表1 GO和GO/MnO 2薄膜闪光还原过程中产气数值研究中使用的参数
Figure PCTCN2022086742-appb-000008
对于纯GO样品，我们将输入的GO质量模拟为6mg(与用于过滤的每张薄膜的输入GO质量相同)。调整x：y：z以确保CO：H 2的输出浓度比与GC-TCD测量值一致(图8)。之后，通过相应地改变GO和MnO 2的输入质量，用相同的模型模拟GO/MnO 2样品。
使用Knudsen扩散模型评估闪蒸后还原气体的扩散。克努森扩散通量(J K)表征了扩散气体的摩尔流速，其计算公式如下(12)：
Figure PCTCN2022086742-appb-000009
其中n表示摩尔浓度，ΔP是frGO网络内部与环境压力之间的压力差，T是温度，l是frGO薄片的长度，R是气体常数。D KA表示还原气体的克努森扩散率，可以从(公式(13))获得：
其中d表示相邻的frGO层之间的间隙，M A是单个还原气体的摩尔质量。
为了估计在闪光后从frGO薄膜逸出的H 2或CO总量，将Knudsen扩散通量(J K)模式简化为高斯脉冲，遵循公式(13)：
Figure PCTCN2022086742-appb-000010
其中x 0是J K达到最大值的时间，而σ表示标准偏差，并且可以根据以下关系式(14)从所获得的J K模式的半峰全宽(FWHM)得出：
Figure PCTCN2022086742-appb-000011
通过积分所描述的Knudsen扩散通量的高斯脉冲，可以计算出闪光后从frGO网络逸出的H 2或CO总量。因此，在气体通过克努森扩散而快速逸出之后，残留在frGO网络中的还原性气体可以通过从闪速辐射产生的全部还原性气体中减去逸出的气体浓度来推导，该总还原性气体可以直接从数值模型中推导出来。
通常，由于H 2的摩尔质量比CO小得多(图2c和d)，因此具有较高的扩散通量。对于H 2和CO，GO，0.5M6GO和3M6GO由于系统内较高的温度和压力而显示出比6M6GO更高的通量，而计算出的6M3GO的通量由于还原气体的量少得多而明显较低。
在图2e中，我们根据每张膜的MnO 2进料质量进一步估算了还原气体的浓度(实现每个样品(蓝条)完全还原MnO 2纳米针所需的H 2和CO的总量，并将其与理想的情况是，残留气体的量应大于将MnO 2完全转化为MnO所需的气体量。图2e，0.5M6GO和6M6GO展示了还原气体充足的场景，其中生成并捕获了足够的还原气体以完全还原MnO 2，而在3M6GO和6M3GO的情况下，观察到还原气体不足的场景，因为还原气体的数量由于气体逸出少于MnO 2完全还原所需的量，表明MnO 2的部分还原。对于6M3GO，GO闪光还原产生的还原气体的量短时照射不足以完全还原MnO 2。对于3M6GO，尽管GO还原后会产生大量还原气体，但薄膜经历了剧烈的气体扩散，与所需量相比，还原气体相对较低，因此在该闪光还原过程中MnO 2还原效率较低。
从仿真研究表明，我们在制膜过程中合成了进料比受控的GO/MnO 2。
分析方法
所有还原膜的热重分析(TGA)是通过TGA Q500分析仪在N 2流下从40℃到800℃在10℃·min -1加热速率下进行的。
还原过程的温度变化通过Optris激光温度计测量。
使用CuKα辐射
Figure PCTCN2022086742-appb-000012
在Bruker D8Discover粉末X射线衍射仪上收集X射线衍射(XRD)图。
在FEI Helios NanoLab 600 Dual Beam FIB-SEM上拍摄的扫描电子显微镜(SEM)图像中揭示了多孔微结构。
为了制备透射电子显微镜(TEM)样品，将xMyG样品在异丙醇溶剂中超声处理3分钟。将超声处理的样品滴铸在多孔碳TEM网格上，并在室温下干燥。使用TEM(1010和2100F)获得了xMyG样品的形态和选定的区域衍射(SAED)模式。使用高分辨率TEM(HRTEM-JEOL 2100F)观察6M6G的晶格条纹。
X射线光电子能谱(XPS)研究是在具有单色AlKαX射线源的AXIS Ultra光谱仪上进行的。
拉曼光谱是通过NTEGRA SPECTRA II AFM-Raman SNOM系统获得的。
通过具有热导检测器(TCD)和火焰离子化检测器(FID)的气相色谱(GC)进行气 体分析。
还原膜的性能分析
在这些独立的薄膜上进行快速照射后，致密堆积的GO片材迅速膨胀并形成了3D海绵状的frGO网络，由于GO的还原和剥落而形成了许多孔和裂纹(图3b)。快速曝光后，xMyG中除0.5M6G以外的MnO 2纳米针(图3a)在还原后仍保持纳米针形状，并且彼此交叉并在frGO纳米片上形成均匀且多孔的覆盖层(图3b，c和图3d，图9，图10)。闪光还原后的6M6G薄膜中C，O和Mn元素的均匀分布也可以从图3d中的能量色散X射线光谱(EDS)元素映射图中看出。这种独特的形态表明赝电容活性材料的高水平表面曝光以及在frGO网络上的良好附着力。此外，沉积在frGO网络上的还原的MnO 2纳米针还为基于石墨烯的薄膜提供了精细的多孔结构，因为它们可以充当frGO层之间的“间隔物”，从而进一步扩大层间距。
为了研究每个样品中MnO x的质量负载，我们在N 2加热下进行了热重量分析(TGA)测量。据计算，发现0.5M6G，3M6G，6M6G的每张膜中的MnO x质量负载分别为27.2wt％，61.2wt％和75.9wt％(图11)。值得注意的是，即使在6M3G薄膜中高达91.7wt％的超高质量负载下，也没有观察到明显的MnO x团聚(图9)。这表明实现了将大量的MnOx材料均匀地加载到frGO网络上。
在图3e中的透射电子显微镜(TEM)图像中也观察到了成功将α-MnO 2还原为纯MnO的情况，其中MnO纳米针均匀分布在frGO薄片上。图3e中的选定区域电子衍射(SAED)图案显示出与MnO(111)，(200)和(220)晶格面相对应的明显衍射环，这证实了在该闪光还原过程中6M6G中MnO纳米针的形成。如图3f所示，还在高分辨率透射电子显微镜(HRTEM)图像中研究了MnO纳米针的晶体结构，其中在MnO纳米针中发现了清晰的(111)和(200)晶格条纹。HRTEM图像还显示出无定形的frGO区域和结晶的MnO区域之间存在折叠的石墨烯层，这表明MnO纳米针和frGO片之间牢固结合，当用作超级电容电极时有利于电子传输和循环稳定性。
X射线光电子能谱(XPS)分析表明，还原后所有样品的C/O比增加(图14，15和表2)和氧-氧含量下降，表明OCFGs在所有样品中均有效解离。包含C1s光谱中的成分(图4b和14)。图4e表明，所有还原的薄膜在C1s峰中均表现出尽管GO和MnO 2的不同进料比，相似的碳-碳键与碳-氧化物键比率水平和占主导地位的碳-碳键约为80％。
表2 闪光还原之前和之后样品中C/O比
Figure PCTCN2022086742-appb-000013
还通过XPS测量研究了frGO网络中MnO的形成。图4c显示了6M6G膜的Mn3s光谱，其中确定了83.7eV和89.7eV处的双峰。Mn3s光谱中的峰间距(ΔE)是由3s核心能级电子与3d价带电子之间的平行自旋耦合产生的，可以直接确定Mn的氧化态。根据文献，Mn 2+和Mn 4+的ΔE(Mn3s)分别指定为6.0和4.7eV。如图4f和16所示，0.5M6G和 6M6G的ΔE(Mn3s)计算为6.0eV，而3M6G和6M3G的ΔE(Mn3s)分别为5.4和5.3eV。与XRD的结果一致，在0.5M6G和6M6G膜中可以从MnO 2完全还原为MnO，而在3M6G和6M3G膜中仅观察到部分还原为MnO 2/MnO。6M6G的Mn2p1/2光谱(图4d)可以解卷积为3个峰，分别为641.5、644.3和647.4eV，与Mn 2+，Mn 4+和Mn 2+卫星峰的价态相对应。尽管Mn3s光谱显示0.5M6G和6M6G均以氧化态占主导地位，但6M6G在所有样品中均表现出最高的MnO 2还原为MnO，这是由于Mn2p光谱中拟合的最大Mn 2+与Mn 4+组成比所致。如模拟结果所示，在0.5M6G和6M6G中向MnO的完全转化可以归因于产生了还原气体充足的情况。
制备frGO/MnO的工作电极
将准备好的xMyG膜，导电碳和聚偏二氟乙烯(PVDF)混合在一起，与N-甲基-2-吡咯烷酮(NMP)溶剂形成浆液，然后将其涂在1厘米乘1.5厘米面积内的铂集电器上，然后在80℃空气干燥。
使用Biologic VMP-300恒电位仪/恒电流仪进行循环伏安法(CV)，循环充放电(CCD)和电化学阻抗谱(EIS)测量。在典型的三电极测试中，铂膜电极和Hg/HgO电极分别用作对电极和参比电极。将1M KOH溶液用作电解质。使用以下公式从CCD曲线计算单电极的比电容(C_electrode，F·g -1)：
Figure PCTCN2022086742-appb-000014
其中I/m是施加到工作电极上的电流密度(A·g -1)，Δt(s)是放电时间，而ΔV(V)是放电过程中的电压窗口。
rGO//6M6G不对称超级电容的性能在1M KOH电解质中进行。将独立的6M6G和frGO薄膜压在镍泡沫盘(直径为15毫米)上，并按照类似三明治的结构组装成纽扣电池(如图7c所示)。frGO//6M6G非对称超级电容(C cell，F·g -1)的比电容是根据以下公式从CCD曲线得出的：
其中I/M是基于两个电极的质量施加到超级电容的电流密度(A·g -1)，Δt(s)是放电时间，而ΔV(V)是放电期间的电压窗口处理。根据以下公式计算frGO//6M6G的能量密度(E cell，Wh·kg -1)和功率密度(P cell，W·kg -1)：
Figure PCTCN2022086742-appb-000015
Figure PCTCN2022086742-appb-000016
6M6G电极和frGO//6M6G超级电容器件的循环稳定性均在CCD测量下的重复充电和放电循环下进行。
为了研究xMyG薄膜的电化学性能，我们使用1M KOH作为电解质对所有样品进行了三电极测试。对于几乎所有的xMyG样品，在循环伏安法(CV)曲线上均出现一对对称的阴极和阳极峰，扫描速率为10mV·s -1，这表明由于K +离子(图5a)的可逆吸附和解吸，Mn具有可逆的法拉第行为。但是，与6M6G和3M6G电极相比，较小的封闭区域使6M3G和0.5M6G的电容值小得多。从循环充放电(CCD)曲线可以得出类似的结论(图5b)，其中6M6G和3M6G的充放电时间比其他样品大得多。除轻微弯曲外，所有xMyG样品的CCD曲线均显示出近似对称的形状，这表明其良好的电容性能同时包含赝电容和双层电容量。6M6G表现出最高的电容性能，因为完全还原为frGO/MnO确保电极材料具有出色的均质性，并且将MnO以高负载量负载到frGO框架上，确保了高容量MnO材料在氧化还原反应中的有效利用。图5c显示了在不同扫描速率下6M6G的CV曲线。可以观察到，在低扫描速率1mV·s -1下出现了多于一对的氧化还原峰。这表明6M6G在缓慢的扫描速率下经历了两步氧化还原反应，而不仅限于在充电/放电过程中Mn 2+和Mn 3+之间的氧化还原反 应，可以描述如下：
Figure PCTCN2022086742-appb-000017
随着Mn 4+的进一步氧化/还原，在缓慢的充电/放电循环中，可以预期6M6G具有出色的电容值。6M6G电极的内部电阻也低于其他样品，这在图5e中的Nyquist图中得到了证明。可以从MnO纳米针的均匀分散来解释这一点，它可以扩大frGO网络的层距离并促进frGO/MnO电极内的离子扩散。
如预期的那样，根据CCD曲线在0.2A·g -1的电流密度下计算出的6M6G电容高达1706F·g -1，并且在20A·g -1的超高电流密度下仍保持108F·g -1(图5d)。3M6G的最大电容为843F·g -1，而其他电极几乎无法达到高于300F·g -1的电容值。0.5M6G的电容性能受损可能是由于掺入frGO网络中的MnO量相对较少。0.5M6G的相对较低的电容性能也可以通过MnO纳米颗粒的聚集来解释，这由TEM图像中平均颗粒宽度的增加来表示(如图10所示)。0.5M6G中MnO物种的聚集可能是由于0.5M6GO还原过程中较高的温度和压力导致的，这使MnO物种与frGO薄片之间的附着变松了。因此，观察到内部电阻较高，并且由于电荷传输不足而限制了电容。结果，尽管在其中实现了完全转化为frGO/MnO，但是0.5M6G薄膜的电容性能受到了显着影响。对于6M3G膜，大量的纳米针覆盖了frGO纳米片的表面(图9)，这阻塞了frGO网络中用于离子吸附和扩散的部分孔和通道。此外，过量的MnO和MnO2材料本质上导电性差，这进一步限制了6M3G电极内的电荷转移。
通过用Dunn法将扩散控制过程和电容控制过程分开来研究电极动力学。在基于Dunn电流扫描速率依赖性方法的电容分离分析中，在CV测量中，对施加的扫描速率的电流响应将根据扩散控制的氧化还原反应或表面(电容)控制的过程而变化。对于电容性过程，电流(i(V))响应随扫描速率(ν)变化，而对于受半无限线性扩散限制的扩散控制的氧化还原反应，(i(V))响应随ν 1/2。因此，当前扫描速率关系可以表示为：
i(V)＝k 1v+k 2v 1/2        (16)
其中，k 1和k 2分别代表电容控制过程和扩散控制过程的系数。公式(17)可以重新排列为：
i(V)/v 1/2＝k 1v 1/2+k2      (17)
根据公式(17)绘制从1mV s -1到10mV s -1的慢扫描速率的i(V)/ν 1/2与ν 1/2对比，可以确定k 1和k 2从每个给定电压下线性拟合直线的斜率和y轴截距得出。此后，针对CV曲线中的每个电压，从k 1ν计算由电容控制过程贡献的电容，并相应地进行绘制，如图18所示。电容控制过程的电容贡献(％)是基于分离的电容控制曲线的积分确定的。
扩散控制过程的电容归因于离子嵌入和固态法拉第氧化还原反应，而电容控制的反应则建立了电化学双层电容(EDLC)。在图6a和b中以1mV·s -1的扫描速率研究了3M6G和6M6G电极的结果。6M6G电极比3M6G电极(18％)显示出更高的电容贡献(20％)，并且由CV曲线中较大的封闭区域表示更高的比电容值。图6c总结并比较了3M6G和6M6G电极在1到10mV s -1的扫描速率下的电容和扩散贡献，其中6M6G电极在所有扫描速率下均显示出比3M6G更高的电容贡献(也显示在图18中)。由于电容控制反应的动力学通常更快，因此6M6G电极中较高的电容贡献表明，与3M6G相比，它们在高电流密度下能够保持较高的电容。这种趋势与图5d所示的电容结果一致。
为了进一步比较经过完全还原和部分还原的电极之间的差异，我们仅基于MnO x材料减去了电容值对6M6G和3M6G电极的贡献(图6d和19)。减法与文献一致，其中frGO片材贡献的电容从电极电容中扣除，并基于每个样品的质量百分比对基于MnO x的电容进行校准。仅基于MnO质量，通过6M6G获得了0.2A·g -1时的2150F·g -1的超高电容，这远远超出了MnO的理论电容(1350F·g -1)，而较小的电容为1178F·g -1基于MnO和未还原的 MnO 2的总质量，通过3M6G实现。值得注意的是，MnO的理论电容是根据Mn 2+和Mn 3+在1V电压范围内的氧化还原反应计算得出的，而在6M6G的缓慢充放电循环中，Mn 3+的额外氧化还原反应如上所述，Mn 2+和Mn 4+参与其中。即使在20A·g -1的超高电流密度下，由6M6G中的MnO贡献的比电容始终高于3M6G中的MnO 2/MnO电容。这可以归因于6M6G中MnO 2完全转化为MnO，从而提高了电化学性能。
6M6G出色的电容性能也归功于高质量frGO网络。导电的多孔frGO网络不仅为电子传输和离子扩散提供了高导电性的通道，还为复合电极贡献了额外的EDLC。因此，通过完全还原的6M6G电极可以获得超过纯MnO理论极限的超高电容值。机械强度高的frGO网络也充当骨架，以紧密支撑MnO纳米针，并防止它们在重复的充电/放电循环中失效。对于6M6G，在5A·g -1的1500次超快充电/放电循环下，电容仍可保持在其原始值的81％以上。电容的逐渐减小主要是由于在快速且重复的充电/放电过程中受损的氧化还原反应所致。但是，鉴于MnO的大量负载和快速的循环速度，电容保持率仍高于81％仍显示出6M6G的良好循环稳定性，可与通过许多复杂工艺生产的其他rGO/MnOx电极相媲美。相比之下，我们的方法很简单，并且可以在几毫秒内完成，这证明了超快速生产具有超高电容的高质量石墨烯/MnO电极的方法。
通过组装独立的6M6G薄膜作为阴极和frGO薄膜作为阳极来制造实用的水基不对称超级电容器件，如图7c所示。将阳极和阴极浸入1M KOH电解质中。图7a显示了组装后的frGO//6M6G非对称SC器件在1.6V的大电压窗口下的CV曲线。水性电解质中变宽的电压窗口可以用阳极和阴极材料在不同的电压窗口下以不同的电化学反应来解释。可以在CV曲线(图7a)和CCD曲线(图20)中识别出明显的氧化还原峰，这证实了MnO造成的赝电容的存在。即使在快速扫描速率和大电流密度下，也不会从CV曲线和CCD曲线中观察到明显的畸变，这可以归因于6M6G和frGO电极内出色的离子和电子传输。理想的电荷传输也可以从图7b中的Nyquist图中看出，从中可以评估出约4.0Ω的较小内部电阻。结果，获得了出色的frGO//6M6G非对称器件的频率响应能力(图21)，只有0.89s的超短弛豫时间甚至比许多基于EDLC材料和商业应用的超级电容器件还要短。如图7c所示，在1.5A·g -1的大电流密度下(基于阳极和阴极的总质量)，优良的比电容值高达75.6F·g -1。通过frGO//6M6G不对称超级电容实现。为了评估稳定性能，在2A·g -1的大电流密度下对frGO//6M6G电池进行反复充电和放电。可以观察到，在连续4500次快速充电/放电循环之后，超级电容保留了其原始电容的84％(图7d)，这证明了frGO//6M6G在实际应用中具有出色的循环稳定性。图7e显示了frGO//6M6G的Ragone图。在1198W·kg -1的高功率密度下可以达到26.8Wh·kg -1的高能量密度。组装后的超级电容器件即使在15696W·kg -1的超高功率密度下也可以保持10.9Wh·kg -1的良好能量密度性能，这比许多已报道的基于石墨烯和MnO x的超级电容器件都优越。
综上所述，在还原性气体充足的条件下，通过简便易行的闪光还原工艺生产了高容量的frGO/MnO电极。这样的过程可以在几毫秒内同时实现高质量的GO还原和从MnO 2到MnO的完全转化。产生的MnO纳米针被均匀地固定在导电的和多孔的frGO网络上。这种独特的结构使电极具有非凡的电容(1706F·g -1/电流密度0.2A g -1)，超出了MnO和原始石墨烯的理论极限。当组装成frGO//6M6G非对称SC器件时，可以在1198W·kg -1的高功率密度下实现高达26.8Wh·kg -1的高能量密度。我们相信，这种独特的生产高性能frGO/MnO电极的方法不仅为有效，一步一步生产基于MnO的储能器件提供了亮点，而且为掺杂石墨烯材料的低成本制造提供了希望用于不同的应用，例如燃料电池，传感器和催化剂。
以上所述仅是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (12)

  1. 一种石墨烯/MnO电极的制备方法，包括以下步骤：
    A)形成包含MnO 2纳米针和氧化石墨烯的混合液；
    所述MnO 2纳米针与氧化石墨烯的质量比为1：(0.5～12)；
    B)将所述混合溶液形成膜；
    C)对所述膜进行闪光还原，得到石墨烯/MnO电极。
  2. 根据权利要求1所述的制备方法，其特征在于，所述先将MnO 2纳米针与水超声混合，得到MnO 2纳米针胶体，再与氧化石墨烯溶液混合，得到混合溶液。
  3. 根据权利要求1所述的制备方法，其特征在于，所述MnO 2纳米针的直径为10～30nm，长度为200～400nm。
  4. 根据权利要求1所述的制备方法，其特征在于，所述MnO 2与氧化石墨烯的质量比为1：(0.8～1.2)。
  5. 根据权利要求1所述的制备方法，其特征在于，所述混合溶液通过真空过滤法形成膜，所述真空过滤使用的过滤膜孔径为0.02～0.03μm。
  6. 根据权利要求1所述的制备方法，其特征在于，所述闪光还原的功率为600～700Ws。
  7. 根据权利要求1所述的制备方法，其特征在于，所述膜中的氧化石墨烯在闪光还原过程中产生足量的还原性气体使MnO 2转化为MnO x，1≤x＜2。
  8. 根据权利要求1所述的制备方法，其特征在于，所述MnO 2纳米针按照以下步骤制备：
    将二价锰盐在有机溶剂中加热回流，加入高锰酸钾，搅拌反应后，收集沉淀物，洗涤，干燥后得到MnO 2纳米针。
  9. 一种如权利要求1～8任意一项所述的制备方法制备得到的石墨烯/MnO电极。
  10. 根据权利要求9所述的石墨烯/MnO电极，其特征在于，所述石墨烯/MnO电极包括还原氧化石墨烯和分布在还原氧化石墨烯层间的MnO x纳米针，1≤x＜2。
  11. 根据权利要求10所述的石墨烯/MnO电极，其特征在于，所述MnO x纳米针的质量分数为27～92wt％。
  12. 一种高能量密度超级电容器，其特征在于，包括权利要求9～11任意一项所述的石墨烯/MnO电极和水基电解液。
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