CN110993375A - Method for preparing compact-structure RGO/MXene-sulfuric acid supercapacitor flexible electrode in one step and application thereof - Google Patents
Method for preparing compact-structure RGO/MXene-sulfuric acid supercapacitor flexible electrode in one step and application thereof Download PDFInfo
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- 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
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- 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
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- H—ELECTRICITY
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- 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
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- 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
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Abstract
The invention belongs to the field of electrochemistry, and particularly relates to a method for preparing a compact structure graphene/MXene-sulfuric acid supercapacitor flexible electrode in one step and application thereof. Firstly, mixing graphene oxide aqueous dispersion and MXene aqueous dispersion, adding sulfuric acid, and uniformly mixing; soaking the metal zinc sheet into the uniformly mixed solution, standing, obtaining a composite film on the surface of the metal zinc sheet, and stripping to obtain RGO/MXene-H2SO4A composite membrane. The invention adopts a layer-by-layer assembly method to prepare the compact structure RGO/MXene-H with ordered arrangement2SO4A composite film, which synchronously and horizontally distributes the molecules of the nonvolatile liquid electrolyte to the electricity in the self-assembly process of the filmAnd the electrode material is fully contacted with the electrolyte on the surface of the electrode material. The method has the advantages of simplicity, strong designability, wide applicability, good electrochemical performance and the like, and has wide application prospect in the fields of electrochemical materials and the like.
Description
Technical Field
The invention belongs to the field of electrochemistry, and particularly relates to a method for preparing a compact-structure RGO/MXene-sulfuric acid supercapacitor flexible electrode in one step and application thereof.
Background
Energy and environmental problems are two major problems that people need to solve at present. In the present days that fossil energy is gradually exhausted, environmental pollution is increasingly serious, and global climate is warmed, it is urgent to seek renewable green energy for replacing traditional fossil energy and to seek harmony between people and the environment. The utilization of new renewable energy sources, such as wind energy, solar energy and the like, the gradual marketization of electric vehicles and hybrid electric vehicles, and the rapid development of various portable electric devices all need high-efficiency, practical and 'green' energy storage and transportation systems. For a novel green energy storage device, the green energy storage device is concerned, and meanwhile, the high power density and the high energy density are important indexes for really replacing a traditional energy storage and transportation system. The super capacitor is an important 'green' energy storage device at present, and the core part of the super capacitor is an electrode material with excellent performance.
Graphene, a novel carbon material, oversized and perfect sp2The hybrid system has incomparable in-plane charge transport performance of 103-104S/m, and the thickness of the monomolecular layer makes the monomolecular layer have ultrahigh theoretical surface area of 2630m2(ii) in terms of/g. Particularly, the graphene ultrathin sheets can be stacked into a three-dimensional conductive network in a self-assembly mode, the special structure is not only beneficial to charge transfer between an electroactive substance and a current collector, but also beneficial to migration and permeation of charged components in an electrolyte, and the diffusion stroke of the graphene ultrathin sheets is greatly shortened, so that the electrochemical reaction is promoted to be rapidly carried out, the graphene ultrathin sheets are expected to have wide application prospects when being used as an electrode material of a super capacitor, and graphene is always accompanied with agglomeration of graphene sheet layers in the preparation process of a flexible electrode of the super capacitor material, so that the specific surface area is reduced.
The discovery of graphene has made two-dimensional nanomaterials a hot spot in research for the last decade. In addition to graphene, the two-dimensional nanomaterial includes black phosphorus, boron nitride, transition metal sulfides, and transition metal oxides. MXene is a novel transition metal carbide two-dimensional crystal and has a structure similar to that of graphene. Chemical formula (II)Is Mn+1XnWherein n is 1, 2 or 3, M is an early transition metal element, and X is carbon or/and nitrogen. This class of materials can be obtained by dissociating the phase a of the layered ceramic material MAX with lithium fluoride and hydrochloric acid, and has good electrical conductivity, low ion diffusion resistance, low open circuit voltage and high storage capacity. However, MXene also has the disadvantage of being prone to agglomeration itself.
The super capacitor has high power density and can realize rapid charge and discharge, and also has the advantages of ultra-long cycle life and simple structure, thus becoming one of the most potential flexible electronic devices. The conventional super capacitor is composed of a positive electrode, a negative electrode, a diaphragm and an electrolyte for conducting electrons, wherein the electrodes are core components of the capacitor, and for the commercialized super capacitor, the electrodes are mainly prepared by scraping slurry on the surface of a current collector, and the slurry generally consists of an electrode material binder and a conductive agent. For the conventional super capacitor, the binder and the current collector are indispensable parts, but in consideration of the electrochemical performance of the whole device, their existence also becomes a big disadvantage of the conventional capacitor. At the same time, the additive has a smaller capacitance, which tends to reduce the energy density of the entire capacitor. Moreover, since the electrodes of the supercapacitor made of graphene and its derivatives are generally porous structures obtained by disordered arrangement of graphene, such disordered porous structures cause a series of structural defects and also cause low volumetric energy density of the whole capacitor. In addition, in order to improve the flexibility of the supercapacitor, a solid or quasi-solid electrolyte is generally adopted, and due to the fact that the wettability of graphene on an electrode material is poor due to the fact that the hydrophobicity of graphene and the mobility of the solid or quasi-solid electrolyte are low, sufficient contact between the electrolyte and the electrode material is an important problem to be solved.
Disclosure of Invention
The invention aims to provide a method for preparing a compact-structure RGO/MXene-sulfuric acid supercapacitor flexible electrode in one step, which realizes full contact between an electrode material and electrolyte and has the advantages of simple method, strong designability, wide applicability, good electrochemical performance and the like.
The method for preparing the RGO/MXene-sulfuric acid supercapacitor flexible electrode with the compact structure in one step comprises the following steps: firstly, mixing graphene oxide aqueous dispersion and MXene aqueous dispersion, adding sulfuric acid, and uniformly mixing; then soaking the metal zinc sheet into the uniformly mixed solution for standing to obtain RGO/MXene-H on the surface of the metal zinc sheet2SO4Composite film, stripping to obtain RGO/MXene-H2SO4And (3) a composite film, namely a flexible electrode of the super capacitor.
Wherein:
the mass of the MXene accounts for 10-40% of the total mass of the graphene oxide and the MXene.
The molar concentration of the sulfuric acid is 0.5-1 mol/L.
The MXene aqueous dispersion is prepared by mixing deionized water and concentrated hydrochloric acid, adding lithium fluoride, mixing, and adding Ti3AlC2And etching, centrifugally washing to neutrality, dispersing washed precipitate into deionized water, ultrasonically treating, centrifuging, and removing precipitate to obtain MXene aqueous dispersion.
The volume ratio of the deionized water to the concentrated hydrochloric acid is 1: 1-2, the concentration of the concentrated hydrochloric acid is 12mol/L, and the lithium fluoride and the Ti are3AlC2The mass ratio of the components is 1-1.5: 1-1.5, the etching temperature is 45-55 ℃, and the etching time is 18-24 hours.
The preparation process of the graphene oxide aqueous dispersion comprises the steps of mixing concentrated sulfuric acid, graphite, sodium nitrate and potassium permanganate, preserving heat in a water bath, adding water for dilution under the ice bath condition, adding hydrogen peroxide, washing with hydrochloric acid and deionized water, performing ultrasonic centrifugation, and taking supernate to obtain the two-dimensional layered graphene oxide aqueous dispersion.
The dosage proportion of the concentrated sulfuric acid, the graphite, the sodium nitrate, the potassium permanganate and the hydrogen peroxide is as follows: 70-90: 1.5-3: 1-1.5: 7-9: 15-20, wherein the concentrated sulfuric acid and the hydrogen peroxide are counted in ml, the graphite, the sodium nitrate and the potassium permanganate are counted in g, and the concentration of the concentrated sulfuric acid is 18.4 mol/L.
The heat preservation temperature is 35-45 ℃, and the heat preservation time is 50-70 minutes.
The application of the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode prepared in one step is as follows: RGO/MXene-H2SO4Drying and cutting the composite film to obtain a flexible electrode slice; the filter paper soaked in sulfuric acid is used as a diaphragm, two identical flexible electrode plates are separated by the diaphragm and finally attached together to form the super capacitor.
The drying temperature is 30-60 ℃.
Further, the graphene/MXene-H with compact structure is prepared in one step2SO4The method of the flexible electrode of the super capacitor comprises the following steps:
(1) preparation of MXene aqueous dispersion:
etching: under the condition of water bath, 5-10 ml of deionized water and 5-10 ml of concentrated hydrochloric acid (12mol/L) are added into a plastic beaker, magnetic stirring is carried out for 10-15 minutes, 0.8-1 g of lithium fluoride is continuously added into the beaker, stirring is continuously carried out for 10-15 minutes, and after uniform stirring is carried out, 0.8-1 g of MAX (Ti) is slowly added3AlC2) And after all the substances are uniformly stirred, sealing the beaker by using a preservative film, and heating in a water bath for 18-24 hours at the temperature of 45-55 ℃. The entire process was operated in a fume hood.
Dispersing: and centrifugally washing the etched solution at the rotating speed of 7500-8000 r/min until the solution is neutral. Dispersing the washed precipitate into 180-200 ml of deionized water, stirring for 18-24 hours, performing ultrasonic treatment for 20-30 min, centrifuging at 3000-3500 r/min, and removing the precipitate to obtain the aqueous dispersion of MXene with the layered structure.
(2) Preparing a graphene oxide aqueous dispersion:
sequentially adding 70-90 ml of concentrated sulfuric acid and 1.5-3 g of graphite into a beaker, stirring for 30-45 minutes at normal temperature, and adding 1-1.5 g of NaNO under the ice bath condition3Continuously stirring for 30-45 minutes, and slowly adding 7-9 g of KMnO4And continuing stirring for 30-45 minutes, wherein the solution is dark green in the reaction process. Water bath, namely, keeping the temperature of the beaker at 30-45 ℃ for 45-60 minutes, removing the water bath, adding 120-140 ml of deionized water under the ice bath condition, stirring for 15-20 minutes, removing the ice bath, and adding 180-200 ml of deionized water at normal temperatureDeionized water is stirred for 8-10 minutes, 15-20 ml of hydrogen peroxide is slowly added into the diluted solution, 12mol/L of concentrated hydrochloric acid and deionized water are mixed with 220-250 ml of diluted hydrochloric acid solution according to the ratio of 8-10: 1, the primarily oxidized graphite is centrifugally washed, and the rotating speed during centrifugation is 7500-8000 r/min. And then washing with water until the solution is neutral, carrying out ultrasonic treatment on the obtained solution for 8-12 hours until no precipitate is formed, centrifuging at 3500-4500 r/min, and taking supernatant to obtain the two-dimensional layered graphene oxide aqueous dispersion.
(3)RGO/MXene-H2SO4The preparation method of the electrode comprises the following steps:
slowly and dropwise adding 5-10 ml of MXene aqueous dispersion with the concentration of 5mg/ml into 5-10 ml of graphene oxide aqueous dispersion with the concentration of 10mg/ml, adding 8-12 ml of 0.5M sulfuric acid, stirring for 30-45 minutes, and uniformly mixing; then soaking the metal zinc sheet into the uniformly mixed solution and standing for 1-1.5 hours, thus obtaining RGO/MXene-H on the metal surface2SO4A composite membrane. Washing the composite membrane, removing graphene oxide physically adhered to the surface, soaking the zinc sheet adhered with the composite membrane into 0.5M sulfuric acid to strip the composite membrane from the zinc surface, and continuously washing away redundant zinc ions on the composite membrane by acid to obtain RGO/MXene-H2SO4And (3) a composite film, namely a flexible electrode of the super capacitor.
(4) Assembling the super capacitor:
the method comprises the following specific steps: RGO/MXene-H2SO4Drying and cutting the composite film to obtain a flexible electrode slice; the filter paper soaked in sulfuric acid is used as a diaphragm, two identical flexible electrode plates are separated by the diaphragm and finally attached together to form the super capacitor which is of a three-layer structure.
The invention prepares the electrode of the super capacitor by a layer-by-layer assembly method, and simultaneously assembles the nonvolatile liquid electrolyte sulfuric acid into the flexible electrode in the electrode assembly process to realize the full contact between the electrode and the electrolyte. The whole electrode is an independent self-supporting electrode without an adhesive current collector. The self-supporting electrode with a proper size is prepared by cutting the composite film and is directly used for the super capacitor without a current collector.
The invention has the following beneficial effects:
the invention adopts a layer-by-layer assembly method to prepare the orderly arranged lamellar RGO/MXene-H2SO4The thin film, RGO and MXene, respectively, act as interlayer filling materials for each other, effectively inhibiting the stacking and agglomeration of materials. In the process of membrane assembly, the effect of full contact between the electrolyte and the electrode material is realized by a method of directly compounding the sulfuric acid electrolyte at a molecular level, the conduction paths of ions and electrons are shortened, the compactness of the electrode is effectively improved, the volume of the electrode is reduced, and the energy density of the capacitor is improved.
The method of adding the electrolyte by adopting a one-step method in the film assembling process solves the defects that the electrolyte wettability of the traditional electrode material is poor and the specific surface area of the electrode can not be fully utilized. Furthermore, for conventional supercapacitors, both binder and current collector are essential parts. The electrode with the independent self-supporting structure is prepared, the constraint of a binder and a current collector is eliminated, and the defect of small capacitance caused by inactive components is overcome, so that the energy density of the whole capacitor is improved.
In conclusion, the invention adopts a layer-by-layer assembly method to prepare the RGO/MXene-H with the orderly arranged compact structure2SO4The composite film synchronously horizontally distributes the molecules of the nonvolatile liquid electrolyte to the surface of the electrode material in the self-assembly process of the film, thereby realizing the full contact between the electrode material and the electrolyte. The method has the advantages of simplicity, strong designability, wide applicability, good electrochemical performance and the like, and has wide application prospect in the fields of electrochemical materials and the like.
Drawings
FIG. 1 is RGO/MXene-H2SO4Scanning photos of the cross section of the composite film;
FIG. 2a is a flow chart of MXene aqueous dispersion preparation;
FIG. 2b is RGO/MXene-H2SO4A flow chart for preparing the composite membrane;
FIG. 2c is RGO/MXene-H2SO4Optical photographs of the composite films;
FIG. 2d is RGO/MXene-H2SO4An optical photograph of the free-standing electrode;
fig. 3a is a scanned photograph of a layered structure MXene;
FIG. 3b is a transmission photograph of an aqueous MXene dispersion;
FIG. 4 is a scanned photograph of a cross-section of an RGO/MXene composite membrane;
FIG. 5a is RGO/MXene-H2SO4A comparison graph of cyclic voltammetry performance of a supercapacitor assembled by a composite membrane electrode and an RGO/MXene electrode;
FIG. 5b is RGO/MXene-H2SO4A cross-flow charge-discharge performance comparison graph of the supercapacitor assembled by the composite membrane electrode and the RGO/MXene electrode;
FIG. 6 is RGO/MXene-H2SO4Cyclic voltammetry curves of the assembled supercapacitor at different scanning rates;
FIG. 7 is RGO/MXene-H2SO4And cross current charging and discharging curves of the assembled super capacitor under different current densities.
Detailed Description
The present invention is further described below with reference to examples.
Example 1
(1) Preparation of MXene aqueous dispersion:
etching: putting a plastic beaker into a water bath kettle, adding 10ml of deionized water and 10ml of concentrated hydrochloric acid (12mol/L) into the beaker, magnetically stirring for 10 minutes, continuously adding 1g of lithium fluoride into the beaker, continuously stirring for 10 minutes, and slowly adding 1g of Ti after uniformly stirring3AlC2After all the materials are stirred uniformly, the beaker is sealed by a preservative film and heated in a water bath for 24 hours at the temperature of 55 ℃. The entire process was operated in a fume hood.
Dispersing: after the etching is finished, the solution after etching is centrifugally washed at the rotating speed of 8000r/min until the solution is neutral. And dispersing the washed precipitate into 200ml of deionized water, stirring for 24 hours, performing ultrasonic treatment for 30min, centrifuging at 3500r/min, and removing the precipitate to obtain the aqueous dispersion of the MXene with the layered structure.
(2) Preparing a graphene oxide aqueous dispersion:
adding 90ml of concentrated sulfuric acid and 3g of graphite into a 500ml beaker in sequence, stirring for 45 minutes at normal temperature, and adding 1.5g of NaNO under the ice bath condition3Stirring was continued for 45 minutes and 9g KMnO was added slowly4Stirring was continued for 45 minutes, and during the reaction, the solution appeared greenish black. And (2) water bath, namely keeping the temperature of a beaker at 45 ℃ for 60 minutes, removing the water bath, continuing ice bath, adding 140ml of deionized water under the ice bath condition, stirring for 20 minutes, after removing the ice bath, continuing adding 200ml of deionized water at normal temperature, stirring for 10 minutes, slowly adding 20ml of hydrogen peroxide into the diluted solution, preparing 12mol/L concentrated hydrochloric acid and deionized water into 250ml of diluted hydrochloric acid solution according to the proportion of 10:1, and centrifugally washing the primarily oxidized graphite at the rotating speed of 7500r/min during centrifugation. And then washing with water for multiple times until the solution is neutral, carrying out ultrasonic treatment on the obtained liquid for 12 hours until no precipitate is formed, centrifuging at 4500r/min, and taking supernatant to obtain the two-dimensional layered graphene oxide aqueous dispersion.
(3)RGO/MXene-H2SO4The preparation method of the electrode comprises the following steps:
slowly and dropwise adding 10ml of MXene aqueous dispersion with the concentration of 5mg/ml into 10ml of graphene oxide aqueous dispersion with the concentration of 10mg/ml, adding 10ml of 0.5M sulfuric acid, stirring for 45 minutes, and uniformly mixing; then soaking the metal zinc sheet into the uniformly mixed solution and standing for 1 hour, thus obtaining RGO/MXene-H on the metal surface2SO4A composite membrane. Washing the composite membrane, removing graphene physically adhered to the surface, soaking the zinc sheet attached with the composite membrane into 0.5M sulfuric acid to strip the composite membrane from the zinc surface, and continuously washing away redundant zinc ions on the composite membrane by acid to obtain RGO/MXene-H2SO4A composite membrane.
(4) Assembling the super capacitor:
mixing RGO/MXene-H2SO4And drying the composite membrane at 40 ℃ for 1 hour, and cutting to obtain the electrode slice. Cutting filter paper, soaking in sulfuric acid, separating two identical electrode plates with the membrane, and bonding to obtain the final productAnd (5) forming.
Example 2
(1) Preparation of MXene aqueous dispersion:
etching: putting a plastic beaker into a water bath kettle, adding 5ml of deionized water and 8ml of concentrated hydrochloric acid (12mol/L) into the beaker, magnetically stirring for 10 minutes, continuously adding 0.8g of lithium fluoride into the beaker, continuously stirring for 15 minutes, and slowly adding 0.8g of Ti after uniform stirring3AlC2After all the materials are stirred uniformly, the beaker is sealed by a preservative film and heated in a water bath for 18 hours at the temperature of 45 ℃. The entire process was operated in a fume hood.
Dispersing: after the etching is finished, the solution after etching is centrifugally washed at the rotating speed of 7500r/min until the solution is neutral. Dispersing the washed precipitate into 180ml of deionized water, stirring for 20 hours, performing ultrasonic treatment for 20 minutes, centrifuging at 3000r/min, and removing the precipitate to obtain the MXene aqueous dispersion.
(2) Preparing a graphene oxide aqueous dispersion:
70ml of concentrated sulfuric acid and 1.8g of graphite are sequentially added into a 500ml beaker, stirred for 35 minutes at normal temperature, and 1g of NaNO is added under the ice bath condition3Stirring was continued for 45 minutes, and 7g of KMnO was slowly added4Stirring was continued for 45 minutes, and during the reaction, the solution appeared greenish black. And (2) water bath, namely keeping the temperature of a beaker at 35 ℃ for 45 minutes, removing the water bath, continuing ice bath, adding 120ml of deionized water under the ice bath condition, stirring for 20 minutes, after removing the ice bath, continuing adding 180ml of deionized water at normal temperature, stirring for 10 minutes, slowly adding 20ml of hydrogen peroxide into the diluted solution, preparing 12mol/L concentrated hydrochloric acid and deionized water into 220ml of diluted hydrochloric acid solution according to the ratio of 8:1, and centrifugally washing the primarily oxidized graphite at the rotating speed of 7500r/min during centrifugation. And then washing with water for multiple times until the solution is neutral, carrying out ultrasonic treatment on the obtained liquid for 8 hours until no precipitate is formed, centrifuging at 4500r/min, and taking supernatant to obtain the graphene oxide aqueous dispersion.
(3)RGO/MXene-H2SO4The preparation method of the electrode comprises the following steps:
slowly and dropwise adding 5ml of MXene aqueous dispersion with the concentration of 5mg/ml to 7ml of graphene oxide water with the concentration of 10mg/mlAdding 8ml of 0.5M sulfuric acid into the dispersion, stirring for 35 minutes, and uniformly mixing; then soaking the metal zinc sheet into the uniformly mixed solution and standing for 1 hour, thus obtaining RGO/MXene-H on the metal surface2SO4A composite membrane. Washing the composite membrane, removing graphene physically adhered to the surface, soaking the zinc sheet attached with the composite membrane into 0.5M sulfuric acid to strip the composite membrane from the zinc surface, and continuously washing away redundant zinc ions on the composite membrane by acid to obtain RGO/MXene-H2SO4A composite membrane.
(4) Assembling the super capacitor:
mixing RGO/MXene-H2SO4And drying the composite membrane at 45 ℃ for 0.5 hour, and cutting to obtain the electrode slice. The filter paper is cut and used as a diaphragm, the diaphragm is soaked in sulfuric acid, two identical electrode plates are separated by the diaphragm and are attached together to form the super capacitor, and the super capacitor is of a three-layer structure.
Example 3
(1) Preparation of MXene aqueous dispersion:
etching: putting a plastic beaker into a water bath kettle, adding 6ml of deionized water and 9ml of concentrated hydrochloric acid (12mol/L) into the beaker, magnetically stirring for 15 minutes, continuously adding 0.9g of lithium fluoride into the beaker, continuously stirring for 10 minutes, and slowly adding 0.9g of Ti after uniform stirring3AlC2After all the materials are stirred uniformly, the beaker is sealed by a preservative film and heated in water bath for 20 hours at the temperature of 50 ℃. The entire process was operated in a fume hood.
Dispersing: after the etching is finished, the solution after etching is centrifugally washed at the rotating speed of 7700r/min until the solution is neutral. Dispersing the washed precipitate into 190ml of deionized water, stirring for 21 hours, performing ultrasonic treatment for 30min, centrifuging at 3500r/min, and removing the precipitate to obtain the MXene aqueous dispersion.
(2) Preparing a graphene oxide aqueous dispersion:
80ml of concentrated sulfuric acid and 2.5g of graphite are sequentially added into a 500ml beaker, stirred for 45 minutes at normal temperature, and added with 1.3g of NaNO under the ice bath condition3Stirring was continued for 40 minutes, and 8g of KMnO was slowly added4Stirring is continued for 45 minutesIn the reaction process, the solution appears dark green. And (2) water bath, namely keeping the temperature of a beaker at 40 ℃ for 60 minutes, removing the water bath, continuing ice bath, adding 130ml of deionized water under the ice bath condition, stirring for 20 minutes, after removing the ice bath, continuing adding 190ml of deionized water at normal temperature, stirring for 10 minutes, slowly adding 18ml of hydrogen peroxide into the diluted solution, preparing 12mol/L concentrated hydrochloric acid and deionized water into 250ml of diluted hydrochloric acid solution according to the ratio of 9:1, and centrifugally washing the primarily oxidized graphite at the rotating speed of 7800r/min during centrifugation. And then washing with water for multiple times until the solution is neutral, carrying out ultrasonic treatment on the obtained liquid for 12 hours until no precipitate is formed, centrifuging at 4500r/min, and taking supernatant to obtain the graphene oxide aqueous dispersion.
(3)RGO/MXene-H2SO4The preparation method of the electrode comprises the following steps:
slowly and dropwise adding 8ml of MXene aqueous dispersion with the concentration of 5mg/ml into 6ml of graphene oxide aqueous dispersion with the concentration of 10mg/ml, adding 12ml of 0.5M sulfuric acid, stirring for 30 minutes, and uniformly mixing; then soaking the metal zinc sheet into the uniformly mixed solution and standing for 1.5 hours, thus obtaining RGO/MXene-H on the metal surface2SO4A composite membrane. Washing the composite membrane, removing graphene physically adhered to the surface, soaking the zinc sheet attached with the composite membrane into 0.5M sulfuric acid to strip the composite membrane from the zinc surface, and continuously washing away redundant zinc ions on the composite membrane by acid to obtain RGO/MXene-H2SO4A composite membrane.
(4) Assembling the super capacitor:
mixing RGO/MXene-H2SO4And drying the composite membrane at 35 ℃ for 2 hours, and cutting to obtain the electrode slice. The filter paper is cut and used as a diaphragm, the diaphragm is soaked in sulfuric acid, two identical electrode plates are separated by the diaphragm and are attached together to form the super capacitor, and the super capacitor is of a three-layer structure.
Comparative example 1
In order to demonstrate the effect of the electrode on enhancing the capacity of the supercapacitor after absorbing the electrolyte, the electrode without adding the sulfuric acid electrolyte was prepared.
The preparation method of the RGO/MXene electrode comprises the following steps:
slowly and dropwise adding 10ml of MXene aqueous dispersion with the concentration of 5mg/ml into 10ml of graphene oxide aqueous dispersion with the concentration of 10mg/ml, stirring for 45 minutes, and uniformly mixing; and then soaking the metal zinc sheet into the uniformly mixed solution, and standing for 1 hour, so that the RGO/MXene composite membrane can be assembled on the metal surface. And (2) washing the composite membrane, removing graphene physically adhered to the surface, soaking the zinc sheet adhered with the composite membrane into 0.5M sulfuric acid to peel the composite membrane from the zinc surface, continuously washing away redundant zinc ions on the composite membrane by using acid, and then washing and drying to obtain the RGO/MXene composite membrane.
In example 1, a supercapacitor was assembled by separating both electrodes with a separator using filter paper having a diameter of 16mm and an electrode material having a diameter of 12mm, using 0.5M sulfuric acid as an electrolyte, and performing an electrochemical test.
In comparative example 1, the procedure was the same as in example 1 except that the preparation of the electrode was carried out without adding sulfuric acid and the steps of washing with water and drying after pickling the composite film. And assembling the super capacitor after obtaining the RGO/MXene composite membrane, and carrying out electrochemical test.
Refer to the drawings of the specification specifically. Wherein FIG. 1 is RGO/MXene-H2SO4Scanning photos of the cross section of the composite film; FIG. 2a is a flow chart of MXene aqueous dispersion preparation; FIG. 2b is RGO/MXene-H2SO4A flow chart for preparing the composite membrane; FIG. 2c is RGO/MXene-H2SO4Optical photographs of the composite films; FIG. 2d is RGO/MXene-H2SO4An optical photograph of the free-standing electrode; fig. 3a is a scanned photograph of a layered structure MXene; FIG. 3b is a transmission photograph of an aqueous MXene dispersion; FIG. 4 is a scanned photograph of a cross-section of an RGO/MXene composite membrane; FIG. 5a is RGO/MXene-H2SO4A comparison graph of cyclic voltammetry performance of a supercapacitor assembled by a composite membrane electrode and an RGO/MXene electrode; FIG. 5b is RGO/MXene-H2SO4A cross-flow charge-discharge performance comparison graph of the supercapacitor assembled by the composite membrane electrode and the RGO/MXene electrode; FIG. 6 is RGO/MXene-H2SO4Cyclic voltammetry curves of the assembled supercapacitor at different scanning rates; FIG. 7 is RGO/MXene-H2SO4And cross current charging and discharging curves of the assembled super capacitor under different current densities.
From the charge-discharge and cyclic voltammograms of the capacitor shown in figure 5, it is clear that the performance of the electrode with the addition of sulphuric acid in a single step is greatly improved. The capacitance of the capacitor of example 1 and the capacitance of the capacitor of comparative example 1 without sulfuric acid during the electrode preparation, 150F g, were calculated-1In contrast, 257F g can be reached-1. FIG. 6 is a cyclic voltammogram of a supercapacitor at different scan rates, each scan rate being 10mV s-1，20mV s-1，50mV s-1，100mV s-1，200mV s-1，500mV s-1. FIG. 6 shows: the cyclic voltammogram of the supercapacitors prepared according to the invention was approximately rectangular over the range of potentials tested, which indicates typical capacitive behavior and low resistance performance. In addition, the capacitor is tested for constant current charge and discharge under different current densities of 0.1-5.0A/g, and as can be seen from FIG. 7, the cross current charge and discharge curves of the super capacitor are all triangular, which shows that the cation reversibility is extremely high in the charge and discharge processes, which shows that the equivalent series resistance EIS of the super capacitor prepared by the invention is very small; and the super capacitor can be charged and discharged well under higher current density, which shows that the rate capability of the super capacitor is better.
Claims (10)
1. A method for preparing a compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode in one step is characterized by comprising the following steps: firstly, mixing graphene oxide aqueous dispersion and MXene aqueous dispersion, adding sulfuric acid, and uniformly mixing; then soaking the metal zinc sheet into the uniformly mixed solution for standing to obtain RGO/MXene-H on the surface of the metal zinc sheet2SO4Composite film, stripping to obtain RGO/MXene-H2SO4And (3) a composite film, namely a flexible electrode of the super capacitor.
2. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 1, wherein: the mass of MXene accounts for 10-40% of the total mass of the graphene oxide and the MXene.
3. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 1, wherein: the molar concentration of the sulfuric acid is 0.5-1 mol/L.
4. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 1, wherein: the MXene aqueous dispersion is prepared by mixing deionized water and concentrated hydrochloric acid, adding lithium fluoride, mixing, and adding Ti3AlC2And etching, centrifugally washing to neutrality, dispersing washed precipitate into deionized water, ultrasonically treating, centrifuging, and removing precipitate to obtain MXene aqueous dispersion.
5. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 4, wherein: the volume ratio of the deionized water to the concentrated hydrochloric acid is 1: 1-2, the concentration of the concentrated hydrochloric acid is 12mol/L, and the lithium fluoride and the Ti are3AlC2The mass ratio of the components is 1-1.5: 1-1.5, the etching temperature is 45-55 ℃, and the etching time is 18-24 hours.
6. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 1, wherein: the preparation process of the graphene oxide aqueous dispersion comprises the steps of mixing concentrated sulfuric acid, graphite, sodium nitrate and potassium permanganate, preserving heat in a water bath, adding water for dilution under the ice bath condition, adding hydrogen peroxide, washing with hydrochloric acid and deionized water, performing ultrasonic treatment and centrifugation, and taking supernate to obtain the graphene oxide aqueous dispersion.
7. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 6, wherein: the dosage proportion of concentrated sulfuric acid, graphite, sodium nitrate, potassium permanganate and hydrogen peroxide is as follows: 70-90: 1.5-3: 1-1.5: 7-9: 15-20, wherein the concentrated sulfuric acid and the hydrogen peroxide are counted in ml, the graphite, the sodium nitrate and the potassium permanganate are counted in g, and the concentration of the concentrated sulfuric acid is 18.4 mol/L.
8. The method for preparing the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 6, wherein: the heat preservation temperature is 35-45 ℃, and the heat preservation time is 50-70 minutes.
9. Use of the one-step preparation of dense structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to any one of claims 1-8, characterized by: RGO/MXene-H2SO4Drying and cutting the composite film to obtain a flexible electrode slice; the filter paper soaked in sulfuric acid is used as a diaphragm, two identical flexible electrode plates are separated by the diaphragm and finally attached together to form the super capacitor.
10. The use of the compact structure RGO/MXene-sulfuric acid supercapacitor flexible electrode according to claim 9, characterized in that: the drying temperature is 30-60 ℃.
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