CN102354609A - Method for preparing graphene-nickel hydroxide composite electrode material for super capacitor - Google Patents

Abstract

A method for preparing a graphene-nickel hydroxide composite electrode material for a supercapacitor is to prepare a graphene substrate film material by chemical vapor deposition of carbon source gas and hydrogen in a plasma-enhanced chemical vapor deposition reaction device, Then, the in-situ growth of graphene-nickel hydroxide is combined by electrochemical deposition of nickel hydroxide. The specific capacitance of the composite electrode material prepared by this method can reach up to 1918F/g, and it can withstand hundreds of cycles of high current charge and discharge. It can still maintain more than 80% after the second time. The method is simple and effective, reduces production costs and has excellent electrochemical performance, and is expected to be used as anode material in supercapacitors for energy storage, improve the overall performance of electrode materials, and expand the development of hybrid energy power and other fields. up the road.

Description

Method for preparing graphene-nickel hydroxide composite electrode material for supercapacitor

Technical field:

The invention relates to a method for preparing a graphene-nickel hydroxide composite electrode material for a supercapacitor, more specifically, the invention relates to a method for preparing a graphene-nickel hydroxide composite positive electrode material in a supercapacitor energy storage device.

Background technique:

With the aggravation of global warming, environmental pollution and other issues, as well as the substantial increase in human demand for energy, scientific research institutions and manufacturers have focused their research and development on energy storage and conversion equipment. Supercapacitors are expected to become the future star of the energy field due to their good power characteristics, long cycle life, and low maintenance costs. Their ideal applications include: emergency power supply, peak power supply for electric vehicle batteries, and other energy storage fields. According to the different energy storage methods, it can be divided into two types: electric double layer capacitor (ion adsorption type) and pseudocapacitor capacitor (fast surface redox reaction type). Pseudocapacitive materials can make supercapacitors have high specific capacitance and large energy density, and have attracted much attention from industrial research institutes. The current research focuses on finding cheap pseudocapacitive electrode materials that can replace noble metal oxides such as RuO2 and IrO2, and at the same time have high specific capacitance, excellent cycle performance and simple and feasible preparation methods. However, electrode materials with high specific capacitance often have poor cycle stability, and the preparation methods are complex and repeatable, and require the use of additives such as binders and conductive agents, which seriously affect the service life and manufacturing costs of electrode materials.

As a two-dimensional material, graphene has high specific surface area and electrical conductivity, good flexibility, high mechanical strength, strong chemical resistance, wide potential window and extremely light weight, making it an ideal growth material with electrochemical properties. It is an ideal substrate material for nanomaterials with active and good conductivity; while nickel hydroxide electrode material has the characteristics of high theoretical specific volume, perfect oxygen reduction characteristics and low cost. The advantage of the composite electrode material formed by the two lies in: while maintaining the electrochemical activity of the pseudocapacitive material, it utilizes the morphology characteristics of the substrate material, high electrical conductivity and is more friendly to the active coating material (nickel hydroxide). The surface stabilization effect of the supercapacitor can maximize its synergistic effect and guide the distribution, growth and stability of the active coating, so as to improve and optimize the overall performance of the supercapacitor. In terms of the preparation of composite electrode materials, complex and cumbersome chemical synthesis routes, high-cost synthetic raw materials, time-consuming preparation processes, and uncontrollable and difficult-to-repeat preparation conditions have become strong obstacles and bottlenecks that limit their development and industrialization.

Invention content:

The purpose of the present invention is to, starting from the above background, propose a simple and effective method for preparing graphene-nickel hydroxide composite electrode material, first use plasma-enhanced chemical vapor deposition as a means, and use methane and hydrogen as reaction gases to prepare A low-defect in-situ growth graphene substrate is produced, and then the nickel hydroxide active layer is deposited by electrochemical deposition to achieve recombination. The prepared composite material can be directly applied to the positive electrode of supercapacitors without any binder or conductive agent, and can have both high specific capacitance and excellent cycle stability performance, which provides technical improvements and product upgrades for supercapacitor electrode materials Technical references are provided.

The preparation method of the present invention that can achieve the above-mentioned purpose is characterized in that: under the method of PECVD (plasma enhanced chemical vapor deposition, plasma enhanced chemical vapor deposition), the metal material is used as the substrate, and the carbon source gas and hydrogen gas are mixed in a ratio of 10:80 ( The unit is sccm, the ratio of standard state milliliters per minute), and the graphene substrate material is prepared under the action of high temperature (above 700°C); then, under the method of electrochemical deposition, Ni(NO3) ₂ is used as the electrolyte, The prepared graphene-nickel foam substrate material is the working electrode, the platinum is the counter electrode, and the saturated calomel electrode is the reference electrode. Nickel hydroxide is electrodeposited on the substrate material to achieve in-situ graphene growth-zero addition complex. Through the above invention, composite electrode materials with high specific capacitance and good cycle stability can be prepared.

Concrete technical scheme of the present invention is:

A method for preparing a graphene-nickel hydroxide composite electrode material for a supercapacitor is to prepare a graphene substrate film material by plasma-enhanced chemical vapor deposition, and then compound nickel hydroxide active material by electrochemical deposition to realize In-situ-zero addition composite of graphene-nickel hydroxide, the method mainly includes the following steps:

Step A: using PECVD technology to deposit a graphene film on the carrier of the graphene film as the base material of the collector of the supercapacitor;

Step B: Place the collector-graphene substrate material prepared in step A in the electrolytic cell, use nickel nitrate solution as the electrolyte, the prepared graphene substrate material as the working electrode, and the platinum sheet as the counter electrode, saturate The calomel electrode is used as a reference electrode for electrochemical deposition of nickel hydroxide;

Step C: controlling the temperature, time and deposition current or potential of electrochemical deposition, and preparing nickel hydroxide on the graphene substrate, thereby obtaining a composite electrode material.

In step A, the prepared graphene film is prepared by PECVD technology, the precursors of the reaction are carbon source gas and hydrogen, and the graphene film material is grown in situ on the base material.

In step A, the base used for depositing graphene film is selected from nickel foam and nickel sheet metal materials, and is used as a collector electrode of supercapacitor at the same time. The preferred hydrogen reducing gas used in the deposition process is a protective gas with a flow rate of 10-20 sccm, and the sccm is The standard state is milliliters per minute, and the pressure is in the range of 100-200Pa; the reaction gas in the vapor deposition process is carbon source gas, preferably methane.

In step A, the reaction temperature is between 700-800°C. When the reaction temperature is reached, the hydrocarbon gas is introduced and the radio frequency plasma reaction is carried out. The radio frequency power is between 150-200W, and the reaction time is controlled within 30-40min. .

In the electrochemical deposition stage of step B, the selected working electrode comes from the carbon-containing substrate prepared by the PECVD method, that is, the carbon material grown by chemical vapor deposition, the carbon material carrier such as nickel foam based on graphene film, nickel nitrate The concentration of the solution is between 0.1-1M, M is the number of moles of solute substances per liter of solution, the electrochemical deposition process is preferably constant current cathodic deposition, the deposition current density is preferably 1-4mA/cm ² , and the deposition time is controlled at 3 -12min.

In the electrochemical stage of step C, the combination of nickel hydroxide and graphene does not require a binder or a conductive agent, and the temperature is preferably room temperature.

In the whole process of the prepared composite electrode material, no bonding treatment, substance addition and follow-up operations including annealing are performed.

The summary of basic technical solution of the present invention is as follows:

Select a conductive material that can be used as a supercapacitor collector material (such as nickel foam, nickel sheet, titanium sheet, etc.) At this time, the graphene substrate material is chemically vapor deposited by plasma action, and then the nickel hydroxide active material is electrochemically deposited as the working electrode to realize the in-situ growth of graphene and the zero-addition recombination of nickel hydroxide.

Concrete technical parameter of the present invention and optimum selection scheme are introduced as follows:

In the present invention, the preparation of the graphene substrate film (then as the substrate of the electrochemically deposited nickel hydroxide active material) is preferably plasma-enhanced chemical vapor deposition technology, and the substrate material is preferably nickel foam. The process can be divided into three main steps:

1) Introduce some kind of gas or certain gases to raise the temperature to a predetermined temperature (reaction temperature), and when the temperature reaches the reaction temperature, introduce carbon source gas;

2) The ratio of carbon source gas and hydrogen is reasonable, that is, C _m H _n //H ₂ =10/80, and the unit is sccm. Adjust the reaction pressure, set the radio frequency power and reaction time, so that the reaction raw materials are fully ionized, decomposed, converted into active groups, and then adsorbed, dissolved, diffused, and precipitated on the surface and interior of the substrate material, and finally form a graphene substrate Material;

3) Cool down to below 100°C with protective gas.

In the present invention, in the preparation process of the graphene substrate film, the carbon source gas is preferably methane, and the back-bottom pressure should be less than 10 Pa, so as to ensure the high purity of the catalyst film.

In the present invention, in the preparation process of the graphene substrate film, in step 1) during the temperature rise etching (or thermal etching) process, the gas is preferably hydrogen, and the heating time is preferably 40 minutes. The purpose of hydrogen heating treatment is to reduce the substrate material that may be partially oxidized, so as to provide conditions for the subsequent plasma chemical vapor deposition process to obtain a continuous, low-defect, high-quality graphene film substrate.

In the present invention, the preparation of the nickel hydroxide active material is preferably 0.1M Ni(NO ₃ ) ₂ solution, the carbon-based material prepared by the above method is used as the working electrode, the platinum sheet is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Electrochemical deposition is carried out, and the deposition method is preferably constant current cathode deposition.

In the present invention, during the preparation process of the nickel hydroxide active material, the electrochemical deposition temperature is preferably room temperature, the deposition current density is preferably -1-4 mA/cm ² , and the deposition time is preferably within 3-12 min.

In summary, the basic composition of preferred technical parameters in the present invention is: base material (as the collector of supercapacitor simultaneously) under the condition that methane (preferably gas), hydrogen coexist, by plasma discharge, prepare graphene The substrate material is used as the working electrode to directly electrodeposit the nickel hydroxide active material to realize the composite. After such steps, simple and effective in-situ preparation of graphene and rapid recombination of nickel hydroxide can be realized. The simplification of the operation process is far superior to the cumbersome chemical preparation methods commonly used at present, reducing the preparation time and cost. The electrode is used as an anode material for supercapacitors. It has high specific capacitance and good cycle stability. It is expected to be put into industrialization and provide conditions for industrial production and product optimization and upgrading.

The present invention has the following obvious advantages:

1) At first, the preparation of graphene substrate material among the present invention adopts the method for plasma-enhanced chemical vapor deposition, directly grows in situ on the substrate that is used for supercapacitor collector material, is different from the chemical preparation method of graphene material, The preparation of the substrate material is completed at one time, the reaction time is short, and the yield is high, which is different from the graphene material prepared by the cumbersome oxidation-reduction method.

2) Secondly, the ratio of carbon source gas and hydrogen gas in the present invention is obtained through repeated experiments and tests, and the experimental parameters can be repeated to ensure the repeatability of the experimental operation.

3) Again, the preparation of the nickel hydroxide active material in the present invention uses the method of electrochemical deposition. Compared with the chemical bath method that is more used at present, the reaction process is simple, easy to operate, and the sample deposition can be completed in a few minutes, and It can be well combined with the substrate graphene film without any additives, which greatly saves time and cost.

4) Finally, for the graphene-nickel hydroxide composite electrode material prepared by the present invention, the entire method flow used has not been reported at present, and while the product has a high specific capacitance, it can be charged at a high current density hundreds of times. Under discharge conditions, the specific capacitance value of more than 80% is maintained, thereby providing favorable technical support for hybrid energy and other fields.

Description of drawings:

Fig. 1 is the SEM picture of the graphene substrate thin film that obtains in embodiment 1, can see that the extremely high large-area carbon film of transparency is distributed on the nickel foam substrate.

Fig. 2 is the TEM picture and corresponding SAED pattern of the graphene substrate thin film that obtains in embodiment example 1.

Fig. 3 is the Raman spectrum of the graphene substrate thin film obtained in implementation example 1.

Fig. 4 is the SEM picture of the graphene-nickel hydroxide composite electrode material that obtains in embodiment example 1.

Fig. 5 is the TEM picture of the graphene-nickel hydroxide composite electrode material obtained in implementation example 1 and the corresponding SAED pattern, it can be seen that the two substances have achieved good compounding, and the diffraction pattern comes from single crystal carbon.

Fig. 6 is the cyclic voltammetry curve figure of the stone graphene-nickel hydroxide composite electrode material obtained in embodiment 1 under different scanning speeds, and potential window is 0-0.5V; Under different scanning speeds, its cyclic voltammetry curve The shape of is basically unchanged, indicating that the prepared composite electrode material has excellent electrochemical performance.

FIG. 7 is a graph showing graphene-nickel hydroxide composite electrode materials obtained in Example 1 for charging and discharging tests at different current densities, correspondingly giving specific capacitance values at different current densities.

Fig. 8 is a comparison chart of the discharge curves of the graphene-nickel hydroxide composite electrode material obtained in Example 1 charged and discharged 700 times at a high current density of 60A/g.

Fig. 9 is the graphene-nickel hydroxide composite electrode material obtained in the implementation example 1, the relationship diagram of the specific capacitance changing with the number of cycles under the charge and discharge current density of 60A/g.

Fig. 10 is the cyclic voltammetry graph of graphene-nickel hydroxide composite electrode material obtained in Example 2 at different scanning speeds.

Fig. 11 is a curve comparison diagram of graphene-nickel hydroxide composite electrode material obtained in Example 2 charged and discharged 300 times at a high current density of 60A/g.

Fig. 12 is the graphene-nickel hydroxide composite electrode material obtained in the implementation example 2, the relationship diagram of the specific capacitance changing with the number of cycles under the charge and discharge current density of 60A/g.

Fig. 13 is the TEM picture and corresponding SAED pattern of the graphene-nickel hydroxide composite electrode material obtained in embodiment example 3.

Fig. 14 is the cyclic voltammetry graph of the graphene-nickel hydroxide composite electrode material obtained in Example 3 at different scanning speeds.

Detailed ways:

Implementation example 1:

1) Use nickel foam as the substrate, use PECVD equipment, heat up to 800°C in a hydrogen atmosphere, and the heating rate is 20°C/min. When this temperature is reached, methane gas is introduced to make the ratio of methane to hydrogen 1:8 , the total pressure is controlled at 4 Torr;

2) In the PECVD equipment, after step 1) is completed, the RF power is turned on, the RF power is controlled at 200W, and the deposition time is 30min;

3) After the reaction is over, continue to pass hydrogen to room temperature;

4) With 0.1M Ni(NO ₃ ) ₂ as the electrolyte, the surface of the graphene-nickel foam substrate material prepared by the above method in contact with the plasma environment is used as the working electrode opposite to the platinum sheet, and the platinum sheet is For the counter electrode, a saturated calomel electrode is used as a reference electrode, and nickel hydroxide is deposited at a constant current of -1mA/cm ² for 12 minutes.

According to the exemplifying method of the above-mentioned invention, the graphite carbon substrate film material can be prepared, and the material has the following characteristics:

1) Scanning electron microscope (SEM) observation is carried out to the sample obtained by the method used in the above invention, it can be found that the transparency of the carbon film is very high, and it is continuous and regular.

2) Observation by transmission electron microscope (TEM) and selected area electron diffraction (SAED) on the sample obtained by the method used in the above invention shows that the film has extremely high transparency and regularity, and its diffraction pattern is consistent with graphite carbon.

3) Raman analysis is carried out on the sample obtained by the method used in the above invention, and it is found that there is no shoulder peak in its D peak (about 1350cm ^-1 Raman shift) and 2D peak (about 2700cm ^-1 Raman shift) , the peak position of the G peak is located at 1587cm ^-1 which matches the structure of graphene, which proves the existence of graphene, and the ratio of I _D / I _G is extremely small, and the surface graphene substrate has few defects and high quality.

According to the exemplifying method of the above-mentioned invention, the in-situ composite of graphene-nickel hydroxide electrode can be realized, and the material has the following characteristics:

1) Observing the composite electrode obtained by the method used in the above invention with a scanning electron microscope (SEM), it is found that the deposited nickel hydroxide grows directional and is evenly distributed on the surface of the substrate;

2) TEM and SAED analysis were carried out on the composite electrode obtained by the method used in the above invention, and it was found that the flocculent nickel hydroxide was evenly distributed on the substrate of the carbon material, and the selected area electron diffraction pattern and the d-phase nickel hydroxide and graphite carbon It is consistent, indicating that the two materials have achieved a good composite;

3) Electrochemical testing is carried out to the composite electrode obtained by the method used in the above-mentioned invention, the electrolyte is 1M KOH solution, the platinum sheet is used as the counter electrode, and the reference electrode is a saturated calomel electrode (the test method is the same in other implementation examples). Under the cyclic voltammetry test (CV), the specific capacitance can reach 1577F/g when the scanning speed is 5mV/s; under the charge-discharge (CD) test, the specific capacitance can reach 1563F/g when the current density is 3A/g. The charge and discharge test was carried out at a high current density of 60A/g, and its specific capacitance was 869F/g, and it could maintain 93% after 700 cycles.

Implementation example 2:

1) Using nickel foam as the substrate, using PECVD equipment, the temperature is raised to 800°C in a hydrogen atmosphere, and the heating rate is 20°C/min. When this temperature is reached, methane gas is introduced so that the ratio of methane to hydrogen is 1:8 , the total pressure is controlled at 4Torr;

2) In the PECVD equipment, after step 1) is completed, the RF power is turned on, the RF power is controlled at 200W, and the deposition time is 30min;

3) After the reaction is over, continue to pass hydrogen to room temperature;

4) Using 0.1M Ni(NO ₃ ) ₂ as the electrolyte, the graphene-nickel foam substrate material prepared by the above method is in contact with the stage of the PECVD reaction chamber (that is, the side that is not in contact with the plasma environment). side) as the working electrode opposite to the platinum sheet, the platinum sheet is the counter electrode, and the saturated calomel electrode is the reference electrode. Nickel hydroxide is deposited at a constant current of -1mA/ ^cm2 for 12min.

Electrochemical testing is carried out on the composite electrode obtained by the method used in the above invention. Under the CV test, when the scanning speed is 5mV/s, the specific capacitance can reach 1918F/g; when the CD test is carried out at a large current density of 60A/g, the specific capacitance It is 1006F/g, and can maintain 86% after 300 cycles.

Implementation example 3:

1) Use nickel foam as the substrate, use PECVD equipment, heat up to 800°C in a hydrogen atmosphere, and the heating rate is 20°C/min. When this temperature is reached, methane gas is introduced to make the ratio of methane to hydrogen 1:8 , the total pressure is controlled at 4 Torr;

2) In the PECVD equipment, after step 1) is completed, the RF power is turned on, the RF power is controlled at 200W, and the deposition time is 30min;

3) After the reaction is over, continue to pass hydrogen to room temperature;

4) With 0.1M Ni(NO ₃ ) ₂ as the electrolyte, the graphene-nickel foam substrate prepared by the above method was used as the working electrode, the platinum sheet was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode. /cm ² constant current deposition of nickel hydroxide, the time is 3min.

According to the exemplifying method of the above-mentioned invention, the in-situ composite of graphene-nickel hydroxide electrode can be realized, and the material has the following characteristics:

TEM and SAED analysis were carried out on the composite electrode obtained by the method used in the above invention, and it was found that the flocculent nickel hydroxide was evenly distributed on the carbon material substrate, indicating that the two materials had achieved good composite;

Electrochemical tests are carried out on the composite electrode obtained by the method used in the above invention. Under the cyclic voltammetry test, when the scanning speed is 5mV/s, the specific capacitance can reach 1462F/g.

Claims (7)

1. A method for preparing a graphene-nickel hydroxide composite electrode material for a supercapacitor, characterized in that, the graphene substrate film material is prepared by plasma-enhanced chemical vapor deposition, and hydrogen is compounded by the method of electrochemical deposition The nickel oxide active material realizes the in-situ-zero addition composite of graphene-nickel hydroxide, and the method mainly includes the following steps: Step A: using PECVD technology to deposit a graphene film on the carrier of the graphene film as the base material of the collector of the supercapacitor; Step B: Place the collector-graphene substrate material prepared in step A in the electrolytic cell, use nickel nitrate solution as the electrolyte, the prepared graphene substrate material as the working electrode, and the platinum sheet as the counter electrode, saturate The calomel electrode is used as a reference electrode for electrochemical deposition of nickel hydroxide; Step C: controlling the temperature, time and deposition current or potential of electrochemical deposition, and preparing nickel hydroxide on the graphene substrate, thereby obtaining a composite electrode material. 2. a kind of method for preparing supercapacitor graphene-nickel hydroxide composite electrode material as claimed in claim 1, is characterized in that, in step A, prepared graphene thin film adopts PECVD technology preparation, reacts The precursors of the method are carbon source gas and hydrogen, and the graphene film material is grown in situ on the substrate material. 3. a kind of method for preparing graphene-nickel hydroxide composite electrode material for supercapacitor as claimed in claim 1, is characterized in that, in step A, the substrate used for depositing graphene film is selected from the group consisting of nickel foam, nickel The sheet metal material is used as the collector of the supercapacitor at the same time. The protective gas used in the deposition process is preferably a hydrogen reducing gas. The flow rate is 10-20sccm, sccm is the standard state of milliliters per minute, and the pressure is in the range of 100-200Pa; The gas is a carbon source gas, preferably methane. 4. a kind of method for preparing supercapacitor graphene-nickel hydroxide composite electrode material as claimed in claim 1, is characterized in that, in step A, reaction temperature is between 700-800 ℃, when reaching reaction After the temperature is reached, the hydrocarbon gas is introduced and the radio frequency plasma reaction is carried out. The radio frequency power is between 150-200W, and the reaction time is controlled within the range of 30-40min. 5. a kind of method for preparing supercapacitor graphene-nickel hydroxide composite electrode material as claimed in claim 1, is characterized in that, in the electrochemical deposition stage of step B, selected working electrode comes from PECVD method The prepared carbon-containing substrate, that is, the carbon material grown by chemical vapor deposition, the carbon material carrier such as nickel foam mainly composed of graphene film, the concentration of the nickel nitrate solution is between 0.1-1M, and M is the concentration per liter of the solution. The number of moles of solute substances, the electrochemical deposition process is preferably constant current cathodic deposition, the deposition current density is preferably 1-4mA/cm ² , and the deposition time is controlled at 3-12min. 6. a kind of method for preparing graphene-nickel hydroxide composite electrode material for supercapacitor as claimed in claim 1 is characterized in that, in the electrochemical stage of step C, the combination of nickel hydroxide and graphene does not need to stick Bonding agent, conductive agent, the temperature is preferably room temperature. 7. a kind of method for preparing supercapacitor graphene-nickel hydroxide composite electrode material as claimed in claim 6 is characterized in that, in the prepared composite electrode material whole process, do not carry out any bonding treatment, material addition and Including subsequent annealing operations.

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