CN115036142A

CN115036142A - Manganese dioxide electrode and preparation method and application thereof

Info

Publication number: CN115036142A
Application number: CN202210678291.4A
Authority: CN
Inventors: 赵俊善; 张明; 施佚涵; 李继涛; 杨定宇
Original assignee: Chengdu University of Information Technology
Current assignee: Chengdu University of Information Technology
Priority date: 2022-06-16
Filing date: 2022-06-16
Publication date: 2022-09-09
Anticipated expiration: 2042-06-16
Also published as: CN115036142B

Abstract

The invention belongs to the technical field of energy storage elements, and discloses a manganese dioxide electrode and a preparation method and application thereof. The invention takes three-dimensional foam nickel as a substrate in NiSO ₄ ，Na ₂ SO ₄ The mixed solution is subjected to electro-reduction to construct a nickel Base (rNi Base) reduced on the foamed nickel with the nano nuclear structure. Then the rNi Base is used as a substrate in Na ⁺ ，K ⁺ ，NH ⁴⁺ Respectively electrodepositing manganese dioxide under three different monovalent cation pre-intercalation treatment conditions to finally obtain rNi/MnO with special nano cauliflower-like structure ₂ &Na ⁺ The electrode has the advantage that the special nanostructure of the electrode improves the electrochemical performance of the electrode.

Description

Manganese dioxide electrode and preparation method and application thereof

Technical Field

The invention relates to the technical field of energy storage elements, in particular to a manganese dioxide electrode and a preparation method and application thereof.

Background

The super capacitor is used as a novel energy storage element between a conventional capacitor and a chemical battery, and is widely applied to the fields of portable electronic equipment, electric automobiles and the like. The super capacitor has the advantages of high discharge power, super capacitance in farad level, high energy, wide working temperature range, extremely long service life, no maintenance, economy, environmental protection and the like, and is paid more and more attention in recent years. The electrode material is a core component that affects the performance of the supercapacitor. Among the numerous types of electrode materials, manganese oxides MnO ₂ The electrode material is considered as the most promising next-generation super capacitor electrode material with abundant storage capacity, low cost, no toxicity, no pollution and higher theoretical specific capacity (1370F/g).

Compared with MnO ₂ The traditional preparation method and the electrodeposition method have a plurality of advantages. First, the Faraday reaction mainly occurs at the surface of the electrode and within a shallow bulk of not more than 500nm, and thus is close to MnO ₂ Theoretical specific capacitance of, MnO ₂ The film thickness should tend to be infinitely small, which speeds up electron and electrolyte ion transport and ensures MnO ₂ The active material is fully applied to energy storage, and MnO is deposited by using an electrochemical method ₂ The electrode can well control the film thickness, improve the material quality utilization rate as far as possible, and further improve the specific capacitance of the electrode. Secondly, preparing MnO by an electrochemical method ₂ The electrode material does not need to introduce a conductive agent and a binder, so that the introduction of redundant mass is avoided, and the specific capacitance of the material is reduced. And the conductive three-dimensional porous framework material can be directly used as a substrate to grow the nano material by adopting an electrodeposition method to obtain the electrode with a high surface area and a hierarchical structure, and the high-conductivity three-dimensional continuous porous support can provide enough binding sites for loading electroactive materials, so that the falling of the active materials caused by the volume change of the electrode in the charge-discharge cycle process is relieved, the insertion and the extraction of electrolyte ions at the electrode/electrolyte interface are facilitated to be accelerated, and the surface reaction rate is improved. The lan g prepares a nano-porous gold film with the thickness of 100 nanometers and promotes MnO ₂ With electrolytesIon diffusion while also providing electric double layer capacitance (Lang X, Hirata A, Fujita T, e)t al., Nanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors[J]Nature Nanotechnology, 2011, 6: 232-. Zhang electrodeposits nickel using self-assembled opals as a template to obtain a bicontinuous electrode, and removal of the template to obtain a nickel inverse opal (porosity of about 74%) that prevents discontinuous ion paths from conformal deposition of electrolytically active material deep into the structure, thereby increasing the charge and discharge rate (hugging Zhang, Xindi Yu, Paul v. However, the scarcity of noble metals and the complexity of the preparation process respectively limit the large-scale application of the noble metals and the preparation process.

In view of this, the invention is particularly proposed.

Disclosure of Invention

To solve the problems of the background art, it is an object of the present invention to provide a simple method for preparing a manganese dioxide electrode. The second purpose of the invention is to apply the electrode to the preparation of a super capacitor.

In order to achieve the purpose, the invention adopts a technical scheme that:

a method of making a manganese dioxide electrode comprising the steps of:

taking the cleaned three-dimensional porous foam Ni substrate as a working electrode, and NiSO ₄ 、Na ₂ SO ₄ The mixed solution is a precursor solution, and a three-electrode system is adopted for electrochemical reduction to obtain a nickel substrate reduced on the foam Ni; and

taking a reduced nickel substrate on the cleaned foam Ni as a working electrode, and MnSO ₄ 、Na ₂ SO ₄ The mixed solution is a precursor solution, and a three-electrode system is adopted to carry out pre-intercalation electrodeposition to obtain an electrode rNi/MnO ₂ &Na ⁺ And (6) drying.

Preferably, the cleaning method of the three-dimensional porous foam Ni substrate comprises the step of sequentially placing the three-dimensional porous foam Ni substrate into dilute hydrochloric acid, deionized water and absolute ethyl alcohol, and carrying out ultrasonic cleaning for 15min respectively.

Preferably, the reference electrode of the three-electrode system is a saturated Ag/AgCl electrode, and the counter electrode is a Pt electrode.

Preferably, the NiSO ₄ 、Na ₂ SO ₄ The molar concentration of (a) is 0.04-0.1 mol.L ^-1 Preferably 0.06 mol.L ^-1 。

Preferably, the MnSO ₄ 、Na ₂ SO ₄ The molar concentration of (a) is 0.04-0.1 mol.L ^-1 Preferably 0.06 mol.L ^-1 。

Preferably, the three-electrode system is treated by ultrasonic wave assistance.

Preferably, the voltage for electrochemical reduction by using the three-electrode system is-0.5 to-2.5V, and the time is 60 to 300s, preferably-1V and 100 s.

Preferably, the deposition voltage of the three-electrode system for pre-intercalation electrodeposition is 0.4-1.0V, the time is 60-300 s, and the preferable voltage is 0.8V and 120 s.

The invention also provides a manganese dioxide electrode obtained by any one of the preparation methods.

The invention adopts another technical scheme that the manganese dioxide electrode is applied to the preparation of the super capacitor. Compared with the prior art, the invention has the following beneficial effects:

the substrate used by the invention is a three-dimensional porous foam Ni substrate, the substrate has larger specific surface area, the mass utilization rate of the active material is increased, and the high-conductivity network of the structure promotes the transport of electrons and electrolyte ions. The invention takes three-dimensional foam nickel as a substrate in NiSO ₄ ，Na ₂ SO ₄ The mixed solution is subjected to electro-reduction to construct a nickel Base (rNi Base) reduced on the foamed nickel with the nano nuclear structure. Then the rNi Base is used as a substrate in Na ⁺ ，K ⁺ ，NH4 ⁺ Respectively electrodepositing manganese dioxide under three different monovalent cation pre-intercalation treatment conditions to finally obtain rNi/MnO with special nano cauliflower-like structure ₂ &Na ⁺ An electrode, the electrochemical performance of which is improved by the special nano structure of the electrode is 1A ‧ g ^-1 Electricity (D) fromHas 598F ‧ g at the flow density ^-1 And is at 20A ‧ g ^-1 At a high current density, the specific capacitance is still as high as 307.5F ‧ g ^-1 At 2A ‧ g ⁻¹ After the charge and the discharge are carried out for 500 times under the current density, the specific capacitance maintenance rate is up to 92.7 percent. In addition, the symmetrical super capacitor assembled by the electrode has ultrahigh specific capacitance (1A ‧ g) ^-1 At a current density of 401.1F ‧ g ^-1 ) Has a specific energy density (599.99W ‧ kg) ⁻¹ 80.22Wh ‧ kg at Power Density ⁻¹ ) Even at 11997.98W ‧ kg ⁻¹ The energy density of the high-power energy-saving material can reach 24.90 Wh ‧ kg ⁻¹ 。

Drawings

FIG. 1 is an SEM image of samples of example 1 and comparative examples 1 to 3;

FIG. 2 is a TEM image of the samples of example 1 and comparative examples 1 to 3;

FIG. 3(a) is a constant current charge and discharge curve of the samples of example 1 and comparative examples 1 to 3;

FIG. 3 (b) is a graph showing the rate capability of the samples of example 1 and comparative examples 1 to 3;

FIG. 3 (c) is a cyclic voltammogram of the samples of example 1, comparative examples 1-3;

FIG. 3 (d) is the area specific capacitance of the samples of example 1 and comparative examples 1-3;

FIG. 3 (e) is a graph showing the change in capacitance performance after 500 cycles of charge and discharge of the samples of example 1 and comparative examples 1 to 3;

FIG. 3 (f) is the cycle retention for the samples of example 1 and comparative examples 1-3 that were charged and discharged 500 times in cycles;

FIG. 4 (a) is a cyclic voltammogram of an assembled capacitor of example 1 and comparative example 3;

FIG. 4 (b) is a GCD curve for the assembled capacitor of example 1 and comparative example 3;

FIG. 4 (c) is a graph of rate capability of the assembled capacitor of example 1 and comparative example 3;

FIG. 4(d) is a graph showing the power density and energy density of the capacitor assembled from example 1 and comparative example 3;

FIG. 4(e) is a graph of the cycling performance of the assembled capacitor of example 1 and comparative example 3;

FIG. 4(f) shows the symmetrical apparatus of example 1 connected in series to illuminate a 3V LED lamp.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the following detailed description and the accompanying drawings. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The raw materials or instruments used are not indicated by manufacturers, and are all conventional products which can be obtained by commercial purchase.

In a first embodiment, the present invention provides a method for preparing a manganese dioxide electrode, comprising the steps of:

taking the cleaned three-dimensional porous foam Ni substrate as a working electrode, and NiSO ₄ 、Na ₂ SO ₄ The mixed solution is a precursor solution, and a three-electrode system is adopted for electrochemical reduction to obtain a nickel substrate reduced on foam Ni; and

taking a nickel substrate reduced on the cleaned foam Ni as a working electrode, and MnSO ₄ 、Na ₂ SO ₄ The mixed solution is a precursor solution, and a three-electrode system is adopted to carry out pre-intercalation electrodeposition to obtain an electrode rNi/MnO ₂ &Na ⁺ And (6) drying.

The above preparation method is explained in detail: the three-dimensional porous foam Ni substrate is preferably processed to 3 x 2 cm ² The substrate is placed into dilute hydrochloric acid, deionized water and absolute ethyl alcohol to be sequentially subjected to ultrasonic cleaning for 15min respectively so as to remove nickel oxide and oil stains on the surface of the nickel substrate, wherein the electro-oxidation effect of the absolute ethyl alcohol can guide the active substances to be rapidly and uniformly deposited, so that the thickness of the film is more uniform and controllable, and the utilization rate of the active substances is higher.

Then adopting electrochemical reduction method, and using molar concentration to be 0.04-0.1 mol.L ^-1 NiSO (D) ₄ 、Na ₂ SO ₄ The mixed solution is used as a precursor solution,in a three-electrode system (a French BioLogic electrochemical workstation, three-dimensional porous foam Ni is used as a working electrode, saturated Ag/AgCl is used as a reference electrode, and a Pt electrode is used as a counter electrode) under the assistance of ultrasonic waves, a reduced nickel substrate (rNi Base) on foam nickel is obtained, the deposition voltage is-0.5V-2.5V, and the deposition time is 60s-300 s. The reaction occurring during the production of rNi Base by the electro-reduction method is shown in formula (1):

（1）

then, the reduced nickel substrate rNi Base on the foamed nickel is placed in deionized water for ultrasonic cleaning and then is dried in a vacuum drying oven. Subsequently, each substrate was used as a working electrode in a three-electrode system with ultrasonic assistance, and the molar concentration was 0.04 mol ^-1 -0.1 mol•L ^-1 MnSO of ₄ 、Na ₂ SO ₄ Performing intercalation treatment and electrodeposition in a precursor solution of the mixed solution in advance to obtain rNi/MnO ₂ &Na ⁺ The deposition voltage is 0.4V-1.0V, the deposition time is 60s-300s, the introduction of ultrasonic oscillation in the deposition process can effectively reduce the concentration range difference caused by the rapid consumption of metal ions near the electrode, so that the deposition is more uniform, and the reaction in the deposition process is shown in a formula (2):

（2）

in order to better understand the technical scheme provided by the invention, the following specific examples respectively illustrate the preparation method, application and performance test of the manganese dioxide electrode provided by the above embodiment of the invention.

Example 1

Three-dimensional porous foam Ni substrate (3 x 2 cm) ² ) And placing the nickel substrate into dilute hydrochloric acid, deionized water and absolute ethyl alcohol to perform ultrasonic cleaning for 15min respectively in sequence so as to remove nickel oxide and oil stains on the surface of the nickel substrate. Then adopting electrochemical reduction method to make the concentration of the catalyst be 0.06 mol ^-1 NiSO (D) ₄ ，Na ₂ SO ₄ Precursor solution of mixed solutionAnd (3) obtaining a reduced nickel substrate (rNi Base) on the foamed nickel in a three-electrode system (a French BioLogic electrochemical workstation, foamed nickel is used as a working electrode, saturated Ag/AgCl is used as a reference electrode, and a Pt electrode is used as a counter electrode) under the assistance of ultrasonic waves, wherein the deposition voltage and the deposition time are respectively-1V and 100 s.

Then putting the rNi Base into a vacuum drying oven for drying after ultrasonic cleaning in deionized water, weighing the substrate quality after drying and recording. Subsequently, each substrate was used as a working electrode in a three-electrode system with the assistance of ultrasonic waves at 0.06 mol ^-1 MnSO ₄ , Na ₂ SO ₄ Performing intercalation treatment and electrodeposition in a precursor solution of the mixed solution in advance to obtain rNi/MnO ₂ &Na ⁺ The deposition voltage was 0.4V and the deposition time was 280 s.

The sample was dried and weighed, and the difference between the two masses before and after the drying was the mass of the electrode sheet active material, and the results are shown in table 1.

TABLE 1

。

rNi/MnO ₂ &Na ⁺ Punching into 14 mm electrode pieces directly with a punching machine, respectively using the two punched electrode pieces as a positive electrode and a negative electrode, using ONKK-MPF30AC-10 as a diaphragm, and 1mol ^-1 Na ₂ SO ₄ The solution was used as an electrolyte, and a CR2016 type battery case was used as a positive and negative electrode case to assemble each of the symmetrical capacitors.

Example 2

Three-dimensional porous foam Ni substrate (3 x 2 cm) ² ) And placing the nickel substrate into dilute hydrochloric acid, deionized water and absolute ethyl alcohol to perform ultrasonic cleaning for 15min respectively in sequence so as to remove nickel oxide and oil stains on the surface of the nickel substrate. Then adopting an electrochemical reduction method to perform reduction at the concentration of 0.04 mol ^-1 NiSO (D) ₄ ，Na ₂ SO ₄ The mixed solution is used as a precursor solution, and foams are obtained in a three-electrode system (a France BioLogic electrochemical workstation, foamed nickel is used as a working electrode, saturated Ag/AgCl is used as a reference electrode, and a Pt electrode is used as a counter electrode) under the assistance of ultrasonic wavesThe nickel substrate (rNi Base) was reduced on nickel at a deposition voltage of-1.5V for 160 s.

Then the rNi Base is placed in deionized water for ultrasonic cleaning and then is dried in a vacuum drying oven. Subsequently, each substrate was used as a working electrode in a three-electrode system with the aid of ultrasound at 0.07 mol.L ^-1 MnSO ₄ , Na ₂ SO ₄ Performing pre-intercalation treatment and electrodeposition in a precursor solution of the mixed solution to obtain rNi/MnO ₂ &Na ⁺ The deposition voltage was 0.6V and the deposition time was 200 s.

Example 3

Three-dimensional porous foam Ni substrate (3 x 2 cm) ² ) And placing the nickel substrate into dilute hydrochloric acid, deionized water and absolute ethyl alcohol to perform ultrasonic cleaning for 15min respectively in sequence so as to remove nickel oxide and oil stains on the surface of the nickel substrate. Then adopting electrochemical reduction method to make the concentration of the active carbon be 0.1 mol.L ^-1 NiSO (D) ₄ ，Na ₂ SO ₄ The mixed solution was used as a precursor solution, and a reduced nickel substrate (rNi Base) on foamed nickel was obtained in a three-electrode system (French BioLogic electrochemical workstation, foamed nickel was used as a working electrode, saturated Ag/AgCl was used as a reference electrode, and Pt electrode was used as a counter electrode) with the assistance of ultrasonic waves, and the deposition voltage and deposition time were-0.5V and 280s, respectively.

Then the rNi Base is placed in deionized water for ultrasonic cleaning and then is dried in a vacuum drying oven. Subsequently, each substrate was used as working electrode in a three-electrode system with the assistance of ultrasound at 0.04 mol ^-1 MnSO ₄ , Na ₂ SO ₄ Performing intercalation treatment and electrodeposition in a precursor solution of the mixed solution in advance to obtain rNi/MnO ₂ &Na ⁺ The deposition voltage was 1.0V and the deposition time was 70 s.

Comparative example 1

Compared with example 1, 0.06 mol.L ^-1 MnSO ₄ , Na ₂ SO ₄ The mixed solution was replaced with 0.06 mol.L ^- ¹ MnSO ₄ , K ₂ SO ₄ The solution was mixed and the remaining process was the same as in example 1 to prepare rNi/MnO of electrode ₂ &K ⁺ . The mass difference of the two times is the active material of the electrode sliceMass, as shown in Table 1.

Comparative example 2

Compared with example 1, 0.06 mol.L ^-1 MnSO ₄ , Na ₂ SO ₄ The mixed solution was replaced with 0.06 mol.L ^- ¹ MnSO ₄ , (NH ₄ ) ₂ SO ₄ The solution was mixed and the remaining process was the same as in example 1 to prepare rNi/MnO of electrode ₂ & NH ⁴⁺ . The mass difference between the two previous and later times is the mass of the active material of the electrode plate, as shown in table 1.

Comparative example 3

Compared with the embodiment 1, the three-dimensional porous foam Ni substrate is not prepared by adopting an electrochemical reduction method, and the specific method comprises the following steps:

the three-dimensional porous foam Ni substrate (Ni Base) is placed in a vacuum drying oven for drying after being ultrasonically cleaned in deionized water. Subsequently, each substrate was used as a working electrode in a three-electrode system with the aid of ultrasound at 0.06 mol ^-1 MnSO ₄ , Na ₂ SO ₄ Performing intercalation treatment and electrodeposition in a precursor solution of the mixed solution in advance to obtain Ni/MnO ₂ &Na ⁺ The sample was dried and weighed, and the difference between the two masses before and after the drying was the mass of the electrode sheet active material, as shown in table 1.

Experimental example 1 characterization of Material morphology

The surface morphology and microstructure of each sample and electrode were observed by scanning electron microscopy (SEM, Zeiss ULTRA 55 SEM) on the samples of example 1 and comparative examples 1-3, and the results are shown in fig. 1. Example 1rNi/MnO was observed using a transmission electron microscope (TEM, FEI Tecnai G2F 20) ₂ &Na ⁺ The results are shown in fig. 2.

It is apparent from fig. 1 that the secondarily constructed rNi Base (example 1, comparative examples 1-2) after the electrochemical reduction treatment exhibits a nano-core structure, compared to the general Ni Base (comparative example 3). Moreover, the substrate morphology has a great influence on the deposition process of the electrode material, MnO ₂ The growth of the nano material shows a staggered nano rod structure on the common Ni Base, and shows fine nano on the secondary constructed rNi BaseThe rice ball is coated on the surface of the irregular core substrate to form a nano cauliflower structure. On the one hand, the surface of the irregular nuclear structure of the rNi Base is MnO ₂ Provide more active sites, and thus MnO grown thereon ₂ The combination between the film and the substrate is more compact, the film is not easy to fall off, and the electrode cycle performance can be enhanced; on the other hand, the surface of the irregular nuclear structure of the rNi Base is uneven, charges are more easily accumulated at the nuclear protuberance, and MnO is guided ₂ The nanorods grow such that they aggregate into a spherical structure.

To further determine the microstructure of the electrode, a Transmission Electron Microscope (TEM) pair rNi/MnO was used ₂ &Na ⁺ The observation was performed, and electron diffraction (SAED), Element mapping (Element mapping) analysis and high-resolution transmission electron microscopy (HR-TEM) analysis were performed, and the results are shown in fig. 2. Combining the results of FIG. 2(a), at rNi/MnO ₂ &Na ⁺ (example 1) the surface of the nano-embroidered sphere structure formed by uniformly wrapping the manganese dioxide nano-material on the surface of the Ni core can be clearly observed, and the structure forms a nano-cauliflower structure in an SEM picture as a unit, and the structure is favorable for providing more Faraday redox reaction sites. FIG. 2(c), (d) is rNi/MnO ₂ &Na ⁺ HR-TEM picture of the electrode can clearly observe the lattice fringes of the material, and the interplanar spacing is d ₁ =0.172 nm，d ₂ =0.202 nm，d ₃ =0.206 nm，d ₄ =0.226 nm, each corresponding to MnO ₂ The (501), (202), (401), and (002) crystal planes of (b). In addition, the Element mapping result shows that Mn, O and Na are uniformly distributed on the surface of the Ni Element, which further shows that MnO is contained ₂ The material is coated on the surface of a Ni core, and simultaneously proves Na ⁺ Successfully pre-inserted into rNi/MnO ₂ And an electrode.

Experimental example 2 detection of electrochemical Properties of electrode

And carrying out electrochemical performance test on the prepared sample electrode by adopting a constant current charge-discharge method and a linear cyclic voltammetry method. The reaction equation during electrochemical charge and discharge can be represented by formula (3):

（3）

at 1 mol.L ^-1 Na ₂ SO ₄ The solution was used as electrolyte in a three-electrode system (sample electrode as working electrode, Ag/AgCl as reference electrode, Pt electrode as counter electrode) on a BioLogic electrochemical workstation, France. The mass specific capacitance of the electrode material is calculated by using a constant current charge-discharge curve and a cyclic voltammetry curve obtained by an electrode performance test and respectively adopting the following formula (4) and formula (5)

And area ratio capacitance

：

（4）

(4) In the formula

Mass current density, Delta, for charging and discharging𝑡M is the mass of the electrode plate of the sample, Delta𝑉The voltage change is complete charge and discharge.

（5）

(5) Wherein s is the area of the sample electrode plate,

is the scan rate, V is the scan interval, the integral multiple𝐼d𝑣Is half of the integrated area of the entire CV curve.

As a result, as shown in FIG. 3, FIGS. 3(a) and (b) are constant current charge/discharge curves of the respective electrodes (each electrode is at 1 A.g) ^-1 At a current density of) and at a different current density (1,2,5,10,20 A.g) from the electrode ^-1 ) The rate performance obtained is as follows. First, it can be observed that compared to normal NThe GCD curves of the electrodes deposited on the i Base and those deposited on the rNi Base more approximate equilateral triangles, indicating that they have highly reversible redox reactions and that the discharge times are significantly longer, and I.R drop is also lower, which is attributable to the fact that the electrodes deposited on the rNi Base with a nuclear structure possess a larger specific surface area. The morphology with the high specific surface area can provide more redox reaction sites, so that the electrode pseudocapacitance is improved, and the electrode pseudocapacitance has smaller resistivity, so that the electrode series equivalent resistance (ESR) is reduced, and finally the purpose of reducing IR drop is achieved.

rNi/MnO ₂ &Na ⁺ The GCD curve shows the longest discharge time, which is beneficial to the unique three-dimensional nanometer cauliflower structure of the electrode, the high specific surface area and the high porosity of the structure can provide more Na ⁺ The active material mass utilization rate is improved at the embedding and de-embedding sites, so that the electrode is arranged at 1,2,5,10,20 A.g ^-1 Respectively possess 598, 484.6, 402.2, 349.2, 307.5 F.g ^-1 Ultra high specific capacitance (compare with previous studies, see table 2).

TABLE 2 comparison of electrode specific capacities

。

Wherein (r) is Zhang M, Yang D, J Li. Supercapactor requirements of MnO ₂ and MnO ₂ / reduced graphene oxide prepared with various electrodeposition time. Vacuum, 2020, 178:109455.

(ii) Mahdi F, Javanbakht M, Shahrokhian S. antioxidant pulse amplification of meso magnetic dioxide nanostructures for high performance supercapacitors. Journal of Alloys and Compounds, 2021:161376.

③ Swain N, Mitra A, Saravanakumar B,et al., Construction of Three-Dimensional MnO ₂ /Ni Network as an Efficient Electrode Material for High Performance Supercapacitors. Electrochimica Acta, 2020, 342: 136041.

cyclic voltammetry is also one of the important means for detecting the performance of the electrode material, and as shown in fig. 3 (c), all samples have a pair of distinct redox peaks at about 0.6-0.9V. And compared with the electrode deposited on the common substrate, the electrode deposited on the two secondary construction substrates rNi Base has the absolute value of the ratio of the sizes of the oxidation reduction peak values close to 1, which shows that the electrode has stronger reversibility of the oxidation reduction reaction. The area specific capacitance of each electrode was obtained from the CV test results in combination with equation (5), as shown in fig. 3. (d). Thanks to the nano cauliflower structure with ultra-high specific surface area, rNi/MnO ₂ &Na ⁺ The area specific capacitance of the sample is highest in each group and reaches 141 mF ^-2 . Each electrode has a cycling performance passing current density of 2 A.g ^-1 1 mol.L of the GCD method ^-1 Na ₂ SO ₄ The charge and discharge cycles were repeated 500 times to obtain (FIG. 3.(e), (f)). The initial degradation of the capacitor performance is mainly due to the presence of manganese dioxide in Na ₂ SO ₄ Dissolution in solution. In fact, we also observed that the sodium sulfate solution turned brown during the test period. rNi/MnO ₂ &Na ⁺ Benefiting from structural stability, MnO ₂ More contact with the substrate and stronger adhesion, a high cycle retention of 92.7% was obtained.

Experimental example 3 electrochemical Performance testing of symmetric supercapacitor

Referring to the method of assembling the capacitor of example 1, comparative example 1 was assembled, and the assembled symmetrical supercapacitor was left to stand for 12 hours and then subjected to an ac impedance test using a Bio-logic electrochemical workstation of france, with a frequency range of 0.01Hz to 100KHz and an amplitude of 5m V. The device was then scanned at a rate of 5 mv.s ^-1 The cyclic volt-ampere test is carried out to determine the voltage window of each device to carry out constant current charge and discharge test. The mass specific capacitance of the device can be calculated according to the formula (4) by the constant current charging and discharging curve of the super capacitor

The energy density (E) (Wh kg) of the electrode at different current densities can be calculated by using the following two formulas (6) and (7) ^-l ) And power density (P) (W kg) ^-1 )。

（6）

（7）

Wherein the content of the first and second substances,

representing the voltage window during charging and discharging,

representing the device discharge time.

With Ni/MnO ₂ &Na ⁺ Comparative example 3 and rNi/MnO ₂ &Na ⁺ (example 1) results of performance testing of the electrode-assembled symmetrical supercapacitor are shown in fig. 4. Fig. 4 (a) is a cyclic voltammogram of each of the symmetric devices, and first, it can be seen that the symmetric device composed of electrodes deposited on the rNi Base obtained a larger CV curve area when the same cations were subjected to the pre-intercalation treatment, which indicates that the specific surface capacitance of the device is improved, and the high specific surface area of the nano cauliflower attributable to the electrodes shows morphology. Secondly, each electrode has a pair of redox peaks in a voltage interval of-0.2-1V, so that the device is subjected to 1,2,5,10, 20A ‧ g in a voltage interval of-0.2-1V ⁻¹ The constant current charge and discharge test of (a) and (b) shows that the GCD curves and the multiplying power performance of the two devices are respectively shown in fig. 8(b) and (c). rNi/MnO ₂ &Na ⁺ Symmetrical devices are at 1,2,5,10, 20A ‧ g ⁻¹ Has the current densities of 401.1, 289.9, 194, 159.1 and 124.5F ‧ g ⁻¹ The ultra-high specific capacity.

The power density (P) and the energy density (E) are also important electrochemical properties of the supercapacitor, and the results obtained by calculation using the equations (6), (7) according to the GCD curve are shown in fig. 4 (d). Compared with electrode deposited on common substratePrepared devices, rNi/MnO ₂ &Na ⁺ The capacitor has higher energy density (599.99W ‧ kg ⁻¹ 80.22Wh ‧ kg at Power Density ⁻¹ ) Even at 11997.98W ‧ kg ⁻¹ The energy density of the high-power energy-saving material can reach 24.90 Wh ‧ kg ⁻¹ . The cycle performance of each device shown in FIG. 4(e) was 2A ‧ g ⁻¹ The material is obtained by constant current charging and discharging for 500 times under current density, the whole performance is similar to that of an electrode cycle performance test, and the reduction of the capacitance performance of the same device in the initial stage is mainly due to MnO ₂ In Na ₂ SO ₄ Dissolution in the electrolyte. rNi/MnO ₂ &Na ⁺ Symmetrical supercapacitors as electrode compositions benefit from the high specific surface area, MnO, of rNi substrate ₂ More contact between the material and the substrate, increased MnO ₂ The adhesive strength of (a) and the structural stability are stronger, and a high cycle retention of 84.8% is obtained. With the same three blocks rNi/MnO ₂ &Na ⁺ The symmetrical super capacitors are connected in series to be used as a power supply for driving, and the LED lamp with the rated voltage of 3V is successfully lightened, as shown in fig. 4 (f).

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The preparation method of the manganese dioxide electrode is characterized by comprising the following steps of:

by reduction on cleaned foam NiThe nickel substrate is a working electrode, MnSO ₄ 、Na ₂ SO ₄ The mixed solution is a precursor solution, and a three-electrode system is adopted to carry out pre-intercalation electrodeposition to obtain an electrode rNi/MnO ₂ &Na ⁺ And (6) drying.

2. The method for preparing a manganese dioxide electrode according to claim 1, wherein the method for cleaning the three-dimensional porous foam Ni substrate comprises the step of sequentially placing the three-dimensional porous foam Ni substrate in diluted hydrochloric acid, deionized water and absolute ethyl alcohol, and performing ultrasonic cleaning for 15min respectively.

3. The method of making a manganese dioxide electrode according to claim 1, wherein the reference electrode of said three-electrode system is a saturated Ag/AgCl and the counter electrode is a Pt electrode.

4. The method of making manganese dioxide electrode of claim 1, wherein said NiSO is ₄ 、Na ₂ SO ₄ The molar concentration of (a) is 0.04-0.1 mol.L ^-1 。

5. The method of making a manganese dioxide/carbon electrode of claim 1, wherein said MnSO is ₄ 、Na ₂ SO ₄ The molar concentration of (b) is 0.04-0.1 mol ^-1 。

6. The method of making a manganese dioxide electrode of claim 1, wherein said three-electrode system is ultrasonically assisted.

7. The method of preparing a manganese dioxide electrode according to claim 1, wherein the electrochemical reduction using the three-electrode system is carried out at a voltage of-0.5 to-2.5V for a time of 60 to 300 s.

8. The method of claim 1, wherein the pre-intercalation electrodeposition is performed using a three-electrode system at a deposition voltage of 0.4 to 1.0V for a period of 60 to 300 seconds.

9. Manganese dioxide electrode obtainable by the process according to any one of claims 1 to 8.

10. Use of manganese dioxide electrode according to claim 9 for the preparation of a supercapacitor.