CN112992558A

CN112992558A - Preparation method of metal-based carbon fiber composite electrode, product and application thereof

Info

Publication number: CN112992558A
Application number: CN202110177102.0A
Authority: CN
Inventors: 赵亚萍; 苏丽访; 金振东; 靳凯丽; 蔡再生
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2021-02-07
Filing date: 2021-02-07
Publication date: 2021-06-18
Anticipated expiration: 2041-02-07
Also published as: CN112992558B

Abstract

The invention discloses a preparation method of a metal-based carbon fiber composite electrode and a product and application thereof.A pretreated and activated carbon fiber is placed in an aqueous solution in which a main metal salt, a reducing agent and a buffering agent are dissolved, and a metal/carbon fiber composite material is obtained by heating reaction; and further carrying out electrooxidation on the obtained metal/carbon fiber composite material to obtain the metal-based carbon fiber composite electrode. Then the metal-based carbon fiber composite electrode is used as weft, the fabric fiber is used as warp, and the weaving process is carried out to obtain the woven super capacitor. Under the premise of not changing carbon fiber as a flexible substrate, the surface of the carbon fiber is metallized by chemical plating, and then electrode active substances are grown on a metal plating layer by utilizing electrooxidation. A hybrid structure of an in-situ synthesized active material and a conductive reinforcing material is formed, so that the reaction kinetics between the metal hydroxide and the electrolyte ion transmission is promoted, the contact resistance of the electrode material is reduced, and the electrochemical performance of the material is improved.

Description

Preparation method of metal-based carbon fiber composite electrode, product and application thereof

Technical Field

The invention relates to the technical field of carbon fiber composite electrodes, in particular to a preparation method of a metal-based carbon fiber composite electrode, and a product and application thereof.

Background

In order to realize the practicability of the flexible wearable electronic equipment, the preparation of an energy storage device with light weight, small volume and high flexibility is urgent. Compared with the traditional flexible energy storage device based on a planar structure, the supercapacitor based on the fiber electrode has the characteristic of being capable of realizing the application of flexible wearable electronic equipment. Besides, the fiber-based super capacitor can be woven into a wearable energy fabric through a textile technology according to the weavability and the tailorability, and the large-scale forming process is convenient to complete. Therefore, the development of a fiber super capacitor with high energy density has far-reaching significance for realizing flexible wearable energy storage.

The carbon material is the most commonly used electrode substrate of the fiber capacitor and has the advantages of high specific surface area, thermal stability, chemical stability, low cost and the like; carbon Fiber (CF) is light, high in specific strength, high in specific stiffness, strong in designability, high in safety and stability, and is an ideal lightweight high-performance material, but its application as an electrode material is limited by low capacitance.

Transition metal hydroxides have a high theoretical capacity by storing/releasing charges by reversible faradaic redox, and have recently received attention from many researchers as a high theoretical capacity electrode material. Studies have shown that transition metal hydroxides have excellent capacitive properties for use in self-supporting electrodes of supercapacitors. Such as Ni (OH)₂Has a theoretical specific mass capacity of 2585F g^-1The material is an ideal high-capacity super capacitor electrode material; however, due to the problems of small specific surface area, poor self-conductivity, short mean free path, slow interlayer ion diffusion and the like, the rate performance is poor, the realization of high theoretical capacitance is seriously hindered, and particularly, the capacitance performance under high charge-discharge rate is limited, so that the application of the capacitor is limited.

Disclosure of Invention

In order to solve the technical problems, the invention provides a preparation method of a metal-based carbon fiber composite electrode, a product and an application thereof, wherein the carbon fiber composite electrode is subjected to chemical plating to metalize the surface of the carbon fiber on the premise of not changing the carbon fiber as a flexible substrate, and then an electrode active substance is grown on a metal plating layer by utilizing electrooxidation. A hybrid structure of an in-situ synthesized active material and a conductive reinforcing material is formed, so that the reaction kinetics between the metal hydroxide and the electrolyte ion transmission is promoted, the contact resistance of the electrode material is reduced, and the electrochemical performance of the material is improved.

One of the technical schemes of the invention is a preparation method of a metal-based carbon fiber composite electrode, which comprises the following steps:

placing the pretreated and activated carbon fiber in an aqueous solution in which a main metal salt, a reducing agent and a buffering agent are dissolved, and heating for reaction to obtain a chemically plated metal/carbon fiber composite material; and further carrying out electrooxidation on the obtained metal/carbon fiber composite material by adopting a cyclic voltammetry method to obtain a metal-based carbon fiber composite electrode.

Further, the pretreatment and activation process of the carbon fiber specifically comprises the following steps:

pretreatment: soaking the carbon fiber in ethanol and then airing to obtain pretreated carbon fiber;

and (3) activation: and (3) soaking the pretreated carbon fiber in an alkaline sodium borohydride solution, airing, and placing in an activating solution for reaction to obtain the pretreated and activated carbon fiber.

Further, the soaking time in the ethanol is 30 min;

further, NaBH in the alkaline sodium borohydride solution₄The concentration is 0.2g/L, and the concentration of NaOH is 0.04 g/L; soaking the carbon fiber in an alkaline sodium borohydride solution for 30 min;

furthermore, the concentration of nickel sulfate in the activation solution is 0.1mol/L, the concentration of sodium hypophosphite is 0.03mol/L, the concentration of trisodium citrate is 0.02mol/L, and the reaction time of the carbon fiber in the activation solution is 10 min.

The pretreatment is used for removing impurities and oil stains on the surface of the carbon fiber;

chemical plating is a reaction between liquid/solid phases, and metal ions are subjected to reduction deposition and grain growth at a substrate/solution interface; in order to ensure the growth of metal grains on a substrate, activation treatment is needed before chemical plating, and the function is to form a layer of discontinuous noble metal particles on the surface of the substrate so that the surface of a machine body has catalytic capability; the method comprises the steps of firstly soaking carbon fibers in a strong reducing agent sodium borohydride, then contacting the carbon fibers with a nickel salt solution, and reducing Ni on the surfaces of the carbon fibers²⁺Forming a Ni simple substance as a catalytic site in a subsequent reduction process, specifically:

further, the main metal salt is a double metal salt; specifically, the concentration ratio of metal ions is (1-4): (1-4) nickel salt and cobalt salt, or metal ion concentration ratio of (1-4): (1-4) a nickel salt and a ferrous salt;

the total concentration of the main metal salt is 0.1 mol/L.

Furthermore, the reducing agent is sodium hypophosphite, and the concentration of the reducing agent is 0.02-0.05 mol/L.

Further, the buffer is trisodium citrate.

Further, the heating reaction temperature is 60-90 ℃.

In the chemical plating process, a weak reducing agent sodium hypophosphite is adopted as a reducing agent, wherein the chemical reaction is involved:

or

In the chemical plating reaction of the double metal salt, the difference of the deposition rates of different metal ions has great influence on the chemical reaction rate, so the concentration ratios of different metal salts play a crucial role; the chemical plating process is a process of reducing metal ions in the plating solution, so that the content of a reducing agent has certain influence on the quality of chemical plating; in the chemical plating system, the reduction process is an endothermic reaction, so the influence on the reaction process by the temperature is large; for the above reasons, the present invention defines the metal ion concentration ratio, the concentration of the reducing agent, and the heating reaction temperature. Tests prove that when the concentration ratio of the metal ions of the nickel salt and the cobalt salt is 3:2, the resistance of the prepared NiCo/CF sample is the minimum; when the concentration of the reducing agent is 0.03mol/L, the reaction rate is optimal; when the heating temperature is 80 ℃, the weight increase of the coating is the largest.

When the main metal salt is nickel salt or ferrous salt, the Fe is²⁺Has a lower standard reduction potential, and the increase of the pH value is favorable for the reduction of metal ions, but the pH value of the solution is too high, so that H is easily caused₂PO^2-Because the side reaction of the oxidation reaction occurs, when ferrous salt is used as auxiliary salt, the pH value of the reaction solution needs to be controlled, and the weight increase of the plating layer is the largest when the pH value is 9.

Side reaction:

further, the electro-oxidation specifically includes: and (2) taking 3mol/L potassium hydroxide as an electrolyte, a metal/carbon fiber composite material as a working electrode, a platinum wire as a counter electrode and a saturated calomel electrode as a reference electrode, and performing electrooxidation circulation for 200 times at a scanning rate of 10mV/s under the condition of a voltage of-0.1-0.6V to obtain the metal-based carbon fiber composite electrode.

In the second technical scheme of the invention, the metal-based carbon fiber composite electrode is prepared by the preparation method of the metal-based carbon fiber composite electrode.

According to the third technical scheme, the metal-based carbon fiber composite electrode is applied to a super capacitor.

In the fourth technical scheme of the invention, the woven supercapacitor is prepared by weaving the metal-based carbon fiber composite electrode as weft and the fabric fiber as warp through a weaving process.

Further, the fabric fiber is one of wool, jute, viscose, ramie, silk, cotton, vinylon, chinlon, acrylic fiber, terylene and polypropylene fiber; the weaving process is plain weave, twill weave or satin weave.

The plain weave fabric has the advantages that the openings of the warps and the wefts are staggered every time, so that the warps are bent more, and the warps and the wefts are interwoven most tightly, so that the plain weave fabric is firm in texture under the same condition; the twill weave has less warp and weft interweaving rate than the plain weave, the woven yarn is easy to close, and the wear resistance and the fastness of the twill weave are not as good as those of the plain weave; the distance between the interweaving points of the satin fabric is long, the floating length of the fabric yarn is long, and the fastness is poor.

Compared with the prior art, the invention has the following beneficial effects:

the invention adopts a chemical plating-electrooxidation method to prepare the composite fiber electrode with uniformly distributed particle and flake multilevel structures on the surface, so that the active specific surface area of the material is increased, and the electrochemical activity is improved. Specifically, bimetallic conductive particles are introduced to the surface of carbon fibers by a chemical plating method, and further the bimetallic conductive particles are used as a metal hydroxide deposition and growth substrate, further electrooxidation is carried out by a cyclic voltammetry method, metal elements grow in a mode of electrochemically oxidizing and etching a matrix, and a nano hierarchical structure compound consisting of bimetallic and layered metal oxides is constructed on the carbon fibers to form a composite fiber electrode; the metal/metal hydroxide on the surface of the carbon fiber is good, so that the conductivity of the electrode material can be improved; the existence of the metal hydroxide two-dimensional nano-sheet increases active sites, improves the circulation stability and realizes high capacity; the active specific surface area of the material is increased by utilizing a metal @ metal hydroxide composite nano hierarchical structure, and the composite fiber electrode material with higher specific capacitance and excellent cycle stability is obtained.

The fiber electrode prepared by the invention can be further used as weft to prepare a woven supercapacitor which has higher specific capacitance and energy density, and the capacitance of the woven supercapacitor is hardly lost under three conditions of being folded for 1 time under a 180-degree bending condition and being folded for 1000 times under a 180-degree bending condition in an unbent state.

Drawings

FIG. 1 is a plain weave pattern of a woven super dot contemporaneous fabric prepared in example 1 of the present invention.

FIG. 2 is a graph showing the effect of the main factors influencing the chemical plating conditions during the NiCo/CF preparation process on the resistance and weight gain in the effect verification of the present invention; wherein FIG. 2a is the ratio of the main salt metal ion concentration, FIG. 2b is the reducing agent concentration, and FIG. 2c is the temperature.

FIG. 3 is an SEM image of an electroless plating sample NiCo/CF in the effect verification of the present invention; wherein FIG. 3a is an apparent topography of an electroless plating sample of NiCo/CF-1, FIG. 3b is an apparent topography of an electroless plating sample of NiCo/CF-2, and FIG. 3c is an apparent topography of an electroless plating sample of NiCo/CF-3.

FIG. 4 is a FESEM image of a sample NiCo @ NiCoDH/CF after electroless-electro-oxidation in the validation of the present invention; wherein FIG. 4a is an apparent topography of an electroless plated sample of NiCo @ NiCoDH/CF-1, FIG. 4b is an apparent topography of an electroless plated sample of NiCo @ NiCoDH/CF-2, and FIG. 4c is an apparent topography of an electroless plated sample of NiCo @ NiCoDH/CF-3.

FIG. 5 is an EDS map of an electroless plated sample NiCo/CF-3; wherein FIG. 5a is an EDS diagram of an electroless plating sample NiCo/CF-3, and FIG. 5b is a Mapping diagram of the electroless plating sample NiCo/CF-3.

FIG. 6 is a graph showing the electrochemical performance of NiCo @ NiCoDH/CF in the effect test of the present invention; wherein FIG. 6a is a CV diagram of a CF electrode and a NiCo @ NiCoDH/CF-3 electrode at a scanning rate of 10mV/s, FIG. 6b is a CV comparison diagram of a NiCo @ NiCoDH/CF electrode, FIG. 6c is an EIS diagram of a NiCo @ NiCoDH/CF electrode, FIG. 6d is a magnification performance diagram of a NiCo @ NiCoDH/CF electrode, FIG. 6e is a CV diagram of a NiCo @ NiCoDH/CF-3 electrode at a scanning rate of 1-10 mV/s, and FIG. 6f is a GCD diagram of a NiCo @ NiCoDH/CF-3 electrode at a current density of 1-20 mA/cm.

FIG. 7 is a graph showing the effect of the major factors affecting the electroless plating conditions on the electrical resistance and weight gain during the NiFe/CF preparation process; FIG. 7a is the ratio of the metal ion concentration of the main salt, FIG. 7b is the pH value, and FIG. 7c is the temperature.

FIG. 8 is an SEM image of an electroless plated NiFe/CF sample in the validation of the effects of the present invention; wherein FIG. 8a is an apparent topography of an electroless plated sample of NiFe/CF-1, FIG. 8b is an apparent topography of an electroless plated sample of NiFe/CF-2, FIG. 8c is an apparent topography of an electroless plated sample of NiFe/CF-3, and FIG. 8d is an apparent topography of an electroless plated sample of NiFe/CF-4.

FIG. 9 is an SEM image of an electroless plated sample NiFe @ NiFeDH/CF-2 in the validation of the effects of the present invention; where FIG. 9a is at 5K magnification, FIG. 9b is at 20K magnification, FIG. 9c is at 50K magnification, and FIG. 9d is at 100K magnification.

FIG. 10 is an EDS chart of an electroless plating sample NiFe/CF-2 in effect verification according to the present invention; FIG. 10a is the EDS map of NiFe/CF-2, and FIG. 10b is the Mapping map of NiFe/CF-2.

FIG. 11 is a graph of the electrochemical performance of NiFe @ NiFeDH/CF-2 in the effect verification of the present invention; FIG. 11a is a GCD curve of NiFe @ NiFeDH/CF-2, FIG. 11b is an EIS diagram of a NiFe @ NiFeDH/CF-2 electrode, and the inset shows an enlarged view at high frequency.

FIG. 12 is a cyclic voltammetry test plot of NiFe @ NiFeDH/CF in the validation of the present invention; wherein FIG. 12a is a CV comparison graph of the three fiber electrodes at a scan rate of 10mV/s, FIG. 12b is a GCD curve of the three fiber electrodes at a current density of 1mV/cm, and FIG. 12c is a graph of the rate capability of the three fiber electrodes.

FIG. 13 is a schematic of the cycles NiFe @ NiFeDH/CF-2 and NiCo @ NiCoDH/CF-3.

FIG. 14 is a graph comparing the CV curve of the prepared wSC-NC folded 1000 times under a 180 ° bend test with the initial CV curve, with the inset being wSC-NC for the original and completed bend states, respectively.

Fig. 15 is a graph comparing CV of viscose and polypropylene woven supercapacitors at the same scan rate.

FIG. 16 is a plot of cyclic voltammetry performance of wSC-NC, wherein FIG. 16a is a CV curve of wSC-NC at different scan rates, FIG. 16b is a GCD curve of wSC-NC at different currents, and FIG. 16c is an AC impedance plot of wSC-NC.

FIG. 17 is a plot of cyclic voltammetry performance for multiple wSC-NC sets in series-parallel; FIG. 17a is a CV diagram of 4 wSC-NC units connected in parallel, and FIG. 17b is a CV diagram of 4 wSC-NC units connected in series.

FIG. 18 is a plot of cyclic voltammetry performance of wSC-NF, where FIG. 18a is a CV curve of wSC-NF at different scan rates, FIG. 18b is a GCD curve of wSC-NF at different currents, and FIG. 18c is an AC impedance plot of wSC-NF.

FIG. 19 is a graph comparing the energy densities of wSC-NC and wSC-NF.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

1 example

1.1 pretreatment and activation of carbon fibers

Soaking carbon fiber in ethanol for 30min to remove surface impurities and oil stain, and air drying at room temperature. Weighing the cleaned carbon fiber by using an analytical balance, and recording the weight as m 1;

putting the pretreated carbon fiber in an alkaline sodium borohydride solution (0.2g/L NaBH)₄0.04g/L NaOH) for 30min, and then dried at room temperature. Then placing the mixture into an activating solution (0.1mol/L nickel sulfate, 0.03mol/L sodium hypophosphite and 0.02mol/L trisodium citrate) to react for 10 min.

1.2 preparation of Nickel-cobalt-based carbon fiber composite electrode

Dissolving nickel sulfate, cobalt sulfate, sodium hypophosphite and trisodium citrate in 100mL of deionized water, adding activated carbon fibers, and reacting at a certain temperature for 1 h. After the reaction is finished, the CF (NiCo/CF) after electroless plating is taken out, washed by distilled water, dried and weighed, and recorded as M2, the weight gain delta M of the carbon fiber is calculated to be M2-M1(mg), and the length resistance (M omega/cm) of the carbon fiber is measured. Three variables were designed in the examples: the concentration ratio of main salt metal ions (nickel salt and cobalt salt), the concentration of a reducing agent and the temperature, and the experimental conditions are shown in table 1;

carrying out electrooxidation on NiCo/CF on a three-electrode system of an electrochemical workstation by adopting a cyclic voltammetry method, using 2mol/L KOH electrolyte, using NiCo/CF as a working electrode, a platinum wire as a counter electrode and a saturated calomel electrode as a reference electrode, and carrying out electrooxidation circulation for 200 times at a scanning rate of 10Mv/s under the condition of 0-0.6V voltage to obtain a NiCo @ NiCoDH/CF fiber electrode;

TABLE 1

1.3 preparation of ferronickel-based carbon fiber composite electrode

Dissolving different reagents (nickel sulfate, ferrous ammonium sulfate, sodium hypophosphite and trisodium citrate) in 100mL of deionized water, adjusting the pH value of the solution by using potassium hydroxide, adding activated carbon fibers, reacting for one hour at a certain temperature, taking out chemically plated CF (NiFe/CF) after the reaction is finished, washing the chemically plated CF (NiFe/CF) by using distilled water, drying and weighing the CF, marking the CF as m2, calculating the weight gain delta m of the carbon fibers as m2-m1(mg), and measuring the length resistance (m omega/cm). Three variables were designed in the examples: the concentration ratio of main salt metal ions (nickel salt and ferrous salt) (the total molar amount of the main salt metal ions is 0.1mol), the pH value and the temperature, and the specific experimental conditions are shown in table 2.

And (2) carrying out electrooxidation on a sample NiFe/CF on a three-electrode system of an electrochemical workstation by adopting a cyclic voltammetry method, using 2mol/L KOH electrolyte, using NiFe/CF as a working electrode, a platinum wire as a counter electrode and saturated calomel as a reference electrode, and carrying out electrooxidation circulation for 200 times under the conditions of-1.0-0.6V voltage and 10Mv/s scanning rate to obtain the NiFe @ NiFeDH/CF fiber electrode.

TABLE 2

Chemical composition	Conditions of the experiment
		NiSO₄·6H₂O(mol/L)	0.08/0.06/0.04/0.02
(NH₄)₂Fe(SO₄)₂·7H₂O(mol/L)	0.02/0.04/0.06/0.08
		NaH₂PO₂·H₂O(mol/L)	0.03
Na₃C₆H₅O₇·2H₂O(mol/L)	0.02
		pH value	7.0/8.0/9.0/10.0
Temperature (. degree.C.)	75/80/85/90
		Time (h)	1

1.4 preparation of nickel-based carbon fiber composite electrode

In order to compare with NiCo @ NiCoDH/CF and NiFe @ NiFeDH/CF fiber electrodes, an electroless plating solution containing 0.1mol/L of nickel sulfate, 0.03mol/L of sodium hypophosphite and 0.02mol/L of trisodium citrate is adopted, and the preparation method of electroless plating is the same as 1.2, so that Ni/CF is prepared. Using an electrochemical workstation and Ni/CF as a working electrode to carry out electro-oxidation on the Ni/CF, and carrying out electro-oxidation circulation 200 times under the conditions of 0-0.6V voltage and 10Mv/s scanning rate to obtain Ni @ Ni(OH)₂a/CF fiber electrode.

1.5 preparation of woven supercapacitor

Weaving on a semi-automatic loom by using a weaving process of a layer of plain fabric with a fiber electrode prepared by 1.2-1.4 as a weft and viscose as a warp; the weave parameters of the plain weave are: r_j＝R_w＝2，S_j＝S _w1, complete warp count in the weave cycle (R)_j) Number of complete weft threads (R)_w) The number of weft yarns (S) spaced between two corresponding interlacing points on two adjacent warp yarns, counted in the warp direction_j) The number of warp threads (S) spaced between two corresponding interlacing points on two adjacent warp threads, counted in the weft direction_w). FIG. 1 shows a plain weave pattern in which (a) shows a plain weave pattern, (b) shows a weft cross-sectional view of a first weft yarn, (c) shows a warp cross-sectional view of a first warp yarn, and (d) shows a weave pattern, and (e). The portion enclosed by the arrow in the figure indicates a weave loop, and 1 and 2 indicate the arrangement order of the warp and weft. In this embodiment, the prepared fiber electrode is used as weft, the adhesive fiber is used as warp, and the weaving process shown in fig. 1 is adopted to weave a woven super capacitor on a semi-automatic loom.

Adding 3g of PVA into 30mL of deionized water, heating and stirring for 1h at the constant temperature of 90 ℃ until the PVA is completely dissolved, reducing the temperature to 70 ℃, dropwise adding dissolved KOH, continuing heating and stirring until the mixture is transparent, and cooling for later use. Two adjacent fibrous electrodes and a KOH/PVA gel electrolyte assembly form a woven supercapacitor (wSC) cell. When the gel solidified at room temperature, wSC was obtained.

In the comparative experiment, polypropylene fiber is used as warp, and the woven supercapacitor is prepared.

2 Effect verification

2.1 methods of testing and characterization

2.1.1 morphology and Structure characterization

(1) The scanning electron microscope used for field emission was model S-4800 from Hitachi, Japan, and was used to observe the microstructure, metal particle deposition, and the size and porosity of the nanosheet-like active material of the samples NiCo/CF, NiCo @ NiCoDH/CF, NiFe/CF, and NiFe @ NiFeDH/CF prepared in this experiment.

(2) The Japanese electronic institute JEM-2100F type field emission transmission electron microscope is adopted for testing and characterization. Is used for determining the appearance of the bimetallic electrooxidation product. Shearing prepared samples, then carrying out ultrasonic treatment on the obtained powder in ethanol for 30min to obtain a suspension, and taking the supernatant for later use.

(3) The samples were subjected to energy spectrum analysis (EDS) and Mapping tests using a Quanta250 environmental scanning electron microscope of RIGAKU, Inc., Japan.

(4) CF, NiCo/CF and NiFe/CF for electroless plating and sample Ni @ Ni (OH) after electrooxidation were measured using a SAXSessmc2 small angle X-ray scatterometer from Austria-Topa Limited₂The crystal phase structure of the/CF, NiCo @ NiCoDH/CF and NiFe @ NiFeDH/CF is tested, the small angle measurement range is 0.11-5 degrees, the voltage is 40kV, and the current is 50 mA.

2.1.2 conductivity test

And testing the resistance of the chemical plating sample by using an RST-9 type double electric testing four-probe tester, wherein the unit is m omega/cm. The smaller the resistance value is, the better the conductivity of the material is. The resistance of 5 different points is selected to this experiment test sample to calculate its average value, in order to get rid of accidental error.

2.1.3 electrode electrochemical Performance testing

Electrochemical performance of the prepared sample was tested using a CHI 760 electrochemical workstation using a three-electrode system, using the prepared sample as a working electrode (all electrodes prepared were 1cm in length), using a saturated calomel electrode Hg₂Cl₂|Cl^-(3mol/L KCl) as reference electrode, platinum wire as counter electrode, and electrolyte 2mol/L KOH.

2.1.4 test of energy storage performance of super capacitor

Electrochemical tests are carried out on the supercapacitor devices, a two-electrode system is adopted, 2mol/L KOH/PVA gel electrolyte is used, and the test items are as follows: cyclic volt-ampere test, constant current charge and discharge test and alternating current impedance test.

2.2 Nickel-cobalt-based carbon fiber composite electrode Performance verification results

2.2.1 Effect of electroless plating conditions on electroless plating sample parameters

(1) Ion ratio of metal concentration of main salt

The effect of the concentration ratio of the main salt metal ions on the chemical plating is discussed under the conditions that the concentration of the main metal salt is 0.1mol/L, the concentration of the sodium hypophosphite is 0.03mol/L and the temperature is 80 ℃. Ni/CF as main salt metal ion only containing Ni²⁺NiCo/CF-1, NiCo/CF-2 and NiCo/CF-3 correspond to the main salt metal ion concentration ratio (c (Ni/CF-3), respectively²⁺):c(Co²⁺) ) 2:3, 1:1 and 3:2, respectively. The sample weight gain and specific resistance are shown in figure 2 a.

Co in chemical nickel-cobalt plating reaction at a certain concentration of main salt²⁺Has a deposition rate constant higher than that of Ni²⁺Activation energy lower than that of Ni²⁺Adding a certain amount of Co²⁺The reaction rate will be increased. As shown in FIG. 2a, the NiCo/CF-3 coating weight gain is significantly increased compared to Ni/CF. However, when c (Ni)²⁺):c(Co²⁺) At 1:1, the plating weight gain is significantly reduced, probably due to Co in the bath²⁺The relative concentration is increased, the Co deposition rate is too high, the content of Ni simple substances in the coating is reduced, and the Ni active catalytic center is relatively reduced, so that the overall deposition rate of the alloy is reduced. When Co is present²⁺Too high a relative concentration will form a complex, i.e. when c (Ni)²⁺):c(Co²⁺) When the ratio is 2:3, the deposition amount of Co is reduced, and the weight increase of the alloy coating is slightly increased. As the conductivity of Ni and Co is not very different, as can be seen from FIG. 2a, the change rule of the resistance of the alloy plating samples (NiCo/CF-1, NiCo/CF-2 and NiCo/CF-3) is consistent with the change rule of the weight gain, i.e. the resistance is smaller when the weight gain is larger, and when c (Ni) is smaller²⁺):c(Co²⁺) At 3:2, the NiCo/CF-3 sample produced had the least resistance.

(2) Concentration of reducing agent

C (Ni) at a main salt concentration of 0.1mol/L²⁺):c(Co²⁺) 3:2, at a temperature of 80 ℃, the influence of the concentration of the reducing agent on the electroless plating is studied, and the weight gain and the resistance of the prepared sample with the sodium hypophosphite concentrations of 0.02mol/L, 0.03mol/L, 0.04mol/L and 0.05mol/L are compared and are shown in fig. 2 b. As shown in FIG. 2b, the coating quality tends to increase and decrease with the increase of the concentration of sodium hypophosphite, and the resistance appearsThe trend is reduced and then increased, the weight increment of the plating layer is the largest when the concentration of the reducing agent is 0.03mol/L, and the resistance is the smallest. Compared with the method that when the concentration of sodium hypophosphite is 0.02mol/L, the weight gain of the obtained sample is increased when the concentration of sodium hypophosphite is 0.03mol/L, namely the reaction rate is accelerated, and the increase of the concentration of reducing agent sodium hypophosphite is beneficial to forward progress of metal reduction reaction; as the concentration of sodium hypophosphite continues to increase to 0.04g/L and 0.05g/L, the weight gain of the sample decreases, because the electroless plating reaction becomes severe when the concentration of sodium hypophosphite is too high, the deposition rate is too fast, a loose-structure plating layer is formed on the fibers and is easily peeled off from the fibers. In addition, the deposition rate is too fast, and metal simple substance precipitation is easily formed in the solution, so that the stability of the plating solution is reduced, and self-decomposition side reaction is caused. In summary, the concentration of sodium hypophosphite was determined to be 0.03 mol/L.

(3) Temperature of

C (Ni) at a main salt concentration of 0.1mol/L²⁺):c(Co²⁺) The ratio of sodium hypophosphite to sodium hypophosphite is 3:2, and the influence of temperature on chemical plating is studied under the condition that the concentration of sodium hypophosphite is 0.03mol/L, and the weight gain and the resistance of a sample prepared at the temperature of 60 ℃, 70 ℃, 80 ℃ and 90 ℃ are respectively shown in figure 2 c. Theoretically, the positive and negative reactions generated in the experiment are endothermic reactions, and the forward reaction is facilitated due to high temperature. As shown in fig. 2c, the weight gain of the sample under four temperature conditions increases and then decreases, and the weight gain of the plating layer reaches the maximum when the temperature is 80 ℃; when the temperature is increased to 90 ℃, the quality and the conductivity of the deposited plating layer are reduced, which should be because the temperature is too high and the reaction is too fast, nickel ions and cobalt ions in the solution are also reduced into simple substances at the same time, and catalytic sites are formed in the solution phase to react and compete with the active sites of the nickel-cobalt simple substances on the carbon fibers, so that the nickel-cobalt plating layer on the carbon fibers is reduced, and the conductivity is deteriorated.

2.2.2 structural characterization and Performance test results

(1) Structural characterization

FIG. 3 is an apparent morphology diagram of an electroless plating sample under different metal ion concentration ratio conditions, wherein FIG. 3a is an apparent morphology diagram of a NiCo/CF-1 electroless plating sample, FIG. 3b is an apparent morphology diagram of a NiCo/CF-2 electroless plating sample, and FIG. 3c is a chemical conversion diagram of NiCo/CF-3An apparent topography of the electroless plated sample; the sample in FIG. 3a corresponds to c (Ni) in the plating bath²⁺):c(Co²⁺) The ratio of the metal particles to the carbon fiber is 2:3, the formed plating layer grows disorderly, the metal particles are gathered together, and a rod-shaped accumulation is formed in the vertical direction of the carbon fiber, has a loose structure and is easy to fall off. The sample in FIG. 3b corresponds to NiCo/CF-2(c (Ni) in the bath²⁺):c(Co²⁺) 1:1), the particle agglomeration phenomenon is less, the arrangement is more orderly, however, part of the fiber surface is exposed, which indicates that the fiber is not completely covered by the plating layer, and the phenomenon is consistent with the condition that the weight increment of the plating layer is obviously reduced under the obtained condition. In contrast, NiCo/CF-3(c (Ni) in FIG. 3c²⁺):c(Co²⁺) 3:2) the plating layer is flat and uniform without defects such as cracks, and the particles are in a unit cell shape and are densely arranged.

FIG. 4 is an SEM image of samples NiCo @ NiCoDH/CF-1 (FIG. 4a), NiCo @ NiCoDH/CF-2 (FIG. 4b), and NiCo @ NiCoDH/CF-3 (FIG. 4c) after electroless-electrolytic oxidation. As can be seen from the figure, Ni is present in the plating solution²⁺And Co²⁺The concentration of (A) has a larger influence on the morphology of NiCo @ NiCoDH/CF after electro-oxidation, although lamellar flakes grow on the surface of the particle, the sizes of gaps formed by adjacent flakes are different, the gaps formed by the flake spaces in NiCo @ NiCoDH/CF-1 are large and the gaps are large, the gaps formed by the flake spaces in NiCo @ NiCoDH/CF-2 are small and the surface particles still exist, and the sizes of the gaps in NiCo @ NiCoDH/CF-3 are medium. This difference in morphology may be caused by the content and distribution of Ni and Co on the surface of the plating layer, and the oxidation rate of Ni and Co during the electro-oxidation process.

(2) Elemental composition and distribution

FIG. 5a is an EDS diagram of an electroless plated sample NiCo/CF-3, and FIG. 5b is a Mapping diagram of the electroless plated sample NiCo/CF-3; NiCo/CF-3 from FIG. 5a contains mainly Ni, Co, P and C elements. The Ni element comes from NiSO in the plating solution₄Ni simple substance obtained by reduction, Co element comes from CoSO in plating solution₄The element Co is obtained by reduction, and the element P is from NaH in the plating solution₂PO₂The P element and the C element which are obtained by reduction mainly come from a CF matrix. Thus, the NiCo coating is a Ni-Co-P alloy coating.

According to the analysis of element content, the Ni atom content of the fiber is 69.33%, the Co atom content is 12.94%, and the C atom content of the fiber is C10.12 percent of Ni atoms, 7.6 percent of P atoms, 77.14 percent of Ni atoms, 14.41 percent of Co atoms and 8.45 percent of P atoms in the NiCo coating layer by calculation, wherein Ni is 5.4 times of the number of Co atoms and c (Ni) in the coating solution²⁺) Is c (Co)²⁺) Higher than 1.5 times, and the side shows that Ni is deposited preferentially in the plating solution. As can be seen from the Mapping chart in FIG. 5b, the Ni, Co and P elements are uniformly distributed along the fiber, the signal of the C element is weak, and it can also be shown that the coating layer covered on the surface of the NiCo/CF-3 sample is dense and almost completely wraps the carbon fiber.

(3) Analysis of electrochemical Performance of electrodes

The CF resistance used in this embodiment is about 80 Ω/cm, and as shown in FIG. 6a, the Cyclic Voltammetry (CV) curves measured in a three-electrode system with CF and NiCo @ NiCoDH/CF-3 as the working electrode respectively has a scan rate of 10mV/s, the CV curve area of the CF electrode is small, and there is substantially no capacitance performance, and the CV curve area of the NiCo @ NiCoDH/CF-3 electrode is large, and CF has substantially no capacitance contribution to NiCo @ NiCoDH/CF-3. As can be seen from FIGS. 6a and 6b, there are two pairs of CV diagrams of NiCo @ NiCoDH/CF-3, which correspond to Ni (OH)₂And Co (OH)₂The oxidation-reduction peak of (2), the reaction taking place is as follows

Wherein, NiCo @ NiCoDH/CF-3 electrode CV curve is Ni (OH)₂And Co (OH)₂The redox peak positions are respectively 0.25V and 0.55V, and 0.36V and 0.39V, the smaller the distance between the redox peaks is, the better the reversibility of the reaction is, which indicates that the NiCo @ NiCoDH/CF-3 sample has better reversibility, and the average voltage of the NiCo @ NiCoDH/CF-3 redox peaks is also the highest, so that the electrode is allowed to exchange more energy under the same current condition. FIG. 6c is an AC impedance plot (Nyquist plot) of three NiCo @ NiCoDH/CF samples, from which the Nyquist plot of the electrode material is seen from high frequencyThe intercept of the region, the semicircle of the middle frequency region and the slope of the low frequency region. Wherein the intercept Rb of the high frequency region with the X-axis represents the solution resistance (including electrolyte resistance, current collector resistance, and cross-sectional contact resistance of the electrode active material with the current collector). As shown in fig. 6c, in the high frequency region, the three curves are all less than 1 intercept with the X-axis, which reflects very low internal resistance. In the medium frequency range, the diameter of the half circle represents the charge transfer resistance, which reflects the amount of resistance to charge transfer experienced by the electrode material upon electrochemical reaction. NiCo @ NiCoDH/CF-3 has the smallest semi-circular diameter and a resistance of 0.25. omega. As shown in FIG. 6d, the specific capacitance decreases to different degrees with the increase of the current density, when the current density is increased from 1mA/cm²Increasing to 10mA/cm, the retention rate of NiCo @ NiCoDH/CF-3 electrode capacitance is 24.5%, the retention rate of NiCo @ NiCoDH/CF-2 electrode capacitance is 19.6%, and the retention rate of NiCo @ NiCoDH/CF-1 electrode capacitance is 16.7%, which is caused by the fact that the electrochemical redox reaction of the pseudocapacitance material is incomplete under high current density, and the discharge capacity is reduced. The NiCo @ NiCoDH/CF-3 electrode has high capacitance retention rate and is related to the shape of the electrode, more sheet metal hydroxides are arranged on the surface of the NiCo @ NiCoDH/CF-3 electrode, the size of surface gaps is moderate, more electrolyte ions can be in contact with an electrode material in the same time, and the capacitance is improved. FIG. 6e is a CV curve of the NiCo @ NiCoDH/CF-3 electrode at a scanning rate of 1-10 mV/s, and with the increase of the scanning rate, the CV curve shows an obvious redox peak at each scanning rate, which indicates that the whole redox process has good electrochemical reversibility. FIG. 6f is a constant current charging and discharging curve (GCD) of NiCo @ NiCoDH/CF-3 electrode at different current densities, when the current densities are 1, 2, 5, 10mA/cm respectively²In time, a distinct charge-discharge plateau appears on the GCD curve, corresponding to the redox peak appearing on the CV curve.

2.3 Nickel-iron-based carbon fiber composite electrode performance verification result

2.3.1 Effect of electroless plating conditions on electroless plating sample parameters

(1) Ion ratio of metal concentration of main salt

NiFe/CF-1, NiFe/CF-2, NiFe/CF-3 and NiFe/CF-4 correspond to the concentration ratio of main salt metal ions (c (Ni)²⁺):c(Fe²⁺) ) 4:1, 3:2, 2:3 and 1:4, respectively; FIG. 7a shows the results for the plating bath as Fe²⁺The weight gain of the plating layer is increased firstly and then reduced with the increase of the relative concentration. Ni in alkaline solution²⁺Has a standard reduction potential of-0.25V, Fe²⁺Has a standard reduction potential of-0.44V, Fe²⁺Standard reduction potential ratio of Ni²⁺Is low. Therefore, in the presence of Ni²⁺And Fe²⁺When a reducing agent is added into the plating solution, elemental nickel is preferentially deposited on the activated CF surface.

The ferrous ammonium sulfate in the plating solution has double functions, on one hand, an iron source is provided for the chemical plating layer, on the other hand, ammonium salt is provided in the plating solution, and the ammonium salt and the trisodium citrate have a certain buffering effect similar to the effect. The ammonium salt can adjust OH in the plating solution to a certain extent^-And the reaction is promoted. Thus, in this electroless plating system, the NiFe/CF-2 weight gain is increased as compared to the NiFe/CF-1 weight gain. When Fe²⁺The relative concentration continues to increase, c (Ni)²⁺):c(Fe²⁺) Increase to 2:3 and 1:4, Ni²⁺Concentration ratio of Fe²⁺When the concentration is low, the Ni content in the deposition layer is low, the catalytic center is less, and the deposition amount of the coating is reduced. Thus, the concentration of the main salt metal ion c (Ni)²⁺):c(Fe²⁺) Preferably, the ratio is controlled to be 3: 2.

(2) pH value

The weight gain and resistance of the samples prepared under the plating solution conditions with pH values of 7.0, 8.0, 9.0, and 10.0, respectively, are shown in fig. 7 b. As shown in fig. 7b, the pH increased from 7 to 9, the plating weight increased steadily, and the plating weight increased abruptly when the pH reached 1. Theoretically, the redox reaction takes place under alkaline conditions, so that the pH value is determined>7 is favorable for the generation of metal simple substances, and when the pH value is too high, the OH in the solution is^-Too many ions accelerate the reaction and also promote side reactions to make the reducing agent ineffective. In the experimental process, the phenomenon that bubbles generated on the surface of the fiber in the plating solution are intensified along with the increase of the pH value of the plating solution can also be observed; when the pH reached 10, black precipitates appeared in the bath at an extremely rapid rate and appeared cloudy. The black precipitate is due to metal ions in solutionThe reduction is generated by agglomeration. Therefore, the pH value of 9 is selected as an appropriate condition according to the resistance and increase of the plating layer.

(3) Temperature of

As shown in fig. 7c, the weight gain of the samples prepared at 75 ℃, 80 ℃, 85 ℃ and 90 ℃ increased and then decreased with increasing temperature, and the effect of temperature was smaller than the other two factors discussed, however, the weight gain was significantly decreased when the temperature reached 90 ℃. In experiments, it was found that when the plating temperature reached 90 ℃, the electroless plating process was too vigorous, a large amount of black precipitates were seen in the reaction solution and agglomerated sharply in the solution, and the plating layer on the fiber surface was also reduced. Therefore 80 ℃ was chosen as the reaction temperature for electroless nickel plating.

2.3.2 structural characterization and Performance testing

(1) As shown in FIG. 8, c (Ni)²⁺):c(Fe²⁺) SEM images at the same magnification of samples prepared at four metal ion concentration ratios of 4:1, 3:2, 2:3, and 1:4, respectively. From FIG. 8a, c (Ni) is seen²⁺):c(Fe²⁺) At 4:1, the deposited particles on the carbon fibers exhibit agglomerated irregular growth due to Ni in the plating solution²⁺The relative concentration is high, the reaction rate is high, and the metal particles are rapidly aggregated; FIG. 8b is c (Ni)²⁺):c(Fe²⁺) 3:2, Ni in plating solution²⁺The relative concentration is low, the agglomeration degree of the particles is obviously reduced, and the metal particles are observed to be in a unit cell shape and arranged more compactly under high magnification; FIG. 8c corresponds to c (Ni)²⁺):c(Fe²⁺) The deposition amount on CF is relatively reduced, and the metal particles are dispersed and distributed under high magnification; when c (Ni)²⁺):c(Fe²⁺) When the ratio is 1:4 (see fig. 8d), a large number of areas of CF not covered with plating were observed. Thus, the morphology change rule is intuitive and proves the influence of the metal ion concentration ratio on the weight gain and the resistance of the sample discussed above.

(2) FIG. 9 is an SEM image of the fiber electrode NiFe @ NiFeDH/CF-2 at different magnifications after electrooxidation of the NiFe/CF-2 sample. It is seen from fig. 9 that uniform pores are formed on the surface of the plating layer after the electro-oxidation treatment, and a relatively regular morphology is formed. Compared with the prepared NiCo @ NiCoDH/CF-3 composite electrode, the NiFe @ NiFeDH/CF-2 composite electrode has the advantages that the pore distribution is more uniform and the sheet structure is more obvious. Under the high power microscope of fig. 9b, c, d, it can be clearly seen that the layered nano-flakes are formed on the surface of the plating layer, and the flakes are connected with each other to form a rich space structure. The contact area of electrolyte ions and active substances is increased when the electrode material undergoes redox, and the electrochemical performance is favorably improved.

(3) In order to research the element content and the element distribution of the coating, the element composition and the element distribution of the NiFe/CF-2 sample are researched by EDS. As shown in FIG. 10a, NiFe/CF-2 contains mainly Ni, Fe, P and C elements. The Ni element comes from NiSO in the plating solution₄The Ni element obtained by reduction, the Fe element comes from the plating solution (NH)₄)₂Fe(SO₄)₂Fe simple substance obtained by reduction, P element comes from NaH of plating solution₂PO₂The P element is obtained by reduction, wherein the C element is from a CF matrix. Thus, the NiFe coating is a Ni-Fe-P alloy coating.

Analyzed from element content, the Ni atom content of the fiber is 82.20%, the Fe atom content is 5.65%, the C atom content is 7.19%, the P atom content is 4.34%, and calculated that Ni is 14.6 times of the Fe atom number, and the Ni is mixed with C (Ni) in the plating solution²⁺) Is c (Fe)² ⁺) The ratio of the metal to the metal is much higher than that of the metal of 1.5 times, the condition of preferential deposition of Ni in the plating solution is shown on the side face, the condition of a NiCo plating layer and the difference of the atomic ratio of two metals in a chemical plating layer can be the main reason of the morphological difference of the subsequently generated hydroxide. As can be seen from the Mapping graph in FIG. 10b, Ni is uniformly distributed on CF, the distribution density of Ni is higher than that of Fe, the signal points of C are fewer, and it is also confirmed that the Ni-Fe-P coating is denser and almost completely wraps the carbon fibers. As can be seen from FIG. 9, the C atom ratio of NiFe/CF-2 is 4.34% and lower than that of NiCo/CF-3 (10.12%), and it is presumed that the NiFe coating layer prepared on the surface of the fiber may be more densely covered than the NiCo coating layer.

(4) Electrochemical performance of electrode

FIG. 11a is a constant current charge-discharge curve of the NiFe @ NiFeDH/CF-2 fiber electrode under different current densities, a GCD test voltage window is set to-1.0-0.5V,the GCD curve of the NiFe @ NiFeDH/CF-2 fiber electrode has an obvious redox platform between 0.4 and 0.5V, and is an active substance Ni (OH)₂A redox reaction occurs. Has a redox peak platform at 0.2V and-0.4 to-0.2V, and is the active substance (hydrogen) ferric oxide to perform redox reaction.

FIG. 11b is an EIS plot of a NiFe @ NiFeDH/CF-2 fiber electrode with the inset showing an enlarged view of the high frequency region. As shown, in the high frequency region, the NiFe @ NiFeDH/CF-2 has an X-axis intercept of about 1. In the medium frequency range, the diameter of the semicircle represents the electron transfer resistance, which reflects the amount of resistance to charge transfer experienced by the electrode material upon electrochemical reaction. The NiFe @ NiFeDH/CF-2 radius is the smallest, with a value of about 0.5 Ω, reflecting the lesser resistance to charge transfer in NiFe @ NiFeDH/CF-2. However, compared with the semi-circle diameter of an EIS curve of a NiCo @ NiCoDH/CF-3 electrode, the diameter of NiFe @ NiFeDH/CF-2 is enlarged by two times, which is probably because the content of cobalt in the nickel-cobalt hydroxide is larger than that of iron in the nickel-iron hydroxide, and the amount of other doped metals has a relatively obvious influence on the performance. The slope of the material in the low frequency region is related to the capacitance performance, with a larger slope indicating that the electrode material is closer to the ideal capacitance. The gradient of an EIS curve of the NiFe @ NiFeDH/CF-2 electrode in a low-frequency region is larger, which shows that the electrochemical performance of the electrode material is better. According to the morphological analysis, the addition of iron possibly enlarges the gaps between the flaky metal hydroxides, is beneficial to the contact of electrolyte and more active substances, and improves the capacitance.

FIG. 12 compares NiFe @ NiFeDH/CF-2, NiCo @ NiCoDH/CF-3, and Ni @ Ni (OH) by Cyclic Voltammetry (CV) test, charge-discharge test (GCD), and rate capability test₂The performance of/CF.

As shown in FIG. 12a, NiFe @ NiFeDH/CF-2 and NiCo @ NiCoDH/CF-3 electrodes were applied at a scan rate of 10mV/sThe area enclosed by the polar CV curve is significantly larger than Ni @ Ni (OH)₂The area surrounded by/CF shows that the electrochemical performance of the nickel-cobalt double-metal hydroxide and the nickel-iron double-metal hydroxide is superior to that of the single-metal nickel hydroxide, and the synergistic effect of the double-component metal and the double-metal hydroxide can improve the intrinsic reaction activity of the fiber electrode material and improve the electrochemical performance of the electrode.

FIG. 12b is NiFe @ NiFeDH/CF-2 and NiCo @ NiCoDH/CF-3 and Ni @ Ni (OH)₂The GCD curve of the three electrodes is shown under the current density of 1mA/cm, and the discharge time of NiFe @ NiFeDH/CF-2 is 3400 s; the discharge time of NiCo @ NiCoDH/CF-3 is 2000 s; ni @ Ni (OH)₂The discharge time/CF is the shortest (300 s). Compared with a NiCo @ NiCoDH/CF-3 electrode, the NiFe @ NiFeDH/CF-2 capacitance improvement is due to the fact that the flaky nickel iron hydroxide is more regular in shape, more gaps among the flakes are beneficial to contact of electrolyte ions with the electrode, and more active substances can participate in reaction at the same time to improve the capacitance.

FIG. 12c is NiFe @ NiFeDH/CF-2 and NiCo @ NiCoDH/CF-3 and Ni @ Ni (OH)₂Multiplying power performance graphs of the three electrodes under different current densities. The specific capacitance is reduced to different degrees along with the increase of the current density when the current density is from 1mA/cm²Increased to 10mA/cm²In the process, the multiplying power performance of NiFe @ NiFeDH/CF-2 is 24.3 percent, which is caused by incomplete electrochemical oxidation-reduction reaction of the pseudocapacitance material under high current density, so that the discharge capacity is reduced.

As an electrode material of a supercapacitor, the cycle stability thereof is an important evaluation criterion. For example, FIG. 13 shows NiCo @ NiCoDH/CF-3 and NiFe @ NiFeDH/CF-2 electrodes at 20mA/cm²The current density of the metal oxide is tested, the specific charge-discharge capacity of each cycle is recorded, a stability test chart is shown in 13, the metal oxide and the metal oxide are cycled for 5000 times under the same current density, the capacity retention rates of the two are more than 99 percent, the conductive NiCo or NiFe coating is introduced to be used as a metal hydroxide deposition and growth substrate, the electrochemical etching component mode is combined to improve the electron and ion transmission performance of the material, and meanwhile, the metal also improves the double metal hydroxideThe stability of the cycle contributes.

2.4 energy storage Performance of woven supercapacitor based on fibrous electrode

(1) The NiCo @ NiCoDH/CF fiber electrode is used as a weft, the viscose fiber is used as a warp, and the woven supercapacitor wSC-NC is woven on a semi-automatic loom by adopting a plain weave process.

FIG. 14 is a CV curve (scan rate 100mV/s) of wSC-NC before and after folding 1 time under 180 DEG bending condition and folding 1000 times under 180 DEG bending condition in the unbent state. The bent and unbent states of the device are shown in the inset of fig. 14. Similar CV curves indicate wSC-NC has good stability under repeated deformation, and the fabric texture is fast and abrasion resistant thanks to the close interweaving between the warp and weft of a plain weave fabric, so there is almost no loss of capacitance under multiple bending tests. Mechanical deformation stability is also an important index for measuring the flexible energy storage device, the super capacitor is woven by using a plain weave structure, fibers between two electrodes play a natural diaphragm role in the weaving process, a weft fiber is used for effectively separating a positive electrode and a negative electrode, and the key problem that wSC-NC is stable in a long-term folding use state is solved by using a weaving forming device.

The moisture absorption and moisture conductivity of the warp have great influence on the transmission of electrolyte ions of the woven supercapacitor, and the difference of the electrochemical performance of the warp woven supercapacitor made of different fibers. The moisture absorption of common fabric fibers is arranged from high to low: wool, jute, viscose, ramie, silk, cotton, vinylon, chinlon, acrylic fiber, terylene and polypropylene fiber, wherein the viscose fiber has excellent water absorption and better spinnability; polypropylene fiber, as an extreme of moisture absorption, is less hygroscopic but has better moisture conductivity, so both are the preferred choice for warp yarns of woven supercapacitors.

FIG. 15 shows CV plots for wSC-NF/viscose and wSC-NF/polypropylene fibers at the same scan rate. The difference of current responses of the capacitors woven by the two fibers on a CV diagram is obvious, under the working voltage of 1.2V, the current response of wSC-NF/polypropylene fiber is close to 12mA, the current response of wSC-NF/viscose fiber is about 1mA, the difference of the current responses is probably because the polypropylene fiber is a common fiber with the worst hygroscopicity, the moisture conductivity is good, the transmission rate of electrolyte by the polypropylene fiber is higher than that of other fibers in the same time, and the areas enclosed on the CV diagram by the capacitors woven by the two fibers are approximately the same from the experimental result, the difference of the specific capacitances of the capacitors is not large because the viscose fiber is good water-absorbing fiber, a part of electrolyte can be stored in the fibers to be beneficial to the working requirement of the capacitors, and the effects of the capacitors on wSC capacitive performance are not large.

To further explore the effect of viscose and polypropylene fibers on the ion transport of wSC electrolytes, EIS plots of these two wSC were tested. The results show that the ohmic impedance of wSC-NF/polypropylene fiber and wSC-NF/viscose fiber in a high-frequency area and a solution is respectively about 3 omega and 6 omega, and the reduction of the ohmic impedance also proves that the polypropylene fiber has good moisture conductivity and is beneficial to the transmission of electrolyte ions. Compared with wSC-NF/viscose fiber, wSC-NF/polypropylene fiber has larger slope in a low frequency region, which shows that the resistance value of interface diffusion is smaller.

(2) Energy storage performance analysis

As shown in fig. 16a, the rectangular CV curve maintained a good shape as the scan rate increased, indicating that the electrons still had a good transport rate under the solid gel electrolyte. FIG. 16b shows wSC-NC with GCD curves having symmetrical triangles at different currents, indicating good capacitive behavior of the wSC-NC device. FIG. 16c is a Nyquist plot of wSC-NC, with a greater contact resistance between the electrode and the gel electrolyte, 6 Ω compared to the three-electrode test system, but the high slope in the low frequency region indicates good diffusion of electrolyte ions in wSC-NC.

To obtain greater capacitance, multiple wSC-NC sets were connected in series-parallel. FIG. 17a is a CV diagram of four wSC-NC units in parallel. Along with the increase of the number of the parallel units, the capacitance is gradually increased, and the good expandability of the woven super capacitor is shown. As shown in FIG. 17b, the wSC-NC cells are in a series configuration, and the output voltage of the series wSC-NC increases linearly with the number of wSC-NC cells. This provides a harmonious operating voltage for driving different types of flexible electronics. These results demonstrate the scalable and reliable scalability of wSC-NC in practical applications.

An NiFe @ NiFeDH/CF-2 fiber electrode is woven to form wSC-NF, and the electrochemical performance test of the electrode is shown in the figure. The electrochemical capacitance characteristics of the wSC-NF device were evaluated by Cyclic Voltammetry (CV), constant current charging and discharging (GCD) and alternating current impedance (EIS) techniques. As shown in fig. 18a, the CV curve still maintained a good shape as the scan rate increased, indicating that the electrode material still has good reversibility at high scan rates. FIG. 18b shows a GCD curve of wSC-NF at different current densities, with a 60% increase in discharge time at a current density of 200uA compared to a wSC-NC capacitor, with a voltage window extending from 0-0.5V to 0-1.0V. FIG. 18c shows that the internal resistance of the wSC-NF capacitor in the frequency region of an EIS spectrum of the wSC-NF capacitor is about 5 omega, and the good conductivity of the wSC-NF capacitor is proved.

FIG. 19 is a Ragon plot of wSC-NF and wSC-NC, where it can be seen that the wSC-NF energy density is higher than wSC-NC at a range of current densities, 0.10, 0.15, 0.25, 0.5mA/cm²The current density of (a) is 6.25-12.50 Wh/m for wSC-NC energy density²The energy density of wSC-NF is 24.00-50.02 Wh/m². This is due to the increased wSC-NF discharge time, the expanded voltage window results in an increased energy density.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.

Claims

1. The preparation method of the metal-based carbon fiber composite electrode is characterized by comprising the following steps of:

placing the pretreated and activated carbon fiber in an aqueous solution in which a main metal salt, a reducing agent and a buffering agent are dissolved, and heating for reaction to obtain a chemically plated metal/carbon fiber composite material; and further carrying out electrooxidation on the obtained metal/carbon fiber composite material by adopting a cyclic voltammetry method to obtain the metal-based carbon fiber composite electrode.

2. The method for producing a metal-based carbon fiber composite electrode according to claim 1,

the pretreatment and activation process of the carbon fiber specifically comprises the following steps:

3. The method for producing a metal-based carbon fiber composite electrode according to claim 2,

soaking in ethanol for 30 min;

NaBH in the alkaline sodium borohydride solution₄The concentration is 0.2g/L, and the concentration of NaOH is 0.04 g/L; soaking the carbon fiber in an alkaline sodium borohydride solution for 30 min;

the concentration of nickel sulfate in the activating solution is 0.1mol/L, the concentration of sodium hypophosphite is 0.03mol/L, the concentration of trisodium citrate is 0.02mol/L, and the reaction time of the carbon fiber in the activating solution is 10 min.

4. The method for producing a metal-based carbon fiber composite electrode according to claim 1,

the main metal salt is a double metal salt, and specifically, the concentration ratio of metal ions is (1-4): (1-4) nickel salt and cobalt salt, or metal ion concentration ratio of (1-4): (1-4) a nickel salt and a ferrous salt;

the total concentration of the main metal salt is 0.1 mol/L;

the reducing agent is sodium hypophosphite, and the concentration of the reducing agent is 0.02-0.05 mol/L;

the buffer is trisodium citrate.

5. The method for preparing a metal-based carbon fiber composite electrode according to claim 1, wherein the heating reaction temperature is 60 to 90 ℃.

6. The method for preparing a metal-based carbon fiber composite electrode according to claim 1, wherein the electro-oxidation specifically comprises: and (2) taking 3mol/L potassium hydroxide as an electrolyte, a metal/carbon fiber composite material as a working electrode, a platinum wire as a counter electrode and a saturated calomel electrode as a reference electrode, and performing electrooxidation circulation for 200 times at a scanning rate of 10mV/s under the condition of a voltage of-0.1-0.6V to obtain the metal-based carbon fiber composite electrode.

7. A metal-based carbon fiber composite electrode produced by the method for producing a metal-based carbon fiber composite electrode according to any one of claims 1 to 6.

8. Use of the metal-based carbon fiber composite electrode according to claim 7 in a supercapacitor.

9. A woven supercapacitor, which is prepared by weaving the metal-based carbon fiber composite electrode according to claim 7 as weft and fabric fibers as warp through a weaving process.

10. The woven supercapacitor according to claim 9, wherein the textile fibers are one of wool, jute, viscose, ramie, silk, cotton, vinylon, nylon, acrylic, polyester and polypropylene; the weaving process is plain weave, twill weave or satin weave.