Preparation method and application of polypyrrole nanotube for flexible supercapacitor

Abstract

The invention relates to a preparation method and application of a polypyrrole nanotube for a flexible supercapacitor, the preparation method adopts a chemical oxidation method, methyl orange and ferric chloride are utilized to form a self-assembled nanotube template, so that polypyrrole is in a one-dimensional nanotube form on a microstructure, and the polypyrrole nanotube is prepared. Compared with traditional zero-dimensional nanospheres, the polypyrrole nanotube prepared by the method has higher electrochemical performance, especially specific capacitance, cycling stability and electrical conductivity; by adjusting the doping concentration of methyl orange, the electrochemical performance of polypyrrole is optimized, the energy storage capacity of the material is further improved, the prepared polypyrrole nanotube can be widely applied to a flexible supercapacitor, the assembled supercapacitor can still keep a high capacitance retention rate in a bending state, and the performance of the supercapacitor is improved. The method has huge application potential in flexible electronic equipment, and an efficient and stable solution can be provided for flexible energy storage equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible capacitors, and in particular to a preparation method of polypyrrole nanotubes for flexible supercapacitors and applications thereof. Background Art

[0002] With the rapid development of flexible electronic technologies such as wearable electronics, flexible displays, and smart textiles, the demand for flexible energy storage devices is growing. Supercapacitors, as a new type of energy storage device, have become ideal energy storage units in flexible electronic systems due to their high power density, long cycle life, rapid charge and discharge capabilities, and good safety. However, traditional supercapacitors use rigid materials and structures, which make it difficult to meet the mechanical flexibility and wearability requirements of flexible electronic devices. Therefore, the development of flexible supercapacitors with excellent electrochemical performance and mechanical flexibility has become an important research direction in the field of energy materials and devices.

[0003] Flexible supercapacitors are usually composed of flexible electrode materials, flexible electrolytes, and deformable packaging. The key lies in how to ensure a flexible structure while taking into account high conductivity, high specific capacitance, and excellent cycle stability. At present, most flexible supercapacitors on the market use polymer materials as electrode active substances. Polypyrrole, as a conductive polymer, is a C, N five-membered heterocyclic conjugated conductive polymer with unique qualities such as simple synthesis, stable oxidation form, strong conductivity, low cost, high energy density, good redox performance and thermal stability. It is widely used in supercapacitor electrodes.

[0004] However, there are some problems when using polypyrrole as a supercapacitor electrode material. First, in most application studies, polypyrrole is usually attached to the surface of other materials in the form of zero-dimensional nanospheres, which leads to low specific surface area and porosity of the material, thereby affecting the ion transfer efficiency between the electrolyte and the active material. Secondly, the crystallinity of zero-dimensional polypyrrole nanospheres is low, and the structure of polypyrrole is easily destroyed during the charge and discharge cycle, resulting in a decrease in specific capacitance and poor cycle stability. Therefore, the electrochemical performance of polypyrrole as an active material for supercapacitors still needs to be further improved; in recent years, studies have found that the morphology of the polymer has an important influence on its electrochemical performance. Compared with zero-dimensional polypyrrole nanospheres, one-dimensional nanostructured conductive polymers can effectively improve their electrochemical performance, especially in terms of conductivity and capacitance. One-dimensional structured polypyrrole can provide more charge storage space and higher ion transfer efficiency. Therefore, the development of highly conductive, one-dimensional structured polypyrrole materials is an important direction for improving the performance of supercapacitors.

[0005] Existing technologies primarily focus on the synthesis and application of polypyrrole nanospheres, while relatively little research has been conducted on the preparation of one-dimensional polypyrrole nanotubes. Therefore, how to prepare one-dimensional polypyrrole nanotubes with excellent electrochemical performance and structural stability and apply them to flexible supercapacitors has become a pressing technical challenge in the current field. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a method for preparing polypyrrole nanotubes for flexible supercapacitors, so as to solve the problems of fast specific capacitance decay and short cycle life caused by low specific surface area, limited ion transmission channels and poor structural stability of polypyrrole nanospheres in the prior art.

[0007] To overcome the above defects of the prior art, the present invention provides a method for preparing polypyrrole nanotubes for flexible supercapacitors, comprising the following steps: S1: Add methyl orange powder to deionized water and stir to dissolve to prepare solution A; S2: Add pyrrole monomer to solution A and continue stirring to prepare solution B; S3: Add anhydrous ferric chloride powder to deionized water and continue stirring until dissolved to prepare solution C; S4: adding solution C dropwise to solution B, stirring continuously until solution C is completely added, to obtain a mixed solution, and reacting the mixed solution; S5: After the reaction of the mixture in step S4 is completed, the mixture is filtered to obtain black polypyrrole powder, and the unreacted methyl orange on the surface of the black polypyrrole powder is washed, followed by drying to obtain polypyrrole nanotube powder.

[0008] Compared with the prior art, the present invention provides a method for preparing polypyrrole nanotubes for flexible supercapacitors, which has the following advantages: Compared with the prior art method of preparing zero-dimensional polypyrrole nanospheres by direct chemical oxidation polymerization, the present invention optimizes the reaction conditions and introduces a methyl orange template, so that the generated polypyrrole material has a more regular nanotube morphology, a larger specific surface area and a higher conductivity, thereby exhibiting excellent specific capacitance and good cycle stability in electrochemical performance, especially in the application of flexible supercapacitors, which has obvious advantages; the preparation method of the present invention controls the molar concentration ratio of methyl orange to ferric chloride and the low-temperature reaction conditions to make the pyrrole monomers directional polymerize along the template to form a one-dimensional nanotube structure. In the preparation method of the present invention, the sulfonic acid group of methyl orange reacts with Fe 3+The nanotube template is formed by self-assembly through electrostatic action, guiding the polymerization of pyrrole monomers along the template surface to form a tubular structure. The polymerization rate is further suppressed by the low-temperature reaction environment, promoting the orderly arrangement of polypyrrole molecular chains, and improving the crystallinity and conductivity. At the same time, in the present invention, the methyl orange doping concentration is positively correlated with the aspect ratio and specific surface area of the nanotubes, thereby optimizing the ion transmission path. Through the above-mentioned conditions of the present invention, the morphology of the prepared nanotubes increases the specific surface area to 51.12 m²·g⁻¹ (more than 10 times that of nanospheres), and the conductivity is as high as 15.33 S·mm⁻¹. At the same time, the mechanical stability of the tubular structure effectively alleviates the volume expansion during the charge and discharge cycle, so that the capacitance retention rate after 2000 cycles is increased to 43.41% (only about 20% of nanospheres), fundamentally solving the problem of limited electrochemical performance of zero-dimensional polypyrrole nanospheres in the background technology due to low specific surface area and disordered stacking. When the prepared polypyrrole nanotubes are used as flexible supercapacitor electrode active materials, they have a capacitance of 5 mV·s -1 The specific capacitance is as high as 389 F·g -1 The capacitance retention rate is 100% when bent 180°, meeting the dual requirements of flexible electronic devices for high energy density and mechanical deformation tolerance.

[0009] In a possible embodiment, in step S1, the stirring and dissolving conditions are: stirring and dissolving at room temperature.

[0010] Compared with the prior art, the present invention adopts the above technical solution and, compared with heating-assisted dissolution or prolonged ultrasonic treatment, dissolves methyl orange by stirring at room temperature, thereby avoiding the destruction of the chemical structures of the azo groups and sulfonic acid groups in the methyl orange molecules by high temperature and preventing the subsequent self-assembly template from being destabilized due to excessive dispersion.

[0011] In a possible implementation, in step S2, the condition for adding the pyrrole monomer to solution A is: adding at a temperature of -10°C.

[0012] Compared with the existing technology, the above-mentioned technical solution slows down the rate of the polymerization reaction under lower temperature conditions (-10°C), allowing the pyrrole monomer to self-assemble into a nanotube structure in a more regular manner, which is crucial for improving the crystallinity, specific surface area and conductivity of polypyrrole. Under low temperature conditions of -10°C, the polymerization reaction occurs through a slow and stable process, avoiding the problems of non-uniform polymerization and irregular arrangement of polymer chains that may occur at high temperatures.

[0013] In a possible implementation, in step S3, the continuous stirring condition is: stirring at a temperature of 50° C. until the anhydrous ferric chloride powder is completely dissolved.

[0014] Compared with the prior art, the above technical solution allows ferric chloride to dissolve at a faster rate and fully contact with other reactants by heating and stirring at 50°C, ensuring that ferric chloride can uniformly catalyze the reaction during the formation of polypyrrole. The stirring temperature is controlled at 50°C, which can ensure that the dissolution process does not cause an overly rapid reaction and maintain good dissolution stability, avoiding incomplete dissolution of ferric chloride, thereby ensuring the controllability of the reaction process and the catalytic effect.

[0015] In a possible embodiment, in step S4, the condition for slowly adding solution C to solution B is: adding at a temperature of -10°C.

[0016] Compared with the existing technology, the above technical solution can effectively control the rate and reaction selectivity of the polymerization reaction. By adding solution C at a temperature of -10°C, the reaction rate can be effectively slowed down, an excessively fast polymerization reaction can be avoided, and sufficient contact between the reactants can be ensured. At the same time, the stability of the reaction system can also be maintained, thereby contributing to the formation of a good structure of polypyrrole nanotubes. During the dropwise addition process, the temperature is maintained at a low temperature, which is beneficial to reducing the generation of by-products, improving the purity of the target product, and making the reactants evenly distributed, thereby obtaining a stable polypyrrole nanotube structure.

[0017] In one possible embodiment, in step S4, the molar concentration ratio of methyl orange, pyrrole, and ferric chloride in the mixed solution is (1-4):60:120, and the reaction conditions of the mixed solution are: reacting at -10°C for 24 hours.

[0018] Compared with the existing technology, the above technical solution can effectively optimize the structural characteristics and electrochemical performance of polypyrrole nanotubes. By controlling the molar concentration ratio of methyl orange, pyrrole and ferric chloride to (1-4): 60:120, the polymerization rate in the reaction system can be adjusted, further improving the crystallinity and order of the polypyrrole nanotubes, avoiding the formation of disordered structures, and thus improving the conductivity and stability of the final product. In the present invention, methyl orange is used as a template molecule. The regulation of its concentration range can not only affect the progress of the reaction, but also control the morphology and size of the final nanotubes, optimize the specific surface area of the material, and enhance its electrochemical performance.

[0019] In a possible embodiment, in step S4, in the mixed solution, the molar concentration of methyl orange is 2.5-10 mM, the molar concentration of pyrrole is 0.15 M, and the molar concentration of anhydrous ferric chloride is 0.3 M.

[0020] Compared with the prior art, the above technical solution can optimize the polymerization rate and control the morphology of the product by further precisely controlling the reaction conditions of the polymerization reaction, especially the molar concentration ratio of methyl orange, pyrrole, and ferric chloride. The selection of the methyl orange concentration range enables the methyl orange to act as a template, guiding the formation of polypyrrole nanotubes, and the size and structure of the nanotubes can be adjusted by precisely adjusting its concentration, thereby improving the specific surface area and conductive properties of the material. The control of the pyrrole concentration ensures the smooth progress of the polymerization reaction, avoids excessive polymerization or incomplete polymerization, and guarantees the quality and yield of the polypyrrole. The molar concentration of anhydrous ferric chloride is maintained at a moderate level, which helps to provide sufficient oxidizing capacity to initiate the polymerization of the pyrrole monomer while avoiding the formation of byproducts caused by excessive ferric chloride.

[0021] In one possible embodiment, in step S5, the cleaning conditions are: removing unreacted methyl orange on the surface of the black polypyrrole powder by multiple rinses with deionized water and anhydrous ethanol; and the drying conditions are: vacuum drying the obtained black polypyrrole powder at 60° C. for 12 hours.

[0022] Compared with the prior art, the above technical solution can effectively remove unreacted methyl orange on the surface of polypyrrole, avoid excessive unreacted products adhering to the surface of polypyrrole nanotubes, not only improve the purity of the final product, but also avoid the interference of methyl orange on the electrochemical performance; and by using deionized water and anhydrous ethanol in the rinsing step, impurities in the solvent can be efficiently removed while retaining the structural integrity of the polypyrrole, ensuring its conductivity and stability. In the above technical solution of the present invention, under vacuum drying conditions, a temperature of 60° C. and a treatment time of 12 hours are used, which can effectively remove moisture and solvent, and due to the effect of the vacuum environment, structural deformation or agglomeration of the polypyrrole during the drying process can be further prevented.

[0023] The second technical problem to be solved by the present invention is to provide a polypyrrole nanotube for a flexible supercapacitor to solve the problems of unsatisfactory morphology, small specific surface area, poor conductivity and unstable electrochemical performance in the prior art.

[0024] In order to overcome the above defects of the prior art, the present invention provides a polypyrrole nanotube for a flexible supercapacitor, wherein the polypyrrole nanotube is prepared by the above preparation method.

[0025] Compared with the prior art, the polypyrrole nanotubes for flexible supercapacitors disclosed in the present application have the following advantages: the polypyrrole nanotubes of the present invention have a higher specific surface area and aspect ratio. The above-mentioned improvements enable them to have a larger effective reaction area, which can better contact with the electrolyte, thereby improving the diffusion efficiency of ions and electrochemical performance; at the same time, the polypyrrole nanotubes of the present invention have high crystallinity and good electrical conductivity, which help to improve the specific capacitance and cycle stability of the supercapacitor. The preparation process of the polypyrrole nanotubes in the present invention adopts a methyl orange doping method, which effectively promotes the formation of nanotubes, making the resulting material more ordered in microstructure, further improving the electrochemical performance and stability.

[0026] The third technical problem to be solved by the present invention is to provide an application of polypyrrole nanotubes for flexible supercapacitors to solve the problems existing in the prior art such as unstable electrochemical performance, small specific surface area, poor conductivity and short cycle life.

[0027] In order to overcome the above defects of the prior art, the present invention provides applications of the polypyrrole nanotubes, including application of the polypyrrole powder in preparing flexible supercapacitors.

[0028] Compared with the prior art, the application of polypyrrole nanotubes for flexible supercapacitors in the present application has the following advantages: the polypyrrole nanotubes of the present invention, as electrode materials for flexible supercapacitors, have a larger specific surface area and better electrical conductivity. The one-dimensional nanotube structure not only increases the contact area between the electrolyte and the active material, but also enhances the diffusion rate of ions and improves the energy storage performance. The good crystallinity and stable structure of the polypyrrole nanotubes can effectively avoid structural damage to the electrode during the charge and discharge process, significantly improving the cycle stability and specific capacitance. Compared with the prior art, the application of the present invention can provide higher specific capacitance and better cycle stability, especially under flexible conditions such as bending and compression, and can maintain a high capacitance retention rate and electrochemical performance stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The conductivity and yield data of the polypyrrole nanospheres prepared in Comparative Example 1 and the polypyrrole nanotubes prepared in Examples 1-4 of the present invention are shown in FIG. Figure 2 is the SEM image of polypyrrole nanotubes; Figure 2 In the figure, (a)-(e) are SEM images of polypyrrole nanospheres prepared in Comparative Example 1 of the present invention and polypyrrole nanotubes prepared in Examples 1-4, respectively; Figure 3 Isothermal adsorption-desorption curve and average pore size distribution of polypyrrole nanotubes; Figure 3Among them, (a)-(e) are the isothermal adsorption-desorption curves and average pore size distribution diagrams of the polypyrrole nanospheres prepared in Comparative Example 1 of the present invention and the polypyrrole nanotubes prepared in Examples 1-4; Figure 4 XRD spectra of the polypyrrole nanospheres prepared in Comparative Example 1 and the polypyrrole nanotubes prepared in Examples 1-4 of the present invention; Figure 5 CV curves of polypyrrole samples at different scan rates and specific capacitance graphs at different scan rates according to an embodiment of the present invention; Figure 5 In the figure, (a)-(e) are CV curves of the polypyrrole samples prepared in Comparative Example 1 and Examples 1-4 of the present invention at different scanning rates; Figure 5 (f) is the specific capacitance of the polypyrrole samples prepared in Comparative Example 1 and Examples 1-4 of the present invention at different scan rates in the CV test; Figure 6 GCD curves of polypyrrole samples at different current densities and specific capacitance graphs at different current densities for the embodiments of the present invention and the comparative example; Figure 6 In the figure, (a)-(e) are GCD curves of the polypyrrole samples prepared in Comparative Example 1 and Examples 1-4 of the present invention at different current densities; Figure 6 (f) is a graph of the specific capacitance of the polypyrrole samples prepared in Comparative Example 1 and Examples 1-4 of the present invention at different current densities in the GCD test; Figure 7 The EIS scatter plot and 2000 cycle charge-discharge curve of the polypyrrole sample of the embodiment of the present invention are shown; Figure 7 In the figure, (a) is the EIS scatter plot of the polypyrrole samples prepared in Comparative Example 1 and Examples 1-4 of the present invention; Figure 7 In the figure, (b) is a 2000 cycle charge-discharge curve diagram of the polypyrrole samples prepared in Comparative Example 1 and Examples 1-4 of the present invention.

[0030] Figure 8 This is a performance diagram of the supercapacitor assembled according to Example 4 of the present invention; Figure 8In the figure, (a) is a CV curve diagram of a supercapacitor assembled with the polypyrrole sample prepared in Example 4 of the present invention at different scan rates; (b) is a CV curve diagram of a supercapacitor assembled with the polypyrrole sample prepared in Example 4 of the present invention at different bending angles; (c) is a GCD curve diagram of a supercapacitor assembled with the polypyrrole sample prepared in Example 4 of the present invention at different current densities; (d) is a GCD curve diagram of a supercapacitor assembled with the polypyrrole sample prepared in Example 4 of the present invention in the states of a single device, two devices in parallel, and two devices in series; (e) is a 2000 cycle charge and discharge curve diagram of a supercapacitor assembled with the polypyrrole sample prepared in Example 4 of the present invention.

[0031] Figure 9 Lighting images of three supercapacitors assembled from polypyrrole samples prepared in Example 4 of the present invention; Figure 9 In the figure, (a) is a diagram showing three supercapacitors assembled using the polypyrrole sample prepared in Example 4 of the present invention, which are connected in series to light up five red LED bulbs under normal conditions; Figure 9 In the figure, (b) is a picture of three supercapacitors assembled using the polypyrrole sample prepared in Example 4 of the present invention, which are connected in series in a bent state to light up five red LED bulbs. DETAILED DESCRIPTION

[0032] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of the present application and are not intended to limit the scope of protection of the embodiments of the present application. Those skilled in the art may adjust them as needed to suit specific application scenarios.

[0033] The present invention provides a method for preparing polypyrrole nanotubes for flexible supercapacitors, comprising the following steps: S1: Add methyl orange powder to deionized water and stir to dissolve to prepare solution A; S2: Add pyrrole monomer to solution A and continue stirring to prepare solution B; S3: Add anhydrous ferric chloride powder to deionized water and continue stirring until dissolved to prepare solution C; S4: adding solution C dropwise to solution B, stirring continuously until solution C is completely added, to obtain a mixed solution, and reacting the mixed solution; S5: After the reaction of the mixture in step S4 is completed, the mixture is filtered to obtain black polypyrrole powder, and the unreacted methyl orange on the surface of the black polypyrrole powder is washed, followed by drying to obtain polypyrrole nanotube powder.

[0034] As a preferred solution, in step S1, the stirring and dissolving conditions are: stirring and dissolving at room temperature.

[0035] As a preferred solution, in step S2, the condition for adding the pyrrole monomer to solution A is: adding it at a temperature of -10°C.

[0036] As a preferred solution, in step S3, the continuous stirring condition is: stirring at a temperature of 50° C. until the anhydrous ferric chloride powder is completely dissolved.

[0037] As a preferred solution, in step S4, the condition for slowly adding solution C to solution B is: adding at a temperature of -10°C.

[0038] As a preferred solution, in step S4, the molar concentration ratio of methyl orange, pyrrole and ferric chloride in the mixed solution is (1-4):60:120, and the reaction conditions of the mixed solution are: reacting at -10°C for 24 hours.

[0039] As a preferred solution, in step S4, in the mixed solution, the molar concentration of methyl orange is 2.5-10 mM, the molar concentration of pyrrole is 0.15 M, and the molar concentration of anhydrous ferric chloride is 0.3 M.

[0040] As a preferred solution, in step S5, the cleaning conditions are: removing unreacted methyl orange on the surface of the black polypyrrole powder by rinsing with deionized water and anhydrous ethanol multiple times; and the drying conditions are: vacuum drying the obtained black polypyrrole powder at 60° C. for 12 hours.

[0041] Compared with the existing technology, the advantages of the preparation method of the present invention are: (1) The preparation method of the present invention prepares polypyrrole nanotubes by chemical oxidation. The preparation method of the material is simple, the preparation cost is low, the product yield is large, and mass production can be achieved; (2) The preparation method of the present invention forms a self-assembled nanotube template by using methyl orange and ferric chloride. The obtained polypyrrole has a nanotube morphology in the microscopic sense, has a large aspect ratio and specific surface area, and at the same time, the lower polymerization temperature slows down the polymerization rate, making the polypyrrole chain more regular and orderly. The finally obtained polypyrrole nanotube powder has a higher specific surface area, crystallinity, conductivity and yield than the bulk polypyrrole nanospheres, and has higher specific capacitance and cycle stability in electrochemical tests; The preparation method of the present invention uses self-assembled nanotubes formed by methyl orange and ferric chloride as a template during the chemical oxidation process of polypyrrole, so that the generated polypyrrole has a nanotube-like microscopic morphology. Performance analysis shows that compared with bulk polypyrrole nanospheres without a dopant, the prepared polypyrrole nanotubes have higher electrical conductivity, yield, thermal stability and crystallinity. Electrochemical performance tests show that the electrochemical performance of the polypyrrole nanotubes is positively correlated with the doping concentration of methyl orange.

[0042] The present invention also provides a polypyrrole nanotube for a flexible supercapacitor, wherein the polypyrrole nanotube is prepared by the above preparation method.

[0043] The present invention also provides applications of the polypyrrole nanotubes, including application of the polypyrrole powder in preparing flexible supercapacitors.

[0044] The flexible supercapacitor prepared using the polypyrrole nanotubes prepared by the present invention as the active material has excellent electrochemical energy storage capacity, especially in the bent state, the capacitance retention rate is almost 100%. It has excellent performance in actual charging and discharging and lighting LED light bulb applications, reflecting the potential of one-dimensional polypyrrole nanotubes in flexible energy storage devices and flexible electronics.

[0045] In combination with the above technical solution, an embodiment combined with specific data is given below to further expand and explain the technical content of the present invention: Example 1: This embodiment provides a polypyrrole powder for a flexible supercapacitor and a preparation method thereof, comprising the following specific steps: S1: Add 0.3273 g (1 mmol) of methyl orange powder to 350 mL of deionized water and stir thoroughly at room temperature to dissolve to prepare solution A. S2: Add 4.165 mL (0.06 mol) of pyrrole monomer to solution A at -10°C with continuous stirring to prepare solution B. S3: Add 19.464 g (0.12 mol) of anhydrous ferric chloride powder to 50 mL of deionized water and continue stirring at 50°C until completely dissolved to prepare solution C. S4: slowly adding solution C dropwise to solution B at -10°C while continuously stirring until solution C is completely added to obtain a mixed solution, and reacting the mixed solution; S5: After the reaction of the mixture in step S4 is completed, the mixture is filtered to obtain black polypyrrole powder, and the unreacted methyl orange on the surface of the black polypyrrole powder is washed, followed by drying to obtain polypyrrole nanotube powder.

[0046] Example 2: This embodiment provides a polypyrrole powder for a flexible supercapacitor and a preparation method thereof. The other steps of the preparation method are the same as those in Example 1, except that step S1 is as follows: 0.6546 g (2 mmol) of methyl orange powder is added to 350 mL of deionized water, and the mixture is thoroughly stirred and dissolved at room temperature to prepare solution A.

[0047] Therefore, in step S4, the molar concentrations of methyl orange, pyrrole, and ferric chloride in the mixed solution are 5 mM, 0.15 M, and 0.3 M, respectively, and the ratio is 2:60:120.

[0048] The remaining operations were the same as those in Example 1 to obtain polypyrrole nanotube powder.

[0049] Example 3: This embodiment provides a polypyrrole powder for a flexible supercapacitor and a preparation method thereof. The other steps of the preparation method are the same as those in Example 1, except that step S1 is as follows: 0.9819 g (3 mmol) of methyl orange powder is added to 350 mL of deionized water, and the mixture is stirred and dissolved at room temperature to prepare solution A.

[0050] Therefore, in step S4, the molar concentrations of methyl orange, pyrrole, and ferric chloride in the mixed solution are 7.5 mM, 0.15 M, and 0.3 M, respectively, and the ratio is 3:60:120.

[0051] The remaining operations were the same as those in Example 1 to obtain polypyrrole nanotube powder.

[0052] Example 4: This embodiment provides a polypyrrole powder for a flexible supercapacitor and a preparation method thereof. The other steps of the preparation method are the same as those in Example 1, except that step S1 is as follows: 1.3092 g (4 mmol) of methyl orange powder is added to 350 mL of deionized water, and the mixture is stirred and dissolved at room temperature to prepare solution A.

[0053] Therefore, in step S4, the molar concentrations of methyl orange, pyrrole, and ferric chloride in the mixed solution are 10 mM, 0.15 M, and 0.3 M, respectively, and the ratio is 4:60:120.

[0054] Comparative Example 1: The comparative example provides a polypyrrole powder for a flexible supercapacitor and a preparation method thereof, the preparation method comprising the following specific steps: S1: Add 0 g (0 mmol) of methyl orange powder to 350 mL of deionized water and stir thoroughly to dissolve at room temperature to prepare solution A. S2: Add 4.165 mL (0.06 mol) of pyrrole monomer to solution A at -10°C with continuous stirring to prepare solution B. S3: Add 19.464 g (0.12 mol) of anhydrous ferric chloride powder to 50 mL of deionized water and continue stirring at 50°C until completely dissolved to prepare solution C. S4: slowly adding solution C dropwise to solution B at -10°C while continuously stirring until solution C is completely added to obtain a mixed solution, and reacting the mixed solution; S5: After the reaction of the mixture in step S4 is completed, suction filtration is performed to obtain black polypyrrole powder, and unreacted methyl orange on the surface of the black polypyrrole powder is washed, followed by drying to obtain polypyrrole powder.

[0055] The remaining operations were the same as those in Example 1 to obtain polypyrrole nanotube powder.

[0056] The polypyrrole nanosphere powder prepared in Comparative Example 1 and the polypyrrole nanotube powder prepared in Examples 1 to 4 were used as active materials to prepare carbon cloth electrodes and flexible strain sensors, respectively: First, weigh polypyrrole, acetylene black, carboxymethyl cellulose powder, and 10% styrene-butadiene rubber dispersion in a mass ratio of 16:2:1:1. Add these to a mixing cup and dropwise add an appropriate amount of deionized water to ensure that the active material, conductive filler, and binder are evenly mixed into a slurry of suitable viscosity. After tightly capping the mixing cup, place it in a planetary degassing stirring device and homogenize for 6 to 8 minutes to obtain a uniform slurry.

[0057] Then, use a small brush to evenly apply the mixed slurry to the surface of a 1.5 cm × 1 cm conductive carbon cloth that has been acidified in advance, with a coating area of approximately 1 cm × 1 cm. Next, bake the coated carbon cloth electrode in an 80°C forced air drying oven overnight to ensure complete evaporation of moisture.

[0058] Subsequently, a small brush was used to evenly coat the remaining slurry on the surface of a 2cm×2cm conductive carbon cloth connected to an external metal sheet, and then baked in an 80°C forced air drying oven overnight. To prepare the electrolyte, the commercially available polyacrylic acid-based hydrogel was first soaked in a 1M H2SO4 electrolyte for more than 12 hours to allow it to fully absorb the electrolyte. The dried electrode sheets were then attached to both sides of the gel electrolyte face to face, and finally packaged in a plastic bag to complete the assembly of the flexible symmetrical supercapacitor.

[0059] Next, the performance analysis and effect verification of the polypyrrole powder, carbon cloth electrode and flexible supercapacitor prepared in the above embodiments and comparative examples of the present invention were carried out: (I) Conductivity and yield test of polypyrrole samples: The polypyrrole powders of Examples 1-4 and Comparative Example 1 were weighed using a precision electronic balance model QL105B, and their respective yields were recorded. Subsequently, the conductivity was tested using a four-probe resistivity tester model FT-343. The results are shown in the figure below. Figure 1 As shown. The product yields of Comparative Example 1 to Examples 1-4 gradually increased, indicating that the doping of methyl orange can effectively increase the yield of polypyrrole powder. In terms of conductivity, as the doping concentration of methyl orange increases, the conductivity first increases and then decreases. The conductivity of Example 3 is the highest, reaching 15.33 S mm -1 , significantly higher than Comparative Example 1.

[0060] (II) Microstructure analysis of polypyrrole samples: The polypyrrole powders of Examples 1-4 and Comparative Example 1 were characterized using a SU-70 scanning electron microscope (SEM). Figure 2 As shown in Figures (a)-(e), without methyl orange doping, the polypyrrole prepared in Comparative Example 1 is a zero-dimensional nanosphere. However, with methyl orange doping, the polypyrroles of Examples 1-4 exhibit one-dimensional nanotube morphology, with the tube diameter gradually decreasing as the methyl orange concentration increases. This phenomenon demonstrates that methyl orange doping effectively increases the aspect ratio of polypyrrole.

[0061] (III) Specific surface area (BET) test of polypyrrole samples: BET test was performed on the polypyrrole powders of Examples 1-4 and Comparative Example 1 using a fully automatic specific surface area adsorption instrument of model ASAP 2460. The results are as follows: Figure 3 (a)-(e) show that the specific surface area of comparative example 1 is relatively small, only 4.97 m 2 •g -1 However, the specific surface areas of Examples 1-4 were 37.33, 38.32, 49.49, and 51.12 m 2 •g -1 ¹, indicating that methyl orange doping significantly improves the structure of polypyrrole. As the methyl orange concentration increases, the specific surface area of the polypyrrole nanotubes further increases, thereby improving the material's contact with the electrolyte, promoting ion diffusion, and providing abundant channels and chemically active sites for enhanced electrochemical performance.

[0062] (IV) X-ray diffraction (XRD) test of polypyrrole samples: XRD test was performed on the polypyrrole powders of Examples 1-4 and Comparative Example 1 using an X-ray powder diffractometer of model D8Advance. The results are as follows: Figure 4As shown. Comparative Example 1 and Examples 1-4 all show two amorphous diffraction peaks near 2θ = 12° and 2θ = 26°. As the concentration of methyl orange increases, the amorphous peak near 12° does not change significantly, while the amorphous peak near 26° is significantly enhanced, indicating that the doping of methyl orange helps optimize the arrangement and stacking of polypyrrole molecular chains and the arrangement of π-π bonds.

[0063] (V) Electrochemical performance analysis of polypyrrole samples: Cyclic voltammetry (CV), constant current charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and 2000 cycles of charge-discharge tests were performed on the polypyrrole carbon cloth electrodes of Comparative Example 1 and Examples 1-4 using a PARSTAT 4000A electrochemical workstation. The CV test results are shown in Table 1. Figure 5 As shown, the ordinate is normalized by dividing the measured current by the mass of the active material. Comparative Example 1 and Examples 1-4 all exhibit oxidation peaks and reduction peaks at around 0.4 V, indicating the embedding and extraction of Cl⁻ in the electrode. Except for Comparative Example 1, the electrodes of the other Examples 1-4 also exhibited another pair of redox peaks near 0.5 V, and as the concentration of methyl orange increased, the redox peaks became more obvious, indicating the reversible oxidation / reduction activity of the azo group in methyl orange. The area enclosed by the CV curve is positively correlated with the specific capacity of the material. The area of the CV curve of Examples 1-4 is significantly larger than that of Comparative Example 1, indicating that methyl orange doping can effectively improve the electrochemical performance, and its effect increases with the increase of methyl orange concentration. At each scan rate, Example 4 has the best specific capacitance performance, with a specific capacitance of up to 389 F•g at 5 mV•s⁻¹. -1 , at 100 mV•s -1 It can still reach 230 F·g -1 , which is 59% of the initial capacitance.

[0064] GCD test results are as follows Figure 6 As shown in the figure, the charge and discharge curves of all examples show an isosceles triangle structure. As the current density increases, the charge and discharge speed of the electrode accelerates. The charge and discharge speed of the electrode in Example 1 is slow, while the discharge time of Examples 1-4 also increases significantly with the increase of methyl orange concentration, further proving that methyl orange doping has a positive effect on the electrochemical performance. At different current densities, Example 4 has the best specific capacity, 1 A·g -1 Specific capacitance up to 395 F·g -1 , at 5 A·g -1 257 F·g -1 , the capacitance retention rate reaches 65%.

[0065] EIS test results are as follows Figure 7As shown in (a), the equivalent series resistance of the electrode of Example 4 in the high-frequency region is slightly higher than that of Examples 3 and 2, at approximately 0.88 Ω. However, the slope of the curve of Example 4 in the low-frequency region is the largest and the semicircle diameter is the smallest, indicating that the interfacial charge transfer rate and ion transport behavior of its electrode material and electrolyte are superior to those of samples with other methyl orange concentrations.

[0066] 2000 cycles of charge and discharge test results are as follows Figure 7 As shown in (b), due to the irreversible volume expansion generated during the ion insertion / extraction process, the specific capacitance of the comparative example and the embodiment decreased. The capacitance retention rate of Example 4 was the highest, which was 43.41% of the initial capacitance.

[0067] (VI) Verification of the electrochemical performance and practical application of the flexible symmetric supercapacitor assembled in Example 4: Since Example 4 demonstrated the best electrochemical performance, the polypyrrole nanotube material was selected to assemble a flexible symmetric supercapacitor. CV testing, GCD testing, 2000 cycle charge-discharge testing, and application of lighting an LED light bulb were performed using a PARSTAT 4000A electrochemical workstation. Figure 8 (a) shows that the supercapacitor exhibits a rectangular closed curve at different scan rates and displays redox peaks near 0.4 V and 0.3 V. Figure 8 (b) shows that the area of the CV curve does not decrease under 180° bending, proving that the device meets the requirements for flexible electronic device applications. Figure 8 (c) shows the -1 At a current density of , the capacitance is 193.91 F·g -1 , indicating good electrochemical performance, Figure 8 (d) shows that the two devices can work normally whether in series or parallel, and the charge and discharge time is slightly longer than that of a single supercapacitor. Figure 8 (e) shows that after 2000 cycles of charge and discharge, the capacitance retention rate is 39.1%, which indicates that the flexible supercapacitor prepared in Example 4 has a high capacitance retention rate and can meet the practical application requirements of flexible electronic devices.

[0068] Through the above examples, it is further proved that the present invention, by constructing a low-temperature self-assembly chemical oxidation polymerization system with methyl orange as a template, synergistically regulates the morphology and molecular structure of polypyrrole, and successfully prepares a high-crystallinity polypyrrole nanotube material with a one-dimensional tubular structure. In the preparation method of the present invention, the electrostatic induced template effect of methyl orange and the joint participation of low-temperature reaction conditions not only achieve the directional growth and orderly arrangement of polymer chains, but also significantly improve the specific surface area and electron migration ability of the material, forming an electrode active material structure with efficient charge transfer and energy storage capacity. This synergistic effect gives the prepared polypyrrole nanotubes superior electrochemical properties, including higher specific capacitance, good rate performance, and capacitance stability after multiple mechanical deformation. In addition, the preparation method proposed in the present invention is simple in process, controllable in parameters, and suitable for large-scale production. The practical application of the obtained polypyrrole nanotubes in flexible supercapacitors shows good structural stability and excellent device performance, and is superior to traditional nanosphere structure materials in terms of cycle life, capacitance decay control, and flexible stress tolerance, significantly alleviating the technical bottleneck of current flexible energy devices in terms of performance and mechanical adaptation. Through the technical path of the present invention, it is expected to be promoted and applied in multiple application scenarios such as flexible wearable devices, smart fabrics and micro energy storage systems in the future, and has good engineering application prospects and industrialization potential.

[0069] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0070] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing polypyrrole nanotubes for flexible supercapacitors, characterized in that: The following steps are involved: S1: Add methyl orange powder to deionized water and stir to dissolve to prepare solution A; S2: adding pyrrole monomer to the solution A obtained in step S1, and continuously stirring to obtain solution B; S3: Add anhydrous ferric chloride powder to deionized water and continue stirring until dissolved to prepare solution C; S4: adding the solution C obtained in step S3 dropwise to the solution B obtained in step S2, and stirring continuously until the solution C is completely added to obtain a mixed solution, and reacting the mixed solution; S5: After the reaction of the mixture in step S4 is completed, the mixture is filtered to obtain black polypyrrole powder, and the unreacted methyl orange on the surface of the black polypyrrole powder is washed, followed by drying to obtain polypyrrole nanotube powder.

2. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 1, characterized in that: In the step S1, the stirring and dissolving conditions are: stirring and dissolving at room temperature.

3. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 1, characterized in that: In the step S2, the pyrrole monomer is added to the solution A at a temperature of -10°C.

4. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 1, wherein: In step S3, the continuous stirring condition is: stirring at a temperature of 50° C. until the anhydrous ferric chloride powder is completely dissolved.

5. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 1, characterized in that: In the step S4, the solution C obtained in the step S3 is added dropwise at a temperature of -10°C.

6. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 1, characterized in that: In step S4, the molar concentration ratio of methyl orange, pyrrole and ferric chloride in the mixed solution is (1-4):60:120, and the mixed solution is reacted at -10°C for 24 hours.

7. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 6, characterized in that: In step S4, in the mixed solution, the molar concentration of methyl orange is 2.5-10 mM, the molar concentration of pyrrole is 0.15 M, and the molar concentration of anhydrous ferric chloride is 0.3 M.

8. The method for preparing polypyrrole nanotubes for flexible supercapacitors according to claim 1, characterized in that: In step S5, the cleaning conditions are as follows: removing unreacted methyl orange on the surface of the black polypyrrole powder by rinsing with deionized water and anhydrous ethanol multiple times; and the drying conditions are as follows: drying the obtained black polypyrrole powder in a vacuum oven at 60° C. for 12 hours.

9. A polypyrrole nanotube for a flexible supercapacitor, characterized in that: The polypyrrole nanotubes are prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the polypyrrole nanotubes according to claim 9, characterized in that: The application includes application of the polypyrrole powder in preparing flexible supercapacitors.

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