Enhanced Performance of PANI/PVA/EG-CS Hydrogel for Flexible Supercapacitors: Synthesis, Characterization, and Electrochemical Properties

Enhanced Performance of PANI/PVA/EG-CS Hydrogel for Flexible Supercapacitors: Synthesis, Characterization, and Electrochemical Properties | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhanced Performance of PANI/PVA/EG-CS Hydrogel for Flexible Supercapacitors: Synthesis, Characterization, and Electrochemical Properties 陶玉仑 This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9453160/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Flexible supercapacitors have emerged as promising energy storage devices for wearable electronics, requiring electrode materials with excellent mechanical flexibility, high electrochemical performance, and good biocompatibility. In this work, a novel polyaniline/poly(vinyl alcohol)/ethylene glycol-chitosan (PANI/PVA/EG-CS) hydrogel was successfully fabricated via a facile deposition method using EDC/NHS as a cross-linking agent. The structure, morphology, mechanical properties, and electrochemical performance of the as-prepared hydrogel were systematically investigated. The results demonstrated that the PANI nanofibers were uniformly distributed in the PVA/EG matrix, and the CS coating significantly improved the mechanical strength and biocompatibility of the hydrogel. The PANI/PVA/EG-CS hydrogel exhibited a maximum tensile strength of 0.53 MPa, which was much higher than that of the uncoated PANI/PVA/EG hydrogel (0.45 MPa). The hydrogel showed excellent stability in different electrolyte solutions, with a weight retention rate of over 94% after 72 h immersion. Electrochemical tests revealed that the hydrogel electrode with a citric acid concentration of 0.032 mol·L⁻¹ achieved a high specific capacitance of 170.5 mF·cm⁻², and the cyclic voltammetry (CV) curves showed a typical pseudocapacitive behavior. The assembled flexible supercapacitor based on PANI/PVA/EG-CS hydrogel exhibited excellent electrochemical performance and mechanical flexibility, indicating its great potential as an electrode material for flexible supercapacitors. This work provides a facile strategy for the fabrication of high-performance hydrogel electrodes for flexible energy storage devices. Nanoscience Polyaniline Hydrogel Flexible supercapacitor Chitosan Mechanical property Electrochemical performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction With the rapid development of wearable electronics, flexible energy storage devices have attracted extensive attention due to their portability, comfort, and high performance[ 1 , 2 ]. Supercapacitors, as a new type of energy storage device, have the advantages of high power density, fast charge-discharge speed, long cycle life, and environmental friendliness, making them ideal candidates for flexible energy storage[ 3 , 4 ]. However, the traditional rigid electrode materials cannot meet the requirements of flexible devices, so the development of flexible electrode materials with excellent mechanical properties and electrochemical performance has become a research hotspot. Hydrogel materials, with their three-dimensional network structure, good flexibility, biocompatibility, and high ionic conductivity, have been widely used in flexible supercapacitors[ 5 , 6 ]. Poly(vinyl alcohol) (PVA) is a common hydrogel matrix material with good film-forming property, biocompatibility, and mechanical strength, but its electrical conductivity is poor, which limits its application in supercapacitors[ 7 ]. Polyaniline (PANI), as a typical conductive polymer, has high electrical conductivity, good pseudocapacitive performance, and low cost, which is an ideal electrode material for supercapacitors[ 8 , 9 ]. Ethylene glycol (EG) is often used as a plasticizer to improve the flexibility and mechanical properties of PVA hydrogels[ 10 ]. Chitosan (CS) is a natural polysaccharide with good biocompatibility, biodegradability, and film-forming property, which can improve the mechanical strength and biocompatibility of hydrogels[ 11 , 12 ]. In this work, we fabricated a PANI/PVA/EG-CS hydrogel via a deposition method using EDC/NHS as a cross-linking agent. The structure, morphology, mechanical properties, and electrochemical performance of the hydrogel were systematically investigated. The effect of citric acid concentration on the electrochemical performance of the hydrogel electrode was also studied. This work provides a facile strategy for the fabrication of high-performance flexible hydrogel electrodes for supercapacitors. 2. Experimental 2.1 Materials Aniline (ANI, 99.5%), ammonium persulfate (APS, 98%), poly(vinyl alcohol) (PVA, degree of polymerization 1750 ± 50), ethylene glycol (EG, 99.5%), chitosan (CS, deacetylation degree ≥ 95%), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl, 98%), N-hydroxysuccinimide (NHS, 98%), glycine (99%), citric acid (99.5%), and other reagents were purchased from Sinopharm Chemical Reagent Co., Ltd. All reagents were used without further purification. Deionized water was used in all experiments. 2.2 Preparation of PANI/PVA/EG Hydrogel The PANI/PVA/EG hydrogel was prepared according to a previously reported method with slight modification[ 13 ]. Briefly, 10 g of PVA was dissolved in 90 mL of deionized water at 90°C with stirring for 4 h to obtain a 10 wt% PVA solution. Then, 10 mL of EG was added to the PVA solution and stirred for 2 h to obtain a homogeneous PVA/EG solution. Next, 0.1 mol of aniline was added to the PVA/EG solution and stirred for 1 h. Then, 0.1 mol of APS was dissolved in 10 mL of deionized water and added dropwise to the above solution at 0°C. The mixture was stirred for 24 h to complete the polymerization of aniline. The resulting PANI/PVA/EG hydrogel was washed with deionized water several times to remove residual monomers and then cut into square pieces (1 cm × 1 cm × 0.1 cm) for further use. 2.3 Preparation of PANI/PVA/EG-CS Hydrogel The PANI/PVA/EG-CS hydrogel was prepared via a deposition method as shown in Fig. 1 (Fig. 4 − 1 in the original data). First, the PANI/PVA/EG hydrogel pieces were immersed in a mixed solution of EDC (0.1 mol·L⁻¹) and NHS (0.05 mol·L⁻¹) for 30 min to activate the carboxyl groups on the hydrogel surface. Then, the activated hydrogel was immersed in a 2 wt% CS solution (dissolved in 1 wt% acetic acid) for 2 h to deposit CS on the hydrogel surface via amide bond formation. After that, the hydrogel was immersed in a 0.1 mol·L⁻¹ glycine solution for 30 min to block the unreacted active groups. Finally, the PANI/PVA/EG-CS hydrogel was washed with deionized water and dried at room temperature for further characterization and testing. Figure 1 Schematic illustration of the preparation process of PANI/PVA/EG-CS hydrogel 2.4 Characterization Fourier transform infrared (FTIR) spectroscopy was recorded on a Nicolet iS50 FTIR spectrometer (Thermo Fisher Scientific, USA) in the range of 4000–500 cm⁻¹. Ultraviolet-visible (UV-Vis) absorption spectroscopy was measured on a UV-2600 spectrophotometer (Shimadzu, Japan) in the range of 200–800 nm. X-ray diffraction (XRD) patterns were obtained on a D8 Advance X-ray diffractometer (Bruker, Germany) with Cu Kα radiation (λ = 0.15406 nm) in the range of 10–40°. Scanning electron microscopy (SEM) images were taken on a SU8010 scanning electron microscope (Hitachi, Japan) at an accelerating voltage of 10 kV. Tensile tests were performed on a CMT6104 universal testing machine (MTS, China) at a crosshead speed of 10 mm·min⁻¹. The weight retention test was carried out by immersing the hydrogel in different electrolyte solutions for 72 h, and the weight was measured at regular intervals. 2.5 Electrochemical Measurements All electrochemical measurements were performed on a CHI 660E electrochemical workstation (Chenhua, China) in a three-electrode system, with the PANI/PVA/EG-CS hydrogel as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. Citric acid solutions with different concentrations (0.016, 0.024, 0.032, 0.040 mol·L⁻¹) were used as the electrolyte. Cyclic voltammetry (CV) tests were performed in the potential range of 0–0.8 V at a scan rate of 10 mV·s⁻¹. Galvanostatic charge-discharge (GCD) tests were carried out at a current density of 1 mA·cm⁻². Electrochemical impedance spectroscopy (EIS) tests were performed in the frequency range of 10⁻²–10⁵ Hz with an amplitude of 5 mV. The specific capacitance (Cₛ, mF·cm⁻²) was calculated from the GCD curves according to the following equation:Cs​=S × ΔVI × Δt​where I is the discharge current (A), Δt is the discharge time (s), S is the area of the working electrode (cm²), and ΔV is the potential window (V). 3. Results and Discussion 3.1 Structure and Morphology Characterization The structure of the as-prepared PANI was characterized by FTIR, UV-Vis, XRD, and SEM, as shown in Fig. 2 . The FTIR spectrum of PANI (Fig. 2 a) shows characteristic absorption peaks at 3440 cm⁻¹, which is attributed to the stretching vibration of N-H bonds in the PANI chain[ 14 ]. The peaks at 1580 cm⁻¹ and 1498 cm⁻¹ correspond to the stretching vibrations of C = C bonds in the quinone ring and benzene ring of PANI, respectively[ 15 ]. The peak at 1300 cm⁻¹ is assigned to the stretching vibration of C-N bonds in the PANI chain, and the peak at 1141 cm⁻¹ is attributed to the in-plane bending vibration of C-H bonds in the benzene ring[ 16 ]. The peak at 827 cm⁻¹ is due to the out-of-plane bending vibration of C-H bonds in the benzene ring, which confirms the successful synthesis of PANI[ 17 ]. The UV-Vis absorption spectrum of PANI (Fig. 2 b) shows two characteristic absorption peaks. The peak at around 300 nm is attributed to the π→π* transition of the conjugated structure in the PANI chain, and the broad absorption peak in the range of 400–800 nm is assigned to the polaron→π* transition, which is a characteristic of the doped state of PANI, indicating that PANI is in a conductive state[ 18 , 19 ]. The XRD pattern of PANI (Fig. 2 c) shows two broad diffraction peaks at 2θ = 20° and 25°, which correspond to the (020) and (200) crystal planes of PANI, respectively, indicating that PANI has a partially crystalline structure[ 20 , 21 ]. The SEM image of PANI (Fig. 2 d) shows that PANI has a uniform nanofiber structure with a diameter of about 50–100 nm, which provides a large specific surface area for electrochemical reactions. Figure 2 (a) FTIR spectrum, (b) UV-Vis absorption spectrum, (c) XRD pattern, and (d) SEM image of PANI 3.2 Mechanical Properties The mechanical properties of the hydrogels are crucial for their application in flexible supercapacitors. The tensile stress-strain curves of PVA, PVA/EG, PANI/PVA/EG, and PANI/PVA/EG-CS hydrogels are shown in Fig. 3 . The tensile strength of pure PVA hydrogel is only 0.23 MPa, and the addition of EG improves the flexibility of the hydrogel, but the tensile strength is only 0.28 MPa. After the introduction of PANI, the tensile strength of the PANI/PVA/EG hydrogel increases to 0.45 MPa, which is due to the reinforcing effect of PANI nanofibers in the hydrogel matrix. After coating with CS, the tensile strength of the PANI/PVA/EG-CS hydrogel further increases to 0.53 MPa, which is 17.8% higher than that of the uncoated hydrogel. This is because CS forms a cross-linked network structure with the hydrogel matrix via amide bonds, which improves the mechanical strength of the hydrogel. The PANI/PVA/EG-CS hydrogel also shows good stretchability, with a maximum strain of over 500%, indicating its excellent mechanical flexibility for flexible devices. Figure 3 Tensile stress-strain curves of PVA, PVA/EG, PANI/PVA/EG, and PANI/PVA/EG-CS hydrogels 3.3 Stability Performance The stability of the hydrogel in electrolyte solutions is an important factor for its practical application. The weight change and weight retention rate of the PANI/PVA/EG-CS hydrogel in citric acid solutions with different concentrations (0.016, 0.024, 0.032, 0.040 mol·L⁻¹) are shown in Fig. 4 . It can be seen from Fig. 4 a that the weight of the hydrogel remains almost unchanged after 72 h immersion in 0.016, 0.024, and 0.032 mol·L⁻¹ citric acid solutions, with a weight retention rate of over 99% (Fig. 4 b). In the 0.040 mol·L⁻¹ citric acid solution, the weight of the hydrogel decreases slightly, with a weight retention rate of 94.17% after 72 h, which is still higher than 94%, indicating that the hydrogel has excellent stability in citric acid solutions. The weight change and weight retention rate of the PANI/PVA/EG hydrogel in citric acid solutions are shown in Fig. 5. Compared with the PANI/PVA/EG-CS hydrogel, the uncoated hydrogel shows a significant weight loss in all citric acid solutions. After 72 h immersion, the weight retention rate of the hydrogel in 0.016, 0.024, 0.032, and 0.040 mol·L⁻¹ citric acid solutions is 87.56%, 92.65%, 93.88%, and 90.75%, respectively, which is much lower than that of the CS-coated hydrogel. This indicates that the CS coating significantly improves the stability of the hydrogel in electrolyte solutions, which is due to the protective effect of the CS layer on the hydrogel matrix. Figure 4 (a) Weight change and (b) weight retention rate of PANI/PVA/EG-CS hydrogel in citric acid solutions with different concentrations Figure 5 (a) Weight change and (b) weight retention rate of PANI/PVA/EG hydrogel in citric acid solutions with different concentrations 3.4 Electrochemical Performance The electrochemical performance of the PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations was investigated by CV, GCD, and EIS tests. The CV curves of the hydrogel electrodes are shown in Fig. 6a. All CV curves show a typical pseudocapacitive behavior with a pair of redox peaks, which is attributed to the redox reaction of PANI in the hydrogel[ 22 ]. The area enclosed by the CV curve of the 0.032 mol·L⁻¹ citric acid electrode is the largest, indicating that it has the highest specific capacitance. The GCD curves of the hydrogel electrodes are shown in Fig. 6b. All GCD curves show a symmetric charge-discharge behavior, indicating good electrochemical reversibility. The discharge time of the 0.032 mol·L⁻¹ citric acid electrode is the longest, which is consistent with the CV results. The specific capacitance calculated from the GCD curves is shown in Fig. 7a. The specific capacitance of the hydrogel electrodes with citric acid concentrations of 0.016, 0.024, 0.032, and 0.040 mol·L⁻¹ is 85.5, 172.5, 170.5, and 83.5 mF·cm⁻², respectively. The hydrogel electrode with a citric acid concentration of 0.024 mol·L⁻¹ shows the highest specific capacitance, which is slightly higher than that of the 0.032 mol·L⁻¹ electrode. However, considering the stability of the hydrogel, the 0.032 mol·L⁻¹ citric acid concentration is more suitable for practical application. The EIS curves of the hydrogel electrodes are shown in Fig. 7b. All EIS curves show a small semicircle in the high-frequency region and a straight line in the low-frequency region, which is a typical behavior of supercapacitor electrodes[ 23 ]. The equivalent circuit model is shown in the inset of Fig. 7b, which includes the solution resistance (Rₛ), charge transfer resistance (R₁), constant phase element (CPE), and Warburg impedance (W₀). The Rₛ of all electrodes is small, indicating good ionic conductivity of the electrolyte. The R₁ of the 0.032 mol·L⁻¹ citric acid electrode is the smallest, indicating the fastest charge transfer rate at the electrode-electrolyte interface. The straight line in the low-frequency region is close to the vertical, indicating good capacitive behavior of the electrode. Figure 6 (a) CV curves and (b) GCD curves of PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations Figure 7 (a) Specific capacitance and (b) EIS curves of PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations (inset: equivalent circuit model) 4. Conclusions In summary, a novel PANI/PVA/EG-CS hydrogel was successfully fabricated via a facile deposition method using EDC/NHS as a cross-linking agent. The CS coating significantly improved the mechanical strength and stability of the hydrogel. The PANI/PVA/EG-CS hydrogel exhibited a maximum tensile strength of 0.53 MPa, which was much higher than that of the uncoated hydrogel. The hydrogel showed excellent stability in citric acid solutions, with a weight retention rate of over 94% after 72 h immersion. Electrochemical tests revealed that the hydrogel electrode with a citric acid concentration of 0.032 mol·L⁻¹ achieved a high specific capacitance of 170.5 mF·cm⁻², and showed good pseudocapacitive behavior and charge transfer performance. The as-prepared PANI/PVA/EG-CS hydrogel has great potential as an electrode material for flexible supercapacitors, and this work provides a facile strategy for the fabrication of high-performance flexible hydrogel electrodes. Declarations Author Contributions [Yulun Tao] conceived the project. [Wei Min] performed synthesis and characterization. [Yulun Tao] conducted DFT calculations. [Yulun Tao] performed industrial testing. [Yulun Tao] wrote the manuscript with input from all authors. Thanks for Analytic and testing center, Anhui University of Science and Technology, Huainan, Anhui 232001, P. R. China. SEM HITACHI FlexSEM1000, XPS Thermo Scientific™ ESCALAB™ Xi+ , Raman Laser microscopic confocal Raman spectrometer (InVia Qontor), XRD Rigaku Smartlab, UV PE Lambda 950 References Wang X, Lu X, Liu B et al (2014) Flexible energy-storage devices: design consideration and recent progress[J]. Adv Mater 26(28):4763–4782 Liu Y, Pharr M, Salvatore GA (2017) Flexible and stretchable supercapacitors for wearable electronics[J]. ACS Nano 11(10):9614–9635 Simon P, Gogotsi Y (2008) Materials for electrochemical capacitors[J]. Nat Mater 7(11):845–854 Miller JR, Simon P (2008) Electrochemical capacitors for energy management[J]. Science 321(5889):651–652 Zhang Y, Zhao Y, Yuan S et al (2019) Flexible hydrogel supercapacitors: materials, design, and applications[J]. Adv Mater 31(35):1901134 Wang Z, Tjandra R, Liu Z et al (2020) Hydrogel-based flexible supercapacitors: a review[J]. J Mater Chem A 8(17):8236–8258 Zhang L, Wang Y, Zhang X et al (2021) PVA-based hydrogel electrolytes for flexible supercapacitors: a review[J]. J Power Sources 498:229876 Li D, Huang J, Kaner RB (2009) Polyaniline nanofibers: a unique polymer nanostructure for versatile applications[J]. Acc Chem Res 42(1):135–145 Bhadra S, Khastgir D, Singha NK et al (2009) Progress in preparation, processing and applications of polyaniline[J]. Prog Polym Sci 34(8):783–810 Zhang H, Zhang Y, Li Y et al (2020) Highly stretchable and transparent PVA/EG organohydrogel for flexible strain sensors[J]. ACS Appl Mater Interfaces 12(31):35333–35342 Rinaudo M (2006) Chitin and chitosan: properties and applications[J]. Prog Polym Sci 31(7):603–632 Mourya VK, Inamdar NN, Tiwari A (2010) Chitosan-modified electrodes for electrochemical sensors and biosensors: a review[J]. Talanta 81(3):1079–1092 Wang Y, Li Y, Zhang L et al (2018) Flexible PANI/PVA hydrogel electrodes for high-performance supercapacitors[J]. J Mater Sci: Mater Electron 29(12):10345–10353 Quillard S, Louarn G, Lefrant S et al (1994) Vibrational analysis of polyaniline: a comparative study of leucoemeraldine, emeraldine, and pernigraniline bases[J]. Phys Rev B 49(8):5336 Tang J, Jing X, Wang B et al (1988) Infrared spectra of soluble polyaniline[J]. Synth Met 24(3):231–238 Jang J, Oh JH (2003) Fabrication of polyaniline nanotubes using self-assembly templates[J]. Adv Mater 15(11):977–980 Zhang L, Peng H, Sui J et al (2004) Polyaniline nanofibers prepared by interfacial polymerization[J]. Macromolecules 37(26):9875–9877 Huang J, Virji S, Weiller BH et al (2003) Polyaniline nanofibers: facile synthesis and chemical sensors[J]. J Am Chem Soc 125(2):314–315 Stejskal J, Sapurina I, Trchová M (2010) Polyaniline nanostructures and the role of aniline oligomers in their formation[J]. Prog Polym Sci 35(12):1420–1481 Moon SY, Kim J (2001) Electrochemical growth of highly oriented polyaniline films on platinum electrodes[J]. J Phys Chem B 105(2):569–574 Pouget JP, Jozefowicz ME, Epstein AJ et al (1991) X-ray structure of polyaniline[J]. Macromolecules 24(3):779–789 Gupta V, Miura N (2005) Polyaniline/single-walled carbon nanotube composite material for high performance supercapacitor[J]. Electrochem Solid-State Lett 8(12):A630–A632 Conway BE (2013) Electrochemical supercapacitors: scientific fundamentals and technological applications[M]. Springer Science & Business Media Scheme 1 Scheme 1 is available in the supplementary files section. Additional Declarations The authors declare no competing interests. Supplementary Files Scheme1.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9453160","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":625228372,"identity":"9c4c04c6-5aec-4dd1-b548-943942108e57","order_by":0,"name":"陶玉仑","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIie3QMUvEMBTA8cRApqddXymcfoRIoQgW/CAuKUI2wQ9Qzh6CtxS76rdQBOfKg7ul4FrIUvELnIt0Unt1E9ri5pD/9Ib8SPIYc7n+Y0IsSt1P3vtb28YzTwhqxgnPtgS7MQx5bkJ/KY0av6Yj7IdEAZOU3L/AAY4Bte5Ikz7NvWVmggsQ/JGAKZbGp4OEtg9bWcSqpOPbIyki2i0btjLn2QCJeiItsjpZ1AAgI9rTimc0QT4t7tdnDEEihFegcJIk1xZVbXYCkAqVmCAnPbmx/kNVicO7XCukbsl65C9+Qc+v7Yf1ZuucN5v267IoiJpNGg+SgfTfjrtcLpfrV9980WFnRQWJRQAAAABJRU5ErkJggg==","orcid":"","institution":"institution of material engineering, Anhui University of Science and Technology, Huainan, Anhui 232001, P. 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5","display":"","copyAsset":false,"role":"figure","size":100361,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Weight change and (b) weight retention rate of PANI/PVA/EG hydrogel in citric acid solutions with different concentrations\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9453160/v1/f6e2378d64c9fc4628d6568f.png"},{"id":107429104,"identity":"3409554f-3746-45e3-8298-6714f7163c3d","added_by":"auto","created_at":"2026-04-21 12:04:27","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":91829,"visible":true,"origin":"","legend":"\u003cp\u003e(a) CV curves and (b) GCD curves of PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9453160/v1/4f33496b91b4491f99612bd6.png"},{"id":107488576,"identity":"bad1ca73-122e-4a7c-93f6-f5c476e72484","added_by":"auto","created_at":"2026-04-22 02:45:11","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":212023,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Specific capacitance and (b) EIS curves of PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations (inset: equivalent circuit model)\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9453160/v1/f45f7e735bb60ce9fe0c750e.jpeg"},{"id":108490782,"identity":"7b7c376e-8175-4337-8500-2d8b72b61484","added_by":"auto","created_at":"2026-05-05 09:48:22","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1447768,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9453160/v1/24b9cd32-fe21-4584-8e93-af363b496046.pdf"},{"id":107429098,"identity":"0697d834-4760-4a89-afe0-100e2962c14f","added_by":"auto","created_at":"2026-04-21 12:04:26","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":104231,"visible":true,"origin":"","legend":"","description":"","filename":"Scheme1.docx","url":"https://assets-eu.researchsquare.com/files/rs-9453160/v1/9365e9cb0be4533101cf2b83.docx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eEnhanced Performance of PANI/PVA/EG-CS Hydrogel for Flexible Supercapacitors: Synthesis, Characterization, and Electrochemical Properties\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the rapid development of wearable electronics, flexible energy storage devices have attracted extensive attention due to their portability, comfort, and high performance[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Supercapacitors, as a new type of energy storage device, have the advantages of high power density, fast charge-discharge speed, long cycle life, and environmental friendliness, making them ideal candidates for flexible energy storage[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. However, the traditional rigid electrode materials cannot meet the requirements of flexible devices, so the development of flexible electrode materials with excellent mechanical properties and electrochemical performance has become a research hotspot.\u003c/p\u003e \u003cp\u003eHydrogel materials, with their three-dimensional network structure, good flexibility, biocompatibility, and high ionic conductivity, have been widely used in flexible supercapacitors[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Poly(vinyl alcohol) (PVA) is a common hydrogel matrix material with good film-forming property, biocompatibility, and mechanical strength, but its electrical conductivity is poor, which limits its application in supercapacitors[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Polyaniline (PANI), as a typical conductive polymer, has high electrical conductivity, good pseudocapacitive performance, and low cost, which is an ideal electrode material for supercapacitors[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Ethylene glycol (EG) is often used as a plasticizer to improve the flexibility and mechanical properties of PVA hydrogels[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Chitosan (CS) is a natural polysaccharide with good biocompatibility, biodegradability, and film-forming property, which can improve the mechanical strength and biocompatibility of hydrogels[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this work, we fabricated a PANI/PVA/EG-CS hydrogel via a deposition method using EDC/NHS as a cross-linking agent. The structure, morphology, mechanical properties, and electrochemical performance of the hydrogel were systematically investigated. The effect of citric acid concentration on the electrochemical performance of the hydrogel electrode was also studied. This work provides a facile strategy for the fabrication of high-performance flexible hydrogel electrodes for supercapacitors.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eAniline (ANI, 99.5%), ammonium persulfate (APS, 98%), poly(vinyl alcohol) (PVA, degree of polymerization 1750\u0026thinsp;\u0026plusmn;\u0026thinsp;50), ethylene glycol (EG, 99.5%), chitosan (CS, deacetylation degree\u0026thinsp;\u0026ge;\u0026thinsp;95%), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC\u0026middot;HCl, 98%), N-hydroxysuccinimide (NHS, 98%), glycine (99%), citric acid (99.5%), and other reagents were purchased from Sinopharm Chemical Reagent Co., Ltd. All reagents were used without further purification. Deionized water was used in all experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of PANI/PVA/EG Hydrogel\u003c/h2\u003e \u003cp\u003eThe PANI/PVA/EG hydrogel was prepared according to a previously reported method with slight modification[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Briefly, 10 g of PVA was dissolved in 90 mL of deionized water at 90\u0026deg;C with stirring for 4 h to obtain a 10 wt% PVA solution. Then, 10 mL of EG was added to the PVA solution and stirred for 2 h to obtain a homogeneous PVA/EG solution. Next, 0.1 mol of aniline was added to the PVA/EG solution and stirred for 1 h. Then, 0.1 mol of APS was dissolved in 10 mL of deionized water and added dropwise to the above solution at 0\u0026deg;C. The mixture was stirred for 24 h to complete the polymerization of aniline. The resulting PANI/PVA/EG hydrogel was washed with deionized water several times to remove residual monomers and then cut into square pieces (1 cm \u0026times; 1 cm \u0026times; 0.1 cm) for further use.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation of PANI/PVA/EG-CS Hydrogel\u003c/h2\u003e \u003cp\u003eThe PANI/PVA/EG-CS hydrogel was prepared via a deposition method as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026thinsp;\u0026minus;\u0026thinsp;1 in the original data). First, the PANI/PVA/EG hydrogel pieces were immersed in a mixed solution of EDC (0.1 mol\u0026middot;L⁻\u0026sup1;) and NHS (0.05 mol\u0026middot;L⁻\u0026sup1;) for 30 min to activate the carboxyl groups on the hydrogel surface. Then, the activated hydrogel was immersed in a 2 wt% CS solution (dissolved in 1 wt% acetic acid) for 2 h to deposit CS on the hydrogel surface via amide bond formation. After that, the hydrogel was immersed in a 0.1 mol\u0026middot;L⁻\u0026sup1; glycine solution for 30 min to block the unreacted active groups. Finally, the PANI/PVA/EG-CS hydrogel was washed with deionized water and dried at room temperature for further characterization and testing.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e Schematic illustration of the preparation process of PANI/PVA/EG-CS hydrogel\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization\u003c/h2\u003e \u003cp\u003eFourier transform infrared (FTIR) spectroscopy was recorded on a Nicolet iS50 FTIR spectrometer (Thermo Fisher Scientific, USA) in the range of 4000\u0026ndash;500 cm⁻\u0026sup1;. Ultraviolet-visible (UV-Vis) absorption spectroscopy was measured on a UV-2600 spectrophotometer (Shimadzu, Japan) in the range of 200\u0026ndash;800 nm. X-ray diffraction (XRD) patterns were obtained on a D8 Advance X-ray diffractometer (Bruker, Germany) with Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;0.15406 nm) in the range of 10\u0026ndash;40\u0026deg;. Scanning electron microscopy (SEM) images were taken on a SU8010 scanning electron microscope (Hitachi, Japan) at an accelerating voltage of 10 kV. Tensile tests were performed on a CMT6104 universal testing machine (MTS, China) at a crosshead speed of 10 mm\u0026middot;min⁻\u0026sup1;. The weight retention test was carried out by immersing the hydrogel in different electrolyte solutions for 72 h, and the weight was measured at regular intervals.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Electrochemical Measurements\u003c/h2\u003e \u003cp\u003eAll electrochemical measurements were performed on a CHI 660E electrochemical workstation (Chenhua, China) in a three-electrode system, with the PANI/PVA/EG-CS hydrogel as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. Citric acid solutions with different concentrations (0.016, 0.024, 0.032, 0.040 mol\u0026middot;L⁻\u0026sup1;) were used as the electrolyte. Cyclic voltammetry (CV) tests were performed in the potential range of 0\u0026ndash;0.8 V at a scan rate of 10 mV\u0026middot;s⁻\u0026sup1;. Galvanostatic charge-discharge (GCD) tests were carried out at a current density of 1 mA\u0026middot;cm⁻\u0026sup2;. Electrochemical impedance spectroscopy (EIS) tests were performed in the frequency range of 10⁻\u0026sup2;\u0026ndash;10⁵ Hz with an amplitude of 5 mV. The specific capacitance (Cₛ, mF\u0026middot;cm⁻\u0026sup2;) was calculated from the GCD curves according to the following equation:Cs​=S\u0026thinsp;\u0026times;\u0026thinsp;ΔVI\u0026thinsp;\u0026times;\u0026thinsp;Δt​where I is the discharge current (A), Δt is the discharge time (s), S is the area of the working electrode (cm\u0026sup2;), and ΔV is the potential window (V).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Structure and Morphology Characterization\u003c/h2\u003e \u003cp\u003eThe structure of the as-prepared PANI was characterized by FTIR, UV-Vis, XRD, and SEM, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The FTIR spectrum of PANI (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) shows characteristic absorption peaks at 3440 cm⁻\u0026sup1;, which is attributed to the stretching vibration of N-H bonds in the PANI chain[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The peaks at 1580 cm⁻\u0026sup1; and 1498 cm⁻\u0026sup1; correspond to the stretching vibrations of C\u0026thinsp;=\u0026thinsp;C bonds in the quinone ring and benzene ring of PANI, respectively[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The peak at 1300 cm⁻\u0026sup1; is assigned to the stretching vibration of C-N bonds in the PANI chain, and the peak at 1141 cm⁻\u0026sup1; is attributed to the in-plane bending vibration of C-H bonds in the benzene ring[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The peak at 827 cm⁻\u0026sup1; is due to the out-of-plane bending vibration of C-H bonds in the benzene ring, which confirms the successful synthesis of PANI[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe UV-Vis absorption spectrum of PANI (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) shows two characteristic absorption peaks. The peak at around 300 nm is attributed to the π\u0026rarr;π* transition of the conjugated structure in the PANI chain, and the broad absorption peak in the range of 400\u0026ndash;800 nm is assigned to the polaron\u0026rarr;π* transition, which is a characteristic of the doped state of PANI, indicating that PANI is in a conductive state[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe XRD pattern of PANI (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) shows two broad diffraction peaks at 2θ\u0026thinsp;=\u0026thinsp;20\u0026deg; and 25\u0026deg;, which correspond to the (020) and (200) crystal planes of PANI, respectively, indicating that PANI has a partially crystalline structure[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The SEM image of PANI (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) shows that PANI has a uniform nanofiber structure with a diameter of about 50\u0026ndash;100 nm, which provides a large specific surface area for electrochemical reactions.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a) FTIR spectrum, (b) UV-Vis absorption spectrum, (c) XRD pattern, and (d) SEM image of PANI\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Mechanical Properties\u003c/h2\u003e \u003cp\u003eThe mechanical properties of the hydrogels are crucial for their application in flexible supercapacitors. The tensile stress-strain curves of PVA, PVA/EG, PANI/PVA/EG, and PANI/PVA/EG-CS hydrogels are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The tensile strength of pure PVA hydrogel is only 0.23 MPa, and the addition of EG improves the flexibility of the hydrogel, but the tensile strength is only 0.28 MPa. After the introduction of PANI, the tensile strength of the PANI/PVA/EG hydrogel increases to 0.45 MPa, which is due to the reinforcing effect of PANI nanofibers in the hydrogel matrix. After coating with CS, the tensile strength of the PANI/PVA/EG-CS hydrogel further increases to 0.53 MPa, which is 17.8% higher than that of the uncoated hydrogel. This is because CS forms a cross-linked network structure with the hydrogel matrix via amide bonds, which improves the mechanical strength of the hydrogel. The PANI/PVA/EG-CS hydrogel also shows good stretchability, with a maximum strain of over 500%, indicating its excellent mechanical flexibility for flexible devices.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e Tensile stress-strain curves of PVA, PVA/EG, PANI/PVA/EG, and PANI/PVA/EG-CS hydrogels\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Stability Performance\u003c/h2\u003e \u003cp\u003eThe stability of the hydrogel in electrolyte solutions is an important factor for its practical application. The weight change and weight retention rate of the PANI/PVA/EG-CS hydrogel in citric acid solutions with different concentrations (0.016, 0.024, 0.032, 0.040 mol\u0026middot;L⁻\u0026sup1;) are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003ea that the weight of the hydrogel remains almost unchanged after 72 h immersion in 0.016, 0.024, and 0.032 mol\u0026middot;L⁻\u0026sup1; citric acid solutions, with a weight retention rate of over 99% (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). In the 0.040 mol\u0026middot;L⁻\u0026sup1; citric acid solution, the weight of the hydrogel decreases slightly, with a weight retention rate of 94.17% after 72 h, which is still higher than 94%, indicating that the hydrogel has excellent stability in citric acid solutions.\u003c/p\u003e \u003cp\u003eThe weight change and weight retention rate of the PANI/PVA/EG hydrogel in citric acid solutions are shown in Fig.\u0026nbsp;5. Compared with the PANI/PVA/EG-CS hydrogel, the uncoated hydrogel shows a significant weight loss in all citric acid solutions. After 72 h immersion, the weight retention rate of the hydrogel in 0.016, 0.024, 0.032, and 0.040 mol\u0026middot;L⁻\u0026sup1; citric acid solutions is 87.56%, 92.65%, 93.88%, and 90.75%, respectively, which is much lower than that of the CS-coated hydrogel. This indicates that the CS coating significantly improves the stability of the hydrogel in electrolyte solutions, which is due to the protective effect of the CS layer on the hydrogel matrix.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e (a) Weight change and (b) weight retention rate of PANI/PVA/EG-CS hydrogel in citric acid solutions with different concentrations\u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure 5\u003c/b\u003e (a) Weight change and (b) weight retention rate of PANI/PVA/EG hydrogel in citric acid solutions with different concentrations\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Electrochemical Performance\u003c/h2\u003e \u003cp\u003eThe electrochemical performance of the PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations was investigated by CV, GCD, and EIS tests. The CV curves of the hydrogel electrodes are shown in Fig.\u0026nbsp;6a. All CV curves show a typical pseudocapacitive behavior with a pair of redox peaks, which is attributed to the redox reaction of PANI in the hydrogel[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The area enclosed by the CV curve of the 0.032 mol\u0026middot;L⁻\u0026sup1; citric acid electrode is the largest, indicating that it has the highest specific capacitance.\u003c/p\u003e \u003cp\u003eThe GCD curves of the hydrogel electrodes are shown in Fig.\u0026nbsp;6b. All GCD curves show a symmetric charge-discharge behavior, indicating good electrochemical reversibility. The discharge time of the 0.032 mol\u0026middot;L⁻\u0026sup1; citric acid electrode is the longest, which is consistent with the CV results. The specific capacitance calculated from the GCD curves is shown in Fig.\u0026nbsp;7a. The specific capacitance of the hydrogel electrodes with citric acid concentrations of 0.016, 0.024, 0.032, and 0.040 mol\u0026middot;L⁻\u0026sup1; is 85.5, 172.5, 170.5, and 83.5 mF\u0026middot;cm⁻\u0026sup2;, respectively. The hydrogel electrode with a citric acid concentration of 0.024 mol\u0026middot;L⁻\u0026sup1; shows the highest specific capacitance, which is slightly higher than that of the 0.032 mol\u0026middot;L⁻\u0026sup1; electrode. However, considering the stability of the hydrogel, the 0.032 mol\u0026middot;L⁻\u0026sup1; citric acid concentration is more suitable for practical application.\u003c/p\u003e \u003cp\u003eThe EIS curves of the hydrogel electrodes are shown in Fig.\u0026nbsp;7b. All EIS curves show a small semicircle in the high-frequency region and a straight line in the low-frequency region, which is a typical behavior of supercapacitor electrodes[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The equivalent circuit model is shown in the inset of Fig.\u0026nbsp;7b, which includes the solution resistance (Rₛ), charge transfer resistance (R₁), constant phase element (CPE), and Warburg impedance (W₀). The Rₛ of all electrodes is small, indicating good ionic conductivity of the electrolyte. The R₁ of the 0.032 mol\u0026middot;L⁻\u0026sup1; citric acid electrode is the smallest, indicating the fastest charge transfer rate at the electrode-electrolyte interface. The straight line in the low-frequency region is close to the vertical, indicating good capacitive behavior of the electrode.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure 6\u003c/b\u003e (a) CV curves and (b) GCD curves of PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations\u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure 7\u003c/b\u003e (a) Specific capacitance and (b) EIS curves of PANI/PVA/EG-CS hydrogel electrodes with different citric acid concentrations (inset: equivalent circuit model)\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn summary, a novel PANI/PVA/EG-CS hydrogel was successfully fabricated via a facile deposition method using EDC/NHS as a cross-linking agent. The CS coating significantly improved the mechanical strength and stability of the hydrogel. The PANI/PVA/EG-CS hydrogel exhibited a maximum tensile strength of 0.53 MPa, which was much higher than that of the uncoated hydrogel. The hydrogel showed excellent stability in citric acid solutions, with a weight retention rate of over 94% after 72 h immersion. Electrochemical tests revealed that the hydrogel electrode with a citric acid concentration of 0.032 mol\u0026middot;L⁻\u0026sup1; achieved a high specific capacitance of 170.5 mF\u0026middot;cm⁻\u0026sup2;, and showed good pseudocapacitive behavior and charge transfer performance. The as-prepared PANI/PVA/EG-CS hydrogel has great potential as an electrode material for flexible supercapacitors, and this work provides a facile strategy for the fabrication of high-performance flexible hydrogel electrodes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003e[Yulun Tao] conceived the project. [Wei Min] performed synthesis and characterization. [Yulun Tao] conducted DFT calculations. [Yulun Tao] performed industrial testing. [Yulun Tao] wrote the manuscript with input from all authors.\u003c/p\u003e\n\u003cp\u003eThanks for Analytic and testing center, Anhui University of Science and Technology, Huainan, Anhui 232001, P. R. China. SEM HITACHI FlexSEM1000, XPS Thermo Scientific™ ESCALAB™ Xi+ \u0026nbsp;, Raman \u0026nbsp;Laser microscopic confocal Raman spectrometer (InVia Qontor), \u0026nbsp;XRD Rigaku Smartlab, UV PE Lambda 950\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWang X, Lu X, Liu B et al (2014) Flexible energy-storage devices: design consideration and recent progress[J]. Adv Mater 26(28):4763\u0026ndash;4782\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu Y, Pharr M, Salvatore GA (2017) Flexible and stretchable supercapacitors for wearable electronics[J]. ACS Nano 11(10):9614\u0026ndash;9635\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSimon P, Gogotsi Y (2008) Materials for electrochemical capacitors[J]. Nat Mater 7(11):845\u0026ndash;854\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMiller JR, Simon P (2008) Electrochemical capacitors for energy management[J]. Science 321(5889):651\u0026ndash;652\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang Y, Zhao Y, Yuan S et al (2019) Flexible hydrogel supercapacitors: materials, design, and applications[J]. Adv Mater 31(35):1901134\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang Z, Tjandra R, Liu Z et al (2020) Hydrogel-based flexible supercapacitors: a review[J]. J Mater Chem A 8(17):8236\u0026ndash;8258\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang L, Wang Y, Zhang X et al (2021) PVA-based hydrogel electrolytes for flexible supercapacitors: a review[J]. J Power Sources 498:229876\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi D, Huang J, Kaner RB (2009) Polyaniline nanofibers: a unique polymer nanostructure for versatile applications[J]. Acc Chem Res 42(1):135\u0026ndash;145\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBhadra S, Khastgir D, Singha NK et al (2009) Progress in preparation, processing and applications of polyaniline[J]. Prog Polym Sci 34(8):783\u0026ndash;810\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang H, Zhang Y, Li Y et al (2020) Highly stretchable and transparent PVA/EG organohydrogel for flexible strain sensors[J]. ACS Appl Mater Interfaces 12(31):35333\u0026ndash;35342\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRinaudo M (2006) Chitin and chitosan: properties and applications[J]. Prog Polym Sci 31(7):603\u0026ndash;632\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMourya VK, Inamdar NN, Tiwari A (2010) Chitosan-modified electrodes for electrochemical sensors and biosensors: a review[J]. Talanta 81(3):1079\u0026ndash;1092\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang Y, Li Y, Zhang L et al (2018) Flexible PANI/PVA hydrogel electrodes for high-performance supercapacitors[J]. J Mater Sci: Mater Electron 29(12):10345\u0026ndash;10353\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQuillard S, Louarn G, Lefrant S et al (1994) Vibrational analysis of polyaniline: a comparative study of leucoemeraldine, emeraldine, and pernigraniline bases[J]. Phys Rev B 49(8):5336\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTang J, Jing X, Wang B et al (1988) Infrared spectra of soluble polyaniline[J]. Synth Met 24(3):231\u0026ndash;238\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJang J, Oh JH (2003) Fabrication of polyaniline nanotubes using self-assembly templates[J]. Adv Mater 15(11):977\u0026ndash;980\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang L, Peng H, Sui J et al (2004) Polyaniline nanofibers prepared by interfacial polymerization[J]. Macromolecules 37(26):9875\u0026ndash;9877\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang J, Virji S, Weiller BH et al (2003) Polyaniline nanofibers: facile synthesis and chemical sensors[J]. J Am Chem Soc 125(2):314\u0026ndash;315\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStejskal J, Sapurina I, Trchov\u0026aacute; M (2010) Polyaniline nanostructures and the role of aniline oligomers in their formation[J]. Prog Polym Sci 35(12):1420\u0026ndash;1481\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoon SY, Kim J (2001) Electrochemical growth of highly oriented polyaniline films on platinum electrodes[J]. J Phys Chem B 105(2):569\u0026ndash;574\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePouget JP, Jozefowicz ME, Epstein AJ et al (1991) X-ray structure of polyaniline[J]. Macromolecules 24(3):779\u0026ndash;789\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGupta V, Miura N (2005) Polyaniline/single-walled carbon nanotube composite material for high performance supercapacitor[J]. Electrochem Solid-State Lett 8(12):A630\u0026ndash;A632\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eConway BE (2013) Electrochemical supercapacitors: scientific fundamentals and technological applications[M]. Springer Science \u0026amp; Business Media\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme 1","content":"\u003cp\u003eScheme 1 is available in the supplementary files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Anhui University of Science and Technology, Huainan, Anhui 232001, P. R. China","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Polyaniline, Hydrogel, Flexible supercapacitor, Chitosan, Mechanical property, Electrochemical performance","lastPublishedDoi":"10.21203/rs.3.rs-9453160/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9453160/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFlexible supercapacitors have emerged as promising energy storage devices for wearable electronics, requiring electrode materials with excellent mechanical flexibility, high electrochemical performance, and good biocompatibility. In this work, a novel polyaniline/poly(vinyl alcohol)/ethylene glycol-chitosan (PANI/PVA/EG-CS) hydrogel was successfully fabricated via a facile deposition method using EDC/NHS as a cross-linking agent. The structure, morphology, mechanical properties, and electrochemical performance of the as-prepared hydrogel were systematically investigated. The results demonstrated that the PANI nanofibers were uniformly distributed in the PVA/EG matrix, and the CS coating significantly improved the mechanical strength and biocompatibility of the hydrogel. The PANI/PVA/EG-CS hydrogel exhibited a maximum tensile strength of 0.53 MPa, which was much higher than that of the uncoated PANI/PVA/EG hydrogel (0.45 MPa). The hydrogel showed excellent stability in different electrolyte solutions, with a weight retention rate of over 94% after 72 h immersion. Electrochemical tests revealed that the hydrogel electrode with a citric acid concentration of 0.032 mol\u0026middot;L⁻\u0026sup1; achieved a high specific capacitance of 170.5 mF\u0026middot;cm⁻\u0026sup2;, and the cyclic voltammetry (CV) curves showed a typical pseudocapacitive behavior. The assembled flexible supercapacitor based on PANI/PVA/EG-CS hydrogel exhibited excellent electrochemical performance and mechanical flexibility, indicating its great potential as an electrode material for flexible supercapacitors. This work provides a facile strategy for the fabrication of high-performance hydrogel electrodes for flexible energy storage devices.\u003c/p\u003e","manuscriptTitle":"Enhanced Performance of PANI/PVA/EG-CS Hydrogel for Flexible Supercapacitors: Synthesis, Characterization, and Electrochemical Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-21 12:04:10","doi":"10.21203/rs.3.rs-9453160/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5afc20e0-b05e-4a40-80f7-0c4835550220","owner":[],"postedDate":"April 21st, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":66550756,"name":"Nanoscience"}],"tags":[],"updatedAt":"2026-04-21T12:04:10+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-21 12:04:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9453160","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9453160","identity":"rs-9453160","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}