Flexible Solid-state Supercapacitors Research Articles

One-step preparation of flexible nanocellulose-based composite hydrogel supercapacitors with high specific capacitance

Supercapacitors (SCs) have ultra-high specific capacitance far exceeding traditional capacitors, and have become an important direction in the field of capacitor research. However, SCs devices based on carbon materials usually require a high temperature environment for N-doping or compounding of pseudocapacitive materials, which greatly increases the manufacturing cost and the difficulty of industrialized production. Herein, we fabricated cellulose-based flexible hydrogel supercapacitors by Fe3+ facilitated one-step ternary composite of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCN)/sulfonated carbon nanotubes (SCNT)/polyaniline (PANI). The combination of these three substances could form a porous and flexible three-dimensional conductive hydrogel just at room temperature. By comparing the performance of supercapacitors prepared with different ratios of three substances, it was found that the best supercapacitors exhibited a high area specific capacitance of 1786 mF/cm2 at a current density of 1 mA/cm2 and excellent flexibility. Therefore, these composite hydrogels are promising for high-performance flexible solid-state supercapacitors.

Chemical vapor deposited graphene-based quasi-solid-state ultrathin and flexible sodium-ion supercapacitor

Flexible electronic devices find wide application in wearable electronics and foldable gadgets. This article reports chemical vapor deposited (CVD) few-layers graphene for a solid-state flexible supercapacitor device. Raman spectroscopy analysis reveals up to five layers in the graphene samples. Polyvinyl alcohol-Na2SO4 hydrogel membrane is used as a gel polymer electrolyte (GPE). 50 nm thick silver (Ag) deposited on polyethylene tere­phthalate (PET) through E-beam deposition served as the flexible current collector for the device. Galvanostatic charge-discharge (GCD) executed on the fabricated device to ana­lyze its electrochemical performance yielded a specific areal capacitance of 15.3 mF cm-2 at 0.05 mA cm-2 current density. The obtained power density of the fabricated device is 0.53 µWh cm-2 at a power density of 25 µW cm-2.

Construction of vacancies-enriched CuS/Fe2O3 with nano-heterojunctions as negative electrode for flexible solid-state supercapacitor

The application of supercapacitor is often restricted by unsatisfactory performance of negative electrodes and limited voltage window. Herein, the CuS/Fe 2 O 3 nano-heterojunction with O and S vacancies is constructed by calcination and selective sulfurization, and applied as negative electrode for asymmetric supercapacitor devices. Compared with bare Fe 2 O 3 and CuS, the heterojunction and defect endow the hybrid with improved conductivity, exposed full electrochemical active sites and enhanced charge transfer. Density functional theory (DFT) calculations suggest that the electronic interface reconstruction between CuS and Fe 2 O 3 optimizes the electronic structure and accelerates the electron transport. Therefore, the heterostructured CuS/Fe 2 O 3 exhibits superior supercapacitor negative performance with high capacitance (921 F g -1 at 1 A g -1 ) and good rate capability. After assembling an asymmetric solid-state supercapacitor (CuS/Fe 2 O 3 //MnO 2 ASC) in a PVA/KOH gel, the device shows a high energy density of 56.6 Wh kg -1 at the power density of 900 W kg -1 . In addition, employing polyvinyl alcohol/sodium alginate (PVA/SA/KOH) gel as the electrolyte, a flexible solid-state supercapacitor (CuS/Fe 2 O 3 //MnO 2 SSC) provides 27.8 Wh kg -1 at 900 W kg -1 . This work designs and fabricates defect-rich heterojunction between metal sulfide and oxide and provides insights into developing high-performance electrode materials for supercapacitors. Vacancy-enriched CuS/Fe 2 O 3 nanoparticles take the advantage of CuS and Fe 2 O 3 to increase its conductivity and expand the potential window, and exhibit excellent negative electrode performance for flexible solid-state supercapacitor. • CuS/Fe 2 O 3 was formed via simple calcination and selective sulfurization. • The composite exhibited an oxygen and sulfur vacancies-rich nano heterostructure. • The hybrid presented increased conductivity and electrochemical active sites. • Compared with CuS and Fe 2 O 3 , the composite showed enhanced specific capacitance. • Flexible solid-state supercapacitor showed excellent energy density.

MXene/Graphdiyne nanotube composite films for Free-Standing and flexible Solid-State supercapacitor

MXene with excellent flexibility, metallic conductivity, and ultra-high capacitance, makes a promising electrode for flexible supercapacitor. But the serious restacking phenomenon between MXene layers undesirably limits the ion transport kinetics and substantially reduces ion storage sites, badly restricting the rate capability and storage capacity of supercapacitor. Here, we constructed a free-standing, flexible, structurally 3D-interconnected and hydronium ion penetrable MXene/Graphdiyne nanotube (MG) composite film by employing graphdiyne nanotubes (GDY-NTs) with inherent in-plane pores for horizontal-vertical intercalation among MXene layers. Benefiting from the above synergistic effect, this composite film presents a greatly-improved capacitance of 337.4 F g−1 (337.4 C g−1) and an obviously-enhanced rate capability of 73 %-remaining at 100 mV s−1, which is much better than those of the pure Ti3C2Tx films (230.8 F g−1, 55 %-remaining). Based on it, we developed an asymmetric solid-state flexible supercapacitor with a high energy density of 19.7 Wh kg−1 at the power density of 750 W kg−1 and a capacitance retention of 88.2 % after 10 000 cycles at 8 A g−1. Evidently, this work provides a new route to solve the restacking issue of MXene for high-performance flexible supercapacitor.

Polyaniline grown on poly(vinyl alcohol)/ionic liquid composite film as electrodes for flexible and self-healable solid-state polymer supercapacitors

Flexible solid-state supercapacitors are considered as one kind of competitive energy storage devices due to the excellent flexibility and high specific capacitance. It attracts considerable attention in recent years. In this paper, binder-free polymer electrodes with outstanding electrochemical performance and mechanical properties were fabricated using poly (vinyl alcohol)/ionic liquid (PVA/IL) composite films as the substrates for the in-suit polymerization of aniline. Scanning electron microscope, cyclic voltammetry, galvanostatic charge-discharge, and tensile test were applied to study the effect of IL content on the structure and properties of the polymer electrodes polyaniline/poly(vinyl alcohol)/ionic liquid (PANI/PVA/IL). The electrode PANI/PVA/IL-1.0 has the optimal comprehensive performance. The specific capacitance and conductivity were 266.6 mF cm −2 and 6.49 S m −1 at 1 mA cm −2 . The tensile strength and elongation at break could reach 1.27 MPa and 509.19%, respectively. PANI/PVA/IL-1.0 was used to assemble the symmetrical polymer supercapacitor with polymer gel electrolyte (PVA/H 2 SO 4 /IL). The area specific capacitance was 251.2 mF cm −2 at 1 mA cm −2 with the capacitance retention of 77.2% after 1000 charge-discharge cycles. Moreover, the solid-state polymer supercapacitor could keep excellent electrochemical performance even under different bending angles or after self-healing, which provides potential applications in electronic encapsulation, flexible energy-storage devices, and high stretchable electric devices etc. The polyaniline/poly(vinyl alcohol)/ionic liquid based electrodes exhibit outstanding electrical and mechanical performance, which endows the solid-state polymer supercapacitors excellent specific capacitance, flexibility and self-healing. • Flexible and self-healable supercapacitors were fabricated using poly(vinyl alcohol)-ionic liquid as substrates. • High tensile strength at break of the polymer indicated its outstanding flexibility due to the presence of ionic liquid. • The fabricated solid-state polymer supercapacitor has good specific capacitance, flexibility and self-healing function.

Compacted N-Doped 3D Bicontinuous Nanoporous Graphene/Carbon Nanotubes@Ni-Doped MnO2 Electrode for Ultrahigh Volumetric Performance All-Solid-State Supercapacitors at Wide Temperature Range.

Developing wide temperature range flexible solid-state supercapacitors with high volumetric energy density is highly desirable to meet the demands of the rapidly developing field of miniature consumer electronic devices and promote their widespread adoption. Herein, high-quality dense N-doped 3D porous graphene/carbon nanotube (N-3DG/CNTs) hybrid films are prepared and used as the substrate for the growth of Ni-doped MnO2 (Ni-MnO2 ). The integrated and interconnected architecture endows N-3DG/CNTs@Ni-MnO2 composite electrodes' high conductivity and fast ion/electron transport pathway. Subsequently, 2.4V solid-state supercapacitors are fabricated based on compacted N-3DG/CNTs@Ni-MnO2 positive electrodes, which exhibit an ultrahigh volumetric energy density of 78.88mWhcm-3 based on the entire device including electrodes, solid-state electrolyte, and packing films, excellent cycling stability up to 10 000 cycles, and a wide operating temperature range from -20 to 70°C. This work demonstrates a design of flexible solid-state supercapacitors with exceptional volumetric performance capable of operation under extreme conditions.

Solvothermal in-situ preparation of poly(1,5-diaminoanthraquinone) grafted graphene with superior electrochemical performance

Poly(1,5-diaminoanthraquinone) (PDAA) has attracted intense interests as electrode materials for supercapacitors. The interaction between PDAA and conductive frameworks plays an important role on the electrochemical performance of the flexible devices. Here, facile and efficient strategy was developed to covalently graft PDAA onto graphene oxide (GO) via solvothermal in-situ chemical oxidation polymerization, in which GO was oxidized and cut into pieces to produce more functional groups for PDAA grafting. Owing to the strong interaction, the PDAA-rGO/rEGO based flexible symmetric solid-state supercapacitors (SSSCs) possessed a capacitance of 203.1 mF cm−2, power density of 241.5 mW cm−2 and energy density of 18.0 mWh cm−2 at 0.50 mA cm−2, with superior capacitance retention of 92.5% and 93.3% after 10000 CV cycles and 300 cycles of 180°-bending.

Synthesis of spongy Mn nanoparticles by electroless reduction for solid-state flexible supercapacitor application

Increasing energy storage capacity through the use of novel nano-ranged structures is advantageous for the generation of high-rate performing supercapacitors. Designing metal electrodes that are easily available on earth, cheap, and have better charge transfer characteristics with high stability is still challenging. Current article assesses the first study to explore the synthesis of Mn nanoparticles with spongy nano flakes-like surface architecture using simple, room temperature electroless route to serve as an active electrode for supercapacitive energy storage device. Interestingly, Mn thin film electrode attained a capacitance of 663 F g−1 with a cyclic retention of 103% at 5000 cycles. Designed bendable solid-state symmetric device exhibits an extraordinary specific power of 1.2 kW kg−1 and an exceptional deformation endurance (96% at 170°), indicating its suitability for advanced flexible energy storage applications.

Synergistic enhancement on flexible solid-state supercapacitor based on redox-active Fe3+ions/natural spidroin modified vertically aligned carbon nanotube arrays

The conductive skeleton and aligned carbon nanotube array (CNTA) structure can greatly shorten the ion transfer path and promote the charge transfer speed, which makes the CNTA an ideal electrode material for energy storage application. However, poor mechanical stability and low specific capacitance greatly impede its practical utilization. Here, we introduce a promising flexible electrode material based on the natural spider silk protein (SSP) modified CNTA(SSP/CNTA) with improved hydrophilicity and mechanical flexibility. The redox-active Fe3+ doped SSP/CNTA flexible solid-state supercapacitor (FSSC) device with superior energy storage performance was assembled in a symmetric ‘sandwich-type’ structure. The synergetic interaction between Fe3+ ions and the SSP are proved to greatly enhance the electrochemical performance especially the long-term cyclic stability. The Fe3+ doped SSP/CNTA FSSCs device achieves an ultra-high volumetric capacitance of 4.92 F cm−3 at a sweep speed of 1 mV s−1. Meanwhile it exhibited an excellent cycling stability with an increased capacitance by 10% after 10 000 charge–discharge cycles. As a control, a Fe3+ doped CNTA composite device without SSP will lose over 74% of the capacitance after 10 000 cycles. The energy storage mechanism analysis confirms the dominated capacitive behavior of the device, which explained a considerable power density and rate performance. Our method thus provides a promising strategy to build up highly-efficient redox-enhanced FSSCs for next generation of wearable and implantable electronics.

Electrochemical Preparation of Hydroxylated Boron Nitride Nanosheets for Solid-State Flexible Supercapacitors Using Deep Eutectic Solvent and Water Mixture as Electrolytes.

One-step and efficient preparation of few-layer hydroxylated boron nitride nanosheets (OH-BNNSs) in electrochemical methods is still challenging. Here, we developed an electrolyte composed of a mixture of deep eutectic solvent (DES, choline chloride-urea) and water for electrochemical methods to enhance the exfoliation and oxidation processes, enabling the one-step preparation of OH-BNNSs. It was found that the obtained OH-BNNSs were an average lateral size of 625 nm and thickness of six layers. Furthermore, the OH-BNNSs and DES were added to the poly(vinyl alcohol) (PVA) substrate to prepare composite gel polymer electrolyte (PVA/DES/OH-BNNSs GPE) for solid-state flexible supercapacitor. The OH-BNNSs can effectively shorten the ionic transport distance and enhance ion conductivity. In addition, their excellent mechanical properties can significantly prevent the electrolyte structure from collapsing during reuse. In the meantime, DES was introduced to improve ionic conductivity and broaden the operating voltage window of supercapacitor. As a result, the symmetric solid-state flexible supercapacitor consisting of activated carbon electrodes and PVA/DES/OH-BNNSs GPE appeared a wide voltage window of 2.3 V, high specific capacitance of 151.22 F g-1 at 0.1 A g-1 and remained 98% capacitance after 1500 charge-discharge cycles. This study not only opened a new pathway to efficient exfoliation of insulating layered materials but also found a novel gel polymer electrolyte for solid-state flexible supercapacitors.

Stretchable and conductive cellulose hydrogel electrolytes for flexible and foldable solid-state supercapacitors

In this study, the anti-freezing conductive hydrogel electrolytes with outstanding mechanical properties were synthesized by a facile and feasible method. The mechanical and anti-freezing properties of the synthesized polyacrylamide/lithium lhloride/water soluble cellulose acetate (PAM/LiCl/WSCA) hydrogels are significantly enhanced with the addition of WSCA and LiCl. The tensile strength and toughness of the gels were gradually increased to 341 KPa and 1.2 MJ/m3, respectively. The hydrogel electrolyte can remain soft and flexible at −80 °C, displaying certain elasticity and electrical conductivity. In addition, the super-capacitor assembled with PAM/LiCl/WSCA hydrogel as electrolyte showed excellent stability in capacitance retention after 500 times of folding cycles and 10,000 times of charge and discharge tests. The capacitor still maintains 64.64 % of its capacity at −40 °C. This facile strategy to fabricate anti-freezing conductive hydrogel electrolyte provides a new idea and way to the application of hydrogels as electrolytes in extreme cold environments.

Integrating MXene waste materials into value-added products for smart wearable self-powered healthcare monitoring

MXenes have gained significant attention for development of flexible or wearable electronics. However, intrinsic sediment waste from the MXene production process is usually discarded, greatly decreasing efficiency. Rational use of MXene waste (trash) in wearables may improve economic benefits. Here, a strategy that integrates MXene nanosheets (treasure) with sediment trash is employed to construct a smart wearable self-powered health monitoring system. A flexible solid-state supercapacitor (FSSC) consisting of a robust MXene/polyamide (MX-PA) film delivers good specific capacitance and mechanical properties. An MXene trash-based pressure sensor realizes effective monitoring of physiological signals. By integrating the FSSC and pressure sensor, the self-powered smart system can remotely receive physiological feedback for evaluating human health status. This work explores a feasible strategy to take full advantage of MXene starting materials and may expand scalable fabrication of MXene-based smart wearables in healthcare fields.

Self-powered and multi-mode flexible sensing film with patterned conductive network for wireless monitoring in healthcare

The flexible and multi-functional strain sensors have attracted extensive research attention due to their promising applications in various wearable electronics. However, it remains a huge challenge to design and fabricate the self-powered flexible sensing micro-system based on a single multifunctional material to relieve the dependence on external rigid and heavy battery. Herein, a self-powered and multi-mode flexible sensing system integrated with triboelectric nanogenerator (TENG), flexible solid-state supercapacitors (FSSC) and strain sensor is developed based on thermoplastic polyurethane film with asymmetric and cross conductive networks through a facile screen printing process. The unique conductive network endows the prepared strain sensor with an independent anisotropic response to the strain applied in different directions. The TENG in single-electrode mode is presented to generate electricity from ubiquitously bio-mechanical energy and stored it in the FSSC immediately, realizing continuous green power supply for the sensor. As proof-of-concept, an all-in-one smart device consisting of energy supply and sensing module is constructed, demonstrating the great convenience and feasibility for practical application in sustainable wearable electronics. Benefiting from the excellent comprehensive sensing performance, the wireless wearable device assembled by the prepared sensor exhibits excellent detection and recognition for various human motion, expressions, phonation, and physiological signal, revealing the broad potential applications in rehabilitation training, human-machine interaction and medical diagnosis. This work proposes an innovative and scalable approach to manufacture multifunctional micro-systems, which will bring new vitality and more possibilities to a new generation of wearable electronics.

Design and realization of binder-free electrodes with leaf-like structure based on Fe-Co binary oxides/graphene enabling efficient energy storage of flexible solid-state supercapacitors

High performance and efficient preparation of electrodes are prerequisites for energy storage devices to adapt to complex usage scenarios in the future. In this work, flexible binder-free electrodes with unique leaf-like structure were designed and prepared based on Fe-Co binary oxides nanoparticles/graphene coated on carbon cloth, which can be directly used in supercapacitors without any subsequent operations or additives. Morphological characterization demonstrates that the structure of the electrodes is similar to that of a leaf, including veins (carbon fibers), blades (graphene layers), and mesophyll cells (evenly distributed CoO particles of 60–80 nm and Fe3O4 particles less than 10 nm). Electrochemical characterization confirms that the electrode exhibits high specific capacitance of 458 F g−1 at 1 A g−1 under a wide operating potential window of 1.45 V. After assembled into a flexible solid-state symmetric supercapacitor with aqueous KOH/PVA as the gel electrolyte, the device exhibits good energy density (20.2 Wh kg−1), ameliorated power density (8910 W kg−1), and excellent cycling stability (capacitance retention of 87% after 3000 continuous cycles at 1 A g−1). Furthermore, after being bent at 60°, 120°, 180° and finally restored to the original state, its cyclic voltammetry curve remains almost unchanged in both shape and area, indicative of its remarkable flexibility and structural stability. All the results prove that this work is promising to further promote the development of supercapacitors.

Flexible Self-Supporting 3D Electrode Based on 3D Graphene-PPy@Fe-MnCo2O4 Nanostructure Arrays toward High-Performance Wearable Supercapacitors

The development of high-performance flexible supercapacitors is desperately desired for application in wearable electronics, but the fabrication of a flexible self-supporting 3D electrode with light weight and high energy density remains challenging. Herein, we report an approach to fabricate the flexible self-supporting and lightweight 3D G-PPy@Fe-MnCo2O4 hierarchical electrode for flexible solid-state supercapacitors (FSSCs), which utilizes the active material 3D G-PPy as a substrate to vertically grow Fe-MnCo2O4 nanowire (NW) arrays. Importantly, the experimental results and DFT simulations indicate that Fe-MnCo2O4 NWs obtain metallic characteristics by doping Fe into a MnCo2O4 lattice, which induces the free propagation of electrons in the electrode. Thus, MnCo2O4 utilization efficiency and cycle performance are both greatly enhanced. The electrode has a high areal specific capacitance of 5136 mF cm–2 (422.4 F g–1) at 2 mA cm–2 with long-term cycle stability. The capacitance retention is about 94.7% after 7000 cycles. It presents a viable design route toward advanced wearable energy storage devices.

Recent advances in solid‐state supercapacitors: From emerging materials to advanced applications

Solid-state supercapacitors (SSCs) hold great promise for next-generation energy storage applications, particularly portable and wearable electronics, implementable medical devices, the Internet of Things (IoT), and smart textiles. This review is intended to present the broad picture of SSC technology by covering various kinds of all-solid-state and flexible solid-state supercapacitors. The review begins with introducing a brief history of the development of supercapacitors and then discusses the fundamentals, charge storage mechanisms, and the performance evaluation methods of SSCs. The next chapter provides an overview of the solid-state electrolytes, notably solid polymer electrolytes, inorganic electrolytes, and redox-active solid electrolytes. In this study, a particular focus is given to the electrode fabrication methods and some emerging electrode materials, such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal nitrides (MNs), MXenes, polyoxometalates (POMs), and black phosphorus (BP). Subsequently, the performance of SSCs with different configurations based on the cell design (ie, symmetric, asymmetric) and the electrode type (ie, freestanding, fiber, interdigitated, flexible) is discussed. This review also presents a comprehensive summary of the latest innovations and state-of-the-art applications of SSCs, including electrochromic, self-healing, shape memory, thermally chargeable, piezoelectric-, photo-SSCs. The final section highlights the future directions and critical technological challenges in the field of SSCs.

Flexible Solid-State Supercapacitor with High Energy Density Enabled by N/B/O-Codoped Porous Carbon Nanoparticles and Imidazolium-Based Gel Polymer Electrolyte

Flexible Solid-State Supercapacitor with High Energy Density Enabled by N/B/O-Codoped Porous Carbon Nanoparticles and Imidazolium-Based Gel Polymer Electrolyte

FeSe and Fe3Se4 encapsulated in mesoporous carbon for flexible solid-state supercapacitor

Metal selenides have been developed as promising alternatives of metal oxides in energy storage field due to their high conductivity and low bandgap. However, the synthesis of selenides usually suffers from the low melting point and strong volatility of selenium at temperatures higher than 217 ℃. Herein, a facile strategy was developed to prepare iron selenides using a template of Se-contained MOF gel, which could in situ immobilize Se powder due to the fast gelation process, resulting a porous, uniform and tight precursor. By adjusting the mole ratio of Fe and Se in the precursor, FeSe@C and Fe3Se4@C were controllably synthesized with rich mesopores and excellent carbon-encapsulation structure. The kinetics analysis indicates that these unique structures are beneficial for improving electrode kinetics, charge/ion-transfer resistance and electrochemical stability. FeSe@C and Fe3Se4@C exhibit significant capacitances (611.0F g−1 and 569.0F g−1 at 1 A g−1), and excellent cycling properties (94.22% and 93.28% retention after 2000 charge–discharge cycles at 5 A g−1). When estimated in practical application, the flexible solid-state symmetric supercapacitor of FeSe@C//Fe3Se4@C delivers a high Csp of 160.1F g−1, the superior energy density of 32.1 W h kg−1 and a high specific power density of 5998 W kg−1 with 89.5% capacitance retention after 5000 cycles, and the outstanding flexibility.

Constructing a novel carbon skeleton to anchor Sn/SnO2 nanodots for flexible supercapacitor with excellent rate capability

Designing SnO2/carbon composites is an effective strategy to improve the conductivity and buffer the volume expansion of SnO2. However, it remains a challenge to combine SnO2 and carbon materials tightly as a stable integration. Herein, a facile and versatile strategy of Sn/SnO2 nanodots anchored tightly into carbon nanofibers (CNFs) with the decoration of graphene quantum dots (GQDs) for high performance supercapacitor is reported. Through a simple electrospinning and carbonization reduction process, a novel multidimensional carbon skeleton of GQD/CNF effectively improves the conductivity, and importantly, abundant Sn–O–C covalent bonds are constructed to anchor SnO2 nanodots tightly into GQD/CNF, suppressing SnO2 aggregation and facilitating electron/ion transfer kinetics. Consequently, as self-supporting and binder-free electrode material, Sn/SnO2/GQD/CNF displays high specific capacitance of 168.6 mA h g−1 (1349 F g−1) at 1 A g−1 with excellent rate capability (88.9% retention at 20 A g−1). Furthermore, a flexible solid-state asymmetric supercapacitor based on Sn/SnO2/GQD/CNF and GQD/CNF achieves a high energy density of 32.3 W h kg−1 at a power density of 800 W kg−1 with remarkable flexibility and cycling stability (86.1% retention after 5000 cycles). The excellent electrochemical performances demonstrate that this novel carbon skeleton anchored active materials shows great potential for electrochemical energy storage applications.

Enhancement of polypyrrole nanotubes stability by gold nanoparticles for the construction of flexible solid-state supercapacitors

Flexible solid-state supercapacitors (FSSCs) have becoming of great interest due to the increasing energy demand of the modern world. Many studies are focusing on the development of different materials for supercapacitor electrodes, however, the combination of high specific capacitance, high stability and low cost in a single material is still a challenge. Herein, we report the fabrication of a FSSC based on a hybrid material of polypyrrole nanotubes (PPy-NTs) and gold nanoparticles (AuNPs). The materials were characterized by scanning and transmission electron microscopies and energy dispersive X-ray spectroscopy and they were also electrochemically characterized in aqueous 1 mol L−1 H2SO4 solution. The FSSC was assembled using a poly(vinyl alcohol) and sodium alginate gel electrolyte and the results showed a high specific capacitance, high stability over 2000 galvanostatic charge/discharge cycles (88%) and good electrochemical performance under bending. The results indicate the great potential to use PPy-NTs/AuNPs hybrid material in flexible all-solid-state symmetric devices.