Facile Co-Electrodeposition Method for High-Performance Supercapacitor Based on Reduced Graphene Oxide/Polypyrrole Composite Film

A Nanofibrous Polypyrrole Membrane with an Ultrahigh Areal Specific Capacitance and Improved Energy and Power Densities

For conductive polymers to be competitive with carbon-based electrode materials, it is critical to increase their surface area and electroactivity. In this work, a thick nanofibrous polypyrrole (PPy) membrane with communicating interfiber spaces was prepared through one-pot interfacial polymerization for the first time. The electrochemical properties and conductivity of the membrane were studied with cyclic voltammetry, electrochemical impedance spectroscopy, and a four-point probe. Its morphology, chemistry, and thermostability were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The areal specific capacitances measured between 0.0 and 0.8 V at 1 mA/cm2 were 19179, 13264, 7238, and 4458 mF/cm2 for the membranes doped with docusate sodium (AOT), camphor-10-sulfonic acid (β) (CSA), Cl-, and poly(sodium 4-styrenesulfonate) (PSS), respectively. The capacity retentions after 1000 cycles were 83, 74, 67, and 61% for the AOT-, CSA-, PSS-, and Cl--doped membranes, respectively. The Coulombic efficiency was above 99% for all of the membranes. They showed energy densities of 1.7, 1.2, 0.7, and 0.4 mWh/cm2 and power densities of 0.61, 0.75, 0.66, and 0.62 mW/cm2 for the AOT-, CSA-, Cl--, and PSS-doped membranes, respectively. The ultrahigh areal specific capacitance of PPy-AOT is due to its nanofibrous structure. A mechanism has been proposed to explain how this structure is formed based on the role of AOT as the surfactant. This nanofibrous PPy membrane is easy to prepare and metal-free and offers a very high areal specific capacitance, making it an excellent candidate to construct electrodes in pseudosupercapacitors.

Innovative modification of cellulose fibers for paper-based electrode materials using metal-organic coordination polymers

Cellulosic paper-based electrode materials have attracted increasing attention in the field of flexible supercapacitor. As a conductive polymer, polyaniline exhibits high theoretical pseudocapacitive capacitance and has been applied in paper-based electrode materials along with cellulose fibers. However, the stacking of polyaniline usually leads to poor performance of electrodes. In this study, metal-organic coordination polymers of zirconium-alizarin red S and zirconium-phytic acid are applied to modulate the polyaniline layer to obtain high-performance cellulosic paper-based electrode materials. Zirconium hydroxide is firstly loaded on cellulose fibers while alizarin red S and phytic acid are introduced to regulate the morphology of polyaniline through doping and coordination processes. The results show that the introduction of dual coordination polymers is effective to regulate the morphology of polyaniline on cellulose fibers. The performances of the paper-based electrode materials, including electrical conductivity and electrochemistry, are apparently improved. It provides a promising strategy for the potential development of economical and green electrode materials in the conventional paper-making process.

Carboxymethylcellulose-polyaniline/carbon nanotube (CMC-PANI/CNT) film as flexible and highly electrochemical active electrode for supercapacitors

Herein, we demonstrate a flexible, structural robust and highly electrochemical active film electrode based on evenly distributed carboxymethylcellulose-polyaniline/carbon nanotube (CMC-PANI/CNT) for supercapacitors. In this process, vertically aligned PANI nanoparticles grow in an orderly manner on CMC fibers. The highly dispersed CNT nanomaterials are then introduced by simple layer-by-layer assembly, eventually forming an interwoven network structure. Mechanical tests have shown that the obtained CMC-PANI/CNT film exhibit excellent robustness and flexibility, and can be used directly as electrodes without any conductive additives and binders. The CMC-PANI/CNT electrode with optimal CMC, PANI and CNT contents demonstrates an excellent area specific capacitance of 3106.3 mF cm^-2 at 5 mA cm^-2 and a gravimetric specific capacitance of 348.8 F g^-1 at 0.5 A g^-1. Furthermore, the symmetric supercapacitor (SSC) assembled with CMC-PANI/CNT exhibits a high energy density of 99.89 μW h cm^-2 at a power density of 400.02 μW cm^-2, and a good cycling stability (with capacitance retention of 89.2 % after 5000 cycles). The cost-effective and eco-friendly preparation method of free-standing CMC-PANI/CNT film electrodes provide a novel insight for developing flexible energy storage devices.

One-step electrodeposition of a polypyrrole/NiO nanocomposite as a supercapacitor electrode

An electrochemical deposition technique was used to fabricate polypyrrole (Ppy)/NiO nanocomposite electrodes for supercapacitors. The nanocomposite electrodes were characterized and investigated by Fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The performance of supercapacitor electrodes of Ppy/NiO nanocomposite was enhanced compared with pristine Ppy electrode. It was found that the Ppy/NiO electrode electrodeposited at 4 A/cm-2 demonstrated the highest specific capacitance of 679 Fg-1 at 1 Ag-1 with an energy density of 94.4 Wh kg-1 and power density of 500.74 W kg-1. Capacitance retention of 83.9% of its initial capacitance after 1000 cycles at 1 Ag-1 was obtained. The high electrochemical performance of Ppy/NiO was due to the synergistic effect of NiO and Ppy, where a rich pores network-like structure made the electrolyte ions more easily accessible for Faradic reactions. This work provided a simple approach for preparing organic-inorganic composite materials as high-performance electrode materials for electrochemical supercapacitors.

Uniform polypyrrole electrodeposition triggered by phytic acid-guided interface engineering for high energy density flexible supercapacitor

Unevenly distributed polypyrrole (PPy) films/coatings with extensive "dead volumes" via electrodeposition have emerged as a main challenge for high energy density flexible supercapacitor. In this work, we have fabricated a phytic acid-guided graphite carbon felt/polypyrrole (GF@PA@PPy) 3D porous composite with less "dead volumes" via electrodeposition. After the activation of phytic acid (PA), the quantity and content of defects and oxygen-containing groups on the surface of carbon felt (GF) have increased. First, these functional groups improve the hydrophilicity of the surface of GF, resulting in the preferential uniform distribution of pyrrole monomer (Py). While significantly, the synergistic effects between the defects and oxygen-containing groups boost the attraction of pyrrole ring, and thus promotes the formation of perfect PPy films with less "dead volume" on GF. Finally, the supercapacitor assembled from the GF@PA@PPy-40 displays a high areal energy density of 0.0732 mWh cm^-2, exceeding the previously reported PPy-based electrodes values. The deeper understanding of the role for the defects and oxygen-containing groups in the synthesis of PPy/carbon materials offers a new strategy to construct advanced PPy-based supercapacitors.

Flexible core/shelled PPy@PANI nanotube porous films for hybrid supercapacitors

Flexibility of the films and the limited ion transport in the vertical direction of film highly restrict the development of flexible supercapacitors. Herein, we have developed hybrid porous films consisting of N-doped holey graphene nanosheets (NHGR) with abundant in-plane nanopores and the vertically aligned polyaniline nanowires arrays on polypyrrole nanotubes (PPy@PANI) via a two-step oxidative polymerization strategy and vacuum filtration. The rational design can efficiently shorten the diffusion path of electrons/ions, alleviate volume variation of electrodes during cycling, enhance electric conductivity of the hybrids, and while offer abundant active interfacial sites for electrochemical reaction. Benefiting from the distinctive structural and compositional merits, the obtained PPy@PANI/NHGR film electrode manifests an excellent electrochemical properties in terms of specific capacity (1348 mF cm^-2at a current density of 1 mA cm^-2), rate capability (81.2% capacitance retention from 1 to 30 mA cm^-2), and cycling stability (capacitance retention of 73.7% at 20 mA cm^-2after 7000 cycles). Matched with NHGR negative electrode, the assembled flexible all-solid-state asymmetric supercapacitor displays a remarkable areal capacitance of 359 mF cm^-2at 5 mA cm^-2, maximum areal energy density of 112.2μWh cm^-2at 3.747 mW cm^-2, and good flexibility at various bending angles while preserving stable cycling performance. The result shows the PPy@PANI/NHGR film with high flexibility and 3D ions transport channels is highly attractive for flexible energy storage devices.

A SnO2QDs/GO/PPY ternary composite film as positive and graphene oxide/charcoal as negative electrodes assembled solid state asymmetric supercapacitor for high energy storage applications

The work demonstrates tin oxide quantum dots/graphene oxide/polypyrrole (SnO2QDs/GO/PPY) ternary composite deposited on titanium foil as a positive electrode and graphene oxide (GO)/charcoal on titanium foil as negative electrode separated by polyvinyl alcohol/potassium hydroxide (PVA/KOH) gel-electrolyte as a solid-state asymmetric supercapacitor for high energy storage applications. Here, tin oxide quantum dots (SnO2QDs) were successfully synthesized by a hydrothermal technique, and SnO2QDs/GO/PPY ternary composite was synthesized by an in situ method with pyrrole monomer, SnO2, and GO. A pH value controlled, which maintained the uniform size of SnO2QDs dispersed on PPY, through GO ternary composite was used for fabricating the asymmetric supercapacitor electrode with the configuration (SnO2QDs/GO/PPY)/GO/charcoal (85 : 10 : 5). The device achieved the highest specific capacitance of 1296 F g-1, exhibited an energy density of 29.6 W h kg-1 and the highest power density of 5310.26 W kg-1 in the operating voltage from 0 to 1.2 V. The device also possessed excellent reliability and retained the capacitance of 90% after 11 000 GCD cycles. This ternary composite is a prominent material for potential applications in next-generation energy storage and portable electronic devices.

Electrochemical approach toward reduced graphene oxide-based electrodes for environmental applications: A review

Graphene has shown great potential in various application fields due to its excellent carrier transportation, ultra-high specific surface area, good mechanical properties, and light transmittance. However, pure graphene still exhibits some insurmountable defects, such as difficulty in simple and large-scale preparation, and limitations in application. The electrochemical method is a simple, clean, and environmentally friendly method. The rapid and simple preparation of graphene and its derivatives by electrochemical methods has important environmental significance. Moreover, rGO-based nanohybrids can be prepared by convenient and quick electrodeposition or cyclic voltammetry (CV), or to change the morphology and structure of graphene and its derivatives to achieve the purpose of improving material properties. This work mainly summarizes electrochemically related graphene from four aspects: (i) the method of electrochemical exfoliation of graphene; (ii) types of electrodeposition rGO-based nanohybrids; (iii) electrochemical regulation of the structure of rGO-based mixtures; (iv) environmental applications of rGO-based nanohybrids prepared by electrodeposition. This article critically discusses the advantages and disadvantages of electrochemical-related graphene, outlines future challenges, and provides insightful views and references for other researchers.

Electropolymerized Poly(3,4-ethylenedioxythiophene)/Screen-Printed Reduced Graphene Oxide-Chitosan Bilayer Electrodes for Flexible Supercapacitors

An electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT)/screen-printed reduced graphene oxide (rGO)-chitosan (CS) bilayer material was coated on carbon cloth to form electrodes for gel-electrolyte flexible supercapacitors. The conductive polymer and carbon-based materials mainly contribute pseudocapacitance (PC) and electrical double-layer capacitance (EDLC), respectively. The high porosity and hydrophilicity of the PEDOT/rGO-CS bilayer material offers a large contact area and improves the contact quality for the gel electrolyte, thereby enhancing the capacitive performance. Cyclic voltammetry (CV) under a potential scan rate of 2 mV/s revealed that a maximum areal capacitance of 1073.67 mF/cm² was achieved. The capacitance contribution ratio PC/EDLC was evaluated to be ∼67/33 by the Trasatti method. A 10,000-cycle CV test showed a capacitance retention rate of 99.3% under a potential scan rate of 200 mV/s, indicating good stability. The areal capacitance remains similar under bending with a bending curvature of up to 1.5 cm^-1.

Nanocomposite Materials Based on Electrochemically Synthesized Graphene Polymers: Molecular Architecture Strategies for Sensor Applications

The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors.

Flexible all-solid-state supercapacitors based on PPy/rGO nanocomposite on cotton fabric

Polypyrrole (PPy) has high electrochemical activity and low cost, so it has great application prospects in wearable supercapacitors. Herein, we have successfully prepared polypyrrole/reduced graphene oxide (PPy/rGO) nanocomposite cotton fabric (NCF) by chemical polymerization, which exhibits splendid electrochemical performance compared with the individual. The addition of rGO can block the deformation of PPy caused by the expansion and contraction. The as-prepared PPy-0.5/rGO NCF electrode exhibits the brilliant specific capacitance (9300 mF cm^-2at 1 mA cm^-2) and the capacitance retention with 94.47% after 10 000 cycles. At the same time, the superior capacitance stability under different bending conditions and reuse capability have been achieved. All-solid-state supercapacitor has high energy density of 167μWh cm^-2with a power density of 1.20 mW cm^-2. Therefore, the PPy-0.5/rGO NCF electrode has a broad application prospect in high-performance flexible supercapacitor fabric electrode.

Carbon Nanomaterials Embedded in Conductive Polymers: A State of the Art

Carbon nanomaterials are at the forefront of the newest technologies of the third millennium, and together with conductive polymers, represent a vast area of indispensable knowledge for developing the devices of tomorrow. This review focusses on the most recent advances in the field of conductive nanotechnology, which combines the properties of carbon nanomaterials with conjugated polymers. Hybrid materials resulting from the embedding of carbon nanotubes, carbon dots and graphene derivatives are taken into consideration and fully explored, with discussion of the most recent literature. An introduction into the three most widely used conductive polymers and a final section about the most recent biological results obtained using carbon nanotube hybrids will complete this overview of these innovative and beyond belief materials.

Design and synthesis of a 3D flexible film electrode based on a sodium carboxymethyl cellulose–polypyrrole@reduced graphene oxide composite for supercapacitors

A novel, environmentally friendly and freestanding 3D flexible film electrode (CMC–PPy@RGO) was prepared by a simple vacuum filtration method.

Ice-interface assisted large-scale preparation of polypyrrole/graphene oxide films for all-solid-state supercapacitors

In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. The morphology, chemical structure and electrochemical property were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS), respectively. The lamellar structure of GO and both strong interaction with ice and pyrrole could promote polymerization of pyrrole and improve the compactness of the film. With the aid of GO, the conjugation length of PPy increased, the resistance of the material decreased, and the electrochemical energy storage of the composite film was significantly enhanced. In the case of 2.5 wt% GO, the prepared PPy/GO nanocomposite supercapacitor exhibited a high area specific capacitance of 97.3 mF cm^-2 at 1 mA cm^-2. Furthermore, the PPy/GO film supercapacitor also showed excellent cycling stability and good flexibility.

Bilayered microelectrodes based on electrochemically deposited MnO2/polypyrrole towards fast charge transport kinetics for micro-supercapacitors

Micro-supercapacitors (MSCs) are promising power solution facilities for miniaturized portable electronic devices. Microfabrication of on-chip MSC with high specific capacitance and high energy density is still a great challenge. Herein, we report a high-performance MnO2/polypyrrole (PPy) microelectrode based MSC (MnO2/PPy-MSC) by modern micromachining technology. Interdigital Au micro current collectors were obtained by photolithography, physical vapor deposition and lift off. A layer of PPy was electrochemically deposited on Au current collectors followed by deposition of urchin-like MnO2 micro/nanostructures. The electrochemical performance of MnO2/PPy-MSC was explored employing LiClO4/PVA gel electrolyte. The assembled MSC demonstrated a high areal capacitance of 13 mF cm-2, an energy density of 1.07 × 10-3 mW h cm-2 and a power density of 0.53 mW cm-2. In addition, the MnO2/PPy-MSC showed an improved cycling stability, retaining 84% of the initial capacitance after 5000 CV cycles at a scan rate of 500 mV s-1. Our proposed strategy provides a versatile and promising method for the fabrication of high-performance MSCs with large-scale applications.

A Universal Electrolyte Formulation for the Electrodeposition of Pristine Carbon and Polypyrrole Composites for Supercapacitors

Electrodeposition of conducting polymer-carbon composites from an electrolyte precursor solution is a facile one-step approach to fabricate device-ready electrodes for energy storage. A key challenge in this approach is the dispersion of the carbon nanomaterials with the aqueous precursor solution with previous approaches either heavily oxidizing the carbon nanomaterials or using high concentrations of anionic surfactants as dopants. However, the former reduces the electrical conductivity of carbon, while the latter reduces the ionic mobility of the conducting polymer due to the large anion size. Herein, for the first time we present a quaternary electrolyte formulation for the fabrication of pristine carbon and polypyrrole (PPy) composites that does not sacrifice either electron or ion mobility. The electrolyte uses lithium perchlorate (20 mM) as a supporting electrolyte and dopant, sodium dodecylbenzenesulfonate at a very low concentration (1.43 mM) as a surfactant, together with pristine carbon nanomaterials and pyrrole monomers. The order of magnitude difference between the concentration of the dopant and surfactant ion allows the as-deposited PPy to be doped predominantly by small-sized and mobile perchlorate anions. Composites of PPy with carbon black, carbon nanotubes, and electrochemical exfoliated graphene (EEG) have been successfully prepared using this new quaternary electrolyte. The as-fabricated PPy/EEG composite electrodes showed a specific capacitance of 348.8 F g^-1 with a high rate capability (190.7 F g^-1 at 71 A g^-1). Supercapacitor devices based on the PPy/EEG composite electrodes exhibit a high rate behavior up to 500 mV s^-1 and a long cycle life of 5000 cycles.

Effect of Deposition Parameters on Electrochemical Properties of Polypyrrole-Graphene Oxide Films

Graphene oxide (GO)-modified polypyrrole (PPy) coatings were obtained by electrochemical methods in the presence of the anionic surfactant, sodium dodecyl sulfate (SDS). The structure, morphology, and electrochemical properties of the coatings were assessed by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry at varying scan rates, respectively. The properties of the obtained coatings were analyzed with the GO and PPy loadings and electrodeposition mode. The hybrid coatings obtained galvanostatically showed a coarser appearance than those deposited by cyclic voltammetry CV mode and improved performance, respectively, which was further enhanced by GO and PPy loading. The capacitance enhancement can be attributed to the SDS surfactant that well dispersed the GO sheets, thus allowing the use of lower GO content for improved contribution, while the choice of suitable electrodeposition parameters is highly important for improving the applicability of GO-modified PPy coatings in energy storage applications.

Multidimensional Hierarchical Fabric-Based Supercapacitor with Bionic Fiber Microarrays for Smart Wearable Electronic Textiles

Flexible textile-based supercapacitors (SCs) have attracted a lot of attention, with the artificial intelligence technology and smart wearable electronic textiles developing rapidly. However, energy-storage performance of common textile-based SCs is always restricted with the low-dimensional substrates (i.e., one-dimensional fibers or two-dimensional fabrics), and hence flexible textile-based SCs with multifarious hierarchical substrates are highly desired. Herein, a multidimensional hierarchical fabric electrode model with a bionic fiber microarray structure has been designed, inspired by the "grasp effect" of the sophisticated arrangement structures of hedgehog spines, and the bionic assembled SCs exhibit an enhanced specific areal capacitance (245.5 mF/cm² at 1 mV/cm²), compared with the planar fabric-based SCs (41.6 mF/cm²), and a high energy density (21.82 μWh/cm² at 0.4 mW/cm²). Besides, the SCs also show a stable capacitance ratio of 83.9% after 10 000 cycles and a mere capacitance loss under different bending states. As a proof of concept, an all-fabric smart electronic switch is fabricated with self-power and wearable properties, along with some other trial applications. Such a hierarchical fabric with a bionic fiber microarray structure is believed to enhance the performance of the assembled SCs. We foresee that the multidimensional hierarchical fabric would bring more promising prospects for flexible textile-based energy-storage systems and be used in smart wearable textile applications.

Electrochemical detection of Salmonella using an invA genosensor on polypyrrole-reduced graphene oxide modified glassy carbon electrode and AuNPs-horseradish peroxidase-streptavidin as nanotag

A rapid and sensitive electrochemical biosensor was constructed to detect Salmonella using invA gene biosensor. The biosensing was based on polyrrole-reduced graphene oxide (PPy-rGO) nanocomposite modified glassy carbon electrode (GCE) and signal amplification with horseradish peroxidase-streptavidin biofunctionalized gold nanoparticles (AuNPs-HRP-SA). PPy-rGO was prepared at 60 °C by chemical reduction of PPy-functionalized graphene oxide (PPy-GO) that was synthesized by in situ polymerization at room temperature. The detection signal was amplified via enzymatic reduction of H₂O₂ in the presence of hydroquinone (HQ) using AuNPs-HRP-SA as nanotag. Under optimal conditions, the differential pulse voltametric (DPV) signal from the biosensor was linearly related to the logarithm of target invA gene concentrations from 1.0 × 10^-16 to 1.0 × 10^-10 M, and the limit of detection (LOD) was 4.7 × 10^-17 M. The biosensor can also detect Salmonella in the range of 9.6 to 9.6 × 10⁴ CFU mL^-1, with LOD of 8.07 CFU mL^-1. The biosensor showed good regeneration ability, acceptable selectivity, repeatability and stability, which bode well as an alternative method for Salmonella screening.

Synthesis of morphology-tunable electroactive biomass/graphene composites using metal ions for supercapacitors

Tannic acid (TA) is a natural polyphenolic biomass, which shows high electro-activity and can be considered for supercapacitor applications. However, the negligible electronic conductivity of TA hinders its direct use as an electrode. In order to achieve the electrochemical activity of TA, herein, a three-dimensional porous TA/graphene composite (TAG) is prepared by mixing TA with graphene oxide (GO) via hydrothermal assembly, and various structural composites are realized by adding metal ions into the system before hydrothermal treatment. Metal ions can chelate with TA molecules and coordinate with GO via electrostatic interactions. As a result, a uniform and well-defined three-dimensional porous network (TAGNi), a regularly arranged scale-like microstructure (TAGCu) and a flower-like structure (TAGFe) are achieved by introducing Ni2+, Cu2+ and Fe3+, respectively. The as-prepared TAG, TAGNi, TAGCu and TAGFe electrodes exhibit a high specific capacitance of 373.6, 412.4, 460.4 and 429.4 F g-1 at 1 A g-1, respectively, and excellent cycling stability. The TAG, TAGNi, TAGCu and TAGFe assembled symmetric supercapacitors display a favorable energy density of 14.76, 16.76, 19.13 and 17.6 W h kg-1 at 300 W kg-1, respectively. The morphology-tunable TA/graphene composites with excellent electrochemical performance are promising for renewable energy storage device applications.

Simultaneous Electrochemical Deposition of Cobalt Complex and Poly(pyrrole) Thin Films for Supercapacitor Electrodes

Supercapacitors are beneficial as energy storage devices and can obtain high capacitance values greater than conventional capacitors and high power densities compared to batteries. However, in order to improve upon the overall cost, energy density, and charge-discharge rates, the electrode material of supercapacitors needs to be fine-tuned with an inexpensive, high conducting source. We prepared a Co(III) complex and polypyrrole (PPy) composite thin films (CoN₄-PPy) that was electrochemically deposited on the surface of a glassy carbon working electrode. Cyclic voltammetry studies indicate the superior performance of CoN₄-PPy in charge storage in acidic electrolyte compared to alkaline and organic solutions. The CoN₄-PPy material generated the highest amount of specific capacitance (up to 721.9 F/g) followed by Co salt and PPy (Co-PPy) material and PPy alone. Cyclic performance studies showed the excellent electrochemical stability of the CoN₄-PPy film in the acidic medium. Simply electrochemically depositing an inexpensive Co(III) complex with a high electrically conducting polymer of PPy delivered a superior electrode material for supercapacitor applications. Therefore, the results indicate that novel thin films derived from Co(III) metal complex and PPy can store a large amount of energy and maintain high stability over many cycles, revealing its excellent potential in supercapacitor devices.

Unveiling high specific energy supercapacitor from layer-by-layer assembled polypyrrole/graphene oxide|polypyrrole/manganese oxide electrode material

A novel layer-by-layer (LBL) based electrode material for supercapacitor consists of polypyrrole/graphene oxide and polypyrrole/manganese oxide (PPy/GO|PPy/MnO₂) has prepared by electrochemical deposition. The formation of LBL assembled nanocomposite is confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction. The field emission scanning electron microscopy images clearly showed that PPy/MnO₂ was uniformly coated on PPy/GO. The PPy/GO|PPy/MnO₂ symmetrical supercapacitor has revealed outstanding supercapacitive performance with a high specific capacitance of 786.6 F/g, an exceptionally high specific energy of 52.3 Wh/kg at a specific power of 1392.9 W/kg and preserve a good cycling stability over 1000 cycles. It is certain that PPy/GO|PPy/MnO₂ has an extraordinary perspective as an electrode for future supercapacitor developments. This finding contributes to a significant impact on the evolution of electrochemical supercapacitor.

Polypyrrole Nanowires with Ordered Large Mesopores: Synthesis, Characterization and Applications in Supercapacitor and Lithium/Sulfur Batteries

In this work, we report the preparation of polypyrrole nanowires with ordered large mesopores (OMPW) by a simple chemical polymerization method from dual templates synthesized by self-assembling silica nanospheres in porous anodic aluminum oxide (AAO) membrane channels. The obtained OMPW showed a large surface area (231.5 m² g⁻¹), high aspect ratio, and interconnected large mesopores (~23 nm). The OMPW was tested as a supercapacitor electrode and showed a specific capacitance of 453 F g⁻¹ at 0.25 A g⁻¹. A sulfur/OMPW (S/OMPW) cathode was fabricated via a simple solution method and a heat-treatment process for lithium/sulfur batteries (LSBs). The S/OMPW composite delivered a large discharge capacity reaching 1601 mAh g⁻¹ at the initial cycle, retaining 1014 mAh g⁻¹ at the 100th cycle at 0.1 C. The great electrochemical performances of the OMPW capacitor electrode and S/OMPW composite were attributed to the large specific surface areas and interconnected mesopores that could supply more active sites for the electrochemical reaction and facilitate mass transfer.

High-Performance Flexible In-Plane Micro-Supercapacitors Based on Vertically Aligned CuSe@Ni(OH)2 Hybrid Nanosheet Films

The orientation and hybridization of ultrathin two-dimensional (2D) nanostructures on interdigital electrodes is vital for developing high-performance flexible in-plane micro-supercapacitors (MSCs). Despite great progress has been achieved, integrating CuSe and Ni(OH)₂ nanosheets to generate advanced nanohybrids with oriented arrangement of each component and formation of porous frameworks remains a challenge, and their application for in-plane MSCs has not been explored. Herein, the vertically aligned CuSe@Ni(OH)₂ hybrid nanosheet films with hierarchical open channels are skillfully deposited on Au interdigital electrodes/polyethylene terephthalate substrate via a template-free sequential electrodeposition approach, and directly employed to construct in-plane MSCs by choosing polyvinyl alcohol-LiCl gel as both the separator and the solid electrolyte. Because of the unique geometrical structure and combination of intrinsically conductive CuSe and battery-type Ni(OH)₂ components, such hybrid nanosheet films can not only resolve the poor conductivity and re-stacking problems of Ni(OH)₂ nanosheets but also create the 3D electrons or ions transport pathway. Thus, the in-plane MSCs device fabricated by such hybrid nanosheet films exhibits high volumetric specific capacitance (38.9 F cm^-3). Moreover, its maximal energy and power density can reach 5.4 mW h cm^-3 and 833.2 mW cm^-3, superior to pure CuSe nanosheets, and most of reported carbon materials and metal hydroxides/oxides/sulfides based in-plane MSCs ones. Also, the hybrid nanosheet films device shows excellent cycling performance, good flexibility, and mechanical stability. This work may shed some light on optimizing 2D electrode materials and promote the development of flexible in-plane MSCs or other energy storage systems.

Laser-Assisted Large-Scale Fabrication of All-Solid-State Asymmetrical Micro-Supercapacitor Array

The micro-supercapacitors are of great value for portable, flexible, and integrated electronic equipments. Here, the large-scale and integrated asymmetrical micro-supercapacitor (AMSC) array is fabricated in virtue of the laser direct writing and electrodeposition technology. The AMSC shows the ideal flexibility, high areal specific capacitance (21.8 mF cm^-2 ), and good rate capability. Moreover, its energy density reaches 12.16 µW h cm^-2 , outperforming most micro-supercapacitors reported previously. Meanwhile, large-scale series-connected AMSCs are integrated on the flexible substrates (e.g., indium tin oxide-polyethylene terephthalate film), which can power a veriety of the commercial electronics. The combination of AMSCs array, solar cell, and electronic device proves the feasibility for practical application in the portable, flexible, and integrated electronic equipments.

Dandelion-like nickel/cobalt metal-organic framework based electrode materials for high performance supercapacitors

Metal-organic frameworks (MOFs), serving as a promising electrode material in the supercapacitors, have attracted tremendous interests in recent years. Here, through modifying the molar ratio of the Ni²⁺ and Co²⁺, we have successfully fabricated Ni-MOF and Ni/Co-MOF by a facile hydrothermal method. The Ni/Co-MOF with a dandelion-like hollow structure shows an excellent specific capacitance of 758 F g^-1 at 1 A g^-1 in the three-electrode system. Comparing with Ni-MOF, the obtained Ni/Co-MOF has a better rate capacitance (89% retention at 10 A g^-1) and cycling life (75% retention after 5000 circulations). Besides, the assembled asymmetric supercapacitor based on Ni/Co-MOF and active carbon exhibits a high specific energy density of 20.9 W h kg^-1 at the power density of 800 W kg^-1. All these results demonstrate that the mixed-metal strategy is an effective way to optimize the morphology and improve the electrochemical property of the MOFs.

Nanocellulose/polypyrrole aerogel electrodes with higher conductivity via adding vapor grown nano-carbon fibers as conducting networks for supercapacitor application

Nanocellulose-based conductive materials have been widely used as supercapacitor electrodes. Herein, electrode materials with higher conductivity were prepared by in situ polymerization of polypyrrole (PPy) on cellulose nanofibrils (CNF) and vapor grown carbon fiber (VGCF) hybrid aerogels. With increase in VGCF content, the conductivities of CNF/VGCF aerogel films and CNF/VGCF/PPy aerogel films increased. The CNF/VGCF₂/PPy aerogel films exhibited a maximum value of 11.25 S cm⁻¹, which is beneficial for electron transfer and to reduce interior resistance. In addition, the capacitance of the electrode materials was improved because of synergistic effects between the double-layer capacitance of VGCF and pseudocapacitance of PPy in the CNF/VGCF/PPy aerogels. Therefore, the CNF/VGCF/PPy aerogel electrode showed capacitances of 8.61 F cm⁻² at 1 mV s⁻¹ (specific area capacitance) and 678.66 F g⁻¹ at 1.875 mA cm⁻² (specific gravimetric capacitance) and retained 91.38% of its initial capacitance after 2000 cycles. Furthermore, an all-solid-state supercapacitor fabricated by the above electrode materials exhibited maximum energy and power densities of 15.08 W h Kg⁻¹, respectively. These electrochemical properties provide great potential for supercapacitors or other electronic devices with good electrochemical properties.

The electrochemical performances of nanocellulose-based electrode materials were improved via building nano-carbon conducting networks.