One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Single-step hydrothermal synthesis of WO3-MnO2 composite as an active material for all-solid-state flexible asymmetric supercapacitor

In present study, new strategy is employed to build composite nanostructure and asymmetric configuration to enhance the capacitive performance of supercapacitor device. The WO₃-MnO₂ composite with mesoporous structure is prepared by single-step hydrothermal method and used to gain superior electrochemical performance in asymmetric configuration. A binder-free and additive-less WO₃-MnO₂ composite electrode exhibits high specific capacitance of 609 F g^?1 at a scan rate of 5 mV s^?1. The flexible asymmetric supercapacitor device with WO₃-MnO₂ as a positive electrode and WO₃ as a negative electrode demonstrates stable operating potential window of 1.4 V with specific capacitance of 103 F g^?1 at a scan rate of 5 mV s^?1 and energy density of 24.13 Wh kg^?1 at power density of 915 W kg^?1. Furthermore, WO₃-MnO₂//WO₃ device exhibits good cycle life with capacity retention of 95% after 2500 cycles and excellent mechanical flexibility. These results reveal the potential of WO₃-MnO₂ composite electrode for fabrication of high-performance supercapacitors.     

Fabrication of core-shell NiMoO4@MoS2 nanorods for high-performance asymmetric hybrid supercapacitors

In this work, core-shell NiMoO₄@MoS₂ nanorods were successfully fabricated via a facile two-step hydrothermal method. By inheriting the merits of high electrical conductivity from MoS₂ nanosheets and high pseudocapacitive activity from NiMoO₄ nanorods, the hierarchical NiMoO₄@MoS₂ nanocomposite was endowed with improved electrical conductivity, enlarged specific surface area and enriched porosity, consequently enabling fast ion/electron transport and rapid Faradaic reactivity. Benefited from the synergism of NiMoO₄ and MoS₂, the NiMoO₄@MoS₂ electrode was superior to the NiMoO₄ and MoS₂ electrode, achieving specific capacitance of 2246.7 F g⁻¹, as well as showing good rate performance and improved cyclic stability (88.4% capacitance retention after 5000 cycles). The asymmetric supercapacitor device composed of the NiMoO₄@MoS₂ nanorods and hierarchical porous carbon exhibited a high energy density of 47.5 Wh kg⁻¹ at a power density of 0.44 kW kg⁻¹. The device also showed superior long-term cycling stability, retaining 80.2% of initial capacitance after 10 000 cycles. This work provides a simple strategy for scalable synthesis of integrated nanostructures, which holds great promise for the development of advanced supercapacitors.     

Supercapacitive properties of activated carbon electrode using ammonium based proton conducting electrolytes

In this study, we demonstrated the usefulness of proton conducting electrolytes (such as ammonium thiocyanate (NH₄SCN) and ammonium nitrate (NH₄NO₃)) for electrochemical energy storage devices using activated carbon (AC) as the electrode material. The cyclic voltammetry analysis revealed the presence of rectangular shaped cyclic voltammograms indicating the presence of electrical double layer capacitance in AC electrode using NH₄SCN and NH₄NO₃ electrolytes. The mechanism of charge-storage in AC electrode using the proton conducting electrolytes has been studied in detail using electrochemical impedance spectroscopy (Nyquist and Bode plots). The galvanostatic charge-discharge analysis revealed that a maximum specific capacitance of AC electrode using NH₄SCN and NH₄NO₃ electrolytes was found to be 136.75 mF cm^?2 and 113.38 mF cm^?2 at a current density of 0.5 mA cm^?2. This study would open a new avenue for the use of ammonium based proton conducting electrolytes for supercapacitor applications.     

Co(OH)2 nanoparticles deposited on reduced graphene oxide nanoflake as a suitable electrode material for supercapacitor and oxygen evolution reaction in alkaline media

In this work, cobalt hydroxide nanoparticles are simply synthesized (size is about 50 nm) and deposited on the reduced graphene oxide nanoflake by the hydrothermal method. Then, the ability of glassy carbon electrode modified with this low-cost nanocomposite is examined as a supercapacitor and oxygen evolution electrocatalysts in 2.0 mol L^?1 KOH by a three-electrode system. The modified electrode as a pseudocapacitor with potential windows of 0.35 V, exhibits a powerful specific capacitance (235.20 F g^?1 at 0.1 A g^?1 current density), energy density, stability (about 90% of the initial capacitance value maintain after 2000 cycles at 1.0 A g^?1) and fast charge/discharge ability. Furthermore, the modified electrode displays a good electrocatalytic activity for oxygen evolution reaction with a current density of 10.0 mA cm^?2 at 1.647 V, small Tafel slope of 56.5 mV dec^?1, good onset potential of 1.521 V vs. RHE and suitable durability.     

Investigation on energy storage and conversion properties of multifunctional PANI-MWCNT composite

Polyaniline-multiwalled carbon nanotube (PANI-MWCNT) composite synthesized through chemical polymerization is investigated as a possible electrode material for supercapacitor as well as an electro-catalyst for hydrogen evolution reaction (HER) in acidic medium. UV–Vis spectroscopy, FTIR spectroscopy and field emission scanning electron microscopy (FESEM) have been used to characterize the electrode material. The binder-free electrodes were prepared and they exhibit a specific capacitance of 540.29 F g^?1 at a scan rate of 2 mV s^?1 in 1 M H₂SO₄ electrolyte. The material exhibits excellent pseudocapacitive behaviour due to the presence of PANI with long-term cyclic stability of 87.4% retention after 5000 cycles. PANI-MWCNT composite also shows good HER activity, with overpotential of ?395 mV.     

Boosting the capacitance of NiCo2O4 hierarchical structures on nickel foam in supercapacitors

A facile method of directly growing NiCo₂O₄ hybrid hierarchical nanostructures on nickel foam is developed by a hydrothermal and post heat-treatment method without using any surfactant, stabilizer or organic binder. Due to the rich porous nanostructures, relative large specific surface area (177.71 m² g^?1) of the NiCo₂O₄ hybrid structure and efficient electrical contact with the conductive nickel substrate, the NiCo₂O₄NF hybrid electrode shows significantly enhanced specific capacitance (3105.1 F g^?1 at 1 A g^?1), outstanding rate properties (1621.3 F g^?1 at 20 A g^?1 and 1191.5 F g^?1 at 50 A g^?1) and high energy density (95.26 Wh kg^?1). This facile and effective design method opens up new possibilities for producing binder-free electrodes in high-performance electrochemical supercapacitors and miniaturized devices.     

Enhanced performance of supercapacitor based on boric acid doped PVA-H2SO4 gel polymer electrolyte system

Proton Conducting gel polymer electrolytes (GPEs) are taking much attention compared to liquid electrolytes for supercapacitor applications because of their physical properties, electrochemical stability and operation over broader temperature window. Among different GPEs PVA/acid blend electrolytes such as PVA/H₂SO₄, has drawn great attention in recent years. In this study, PVA-H₂SO₄-H₃BO₃ GPE was introduced for electric-double layer capacitor (EDLCs) application, in which electrospun free-standing carbon nanofibers are used as electrodes. Introduced PVA-H₂SO₄-H₃BO₃ GPE serves as both separator and the electrolyte in the supercapacitor. Symmetric Swagelok cells including GPEs were assembled via using two electrode arrangements and the electrochemical properties were searched. Electrochemical performance studies demonstrated that PVA-H₂SO₄-H₃BO₃ GPE had a maximum specific capacitance (Cs) of 134 F g^?1 and showed great capacitance retention (%100) after 1000 charge/discharge cycles. Furthermore, PVA-H₂SO₄-H₃BO₃GPE yielded an energy density of 67 Wh kg^?1 with a corresponding power density of 1000 W kg^?1 at a current density of 1 A g^?1.     

Synthesis of CuCo2S4 nanosheet arrays on Ni foam as binder-free electrode for asymmetric supercapacitor

Recently more and more concerns have been paid on ternary metal sulfides for use in supercapacitors because of their better electrochemical performances compared with binary counterparts. In this work, CuCo₂S₄ nanosheet arrays on Ni foam were prepared by a sequential ion-exchange strategy under hydrothermal conditions, where Co₃O₄ was converted into Co₄S₃ by an anion-exchange reaction between Co₃O₄ and S^2? ions, subsequently the Co₄S₃ was transformed into CuCo₂S₄ through a cation-exchange reaction with Cu²⁺ ions. The as-prepared CuCo₂S₄ was characterized by powder X-ray diffraction, high-resolution X-ray photoelectron spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The CuCo₂S₄ arrays were composed of interconnected thin nanosheets with thickness of about 10 nm. The CuCo₂S₄ nanosheet arrays on Ni foam were directly employed as a binder-free electrode showing a high specific capacitance of 3132.7 F g^?1 at a current density of 1 A g^?1. Besides, an asymmetric supercapacitor based on this synthesized CuCo₂S₄ electrode as positive electrode and active carbon as negative electrode can deliver a high energy density of 46.1 Wh kg^?1 at a power density of 991.6 W kg^?1, and exhibits good rate capability and cycling stability.     

One-step synthesis of 3D sulfur-doped porous carbon with multilevel pore structure for high-rate supercapacitors

In this work, three-dimensional (3D) interconnected S-doped porous carbon materials are fabricated using bio-waste sodium lignosulfonate as carbon and sulfur precursor by in situ carbonization and subsequent KOH activation process. The as-obtained S-PC-50 has high specific surface area of 1592 m² g^?1, high S weight percentage up to 5.2 wt% and interconnected porous framework consisting of micro-, meso- and macropores. As a result, the S-PC-50 exhibits a high specific capacitance of 320 F g^?1 at 0.2 A g^?1, excellent rate performance with 76.5% capacitance retention after a current density increasing from 2 A g^?1 (200 F g^?1) to 100 A g^?1 (153 F g^?1) and 99% capacitance retention after 10,000 cycles at 5 A g^?1. Besides, the symmetric supercapacitor can deliver a high energy density up to 8.2 Wh kg^?1 at 50 W kg^?1.     

Nickel-cobalt layered double hydroxide ultrathin nanosheets coated on reduced graphene oxide nonosheets/nickel foam for high performance asymmetric supercapacitors

Here in, for the first time, we report a new and simple procedure for preparing reduced graphene oxide/nickel-cobalt double layered hydroxide composite on the nickel foam (Ni-Co LDH/rGO/NF) via a fast and simple two-step electrochemical method including potentiostatic routes in the presence of CTAB as a cationic surfactant. Graphene oxide coated nickel foam prepared by simple immersion method. After that, the prepared electrode reduced electrochemically to obtain rGO/NF electrode. Finally, the rGO/NF electrode was used as cathode for electrodeposition of Ni-Co LDH in the presence of CTAB as cationic surfactant. The prepared electrodes were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDS), Brunauer, Emmett and Teller (BET) and electrochemical techniques such as voltammetry (CV), galvanostatic charge-discharge curves (GCD) and electrochemical impedance spectroscopy (EIS). The resulting electrode which prepared in the presence of CTAB afforded extremely high specific capacitance of 2133.3 F g^?1 at a current density of 4 A g^?1. FE-SEM, TEM and EDS mapping results showed that Ni-Co LDH nanosheets uniformly covered the surface of rGO/NF in the presence of CTAB, and is closely packed and thinner in thickness compared with the sample prepared in similar way without using surfactant. Such new thin and dense morphology facilitates electrolyte ions diffusion through the prepared electrode. A good cycling stability was obtained for the electrode in alkaline media. EIS measurements showed low values of internal resistance (R_s) and charge transfer resistance (R_ct), indicating that the prepared nanocomposite is a promising candidate for supercapacitor applications. The asymmetric supercapacitor (ASC) based on the Ni-Co LDH/CTAB/rGO/NF as a positive electrode and rGO/NF as a negative electrode was assembled and it exhibited a C_s of 71.4 F g^?1 at a current density of 2 A/g and correspondingly energy density of as high as 68 Wh kg^?1.     

Preparation of mesoporous Ni2P nanobelts with high performance for electrocatalytic hydrogen evolution and supercapacitor

The development of bifunctional electrochemically-active materials for both hydrogen evolution reaction (HER) and supercapacitors enables the possibility to integrate energy storage and production into one single system. Here, we report a novel bifunctional mesoporous Ni₂P nanobelt-like architecture prepared via the hydrothermal synthesis of Ni(SO₄)_0.3(OH)_1.4 nanobelt precursor and subsequent low temperature phosphorization process under Ar atmosphere. Composed of numerous cross-linked Ni₂P nanoparticles, the as-obtained Ni₂P nanobelts exhibit a two dimensional leaf-like morphology, allowing remarkable enhancement of mesoporosity as well as active surface area. The HER electrocatalytic test in acid medium show a current density of 16 mA cm^?2 at an overpotential of 187 mV, Tafel slope of 62 mV dec^?1 and long-term durability. Investigation of this Ni₂P nanobelts as supercapacitor materials in 2M KOH electrolyte display a high specific capacity ranging from 1074 F g^?1 at 0.625 A g^?1 to 554 F g^?1 at 25 A g^?1, and notable cycling life with 86.7% retention after 3000 cycles at 10 A g^?1. With the simplicity of the synthetic routine and the outstanding performance as both HER catalysts and supercapacitors, the Ni₂P nanobelts provide promising potential for energy devices.     

Ni@NC@NiCo-LDH nanocomposites from a sacrificed template Ni@NC@ZIF-67 for high performance supercapacitor

A metal porous carbon (Ni@NC) supported nickel/cobalt layered double hydroxide (NiCo-LDH) (Ni@NC@NiCo-LDH) with a cauliflower morphology was synthesized by a successive double template method. At first a nickel metal-organic framework (Ni-MOF) was prepared and used as a sacrifice template to produce metal porous carbon (Ni@NC). Then the prepared conductive porous carbon material was exploited as a substrate for in-situ growing of ZIF-67 on its surface. Lastly the obtained Ni@NC@ZIF-67 was further used as a sacrifice template to prepare the final electrode material Ni@NC@NiCo-LDH by Ni²⁺ etching and co-precipitation. The cooperation of Ni@NC with excellent conductivity and NiCo-LDH with superior pseudocapacitive property yielded a synergistic effect, which effectively improved the electrochemical performance of the resulted electrode material. And the special flower morphology exposed more redox active sites and provided proper charge transport path for enhanced electrochemical performance. The prepared Ni@NC@NiCo-LDH exhibited a high specific capacitance of 1761.8 F·g^?1 at the current density of 1 A·g^?1. The assembled Ni@NC@NiCo-LDH//AC asymmetric supercapacitor also displayed an acceptable energy density (39.27 Wh·kg^?1 at the power density of 757.21 W·kg^?1) and ultrahigh cycling stability (94.74% capacitance retention after 25000 cycles at 10 A g^?1).     

Microwave synthesis of Sb2Se3/polyacrylonitrile-based carbon fiber mat electrodes for high-performance flexible capacitors and hydrogen evolution reaction

The development of bifunctional electrodes with good capacitive performance and efficient hydrogen evolution reaction activity is one of the potential solutions to combat energy depletion. In this study, flexible polyacrylonitrile-based carbon fiber mat with nitrogen doping and oxygen-containing functional group carbon structure was selected as the flexible substrate, and binder-free flexible Sb₂Se₃/polyacrylonitrile-based carbon fiber mat composite electrode was successfully prepared within 120 s using microwave synthesis. The electrode not only has a capacitance of 478.0C g^?1 and retains 97.4% of the initial capacitance after 50,000 charge–discharge tests but also exhibits good HER activity of low overpotential (152 mV) and Tafel slope (78.4 mV/dec) in alkaline electrolyte. The performance of the assembled flexible asymmetric supercapacitor is almost unaffected by bending up to 180°. The device has an energy density of 21.3 Wh kg^?1 at a power density of 800.0 W kg^?1, indicating that the electrode has good prospects for portable energy storage applications.     

Polyaniline-silver-manganese dioxide nanorod ternary composite for asymmetric supercapacitor with remarkable electrochemical performance

Metal oxide incorporated with a conductive polymer have shown great potential as high-performance energy storage devices. In this report, polyaniline wrapped silver decorated manganese dioxide (PANI/Ag@MnO₂) nanorods were successfully synthesized and used as positive electrode material. Cyclic voltammetry, galvanostatic charge discharge and electrochemical impedance spectroscopy were employed to investigate the electrochemical activities. The overall result demonstrates that as prepared PANI/Ag@MnO₂ nanorod performed better supercapacitor activities compared to Ag@MnO₂ and pure MnO₂. The PANI/Ag@MnO₂ nanocomposite exhibited a high specific capacitance of 1028.66 F g^?1 at a current density of 1 A g^?1 (nearly close to the theoretical capacitance of MnO₂). A detail investigation of the synergic effect of PANI, Ag and MnO₂ on electrochemical properties is presented sequentially. The assembled (PANI/Ag@MnO₂//AC) asymmetric supercapacitor device showed a high energy density of 49.77 W h kg^?1 at power density of 1599.75 W kg^?1. The facile and cost-effective production of PANI/Ag@MnO₂ demonstrates a high specific capacitance and energy density with long life cycle introduces this material as a prospective candidate for energy management.     

Synthesis of hierarchical tube-like yolk-shell Co3O4@NiMoO4 for enhanced supercapacitor performance

Transition metal oxides with three-dimensional architectures have attracted great interest as high-performance supercapacitor electrodes. In this work, tube-like yolk-shell Co₃O₄@NiMoO₄ composite were prepared via a two-step synthesis for the first time. Ultrathin NiMoO₄ nanosheets arrayed randomly to form porous shell, which fully covered around Co₃O₄ fibers with interspaces between core and shell. Benefitting from unique structure and chemical composition, the Co₃O₄@NiMoO₄ composite as supercapacitor electrodes exhibited enhanced specific capacitance of 913.25 F g^?1 at high current density of 10 A g^?1 and large capacitance retention of 88% with current density increased from 0.5 to 20 A g^?1 as well as remarkable cycling stability. In addition, NiCo₂O₄@NiMoO₄ and NiFe₂O₄@NiMoO₄ composites with similar morphologies were obtained. Namely, this work exhibits a general approach to reasonable construct and preparation hierarchical structure for high performance supercapacitor electrodes.     

Designing a hierarchical structure of nickel-cobalt-sulfide decorated on electrospun N-doped carbon nanofiber as an efficient electrode material for hybrid supercapacitors

The intent of designing and exploring novel active electrode materials is to enhance the electrochemical performance of supercapacitors. Herein, a hierarchical structure of nickel-cobalt-sulfide nanostructures (NiCo₂S₄) decorated on the electrospun N-doped carbon nanofiber (CNF), NiCo₂S₄@CNF, is manipulated using a one-step and simple hydrothermal approach. The fabricated hierarchical structure of the NiCo₂S₄@CNF is featured by a large surface area and a high porosity that serve as ion diffusion channels. Therefore, it manifests high specific capacitance and specific capacity values of 377.2 C g^?1 and 754.4 F g^?1 at a current density of 1 A g^?1, respectively. Furthermore, a NiCo₂S₄@CNF//CNF hybrid supercapacitor in which a positive electrode of NiCo₂S₄@CNF is assembled with a negative electrode of CNF to estimate the electrochemical performance of the NiCo₂S₄@CNF. As a result, the device has a superior energy density of 65.6 and 52.5 Wh kg^?1 at a power density of 665 and 1313.8 W kg^?1, respectively. Moreover, the device reveals good stability with capacitance retention of 72% after 3000 charge/discharge cycles. These outstanding results enable the designed hierarchical structure of the NiCo₂S₄@CNF to be a promising electrode material for supercapacitors (SCs) applications.     

Microwave-synthesized self-supporting CoSe2/carbon fiber felt electrode for ultra–high cycling life flexible supercapacitors

Flexible electrodes are candidate for portable and wearable electronic storage devices. In this work, high-performance flexible self-supporting CoSe₂/carbon fiber felt (CoSe₂/CFF) electrode was prepared via the microwave method without any binder. The CoSe₂/CFF electrodes exhibited superior electrochemical performance (621 F g^?1 at 1 A g^?1) and an ultra-high cycling life (84.7% capacitance retention after 100,000 cycles). When the CoSe₂/CFF was used as the positive electrode for the flexible supercapacitor, the assembled device exhibited an outstanding energy density of 22.43 W h Kg^?1 at a power density of 823.12 W kg^?1. Because of the excellent mechanical stability of the device, it maintained 91.3% of its initial C after bending from 0° to 180°. The CoSe₂/CFF proposed in this work shows electrode promising applicability to a low-cost, small-sized wearable and portable energy storage device.     

Nitrogen and oxygen dual-doped porous carbons prepared from pea protein as electrode materials for high performance supercapacitors

Porous carbons as electrode materials are highly desired for use in energy storage/conversion devices. Herein, the development of a series of highly porous nitrogen and oxygen co-doped carbons by using pea protein (PP) as a cost-effective, sustainable and nitrogen-rich precursor is reported. Pea protein derived carbons (PPDCs) have been prepared by applying a straightforward two-step synthetic route including pyrolysis and KOH-chemical activation. Potassium hydroxide has been employed to generate porosity and introduce oxygen functionalities into the framework of carbon. The heteroatoms doping content and porosity parameters have been tuned by varying the synthesis temperature and activator to precursor ratio. The carbon obtained with optimal synthetic parameters (T = 800 °C and KOH/Precursor = 4) featured the highest surface area, the maximal pore volume and N-/O doping level of 3500 m² g^?1, 1.76 cm³ g^?1, and 2.5-/17.9 at%, respectively. PPDC-4-800 as supercapacitor presented a very high specific capacitance (413 F g^?1 at 1.0 A g^?1 in 1 M KOH), remarkable cycling stability (92% retention after 20000 cycles) and outstanding rate capability (210 F g^?1 at 30 A g^?1). The cooperative effects of the well-developed porous architecture and surface modification of PPDCs resulted in enhanced electrochemical performances, suggesting their potential application for energy storage devices.