Converting of the 2D graphene to its 3D by chicken red blood cells as sheets separator for construction supercapacitor electrode

Here, we report on a facile green and scalable method for the fabrication of porous 3D graphene as a well-known carbon-based material used in many energy storage devices. Chicken red blood cells were used as sheets spacer and heteroatom sources in the construction of 3D graphene. First, the red blood cells were separated from the blood and mixed with graphene oxide. Then, the mixture was freeze-dried and carbonized at 700 °C. The resulted 3D graphene containing heteroatoms was used as a supercapacitor electrode modifier on a glassy carbon electrode and tested with various electrochemical techniques. The supercapacitor electrode showed a specific capacitance of 330 F g⁻¹ at a current density of 1 A g⁻¹, maximum power density of 1958 W kg⁻¹, and maximum energy density of 85 Wh kg⁻¹. Furthermore, the supercapacitive performances were tested in a two-electrode symmetrical system which exhibited a specific capacitance of 238 F g⁻¹ for 1 A g⁻¹. It also showed a power density of 2200 W kg⁻¹ and an appreciable energy density of 160 Wh kg⁻¹. The excellent electrochemical behavior of 3D graphene indicates the promising abilities of the composite for other applications such as biosensors, batteries, electrocatalysts, etc.     

Synthesis and performance of nickel hydroxide nanodiscs for redox supercapacitors

Herein, we report the facile synthesis of β-Ni(OH)₂ nanodiscs by chemical precipitation method and their use in supercapacitors. β-Ni(OH)₂ nanodiscs are characterized by FTIR, XRD, FESEM, XPS and TGA analysis. Morphological analysis revealed the uniform nanodisc morphology of β-Ni(OH)₂. The supercapacitor behavior is evaluated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy measurements in 1-M aqueous KOH solution with 0- to 0.6-V potential window. The specific capacitance of β-Ni(OH)₂ nanodiscs is found to be 400 F g⁻¹. The energy and power densities of the β-Ni(OH)₂ nanodiscs are found to be 7.15 W h kg⁻¹ and 1716 W kg⁻¹, respectively, at the current density of 1 A g⁻¹. The cycle life test shows the good stability of the electrode with 83 % retention capacitance even after 1500 cycles.

     

Mechanochemical synthesis of poly(2,5-dimethoxy aniline) nanobelts and its electrochemical performance in hybrid supercapacitors

A solvent-free mechanochemical route for the preparation of poly(2,5-dimethoxyaniline) hydrochloride nanostructures is developed and reported in the article. High conductivity, good crystallinity, and nanostructured morphology are observed for the prepared polymer. This polymeric powder is utilized as a cathode material in hybrid supercapacitor and its electrochemical performance is evaluated and discussed in this short report. The maximum specific capacitance of the poly(2,5-dimethoxyaniline) hydrochloride/activated carbon hybrid supercapacitor is found to be 125 F g⁻¹ at 1 mA cm⁻² current density. The cell delivers a specific energy as high as 50 Wh kg⁻¹ at a specific power of 97 W kg⁻¹ and also exhibits an excellent cycle performance with more than 99% coulombic efficiency and the maintenance of 85% of its initial capacitance after 1,000 cycles.     

Effect of growth time of hydrothermally grown cobalt hydroxide carbonate on its supercapacitive performance

We present the time-dependent synthesis of cobalt hydroxide carbonate nanorods by hydrothermal method with a systematic increase of different parameters such as specific surface area and specific capacitance as a function of different synthesis time. Morphological characterization of the cobalt hydroxide carbonate nanorods were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that variation of the time of reaction plays a crucial role in the transformation of samples’ morphology. Cobalt hydroxide carbonate nanorods synthesized with 12 h reaction time, which is the reaction just before the materials transforms into cobalt oxide under the same synthesis conditions exhibited the highest specific capacitance of 466 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH electrolyte and also showed excellent stability with ∼99% capacitance retention after 2000 cycles at a current density of 10 A g⁻¹. Based on the above results, the cobalt hydroxide carbonate nanorods show a considerable potential as electrodes materials for supercapacitor applications.     

Longitudinal unzipping of carbon nanotubes and their electrochemical performance in supercapacitors

The capacitive properties of graphene nanoribbons (GNRs) with different reduction levels were investigated. GNRs have been synthesized through thermal reduction of oxidized GNRs in the temperature range 100–400 °C. Oxidized GNRs were synthesized by longitudinal unzipping of multi-walled carbon nanotubes (MWCNTs) by means of chemical treatments. Scanning electron microscopy and transmission electron microscopy observations showed, that the efficient tube unzipping yielded improved effective surface area without any tube annihilation by the unzipping process of MWCNTs. Electrochemical studies indicated that through unzipping of MWCNTs, specific capacitance increased from 8 to 28 F g⁻¹ at discharge current density of 0.5 A g⁻¹, confirming increased active surface area and increased defect density in the MWCNTs surface. Unzipping of MWCNTs resulted in decreased rate capability of the electrode because of low electrical conductivity due to oxidization during the unzipping process. Thermal reduction of unzipped sample affected both specific capacitance and rate capability of electrodes. The highest specific capacitance of 62 F g⁻¹ at discharge current density of 0.5 A g⁻¹ was obtained for the sample unzipped and thermally annealed at about 150 °C. The amount of oxygen-containing groups was shown to be an important factor influencing the performance of the GNRs. These results make unzipped MWCNTs promising electrode materials for supercapacitor applications.     

Free-standing 3D Co3O4@NF micro-flowers composed of porous ultra-long nanowires as an advanced cathode material for supercapacitor

The development of smart structured cathode materials for supercapacitors (SCs) has sparked tremendous interest. However, the appropriate design to achieve high capacitance and energy density-based cathode materials remains a major problem for energy storage systems. This article describes the effective synthesis of self-supported 3D micro-flowers composed of ultrathin nanowires array of Co₃O₄ on Ni foam (NF) using hydrothermal conditions (Co₃O₄@NF). The mesoporous Co₃O₄@NF with a high surface area, providing a rich active state for the Faraday redox reaction and increasing the diffusion rate of the electrolyte ions. The optimized Co₃O₄@NF-16h electrode exhibited supreme electrochemical performance by delivering a high specific capacitance of 1878, (1127) and 1200 (720 C g⁻¹) F g⁻¹ at 1.0 and 20 A g⁻¹, respectively. The Co₃O₄@NF electrode retained good capacitance stability of 91% over 10000 cycles at 20 A g⁻¹ with excellent rate-performance of 67% at 20 folded high current values. The obtained results for the Co₃O₄@NF electrode are presented the enhanced pseudocapacitive performance, indicating the substantial potential for high-performance supercapacitor applications.     

Fabrication of Ni-Co binary oxide/reduced graphene oxide composite with high capacitance and cyclicity as efficient electrode for supercapacitors

Nickel-cobalt binary oxide/reduced graphene oxide (G-NCO) composite with high capacitance is synthesized via a mild method for electrochemical capacitors. G-NCO takes advantages of reduced graphene oxide (RGO) and nickel-cobalt binary oxide. As an appropriate matrix, RGO is beneficial to form homogeneous structure and improve the electron transport ability. The binary oxide owns more active sites than those of nickel oxide and cobalt oxide to promote the redox reaction. Attributed to the well crystallinity, homogeneous structure, increased active sites, and improved charge transfer property, the G-NCO composite exhibits highly enhanced electrochemical performance compared with G-NiO and G-Co₃O₄ composites. The specific capacitance of the G-NCO composite is about 1750 F g^?1 at 1 A g^?1 together with capacitance retention of 79 % (900/1138 F g^?1) over 10,000 cycles at 4 A g^?1. To research its practical application, an asymmetric supercapacitor with G-NCO as positive electrode and activated carbon as negative electrode was fabricated. The asymmetric device exhibits a prominent energy density of 37.7 Wh kg^?1 at a power density of 800 W kg^?1. The modified G-NCO composite shows great potential for high-capacity energy storage.     

Preparation and electrochemical investigation of the cobalt hydroxide carbonate/activated carbon nanocomposite for supercapacitor applications

Cobalt hydroxide carbonate/activated carbon (AC) composite was successfully synthesized by hydrothermal method. Morphological characterizations of cobalt hydroxide carbonate/AC composite were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results show that the cobalt hydroxide carbonate nanorods are well dispersed on the AC. Due to the synergistic effects arising from cobalt hydroxide carbonate nanorods and AC, the electrochemical performances of pure cobalt hydroxide carbonate material is significantly improved by the addition of AC. The composite shows a specific capacitance of 301.44 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH electrolyte and exhibits good cycling stability. Based on the above results, the cobalt hydroxide carbonate/AC composite shows a considerable promise as electrode for electrochemical applications.     

Amorphous Cobalt Coordination Nanolayers Incorporated with Silver Nanowires: A New Electrode Material for Supercapacitors

The 2D amorphous cobalt coordination framework/silver nanowires nanocomposites (A‐CoL/Ag NC) are successfully synthesized by one‐step solution agitation at room temperature. The experimental data reveal that the hybrid provides sufficient contact between active materials and electrolyte, and facilitates the transfer of ions/electrons, resulting in high specific capacitance, high output potential, great rate capacity at high current density, and good cycle stability. As supercapacitor electrode materials, the as‐prepared A‐CoL/Ag NC electrode exhibits a great specific capacitance which can reach up to 1467 mF cm^?2 at 1.0 mA cm^?2, and 1060 mF cm^?2 even at 10.0 mA cm^?2. The A‐CoL/Ag NC// activated carbon asymmetric supercapacitor (AC ASC) displays a maximum energy density (110 W h kg^?1 at 760 W kg^?1) and maximum power density (6410 W kg^?1 at 63 W h kg^?1) in 3.0 m KOH. Moreover, the developed solid‐state A‐CoL/Ag NC//AC ASC has a broad operated potential window within 0–1.6 V, long cycle life (95.2% after cycling 7000 cycles), delivering an energy density of 151 W h kg^?1 (at 790 W kg^?1), and a power density of 7972 W kg^?1 (at 70 W h kg^?1). The well‐synthesized nanocomposite provides a novel way to synthesize prominent electrode materials for supercapacitors.     

Facile Construction of 3D Reduced Graphene Oxide Wrapped Ni3S2 Nanoparticles on Ni Foam for High‐Performance Asymmetric Supercapacitor Electrodes

3D reduced graphene oxide (rGO)‐wrapped Ni₃S₂ nanoparticles on Ni foam with porous structure is successfully synthesized via a facile one‐step solvothermal method. This unique structure and the positive synergistic effect between Ni₃S₂ nanoparticles and graphene can greatly improve the electrochemical performance of the NF@rGO/Ni₃S₂ composite. Detailed electrochemical measurements show that the NF@rGO/Ni₃S₂ composite exhibits excellent supercapacitor performance with a high specific capacitance of 4048 mF cm^?2 (816.8 F g^?1) at a current density of 5 mA cm^?2 (0.98 A g^?1), as well as long cycling ability (93.8% capacitance retention after 6000 cycles at a current density of 25 mA cm^?2). A novel aqueous asymmetric supercapacitor is designed using the NF@rGO/Ni₃S₂ composite as positive electrode and nitrogen‐doped graphene as negative electrode. The assembled device displays an energy density of 32.6 W h kg^?1 at a power density of 399.8 W kg^?1, and maintains 16.7 W h kg^?1 at 8000.2 W kg^?1. This outstanding performance promotes the as‐prepared NF@rGO/Ni₃S₂ composite to be ideal electrode materials for supercapacitors.     

Cobalt terephthalate MOF-templated synthesis of porous nano-crystalline Co3O4 by the new indirect solid state thermolysis as cathode material of asymmetric supercapacitor

In this work, two different types of Co₃O₄ nano-crystals were synthesized by (i) conventional direct solid state thermolysis of cobalt terephthalate metal-organic framework (MOF-71) and (ii) new indirect solid state thermolysis of Co(OH)₂ derived by alkaline aqueous treatment of MOF-71. The products were then characterized by X-ray diffraction technique (XRD), Fourier transforms infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Reflection electron energy loss spectroscopy (REELS), Brunauer, Emmett, and Teller (BET), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. By REELS analysis the energy band gap of MOF-71 was determined to be 3.7 eV. Further, electrochemical performance of each Co₃O₄ nanostructure was studied by the cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a three-electrode system in KOH electrolyte. An asymmetric supercapacitor was fabricated using indirect Co₃O₄ nanoparticles as cathode and electrochemically reduced graphene oxide as anode, and the electrochemical properties were studied and showed a high energy density of 13.51 Wh kg⁻¹ along with a power density of 9775 W kg⁻¹ and good cycling stability with capacitance retention rate of 85% after 2000 cycles.     

A facile synthesis about amorphous CoS<Subscript>2</Subscript> combined with first principle analysis for supercapacitor materials

The structure and electrochemical properties of amorphous CoS₂ and crystalline CoS₂ have been studied with both experimental characterization and theoretical calculations. In the field of experimental characterization, a facile chemical precipitation method is used to synthesize amorphous and crystalline CoS₂ samples with calcining temperatures of 200 and 280 °C, respectively. Comparing with crystalline CoS₂, amorphous structure of CoS₂ manifests great electron conductivity, effective porous structure, and exhibit a high specific capacitance of 996.16 F g^?1 at current density of 0.5 A g^?1, excellent rate capability of 89.8% retention with the current density ranging from 0.5 to 5 A g^?1, and a great cycling stability of 97.6% retention after 10,000 cycles at 2 A g^?1 in 6 mol L^?1 KOH aqueous electrolyte. In the area of theoretical calculation, we used the first principle and obtained the band structure with band gap of 0.00369 eV and DOSs with high locality of D-orbital from 69.88689 electrons/eV main peak, in the CoS₂ amorphous. The result confirms that amorphous CoS₂ have higher conductivity than crystalline CoS₂ in theory. In addition, the as-assembled asymmetric supercapacitor of Co-S-200//AC also exhibits the maximum specific capacitance of 104 F g^?1 within a cell voltage from 0 to 1.5 V at current density of 0.5 A g^?1 and indicates a great cycling stability of 95.68% and excellent capacitance behavior. All results demonstrate a great potential of amorphous CoS₂ active material for supercapacitors.     

Nickel–cobalt oxide/activated carbon composite electrodes for electrochemical capacitors

Nanostructured synthesis of nickel–cobalt oxide/activated carbon composite by adapting a co-precipitation protocol was revealed by transmission electron microscopy. X-ray diffraction analysis confirmed that nickel–cobalt oxide spinel phase was maintained in the pure and composite phases. Cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy were employed to elucidate the electrochemical properties of the composite electrodes in 1.0 M KCl. The specific capacitance which was the sum of double-layer capacitance of the activated carbon and pseudocapacitance of the metal oxide increased with the composition of nickel–cobalt oxide before showing a decrement for heavily-loaded electrodes. Utilisation of nickel–cobalt oxide component in the composite with 50 wt. % loading displayed a capacitance value of ～59 F g^?1. The prepared composite electrodes exhibited good electrochemical stability.     

Controllable synthesis of layered Co–Ni hydroxide hierarchical structures for high-performance hybrid supercapacitors

A facile solvothermal method is developed for synthesizing layered Co–Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co–Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co_0.5Ni_0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g⁻¹ at a galvanic current density of 1 A g⁻¹ and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co–Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.     

Electrical studies on ionic liquid-based gel polymer electrolyte for its application in EDLCs

Ionic liquid-based gel polymer electrolyte (GPE) has been synthesized using standard solution cast technique. Different weight percent of ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl) and liquid electrolyte, ethylene carbonate (EC)–propylene carbonate (PC)–tetra ethyl ammonium tetra fluoro borate (TEABF₄) was incorporated in polymer, poly(vinylidene fluoride-co-hexafluoro propylene (PVdF-HFP) to obtain mechanically stable gel polymer electrolyte film (GPE) having maximum conductivity of ~10⁻³ S cm⁻¹ at room temperature, which is acceptable from device fabrication point of view. Potential window and ionic transference number has been obtained to examine the potential limit and ionic characteristics of optimized GPE system. Temperature dependence behavior of electrical conductivity curve follows Arrhenius nature in the temperature range of 303–373 K. Pattern of dielectric constant and its loss as a function of frequency and temperature have been studied and is being explained on the basis of electrode interfacial polarization effect. Frequency-dependent conductivity spectra obey the Jonscher’s power law. Further, optimized composition of GPE has been tested successfully for its application in supercapacitor fabrication with activated charcoal as an electrode material. Maximum specific capacitance of 118.6 mF cm⁻² equivalent to single electrode specific capacitance of 61.7 F g⁻¹ have been observed for the optimized GPE film.

     

Ultrasound-assisted facile one-pot synthesis of ternary MWCNT/MnO2/rGO nanocomposite for high performance supercapacitors with commercial-level mass loadings

Commercial application of supercapacitors (SCs) requires high mass loading electrodes simultaneously with high energy density and long cycle life. Herein, we have reported a ternary multi-walled carbon nanotube (MWCNT)/MnO₂/reduced graphene oxide (rGO) nanocomposite for SCs with commercial-level mass loadings. The ternary nanocomposite was synthesized using a facile ultrasound-assisted one-pot method. The symmetric SC fabricated with ternary MWCNT/MnO₂/rGO nanocomposite demonstrated marked enhancement in capacitive performance as compared to those with binary nanocomposites (MnO₂/rGO and MnO₂/MWCNT). The synergistic effect from simultaneous growth of MnO₂ on the graphene and MWCNTs under ultrasonic irradiation resulted in the formation of a porous ternary structure with efficient ion diffusion channels and high electrochemically active surface area. The symmetric SC with commercial-level mass loading electrodes (∼12 mg cm⁻²) offered a high specific capacitance (314.6 F g⁻¹) and energy density (21.1 W h kg⁻¹ at 150 W kg⁻¹) at a wide operating voltage of 1.5 V. Moreover, the SC exhibits no loss of capacitance after 5000 charge−discharge cycles showcasing excellent cycle life.     

Electrochemical characterization on layered lithium ruthenate for electrochemical supercapacitors

Electrochemical characteristics of lithium ruthenate (Li_xRuO_2+0.5x·nH₂O) for electrochemical capacitors' electrode material were first examined in this paper by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Results show that Li_xRuO_2+0.5x·nH₂O has electrochemical capacitive characteristic within the potential range of − 0.2–0.9 V (vs. SCE) in 1 M Li₂SO₄ solution. The capacitance mainly arises from pseudo-capacitance caused by lithium ions' insertion/extraction into/out of the Li_xRuO_2+0.5x·nH₂O electrode. The specific capacitance of 391 F g^− 1 can be delivered at 1 mA charge–discharge current for Li_xRuO_2+0.5x·nH₂O electrode with an energy density of 65.7 W h kg^− 1. This material also exhibits an excellent cycling performance and there is no attenuation of capacitance over 600 cycles.     

Facile hydrothermal synthesis of ultrahigh-aspect-ratio V2O5 nanowires for high-performance supercapacitors

Ultrahigh-aspect-ratio V₂O₅ nanowires were successfully prepared using [VO(O₂)₂(OH₂)]⁻ as the starting material by a template-free hydrothermal route without the addition of organic surfactant or inorganic ions. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The results revealed that the peroxovanadium (V) complexes can be easily transformed to V₂O₅ nanowires by this hydrothermal route. The uniform nanowires were with width about 50 nm and length about dozens of micron. The BET analysis showed the V₂O₅ nanowires had a high specific surface area of 25.6 m² g⁻¹. The synthesized V₂O₅ nanowires performed a high capacitance of 351 F g⁻¹ when used as supercapacitor electrode in 1 mol L⁻¹ LiNO₃.     

Hydrophilic polyaniline nanofibrous architecture using electrosynthesis method for supercapacitor application

An electrosynthesis process of hydrophilic polyaniline nanofiber electrode for electrochemical supercapacitor is described. The TGA–DTA study showed polyaniline thermally stable up to 323 K. Polyaniline nanofibers exhibit amorphous nature as confirmed from XRD study. Smooth interconnected fibers having diameter between 120–125 nm and length typically ranges between 400–500 nm observed from SEM and TEM analysis. Contact angle measurement indicated hydrophilic nature of polyaniline fibers. Optical study revealed the presence of direct band gap with energy 2.52 eV. The Hall effect measurement showed room temperature resistivity ∼3 × 10⁻⁴ Ω cm and Hall mobility 549.35 cm⁻²V⁻¹ s⁻¹_. The supercapacitive performance of nanofibrous polyaniline film tested in 1 M H₂SO₄ electrolyte and showed highest specific capacitance of 861 F g⁻¹ at the voltage scan rate of 10 mV/s.