Amaryllis-like NiCo2S4 nanoflowers for high-performance flexible carbon-fiber-based solid-state supercapacitor

Low-cost dynamic materials for Faradaic redox reactions are needed for high-energy storage supercapacitors. A simple and cost-effective hydrothermal process was employed to synthesize amaryllis-like NiCo₂S₄ nanoflowers. The sample was characterized by X-ray powder diffraction, Brunauer–Emmett–Teller method, scanning electron microscopy, and transmission electron microscopy. NiCo₂S₄ nanoflowers were coated onto carbon fiber fabric and used as a binder-free electrode to fabricate a solid-state supercapacitor compact device. The solid-state supercapacitor exhibited excellent electrochemical performance, including high specific capacitance of 360 F g⁻¹ at scan rate of 5 mV s⁻¹ and high energy density of 25 W h kg⁻¹ at power density of 168 W kg⁻¹. In addition, the supercapacitor possessed high flexibility and good stability by retaining 90% capacitance after 5000 cycles. The high conductivity and Faradic-redox activity of NiCo₂S₄ nanoflowers resulted in high specific energy and power. Thus, NiCo₂S₄ nanoflowers are promising pseudocapacitive materials for low-cost and lightweight solid-state supercapacitors.     

Straightforward synthesis of hierarchical Co3O4@CoWO4/rGO core–shell arrays on Ni as hybrid electrodes for asymmetric supercapacitors

Hierarchical Co₃O₄@CoWO₄/rGO core/shell nanoneedles arrays are successfully grown on 3D nickel foam using a simple, effective method. By virtue of its unique structure, Co₃O₄@CoWO₄/rGO demonstrates an enhanced specific capacitance of 386 F g⁻¹ at 0.5 A g⁻¹ current density. It can be used as an integrated, additive-free electrode for supercapacitors that boasts excellent performance. As illustration, we assemble an asymmetric supercapacitor (ASC) using the as-prepared Co₃O₄@CoWO₄/rGO as the positive electrode and activated carbon as the negative electrode. The optimized ASC displays a maximum energy density of 19.99 Wh kg⁻¹ at a power density of 321 W kg⁻¹. Furthermore, the ASC also presents a remarkably long cycle life along with 88.8% specific capacitance retention after 5000 cycles.     

Facile synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres as high-performance electrode materials for supercapacitors

In this work, we reported the synthesis of three dimensional flower-like Co₃O₄@MnO₂ core-shell microspheres by a controllable two-step reaction. Flower-like Co₃O₄ microspheres cores were firstly built from the self-assembly of Co₃O₄ nanosheets, on which MnO₂ nanosheets shells were subsequently grown through the hydrothermal decomposition of KMnO₄. The MnO₂ nanosheets shells were found to increase the electrochemical active sites and allow faster redox reaction kinetics. Based on these advantages, when used as an electrode for supercapacitors, the prepared flower-like Co₃O₄@MnO₂ core-shell composite electrode demonstrated a significantly enhanced specific capacitance (671 F g⁻¹ at 1 A g⁻¹) as well as improved rate capability (84% retention at 10 A g⁻¹) compared with the pristine flower-like Co₃O₄ electrode. Moreover, the optimized asymmetric supercapacitor device based on the flower-like Co₃O₄@MnO₂//active carbon exhibited a high energy density of 34.1 W h kg⁻¹ at a power density of 750 W kg⁻¹, meaning its great potential application for energy storage devices.     

3D NiCo2S4 nanorod arrays as electrode materials for electrochemical energy storage application

It is essential to develop new electrode materials for electrochemical energy storage to meet the increasing energy demands, reduce environmental pollution and develop low-carbon economy. In this work, binder-free NiCo₂S₄ nanorod arrays (NCS NRAs) on nickel foam electrodes are prepared by an easy and low energy-consuming route. The electrodes exhibit superior electrochemical properties both for alkaline and Li-ion batteries. In 3 M KOH electrolyte, the NCS NRAs achieve a specific capacity of 240.5 mA h g⁻¹ at a current density of 0.2 A g⁻¹, and 105.7 mA h g⁻¹ after 1500 cycles at the current density of 5 A g⁻¹ with capacity retention of 87.3%. As the anode for LIBs, it shows a high initial capacity of 1760.7 mA h g⁻¹ at the current density of 100 mA g⁻¹, corresponding coulombic efficiency of 87.6%, and a rate capacity of 945 mA h g⁻¹ when the current density is improved 10 times. Hence, the NiCo₂S₄ nanorod arrays are promised as electrode materials with competitive performance.     

Preparation of scale-like nickel cobaltite nanosheets assembled on nitrogen-doped reduced graphene oxide for high-performance supercapacitors

Ultrathin scale-like nickel cobaltite (NiCo₂O₄) nanosheets supported on nitrogen-doped reduced graphene oxide (N-rGO) are successfully synthesized through a facile co-precipitation of Ni²⁺ and Co²⁺ in the presence of sodium citrate and hexamethylenetetramine and subsequent calcination treatment. The composition and morphology of NiCo₂O₄ nanosheets@nitrogen-doped reduced graphene oxide (denoted as NiCo₂O₄ NSs@N-rGO) were characterized by Scanning electron microscope, Transmission electron microscope, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller and thermogravimetric analysis. The thickness of NiCo₂O₄ nanosheets anchored on the reduced graphene oxide is around 4 nm. The capacitance of NiCo₂O₄ NSs@N-rGO is evaluated by cyclic voltammogram and galvanostatic charge/discharge with the result that the NiCo₂O₄ NSs@N-rGO could deliver a specific capacitance of 1540 F g⁻¹ after 1000 cycles at 10 A g⁻¹.     

NiCo2O4 nanosheets and nanocones as additive-free anodes for high-performance Li-ion batteries

Development of novel electrode materials with high energy and power densities for lithium-ion batteries (LIBs) is the key to meet the demands of electric vehicles. Transition metal oxides that can react with large amounts of Li⁺ for electrochemical energy storage are considered promising anode materials for LIBs. In this work, NiCo₂O₄ nanosheets and nanocones on Ni foam have been synthesized via general hydrothermal growth and low-temperature annealing treatment. They exhibit high rate capacities and good cyclic performance as LIB anodes owing to their architecture design, which reduces ion and electron transport distance, expands the electrode–electrolyte contact, increases the structural stability, and buffers volume change during cycles. Notably, NiCo₂O₄ nanosheets deliver an initial capacity of 2239 mAh g⁻¹ and a rate capacity of 964 mAh g⁻¹ at current densities of 100 and 5000 mA g⁻¹, respectively. The corresponding values of nanocones are 1912 and 714 mAh g⁻¹. Hence, the as-synthesized NiCo₂O₄ nanosheets and nanocones, which are carbon-free and binder-free with higher energy densities and stronger connections between active materials and current collectors for better stability, are promising for use in advanced anodes for high-performance LIBs.     

Decoration of carbon cloth by manganese oxides for flexible asymmetric supercapacitors

Here we describe the production of carbon cloth coated with MnO₂ nanosheets or MnOOH nanorods through a normal temperature reaction or a hydrothermal approach, respectively. Of note, the electrochemical performance of MnO₂-coated carbon cloth was better (429.2 F g⁻¹) than that of MnOOH-coated carbon cloth. When the MnO₂-coated carbon cloth is introduced as the positive electrode and the Fe₂O₃-coated carbon cloth as the negative electrode, a flexible asymmetric supercapacitor was obtained with an energy density of 22.8 Wh kg⁻¹ and a power density of 159.4 W kg⁻¹. Therefore, such a hierarchical MnO₂-coated carbon cloth nanocomposite is a promising high-performance electrode for flexible supercapacitors.     

Core/shell-structured nickel cobaltite/onion-like carbon nanocapsules as improved anode material for lithium-ion batteries

Core/shell-structured nanocapsules consisting of a nickel cobaltite (NiCo₂O₄) nanoparticle core encapsulated in an onion-like carbon (C) shell are synthesized by arc-discharge and air-annealing methods. Void spaces between NiCo₂O₄ core and the carbon shell are observed in the NiCo₂O₄/C nanocapsules. Lithium-ion batteries fabricated using the nanocapsules as the anode material exhibit enhanced initial coulombic efficiency of 82.3% and specific capacity of 1197.2 mA h/g after 300 cycles at 0.2 A g⁻¹ current density. Varying the rate of charge/discharge current from 0.2 to 4 A/g does not show negative effects on the recycling stability of the nanocapsules and a recoverable specific capacity as high as 1270.4 mA h/g is obtained. The introduction of the onion-like C shell and the presence of the void spaces are found to increase the contact areas between the electrolyte and the nanocapsules for improved electrolyte diffusion, to enhance the electronic conductivity and ionic mobility of the NiCo₂O₄ nanoparticle cores, and to accommodate the change in volume during the lithium-ion insertion/extraction process.     

Materials and electrode designs of high-performance NiCo2S4/Reduced graphene oxide for supercapacitors

NiCo₂S₄ is one of the most promising bimetallic sulfides for use in energy-storage systems, but more studies are needed to endow NiCo₂S₄ with a high electrochemical reaction capability and reversibility. In this work, we present rationally materials design of an optimal NiCo₂S₄ nanoparticle in a reduced graphene oxide (RGO) matrix as a NiCo₂S₄/RGO nanocomposite. Furthermore, we report the improvements in the materials technology, demonstrating the NiCo₂S₄/RGO nanocomposite electrode with an excellent specific capacitance of 963–700 F g⁻¹ at 1–15 A g⁻¹, high capacitance retention of 70%, and long cycle life of 3000 cycles. The practical application is showcased in an asymmetric supercapacitor with a high active-material loading. The NiCo₂S₄/RGO nanocomposite shows a high energy density of 31 Wh kg⁻¹ at a power density of 987 W kg⁻¹ and maintains an excellent density of 23 Wh kg⁻¹ at a high power density of 7418 W kg⁻¹. The outstanding electrochemical utilization and stability of the NiCo₂S₄/RGO nanocomposite confirm that our systematic optimization in the materials science and technology in terms of the active-material synthesis, the electrode development, and the device design/fabrication would benefit the future development of high-performance supercapacitors.     

Ni@NiCo2O4 core/shells composite as electrode material for supercapacitor

A novel Ni@NiCo₂O₄ core/shells structure consisting of the Ni microspheres skeletons and nanosheet-like NiCo₂O₄ skins was designed and investigated as the electrochemical electrode for supercapacitor. Due to the unique architecture with Ni microspheres as the highly conductive cores improving the electrical conductivity of electrode and external nanosheet-like NiCo₂O₄ shells as the efficient electrochemical active materials facilitating the contact between the electrode and electrolyte, the as-prepared Ni@NiCo₂O₄ exhibited excellent electrochemical performance with high specific capacity of 597 F g⁻¹ (1 A g⁻¹) as well as remarkable capacitance retention of 96% (3000 cycles). These impressive results pave the way to design high-performance electrode materials for energy storage.     

Synthesis of 3D nanoflower-like mesoporous NiCo2O4 N-doped CNTs nanocomposite for solid-state hybrid supercapacitor; efficient material for the positive electrode

In this research work, we report a novel method for developing ternary NiCo₂O₄ compounds using deep eutectic solvents (DESs) and a strategy for improving their pseudocapacitive performance. NiCo₂O₄ composites with N-doped carbon nanotubes (NCNTs) were fabricated on Ni foam using a hydrothermal method. The electrochemical performance of the NiCo₂O₄ was altered with the change in the reaction temperature. The composite of NiCo₂O₄ and NCNTs demonstrated a maximum value of specific capacity of 303 mAh g⁻¹ at a scan rate of 5 mV s⁻¹. The specific capacity for the composite compound was 1.3-fold greater than that of the pristine NiCo₂O₄ sample. For practical applications, we constructed a flexible solid-state hybrid supercapacitor comprised of NiCo₂O₄/NCNTs//activated carbon (AC) cells with an excellent energy density of 12.31 Wh kg⁻¹, outstanding power density of 8.96 kW kg⁻¹, and tremendous electrode stability. The three-dimensional mesoporous nanoflowers and nanotubes-like nanostructures of NiCo₂O₄ are well-suited for use in hybrid devices as well as convenient for flexible electronic devices.     

Influence of sintering aids and excess Lithium on the conductivity of perovskite-type Li3/8Sr7/16Zr1/4Nb3/4O3 solid electrolyte

Perovskite-structured Li_3/8Sr_7/16Zr_1/4Nb_3/4O₃ solid-state Lithium-conductors were prepared by conventional solid-state reaction method. Influence of sintering aids (Al₂O₃, B₂O₃) and excess Lithium on structure and electrical properties of Li_3/8Sr_7/16Zr_1/4Nb_3/4O₃ (LSNZ) has been investigated. Their crystal structure and microstructure were characterized by X-ray diffraction analysis and scanning electron microscope, respectively. The conductivity and electronic conductivity were evaluated by AC-impedance spectra and potentiostatic polarization experiment. All sintered compounds are cubic perovskite structure. Optimal amount of excess Li₂CO₃ was chosen as 20 wt% because of the total conductivity of LSNZ-20% was as high as 1.6×10⁻⁵ S cm⁻¹ at 30 °C and 1.1×10⁻⁴ S cm⁻¹ at 100 °C, respectively. Electronic conductivity of LSNZ-20% is 2.93×10⁻⁸ S cm⁻¹, nearly 3 orders of magnitude lower than ionic conductivity. The density of solid electrolytes appears to be increased by the addition of sintering aids. The addition of B₂O₃ leads to a considerable increase of the total conductivity and the enhancement of conductivity is attributed to the decrease of grain-boundary resistance. Among these compounds, LSNZ-1 wt%B₂O₃ has lower activation energy of 0.34 eV and the highest conductivity of 1.98×10⁻⁵ S cm⁻¹ at 30 °C.     

Synthesis and characterization of S2O82 −/ZnFexAl2 − xO4 solid acid catalysts for the esterification of acetic acid with n-butanol

New spinel-types of S₂O₈^2 −/ZnFe_xAl_2 − xO₄ solid acid catalysts were prepared by sol–gel method. Their catalytic performances for the synthesis of n-butyl acetate were investigated. The catalysts were characterized by means of XRD, IR, XPS, FT-IR of adsorbed pyridine and NH₃-TPD. The experimental results showed that S₂O₈^2 −/ZnFe_xAl_2 − xO₄ solid acid catalysts maintained the spinel structure as well as the support of ZnFe_xAl_2 − xO₄. Fe^3 + ions were well incorporated and highly dispersed into the spinel lattice. S₂O₈^2 −/ZnFe_0.15Al_1.85O₄ exhibited the maximum conversion of acetic acid with 98.2%. Moreover, S₂O₈^2 −/ZnFe_0.15Al_1.85O₄ showed better reusability, which remained above 72.7% conversion of acetic acid even after being used five times.     

Effect of core-shell reversal on the structural,magnetic and adsorptive properties of Fe2O3-GO nanocomposites

Effect of core-shell reversal on the nanocomposites of graphene oxide (GO) and ferric oxide (Fe₂O₃) was studied. Fe₂O₃@GO core-shell nanosheets were synthesized by sonication method, while the GO@Fe₂O₃ core-shell nanospheres by employing N,N′-dicyclohexylcarbodimide as the binding agent for the wrapping of GO sheets on pre-formed Fe₂O₃ nanoparticles (NPs). The phase composition, crystallinity and morphology of the nanocomposites were characterized by FT-IR, TEM, SEM-EDS, VSM, BET surface area study and XRD techniques. The saturation magnetization (M_s) was 1.25 and 0.51 emu g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO respectively owing to the dependence of magnetic properties on the reversal of core-shell. BET analysis revealed the surface area of 100.32 m² g⁻¹ and 45.69 m² g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO nanocomposites respectively. The fabricated nanocomposites were analyzed as adsorbents for the uptake of Pb (II) ions. The impact of various factors affecting adsorption process such as pH, adsorbent dose, contact time, temperature and metal ion concentration was also investigated. GO@Fe₂O₃ core-shell nanospheres showed a higher adsorption capacity for Pb (II) ions as compared to Fe₂O₃@GO core-shell nanosheet with the maximum adsorption capacities (q_m) of 303.0 and 125.0 mg g⁻¹ respectively. The equilibrium data was estimated by Freundlich, Langmuir, D-R and Temkin isotherm models. Thermodynamic analysis confirmed the spontaneous and exothermic nature of the adsorption process. The adsorption kinetics was significantly fitted to pseudo-second order model. The results confirmed that core-shell reversal can significantly alter the adsorptive properties of Fe₂O₃-GO nanocomposite     

3D network-like porous MnCo2O4 by the sucrose-assisted combustion method for high-performance supercapacitors

3D network-like porous MnCo₂O₄ nanostructures have been successfully fabricated through a facile and scalable sucrose-assisted combustion route followed by calcination treatment. Benefiting from its advantages of the unique 3D network-like architectures with large specific surface area (216.15 m² g⁻¹), abundant mesoporosity (2–50 nm) and high electronic conductivity, the as-prepared MnCo₂O₄ electrode displays a high specific capacitance of 647.42 F g⁻¹ at a current density of 1 A g⁻¹, remarkable capacitance retention rate of 70.67% at current density of 10 A g⁻¹ compared with 1 A g⁻¹, and excellent cycle stability (only 6.32% loss after 3000 cycles). The excellent electrochemical performances coupled with facile and cost effective method will render the as-fabricated 3D network-like porous MnCo₂O₄ as a promising electrode material for supercapacitors.     

Honeycomb-like NiCo2O4@Ni(OH)2 supported on 3D N−doped graphene/carbon nanotubes sponge as an high performance electrode for Supercapacitor

In order to increase the energy density of supercapacitor, a new kind electrode material with excellent structure and outstanding electrochemical performance is highly desired. In this article, a new type of three-dimensional (3D) nitrogen-doped single-wall carbon nanotubes (SWNTs)/graphene elastic sponge (TRGN?CNTs?S) with low density of 0.8 mg cm^?3 has been successfully prepared by pyrolyzing SWNTs and GO coated commercial polyurethane (PU) sponge. In addition, high performance electrode of the honeycomb-like NiCo₂O₄@Ni(OH)₂/TRGN-CNTs-S with core-shell structure has been successfully fabricated through hydrothermal method and then by annealing treatment and electrochemical deposition method, respectively. Benefited from 3D structural feature, the compressed NiCo₂O₄@Ni(OH)₂/TRGN-CNTs-S electrode exhibits high gravimetric and volumetric capacitance of 1810 F g^?1, 847.7 F cm^?3 at 1 A g^?1. The high rate performance and long-term stability was also obtained. Furthermore, an asymmetric supercapacitor using NiCo₂O₄@Ni(OH)₂/TRGN-CNTs-S cathode and NGN/CNTs anode delivered high gravimetric and volumetric energy density of 54 W h kg^?1 at 799.9 W kg^?1 and 37 W h L^?1 at 561.5 W L^?1. In summary, an excellent electrochemical electrode with new elastic 3D SWNTs/graphene supports and binder free pseudocapacitive materials was introduced.     

Hollow core–shell ZnMn2O4 microspheres as a high-performance anode material for lithium-ion batteries

The hollow core–shell ZnMn₂O₄ microspheres are successfully prepared by a solvothermal carbon templating method and then a annealing process. The crystal phase and particle morphology of resultant ZnMn₂O₄ microspheres are characterized by XRD and TEM. The electrochemical properties of the ZnMn₂O₄ microspheres as an anode material are investigated for lithium ion batteries. The results show that the ZnMn₂O₄ microspheres exhibit a reversible capacity of 855.8 mA h g⁻¹ at a current density of 200 mA g⁻¹ after 50 cycles. Even at 1000 mA g⁻¹, the reversible capacity of the ZnMn₂O₄ microspheres is still kept at 724.4 mA h g⁻¹ after 60 cycles. The enhanced electrochemical performance suggests the promising potential of the hollow core–shell ZnMn₂O₄ microspheres in lithium-ion batteries.     

Effects of B2O3 on microstructure and ionic conductivity of Li6.5La3Zr1.5Nb0.5O12 solid electrolyte

Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZN) garnet-type structure was synthesized at low temperature with B₂O₃ addition by solid state reaction method. The effects of B₂O₃ content on the formation, microstructure, ionic conductivity and activation energy of the LLZN solid electrolytes have been investigated by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and alternate current (AC) impedance spectroscopy. The cubic LLZN phase was obtained after calcining at 850 °C for 6 h and no phase evolution was observed after sintering at 1100 °C for 6 h. The relative density and lithium ion conductivity increased first and then decreased with increasing B₂O₃ content, reaching the maximum value of 92.4% and 1.86×10⁻⁴ S cm⁻¹ respectively in the sample with 1.4 wt% B₂O₃. By contrast, the activation energy reached a minimum value of ~31.5 kJ mol⁻¹.     

Two-dimensional mesoporous carbon sheet-like framework material for high-rate supercapacitors

Two-dimensional mesoporous carbon sheet-like framework (MCSF) material has been prepared using mesoporous SiO₂ nanosheet as template and coal tar pitch as carbon precursor. MCSF sheets consisting of numerous mesopores have a specific surface area of 582.7 m² g⁻¹. As a result, the MCSF electrode possesses a maximum specific capacitance of 264 F g⁻¹ at 5 mV s⁻¹, excellent rate capability (74% retention ratio at 1000 mV s⁻¹), and impressive cycling stability with 91% initial capacitance retained after 5000 cycles at 200 mV s⁻¹ in 6 mol L⁻¹ KOH. MCSF symmetric supercapacitor exhibits a maximum energy density of 9.6 Wh kg⁻¹ at 5 mV s⁻¹ and a maximum power density of 119.4 kW kg⁻¹ based on the total mass of the two electrodes in 1 mol L⁻¹ Na₂SO₄ electrolyte.     

Ionic conductivity of Mn2+ doped dense tin pyrophosphate electrolytes synthesized by a new co-precipitation method

Mn²⁺-doped Sn_1−xMn_xP₂O₇ (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at <150 °C. The dopant Mn²⁺ acts as a sintering aid and leads to dense Sn_1−xMn_xP₂O₇ samples on sintering at 1100 °C. Though conductivity of Sn_1−xMn_xP₂O₇ samples in the ambient atmosphere is 10⁻⁹–10⁻⁶ S cm⁻¹ in 300–550 °C range, it increases significantly in humidified (water vapor pressure, pH₂O = 0.12 atm) atmosphere and reaches >10⁻³ S cm⁻¹ in 100–200 °C range. The maximum conductivity is shown by Sn_0.88Mn_0.12P₂O₇ with 9.79 × 10⁻⁶ S cm⁻¹ at 550 °C in ambient air and 2.29 × 10⁻³ S cm⁻¹ at 190 °C in humidified air. It is observed that the humidification of Sn_1−xMn_xP₂O₇ samples is a slow process and its rate increases at higher temperature. The stability of Sn_1−xMn_xP₂O₇ samples is analyzed.