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Abstract Birnessite-type MnO 2 synthesized on the surface of carbon nanotubes (CNTs) via facile hydrothermal reflux technique to produce MnO 2 -CNT nanocomposite and 3D microporous nanostructured activated carbon (AC) derived from cork (Quercus Suber) with good microstructural, morphological and electrochemical properties are herein reported. A hybrid supercapacitor device comprising of MnO 2 -CNT nanocomposite as positive electrode and AC as the negative electrode was successfully fabricated and tested for energy storage application. The device displayed a maximum working potential of up to 2 V due to the excellent synergistic contribution from the MnO 2 -CNT nanocomposite and AC material derived from cork (Quercus Suber). The fabricated device displayed good electrochemical performance having an energy density of ∼25 Wh Kg−1 that corresponds to a power density of 500 W Kg−1 at a current density of 0.5 A g−1 in a 1 M Li 2 SO 4 aqueous neutral electrolyte. The device exhibited an excellent stability of ∼100% coulombic efficiency after 10,000 charge-discharge cycles and excellent capacitance retention after potentiostatic floating test for 60 h. Graphical abstract Image Highlights • Birnessite-type manganese oxide decorated on uncapped carbon nanotubes was synthesized via facile. • Activated carbon (AC) was derived from a cork (Quercus Suber). • A hybrid device was successfully fabricated using MnO 2 -CNT as the positive electrode and AC as negative electrode. • The electrode materials exhibited good electrochemical performance. [ABSTRACT FROM AUTHOR]

Multidimensional CoMoO 4 @Ni(OH) 2 nanocomposite materials are fabricated on the nickel modified surface and channels of an ordered macro-porous electrode plate (OMEP) by a multistep high temperature hydrothermal method as the supercapacitor electrode in a high power density energy storage device. The effects, morphology, capacitive properties, and formation mechanism of the CoMoO 4 @Ni(OH) 2 composite materials are systematically investigated. Compared to nanostructured nickel grown on the OMEP or CoMoO 4 @Ni(OH) 2 on nickel plate with the same area, the CoMoO 4 @Ni(OH) 2 /OMEP shows enhanced electrochemical energy storage properties such as high energy capacitance of 8.55 F cm −2 (1812.42 F g −1 ) at 2 mA cm −2 and good cycling stability of 87.42% capacity retention after 5000 cycles. An asymmetrical supercapacitor (ASC) device is assembled with a polyethylene (PE) membrane, CoMoO 4 @Ni(OH) 2 /OMEP, and active carbon covered nickel foam. The ASC with the CoMoO 4 @Ni(OH) 2 /OMEP has an energy density of 9.66 Wh Kg −1 even at a power density of 3000 W Kg −1 as well as stable power characteristics with 86.5% retention after 10,000 cycles at a current of 0.06 A. The device produces large instantaneous power after charging at 2.8 V for 10 s one ASC can power a 5 mm red LED with high efficiency. [ABSTRACT FROM AUTHOR]

Hybrid supercapacitors, which combine a capacitive negative electrode and a faradaic positive electrode operating in an aqueous media, have many potential applications such as frequency regulation on the electrical grid, in particular when used in conjunction with intermittent energy sources. The purpose of this work is to study alternative designs to the aforementioned hybrid devices, by using composite materials which combine faradaic and capacitive contributions in the same electrode in order to maximize both energy and power densities. Cu 2 O:graphene composite materials have been synthesized using a simple precipitation technique in order to improve the energy of capacitive graphene-based negative electrode materials. Cuprous oxide (Cu 2 O) has been chosen due to its high theoretical capacity of 375 mAh.g −1 associated with an active electrochemical window in the range −0.85 V to −0.20 V vs Hg/HgO (1 M KOH), thus being a potential candidate to serve as a negative electrode to combine with the known carbon/Ni(OH) 2 positive electrode in internal hybridized cell. An interesting initial capacity of more than 275 mAh g −1  has been obtained for the Cu 2 O:graphene composite material when cycled in a 6 M KOH solution at 0.1 mV s −1 , despite a progressive fading of the specific capacity upon cycling. [ABSTRACT FROM AUTHOR]

Mixed transition metal oxides have attracted great attention due to their improved properties over simple oxides in energy storage applications. Herein, we report facile hydrothermal synthesis of novel porous NiCoMn ternary metal oxide flakes with reduced graphene oxide (NCMO_rGO) and their application in high performance aqueous-based energy storage devices. The effect of reaction time on composition and morphology was studied by X-ray diffraction, Raman spectroscopy, thermal gravimetric analysis, transmission electron microscopy, and N 2 ad/de-sorption measurements. Accordingly, a high specific surface area of 200 m 2  g −1 was achieved for the optimized sample. The sample was electrochemically investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. Porous NCMO_rGO hybrid exhibited a high capacity of 115 mAh·g −1 at 1 A g −1 . Subsequent integration of the hybrid material as a positive electrode with rGO negative electrodes resulted in asymmetric aqueous devices having a specific energy as high as 27 Wh·kg −1 . Moreover, this NCMO_rGO//rGO hybrid device showed an excellent cycling stability of 96% over 2000 cycles. This work not only reports for the first time the rational design and fabrication of porous NCMO_rGO nanoflakes as high performance electrodes for energy storage but also paves the path towards facile synthesis of mixed metal oxide nanocomposites for other applications. [ABSTRACT FROM AUTHOR]

A novel strategy for the development of high energy density supercapacitors (SC) is explored. The new devices contain two electrolytes that are different in nature, an aqueous electrolyte in one half-cell and an ionic liquid in the other. These systems, referred to as biliquid SCs, make it possible to combine the best electrode/electrolyte in terms of individual electrode capacitance and cathodic/anodic stability limits. Furthermore, other asymmetries that combine different electrodes, electrolytes and storage mechanisms can be incorporated. Synchronous cyclic chronopotenciometry was used to monitor the performance of these novel complex systems. It is expected that this approach will help scientists working in this field to develop new devices that overcome the energy density limitations of current SCs, thereby extending the scope of their application. [ABSTRACT FROM AUTHOR]

Thin Co-Mn layered double hydroxide (LDH) nanoflakes and Activated carbon (AC) from cork raw material (Quercus Suber) with highly porous structure and good textural properties was synthesized by a facile solvothermal and two-step eco-friendly hydrothermal syntheses routes respectively. A hybrid device was successfully fabricated using Co-Mn LDH as the positive electrode and AC as negative electrode. The device exhibited a high energy density of 20.3 W h kg −1 and corresponding power density of up to 435 W kg −1 at 0.5 A g −1 current density in 1 M KOH aqueous electrolyte. The device also displayed a very high stability with 99.7% capacitance retention after 10,000 continuous charge-discharge cycles and negligible degradation after subsequently subjecting it to voltage holding test at its maximum operating voltage for 70 hours. These results showcase the potential use of this hybrid device as possible electrodes for high energy density supercapacitor application. [ABSTRACT FROM AUTHOR]

Lithium ion capacitors have attracted enormous interest in recent years due to their high energy density, high power density as well as long cycle stability. However, it remains as a grand challenge to find a suitable battery-type anode material with low Li-ion insertion potential and fast electrochemical kinetics. In this work, we demonstrate that the 3D porous Li 3 VO 4 @C composites synthesized by a facile freeze-drying-assisted thermal treatment method can be favorably used for high-performance lithium ion capacitors. Benefiting from the uniformly distributed Li 3 VO 4 nanoparticles and interconnected conductive carbon networks, the 3D porous Li 3 VO 4 @C anode displays a fast kinetics for both charge-transfer and ion-diffusion, excellent rate capability (317 mAh/g even at a high rate of 10 A/g) and superior cycling stability (322 mAh/g at 5A/g after 2000 cycles). A lithium ion capacitor based on these 3D porous Li 3 VO 4 @C composites delivers high energy/power densities (129.7 Wh/kg at 251.8 W/kg, 52.8 Wh/kg even at 15.2 kW/kg), revealing the promising potential applications in high-performance and long life Lithium ion capacitors. [ABSTRACT FROM AUTHOR]

Nanorods/fibers, nanosheet and nano-flower like structure were effectively synthesized from sulphur-reduced graphene oxide (RGO-S) and sulphur-reduced graphene oxide/manganese dioxide (RGO-S/MnO 2) composites for supercapacitor applications. Structural, chemical composition and morphological analysis reveal an effective synthesis of the RGO-S and RGO-S/MnO 2 composite. Electrochemical measurements of the optimized mass loading of MnO 2 on RGO-S in a three electrode configurations revealed a specific capacitance of 180.4 F g−1 compared to 75.2 F g−1 of the pristine sample at 1 A g−1 in 2.5 M KNO 3 electrolyte. An assembled asymmetric device consists of optimized RGO-S/MnO 2 as positive electrode and activated carbon from peanut shell (AC-PS) as a negative electrode delivered a high specific energy of 71.74 Wh kg−1 with its corresponding specific power of 850 W kg−1 at 1 A g−1. It was observed that even at high specific current of 5 A g−1 the device was able to maintain a specific energy of 55.30 Wh kg−1. An excellent stability with capacitance retention of 94.5% and columbic efficiency of 99.6% up to 10, 000 cycles was recorded for the device at 5 A g−1. The device demonstrated a very good stability after being subjected to a voltage holding of up to 90 h and an outstanding self-discharge of about 1.45 V was recorded within the first 10 h and 1.00 V after 72 h from its maximum potential of 1.7 V. Image 1 • RGO-S and RGO-S/MnO 2 composites were successfully synthesized. • Electrochemical performance of RGO-S/MnO 2 has been improved by introduction MnO 2. • The RGO-S/MnO 2 was adopted as positive electrode in asymmetric device. • The fabricated device proves to be of great potential for supercapacitors applications. [ABSTRACT FROM AUTHOR]

The cation exchange process is an effective method for improving the electrochemical performance of electrodes in supercapacitors. In this study, the cation (Cu) and co-cation (Cu–Fe) exchanges were achieved in the form of a cobalt oxide crystallite using a chemical bath deposition method, followed by high-temperature calcination. Interestingly, the nanoneedle structure of the as-formed Cu–Fe–Co ternary oxide remained unchanged after calcination, with the crystal phase preserved in the cation exchange process. The novel trimetallic oxide delivered a high specific capacity of 737 C g−1 at 1 A g−1. The Cu–Fe–Co ternary oxide electrode exhibited a low fading rate of only 0.000238% per cycle over 4200 charge-discharge cycles. A fabricated hybrid supercapacitor (HSC) delivered a high-energy density of 48 W h kg−1 and a high-power density of 4800 W kg−1. Integration of the HSC device with solar cells successfully illuminated 52 red LEDs, demonstrating the viability of the prepared electrodes for practical and commercial use. Bio-inspired nanostructures and crystal phases were preserved during cation exchange process. The two HSC devices were charged from solar panels and successfully illuminated 52 red light emitting diodes. Image 1 • Novel electrode preparation with dual cation exchange process by CBD method. • Morphology of the crystalline structure has been preserved. • A hybrid supercapacitor (HSC) device has been fabricated. • The HSC device showed higher energy and power densities than the reported. • Integration of solar cells (conversion) and supercapacitors (storage) have been studied. [ABSTRACT FROM AUTHOR]