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Nickel ferrites have served as electrode materials in energy storage applications such as batteries and supercapacitors in comparison to other metal oxides, they have a higher theoretical capacitance range. Pristine metal oxides are poor candidates as electrode components in electrochemical applications because of their tendency to aggregate and their less specific surface areas. Herein, we reported wet impregnation method to incorporate Nickel Ferrite (NiFe2O4) to multiwalled carbon nanotubes (MWCNTs) for improved electrochemical performance of nickel ferrites (NiFe2O4). The synthesized materials attained good crystallinity confirmed by X-ray diffraction (XRD). NiFe2O4 nanoparticle adhesions on multiwalled carbon nanotubes have been confirmed by scanning electron microscopy (SEM). UV-DRS was used to measure the bandgap for optical studies. Cyclic Voltammetry (CV), Galvanostatic Charge/Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) investigations for supercapacitor applications revealed that synthesized materials demonstrated good electrochemical potential, but MWCNTs supported NiFe2O4 composite attained exceptionally high specific capacitance (CV: 830 F g−1 at 5 mV s−1, GCD:343 F g−1 at current density of 0.1 A g−1) with capacitance retention of 98% at the current density of 0.8 A g−1 after 3500 stability cycles. [ABSTRACT FROM AUTHOR]

A tremella-like NiCo 2 O 4 @graphene quantum dots (GQDs) composite is prepared where the tremella-like NiCo 2 O 4 is homogeneously encapsulated by GQDs. Herein, the GQDs based on π-conjugated core with abundant edge sites, make NiCo 2 O 4 favorable for advanced electric energy storage (EES). In terms of the synergistic effect between the conductive GQDs and tremella-like NiCo 2 O 4 , the as prepared NiCo 2 O 4 @GQDs composite exhibits an excellent specific capacitance of 1242 F g−1 at 30 A g−1 in 2.0 M KOH electrolytes, much higher than that of pristine NiCo 2 O 4 (790 F g−1 at 30 A g−1). Also, it manifests outstanding cycle stability (99% capacitance retention after 4000 cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by pairing NiCo 2 O 4 @GQDs composite as positive electrode and activated carbon (AC) as negative electrode (NiCo 2 O 4 @GQDs//AC), and its specific energy density is as high as 38 W h kg−1 at a power density of 800 W kg−1. Image 1 [ABSTRACT FROM AUTHOR]

NiMn 2 O 4 (NMO) powders are synthesized by the sol–gel route and the NMO1 electrode is fabricated from the powder synthesized at a calcination temperature of 500 °C. The specific capacitance of the NMO1 electrode is improved from 571 Fg−1 to 762 Fg−1 at a scan rate of 5 mVs−1 , with an increase in the concentration of KOH electrolyte from 1 M to 6 M. [Display omitted] NiMn 2 O 4 (NMO) powders have been prepared by facile sol–gel route, and the effect of annealing temperature and the concentration of KOH electrolyte on its electrochemical performance has been investigated. The electrochemical performance of the NMO electrodes is tested via a three electrode arrangement in KOH electrolyte. The NMO electrode (NMO1) prepared from the powder synthesized at a temperature of 500 °C with an approximate crystallite size of 10 nm exhibits maximum specific capacitance of 571 Fg−1 at a scan rate of 5 mVs−1 in 1 M KOH electrolyte. The specific capacitance of the NMO1 electrode is found to be improved from 571 Fg−1 in 1 M KOH to 762 Fg−1 in 6 M KOH electrolyte. The improvement in the specific capacitance of the NMO1 working electrode in 6 M KOH electrolyte can be attributed to good electrochemical utilization and an effective charge storage mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • A one-step facile synthetic strategy for spinel/carbon composites is proposed. • Graphite nanoflakes matrix is obtained via the low-cost physical exfoliation. • The introduction of GNF significantly enhances the performance of spinels. • Good electrochemical performances are achieved in the MXO/GNF//rGO ACS devices. We put forward a facile one-pot hydrothermal strategy to synthesize the MnX 2 O 4 (X = Co, Ni) spinel/graphite nanoflakes (GNF) composites. Note that the physical exfoliation toward GNF frees the method from the complex and expensive conventional chemical treatments. The obtained MnCo 2 O 4 /GNF (MCO/GNF) and MnNi 2 O 4 /GNF (MNO/GNF) exhibit high specific capacitance (1712 F g−1 for MCO/GNF and 1622 F g−1 for MNO/GNF at 1 A g−1) and good cycling performance (almost 80 % capacitance retention after 3500 cycles at 5 A g−1 for both MCO/GNF and MNO/GNF). Furthermore, the asymmetric supercapacitor (ASC) with MCO/GNF or MNO/GNF as positive electrode and rGO as the negative electrode is assembled. The optimized ASC is able to show high energy density up to 22.5 Wh kg−1. Together with the facile synthetic strategy, such good electrochemical performance may promote the spreading of the next-generation energy storage electrodes. [ABSTRACT FROM AUTHOR]