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The nano‐sized bush‐like α‐Fe2O3 particles were synthesized using sol‐gel auto combustion route. The structural characterization of obtained α‐Fe2O3 was performed by X‐ray diffraction (XRD) method to confirm its phase and crystallinity. The Scanning Electron Microscopy (SEM) confirmed the formation of bush‐like nanostructure which was further used for the electrochemical charge storage performance testing. The electrochemical performances of the synthesized electrode material were studied by using Cyclic Voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis in a three electrode configuration. The variation of specific capacitance values with the different molar concentration of electrolyte has been discussed. An enhancement in the specific capacitance has been observed up to 3 M KOH electrolyte solution. The maximum value of specific capacitance is 202.2 F g−1 which is obtained at a scan rate of 2 mV s−1 for 3 M aqueous KOH solution as electrolyte. [ABSTRACT FROM AUTHOR]

In this paper, we compared the electrochemical performances of ordered MnO 2 -Graphene (MnO 2 -GO) oxide with the disordered system of the same composite. The ordered system is fabricated using electrospinning while the disordered system is fabricated dropcasting the same precursor under similar synthesis condition. This fiber-like ordered structure exhibits excellent electrochemical properties both in terms of specific capacitance and cyclic stability because of excellent connectivity between the individual nanoparticles. The electrospun sample having MnO 2 : GO = 5:2 (by weight) demonstrates the highest specific capacitance of 892.8 F g−1 whereas the disordered sample having same ratio of MnO 2 and GO demonstrates 546.9 F g−1 at 2 mV s−1. To correlate the superior electrochemical performance of the ordered sample compared to the disordered one, room temperature dielectric measurements are performed which reveals various parameters like conductivity; diffusivity and mobility of charge carriers. An asymmetric supercapacitor device is fabricated using the fiber-like ordered structure as an active electrode. The device offers maximum power density of 2.8 kW kg−1 and maximum energy density of 96.75 Wh kg−1 with a 93.3% retention after 5000 GCD cycles. Image 1 • Ordered and disordered systems of MnO 2 -GO composite have been fabricated. • Ordered electrospun sample offers better conductivity and storage capacity. • Dielectric measurement has been used to evaluate different parameters. • Two electrode device performance is demonstrated. [ABSTRACT FROM AUTHOR]

• Wool ball like CuO/NiO/CNT nanohybrids were synthesized by solvothermal route. • Highly ordered mesoporous CNC1 hybrid offers high specific surface area of 262 m2 g−1. • Electrode materials CNC1 provided a high specific capacitance of 786 F g−1 at a current density of 2 A g−1. • The asymmetric device exhibited a high specific capacity of 156 F g−1 at a scan rate of 2 mV s−1. • The device offered high energy and power density with excellent cyclic stability. [Display omitted] In the present work, some CuO@NiO@MWCNT (CNC) ternary hybrid nanostructures have been synthesized solvothermally in a well-controlled manner by varying the amount of MWCNT for energy storage application with superior electrochemical performance. Among three CNC1 (CuO@NiO:40 mg MWCNT), CNC2 (CuO@NiO:40 mg MWCNT; in one-step method) and CNC3 (CuO@NiO:60 mg MWCNT) nanocomposites, the CNC1 has emerged out with the best performance due to its well-designed components and synergistic effects, wool ball-like morphology and a mesoporous structure containing more active sites, a shortest conductive pathway for electron-ion transportation. The CNC1 hybrid with a highly ordered mesoporous structure (pore radius ~1.9 nm) offers a high specific surface area of 262 m2 g−1. The structure and microstructure of these ternary hybrid nanocomposites are characterized by analyzing respective X-ray diffraction patterns, HRTEM, FESEM images, and XPS spectra. HRTEM and FESEM images reveal the uniform distribution of the MWCNT network and the growth of spherical NiO nanoparticles of 8–10 nm in these CNT. The optimized ternary wool ball-like CNC1sample exhibits a high specific capacitance of 786 F g−1 and high areal capacitance of 3.144 F cm−2at a current density of 0.6 A g−1 with a significant rate capability. A two-electrode asymmetric device has been designed with the CNC1 sample as the positive electrode and activated carbon as the negative electrode in a 1 M Na 2 SO 4 electrolyte medium. This device offers maximum specific energy of 32.21 Wh Kg−1, a maximum power density of 3923 W Kg−1, excellent cyclic stability and a high Coulomb efficiency. The optimum use of MWCNT in CNC1 ternary nanostructures results in better morphology, leading to a significant reduction in charge transfer parameters,as revealed by EIS spectroscopy. [ABSTRACT FROM AUTHOR]

• One-step solvothermal synthesis of ethylene glycol functionalized MnFe 2 O 4 nanoparticles and its rGO composite. • MnFe 2 O 4 /rGO nanocomposites showed superior charge storage behavior and electrochemical properties compared to bare MnFe 2 O 4. • MnFe 2 O 4 /rGO showed high specific capacitance of 253 Fg−1 at current density 10 Ag−1. • The composite attains significantly improved energy density of 76.06 Wh kg−1 with a power density of 7.49 kW kg−1. • MnFe 2 O 4 /rGO nanocomposite showed 96 % cyclic stability at the end of 5000 cycles. A single-step solvothermal method has been employed to synthesize MnFe 2 O 4 composite nanoparticles where graphene sheets were incorporated into spherical MnFe 2 O 4 nanoparticles of size ∼57 nm. The synthesized MnFe 2 O 4 /reduced graphene oxide (rGO) composite exhibits enhanced electrochemical properties due to its improved porosity, surface area, and conductivity. FTIR, Raman, and XPS studies confirmed the effective reduction of GO and the successful formation of MnFe 2 O 4 /rGO composite. When employed as an electrochemical cell electrode, the MnFe 2 O 4 /rGO composite showed an enhanced specific capacitance of 253 F g−1, as opposed to 133 F g−1 for the bare nanoparticles. The composite attains significantly improved energy density of 76.06 Wh kg−1 and power density of 7.49 kW kg−1 at current density of 10 A g−1. The unification of 2D graphene and MnFe 2 O 4 nanoparticles yields enhanced electrochemical performance and an outstanding 96 % cyclic stability (after 5000 cycles), which offers a viable approach for developing better supercapacitor electrode materials in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

• MnO 2 microfiber of diameter 5 μm is prepared via Rotary-Jet spin technique. • Microfiber offers excellent supercapacitive properties due to ordered morphology. • Highest specific capacitance of 663 F g−1 is obtained in three electrode system. • The asymmetric two electrode device shows excellent charge storage capability. In this study, we have prepared MnO 2 microfiber using Rotary-Jet Spin (RJ-Spin) to fabricate supercapacitor electrodes. The viscous suspension of MnO 2 -polyvinyl alcohol (MnO 2 -PVA) is allowed through small holes of a rotating head under the action of centrifugal force to form metal oxide fiber. Because of good interconnection between the individual redox active sites, the microfiber offers high specific capacitance of 663 F g−1 at a scan rate of 2 mV s−1 with excellent long-term cyclic stability. A two electrode asymmetric device is fabricated which demonstrates maximum specific capacitance of 135.6 F g−1 with a maximum power density of 3.2 kW kg−1 and maximum energy density of 56.7 Wh kg−1. [ABSTRACT FROM AUTHOR]

In this report, we have demonstrated the morphological effect on the electrochemical performances of hydrothermally synthesized NiMn 2 O 4. Morphologies of the nanoparticles are varied using different surfactants and mineralizer during synthesis. Three different surfactants namely cetyl trimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and glucose and one mineralizer ammonium fluoride (NH 4 F) are used all of which result in a spherically shaped particles with varying sizes. We have seen that addition of SDS results in an agglomeration of spherical nano-particles of NiMn 2 O 4 with good interconnection between them. Brunauer–Emmett–Teller (BET) surface area analysis confirms this sample offers highest surface area with mesoporous structure amongst all these samples. A specific capacitance of 1937 F g−1 is obtained for the same at 2 mV s−1 scan rate in 1 M aqueous Na 2 SO 4 electrolyte. A two-electrode asymmetric device has been fabricated using the sample as positive electrode and activated carbon as negative electrode. The device offers a specific capacitance of 270 F g−1 with excellent cyclic stability and good power and energy density. The superior performance of the device has been validated by demonstrating the capability of the device to harvest energy from a solar cell and to deliver the same through a LED. Image 1 • NiMn 2 O 4 has been synthesized using hydrothermal technique. • Surfactants and mineralizer have been used separately to tune the morphology. • A maximum specific capacitance of 1937 F g−1 is obtained in three electrode system. • The two electrode asymmetric device shows excellent charge capability. • The device has been used to store energy from commercial solar cell. [ABSTRACT FROM AUTHOR]

In the present work, hydrothermal and wet chemical methods are adopted to fabricate NiCo 2 O 4 nanowires (NiCo-NW) and NiCo 2 O 4 nanoparticles (NiCo-NP) respectively. Owing to the mesoporous nature of these subunits, fast and convenient electron-ion transport and redox reaction, NiCo-NW achieves excellent electrochemical performance. Structure and microstructural characterizations of these samples are carried out by analyzing X-ray diffraction data employing the Rietveld method of structure refinement method and analyzing HRTEM, FESEM images and FTIR spectra. The low dimensional NiCo-NP is found to provide superior electrochemical performance than the NiCo-NW (∼13 nm) due to its smaller particle size (∼9 nm). This porous structure effectively helps in better transport of ions in the electrolyte. It manifests high specific capacitance 1066.03 F g−1 and enormous areal capacitance up to 5.96 F cm−2 whereas NiCo-NW exhibits specific capacitance up to 880.72 F g−1 and high areal capacitance of 4.93 F cm−2. An asymmetric supercapacitor (ASC) has been fabricated with NiCo-NP and activated carbon as positive and negative electrodes respectively in 1 M Na 2 SO 4 electrolyte medium. This device offers maximum specific energy 59.56 Wh Kg−1 and maximum power density 3403 W kg−1 with a high energy density of 4.197 Wh Kg−1 and shows excellent cyclic stability. • Hydrothermal and wet chemical method were adopted to fabricate Nickel cobaltite. • High areal capacity: 5.96 F cm−2 and 4.93 F cm−2 achieved by two materials. • ASC device: maximum power density 3403 w kg−1 with a energy density of 4.1 Wh kg−1 • ASC device:Excellent long term cyclic stability: 1% loss after 2700 cycles. [ABSTRACT FROM AUTHOR]

Summary: The current study emphasizes the influence of electrochemical active surface area (ECSA) on the electrochemical oxygen evolution reaction (OER) and supercapacitive performances of MnO2‐multiwalled carbon nanotube (MC) composites. The best sample exhibits an ECSA of 8.6 cm2. With the increase of ECSA both OER activity and the supercapacitive performance of the composites increases. The MC composite exhibits a low over potential (0.385 V) for OER activity. The composite displays outstanding catalytic activity for OER in the alkali medium as well as exhibits excellent supercapacitive activity (specific capacitance of 1039 F g−1 at a scan rate of 2 mV s−1). An asymmetric supercapacitor has also been developed which shows very high specific capacitance within a wide working potential of 1.8 V. This device can supply an energy and power density of 60.55 Wh kg−1 and 8.45 kW kg−1, respectively. The role of ECSA has been investigated in both oxygen evolution and supercapacitive process showing the promise of this multifunctional MnO2‐MWCNT composite for both energy storage but also in conversion. [ABSTRACT FROM AUTHOR]

Summary: Strontium (Sr) incorporated LaMnO3 (La0.7Sr0.3MnO3) nanoparticles have been synthesized by ball‐milling‐assisted solid‐state reaction to study their performance as electrode material for energy storage applications. The La0.7Sr0.3MnO3 nanoparticles exhibit superior electrochemical performance in neutral aqueous electrolyte (1 M Na2SO4) in comparison to LaMnO3 and SrMnO3 nanoparticles. This neutral electrolyte provides relatively higher ionic conductivity and viscosity compared to the ionic liquids and a wider potential window compared to the alkaline electrolytes. Electrochemical study of the electrodes prepared using La0.7Sr0.3MnO3 nanoparticles reveals pseudocapacitive behaviors with fast reversible Faradaic charge storage, which plays a key role in charge storage. The composite materials exhibit highest specific capacitance of 393.5 F g−1 at a scan rate of 2 mV s−1. Asymmetric supercapacitors fabricated using La0.7Sr0.3MnO3 nanoparticle and activated carbon operates over a wide potential window of 1.8 V, and it reveals high specific capacitance (197 F g−1) as well as high capacitive retention (87%) even after 4000 charge–discharge cycles. [ABSTRACT FROM AUTHOR]

Nickel-oxide-Carbon nanotube (NiO-CNT) composite has been synthesized and its multifunctional electrochemical properties have been demonstrated by investigating the supercapacitive performance and the oxygen evolution reactivity. The composite exhibits interlinked porous structure and offers high surface area which has been observed by X-ray diffraction, Field emission scanning electron microscopy, Transmission electron microscopy and Brunauer-Emmett-Teller surface area analysis. NiO-CNT composite offers a specific capacitance of 878.19 F g −1 at a scan rate of 2 mV s −1 along with high cyclic stability. Asymmetric supercapacitor has been fabricated with the composite material as positive electrode and activated carbon as negative electrode and 1 M Na 2 SO 4 electrolyte medium. The device offers a specific capacitance of 197.7 F g −1 at a scan rate of 2 mV s −1 . It exhibits specific energy and specific power 85.7 Wh kg −1 and 11.2 kW kg −1 , respectively. The device is capable of powering LED and DC motor for several minutes. Moreover, NiO-CNT composite shows excellent activity as a catalyst for Oxygen Evolution Reaction. The composite offers an overpotential of 0.301 V. The material shows excellent long term performance. This multifunctional composite material is a promising candidate for future applications in energy storage and conversion. [ABSTRACT FROM AUTHOR]

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 H 2 SO 4 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. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sol-gel derived spinel NiMn 2 O 4 is synthesized in pure phase. • The structural analysis has been carried out using Rietveld refinement. • The dependence of EIS on potential is extensively demonstrated for first time. • NiMn 2 O 4 electrode exhibits maximum specific capacitance of 875 F g−1. • NiMn 2 O 4 electrode shows excellent ASC device performance. Abstract We report the synthesis of porous spinel-structured binary NiMn 2 O 4 metal oxide nanoparticles and their performance as electrode material for supercapacitors. Spherical NiMn 2 O 4 nanoparticles of ∼8 nm average diameter have been synthesized using inexpensive and simple sol-get method, and characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The electrodes made of this single phase spinel nanoparticles exhibit superior electrochemical performance with excellent rate capability, offering highest specific capacitance value of 875 F g−1 at 2.0 mV s−1 scan rate in 1 M Na 2 SO 4 electrolyte solution. Furthermore, an asymmetric supercapacitor is also assembled and possesses a wide operating voltage window of 1.8 V, exhibiting an energy density of 75.01 W h kg−1 at a power density of 2250.91 W kg−1. The results infer this highly porous binary metal oxide nanostructures are promising candidates for high performance energy storage applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Interlinked V 2 O 5 -PANI composites are synthesized by chemical polymerization. • V 2 O 5 -PANI exhibits the highest capacitance of 529.56 F g−1 with wide window of 1.6 V. • Correlation between electrochemical performances with IR peak shifts is studied. • Inorganic-organic synergistic effect plays crucial role for wide working window. • Asymmetric supercapacitor exhibits high energy and power in wide potential windows. Abstract To meet the demand of high-energy density supercapacitors, development of suitable electrode material with a wide potential window and high specific capacitance is most important. In this report, we have synthesized V 2 O 5 -PANI nanocomposite through in-situ intercalation and polymerization reaction of aniline with V 2 O 5 , which shows a wide potential window as well as high specific capacitance. XRD, SEM and FTIR have been used to characterize the electrode materials. Their electrochemical activity and pseudocapacitive performances were investigated. The correlation between morphology and electrochemical performances were investigated which is a vital way for the selection of electrode materials. Due to the organic-inorganic compatibility, V 2 O 5 -PANI exhibits good electrochemical charge storage in a wide potential window of 1.6 V (ranging between −0.4 V to 1.2 V) with excellent stability of 84.2% capacitance retention after 5000 GCD cycles. Moreover, asymmetric supercapacitor was assembled V 2 O 5 -PANI composite and NiMn 2 O 4 electrodes which yield remarkable energy and power density. [ABSTRACT FROM AUTHOR]