Highlights• VS 2 nanosheets electrode material was synthesized by the hydrothermal method.• C-Fe/PANI was synthesized on nickel foam by pyrolysis of the iron-PANI mixture.• The device was fabricated using VS 2 as a cathode and C-Fe/PANI as an anode.• VS 2 //C-Fe/PANI asymmetric device exhibited good electrochemical performance.ABSTRACT VS 2 nanosheets electrode material was successfully synthesized by the hydrothermal method, and the electrode material (C-Fe/PANI) based on the carbonization of Fe cations adsorbed onto polyaniline (PANI) was directly synthesized on a nickel foam (current collector) by pyrolysis of the iron-PANI mixture coated on nickel foam in a tube furnace under the N 2 atmosphere. The structural and morphological characterization of the as-synthesized electrode materials was carried out using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The electrochemical behavior of each working electrode was analyzed in a three-electrode cell configuration using 6 M KOH electrolyte, and thereafter, a hybrid (asymmetric) device was successfully fabricated using VS 2 nanosheets as the positive electrode and C-Fe/PANI as a negative electrode. The fabricated VS 2 //C-Fe/PANI asymmetric device was found to perform at a high applied potential difference of 1.7 V in 6 M KOH. At a current density of 2 A g -1 , this device exhibited high energy and power densities of 27.8 Wh kg -1 and 2991.5 W kg -1 respectively. In addition, a VS 2 //C-Fe/PANI 2 device showed excellent cycling stability with 95% capacity retention over 10 000 galvanostatic charge-discharge cycles at a current density of 5 A g -1 . storage 1. INTRODUCTION Supercapacitors (SCs) which are also referred to as electrochemical capacitors (ECs) have attracted great interest for the important application in the area of electrochemical energy storage because of increasing demand for digital communication, electric vehicles and other electric devices at high pulse power level [1-7]. Since, SCs are high power-delivery storage devices which are able to discharge in a shorter time by exploiting their fast surface or near surface reactions and delivering high power compared to conventional batteries [2,8-10]. Though, SCs are high power-delivery storage devices (have high power density) they have low energy density especially compared to rechargeable batteries (Li-ion batteries) [2,11]. Accordingly, researchfocus in SCs is on improving their energy density (i.e. ~5˗8 Wh kg -1 ) without compromising their high power density (i.e. ~5˗30 kW kg -1 ), unlike in rechargeable batteries which already have high energy density in the range of 120˗200 Wh kg -1 , the focus will be on improving the power density which is in the range of 0.4˗3 kW kg -1 [2,8,9,12]. Recently, asymmetric (hybrid) systems have been explored to increase the operating electrode potential to improve the energy density of the SCs. Generally, the behavior of the SCs is mainly influenced by the charge storage mecha...

Highlights • Thin Co-Mn LDH nanoflakes was synthesized by a facile solvothermal technique. • AC was synthesized by a two-step eco-friendly hydrothermal synthesis. • A device was fabricated using Co-Mn LDH as positive and AC as negative electrode. • The electrode materials exhibited good electrochemical performance.

Activated carbon (ACB) obtained from tree bark waste biomass was obtained by adopting an optimized activation and carbonization route using potassium hydroxide (KOH) pellets. The morphological and structural characteristics of the optimized carbon material revealed a porous network suitable for charge storage. The potential of the ACB material as a suitable supercapacitor electrode was investigated in a symmetric two electrode cell configuration using a polymer-gel/KOH active electrolyte. The KOH was included to improve ionic mobility within the polyvinyl alcohol (PVA) gel, while carbon acetylene black and a polymer-fullerene blend acted as the conductive additives. The cell exhibited an EDLC behaviour in all electrolytes with the PVA/KOH/carbon black (PKCB) electrolyte portraying the best electrochemical response with a 1.4 V voltage window. A specific capacitance (C SP ) of $227 F g À1 was obtained with a corresponding energy density of 15.5 W h kg À1 and power density of 700 W kg À1 at a current density of 0.5 A g À1. An excellent stability was exhibited with a coulombic efficiency of 98% after 5000 continuous cycles at 5.0 A g À1 and a slight deterioration of the ideal electrochemical behavior was observed after further subjecting the electrode to a floating test for 120 h (5 days) at 1.4 V. Interestingly, the gel-based electrolyte showed a peculiar "recuperating behavior" after further floating process and negligible charge loss after a self-discharge process for 30 h at 1.0 A g À1 which demonstrates the viability for adopting gel-electrolytes in SC devices from plant biomass waste.