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Abstract The role of redox additive electrolytes in supercapacitors is gaining an increased significance. The present research work, for the first time, investigates the supercapacitor performance of a rGO/TiO 2 nanosheet composite (prepared via facile one step hydrothermal reaction route) electrode in combination with a redox additive electrolyte, i.e., 0.2 M K 3 [Fe(CN) 6 ] in 1 M Na 2 SO 4. The synergistic effects between the porous rGO/TiO 2 nanosheet electrode and the optimized redox electrolyte have helped to achieve a significantly high specific capacitance of 1565 F/g at a current density of 3 A/g (working potential window = −0.1–0.5 V). This value of specific capacitance is much higher than achievable with the application of a plain aqueous electrolyte (e.g., 1 M Na 2 SO 4). Furthermore, rGO/TiO 2 nanosheet electrodes have been used to fabricate a symmetrical supercapacitor device which has delivered an excellent specific capacitance value of 204.5 F/g at a current density of 1.5 A/g. The device also yielded promising values of energy density (15.5 Wh/kg) and power density (1.1 kW/kg) apart from showing a long-term cyclic stability (∼87%) even after 1000 continuous charge-discharge cycles. Graphical abstract Image 1 Highlights • A composite of rGO/TiO 2 nanosheets has been explored as a supercapacitor electrode. • 0.2 M K 3 [Fe(CN) 6 ] in 1 M Na 2 SO 4 has been used as an optimized electrolyte. • Selection of above electrode and electrolyte yielded high specific capacitance. • A specific capacitance of 1565 F/g has been achieved at a current density of 3 A/g. • High values of energy (15.5 Wh/Kg) and power (1.1 kW/kg) densities were achieved. [ABSTRACT FROM AUTHOR]

Abstract In pursuit of high specific capacitance and high energy density; morphology, specific surface area and conductivity of electrode material are key factors. In this context, Ni 1-x Mg x Co 2 O 4 @C (x = 0.0, 0.5) nanostructures are synthesized via facile hydrothermal route using the cotton template. Notably; the morphology altered from flowers to rods with the incorporation of cotton templates. Additionally, Mg dopant ion helps to attain greater electrical conductivity while preventing the morphology. Besides, Influence of Mg doping on the pseudocapacitance of NiCo 2 O 4 electrode was investigated by electrochemical analysis in 6 M KOH electrolyte. This remarkable synergy display superb electrochemical performance for Ni 0.5 Mg 0.5 Co 2 O 4 @C rods, i.e a high specific capacitance of 1340 Fg-1 at a current density of 1 Ag-1 and admirable cyclic stability of ∼97% up to 2000 charge-discharge cycles (at 15 Ag-1). Further, the proposed Ni 0.5 Mg 0.5 Co 2 O 4 @C rods electrode delivered high values of energy (59.5 Wh/Kg) & power (799.2 W/Kg) densities at a current density of 1 Ag-1, which is 2 times more as compared to flowers structured material. This can be attributed to increase in the specific surface area with more porous nature of rods. This work conveys the deeper understanding of the morphology and chemical composition effect on the supercapcitive performance of Ni 0.5 Mg 0.5 Co 2 O 4 @C. Thus, Ni 0.5 Mg 0.5 Co 2 O 4 @C (NMCo@C) rods may be an excellent electrode material for high-performance supercapacitor due to its exceptional electrochemical performances. Graphical abstract Image 1 Highlights • Highly porous rods structure of specific surface area of 51.78 m2g-1 is fabricated. • The specific capacitance of 1340 Fg-1 is obtained for Ni 0.5 Mg 0.5 Co 2 O 4 @C rods. • Ni 0.5 Mg 0.5 Co 2 O 4 @C rods delivers maximum energy density of 59.5 WhKg−1. • The capacitance retention of ∼97% up to 2000 charge-discharge is maintained. [ABSTRACT FROM AUTHOR]