Manganese phosphate (Mn(PO) hexagonal micro-rods and (Mn(PO) with different graphene foam (GF) mass loading up to 150mg were prepared by facile hydrothermal method. The characterization of the as-prepared samples proved the successful synthesis of Mn(PO) hexagonal micro-rods and Mn(PO)/GF composites. It was observed that the specific capacitance of Mn(PO)/GF composites with different GF mass loading increases with mass loading up to 100mg, and then decreases with increasing mass loading up to 150mg. The specific capacitance of Mn(PO)/100mg GF electrode was calculated to be 270Fg as compared to 41Fg of the pristine sample at a current density of 0.5Ag in a three-electrode cell configuration using 6M KOH. Furthermore, the electrochemical performance of the Mn(PO)/100mg GF electrode was evaluated in a two-electrode asymmetric cell device where Mn(PO)/100mg GF electrode was used as a positive electrode and activated carbon (AC) from coconut shell as a negative electrode. AC//Mn(PO)/100mg GF asymmetric cell device was tested within the potential window of 0.0-1.4V, and showed excellent cycling stability with 96% capacitance retention over 10,000 galvanostatic charge-discharge cycles at a current density of 2Ag.

This work presents the effect of different contents of graphene foam (GF) on the electrochemical capacitance of nickel phosphate Ni3(PO4)2 nano-rods as an electrode material for hybrid electrochemical energy storage device applications.

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Banana peels, a common fruit waste was adopted as a material precursor in this study to synthesize highly porous activated carbon from banana peels (ABP) which serves as an electrode material for a symmetric supercapacitor device. The activation was done using KOH pellets at different carbonization temperatures ranging from 750 °C to 950 °C. The ABP sample obtained from the 900 °C carbonization temperature (ABP900) exhibited unique material properties such as hierarchical porous nano-architecture containing micropores, and mesopores with the highest specific surface area (1362 m 2 g-1). Electrochemical performance investigation in different neutral aqueous electrolytes showed that the best response was obtained in NaNO 3 for the ABP900 electrode. The symmetric device subsequently assembled using 1M NaNO 3 operated in a potential window of 1.8 V, exhibited a specific capacitance of 165 F g-1 with a corresponding energy density of 18.6 W h kg-1 at 0.5 A g-1. A 100% capacitance retention and columbic efficiency were obtained after 10000 continuous charge-discharge cycles at 5 A g-1. Remarkably, after subjecting the symmetric device to a voltage holding test for 60 hours, the specific capacitance was observed to increase from 165 F g-1 to 328 F g-1 with a corresponding increased energy density to about 36.9 W h kg-1 at 0.5 A g-1 , suggesting a 98% increase in device energy density from its initial value after voltage holding. Thus, the results reported showcase the ABP900 material as a potential nanostructured porous material useful in the design of high-performance electrodes for stable electrochemical capacitors.

Highlights •NiCo/NiCoMn-mixed hydroxides, ternary NiCo-MnO 2 nanostructures were successfully synthesised. •The samples were used as electrodes for electrochemical supercapacitor in 1 M KOH. •The electrode materials exhibit good charge storage capability on both regions. •Assembled NiCo-MnO 2 /C-FP hybrid supercapattery displays high electrochemical performance.

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