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.

Activated carbon from tree bark (ACB) has been synthesized by a facile and environmentally friendly activation and carbonization process at different temperatures (600, 700, and 800 °C) using potassium hydroxide (KOH) pellets as an activation agent with different mass loading. The physicochemical and microstructural characteristics of the as-obtained material revealed interconnected micro/mesoporous architecture with increasing trend in specific surface area (SSA) as carbonization temperatures rises. The SSA values of up to 1018 m 2 g -1 and a high pore volume of 0.67 cm 3 g -1 were obtained. The potential of the ACB material as suitable supercapacitor electrode was investigated in both a three and two electrode configuration in different neutral aqueous electrolytes. The electrodes exhibited EDLC behaviour in all electrolytes with the Na 2 SO 4 electrolyte working reversibly in both the negative (-0.80 V to -0.20 V) and positive (0.0 V to 0.6 V) operating potentials. A specific capacitance (C S ) of up to 191 F g -1 at a current density of 1 A g -1 was obtained for the optimized ACB electrode material in 1 M Na 2 SO 4 electrolyte. A symmetric device fabricated exhibited specific C S of 114 F g -1 at 0.3 A g -1 and excellent stability with a coulombic efficiency of a 100% after 5000 constant charge-discharge cycles at 5.0 A g -1 and a low capacitance loss for a floating time of 70 h.

In this study, the synthesis of porous activated carbon nanostructures from peanut (Arachis hypogea) shell waste (PSW) was described using different porosity enhancing agents (PEA) at various mass concentrations via a two-step process. The textural properties obtained were depicted with relatively high specific surface area values of 1457 m2 g−1, 1625 m2 g−1 and 2547 m2 g−1 for KHCO3, K2CO3 and KOH respectively at a mass concentration of 1 to 4 which were complemented by the presence of a blend of micropores, mesopores and macropores. The structural analyses confirmed the successful transformation of the carbon-containing waste into an amorphous and disordered carbonaceous material. The electrochemical performance of the material electrodes was tested in a 2.5 M KNO3 aqueous electrolyte depicted its ability to operate reversibly in both negative and positive potential ranges of 0.90 V. The activated carbon obtained from the carbonized CPSW:PEA with a mass ratio of 1:4 yielded the best electrode performance for all featured PEAs. The porous carbons obtained using KOH activation displayed a higher specific capacitance and the lower equivalent series resistance as compared to others. The remarkable performance further corroborated the findings linked to the textural and structural properties of the material. The assembled device operated in a neutral electrolyte (2.5 M KNO3) at a cell potential of 1.80 V, yielded a ca. 224.3 F g−1 specific capacitance at a specific current of 1 A g−1 with a corresponding specific energy of 25.2 Wh kg−1 and 0.9 kW kg−1 of specific power. This device energy was retained at 17.7 Wh kg−1 when the specific current was quadrupled signifying an excellent supercapacitive retention with a corresponding specific power of 3.6 kW kg−1. These results suggested that peanut shell waste derived activated carbons are promising candidates for high-performance supercapacitors.

In this work, we present the synthesis of low cost carbon nanosheets derived from expanded graphite dispersed in Polyvinylpyrrolidone, subsequently activated in KOH and finally .This electrical double layer capacitor electrode also exhibits excellent stability after floating test for 120 h in 6 M KOH aqueous electrolyte. These results suggest that this activated expanded graphite (AEG) material has great potential for high performance electrode in energy storage applications.

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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VS 2 nanosheets as the positive electrode and the activated carbon (AC) as the negative electrode with a 6 M KOH solution as electrolyte were fabricated as an asymmetric supercapacitor. These materials were combined to maximize the specific capacitance and to enlarge the potential window, therefore improving the energy density of the device. A specific capacitance of 155 F g -1 at 1 A g -1 with a maximum energy density as high as 42 Wh kg -1 and a power density of 700 W kg -1 was obtained for the asymmetric supercapacitor within the voltage range of 0 -1.4 V. The supercapacitor also exhibited a good stability with ∼ 99% capacitance retention and no capacitance loss after 5000 cycles at a current density of 2 Ag -1 .