N-Doped Carbon Nanosheets from Biomass for Ultra Long-Cycling and High Energy Density Symmetric Supercapacitors

The demand for high performance energy storage devices has stimulated much interests in developing high-energy density supercapacitors. Herein, we report N-doped peanut hull derived activated carbon (PHAC) nanosheets as high-performance supercapacitor electrode by low-cost approach. Electron microscope and physiochemical characterization of PHAC confirm multi-layered sheet like nanostructures with self-doped nitrogen. Tuning of KOH activation temperature in a narrow range between 700 °C and 750 °C has a significant effect over specific surface area which increases up to ∼2300 m 2 g −1 for 720 °C activated PHAC compared to 501 m 2 g −1 for 700 °C treated sample. Investigation of PHACs as supercapacitor electrode in 1.0 M H 2 SO 4 electrolyte delivers high capacitance of 195 Fg −1 at an applied current density of 1 Ag −1 with superior capacitance retention of 98.6% after 15000 cycles. More importantly, PHACs electrode shows high stability even at a current density of 50 Ag −1 with an impressive capacitive retention of 49.2%. In a symmetric cell configuration, the PHAC constructed electrode shows a maximum power density of 25 KW kg −1 with energy density of 8.96 Wh kg −1 . Such an exquisite charge storage performance of N-doped peanut hull based carbon nanosheets is attributed to very large surface area, porosity, high N-content vis-ẚ-vis electrical conductivity.