Biomass-derived ultrathin mesoporous graphitic carbon nanoflakes as stable electrode material for high-performance supercapacitors

With the motivation of materializing a high-performance electrode material for the high-energy supercapacitor, ultrathin mesoporous graphitic‑carbon was synthesized from biomass green-tea wastes via the KOH activation process combined with either of the water or the hydrochloric acid treatment. The water-treated graphitic‑carbon showed an interconnected ultrathin-nanoflake structure with a high porosity, while the hydrochloric acid-treated graphitic carbon exhibited an aggregated structure of irregular nanoparticles. The supercapacitor with an electrode of water-treated graphitic‑carbon nanoflakes displayed an enhanced specific capacitance of 162F/g at 0.5 A/g. Furthermore, the device revealed an excellent cycle stability after multiple cyclic charge-discharge operations (i.e., 121% cyclic capacitance retention over 5000cycles). These may open up a new avenue toward the recycling of biomass carbonaceous resources (e.g., green tea wastes) for inexpensive high-performance electrochemical energy-storage devices such as high-energy supercapacitors.