Mesoporous structure favorable for high voltage and high energy supercapacitor based on green tea waste-derived activated carbon

Abstract

Designing high voltage, high energy, and activated carbon-based supercapacitors has been a long-time wish for meeting various electronic module requirements. This paper focuses on the approach of synthesizing the hierarchical porous activated carbon with dominant mesopores using eco-friendly green tea waste. The desirable ample pore space achieved by changing the weight ratio of KOH activating agent renders more ionic accessibility and space charge distribution. This feature leads to the achievement of 4 V double layer supercapacitor with a remarkable specific energy of 142 Wh kg−1 and specific power of 3192 W kg−1, respectively using an acetonitrile organic electrolyte. The fabricated cell also exhibits a superior 104% capacitance retention after 25 000 charge-discharge cycles at the working potential of ≥3 V. Besides, the hierarchical porous activated carbon soaked in an aqueous KOH electrolyte shows a high specific capacitance of 397 F g−1 at 5 mA cm−2, high rate capability of 100 mA cm−2, and excellent cycle life of 116% capacitance retention after 50 000 cycles tested at 200 mA cm−2. The larger Debye length of the diffuse ion layer permitted by the mesopores is proposed to explain the higher voltage window as against low voltage of micropore dominated commercial activated carbon. The present research may pave the way toward the design of high-energy supercapacitors through recycling tea waste.