Manipulating the overall capacitance of hierarchical porous carbons via structure- and pore-tailoring approach

Abstract

Herein, we present pore architecture-tailorable porous carbons through a time-adjustable hydrothermal reaction and subsequent KOH chemical activation method. Accordingly, platanus spiky (Ps) fruits, taro (T) roots, and green bell peppers (Pp) biowaste substrates were utilized as sustainable precursors to construct novel hierarchical porous carbons (HPCs) with highly interconnected porous frameworks and smart micro/meso/macroporous architecture for supercapacitors. The heterogeneous feedstocks were pre-carbonized under hydrothermal conditions for different hold durations (12 h, 24 h, 36 h) at 200 °C. The optimized Ps-24h material exhibits a high capacitance of 371.6 F g−1 at 1 A g−1 in an aqueous Na2SO4 electrolyte and an outstanding rate performance (94% capacitance retention after 10,000 charge-discharge cycles). Surprisingly, the specific gravimetric capacitance of HPCs can be significantly manipulated by establishing a high-performance redox electrolytic system. In particular, the tailored Ps-24h-based electrode delivers a superior capacitance of 843 F g−1 at 1 A g−1 with an exceptional rate capability (64.7% capacitance retention from 1 to 20 A g−1 in K3[Fe(CN)6]/Na2SO4 electrolyte). Consequently, the as-integrated Ps-24h//Ps-24h symmetric supercapacitor device with a working voltage of 1.8 V presents enhanced energy/power outcomes (63.8 W h kg−1/900.2 W kg−1) with remarkable long-term cyclic durability (90.4% capacitance retention after 15,000 cycles) in a redox electrolytic system.