KOH activation of wax gourd-derived carbon materials with high porosity and heteroatom content for aqueous or all-solid-state supercapacitors.

Biomass precursors with natural porous structure and multifarious heteroatoms are desirably sustainable precursors for synthesis of carbon materials for energy and environmental applications. Herein, we reported wax gourd based porous carbons (WGPCs) with developed micro/mesoporous structures via potassium hydroxide (KOH) chemical activation. The optimized material that is denoted as WGPC-4 exhibits high specific surface area (2919 m2 g-1) with oxygen and nitrogen contents of 17.9 at.% and 1.0 at.%, respectively. In a three-electrode system, the WGPC-4 electrode presents high specific capacitance of 333 F g-1 at current density of 1 A g-1. Meanwhile, the assembled symmetrical cell using aqueous electrolyte (0.5 M Na2SO4) has high specific capacitance (167 F g-1 at 1 A g-1), stable cycling characteristics (93% capacitance retaining after 5000 runs) and excellent energy density of 19.2 Wh kg-1. Furthermore, these WGPC-4 electrodes were assembled into an all-solid-state supercapacitor using KOH/polyvinyl alcohol (PVA) gel as solid electrolyte, whose specific capacitance is 258 F g-1 at 1 A g-1, retention at the 2500th run is 87% and energy density is 13.0 Wh kg-1 under a high power density. These materials with excellent structural characteristics are an ideal candidate for high-performance supercapacitors.