Biowaste-derived 3D honeycomb-like porous carbon with binary-heteroatom doping for high-performance flexible solid-state supercapacitors

Abstract

Corncob sponge is a type of agricultural abandoned byproduct and abundant around the world. Herein, a facile one-pot carbonization and activation method is developed to convert corncob sponge into three-dimensional (3D) interconnected honeycomb-like porous carbon, followed by an effective binary-heteroatom doping to fabricate nitrogen and sulfur co-doped activated corncob sponge (denoted as N,S-ACS). The resultant products possess a high accessible surface area (1874 m² g⁻¹) induced by the 3D honeycomb-like framework and a highly porous structure that benefits a large ion storage and a rapid ion transfer. In addition to the electrical double layer capacitance, heteroatom doping evokes faradic contribution. N,S-ACS demonstrates a remarkable specific capacitance of 404 and 253 F g⁻¹ at the current densities of 0.1 and 10 A g⁻¹ in a 6 mol L⁻¹ KOH electrolyte, respectively, along with a high cycling stability with only 1% loss over 10 000 cycles. Furthermore, the assembled symmetric flexible solid-state supercapacitors with the electrode of N,S-ACS and the electrolyte of a PVA/KOH gel display a high integrated energy–power density of 30 W h kg⁻¹ at 8 kW kg⁻¹ and a 99% capacitance retention after 10 000 cycles at 3 A g⁻¹. The fascinating performance significantly endows N,S-ACS with great prospects as a supercapacitor electrode.