Insights into the KOH activation parameters in the preparation of corncob-based microporous carbon for high-performance supercapacitors

Abstract

High-performance supercapacitors extremely depend on reasonable microstructure of electrode materials, but how to efficiently control the pore structure of principal carbon materials remains a challenge. In this study, corncob-based porous carbon (CPCX) with controllable pore structures is synthesized by means of KOH activation strategy, and the technical parameters of KOH activation are comprehensively investigated including activation temperature, activation time and KOH/biochar ratio. The optimal sample with a KOH/biochar mass ratio of 3 activated at 650 °C for 1 h (denoted as CPC650–1-3) possesses sub-nanopores concentrated at 0.6 nm and 0.8 nm, and larger micropores distribute at 1.2 nm and 1.5 nm. These highly cross-linked microporous structures provide accessible specific surface area (SSA) for electrode materials and act as high-speed channels for fast ion diffusion and transfer. The activated carbon material has a high SSA (2998 m2 g−1) and a large Vmicro/Vmeso ratio of 8.26. The specific capacitance of CPC650–1-3 reaches 258 F g−1 at 0.5 A g−1 and remains a satisfied retention of 74 % even at 10 A g−1. Moreover, CPC650–1-3//CPC650–1-3 symmetric supercapacitors exhibit a high energy density of 6.4 Wh kg−1 at power density of 500.1 W kg−1. It also has a capacitance retention of 90.1 % after 10,000 cycles, highlighting its excellent cycle stability. These results indicate that corncob-based microporous carbon materials have broad application prospects in promoting the high added-value utilization of biomass waste and the development of high-performance supercapacitors.