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

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 (CPC X ) 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 CPC 650 – 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 m 2 g −1 ) and a large V micro /V meso ratio of 8.26. The specific capacitance of CPC 650 – 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, CPC 650 – 1-3 //CPC 650 – 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. • Microporous carbons were prepared from agricultural waste corncob. • The pore structure of materials was regulated by changing the activation conditions. • The relationships among activation conditions, V micro /V meso , specific surface area and specific capacitance were investigated. • A remarkable capacitance retention of 90.1 % after 10,000 cycles at 10 A g −1 .