High performance electrode materials for electric double-layer capacitors based on biomass-derived activated carbons

Activated carbons (ACs) are successfully synthesized from corncob by a simple chemical activation methodology and demonstrated as novel, suitable electrode materials for electric double-layer capacitors (EDLCs). The as-prepared samples were characterized by SEM, TEM, XPS, FT-IR and N2-sorption followed by further electrochemical characterization. All samples exhibit a high specific surface area, favorable pore size distribution combining good electrical conductivity and excellent capacitive performance. The optimal sample achieved not only high specific capacitance (401.6 F g−1 in 0.5 M H2SO4 and 328.4 F g−1 in 6 M KOH aqueous electrolyte at a current density of 0.5 A g−1), but also showed excellent cycling performance, with 100% and ∼91% retention over 10000 cycles at 5 A g−1 in the above mentioned electrolytes. Furthermore, the sample also displayed improved rate capability with discharge capacitance retention of ∼60% at 20 A g−1 in 0.5 M H2SO4 and ∼75% at 20 A g−1 in 6 M KOH. The results indicate surface functional groups associate with high surface area and appropriate microstructure affect the capacitive performance of corncob-based ACs significantly. Herein, ACs prepared from corncobs are presented as a promising substitute to conventional electrode materials for EDLCs.