Biomass-derived activated carbon electrode coupled with a redox additive electrolyte for electrical double-layer capacitors

Electrical double-layer capacitors (EDLCs) using a biomass-derived activated carbon electrode with Na2SO4–NaI–KI as a redox additive electrolyte were investigated. Biomass-derived activated carbon materials from pomelo peels were prepared by chemical activation in potassium hydroxide followed by carbonization. The biomass-derived activated carbon has a high specific surface area of 1360 m2 g−1, which is suitable for electrode materials. Moreover, a stable couple inorganic redox additive electrolyte were studied by the addition of NaI and KI to Na2SO4 forming a redox additive electrolyte. The electrical double-layer based on activated carbon/Na2SO4–NaI–KI/activated carbon has an excellent specific capacitance (334.3 F g−1), which is 412% higher in comparison with that of activated carbon/Na2SO4/activated carbon (81.14 F g−1) at the same current density of 0.5 A g−1. The EDLC using Na2SO4–NaI–KI electrolyte has a high energy density of 22.75 W h kg−1, which is approximately four times higher than EDLCs based on Na2SO4 (5.52 W h kg−1).