High-surface area carbons from renewable sources with a bimodal micro-mesoporosity for high-performance ionic liquid-based supercapacitors

Abstract

Highly porous materials with a bimodal pore size distribution in the micro-mesopore range have been produced from biomass by adding melamine to the hydrochar/KOH mixture used in the activation process. These carbons are characterized by BET surface areas in excess of ∼3300 m2 g−1 and a porosity equally distributed between micropores and mesopores. The use of melamine in the synthesis process not only extends the pore size distribution into the mesopore region, but leads to the incorporation of a certain amount of nitrogen atoms into the carbon framework. These materials combine high ion adsorption capacities (micropores) and enhanced ion-transport kinetics (mesopores) leading to an outstanding capacitive performance in ionic liquid-based supercapacitors. Thus, they have specific capacitances >160 F g−1 at 1 A g−1 and >140 F g−1 at 60 A g−1 in both pure ionic liquid and in acetonitrile-diluted ionic liquid, enabling these materials to store up to a maximum of ca. 60 W h kg−1 in both kinds of electrolytes and deliver ca. 20 W h kg−1 at ∼42 kW kg−1 (discharge time ca. 2 s) in pure ionic liquid and ∼25–30 W h kg−1 at ∼97–100 kW kg−1 (discharge time ∼1 s) in acetonitrile-diluted ionic liquid.