Waste soybean dreg-derived N/O co-doped hierarchical porous carbon for high performance supercapacitor

Soybean dreg is a byproduct of soybean oil extraction, also called “soybean meal”. Here, we demonstrate that a N/O co-doped hierarchical porous carbon can be derived from soybean dreg through a facile KOH activation and high-temperature carbonization for high performance electrode material of supercapacitor in both aqueous (6.0 M KOH) and ionic liquid (EMIMBF4) electrolytes. The material carbonize at 800 °C possesses a high ion-accessible surface (1837.26 m2 g−1) induced by the interconnected 3D network and a high level of micropores (0.71 cm3 g−1), which are beneficial for large-scale ion storage and high-speed ion transport. Furthermore, high contents of nitrogen (1.58 at.%) and oxygen (11.41 at.%) can induce the contribution of faradaic pseudocapacitance for electric double-layer capacitor (EDLCs). As a result, the N/O co-doped hierarchical porous carbon derived from waste soybean dregs displays a superior specific capacity of 321.1 F g−1 at the current density of 1 A g−1, high rate capability of 249.7 F g−1 at 30 A g−1 and excellent cycling durability of 99.5% at 1 A g−1 after 10 000 cycles in three electrode system using 6 M KOH electrolyte. Notably, an excellent energy density can reach as high as 22.1 Wh kg−1 at the power density of 875.0 W kg−1 in two-electrode system using EMIMBF4 electrolyte. This green, renewable and eco-friendly biomass porous carbon might be widely used in the fields of energy conversion device for now and in the foreseeable future.