Walnut septum-derived hierarchical porous carbon for ultra-high-performance supercapacitors

The conversion of biomass waste into economical and high-performance energy storage devices receives significant attention. Herein, a facile and green method to prepare porous active carbon from walnut septum is applied to the electrode materials of supercapacitors. The effect of chemical etching reagent (KOH) on the microstructure and specific capacitance of the porous carbon are explored. The modified BC-2.0, with a KOH/walnut septum mass ratio of 2:1, exhibits large specific surface area of 1003.9 m2·g−1 with hierarchical micro-mesoporous structures. BC-2.0 reveals a superior specific capacitance of 457 F·g−1 at 1 A·g−1. The flexible symmetric supercapacitor in gel electrolyte (KOH/PVA) exhibits considerable synergetic energy–power output performance. The results indicate that walnut septum is a better precursor to obtain activated carbons relative to other biomass carbon sources. The large mesoporosity after activation effectively boosts the electrochemical properties of supercapacitor. Consequently, the walnut septum has potential to be a superior electrode material for supercapacitors.Graphical abstract