Simple and scalable synthesis of hierarchical porous carbon derived from cornstalk without pith for high capacitance and energy density

A sustainable one-pot route for the synthesis of hierarchical porous carbons (HPCs) from cornstalk without pith is developed. Calcium carbonate (CaCO3) as a hard template can promote the activation process and manipulate the pore structure. The interaction of CaCO3 and the activating agent (potassium oxalate) gives rise to an etching effect and gasification, which can tailor the porosity of the carbon. The removal of loose and spongy pith can improve the meso/micropore ratio, significantly increasing the electrochemical capacitance and rate capability. The as-prepared cornstalk rind-based hierarchical porous carbon (CRHPC) with an interconnected pore structure exhibits a high capacitance of 461 F g(-1) at 0.5 A g(-1) in 1 M H2SO4. Meanwhile, it displays good cycling stability, with a high capacitance retention of 90.4% at 10 A g(-1) after 10 000 cycles. Furthermore, the symmetric supercapacitor shows a high energy density of 42.5-33.3 W h kg(-1) at a power density of 0.4-9.3 kW kg(-1) and superior rate capability (78.0% capacitance retention at 20 A g(-1)). The simple removal of loose pith endows the carbon materials with an increased mesopore ratio and graphitization degree, which greatly contribute to rapid ion transportation, low internal resistance and high capacitance and energy density. This low-cost strategy holds great promise in the large-scale production of highly porous carbons from lignocellulose for advanced and efficient energy storage.