Hierarchical hollow-tubular porous carbon microtubes prepared via a mild method for supercapacitor electrode...

In this paper, hollow-tubular porous carbons were synthesized from abundant biomass Cycas fluff (CF) through simple carbonization followed by an NaHCO₃ mild activation process. After activation, the tubular structure of the CF was retained, and a hierarchical structure of micropores, mesopores and macropores was formed. When the optimal mass ratio of NaHCO₃/CF is 2, the obtained porous carbon CF-HPC-2 sample has a large specific surface area (SSA) of 516.70 m² g^-1 in Brunauer-Emmett-Teller (BET) tests and a total pore volume of 0.33 cm³ g^-1. The C, O, N and S contents of CF-HPC-2 were tested as 91.77 at%, 4.09 at%, 3.54 at%, and 0.6 at%, respectively, by elemental analysis. Remarkably, CF-HPC-2 exhibits a high volume capacitance (349.1 F cm^-3 at 1 A g^-1) as well as a higher rate capability than other biomass carbon materials (289.1 F cm^-3 at 10 A g^-1). Additionally, the energy density of the CF-HPC-2 based symmetric supercapacitor in 2 M Na₂SO₄ electrolyte at 20 kW kg^-1 is 27.72 W h kg^-1. The particular hollow tubular morphology and activated porous structure determine the excellent electrochemical performance of the material. Hence, this synthetic method provides a new way of storing energy for porous carbon as high volumetric capacitance supercapacitor materials.