Pyrolysis of loofah sponge into N/O self-doped three-dimensional porous carbon for supercapacitor

Electronic-double-layer supercapacitors (EDLC) usually use activated carbon with large specific surface area and abundant pore structure as the electrode active material for adsorption/desorption of electrolyte ions. Featuring huge yield, low price, multi-level structure, and inherent heteroatoms/functional groups, biomass-derived activated carbon has been demonstrating excellent specific capacitance, low electrochemical impedance, and long-term durability in supercapacitor applications. Loofah sponge is an ideal precursor for activated carbon because of its unique cross-linked parallel channel structure that facilitates ion transfer and storage in super- capacitor. Upon pre-carbonization combined with KHCO3-incorporated activation pyrolysis in this study, the loofah sponge is transformed into a three-dimensional hierarchical porous structured carbon (LC-K1-800), while retaining the primary skeleton and heteroatoms (oxygen and nitrogen) of the biomass. The specific capacitance of LC-K1-800 at a current density of 0.2 A g-1 is measured to be 344 F g-1, and that at a current density of 1 A g-1 is 296 F g-1. Moreover, the symmetric two-electrode device assembled by the LC-K1-800 has a specific capacitance of 216 F g-1 at the current density of 0.2 A g-1 and a capacitance retention rate of 103.4 % after 10,000 charge/discharge cycles at the current density of 10 A g- 1, showcasing exceptional cycling stability. Additionally, the symmetric supercapacitor assembled with 1 M Na2SO4 electrolyte has achieved an energy density of 18 Wh kg-1 in a 1.6 V voltage window. The impressive performance of the LC-K1-800 assembled EDLC is derived from the well-developed hierarchical porous structure, robust carbon skeleton, high specific surface area, as well as the superior hydrophilicity of loofah sponge-derived activated carbon. This work provides an outstanding option for high-performance and cost-effective carbon-based EDLC.