Honeycomb-like Hierarchical Porous Activated Carbons from Biomass Waste with Ultrahigh Specific Surface Area for High-Rate Electrochemical Capacitors

Although highly porous carbon electrode materials from biomass wastes for high-performance electric double-layer capacitors (EDLCs) have attracted great attention recently, the fast charge-discharge performance under ultrahigh current density (100 A g(-1)) still remains a challenge. Herein, we develop a promising route to massively prepare honeycomb-like activated carbon (AC) with hierarchical porous features from spent lotus stems (SLSs) exhibiting an ultrahigh specific surface area of 4190 m(2) g(-1). The preparation process of the SLSAC samples includes carbonization at 400 degrees C in argon (denoted as c-SLS) and followed a KOH chemical activation using various KOH/c-SLS mass ratios at 800 degrees C for 1 h. The SLSAC-5-based electrode (KOH/c-SLS = 5/1) displays a good gravimetric capacitance of 330 F g(-1) at 0.5 A g(-1) with a superior high-rate capacitance of 243 F g(-1) at 100 A g(-1) and presents remarkable cycling stability with a capacitance retention near 100% over 10,000 cycles at 2 A g(-1) using 6 M KOH aqueous electrolyte. Additionally, the SLSAC-5-based sample delivers an energy density of 18.6 W h kg(-1) at 199.2 W kg(-1) with 1 M Na2SO4 electrolyte. Herein, we reveal a simple, promising route to massively generate SLSAC-based samples and investigate prominent electrochemical properties in ultra-fast charge-discharge EDLCs.