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 m2 g−1. The preparation process of the SLSAC samples includes carbonization at 400 °C in argon (denoted as c-SLS) and followed a KOH chemical activation using various KOH/c-SLS mass ratios at 800 °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.