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

Abstract

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.