Facile synthesis of porous helical activated carbon fibers from waste tea and their electrochemical energy storage

As a hopeful material for energy storage, helical carbon fibers (HCFs) have attracted wide attention due to their unique morphology and superior properties. However, the facile synthesis of HCFs with high specific surface area (SSA) and good electrochemical performance is still a challenge. In this study, we synthesized HCFs through a catalyst-free strategy using the helical vessels (HVs) extracted from tea as the bio-template and further obtained the helical porous activated carbon fibers (HPACFs) by KOH activation. The as-prepared HPACFs exhibited a high SSA (3124 m 2 ·g −1 ) and developed pore structure, which provided efficient migration of electrolyte ions and electrons, and thus exhibited excellent electrochemical performance for energy storage. For example, HPACF-5 exhibited a specific capacitance of 488 F·g −1 (at 0.5 A·g −1 ) in a three-electrode system and 187 F·g −1 (1 A·g −1 ) in a two-electrode system, with good cyclic stability (loss ~7% after 3000 cycles at 20 A·g −1 ). The helical porous structure with such high SSA provided a combination of defect sites, sufficient active sites, and nanoporous regions in the bends for ion storage. In addition, these structures also improve the ion diffusion and charge transfer during the discharge process, which is in favor of optimized electrolyte ion and energy storage equipment.