High yield conversion of biowaste coffee grounds into hierarchical porous carbon for superior capacitive energy storage
Xiaoguang Liu, Shuai Zhang, Xin Wen, Xuecheng Chen, Yanliang Wen, Xiaoze Shi, Ewa Mijowska
Abstract
Abstract Recently great efforts have been focused on converting biowastes into high-valued carbon materials. However, it is still a great challenge to achieve high carbon yield and controllable porous distribution in both industrial and academic research. Inspired by the multi-void structure of waste coffee grounds, herein we fabricated hierarchical porous carbon via the combination of catalytic carbonization and alkali activation. The catalytic carbonization process was applied to obtain well-defined mesoporous carbon with carbon yield as high as 42.5 wt%, and subsequent alkali activation process produced hierarchical porous carbon with ultrahigh specific surface area (3549 m 2 g −1 ) and large meso-/macropores volume (1.64 cm 3 g −1 ). In three-electrode system, the electrode exhibited a high capacitance of 440 F g −1 at 0.5 A g −1 in 6 M KOH aqueous electrolyte, superior to that of many reported biomass-derived porous carbons. In two-electrode system, its energy density reached to 101 Wh kg −1 at the power density of 900 W kg −1 in 1-Ethyl-3-Methylimidazolium Tetrafluoroborate (EMIMBF 4 ). This work provided a cost-effective strategy to recycle biowastes into hierarchical porous carbon with high yield for high-performance energy storage application.