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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 highperformance energy storage application.In recent years, with the purpose of turning waste into treasure and reducing environmental hazard, waste management for the production of high-valuable carbon materials has received considerable attention 1 . Specially, biowastes are viewed as the most outstanding natural carbon precursors by virtue of their rich source, low-cost and sustainability 2-4 . So far, many biowastes have been recycled to synthesize carbon materials, but their applications are still limited by low carbon yield and unsatisfied pore structure 5-7 . Thus, effective methods are necessary to control carbonization process and optimize pore distribution for meeting the demands of various intended applications.Until now, several strategies have been developed for the fabrication of porous carbons, including hydrothermal carbonization 8 , hard template 9 and molten-salt route 10 , etc. Generally the widely used carbon-rich precursors are polymers 11 , metal-organic frameworks 12 , organic complex 13 and carbohydrates 14 . Meanwhile, natural biomass is also widely used as carbon precursors, such as salvia splendens 15 , clover stems 16 , moringa oleifera branches 17 , ginkgo leaves 18 , and pollens 19 . Moreover, with considering environmental protection and resource recycle, biowastes are viewed as more promising natural carbon precursors 20 . Currently, various biowastes from plants or animals have been used for porous carbons production, such as kraft lignin 21 , soybean residue 22 , dairy manure 23 , bagasse wastes 24 and peanut shell 1 . In many cases, the added catalysts (or activators) are difficult to penetrate into the inside of carbon precursors, resulting in low carbon yield and unmanageable pore distribution 25 . Besides, many kinds of biowastes are difficult to collect or have a low production. I...

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Converting waste plastics into valuable carbon materials has obtained increasing attention. In addition, carbon materials have shown to be the ideal electrode materials for double-layer supercapacitors owing to their large specific surface area, high electrical conductivity, and stable physicochemical properties. Herein, an easily operated approach is established to efficiently convert waste poly(ethylene terephthalate) beverage bottles into porous carbon nanosheet (PCNS) through the combined processes of catalytic carbonization and KOH activation. PCNS features an ultrahigh specific surface area (2236 m 2 g −1 ), hierarchically porous architecture, and a large pore volume (3.0 cm 3 g −1 ). Such excellent physicochemical properties conjointly contribute to the outstanding supercapacitive performance: 169 F g −1 (6 M KOH) and 135 F g −1 (1 M Na 2 SO 4 ). Furthermore, PCNS shows a high capacitance of 121 F g −1 and a corresponding energy density of 30.6 Wh kg −1 at 0.2 A g −1 in the electrolyte of 1 M TEATFB/PC. When the current density increases to 10 A g −1 , the capacitance remains at 95 F g −1 , indicating the extraordinary rate capability. This work not only proposes a facile approach to synthesize PCNS for supercapacitors, but also puts forward a potential sustainable way to recycle waste plastics and further hopefully mitigates the waste plastics-related environmental issues.