Clean production of N, O-doped activated carbon by water vapor carbonization/activation of expired coffee for high-volumetric supercapacitor

Clean production of activated carbon from household expired food provide an alternative way to get value-added product thus benefits waste reutilization and environmental protection. Herein, we fabricated N, O co-doped activated carbons (HCDC) from expired coffee to by a green route of direct water vapor carbonization/activation approach. In our approach, the expired coffee was firstly grinded and then carbonized under water vapor atmosphere. The derived HCDC owns low surface area (172-184 m(2)/g), large packing density (1.81-1.83 cm(3)/g), rich redox-active nitrogen (4.5 atom%) and oxygenic (12.0 atom%) functionalities. As electrode for super capacitor, the HCDC achieves a high gravimetric capacitance of 312F/g at 1.0 A/g (vs 258F/g of commercial AC) and the value can be maintained 223F/g at 20 A/g, showing a high rate capability of 71.5%. Particularly, because of the large packing density, the HCDC exhibits an excellent volumetric supercapacitor performances: ultrahigh volumetric capacitance of 567F/cm(3) (vs 165F/cm3 of commercial AC) and large energy density of 27.8 Wh/L@1820 W/L (vs 7.5 Wh/L@576 W/L for commercial AC) and superlong cycling stability with near 100 capacitance retention after continual 30 000 cycles at large current density of 9.0 A/g, suggesting a promising application for practical energy storage devices.