Electrochemical performances of hydrothermal tannin-based carbons doped with nitrogen

Six porous carbon materials, produced by hydrothermal treatment of flavonoid tannin and subsequent carbonization at 1173 K, were tested as electrodes of supercapacitors. Four of these carbons were doped with nitrogen by putting tannin in contact with ammonia before or during the hydrothermal treatment. The pyrolyzed hydrothermal carbons had moderate surface areas, within the range 442-684 m(2) g(-1), and nitrogen contents ranging from 0.7 to 8.0 wt.%. Specific capacitances as high as 320 F g(-1) and normalized capacitances as high as 58 mu F cm(-2) were measured at 2 mV s(-1). These performances are comparable with those obtained with high surface area-activated carbons, whereas, normalized capacitances values are among the highest ever reported. Mesostructuration, within the range 3-13 nm, of these materials appears to be a good strategy to improve their electrochemical performances at higher scan rates. We confirmed the beneficial role of oxygen up to 18 wt.%, while an optimum in nitrogen content exists from 3 to 6 wt.%. (C) 2015 Elsevier B.V. All rights reserved.