Electrochemical behaviour of activated carbons obtained via hydrothermal carbonization

Activated carbons were prepared by chemical activation of hydrochars, obtained by hydrothermal carbonisation (HTC) using low cost and abundant precursors such as rye straw and cellulose, with KOH. Hydrochars derived from rye straw were chemically activated using different KOH/precursor ratios, in order to assess the effect of this parameter on their electrochemical behaviour. In the case of cellulose, the influence of the hydrothermal carbonisation temperature was studied by fixing the activating agent/cellulose ratio. Furthermore, N-doped activated carbons were synthesised by KOH activation of hydrochars prepared by HTC from a mixture of glucose with melamine or glucosamine. In this way, N-doped activated carbons were prepared in order to evaluate the influence of nitrogen groups on their electrochemical behaviour in acidic medium. The results showed that parameters such as chemical activation or carbonisation temperature clearly affect the capacitance, since these parameters play a key role in the textural properties of activated carbons. Finally, symmetric capacitors based on activated carbon and N-doped activated carbon were tested at 1.3 V in a two-electrode cell configuration and the results revealed that N-groups improved the capacitance at high current density.

The authors thank the Spanish MINECO, GV and FEDER (PROMETEOII/2014/010, Projects CTQ2012-31762 and MAT2013-42007-P) and D.S.T. is indebted to MINECO for a predoctoral FPI grant (BES-2010-035238). M. Titirici, Li Zhao and Linghui Yu would like to acknowledge financial support from the Max-Planck Society. Li Zhao is grateful to China Scholarship Council for awarding her a PhD fellowship in Germany.