Nanoporous Carbon Derived from Green Material by an Ordered Activation Method and Its High Capacitance for Energy Storage.

Carbon materials have been widely used as electrode materials for supercapacitors, while the current carbon precursors are mainly derived from fossil fuels. Biomass-derived carbon materials have become new and effective materials for electrodes of supercapacitors due to their sustainability, low pollution potential, and abundant reserves. Herein, we present a new biomass carbon material derived from water hyacinth by a novel activation method (combination of KOH and HNO3 activation). According to the electrochemical measurements, the material presents an ultrahigh capacitance of 374 F g-1 (the current density is 1 A g-1). Furthermore, the material demonstrates excellent rate performance (105 F g-1 at a higher density of 20 A g-1) and ideal cycling stability (87.3% capacity retention after 5000 times charge-discharge at 2 A g-1). When used for a symmetrical supercapacitor device, the material also shows a relatively high capacity of 330 F g-1 at 1 A g-1 (a two-electrode system). All measurements suggest the material is an effective and noteworthy material for the electrodes of supercapacitors.