Agricultural waste-derived activated carbon/graphene composites for high performance lithium-ion capacitors

Agricultural waste, corncob-derived activated carbon (AC) is prepared by pre-carbonization of the precursors and activation of KOH of the pyrolysis products. The AC oxidized by HNO₃ is called OAC. The OAC/reduced graphene oxide (rGO) composites are prepared by urea reduction (aqueous mixture of OAC and graphene oxide). The influence of the mass ratio of graphene oxide (GO) on the electrochemical properties of OAC/rGO composites as electrode materials for electrochemical capacitors is studied. It is found that the rGO sheets were used as a wrinkled carrier to support the OAC particles. The pore size distribution and surface area are dependent on the GO mass ratio. In addition, the rate capability of OAC is improved by introducing GO. For the OAC/rGO composites prepared from precursors with a GO mass ratio of 5%, the best rate performance was achieved. The lithium ion capacitor, based on OAC/rGO as cathode and Si/C as anode, exhibits a high energy density of 141 W h kg^-1 at 1391 W kg^-1. 78.98% capacity retention is achieved after 1000 cycles at 0.4 A g^-1.