LAUSR

Abstract Low-cost easily available walnut shells were used as the carbon source to prepare the porous carbon materials. The walnut shell derived porous carbon material was prepared using a simple hydrothermal method followed by the activation routes with K 2 CO 3 . The specific capacitance of this carbon material was 255 F/g at 0.5 A/g. Meanwhile, the obtained carbon material was used as the electrode material in a symmetric all-solid-state supercapacitor. The assembled all-solid-state supercapacitor device exhibits good electrochemical performances including a high specific capacitance (138 mF/cm 2 at 1 mA/cm 2 ) and good stability (96% capacitance retention after 3000 cycles). This new material makes full use of walnut shell waste to provide a useful material for energy storage.