Hierarchically porous graphene/wood-derived carbon activated using ZnCl2 and decorated with in situ grown NiCo2O4 for high–performance asymmetric supercapacitors

Abstract

Although wood-derived carbon (WC) and its derivatives are promising electrodes for supercapacitors because of their hierarchically porous architecture, superior mechanical flexibility, and environmental friendliness, pure WC electrodes usually exhibit poor wettability, inferior areal capacitance, and unsatisfactory electrical conductivity. Herein, hierarchically porous graphene/wood-derived carbon (GWC) aerogels are fabricated for high-performance supercapacitor electrodes by chemical reduction of graphene oxide/wood hydrogels, followed by directional-freezing, freeze-drying, and carbonization at 1000 °C. An activated GWC (AGWC) anode is prepared by activating GWC using ZnCl₂ to create more mass transport paths and increase wettability, while the cathode is synthesized by in situ growth of NiCo₂O₄ (NCO) in the channels of GWC to bring about pseudocapacitance and increase energy storage sites. The resultant NCO@GWC cathode and AGWC anode exhibit superior capacitances of 8540 and 10 965 mF cm⁻² (854 and 183 F g⁻¹) at 1 mA cm⁻², respectively. The assembled NCO@GWC//AGWC asymmetric supercapacitor exhibits a superior areal capacitance of 7116 mF cm⁻² at 1 mA cm⁻², a high energy density of 2.2 mW h cm⁻² (5.6 mW h cm⁻³), a power density of 45.1 mW cm⁻² (112.8 mW cm⁻³), and an excellent cycling stability of 100% capacitance retention over 1000 cycles at 10 mA cm⁻².