Facile synthesis of mesoporous ZnCo.sub.2O.sub.4 nanosheet arrays grown on rGO as binder-free electrode for high-performance asymmetric supercapacitor

Asymmetric supercapacitor (ASC) with high energy density has been developed successfully using rGO/ZnCo.sub.2O.sub.4 composite as positive electrode and activated porous carbon (AC) derived from lotus leaves as negative electrode in KOH solution. Mesoporous ZnCo.sub.2O.sub.4 nanosheet arrays grown on rGO were prepared via a simple hydrothermal method followed by calcination. RGO/ZnCo.sub.2O.sub.4 composite exhibited excellent electrochemical performance, which can achieve a specific capacity of 680 F g.sup.-1 at current density of 1 A g.sup.-1. Due to the high capacitance of porous rGO/ZnCo.sub.2O.sub.4 nanosheet structure and synergistic effect between the positive and negative electrodes, the RGO/ZnCo.sub.2O.sub.4//AC ASC showed excellent performance with high specific capacitance of 110 F g.sup.-1 at 0.5 A g.sup.-1 and good cycling stability with only 2.7% loss of available specific capacitance after 3000 cycles. More importantly, the maximum energy density of this ASC can achieve 31.25 W h kg.sup.-1 at a power density of 375 W kg.sup.-1. In addition, this ASC can store charge efficiently and two ASCs in series can light up a LED, which can last for over 15 min. These encouraging results show its great potential in the application of energy storage devices.