MnO 2 /ZnCo 2 O 4 with binder-free arrays on nickel foam loaded with graphene as a high performance electrode for advanced asymmetric supercapacitors.

ZnCo 2 O 4 nanosheets were successfully arrayed on a Ni foam surface with graphene using a hydrothermal method followed by annealing treatment; then MnO 2 nanoparticles were electrodeposited on the ZnCo 2 O 4 nanosheets to obtain a synthesized composite binder-free electrode named MnO 2 /ZnCo 2 O 4 /graphene/Ni foam (denoted as MnO 2 /ZnCo 2 O 4 /G/NF). After testing the binder-free composite electrode of MnO 2 /ZnCo 2 O 4 /G/NF via cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy testing, we found that it exhibited ultrahigh electrochemical properties, with a high specific areal capacitance of 3405.21 F g -1 under a current density of 2 A g -1 , and wonderful cycling stability, with 91.2% retention after 5000 cycles. Moreover, an asymmetric supercapacitor (ASC) based on MnO 2 /ZnCo 2 O 4 /G/NF//G/NF was successfully designed. When tested, the as-designed ASC can achieve a maximum energy density of 46.85 W h kg -1 at a power density of 166.67 W kg -1 . Finally, the ASC we assembled can power a commercial red LED lamp successfully for more than 5 min, which proves its practicability. All these impressive performances indicate that the MnO 2 /ZnCo 2 O 4 /graphene composite material is an outstanding electrode material for electrochemical capacitors.