MnO2/ZnCo2O4 with binder-free arrays on nickel foam loaded with graphene as a high performance electrode for advanced asymmetric supercapacitors

Abstract

ZnCo₂O₄ nanosheets were successfully arrayed on a Ni foam surface with graphene using a hydrothermal method followed by annealing treatment; then MnO₂ nanoparticles were electrodeposited on the ZnCo₂O₄ nanosheets to obtain a synthesized composite binder-free electrode named MnO₂/ZnCo₂O₄/graphene/Ni foam (denoted as MnO₂/ZnCo₂O₄/G/NF). After testing the binder-free composite electrode of MnO₂/ZnCo₂O₄/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 MnO₂/ZnCo₂O₄/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 MnO₂/ZnCo₂O₄/graphene composite material is an outstanding electrode material for electrochemical capacitors.