MnO2 nanosheet-coated Co3O4 complex for 1.4 V extra-high voltage supercapacitors electrode material

Abstract

Transition metal oxide-based aqueous supercapacitors rarely possess the ability of high potential windows (1.8–2.4 V), which tremendously restricts the possibility of constructing supercapacitors devices with superior energy density. Therefore, a novel strategy is conceived to synthesize a hierarchical Co3O4/MnO2 composite material which broadens the window voltage of the supercapacitors greatly. The MnO2 nanosheets are covered on the surface of Co-MOF-drived Co3O4 nanocages. The morphology and coverage density of MnO2 can be adjusted by the amount of KMnO4. The optimized electrode Co3O4/MnO2-3 exhibits excellent specific capacitance (292 F g−1 at 4 A g−1) and remarkable cycling stability (87.4% retention after 5000 cycles) in 1 M Na2SO4 aqueous electrolyte when the working voltage extends to 1.4 V (vs Ag/AgCl). Furthermore, Asymmetric aqueous supercapacitors assembled with Co3O4/MnO2 as the cathode and activated carbon as the anode displays maximal window voltage of 2.4 V with negligible oxygen evolution reaction, high energy density (46.2 W h kg−1) and excellent cycling stability (84.5% capacitance retention after 5000 cycles). The LED is successfully lit by only one device without any other energy assistance.