Tremella-like NiO microspheres embedded with fish-scale-like polypyrrole for high-performance asymmetric supercapacitor

Tremella-like NiO microspheres embedded with fish-scale-like polypyrrole (PPy) were synthesized by polymerizing pyrrole (Py) onto uniform NiO nanosheets. PPy has a fish-scale-like appearance with a thickness of approximately 10 nm, and is connected to the NiO nanosheet surface. NiO/PPy microspheres (diameter of ∼4 μm) were applied as the electrode material in a supercapacitor. The NiO/PPy-6 obtained under a NiO : Py molar ratio of 6 shows a high specific capacitance of 3648.6 F g−1 at 3 A g−1 and good rate capability (1783 F g−1 at a high current density of 30 A g−1). An asymmetric supercapacitor (ASC) was fabricated using NiO/PPy-6 and activated carbon (AC) as the positive electrode and the negative electrode, respectively. NiO/PPy-6//AC can achieve a high specific capacitance of 937.5 F g−1 at 3 A g−1 and a high energy density of 333.3 W h kg−1 at a power density of 2399.99 W kg−1. The excellent supercapacitor performance is assigned to the combined contribution of both components and the unique heterostructure in NiO/PPy-6.