Formation of ultrafine three-dimensional hierarchical birnessite-type MnO₂ nanoflowers for supercapacitor

Ultrafine (50-100 nm in diameter) birnessite-type MnO₂ nanoflowers assembled by numerous ultrathin nanosheets (3-6 nm in thickness and 30-50 nm in width) have been synthesized via a simple and scalable solution route under ambient conditions. The ratio of reactants plays a significant role in the formation of MnO₂ nanoflowers and the as-prepared MnO ₂ hierarchical nanostructure exhibits excellent electrochemical performance with high specific capacitance (251.3 F g^-1 at 0.5 A g^-1) and superior cycling stability (only 7.5% SC loss after 10,000 cycling test) and good rate capability. The unique microstructures of MnO ₂ nanoflowers are responsible for their superior electrochemical properties, and thus it may be a promising for supercapacitor application.