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

• Ultrafine mesoporous birnessite-type MnO2 nanoflowers have been synthesized via a solution route.
• Hierarchical MnO2 nanoflowers are made up of numerous two-dimensional ultrathin nanosheets.
• MnO2 nanoflowers electrode exhibits superior electrochemical performance.
• It is promising for supercapacitor application.

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 MnO2 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 MnO2 nanoflowers are responsible for their superior electrochemical properties, and thus it may be a promising for supercapacitor application.