Paramecium-like α-MnO2 hierarchical hollow structures with enhanced electrochemical capacitance prepared by a facile dopamine carbon-source assisted shell-swelling etching method†
Abstract
Enhancement of the electrochemical performances of electrode materials is a great challenge in the electrochemical capacitor field. Herein, a novel paramecium-like α-MnO2 hierarchical hollow structure used as an electrode material has been successfully prepared, which possesses an ultra-high specific surface area (285 m2 g−1), uniform crystal orientation, and high specific capacitance (554.3 F g−1 at 1 A g−1) and exhibits 97.9% capacitance retention after 5000 cycles. The earlier carbonaceous coating transformed from dopamine plays an important role in forming this novel paramecium-like morphology. The shells are constructed of ultra-thin α-MnO2 nanoflakes with highly uniform and preferentially exposed [001] crystal orientation. The high specific surface area increases the electrolyte–electrode contact area and the unique orientated structure effectively facilitates ion transportation. Quasi in situ electron energy-loss spectroscopy (EELS) analysis for both hierarchical hollow structures and commercial products at different charge–discharge stages indicates that Mn in our products can be almost completely restored to its original oxidation valence state due to a complete redox reaction, while there is still a fraction of Mn in the commercial product that cannot be restored, which causes the reduction of specific capacitance and retention. All the results suggest that this novel α-MnO2 hierarchical hollow structure with selective growth orientation might become an attractive type of electrode material.