A challenge still remains to develop high‐performance and cost‐effective air electrode for Li‐O2 batteries with high capacity, enhanced rate capability and long cycle life (100 times or above) despite recent advances in this field. In this work, a new design of binder‐free air electrode composed of three‐dimensional (3D) graphene (G) and flower‐like δ‐MnO2 (3D‐G‐MnO2) has been proposed. In this design, graphene and δ‐MnO2 grow directly on the skeleton of Ni foam that inherits the interconnected 3D scaffold of Ni foam. Li‐O2 batteries with 3D‐G‐MnO2 electrode can yield a high discharge capacity of 3660 mAh g−1 at 0.083 mA cm−2. The battery can sustain 132 cycles at a capacity of 492 mAh g−1 (1000 mAh gcarbon −1) with low overpotentials under a high current density of 0.333 mA cm−2. A high average energy density of 1350 Wh Kg−1 is maintained over 110 cycles at this high current density. The excellent catalytic activity of 3D‐G‐MnO2 makes it an attractive air electrode for high‐performance Li‐O2 batteries.

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In this work we present a controllable synthesis of hollow nanostructures of a-Fe 2 O 3 by a facile hydrothermal route using FeCl 3 ?6H 2 O as the iron source and NH 4 H 2 PO 4 as the shape-directing agent. We found that the morphology of a-Fe 2 O 3 experienced a continuous change from thin nanospindles to flat nanodisks via finely tuning the phosphate ion concentration due to the selective absorption of phosphate ions onto the Fe 2 O 3 nanostructures. At a given phosphate ion concentration, prolonging the reaction time led to the formation of hollow nanostructures (nanotubes, nanobeads, and nanorings) due to the dissolution and re-crystallization of Fe 2 O 3 . We also found that morphology-preserved conversion from a-Fe 2 O 3 to magnetic Fe 3 O 4 /C can be achieved during the CVD reactions in C 2 H 2 . The Fe 3 O 4 /C nanocomposites with uniformly coated carbon layers exhibited morphology-dependent magnetic properties.