▎ 摘　　要

The facile synthesis of MnO2 crystals with a controllable structure was achieved through a simple hydrothermal reaction. The MnO2 grew to form a quasicolumnar shape with a structure that can be controlled through the simple variation of the pH during the synthesis. This control strategy could be applied to other solvents to obtain materials with unique structures. Furthermore, composites of the as-synthesized hollow MnO2 with N-doped graphene (rGN) are electrocatalysts for the oxygen reduction reaction under mild conditions. The electrocatalysts were characterized through X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and electrochemical measurements. The prepared composite exhibited excellent catalytic performance as well as improved durability and tolerance to methanol relative to those of a commercial catalyst (20 wt.-% Pt/C); thus, such materials show potential for application as electrocatalysts.