标题：3D hierarchical nitrogen-doped carbon nanoflower derived from chitosan for efficient electrocatalytic oxygen reduction and high performance lithium–sulfur batteries

Abstact：Despite diverse carbon materials being intensively applied in energy storage and conversion, efficient optimization of the carbon structure to further improve its performance is still a great challenge. Herein, we design and fabricate a highly uniform 3D hierarchical N-doped carbon nanoflower (NCNF) using lowcost chitosan as the nitrogen and carbon source by a silica template method. The as-prepared NCNF with abundant meso-porous channels displays a high surface area (907 m2 g1) and large pore volume (1.85 cm3 g1), thereby demonstrating high performance as a bifunctional material for the electrocatalytic oxygen reduction reaction (ORR) and in lithium–sulfur batteries. As a metal-free ORR electrocatalyst, the NCNF exhibits excellent electrochemical activity comparable to that of commercial Pt/C (20 wt%), and much better methanol tolerance and durability. As sulfur accommodation for a Li–S battery cathode, the NCNF high loading content of sulfur (80 wt%) achieves an extremely high capacity (1633 mA h g1 at 0.2C), excellent rate capability (916 mA h g1 at 5C) and good cycling performance with a capacity decay of 0.07% per cycle over 500 cycles at 1C. Even when the area density is improved to 4.5 mgsulfur cm2, the battery delivers a high areal capacity of 5.5 mA h cm2 (0.37 mA cm2) and still maintains 3 mA h cm2 after 200 cycles with a smaller capacity decay of 0.07% per cycle at a high area current density of 3.77 mA cm2. Significantly, the carbon materials recycled from the Li–S cathode after 500 cycles are reused as ORR electrocatalysts, displaying more excellent electrocatalytic activity than Pt/C (20 wt%)

原文：