Understanding the role of nitrogen and sulfur doping in promoting kinetics of oxygen reduction reaction and sodium ion battery performance of hollow spherical graphene

摘要

Here, a simple, economical one-step doping strategy is adopted to prepare N, S co-doped graphene hollow spheres (NSGHS). The NSGHS exhibits remarkable oxygen-reduction-reaction (ORR) activity with a high half-wave potential (E-1/2) of 0.847 V vs. RHE and considerable long-term stability. When applied as anode materials for sodium-ion batteries (SIBs), it could deliver a high reversible capacity of 385 mAh g(-1) at 500 mA g(-1), excellent rate performance of 308 mAh g(-1) at even 20 A g(-1) and superior cycling performance at 10 A g(-1) during 5000 cycles with negligible capacity fade. DFT calculation reveals that the doping of N and S endows the surrounding carbon with high positive charge and spin density, respectively, making them be highly active ORR catalytic sites except for S itself. Despite the possible oxidization of C-S-C active sites, the rest C atoms of NSGHS will still hold a considerably high catalytic activity superior to those of mono-doped or undoped cases. In addition, S doping will improve the binding between Na and graphene substrate to get a high capacity and N doping effectively curbs the rising of oxygen levels and oxidization of S in C-S-C active sites, thus the excellent stability for ORR and SIBs.

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