Mo2C quantum dots decorated ultrathin carbon nanosheets self-assembled into nanoflowers toward highly catalytic cathodes for Li-O2 batteries

[Display omitted] Mo2C quantum dots decorated ultrathin carbon nanosheets self-assembled into porous nanoflowers (Mo2C/C) are fabricated for Li-O2 batteries. The Mo2C quantum dots with an average size of ≈3 nm are uniformly dispersed on the ultrathin carbon nanosheets. The overpotential of the Mo2C/C is about 1.2 V, which is much lower than that of pure C (1.8 V), revealing the Mo2C/C exhibits higher ORR and OER catalytic activity. The porous structure provides sufficient space between neighboring nanosheets that could allow Li+ ions transport into inner region of the nanoflowers. •The 3D porous Mo2C/C nanoflowers are fabricated through in situ synthesis strategy.•The Mo2C quantum dots (3 nm) are uniformly dispersed on ultrathin cabon nanosheets.•The ultrathin nanosheets and porous structure ensure the fast Li+ and O2 diffusion.•The Mo2C/C nanoflowers show low overpotential and high ORR and OER activities. A desirable oxygen electrode is critical for achieving high capacity Li-O2 battery. Here we have fabricated porous Mo2C/C nanoflowers assembled by ultrathin carbon nanosheets decorated with Mo2C quantum dots using in situ synthesis technique and the subsequent anneal treatment. When evaluated as cathode for Li-O2 battery, the Mo2C/C delivers a relatively high specific capacity of 7500 mAh g-1. With a cut-off capacity of 500 mAh g-1, the Li-O2 battery exhibits an excellent cycling stability for 100 cycles without obvious capacity fading. The battery shows the low discharge/charge gaps of 1.2 V in the first cycle, suggesting the excellent catalytic activity of Mo2C/C for ORR and OER. The excellent performance maybe ascribed to the synergistic effect of ultrathin carbon nanosheets, highly-dispersed Mo2C quantum dots and the special porous structure. The ultrathin carbon nanosheets not only effectively prevent the Mo2C quantum dots from agglomeration, but also improve the conductivity of Mo2C. In addition, the ultrathin carbon nanosheets and porous Mo2C/C nanoflowers could ensure the fast Li+ and O2 diffusion.