Porous NiCo₂O₄ nanotubes as a noble-metal-free effective bifunctional catalyst for rechargeable Li-O₂ batteries

Porous NiCo₂O₄ nanotubes have been successfully synthesized using a facile and cost-effective electrospinning method and used as a noble-metal-free catalyst for rechargeable Li-O₂ batteries. The as-synthesized NiCo₂O₄ nanotubes possess hollow cavities and porous walls, and were found to significantly improve the electrochemical performance of Li-O₂ batteries, by endowing them with a high initial discharge capacity, reduced overpotential as well as good rate capability. Excellent cycling stability over 110 cycles with a highly discharged voltage platform of 2.4 V at 200 mA g_c^-1 was achieved. By means of FESEM, XRD, Raman spectroscopy and GITT analysis, toroidal-shaped Li₂O₂ particles were identified as the dominant discharge product and it was revealed that the Li₂O₂ can be completely decomposed during the charging process, indicating its superior reversibility as an effective bifunctional catalyst for Li-O₂ batteries. All the results indicated that the porous NiCo₂O₄ nanotubes expressed intriguing properties and great potential applications as a noble-metal-free effective bifunctional catalyst for rechargeable Li-O₂ batteries.