Hollow NiCo2O4 nanospheres supported on N-doped carbon nanowebs as efficient bifunctional catalyst for rechargeable and flexible Zn-air batteries

A novel NiCo2O4/N-doped carbon nanowebs serving as a bifunctional electrocatalyst, consisting of hollow NiCo2O4 nanospheres and N-doped carbon nanowebs are prepared through a liquid-phase synthesis method accompanied by subsequent heat treatment. The N-doped carbon nanowebs mainly contribute to the high activity for oxygen reduction reaction, whereas the NiCo2O4 nanospheres act as an active phase for oxygen evolution reaction. The electrocatalytic performance is promoted by the synergistic effect between NiCo2O4 and N-doped carbon nanowebs. Benefiting from the hollow and N-doped structure with merits of more activity sites, fast charge and mass transport, the NiCo2O4/N-doped carbon nanowebs exhibit an excellent bifunctional catalytic activity, high selectivity of the apparent 4e(-) pathway, small Delta E values and long-term durability. Rechargeable Zn-air batteries using NiCo2O4/N-doped carbon nanowebs as catalyst display a lower overpotential, a high capacity (826.9 mAh g(-1)), a high energy density (954.2 Wh Kg(-1)) and long-term stability (600 cycles at 5 mA cm(-2)), when compared to commercial Pt/C + Ir/C. Furthermore, the NiCo2O4/N-doped carbon nanowebs is directly used as air catalyst in flexible Zn-air batteries, which also exhibit superior flexibility and cycling stability. This work provide a new method for developing highly efficiency electrocatalyst, rechargeable and flexible Zn-air batteries. (C) 2019 Elsevier Ltd. All rights reserved.