N-Doped Hollow Carbon Tubes Derived N-HCTs@NiCo2O4 as Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc-Air Batteries

It is paramount important to design and explore excellent bifunctional oxygen electrocatalysts to conquer or weaken the shortcomings encountered by Zinc-air batteries at present. Herein, a novel N-doped hollow carbon tubes modified by uniform NiCo2O4 nanocrystals (N-HCTs@NiCo2O4), has been developed as an extremely efficient bifunctional catalyst. The hollow structure of N-HCTs possesses a large specific surface area of 610.60 cm g-1 which provides abundant active N-dopant sites for the oxygen reduction reaction, whereas the NiCo2O4 nanocrystals serve as the positive phase for the oxygen evolution reaction. It is found that the efficient bifunctional activity is obtained by establishing a coupling interface between N-HCTs and NiCo2O4. The N-HCTs@NiCo2O4 composite has a half-wave potential of 0.81 V toward ORR and the overpotential of 330 mV at a current density of 10 mA cm-2 toward OER as compared with noble metal catalysts. The N-HCTs@NiCo2O4 as the cathode catalyst for Zinc-air batteries exhibits superior peak power density (150 mW cm-2), specific capacity up to 779 mAh g-1, and good stability even after 100 h of cyclic charge/discharge cycles N-HCTs@NiCo2O4 has good prospects for practical applications of non-precious metal catalysts in the cathode of Zinc-air batteries.