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 NiCo 2 O 4 nanocrystals ( N -HCTs@NiCo 2 O 4 ), 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 NiCo 2 O 4 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 NiCo 2 O 4 . The N -HCTs@NiCo 2 O 4 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@NiCo 2 O 4 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@NiCo 2 O 4 has good prospects for practical applications of non-precious metal catalysts in the cathode of Zinc-air batteries.