Boosting oxygen reduction catalysis with tailorable active-N-dominated doped defective CNTs

Controlled doping of specific N species is considered to be an effective yet a challenging strategy to boost the ORR performance of the N-doped carbon. Herein, we report a facile synthesis of tailored active-N-dominated doped defective carbon nanotube (CNT) catalysts by in-situ pyrolysis of defective CNT (OCNT) coated with cobalt(II) ions in ammonia atmosphere. With the guidance of defects and cobalt(II) ions, more active N species (pyridinic-N, graphitic-N and Co-Nx) related to ORR activity are inductively doped into the OCNT forming the active-N-dominated doped OCNT-N catalyst. The resulting OCNT-N shows more favorable ORR activity with an onset potential of 0.94 V vs. RHE, half-wave potential of 0.82 V vs. RHE and better selectivity toward four electron path of ORR due to the synergistic effect of these active nitrogen species and structural defects. Most encouragingly, the according Zn-air batteries using OCNT-N as cathode catalysts can achieve a peak power density of 170.2 mW cm−2 and show a slight voltage loss of only 0.86% after continuous discharge for 12 h at 10 mA cm−2. Our findings demonstrate that the resulting synergy of active N species induced by defects and cobalt(II) ions and defect sites considerably may contribute to boost ORR catalytic activity. [Display omitted] •Pre-oxidization renders carbon nanotubes more structural defects liable to N doping.•More oxygen functional groups related to defects induce the doping of active nitrogen species.•A tailored active-N-dominated doped CNT prepared by pyrolysis of OCNT coated with Co2+ in ammonia atmosphere.•Defects tailored N-doped CNT shows enhanced activity toward ORR.