Applied Surface Science, 2018, 456, 959-966

Junxia Guo, Binling Chen, Qian Hao, Jun Nie, Guiping Ma*

In this report, novel pod-like nitrogen-doped carbon fibers encapsulated with cobalt/cobalt oxide nanoparticles (Co/CoOx-N-C) were prepared by a facile method. Co/CoOx-N-C can be readily obtained from the carbonization of electrospun ZIF-67@PAN fiber. Both effects of ZIF-67 crystal size and pyrolysis temperature on the ORR were investigated. The optimal Co/CoOx-N-C-l, which has an average ZIF-67 size of 370 nm and a carbonization temperature of 800 °C, presents features of 1D hierarchical porosity pod-like structure, dispersion of nanoparticles, high content of N dopant, and high degree of graphitization, resulting in an excellent ORR performance. Co/CoOx-N-C-l presents an onset potential of -0.07 V (vs Ag/AgCl), a half-wave potential of -0.144 V, and a diffusion limited current density at 0.6 V of 4.9 mA/cm².The relative current of Co/CoOx-N-C-l (90.1%) is much higher than that of the 20 wt% Pt/C (79.8%) after a 36,000 s of continuous operation. In addition, Co/CoOx-N-C-l was further applied as a cathode catalyst of the Zn-air battery. It exhibited an outstanding discharge specific capacity (610 mAh/g) and a comparable discharge voltage to that of 20 wt% Pt/C and RuO₂. This study may provide a novel strategy to generate pod-like structured nanocomposites for energy devices.