Carbon-nanotube-grafted and nano-Co3O4-doped porous carbon derived from metal-organic framework as an excellent bifunctional catalyst for zinc-air battery

In this study, carbon-nanotube (CNT)-grafted and nano Co3O4-doped porous carbon was prepared by the carbonization of a synthesized zeolitic imidazolate framework compound (ZIF-67/ZIF-8) followed by an oxidation treatment. The novel catalyst demonstrated excellent ORR and OER because of the Co3O4 nano-particles and nitrogen-doped in the carbon framework (NC). In addition, the carbon nanotube grafted on the framework provided a good electrical conductivity while the carbon framework matrix provided a porous skeleton which is beneficial for the mass transfer of electrolyte. In the ORR study, the novel catalyst, CNT-Co3O4/NC, showed a half-wave potential of 0.124 V at 0.1 M KOH (Pt/carbon: -0.152 V) while the limited current density is 4.84 mA/cm(2) (Pt/carbon: 4.9 mA/cm(2)). In terms of OER performance, the potential is 0.819 V at current density of 10 mA/cm(2) (Ir/carbon: 0.771 V). The CNT-Co3O4/NC catalyst shows a specific capacitance of 814 mAh/g (1.19 V at 50 mA/cm(2)), which is very close to the theoretical capacitance (820 mAh/g) and the maximum power density was 267 mW/cm(2) (0.746 V at 385 mA/cm(2)) while 255 mW/cm(2) (0.711 Vat 360 mA/cm(2)) was obtained using Pt/carbon catalyst. We believe that the novel CNT-Co3O4/NC can be used as an excellent catalyst in the zinc-air battery.