Facile synthesis of CO/N-doped carbon nanotubes and the application in alkaline and neutral metal-air batteries

Nonprecious transition metals [e.g., cobalt (Co), iron (Fe), and zinc (Zn)], and nitrogen doped carbon materials are considered to be the most attractive alternatives to precious metal catalysts. Herein, Cobalt decorated nitrogen-doped carbon nanotubes were synthesized via a facile hydrothermal method and calcination. Benefiting from the N-doping, etching of Co nanoparticles to carbon nanotubes and synergistic effect between the components, the as-prepared Co/nitrogen-doped carbon nanotubes (Co-NCNT) displays a half-wave potential of 0.88 V (vs. RHE), a limiting current density of 5.6 mA cm−2, and electron transfer number of 3.9 in 0.1 M KOH. When applied in metal-air batteries, it delivered maximum power densities of 130.0 mW cm−2, 117.3 mW cm−2 and 58.6 mW cm−2 in alkaline Zn-air, Al-air batteries and neutral Mg-air batteries respectively, outperforming the commercial Pt/C. These demonstrate that the synthesized Co-NCNT is a promising candidate for ORR in metal-air batteries with both alkaline and neutral electrolytes.