Cobalt nanoparticles encapsulated in N-doped graphene nanoshells as an efficient cathode electrocatalyst for a mechanical rechargeable zinc-air battery

Air-cathodes with properties of efficiency, durability and low cost are essential for high performance metal-air batteries and fuel cells for practical applications. In this study, non-precious metal ORR electrocatalysts derived by the encapsulation of Co nanoparticles in N-doped graphene nanoshells were synthesized by a typical one-step pyrolysis process. Compared with commercial Pt/C catalysts, the prepared Co-30@N-G hybrid electrocatalyst showed a high ORR activity at the same level in an alkaline medium. Subsequently, the Co-30@N-G hybrid electrocatalyst has been used as a cathode of Zn-air batteries, which displays equivalent performance to the systems derived using a commercial Pt/C catalyst. The Co-30@N-G derived mechanical rechargeable Zn-air battery showed a persistent flat discharge curve with minimum voltage loss at a high discharge rate of 40 mA cm(-2). The robustness of the Co-30@N-G ORR catalyst can allow the batteries to work constantly by periodically replacing the Zn anode and electrolyte, presenting an efficient and economical cathode for Zn-air flow batteries or Zn-air fuel cells.