N,O-codoped carbon spheres with uniform mesoporous entangled Co3O4 nanoparticles as a highly efficient electrocatalyst for oxygen reduction in a Zn-air battery.

Highly efficient electrochemical catalysts for oxygen reduction reactions (ORRs) are urgently needed for various energy conversion and storage devices to overcome sluggish ORR kinetics. Here, N,O-codoped carbon spheres with uniform mesopores and a high specific surface area were used as supports for decorating Co3O4 nanoparticles via a facile immersion route. In addition to the benefit of ions and gas mass transfer, the abundant mesopores present in the three-dimensional (3D) carbon spheres also confine and isolate the Co3O4 nanoparticles growing in it, which help to provide rich Co3O4 active sites. The resulting hybrid material exhibits superior ORR activity in terms of even-better half-wave potential and stability than that of commercial Pt/C (40 wt%) in 0.1 M KOH electrolyte. To verify its catalytic activity, the hybrid material was employed as the cathode catalyst in a flexible solid-state zinc-air battery, which achieves a high power density of 227 mW cm-2; this power density is much higher than that of a Pt/C catalytic zinc-air battery (133 mW cm-2) under identical conditions. The improvement in catalytic activity in both aqueous and nonaqueous electrolytes can be attributed to the abundant active sites of the entangled Co3O4 nanoparticles, as well as the novel N,O-codoped carbon structure.