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.