Light-weight 3D Co-N-doped hollow carbon spheres as efficient electrocatalysts for rechargeable zinc-air batteries.

Rational design of cost-effective, nonprecious metal-based catalysts with a desirable oxygen reduction reaction (ORR) performance by a simple and economical synthesis route is a great challenge for the commercialization of future fuel cell and metal-air batteries. Herein, light-weight 3D Co-N-doped hollow carbon spheres (Co-NHCs) have been fabricated via a facile emulsion approach followed by carbonization. The prepared 0.1-Co-NHCs catalyst with suitable Co doping content exhibits favorable ORR catalytic activity (onset potential of 0.99 V and half-wave potential of 0.81 V vs. RHE), comparable to that of commercial Pt-C (onset potential of 1.02 V and half-wave potential of 0.83 V vs. RHE) and rivals that of Pt-C with better cycling stability. The excellent performance of the catalyst is attributed to the synergetic effect of Co and N doping with a high total ratio of active sites, high surface area and good conductivity of the material. More impressively, the assembled rechargeable zinc-air batteries based on the 0.1-Co-NHCs catalyst outperform those afforded by commercial Pt-C. The progress presented in this reported work is of great importance in the development of outstanding non-noble metal based electrocatalysts for the fuel cell and metal-air battery industry.