Nitrogen-Doped Defect-Rich Graphitic Carbon Nanorings with CoOx Nanoparticles as Highly Efficient Electrocatalyst for Oxygen Electrochemistry

Low-cost and high-performance electrocatalysts for electrochemical reactions are of crucial importance for renewable and sustainable energy technologies including rechargeable metal-air batteries and fuel cells. Nanocarbon materials, as a promising alternative to replace the state-of-theart noble metal electrocatalysts, have attracted much interest, whereas the balance of the defect engineering and electric conductivity for them is still challenging. This work reports a discrete CoOx nanoparticles (CoO(x)NPs) situated in N-doped graphitic carbon nanorings (CoOx@NGCR), featuring graphitic but defect-rich characteristics, through a facile process of hydrothermal synthesis and subsequent high-temperature pyrolysis with in situ catalytic graphitization. The synergy arising from defect engineering and enhanced electric conductivity as well as hollow ring-shaped nanostructure of the fabricated CoOx@NGCR significantly boost the electrocatalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an alkaline system. CoOx@NGCR exhibits extraordinary ORR activity in terms of the positive onset potential (0.91 V), half-wave potential (0.80 V), and large limiting current density (4.9 mA cm(-2)), even comparable to those of the Pt/C benchmark. Furthermore, CoOx@NGCR shows impressive performance for OER along with robust durability. High bifunctional activity and excellent stability of CoOx@NGCR are further confirmed in an assembled Zn-air battery with a high power density and long-time operation stability, revealing great potential in practical applications.