Carbon-Encapsulated Co Nanoparticle and Hollow Carbon Sphere Composites as High-Performance Catalysts for Oxygen Reduction Reaction

Nitrogen and cobalt doped carbon materials are promising alternative catalysts for the oxygen reduction reaction (ORR) to replace more expensive Pt-based catalysts. However, the activity and stability of these materials remain largely subpar to those of Pt-based materials. In this work, a N, Co doped carbon composite with a hierarchical structure of few-carbon-layer encapsulated Co nanoparticles attached on hollow carbon spheres was successfully synthesized and demonstrated to have excellent ORR activity and long-term stability in 0.1 M KOH. The optimal catalyst showed a half-wave potential of 0.865 V, and it only shifted negatively by 17 mV after 50000 potential cycles between 0.4 and 1.2 V (vs RHE). These performance markers are better than those of commercial Pt/C catalysts. The high density of accessible active sites, the modification of the electronic structure of Co-Nx active sites and the carbon layer work function, together with the nonplanar active site structure, are potential contributors to such a high performance.