Co Nanoparticles Encapsulated in N‐Doped Carbon Nanotubes Grafted CNTs as Electrocatalysts for Enhanced Oxygen Reduction Reaction

Abstract The exploration of high‐efficiency and inexpensive electrocatalysts for oxygen reduction reaction (ORR) is of critical significance for renewable energy conversion. Herein, an in situ catalytic transformation strategy toward a unique hierarchical nanostructure is reported. In the architecture, Co nanoparticles encapsulated at the tip of bamboo‐like N‐doped carbon nanotubes (NCNTs) are grafted on N‐doped polypyrrole‐derived CNTs. Thanks to the smart design of unique 3D architecture, the NPCN@Co‐NCNTs catalyst displays an extraordinary ORR activity in 0.1 m KOH solution (the onset and half‐wave potentials are 0.96 and 0.90 V vs RHE, respectively), which is similar to commercial Pt/C catalyst (0.99 and 0.88 V vs RHE, respectively). Meanwhile, the catalyst shows the low Tafel slope of 78 mV dec −1 and long‐time stability. Experimental and theoretical results verify that the improved ORR performance is mainly related to the existence of Co nanoparticles protected by pyridinic‐N‐doped carbon, which lowers the theoretical overpotential of ORR. Density functional theory calculations reveal that Pyridinic‐NCCo site is the reactive site with the lowest overpotential for ORR (0.57 V). These results unambiguously indicate that the NPCN@Co‐NCNTs represent a low‐cost yet high‐efficiency electrocatalyst for the electrocatalytic ORR.