Core-shell Co-NC@NC nanomaterial for efficient oxygen reduction reaction

Transition metal and nitrogen doped carbons (M-N-C) catalysts present significant potential as substitutes for platinum-carbon (Pt/C) in catalyzing oxygen reduction reaction (ORR). Hence, we employ an epitaxial growth strategy to prepare Zn/Co-ZIF@ZIF-8 crystals with core-shell structure. Subsequent pyrolysis and acid etching produce highly porous cobalt-doped nitrogen materials for ORR investigation. The resulting Co-NC@NC catalyst demonstrates a graded porous structure alongside remarkable conductivity, possessing a specific surface area measuring 623 m2 g-1. It showcases heightened ORR activity with a half-wave potential (E1/2) of 0.886 V, superior kinetic performance (illustrated by an extremely low Tafel slope measuring 45.98 mV/dec), and strengthened stability (with mere 25 mV day after 40,000 cycles) when contrast with Pt/C catalysts in 0.1 M KOH. Additionally, it exhibits notable activity and stability in acidic environments. These remarkable attributes are attributable to the graded structure, which facilitates rapid mass transfer, a high electrochemically active area that exposes highly dispersed active sites, and a conductive carbon skeleton network that promotes electron transfer.