Fabrication of core-shell structured cobalt nanoparticle/carbon nanofiber as a bifunctional catalyst for the oxygen reduction/evolution reactions

One-dimensional (1D) catalysts composed of non-precious metal nanoparticles (NPs) and carbon materials exhibit characteristics that make them attractive for electrochemical applications. However, metal NPs with catalytic activity are mostly buried in the carbon material, significantly limiting the surface catalytic reaction. In the present study, a 1D core-shell structured catalyst was designed to secure enhanced number of active sites by placing cobalt NPs on the surface of the catalyst. The proposed 1D core–shell-structured Co NP/carbon nanofiber, Co-CSNF, was realized by facile coaxial electrospinning process followed by the two-step heat treatment process. Through the position control of cobalt nanoparticles, the Co-CSNF showed improved catalyst performance in both ORR and OER compared to Co NP/carbon nanofiber electrospun with a single nozzle (Co-NF). The Co-CSNFs showed excellent oxygen reduction performance with a 4 electron path and a half-wave potential (E_1/2) of 0.86 V to RHE, and achieved a low oxygen evolution reaction of 322 mV (@10 mA cm⁻² at 1.0 M KOH). It was demonstrated that the Co-CSNF-based zinc–air battery (ZAB) exhibited a lower discharge and charge overpotential than the ZAB with Pt/C+IrO₂ with a stable cycling time of 366 h.