Bead-like carbon fibers consisting of abundantly exposed active sites for the oxygen reduction reaction.

Rational design is essential in the synthesis of electrocatalysts for the oxygen reduction reaction (ORR). Herein, we introduced zeolitic imidazolate framework-8 (ZIF-8) and polyvinyl pyrrolidone (PVP) into the electrospinning process of the polyacrylonitrile (PAN) and hemin to increase the active site loading and exposed active area of the final product with empty bead-like structures. In this method, ZIF-8 acts as a carbon skeleton to provide a rich microporous structure that can support active sites, and as a nitrogen dopant to improve nitrogen contents. PVP changes the properties of the spinning solution, adjusts the fiber morphology, and to increase the exposed area of active sites as a pore former. The obtained Fe-N-C ORR catalyst delivered a half-wave potential ( E 1/2 ) of 0.924 V in a 0.1 M KOH solution and 0.77 V in a 0.1 M HClO 4 solution. A homemade zinc air battery with power density of 236 mW cm -2 demonstrated the excellent performance of the catalyst under working conditions.