Long-term durability of platelet-type carbon nanofibers for OER and ORR in highly alkaline media

Abstract

Highly durable air electrodes for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in highly alkaline media are necessary to catalyze reactions in metal-air secondary batteries. Carbon is able to provide electronic conductivity and co-catalyze reactions, however, is typically oxidized under high-potential conditions above 1.1 V vs RHE. Herein, we demonstrate highly durable platelet-type carbon nanofibers (pCNFs) for OER/ORR in alkaline media. The pCNFs have graphene layers arranged perpendicularly to the fiber axis of the nanofibers. Such a specific configuration of the graphene layers in combination with a high degree of graphitization was found to be highly efficient in providing long-term durability combined with a state-of-the-art brownmillerite-type Ca2FeCoO5 catalyst. The improved oxidation resistance of the pCNF carbon is associated with the high degree of graphitization and the extremely slow oxidation rate of carbon edge planes at the sidewalls of the nanofibers.