Reduced Graphene Oxide-Wrapped Co9-x Fex S8 /Co,Fe-N-C Composite as Bifunctional Electrocatalyst for Oxygen Reduction and Evolution.

Searching for highly efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) using nonnoble metal-based catalysts is essential for the development of many energy conversion systems, including rechargeable fuel cells and metal-air batteries. Here, Co9-x Fex S8 /Co,Fe-N-C hybrids wrapped by reduced graphene oxide (rGO) (abbreviated as S-Co9-x Fex S8 @rGO) are synthesized through a semivulcanization and calcination method using graphene oxide (GO) wrapped bimetallic zeolite imidazolate framework (ZIF) Co,Fe-ZIF (CoFe-ZIF@GO) as precursors. Benefiting from the synergistic effect of OER active CoFeS and ORR active Co,Fe-N-C in a single component, as well as high dispersity and enhanced conductivity derived from rGO coating and Fe-doping, the obtained S-Co9-x Fex S8 @rGO-10 catalyst shows an ultrasmall overpotential of ≈0.29 V at 10 mA cm-2 in OER and a half-wave potential of 0.84 V in ORR, combining a superior oxygen electrode activity of ≈0.68 V in 0.1 m KOH.