Oxygen-based
electrocatalysis is an integral aspect of a clean
and sustainable energy conversion/storage system. The development
of economic bifunctional electrocatalysts with high activity and durability
during reversible reactions remains a great challenge. The tailored
porous structure and separately presented active sites for oxygen
reduction and oxygen evolution reactions (ORR and OER) without mutual
interference are most crucial for achieving desired bifunctional catalysts.
Here, we report a hybrid composed of sheath–core cobalt oxynitride
(CoO
x
@CoN
y
) nanorods grown perpendicularly on N-doped carbon nanofiber (NCNF).
The brush-like CoO
x
@CoN
y
nanorods, composed of metallic Co4N cores and oxidized
surfaces, exhibit excellent OER activity (E = 1.69
V at 10 mA cm–2) in an alkaline medium. Although
pristine NCNF or CoO
x
@CoN
y
alone had poor catalytic activity in the ORR, the
hybrid showed dramatically enhanced ORR performance (E = 0.78 V at −3 mA cm–2). The experimental
results coupled with a density functional theory (DFT) simulation
confirmed that the broad surface area of the CoO
x
@CoN
y
nanorods with an oxidized
skin layer boosts the catalytic OER, while the facile adsorption of
ORR intermediates and a rapid interfacial charge transfer occur at
the interface between the CoO
x
@CoN
y
nanorods and the electrically conductive
NCNF. Furthermore, it was found that the independent catalytic active
sites in the CoO
x
@CoN
y
/NCNF catalyst are continuously regenerated and sustained without
mutual interference during the round-trip ORR/OER, affording stable
operation of Zn–air batteries.
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