A SiO2-assisted strategy is a promising approach to
prepare high-performance oxygen reduction reaction (ORR) catalysts.
In this work, atomically dispersed FeN2 on rich nitrogen
doping-hollow carbon nanosphere catalysts were prepared by silica
interface assists. The Fe–N/C@SiO2 catalysts with
an ultrathin SiO2 layer (∼3 nm) were derived from
ZIF-8@Fe/SiO2 composites. A porous SiO2 thin
layer was wrapped on a ZIF-8 surface while loading Fe atoms inside
silica by one-step synthesis. Different from the conventional synthetic
strategy, no additional post-treatments such as etching of SiO2 coatings and second pyrolysis are required. The ORR activity
and stability are highly dependent on the thickness of the SiO2 layer. The rigid SiO2 layer not only traps the
volatile nitrogen species on the surface to achieve a high nitrogen
doping (11.14%) but also prevents the ZIF framework from collapse,
forming hierarchical porous structures. Also more importantly, single
Fe atoms are anchored in situ on the outer surface of the catalysts
in the form of FeN2 configuration, thus greatly boosting
the ORR activities. Remarkable stability (only 1% activity attenuation
after 14 h of operation) is achieved in alkaline media due to the
assist of inactive silica layers.
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