Atomically Dispersed FeN₂ at Silica Interfaces Coupled with Rich Nitrogen Doping-Hollow Carbon Nanospheres as Excellent Oxygen Reduction Reaction Catalysts

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.