Isolating Fe Atoms in N-Doped Carbon Hollow Nanorods through a ZIF-Phase-Transition Strategy for Efficient Oxygen Reduction.

Transition metal-nitrogen-carbon (TM-N-C) catalysts have been intensely investigated to tackle the sluggish oxygen reduction reactions (ORRs), but insufficient accessibility of the active sites limits their performance. Here, by using solid ZIF-L nanorods as self-sacrifice templates, a ZIF-phase-transition strategy is developed to fabricate ZIF-8 hollow nanorods with open cavities, which can be subsequently converted to atomically dispersed Fe-N-C hollow nanorods (denoted as Fe 1 -N-C HNRs) through rational carbonization and following fixation of iron atoms. The microstructure observation and X-ray absorption fine structure analysis confirm abundant Fe-N 4 active sites are evenly distributed in the carbon skeleton. Thanks to the highly accessible Fe-N 4 active sites provided by the highly porous and open carbon hollow architecture, the Fe 1 -N-C HNRs exhibit superior ORR activity and stability in alkaline and acidic electrolytes with very positive half-wave potentials of 0.91 and 0.8 V versus RHE, respectively, both of which surpass those of commercial Pt/C. Remarkably, the dynamic current density (J K ) of Fe 1 -N-C HNRs at 0.85 V versus RHE in alkaline media delivers a record value of 148 mA cm -2 , 21 times higher than that of Pt/C. The assembled Zn-air battery using Fe 1 -N-C HNRs as cathode catalyst exhibits a high peak power density of 208 mW cm -2 .