Nitrogen-Rich Mesoporous Carbon Nanospheres with Atomic Fe-N4 Sites for Efficient Oxygen Reduction

Abstract

The development of efficient and stable non-precious metal electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the commercialization of clean energy technologies such as Zinc-Air batteries (ZABs). In this work, we report the synthesis of Fe-doped high nitrogen containing mesoporous carbon nanospheres (Fe-NMCSs) with an exceptional nitrogen content of up to 13.9 wt%. Comprehensive characterization results confirm the atomic dispersion of Fe species forming Fe-N4 active sites within the nitrogen-rich carbon matrix. The hierarchical pore structure results in a significant increase in specific surface area (448 m2 g-1 ), while the ordered mesoporous structure enhances the exposure of active sites and improves mass transport channels. Electrochemical tests demonstrate that Fe-NMCSs catalyst exhibits outstanding ORR activity in alkaline media, with a half-wave potential (E1/2) of 0.886 V (vs. RHE), surpassing commercial Pt/C (20 wt%, 0.870 V vs. RHE). When assembled as an air cathode in ZABs, it delivers superior open-circuit voltage, specific capacity, and power density compared to the benchmark Pt/C + RuO2, along with excellent rate capability and cycling stability over 200 h. This work underscores the critical role of high nitrogen doping in conjunction with mesoporous structure for designing high electrocatalytic performance single-atom catalysts.