Iron–nitrogen-doped eggshell carbon microsphere-encapsulated hollow nanoparticle catalysts for enhanced oxygen reduction reaction in zinc–air batteries

Iron‑nitrogen-doped carbon materials (Fe-N-C) have gained widespread attention due to their low cost and excellent catalytic activity toward the oxygen reduction reaction (ORR). However, nanoscale Fe-N-C tend to agglomerate, impairing their catalytic activity. Porous carbon materials, with their high specific surface area and good conductivity, are an ideal support framework for the preparation of these catalysts. In this study, we demonstrate a novel iron‑nitrogen-doped carbonized polystyrene eggshell-like microspheres encapsulating hollow nanoparticle catalyst (Fe-N-CMS) by an environmentally friendly and facile synthesis method using the suspension polymerization technology. The experimental results demonstrate that the hydrophobicity of the pore-forming agent plays a key role in controlling the catalyst structure and an optimal Fe content to form Fe N complex determines the ORR activity. With the unique structure, the optimized Fe-N-CMS catalyst exhibits a half-wave potential of 0.932 V, and the peak power density in the zinc-air battery (ZAB) test reaches 130.8 mW cm −2 , which is comparable to that of 20% Pt/C (128.6 mW cm −2 ), along with a specific capacity of 804.46 mAh g −1 at 10 mA cm −2 and excellent long-term stability, maintaining a discharge voltage of approximately 1.12 V and 2.01 V over 120 h (720 cycles) with negligible polarization growth. Thus, this work presents an effective strategy for fabricating Fe-N-C catalysts to strengthen catalytic activity toward the ORR in the energy storage and conversion field.