Formulating N‐Doped Carbon Hollow Nanospheres with Highly Accessible Through‐Pores to Isolate Fe Single‐Atoms for Efficient Oxygen Reduction

Abstract It is challenging yet promising to design highly accessible N‐doped carbon skeletons to fully expose the active sites inside single‐atom catalysts. Herein, mesoporous N‐doped carbon hollow spheres with regulatable through‐pore size can be formulated by a simple sequential synthesis procedure, in which the condensed SiO 2 is acted as removable dual‐templates to produce both hollow interiors and through‐pores, meanwhile, the co‐condensed polydopamine shell is served as N‐doped carbon precursor. After that, Fe─N─C hollow spheres (HSs) with highly accessible active sites can be obtained after rationally implanting Fe single‐atoms. Microstructural analysis and X‐ray absorption fine structure analysis reveal that high‐density Fe─N 4 active sites together with tiny Fe clusters are uniformly distributed on the mesoporous carbon skeleton with abundant through‐pores. Benefitted from the highly accessible Fe─N 4 active sites arising from the unique through‐pore architecture, the Fe─N─C HSs demonstrate excellent oxygen reduction reaction (ORR) performance in alkaline media with a half‐wave potential up to 0.90 V versus RHE and remarkable stability, both exceeding the commercial Pt/C. When employing Fe─N─C HSs as the air‐cathode catalysts, the assembled Zn–air batteries deliver a high peak power density of 204 mW cm −2 and stable discharging voltage plateau over 140 h.